HX64086496 QP34 .B83 1 905 A text-book of human RECAP QP54 £^3 Columbia (Hnttier^ttp mtI)f€itpoflfttjgork College of ^ijpsiicianfi anli ^urgeong Hibrarp h Presentea by I, DR. WILLIAM J. OILS 1^ /d enric.i flie lil^r^rv resonncs ^ViXilckblt to holders ofthe mi OILS FELLOWSHIP in Bioloyc&l Chemistry Digitized by the Internet Archive in 2010 with funding from Columbia University Libraries http://www.archive.org/details/textbookofhumanpOObrub A TEXT-BOOK OF HUMAN PHYSIOLOGY. BRUBAKER A TEXT-BOOK OF HUMAN PHYSIOLOGY. INCLUDING A SECTION ON PHYSIOLOGIC APPARATUS. BY ALBERT P. BRUBAKER, A.M., M.D., PROFESSOR OF PHYSIOLOGY AND HYGIENE IN THE JEFFERSON MEDICAL COLLKGE ; PROFESSOR OF PHYSIOLOGY IN THE PENNSYLVANIA COLLEGE OF DENTAL SURGERY ; LECTURER ON PHYSIOLOGY AND HYGIENE IN THE DREXEL INSTITUTE OF ART, SCIENCE, AND INDUSTRY. Secon& lEMtion. 1Revise& an^ }£nlaroe^. Mitb Colored ipiatcs an& 356 IFUustrations. PHILADELPHIA : P. BLAKISTON'S SON & CO., I0I2 WALNUT STREET. 1905. /7 ^^^ Copyright, 1905, by P. Blakiston's Son & Co. PKESS or WM. f. FELL COMPA^ PMILADELPHI K. TO HENRY C. CHAPMAN, M.D., PROFESSOR OF INSTITUTES OF MEDICINE AND MEDICAL JURISPRUDENCE IN THE JEFFERSON MEDICAL COLLEGE, IN GRATEFUL RECOGNITION OF THE MANY KINDNESSES RECEIVED FROM HIM, DURING A PERIOD OF TWENTY-FIVE YEARS, THIS VOLUME IS RESPECTFULLY DEDICATED BY THE AUTHOR. PREFACE TO SECOND EDITION. In the preparation of a second edition the opportunity has been taken to eliminate inaccuracies, to revise paragraphs with a view of removing obscurities and to insert additional material which it is believed will render the consideration of certain topics more complete and accurate. The additional statements will be found in the sections relating to the chemistry of the proteids, the chemistry of digestion, the movements of the intestines, the production of lymph, the nerve mechanism of the heart, and the physiology of vision. These insertions have increased the size of the volume by about seventeen pages. I wish to express my thanks for the generous reception of this text-book by both teachers and students and trust that it may continue to merit their approval. A. P. B. PREFACE. The object in view in the preparation of this volume was the selection and presentation of the more important facts of physiology, in a form which it is believed will be helpful to students and to practitioners of medicine. Inasmuch as the majority of students in a medical college are preparing for the practical duties of professional life, such facts have been selected as will not only elucidate the normal functions of the tissues and organs of the body, but which will be of assistance in understanding their abnormal manifestations as they present themselves in hospital and private work. Both in the selection of facts and in the method of presentation the author has been guided by an experience gained during twenty years of active teaching. The description of physiologic apparatus and the methods of investigation, other than those having a clinical interest, have been largely excluded from the text, for the reason that both are more appropriately considered in works devoted to laboratory methods and laboratory instruction, and for the further reason that the student receives this information while engaged in the practical study of physiology in the laboratory, now an established feature in the curriculum of the majority of medical colleges. For those who have not had laboratory opportunities a brief account of some essential forms of apparatus and the purposes for which they are intended will be found in an appendix. I wish to acknowledge my indebtedness to Professor Colin C. Stewart for many valuable suggestions in the preparation of different sections of the volume; to Dr. Carl Weiland for assistance in the chapter on vision; to Dr. Joseph P. Bolton for excellent suggestions on questions relating to physiologic chemistry. TABLE OF CONTENTS. CHAPTER I. PAGE Introduction, 17 CHAPTER II. Chemic Composition of the Human Body, 24 CH.\PTER III. Physiology of the Cell, 43 CHAPTER IV. Histology of the Epithelial and Connective Tissues, 49 CHAPTER V. The Physiology of the Skeleton, 60 CHAPTER VI. General Physiology of Muscle-tissue, 65 CHAPTER VII. The General Physiology^ of Nerve-tissue, 105 CHAPTER VIII. Foods, 136 CHAPTER IX. Digestion, 154 CHAPTER X. Absorption, 221 CHAPTER XI. The Blood, 238 CHAPTER XII. The Circulation of the Blood, 272 CHAPTER XIII. Respiration, 350 CHAPTER XIV. Animal HE-i^T, 401 CHAPTER XV. Secretion, 411 xii TABLE OF CONTENTS. CHAPTER XVI. PAGE Excretion, 43 6 CHAPTER XVII. The Central Organs of the Nerve System and their Nerves, 456 CHAPTER XVIII. The Medulla Oblongata; the Isthmus of the Encephalon; the Basal Ganglia, 483 CHAPTER XIX. The Cerebrum, 502 CHAPTER XX. The Cerebellum, 530 CHAPTER XXI. The Cranial Nerves, 538 CHAPTER XXII. The Sympathetic Nerve System, 577 CHAPTER XXIII. Phonation; Articulate Speech, 588 CHAPTER XXIV. The Special Senses, 601 CHAPTER XXV. The Sense of Sight, 614 CHAPTER XXVI. The Sense of Hearing, 653 CHAPTER XXVII. Reproduction, 666 APPENDIX. Physiologic Apparatus, 687 Index, 709 TEXT-BOOK OF PHYSIOLOGY. CHAPTER I. INTRODUCTION. An animal organism in the living condition exhibits a series of phenomena which relate to growth, movement, mentality, and re- production. During the period preceding birth, as well as during the period included between birth and adult hfe, the individual grows in size and complexity from the introduction and assimilation of material from without. Throughout its life the animal exhibits a series of movements, in virtue of which it not only changes the relation of one part of its body to another, but also changes its posi- tion relatively to its environment. If, in the execution of these movements, the parts are directed to the overcoming of opposing forces, such as gravity, friction, cohesion, elasticity, etc., the animal may be said to be doing work. The result of normal growth is the attainment of a physical development that will enable the animal, and, more especially, man, to perform the work necessitated by the nature of its environment and the character of its organization. In man, and probably in lower animals as well, mentality manifests itself as intellect, feehng, and voUtion. At a definite period in the life of the animal it reproduces itself, in consequence of which the species to which it belongs is perpetuated. The study of the phenomena of growth, movement, mentality, and reproduction constitutes the science of animal physiology. But as these general activities are the resultant of and dependent on the special activities of the individual structures of which an animal body is composed, physiology in its more restricted and generally accepted sense is the science which investigates the actions or functions of the individual organs and tissues of the body and the physical and chemic conditions which underlie and determine them. This may naturally be divided into: I. Special physiology, the object of which is a study of the ^^tal phenomena or functions exhibited by the organs of any individual animal. 17 i8 TEXT-BOOK OF PHYSIOLOGY. 2. Comparative physiology, the object of which is a comparison of the vital phenomena or functions exhibited by the organs of two or more animals of different species, with a view to un- folding their points of resemblance or dissimilarity. Human physiology is that department of physiologic science which has for its object the study of the functions of the organs of the human body in a state of health. Inasmuch as the study of function, or physiology, is associated with and dependent on a knowledge of structure, or anatomy, it is essential that the student should have a general acquaintance not only with the structure of man, but with that of typical forms of lower animal life as well. If the body of any animal be dissected, it will be found to be composed of a number of well-defined structures, such as heart, lungs, stomach, brain, eye, etc., to which the term organ was originally applied, for the reason that they were supposed to be instruments capable of performing some important act or function in the general activities of the body. Though the term organ is usually employed to designate the larger and more famihar structures just mentioned, it is equally applicable to a large number of other structures which, though possibly less obvious, are equally important in maintaining the hfe of the individual — e. g., bones, muscles, nerves, skin, teeth, glands, blood-vessels, etc. Indeed, any complexly organized struc- ture capable of performing some function may be described as an organ. A description of the various organs which make up the body of an animal, their external form, their internal arrangement, their relations to one another, constitutes the science of animal anatomy. This may naturally be divided into: 1. Special anatomy, the object of which is the investigation of the construction, form, and arrangement of the organs of any individual animal. 2. Comparative anatomy, the object of which is a comparison of the organs of two or more animals of different species, with a view to determining their points of resemblance or dissimilarity. If the organs, however, are subjected to a further analysis, they can be resolved into simple structures, apparently homogeneous, to which the name tissue has been given — e. g., epithelial, connective, muscle, and nerve tissue. When the tissues are subjected to a microscopic analysis, it is found that they are not homogeneous in structure, but composed of still simpler elements, termed cells and fibers. The investigation of the internal structure of the organs, the physical properties and structure of the tissues, as well as the structure of their component elements, the cells and fibers, con- stitutes a department of anatomic science known as histology, INTRODUCTION. 19 or as it is prosecuted largely with the microscope, microscopic anatomy. Human anatomy is that department of anatomic science which has for its object the investigation of the construction of the human body. GENERAL STRUCTURE OF THE ANIMAL BODY. The body of every animal, from fish to man, may be divided into — 1. An axial portion, consisting of the head, neck, and trunk; and — 2. An appendicular portion, consisting of the anterior and posterior limbs or extremities. The axial portion of all mammals, to which class man zoologi- cally belongs, as well as of all birds, reptiles, amphibians, and os- seous fish, is characterized by the presence of a bony, segmented axis, which extends in a longitudinal direction from before backward, and which is known as the vertebral column or backbone. In virtue of the existence of this column all the classes of animals just men- tioned form one great division of the animal kingdom, the Vertehrata. Each segment, or vertebra, of this axis consists of — 1. xA. solid portion, known as the body or centrum, and 2. A bony arch arising from the dorsal aspect and surmounted by a spine-Hke process. At the anterior extremity of the body of the animal the vertebrae are variously modified and expanded, and, with the addition of new elements, form the skull; at the posterior extremity they rapidly diminish in size, and terminate in man in a short, tail-Uke process. In many animals, however, the vertebral column extends for a considerable distance beyond the trunk into the tail. The vertebral column may be regarded as the foundation element in the plan of organization of all the higher animals and the center around which the rest of the body is developed and arranged with a certain degree of conformity. In all vertebrate animals the bodies of the segments of the vertebral column form a partition which serves to divide the trunk of the body into two cavities — viz., the dorsal and the ventral. (See Fig. i.) The dorsal cavity is found not only in the trunk, but also in the head. Its walls are formed partly by the arches which arise from the posterior or dorsal surface of the vertebras and partly by the bones of the skull. If a longitudinal section be made through the center of the vertebral column, and including the head, the dorsal cavity will be observed running through its entire extent. Though for the most part it is quite narrow, at the anterior ex- TEXT-BOOK OF PHYSIOLOGY tremity it is enlarged and forms Fig. I. — Diagrammatic Longitud- inal Section of the Body. V, V. Bodies of the vertebrae which divide the body into the dorsal and ventral cavities, a, a'. The dorsal cavity. C, p'. The abdominal and thoracic divisions of the ventral cavity, separated from each other by a trans- verse muscular partition, the diaphragm d. B. The brain. Sp. C. The spinal cord. e. The esophagus. S. The stomach, from vv^hich continues the intes- tine to the opening at the poste- rior portion of the body. /. The hver. p. The pancreas, k. The kidney, o. The bladder. /'. The lungs, h. The heart. the cavity of the skulL This cavity is hned by a membranous canal, the neural canal, in which are con- tained the brain and the neural or spinal cord. Through openings in the sides of the dorsal cavity nerves pass out which connect the brain and spinal cord with all the struc- tures of the body. The ventral cavity is confined mainly to the trunk of the body. Its walls are formed by muscles and skin, strengthened in most animals by bony arches, the ribs. Within the ventral cavity is con- tained a musculo-membranous tube or canal known as the ahmentary or food canal, which begins at the mouth on the ventral side of the head, and, after passing through the neck and trunk, terminates at the posterior extremity of the trunk at the anus. It may be divided into mouth, pharynx, esophagus, stomach, small and large intestines. In all mammals the ventral cavity -is divided by a musculo- membranous partition into two smaller cavities, the thorax and abdomen. The former contains the lungs, heart and its great blood- vessels, and the anterior part of the ahmentary canal, the gullet or esophagus; the latter contains the continuation of the alimentary canal — that is, the stomach and intestines — and the glands in con- nection with it, the liver and pan- creas. In the posterior portion of the abdominal cavity are found the kidneys, ureters, and bladder, and in the female the organs of repro- duction. The thoracic and ab- dominal cavities are each hned by a thin serous membrane, known. INTRODUCTION. 21 respectively, as the pleural and peritoneal membranes, which, in addition, are reflected over the surfaces of the organs contained within them. The alimentary canal and the various cavities con- nected with it are lined throughout by a mucous membrane. The surface of the body is covered by the skin. This is com- posed of an inner portion, the derma, and an outer portion, the epi- dermis. The former consists of fibers, blood-vessels, nerves, etc. ; the latter of layers of scales or cells. Embedded within the skin are numbers of glands, which exude, in the different classes of animals, sweat, oily matter, etc. Projecting from the surface of the skin are hairs, bristles, feathers, claws. Beneath the skin are found muscles, bones, blood-vessels, nerves, etc. The appendicular portion of the body consists of two pairs of symmetric limbs, which project from the sides of the trunk, and which bear a determinate relation to the vertebral column. They con- sist fundamentally of bones, surrounded by muscles, blood-vessels, nerves and lymphatics. The limbs, though having a common plan of organization, are modified in form and adapted for prehension and locomotion in accordance with the needs of the animal. Anatomic Systems. — All the organs of the body which have certain peculiarities of structure in common are classified by anato- mists into systems — e. g., the bones, collectively, constitute the bony or osseous system; the muscles, the nerves, the skin, constitute, respectively, the muscle, the nerve, and the tegumentary systems. Physiologic Apparatus. — ]\Iore important from a physiologic point of view than a classification of organs based on similarities of structure is the natural association of two or more organs acting together for the accomphshment of some definite object, and to which the term physiologic apparatus has been applied. While in the community of organs which together constitute the animal body each one performs some definite function, and the harmonious co- operation of all is necessary to the life of the individual, everywhere it is found that two or more organs, though performing totally dis- tinct functions, are cooperating for the accomphshment of some larger or compound function in which their individual functions are blended — e. g., the mouth, stomach, and intestines, with the glands connected with them, constitute the digestive apparatus, the object or function of which is the complete digestion of the food. The capillary blood-vessels and lymphatic vessels of the body, and espe- cially those in relation to the vilh of the small intestine, constitute the absorptive apparatus, the function of which is the introduction of new material into the blood. The heart and blood-vessels con- stitute the circulatory apparatus, the function of which is the dis- tribution of blood to all portions of the body. The lungs and trachea. 22 TEXT-BOOK OF PHYSIOLOGY. together with the diaphragm and the walls of the chest, constitute the respiratory apparatus, the function of which is the introduction of oxygen into the blood and the elimination from it of carbon dioxid and other injurious products. The kidneys, the ureters, and the bladder constitute the urinary apparatus. The skin, with its sweat- glands, constitutes the perspiratory apparatus, the functions of both being the excretion of waste products from the body. The liver, the pancreas, the mammary glands, as well as other glands, each form a secretory apparatus which elaborates some specific material necessary to the nutrition of the individual. The functions of these different physiologic apparatus — e. g., digestion, absorption of food, elaboration of blood, circulation of blood, respiration, production of heat, secretion, and excretion — -are classified as nutritive functions, and have for their final object the preservation of the individual. The nerves and muscles constitute the nervo-muscular apparatus, the function of which is the production of motion. The eye, the ear, the nose, the tongue, and the skin, with their related structures, constitute, respectively, the visual, auditory, olfactory, gustatory, and tactile apparatus, the function of which, as a whole, is the reception of impressions and the transmission of nerve impulses to the brain, where they give rise to visual, auditory, olfactory, gustatory, and tactile sensations and volitional impulses. The brain, in association with the sense organs, forms an appa- ratus related to mental processes. The larynx and its accessory organs — the lungs, trachea, respiratory muscles, the mouth and resonant cavities of the face — form the vocal and articulating appa- ratus, by means of which voice and articulate speech are produced. The functions exhibited by the apparatus just mentioned — viz., motion, sensation, language, mental and moral manifestations — are classified as functions of relation, as they serve to bring the individual into conscious relationship with the external world. The ovaries and the testes are the essential reproductive organs, the former producing the germ-cell, the latter the sperm element. Together with their related structures, — the fallopian tubes, uterus, and vagina in the female, and the urogenital canal in the male, — they constitute the reproductive apparatus characteristic of the two sexes. Their cooperation results in the union of the germ-cell and sperm element and the consequent development of a new being. The function of reproduction serves to perpetuate the species to which the individual belongs. The animal body is therefore not a homogeneous organism, but one composed of a large number of widely dissimilar but related organs. As all vertebrate animals have the same general plan of organization, there is a marked similarity both in form and struc- ture among corresponding parts of different animals. Hence it is INTRODUCTION. • 23 that in the study of human anatomy a knowledge of the form, con- struction, and arrangement of the organs in different types of animal life is essential to its correct interpretation; it follows also that in the investigation and comprehension of the complex problems of human physiology a knowledge of the functions of the organs as they manifest themselves in the different types of animal hfe is indispensable. As many of the functions of the human body are not only complex, but the organs exhibiting them are practically inaccessible to in- vestigation, we must supplement our knowledge and judge of their functions by analogy, by attributing to them, within certain limits, the functions revealed by experimentation upon the corresponding organs of lower animals. This experimental knowledge, corrected by a study of the clinical phenomena of disease and the results of post-mortem investigations, forms the basis of modern human physi- ologv. CHAPTER 11. CHEMIC COMPOSITION OF THE HUMAN BODY. Since it has been demonstrated that every exhibition of functional activity is associated with changes of structure, it has been apparent that a knowledge of the chemic composition of the body, not only when in a state of rest, but to a far greater degree when in a state of activity, is necessary to a correct understanding of the intimate nature of physiologic processes. Though the analysis of the dead body is comparatively easy, the determination of the successive changes in composition of the living body is attended with many difficulties. The hving material, the bioplasm, is not only complex and unstable in composition, but extremely sensitive to all physical and chemic influences. The methods, therefore, which are employed for analysis destroy its composition and vitahty, and the products which are obtained are peculiar to dead rather than to living material. Chemic analysis, therefore, may be directed — 1. To the determination of the composition of the dead body. 2. To the determination of the successive changes in composition which the living bioplasm undergoes during functional activity. A chemic analysis of the dead body, with a view to disclosing the substances of which it is composed, their properties, their intimate structure, their relationship to one another, constitutes what might be termed chemic anatomy. An investigation of the living ma- terial and of the successive changes it undergoes in the performance of its functions constitutes what has been termed chemic physi- ology or physiologic chemistry. By chemic analysis the animal body can be reduced to a number of liquid and solid compounds which belong to both the inorganic and organic worlds. These compounds, resulting from a proximate analysis, have been termed proximate principles. That they may merit this term, however, they must be obtained in the form under which they exist in the living condition. The organic compounds consist of representatives of the carbohydrate, fatty, and proteid groups of organic bodies; the inorganic compounds consist of water, various acids, and inorganic salts. The compounds or proximate principles thus obtained can be further resolved by an ultimate analysis into a small number of chemic elements which are identical with elements found in many other organic as well as inorganic compounds. The different chemic 24 CHEMIC COMPOSITION OF THE HUMAN BODY. 25 elements which are thus obtained, and the percentages in which they exist in the body, are as follows — viz., oxygen, 72 per cent.; hydrogen, 9.10; nitrogen, 2.5; carbon, 13.50; phosphorus, 1.15; calcium, 1.30; sulphur, 0.147; sodium, o.io; potassium, 0.026; chlorin, 0.085; fluorin, iron, silicon, magnesium, in small and variable amounts. THE CARBOHYDRATES. The carbohydrate compounds, which enter into the composition of the animal body, are mainly starches and sugar. In many re- spects they are closely related, and by appropriate means are readily converted into one another. In composition they consist of the elements carbon, hydrogen, and oxygen. As their name imphes, the hydrogen and oxygen are present in these compounds in the proportion in which they exist in water, or as 2 : i. The molecule of the carbohydrates above mentioned consists of either six atoms of carbon or a muUiple of six; in the latter case the quantity of hydrogen and oxygen taken up by the carbon is increased, though the ratio remains unchanged. The carbohydrates may be divided into three groups — viz.: (i) amyloses, including starch, dextrin, glycogen, and cellulose; (2) dextroses, including dextrose, levulose, galactose; (3) saccharoses, including saccharose, lactose, and maltose. According to the number of carbon atoms entering into the second group (six), they are fre- quently termed monosaccharids; those of the third group, disaccharids — twice six ; those of the first group, polysaccharids — multiples of six. Though but few of the members of the carbohydrate group are constituents of the human body, many are constituents of the foods; on account of their importance in this respect, and their relation to one another, the chemic features of the more generally consumed carbohydrates will be stated in this connection. I. AMYLOSES, (CeHioOj),,. Starch is widely distributed in the vegetable world, being abundant in the seeds of the cereals, leguminous plants, and in the tubers and roots of many vegetables. It occurs in the form of microscopic granules, which vary in size, shape, and appearance, according to the plant from which they are obtained. Each granule presents a nucleus, or hilum, around which is arranged a series of eccentric rings, alternately light and dark. The granule consists of an envelope and stroma of cellulose, containing in its meshes the true starch material — gramdose. Starch is insoluble in cold water and alcohol. When heated with water up to 70° C, the granules swell, rupture, and liberate the granulose, which forms an apparent solution; if present in sufficient quantity, it forms a gelatinous mass termed 26 TEXT-BOOK OF PHYSIOLOGY. starch paste. On the addition of iodin, starch strikes a characteristic deep blue color; the compound formed — iodid of starch — is weak, the color disappearing on heating, but reappearing on cooling. BoiUng starch with dilute sulphuric acid (twenty-five per cent.) converts it into dextrose. In the presence of vegetable diastase or animal ferments, starch is converted into maltose and dextrose, two forms of sugar. Dextrin is a substance formed as an intermediate product in the transformation of starch into sugar. There are at least two principal varieties — erythrodextrin, which strikes a red color with iodin, and achroodextrm, which is without color when treated with this reagent. In the pure state dextrin is a yellow-white powder, soluble in water. In the presence of vegetable ferments erythro- dextrin is converted into maltose. Glycogen is a constituent of the animal liver, and, to a sHght extent, of muscles and of tissues generally. In the tissues of the embryo it is especially abundant. When obtained in a pure state it is an amorphous, white powder. It is soluble in water, forming an opalescent solution. With iodin it strikes a port- wine color. In some respects it resembles starch, in others dextrin. Like vegetable starch, glycogen or animal starch can be converted by dilute acids and ferments into sugar (dextrose). Cellulose is the basic material of the more or less sohd framework of plants. It is soluble in ammoniacal solution of cupric oxid, from which it can be precipitated by acids. It is an amorphous powder; dilute acids can convert it into dextrose. 2. DEXTROSES, CeHuOe. Dextrose, glucose, or grape-sugar is found in grapes, most sweet fruits, and honey, and as a normal constituent of liver, blood, muscles, and other animal tissues. In the disease diabetes mellitus it is found also in the urine. When obtained from any source, it is soluble in water and in hot alcohol, from which it crystalhzes in six-sided tables or prisms. As usually met with, it is in the form of irregular, warty masses. It is sweet to the taste. When examined with the polariscope, dextrose turns the plane of polarized light to the right. It is therefore termed dextro-rotatory. It has for a long time been known that when sugar, cupric hydroxid, and an alkali — e.g., sodium or potassium — are present in solution, the sugar will abstract from the cupric hydroxid a portion of its oxygen, thus reducing it to a lower stage of oxidation giving rise to cuprous oxid. Sugar has a similar action on both silver and bismuth. On this property of sugar a standard solution of cupric hydroxid was suggested by Fehhng which may be employed for both quahtative and quantitative tests for the presence of sugar in solution. CHEMIC COMPOSITION OF THE HUMAN BODY. 27 Fehling's Test Solution. — This is a solution of cupric hydroxid made alkaline by an excess of sodium or potassium hydroxid with the addition of sodium and potassium tartrate. It is made by dissolving cupric sulphate 34.64 grams, potassium hydroxid 125 grams, sodium and potassium tartrate 173 grams, in distilled water sufficient to make one liter. The reaction is expressed by the following equation: CUSO4 + 2KOH = Cu(OH)2 + KjSO^. The object of the sodium and potassium tartrate is to dissolve the cupric hydroxid and hold it in solution. For qualitative analysis it is only necessary to boil a few cubic centimeters of this solution in a test-tube; then add the suspected solution and again heat to the boihng-point. If sugar be present, the cupric hydroxid is reduced to the condition of a cuprous oxid, which shows itself as a red or orange-yellow precipitate. The color of the precipitate depends on the relative excess of either copper or sugar, being red with the former, orange or yellow with the latter. The delicacy of this test is shown by the fact that a few minims of this solution will detect in i c.c. of water the -j^j of a milhgram of sugar. For quantitative analysis, 10 c.c. of Fehhng's solution, diluted with 40 c.c. of water, are heated in a porcelain capsule, to which the suspected solution is cautiously added from a buret until the blue color entirely disappears. The strength of this solution is such that I c.c. is decolorized by 5 milHgrams of sugar (dextrose), from which the percentage of sugar in any solution can be determined. All the sugars, with the exception of chemically pure saccharose, may be tested for with this solution. The Fermentation Test. — All the sugars with the exception of lactose undergo reduction to simpler compounds, mainly alcohol and carbon dioxid, under the action of the yeast plant, Saccharomyces cerevisicB. The change with dextrose is expressed in the following equation: CeHijOe = aCjHeO + 2CO2. Dextrose = Alcohol — Carbon Dioxid. About 95 per cent, of the dextrose is so changed, the remaining 5 per cent, yielding secondary products — succinic acid, glycerin, etc. As a means of testing any solution for the presence of sugar this method may be adopted. It is generally very satisfactory. From the quantity of carbon dioxid and alcohol thus produced the quantity of sugar in the solution may be determined. Levulose, or fruit-sugar, is found in association with dextrose as a constituent of many fruits. It is sweeter than dextrose and more soluble in both water and dilute alcohol. From alcohohc 28 TEXT-BOOK OF PHYSIOLOGY. solutions it crystallizes in fine, silky needles, though it usually occurs in the form of a syrup. Levulose is distinguished from dextrose by its property of turning the plane of polarized light to the left ; the extent to which it does so, however, varies with the temperature and concentration of the solution. Under the influence of the yeast plant it slowly undergoes fer- mentation, yielding the same products as dextrose. It also has a reducing action on cupric hydroxid. Galactose is obtained by boihng milk-sugar (lactose) with dilute sulphuric acid. In many chemic relations it resembles dextrose. It is less soluble in water, however, crystallizes more easily, and has a greater dextro-rotatory power. It also undergoes fermentation with the yeast plant. 3. SACCHAROSES, CisHjjO,,. Saccharose, or cane-sugar, is widely distributed throughout the vegetable world, but is especially abundant in sugar-cane, sor- ghum cane, sugar-beet, Indian corn, etc. It crystallizes in large monoclinic prisms. It is soluble in water and in dilute alcohol. Saccharose has no reducing power on cupric hydroxid, and hence its presence can not be detected by Fehling's solution. It is dextro- rotatory. Boiled with dilute mineral, as well as with organic acids, saccharose combines with water and undergoes a change in virtue of which it rotates the plane of polarized light to the left, and hence the product was termed invert sugar. This latter has been shown to be a mixture of equal quantities of levulose and dextrose. This inversion of saccharose through hydration and decomposition is expressed in the following equation : C12H22O11 + H2O = CeHijOg -t- CgHijOg Saccharose -I- Water = Le\Tilose -f- Dextrose Invert Sugar. Saccharose is not directly fermentable by yeast, but through the specific action of a ferment, invertin or invertase, secreted by the yeast plant, or the inverting ferment of the small intestine, it under- goes inversion, as previously stated, after Avhich it is readily fermented, yielding alcohol and carbon dioxid. Lactose is the form of sugar found exclusively in the milk of the mammalia, from which it can be obtained in the form of hard, white, rhombic prisms united with one molecule of water. It is soluble in water, insoluble in alcohol and ether. It is dextro-rotatory. It reduces cupric hydroxid, but to a less extent than dextrose. Dilute acids decompose it into equal quantities of dextrose and galactose. Lactose is not fermentable with yeast, but in the presence of the CHEMIC COMPOSITION OF THE HUMAN BODY. 29 lactic acid bacillus it is decomposed into lactic acid, and finally into butyric acid, as expressed in the following equation: CijHsjOn + H2O = 4C3H6O3 Lactose ~ Water =; Lactic Acid. 2C3He03 = C.HsOz + 2CO2 + 2H2 Lactic Acid = Butyric Acid — Carbon — Free Dioxid Hydrogen. Maltose is a transformation product of starch, and arises when- ever the latter is acted on by malt extract or the diastatic ferments in sahva and pancreatic juice. The change is expressed by the fol- lowing equation: 2CeHio05 + H2O = CnHj^On Starch. Water. Maltose. Maltose crystalhzes in the form of white needles, which are soluble in water and in dilute alcohol. It is dextro-rotatory. In the presence of ferments and dilute acids maltose undergoes hydra- tion and decomposition, giving rise to two molecules of dextrose. It has a reducing action on cupric hydroxid. Fermentation is readily caused by yeast, but w^hether directly or indirectly by inversion is somewhat uncertain. Osazones. — All the sugars w^hich possess the power of reducing cupric hydroxid are capable of combining with phenyl-hydrazin, with the formation of compounds termed osazones. The osazones so formed are crystalline in structure, but have different melting- points, varying degrees of solubility and optic properties, all of which serve to detect the various sugars and to distinguish one from the other. Of the different osazones, phenyl-glucosazone is the most characteristic, and occurs in the form of long, yellow needles. It may be obtained from dextrose by the following method: To 50 c.c. of a dextrose solution add 2 gm. of phenyl-hydrazin and 2 gm. of sodium acetate, and boil for an hour. On cooling, the osazone cr}^stalhzes in the form of long, yellow needles. THE FATS. The fats constitute a group of organic bodies found in the tissues of both vegetables and animals. In the vegetable world they are largely found in fruits, seeds, and nuts, where they probably originate from a transformation of the carbohydrates. In the animal body the fats are found largely in the subcutaneous tissue, in the marrow of bones, in and around various internal organs and in milk. In these situations fat is contained in small, round or polygon-shaped vesicles, which are united by areolar tissue and surrounded by blood- vessels. At the temperature of the body the fat is hquid, but aftei death it soon sohdifies from the loss of heat. 30 TEXT-BOOK OF PHYSIOLOGY. The fats are compounds consisting of carbon, hydrogen, and oxygen, of which the first is the chief ingredient, forming by weight about 75 per cent., while the last is present only in small quantity. The fat found in animals is a mixture, in varying proportions in different animals, of three neutral fats — stearin, palmitin, and olein. Each fat is a derivative of glycerin and the particular acid indicated by its name — e. g., stearic acid, in the case of stearin, etc. The reaction which takes place in the combination of glycerin and the acid is expressed in the following equation: C3H5(HO)3 + (HCi8H,502)3 = C,U,{C,siis,02)3 + 3H2O. Glycerin. Stearic Acid. Stearin. Water. Hence, strictly speaking, the fats are compound ethers, in which the hydrogen of the organic acid is replaced by the trivalent radicle, tritenyl, C3H5. Stearin, €3115(0^8113502)3, is the chief constituent of the more solid fats. It is solid at ordinary temperatures, melting at 55° 0., then solidifying again as the temperature rises, until at 71° 0. it melts permanently. It crystaUizes in square tables. Palmitin, 03115(016113^02)3, is a semifluid fat, solid at 45° 0. and melting at 62° 0. It crystalhzes in fine needles, and is soluble in ether. Olein, 03115(0^8113302)3, is a colorless, transparent fluid, liquid at ordinary temperatures, only soHdifying at 0° 0. It possesses marked solvent powers, and holds stearin and palmitin in solution at the temperature of the body. Saponification. — When subjected to the action of superheated steam, a neutral fat is saponified — i. e., decomposed into glycerin and the particular acid indicated by the name of the fat used: e. g., stearic, palmitic, or oleic. The reaction is expressed as follows: C3H5(C,8H3303)3 + 3H3O = C3H5(HO)3 + 3(Cl8H3402) Olein. Water. Glycerin. Oleic Acid. The fatty acids thus obtained are characterized by certain chemic features, as follows : Stearic acid is a firm, white soHd, fusible at 69° 0. It is soluble in ether and alcohol, but not in water. Palmitic acid occurs in the form of white, ghstening scales or needles, melting at 62° 0. Oleic acid is a clear, colorless Hquid, tasteless and odorless when pure. It crystalhzes in white needles at 0° 0. If this saponification takes place in the presence of an alkali, — e. g., potassium hydroxid or sodium hydroxid, — the acid produced combines at once with the alkaH to form a salt known as a soap, while the glycerin remains in solution. The reaction is as follows: 3KHO + (C,8H3,02)3 = sCKC.sHgjO^) + 3H2O Potassium. Oleic Acid Potassium Oleate. Water. CHEMIC COMPOSITION OF THE HUMAN BODY. 31 All soaps are, therefore, salts formed by the union of alkalies and fatty acids. The sodium soaps are generally hard, while the potas- sium soaps are soft. Those made with stearin and palmitin are harder than those made with olein. If the soap is composed of lead, zinc, copper, etc., it is insoluble in water. Emulsification. — ^When a neutral oil is vigorously shaken with water or other fluid, it is broken up into minute globules that are more or less permanently suspended; the permanency depending on the nature of the hquid. The most permanent emulsions are those made with soap solutions. The process of emulsification and the part played by soap can be readily observed by placing on a few cubic centimeters of a solution of sodium carbonate (0.25 per cent.) a small quantity of a perfectly neutral oil to which has been added 2 or 3 per cent, of a fatty acid. The combination of the acid and the alkali at once forms a soap. The energy set free by this combination rapidly divides up the oil into extremely minute globules. A spontaneous emulsion is thus formed. In addition to the ordinary fats, there are present in different tissues several compounds which, though usually regarded as fats, nevertheless differ materially from them in composition, containing, as they do, both nitrogen and phosphorus. These nitrogenized or phosphorized fats are as follows: Lecithin, C^^HggN.POg, is found in blood, lymph, red and white corpuscles, nerve tissue, yolk of eggs, etc. When pure, it presents itself generally under the form of a white, crystalHne powder, though sometimes as a white, waxy mass. Lecithin is easily decom- posed, yielding, with various reagents, glycero-phosphoric acid, cholin and stearic acid. Protagon, Cj^oHa^gNgPOgs, is found most abundantly in the brain tissue, especially in the white portion. It crystalhzes from warm alcohohc solutions, on coohng, in the form of white needles, generally arranged m groups. It melts at 200° C, and forms a syrupy Hquid. Cerebrin, Cj^HggN.Og, is found largely in the brain, in nerves, and in pus-corpuscles. It is a soft, white, amorphous powder, in- soluble in water, but swelling up like starch in boiling water. When boiled with dilute acids, it is decomposed, yielding a fermentable dextro-rotatory sugar, identical with galactose. Cerebrin may, therefore, be regarded as a glucosid. THE PROTEIDS. The proteids constitute a group of organic bodies which are found in both vegetable and animal tissues. Though present in all animal tissues, they are especially abundant in muscles and 32 TEXT-BOOK OF PHYSIOLOGY. bones, where they constitute 20 per cent, and 30 per cent, respectively. Though genetically related, and possessing many features in common, the different members of the proteid group are distinguished by characteristic physical and chemic properties which serve not only for their identification, but for their classification into more or less well-defined groups as follows: SIMPLE PROTEIDS. ALBUMINS. The members of this group are soluble in water, in dilute saUne solutions, and in saturated solutions of sodium chlorid and mag- nesium sulphate. They are coagulated by heat, and when dried form an amber-colored mass. (a) Serum-albumin. This most important proteid is found in blood, lymph, chyle, and some tissue fluids. It is obtained readily by precipitation from blood-serum, after the other proteids have been removed, on the addition of ammonium sulphate. When freed from sahne constituents, it presents itself as a pale, amorphous substance, soluble in water and in strong nitric acid. It is coagulated at a temperature of 73° C, as well as by various acids — e. g., citric, picric, nitric, etc. It has a rotatory power of — 62.6°. (b) Egg-albumin. — Though not a constituent of the human body, egg-albumin resembles the foregoing in many respects. When obtained in the solid form from the white of the egg, it is a yellow mass without taste or odor. Though similar to serum-albumin, it differs from it in being precipitated by ether, in coagulating at 54° C, and in having a lower rotatory power, —35.5°. (c) Lact-albumin. — As its name impHes, this proteid is found in milk. It can be precipitated from milk-plasma by sodium sulphate after the precipitation of the other proteids by half saturation with ammonium sulphate. It slowlv coagulates at 77° C. (d) Myo-albumin. — This proteid is found in muscle-plasma from which it subjects the plasma to fractional heat coagu- lation. At 73° C. myo-albumin coagulates. GLOBULINS. The members of this group are insoluble in water and in saturated solutions of sodium chlorid and magnesium sulphate and ammonium sulphate. They are soluble, however, in dilute sahne solutions — e. g., sodium chlorid (i per cent.), potassium chlorid, ammonium chlorid, etc. They are coagulated by heat. CHEMIC COMPOSITION OF THE HUMAN BODY. S3 (a) Serum-globiilin or Paraglobulin. — This proteid, as its name implies, is found in blood-serum, though it is present in other animal fluids. When precipitated by magnesium sulphate or carbon dioxid, it presents itself as a flocculent substance, insoluble in water, soluble in dilute acids and alkaHes, and coagulating at 75° C. (b) Fibrinogen. — This proteid is found in blood-plasma in asso- ciation with serum-globuHn and serum-albumin. It is also present in lymph-tissue fluids and in pathologic transudates. It can be obtained from blood-plasma which has been pre- viously treated with magnesium sulphate on the addition of a saturated solution of sodium chlorid. It is soluble in dilute acids and alkahes, and coagulates at 56° C. (c) Para-myosinogen. — This proteid is a constituent of the muscle-plasma from which it can be precipitated by a tem- perature of 47° C. (d) Myosinogen. — This proteid is the chief constituent of the muscle-plasma and is of great nutritive value. During the living condition it is hquid, but after death it readily under- goes a chemic change and contributes to the formation of an insoluble proteid known as myosin. It is soluble in dilute hydrochloric acid and dilute alkalies. It coagulates at 56° C. (e) Globin. — This is a product of the spontaneous decomposition of the coloring-matter of the blood, — hemoglobin, — and arises when the latter is exposed to the air. (/) Crystallin or Globulin. — This is obtained by passing a stream of CO, through a watery extract of the crystalhne lens. DERIVED ALBUMINS OR ALBUMINATES. The proteids of this group are derived from both albumins and globuhns by the gradual action of dilute acids and alkahes, and may be regarded as compounds of a proteid with an acid or an alkali. (a) Acid-albumin. — This is formed when a native albumin is digested with dilute hydrochloric acid (0.2 per cent.) or dilute sulphuric acid for some minutes. It is precipitated by neu- tralization with sodium hydroxid (o.i per cent, solution). After the precipitate is washed, it is found to be insoluble in distilled water and in neutral saline solutions. In acid solutions it is not coagulated by heat. (b) Alkali-albumin. — This is formed when a native albumin is treated with a dilute alkali — e. g., o.i per cent, of sodium hydroxid — for five or ten minutes. On careful neutrahzation with dilute hydrochloric acid, it is precipitated. It is also insoluble in distilled water and in saline solutions; it is not coagulable by heat. 3 34 TEXT-BOOK OF PHYSIOLOGY. COAGULATED PROTEIDS. Although these proteids are not found as constituents of the animal organism, they possess much interest on account of their relation to prepared foods and to the digestive process. They are produced when solutions of egg-albumin, serum-albumin, or globuhns are subjected to a temperature of ioo° C. or to the prolonged action of alcohol. They are insoluble in water, in dilute acids, and in neutral sahne solutions. In this same group may be included also those coagulated pro- teids which are produced by the action of animal ferments on soluble proteids — e. g., fibrin, myosin, casein. (a) Fibrin. — Fibrin is derived from a soluble proteid — fibrinogen — by the action of a special ferment. It is not present under normal circumstances in the circulating blood, but makes its appearance after the blood is withdrawn from the vessels and at the time of coagulation. It can also be obtained by whipping the blood with a bundle of twigs, on which it accu- mulates. When freed from blood by washing under water, it is seen to consist of bundles of white elastic fibers or threads. It is insoluble in water, in alcohol, and ether. In dilute acids it swells, becomes transparent, and finally is converted into acid-albumin. In dilute alkalies a similar change takes place, but the resulting product is an alkali-albumin. Fibrin pos- sesses the property of decomposing hydrogen dioxid, HjOj — i. e., liberating oxygen, which accumulates in the form of bubbles on the fibrin. On incineration fibrin yields an ash which contains calcium phosphate and magnesium phosphate. (b) Myosin. — Myosin develops in muscles after death and is the cause of the stiffening of the muscles. It has been regarded as a derivative of the soluble proteid myosinogen alone, but there is evidence that in its form ation both paramyosinogen and myosinogen take part. It is not definitely known whether this is the result of the action of a special ferment or not. (c) Casein. — Casein is derived from the chief proteid of milk — caseinogen — by the action of a special ferment known as rennin or chymosin. This ferment is a constituent of gas- tric juice. PROTEOSES AND PEPTONES. During the progress of the digestive process, as it takes place in the stomach and intestines, there is produced by the action of the gastric and pancreatic juices, out of the proteids of the food, a series of new proteids, knowm as proteoses and peptones. The chemic properties of these substances will be considered in connection with the process of digestion. CHEMIC COMPOSITION OF THE HUMAN BODY. 35 CONJUGATED OR COMBINED PROTEIDS. The different members of this group are capable of being de- composed by chemic methods into a proteid and a non-proteid sub- stance; e. g., a coloring matter, a carbohydrate, or a nuclein. The chemic character of the non-proteid substance furnishes the basis for the following classification: CHROMO-PROTEIDS. (a) Hemaglobin. — Hemoglobin is the coloring matter of the red corpuscles, of which it constitutes about 94 per cent. It possesses the power of absorbing oxygen as it passes through the lung capillaries and of yielding it up to the tissues as it _ passes through the tissue capillaries. In the arterial blood it is known as oxyhemoglobin, and in the venous blood as deoxy- or reduced-hemoglobin. When hydrolysed by acids or alkahes, hemoglobin undergoes a cleavage into a proteid, globin, and a pigment hematin. (b) Myohematin. — Myohematin is a proteid supposed to be present in muscle. It has never been isolated, hence its chemic features are unknown. Spectroscopic examination in- dicates that it is capable of absorbing and again yielding up oxygen. For this reason it is believed to be a derivative of hemoglobin. GLUCO-PROTEIDS. (a) Mucin. — Mucin is the proteid which gives the mucus, secreted by the epithelial cells of the mucous membranes and related glands, its viscid, tenacious character. It is also a constituent of the intercellular substance of the connective tissues. It is readily precipitated by acetic acid. When heated with dilute acids, mucin undergoes a cleavage into a simpler pro- teid and a carbohydrate termed mucose, which is capable of reducing Fehhng's solution. (b) Mucoids. — The mucoids resemble the mucins though differ- ing from them in solubility and in not being precipitable from alkaline solutions by acetic acid. They are found in the vitreous humor, white of egg, cartilage, and in other situations. They differ slightly one from the other in proper- ties and chemic composition. They yield on decomposition a carbohydrate. NUCLEO-PROTEIDS. The nucleo-proteids are obtained from the nuclei and cell-sub- stance of tissue-cells. Chemically they are characterized by the presence of phosphorus in relatively large amounts. When hydrolysed, they separate into a proteid and a nuclein. 36 TEXT-BOOK OF PHYSIOLOGY. The nucleins derived from cell nuclei can be still further sepa- rated into a simpler proteid and nucleic acid, which latter in turn yields phosphoric acid and the so-called purin bases, xanthin, hypoxanthin, adenin, and guanin. All nucleins which yield the purin bases are termed true nucleins. The nucleins derived from caseinogen, vitellin, and probably cell protoplasm can be separated by chemic methods into a pro- teid and phosphoric acid only. For the reason that they do not give origin to purin bases they are termed pseudo- or paranucleins. {a) Caseinogen. — This is the principal proteid of milk, in which it exists in association with an alkah, and hence was formerly regarded as an alkah-albumin. It is precipitated by acetic acid and by magnesium sulphate. It is coagulated by rennet — that is, separated into an insoluble proteid, casein or tyrein, and a soluble albumin. Calcium phosphate seems to be the natural alkali necessary to this process, for if it be removed by dialysis, or precipitated by the addition of potassium oxalate, coagulation does not take place. (&) Vitellin. — Vitellin is a constituent of the vitelhs or yolk of eggs. It diiTers from other proteids in the fact that it is semicrystalline in character. Though usually regarded as a nucleo-proteid it is not definitely known whether or not it contains phosphorus in its composition. ALBUMINOIDS. The albuminoids constitute a group of substances similar to the proteids in many respects, though differing from them in others. When obtained from the tissues, in which they form an organic basis, they are found to be amorphous, colloid, and when decom- posed yield products similar to those of the true proteids. The principal members of this group are as follows: {a) Collagen, Ossein. — These are two closely alhed, if not identical, substances, found respectively in the white fibrous connec- tive tissue and in bone. When the tendons of muscles, the ligaments, or decalcified bone are boiled for several hours, the collagen and ossein are converted into soluble gelatin, which, when the solution cools, becomes solid. (h) Chondrigen. — This is supposed to be the organic basis of the more permanent cartilages. When the latter are boiled, they yield a substance which gelatinizes on cooling, and to which the name chondrin has been given. Chondrin, how- ever, is not a pure gelatin, but has associated with it a com- pound proteid known as chrondro-mucoid. CHEMIC COMPOSITION OF THE HUMAN BODY. 37 (c) Elastin is the name given to the substance composing the fibers of tlie yellow, elastic connective tissue. {d) Keratin is the substance found in all horny and epidermic tissues, such as hairs, nails, scales, etc. It differs from most proteids in containing a high percentage of sulphur. The average percentage composition of several proteids is shown in the following analyses: c. H. M. o. s. Egg-albumin, 52.9 7.2 15.6 23.9 0.4 (Wiirtz). Serum-albumin, 53.0 6.8 16.0 22.29 i-77 (Hammersten). Casein, 53.3 7.07 15.91 22.03 0.82 (Chittenden and Painter). Myosin, 52-82 7. 11 16.77 21.90 1.27 (Chittenden and Cummins). The molecular composition of the proteids is not definitely known, and the formulae which have been suggested are therefore only approximative. Leow assigns to albumin the formula C-jHjjjNjg- O22S, while Schiitzenberger raises the numbers to C24oH392Ng5075S3, either of which shows that the proteid molecule is extremely complex. As a class, the proteids are characterized by the following prop- erties : 1. Indiffusibility. — None of the proteids normally assumes the crystalline form, and hence they are not capable of diffusing through parchment or an animal membrane. Peptone, a product of the digestion of proteids, is an exception as regards its diffu- sibility. As met with in the body, all proteids are amorphous, but vary in consistence from the liquid to the soHd state. The colloid character of the proteids permits of their separation and purification from crystalloid difi'usible compounds by the process of dialysis. 2. Solubility. — Some of the proteids are soluble in water, others in solutions of the neutral salts of varying degrees of concentration, in strong acids and alkalies. All are insoluble in alcohol and ether. 3. Coagulability. — Under the influence of heat and various acids and animal ferments, the proteids readily pass from the soluble liquid state to the insoluble soHd state, attended by a permanent alteration in their chemic composition. To this change the term coagulation has been given. The various proteids not only coagulate at different temperatures, but with different chemic reagents— distinctive features which permit not only of their detection, but separation. Proteids are capable of pre- cipitation without losing their solubility by ammonium sulphate, sodium chlorid, and magnesium sulphate. 4. Fermentability. — In the presence of specific microorganisms — ■ bacteria — the proteids, owing to their complexity and instability, are prone to undergo disintegration and reduction to simpler 38 . TEXT-BOOK OF PHYSIOLOGY. compounds. This decomposition or putrefaction occurs most readily when the conditions most favorable to the growth of bacteria are present — viz., a temperature varying from 25° C. to 40° C, moisture, and oxygen. The intermediate as well as the terminal products of the decomposition of the proteids are numerous, and vary with the composition of the proteid and the specific physiologic action of the bacteria. Among the intermediate products is a series of alkaloid bodies, some of which possess marked toxic properties, known as ptomains. The toxic symptoms which frequently follow the ingestion of foods in various stages of putrefaction are to be attributed to these compounds. The terminal products are represented by hydrogen sulphid, ammonia, carbon dioxid, fats, phosphates, nitrates, etc. Color Tests for Proteids. — When proteids are present in solu- tion, they may be detected by the following color reactions — viz.: 1. Xanthoproteic- The solution is boiled with nitric acid for several minutes, when the proteid assumes a light yellow color. After the solution has cooled, the addition of ammonia changes the color to an orange or amber-red. 2. The rose-red reaction. The solution is boiled with acid nitrate of mercury (Millon's reagent) for a few minutes, when the coagulated proteid turns a purple-red color. 3. The blue- violet reaction. A few drops of copper sulphate solution are first added to the proteid solution, and then an excess of sodium hydroxid. A blue- violet color is produced, which deepens somewhat on heating, but no further change ensues. INORGANIC CONSTITUENTS. The inorganic compounds and mineral constituents obtained from the solids and fluids of the body are very numerous, and, in some instances, quite abundant. Though many of the compounds thus obtained are undoubtedly derivatives of the tissues and necessary to their physical and physiologic activity, others, in all probability, are decomposition products, or transitory constituents introduced with the food. Of the inorganic compounds, the following are the most important: WATER. Water is the most important of the inorganic constituents, as it is indispensable to hfe. It is present in all the tissues and fluids without exception, varying from 99 per cent, in the saliva to 80 per cent, in the blood, 75 per cent, in the muscles to 2 per cent, in the enamel of the teeth. The total quantity contained in a body CHEMIC COMPOSITION OF THE HUMAN BODY. 39 weighing 75 kilograms (165 pounds) is 52.5 kilograms (115 pounds). Much of the water exists in a free condition, and forms the chief part of the fluids, giving to them their characteristic degree of fluidity. Possessing the capability of holding in solution a large number of inorganic as well as some organic compounds, and being at the same time dift'usible, it renders an interchange of materials between all portions of the body possible. It aids in the absorption of new material into the blood and tissues, and at the same time it transfers waste products from the tissues to the blood, from which they are finally ehminated, along with the water in which they are dissolved. A portion of the water is chemically combined with other tissue con- stituents and gives to the tissues their characteristic physical properties. The consistency, elasticity, and pliability are, to a large extent, con- ditioned by the amount of water they contain. The total quantity of water eliminated by the kidneys, lungs, and skin amounts to about 3 kilograms (6| pounds). CALCroM COMPOUNDS. Calcium phosphate, Ca3(P04)2, has a very extensive distribu- tion throughout the body. It exists largely in the bones, teeth, and to a sught extent in cartilage, blood, and other tissues. Milk con- tains 0.27 per cent. The sohdity of the bones and teeth is almost entirely due to the presence of this salt, and is, therefore, to be regarded as necessary to their structure. It enters into chemic union with the organic matter, as shown by the fact that it can not be separated from it except by chemic means, such as hydrochloric acid. Though insoluble in water, it is held in solution in the blood and milk by the proteid constituents, and in the urine by the acid phosphate of soda. The total quantity of calcium phosphate which enters into the formation of the body has been estimated at 2.5 kilograms. The amount ehminated daily from the body has been estimated at 0.4 gm., a fact which indicates that nutritive changes do not take place with much rapidity in those tissues in which it is contained. Calcium carbonate, CaCOg, is present in practically the same situations in the body as the phosphate, and plays essentially the same role. It is, however, found in the crystalline form, aggregated in small masses in the internal ear, forming the otoliths, or ear stones. Though insoluble, it is held in solution by the carbonic acid diffused through the fluids. Calcium fluorid, CaF,, is found in bones and teeth. SODIUM COMPOUNDS. Sodium chlorid, NaCl, is present in all the tissues and fluids of the body, but especially in the blood, 0.6 per cent., lymph, 0.5, 40 TEXT-BOOK OF PHYSIOLOGY. and pancreatic juice, 0.25 per cent. The entire quantity in the body has been estimated at about 200 gm. Sodium chlorid is of much importance in the body, as it determines and regulates to a large extent the phenomena of diffusion which are there constantly taking place. This is illustrated by the fact that a solution of albumin placed in the rectum without the addition of this salt will not be absorbed. When the salt is added, absorption takes place. The ingested water is absorbed into the blood largely in consequence of the percentage of this salt which it contains. The normal percentage of sodium chlorid in the blood-plasma assists in maintaining the shape and structure of the red blood-corpuscles by determining the amount of water entering into their composition. The same is true of other tissue elements. Sodium chlorid also influences the general nutritive process, in- creasing the disintegration of the proteids, as shown by the increased amount of urea excreted. During its existence in the body it under- goes chemic transformations or decompositions, yielding its chlorid to form the potassium chlorid of the blood-corpuscles and muscles and to form the hydrochloric acid of the gastric juice. Sodium phosphate, Na2HPO^, is found in all sohds and fluids of the body, to which, with but few exceptions, it imparts an alkahne reaction. This is especially true of blood, lymph, and tissue fluids generally. It is essential to physiologic action that all tissue elements should be bathed by an alkahne medium. Sodium carbonate, NajCOg, is generally found in association with the preceding salt. As it is an alkahne compound, it also assists in giving to the blood and lymph their characteristic alkalinity. In carnivorous animals the sodium phosphate is the more abundant, while in the herbivorous animals the sodium carbonate is the more abundant. Sodium sulphate, Na^SO^, is present in many of the tissues and fluids, especially in the urine. Though introduced in the food, it is also, in all probabihty, formed in the body from the decomposition and oxidation of the proteids. POTASSroM COMPOUNDS. Potassium chlorid, KCl, is met with in association with sodium chlorid in almost all situations in the body. It preponderates, how- ever, in the tissue elements, especially in the muscle tissue, nerve tissue, and red corpuscles. The plasma with which these structures are bathed contains but a very small amount of this salt, but, as previously stated, a relatively large quantity of sodium chlorid. Though introduced to some extent in the food, it is very likely that it is also formed through the decomposition of the sodium chlorid. CHEMIC COMPOSITION OF THE HUMAN BODY 41 Potassium phosphate, KjHPO^, is found in association with sodium phosphate in all the fluids and sohds. As it has similar chemic properties, its functions are practically the same. Potassium carbonate, KgCOg, is generally found with the pre- ceding salt. MAGNESIUM COMPOUNDS. Magnesium phosphate, Mg3(POj2> is found in all tissues, in association with calcium phosphate, though in much smaller quantity. Magnesium carbonate, MgCOg, occurs only in traces in the blood. Both of these compounds have functions similar to the calcium compounds, and exist, in all probabihty, under similar conditions. IRON COMPOUNDS. Iron is a constituent of the coloring-matter of the blood. Traces, however, are also found in lymph, bile, gastric juice, and in the pigment of the eyes, skin, and hair. The amount of iron contained in a body weighing 75 kilograms is about 3 gm. It exists under various forms — e. g., ferric oxid, and in combination with organic compounds. Chemic analysis thus shows that the chemic elements into which the compounds may be resolved by an ultimate analysis do not exist in the body in a free state, but only in combination, and in char- acteristic proportions, to form compounds whose properties are the resultant of those of the elements. Of the four principal elements which make up 97 per cent, of the body, O, H, N are extremely mobile, elastic, and possessed of great atomic heat. C, H, N are distinguished for the narrow range of their affinities, and for their chemic inertia. C possesses the great atomic cohesion. O is noted for the number and intensity of its combinations. As the properties of the compounds formed by the union of elements must be the resultants of the properties of the elements themselves, it follows that the ternary compounds, starches, sugars, and fats must possess more or less inertia, and at the same time instability; while in the more complex proteids, in which sulphur and phosphorus are frequently combined with the four principal elements, molecular instabihty attains its maximum. As all the foregoing compounds possess in varying degrees the properties of inertia and instability, it follows that hving matter must possess corresponding properties, and the capability of undergoing unceas- ingly a series of chemic changes, both of composition and decom- position, in response to the chemic and physical influences by which it is surrounded, and which underhe all the phenomena of Hfe. 42 TEXT-BOOK OF PHYSIOLOGY. PRINCIPLES OF DISSIMILATION. In addition to the previously mentioned compounds, — viz., carbohydrates, fats, proteids, and inorganic salts, — there is obtained by chemic analysis from the tissues and fluids of the body: 1. A number of organic acids, such as acetic, lactic, oxahc, butyric, propionic, etc., in combination with alkaline and earthy bases. 2. Organic compounds, such as alcohol, glycerin, cholesterin. 3. Pigments, such as those found in bile and urine. 4. Crystalhzable nitrogenized bodies, such as urea, uric acid, xanthin, hippuric acid, creatin, creatinin, etc. While some few of these compounds may possibly be regarded as necessary to the physiologic integrity of the tissues and fluids, the majority of them are to be regarded as products of dissimilation of the tissues and foods in consequence of functional activity, and represent stages in their reduction to simpler forms previous to being eliminated from the body. CHAPTER III. PHYSIOLOGY OF THE CELL. A microscopic analysis of the tissues shows that they can be resolved into simpler elements, termed cells, which may, therefore, be regarded as the primary units of structure. Though cells vary considerably in shape, size, and chemic composition in the different tissues of the adult body, they are, nevertheless, descendants from typical cells, known as embryonic or undifferentiated cells, examples of which are the leukocytes of the blood and lymph and the first offspring of the fertihzed ovum. Ascending the Une of embryonic development, it will be found that every organized body originates in a single cell — the ovum. As the cell is the elementary unit of all tissues, the function of each tissue must be referred to the function of the cell. Hence the cell may be defined as the primary anatomic and physiologic unit of the organic world, to which every exhibition of hfe, whether normal or abnormal, is to be referred. Structure of Cells. — Though cells vary in shape and size and internal structure in dift'erent portions of the body, a typical cell may be said to consist mainly of a gelatinous substance forming the body of the cell, termed protoplasm or bioplasm, in which is embedded a smaller spheric body, the nucleus. The shape of the adult cell varies according to the tissue in which it is found; when young and free to move in a fluid medium, the cell assumes a spheric form, but when subjected to pressure, may become cyHndric, fusiform, polygonal, or stellate. Cells vary in size within wide hmits, ranging from -3x00 of an inch, the diameter of a red blood- corpuscle, to -j^ of an inch, the diameter of the large cells in the gray matter of the spinal cord. (See Fig. 2.) The cell protoplasm consists of a soft, semifluid, gelatinous material, varying somewhat in appearance in different tissues. Though frequently homogeneous, it often exhibits a finely granular appearance under medium powers of the microscope. Young cells consist almost entirely of clear protoplasm. Mature cells contain, according to the tissue in which they are found, material of an en- tirely different character — e. g., small globules of fat, granules of glycogen, mucigen, pigments, digestive ferments, etc. Under high powers of the microscope the cell protoplasm is found to be pervaded by a network of fibers, termed spongio plasm, in the meshes of which is contained a clearer and more fluent substance, the hyaloplasm. 43 44 TEXT-BOOK OF PHYSIOLOGY. The relative amount of these two constituents varies in different cells, the proportion of hyaloplasm being usually greater in young cells. The arrangement of the fibers forming the spongioplasm also varies, the fibers having sometimes a radial direction, in others a concentric disposition, but most frequently being distributed evenly in all directions. In many cells the outer portion of the cell proto- plasm undergoes chemic changes and is transformed into a thin, transparent, homogeneous membrane, — the cell membrane, — v^hich completely incloses the cell substance. The cell membrane is permeable to water and watery solutions of various inorganic and organic substances. It is, however, not an essential part of the cell. The nucleus is a small vesicular body embedded in the proto- plasm near the center of the cell. In the resting condition of the cell Nuclear membrane. ^ Linin. Nuclear fluid (matrix). Nucleolus. Chromatin-cords (nuclear network). Nodal enlargements of the chromatin. Cell membrane. Exoplasm. Microsomes. Centrosoma. Spongioplasm. Hyaloplasm. Foreign inclosures. Fig. 2. — Diagram of a Cell. Microsomes and spongioplasm are only partly drawn. — (Stohr.) it consists of a distinct membrane, composed of amphipyrenin, in- closing the nuclear contents. The latter consists of a homogeneous amorphous substance, — the nuclear matrix, — in which is embedded the nuclear network. It can often be seen that a portion of one side of the nucleus, called the pole, is free from this network. The main cords of the network are arranged as V-shaped loops about it. These main cords send out secondary branches or twigs, which, uniting with one another, complete the network. The nuclear cords are composed of granules of chromatin, — so called because of its affinity for certain staining materials, — held together by an achromatin substance known as linin. Besides the nuclear network, there are embedded in the nuclear matrix one or more small bodies composed PHYSIOLOGY OF THE CELL. 45 of py renin, known as nucleoli. At the pole of the nucleus, either within or just without in the protoplasm, is a small body, the centro- some, or pole corpuscle. Chemic Composition of the Cell. — The composition of hving protoplasm is ditiicult of determination, for the reason that all chemic and physical methods employed for its analysis destroy its vitality, and the products obtained are pecuhar to dead rather than to Uving matter. Moreover, as protoplasm is the seat of constructive and destructive processes, it is not easy to determine whether the products of analysis are crude food constituents or cleavage or disintegration products. Nevertheless, chemic investigations have shown that even in the living condition protoplasm is a highly complex compound — the resultant of the intimate union of many different substances. About 75 per cent, of protoplasm consists of water and 25 per cent, of sohds, of which the more important compounds are various nucleo-proteids (characterized by their large percentage of phos- phorus), globuhns, traces of lecithin, cholesterin, and frequently fat and carbohydrates. Inorganic salts, especially the potassium, sodium, and calcium chlorids and phosphates, are almost invariable and essential constituents. MANIFESTATIONS OF CELL LIFE. Growth, Nutrition, and Reproduction. — All cells exhibit the three fundamental properties of hfe — viz., growth, nutrition, repro- duction. All cells when newly reproduced are extremely small, but b}^ the absorption of nutritive material from their surrounding me- dium, the h-mph, they gradually grow until they attain their mature size. This is accomplished by the power which living material pos- sesses of not only absorbing nutritive material, but of subsequently assimilating it, organizing it, transforming it into material like itself and endowing it with its own ph}'siologic properties. In the physiologic condition the hving material of the cell, the bioplasm, is the seat of a series of chemic changes which vary in activity from moment to moment, and on the continuance of which its vitality depends. Some of these changes are destructive or dis- integrative in character, whereby the hving material is reduced through a series of descending chemic stages to simpler compounds such as urea, uric acid, carbon-dioxid, etc., and which are finally eliminated from the body. To these disintegrative changes the terms dissimilation and kataholism are applied; other of the changes are constructive or integrative in character, whereby the hving ma- terial is repaired and restored to its former condition, and out of new" nutritive material through a series of ascending chemic stages. 46 TEXT-BOOK OF PHYSIOLOGY. To these integrati\'e changes the terms assimilation and anabolism are given. The sum total of all changes which go on in the cell, both assimilative and dissimilative, are embraced under the general term nulrltion, or metabolism. During the course of its physiologic activities the bioplasm of the cell produces material of an entirely different character which varies with the cell, such as fat, glycogen, mucigen, ferments, etc., which are frequently spoken of as meta- bolic products. Every cell presents in its nutritive activities an epitome of the nutritive activities of the body as a whole. Physiologic Properties of Protoplasm. — All Hving protoplasm possesses properties which serve to distinguish and characterize it — viz., irritability, conductivity, and motility. Irritability, or the power of reacting in a definite manner to some form of external excitation, whether mechanic, chemic, or electric, is a fundamental property of all living protoplasm. The character and extent of the reaction will vary, and will depend both on the nature of the protoplasm and the character and strength of the stimulus. If the protoplasm be muscle, the. response will be a con- traction; if it be gland, the response will be secretion; if it be nerve, the response will be a sensation or some other form of nerve activity. Conductivity, or the power of transmitting molecular disturbances arising at one point to all portions of the irritable material, is also a characteristic feature of all protoplasm. This power, however, is best developed in that form of protoplasm found in nerves, which serves to transmit, with extreme rapidity, molecular disturbances arising at the periphery to the brain, as well as in the reverse direction. Muscle protoplasm also possesses the same power in a high degree. Motility, or the power of executing apparently spontaneous movements, is exhibited by many forms of cell protoplasm. In addition to the molecular movements which take place in certain cells, other forms of movement are exhibited, more or less constantly, by many cells in the animal body — e. g., the waving of cilia, the ameboid movements and migrations of white blood-corpuscles, the activities of spermatozooids, the projection of pseudopodia, etc. These movements, arising without any recognizable cause, are fre- quently spoken of as spontaneous. Strictly speaking, however, all protoplasmic movement is the resultant of natural causes, the true nature of which is beyond the reach of present methods of investi- gation. Reproduction. — Cells reproduce themselves in the higher ani- mals in two ways — by direct division and by indirect division, or karyokinesis. In the former the nucleus becomes constricted, and divides without any special grouping of the nuclear elements. It is probable that this occurs only in disintegrating cells, and never in PHYSIOLOGY OF THE CELL. 47 a physiologic multiplication. In division by karyokinesis (Fig. 3) there is a progressive rearranging and definite grouping of the nucleus, the result of which changes is the division of the centrosome, the chromatin, and the rest of the nucleus into two equal portions, which form the nuclei. Following the division of the nuclei, the proto- plasm divides. The process may be divided into three phases: I. Prophase. — The centrosome, at first small and lying within the nucleus, increases in size and moves into the protoplasm, where it lies near the nucleus, surrounded by a clear zone, from which delicate threads radiate throudi an area known as the attraction Close Skein (^■iewed from the side). Polar field. Loose Skein (viewed from above — i. e., from the pole). Mother Stars (\iewed from the side). Spindle. Mother Star (\-iewed Daughter Star from above). %i.*^ Beginning Completed Di\ision of the Protoplasm. Fig. 3.— Karyokinetic Figures Observed in the Epithelium of the Or.a.l Cavity of a Sal,a.maxder. The picture in the upper right-hand corner is from a section through a dividing egg of Siredon pisciformis. Neither the centrosomes nor the first stages of the development of the spindle can be seen by this mag- nification. X 560. — {Stohr.) Sphere. The nucleus enlarges and becomes richer in chromatin. The lateral twigs of the chromatin cords are drawn in, while the main cords become much contorted, These cords have a general direction transverse to the long axis of the cell, and parallel to the plane of future cleavage. They are seen as V-shaped segments or loops, chromosomes, having their closed ends directed toward a common center, the polar field, while the other ends interdigitate on the opposite side of the nucleus — the anti-pole. The polar field corresponds to the area occu-. 48 TEXT-BOOK OF PHYSIOLOGY. pied by the centrosome. This arrangement is known as the close skein; but as the process goes on, the chromosomes become thicker, shorter and less contorted, producing a much looser arrangement, known as the loose skein. During the formation of the loose skein, the centrosome divides into two portions, which move apart to positions at the opposite ends of the long axis of the nucleus. At the same time dehcate achromatin fibers make their appearance, arranged in the form of a double cone, the apices of which correspond in position to the centro- somes. This is known as the nuclear spindle. During the prophase the nuclear membrane and the nucleoli disappear. 2 The Metaphase. — The two centrosomes are at opposite ends of the long axis of the nucleus, each surrounded by an attraction sphere, now called the polar radiation. The chromosomes become yet shorter and thicker, and move toward the equator of the nucleus, where they lie with their closed ends toward the axis, presenting the appearance, when seen from the poles, of a star, — the so-called mother star, or monaster. While moving toward the equator of the nucleus, and often earher, each chromosome undergoes longitudinal cleavage, the sister loops remaining together for a time. Upon the completion of the monaster, one loop of each pair passes to each pole of the nucleus, guided, and perhaps drawn by the threads of the nuclear spindle. The separation of the sister segments begins at their apices, and as the open ends are drawn apart they remain connected by delicate achromatin filaments drawn out from the chromo- somes. This separation of the daughter chromosomes, and their movement toward the daughter centrosomes, is called metakinesis. As they approach their destination, we have the appearance of two stars in the nucleus — the daughter stars, or diasters. 3. Anaphase. — The daughter stars undergo, in reverse order, much the same changes that the mother star passed through. The chromosomes become much convoluted, and perhaps united to one another, the lateral twigs appear, and the chromatin resumes the appearance of the resting nucleus. The nuclear spindle, with most of the polar radiation, disappears, and the nucleoh and the nuclear membrane reappear, thus forming two complete daughter nuclei. Meanwhile the protoplasm becomes con- stricted midway between the young nuclei. This constriction gradually deepens until the original cell is divided, with the formation of two complete cells. CHAPTER IV. HISTOLOGY OF THE EPITHELIAL AND CONNECTIVE TISSUES. I. EPITHELIAL TISSUE. The epithelial tissue consists of one or more layers of cells resting on a homogeneous membrane, the other side of which is abundantly supphed with blood-vessels and nerves. The form of the epithelial cell varies in different situations, and may be flattened, cuboid, spheroid, or columnar. (See Figs. 4, 5, and 6.) The form of the cell in all instances is related to some specific function. When arranged in layers or strata, the cells are cemented toorether bv an intercellular substance. Fig. 4. — Epithelial Cells of Rabbit, Isolated. X 560. i. Squamous cells (mucous membrane of mouth). 2. Columnar cells (corneal epithelium). 3 Columnar cells, with cuticular border, s (intestinal epithelium). 4. Ciliated cells; h, cilia (bronchial epithelium) .^(^/o/tr.) The epithehal tissue forms a continuous covering for the surfaces of the body. The external investment (the skin) and the internal investment (the mucous membrane, which lines the entire ahmentary canal as well as associated body cavities) are both formed, in all situations, by the homogeneous basement membrane, covered with one or more layers of cells. The glands of the skin, the lungs and the glands in connection with the alimentary canal and the uro-geni- tal apparatus are formed of the same elemental structures. All materials, therefore, whether nutritive, secretory, or excretory, must pass through epithehal cells before they can enter into the formation of the blood or be eliminated from it. The nutrition of the epithelial tissue is maintained by the nutritive material derived from the blood 4 49 50 TEXT-BOOK OF PHYSIOLOGY. diffusing itself into and through the basement membrane. Chemi- cally, the epithehal cells of the epidermis — hair, nails, etc. — are composed of an albuminoid material (keratin), a small quantity of water, and inorganic salts. In other situations, especially on the mucous membranes, the cells consist largely of mucin, in associa- tion with other proteids. The consistency of epithehum varies in accordance with external influences, such as the presence or absence of moisture, pressure, friction, etc. This is well seen in the skin of the palms of the hands and the soles of the feet — situations where it acquires its greatest density. In the aHmentary canal, in the lungs, and in other cavities, where the reverse conditions prevail, the epi- thelium is extremely soft. Epithelial tissues also possess varying degrees of cohesion and elasticity — physical properties which en- able them to resist considerable pressure and distention without ^ having their physiologic in- - tegrity destroyed. Inasmuch I Fig. 5. — Stratified Squamous Epi- thelium (Larynx of Man). X 240. I. Columnar cells. 2. Prickle-cells. 3. Squamous cells. —{Stohr.) Fig. 6. — Stratified Ciliated Epi- thelium. X 560. From the res- piratory nasal mucous membrane of man. i. Oval cells. 2. Spindle- shaped cells. 3. Columnar cells. —{Stohr.) as these tissues are poor conductors of heat, they assist in preventing too rapid radiation of heat from the body, and cooperate with other mechanisms in maintaining the normal temperature. The physiologic activity of all epithehal tissue depends on a due supply of nutritive material derived from the blood, which not only maintains its nutrition, but affords those materials out of which are formed the secretions of the glands, whether of the skin or mucous membrane. The cells hning the blood-vessels, the lymph-vessels, the peri- toneal, pleural, pericardial, and other closed cavities are usually termed endothelial cells. These cells are flat, irregular in shape, with borders more or less wavv or sinuous in outline. THE CONNECTIVE TISSUES. 51 Functions of Epithelial Tissue. — In succeeding chapters the form, chemic composition, and functions of epithelial cells will be considered in connection with the functions of the organs of which they constitute a part. In this connection it may be stated in a general way that the functions of the epithehal tissues are: 1 . To serve on the surface of the body as a protective covering to the underlying structures which collectively form the true skin, thus protecting them from the injurious influences of moisture, air, dust, microorganisms, etc., which would otherwise impair their vitality. Wherever continuous pressure is applied to the skin, as on the palms of the hands and soles of the feet, the epithelium increases in thickness and density, and thus prevents undue pressure on the nerves of the true skin. The density of the epidermis enables it to resist, within limits, the injurious influence of acids, alkalies, and poisons. 2. To promote absorption. Inasmuch as the skin and mucous mem- branes cover the surfaces of the body, it is obvious that all nutritive material entering the body must first traverse the epi- thelial tissue. Owing to their density, however, the epithelial cells covering the skin play but a feeble role as absorbing agents in man and the higher animals. The epithelium of the mucous membrane of the ahmentary canal, particularly that of the small intestine, is especially adapted, from its situation, consistency, and properties, to play the chief role in the absorption of new materials into the blood. The epithelium Hning the air-vesicles of the lungs is engaged in promoting the absorption of oxygen and the exhalation of carbon dioxid. 3. To form secretions and excretions. Each secretory gland con- nected with the surfaces of the body is Hned by epithelial cells, which are actively concerned in the formation of the secretion peculiar to the gland. Each excretory organ is similarly provided with epithelial cells, which are engaged either in the production of the constituents of the excretion or in their removal from the blood. 2. THE CONNECTIVE TISSUES. The connective tissues, in' their collective capacity, constitute a framework which pervades the body in all directions, and, as the name imphes, serve as a bond of connection between the individual parts, at the same time affording a basis of support for the muscle, nerve, and gland tissues. The connective-tissue group includes a number of varieties, among which may be mentioned the areolar, adipose, retiform, white fibrous, yellow elastic, cartilaginous and osseous. Notwithstanding their apparent diversity, they possess many points of similarity. They have a common origin, developing 52 TEXT-BOOK OF PHYSIOLOGY. from the same embryonic material; they have much the same struc- ture, passing imperceptibly into one another, and perform practically the same functions. Areolar Tissue. — This variety is found widely distributed throughout the body. It serves to unite the skin and mucous mem- brane to the structures on which they rest; to form sheaths for the support of blood-vessels, nerves, and lymphatics; to unite into com- pact masses the muscular tissue of the body, etc. Examined with the naked eye, it presents the appearance of being composed of bundles of fine fibers interlacing in every direction. In the embryonic state the elements of this form of connective tissue are united by a ground substance, gelatinous in character. In the adult state this substance shrinks and largely disappears, leaving intercommunicating, spaces of varying size and shape, from which the tissue takes its name. When subjected to the action of various reagents, and examined microscopically, the bundles can be shown to consist of extremely dehcate, colorless, transparent, wavy libers, which are cemented together by a ground substance composed In super- posed layers Fig. 7. — Adipose Tissue. — {Stdhr.) Fig. 8. — Fat-Cells from the Axilla OF Man. I. The equator of the cell in focus. 2. The objective somewhat elevated. 3, 4. Forms changed by pressure, p. Traces of protoplasm in the vicinity of the flat nucleus k. — {Stolir.) largely of mucin. Other fibers are also observed, which are dis- tinguished by a straight course, a sharp, well-defined outhne, a ten- dency to branch and unite with adjoining fibers, and to curl up at their extremities when torn. From their color and elasticity they are known as yellow elastic fibers. Distributed throughout the meshes of the areolar tissue are found flattened, irregularly branched, or stellate corpuscles, connective -tissue corpuscles, plasma cells, and granule cells. Adipose Tissue. — This tissue, which exists very generally throughout the body, though found most abundantly beneath the THE CONNECTIVE TISSUES. 53 skin, around the kidneys, and in the bones, is practically but a modification of areolar tissue. In these situations it presents itself in small masses or lobules of varying size and shape, surrounded and penetrated by the fibers of connective tissue. (See Fig. 7.) Microscopic examination shows that these masses consist of small vesicles or cells, round, elliptical, or polyhedral in shape, depending somewhat on pressure. (See Fig. 8.) Each vesicle consists ojf a thin, colorless, protoplasmic membrane, thickened at one point, in which a nucleus can usually be detected. This membrane incloses a globule of fat, which during life is in the liquid state. It is composed of olein, stearin, and palmitin. The origin of the fat is> to be referred to a retrograde change in the protoplasmic material of the connective-tissue cells. When this protoplasm becomes rich in carbon and hydrogen, it is speedily converted into fat, which makes its appearance in the form of minute drops in different por- tions of the cell. As the drops accu- mulate, at the expense of the cell protoplasm, they gradually coalesce, until there remains but a thin stratum / of the protoplasm, which forms the wall of the vesicle. Adipose tissue may, therefore, be regarded as areolar ,% tissue, in which, and at the expense of some of its elements, fat is stored for fj the future needs of the organism. A . : ^ diminution of food, especially of fat _ and carbohydrates, is promptly fol- ""^i^ lowed by an absorption of fat by fig. 9. — Connective -Tissue the blood-vessels and by its transfer- Bundles of Various Thick- enre to the tissues where it is either nesses of the Intermuscu- ence to tne tissues, wneie it is eitner ^^ connective Tissue of utilized for tissue construction or for man. X 240.— (Stohr.) oxidation purposes. In the situations in which adipose tissue is found it seems, by its chemic and physical properties, to assist in the prevention of a too rapid radia- tion of heat from the body, to give form and roundness, and to diminish angularities, etc. Retiform and adenoid tissue are also modifications of areolar tissue. The meshes of the former contain but Httle ground sub- stance, its place being taken by fluids; the meshes of the latter contain large numbers of lymph corpuscles. Fibrous Tissue. — This variety of connective tissue is widely distributed throughout the body. It constitutes almost entirely the ligaments around the joints, the tendons of the muscles, the mem- branes covering organs such as the heart, liver, nervous system, bones, etc. All fibrous tissue, wherever found, can be resolved into 54 TEXT-BOOK OF PHYSIOLOGY. elementary bundles, Avhich on microscopic examination are seen to consist of delicate, wavy, transparent, homogeneous fibers, which pursue an independent course, neither branching nor uniting with adjoining fibers. (See Fig. 9.) A small amount of ground substance serves to hold them together. Fibrous tissue is tough and inexten- sible, and in consequence is admirably adapted to fulfil various mechanical functions in the body. It is, however, quite pliant, bend- ing easily in all directions. When boiled, fibrous tissue yields gelatin, a derivative of collagen. Elastic Tissue. — -The fibers of elastic tissue are usually associated in varying proportions with the white fibrous tissue; but in some structures — as the ligamentum nuchae, the ligamenta subflava, the Fig. 10. — Elastic Fibers. X 560. A. Fine elastic fibers, /, from intermuscular connective tissue of man; b, connective-tissue bundles swelled by treatment with acetic acid. B. Very thick elastic fibers, /, from ligamentum nuchas of ox; b, connective-tissue bundles. C. From a cross-section of the ligamentum nuchae of ox; /, elastic fibers; b, connective-tissue bundles. — (Stohr.) middle coat of the larger blood-vessels — the elastic fibers are almost the only elements present, and give to these structures a distinctly yellow appearance. The fibers throughout their course give off many branches, which unite with adjoining branches to form a more or less close network. As the name implies, these fibers are highly elastic, and are capable of being extended as much as 60 per cent, before breaking. (See Fig. 10.) Cartilaginous Tissue. — This form of connective tissue differs from the preceding varieties chiefly in its density. As a rule, it is firm in consistency, though somewhat elastic. It is opaque, bluish- white in color, though in thin sections translucent. All cartilaginous THE CONNECTIVE TISSUES. 55 tissues consist of connective-tissue cells embedded in a solid ground substance. According to the amount and texture of the ground substance, three principal varieties may be distinguished: I. Hyaline cartilage, in which the cells, relatively few in number, are embedded in an abundant quantity of ground substance (Fig. 1 1). The body of the cells is in many instances distinctly marked off from the surrounding substance by concentric hues or fibers, which form a capsule for the cell. Repeated division of the cell substance takes place, until the whole capsule is completely occupied by daughter cells. The ground substance is pervaded by minute channels, which communicate on one hand with the li \ Fig. II. — Hyaline C.-^rtilage. X 240. A. Surface view of the ensiform process of frog, fresh; p, protoplasm of cartilage-cell, which entirely tills the lacuna; k, nucleus; g, hyaline matrix. B. Portion of cross-section of human rib-cartilage several days after death; e.xamined in water: the protoplasm, s, of the cartilage- cells has withdrawn from the walls of the lacunae, h; the nuclei are invisible. I. Two cells within one capsule, k; x, a developing partition. 2. Five cartilage- cells within one capsule; the lowest cell has fallen out, and here only the empty space is seen. 3. Capsule cut obliquely, and apparently thicker on one side. 4. Capsule not cut, but showing the cell within, g. Hyaline matri.x transformed into rigid fibers, /. — (Slohr.) spaces around the cells, and on the other with lymph-spaces in the connective tissue surrounding the cartilage. By means of these channels, nutritive fluid can permeate the entire structure. Hyahne cartilage is found on the ends of the long bones, where it enters into the formation of the joints; between the ribs and sternum, forming the costal cartilage, as well as in the nose and larynx. 2. White fibro-cartilage, the ground substance of which is pervaded by white fibers, arranged in bundles or layers, between which 56 TEXT-BOOK OF PHYSIOLOGY Fig, are scattered the usual encapsulated cells. (See Fig. 12.) White fibro-cartilage is tough, resistant, but flexible, and is found in joints where strength and fixcd- ^ ness are required. Hence it is \ " f; present between the vertebrae, fy forming the intervertebral V discs, between the condyle of the lower jaw and the glenoid fossa, in the knee-joint, around the margins of the joint cavities, etc. In these situations it as- sists in maintaining the ap- position of the bones, in giving a certain degree of mobility to the joints, and in diminishing the effects of shock and pres- sure imparted to the bones. , Yellow fibro-cartilage, the ground substance of which is pervaded by opaque, yellow elastic fibers, which form, by the interlacing of their branches, a compUcated network, in the meshes of which are to be found the usual cor- puscles. (See Fig. 13.) As these fibers are elastic, they impart to the cartilage a very considerable degree of elasticity. 12. — From a Horizontal Sec- tion OF THE Intervertebral Disc of Man. g. Fibrillar con- nective tissue. 2. Cartilage-cell (nucleus invisible), k. Capsule surrounded by calcareous gran- ules. X 240. — (Stohr.) f^S^ •■^SsiiSE'^ ^it-^^mff Fig. 13. — Elastic Cartilage. X 240. i. Portion of section of vocal process (ante- rior angle) of arytenoid cartilage of a woman thirty years old; the elastic substance in the form of granules. 2 and 3. Portions of sections of epiglottis of a woman sixty years old; a fine network of elastic fibers in 2, a coarser network in 3. z. Cartilage-cell, nucleus not visible; k, capsule. — [Stohr.) Yellow fibro-cartilage is well adapted, therefore, for entering into the formation of the external ear, epiglottis. Eustachian tube, etc. — structures which require for their functional activity a certain degree of flexibility and elasticity. THE CONNECTIVE TISSUES. 57 Osseous Tissue. — Osseous tissue, as distinguished from bone, is a member of the connective-tissue group, the ground substance of which is permeated with insoluble lime salts, of which the phosphate and carbonate are the most abundant. Immersed in dilute solutions of hydrochloric acid, they can be converted into soluble salts and dis- solved out. The osseous matrix left behind is soft and phable. When boiled, it yields gelatin. A thin, transverse section of a decalcified bone, when examined microscopically, reveals a number of small, round, or oval openings, which represent transverse sections of canals which run through the bone, for the most part in a longitudinal direction, though frequently anastomosing with one another. These so-called Haversian canals in the living state contain blood-vessels and lymphatics. (See Fig. 14.) Periosteum. Outer ground lamellae. "^5;^. ^-f"^ Haversian canals. Haversian lamellae. I ,, Interstitial lamellie. Y^^^ Inner ground laraelUe. ■ , ' Marrow. Fig. 14.— From a Cross-section of a Metacarp of Man. X 50. The Haversian canals contain a little marrow (fat-cells). Resorption line at h. — {Slohr.) Around each Haversian canal is a series of concentric laminae, composed of white fibers. Between every two laminae are found small cavities (lacunse), from which radiate in all directions small canals (canaliculi), which communicate freely with one another. The Haversian canals, with their associated lacunas and canalicuh, form a system of intercommunicating passages, which circulate lymph destined for the nourishment of bone. Each lacuna contains the bone corpuscle, which bears a close resemblance to the usual branched connective-tissue corpuscle, and whose function appears to be the maintenance of the nutrition of the bone. The surface of every bone in the living state is invested with a fibrous membrane, the periosteum, except where it is covered with cartilage. The inner surface of this membrane is loose in texture, and supports a fine plexus of capillary blood-vessels and numerous protoplasmic cells — the osteoblasts. As this layer is directly con- 58 TEXT-BOOK OF PHYSIOLOGY. cerned in the formation of bone, it is spoken of as the osteogenetic layer. A section of a bone shows that it is composed of two kinds of tissue — compact and cancellated. The compact is dense, resembling ivory, and is found on the outer portion of the bone; the cancellated is spongy, and appears to be made up of thin, bony plates, which intersect one another in all directions, and is found in greatest abun- dance in the interior of the bones. The shaft of a long bone is hollow. This central cavity, which extends from one end of the bone to the other, as well as the interstices of the cancellated tissue, is filled in the hving state with marrow. The marrow or medulla is composed of a connective-tissue framework supporting blood-vessels. In its meshes are to be found characteristic bone ceils or osteoblasts, the function of which is supposed to be the formation of bone. In the long bones the marrow is yellow, from the presence in the connective-tissue corpuscle of fat globules, which arise through the transformation of the cell protoplasm. In the cancellated tissue, near the extremities of the long bones, this fatty transformation does not take place to the same extent, and the marrow appears red. The cells of the red marrow are beheved to give birth indirectly to the red blood-cor- puscles. Physical and Physiologic Properties of Connective Tissues. — Among the physical properties may be mentioned consistency, cohesion, and elasticity. Their consistency varies from the semi- liquid to the solid state, and depends on the quantity of water which enters into their composition. Their cohesion, except in the softer varieties, is very considerable, and offers great resistance to traction, pressure, torsion, etc. In all the movements of the body, in the con- traction of muscles, in th& performance of work, the consistence and cohesion of these tissues play most important roles. Wherever the various forms of connective tissue are found, their chemic com- position and structure are in relation to their functions. If traction be the preponderating force, the structure becomes fibrous, as in ligaments and tendons, and the cohesion greatest in the longitudinal direction. If pressure be exerted in all directions, as upon mem- branes, the fibers interlace and offer a uniform resistance. When pressure is exerted in a definite direction, as on the extremities of the long bones, the tissue becomes expanded and cancellated. The lamellae of the cancellated tissue arrange themselves in curves which correspond to the direction of the greatest pressure or traction. Ex- tensibihty is not a characteristic feature, except in those forms con- taining an abundance of yellow elastic fibers. The elasticity is an essential factor in many physiologic actions. It not only opposes and Hmits forces of traction, pressure, torsion, etc., but on their cessation returns the tissues or organs to their original condition. Elasticity THE CONNECTIVE TISSUES. 59 thus assists in maintaining the natural form and position of the organs by counterbalancing and opposing temporarily acting forces. The Skeleton. — The connective tissues in their entirety con- stitute a framework which presents itself under two aspects: (i) As a soHd, bony skeleton, situated in the trunk and hmbs, affording attachment for muscles and viscera; (2) as a line, fibrous skeleton, found everywhere throughout the body, connecting the various viscera and affording support for the epithehal muscle, and nerve tissues. THE ANIMAL BODY AS A MACHINE FOR DOING WORK. The animal body is characterized by the power of executing a great variety of movements, all of which have reference to a change of relation of one part of the body to another, or to a change of posi- tion relatively to the environment, as in the various acts of locomotion. Since in the execution of these movements the different parts are of necessity applied or directed to the overcoming of opposing forces in the environment, the animal is said to be doing work. In the conception of the animal body as a machine for the accomphsh- ment of work the skeleton, the muscle and nerve tissues constitute the three primary mechanisms, all of which bear certain definite relations one to another. CHAPTER V. THE PHYSIOLOGY OF THE SKELETON. The Skeleton is the passive framework of the body, the axial portion of which (the vertebral column, head, ribs, and sternum) imparts more or less fixity and rigidity, while the appendicular por- tions (the bones of the arms and legs) impart extreme mobility. The bones of the arms and legs more especially may be looked upon as constituting a system of levers, the fulcra of which, the points of rest around which they move, lie in the joints. That a lever may be effective as an instrument for the accom- pHshment of work, it must not only be capable of moving around its fulcrum, but it must at the same time be acted on by two opposing forces, one passive, the other active. In the movement of the bony levers of the animal body, the passive forces are largely those con- nected with the environment, e. g., gravity, cohesion, friction, elas- ticity, etc. The active forces by which these latter are opposed and overcome through the intermediation of the bony levers are found in the muscles attached to them. For the execution of all these move- ments, it is essential that the relation of the various portions of the bony skeleton to one another shall be such as to permit of movement while yet retaining close apposition. This is accomplished by the mechanical conditions which have been evolved at the points of union of bones, and which are technically known as articulations or joints. A consideration of the body movements involves an account of (i) the static conditions, or those states of equilibrium in which the body is at rest — e. g., standing, sitting; (2) the dynamic conditions, or those states of activity characterized by movement — e. g., walking, running, etc. In this connection, however, only those physical and physiologic pecuharities of the skeleton, especially in its relation to joints, will be referred to, which underhe and determine both the static and dynamic states of the body. Structure of Joints. — The structures entering into the formation of joints are : I. Bones, the articulating surfaces of which are often more or less expanded, especially in the case of long bones, and at the same time variously modified and adapted to one another in accordance with the character and extent of the movements which there take place. 60 THE PHYSIOLOGY OF THE SKELETON. 6i 2. Hyaline cartilage, which is closely appHed to the articulating end of each bone. The smoothness of this form of cartilage facih- tates the movements of the opposing surfaces, while its elasticity diminishes the force of shocks and jars imparted to the bones during various muscular acts. In a number of joints, plates or discs of white fibro-cartilage are inserted between the surfaces of the bones. 3. A synovial membrane, which is attached to the edge of the hyaline cartilage, entirely inclosing the cavity of the joint. This mem- brane is composed largely of connective tissue, the inner surface of which is lined by endotheUal cells, which secrete a clear, colorless, viscid fluid — the synovia. This fluid not only fills up the joint-cavity, but, flowing over the articulating surfaces, diminishes or prevents friction. 4. Ligaments, — tough, inelastic bands, composed of white fibrous tissue, — which pass from bone to bone in various directions on the dift'erent aspects of the joint. As white fibrous tissue is in- extensible but phant, hgaments assist in keeping the bones in apposition, and prevent displacement while yet permitting of free and easy movements. Classification of Joints. — All joints may be divided, according to the extent and kind of movements permitted by them, into (i) diarthroses; (2) amphiarthroses; (3) synarthroses. I. Diarthroses. — In this division of the joints are included all those which permit of free movement. In the majority of instances the articulating surfaces are mutually adapted to each other. If the articulating surface of one bone is convex, the opposing but corresponding surface is concave. Each surface, therefore, represents a section of a sphere or a cylinder, which latter arises by rotation of a line around an axis in space. According to the number of axes around which the movements take place all diarthrodial joints may be divided into: I. Uniaxial Joints. — In this group the convex articulating surface is a segment of a cylinder or cone, to which the opposing surface more or less completely corresponds. In such a joint the single axis of rotation, though nearly, is not exactly at right angles to the long axis of the bone, and hence the movements — flexion and extension — which take place are not confined to one plane. Joints of this character — e. g., the elbow, knee, ankle, the pha- langeal joints of the fingers and toes — are, therefore, termed ginglymi, or hinge-joints. Owing to the obliquity of their articulating surfaces, the elbow and ankle are cochleoid or screw- ginglymi. Inasmuch as the axes of these joints on the opposite sides of the body are not coincident, the right elbow and left ankle are right-handed screws; the left elbow and right ankle, 62 TEXT-BOOK OF PHYSIOLOGY. left-handed screws. In the knee-joint the form and arrangement of the articulating surfaces are siich as to produce that modifica- tion of a simple hinge known as a spiral hinge, or helicoid. As the articulating surfaces of the condyles of the femur increase in convexity from before backward, and as the inner condyle is longer than the outer, and, therefore, represents a spiral surface, the line of translation or the movement of the leg is also a spiral movement. During flexion of the leg there is a simultaneous inward rotation around a vertical axis passing through the outer condyle of the femur; during extension a reverse movement takes place. Moreover, the slightly concave articulating surfaces of the tibia do not revolve around a single fixed transverse axis, as in the elbow- joint, for during flexion they shde backward, during extension forward, around a shifting axis, which varies in posi- tion with the point of contact. In some few instances the axis of rotation of the articulating surface is parallel with rather than transverse to the long axis of the bone, and as the movement then takes place around a more or less conic surface, the joint is termed a trochoid or pulley— e. g., the odonto-atlantal and the radio-ulnar. In the former the collar formed by the atlas and its transverse ligament rotates around the vertical odontoid process of the axis. In the latter the head of the radius revolves around its own long axis upon the ulna, giving rise to the movements of pronation and supination of the hand. The axis around which these two movements take place is continued through the head of the radius to the styloid process of the ulna. 2. Biaxial Joints. — In this group .the articulating surfaces are un- equally curved, though intersecting each other. When the sur- faces lie in the same direction, the joint is termed an ovoid joint — e. g., the radio-carpal and the atlanto-occipital. As the axes of these surfaces are vertical to each other, the movements per- mitted by the former joint are flexion, extension, adduction, and abduction, combined with a slight amount of circumduction; the latter joint permits of flexion and extension of the head, with inclination to either side. When the surfaces do not take the same direction, the joint, from its resemblance to the surfaces of a saddle, is termed a saddle-joint — e. g., the trapezio-metacarpal. The movements permitted by this joint are also flexion, exten- sion, adduction, abduction, and circumduction. 3. Polyaxial Joints. — In this group the convex articulating surface is a segment of a sphere, which is received by a socket formed by the opposing articulating surface. In such a joint, termed an enarthrodial or ball-and-socket joint, — e. g., the shoulder-joint, hip-joint, — the distal bone revolves around an indefinite number THE PHYSIOLOGY OF THE SKELETON. 63 of axes, all of which intersect one another at the center of rotation. For simplicity, however, the movement may be described as taking place around axes in the three ordinal planes — viz., a transverse, a sagittal, and a vertical axis. The movements around the transverse axis are termed flexion and extension; around the sagittal axis, adduction and abduction; around the vertical axis, rotation. When the bone revolves around the surface of an imaginary cone, the apex of which is the center of rotation and the base the curve described by the hand, the movement is termed circumduction. 2. Amphiarthroses. — In this division are included all those joints which permit of but slight movement — e. g., the intervertebral, the interpubic, and the sacro-iHac joints. The surfaces of the opposing bones are united and held in position largely by the intervention of a firm, elastic disc of fibro-cartilage. Each joint is also strengthened by hgaments. 3. Synarthroses. — In this division are included all those joints in which the opposing surfaces of the bones are immovably united, and hence do not permit of any movement — e. g., the joints between the bones of the skull. The Vertebral Column. — In all static and dynamic states of the body the vertebral column plays a most essential role. Situated in the middle of the back of the trunk, it forms the foundation of the entire skeleton. It is composed of a series of superimposed bones, termed vertebrae, which increase in size from above downward as far as the brim of the pelvic cavity. Superiorly, it supports the skull; laterally, it affords attachment for the ribs, which in turn support the weight of the upper extremities; below, it rests upon the pelvic bones, which transmit the weight of the body to the inferior extremities. The bodies of the vertebras are united one to another by tough elastic discs of fibro-cartilage, which, collectively, constitute about one- quarter of the length of the vertebral column. The vertebras are held together by Hgaments situated on the anterior and posterior surfaces of their bodies, and by short, elastic ligaments between the neural arches and processes. These structures combine to render the vertebral column elastic and flexible, and enable it to resist and diminish the force of shocks communicated to it. The amphiarthrodial character of the intervertebral joints endows the entire column with certain forms of movement which are neces- sary to the performance of many body activities. While the range of movement between any two vertebree is shght, the sum total of movement of the entire series of vertebras is considerable. In dift'erent regions of the column the character, as well as the range of move- ment, varies in accordance with the form of the vertebrae and the inclination of their articular processes. In the cervical and lumbar 64 TEXT-BOOK OF PHYSIOLOGY. regions extension and flexion are freely permitted, though the former is greater in the cervical, the latter in the lumbar region, especially between the fourth and fifth vertebrae. Lateral flexion takes place in all portions of the column, but is particularly marked in the cer- vical region. A rotatory movement of the column as a whole takes place through an angle of about twenty-eight degrees. This is most evident in the lower cervical and dorsal regions. The skeleton may, therefore, be regarded as a highly developed framework, which determines not only the form of the body, and affords support and protection to the various softer organs and tissues, but also, through the mobility of its joints, permits of a great variety of compHcated movements. CHAPTER VI. GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. The muscle-tissue, which closely invests the bones of the body and which is famihar to all as the flesh of animals, is the immediate cause of the active movements of the body. This tissue is grouped in masses of varying size and shape, which are technically known as muscles. The majority of the muscles of the body are connected with the bones of the skeleton in such a manner that, by an alteration in their form, they can change not only the position of the bones with reference to one another, but can also change the individual's relation to surrounding objects. They are, therefore, the active organs of both motion and locomotion, in contradistinction to the bones and joints, which are but passive agents in the performance of the corre- sponding movements. In addition to the muscle masses which are attached to the skeleton, there are also other collections of muscle- tissue surrounding cavities such as the stomach, intestine, blood- vessels, etc., which impart to their walls motihty, and so influence the passage of material through them. Muscles produce movement of the structures to which they are attached by the property with which they are endowed of changing their shape, shortening or contracting under the influence of a stim- ulus transmitted to them from the nervous system. Muscles are divided into: 1. Voluntary muscles, comprising those the activity of which is called forth by an act or effort of volition. 2. Involuntary muscles, comprising those the activity of which is entirely independent of the voHtion. The voluntary muscles are also known from their attachment to the skeleton as skeletal, and from their microscopic appearance as striped or striated muscles. Though for the most part these muscles are red, there are certain muscles in man and other animals which are pale in color. The involuntary muscles, from their relation to the viscera of the body, are known also as visceral, and from their micro- scopic appearance as plain, smooth, or non-striated muscles. THE VOLUNTARY OR SKELETAL MUSCLE. All skeletal muscles consist of a central fleshy portion, the body or belly, provided at either extremity with a tendon in the form of a 5 65 66 TEXT-BOOK OF PHYSIOLOGY. cord or membrane. The body is the active, contractile region, the source of the movement; the tendon is the inactive region, the passive transmitter of the movement to the bones. A skeletal muscle is a complex organ consisting of a framework of connective tissue, supporting muscle-fibers, blood-vessels, nerves, and lymphatics. The general body of the muscle is covered by a dense layer of connective tissue, the epi-mysium, which blends with and partly forms the tendon. From the under surface of this covering, septa of connective tissue pass inward, dividing and grouping the fibers into larger and smaller ^s\ bundles, termed fasciculi. The fasciculi, invested by a special sheath, the peri-mysium, are prismatic in shape and on cross-section present an ir- regular outline. The muscle- fibers composing the fasciculi are separated one from an- other and supported by a very delicate connective tissue, the endo-mysium. The connec- tive tissue thus surrounding and penetrating the muscle binds the fibers into a dis- tinct organ and affords sup- port to all remaining struc- tures (Fig. 15). Histology of the Skeletal Muscle-fiber. — The muscle- fibers for the most part are arranged parallel one to an- other and in a direction cor- responding to the long axis of the muscle. They vary in length from 30 to 40 milli- meters and in breadth from 20 to 30 micromilhmeters. There are exceptional fibers, however, which have a much greater length. As the fibers have but a hmited length in the vast majority of muscles, each end, more or less pointed or beveled, is united to adjoining fibers by cement. In this way a muscle is increased in length. When examined with the microscope, the muscle-fiber is seen to be cyhndric or prismatic in shape and to consist of a thin transparent membrane, the sarcolemma, in which is contained the true muscle or sarcous substance. The sarcolemma is elastic and adapts itself Fig. 15. — From a Cross-section of the Adductor Muscle of a Rabbit. P. Peri-mysiura, containing two blood-ves- sels, at g; m, muscle-fibers; many are shrunken and between them the endo- mysium, p, can be seen; at x the sec- tion of muscle-fiber has fallen out. X 60.— (Stohr.) GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 67 3 i',. Fig. 16.- a. iJarK uanu. Jh OF A Rabbit. Light band. c. Intermediate line. n. Nucleus. — Landois and Stirline. to all changes of form the sarcous substance undergoes. Beneath the sarcolemma there are several nuclei surrounded by granular material. Each fiber also presents a series of transverse bands alternately dim and bright which give to it a striated appearance. If the bright bands are examined with high magnifying powers, each one is seen to be crossed by a fine dark fine which at the time of its discovery was regarded as the optic expression of a membrane attached laterally to the sarco- lemma. It has since been re- solved into a row of granules (Fig. 16). The muscle-fiber also presents a longitudinal striation which in- dicates that it is composed of finer elements placed side by side, termed fibrillae. The fibrillas extend throughout the entire length of the fiber, though they are not of uniform thickness (Fig. 17). That portion of the fibril corresponding in position to the dim band is thick, prismatic, or rod-hke in shape, and termed a sarcostyle; that portion corresponding in po- sition to the bright band is ex- tremely thin and narrow and pre- sents at its middle a sHght enlarge- ment or granule. The fibrillae are embedded in a clear transparent fluid which, from its supposed nutritive character, is termed sar- coplasm. The diminution in cah- ber of the fibrillae at different levels permits of the accumulation and storage of a larger amount of nutritive material than could otherwise be the case. It is for this reason that the fiber at these points presents a brighter appear- ance. When the muscle-fiber is ex- amined under crossed Nichol prisms, the dim band appears bright and the bright band appears dim against a dark background, indi- FiG. 17. — A. Diagram of arrangement of the contractile substance ac- cording to the \'iew of Rollett; the granular figures represent the con- tractile elements, the intervening light areas the sarcoplasm. B. Small muscle-fiber of man; the corresponding parts in the two figures are indicated; /, i, I, respec- tively the transverse, the interme- diate, and lateral discs, n. Muscle nuclei. — (Piersol.) 68 TEXT-BOOK OF PHYSIOLOGY. MUSCLE FIBER ..-CAPILLARY BLOOD VESSEL eating that the former is doubly refracting or anisotropic, the latter singly refracting or isotropic. The Blood-supply. — Muscles in the physiologic condition re- quire for the maintenance of their activity a large amount of nutritive material. This is obtained directly from the lymph and indirectly from the blood furnished by the blood-vessels. The vascular supply to the muscles is very great and the disposition of the capillary vessels with reference to the muscle-fiber is very characteristic. The arterial vessels, after entering the muscle, are supported by the peri-mysium; in this situation they give off short, transverse branches, which immediately break up into a capillary network of rectangular shape within which the muscle-fibers are contained. The relation of the capillary vessel to the muscle-fiber is shown in Fig. i8. The muscle-fiber, in inti- LYMPH SPACE mate relation with the capil- lary, is bathed with lymph derived from it. Its contrac- tile substance, however, is separated from the lymph by its own investing membrane, through which all interchange of nutritive and waste mate- rials must take place. The nutritive material passes through the capillary wall into the lymph-space, then through the sarcolemma into the interior of the fiber, where it comes into relation with the Hving muscle mate- rial. The waste products aris- ing in the muscle as a result of nutritive changes pass in the reverse direction into the blood, by which they are car- ried away to ehminating organs. Lymphatics are present in mus- cle, but confined to the connective tissue, in the spaces of which they take their origin. The Nerve-supply. — The nerves which carry the stimuh to a muscle enter near its geometric center. Many of the fibers pass directly to the muscle-fibers with which they are connected; others are distributed to blood-vessels. Every muscle-fiber is supphed with a special nerve-fiber except in those instances where the nerve- trunks entering a muscle do not contain as many fibers as the muscle. In such cases the nerve-fibers divide near their termination until the Fig. i8. -Relation of the Blood-vessel TO THE Muscle-fiber. GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 69 number of branches equals the number of muscle-fibers. The individual muscle-fiber is penetrated near its center by the nerve where it terminates; the ends being practically free from nerve in- fluence. The stimulus that comes to the muscle-fiber acts primarily upon its center, the effect of which then travels in both directions to the ends. The manner in which the nerve-fibers terminate in muscle will be more fully described in connection with the histology of the nerve tissue. CHEMIC COMPOSITION OF MUSCLE. The chemic composition of living muscle is but imperfectly under- stood owing to the fact that shortly after death some of its constituents undergo a spontaneous coagulation and for the reason that the methods employed for analysis also tend to alter its composition. To human muscle, the following average percentage composition has been given : Water, __- 73.5 Proteids, including those of sarcolemma, connective- tissue, pigments, 18.02 Gelatin, 1.99 Fat, 2.27 Extractives, 0.22 Inorganic salts, 3-i2. (Halliburton.) (The composition of muscles of different animals, consumed as foods, will be found in the chapter on Foods.) When fresh muscle is freed from fat and connective tissue, frozen, rubbed up in a mortar, and expressed through hnen, a shghtly yellow syrupy alkahne or neutral liquid is obtained which has been termed muscle-plasma. This fluid at normal temperatures coagulates spontaneously, the phenomena resembhng in many respects those observed in the coagulation of blood-plasma. The coagulum subse- quently contracts and squeezes out an acid muscle-serum. The coagulated proteid is known as myosin and belongs to the class of globuhns. Inasmuch as it is not present in hving muscle and only makes its appearance under conditions not strictly physiologic, it is regarded as a derivative of a pre-existing proteid which has been termed myosinogen. According to Halhburton, the proteids of living muscle are four in number, distinguished by their varying solubilities in different salts and by the varying temperatures at which they coagulate. From muscle-plasma may then be obtained: (i) Para- myosinogen and (2) myosinogen, the former coagulating at 47° C, the latter at 56° C. It is myosinogen which is converted into myosin under the influence of some special ferment, though both enter into the formation of the muscle-clot. From the muscle-serum may also be obtained at 68° C. a globulin body termed myoglobulin and a 70 TEXT-BOOK OF PHYSIOLOGY. small quantity of myoalbumin. Among the proteids may be men- tioned hemoglobin, which gives the color to the muscles. Spectro- scopic investigation reveals the presence of a special pigment, myo- hematin, which is supposed to have a respiratory function, inasmuch as its absorption bands change by oxidation and reduction. Among the extractives containing nitrogen may be mentioned creatin, creatinin, xanthin, carnin, urea, uric acid, carnic acid, etc. Among the extractives free of nitrogen, glycogen, dextrose, inosite, lactic acid, fat, are the most important. Inorganic salts are relatively abundant, of which potassium is the most abundant among the bases, and phosphoric acid among the acids. THE PHYSICAL AND PHYSIOLOGIC PROPERTIES OF MUSCLE- TISSUE. Consistency. — The consistency of muscle-tissue during hfe varies considerably in accordance with different states of the muscle. In a state of tension it is hard and resistant ; in the absence of tension it is soft and fluctuating to the sense of touch. Tension alone gives rise to hardness. Cohesion. — The cohesion of a muscle is largely dependent on the quantity of connective tissue it contains. A band of fresh human muscle one square centimeter in cross-section was able to resist a weight of 14 kilograms without rupture (McAhster). Cohesion resists the forces of traction and pressure. Elasticity. — Muscle, in common with many other organic as well as inorganic substances, is capable of being extended beyond the normal length through the action of external forces and of resuming the normal length w^hen these forces cease to act. All such bodies are said to be elastic; and the greater the variations between the natural and acquired lengths, the greater is their elasticity said to be. Muscle therefore possesses extensibihty and elasticity.* If the muscle of a frog, preferably the sartorius, the fibers of which are arranged in a practically parallel manner, be fastened at one ex- tremity by a clamp, and then extended by a series of successive weights which differ by a common increment, it will be found that the extensibihty of muscle does not follow the law of elasticity as determined for inorganic bodies; i. e., directly proportional to the weight and to the length of the body extended; but that while in- creasing in length with each successive weight, the increase is always in a diminishing ratio. Thus, for example, as shown in Fig. 19: The extension produced by 5 grams is 5 milhmeters, that produced by 10 grams is only 4 milhmeters more, and so on with additional *By this latter term is here meant the power by virtue of which the muscle returns to its original length and is used synonymously with perfect retractibility. GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 71 . 10. — Extension Curve OF Muscle. — (Gad.) weights until the increase in passing from 25 to 30 grams is only i millimeter. The extensibihty is thus shown to be proportionately greater with small than with larger weights. It is, however, actually greater with the larger weights. The ex- tention curve A B formed by joining the —ptrm ends of the muscle approximates that of a parabola. The muscle in returning to its original length also show^s a variation from the behavior of inorganic bodies. With the successive removal of the weights, the elasticity of the muscle asserts itself with gradually increasing energy until its nor- mal length is nearly, if not entirely, re- gained (Fig. 20). Though it is usually stated that the elasticity of muscle is in- complete, it must be borne in mind that the experiments have usually been made on muscles removed from the body, de- prived of blood and nerve influences, and hence under abnormal conditions. It is highly probable that in the living body muscles possess perfect elasticity which enables them to completely return to their normal length after extension. The extension and elastic recoil of muscle depends on the maintenance of physiologic condi- tions. If the nutrition is impaired by fatigue, deficient blood-sup- ply, or any pathologic condition, the elasticity is at once impaired. Tonicity. — This is a property pos- sessed by all muscles in the body in con- sequence of being stretched to a slight extent beyond their normal length. This may be due to the action of antagonistic muscles or to their mode of growth, the muscles growing somewhat more slowly than the bones to which they are at- tached. That muscles are so stretched is shown by the shortening which at once takes place when their tendons are di- vided. This muscle tonus or tension is closely connected with the elasticity and plays an important role in muscle con- traction; being always on the stretch, the muscle loses no time in acquiring that degree of tension necessary to immediate action on the bone to which it is attached. The working power of a muscle is also increased by the presence, within limits, of some resistance to Fig. 20. — Curve of Elas- ticity Produced by Continuous Extension AND Recoil of a Frog's Muscle, o x. Abscissa before; x', after extension. — {Landois and Stirling.) 72 TEXT-BOOK OF PHYSIOLOGY. the act of contraction. According to Marey, the amount of work is considerably increased when the muscle energy is transmitted by an elastic body to the mass to be moved, while at the same time the shock of the contraction is lessened. The position of a passive limb is the resultant also of the elastic tension of antagonistic groups of muscles. Another explanation for the tonicity of muscle is found in the fact that the skeletal muscles of the body receive continuously nerve impulses from the thermogenic centers. The chief function of the tonicity would thus be the production of heat, other functions which the tone subserves being merely secondary. Irritability, Contractility. — These are terms employed to de- note that property of muscle-tissue in virtue of which it responds by a change of form, becoming shorter and thicker on the application of any external agent which acts as a stimulus. On the withdrawal of the stimulus the muscle again undergoes a change of form, becoming longer and narrower, and returns to its original con- dition. All muscles which possess this capability are irritable and contractile; and all agents which excite the muscle to action are stimuli. The rapid change of form which a highly irritable muscle undergoes in response to the action of a stimulus of short duration is usually termed a twitch or pulsation. With appropriate apparatus it can be shown that the muscle at the time of the twitch becomes warmer and exhibits electric phenomena. The muscle is therefore an apparatus for the conversion of potential into kinetic energy: viz., heat, electricity, and mechanic motion. Though usually associated with the activity of the nervous system, and to some extent dependent on it, irritability is nevertheless an independent endowment of the muscle and persists for a longer or shorter period, as shown by many experiments, after all nerve connections have been destroyed. Among the proofs which may be presented in support of this view is the following: The introduction of the drug curara into the body of an animal produces in a short time complete paralysis. Experiment has shown that curara sus- pends the conductivity of the intramuscular terminations of the nerve-fiber and thus separates the muscle entirely from the nerve. Though the animal is incapable of executing a single movement, its muscles respond promptly on the apphcation of a stimulus. More- over, portions of muscles exhibit irritability in which there is no trace of nerve structure. This is the case with the ends of the sartorius muscle of the frog and the anterior end of the retractor muscle of the eyeball of the cat. These and other facts demonstrate the in- dependence of muscle irritabihty. In the hving body irritabihty and nutritive activity, with which it is closely associated, are maintained by a due supply of oxygen, of nutritive material, the removal of waste products, and a nor- GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 73 mal temperature. The muscles of the cold-blooded animals, and especially the frog, retain their irritabihty for a much longer period than the muscles of the warm-blooded animals. This is the case also with the individual muscles after removal from the body of the animal. The reason for this is found in all probability in the difference in the rate of their nutritive activities and in the quantity of nutritive mate- rial stored up in their cells. The duration of the irritability of isolated muscles can be considerably prolonged by keeping them moist. Muscle Stimuli. — Though consisting of a highly irritable tissue, muscles do not possess spontaneity of action. They require for the manifestation of their characteristic activity the application of a stimulus. In the living body all contractions, at least of the skeletal muscles, occurring under normal or physiologic conditions are caused by the action of "nerve impulses" transmitted by the nerves from the central nervous system to the muscles. The nerve impulse is the normal or physiologic stimulus. After removal from the body and freed from nerve connections muscles can be excited to action by various agents — e. g., mechanic, chemic, thermic, electric. These are artificial or non-physiologic stimuli. 1 . Mechanic Stimuli. — Cutting, pinching, sharply tapping the muscle \vill cause it to contract, providing the stimulus has sufficient intensity. With each stimulation a short, fleeting contraction ensues. If repeated with sufficient rapidity, a series of con- tinuous but irregular pulsations are produced. 2. Chemic Stimuli. — Various chemic substances in solution will excite single or continuous pulsations if the strength of the solu- tion is not such as to destroy at once the irritabihty. They owe their efficiency as stimuh to the rapidity with which they alter the composition of the muscle-substance. Among these may be mentioned solutions of potassium and sodium, weak solutions of the mineral and organic acids, ammonium vapor, distilled water, glycerin, and sugar. 3. Thermic Stimuli. — The application of a heated object, such as a hot wire, causes the muscle to rapidly contract. 4. Electric Stimuli. — The most efficient stimulus and the one least injurious to the tissue is the electric current. Either the con- stant or the induced current may be used.* The Constant Current. — If the ends of the wires in connection with an electric cell be provided Avith non-polarizable electrodes and the * Since the study of the physiologic properties of both muscle-tissue and nerve- tissue involves the employment of electricity as a stimulus, it becomes necessary for the student to familiarize himself with certain forms of apparatus by which it is gen- erated, controlled, and applied. For the purpose of not interrupting the continuity of the text this information is embodied in an appendix. The facts therein contained should be mastered bv the student. 74 TEXT-BOOK OF PHYSIOLOGY. latter placed on opposite ends of a freshly prepared sartorius muscle of a frog which has been previously curarized, it will be found on closing or making the circuit that the muscle will exhibit a short quick pulsation. During the actual passage of the current, especially if it is weak, there may be no apparent change in the muscle. If the current is strong, the muscle may, on the contrary, remain in a state of continuous contraction. With the opening or breaking of the current the muscle at once relaxes, or perhaps again contracts and then relaxes. The extent of the contraction depends mainly on the strength of the current, being greater with strong, less with weak currents. When the current is sufificiently strong to elicit both making and breaking contractions, it is found that the contraction occurring on the make or closure of the circuit is always greater than that occurring on the break or opening of the circuit. More- over, it has been shown in many ways that the contraction occur- ring on the closure of the circuit has its origin at the point where the current is leaving the muscle — i. e., in the immediate neighbor- hood of the negative pole or cathode — and propagates itself to the opposite extremity; while the contraction occurring on the opening of the circuit has its origin at the point where the current is entering the muscle, i. e., in the neighborhood of the positive pole or anode. The Induced Current. — If the primary spiral of the inductorium be connected with an electric cell and the secondary spiral be con- nected with a muscle, it will be found that the current induced in the secondary circuit, both on the make and break of the primary, will also cause the muscle to sharply and rapidly pulsate if the two spirals are sufhciently near each other. Observation, however, makes it evident that the pulsation occurring with the break of the primary circuit is more energetic than that occurring with the make, a result the opposite of that obtained with the constant current. This is not due to any difference in the electricity, however, but to pecuharities in the construction of the inductorium. When the primary circuit is interrupted with sufficient frequency, as it can be by throwing into the circuit Neef's hammer or some other form of interrupter, the con- tractions excited by the induced currents may be made to succeed one another so rapidly that they become fused together, producing a spasm or tetanus of the muscle. The rapidity with which the induced current appears and disappears, its brief duration, the ease with which its strength can be regulated, combine to render it a most efficient stimulus for either muscle or nerve. Conductivity. — All muscle protoplasm possesses conductivity. The change excited in a muscle-fiber by the arrival of a nerve impulse is at once conducted with great rapidity in opposite directions to the end of the fiber; the advance of the excitation process is im- mediately succeeded by the contraction process, the change of form GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 75 which constitutes the contraction. With the disappearance of the former, the latter also disappears and the muscle resumes its pre- vious passive condition. There is no evidence, however, that the excitation process travels transversely, — that is, into adjoining fibers, — being prevented from doing so by the presence of the hmiting membranes, the sarcolemmata. The fact that each muscle-fiber receives its own, or at least a branch of a nerve-fiber, and hence its own nerve impulse or stimulus, would also indicate that the excitation process can not be conducted longitudinally into adjoining fibers, or at least with sufficient rapidity for the purposes of ordinary muscle actions. Nevertheless if a long muscle, such as the sartorius, from a curarized frog be stimulated at one end with an induced electric cur- rent, the excitation and the contraction processes will be conducted with extreme rapidity to the opposite end of the muscle. The rapidity of conduction in human muscles has been estimated at from 10 to 13 meters per second, and in frog's muscle at from 3 to 4.5 meters per second. The contraction process, the thickening of the muscle, is termed the contraction wave. As it is the result of the excitation process and immediately succeeds it, its rate of conduction must be the same as that given above. With appropriate apparatus the duration of the wave at any given point has been shown to be, in the frog's muscle, one-tenth of a second and its length three-tenths of a meter. PHENOMENA ATTENDING A MUSCLE CONTRACTION. PHYSICAL PHENOMENA. The most obvious change in a muscle during the contraction is that relating to its form. The muscle not only becomes shorter, but at the same time thicker. The extent to which it may shorten when unopposed may amount to 30 per cent, or more of its original length. The increase in thickness practically compensates for the diminution in length, for there is no observable diminution in volume. The change in form of the entire muscle results from a corresponding change of form of its individual fibers as determined by microscopic examination, each of which becomes shorter and thicker. The successive changes in both the muscle and the individual fibers are represented in Fig. 21. When the contraction begins, the dim band increases and the bright band diminishes in width. This Engelmann attributes to the passage of fluid material from the bright into the dim band. At the time of relaxation there is a return of this material and the bands assume their original shape and volume. As the contraction wave reaches its maximum the optic properties of the bright and dim bands change. The former now becomes darker and less transparent 76 TEXT-BOOK OF PHYSIOLOGY. until at the crest of the wave it assumes the appearance of a distinct dark band; the latter now becomes clear and bright in comparison. This change in the appearance of the fiber is due to an increase in refrangibihty of the bright and a decrease in the refrangibility of the dim band coincident with the passage of the fluid from the former into the latter. There is at the height of the contraction a complete reversal in the positions of the striations. At a certain stage between the beginning and the crest of the wave the strias almost entirely dis- appear, giving to the fiber an appearance of homogeneity. There is, however, no change in refractive power as shown by the polarizing apparatus. When the contraction wave has reached the stage of greatest intensity, there is^a reversal of the above phenomena as the fiber returns to its former condition, that of relaxation. ^iri IIIIIIMHIjIIIIIIII m Fig. 21. — Showing the Changes in a Muscle and Muscle-fiber during Con- traction. Elasticity. — During the contraction of a muscle there is a greater or less alteration in its elasticity, as shown by the fact that it is ex- tended to a greater degree by the same weight in the active than in the passive condition. The degree to which the extensibihty is in- creased and the elasticity decreased is dependent on the amount of the resisting force. These facts, as determined experimentally, are represented in Fig. 22. Let A B and A b represent the length of the normal unweighted muscle, passive and active states respectively; the line B B', the extension curve of the passive muscle produced by successive weights, 5, 10, 15, 20, 25, 30 grams, differing by a com- mon increment; the fine b B', the extension curve of the active con- tracted muscle when weighted with the same weights ; A' B' the length of the muscle when the weight is sufficiently great to prevent shorten- ing. It will be observed from these facts that while the muscle is extended in both the passive and active states by corresponding GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 77 weights, the extension during the latter is progressively greater, until with a given weight the length of the muscle is the same. Under such circumstances, there being no shortening of the muscle, the energy of its contraction manifests itself physically merely as tension. In the successive actions of the muscle represented in the same figure there is to be observed also a combination of a change of lensfth and Fig. 22. — Extension Curves: B B', of the resting; b B', of the contracting muscle. a change of tension, the ratio of the one to the other being deter- mined by the amount of the supported weights. When the weight is slight in amount, the shortening of the muscle reaches a maximum and the tension a minimum; when the weight is large in amount, the reverse conditions obtain. THE CONTRACTION PROCESS. METHODS OF INVESTIGATION. The contraction of a muscle as it takes place in the living body and under normal physiologic conditions is a complex act, persisting for a variable length of time in accordance with the number of stimuh transmitted to it in a given unit of time, and as determined experi- mentally is the resultant of the fusion of a greater or less number of separate and individual contractions or pulsations. To this enduring contraction the term tetanus has been given. With the aid of ap- propriate apparatus it has become possible to obtain and record single muscle contractions, to analyze and decompose them into their constituent elements, or to combine them in such a manner as to pro- duce practically a normal physiologic tetanus. As in the experi- mental study of the phenomena of a muscle contraction it frequently becomes necessary to remove the muscle from the body of the animal, the muscles of warm-blooded animals are not w^ell adapted for this purpose, owing to the rapid alteration in composition they undergo. 78 TEXT-BOOK OF PHYSIOLOGY. with a consequent loss of irritability, when deprived of their normal blood-supply. The excised muscles of cold-blooded animals, par- ticularly of the frog, — in which, owning to the relatively slow rate of the nutritive activities, the irritabihty and contractility endure for a long period of time, even though deprived of blood, — are particularly valuable for experimental studies. The muscles generally employed are the gastrocnemius, the sartorius, and the hyoglossus. If kept at a normal temperature and moistened with 0.6 per cent, solution of sodium chlorid, such a muscle will contract for a long period of time on the application of any form of stimulus, but especially the electric. Graphic Record of a Muscle Contraction. — Inasmuch as the changes in the form of a muscle during a single contraction take place with extreme rapidity, their succession, peculiarities, and time re- FiG. 23. — Myograph. K. Recording cylinder. M. Moist chamber, ing lever. W. Weight. I. Induction coil. L. Record lations cannot be determined with any degree of accuracy by the unaided eye. This difficulty can largely be overcome by the employ- ment of the graphic method, the principle of which consists in record- ing the movements by means of a pen on some appropriate moving and receiving surface. To accomphsh this object the muscle is at- tached at one extremity by a clamp to a firm support, and at the other extremity to a weighted lever, which is, however, sufficiently light to enable it to take up, reproduce, and magnify its movements. The end of the lever provided with a pen is apphed to a smooth surface, such as glazed paper on a cyhnder or plate, and covered with lamp- black. If the surface is stationary, the contraction is recorded as a vertical line; if it is placed in movement at a uniform rate by clock- GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 79 work, the contraction is recorded in the form of a curve, the width of the arms of which will depend on the rate of movement. The time relations of the phases of the contraction can be obtained by placing beneath the lever a pen attached to an electro-magnet thrown into action. by a tuning-fork vibrating in hundredths of a second. In order to determine the rapidity with which the contraction follows the stimulation, it is essential that the moment of the latter be also recorded. This is accomphshed by an automatic key, the opening or closing of which develops the stimulus which excites the muscle. A combination of these different appliances constitutes a myograph and the curve of contraction a myogram. (See Fig. 23.) The Isotonic Myogram. — With the object of obtaining a curve of successive changes in the length of a muscle during a single con- traction and at the same time avoiding changes in tension, the weight Fig. 24. — The Isotonic Myogram. attached to the lever should be appHed close to its axis, a mechanic condition which practically maintains a uniform tension throughout the contraction. To this method the term "isotonic" has been given and the curve so obtained an isotonic myogram.* The Character of an Isotonic Myogram. — With the muscle arranged as previously described and stimulated directly with a single induction shock, the contraction will be recorded in the form of a curve similar to that represented in Fig. 24, in which the line t t repre- sents the abscissa of time; a, the moment of stimulation; and bed, the degree of shortening at each successive moment. The undulating hne shows the time relations, the distance from crest to crest represent- * In the ordinary method of recording a muscular movement, i. e., with the weight attached to the lever immediately beneath the muscle and known as the "loaded method," a certain momentum is imparted to the weight, which continues after the muscle has ceased to act, both when shortening and relaxing, and so imparts to the re- cording lever additional movements which \atiate the true character of the curve. 8o TEXT-BOOK OF PHYSIOLOGY. ing hundreths of a second. The curve may be divided into three portions: 1. A short but measurable portion between the point of stimulation and the first evidence of the shortening, a b, known as the "latent period." The duration of this period for the skeletal muscle of the frog was originally determined to be o.oi second, but with the employment of more accurate apparatus it has been reduced to 0.0025 to 0.004 second. During this period it is supposed that certain chemic changes are taking place prepara- tory to the exhibition of the movement. The duration of the latent period is influenced by a variety of conditions, e. g., tem- perature, fatigue, strength of stimulus, etc. 2. An ascending portion, b c, the contraction or period of increasing energy. The contraction as shown by the character of the curve begins slowly, then proceeds rapidly, and again slowly as the shortening reaches its maximum. The contraction may be said to end when the tangent to the curve becomes parallel with the abscissa. 3. A descending portion, c d, the relaxation or period of decreasing energy. The relaxation as shown by the character of the curve begins slowly, then proceeds rapidly, and again slowly as the muscle attains its original length. The termination of the re- laxation is at the point where the curve cuts the abscissa. The curve beyond this point may be comphcated by the presence of one or more residual or after- vibrations, which are probably due to the inertia of the lever as well as to changes in the muscle elasticity. The duration of the period of shortening is about 0.04 second, and of the period of relaxation 0.05 second. A single pulsation of the isolated muscle of the frog therefore occupies, from the moment of stimulation to termination, the tenth of a second. Muscles of many other animals have a contraction period the duration of which varies considerably from this. Thus, in man the time of a single contrac- tion is one-twentieth of a second, in some insects one three-hundreth of a second, and in the turtle one second. Pale muscles have a shorter period than the red. Influences Modifying the Contraction Process. — The con- traction process in its entirety as well as in its individual parts is considerably modified by external conditions, among which may be mentioned the following: I. Stimulus. As the contraction is the response of the muscle to a stimulus, the vigor of the former is proportional, within limits, to the strength of the latter. Thus, with single induction shocks the height of the contraction or the degree of shortening increases as the strength of the stimulus increases from a minimum to a GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 8i maximum value (Fig. 25). The rate at which the muscle is stimulated with a given stimulus will also influence the character of the contraction process. If the intervals between the successive stimulations be such as permit the muscle to recover from the effects of the contraction, it may contract as many as a thousand times without showing any particular variation from the normal form. In the earlier period of stimulation there is apparently a decrease in the irritability and consequently in the energy of the contraction for a short time. This is followed by an in- crease in the irritability, as shown by a gradual increase in the height of the curve until a certain maximum is reached and maintained (Fig. 26). These so-called staircase contractions have been observed in the muscles of both cold-blooded and warm- blooded animals. In time, however, as the muscle becomes fatigued the effects of repeated contractions manifest themselves in a lengthening of the latent period, a diminution in the rapidity and extent of the contraction, and an increase in the Fig. 25. — Showing the Ef- fects OF Increasing Strength of Stimulus. Fig. 26. — Showing Staircase Con- tractions. time of relaxation. If the intervals between successive stimu- lations be not sufficient for the muscle to recover itself, the same phenomena arise, though more quickly. Temperature. The temperature at which all phases of the con- traction process, as represented by the myogram, attain their physiologic maximum value is about 30° C. If the temperature of the muscle falls to 20° C. there is a corresponding decHne in activity, as shown by an increase of the latent period, a decrease in the height of curve, — i. e., in the shortening of the muscle, — an increase both in the contraction and relaxation periods. As the temperature approaches 0° C. the height of the curve again suddenly increases, indicating, for some unknown reason, an increase in the irritabihty. This is, however, scarcely a physio- logic condition. At a temperature of 40° C. to 50° C. the muscle suddenly contracts and passes into the condition of heat rigor. The proteid constituents of the muscle are coagulated and the irritability destroyed (Fig. 27). 6 82 TEXT-BOOK OF PHYSIOLOGY. The Load. The extent to which a muscle is loaded or weighted will not only determine the height of the contraction, but also the time relations of all its phases. This is apparent from an ex- amination of Fig. 28, in which it is shown that with an increase in load there is a decrease in the height of the contraction, an increase in the latent period, and a general decrease in the dura- tion of both the periods of rising and falling energy. Fig. -Single Contractions of the Gastrocnemius at Different Tempera- tures. Time Tracing, 200 per Second. — (Brodie.) Muscle Fatigue. Prolonged or excessive activity of our own muscles is accompanied by a feehng of stiffness or soreness and lassitude. There is at the same time a diminution in the rate and vigor of the contractions and the power of doing work. To this condition the term fatigue has been given. The cause of the fatigue is attributed to a diminution in the amount of the energy- holding compounds as well as to the production and accumulation Fig. 28. — Contractions of a Gastrocnemius with Different Loads. — (Brodie.) of waste products resulting from activity. Among the waste products phosphoric acid, potassium phosphate, lactic acid, and carbon dioxid are the most important. The more rapidly they are removed, the sooner is a fatigued muscle restored to its normal condition. It is highly probable that the nerve-centers are more easily fatigued than the muscles. The condition of fatigue with GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 83 its attendant phenomena is shown by an excised frog muscle when stimulated for a long period of time by induction shocks at intervals of one second. In a variable period of time the muscle shows an increase in the duration of the latent period, a diminution of the height of the contraction, in the power of doing work, and an increase in the time required for relaxation. If the stimulation continues, the contractions gradually dechne as the muscle becomes exhausted. (See Fig. 29.) Fig. 29. — Fatigue Curves. Every Twentieth Contraction Recorded. 5. Nutrition. — The irritability of a muscle which conditions the con- traction process is dependent on the maintenance of its nutrition ; hence a continuous and sufiticient supply of nutritive material and a rapid removal of waste products are essential conditions for the exhibition of normal contractions. A diminution of blood-supply or an accumulation of waste products sooner or later impairs the irritabihty and diminishes the vigor and extent of the contraction. Various drugs — e. g., veratrin, barium, etc. — introduced into the circulation and finding their way into the muscle modify the contraction process, as shown by a very great increase in the duration of the relaxation period. The Isometric Myogram. — With the object of obtaining a curve of the increase and de- crease in the tension of a muscle during a single contraction, with the exclusion as far as possible of a change in length, the muscle may be made to contract against a strong spring or similar resistance sufficient to practically though not absolutely prevent shorten- ing. To this method the term isometric has been given, and the curve so obtained an isometric myogram or a tonogram. The recording portion of the lever is prolonged some distance so that the Fig. 30. — a. Diagram of Isotonic; b, of Isometric Muscle Curves. — {Landois and Stirling.) 84 TEXT-BOOK OF PHYSIOLOGY. very slight upward movement at its axis, close to which the muscle is attached, will be considerably magnified. That the ordinate value of an isometric curve may be known, the apparatus must be graduated by subjecting the spring to a series of weights playing over a pulley supported by the muscle clamp. The curve of the variation in tension obtained by the isometric method is shown in Fig. 30, b, in which the two curves are con- trasted. The form of the curve indicates that the muscle attains its maximum of tension more rapidly than its maximum of shortening; that the tension endures for a certain period of time unchanged ; that the fall in tension takes place more rapidly than the muscle relaxes. The Work Accomplished by a Muscle during the Time of a Single Contraction. — By work is meant the overcoming of opposing forces. In the physiologic activities of the body the muscles at each contraction not only overcome the resistances of antagonistic muscles, the weight of the limbs, the friction of joints, etc., but in addition overcome various external resistances connected with the environ- ment — e. g., gravity, cohesion, friction, elasticity, etc. The muscles may therefore be regarded as machines for the accomphshment of work. Experimentally the work done by an isolated muscle may be calculated by multiplying the weight by the height through which it is lifted. In the following table it will be observed that the extent to which a muscle will shorten in response to a maximal stimulus is greatest when it is unweighted ; but as weights differing by a com- mon increment are added, the height of the contraction diminishes until with a given w'eight it is nil. The work done is show^n in the following table: Weight. He GHT. Work DONE. grams 14 mm. gram- millimeters 50 " 9 450 100 " 7 700 150 " 5 750 200 " 2 400 250 " From the preceding figures it is evident that the mechanical work of a muscle increases with increasing weights up to a certain maximum, and then declines to zero. Equally when the muscle contracts to its maximum without being weighted, and when it does not contract at all from being overweighted, no work is done. Between these two extremes the muscle performs varying amounts of work. The maximum amount of force which a muscle puts forth during a contraction is naturally measured by the amount of work done; but as this varies with the degree to w^hich the muscle is weighted, another measure has been adopted, to which the term absolute muscle force or static force has been given. The absolute force is measured by GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 85 the weight which is sufficient to prevent the muscle from shortening. This is best determined by the method of after-loading in which the muscle is not extended by the weight previous to the contraction. It has been found that the absolute force of a muscle is directly de- pendent on the number and not the length of the fibers it contains and proportional to the physiologic transverse section of the muscle. The transverse section of a muscle is obtained by dividing the volume 1058 (obtained by dividing its weight by the specific weight of mus- cle-tissue) by the average length of the fibers. For purposes of comparison it is customary to refer the absolute force to units of diameter — viz., one square centimeter. Rosenthal estimates the force for the square centimeter of the muscle of the frog at from 2 to 8 kilograms; for the muscles of man at 6 to 8 kilograms; Koster at about ten kilograms for the muscles of the leg and 7 or 8 kilograms for the muscles of the arm. Action of Successive Stimuli. — If a series of successive stimuh be applied to a muscle, the effect will vary according to the rapidity with which they follow one another. As previously stated, if the Summation Curve. interval preceding each stimulus be sufficiently long to enable the muscle to recover from the effects of the previous contraction, there will be no eft'ect for a long time except a shght increase, in the early period, of the irritabihty as shown by the increased height of the curve or shortening of the muscle. If, however, a second stimulus be applied to a muscle during the period of relaxation, a second con- traction immediately follows which is added to or superposed on the first ; the eft'ect produced will be greater than that produced by either stimulus separately. A third stimulus applied during the relaxation of the second con- traction produces a third contraction which adds itself to the second, and so on (Fig. 31). The increment of increase in the extent of the successive contractions gradually diminishes, however, until the muscle reaches a maximum of contraction. The superposition of the second contraction on the first, the third on the second, and so on, is termed summation 0} effects. Experiment has shown that the greatest effect of a second stimulus — that is, the highest contraction — is produced 86 TEXT-BOOK OF PHYSIOLOGY. when the stimulus is apphed during the last third of the period of rising energy, when the sum of the two contractions is almost twice as great as the first contraction (Fig. 32). The effects following both maximal and submaximal stimuh indicate that the muscle cannot attain its maximum of shortening except through a summation of several stimuh. If a second maximal stimulus enter a muscle dur- ing the latent period following the first, the effect produced will be no greater than that produced by a single stimulus. The muscle during this period is said to be refractory or non-responsive to a second stimulus. If, however, the stimuli are submaximal they add themselves together, and though the effect is but a single contrac- tion, it is larger than either would have produced separately. This is termed the summation of stimuli. Still further, if a series of subminimal stimuh, each of which is alone insufficient to produce a contraction of the muscle, be applied in rapid succession, a contraction frequently results. This is termed the summation of subminimal stimuli. Tetanus. — When a muscle is stimulated by a series of induced currents at the rate of four or six per second, it undergoes a corre- sponding number of contractions of about equal extent. If the rate of stimulation is increased up to the point when the interval between each stimulus is less than the duration of the entire contraction pro- cess, the muscle does not have time to completely relax before the arrival of the succeeding stimulus, and hence remains in a more or less contracted state, during which it exhibits a series of alternate partial contractions and relaxations. To this condition of muscle activity the term incomplete tetanus or clonus is apphed. A graphic record of an incomplete tetanus is given in Fig. 33. In such a tracing it is observed that the second stimulation, oc-. curring before the muscle had time to relax, gave rise to a second contraction, which was superposed on the first; the same result fol- lowed the third stimulus, the fourth, the fifth, and so on. Owing largely to this summation of the contractions there is a gradual rise in the height of the contraction curve. This condition of the muscle, viz., continued contraction, combined with diminished power of relaxation, is termed contracture. The tracing also shows that as the stimulus continues, the base hne, that connecting the lowest points of the contractions, gradually rises and takes the form of a curve which increases in height with the stimulation. The apex line, that connecting the highest points of the contractions, also rises at the same time, indicating a continuous increase in the height of the contractions. The duration of incomplete tetanus depends on a variety of circumstances, e. g., character of muscle, rate and strength of stimulation, etc., but mainly on the rapidity with which the muscle becomes fatigued. With the oncoming of fatigue the muscle begins GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 87 to relax, and ultimately returns to its normal condition, notwith- standing the continued stimulation. If the stimulation be with- drawn, the muscle does not at once return to its original length but remains more or less contracted for a variable time. This contrac- tion after stimulation is known as the contraction-remainder. If the stimulation be still further increased in frequency, the individual contractions become fused together and the curve described by the lever becomes a continuous hne. (See Fig. 7,^.) Notwith- standing the fact that the individual contractions are no longer visible, it can be shown by other methods that the muscle is undergoing a series of shght alternate contractions and relaxations or vibrations at least. After a varying length of time the muscle becomes fatigued, relaxes, and returns to its natural condition even though the stimu- lation continues. The number of stimuh per second necessary to develop tetanus will depend under normal circumstances on the Fig. ^5. — -Curves Showing the Analysis of Tetanus of a Frog's Muscle (Gas- trocnemius). The numbers under the curves indicate the number of shocks per second appHed to the muscle. There is almost complete tetanus with twenty- five per second, and it is a little lower than the previous one because the muscle was slightly fatigued. — {Stirling.) period of duration of the individual contractions. The longer this period, the less the number of stimuli required, and the reverse. Hence the number of stimuli will vary for different classes of animals and for different muscles in the same animal, e. g., 2 or 3 for the muscles of the tortoise, 10 for the muscles of the rabbit, 15 to 20 for the frog, 70 to 80 for birds, 330 to 340 for insects. Voluntary Tetanus. — The voluntary contractions as they occur in the hving body are to be regarded as states of tetanus more or less complete; for the simplest voluntary contraction, however rapidly it takes place, has always a longer duration than a single con- traction caused by a single induction shock. As tetanus experi- mentally produced is the result of a certain number of successive stimulations per second, it is assumed that a voluntary tetanus is the result of the transmission to the muscles of a certain number of nerve 88 TEXT-BOOK OF PHYSIOLOGY. stimuli per second. In other words, the voluntary tetanus is also the result of a discontinuous stimulation. The number of stimuh trans- mitted to a muscle has been estimated by the employment of the graphic method to vary from 8 to 13 per second, 10 being about the average. Unless the contraction process of human muscle differs from that of frogs, it is difficult, however, to see how 10 stimulations per second can give rise to even an incomplete tetanic contraction. Muscle Sound. — Providing a muscle be kept in a state of tension during its contraction, the intermittent variations in tension cause the muscle to emit an audible sound. This so-called muscle-sound or tone is an evidence that the stimulation of the muscle is not continu- ous, but discontinuous. If the muscle is tetanized by induction shocks, the pitch of the tone will correspond with the number of stimuh. A voluntary contraction is attended by a tone having a vibration frequency of about 36 to 40 per second, which is regarded as the first overtone of the muscle tone, which would have a vibration frequency in consequence of from 18 to 20 per second. This was formerly regarded as an indication of the rate of stimulation of volun- tary contraction. This view, however, is no longer sustained. CHEMIC PHENOMENA. The chemic changes which underlie the transformation of energy in the living muscle even when in a state of rest are active and com- plex, though but little is known as to their exact character. As shown by an analysis of the blood flowing to and from the resting muscle, it has, while flowing through the capillaries, lost oxygen and gained carbon dioxid. The amount of oxygen absorbed by the muscle (9 per cent.) is greater than the amount of carbon dioxid (6.7 per cent.) given off. Notwithstanding the relation of the oxygen ab- sorbed to the carbon dioxid produced, there is no parallelism between these two processes, as the carbon dioxid will be given off in the absence of free oxygen or in an atmosphere of nitrogen. In the active or contracting muscle all the chemic changes are increased, as shown both by an increased absorption of oxygen and an increased production of carbon dioxid, though the ratio existing between them differs considerably from that of the resting muscle. Thus, according to Ludwig, an active muscle absorbs 12.26 per cent, of oxygen and gives oft" 10.8 per cent, carbon dioxid. During the activity of a muscle its tissue changes from a neutral to an acid reaction, from the development of sarcolactic acid and possibly phosphoric acid. The degree of the acidity depends to some extent on the duration of the contraction periods. Chemic analysis of a tetanized muscle shows that it contains less glycogen than a resting muscle, and that it contains a larger amount of water. Coincident GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 89 with muscular contraction, the blood-vessels become widely dilated, leading to a large increase in the blood-supply and a rapid removal of the products of decomposition. Rigor Mortis. — A short time after death the muscles pass into a condition of extreme rigidity or contraction which lasts from one to five days. In this state they offer great resistance to extension. Their tonicity disappears, their cohesion diminishes, and their irri- tabihty ceases. The time of the appearance of this postmortem rigidity varies from a quarter of an hour to seven hours. Its onset and duration are influenced by the condition of the muscle irrita- bihty at the time of death. When the irritabihty is impaired from any cause, such as chronic disease or defective blood-supply, the rigidity appears promptly but is of short duration. After death from acute diseases it is apt to be delayed, but will continue for a longer period. The rigidity first appears in the muscles of the lower jaw and neck; next in the muscles of the abdomen and upper extremities; finally in the trunk and lower extremities. It disappears in prac- tically the same order. Chemic changes of a marked character accompany this process. The muscle becomes acid in reaction from the development of sarcolactic acid and there is a large increase in the amount of carbon dioxid given off. The immediate cause of the rigidity appears to be coagulation of the myosinogen within the sarco- lemma with the formation of an insoluble proteid, myosin. In the early stages of the coagulation restitution is possible by the circula- tion of arterial blood through the vessels. The final disappearance of this postmortem rigidity is due to the action of acids which render the myosin soluble, and possibly to the action of various micro- organisms which give rise to putrefactive changes. Source of the Muscle Energy. — Notwithstanding many in- vestigations, the nature of the materials which are the immediate source of the muscle energy is not known. The absence of any notice- able increase in the quantity of urea or other nitrogen-holding com- pounds excreted renders it probable that the energy does not come from the metaboHsm of proteid materials. The marked production of carbon dioxid and sarcolactic acid points to the decomposition of some unstable compound, of a carbohydrate character, rich in carbon and oxygen. It has been suggested that glycogen furnishes the energy, inasmuch as this substance, generally present in muscle, dis- appears during activity. A muscle which has been tetanized contains less glvcogen than the corresponding muscle at rest. A muscle which has been separated from the nervous system by division of its nerves and thus prevented from contracting accumulates glycogen. Bunge is of the opinion that though the carbohydrates are the main, they are not the only sources of muscle energy. If there is a deficiency or absence of carbohydrate food, the muscle will utihze fat and pro- 90 TEXT-BOOK OF PHYSIOLOGY. teid, for experiment has shown that the available glycogen is entirely consumed the second or third day. The mechanism by which the energy is liberated, whether by decomposition or direct oxidation, is unknown. The fact that muscle will contract in an atmosphere free of oxygen, that no free oxygen can be obtained from muscle, would support the idea that the mechanism is one of decomposition. Hermann suggests that the energy of a contraction is liberated by the sphtting and subsequent re-formation of a complex body belonging neither to the carbohydrates nor fats, but to the proteids — to this hypo- thetic body the term inogen is given. This complex molecule, the product of the nutritive activity of the muscle-cell in undergoing decomposition, would yield carbon dioxid, sarcolactic acid, and a proteid residue resembhng myosin. On the cessation of the con- traction the muscle-cell recombines the proteid residue with oxygen, carbohydrates, and fats, and again forms the energy-holding com- pound, inogen.' The phenomena of rigor mortis support this view. At the moment of this contraction the muscle gives off COj in large amount, develops sarcolactic acid and myosin. There is thus a close analogy between the two processes ; in other words, a contraction is a partial death of the muscle. If this view is correct, then the oxygen is required mainly for heat production through oxidation processes. THERMIC PHENOMENA. The potential energy Uberated during a contraction is transformed into kinetic energy — viz., heat and mechanic motion. Though heat production is taking place even during the passive condition, prob- ably through oxidation processes, it is largely increased by muscle activity. The skeletal muscle of the frog, the gastrocnemius, shows after tetanization an increase in temperature from 0.14° C. to 0.18° C, and after a single contraction from 0.001° C. to 0.005° C. The amount of heat thus produced will vary with a variety of conditions, as strength of stimulus, tension, work done, etc. Stimulus. — It has been experimentally determined that an in- crease in the strength of the stimulus from a minimal to a maximal value increases the amount of heat hberated. This is the direct result of increased chemic change naturally following increased stimulation. Tension. — The greater the tension of a muscle, the greater, other conditions being the same, is the amount of heat liberated. If the muscle is securely fastened at both extremities so that shortening is practically impossible during the stimulation, the maximum of heat production is reached. In the tetanic state the great increase in tem- perature is due to the tension of antagonistic and strongly contracted muscles. In both instances, mechanic motion being prevented, the liberated energy is transformed into heat. GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 91 Mechanic Work. — If the muscle is permitted to shorten and raise a weight, some of the energy Hberated takes the form of mechanic motion. If the weight is removed at the height of the contraction, external work is accomphshed. The greater the weight raised, within limits, the greater is the percentage of energy which takes the direction of mechanic motion. In accordance with the law of the conservation of energy, the heat produced, stated in calories, plus the energy required in the raising of the weight, expressed in kilogram- meters of work, must equal the potential energy transformed. A muscle during a tetanic contraction of short duration accom- plishes more work than during a single contraction; the weight in each case being the same. In the former condition the height of contraction through summation, and hence the work done, is greater than in the latter. The work done by a short tetanic contraction may be two or three times that of a single contraction, but after the muscle reaches its maximum degree of shortening and then con- tinues in a state of tetanus, no further w^ork is done. Internal work is done, however, as shown by an increase in the temperature. When a weight which is hfted by a muscle during a single con- traction is allowed to act on the muscle during the relaxation, no external work is accomphshed. All the energy set free manifests itself as heat. Internal work is done, as shown by the fact that the muscle becomes fatigued. ELECTRIC PHENOMENA. Electric Currents from Injured Muscles. — The energy liber- ated during a muscle contraction is not only transformed into heat and mechanic motion, but to some extent also into electric energy. The presence of points of different potential on the surface of the muscle, the necessary condition for the development of electric currents, is tested by means of non-polarizable elec- trodes connected by wires with a sensitive galvanometer or capil- lary electrometer. When such electrodes are brought in contact with a muscle properly prepared, there is at once developed and con- ducted to the galvanometer an electric current the intensity and direc- tion of which are indicated by the deflection of the galvanometer needle. The existence of this current is most conveniently demonstrated with single muscles the fibers of which are parallel — e. g., the sartorius, or the semimembranosus of the frog. If the tendinous ends of either of these muscles be removed by a section made at right angles to the long axis, a muscle prism is obtained which presents a natural longitudi- nal surface and two artificial transverse surfaces. A hne drawn around the surface of such a muscle prism at a point midway between the two transverse sections constitutes the equator. 92 TEXT-BOOK OF PHYSIOLOGY. When the natural longitudinal and artificial transverse surfaces are connected with the wires of a galvanometer the terminals of which are provided with non-polarizable electrodes, an electric current is at once developed. In all instances the current, as shown by the deflection of the needle, originates at the transverse surface, passes through the muscle to the longitudinal surface, thence through the galvan- ometer to the transverse surface. The longitudinal surface is, there- fore, electropositive, the transverse surface electronegative. The two points exhibiting the greatest difference of potential, and hence the most powerful current, he in the equator and in the center of the transverse surface. Currents of grad- ually diminishing intensity are ob- tained when the electrode placed on the longitudinal surface is removed toward either end. Feeble currents are developed when two points situ- ated at unequal distances, either on corresponding or opposite sides of the equator, are connected; in either case the current flows from the point lying nearest the equator to the point farth- est from it. Similar currents are ob- tained when two points on the cross- section situated at unequal distances from the central axis are connected, in which case the direction of the current will be from the point lying nearest the periphery toward the center. On the contrary, no current is developed when two points on the longitudinal surface equally distant from the equa- tor, or two points on the transverse surface equally distant from the cen- tral axis, are connected. Such points are said to be isoelectric. These facts are shown in Fig. 34. The natural ends of the muscle, enclosed by sarcolemma and tendon, do not exhibit, if carefully preserved from injury, the negativity characteristic of the artificial transverse ends. Similar electric conditions are exhibited by the muscles of man and other mammals, by the muscles of birds, reptiles, amphibia, etc. The currents developed by connecting the equator on the longitu- dinal surface with the axis of the transverse surface have an electromo- tive force in the frog muscle of from 0.037 to 0.075 of a Daniell cell. The electric currents in the muscle are intimately associated with Fig. 34. — Diagram to Illustrate THE Current in Muscle. The arrowheads indicate the direction; the thickness of the lines indicates the strength of the currents. — {Landois and Stirling.) GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 93 the chemic changes underlying its nutrition, and hence their intensity rises and falls with all the conditions which maintain or impair mus- cle nutrition and irritabihty. The currents observed in the injured muscle during the inactive state have been termed currents 0} rest. du Bois-Reymond regarded them as preexistent, intimately connected with the Hving condition of the muscle, and essential to the performance of its functions, and to be explained by the view that the entire muscle is composed of molecules each of which exhibits the same difference of potential on its longitudinal and transverse surfaces as the muscle prism itself. Hermann denies the existence of currents in normal resting muscle and attributes them to injuries of the surface, due to methods of preparation, in consequence of which the tissue dies and becomes electronegative to the uninjured area, which remains electro- positive. These currents Hermann terms "demarcation currents." Negative Variation of the Muscle Current. — If a muscle exhibiting a current of injury be excited to activity by tetanizing in- duced currents apphed to the opposite end of the /"T"^ muscle, it will be ob- served that as the con- traction wave passes over the muscle there is a movement of the galvan- ometer needle toward the zero point, indicating a diminution of the poten- tial on the longitudinal ^"^ ^-l,*-"-- surface. To this dimi- Fig. 35.— The Negative Variation of the De- v,,,+;^v, ;v, +v,^ r.f>.^»,^fV, r.f M.A.RCATION Current. A. The contraction nution m the strength of ^^^.^^ ^^^^ ^^ .^ ^^^^^^ ^^^^^^^ ^^^ ^1^^^^^^^ the current the term at B causes a diminution of potential. negative variation was given. On the withdrawal of the stimulus the needle again returns in a short time to its former position. The diminution of potential on the longitudinal surface of the muscle is now attributed to the passage of the excitation and contraction pro- cesses, to a temporary disintegration of the muscle substance (Fig. 35). With their disappearance and the subsequent restoration of the nutrition of the muscle, the former electric condition returns. The primary deflection of the galvanometer needle is due to the demarcation current which arises as a result of the difference in electric potential produced by the destructive chemic changes taking place at the cut end of the muscle. The negative variation is caused by the fact that the activity of the muscle, with its attendant chemic changes, will always be greater in the uninjured equatorial region, and hence will always tend to counterbalance the original source of difference in electric potential. 94 TEXT-BOOK OF PHYSIOLOGY. Electric Currents from Non-injured Muscles. — Though per- fectly normal resting muscle, according to Hermann, is isoelectric, nevertheless electric currents are developed during activity to which he has given the term action currents, and which are attributed to the propagation of the contraction wave. ^r'j/*Action Currents.— When two isoelectric points on the longitu- dinal surface of a muscle are connected with a galvanometer and a single stimulus applied directly to one extremity, it can be shown that as the contraction wave passes beneath A, Fig. 36, the muscle- tissue at that point becomes electronegative toward B and a cur- rent at once passes through the galvanometer from B to A, as shown by the deflection of the needle toward A. As the con- traction wave passes beneath B it in turn becomes electronegative, Fig. 36. — The Condition Leading to the Development of the First Action Current. and a temporary condition of equal potential is established when the needle returns to the zero point. In a very short time the nutrition of A is restored and becomes electropositive toward B, when a current will pass through the galvanometer in the opposite direction from A to B, as shown by the movement of the needle toward B, Fig. 37. As the contraction wave passes beyond B its nutrition is restored and becomes of equal potential with A. The term phasic is apphed to these currents. The first current flows in the muscle in the direction of progress of the contraction wave — first phase ; the second current flows in the reverse direction — second phase; the current is therefore diphasic. When a muscle is tetanized, there is but a single current observed, which, however, endures so long as the tetanic contrac- GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 95 tion is maintained. To this current the term decremential is given. When a muscle is excited to action by the nerve impulse which en- ters at its center, two contraction waves are developed, one in each half of the muscle, and hence there are two sets of diphasic action currents. The presence of action currents in the muscle of the Hving body during a single contraction was demonstrated by Hermann in the mus- cles of the forearm. The arrangement of the experiment was, briefly, as follows : The forearm was surrounded by two twine electrodes sat- urated with zinc solution, one being placed at the physiologic middle — the nervous equator — the other at the wrist. Both electrodes were then connected with the galvanometer. When the brachial plexus was stimulated in the axillary space, the deflections of the galvanometer Fig 37. — The Condition Leading to the Development of the Second Action Current. needle, when analyzed with the repeating rheotome, indicated phasic currents with a single contraction. In the first phase — atterminal — the wrist became positive and the current passed in the muscle toward its termination; and in the second — abterminal — it became negative and the current now passed in the reverse direction. The action currents which are observed in the frog's muscle were thus shown to be present in the living human muscle, with this difference, how- ever: that the second phase, — abterminal, — instead of being weaker in man, is equally strong with the atterminal. This experiment also revealed the fact that the rapidity of propagation of the excitation wave was much greater in man, amounting to about twelve meters per second. Hermann therefore denies the preexistence of electric currents and regards them as due to localized temporary disintegra- 96 TEXT-BOOK OF PHYSIOLOGY. tion of the muscle in consequence of activity, as they disappear on the restoration of the muscle to its normal condition. Work Done Daily. — The muscle system in its entirety is to be regarded as a machine for the transformation of potential into kinetic energy, and in so doing accomphshes work. Through the inter- mediations of the bones of the skeleton which play the part of levers the individual not only changes his position in space, but overcomes to some extent the resistances offered by the environment. The employment of artificial levers, tools, as distinguished from natural levers, bones, materially adds to the effectiveness of the muscle machine. The amount of work which a man of average physical development weighing 72 kilos can perform in eight hours has been variously estimated. It will naturally vary according to the character of the occupation. If the work done be calculated from the number of kilograms raised one meter, the average laboring-man performs about 300,000 kilogrammeters. SPECIAL ACTION OF MUSCLE GROUPS. The individual muscles of the axial and appendicular portions of the body are named with reference to their shape, action, structure, etc.; e. g., deltoid, flexor, penniform, etc. In different localities a group of muscles having a common function is named in accordance with the kind of motion it produces or to which it gives rise: e. g., groups of muscles which alternately diminish or increase the angular distance between two bones are known respectively as flexors and extensors; such muscle groups are usually found in association with ginglymus joints. Muscles which rotate the bone to which they are attached around its own axis without producing any great change of position are known as rotators, and are found in association with enarthrodial or ball-and-socket joints. Muscles which impart an angular movement to the extremities to and from the median line of the body are termed adductors and abductors respectively. In addition to the actions of individual groups of muscles in pro- ducing special movements, in some regions of the body, several groups of muscles are coordinated for the accomplishment of certain definite functions; e. g., the functions of respiration, mastication, etc. The coordination of axial and appendicular muscles enables the individual to assume certain postures, such as standing, sitting, and lying; to engage in various acts of locomotion, as walking, running, dancing, swimming. Levers. — The function or special mode of action of individual muscles can be understood only when the bones with which they are connected are regarded as levers whose fulcra or fixed points lie in the joints where the movement takes place, and the muscles as sources w F A P i A W 1 P (0 GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 97 of power for imparting movement to the levers with the object][of overcoming resistance. In mechanics levers of three kinds or orders are recognized according to the relative positions of the fulcrum or axis of motion, the applied power, and the weight to be moved. (See Fig. 38.) In levers of the first order the fulcrum, F, lies between the weight or resistance, W, and the power or moving force, P. The distance P F is known as the power arm and the dis- tance W F as the weight arm. As examples of this form of lever found in the human body may be mentioned : 1. The elevation of the trunk from the . _ flexed position. The axis of move- a W p^^^ ment, the fulcrum, lies in the hip-joint; the weight, that of the trunk, acting as ^ 5 — t(3) if concentrated at the center of gravity, ^^^ 38.— The Three Or- which lies close to the tenth dorsal ver- ' ders of Levers. tebra; the power, the muscles attached to the tuberosity of the ischium. The opposite movement is equally one of the first order, but the relative positions of P and W are reversed. 2. The head in its movement backward and forward on the atlas. In levers of the second order the weight Hes between the power and the fulcrum. As illustration of this form of lever may be men- tioned : 1. The depression of the lower jaw, in which movement the fulcrum is the temporomaxillar\' articulation; the resistance, the tension of the elevator muscles; the power, the contraction of the de- pressor muscles. 2. The raising of the body on the toes, in which movement the ful- crum is the toes, the weight that of the body acting through the ankle, the power the gastrocnemius muscle applied to the heel bone. In levers of the third order the power is applied at a point lying between the fulcrum and the weight. As examples of this form of lever may be mentioned : 1. The flexion of the forearm, in which the fulcrum is the elbow- joint, the power the biceps and brachialis anticus muscles ap- phed at their points of insertion, the weight that of the forearm and hand. 2. The extension of the leg on the thigh. When levers are employed in mechanic operations, the object aimed at is the overcoming of a great resistance by the application of a small force acting through a great distance, so as to obtain mechanic advantage. In the mechanism of the human body the reverse gener- 7 98 TEXT-BOOK OF PHYSIOLOGY. ally obtains, viz., the overcoming of a small resistance by the appli- cation of a large force acting through a short distance. As a result there is a gain in the extent and rapidity of the movement of the lever. The power, however, owing to its point of application, acts at a great mechanic disadvantage in many instances, especially in levers of the third order. Postures. — Owing to its system of joints, levers, and muscles the human body can assume a series of positions of equilibrium, such as standing and sitting, to which the term posture has been given. In order that the body may remain in a state of stable equilibrium in any posture, it is essential that the vertical line passing through its center of gravity shall fall within the base of support. Standing is that position of equilibrium in which a line drawn through the center of gravity of the entire body falls within the base of support. This position is maintained largely by the mechanical conditions of the joints, apparently for the purpose of reducing to a minimum muscular action, so that it can be prolonged for some time without giving rise to fatigue. In the military position, which may be assumed as the normal position, all the joints must be in such a condition of extension and fixation that the body will represent a rigid column resting on the astragalus and supported by the arch of the foot. This is accomplished : 1. By balancing the head on the apex of the vertebral column. This is done by the action of the muscles on the back of the neck. The muscular effort is, however, very sHght, as the center of gravity of the head lies but a short distance in front of the articulation. 2. By making the vertebral column erect and rigid. This is brought about by the action of the common extensor muscles of the trunk. In this condition the center of gravity lies just in front of the tenth dorsal vertebra. The head, trunk, and upper extremities are now supported by the hip-joints; and in order that this sup- port may give to the body a certain degree of stable equilibrium, independent of muscular action, the line of gravity falls behind the line uniting the center of rotation of the two joints. In conse- quence the body would fall backward were it not prevented by the tension of the iliofemoral hgament and the fascia lata. The line of gravity, continued downward, passes through the knee- joint posterior to the axis of rotation, and hence the body would now fall backward were it not prevented by the tension of the lateral ligaments and the contraction of the quadriceps femoris muscle. Though the body is supported by the astragalus, the line of grav- ity does not pass through the line uniting the two joints, for in so doing constant muscular effort would be required to maintain stable equilibrium; passing a short distance in advance of this Hne, there GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 99 would be a tendency of the body to fall forward, which is prevented by the extensor muscles of the foot. When the body is in the erect or mihtary position, the center of gravity lies between the sacrum and last lumbar vertebra. Standing is thus an act of balancing, and requires not only the static conditions of joints, but the dynamic conditions of various groups of muscles, and hence is not a position of absolute ease and cannot be maintained for any length of time without experiencing discomfort and fatigue. Sitting erect is an attitude of equilibrium in which the body is balanced on the tubera ischii, when the head and trunk together form a rigid column. Locomotion is the act of transferring the body as a whole through space, and is accomplished by the combined action of its own muscles. The acts involved consist of walking, running, jumping, etc. Walking is a complicated act involving almost all the voluntary muscles of the body either for purposes of progression or for bal- ancing the head and trunk, and may be defined as a progression in a forward horizontal direction due to the alternate action of both legs. In walking one leg becomes for the time being the active or supporting leg, carrying the trunk and head; the other the passive but progressing leg, to become in turn the active leg when the foot touches the ground. Each leg is therefore alternately in an active and passive state. Running is distinguished from walking by the fact that at a given moment both feet are off the ground and the body is raised in the air. THE VISCERAL MUSCLE. The visceral muscle, as the name implies, is found in the walls of hollow viscera, where it is arranged in the form of a membrane or sheet. It is present in the walls of the alimentary canal, blood- vessels, respiratory tract, ureter, bladder, vas deferens, uterus, fallopian tubes, iris, etc. In some situations it is especially thick and well developed — e. g., uterus and pyloric end of the stomach; in others it is thin and slightly developed. The Histology of the Visceral Muscle-fiber. — When examined with the microscope, the muscle sheet is seen to be composed of fibers, narrow, elongated, and fusiform in shape. As a rule, they are extremely small, measuring only from 40 to 250 micromillimeters in length and from 4 to 8 micromillimeters in breadth. The center of each fiber presents a narrow, elongated nucleus. The muscle- protoplasm w^hich makes up the body of the fiber appears to be enclosed by a delicate elastic membrane resembling in some respects the sarcolemma of the skeletal muscle. In some animals the visceral fiber presents a longitudinal striation suggesting the existence of fibrillae surrounded by sarcoplasm (Fig. 39). The fibers are united lOO TEXT-BOOK OF PHYSIOLOGY. longitudinally and transversely by a cement material. The muscle is increased in thickness by the superposition of successive layers. At varying intervals the fibers are grouped into bundles or fasciculi by septa of connective tissue (Fig. 40). Blood-vessels ramify in the connective tissue and furnish the necessary nutritive material. The visceral muscle receives stimuli from the spinal cord, not directly, however, as in the case of the skeletal muscle, but indirectly Fig. 39. — Two Smooth Muscle-fibers from Small Intestine of Frog. X 240. Isolated with 35 per cent, potash-lye. The nuclei have lost their characteristic form through the action of the lye. — (Stohr.) through the intermediation of ganghon cells, vv^hich may be located at some distance from the muscle or near the walls of the viscera. Non-medullated fibers from the ganglion pass directly into the muscle, where they frequently unite to form a general plexus. From this plexus fine branches take their origin and ultimately become physiologically associated with the muscle-fiber. Physiologic Properties. — The visceral muscles which have been subjected to experiment are mainly those of the stomach, in- testine, bladder, ureter, and iris. From the results of the experiments which have been published, it is evident that all visceral muscles possess elasticity, tonicity, irrita- bihty, and conductivity. The elasticity of the bladder muscle of the cat was strikingly shown in the experiments pub- lished by Dr. Colin C. Stewart. When this muscle was weighted with weights differing by a com- mon increment, it was extended on the addition of each weight, though to a progressively less extent. On the removal of the weights the muscle eventually returned to its former length. The records of the extension were similar to, if not identical with, those of the skele- tal muscle. Tonicity is a property common to all visceral muscles. Each muscle is continuously in a state of contraction intermediate between that of complete contraction and that of relaxation. In how far this is due to local and inherent causes or to stimuli reflected from the Connective-tissue septum. Nucleus. Smooth muscle-fiber in transverse section. Fig. 40. — Section of the Circular Layer of the Muscular Coat of THE Human Intestine. — {Stohr.) GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. loi nervous system as a result of peripherally acting causes is not in individual instances readily determinable. From time to time the tonicity varies, increasing and decreasing in response to these various stimuh and in accordance with the functional activities of the organs in which the muscle is found. The irritability manifests itself by a change of form, and doubt- less by the hberation of heat on the appHcation of any form of stimulus — ^mechanic, chemic, thermic, electric. The conductivity is less marked in the visceral than in the skeletal muscle, and, contrary to what is observed in the latter, the conduction extends laterally as well as longitudinally from fiber to iiber. This is shown by stimulation of the exposed intestine. Shortly after the stimulus is applied the muscle contracts longitudinally — i. e., in a direction at right angles to the long axis of the intestine, partially obliterating its lumen. From this point the conduction process indi- cated by the contraction wave passes in opposite directions for some distance along the canal. As to whether this is accomplished by protoplasmic processes extending from fiber to fiber, or whether the uniting membrane differs in conducting power from the sarcolemma, is as yet a matter of doubt. From the fact that the upper two-thirds of the ureter, though free of nerve-cells, exhibits lateral conduction, it is evident that it may take place independent of the nervous system. The Contraction of the Visceral Muscle. — The general character of the contraction may be witnessed on opening the abdomen of a recently killed animal, especially the rabbit. Shortly after exposure to the air the walls of the intestine begin to contract in a most vig- orous manner. The contraction wave beginning at various points is propagated in both directions, running along the intestinal wall for a variable distance. A succession of similar waves may be ob- served for some minutes. To the alternate contraction and relaxa- tion of the muscle-fibers, which are circularly arranged, the term peristalsis is usually given. The excised stomach of a dog kept under suitable conditions will exhibit similar movements. The same holds true of the bladder muscle of the cat, the muscle of the ureter, etc. Careful observation shows a certain periodicity in the movements. Inasmuch as the cause is not apparent, these contrac- tions are termed spontaneous or automatic. Graphic Record of the Contraction. — For experimental pur- poses narrow transverse sections of the stomach of the frog or the entire bladder muscle of the cat, excised or in situ, according to the method of Dr. Colin C. Stewart, may be employed. If kept moist, they will retain their irritabihty for some hours. The changes of form may be recorded with the usual muscle lever. When thus pre- pared, the muscle may exhibit for several hours a series of pulsa- tions, rhythmic in character. With spontaneously acting mammahan I02 TEXT-BOOK OF PHYSIOLOGY. muscle the contraction and relaxation periods are of equal duration. With the amphibian muscle they are of unequal duration, as a rule. In both classes of animals the character of the record, a succession of large and small contractions, would indicate that the general rhythmic movement is compounded of two or three secondary rhythms which differ in rate and character. A single pulsation may be recorded by stimulating the bladder muscle with the induced or the make and break of the constant current. A curve of such a contrac- tion is shown in Fig. 41. The contraction takes place more rapidly than the relaxation; the two phases occupying five and thirty- five seconds respectively. The latent period covered 0.25 second. With other muscles the time relations are slightly different. Tetanization of the bladder muscle of the cat occurred when the stimuh succeeded each other with a certain rapidity; the interval between stimuli approxi- mating a period somewhat less than two sec- onds. This muscle responds to variations in temperature, to strength of stimulus, to the load, in a manner similar to, if not identical with, the skeletal muscle . The Function of the Visceral Muscle. — In a general way it may be said that the vis- ceral muscle determines and regulates the pas- sage through the viscus or organ of the material contained within it. The food in the stomach and intestines is subjected to a churning pro- cess by the muscles, in consequence of which the digestive fluids are more thoroughly incor- porated and their characteristic action in- creased. At the same time the food is carried through the canal, the absorption of the nutri- tive material promoted, and the indigestible residue removed from the body. The blood is delivered in larger or smaller volumes ac- cording to the needs of the . tissues through a relaxation or contrac- tion of the muscle-fibers of the blood-vessels. The urine is forced through the ureter and from the bladder by the contraction of their respective muscles. The mode of action of the individual muscles will be described in successive chapters. Ciliary Movement. — The free surface of the epithehum cover- ing the mucous membrane in certain regions of the body is charac- terized by the presence of delicate filamentous processes termed cilia. (See Fig. 42.) Cihated epithelium is found in man and mammals generally, in the nose, Eustachian tube, larynx, with the exception of the vocal membranes, trachea and bronchial tubes as ii,r;Mininir»ii»iii[rnriiiiir;rN..ii Fig. 41. — The Curve OF Contraction OF THE Bladder Muscle at Body- temperature in Response to a Single Induction Current. The time is indicated in seconds. — (Slewart.) GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 103 far as the pulmonary lobules, Fallopian tubes, uterus, and epididymis. The lumen of the central canal of the spinal cord and the cavities of the brain are lined, especially in childhood, by cells provided with similar ciHa. Cihated epithelium is also found in all classes of ani- mals, and especially in the invertebrates. The ciha found in the human body vary in length from 0.003 ^^• to 0.005 ^^^^- They are apparently structureless and colorless, and appear to have their origin in and to be a prolongation of a trans- parent material on the outer surface of the cell material. The number of ciha present on the surface of any individual cell varies approximately from five to twenty-five. When cihated epithehal cells, freshly removed from the mucous membrane and moistened with normal sahne, are examined with the microscope, it will be found that the ciha are in continuous and rapid vibratile movement, so much so that the individual cihum cannot be distinguished. In time, however, their vitahty declines and the rapidity of movement diminishes. When the movement of the individual cihum falls to about eight or ten per second, its character can be readily determined. It will then be seen that the movement is, as a rule, alter- nately a backward and a forward one, the cihum lowering and then raising itself, the latter taking place more quickly and ener- getically than the former. As the cihum raises itself it becomes somewhat flexed in a direction corresponding to that of the general movement. The movement, how- fig. 42.— Ciliated Epi- ever, varies in character in different situa- thelium. tions and in different animals. The cause of the movements and the mechanism of their coordination are unknown. They are, as far as known, independent of the nervous system. The force of ciliary motion is very great. A load of twenty grams can be supported and carried forward by the cilia on the mucous membrane of the mouth and esophagus of the frog. The activity of the ciha is associated with the nutrition of the cell of which they are a part and rises and falls with it. Experimentally it has been found that the rate and energy of the movement are greatest at a temperature of about 35° to 40° C, especially if they are bathed with normal saline, rendered slightly alkahne. Low temperatures, acids, alkahes, carbon dioxid, etc., retard the move- ment. ■ The function of the ciha, though not always apparent, is asso- ciated with the function of the passages in which they are found. As the surfaces of these passages are swept by a current of considerable power, it is probable that they assist in the passage of the materials I04 TEXT-BOOK OF PHYSIOLOGY. which ordinarily traverse them. Mucus and particles of dust are carried upward through the air-passages; the ovarian cell is carried from the ovary toward the uterus; the spermatozoa, as well as the fluid in which they are contained, are carried forward through the epididymis ducts. CHAPTER VII. THE GENERAL PHYSIOLOGY OF NERVE-TISSUE. The nerve-tissue, which unites and coordinates the various organs and tissues of the body and brings the individual into relation- ship with the external world, is arranged in two systems, termed the encephalospinal or cerebrospinal and the sympathetic. The encephalospinal system consists of: 1. The brain and spinal cord, contained within the cavities of the cranium and the spinal column respectively, and 2. The cranial and spinal nerves. The sympathetic system consists of: 1. A double chain of ganglia situated on each side of the spinal column and extending from the base of the skull to the tip of the coccyx. 2. Various collections of ganglia situated in the head, face, thorax, abdomen, and pelvis. All these ganglia are united by an elab- orate system of intercommunicating nerves, many of which are connected with the cerebrospinal system. HISTOLOGY OF NERVE-TISSUE. The Neuron. — The nerve-tissue has been resolved by the in- vestigations of modern histologists into a single morphologic unit, to which the term neuron has been apphed. The entire nerve system has been shown to be but an aggregate of an infinite number of neurons, each of which is histologically distinct and independent. Though having a common origin, as shown by embryologic investi- gations, they have acquired a variety of forms in different parts of the nervous system in the course of development. The old conception that the nerve system consisted of two distinct histologic elements, nerve-cells and nerve-fibers, which differed not only in their mode of origin, but also in their properties, their relation to each other, and their functions, has been entirely disproved. The neuron, or neurologic unit, is histologically a nerve-cell, the surface of which presents a greater or less number of processes in varying degrees of differentiation. As represented in figure 43, A, the neuron may be said to consist of: (i) The nerve-cell, neurocyte, or corpus; (2) the axon, or nerve process; (3) the end-tufts, or terminal branches. Though these three main histologic features are every- where recognizable, they exhibit a variety of secondary features in 105 io6 TEXT-BOOK OF PHYSIOLOGY. different situations in accordance with peculiarities of function. Though the nerve-cell and the nerve-fiber are but part of the same neuron, it is convenient at present to describe them separately. The Nerve-cell. — The nerve-cell, or body of the neuron, presents a variety of shapes and sizes in different portions of the nervous system. Originally ovoid in shape, it has acquired, in course of de- velopment, pecuharities of form which are described as pyramidal, stellate, pear-shaped, spindle-shaped, etc. The size of the cell varies considerably, the smallest having a diameter of not more than ■g-Q^Q-jj of an inch, the largest not more than -^}y^ of an inch. Each cell 1^" Ferminal nches. Xeurilemma. . Xerve-cell. Terminal branches. Fig. 43. — A. Efferent neuron Afferent neuron. consists of granular, striated protoplasm, containing a distinct ves- icular nucleus and a well-defined nucleolus. A cell membrane has not been observed. From the surface of the adult cell portions of the protoplasm are projected in various directions, which portions, rapidly dividing and subdividing, form a series of branches, termed dendrites or dendrons. In some situations the ultimate branches of the dendrites present short lateral processes, known as lateral buds, or gemmules, which impart to the branches a feathery appearance. This characteristic is common to the cells of the cortex of the cere- brum and of the cerebellum. The ultimate branches of the den- GENERAL PHYSIOLOGY OF NERVE-TISSUE. 107 drites, though forming an intricate feltwork, never anastomose with one another nor unite with dendrites of adjoining cells. According to the number of axons, nerve-cells are classified as monaxonic, diaxonic, polyaxonic. Most of the cells of the nervous system of the higher vertebrates are monaxonic. In the gangha of the posterior or dorsal roots of the spinal and cranial nerves, however, they are diaxonic. In this situation the axons, emerging from opposite poles of the cell, either remain separate and pursue opposite directions, or unite to form a common stem, which subsequently divides into two branches, w^hich then pursue opposite directions. (See Fig. 43, B.) The nerve-cell maintains its own nutrition, and presides over that of the dendrites and the axon as well. If the latter be separated in any part of its course from the cell, it speedily degenerates and dies. The axon, or nerve process, arises from a cone-shaped projection from the surface of the cell, and is the first outgrowth from its pro- toplasm. At a short distance from its origin it becomes markedly differentiated from the dendrites which subsequently develop. It is characterized by a sharp, regular outhne, a uniform diameter, and a hyahne appearance. In structure, the axon appears to consist of fine fibrillae embedded in a clear, protoplasmic substance. Shafer advocates the view that the fibrillag are exceedingly fine tubes filled with fluid. The axon varies in length from a few milhmeters to one meter. In the former instance the axon, at a short distance from its origin, divides into a number of branches, which form an intricate feltwork in the neighborhood of the cell. In the latter instance the axon continues for an indefinite distance as an individual struc- ture. In its course, however, especially in the brain and spinal cord, it gives off a number of collateral branches, which possess all its his- tologic features. The long axons serve to bring the body of the cell into direct relation with peripheral organs, or with more or less re- mote portions of the nerve system, thus constituting association or commissural fibers. The more or less elongated axon becomes invested, as a rule, at a short distance from the cell with nucleated oblong cells, which subse- quently become modified and constitute the medullary or myehn sheath. This is invested by a thin, cellular membrane — the neu- rilemma. These three structures thus constitute what is known as a medidlated nerve-fiber. In the brain and spinal cord the outer sheath, however, is frequently absent. In the sympathetic system the myelin is also frequently absent, though the axon is inclosed by the neurilemma, thus constituting a non-mediillated nerve-fiber. The end-tii}ts or terminal organs are formed by the sphtting of the axon into a number of filaments, which remain independent of one another and are free from the medullary investment. The histologic pecuHarities of the terminal organs vary in different situations, and in io8 TEXT-BOOK OF PHYSIOLOGY. many instances are quite complex and characteristic. In peripheral organs, as muscles, glands, blood-vessels, skin, mucous membrane, the tufts are in direct histologic and physiologic connection with their cellular elements. In the brain and spinal cord the tufts are in more or less intimate relation with the dendrites of adjacent neurons. The neurons in their totahty constitute the neuron or nerve tissue. From the fact that they are arranged both serially and col- laterally into a regular and connected whole, they collectively con- stitute a system known as the neuron or nerve system. Neurons, moreover, are grouped into more or less completely organized masses, termed organs, which in accordance with their locations may for convenience be divided into central and peripheral organs. The central organs of the nerve system consist of the encephalon or brain and the spinal cord; the peripheral organs consist of the cranial nerves, the spinal nerves, the sympathetic ganglia and their branches. Nerve-fibers. — The nerve-fibers which constitute by far the larger part of both the peripheral and central organs of the nerve system, are simply the axonic processes of neurons with their second- ary investments, the myelin and neurilemma; according as they possess or do not possess the medullary sheath, they may be divided into two groups — viz., medullated and non-meduUated libers. Medullated Nerve-fibers. — These consist for the most part of three distinct structures: 1. An external investing sheath, tubular in shape, termed the neuri- lemma. 2. An intermediate semifluid substance — the medulla or myelin, 3. An internal dark thread — the axis-cylinder. The neurilemma is a thin, transparent, homogeneous membrane closely adherent to the medulla. Owing to its colorless appearance, it can be seen only with difficulty in fresh tissue. When treated with various reagents, it becomes distinct. Physically, it is quite resistant and elastic. Its function is doubtless that of a protective agent to the structures within. The medulla, myelin, or white substance 0} Schwann completely fills the neurilemma and closely invests the axis-cyhnder or axon. In fresh tissue the medulla is clear, homogeneous, semifluid, and highly refracting. In composition it is oleaginous. When the nerve is treated with various reagents which alter its composition, the medulla becomes opaque and imparts a white, glistening appearance. The function of the medulla is quite unknown. At intervals of about seventy-five times its diameter the medul- lated nerve-fiber undergoes a remarkable diminution in size, due to an interruption of the medullary substance, so that the neurilemma lies directly on the axis-cylinder. These constrictions, or 7iodes 0} GENERAL PHYSIOLOGY OF NERVE-TISSUE. 109 Ranvier, taking their name from their discoverer, occur at regular intervals along the course of the nerve, separating it into a series of segments. The portion between the nodes is termed the internodal segment. It has been suggested that in consequence of the absence of the myehn at these nodes, a free exchange of nutritive material and decomposition products can take place between the axis-cyhnder and the surrounding plasma. The axis-cylinder, or axon, the direct outgrowth of the nerve-cell, is the most essential element of the nerve-fiber, as it alone is uni- formly continuous throughout. In the natural condition it is trans- parent and invisible; but when treated with proper reagents, it presents itself as a pale, granular, flattened band, more or less solid and somewhat elastic. It is albuminous in composition. With Fig. 44. ^^^^^S^^^r^^jf -Transverse Section of a Nerve (Median), ep. Epineurium. pe. Perineurium, ed. Endoneurium. — (Landois and Stirling.) high magnification the axis presents a longitudinal striation, indicating a fibrillar structure. The hbrillse appear to be embedded in an intervening semifluid substance, the neuroplasm. Non-medullated Nerve-fibers. — These consist, for the most part, only of the axis- cylinder, though in some portions of the nerve system a neurilemma is also present. Though much less abundant than the former variety, they are distributed largely throughout the nerve system, but are particularly abundant in the sympathetic. Owing to the absence of a medulla, they present a rather pale or grayish appearance. Sympathetic Ganglia. — A sympathetic gangHon consists essen- tially of a connective-tissue capsule with an interior framework. no TEXT-BOOK OF PHYSIOLOGY. The meshes of this framework contain nerve-cells provided v^ith dendrites and branching axons. The majority of the axons are non- medullated. In all instances, with the exception of the ganglion cells of the heart, the axons are distributed to nonstriated muscle tissue and to the epithehum of glands. The nerve-cells of the ganglia are also in histologic connection with the terminal branches of fine medullated nerve-fibers which leave the spinal cord by way of the nerve-trunks. These nerve- fibers are designated pre- ganglionic fibers, while those emerging from the cells are designated post- ganglionic fibers. The Peripheral Organs of the Nerve System. — These consist of the cranial and spinal nerves and the sympathetic gangha. Each nerve consists of a variable number of nerve-fibers united into firm bundles by connective tissue which supports blood-vessels and lym- phatics. The bundles are technically known as nerve-trunks or nerves. The nerve-trunks connect the brain and cord with all the re- maining structures of the body. Each nerve is invested by a thick layer of lamellated connective tissue, known as the epineurium. A transverse section of a nerve shows (see Fig. 44) that it is made up of a number of small bundles of fibers, each of which possesses a separate investment of connective tissue — the perineurium. With- in this membrane the nerve-fibers are supported by a fine stroma — the endoneurium. After pursuing a longer or shorter course, the nerve-trunk gives off branches, which interlace very freely with neighboring branches, forming plexuses, the fibers of which are distributed to associated organs and regions of the body. From their origin to their termination, however, nerve-fibers retain their individuality, and never become blended with adjoining fibers. As nerves pass from their origin to their peripheral terminations, they give off a number of branches, each of which becomes invested with a lamellated sheath — an offshoot from that investing the parent trunk. This division of nerve-bundles and sheath continues through- out all the branchings down to the ultimate nerve-fibers, each of which is surrounded by a sheath of its own, consisting of a single layer of endothelial cells. This delicate transparent membrane, the sheath of Henle, is separated from the nerve-fiber by a considerable space, in which is contained lymph destined for the nutrition of the fiber. Near their ultimate terminations the nerve-fibers themselves undergo division, so that a single fiber may give origin to a number of branches, each of which contains a portion of the parent axis- cyhnder and myelin. Blood-supply. — Nerves being parts of living cells require for the maintenance of their nutrition a certain amount of blood. This is furnished by the blood-vessels ramifying in and supported by the connective-tissue framework. Here as elsewhere there is a constant GENERAL PHYSIOLOGY OF NERVE-TISSUE. m exchange, through the capillary wall and the neurilemma, of nutritive material to the nerve proper and of waste materials to the blood. .The Chemic Composition and Metabolism. — Chemic analysis of nerve-tissue has shown the presence of water, proteids (two glob- ulins and a nucleo-proteid), neurokeratin and nuclein, two phos- phorized bodies (protagon and lecithin), several cerebrosides (nitro- gen-holding bodies of a glucoside character, as shown by their yielding the reducing carbohydrate galactose), inorganic salts, and a series of nitrogen-holding bodies such as creatin, xanthin, urea, leucin, etc. As to the metabolism that is taking place in nerve-cells and fibers, practically nothing definite is known. That such changes, how- ever, are taking place would be indicated first by the blood-supply, and second by the fact that withdrawal of the blood-supply is followed by a loss of irritability. The metabolism of the central organs of the nerve system is more active and extensive. In this situation any with- drawal of blood from compression or occlusion of blood-vessels is followed by impairment of nutrition and loss of function. THE RELATION OF THE PERIPHERAL ORGANS TO THE CENTRAL ORGANS OF THE NERVE SYSTEM. Spinal Nerves. — The nerves in connection with the spinal cord are thirty-one in number o;i each side. If traced toward the spinal column, it will be found that the nerve-trunk passes through an intervertebral foramen. Near the outer Hmits of the foramina each nerve-trunk divides into two branches, generally termed roots, one of which, curving shghtly forward and upward, enters the spinal cord on its anterior or ventral surface, while the other, curving back- ward and upward, enters the spinal cord on its posterior or dorsal surface. The former is termed the anterior or ventral root; the latter, the posterior or dorsal root. Each dorsal root presents near its union with the ventral root a small ovoid grayish enlargement known as a ganghon. Both roots previous to entering the cord subdivide into from four to six fascicuh. A microscopic examination of a cross-section of the spinal cord shows that the fibers of the ventral roots can be traced directly into the body of the nerve-cells in the anterior horns of the gray matter. The fibers of the dorsal roots are not so easily traced, for they diverge in several directions shortly after entering the cord. In their course they give off collateral branches which, in common with the main fiber, end in tufts which become associated with nerve-cells in both the anterior and posterior horns of the gray matter. Cranial Nerves. — The nerves in connection with the base of the brain are known as cranial nerves; some of these nerves present a similar gangHonic enlargement, and therefore may be regarded as 112 TEXT-BOOK OF PHYSIOLOGY. dorsal nerves, while others may be regarded as ventral nerves. Their relations within the medulla oblongata are similar to those within the spinal cord. Efferent and Afferent Nerves. — Nerves are channels of com- munication between the brain and spinal cord, on the one hand, and the muscles, glands, blood-vessels, skin, mucous membrane, viscera, etc., on the other. Some of the nerve-fibers serve for the transmission of nerve energy from the brain and spinal cord to certain peripheral organs, and so increase or retard their activities; others serve for the transmission of nerve energy from certain peripheral organs to the brain and spinal cord which gives rise to sensation or other modes of nerve activity. The former are termed efferent or centrifugal, the latter afferent or centripetal nerves. Experimentally it has been de- termined that the anterior or ventral roots contain all the efferent fibers, the posterior or dorsal roots all the afferent fibers. THE PERIPHERAL ENDINGS OF NERVES. The efferent nerves as they approach their ultimate terminations lose both the neurilemma and myehn sheath. The axon or axis- cyhnder then divides into a number of branches which become directly and intimately associated with tissue-cells. The particular Nerve-fiber bundle. Fig. 45. — Motor Nerve-endings of Intercostal Muscle-fibers of a Rabbit. X ISO.— {Sidhr.) mode of termination varies in different situations. These terminations are generally spoken of as end-organs, terminal organs, or end-tufts. In the skeletal muscle the nerve-fiber loses both neurilemma and myehn sheath at the point where it comes in contact with the muscle- GENERAL PHYSIOLOGY OF NERVE-TISSUE. 113 fiber. After penetrating the sarcolemma, the axon or axis-cyhnder divides into a number of small branches which appear to be embedded in a relatively large mass of sarcoplasm and nuclei, the whole form- ing the so-called "motor plate." Each muscle-fiber possesses one such plate or end-organ in mammalia, several in the frog. In the visceral muscle the terminal nerve-fibers derived from sympathetic or peripheral neurons are primarily non-meduUated, The axons divide and subdivide and form plexuses which surround the muscle-cell bundles. Fine fibers from the plexuses are given off which ultimately come into relation with each individual cell, on the surface of which they terminate in the form of one or more granular masses. In the glands, taking as an illustration the parotid and mammary glands, the nerve-fibers, also derived from sympathetic or peripheral neurons, pass into the body of the gland and ultimately reach the acini, on the outer surface of which they ramify and form a plexus. From this plexus fine fibers penetrate the acinus wall and end on the gland-cell. The fibers pre- sent a varicose appearance (Fig. 46). The afferent nerves as they approach their ultimate termina- tions undergo similar changes. The end-tufts become associated, ^^^ 46.-Terminations of Nerve- in some situations, with special- fibers in the Gland-cells. A. ized end-organs which are ex- Cell of the parotid gland of a rabbit , , iV, i.- B. Cells of the mammary gland tremely complex; e. g., the retina ^j ^ ^^t in gesuiion.-{Doyon a,id in the eye, the organ of Corti in Moral.) the ear, the taste-beakers in the tongue, the olfactory cells in the nose. In the skin and mucous membranes the mode of termination varies considerably. The following are some of the principal modes : 1. Free endings in the epithelium. 2. Tactile cells of Merkel. 3. Tactile corpuscles in the papillae of the true skin. 4. Pacinian corpuscles found attached to the nerves of the hand and feet, to the intercostal nerves, and to nerves in other situations. 5. End-bulbs of Krause in the conjunctiva, chtoris, penis, etc. (A consideration of these end-organs will be found in the chapters devoted to the organs of which they form a part.) In the skeletal muscles afferent fibers become associated with small spindle-shaped structures known as muscle-spindles or neuromuscle end-organs. These spindles vary in length from i mm. to 4 mm. They consist of a capsule of fibrous tissue containing from five to twenty muscle-fibers. After penetrating the several layers of the 114 TEXT-BOOK OF PHYSIOLOGY. Posterior GoAfflian^ capsule, the nerve-fibers lose the neurilemma and myelin sheaths. The axons or axis-cyhnders then divide into several long narrow branches which wind themselves in a spiral manner around the con- tained muscle-fiber and terminate in small oval-shaped discs. Similar endings have been observed in the tendons of muscles. Development and Nutrition of Nerves. — The efferent nerve- fibers, which constitute some of the cranial nerves and all the ventral roots of the spinal nerves, have their origin in cells located in the gray mat- ter beneath the aqueduct of Sylvius, beneath the floor of the fourth ventricle, and in the anterior horns of the gray matter of the spinal cord. These cells are the modified descendants of independent, oval, pear-shaped cells — the neuroblasts — which migrate from the medullary tube. As they approach the surface of the cord their axons arc directed toward the ventral surface, which eventually they pierce. Emerging from the cord, the axons continue to grow, and become invested with the myehn sheath and neurilemma, thus constituting the ventral roots. The afferent nerve-fibers, which constitute some of the cranial nerves and all the dorsal roots of the spinal nerves, develop outside of the central nervous system and only subsequently become con- nected with it. (See Fig. 47.) At the time of the closure of the medullary tube a band or ridge of epithelial tissue develops near the dorsal surface, which, becoming segmented, moves outward and forms the rudimentary spinal ganglia. The cells in this situation develop two axons, one from each end of the cell, which pass in opposite directions, one toward the spinal cord, the other toward the per- iphery. In the adult condition the two axons shift their position, unite, and form a T-shaped process, after which a division into two branches again takes place. In the ganglia of all the sensori-cranial and sensori-spinal nerves the cells have this histologic peculiarity. The efferent fibers are therefore to be regarded as outgrowths from the nerve-cells in the ventral horns of the gray matter, and serve to bring the cells into anatomic and physiologic relationship directly with the skeletal muscles and indirectly, through the intermediation Anferivr £006 Fig. 47. — Diagram Showing the Mode of Origin of the Ventral and Dorsal Roots. — {Edinger, after His.) GENERAL PHYSIOLOGY OF NERVE-TISSUE. 115 of ganglia (see sympathetic nervous system), with visceral muscles and glands. The afferent fibers are to be regarded as outgrowths from the cells of the dorsal nerve gangha, and serve to bring the skin, mucous membrane, and certain visceral structures into relation with special- ized centers in the central nervous system. Nerve Degeneration. — If any one of the cranial or spinal nerves be divided in any portion of its course, the part in connection with the periphery in a short time exhibits certain structural changes, to which the term degeneration is appHed. The portion in connection with the brain or cord retains its normal condition. The degenerative process begins simultaneously throughout the entire course of the nerve, and consists in a disintegration and reduction of the medulla and axis-cyhnder into nuclei, drops of myehn, and fat, which in time disappear through absorption, leaving the neurilemma intact. Coin- cident with these structural changes there is a progressive alteration Fig. 48. — DEGENEitA.TiON OF Spinal Nerves and Nerve-roots after Section. A. Section of nerve-trunk beyond the ganglion. B. Section of anterior root. C. Section of posterior root. D. E.xcision of ganglion, a. Anterior root. p. Posterior root. g. Ganglion. — (Dalton.) and diminution in the excitabihty of the nerve. Inasmuch as the central portion of the nerve, which retains its connection with the nerve-cell, remains histologically normal, it has been assumed that the nerve-cells exert over the entire course of the nerve-fibers a nutritive or a trophic influence. This idea has been greatly strength- ened since the discovery that the axis-cyhnder, or the axon, has its origin in and is a direct outgrowth of the cell. When separated from the parent cell, the fiber appears to be incapable in itself of maintaining its nutrition. The relation of the nerve-cells to the nerve-fibers, in reference to their nutrition, is demonstrated by the results which follow section of the ventral and dorsal roots of the spinal nerves. If the anterior root alone be divided, the degenerative process is confined to the peripheral portion, the central portion remaining normal. If the ii6 TEXT-BOOK OF PHYSIOLOGY. posterior root be divided on the peripheral side of the ganghon, de- generation takes place only in the peripheral portion of the nerve. (See Fig. 48.) If the root be divided between the ganglion and the cord, degeneration takes place only in the central portion of the rooi. From these facts it is evident that the trophic centers for the ventral and dorsal roots lie in the spinal cord and spinal nerve gangha, respectively, or, in other words, in the cells of which they are an integral part. The structural changes which nerves undergo after separation from their centers are degenerative in character, and the process is usually spoken of, after its discoverer, as the Wallerian degeneration. When the degeneration of the efferent nerves is completed, the structures to which they are distributed, especially the muscles, un- dergo an atrophic or fatty degeneration, with a change or loss of their irritability. This is, apparently, not to be attributed merely to in- activity, but rather to a loss of nerve influences, inasmuch as inactivity merely leads to atrophy and not to degeneration. CLASSIFICATION OF NERVES. The efferent nerves may be classified, in accordance with the characteristic form of activity to which they give rise, into several groups, as follows : 1. Muscle or motor nerves, those which convey nerve energy or nerve impulses to muscles and excite them to activity. 2. Gland or secretor nerves, those which convey nerve impulses to glands, and cause the formation and discharge of the secretion peculiar to the gland. 3. Vascular or vaso-motor nerves, those which convey nerve impulses to blood-vessels, and cause, either by stimulation or inhibition of the mechanism of their walls, a contraction (vaso-constrictors) or dilatation (vaso-dilatators) of the vessel. 4. Inhibitor nerves, those conveying nerve impulses that cause a slowing or complete cessation of the rhythmic action of organs. 5. Accelerator nerves, those conveying impulses that cause an increase in the rhythmic action of certain organs. The efferent nerves have been somewhat differently classified by Gaskell as follows: 1. Nerves to skeletal muscles. 2. Nerves to vascular muscles. (a) Vaso-motor, i. e., vaso-constrictors; accelerators and aug- mentors of the heart. (6) Vaso-inhibitor, i. e., vaso-dilatators; and inhibitors of the heart. GENERAL PHYSIOLOGY OF NERVE-TISSUE. 117 3. Nerves to visceral muscles. {a) Viscero- motor, (b) Viscero-inhibitor. 4. Nerves to glands. The afferent nerves may also be classified, in accordance with the character of the sensations or other modes of nerve activity to which they give rise, into several groups, as follows : 1. Sensorijacient nerves, those conveying nerve impulses that give rise in the brain to conscious sensations. They may be sub- divided into — (a) Nerves of special sense — e. g., olfactory, optic, auditory, gusta- tory, tactile, thermal, pain, pressure, muscle — giving rise to correspondingly named sensations. (b) Nerves of general sense — e. g., the visceral afferent nerves — those which give rise normally to vague and scarcely percept- ible sensations, such as the general sensations of well-being or discomfort, hunger, thirst, fatigue, sex, want of air, etc. 2. Reflex nerves, those which convey nerve impulses to the nerve- centers and cause a discharge and transmission of nerve impulses outward through efferent nerves to muscles, glands, or blood- vessels, and thus influence their activity. It is quite probable that one and the same nerve may subserve both sense and reflex action, owing to the collateral branches which are given off from the posterior roots as they ascend the posterior column of the cord. 3. Inhibitor nerves, those which are capable reflexly of retarding or inhibiting the activity of either nerve-centers or peripheral organs. PHYSIOLOGIC PROPERTIES OF NERVES. Nerve Irritability or Excitability and Conductivity. — These terms are employed to express that condition of a nerve which enables it|to develop and to conduct nerve impulses from the center to the periphery, or from the periphery to the center, in response to the action of stimuli. A nerve is said to be excitable or irritable so long as it possesses these capabilities or properties. For the manifestation of these properties the nerve must retain a state of physical and chemic integrity; it must undergo no change in structure or chemic composi- tion. The irritability of an efferent nerve is demonstrated by the contraction of a muscle, by the secretion of a gland, or by a change in the cahber of a blood-vessel, whenever a corresponding nerve is stimulated. The irritability of an afferent nerve is demonstrated by the production of a sensation or a reflex action whenever it is stimu- lated. The irritability of nerves continues for a certain period of time after separation from the nerve-centers and even after the death ii8 TEXT-BOOK OF PHYSIOLOGY. of the animal, the time varying in different classes of animals. In the warm-blooded animals, in which the nutritive changes take place with great rapidity, the irritabihty soon disappears — a result due to disintegrative changes in the nerve, caused by the withdrawal of the blood-supply and other non-physiologic conditions. In cold-blooded animals, on the contrary, in which the nutritive changes take place relatively slowly, the irritabihty lasts, under favorable conditions, for a considerable time. Other tissues besides nerves possess irritability, that is, the property of responding to the action of stimuli — e. g., glands and muscles, which respond by the production of a secretion or a contraction. Independence of Tissue Irritability. — The irritability of nerves is distinct and independent of the irritability of muscles and glands, as shown by the fact that it persists in each a variable length of time after their histologic connections have been impaired or destroyed by the introduction of various chemic agents into the circulation. Curara, for example, induces a state of complete paralysis by modifying or depressing the conductivity of the end-organs of the nerves just where they come in contact with the muscles, without impairing the irrita- bility of either nerve-trunks or muscles. Atropin induces complete suspension of gland activity by impairing the terminal organs of the secretor nerves just where they come into relation with the gland- cells, without destroying the irritability of either gland-cell or nerve. Nerve Stimuli. — Nerves do not possess the power of spon- taneously generating and propagating nerve impulses; they can be aroused to activity only by the action of an external stimulus. In the physiologic condition the stimuli capable of throwing the nerve into an active condition act for the most part on either the central or peripheral end of the nerve. In the case of motor nerves the stimulus to the excitation, originating in some molecular disturbance in the nerve-cells, acts upon the nerve-fibers in connection with them. In the case of sensor or afferent nerves the stimuH act upon the peculiar end -organs with which the sensor nerves are in connection, which in turn excite the nerve-fibers. Experimentally, it can be demonstrated that nerves can be excited by a sufficiently powerful stimulus applied in any part of their extent. Nerves respond to stimulation according to their habitual func- tion; thus, stimulation of a sensor nerve, if sufficiently strong, re- sults in the sensation of pain; of the optic nerve, in the sensation of light; of a motor nerve, in contraction of the muscle to which it is distributed; of a secretor nerve, in the activity of the related gland, etc. It is, therefore, evident that peculiarity of nerve function de- ])ends neither upon any special construction or activity of the nerve itself nor upon the nature of the stimulus, but entirely upon the pecu- liarities of its central and peripheral end-organs. GENERAL PHYSIOLOGY OF NERVE-TISSUE. 119 Nerve stimuli may be divided into — 1. General stimuli, comprising those agents which are capable of exciting a nerve in any part of its course. 2. Special stimuli, comprising those agents which act upon nerves only through the intermediation of the end-organs. The end-organs are speciahzed highly irritable structures placed between the nerve-fibers and the surface. They are especially adapted for the reception of special stimuli and for the liberation of energy, which in turn excites the nerve-fiber to activity. General stimuli: 1. Mechanic: Sharp taps, sudden pressure, cutting, etc. 2. Thermic: Sudden application of heated object. 3. Chemic: Contact of various substances which alter their chemic composition quickly, e. g., strong acids or alkalies, sol. sodium chlorid 15 per cent., sugar, urea, etc. 4. Electric: Either the constant or induced current. Special stimuli: For afferent nerves — 1. Light or ethereal vibrations acting upon the end-organs of the optic nerve in the retina. 2. Sound or atmospheric undulations acting upon the end-organs of the auditor}^ nerve. 3. Heat or vibrations of the air acting upon the end-organs in the skin. 4. Chemic agencies acting upon the end-organs of the olfactory and gustatory nerves. For efferent nerves — A molecular disturbance in the central nerve-cells from w^hich they arise, the nature of which is unknown. Nature of the Nerve Impulse. — As to the nature of the nerve impulse generated by any of the foregoing stimuli, either general or special, but little is known. It has been supposed to partake of the nature of a molecular disturbance, a combination of physical and chemic processes attended by the liberation of energy, w^hich propa- gates itself' from molecule to molecule. The passage of the nerve impulse is accompanied by changes of electric tension, the extent of which is an indication of the intensity of the molecular disturbance. Judging from the deflections of the galvanometer needle it is probable that when the nerve impulse makes its appearance at any given point it is at first feeble, but soon reaches a maximum development, after which it speedily declines and disappears. It may, therefore, be graphically represented as a wave-like movement with a definite length and time duration. Under strictly physiologic conditions the nerve impulse passes in one direction only; in efferent nerves from the center to the periphery, in afferent nerves from the periphery to the center. Experimentally, however, it can be demonstrated that TEXT-BQOK OF PHYSIOLOGY. when a nerve impulse is aroused in the course of a nerve by an ade- quate stimulus it travels equally well in both directions from the point of stimulation. When once started, the impulse is coniined to the single fiber and does not diffuse itself to fibers adjacent to it in the same nerve-trunk. Rapidity of Conduction of the Nerve Impulse. — The passage of a nerve impulse, either from the brain to the periphery or in the reverse direction, requires an appreciable period of time. The velocity with which the impulse travels in human sensory nerves has been estimated at about 50 meters a second, and for motor nerves at from 28 to T,T, meters a second. The rate of movement is, however, somewhat modified by temperature, cold lessening and heat increas- ing the rapidity; it is also modified by electric conditions, by the action of drugs, the strength of the stimulus, etc. The rate of transmission through the spinal cord is considerably slower than in nerves, the average velocity for voluntary motor impulses being only 1 1 meters a second, for sensory impulses 12 meters, and for tactile impulses 40 meters a second. Nerve Fatigue .^ — Inasmuch as nerves are parts of living cells, the seat of nutritive changes, it might be supposed that the passage of nerve impulses would be attended by the disruption of energy-holding compounds, the production of waste products, the liberation of heat, and in time by the phenomena of fatigue. Though it is probable that changes of this character occur, yet no reliable experimental data have been ob- tained which afford a clue as to the nature or extent of any such changes. Stimulation of motor nerves with the induced electric current for four hours appears to be without influence either on the intensity of the nerve impulse or the rate of its conduction. Identity of Efferent and Afferent Nerves and Nerve Impulses. — Notwithstanding the classification of nerve-fibers based on dift'er- ences of physiologic actions, there are no characters, either histologic or chemic, which serve to distinguish them from one another. More- over, as the nerve impulse is conducted through a nerve-fiber equally well in both directions, as determined by experiments, it is probable that it does not differ in character in the two classes of nerves. That the efferent fibers conduct the nerve impulses from the nerve-centers to the periphery, and the aft'erent nerves from the periphery to the centers, is because of the fact that they receive their stimulus physio- logically only in the centers or at the periphery. The fundamental Fig. 49. — Nerve- muscle Prep- aration OF A Frog. F. Fe- mur. S. Sciatic nerve. I. Tendo Achillis. — (Lan- dois and Stir- ling.) GENERAL PHYSIOLOGY OF NERVE-TISSUE. 121 reason for difference of effects produced by stimulation of dift'erent nerves is the character of the organ to which the nerve impulse is conducted. A nerve is merely the transmitter of the nerve im- pulse, which if conducted to a muscle excites contraction; to a gland, secretion; to a blood-vessel, variation in caliber; to special areas in the brain, sensations of hght, sound, pain, etc. Electric Excitation of Nerves. — For the purpose of studying the physiologic activities of nerves it has been found convenient to employ the nerve-muscle preparation (the gastrocnemius muscle and sciatic nerve) and to use as a stimulus the induced electric current. (See Fig. 49.) When kept moist, this preparation is extremely sensitive to either the galvanic or the induced current. Though the development and conduction of a nerve impulse may be demonstrated by the deflection of the galvanometer needle or the movement of the mercury in the capillary electrometer, it is more conveniently demonstrated by the contraction of a muscle, the vigor of which, within Hmits, may be taken as a measure of the intensity of the impulse. The preparation should be enclosed in a moist chamber and the nerve connected with the inductorium through the intervention of non-polarizable electrodes. The muscle may be attached to the muscle-lever and its contractions recorded. A single shock of an induced current develops, it is beheved, a single nerve impulse followed by a single muscle contraction. A minimal contraction following a minimal electric stimulus presupposes the development of a nerve impulse of low intensity. Within certain limits a maximal contraction following a maximal electric stimulus presupposes the development of a nerve impulse of high intensity. Intermediate contractions indicate nerve impulses of corresponding intensity. Tetanization of a muscle indicates that the nerve impulses arrive at the muscle with a frequency so great that the muscle does not succeed in relaxing from the effect of one stimulus before the next arrives. Incomplete as well as complete tetanus may be developed by gradually increasing the frequency of the stimulus. The character of the contraction caused by indirect stimulation — i. e., though the nerve — does not differ in any essential respect from that due to direct stimulation. ELECTRIC PHENOMENA OF NERVES. Electric Currents from Injured Nerves. — It was discovered by du Bois-Reymond that electric currents can be obtained from nerves as well as from muscles, and that the electric properties of the former correspond in most respects to those of the latter. The laws governing the development and mode of action of the currents TEXT-BOOK OF PHYSIOLOGY. derived from muscles are equally applicable to the currents derived from nerves. A nerve-cylinder obtained by making two transverse sections of any given nerve presents, as in the case of muscles, a natural and tv\^o artificial transverse surfaces. A line drawn around the cylinder at a point lying midway between the two end surfaces constitutes the equator. From such a cyHnder strong currents are obtained when the natural longitudinal surface and the transverse surface are connected with the electrodes of the galvanometer circuit. The strength of the current thus obtained will di- minish or increase according as the electrode on the longitudinal surface is removed from or brought near to the equator. If two symmetric points on the longitudinal surface equidistant from the equator are united, no cur- rent is obtainable. When asymmetric points on the longitudinal surface are connected, weak currents are obtained, in which case the point lying nearer the equator becomes positive to the point more distant, which becomes negative. From these facts it is evi- dent that all points on the longitudinal surface are electrically positive to the transverse surface and that the point of greatest positive tension is situated near the equator (Fig. 50). The electromotive force of the nerve-current varies in strength with the length and thickness of the nerve. The strongest current obtained from the nerve of the frog is equal to the 0.002 of a Daniell cell; that obtained from the nerve of the rabbit, 0.026 of a Daniell. The existence of the nerve, its strength, duration, etc., depend largely on the mainte- nance of physiologic conditions. All influences which impair the nutrition of the nerve diminish the current. With the death of the nerve all electric phenomena disappear. Negative Variation of the Nerve Current. — During the pas- sage of the nerve impulse the resting nerve current, or the demarca- tion current, diminishes more or less completely in intensity, undergoes a negative variation, as shown by the return of the galvanometer needle, due to a change in its electromotive condition or to a diminu- FiG. 50. — Diagram to Illus- trate THE Currents in Nerves. The arrowheads indicate the direction; the thickness of the lines indicates the strength of the currents. — {Landois and Stirling.) GENERAL PHYSIOLOGY OF NERVE-TISSUE. 123 tion of the difference in potential between the positive longitudinal and negative transverse sections. This negative variation of the de- marcation current is observed equally well from either the central or peripheral end of the nerve. If the two ends of the nerve are con- nected with galvanometers and the nerve stimulated in the middle, the demarcation currents simultaneously undergo a negative variation. This may be taken as a proof that the excitation process propagates itself equally well in both directions. The negative variation is inti- mately connected with changes in the molecular condition of the nerve and is not due to any extraneous electric or other influence. And du Bois-Reymond was also enabled to obtain a negative variation of the current in the nerves of a Hving frog which were yet in connection with the spinal cord. In this experiment the sciatic nerve was divided at the knee and freed from its connections up to the spinal column; the transverse and longitudinal surfaces were then placed in connection with the electrodes of the galvanometer wires and the current per- mitted to influence the needle. The animal was then subjected to the action of strychnin. Upon the appearance of the muscle spasms the needle was observed to swing backward toward the zero point to the extent of from i to 4 degrees, and upon the cessation of the spasms to return to its previous position. In an experiment of this nature it is obvious that the negative variation was the result of a physiologic stimulation of the nerve arising within the spinal cord. The question also here arises as to whether the negative variation is due to a steady, continuous decrease of the natural current, or whether it is due to successive and rapidly following variations in its intensity, similar to that observed in muscles. Though this cannot be demonstrated Avith the physiologic rheoscope, as was the case with the muscle, there can be no doubt, both from experimentation and analogy, that the latter supposition is the correct one. It has been shown that when non-polarizable electrodes connected with Siemen's telephone are placed in connection with the longitudinal and trans- verse sections of a nerve, low, sonorous vibrations are perceived during tetanic stimulation, — a proof that the active state of the nerve is connected with the production of discontinuous electric currents. The oscillations of the mercurial column of the capillary electrom- eter also reveal similar electric changes. It was also demonstrated by Bernstein with a specially devised apparatus, the repeating rheo- tome, that the negative variation is composed of a large number of single variations which succeed each other in rapid succession and summarize themselves in their effect on the needle. Electric Currents from Uninjured Nerves. — The pre-existence of electric currents in living and wholly uninjured nerves while at rest has also been denied by Hermann, who regards all portions of 124 TEXT-BOOK OF PHYSIOLOGY. the nerve as isoelectric, any difference of potential being the result of some injury to its surface. Action Currents. — For reasons to be stated below, it is very diffi- cult to determine the presence of diphasic action currents during the passage of an excitatory impulse through the nerve-fiber. The so- called negative variation of the resting nerve current, — the demarca- tion current, — which is occasioned by tetanic stimulation, Hermann regards as the expression of an action current which flows in the nerve in a direction opposite to the demarcation current. The origin of this action current is to be sought for in the continuous negativity of that portion of the longitudinal surface of the nerve in contact with the diverting electrode, while the dying substance of the transverse surface takes no part in the excitation. This tetanic action current, or nega- tive variation, was discovered by du Bois-Reymond, and Bernstein later succeeded in obtaining this action current during the passage of a single excitation process. That the return of the galvanometer needle toward the zero point is not due to an annulment of the demar- cation current itself, but to the appearance of an action current, is shown by the fact that if the former be compensated by a battery current until the needle rests on the zero point the appearance of the latter current will cause the needle to swing in a direction the opposite of that caused by the demarcation current. The negative variation and action current may therefore be regarded as one and the same thing. It is the expression of the change the nerve is undergoing during the passage of the nerve impulse. The rapidity with which the negative variation or action current travels, the variation in its intensity from moment to moment, the time required for it to pass a given point, would express the change in the nerve to which the term nerve impulse is given. From experiments made with the differential rheotome, Bernstein calculated that the speed of the negative variation is about 28 meters a second; that it is at first feeble, soon rises to a maximum, and then decHnes; that it requires 0.0006 to 0.0008 of a second to pass a given point. From these data it is evident that the negative variation or action current has a space value of about 18 mm. Transferring these statements to the nerve impulse, it may be said that it is a molecular disturbance, traveling at the rate of about 28 meters a second, is wave-like in character, the wave being 18 millimeters in length, and occupying from 0.0006 to 0.0008 of a second in passing any given point. Absence of Diphasic Action Currents. — When any two points on the longitudinal surface which do not exhibit a current are connected with the galvanometer and a single wave of excitation passes beneath the electrodes, it might be expected that, as in the case of the muscle, a diphasic action current would be observed, from the fact that the portions of the nerve beneath the electrodes become alternately neg- GENERAL PHYSIOLOGY OF NERVE-TISSUE. 125 ative with reference- to all the rest of the nerve. This, however, is not the case, the absence of the two opposing phases of the action current being explained on the supposition that the negativity of the two led-off points is of equal amount, and that, owing to the great rapidity with which the excitation wave travels, the two phases fall together too closely in time to alternately influence the galvanometer needle. During stimulation of the nerve, when two currentless or iso- electric points are connected, there is also an absence of the action current, as was observed first by du Bois-Reymond, and which is to be explained on similar grounds. It is true that an apparent action current is sometimes seen when the stimulating current is very power- ful or the seat of stimulation too near the diverting electrodes. This, however, must be attributed to an electrotonic state of the nerve. The Effects of a Galvanic Current on a Nerve.— When a con- stant galvanic current of medium strength is made to pass through a portion of a nerve, several distinct effects are produced: 1. The development 0} a nerve impulse at the moment the current enters and at the moment the current leaves the nerve, i. e., at the moment the circuit is made and at the moment it is broken. The development of the nerve impulse is made evident by the contraction of the muscle if the nerve-muscle preparation be used. If the current be either very weak, or very strong, the muscle contraction may not always take place. 2. The development of electric currents on each side of the positive pole or anode, and the negative pole or cathode (see Fig. 51), which can be led off by means of wires into a galvanometer circuit from either the artificial transverse and longitudinal surfaces, or from any two points on the longitudinal surface as shown by the deflection of the galvanometer needle. The direction of these electric cur- rents in the nerve coincides with that of the galvanic or "polarizing current." The "natural nerve currents," the currents of injury or demarcation currents, as they are variously termed, are at the same time increased and decreased at opposite extremities of the nerve according to the direction of the polarizing current. To this changed condition of the electromotive forces in a nerve the term electrotonus was given (du Bois-Reymond). The currents themselves are known as electrotonic currents; from their relation to the anode and cathode, they are termed anelectrotonic and cat- electrotonic currents. The condition of the nerve around the poles both in the intra-polar and extra-polar regions is known as an- electrotonus and catelectrotonus. The electrotonic currents vary considerably in strength and ex- tent, according to the intensity of the polarizing current, increasing steadily with the intensity of the latter up to the point at which the polarizing current begins to destroy the physical and chemic integrity 126 TEXT-BOOK OF PHYSIOLOGY. of the nerve. The electrotonic currents are strongest in the imme- diate neighborhood of the electrodes, but gradually diminish in strength as the distance between the polarized and led-off portions is increased. The distance to which the electrotonic currents extend along the nerve will depend very largely upon the strength of the polarizing current, though it is conditioned by the physical state of the nerve; for if it be ligated or injured beyond the polarized portion, the electrotonic cur- rents are abolished. The electrotonic currents have no necessary connection with the natural nerve currents, nor are they to be regarded as branchings of the galvanic current. They are in all probabihty of artificial origin, due to an inner positive and negative polarization of the nerve which extends for a variable distance on each side of the poles, and due to the action of the polarizing or the galvanic current. 3. An alteration in the excitability and conductivity of the nerve in the neighborhood of the poles, whereby the results of nerve stimu- lation — that is, muscle contraction, sensation, and inhibition — are increased or decreased according to the strength and direction of the ^- POLARIZING J o'j? CURRENT •/ + ^ 1 i^^ 'j^£Y -^ /^ L GALVANOMETER anelectrotonic katelectroton ic current5 currents Fig. 51. — Electrotonic Currents. current. To this condition the term electrotonus was also given (Pfiiiger). This word has thus been employed to express two distinct series of effects exhibited by a nerve through a portion of which a con- stant galvanic current is passing. It appears desirable, for the sake of clearness, to limit the term electrotonus to the electric or electrotonic currents which can be led off from either extremity of the nerve, and to apply to the modifications of irritability which accompany electro- tonus the expression, electrotonic alteration of excitability and con- ductivity. During the passage of the current the excitabihty of the intra- polar as well as the extra-polar regions undergoes a change which, as shown on examination, is found to be diminished in the neigh- borhood of the anode or positive pole and increased in the neigh- borhood of the cathode or negative pole. These alterations in the excitability are most marked in the immediate vicinity of the elec- trodes, though they extend for some distance into both the extra- polar and intra-polar regions, though with gradually diminishing GENERAL PHYSIOLOGY OF NERVE-TISSUE. 127 intensity, until they finally disappear. Between the electrodes there is a point where the excitability is unchanged and known as the neutral or indifferent point (Fig. 52). The extent to which the ex- citability is modified as well as the position of the neutral point will depend largely on the strength of the polarizing or galvanic current. ,,-T-^ Fig. 52. — Scheme of the Electrotonic Excitability. — {Landois and Stirling.) The electrotonic alterations of excitability and conductivity can be experimentally demonstrated on the muscle-nerve preparation in the following manner: I. With a descending current of medium strength. Previous to the closure of the polarizing current, the nerve is stimulated first ^\ + ANODE \ REGION OF VNCREASED EXCITABILITY KATHODE SECONDARY COIL Fig. 53. — Diagram Showing the Region of Increased Excitability Caused by THE Passage of a Galvanic Current, Stimulation of which Gives Rise TO Incrj;ased Contraction. in the extra-polar anodic region and the extra-polar cathodic region with an induction shock of medium intensity and the height of the contraction recorded. On repeating the stimulation ajter closure of the polarizing current the contraction resulting from stimulation of the anodic region will be enfeebled or mav be 128 TEXT-BOOK OF PHYSIOLOGY. entirely wanting, while the contraction from stimulation of the cathodic region will be decidedly increased. (See Fig. 53.) With an ascending current of the same strength. After prelimi- nary testing of the excitability and the subsequent closure of the polarizing current, it will be found that stimulation of the extrapolar anodic region will provoke a much less energetic contraction or perhaps none at all. Stimulation of the extra- cathodic region, though of increased excitability, as shown by the previous experiment, may also fail to provoke a contraction, owing to the diminished conductivity of the region in the neighbor- hood of the anode. The impulse on reaching this region is blocked in its passage. A similar if not more marked decrease in the conductivity may be developed in the region of the cathode if the current strength be veiy great. (See Fig. 54.) REGION OF DECREASED EXCITABILITY Fig. 54. — Diagram Showing the Region of Decreased Excitability Caused BY THE Passage of a Galvanic Current, Stimulation of which Gives Rise to Decreased Contraction. The Law of Contraction; Polar Stimulation.— It was stated in a previous paragraph that when a galvanic current of medium strength is made to enter a nerve, and when it is withdrawn from the nerve, there is a contraction of its related muscle. These are generally known as the make and break effects. During the actual passage of the current no effect is observed so long as its strength remains uniform. Any sudden variation in the strength of the curjrent at once arouses the nerve to activity, as shown by a muscle contraction. The muscle response to the make and break of the constant current is more or less variable unless the direction of the current as well as its strength be taken into consideration. If the current is made to flow from the central toward the peripheral end of the nerve it is termed a direct, descending, or centrifugal current; if it is made to flow in the reverse direction, it is termed an indirect, ascending, or GENERAL PHYSIOLOGY OF NERVE-TISSUE. 129 centripetal current. The strength of the current is determined and regulated by means of a rheocord. The make and break of currents of different but known strengths and directions give rise to contractions which occur with more or less regularity. The order in which they occur under these varying conditions of experimentation has been determined and tabulated as follows by Pfiuger, and is termed the law 0} contraction: Ascending Current. Descending Cdrrent. Make. Break. Make. Break. Weak, Medium, Strong, Contraction. Contraction. Rest. Rest. Contraction. Contraction. Contraction. Contraction. Contraction. Rest. Contraction. Rest or weak contraction. The results as above tabulated are sometimes compHcated on the opening of the circuit by a series of irregular pulsations of the muscle, an apparent tetanus, and long known as the opening tetanus of Ritter, which is attributed to rapid changes in the irritabihty of the nerve, in the region of the anode. A similar tetanic contraction of the muscle is sometimes observed on the closure of the circuit due to continued excitation in the region of the cathode. This is known as the closing tetanus of Wundt. All the phenomena of the law of contraction were explained by Pfliiger on the assumption that the current stimulates the nerve only at the one electrode, at the cathode on closing, and at the anode on opening; or, in other words, by the appearance of catelectrotonus or by the disappearance of anelectro- tonus, both conditions being attended by a rise of excitabihty — not, however, by the opposite changes. It is further assumed that the appearance of catelectrotonus is more effective as a stimulus than the disappearance of anelectrotonus. For these reasons the term polar stimulation is generally employed in discussing the make and break effects of the galvanic current. The law of contraction may then be explained as follows: Very feeble currents, either ascending or de- scending, produce contraction only upon the closure of the circuit, the sudden increase 0} the excitability in the catelectrotonic area being alone sufficient to generate an impulse. The contraction which follows the closing of the weak ascending current depends upon the fact that the decrease of excitability and conductivity at the anode is insufficient to interfere with the conduction of the cathodal stimulus. Medium currents, either ascending or descending, produce contrac- tion both on closing and opening the circuit. The appearance of catelectrotonus and the disappearance of anelectrotonus are both sufficiently powerful to generate an impulse without, however, seri- ously impairing the conductivity of the nerve. 130 TEXT-BOOK OF PHYSIOLOGY. Very strong currents produce contraction only upon the opening of the ascending and closure of the descending currents, or upon the passage of the excitability in the former from the marked aneleclro- ionic decrease to the normal condition, and in the latter from the nor- mal to that of catelectrotonic increase. The absence of contraction upon the closure of the ascending current is dependent upon the blocking of the cathodal stimulus by the decrease of the excitability and conductivity at the anode. With the opening of the descending current the disappearance of anelectrotonus should also be followed by contraction, which would indeed be the case if the stimulus so generated was not blocked by the decrease of the conductivity at the cathode. The order in which the contractions occur may be tabulated as follows : With Ascending Current. With Descending Current. Weak, I. K. C. C* _. K. C. C. Medium, 2. K. C. C A. O. C.f K. C. C. A. O. C. Strong, 3. -_ A. O. C. K. C. C. A. O. C.(?) Polar Stimulation of Human Nerves. — The preceding state- ments as to changes in the excitabihty caused by the passage of a constant current, as well as to the law of contraction, are based en- tirely on experiments made with the isolated nerve of the frog. It is probable, however, that the same phenomena would have been observed had the nerve of a mammal been used and its excitability been maintained. If the electrodes connected with the wires of a sufficiently strong galvanic battery be applied to the skin over the course of a superficially lying nerve, e. g., the brachial, it will be found that there occurs on the closure of the circuit an increase in the excitability in the extra- polar anelectrotonic region and a decrease in the excitability in the extra-polar catelectrotonic region, as shown by stimulating the nerve in the extra-polar regions with the induced current — results which are in apparent contradiction to those obtained with the isolated nerve. This want of accordance in the results of the two classes of experi- ments arises from a failure to recognize the fact that the physiologic anode and cathode do not coincide with the physical anode and cathode. It has been experimentally demonstrated that owing to the large amount of readily conducting tissue by which the nerve is surrounded, the current density, though great immediately under the electrode, quickly decreases at a short distance from it, so that for the nerve it becomes almost nil. The current, therefore, shortly after entering, again leaves the nerve at various points which become physiologic * K. C. C, cathodal closing contraction, f A. O. C, anodal opening contraction. GENERAL PHYSIOLOGY OF NERVE-TISSUE. 131 cathodes. Stimulation of this physiologic cathode with the induced current gives rise, therefore, to the phenomenon of increased excita- bility in the region of the anode. If, however, the galvanic and stimulating current be combined in one circuit and both be applied to the same tract of nerve, results will be obtained which harmonize with those obtained with the frog's nerve. The changes in the excitability of a nerve of a living man and the contractions which follow the closing and opening of the constant current have been thoroughly studied by Waller and de Watteville. These observers employed a method similar to that of Erb, conjoin- ing in one circuit the testing and polarizing currents. By the graphic method they recorded first the contraction produced by an induc- tion shock alone; and, secondly, the contraction produced by the same stimulus under the influence of the polarizing current. As a result of many experiments, they also demonstrated an increase of Fig. 55. — .\node of Battery. Polar region of nerve is anodic. Peri- polar region of nerve is cathodic. Fig. 56.— Cathode of Battery. Polar region of nerve is cathodic. Peri- polar region of nerve is anodic. — (Waller.) the excitability in the polar region when it is cathodic, and a decrease when it is anodic. Following the suggestion of Helmholtz, that the current density quickly decreases with the distance from the elec- trodes, they recognize, at the point of entrance and exit of the current from the nerve, two regions — a polar, having the same sign as the electrode, and a peripolar, having the opposite sign (Figs. 55 and 56). The peripolar regions also experience similar alterations of excita- bility, though less in degree, according as they are cathodic or anodic. As it is impossible to confine the current to the tnmk of the nerve when surrounded by living tissues, as is easily the case when experi- menting with the frog's nerves, it is incorrect to speak of either ascending or descending currents. Waller,* who has thoroughly studied the electrotonic effects of the galvanic current from this point of view, sums up his conclusions in the following words: "We must apply one electrode only to the nerve and attend to its effects alone, *" Human Physiology-," p. 363, 1891. 132 TEXT-BOOK OF PHYSIOLOGY. completing the circuit through a second electrode, which is applied according to convenience to some other part of the body. "Confining our attention to the first electrode, let us see what will happen according as it is anode or cathode of a galvanic current (Figs. 55 and 56). If this electrode be the anode of a current, the latter enters the nerve by a series of points and leaves it by a second series of points; the former, or proximal series of points, collectively constitutes the polar zone or region; the latter, or distal series of points, collectively constitutes the peripolar zone or region. In such case the polar region is the seat of entrance of current into the nerve — i. e., is anodic; the peripolar region is the seat of exit of current from the nerve — i. e., is cathodic. If, on the contrary, the electrode under observation be the cathode of a current, the latter enters the nerve by a series of points which collectively constitute a 'peripolar' region, and it leaves the nerve by a series of points which collectively con- stitute a 'polar' region. The current, at its entrance into the body, diffuses widely, and at its exit it concentrates; its 'density' is greatest close to the electrode, and, the greater the distance of any point from the electrode, the less the current density at that point; hence it is obvious that the current density is greater in the polar than in the peripolar region. These conditions having been recognized, we may apply to them the principles learned by study of frogs' nerves under simpler conditions. Seeing that, with either pole of the battery, whether anode or cathode, the nerve has in each case points of en- trance (constituting a collective anode) and points of exit to the cur- rent (constituting a collective cathode), and admitting as proved that make excitation is cathodic, break excitation anodic, we may, with a sufficiently strong current, expect to obtain a contraction at make and at break with either anode or cathode applied to the nerve; and we do so, in fact. When the cathode is applied, and the current is made and broken, we obtain a cathodic make contraction and a cathodic break contraction; when the anode is applied, and the current is made and broken, we obtain an anodic make contraction and an anodic break contraction. These four contractions are, however, of very different strengths; the cathodic make contraction is by far the strongest; the cathodic break contraction is by far the weakest; the cathodic make contraction is stronger than the anodic make con- traction; the anodic break contraction is stronger than the cathodic break contraction. Or, otherwise regarded, if, instead of comparing the contractions obtained with a sufficiently strong current, we ob- serve the order of their appearance with currents gradually increased from weak to strong, we shall find that the cathodic make contraction appears first, that the cathodic break contraction appears last, and the formula of contraction for man reads as follows: GENERAL PHYSIOLOGY OF NERVE-TISSUE. 133 "Weak current, K. C. C. Medium current, K. C. C A. C. C. A. O. C. Strong current, K. C. C. A. C. C. A. O. C. K. O. C. The constant or the galvanic current is frequently used for thera- peutic and diagnostic purposes. In accordance with the statements above quoted, one electrode should be appHed to the part to be in- vestigated, the other to some indifferent region. The electrode con- veying the current to or from this part should be of a size sufficient to locahze the current and to increase its density. It was discovered by Duchenne that there are certain points all over the body stimula- tion of which is more quickly followed by muscle contraction than M. biceps brachii. M. brach. anticus. N. medianus M. pronator teres. M. flex, digitor. coinraun. profund. M. flex, carpi radialis. M. flex, digitor. sublim. M. flex. dig. subl. (dig. ind. et min.) \M. ttex.poU. lougus N. med- N.ulnaris. M. flexor carpi ulnaris. N. ulnaris. Fig. 57. — Motor Points of the Median and Ulnar Nerves, with the Muscles Supplied by Them. — {Landois and Stirling) Others. It was subsequently discovered by Remak that these points coincide with the entrance of the nerve into the muscle. It is to these motor points that the one electrode should be appUed. The position of some of these points on the forearm is shown in Fig. 57- Reactions of Degeneration. — In consequence of the degen- eration and changes in irritabihty which occur in nerves when separ- ated from their centers and in muscles when separated from their related nerves, either experimentally or as the result of disease, the response of these structures to the induced, and the make and break of the constant current, differs from that observed in the physiologic condition. The facts observed under the apphcation of these two 134 TEXT-BOOK OF PHYSIOLOGY. forms of electricity are of importance in the diagnosis and thera- peutics of the precedent lesions. The principal difference of behavior is observed in the muscles, which exhibit diminished or abohshed excitabihty to the induced current, while at the same time manifesting an increased excitability to the constant current; so much so is this the case that a closing contraction is just as likely to occur at the positive as at the negative pole. This peculiarity of the muscle response is termed the reaction of degeneration. The synchronous diminished excitability of the nerves is the same for either current. The term "partial reaction of degeneration" is used when there is a normal reaction of the nerves, with the degenerative reaction of the muscles. This condition is observed in progressive muscular atrophy. Reflex Action.^ — Inasmuch as many of the muscle movements of the body, as well as the formation and discharge of secretions from glands, variations in the cahber of blood-vessels, inhibition and acceleration in the activity of various organs, are the result of stimu- lations of the terminal organs of afferent nerves, they are termed, for convenience, reflex actions, and, as they take place for the most part through the spinal cord and medulla oblongata and independently of the brain or of volitional influences, they are also termed involun- tary actions. A reflex action, therefore, may be defined as an action which takes place independent of volition and in response to per- ipheral stimulation. As many of the processes to be described in succeeding chapters are of this character, requiring for their per- formance the cooperation of several organs and tissues associated through the intermediation of the nerve system, it seems advisable to consider briefly, in this connection, the parts involved in a reflex action, as well as their mode of action. As shown in Fig. 58, the necessary structures are as follows : 1. A sentient surface, skin, mucous membrane, sense-organ, etc. 2. An afferent nerve-fiber and cell. 3. An emissive cell, from which arises — 4. An efferent nerve, distributed to a responsive organ, as 5. Muscle, gland, blood-vessel, etc. Such a combination of structures constitutes a reflex mechanism or arc, the nerve portion of which is composed of but two neurons — an afl"erent and an efferent. An arc of this simplicity would of neces- sity subserve but a simple movement. The majority of reflex activ- ities, however, are extremely complex, and involve the cooperation and coordination of a number of nerve centers situated at different levels of the spinal cord on the same and opposite side, and of re- sponsive organs frequently situated at distances more or less remote from one another. This implies that a number of neurons are associated in function. The afferent neurons are brought into re- lation with the dendrites of the efferent neurons by the end-tufts of GENERAL PHYSIOLOGY OF NERVE-TISSUE. 135 the collateral branches, which may extend for some distance up and down the cord before passing into the various segments. For the excitation of a reflex action it is essential that the stimulus applied to the sentient surface be of an intensity sufficient to develop in the terminals of the afferent nerve a series of nerve impulses, which, traveling inward, will be distributed to and re- ceived by the dendrites of the emissive or motor cell. With the reception of these im- pulses there is apparently a a disturbance of the L-cS^y pf^ ~ equihbrium of its molec- '~^ ules, a liberation of en- ergy, and, in conse- quence, a transmission outward of impulses through the efferent nerve to muscle, gland, or blood-vessel, separ- ately or collectively, with the production of muscu- lar contraction, glandular secretion, vascular dila- tation or contraction, etc. The reflex actions take place, for the most part, through the spinal cord and medulla oblongata, which, in virtue of their contained centers, coordinate the various organs and tissues concerned in the performance of the organic functions. The movements of mastica- tion; the secretion of saHva; the muscular, glandular, and vascular phenomena of gastric and intestinal digestion; the vascular and respiratory movements; the mechanism of micturition, etc., are illus- trations of reflex activitv. . 58. — Diagram Showing Structures Con- nected WITH Reflex Actions. A. Trans- verse section of spinal cord with centers in the anterior horn of the gray matter for muscles m, glands, g, and blood-vessels, h. ej.n. Efferent nerves which convey nerve impulses to these organs. 5. Sensory surface, af.n. Afferent nerve conveying nerve impulses to the centers in the spinal cord. CHAPTER VIII. FOODS. ^The functional activity of every organ and tissue of the body is accompanied by a more or less active disintegration of the living material, the bioplasm, of which it is composed. The complex and highly unstable molecules of this living material are continually undergoing disruption and falhng into less complex and more stable compounds; these, through oxidative processes, are eventually re- duced through a series of descending chemic stages to a small number of simpler compounds w^hioh, being of no further value to the organ- ism, are ehminated by the various ehminating or excretory organs, the lungs, skin, kidney, liver. Among these excreted compounds the more important are urea, uric acid, and carbon dioxid. Many other compounds, organic as well as inorganic, are also eliminated from the body in the various excretions, though they are present in but small amounts. Coincident with this disintegration of living material there is a transformation of its potential into kinetic energy,* which manifests itself for the most part as heat and mechanic motion. In order that the organs and tissues may continue in the per- formance of their functions, it is essential that they be supplied with nutritive materials similar to those which enter into their own com- position: viz., proteids, fat, carbohydrates, water, and inorganic salts. These compounds, though originally derived from the food, are immediately derived from the blood as it flows through the capil- lary blood-vessels. The blood is therefore to be regarded as a reser- voir of nutritive material in a condition to be absorbed and trans- formed into utilizable and living material. Inasmuch as the mate- rials lost to the body daily, through- disintegration and oxidation, though considerable, are supplied by the blood, it is evident that this fluid would diminish rapidly in volume, with a corresponding decline in functional activity, were it not restored by the introduction into the body of new material in the food. With the diminution of the volume of the blood and an insufficient supply to the tissues, there arise the sensations of hunger and thirst, which lead to the consump- tion of food and the subsequent restoration of the physiologic condi- tion of the tissues. These two sensations are also partially dependent on the empty condition of the stomach and the dryness of the mucous membrane of the mouth and throat. 136 FOODS. 137 The foods which are consumed daily in response to the sensations of hunger and thirst are complex in composition and contain, though in varying amounts, proteids, fats, carbohydrates, water, and inor- ganic salts, which, in contradistinction to foods, are termed food principles or nutritive principles. In these compounds is also to be found the potential energy necessary to maintain the dynamic equi- librium of the body and which will become manifest as heat and mechanic motion in the transformations of the material underlying the nutritive processes. The animal body may be therefore regarded as a machine capable each day of performing a certain amount of work by the expendi- ture of a definite amount of energy. In the performance of its work, whether it be the raising of weights against gravity, the overcoming of friction, cohesion, or elasticity, the machine suffers disintegration and loses a portion of its available energy. Unlike other machines, however, it possesses the power, within limits, of self-renewal, self- adjustment, when supplied with foods in proper quantity and quality. QUANTITIES OF FOOD PRINCIPLES REQUIRED DAILY. In order that the body may continue in the performance of its work and yet retain a given weight, it is essential that the loss to the body daily shall be exactly compensated by the introduction and assimilation of a corresponding amount of food principles. If this condition is realized, the body neither gains nor loses, but remains in a condition of nutritive equilibrium. The determination of the exact quantities of the different food principles required daily and their ratio one to another is made from an examination of the quantity and composition of the daily excretions. Since the proteids disintegrated are represented in the excretions by urea and similar nitrogen-holding compounds and the fats and carbohydrates by carbon dioxid, it becomes possible to determine from them the quantities required to restore equihbrium under any given condition. But as the activity of the nutritive changes will vary in accordance with climatic condi- tions, work done, etc., and as the excreted products will vary in the same ratio, it is obvious that the required amounts of food will vary in accordance with these varying conditions, if equilibrium is to be maintained. Various estimates have been made by different investigators as to the amounts of the excreted products and the food principles re- quired daily, which, though differing to some extent, have, neverthe- less, an average nutritive and energy-producing value. The follow- ing table shows the diet scale of Vierordt and the excretions to which it would give rise. As the income and outgo practically balance, there would be no change in the weight. 138 TEXT-BOOK OF PHYSIOLOGY. COMPARISON OF THE INCOME AND OUTGO. Incomi;. Proteid, Fat, Carbohydrates, -. Salts, Water, j 2 Oxygen, Grams. Ounces. 120 4-25 90 3-17 330 11.64 32 I-I3 2818 99-30 756 4146 26.66 146.13 Outgo. Water, Urea, Feces, dry, Salts, Carbon dioxid, Water formed in body, Gram.s. Ounces. 2818 99-3° 40 1.40 38 1.60 32 1-13 922 32-37 296 IO-33 4146 146.15 Other estimates as to the amounts of the organic food principles required daily are as follows : Ranke. Voit. Moleschott. Atwater. Hultgren. Grams. Grams. Grams. Grams. Grams. Proteid, 100 118 130 125 134 Fat, 100 56 84 125 79 Starch, 250 500 550 400 522 In arranging tables showing the relation between the income and the outgo, it is generally customary to state merely the amounts by weight of the nitrogen and carbon each contains. This method furnishes sufficiently accurate information regarding the metabolism of the body, for the reason that the nitrogen represents the proteid, and the carbon, with the exception of that contained in the proteid, the fat and carbohydrates which have undergone disintegration or metabolism. The following balance table, as given by Ranke, shows the rela- tion of the nitrogen to the carbon in the average mixed diet and in the excretions of a man weighing 70 kilograms, in a condition of nutritive equilibrium : Income. Grams. 100 N. c. Proteid, . 15-5 53-0 79.0 93 -o Fat, . . Carbohydrates, — 250 15-5 225.0 Outgo. Grams Urea, _ _ . Uric acid. Feces, --. CO,, --. 10.84 208.00 225.00 FOODS. 139 From the above it will be observed that the daily discharge for each kilogram of body-weight is 0.21 gram nitrogen and 3.03 grams of carbon; the relation of the two being -^ = 14.5. On a diet in which there is an excess of either proteid or carbohydrates this ratio necessarily changes. CLASSIFICATION OF FOOD PRINCIPLES. Though the food principles are grouped as proteids, fats, carbo- hydrates, etc., the members of each group differ somewhat in chemic composition, digestibility, and nutritive value. These groups are as follows: I. Peoteids. Principle. Where found. Myosin, . Flesh of animals. Albumin, vitellin, White of egg, yolk of egg. Caseinogen, Milk. Serum-albumin, fibrin, Blood contained in meat. Glutin, Grain of wheat and other cereals. Vegetable albumin, Soft-growing vegetables. Legumin, Peas, beans, lentils, etc. 2. Fats. Animal fats, In adipose tissue of animals. Vegetable oils, In seeds, grains, nuts, fruits, and other vegetable tissues. 3. Carbohydr.^tes. Dextrose or grape-sugar ) j^ ^^.^^_ Levulose or fruit-sugar, I Lactose or milk-sugar, Milk. Saccharose or cane-sugar, Sugar-cane, beet roots. Maltose, Malt and malted foods. q , I Cereals, tuberous roots, and legumin- , cause the lower teeth to project Anterior fibers of temporal j beyond the upper. Posterior fibers of temporal Internal portion of masseter f Draw the lower jaw back to its Digastric, mylohyoid, and genio- I normal position. hyoid J Internal pterygoids \ Contracting alternately, draw the External pterygoids J jaw to the opposite side. Pterygoids, external and interna 1 t> . • .• ^ c ^ ■[ [ Produce gnnding movements of M3er J the lower jaw. The action of the depressor muscles becomes apparent when their points of origin and insertion are considered. The anterior belly of the digastric, the mylohyoid, the geniohyoid muscles, agree in having a similarity of origin — the hyoid bone — and a common area of insertion, the anterior portion of the inferior maxillary. Their anatomic relation is such that their combined action will depress the lower jaw and open the mouth. The elevator muscles arise from various points on the side of the head, and are inserted into the coronoid process, ramus, and internal surface of the angle of the lower jaw. When the mouth has been opened, the simultaneous contraction of these muscles elevates the jaw and closes the mouth with considerable force. The power of these muscles is very great, and depends on the shortness and thickness of the muscle-bundles. The action of the rotator muscles, those which give rise to the lateral movements of the jaw, depends in hke manner on their origin and insertion. Arising from the superior maxillary and sphenoid bones, they are inserted into the neck of the condyle and angle of the lower jaw respectively. When they contract, the condyle on the corresponding side is drawn forward, while the opposite condyle remains stationary. As a result, the symphysis of the jaw is directed to the opposite side. The grinding movements of the jaw are pro- duced by the coordinated action of all the groups of muscles acting more or less successively. For the proper mastication of the food it is essential that it be kept between the opposing surfaces of the teeth. This is accom- plished by the contraction of the orbicularis oris and buccinator muscles from without and the tongue muscles from within. i6o TEXT-BOOK OF PHYSIOLOGY. The Nerve Mechanism of Mastication.* — The movements of mastication, though originating in efforts of the will and under its control, are for the most part of an automatic or reflex character; for when once initiated by a voluntary effort they continue for an inde- finite period — so long, in fact, as the impressions which the food makes upon the afferent nerves are received by the nerve-centers which regulate and control them. That the masticatory movements are of this reflex nature is shown by the fact that they will be maintained even though the voluntary effort which called them forth has sub- sided and the attention has been directed to some entirely different subject. It would appear that all that is necessary under such con- ditions is the exciting action of the food upon the periphery of the afferent nerves distributed to the tongue and mouth. The nerves involved in this reflex are shown in the following table : Afferent Nerves. Efferent Nerves. 1. Lingual branch of fifth nerve. i. Inferior maxillary division of fifth nerve. 2. Glossopharyngeal. 2. Hypoglossal or sublingual. 3. Facial or portio dura. The nerve-center coordinating the movements of mastication is situated in the medulla oblongata. The afferent or excitor nerves which receive the impressions of the food are distributed largely to the mucous membrane of the tongue. When these impressions are received by the center in the medulla oblongata, it discharges nerve impulses, which, passing outward through motor nerves, excite con- traction in the masticatory muscles. The motor nerves innervating the muscles are: (i) The small root of the fifth nerve, which, after emerging from the cavity of the cranium through the foramen ovale, joins the inferior maxillary division of the large sensor root. It then is distributed to the masseter, temporal, internal, and external pterygoids, anterior belly of the digastric, and mylohyoid muscles, and controls their movements. (2) The hypoglossal nerve, which, after emerging through the anterior condyloid foramen, passes down- ward and forward to be distributed to the extrinsic and intrinsic muscles of the tongue. (3) The facial or portio dura, which, after emerging from the stylomastoid foramen, is distributed to the mus- cles of the face. Irritation of any one of these nerves produces con- vulsive movements in the muscles to which it is distributed, while their division is followed by paralysis of these muscles. The medulla not only generates the impulses which are directly responsible for the movements of mastication, but also coordinates them in such a manner that the movements of mastication may be directed toward the accompHshment of a definite purpose. *By this term is meant a combination of nerves, afferent and efferent, and nerve centers which when stimulated coordinates the actions of the organs with which it is associated. DIGESTION. i6i INSALIVATION. Insalivation is the incorporation of the sahva with the food, and takes place for the most part during mastication. The sahva ordi- narily present in the mouth is a complex fluid composed of the various secretions of the parotid, submaxillary, and subhngual glands and the muciparous folhcles of the mouth, which collectively constitute the sahvary apparatus (Fig. 6i). The parotid gland is situated in front of and partly below the external ear, where it is held in position by the fascia and skin. From the anterior border of the gland there emerges a duct (Sten- sen's), which, after crossing the masseter muscle to its anterior border, turns in- ward, pierces the buccin- ator, and opens on the sur- face of the cheek opposite the second upper molar tooth. The submaxillary gland is situated below the jaw in the anterior part of the submaxillary triangle. From the gland there emerges a duct (Wharton's) which opens into the mouth by a minute orifice on the surface of a papilla by the side of the tongue. The sublingual gland is situated just beneath the mucous membrane in the anterior part of the mouth, where it forms a projection between the gums and tongue. The posterior part of the gland gives origin to a duct (the duct of Rivinus, described also by Bartho- hn) which opens into the mouth with or very near to the duct of Wharton. The anterior part of the gland gives origin to a varying number of ducts (Walthers) which open separately along the edge of the sublingual plica of the mucous membrane. Histologic Structure of the Salivary Glands.^ — In their uki- mate structure the sahvary glands bear a close resemblance to one Fig. 6i. — Salivary Glands, i, 2. Parotid. 3. Duct of Steno. 4. Submaxillary. 5. Sublingual. 6. Mylohyoid muscle. 7. Lingual branch of the fifth nerve. 8. Duct of Wharton. 9. Digastric muscle. 10. Sternomastoid muscle. 11. External jugu- lar vein. 12. Facial vein. 13. Temporal vein. 14, 15. Internal jugular vein. 16. Branch of the cervical plexus. 17. Sub- lingual nerve. — {Le Bon.) l62 TEXT-BOOK OF PHYSIOLOGY. lixcrelory duct. another. They are compound tubulo-alveolar glands composed of small irregularly shaped lobules united by areolar tissue and con- nected by branches of the sahvary ducts. Each lobule is made up of a number of small alveoli or acini more or less tubular in shape which are the terminal expansions of the smallest ducts. (See Fig. 62.) The wall of the acinus is formed by a reticulated basement mem- brane, surrounded externally by blood-vessels, the spaces between which constitute lymph-spaces or channels. The inner surface of the acinus membrane supports a single layer of irregular spheric or polygonic epithelial cells. The ceHs do not entirely fill up the cavity of the acinus, but leave an intercellular space, the lumen, which constitutes the beginning of the duct for the transmission of the secretion to the mouth. From each acinus there passes a narrow intercalary duct lined by a layer of flattened cells. The common ex- cretory duct — formed by the union of the intralobular and interlobular ducts — consists also of a basement membrane, lined, however, by tall columnar epithelial cells. The sali- vary glands are abundantly supphed with blood-vessels and nerves which are closely related to their activity. Based partly on the character of their secretions and partly on the microscopic appearance of their secreting cells, the salivary glands have been divided by Heidenhain into two classes: viz., serous or al- buminous, and mucous glands. To the first class belong the parotid, a portion of the submaxillary, and a portion of the glands of the tongue. To the second class belong a portion of the submaxillary gland, the subHngual, a portion of the glands of the tongue, the glands of the cheeks, hps, palate, and pharynx. It is possible that a single alveolus of any gland may contain both albuminous and mucous cells. In the serous glands the cells are more or less spheric in shape, nucleated, and almost completely filled with dark granular material (Fig. 63). In the mucous glands the cells are large, clear in appear- ance, and loaded with a highly refracting material resembling mucin (Fig. 64). Between the basement membrane and the clear cells are to be found in the acini of the submaxillary glands small crescentic shaped cells filled with granular material which stains deeply with vari- FiG. 62. — Scheme of the Human Submaxillary Gland. — {Stdhr.) DIGESTION. i6: ous coloring-matters. These are known as the demilunes of Heiden- hain. At one time it was supposed that they were young cells des- tined to take the place of the clear cells which were beheved to be exhausted and to have undergone disintegration. At the present time they are regarded as albuminous or serous cells which exhibit changes similar to the cells of the parotid gland. The glands embedded in the mucous membrane covering the tongue, lips, cheek, palate, and pharynx are for the most part lined with epithelial cells which contain a highly refracting matter similar to, if not identical with, that found in the cells of the submaxillary and sublingual glands. Nerve-supply. — Experimental research has demonstrated that each salivary gland receives nerve-fibers which influence the produc- tion of the secretion (secretor nerves) and fibers which dilate or con- strict the blood-vessels (vaso-dilatator and vasoconstrictor nerves). Fig. 63. — Section of Human Paro- tid Gland Including Several Acini, d. Cut intralobular duct. — {Pier sol.) Fig. 64.— Section of Hum.an Sublin- gual Gland. Among the clear cells Lining the mucous acini are nests {g, g) of granular elements which constitute the demilunes of Heidenhain. — {Pier sol.) The secretor fibers penetrate the basement membrane and finally terminate between and on the surface of the secretory cells. The vaso-motor fibers terminate between and on the muscle-cells in the walls of the blood-vessels. The nerve-fibers in direct relation with the cells and blood-vessels of the parotid gland are derived from the otic ganglion. The cells of this ganglion are, however, invested by the terminal branches of other nerve-fibers (preganglionic) derived from the medulla oblongata. The relation of these preganghonic fibers to the blood-vessels and cells is shown by the increase in secretion and a change in the caliber of the vessels when they are subjected to electric stimulation. The nerve-fibers which are in direct relation with the vessels and cells of the submaxillary and sublingual glands are derived from the submaxillary, the subhngual, and the superior cervical ganglia. These local ganglion cells are also closely invested by the terminal branches or arborizations of the i64 TEXT-BOOK OF PHYSIOLOGY. fibers of nerves (preganglionic fibers) coming direct from the medulla oblongata and spinal cord. The Parotid Saliva. — The parotid saliva, as it flows from the orifice of Stensen's duct, is clear, limpid, free from viscidity, dis- tinctly alkaline in reaction, with a specific gravity of 1.003. Chemic analysis shows that it consists of water, a small quantity of proteid matter, a trace of a sulphocyanogen compound, and inorganic salts. The secretion is increased during mastication, and especially on the side engaged in mastication. Dry food causes a larger flow than moist food. The situation of the orifice of the parotid duct is such that as the secretion is poured into the mouth it is at once incorporated with the food by the movements of the lower jaw, and thus fulfils the physical function of softening and moistening it. The Submaxillary Saliva. — The submaxillary saliva is clear, slightly viscid, alkaline in reaction, and has a specific gravity of 1.002. It consists of water, proteid matter (mucin), and inorganic salts. The Sublingual Saliva.— The subhngual saliva is clear, extremely viscid, and strongly alkaline in reaction. It consists of water, proteid matter (chiefly mucin), and inorganic salts. The small racemose glands embedded in the mucous membrane on the inner surface of the cheeks and Hps, on the hard and soft palate, on the tongue and pharynx, secrete a fluid which is grayish in color, extremely viscid and ropy. It contains a large amount of mucin. Mixed Saliva. — The saHva of the mouth is a complex fluid com- posed of the secretions of all the salivary glands. As obtained from the mouth it is frothy, colorless, shghtly turbid, and somewhat viscid. The specific gravity is low, ranging from 1.003 to 1.006. The re- action is usually distinctly alkahne. It may, however, be neutral or even acid in reaction if there is any fermentation of food particles in the mouth or as a result of disorders of the alimentary canal. When examined with the microscope, the saliva is seen to contain epithelial cells, salivary corpuscles resembling leukocytes, particles of food, various microorganisms, and especially Leptothrix huccalis. The chemic composition of the saliva is shown in the following table : COMPOSITION OF HUMAN SALIVA. Water, 995-i6 994.20 Epithelium, ; 1.62 2.20 Soluble organic matter, 1.34 1.40 Potassium sulphocyanid, 0.06 0.04 Inorganic salts, 1.82 2.20 1000.00 1000.04 (Jacubowitsch.) (Hammerbacher.) DIGESTION. 165 Water constitutes the main ingredient, amounting to 99.5 per cent. The soluble organic matter is proteid in character and is a mixture of mucin, globuhn, and serum-albumin. The potassium sulpho- cyanid is mainly derived from the parotid gland. Its presence can be demonstrated by the addition of a few minims of a dilute solution of slightly acidulated ferric chlorid, when a characteristic red color is developed. The inorganic constituents comprise the sodium, calcium and magnesium phosphates, sodium carbonate, sodium and potas- sium chlorids. Quantity of Saliva.— The estimation of the total quantity of mixed sahva secreted in twenty-four hours is exceedingly difficult, and the results obtained must be only approximative. It is, of course, subject to considerable variation, depending upon habit, the nature of the food, etc. The experiments of Professor Dalton and the results obtained by him are eminently trustworthy, and in all probabihty represent as nearly as possible the exact amount secreted. He found that without any artificial stimulus he was enabled to collect from the mouth about 36 grams (540 grains) of saliva per hour, but that upon the introduction of any stimulating substance into the mouth the quantity could be greatly increased. During mastication the saUva was poured out in greater abundance, the amount depending upon the relative dryness of the food. He found that wheaten bread ab- sorbed 55 per cent, of its weight, and fresh cooked meat 48 per cent. If, therefore, the average quantity of bread and meat required daily by a man of ordinary physical development and activity be assumed to be 540 grams (19 oz.) of the former and 450 grams (16 oz.) of the latter, these two substances would absorb respectively 297 grams (4573.8 grains) and 216 grams (3326.4 grains), making a total of 513 grams (7900 grains). If, therefore, the amount secreted and mixed with the food during an estimated two hours of mastication be added to the amount secreted during the remaining twenty-two hours, supposing that it continues at the rate of 36 grams per hour, we have a total amount of 513 + 792 grams, or 1305 grams (19,780 grains), or about 2.8 pounds. Histologic Changes in the Salivary Glands during Secretion. — During and after secretion very remarkable changes take place in the cells lining the acini, which are in some way connected with the production of the essential constituents of the salivary fluids. In the case of the parotid gland, which may be regarded as the type of a serous or albuminous gland, the following changes have been observed by Langley (Fig. 65). During the period of rest and just previous to secretory activity, the epithelial cells are enlarged and swollen, and encroach on the lumen of the acinus. The protoplasm of the cells is so completely filled with dark fine granules as not only to obscure the nucleus, but to almost obliterate the line of union of the cells. 1 66 TEXT-BOOK OF PHYSIOLOGY. As soon as secretion becomes active, however, the granules begin to disappear from the outer region of the cell and move toward the inner border and into the lumen of the acinus. From these observations it might be inferred that during rest the protoplasm of the cells gives rise to granular material, and that during and after secretory activity Fig. 65. — Cells of the Alveoli of a Serous or Watery Salivary Gland. A. After rest. B. After a short period of activity. C. After a prolonged period of activity. — {Yeo's " Text-Book of Physiology.") there is an absorption of new material from the lymph and a recon- struction of the granular material. In the submaxillary gland, a portion of which may be taken as a type of a mucous gland, similar changes have been observed (Fig. 66). During rest the epithehal cells are large, clear in appear- ance, highly refractive, and loaded with small globules resembling mucin. The nucleus, surrounded by a small quantity of proto- plasm, lies near the margin of the cell. That the granules are not protoplasmic in char- acter is shown by the fact that they do not stain on the addition of carmine. When treated with water or dilute acids, the globules swell up, coalesce, and form a uniform mass. The chemic relations of this substance indicate that it is the precursor of mucin — namely, mucigen. During secretory activity the cells dis- charge these mucigen granules into the lumen of the acinus, where they are transformed into mucin. Though the appearance of the gland-cell appears to in- dicate it, there is no evidence for the view that the cell itself undergoes disintegration in the process. The Physiologic Actions of Saliva. — The constant presence of sahvary glands in the different classes of animals and the large amount m\ Fig. 66. — The Appearance Presented by THE Cells of the Submaxillary Gland of the Dog after Prolonged Secretion. — {Modified from Landois and Stirling.) DIGESTION. 167 of secretion they pour daily into the ahmentary canal point to the conclusion that this mixed fluid plays an important role in the general digestive process. Experiment has demonstrated that it has a two- fold action, physical and chemical. Physically, saliva softens and moistens the food, unites its par- ticles into a consistent mass by means of its contained mucin, and thus facihtates swallowing. Chemically it converts starch into sugar. This action is more marked with boiled than wdth raw starch, a fact which depends on the physical structure of the starch grain. In the natural con- dition each starch grain consists of a cellulose envelope or stroma in the meshes of which is contained the true starch material, the granulose. When boiled for some minutes, the starch grain absorbs water, the granulose swells and ruptures the cellulose envelope, after which it passes into an imperfect opalescent solution more or less viscid, depending on the relative amounts of water and starch. This is the change largely brought about by the process of cooking. If a portion of this hydrated starch be kept in the mouth for a few minutes it will be converted into sugar, a fact made evident by the sense of taste. The chemic action of sahva in converting starch into sugar, as well as the intermediate stages, can be experimentally shown in the following manner : To 5 volumes of a thin starch solution in a test- tube add two volumes of filtered saliva. Place the mixture in a water-bath at a temperature of 35° C. In a few minutes the starch passes into a soluble condition and the fluid becomes clear and trans- parent. On testing the solution from time to time with iodin the characteristic blue reaction will be found to gradually disappear, the color passing from blue to violet, to red, to yellow. If now the solu- tion be boiled with a solution of cupric hydroxid (Fehling's solution) a copious red or yellow precipitate of cuprous oxid is formed, which indicates the presence of sugar. The polariscope shows that this sugar is maltose, Cj2H220ir During the conversion of the starch intermediate substances are formed to which the term dextrin is applied. After the starch has been rendered soluble it undergoes a cleavage into maltose and a dextrin, which, as it gives rise to a red color with iodin, is termed erythrodextrin. At a later stage this erythrodextrin also undergoes a cleavage into maltose and a second variety of dextrin, which, as it does not give rise to any color with iodin, is termed achroodextrin. It is claimed by some investigators that this form can also in time be transformed into sugar. It is possible that a small quantity of dextrose is also formed. The successive stages of the conversion of starch into sugar may be represented by the following schema : 1 68 TEXT-BOOK OF PHYSIOLOGY. 1^ ., J . . f Achroodextrin. Starch = Soluble Starch = f Erythrodextnn -= | Maltose. ^ Maltose. This change consists in the assumption by the starch of a molecule of water, and for this reason the process is termed hydrolysis. The nature of the chcmic change is shown in the following formula: 3(CeHio05) + HjO = C.jHj^Ou + CeH.oOs Starch + Water ^ Maltrose + Dextrin. The amylolytic or starch-changing action of saliva depends on the presence of an unorganized ferment or enzyme known as ptyalin. This enzyme is present in the secretion of each of the salivary glands. The chemic character of ptyalin is unknown, though there are reasons for believing that it partakes of the nature of a proteid. It is a product in all probability of the katabolic activity of the secre- tory cells. According to Latimer and Warren, ptyaHn is a deriva- tive of the zymogen, ptyalogen. This latter compound has been shown to be present in the glands of the dog, cat, and sheep. Ptyalin effects the transformation of starch merely by its presence, and undergoes no perceptible consumption in the process. The activity of this enzyme is very great, and unless interfered with by an excess of sugar and dextrin, it acts practically indefinitely. The activity of ptyalin is modified by various external conditions, among which may be mentioned the chemic reaction of the medium in which it is placed. It is most active when the medium is moder- ately alkaline. Its activity is arrested either by strong alkalies or acids, though the presence of a small percentage of an acid does not appear to have any effect in either hastening or retarding the process. This fact has a bearing upon the question as to whether the action of the saHva is interfered with in the stomach by the presence of the gastric juice. At present it is a disputed matter, but the weight of authority is in favor of the view that the transforming action may continue for almost half an hour during the early stages of gastric digestion. .The temperature also influences the rapidity with which the transformation of the starch is effected. At a temperature of 95° to io6° F. the ptyalin acts most energetically, while its activity is entirely arrested by reducing the temperature to the freezing-point or raising it to the boihng-point. The Nerve Mechanism of the Secretion of Saliva. — The secretion of the saliva is a complex act and involves the cooperation of gland-cells, blood-vessels, and nerves. During the intervals of mastication the glands are practically at rest as far as the discharge of saliva is concerned. The cells, however, are actively engaged in absorbing from the surrounding lymph-spaces materials derived from the blood from which they construct their characteristic con- DIGESTION 169 tents. The blood-vessels possess that degree of dilatation necessary for nutritive purposes. With the beginning of mastication the blood-vessels suddenly dilate, the blood-supply is increased, and the gland-cells begin to dis- charge water, inorganic salts, and their organic constituents into the lumen of the acinus. This continues until mastication ceases, when all the structures return to their former condition of relative inactivity. The entire process is reflex in character and takes place through the medulla oblongata. It requires the usual mechanism necessary for all reflex acts — viz., a sentient surface, afferent nerves, emissive cells, efferent nerves, and the responsive organs. With the introduction of food into the mouth impressions are made on the terminal branches of the afferent nerves distributed in the mucous membrane. Nerve impulses developed by the mechanic and chemic action of the food are then transmitted to the medulla oblongata and received by emissive cells. These in turn discharge nerve impulses which are transmitted through efferent ner\"es to the structures, producing the vascular and secretory effects already stated. The nerves and nerve-centers which constitute the reflex mechan- ism for the secretion of saliva are shown in the following table: Afferent Nerves. Nerve-centers. Efferent Nerves. 1. Lingual branch of fifth Medulla oblongata. Chorda tympani for the submax- nerve. illary and subUngual glands, auriculotemporal branch of the 2. Taste fibers in the fifth nerve for the parotid chorda tympani. gland. 3. Glossopharyngeal. Sympathetic nerve. That the secretion of the saliva is regulated by the above mechan- ism, and that the lingual branches of the fifth nerves and the glossopharyngeal are the afjerent nerves, can be demonstrated by exposing the glands and their nerve connections and subjecting them to experiment. Under such circumstances, if a cannula be placed in the duct of the submaxillary gland, and the lingual nerve stimu- lated by an induced electric current of moderate strength, a copious flow of saliva at once takes place. If now the glossopharyngeal nerve be stimulated in a similar manner, the effect on the secretion will be the same. Division of these two nerves in an animal, in such a way as to prevent the nerve impulses from reaching the medulla oblongata, is followed by a marked diminution in the amount of saliva secreted. The reflex centers, however, may receive impulses and be excited to activity by impulses coming through other nerves — e. g., the pneumo- gastric, when the mucous membrane of the stomach is stimulated; the sciatic, when after division its central end is stimulated; through nerve-fibers that originate higher up in the brain and are stimulated by ideas and emotions. 170 TEXT-BOOK OF PHYSIOLOGY. Whenever these centers are stimulated, either by nerve impulses coming through afferent nerves, from the periphery or from the brain, impulses are generated which pass outward through efferent nerves — the chorda tympani nerve to the submaxillary and sublingual glands, and the auriculo-temporal nerve to the parotid gland. The chorda tympani nerve is a branch of the facial, the trunk of which it leaves in the aqueduct of Fallopius. It then crosses the tympanic cavity, emerges through the Glaserian fissure, and joins the lingual branch of the inferior maxillary division of the fifth Glosso-Pnaryntfe al Otic GanrjUon^ rarotid via, Oiih Maxillary Ulan uAarcla. Tympani Oup.Ceroicul' Uanollon. Sympathetic Nerves Fig. 67. — Scheme of the Nerves Involved in the Secretion of Saliva. nerve. After passing forward as far as the sublingual gland, nearly all of the original fibers leave the lingual nerve by four or five strands to become connected by terminal branches with nerve-ganglion cells in relation with the submaxillary and sublingual glands. (See Fig. 67.) The nerve-fibers which conduct nerve impulses outward from the medulla to the parotid gland are beheved to pass through the glossopharyngeal nerve, through the tympanic branch or nerve of Jacobson, to the otic ganglion, with which they become connected. From this ganghon new nerve-fibers arise, the terminal branches of which become connected with the secretory cells of the gland. DIGESTION. 171 The effects on the secretion and flow of sahva from the submaxil- lary gland which follow division and stimulation of the chorda tym- pani nerve are shown in the following way: a cannula is inserted into Wharton's duct and the rate of flow estimated; the nerve is then divided, after which the flow ceases. The peripheral end of the nerve is then stimulated with the induced electric current, when a copious secretion of a thin saliva takes place, accompanied by a marked dilatation of the blood-vessels of the gland. The quantity of blood passing through the vessels is so great as to give to the venous blood an arterial hue and to the small veins a distinct pulsation. It would appear from these effects that the chorda contains two sets of fibers, one of which inhibits the action of a local vaso-motor mechan- ism permitting the blood-vessels to dilate (vaso-dilatator fibers), the other of which stimulates the secretor cells to activity, either directly or through the intermediation of local gangha. That local ganglia are involved is shown by the effects which follow the injection of nicotin into the circulation. After a sufficient dose — 10 miUi- grams for the cat — stimulation of the chorda has no effect. Stimu- lation of the nerve-plexus beyond the ganglion, however, is at once followed by vascular dilatation and secretion. It might be inferred that the increase in the flow of saliva is due to filtration, the result of the increased blood-supply to the gland, and not to the influence of any true secretor fibers stimulating the activities of the secretor cells. That this is not the case, however, can be demonstrated in several ways: First, the pressure in the duct of the submaxillary gland, as shown by the mercurial manometer, rises, when the gland is secreting, considerably above the pressure in the carotid artery, which could not be the case if it were due to a mere filtration; for if pressure alone were the cause, the flow of saliva would cease as soon as the pressure in the tube equaled the pressure in the blood-vessels. Second, even in the absence of blood the gland can be made to yield a secretion, as shown by stimulating the nerve in a recently killed animal. Third, after the injection of atropin into the circulation the secretion is abolished, but the local vasomotor mechan- ism is unimpaired, for stimulation of the nerve, as in the previous instance, gives rise to a dilatation of the vessels and an increased blood-supply. There is thus abundant proof that the chorda tym- pani contains two sets of fibers — one regulating the blood-supply to the gland, the other stimulating the secretory cells. The influence of the auriculo-temporal branch of the fifth nerve upon the parotid gland is similar to the action of the chorda tympani on the submaxillary gland. The active fibers of this nerve are prob- ably derived from the ninth nerve or glossopharyngeal. If the nerve be stimulated by the induced electric current, there follows a dilata- tion of the blood-vessels and an abundant discharge of a thin saliva, 172 TEXT-BOOK OF PHYSIOLOGY. rich in water and salts, but containing a small amount of organic matter. Division of the nerve, extirpation of the otic ganglion, division of Jacobson's nerve, is followed by a loss of reflex secretion. Stimulation of Jacobson's nerve, as shown by Heidenhain, gives rise to the secretion. The sympathetic fibers which influence the salivary secretion emerge from the spinal cord mainly through the second, third, and fourth thoracic nerves. After passing into the sympathetic chain they ascend to the superior cervical ganglion, with the cells of which they become connected through the intermediation of fine terminal branches. From this point non-medullated nerve-fibers follow the branches of the external carotid artery to the different glands. There is no evidence that these fibers have any connection, anatomic or physiologic, with local ganglia at or near the submaxillary or sub- lingual glands. If the sympathetic nerve in the neck, especially in the dog, be divided and the peripheral end stimulated with the in- duced electric current, there is at once a contraction of the smaller blood-vessels of the gland and a diminution of the blood-supply, a result showing the presence of vaso-constrictor fibers. Nevertheless both the submaxillary and sublingual glands pour out a saliva which is different from that poured out when the chorda 'tympani is stimu- lated. The quantity is less, it is more viscid, richer in organic matter, of a higher specific gravity, and more active in the transformation of starch into sugar. Stimulation of the fibers passing to the parotid gland is followed by contraction of the vessels and an abolition of the secretion; but at the same time there is an increased activity of the secretor cells, for subsequent stimulation of the auriculo-temporal nerve not only causes an increase in the amount of water and in- organic salts, but an increase also in the amount of organic matter far beyond that produced when the auriculo-temporal has alone been stimulated. Histologic examination shows that the^small ducts of the gland are filled with thick organic matter after stimulation of the cervical sympathetic. DEGLUTITION. Deglutition is that part of the digestive process which is concerned in the transference of the food from the mouth through the pharynx and esophagus into the stomach. This is an extremely complex act and involves the action of a large number of structures, all of which are made to act in proper sequence under the coordinating influence of the nervous system. The deglutitory canal consists of the mouth, pharynx, and esophagus, each of which presents certain anatomic features on which its physiologic action depends. The cavity of the mouth communicates posteriorly with the pharynx by a narrow orifice, the isthmus of the fauces. This orifice DIGESTION. 173 is bounded above by the soft palate, laterally by the anterior and posterior half arches, and below by the tongue. The pharynx is an oval-shaped cavity extending from the base of the skull to the lower border of the cricoid cartilage, a distance of /ML) MtT^s Z7 Fig. 68. — Vertical Section of the Nasal Fossa and Mouth, i. Left nares 2. Lateral cartilage of the nose. 3. Portion of the internal alar cartilage form- ing the skeleton of the lower part. 4. Superior meatus. 5. Middle meatus. 6. Inferior meatus. 7. Sphenoidal sinuses. 8. External boundary of the pos- terior nares. 9. Internal elUptical opening of the Eustachian tube. 10. Soft palate. 11. Vestibule of the mouth. 12. Vault of palate. 13. Genioglossus muscle. 14. Geniohyoid muscle. 15. Cut margin of the mylohyoid muscle. 16. Anterior pillar of the palate (anterior half-arch), presenting a triangular figure with the base inferiorly, covering partly the tonsil. 17. Posterior pillar (poste- rior half-arch) of the palate. 18. Tonsil. 19. FoUicular (mucous) glands at the base of the tongue. 20. Cavity of the larynx. 21. Ventricle of the larynx. 22. Epiglottis. 23. Cut OS hyoides. 24. Cut thyroid cartilage. 25. Thyro- hyoid membrane. 26. Section of posterior portion of the cricoid cartilage. 27. Section of the anterior portion of the same cartilage. 28. Crico-thyroid membrane . — (5a ppey.) about 12 centimeters. (See Fig. 68.) Its walls are formed mainly by three pairs of muscles — the superior, middle, and inferior constrictors — each consisting of red, striated muscle- fibers, and hence capable of rapid and energetic contractions. Superiorly the pharynx is attached to and supported by the basilar process of the occipital bone; inferiorly it becomes continuous with the esophagus. The 174 TEXT-BOOK OF PHYSIOLOGY. anterior wall of the pharynx is imperfect and presents openings which communicate with the nasal chambers, the mouth, and the larynx. The lateral wall on either side presents the opening of the Eustachian tube which leads directly into the cavity of the middle ear. The interior of the pharynx is lined by mucous membrane. The pharynx is partially separated from the mouth by the velum pendulum palati, a muscular structure attached above to the hard palate; its lower edge or border is directed downward and backward and presents in the middle hne a conical process, the uvula. On either side the palate presents two curved arches, the anterior and posterior, formed re- spectively by the palato-glossei and palato-pharyngei muscles. The laryngeal orifice or glottis is placed just beneath the base of the tongue. It is triangular in shape, wide in front, narrow behind, and directed downward and backward. It is bounded above by a thin plate of cartilage, the epiglottis, placed just behind the tongue and so arranged that it can easily be depressed and elevated. The esophagus, the continuation of the deglutitory canal, extends downward from the lower border of the cricoid cartilage for a dis- tance of from 2 2 to 25 centimeters, to a point opposite the ninth thoracic vertebra, where it expands into the stomach. Its walls are composed of an internal or mucous and an external or muscular coat, united by areolar tissue. The muscular coat consists of an external layer of longitudinal fibers arranged in three bands and of an internal layer composed of fibers arranged circularly in the upper part and obhquely in the lower part of the esophagus. In the upper third the fibers are striated; in the middle third they are a mixture of both striated and non-striated; in the lower third they are entirely non- striated. The muscle fibers surrounding the esophago-gastric orifice are arranged in the form of and play the part of a sphincter muscle, and for this reason may be termed the sphincter cardiae muscle. By its action it prevents a return under normal conditions of food into the esophagus. The deglutitive act may be for convenience divided into three stages, viz.: 1. The passage of the food from the mouth into the pharynx. 2. The passage of the food through the pharynx into the esophagus. 3. The passage of the food through the esophagus into the stomach. In the first stage the bolus of food is placed on the superior surface of the tongue. The mouth is then closed and respiration is momen- tarily suspended. The tip of the tongue is placed against the pos- terior surfaces of the teeth. The tongue, because of its intrinsic musculature, then arches from before backward against the roof of the mouth and pushes the bolus of food through the isthmus of the fauces into the pharynx. This completes the first stage. It is a DIGESTION. 175 voluntary effort and accomplished partly by the tongue, though, as shown by Meltzer, mainly by the mylohyoid muscles. The second and third stages, or the passage of the food through the pharynx and esophagus into the stomach, have been attributed until quite recently entirely to peristaltic movements of their muscu- lature. It has been stated that with the passage of the food through the isthmus of the fauces the posterior wall of the pharynx advances and seizes the food, and in consequence of a rapid peristaltic move- ment running through its constrictor muscles from above downward is transferred to the esophagus; that with the entrance of the food into the esophagus a similar peristalsis, varying in rapidity in different sections in consequence of a change in the character of its muscula- ture, gradually transfers the food into the stomach. There can be but shght doubt that by this method the bolus of food, especially if it is of iirm consistence and of a size sufficient to distend the esoph- agus, is transferred into the stomach, but that it is the exceptional rather than the usual method has been demonstrated by Kronecker, Falk, and Meltzer. In 1880 the first of these experimenters made the observation that the sensation in the stomach following the swallowing of a mouthful of cold water occurred too quickly to be explained by the prevalent behef that its transference was caused by ordinary peristalsis, the rate of progression of which was known to be slow. Falk then discovered the fact, by introducing through the mouth into the pharynx a tube connected externally with a water manometer, that during the act of swallowing there is a sudden rise of pressure equal to about twenty centimeters of water. These experiments demonstrated that at the beginning of degluti- tion there is a sudden rise of pressure, the result of a quickly acting force resident in the mouth or pharynx, in consequence of which the food is rapidly thrown down into the stomach, peristalsis playing no part in the process. The proof, however, of these statements was furnished by Meltzer. This observer introduced into the pharynx and esophagus rubber tubes, the ends of which were provided with thin-walled rubber balloons which could be distended with air. The outer ends of the tubes were connected with Marey's recording tambours. Any compression of the balloon would be followed by the passage of the air into the tambour and an elevation of the lever. With one balloon in the pharynx and the other in the esophagus at varying depths, and the recording levers of the tambours applied against the surface of a revolving cylinder, it became possible, with the addition of a chronogram, to obtain a graphic representation of the time relations of simultaneous and successive compressions of the two balloons. 176 TEXT-BOOK OF PHYSIOLOGY. It was found as the result of many experiments that no matter how deep the position of the esophageal balloon, it was compressed simultaneously with the pharyngeal balloon, as shown by the rise of the levers on swallowing a mouthful of water. The interval of time between the rise of the two levers did not amount to more than the tenth of a second. The inference was that the water was projected or shot down the pharynx and esophagus in this period of time, and in its passage compressed both balloons practically at the same in- stant. The same was found to be true when small masses of more consistent food were swallowed. The curves of the entire deglutitive act recorded by the two levers are, however, different in form. (See Fig. 69.) The pharyngeal curve, I, presents two crests, the first, A, being due to the compression caused Fig. 69. — Tracing of the Act of Deglutition, i. A indicates the compression of the elastic bag caused by the bolus projected by the contraction of the mylohyoid muscles. B. Contraction of the pharynx. 2. Line marking seconds. 3. Trac- ing of the bag in the esophagus 12 cm. from the teeth. C. Compression of the bag by the bolus corresponding to A. D. Compression by the residues of the bolus carried on by the contraction of the pharynx, B. E. Contraction of the esophagus. — (Landois and Stirling.) by the passage of the bolus, the second, B, due to the compression exerted by the contraction of the pharyngeal muscles. The interval of time between these two crests amounts to not more than 0.3 second. In the esophageal curve, 3, the elevation, C, corresponds to the elevation. A, and is likewise due to the compression exerted by the bolus. The interval of time between the beginning of the first and second curves was not more than o.i second, regardless of the depth to which the esophageal balloon was plunged. At a later period a second rise of the lever was recorded ; the time of its appear- ance, height, duration, etc., were found to increase with the depth of the balloon. These facts demonstrate that deglutition consists of two phases: (i) a rapid rise of pressure in the pharynx, as a result of which the DIGESTION. 177 bolus is suddenly shot down to the stomach; (2) a peristaltic con- traction of the musculature of the canal, which, acting as a supple- mentary force, carries onward any particles of food in the canal and forces the bolus through the closed sphincter at the end of the esoph- agus. The immediate cause of the sudden rise of pressure was shown by Meltzer to be the contraction of the mylohyoid muscles. When the nerves going to these muscles were divided in a dog, deglutition was practically abohshed. These muscles are probably assisted in their action by the contraction of the hyoglossus muscles as well as the tongue itself. It was also demonstrated in these experiments that the contrac- tion of the esophagus did not partake of the character of ordinary peristalsis. It was found that the esophagus contracted in three distinct segments, corresponding in all probability to the difference in the character of their muscular fibers. The first segment, about six centimeters in length, was found to begin to contract about 1.2 seconds after the beginning of the first curve and lasting 2 seconds; the second segment, about twelve centimeters in length, beginning to contract about 1.8 seconds or 3 seconds after the beginning of the first section, and lasting for from 5 to 7 seconds; the third segment, six centimeters in length, contracting from 6 to 7 seconds. The beginning and the end of the contraction for each segment oc- curred simultaneously throughout its entire extent. If, however, a series of deglutitory acts follow each other in quick succession, there is an inhibition of the peristaltic contractions until after the final swallow. An examination of the action of the esophagus during degluti- tion, made by Cannon and Moser with x-rays and the fluoroscope, disclosed the fact that the method of food transmission varied in different animals. In the cat and dog the transmission was effected bv peristalsis alone. The time required for the food to reach the stomach varied in the cat from nine to twelve seconds and in the dog from four to five seconds. The descent of the bolus was more rapid in the upper than in the lower part of the esophagus. In man, hquids descended rapidly, at the rate of several feet a second, in consequence of the rapid and energetic contraction of the mylo- hyoid muscles. A peristaltic contraction, passing over the entire esophagus, was necessar}- to the passage of soHd and semisoHd food through it. Closure of the Posterior Nares and Larynx. — Notwithstand- ing the rise of pressure in the pharynx during the act of swallowing, it is seldom under normal circumstances that any portion of the bolus ever finds its way either into the lar}mx or nasal chambers, 178 TEXT-BOOK OF PHYSIOLOGY. for the reason that the openings of these cavities are fully closed by appropriate means. At the moment the food passes into the pharynx the posterior nasal openings are closed against the entrance of the food by a septum formed by the pendulous veil of the palate and the posterior half arches. The palate is drawn upward and backward until it meets the posterior wall of the pharynx, and at the same time is made tense, by the action of the levator palati and tensor palati muscles respec- tively (Fig. 70). This septum is completed by the advance toward the middle line of the posterior half arches caused by the contrac- tion of the muscles which compose them — the palato-pharyngei. When these structures are impaired in their functional activity, as in diphtheritic paralysis and ulcerations, there is not infre- quently a regurgitation of food, especially liquids, into the nose. The larynx is equally pro- tected against the entrance of food during deglutition under normal circumstances. That this accident occasionally hap- pens, giving rise to severe spas- modic coughing, and even in extreme cases to suffocation, is abundantly shown by the records of chnical medicine. Usually it does not occur, for the following reasons: Just preceding and during the act of deglutition there is a com- plete suspension of the act of inspiration by which particles of food might otherwise be drawn into the larynx; at the same time the larynx is always drawn well up under the base of the tongue and its entrance closed by the downward and backward movement of the epiglottis. The glottis itself is also closed by the constrictor muscles which surround it. The action here attributed to the epiglottis has been denied by Stuart and McConnick. These observers had the opportunity of looking into a naso-pharynx which had been laid open by a sur- gical operation for the removal of a morbid growth. In this patient, the epiglottis, at the time of deglutition, was always more or less erect and closely applied to the base of the tongue. So comj^lete Fig. 70. — Diagram showing the Manner OF Closure of the Posterior Nares AND Larynx during Deglutition. — {Landois and Stirling.) DIGESTION. 179 was this that the food passed over its posterior or inferior surface for a certain distance. In no instance was it ever observed to fold backward Hke a lid. Because of the possibihty that this position of the epiglottis was due to pathologic causes, Kanthack and Anderson instituted a new series of experiments with a view of determining the action of the epiglottis. As a result of many experiments on animals and of ob- servations on themselves, these observers reathrm the generally accepted view, that under normal conditions, the entrance of the larvnx is always closed by the epiglottis after the manner of a lid. The Nerve Mechanism of Deglutition. — Deglutition is almost exclusively a reflex act throughout its entire extent, and requires for its inauguration merely a stimulus to some portion of the mucous membrane of the deglutitory canal. The first stage is primarily voluntary, but from inattention to the process may become second- arily reflex. The origin and course of the afferent nerves, stimu- lation of which excite reflexly the movements of the pharynx and esophagus, however, are practically unknown. In the rabbit deg- lutition can be excited by stimulating the anterior central part of the soft palate. In man it has not yet been possible to locate an area stimulation of which will give rise to a reflex deglutitory act. Though electric stimulation of the superior laryngeal nerve will cause reflex deglutitory movements, it is obvious that the terminals of this nerve can not be the source of the natural afferent impulses. Stimu- lation of the glossopharyngeal nerve causes an inhibition of the movements. The center from which emanate nerve impulses which excite the various muscles to action has been located experimentally in the medulla oblongata just above the alas cinereae. The efferent nerves comprise branches of the facial, hypoglossal, motor filaments of the third division of the fifth ner\'e, motor filaments of the glossopharyn- geal and vagus derived in all probability directly from the medulla oblongata. Inasmuch as the different mechanisms act not only in a coordinate but sequential manner, it is possible that the deglutition center is not a single circumscribed collection of cells, but a series of centers corresponding to the origin of the efferent nerves, the activi- ties of which are coordinated by some single true deglutition center. GASTRIC DIGESTION. After the food has passed through the esophagus it is received by the stomach, where it is retained for a variable length of time, during which important changes are induced in its physical and chemic com- position. The disintegration of the food inaugurated by mastication and insalivation is still further carried on in the stomach by the sol- i8o TEXT-BOOK OF PHYSIOLOGY. vent action of the acid fluid there present, until the entire mass is reduced to a hquid or semi-Hquid condition. The stomach is a dilated and highly specialized portion of the alimentary canal intervening between the esophagus and small intes- tine. When moderately distended with food, it is somewhat conical or pyriform in shape and shghtly curved on itself. It is situated obliquely and in some individuals almost vertically in the upper part of the abdominal cavity, extending from the left hypochondrium to the right of the epigastrium. The dimensions and capacity of the stomach undergo considerable periodic variation according to the extent to which it is distended by food. In the average condition it measures in its long diameter from 25 to 35 centimeters, in its vertical diameter at the cardia 15 centimeters, in its antero-posterior diameter from II to 12 centimeters. The capacity of the stomach varies from 1500 to 1700 c.c. In the empty condition its walls are collapsed and partly in contact, and the entire organ is drawn up into the upper part of the abdominal cavity. The opening through which the food passes into the stomach is known as the esophago-gastric orifice or the cardia. The opening through which it passes into the intes- tine is known as the pylorus, the pyloric or gastro-duodenal orifice. Between these two orifices the stomach along its upper border pre- sents a curve and along its lower border a much larger curve, known as the lesser and greater curvatures respectively. The left end of the stomach is termed the fundus or cardiac end; the right, the pyloric end. Passing from the fundus toward the pylorus, the stomach gradually narrows, and at a point situated about 5 cm. from the pyloric opening it frequently presents a constriction which divides the general cavity into two portions: viz., the fundus and the antrum of the pylorus. The walls of the stomach are formed by four distinct coats united by areolar tissue and named, from without inward, as the serous, muscle-, submucous, and mucous. The external or serous coat is thin and transparent and formed by a reduplication of the general peritoneal membrane. The middle or muscle-coat consists of three layers of non-striated muscle-fibers, named from their direction the longitudinal, circular, and oblique (Fig. 71). The longitudinal fibers are most abundant along the lesser curvature and are a continuation of those of the esophagus; over the remainder of the stomach they are thinly scat- tered, but toward the pyloric orifice they are more numerous and form a tolerably thick layer which becomes continuous with the fibers of the small intestine. The circular fibers form a complete ayer encircling the entire organ, with the exception, perhaps, of a portion of the fundus. The fibers of this coat cross the longitudinal fibers at right angles. At the lower end of the esophagus and sur- DIGESTION. i8i rounding the cardia the circular muscle fibers form a true sphincter which is known as sphincter cardies. At the junction of the fundus with the pyloric antrum the circular fibers are arranged in a well-de- fined bundle termed the sphincter antri pylorici. In the pyloric region the circular fibers are more closely arranged, forming thick well- defined rings. At the pyloric opening the circular fibers are again crowded together and form a distinct muscle band, — the sphincter pylori, — which projects for some distance into the interior of the stomach. It has been stated by Riidinger that the inner fibers of the longitudinal coat become connected with this circular band and con- stitute a distinct muscle, the dilatator pylori. The oblique fibers are Fig. 71. — Fibers Seen WITH THE Stomach Everted. 1,1. Esophagus. 2. Circular fibers at the esophageal opening. 3, 3. Circular fibers at the lesser curvature 4, 4. Circular fibers at the pylorus. 5, 5, 6, 7, 8. Oblique fibers. 9, 10. Fibers of this layer covering the greater pouch. 11. Portion of the stomach from which these fibers have been removed to show the subjacent circular fibers. — (Sappey.) most distinct over the cardiac portion of the stomach, but extend from left to right as far as the junction of the middle and last thirds of the stomach. They are continuations of the circular fibers of the esophagus. The submucous coat consists of loose areolar tissue carrying blood-vessels, nerves, and lymphatics. It serves to unite the muscle to the mucous coat. Its inner surface bears a thin layer of muscular tissue, the muscularis mucosa, which supports the mucous membranes. The internal or mucous coat is loosely attached to the muscular coat. In the empty and contracted state of the stomach it is thrown into longitudinal folds or rugae, which are, however, obliterated when I«2 TEXT-BOOK OF PHYSIOLOGY. :^?f'*».. y'f"': Mucosa. ■r-' the organ is distended with food. The mucous membrane in aduU life is smooth and velvety in appearance, gray in color, and covered with a layer of mucus. Its average thickness is about one millimeter. The surface of the membrane is covered with a layer of columnar epithelial cells, each of which possesses a nucleus and nucleolus. At the pylorus there is a circular involution of the mucous membrane which is known as the pyloric valve. This is strengthened by fibrous tissue and embraced by the sphincter muscle previously described. Gastric Glands. — The surface of the mu- cous membrane when examined with a low magnifying power pre- sents throughout in- numerable depressions polygonal in shape and separated by slightly elevated ridges. At the bottom of these spaces are to be seen small orifices, which are the mouths of the glands embedded in the mucous membrane. A vertical section of the gastric walls (Fig. 72) shows not only the position and ap- pearance of the glands, but the relation of the various tissues which en- ter into the formation of these walls. An exam- ination of the mucous membrane in different regions of the stomach Epilhelium. Tunic J propria. Muscularis mucosae. SubniiKosa. Inner cir- cular layer of muscle. /I Muscu- laris. Outer longi- tudinal layer of muscle. Serosa. Fig. 72.^-Tr.'^nsverse Section or the Wall of a Human Stomach. X i5- The tunica propria contains glands standing so close together that its tissue is visible only at the base of the glands toward the muscularis mucosas. — {Stolir.) reveals two distinct types of glands, cardiac or fundic, and pyloric, which differ not only in histologic structure, but also in function. Both types extend through the entire thickness of the mucosa. The cardiac, jundic, or peptic glands, are formed by an involution of the basement membrane of the mucosa and hned by epithehal cells. Each gland may be said to consist of a short duct, or neck, and a body or fundus (Fig. 73). The latter portion is wavy or tortuous and frequently subdivided into as many as 8 to 10 distinct and separate tubules. The duct is lined by columnar epithehal cells DIGESTION. 183 similar to those covering the surface of the mucosa. The lumen of the fundus is bordered by epithelial cells, cuboid in shape, and con- sisting of a granular protoplasm containing a distinct spherical nucleus. These cells are generally spoken of as the chief or central cells. In addition to the chief cells, the fundus contains a second variety of cell, which is of a larger size, of a triangular or oval shape, and consisting of a finely granular protoplasm. From this situation just beneath the gland wall they have been termed parietal or border cells. Each parietal cell appears to be surrounded and penetrated by a system of pas- sages which open into the lumen of the gland by means of a deli- cate cleft or canaliculus (Fig. 74). Glands with these histo- logic features are most abundant - Lumen. V^*^ Secretory capillaries Fig. 73. — Peptic Gland from Stomach of Dog. a. Wide mouth and duct which receive the terminal di\dsions of the gland, b, c. Neck and fun- dus of the tubes, e. Central or chief cells, d. Parietal or acid cells. — (AJler Piersol.) Fig. 74. — Section of Fundus Gland OF Mouse. Left upper half drawn after an alcohol preparation, right upper half after a Golgi prepara- tion. The entire lower portion is a diagrammatic combination of both prepara tions . — {Stoh r . ) in the middle zone of the stomach. Toward the extreme left end of the fundus the glands are largely, if not entirely, devoid of pari- etal cells. The pyloric glands are also formed by an involution of the mucous membrane and lined by epithelial cells (Fig. 75). The 1 84 TEXT-BOOK OF PHYSIOLOGY. ducts are much longer than the ducts of the fundic glands. At its extremity each duct becomes branched, giving rise to a num- ber, from 2 to 1 6, of short tubes, each of which has a large lumen and communicates with the duct by a narrow short neck. The ducts are lined throughout by columnar epithelium. Accord- ing to Mall, the total number of openings on the surface of the raucous membrane of the dog's stomach is somewhat over i,ooo,- ooo, and the total number of blind tubes opposite the muscularis mucosa exceeds 16,500,000. According to Sappe}*, the surface of the mucous membrane of the human stomach presents over 5,000,000 orifices of gastric glands. Blood-vessels, Nerves, and Lymphatics. — The blood-vessels of the stomach after entering the mucosa break up into a number of branches which are distributed to the muscular and mucous coats. The branches to the latter soon form a capillary network with oblong meshes which not only surround the tubules but form a network just beneath the surface of the mucosa. Veins grad- ually arise from the capillaries which empty into the larger veins of the mucosa. The glands are also sup- ported by processes of smooth mus- cle-fibers passing up from the muscul- aris mucosa. The nerve-fibers distributed to the stomach are derived from the vagus and the sympathetic branches of the solar plexus. After piercing the ser- ous coat the fibers form or unite with a plexus of fibers situated between the circular and longitudinal layers of the muscle- coat. At the nodal points of this plexus large nerve-ganghon cells are to be found, the whole forming the mechanism known as Auerbach's plexus. A similar plexus of cells and fibers in more or less intimate anatomic connection with the foregoing is found between the muscle and submucous coats, and is known as Meissner's plexus. From this plexus fine nerve filaments are distributed to muscle-fibers, blood-vessels, and glands. In the latter structure terminal arbori- zations have been detected in close contact with the secreting cells themselves. The lymphatics, which are quite numerous, originate in the Fig. 75. — Section of Pyloric Glands from Human Stom- ach, a. Mouth of gland leading into long, wide duct {b), into which open the ter- minal divisions, c. Connec- tive tissue of the mucosa. — (After Piersol.) DIGESTION. 185 meshes of the mucosa. The larger trunks enter lymph-glands lying along the greater and lesser curvatures of the stomach. Gastric Fistulae. — The general process of digestion, as it takes place in the stomach, has been studied in human beings and animals with a fistula in the walls of the stomach and abdomen, the result either of accident or of necessary surgical or experimental procedures. The earliest observations on gastric digestion were made by Dr. Beaumont on Alexis St. Martin, who, as the result of a gunshot wound, was left with a permanent fistulous opening into the fundus of the stomach. This opening two years after the accident was about two and a half inches in circumference and usually closed from within by a fold of mucous membrane which prevented the escape of the food. This valve could be readily displaced by the finger and the interior of the stomach exposed to view. After the complete recovery of St. Martin, Dr. Beaumont during the years between 1825 and 1831 at intervals made numerous experiments on the nature of gastric diges- tion. As the result of an admirable series of investigations it was estabhshed that the digestion of the food is largely a chemic act, due to the presence of an acid fluid secreted by the mucous membrane; that this fluid is secreted most abundantly after the introduction of food into the stomach; that different articles of food possess varying degrees of digestibihty; that the duration of digestion varies according to the nature of the food, exercise, mental states, etc., and that the process is aided by continuous movements of the muscular walls. Since Dr. Beaumont's time the estabhshing of a gastric fistula in human beings has been necessitated by pathologic conditions of the esophagus. After recovery these cases offered fair facihties for the study of the process when the food was introduced through the opening. Similar fistulce have been established in both carnivorous and herbivorous animals with a view of studying the process as it takes place in them. The results obtained in these instances in many respects corroborate those obtained by Dr. Beaumont, though many new facts, unobserved by him, have been brought to light. Gastric Juice. — The gastric juice obtained from the human stomach free from mucus and other impurities is a clear, colorless fluid with a constant acid reaction, a slightly saline and acid taste, and a specific gravity varying from 1.002 to 1.005. The juice ob- tained from the dog's stomach possesses essentially the same char- acteristics, though its acidity as well as its specific gravity are shghtly greater. When kept from atmospheric influences, it resists putre- factive change for a long period of time, undergoes no apparent change in composition, and loses none of its digestive power. It will also prevent and even arrest putrefactive change in organic matter. The chemic composition of the gastric juice has never been satisfactorily determined, owung to the fact that the secretion i86 TEXT-BOOK OF PHYSIOLOGY. as obtained from fistulous openings has not been absolutely normal. The following analyses represent the composition of a sample obtained by Schmidt from the stomach of a woman who had a fistula, but who was nevertheless in good health; also the composition of the juice from a dog: COMPOSITION OF GASTRIC JUICE. Human. Dog. Water, 994.40 973.06 Organic matter, 3.19 ^7-^3 Hydrochloric acid, 0.20? 3.34 Calcium chlorid, 0.06 0.26 Sodium chlorid, 1.46 2.50 Potassium chlorid, 0.55 1.12 Calcium phosphate "| 1.73 Magnesium " > 0.12 0.23 Ferric " J 0.08 Ammonium chlorid, 0.47 The organic matter present in gastric juice is a mixture of mucin and a proteid, products of the metabolic activity of the epithehal cells on the surface of the mucous membrane and of the chief or central cells of the gastric glands respectively. Associated with the proteid material are two ferment or enzyme bodies, termed pepsin and rennin. As is the case with other enzymes, their true chemic nature is practically unknown. Pepsin, though present in gastric juice, is not present as such in the chief cells of the glands, but is derived from a zymogen, pro- pepsin or pepsinogen, when the latter is treated with hydrochloric acid. This antecedent compound is related to the granules ob- served in and produced by the cell protoplasm during the period of rest. Though pepsin is largely produced by the central cells of the fundic glands, it is also produced, though in less amount, by the cells of the pyloric glands. Pepsin is the chief proteolytic agent of the gastric juice and exerts its influence most energetically in the presence of hydrochloric acid and at a temperature of about 40° C. Other acids — e. g., phosphoric, nitric, lactic, etc.- — are also capable of exciting it to activity, though with less intensity. Rennin or pexin is present in the gastric juice not only of man and all the mammaha, but also of birds and even fish. In its origin from a zymogen substance, in its relation to an acid medium and an optimum temperature, it bears a close resemblance to pepsin. Its specific action is the curdling of milk, a condition due to the coagulation of caseinogen. Hydrochloric acid is the agent which gives to the gastric juice its normal acidity. Though the juice frequently contains lactic, acetic, and even phosphoric acids, it is generally believed that they are the result of fermentation changes occurring in the food, the result of DIGESTION. 187 bacterial action. The percentage of hydrochloric acid has been the subject of much discussion. The analysis of human gastric juice made by Schmidt shows a percentage of 0.02, while that of the dog is 0.34. It is probable, however, that the low percentage of HCl in human gastric juice was due to the admixture with saliva. At present it is beheved from analyses made for clinical purposes that the acid is present to the extent of at least 0.2 per cent. This degree of acidity is not constant during the entire process of digestion. In the earlier as well as in the later stages it is much less. The immediate origin of the hydrochloric acid is difficult of ex- planation. That it is derived, however, primarily from the chlorids of the food and secondarily from the blood-plasma has been estab- lished by direct experiment. If all the chlorids be removed from the food and all chlorids be withdrawn from the animal tissue by the administration of various diuretics, — e. g., potassium nitrate, — there will be a total disappearance of hydrochloric acid from the stomach. On the addition of sodium or potassium chlorids to the food, there is at once a reappearance of the acid. As to the nature of the process by which the acid is formed, noth- ing definite is known. Various theories of a chemic and physical character have been offered, all of which are more or less unsatis- factory. As no hydrochloric acid is found either in the blood or lymph, the most plausible view as to its origin is that which regards it as one of the products of the metaboHsm of the gland-cells, and more particularly of the parietal or border cells, and which for this reason have been termed acid-producing or oxyntic cells. From the chlorids furnished by the blood the chlorin is derived, which, uniting with hydrogen, forms the HCl. The base set free returns to the blood, which in part accounts for its increased alkahnity during digestion as well as the diminished acidity of the urine. The acid thus formed passes through the canalicuh, which penetrate and surround the cells, into the lumen of the gland. Hydrochloric acid exerts its influence in a variety of ways. It is the main agent in the derivation of pepsin and rennin or pexin from their antecedent zymogen compounds, pepsinogen and pexinogen (Warren) ; it imparts activity to these ferments ; it prevents and even arrests fer- mentative and putrefactive changes in the food by destroying micro- organisms; it softens connective tissue, it dissolves proteids and acid- ifies the proteids, thus making possible the subsequent action of pepsin. The inorganic salts of the gastric juice are probably only inci- dental and play no part in the digestive process. Mode of Secretion. — The observations of Dr. Beaumont and the experiments of many physiologists have made it certain that the secretion of the gastric juice is intermittent and not continuous, that it is only on the introduction and digestion of the food that the normal i88 TEXT-BOOK OF PHYSIOLOGY. amount is poured out. During the intervals of digestive activity the stomach is practically free from all traces of the juice. The mucous membrane is pale and covered with a layer of mucus having an alka- line or neutral reaction. The introduction, however, of small por- tions of food or irritation with a glass rod causes a change in the appearance of the mucous membrane. At the points of irritation the membrane becomes red and vascular and in a few minutes small drops of the secretion make their appearance; these coalesce and run down the sides of the stomach. The chemic reaction then changes from alkalinity to acidity. Though the secretion of the gastric juice can be excited by these artificial means, the amount secreted, owing to the local character of the stimulation, is but slight compared with the quantity secreted when the natural stimulus — well-masticated food saturated with alkaline saliva — passes into the stomach. Under such circum- stances, the stimulus being general, the blood-vessels dilate, the mucous membrane becomes uniformly red, and in a short time the secretion makes its appearance. From experimental investigations there is reason to believe that the physical contact of the food with the mucous membrane is not sufficient to maintain a continuous secretion, and that other factors must be invoked. For it is not until digestion is well under way that the juice is secreted in normal and necessary quantity. Attempts have been made to determine the relative degree of influence of different articles of food on the rate of secretion. Of all substances capable of increasing the flow none are so efficient as peptones, their introduction into the stomach being followed by a copious secretion. For this reason it has been asserted that after the primary physical stimulation of the food there is a secondary chemic stimulation by peptones, the result of the digestive process. As to whether they are absorbed by the mucous membrane and directly stimulate the gland- cells, or whether they act as chemic stimuli to afferent nerves in the mucosa, nothing definite can be stated. Histologic Changes in the Gastric Cells during Secretion. — During the periods of rest and secretory activity the cells of the gastric glands undergo changes in histologic structure which are believed to be connected with the production of the ferments and acid. In the resting period the protoplasm of the chief or central cells of the fundus glands becomes crowded with large and well- defined granules, which during the period of secretory activity largely disappear, so much so, that only the luminal border of the cell is occupied by them, the outer border being clear and hyaline in appear- ance. The parietal cells during rest are large and finely granular, but after secretion they are smaller in size though still granular. (See Fig. 76, A and B.) DIGESTION. 189 The cells of the pyloric glands, though containing granules, do not show any marked difference between the resting and active condition. According to some observers, they contain pepsinogen; according to others, mucin. The epithelial cells lining the ducts of the pylorus and fundus glands, if not identical with the epithehal cells on the sur- face of the mucous membrane, pass by transitional forms into them. Among these cells are found many goblet cells which secrete a portion of the mucus found in the stomach and gastric juice. In the period of rest the protoplasm of the epithelial cells absorbs and assimilates from the surrounding lymph-spaces material which eventually makes its reappearance as a product of metabolism in the form of granules br a, 9 .„ ..C b nW. B Fig. 76. — Sections of Deep Ends of Fundus Glands of the Cat in Different Secretfve Phases. X 1000. — (Bensley.) A. From a fasting stomach. The chief cells are filled with large zymogen granules; nuclei near the outer ends of ceils. Gentian-violet preparation, b b b. Border cells. B. Six hours after an abundant meal of raw flesh. The chief cells exhibit two zones, the inner occupied by large zymogen granules, the outer by a deeply staining, obscurely fibrillar element, prozymogen; the nuclei lie at the junction of the two zones, b bb. Border cells, pr. Prozymogen. c. Mucin-secreting cell, similar to those found in the neck of the gland. Gentian-violet preparation. — {Hemmeter after Bensley.) and hydrochloric acid. With the onset of digestive activity there is a dilatation of the blood-vessels, an increase in the blood-supply, a stimulation through the nerve-supply of the cells, and an output of a fluid to which the name gastric juice is given. Influence of the Nerve System. — The secretion of gastric juice is largely a reflex act and under the control and influence of the central nerve system. Though the mechanism involved is ob- scure, it has frequently been observed that the sight of food or the chewing of food without its passage into the stomach is attended by a dilatation of the blood-vessels and a copious flow of gastric juice I90 TEXT-BOOK OF PHYSIOLOGY. within a few minutes, showing the cooperation of vaso-motor and secretor nerve influences, a result similar to that which occurs when the food comes into contact with the mucous membrane itself. It was also observed by Dr. Beaumont that mental emotions, such as fear and anger, will arrest the normal secretion. Many attempts have been made with var}dng degrees of success to determine the paths of the efferent impulses to the glands. As the vagus is the only cranial nerve connecting the stomach with the central nerve system, it has been the subject of much experimenta- tion. The results obtained, however, have not been uniform. The recent investigations of Pawlow are most reliable. He found that division of both vagi was followed by a loss of reflex action. Stimu- lation of the peripheral ends with induction shocks, one per second, after a latent period of about seven minutes, caused a flow of gastric juice. The Physiologic Action of Gastric Juice. — In the study of the physiology of gastric digestion as it takes place under normal con- ditions it is important to bear in mind that the foods introduced into the stomach are heterogeneous compounds consisting of both nutritive and non nutritive materials, and that before the former can be digested and utilized for nutritive purposes they must be freed from their combinations with the latter. This is accomphshed by the solvent action of the gastric juice, which in virtue of the chemic activity of its constituents on proteids, gradually disintegrates the food and reduces it to the liquid or semi-liquid condition. The nature of this change and the respective influence which the acid and pepsin exert can be studied w'ith almost any form of proteid. The most suitable form, however, is coagulated fibrin obtained from blood by wdiipping and thoroughly freed from blood by washing under a stream of water. The chemic features of proteids, as well as the typical forms contained in the different articles of food, have been considered in connection with the chemic composition of the body and the composition of foods (see pages 31 and 136). For purposes of experimentation artificial gastric juice may be employed. This is as effective as the normal secretion and in no essential respect differs from it. A glycerin extract of the mucous membrane acidulated with 0.2 per cent, hydrochloric acid is probably the best. If small pieces of fibrin be suspended in clear gastric juice and kept at a temperature of 104° F. (40° C.) for an hour or two, they will be dissolved and will entirely disappear, giving rise to a slightly opalescent mixture. In the early stages of the process the fibrin be- comes swollen and transparent and partly dissolved. If at this time the solution be carefully neutralized, the dissolved portion can be regained in the form of acid-albumin or syntonin — a fact which in- dicates that the first effect of the gastric juice is the acidification of the DIGESTION. 191 proteids. This having been accompUshed, the pepsin becomes opera- tive, and in a varying length of time transforms the acid-albumin into a new form of proteid, termed peptone. This form of proteid differs from all other forms of proteid in being soluble in both acids and alkalies and non-coagulable by heat. In the transformation of acid- albumin into peptone it is possible to isolate by the addition of magnesium sulphate and ammonium sulphate intermediate bodies to which the term alhumoses or proteoses has been given, and which differ somewhat in their solubility. The proteoses are termed, from the order in which they make their appearance, primary and second- ary. The primar}^ proteoses are precipitated by magnesium sulphate, the secondar}^ by ammonium sulphate. As some of the primar}- proteoses are soluble in water while others require in addition so- dium chlorid for their solution, they have been divided into two groups — -viz.: proto- and hetero-albumoses. The secondary proteoses or deutero-albumoses are soluble in water. Though in the subjoined scheme two forms of dcutero-albumose are represented and two forms of peptone developed out of them, the results of chemic investiga- tion would indicate that there is but one form of deutero-albumose and hence but one form of peptone. This supposed change pro- duced by gastric juice is represented by the following scheme: Albumin Acid-albumin Proto-albumose = ( -n . ' = Hetero-albumose ■ Proteoses ' Deutero-albumose ( 'ti <. ' I = Deutero-albumose Proteoses ' Peptone (Ampho-peptones) Peptone. From the fact that when peptones are subjected to the prolonged action of pancreatic juice there arise compounds such as leucin, tyrosin, aspartic acid, arginin, etc., it was believed that two kind of peptones were formed out of a simple proteid one of which suc- cumbed to the destructive action of pancreatic juice, while the other resisted it; for this reason the latter was termed anti- and the former hemi-peptone. The two were included under the term ampho-pep- tone. It is generally admitted now, however, that the body termed anti-peptone is not a peptone at all, but a compound termed carnic acid and which is also separable into leucin, tyrosin, etc. Hemi- peptone has never been isolated. The probabilities are, therefore, that but one form of peptone is developed from any given simple pro- teid. 192 TEXT-BOOK OF PHYSIOLOGY. Nearly all forms of proteid are in a similar manner transformed into peptones by gastric juice. Beyond this stage, however, there does not seem to be any further change, peptones apparently being the final products of gastric digestion. The intimate nature of this change is practically unknown, but there are reasons for thinking that it is a process of hydration, attended by cleavage, with increasing solubility of the resulting products. Characters 0} Peptones. — The peptones resulting from the diges- tion of different proteids, though resembling each other in many re- spects, yet possess different chemic characteristics, as shown by their reaction to various chemic reagents. Though having some resem- blance to the proteids from which they are derived, they are to be distinguished from them by the following general characteristics: 1. They are not coagulable either by heat or by nitric acid. 2. They are soluble in water, either hot or cold, and in acid and alkahne solutions. 3. They are diffusible, passing through animal membranes with great rapidity. It has been demonstrated that peptones diffuse about twelve times as rapidly as the proteids from which they are derived. Neither on fat nor starch has gastric juice any appreciable effect, and when these substances are introduced into the stomach they pass into the intestine unchanged. It has been stated, however, that the gastric mucosa produces a fat-splitting enzyme, but that its action is prevented by the presence of the hydrochloric acid. Not- withstanding the fact that dilute solutions of hydrochloric acid (0.3 per cent.) will promptly invert cane-sugar into dextrose and lewilose, and that gastric juice will accomphsh the same result in test-tubes, there is no strong evidence for the behef that the inversion of cane- sugar takes place to any marked extent in the stomach under normal conditions. The starch, however, which has been subjected to the action of the saliva still continues to be converted into maltose during the first fifteen to thirty minutes or e\'en longer. Even though gastric juice is being secreted and though hydrochloric acid solutions with a strength of 0.3 per cent, will arrest the action of ptyalin, starch digestion continues for the reason that the acid combines with the proteids and is thus rendered inoperative and for the further reason that the food is largely retained in the extreme cardiac end of the stomach where the gastric juice is not abundant. After the above-mentioned period, free acid makes its appearance when saUvary digestion ceases. Action of Gastric Juice on Foods. — The action of gastric juice on proteids affords a key to its influence in the reduction of foods to the liquid or semi-Hquid condition. It is evident that it will be most active in the digestion of food consisting largely of proteid DIGESTION. 193 materials, such as meat, eggs, milk, etc. Meat is disintegrated first by the conversion of the proteids of the connective tissue, which have been more or less gelatinized by cooking, into peptones. The sarcolemma of the muscle-fibers which have been thus separated is in a similar manner attacked and converted into peptones. The true muscle or sarcous substance, consisting largely of myosin, un- dergoes a corresponding change. If the quantity of meat be not too large and the gastric juice be secreted in proper amount, it is possible that all the meat will be digested in the stomach. It is quite probable, however, that this is not the case and that a portion of the semi- digested meat passes into the intestine, where its final solution is effected. The white of egg, especially when slightly boiled, is much more readily digested than when raw or firmly coagulated by prolonged boihng. In either condition, however, the connective tissue is dis- solved and peptonized, after which the native albumin undergoes the same change. The yolk of the egg consists largely of fat held in sus- pension by a proteid substance, vitellin, which is also capable of transformation into peptone. Adipose tissue is similarly reduced. The proteids of the con- nective tissue and of the fat vesicles are dissolved and peptonized and the fat-drops set free. Milk undergoes a peculiar change in composition before its proteid constituents can be transformed into peptones. The case- inogen in the presence of calcium salts is always in the soluble state. When acted on by the gastric juice, the caseinogen under- goes coagulation which consists in the formation of a solid com- pound, casein, and a soluble albumin. This change is due to the presence and activity of the ferment, rennin. The necessity for this change, how^ever, is not apparent. The coagulated casein presents itself in the form of a flocculent curd, which is finer in human than in cow's milk, and hence more easily digestible. The casein is acidified by the hydrochloric acid and then converted by the pepsin into peptone. Vegetables, though consisting of a woody or cellulose framework, undergo a partial disintegration in the stomach. When boiled and physically disintegrated by the teeth, the gastric juice is enabled to penetrate the framework and dissolve and peptonize the various proteid constituents. As a general rule, the vegetable proteids are more difficult of digestion than the animal proteids. Duration of Gastric Digestion. — The length of time the food remains in the stomach and the relative digestibihty of different articles of food were carefully studied by Dr. Beaumont on St. Martin, and though the results obtained by him may not be absolutely correct, viewed in the light of recent knowledge of the digestive process, yet 194 TEXT-BOOK OF PHYSIOLOGY. in the main they have been corroborated in various ways. As a result of many observations Dr. Beaumont came to the conclusion that the average length of time an ordinary meal consisting of meat, bread, potatoes, etc., remained in the stomach undergoing digestion was about three and a half hours, the duration of the process, how- ever, being increased when an excessive quantity of food was taken or the quantity and quaUty of the gastric juice impaired by abnormal conditions of the system. As soon as the food is liquefied by the gastric juice that portion not absorbed by the gastric vessels passes into the intestines, this continuing for two to three hours until the stomach is completely emptied. The relative digestibihty of the dif- ferent foods was also made the subject of many experiments by Dr. Beaumont. After repeating and verifying his observations made under varying conditions, he summed up his results in a table, of which the following is an abstract, in which the mode of preparation and the time required for the digestion of different foods are exhibited : TABLE SHOWING DIGESTIBILITY OF VARIOUS ARTICLES OF FOOD Hours. Minutes. Eggs, whipped, i 20 " soft boiled, 3 " hard boiled, 3 30 Oysters, raw, 2 55 " stewed, 3 30 Lamb, broiled, 2 30 Veal, broiled, 4 Pork, roasted, 5 15 Beefsteak, broiled, 3 Turkey, roasted, 2 25 Chicken, boiled, 4 __ " fricasseed, 2 45 Duck, roasted, 4 Soup, barley, boiled, 1 30 " bean, " 3 " chicken, " 3 " mutton, " 3 30 Liver, beef, broiled, 2 Sausage, " 3 20 Green corn, boiled, 3 45 Beans, " 2 30 Potatoes, roasted, 2 30 " boiled, 3 30 Cabbage, " 4 30 Turnips, " 3 30 Beets, " 3 45 Parsnips, " 2 30 Movements of the Stomach. — During the period of gastric digestion the muscle walls of the stomach become the seat of a series of movements, peristaltic in character, which not only incor- porate the gastric juice with the food, but also serve to eject the liquefied portions of the food into the small intestine. DIGESTION. 195 The movements of the human stomach as described by Beau- mont, as well as the movements of the dog's stomach as stated by different observers, are not in agreement in all respects, and are, moreover, open to question for the reason that they were not ob- served under strictly physiologic conditions. The more recent investigations of Cannon have thrown new light on this subject. By means of the Rontgen rays he has been enabled to study the movements in the living animal and under normal conditions. The animal (the cat) was fed with bread and milk, to which was added subnitrate of bismuth. This substance, being opaque, rendered the movements of the stomach walls visible on the fluorescent screen. With paper placed over the screen it was pos- sible to sketch the changes in shape that the stomach undergoes at different periods of the digestive act. Some of these changes are represented in Fig. 77. The anatomic features of the cat stomach of interest in this connection are represented in Fig. 78. These investigations show that different portions of the stomach walls exhibit different forms of activity, which for convenience of description are separately described by Cannon as follows: I. The Movements 0} the Pyloric Part. — Within five minutes after a cat has finished a meal of bread there is visible near the du- odenal end of the antrum a slight annular contraction which moves peristaltically to the pylorus; this is followed by several waves re- curring at regular intervals. Two or three minutes after the first movement is seen, very slight constrictions appear near the middle of the stomach, and, pressing deeper into the greater curvature, course slowly tovv'ard the pyloric end. As new regions enter into constric- tion, the fibers just previously contracted become relaxed, so that there is a true moving wave, with a trough between two crests. When a wave swings round the bend in the pyloric part, the indenta- tion made by it deepens; and as digestion goes on the antrum elongates and the constrictions running over it grow stronger, but, until the stomach is nearly empty, they do not entirely divide the cavity. After the antrum has lengthened, a wave takes about thirty-six sec- onds to move from the middle of the stomach to the pylorus. At all periods of digestion the waves recur at intervals of almost exactly ten seconds. It results from this rhythm that when one wave is just beginning several others are already running in order before it. Between the rings of constriction the stomach is bulged out, as shown in the various outlines in Fig. 77. Movements of the Pyloric Sphincter, — During the first ten or fifteen minutes after the first constriction of the antrum the pylorus is tightly closed. After this period it opens at irregular intervals to permit the passage of liquefied food which is ejected by peristaltic waves for a distance of two or three centimeters into the duodenum. 196 TEXT-BOOK OF PHYSIOLOGY. The frequency with which the pylorus opens depends apparently on the degree to which the food is softened. When the food is hard, the pylorus closes more tightly and remains closed a longer period than when it is soft. The Activity 0} the Cardiac Portion. — As digestion proceeds, the pre-antral part of the stomach elongates and assumes the shape of a tube, which becomes the seat also of peristaltic constriction waves. As a result, some of the food is gradually forced into the antrum to succeed that which has been prepar- ed and ejected into the duodenum. As the pre-antral tube is emptied of its contents the longitudinal and circular fibers of the fundus stead- ily contract and gradually force its contents into the tubular portion. This continues until the fundus is completely emptied. The changes Left Fig. 77. — Shadow Sketches OF THE Outlines of THE Stomach of a Cat Immediately after a Meal (ii.o), and at Various Intervals Afterward (at 12.0, at 2.0, 3.30, 4.30).— (PF. B. Cannon.) Post Fig. 78. — The cardiac portion is all that part to the left, as the stomach Ues in the body, of WX. The cardia is at C The pylorus is at P, and the pyloric portion is the part between P and WX. This has two divisions: the antrum, between P and YZ, and the pre-antral part, be- tween WX and YZ. The lesser curva- ture is on the top of the outline between C and P, and the greater curvature be- tween the same points along the lower border. — (Amer. Jour, of Physiology, Cannon.) in shape which the cardiac portion undergoes during digestion are represented in Fig. 77. The fundus acts as a reservoir for the food and forces out its contents a httle at a time as the antral mechan- ism is ready to receive them. Since peristaltic movements are DIGESTION. 197 absent from the cardiac portion the food is not mixed with gastric juice, and therefore sahvary digestion can continue for a considerable period. There is no evidence of a circulation of food in the stomach as usually described. On the contrary, the movement through the pre-antral tube and antrum is in general a progressive though an oscillating one. As the constriction waves rapidly pass over the food it is advanced toward the pyloric opening, but as this is closed the food is forced backward through the advancing constricted ring for a variable distance. The effect of the constriction waves is to mix the food with the gastric juice, triturate and soften it. So soon as this is eft'ected, the pylorus relaxes, when the advancing constriction \vave expels it into the intestine. With its expulsion room is afforded for an additional quantity of food, and hence there is a general advance of the food mass toward the pylorus. Though these observations were made on the cat, evidence is accumulating which goes to show that in human beings the walls of the stomach exhibit constriction waves which are similar in all respects to those above described. The Nerve Mechanism of the Stomach. — In preceding para- graphs it was stated that during the period of gastric digestion the food is retained in the stomach because of the closure of the cardia (the esophago-gastric orifice) and of the pylorus (the gastro-duode- nal orifice) both orifices being tightly closed by the tonic contraction of sphincter muscles; that both sphincters relax from time to time, the one to permit the entrance of food into the stomach for further digestion, the other to permit the exit of food into the intestine after its more or less complete digestion, after w^hich in both instances the sphincters again contract and close the orifices; that the pyloric or antral muscles are vigorously active throughout the digestive period, triturating the food, mixing it with gastric juice, and finalh' driving it through the temporarily open pylorus into the intestine. These separate but related groups of muscle-fibers, by reason of their endowments, and possibly by virtue of the presence of local nerve mechanisms, exhibit activities wiiich are independent of the central nerve svstem. Thus the isolated stomach of the dog and of other animals as well, if kept warm and moist, will exhibit rhythmic movements for a period of time varying from an hour to an hour and a half. Though nerve-cells and nerve-fibers (Auerbach's plexus) are present in the vvalls of the stomach between the layers of muscle- fibers, it is not believed that they are the immediate sources of the stimulus to the contraction, though they may act as a coordinating mechanism. The stimulus in all probability develops in the muscle- fiber itself and is therefore myogenic in origin. The degree of acti\dty of both the sphincter and antral muscles 198 TEXT-BOOK OF PHYSIOLOGY. is modified by the central nerve system cither in the way of inhibition or augmentation and in response to gastric stimulation. The nerves more especially concerned in the maintenance and regulation of the gastric contractions, are the vagi and the splanchnics. The afferent fibers through which nerve impulses pass to the nerve centers are in all probability contained in the trunk of the vagus nerve; the efjerent fibers through which nerve impulses from the centers reach the stomach, are contained partly in the trunk of the vagus and partly in the trunk of the splanchnic nerve. If the vagus nerves are divided in the neck, there is a loss of muscle tonus though the contractions do not wholly disappear. Stimulation of the peripheral end of one divided vagus is followed by an augmentation in the vigor of the contraction of the antral muscles an increase in the tone of the fundus muscles as well as an increase in the contraction of the sphincter pylori and sphincter cardiac. Though this is the usual result there may be a primary relaxation or inhibition of short duration of one or all of these structures before the augmicntation occurs. May states that this was alwa}"S the case in his experiments. A similar inhibition may be brought about reflexly by stimulation of the central end of a divided vagus. This result will not be produced if the opposite vagus has previously been divided. The vagi, therefore, contain both inhibitor and augmentor nerve- fibers lor the gastric musculature. Stimulation of the peripheral end of a divided splanchnic is followed by an inhibition of the peristalsis and a loss of tone. Morat, however, has observed a primary opposite effect. From these facts it would appear that the gastric muscles receive both inhibitor and augmentor fibers from two different sources. The excitatory cause for the activity of this mechanism is doubtless connected with the chemic and mechanic stimulation by the gastric contents. The relaxation or inhibition of the sphincter p}lori ap- pears to be caused by the presence of free acid at the pylorus: its contraction, by the presence of acids in the duodenum. Similar conditions throughout the interior of the stomach may be the cause of the cooperative antagonism of these specialized muscle structures. INTESTINAL DIGESTION. The physical and chemic changes which the ahmentary principles undergo in the small intestine, and which collectively constitute in- testinal digestion, are probably more important and complex than those taking place in the stomach, for the food is, in this situation, subjected to the solvent action of the pancreatic and intestinal juices, as well as to the action of the bile, each of which exerts a transforming influence on one or more substances and still further prepares them for absorption into the blood. DIGESTION. 199 To i-ightly appreciate the physiologic actions of the digestive juices poured into the intestine, the nature of the partially digested food as it comes from the stomach must be kept in mind. This consists of water, inorganic salts, acidified proteids, albumoses, pep- tones, starch, maltose, liquefied fat, saccharose, lactose, dextrose, cellulose, and the indigestible portion of meats, cereals, and fruits. Collectively they are known as chyme. As this acidified mass passes through the duodenum its contained acids excite a reflex secretion and discharge of the intestinal fluids: e. g., pancreatic juice, bile, and intestinal juice. Inasmuch as these fluids are alkahne in re- action they exert a neutrahzing and precipitating influence on vari- ous constituents of the chyme. As soon as this has taken place, gastric digestion ceases and those chemic changes are inaugurated which eventuate in the transformation of all the remaining undigested nutritive materials into absorbable and assimilable compounds which collectivelv constitute intestinal digestion. THE SMALL INTESTINE. The small intestine, in which this stage of digestion takes place, is a convoluted tube, measuring about seven meters in length and 3.5 cm. in diameter, and extending from the pyloric orifice of the stomach to the beginning of the large intestine. The intestine consists of four coats: viz., serous, muscular, sub- mucous, and mucous. The serous coal is the most external and is formed by a reflection of the general peritoneal membrane. It is, however, wanting in the duodenal portion. The muscle coat, situated just beneath the former, surrounds the entire intestine. It is composed of non-striated fibers which are more abundant and better developed in the upper than in the lower portions of the intestine. The muscle coat consists of two layers of fibers: (i) an external or longitudinal, and (2) an internal or circular layer. The longitudinal fibers are most marked at that border of the intestine free from peritoneal attachment, though they form a thin layer all over the intestine. The circular fibers are much more numerous, and completely encircle the intestine throughout its entire extent. It has been demonstrated that at the junction of the ileum and colon, and surrounding the orifice, the ileo-colic, common to both, the muscle-fibers are arranged in the form of, and play the part of, a sphincter muscle, which has been turned the ileo-colic sphincter. It is usuallv in a state of tonic contraction and regulates the passage of materials from the small into the large intestine, and possibly also in the reverse direction under special circumstances. The submucous coat consists of areolar tissue and serves to unite 200 TEXT-BOOK OF PHYSIOLOGY. the muscular with the mucous coat. A thin layer of muscle-fibers, the muscularis mucosa, is placed on its inner surface. The mucous coat is soft and velvety in appearance and covered by a single layer of columnar epithelium. Its entire surface is covered with small conical projections termed villi. Throughout its entire extent, with the exception of the lower portion of the ileum and the duodenum, the mucous membrane presents a series of transverse folds — the valvulae conniventes, or valves of Kirkring. These folds vary from one-fourth to half an inch in width and extend one-half to two-thirds of the distance around the interior of the bowel. Each valve consists of two layers of the mucous membrane perman- ently united by fibrous tissue. It is beheved that the valves retard to some extent the passage of the food through the intestine and present a greater surface for absorption. Blood-vessels, Nerves, and Lymphatics. — The blood-vessels, of the small intestine, which are very numerous, are derived mainly from the superior mesenteric artery. After penetrating the intestinal walls the smaller vessels ramify in the submucous coat and send branches to the muscle and mucous coats, supplying all their struc- tures with blood. After circulating through the capillary vessels the blood is returned by small veins, which subsequently unite to form the superior mesenteric vein, which, uniting with the splenic and gas- tric veins, forms the portal vein. The nerves are derived from the lower part of the solar plexus. The branches follow the blood-vessels and become associated with two plexuses, one (Auerbach's) lying between the muscle coats, the other (Meissner's) lying in the sub- mucous coat. The lymphatics, which originate in the mucous and muscle coats, are very abundant. They unite to form those vessels seen in the mesentery and empty into the thoracic duct. Intestinal Glands. — The gland apparatus of the intestine by which the intestinal juice is secreted consists of the duodenal (Brun- ner's) and the intestinal (Lieberkiihn's) glands. The duodenal glands are situated beneath the mucous membrane and open by a short wide duct on its free surface. They are racemose glands lined by nucleated epithelium. The secretion of these glands is clear, slightly viscid, and alkaline. Its chemic composition and function are unknown. The intestinal glands or foUicles are distributed throughout the entire mucous membrane in enormous numbers. They are formed mainly by an inversion of the mucous membrane and hence open on its free surface. Each tubule consists of a thin basement membrane lined by a layer of spheric epithelial cells, some of which undergo distention by mucin and become converted into mucous or goblet cells. The epithelial secreting cells consist of granular protoplasm containing a well-defined nucleus. The intestinal foUicles constitute DIGESTION. 20I the apparatus which secretes the chief portion of the intestinal juice. Intestinal Juice. — Owing to its admixture with other secretions and to the profound disturbance of the digestive function, caused by the estabhshment of intestinal fistulas, this fluid has rarely been ob- tained in a state of purity or in quantities sufficient for accurate analyses or for experimental purposes. Its physiologic properties and functions are therefore imperfectly known. Various attempts have been made by physiologists, by the employment of different methods, to obtain this secretion. The method usually employed is that of Thiry and Vella. This consists in dividing the intestine at two places, about eight or ten inches apart, restoring the continuity of the intestine, and then uniting the two ends of the resected portion to the edges of two openings in the abdominal walls. The resected portion, being supplied with blood-vessels and nerves, maintains its nutrition and secretes a more or less normal juice. When obtained from a dog under these circumstances the intes- tinal juice is watery in consistence, slightly opalescent, light yellow in color, alkahne in reaction, with a specific gravity of i.oio. Chemic analysis reveals the presence of proteids, mucin, and sodium car- bonate. The intestinal juice obtained by Tubbey and Manning from a small portion of the human intestine (ileum) was opalescent, occa- sionally brownish in color, alkaline, and had a specific gravity of 1.006. On the addition of hydrochloric acid, carbonic acid was given off, showing the presence of carbonates. It contained proteids and mucins. PANCREAS. The pancreas is a long flattened gland, situated deep in the abdominal cavity, lying just behind the stomach. It measures from six to eight inches in length, two and a half in breadth, and one in thickness. It is usually divided into a head, body, and tail. The head is directed to the right side and is embraced by the curved portion of the duodenum; the tail is directed to the left side and extends as far as the spleen (Fig. 79). The pancreas communicates with the intestine by means of a duct. This duct commences at the tail and runs transversely through the body of the gland. As it approaches the head of the gland it gradually increases in size until it measures about one-tenth of an inch in diameter. It then curves downward and forward and opens into the duodenum. In its course through the gland it receives branches which enter it nearly at right angles. The pancreas is richly supplied with blood-vessels and nerves, the latter coming from the solar plexus. 20:; TEXT-BOOK OF PHYSIOLOGY. Histologic Structure. — In its structure the pancreas resembles the salivary glands. It consists oi a connective-tissue framev^ork which divides the gland tissue into lobules. Each lobule is com- posed of a number of acini or alveoH, more or less elongated or Tail. Pancreatic ducts Common bile duct Primary pancreatic duct Fig. 79. — Pancreas and Duodenum Removed from the Body and Seen from Behind. The Gland is Cut to Show the Ducts. — {Landois and Stirling.) tubular in shape. Each acinus gives origin to a small duct which, uniting with adjoining ducts, forms the lobular duct, which becomes tributary to the main duct. The acinus is lined by a layer of cylin- dric epithehal cells characterized by a difference in structure be- FiG. 80. — Section of Hum.an Pan- creas, INCLUDING Several Acini AND Two Ducts. The Cells Present a Central Granular AND A Peripheral Clear Zone. — (Piersol.) Fig. 81. — Section of Human Pan- creas SHOWING, a, a. Islands OF LANGERHANS, AND b THE Usual Acini. — {Piersol). tween the central and peripheral ends (Fig. 80). The central end, that bordering the lumen of the acinus, is dark in appearance and filled with dark granules, while the peripheral end is clear ahd homo- geneous. The relative depth of these two zones varies according to DIGESTION. 203 the functional activity of the gland. During the intervals of digestion the granular layer is very deep and occupies almost the entire cell; after active digestion the granular layer is very narrow, while the clear zone is largely increased in depth. The blood-vessels of the pancreas are arranged around the acini in a manner similar to that observed in the salivary glands. The ultimate terminations of the nerves in the epithelium are probably by means of the usual end-tufts. The Islands of Langerhans . — Throughout the body of the pan- creas and especially in the outer extremity there are found between and among the acini collections of globular cells arranged in the form of rods or columns, separated from the acini and from one another by layers of connective tissue in which ramify large tortuous capillary blood-vessels. These columnar bodies, seen in cross- section in Fig. 81, have been named, after their discoverer, the islands of Langerhans. Embryologic investigations have shown that these cells are outgrowths from the primitive acini, to which they remain attached for some time by means of a foot-stalk. This subsequently becomes constricted by the connective tissue and the cells become completely detached. The cells then assume the columnar arrangement, after which vascularization takes place. From the fact that complete extirpation of the pancreas as well as its various diseases is followed by serious disturbances of the carbohy- drate metabolism it has been suggested that the islands of Langerhans have a function separate and distinct from that of the glandular portion of the pancreas; that they secrete a specific material which partakes of the nature of an internal secretion which is absorbed by the blood circulating around them and carried to different tissues. The effect on the metabolism of the body which follows extirpation of the pan- creas will be referred to in a subsequent chapter. Pancreatic Juice. — The pancreatic juice may be obtained by introducing a silver cannula, through an opening in the abdominal wall, into the duct, and securing it by a ligature. In a short time the juice flows from the distal end of the cannula, when it can be collected. According to Bernard, normal juice can only be ob- tained during the first twenty-four hours. The juice obtained from a temporary fistula is clear, slightly opalescent, viscid, of a decidedly alkaline reaction, and has a specific gravity in the dog of 1.040. When cooled to 0° C, it assumes a gelatinous consistence. At 100° C. it completely coagulates. When obtained from a permanent fistula, the juice is watery and the solid constituents are very much diminished in amount. The chemic composition of the pancreatic juice of the dog as deter- mined by Schmidt is as follows: water, goo. 76; organic matter, 90.44; inorganic salts, 8.80. Of the inorganic salts, sodium carbonate is 204 TEXT-BOOK OF PHYSIOLOGY. probably the most essential, as it is this salt which gives to the juice its alkaline reaction. Mode of Secretion. — The secretion of the juice is, in the rabbit and dog at least, almost continuous during a period of twenty-four hours after a single average meal, though the rate of flow varies con- siderably during this period. As soon as food enters the stomach the flow of the pancreatic juice begins and steadily increases in amount until about the third hour, when it reaches its maximum; after this period the flow diminishes until the sixth hour, when it again increases for about an hour. It then gradually diminishes until it ceases entirely. During the period of secretory activity the gland becomes red and vascular from a dilatation of the blood-vessels. The discharge of the juice associated with the introduction of food into the stomach is brought about in all probability through the agency of the nerve system, though the exact mechanism is imperfectly understood. It is probable that impressions made on the terminal filaments of the pneumogastric nerve ascend to the medulla, whence impulses pass outward through vaso-motor and secretor nerves to the blood-vessels and secreting cells of the glands. Stimulation of the peripheral end of the divided vagus gives rise to increased secretion. Inasmuch as various agents, such as mineral and organic acids, placed on the duodenal mucous membrane excite the flow, it is quite probable that the passage of the acid contents of the stomach through the duodenum also acts as a powerful stimulus to the discharge of the juice. But as the secretion and discharge of the juice is excited by the same conditions after the division of all related nerves, other explanations were sought for. Bayliss and Starhng made the discovery that the secretory activity of the pancreas is initiated and maintained by the action of a specific substance to which they have given the term secretin. This substance is developed in the duodenal glands out of a precursor, prosecretin, in consequence of the action of the acids in the chyme, after which it is carried by the blood-stream to the pancreas. An extract of the duodenal mucous membrane made with hydrochloric acid 0.4 per cent, and presumably containing secretin, when injected into the blood will evoke a pro- fuse discharge of pancreatic juice. Hydrochloric acid alone will not have this effect. The total amount of pancreatic juice secreted in twenty-four hours has been only approximately determined; the estimates based upon the amount obtained from dogs vary from 175 to 800 grams. Histologic Changes in the Cells during Secretory Activity.— Reference has already been made to the fact that the cells lining the acini consist of two zones: an outer one, clear and homogene- ous; and an inner one, dark and granular. The position of the nucleus of the cell varies, being at one time in the outer, at an- DIGESTION. 205 \ -'v other time in the inner, zone. If the pancreas be examined microscopically during the intervals of digestion, it will be ob- served that the inner zone is broad, highly granular, occupying nearly the entire cell, while the outer zone is narrow and clear. If, however, the gland be examined shortly after a period of active secretion, the reverse conditions will be observed; that is, the inner zone will be narrow, containing relatively few granules, while the outer zone will be clear and wide. This change in the cell has been witnessed in the pancreas of the Hving animal — rabbit — by Kiihne and Lea. They observed that as soon as digestion set in, the granules of the broad inner zone began to pass toward the lumen of the acinus and to gradually disappear as the secretion was poured out, while the outer zone in- creased in width un- til almost the entire cell became clear and homogeneous. (See Fig. 82.) After secre- tion ceased the gran- ules again made their appearance, the result, in all probability, of metabolic activity. Physiologic Ac- tion of Pancreatic Juice . — Exper i m e n - tal investigations have demonstrated the fact that pancreatic juice is the most complex in its physiologic action of all the digestive fluids. In virtue of its contained enzymes, pancreatic juice acts: 1. On starch. When normal pancreatic juice or a glycerin extract of the gland is added to a solution of hydrated starch, the latter is speedily transformed into maltose, passing through the inter- mediate stage of dextrin. The process is in all respects similar to that observed in the digestion of starch by saliva. Pancreatic juice, however, is more energetic in this respect than sahva. The enzyme which effects this change is termed amylopsin. When the starch which escapes salivary digestion passes into the small intestine and mingles with pancreatic juice, it is very promptly converted into maltose by the action or in the presence of this enzyme. 2. On proleid. When proteid bodies are subjected to the action Fig. 82. Fig. 83. One Saccule of the Pancreas of the Rabbit in Different States of Activity. Fig. 82. — After a period of rest, in which case the outlines of the cells are indistinct and the inner zone — i. e., the part of the cells (a) next the lumen (c) — is broad and filled with fine granules. Fig. 83. — After the gland has poured out its secretion, when the cell outUnes {d) are clearer, the granular zone (a) is smaller, and the clear outer zone is wider. — {Yeo's "Texl-hook of Physiology," ajter Kiihne and Lea.) 2o6 TEXT-BOOK OF PHYSIOLOGY. of pancreatic juice, they are transformed into peptones which do not differ in essential respects from those formed by gastric juice. The intermediate stages, however, are beheved to be somewhat different. The enzyme which effects this change is termed trypsin. When fibrin, for example, is added to trypsin in a solution rendered alkaline by sodium carbonate, it does not swell up and become trans- lucent, as it does when treated with hydrochloric acid and pepsin. On the contrary, it becomes corroded on the surface, fragile, and in a short time undergoes solution. The first product is a compound termed alkali-albumin. After solution has taken place, various chemic changes are initiated which eventuate in the production of peptone and certain nitrogenized bodies, leucin, tyrosin, aspartic acid, etc. The intermediate stages in this process have not been satisfactorily deter- mined. At no time during artificial pancreatic digestion is there any evidence of the presence of the primar}^ proteoses (proto-albumose and hetero-albumose). The secondary proteoses (deutero-albumose) are usually present. It will be recalled that when the peptone of peptic digestion is subjected to the action of trypsin a portion of it is decomposed into leucin and tyrosin, while another portion pre- sumably is not so decomposed, for which reason the latter was called anti- and the former, Aewi-peptone. It is now believed that anti- peptone is not a peptone at all, but a compound termed carnic acid, which can be decomposed into simpler nitrogen-holding bodies such as leucin, tyrosin, arginin, etc. The action of tr\psin on proteids in an alkaline medium may be illustrated by the following scheme: » Proteid Alkali-albumin Deutero-proteose or deutero-albumose Peptone Leucin Tyrosin Aspartic acid Arginin Ammonia When the proteids which have escaped digestion in the stomach pass into the small intestine and mingle with the pancreatic juice, they are doubtless digested in the course of the intestinal canal, passing through the stages just described. As leucin and tyrosin are found in the intestine during digestion, it is probable that a portion of the peptone undergoes decomposition into these bodies; but as to the extent to which this takes place or in how far it is a necessary process under normal conditions, nothing definite can be said. It is probable that it takes place when there is an excess of proteid food or when for any reason digestion is prolonged or absorption is delayed. While the view that the final stage in the digestion of proteids is DIGESTION. 207 the formation of peptones, which in due time are absorbed and syn- thetized into blood albumin, is generally accepted, there is some evidence that it is not wholly true, and that the final stage may be the formation of the nitrogen-holding compounds above mentioned; in other words, that the cleavage of the proteids is far more com- plete than has heretofore been assumed. Ever since the discovery by Cohnheim of the existence in the intestinal juice of a substance termed by him erepsin, which is capable of splitting proteoses and peptones into simple nitrogen-holding compounds, there has been slowly developing the idea that normally during intestinal digestion the proteoses and peptones are reduced by this agent to leucin, tyrosin, histidin, arginin, aspartic acid, etc., which in turn are absorbed and synthetized to blood or tissue albumin. The discovery by Vernon of erepsin in pancreatic juice lends further support to this view. Until more convincing evidence is furnished, however, it may be assumed that peptone represents the final stage in the digestion of proteids. 3. On jat. If pancreatic juice be added to a perfectly neutral fat — olein, palmitin, or stearin — and kept at a temperature of about 100° F. (38° C), it will at the end of an hour or two be partially de- composed into glycerin and the particular fatty acid indicated by the name of the fat used — e. g., oleic, palmitic, stearic. The oil will then exhibit an acid reaction. The reaction is represented in the following formula: CsHjCCsHjjO^), + 3H2O = (CisHj.Oj), -f C3H5(HO)3 Triolein. Water. Oleic Acid. Glycerin. If to this acidified oil there be added an alkah, e. g., potassium or sodium carbonate, the latter will at once combine with the fatty acid to form a salt known as a soap. The reaction is expressed in the following equation: Sodium Carbonate. Oleic Acid. Sodium Oleate. Carbonic Acid. NajCOa + CjaHj^Oj = NajOCigHjjOj + H2CO3 Coincident with the formation of the soap the remaining neutral oil undergoes division into drops of microscopic size, which float in the soap solution, forming what has been termed an emulsion, which is white and creamy in appearance. The action of the pancreatic juice may then be said to consist in the cleavage of the neutral fats into fatty acids and glycerin, after which the formation of the soap and the division of the fat takes place spontaneously. The enzyme which produces the cleavage of the neutral fats has been termed stcapsin. The extent to which the cleavage of the fat takes place in the intestine has not been definitely determined. There are some who think the amount is relatively small, while others consider that it is large, practically all of the fat undergoing this decomposition, with the formation of soap and glycerin prior to their absorption. 2o8 TEXT-BOOK OF PHYSIOLOGY. According to Pawlow, the relative amounts of the pancreatic enzymes produced are conditioned by the character and amounts of the food principles consumed. Thus, if chyme contains an ex- cess of either starch, proteid, or fat, there is a corresponding increase in the amount of either amylopsin, trypsin, or steapsin produced. The pancreas apparently adapts its activities to the character of the food. Though it is probable that each enzyme is a derivative of a special zymogen, it is only positively known that this is the case with trypsin. This enzyme is a derivative of the zymogen, trypsin- ogen, the production of which is thought to be the special function of secretin. The pancreatic juice at the moment of its discharge into the intestine does not contain trypsin but trypsinogen. The transformation of the latter into the former is accomplished, ac- cording to Pawlow, by a special ferment secreted by the epithelium of the small intestine and termed enter okinase. The rapidity with which pancreatic juice in the presence of bile and hydrochloric acid (under conditions such as are present in the duodenum) can develop sufhcient fatty acid to form an emulsion was determined by Rachford to be two minutes. The activity of steapsin is thus shown to be very great. Physiologic Action of the Intestinal Juice. — The part played by the intestinal juice in the digestive process is yet a subject of dis- cussion, as the results obtained by different observers are in some respects contradictory, due to the fact that animals, including human beings, have been the subjects of experimentation. Notwithstanding the actions of saliva, gastric and pancreatic juice, there yet remain in the food saccharose, maltose, and lactose, three forms of sugar which are believed by most observers to be non-assimilable and therefore require some change before they can be absorbed and assimilated. An extract of the intestinal mucous membrane or the intestinal juice of a dog, added to a solution of saccharose, will in a very short time convert it into dextrose and levulose, which together constitute invert sugar. The enzyme by which this inversion is produced, though nothing definite is known as to its nature, has been termed invertin. Tubbey and Manning state that the human intes- tinal juice as obtained by them has the same action. In the case of intestinal fistulae reported by Busch, which were supposed to be located in the upper third of the intestine, it was found that when saccharose was introduced into the lower opening, it was not inverted but appeared in the feces unchanged. Maltose is also rapidly transformed into dextrose. Lactose appears to be unaffected by the pure juice. As it is non-assimilable it has been supposed to undergo conversion into dextrose and galac- tose while passing through the epithelial cells of the intestinal mu- DIGESTION. 209 cosa. In either case the transformation is brought about by two ferments known respectively as maltase and lactase. Intestinal juice also has a sHght diastatic action on starch. THE LIVER. The liver is a highly vascular conglomerate gland situated in the right hypochondriac region and connected with the intestine by a duct. Inasmuch as the liver performs several functions related to both secretion and excretion, a consideration of its structure and its vari- ous functions will be deferred to a subsequent chapter. In this connection the bile, its physical properties and chemic composition in relation to the digestive process, will only be considered. The bile is a product of the secretory activity of the liver cells. As it is poured into the intestine in man and most mammals at a point corresponding to the orifice of the pancreatic duct, 'and most abundantly at the time the food is passing through the duodenum, it is usually regarded as a digestive fluid possessing an influence favorable if not necessary to the completion of the general digestive process. Anatomic Relations of the Biliary Passages. — After its forma- tion by the liver cells the bile is conveyed from the hver by the bile capillaries, which uniting finally form the main hepatic duct. This duct emerges from the liver at the transverse fissure. At a distance of about 5 centimeters it is joined by the cystic duct, the distal ex- tremity of which expands into a pear-shaped reservoir, the gall- bladder, in which the bile is temporarily stored (Fig. 84). The duct formed by the union of the hepatic and cystic ducts, the common bile-duct, passes downward and forward for a distance of about 7 centimeters, pierces the walls of the intestine and passes obhquely through its coats for about a centimeter and opens on the surface of a papilla in conjunction with the pancreatic duct. The walls of the bihary passages are composed of a mucous membrane internally, a fibrous and muscular coat externally. The termination of the common bile-duct is 'provided with a distinct band of circularly disposed muscle-fibers, which when in action completely close the orifice and prevent the discharge of bile. It may therefore be re- garded as a true sphincter muscle. Small racemose glands are embedded in the mucous membrance of the main ducts. Physical Properties and Chemic Composition of Bile. — The bile obtained directly from the hver through a fistulous opening in the hepatic duct is always thin and watery, while that obtained from the gall-bladder is more or less viscid from admixture with mucin, the degree of this viscidity depending on the length of time it remains 14 2IO TEXT-BOOK OF PHYSIOLOGY. in this reservoir. The specific gravity of human bile varies within normal limits from i.oio to 1.020. The reaction is invariably alka- line in the human subject when first discharged from the liver, but may become neutral in the gall-bladder. The alkahnity depends on the presence of sodium carbonate and sodium phosphate. When fresh, it is inodorous; but it readily undergoes putrefactive changes, and soon becomes offensive. Its taste is decidedly bitter. When shaken with water, it becomes frothy — a condition which lasts for Fig. 84. — Gall-bladder, Hepatic, Cystic, and Common Ducts, i, 2, 3. Duode- num. 4, 4, 5, 6, 7, 7. 8. Pancreas and pancreatic ducts. 9, 10, 11, 12, 13. Liver. 14. Gall-bladder. 15. Hepatic duct. 16. Cystic duct. 17. Common duct. 18. Portal vein. 19. Branch from the ceHac axis. 20. Hepatic artery. 21. Coro- nary artery of the stomach. 22. Cardiac portion of the stomach. 23. Splenic artery. 24. Spleen. 25. Left kidney. 26. Right kidney. 27. Superior mesen- teric artery and vein. 28. Inferior vena cava. — (Sappey.) some time and which is due to the presence of mucin. In ox bile the mucin is replaced by a nucleo-proteid. The color of bile obtained from the hepatic duct is variable, usually a shade between a greenish-yellow and a brownish-red. In different animals the color varies. In the herbivorous animals it is usually green; in the carnivorous animals it is orange or brown. In man it is green or a golden yellow. The colors are due to the pres- ence of pigments. Microscopic examination does not show the presence of structural elements. DIGESTION. 211 Human bile obtained from an accidental biliary fistula was shown by Jacobson to contain the following ingredients, viz. : COMPOSITION OF HUMAN BILE. Water, 1 9774o Sodium glycocholate, 9.94 Sodium taurocholate, a trace Cholesterin, c.54 Free fat, ^.. o.io Sodium palmitate and stearate, 1.36 Lecithin, 0.04 Other organic matters, 2.26 Sodium chlorid, 5.45 Potassium chlorid, 0.28 Sodium phosphate, 1.33 Calcium phosphate, 0.37 Sodium carbonate, l 0.93 1000.00 In this analysis the soHd ingredients constitute 22.5 parts per 1000, of which two-thirds are organic and one-third inorganic. The amount of sohds varies according to the animal from which the bile is obtained. Sodium Glycocholate and Taurocholate. — Of the various in- gredients of the bile none are more important than these two salts, usually known as the bile salts. The sodium glycocholate is found most abundantly in the bile of herbivora, the sodium taurocholate in the bile of the carnivora. These salts are compounds of sodium and glycocholic and taurocholic acids. When separated from the sodium, the acids will crystallize in the form of fine acicular needles. Under the influence of hydrating agents, such as dilute acids and alkalies, both acids will undergo cleavage into their respective com- ponents — e. g., glycocoll and cholalic acid, taurine and cholahc acid. Glycocoll and taurine are crystallizable nitrogenized compounds known chemically as amido-acetic and amido-isothionic acids re- spectively. The bile salts are produced in the liver by a true act of secretion, as they are not found in any of the tissues and fluids of the body. After being discharged into the intestine they undergo chemic changes, after which they can no longer be recognized. In all probability they are reabsorbed into the blood and play some ulterior part in the nutrition of the body. Cholesterin. — Cholesterin is a constant ingredient of bile, though it is not confined to this fluid, as its presence has been determined in the crystaUine lens, blood-corpuscles, nerve-tissue, and various patho- logic fluids. It is an organic non-nitrogenized substance resembling the fats in some particulars, but differing from them in not being capable of saponification with alkahes. It presents itself in the form of thin transparent rectangular crystals, insoluble in water but soluble 212 TEXT-BOOK OF PHYSIOLOGY. in ether and boiling alcohol (Fig. 85). It is held in solution in bile by the bile salts. If they are deficient in amount, the cholesterin may pass out of solution, collect around some foreign matter, and form a gall-stone. Cholesterin is a product of the metabolism largely of nerve-tissue, from which it is absorbed by the blood, carried to the liver, and excreted. In the intestine it is converted into stercorin and discharged from the body in the feces. Bilirubin, Biliverdin. — These two pig- ments impart to the bile its red and green colors respectively. Bilirubin is present in ^ the bile of human beings and the carnivora, ^'^'c^ivTx^A'^s.-CWoil'^biHverdin in the bile of the herbivora. As and Stirling.) the former pigment readily undergoes oxi- dation in the gall-bladder, giving rise to the latter pigment, almost any specimen of bile may present any shade of color between red and green. Bihrubin is regarded as a derivative of hematin, one of the cleavage products of hemoglobin, the coloring- matter of the blood. In. the liver the hematin combines with water, loses its iron, and is changed to bilirubin. By continuous oxidation there are formed bihverdin, bihcyanin, and choletelin. After their discharge into the intestine the bile pigments are finally reduced to hydrobilirubin, which becomes one of the constituents of the feces. An oxidation of the bilirubin can be produced by nitroso-nitric acid. If this agent is added to a thin layer of bile on a porcelain surface, a series of colors will rapidly succeed one another, commencing with green and passing to blue, orange, purple, and yellow. This is the basis of the well-known test for bile pigments suggested by Gmelin. Lecithin is one of the products of the metabolism of nerve-tissue. It is removed from the blood by the liver cells and thus becomes one of the constituents of the bile, in which it is held in solution by the bile salts. The Mode of Secretion and Discharge of Bile.^ — The manner in which the bile flows from the liver into the main hepatic ducts, the variations in the rate of its discharge into the intestine, as well as the total quantity secreted daily, have been approximately de- termined by fistulous openings either in the hepatic ducts or in the gall-bladder. Although the liver presents some physiologic peculi- arities, there is no reason to believe that the conditions of secretion therein are different from those in any other secretory organ, or that any other structure than the cell is engaged in this process. As shown by chemic analysis, the bile consists of compounds, some of which, like the bile salts, are formed in the fiver cells out of ma- terial furnished by the blood, by a true act of secretion, while others, such as cholesterin and lecithin, principles of waste, are merely ex- DIGESTION. 213 creted from the blood to be finally eliminated from the body. The bile is thus a compound of both secretory and excretory principles. The flow of bile from the liver is continuous but subject to con- siderable variation during the twenty-four hours. The introduction of food into the stomach at once causes a shght increase in the flow, but it is not until about two hours later that the amount secreted reaches its maximum; after this period it gradually decreases up to the eighth hour, but never entirely ceases. During the intervals of digestion though a small quantity passes into the intestine, the main portion is diverted into the gall-bladder, because of the closure of the common bile-duct by the sphincter muscle near its termination, where it is retained until required lor digestive purposes. When acidulated food passes over the surface of the duodenum there is excited, through reflex action, a contraction of the muscle walls of the gall-bladder and ducts, a relaxation of the sphincter, and a gush of bile into the intestine, the discharge continuing intermittently until digestion ceases and the intestine is emptied of its contents. The storage and the discharge of bile, brought about by the alternate contraction and relaxation of the muscle walls of the gall- bladder and of the sphincter is regulated by the nerve system. As the result of his experiments Doyon concludes, that during the inter- vals oi intestinal digestion the vagus nerve is carr} ing nerve impulses which on the one hand augment the contraction of the sphincter and inhibit the contraction of the walls of the gall-bladder, thus estabhshing the concitions lor the storage of bile; but when intesti- nal digestion is inaugurated the splanchnic nerve carries nerve im- pulses which inhibit the sphincter and augment the contraction of the walls of the gall-bladder, thus establishing the condition for the discharge ol the bile. The total quantity of bile secreted daily has been estimated to be from 500 to 800 grams. Physiologic Action of Bile.— Notwithstanding our knowledge of the complex composition of bile, the quantity discharged daily, and the time and place of its discharge, its exact relation to the digestive process has not been fully determined. No specific action can be attributed to it. It has but a slight, if any, diastatic action on starch. It is without influence on proteids. By virtue of the bile salts it con- tains, it hastens the action of pancreatic juice in sphtting neutral oils into fatty acids and glycerin, and in this way aids in their digestion. The bile salts also dissolve insoluble soaps, which may be formed during digestion. Bile favors the digestion of fat. If it be excluded from the intes- tine there is found in the feces from 22 to 58 per cent, of the ingested fats. At the same time the chyle, instead of presenting the usual white creamy appearance, is thin and shghtly yellow. The manner 214 TEXT-BOOK OF PHYSIOLOGY. in which the bile promotes fat digestion is yet a subject of investiga- tion. If all the fat is converted into fatty acid and glycerin, with the formation of soaps, as seems probable, the action of the bile becomes more apparent from the fact, already stated, that it dissolves and holds in solution the soaps so formed which would be necessary to their absorption by the epithelial cells. As an aid to digestion the bile has been regarded as important, for the reason that its entrance into the intestine is attended by a neutralization and precipitation of the proteids which have not been fully digested and are yet in the stage of acid-albumin. In this way gastric digestion is arrested and the foods are prepared for intestinal digestion. Though bile possesses no antiseptic properties outside the body, itself undergoing putrefactive changes very rapidly, it has been believed that in the intestine it in some way prevents or retards putre- factive changes in the food. There can be no doubt that if the bile be prevented from entering the intestine there is an increase in the formation of gases and other products which impart to the feces certain characteristics which are indicative of putrefaction. As to the manner in which bile retards this process nothing definite can be stated. Bile has been supposed to be a stimulant to the peristaltic move- ments of the intestine, inasmuch as these movements diminish when bile is diverted from the intestine. Though no definite nor specific action on any of the different classes of food principles can be attributed to the bile, there is abun- dant evidence to show that its presence in the alimentary canal during digestion is essential to the maintenance of the nutrition of the body. That the bile as a whole, or at least part of its constituents, favorably influences digestion and general nutrition is evident from the phenomena which follow its total exclusion from the intestine, as when the common bile-duct is ligated and a fistula of the gall-bladder is established. The following phenomena were observed in a young dog so prepared by Professor Flint. During the first five days succeeding the operation the abdomen was tumid and there was some rumbling in the bowels. Though the animal ate every day, the discharge of fecal matter became infrequent, the matter passed being grayish in color and highly offensive. After two weeks the alvine discharges took place three and four times daily. For four days the weight remained normal; afterward it began to diminish, and from this time the animal continued to lose strength and weight until its death, thirty-eight days after the operation. Ten days after the oper- ation the appetite, which had been very good, increased, but did not become ravenous until a few days before death. The animal usually ate from a pound to a pound and a half of beef-heart daily, always refusing fat. There was an absence at all times of jaundice, DIGESTION. 215 fetor of the breath, and falhng of the hair. Postmortem examination showed that the bile-duct was obhterated, and there was no evidence that any bile could have passed into the intestine. The results of this and similar cases go to show that that portion of the bile which is secretory in character is essential to digestion and the nutrition of the body — that, though large quantities of food are consumed, pro- gressive diminution of weight takes place until nearly 40 per cent, of the body is consumed. In some instances the breath becomes fetid and there is a falling of the hair, showing some profound disturbance of the general nutritive process. The Movements of the Intestine. — The movements of the intestine have been studied by means of the Roentgen rays by Cannon. The method adopted was to mix with the food, subnitrate of bismuth, which being opaque rendered the movements of the intestinal con- tents and thereby the movements of the intestinal walls visible, on the fluorescent screen. These investigations revealed the presence of two forms of activity, one of which is more or less stationar}^ and due to rhythmic contraction of circular muscle-fibers, the other progres- sive, passing from abo^•e downward and due to the contraction of circular and longitudinal muscle-fibers. The former activity, which is by far the more common, results in a division of the intestinal contents into small segments and for this reason was termed by Can- non, rhvtlimic segmentation; the latter activity is the well-known peristaltic wave. Alter bands of circular muscle-fibers, situated at variable dis- tances one from another, contract and divide a mass of food into seg- ments, they at once relax and are followed by contraction of other bands in the segments of the intestines overlying the segments of food. The result is again a division of the food into two new seg- ments. The lower hah of each segment then unites with the upper half of the segment below to commingle with it and expose new sur- faces of the lood mass to contact with the actively absorbing mu- cosa. The continual repetition of this process results in a thorough mixing of the food with the digestive juices. From the manner in which these contractions make their appearance it would seem that the mere presence of a segment in the lumen of the intestine is suffi- cient to excite the overhing fibers to activity. In certain regions of the intestine rhythmic segmentation may continue for half to three-quarters of an hour without moving the food forward to any marked extent. In the cat the segmentation may proceed at the rate of thirty divisions a minute. Ba}hss and Starling state, from observations made on the ex- posed intestine of a dog, that in addition to the usual peristaltic movement the intestinal coils exhibit a swaying or pendulum move- ment accompanied by shght waves of contraction which may arise 2i6 TEXT-BOOK OF PHYSIOLOGY. apparently at any point and pass down the intestine. These con- tractions may occur from ten to twelve times a minute and travel at a rate varying from two to five centimeters a second. In how far this movement represents the normal movement as it takes place under ph}siologic conditions and as observed by Cannon, remains for further investigators to decide. Alter the food has been prepared by the process above described, it is then slowly carried downward by what is known as the vermicular or peristaltic wave. This wave is characterized by a contraction of the circular fibers behind a bolus and a relaxation of the fibers in advance of it. The result is a movement forward of the bolus, and as it moves it is followed by a ring of constriction and preceded by a ring of relaxation or inhibition. The rate of movement of the peri- staltic wave is extremely slow. The Nerve Mechanism of the Intestine. — The causes of these two forms of intestinal activity, rhythmic segmentation or pendulum movement and peristalsis, have been the subject of much investiga- tion. Because of the presence of a network or plexus (Auerbach's and Meissner's) of nerve cells and nerve-fibers in the walls of the intestines and in close relation to the muscle cells, and because of the fact that the intestines will contract for some time alter removal from the body of the animal, it has been difficult to decide whether the contractions are of myogenic or neurogenic origin. As the rhythmic contractions continue, though the peristaltic are abolished by the introduction of nicotin into the blood, an agent which temporarily paral}ses peripheral nerve cells, it was concluded by Bayhss and Starling that the rhythmic contractions are of myo- genic origin and propagated from fiber to fiber and that the peri- staltic contractions are reflex in character, the coordination being carried out by the local nerve mechanisms and initiated by stimu- lation of the intestine. Whether this is the case or not, the general contractions of the intestine are augmented and inhibited by the central nerve system through the vagus and splanchnic nerves. Stimulation of the vagus is followed by an augmentation of the contraction, though not inlrequently there is a primary inhibition of short duration. Stimulation of the splanchnic is followed by a relaxation or inhibition of the contraction, though according to some observers there is at times an opposite effect. The Large Intestine. — The large intestine is that portion of the alimentary canal situated between the termination of the ileum and the anus. It varies in length from four and a half to five feet, in diameter from one and a half to two and a half inches. It is divided into the cecum, the colon (subdivided into an ascending, transverse, and descending portion, including the sigmoid flexure), and the rectum. DIGESTION. 217 The cecum is situated in the right iliac fossa. It is that dilated portion of the large intestine below the orifice of the small intestine. The posterior and inner wall presents a small opening which leads into a narrow round process about four inches in length — the vermi- form appendix. The opening of the small intestine into the cecum is narrow and elongated and bordered by two folds of mucous mem- brane strengthened by fibrous and muscle-tissue. These folds constitute the so-called ileo-cecal valve. When the cecum is dis- tended the margins of these folds are approximated and effectually prevent the return of material into the small intestine. The closure of this opening is now attributed to a sphincter mus- cle — the ileo- colic — the action of which is regulated by the nerve system. The colon ascends to the under surface of the hver, where it bends at a right angle, crosses the abdominal ca-\dty to the spleen, bends again, and descends to the left iliac fossa. At this point it turns upon itself to form the sigmoid flexure. The rectum is a dilated pouch, situated within the true pehis. It measures from 15 to 18 centi- meters in length. Within an inch of its termination at the anus it presents a constriction formed by a circular band of muscle-fibers known as the internal sphincter. The margin of the anus is also surrounded by bands of muscle-fibers known collectively as the ex- ternal sphincter. The walls of the large intestine consist of three coats: viz., serous, muscular, and mucous. The serous is a reflection of the general peritoneal membrane. The muscle is composed of both longitudinal and circular fibers. The longitudinal fibers are collected into three narrow bands which are situated at points equidistant from one another. At the rectum they spread out so as to completely surround it. As the longitudinal bands are shorter than the intestine itself, its surface becomes sacculated, each sac being partially separated from adjoining sacs by narrow constrictions. The circular fibers are arranged in the form of a thin layer over the entire intestine. Between the sac- cuH, however, they are more closely arranged. In the rectum they are well developed, and at a point an inch above the anus they form, as stated above, the internal sphincter. The mucous membrane of the large intestine possesses neither vilH nor valvulce conniventes. It contains a large number of tubules consisting of a basement membrane lined by columnar epithehum. They resemble the follicles of Lieberkiihn. The secretion of these glands is thick and \'iscid and contains a large quantity of mucin. Contents of the Large Intestine. — ^As a result of the actions of saliva, of gastric, intestinal, and pancreatic juice, and of the bile, the food is disintegrated and hquefied. The nutritive principles, proteid, starches, sugars, and fats, undergo chemic changes and are 2i8 TEXT-BOOK OF PHYSIOLOGY. transformed into peptones, dextrose, soap and glycerin, fatty acids, under which forms they are absorbed. After the more or less com- plete digestion and absorption of these nutritive substances the residue of the food, comprising the indigestible and undigested matter, passes out of the small intestine into the large intestine and forms a portion of its contents. This residue consists of the hard parts of the cereals, vegetable seeds, cellulose, etc., the quantity and variety of which depend on the nature of the food. These substances, passing into the large intestine along with the excrementitious matters of the bile, become incorporated with the mucous secretions and assist in the formation of the feces. Under the influence of a peristaltic movement similar to that witnessed in the small intestine, all this excrementitious matter, deprived by absorption of the excess of its contained water and nutritive material is gradually carried downward to the sigmoid flexure, where it accu- mulates prior to its extrusion from the body. The efi'ects of the peristaltic waves are to some extent interfered with by anti-peristaltic waves which beginning in the transverse colon nm toward and to the cecum. An antiperistaltic wave occurs in the cat about every fifteen minutes and lasts for about five min- utes. The intestinal contents are thereby driven back toward the cecum. The effect is a still further admixture with the secretions and exposure to the absorbing mucosa. There is some evidence also that the antiperistaltic wave may force some of the liquefied con- tents through the ileo-colic opening into the small intestine because of the relaxation of the sphincter muscle. Intestinal Fermentation. — Owing to the favorable conditions in the intestine for fermentative and putrefactive processes — e. g., heat, moisture, oxygen, and the presence of various microorganisms — the food, when consumed in excessive quantity or when acted on by defective secretions, undergoes a series of decomposition changes which are attended by the production of gases and various chemic compounds. Dextrose and maltose are partially reduced to lactic acid; this to butyric acid, carbon dioxid, and hydrogen. Fats are reduced to glycerol and fatty acids; the glycerol, according to the organisms present, yields succinic acid, carbon dioxid, and hydrogen. The proteids under the prolonged action of the pancreatic juice are decomposed, with the production of leucin and tyrosin. These crystalline compounds are in turn reduced to simpler forms. The former yields valerianic acid, ammonia, and carbon dioxid; the latter gives rise to indol, which is the antecedent of indican, found in the urine. Skatol, another derivative of the proteid molecule, due to bacterial action, gives the characteristic odor to the feces. Feces. — The feces consist of water, mucin, the indigestible resi- due of the food, decomposition products, and inorganic salts. The DIGESTION. 219 consistency of the fecal matter varies from fluid to semi-fluid, depend- ing largely on the length of time it remains in the intestine and the extent to which absorption of its watery portion has taken place. The odor is due to the presence of sulphuretted hydrogen and skatol. The color is due partly to the altered coloring-matter of the bile, hydro- bilinibin or stercohilin, and partly to the character of the food. The total quantity discharged daily varies from four to six ounces. Defecation. — Defecation is the final act of the digestive process and consists in the expulsion of the indigestible residue of the food from the intestine. This act usually takes place in the human being but once in twenty-four hours, as the diet contains but a minimum quantity of indigestible matter. Previous to their expulsion the feces which have accumulated in the sigmoid flexure must pass downward into the rectum. In so doing they develop the sensation which leads to the act of defecation. The descent of the feces is accompUshed by the peristaltic contraction of the intestinal wall. Coincident with the passage of the feces into the rectum there is a relaxation of the sphinc- ter muscles and a contraction of the longitudinal and circular mus- cular fibers, in consequence of which the feces are expelled. These complex muscular actions are also aided by the voluntary contrac- tions of the diaphragm and abdominal muscles. Nerve Mechanism of Defecation. — The act of defecation is primarily reflex, though somewhat influenced by voluntary efforts. Under normal conditions the sphincter muscles governing the anal orifice are firmly contracted, thus preventing the escape of gases or semi-sohd matter. This tonic contraction is maintained by a nerve- center located in the lumbar region of the spinal cord. The circu- lar and longitudinal muscle-fibers of the rectum are at the same time in a relaxed condition. When the desire to evacuate the bowels is experienced, the impressions made by the feces on the afferent nerves of the rectal mucous membrane develop nerve impulses, which transmitted to the rectal center and to the brain, influence in one direction or another, their activities. If the act of defecation is to take place there is an inhibition of the contraction of the sphincter ani muscles and an augmentation of the contraction of the rectal muscles. In their expulsive efforts, these latter muscles are assisted by the contraction of the diaphragm, abdominal and other muscles. After the expulsion of the feces there is a return to the former con- dition, viz., a relaxation of the rectal muscles and a contraction of the sphincters. If the act is to be suppressed, the controlling influence of the rectal or sphincter center is strengthened and the reflex mechanism for a while held in abeyance. The exact course of the afferent and efferent nerves concerned in this reflex is yet a subject of investigation. 220 TEXT-BOOK OF PHYSIOLOGY. The nerve supply for the circular and longitudinal muscles of the lower part of the colon and rectum varies somewhat in different animals, though it is usually derived from the second, third, and fourth lumbar and the second and third sacral or pelvic nerves. The lumbar nerves pass into and through the sympathetic chain and thence to the inferior mesenteric ganglion, around the cells of which most of the nerves arborize. From this ganghon nerve- fibers pass to both the circular and longitudinal fibers. The sacral or pelvic nerves pass to the hypogastric plexus and are ultimately connected with ganghon cells, which in turn send fibers to both the longitudinal and circular fibers. The explanation of the action of this complex mechanism is a subject of discussion because of the want of agreement in the results that follow stimula- tion of these nerves. CHAPTER X. ABSORPTION. Absorption is the process by which nutritive material is trans- ferred from the tissues, from the serous cavities, and from the mucous surfaces of the body, into the blood. The most important of these surfaces, especially in its relation to the formation of blood, is the mucous surface of the alimentary canal, for it is from this organ that the new materials are derived which maintain the quantity and quahty of the blood. The absorption of material from the inter- stices of the tissues and from the serous cavities may be regarded as an act of resorption, or a return to the blood of liquid nutritive material which has escaped through the walls of the capillary blood-vessels for purposes of nutrition, and which, if not returned, would lead to an accumulation and the development of edematous conditions. The anatomic mechanisms involved in the absorptive process are, primarily, the tissue or lymph-spaces, the lymph- and blood- capillaries; secondarily, the lymph-vessels and the veins. • Tissue or Lymph-spaces; Lymph-capillaries. — Everywhere throughout the body, in the connective-tissue system and in the inter- stices of the several structures of which an organ is composed, are found spaces or clefts of irregular shape and size, determined largely by the structure of the organ in which they are found, which have been termed tissue or lymph-spaces, from the fact that they contain a clear fluid, the lymph. These spaces are devoid for the most part of any endothehal lining, but as they communicate more or less freely one with another, there is a circulation of lymph through them and around the islets of tissue (Fig. 86). In addition to the connective- tissue lymph-spaces, different observers have described special spaces or clefts in organs such as the kidney, liver, spleen, testicle, and in all secreting glands between their basement membrane and the sur- rounding blood-vessels, all of which contain a greater or less quan- tity of lymph. Within the brain, spinal cord, bone, and other tissues it has been shown that the smallest blood-vessels and capillaries are bounded and limited by a cylindrical sheath containing lymph, which is known as a perivascular lymph-space. A similar sheath surrounds the smallest nerve-bundles and fibers, enclosing a perineural lymph- space. The large serous cavities of the body, pleural, peritoneal, pericardial, etc., are also to be regarded as lymph-spaces. The sur- faces of these cavities, however, are covered with a layer of endo- TEXT-BOOK OF PHYSIOLOGY. thclial cells with sinuous margins. At intervals between these cells are to be found small free openings which have received the name of stomata. The lymph-capillaries in which the lymph-vessels proper take their origin are arranged in the form of plexuses of quite irreg- ular shape. In most situations they are intimately interwoven with the blood-vessels, from which they can be readily distinguished by their larger caliber and irregular expansions. The wall of the lymph-capillary is formed by a single layer of endothelial cells with characteristic sinuous outlines. These capillaries anastomose very freely one with an- other and communicate, on the one hand, with the lymph-spaces and on the other with the lymph - vessels proper. As the shape, size, etc., of both lymph -spaces and capillaries are de- termined largely by the nature of the tissue in which they are found, it is not always possible to separate one from the other. Their function, however, may be re- garded as similar: viz., the reception and collec- tion of the lymph which has transuded through the walls of the blood- vessels and its transmis- sion onward into the regular lymph- vessels. The blood-capilla- ries not only permit of a transudation of the Hquid nutritive material from the blood through their delicate walls, but are also engaged, if not in the reabsorption of a portion of this transudate, at least in the absorption of waste products resulting from tissue metabolism. Lymph-vessels. — The lymph-vessels constitute a system of minute, delicate, transparent vessels found in nearly all the organs and tissues of the body, and take their origin from the lymph- capillaries and spaces above described. From their origin they gradually converge toward the trunk of the body, and finally empty into the thoracic duct. In their course they anastomose very Fig. 86. — Origin of Lymphatics from the Cen- tral Tendon of the Diaphragm Stained with Nitrate of Silver, s. The lymph- spaces and lymph-canals, communicating at x with the lymphatics, a. Origin of the lym- phatics by the confluence of several juice canals. B. Capillary blood-vessel. — {Landois and Stirling.) ABSORPTION. 223 freely with adjoining vessels. The diameter of a lymph-vessel varies from i to 2 mm. After the lymphatics have emerged from the lymph-capillaries they acquire three distinct coats, each of which possesses definite histologic features. The internal coat is composed of a delicate lamina of longitudinally disposed elastic fibers covered with a layer of flattened nucleated endothelial cells with wavy outlines. The middle coat consists of white fibrous tissue arranged longi- FiG. 87. — Lymph-vessels and Lymph-glands of the Head and Neck. — (From Gould's Dictionary.) tudinally and of non-striated muscle and elastic fibers arranged transversely. The external coat consists of practically the same structures, though the muscle-fibers are longitudinally disposed. The lymphatics are provided with valves which are so numerous and located at such short intervals as to give the vessels a beaded appearance. These valves are arranged in pairs and consist of two semilunar folds with their concavities directed toward the larger vessels. They are formed by a reduplication of the Hning membrane, 224 TEXT-BOOK OF PHYSIOLOGY. which is strengthened by fibrous tissue derived from the middle coat. Lymph-glands. — In their course toward the thoracic duct the lymph-vessels pass through a num- ber of small lenticular bodies termed lymph-glands. These are exceedingly abundant in some situ- ations, as the cervical, axillary, and inguinal regions, and the abdominal cavity. As the lymph-vessels ap- proach a gland they divide into a number of branches before entering it, known as the afferent vessels. From the opposite side of the gland the lymphatics again emerge as efferent vessels to unite to form larger trunks. A section of a gland shows that it consists of an outer dense cortical and an inner soft pulpy medullary portion. Each gland is covered externally by a dense membrane of fibrous tissue containing in its meshes non-stri- ated muscle-fibers. From the inner surface of this membrane there pass inward septa of connective tissue which, as they converge toward the center of the gland, divide the outer zone of the gland into small conical compartments or alveoli. When the septa reach the medullary portion, they subdivide and form bands or cords which interlace in every direc- tion and constitute a loose mesh- work the spaces of which communi- cate with one another and with the alveoli (Fig. 90). Within the meshes of this framework the proper gland substance is contained. In the cor- tical compartments it is moulded into pear-shaped masses; in the medullary mesh work it assumes the form of rounded cords which are connected with one another. In both regions, however, it is separated from the septa by a space termed a lymph sinus, through which the lymph flows as it passes —Lymph-vessels Arm. — {Deaver. ) ABSORPTION. 225 through the gland. The lymph sinus is crossed by a network of retiform connective tissue which offers considerable resistance to the passage of the lymph. The gland substance consists also of a framework of retiform connective tissue in the meshes of which large numbers of lymph-corpuscles are contained. The gland substance is separated from the lymph sinus by a dense layer of a reticulum, which, however, does not prevent lymph and even corpuscles from passing through it into the lymph sinus. The lymph-glands are abundantly supphed with blood-vessels. The arteries enter the gland at the hilum, penetrate into the medullary substance, and terminate in a line capillary plexus which is supported by the connective tissue. The veins arising from this plexus leave the gland also at the hilum. Fig. 89. — Diagrammatic Section of a Lymph-gland, a. I., Afferent, e. I., Efferent lymphatics. C. Cortical substance. M. Reticular cords of medulla. /. 5. Lymph sinus, c. Capsule, with trabeculas, tr.- — (Landois and Stirling.) The lymph-vessels which enter a gland first ramify in the in- vesting membrane and then open directly into the lymph sinus. The vessels which leave the gland are also in communication with the sinus. After the lymphatics enter the gland they lose their external and middle coats, retaining only the internal or endothehal coat, which lines the inner surface of the lymph sinus. The current of lymph, therefore, is from the afferent vessels through the lymph sinus into the efferent vessels. In addition to this primary current, there is a secondary current flowing from the capillary blood-vessels outward and into the sinus, which carries with it large numbers of lymph-corpuscles. It is quite probable that the movement of the 15 226 TEXT-BOOK OF PHYSIOLOGY. lymph through this compHcated system of passages is aided by the contraction of the muscle-fibers in the capsule of the gland. The lymph-corpuscles or lymphocytes originate for the most part in the gland substance of the cortical alveoli. In this situation there Fig. 90. — Diagram showing the Course of the Main Trunks of the Absorbent System. The lymphatics of lower extremities (D) meet the lacteals of intestines (LAC) at the receptaculum chyli (RC), where the thoracic duct begins. The superficial vessels are shown in the diagram on the right arm and leg (S), and the deeper ones on the arm to the left (D). The glands are here and there shown in groups. The small right duct opens into the veins on the right side. The thoracic duct opens into the union of the great veins of the left side of the neck (T). — {Yeo's " Text-book of Physiology.") are groups of cells, so-called germ centers, which divide very rapidly by mitosis and give rise constantly to groups of young cells which soon find their way into the lymph stream. ABSORPTION. 227 The Thoracic Duct. — The thoracic duct is the general trunk of the lymph system, into which the vessels of the lower extremities, of the abdominal organs, of the trunk, of the left arm, and of the left side of the head empty their contents. It is about fifty centimeters in length and four millimeters in diameter. It extends upward from the third lumbar vertebra along the vertebral column to the seventh cervical vertebra, where it empties into the venous system at the junction of the internal jugular and subclavian veins on the left side. The thoracic duct wall has the same general structure as the wall of the lymph-vessel: viz., an internal or endothelial; a middle elastic and muscular; an external or fibrous. It is also provided with numerous valves. The lymph-vessels of the right side of the head, of the right arm, and a portion of the right side of the trunk terminate in the right thoracic duct, which is about 25 to 30 mm. in length and which emp- ties into the venous system at the junction of the internal jugular and subclavian veins on the right side. The general arrangement of the lymphatic system is diagrammatically shown in Fig. 90. LYMPH. Lymph is the clear fluid found within the tissue spaces and with- in the lymph-vessels. Inasmuch as there are reasons for the view that lymph varies in composition, as well as in function, in these different regions it will be found conducive to clearness to designate the lymph found in the tissue spaces as intercellular lymph, and that found in the lymph-vessels as intravascular lymph. The Physical Properties of Lymph. — Whether obtained from tissue spaces or from lymph-vessels, the lymph presents practically the same physical properties. The lymph obtained from the tho- racic duct during the intervals of digestion or from one of the large trunks of the leg is a clear, colorless or slightly opalescent fluid hav- ing an alkaline reaction and a specific gravity of 1.020 to 1.040. Examined microscopically it is seen to hold in suspension a large number of corpuscles similar to those seen in the lymph glands and to the white corpuscles of the blood. Their number has been esti- mated at about 8200 per cubic millimeter, though this count will vary within wide Hmits according as the lymph examined has passed through a large or smaller number of glands. The lymph corpuscle consists of a small quantity of protoplasm in which is embedded a distinct nucleus. Some of these lymphocytes contain distinct gran- ules, more or less refractive, which impart to the corpuscle a dis- tinctly granular appearance. When withdrawn from the vessels lymph undergoes a spontaneous coagulation, though the coagulum is never as firm as that observed in the coagulation of the blood. 228 TEXT-BOOK OF PHYSIOLOGY. The cause of the coagulation is the appearance of librin. After a variable length of time the coagulum separates into a liquid and a solid portion, the serum and the clot. The Chemic Composition of Lymph. — Although the lymph obtained from the tissue spaces, from the lymph-vessels, as well as from the so-called serous cavities has the same general chemic char- acteristics, there is reason for the view that it varies in its ultimate composition according as it is derived from one region of the body or from another. The needs of any individual tissue as well as the character of its metabolic products will in all probability not only change its normal composition, but also the relative amounts of its normal constituents. Chemic analysis has shown that the lymph from the thoracic duct contains from 3.4 to 4.1 per cent, of proteids (serum-albumin, fibrin- ogen), 0.046 to 0.13 per cent, of substances soluble in ether (probably fat), 0.1 per cent, of sugar, and from 0.8 to 0.9 per cent, of inorganic salts, of which sodium chlorid (0.55 per cent.) and sodium carbonate (0.24 per cent.) are the most abundant (Munk). There are usually in most specimens small quantities of potassium, calcium, and mag- nesium salts. Fibrinogen is seldom present beyond o.i per cent., which will account for the feeble and slow coagulation. Lymph contains both free oxygen and carbon dioxid. Of the former, how^- ever, there is but a small percentage; of the latter, about 45 vols, per cent., partially in the free state and partially combined with sodium. Urea is also present in very small amounts. This analysis indicates that lymph resembles blood-plasma in the character of its constitu- ents, though their relative quantities vary considerably. With the exception that it contains no red corpuscles, lymph may be regarded as a diluted blood. The Production of Lymph. — Though blood is the common res- ervoir of nutritive material, the latter is not available for nutritive purposes as long as it is confined within the blood-vessels. The capillary wall, thin as it is, and composed of but a single layer of endothehal cells, would be sufficient to prevent its utilization by the tissues, if it were not permeable to the liquid portion of the blood. As this is the case, however, it is found that as the blood flows through the capillary vessels a portion of the blood-plasma passes through the capillary wall and is received into the tissue spaces, where it comes into intimate contact with the tissue-cells. The forces concerned in the passage of the constituents of the blood-plasma across the capillary wall have been the subject of much investigation. According to some investigators, diffusion, osmosis and filtration are sufficient to account for all the phenomena. It is assumed tha the capillar}^ wall, being an animal membrane, is freely permeable to water and crystalloid bodies generally ; less so, however, ABSORPTION. 229 to colloid bodies, such as the proteids of the blood-plasma; moreover, it is further assumed that the physiologic conditions of the capillary walls are such as not only to permit of the passage of the constituents of the blood into the tissue spaces, but also the passage of the con- stituents of the inter-cellular l}Tnph into the blood, according to laws similar at least to those determining the passage of substances through animal membranes as determined experimentally. The force giving rise to filtration is the difference of pressure between that exerted by the blood within the capillar}^ vessels and that ex- erted by the fluid in the tisssue spaces ; hence any increase or decrease of this difference of pressure is attended by an increase or decrease in the production of lymph. Thus compression of the veins of a part which interferes with the outflow of blood from the capillaries, or a dilatation, of the arterioles which increases the inflow of blood to them will increase the capillary pressure and therefore the production of l\Tnph. The reverse conditions will, of course, diminish the intra- capillar}' pressure and lymph production. Hemorrhages which lower the general blood-pressure may so lower the capillar)^ pressure as not only to stop the flow of hrniph to the tissues, but may give rise to a diffusion current from the tissues into the blood. The quantitative composition of the lymph compared with that of the blood indicates that it is produced by difl'usion, osmosis, and filtration. In the lymph the concentration of the inorganic salts is practically the same as in the blood; the concentration of the pro- teids, however, is somewhat less. These facts are in accordance with what is known regarding the diffusibihty of both crystalloids and colloids through animal membranes. According to other investigators, the production of lymph is not so much due to intracapillary pressure as it is to the speciahzed activities of the endothelial cells, activities which indicate that lymph is a secretion the composition of which varies in different situations by virtue of a difference in the molecular structure of the endothehal cells. As is the case with many of the secreting cells of the body, the injection of various substances into the blood apparently increases the activity of the endothehal cells, as shown by an increased lymph production without any appreciable increase of intracapillary pressure. Thus it has been shown that after the injection into the blood of sugar, sodium chlorid, sodium sulphate, urea, etc., there is an increase in the flow of lymph from the thoracic duct. The lymph, however, under these circumstances is richer in water than is normally the case. As the blood at the same time increases its percentage of water, it is assumed that the water is extracted from the tissues, by reason of an increased percentage of salts in the tissue spaces due to increased activity of the endothehal cells. A higher percentage of 230 TEXT-BOOK OF PHYSIOLOGY. salts in the lymph than in the blood is difficult to account for on the diffusion-filtration theory. The injection of peptones, albumin, the extract of the muscles of the leech, crab, mussel, etc., is also followed by an increase in the amount of lymph discharged from the thoracic duct; but in this instance the lymph possesses a higher degree of con- centration, being richer not only in inorganic but also organic constit- uents. The cause of this increase in both the quantity and quality of the lymph is believed to be an increased activity in the secreting power of the endothelial cells. The more recent experiments of Starhng indicate that in addition to the difference of pressure be- tween the blood in the capillaries and the l3miph in the tissue spaces, a new factor must be considered and that is, the permeability of the capillary wall. This he finds to vBiVy considerably in different parts of the vascular apparatus, being greatest in the capillaries of the liver, less in the capillaries of the intestines and least in the capillaries of the extremities. It also varies doubtless in all other situations. The increase in the production of lymph by the injection of peptones, extract of muscles of the leech, the crab, etc.. Starling explains by the assumption that these substances alter the properties of the capillary wall and thus increase its permeabihty. The difference of pressure, therefore, between blood and lymph taken in connection with the degree of permeability of the capillary wall will account for the pro- duction of lymph in all regions of the body. It is possible that all these facts may be otherwise interpreted; the subject is yet a matter of investigation. The Functions of Intercellular Lymph. — The origin and composition of lymph, its situation and relation to the tissue cells indicate that its function is to provide the tissue cells with those nutritive materials necessary to their growth, repair, and functional activities, and to receive from the tissue cells their waste products prior to their removal by the blood- and lymph-vessels. The necessity for the production of lymph becomes apparent when the chemic changes which the tissues undergo at all times are considered. Thus whether in a state of relative rest or in a state of activity, disintegrative changes are constantly taking place and al- ways in direct proportion to the degree and continuance of the activity. If the tissues are to continue in the performance of their customary activities, it is essential that repair and restoration be at once estab- lished. This is made possible by the presence of lymph, and by the power which living material possesses of absorbing from the lymph the necessary nutritive materials, of assimilating them and transform- ing them into material like unto itself and endowing them with their own physiologic properties. Coincidently with the loss of nutritive material, the lymph receives the waste products of the tissues and hence changes in composition. ABSORPTION. 231 Should this change in composition continue for any length of time, the lymph would lose its restorative character and become destruc- tive to tissue vitality. Therefore it is essential that the nutritive material be renewed as rapidly as consumed and the waste products be carried away as rapidly as produced. Both these conditions are fulfilled by the blood- and lymph- vessels. The Absorption of Intercellular Lymph. — From the fact that lymph is being discharged from the thoracic duct into the blood, more or less continually, it is evident that hnnph is being absorbed from the intercellular spaces; from which fact it may be inferred that the production of lymph is a continuous process and that it is passing through the capillaries in amounts greater than is necessary for the immediate needs of the tissues. Should this excess accumu- late there would soon arise the condition of edema and an interference with the functional activities of the tissues. Therefore so soon as the accumulation attains a certain volume it is absorbed in large measure by the lymph capillaries and transmitted to the lymph- vessels and thoracic duct. Because of the general behef that the lymph capillaries were in open communication with the tissue spaces it was assumed that the absorption of lymph and its flow through the lymph-vessels was the result of a difference of pressure between the lymph in the tissue spaces and the blood in the innominate veins. But if the lymph capillaries are closed vessels, as recent investiga- tions indicate, then additional factors, in explanation of lymph ab- sorption, must be sought for. It is quite possible under even normal conditions of pressure in the tissue spaces that some of the more dilfusible constituents of the lymph should be absorbed by the capillary blood-vessels. As to whether the relatively feebly diffusible colloids should be so resorbed is as yet a matter of investigation. ABSORPTION OF FOODS. The most important of the absorbing surfaces, especially in its relation to the absorption of new material, is the mucous membrane of the ahmentary canal, and more particularly that portion lining the small intestine, provided as it is with specialized absorbing structures — the villi. Though certain substances can be absorbed from the mouth, it is not probable that any food is so absorbed. From the changes which the food principles undergo in the stomach it might naturally be inferred that their absorption would promptly follow. Experimental researches have demonstrated, however, that this takes place, if at all, but to a shght extent. If, however, solutions of inor- ganic salts, sugars, and peptones possessing a concentration of at least 5 per cent. — a degree of concentration seldom realized under 232 TEXT-BOOK OF PHYSIOLOGY. normal conditions — are introduced into the stomach, their absorption will be effected, the rate of absorption following in a general way the increase, within limits, in concentration. Water is practically not absorbed from the stomach. The absorption of the products of digestion — i. e., dextrose, levulose, peptones, soaps, glycerin, fatty acids, salts, along with water, in which for the most part they are Fig. 91. — Longitudinal Sec- tion OF A Villus from In- testine OF the Dog, Highly Magnified. a. Columnar epithelium containing goblet- cells (b) and migratory leuko- cytes (h). c. Basement mem- brane, d. Plate-like connec- tive-tissue elements of core. e, e. Blood-vessels. /. Ab- sorbent radical or lacteal. — (Piersol.) Fig. 92. — Section of Injected Small Intestine of Cat. a, b. Mucosa. g. Villi, i. Their absorbent vessels. h. Simple follicles, c. Muscularis mu- cosae. 7. Submucosa. g, e'. Circular and longitudinal layers of muscle. /. Fibrous coat. All the dark lines represent blood-vessels filled with the injection mass. — (Piersol.) held in solution — is therefore hmited very largely to the small intes- tine, and is accomphshed by the villous processes projecting from the surface of the mucous membrane. Structure of the Villi. — The vilh are small fiHform or conical processes, from 0.5 to i mm. in length, and from 0.2 to 0.5 mm. in ABSORPTION. 233 within the basement breadth, covering the surface of the mucous membrane from the pyloric orifice to the upper surface of the ileo-cecal valve. Each villus consists of a basement membrane (see Fig. 91) supporting tall columnar epithelial cells. Each cell is composed of granular bio- plasm containing a distinct nucleus. At its free extremity a narrow border of the cell presents a striated appearance, as if it were com- posed of small rods embedded in some cement substance. Goblet or mucin-holding cells are also to be found among the columnar cells. The body of the villus, that portion membrane, consists of a reticu- lated connective tissue support- ing arteries, capillaries, veins, and lymphoid corpuscles. In the center of the villus there is usually a single though at times a double club-shaped lymph- capillary, the walls of which are composed of epithelioid cells with sinuous margins. This capillary probably begins by a blind extremity and opens at the base of the villus into the subjacent lymph -vessels. The communicating orifice is guard- ed by a valve. It is also sur- rounded by a layer of non-stri- ated muscle-fibers, arranged longitudinally, derived from the muscularis mucosae and at- tached to the apex of the body of the villus. The arteries which penetrate the villi are derived from those of the submucous coat of the intestine, which are the ultimate branches of the intestinal artery, and serve the purpose of dehv- ering nutritive material to the capillary plexus (Fig. 92). While passing through the latter a portion of the blood-plasma transudes through the capillary walls into the spaces of the reticulated tissue, constituting lymph. At the same time products of tissue metab- olism pass through the capillary walls into the blood. The blood then passes into the venules, which, leaving the villus at its base, unite with the veins of the submucous coat to form the intestinal veins. These finally unite with the gastric and splenic veins to form Fig, 93. — Diagram of the Portal Vein {pv) arising in the Alimen- tary Tract and Spleen (5), and Carrying the Blood from These Organs to the Liver. — ( Yeo's " Text-book of Physiology.") . 234 TEXT-BOOK OF PHYSIOLOGY. the portal vein, which enters the hver at the transverse fissure (Fig. 93). The excess of lymph within the villus passes into the club- shaped lymph-capillary, to be finally carried by the lymphatics of the mesentery into the thoracic duct. During the intervals of digestion and in the absence of food from the intestine there is, of course, no absorption of food nor the removal from the villus of anything but the excess of lymph and metabohc products. Function of the Villi. — The viUi, and especially the epithelial cells covering them, are the essential agents in the absorption of the products of digestion. It is by the activity of these cells that the new materials are taken out of the ahmentary canal and transferred into the lymph-spaces, in the body of the vilh, from which they are subsequently removed by the blood-vessels and lymphatics. As to the mechanism by which the epithelial cells accomphsh this result, nothing definite can be asserted. Inasmuch as the absorption of food does not take place in accordance with the laws of osmosis as at present understood, it has been suggested that the cells possess a "selective action" dependent on their organization and living con- dition, an action which is to a great extent conditioned and limited by the degree of diffusibihty of the substances to be absorbed. Absorption 0} Water and Inorganic Salts. — Water and inorganic salts after their absorption from the intestine and transference into the lymph-spaces of the villi pass through the walls of the capillary blood-vessels and are carried by the way of the portal vein into the liver. Unless water be present in excessive amounts, there is no appreciable absorption of water by the lymphatics. Absorption 0} Sngar. — As previously stated, all the carbohydrates, with the exception possibly of lactose, are transformed by the diges- tive fluids into either dextrose or levulose, under which forms they are absorbed by the epithelial cells. It is possible, however, that soluble dextrin may also be absorbed. Whatever the form under which the carbohydrates are absorbed, they never leave the epithe- lial cells except as dextrose and levulose. Direct experimentation has shown that the sugars are taken up by the capillary blood-vessels and carried direct to the liver. Analysis of the blood of the portal vein after the ingestion of large quantities of sugar may reveal an increase of 0.2 5 per cent.; while after the injection of sugar into the intestine the percentage may rise as high as 0.4. As chemic analysis of lymph obtained from the thoracic duct shows no increase in the percentage of sugar beyond that normally present (o.i per cent.), it is assumed that sugar is not removed from the vilh by the lymphatics. Absorption of Proteids. — Since most of the proteidsare transformed through hydration and cleavage by the action of the gastric and pan- creatic enzymes into peptones, there is reason to believe that this change is necessary to their complete and rapid absorption. Never- ABSORPTION. 235 theless it has been shown by the resuhs of experimentation that unchanged native proteids, such as egg-albumin, and partially digested proteids, such as acid and alkah albumin, albumoses, may hkewise be absorbed from the smah intestine, though in far less amounts. It has also been demonstrated that native proteids can be absorbed from the large intestine. Inasmuch as chemic analysis has failed to detect more than a trace of either peptone or native pro- teid in the portal blood or in the lymph of the thoracic duct, it must be assumed that the epithehum after absorbing must also synthetize them into some form of coagulable proteid (serum-albumin) which is readily assimilable by the blood. That such a reconversion is neces- sary would appear from the fact that the introduction of peptones even in small amounts into the blood is followed by their elimination unchanged in the urine. When injected into the blood in large amounts, they act as toxic agents, giving rise to a fall of blood-pres- sure, a diminished coagulability of the blood, coma, and death. After passing through the epithelium into the spaces of the villi they are removed by the blood-vessels and carried direct to the liver. Even though there is no appreciable increase in the amount of pro- teid in the portal blood during digestion, there is every reason to think that this is the route by which it reaches the general circulation. Ligation of the thoracic duct does not interfere with proteid absorp- tion nor with the normal elimination of urea nor with the weight of the animal. Absorption 0} Fat. — As previously stated, there are two views as to the changes which fats undergo during digestion. According as the one or the other is accepted will depend the view as to the nature of the absorptive process. If it be assumed that the final stage in the digestion of fat is a purely physical one, the production of an emulsion in which the fats present themselves as fine granules, it is diflficult to give any satisfactory explanation of the mechanism by which the epithehal cells take them up. Various theories have been advanced to explain the process, but none are free from serious ob- jections. This view of fat absorption has largely been based on the observation that during digestion fatty granules can be seen in all portions of the cell apparently passing toward the interior of the villus. If, on the contrary, it be admitted that the final stage in the digestion of fats is the formation of soaps and glycerin, both of which are soluble, their absorption can more readily be accounted for. According to this view, the soaps and glycerin are again synthetized by a process the reverse of that which is produced by the pancreatic enzyme, with the appearance of minute granules of fat. That this is the more probable view as to the mechanism of fat absorption is evident from the fact that when animals are fed with alkaline soaps 236 TEXT-BOOK OF PHYSIOLOGY. and glycerin, or with fatty acids alone, globules of fat are found in the epithehal cells and in the interior of the villus. With the passage of the fat-granules into the interior of the villus they at once enter the lymph-radicle and become constituents of the lymph-stream, to which they impart a white, milky appearance. If the abdomen of an animal in full digestion be opened, the lymph- vessels of the mesentery present themselves as distinct white threads. An examination of the fluid they contain, known as chyle, shows the presence of fat-granules of microscopic size. With the passage of the chyle into the thoracic duct it also presents the same milky ap- pearance. For this reason the lymphatics of the mesentery were erroneously termed lacte.als. The chyle as obtained from these lymph- vessels possesses the same qualitative though not quantitative composition as lymph, the difference being mainly in the large excess of fat in the former. Indeed, chyle may be regarded as lymph plus fat. Routes for the Absorbed Food. — Physiologic experiments have demonstrated that the agents concerned in the removal of the products of digestion after their absorption from the interior of the villus are: 1, The blood-vessels of the gastro-intestinal tract, which unite to form the portal vein. 2. The lymph- vessels of the small intestine, which converge to empty into the thoracic duct. The products of digestion find their way into the general circu- lation by these two routes, as follows : The water, inorganic salts, proteids, and sugar after entering the blood-vessels of the villus are carried by the blood directly into the hver by the portal vein; after circulating through the capillaries of the Hver and being influenced by the hver cells, they are discharged by the hepatic veins into the ascending vena cava. The fats after entering the lymph-radicle of the villus are carried by the lymph-stream into the thoracic duct, by which they are poured into the blood at the junction of the left subclavian and in- ternal jugular veins. Forces Aiding the Movement of Lymph and Chyle. — The force which primarily determines the movement of the lymph has its origin in the beginnings of the lymph- vessels, the lymph- spaces, and depends on a difference in pressure here and at the termination of the thoracic duct. The rise of pressure in the lymph-spaces is due to the continual production of lymph, either by filtration or secretory activity of the capillary walls. As soon as the pressure rises above that in the thoracic duct a forward movement of lymph takes place. Other things being equal, the rate of movement will be proportional to the difference of pressure. The first movement of the chyle, its passage from the lymph-capillary in the villus into ABSORPTION. 237 the subjacent lymph- vessel, has been attributed to a shortening of the villus and a compression of the capillary by the contraction of the non-striated muscle-fibers by which it is surrounded. With the entrance of the chyle into the subjacent lymph-vessel there is a distention of the vessel and a rise in pressure. When the muscle- fibers relax, regurgitation is prevented by the closure of the valves at the base of the villus. The elastic tissue of the lymph-vessel now re- coils and forces the chyle toward the thoracic duct. After the empty- ing of the lymph-capillary the conditions as far as pressure is con- cerned are favorable to the absorption of new material. The rhythmic contractions of the intestinal wall undoubtedly aid in the movement of lymph and chyle. It is quite possible that the walls of the general lymphatic system aid the forward movement of lymph by more or less rhythmic con- tractions of their contained muscle-fibers. Inasmuch as the lymph- vessels lie in situations in which they are subject to compression by muscles during contraction, it is prob- able that the fluid in the vessels will be forced onward toward the thoracic duct at each compression, a backward movement being prevented by the closure of the valves which are everywhere present in the vessels. Experimental observations have demonstrated the truth of this supposition. Alternate contraction and relaxation of the muscles of the leg will, in an animal at least, increase considerably the flow as well as the production of lymph from the thoracic duct. Massage has a similar influence. The respiratory movements also aid the flow of both lymph and chyle from the thoracic duct and larger lymph-vessels into the venous blood. During inspiration the negative pressure of the thorax is increased, the increase being pro- portional to the extent of the inspiration. The positive pressure of the air within the lungs on the thoracic structures, venae cavae, thoracic duct, etc., being at the same time diminished, there is an expansion of and a fall of pressure in the thoracic duct and venae cavae. As the lymph in the abdominal portion of the thoracic duct is subjected to the higher intra-abdominal pressure, its contents are forced ener- getically toward the end of the thoracic duct. During expiration the reverse conditions obtain. As the negative pressure diminishes and the positive intrapulmonary pressure increases the upper part of the thoracic duct is compressed and the lymph is forced into the subclavian vein at its junction with the internal jugular. Regurgita- tion here is prevented by a closure of the valves. CHAPTER XL THE BLOOD. The blood is a highly complex nutritive fluid, the presence and proper circulation of which in the living organism are essential to the maintenance and activity of all physiologic processes. The escape of the blood from the vessels, especially in the higher animals, is followed by a loss of the physiologic properties of all the tissues within a short period of time. The immediate dependence of the functional activities of the tissues and organs on the presence of the blood can be demonstrated by the following experiment : If the nozzle of a syringe, adapted to the size of the animal, be introduced through the jugular vein into the right side of the heart and the blood be sud- denly withdrawn, there is an immediate cessation in the activity of all the organs; the return of the blood to the vessels within a limited period of time is promptly followed by a renewal of their activity. Though contained within a practically closed system of vessels, the blood is brought into intimate relation with all the tissue elements through the intermediation of the capillaries. As the blood flows through these delicate vessels, portions of its soluble nutritive con- stituents, including oxygen, are given up to the tissues, by which they are utilized for growth, repair, and functional activity. At the same time the tissues yield up to the blood a series of decomposition prod- ucts, resulting from their activity, which vary in quantity and quality according as the blood traverses the muscles, nerves, glands, or other tissues. The blood may be regarded, therefore, as a reservoir of nutritive materials prepared by the digestive apparatus and absorbed from the food canal; of oxygen, absorbed from the respiratory surface of the lungs; of decomposition products, produced by and absorbed from the tissues. Though the blood varies in composition in different parts of the body in consequence of the introduction of both nutritive material and decomposition products, it nevertheless presents certain average physical, morphologic, and chemic properties which dis- tinguish it as an individual tissue. Constituents of Blood. — A microscopic examination of the blood as it flows through the capillary vessels of the web of the frog or the mesentery of the rabbit shows that it is not a homogeneous fluid, but that it consists of two distinct portions: viz., (i) a clear, transparent, slightly yellow fluid, the plasma or liquor sanguinis; (2) small par- 238 THE BLOOD. 239 tides termed corpuscles floating in it, of which there are two varieties, the red and white. By appropriate methods it can be shown that a third corpuscle, colorless in appearance and smaller in size than the ordinary white corpuscle, is present in the blood stream and known as the blood-plate or plaque. The different constituents can be roughly separated by appropriate means when the blood is with- drawn from the body. If the blood of the horse is allowed to flow directly into a tall cylindric glass vessel, surrounded by ice, it sep- arates in the course of a few hours into three distinct layers in ac- cordance with their specific gravities. The lower layer is dark red and consists of the red corpuscles ; the middle layer is grayish in color and consists of the white corpuscles; the upper layer is clear and transparent and consists of the plasma. The red corpuscles occupy almost one-half, the white one-fortieth, the plasma a trifle more than one-half of the height of the entire blood-column, which indicates approximately the different volumes of each. The same result can be obtained with human blood by the use of the centrifuge or hema- tocrit. PHYSICAL PROPERTIES OF BLOOD. 1. Color. — Within the blood-vessels two kinds of blood are dis- tinguished — the arterial, the color of which is a bright scarlet, and the venous, the color of which is a dark bluish-red or purple. The cause of the color as well as the difference in color is the presence in the red corpuscles of a coloring-matter, hemoglobin, in different degrees of combination with oxygen. The intensity of the color in either kind of blood is dependent on the thickness of the blood-stream, for in the finest capillaries, as seen under the microscope, there is an almost total absence of color. As the arterial blood passes into and through the systemic capillaries, the hemoglobin yields up a portion of its oxygen to the tissues and changes in color, though the change is not appreciable by the eye. On passing into the veins, however, the blood-stream soon presents its characteristic dark bluish color, which deepens as it approaches the lungs. On passing into and through the capillary vessels of the lungs the hemoglobin absorbs a new volume of oxygen, changes in color, and on emerging from the lungs the blood presents its characteristic scarlet color. 2. Opacity. — Owing to the fact that the corpuscles have a re- fracting power different from the plasma, the blood, even in thin layers, is opaque. The repeated refractions and reflections which light undergoes in passing through plasma and corpuscles is attended by such a dissipation that it is impossible to see printed matter through it. That the opacity is due to the shape of the corpuscles rather than to their contained coloring-matter is evident from the fact that when the hemoglobin is caused to separate from the corpuscles by the 240 TEXT-BOOK OF PHYSIOLOGY. addition of chemic reagents, the blood, though it deepens in color, becomes at once transparent. 3. Odor. — When freshly drawn the blood possesses a peculiar characteristic odor which has been attributed to the presence of a volatile fatty acid in combination with an alkaline base. The in- tensity of the odor may be increased by the addition of concentrated sulphuric acid, by means of which the volatile acid is set free. 4. Specific Gravity. — The specific gravity of blood lies within the limits of 1.051 and 1.059, averaging in man 1.056 and in woman 1 .053. Normally, variations from these values are only temporary and are connected with variations in physiologic processes. The specific gravity is diminished by the ingestion of liquids and abstinence from solid food. It is increased by abstinence from liquids, by the inges- tion of dry food, and by the elimination of large quantities of water by the lungs, skin, and kidneys. 5. Alkalinity. — The reaction of the blood is alkaline from the presence of the disodium phosphate (Na2HPO^) and the sodium car- bonate, NajCOa. The alkalinity can be readily shown by allowing the blood to remain for a few seconds on slightly reddened glazed litmus paper. On washing off the blood a distinct blue color pre- sents itself against a red or violet background. The alkalinity varies within narrow limits in consequence of variations in physiologic processes. It is increased in the early stages of digestion and de- creased in the later stages. It is decreased after muscular exercise in consequence of the increased production and absorption of acids. According to v. Jaksch, the alkalinity corresponds to from 260 to 300 milligrams of sodium hydrate, NaOH, for every 100 c.c. of blood; according to Lowy, from 300 to 325 milhgrams. The hitherto un- avoidable error in these estimates is about 30 milligrams. 6. Temperature. — The temperature varies from 36.78° C. (98.2° F.) in the superior vena cava to 39.7° C. (103.4° F.) in the hepatic vein, the mean being about 38° C. (100° F.). Coagulation of the Blood. — Within a few minutes after the blood is withdrawn from the vessels of a hving animal it begins to lose its fluidity, becomes somewhat viscid, and if left undisturbed passes rapidly into a semi-solid or jelly-like state. To this change in the physical condition of the blood the term coagulation has been applied. The blood, during the progress of coagulation, not only assumes the shape of the vessel in which it is contained, but becomes so firmly adherent to its walls that it may be inverted without the coagulum becoming dislodged. If a portion of such a jelly-like mass be examined microscopically, it will be found to be penetrated in all directions by a felt-work of extremely fine delicate fibrils, which, having made their appearance before the corpuscles had time to THE BLOOD. 241 settle to the bottom of the fluid, have entangled them in the meshes so that the entire mass retains its characteristic color. These fibrils are collectively known as fibrin (Fig. 94). If the coagulated blood be allowed to remain undisturbed, a clear, transparent, sHghtly yellowish fluid makes its appearance on the surface of the mass, which as it accumulates forms a layer of varying degrees of thickness. Within a few hours the blood-mass detaches itself from the sides of the vessel in consequence of the re- traction of the fibrils, while at the same time the clear fluid increases in amount and accumulates along the sides and bottom of the vessel. The shrinkage in the volume of the red coagulum and the increase of the volume of the clear fluid which is expressed from its meshes continue for a period varying from ten to fifteen hours, according to certain external conditions. The blood has now become separated into two distinct portions: viz., a sohd contracted red mass, termed clot, and a clear fluid, termed serum. The clot consists of the fibrin containing in its meshes the red and white corpuscles; the serum Fig. 94. — Diagram to Illustrate the Process of Coagulation, i. Fresh blood, plasma, and corpuscles. 2. Coagulating blood (birth of fibrin). 3. Coagulated blood (clot and serum). — {Waller.) consists of all the constituents of the plasma except the antecedents of the fibrin. The stages of coagulation are shown in Fig. 94. If the blood coagulates slowly the red corpuscles, owing to their greater specific gravity, subside to the bottom of the blood-mass, giving to it a deeper color; the white corpuscles, owing to their lesser specific gravity, remain near the surface of the clot and give to it a more or less whitish appearance, producing the so-called hufjy coat. In certain inflammatory conditions the coagulating power of the blood is much diminished, and the corpuscles, having time to subside, a well- developed buffy coat is formed which at one time had much interest for pathologists. As the contraction of the fibrin takes place more actively in the center, there being here less resistance than at the sides of the coagulum, the upper surface usually becomes depressed or cupped. Coagulation of Plasma. — Clear plasma may be obtained by means of the centrifuge from blood to which sufficient magnesium sulphate has been added to prevent coagulation, or from horse's 16 242 TEXT-BOOK OF PHYSIOLOGY. blood which has been allowed to How into a tall vessel surrounded by a cooling mixture so as to prevent coagulation and thus permit the red corpuscles to subside. If such plasma be subjected to room-tem- perature, it very shortly undergoes coagulation, exhibiting practically the same phenomena as blood itself. After a variable length of time it also separates into a soft, colorless coagulum or clot consisting of fibrin, and a clear fluid, the serum. The presence of the red cor- puscles is therefore not essential to the process of coagulation. Rapidity of Coagulation. — The rapidity with which the blood coagulates varies in dilferent classes of animals under the same con- ditions: e. g., the blood of the pigeon coagulates immediately; that of the dog, in from one to three minutes ; that of the horse, in from five to thirteen minutes; that of man, in from four to seven minutes. The time, however, can be lengthened or shortened by either chang- ing the external conditions or by altering temporarily the normal composition of the blood. Coagulation is retarded or prevented by the following agents, viz.: (i) A low temperature, especially that of melting ice. (2) The addition of magnesium sulphate Cr volume of a 25 per cent, solution to 3 volumes of blood); of sodium sulphate (i volume of a saturated solution to 7 volumes of blood). (3) The addition of potassium oxalate (i volume of a i per cent, solution to 3 volumes of blood). (4) The injection into the blood of commercial peptone. (5) The mouth secretion of the leech. Coagulation is hastened by the following agents, viz.: (i) A gradually increasing temperature from 38° C. to 50° C. (2) The addition of water in not too large amounts. (3) The presence of foreign bodies. (4) Agitation of the blood — e. g., stirring. Fibrin and Defibrinated Blood. — If freshly drawn blood is stirred with a bundle of twigs or glass rods for a few minutes, the fibrin collects on them in the form of thick bundles* or strands; after washing it with water the entangled corpuscles are removed, when the fibrin assumes its natural white appearance. The strands can be resolved into a large number of dehcate fibers which possess ex- tensibility and retractibility, and are therefore elastic. The chemic features of fibrin have already been considered (see page 34). The remaining fluid, similar in its physical appearance to the blood, is termed defibrinated blood. When such blood is allowed to remain at rest for a few days, the remaining red corpuscles gradually sink to the bottom of the fluid, above which will be found the clear serum. COMPOSITION OF PLASMA AND SERUM. Plasma.— The plasma obtained by any of the methods previously described is a clear, colorless, transparent, slightly viscid fluid, with THE BLOOD. 243 a specific gravity of 1.026 to 1.029. ^^ ^s composed largely of water holding in solution proteids, sugar, fatty matter, inorganic salts, urea, cholesterin, lecithin, etc. In composition it is quite complex, con- taining as it does not only the nutritive materials derived from the digestion of the food, but also the substances resulting from the disintegration of the tissues consequent on their functional ac- tivity. Serum. — The serum is the clear, transparent, slightly yellow fluid expressed from the coagulated blood during the contraction of the fibrin. It consists practically of the ingredients of the plasma, with the exception of those substances which entered into the for- mation of fibrin. The average composition of plasma is shown in the following table: COMPOSITION OF PLASMA. Water, 90.00 [Serum-albumin, 4.50 Proteids ^ Paraglobulin, 3.40 ( Fibrinogen, 0.30 Fatty matters, 0.25 Sugar, CIO Extractives, 0.60 Inorganic salts, 0.85 100.00 Serum-albumin. — Of the proteid constituents of the blood, serum-albumin is the most abundant, existing to the extent of from 4 to 5 per cent. From its similarity to egg-albumin it is regarded as holding an important position as a nutritive agent, for it is out of this common proteid that in all probability each individual tissue elabor- ates the special proteid characteristic of it, since during starvation the albumin steadily diminishes in amount. As it passes through the walls of the capillary vessels it is found in the hmiph, pericardial fluid, and similar secretions in various parts of the body, as well as in various pathologic transudates. It is also present in serum. While circulating in the lymph-spaces the serum-albumin is utilized in replacing the proteids which have undergone disintegration during tissue metabolism. Its supply in the blood is maintained by the absorption of peptones which are formed from the proteids of the food and which during the time of absorption are changed in some unknown way into serum-albumin. It is readily obtained from plasma or serum by saturating either of these fluids with magnesium sulphate, when all the proteids except serum-albumin are precipitated. After their removal the remaining fluid is subjected to a temperature of from 70° to 75° C, when the serum-albumin is precipitated in a coagulable form, after which it can be removed and its chemic features determined. 244 TEXT-BOOK OF PHYSIOLOGY. Paraglobulin. — This proteid, though present in plasma, is best obtained from scrum when this fluid is saturated with magnesium sulphate. As the line of saturation is approached the fluid becomes turbid, and after a few minutes a fine white precipitate occurs. It can then be collected on a filter, dried, and its chemic properties determined. In its reactions it resembles the various members of the globulin class. The amount varies from 2 to 4 per cent, in the blood of man. As to the physiologic importance or antecedents of para- globulin nothing is definitely known. Its constant presence in the blood would indicate that it plays an equally important, though per- haps different, part with serum-albumin in the nutrition of the body. Fibrinogen. — This proteid can be obtained from plasma, lymph, pericardial, and peritoneal fluids, as well as from hydrocele fluid. It is, however, not to be obtained from serum, as it is removed from the blood during the formation of sohd fibrin. It is normally present in the blood in very small quantity, amounting to not more than 2.2 to T,.T, parts per thousand. Fibrinogen may be obtained from plasma which has been prevented from coagulating, by the addition of mag- nesium sulphate in certain quantities or by the addition of a satu- rated solution of sodium chlorid. In a few minutes a flaky precipitate occurs. By repeated washing and precipitation with sodium chlorid solutions of varying strength the fibrinogen may be obtained in a pure state. The history of fibrinogen is unknown. Beyond the fact that it contributes to the formation of fibrin there is no positive knowledge either as to its origin, its nutritive value, or its final dis- position in the blood under normal conditions. Fat. — The plasma as well as the serum contains a very small quantity of fat in the form of microscopic globules. Though the percentage is normally not above 0.25, yet just after a meal rich in fatty matter the amount may be so great as to give to the blood a milky or opalescent appearance. Within a few hours, however, this excess of fat disappears from the blood, though its immediate disposition is unknown. Soaps or alkaline salts of the fatty acids, though formed during the digestion of fats, are not present in the blood. Lecithin and cholesterin are present in very small quantities. Sugar. — Sugar is present in the blood in the form of dextrose, and is now regarded as a normal constituent. The amount is about I part per thousand, though it may be present to the extent of 3 parts per thousand. Beyond this, the excess soon appears in the urine. Extractives. — The blood contains a series of nitrogenized bodies, such as urea, uric acid, creatin, creatinin, xanthin, etc., which result from the katabolic changes in nerve- and muscle-tissues as well as from subsequent chemic combinations and decompositions. Though constantly absorbed from the tissues, they seldom accumu- THE BLOOD. 245 late beyond a small amount, since they are constantly being elimi- nated from the blood by the various excretory organs. Inorganic Salts. — The inorganic salts of the plasma are chiefly sodium and potassium chlorids, sulphates, and phosphates, together with calcium and magnesium phosphates. Of the salts, sodium chlorid is the most abundant, amounting to 5.5 parts per thousand. Some of the salts are alkahne and impart to the blood its alkalinity. Calcium phosphate is present in small quantity — 2 parts per 1000. This salt is wanting in serum for the reason that it became a constitu- ent of fibrin at the time of coagulation. In other respects serum differs but slightly from plasma in the proportions of its sahne con- stituents. HISTOLOGY OF THE RED CORPUSCLES OR ERYTHROCYTES. The histologic features of the red corpuscles are readily observed in a drop of freshly drawn blood when examined microscopically. The field of the microscope will be seen to be crowded with red corpuscles floating in a clear transparent fluid — the plasma. Here and there will also be seen a white corpuscle, round or irregular in shape, and granular in appearance. Within a short time a char- acteristic phenomenon takes place: viz., the arranging of the corpuscles in the form of columns of var}'- ing length, resembling rolls of coins. These rolls in- terlace with each other at all angles and form a net- work in the meshes of which lie individual red and white corpuscles. (See F^g- 95-) The cause of this tendency of the cor- puscles to adhere to one another is not definitely known. Since it does not take place in circulating blood, and since it is to a great extent prevented by defibrinating the blood, it has been supposed to be dependent on the formation of some adhesive substance connected with the formation of fibrin. Color. — When viewed by transmitted light, a single corpuscle is slightly yellow or greenish in color; but when a number are grouped Fig. 95. — Corpuscles from Human Sub- ject. A few colorless corpuscles are seen among the colored discs, many of which are arranged in rouleaux. — (Ftmke.) 246 TEXT-BOOK OF PHYSIOLOGY. together, the color deepens and the corpuscles appear red. In either case the color is due to the presence in the corpuscle of a specific coloring-matter, hemoglobin. Shape. — The red corpuscle is a circular, flattened disk with rounded edges. Each surface is perfectly smooth and presents a shallow depression in its center, so that it is also biconcave. A longitudinal section of a corpuscle would present, when viewed edgewise, an outline similar to that of Fig. 96. This difference in the thickness of the peripheral and central portions of the corpuscle gives rise to differences in optical e-.-.j!-^^^;^,. — ,. appearances when examined micro- • Jb scopically. At a certain distance of -—- i — --^^.^^^^ y. the object-glass the corpuscle pre- ""a "" sents in its peripheral portion a Fig. 96.-IDEAL Transverse Sec- \^^\aVs.\. rim, and in its central por- TiON OF A Human Red Corpus- . ° , ' tt i 1 • • CLE. (Magnified 5000 times.) tion a dark spot. If the objective a, h. Diameter, c, d. Thickness, be brought nearer and the center accurately focused, the reverse ap- pearance obtains ; the central portion becomes bright and the periph- eral portion dark. The cause of this difference in optical appear- ance is the unequal distribution of the transmitted hght in conse- quence of the shape of the corpuscle. .Size. — The diameter of a typical well-developed red corpuscle under normal conditions is 0.0075 mm.; its greatest thickness is 0.0019 mm. Though this may be assumed as the average diameter, there is a small percentage of distinctly smaller and a small per- centage of distinctly larger corpuscles. The following table shows the results of measurement made by different observers: Normal Limits. Average Diameter. Welcker, diameter 0.0045-0.0095 0.0070 Hayem, " 0.0060-0.0088 0.0075 Gram, " 0.0067-0.0093 0.0078 Melassez, " 0.0076 0.00747 (32V0 inch) Structure. — The red corpuscle of man as well as all other mam- mals possesses neither a nucleus nor a hmiting membrane, but appears to consist of a homogeneous substance more or less semisolid in con- sistence. Under the influence of certain reagents the corpuscle separates into two distinct portions: viz., a colorless protoplasmic stroma and a coloring-matter which diffuses into the surrounding liquid. The presence of the former can be demonstrated by the addition of iodin, which imparts to it a faint yellow color. The stroma is elastic, and determines not only the shape of the corpuscle but gives to it the properties of extensibility and retractibility. THE BLOOD. 247 Number of Red Corpuscles.— In any given specimen of blood the corpuscles are so numerous and the spaces between them so small that it seems almost impossible to determine their number. This, however, has been accomphshed for a cubic miUimeter of blood by various observers employing different methods with compara- tively uniform results. The average normal number of corpuscles in one cubic milhmeter of blood is, for men, 5,000,000; and for women, 4,500,000. This value, however, will vary within shght hmits, with variations in the activity of physiologic processes and to a large extent at times in pathologic states of the blood or body. The number is increased in the cutaneous veins by all influences which cause a diminution in the quantity of water in the blood — e. g., copious •sweating, acute watery diarrhea, fasting, abstinence from Hquids; the number is diminished by influences which dilute the blood — e. g., the ingestion of hquids, the absorption of fluids from the tissue spaces, etc. But it is well to remember that these influences which produce changes in the number of corpuscles per cubic millimeter do not necessarily produce corresponding changes in the total number of red corpuscles in the body. In women lactation, menstruation, and the act of parturition diminish the number. High altitudes appar- ently increase the number of corpuscles, as shown by their increase in the blood of the peripheral vessels. Whether this is an indication that there is a corresponding increase of the total number in the general volume of the blood is uncertain. The following table will show the increase in the count per cubic miUimeter at different altitudes: Place. Height above Sea-level. Red Cells. 4.974.000 5,225,000 5,322,000 5,752,000 5,748,000 5,900,000 7,000,000 8,000,000 Author. Christiania, Gottingen, Xiibingen, __ meter 148 meters 314 414 425 700 " 1800 " 4.392 Laache. Schaper. Reinert. Zurich, Auerbach, Reibaldsgriin, Arosa, The Cordilleras, Moro cocha. Steirlin. Koppe. Egger. Viault. (Koppe.) This increase in the number of corpuscles takes place, according to Viault's observations, within two or three weeks, and is apparently not connected with either diet or mode of life, but rather with dimin- ished atmospheric, if not oxygen, pressure. On returning to sea- level there is a gradual reduction, without any apparent destruction of the corpuscles, to their normal number. The reason for these variations is not clear. The method of counting corpuscles introduced by Vierordt and 248 TEXTBOOK OF PHYSIOLOGY. Welckcr has been modified by different observers, and especially by Thoma and Zeiss. On account of the great number of corpuscles in I cubic millimeter of blood, it becomes necessary for purposes of enumeration that the blood be diluted a definite number of times and that the diluted mixture be placed in a counting chamber possessing a definite capacity. By means of the pipette or melangeur of Potain and the counting chamber of Thoma both these objects are attained. ^ The pipette consists of a capillary tube (Fig. gy) provided with an enlargement containing a freely mov- able small glass ball, a. One end of the tube is pointed, vdiile to the other end is attached a rubber tube for the purpose of facilitating the introduction of the blood and the diluting fluid. The capillary tube, which is accurately calibrated, carries marks, ^, i, loi, which signify that if the tube be filled with blood up to the mark i and the diluting fluid be sucked into the tube up to the mark loi, the blood will be diluted loo times. If the blood be sucked up to the mark J and the diluting fluid to loi, then the blood will be diluted 200 times. In using the pipette the point is introduced into a drop of blood derived from a small wound in the skin of the lobe of the ear or finger and sucked into the tube by introducing the rubber tube into the mouth. The tube is then quickly inserted into a solution, similar in specific gravity to the plasma, which will preserve the shape and size of the corpuscles, such as Gowers's sodium sulphate solution, sp. gr. 1.025, or a 3 per cent, sodium chlorid solution,* and the fluid sucked into the tube up to the mark loi. On shaking the pipette for a few minutes, the admixture will take place, aided by the movements of the glass ball. Fig. 98 shows both a section view. A, and a surface view, C, of the counting chamber. This con- sists of an oblong glass plate on which are cemented two small pieces of glass, one of which has in the center a circular opening in which is placed the other, a circular disc or Fig. 97. — Melan- geur OR Pipette. — (Landois and Stirling. ) * Various solutions have been devised for diluting blood, any one of which may be employed, e. g.: Toisson's Fluid: Aquae destillat., 160.00 parts. Glycerins, 30.00 " Sodium sulphate, __ 8.00 " Sodium chlorid, i.oo " Methyl-violet, 0.025 part. Hayem's Fluid: Hydrarg. bichior., 0.5 gm Sodium sulphate, 5.0 " Sodium chlorid, 2.0 " Aquae destillat., 200.0 " Gowers's Fluid: Sodium sulphate, gr. 104 Acid, acetic, .^j Aquae dest., q. s. ad ^^iv. THE BLOOD. 249 stage. Their relation is such that a narrow groove or moat separates the one from the other, the floor of which is formed by the glass plate. The surface of the circular stage is exactly o.i mm. lower than that of the cover-glass, a. On the surface of the glass stage a series of small squares is engraved, each one of which has a side length of ^^ mm. and an area of :f^o square mm., B. To faciHtate counting, a group of i6 squares is surrounded by a heavy dark line. This group is a b separated from adjoining groups, also enclosed by dark lines, by an inter- mediate light line, which serves as a guide in pass- ing from one group to another. When a cover- glass is accurately applied to the glass, b, each one of the small squares will have a cubic capacity of ,:-^^_X O.I, or 4oVo cubic millimeter, and every four such squares will have therefore a capacity of yoVtt cubic millimeter. Before placing the di- luted blood on the coimt- ing stage, the fluid in the tube of the pipette should be blown out and dis- carded, as it contains no portion of the blood. A few drops are then placed on the glass stage and covered with the cover- glass. After a few min- utes the corpuscles settle over the ruled spaces and are ready for counting. The number of corpuscles in a horizontal series of 4 squares is then counted; this number is then multiplied by 1000 in order to get the number in i cubic millimeter of the diluted blood, and this product by 100 or 200 according to the extent of the dilution: e. g., four squares contain 50 corpuscles; multiplied by 1000 and then by 100 = 5,000,000. The accuracy of the comiting is proportional to the number of squares counted. If 200 squares are counted and the average taken, the probable limit of error will not be more than 2 per cent. Effects of Reagents on the Red Corpuscles. — Within the blood-vessels the composition of the plasma is such that both the Fig. 98. — Apparatus of Thoma and Zeiss FOR Counting the Corpuscles. A. In section. C. Surface view without cover- glass. B. Microscopic appearance with the blood-corpuscles. — {Landois aiid Stirling.) 250 TEXT-BOOK OF PHYSIOLOGY. form and composition of the corpuscles arc maintained under normal physiologic conditions. This fluid, therefore, is preservative of the structure and function of the corpuscle. When examined micro- scopically with a view of determining their histologic features, the plasma must be diluted, and in consequence they rapidly undergo physical and chemic changes from the absorption or loss of water. To prevent these elTects the corpuscles must be immersed in a fluid containing a percentage of salts approximating that of the plasma. Under such circumstances they will neither absorb nor give up water. Such a fluid is found in the physiologic salt solution, which contains 0.64 per cent, sodium chlorid. This fluid maintains the chemic equilibrium of the corpuscles, and is therefore said to be isotonic to the corpuscle. If distilled water be added to the drop of blood, the corpuscle absorbs it, swells, and assumes a more or less spheric form, some- times cup-shaped. The hemoglobin dissolves out and the stroma becomes almost invisible. Its presence can be detected by the addition of iodin. The addition of salt solutions, — e. g., sodium chlorid, sodium sulphate, ammonium chlorid, etc.,— which increase the density of the plasma, cause a shrinkage of the corpuscles so that they assume a crenated or notched appearance. Dilute solutions of acetic acid, of alkalies, especially potassium and sodium hydrate, cause the corpuscles to swell, to lose their color, dissolve, and en- tirely disappear. Many other agencies of a physical and chemic nature, such as heat 60° C, electricity, bile salts, the vapor of chloroform, ether, ammonium sulphocyanid, etc., also destroy the integrity of the corpuscles, and cause the hemoglobin to separate from the stroma and diffuse into the plasma without itself under- going any appreciable change in composition. The blood at the same time will become transparent and cliange to a dark red color, to which the term "lake color" has been given. The Corpuscles of Other Vertebrated Animals. — In all mam- mals, with the exception of the camel, llama, and dromedary, the red corpuscles present the same shape and structure as the corpuscles of man, and may be described as circular, flattened, biconcave disks. In the animals excepted the corpuscles are oval. The size, however, varies in different animals from 0.0092 mm. (2TTT inch) in the ele- phant to 0.0023 nim. (y-jiTT inch) in the musk-deer, while in most animals the average lies between 0.0084 nim. and 0.0050 mm. Inas- much as the question may arise as to whether the corpuscles of any given specimen of blood are those of a human being or of some other mammal, a knowledge of the size of the corpuscles becomes a matter of medicolegal as well as of physiologic interest. Though the differences in size are slight, yet it is possible for skilled microscopists, when examining fresh blood, to make a diagnosis between the cor- THE BLOOD. 251 puscles of man and those of the domesticated animals, with the ex- ception, perhaps, of the guinea-pig. Tlie diagnosis of the corpuscles of dried blood which have been altered by the action of various ex- ternal agents, even though capable of a certain degree of restoration, is most difficult, and should not be attempted in criminal cases with- out large experience in microscopy, in measurements and methods of preparation of all kinds of blood-corpuscles, and a proper per- ception of corpuscular forms and sizes. In the following table the average results of the measurements of the corpuscles in different classes of animals are given (abstracted from Formad's compilation) : Gulliver. WORMLEY. C. Schmidt. Malunin. French Medico- legal Soc. Welcker. Form AD. Inch. 1 3200 1-3538 1-3532 1-3607 1.4267 1.4230 1.4600 1.4404 1.5300 1.6366 Mm. Inch. Mm. Inch. Mm. Inch. Mm. Inch. Mm. Man Guiaea-pig.. Dog Rabbit, Ox Pig Horse Cat Sheep Goat 0.0079 0.0071 0.0071 0.0070 0.0060 0.0060 0.0057 0.0058 0.0048 0.0040 3250 3223 3561 3653 4219 4268 4243 4372 4912 6189 0.0078 0.0079 0.0071 0.0070 0.0060 0.0059 0.0059 0.0058 00031 0.0041 1.3300 1.3300* 1.3636 1-3968 1-4354 1 .4098 1.4464 1-4545 1.5649 1.6369 0.0077 0.0077 0.0070 0.0064 0.0058 0.0062 0.0057 0.0056 0.0045 0.0040 3257 3213T 348s 3653 4545 4098 4545 3922 5076 SS2S 0.0078 0.0079 0.0073 0.0069 0.0056 0.0062 0.0056 0.0065 0.0059 0.0046 1.3200 1.3400 1-3580 1.3662 1.4200 1.4250 1. 43 10 1.5000 1. 6100 0.0079 0075 0.0071 0.0069 0.0060 0.0060 0.0059 0.0051 0.0042 In birds, reptiles, and amphibians the corpuscles are larger than in mammals, are oval in shape, and nucleated. (See Figs. 99 and 100.) As the scale of animal life is descended the corpuscles in- crease in size, until in the proteus and am- phiuma the long diameter attains an average length of 0.058 mm. and 0.077 mm. respec- tively. In fish the corpuscles are smaller, oval, and nucleated, with the exception of the lam- prey eels, in which they are circular, biconcave, and nucleated, though the nucleus is gener- ally concealed in the peripheral portion of the corpuscle. As in these animals, the cor- puscles are almost twice the size of the human red corpuscles, they can, notwithstanding the similarity of shape, be readily distinguished from them. Function of the Red Corpuscles. — The red corpuscles, in virtue of the capacity of their contained hemoglobin for oxygen absorption, may be regarded as carriers of oxygen from the lungs to the tissues, and therefore important factors in the general respiratory Fig. 99. Fig. 100. Amphibian Colored b l o o d-c o r p u s cles. Fig. 99, on the flat; Fig. 100, on edge. — (Landois and Stirling.) * Masson. t Woodward. 252 TEXT-BOOK OF PHYSIOLOGY. process. The size as well as the number of the corpuscles in different classes of animals appears to be directly related to the activity of the respiratory process. In those animals in which the corpuscles are small and numerous and the total superficial area large, respiration is active, the quantity of oxygen absorbed is large, and the energy evolved through oxidation great. In those animals, on the contrary, in which the corpuscles are large and relatively few in number, the reverse conditions obtain. This is in accordance with the fact that the superficial area of any given volume of substance is increased in proportion to the extent to which it is subdivided. The superficial area of a single human red corpuscle has been estimated at 0.000128 sq. mm. If the number of corpuscles in i cubic milhmeter of blood averages 5,000,000, the superficial area would amount to 640 square miUimeters; and if the amount of blood in the body of a man weighing 75 kilos is taken as one-thirteenth of this weight, — that is, 5769 grams (5463 c.c), — the total area of the corpuscular surface will amount to 3496 square meters. Life-history of Red Corpuscles. — In the performance of their functions the red corpuscles undergo more or less disintegration and finally destruction; but as the average number is maintained under normal physiologic conditions, there must be a constant renewal of corpuscles from day to day. The evidence of destruction of red corpuscles is furnished by the presence in the blood, in various situ- ations of the body, of a pigment containing iron and the presence of pigments in the bile and urine, all of which are believed to be deri- vatives of effete hemoglobin. The blood-pigment (hematin), which contains the iron of the hemoglobin, is found in the capillaries of the fiver, in the cells of the splenic pulp, and in the marrow of the bones. Whether the presence of the pigment in these organs is a proof that the corpuscles are destroyed here, or whether they are to be regarded merely as agents concerned in the further reduction and efimination of the hematin, is uncertain. The genetic rela- tionship between bile-pigment and hemoglobin is shown by the fact that any artificial destruction of hemoglobin or its injection into the blood is attended by an increase in the quantity of bile-pigment eliminated. It appears also from chemic considerations that the hemoglobin will undergo cleavage into a globuHn body and hematin, which by the loss of its iron is readily converted into the bile-pig- ment, bihrubin. The amount of this latter pigment may therefore be taken as an index of the extent of corpuscular destruction. This gradual decay of corpuscles as well as the losses occasioned by hemorrhages necessitate a continuous formation of new cor- puscles, so that the normal number may be maintained. The rapidity with which corpuscles may be renewed, in the woman at least, is shown by a computation of Mr. Charles L. Mix. A woman loses THE BLOOD. 253 during a menstrual period 150 c.c. of blood. At the end of twenty- eight or thirty days this volume is restored, so that in one day 5 c.c, or 5000 c.mm., of blood must be formed, or 208 c.mm. per hour and 3^ c.mm. per minute. That is, during a certain number of years 15,750,000 corpuscles must be formed every minute, and this inde- pendent of the daily loss due to functional activity. At the present time there is a general agreement among histolo- gists that in adult life the red corpuscles are derived from embryonic forms, the so-called erythroblasts, which are found chiefly in the marrow of the long bones.* In this situation both arterial and venous capillaries are relatively large and the blood is separated from the surrounding marrow by extremely thin walls. In the passages of this capillary network the erythroblasts make their appearance most probably by a transformation of preexisting marrow cells. At first they are large, homogeneous, colorless, perhaps slightly tinged with hemoglobin and distinctly nucleated. They increase in number by karyokinesis and at the same time increase in their hemoglobin con- tent. The nucleus is finally extruded, carrying with it a portion of the perinuclear cytoplasm, after which the remainder of the cor- puscle assumes the shape and size of the adult corpuscle and is carried out into the general circulation. After severe hemorrhage the forma- tive processes in the marrow may become so active that erythroblasts make their appearance in the blood-stream before the extrusion of the nucleus has taken place. CHEMIC COMPOSITION OF RED CORPUSCLES. Hemoglobin. — The red corpuscle consists of a stroma and a coloring-matter, hemoglobin. In the normal condition the latter is amorphous and in- some unknown way combined with the former and not merely diffused in its meshes. The amount of hemoglobin per corpuscle is estimated at 90 per cent., so that the corpuscle may be conceived of as a mass of hemoglobin supported and enclosed by a protoplasmic stroma. If blood w^hich has been rendered laky, by water or any other of the known agencies, be allowed to slowly evaporate, the dissolved hemoglobin undergoes crystaUization. The rapidity with which the crystals form varies in the blood of different animals under similar conditions. According to the ease with which crystallization takes place, Preyer has classified various animals as follows: (i) Very difficult — calf, pigeon, pig, frog; (2) difficult — man, monkey, rab- * For an admirable resume of the various views regarding the origin and formation of red corpuscles see the paper of Mr. Charles L. Mix, Boston Med. and Surg. Journal, 1892, Nos. II and 12; also paper by Prof. W. H. Howell, Journal of Morphology, vol. IV, 1802. 2 54 TEXT-BOOK OF PHYSIOLOGY. bit, sheep; (3) easy — cat, dog, mouse, horse; (4) very easy — guinea- pig, rat. The hemoglobin crystals vary in shape according to the blood from which they are obtained (Fig. loi). Those obtained from the guinea-pig are tetrahedral; those from man and most mammals are prismatic rhombs; those from the squirrel are in the form of hexagonal plates. Notwith- standing these shght differences, all forms belong to the same crystal system, with the excep- tion of those from the squirrel. A simple but very effective method of obtaining blood-crys- tals suggested by Reichert is to lake defibrinated blood, espe- cially that of the dog, rat, guinea- pig, and horse, with acetic or ethyhc ether and then add a solution, I to 5 per cent., of ammonium oxalate. A drop of this mixture placed under the microscope will show crystal for- mation in a very few minutes. Chemic Composition of Hemoglobin. — By appropriate methods hemoglobin can be ob- tained in a practically pure form, and when subjected to a tem- perature of 100° C. its water of crystallization is driven off, after which it can be analyzed. In the subjoined table the results of several analyses are given for 100 parts of hemoglobin. Fig. ioi. — Crystallized Hemoglobin. a, b. Crystals from venous blood of man. c. From blood of cat. Guinea-pig. e. Of marmot, squirrel. — (Gaulier). Of Of c, - o,. H,. N,. S, . Fe, THE BLOOD. 255 The elementary composition of hemoglobin is thus seen lo vary slightly in different animals, suggesting that there may be different kinds of hemoglobin. The rational molecular formula is not known. On the assumption that each molecule contains one atom of iron, Preyer suggested the following empirical formula: CgooHgggNjj^Oj^j,- SgFe, with a molecular weight of 13,332; Jaquet has suggested a different formula: viz., Cj5gHj2,,3Nj9502,8S3Fe, with a molecular weight of 16.669. It is very evident from this that the molecule is of enor- mous size and exceedingly complex. Quantity of Hemoglobin. — The quantity of hemoglobin in blood as determined by chemic, chromometric, and spectro-photometric methods amounts to about 14 per cent, in man and 13 per cent, in woman. Of the chemic methods, that based on the amount of iron is the most familiar. Chemic analysis has shown that hemoglobin contains 0.43 per cent, and blood 0.056 per cent, of iron; with these two factors the quantity of hemoglobin can be determined by the following formula: x = '°° ^ ° °^^ = 13.33 P^^ cent. The total quantity of hemoglobin in the blood, assuming the latter to be about 5769 grams (one-thirteenth of the body-weight, 75 kilos) will therefore amount to 769 grams; e. g., x = 5769 x 13.33 ^ ^5^^ 'pj^g |-Q^g^[ amount of iron in the blood is obtained by the following formula: viz., x = s769j^o^s6 _ grams. 100 "-' "JO Under normal physiologic conditions the percentage of hemo- globin undergoes but slight variation. In pathologic states there is frequently a great diminution in the amount, especially in chlorosis, splenic leukemia, and pernicious anemia, diseases in w^hich it dimin- ishes to 2^ per cent, in many instances. For the determination of these variations in the hemoglobin for clinical purposes two chromo- metric methods are at present largely employed, that of Gowers and V. Fleischl. All chromometric methods are based on the principle that if two equally thick and equally well-illuminated solutions pre- sent the same intensity of color, their richness in coloring-matter is the same. There are two methods by which this can be done: (i) By diluting the blood to be examined wdth water until the shade of color corresponds to that of a solution of hemoglobin of known strength (Gowers). (2) Diluting a given quantity of blood with a given quantity of water and then finding an identical color which repre- sents a previously determined quantity of hemoglobin (v. Fleischl). Gowers' hemoglobinometer consists (Fig. 102) of two glass tubes of exactly the same size. One, A, contains glycerin jelly colored with picro-carmine the shade of which corresponds to that of normal blood diluted 100 times, 20 c.mm. in 2000 c.mm. of water repre- senting a I per cent, solution. The other tube, B, is ascendingly graduated with 120 divisions, each one of which corresponds to 20 256 TEXT-BOOK OF PHYSIOLOGY. c.mm. With a graduated pipette 20 cubic millimeters of blood are accurately measured and blown into the bottom of the tube B, in which a few drops of distilled water have been placed so as to prevent coagulation. Water is then added drop by drop until the color of the diluted blood is exactly that of the standard. The division of the scale reached by the dilution will represent the relative per- centage of hemoglobin. If this tint is not obtained until the dilu- tion reaches 100 divisions, the quantity of hemoglobin is normal. If more water must be added, it is in excess; if less, it is diminished. If, for example, the 20 cubic miUimeters of blood from an anemic patient gave the standard tint at 60 divisions, the blood contained but 60 per cent, of the normal amount of hemoglobin. Fig. 102. — GowERs' Hemoglobinometer. A. Pipette bottle for distilled water. B. Capillary pipette. C. Graduated tube. D. Tube with standard dilution. F. Lancet for pricking the finger. — {Landois and Stirling.) Von Fleischl's hemometer consists of a metallic cell divided into two compartments, a and a', by a vertical partition (Fig. 103). In the former a definite quantity of blood is placed and diluted with a known quantity of water. Beneath the compartment a' is placed a glass wedge stained with the golden purple of Cassius or simi- lar pigment, the color of which passes from a deep red at one end to clear glass at the other (Fig. 104). To the side of this wedge is placed a scale ranging from o to 120. By means of the screw, R T, the glass wedge is moved until the color of the glass and diluted blood is identical. The illumination of the blood and glass wedge is accompanied by lamplight reflected from the white reflect- ing surface beneath. The depth of color of the glass opposite 100 on THE BLOOD. 257 the scale corresponds to that of normal blood. If, therefore, the colors are identical at 75 divisions, the blood contains but 75 per cent, of hemoglobin. Very frequently the diminution of corpuscles and hemoglobin Fig. 103. — Von Fleischl's Hemometer. K. Red colored wedge of glass moved by R. G. Mixing vessel vs^ith two compartments, a and a'. M. Table with hole to read off the percentage of hemoglobin on the scale P. T. To move K. S. Mirror of plaster-of-Paris. proceeds along parallel lines, in which case the amount of hemoglobin per corpuscle is supposed to be normal and the color-index = i. If the hemoglobin diminution is greater than the corpuscles, as is the case in many pathologic conditions, the color-index is less than unity. If the percentage of corpuscles is determined by the method of counting to be 80 per cent. (4,000,000 per cubic milli- meter) and the percentage of hemoglobin 60, the color- index is obtained by dividing the latter by the former; e. g., •f^ = 0.75. In other words, each corpuscle has but 0.75 per cent, of the normal amount of hemoglobin. Absorption Spectra. — Both oxyhemoglobin and reduced hemo- globin, Hke other soluble pigments, have an absorbing influence on certain waves of light, and hence give rise to absorption bands which 17 Fig. 104. — Tinted Glass Wedge of the VON Fleischl Hemometer. — {Da Costa's Hematology.) 258 TEXT-BOOK OF PHYSIOLOGY. can be studied with the spectroscope, and which are so character- istic as to serve for their identification. In principle a spectroscope consists of a prism which decomposes the hght from a narrow sht into a band of all the spectral colors. A form of spectroscope in common use is that shown in Fig. 105. It consists of a tube, B, which has at one end a sht that can be narrowed or widened by means of a screw. The light, having passed through it, falls on an achromatic convex lens (called the colhmator) at the opposite end of the tube which renders the diver- gent rays of light parallel. These parallel rays subsequently fall on the prism, by which they are dispersed and directed into the F13. 105. — The Spectroscope. A. Telescope. B. Tube for the admission of light and carrying the collimator. C. Tube containing a scale, the image of which when illuminated is reflected above the spectrum. D. The fluid exam- ined. — {Landois and Stirling.) tube. A, which is nothing more than a small telescope. On looking into it at the ocular end the spectral colors are seen If the light has been derived from the sun, the spectrum will present vertical dark hues, the so-called Fraunhofer's lines. They are given from A to F in Fig. 106. If a colored medium be held in front of the sht so that the light has to pass through it first, certain dark bands will appear in the spectrum, owing to the absorption of certain rays. Dilute solutions of arterial blood show two absorption bands between the Fraunhofer fines, D and E, in the green and yellow THE BLOOD. 259 portion of the spectrum. (See Fig. io6.) The band nearest D frequently designated as alpha is dark in the center and sharply defined. The band which lies toward E is broader and less sharply defined. As the amount of light absorbed varies with the concentration of the solution as well as its thickness, and gives rise to absorption bands of different widths and intensities, it becomes necessary, in order to obtain the characteristic bands, to employ only dilute solutions. The absorption spectra, as seen with different strengths of solu- tion one centimeter thick, are shown grapically in Fig. 107. It will be observed that solutions varying in strength from o.i per cent, to 0.6 per cent, give rise to the two characteristic bands, but with gradually Red. Orange. Yellow. Green. Cyan Blue. A a B C 40 50 Fig. 106. — Spectra of Hemoglobin and Some of its Compol^nds. Stirlhig.) Reduced Hemoglobin -{Landois and increasing breadths. With a percentage greater than 0.65 per cent, the light between D and E, the yellow-green, becomes extinguished and the two bands fuse together, forming a single band overlapping slightly the fines D and E. At the same time there is a progressive darkening of the violet end of the spectrum. At 0.85 per cent., all the fight is absorbed with the exception of a small amount of the red. Solutions less than o.oi per cent, to 0.003 P^^ cent, show but a single absorption band — that nearest D. A solution of venous blood or of reduced hemoglobin shows but a single absorption band (see Fig. 106), frequently designated as gamma, broader and less marked between the lines D and E, but extending sfightly beyond D. Fig. 108 shows in the same graphic 26o TEXT-BOOK OF PHYSIOLOGY. manner the increasing breadth of the absorption band with increas- ing strengths of solution, as well as the simultaneous absorption of light at both the red and violet ends of the spectrum. Compounds of Hemoglobin. — The .coloring-matter of the blood is characterized by the property of combining with and of again yielding up oxygen. The union is a chemic one, taking place under certain pressure conditions. It therefore may exist in two states of oxidation, distinguished by a difference in color and their absorption spectra. If- hemoglobin either in blood or in solution be shaken with air, it at once combines with oxygen and is con- verted into oxyhemoglobin, which imparts to the blood or solution a bright red or scarlet color. If the blood or solution be now deprived Fig. 107. — Graphic Representation OF THE Absorption of Light in A Spectrum by Solutions of Oxyhemoglobin of Different Strengths. The shading indi- cates the amount of absorption of the spectrum, and the numbers at the side the strength of the solu- tion. aCB D Fig. 108. — Graphic Representation OF THE Absorption of Light in a Spectrum by Solutions OF Hemoglobin of Different Strengths. The shading indi- cates the amount of absorption of the spectrum, and the numbers at the side the strength of the solu- tion. of oxygen, the oxyhemoglobin is converted into reduced hemoglobin, which imparts to the blood or solution a dark bluish or purple color. The quantity of oxygen absorbed by i gram of hemoglobin is estimated at 1.56 c.c. measured at 0° C. and 760 mm. of mercury. The compound formed by the union of oxygen and hemoglobin is a very feeble one ; for when the pressure is lowered the union becomes less stable, and as the zero point is approached, as in the Torricelhan vacuum, a rapid dissociation of the oxygen takes place. This, how- ever, is not due entirely to a fall of pressure but partly to the dis- sociating force of heat, which increases in power as the pressure falls. The same dissociation of oxygen can be brought about by passing through blood indifferent gases, such as hydrogen, nitrogen, carbon THE BLOOD. 261 dioxid, which lower oxygen pressure, or by the addition of reducing agents, such as ammonium sulphid or Stokes' fluid. These experimental determinations of the relation of oxygen to hemoglobin partly explain the oxidation and deoxidation of the hemoglobin in the lungs and tissues. As the blood passes through the lungs and is subjected to the oxygen pressure there, the hemoglo- bin combines with a definite quantity of oxygen, and on emerging from the lungs exhibits a bright red or scarlet color; as the blood passes through the systemic capillaries where the oxygen pressure in the surrounding tissues is low, the oxyhemoglobin yields up a por- tion of its oxygen, becoming deoxidized or reduced, and the blood on emerging from the tissues exhibits a dark bluish color. The portion of oxygen given up to the tissues is termed respiratory oxygen. In 100 parts of arterial blood the coloring-matter presents itself almost exclusively in the form of oxyhemoglobin. In passing through the capiharies about 5 per cent, only gives up its oxygen and becomes reduced, so that both kinds are present in venous blood. In asphyx- iated blood only reduced hemoglobin is present. It is this capa- bihty of combining with and of again yielding up oxygen, that enables hemoglobin to become the carrier of oxygen from the lungs to the tissues. Carbon Monoxid Hemoglobin. — Carbon monoxid is a con- stituent of both coal-gas and water-gas. From either source it is likely to accumulate in the air, and if inspired for any length of time produces a series of effects which may eventuate in death. If blood be brought into contact with this gas, it assumes a bright cherry-red color, which is quite persistent and due to the displacement of the loosely combined oxygen and the union of the carbon monoxid with the hemoglobin. The compound thus formed is very stable and resists the action of various reducing agents. The passage of air or of some neutral gas through the blood for a long period of time will gradually displace the carbon monoxid and enable the hemoglobin to again absorb oxygen. It is for this reason that partial poisoning with the gas is not fatal. It is to its power of displacing oxygen and form- ing a stable compound with hemoglobin and thus interfering with its respiratory function that carbon monoxid owes its poisonous properties. Examined spectroscopically, solutions of carbon mon- oxid hemoglobin exhibit two absorption bands closely resembling in position and extent those of oxyhemoglobin; but careful examina- tion shows that they are slightly nearer the violet end of the spectrum and closer together. (See Fig. 106.) A useful test for CO blood is the addition of caustic soda, which produces a cinnabar red pre- cipitate. Methemoglobin. — This is a pigment, closely related to oxy- hemoglobin, found in the blood after the administration of various 262 TEXT-BOOK OF PHYSIOLOGY. drugs, in cysts and in the urine in hematuria and hemoglobinuria. It is also produced when a solution of hemoglobin is exposed to the air and becomes acid in reaction and brown in color. The spectrum shows two absorption bands similar to oxyhemoglobin, but in addition a new and quite distinct band near the hne C, in the red. If the acid solution be rendered alkahne by the addition of ammonia, this band disappears and another makes its appearance near the line D. The addition of ammonium sulphid develops reduced hemoglobin, which, on the absorption of oxygen, produces again oxyhemoglobin, as shown by the spectroscope. Hematin. — Boiling hemoglobin or adding to it acids or alka- lies decomposes it and develops one or more proteid bodies to which the general term globulin has been given, and an iron-holding pigment termed hematin. This is regarded as an oxidation product of hemoglobin and constitutes about 4 per cent, of its composition. When obtained in a pure state, it is a non-crystalHzable blue-black powder with a metalHc luster. According as it is treated with acids or alkahes, two forms of hematin can be obtained (acid and alkahne), each of which has special properties, giving rise to different absorp- tion bands. Hemochromogen. — This pigment is derived from hemoglobin, of which it constitutes about 96 per cent., during decomposition in the absence of oxygen. In solution it produces a purple color, but soon absorbs oxygen and is converted into hematin. Hemin. — This pigment is a derivative of hematin, presenting itself in the form of microscopic rhombic plates or rods (Teichmann's crystals), which are so characteristic as to serve as tests for blood- stains in medico-legal inquiries. These crystals are readily obtained by adding to a small quantity of dried blood on a glass shde a few drops of glacial acetic acid and a crystal of sodium chlorid; after heating gently for a few minutes over a spirit lamp and then allowing the mixture to cool, crystallization of the hemin soon takes place. Hematoidin. — This term has been applied to a pigment which occurs in the form of yellow crystals in old blood-clots or in blood which has been extravasated into the tissues. In its chemic com- position and in its reactions it closely resembles bilirubin, the pigment of the bile, exhibiting the same characteristic play of colors on the addition of nitric acid. The Stroma. — The stroma of the red corpuscles obtained by the methods which dissolve out the hemoglobin has been shown by analysis to consist of from 60 to 70 per cent, of water and 40 to 30 per cent, of solid material, containing a proteid resembling cell- globulin, lecithin, cholesterin, and inorganic salts, among which potassium phosphate is especially abundant. THE BLOOD. 263 HISTOLOGY OF THE WHITE CORPUSCLES OR LEUKOCYTES. The histologic features of the white corpuscles can readily be observed under the same conditions as in the case of the red corpuscles. Within the smaller blood-vessels they are seen adhering to the walls of the vessel ; in a drop of freshly drawn blood they are found in the spaces between the rouleaux of red corpuscles. (See Fig. 96, p. 236.) Shape and Size. — In the resting condition, whether seen in the vessel or on the stage of the microscope, the white corpuscle, as its name implies, is grayish in color, round or globular in form, though often presenting a more or less irregular surface. Its diameter varies from 0.0004 to 0.0013 mm., though the average is about o.ooii mm. or about -jtwo inch. Structure. — A typical white corpuscle consists of a ground- substance uniformly transparent and apparently homogeneous, in which are embedded a number of granules of varying size, some of which are very fine, while others are larger. By various reagents it has been demonstrated that the granules are fatty, proteid, and carbohydrate (glycogen) in character. In the fresh cells the ex- istence of a nucleus is difficult of detection, though its presence can be demonstrated by the addition of acetic acid, which renders the perinuclear cytoplasm more transparent and makes the nucleus conspicuous and sharply defined. From its structure it is apparent that the white corpuscle belongs to the group of undifferentiated tissues and resembles the cells of the embryo in its earhest stages as well as the unicellular organism, the amoeba. Number of White Corpuscles. — The number of white cor- puscles per cubic millimeter of blood is much less than the number of red corpuscles, the ratio being in the neighborhood of i white to 700 red. This ratio, however, varies within wide hmits in different portions of the body and under normal variations in physiologic conditions. In the blood of the splenic artery there is but i white to 2260 red, while in the splenic vein there is i white to every 60 red; or about thirty-eight times as many as in the artery. In the portal vein there is i white to 740 red, while in the hepatic vein there is i white to 170 red. The total number of white corpuscles per cubic millimeter has been estimated at from 5000 to 10,000, though the average is about 7500. The number, however, is influenced by a variety of physio- logic conditions. The ingestion of food rich in proteid material raises the count from 30 to 40 per cent., as compared with the count before the meal. Fasting for a few days always lowers the count, and in a case of total abstinence of food for a week, reported by Luciani, the count fell to 861 per cubic milhmeter, after which it rose to 1530, where it practically remained for the succeeding three 264 TEXT-BOOK OF PHYSIOLOGY. Fig. 109. — Human Leukocytes show- ing Ameboid Movements. — (Frey.) weeks of the fasting period. In the new-born the number is greater than in adults — 17,000 to 20,000 per cubic milHmeter. Cabot states that 30,000 is never a high count after a meal in infants under two years. In the later months of pregnancy, especially in primi- parae, the number increases to 16,000 to 18,000. Many patho- logic conditions of the body also influence the count very con- siderably. The method for counting the white corpuscles is similar to that used in counting the red. The given volume of blood should, however, be diluted with 10 vol- umes of a one-third of one per cent, solution of acetic acid, which renders the red corpuscles invisible and thus facilitates the counting of the white. The pip- ette should have a larger bore than that used for the red, and a greater number of squares in the counting chamber should be counted, so as to diminish the percent- age of error. Physiologic Properties. — The white corpuscles possess the characteristic property of exhibiting movements simi- lar to those observed in the amoeba, and are therefore termed ameboid. These movements consist in alter- nate protrusions and re- tractions of portions of the cell body, as a result of which they exhibit a great variety of forms. (See Fig. 109.) The protruded pro- cess can also attach itself to some point of the sur- face on which it rests, and then draw the body of the corpuscle after it. By a repetition of this process the corpuscle can slowly creep about and change its position in space. In virtue of these Fig. iio. — Small Vessel of a Frog's Mesen- tery SHOWING DiAPEDESIS. W, W. Vas- cular walls, a, a. Poiseuille's space, r, r. Red corpuscles. /, /. Colorless cor- puscles adhering to the wall, and, c, c, in various stages of extrusion. /, /. Ex- truded corpuscles. — {Landois and Stirling.) {Triacid Stain.) I, 2, 3, 4. Small Lymphocytes. Contrast the faintly coIoilcI protoplasm of these cells in the triple stained specimen with their intensely basic protoplasm in the film stained with eosin and methylene- blue, 17 and 18. The cell body of 1 is invisible. Note the kidney-shaped nucleus in 4. 5, 6. Large Lymphocytes. With this stain the nucleus reacts more strongly than the protoplasm; with eosin and methylene-blue (19, 20), on the contrary, the protoplasm is so deejjly stained that the nucleus appears pale by contrast. This peculiarity is also observed in the smaller forms of lymphocytes. 7, 8. Transitional Forms. Note the moderately basic and indented nucleus, and the almost hyaline non- granular protoplasm. Compare 8 with the myelocyte, 7, Plate I, these cells differing chiefly in that the myelocyte contains neutrophile granules. 9, 10, II. Polynuclear Neutrophiles. These ceils are characterized by a polymorphous or polynuclear nucleus, sur- rounded by a cell body filled with fine neutrophile granules. In 11 the nuclear structure is obviously separated into four parts; in 9 it is moderately, and in 10 markedly, polymorphous. 12, 13. Eosinophiles. The nuclei are not unlike those of the polynuclear neutrophile, except that they are somewhat less convoluted, and poorer in chromatin, staining less intensely. The protoplasm is filled with coarse eosinophile granules, the characteristics of which are clearly illustrated by 13, a "fractured" eosinophile. 14. Eosinophilic Myelocyte. Compare with 15 15, 16. Myelocytes. {Neutrophilic.) These cells are morphologically similar to 14, except that they contain neutrophile instead of eosinophile granules. Note that the granules of the myelocyte are identical with those of the polynuclear neutrophile. A dwarf form of myelocyte is represented by 16. {Eosin and Methylene-blue.) i-j, 18. Small Lymphocytes. Note the narrow rim of pseudo-granular basic protoplasm surrounding the nucleus, and the pale appearance of the latter. 19, 20. Large Lymphocytes. Budding of the basic zone of protoplasm is represented by 20. Both of these cells belong to the same type as 5 and 6. 2£, 22. Large Mononuclear Leukocytes. Compared with 19 and 20, these cells have a decidedly less basic protoplasm, but a somewhat more basic nucleus. In the triple stained film these differences can- not be detected, so that they must be classed as large lymphocytes. 23. Transitional Form. The distinction between this cell and 24 is not marked; the nucleus of the latter simply being somewhat more basic and convoluted. 24, 25, 26, 27. Polynuclear Neutrophiles. With this stain these cells show a feebly acid protoplasm, and lack granules. Note that the more twisted the nucleus the deeper it is stained. Compare with 9, 10, and II. 28, 29. Eosinophiles. Compare with 12 and 13. 30. Eosinophilic Myelocyte. Compare with 14. 31. Basophile. {Finely granular.) This cell is characterized by the presence of exceedingly fine ''-granules, staining the pure color of the basic dye. The nucleus is markedly convoluted and deficient in chromatin. The cell here shown was found in normal blood. 32. ^T„ 34, 35, 36. Mast Cells. . The granules take a modified basic color, as shown by their royal-purple tint in this illustration. Note their unusually large size and ovoid shape in 35, their pecuHar distribution in 35 and 36, and their irregularity in size in 32 and 36. With the triacid mixture these granules, as well as those of the finely granular basophile, 31, remain unstained, showing as dull-white stippled areas in the cell body. The nuclear chromatin of the mast cell is so delicate and so feebly stained that it is barely visible. These cells were found in the blood of a case of spleno- medullary leukemia. PLATE I. Q ••:■ •?.•*• 13 '°§o<4»J'>'« 17 18 ^..^■■~- ^■^^x oo( )0 26 27 34 •3'5|?»' 35 f* 36 '%.#«.«•• The Leukocytes. (i-i6, Triacid Stain; 17-36, Eosin and Melhylene-blue.) (E. F. Faber, lee.) (From DaCosta's '-Clinical Hematology.") THE BLOOD. 265 ameboid movements the corpuscle can appropriate small particles of pigment, such as indigo or carmine, and after a short time eliminate them from various parts of the surface. It is also capable of thrusting a process into and through the wall of the capillary vessel, after which the remainder of the corpuscle follows (Fig. no). This continues until the corpuscle is outside the vessel and in the lymph-space, where it resumes its original shape and movement. This process is best observed in inflammatory conditions, when the blood has come to rest and the vessels are occluded with both red and white corpuscles. To this passage of the white blood-corpuscles through the capillary wall the term diapedesis is given. The move- ments of the white corpuscles are increased by a rise in temperature up to 40° C, beyond which they cease, owing to the coagulation of the cell-substance. A low temperature also arrests the movements. Induced electric currents also cause contraction and death of the cell. Moisture and oxygen are necessary to their activity. From their similarity to lower organisms the white corpuscles may be regarded as independent organisms living in the animal fluids, just as the amoeba Uves in its natural Hquid medium. Classification. — With the aid of the tricolor staining fluid of Ehrhch four distinct forms of white corpuscles or leukocytes can be demonstrated to be present in the blood, viz.: 1. Small lymphocytes, so called from their resemblance to the cor- puscles of the lymph-glands, consisting of a small dark nucleus surrounded by a very thin layer of cytoplasm. 2. Large mononuclear lymphocytes, which represent the preceding type at a later stage of development and in the possession of a large amount of perinuclear cytoplasm more or less hyahne and devoid of granules. The nucleus is often deeply notched, resembhng a horseshoe in shape. This cell is capable of executing ameboid movements. 3. Polymorphonuclear leukocytes or neutrophiles, which represent the adult condition of the cell. The nucleus is irregular and assumes a variety of shapes in different cells, a feature which has suggested the name given to the cell. The perinuclear cyto- plasm contains a number of granules which are made evident when stained with the neutral mixture of Ehrlich. These cells exhibit active ameboid movements. They make up about 60 to 70 per cent, of the whole number of the white blood-cells. 4. Eosinophile cells, the granules of which stain most readily with acid stains like eosin. The granules are spheric and larger than in the previous cell. The nucleus is pale and irregular in shape. The eosinophile cell is regarded as the old or "over- ripe" cell and is the most actively ameboid of all the cells. It is present to the extent of from | to 4 per cent. 266 TEXT-BOOK OF PHYSIOLOGY. Origin of White Corpuscles. — The white corpuscles which are present in the blood are believed to be derived from the lymphocytes or lymph-corpuscles which find their way into the blood at the points where the lymph-ducts discharge their lymph: viz., at the junc- tions of the internal jugular and subclavian veins. Along the course of the lymph-vessels are to be found, in different regions of the body, numerous lymph-glands the meshes of which are filled with small, colorless, nucleated cells, which arise by self-division and rep- resent the early stages in the development of lymphocytes. Similar corpuscles are found in the mucous membranes, skin, spleen, and the fluids of the tissues. As the lymph flows through the glands these cells are washed out and carried direct to the blood. In their passage they grow in size by increasing the amount of their cytoplasm and even- tually become normal adult leukocytes. After an unknown period of life they undergo dissolution and disappear. Chemic Composition. — The chemic composition of the white corpuscles has been inferred from an analysis of pus-corpuscles, with which they are practically identical, and of lymph-corpuscles from the lymph-glands. Of the corpuscle about 90 per cent, is water and the remainder soHd matter consisting mainly of proteids, of which nuclein, nucleo-albumin, and cell globulin are the most abundant. The two former are characterized by the presence of a considerable quantity of phosphorus, amounting to as much as 10 per cent. Lecithin, fat, glycogen, and earthy and alkahne phos- phates are also present. Functions. — The functions of the white corpuscles are but im- perfectly known, and at present no positive statements can be made. It has been suggested that wherever found in the body, whether in blood or tissues, they are engaged in the removal of more or less in- soluble particles of disintegrated tissues, in attacking and destroying more or less effectively various forms of invading bacteria and thus protecting the body against their deleterious actiVity. This they do by surrounding, enveloping, and incorporating either the tissue par- ticle or bacterium and digesting it. On account of this swallowing action these cells were termed by Metchnikoff phagocytes and the process phagocytosis. He regards them as the general scavengers of the body. It has been suggested that they are also engaged in the absorption of fat from the lymphoid tissue of the intestine. In their dissolution they contribute to the blood-plasma certain proteid materials which assist under favorable circumstances in the coagu- lation of the blood. HISTOLOGY OF THE BLOOD-PLATES. The blood-plates or plaques are small histologic elements circu- lating in the blood-plasma. They were discovered by Hayem, who THE BLOOD. 267 applied to them the term hematoblasts, on the supposition that they were the early stages in the development of the red corpuscles. This is now known to be erroneous. On account of their specific, distinct characters, and their constant presence in the blood of hving animals (guinea-pig and bat), they are now regarded as normal constituents of the blood and designated as the third corpuscle. When blood is freshly drawn from the body, the plaques rapidly undergo disintegra- tion and disappear; but by treating the blood with osmic acid, the form and structure of the plaque may be retained. The blood-plaque may be defined as a colorless, grayish-white, homogeneous or finely granular protoplasmic disk, varying in diam- eter from 1.5 to 3.5 micro-millimeters. The edges are rounded and well defined, but it is not certain whether they are only flattened or are shghtly biconcave. There is, however, no nucleus. The ratio of the plaques to the red corpuscles is i to 18 or 20, and the total number per cubic miUimeter has been estimated to be 250,000 to 300,000. When blood is shed they tend to adhere to each other and form irregular masses known as Schultze's granular masses. If threads are suspended in blood, the plaques accumulate in enormous numbers upon them and appear to form a center from which fibrin filaments radiate as coagulation proceeds. The white thrombi which form in blood-vessels in consequence of diseased states — e. g., endocarditis, atheromatous ulceration, etc. — are composed very largely of blood- plaques and fibrin threads. The function of the blood-plaques is unknown, but it has been surmised that in some way they are, like the leukocytes, concerned in the coagulation of the blood. When- ever they are diminished in number, as in purpura and hemophilia, coagulation takes place very slowly. The blood-plaques can be seen with high powers of the micro- scope in the blood-vessels of the omentum of the guinea-pig and rat, especially when the blood-stream begins to slow. They are also readily seen in the blood-vessels of subcutaneous connective tissue of various animals, and especially in that of the new-born rat. A small quantity of this tissue moistened with normal saline and exam- ined microscopically with suitable powers will show large numbers of plaques within the blood-vessels. THE TOTAL QUANTITY OF THE BLOOD; ITS GENERAL COMPOSITION. The determination of the total quantity of the blood in an animal is best made by the chromometric method, somewhat modified at present, of Welcker. This consists, first, in bleeding an animal, collecting all the blood it yields, and weighing it ; second, in washing out the vessels with a normal saline solution until the fluid comes from the veins clear and free from blood ; third, in mincing the tissues 268 TEXT-BOOK OF PHYSIOLOGY. of the body, after removal of the contents of the alimentary canal, soaking them in water for twenty-four hours, and then expressing them. All the washings are collected and weighed. A given volume of the normal defibrinatcd blood, treated with carbon monoxid so as to give it uniform color, is then diluted with water until its tint is identical with that of the washings similarly treated with carbon monoxid. From the quantity of water necessary to dilute the blood the quantity of blood in the washings is readily determined. The animal having been previously weighed and the weight of the contents of the alimentary canal deducted, the ratio of the total weight of the blood to the weight of the body at once becomes apparent. By this method it has been shown that the ratio of blood to body- weight in a human adult is i : 13; in an infant, 1 : 19; in a dog, i : 13; in a cat, i : 21. Thus an adult man of 75 kilos weight would have 5769 grams of blood. The amount of blood in the different organs has been determined by hgating the blood-vessels in the living animal, removing the organ, and after allowing the blood to escape subjecting the tissues to the chromometric methods described above. According Jo Ranke, the volume of the blood is distributed as follows : Heart, lungs, arteries, and veins, l; liver, I; muscles, J; other organs, ^. General Composition. — The results of the analyses of the blood will vary with the animal and the methods employed. The following table, taken from Gad, shows the average composition, expressed in whole numbers, of horse's blood. In essential respects the ratio of the constituents in human blood would not be materially different. One thousand parts of blood contain: {Water, 200 200 f Hemoglobin, 116 Solids, 128 ^ Other organic matter, 10 (Salts, 2 fWater, 604 604 Plasma...... 672 -j [ ISumin7::::i::.":::-":"i:-i:i 5I ^Solids, 68-^^.,' ' "7 ' Other orgamc matter, 3 I Potassium and sodium salts, 4 [Calcium and magnesium salts, i CHEMISTRY OF COAGULATION. The changes which eventuate in the formation of fibrin, and hence all the subsequent phenomena of coagulation, are chemic in character; but as these changes take place in organic compounds the composition of which is but imperfectly known, the intimate nature of the process is quite obscure. All the theories which have been advanced in explanation, though approximating the truth, are more or less incomplete and in some respects contradictory. Since the THE BLOOD. 269 coagulation is coincident with the appearance of the fibrin, the ante- cedents of this substance, the physical and chemic conditions which condition its development, and the succession of chemic changes in- volved must be determined, before any consistent theory can be established. Extra-vascular Coagulation. — At present it is generally be- lieved that the immediate factors concerned in extra-vascular coagu- lation are fibrinogen, a calcium salt, and a ferment-body. As to the manner in which these three bodies react one with another there is a diversity of opinion. At least five different theories are current at the present time, all of which have some features in common, though presenting points of difference. Alexander Schmidt long contended that fibrin was the result of a union of fibrinogen and paraglobuhn ; that the union was brought about by a ferment-body; that the presence of the neutral salts of the plasma was necessary to the activity of the ferment. Previous to his death in 1893 Schmidt modified his view as follows: The insoluble fibrin is developed out of a soluble fibrin derived from paraglobuhn, which in turn is a product of general cell disintegration; the conver- sion of the fibrinogen into fibrin is due to the activity of a ferment, thrombin, a derivative of pro-thrombin, a product of the disintegra- tion of leukocytes, lymph-cells, etc.; that the production of thrombin is conditioned by the presence of the neutral salts of the plasma in normal percentages; that no one of these salts, calcium included, acts in a specific manner; finally, that fibrin is not a compound of a pro- teid and calcium. Hammersten, as a result of many years of investigation, believes that paraglobuhn is not necessary to the process, fibrinogen alone being transformed into fibrin under the influence of the ferment, in the presence of a neutral salt, especially calcium, which acts specifically in a manner different from the sodium salts. Inasmuch as the quan- tity of fibrin produced is always less than the quantity of fibrinogen previously present, Hammersten concludes that the latter substance, under the influence of the ferment, undergoes a cleavage into two unequal portions, one of which remains in solution, the other solidify- ing as fibrin. While admitting that the calcium salts act specifically, he believes that they are concerned rather with the production of the ferment than the fibrin, for if the ferment is present in sufficient quantity coagulation takes place in a typical manner even in the total absence of calcium. Arthus and Pages conclude that for the transformation of fibrin- ogen into fibrin the calcium salts are absolutely essential and act in a specific manner; that the ferment causes a cleavage of fibrinogen into two substances, one of which remains in solution, the other com- bines with calcium to form fibrin. They offer in support of this 270 TEXT-BOOK OF PHYSIOLOGY. view the fact that if a i per cent, solution of potassium oxalate be added to blood in quantity sufficient to precipitate the calcium, coagu- lation will not take place; but if calcium is restored coagulation proceeds in the usual manner. They transfer the sphere of influence of calcium to the formation of the fibrin rather than to the formation of the ferment. Pekelharing's researches led him to the conclusion that there arises from the disintegration of the leukocytes a nucleo-proteid, pro-thrombin, which combining with the calcium salt forms the ferment thrombin. This compound then transfers the calcium to the fibrinogen, which in turn becomes fibrin; the latter is therefore a proteid-calcium compound. Lilienfeld asserts that fibrin formation is a cleavage process by which fibrinogen is separated into two bodies, one an albumose which remains in solution, the other a proteid to which he has given the name thromhosin. This cleavage is attributed to the action of the usual ferment, a product of the disintegration of leukocytes. Throm- bosin combines, according to Lilienfeld, with calcium to form fibrin. In a critical examination of these different theories Hammersten denies that fibrin is a compound of a proteid and calcium ; for chemic analysis of both fibrinogen and fibrin shows that the former contains as much calcium as the latter, and that therefore the view of coagu- lation according to which fibrinogen unites with calcium to form fibrin is without foundation. On the contrary, he maintains that the specific influence of the calcium is directed toward the production of the ferment, for if this be present in sufficient quantity coagulation takes place in a typical manner, no matter whether the blood has been decalcified by potassium oxalate or not. Intra-vascular Coagulation. — So long as the relations of the blood and the vascular system remain physiologic no coagulation occurs in the vessels. The reason assigned for this is that the fer- ment, though continually being produced, is as rapidly being de- stroyed, and hence never accumulates in amount sufficient to develop fibrin. This view is supported by the fact that if a solution of cell- protoplasm, leukocytes, lymph-corpuscles, etc., presumably contain- ing a large amount of the ferment, be injected into the blood-vessels, extensive intra-vascular coagulation promptly follows. It is also believed that the lining of the blood-vessel in some unknown way restrains the coagulation process even though the circulation has come to rest. Under pathologic conditions of the circulatory apparatus, espe- cially of the internal lining, intra-vascular coagulation frequently arises, though the process can not be considered as identical with extra-vascular coagulation. Many pathologists assert that in its origin, mode of formation, and structure the intra-vascular coagulum THE BLOOD. 271 or thrombus is not a true coagulum as ordinarily understood, but rather a conglutination of blood-plaques and leukocytes. Whenever the integrity of the internal wall of the vessel is impaired by disease or by the introduction of foreign bodies, there is primarily a de- position and accumulation of blood-plaques at the injured area or on the foreign body which constitutes to a large extent the mass of the thrombus which at once forms. The thrombi which form on the surface of atheromatous ulcers, on the valves of the heart, and in the veins in consequence of diseased states, on threads or needles passed through the vessels, at the orifices of torn blood-vessels, consist largely of blood-plaques. A thrombus so formed may con- tain a number of dehcate fibrin threads, which, however, present a different appearance from the fibrin of the extra- vascular clot. In the thrombi which form around foreign bodies there is always a larger quantity of fibrin than in those originating from causes wholly within the vessel. CHAPTER XII. THE CIRCULATION OF THE BLOOD. Each organ and tissue of the body is the seat of a more or less active metaboHsm, the maintenance of which is essential to its physio- logic activity. This metabohsm is characterized by the assimilation of food materials and the production of waste products; that it may be maintained it is imperative that there shall be a continuous supply of the former and a continuous removal of the latter. Both condi- tions are subserved by the blood. In order, however, that this fluid may fulfil these functions it must be kept in continuous movement, must flow into and out of the tissues in volumes varying with their activity, under a given pressure and with a certain velocity. The apparatus by which these results are attained is termed the circulatory apparatus. This consists of a central organ, the heart; a series of branching diverging tubes, the arteries; a net- work of minute passageways with extremely dehcate walls, the capil- laries ; a series of converging tubes, the veins. These structures are so arranged as to form a closed system of vessels within which the blood is kept in continuous movement mainly by the pressure pro- duced by the pumping action of the heart, though aided by other forces. (See Fig. 1 1 1 .) In this system a particle of blood which passes any given point will eventually return to the same point, no matter how intricate or tortuous the route may be through which it in the meanwhile travels ; for this reason the blood is said to move in a circle, and the movement itself is termed the circulation. In order to understand the reasons for the movement of the blood in one direction only, as well as for many other phenomena connected with the circulation, a knowledge of the structure of the heart and its internal mechanism is of primary importance. THE PHYSIOLOGIC ANATOMY OF THE HEART. The heart is a cone or pyramid-shaped hollow muscular organ situated in the thorax just behind the sternum. The base is directed upward and to the right side ; the apex downward and to the left side, extending as far as the space between the cartilages of the fifth and sixth ribs. In this situation the heart is enclosed and suspended in a fibroserous sac, the pericardium, attached to the great vessels at its base. 272 THE CIRCULATION OF THE BLOOD. 273 The heart is a double organ, consisting of a right and a left half, separated by a vertical septum. The general cavity of each side is partially subdivided by a transverse constriction into two smaller cavities, an upper and a lower, known respectively as the auricle and the ventricle. The heart may therefore be said to consist of four cavities, the walls of which are composed of muscle-tissue. Of these four cavities, the right auricle and the right ventricle constitute the venous heart; the left auricle and the left ventricle, the arterial heart. The right auricle is quadrangular in shape and presents on its posterior aspect two large openings, the termi- nations of the two final trunks of the venous system, the superior and in- ferior vence cava (Fig. 112). Below, the auricle communicates with the ven- tricle by a large opening which, from its position, is termed the auriculo- ventricular opening. The walls of the auricle are extremely thin, not meas- uring more than two milhmeters in thickness. The right ventricle, as shown on cross-section, is crescentic in shape owing to the projection of the ven- tricular septum. It presents at its upper left angle a cone-shaped pro- longation, the comis arteriosus. From this prolongation, and continuous with it, arises the pulmonary artery. The wall of the ventricle measures in the middle about four milhmeters in thick- ness. The inner surfaces of the ven- tricle show: (i) a complicated system of muscle ridges and bands, the col- umned carnecB (fleshy columns), and (2) a set of muscle projections, the musculi papillares (papillary muscles), which arise by a broad base from the walls of the ventricle and project upward toward the auriculo- 18 Fig. III. — Diagram of Circula- tion. I. Heart. 2. Lungs. 3. Head and upper extremi- ties. 4. Spleen. 5. Intestine. 6. Kidney. 7. Lower extremi- ties. 8. Liver. — (Dalton.) 274 TEXT-BOOK OF PHYSIOLOGY. ventricular opening. From the apex of each papillary muscle there are given off fine tendinous cords, the chorda tendinccE, which become attached above to the auriculo-vcntricular valve. Fig. 112. — The Right Auricle and Ventricle Opened, and a Part of Their Right and Anterior Walls Removed, so as to show Their Interior. i — I- Superior vena cava. 2. Inferior vena cava. 2'. Hepatic veins cut short. 3 Right auricle. 3'. Placed in the fossa ovalis, below which is the Eustachian valve. 3". Is placed close to the aperture of the coronary vein. H — h- Placed in the auriculo-ventricular groove, where a narrow portion of the adjacent walls of the auricle and ventricle has been preserved. 4, 4. Cavity of the right ventri- cle; the upper figure is immediately below the semilunar valves. 4'. Large columna carnea or musculus papillaris. 5, 5', 5". Tricuspid valve. 6. Placed in the interior of the pulmonary artery, a part of the anterior wall of that vessel having been removed, and a narrow portion of it preserved at its commencement, where the semilunar valves are attached. 7. Concavity of the aortic arch close to the cord of the ductus arteriosus. 8. Ascending part or sinus of the arch cov- ered at its commencement by the auricular appendix and pulmonary artery. 9. Placed between the innominate and left carotid arteries. 10. Appendi.x of the left auricle. 11, 11. The outside of the left ventricle, the lower figure near the apex. — {Allen Thomson.) The left auricle, similar in general shape to the right, presents posteriorly four openings, the terminations of the four final trunks of the venous system of the lungs, the pulmonary veins. Below is THE CIRCULATION OF THE BLOOD. 27s placed the corresponding auriculo-ventricular opening. The wall of the auricle measures about 3 mm. in thickness. The left ventricle (Fig. 113) is conic in shape from above downward and oval or cir- cular in shape on cross-section. At its upper right angle it presents Fig. 113. — The Left Auricle and Ventricle Opened and a Part of Their Anterior and Left Walls Removed. J. — The pulmonary artery has been divided at its commencement; the opening into the left ventricle is carried a short distance into the aorta between two of the segments of the semilunar valves; and the left part of the auricle with its appendix has been removed. The right auricle is out of view. i. The two right pulmonar}' veins cut short; their open- ings are seen within the auricle, i'. Placed mthin the cavity of the auricle on the left side of the septum and on the part which forms the remains of the valve of the foramen ovale, of which the crescentic fold is seen toward the left hand of i'. 2. A narrow portion of the wall of the auricle and ventricle preserved round the auriculo-ventricular orifice. 3, 3'. The cut surface of the walls of the ventricle, seen to become ver}' much thinner toward 3", at the apex. 4. A small part of the anterior wall of the left ventricle which has been preserved with the principal anterior columna carnea or musculus papillaris attached to it. 5' 5- Musculi papillares. 5'. The left side of the septum, between the two ventricles, within the cavity of the left ventricle. 6, 6'. The mitral valve. 7. Placed in the interior of the aorta, near its commencement and above the three segments of its semilunar valve which are hanging loosely together. 7'. The exterior of the 276 TEXT-BOOK OF PHYSIOLOGY. a circular orifice, the margins of which give attachment to the walls of the aorta, the main arterial trunk of the systemic circulation. The inner surfaces of the ventricle show a similar though better devel- oped system of columnae carneas, muscuH papillares, chordae tendineae, etc. The wall of the left ventricle measures about 11,5 mm. in thick- ness in the middle. The Endocardium. — The cavities of both the right and left sides of the heart are lined by a thin firm connective-tissue membrane, closely adherent to the muscle- tissue, termed the endocar- dium. It also contains elastic fibers and smooth muscle- fibers. Its entire surface is covered over with a layer of polygonal endothelial cells. This membrane serves to re- sist undue distention of the heart during contraction and to prevent separation of the muscle-fibers. The endocar- dium is continuous with the lining membrane of the blood- vessels. The Cardio- pulmonary Vessels. — Though the two sides of the heart are separ- ated from each other by a vertical septum, they are ana- tomically and physiologically connected by the intermedia- tion of the pulmonary system of vessels: viz., the pulmonary artery, capillaries, and veins (Fig. 114). The pulmonary artery arises from the conus arteriosus of the right ventricle. After a short upward course it divides into a right and a left branch, which enter corresponding lungs. The vessel at once divides and subdivides into a number of branches, which, after fol- lowing the bronchial tubes to their termination, give origin to capil- laries that surround the air-cells of the pulmonary lobules. The capillaries in this situation are extremely abundant and well Fig. 114. — Diagram of the Heart and Pulmonary Circulation in Mamma- lians, a. Right auricle, b. Right ven- tricle, c. Pulmonary artery, d. Lungs. e. Pulmonary vein. /. Left auricle, g. Left ventricle, h. Aorta, i. Vena cava. — (Dalton.) great aortic sinus. 8. The root of the pulmonary artery and its semilunar valves. 8'. The separated portion of the pulmonary artery remaining attached to the aorta by 9, the cord of the ductus arteriosus. 10. The arteries rising from the summit of the aortic arch.- — {Allen Thomson.) THE CIRCULATION OF THE BLOOD. 277 developed. They lie close to the inner surfaces of the air-cells. The blood is thus brought into intimate relationship with the pulmonary air, and the exchange of gases — the excretion of carbon dioxid and the absorption of oxygen — for which the cardio-pulmonary vessels exist, is readily accomplished. The pulmonary veins which return the blood to the heart are formed by the convergence and union of the small veins which emerge from the capillary sys- tem. The final trunks thus formed, the four pulmonary veins, — two from each lung, — enter the posterior wall of the left auricle. The Course of the Blood through the Heart. — There is thus established a pathway between the venae cavas on the right side and the aorta on the left side, by way of the right side of the heart, the cardio- pulmonary vessels, and the left side of the heart. The venous blood flowing toward the heart is emptied by the supe- rior and inferior venae cavas into the right auri- cle, from which it passes through the auriculo- ventricular opening into the right ventricle (Fig. 115); thence into and through the pulmonar}' artery and its branches to the pulmonary capil- laries, where it is arterialized by the exchange of -gases — the giving up of a portion of carbon dioxid to the lungs and the absorption of oxygen — and changed in color from bluish-red to scarlet. The arteriahzed blood, flowing toward the heart, is emptied by the pul- monary veins into the left auricle, from which it passes through the auriculo-ventricular opening into the left ventricle; thence into the aorta and its branches to the systemic capillaries, where it is Fig. 1 1 5 . — Diagram of Course of Blood through THE Heart, i, 2. Superior and inferior venae cavse. 3. Right auricle. 4. Right ventricle. 5, 5, 5. Pulmonary artery and branches. 6, 6. Pulmonary veins. 7. Left auricle. 8. Left ventricle. 9. Aorta. 10. Innominate artery. II. Left carotid artery. 12. Left subclavian arter}'. — -{After Moral and Doyon.) 278 TEXT-BOOK OF PHYSIOLOGY de-arterialized by a second but opposite exchange of gases — the giving up of a portion of its oxygen to the tissues and the absorption of carbon dioxid from the tissues — and changed in color from scarlet to bluish-red. The venous blood is again returned by the systemic veins to the venas cavae. Though the blood is thus described as flowing first through the right side and then through the left side, it must be kept in mind that the two sides fill synchronously; that while the blood is flowing into the right side from the venae cava;, it is also flowing from the pulmonary veins into the left side in equal quantities and velocities. Though there is but one set of capillaries, as a rule, between arteries and veins, there is an exception in the case of the arteries and veins of the abdominal viscera. Thus the veins emerging from the capillaries of the stomach, intestines, pancreas, and spleen, instead of passing directly to the inferior vena cava, unite to form a large vein — the portal vein — which enters the liver. In this organ the portal vein divides to form a second capillary system which is in close relation to the liver cells and from which arise the veins which unite to form the hepatic veins. These latter vessels empty into the inferior vena cava just below the diaphragm. From the foregoing facts physiologists frequently divide the general circulation into: 1. The pulmonary circulation, which includes the course of the blood from the right side of the heart through the lungs, to the left side of the heart. 2. The systemic circulation, which includes the course of the blood from the left side of the heart through the aorta and its branches, through the capillaries and veins to the right side of the heart. 3. The portal circulation, which includes the course of the blood from the capillaries of the stomach, intestines, pancreas, and spleen through the portal vein to the liver. Orifices and Valves. — The movement of the blood along the path of the circle above outhned is accomphshed by the alternate contraction and relaxation of the muscle walls of the heart. That the movement may be a progressive one, that there shall be no regurgitation during the relaxation, it is essential that some of the orifices of the heart be closed. This is accomphshed by the heart valves. The right auriculo-ventricular opening is surrounded and strength- ened by a ring of fibrous tissue to which is attached a membrane par- tially subdivided into three portions or cusps, which during the period of relaxation are directed into the ventricle (Fig. 116); during the period of contraction they are raised and placed in complete apposi- tion, when they act as a valve preventing a backward flow into the auricle (Fig. 117). In the former position the valve is open; in the THE CIRCULATION OF THE BLOOD. 279 Fig. 116. — Right Cavities of the Heart. Auriculo-ventricular valves open, arte- rial valves closed. — (Dai/on.) latter, shut. For these reasons this structure is known as the tri- cuspid valve. This valve is formed of fibrous tissue de- rived from the fibrous ring, some muscle-fibers, covered over by a reduplication of the endocardium. To the under surface and to the edges of this valve the ten- dinous cords of the papillary muscles are firmly and intri- cately attached. These cords are just sufficiently long to permit closure of the valve and to prevent their being floated into the auricle. The orifice of the pul- monary artery is also sur- rounded by a ring of fibrous tissue to which are attached three semilunar or pocket- shaped membranes, the semilunar valves. Each valve is formed by a reduplication of the endocardium strengthened by fibrous tissue. In the center of the free edge of the valve there is a small nodule of fibro- cartilage (the corpus Aur- antius). The outer edge of the valve is strengthened by a delicate fibrous band. A similar band strengthens the convex attached por- tion of the valve just where it is joined to the fibrous ring. A third set of fibers pass toward the nodule, in- terlacing in all directions. Two narrow crescentic- shaped areas (the lunulas) near the free edge are de- void of these fibers. Dur- ing the period of relaxation ^ ^ ^ , of the heart the edges of Fig. 117. — Right C.a.vities of the Heart. , , _ . 1 Auriculo-ventricular valves closed, semi- "-^^ val\ es aie m CiOSC lunar valves open. — (Daiton.) apposition and prevent a 28o TEXT-BOOK OF PHYSIOLOGY. return of the blood into the ventricle (Fig. ii6); during the con- traction they are directed into the artery (Fig. 117). In the former position they are shut; in the latter, they are open. The left auriculo-ventricular opening is provided with a similar though better developed fi- brous ring and membran- ous valve. It is, however, subdivided into but two portions or cusps, and is therefore termed the bi- cuspid valve, or, from its fancied resemblance to a bishop's mitre,, the mitral valve. The general ar- rangement, connections, and mode of action of this valve are similar in all re- spects to those of the tricus- pid valve. The orifice of the aorta is also surrounded by a ring of fibrous tissue to which are attached three semilunar or pocket-shaped valves (Fig. 113), which in their arrangement, connections, and mode of action are similar in all respects to those at the orifice of the pulmonary artery. The anatomic relations of the cardiac orifices one to the other and the appearance presented by the valves when closed are repre- sented in Fig. 118. The Heart Muscle-fibers and Their Ar- rangement. — The muscle-fibers of the heart, though transversely striated and nucleated, diijfer in shape and arrangement from those found in any other situation. The individual fiber is short and broad and usually divided at one or both ends. By this means the fibers are united not only longitudinally, but laterally. (See Fig. 119.) The fibers are devoid of a sarcolemma and united one to the other by a cement material. The entire musculature is permeated and supported by connective tissue which is so arranged as to group the fibers in bundles or fasciculi of varying size. The arrangement of the muscle bundles is quite comphcated and in accordance with the functions of the individual portions of the Fig. 118. — Valves of the He.4rt. i. Right auriculo-ventricular orifice, closed by the tricuspid valve. 2. Fibrinous ring. 3. Left auriculo-ventricular orifice, closed by the mitral valve. 4. Fibrinous ring. 5. Aortic orifice and valves. 6. Pulmonic orifice and valves. 7, 8, 9. Muscular fibers. — {Bonamy and Bean.) Fig. 119. — Muscle- fibers FROM the Heart of a Mam- mal. — {Landois and Sliding.') THE CIRCULATION OF THE BLOOD. heart. In the auricles the bundles are arranged in two sets : an outer transverse set, which pass from auricle to auricle, and an inner longi- tudinal set, which pass over the auricles to be attached anteriorly and posteriorly to the connective tissue of the auriculo-ventricular groove. The longitudinal fibers of each auricle are practically in- dependent of each other. Circularly arranged fibers are present near the terminations of the vense cavae and pulmonary veins. In the ventricles the muscle-bundles are also arranged in two sets, a superficial longitudinal and a deep transverse, though their arrangement is some- what more complicated than that observed in the auricles. In a gen- eral way it may be said that the superficial lon- gitudinal fibers on both the anterior and poste- rior surfaces from their origin in the connective tissue of the auriculo- ventricular groove pass obliquely downward and forward from right to left toward the apex, where they turn back- ward and inward in a vortex, after which they ascend to terminate in the wall of the septum, the columnae carneae and musculi papillares. Longitudinal fibers are also found on the inner surface. The transverse fibers are very abundant and surround each ven- tricle separately. Between the superficial longitudinal and deep transverse fibers there are several layers of fibers which possess varying degrees of obliquity. The general arrangement of the fibers is such as to ensure a complete and simultaneous discharge of blood from both auricles and ventricles (Fig. 120). Fig. 120. — Muscle-fibers of the Ventricles. I. Superficial fibers, common to both ventri- cles. 2. Fibers of the left ventricle. 3. Deep fibers, passing upward toward the base of the heart. 4. Fibers penetrating the left ventricle. — {Sappey, after Bonamy and Beau.) 282 TEXT-BOOK OF PHYSIOLOGY. THE MECHANICS OF THE HEART. The immediate cause of the movement of the blood through the vessels is the contraction and relaxation of the muscle -walls of the heart, and more particularly of the walls of the ventricles, each of which plays alternately the part of a force-pump, and to a shght extent of a suction-pump. The motive power is furnished by the heart itself, by the transformation of potential energy, stored up during the period of rest, into kinetic energy — /. e., heat and mechanic motion. The contraction of any part of the heart is termed the systole; the relaxation, the diastole. As each side of the heart has two cavities the walls of which contract and relax in succession, it is customary to speak of an auricular systole and diastole, and a ventricular systole and diastole. As the two sides of the heart are in the same anatomic relation to each other, they contract and relax in the same periods of time. The movements of the heart, as well as many phenomena con- nected with the flow of blood through its cavities, have been deter- mined by observation of, and experiment on, the exposed heart of a mammal, — e. g., dog, cat, rabbit, — supplemented and corrected by experiments on the heart in its normal relations. V^aluable informa- tion as to the heart-beat and the influences which modify it has been obtained from experiments made on the isolated heart of the turtle, frog, and allied animals. If the thorax of a dog completely anesthetized is opened and artificial respiration established, the heart will be observed in active movement inside the pericardium. If this sac is divided and turned aside, the heart will be fully exposed to view. At the normal rate of movement characteristic of the dog it will be almost impossible to determine either the succession of events or their duration. But by observing the heart under different conditions at different rates of movement and with instrumental aids physiologists have succeeded not only in analyzing the movements, but in describing their sequence and in estimating their time duration. Thus it has been determined that the heart presents two distinct movements which alternate with each other in quick succession. One is the movement of contraction, or the systole, by which the blood contained within its cavities is ejected into the arteries — pulmonary artery and aorta; the other is the movement of relaxation, or the diastole, followed by a pause during which the cavities again fill up with the blood from the venag cavae and pulmonary veins. Sequence of Events. — It has been ascertained that the contrac- tion of the auricles and ventricles as well as their subsequent relaxations, though occurring with extreme rapidity, do not take THE CIRCULATION OF THE BLOOD. 283 place simultaneously but successively; that the contraction process passes over the heart in the form of a wave; that it begins, indeed, at the terminations of the great veins, then passes to and over the auricles, thence to and over the ventricles from base to apex with great rapidity, but occupying in these different regions unequal periods of time; that the relaxation immediately succeeds the con- traction, in the same order, and that at the close of the ventricular relaxation there is a period during which the whole heart is in repose, passively filling with blood. Changes in Position and Form. — In passing from the diastolic to the completed systolic condition the exposed heart undergoes changes both of position and form as the contraction rises to its maximum. This having been attained, the heart undergoes reverse changes until the original diastolic condition is regained. Thus at the time of the ventricular systole the apex is tilted upward, the entire heart is twisted on its axis from left to right and forced down- ward by the expansion and elongation of the pulmonary artery and aorta. At the time of the diastole, the reverse movements take place. It is probable, however, that these movements are not permitted to the same extent in the unopened chest, for the following reasons: the heart is enclosed in the pericardium, is supported posteriorly by the expanded lungs, and both posteriorly and inferiorly by the diaphragm, all of which cooperate in keeping the heart, and more particularly the right ventricle, in close contact with the chest- waU and limiting its movements By means of needles inserted into the apex of the heart, through the chest-walls, it has been shown by their slight movement that the apex is practically a fixed point. In the diastolic condition the shape of the heart near the base is eUiptic on cross-section, the' long diameter extending from side to side. In the completed systolic condition the shape of the same cross-section is that of a circle. In passing from the diastolic to the systolic con- dition the transverse diameter diminishes while the antero-posterior diameter increases, while the whole heart becomes somewhat more conic in shape. It is questionable if the vertical diameter per- ceptibly shortens. During the systole the heart hardens, increases in convexity, and is more forcibly pressed against the chest-wall. As this takes place suddenly, it gives rise to a marked vibration of the chest-wall, knovv'n as the cardiac impulse. This is princi- pally observed in the space between the fourth and fifth ribs, between the left edge of the sternum and a hne drawn vertically through the nipple. The cardiac impulse is synchronous with the cardiac svstole. 284 TEXT-BOOK OF PHYSIOLOGY. The Cardiac Cycle. — The entire period of the heart's pulsation may be divided into three phases, viz. : 1. The auricular contraction. 2. The ventricular contraction. 3. The pause or period of repose, during which both auricles and ventricles are at rest. These three phases collectively constitute a cardiac cycle or a cardiac revolution. The duration of a cycle, as well as the duration of each of its three phases, varies in different animals in accordance with the number of cycles which recur in a unit of time. In human beings in adult hfe there are about 72 cycles to the minute; the average duration therefore is 0.83 second. From this it follows that the time occupied by any one of the three phases must be extremely short and difficult of determination. From observations made on human beings and from experiments on animals the following estimates have been made and accepted as approximately correct: I. The auricular systole, 0.16 second. 2. The ventricular systole, 0.32 second. 3. The period of rest for both auricles and ventricles, c.32 second. The relations of these three phases to one another may be illustrated by the following dia- gram (Fig. 121), in which the space 1-2 is the duration of a cardiac cycle divided into eight equal spaces, each of which re- presents one-tenth of a second. The line A represents the auric- ular, the line V the ventricular phase. The rise in the line A represents the contraction; the fall and subsequent continuation, the relaxation and pause. The rise in the line V and its continuation represent the contraction; the fall and subsequent continuation, the relaxation and the pause. From this it is apparent that the auric- ular contraction or systole has a brief duration, 0.16 second, while the relaxation or diastole has a long duration, 0.64 second; that the ventricular contraction immediately following the auricular has a duration of 0.32 second, while the relaxation and diastole have a duration of 0.48 second; that the pause of the entire heart, that is, the period between the termination of the ventricular systole and the be- ginning of the next auricular systole, is only 0.32 second. The frequency of the heart-beat varies with a variety of con- ditions: e. g., age, sex, posture, exercise, etc. Fig. 121.- -The Phases of the Heart's Pulsation. THE CIRCULATION OF THE BLOOD. 285 Age. — The most important normal condition which modifies the activity of the heart is age. Thus : Before birth, the number of beats a minute averages 140 During the first year it diminishes to 128 During the third year it diminishes to 95 From the eighth to the fourteenth year it averages 84 In adult life it averages 72 Sex. — The heart-beat is more rapid in females than in males. Thus while the average beat in males is 72, in females it is usually 8 or 10 beats more. Posture. — Independent of muscle efforts the rate of the beat is influenced by posture. It has been found that when the body is changed from the lying to the sitting and to the standing position, the heart will vary as follows — from 66 to 71 to 81 on the average. Exercise and digestion also temporarily increase the number of beats. The Action of the Valves. — As previously stated, the forward movement of the blood is permitted and regurgitation prevented by the alternate action of the auriculo-ventricular and the semilunar valves. As a point of departure for a consideration of the action of the valves and their relation to the systole and diastole of the heart, the close of the ventricular systole may be conveniently selected. At this moment, if the blood is not to be returned to the ventricles, the semilunar valves must be instantly and completely closed. This is accomplished in the following manner: During the outflow of blood from the ventricles the valves are pushed outward toward the walls of the vessels, though not coming into contact with them; for behind them are the pouches of Valsalva, containing blood, continuous with and under the same pressure as that in the vessels themselves. With the cessation of the outflow and the beginning of the relaxation the pressure of the blood behind the valves suddenly forces them inward until their free edges, including the lunulee, come into complete appo- sition. By this means the orifices of the pulmonary artery and aorta are securely closed and a return flow prevented. Reversal of the valves is prevented by their mode of attachment to the fibrous rings of the orifices. During the ventricular systole the relaxed auricles have been filling with blood. With the ventricular relaxation this volume, or its equivalent, flows readily into the empty and easily distensible ventricles, its place being taken by an additional volume of blood flowing from the venae cavae and pulmonary veins. Whether the ventricles exert a suction power at the moment of their relaxation is an undecided question. A steady stream of blood into the auricles and ventricles continues throughout the entire period of rest until both cavities are filled. The tricuspid and bicuspid valves which hang down into the ventricular cavities are now floated up by cur- 286 TEXT-BOOK OF PHYSIOLOGY. rents of blood welling up behind them until they are nearly closed. The auricles now contract, forcing their contained volumes, or at least the larger portions of them, into the ventricles, which become fully distended. With the cessation of the auricular systole the ventricular systole begins. If the blood is not to be returned to the auricles at this moment, the tricuspid and mitral valves must be suddenly and com- pletely closed. This is readily accomplished by reason of the position of the valves, which have been floated up and placed almost in apposi- tion by the blood itself. With the beginning of the ventricular pressure the blood is forced upward against the valves until their free edges are brought together and the orifices closed. Reversal of these valves is prevented by the contraction and shortening of the papil- lary muscles, which in consequence exert a traction on their under surfaces. The blood now confined in the ventricle between the closed auriculo- ventricular and semilunar valves is subjected j to pressure from all sides. As the pressure rises proportionately to the vigor of the contraction, there comes a moment when the intra- ventricular pressure exceeds that in the aorta and pulmonary artery. Immediately the semilunar valves of both vessels are thrown open and the blood discharged. Both contraction and outflow continue until the ventricles are practically empty, after which ventricular relaxa- tion sets in, attended by a rapid fall of pressure. Under the influence of the positive pressure of the blood in the sinuses of Valsalva the semilunar valves are again closed, the column of blood supported, and regurgitation is prevented. With the accumulation of blood in the auricles the cardiac cycle is completed. Relative Functions of Auricles and Ventricles. — Though both auricles and ventricles are essential to the continuous movement of blood, they possess unequal values in this respect. The passage of the blood through the pulmonary and systemic vessels is accom- plished by the driving power of the right and left ventricles respec- tively, aided, however, by minor extra-cardiac forces. They may be regarded therefore as force-pumps. If the heart consisted of ventricles only, the flow of blood from the venae cavae and pulmonary veins would be temporarily arrested during their systole and their subsequent refilling delayed. This is obviated, however, by the addition of the auricles; for during the ventricular systole the blood continues to flow into the auricles, in which it is temporarily stored until the ventricular relaxation sets in. With this event the accumulated blood passes into the ventricles, which are thus practically filled before the auricular systole occurs by which the fining is completed. By this means there is no delay in the filhng of the ventricles, and hence their effective working as force-pumps is more readily secured. The auricles may therefore be regarded as feed-pumps. For this reason it is probable, notwithstanding the THE CIRCULATION OF THE BLOOD. 28: contraction of the circular muscle-libers at the terminations of the venous system, the flow of blood into the auricles is never entirely arrested. Regurgitation in these vessels does not occur for the reason that the pressure in the auricles is not higher than, if as high as, in the great veins. Synchronism of the Two Sides of the Heart. — If the balance of the circulation is to be maintained, the two sides of the heart must act synchronously. That they do so can be shown by attaching levers to their walls and thus recording their activities. The syn- chronism is so perfect that until recently it was generally believed to be dependent on nerve connections; but Porter has shown that if the ventricles are cut away from the auricles, in which the nerve mechan- ism seemed to lie, the synchronism of the former is not interfered with; that the apical halves of the ventricles will beat synchronously if perfused with blood through an artery; that a very small bridge of muscle-tissue will carry the wave of excitation from one part to neigh- boring parts of the ventricle. It is therefore probable that tlie syn- chronism is accomplished through muscle connections only. The left ventricle, in keeping with the greater work it has to do, has a greater development than the right, and therefore contracts more energetically. The ratio between the energy of the left and right sides is approximately 3 to i. Intra-cardiac Pressure. — It has been stated that during the pause of the heart when its cavities are filling with blood the semilunar valves are kept closed by the pressure of the blood in the pulmonary artery and aorta, a pressure due to the resistance, as will be explained later, offered to the flow of the blood mainly by the smaller arteries and capillaries; that max valve they are opened only when the press- ure of the blood within the ventricle exceeds that in the arteries. It be- comes, therefore, a matter of impor- tance to determine the extent of this pressure as well as its variations dur- ing the course of a cardiac cycle. This can be done by inserting a long catheter into either the right or left ventricle, through the jugular vein or the carotid artery respectively, and connecting its free extremity with a mercurial manometer. By the inter- position of a double valve such as represented in Fig. 122, it becomes possible, according to the direction the blood is permitted to .Tianometer mm valve to heart Fig. 122. — V. Fr.\xk's Valve. This is placed in the course of the tube between heart and manometer, so that the latter may be used as a maximum, minimum, or ordinary man- ometer according to the tap which is left open. — {Starling.) 288 TEXT-BOOK OF PHYSIOLOGY. to flow, to obtain either the maximal or the minimal pressure that occurs in the heart during a series of cycles. Thus Goltz found in the left ventricle of the dog a maximal pressure of 114 to 135 mm.; in the right ventricle, a pressure of 35 to 62 mm. Minimal pres- sures of — 23 to — 52 mm. for the left ventricle have also been obtained. The maximal pressure in the ventricles during the systole, though always higher than that in the arteries, is not a fixed or an invariable pressure, as it rises and falls with the latter from moment to moment. Within hmits the cardiac power, and therefore the intra-cardiac I)ressure, is capable of considerable increase. The function of the heart is to drive the blood through the vessels with a given velocity. This is only possible by first overcoming the resistance to the flow offered by the vessels, as indicated by the arterial pressure. As this is a variable factor, rising and falHng very considerably at times, the teart must meet and exceed each rise, if the circulation is to be main- tained. The power put forth by the heart is proportional to the work it has to perform. If the arterial pressure continues higher than the average for any length of time, the heart meets the condition by an hypertrophy of its walls. The Intra-ventricular Pressure Curve. — An accurate interpre- tation of the play of the heart mechanism necessitates the obtaining of a graphic record of the course of the intra-ventricular pressure, its varia- tions and time relations. With such a record may be compared the records of the pressures in the venae cavae, on the one hand, and in the aorta, on the other hand, and their relations one to another accurately defined. The intra-ventricular pressure has been obtained by specially de- vised manometers or tonometers or tono graphs, as they are variously termed, the construction of which is such as to enable them to respond instantly to the very rapid variations of the pressure which occur during the brief cardiac cycle. One of the best is that of Hiirthle. This consists of a small metallic tambour 5 or 6 millimeters in diam- eter, covered by a thin rubber membrane. A small button resting on the membrane plays against an elastic steel spring, by the tension of which the pressure of the blood is counterbalanced. The move- ments of the membrane are taken up, magnified, and recorded by a suitable lever. A long cannula is inserted into the right ventricle through the jugular vein or into the left ventricle through the carotid artery. Both cannula and tambour are filled with an alkahne solu- tion to prevent coagulation of the blood, and then joined air-tight. The pressure of the blood in the ventricle is thus transmitted by a hquid column to the tambour and to its attached lever. With such a manometer a curve is registered similar to that shown in Fig. 123. To obtain the absolute value of this curve in millimeters of mercury THE CIRCULATION OF THE BLOOD. y /\AMA/WWV\M/WV /V MAA/WWWWV O/ 2 J4 J it is necessary to previously graduate the instrument. An examination of the curve shows that previous to the ventricular contraction there is a very shght rise of pressure above that of the atmosphere, repre- sented by the hne a — b. This may be due to the inflow of blood from the auricle during the diastole. At o the pressure suddenly rises, passes quickly to its maximum value, (2), which is maintained with slight variations for some time, and then suddenly (3) begins to fall, and, rapidly reaches the hne of atmospheric pressure, or even passes below it, becoming negative in fact for a short period. The curve may also be taken as a record of the ventricular contraction, for there are reasons to beUeve that the two closely coincide through- out their entire course. A characteristic feature of this curve is the more or less horizontal portion comprised between the points 2 and 3, marked by several elevations and depressions, which has been termed the systolic plateau. With other forms of elastic man- ometers, especially those in which the transmission of the intra-ven- tricular pressure is effected by air or by a combination of air and li- quid, this portion of the curve is represented by a single peak, which is taken as an indication that the maximum pressure once reached is not maintained, but immediately begins to fall to its original level, notwithstanding the continued con- traction of the ventricle. Those who adhere to this view attribute the plateau to the closure of the orifice of the catheter by the con- tracting and approximating walls of the ventricle. There are reasons for believing, however, that the former curve is the more correct re- presentation of the course of the intra- ventricular pressure. Bayliss and Starhng photographed on a moving surface the oscillations of a fluid, a solution of sodium sulphate, in a capillary glass tube one end of whicli was closed, the other end placed in connection with an intracardiac catheter, the oscillations representing the variations in pressure. The photogram thus obtained resembles the curve obtained by Hiirthle's membrane manometer. The Relation of the Intra-ventricular Pressure Curve to the Intra-cardiac Mechanisms. — By itself the curve of the intra- ventricular pressure affords no indication as to events occurring within the heart: i. e., as to the times during the systole, of the closure of the auriculo-ventricular valves and the opening of the 19 '/ -2 a-tf s Fig. 123. — V. Curve of the pressure in the ventricle of the dog. — {Hilrthle.) A. Curve of the pres- sure in the aorta. The curves were taken simultaneously. s. Tuning-fork vibrations, loo per second. 290 TEXT-BOOK OF PHYSIOLOGY. semilunar valves, or the times during the diastole, of the closure of the semilunar valves and the opening of the auriculo-ventricular valves. By registering the curve of pressure in the aorta simultaneously with the pressure in the left ventricle (Fig. 123), and by comparing these with the curve of the successive differences of pressure in these two cavities as determined by the "differential manometer," it be- comes possible to mark on the ventricular pressure curve the points at which the foregoing events take place. During the systoHc plateau the blood is passing from the ventricle into the aorta. Independent of the slight elevations and depressions there is an absolute fall of pressure between the beginning and the end of the plateau. There is also a corresponding fall in the aortic pressure, corresponding to these two points. The curve of the dif- ference of pressure shows, however, that the ventricular pressure is slightly higher than the aortic. This fall in both ventricular and aortic pressures is due to the escape of blood from the arterial into and through the capillary system. At 3, however, whether completely emptied or not, the ventricle suddenly relaxes, and its pressure soon falls below that in the aorta. As soon as this takes place the semilunar valves must close, if regurgitation into the ven- tricular cavity is to be prevented. A comparison of the aortic pres- sure curve shows a shght notch, the "dicrotic notch," just preceding a slight elevation, the "dicrotic" wave. This notch is taken as the moment when the semilunar valves close. The corresponding point on the ventricular pressure curve has been placed just where the ordinate 4 cuts the descending portion. As yet, however, the pressure is higher in the ventricle than in the auricle, and so continues until near the line of atmospheric pressure. At this point the pressure in the auricle, due to the accumulation of blood during the ventricular systole, now forces open the mitral valve and the blood flows into the ventricle. The opening of the mitral valve occurs about the point where the ordinate 5 cuts the curve. The ventricular pressure curve affords but shght, if any, indication of the auricular systole. It apparently does not give rise to any noticeable increase in the ventricular pressure. The slight rise in the pressure curve, which just precedes the abrupt rise due to the ventricular systole, may be taken as an indication of an increasing pressure due to the inflow of blood from the auricle. As soon as the pressure in the ventricle exceeds that in the auricle the mitral valve closes. This is marked on the curve where the ordinate cuts it, at o. Coincident with this, the ventricular systole begins, and as the blood is contained within a closed cavity the pressure abruptly rises. A comparison of the aortic curve shows that for a short time during the ventricular systole, the pressure is falling, but at one point it turns at a sharp angle and rapidly rises. This is an indication that THE CIRCULATION OF THE BLOOD. 291 the semilunar valves are suddenly thrown open and the blood begins to pass into the aorta. This event occurs at a moment marked on the ventricular curve by the ordinate i. Beyond this point the pres- sure continues to rise, for the aortic pressure must not only be ex- ceeded, but a certain velocity must be imparted to the blood. Between the ordinates i and 4, the semilunar valves remain open and the blood passes into the aorta. In accordance with the foregoing the ventricular systole may be subdivided into two periods : 1. The period of rising tension, from the beginning of the systole to the opening of the semilunar valves, occupying from 0.02 to 0.04 second. 2. The period of ejection, from the opening of the semilunar valves to the end of the systole, occupying about 0.2 second. The ventricular diastole may also be divided into two periods : 1. The period of falling tension or relaxation, from the end of the systole to the time of lowest pressure in the ventricle, occupying about 0.05 second. 2. The period of filling, from the opening of the mitral valve to the beginning of the systole. Negative Pressure. — As shown by the ventricular pressure curve there is a moment when the pressure falls below atmospheric pres- sure, becoming negative to it. The extent to which this takes place, its duration and frequency, have never been satisfactorily determined. The cause of the negative pressure, its influence on the opening of the auriculo- ventricular valves, and on the entrance of blood into the ventricles are equally unknown. The most probable cause is an expansion of the base of the ventricles due to the enlargement of the aorta and pulmonary artery. That it is not due to the expansion of the thorax is evident from the fact that it is occurs when the thorax is open and the heart exposed. Heart-sounds. — Two sounds accompany each pulsation of the heart, both of which may be heard by applying the ear or the stetho- scope to the chest- walls, especially over the region of the heart. One of these sounds is low in pitch, dull and prolonged; the other is high in pitch, clear and short. These sounds can be approximately repro- duced by pronouncing the syllables lubb-dupp, lubb-dupp. The long dull sound occurs with the systole, the first phase of a new cardiac cycle, and is therefore termed the jirst sound; the short clear sound occurs at the beginning of the diastole, with the second phase of the cardiac cycle, and is therefore termed the second sound. The first sound is the systolic, the second the diastolic, sound. With the ear it can readily be determined that there is a brief pause between the first and second sounds, and a longer pause between the second and the first sounds. The duration of the first sound is almost equal to the 292 TEXT-BOOK OF PHYSIOLOGY. duration of the systole — viz., 0.3 second; the duration of the second sound is not more than o.i second. The systoHc sound is heard most distinctly over the body of the heart; the diastohc sound is heard most distinctly in the neighborhood of the third rib to the right of the sternum. The causes of the heart-sounds have enlisted the attention of clinicians and physiologists for years, and many factors have been assigned for their production. At present it is generally believed that the first sound is the product of at least two, possibly three, factors: viz., the contraction of the muscular v^alls of the ventricles, the simultaneous closure and subsequent vibration of the tricuspid and mitral valves, and the sudden increase of pressure of the apex of the heart against the chest- wall. That the contraction of the ventricular muscle gives rise to a sound is certain from the fact that it is per- ceptible in an excised heart when the cavities are free from blood and when the valves are prevented from closing. The explanation of this sound is extremely difficult, as the contraction, though prolonged, is not of the nature of a tetanus and therefore not char- acterized by rapid variations of tension. The apex element may be ehminated by plac- ing the individual in the recumbent position. Fig. 124.— Scheme of a 'pj^g second sound is the product of the Cardiac Cycle Trie . inner circle shows what simultaneous closure and subsequent vibra- events occur in the tion of the aortic and pulmonary valves heart, and the outer, ^^^^ ^ ^j^ beginning of the ven- the relation of the . i i i i sounds and silences to tricular diastole as the blood surges back these events. against the closed valves. This has been definitely proved by the fact that the sound disappears when the valves are destroyed or held back by hooks introduced into the aorta and pulmonary artery. It is also possible that the vibration of the column of blood produces an additional tone which adds itself to that produced by the valves. The relation of the sounds to the systole and diastole of the heart is represented in Figs. 124 and 121. The Blood-supply to the Heart. — The nutrition of the heart, its contractihty, the force and frequency of the beat, are dependent on and maintained by the introduction of arterialized blood into and the removal of waste products from its tissue. This is accomphshed by the coronary arteries, on the one hand, and the coronary veins, on the other. The arteries, two in number, the right and left, arise from the aorta in the pouches of Valsalva just above the right and left semilunar valves. Turning in opposite directions, they ultimately THE CIRCULATION OF THE BLOOD. 293 anastomose, forming a circle around the base of the ventricles. From both the right and left artery branches are given off which run over the walls of both auricles and ventricles, the most important of which in man are the anterior and posterior interventricular. These main vessels lie in grooves on the surface of the heart beneath the visceral pericardium, surrounded by connective tissue and fat. Small branches penetrate the heart-muscle in which they break up into capillaries. From the capillary areas small veins arise which, passing backward, converge to form the coronary veins. These follow the course of the arteries and finally terminate in the coronary sinus, located in the auriculo-ventricular groove on the posterior surface of the heart. This sinus opens into the right auricle between the opening of the inferior vena cava and the auriculo-ventricular opening. Its orifice is guarded by a valve, which is usually single, though sometimes double. While by far the larger portion of the blood is returned by the coronary veins, it is also certain that some of it is returned by small veins which open into little pits or depressions on the inner surface of the heart-walls, known as the foramina Thebesii. It has been lately shown by Pratt that these foramina are present not only in the auricular wall, as generally stated, but in the walls of all the cavities. These foramina communicate through a capillary plexus with both arteries and veins, and by special large passages with the veins alone. During the systole the intra-mural vessels are compressed and the blood driven out of the capillaries into the veins; during the diastole, the vessels again dilate and permit the blood to re-enter freely from the arteries. The greater the force and frequency of the beat, the greater the volume of blood passing through the coronary system. The period of time in the cardiac cycle during which the coronary arteries are filled with blood, whether during the systole or the dias- tole, has been a subject of much discussion. At present, however, as the result of many experiments it is generally believed that they are filled at the time of the systole. A comparison of the tracings of the pulse-wave taken simultaneously in the carotid and coronary arteries shows that the pressure rises and falls simultaneously in both vessels; that there is a complete agreement between the two trac- ings, and as a corollary both vessels are filled during the systole. But because of the pressure which the heart muscle must exert upon the smaller arteries and veins within its own substance during systole, it is probable that there is a freer circulation in the coronary vessels during the period of diastolic repose. In mammals the nutrition of the heart-muscle, its irritabihty and contractihty, depend on the blood-supply derived from the coronary vessels. This is shown by the effects which follow its withdrawal. Ligation of both coronary arteries in the dog is followed by a diminu- 294 TEXT-BOOK OF PHYSIOLOGY. tion in the force and frequency of the heart-beat, and in a few minutes by complete cessation. Ligation of even a single branch of a coro- nary artery, provided it supply a sufficiently large territory, — e. g., the arteria circumflcxa, — is sufficient to cause arrest in at least 80 per cent, of animals (Porter). With the ligation of this vessel there occurs a gradual diminution in the force and frequency of the systole. As the power of coordinate contraction ceases the heart-muscle frequently exhibits a series of independent contraction of individual fibers and cells known as fibrillary contraction. All the results which follow ligation are to be attributed in the light of experiment to the sudden anemia which is thus established. The removal of the ligature and the return of the blood will restore the nutrition and re- establish coordinate contractions. The excised heart of the mammal may be again made to beat by passing warm defibrinated blood through the coronary vessels under a suitable pressure. In frogs and allied animals the heart is nourished by blood flow'- ing, during the diastole, from the interior of the heart into a system of irregular channels which penetrate the walls in all directions. With the systole the blood is returned to the cavities. The excised heart of the mammal- — e. g., the cat — may be partially nourished in a similar manner through the foramina Thebesii. If the w^arm defibrinated blood of the same animal be introduced into the ventricle under a pressure of about 75 mm. of blood, the heart will recommence and continue to beat for a period varying from one to several hours. The Causation of the Heart-beat. — The beat of the heart, its frequency and regularity, its continuance from the early stages of fetal development till death, has long been an interesting subject for physiologic investigation. Though related to the functional activities of the body at large, the activity of the heart is in a sense independent of them, for it will continue for a variable length of time after they have ceased. The heart of the frog and the turtle will continue to beat under appropriate conditions for some hours after separation of all its anatomic connections and removal from the body. The heart of the dog or cat will, however, beat but for a few minutes. The human heart would in all probabihty act in the same way. The reason for the longer continuance of the beat of the excised heart of the cold-blooded animal beyond that of the warm-blooded animal lies probably in the difference in the rate of their respective metabolisms. There is reason to believe that each cell of the heart- muscle, in common with other tissue-cells, during life stores up and holds in reserve a larger quantity of nutritive material than is necessary for its immediate needs. When separated from the general blood- supply, the cells at once begin to utilize this reserved material. With its exhaustion the irritabihty declines and in a short time disappears. As the metabolism is far more rapid in the warm-blooded than in the THE CIRCULATION OF THE BLOOD. 295 cold-blooded animal, it is probable that the reserved nutritive material is utilized much more quickly in the former than in the latter. So long as it lasts in either class, the irritability and contractihty persist. The passage of defibrinated oxygenated blood through the vessels of the excised heart of the dog may maintain the duration of the irri- tabihty for a period of from one to six hours. Whatever the immediate or exciting cause of the heart contraction may be, the fundamental condition for its manifestation is the main- tenance of the irritability. So long as this persists at the normal level the heart-muscle will contract in response to the appropriate stimulus. Nature of the Stimulus. — As the heart continues to beat after removal from the body, it is evident that the stimulus does not origi- nate in the central nerve system but in the heart itself. Two views have been held as to its origin and nature: 1. That it originates in the nerve-cells found in various parts of the heart-muscle; that it is a nerve impulse rhythmically and auto- matically discharged by these cells and transmitted by their axons to the heart-muscle cells. 2. That it originates in the muscle-cells themselves; that it is chemic in character and due to a reaction between the inorganic salts in the muscle cells and those in the lymph by wliich they are surrounded. According to the first view the stimulus is neurogenic, according to the second view myogenic, in origin. The presence of nerve-cells; their relation to the muscle-cells; the pronounced rhythmic activity of the sinus and auricles in which the nerve-cells are abundant ; the feeble activity of the apex, in which they are wanting, — these and other facts lend support to the view that the stimulus originates in the nerve-cells. To them have been attributed the power of automatic activity. The absence of nerve cells in portions of the heart-muscle, which nevertheless exhibit rhythmic contractions for quite a long period of time; the rhythmic beat of the embr}'omc heart before the migra- tion of nerve-cells to its walls shows that the stimulus does not neces- sarily originate in nerve-cells. Moreover, Porter has conclusively shown that the apex of the dog's heart, which is generally beheved to be totally devoid of nerve-cells, can be made to beat for hours by feeding it through its nutrient artery with warm defibrinated blood. Unless it be assumed that the heart-muscle contracts automatically, without cause, it is a fair assumption that the exciting cause of the contraction arises within the muscle-cells themselves, and that it is in all probability the outcome of a reaction between the chemic con- stituents of the blood or lymph on the one hand, and the chemic constituents of the muscle-cells on the other. Attempts have been made to isolate these constituents, to determine not only their 296 TEXT-BOOK OF PHYSIOLOGY. individual, but also their cooperative action, when combined in pro- portions approximating those in which they exist in the blood. Action of Inorganic Salts. — The agents known to be direct- ly concerned in exciting and sustaining the heart-beat are sodium chlorid, calcium phosphate or chlorid, and potassium chlorid. Rin- ger's combination of these salts is made by saturating a 0.65 per cent, solution of sodium chlorid with calcium phosphate, and then adding to each 100 c.c, 2 c.c. of a i per cent, solution of potassium chlorid. A frog's heart immersed in this solution will continue to beat for several hours. A combination of the chlorids of sodium, calcium, and potassium is equally efificient in maintaining the heart-beat. The collective as well as the individual actions of these salts have been strikingly brought out by the experiments of Professors Howell and Green, from whose papers the following statements are derived. In these experiments strips from the terminations of the venae cava^ and from the ventricle of the terrapin's heart were employed. The proportion of these salts most favorable to the contraction of the venae cavas strips is the following: viz., sodium chlorid, 0.7 per cent.; calcium chlorid, 0.026 per cent.; potassium chlorid, 0.03 per cent.; for the contraction of the ventricular strips a larger percentage of the calcium is required: viz., 0.04 to 0.05. From this fact it is inferred that the venae cavas region is more sensitive to the action of the com- bined salts than the ventricle. With the latter strength of the solu- tion, the ventricular strips may contract for several days. In the first proportion as well as in serum the ventricular strips do not con- tract, but are kept in good condition for contraction for several days. An increase in the quantity of the calcium chlorid sufficient to raise the percentage to 0.04 or 0.05 wnll after a brief latent period give rise to rapid and energetic contractions. The action of the individual salts is also best shown with ven- tricular strips. In a 0.7 per cent, sodium chlorid solution the strip beats rhythmically and energetically, but for a short period and with gradually diminishing force, until it entirely ceases. A reason assigned for this is the removal of other salts necessary to the excita- tion of the contraction. In a calcium chlorid solution — 0.9 per cent. — i. e., isotonic with the sodium chlorid — the heart strip is thrown into strong tone, but does not rhythmically contract. If, however, the strip is placed in normal sahne, and calcium chlorid added in amounts equal to that present in the blood, it will after a very short latent period begin to contract rapidly and energetically and for a longer tiine than when in sodium chlorid solution alone. The contractions not infrequently occur before relaxation is completed, so that the strip passes into the condition of contracture. In potassium chlorid solutions isotonic — 0.9 per cent.^ — with sodium chlorid solution the heart strip also fails to contract. This THE CIRCULATION OF THE BLOOD. 297 is the case also when the potassium is added to the sodium chlorid in amount practically equal to that found in the blood. With the foregoing combination of inorganic salts (Ringer's or Howell and Green's) in which the heart continues to contract for many hours, it is believed that the sodium chlorid maintains the osmotic pressure between the heart tissues and the surrounding fluid; that the calcium salt prevents the washing out of the calcium salts, and at the same time acts as a stimulus to the heart-cells; that the potassium chlorid acts antagonistically to the calcium. From these facts it may be inferred that the stimulus is chemic in character and, though continuously acting, calls forth but periodic contractions. Th. W. Engelman concludes, as a result of long continued experi- mentation, that a stimulating action cannot be ascribed to the above- mentioned inorganic salts either alone or in combination with or- ganic matter and ox}-gen. Blood and lymph with their contained ingredients merely furnish the conditions favorable to the develop- ment of the excitation process. The stimulus, according to this experimenter, arises as a result of metabolic processes occurring within the cells themselves so long as they are conditioned by the factors just mentioned. PROPERTIES OF THE HEART-MUSCLE. 1. Irritability. — The heart-muscle in common with other muscles possesses irritability in virtue of which it responds by a change of form to the action of a stimulus. Whatever the stimulus, here, as elsewhere, there is a conversion of potential into kinetic energy — heat and mechanic motion. The normal physiologic stimulus is at present undetermined. In common with other forms of muscle tissue, the heart may be made to contract by artificial stimuli — e. g., mechanic, thermic, chemic, and electric. The irritabihty depends on the nutrition, and so long as this is maintained the muscle will respond by a contraction to any stim- ulus. The irritability is most marked in the neighborhood of the venae cavns terminations. It is least marked in the ventricles. 2. Conductivity. — The heart-muscle possesses conductivity. The excitation process and the subsequent contraction wave, both of which take their rise under physiologic conditions near the venae cavae terminations, are conducted over the auricles, thence to the ventricles from base to apex. The propagation of both processes is accomplished by muscle-tissue alone, independently of the nerve systems. The conductivity, however, is not equally well developed in every part of the heart. This is especially true of the tissue at the auriculo- ventricular junction. At this point the contraction wave is delayed for an appreciable period, a condi- tion due to the embryonic character of the muscle-tissue. In the TEXT-BOOK OF PHYSIOLOGY. frog's heart the excitation process begins in the sinus venosus, from which it passes to the auricles, thence to the ventricles. The excitation process as well as the contraction wave is de- layed both at the sinu-auricular and auriculo-ventricular junc- tions. In Fig. 125, which is a graphic record of the heart-beat, the two elevations of the lever on the up-stroke, a and h, repre- sent the contraction of the sinus and the auricle respectively, while the two depressions c and d in- dicate the delay in the transmission of the contraction wave at the two junc- tions. There is here an anatomic obstacle to the conduction of the con- traction. This may be artificially in- creased by compressing the heart be- tween the auricles and ventricles with a clamp. By carefully regulating the pressure it is possible to so block the wave that three or four auricular con- tractions may occur before a single ventricular contraction (Fig. 126). A similar blocking of the contraction wave in the dog's heart has been accomplished by Erlanger, by compression of the auriculo-ventricular groove by means of a specially devised hook-clamp. When the structures — the muscle-band of His — Fig. 125.— Record of the Contraction of the Frog's Heart. Aur. Fig. 126.- Vent -Record of the Auricular and Ventricular Contractions before AND after the CLOSURE OF THE ClAMP AT a. were completely compressed, the auricles and ventricles beat with an independent rhythm, the relation of the auricle to ventricle being as 3 to i . This experiment affords a possible explanation of the altered rhythm of the auricles and ventricles in that pathologic condition known as Stokes- Adams disease. Erlanger has demonstrated from a study of the cardiac impulse, the brachial and the jugular pulse, that the cardiac disturbances THE CIRCULATION OF THE BLOOD. 299 are due to a diminution in conductivity at the auriculo- ventricu- lar junction. Since the ventricular rhythm was at times in- dependent of the auricular, the blocking must have been com- plete. Thus in one determination the rate of the ventricular beats was 27.6 per minute, while the rate of the auricular beats was 98 per minute. Rhythmicity. — The beat of the heart is a uniform movement, occurring at regular intervals. Each phase of each beat occupies a regular measure of time. The beat is therefore rhythmic in char- acter. The heart-muscle as a whole varies in rhythmic power in its different parts. It is best developed in the frog and tortoise, in the sinus venosus, less so in the auricles, least in the ventricles. This may be shown by division of the tissue between sinus and auricles in situ. At once the auriculo-ventricular portion ceases to beat, while the sinus continues contracting as usual. In a short time the auricles and ventricles begin to beat, though less rapidly than formerly. Separation of the auricle from the ven- tricle is again followed by rest. In due time the auricle begins to beat, while the ventricle remains quiescent. If the ventricle be now stimulated in a rhythmic manner, it may resume rhyth- mic activity. These facts are taken as an indication that the rhythmic power is developed in unequal degree in the three divisions of the heart. The same difference in the rhythmicity of the auricles and ventricles of the mammalian heart also exists, though perhaps not to the same extent. Automatic ity. — The heart-muscle continuing to contract rhythmi- cally, even after removal from the body and without the aid of any external stimulus is said to be automatic in action. This, however, does not exclude the action of an internal stimulus. Tonicity. — The heart-muscle, Hke the vascular muscle, main- tains continuously a certain degree of contraction, termed tone, upon which the efficiency of the heart as a pumping organ is largely dependent. This tone may, however, be increased or decreased by the action of various external agents. Thus the passage of dilute solutions of various drugs — e. g., alkalies, digitalis — through the cavities of the excised heart will so in- crease the tone, or the contractile power, that complete relaxa- tion is prevented, until finally the heart comes to a standstill in the condition of systole. The passage of dilute solutions of lactic acid, muscarine, etc., through the heart will, on the con- trary, so decrease the tone or the contractile power that the normal contraction is not attained. The relaxation therefore gradually increases until the heart finally comes to a stand- still in the condition of diastole. In the first instance the tonicity is said to be increased; in the second instance, decreased. 300 TEXT-BOOK OF PHYSIOLOGY. The Response of the Heart to the Action of a Stimulus. — The heart of the frog as well as of some other animals may be brought to a standstill by the ligation of the tissues between the sinus veno- sus and the auricle, a procedure first introduced by Stannius and now known as the first Stannius ligature. Under such circumstances the heart may be made to contract by stimulating it with the single induced current. With each passage of the current the heart con- tracts. Contrary to what is observed in other muscles, the heart- muscle, if it contracts at all, at once reaches its maximal value. Any increase in the strength of the stimulus above the threshold value has no greater effect on the extent or force of the contraction than the minimal stimulus. A conclusion which may be drawn from this fact, according to Engelman, is as follows : By reason of the fact that the heart contracts at its maximum value to the action of any strength of stimulus, under given conditions, there is alwa}"s ensured a complete emptying of the ventricular contents and a uni- form discharge of blood into the arteries, which would not be the case if the extent of the contraction varied with the strength of the stimulus; and there are reasons for believing that the normal stimu- lus for the contraction varies within wide limits above the threshold value both in normal and abnormal conditions of the heart. The changes in the extent or force of the contraction are the result, not of changes in the intensity of the stimulus, but of changes in the heart- muscle, caused by variations in mechanical resistances. The periodicity of the heart's action or its rhythm may also be elucidated by the foregoing fact. There are reasons for believing that at the time of the contraction practically all of the available energy-holding material is completely utilized, after which the heart relaxes and remains at rest in the diastohc condition for a given period; and before a second excitation wave can pass from the si- nus over the heart there must be a re-accumulation of energy-holding material. This is accomplished during the diastole. By virtue of this fact the heart cannot act otherwise than in a periodic or rhyth- mic manner. Inasmuch as there is a conversion of potential into kinetic energy during the systole, there is of necessity a lowering of the irritability, and for this reason the heart will not respond to the action of a second stimulus during the systolic period. This non-responsive- ness of the heart may be shown by throwing into it a second stimulus at any moment during the systole. Whatever the moment, the extent of the contraction remains the same. During the systohc period the heart is said, therefore, to be refractory to a second stimulus; and if the stimulus be a weak one it may continue refrac- tory throughout the relaxation and even possibly during a portion of the diastole. THE CIRCULATION OF THE BLOOD. 301 If, however, the second stimulus be of average strength and thrown into the heart during the relaxation, a second contraction or extra systole is developed which superposes itself on the first, but the height of the contraction is no greater than the first (Fig. 127). There is, therefore, no summation of effects such as occurs when skeletal muscles are similarly stimulated. For- this reason a tetanic condition of the heart cannot arise. With the relaxation of the heart after the extra systole a considerable pause in the heart's action oc- curs to which the term compensatory pause is given, which is as long as the usual relaxation period was shortened by the extra systole plus the length of the usual pause. The duration of the pause must in any instance be sufficient to pemiit of a storage of energy- holding compounds and a restoration of the normal period- icity or rhythm. The explanation that may be offered for the development of 1 the second contraction is either that the p^^ 127— The Extra Con- energ}'-holding material was not wholly traction and the Com- destroved or that during the short time pensatory Pause. The ^•^'^ jir .1 ^ ,• 1 break in the horizontal which elapsed before the second stimulus ^ne indicates the moment new material had been generated. the electric current passes If a series of successive stimuli be through the heart, thrown into the heart-muscle the effect will vary in accordance with their time intervals. Should this be less than about three seconds there will be a gradual increase in the height for some half dozen contractions, a result to which the term "staircase" has been given. This increase in the height of the contraction is attributed to an increase in the irritability and con- tractility of the muscle the result of the stimulation. A similar beneficial effect follows successive stimulation of skeletal muscle. Though many of the experiments relating to the properties of the heart-muscle have been made on the hearts of frogs, turtles, and aUied animals, there is every reason for believing that the results so obtained hold true, with minor exceptions, for the heart of the mammal. THE NERVE MECHANISM OF THE HEART. By this term is meant a combination of nerves and nerve-centers which cooperate to increase or decrease either the rate or force — or both — of the heart's contraction in accordance with the needs of the system. That the heart is normally influenced by the central organs of the nerve system in response to the action of nerve impulses re- flected to them from many organs of the body is a matter of per- sonal experience; that it is abnormally influenced by the same or other organs in response to nerve impulses reflected to them in conse- 302 TEXT-BOOK OF PHYSIOLOGY. quence of pathologic and traumatic processes occurring in different regions of the body, and that both heart and nerves are modified in different ways by the action of drugs introduced into the body, are matters of daily chnical experience. —3notio rial Centers I Ech'darating (Blue) ) Depressing (Red) Cardio -Inhibitor Centef Ganglion Stdlatum Intra- Cardiac Nerue Cells CardioGccelerator Center Ya^usNerue [Inhibitor (Red) j Sensor (Black) Sympathetic Nerves I fttreehra.tor&G'iiffmen.torj Fig. 127 A. Diagram of the nerve mechanism of the heart. The nerves comprising this mechanism and the relation they bear one to another are represented in Fig. 127 A. It was stated in a previous paragraph, page 294, that the con- traction of the heart-muscle is independent of its connection with THE CIRCULATION OF THE BLOOD. 303 the central organs of the nerve system, and that it will continue to contract in a rhytlimic manner for a variable length of time even after its removal from the body of the animal, the length of time vandng with the animal and the conditions to which it is subjected ; that the stimulus is myogenic in origin and chemic in character, the result of a reaction between the inorganic salts in the muscle-cells and those in the lymph by which they are surrounded. It has also been further shown that even in the living animal the heart will con- tinue to beat and fulfil its functions after division of all nerves in con- nection with it. A dog thus experimented on hved for eleven months, and be}ond the fact of becoming fatigued more readily upon exertion than formerly, exhibited no striking disturbance of his functions. Nevertheless groups of nerve-cells are present in certain portions of the heart in all classes of vertebrate animals, which bear an anatomic and physiologic relation to the heart-cells on the one hand, and to the nerves connecting them with the central organs of the nerve system on the other hand. Intra-cardiac Nerve-cells. — In the frog heart a group of nerve- cells is found in the sinus at its junction with the auricle, known as the crescent or ganghon of Remak; a second group is found at the base of the ventricle on its anterior aspect, and known as the gan- glion of Bidder; a third group is found in the auricular septum, known as the septal ganglion, or v. Bezold's or Ludwig's. The majority of the cells are situated on the surface of the heart just beneath the pericardium. From the cell-body fine non-medullated fibers pass into the substance of the heart, to become histologically and physiologically related with the muscle-fiber. These nerve-cells were formerly regarded as the sources of the stimuli for the heart's activities. They are regarded by Gaskill as trophic in function, and exerting a favorable influence on the nutrition of the heart-muscle. In the dog heart the nerve-cells are not arranged in such definite groups, but are distributed in the terminations of the venae cavse, pulmonary veins, the walls of the auricles, and in the neighborhood of the base of the ventricles. Extra-cardiac Nerves. — The nerves which connect the heart with the central nerve system are two: viz., the vagus or pneumo- gastric, and the sympathetic. The Vagus. — Histologic investigatioji has shown that the vagus nerve-trunk contains meduUated fibers of large and small size. Ex- periment has shown that the large fibers are afferent, the small fibers efferent in function. The large afferent fibers arise in the gangha situated on the tmnk of the nerve. From their contained nerve- cells a short-axon process proceeds which soon divides into a central and a peripheral branch. The central branch passes toward and into the grav matter beneath the floor of the fourth ventricle where 304 TEXT-BOOK OF PHYSIOLOGY. Viif/iis its end-tufts arborize around ncrvc-cclls; the peripheral branch passes toward the general periphery to be distributed to the mucous membrane of the lungs, stomach, intestine, etc. The small efferent fibers are the peripherally coursing axons of nerve-cells situated in the gray matter beneath the floor of the fourth ventricle at the tip of the calamus scriptorious. The exact course of these fibers is not definitely known. According to some investigators, they leave the medulla by way of the spinal accessory nerve and enter the trunk of the vagus through the internal or anastomotic branch ; according to recent investigations made by Schaternikoff and Fried enthal, they leave the medulla along the path by which the afferent fibers enter and never become associated with the spinal accessory nerve at its origin. Below the origin of the inferior or recurrent laryngeal nerves, branches containing the efferent fibers are given off, which pass to the heart. The terminal branches of the fibers are not distributed directly to the heart- muscle, but to the nerve-cells, around the bodies of which they end in basket- like formations. The fibers in the vagus are pre-ganglionic ; those of the nerve-cells post-ganglionic. (See Fig. 128.) The Sympathetic. — Histologic investigation has shown that the sympathetic nerves which pass to the heart are non-meduUated. Experi- ment has shown that they are also efferent in function. The fibers are peripherally coursing axons of nerve- cells situated in the ganglion stellatum and inferior cervical ganglion. After reaching the heart they may terminate directly in the muscle- cell or indirectly through the intervention of the heart nerve-cells. The former method is the njore probable. The nerve cells in these ganglia are in relation with small medullated nerve-fibers which, emerging from the cord in the anterior roots of the second and third thoracic nerves pass through the white rami communicantes, and thence to the ganglion stellatum, and the inferior cervical gan- glion, where their end branches arborize around the nerve-cells. The nucleus of origin of these medullated fibers is probably in the medulla oblongata. The fibers emerging from the cord are pre- ganglionic, those emerging from the ganglion, post-ganglionic. In the frog these two sets of nerve-fibers, viz., the efferent vagus fibers and the sympathetic fibers, pass to the heart in the common thetic yeitron Cell Fig. 128. — Diagram showing THE Relation of the Vagus TO THE Heart Muscle-cell. THE CIRCULATION OF THE BLOOD. 305 sheath of the vagus nerve. The s}Tnpathetic fibers proper, the post- ganghonic libers, arise from nerve-cells in the third s}-mpathetic ganglion. From this origin they ascend, passing successively through the second sympathetic ganglion, the annulus of Vieussens, the first sympathetic ganghon, to the ganglion on the trunk of the vagus, at which point they enter the sheath of this nerve. For this reason the common tnmk which descends to the heart is generally spoken of as the va go-sympathetic nerve. The pre-ganglionic fibers emerge from the cord in the anterior roots of the third spinal nerve, pass through the rami communicantes to the third sympathetic ganglion, around the cells of which the nerve-fibers arborize. In man and some other mammals the sympathetic fibers arising in the ganglion stellatum pass direct to the heart without any anatomic connection with the vagus trunk. The Physiologic Action of the Vagus and Sympathetic Nerves.— The information noAV possessed regarding the influence which the cen- tral nerve sys- tem exerts upon the heart has been derived largely from ex- periments made on the nerves of the frog, toad and turtle. To demonstrate the respective actions of the two sets of fibers they must be stimulated or divided before their union at the vagus ganghon. Stimulation of the intra-cranial roots of the vagus with very weak induced currents is followed by a gradual diminution in the rate or rhythm and a diminution in the force of the heart-beat. If the in- duced currents are moderate in strength, the heart will at once come to a standstill in diastole. Since stimulation of the nerve, which in all probabihty exaggerates its normal function, is followed by a period of rest or inactivity, the vagus is said to have a retarchng or an inhibi- tor influence on the beat of the heart. After cessation of the stimulation, the heart resumes its activity. At first the beat usually is slow and feeble, but with each succeeding beat both rate and force increase, until they attain or exceed that observed prior to the stimulation. The duration of the inhibitory effect varies with the duration of the stimulation. Thus during and after a stimulation of thirty-eight seconds the heart of the toad re- mained at rest for 292 seconds (Gaskell). iMiMwmjmTOMvmTOmMW.wmvw.wwMvwwtfA'iMmmm ■ Fig. 129. I'RACING SHOWIXG THE DIMINUTION IN THE Rate of the Heaet-beat following Weak Tetanization of the Vagus Trunk. 3o6 TEXT-BOOK OF PHYSIOLOGY. Stimulation of the sympathetic fibers prior to their union with the vagus is followed by an increase in the rate or an augmenta- tion in the force of the heart-beat or both at the same time. With the cessation of the stimulation the heart returns to its normal con- dition. From the foregoing facts the sympathetic is said to have an accelerator or an augmentor influence on the heart, according as it accelerates the rate or augments the force of the beat. Stimulation of the trunk of the vagus in the frog or the toad with weak tetanizing induced electric cur- rents is followed by increase in the mmummmmijmmiiiiHimmimimmiiiiiit Fig. 130. — Tracing showing Complete Inhibition FOLLOWING Strong Tetanization of the Vagus Trunk. an mcrease m rate of the heart-beat because of the stimulation of the accelerator fibers which apparently respond before the inhibitor fibers; stimu- lation with somewhat stronger currents is followed by a diminution in the rate of the beat because of the greater effect on the inhibitor nerve-fibers (Fig. 129). Stimulation with strong tetaniz- ing currents is followed by complete inhibition, and for a short time the heart remains quiescent; but not withstanding the continued stimulation, the heart commences again to beat (Fig. 130). Though at lirst the beat is feeble, it soon re- gains and far exceeds its former rate and force. This may be attributed to a fatigue of the terminals of the in- hibitor fibers or to an over- powering action of the aug- mentor fibers arising after a rather long latent period. The foregoing facts are also illustrated in Figs. 131 and 132, as published by Gaskell. In these experiments the heart was suspended and clamped in the auriculo-ventricular groove, thus permitting both auricle and ven- tricle to be attached to recording levers. In addition to the changes in the rate and force of the heart caused by stimulation of the inhibitor and the augmentor nerves, it is stated by Gaskell that there is also during the inhibition a decrease in the conductivity of the heart at both the sinu-auric- Fig. 131. — Tracing showing Diminished Amplitude and Slowing of the Pul- sations OF the Auricle and Ventri- cle without Complete Stoppage during Irritation of the Vagus. — (From Brunton, after Gaskell.) THE CIRCULATION OF THE BLOOD. 307 Aur. Vent. m C.8. '^'''^mmmmmmm ular and auriculo-ventricular junctions, and an increase in the conductivity during acceleration of the beat. The decrease in con- ductivity may be so pronounced that only every second or third contraction of the auricle will be followed by a contraction of the ven- tricle. In other instances both auricles and ventricles remain at rest while the sinus maintains its usual rate. The increase in conductivity is shown by first artificially block- ing the contraction wave at the auriculo-ventricular junction with the clamp, until only every second or third auricular contraction is conducted to the ventricle, and then stimulating the sympathetic. At once the auricular contraction forces the block, and passes to the ventricle, calling forth a normal contraction. In the mammal the same effects follow stimulation of the vagus and the sympa- thetic as in the frog. If the thorax of a dog is opened and artificial respiration maintained, the heart will continue to beat in a practic- ally normal manner for a long time. Stimulation of the vagus with induced cur- rents of moderate strength will be followed by a com- plete standstill of the heart in diastole, during which the walls are relaxed and the heart-cavities filled with blood. If the currents are of feeble strength, the heart will come to rest gradually through a gradual diminu- tion in the rate and force of the contraction. Stimulation of the sympathetic may be followed by only a slight increase in the rate, especially if the heart action is normally very rapid. There is, however, an augmentation of the force and an increase in conductivity (Fig. 133). The Cardio-inhibitor Center. — In the dog, and probably in many other mammals also, the cardio-inhibitor center, in the medulla, exerts a more or less constant inhibitor or restraining in- fluence on the heart's activity. This is indicated by the fact that the rate of the heart-beat is very much increased by simultaneous divi- sion of both vasi. For this and other reasons it is believed that this Fig. 132. — Tracing showing the Actions OF THE Vagus on the Heart. Aur., Auricular; Vent., ventricular tracing. The part between perpendicular lines indicates period of vagus stimulation. C.8 indicates that the secondary coil was 8 cm. from the primary. The part of tracing to the left shows the regular contractions of moderate height before stimulation. During stimulation, and for some time after, the beats of auricle and ventricle are arrested. After they commence again they are single at first, but soon acquire a much greater ampli- tude than before the application of the stimulus. — {From Brunton, ajter Cas- kell.) 3o8 TEXT-BOOK OF PHYSIOLOGY. center is in a state of tonic activity, discharging nerve impulses which exert a regulative influence on the cardiac mechanism in accordance with its needs, and especially in reference to the variable resistances offered to the flow of blood which the heart must overcome. The question has been raised as to whether the tonic activity of the center is maintained by causes within itself, the result of an interaction of cell substance and the surrounding lymph, or by nerve impulses reflected to it through aft'erent or sensor nerves. The latter suppo- sition is supported by the results of experimentation, though both factors are undoubtedly of importance. Stimulation of the sensor nerves in almost any region of the body is followed by a slowing of the heart's action. Thus stimulation of the posterior roots of the spinal nerves, the trunks of the cranial sensor nerves, the splanchnic nerves, the pulmonary branches of the vagus, etc., give rise to a more or less pronounced inhibition. As a i:rc.J"JV:Acc.y Fig. 133. — Increase in the Force of the Ventricular Contraction (Curve of Pressure in Right Ventricle) from Stimulation of the Sympathetic Fibers. There is Little or no Ch.^nge in Frequency. — {Franck.) rule, stimulation of the peripheral terminations of these nerves is more effective than stimulation of their trunks, hence an explanation is at hand for the cardiac inhibition which results from sudden dis- tention of the stomach, intestines, or lungs, or operative procedures in the nose, mouth, and larynx. The Cardio-accelerator Center. — The exact location of this center is not as yet determined. It is probably in the medulla ob- longata. The experiments of Hunt would indicate that this center is also in a condition of tonic activity, increasing both the rate and force of the heart's action; that it antagonizes the action of the inhibitory center and is in time antagonized by it; that the normal rate of the heart from moment to moment is the resultant of the action of these two opposing forces. These experiments also support the view that the acceleration of the heart observed during stimulation of certain afferent nerves is not due to a reflex stimulation of the accelerator center, but to an inhibition of the cardio-inhibitor center. It must THE CIRCULATION OF THE BLOOD. 309 therefore be assumed that the afferent nerves contain two sets of nerve-fibers, one of which inhibits, the other excites, the cardio- inhibitor center. The cardio-inhibitor and the cardio-accelerator centers may be increased in activity also by nerve impulses descending from the cerebrum, the result of emotional states; thus depressing emotions according to their intensity may so increase the activity of the cardio- inhibitor center, that the heart's action may not only be retarded but even completely inhibited; joyous emotions, as the contrary may so increase the activity of the cardio-accelerator center that the heart's action will be increased in both its rate and force. The Depressor Nerve. — The vagus trunk also contains afferent fibers stimulation of which not only brings about a reflex inhibition of the heart, but also a dilatation of the peripheral arteries and a fall of blood-pressure through a depressive influence on the vaso-motor centers. To this nerve the term depressor has been given. A con- sideration of the physiologic action of this nerve will be found in the section devoted to the nerve mechanisms concerned in the mainte- nance of the blood-pressure. THE VASCULAR APPARATUS: ITS STRUCTURE AND FUNCTIONS. The systemic vascular apparatus consists of a closed system of vessels extending from the left ventricle to the right auricle, and includes the arteries, capillaries, and veins. Though serving as a whole to transmit blood from the one side of the heart to the other, each one of these three divisions has separate but related functions, which are dependent partly on differences in structure and physio- logic properties, and partly on their relation to the heart and its physiologic activities. The Structure, Properties and Functions of the Arteries. — The arteries serve to transmit the blood ejected from the heart to the capillaries; that this may be accompHshed they divide and sub- divide and ultimately penetrate each and every area of the body. Their repeated division is attended by a diminution in size, a de- crease in the thickness and a change in the structure of their walls. A typical artery consists of three coats: an internal, the tunica intima; a middle, the tunica media; an external, the tunica adven- titia. The internal coat consists of a structureless elastic basement membrane, on the inner surface of which rests a layer of elongated spindle-shaped endothehal cefls. The middle coat consists of several layers of circularly disposed, non-striated muscle fibers, between which are networks of elastic fibers. The external coat consists of bundles of connective tissue of the white fibrous and 3IO TEXT-BOOK OF PHYSIOLOGY. yellow elastic varieties. Between the external and middle coats there is an additional elastic membrane. In the small arteries there is but a single layer of muscle-fibers. In the large arteries the elastic tissue is very abundant, exceeding largely in amount the muscle-tissue. It is also more closely and compactly arranged. The external coat is well developed in the large arteries (Figs. 135 and 136). In virtue of the presence in their walls of both elastic and con- tractile elements, the arteries possess the two properties of elasticity and contractility. The elasticity is especially well developed in the large arteries, which are capable, therefore, of both disten- tion and elongation, and, when the distending force is withdrawn, of re- turning to their previous condition. The elasticity permits of a wide vari- ation in the amount of blood the arterial system can hold between its minimum and maximum disten- tion. Thus the capacity of the aorta and carotid artery of the rabbit can be increased four times and six times respectively by raising the intra- arterial pressure from o to 200 mm. of mercur}\ The elasticity also con- verts the intermittent movement of the blood imparted to it by the heart as it is ejected from the ventricle, into a remittent movement in the arteries and finally into the continuous and equable movement observed in the capillaries. This is accomplished in the following manner: With each contraction of the left ventricle more blood is ejected into the aorta than the arteries can discharge into the capillaries and veins during the time of the contraction. The portion not so discharged exerts a lateral pressure against the walls of the arteries which at once dilate until a condition of equilibrium is established between the pressure from within and the elastic reaction of the arterial walls from without. With the cessation of the contraction the elastic walls recoil and propel the blood toward the capillaries. The intermittent action of the heart is thus succeeded by the continuously reacting arterial wall. Fig. 134. — Coats or a Small Artery, a. Endothelium, b. Internal elastic lamina, c. Cir- cular muscular fibers of the middle coat. d. The outer coat. — {Landois and Stirling.) THE CIRCULATION OF THE BLOOD. 311 As the blood advances toward the periphery of the arterial system and larger amounts pass into the capillaries both the distension and the elastic recoil diminish, and by the time the blood reaches the capillaries its intermittency of movement has been so far obhter- ated by the elastic recoil that as it enters the capillaries the move- ment becomes equable and continuous. The elasticity thus serves the purpose of equalizing the movement of the blood throughout the arterial system. In youth the arterial walls are highly distensible and elastic; in advanced years they are frequently relatively rigid and inelastic; and in consequence the flow of blood toward and into the capillaries approximates in its characteristics the flow of a fluid through a rigid tube under the intermittent action of a pump; that is, the intermit- tent movement im- parted by the heart is not so completely con- verted into a continu- ' . ous movement, and i: hence the blood flows through the capillaries ^ durjing the systole ^ with greater velocity, and during the dias- Fig. tole with less veloc- ity, than is the case when the vessel is normally elastic. For these and other rea- sons the tissues are not so well nourished and hence their nutrition and functional activities decline. The contractility permits of a variation in the amount of blood passing into a given capillary area in a unit of time. Normally each artery has a certain average caliber due to a given contraction of the muscle coat. Beyond this average condition the artery can pass in one direction or the other by either a relaxation or increased contraction of the muscle coat. During the functional activity of any organ or tissue there is need for an increase in the amount of blood beyond that supplied during inactivity or rest. This is ac- complished by a relaxation of the muscle-fibers. With the cessation of activity the muscle-fibers again contract and reduce the amount of blood to that required for nutritive purposes only. An increased contraction of the muscle-fibers beyond the average diminishes the outflow of blood, and if sufficiently great may give rise to anemia and pallor. The contractile elements at the periphery of the arterial 135. — Transverse Section of Part of the Wall of the Posterior Tibial Artery (Man). — (Schafer.) a. Endothelium lining the vessel, appearing thicker than natural from the contrac- tion of the outer coats, b. The elastic layer of the intima. c. Middle coat composed of muscle- fibers and elastic tissue, d. Outer coat consisting chiefly of white fibrous tissue. — {Front Yeo's "Phys- iology. ") 312 TEXT-BOOK OF PHYSIOLOGY. system, in the so-called arteriole region, therefore regulate the supply of blood to the tissues in accordance with their functional needs. The Structure, Properties and Functions of the Capil- laries. — The capillaries are small vessels that connect the arteries with the veins. Though different in structure from a small artery or vein, there is no sharp boundary between them, as their structures pass imperceptibly one into the other. A true capillary, however, is of uniform size in any given tissue and does not undergo any noticeable decrease in size from repeated branchings. The diameter varies in different tissues from 0.0045 mm. to 0.0075 mm., just sufficiently large to permit the easy passage of a single red corpuscle. The length varies from 0.5 mm. to I mm. The wall of the capillary (Fig. 136) is composed of a single layer of nucleated endo- thelial cells v/ith serrated edges united by a cement material. Though extremely short, the capillaries divide and subdivide a number of times, forming meshes or networks, the close- ness and general ar- rangement of which vary in different localities. As the endothelial cells are living structures and characterized by irritabihty, contractility and tonicity, it may be assumed that the capillary w^all as a whole is characterized by the same properties. Upon the possession of these properties, the func- tions of the capillary depend. The junction of the capillar}^ wall is to permit of a passage of the nutritive materials of the blood into the surrounding tissue spaces and of waste products from the tissue spaces into the blood. The structure of the capillary wall is well adapted for this purpose. Com- posed as it is of but a single layer of endothelial cells, the diameter of which defies accurate measurement, it readily permits, under cer- tain conditions, of the necessary exchange of materials between the blood and the tissues. The forces which are concerned in the pas- sage of materials across the capillary wall are embraced under the Fig. 136. — Capillaries. The Outlines of the Nucleated Endothelial Cells with the Cement Blackened by the Action of Sil- ver Nitrate. — {Landois and Stirling.) THE CIRCULATION OF THE BLOOD. 313 terms diffusion, osmosis, and filtration. As a result of the interchange of materials the tissues are provided with nourishment and relieved o the presence of waste products. The blood at the same time changes in composition; because of the loss of oxygen and the gain of carbon dioxid it changes in color from red to bluish red. The Structure, Properties and Functions of the Veins. — The veins serve to collect the blood from the capillary areas and return it to the right side of the heart. As they emerge from the capillary areas the veins, which in these regions are termed venules, are quite small. By their convergence and union the veins gradually increase in size in passing from the periphery toward the heart. Their walls at the same time correspondingly increase in thickness. The veins from the lower extremities, the trunk, and abdominal organs finally terminate in the inferior vena cava. The veins from the head and upper extremities terminate in the superior vena cava. Both venae cavas empty into the right auricle. A typical vein consists of the same three coats as ''^ the artery: viz., the tunica intima, the tunica media, and the tunica adventitia. The media, however, does not possess as much of either the elastic or muscle tissues as the artery, but a larger amount of the fibrous tissue. Hence they readily collapse when empty. In virtue of their structure the veins also possess both elasticity and contractility, though in a far less degree than the arteries. These Fig. 137.— Valves properties come into play and are of value in °^ ^ \-£.i^. furthering the movement of the blood toward the valve, i. Free heart, especially after a temporary obstruction. edge of the Veins are distinguished by the presence of valves l^/soit) '^' throughout their course. These are arranged in pairs and formed by a reduplication of the internal coat, strength- ened by fibrous tissue. They are always directed toward the heart and in close relation to the walls of the veins, so long as the blood is flowing forward (Fig. 137). An obstruction to the flow causes the valves to turn backward until they meet in the middle line, when they act as a barrier to regurgitation. Under these circumstances the elastic tissue permits the veins to distend and accommodate the blood. With the removal of the obstruction the recoil of the elas- tic tissue, and perhaps the contraction of the muscle-tissue, forces the blood quickly onward. The Stream-bed. — The stream-bed, the path along which the blood flows, varies widely in its total sectional area in different parts of its course, being greatest in the capillaries, least in the aorta and venae cavae. In passing from the base of the aorta toward the capil- laries the sectional area of individual arteries, in consequence of 314 TEXT-BOOK OF PHYSIOLOGY. repeated branching, diminishes, though their total sectional area increases and in direct proportion to their distance from the heart. In the capillary system the sectional area of an individual capillary at- tains its minimal value, though the total sectional area attains its maxi- mal value. Comparing one with the other, it has been estimated that the total sectional area of the aortic bed is to the total sectional area of the capillary bed as i is to 600 or 800. In passing from the capil- lary into the venous system the sectional area of individual veins in- creases, though the total sectional area decreases and in direct pro- portion to their distance from the capillaries. The stream-bed in the aorta is relatively narrow, but widens Capillaries. Fig. 138. — Scheme of the Circulatory Apparatus. gradually as it approaches the capillaries, where it attains its maxi- mum width; it again narrows gradually as it passes into the veins, until in the venae cavae it becomes almost as narrow as in the aorta. As the combined sectional areas of the venae cavae are greater than the sec- tional area of the aorta, the stream-bed of the former never becomes as narrow as that of the latter. These facts will become apparent if the vascular apparatus is conceived of as a system of symmetri- cally branching vessels and all vessels of the same diameter sym- metrically disposed one to the other (Fig. 138). The gradual increase in the width of the stream-bed which results from this repeated branching, as well as its relative width in the arteries, capillaries, and veins, is graphically shown in Fig. 139. BLOOD PRESSURE. The immediate cause of the movement of the blood from the beginning of the aorta through the arteries, the capillaries, and the veins to the right side of the heart, is a difference of pressure between these two points. The fact that the blood flows from the aorta to the venae cavae indicates that there is a higher pressure in the former than in the latter. The same holds true for the pulmonary artery and veins. So long as this is the case, the blood must flow from the point of high to the point of low pressure. THE CIRCULATION OF THE BLOOD. 315 To this pressure the term blood-pressure is given, and may be defined as the pressure exerted radially or laterally by the mo\dng blood-stream against the sides of the vessels. That there is such a pressure within the arteries, capillaries, and veins, different in amount in each of these three divisions of the vascular apparatus, is evident from the results which follow division of an artery or a vein of corresponding size. When an artery is divided, the blood spurts from the opening for a considerable distance and with a certain velocity. When a vein is divided, the blood as a rule merely wells out of the opening with but shght momentum. These results indicate that the blood in the arteries stands under a pressure con- FiG. 139. — Diagram Intended to Give ax Idea of the Aggregate Sectional Area of the Different Parts of the A'ascttl-ar System. A. Aorta. C. Capillaries. \'. \'eins. The transverse measurement of the shaded part may be taken as the width of the various kinds of vessels, supposing them fused together. -{Yeo.) siderably higher than that of the atmosphere, and that in the veins it stands under a pressure perhaps but shghtly above that of the atmosphere. Especially true is this of the larger veins. The same facts may be demonstrated in another and more striking way. A dog or cat is anesthetized and securely fastened in an appro- priate holder. The carotid arten,- on the right side and the jugular vein on the left side are freely exposed and clamped. Into the artery there is inserted on the distal side of the clamp and in the direction of the heart a cannula to which is connected a tall glass tube, 200 cm. high and of about 4 mm. internal diameter. Into the vein there is passed on the proximal side of the clamp and in the direction of the 3i6 TEXT-BOOK OF PHYSIOLOGY. capillaries a second cannula, to which is connected a similar tube, though of less height. If the two clamps are removed at the same time, the blood will mount in both tubes simultaneously. In the arterial tube the blood will ascend by leaps corresponding to the heart-beats until a certain height is reached, when the column becomes stationary, being kept in equilibrium by the blood-pressure within the vessel and the atmospheric pressure without. Though stationary in a general sense, the blood-column oscillates, rising and falHng with each contraction and relaxation of the heart. Not infrequently larger excursions of the column are seen which correspond in a general way to the respiratory movement. This experiment was originally per- formed on the horse, by the Rev. Stephen Hales (1732). In the venous tube the blood also rises to a certain height, after which it remains quite stationary, as the effect of the cardiac con- traction is not propagated under normal conditions beyond the arterial system. The height to which it rises is but slight as com- pared with that in the arterial tube. The pressure in both vessels is thus recorded in milhmeters of blood. The absolute pressure on any given unit of vessel surface — e. g., 1 square mm. — is obtained by multiplying the height of the column, expressed in millimeters, by the unit of surface, and then determining the weight of this mass of blood. Thus if the height of the column of blood in the carotid artery tube is 2000 mm., then the pressure on i sq. mm. is 2000 mm. of blood. The weight of 2000 c.mm. of blood is equal to 2.1 grams. The Arterial Pressure. — For accurate and long-continued ob- servation the arterial blood-pressure is more conveniently studied by means of a U-shaped tube (a manometer) partially filled with mercui"y. One limb of the manometer is connected by means of a tube and a cannula with an artery. For the purpose of retarding coagulation of the blood and for preventing the escape of a large volume of blood from the vessels, the system is filled with a solution of carbonate of soda of sp. gr. 1060 and under a pressure approxi- mately equal to that in the vessel of the animal as determined in previous experiments. When communication is established between the vessel and the cannula, the mercurial column adjusts itself to the pressure in the artery. It at once begins to exhibit the same cardiac and respiratory oscillations and undulations as did the column of blood in the previous experiment. The height of the mercurial column kept in equiHbrium by the pressure of the blood within and the pressure of air without the vessel is that between the lower level of the mercury in the proximal and the higher level in the distal limb of the manometer, both of which can be read off on a scale placed between the two limbs. The height of the mercury as well as its oscillations in the distal limb may be recorded by placing on the top of the mercury a light THE CIRCULATION OF THE BLOOD. 317 float, the upper end of which carries a writing point. When the latter is placed in contact with the moving blackened surface of a recording cylinder or kymograph, the height and the oscillations are recorded in the form of a tracing similar to that shown in Figs. 140 and 141, in which the larger curves represent the respiratory, the smaller curves the cardiac oscillations. The height of the mercurial B P TRACING ABSCISSA Fig. 140. — Diagram to show the Rel.a.tiox of the Mercurial Manometer to THE Artery, on One H.and, and to the Recording Cylinder, on the Other Hand, when Arr.anged for Recording Blood-pressure. column kept in equihbrium at any particular moment is determined by measuring the distance between a base-hne or abscissa, which represents the position of the mercury at atmospheric pressure, and any given point on the trace above, and multiplying it by 2, for the reason that the mercury sinks in the proximal hmb as high at it rises in the distal limb of the manometer. Fig. 141. — Blood-pressure Tr.acing. The blood-pressure as revealed by the tracing may be resolved into two components: viz., (i) the pressure in the arteries during the period of the cardiac diastole, which is termed the arterial pres- sure; and (2) that additional pressure occurring at the time of the 3i8 TEXT-BOOK OF PHYSIOLOGY. cardiac systole, which is termed the cardiac pressure. The arte- rial pressure is represented by the distance between the base-line and the points of the curve corresponding to the diastolic rest; the cardiac pressure, by the increase of distance between these points and the apices of the smaller oscillations. The relation of these two components varies in different animals and in the same animal at different times. If the arterial pressure is low, the cardiac increase may be considerable; if the former is high, the latter may be slight. The relation, however, of these components is not so accurately shown by the mercurial manometer, owing to the inertia of the mercury, as by one of the various forms of quickly responsive spring manometers used in determining the rapid variations of intra-cardiac pressure. These instruments show a much larger rise of pressure during the systole, often amounting to as much as one-third or one-fourth of the arterial pressure. In- a series of experiments it will be found that the arterial pressure, though rising and falhng a certain number of milhmeters, yet retains a fairly constant general average, the result of an adjust- ment between the number of heart-beats per minute and the amount of the resistance offered to the escape of blood into the capillaries and veins. In a tracing in which the respiratory undulations are absent, the arterial pressure, plus one-half of the cardiac increase, represents the mean arterial pressure. If the respiratory undulations are pres- ent, as is generally the case, the mean pressure may be represented by a line drawn horizontally across the tracing midway between the apex and trough of the undulation. Estimates of the Arterial-Pressure. — By means of the kymo- graphic methods previously mentioned the pressure in the larger arteries has been determined for all classes of animals. In the carotid artery of the dog it ranges from 140 to 160 mm.; in the horse, from 160 to 170 mm.; in the rabbit, from 90 to 100 mm. In two obser- vations made on human beings during amputation of the limb the pressure was found in the brachial artery of one patient to range from no to 120 mm., and in the anterior tibial of the other patient from no to 160 mm. The Estimation of the Arterial-Pressure in Man. — The fore- going method of obtaining the blood-pressure is not of general apphcation to human beings for obvious reasons, hence special instruments have been devised by means of which the pressure may be determined at least approximately without any surgical procedure. Such instruments are termed sphygmomanometers. One of the best is that of Mosso, represented in Fig. 142. It consists essentially of rubber capsules, contained within metallic tubes and into which two fingers of each hand are inserted. This system is connected, on the one hand, with a pressure apparatus, and, on the other, with a THE CIRCULATION OF THE BLOOD. 319 manometer provided with a scale. A float and writing-pen record the movements of the mercurial column on a moving blackened surface. In using this apparatus the pressure is raised to the point at which the mercurial column exhibits the greatest oscillations. This sphygmomanometer, as well as the interpretation of the results obtained with it, are based on the theory that the greatest oscillations of the arterial walls, and hence the greatest oscillations of the mercurial column, take place when the external pressure is just equal to the mean arterial pressure, the latter being the mean between the maximum pressure during the systole and the minimum pressure during the diastole of the heart. It is only necessary, there- fore, to take the mean of the readings corresponding to the excursions Fig. 142. — The Sphygmomanometer of Mosso. of the mercurial column and determine from them the mean arterial pressure. It has been experimentally demonstrated, however, by Howell and Brush that this interpretation is not correct, but that the greatest oscillation takes place when the external pressure justs equals the pressure in the artery at the end of the cardiac diastole. These ex- perimenters found when the carotid artery of one side w^as connected with a minimum valve and the carotid artery of the opposite side was surrounded by a plethysmograph in connection with a manometer, that the diastolic pressure indicated by the valve just equaled the lowest point of the greatest oscillation indicated by the manometer. Hence it is to be inferred that the greatest oscillations record the diastolic pressure. 320 TEXT-BOOK OF PHYSIOLOGY. An excellent sphygmomanometer, especially adapted for clinical use, is that devised by Stanton (Fig. 143 *). In this apparatus the systohc pressure is determined by noting the point at which the pulse reappears after obhteration, while the diastohc pressure is estimated by recording the point at which the greatest oscillations occur in the mercury column of the manometer. The pressure is applied to the arm by the rubber armlet h, which is 2,1 inches wide. This is the widest armlet that can be adjusted to the average-sized arm and presents distinct advantages over the Fig. 143. — Stanton's Sphygmomanometer. narrow armlet hitherto employed. This armlet is prevented from expanding outward by a cuff, f, of double thick canvas with inserted strips of tin, which is held in place by two straps which completely encircle the cuff. On the rigidity of this depends to a large extent the transmission of pulsation. The rubber armlet is connected by glass with a stiff-walled rubber tube, g, which in turn connects with the manometer. The manometer is perhaps the most important part of the apparatus. It is constructed entirely of metal except for the * The following description of this apparatus is abstracted from the Univ. of Pa. Medical Bulletin, Feb., 1903. THE CIRCULATION OF THE BLOOD. 321 glass tube containing the mercury column. The chamber c com- municates by means of a metal tube with the glass column d, which is connected by a screw-thread at 3, the caliber of c being approx- imately 100 times that of D. The cap of the chamber, which screws on, is provided with a metal T which is connected at 2 with the rubber armlet and at i with the bulb, used as an air-pump. At A is a stop-cock shutting the rubber bulb completely from the rest of the apparatus, while at b is a screw-valve which allows the air to escape from the closed system. When desired, the manometer can be made portable (without removing the mercury) by screwing the caps i and 2 into either end of the T at i and 2. The manometer is then tilted away from the glass column d until all the mercury has run into the chamber, the glass is then unscrewed and cap 3 screwed in. Before removing cap 3 the manometer must always be tilted, else the mercury will be lost. The rubber bulb is similar to those found on atomizers. In using this apparatus the pressure is raised by the air-bulb forcing air into the closed system — distending the rubber armlet and with the same degree of force displacing the mercury in c, driving it up the glass column d. When the pulse is no longer felt, the bulb still being compressed, the arm of valve A is turned until it is at right angles with the thumb and finger. The valve b is now slowly unscrewed until the mercury column begins to fall. With the eye on the scale the point at which the pulse reappears is mentally noted as the systohc pressure. Often considerably before the reappearance of the pulse to palpation, a pulsation is seen in the mercury column. As the column slowly falls this increases up to its greatest oscillation and then diminishes. The lowest point of the greatest pulsation is noted as the diastolic pressure. From experimental data and from theoretic reasoning it is certain that the pressure in the carotid and femoral arteries is less than in the aorta and greater than in the small peripheral arteries. In other words, there is a fall of pressure from the beginning of the aorta to the arteriole region. The fall in pressure, however, is not great in the larger vessels of the arterial system. It is only in the smallest arteries, before their passage into the capillaries, that an abrupt fall in pressure takes place. The Capillary Pressure. — The small size of the capillaries pre- cludes an investigation of their pressure by manometric methods. It may be stated, however, to be approximately equal to the pressure required to obliterate their lumen and to whiten the skin. The apparatus of v. Kries is based on this theory. A small glass plate, from 2.5 to 5 sq. mm., is fastened to the under surface of a support of suitable size carr\ang a small scale pan. The glass plate is placed on the skin near the root of a finger-nail and the scale pan gradually 322 TEXT-BOOK OF PHYSIOLOGY. weighted until the vessels are obhterated, as shown by the blanching of the skin. From results obtained with this apparatus v. Kries estimated the pressure in the capillaries of the hand at 37 mm. Hg, and in the ear at 20 mm. The Venous Pressure. — In passing from the capillaries to the heart the pressure continues to fall. The increasing size of the veins permits again of manometric observations in different regions. In the crural vein the pressure has been found to be equal to 14 mm. Hg, and in the brachial vein 9 mm. of Hg. In the jugular and subclavian and other vessels near the heart it is zero or even negative; that is, less than atmospheric pressure to the extent of from i to 10 mm. of mercury. >.The amount and relation of the pressures in the three divisions of the systemic vascular apparatus are approximately shown in Fig. 144. Fig. 144. — Diagram showing the Relative Height of the Blood-pressure in THE Different Regions of the Vessels. H. Heart. A. Arteries. C. Capil- laries. V. Large veins. 0, 0, being the zero line ( =atmospheric pressure), the pressure is indicated by the height of the curve. The numbers on the left give the pressure (approximately) in millimeters of mercury, h. Pressure in heart. a. Arteriole region showing sudden fall of pressure, c. The fall of pressure in the capillaries, v. The negative pressure in the large veins. — (Yeo.) The Causes of the Blood-pressure. — A conception of the blood- pressure as well as of the factors which cooperate to develop it in the different divisions of the vascular apparatus will be more readily ob- tained if the phenomena attending the flow of a fluid through an appar- atus similar to that represented in Fig. 144 A, be first understood. This apparatus consists of a reservoir or pressure vessel, R, provided with a horizontal tube with rigid walls, the diameter of which varies in its three divisions a, b, c. Into the horizontal tube, vertical tubes are inserted at equal distances. If the reservoir be filled with fluid the latter will exert a downward THE CIRCULATION OF THE BLOOD. 323 pressure, the degree of which will depend on the height of the column and may be represented by P. Under given conditions this pressure will act as a driving or propelling power. If the stop-cock at be opened the fluid will be driven into and through the horizontal tube with a detinite velocity. As the fluid flows through the horizontal tube it meets with re- sistance due to friction between the fluid and the sides of the tube which progressively diminishes the primary propelling power. The resistance offered to the flow of the fluid gives rise to a lateral pressure against the sides of the tube which varies in the three divisions as shown by the height to which the fluid rises in the vertical tubes. In the division c the pressure is low, for the reason that the resistance to be overcome by the moving fluid is but slight in amount; in the division b the pressure is higher because of its narrower caliber and its greater distance from the outflow orifice. In the division a the pressure is highest because of the friction offered by its walls in addition to that offered by the walls of b and c. The resistance to be overcome by the moving fluid at any given point of the horizontal tube is Fig. 144 A. — A Pressure Vessel, R, with out-flow tube a, b, c, and manometers inserted at different points. represented therefore by the degree of the lateral pressure, and, conversely the pressure at any given point is proportional to the resistance yet to be overcome. (In the conduct of an experiment, the propelling power should be kept constant by permitting fluid to flow into the reservoir as rapidly as it flows out of the horizontal tube.) If the horizontal tube were of uniform caliber throughout, the fall of pressure would be directly proportional to its length; but as it is not uni- form but unequal in diameter in its three divisions, the fall of pressure from the beginning to the end is unequal and may be represented by the irregular line which unites the upper limits of the fluid in the vertical tubes and which, if continued, would meet the reservoir at the point y. The height of the fluid at this point indicates approximately the amount of the pro- pelling power utilized in overcoming the resistance offered by the hori- zontal tube to the flow of the fluid through it. The remainder of the propelling power, represented by the portion of the column between x 324 TEXT-BOOK OF PHYSIOLOGY. and y, indicates approximately the amount utilized in imparting velocity to the fluid. The primary propelling power is thus utilized in overcoming the resistance represented by the pressure and in imparting velocity to the fluid. The pressure in the horizontal tube is therefore the resultant of two factors, viz., the propelling power of the fluid in the reservoir and the resistance offered by the walls of the tube. Variations of the Pressure. — So long as the foregoing factors remain constant the pressure remains constant. If either factor changes in one direction or another there will arise a change in the relative degree of pres- sure in the different divisions of the system. Thus if the diameter of the tube h is increased the resistance at once diminishes and there will be a tendency towards an equalization of pressure in all parts of the tube, as indicated by the dotted line t t: the pressure will fall in a, and in the ad- joining part of b, and rise in c, and in the adjoining part of b. If the diameter of the tube c is decreased the reverse conditions will obtain. For the reason that the walls of the outflow tube are rigid any increase or de- crease in the propelling power would be attended by a proportional increase or decrease of the pressure in a, b, and c. The phenomena presented by the flow of a fluid through elastic tubes are somewhat different and more complicated than those presented by rigid tubes, and they are still further complicated when the propelling power is periodic in action rather than constant. Nevertheless the fore- going facts serve to explain in a general way certain phenomena presented by the circulatory apparatus. In correspondence with the lavv^s of the flow of fluids through both rigid and elastic tubes, the flow of blood through the blood- vessels under the driving-power of the heart encounters friction. This is to be sought for not between the blood and the inner surface of the vessel, but rather in the cohesion of the particles of blood. This it is which offers resistance to the onward movement of the blood and which must be overcome if the circulation is to be maintained. Close to the inner surface of the vessel there is a layer of blood which is motionless, known as the still layer, caused by an adhesion between the blood and the vessel. Between this layer and the axis of the stream there is an infinite number of layers. The cohesion between these layers gradually diminishes in passing from the periphery to the center of the stream. The larger the stream, the less is the cohesion, and the reverse. In the large arteries the still layer is small in amount as compared with the total volume of blood passing through them ; hence the axial cohesion is readily overcome and the friction is but slight. In the smallest arteries and capillaries the ratio changes and the friction rapidly increases and to a considerable extent. In the veins the ratio again changes, approximating that in the arteries. As the veins pass from the periphery toward the heart and their individual sectional areas increase there is again a diminution of the friction. THE CIRCULATION OF THE BLOOD. 325 As a consequence of the friction throughout the entire vascular apparatus the blood experiences a resistance to its onward move- ment which, working backward, causes the blood to exert a lateral or radial pressure against the walls of the vessels. The high pres- sure in the aorta is the result of the total resistance of the vascular system, and the pressure at any point of the system represents the resistance yet to be overcome. The larger part of the pressure in the arterial system, however, is due to the resistance offered by the smallest arteries and capillaries, and when peripheral resistance is alluded to as a factor in the production or in the variation of blood- pressure, the resistance of these vessels is mainly understood. The primar}^ factor in the production of the pressure is the pump- ing action of the heart. Should there be any cessation in its activity, the elastic walls of the arteries would recoil and force the blood into the veins. There would be coincidently a fall of pressure equal to that of the atmosphere. Even under normal circumstances this condition is approximated during the diastole. The recoil of the arterial wall by which the forward movement of the blood is main- tained is attended by a fall in pressure. But before this reaches any considerable extent, the heart again contracts and forces its contained volume of blood into the arteries. That this may be accomplished it is essential that the cardiac energy be sufficient not only to drive a portion of the blood through the capillaries into the veins, but to oppose the recoihng arteries, and to distend them to their previous extent, so that the incoming volume of blood may be accommodated. This at once reestablishes the pressure at its former level. The alternate rise and fall of the pres- sure is represented by the oscillations of the mercurial column or by the small elevations and depressions on the kymographic tracing. During the contraction of the heart the kinetic energy is trans- formed into potential energ}% represented by the tense distended walls of the arteries. With the relaxation of the heart and the closure of the semilunar valves the potential energy of the arteries is again trans- formed into kinetic energy, represented by the moving blood. The arter}^ thus continues the work of the heart during its period of in- activity. The rapidity with which the cardiac contractions succeed each other prevents the pressure from sinking below a certain average level. The uniform level of the arterial pressure depends on the fact that though more blood enters the arteries during the systole than escapes into the capillaries and veins, as shown by the rise of the mercurial column in the manometer, this is compensated for by a continued escape during the diastole as shown by the fall of the mercurial col- umn. So long as the inflow of blood is equaled by the outflow, there is a balancing of opposing forces and the pressure is maintained at a uniform level. 326 TEXT-BOOK OF PHYSIOLOGY. VARIATIONS IN THE BLOOD PRESSURE, A. In the Arterial Pressure. — It is evident from the preced- ing statements that the arterial blood-pressure as a whole may be increased by: 1. An increase in the rate or force of the heart's contraction. 2. An increase in the peripheral resistance. 3. An increase in the general volume of the arterial blood. And that it may be decreased by : 1. A decrease in the rate and force of the heart's contraction. 2. A decrease in the peripheral resistance. 3. A decrease in the general volume of blood. If when the arterial pressure is in a condition of equilibrium the heart ejects into the arteries in a given period of time an increased quantity of blood as a result of an increased rate of contraction, there will be an accumulation of blood temporarily in the arteries (the peripheral resistance remain- ing the same), for the press- ure is only sufficient to force into the capillaries a given volume. The same result could be brought about by an increase in the force or power of the contraction, the frequency re- maining the same. An in- crease in the volume of blood ejected at each contraction will necessarily lead to an ac- cumulation. With the accu- mulation there goes an in- creased distention of the artery and a corresponding increase of press- ure. In a short time, therefore, the increased pressure will force out of the arteries at a higher rate of speed this excess of blood until the outflow again equals the inflow. This restores the equilibrium but establishes the mean pressure at a higher level. If the peripheral resistance is increased by a contraction of the muscular walls of the arterioles, the frequency and force of the heart remaining the same, there will also be an accumulation of blood in the arteries until their increased distention and consequent rise of pressure become sufficient to increase the rapidity of outflow until it counterbalances the inflow. The converse of these statements also holds true. If when the general arterial pressure is in a condition of equilibrium the heart Fig. 145. — Fall of Blood-pressure from 1 Arrest of the Heart's Action due TO Stimulation of the Vagus begun AT a and Stopped at b. — {Landois and Stirling.) THE CIRCULATION OF THE BLOOD. 327 ejects into the arteries in a given period of time a decreased quantity of blood, either as a result of a decrease in the rate or power or both, there will soon be a diminution of the arterial distention and a con- sequent fall in pressure (Fig. 146). This continues until the outflow no longer exceeds the inflow. Equihbrium will again be established, but the pressure will be at a lower level. If the peripheral resistance is diminished by a dilatation of the arterioles, the heart's contractions remaining the same, the existing pressure soon diminishes. The outflow of blood at once lessens in rapidity and so continues until it counterbalances the inflow. The equilibrium is again restored, but the pressure is at a lower level. B. In Capillary Pressure. — The pressure in the capillaries, though for the most part possessing a permanent value, is sub- ject to variations in accordance with variations in the pressure in either the arterial or venous systems or both. The marked difference in the pressure in the large arteries and the capillaries is partly due to Fig. 146. — Fall of Blood-pressure from Diminution of the Peripheral Resist- ance, THE Result of a Dilatation of the Arterioles, brought about by Stimulation of the Central End of the Depressor Is-erve. Stimulation begun at a, and stopped at b. — {Landois and Stirling.) the resistance offered by the narrow arterioles. If the latter dilate in any given area, the capillary pressure increases because of the propagation into them of the arterial pressure. The reverse condition would decrease the pressure. On the other hand, any interference with the outflow from any given area, due to venous compression, would Hkewise increase the pressure ; any factor which would, on the contrary, favor the outflow would decrease the pressure. Indepen- dent of any change in the arteriole resistance, it is evident that a rise in arterial pressure alone would increase the capillary pressure. If both arterial and venous pressures rise, the capillary pressure increases ; if both fall, it decreases. C. In Venous Pressure. — Independent of any change in the venous pressure in a given area from local or temporarily acting causes, — e. g., aspiration of the thorax or heart, muscle contrac- tions, change of position, etc., — the general venous pressure will be increased by a decrease in the value of those factors which produce 328 " TEXT-BOOK OF PHYSIOLOGY. the difference of pressure between the arteries and veins. An in- crease in the value of these factors would necessarily decrease the pressure. THE VELOCITY OF THE BLOOD. From the number of heart-beats per minute, 72, and the amount of blood discharged from the left ventricle at each beat, 180 c.c, it is evident that the blood must be flowing through the vascular appa- ratus with a certain velocity, for during the minute the entire volume of blood, 5769 grams, must have passed twice through the heart. Direct observation of the escape of blood from the central end of a divided artery, and from the peripheral end of a divided vein, as well as of the flow through the capillaries as seen with the microscope, shows that the velocity of the flow varies in different parts of the vascular apparatus. In the arteries, moreover, the flow is not quite uniform, but experiences alternate acceleration and retardation with each heart-beat. In the capillaries and veins the flow is continuous and uniform, as the conditions of the arterial walls are such as to completely overcome the intermittency. If the systemic vascular apparatus be conceived of as a system of tubes which have symmetrically divided and subdivided, and have again united and reunited in a corresponding manner, it is clear that the total sectional area will steadily increase from the beginning to the middle of the system, and then as steadily decrease from the middle to the end of the system. In such a system the same volume of blood must pass through any given section in a unit of time if the balance of the circulation is to be maintained. As the velocity of a fluid is inversely as the sectional area of the tubes through which it flows, it foUows that the initial mean velocity of the blood in the aorta will steadily decrease as it flows into the steadily enlarging blood-path until it reaches a minimal value in the middle of the capillary system ; and that it will again steadily increase as it flows into the narrowing blood-path until it reaches the heart. The initial mean velocity of the blood in the aorta wiU not be attained in the venae cavae, for the reason that the total sectional area of the latter is somewhat greater than that of the former. The same facts hold true for the pulmonic vascular system. The Velocity in the Aorta. — From the well-known fact that the velocity with which a fluid is flowing through a tube may be deter- mined by dividing its sectional area into the quantity discharged in a unit of time, attempts have been made to determine the mean velocity of the blood at the beginning of the aorta. If it be assumed that the volume discharged at each contraction is 180 c.c, as stated by Vierordt, and the number of heart-beats per minute at 72, THE CIRCULATION OF THE BLOOD. 329 the total volume discharged per minute would be 12,960 c.c, or 215 c.c. per second. The sectional area of the aorta at its origin is 6.15 sq. cm. On the principle above stated, these two factors would show a velocity of 350 mm. per ^^ second. An objection to this esti- ? mate is that the amount of blood discharged — /. e., the contraction volume — is much larger than recent investigations warrant. Different observers have estimated that in man the contraction volume is con- siderably less, probably not more than So c.c. Fig. 147. — Volkmann's Hemodromometer C, C. Arterial cannulas. Fig. 148. — LuDwiG and Dogiel's Rheometer. X, Y. Axis of rotation. A, B. Glass bulbs. h, k. Cannulas inserted in the divided artery, e, e^, rotates on g, f. c, d. Tubes. The Velocity in the Arteries. — The mean velocity of the blood in the larger and more superficially lying arteries has been determined 330 TEXT-BOOK OF PHYSIOLOGY. by Volkmann with the hemodromometer, by Ludwig and Dogiel with the stromuhr, and by other investigators with different forms of apparatus. Since neither the blood nor any particle placed in it can be seen through the walls of the artery, it occurred to Volkmann to inter- calate along the course of a vessel a U-shaped glass tube about one meter in length with a lumen the diameter of that of the selected vessel, into and through which the blood could be made to flow. The mechanic construction of the apparatus is such (Fig. 147) that the blood can be made to flow directly into the distal portion of the artery across the base or indirectly by way of the glass tube. Pre- vious to the intercalation of the tube it is filled with serum or normal saline solution. With the turn- ing of the cocks at B the blood enters the glass tube and drives the serum ahead of it into the arterial system. From the difference in time between the moment the blood enters and the moment it leaves the tube and from the length of the tube the velocity is deter- mined. The stromuhr or rheo- meterof Ludwig (Fig. 148) is constructed on the same principle, but instead of the glass tube having the same diameter it is considerably enlarged on its two sides. The bulbs are fastened to a metalhc disk which rotates around an axis in the metalhc base which carries the tubes to be inserted into the arteries. With this device it is possible to place either bulb in connection with the proximal end of the artery. Previous to the experiment the proximal bulb is filled with oil, the distal bulb with serum or normal sahne. On removing the clips on the artery the blood flows into the proximal bulb and drives the oil into the distal bulb. As soon as ' the former is filled with blood the bulbs are reversed and the same relative conditions are attained. This is repeated a number of times. Knowing the capacity of the bulbs, and the number of times they are filled in a given period, the total quantity of blood Fig. 149. — The Hemodromograph of Chau- VEAU AND LoRTET. A, B. Tube inserted in artery. C. Lateral tube connected with a manometer. h. Index moving in a caoutchouc membrane, a. G. Handle. THE CIRCULATION OF THE BLOOD. 331 discharged is obtained. This divided by the sectional area of the artery gives the velocity. The following values have thus been obtained: For the carotid of the dog, 205 to 357 mm. per second; for the carotid of the horse, 306 mm. ; for the metatarsal artery of the horse, 56 mm. (Volkmann). For the carotid of rabbits, 94 to 226 mm.; for the carotid of the dog, 349 to 733 mm. (Dogiel). The variations in the velocity of the blood in the arteries during the different phases of the cardiac cycle have been determined by Chauveau and Lortet with the hemodromograph (Fig. 149). This consists of a metaUic tube carrying a graduated disk. At one point the tube is perforated but covered with a rubber band through which passes an index. When the tube is inserted into the divided ends of an artery, the current of blood strikes the short arm of the index and gives to the outer long arm a movement in the opposite direction. ;; — -...^^^ ^^^>\ r 1 --''''' 1 ,,-- ^\ \ ' 1 ^^' ^^x \( 1 '\ \ \ /''' . \/ /; \ A /: \ '' \ V \ / ; i\ \ / 1 „/ I X. •»->. o-^ > /' ^-v^ ~~~"'-~^ 0-^' '^ / ^.^^ ' t- — ■ ^ 1 '^"~~ — Arteries. Fig. 150. Capillaries. -, Blood-pressure. , Velocity. — o- Veins. -o, Sectional area. The extent of the excursion indicates the velocity. The apparatus is first graduated with currents of water of known velocity. With this instrument Chauveau found that in the horse the velocity during the systole was 520 mm. per second, at the beginning of the diastole 220 mm. per second, and during the pause 150 mm. per second. The Velocity in the Capillaries. — The rate of flow in the capil- lary vessels can not be experimentally determined. It has been esti- mated by Vierordt at 0.5 mm. per second in his own retinal capillaries; by Weber at 0.8 mm. In frogs the velocity can be fairly well deter- mined by observing the time required for a corpuscle to pass over one or more divisions of an ocular micrometer. Weber calculated in this way that the velocity is 0.5 mm. per second. As the velocity varies inversely with the sectional area, it becomes possible to approximately determine the relation of the sectional area 332 TEXT-BOOK OF PHYSIOLOGY. of the capillary system to that of the aorta from the above-mentioned velocities. If it be assumed that the velocity in the aorta averages 300 mm. and in the capillaries 0.5 mm. per second, then the sectional area of the capillaries is to that of the aorta as 600 to i. The Velocity in the Veins. — In the venous system the velocity increases in proportion as the sectional area decreases. In the jugu- lar vein Volkmann found the velocity 225 mm. per second, which was about one-half that in the aorta of the same animal. The reason for the slow rate of movement in the jugular vein is to be found in the fact that the sectional area of the combined venae cavae is about twice that of the aorta; hence the relation of the sectional area of the cap- illary system to the sectional area of the venae cavae is about 300 to i. The blood-pressure, the velocity of the blood, the sectional area of the vascular apparatus, and their relation one to the other are shown in Fig. 150. THE PULSE. The pulse may be defined as a periodic expansion and recoil of the arterial system. The expansion is caused by the discharge from the heart into the arteries of a volume of blood during the systole; the recoil is due to the elastic reaction of the arterial walls on the blood, driving it forward into and through the capillaries, during the dias- tole. At the close of the cardiac diastole the arterial system is full of blood and considerably distended. During the occurrence of the succeeding systole a definite volume of blood is again discharged into the aorta. The incoming volume of blood is now accomodated by the discharge of a portion of the general blood volume into the capillaries and by the expansion of the arteries. The expansion naturally begins at the root of the aorta and at the beginning of the systole. As the blood continues to be discharged from the heart, adjoining segments of the aorta and its branches expand in quick succession, and by the time the systole is completed the expansion has traveled over the entire arterial system as far as the capillaries. With the cessation of the systole, the recoil of the arterial walls at once occurs. This expansion movement which thus passes from the beginning to the end of the arterial system in the form of a wave is known as the pulse-wave or pulse. Coincident with the expansion and recoil of the arterial system there is a slight alternate increase and decrease of the general blood-pressure, as shown by the small curves on a blood- pressure tracing, and for this reason the expansion and recoil is termed the pressure pulse. The pulse-wave which thus spreads itself over the entire arterial system with each systole of the heart can be perceived in certain THE CIRCULATION OF THE BLOOD. 333 localities by the eye, by the sense of touch, and investigated with various forms of apparatus or instrumental means. The pulse- wave, or at least the elevation of the soft tissues overlying it, can be seen in the radial artery, where it passes across the wTist- joint, in the carotid artery, in the temporal SLTtery, in the arteries of the retina under certain conditions, with the ophthalmoscope. If the ends of the fingers are firmly placed over the radial artery, not only the increase and de- crease of pressure, but also many of the peculiarities of pulse-wave, may be perceived. Without much difficulty it may be perceived that the expansion takes place quickly, the recoil relatively slowly; that the waves succeed one another with a certain frequency, corresponding to the heart-beat; that the pulsations are rhythmic in character, etc. Inasmuch as the individuality of the pulse-wave varies at different periods of life and under different physiologic and pathologic condi- tions, various terms more or less expressive have been suggested for its var}dng pecuharities. Thus the pulse is said to be jrequent or infrequent according as it exceeds or falls short of a certain average number — 72 per minute; quick or slow, according to the suddenness with which the expansion takes place or strikes the fingers; hard or soft, tense or easily compressible, according to the resistance which the vessel offers to its compression by the fingers; large, full, or small, according to the volume of blood ejected into the aorta, or, in other words, the degree of fullness of the arterial system. Frequency of the Pulse. — As the pulse or the arterial expansion is the direct result of the heart's action, its frequency must, under physiologic conditions, coincide with that of the heart. All condi- tions which modify the rate of the heart will modify at the same time the rate of the pulse. (See page 285). The Velocity of Propagation of the Pulse-wave. — The propa- gation of the pulse- wave from its origin at the root of the aorta to any given point of the arterial system occupies an appreciable period of time. The difference in time between the systole and the appearance of the pulse- w^ave at the dorsal artery of the foot can be appreciated by the sense of touch. The absolute time occupied by the wave in reaching this point was determined by Czermak to be 0.193 second. The rate at which the wave is propagated over the vessels of the lower extremity has been estimated by the same observer at 11. 16 meters per second, and for the upper extremities at but 6.7 meters per second. Other experimenters have obtained for the lower extremities some- what different results, varying from 6.5 to 11 meters per second. Weber's original estimate was from 7.92 to 9.24 meters per second. The slower rate of movement in the vessels of the upper extremities has been attributed to a greater distensibility of their walls, a condi- tion unfavorable to rapid propagation. For this reason a low arterial tension will occasion a delay in the appearance of the pulse-wave in 334 TEXT-BOOK OF PHYSIOLOGY. any portion of the body; a high arterial tension will of course have the opposite effect. The difference in the speed of the pulse-wave and the blood-current shows that they are not identical and must not be confounded with each other. ■^The Sphygmograph. — The alternate expansion and recoil of an Fig. 151. — Von Frey's Sphygmograph. G. S. Metal framework. P. Button attached to spring. F. Vertical rod. U. Clock-work which turns the recording cylinder. VI. Time marker. artery caused by the temporary increase and decrease of pressure following each heart-beat can be graphically recorded on a travehng surface by means of a special apparatus, the sphygmograph or pulse- writer. The tracing obtained in the form of a curve is termed the pulse-curve or the sphygmogram. Different forms of this apparatus have been devised by Marey, Dudgeon, V. Frey, and many others. The in- strument of V. Frey is shown in Fig. 151. This consists first of a metal framework by which the apparatus is fastened to the arm and support given to the lever, recording surface, etc. The essential part is the spring carry- ing a button which is placed over the artery, usually the radial, before it crosses the wrist-joint. A vertical rod transmits the movement of the spring to the recording lever; the movements of the latter are recorded on a small cylinder inclined slightly so that the upstroke may be vertical. A small electro-magnet serves to -record the Fig. 152. — The Pulse Curve or Sphygmogram. TPIE CIRCULATION OF THE BLOOD. 335 time relations of the changes in the blood pressure. An average tracing taken from the radial artery is shown in Fig. 152. This, however, is not a tracing of the pulse-wave, but rather a record of the changes in pressure, their succession and time relations, which follow each beat of the heart. The artery usually selected for obtaining a sphygmogram is the radial. This artery lies quite superficially, covered only by connective tissue and skin and sup- ported by the flat surface of the radial bone, conditions most favor- able to technical investigation. The sphygmogram or pulse-curve may be divided into two portions : viz., a line of ascent from a to b, and a line of descent from b to d (Fig. 152). In normal tracings the former is almost vertical and caused by the sudden expansion of the artery immediately following the ventricular contraction; the latter is in general obhque, due to the recoil of the arterial walls, occupies a longer period of time, and is marked by several elevations and depressions, both of which indicate that the restoration to equihbrium is neither immediate nor uncom- phcated. One of these elevations is quite constant and known as the dicrotic wave, c; the depression or notch just preceding it is known as the dicrotic notch. Pre- and post-dicrotic waves are not infrequently present. The summit is generally sharp and pointed. The vertical direction of the hne of ascent is taken as an indica- tion that the arterial walls expand readily, that the blood is dis- charged quickly, and that the ventricular action is not impeded. An oblique direction of the hne of ascent is an indication that the reverse conditions obtain. The height varies inversely as the arterial pressure, other things being equal; being high with a low pressure, and low with a high pressure. The dicrotic elevation shows that a second expansion wave is de- veloped which interrupts temporarily the recoil of the arterial walls. The origin of this second expansion has been the subject of much investigation, and at present it may be said that the question is not fully decided. It is asserted by some investigators that it is central in origin, beginning at the base of the aorta and passing to the pe- riphery; by others, that it is peripheral in origin, beginning near the capillary region and reflected to the heart. The former view is the one more generally accepted. According to it, the expansion is the result of the sudden closure of the aortic valves, a backward surge of the blood-column against them. The sudden arrest of the blood and its accumulations again expands the aorta. The dicrotic notch is therefore taken as the moment at which the ventricular systole ceases and the aortic valves close. From this fact it is evident that immediately after the first expansion the pressure begins to fall, even though the ventricular systole continues, owing to the discharge of blood from the arterial into the capillary and 33^ TEXT-BOOK OF PHYSIOLOGY. venous systems. The height of the dicrotic wave or the depth of the dicrotic notch is favored by low arterial tension and highly elastic arteries. Both features are diminished by the reverse conditions. The apex is sometimes rounded and even fiat, indicative of a great diminution in arterial elasticity. The sphygmogram not infrequently varies considerably from the normal type in different pathologic conditions of the circulatory apparatus. A consideration of these variations does not fall within the scope of this work. The Volume Pulse. — If an individual artery expands with each systole and recoils with each diastole of the heart, the same is true of all arteries, and as a result the volume of any organ or part of the body must undergo similar changes. To such alternate changes in volume the term volume pulse is given. The extent to which an organ will increase in volume will depend to some extent on its elasticity. The reason for the increase in volume is the resistance offered to the flow Fig. 153. — Mosso's Plethysmogeaph. G. Glass vessel for holding a limb. F. Flask for varying the water-pressure in G. T. Recording apparatus. — {Landois and Stirling.) of blood into and through the capillaries; the decrease in volume to the overcoming of the resistance through the arterial recoil. The variations in volume may be recorded by enclosing the organ in a rigid glass or metal vessel, which at one point is in com- munication with a recording apparatus, e. g., a tambour with a lever or mercurial manometer with float and pen. The space be- tween the organ and vessel is filled with normal saline, air, or oil. Such an apparatus is known as a plethysmograph. A well-known form of plethysmograph is that of Mosso (Fig. 153). Many forms of this apparatus have been devised in accordance with the character of the organ — spleen, kidney, etc. — to be investigated, though the principle underlying them is essentially the same. In addition to changes in volume due to the heart's action, most organs undergo additional changes in volume from respiratory and vaso-motor causes. THE CIRCULATION OF THE BLOOD. 337 THE CAPILLARY CIRCULATION. In certain regions of the body of many animals it is possible, on account of the delicacy and transparency of the tissues, to observe not only the flow of blood through the smaller arteries, capillaries, and veins, but many of the phenomena connected with it, to which reference has already been made. The structures usually selected for the observation of these phenomena are the interdigital mem- branes, the tongue, the lung, the bladder, and the mesentery of the frog. Though any one of these structures will afford an admirable view of the blood-flow, the mesentery for many reasons is the most satisfactory. For a comparison of the phenom- ena observed in the cold- blooded animals with those in the warm-blooded animals the omentum of the guinea-pig may be employed. If the frog is the subject of experiment, it should be slightly curarized and the brain destroyed by pithing. The animal is then placed on a small board cap- able of adjustment to the stage of the microscope. The abdo- men is then opened along the side and a loop of intestine withdrawn and placed around a cork ring which surrounds an opening in the side of the frog board. The loop of the intestine should be so placed that it will lie between the ob- server and the body of the frog. The mesentery thus exposed must be kept moist with normal saline solution. When examined with low powers of the microscope, arteries, veins, and capillaries will be found occupying the field of vision. Their general arrangement, their size and connections, can be readily deter- mined. After a few preliminary adjustments a region will be found in which the blood is flowing in opposite directions. The vessel apparently carrying blood away from the observer is an artery; the vessel apparently carrying blood toward the observer is a vein; the smallest vessels are capiflaries. The blood in the artery is of a brighter color than the blood in the vein; the blood in the capilla- ries is almost colorless. The arterial blood-stream not infrequently Fig. 154. — The Vessels of the Frog's Web. — a. Trunk of vein, and {b, b) its tributaries passing across the capillary network. The dark spots are pigment cells. — {Yeo's "Physiology. ") 338 TEXT-BOOK OF PHYSIOLOGY. shows remittancy, an alternate acceleration and retardation, corre- sponding to each heart-beat; the capillary and venous streams are uniform and continuous. The relative velocities in the three sets of vessels are indicated by the movement of the red corpuscles. In the arteries they pass before the eye so rapidly that they can not be distinguished; in the capillaries they pass so slowly that both form and structure may be determined; in the veins, though again mov- ing rapidly, they can often be distinguished. The relative positions of the red and white corpuscles in the blood-stream are also apparent; the former occupy the central, the latter the peripheral portion, at the same time adhering to the sides of the vessel. Between the axial portion of the stream occu- pied by the red corpuscles and the wall of the vessel there is a clear still layer of plasma, the re- y^ suit of an adhesion of the plasma to the wall. It is this feature which gives rise to the friction between suc- cessive layers of the blood- stream, the resistance to the blood-flow, and the devel- opment of blood-pressure. The relative breadth of the still layer and amount of friction are greater in small than in large vessels. The volume of blood passing into any given cap- illary area is determined by the degree of contraction of the arterioles. Thus on the apphcation of warm sa- line solution, which relaxes the arterioles, there is a large increase in the inflow of blood; vessels previously invisible suddenly come into view as the blood with its corpuscles passes into them. On the apphcation of cold water, which contracts the arterioles and dimin- ishes the inflow, many of the smaller vessels entirely disappear from view. The alternate contraction and relaxation of the arterioles will therefore determine the quantity of blood flowing into and through the capillary system. Migration of the White Corpuscles. — ^A phenomenon fre- quently observed in the capillary vessels of the mesentery or of the bladder of the frog is the passage of the white corpuscles through the walls into the surrounding lymph-spaces. To this pro- cess the term migration or diapedesis is given. After the tissues Fig. 155. — Small Vessel of a Frog's Mesen- tery SHOWING Diapedesis. w, w. Vas- cular walls, a, a. Poiseuille's space, r, r. Red corpuscles. /, /. Colorless corpuscles adhering to the wall, and c, c, in various stages of extrusion. /, /. Extruded cor- puscles. — {Landois and Stirling.) THE CIRCULATION OF THE BLOOD. 339 have been exposed to the air for some time or subjected to an irritant, the vessels dilate and become distended with blood. In a short time the blood- stream slows, and finally comes to rest. The condition of stasis is then estabhshed. During the develop- ment of this condition the white corpuscles accumulate in large numbers along the inner surface of the vessels and soon begin to pass through the vessel- walls. This they do by protruding a portion of their substance and inserting it into and through the vessel- wall. This once accomphshed, the remainder of the cell in due time follows until it has entirely passed out into the tissue-space. The opening in the cell-wall now closes. The successive steps in this process are shown in Fig. 155. As this migration occurs mainly after the circulation has ceased or when the tissues present the phenomena of approaching inflammation, it is difficult to state in how far it is strictly a physiologic process. The Venous Circulation. — The blood, having passed through the capillary vessels, is gathered up by the veins and conveyed to the right side of the heart. As the veins converge and unite to form larger and larger trunks the sectional area gradually diminishes, and hence the velocity of the blood-flow increases, though it never attains the velocity, even in the vense cavae, that it had in the aorta, for the reason that the sectional area of the venae cavse is considerably larger than that of the aorta. The pressure also is very low in the larger veins because the friction still to be overcome is relatively very slight. The capacity of the venous system is considerably greater than that of the arterial system, as there are usually two and even three veins accompanying each artery. This, taken in connection with its greater distensibihty, makes of the venous system a reservoir in which blood can be stored. On this reservoir the arterial system can call for that amount of blood necessary for the maintenance of its normal volume and pressure, and into it any excess can be discharged. The relative amounts contained in the two systems are regulated by the nervous system. The movement of the blood through the veins is accomplished by the cooperation of several forces, reference to which will be made in a following paragraph. THE PULMONIC VASCULAR APPARATUS. The pulmonic vascular apparatus consists of a closed system of vessels extending from the right ventricle to the left auricle, and includes the pulmonary artery, capillaries, and pulmonary veins. In its anatomic structure and physiologic properties it closely resembles, if it is not identical with, the systemic apparatus. The stream-bed widens from the beginning of the pulmonary artery to the middle of the capillary system; it again narrows from this point to the terminations of the pulmonary veins. 340 TEXT-BOOK OF PHYSIOLOGY. The movement of the blood from the beginning to the end of the system is due to a difference of pressure between these two points, the result of the friction between the blood and the vascular walls. From the difference in the extent of the pulmonic and systemic systems it is evident that, other things being equal, the friction is less, and therefore also the pressure is less in the former than in the latter. This view is supported by the difference in the thickness of the walls of the right and left sides of the heart. The pressure in the pulmonary artery of the dog was shown by Beutner to be about one-third that in the aorta; by Bradford and Dean to be one-fifth. The velocity of the blood-stream in each of the three divisions of the system can not wtU be determined. The time occupied by a particle of blood in passing from the right to the left ventricle has been estimated at one-fourth the time required to pass from the left to the right ven- tricle. Assuming the latter to be thirty seconds, the former would be seven and one-half seconds. The capillary vessels are spread out in a very elaborate manner just beneath the inner surface of the pulmonary air-cells, and form by their close relation to it, a mechanism for the excretion of carbon dioxid and the absorption of oxygen. The extent of the capillary surface is very great. It has been estimated at 200 square meters. The amount of blood flowing through this system hourly and exposed to the respiratory surface is about 800 liters. The reason for the existence of the pulmonary circulation is the renewal of the oxygen volume in the blood and the ehmination of the carbon dioxid; for the accomplishment of both objects ample provision is here made. The flow of blood through the cardio-pulmonary vessels is subject to variation during both inspiration and expiration in consequence of their relation to the respiratory apparatus. The mechanism by which these variations are produced will be considered in the chapter devoted to Respiration. FORCES CONCERNED IN THE CIRCULATION OF THE BLOOD. The Contraction of the Heart. — The primary forces which keep the blood flowing from the beginning of the aorta to the right side of the heart and from the beginning of the pulmonary artery to the left side are the contractions of the left and right ventricles respectively. This is evident from the fact that each ventricle at each contraction not only overcomes the pressure in the aorta and pulmonary artery, the sum of all resistances, but imparts a given velocity to the blood. Since the pressure continuously falls from the beginning to the end of each system, it follows that the blood must flow from the point of high to the point of low pressure During the interval of the heart's activity the walls of THE CIRCULATION OF THE BLOOD. 341 the arteries, to which the heart's energy was largely transferred, now take up and continue the work of the heart, and by recoiling drive the blood forward and into the venous system. Though the heart's energy is probably sufficient to drive the blood into the opposite side of the heart, it is supplemented by other forces — e. g. : 2. Muscle Contraction. — As a result of the relation which the veins bear to the muscles in all parts of the body it is clear that with each contraction and relaxation of the muscles there will be exerted an intermittent pressure on the veins. With each contraction the blood on the proximal side will at once be driven forward with increased velocity, while that on the distal side will be re- tarded, will accumulate and distend the veins, owing to the closure of the valves ; with the relaxation of the muscle the elastic and contractile tissues in the walls of the veins will come into play and force the blood forward. 3. Thoracic Aspiration. — The inspiratory movement aids the flow of blood through the venae cavae and their tributaries. With each inspiration the pressure within the thorax but outside the lungs undergoes a diminution more or less pronounced in ac- cordance with the extent of the movement. As a result, the blood in the large veins, now subjected to a pressure greater than that in the thorax, flows more rapidly toward the heart. With each expiration the reverse obtains. 4. Action of the Valves. — It is quite probable that gravity opposes to some extent the flow of blood through the veins below the level of the heart. This opposition to the upward flow is largely pre- vented by the valves, for each retardation is immediately checked by their closure and support given to the column of blood. The influence of gravity is shown when the relation of the arm to the heart is changed. Thus, if the arm be allowed to hang pas- sively by the side of the body, the veins, especially on the back of the hand, will become distended with blood. If now the arm be raised, the blood will flow rapidly toward the heart, as shown by the rapid emptying of the veins. Work Done by the Heart. — The work which the left ventricle performs at each contraction when it discharges its contained volume of blood into the aorta is : 1. To overcome the total resistance of the systemic vascular appa- ratus expressed in terms of aortic pressure ; and — 2. To impart velocity to the blood. The pressure in the aorta is not absolutely determined, though for many reasons it may be assumed to be about 250 mm. Hg, or its equivalent, a column of blood 3.21 meters in height. As the heart discharges 188 grams, the work done may be calculated by 342 TEXT-BOOK OF PHYSIOLOGY. multiplying the weight by the height : viz., 0.188 X 3.2 = 0.6016 kilo- grammeter. The velocity of the blood in the aorta has been approximately estimated at 0.5 meter per second. The work done in imparting this velocity to 188 grams is estimated by squaring the velocity and dividing by the accelerating force of gravity {^~J^Yi) ^^^ multiplying the quotient by 0.188. The quotient of the first two values represents the distance a body would have to fall to acquire this velocity: viz., 0.0127 meter. The work done is therefore 0.188 X 0.0127, or 0.0023 kilogrammeter. The entire work of the left ventricle is the sum of these two amounts, or 0.604 kilogrammeter. Assuming that the heart beats 72 times per minute, the work done daily would be 0.604 X 72 + 60 X 24, or 62.622 kilogrammeters. The right ventricle approxi- mately performs about one-third of this amount of work in over- coming the resistance offered by the pulmonary system and in imparting velocity to its contained volume of blood. The work of the entire heart would therefore be for the twenty-four hours about 83.496 kilogrammeters. THE NERVE MECHANISM OF THE VASCULAR APPARATUS. The middle coat of the arteries, and especially of those in the peripheral region of the arterial system, consists of a well-defined layer of non-striated muscle-fibers arranged in a circular direction or at right angles to the long axis of the vessel. In the physiologic con- dition these fibers are in a state of continuous contraction, more or less pronounced, and give to the arteries a certain average caliber which permits a definite volume of blood to flow through them in a given unit of time. The cause of this tonic contraction is not definitely known. It has been attributed to the action of local nerve-ganglia, to the pres- sure of blood from within, to the influence of organic substances in the blood, the products of gland activity: e. g., adrenalin or epinephrin. This tonic contraction of the vascular muscle is subject to increase or decrease in accordance with the action of various agents. In- creased contraction will result in a decrease of the caliber and a reduction in the outflow of blood. Decrease of the contraction or relaxation will result in an increase both of the caliber and outflow of blood. The small arteries thus determine the volume of blood passing to any given area or organ in accordance with its functional activities. The Vaso-motor Nerves. — The activities of the vascular muscle are regulated by the central nerve system through the intermedia- tion of nerve-fibers, termed vaso-motor nerves. Of these there are THE CIRCULATION OF THE BLOOD. 343 two kinds, one which increases or augments the contraction, the vaso-constrictors or vaso-augmentors ; another which decreases or inhibits the contraction, the vaso-dilatators or vaso-inhihitors. The vaso-motor nerves of both classes, unhke the ordinary motor nerves, do not pass directly to the muscle-fiber, but indirectly by way of the ganglia of the sympathetic nerve system. In these ganglia the vaso-motor nerves, which come from the central nerve system, terminate, breaking up into tufts, which arborize around the nerve- cells. From the cells new nerve-fibers arise which then pass without interruption to their final destination. The nerve-fibers which emerge from the central nerve system are extremely fine in caliber and medullated; those which emerge from the sympathetic ganglia are equally fine, but non-medullated. The former are termed pre- ganglionic, the latter post- ganglionic fibers. The ganglion in which the pre-ganglionic fibers end is not necessarily found in the pre-vertebral or lateral chain; it may be found in the collateral or even in the peripheral group. The vaso-constrictor nerves take their origin from nerve-cells located in the anterior horns and lateral gray matter of the spinal cord. They emerge from the cord in company with the fibers which compose the anterior roots of the spinal nerves from the second thoracic to the second or third lumbar nerves inclusive. A short distance from the cord they leave the anterior roots as the white rami communicantes and enter the pre-vertebral or lateral sympathetic ganglia. From the results of many observations and experiments it is probable that the great majority of the vaso-constrictor nerves terminate in these ganglia; that is to say, it is here that the pre- ganglionic fibers arborize around the contained nerve-cells. From the nerve-cells new fibers arise, the post-ganglionic, which pass to the blood-vessels of the head, to the upper and lower extremities, and to the thoracic and abdominal viscera. The vaso-constrictors for the head emerge from the spinal cord in the first four thoracic nerves, thence pass successively into and through the ganglion stellatum (the first thoracic), the annulus of Vieussens, the inferior cervical ganglion, the sympathetic cord to the superior cervical ganglion, around the cells of which they arborize. From this ganglion the new fibers follow the carotid artery and its branches to their terminations. The vaso-constrictors for the fore-limbs emerge from the cord in the roots of the fourth to the tenth thoracic nerves inclusive. Through the white rami they pass into the sympathetic chain, after which they take an upward direction and terminate around the cells of the gan- glion stellatum. From this ganglion the new fibers enter, by way of the gray rami communicantes, the trunks of the cervical nerves which unite to form the brachial plexus and by this route pass to the blood- vessels. 344 TEXT-BOOK OF PHYSIOLOGY. The vaso-constrictors for the hind-Hmbs emerge from the cord in the roots of the eleventh dorsal to the second or third lumbar nerves inclusive. They then pass through the white rami to the lower lumbar and upper sacral ganglia. Thence by way of the gray rami they pass into the nerve-trunks which unite to form the sacral nerves and by this route pass to the blood-vessels. The vaso-constrictors for the viscera of the abdominal cavity pass by way of the splanchnic nerves directly into the collateral gangha, the semilunar, the superior mesenteric, the inferior mesenteric, and the sacral. From these ganglia an elaborate network of non-medul- lated fibers passes to the blood-vessels of the stomach, intestines, and other viscera. The great splanchnic nerve is one of the most im- portant vaso-constrictor trunks of the body, on account of the large vascular area it controls. The existence, course, distribution, and functions of the vaso- constrictor nerves have been determined by a variety of methods, physiologic and anatomic. Stimulation of the nerve-trunks under appropriate conditions gives rise to a contraction, division to a dilata- tion of the blood-vessels. The physiologic continuity of the pre- ganglionic fibers with the nerve-cells of the sympathetic ganglia has been shown by the intra- vascular injection or the local applica- tion of nicotin. This agent, as shown by Langley, has a selective action on the arborizations of the pre-ganglionic fibers, and when given in sufficient doses suspends their conductivity; hence stimu- lation of the pre-ganglionic fibers is without effect, though stimulation of the post-ganghonic fibers is followed by the usual contraction. The following will serve as illustrations of the functions of vaso- constrictor nerves. Division of the great splanchnic is followed by a marked dilatation of the blood-vessels of the intestinal tract ; stimu- lation of the peripheral end by their contraction. Division of the cervical cord of the sympathetic is followed by dilatation of the blood- vessels of the side of the head; stimulation of the peripheral end by their contraction. The vaso-dilatator nerves have their origin for the most part in nerve-cells situated in the region of the spinal cord included between the origins of the second dorsal to the second lumbar nerves inclusive, though they are not confined to this region. Some vaso-dilatator fibers have their origin in the medulla oblongata, others in the sacral region of the spinal cord. The general course of the dilatator fibers for the intestinal tract is the same as that of the vaso-constrictors, though instead of becom- ing related to the nerve-cells in the pre-vertebral ganglia, they pass by way of the splanchnics to the collateral ganglia, the semilunar, the superior and inferior mesenteric, and perhaps to peripheral ganglia in or near the blood-vessels themselves. THE CIRCULATION OF THE BLOOD. 345 The vaso-dilatators for the hmbs are found in the common nerve- trunks associated with the usual motor and sensor fibers, though the exact route by which they pass from the spinal cord to the peripheral nerves has not in all cases been determined. Their cell stations have not been definitely located. The vaso-dilatator nerves for the blood- vessels of the submaxillary gland arise in the medulla, pass outward in the trunk of the facial nerve, and reach the gland by way of the chorda tympani branch. Their cell station is in the. ganghon near the hilum of the gland. The vaso-dilatator nerves for the blood- vessels of the corpora cavernosa of the penis, the nervl erigenles, have their origin in the sacral region of the spinal cord; and emerge in the roots of the second and third sacral nerves. Their cell station is in the ganglion near the organ. The existence, course, distribution, and functions of the vaso- dilatator fibers have been determined by the same methods employed in the investigation of the vaso-constrictors. Thus division and stimulation of the peripheral end of the chorda tympani nerve are at once followed by an active dilatation of the blood-vessels of the submaxillary gland. The inflow of blood is so great that the gland becomes bright red in color. Its tissues being unable to appropriate all the oxygen, the blood emerges in the veins almost arterial in char- acter. Stimulation of the peripheral ends of the divided nervi erigentes is followed by similar effects in the blood-vessels of the corpora cavernosa. Slow stimulation, once per second, of the periph- eral end of a divided sciatic nerve is followed by dilatation of the blood-vessels of the leg. From these and many other facts of a similar character it is highly probable that the blood-vessels of each organ are under the control of two antagonistic classes of nerve-fibers, one augmenting the degree of their contraction, the vaso-constrictors, the other diminish- ing it through inhibition, the vaso-inhibitors. Through the coopera- tive antagonism of these two classes of nerves the cahber of the blood- vessels and thereby the volume of the blood is accurately adapted to the needs of each organ both during rest and during activity. It is also to the alternate activity of these nerves that the variations occurring from time to time in the volume of organs are to be at- tributed. The vaso-constrictors and the vaso-dilatators differ somewhat in their physiologic properties, as shown by the results of experiment. Thus, when a mixed nerve, i. e., one containing both classes of fibers, — e. g., the sciatic, — is stimulated with frequently repeated induced currents, the constrictor effect is the more pronounced, the dilatator effect being wanting or prevented; when stimulated with slowly repeated induced currents, the dilatator effect is the more 346 TEXT-BOOK OF PHYSIOLOGY. pronounced. These different effects are strikingly shown in Fig. 156, A and B. In the experiment of which these tracings are the result the leg of a cat was enclosed in a plethysmograph and the variations in volume due to dilatation or contraction of the vessels, following stimulation of the sciatic nerve, were recorded by means of a tambour and lever on a slowly revolving cylinder. In A the fall of the curve indicates a diminution of volume, from contraction of blood-vessels following a rate of stimulation of the sciatic nerve of 16 per second for fifteen seconds. In B the rise of the curve indicates an increase in volume from dilatation of the vessels following a rate of stimulation of i per second for fifteen seconds (Bowditch and Warren). With different rates of stimulation somewhat different results are obtained. After division of a mixed nerve the vaso-constrictors degenerate and lose their influence over the blood-vessel in from four to five days, the vaso- dilatators in from seven to ten days, as shown by the response to electrical stimulation. ^mm^ 1 i /%Krtl Fig. 156. — Plethysmogeams of the Hind-leg of the Cat following Stimulation OF the Sciatic Nerve. In A the rate of stimulation was sixteen per second, in B one per second for fifteen seconds. When a nerve is cooled, the vaso-constrictors lose their irritability before the vaso-dilatators. Vaso-motor Centers. — The nerve-cells throughout the spinal cord from which the vaso-motor nerves take their origin may be regarded as nerve-centers which through their related nerve-fibers exert from time to time either a constrictor or a dilatator influence over the blood-vessels. Though both the vaso-constrictor and vaso- dilatator centers are in a state of continuous activity, the former decidedly preponderates, as shown by the maintenance of a tonic contraction of the blood-vessels. The activity of both centers may be increased or decreased, augmented or inhibited, by nerve impulses reflected to them from the periphery through afferent nerves or THE CIRCULATION OF THE BLOOD. 347 through nerve-fibers descending the cord from higher levels of the nervous system. Experiment has shown that when a definite region of the medulla oblongata is punctured or in anywise destroyed there is an immediate dilatation of the blood-vessels throughout the body and a fall of blood-pressure below one-half or one-third of the normal value. This region has a width of one and a half millimeters and extends longitudinally for a distance of four or five miUimeters, terminating at a point four milhmeters above the tip of the calamus scriptorius. A transection of the medulla above the upper Hmit of this area is without effect on the blood-pressure. A similar section below it, however, is at once followed by vascular dilatation, a loss of vascular tone, and a general fall of blood-pressure. Subsequent stimulation of the peripheral end of the divided medulla, the animal being curar- ized and artificial respiration maintained, will give rise to a marked contraction of the blood-vessels and a rise of blood-pressure up to and far beyond the normal value. If the experimental lesion is limited to the area mentioned in the foregoing paragraph, the vascular dilatation passes away after a time, the blood-vessels regain their normal tone, and the pressure again rises. These facts indicate that the area is to be regarded as the general vaso-motor {constrictor) center which maintains the tonus of the blood-vessels through its dominating influence over the vaso- motor centers in the cord, the latter acting in a subsidiary manner to the former. The nerve-fibers which transmit the regulative nerve impulses from the general to the subsidiary centers are found in the lateral columns of the cord. There is no evidence for the existence of a general vaso-dilatator center in the medulla. Since the blood- vessels maintain a more or less constant tone, it is assumed that the vaso-motor centers are in a state of continuous activity. In how far, however, this activity is the result of chemic changes between the cells and the surrounding lymph and blood, or the result of con- stantly arriving nerve impulses reflected from the periphery or from higher regions of the nervous system, is not readily determinable. Both factors are probably involved. Direct Stimulation of the Vaso-motor Centers. — The general vaso-motor (constrictor) center at least is markedly influenced by the quantity and quality of blood and lymph circulating around and through it. If the blood-supply to the medulla and associated structures be diminished by compression of the carotid arteries, the activity of the center is at once increased, as shown by increased vas- cular contraction and a rise of pressure. Restoration of the blood- supply is followed by a return of the center to its normal degree of activity. Increased blood-supply, as in cerebral hyperemia, is at- tended by a fall in blood-pressure indicating a decrease in the activity 34S TEXT-BOOK OF PHYSIOLOGY. of the center. A diminution in the percentage of oxygen or an in- crease in the percentage of COj in the blood will increase the activity of the center. In asphyxia especially, the center is extremely excit- able, as shown by a rise of the arterial tension. The subsidiary centers in the spinal cord are influenced by corresponding conditions. Reflex Stimulation of the Vaso-motor Centers. — The results of experiment make it certain that the degree of vascular contraction maintained by the cooperative antagonism of the vaso-motor centers can be increased or decreased by nerve impulses reflected to the cord and medulla from the periphery or from the brain. The effect may be general, or local and confined to the area from which the im- pulses arise. The following experiments may be cited as illustrations : Stimulation of the central end of a divided posterior root of a spinal nerve gives rise to increased vascular contraction, as shown by the rise of blood-pressure. The same holds true for any sensory nerve. Stimulation of the central end of the divided sciatic will give rise to opposite results, according to the strength of the stimulus, weak stimuli producing dilatation, strong stimuli producing contrac- tion of the vessels. Stimulation of the central end of the divided vagus gives rise to dilatation of the vessels of the lips, cheeks, and nasal and palatal mucous membranes. Stimulation of the auricular nerve in the rabbit will, according to the strength of the currents, give rise to either contraction or dilatation. Stimulation of the tongue is followed by dilatation of the vessels of the submaxiUary gland. In explanation of these different results it has been assumed that in the afferent nerves there are two classes of fibers, one which in- creases, the other decreases the activity of the vaso-constrictor centers. The first is termed pressor, the second depressor. Inasmuch as the vascular dilatation is often greater than the dilatation which follows division of the vaso-motor fibers themselves, it has been assumed by some that the general vascular tonus, as well as its variations from time to time, is the resultant of the simultaneous activity and varia- tions in activity of both vaso-constrictor and vaso-dilatator centers; that in the afferent nerves there are fibers which when stimulated augment, for example, the vaso-constrictor center and inhibit the vaso-dilatator centers, or the reverse. The result, either contraction or dilatation, which follows stimulation of their peripheral termina- tions will depend on the character of the physiologic stimulus. In a similar manner the vaso-motor centers are influenced by emotional states, fear causing a contraction, shame a dilatation, of the vessels of the face and neck. It is probable that these effects are due to the transmission of nerve impulses from the cortex to the vaso- motor centers in the medulla. The Depressor Nerve.— In the rabbit there is a small nerve formed by the union of a branch from the trunk of the vagus with a THE CIRCULATION OF THE BLOOD. 349 branch from the superior laryngeal. The peripheral distribution of this nerve is over the wall of the ventricle. The same nerve is found in many other animals. In some, as the dog, it is bound up in the vago-sympathetic. In man it is also present, though shortly after its origin it enters the trunk of the vagus. Division of this nerve is without effect either on the heart or the vessels. Stimulation of the peripheral end has neither an accelerator nor an inhibitor action on the heart. Stimulation of the central end is followed by a fall in blood-pressure, frequently to a level below one-half the normal value ; at the same time there is a diminution, brought about reflexly, in the rate of the heart-beat. The fall in pressure, however, is not due to this cause, for it occurs equally well after division of all the cardiac nerves. For this reason the nerve was termed the depressor nerve. On exposure of the abdominal cavity, it is observed during stimulation of the depressor that there is a notable dilatation of the intestinal vessels. From this fact it was assumed that the action of the depressor nerve was to lower the general pressure through reflex dilatation of these vessels. It has been shown by Porter and Beyer that if the splanchnics are divided and the peripheral end stimulated so as to maintain the tonus of the intestinal vessels, and hence the general pressure, stimulation of the depressor nerve will nevertheless be followed by a fall of the blood-pressure almost as great as when the splanchnics are intact. From this it is evident that the depressor nerve is related to centers which influence the vascular apparatus in its entirety. It has been supposed that through it the heart can protect itself from injurious results of an excessive rise of arterial pressure. CHAPTER XIII. RESPIRATION. Respiration is a process by which oxygen is introduced into, and carbon dioxid removed from, the body. The assimilation of the former and the evolution of the latter take place in the tissues as a part of the general process of nutrition. Without a constant supply of oxygen and an equally constant removal of the carbon dioxid, those chemic changes which underhe and condition all life phenom- ena could not be maintained. The general process of respiration may be considered under the following headings, viz. : 1. The anatomy and general arrangement .of the respirator}' ap- paratus. 2. The mechanic movements of the thorax by which an interchange of atmospheric and intra-pulmonary air is accomphshed. 3. The chemistry of respiration, the changes in composition ex- perienced by the air, blood, and tissues. 4. The nerve mechanism by which the respiratory movements are maintained. THE RESPIRATORY APPARATUS. The respiratory apparatus consists essentially of: 1. The lungs and the air-passages leading into them: viz., the nasal chambers, mouth, pharynx, larynx, and trachea. 2. The thorax and its associated structures. The nasal chambers are the natural entrances for the inspired air. Their comphcated structure slightly retards the movement of the air, in consequence of which its temperature and moisture are adjusted to the physiologic conditions of the lower respiratory pas- sages. The mouth, though frequently serving as an entrance for air, is not primarily a respiratory passage. Both the nasal chambers and the mouth communicate posteriorly with the pharynx, in which the respiratory and the deglutitory passages cross each other, the former leading directly into the \a.rynx. The larynx is a comphcated mechanism serving the widely different though related functions of respiration and phonation. It consists of a framework of cartilages, articulating one with another, united by hgaments and moved by muscles; it is covered externally with fibrous tissue and hned with mucous membrane. The superior 350 RESPIRATION. 351 opening of the larynx, the glottis, is triangular in shape, the base being directed upward and forward, the apex downward and back- ward. The inchnation of the glottic opening is almost vertical. Kt The cavity of the larynx is partially subdivided by the inter- position of the vocal bands into a superior and an inferior portion. Fig. 157. — Trachea and Bronchial Tubes, i, 2. Larynx. 3, 3. Trachea. 4. Bifurcation of trachea. 5. Right bronchus. 6. Left bronchus. 7. Bronchial division to upper lobe of right lung. 8. Division to middle lobe. 9. Division to lower lobe. 10. Division to upper lobe of left lung. 11. Division to lower lobe. 12, 12, 12, 12. Ultimate ramifications of bronchi. 13, 13, 13, 13. Lungs, represented in contour. 14, 14. Summit of lungs. 15, 15. Base of lungs. — {Sappey.) The opening, bounded by the vocal bands, is also triangular in shape, though in this case the base is directed backward, the apex forward. (See chapter on Voice and Speech.) The introduction of the vocal bands narrows at this level the air- passage and to some extent interferes with the free entrance of air. 352 TEXT-BOOK OF PHYSIOLOGY. According to the investigations of Semon, the area of the air-passage above and below the phonatory apparatus is about 200 sq. mm.; while the area bounded by the vocal apparatus is but 155 sq. mm. during quiet respiration. The trachea is a tube, some 12 centimeters in length, from one- half to three-fourths of a centimeter in breadth, extending from the lower border of the larynx to a point opposite the fifth dorsal verte- bra. It consists of an external fibrous and an internal mucous membrane, between which is a series of superposed C-shaped arches or rings of elastic cartilage, some 18 or 20 in number. Between the fibrous and mucous coats posteriorly, and occupying the space be- tween and attached to the free ends of the cartilages, there is a layer of transversely arranged non-striated muscle-fibers, known as the tracheal muscle. The contraction of this muscle would approximate the ends of the arches and so di- minish the caliber of the tube. The surface of the mucous mem- brane is covered by a layer of stratified columnar ciHated epi- thelium (Fig. 158). In the sub- mucous tissue there are a number of glands the ducts of which open on the free surface. Opposite the fifth dorsal ver- tebra the trachea divides into a right and a left bronchus. Each bronchus again subdivides into two or three branches, which penetrate the corresponding lung. The lungs in the physiologic condition, occupy the greater part of the cavity of the thorax. They are separated from each other by the contents of the mediastinal space: viz., the heart, the large blood-vessels, the esophagus, etc. Each lung is somewhat pyramidal in shape with the apex directed upward. The outer surface is con- vex and corresponds to the general conformation of the thorax. The inner surface is concave and accommodates the contents of the mediastinal space. At about the middle of the inner surface there enter the lung, the bronchi, and blood-vessels. The under surface of the lung is concave and rests on the diaphragm. The posterior border is convex; the anterior border is thin. A histologic analysis of the lung shows it to consist of the branches of the bronchi, their subdivisions and ultimate terminations, blood- vessels, lymphatics and nerves, imbedded in a stroma of fibrous and elastic tissue. The anatomic relations which these structures bear one to another is as follows: — Fig. 158. — Transverse Section of THE Trachea of a Kitten. — ■ {Stirliftg.) RESPIRATION. 153 Bronchiole. .. Infundibulum Fig. 159. — Scheme or a Bronchiole Terminat- ing IN Alveolar Passages, those Leading into Infundibula beset with Air-cells. — {Landois and Stirling.) Within the substance of the lung the bronchi divide and subdivide, giving origin to a large number of smaller branches, the bronchial tubes, which penetrate the lung in all directions. With this repeated sub- division the tubes become narrower, their walls thin- ner, their structure sim- pler. In passing from the larger to the smaller tubes the cartilaginous arches become shorter and thinner, and finally are represented by small angular and irregularly disposed plates. In the smallest tubes the carti- lage entirely disappears. With the diminution of the caliber of the tube and a decrease in the thickness of its walls, there appears a layer of non-striated muscle- fibers between the mucous and submucous tissues, which completely surrounds the tube and becomes especially well developed in those tubes devoid of cartilage. The fibrous and mucous coats at the same time diminish in thickness. When the bronchial tube has been re- duced to the diameter of about one milli- meter, it is known as a bronchiole or a ter- minal bronchus. From the sides of the terminal bronchus and from its final ter- mination there is given off a series of short branches which soon expand to form lobules or alveoh (Fig. 159). The cavity of the alveolus is termed the infundibulum. From the inner surface of the alveolus and of the passageway leading into it, there project thin partitions which subdivide the outer portion of the general cavity or in- fundibulum into small spaces the so-called air-sacs or air-cells (Fig. 160). The wall of the alveolus is extremely 23 Fig. 160. — Single Lobule OF Human Lung. a. Alveolar passage, b. Cavity of lobule or in- fundibulum. c. Pul- monary sacs. — {Dal- ton.) 354 TEXT-BOOK OF PHYSIOLOGY. thin and consists of fibro-elastic tissue, supporting a very elaborate capillary network of blood-vessels. The bronchial system as far as the alveolar passages is lined by ciliated epi- thelium. The air- sacs are lined by flat epithehal plates of ir- regular shape, termed the respiratory epithe- lium (Fig. i6i). The alveoli are united one to another by fibro- elastic tissue. In consequence of the presence of the elastic tissue, the lungs are distensible and elastic. After re- moval from the body the elastic tissue at once recoils, forcing out a portion of the contained air. The Under pressure, how- These proper- FlG, i6i. — Section of Silvered Lung of Kitten, INCLUDING Portions of Infundibulum and Air-sac. a. Small polyhedral epithelial cells covering the wall of the infundibulum. b. Fibro- elastic framework, c. Large flattened epithelial plates lining air-sac, among which lie small groups of small cells {d). — {Pier sol.) condition of the lung is now one of collapse ever, the lung can be readily distended or inflated. ties endure for a long period after death, if not indefinitely, if the lungs are properly preserved. The capacity of the lungs can be made to vary within rather wide limits in virtue of the presence of the elastic tissue. The Pulmonary Blood-ves- sels. — The pulmonary artery which conducts the venous blood from the heart to the lungs di- vides beneath the arch of the aorta into a right and a left branch. Each branch with its subdivisions enters the lung at the hilum in company with the larger divisions of the bronchi. Within the lung the arteries di- vide and subdivide in a manner corresponding to that of the bron- chial tubes, which they follow to their ultimate terminations. As Fig. 162. — The Relation of the Pul- monary Artery, PA, and the Pul- monary Vein, PV, to the Lobules, A A. B. The Bronchiole. RESPIRATION. 355 the pulmonary lobules are approached, a small arterial branch plunges into the wall of the lobule (Fig. 162), in which it forms an elaborate capillary network which surrounds and embraces the air-sacs on all sides. As this network is to subserve the respir- atory exchange of gases it lies nearer the inner than the outer surface of the lobule and in close relation to the respiratory epithelium. The air and blood are thus brought into intimate relationship, being separated only by the respiratory epithelium and the wall of the capil- FiG. 163. — Bronchi and Lungs, Posterior View. 1,1. Summit of lungs. 2, 2. Base of lungs. 3. Trachea. 4. Right bronchus. 5. Division to upper lobe of lung. 6. Division to lower lobe. 7. Left bronchus. 8. Di\ision to upper lobe. g. Division to lower lobe. 10. Left branch of pulmonar}' artery. 11. Right branch. 12. Left auricle of heart. 13. Left superior pulmonary vein. 14. Left inferior pulmonary vein. 15. Right superior pulmonary vein. 16. Right inferior pul- monary vein. 17. Inferior vena cava. 18. Left ventricle of heart 10. Ri.'ht ventricle. — (Sappey.) lary vessel. The blood emerging from the capillary ^•essels is con- ducted by a corresponding converging system of vessels, the pulmon- ary veins, out of the lungs and into the left auricle of the heart. The main function of the pulmonary apparatus and the pulmonar}^ divi- sion of the circulatory apparatus is to afford a ready means for the exhalation of the carbon dioxid and the absorption of oxygen. In consequence of this exchange of gases the blood changes in color from dark bluish-red to scarlet red. The relations of the heart and its vessels to the lungs and bronchial tubes are shown in Fig. 163. 356 TEXT-BOOK OF PHYSIOLOGY. The Thorax. — The thorax, in which the respiratory organs and their associated structures are lodged, is conic in shape, though somewhat compressed from before backward. Its apex is directed upward, its base downward. The walls of the thorax are composed, first, of a bony framework or skeleton and, second, of muscles and fascia. The bony framework is formed posteriorly by the thoracic vertebrae and the posterior extremities of the ribs, laterally by the ribs, and anteriorly by the costal cartilages and the sternum. The superior opening, through which pass the trachea, esophagus, and blood-vessels, is oval in outhne and measures from side to side about 12.5 cm., and from before backward about 6.25 cm. The interior opening is of large size, but irregular in its boundaries from the upward inclination of the ribs and the downward pro- jection of the sternum. The ribs which form a large part of the thoracic walls consti- tute a series of bony arches at- tached posteriorly to the vertebrae and anteriorly to the sternum through the intermediation of their cartilages. The last two form an exception. The ribs are somewhat twisted upon them- selves and pursue an obhque direction from above downward and forward. As a result the anterior extremity lies at a lower level than the posterior. The costal cartilages are directed upward and forward, with the exception of the upper three, which are almost horizontal. The general arrangement and appearance of the thorax are shown in Fig. 164. The costo-vertebral and costo-chondral and the chondro-sternal articulations are diarthrodial in character and endow the thoracic walls with a considerable degree of mobility. The costo-vertebral joints are two in number, the first being formed by the beveled head of the rib and the bodies of two adjoining vertebrae; the second, by the tubercle of the rib and the transverse process. The costo-chon- FiG. 164. — Thorax, Anterior View. I. Manubrium sterni. 2. Gladio- lus. 3. Ensiform cartilage of xiphoid appendix. 4. Circumference of apex of thorax. 5. Circum- ference of base. 6. First rib. 7. Second rib. 8, 8. Third, fourth, fifth, sixth, and seventh ribs. 9. Eighth, ninth, and tenth ribs. 10. Eleventh and twelfth ribs. 11, 11. Costal cartilages. RESPIRATION. 00/ dral and the chondro-sternal articulations, as their names imply, are formed by the ribs, cartilages, and sternum. The muscles which complete the formation of the thoracic walls are as follows: the diaphragm, the intercostales externi and interni, the levatores costarum, the triangularis sterni, and the infra-cos- tales. The diaphragm is the musculo-membranous sheet which closes the inferior open- ing of the thorax and completely separates its cav- ity from that of the abdomen. It consists of two muscles which arise from the bodies of the first three or four lumbar vertebras and neighboring fascia, from the border of the six lower ribs, and from the ensi- form cartilage (Fig. 165). From this extensive origin the mus- cle fibers pass centrally to be inserted into a common tendon. As the direction of the fibers is from below upward and inward, the diaphragm is somewhat dome- shaped. Its inferior border is for a short distance in contact with the sides of the thorax. The intercostales externi, eleven in number on each side, occupy the spaces between the ribs to which they are attached from the tubercle to the anterior extremity (Fig. 166 and 167). Their fibers, which are arranged in parallel bundles, are directed from above downward and from behind forward. The point of attachment, therefore, of any given bundle of fibers to the rib above, lies nearer the vertebral column, nearer the fulcrum, than the point of attach- ment below. Fig. 165. — Diaphragm, Inferior Aspect, i. Anterior and middle leaflet of central tendon. 2. Right leaflet. 3. Left leaflet. 4. Right crus. 5. Left crus. 6, 6. In- tervals for phrenic nerves. 7. Muscular fibers, from which the Hgamenta arcuata originate. 8. Muscular fi- bers that arise from the inner surface of the six lower ribs. 9. Fibers that arise from ensiform cartilage. 10. Open- ing for inferior vena cava. 11. Opening for esophagus. 12. Aortic opening. 13, 13. Upper portion of trans- versaUs abdominis, turned upward and outward. Anterior leaflet of transversalis aponeurosis. 15, Quadratus lumborum. 16, 16. Psoas magnus. Third lumbar vertebra. 14. 15- 17- 358 TEXT-BOOK OF PHYSIOLOGY. The intercostales interni, eleven in number, occupy the spaces between and are attached to the ribs from the tubercle to the anterior extremity of the cartilages. Their fibers, which are also arranged in parallel bundles, are directed from above downward and back- ward (Fig. 1 66 and 167). The levatores costarum are twelve in number on either side. They arise from the tips of >2^ - the transverse pro- cesses of the last cervi- cal and the thoracic vertebrae with the ex- ception of the last. From the point of origin the fibers pass downward and out- ward in a diverging manner to be inserted into the ribs between the tubercle and the angle. Their action, as their name implies, is to elevate the pos- terior portion of the ribs (Fig. 167). The triangularis sterni arises from the side of the posterior surface of the lower third of the sternum and is inserted by fleshy shps into the cartilages of the ribs from the second to the sixth. From the fact that the inferior opening of the thorax as well as the intercostal spaces are completely closed by the foregoing muscles, and from the further fact , that the superior is closed by fascia except at those points through which pass the trachea, blood- vessels and esophagus, the cavity of the thorax is absolutely air-tight. Fig. 166. — Showing the Situation, the Points of Attachment, and Direction of the Inter- costal Muscles, i. The intercostales externi. 2. The intercostales interni. 3. The intercarti- laginei. — (Deaver.) RESPIRATION. 359 The Pleurae. — Each lung is surrounded by a closed invaginated serous sac, the pleura, of which the inner portion is reflected over and is closely adherent to the surface of the entire lung as far as its root; the outer portion is reflected over the inner wall of the thorax, the superior surface of the diaphragm, and the viscera of the mediastinum. Under normal conditions these two layers of the pleura, the visceral and parietal, are in contact, or at most separated only by a thin capillary layer of lymph. The presence of this fluid prevents friction as the two surfaces play against each other in consequence of the movements of the lungs. THE MECHANIC MOVEMENTS OF THE THORAX. The blood receives oxygen from, and yields carbon dioxid to, the alveoh of the lungs, as it flows through the pulmonary capillaries. That this exchange of gases may continue, it is of primary impor- tance that the air within the alveoh be removed as rapidly as it is vitiated. This is accomphshed by an alternate increase and decrease in the capacity of the thorax, accom- panied by corresponding changes in the capacity of the lungs. During the former there is an inflow of atmospheric air (inspiration), during the latter an outflow of intrapul- monary air (expiration). The con- tinuous recurrence of these two movements brings about that de- gree of pulmonary ventilation nec- essary to the normal exchange of gases between the blood and the air. The two movements together con- stitute a respiratory act or cycle. In the course of the respiratory cycles the thorax presents alter- nately a short period of rest — viz., between the end of an expiration and the beginning of an inspiration — and a relatively long period of activity, including both inspiration and expiration. The former may be regarded as the static, the latter as the dynamic condition of the thorax. In the static condi- tion, the thorax and its contained and associated organs sustain a definite relation one to another; in the dynamic conditions these Fig. 167. — View from behind of Four Dorsal Vertebrae and Three Attached Ribs, show- ing THE Attachment of the Elevator Muscles of the Ribs and the Intercostals. I Long and short elevators. 2. External intercostal. 3. Internal intercostal. — {A llefi Thomson.) 36o TEXT-BOOK OF PHYSIOLOGY. relations undergo a change the extent of which is proportional to the extent of the movements.* THE STATIC CONDITION. Relation of the Thoracic Organs. — Intra-pulmonary Pres- sure: Intra-thoracic Pressure. — In the static condition of the thorax the lungs, by virtue of their distensibility, completely till all parts of the thoracic cavity not occupied by the heart and great blood-vessels (Fig. i68). This condition is maintained by the pressure of the air within the lungs, the intra- puhnonary pressure, which with the respiratory passages open, is that of the atmosphere, 760 mm. Hg. This relation persists so long as the thoracic cavity remains air-tight. If the skin and muscles covering an intercostal space be re- moved the lung can be seen in close contact with the parietal layer of the pleura gliding by with each inspiration and expiration. If, how- ever, an opening be now made in the pleura sufficient to admit air, the lung immediately collapses and a pleural cavity is estabhshed (pneu- mothorax). The pressure of air within and without the lung counter- balancing, at the moment the opening is made, the elastic tissue at once recoils and forces a large part of the air out of the lung. This is a proof that in the normal condition, the lungs, distended by at- mospheric pressure from within, are in a state of elastic tension and ever endeavoring to pull the visceral layer of the pleura away from the parietal layer. That they do not succeed in doing so is due to the fact that the atmospheric pressure from without is prevented from acting on the lung by the firm unyielding walls of the thorax. Intra-thoracic Pressure. — As a result of the elastic tension of the lungs a fractional part of the intra-pulmonary pressure, 760 mm. Hg, is counterbalanced or opposed, so that the heart and great vessels and other intra-thoracic viscera are subjected to a pressure somewhat less than that of the atmosphere; the amount of this pressure will be that of the atmosphere less that exerted by the elastic tissue of the lung in the opposite direction, expressed in terms of millimeters of mercury. In the thorax, but outside the lungs, there then prevails a pressure, intra-thoracic pressure, negative to the pressure inside the lungs. The amount of this intra-thoracic pressure can be approximately * It is a matter of dispute as to whether or not there is an absolute cessation of movement of the thoracic walls at the end of expiration. A graphic record of the movement shows that if there is no absolute cessation, the movement is so slight that, for the purposes here intended, a pause may be admitted. With this admission it is, however, recognized that the forces, both elastic and muscular, which are always acting on the thoracic walls, though in opposite directions, have not ceased to act, but have become so nearly equal that for a brief period they are practically in a con- dition of equilibrium, during which the thoracic walls are stationary. RESPIRATION. !6i determined in several ways. Thus, if shortly after death a mer- curial manometer be inserted air-tight into the trachea of a human being and the thorax opened, the lungs will recoil and compress their contained air. The mercurial manometer will at once show an excess of pressure in the trachea of about 6 mm. This was taken by Bonders as a measure of the force with which the lungs endeavor to recoil. The intra-thoracic pressure would be, therefore, atmos- pheric pressure, 760 mm,, less 6 mm., or 754 mm. Hg. Another method is to insert a rubber catheter through a small opening in an intercostal space into the thoracic cavity. The air which enters Fig. 168. — Section of Thorax with the Lungs, Heart, and Principal Vessels 5. Catheter introduced into the pleural space and connected with a manometer. — {After Moral and Doyen.) through the open extremities of the catheter and leads to a collapse of the lungs may be subsequently aspirated, when the lung returns to its normal position. The catheter is then placed in connection with a ' water manometer. On establishing a communication between them, by the turning of a stopcock, the water will rise in the proximal and fall in the distal hmb of the manometer, indicating a pressure in the thorax negative to that in the lung. The difference in the level of the water in the two limbs of the manometer, expressed in milUmeters of mercury, would also represent the force with which the elastic tissue strives to recoil, the extent to which it opposes 362 TEXT-BOOK OF PHYSIOLOGY. the atmospheric pressure. This subtracted from the atmospheric pressure would give the intra-thoracic pressure. In the Hving dog this latter is less than the former, to the extent of from 3-5 to 5.5 mm. For the same reason the superior surface of the diaphragm also ex- periences a pressure less than that of the atmosphere. Owing to the soft and yielding character of the abdominal walls the atmospheric pressure is transmitted through the abdominal organs to the inferior surface of the diaphragm. The pressure being greater from below than above, the diaphragm is forced upward until it assumes the dome- hke appearance it usually presents. (These relations are shown in Fig. 168.) The cause of the negativity of the intra-thoracic pressure is con- nected with the change in the relation of the lungs to the thorax attending the first inspiration. Previous to birth the walls of the alveoli and bronchioles are collapsed and in apposition. The larger bronchial tubes in all probability contain fluid. The lungs therefore are devoid of air (atelectatic), and, having a specific gravity greater than water, readily sink when placed in this fluid. The capacity of the thorax does not exceed the volume of the lungs. With the first inspiration, however, the thoracic walls take a new position. The air at once rushes into the lungs and distends them. But as the capacity of the thorax even at the end of the expiration is now greater than the volume whicli the lungs could assume without consider- able distention, there at once arises the elastic recoil in the opposite direction, the condition which gives rise to the negativity of the pressure in the thoracic cavity. It is also probable that as the child develops, the thorax grows more rapidly than the lungs, giving rise to a condition which would increase and accentuate the elastic tension and thus increase the negativity of the intra-thoracic pressure. THE DYNAMIC CONDITION. In the dynamic condition as previously stated these relations and pressures change. Thus the diaphragm descends, the ribs ascend, the sternum advances and the lungs expand. The intra- pulmonary pressure varies during both inspiration and expiration. With the enlargement of the thorax through muscle activity, there goes a corresponding increase in the size and capacity of the lungs in consequence of the expansion and pressure of the air in the pulmonary alveoli. With the expansion of the air its pressure falls; but though it is now less than atmospheric, it is yet much greater than the opposing force of the lung tissue. As a result of the fall of intra-pulmonary pressure there is a rapid inflow of air, which continues until atmospheric pressure is restored; that is, at the end of the inspiration. With the diminution of the thorax, through the recoil of the elastic tissue of the thoracic and abdominal walls, there goes a corresponding decrease of lung capacity, in consequence RESPIRATION. 563 Insp Intra-pulmonary pressure. Exp. of the recoil of the elastic tissue of the lungs. As a result, the air in the lungs becomes compressed, its pressure rises above that of 'the atmosphere, and a rapid outflow of air takes place, which continues until atmospheric pressure is again restored; that is, at the end of the expiration. The cause for the fall of intra-pulmonary pressure during in- spiration and the rise during expiration is to be found in the resist- ance offered by the air-passages to the movement of the air, through- out their entire extent, and especially at the level of the vocal bands. The greater the resistance, from whatever cause, physiologic or pathologic, the greater the variations of the pressure. In quiet inspiration the fall of pressure, as indicated by a man- ometer inserted into one nostril, seldom amounts to more than 1.5 mm. ; the rise in expiration, 2.5 to 3 mm. In forcible inspiratory and ex- piratory efl'orts these hmits may be largely exceeded. Thus it was found by Bonders that with one nostril closed and a mercurial manometer inserted into the other the pressure by voluntary efforts could be made to fall 57 mm. during inspiration and to rise 87 mm. during expira- tion. The changes in intra-pulmonary pres- sure are graphically represented in the up- per half of Fig. 169. The intra-thoracic pressure also varies during both inspiration and expiration. As the intra-pulmonary pressure falls, the recoil of the elastic tissue in- creases, with the result of diminishing the intra-thoracic pressure, though not in a steadily progressive manner. The fall of intra- thoracic pressure at the end of a quiet inspiration amounts to about 9 mm. Hg. In forcible inspiratory efforts this fall in intra-thoracic pressure may amount to 30 or 40 mm. of Hg. As the intra- pulmonary pressure rises above the atmospheric pressure during expiration, the recoil of the elastic tissue is again opposed, with the result of increasing the intra-thoracic pressure, though not in a steadily progressive manner. The changes in intra-thoracic pressure are graphically represented in the lower half of Fig. 169. Respiratory Movements. — ^As previously stated,' the ventilation of the lungs is accomplished by an alternate increase and decrease in the capacity of the thorax, accompanied by corresponding changes 760 mm C 760 mm Intra-thoracic pressure. Fig. 169. — Representing the Changes, i, in the Intra-pulmonary, and, 2, in the Intr.\-tho- RAcic Pressures during Inspiration and Ex- piration. 364 TEXT-BOOK OF PHYSIOLOGY. in the lungs, the two movements being known as inspiration and expiration respectively. During the increase in the thoracic capacity, the air passively flows into the lungs; during the decrease in the thoracic capacity, the air passively flows out of the lungs. In both movements the lungs play an entirely passive part, their movements being detemiined by the pressure of air within them and by the tho- racic walls, with which they are in close contact. 1. Inspiration is an active process, the result of muscle activity. 2. Expiration is a passive process, the result mainly of the recoil of the elastic tissue of the walls of the thorax and abdomen and of the elastic tissue of the lungs. In inspiration the thorax is enlarged in all its diameters: viz., ver- tical, transverse, and antero-posterior. In expiration these diameters are again decreased as the thorax returns to its previous condition. Inspiratory Muscles. — The muscles which from their origin, direction, and insertion contribute to the enlargement or expansion of the thorax are quite numerous, and include those muscles which enter into the formation of the thoracic walls (intrinsic muscles), as well as certain muscles which, having their origin elsewhere, are attached to the thoracic walls at different points (extrinsic muscles), though the extent to which they are called into activity depends on the necessity for either tranquil or energetic inspirations. The gradations between a minimum and a maximum inspiration are very slight, and it is difficult to state at what particular instant any given muscle begins to act. It is customary, however, to divide the muscles into two groups: (i) Those active in the average or ordinary inspirations, and (2) those active in maximum or extra- ordinary inspirations. Among the muscles active in ordinary in- spirations may be mentioned the diaphragm, the intercostales externi, the inter cartilagenei, the levatores costariim, the scaleni, and the ser- ratus posticus superior. Among the muscles active in extraordi- nary inspirations may be mentioned, in addition to the foregoing, the sterno-cleido-mastoideus , the trapezius, and the pectorales minor and mijor. The vertical diameter is increased by the contraction and descent of the diaphragm, and more especially of its lateral muscular portions. At the end of an expiration the diaphragm is relaxed, and the lower portion closely applied to the walls of the thorax. At the beginning of an inspiration the muscle-fibers contract, shorten, and approxi- mate a straight line, whereby not only is the convexity of the dia- phragm diminished, but that portion in contact with the thorax is drawn away, thus making a large free space into which the lat- eral and posterior portions of the lungs at once descend. The attachment of the central tendon of the diaphragm to the peri- cardium prevents any marked descent of this portion except in forcible RESPIRATION. ;65 inspirator}' efforts (Fig. 170). The vertical diameters are thus enlarged, though unequally in dift'erent regions of the thorax. As the diaphragm descends it displaces the abdominal viscera, forcing them downward and outward against the abdominal walls, which advance and become more convex. In forcible inspiration the diaphragm, acting from the central tendon as the more fixed point, would draw the lower portion of the thorax inward were this not prevented by the outward pressure of the displaced viscera. The antero- posterior and transverse diameters are increased by the elevation and outward rotation of the ribs and an advance of the sternum, both movements made possible by the construction and arrangement of the costo-vertebral and costo-chondral and chondro- sternal articulations. The construction of these articulations is such as to permit at the first a shght elevation and depression of the head of the rib, and at the second a ghding of the tubercle on the transverse process. The axis around which the rib rotates practically coincides with the axis of the rib neck, which in the upper part of the thorax is almost horizontal, in the lower part somewhat sagittal in direction. Hence when the ribs are elevated the upper part of the thorax increases in its antero-posterior, the lower part in its transverse diameters. At the same time, the lower portion of the sternum is pushed forward and upward by the elevation of the anterior extremity of the ribs and the widening of the angle of the costo-chondral articulation. With the ele- vation of the ribs there goes an eversion or outward rotation which gives an additional increase to the transverse diameters. This elevation and outward rotation of the ribs is the resultant of the cooperation of the follow- ing muscles, viz. : the intercostales exierni, the intercartilagenei, the levator es cost arum, the scaleni and the serratus posticus superior. The action of the external intercostal muscles has been a subject of much discussion. Some investigators have maintained that they are elevators of the ribs, and therefore inspiratory; others that they are depressors of the ribs, and therefore expiratory in function. At the present time the general consensus of opinion is that the former view is the one most in accordance with the facts. The situation of the muscles and the shortness of their fibers render it extremely diffi- cult to obtain myographic tracings of their action. This is supposed, however, to be disclosed by the play of the apparatus suggested Fig. 170 ING Diagram show- Interval BE- TWEEN THE Position OF the Diaphragm IN Expiration (e, e) AND Inspiration {i, i). The Increase in Capacity is shown BY THE White Areas. — {Yeo.) 365 TEXT-BOOK OF PHYSIOLOGY. originally by Bernouilli, which consists, as shown in Fig. 171, of a vertical support carrying two freely movable parallel bars united at their outer extremities by a short vertical strip, representing respec- tively the vertebral column, two adjoining ribs, and a piece of the sternum. The parallel bars are joined to each other by a short elastic band having the direction of and representing the external in- tercostal muscles. If the bars are depressed, the elastic band is elongated and made tense. On releasing the bars the band at once recoils and elevates them. Although the elastic force is the same in both directions, the bars are yet elevated for the reason that in ac- cordance with the parallelogram of forces the component acting upward on the long arm of the lever preponderates over the com- ponent acting downward on the short arm of the lever. The action of the band is supposed to disclose and illustrate the action of the muscle. The intercartilaginei, those portions of the intercostales intern! which occupy the space between the costal cartilages from the sternum to their outer extremity, bear the same relation to the cartilages in reference to the sternum that the external intercostals bear to the ribs in reference to the vertebral column; that is, the point of attachment to the cartilage above, lies nearer the sternum, nearer the fulcrum, than the point of attachment below. Hence the same action is at- tributed to them as to the external intercostals: viz., elevation of the cartilages and the anterior extremities of the ribs. The levatores costarum, as is evident from their points of origin and insertion, elevate the ribs posteriorly. The scaleni muscles, anticus, medius, and posticus, arise from the transverse processes of the cervical vertebrae, and after pursuing a downward and forward direction are inserted into the sternal end of the first and second ribs. The action of the first two, at least, is to elevate the first rib and thus estabHsh a fixed point from which the intercostal muscles can act. The posticus has doubtless a similar action on the second rib. The serratus posticus superior, a quadrilateral sheet of muscle- fibers, arises mainly from the spines of the last cervical and first and second thoracic vertebrae. The anterior extremity is serrated and attached to the outer surfaces of the second, third, fourth, and fifth ribs beyond the angle. The action of the muscle is the elevation of the ribs to which it is attached. In forcible or extraordinary inspirations, whereby the capacity of the thorax is still further increased, the foregoing muscles are rein- forced by the sternocleidomastoideus, the trapezius, and the pec- torales minor and major. Their functions will become apparent from a consideration of their origins and insertions. RESPIRATION. 367 Expiratory Forces and Muscles. — Expiration, as previously stated, is a passive process brought about by the recoil of the elastic tissues of the thoracic and abdominal walls, and of the lungs, aU of which have been stretched and made tense during inspiration. With the cessation of the inspirator}- effort the elastic forces, assisted by the weight of the ribs, sternum, and soft tissues, return the thorax to its former condition. The result is a diminution of all the diameters of the thorax. The vertical diameter is diminished by the recoil of the tense abdominal walls, the replacement of the abdominal organs and the consequent ascent of the diaphragm to its former position. The transverse and antero- posterior diameters are diminished by the descent of the ribs, sternum, and lungs. It is somewhat uncertain if a normal expirator}- movement necessitates active muscle contrac- Fig. 171. — Diagram illustrating the Action of A, the External Intercostal AND B, the Internal Intercostal Muscles. V, V. Vertical support. R, R'. Parallel bars. S. Vertical strip, representing respectively the vertebral column, two ribs, and sternum. tion. If, however, there is any impairment of the elasticity of the lungs or ribs, or any interference with the free exit of the intra- puhnonan- air, it is highly probable that the elastic forces are assisted by the internal intercostal and triangularis stemi muscles. The action of the internal intercostals is less clearly understood than that of the externals, and for the same reasons. If, however, Bernouilli's model discloses the action of the latter, it equally well discloses the action of the former. Thus, if the parallel bars be joined by an elastic band having the direction of and representing the inter- nal intercostals, and then forcibly elevated, the band is elongated and made tense. On releasing the bars, the elastic band at once recoils and depresses them. Here, again, though the elastic force is the same in both directions, the bars are depressed, for the reason that the 368 TEXT-BOOK OF PHYSIOLOGY. component acting downward on the long arm of the lever pre- ponderates over that acting upward on the short arm of the lever. The action of the band is supposed to disclose and illustrate the action of the muscle. The triangularis sterni muscle, judging from its anatomic re- lations, in all probabihty assists in expiration by depressing the car- tilages to which it is attached and as a further result the anterior extremities of the ribs. After the elastic forces have ceased to act and the normal expira- tory movement has been brought to a close, the thorax can be, to a considerable extent, still further diminished in all its diameters by the contraction, through volitional effort, of abdominal and thoracic muscles. To this decrease in the capacity of the thorax, as a result of which a much larger volume of air is expelled from the lungs than during passive expiration, the term forced expiration has been given. With the cessation of muscle activity the elastic forces of the now- compressed thoracic walls, aided by the return of upward displaced abdominal organs, at once restore the thoracic walls to the position they had attained at the eni of passive expiration. Of the muscles active in forced expiration in addition to the intercostales interni and the triangularis sterni, the following may be mentioned, viz.: the abdominales, the serratus posticus inferior, and the quadratus lum- borum. The externus abdominis arises by a series of muscle slips from the outer surface of the lower eight ribs. After pursuing an oblique direction downward and forward, the slips blend to form a single muscle, which is inserted mainly into the outer Hp of the anterior half of the crest of the ihum and into the central abdominal tendon or aponeurosis. The internus abdominis arises mainly from the anterior two-thirds of the inner crest of the ihum and the lumbar fascia. Its fibers pass upward and forward to be inserted into the cartilages of the last three ribs and into the central abdominal tendon. The rectus abdominis arises from the crest of the pubes and is inserted above into the cartilages of the fifth, sixth, and seventh ribs, and occasionally into the ensiform cartilage. The transversalis arises from the cartilages of the last six ribs, the lumbar fascia, and the anterior half of the crest of the ilium. After passing transversely across the abdomen, the fibers are inserted mainly into the linea alba. The conjoint action of these muscles is to diminish the convexity of the abdominal walls and to exert a pressure on the abdominal organs. These, taking the Hne of least resistance, are forced upward against the inferior surface of the diaphragm, which in consequence becomes more strongly curved and ascends higher into the thorax. RESPIRATION. 369 The vertical diameter of the thorax is thus diminished. Acting from the pelvis as a fixed point, these muscles will also draw downward and inward the lower end of the sternum and the lower ribs and diminish the antero-posterior and transverse diameters. The serratus posticus inferior arises from the spines of the last two thoracic and first. two lumbar vertebrae. The fibers pass upward to be inserted into the lower border of the last four or five ribs beyond the angle. Their action is to depress the ribs and assist in expira- tion. The quadratus lumhorum has a similar action on the last rib. Movements of the Lungs. — As the thorax is enlarging in all its diameters during inspiration, through muscle activity, the lungs are correspondingly enlarging in all their diameters, by virtue of their distensibility, through the pressure of the air within them. The lungs must therefore move downward, outward, and forward. That this is the case is made evident both by an examination of the lungs through an intercostal space after removal of the skin and intercostal muscles and by the methods of percussion. The inferior border of each lung descends from the lower border of the sixth to the eleventh rib, inserting itself into the space developed between the thorax and diaphragm as the latter contracts and is drawn away from the former. In consequence of the lateral expansion the anterior border of each lung advances toward the middle line until the heart is almost cov- ered. With the beginning and continuance of expiration the lungs exhibit a reverse movement which continues until they reach their original position. At all times, however, the movements of the lungs are entirely passive and determined by the movements of the thorax. The succession of events in the thorax at the time of a respirator)' act may be summarized as follows: During Inspiration. 1. Enlargement of the thoracic diameters by muscle action. 2. Expansion of intra-pulmonary (alveolar) air. 3. Expansion of the lungs. 4. Lowering of the intra-pulmonar}' air pressure below the atmospheric air pressure. 5. Increase in the negativity of the intra-thoracic pressure. 6. Inflow of atmospheric air, in consequence of its higher pres- sure, until the intra-pulmonary air pressure rises to that of the atmosphere. During Expiration. 1. Diminution of the thoracic diameters by the action of elastic forces. 2. Recoil of the lungs. 3. Compression of the intra-pulmonary (alveolar) air. 24 37© TEXT-BOOK OF PHYSIOLOGY. 4. Rise of intra-pulmonary air pressure above the atmospheric air pressure. 5. Decrease in the negativity of the intra- thoracic pressure. 6. Outflow of intra-puknonary air, in consequence of its higher pressure, until the intra-puhnonar)^ air pressure falls to that of the atmosphere. Respiratory Movements of the Upper Air-passages. — The resistance to the entrance of air into and through the respiratory tract is much diminished by respiratory movements of the nares and larynx which are associated and occur synchronously with the move- ment of the thorax. The nares at each inspiration are dilated by the outward move- ment of their alae or wings, the result of muscle activity. At each expiration they are diminished by the return of their cartilages through the play of elastic forces. The larynx, as shown by observation with the laryngoscope, exhibits corresponding movements of the vocal membranes. Their introduction at this level naturally narrows the tract, and would interfere with both the entrance and the exit of air were they not kept widely asunder during the time they are not re- quired for purposes of phonation. This is accomphshed by the tonic contraction of the posterior crico-arytenoid muscles, which are entirely respiratory in function. It is not infrequently stated that these membranes exhibit consider- able oscillations, outward and inward, corresponding to the periods of inspiration and expiration. The statements of the majority of laryngologists do not favor this view. During tranquil breathing the membranes are widely separated and almost stationary, seldom moving in either direction more than a few milhmeters. In labored respirations these movements are naturally increased in extent. The reflex movements of the membranes occasioned by the unskilful use of the laryngoscope, especially with nervous patients, are not to be re- garded as strictly physiologic. The respiratory space in quiet breath- ing is an isoceles triangle, with a length of 20 mm. and a width at the base of 15.5 mm. Respiratory Types. — Observation of the respiratory movements in the two sexes shows that while the enlargement of the thoracic cavity is accomphshed both by the descent of the diaphragm (as shown by the protrusion of the abdomen) and the elevation of the thoracic walls, the former movement preponderates in the male, the latter in the female, giving rise to what has been termed in the one case the diaphragmatic or abdominal and in the other the thoracic or costal type of respiration. The cause of this greater mobility and activity of the thorax in the female has been a subject of much discus- sion. It has been attributed, on the one hand, to the necessity for a physiologic adjustment between respiration and child-bearing, and RESPIRATION. 371 therefore a specific sex peculiarity; on the other hand, it has been attributed to persistent constriction of the waist, in consequence of which the full play of the diaphragm is prevented and the burden of inspiration is thrown on the thoracic muscles. It has been assumed that if inspiration were confined in women to the diaphragm, there would arise in the latter stages of gestation such an increase in intra- abdominal pressure that not only would respiratory exchanges be interfered with, but fetal fife might be unfavorably influenced, if not endangered. Modern investigations have not confirmed this assump- tion, but, on the contrary, have corroborated the view that the pre- ponderance of thoracic movement is due to the influences of dress restrictions, for with their removal the so-called costal type of breath- ing entirely disappears. While gestation may lead to a greater activity of the thorax, this is but temporary, for with its termination there is a return to the diaphragmatic type of breathing. Number of Respirations per Minute. — The number of respira- tions which occur in a unit of time varies with a variety of conditions, the most important of which is age. The results of the observa- tions of Quetelet on this point, which are generally accepted, are as follows : Age. Respirations per Minute. o- I year, 44 5 years, 26 15-20 " 20 Age. Respirations per Minute. 20-25 years, 18.7 25-30 " 16.0 30-50 " 18.0 From these observations it may be assumed that the average number of respirations in the adult is eighteen per minute, though varying from moment to moment from sixteen to twenty. During sleep, however, the respiratory movements often diminish in number as much as 30 per cent., at the same time diminishing in depth. Rhythm. — Each respiratory act takes place normally in a regular methodic manner, each event occurring in a definite sequence and occupying the same relative period of time. This rhythm, however, is not infre- quently temporarily disturbed by emo- tions, volitional acts, muscle activity, pho- nation, changes in the composition of the blood, etc. ; with the removal of these disturbing factors, the respiratory mechanism soon returns to its normal condition. A graphic representation of the excursions of the thoracic walls, rhythmic or otherwise, is obtained by fastening to the thorax an Fig. 172. — Pneumograph. — (Fitz.) 372 TEXT-BOOK OF PHYSIOLOGY. apparatus, a stethomeier or a pneumograph, which by means of a tam- bour takes up and transmits the movement to a second tambour provided with a recording lever. A simple form of pneumograph, suggested by Fitz (Fig. 172), consists of a coil of wire two and a half centimeters in diameter and about 40 centimeters in length, enclosed by thin rubber tubing, one end of which is closed, the other placed in communication with either a tambour and lever or with a piston recorder. By means of an inelastic cord or chain the apparatus is securely fastened to the chest. With each inspira- tion the spring is elongated, the air within the system is rarefied, and as a result the lever falls; with each expiration the reverse conditions obtain and the lever rises. If the lever be applied to the recording surface of a moving cyhnder, a curve of the thoracic movement, a pneumaiogram, is obtained (Fig. 173), from which it is apparent that inspiration takes place more abruptly and occupies a shorter period of time than expiration; that expiration immediately follows inspiration, but that there is a slight pause between the end of the expiration and the beginning of the inspiration. The time relations of the two movements can be obtained by a magnet-sig- nal actuated by an electric current interrupted once a second. The ratio of inspiration to expiration has been represented as 5 to 6, or 6 to 8. 173— A pneumatogram— (,4//er Volumes of Air Breathed. Marey.) — 'pj^g volumes of air which enter and leave the lungs with each inspiration and expiration naturally vary with the extent of the movement, though four at least may be determined: (i) that of an ordinary inspiration; (2) that of an ordinary expiration; (3) that of a forced inspiration; (4) that of a forced expiration. The apparatus employed for the determination of these different volumes is the spirometer, a modification of the gasometer. The form introduced by Jonathan Hutchinson (Fig. 174) consists of tw^o metallic cylinders, one (a) containing water, the other (b) containing air, the latter being inserted into the former. The air cylinder is balanced by weights so accurately that it remains stationary in any position. A tube, penetrating the base of the water cyhnder, is con- tinued upward through and above the level of the water. The air-space above is thus placed in free communication with the ex- ternal air. A stopcock at the outer end of this tube prevents the escape of the air when this is not desirable. To the free end of the tube a rubber tube provided with a suitable mouthpiece is attached, through which air can be breathed into or out of the air-cylinder. RESPIRATION. 373 With each inspiration the air-cyhnder descends; with each expiration it ascends. A scale, on one of the side supports, graduated in cubic inches or centimeters, indicates the volume of air inspired or expired. With this apparatus Hutchinson, from a long series of observa- tions, deiined and determined the above-mentioned four volumes as follows: 1. The tidal volume, that which flows into and out of the lungs with each inspiration and expiration, which varies from 20 to 30 cubic inches (312 to 468 c.c). 2. The complemental volume, that which flows into the lungs, in addi- tion to the tidal volume, as a result of a forcible inspiration, and which amounts to about no cubic inches (1748 c.c). 3. The reserve volume, that which flows out of the lungs, in addition to the tidal volume, as a result of a forcible expiration, and which amounts to about 100 cubic inches (1562 c.c). After the expulsion of the reserve volume there yet remains in the lungs an unknown volume of air which serves the mechanic function of distending the air-cells and alveolar passages, thus maintaining the conditions essen- tial to the free movement of blood through the capillaries and to the ex- changes of gases between the blood and alveolar air. As this air can not be displaced by voHtional effort, but resides permanently in the alveoli and bronchial tubes though constantly un- yig. dergoing renewal, it was termed — 4. The residual volume, the amount of which is difficult of determination, but has been estimated by different observers at 914 c.c, 1562 c.c, 1980 c.c. The Vital Capacity of the Lungs. — From foregoing statements it is clear that the thorax and lungs are capable of a maximum degree of expansion, at which moment the lungs contain their maximum volume of air. This volume, whatever it may be, represents the entire capacity of the lungs in the physiologic condition, and includes the tidal, the complemental, the reserve, and the residual volumes. Mr. Hutchinson, however, defined the vital or respiratory capacity of the lungs as the amount of air which can be expelled by the most 74. — Spirometer.— {Hutchinson.) 374 TEXT-BOOK OF PHYSIOLOGY. Fig. 175. — Pneumatograph. — {Gad.) forcible expiration after the most forcible inspiration, and which therefore excludes the residual volume. The vital capacity was sup- posed to be an indication of an individual's respiratory power, not only in physiologic but also in pathologic conditions. Though averaging about 230 cubic inches (3593 c.c.) for an individual 5 feet 7 inches in height, the vital capacity varies with a number of conditions, the most im- portant of which is stature. It is found that between 5 and 6 feet the capacity increases 8 inches (125 c.c.) for each inch increase in height. The volume changes of the thorax indicated by the vol- umes of air entering and leav- ing the lungs can be not only determined but graphically represented by means of an apparatus similar in principle to the spirometer, de- vised by Gad and known as the pneumatograph or aero plethy sinograph (Fig. 175). This consists of a quadrangular box with double walls, the space between which is filled with water. The center of the box is an air chamber. A thin- walled mica box sinks into the water. Posteriorly it is attached to and rotates around an axis, which permits of an elevation or depression of the anterior portion. It is also carefully counterpoised. A light lever attached to the mica box records its movements. The interior of the box communicates by a tube with a large reservoir into which the individual breathes, the object being to prevent a too rapid vitiation of the air. Inspiration causes the lever to descend, expiration to as- cend. Previous graduation of the apparatus is necessary to determine the volumes breathed. A graphic record of the volume changes is shown in Fig. 176. Respiratory Sounds. — On applying the ear over the trachea and bronchi there is heard during both inspiration and expiration a well-defined sound, loud, harsh, and blowing in character, which from its situation is known as the bronchial sound. It is especially Fig. 176. — Representing the Volume Changes of the Thorax and Lungs (Diagrammatic). RESPIRATION. 375 well heard between the scapulae above the fourth dorsal vertebra. This sound is produced in the larynx, for with its separation from the trachea the sound disappears. The cause of the sound is to be found in the narrowing of the air-passage at the level of the vocal membranes, though the mechanism of its production is un- certain. On applying the ear to almost any portion of the chest- wall, but especially to the infrascapular area, there is heard during both inspiration and expiration a dehcate, sighing, rusthng sound, which from its supposed seat of origin, the air-vesicles or -cells, is known as the vesicular sound. This sound is supposed to be due to the sudden expansion of the air-cells during inspiration and to the friction of the air in the alveolar passages. THE CHEMISTRY OF RESPIRATION. The general nutritive process as it takes place in the tissues in- volves the assimilation of oxygen and the evolution of carbon dioxid. The former is the first, the latter the last, of a series of chemic changes the continuance of which is essential to the maintenance of all hfe phenomena. A constant supply of oxygen and an equally constant removal of carbon dioxid are necessary conditions for tissue activity. The respiratory movements constitute the means by which the oxygen of the air is brought into, and the carbon dioxid expelled from, the lungs into the surrounding air. The blood is the medium by which the oxygen is transported from the lungs to the tissues and the carbon dioxid from the tissues to the lungs. The exchanges between blood and tissues constitute internal respiration, in contradistinction to the thoracic movements by which the air is brought into relation with the blood, and which constitute external respiration. The transfer of the oxygen by the blood from the interior of the lungs to the tissues, and of the carbon dioxid from the tissues to the interior of the lungs, is the outcome of a series of chemic changes which are related to the exchange of gases between the air in the lungs and the blood, on the one hand, and between the blood and tissues, on the other. In consequence of the many and complex chemic changes which attend these gaseous exchanges, there arise changes in composition of; 1. The air breathed. 2. The blood, both arterial and venous. 3. The tissue elements and the lymph by which they are surrounded. The investigation of the nature of these changes, the mechanism of their production, and their quantitative relations constitutes the subject-matter of the chemistry of respiration. 376 TEXT-BOOK OF PHYSIOLOGY. CHANGES IN THE COMPOSITION OF THE AIR. Experience teaches that the air during its sojourn in the lungs undergoes such a change in composition that it is rendered unfit for further breathing. Chemic analysis has shown that this change involves a loss of oxygen, a gain in carbon dioxid, watery vapor and organic matter. For the correct understanding of the phenom- ena of respiration it is essential, that not only the character but the extent of these changes be known. This necessitates an analysis of both the inspired and expired airs, from a comparison of which certain deductions can be made. The results which have been obtained are represented in the following table: Inspired Air. Expired Air. (Oxygen, 20.80. f Oxygen, 16.02. Carbon dioxid, traces. 100 | Carbon dioxid, 4-38. Nitrogen, 79.20. vols. -I Nitrogen, 79.60. Watery vapor, variable. Watery vapor, saturated. i Organic matter. These analyses indicate that under ordinary conditions the air loses oxygen to the extent of 4.78 per cent, and gains carbon dioxid to the extent of 4.38 per cent. ; that it gains in nitrogen to the extent of 0.4 per cent, and in watery vapor from its initial amount to the point of saturation, as well as in organic matter. It is to these changes in their totality that those disturbances of physiologic activity are to be attributed which arise when expired air is re-breathed for any length of time without having undergone renovation. Special forms of apparatus have been devised for the collection and analysis of gases. Their construction as well as the methods of analysis involved are complicated and need not be described in this connection. The presence of the carbon dioxid, however, may be readily shown by breathing through a glass tube into a vessel con- taining barium or calcium hydrate. The turbidity which immediately follows is due to the formation of barium or calcium carbonate, which can be due only to the presence of carbon dioxid. That this turbidity is not due to the carbon dioxid normally present in the air is shown by the fact that the solution remains clear until the passage of the atmos- pheric air has been maintained for some time. From the percentage loss of oxygen and gain in carbon dioxid, the total oxygen absorbed and carbon dioxid exhaled may be approximately calculated. Thus, if the volume of air breathed daily be accepted at either 10,800 or 12,- 240 liters, and the percentage loss of oxygen be 4.78, the total oxygen absorbed may be obtained by the rule of simple proportion, e. g.: 100 : 4.78 :: 10,800 : x = 516 liters Or 100 : 4.78 :: 12,240 : x = 585 liters. RESPIRATION. 377 By the same method the total carbon dioxid exhaled is found to be either 473 or 526 liters; volumes in both instances which agree very well with volumes obtained by other methods. From the fact that when one volume of oxygen combines with carbon it gives rise to but one volume of carbon dioxid, it is evident that of the oxygen absorbed the greater portion by far is utilized in the oxidation of the carbon, while the smaller portion is utilized in the oxidation of other substances, but especially hydrogen, as shown by the increase in water eliminated beyond that consumed. These amounts, however, are not fixed but variable, and depend on the quality and quantity of the foods, exercise, etc. The ratio of the volume of the carbon dioxid exhaled to the volume of oxygen absorbed is known as the respiratory quotient, and is usually represented by CO > the symbol q-. Thus in the foregoing analysis the respiratory quotient is 0.916. The gain in nitrogen is a variable factor, ranging from zero to 0.9 per cent. This gain is probably of accidental occurrence, due to absorption from the large intestine, in which decomposition of nitrogen-holding compounds is taking place. It is generally believed that free nitrogen plays no part in any phenomenon of combination or decomposition within the body. The gain in watery vapor will depend on the amount previously present in the air. This is conditioned by the temperature. With a rise in temperature the percentage of water increases; with a fall, it decreases. By breathing into a vessel containing pumice stone saturated with sulphuric acid, the vapor may be collected. The difference observed between the weight before and after breathing is an indication of the amount by weight of water exhaled during the time of breathing. It has been calculated that the amount of water exhaled daily approximates 500 grams. Though invisible at ordinary temperatures, it becomes visible at low temperature as soon as it emerges from the respiratory tract. The loss of heat is followed by a condensation of the vapor, which appears at once as a cloudy pre- cipitate. The gain in organic matter is also variable. The amount present is not sufficient to permit of a thorough chemic analysis, but there are reasons for beheving that it belongs to the proteid group of bodies. If it accumulates in the air, especially at high temperatures, it readily undergoes decomposition, with the production of offensive odors. Traces of free ammonia have also been found in the expired air. In addition to these chemic changes, the air experiences physical changes; e. ^., a rise in temperature and an increase in volume. The rise in temperature can be shown by breathing through a suitable mouthpiece into a glass tube containing a thermometer. By this means it has been shown that inspired air at 20° C. rises in tern- 378 TEXT-BOOK OF PHYSIOLOGY. perature to 37° C; at 6.3° to 29.8° C. The increase in the tem- perature will depend upon that of the air inspired and the time it remains in the lungs. If retained a sufficient length of time it will always become that of the body. As a result of the heat absorption the expired air increases in volume about one-ninth over that of the inspired air. When corrected for temperature and pressure and freed from aqueous vapor, the volume of the expired air is less than that of the inspired air by about one-two hundred and fiftieth. The Composition of the Alveolar Air. — The foregoing state- ment of the composition of the expired air, derived in part from the upper air-passages, trachea, and bronchi, does not necessarily repre- sent the composition of the alveolar air. It is very probable that the percentage of carbon dioxid is greater, the percentage of oxygen less, in the latter than in the former. This is made evident by collecting in several portions the expired air as it escapes from the respiratory tract and subjecting it to analysis. The last portion always contains a larger amount of carbon dioxid and a smaller amount of oxygen than the first portion. The determination of the composition of the alveolar air is extremely difficult. It has been estimated to contain from 5 to 6 per cent, of carbon dioxid and from 14 to 18 per cent.'__of oxygen. Pulmonary Ventilation. — It is owing largely to this inequahty of volumes and consequently of the " partial pressures" of these two gases in the trachea and alveoli that the degree of ventilation necessary to exchange of gases between lungs and air is maintained. Though the respiratory movements doubtless create currents in the air-passages which carry, on the one hand, a portion of the inspired air directly into the alveoh, and, on the other hand, carry a portion of the alveolar air directly out of the body, other portions find their way into and out of the alveoli in accordance with the laws of diffusion. If the tension of the oxygen in the trachea is 158 mm. Hg and in the alveoh 114 mm. Hg, diffusion downward will take place. Equilibrium, however, is never estabhshed, as the oxygen is continually disappearing by passing into the blood. On the contrary, if the carbon dioxid tension in the alveoli is 38 to 40 mm. Hg, and in the trachea 0.3 mm. Hg, diffusion will take place upward. EquiUbrium will never be estab- hshed, however, as the carbon dioxid is constantly coming out of the blood. Pulmonary ventilation may also be aided by those alternate changes in volume of the heart, great vessels, and lungs occurring as the result of the heart-beat and producing the so-called cardio-pneumatic movements. CHANGES IN THE COMPOSITION OF THE BLOOD.* The blood which flows into the lungs through the pulmonary artery is dark bluish-red, that which flows from the lungs into the RESPIRATION. 379 pulmonary veins is scarlet red, in color. The blood is changed, while flowing through the lung capillaries, from the venous to the arterial condition. As the air in the lungs gains carbon dioxid and loses oxygen, it is fair to assume that what the air gains the blood loses, and what the air loses the blood gains. In other words, the blood, while passing through the lungs, is changed from venous to arterial by the loss of carbon dioxid and the gain of oxygen. The change in color of venous blood from dark bluish to scarlet red is strikingly shown by shaking it in a test-tube with oxygen or atmospheric air. The blood which flows into the tissues through the arteries is red, that which flows from the tissues into the veins is bluish, in color. The blood while flowing through the tissue capillaries is changed from the arterial to the venous condition. Since arterial blood when deprived of oxygen becomes bluish-red, the indication is that the change in color is associated with, if not entirely due to, the escape of oxygen into the tissues. The constant ehmination of carbon dioxid from the blood into the lungs indicates that the carbon dioxid is as constantly passing from the tissues through the capillary walls into the blood. These considerations are confirmed by the results of analyses which have been made of both venous and arterial blood. The presence of gas in the blood is demonstrated by subjecting it under appropriate conditions to the vacuum of the mercurial air-pump, into which it at once escapes. From 100 volumes, an average of 60 volumes of gas at standard pressure, 760 mm. Hg and temperature 0° C, can thus be obtained. Gases of the Blood. — An analysis of the volumes of gas removed from both venous and arterial blood shows that each consists of oxygen, carbon dioxid, and nitrogen, though in different amounts. An average composition of the gases extracted from dog's blood obtained from the right ventricle and carotid artery is given in the following table: 1,1 J fOxvs^en, 0-12 vols. » .. • 1 ui j f Oxvgen, 20 vols. enous blood ^ -^ ,. . , ^ _ „ Arterial blood ^ ^-P ,■ ., <, , i Carbon dioxid, 4=; 1 i Carbon dioxid, 40 100 vols. .-, ^^ ,{ 100 vols. -.TV " t>^itrogen, i- 2 I. Nitrogen, — 1-2 The changes produced in the blood by respiration, both external and internal, become apparent from a comparison of these analyses. The venous blood while passing through the lungs gains from eight to eleven volumes per cent, of oxygen and loses five volumes per cent, of carbon dioxid. The arterial blood while passing through the tissues loses ox}^gen and gains carbon dioxid in corresponding amounts. The volume of nitrogen is not appreciably changed. The Relation of the Gases in the Blood. — The mechanism by w^hich the gases become associated with the blood at the moment 38o TEXT-BOOK OF PHYSIOLOGY. of their entrance into it, and again become dissociated just prior to their exit from it, as well as their relation while in transit, will be more readily understood after reference to & few elementary facts relative to the absorption of gases in general and the conditions of temperature and pressure by which it is influenced. It is well known that Hc^uids will take up, absorb, or dissolve unequal volumes of different gases in accordance with their solu- bilities and with variations in temperature and pressure. Water, for example, will absorb oxygen, carbon dioxid, and nitrogen as well as other gases in amounts varying with the foregoing conditions. The amount of any gas absorbed by one volume of a liquid at a tem- perature of o° C. and a pressure of 760 mm. Hg is known as the co- efficient of absorption. The coefficient of absorption of i volume of distilled water for oxygen is 0.0489 volume; of carbon dioxid, 1.797 volumes; of nitrogen, 0.023 volume. With a rise in tem- perature, however, the absorptive power of water for each one of these gases diminishes. On the contrary, as the pressure rises the quantity of the gas absorbed increases, and as it falls, decreases. In all gaseous determinations, therefore, it is always necessary, for purposes of comparison, to reduce the obtained volumes to standard temperature (0° C.) and pressure (760 mm. Hg). If water be exposed to atmospheric air consisting of oxygen, carbon dioxid, and nitrogen in the ordinary proportions, at any given temperature and pressure, the water will absorb unequal volumes of each of the three gases. The pressure under which each gas is absorbed is a part only, however, of the total atmos- pheric pressure at the time. The pressure exerted by any one of these three gases is known as its partial pressure, and depends on the percentage volume of the gas present. If atmospheric air contains at standard pressure and temperature 79.15 volumes per cent, of nitrogen, its partial pressure will be ^{^ of 760, or 601.54 mm. Hg; if the air contains 0.04 volume per cent, of carbon dioxid and 20.85 volumes per cent, of oxygen, the partial pressure of each will be 0.30 mm. Hg and 158.46 mm. Hg respectively. The absorption of each gas is independent of all the rest, and is the same for nitrogen, for example, as if it alone were present at a pressure of 601.54 mm. Hg. Again, if water holding in solution a certain volume of a gas — carbon dioxid, for example — be exposed to an atmosphere containing but 0.04 volume per cent, of carbon dioxid, and having therefore a pressure of but 0.3 mm. Hg, the gas will at once begin to leave the water, and continue to do so until the pressure of the carbon dioxid in the atmosphere balances the tension of the gas in the water, at which moment the escape of the gas ceases. The tension of a gas in a liquid is equal to that pressure in milhmeters of mercury of the same gas in the atmosphere which is required to keep it in solution. Pressure RESPIRATION. 3S1 and tension are therefore in this case convertible terms. What is true for the carbon choxid is true for any other gas that may be in solution. It will be recalled that the blood yields up its gases when subjected to the vacuum of the mercurial pump; that is, to a diminu- tion or complete removal of the atmospheric pressure. From this it might be inferred that the gases are merely held in solution by pressure, and at once escape the moment they are exposed to a space in which there is a very slight or a total absence of pressure. It is therefore necessary to test this supposed condition of the gases in the blood by subjecting the latter to gradually diminishing pres- sures, with a view of determining in how far the evolution of the gases follows the law of partial pressures. For convenience the conditions of each gas will be considered separately. Oxygen. — If blood is subjected to a succession of pressures pro- gressively less than the standard, it is found that though oxygen is evolved, its evolution is not in accordance with the law of partial pressures ; that is, in proportion to the diminution of pressure. Within wide limits — e. g., from 760 to 238 mm. atmospheric pressure, to which correspond oxygen pressures of 160 and 50 mm. respec- tively — there is but a shght increase in the amount of oxygen evolved ; and it is not until the pressure of the oxygen falls to about 40 to 3c mm. that it begins to be liberated in large amounts. From this on, the oxygen continues to be liberated with decreasing pressures, until the zero point is reached, when all gaseous discharge ceases. Co- incidently the blood changes in color from a bright red to a deep bluish- red. It is evident from the results of this procedure that the con- dition of the oxygen in the blood is but to a shght extent one of physical absorption. The indications are that it partakes of the nature of a chemic combination. If the red corpuscles be removed from the blood and the plasma alone be treated in the manner above described, it will be found that the oxygen liberated now follows the law of partial pressure. The amount so liberated, however, is small — about one per cent, of the total oxygen of the blood. The agent therefore which holds the oxygen in com- bination is the red corpuscle, and more especially the hemoglobin, which constitutes about 94 per cent, of its volume. This is proved by the fact that a solution of gas-free hemoglobin of a strength equivalent to that of the blood (14 per cent.), exposed to gradually increasing pressures from zero up to 30 or 40 mm. oxygen pressure, will absorb large quantities of oxygen; beyond this point the amount absorbed is again small in comparison. At 70 mm. pressure the hemoglobin is almost saturated. Coincidently with this absorption the hemo- globin changes in color from dark blue to bright red; changes from hemoglobin to oxyhemoglobin. The reverse method, that of subjecting oxyhemoglobin to gradually diminishing pressures, yields opposite 382 TEXT-BOOK OF PHYSIOLOGY. results. As one gram of hemoglobin combines with 1.59 c.c. of oxygen, and as the percentage of hemoglobin is 13.50 to 14, it is evident that there is sufficient hemoglobin to combine with practically all the oxygen usually present in the blood. The relation of the oxygen in the blood is therefore partly physi- cal, partly chemical. One per cent, is physically absorbed by or dissolved in the plasma; the remainder is chemically combined with the hemoglobin. The association or combination of oxygen is favored by a pressure of at least from 30 to 50 mm. Hg and upward; the dissociation, by diminution of pressure. In the conversion of hemoglobin into oxy- hemoglobin two antagonistic forces are at work, heat and chemic affinity. The former endeavors to prevent, the latter to favor, the union. Chemic affinity increases with the influence of mass, that is, in proportion to the number of atoms in a unit of volume, with the density and with the partial pressure of the oxygen. Diminution of pressure reduces the mass influence and permits the heat to bring about dissociation (Bunge). The following table by Hiifner shows the relative proportion of hemoglobin and oxyhemoglobin in blood containing 14 per cent, hemoglobin and exposed to air at gradually diminishing pressures: HERic Pressure ! MM. Hg. Partial Pressure of Oxygen in mm. Hg. Hemoglobin Percentage. Oxyhemoglobin Percentage. 760 524.8 357-8 2380 159-3 no . 75 50 1.49 2.14 3-II 4.60 98.51 97.86 96.89 95-4° 119 3 47-7 . 23.8 25 10 5 8.79 19.36 32-51 91.21 80.64 67.49 0.0 0.0 I03.00 o.oo Carbon Dioxid. — The blood yields up its contained carbon dioxid to the vacuum of the gas-pump as completely as it does its oxygen. The same is not the case, however, if the red corpuscles are first removed and the experiment made with either plasma or serum. Even at zero pressure the fluid contains carbon dioxid, as shown by its liberation on the addition of some weak acid, as tartaric or phos- phoric, an indication that it exists in a state of firm combination. The same result follows the addition of the red blood-corpuscles, which act in a manner similar to the acids just mentioned. This property of the corpuscles has* been attributed to hemoglobin, and especially when in the state of oxyhemoglobin. It is for this reason that blood yields all its carbon dioxid to the vacuum of the gas-pump. The Hmit of pressure at which the plasma ceases to physically absorb carbon dioxid and begins to chemically combine it is not very clearly defined. It has been estimated that of the entire amount, 38 to 45 volumes, only about 2.5 volumes are so absorbed, the re- mainder beino; in a condition of both loose and stable combination. RESPIRATION. 383 An analysis of the serum, and presumably of the plasma, shows the presence of sodium salts, with which the carbon dioxid could enter into combination, viz.: sodium carbonate and dibasic sodium phosphate. The sodium is thus partly divided between carbonic acid and phosphoric acid. The amount of the sodium which falls to carbon dioxid will depend on the mass influence of the latter; that is, its partial pressure. At its origin in the tissues the carbon dioxid acquires a consider- able tension, and its mass influence is correspondingly large. On entering the blood it combines with sodium carbonate, with the formation of sodium bicarbonate, as shown in the following equation : NajCOa + CO2 + HjO = 2NaHC03. At the same time, having a greater mass influence than the phos- phoric acid, it wdll withdraw from the dibasic sodium phosphate one-half of its sodium, with the formation of sochum bicarbonate and monobasic sodium phosphate, as shown in the following equation: NajHPO^ + CO2 -f H2O = NaHCOj -t- NaHjPO,. With the diffusion of the carbon dioxid from the blood into the alveoH its tension in the venous blood falls, its mass influence dimin- ishes, while that of the phosphoric acid relatively increases. As a result, the sodium is withdrawn from the sodium bicarbonate, an additional liberation of carbon dioxid takes place and dibasic sodium phosphate is re-formed. The association or combination of the carbon dioxid with the basic salts depends on its partial pressure; its dissociation in the lungs, on a diminution of pressure. Nitrogen. — This gas exists in both arterial and venous blood in a state of solution. There is no evidence that it enters into com- bination with any other element. Tension of the Gases in the Blood. — It will be recalled that a Hquid holding in solution one or more gases will on exposure to an atmosphere composed of the same gases either give up or absorb volumes varying in amount and in accordance with their partial pressures until equihbrium is established. If the pressure of any one gas in the atmosphere is greater than in the liquid, it is absorbed; if the pressure is less, it is discharged. Knowing the pressure of the gases in percentages of an atmosphere, at the beginning and the end of an experiment, the original tension or pressure of the gases in the liquid can be easily calculated. On this principle various forms of apparatus known as aerotonometers have been devised by which the tension of the gases in the blood can be determined. These apphances consist essentially of a glass tube containing oxygen and carbon dioxid in known amounts and tensions. The 384 TEXT-BOOK OF PHYSIOLOGY. blood from an animal is then allowed to flow directly from an artery or vein into the tube. As it flows down its sides in a thin layer it presents a large surface to the action of the contained gases. In the aerotonometer of Fredericq the blood made non-coagulable by the injection of peptone is returned from the opposite extremity of the tube to the animal. This enables the experiment to be continued for an hour or more. A knowledge of the tensions of the blood gases is of interest, as it affords a clue to the mechanism by which the interchange takes place between the lungs and the blood, on the one hand, and the blood and tissues, on the other. The results, however, of different observers are not sufliciently in accord to permit of positive deductions. In the well-known and generally accepted experiments of Strass- burger, the tension of the oxygen in the arterial blood of the dog was found to be 29.64 mm. Hg, or 3.9 per cent, of an atmosphere, and in the venous blood 22.04 mm. Hg, or 2.9 per cent. The tension of the carbon dioxid in the venous blood was found to be 41.04 mm, Hg, or 5.4 per cent, of an atmosphere, and in the arterial blood 21.8 mm. Hg, or 2.8 per cent. In the experiments of Fredericq the oxygen tension in the arterial blood was found to be 106 mm. Hg, or 14 per cent, of an atmosphere. CHANGES IN THE COMPOSITION OF THE TISSUES AND LYMPH. From previous statements the inferences can be drawn that the oxygen leaves the blood as the latter flows through the capillaries; that it passes through the capillary wall into the surrounding lymph and so to the tissue-cells; that it oxidizes food materials in the tissue- cells whereby the potential energy of the former is hberated as kinetic energy; that the carbon dioxid so evolved passes into the lymph and through the wall of the capillary into the blood. While this is doubtless the case, the presence of free oxygen in the tissues can not be demonstrated by the usual methods of gas analysis. Only in the saHva and in the blood of the placental umbiHcal vein can it be shown that oxygen has directly passed through the capiUary wall. For this reason it has been claimed by a few investigators that oxygen does not leave the blood, but that the field of its activity as an oxidizing agent is limited to the blood-current, where it meets with and oxidizes easily reducible substances entering from the tissues. On this view the potential energy of the food would be liberated by mere decom- position or cleavage in consequence of cell activity. Nevertheless many facts from the fields of comparative physi- ology and physiologic chemistry combine to support the view that oxygen is absolutely necessary to the maintenance of the life of all tissue-cells. Though thev will continue to manifest their character- RESPIRATION. 385 istic activities — e. g., contraction on the part of a muscle, secretion by a gland, the conduction of a nerve impulse by the nerve, etc. — for a variable length of time after oxygen is prevented from gaining access to them, nevertheless they will in due time die. The necessity for oxygen on the part of the tissues and the avidity with which they absorb it, is shown by their power of reducing pig- ments such as alizarine blue. If this pigment be injected into the blood-vessels of an animal and the animal killed in about ten minutes, it will be found that while the blood exhibits a deep blue color the tissues present their usual colors. But after exposure to the air or to free oxygen the latter also acquire the characteristic blue color. The explanation offered for this fact is that the tissues in their need for oxygen absolutely extract it from the pigment, reducing it to a color- less compound, which, however, on exposure recombines with oxygen and regains the original color. Though free oxygen can not be shown to be present in the tissues, there are many reasons for beheving that it is continually passing into them by way of the lymph-stream. Its rapid disappearance would indicate that it is immediately utihzed for the production of carbon dioxid (which is improbable on other grounds), or that the tissues possess a capacity for oxygen storage, of placing it in reserve under some combination or other, by which it can be securely retained until required for oxidation purposes. This is rendered probable from the fact that the carbon dioxid evolved at any given moment is not necessarily dependent on the oxygen just absorbed, for if oxygen be withheld from a nutritive fluid which is being artificially circulated through a recently isolated organ, carbon dioxid will continue to be discharged for some time. A muscle, or even a living animal, — e. g., a frog, — placed in an atmosphere of pure nitrogen will remain active and evolve COj for even several hours. Naturally the absorption of oxygen and the discharge of carbon dioxid and the changes of composition which are incident to nutri- tion will be most marked in those tissues characterized by the greatest degree of physiologic activity. ^luscle-tissue exhibits these changes to a greater degree than bone. Tissues with inter- mediate degrees of activity should exhibit corresponding degrees of respiratory change. Experiment confirms this view. Thus, 100 grams each of muscle, spleen, and broken bone from a recently Hving animal exposed to the air for twenty-four hours absorbed respectively 50.8 c.c, 27.3 c.c, and 17.2 c.c. of oxygen, while each discharged during the same period 56.8 c.c, 15.4 c.c, and 8.1 c.c of carbon dioxid respectively. In another series of experiments by a different observer 100 grams of muscle absorbed in three hours 23 c.c. of oxygen, and 100 grams of bone 5 c.c. of oxygen. Both tissues discharged carbon clioxid in amounts proportional to the 386 TEXT-BOOK OF PHYSIOLOGY. ATMOSPHERIC AIR. 0-I58 MM MG,OR 20.85 P.C CO 0.3 MM HG OR 0.04- PC O-TEN SION 2.Z. 0+ M M HG OR 2.. 9 P.C. CO_ TENSION 2. ■♦I.04- M M H G OR 5.4 PC. AL-VEOLUS oxygen absorbed. The same respiratory changes may be more satisfactorily demonstrated by passing blood through the tissues of isolated organs and the tissues of recently living animals. The analysis of the blood before and after perfusion shows a loss of oxygen and a gain in carbon dioxid. Tension of the Gases in the Tissues. — As the presence of free oxygen can not be demonstrated, its tension there must be regarded as nil. The tension of the carbon dioxid is quite high, though difficult of exact determination. It has been estimated at from 45 to 68 mm. Hg, or from 6 to 9 per cent, of an atmosphere. ■ The variations of tension or pres- sure of these two gases in the lungs, in different parts of the vascular ap- paratus, and in the tissues, and their re- lations to each other, are shown in Fig. 177, expressed in mm. Hg and per- centages of an at- mosphere. The Mechan- ism of the Gas- eous Exchange. — In these pressure differences s u f f i - cient cause is found for the exchange of the gases. The oxygen pressure in the alveoli being in excess of that in the blood, the gas passes through the thin al- veolo-capillary wall into the plasma. As the pressure in the plasma rises, the oxygen combines with the hemoglobin, until the latter is al- most saturated. On passing into the systemic capillaries the blood enters a region in which the oxygen tension of the surrounding tissues is nil. At once a dissociation of the oxyhemoglobin and oxygen takes place, after which the latter passes through the capillary wall into the plasma and so to the tissue-cells, in which it is stored and utilized. The sojourn of the blood in the capillaries being of VENOUS BI.OOD ARTERIAL BLOOD O -TENSION o. 00 M M H a CO - TENSION -TENSION 29. S* M M HC OR 3 9 P.C. CO —TENSION TISSUES Fig. 177. — Diagram showing the Relative Tension OF Oxygen and Carbon Dioxid in the Lungs, IN the Blood, and in the Tissues. RESPIRATION. 387 short duration, the oxyhemoglobin can part with but a portion of its oxygen, sufficient, however, to satisfy the needs of the tissues. The carbon dioxid pressure in the tissues being in excess of that in the blood, it passes through the capillary wall into the blood, where it exists in the free and combined states. On passing into the pul- monic capillaries the blood enters a region in which the carbon dioxid in the alveoli is less than in the blood. At once a diffusion and dissociation of the carbon dioxid takes place through the alveolo- capillary wall until equilibrium is established. This, however, is of very short duration, for the carbon dioxid so eliminated is rapidly removed from the lungs by the respiratory movements. While diffusion, in response to physical and chemic conditions, thus plays a large part in, and is suthcient to account for, the ex- changes of gases, it is possible that the alveolar or respiratory epithe- lium may also play an essential role. It is believed by some in- vestigators that it is active in both the absorption of oxygen and the excretion of carbon dioxid. This view has been suggested as a means of interpreting the results of the experiments of more recent investigators, made with a view of determining the tension of the blood gases. It was found by Bohr that the tension of the oxygen in arterial blood was often as high as loi to 144 mm. Hg, and in many instances higher than the tension of the oxyen in the trachea, while the carbon dioxid tension in the trachea was higher than in the blood. Haldane and Smith by a different method found an oxy- gen tension in the arterial blood of 200 mm. Hg. If these results should prove to be correct, though they are at present subject to con- siderable criticism and not generally accepted, some other force than diffusion would have to be found to explain the facts. It would then remain to determine in how far the alveolar epithelium could be regarded as an active agent in both absorption and excretion in opposition to pressure. THE TOTAL RESPIRATORY EXCHANGE. The total quantities of oxygen absorbed and carbon dioxid dis- charged by a human being in twenty-four hours are measures of the intensity of the respiratory process, and an indication of the extent and character of the chemic changes attending all life phenomena. Their determination and their relation to each other are matters of interest and importance. The quantities which have been obtained by differ- ent observers are the outcome of calculations based on certain groups of data and of experiments made with special forms of apparatus. Thus from the total air breathed daily, estimated from the amounts obtained during a longer or shorter period, of experiments with spiro- metric apparatus, and from the percentage loss of oxygen and gain of 388 TEXT-BOOK OF PHYSIOLOGY. carbon dioxid shown by an analysis of the respired air, it can be cal- culated at least approximately what the total amounts of oxygen ab- sorbed and carbon dioxid exhaled must be. If it be assumed that the minimum daily volume of air breathed is io,8co liters and the maximum volume 12,240 liters, and the percentage loss of oxygen is 4.78, then the total volume of oxygen absorbed is 516 liters (735.17 grams) or 585 liters (836.42 gramsj. By the same method the total carbon dioxid exhaled daily is found to be either 473 liters (931.8 grams) or 526 liters (1036 grams). The direct experiments which have been made with specially devised forms of apparatus, both on human beings and animals, have yielded similar results. With those forms which are adapted for both human beings and animals — Scharhng's, Petten- kofer and Voit's — it is only possible, however, to determine the amount of carbon dioxid and water, and from these to calculate the amount of oxygen absorbed. This is done by deducting the loss in weight by the man or animal during the experiment from the combined weights of the carbon dioxid and water discharged. The difference represents the oxygen absorbed. The Pettenkofer-Voit apparatus (Fig. 178) consists essentially of a chamber large enough to admit a man and capable of being made air-tight with the exception of an inlet for air for breathing purposes. The respired air is drawn through a tube and measured by a large meter turned by a water or gas motor. By means of a side tube a fractional quantity of the main column of air is diverted to an absorption apparatus by a small pump. This air first passes into a vessel containing H2S0^, by which the water is collected; then into long tubes containing barium hydroxid, by which the carbon dioxid is absorbed ; thence into a small meter, by which its amount is registered. From the amount of water and carbon dioxid thus ob- tained the amounts of both in the total air breathed are calculated. The water and carbon dioxid previously present in the air are simulta- neously determined by a corresponding absorption apparatus and de- ducted from the amounts obtained from the respired air. As the apparatus is traversed constantly by a column of air of normal composition and the waste products removed as rapidly as discharged, the experiment can be continued for periods varying from six to twenty-four hours without detriment to the subject of the experiment. With those forms adapted only for animals — Regnault's and Reiset's, or Jolyet and Rcgnard's — it is possible to determine simul- taneously the absorption of oxygen and the discharge of carbon dioxid. As the apparatus employed is completely closed, the carbon dioxid must be removed as soon as discharged and the oxygen re- newed as soon as absorbed. The former is accomplished by the as- piratory action of moving bulbs containing an alkah, the latter by a steadily acting pressure on a reservoir of oxygen. This apparatus RESPIRATION. 389 >.-a 390 TEXT-BOOK OF PHYSIOLOGY. (Fig. 179) consists essentially of a bell-jar in which the animal is placed. This is brought into connection by tubes, on the one hand, with the oxygen reservoir, and, on the other hand, with the aspiratory bulbs, kept in motion by some form of motor. The construction of each of these forms of apparatus is so complex, the conduct of an experiment and the final determination of the results Fig. 179. — Regnault's and Reiset's Respiration Apparatus. A. Bell-jar for the reception of the animal, surrounded by a compartment, B, containing water. N, N, N. Reservoirs of oxygen communicating, on the one hand, with the animal chamber, and, on the other hand, with pressure bottles, P, by which the oxygen is driven into the animal chamber. G, G. Aspiratory bulbs containing sodium hydro.xid in solution for the absorption of the carbon dioxid. The bulbs are given an alternate up-and-down movement by a falling weight or electric motor. SO complicated, that a detailed description would be out of place in a work of this character.* Among the results obtained by these and other methods a few are given in the following table: * Both forms of apparatus are in use in the Physiological Laboratory of the Jeffer- son Medical College and are fully described by Prof. H. C. Chapman in his text- book on Physiology, to which the reader is directed for further information. RESPIRATION. 391 Oxygen Absorbed. Observer. Carbon Dioxid Discharged 746 grams. Vierordt. 876 grams. 700 " Pettenkofer and \'oit. 800 663 " Speck. 770 The amounts of oxygen absorbed in Pettenkofer and Voit's experi- ments varied from 594 to 1072 grams; of carbon dioxid exhaled, from 686 to 1285 grams. In all these results it is evident on examination that the volume of oxygen absorbed is always greater than the volume of carbon dioxid exhaled, or, what amounts to the same thing, the weight of the oxygen absorbed is always greater than the weight of the oxygen entering into the formation of the carbon dioxid exhaled. The reason for this difference between the amounts of oxygen in the inspired air and in the CO2 exhaled is found in the fact that on a mixed diet — one containing fat — a portion of the oxygen is utiHzed in the oxidation of the hydrogen of the fat with the formation of water. Under such a diet the respiratory quotient is always less than unity, usually 0.907. On a purely carbohydrate diet — one in which there is no surplus hydrogen — all the oxygen will combine with carbon and be returned as carbon dioxid, and hence the respiratory quotient will be unity. The respiratory quotient therefore indicates the extent to which the oxygen absorbed is utilized in oxidizing carbon, on the one hand, and hydrogen, on the other. Since the total oxygen absorbed and carbon dioxid discharged will vary considerably with the size of 'the animal, it is customary, for purposes of comparison, to reduce all total results to the unit of body- weight (one kilogram) and to the unit of time (one hour). Respiratory Activity. — The activity or the intensity of the respiratory process may be measured either by the oxygen absorbed or the carbon dioxid discharged. But as the carbon dioxid is more easily estimated than the oxygen, it is usually taken as the index of the activity, though there are reasons for believing that it would be more accurately indicated or represented by the oxygen. Whatever factor may be accepted as the measure, it is certain that the respiratory activity varies in different tissues in accordance with their functional activities, being least in bones and greatest in muscles. This is shown by the relative amounts of oxygen absorbed and carbon dioxid discharged by equal amounts of each of these and other tissues in twenty-four hours, as shown in the following table: QUANTITY OF O AND CO 2 ABSORBED AND EXHALED DURING TWENTY-FOUR HOURS, IN CUBIC CENTIMETERS. By 100 Grams of: Oxygen Absorbed. Carbonic Acid Exhaled. Muscle, 50.8 c.c; 56.8 c.c. Brain, Kidneys, Spleen, Testicles, Pounded bones, 4.S-8 42.8 ' 37-0 15.6 ' 2 7-.S 15-4 ' 18.3 27.5 ' 17.2 8.1 ' 392 TEXT-BOOK OF PHYSIOLOGY. The total respiratory change therefore of the body as a whole is the resultant of the respiratory changes of its individual organs and tissues, and is conditioned by all influences which retard or hasten their activity. Among these influences the more imi)ortant are the following: Muscle Activity.^ — As the muscles constitute a large part of the body, about 40 per cent., and as muscle-tissue absorbs and discharges relatively large quantities of oxygen and carbon dioxid, it is readily apparent that an increase in their activity would be followed or attended by an increase in the respiratory exchange. In passing from a condition of body repose to one of marked activity there ought to be an increase in the amount of oxygen absorbed and COj dis- charged. Pettenkofer and Voit found that a man in repose who absorbed daily 807.8 grams of oxygen and discharged 930 grams COj absorbed during work 1006 grams of oxygen and discharged 1 137 grams of CO,. Edward Smith, who estimated only the COj, found that a man in repose who discharged carbon dioxid at the rate of 161. 6 c.c. per minute increased the amount while walking at the rate of two and three miles an hour to 569 c.c. and 851 c.c. respec- tively. Similar results have been obtained by other investigators. Digestive Activity. — The activity of the alimentary canal, involving contraction of its muscle coat through its entire length as well as secretion of its related glands called forth by the inges- tion of food, materially influences the absorption of oxygen and discharge of carbon dioxid, independent of the increase due to the oxidation of food materials after absorption. It was found that in a fasting man a dose of sodium sulphate increased the absorption of oxygen as much as 17 per cent, and the discharge of CO2 24 per cent. (Lowy). It is difficult to determine how much of the increase after a meal is therefore due to food oxidation and how much to functional activity of the canal itself. The consumption of nitrogenized meals, however, has a greater effect than non-nitrogenized meals. Temperature. — A rise in temperature of the surrounding air has as an effect a diminution in the amounts of oxygen consumed and carbon dioxid discharged. A fall in temperature has the opposite effect. Thus a cat at a temperature of — 3.2° C. consumed during a period of six hours 21.39 grams of oxygen and discharged 22 gram.s of carbon dioxid, while at a temperature of 29.6° C. the correspond- ing amounts for the same period of time were for oxygen 13.9 grams and for carbon dioxid 13.12 grams. Lavoisier and Sequin, having reference only to the oxygen, found that a man at a temperature of 15° C. consumed 38.31 grams of oxygen, while at a temperature of 32.8° C. the corresponding amount was but 35 grams. Similar results have been obtained by other observers with different animals. The explanation of these facts is to be found in the increased activity RESPIRATION. 393 of all physiologic mechanisms coincident with a fall, and in the decreased activity, coincident with a rise in temperature. The lower temperatures act as a stimulus to the peripheral terminations of the nerve system, bringing about reflexly increased activity of the body at large. The muscles especially are not only reflexly but vohtionally excited to greater activity. This leads naturally to an increase in the consumption of oxygen and in the production of carbon dioxid and in the evolution of heat. In cold-blooded animals the respiratory exchange is influenced in a manner the reverse of that observed in warm-blooded animals. With a rise of external temperature and a corresponding ris^ of body-temperature the discharge of carbon dioxid steadily increases. Thus a frog in an atmosphere at 0° C. with a body-temperature of 1° C. discharged per kilogram per hour 4.31 c.c. of carbon dioxid; in an atmosphere of 35° C. with a body-temperature of 34° C. there was discharged 325 c.c. per kilo per hour. Intermediate tempera- tures were attended by corresponding increases in the amounts of COj discharged. The reason for this difference in the two classes of animals is probably to be found in the want, in the cold-blooded animals, of a self-adjusting heat-regulating mechanism. Age. — In early youth, as a result partly of the more pronounced activity of the nutritive energies and partly of a cutaneous surface relatively greater, as compared with the mass of the body, than in adult life, the absorption of oxygen and the discharge of carbon dioxid are greater both absolutely and relatively. Thus, in a boy of nine and a half years with a weight of 22 kilograms it was found that in twenty-four hours there was a discharge of carbon dioxid amounting to 488 grams, or 0.92 gram per kilo per hour, and in man with a weight of 65.5 kilograms there was a discharge of 804.72 grams, or 0.51 gram per kilo per hour. MODIFICATIONS OF RESPIRATORY RHYTHM. The character of the respiratory movements is materially modified by a change in the quantitative and qualitative composition of the air and blood as well as by changes of a pathologic nature of the re- spiratory apparatus itself. Eupnea." — So long as the air retains its normal composition and the respiratory mechanism its structural integrity, so long do the respiratory movements exhibit a normal rhythm and frequency. To the condition of easy tranquil breathing the term eupnea is given. In this condition the percentages of oxygen and carbon dioxid in the blood are such as to favor at least the rhythmic discharge of nerve impulses to the respiratory muscles, of sufficient energy and frequency for the maintenance of normal respiration. 394 TEXT-BOOK OF PHYSIOLOGY. Hyperpnea. — The normal rate of the respiratory movements is increased by a rise in body-temperature, by active exercise, and by emotional states. Whatever the cause, the increase in rate and prob- ably in depth is termed hyperpnea. Febrile states characterized by a rise in the temperature of the blood increase considerably the respiratory activity. This is due in all probability to a warming of the respiratory center, in consequence of which its excitabihty is heightened; for surrounding the carotid arteries with warm tubes and heating the blood on its way to the medulla has the same effect. It is also possible, however, that the high temperature of febrile conditions may interfere with the absorb- ing power of hemoglobin, and thus by diminishing the quantity of oxygen absorbed lead to more frequent respirations. To the hy- perpnea induced by heat the term thermo- polypnea is frequently given. Muscle activity, especially if it is violent and indulged in by those unaccustomed to exercise, is generally followed by increased rate and depth of breathing, and not infrequently it is attended with such extreme difficulty that the condition approximates that of dyspnea. This condition is attributed to the production and dis- charge into the blood of unknown waste products which act as irritants to the respiratory center and thus increase its activity. As they apparently can not be isolated and their chemic nature deter- mined, it is presumable that they are speedily oxidized or reduced in the blood. Experiment has shown that the increase of carbon dioxid does not account for the increased rate of breathing. Emo- tional states temporarily increase respiratory activity. With their disappearance the normal condition returns. Apnea. — If the respiratory movements be voluntarily increased in frequency and depth for a short time it will be found on cessation that for a variable length of time the respiratory mechanism remains in a condition of complete rest or inaction. To this complete cessation of activity the term apnea is given. The same phenomenon is witnessed in animals when the lungs are rapidly inflated with air by means of bellows. At one time this was attributed to an excess of oxygen in the blood (the result of the forced ventilation of the lungs), complete saturation of the plasma and hemoglobin, in consequence of which the respiratory center remained inactive. This has been dis- proved, however, by modern chemic analyses of the blood. The condition is now attributed: 1. To increased ventilation of the lungs and an increased percentage of oxygen in the alveoli, as a result of which the normal percentage of oxygen in the blood can be maintained for a longer period than usual. 2. To a stimulation of the peripheral terminations of the pneumo- RESPIRATION. 395 gastric nerve whereby the discharge of nerve impulses from the respiratory center is temporarily inhibited. Division of the pneumogastric nerve prevents the development of the apneic condition. Dyspnea. — Excessive and laborious respiratory movements constitute a condition known as dyspnea. Movements of this char- acter indicate that the blood is deficient in oxygen or overcharged with carbon dioxid. In either case the excitability of the respiratory center is abnormally heightened. These conditions of the blood may be caused: (i) By all those pathologic conditions of the respiratory apparatus which limit the free entrance of oxygen into and the free exit of carbon dioxid from the blood; (2) by those alterations in the composition of the air and subsequently in the blood which arise when the individual is confined in a space of moderate size with imperfect ventilation. The want of oxygen in the blood gives rise to more forcible inspirations; the presence of CO2 in excess, to more forcible expirations — showing that the former condition affects the inspiratory portion of the respiratory center, the latter condition the expiratory portion. A deficiency in the amount or quality of the hemoglobin is usually attended with dyspnea. Asphyxia. — If the state of the blood observed in dyspnea be ex- aggerated, — that is, if the decrease in the percentage of oxygen and the increase in the percentage of carbon dioxid become more marked, — the respiratory movements become more laborious. A continuance of this changed composition of the blood eventuates in death. Before this occurs the individual exhibits a succession of phenomena, to the totality of which the term asphyxia is given. Asphyxia may be caused: (i) By a sudden interference with the entrance of oxygen into and the exit of carbon dioxid from the blood, as in drowning, occlusion of the trachea from any cause, double pneumothorax, etc. (2) By confinement in a small space the air of which speedily undergoes a loss of oxygen and an accumulation of carbon dioxid. In the first instance death may occur in a few minutes ; in the second instance it may be postponed several hours or more, the time varying with the size of the space. The succession of phenomena presented by an individual in the asphyxiated condition is as follows: Increased rate and depth of the respiratory movements, passing rapidly from hyperpnea to dyspnea, with an active contraction of all the muscles concerned in respira- tion, ordinary and extraordinary; a blue cyanosed condition of the face from the rapid accumulation of carbon dioxid and disappearance of the oxygen of the blood; a diminution in the depth of inspiration and an increase in the force and extent of expiration, followed by general convulsions; collapse, characterized by unconsciousness, loss of the reflexes, relaxation of the muscles, a weak action of the heart, 396 TEXT-BOOK OF PHYSIOLOGY. a disappearance of the pulse and death. As shown by observation of the circulatory apparatus in artificially induced asphyxia, there is primarily an increase in the activity of the heart, soon followed by retardation; a rise of blood-pressure in the early stages and a fall to zero after collapse has set in. The retardation and final cessation of the heart, as well as the rise of the blood-pressure, are to be attributed to stimulation of the cardio-inhibitory and vasomotor centers from the accumulation of the carbon dioxid. With the exhaustion of the nerve-centers, there is a general relaxation of the muscles and a fall of the pressure. THE NERVE MECHANISM OF RESPIRATION. The nerve mechanism by which the respiratory muscles are ex- cited to action is extremely complex and involves the action of both afferent and efferent nerves and their related nerve-centers in the cen- tral nerve system. For the free introduction of air into the lungs it is essential that the nasal and laryngeal passages and the cavity of the thorax be simultaneously enlarged. The muscles by which these results are accomplished have already been mentioned and described. Their simultaneous and coordinate contraction implies the coordinate activity of motor nerves and their centers; thus, the nasal and laryn- geal muscles (the dilator naris and the posterior crico-arytenoid) involve the activity of the facial and inferior laryngeal nerves re- spectively, the centers of origin of which lie in the gray matter beneath the floor of the fourth ventricle; the diaphragm and intercostal muscles involve respectively the activity of the phrenic and inter- costal nerves, the centers of origin of which lie in the anterior horn of the gray matter of the spinal cord at a level, for the phrenic, of the fourth, fifth, and sixth cervical nerves, and for the intercostals at the level of the upper thoracic nerves. Division of any one of these nerves is followed by paralysis of its related muscle. The coordinate contraction of the inspiratory muscles implies a practically simultaneous discharge of nerve impulses from each of the foregoing nerve-centers, accurately graduated in intensity in accordance with inspiratory needs. This has been supposed to necessitate the existence in the central nerve system of a single group of nerve-cells from which nerve impulses are rhythmically discharged and conducted to the previously mentioned nerve-centers in the medulla oblongata and spinal cord, by which they are in turn excited to activity. To this group of cells the term "inspiratory center" has been given. For the free exit of air from the lungs it is not only essential that the air-passages be open, but that the air in the lungs be compressed until its pressure rises above that of the atmosphere. This is accomplished by the recoil of the elastic tissue RESPIRATION. 397 of the lungs and thorax, the return of the displaced abdominal organs aided by atmospheric pressure, and the contraction of the expiratory muscles. In how far muscle action is necessary for expiratory pur- poses will depend on the resistance offered to the outflow of air and on the degree of efficiency of the elastic forces. The simultaneous and coordinate activity of the expiratory muscles also involves the action of motor nerves and nerve-centers. The simultaneous and coordinate discharge of nerve impulses, also graduated in intensity for expiratory needs, apparently implies the existence in the central nerve system of a single center from which nerve impulses are rhythmically dis- charged which excite and coordinate the lower nerve-centers. To this group of cells the term "expiratory center" has been given. The two centers taken together constitute the so-called "respiratory center." The existence, however, of a definite group of cells which initiates the respiratory movements has not as yet been demonstrated. Never- theless there is in the dorsal portion of the medulla oblongata, at the level of the sensory end-nucleus of the vagus nerve, a region the sudden destruction of which on one side is followed by a cessation of respira- tory movements on the corresponding side, though they continue on the opposite side, a fact which indicates that the area, though acting as a unit, is bilateral. The bilateral character of the area is also shown by the continuance of the respiratory movements on both sides after longitudinal division of the medulla. Destruction of the entire region is followed by a complete cessation of respiratory activity and death of the animal. For this reason the term "noeud vital" was apphed to it. In this area the respiratory center was located. It has, however, been shown by Gad that if this area be gradually destroyed by cauterization the respiratory movements do not cease, but con- tinue until the cauterization has reached a point far forward in the formatio reticularis, in which the respiratory center was assumed to lie. Though its existence has not been anatomically determined beyond question, it is permissible to speak of the central mechanism as a "center" located in the medulla oblongata. The activity of the respiratory center has long been described as automatic or autochthonic (Gad) in character, expressive of the idea that the rhythmic discharge of nerve impulses is conditioned by the composition of the blood or lymph by which it is surrounded. Thus so long as the blood retains its normal composition the respiratory movements are normal. If, however, the blood becomes richer in oxygen and poorer in carbon dioxid, the rate of discharge of nerve impulses and the inspiratory movements diminish until the condition of apnea results. If, on the contrary, the blood becomes poorer in oxygen and richer in carbon dioxid, the reverse condition obtains: 398 TEXT-BOOK OF PHYSIOLOGY. viz., an increased rate of discharge of nerve impulses, increased fre- quency of respiration, hyperpnea, and dyspnea. This view is ap- parently supported by the fact that after division of the fifth and vagus nerves the respiratory movements continue, though changed in character, becoming less frequent and deeper. Whether they would continue after division of ail afferent nerves it is impossible to state, since from the nature of the case such an experiment would be most difficult to perform. The first inspiration after birth is supposed to be due to the direct stimulation of the respiratory center by the increase in the carbon dioxid present in the blood, though it may be aided by the cooling of the skin due to vaporization of the amniotic fluid. Whether the respiratory center is automatic in character or not, it may be influenced directly by nerve impulses descending from the brain in consequence of volitional acts or emotional states, and in- directly by nerve impulses reflected to it from the general periphery through various afferent nerves, in consequence of agencies acting on their peripheral filaments: e. g., cold applied to the skin, irritating gases to the nasal and bronchial mucous membrane, distention and collapse of the pulmonary alveoli. Of all afferent nerves, the vagus appears to be the most influential in maintaining the rhythmic discharge of nerve impulses from the respi- ratory center. Thus, if while the animal is breathing regularly and quietly both vagi are cut, the respiratory movements become much slower, falling perhaps to one-third their original number per minute. If the central end of the divided vagus be stimulated with weak faradic currents, the respiratory movements are increased in fre- quency and their depth diminished until the normal rate is restored. With the cessation of the stimulation the former condition at once returns. This would indicate that in the physiologic state afferent impulses are ascending the vagus fibers which influence the rate of discharge from the respiratory center. If, however, the stimulation is increased in strength, the inspiratory movement gradually so ex- ceeds the expiratory that the muscles pass into the tetanic state and the chest-walls come to rest in the condition of forced inspiration. The vagus evidently contains fibers which augment the activity of the inspiratory center and inhibit the activity of the expiratory center. If, on the other hand, the central end of the divided superior laryngeal nerve be stimulated with faradic currents, the opposite effect is pro- duced: viz., an excess of the expiratory over the inspiratory move- ment until the chest-waUs come to rest in the condition of forced expiration. The superior laryngeal nerve evidently contains fibers which augment the activity of the expiratory center and inhibit the activity of the inspiratory center. The same result not infrequently follows stimulation of the divided RESPIRATION. 399 vagus and always after the administration of large doses of chloral. The vagus contains two classes of fibers, one of which augments the activity of the inspiratory while inhibiting the activity of the ex- piratory; the other inhibiting the inspiratory while augmenting the expiratory. The stimulus adequate to the excitation of the nerve- fibers in the physiologic condition was formerly believed to be the chemic action of carbon dioxid; it is now believed to be a mechanic action, the result of the alternate distention and collapse of the walls of the pulmonary alveoli. Thus, it has been shown by Head that if the lungs are actively inflated there will be produced an inhibition of the inspiratory and an augmentation of the expiratory movement until the chest comes to rest, a result similar in all respects to that produced by stimulation of the superior laryngeal nerve. On the other hand, if the lungs are collapsed by the artificial withdrawal of air, there will be produced an augmentation of the inspiratory and an inhibition of the expiratory movements until the chest comes to rest in extreme inspiration, a result similar in all respects to that produced by powerful stimulation of the central end of the divided vagus. These facts indicate that the respiratory mechanism is reflex and self-regulating in character, and the stimulus, the alternate collapse and distention of the pulmonary alveoli ; collapse augmenting the inspiratory and inhibiting the expiratory, distention, inhibiting the inspiratory and augmenting the expiratory center. THE EFFECT OF THE RESPIRATORY MOVEMENTS ON THE FLOW OF BLOOD THROUGH THE INTRA-THORACIC VESSELS AND ON THE ARTERLAL PRESSURE. I. On the Intra-thoracic Vessels. — The forces which cause the air to flow into and out of the lungs will at the same time and in the same way cause the blood of the systemic vessels to flow into, through, and out of the intra-thoracic vessels. From the tendency of the pul- monary elastic tissue to recoil, the blood-vessels in the thorax at the end of an expiration sustain a positive pressure, about six millimeters of mercury less, than that in the lungs, or, in other words, a pressure negative to that of the atmosphere by six millimeters. As a result the blood in the systemic vessels standing under atmospheric pressure will flow steadily tow^ard the intra-thoracic veins, the venae cavag, and the right side of the heart; i. e., from a point of high to a point of low pressure. Since during inspiration, with the increasing tendency to pulmonary recoil, the positive pressure on the veins and heart may diminish by thirty millimeters of mercury, the blood will flow in increased volume from the systemic to the intra-thoracic vessels. The right heart, being more generally filled with blood, will discharge a larger volume with each contraction into the pulmonary artery. 400 TEXT-BOOK OF PHYSIOLOGY. Coincident with these effects a similar effect is produced in the arterioles and capillaries of the pulmonary alveoli. Situated between the two elastic layers of the alveolar wall, embedded in a meshwork of connective tissue, the pressure to which they are subjected at the end of an expiration will also be a few millimeters less than that of the intra-pulmonary air; and at the end of an inspiration it will be considerably less. With the inspiration there will occur a dilatation of the vessels, a larger flow of blood through them and into the pul- monary veins. The left heart, being in consequence more generously filled with blood, will discharge a larger volume into the aorta at each contraction. During expiration the flow of blood through the intra- thoracic vessels will be diminished for the reverse reasons. 2. On the Arterial Pressure. — An examination of a tracing of the arterial pressure will show that it is characterized by small un- dulations due to the cardiac beat and large undulations due to the respiratory movements, inspiration being accompanied by a rise, expiration by a fall of pressure. These results are readily accounted for by the difl'erence in the volume of blood discharged by the left heart into the aorta during the time of the two movements. If a tracing of the respiratory movements and of the blood-pressure be taken simultaneously, it will be found that the rise of pressure does not exactly correspond with inspiration, nor the fall of pressure with expiration ; for a certain period after the beginning of an inspiration the pressure continues to fall, and for a certain period after the beginning of an expiration the pressure continues to rise. During the remainder of the period, however, inspiration is attended by a rise, expiration by a faff of pressure. The explanation of these results lies in the fact that at the beginning of the inspiration, when the vessels dilate, the blood-flow momentarily slows; the left heart continuing to discharge small volumes into the aorta, the pressure continues to fall. So soon as the left heart begins to be better filled, the pressure at once begins to rise, x^t the end of an expiration the flow of blood into the left heart continues and the pressure rises, but with the return of the intra-thoracic pressure the vessels diminish in caliber, the volume of blood transmitted by them becomes less, the output of the left heart dechnes, and the pressure faUs. CHAPTER XIV. ANIMAL HEAT. The chemic changes which take place in the tissues and organs of the living body and which underlie all manifestations of life are attended by the evolution of heat. In consequence of this each animal acquires a certain body-temperature. In man, as well as in other mammals and in birds, the chemic changes are extremely active and the evolution of heat very great. Through some special heat- regulating mechanism, by wdiich heat- production and heat-dissipation are kept in equilibrium, these animals have acquired and maintain within limits a constant temperature which is independent of and generally above that of the surrounding atmosphere. As the temperature of these animals is high and per- ceptible to the sense of touch, they were originally designated "warm- blooded" animals. As this temperature is constant notwithstanding the great variations in external temperature during the summer and winter seasons, they are more appropriately termed constant-tem- peratured or homoiothermous animals. The intensity of the body- temperature determined by the insertion of a thermometer in the rectum varies in different classes of mammals from 37.2° C. to 40° C. The causes of this variation are doubtless connected with peculiarities or organization. In birds the rectal temperature is usually higher, var}dng from 40.9° C. in the pigeon to 44° C. in the titmouse and the swift. In reptiles, amphibians, and fish chemic changes, as a rule, are not very active and heat-production relatively slight. As they are devoid of a sufficiently active heat-regulating mechanism, the tem- perature of the body is largely dependent on that of the medium in which they live, though it is always one or more degrees above it. In winter the body-temperature of frogs, for example, may decline as low as 8.9° C, the temperature of the surrounding medium being 6.7° C. When subjected to temperatures below zero, the temperature of the body may fall below the freezing-point also, when the lymph and fluids of the body become ice. Though apparently dead, the gradual elevation of the temperature restores their vitality. In summer-time, on the contrary, the body-temperature may attain to 38° C. Similar variations have been observed in other animals. As the temperature of these animals is low and perceptibly below that of our own bodies, they were originally termed "cold-blooded" animals; 26 401 402 TEXT-BOOK OF PHYSIOLOGY. as their temperature is inconstant, varying with the temperature of the surrounding medium, they are more appropriately termed "varia- ble tempcratured " or poikilo-thermous animals. THE TEMPERATURE OF THE HUMAN BODY. The determination of the temperature of the human body under the changing conditions of life is a matter of the greatest physiologic and chnical interest. The temperature of the superficial portions of the body may be obtained by the introduction of a thermometer into the mouth, the rectum, the vagina, or the axilla. As a result of many observations it has been found that the temperature of the rectum is, on the average, 37.2° C; that of the mouth, 36.8° C; that of the axilla, 36.9° C. Owing to radiation and conduction the surface tem- perature is lower than that of either the mouth or rectum, and varies to a slight extent in different regions of the body: e. g., at a room- temperature of 20° C. the skin of the pectoral region has a tem- perature of 34.7°; that of the cheek, 34.4°; that of the calf, 33.6°; that of the tip of the ear, only 28.8°, etc. In the interior of the body, especially in organs in which oxidation takes place rapidly, and which at the same time are protected by their anatomic surroundings from rapid radiation, the temperature is higher than that observed in the rectum. From an investigation of the temperature of the blood as it emerges from the liver, the muscles, the brain, alimentary canal etc., it is evident that these organs have a higher temperature than the rectum. As the chemic changes underlying physiologic activity vary in intensity and extent in different regions of the body, there would be marked variations in their temperature were it not that the blood, having a large capacity for heat-absorption, distributes the heat almost uniformly to all portions of the body, so that at a short distance beneath the surface the temperature does not vary but within a few degrees. In the dog the temperature of the blood in the aorta and in its principal branches is approximately 38.3° C. In passing through the systemic capillaries the temperature falls from radiation and con- duction to surface temperature, to again rise as the venous blood approaches the deeper regions of the body. In the neighborhood of the renal veins and in the superior vena cava the temperature is again that of the aorta. In the portal vein the temperature rises to 40.2° C. ; in the hepatic vein, to 40.6° C. In the right ventricle, owing to the admixture of blood from different localities having different temperatures, the temperature falls to 38.2° to 40.4°. In passing through the pulmonary capillaries the temperature of the blood again falls, so that in the left ventricle it will register from 38° C. to 40.2° C ANIMAL HEAT. 403 There is thus usually a difference between the two sides of the heart of about 0.2° C. Variations in the Mean Temperature. — The mean tempera- ture of the human body for twenty-four hours, which for the mouth and rectum may be accepted at 36.7° C. and 37.2° C. respectively, is subject to variations from a variety of circumstances, such as age, periods of the day, food, exercise, etc. Age. — i\t birth the temperature of the infant is slightly higher than that of the mother, registering in the rectum about 37.5° C. In a few hours it rapidly declines to about 36.5°, to be followed in the course of twenty-four hours by a rise to the normal or slightly beyond. During childhood the temperature gradually approximates that of the adult. In old age the temperature rises, as a rule, and attains a maximum at eighty years of 37.4° C. Periods 0} the Day. — The observations of Jiirgensen show that there is a diurnal variation in the mean temperature of from 0.5° C. to 1.5° C, the maximum occurring late in the afternoon, from 5 to 7 o'clock, the minimum early in the morning, from 4 to 7 o'clock. This diurnal variation in the mean temperature is related to corresponding variations in many other physiologic processes, and its causes are to be found in the ordinary habits of hfe as regards the time of meals, periods of exercise, sleep, etc. Food and Drink. — The ingestion of a hearty meal increases the temperature but slightly — not more than 0.5° C. Insufficiency of food lowers the temperature^ total withdrawal of food, as in starva- tion, is followed by a steady though shght decline, until just preceding the death of the animal, when it falls abruptly to from 6° to 8° C. Cold drinks lower, hot drinks raise the temperature. Food and drinks, however, only temporarily change the mean temperature, and after a short period equilibrium is restored through the activity of the heat-regulating mechanism. Alcoholic drinks lower the tem- perature about 0.5° C. In large toxic doses in persons unaccustomed to their use the temperature may be lowered several degrees. This is attributed not to a diminution in heat-production, but rather to an increase in heat-dissipation (Reichert) from increased action of the heart, dilatation of the blood-vessels of the skin, and increased activity of the sweat-glands. Exercise. — The temperature may be raised by active muscular exercise from 1° to 1.5° C. as a result of increased activity in chemic changes in the muscles themselves. A rise beyond this point is prevented by the increased activity of the circulatory apparatus, the removal of the heat to the surface, and its rapid radiation. External Temperature. — The external temperature influences but slightly the mean temperature of the human body. In the tropic as well as in the arctic regions, notwithstanding the change in the 404 TEXT-BOOK OF PHYSIOLOGY. temperature of the air, that of the body remains almost constant. The same is true for the seasonal variations in the temperature of the temperate regions. THE SOURCE AND TOTAL QUANTITY OF HEAT PRODUCED. The Source of Heat. — The immediate source of the body-heat is to be found in the chemic changes which take place in all the tissues and organs of the body. Each contraction of a muscle, each act of secretion, each exhibition of nerve-force, is accompanied by the evolution of heat. The chemic changes are for the most part of the nature of oxidations, the union of oxygen v^ith the elements, carbon and hydrogen, of the food principles either before or after they have become constituents of the tissues. The ultimate source of the body- heat is the latent or potential energy in the food principles, which was absorbed from the sun's energy and stored up during the growth of the vegetable world. In the metaboHsm of the animal body the food principles are again reduced through oxidation, directly or indirectly, to relatively simple bodies, such as urea, carbon dioxid, and water, with a Hberation of a large portion of their contained energy which manifests itself as heat and mechanic motion. The Total Quantity. — The total quantity of heat liberated in the body daily may be approximately determined in at least two ways : (i) By determining experimentally the heat values of different food principles by direct oxidation; (2) by collecting and measuring with a suitable apparatus, a calorimeter, the heat evolved by the oxidation of the food within, and dissipated from, the body daily. I. Direct Oxidation. — The amount of heat which any given food principle will yield can be determined by burning a definite amount — e. g., I gram — to carbon dioxid and water and ascertaining the extent to which the heat thus liberated will raise the temperature of a given amount of water: e. g., 1 kilogram. The amount of heat may be expressed in gram or kilogram degrees or calories; a gram calorie or kilogram calorie being the amount of heat required to raise the temperature of a gram or a kilogram (1000 grams) of water 1° C. The apparatus employed for this purpose is termed a calorimeter, which consists essentially of a closed chamber, in which the oxidation takes place, surrounded by a water-jacket. The rise in temperature of the water indicates the amount of heat produced. The results obtained by investigators employing different calor- imeters and different food principles of the same class vary, though within narrow limits: e. g., i gram casein yields 5.867 kilogram calories; i gram of lean beef, 5.656; i gram of fat, 9.353, 9.423, 9.686 calories; i gram of starch or sugar, 4.1 16, 4.182, 4.479, etc., calories. These results are, however, physical values, and indicate the quan- ANIMAL HEAT. 405 tity of heat such quantities of foods give rise to when completely oxidized to carbonic acid and water. In the human body the carbo- hydrates and the fats, with the exception of the small portion which escapes digestion, are reduced to carbon dioxid and water, and hence practically liberate as much heat as they do when oxidized outside the body. The proteids, however, are only reduced to the stage of urea. As this compound is capable of further reduction in the calor- imeter to carbon dioxid and water, with the liberation of heat, the quantity of heat it contains must therefore be deducted from the physical heat value of the proteid. According to Rubner, i gram of urea will yield 2.523 kilogram calories. As about one-third of a gram of urea results from the oxidation of i gram of proteid, the amount of heat to be deducted from the heat value of the proteid is J of 2.523, or 0.841 calorie. It has also been shown by the same in- vestigator that some of the ingested proteid is found in the feces, the heat value of which must also be determined and deducted. This having been done, the physiologic heat value becomes 4.124 calories. The following estimates give approximately the number of kilo- gram calories which should be liberated within the body when the proteid is burned to the stage of urea, and the fat and carbohydrate to the stage of carbon dioxid and water: 1 gram of proteid 4-124 calories I " fat 9.353 I " carbohydrate 4. 116 " The total number of kilogram calories yielded by the various diet scales can be readily determined by multiplying the quantities of the food principles consumed by the foregoing factors. The diet scale of Vierordt, for example, yields the following: 120 grams of proteid 404.88 calories 90 " fat 841.77 " 330 " starch 1358.28 " Total, 2694.93 " The total calories obtained from other diet scales would be as follows : Ranke's, 2335; Voit's, 3387; Moleschott's, 2984; Atwater's, 3331; Hultgren's, 3436. These numbers indicate theoretically the total heat-production in the body daily. 2. Calorimetric Measurements. — By this method the heat dissi- pated from the body of an animal is directly collected and measured, and the amount so obtained is taken as a measure of the heat evolved by the oxidation of the food. A calorimeter is therefore an apparatus for the direct estimation of the quantity of heat dissipated from the body in a given time. The substance employed for collecting and measuring the heat is either water or air. The calorimeters in 4o6 TEXT-BOOK OF PHYSIOLOGY. general use consist essentially of two metallic boxes placed one within the other, though separated by a space sufficiently large to hold a definite amount of water (Fig. i8o). The animal is placed in the inner box, which is also provided with tubes for the entrance of fresh and the exit of expired air. The heat radiated is absorbed by the water and its temperature raised. To prevent loss by radiation and to render it independent of changes in the surrounding temperature the calorimeter is surrounded by a poorly conducting material, such as wool. The temperature of the animal is taken at the beginning and the end of the experiment. If the temperature of the animal remains the same at the end of the experiment, then the heat absorbed by the water represents the amount produced by the animal. If, on the con- trary, the temperature of the animal rises or falls, the number of calories so retained or lost must be added to or sub- tracted from the amount absorbed by the calor- imeter. In the determi- nation of the absolute amount of heat retained lost by the animal sc-sssEiKiimin or Fig . 1 80. — Water Calorimetek of Dulong. D and D'. Tubes for the entrance and exit of air. T and T'. Thermometers for ascertain- ing the temperature of the water. S. A mechanic contrivance for stirring the water for the purpose of distributing the absorbed heat uniformly. To prevent the escape of heat with the expired air, the tube D' is wound many times in the water-space beneath the animal cage. above or below the initial temperature, as well as that absorbed by the materials of the appara- tus in these various in- stances, the w^ater equiv- alent of the tissues of the animal and the materials of the calorimeter must be obtained, and then added to or subtracted from, as the case may be, the amount of water in the calorimeter, and the amount thus ob- tained multiplied by its rise in temperature. In properly conducted experiments in which the sources of error are reduced to a minimum there is a very close correspondence between the total physiologic heat value of the food and the amount collected by the calorimeter. Thus, in an experiment detailed by Rubner a dog was given during twelve days 228.06 grams of proteid and 340.4 grams of fat the physical heat value of which was estimated at 4429 calories. The urine and feces during this period were collected and their heat value determined, which amounted to 305 calories. The heat which theoretically ANIMAL HEAT. 407 should have been produced was 4124 calories. During the experi- ment the calorimeter actually absorbed 3958 calories, a difference between the theoretic and experimental results of 156 calories. Calorimetric experiments on man corresponding to those made by Rubner on dogs have not been successful, owing purely to tech- nical difficulties. Various attempts have been made, however, to determine the daily heat-dissipation. Liebermeister immersed a man in a bath with a temperature lower than that of the man's body. From the rise in temperature of the water it was calculated that the man produced daily 3525 calories. Leyden placed the leg alone of a man in a calorimeter. In one hour 6 calories were absorbed. Assuming that the total superficial area of the body was fifteen times that of the leg, he calculated, taking into consideration various sources of error, that the entire body would produce daily 2376 cal- ories. Ott, employing a w^ater calorimeter, found that the body of a man produced 103 calories during an afternoon, or at the rate of 2472 calories daily. These and similar experiments, while not free from many objections, furnish results which indicate that the heat dissipated from the body approximates the physiologic heat values of the foods. HEAT-DISSIPATION AND REGULATION OF THE TEMPERATURE. Heat-dissipation.— From the preceding statements it is evident that the body is continually evolving heat in amounts daily far in excess of that necessary for the maintenance of the body-temperature. Should this heat be retained, the temperature of the body would be raised at the end of twenty-four hours an additional 18° or 20° C, — a temperature far in excess of that compatible with the maintenance of physiologic processes. That the body may be kept at the mean temperature of 37.8° C. it is essential that the heat evolved be dissi- pated as fast as produced. This is accomplished in several ways: (i) In warming the food and drink to the temperature of the body. (2) In warming the inspired air to the same temperature. (3) In the evaporation of water from the lungs. (4) In evaporating water from the skin. (5) In radiation and conduction from the skin. The quantities of heat lost to the body by these different processes it is difficult for obvious reasons to accurately determine, and the estimates usually given must be regarded only as approximative. Assuming 2500 calories to be an average amount of heat liberated during a day of repose, the losses, in the ways stated above, may be given as follows : I. In Warming Food and Drink. — The average temperature of food and drink is about 12° C; the amount of both together is about 3 kilograms; the specific heat of food about 0.8. The absorption 4o8 TEXT-BOOK OF PHYSIOLOGY. of body-heat therefore amounts to 3 X 0.8 X 25° C. = 60 calories = 2.8 per cent. With the removal of the end-products of the foods and drink from the body an equal amount of heat is carried out. 2. In Warming the Inspired Air. — The average temperature of the air is 12° C; the amount of inspired air, about 15 kilograms; the specific heat of air, 0.26. The absorption of body-heat by the air therefore amounts to 15 X 0.26 X 25° = 97.5 = 3.8 per cent. The expired air removes from the body a corre- sponding volume. 3. In the Evaporation 0} Water from the Lungs. — The quantity of water evaporated from the lungs may be estimated at 400 grams ; as each gram requires for its evaporation 0.582 calorie, the quantity of heat lost by this channel would be 400 X 0.582 = 232.8° C. = 9.4 per cent. 4. In the Evaporation 0} Water from the Skin. — The quantity of water evaporated from the skin may be estimated at 660 grams, causing a loss of heat by this channel of 660 X 0.582 = 384.1° C. = 15.3 per cent. 5. In Radiation and Conduction from the Skin. — The amount of heat lost by this process can be indirectly determined only by subtracting the total amount lost by the above-mentioned channels from the total amount produced. Thus, 2500 — 774-4 = 1725.6 = 69 per cent, would represent the average amount lost by radiation and conduction. Regulation of the Mean Temperature. — In order that the mean temperature of the body may remain practically constant, the heat produced must be exactly balanced by the heat dissipated. Should there be any want of correspondence between the two processes, there would arise either an increase or a decrease in the mean temperature. As both lieat-production and heat-dissipation are variable factors, dependent on a variety of internal and external conditions, their adjustment is accomphshed by a complex self-regulating mechanism involving muscular, vascular, and secretory elements, coordinated by the nerve system. Heat-production varies in intensity and amount, in accordance with a number of conditions, but principally with variations in physiologic activity, the quantity and quahty of the food, and changes in the external temperature. All physiologic and especially muscle activity is attended by chemic changes and the evolution of heat. The greater the activity, the larger is the volume of heat. Foods have different physiologic heat values. If the food consumed contains much potential energy and the quantity con- sumed be larger than the average daily requirements, there will be an increase in heat-production. A lowering of the external tem- perature, as in the winter season, leads to increased heat-production ANIMAL HEAT. 409 through stimulation of the nerve-centers. When all these conditions, increased muscular activity, increased amount of food of high poten- tial energy, and a low external temperature coexist, heat-production attains its maximum, amounting to as much as 4726 calories daily (Hultgren). Heat-dissipation varies in rapidity in accordance with variations of a number of factors, but principally with variations in the external temperature and the activity of the perspiratory apparatus. The heat is dissipated mainly by the skin, 69 per cent., in consequence of radiation and conduction and by the evaporation of the sweat. The loss by this channel as well as from the lungs is dependent for the most part on a difference of temperature of the surrounding air and of the body. If the surrounding temperature is high, there is an increase in the activity of both the circulatory and respiratory mechan- isms, brought about by the central nervous system. In addition to an increased action of the heart, the blood-vessels of the skin dilate and dehver to the surface a larger volume of blood in a given time, thus increasing the conditions favorable to radiation. The sweat- glands at the same time are stimulated to increased activity, and in consequence of the additional volumes of blood brought to the skin a larger amount of sweat is secreted, which speedily undergoes evap- oration. As each gram of water for its evaporation requires 0.582 of a calorie, it is evident that increased secretion of sweat favors heat- dissipation. The nerve-centers influencing the activity of the sweat- glands may be stimulated not only refiexly, but directly by an excess of heat in the blood. If, however, the atmosphere itself possesses a high percentage of moisture, evaporation from the body is much diminished and the value of sweating as a means of lowering the body-temperature is much impaired. Evaporation is hastened by air in motion. Hastened respiratory movements and the dilatation of blood-vessels of the respiratory surface also increase the evaporation of water from the lungs and thus occasion a greater loss of heat. If the external temperature falls there is a decrease in the physio- logic activity of the skin from a contraction of the blood-vessels, a diminution of the blood-supply, and a cessation in the secretion of sweat. The blood, being prevented from coming to the surface, is retained in the deeper portion of the body, and in consequence the conditions for radiation are diminished. These variations in the cutaneous circulation in response to variations in the external tem- perature are brought about by the vasomotor nerve mechanism ; and as they take place with extreme promptness heat-dissipation and heat- production are quickly adjusted and the mean temperature main- tained. Radiation from the skin is modified to some extent by clothing. An excess of clothing diminishes, a diminution of clothing increases 4IO TEXT-BOOK OF PHYSIOLOGY. radiation. Tlie quality of clothing is also an important factor. Wool is a poor conductor of heat but a good absorber and retainer of moisture, and hence is adapted for cold weather. Linen and cotton possess the opposite qualities, and hence are adapted for warm weather. Radiation from the skin is somewhat interfered with by subcutaneous fat, the extent of the interference being dependent on its amount. The foregoing estimates as to the amounts of heat produced have reference only to the body in repose. When the body passes into a state of muscle activity, there is at once a notable increase in heat- production in consequence of the increase in the activity of the chemic changes which underhe body activity, as shown by the increase in the consumption of oxygen and the production of carbon dioxid. Not all of the potential energy set free, however, appears as heat; for if the muscles are engaged in doing work a part of the energy which would otherwise manifest itself as heat is converted into mechanic motion. From the work done during a period of eight hours it has been estimated that about 500 calories are so transformed or utihzed. Hirn calculated from an average of five experiments that a man weighing 67 kilos in repose produced 154.4 calories per hour and absorbed 30.7 grams of oxygen per hour; but when engaged in active muscle movements produced 271.2 calories and absorbed 119.84 grams of oxygen per hour. The increase in heat-production per hour during activity was thus almost doubled, though the sum total pro- duced daily in which there was a working period of eight or ten hours was only about one-third more than during a day of repose. During sleep there is a greatly diminished heat-production, not more than 40 calories per hour being produced. The preceding data may be tabulated as follows (Martin) : Day of Rest. Day of Work. Heat units (calor-1 ^sst 16 hrs. Sleep 8 hrs. Rest 8 hrs. WorkShrs. .Sleep8hrs. ies) produced.. I 2470.4 320 1235.2 2160.6 320 ^ 2790.4 3724-8 CHAPTER XV. SECRETION. Secretion. — As the blood flows through the capillaries of the body certain of its nutritive principles are separated by the activity of the epithelial cells of the capiUary wall, aided by the physical processes of filtration and diffusion. To this process the term secretion may be applied. This separated or secreted material may be utilized in several ways: 1. For the repair of the tissues, for growth, for the hberation of energy. 2. For the elaboration or production by specialized organs of a variety of complex fluids of widely different application. The fluids thus formed are utilized for the most part to meet some special need of the body. All such fluids are termed secretions. The organs concerned in the elaboration of the various secretions are covered or lined by epithelium to the activity of which the secretion is to be referred. To all these organs the term gland may be applied. As these fluids are poured out on the surface of the body, they have been termed external secretions: e. g., mucus, saliva, gastric juice, milk, sebaceous matter, etc. Within recent years it has been demonstrated that the epithehum of glands and particularly of those which do not possess a duct, such as the thyroid, thymus, adrenals, hypophysis, etc., also produces certain specific constituents which are reabsorbed into the blood, and which in some unknown but yet favorable way influence the general nutrition. To such prod- ucts of these glands the term internal secretions has been given. The blood, in addition to its nutritive constituents, contains a number of principles, derived from the tissues, which are to be regarded as waste products, the outcome of the metabolic activity of the tissues and of no further use to the body. If retained, they would seriously if not fatally interfere with the normal physiologic activities of the different tissues. They are therefore removed by specialized organs after their separation from the blood-stream. The waste products in solution thus removed are not capable of being utilized for any special purpose, and are therefore termed excre- tions: e. g., urine, perspiration, etc. Excretion, however, is per- formed by the activities of epithehal cells aided by the physical forces of diffusion and filtration; and though a distinction is made 411 412 TEXT-BOOK OF PHYSIOLOGY. between the two classes of fluids, no sharp Hne can be drawn between the cell processes which take place in secretory and excretory organs. All secretory organs may be divided into — 1. Epithelial. 2. Reticular and vascular, the latter term indicating merely their re- lation to blood-vessels. The Epithelial Secretory Apparatus. — The apparatus essential to the production of a secretion is a dehcate homogeneous mem- brane, on one side of which and in close contact is a layer of capillary blood-vessels, lymphatics, and nerves; on the other side, a layer of epithelial cells, the physiologic function of which varies in different situations. The epithelial organs may consist of a single layer of cells or a group of cells, and may be subdivided into — 1. Secreting membranes. 2. Secreting glands. The secreting membranes are the mucous membranes lining the gastro-intestinal, the pulmonary, and the genito-urinary tracts, and the serous membranes lining closed cavities, such as the pleural, pericardial, peritoneal, and synovial membranes. The mucous membranes are soft and velvety in character and are composed of a condensed connective tissue forming a basement membrane beneath which is a layer of blood-vessels and muscle-fibers, and on which is a layer of epithelium, the histologic as well as physio- logic characters of which vary in different situations. The mucus secreted by the various epithelial forms will very naturally possess a somewhat different composition, according to the locality in which it is formed. In a general way it may be said that mucus is a pale, semitransparent, alkaline fluid, containing leukocytes and epithelial cells. It is composed chemically of water, mineral salts, and an albuminoid body, mucin, to the presence of which it owes its vis- cidity. Much of the mucus is secreted by the goblet cells on the surface of the mucous membranes. The principal varieties of mucus are the nasal, bronchial, vaginal, urinary, gastro-intestinal. The serous membranes are composed of thin membrane formed by a condensation of connective tissue and covered by a single layer of large, flat, nucleated cells with irregular margins. These mem- branes enclose what are practically large lymph sacs or spaces, and the fluid they contain resembles lymph in all respects and is prac- tically identical with it. It serves to diminish friction when the viscera they enclose move over one another. The most important of the serous membranes are the pleural, pericardial, and peritoneal. The synovial membranes in and around joints resemble serous membranes. The cells covering them, however, secrete a clear colorless fluid resembling lymph, but differing from it in containing SECRETION. 413 a mucin-like substance, a nucleo-albumin, which imparts to it con- siderable viscidity. This synovial fluid serves to diminish friction between the opposing surfaces of the bones as they ghde over one another during movement. Other secretions, such as the aqueous and vitreous humors of the eye, the fluid of the internal ear, the cerebrospinal fluid, etc., will be considered in connection with the organs with which they are asso- ciated, as have been the digestive secretions. The secreting glands are formed of the same histologic elements as the secreting membranes. They are formed by an involution of the mucous membrane or skin the epithehum of which is variously modified structurally and functionally in the various situations in which they are formed. Like the membranes themselves, the glands are invested by capillary blood-vessels and supphed with lymphatics and nerves, of which the latter are in direct connection with the blood- vessels and epithelial cells. The interior of each gland is in com- munication with the free surface by one or more passageways known as ducts. These glands may be classified according as the involution is cyhndrical or dilated as — 1. Tubular. The tubular glands may be simple — e. g., sweat- glands, intestinal glands, fundus glands of the stomach; or compound — e. g., kidney, testicle, saHvary, and lachrymal glands. 2. Alveolar. The alveolar glands may also be simple — e. g., the sebaceous glands, the ovarian folHcles, meibomian glands; or compound, as the mammary glands and salivary glands. For the production of a secretion it is necessary that the plasma of the blood, the common material, be dehvered to the lymph-spaces with which the epithelial cells are in close relation. The processes involved in the passage of the plasma across the capillary wall have already been considered in connection with the production of lymph. They include the physical processes, difi'usion, filtration, and osmosis, combined with a secretory activity of the cells of the capillary wall. The question as to which of these processes is the more active is yet a subject of investigation. As the chemic composition and the chemic features of the organic constituents of all secretions have been demonstrated to be the out- come of metaboHc processes going on within the epithehal cells, it must be assumed at least that these dift'erences are correlated with differences in the histologic features and molecular structure of the epithehum. The discharge of the secretion is, as a rule, intermittent ; that is, there are periods of activity on the part of the gland fol- lowed by periods of inactivity or rest. In rest more especially the epithelial cells, after the assimilation of lymph, accumulate within themselves such characteristic products as globules of mucin, gran- 414 TEXT-BOOK OF PHYSIOLOGY. ules which apparently are the antecedents of the digestive enzymes, granules of glycogen, globules of fat, sugar, and proteid, as in the case of the mammary gland. In how far all these compounds are the result of secretory activity or of a cell degeneration and disinte- gration it is impossible to state in the light of present knowledge. During the period of gland rest the blood-supply to the gland is merely sufficient for nutritive purposes. When the occasion arises for gland activity, the blood-vessels, under the influence of the vasomotor nerves, dilate and dehver to the gland an amount of blood far beyond that required for nutritive purposes. As a result the gland becomes red and vascular and the blood emerging by the veins fre- quently retains its customary arterial color. The increased blood-supply favors a rapid transudation of water and salts into the lymph-spaces where they are speedily absorbed and transmitted by the epithelial cells into the interior of the gland lumen. Coincident with the passage of water through the cell, the organic constituents are extruded from the end of the cell bordering the lumen to become dissolved, or in the case of fat to be suspended, in the water. The secretion thus formed accumulates, and with the rise of pressure which inevitably follows it at once passes into the ducts to be discharged on the surface of the mucous membrane or skin, as the case may be. Influence of the Nerve System. — The activity of every gland is controlled by nerve-centers situated in the central nerve system. These centers may be excited to activity either by impressions made on the peripheral terminations or by emotional states, or, possibly, by changes in the composition of the blood itself. As a rule, all normal secretion is a reflex act involving the usual mechanism: viz., a sentient surface (skin, mucous membrane, or sense-organ), an afferent nerve, an emissive cell from which emerges an efferent nerve to be distributed to a responsive organ, the gland epithelium. For the production of the secretion by the epithelial cell it is beheved by some experimenters that two physiologically dis- tinct, efferent nerve-fibers are involved — one stimulating the pro- duction of the organic constituents {trophic nerves), the other stimu- lating the secretion of water and inorganic salts (secretor nerves). The evidence for the influence of the nerve system on secretion and the mode of connection of the nerve-fibers with the gland-cells have been alluded to and will again be in subsequent chapters. The reticular and vascular glands, though not possessing any common histologic features, are grouped together merely for con- venience, and will be considered in a separate chapter in connection with the problems of internal secretion. SECRETION. 415 MAMMARY GLANDS. The mammary glands, which secrete the milk, are two more or less hemispheric organs situated in the human female on the anterior surface of the thorax. Though rudimentary in childhood, they gradually increase in size as puberty approaches. The gland pre- sents at its convexity a small conical eminence termed the mammilla or nipple, surrounded by a circular area of pigmented skin, the areola. The gland proper is covered by a layer of adipose tissue anteriorly and is attached posteriorly to the pectoral muscles by a network of fibrous tissue. During utero-gestation the mammary glands become larger, firmer, and more lobulated; the areola darkens and the blood- vessels, especially the veins, be- come more prominent. At the period of lactation the gland is the seat of active histologic and physiologic changes correlated wdth the production of milk. At the close of lactation these Fig. 181. — Mammary Gland. 1. Lactiferous ducts. 2. Lobuli of the mammary gland. Fig. 182. — Acini of the Mammary Gland of a Sheep during Lacta- tion, a. Membrana propria, b. Secretory epithelium. activities cease, the glands diminish in size, undergo involution, and gradually return to their former non-secreting condition. ^ Structure of the Mammary Gland. — Each mammar}' gland consists of an aggregation of some 15 or 20 irregular pyramidal lobes, each of which is surrounded by a framework of fibrous tissue. This tissue affords support for blood-vessels, lymphatics, and nerves. Each lobe is provided with a single excretory duct, the lactiferous duct, which as it approaches the areola expands into a fusiform ampulla or reservoir. At the base of the nipple the ampullae contract to form some 16 or 18 narrow ducts, which, ascending the nipple, open by constricted orifices 0.5 mm. in diameter on its apex (Fig. 181). 4i6 TEXT-BOOK OF PHYSIOLOGY. On tracing the lactiferous duct into a lobe, it is found to divide and subdivide into a number of branches, which pass into smaller masses — the lobules. The lobule in turn is composed of a large number of tubular acini or alveoli, the final terminations of the lobu- lar ducts. Each acinus consists of a basement membrane lined by a single layer of low cuboidal epithehal cells (Fig. 182). Externally the acinus is surrounded by blood-vessels, nerves, and lymphatics. MILK. Milk as obtained during active lactation is an opaque bluish- white fluid, almost inodorous, with a sweet taste, an alkahne reaction, and a specific gravity of from 1.025 to 1.040. Examined micro- scopically, it is seen to consist of a clear fluid, the milk plasma, hold- ing in suspension an enormous number of small, highly refractive oil-globules, which measure on the average about yo (TTrrr of 3-^ inch in diameter. It has been asserted by some observers that each globule is surrounded by a thin proteid envelope which enables it to maintain the discrete form. This, however, is at present disbelieved. The quantity of milk secreted daily by the human female averages about 1200 c.c. Chemic analysis has shown that the milk of all the mammalia consists of all the different classes of nutritive principles, though in different proportions, which are necessary to the growth and devel- opment of the body. The only exception appears to be an insuffi- cient amount of iron for the formation of the coloring-matter of the blood, the hemoglobin. Caseinogen is the chief proteid constituent of milk. Associated with it, however, are two other proteids, lactalbumin and lactoglob- ulin, both of which are present in but small quantity. When milk is treated with acetic acid, sodium chlorid, or magnesium sulphate to saturation, the caseinogen is precipitated as such, and after the re- moval of th^ fat with which it is entangled may be collected by ap- propriate chemic methods. On the addition of rennet prepared from the mucous membrane of the calf's stomach, which contains the enzyme rennin or pexin, the caseinogen undergoes cleavage into an insoluble proteid, casein or tyrein, and a small quantity of a new soluble proteid. To this process the term coagulation has been given. The presence of calcium phosphate appears to be essential to this process, inasmuch as it does not take place if the milk be completely decalcified by the addition of potassium oxalate. After coagulation^ the more or less solid mass of milk separates into a liquid portion, the serum, and a solid portion, the coagulum. The former, generally termed whey, consists of water, salts, lactalbumin, sugar; the latter, the curd, consists of the casein and entangled fat. Boiling the milk SECRETION. 417 retards and even prevents the coagulation by rennet, owing to the precipitation of the calcium phosphate. When milk is taken into the stomach, it is probable that the rennin coagulates the caseinogen in a manner similar to, if not identical with, this process, which appears to be essential to the normal digestion of the milk. The fat of milk is more or less solid at ordinary temperatures. It is a compound of olein, palmitin, and stearin with small quantities of butyrin and caproin. The melting-point of butter varies between 31° and 34° C. When milk is allowed to stand for some time, the fat-globules rise to the surface and form a thick layer known as cream. Churning the milk or cream causes the fat-globules to run together and form a coherent mass termed butter. Lactose is the particular form of sugar characteristic of milk. It belongs to the saccharose group and has the following composition: Cj2H220jj. Though incapable of undergoing fermentation by the action of the yeast plant, it is readily reduced by the Bacillus acidi iactici to lactic acid and carbon dioxid, the former of which imparts to milk an acid reaction and a sour taste. With the accumu- lation of the lactic acid the caseinogen is precipitated as a more or less consistent mass. The inorganic salts of milk are chiefly potassium, sodium, calcium, and magnesium phosphates and chlorids. Iron is also present in small amount. The following table of Bunge gives the quantitative amounts of these constituents in both human and cow's milk: In iooo Parts. POTAS- „ siuM. Sodium. Calcium. Magne- sium. Iron OXID. Phos- phoric Acid. Chlorin Human milk, Cow's milk, 0.78 0.25 1.76 I. II 0-33 1-59 0.06 0.0036 0.21 0.0030 0.47 I.Q7 0-43 1.69 Mechanism of Milk Secretion. — During the time of lactation the mammar}^ gland exhibits periods of secretory activity which alternate with periods of repose. Coincidently with these periods certain histologic changes take place in the secreting epithelium. At the close of a period of active secretion and after the discharge of the milk each acinus presents the following features: The epithelial cells are short, cubical, nucleated, and border a relatively wide lumen, in which is found a variable quantity of milk. After the gland has rested for some time active metabolism again begins. The cells grow and elongate; the nucleus divides into two or three new nuclei; constriction takes place and the inner portion is detached and discharged into the lumen of the acinus. During the time these changes are taking place oil-globules make their appearance in the cell 27 4iJ TEXT-BOOK OF PHYSIOLOGY. protoplasm, some of which are discharged separately into the lumen, while others remain for a time associated with the detached portion of the cell (Fig. 183). From these histologic changes it is inferred that the caseinogen and fat are products of the metabolism of the cell protoplasm and not derived directly through the lymph from the blood. The lactose apparently has a similar origin, as appears from the fact that it is not found either in the blood or any other tissue, and that it is formed independently of carbohydrate food. The water, and especially the inorganic salts, are the result of secretory activity, rather than of diffusion and filtration. This is rendered probable from the fact that the proportions of the inorganic salts of milk are more closely allied to those of the tissues of the new-born child than to blood. With the passage of the water and salts into the lumen of the acinus the proteids undergo disintegration and solution and the liquid assumes the characteristics of milk. The discharge of milk is occasioned by the suction efforts on the part of the child, aided by atmospheric pressure and the contractions of the non-striated mus- cle-fibers of the lactiferous ducts. Influence of the Nerve System. — Judging from analogy, it is probable that the secretion of milk is regulated by influences emanating from the nerve system, though the exact nerve-channels for the transmission of such influences have not been determined experimentally. Various attempts have been made to isolate and study these nerves, but the results are inconclusive. It is well known tliat emotional states on the part of the mother modify the quantity as well as quahty of milk, indicating a connection between the gland- cells and the central organs of the nerve system. Nerve terminals have been discovered in and around the epithehal cells — a fact \vhich supports this view. Colostrum. — Within a day or two after parturition the alveoli become filled with a fluid which in some respects resembles milk and which has been termed colostrum. This is a watery fluid con- taining disintegrated epithehal cells, fat-globules, as wefl as colos- trum corpuscles, which are probably emigrated leukocytes. Colos- trum is distinguished from milk in being richer in sugar and inorganic salts. It is said to possess constituents which act as a laxative to the young child. Fig. 183. — Section of the Mammary Gland of a Cat in, the Early Stages of Lactation. A. Cavity of alveoli filled with granules and globules of fat. I, 2, 3. Epithe- lium in various stages of milk-formation. — ( Yeo.) SECRETION. 419 THE LIVER. The liver is a large gland situated in the upper and right side of the abdominal cavity, where it is held in position largely by hga- ments formed by redupHcations of the peritoneal investment. In the adult it weighs, freed of blood, from 1300 to 1700 grams. The liver is connected with the duodenal portion of the intestine by the hepatic duct. It receives blood both from the hepatic artery and from the portal vein, and in this respect differs from all other glands in the body. The epithehal structures of the Uver are inclosed by a firm fibrous membrane, known as Ghsson's capsule. At the trans- verse fissure it invests and follows the blood-vessels, which there enter, in all their ramifications through the gland. Structure of the Liver. — The fiver is composed of an enor- number of ev 2- Vi nious small masses, rounded, ovoid, or polygonal in shape, called lo- bules, measuring about one milhmeter in diameter and sepa- rated from one an- other by a narrow space in which are to be found blood- vessels, lymphatics, hepatic ducts, sup- ported by connective tissue. In the pig this space and its con- tained elements is quite distinct, sharply marking out the border of the lobule (Fig. 184). This is not so apparent in man. Each lobule is made up of irregular or polygonal shaped cells measur- ing about 30 to 40 micromiUimeters in diameter. These cells are arranged in a radial manner from the center to the circumference of the lobule (Fig. 185). Each cell possesses one and at times two nuclei. There is no evidence for the existence of a distinct cell-wall. The cell protoplasm frequently contains globules of fat, granules of a proteid nature, granules of glycogen, pigment material, etc. The appearance presented by the cell will vary considerably, according to the time it is observed. Thus there may be a complete absence of these constituents, when the cell may present a series of vacuoles separated by bands of protoplasm. The cells are the secreting Fig. 1S4. — Section of Liver of Pig, showing very DiAGRAiiMATiCALLY THE LoBULES. a. Interlobu- lar connective tissue, b, c. Branches of portal vein and of hepatic artery, d. Bile-ducts. e. Intra- lobular vein. — {Piersol.) 420 TEXT-BOOK OF PHYSIOLOGY. Trabeculae of hepatic cells. Central vein. which uhimately oc- space between the structures of the hver, and hence are in close relation with capillary blood-vessels, lymphatic spaces, nerves, and irregular channels or passageways. The latter running between the epithelial cells may be compared to the lumen of other secreting glands. Blood-vessels and Their Distribution. — The blood-vessels which are in relation with the hver are : 1. The portal vein. 2. The hepatic artery. 3. The hepatic vein. The portal vein and the hepatic artery enter the hver at the trans- verse fissure. After penetrating its substance they divide and sub- divide into smaller and smaller branches, cupy the lobules, completely surrounding and hmiting them. From their situation they are termed inter- lohidar veins and arteries. The interlobular veins give off small capillary vessels which penetrate the lobule at all points of its surface. These capillaries, though frequently anastomosing, form a radial meshwork which converges toward the center of the lobule. In the meshes of this plexus are found, arranged in a corresponding radial man- ner, the hver cells. The inter- lobular arteries are distributed to the walls of the portal vein, to the connective tissue, and finally terminate in the portal vein capil- laries. The intralobular capil- laries thus receive and transmit blood which is an admixture of both arterial and venous blood. In the center of each lobule there is a large vein, formed by the union of the intralobular capillaries, known as the intralohilar vein, which collects ah the blood of the lobule and transmits it through the lobule to an underlying or sublobular vein (Fig. 186). These latter vessels, uniting and reuniting, ultimately form the hepatic vein, which empties the blood into the inferior vena cava. Bile Capillaries and Hepatic Ducts. — The bile capillaries are narrow channels which penetrate the lobule in all directions and are generally found running along the sides of the ceHs. These channels. Interlobular vein. Hepatic duct. Fig. 185. — Scheme of a Hepatic Lob- ule, REPRESENTED IN TRANSVERSE Section below and, by Partial Leveling, in Longitudinal Sec- tion above. In the left half the blood-vessels are drawn; in the right half only the cords of hepatic cells. X 20.— {Stohr.) SECRETION. 421 which are devoid of walls, receive from the cells some of the products of their secretory activity, and hence are comparable to the lumen of the alveoH of other secreting glands. At the periphery of the lobules the bile capillaries communicate with larger channels which are the beginnings of the hepatic or bile-ducts lying in the interlobular spaces. The interlobular bile-ducts possess a distinct wall Hned by flattened epitheHum. There is, however, no distinct Hne of demarca- tion between the cells of the interlobular ducts and the secreting cells of the Uver proper, as the two blend insensibly, the one into the other. As the hepatic ducts increase in size they gradually acquire the structure characteristic of the main hepatic duct: viz., a mucous, a muscle, and a fibrous coat. Fig. 186. — Transverse Section of a Single Hepatic Lobule, i. Intralobular vein, cut across. 2, 2, 2, 2. Afferent branches of the intralobular vein. 3, 3, 3' 3' 3> 3> 3' 3' 3- Interlobular branches of the portal vein, with its capillary branches, forming the lobular plexus, extending to the radicles of the intralobular vein. — (Sappey.) Nerves. — Experimental investigations have demonstrated that the Hver is supplied with nerves derived from the central nerve system. The route of these nerves is probably by way of the splanch- nics and the vagi. Many of the nerves which enter the liver are vasomotor in function ; as to whether others are secretory in character is yet a subject of investigation. It has been asserted that nerve terminals have been demonstrated running between the cells and even penetrating their substance. This fact would indicate that the metaboHc processes of the liver are under the control of the central nerve system. Functions of the Liver.— The anatomic and histologic pecu- 422 TEXT-BOOK OF PHYSIOLOGY. liarities of the liver would indicate that it has a variety of relations to the general processes of the body. Experimental investigation has brought some of these relations to light. Though its physiologic actions are not yet v^holly understood, it may be said that it — 1. Secretes bile. 2. Produces and stores glycogen. 3. Assists in the formation of urea. Secretion of Bile. — The physical properties and chemic com- position of the bile have already been considered (page 203). The characteristic salts of the bile, sodium glycocholate and tauro- cholate, do not pre-exist in the blood, and therefore must be formed by the hver cells out of materials derived from the blood of the intralobular capillaries. The antecedents of the bile salts, glycocoU and taurin, are crystalhzable nitrogenized compounds, and known chemically as amido-acetic and amido-ethylsulphonic acids. Their chemic composition indicates that they are derivatives of the proteids or the albuminoids, though the intermediate stages in their produc- tion are unknown. The origin of the cholahc acid with which they are combined is equally obscure. The bile salts as they are found in the bile are produced in the hver cells by metabolic activity. The primary coloring-matter of the bile, bihrubin, has been shown to be a derivative of hematin, a product of the disintegration of hemo- globin. It is supposed that the hver cells bring about this change by combining water with hematin, with the abstraction of iron. The product thus formed is bilirubin, which is excreted, while the iron is for the most part retained. Cholesterin is a waste product derived largely from the nerve- tissue. It is brought to the liver and simply excreted by the cells. The remaining constituents of the bile, water and inorganic salts, are secreted here as in all other glands. When once formed, the hver cells discharge these various com- pounds into the channels by which they are surrounded; they then pass into the open mouths of the bile-ducts at the periphery of the lobules. Under the increasing pressure which arises from the secre- tion and accumulation of bile, this fluid flows from the smaller into the larger bile-ducts, and finally is emptied either directly into the in- testine or into the gall-bladder, where it is stored until required for digestive purposes. The secretion of bile, as observed by means of a biliary fistula, is continuous and not intermittent, though the rate of flow is subject to considerable variation. The hver cells, as far as the secretion of bile is concerned, appear to be independent of the nerve system. Their activity, however, is stimulated by the increased blood-supply which arises during digestion in consequence of the dilatation of the intestinal vessels, since it is at this period that the rate of discharge is the greatest. SECRETION. 423 The same results have been shown by experiment. Thus, division of the splanchnic nerves is followed by an increased discharge of bile, apparently due to the dilatation of the portal vessels; stimula- tion of their peripheral ends is followed by a decreased discharge of bile in consequence of the contraction of the portal vessels. The bile salts appear to be the most efficient stimulants to the activity of the liver cells, for their administration and absorption is followed by an. increase not only in the amount of water, but of the inorganic salts and other soUd constituents as well. The flow of bile from the bile capillaries to the main hepatic duct, though primarily dependent on differences of pressure, is aided by the contraction of the muscular walls of the bile-ducts and the inspiratory movements of the diaphragm, xlny obstacle to the dis- charge of bile leads to its accumulation, a rise of pressure beyond that of the capillary blood-vessels, and a reabsorption by the lymph- atics of the bile constituents. After their discharge into the blood from the thoracic duct these constituents are deposited in various tissues, giving rise to the phenomena of jaundice. The Production of Glycogen. — In 1857 Bernard discovered the fact that the hver normally during Hfe produces a sugar-forming substance, analogous in its chemic composition to starch, to which he gave the name glycogen. This substance can be obtained by the following method: Small pieces of the liver of an animal recently killed, preferably after a meal rich in carbohydrates, are placed in acidulated boihng water for a few minutes; then rubbed up in a mortar with sand, again boiled, after which the proteids are removed by filtration. The filtrate thus obtained is opalescent and resembles a solution of starch. The glycogen may be precipitated from this solution with alcohol as a white amorphous powder, soluble in water. Chemic analysis shows that it consists of CgH^gOj, or a multiple of it. When either the original solution obtained by boihng or a solution of this amorphous powder is treated with iodin, it strikes a port- wine color. When digested with saHva, pancreatic juice, or boiled with dilute acids, the solution becomes clear, and testing with Fehhng's solution reveals the presence of sugar. If the liver be allowed to remain in the body of an animal for a period of twenty-four hours before the decoction is made as above described, it will be found that the solution contains only a small amount of glycogen but a relatively large amount of sugar. The inference drawn is that after death the glycogen is transformed by some agent, possibly a ferment, into sugar (dextrose). The presence of glycogen in the hver cells can be shown micro- scopically in the form of discrete hyaline and refractive granules. As they are soluble in water they can be readily dissolved out from 424 TEXT-BOOK OF PHYSIOLOGY. the cells, leaving small vacuoles separated from one another by strands of cell substance. The amount of glycogen in a well-fed animal varies from 1.5 to 4 per cent, of the total vv^eight of the liver. The production of glycogen is dependent very largely on the con- sumption of carbohydrates, the greater the amount of sugar and starch in the food, the greater being the production of glycogen. On a pure proteid diet it is still produced, though in small amounts. Glycogen is present also in muscles, in the placenta, in the tissues of the embryo — wherever, indeed, active tissue changes and growth are taking place. The facts connected with the formation of glycogen, as well as its disposition as at present generally accepted, may be stated as follows : The dextrose into which the carlDohydrates are converted by the action of the digestive fluids is absorbed into the blood of the portal vein and carried direct into the liver, where by the action of the cells it is abstracted, dehydrated, and temporarily deposited under the form of the non-diffusible body glycogen. At a subsequent period and in proportion to the needs of the system the liver cells, through the agency of a ferment, transform the glycogen into dextrose, return it to the circulation, by which it is transported to the systemic capillaries, where it disappears. The blood of the hepatic vein therefore contains more sugar than the blood of any other part of the body, and the blood of the arteries more than the blood of the other veins. Should there be a failure on the part of the liver cells to abstract the sugar, it would pass through the liver into the general circulation, from which it would be eliminated by the kidneys. The final fate of the sugar is uncertain. It is, however, probable that after its delivery to the muscles, for example, it may be directly oxidized, or stored as glycogen, or possibly utihzed in the formation of living material. Ultimately, however, through oxidation it yields heat, and contributes to the production of muscle energy. In opposition to this view, Dr. Pavy, after years of accurate ex- perimentation, states that the blood on the cardiac side of the liver never under normal circumstances contains a larger percentage of sugar than is to be found in any part of the circulation, except in the portal vein. He states that glycogen is never reconverted into sugar, and denies that the liver produces sugar, to be discharged into the blood ; that the function of the liver is merely to arrest the passage of sugar, and so to shield the general circulation from an excess ; that the sugar which arises in the liver after death is a postmortem product and not an illustration of what takes place during life. Dr. Pavy, having apparently demonstrated the glucoside constitution of proteid material in general, accounts for the presence of glycogen in muscles and other tissues on the assumption that during the cleavage of the proteid molecule the carbohydrate element is set free and temporarily SECRETION. 425 stored as glycogen. He thus accounts for the production of sugar in the body, even in the absence of all sugar and starch from the food. Pavy believes that the glycogen produced in the liver is utiHzed in the formation of fat and the synthesis of complex proteids necessar}' to the construction of the tissues. Influence of the Nerve System. — The nerve system influ- ences in some way the glycogenic function of the liver. It was discovered by Bernard that puncture of the floor of the fourth ven- tricle at a point between the acoustic and vagus nerves, near the middle line is followed within an hour or two by the appearance of sugar in the urine, which lasted for twenty-four or thirty-six hours. To this area, in close relation to the vasomotor center, he gave the name "diabetic area." The quantity of sugar excreted in the urine will depend on the amount of sugar previously present in the liver. Through some agency the stored-up glycogen is rapidly converted into sugar discharged into the blood and eliminated by the kidneys. There is no positive evidence that the puncture destroys the vaso- motor center for the blood-vessels of the liver, or that there is any change in the relation of the blood-vessels to the liver-cells. Never- theless powerful stimulation of the sciatic nerve, or the central end of the vagus which impairs or depresses the vasomotor center, will give rise to a similar production and elimination of sugar. The pathway for the passage of these influences beyond the first thoracic ganglion is unknown, but that it is not by way of the splanchnics or the vagi is evident from the fact that division of either of these nerves is not followed by the appearance of sugar in the urine. Diabetes. — Diabetes is a chronic disease characterized by the appearance of sugar in the urine in variable amounts. This patho- logic condition has usually been associated with derangements of the glycogenic function of the liver, though doubtless derangements of other organic functions will produce the same condition. At the present time it is believed that the excretion of sugar by the kidneys depends on two causes: (i) An ineffectual abstraction and storage of sugar due to some impairment in the activity of the liver cells; (2) a rapid cleavage of the proteid constituents of the tissues, in conse- quence of some profound alteration in the nutritive process, whereby their glucose radicals are Hberated in unusual amounts. The physi- ologic mechanism by which the normal metabolism of the carbohy- drates is regulated is unknown. That it is complex in character is shown by the phenomena which follow not only puncture of the medulla, but also removal of the pancreas and the administration of various poisons. Removal of the pancreas from the body of a dog or other ani- mal is at once followed by a rise in the percentage of sugar in the blood and its elimination by the kidneys. In a short time acetone. 426 TEXT-BOOK OF PHYSIOLOGY. aceto-acetic and oxybutyric acids make their appearance, attended by the usual symptoms characteristic of glycosuria in man. The quantity of sugar excreted and the gravity of the attendant symptoms may be much diminished by allowing a portion of the gland to remain in situ, even though its capacity for the production of pancreatic juice is entirely abolished. Transplantation of the pancreas to the subcutaneous tissue or to the abdominal cavity will practically pre- vent the glycosuria. The explanations which have been offered as to the manner in which the pancreatic tissue prevents and its absence gives rise to the excretion of sugar are purely hypothetical. It has been claimed by some investigators that the pancreas secretes a specific material, which enters the blood and promotes oxidation of the sugar. In the absence of this material the sugar accumulates, and is finally ehminated by the kidneys. Since the discovery of the islands of Langerhans it has been suggested by some investigators that the production of the material which regulates carbohydrate metabo- Usm should be attributed to them rather than to the pancreas as a whole. The sugar excreted doubtless in part comes from the glycogen of the liver, as this disappears in a short time. But as sugar con- tinues to be excreted, even though all carbohydrates be withdrawn from the food, the conclusion is justifiable that it arises in conse- quence of increased proteid metabohsm. This supposition is strengthened by the fact that the quantity of urea excreted rises and falls with the quantity of sugar excreted. Phloridzin, a glucoside obtained from the root bark of the cherry and plum tree, gives rise to the appearance of sugar in the urine, in amounts beyond that which might come from the glucose normally present in the blood or from the glycogen of the liver. As there is a concomitant increase in the amount of urea excreted, the supposition is that phloridzin increases proteid metabolism. Curara, in doses sufficient to paralyze the muscles, also gives rise to the appearance of sugar in the urine. This is not due, however, to an increased production on the part of the liver, but rather to a want of consumption on the part of the muscles, due to their inac- tivity. The accumulation of the sugar in the blood which takes place for this reason leads very promptly to its removal by the kidneys. The Formation of Urea. — It is now generally beheved that the hver is the most active of all the organs which may be engaged in the production of urea. This belief is based on numerous physiologic and pathologic data. The compounds out of which the hepatic cells construct urea have been for chemic reasons asserted to be the ammonium salts, e. g., the carbonate, lactate, carbamate, which are constantly present in the blood. These salts, which result from proteid metabolism, are absorbed from the tissues, carried to the liver, and there synthesized to urea. This supposition is supported SECRETION. 427 by an experiment as follows: The liver of an animal recently living is removed from the body and its vessels perfused continuously with blood (the urea content of which is known) containing the ammonium salts. An analysis of this blood shows, after a time, a diminution of these salts, and a large increase in the amount of the urea. The leucin and tyrosin which result from the prolonged action of pan- creatic juice on hemi-peptone are also capable of being converted to urea by the hepatic cells, and in all probability are so disposed of. Destructive diseases of the liver — e. g., acute yellow atrophy, sup- puration, cirrhosis — largely diminish the production of urea, but in- crease the quantities of the ammonium salts in the urine. The same is true when the liver cells are destroyed during acute phosphorus- poisoning. VASCULAR OR DUCTLESS GLANDS. INTERNAL SECRETIONS. The metaboHsm of the body generally, as well as that of individual organs, has been shown to be related not only to the physiologic ac- tivity of such organs as the hver and pancreas, but also to the activity of the so-called vascular or ductless glands. The influence of the pancreas in regulating the production of glycogen by the liver, and the influence of the hver in the maintenance of the general metabo- lism through the production of glycogen and the formation of urea, are now established facts. That the vascular or ductless glands to an equal extent, though perhaps in a different way, assist in the main- tenance of physiologic processes, appears certain from the results of animal experimentation. The explanation given for the influence of these glands is that they produce specific substances, which are poured into the blood or lymph and carried direct to the tissues, to the activities of which they appear to be essential; for without these substances the nutrition of the tissues declines and in a short time a fatal termination ensues. Inasmuch as these partly unknown substances are formed by cell activity and are poured into the interstices of the tissues, they have been termed "internal secretions." Though the term internal secre- tions is appHcable to all substances which arise in consequence of tissue metabohsm, and which, after being poured into the blood, influence in varying degrees and ways physiologic processes, yet the term in this connection will be applied only to the secretions of the thyroid gland, hypophysis cerebri, and adrenal bodies. Thyroid Gland. — The thyroid gland or body consists of two lobes situated on the lateral aspect of the upper part of the trachea. Each lobe is pyriform in shape, the base being directed downward and on a level with the fifth or sixth tracheal ring. The lobe is about 50 mm. in length, 20 mm. in breadth, and 25 mm. in thickness. As a rule, 428 TEXT-BOOK OF PHYSIOLOGY. the lobes are united by a narrow band or isthmus of the same tissue. The gland is reddish in color, and abundantly suppHed with blood- vessels and lymphatics. Microscopic examination shows that the thyroid consists of an enormous number of closed sacs or vesicles, variable in size, the largest not measuring more than o.i mm. in diameter. Each sac is composed of a thin homogeneous membrane hned by cuboid epithe- lium. The interior of the sac in adult Hfe contains a transparent, viscid fluid containing albumin and termed "colloid" substance. Externally, the sacs are surrounded by a plexus of capillary blood- vessels and lymphatics. The individual sacs are united and sup- ported by connective tissue, which forms, in addition, a covering for the entire gland. ^ Function of the Thy- roid. — The knowledge at present possessed as to the function of the thyroid gland, especially in mam- mals, is the outcome of a study of the effects which follow its arrested develop- ment in the child, its de- generation in the adult, and its extirpation in the human being as well as in animals. The results, how- ever, which follow its ex- tirpation are not always uniform in all animals, though sufficient reasons for the lack of uniformity can not always be assigned. Cretinism, a condition characterized by a want of physical and mental development, is associated with, if not directly dependent on, a congenital absence of the thyroid or its arrested development dur- ing the early years of childhood. Myxedema, a condition of the skin in which there is a hyperplasia of the connective tissue, of an embryonic type, rich in mucin, is gener- ally regarded as one of the effects of degenerative processes in the thyroid. Partly in consequence of this change in the skin the face becomes broader, swollen, and flattened, giving rise to a loss of ex- pression. At the same time the mind becomes dull, clouded, even approximating the idiotic type. This supposed infiltration of the skin with mucin was termed myxedema by Ord, who at the same time associated it with a change in the structure of the thyroid as a result of which it became functionally useless. Fig. 187. — View of Thyroid Body. i. Thy- roid isthmus. 2. Median portion of crico- thyroid membrane. 3. Crico-thyroid muscle. 4. Lateral lobe of thyroid body. — {After Morris.) SECRETION. 429 Extirpation of the thyroid, for rehef from symptoms due to grave pathologic changes, has been followed in human beings by symptoms similar to those of myxedema. To this condition the terms operative myxedema and cachexia strumipriva have been applied. After the pubhcation of the history of the myxedema which fol- lowed surgical removal of the thyroid, Schiff, in 1887, repeated his earlier experiments on dogs, and found again that removal of the thyroid was speedily followed by tremors, convulsions, and death. Similar experiments were made by Horsley on monkeys, with results which resembled those characteristic of myxedema. Among the symptoms which developed within a few days after the removal of the gland may be mentioned loss of appetite ; fib- rillar contractions of muscles; tremors and spasms; mu- cinoid degeneration of the skin, giving rise to pulSness of the eyehds and face and to a swollen condition of the abdomen ; hebetude of mind, frequently terminating in idiocy ; fall of blood- pressure; dyspnea; albuminuria ; atro- phy of the tissues, followed by death of the animal in the course of from five to eight weeks. The complexus of symptoms observed in monkeys was divided by Horsley into three stages: viz., the neurotic, the mucinoid, and the atrophic. It is evident that the presence of the thyroid is essential to the normal activity of the tissues generally. As to the manner in which it exerts its favorable influence, there is some difference of opinion. The view that the gland removes from the blood cer- tain toxic bodies, rendering them innocuous and thus preserving the body from a species of auto-intoxication, is gradually yielding to the more probable view that the epithelium is engaged in the secre- tion of a specific material, which finds its way into the blood or lymph Fig. 188. — A Lobule from a Thin Section of the Thyroid Gland of an Adult Man. 1. Colloid substance. 2. Epithelium. 3. Tangential section of a tubule, the epithelium viewed from the surface. 4. Tubule in transverse section. 5. Connective tissue. —{Stohr.) 430 TEXT-BOOK OF PHYSIOLOGY. and in some unknown way influences favorably tissue metabolism. This view of the function of the thyroid is supported by the fact that successful grafting of a portion of the thyroid beneath the skin or in the abdominal cavity will prevent the usual symptoms which follow thyroidectomy. The same result is obtained by the intravenous injection of thyroid juice or by the administration of the raw gland. It was shown by Murray that myxedematous patients could be bene- fited, and even cured, by feeding them with fresh thyroids or with the dry extract. The chemic features of the material secreted and obtained from the structures of the thyroid indicate that it is a complex proteid con- taining iodin, which, under the influence of various reagents, under- goes cleavage, giving rise to a non-proteid residue, which carries with it the iodin and phosphorus. The amount of iodin in the thyroid varies from 0.33 to i milligram for each gram of tissue. To this compound the term thyroiodin has been given. The administration of this compound produces efl'ects similar to those which follow the therapeutic administration of the fresh thyroid itself: viz., a diminu- tion of all myxedematous symptoms. In normal states of the body, thyroiodin influences very actively the general metabohsm. It gives rise to a decomposition of fats and proteids and to a decline in body- weight. In large doses it may produce toxic symptoms: e. g., in- creased cardiac action, vertigo, and glycosuria. The Pituitary Body. — This is a small body lodged in the sella turcica of the sphenoid bone. It consists of an anterior lobe, somewhat red in color, and a posterior lobe, yellowish-gray in color. The former is much the larger and partly embraces the latter. The anterior lobe is developed from an invagination of the epiblast of the mouth cavity, and consists of distinct gland tissue. The posterior lobe is an outgrowth from the brain, and is connected with the infundibulum by a short stalk. It has been suggested that the term infundibular body be reserved for the posterior lobe, and the term hypophysis cerebri for the anterior lobe. This distinction appears to be desirable, inasmuch as in their origin and structure they are separate and distinct bodies. Removal of the hypophysis cerebri, or the pituitary body, is always followed by a fatal result, preceded by symptoms not unlike those which follow removal of the thyroid: viz., anorexia, tremors, spasms, etc. Degeneration of the pituitar}^ body has been found in connection with a hypertrophic condition of the bones of the face and extremities, to which the term acromegalia has been given. Intravenous injection of an extract of the pituitary increases the force of the heart-beat without any change in its frequency, and causes a rise of blood-pressure from a stimulation of the arterioles (Schafer and Ohver). The material secreted by the pituitary has SECRETION. 431 not been isolated, hence its chemic features are unknown. After its formation it probably passes through a system of ducts into the cerebrospinal fluid, after which it influences the metabolism of the nerve and osseous tissues as well as the force of the heart muscle. An extract of the anterior lobe itself exerts no appreciable effect on the blood-pressure or on the rate of the heart-beat, nor does it in- fluence the circulatory and respiratory organs. An extract of the infundibular body intravenously injected, how- ever, gives rise to increased blood-pressure and to a slowing of the heart-beat (Howell). Adrenal Bodies, or Suprarenal Capsules. — These are two flattened bodies, somewhat cres- centic or triangular in shape, situated each upon the upper extremity of the corresponding kidney, and held in place by connective tissue. They measure about 40 mm. in height, 30 mm. in breadth, and from 6 to 8 mm. in thickness. The weight of each is about 4 gm. Function of the Adrenal Bodies. — It was observed by Addison that a profound disturbance of the nutrition, characterized by a bronze-Hke discoloration of the skin and of the mucous membranes of the mouth, extreme muscular weakness, and profound anemia, was associated with, if not dependent on, pathologic conditions of the suprarenal glands. In the progress of the disease the asthenia gradually increases, the heart becomes weak, the pulse small, soft, and feeble, indicating a general loss of tone of the muscular and vascular apparatus. Death ensues from paralysis of the respiratory muscles. The essen- tial nature of the lesion which gives rise to these symptoms has not been determined. Removal of these bodies from various animals is invariably and in a short time followed by death, preceded by some of the symptoms char- acteristic of Addison's disease. Their develop- ment, however, is more acute. From the fact that animals so promptly die after extirpation of these bodies, and the further fact that the blood of such animals is toxic to the subjects of recent extirpation, but not to normal animals, the conclusion was drawn that the function of the adrenal bodies is to remove from the blood some toxic product of muscle metabolism. Its accumulation after extirpation gives rise to death through auto-intoxication. On the supposition that the adrenals might secrete and pour into Fig. 189. — Sagittal Section of the Pituitary Body AND Infundi- BULUM with Adjoining Part of Third Ventricle. a. Anterior lobe. a'. A projection from it toward the front of the infundibulum. b. Posterior lobe connected by a stalk with the infundibulum, i. I.e. Lamina cin- erea. o. Right optic nerve, ch. Section of optic chiasm, r.o. Re- cess of ventricle above the chias- ma. cm. Corpus mammillare. — (Schwalbe, from Qiiain.) 432 TEXT-BOOK OF PHYSIOLOGY. the blood a specific material which favorably influences general metabolism, Schafer and Oliver injected hypodermically glycerin and water extracts, and observed at once an increased activity of the heart-beats and of the respiratory movements. The effects, however, were only transitory. When these extracts are injected into the veins directly, there follows in a short time a cessation of the auricular contraction of the heart, though the ventricular contraction continues with an independent rhythm. If the vagi are cut previous to the injection or if the inhibition is removed by atropin, the rapidity and vigor of both auricles and ventricles are increased. Whether the inhibitory influence is removed or not, there is a marked increase in the blood-pressure, though it is greater in the former instance. This is attributed to a direct stimulation and contraction of the muscle- fibers of the arterioles themselves, and not to vasomotor influences, as it occurs also after division of the cord and destruction of the bulb. The contraction of the arterioles is quite general, as shown by plethysmographic studies of the limbs, spleen, kidney, etc. Applied locally to the mucous membranes, adrenal extract produces contrac- tion of the blood-vessels and pallor. The skeletal muscles are affected by the extract very much as they are by veratrin. The duration of a single contraction is very much prolonged, especially in the phase of relaxation or of decreasing energy. It is evident from these experiments that the adrenal bodies are engaged in elaborating and pouring into the blood a specific material which stimulates to increased activity the muscle-fibers of the heart and arteries, and thus assists in maintaining the normal blood-pres- sure as well as the tonicity of the skeletal muscles. An alkaloidal substance was isolated by Abel from extracts of this gland, to which the term epinephrin was given. A crystallizable substance was iso- lated first by Takamine and later by Aldrich, to which the term adrenalin was given. Both substances are apparently equally efficacious in causing contraction of the blood-vessels and in raising the blood pressure. The question as to which of these twO' substances represents the active principle of the gland is as yet a subject of discussion. The Spleen. — The spleen is a soft bluish-red organ, oval in shape, from twelve to fifteen centimeters long by eight broad and four thick. It is situated in the left hypochondrium between the stomach and the diaphragm. In this situation it is held in position by a fold of the peritoneum which passes from the upper border to the diaphragm. Structure. — A section of the spleen shows that it consists of connective tissue, blood-vessels, lymph corpuscles, and lymphoid tissue. The surface of the spleen is covered by a capsule composed of dense fibrous tissue, from the inner surface of which septa or SECRETION. 433 trabeculae pass inward toward the center of the organ. In their course they give off a series of processes which unite freely, forming a spongy connective-tissue framework. The capsule and the main trabeculae in some animals contain numerous non-striated muscle- fibers. In man they are relatively few in number. The blood- vessels which enter the spleen are supported by the connective- tissue septa. As they pass toward the center of the organ they divide very rapidly and soon diminish in size. In their course small branches are given off, which penetrate the intertrabecular tissue and become encased with spheric or cylindric masses of adenoid tissue known as Malpighian corpuscles. These corpuscles are composed largely of leukocytes. In some animals the leukocytes, instead of being arranged in masses, are distributed along the walls of the artery as a continuous layer. Within the corpuscles the arteries pass into capil- laries, whether the artery passes directly to the splenic pulp or indirectly by way of the corpuscles, its ultimate branches terminate in capil- laries v^hich open into the spaces of the splenic pulp. From these spaces a net- work of venules gathers the blood and transmits it to the veins. It is a disputed question as to whether the spaces are lined by epithe- Uum, thus forming a con- tinuous blood channel, or whether they are wanting in this histologic element. The Splenic Pulp. — The spaces of the connective-tissue frame- work are filled with a dark red semifluid mass known as the splenic pulp. When microscopically examined, the pulp presents a fine loose network of adenoid tissue, large numbers of leukocytes or lymph corpuscles, red corpuscles in various stages of disintegra- tion, and pigment granules. Chemic analysis reveals the presence of a number of nitrogen-holding bodies, e. g., leucin, tyrosin, xanthin, uric acid; organic acids, e. g., acetic, lactic, succinic acids; pigments containing iron, and inorganic salts. The Functions of the Spleen. — Notwithstanding all the ex- periments which have been made to determine the functions of the 28 Fin. I go. — Malpighian Corpuscle of a Cat's Spleen Injected, a. Artery. 6. Meshes' of the pulp injected, c. The artery of the corpuscle ramifying in the lymphatic tis- sue composing it. 434 TEXT-BOOK OF PHYSIOLOGY. spleen, it can not be said that any very definite results have been obtained. The fact that the spleen can be removed from the body of an animal without appreciably interfering with the normal metabo- lism would indicate that its function is not very important. The chief changes observed after such a procedure are an enlargement of the lymphatic glands and an increase in the activity of the red marrow of the bones. The presence of large numbers of leukocytes in the splenic pulp and in the blood of the splenic vein suggested the idea that the spleen is engaged in the production of leukocytes, and to this extent contributes to the formation of blood. The presence of disintegrated red blood-corpuscles has suggested the view that the spleen exerts a destructive action on functionally useless red corpuscles. These and other theories as to splenic func- tions have been offered by different observers, but all are lacking posi- tive confirmation. Volume Variations of the Spleen. — It was shown some years since by Roy, with the aid of the plethysmograph, that the spleen undergoes rhythmic variations in volume from moment to moment. In the cat and in the dog the diminu- tion in the volume (the systole) and the increase in volume (the diastole) together occupied about one minute. This fact was determined by withdrawing the spleen through an opening in the abdominal wall and enclosing it in a box with rigid walls, the interior of which was connected with a piston record- ing apparatus. The system being filled with oil, each variation in volume was attended by a to-and-fro displacement and a cor- responding movement of the recording lever. The special form of plethysmograph used for this purpose is known as the oncometer or bulk measurer, and the recording apparatus as the oncograph (Fig. 191 and Fig. 196). The cause of these variations in volume Roy attributed to a rhythmic contractility of the non-striated muscle-fibers in the capsule and trabecular, and not to changes in the arterial blood-pressure, as the curve of the pressure taken simultaneously remained prac- FiG. iQi. — Spleen Oncometer Laid Open. SECRETION. 435 tically uniform. The effect of the rhythmic contractions of the splenic muscle tissue is to force the blood through the organ, a condition necessitated perhaps by the pressure relations within, though what function is thereby fulfilled is not apparent. It was subsequently shown by Schafer and Moore that the splenic volume is extremely responsive to all fluctuations of the arterial blood-pressure; that though the spleen may passively expand and recoil in response to the rise and fall of the blood-pressure, never- theless the reverse conditions may obtain: viz., that the splenic volume may diminish as the pressure rises, if the splenic arterioles contract simultaneously with the contraction of the arterioles gener- ally. On the contrary, the splenic volume may increase coincident with a dilatation of the splenic and systemic arterioles. In addition to the rhythmic variations, the spleen steadily increases in volume for a period of five hours after digestion, and then gradually returns to its former condition. Influence of the Nerve System. — The nerves which supply the vascular and visceral muscles in the spleen are derived directly from the semilunar ganglion (post-ganglionic fibers) and pass to it in company with the splenic artery. The nerve-cells from which they arise are in physiologic relation with nerve-fibers (pre-ganglionic fibers) which emerge from the spinal cord in the anterior roots of the third thoracic to the first lumbar nerves inclusive, though they are found most abundantly in the sixth, seventh, and eighth thoracic nerves. Their center of origin is in the medulla oblongata. Stimulation of the nerves in any part of their course gives rise to a diminution in splenic volume; division of the nerves is followed by an increase in the volume. In asphyxia the spleen is small and contracted, a condition attributed to a stimulation of the centers in the medulla by the venosity of the blood. The musculature of the spleen may also be excited to contraction by reflex influences, as show^n by the fact that stimulation of the central end of a sensory nerve is attended by a diminution of volume. Inasmuch as the excised spleen will continue to exhibit variations in volume when perfused with blood, it would appear that it possess some mechanism independent to some extent of the nerve system. CHAPTER XVI. EXCRETION. As stated in the preceding chapter, the term excretion is limited to the process by which the end-products of tissue metabohsm are re- moved from the body, the nature of the process, however, differing in no essential particulars from that underlying the process of secre- tion. The histologic structures involved and the forces at work being of the same general character, it is impossible to draw any sharp hne of distinction between them. As a general fact it may be stated that in their composition all the characteristic ingredients of the excretions are incapable either of entering into the formation of tissue or of undergoing oxidation for the purpose of heat-production. As the retention of these end-products in the body would exert a deleterious influence on normal metabolism, their prompt removal becomes essential to the maintenance of physiologic activity. The principal excretions of the body — urine, perspiration, and bile — are complex fluids in which, with the exception of those given off in the lungs, are to be found in varying proportions the chief end-products of metabohsm. THE URINE. Normal urine has a pale yellow or amber color, an aromatic odor, an acid reaction, and a specific gravity of 1.020. As a rule, it is perfectly transparent, though its transparency may be diminished from the presence of mucus, calcium and magnesium phosphates, and mixed urates. The color, which varies within physiologic hmits from a pale yellow to a reddish-brown, is due to the presence of the coloring- matters urobilin, urochrome, and uroerythrin, all of which are de- rivatives from the bile pigments absorbed from the liver or the alimentary canal. The reaction of the urine is acid, owing to the presence of the acid phosphates of sodium and calcium. The degree of acidity, however, varies at different periods of the day. Urine passed in the morning is strongly acid, while that passed during and after digestion, espe- cially if the food be largely vegetable in character and rich in alkaline salts, is either neutral or alkahne in reaction. The diminished acidity after meals is attributed to the formation of hydrochloric acid by the gastric glands and the consequent liberation of bases which are ex- creted in the urine. The phosphoric acid which enters into com- 436 EXCRETION. 437 bination with sodium and potassium bases is a product of tissue metabolism. The specific gravity is about 1.020, though it varies from 1.015 to 1.025. It will diminish, other things being equal, with increased consumption of water and diminished activity of the skin; it will be increased of course by the opposite conditions. The quantity of urine excreted in twenty-four hours varies from 1200 to 1700 c.c. Amounts both above and below these are fre- quently passed from a variety of causes. The odor of the urine is characteristic and due to the presence of aromatic compounds. COMPOSITION OF URINE. Water, 1500.00 c.c. Total solids, 72.00 grams. Urea, 33-i8 Uric acid, (urates), 0.55 " Hippuric acid, ( hippurates.) 0.40 " Kreatinin, .xanthin, hypoxanthin, guanin, ammo- \ ,< nium salts, pigment, etc. j Inorganic salts: sodium and potassium sulphates, ] phosphates, and chlorids; magnesium and cal- j cium phosphates, |- 27.00 " Organic salts: lactates, acetates, formates in small j amounts, J Sugar, a trace Gases nitrogen, and carbonic acid. The estimation of total urinary solids in any given sample of urine is frequently a matter of chnical interest. This may approxi- mately be attained by multiplying the last two figures of the specific gravity by the coefficient of Haeser or Christison, 2.33. The result expresses the total sohds in looo parts: e.g., urine with a specific gravity of 1.020 would contain 20X2.33, or 46.60 grams of sohd matter per looo c.c. If the amount passed in twenty-four hours be 1500 c.c, the total solids would amount to 69.9 grams. The Water of the Urine. — The amount of urinary water and its ratio to the solid constituents will vary with the amount consumed and the activity of the skin and lungs. In summer the foods, liquid and solid, remaining the same, the quantity of water in the urine is diminished in consequence of increased activity of skin and lungs and the ratio of water to solids decreased. In winter the reverse conditions obtain. The food remaining the same, the consumption of large quantities of water hastens at least the removal of end- products from the tissues and thus increases the urinary solids. Urea is the most abundant of the organic constituents of the urine and is present to the extent of from 2 to 3 per cent. It is a colorless neutral substance, crystallizing under varying conditions in long silky needles or in rhombic prisms. It is soluble in water and alcohol. It is composed of CONjH^. When subjected to pro- longed boihng, it combines with water, giving rise to ammonium 438 TEXT-BOOK OF PHYSIOLOl^Y. carbonate. The presence of Micrococcus urece in urine will also convert the urea, by combining it with two molecules of water, into ammonium carbonate, C0N2H^ + 2H20 = (NHJ2C03. The average amount of urea excreted daily varies from 30 to 34 grams. As urea is now known to be the principal end-product of proteid metabolism within the body, it is evident that the quantity produced and eliminated in the twenty-four hours will depend on the quantity of proteid food consumed and on the extent to which the proteid constituents of the tissues are metabolized. In the condition of nutritive equilibrium, when the proteid ingested is 100 grams and the urea egested 31.5 grams, it is difficult to state the percentage of urea which is derived from the metabolism of the proteid food (circulating proteid) and that derived from the metabolism of the proteids of the tissues (organ proteid). In this condition, however, it is found that if the proteid consumed is varied within hmits above or below the standard amount of 100 grams, the quantity of urea excreted rises and falls in practically the same ratio, indicating apparently that the production of urea is directly dependent on the proteid supply. On the contrary, it has been observed in human beings in the fasting condition that for a period of ten days there is a daily excretion of about 21 grams of urea, equivalent to about 70 grams of proteid. Again, contrary to former views, the metabolism of proteid and the production of urea are practically independent of muscular work. Even after severe labor extending over a period of some hours there is no noticeable increase in the urea eliminated. Seat of Urea Formation. — It is quite certain in the light of present knowledge that urea is partly formed in the liver by the action of the cells out of cleavage products of proteid metabolism. The par- ticular compounds out of which the cells synthetize urea are the ammonium salts, especially the carbamate and carbonate. The experimental reasons for this view have already been stated on page 426. Uric acid is one of the constant ingredients of the urine. It is a crystalhne nitrogen-holding body closely resembhng urea, its formula being CgH^N^Og. The total quantity excreted daily varies from 0.2 to I gram. It is doubtful if uric acid exists in a free state in the urine, the indications being that it is combined with sodium and potassium in the form of a quadriurate. The urates are frequently deposited when in excess from the urine as a brick-red sediment, the color being due to their combination with the coloring-matter uroerythrin. When pure, uric acid crystalhzes in the rhombic form, though it assumes a variety of forms. Uric acid was long regarded as a product of general proteid metaboHsm and for chemic reasons an antecedent of urea. This view has been abandoned. At present it is believed that it is a cleavage product of nuclein, a constituent of all cell nuclei. In the metabolism of nuclein a proteid and nucleic EXCRETION. 439 acid are formed, from the latter of which uric acid is derived. Nu- cleic acid when decomposed yields a series of bases, such as xanthin, hypoxanthin, adenin, guanin, etc. Because of the fact that these bodies can also be obtained from a s}nthetized body termed purin they are known collectively as the purin bases. Though there is a close relationship between uric acid and the purin bases, it has been impossible to experimentally derive one from the other. When hy- poxanthin, however, is given internally it is oxidized and converted into uric acid. It is extremely probable, therefore, that uric acid is an oxidation product of one or more of the purin bases. It is probable, however, that not all of the uric acid eliminated is derived from the nuclein of tissue-cells and their decomposition products, the purin bases. Some of it is undoubtedly derived from the nucleins contained in foods. The uric acid eliminated is there- fore partly endogenous and partly exogenous in origin. Xanthin, hypoxanthin, guanin, etc., are also found in urine in small but variable amounts. They are nitrogenized compounds derived mainly from the metabolism of the nuclein bodies. Kreatinin is a crystalline nitrogenous compound closely resem- bling kreatin, one of the constituents of muscular tissue. The amount excreted daily is about i gram. Though kreatinin may arise in conse- quence of proteid metabohsm, it is probable that it is largely derived from a transformation of the kreatin contained in the meat consumed as food. Hippuric acid in combination with sodium and potassium is very generally present in urine, though in small amounts. It is more abundant in the urine of the herbivora than the carnivora. In man the amount excreted daily is about 0.7 gram, though the amount may be raised by a diet of asparagus, plums, cranberries, etc., and by the administration of benzoic and cinnamic acids. There is evidence that hippuric acid is formed in the kidney from benzoic acid, its pre- cursors, or related bodies. Various compounds of this class are found in vegetable foods, a fact which may account for the increase in the excretion of hippuric acid on a vegetable diet. Leucin, tyrosin, phenol, cystin, indoxyl, skatoxyl, are found in small amounts even under normal conditions. They arise from putrefactive change in the intestine. Inorganic Salts. — Sodium and potassium phosphates, known as the alkaline phosphates, are found in both blood and urine. The total quantity excreted daily is about 4 grams. Calcium and magnesium phosphates, known as the earthy phosphates, are present to the extent of i gram. Though insoluble in water, they are held in solution in the urine by its acid constituents. If the urine be rendered alkaline, they are at once precipitated. Sodium and potassium sulphates are also present to I he extent of about 440 TEXT-BOOK OF PHYSIOLOGY. 2 grams. The phosphoric and sulphuric acids which are combined with these bases enter the body for the most part in the foods, though there is evidence that they also arise by oxidation in consequence of the metabolism of protcids which contain phosphorus and sulphur. Sodium chlorid is the most abundant of the inorganic salts. It is derived mainly from the food. The amount excreted is about 15 grams in twenty-four hours. THE KIDNEYS. The kidneys are the organs engaged in the excretion of the urinary constituents from the blood. They resemble a bean in shape, are from 10 to 12 centimeters in length, 2 in breadth, and weigh from 144 to 170 grams. They are situated in the lumbar region, one on each side of the vertebral column behind the peritoneum, and extend from the eleventh rib to the crest of the ihum. The anterior surface is convex, the posterior surface concave. The latter presents a deep notch — the hilum. The kidney is surrounded by a thin smooth membrane composed of white fibrous and yellow elastic tissue; though it is attached to the surface of the kidney by minute processes of connective tissue, it can very readily be torn away. The sub- stance of the kidney is dense but friable. Upon making a longitudinal section of the kidney it will be ob- served that the hilum extends into the interior of the organ and expands to form a cavity known as the sinus, in which are found the blood-vessels, nerves, and duct (Fig. 192). This cavity is mainly occupied by the upper part of the renal duct, the ureter, the interior of which is termed the pelvis. The ureter divides into several por- tions which terminate in small caps or calyces which receive the apices of the pyramids. The parenchyma of the kidney consists of two portions : viz. — 1. An internal or medullary portion, consisting of a series of pyramids or cones, some twelve or fifteen in number, which present a dis- tinctly striated appearance. 2. An external or cortical portion, half an inch in thickness and dis- tinctly friable in character. The Histology of the Kidney. — The kidney is composed of a connective-tissue framework supporting secreting tubules, blood- vessels, lymphatics, and nerves, all of which are directly connected with the removal of the urinary constituents from the blood. The kidney is structurally a compound tubular gland. If the apex of each pyramid be examined with a lens, it will present a number of small orifices which may be regarded as the beginnings of the urinifer- ous tubules. From this point the tubules pass outward in a straight but somewhat diverging manner toward the cortex, giving off at EXCRETION. 441 acute angles a number of branches (Fig. 193). From the apex to the base of the pyramids they are known as the tubules of Bellini. In the cortical portion of the kidney the tubule becomes enlarged and twisted, and, after pursuing an extremely convoluted course, turns backward into the medullary portion for some distance, form- ing the ascending limb of Henle's loop; it then turns upon itself, forming the descend- ing limb of the loop, re- enters the cortex, again expands and becomes convoluted, and finally terminates in an ovoid enlargement known as Miiller's or Bowman's capsule, in which is contained a small tuft of blood-vessels — the glomerulus. Each tubule consists of a basement membrane hned throughout its entire extent by epi- thelial cells. The epi- thelium as well as the tubule vary in shape and size in different parts of its course. In the capsule the epi- thelium is flattened, lining not only the inner surface of the capsule but reflected over the blood-vessels as well. This is knowai as the glomer- ular epithelium. In the convoluted por- tions of the tubules the epithehum is cuboidal, granular, and some- what striated ; in Henle's loop it is more or less flattened. The Blood-vessels of the Kidney. — The renal artery enters the kidney at the hilum behind the ureter; it soon divides into several Fig. 192. — Longitudinal Section through the Kidney, the Pelvis of the Kidney, and a Number of Renal Calyces. A. Branch of the renal artery. U. Ureter. C. Renal calyx. i. Cortex, i'. Medullary rays. i". Labyrinth, or cortex proper. 2. Medulla. 2'. Papillary por- tion of medulla, or medulla proper. 2". Border layer of the medulla. 3, 3. Transverse section through the axes of the tubules of the border layer. 4. Fat of the renal sinus. 5, 5. Arterial branches. *. Transversely coursing medulla rays. — {Tyson, after Henle.) 442 TEXT-BOOK OF PHYSIOLOGY. large branches which penetrate the substance of the kidney between the pyramids and pass outward into the cortex. At the base of the Lobule. Lobule. Renal corpuscle Thin division of tlu- loop of Hen Collectin.:; tubule. runica albuginea. . Stellate vein. . Interlobular artery. - Interlobular vein. . Arciform artery. ,. Arciform vein. Interlobar artery. » Interlobar vein. Papillary duct -f-.t; Fig. IQ1!.— Scheme of the Course of the Uriniferous Tubules and the Renal Vessels. EXCRETION. 443 pyramids branches of the arteries form an anastomosing plexus. From this plexus vessels are given off, some of which follow the straight tubules toward the apex of the pyramids, vasa recta, while others enter the cortex and pass to its surface (Fig. 193). In the course of the latter small branches are given off, each of which soon divides and subdivides to form a ball of capillary vessels known as the glomer- ulus. These capillaries, however, do not anastomose, but soon re- unite to form an efferent vessel the caliber of which is less than that of the afferent artery. In consequence of this, there is a greater re- sistance to the outflow of blood than to the inflow, and therefore a higher blood-pressure in the glomerulus than in capillaries generally. The relation of the glomer- ulus to the tubule is im- portant from a physiologic point of view. As stated above, the glomerulus is received into and sur- rounded by the terminal expansion or capsule of the tubule. This capsule, formed by an indentation of the terminal portion of the tubule, consists of two walls, an outer one consist- ing of an extremely thin basement membrane, covered by flattened epi- thehal cells, and an inner one consisting apparently only of flattened epithelium which is reflected over and closely invests the glomer- ular blood - vessels (Fig. 194). The blood is thus separated from the interior of the capsule by the epithehal wall of the capillary and the epithehum of the re- flected wall of the capsule. During the periods of secretory activity the blood-vessels of the glomerulus are filled with blood to such an extent that the sac cavity is almost obhterated. After its exit from the capsule the efferent vessel of the glomerulus soon again divides and subdivides to form an elaborate capillary plexus which surrounds and closely invests the convoluted tubules. From this plexus as well as from the plexus wiiich surrounds the straight tubules veins arise which pass toward and empty into veins at the base of the pyra- mids. The renal vein formed by the union of these latter veins emerges from the kidney at the hilum and finally empties into the vena cava inferior. Fig 194. — Scheme of the Rexal or Mal- PiGHiAN Corpuscle, i. Interlobular ar- tery. 2. Afferent vessel. 3. Efferent vessel. 4. Outer wall. 5. Inner wall. 6. Glom- erulus. 7. Neck of tubule. — {Stohr.) 444 TEXT-BOOK OF PHYSIOLOGY. The nerves of the kidney are derived from the renal plexus and follow the course of the blood-vessels to their termination. The Renal Duct. — The excretory duct of the kidney, the ureter, is a musculo-mcmbranous tube about 5 mm. in diameter when dis- tended, 30 cm. in length, and extends from the hilum to the base of the bladder. The upper extremity is expanded and within the renal sinus becomes irregularly branched, giving rise to a number of short tubes, called calyces, each of which embraces the apex of a Malpighian pyramid. The interior of the expanded portion of the ureter is known as the pelvis. The wall of the ureter consists of a mucous membrane, a muscle coat, and an external fibrous investment. MECHANISM OF URINE SECRETION. The secretion of urine is a complex process and susceptible of several interpretations. It was originally inferred by Bowman that, as the kidney presents anatomically an apparatus for filtration, the capsule with its enclosed glomerulus, and an apparatus for secretion, the epithelium of the urinary tubules, the elimination of the urinary constituents from the blood is accomplished by the two processes of filtration and secretion; that the water and highly diffusible inorganic salts simply pass by diffusion, under pressure, through the walls of the glomerular capillaries, while the organic constituents are removed by the epithelium lining the tubules. Influenced largely by the facts of blood-pressure Ludwig advanced the view that the factors concerned in the secretion of urine were purely physical; that in consequence of the high pressure in the vessels of the glomeruh, due to the resistance offered by the smaller efferent vessel, all the urinary constituents were filtered off in a state of extreme dilution. In order to account for the higher per- centage of the organic constituents in the urine, it was assumed that as the dilute urine passed through the tubules the water was partly reabsorbed, passing by diffusion into the lymph and blood until the urine acquired its normal characteristics. In support of this view, a large number of facts relating to the influence of an increase and a decrease of pressure in the blood-vessels of the glomeruh, the velocity of the blood-stream, etc., in determining the rate of urinary flow were adduced, all of which apparently indicated that the former stood to the latter in the relation of cause and effect, and that the formation of urine was accomplished entirely by physical forces. The progress of physiologic investigation, however, has thrown some doubt on the vaHdity of this physical interpretation, and has rather served to support the view of Bowman that the organic con- stituents at least are removed from the blood by a process of selection on the part of the epithelium of the convoluted part of the urinary EXCRETION. 445 tubules; in other words, that the secretion of urine is physiologic rather than physical. Heidenhain has brought forward a series of facts which support this view. As evidence that the cells possess a selective power, he presents the following experiment : The spinal cord of an animal is divided in the neck for the purpose of lowering the blood-pressure in the kidney below the pressure at which the urine is secreted; a solution of indigo-carmine is injected into the blood- vessels; after the lapse of ten minutes the animal is killed, the blood- vessels washed out with alcohol for the purpose of precipitating the indigo-carmine in situ. Section of the kidney shows a uniform blue stain of the cortex alone. Microscopic examination reveals the fact that the blue stain is due to the deposition of the pigment in the lumen and in the lumen border of the cells of the convoluted tubules and the ascending Hmb of Henle's loop; while the epithehum of Bow- man's capsule as well as the glomerular epithelium present no evi- dence of pigmentation. Nussbaum attempted to establish the secretory power of the epi- thehum in another way. In the frog the kidney receives blood from two sources: the glomeruli receive their blood from the renal artery, the tubules from the capillaries formed by the anastomosis of branches of the efferent vessel of the glomerulus and the branches of the renal portal vein. Nussbaum believed that by ligating the renal artery all glomerular activity could be aboHshed and the part played by the epithelium could be estabhshed. After so doing the flow of urine was at once checked; the injection of urea at once reestablished it. This fact was taken as a proof that the tubular epithehum not only ex- creted urea, but water and perhaps other constituents as well. It was also found that sugar, peptones, carmine, etc., which are always ehminated from the blood under normal conditions, are not removed after ligation of the renal artery. It was concluded from these ex- periments that the secreting structures of the kidney consist of two distinct systems, the glomerular and the tubular; the former secreting water, salts, sugar, peptone, etc.; the latter urea, uric acid, etc. These and similar facts indicate that the renal epithehum possesses a secretory rather than an absorptive function. Heidenhain and those who agree with him assert that even the water and inorganic salts which pass through the glomerular epithelium do so in conse- quence of cell selection and cell activity; that the entire process is one of secretion, though conditioned by blood-pressure, blood velocity, etc. Influence of Blood-pressure. — Whether the ehmination of the urinary constituents is entirely secretory (physiologic) in character or not there can be no doubt that the whole process is largely deter- mined by the pressure and velocity of the blood in the glomerular capillaries, or, to state it more accurately, on the dilTerence of pres- sure between the blood in the capillaries and the urine in the capsules. 446 TEXT-BOOK OF PHYSIOLOGY. As a rule, this latter pressure is at a minimum. If the urine should accumulate in the ureter and tubules cither from ligation or mechan- ical obstruction until its pressure approximates that of the blood, the secretion would be diminished if not abolished. It is difficult to determine the average pressure or velocity of the blood in the glomerular capillaries, though they both must be greater than in capillaries in other parts of the body, from the fact that the efferent vessel is narrower than the afferent, and therefore offers great resistance to the outflow of blood, a condition most favor- able to the production of a high pressure in the glomerulus. The pressure of the blood in the glomeruli may be raised and the velocity increased: 1. By an increase in blood-pres- sure generally. 2. By an increase in the pressure of the renal artery alone. The first condition may be brought about by an increase in either the force or frequency of the heart's action or by a con- traction of the arterioles of vas- cular areas in any or all parts of the body, excepting, of course, the renal vascular area. The second condition is brought about by a dilatation of the renal artery alone and possibly by a contrac- tion of the efferent vessels of the glomeruli. The pressure of the blood in the glomeruli may be diminished and the velocity decreased — 1. By a decrease in the blood-pressure generally. 2. By a decrease in the pressure of the renal artery alone. The first condition is brought about by a decrease in either the force or frequency of the heart's action or by a dilatation of the arteri- oles of large vascular areas in any or all parts of the body. The second condition is brought about by contraction of the renal arter\' alone and possibly by a dilatation of the efferent vessels of the glom- eruli. The effect of the contraction and relaxation of either the afferent or efferent vessels on the pressure within the glomerulus is shown in figure 195. Fig. 195. — To Illustrate the Effect OF Active Changes in the Yasa Afferentia and Efferentia on THE Pressure in the Glomerul.ar Capillaries. A. Renal arteries. G. Glomerular capillaries. C. Tubular capillaries. V. Vein. The short thick lines represent the vasa afferentia and efferentia. The con- tinuous heavy line represents the mean average pressure. If the vas afferens dilates and the vas efferens contracts separately or conjointly, the pressure will rise, as indicated by the upper dotted Una. If the vas afferens contracts and the vas efferens dilates separately or con- jointly, the pressure wfill fall, as in- dicated by the lower dotted line. — {Ajter Moral and Starling.) EXCRETION. 447 Coincident with the rise and fall of pressure in the glomerular capillaries there is a rise and fall in the rate of urinary flow. Thus it has been found that an increase in the aortic pressure from 127 to 142 mm. of mercury, by ligation of the carotid, femoral, and vertebral arteries, increased the rate of urinary flow from 8.7 grams in thirty minutes to 21.2 grams. On the contrary, a decrease in aortic pres- sure below 40 mm. of mercury caused by division of the spinal cord is followed by a total abolition of the urinary flow. These facts serve to indicate the dependence of the secretion on blood-pressure. That there is an increase in the volume of the blood flowing: through the kidney during its functional activity is apparent from inspection. It is enlarged, swollen, and red in color. The blood in the renal vein is bright red in color and contains more oxygen and less carbon dioxid than venous blood generally. During the intervals ^1 -*'- ^ ^^^ T(i:iz [• a Fig. 196. — Oncometer. K. Kidney; the thick line is the metallic capsule, h. Hinge. I. Tube for filling apparatus. T. Tube to connect with T,. a, v, u. Artery, vein, ureter. — {Stirling, after Roy.) Fig. 197. — Oncograph. C. Chamber filled with oil, communicating by T, with T. p Piston. /. Writing-lever. — {Stirling, after Roy.) of activity the kidney diminishes in size, is pale in color and the blood of the renal vein dark and venous in character. These varia- tions in the volume of the kidney have also been experimentally deter- mined and registered by means of the oncometer and oncograph devised by Roy (Figs. 196 and 197). The oncometer consists of a metalhc box (Fig. 196) composed of halves which open and close by means of a hinge. It is con- nected with a recording apparatus, the oncograph (Fig. 197), through the tube T. The kidney, withdrawn from the body, is placed within the oncometer. Through an opening in the side pass the arter}% vein, and ureter. Between the kidney and the wall of the capsule there is placed a thin membrane. Oil is then poured through the side tube I until the space between the capsule and 448 TEXT-BOOK OF PHYSIOLOGY. the kidney, as well as the tube leading to the chamber of the onco- graph, are completely filled. When the tube I is closed, the condi- tions are such that all variations in the volume of the kidney are taken up and reproduced by the recording lever attached to the piston of the oncograph. A curve of the variations in the volume of the kidney is shown in figure 198, taken simultaneously with the curve of the blood-pressure. An examination of this curve shows that the volume-changes coincide with changes in the blood-pressure, exhibiting not only the respiratory but also the cardiac undulations. Influence of the Nerve System. — The influence of the nerve system in regulating the blood-supply to the kidney is evident from the results of experimentation. If the nerves which accom- pany the renal artery into the kidney are divided, the artery at once dilates, the kidney enlarges, and a copious flow of urine takes place. If the peripheral ends of these nerves be stimulated with the induced electric current, the artery contracts, the kidney B.P. BLOOD PRESSURE CURVE KIDNEY CURVE Fig. 198. — B. P. Blood-pressure curve. K. Curve of the volume of the kidney. T Time curve; intervals indicate a quarter of a minute. A. Abscissa. — {Stirling, after Roy.) diminishes in size, and the flow of urine ceases. In addition to these vaso-constrictor nerves, there is evidence that the kidney also receives vaso-dilator nerves which emerge from the spinal cord and are found in the anterior roots of the eleventh, twelfth, and thirteenth dorsal nerves, in the dog. Direct and reflex stimulation of these nerves gives rise to a dilatation of the artery, a swelling of the kidney, and an increase in secretion, independent of any variation in general blood-pressure. The route of the vaso-constrictor nerves is, in the dog at least, through the splanchnics. Section of these nerves is followed by a dilatation of the renal vessels and an increase in the flow of urine. Stimulation of the peripheral ends is followed by a constriction of the vessels and a cessation of the flow of urine. The vasomotor center for the blood-vessels of the kidney is in all probability situated in the medulla oblongata in close proximity to the general vasomotor centers, though subordinate centers are doubt- EXCRETION. 449 less present in the spinal cord. It was found by Bernard that punc- ture of the medulla was occasionally followed by a profuse secretion of urine without the presence of sugar. The route of the vaso-motor impulses which influence the renal blood-supply is down the cord through the splanchnics and through the renal plexus. Influence of Variations in the Composition of the Blood. — As it is the function of the kidneys to excrete water, inorganic salts, and various end-products from the blood and thus maintain a gen- eral average composition, it is highly probable that as soon as they accumulate beyond a certain percentage they themselves act as stimu- lants to renal activity, either by acting directly on the renal epithelium or by increasing the glomerular pressure. There is evidence at least that urea acts in the former manner. An excess of water in the blood that from copious drinking or from a sudden checking of the skin from a fall of temperature will act in the latter way. The introduction into the blood of inorganic salts, such as potassium nitrate, sodium acetate, etc., will in a short time lead to increased activity of the kidneys, as shown by an increase in the quantity of urine excreted. The manner in which these agents and other members of their class, the so-called saline diuretics, increase renal activity is yet a subject of discussion. On the one hand, it is stated that they promote an absorption of water from the tissues to such an extent that a condition of hydremic plethora is produced, which in itself increases not only the general blood-pressure but the local renal pressure as well, and that it is this factor which is the cause of the increased flow of urine. On the other hand, it is asserted that though the salts increase the local pressure and the volume of the kidney, they nevertheless act specifically on the renal epithelium, and therefore may be re- garded as secreto-motor agents. An increase in the percentage of sugar or urea in the blood has a similar influence on the kidney. The Storage and Discharge of Urine. — Urination. — The uri- nary constituents, as soon as they are eliminated from the blood, pass into and through the uriniferous tubules and by them are dis- charged into the pelvis of the kidney. They then enter the ureter bv which they are conducted to the bladder. The immediate cause of this movement is undoubtedly a difference of pressure between the terminal portions of the tubules and the terminal portion of the ureter, aided by the peristaltic contraction of the muscle wall of the ureter. The bladder is a reservoir for the temporary reception of the urine prior to its expulsion from the body. When distended it is ovoid in shape and is capable of holding from 600 to 800 cu. cm. The bladder is composed of four coats: viz., serous, muscle, areolar, and mu- cous. The muscle coat consists of external longitudinal and inter- nal circular and obhque layers of fibers of the non-striated variety 29 450 TEXT-BOOK OF PHYSIOLOGY. which collectively encircle the entire organ. As these fibers by their contraction expel the urine from the bladder, they are known col- lectively as the detrusor urince muscle. At the exit of the bladder the circular fibers are somewhat increased in number, giving rise to the appearance of a distinct muscle which has been termed the sphincter vesica muscle. The presence of this muscle has, however, been denied and the retention of the urine has been attributed to mechanic conditions at the neck of the bladder. The urethra just beyond the bladder is provided with a distinct circular muscle com- posed of striated fibers, the sphincter urethra muscle. When the urine passes into the bladder it is retained there and prevented from escaping by the contraction of this latter muscle. Under normal conditions the urine accumulates to a considerable extent before the intra-vesic pressure gives rise to a characteristic sensation and the desire for urination. The Nerve Mechanism of Urination. — The muscle mechan- isms which retain as well as expel the urine are under the control of the nerve system. The sphincter urethrae muscle, which by the orifice of the bladder is closed, is kept in a state of tonic contraction by nerve impulses coming from the spinal cord through the anterior roots of the third and fourth sacral nerves. The detrusor urinae muscle is excited to contraction by impulses coming likewise through the sacral nerves and through the upper lumbar nerves irom the cord. The centers of origin for these two sets of motor nerves are located in the cord in the neighborhood of the fifth lumbar vertebra. The expulsion of the urine is largely a reflex act, though under the con- trol of the will. When the desire to urinate is experienced, nerve impulses are coming through sensory nerves from the mucous mem- brane of the bladder which are reflected to the centers governing the sphincter urethrae and detrusor urinae muscles and to the brain. The elfect of the reflected impulses is to inhibit the sphincter center and to stimulate the detrusor center. If the act of urination is to be permitted, vohtional impulses descend through the spinal cord which have the effect of still further inhibiting the sphincter center and stimulating the detrusor center, the result being a re- laxation of the sphincter muscle and a contraction of the detrusor muscle and the expulsion of the urine. If the act of urination is to be suppressed, volitional impulses inhibit the detrusor center and stimulate the sphincter. PERSPIRATION; SEBUM. The perspiration or sweat, the chief secretion of the skin, is a clear colorless fluid, sHghtly acid in reaction and saline to the taste. Its specific gravity varies from 1.003 to 1.006. Unless collected from the soles of the feet and the palms of the hand, it is apt to be mixed with epithehal cells and sebum. The total quantity of perspiration EXCRETION. 451 secreted daily has been variously estimated at from 700 to 1000 grams; the exact amount, however, is difficult of determination, for the reason that the rate of secretion varies readily with variations in tempera- ture, food, drink, season of the year, etc. Chemic analysis of the sweat shows that it contains but from 0.5 to 2.5 per cent, of solid constituents, the variation in the percentage depending on the quantity of water secreted. The solids consist of traces of urea, neutral fats, lactic and sudoric acids in combination with alkaline bases, and inorganic salts (Fovel). Other observers, however, have not been able to detect the presence of either lactic or sudoric acid. Urea is a constant ingredient, though its percentage is extremely small, possibly not more than o.i per cent. The amount, however, may be very much increased in uremic conditions, the result of acute or chronic disease of the kidneys. The inorganic constituents consist mainly of sodium chlorid and alkahne and earthy phosphates. Carbonic acid is also present in the free state as well as in combination with alkaline bases. The very small quantity of the sohd constituents in the sweat, taken in connection with the fact that it is excreted most abundantly when the external temperature is high, indicates that it is not so im- portant as an excrementitious fluid as it is as a means for the regula- tion of the temperature of the body. The sweat is a product of the secretory activity of speciahzed glands, the sweat-glands, embedded in the skin, to the histologic structures of which they bear a special relation. THE SKIN. The skin is a complexly organized structure investing the entire external surface of the body. Its total area varies from 16 to 20 feet in man and from 12 to 16 feet in woman. It varies in thickness in different localities of the body from ^ to yIt of an inch. The skin consists of two principal layers: viz., a deep layer, the derma or corium, and a superficial layer, the epidermis. The derma on corium may be subdivided into a reticulated and a papillary layer. The reticulated layer consists of white fibrous and yellow elastic tissue, non-striated muscle fibers, woven together in every direction and forming an areolar network, in the meshes of which are deposited masses of fat and a structureless amorphous matter; the papillary layer consists mainly of club-shaped elevations or projections of the amorphous matter constituting the papillae. The reticulated layer serves to connect the skin with the underlying structures and to afl'ord support for the blood-vessels, nerves, and lymphatics which are distributed to the papillae (Fig. 199). The epidermis is an extra- vascular structure consisting entirely of epithelial cells. It may also be subdi\dded into two layers — the Malpighian or pigmentary layer, and the corneous or horny layer 452 TEXT-BOOK OF PHYSIOLOGY. ,"3- 3^-tc^ A:_ The former is closely applied to the papillary layer of the true skin and is composed of large nucleated cells, the lowest layer of which, the "prickle cehs," contains the pigment granules which give to the skin its varying hues in different individuals and in different races of men ; the corneous layer is composed of flattened cells which from their exposure to the atmosphere, etc., are hard and horny in texture. The Sweat-glands. — These glands are tubular in shape, the inner extremity of each being coiled upon itself a number of times, forming a little ball situated in the derma or the subcutaneous connective tissue. From this coil the duct passes up in a straight direction to the epidermis, where it makes a few spiral turns, after which it opens obliquely on the surface. The gland consists of a base- ment membrane lined with epithelial cells. It is sup- plied abundantly with blood-vessels and nerves. The sweat - glands are extremely numer- ous all over the cutaneous surface, though they are more thickly dis- posed in some situ- ations than others. They probably average 2500 to the square inch; the total number has been estimated at from 2,000,000 to 2,500,000. The Influence of the Nerve System on the Production of Sweat. — The secretion of sweat, though a product of the activity of epithehal cells and dependent on a variety of conditions, is reg- ulated to a large extent by the nerve system. Here as in other secreting glands the fluid is derived from materials in the lymph- spaces, furnished by the blood. Generally the two conditions, in- >=^,- ^%. ■<^^^'s/. ■*^iiii^ Fig 199. — Section Perpendicularly Through the Healthy Skin. a. Epidermis, or scarfskin. b. Rete mucosum, or rete malpighii. c. Papillary layer, d. Derma, corium, or true skin. e. Pan- niculus adiposus, or fatty tissue. /, g, h. Sweat- gland and duct, i, k. Hair, with its follicle and papilla. /. Sebaceous gland. EXCRETION. 453 creased blood-flow and increased glandular action, coexist. At times, however, a profuse clammy perspiration is secreted with dimin- ished blood-flow. Two sets of nerves are evidently concerned in this process: viz., vaso-motor nerves, which regulate the blood-supply, and secretor nerves, which stimulate the gland-cells to activity. The nerve-centers which control the sweat-glands are situated in the spinal cord, though the number of such centers and their exact location for the different regions of the body have not yet been satisfactorily determined. In a general way it may be stated that the centers for the head and face he in the upper cervical portion of the cord; for the upper extremities, in the lower cervical portion; for the lower extremities, in the lower dorsal and upper lumbar portion. The secretor nerves which emerge from these centers reach the glands of the face and head through the cervical sympathetic; of the arms and legs, through the brachial plexus and the sciatic nerves. It is probable that there is also a general dominating sweat center located in the medulla oblongata. That the sweat-glands are stimulated to activity by nerve impulses is shown by the fact that stimulation of the peripheral end of the divided cervical sympathetic, of the brachial plexus, or of the sciatic nerve is followed in a few seconds by a profuse secretion. Though under physiologic conditions there is a simultaneous dilatation of the blood-vessels and an increased supply of blood, this is merely a condition and not a cause of the secretion; for the secretion can be excited and the flow maintained for a period of from ten to fifteen minutes after hgation of the blood-vessels of the limb or even after its amputation, when the corresponding nerve is stimulated. The sweat-glands may be excited to activity by their related nerve- centers, either by central, reflex, or peripheral influences. Among the first may be mentioned mental emotions, venosity of the blood, increased temperature of the blood, hot drinks, violent muscular exercise, etc. Among the second may be mentioned powerful stimulation of various afferent or sensor nerves, heightened external temperature, etc. Among the last may be mentioned various drugs. Pilocarpin injected into the blood causes a profuse secretion even when the nerves have been divided. Its action is supposed to be exerted on the terminal branches of the nerves and possibly on the cells themselves. As in the case of the sahvary glands atropin suspends the activity of the terminal branches of the secretor nerves. Hairs. — Hairs are found in almost all portions of the body, and can be divided into — 1. Long, soft hairs, on the head. 2. Short, stiff hairs, along the edges of the eyelids and nostrils. 3. Soft, downy hairs on the general cutaneous surface. 454 TEXT-BOOK OF PHYSIOLOGY. They consist of a root and a shajt. The shaft is oval in shape and about ^^^^^ of an inch in diameter; it consists of fibrous tissue, covered externally by a layer of imbricated cells, and internally by cells containing granular and pigment material. The root of the hair is embedded in the hair-follicle, formed by a tubular depression of the skin, extending nearly through to the subcutaneous tissue; its walls are formed by the layers of the corium, covered by epidermic cells. At the bottom of the folhcle there is a papillary projection of amorphous matter, corresponding to a papilla of the true skin, containing blood-vessels and nerves, upon v^hich the hair-root rests. The investments of the hair-roots are formed of epithelial cells, constituting the internal and external root-sheaths. The lower portion of the hair follicle is connected with the upper surface of the derma by bundles of non-striated muscle-fibers which are termed arrectores pilorum muscles. Their inclination and insertion are such that their contraction is fol- lowed by erection of the hair follicle and hair shaft. These muscles are excited to action by nerves termed pilo-motor nerves. THE SEBUM. The sebum or sebaceous matter is a pecuhar oily material produced by specialized glands in the skin. It consists of water, epi- thelium, proteids, fat, cholesterin, and inorganic salts. The sebaceous glands are simple and compound racemose glands opening by a common excretory duct on the surface of the epidermis or into the shaft of a hair- folhcle (Fig. 200). These glands are extremely numerous and found in all portions of the body, with the exception of the palms of the hands and soles of the feet, and most abundantly in the face. They are formed by a dehcate structureless membrane lined by polyhedral epithe- hum. The sebum is not produced by an act of true secretion, but is formed by a proliferation and degeneration of the gland epithehum. When first poured on the surface, the sebum is oily and semi-hquid in character, but soon hardens and acquires a cheese-Hke consistence. Fig. 200. — Large Sebaceous Gland. I. Hair in its follicle. 2, 3, 4, 5. Lobules of the gland. 6. Excre- tory duct traversed by the hair. — {Sappey.) EXCRETION. 455 It serves to lubricate the hair and skin and prevent them from be- coming dry and harsh. The surface of the fetus is generally covered with a thick layer of sebaceous matter, the vernix caseosa, which possibly keeps the skin in a normal condition by protecting it from the effects of the long- continued action of the amniotic fluid in which the fetus is suspended. CHAPTER XVII. THE CENTRAL ORGANS OF THE NERVE SYSTEM AND THEIR NERVES. The central organs of the nerve system are the encephalon and the spinal cord lodged within the cavity of the cranium and the cavity of the spinal or vertebral column respectively. The general shape of these two portions of the nerve system corresponds with that of the cavities in which they are contained. The encephalon is broad and ovoid, the spinal cord is narrow and elongated. The encephalon is subdivided by deep fissures into four distinct, though closely related portions: viz., (i) the cerebrum, the large ovoid mass, occupying the entire upper part of the cranial cavity; (2) the cerebellum, the wedge-shaped portion placed beneath the posterior part of the cerebrum and lodged within the cerebellar fossae of the cranium; (3) the isthmus of the encephalon, the more or less pyramidal-shaped portion connecting the cerebrum and cerebellum with each other and both with (4) the medulla oblongata. (Fig. 201.) The spinal cord is narrow and cylindric in shape. It occupies the spinal canal as far as the second or third lumbar vertebra. The central nerve system is bilaterally symmetric, consisting of distinct halves united in the median line. The cerebrum is subdivided by a deep fissure, running antero-posteriorly, into two ovoid masses termed cerebral hemispheres; the cerebellum is also partially subdivided into hemispheres ; the isthmus likewise presents in the median line a partial division into halves; the medulla oblongata and spinal cord are subdivided by an anterior or ventral and a posterior or dorsal fissure into halves, a right and a left. The nerves in anatomic and physiologic relation with the central organs of the nerve system are the encephalic and the spinal nerves. The encephahc nerves, twelve in number on each side of the median line, are in relation with the base of the encephalon, and because of the fact that they pass through foramina in the walls of the cranium they are usually termed cranial nerves. The spinal nerves, thirty-one in number on each side, are in relation with the spinal cord, and because of the fact that they pass through foramina in the walls of the spinal column they are termed spinal nerves. As both cranial and spinal nerves are ultimately distributed to the structures of the body, — i. e., the general periphery, — they collectively constitute the peripheral organs of the nerve system. 456 THE ENCEPHALO-SPINAL MEMBRANES. 457 The central organs of the nerve system are supported and protected by three membranes named, in their order from without inward, the dura mater, the arachnoid, and the pia mater. The dura mater is a tough membrane composed of fibrous tissue. It consists of two layers, the outer of which lines the cranial cavity and forms an internal peri- osteum; the inner layer is closely attached to the outer except at certain regions where it separates and forms supporting structures, such as the falx cerebri, falx cerebelli, tentorium cerebelH, etc.; at the margin of the foramen magnum the outer layer be- comes continuous with the periosteal tissue, while the inner layer invests the cord down to its ultimate termination. (Fig. 202.) The arachnoid is a delicate serous membrane. The external surface is smooth and well defined and separated from the dura by a narrow space, the subdural space. The inner surface sends inward fine con- nective-tissue processes which interlace in every direction, constituting the subarach- noid tissue. This tissue is abundant in the cranium, much less so in the spinal canal. The spaces between the connective tissue, taken collectively, constitute the general sub- arachnoid space. Around the spinal cord this space is well defined, and at the base of the encephalon expands to form large cavi- ties known as the cisterna magna, cisterna pontis, etc. The pia mater is a delicate membrane composed of areolar tissue. It closely invests the encephalon and spinal cord, dipping into the various fissures. It is exceedingly vascular and sends small blood- vessels for some distance into the brain and spinal cord. The Encephalo-spinal Fluid. — The general subarachnoid space, as well as cer- tain cavities within the encephalon, contain a clear transparent fluid, termed the en- cephalo-spinal. This fluid has an alkaline reaction and a specific gravity of 1.007 o^ 1.008. It is composed of water, proteids (pro- FlG, , 201. — The Central Organs of the Nerve System, f. t. o. Fron- tal, temporal, and oc- cipital lobes of the cerebrum, c. Cerebel- lum, p. Pons. mo. Medulla oblongata. ms., ms. The upper and lower limits of the spinal cord. The re- maining letters indicate the region and number of the spinal nerves. — {Quain, after Bourgery.) 458 TEXT-BOOK OF PHYSIOLOGY. teoses and serum-globulin), and a compound pyrocatechin, capable of reducing copper salts, though not exhibiting any other of the properties of sugar. In many respects this fluid resembles lymph. The subarachnoid space and the general encephalic cavities, termed ventricles, communicate with one another by an opening in the pia mater (the foramen of Magendie) as it passes over the lower part ofjthe fourth ventricle. The Functions of the Nerve System. — The functions of the nerve system are twofold: (i) It unites and coordinates the organs and tissues of the body in such a man- ner that they are enabled to cooperate for the accomplishment of a definite object. (2) It serves to arouse in the individual a consciousness of the ex- istence of an external world, by virtue of the impressions which it makes on his sense organs, and to enable him therefore to adjust himself to his en- vironment. By virtue of the coordination, a stimulus, if of sufficient intensity, ap- plied to one organ or tissue will call forth activity in one or more organs near or remote from the part stimula- ted . This coordination is accomphshed mainly by the spinal cord and the me- dulla oblongata. All such actions tak- ing place independently of voHtion are termed reflex actions. The reflex activities connected with digestion, the circulation of the blood, with res- piration, excretion, etc., are illustra- tions of the coordinating capabilities of the nerve-centers located in these portions of the central nerve system. Consciousness of the existence of the external world and of the relation existing betw^een it and the individual is associated with the physiologic activities of the encephalon, and more particularly of the cerebral hemispheres. This portion of the nerve system is the chief, though perhaps not the sole, organ of the mind, and its main functions are for the most part mental. The function of a part at least of the peripheral nerve system is to afford a means of communication between the central nerve system and the remaining structures of the body. The nerve-trunks con- stituting this part may be divided into two groups, as follows: Fig. 202. — The Membranes of THE Spinal Cord. i. Dura mater. 2. Arachnoid. 3. Posterior root of spinal nerve. 4. Anterior root of spinal nerve. 5. Ligamentum den- tatum. 6. Linea splendens. — {Morris, after Ellis.) THE SPINAL CORD. 459 1. The first group comprises nerves in connection with the special sense-organs, e. g., eye, ear, nose, tongue, skin, as well as nerves in connection with the general or organic sense-organs, e. g., mu- cous membranes, viscera, etc., which transmit nerve impulses to certain localized areas in the cerebral cortex, where they are translated into conscious sensations. These sensations, both special and general, by their grouping and combinations are the primary elements of intelHgence. 2. The second group comprises those nerves which terminate in the muscle apparatus and which transmit nerve impulses, by way of the medulla and spinal cord, from locahzed areas in the cerebral cortex to the muscles of the face, trunk and extremities, which are in consequence excited to activity. The muscle movements thus become physical expressions of mental states, and if directed in a definite manner to the overcoming of the resistances offered by the external world become capable of modifying it in accordance with the mental states. The first group of nerves, the afferent, especially those connected with the special sense-organs, are excited to activity by impressions made on their peripheral terminations by agencies in the external world, and thus become a means of communication between the physical and the mental worlds. The second group of nerves, the efferent, are excited to activity by those molecular disturbances in their related nerve-cells which accompany vohtional efforts, and thus they become a means of com- munication between the mental and the physical worlds. The central nerve system is thus composed of a number of separate though closely related parts, to each of which a separate function has been assigned. In the study of the structure and func- tion of these separate parts it will be found convenient, and con- ducive to clearness, to consider them in the order of their complexity, beginning with the spinal cord and ending with the cerebrum. THE SPINAL CORD. The spinal cord is the narrow elongated portion of the central nerve system contained within the spinal canal. It is cyhndric in shape though presenting an enlargement in both the lower cervical and lower lumbar regions corresponding to the origins of the nerves distributed to the upper and lower extremities. The cord varies in length from 40 to 45 cm., measures 1 2 mm. in diameter, weighs 42 gms, and extends from the atlas to the second lumbar vertebra, beyond which it is continued as a narrow thread, the filum terminale. (Fig. 203.) It is divided by the anterior and posterior longitudinal fissures into halves, and is therefore bilaterally symmetric. A transverse sec- tion of the cord shows that it is composed of both white and gray mat- ter, the former covering the surface, the latter occupying the center. 460 TEXT-BOOK OF PHYSIOLOGY. Structure of the Gray Matter. — The gray matter is arranged in^the form of two crescents, united in the median hne by a trans- verse band or commissure forming a figure resembhng the letter H. Though varying in shape in different regions of the cord, the gray matter in all situations presents on either side an anterior or ventral Superior or Cervical Segment of Spinal Cord. Middle or Dorsal Portion of Cord. Inferior Portion of Cord and Cauda Equina. Fig. 203. — Superior, Middle, and Inferior Portions of Spinal Cord. — I. Floor of fourth ventricle. 2. Superior cerebellar peduncle. 3. Middle cerebellar peduncle. 4. Inferior cerebellar peduncle. 5. Enlargement at upper extremity of postero-median column. 6. Glosso-pharyngeal nerve. 7. Vagus. 8. Spinal accessory, g, 9, 9, q Ligamentum denticulatum. 10, 10, 10, 10. Posterior roots of spinal nerves. 11, 11, 11, 11. Postero-lateral fissure. 12, 12, 12, 12. Ganglia of posterior roots. 13, 13. Anterior roots. 14. Division of united roots into anterior and posterior nerves. 15. Terminal extremity of cord. 16, 16. Filum terminale. 17, 17. Cauda equina. I, VIII. Cervical nerves. I, XII. Dorsal nerves. I, V. Lumbar nerves. I, V. Sacral nerves. — {Sappey.) and a posterior or dorsal horn. Between the two horns there is a portion termed the intermediate gray substance. The commissure presents in its center a narrow canal which extends throughout the entire length of the cord. This canal is lined by cylindric epithelium and surrounded by gelatinous material. (Fig. 204.) THE SPINAL CORD. 461 The anterior horn is short and broad and entirely surrounded by white matter. The posterior horn is narrow and elongated and extends quite up to the surface of the cord, where it is capped by gelatinous matter, the substantia gelatinosa. in the lower cervical and thoracic regions a portion of the intermediate gray substance projects outward and forms the so-called lateral horn. The gray matter fundamentally consists of a framework of fine neuroglia supporting blood-vessels, lymphatics, medullated and non-medullated nerves, and groups of nerve-cells. The Nerve-cells. — The nerve-cells of the cord are very numerous and present a variety of shapes and sizes in different regions. They are usually ar- ranged in groups which extend for some distance up and down the cord, forming columns more or less continuous. In the anterior horn two well- marked groups are found, one situated at the anterior and inner angle, known as the antero-median group, the other situated at the posterior and lateral angle and known as the postero-lateral group. In the lower cervical and upper thoracic regions, in the region of the lateral horn, another group of cells is found, known as the intermediate group. In the central portion of the horn there is also a central group. The cells of the anterior horns are of large size, nucleated and multipolar. They are the modified descendants of pear-shaped cells, the neuroblasts, which migrated from the medullary tube (see page 114). In the course of their migration they developed den- drites which form an intricate felt- work throughout the anterior horn. One of the processes, the axon, approached the surface of the cord, penetrated it, grew outward, became covered with myelin and neurilemma, and developed into D Fig. 204 Sections Through Different Regions of the Spinal Cord. A. At the level of the sixth cervical nerve. B. At the mid-dorsal region. C. At the center of the lumbar enlargement. D. At the upper part of the conus medullaris. i. Poste- rior roots. 2. Anterior roots. 3. Posterior fissure. 4. Ante- rior fissure. 5. Central canal. — {Morris' "Anatomy,'' after Schwalbe.) 462 TEXT-BOOK OF PHYSIOLOGY. an anterior root-fiber. These nerve-cells, with their dendrites, axons, and terminal branches, form efferent neurons of the first order. The intimate histologic and physiologic relationship existing between the nerve-cell and the axon is revealed by the degenerative changes which arise in the latter when separated from the former. The cell apparently determines the nutrition of the axon and may be regarded as trophic in function. Some of the cells of the ante- rior horn send their axons into the white matter of the same side. Fig. 205.— Diagram Illustrating the Chief Cellular Elements of the Spinal Cord, and the Probable Relations between the Cells and the Fibers and the Principal Tracts; the Left Half of the Figure Exhibits the Communications OF the Several Varieties of Nerve-cells. A, P. Ventral or anterior and dorsal or posterior horns. PR. Posterior root bundles. DP. Direct pyramidal tract. CP. Crossed pyramidal tract. DC. Direct cerebellar tract. GB. Gowers's tract, a. Alotor cells passing directly into fibers of ventral roots, b. Various cells of the antero-lateral column. Some give off collateral branches of remarkable size. c. Commissural (heteromeral) cells, d. Cells to dorsal column (tautomeral). e. Golgi cells of dorsal horn. The right half of the diagram shows the communications established by means of the collateral fibers. — {Piersol, after Lenhossek.) after which they divide into two branches, one passing up, the other down, the cord, to re-enter the gray matter at different levels. They are probably associative in function. Other cells send their axons into that portion of the white matter on the same and opposite sides known as Gowers's antero-lateral tract. (Fig. 205.) In the posterior horn nerve-cells are also present, though they are not so numerous as in the anterior horn. At the base of the horn THE SPINAL CORD. 463 and on its inner side there is a well-marked group of cells which ex- tends from the seventh or eighth cervical nerves downward to the second or third lumbar nerves, being most prominent in the thoracic region. This column is known as Clarke's vesicular column. From the nerve-cells constituting this column axons pass obhquely outward into that portion of the white matter known as the direct cerebellar tract. Classification of Nerve-cells. — The cells of the gray matter may be divided into three main groups: viz., intrinsic, efferent, and afferent. The intrinsic cells are associative in function. The axons to which these cells give origin pass more or less horizontally into the white matter, where they divide into two branches, one of which passes upward, the other downward. At various levels they reenter the gray matter and arborize around other intrinsic cells. The efferent cells, independently of their trophic influence, are also motor in function, inasmuch as the excitation arising in them is transmitted outwardly through their axons to muscles, blood- vessels, glands and viscera, imparting to them motion, either molar or molecular. As the efferent fibers in the ventral roots of the spinal nerves are classified (see page 116) in accordance with their physio- logic action into motor, vaso-motor, secretor, inhibitor and accelerator nerves, so the nerve-cells of which the nerves are integral parts may be classified physiologically as motor, vaso-motor, secretor, inhibitor, and accelerator. Collections or groups of such cells are termed "centers." The afferent cells are largely sentient or receptive in function, inasmuch as the excitations brought to the spinal cord by the afferent nerves in the dorsal roots from the general periphery are received by them and transmitted through their axons toward the cortex of the cerebrum, where they are translated into conscious sensations. As the nerve-fibers in the dorsal roots of the spinal nerves are classified, in accordance with the sensations to which they give rise, as sensor, thermal, tactile, etc., so these nerve-cells may be similarly classified according as they transmit their excitations to those specialized areas in the cerebral cortex in which these different sensations arise. Structure of the White Matter. — A transverse section of the cord shows that the white matter completely covers the gray matter except where the posterior horns reach the surface. Anteriorly the white matter of each lateral half is connected by a narrow strip or bridge of white matter, the anterior commissure. Microscopic examination shows that the white matter is composed of vertically disposed medullated nerve-fibers which are devoid of a neurilemma. These fibers are supported partly by a framework of connective tissue, and partly by neuroglia. The white matter of each side of the cord is anatomically divided into an anterior, a lateral, and a posterior column by the anterior and posterior roots of the spinal nerves. 464 TEXT-BOOK OF PHYSIOLOGY. Classification of the Nerve-fibers. — From a study of the embryologic development of the white matter and of the degenerative changes which follow its pathologic and experimental destruction, it has been differentiated into a number of specialized tracts which have different origins, destinations, and functions. They may be divided, however, into efferent, afferent, and associative fibers. (Fig. 206.) I. The anterior column, comprising that portion between the anterior longitudinal fissure and the anterior roots, has been sub- divided into: (a) The direct pyramidal tract, or column of Tiirck. This tract borders the longitudinal fissure and extends from the upper extremity Cnhimn of Lissauer. Fig. 206. — Transection of the Cervical Spinal Cord Showing Its Chief Sub- divisions. — {From Mills' ^^ Diseases of the Nervous System.") of the cord as far down as the mid-thoracic region. From above downward this tract diminishes in size, for the reason that its fibers or their collaterals cross at successive levels to the opposite side of the cord by way of the anterior commissure to enter the gray matter of the anterior horn. The cells of these axons are located in the cortex of the cerebral hemisphere of the same side. The terminal filaments of these fibers or axons are in physiologic relation with the dendrites of the cornual cells. When divided in any part of their course, these fibers undergo descending degeneraion. They are therefore efferent neurons and of the second order. (h) The anterior root zone. This tract lies external to the pyram- THE SPINAL CORD 465 idal tract, surrounds the anterior horn of the gray matter and ex- tends throughout the length of the cord. It is composed of short com- missural fibers which come from nerve-cells in the gray matter from the same and opposite sides of the cord. After entering the white matter they divide into two branches, pursue opposite directions, then re-enter the gray matter at higher and lower levels and come into relation with other nerve-cells. (c) The antero -lateral tract of Marchi and Lowenthal. This tract is situated at the inner and anterior angle of the anterior column. After removal of the one-half of the cerebellum it degenerates downward. 2. The lateral column, comprising that portion between the ventral and dorsal roots, has been divided into: {a) The antero-lateral tract of Gowers. This tract is somewhat crescentic in shape and situated on the lateral aspect of the cord external to the anterior root zone. It extends throughout the entire length of the cord. When divided it undergoes ascending degenera- tion, which would indicate that the axons originate in nerve-cells in the gray matter. This tract is therefore afferent in function. {h) The lateral limiting tract. This tract, which is quite narrow, lies close to the external border of the gray matter. It is composed of fibers which do not degenerate to any considerable extent and are in all probability associative fibers which come from nerve-cells in the gray matter to re-enter at lower and higher levels. (c) The crossed pyramidal tract. This tract occupies the posterior portion of the lateral column, though its exact position varies some- what in different regions of the cord. In the cervical and thoracic regions it is covered by a layer of fibers. In the lumbar region, however, it comes to the surface. From above downward this tract gradually diminishes in size, for the reason that its fibers and their collaterals enter the gray matter at successive levels. The terminal branches of these fibers are in close physiologic relation with the dendrites of the cornual cells. The cells of these axons are located in the cortex of the cerebral hemispheres of the opposite side. When divided in any part of their course, they undergo descending de- generation. They are therefore efferent neurons and of the second order. {d) The direct cerebellar tract, or column of Flechsig. This tract is situated on the surface of the lateral column external to the crossed pyramidal tract. It slightly increases in size from below upward. It is composed of fibers the cells of which are found on the inner side and base of the posterior horn (Clark's vesicular column). From this origin the fibers pass obliquely outward to the surface and then directly upward to terminate, as its name implies, in the cerebellum. Decussation of these fibers takes place in the superior vermiform lobe of the cerebellum. When divided this tract degenerates upward. It 30 466 TEXT-BOOK OF PHYSIOLOGY. is therefore in all probability an afferent tract and of the second order. 3. The posterior column, comprising that portion between the dorsal roots and the posterior longitudinal fissure, has been sub- divided into : (a) The postero-external tract of Burdach. This tract hes just within the posterior horns. A portion of this tract is composed of ground fibers which, though vertically disposed, have but a short course. They take their origin in cells in the gray matter, and after entering this tract divide into ascending and descending branches, which with their collaterals re-enter the gray matter at different levels. Another portion of this tract is made up of nerve-fibers de- rived from the dorsal roots of the spinal nerves, which cross this column toward the median line in an obhque or horizontal direction. The fibers of the upper portion of this tract terminate around the nucleus cuneatus at the medulla oblongata. When divided, these fibers degenerate for but a short distance. The ground fibers are probably associative in function. (6) The postero-median internal tract, or column of Goll. This tract is separated from the former by a septum of connective tissue which is most marked above the eleventh thoracic segment. The fibers which compose this tract are long and derived for the most part from the dorsal roots of the spinal nerves of the same side. This is shown by the fact that division of these roots central to the ganglion is followed by ascending degeneration of the column of Goll as far as the nucleus gracilis in the medulla. Fibers derived from cells in the gray matter are also contained in this column. This tract is afferent in function. (c) The septo -marginal tract. This is an oval-shaped tract situated along the margin of the posterior longitudinal fissure. {d) The cornu-commissural tract. This is formed along the border of the anterior portion of the posterior column as far forward as the posterior commissure. Both of these tracts are best developed in the lumbo-sacral region. They arise from nerve-cells in the gray matter. They undergo descending degeneration when divided, but not after division of the dorsal roots. (e) Lissauer^s tract. This tract embraces the tip of the posterior horn and is composed principally of fibers from the dorsal roots of the spinal nerves. After entering the tract the fibers divide into ascend- ing and descending branches, which finally terminate around cells in the posterior horn. (/) The comma tract. This is a narrow tract of fibers situated in the anterior portion of the column of Burdach. When divided, its fibers degenerate downward. The Relation of the Spinal Nerves to the Spinal Cord. — The spinal nerves present near the spinal cord two divisions which from THE SPINAL CORD. 467 their connection with the anterior or ventral and the posterior or dorsal surfaces are known as the ventral and dorsal roots. The ventral roots are the axons of various groups of cells in the anterior horns. From their origin these axons pass almost horizontally forward through the anterior column in three distinct bundles. After emerging from the cord they curve downward and backward to join the poste- rior root. The dorsal roots are the central axons of nerve-cells in the spinal gangha. After entering the cord they divide into two main groups, a lateral and a mesial. A portion of the lateral group enters the posterior horn directly through the caput cornu; the other portion turns upward and runs through Lissauer's tract and ultimately enters the posterior horn. The mesial group passes into the postero- external column (Burdach), where the fibers divide into descending and ascending branches. The former constitute the comma tract, the terminal branches of which surround cells in the gray matter; the latter (ascending) cross the column obhquely and enter the postero-internal column (Goll), in which they pass upward to ter- minate around the cells of the nucleus gracilis of the same side. As these root fibers pass up and down the cord, collateral branches are given off which enter the gray matter at successive levels and come into physiologic relation with the cells of Clark's vesicular column on the same and opposite sides and with the cells of the anterior horn. Experimentally, it has been determined that the anterior or ventral roots contain all the efferent fibers, the posterior or dorsal roots all the afferent fibers. The proofs in support of this view are as follows: Stimulation of the ventral roots produces : 1. Convulsive movements of muscles. 2. The discharge of a secretion from glands. 3. Changes in the caliber of blood-vessels. 4. Inhibition of the rhythmic activity of certain organs. Division of these roots is followed by: 1. Loss of muscle movement (paralysis of motion). 2. Cessation of normal secretion. 3. Cessation of active vascular changes. Stimulation of the dorsal roots causes : 1. Reflex activities. 2. Conscious sensations. 3. Inhibition of the rhythmic activity of certain organs. Division of these roots is followed by: 1. Loss of reflex activities, and 2. Loss of sensation in all parts to which they are distributed. The ventral roots are, therefore, efferent in function, transmitting nerve impulses from the spinal cord to the periphery. The dorsal roots are afferent in function, transmitting nerve impulses from the general periphery to the spinal cord. 468 TEXT-BOOK OF PHYSIOLOGY. The classification of the nerve-fibers in the ventral and dorsal roots of the spinal nerves in accordance with the functions they sub- serve will be found on page ii6. Though both the efferent and afferent fibers of the spinal nerves are directly connected with nerve-cells in the spinal cord, they are also indirectly connected by efferent and afferent nerve-tracts with the cerebral cortex. FUNCTIONS OF THE SPINAL CORD. Physiologic investigation has demonstrated that the spinal cord, by virtue of the presence of nerve-cells and nerve-fibers, may be re- garded as composed of: 1. Independent nerve-centers, each of which has a special function; and — 2. Conducting paths by which these centers are brought into relation with one another and with the cerebrum and its subordinate or underlying parts. The cord, moreover, may be considered as consisting physiologically of a series of segments placed one above the other, the number of segments corresponding to the number of spinal nerves. In other words, a spinal segment comprises that portion of the cord to which is attached a pair of spinal nerves. The nerve-cells in each segment are in histologic and physiologic relation with definite areas of the body, embracing muscles, blood-vessels, glands, skin, etc. The Spinal Cord as an Independent Center. — The efferent cells of the spinal segments are the immediate sources of the nerve energy which excites activity in muscles, blood-vessels, glands. The discharge of their energy may be caused: 1. By variations in the composition of the blood or lymph by which they are surrounded. The activity of the cell thus occasioned is termed automatic or autochthonic (Gad). 2. By the arrival of nerve energy coming through afferent nerves from the general sentient periphery, skin, mucous membrane, etc. 3. By the arrival of nerve energy descending the spinal cord from the cerebrum or subordinate structures. The peripheral activity in the former instance is said to be reflex or peripheral in origin ; in the latter instance, direct or cerebral in origin. In this latter instance, also, the muscle movements are due to volitional, the vascular variations and glandular discharges to emotional, forms of cerebral activity. Each segment of the spinal cord may be regarded, therefore, because of its contained nerve-cells : 1. As a center for automatic activity. 2. As a center for the reception of excitations arising either at the periphery or in the cerebrum, and for their subsequent trans- mission through efferent nerves to various peripheral organs. THE SPINAL CORD. 469 Automatism. — The growth, the nutrition and multiplication of the cells of various tissues, and their continuous and rhythmic activity, have been attributed to an automatic action of the spinal nerve- cells. By this expression is meant a discharge of energy from the cells occasioned by a change in their environment, i. e., in the chemic composition of the blood or lymph by which they are surrounded, and independent of any excitation coming through afferent nerves. If the cell activity is continuous, though variable in degree from time to time, it gives rise to what is termed tonus, e. g., trophic tonus, vas- cular, muscle tonus, etc. If the cell activity is intermittent, it imparts to muscles a certain rhythmic activity, e. g., the respiratory movements. As no eft'ect arises without a sufficient cause, the term automatic has been objected to and the term autochthonic has been suggested (Gad), expressive of the idea that the energy originates in the nerve- cell as a result of a reaction between the cell and its ever-changing environment. A center so acting could not be regarded as primarily a center for reflex action, however much it might be influenced or conditioned secondarily by afferent impulses. Though automatic activity of the spinal cord centers is advocated by some physiologists, the fact must be recognized that with increasing knowledge of reflex activities some of the phenomena hitherto regarded as automatic have been found to be reflex in origin. Whether this will eventually be found true for all forms of so-called automatic or autochthonic activity remains to be seen. Trophic Tonus. — The normal metabohsm of muscle, gland, and connective tissue which underlies the assimilation of food, the storing of energy, and the production of new compounds, is dependent, in the higher animals at least, on the connection of these tissues with the central nerve system; for if the eft'erent nerves be divided, not only will they undergo degeneration in their peripheral portions, but the muscles, glands, and connective tissues to which they are distributed will also undergo similar changes. This is to be attributed not merely to inactivity, but rather to a loss of nerve influence, inasmuch as inactivity leads merely to atrophy and not to degeneration. It would appear from facts of this character that the normal metabolism is dependent for its continuance on nerve influences. There is no evidence, however, as to the existence of special trophic nerves, separate from those which impart to glands and muscles their cus- tomary activities. The trophic centers and the motor centers are iden- tical, though the two modes of their activity are separate and distinct. Vascular Tonus. — The state of moderate contraction of the arterioles throughout the body, in consequence of which the average arterial pressure is maintained, is attributed to constant activity of the vaso-motor centers, this activity being conditioned by variations in the composition of blood, either an increase in the quantity of carbon dioxid or a decrease in the quantity of oxygen. The vaso- 470 TEXT-BOOK OF PHYSIOLOGY. motor centers are regarded as primarily automatic, though capable of being influenced secondarily by reflected excitations from the periphery or direct excitations from the cerebrum. Muscle Tonus. — It is wefl known that if a muscle be divided in the living animal the two portions will contract and separate them- selves to a certain distance. This indicates that the muscle when in a state of rest is in a sHght degree of contraction. This condition of the muscle, to which the term muscle tonus is given, was formerly attributed to an automatic and continuous discharge of energy from the nerve-cells. Brondgeest, however, showed that this tonus is entirely reflex in origin and immediately disappears on division of the posterior roots of the spinal nerves, which would not be the case if the cells in the cord were acting automatically. The afferent nerves in this reflex arise in the muscle or its tendons, and the stimulus is the slight degree of extension to which the muscle is subjected in virtue of its attachments and the ever- varying position of the Hmbs and trunk. Fig 207.— Diagram of a Simple Reflex Arc. i. Sentient surface. 2. Afferent nerve. 3. Emissive or motor cell. 4. Efferent nerve. 5. Muscle. — (After Moral and Dayoii.) The tonic contraction of the visceral muscles, — e. g., the pyloric, the vesical, the anal sphincters, — though regarded as automatic by some, is probably reflex in origin, dependent on the arrival of afferent impulses from the periphery. It is probable that future investi- gation will disclose the existence and pathway of these afferent fibers. Reflex Actions. — It has already been stated that the nerve-cells in the spinal cord are capable of receiving and transforming afferent nerve impulses into efferent nerve impulses, which are transmitted outward to muscles, exciting contraction; to glands, provoking secre- tion; to blood-vessels, changing their caliber; and to organs, inhibit- ing or accelerating their activity. All such actions taking place through the spinal cord and medulla oblongata independently of sensation or volition are termed reflex actions. The mechanism in- volved in every reflex action consists of at least the following struc- tures (Fig. 207) : I. A sentient surface; e. g., skin, mucous membrane, sense organ, etc. THE SPINAL CORD. 471 2. An afferent fiber and cell. 3. An emissive cell, from which arises — 4. An efferent nerve, distributed to a responsive organ, as — 5. Muscle, gland, blood-vessel, etc. In this connection the reflex contractions of skeletal muscles only will be considered. If a stimulus of sufficient intensity be applied to the sentient surface, there will be developed in the terminals of the afferent nerve a series of nerve impulses which will be transmitted by the afferent nerv^e to, and received by, the dendrites of the emissive cell in the anterior horn of the gray matter. With the reception of these impulses there will be a dis- turbance in the equilibrium of the molecules of the cell, a liberation of energy and a transmission of nerve impulses outward through the efferent nerve to the muscle. A reflex mechanism or arc of this simplicity would subserve but a simple movement. The majority of the reflexes, however, are extremely com- plex and involve the cooperation and coordination of a number of centers at different levels, of the spinal cord and medulla, on the same and opposite sides, and of muscles situated at dis- tances more or less remote from one another. The transference of nerve impulses coming from a localized area of a sentient surface, to emissive cells situated at different levels is accom- plished by the intermediation of a third neuron situated in the gray matter which is in connection, on the one hand, with the central terminals of the afferent nerve, and, on the other hand, with the dendrites of the emissive or motor cells (Fig. 208). A histologic and physiologic mechanism of this character readily explains how a localized stimulation can give rise to reflex actions extremely complex in character. The reflex contractions of skeletal muscles are best studied after division of the central nerve system at the upper limit of the spinal cord. After this procedure the spinal centers can act independently of, and uninfluenced by either sensation or volitional efforts on the part of the animal. Though it is possible to provoke reflex contrac- tions under such circumstances in w^arm-blooded animals, they are. Fig. 208. — Diagram Showing THE Relation of the Third Neuron a, to the Afferent Neuron h, and' to the Ef- ferent Neurons c, c, c. — {Ajter Kdllikcr.) 472 TEXT-BOOK OF PHYSIOLOGY. as a rule, incomplete and of short duration, owing to disturbances of the circulation and respiration and the consequent loss of tissue irritability. In frogs and in cold-blooded animals generally, the spinal cord retains its irritability for a long period of time after re- moval of the brain, and therefore is well adapted for the study of reflex actions. The division of the spinal cord can be readily effected by inserting a spear-shaped knife between the occipital bone and the atlas. The skin, occipito-atlantal membrane, and medulla can be divided with one plunge of the knife. The brain can then be destroyed by the insertion of a fine wire into the brain cavity. A frog so prepared, and placed on the table and allowed to remain at rest for a few moments until the shock of the operation passes away, will draw the limbs close to the body and assume a position not unlike that of a normal frog. If then the posterior limbs be extended, they will immediately be drawn close to the side of the trunk in the usual flexed position. If the toes are pinched with forceps, the foot will execute a series of movements as if it were trying to free itself from the source of irritation. If the frog be suspended, the hmbs, through the force of gravity, will be gradually extended and hang down freely. In this, as in the sitting position, the animal will remain perfectly quiet and will not exhibit spontaneous movements. Any stimulus apphed to the skin, however, provided it is of sufficient intensity, will be followed by a more or less pronounced movement. Mechanic, chemic and electric stimuli apphed to any part of the skin will call forth the characteristic reflex movements. Chemic stimuli such as weak solutions of sulphuric or acetic acid placed on the toes will be followed by feeble flexion of the corresponding leg, to be succeeded in a short time by extension. Stronger solutions will produce more extensive and vigorous movements, the foot at the same time being rubbed against the thigh, apparently for the purpose of freeing it from the irritant. Similar phenomena follow the apphcation of the acid to the fingers or the trunk. As a rule, the extent and complexity of the movement is within limits proportional to the strength of the stimulus. By hmiting the sphere of action of the stimulus to definite but different areas of the skin a great variety of movements, more or less complex and coordinated and apparently purposive and defensive in character, can be produced. The coordinated and purposive character of the movements exhibited by a brainless frog led Pfliiger to the assump- tion that the spinal cord in this as well as in other cold-blooded ani- mals is possessed of sensorial functions, is endowed with rudimentary consciousness. This view, however, is not generally accepted, the movement being attributed to specialized mechanisms in the cord, partially inherited, which permit of one and the same movement with THE SPINAL CORD. 473 mechanic regularity and precision, so long as the conditions of the experiment remain the same. In warm-blooded animals similar results may be obtained for a short time after division of the cord, especially if artificial respiration is maintained and the circulation of the blood continued. The cord will then retain its irritability for some time. If the conditions of experimentation were favorable, it is highly probable that the human spinal cord would execute similar movements. Thus it was observed by Robin in a man who had been decapitated that reflex muscle con- tractions could be ehcited by stimulating the skin after the lapse of an hour after execution. "While the right arm was lying extended by the side, with the hand about 25 centimeters distant from the upper part of the thigh, I scratched with the point of a scalpel the skin of the chest at the areola of the nipple, for a space of 10 or 11 centimeters in extent, without making any pressure on the subjacent muscles. We immediately saw a rapid and successive contraction of the great pectoral muscle, the biceps, probably the brachialis anticus, and lastly the muscles covering the internal condyle. The result was a movement by which the whole arm was made to approach the trunk, with rotation inward and half- flexion of the forearm upon the arm; a true defensive movement, which brought the hand toward the chest as far as the pit of the stomach. Neither the thumb, which was partially bent toward the palm of the hand, nor the fingers, which were half bent over the thumb, presented any movements. The arm being replaced in its former position, we saw it again execute a similar movement on scratching the skin, in the same manner as before, a little below the clavicle. This experiment succeeded four times, but each time the movement was less extensive; and at last scratching the skin over the chest produced only contractions in the great pectoral muscle which hardly stirred the limb" (Dalton). Laws of Reflex Action (Pfliiger). 1. Law of Unilaterality. — If a feeble irritation be applied to one or more sensory nerves, movement takes place usually on one side only, and that the same side as the irritation. 2. Law 0} Symmetry. — If the irritation becomes sufficiently intense, motor reaction is manifested, in addition, in corresponding muscles of the opposite side of the body. 3. Law of Intensity. — Reflex movements are usually more intense on the side of irritation; at times the movements of the opposite side equal them in intensity; but they are usually less pronounced. 4. Law of Radiation. — If the excitation still continues to increase, it is propagated upward, and motor reaction takes place through centrifugal nerves coming from segments of the cord higher up. 5. Law of Generalization. — When the irritation becomes very intense, it is propagated in the medulla oblongata; motor reaction then 474 TEXT-BOOK OF PHYSIOLOGY. becomes general, and it is propagated up and down the cord, so that all the muscles of the body are thrown into action, the medulla oblongata acting as a focus whence radiate all reflex movements. Special Reflex Movements. — Among the reflexes connected with the more superficial portions of the body there are some which are so frequently either increased or diminished in pathologic conditions of the spinal cord that their study affords valuable indi- cations as to the seat and character of the lesions. They may be divided into: 1. The skin or superficial, and 2. The tendon or deep reflexes. The skin reflexes, characterized by contraction of underlying mus- cles, are induced by stimulation of the skin — e. g., pricking, pinching, scratching, etc. The following are the principal skin reflexes : 1 . Plantar reflex, consisting of contraction of the muscles of the foot, induced by stimulation of the sole of the foot; it involves the integrity of the reflex arc through the lower end of the cord. 2. Gluteal reflex, consisting of contraction of the glutei muscles when the skin over the buttock is stimulated; it takes place through the segments giving origin to the fourth and fifth lumbar nerves. 3. Cremasteric reflex, consisting of a contraction of the cremaster muscle and a retraction of the testicle toward the abdominal ring when the skin on the inner side of the thigh is stimulated; it depends upon the integrity of the segments giving origin to the first and second lumbar nerves. 4. Abdominal reflex, consisting of a contraction of the abdominal muscles when the skin upon the side of the abdomen is gently scratched; its production requires the integrity of the spinal segments from the eighth to the twelfth dorsal nerves. 5. Epigastric reflex, consisting of a slight muscular contraction in the neighborhood of the epigastrium when the skin between the fourth and sixth ribs is stimulated; it requires the integrity of the cord between the fourth and seventh dorsal nerves. 6. The scapular reflex consists of a contraction of the scapular muscles when the skin between the scapulas is stimulated; it depends upon the integrity of the cord between the fifth cervical and third dorsal nerves. The skin or superficial reflexes, though variable, are generally present in health. They are increased or exaggerated when the gray matter of the cord is abnormally excited, as in tetanus, strychnin- poisoning, and disease of the lateral columns. The so-called ''tendon reflexes," characterized by the con- traction of a muscle, also are of much value in the diagnosis THE SPINAL CORD 475 of lesions of the cord and are elicited by a sharp tap on a given tendon. The term, tendon reflex, is, however, somewhat in- accurate. The fundamental condition for the production of the tendon reflex is the normal tone of the muscle, which is a true reflex, maintained by afferent nerve impulses developed in the muscle itself in consequence of its extension and hence compression of the end- organs of the afferent nerves, the muscle spindles. When the muscle is passively extended, as it is when the reflex is to be elicited, there is an exaltation of the tonus and an increase in the irritability. To this condition of the muscle due to passive tension, the term m}Otatic irritability has been given. If the muscle extension be now suddenly increased, as it is when the tendon is sharply tapped, the increased compression of the muscle spindles will develop additional afferent impulses which af ler transmission to the spinal cord will give rise to contraction of the corresponding muscle. The following are the principal forms of the tendon reflexes : 1. Patellar reflex or knee-jerk, consisting of a contraction of the ex- tensor muscles of the thigh when the ligamentum patellae is struck between the patella and tibia. This reflex is best ob- served when the legs are freely hanging over the edge of a table. The patella reflex is generally present in health, being absent in only 2 per cent.; it is greatly exaggerated in lateral sclerosis, in descending degeneration of the cord; it is absent in locomotor ataxia and in atrophic lesions of the anterior gray cornua. 2. Ankle- jerk or ankle reflex. — If the extensor muscles of the leg be placed on the stretch and the tendo Achillis be sharply struck, a quick extension of the foot will take place. 3. Ankle Clonus. — This consists of a series of rhythmic reflex con- tractions of the gastrocnemius muscle, varying in frequency from six to ten per second. To ehcit this reflex, pressure is made upon the sole of the foot so as to suddenly and energetically flex the foot at the ankle, thus putting the tendo Achillis and the gas- trocnemius muscle upon the stretch. The rhythmic movements thus produced continue so long as the tension within limits is maintained. Ankle clonus is never present in health, but is very marked in lateral sclerosis of the cord. The toe reflex, peroneal reflex, and wrist reflex are also present in sclerosis of the lateral columns and in the late rigidity of hemiplegia. Reflex Irritability. — The general irritability or quickness of response of the mechanism involved in reflex action can be approxi- mately determined by observation of the length of time that elapses between the application of a minimal stimulus and the appearance of the muscle response. The method of Tiirck is sufficiently accurate for general purposes. This consists in suspending a frog, after removal of the brain, and immersing the foot in a 0.2 per cent, solu- 476 TEXT-BOOK OF PHYSIOLOGY. tion of sulphuric acid. The time is determined by means of a metro- nome beating one hundred times a minute. Stimulation of the skin can also be effected by the induced electric current, as suggested by Gaskell. A single shock is, however, ineffective. When the shocks follow each other with sufficient rapidity, they give rise to a summa- tion of effects in the nerve-centers which will soon be followed by a muscle response. It is highly probable that the chemic stimulation gives rise to a similar summation of effects. The period of time thus obtained is distributed over the entire mechanism. The true reflex time, however, — i. e., the time occupied in the passage of the nerve impulses across the spinal mechanism, — is shorter and is obtained by subtracting from the whole period the time occupied by the passage of the impulses through the afferent and efferent nerves as well as the latent period of muscle contraction. This corrected period, the true reflex time, has been found to be twelve times longer than the time occupied by the passage of the nerve impulse through the nerves, including the latent period of the muscle. The reflex irritability is increased by: 1. Separation of the Brain from the Cord. — This is at once followed by an increase in reflex irritabihty, and is taken as evidence that the brain normally exerts an inhibitory influence over the reflex centers of the cord. The same increase is observed upon hemi- section of the cord, though the increase is limited to the same side. 2. The Toxic Action of Drugs. — Strychnin even in small doses in- creases the irritabihty to such an extent that a minimal stimulus is sufficient to call forth spasmodic contractions of all the skeletal muscles. Under its influence the usual coordinated reflexes disappear and are succeeded by incoordinated reflexes. The explanation of this fact is believed to be a diminution in the resistance offered by the cord to the passage of the afferent im- pulses rather than to a direct stimulation of the efferent cells. So much is this resistance decreased that the nerve impulses, instead of being confined to their accustomed paths, are radiated in all directions. Absolute repose of the animal and the exclu- sion of all external stimuli greatly diminish the tendency to the occurrence of spasms. 3. Degeneration of the Pyramidal Tracts. — In primary lateral scle- rosis, a pathologic condition characterized primarily by a degen- eration of the terminal filaments of the pyramidal tract fibers, the reflex activity of the cord becomes exalted. As the disease progresses the irritability increases to such an extent that violent spasmodic contractions of the arms and legs arise when the skin or tendons are mechanically stimulated. The explanation THE SPINAL CORD. 477 offered is practically the same as in division of the cord: viz., withdrawal of the inhibitor and controlhng influence of the brain. The reflex excitability may be decreased by: 1. Stimulation of Certain Regions of the Brain. — It was discovered by Setchenow that when the frog brain is divided just anterior to the optic lobes and the reflex time subsequently determined according to the method of Tiirck, that the time can be considerably lengthened by stimulation of the optic lobes. This is readily accomplished by placing small crystals of sodium chlorid on the optic lobes. It was concluded from this fact that these lobes contain centers which exert an inhibitory influence over centers in the spinal cord through descending nerve-fibers This conclusion is strengthened by the fact that division of the brain just behind the optic lobes causes a temporary inhibition of the reflexes in consequence of a mechanical irritation of these fibers. It is quite probable that the volitional inhibition of certain reflexes is accomplished through the intermediation of this center localized by Setchenow. 2. Stimulation of Sensor Nerves. — If during the application of a stimulus sufficient to call forth a characteristic reaction in a definite period of time, a sensor nerve in a distant region of the body be simultaneously stimulated, it will be found that the reflex time will be lengthened or the reaction completely inhibited. The explanation of this phenomenon is not apparent. 3. Lesions of the spinal cord; e. g., atrophy of the multipolar cells of the anterior horns of the gray matter; degeneration of the terminals of the posterior fibers. 4. The toxic action of various drugs, — e. g., chloroform, chloral, — which are believed to exert their depressing action on the nerve- cells themselves. The Spinal Cord as a Conductor. — The white matter of the spinal cord consists of nerve-fibers the specific function of which is 1 . To conduct nerve impulses from one segment of the cord to another. 2. To conduct ner^'e impulses coming to the cord through afferent nerves, directly or indirectly to various areas of the encephalon. 3. To conduct nerve impulses from the encephalon to the spinal cord segments. Intersegmental or Associative Conduction. — The spinal cord consists of a series of physiologic segments each of which has specific functions and is associated through its related spinal nerve with a definite segment of the body. For the harmonious cooperation and coordination of all the spinal segments it is essential that they should be united by commissural or associative fibers. This is, in fact, accomplished by the axons of the intrinsic cells of the gray matter, 478 TEXT-BOOK OF PHYSIOLOGY. which constitute such a large part of the anterior and posterior root zones. In consequence of tliis association, the cord becomes capable of complex coordinated and purposive reflex actions. Spino-encephalic or Sensor Conduction. — The nerve impulses that arise in consequence of impressions made on the terminals of the nerves in the cutaneous and mucous surfaces, in the viscera and in the muscles, are transmitted through the dorsal roots of the spinal nerves to the cord. When transmitted through the cord to the cere- bral hemispheres directly or indirectly, they are received by specialized nerve-cells in the cortex and translated into conscious sensations. The sensations thus arising may be divided into special and general sensations. Of the former may be mentioned pain, touch, tem- perature; of the latter may be mentioned hunger, thirst, fatigue, well-being, etc. The pathways through the spinal cord that conduct these afferent impulses to the brain are ill defined and imperfectly known, and only for a few sensations can it be said that their pathways have been determined. The reason for this obscurity hes partly in the diffi- culties of experimentation, partly in the difficulties of interpretation. Clinical observations are for special reasons more or less untrust- worthy. Section of one lateral half of the cord, or a lesion involving the one lateral half, as a rule abolishes all forms of cutaneous sensibility on the opposite side below the injury. This would seem to prove that the nerve impulses cross the median line of the cord immediately or very shortly after entering. At the same time, muscle sensibihty is abolished on the corresponding side below the injury. This would seem to prove that the fibers of the posterior roots which enter and cross the column of Burdach and ascend in the column of Goll are derived mainly from the muscles. It is, however, believed by some investigators that those fibers which subserve the sense of touch do not decussate at once, but ascend in the column of Goll as far as the medulla oblongata, where they, in common with the fibers coming from the muscles, arborize around the nerve-cells in the gracile and cuneate nuclei. The afferent path is then continued by new nerve- fibers which emerge from these cells, and which, after crossing the median plane and decussating with the fibers coming from the oppo- site side, join the afferent path from the spinal cord. These fibers are known as the internal arcuate fibers and assist in the formation of the lemniscus or fillet. (Fig. 209.) The sensor pathway decus- sates in part at different levels of the spinal cord and in part at the level of the gracile and cuneate nuclei. The former is often termed the lower, the latter the upper sensor decussation. The pathways for the impulses that give rise to the different sen- sation have been variously located by different observers, e. g., in the THE SPINAL CORD. 479 gray matter, in the limiting layer, and in the antero-lateral tract of Gowers ; the pathway for the impulses that give rise to temperature sensations has been located in the gray matter; the pathway for tactile impressions has been located in the posterior columns, though this is not beyond dispute. The pathway for pain sensations has been located in Gowers' tract. Fig. 209. — Diagram of the Sensor Pathways in the Spinal Cord Augmented ABOVE BY Fibers of the Sensor Cranial Nerves and Nerves of Special Sense. V. The trifacial Nerve. VIII. The vestibular branch of the acoustic nerve. IX. The glosso -pharyngeal nerve. X. The pneumogastric nerve. — {Van Gehiichten). Encephalo-spinal or Motor Conduction. — At birth the child is capable of performing all the functions of organic life, such as sucking, swallowing, breathing, etc. It is, however, deficient in psychic activity and in volitional control of its muscles. Its movements are therefore largely, if not entirely, reflex in character. 48o TEXT-BOOK OF PHYSIOLOGY. Embryologic and histologic examination of the spinal cord and medulla show that so far as their mechanisms for independent phys- iologic activities are concerned both are fully developed. Similar investigations of the cerebral hemispheres and of the nerve-fibers which bring their nerve-cells into relation with the spinal segments show that the cells of the cortex are not only immature, but that their descending axons are incompletely invested with myelin. With the growth of the child, psychic life unfolds and volitional control of mus- cles is acquired. Coincidently the cells of the cerebral cortex grow and develop and the fibers become covered with myelin. The nerve-fibers which have their origin in the cells of the cerebral cortex, and which terminate in tufts around the cells in the anterior horns of the gray matter of the spinal segments, are to be regarded as long commissural tracts uniting and associating these two portions of the central nerve system. Experimental investigations and observations of pathologic lesions accord with the view that physiologically these fibers are efferent pathways for the transmission of motor or volitional impulses from the cortex to the spinal segments. The nerve-cells in which the motor impulses originate are located for the most part, as will be fully stated later, in the central portion of the cortex of the cerebral hemi- spheres in the neighborhood of the central or Rolandic fissure. The axons of these cells from each hemisphere descend through the corona radiata to and through the internal capsule, along the inferior surface of the crura cerebri, behind the pons to the medulla, of which they constitute the anterior pyramids. (Fig. 210.) At this point the pyramidal tract* of each side divides into two portions, viz.: r. A large portion, containing from 80 to 90 per cent, of the fibers, which decussates at the lower border of the medulla and passes downward in the posterior part of the lateral column of the opposite side, constituting the crossed pyramidal tract; as it descends it gradually diminishes in size as its fibers or their collaterals enter the gray matter of each successive segment. 2. A small portion, containing from 20 to 10 per cent, of the fibers,, which does not decussate at the medulla but passes downward on the inner side of the anterior column of the same side, con- stituting the direct pyramidal tract or column of Tiirck. This tract can be traced down, as a rule, only as far as the mid-dorsal region. As it descends it becomes smaller as its fibers cross the anterior commissure to enter the gray matter of the opposite * From the fact that the region included between the origin of these fibers and the internal capsule presents somewhat the form of a pyramid with four sides, Charcot designated it the pyramidal region and the fibers composing it the pyram- idal tract. The base of the pyramid includes the cortex of the convolutions around the Rolandic fissure. The summit of the pyramid is truncated and covers the pyramidal region of the Internal capsule. THE SPINAL CORD. 481 side. Thus all the fibers of the pyramidal tract from each cerebral hemisphere eventually are brought into relation with the cells of the gray matter of the opposite side of the cord. Fig. 210. — Diagram of the Pyramidal Tract or Motor Path. III. Common oculo-motor nerve. IV. Pathetic nerve. V. Motor division of the trigeminal nerve. VI. The abducens nerve. VII. Facial nerve. IX. and X. Motor divisions of the glosso-pharyngeal and pneumogastric nerves. XI. Spinal accessory nerve. XII. Hypoglossal nerve. — -{Van Gehiichten.) That the pyramidal tracts arc the conductors of volitional impulses throughout the length of the cord to its various seg- ments has been made evident by the results of section, electric stimu- lation, and disease. Division of the anterior and lateral columns 31 482 TEXT-BOOK OF PHYSIOLOGY. of one side of the cord in any part of its extent is invariably followed by a loss of motion or paralysis of the muscles below the section, while electric stimulation of the peripheral end of the isolated crossed pyramidal tract is followed by marked characteristic movements of the muscles. Similar results follow division of the pyramidal tract in any part of its course from the cerebral cortex downward. Electric stimulation of the cortical cells which give origin to the pyramidal tract is also followed by contraction of the muscles of the opposite side, while their destruction is attended by paralysis of the same muscles. As the nutrition of the fibers is governed by the cells, it follows that when the axon is separated from its cell it degenerates. It has been found that a lesion of the pyramidal tract in any part of its course is followed by descending degeneration, which is taken in evidence that it conducts nerve impulses from above downward. Thus experimental investigation and pathologic observation are in accord in the view that physiologically these nerve-fibers are the pathways for the transmission of motor or vohtional impulses from the encephalon to the spinal cord. The relation of the motor and sensor pathways to each other in the spinal cord and brain are shown in Plate II. The afferent fibers which decussate at various levels through the spinal cord are not represented. Diagram Indicating the Course of the Motor and Sensory Fibers of the Spinal Cord and Medulla. — {Gordinier.) a, a. Motor cells of the cerebral cortex, b, b. Arborizations of the fibers of the sensory tract in the cerebral cortex, c. Nucleus of the column of Burdach, showing ter- minal arborizations of the long sensory fibers of the cord. d. Nucleus of the column of GoU, showing terminal arborizations of the long sensory fibers of the cord. e. Section of the medulla, showing sensory decussation. /. Section of medulla, showing motor or pyramidal decussation, g, g. Motorial end plates. h. Section through the cervical region of the cord, showing termination in the anterior horn of the motor fibers of the direct pyramidal tract after they have crossed in the anterior commissure; also fiber of crossed pyramidal tract ending about anterior horn cell of same side, i, i. Posterior spinal ganglia, j, k. Sensory fibers of short course. /. Sensory fibers of long course, terminating in medulla. m, m, m. Sensory end organs, n. Section through lumbar cord. Plate II. CHAPTER XVIII. THE MEDULLA OBLONGATA; THE ISTHMUS OF THE ENCEPHALON; THE BASAL GANGLIA. THE MEDULLA OBLONGATA. The medulla oblongata is that portion of the central nerve system immediately superior to and continuous with the spinal cord. It has the shape of a truncated cone, the base of which is directed upward, the truncated apex downward. It is 38 mm. in length, 18 mm. in breadth, and 12 mm. in thickness. By the continuation upward of the anterior and posterior median fissures, the medulla is divided into symmetric halves (Figs. 211 and 212). Like the cord, of which it is a continuation, it is composed of white matter externally and gray matter internally. Structure of the Gray Matter. — The gray matter of the medulla is continuous with that of the cord, though owing to the shifting of position of the different tracts of the white matter it is arranged with much less regularity. The appearance which the gray matter presents on transverse section varies also at different levels. At the level of the first cervical nerve the posterior horns are narrow, elongated, and directed outward. The lateral horns are well developed and present a collection of cells near their bases which can be traced forward and backward for some distance. At the level of the decussation of the pyramidal tracts the head of the anterior horn becomes completely detached from the rest of the gray matter and is pushed backward toward the posterior horn; the bases of the anterior horns become spread out to form a layer of gray matter near the dorsal aspect of the medulla. Transverse sec- tions of the medulla at all levels show a more or less extensive network of nerve-fibers known as the reticular formation. In its meshes are found collections of nerve-cells of varying size. Toward the dorsal aspect of the medulla special groups of cells are found from which axons arise to become the fibers of various efferent cranial nerves, e. g., the hypoglossal, the efferent fibers of the vagus, and glosso-pharyngeal. Structure of the White Matter. — The white matter is com- posed of nerve-fibers supported by connective tissue and neuroglia. It is subdivided on either side by grooves into three main columns: viz., an anterior column or pyramid, a lateral column, and a posterior column. 483 484 TEXT-BOOK OF PHYSIOLOGY. The anterior column or pyramid is composed partly of fibers continuous with those of the anterior column of the spinal cord (the direct pyramidal tract), and partly of fibers continuous with those of the lateral column of the cord of the opposite side (the crossed pyram- idal tract), which decussate at the anterior portion of the medulla. The united fibers can be traced upward to the pons, where they disappear from view. The lateral column is composed of fibers continuous with those of the lateral column of the cord. As the fibers pass upward, how- ever, they diverge in several directions. The fibers of the crossed pyramidal tract cross the median hne, as previously stated, to enter into the formation of the anterior column; the fibers of the direct cerebellar tract gradually curve backward, and in so doing unite with other fibers to form the restiform body, after which they enter the cerebellum by way of the inferior peduncle. Situated between the anterior pyramid and the restiform body is a small oval mass, the olivary body, composed of both white and gray matter. The posterior column is composed largely of fibers continuous with those of the posterior column of the cord. The subdivision of this column into a postero- external (Burdach) and a postero-internal (GoU) is more marked in the medulla than in the cord. The former is here known as the funiculus cuneatus, the latter as the funiculus gracilis. These two strands of fibers are apparently continued into the restiform body. Owing to the divergence of the restiform bodies a V-shaped space is formed, the floor of which is covered with epithe- lium resting on the ependyma. At the upper extremity of the funiculus cuneatus and funiculus gracihs, two collections of gray matter are found, known respectively as the nucleus cuneatus and nucleus gracilis. Around the cells of these nuclei many of the fibers of the posterior column end in brush-like expansions. The Fillet or Lemniscus. — From the ventral surface of the cu- neate and gracile nuclei axons emerge which pass forward and upward through the gray matter and decussate with corresponding fibers coming from the opposite nuclei. They then assume a position just posterior to the pyramids and between the ohvary bodies. These fibers thus form a new distinct tract, termed the fillet or lemniscus. As this tract ascends toward the brain it receives additional axons from the sensory end-nuclei of all the afferent cranial nerves of the opposite side with the exception of the auditory. From the end-nuclei of the auditory nerve new axons ascend as a distinct tract situated near the lateral aspect of the pons. From their position these two separate tracts have been termed the mesial and lateral fillets respectively. Before proceeding to a consideration of the functions of the medulla oblongata it will be found conducive to clearness to sketch the saHent anatomic features of the parts anterior to it and their relations one to another. MEDULLA OBLONGATA. 485 Fig. 211. — Anterior or Ventral View of the Medulla Ob- longata AND Isthmus, i. In- fundibulum. 2. Tuber ciner- eum. 3. Corpora albicantia. 4. Cerebral peduncle. 5. Tuber annulare. 6. Origin of the mid- dle peduncle of the cerebellum. 7. Anterior pyramids of the medulla oblongata. 8. Decussa- tion of the anterior pyramids. 9. Olivary bodies. 10. Restiform bodies. 11. Arciform fibers. 12. Upper extremity of the spinal cord. 13. Ligamentum denticu- latum. 14, 14. Dura mater of the cord. 15. Optic tracts. 16. Chiasm of the optic nerves. 17. Motor oculi communis. 18. Patheticus. 19. Fifth nerve. 20. Motor oculi e.xternus. 2 1 . Facial nerve. 22. .A.uditory nerve. 23. Nerve of Wrisberg. 24. Glosso- pharyngeal ner\'e. 25. Pneumo- gastric. 26, 26. Spinal accessory. 27. Sublingual nerve. 28, 29, 30. Cervical nerves. — (Sappey.) Fig. 212. — Posterior or Dorsal View of the Medulla Oblongata, Isthmus, AND Basal Ganglia. i. Corpora quadrigemina. 2. Corpus quadrige- minum anterior (pregeminum). 3. Cor- pus quadrigeminum posterior (post- geminum). 4. Tract of fibers (bra- chium) passing to the corpus genicula- tum externum. 5. Tract of fibers (brachium) passing to 6, the corpus geniculatum internum. 7. Posterior commissure. 8. Pineal gland. 9. Su- perior cerebellar peduncle. 10, 11, 12. The valve of Vieussens. 13. The pa- thetic nerve. 14. Lateral groove of the isthmus. 15. Triangular bundle of the isthmus. 16. Superior cerebellar pedun- cle. 17. Middle cerebellar peduncle. 18. Inferior cerebellar peduncle. 19. Antero-inferior wall of the fourth ven- tricle. 20. Acoustic nerve. 21. Spinal cord. 22. The postero-median column. 23. The posterior pyramids. — (Sappey.) 486 TEXT-BOOK OF PHYSIOLOGY. THE ISTHMUS OF THE ENCEPHALON. The isthmus of the encephalon comprises that portion of the central nerve system connecting the cerebrum above, the cerebellum behind, and the medulla below. Its ventral surface presents below an enlargement, convex from side to side, the pons Varolii. On each side the fibers of which the pons consists converge to form a compact bundle, the middle peduncle, which enters the correspond- ing half of the cerebellum. Above the pons, this surface presents two large columns of white matter which, diverging somewhat from below upward, enter the base of the cerebrum and are known as the crura cerebri. Embracing the crura above are two large bands of white matter, the optic tracts (Fig. 211). The dorsal surface presents below two diverging columns of white matter, the inferior peduncles; above, two converging columns, the superior peduncles of the cerebellum (Fig. 212). At the extreme upper part of this surface there are four small grayish eminences, the corpora quadrigemina. From the disposition of the white matter on the dorsal surface of the isthmus and medulla, there is formed a lozenge- shaped space, the fourth ventricle. This space is merely an expansion of the central cavity of the cord, the result of the changed relations of the white and gray matter in this region of the central nerve system. Above, this ventricle communicates by a narrow canal, the aqueduct of Sylvius, with the third ventricle. The floor of the fourth ventricle is covered with a layer of epithehum resting on the ependyma continuous with that lining the central canal of the cord. Beneath this is a layer of gray matter. The pons Varolii comprises in a general way that portion of the central nerve system situated between the medulla oblongata and the crura cerebri. The ventral surface is convex from side to side; the lateral surface, owing to the convergence of the fibers of which it is composed, is contracted to form the middle peduncle of the cerebellum; the posterior surface is flat and forms the upper half of the floor of the fourth ventricle. The pons consists of white fibers and gray matter supported by connective tissue and neuroglia. Trans- verse sections of the pons show that it is divided into an anterior or ventral, and a posterior or dorsal portion, the latter being usually termed the tegmentum. The ventral portion consists for the most part of white fibers, ar- ranged longitudinally and transversely (Fig. 213). The longitudinal fibers are largely continuations of the pyramidal tracts, or the fibers composing the anterior pyramid of the medulla. In the lower part of the pons these fibers are compactly arranged, but at higher levels they are separated into a number of bundles by the interlacing of the trans- verse fibers. The transverse fibers are divided into a superficial and ISTHMUS OF THE ENCEPHALON. 487 a deep set. Among these fibers are groups of nerve-cells which collectively are known as the nucleus pontis. Some of the transverse fibers, especially the superficial ones, are commissural in character — i. e., they connect corresponding parts of the gray matter of the lateral halves of the cerebellum; others coming from the gray matter of the cerebellum cross the median fine and terminate around the cells of the nucleus pontis; others again are connected with the gray cells of the same side. Through the intermediation of the nucleus pontis and certain of the longitudinal fibers of the pons, the cerebellum is brought into relation with the cerebrum. The dorsal or tegmental portion consists of: (i) The fillet; (2) the formatio reticularis; (3) the posterior longitudinal bundle; (4) the substantia ferruginosa; (5) groups of nerve-cells from which arise various cranial nerves — e. g., the fifth, sixth, sev^enth, and eighth. The fillet or lemniscus in this region is divided into a mesial and a lateral portion. The fibers of the mesial por- tion are partly the axons of the nerve- cells of the gracile and cuneate nuclei of the opposite side of the medulla, and partly of the axons of the sensor nerve-cells of the afferent cranial nerves with the exception of the auditory. The fibers of the lateral portion are mainly the axons of the cells in the floor of the fourth ventricle around which the auditory nerve-fibers end. They are therefore a continuation of the auditory tract. The formatio reticularis is a con- tinuation of that of the medulla. The posterior longitudinal bundle is triangular in shape and situated behind the formatio reticularis and close to the median fine. The fibers composing it are largely derived from the ground fibers of the antero-lateral column of the spinal cord. The superior olive is a cylindric mass of gray matter situated in the pons in the anterior part of the formatio reticularis. It consists of nerve-cells the axons of which pass dorso-laterally, decussate in the median line, and form the lateral fillet of the opposite side. Some few axons go to the lateral fillet of the same side. The substantia }errugi?tosa is composed mainly of pigmented cells. The groups of nerve-cells lying just beneath the floor of the fourth ventricle give origin to axons of the motor portion of the fifth. Fig. 213. — Traxsection of the Pons through its Middle Portion, Showing the Relation of the Nerve Tracts of Which it is Composed. D. I. f. Dorsal longitudinal fasciculus. L.c. and c. Locus ceruleus. L.f. Lateral fillet. TEXT-BOOK OF PHYSIOLOGY. the sixth, the seventh cranial nerves. Some of the groups are the sensor end-nuclei of the fifth and eighth cranial nerves. The crura cerebri comprise that portion of the central nerve sys- tem situated between the pons below and the cerebrum above. They are composed of strands of nerve-fibers which are divided, as shown on cross-section, into a ventral and a dorsal portion by a crescentic shaped layer of gray matter, the substantia nigra (Fig. 214). Of the fibers which compose the ventral portion of each crus, the crusta or pes, the larger part is continuous below, through the longitudinal fibers of the pons, with the pyramid of the medulla and the pyramidal tract; above they assist in the formation of the internal capsule. On the inner and on the outer .2Q . side of each crusta there is a bundle of fibers derived from the frontal, and from the temporal and occipital por- tions of the cerebrum, respec- tively. These fibers are con- nected directly with the nuclei pontis and indirectly with the cerebellum of the same and opposite sides. The fibers which compose the dorsal portion, the tegmentum, are continuous with those which pass upward from the medulla and pons, e. g., the fillet, both mesial and lateral, the formatio reticularis, the posterior longitudinal bundle, and, in addition, the fibers of the superior peduncles of the cerebellum. Above, the fibers terminate largely in collections of gray matter at the base of the cerebrum. The aqueduct of Sylvius is a short narrow canal which connects the cavity of the fourth with the cavity of the third ventricle. It is lined by the ependyma and surrounded by a layer of gray matter continuous with that forming the floor of the fourth ventricle. In that portion of the gray matter lying beneath or ventral to the aqueduct there are groups of nerve-cells which give origin to axons which unite to form the third and fourth cranial nerves. Fig. 214. — Scheme of Transverse Sec- tion OF THE Cerebral Peduncles. CQ. Corpora quadrigemina. Aq. Aque- duct, p.l.b. Posterior longitudinal bun- dle. F. Fillet or lemniscus. RN. Red nucleus. SN. Substantia nigra. III. Third nerve. Py. Pyramidal tracts. FC. Fronto-cerebellar; and TOC, tem- poro-occipital fibers of the crusta. CC. Caudate-cerebellar fibers in upper part of crusta. — {After Wernicke and Cowers.) CORPORA QUADRIGEMINA. THE CORPORA QUADRIGEMINA. The corpora quadrigemina are four small grayish eminences situated beneath the posterior border of the corpus callosum and be- hind the third ventricle. They rest upon the lamina quadrigemina, which fonns the roof of the aqueduct of Sylvius. The anterior pair are termed the nates, or the pregemina, the posterior pair the testes, or the postgemina. From the external surface of each body there pass outward bundles of fibers termed hrachia. The fibers which compose the brachium of the pregeminum pass outward and enter a small col- lection of gray matter, the corpus geniculatum extenmm, and the optic tract. The fibers which compose the brachium of the postgeminum are divided into two bundles, one of which enters a second small collection of gray matter, the corpus geniculatum internum, while the other passes forward beneath this body to enter the internal capsule, beyond which it passes to the cortex of the temporal region of the cerebrum (Fig. 212). Though these bodies are closely associated anatomically, they differ in origin, in their relations and in their functions. Microscopic examination of sections of the quadrigeminal bodies shows that they are composed of nerve-cells and nerve-fibers, both of which are so intricately arranged that it is difficult to trace their relation one to another and to adjoining structures. Some of the cells of the pregeminum give off axons which course outward and forward, enter the internal capsule, and pass through the optic radiation to the cortex of the occipital region of the cerebrum. Many fibers of the optic tract, axons of the cells of the retina, end in brush-like expansions around these same cells. There is thus formed a connected pathway between the retina and the occipital cortex. The cells of the occipital cortex, however, send axon fibers in the reverse direction through the optic radiation to terminate around the cells of the pregeminum, while axons of pregeminal cells pass for- ward to the retina and to the cells of origin of the third nerve. The cells of the postgeminum give origin to axons which pass upward, forward, and outward, enter the internal capsule, and pass by way of the auditory tract to the cortex of the temporo-sphenoidal region of the cerebrum. ]\Iany of the fibers of the lateral fillet, a portion of the auditory tract, terminate in brush-like expansions around these same cells. There is thus established a connected pathway between the cochlea and the temporo-sphenoidal cortex. The cells of the temporal cortex, however, send axons in the re- verse direction by way of the auditory tract to the cells of the postgeminum. There is thus established a double communication between the occipital and temporal region of the cerebral cortex, and the pregeminal and postgeminal bodies respectively. 490 TEXT-BOOK OF PHYSIOLOGY. THE BASAL GANGLIA; THE CORPORA STRIATA AND OPTIC THALAMI. The basal ganglia surmount the crura cerebri, but are only made visible by removal of the cerebrum (Fig. 215). Fig. 215.— Dissection of Brain, from above, Exposing the Lateral Fourth AND Fifth Ventricles with the Surrounding Parts, i. — a. Anterior part, or genu of corpus callosum. b. Corpus striatum, b'. The corpus striatum of left side, dissected so as to e.xpose its gray substance, c. Points by a line to the taenia semicircularis. d. Optic thalamus, e. Anterior pillars of fornix divided; below they are seen descending in front of the third ventricle, and between them is seen part of the anterior commissure; in front of the letters is seen the slit-like fifth ventricle, between the two laminae of the septum lucidum. /. Soft or middle commissure; g is placed in the posterior part of the third ventricle; immediately behind the latter are the posterior commissure (just visible) and the pineal gland, the two crura of which extend forward along the inner and upper margins of the optic thalami. h and /. The corpora quadrigemina. k. Superior crus of cerebellum. Close to k is the valve of Vieussens, which has been divided so as to expose the fourth ventricle. /. Hippocampus major and corpus fimbria- tum, or tasnia hippocampi, m. Hippocampus minor, n. Eminentia collaterahs. o. Fourth ventricle, p. Posterior surface of medulla oblongata, r. Section of cerebellum, s. Upper part of left hemisphere of cerebellum exposed by the removal of part of the posterior cerebral lobe. — {Hirschfeld and Leveille.) The corpora striata are two large ovoid collections of gray and white matter situated at the base of the cerebrum. The larger portion of each body is embedded in the cerebral white matter, while the BASAL GANGLIA. 491 smaller portion projects into the anterior part of the lateral ventricle. A transection of the corpus striatum shows that it is divided by a band of white matter into two portions, viz.: 1. The caudate nucleus, the intra- ventricular portion, convex in shape with its base directed forward, its apex or tail directed backward and downward. 2. The lenticular nucleus, the extra-ventricular portion, somewhat biconvex in shape and embedded largely in the white matter. Each lenticular nucleus is sub- divided by two lamina of white matter into three portions. The two inner, from their pale yellow color, form the globus pallidus; the outer, somewhat darker in color, is the putamen. The Internal Capsule. — The band of white matter separating the caudate from the lenticular nucleus has been termed the internal capsule from the manner in which it embraces the inner surface of the lenticular nucleus. It consists of nerve-fibers which associate histologically and physiologically all por- tions of the cerebral cortex with the optic thalamus, pons, medulla, spinal cord, and cerebellum. The relation of the capsule to the nuclei through which it passes is readily shown on cross-section (Fig. 216). The appearance which it presents, how- ever, varies considerably at different levels. At a given level it may be said to con- sist of two segments or limbs, an anterior, situated between the caudate nucleus and the anterior extremity of the lenticular nucleus, and a posterior, situated between the optic thalamus and the posterior extremity of the lenticular nucleus. The two segments unite at an obtuse angle, termed the knee, which is directed toward the median hne. The optic thalami are two oblong masses of gray matter situated upon the crura cerebri and behind the corpora striata. The anterior and posterior extremities of each thalamus present enlargements known respectively as the anterior tubercle and the posterior tubercle or pulvinar. The mesial surface of the thalamus forms the lateral wall of the third ventricle and is covered by epithehum resting on a thin layer of ependyma. Fig. 216. — Horizontal Sec- tion OF THE Internal Capsule showing its Relations to the Cau- date Nucleus, Optic Thalamus, and the Lenticular Nucleus, i. Caudate nucleus. 2. An- terior segment of the in- ternal capsule. 3. Exter- nal capsule. 4. Lenticu- lar nucleus. 5. Claus- trum. 6. Posterior seg- ment of internal capsule. 7. Optic thalamus. — {Modified from Landois.) 492 TEXT-BOOK OF PHYSIOLOGY. A transection of the thalamus shows that it is not only covered externally but penetrated by white matter, which subdivides its con- tained gray cells into four more or less distinct masses termed nuclei, viz., an anterior, a lateral, occupying the external part of the thalamus, a ventral, close to the entire ventral surface, and a posterior, situated beneath the pulvinar. Beneath and somewhat internal to each optic thalamus there is a region, the subthalamic, consisting of an intricate network of nerve-fibers and several nuclei of gray matter, e. g., the red or tegmental nucleus, the subthalamic nucleus, or Luys' body, and the substantia nigra. Though the thalamus has extensive connections with many por- tions of the central nerve system, the most important are with the cortex, the tegmentum, and the optic tracts. From the cells of these various nuclei axons emerge which pass into the internal capsule, and through the corona radiata to all portions of the cortex. Those axons which come from the pulvinar and pass to the occipital lobe constitute a part of the optic radiation; those from the lateral and ventral nuclei ultimately reach the parietal lobe; those from the anterior nucleus pass to the hippocampal and unci- nate convolutions. In a similar manner all portions of the cortex are brought into relation with the thalam.us, axons from the cortical cells passing downward to terminate in tufts around the thalamic nuclei. The tegmentum is intimately related to the thalamus, though the exact distribution of various strands of fibers is a subject of much discussion. Most of the fibers of the mesial fillet end in tufts around the cells of the ventral and lateral nuclei; other fibers pass directly to the cortex. The optic tract sends fibers directly into the pulvinar, around the cells of which they terminate in brush-like expansions. SUMMARY OF THE STRUCTURE OF THE MEDULLA, ISTHMUS, AND BASAL GANGLIA. Structure of the Central Gray Matter. — Though the general arrangement of the central gray matter has been incidentally alluded to in the foregoing presentation of the anatomic features of the medulla and isthmus, it will be convenient to summarize its arrange- ment and structure at this point. The gray matter of the cord, of the dorsal aspect of the medulla and pons, of the region surrounding the aqueduct of Sylvius, and of the fining of the third ventricle, constitute practically a continuous system, though presenting modifications in various parts of its extent. In the transition region of the spinal cord and medulla the gray matter of the former becomes much changed in shape owing to the shifting of position of the various tracts of white matter, until in the medulla MEDULLA AND BASAL GANGLIA. 493 and pons it is spread out in the form of a thin layer near tlieir dorsal surfaces, where, together with the ependyma, it forms the floor of the fourth ventricle. In the region of the aqueduct of Sylvius the gray matter again converges and ultimately surrounds the canal, to again expand at its anterior extremity, to form the hning of the third ventricle The Nerve-cells. — The nerve-cells in these different regions do not differ morphologically from those in the gray matter of the spinal cord. The corpus, or body of the cell, presents a number of den- drites as well as the sharply defined axon. As a rule, the cells are arranged in groups, or clusters, or nests, partially surrounded and enclosed by supporting tissue, and situated beneath the floor of the fourth ventricle and the floor of the aqueduct of Sylvius. From some of the cell groups axons pass ventrally through the white matter to emerge on the ventral and lateral surfaces of the medulla, pons, and crura, where they are known as efferent or motor cranial nerves. From other groups of cells, axons cross the median line, and after joining the mesial fillet ascend toward the cerebrum. Around these latter cells the terminal filaments of the afferent or sensor cranial nerves arborize. The collection of cells formed in the central gray matter may be divided into two groups — efferent and afferent. The efferent cells, like those of the cord independent of a trophic influence, are motor in function, inasmuch as the excitation arising in them is transmitted outward through their related axons to mus- cles, glands, or blood-vessels, imparting to them motion, either molar or molecular. The afferent cells are largely sentient or receptive in function, inasmuch as the excitations brought to them by the afferent cranial nerves from skin and mucous membranes and from sense-organs, such as the tongue and ear, are received by them and transmitted through their ascending axons to the cortex of the cerebrum, where they are translated into conscious sensations. Structure of the White Matter.— The white matter is com- posed of medullated nerve-fibers, and though arranged in a very complex manner may be divided into longitudinal and transverse fibers. The longitudinal fibers which compose the main portion of the isthmus may be subdivided into (i) a ventral or pedal portion and (2) a dorsal or tegmental portion. The fibers constituting the ventral or pedal portion may for convenience be said to extend from the cerebral cortex to the pons, medulla, and spinal cord. They may be divided into three distinct tracts: e. g., the pyramidal tract, the fronto-cerebellar tract, and the occipito-temporo-cerebellar tract (Fig. 217). The pyramidal tract descends from the cortex of the cerebrum 494 TEXT-BOOK OF PHYSIOLOGY. bordering the fissure of Rolando, passes through the posterior one- third of the anterior segment and the anterior two-thirds of the posterior segment of the internal capsule, the middle two-fifths of the crusta, behind the transverse fibers of the pons, to become the anterior pyramids of the medulla, beyond which it divides into the direct and crossed pyramidal tracts of the cord. In its course some of the fibers and their collaterals arborize around efferent cells from the anterior extremity of the aqueduct of Sylvius to the termination of the spinal cord. Fig 217. — Diagrammatic Arrangement of the Projection Tracts Connecting THE Cerebral Cortex with the Lower Nerve-centers. A. Fronto- cerebellar tract. B. The pyramidal or motor tract. C. Sensory tract. D. Visual tract from optic thalamus (O.T.) to the occipital lobe. E. Central audi- tory tract. F. Superior cerebellar peduncle. G. Middle cerebellar peduncle. H. Inferior cerebellar peduncle. C.N. Caudate nucleus. C.Q. Corpora quad- rigemina. Vt. Fourth ventricle. The numerals refer to cranial nerves. J. Eighth nerve nucleus. — (After Starr.) The jronto-cerehellar tract descends from the cortex of the frontal portion of the anterior lobe, passes through the anterior portion of the anterior segment of the internal capsule, the inner fifth of the crusta to the pons, where its fibers terminate or arborize around the nucleus pontis of the same and opposite sides. The occipito-temporo-cerebellar tract descends from the occipital and temporal lobes, passes to the inner side of the lenticular nucleus, MEDULLA OBLONGATA AND ISTHMUS. 495 and continues downward on the outer side of the crusta, occupying about one-fifth of its bulk, to the pons, wliere its fibers also arborize around the nucleus pontis of the same and opposite sides. By means of fibers in the middle peduncle these descending fibers are brought into relation with the cerebellum. The fibers constituting the dorsal or tegmental portion of the longitudinal system may be said for convenience to extend from the posterior portion of the medulla and pons to the optic thalamus and cerebrum. They may be subdivided into several tracts: viz., the fillet, the posterior longitudinal bundle, Gowers' tract, etc. The fillet or lemniscus, consisting of fibers having their origin partly from the cells of the cuneate and gracile nuclei and partly from the cells of the sensor end-nuclei of various sensor cranial nerves, occupies a region in the ventral and mesial portion of the tegmentum throughout its entire extent. Superiorly this mesial fillet divides into two portions, one of which passes to the thalamus and pregem- inum (anterior corpus quadrigeminum), the other to the cortex of the parietal and limbic lobes. The fibers coming from the sensor end-nucleus of the auditory nerve (the lateral fillet) lie on the lateral aspect of the pons and crus. Superiorly they terminate in the post- geminum (the posterior corpus quadrigeminum). The posterior longitudinal bundle, an upward extension of the fibers composing a portion of the ground bundle of the spinal cord, is located on either side of the median line just beneath the floor of the fourth ventricle and the aqueduct of Sylvius. As it passes upward collateral branches are given off, some of which arborize around the cell nuclei of the third, fourth, and sixth cranial nerves of the same side, while others cross the median line and arborize around the corresponding cell nuclei of the opposite side. Superi- orly some of the fibers become related to cells in the thalamus and subthalamic region. This bundle of fibers appears to be mainly commissural in character. Gowers' tract, the antero-lateral tract of the spinal cord, occupies a position in the lateral region of the formatio reticularis both in the medulla and pons. Continuing upward, it enters the mesial fillet, and in company with it passes through the posterior division of the internal capsule and finally terminates around cells in the cortex of the parietal lobe. The transverse fibers of the isthmus are found in the pons. The fibers of the ventral as well as those of the more dorsal regions have their origin in nerve-cells in the cortex of the cerebellum. From their origin they pass through the cerebellar white matter, and through the middle peduncle as far as the median line, where they decussate with fibers coming from the opposite side. Beyond this point they pass to the cerebellar cortex. From their anatomic relations it is prob- 496 TEXT-BOOK OF PHYSIOLOGY. able that these transverse fibers are commissural in character, bring- ing into relation opposite but corresponding regions of the cerebellar cortex. In addition to the commissural fibers other transverse fibers associate the cerebellar cortex with the gray matter in the pons on both the same and opposite sides. In this way the cerebellum is brought into relation with longitudinal fibers coming from and going to the cerebrum. FUNCTIONS OF THE MEDULLA OBLONGATA, ISTHMUS, AND BASAL GANGLIA. Microscopic examination of the white and gray matter of these various parts of the central nerve system shows that they are com- posed of nerve-cells and nerve-fibers which morphologically do not differ in essential respects from those found in the spinal cord, though their arrangement is far more complicated and involved. The func- tions of these closely related structures are in consequence equally complex and involved and but imperfectly known. In a general way it may be said that by virtue of the presence of nerve-cells and definite tracts of nerve-fibers these structures col- lectively may be regarded as consisting: 1. Of centers for reflex actions; and — 2. Of conducting paths by which the various parts are brought into relation one with another and with the spinal cord, the cerebel- lum, and the cerebrum. The Medulla Oblongata and Pons. — The gray matter situated in these structures — i. e., just beneath the floor of the fourth ventricle — contains nerve-cells arranged in more or less well-defined groups which may be divided into efjerent and afferent. The efferent cells are the immediate sources of energy which is transmitted through efferent axons to various peripheral organs — muscles, glands, and blood-vessels. Their activity may be excited by the same influences which excite the efferent cells of the spinal cord: e. g., variations in the composition of the blood or lymph; the arrival of nerve energy coming through afferent pathways in the spinal cord and through afferent cranial nerves; the arrival of nerve energy coming through efferent pathways from the cerebrum. The peripheral activity resulting from their excitation may therefore be automatic or autochthonic, peripheral (reflex) or cerebral (volitional) in origin. The afferent cells are sentient or receptive in function, inasmuch as they receive nerve energies coming through lower afferent pathways and transmit them through their related axons to the cortex of the cerebrum, where they are translated into conscious sensations. N'- The efferent cells give origin to nerve-fibers which pass ventrally and become the efferent or motor cranial nerves. FUNCTIONS OF THE MEDULLA OBLONGATA. 497 The afferent cells give origin to fibers which pass to the cerebral cortex. Around both groups of cells, the afferent or sensor cranial nerves terminate in tuft-like expansions. In a subsequent section the origin, course, and distribution of the various cranial nerves will be considered. But as the function of the nerve is but to transmit energy from the cell of which it constitutes a part, the function ascribed to it may without impropriety be transferred to the cell itself. Since it is by means of nerve-cells and their associated fibers that many important functions of organic life are initiated and maintained, it would naturally be expected from its extensive nerve connections that this region of the nerve system plays an extensive role in this respect. As the accomplishment of these functions requires the cooperation and coordination of a number of separate but related structures, it is evident that there must exist in the medulla and pons a number of coordinating mechanisms consisting of nerve-cells and nerve-fibers which are associated in various ways for the accomplish- ment of definite functions. To such a coordinating mechanism the term "center" has been given: e. g., respiratory, cardiac, deglutitory, etc.* As centers for reflex activities. Experimentation has shown that the medulla and pons contain a number of such centers, the more important of which are as follows : 1. A cardiac center, which exerts (i) an accelerator influence over the heart's pulsations through nerve-fibers emerging from the spinal cord in the roots of the first and second dorsal nerves and reach- ing the heart through the sympathetic nerve; (2) an inhihiior or retarding influence on the action of the heart through efferent fibers in the trunk of the pneumogastric nerve. (See page 303.) 2. A vaso- motor center, which regulates the cahber of the blood- vessels throughout the body in accordance with the needs of the organs and tissues for blood, through nerve-fibers passing by way of the spinal nerves to the walls of the blood-vessels. (See page 342.) 3. A respiratory center, which coordinates the muscles concerned in the production of the respiratory movements, (See page 397-) 4. A mastication center, which excites to activity and coordinates the muscles of mastication. (See page 160.) 5. A deglutition center, which excites and coordinates the muscles * By the term center as here employed is meant a collection of nerve-cells and nerve-fibers occupying an area of greater or less extent, though its exact anatomic limits may not be accurately defined. That an area may merit the term center, it is necessary that its stimulation should increase, its destruction should abolish or impair, functional activity. 32 498 TEXT-BOOK OF PHYSIOLOGY. concerned in the transference of the food from the mouth to the stomach. (See page 179.) 6. An articulation center, which coordinates the muscles necessary to the production of articulate speech. In addition, the gray matter contains centers which influence the secretion of saliva, provoke vomiting, coordinate the muscles of the face concerned in expression, and control the secretion of the per- spiration. As conducting pathways. The anterior pyramids of the medulla and their continuations through the more ventral portions of the pons, being portions of the general pyramidal tract, serve to conduct volitional efferent nerve impulses from higher portions of the brain to the spinal cord. Division of either of these pathways is at once followed by a loss of volitional control of the muscles below the section. The dorsal or tegmental portion, containing the fillet and Gowers' tract, serves to transmit afferent nerve impulses from the spinal cord to higher portions of the brain. Transverse division of one-half of the dorsal portion of the pons is followed by complete anesthesia of the opposite half of the body without any impairment of motion. The restiform bodies constitute a pathway between the spinal cord and the cerebellum. The transverse fibers of the pons associate opposite but corresponding portions of the cerebellar hemispheres. The Crura Cerebri. — The crura cerebri consist ventrally of fibers which are largely derived from the pyramidal tracts and are con- tinuous with the longitudinal fibers of the ventral portion of the pons and medulla; and dorsally of fibers continuous with those coming through the lower portions of the tegmentum. Hence they are con- ductors of motor impulses in the former and of sensor impulses in the latter region. It is not definitely known as to whether reflex actions take place through the gray matter, the locus niger, or not. The gray matter beneath the aqueduct of Sylvius contains nerve- cell groups which are centers for reflex actions in connection with ocular movements: e. g., closure of the lids, contraction of the sphinc- ter pupillas, convergence of the eyes, etc. The Corpora Quadrigemina. — From the anatomic relation of the anterior quadrigeminal body (the pregeminum) to the optic tract, on the one hand, and to the optic radiation, on the other, the in- ference can be drawn that it is in some way essential to the per- formance of the visual process. Experimental investigations and pathologic changes support the inference. Irritation of the pregeminum in monkeys on one side is followed by dilatation of the pupils first on the opposite side and then almost immediately on the same side. The eyes at the same time are also widely opened and the eyeballs turned upward and to the opposite FUNCTIONS OF THE BASAL GANGLIA. 499 side. If the irritation be continued, motor reactions are exhibited in various parts of the body. Destruction of the pregeminum in both monkeys and rabbits is followed by bhndness, dilatation and immo- bility of the pupils, with marked disturbance of equihbrium and locomotion (Ferrier). From the anatomic relation of the posterior quadrigeminal body (the postgeminum) to the lateral fillet, the basal tract for hearing, the inference may be drawn that it is in some way connected with the auditory process. Stimulation of the postgeminum gives rise to cries and various forms of vocalization. Pathologic states of this body are also attended by impairment of hearing and disorders of the equilibrium. From the foregoing facts it is probable that the corpora quadrigem- ina are associated with station and locomotion. Ferrier assumes that in these bodies "sensory impressions, retinal and others, are coordinated with adaptive motor re- actions such as are in- volved in equilibration and locomotion." The Corpora Striata. — The relation of these bodies to the pyramidal motor tract would indi- cate that they are in some way connected with motor activities. Their function, however, is ob- scure. While stimulation of one corpus produces convulsion of the muscles of the opposite side of the body, and destruction gives rise to paralysis of the corresponding muscles, it is difficult, owing to the intimate association of the white and the gray matter, to state to which the phenomena are to be attributed. The evidence at hand points to the conclusion that if a lesion is limited to the gray matter the paralysis which might resuk would be but temporary and of short duration. The pathologic evidence is of a similar character. Gowers Fig. 218. — Horizontal Section of the Internal Capsule Showing the Position and Rela- tion OF THE Motor Tracts for the Eye, Head (Hd.), Tongue (Tg.), Mouth (Mth.), Shoulder (Shi.), Elbow (Elb.), Digits of Hand (Dig.), Abdomen (Abd.), Hip, Knee (Kn.), Digits of Foot (Dig.). S. Sensor tract. O. T. Optic tract. A. T. Auditory tract. I. Caudate nucleus. 2. Anterior seg- ment of internal capsule. 3. E.xternal capsule 4. Island of Reil. 5. Lenticular nucleus. 6. Claustrum. 7. Posterior segment of internal capsule. — {Modified from Landois.) 500 TEXT-BOOK OF PHYSIOLOGY. is of the opinion, that if the lesion is small and at a sufficient distance from the white fibers of the capsule, there may even be no initial hemiplegia; neither motor nor sensory paralysis will arise if the lesion is confined to the gray matter. It is stated by some experimenters that localized injuries, both experimental and pathologic, are followed by a persistent rise of temperature, varying from i° to 2.6° C. The Optic Thalami. — From the anatomic relation of the optic thalami to the general and special sense nerve-tracts, on the one hand, and to the cerebral cortex, on the other hand, it is assumed that they are connected with the production of sensations both general and special, and act as intermediates between the peripheral sense- organs and the cortex. The results of ex- perimental stimulation and destruction of the thalami are extremely contradictory and fail to throw much light on their functions. Ferrier states that destruction of the posterior part of one thalamus produced blindness in the opposite eye and impairment of the sense of touch and pain in the opposite side of the body. In a pa- tient under the care of Hughhngs-Jackson there was blindness in the right half of each eye, loss of hearing in the left ear, impairment of taste on the left side of the tongue, and a diminu- tion of the sense of touch on the left side of the body. Postmortem examination showed a patch of softening in the posterior part of the right thalamus, the remainder of the organ being normal. It is probable that in the thalamus visual, tactile, and labyrinthine impressions are received, coordinated, and reflected outward, with the result of producing various adaptive motor reactions connected with station and equilibrium. It is also beheved by some investigators Fig. 219. — Vertical Section Through the Right Cerebral Hemisphere in Front of the Gray Commissure, i. Caudate nucleus. 2. Corpus callosum. 3. Pillars of the fornix. 4. Internal capsule. 5. Optic thalamus. 6. Gray commissure. 7. External capsule. 8. Claustrum. — {Landois.) FUNCTIONS OF THE INTERNAL CAPSULE. 501 to act as an intermediate between emotional states and their expres- sion in the muscles of the face, this power being lost in certain patho- logic conditions. The power of regulating the temperature of the body has also been assigned to the thalamus, as destruction of its anterior extremity is usually followed by a rise in temperature. The Internal Capsule. — The internal capsule has been shown by the results both of experiment and of pathologic processes to be, first, a pathway for the transmission of nerve impulses from the cerebral cortex to the pons, medulla, and spinal cord, which give rise to contraction of the muscles of the opposite side of the body; and, second, a pathway for the transmission of nerve impulses coming from skin, mucous membrane, muscles, and special sense-organs to the cortex, where they give rise to sensations general and special. It is therefore the common motor and sensor pathway. For the reason that it transmits both motor and sensor impulses, and for the further reason that it is frequently the seat of pathologic lesions which are followed by either a loss of motion or sensation or both, the internal capsule is one of the most important parts of the central nerve system. As shown in Fig. 218, it consists of two segments or hmbs united at an obtuse angle, the knee or elbow, which is directed toward the median line. The motor tract is confined to the posterior one-third of the anterior segment and the anterior two-thirds of the posterior segment. The sensor tract is confined to the posterior one-third of the posterior segment, the extreme end of which also contains the optic and auditory tracts. The regioh of the anterior segment in front of the motor tract contains the fibers of the fronto-ccrebellar tract, the function of which is unknown. The motor region contains fibers which descend from the cerebral cortex to nerve-centers situated in the gray matter beneath the aqueduct of Sylvius, in the gray matter beneath the floor of the fourth ventricle, and in the anterior horns of the gray matter of the spinal cord, and which in turn are connected by the cranial and spinal nerves with the muscles of the eye, head, face, trunk, and hmbs. The positions occupied by these dift'erent tracts are shown in Fig. 218. The relation of the internal capsule to the caudate nucleus and the optic thalamus internally, and to the lenticular nucleus exter- nally, is also shown in a vertical section of the cerebrum made in front of the gray commissure (Fig. 219). From the fact that the internal capsule contains efferent or motor tracts, and afferent or sensor tracts, it is evident that a destructive lesion of the motor tract would be followed by a loss of motion; and of the sensor tract, by a loss of sensation on the opposite side of the body. CHAPTER XIX. THE CEREBRUM. The cerebrum is the largest portion of the encephalon, constitut- ing about 85 per cent, of its total weight. In shape it is ovate, convex on its outer surface, narrow in front and broad behind. It is divided by a deep longitudinal cleft or fissure into halves, known as the cerebral hemispheres. The hemispheres are completely separated anteriorly and posteriorly by this fissure, but in their middle portions are united by a broad white band, the corpus callosum. Each hemisphere or hemi-cerebrum is convex on its outer aspect, and corresponds in a general way with the cavity of the skull; the inner or mesial surface is fiat and forms the lateral boundary of the longi- tudinal fissure. The surface of each hemi-cerebrum presents a series of alternate indentations and elevations, known respectively as fissures or sulci, and convolutions or gyres. A knowledge of the situation and extent of the principal fissures and convolutions, as well as of their relation one to another, is essential to a clear understanding of many phys- iologic processes, clinical phenomena, and surgical procedures. The general arrangement of the primary fissures and convolutions is represented in Figs. 220 and 221. Fissures. — 1. The fissure 0} Sylvius, one of the most important of the primary fissures, is found on the side of the cerebrum. It begins at the base and extends upward, outward, and backward to a point corresponding to the eminence of the parietal bone, where it usually terminates. Anteriorly a short branch is given of? which passes upward and forward into the frontal lobe. The Sylvian fissure is the first to appear in the development of the fetal brain, becoming visible at the third month. In the adult it is deep and well marked and divides the hemi-cerebrum into a frontal and a temporo-sphenoidal lobe. 2. The fissure 0} Rolando, or central fissure, equally important, is found on the superior and lateral aspects of the cerebrum. It runs from a point on the convexity of the hemisphere near the median line transversely outward and downward toward the fissure of Sylvius, but as a rule does not pass into it. It divides the frontal from the parietal lobe. The inchnation of the 502 CEREBRUM. 503 central fissure is such as to form with the longitudinal fissure an angle of about 67 degrees. The intra- parietal fissure arises a short distance behind the central fissure. It then runs upward, backward, and downward to terminate near the posterior extremity of the hemisphere. It divides the parietal lobe into a superior and an inferior portion. Fig. 220. — Diagram Showing Fissures and Convolutions of the Left Side of THE Human Brain. F. Frontal. P. Parietal. O. Occipital. T. Temporo- sphenoidal lobe. S. Fissure of Sylvius. S'. Horizontal. S". Ascending ramus of S. c. Sulcus centralis, or fissure of Rolando. A. .A^scending frontal, and B. Ascending parietal, convolution. Fj. Superior, F,. Middle, and F,. Inferior frontal convolutions, f,. Superior, fj. Inferior, frontal fissures, fs. Sulcus prje- centralis. P. Superior parietal lobule. P,. Inferior parietal lobule, consisting of Pj. Supramarginal gyrus, and Pj'. Angular gyrus, ip. Sulcus interparietalis. cm. Termination of callosomarginal fissure. O,. First, O2. Second, O3. Third, occipital convolutions, po. Parieto-occipital fissure, o. Transverse occipital fissure. 02- Inferior longitudinal occipital fissure. Tj. First, Tj. Second, T3. Temporo-sphenoidal, convolutions. /,. First, (2. Second, temporo-sphenoida] fissures. — {Landois' ^'Physiology," after Ecker.) 4. The parieto-occipital fissure, situated on the mesial surface of the hemisphere, divides the latter into a parietal and an occipital lobe. It begins as a deep notch on the surface of the hemisphere, and is then continued downward and forward until it enters the calcarine fissure. 504 TEXT-BOOK OF PHYSIOLOGY. The calcarine fissure begins on the posterior extremity of the mesial surface of the occipital lobe. From this point it passes downward and forward to unite with the parieto-occipital fissure. The calloso-marginal fissure is a deep cleft on the mesial surface of the hemisphere. It begins below the anterior extremity of the corpus callosum and in a general way follows the course of this structure as far as its posterior extremity, where it turns upward to terminate at the margin of the hemisphere just posterior to the fissure of Rolando. P'iG. 221. — Diagram Showing Fissures and Convolutions on Mesial Aspect OF THE Right Hemisphere. Median aspect of the right hemisphere. CC. Corpus callosum divided longitudinally. Gf. Gyrus fornicatus. H. Gyrus hip- pocampi, h. Sulcus hippocampi. U. Uncinate gyrus, cm. Calloso-marginal fissure. F. First frontal convolution, c. Terminal portion of fissure of Rolando. A. Ascending frontal, B. Ascending parietal, convolution and paracentral lobule. P/. Precuneus or quadrate lobule. Oz. Cuneus. Po. Parieto-occipital fissure. Op Transverse occipital fissure, oc. Calcarine fissure, oc'. Superior, oc". Inferior, ramus of the same. D. Gyrus descendens. T4. Gyrus occipitotemporalis lateralis (lobulus fusiformis). T5. Gyrus occipitotemporalis medialis (lobulus lingualis). — (Ecker.) Secondary fissures of more or less importance are present in the different lobes, subdividing the surface into convolutions: e. g., in the frontal lobe are found the pre-central, the superior and middle frontal fissures; in the temporo-sphenoidal lobe the superior and injerior or the first and second temporo-sphenoidal fissures; in the occipital lobe, the transverse and inferior longitudinal fissures. Convolutions. — The convolutions or gyres are the portions of the cerebral surface comprised between the fissures. The arrange- CEREBRUM. 505 ment of the surface is such that only the more superficial portions are visible. The depth of the convolution, the portion bordering the fissure, is concealed from view. Each lobe presents a series of such convolutions, which differ considerably in their relative physiologic importance. The Frontal Lobe. — The frontal lobe presents on its convex surface four convolutions: viz., the anterior or pre-central convolution, and the superior, middle, and inferior frontal convolutions. 1. The anterior or pre-central convohition is situated just in front of the Rolandic or central fissure, with which it corresponds in direction. It is continuous above with the superior frontal and below with the inferior frontal convolution. 2. The superior jrontal convolution is bounded internally by the longitudinal fissure and externally by the superior frontal fissure. From the upper end of the pre-central convolution, with which it is continuous, it runs forward and downward to the anterior extremity of the frontal lobe, where it turns backward and rests on the orbital plate of the frontal bone. 3. The middle jrontal convolution is situated on the side of the lobe, between the superior frontal fissure above and the middle frontal fissure below. Its general direction is downward and forward. 4. The inferior jrontal convohition winds around the ascending branch of the fissure of Sylvius in the anterior and inferior por- tion of the cerebrum. It is continuous posteriorly with the lower end of the pre-central convolution. The Parietal Lobe. — The parietal lobe presents three well- marked convolutions: viz., the posterior or post-central convolution, and the superior and inferior parietal. 1. The posterior or post-central convolution is situated just behind the Rolandic or central fissure, with which it corresponds in direction. Above, it is continuous with the superior parietal convolution; below, with the inferior parietal and the pre-central convolutions. 2. The superior parietal convolution is bounded internally by the longitudinal fissure and externally by the intra-parietal fissure. From the upper end of the post-central convolution, with which it is connected, it runs downward and backward as far as the parieto-occipital fissure. 3. The inferior parietal convolution is connected anteriorly with the post-central convolution. Passing backward, it winds around the superior extremity of the fissure of Sylvius, in which situa- tion it is known as the supra-marginal convolution. Beyond this point it divides into two portions, one of which runs forward into the temporal lobe above the first temporal fissure, while the other runs downward and backward, following the intra- 5o6 TEXT-BOOK OF PHYSIOLOGY. parietal fissure to its termination. At this point it makes a sharp bend and runs forward into the temporal lobe just beneath the first temporal fissure. In the neighborhood of the bend it is generally known as the angular convolution or gyrus. The Temporo-sphenoidal Lobe. — The temporo-sphenoidal lobe presents on its external surface three well-marked convolutions: viz.,- the superior, the middle, and the inferior temporal, separated by the first and second temporal fissures. These three convolutions are in a general way parallel with each other, and pursue a direction from before backward and upward. Anteriorly, they are fused to- gether, but posteriorly their connections are somewhat different. The superior temporal is continuous behind and above with the supra-marginal convolution, and behind and below with the angular convolution or gyre. The middle temporal blends with the preceding and with the middle occipital. The inferior temporal is continuous with the inferior occipital. The Occipital Lobe. — The occipital lobe is triangular in shape and forms the posterior apex of the hemisphere. Its base on the external surface is formed by an imaginary line drawn from the parieto-occipital fissure to the pre-occipital notch on the inferior and lateral border. The external surface presents three convolutions — the superior, middle, and inferior occipital. The inner or mesial surface of the hemisphere, formed in part by the frontal, the parietal, the occipital, and the temporal lobes, pre- sents several convolutions of much physiologic interest, viz. : 1. The gyrus fornicatus, situated between the calloso-marginal fissure and the corpus callosum. From its origin anteriorly at the base of the brain this convolution passes backward, gradually increasing in width as it approaches the posterior extremity of the corpus callosum. At this point it again narrows and descends between the calcarine and hippocampal fissures to blend with the hippocampal convolution. 2. The gyrus hippocampus, formed by the union of the posterior extremity of the gyrus fornicatus and the median occipito-tem- poral convolution (the Hngual lobule), is situated just below the dentate or hippocampal fissure. Anteriorly it becomes enlarged, and just behind the apex of the temporal lobe turns backward and inward to form a hook-shaped eminence, the uncinate gyrus or uncus. The limbic lobe is the name given to an area of the brain which includes, among other structures, the gyrus fornicatus, the gyrus hippocampus, and the uncus. As forming a part of this general lobe may be mentioned the dentate fascia, the striae and peduncle of the corpus callosum, the septum lucidum, the fornix, and the infracallosal gyrus. CEREBRUINI. 507 3. The temporo-occipiial gyrus is bounded by the cohateral fissure above, and its inferior border extends from the occipital lobe to the anterior pole of the temporal lobe. 4. The quadrate lobule, a square-shaped convolution, is situated between the posterior termination of the calloso-marginal fis- sure and the parieto-occipital fissure. It blends with the gyrus fornicatus, on the one hand, and with the parietal lobule on the other. 5. The ameiis, a triangular or wedge-shaped convolution or lobule, is situated on the mesial surface of the occipital lobe between the parieto-occipital and calcarine fissures. The Insula or Island of Reil. — This anatomic structure con- sists of a triangular shaped cluster of six small convolutions situated at the bifurcation of the Sylvian fissure and concealed from view by the convolutions bordering it, spoken of collectively as the oper- culum. These convolutions are connected with the frontal, the parietal, and the temporal lobes. Structure of the Gray Matter or the Cortex. — The gray matter, the cortex of the cerebrum, varies from two to four millimeters in thickness. When examined with a lens of low power, it presents a laminated appearance, due to differences in color and arrangement of its constituent elements. With higher magnification the cortex is seen to consist of neuroglia cells, nerve-cells with specialized dendrites and axons, medullated and non-medullated nerve-fibers, blood-vessels, connective tissue, etc., — all of which are arranged and interblended in a most intricate manner. Notwithstanding the com- plexity of its structure, modern histologic methods have enabled Cajal to divide it into four fairly distinct layers or zones, from without inward, as follows (Fig. 222): 1. The Molecular Layer. — The most superficial portion of this layer consists mainly of neuroglia or glia cells, the processes of which interlace in all directions, forming a distinct sheath just beneath the pia. The deeper portions of this layer contain a specialized type of nerve-cell (Cajal cells), of which there are several varie- ties. These cells give off nerve-fibers which pursue a horizontal direction for a variable distance, but in their course give off collateral branches which ascend to the outer surface of the layer. Among these structures are to be found, also, dendritic processes of cells situated in the subjacent layer. The terminal filaments of medullated nerve-fibers coming from nerve-cells in lower regions of the encephalo-spinal axis are also present, but for the most part they pursue a tangential direction. 2. The Layer 0} Small Pyramidal Cells. — This layer consists mainly of nerve-cells, the majority of which are pyramidal in shape and of small size. Other cells, however, are present, which 5o8 TEXT-BOOK OF PHYSIOLOGY. present a variety of shapes, for which reason the layer was at one time termed the ambiguous layer. The apical process of the pyramidal cells is broad at the base, but narrows rapidly as it passes upward. It frequently divides into several branches, each of which develops club- shaped processes or gemmules, which give to it a feathery appear- ance. Dendrites are also given off from the sides and base of the cell-body. From the base a single axon descends which ulti- mately becomes the axis-cylinder of a medullated nerve. The Layer of Large Pyramidal Cells. — The nerve-cells of this layer, as the name implies, are also pyramidal in shape, but of large size. Each cell presents the same features as the cells of the preceding layer, with the exception that the apical process is larger, better developed, and branches more freely. All the dendrites are extensively provided with gemmules. The axon is well developed, sharply defined, and smooth. After giving off collateral branches, the axon descends into the cerebrum and becomes a medullated nerve-fiber. The Layer of Polymorphous Cells. — In this layer the nerve-cells pre- sent a variety of forms: e. g., spindle, polygonal, pyramidal, etc. The spindle form is the most common. From either end of the spindle a large dendrite emerges which soon branches and becomes gemmulated. The axon is well defined and it soon descends into the white matter. The Number of Cortical Cells. — x-Yttempts have been made by various histologists to estimate the total number of functional nerve- cells in the cerebral cortex of man. Though the estimates are widely different, the lowest presents numbers which are beyond compre- FiG. 222. — Section of the Cere- bral Cortex (Motor Area) OF Child, Stained by GoLGi's Silver Method. A. Layer of neuroglia cells. B. Layer of small pyramidal ganglion cells. C. Layer of large pyramidal cells. D. Layer of irregular smaller cells.— {Pier sol.) CEREBRUM 509 hension. Thus, Meynert's estimate is 612 millions; Donaldson's 1200 millions; while Thompson's is 9200 millions. Structure of the White Matter.— The white matter of the cerebrum consists of meduUated nerve-fibers which, though in- tricately arranged, may be divided into three systems: viz., the commissural, the association, and the projection. 1. The commissural system. The fibers which compose this system unite corresponding areas of the cortex of each hemisphere. The fibers from the frontal, parietal, and occipital lobes cross in the median line and form a band of transversely arranged fibers, the corpus callosum. The fibers which unite the corre- sponding areas of the temporo-sphenoid lobes cross in the anterior commissure. All the commissural fibers are the axons of nerve-cells in the cortex, the terminals of which are to be found in the cortex of the opposite side. 2. The association system. The fibers w^hich compose this system unite neighboring as well as distant parts of the same hemi- sphere, and may therefore be divided into long and short fibers. They associate the inexcitable or association areas with the excitable or projection areas. 3. The projection system. The fibers composing this system unite certain areas of the cortex of the cerebrum with the basal ganglia, the pons, medulla oblongata, and spinal cord. They may be divided into: (i) afferent fibers which have their origin in the lower nerve-centers at different levels and thence pass to the cortex; and (2) efferent fibers which have their origin in the cortex and thence pass to the lower nerve-centers, terminating at different levels. The former are also termed the cortico- afjerent or cortico- petal; the latter, cortico-efjerent or cortico-jugal. The afjereiit fibers, the so-called sensor tract, which transmit nerve impulses coming from the general periphery and the_ sense- organs, pass through the tegmentum as the mesial and lateral fillets, and thence to the cortex directly by way of the internal capsule, or indirectly through the intermediation of the thalamic and subthalamic nuclei. The distribution of these fibers to the various areas of the cortex will be found in following paragraphs. The efferent fibers of the so-called motor tract which transmit motor or volitional nerve impulses from the cortex to the pons, medulla, and spinal cord, emerge from the layer of pyramidal cells of the gray matter of the anterior or the pre-central convolution, the paracentral lobule and immediately adjacent areas. From this origin the axons descend through the white matter of the corona radiata, converging toward the internal capsule, into and through which they pass, occupying the anterior two-thirds of the posterior limb or segment. Beyond the capsule they continue to descend, 5IO TEXT-BOOK OF PHYSIOLOGY. occupying the middle three-fifths of the pes or crusta of the crus cerebri, the ventral portion of the pons, and eventually the anterior pyramid of the medulla oblongata. At this point the tract divides into two portions, viz. : 1. A large portion, containing from ninety-one to ninety-seven per cent, of the libers, which decussates at the lower border of the medulla and passes down the lateral column of the cord, con- stituting the crossed pyramidal tract. 2. A small portion, containing from three to nine per cent, of the fibers, which does not decussate at the medulla, but passes down the inner side of the anterior column of the same side, constituting the direct pyramidal tract or column of Tiirck. After passing through the internal capsule, and as it descends through the crus, pons, and medulla, the cortico-efferent tract gives off a number of fibers which cross the median line and arborize around the nerve-cells in the gray matter beneath the aqueduct of Sylvius (the nuclei of origin of the third and fourth cranial nerves), and around the nerve-cells in the gray matter beneath the floor of the fourth ventricle (the nuclei of origin of the remainder of the motor cranial nerves). The remaining fibers go to form the crossed and direct pyramidal tracts and arborize around the cells in the anterior horn of the gray matter of the opposite side of the cord at successive levels. By this means the cortex is brought into anatomic and phys- iologic relation with the general musculature of the body through the various cranial and spinal motor nerves, (See Fig. 210, page 481.) The jronto-cerehellar and the occipito-temporo-cerebellar tracts are also efferent tracts and parts of the projection system. The fronto-cerebellar, originating in the nerve-cells of the cortex of the frontal lobe, passes clown to and through the internal capsule, occupy- ing the anterior one-third of the anterior segment. It then descends along the inner side of the crus cerebri to the pons, where its fibers arborize around the cells of the nucleus pontis. Through the inter- mediation of these cells this tract is brought into relation with the cerebellum of the same but chiefly of the opposite side. The occipito- temporal tract, originating in the cells of the cortex of both the occipital and temporal lobes, passes downward and inward toward the lenticular nucleus, beneath which it passes to enter the outer one-fifth of the crusta. It then enters the pons, and through the nucleus pontis also comes into relation with the cerebellum of both sides. (See Fig. 217, page 494.) THE FUNCTIONS OF THE CEREBRUM. The functions of the cerebrum comprehend, in man at least, all that pertains to sensation, cognition, feehng, and voHtion. All subjective experiences, which in their totality constitute mind, are CEREBRUM. 511 dependent on and associated with the anatomic integrity and the physiologic activity of the cerebrum and its related sense-organs, the eye, ear, nose, tongue, etc. From an examination of the anatomic development of the brain in different classes of animals, in different men and races of men, and from a study of the pathologic lesions and the results of ex- perimental lesions of the brain, evidence has been obtained which reveals in a striking manner the intimate connection of the cerebrum and all phases of mental activity. 1. Comparative anatomic investigations show that there is a general connection between the size of the brain, its texture, the depth and number of convolutions, and the exhibition of mental power. Throughout the entire animal series an increase in intelhgence goes hand in hand with an increase in the development of the brain. In man there is an enormous increase in size over that of the highest animals, the anthropoid apes. The most culti- vated races of men have the greatest cranial capacity, that of the educated European or American being approximately 92.1 cubic inches (1835 c.c); while that of the Austrahan is but 81.7 cubic inches (1628 c.c). Men distinguished for great mental power usually have large and well developed brains; e.g., that of Cuvier weighed 64.4 ounces (1830 grams); that of Abercrombie, 63 ounces (1786 grams). A large intelligence, however, is not incompatible with a much smaller brain weight; thus, the brain of Helmholtz weighed but 50.8 ounces (1440 grams); that of Leidy, 49.9 ounces (1415 grams); that of Liebig, 47.7 ounces (1352 grams). The average arithmetic brain weight of 96 distinguished men was found to be 51.9 ounces (1473 grams) (Spitzka). 2. Pathologic lesions and mechanic injuries which disorganize the cerebrum are at once followed by a disturbance or an entire suspension of mental activity. Concussion of the brain or sudden compression from a hemorrhage destroys consciousness. Physical and chemic alterations of the gray matter of the cere- brum have been shown to coexist with insanity, loss of memory, of articulate speech, etc. Congenital defects of organization are accompanied by a deficiency in mental capacity and the higher instincts. Under such circumstances no great advance in brain development is possible and the intelligence remains at a low level. In congenital idiocy the brain is small, imperfectly developed, and wanting in proper chemic composition. 3. Experimental lesions of the brain in lowxr animals are attended by results similar to those observed in disease or after injury in man. Removal of the cerebrum in the pigeon completely abolishes intelligence and destroys the capability of performing 512 TEXT-BOOK OF PHYSIOLOGY. volitional movements. The pigeon remains in a state of profound stupor, though retaining the capability of executing reflex or instinctive movements. It can temporarily be aroused by loud noises, light placed before the eyes, pinching of the toes, etc., but it soon relapses into a condition of quietude. Coincident with the destruction of the cerebrum there occurs a loss of memory, reason, and judgment, and the animal fails to associate the impressions with any previous train of ideas. The higher the animal in the scale of development, the more striking is the loss of mentality after removal of the cerebrum. 4. Experimental interference with the blood-supply to the cerebrum is followed by a diminished or complete cessation of its activities. There is perhaps no organ of the body that is so directly depend- ent upon its blood-supply for the continuance of its activities as the cerebrum. The supply of blood is furnished by four large blood-vessels: viz., the two carotid and the two vertebral arteries. These vessels, after entering the cavity of the skull, give off branches which unite to form the "circle of Willis." From this circle, large branches are given off which enter the cerebrum and distribute blood to all its parts. After passing through the capillaries the blood, greatly altered in chemic composition, is returned by large veins. The large volume of blood that is present in the brain and the marked changes in composition that it undergoes while passing through the brain indicate a very active and complex metabolism in this organ. By means of the anatomic arrangement of the blood-vessels at the base of the brain, the blood-supply is equalized. It also explains why, when one, or even two, of the four large vessels are oc- cluded by pathologic deposits or surgical procedures, brain activity continues, though perhaps diminished in degree. Occlu- sion of all four vessels, however, is at onCe followed by a complete abolition of all forms of cerebral activity. An experiment per- formed by Brown-Sequard illustrates the dependence of cerebral activity on the blood-supply. A dog was beheaded at the junction of the neck and chest. After a period of ten minutes all evidences of Hfe had entirely ceased. Four tubes connected with a reservoir of warm defibrinated blood were then connected with the four arteries of the head. By means of a pumping apparatus imitating the action of the heart the blood was driven into and through the brain. After a few minutes cerebral activity returned, as shown by contraction of the muscles of the face and eyes. The character of the contractions were such as to convey the idea that they were directed by the will. These vital manifestations continued for a period of fifteen minutes, when on the cessation of the artificial circulation they disap- THE CEREBRUM. 513 peared, and the head exhibited once again the usual phenomena observed in dying: viz., contraction and then dilatation of the pupils and convulsive movements of the muscles of the face. Localization of Functions in the Cerebrum. — By the term localization of functions is meant the assignment of definite phys- iologic functions to definite anatomic areas of the cerebral cortex. From experiments made on the brains of animals, by the observa- tion and association of chnical symptoms with pathologic lesions of the central nerve system, and from observation of the developmental stages of the embryonic brain, it has been established in recent years : 1. That the general and special sense-organs of the body are as- sociated through afferent nerve-tracts with definite though per- haps not sharply delimited areas of the cerebral cortex; and — 2. That certain areas of the cortex are associated through efl'erent nerve-tracts with special groups of skeletal or voluntary muscles. Experimental excitation of a cortical area associated with a sense- organ is undoubtedly attended by the production of a sensation at least similar to that produced by peripheral excitation of the sense- organ itself; destruction of the area is followed by an abolition of all the sensations associated with the sense-organ. For these reasons such areas are termed sensor. Excitation of a cortical area associated with a group of skeletal muscles is attended by their contraction; destruction of the area is followed by their relaxation or paralysis. For these reasons such areas are termed motor. Since the sense-organs are remote from the brain and the impres- sions made upon them by the objective world can be utilized by the mind, only after they have been reproduced in the cortical areas, it may be said that each sense-organ has its special area in the cortex by which it is represented, or, in other words, each sense-organ has a cortical area of representation. Since the muscles are remote from the brain and since they contract in response to the discharge of nerve impulses from the cells of the cortical motor areas, it may be said that the activities of the motor areas are represented by the contractions of the muscles; in other words, that the cortical motor areas have areas of representa- tion in the general skeletal musculature. It is usually stated, how- ever, in the reverse way: viz., that the muscle movements have areas of representation in the cortex. The cortex of the cerebrum may therefore be compared to a mosaic made up, partially at least, of sensor and motor areas which respectively represent sense organs and motor organs, and which bear a deiinite anatomic and physiologic relation one to the other. Their cooperation is essential to the normal performance of all forms of cerebral activity. 514 TEXT-BOOK OF PHYSIOLOGY. A knowledge of the situation of these areas, the order of their development, the effects that arise from their stimulation or follow their destruction, are matters of the highest importance in the study of cerebral activity and indispensable to the physician in the localiza- tion of lesions which manifest themselves in perversions or aboHtion of sensations and in convulsive seizures or paralyses. The Sensor Areas. — The sensor areas which should theoret- ically be present in the cortex are primarily those which receive and translate into conscious sensations nerve impulses, developed by changes going on in the body itself; and secondarily those which receive and translate into conscious sensations the nerve impulses developed in the special sense-organs by the impact of the external or objective world. In the former areas, are received the nerve im- pulses that come from the skin, mucous membranes, muscles, viscera, etc., and give rise to cutaneous, muscle, and visceral sensations. In the latter are received the nerve impulses that come from the sense- organs and give rise to tactile, gustatory, olfactory, auditory, and visual sensations. A number of such sense areas may be predicated : e. g., areas of cutaneous and muscle sensibility, of gustatory, olfactory, auditory, and visual sensibility. The Motor Areas. — The motor areas which should theoretically be present in the cortex are those which in consequence of the dis- charge of nerve impulses excite contraction of special groups of muscles and which, from their coordinate and purposive character, are conventionally termed vohtional. Five such general motor areas may be predicated: e. g., one for the muscles of the head and eyes, one for the muscles of the face and associated organs, and areas for the muscles of the arm, leg, and trunk. They are usually designated as head and eye, face, arm, leg, and trunk motor areas. The existence and anatomic location of these areas in the cortex of animals have been determined by the employment of two methods of experimentation: viz., stimulation and destruction or extirpation; the first by means of the rapidly repeated induced electric currents, the second by the electric cautery and the knife. If the stimulation or excitation of any given area is followed by contraction and its destruction by paralysis of muscles, it is assumed that the area is motor in function — is a center of motion. If the stimulation of a given area is attended by phenomena which indicate that the animal is experiencing sensation, and its destruction by a loss of this capability or the loss of a special sense, it is assumed that the area is sensor in function — is an area of special sense. The animals generally employed for experiments of this character are dogs and monkeys, though other animals have frequently been employed by different investigators. Of all animals, the monkey is the most fre- quently selected, as the configuration of the brain in its general out- THE CEREBRUM. 515 lines more closely resembles that of man than does the brain of any other animal. The results therefore which are obtained, there is every reason to believe, are the results, in their general outlines, that would follow stimulation of the human brain if this were possible under the same conditions. Indeed, the clinical symptoms which arise during the development of pathologic processes, and the phenomena which occur during surgical procedures for the removal of growths and pathologic cortical areas, justify the conclusion that the chart of the motor and sensor areas of the monkey brain may be transferred to the human brain without introducing any serious errors. The Sensor Areas of the Monkey Brain. — From experiments made on the brains of monkeys, Fcrrier, Schafer, Horsley, and many Fig. 223. — Diagram of the Motor and Sensor Areas on the Lateral Sur- face OF the Monkey Brain. — (After Horsley and Schafer.) Others have mapped out, though not with a high degree of definite- ness and certainty, the sensor areas, stimulation of which gives rise to sensation, destruction to loss of sensation. A diagrammatic repre- sentation of these areas is shown in Fig. 223 and Fig. 224. The tactile area or area of tactile perception has not been accu; rately or definitely located. Ferrier assigned it to the hippocampal region. Schafer and Horsley assigned it to the limbic lobe, and especially to that portion known as the gyrus fornicatus, as destruction of this convolution was followed by hemianesthesia of the opposite side of the body which was more or less marked and persistent. These observers conclude that the limbic lobe "is largely if not exclusively concerned in the appreciation of sensation, painful and 5i6 TEXT-BOOK OF PHYSIOLOGY. tactile." Other experimenters question this conclusion and locate the area near to, if not within, the Rolandic area. The difference of opinion regarding the location and probable limitation of the area of tactile sensibility renders necessary additional and more conclusive experiments. The olfactory and gustatory areas or areas oj oljactory and gusta- tory perception have been located in the uncinate gyrus and the adjacent region, though their exact limits have not been determined by the experiments thus far performed. The auditory area or area of auditory perception was located by Ferrier in the upper two-thirds of the superior tcmporo-sphenoidal Fig. 224. — Diagram of the Motor and Sensor Areas on the Mesial Sur- face OF THE Monkey Brain. — {Ajter Horsley and Sckdjer.) convolution. Bilateral cauterization of this region gave rise to com- plete deafness, which endured to the time of the animal's death, more than a year later. Unilateral destruction of this region gave rise to deafness in the opposite ear only. The results of experiments made subsequently by other observers would indicate that the audi- tory area is somewhat more extended than that designated by Ferrier, as apparently animals recovered their hearing, to some extent at least, after complete recovery from the operation. The limit or extension of the area is, however, unceitain. The visual area or area of visual perception has been located in the occipital lobe, though in this, as in the previous instances, its exact limits have not been positively determined Experimenters also are not in accord as to the relative functions of its different parts. THE CEREBRUM. 517 Ferrier located this area in the occipital lobe and that adjacent por- tion of the parietal lobe on the outer surface known as the angular gyrus. He found that extirpation of the angular gyrus alone was followed by a temporary blindness of the opposite eye, which was, however, not hemiopic in character.* He also found that destruction of the occipital lobe together with the angular gyrus gave rise to a more or less enduring hemianopsia, in addition to the transient blindness of the opposite eye. From these and similar facts he con- cluded that the angular gyrus is the area of representation for the macular or central region of the retina, and the occipital lobe for the corresponding halves of the peripheral portions of the retina. It was, however, found by Munk, Schafer, and others that the angular gyrus was not concerned in any way with vision; that extir- pation of the occipital lobe alone, especially if the line of division be carried a little further forward on the mesial and inferior sur- faces, was followed by homonymous hemiopia (loss of retinal func- tion on the same side), and therefore homonymous hemianopsia. Additional experiments lead to the conclusion that the area for macular vision is near the anterior extremity of the calcarine fissure, while the area for peripheral vision is in the posterior portion of the mesial surface and for a variable distance on the outer surface. Moreover, there is reason to believe that the area for macular vision is in relation with homonymous halves of the two macules lutese. The supposed error, the assignment of macular vision to the angular gyrus, has been attributed to destruction of the fibers of the optic radiation, which in their course to the occipital lobe pass close to this gyrus. The Motor Areas of the Monkey Brain. — From experiments made on the brains of monkeys Ferrier mapped out a number of * In a consideration of this subject certain facts connected with visual perception, both in physiologic and pathologic conditions, must be kept in mind. Thus, visual sensation may arise from stimulation of either the central portion, the macula, or the peripheral portion of the retina or both. In the first instance the vision is termed central or macular; in the second instance, peripheral or retinal. Macular vision is clear, sharp, and distinct; retinal vision progressively indistinct from the center toward the periphery. Division of one optic tract is followed, in consequence of the partial decussation of the optic nerve-fibers at the chiasma, by a loss of function in the outer two-thirds of the retina of the same side, both in the central (macular) as well as in its peripheral portions, and the inner one-third of the retina of the oppo- site side. To this condition the term hemiopia has been apphed. .A.s a result of this want of functional activity of these retinal portions on the side of the lesion, rays of light emanating from olDJects situated in the opposite side of the field of vision will not be perceived when both eyes are directed to the fLxation point. To this "blind- ness" in the opposite half of the field of vision the name hemianopsia is given. In the lesion under consideration (di\asion of one optic tract) the hemianopsia is bilateral, and as it affects the corresponding portions associated in normal vision it is of the homonymous variety. Division of the right optic tract is followed by left lateral homon- ymous hemia>iopsia, indicative of the fact that objects in the field of vision to the left of the binocular fixation point are invisible. 5i8 TEXT-BOOK OF PHYSIOLOGY. areas stimulation of which gives rise to muscle contractions on the opposite side of the body which are so purposive and coordinate in character that they may be regarded as identical with those produced volitionallv. Destruction of these areas is followed by paralysis. The results of Ferrier's earlier work are represented in Fig. 225, the descrip- tive text to which renders them intelhgible. In a general way it may be said that the upper third of the anterior and pos- terior central convolu- tions presides over the movements of the leg of the opposite side of the body; the middle third over the movements of t h e arm ; the inferior third over the move- ments of the face and tongue. Collectively these areas are known as the motor area or motor zone; and as it is ranged along the Rolandic fis- sure, it is sometimes termed the Rolandic. area. The experiments of Horsley and Schafer added additional facts and enabled them to con- struct a new diagramma- tic representation of the motor area and more accurately define the special areas upon the lateral and mesial as- pects of the brain of the monkey. The bound- aries of the general and special areas, as deter- mined by these observers, will be readily apparent from an examina- tion of Fig. 223. Their experiments have enabled them also to subdivide the general into special areas as follows: I. The head area or area for visual direction into areas excitation of which causes "opening of the eyes, dilatation of the pupils and Fig. 225. — Left Hemisphere or Monkey, Show- ing Details of Motor Areas Indicated by THE Movements Following Stimulation of: I. Superior parietal lobule; exciting ad- vance of the hind limb. 2. Top of ascending frontal and parietal convolutions; flexion and outward rotation of thigh; flexion of toes. _ 3. On ascending frontal convolution near semilu- nar sulcus; movements of hind limb, tail and extremity of trunk. 4. On adjacent margins of ascending frontal and parietal convolution; adduction and extension of arm, pronation of hand. 5. Top of ascending frontal near supe- rior frontal convolution; forward extension of arm. a, b, c, d. On ascending parietal; move- ments of various muscles of the forearm. 6. Ascending frontal convolution; flexion of forearm and supination of hand which is brought toward mouth. 7. Retraction and elevation of corner of mouth. 8. Elevation of nose and lip. q and 10. Opening mouth and motions of tongue. 11. Retraction of angle of mouth. 12. Middle and superior frontal convolutions; movements of head and eyelids. 13 and 13'. Anterior and posterior limbs of angular gyrus; movements of eyeballs. 14. Superior temporo-sphenoidal convolution, ear pricked and head moved. 15. Movement of lip and nostril. — {Ferrier.) THE CEREBRUM. 519 turning the head to the opposite side with conjugate deviation of the eyes to that side." 2. The leg area may be subdivided into (a) an area both on the lateral and mesial surfaces which presides over the movements of the hip and thigh; {h) an area in the posterior part which presides over the movements of the legs and toes; (c) an area in the paracentral lobule for the movements of the hallux or great toe. 3. The trunk area, situated largely on the mesial surface, may be subdivided into an anterior and a posterior area, which respec- tively preside over the movements of the spinal column as arch- ing and rotation, and the movements of the pelvis and tail. 4. The arm area may be subdivided as follows: {a) an area supe- riorly which controls the movements of the shoulder; {h) an area posteriorly and below this, which controls the movements of the elbow; (c) an area anteriorly and below the preceding, govern- ing the movements of the wrist and lingers; {d) an area pos- teriorly and below governing the movements of the thumb. 5. The jace area may be divided into an upper part, comprising about one-third, and a lower part, comprising the remaining two-thirds. In the upper part are areas governing the move- ments of the opposite angle of the mouth and of the lower face. In the lower part anteriorly there is an area governing the move- ments of the vocal membranes or bands (the laryngeal area); posteriorly areas governing the opening and closing of the mouth, the protrusion and retraction of the tongue. Electric stimulation of the sensor areas is attended by certain motor reactions which vary in accordance with the area stimulated. Thus, when the electrodes are applied to different portions of the occipital lobe the eyeballs are conjugately turned upward, dow^nward, or laterally and to the opposite side; when placed on the upper por- tion of the superior temporal convolution, the ear is pricked up or retracted, the head is turned to the opposite side and the pupils are dilated ; when placed on the hippocampal convolution, there is movement of torsion of the nostril and lips of the same side. Ferrier assumed that these movements were the result of the origination of subjective 'sensations and not an evidence that the area in question is a motor area, in the sense that this term is applied to the areas of the Rolandic region, especially as their destruction is not followed by paralysis of any of the corresponding muscles. This interpretation is supported by the experiments of Schafer, which showed that the contraction of the eye-muscles which followed stimulation of the occipital lobe took place between 0.2 and 0.3 second later than when the frontal lobe was stimulated; and that as the motor reaction takes place after extirpation of the frontal region. 520 TEXT-BOOK OF PHYSIOLOGY. the route of the efferent impulse cannot be to and through the frontal lobe, but probably through some lower center. The same facts hold true for the reactions of the ear-muscles following stimu- lation of the temporal lobe. The view that the cortex of the cerebrum can be divided into separate and independent though physiologically related motor and sensor areas has been questioned in recent years, and a somewhat different interpretation given to the facts. It is believed by many physiologists and neurologists that the so-called motor and sensor areas are so closely related that it is almost impossible to distinguish one from the other either anatomically or physiologically. Thus the Rolandic region is believed to be both motor and sensor in function, the former, however, being more predominant in the pre-central, the latter in the post-central, convolution. As these two functions are so intimately blended and their anatomic substrata so difficult of separation, it is thought the term sensori-motor should be em- ployed as more descriptive and more in accordance with the facts to the entire Rolandic region. This view has been strengthened by the results of the embryo- logic investigation of Flechig, which show that different nerve-tracts become medullated or receive their myelin investment at successively later periods and that the tracts which first become myelinated and are hence first functionally active, belong to the afferent system. Among the first to undergo myelinization are three tracts numbered by Flechsig i, 2, and 3, which arise largely from the median nucleus of the thalamus and the medial lemniscus and pass to the anterior and posterior convolutions, to the para-central lobule and foot of the superior frontal convolution, and to the foot of the third frontal convolution respectively. It is these fibers which convey nerve im- pulses to the cortex and furnish information regarding changes taking place in the body itself and thus lead to the performance of muscle movements. This area is therefore primarily a sensor area, an area for body-feelings, cutaneous, tactile, muscle, and visceral, and second- arily a motor area. The afferent fibers to this region become mye- linated during the ninth month of intra-uterine life, the efferent fibers from it become mvelinated during the third month of extra-uterine hfe. By the same method of reasoning the gustatory, olfactory, audi- tory, and visual sense areas are to be regarded as sensori-motor in character, for embryologic investigations show that subsequently to the myelinization of the afferent tracts connecting the sense-organs with the cortex, efferent nerve-tracts arise from or near to the same centers and undergo myehnization. In other words, these areas are primarily sensor and secondarily motor, and therefore should be termed sensori-motor. In Flechsig's own terminology THE CEREBRUM. 521 each cortico-petal or afferent tract is accompanied by a cortico-fugal or efferent tract. In this view sensations, or the mental processes the outcome of sensations, are the immediate cause of the movements of the mus- cles connected with both the sense-organs and skeletal structures. Though this interpretation — viz., the coincidence of sensor and motor areas — appears more in accordance with the facts than the earlier view, it must be admitted that there are many facts both of a physiologic and pathologic character which it is difficult to har- monize with it. The Motor Area of the Chimpanzee Brain. — In a series of experiments made by Sherrington and Griinbaum on the brain of the chimpanzee it was discovered that the so-called motor area was not so widely distributed as in the monkeys generally, but was confined almost exclusively to the convolution just in front of the fissure of Rolando, as it was impossible to obtain any movement on direct stimulation of the convolution just behind it. All points on the surface of the pre-central convolution, including the portion forming the wall of the Rolandic fissure itself, were found to be excitable and productive of movement when stimulated. The sequence of representation from below upward is similar to that observed in the monkey. One pecuharity, however, was the location of the area for conjugate deviation of the eyeballs to the opposite side. This is situated far forward in the middle and inferior frontal convolutions, and separated from the areas in the pre-central convolution by a region apparently inexcitable. These facts are of great interest and value in the assignment of the motor areas in the cortex of the human brain, as in its development and configuration the chimpanzee brain more closely resembles the human brain than does the monkey's. The Localization of Sensor and Motor Areas in the Human Brain. — The observation of chnical symptoms and their interpreta- tion by postmortem findings, the phenomena observed during surgical procedures, and the results of embryologic investigations, point to the conclusion that corresponding areas both for sensations and move- ments exist in the cerebral cortex of the human brain, though it is probable that their locations do not in all respects coincide with those characteristic of the monkey or even the ape brain. In the fol- lowing diagrams (Figs. 226 and 227), the sensor and motor areas are at least provisionally located, in accordance with recent obser- vations. They are represented as limited or bounded by a serrated line to indicate, as suggested by Mills, that they are not sharply defined, but that they interfuse or interdigitate with surrounding regions. The Sensor Areas. — The sensor areas occupy regions corre- sponding in a general way with those of the monkey brain. 522 TEXT-BOOK OF PHYSIOLOGY. The cutaneous and muscle sense areas have been assigned to the post-central, a portion of the superior and inferior parietal convolu- tions on the lateral aspect, and to portions of the frontal convolution and of the gyrus fornicatus on the mesial aspect. It is also probable that the tactile (cutaneous) area may be assigned, though in less degree, to the pre-central convolution, the general motor area. This is in accordance with the embryologic investigations of Flechsig, who concludes that the entire Rolandic region is to be regarded as sensor as well as motor in function, and names it the area of body feelings, or the somesthetic area. CONCRtTE CONCEPT Fig. 226. — The Areas and Centers of the Lateral Aspect of the Human Hemi-cerebrum. — (C. A'. Mills.) The clinical and postmortem evidence as to the extent of the area of tactile sensibility and its coincidence with the motor area is somewhat contradictory, and in some respects apparently in opposi- tion to the view of Flechsig. Thus, Dr. C. K. Mills, whose skill in interpreting the phenomena of disease is well known, states in this con- nection in his work on nervous diseases that " innumerable cases have been reported of lesions of the motor cortex without the shghtest impairment of sensibility." In several cases of excision of the human cortex in the Rolandic region by surgical operations careful studies of the patients failed to show any impairment of sensation. Other competent observers, however, have reported a number of cases in THE CEREBRUM. 523 which anesthesia more or less pronounced and persistent has accom- pan ed lesions of the motor area. The explanation of these contra- dictory observations is not apparent. The olfactory area has been assigned to the uncinate convolution, the anterior part of the gyrus fornicatus, and the posterior part of the base of the frontal lobe. Lesions in this region are frequently accompanied by subjective olfactory sensations. The gustatory area has been assigned to the fourth temporal convolution. The auditory area has been assigned to the posterior portion of the superior temporal convolution and to the retro-insular convolu- tions, the island of Reil. Unilateral destruction of this region is followed by only a partial loss of hearing in the opposite ear (owing to the partial decussation of the cochlear nerve), which, however, may be recovered from after a time, owing probably to a compensatory activity of the insular convolutions. Bilateral disease of this region is followed by complete deafness. Within this area there is a smaller region, disease of which is accompanied by word-deajness only, the patient being unable to distinguish the tone intervals between words and syllables and therefore hearing only confused noises. Object hearing has also a separate area of representation. The visual area has been assigned to a triangular shaped area on the mesial surface of the occipital lobe, which includes the gray matter above and below the calcarine fissure (the cuneus and upper part of the lingual lobe), and to the gray matter of the first occipital convo- lution on the lateral aspect of the occipital lobe. Focal lesions of this area on one side are followed by lateral homonymous hemianopsia, which, however, does not involve, as a rule, the fovea or macula. It is, therefore, the area of homonymous half-retinal representation. The location of the area for macular or central vision is uncertain. Henschen locates it in the anterior part of the area near the ex- tremity of the calcarine fissure, and asserts that in each area both maculae are represented. From experiments made on monkeys Schafer locates it in the same region. Beyond the limits of this visual area and on the lateral aspect of the parietal lobe there is a region (the supra-marginal convolution and angular gyrus) in which impressions of words and letters seen have their representation. Destruction of this area by diseases is follow^ed by word- and per- haps letter-blindness, the patient being unable to recognize words and letters seen because of failure to revive the memory images of words and letters. The areas for visual sensations and optic memory pictures are therefore separate, a fact w-hich has led to a division of the visual area into a lower and a higher area. It was stated in a previous paragraph that electric stimulation of the sensor areas of the monkey brain is attended by certain motor 524 TEXT-BOOK OF PHYSIOLOGY. reactions which vary with the area stimulated. Corresponding areas are beheved to be present in the human brain and that their stimula- tion would be followed by similar motor reactions. Their location is shown in Figs. 226 and 227, and named visual, auditory, olfactory, and gustatory motor. The stereognostic area or area of stereognostic perception, by which objects are recognized through their form independent of vision and by the sense of touch alone, has been located in the superior parietal convolution and the precuneus (Mills). The existence of such an area is rendered probable by the fact that cases have been recorded in which there was a loss of this power (astereognosis) unaccompanied Fig. 227. — The Areas and Centers of the Mesial Aspect of the Human Hemi-cerebrum. — (C. K. Mills.) by either sensor or motor disturbances. Postmortem investigations showed that in these cases there was a destruction of the superior parietal convolution. Equilibratory, intonation, and orientation areas have been pro- visionally located in the sphenotemporal lobe. The Motor Area. — The general motor area (Fig. 226) is repre- sented as occupying the pre-central convolution, the base of the first convolution, both on its lateral and mesial aspects, and the paracentral lobule. The exclusion of the post-central convolution from the motor area is in accordance with the embryologic researches of Flechsig, which indicate that the efferent fibers which compose the pyramidal tract come from the region anterior to the central fissure, and with the THE CEREBRUM. 525 experiments of Sherrington and Grlinbaum on the brain of the chim- panzee, which demonstrate that the post-central convolution is absolutely inexcitable to electric stimulation. It is quite probable that with the growth of the brain in size and complexity, the motor area has come to occupy a position somewhat farther forward in the human brain than in the monkey brain. This general area is also capable of subdivision into areas of variable size, in which the movements of the face and associated structures, the head and eyes, the arm, trunk, and leg, are represented. The sequence of their representation from below upward is similar to that observed in the monkey and chimpanzee. A localized irritative lesion of any one of these areas gives rise to convulsive movements of the muscles of the opposite side of the body, similar in character to those resulting from electric stimulation of the corresponding areas of the monkey and ape brains. Destruction of these areas from the growth of tumors, softening, etc., is followed by paralysis of the muscles. Electric stimulation of the human brain for the purpose of localizing obscure irritative lesions prior to surgical procedures on the brain gives rise to the same convulsive movements. Language. — The succession of motor acts by which ideas are expressed, is known as language, which may be divided into (i) articulate or spoken, and (2) written. The expression of ideas both by words and signs depends primarily on the power of reviving the images or memories of words and letters heard and seen; and secondarily on the power of reviving the images or memories of the muscle movements which were previously em- ployed in an eflPort to imitate or reproduce the words (speech) or the verbal signs (writing). Clinico-pathologic investigations have shown that words and letters heard and seen have areas of representation in the cortex, the former in the general auditory area, the latter in the supra-marginal convolution and angular gyrus (Fig. 226). Destruction of these areas is followed by word-deafness and word-blindness respectively. The same methods of investigation have shown that the muscle movements employed to reproduce the words and the verbal signs also have areas of representation in the cortex; the former in the third frontal convolution (Fig. 226), and probably in the adjacent region, the island of Reil, on the left side in the great majority of people ; the latter in front of the arm region of the general motor area. Destruction of these areas is followed in the first instance by a loss of the power of executing the movements of the muscles employed in speech, and in the second instance, of those employed in writing. These different areas are connected with one another by associa- tion fibers, and, taken collectively, constitute the language zone. Their situation and relations are shown in Fisj. 228. In this figure TEXT-BOOK OF PHYSIOLOGY. the dotted lines coming from the ear (a) and the eye (v) represent the auditory and visual tracts through which nerve impulses pass to the auditory (A) and the visual centers (V) respectively. Similar lines coming from the muscles involved in speech and writing might also be represented to indicate the paths of the nerve impulses to the motor speech (M) and the motor writing center (E). The continuous lines on the surface of the cortex represent nerve-fibers which associate the auditory and visual centers with the speech and writing centers and with higher psychic centers (O O) as well. The dotted Unes coming from the speech and writing centers represent the tracts through which nerve impulses pass to the muscle of the larynx, tongue, mouth, and hps, and to the muscles of the hand. The anatomic and physiologic association of the various areas is essential to the registration of the impressions made on the ear and eye and for the expression of the ideas evolved from them by words (speech) and signs (writing). Their collective action is essential to the acquisition of language. Destruction of any part of this cerebral mechanism is attended by an impairment or a total loss either in the power of obtaining auditory images of words heard and visual images of words seen, or in the power of expressing ideas by speech and writing. To this pathologic condition the term aphasia has been given. Aphasia. — It was discovered by Bouillaud that a destructive lesion of the third frontal convolution on the left side was accom- panied by a partial or complete loss of the faculty of articulate speech, t'^iG. 228. —Diagram Showing the Relation of the Centers of Language and their Principal Associations. A. Auditory center. V. Visual center. M. Motor speech center. E. Motor writing center. O O. Intellectual center. — (Afier Grasset.) THE CEREBRUM. 527 the power to express ideas with words. To this condition the term aphasia was given. Though of hmited apphcation etymologically, the word is now employed in a wider sense to signify " partial or com- plete loss of the power of expression or comprehension of the con- ventional signs of language, " words either spoken or written, due to lesions of different portions of the cortex, and especially on the left side. Aphasias are of many degrees and kinds, though they may be in- cluded in the two general divisions, motor and sensor. i Motor aphasia may be either ataxic or agraphic. In ataxic aphasia the patient is unable to express or communicate his thoughts by spoken words, owing to an inabihty to execute those movements of the mouth, tongue, etc., necessary for speech without there being any paralysis of these muscles. The lesion is usually in the third frontal convolution and most frequently associated with right hemiplegia. In agraphic aphasia the patient is unable to com- municate his ideas by wTiting through an inability to execute the necessary movements, though retaining his mental processes. In this form of aphasia the lesion is in the writing area. These two forms of motor aphasia are not infrequently associated. Sensor aphasia or amnesia may be either visual or auditory. In visual aphasia or amnesia the patient is unable to recognize a letter or word, printed or written (though capable of seeing other objects), a condition known as letter- or word-blindness. It is usually associated with lesions in the neighborhood of the supra-marginal convolution. In auditory aphasia or amnesia the patient cannot understand articulate or vocal speech, though capable of hearing and understand- ing other sounds, through an inability to distinguish tone intervals of words and letters — a condition known as ivord-deafness. It is associated with lesions of the auditory area. Paraphasia is an inabihty to recall the proper words to associate with ideas and necessary to their expression. Concept aphasia is the inability to recall the names of objects. It is associated with lesions of the cortex of the mid-temporal or third temporal convolution (Mills). This area is known as the concept or naming area. Bilateral Representation. — Though highly speciahzed move- ments, such as those performed by the arms and hands, legs and feet, have their areas of representation on one side of the cerebrum only, and that, opposite to the side of the movement, less highly specialized movements, such as the masticatory, phonatory, respiratory, and various trunkal movements, which require for their performance the cooperation of muscles on both sides of the body, have their areas of representation on both sides of the cerebrum; the area of either side exciting to action the muscles on both sides of the body. 528 TEXT-BOOK OF PHYSIOLOGY. In the case of specialized movements the representation is unilat- eral; in the case of the more general movements the representation is bilateral. Motor and tactile area. Parietal association aren , ,<^ ■—^'^y^ / VV i ^ > ; Frontal association area. Island of Reil. Occipito-temporal association area. .^uditorv area. Motor and tactile area. ^■om^ Parietal association uo (Precuneus). Visual area (cuneus). Occipito-temporal association area. Olfactory lobe. Olfactory tract. ^ Olfactory area. Gyrus hippocampus. Fig. 229. — -Di.^GRAMS to show the Position and the Relation of the Association and Projection Areas. The Projection Areas are Dotted. ^(/l//fr Flechsig.) Association Centers. — The sensor and motor areas to which specific functions have been assigned do not constitute more than one-third of the total cerebral cortex. There yet remain large THE CEREBRUM. 529 regions to which it has not been possible to assign specific functions based on physiologic experiments. Three or four such regions separated by the sensor and motor centers are to be recognized on the lateral and mesial aspects of the hemisphere. In Fig. 229 the location, extent, and names of these regions are represented. The fibers which are found in these regions belong almost exclusively to the association system, and become medullated at a later period than do the fibers of the projection system; moreover, from the method of their medullization it would appear that many of these fibers grow out directly from the sensor centers into these regions and become related to the nerve-cells of their convolutions, while others grow out from adjacent as well as distant convolutions. From histologic and pathologic evidence these regions were termed by Flechsig association centers or areas, implying the idea that through the in- tervention of their cell mechanisms the sense areas are indirectly associated anatomically and physiologically, and together constitute a mechanism by which sensations are associated and elaborated into concrete forms of knowledge or related to definite forms of move- ment. It has been assumed by Flechsig that the frontal association center, from its connections with the sensor and motor areas of the Rolandic region, the olfactory, and perhaps other regions, is engaged in as- sociating and registering body sensations and vohtional acts, and that the knowledge thus gained has reference largely to the personal- ity of the individual; that the par ieto- occipital association area, from its relation to the visual, auditory, and tactile sense areas, is engaged in associating and registering visual, auditory, and tactile sensations, and that the knowledge thus gained has reference mainly to the external world. These assumptions in a general way are supported by the phenomena of disease. In certain lesions of the frontal lobe the symptoms indicate a loss or change of ideas regarding personality rather than of the objective w^orld, while the reverse is true in disease of the parieto-occipital lobe. 34 CHAPTER XX. THE CEREBELLUM. The cerebellum is situated in the inferior fossae of the occipital bone, beneath the posterior lobes of the cerebrum, from which it is separated by the tentorium cerebelli, a semilunar fold of the dura mater. It is partially divided into hemispheres by a longi- tudinal fissure, more apparent on the inferior surface, though united by a central lobe, the vermiform process. Each hemisphere is con- nected with the cerebrum, the pons, medulla and spinal cord by three bundles of nerve-fibers known respectively as the superior, middle, and inferior peduncles. The surface of the cerebellum presents a series of lobes and fissures of which the former have received more or less fanciful names. A section of the cerebellum shows that it is composed of gray matter externally and white matter internally. The general appearance presented on section is shown in Fig. 230. Structure of the Gray Matter. — The gray matter consists mainly of nerve-cells of varying size and shape, which are arranged in two layers: viz., an outer or molecular and an inner or granular. The molecular layer consists of stellate and multipolar cells of small size, from which dendrites and axons pass horizontally and vertically. The granular layer consists, as its name implies, of granular shaped cells and large stellate cells. These cells are characterized by the possession of dendrites and axons, the course and relation of which have not been clearly determined. The inner border of the molecular layer presents a series of large cells originally described by Purkinje and known by his name. From the outer end of the cell-body one or more dendrites emerge which soon divide and subdivide into a number of branches which pass toward the cerebellar surface. The general arrangement of these dendrites gives to the entire cell a tree-like appearance (Fig. 231). From the inner end of the cell an axon emerges which- passes centrally into the w^hite matter. Structure of the White Matter. — The white matter consists of nerve-fibers which are arranged in association and projection systems. The Association System.—Th.e fibers which compose this system are of variable lengths and unite adjacent as well as distant regions of the cerebellar cortex. They doubtless associate them both anatom- ically and physiologically. 530 THE CEREBELLUM. 531 The Projection System. — The fibers composing this system con- nect the cerebellar cortex with certain structures in the cerebrum, pons, medulla, and spinal cord. They may be divided into efferent and afferent systems. The efferent fibers have their origin in the cells of Purkinje and the dentate nucleus. Some of these fibers emerge from the cere- bellum in the superior peduncles through which they pass to- ward and beneath the corpora quadrigemina to terminate around the cells of the red nucleus. As they ap- proach this nucleus some of the fibers cross the median line and decussate with those coming from the opposite side, while others pursue a straight direction, terminating on the same side. Through the intervention of fibers which arise from the red nucleus and ascend to the cerebral cortex, the cortex is thus connected with both sides of the cerebellum, though chiefly with the oppo- site side. Efl'erent fibers also leave the cerebellum by the middle peduncle and pass directly to the nucleus pontis, around the cells of which their terminals arborize. Efferent fibers also descend the inferior peduncles and constitute the tract known as the Lowenthal and Marchi tract, situated in the antero-lateral region of the spinal cord in its upper part. The afferent fibers come from a variety of sources. Those found in the superior peduncles come from the red nucleus; those in the middle peduncles from the nucleus pontis of the opposite side, having Fig. 230. — View of Cerebellum in Section, AND OF Fourth Ventricle, with the Neighboring Parts. — {From Sappey.) I. Median groove fourth ventricle, ending below in the calamus scriptorius, with the longitudinal eminences formed by the fas- cicvili teretes, one on each side. 2. The same groove, at the place where the white streaks of the auditory nerve emerge from it to cross the floor of the ventricle. 3. Inferior peduncle of the cerebellum, formed by the restiform body. 4. Posterior pyramid ; above this is the calamvis scriptorius. 5, 5. Superior peduncle of cerebellum, or pro- cessus e cerebello ad testes. 6, 6. Fillet to the side of the crura cerebri. 7, 7. Lateral grooves of the crura cerebri. 8. Corpora quadrigemina. — -{After Hirschfcld and Lc- veille.) 532 TEXT-BOOK OF PHYSIOLOGY. crossed or decussated at the raph6 near the anterior surface of the pons; those contained in the inferior peduncles are the most abundant and important, and are represented by (i) the direct cerebellar tract, which terminates in the superior vermis after decussation; (2) the anterior and posterior arcuate fibers, the former coming from the gracile and cuneate nuclei of the opposite side, the latter from the same side, which also pass to the superior vermis; (3) the acustico- cerebellar tract, composed of fibers the axons of the sensory end nuclei (Deiters) of the vestibular portion of the auditory nerve. It is probable that all these fibers de- cussate prior to their final termina- tion. The cerebellum through this system of efferent and aft'erent fibers is brought into relation with many different regions of the cerebrum, pons, medulla, and spinal cord. Each half of the cerebellum is con- nected with the foregoing structures of the same side, but more especially of the opposite side. Fig. 231. — Section of Cere- bellar Cortex. A. Outer or molecular layer. B. Inner or granular laver. C. White matter, a. Cell of Purkinje. b. Small cells of inner layer, c. Dendrites of these cells, d. A similar cell lying in the white matter. — (Stirling.) THE FUNCTIONS OF THE CEREBEL- LUM. From the observations of the results of experimental lesions, from analysis of clinico-pathologic facts, and from its comparative anatomic development in different animals, the deduction has been drawn that the cerebellum coordinates and har- monizes the action of those muscles the activities of which are necessary to the maintenance of body equihbrium both during station and progression. By equilibrium of the body is understood a condition which may be maintained for a variable length of time without displacement, and is possible only so long as a hne passing through the center of gravity falls within the base of support. The support offered by the earth to the feet neutralizes and counteracts the force of gravity. In station, when the body is in the erect or mihtary position, the arms by the side, the center of gravity lies between the sacrum and the last lumbar vertebra, and the line of gravity falls between the feet and within the base of support. The entire skeleton for the time being is ren- dered fixed and rigid at all its joints by the combined action of the THE CEREBELLUM. 533 muscles connected with it. That this position may be maintained all the different groups of antagonistic but cooperative muscles must be accurately coordinated in their actions. Any failure in this respect is at once attended by a disturbance of the equilibrium and displacement. In progression, walking, running, dancing, etc., the body is trans- lated from point to point by the alternate action of the legs. Whether the direction of the translation be linear or curvilinear, as the legs change their position from moment to moment, the center of gravity also changes, and at once the equihbrium is menaced. If it is to be maintained and displacement prevented there must be a prompt readjustment in the relation of all parts of the body so that the line of gravity falls again within the base of support. The more com- plicated the movements of progression, or the narrower the base of support, the greater is the danger to the equilibrium, and hence the necessity for rapid and compensatory changes in coordinated muscle activity. All movements of this character, in man at least, are pri- marily volitional and require for their performance the constant exercise of the attention. With frequent repetition they gradually come to be performed independently of consciousness and fall into the cate- gory of secondary or acquired reflexes. Though coordinating power is exhibited by the spinal cord, medulla, and basal ganglia, it is only in the cerebellum that this power attains its highest development and differentiation. To it is assigned the power of selecting and grouping muscles, not in any restricted part, but in all parts of the body, and coordinating their actions in such a manner as to preserve the equilibrium. The Results of Experimental Lesions. — If the cerebellum in its totality, coordinates and harmonizes the action of the muscles on the opposite sides of the body, any derangement of its structure or its connections with the cord, medulla, pons, or basal ganglia should at once be followed by incoordination of muscles and a want of har- mony in their action. Experimental lesions of the cerebellum are attended by such results. The phenomena observed are many and complex. They differ in extent and character in different animals and in accordance with the extent and location of the lesion, though the note of incoordination runs through them all. Removal of one lateral half of the cerebellum in the dog is followed by an inability to maintain the equihbrium necessary to the erect position. On attempting to stand, the animal at once falls toward the side of the lesion, the muscles of which at the same time contract and give to the body a distinctly curved condition (Fig. 232). The anterior hmbs are extended to the opposite side. On making efforts to regain the standing position, the animal may roll over around the long axis of its body. Conjugate deviation of the eyes is frequently observed as well as nvstagmus. 534 TEXT-BOOK OF PHYSIOLOGY. After a few days the symptoms partially subside and the animal acquires the power of sitting on the abdomen when the anterior limbs are widely extended (Fig. 233). As the days go by the improve- ment continues, and the animal recovers the power of walking, though each step is attended with tremor and oscillations of the body. Any Fig. 232. — Attitude Assumed After Destruction of the Left Half OF THE Cerebellum. — {Morat and Doyoii, after Thomas.) change in the center of gravity such as results when one leg is Hfted may result in a fall toward the side of the lesion, owing to an inabihty to promptly bring about the necessary compensatory muscle actions. With time the animal continues to improve in its power of adjustment, though it never completely recovers it. Move- ments of progression are apt \ to be characterized by stiffness and accompanied by tremor suggestive of volitional efforts. Total removal of the cere- bellum is followed by a differ- ent train of symptoms. The extensor muscles apparently preponderate in their action, for the limbs are extended and abducted, the head and neck are retracted, and opis- thotonos is established. In time these effects also partially subside, though all attempts at walking are permanently accompanied by tremor and oscillations. The characteristic effect which follows section of the peduncles is again incoordination, manifesting itself in deviation of the head, eyes, inability to walk, tremor on exertion, etc. The effects vary, however, according to the peduncle divided. Section of the middle peduncle gives rise to the most pronounced eft'ects. The head and the anterior part of the body are at once drawn toward the pelvis on the side of the section. Fig. 233. the —Attitude in Repose after Complete Removal of the Cerebellum but during the Period of Restoration of Func- tion. — {Morat and Doyon, after Thomas.) THE CEREBELLUM. 535 A voluntary effort on the part of the animal causes it to lose all control of its muscles and the body is rotated in the direction of its longitudinal axis from 40 to 60 times a minute before it comes to rest. According as the lesion is made from behind or before, the rotation is from or to the side of the section. In time these symptoms subside, though the animal never completely recovers. The partial recovery of the power of coordination, observed after removal of a portion or the whole of the cerebellum, indicates that the centers in the cord, medulla, pons, and cerebrum endowed with corresponding though less developed power, develop compensatory activity and acquire to some extent the capabilities of the cerebellum itself (Fig. 234). Clinico- pathologic facts partly corroborate the results of phys- iologic investigations. In various forms of uncomplicated cere- bellar disease, vertigo, tremor on making voluntary efforts, difficulty in maintaining the erect position, unsteadiness in walking, opisthotonos, pleurothotonos, are among the symptoms generally observed. Comparative anatomic investigations reveal a remarkable correspond- ence between the de- velopment of the cerebel- lum and the complexity of the movements ex- hibited by animals. In those animals whose movements are complex and require for their performance the cooperation of many groups of muscles the cere- bellum attains a much greater development in reference to the rest of the brain than in animals whose movements are relatively simple in character. This relative increase in the development of the cerebellum is found in many animals, such as the kangaroo, the shark, the swallow, and the predaceous birds generally. The Coordinating Mechanism. — Though it is not known how the cerebellum selects and coordinates groups of muscles for the per- formance of any complex movement, it is known that its activity is largely reflex in origin and excited by impulses reflected to it from peripheral organs. In this as in other forms of reflex activity the mechanism involves (i) afferent nerves, e. g., cutaneous, muscle, optic, and vestibular, and their related end-organs, tactile corpuscles, muscle spindles, retina, and semicircular canals, all indirectly con- nected with (2) the cerebellar centers; (3) efferent nerves indirectly Fig. 234. — Progression after Destructiox OF THE Vermis. — {Moral and Doyon, after Thomas.) 536 TEXT-BOOK OF PHYSIOLOGY. connected with (4) the general musculature of the body. Both station and progression are directly dependent on the development and trans- mission of afferent impulses from the previously mentioned periph- eral sense-organs to the cerebellum. Tactile, muscle, visual, and labyrinthine impressions and sensations not only cooperate in the development and organization of the motor adjustments necessary to the maintenance of the equilibrium and locomotive coordination, but even after their organization they are necessary to the excitation of cerebellar activity. The manner in which they lead to the develop- ment of this capabihty on the part of the cerebellum is conjectural. Their ever-present influence is shown by the effects which follow their removal, as the following facts indicate. The prevention of the development of tactile impulses by freezing or anesthetizing the soles of the feet, and the blocking of normally de- veloped impulses through destruction of afferent pathways in diseases of the spinal cord lead at once to marked impairment in the coordinat- ing power. The removal of the skin from the hind legs of the frog, previously deprived of its cerebrum, destroys its coordinating power, which it would otherwise possess in a high degree. The blocking in consequence of destructive lesions of the spinal cord, of the impulses, which come from the muscles, tendons, etc., and which inform us of the activity and the degree of activity of our muscles, the location of the hmbs, the amount of effort necessary to produce a given movement, etc., also gives rise to much incoor- dination. A blocking of both tactile and muscle impulses frequently exists in degeneration or sclerosis of the posterior columns of the spinal cord. The coordinating power is so much impaired in this disease that the patient is unable to maintain, without strained effort, the erect position and especially if the directive power of the eyes be removed by closure of the hds. Walking becomes extremely difficult ; the gait is irregular and jerky, and equilibrium is maintained only by keeping the eyes fixed on the ground in front and by artificially increasing the basis of support by the use of canes. An interference with the development of the customary visual impressions which in a measure maintain the sense of relation of the individual to surrounding objects also gives rise to equihbratory dis- turbances. A rapid change in the relation of the individual to sur- rounding objects or the reverse; a change in the direction of one optic axis from the use of a prism or from paralysis of an eye muscle ; the destruction of an eye; — these and similar conditions frequently give rise to such marked disturbances of the equihbratory power that displacement is difficult to prevent. An interference with the development of the so-called labyrin- thine impressions by destruction of the semicircular canals gives rise to the most remarkable disturbances in this respect. Section of one THE CEREBELLUM. 537 horizontal canal* in the pigeon is followed by oscillations of the head in a horizontal plane around a vertical axis. Bilateral section so increases these oscillations that the pigeon is unable to maintain equilibrium and forced to fall and turn continuously around the vertical axis. Bilateral section of the posterior vertical canals gives rise to oscillations around a horizontal axis which frequently become so exaggerated as to eventuate in the turning of backward somersaults, head over heels. Similar phenomena follow division of the superior vertical canals. Bilateral destruction of both sets of canals is attended by extra- ordinary disturbances in the equihbrium. From the moment of the operation the animal, the pigeon, loses all control of its motor mechan- isms. It can neither maintain a fixed attitude nor execute orderly movements of progression ; its activity, continuous and uncontrollable, is characterized by spinning around a vertical axis, turning somer- saults, dashing itself against surrounding objects until hfe is endan- gered. If the animal be protected from injury, these disturbances gradually subside, and in the course of a few months the equihbratory power is so far regained that standing and walking at least become possible. In this condition, however, the coordinating power is directly dependent on visual impulses, for with the closure of the eyes all the previous motor disturbances at once recur. These and similar facts indicate that the semicircular canals are the peripheral sense-organs from which come the nerve impulses most essential to the excitation of the cerebellar coordinative centers in their control of equilibrium and of progression. The cerebellum may therefore be regarded as the essential, most highly differentiated portion of the coordinating mechanism con- cerned in the maintenance of equihbrium, during both station and progression. The manner in which the cerebellum accomplishes this result is unknown, though it is certain, from the foregoing facts, that its special mode of activity is dependent on the excitatory action of nerve impulses reflected from a variety of peripheral sense-organs. * The physiologic anatomy of the semicircular canals is described in the chapter devoted to the ear, to which the reader is referred. CHAPTER XXI. THE CRANIAL NERVES. The nerve-trunks which serve as channels of communication between the encephalon and the structures of the head, the face, and in part the organs of the thorax and abdomen, pass through foramina in the walls of the cranium, and for this reason are termed cranial nerves. According to the classification now generally adopted, there are twelve cranial nerves on either side of the median line, which, enu- merated from before backward, are as follows (Fig. 235): First or Olfactory. Seventh or Facial. Second or Optic. Eighth or Auditory. Third or Oculo-motor. Ninth or Glosso-pharyngeal. Fourth or Patheticus. Tenth or Pneumogastric or Vagus. Fifth or Trigeminal. Eleventh or Spinal Accessory. Sixth or Abducens. Twelfth or Hypoglossal. The cranial nerves may be classified physiologically in accordance with their functional manifestations into three groups, viz. : 1. Nerves of Special Sense: e.g., Olfactory, Optic, Auditory, Gustatorj' (Glosso- pharyngeal). 2. Nerves of General SensibiKty: e.g., Large root of the Trigeminal, Glosso- pharyngeal, and Pneumogastric. 3. Nerves of Motion: e.g., Oculo-motor, Patheticus, the small root of the Trigeminal, Facial, Spinal Accessory, and Hypoglossal. Though this classification in the main holds true, it must be borne in mind that modern investigations have demonstrated that the glosso- pharyngeal and pneumogastric nerves contain even at their junction with the medulla oblongata a number of efferent or motor fibers, and to this extent are mixed nerves. The Origins of the Cranial Nerves. — In accordance with modern views as to the origins of nerves in general, it may be stated that— The nerves 0} special sense have their origin respectively in the neuro- epithelial cells in the mucous membrane of the olfactory region of the nose, in the ganghon cells of the retina, in the cells of the spiral ganghon of the cochlea and the ganglion of Scarpa, and in the cells of the petrous and jugular gangha. From the cells of these gangha dendrites pass peripherally to become associated with speciahzed end- organs, while axons pass centrally in well-defined bundles to 538 THE CRANIAL NERVES. 539 become related by means of their end-tufts with primary basal gangha. The nerves of general sensibility have their origin in the ganglia on their trunks, and in this respect resemble the spinal nerves. From the ganglion cell there emerges a short axon process which soon divides into a central and a peripheral branch. The former passes toward and into the gray matter located beneath the floor of the fourth ventricle, where its end- tufts arborize about nerve-cells. The latter (the peripheral branch) passes toward the general periph- ery to be distributed to skin and mucous membranes (Fig. 236). The nerves 0} motion have their origin in the nerve-cells in the gray matter beneath the aqueduct of Sylvius and beneath the floor of the fourth ventricle (Fig. 237). The axons emerging from these cells course per- ipherally to be distributed to skeletal muscles. In some of the motor nerves, and in some sensory nerves as well, there are to be found efferent fibers of smaller size which have a similar origin and which become related through the intervention of sympathetic ganglia (peripheral neurons) with visceral muscles and glands. These nerves have been termed autonomic nerves. The Cortical Connections of the Cranial Nerves. — Each of these three groups of cranial nerves has special connections with the cerebral cortex. The nerves of special sense for the most part terminate in primary basal gangha, around the cells of which their central end-tufts ar- borize. From these cells axons arise which pass upward and directly or indirectly come into physiologic relation with sensor nerve-cells in the cerebral cortex. The nerves of general sensibility terminate in the gray matter beneath the floor of the fourth ventricle, around the nerve-cells of which their end-tufts arborize. These groups of nerve-cells are Fig. 2- -Superficial Origin of the Cranial Nerves from the Base OF THE Encephalon. I. Olfactory. 2. Optic. 3. Motor oculi. 4. Patheticus. 5. Trigeminal. 6. Abdu- cens. 7. Facial. 7'. Nerve of Wrisberg. 8. Auditory. 9. Glosso- pharyngeal. 10. P'neumogastric. II. Spinal accessory. 12. Hypo- glossal. — {Morat and Doyon.) S40 TEXT-BOOK OF PHYSIOLOGY. known as sensor end-nuclei. Though once regarded as the centers of origin of the sensor nerves, they are now regarded as the centers of origin of axons which pass upward to the cortex of the cerebrum, where they also come into physiologic relation with sensor nerve- cells. Fig. 236. — Ganglia of Origin of the Sensor Cranial Nerves, i. Tri- geminal (ganglion of Gasser). 2. Nerve of Wrisberg. 3. Auditory (ganglion of Scarpa). 4. Glosso- pharyngeal (ganglion of Andersch). 5. Pneumogastric (ganglion plexi- formis). — {After Moral and Doyon.) Fig. 237. — Nuclei of Origin of the Motor Cranial Nerves. 1. Motor oculi. 2. Patheticus. 3. Motor root of the trigeminal. 4. Abducens. 5. Facial. 6. Mixed nucleus for efferent fibers of the glosso-pharyngeal vagus and spinal accessory. 7. Hypoglossus. 8. Spinal accessory. 9. Spinal nerves. — (After Moral and Doyon.) The axons in both of these classes of nerves thus originate in the cells of the central nerve system and continue upward to the cere- brum, the primary afferent path. The motor nerves which have their origin in the cells of the gray matter beneath the aqueduct of Sylvius and beneath the floor of the fourth ventricle are in physiologic relation with nerve-cells in the THE CRANIAL NERVES. 541 motor region of the cortex through descending axons contained in the pyramidal tract. The end-tufts of these axons arborize around the nerve-cells. The efferent path beginning in the cerebral cortex is thus continued by the motor nerves to the general periphery. The three groups of nerves, those of special sense, of general sensibility, and the motor nerves, are neurons of the first order; the nerve-cells and fibers which constitute the cerebral connections are neurons of the second order. It is possible that the sensor cells in the cerebral cortex are neurons of a third order. FIRST PAIR. THE OLFACTORY. The first cranial nerve, the olfactory, is situated in the upper third of the nasal fossa, in the regio oljactoria. It consists of from 20 to 30 branches, the fibers of which are non-meduUated. Origin. — The olfactory nerve is composed of centrally coursing axons which have their origin in the central ends of bipolar, rod-shaped, or spindle-shaped nerve-cells interspersed among the epi- thelial cells covering the mucous membrane in the regio ■ olfactoria ; the per- ipheral ends of these cells give oft' a number of den- drites which are spread out to form a delicate feltwork over the surface of the mucous membrane. From their origin the axons gradually converge to form bundles which ascend to the cribriform plate of the ethmoid bone, through the foramina of which they pass to become related by their end-tufts mth structures in the gray matter of the olfactory bulb (Fig. 238). Cortical Connections. — The olfactory bulb and olfactory tract, formerly called the olfactory nerve, are portions of the cerebrum (the olfactory lobe) which arise embryologically by a protrusion of the walls of the cerebral ca\dty. The bulb is oval-shaped Fig. 238. — The Relation of the Olfactory Nerves to the Olfactory Tract, i Olfactory nerve-cell. 2. Axon process. 3. Epithelial cells. 4. Glomerulus. 5. Mitral cells. 6. Centrally coursing axons of the olfactory tract. — {Moral and Doyon.) 542 TEXT-BOOK OF PHYSIOLOGY. il'illfS, and consists of both gray and white matter. It rests on the cribriform plate of the ethmoid bone and is embraced by the olfactory nerves. As seen on sagittal section, there is just beneath the surface a layer of large pyramidal and spindle-shaped cells (termed also mitral cells), each provided with an apical and two lateral dendrites. The apical dendrite passes toward the surface and ends in a brush- or basket-Hke expansion which interlaces with the end-tufts of the olfactory nerves, forming what are known as the olfac- tory glomerules. The lateral dendrites end free. The axons of the pyramidal cells pass toward the center of the bulb and bend at right angles, after which they pursue a horizontal direction toward and into the olfactory tract. This tract is about five centimeters in length, prismatic in shape on cross-section and di- visible into a ventral and a dorsal portion. It emerges from the posterior extremity of the bulb, passes back- ward to the posterior part of the anterior lobe, where it divides into three roots: viz., a lateral or external, a mesial or internal, a middle or dorsal. The fibers of the lateral and mesial roots are derived almost exclusively from the ventral portion of the tract, the fibers of which come from the mitral cells in the bulb. The lateral root-fibers pass outward into the fossa of Sylvius and come into relation with nerve-cells in the inferior extremity of the gyrus hippocampus and the gyrus uncinatus. The mesial fibers pass inward and come into relation with nerve-cells in the pre-callosal part at least of the gyrus fornicatus. The fibers thus far considered are undoubtedly true olfactory fibers, pursuing Fig. 239. — Olfactory Lobe of the Human Brain. — Bii. Olfactory bulb. T. Tract. Tr.o. Trigone. R. Rostrum of corpus callosum. p. Peduncle of cor- pus callosum, passing into G.s., gyrus subcallosus (diagonal tract, Broca). Br. Broca's area. P.p. Fissura prima. F.s. Fissura serotina. C.a. Posi- tion of anterior commissure. L.t. Lamina ter- minalis. Ch. Optic chiasma. T.o. Optic tract. p.olf. Posterior olfactory lobule (or anterior per- forated space). 7n.r. Mesial root. l.r. Lateral root of tract. — (His.) — (After Quain.) THE CRANIAL NERVES. 543 a centripetal direction, carrying nerve impulses from the olfactory cells to the cerebrum (Fig. 239). Histologic and embryologic methods of research have shown that some of the fibers in the olfactory tract are centrifugal in direction. They originate in the olfactory cortical areas, pass toward the peripher}' as far as the anterior commissure, where they cross to become the dorsal root, enter the olfactory tract, and finally terminate in the bulb. This tract serves to connect the cortex with the bulb of the opposite side, and carries impulses from the cortex to the bulb. The two opposite cerebral olfactory areas are also united by com- missural fibers which decussate at the anterior commissure. Functions. — The olfactor}' nerves, including the olfactory tract, are channels of communication between the olfactor}' region in the nose and the cerebral cortex. The stimulus to its excitation is the impact and chemic action of gaseous or volatile organic matter on the dendrites of the olfactory cells. The energy set free develops nerve impulses which, travehng through the entire olfactory tract to the cortex, evoke the sensation of odor. The sensitiveness of the olfactory end-organ to the action of many substances is remarkable, responding, for example, to the tto i. oinr of a gram of oil of roses and to the o-.Te^TT.Toir of a gram of mercaptan. Division or destruction of the olfactory path at any point is fol- lowed by an abolition of the sense of smell on the corresponding side. Destructive lesions of the hippocampal and uncinate gyri are fol- lowed bv similar results. SECOND PAIR. THE OPTIC. The second cranial nerve, the optic, consists of centrally coursing axons of neurons, which connect the essential part of the organ of vision, the retina, with sensory end-nuclei or ganglia situated at the base of the cerebrum. Origin. — The axons which constitute the optic nerve have their origin in the ganglionic cells in the anterior part of the retina. Through their dendrites these cells are brought into relation pos- teriorly with successive layers of cells which collectively constitute the retina. Though the retina is said to consist of ten or eleven layers, it may be reduced practically to three, viz. (Fig. 240) : 1. The layer of visual cells. 2. The layer of bipolar cells. 3. The layer of ganglionic cells. The visual cells present peripherally modified dendrites, known as the rods and cones; centrally they give off an axon which after a short course terminates in an end-tuft. The bipolar cells also possess dendrites and an axon; the former interlace with the end- 544 TEXT-BOOK OF PHYSIOLOGY. tufts of the visual cell axon, the latter with the dendrites of the gang- lion cell. The retina may be regarded therefore as the peripheral end-organ in which the optic nerve originates. From their origin the axons turn backward, at the same time converging to form a distinct bundle which passes through the chorioid coat and sclera. After emerging from the eyeball the nerve-bundle (the optic nerve) passes backward as far as the sella turcica, traversing in its course the or- bit cavity and the optic foramen. At the sella turcica there is a union and partial decussation in man and other mammals of the two nerves, forming the optic chiasm. Decussation of the Optic Nerves. — The results of various methods of research would seem to indicate that the fibers from the nasal third of the retina of the left eye cross in the chiasm to unite with the fibers from the temporal two-thirds of the retina of the right eye. In a 'similar manner the fibers from the nasal third of the retina of the right eye cross in the chiasm and unite with the fibers from the temporal two-thirds of the retina of the left eye. Posterior to the chiasm the crossed and uncrossed fibers form the so-called optic tracts, which after winding around the crura cerebri enter the optic 'basal ganglia. Transection of the optic nerve shows that it is composed of an enormous number of non-medullated nerve-fibers, estimated by;Salzer at from 450,000 to 800,000, enclosed in a sheath of the dura mater. In the central portion of the nerve there is seen a distinct bundle of fibers, triangular in shape, that come from the region of the macula lutea. At the chiasm this bundle of fibers undergoes a partial decussation similar to that of the fibers coming from the more peripheral portions of the retina. In the left optic tract, therefore, fibers from four different regions are to> be found: viz., the two-thirds of the temporal side of the left retina, the temporal half of the left macula, the nasal third of the right retina, and the nasal half of the right macula. Corresponding fibers are to be found in the right optic tract. As the optic tract passes around the crus cerebri it divides into a lateral or outer, and a mesial or inner bundle, which then terminate in the optic basal ganglia. The fibers of the lateral bundle are traceable into the external geniculate body (the pre-geniculum), the pulvinar of the optic thalamus, and the anterior quadrigeminal body (the pregeminum). These are in all probabihty the true visual fibers. The fibers of Fig. 240. — Retinal Cells, s', z'. Visual cells with their peripheral terminations. 5. Rods. z. Cones. b. Bipolar cells. g. Ganglion cells from which arise the axons of the optic nerve. THE CRANIAL NERVES. 545 VISUAL NEW VISUAL nELD the mesial bundle are traceable into the internal geniculate body (the post-geniculum) and the posterior quadrigeminal body (the post- geminum). Cortical Connections. — ^After entering the basal gangha the visual fibers terminate in end-tufts which arborize around nerve- cells. From these cells new axons arise which ascend through the posterior part of the internal capsule, at the same time curv- ing backward to form the op- tic radiation of Gratiolet, and terminate finally around nerve-cells in the gray matter of the cuneus and in the gray matter bordering the calcarine fissure, both situated on the mesial aspect of the occipital lobe. Cenlrijugal Fibers of the Optic Nerve. — All the fibers previously alluded to have been aft'erent or centripetal in direction; but the optic nerve also contains efferent or centri- fugal fibers which come from nerve-cells in the basal ganglia and ramify around special cells, the amacrine cells, in the retina. Their function is unknown. It has been sug- gested that they regulate the vascular supply to the retina. Centrifugally coursing fibers also connect the visual areas of the cortex ^vith the basal ganglia. Functions. — The optic nerve apparatus in its entirety connects the visual cells of the retina with the cells of the cerebral cortex. The excitation of this appa- ratus evokes the sensation of light and its dift"erent quahties — colors. The specific physiologic stimulus of the visual retinal cells is the impact of the undulations of the ether. The energy set free excites in the optic nerve, nerve impulses which are transmitted first to the optic ganglia and then to the cerebral cortex, where they evoke the sensations of light and color. Iris Reflex. — The optic nerve also assists in the automatic reg- 35 Fig. 241. — Diagram Illustrating Left Homonymous Lateral Hemianopsia FROM A Lesion of the Right Optic Tract or the Right Cuneus. The Shaded Lines in the Visual Fields Indicate the D.\rkened Area. 546 TEXT-BOOK OF PHYSIOLOGY. ulation of the size of the pupil. Some of its fibers form the afferent part of the reflex nerve mechanism by which the circular fibers of the iris (the sphincter pupillae) are excited to contraction. These fibers arborize around nerve- cells in the anterior quadrigeminal body, from which axons descend in the posterior longitudinal bundle. In their course they give off collateral branches to the nuclei of origin of the oculo-motor nerve, from which nerve-fibers pass to the iris. Light falling on the retina generates nerve impulses which, when conducted through the aflPerent and efferent pathways just mentioned, stimulate the circular fibers to contraction. The extent of the con- traction will depend on the in- tensity of the fight. In the absence of all fight the muscle completely relaxes. Hemiopia and Hemian- opsia. — Division of the optic nerve between the eyeball and the optic chiasm is fol- lowed by complete blindness in the eye of the corresponding side. Owing to the partial decussation of the fibers in the chiasm, division of an optic tract is followed by a loss of sight in the outer two-thirds of the eye of the same side and in the inner third of the eye of the opposite side. To this loss of visual power in the retina the term hemiopia is given. In consequence of this loss of vis- ual power in the retina there is a corresponding obscuration or total obliteration of nearly one-half of the visual field, to which the term hemianopsia is given. If, for example, the right optic tract is divided there will be hemiopia in the outer two-thirds of the right eye and the inner third of the left eye, with lejt lateral hemian- opsia, and as the portions of the retina which are affected are associated in vision the loss of the visual fields is spoken of as homonymous hemianopsia (Fig. 241). A destructive lesion of the cerebral visual area, the cuneus and the adjacent gray matter on the right side, is also followed by left lateral hemianopsia.* Fig. 242. — Diagram to Show the Exist- ence OF Hemianopsia. The lesion is supposed to be in the right optic tract. * It should be borne in mind that in both instances the retina itself is unaffected. The impact of light generates, as usual, nerve impulses which proceed as far back- ward as the point of division or destruction. In consequence those portions of the cerebral cortex stimulation of which evokes the sensation of light remain unaffected THE CRANIAL NERVES. 547 The existence of an homonymous hemianopsia becomes evident when the individual is directed to focus the vision on an object placed directly in front and with its center in the median plane of the body, when if the lesion be on the right side, the left half of the object will be invisible. The reason for this will be apparent on reference to Fig. 242. All the hght rays emanating from the left half of the object fall on the retina on the side of the injury, and hence there will be no sensation. If, however, the object be moved to the right without change in the position of the head, the entire object will be visible, as all the rays fall on the normal side. If, on the contrary, the object be moved to the left, it will be invisible for the opposite reason. Hemianopsia may be the result of either destruction of the optic tract or of the cortical visual area. The seat of lesion in any given case is indicated by a peculiarity of the iris reflex pointed out by Wernicke, which will be referred to in connection with the considera- tion of the oculo-motor nerve. THIRD PAIR. THE OCULO-MOTOR. The third cranial nerve, the oculo-motor, consists of some 15,000 peripherally coursing nerve-fibers which serve to bring the nerve-cells from which they arise into relation with a large portion of the general musculature of the eye. Origin. — The axons composing the third nerve arise from a series of seven or eight groups of nerve-cells, located in the gray matter beneath the floor of the aqueduct of Sylvius. From each of these groups or nuclei, bundles of axons emerge, which after a short course unite to form the common trunk. The large majority of the fibers in the nerve come directly from the nuclei of the same side; the remain- der come from a group of cells on the opposite side of the median line. There is thus a partial decussation of its fibers (Fig. 243). The different groups of cells, the nuclei of origin, are arranged in a serial manner. The anatomic arrangement of these nuclei would indicate that each nucleus is related to an individual member of the eye-group of muscles. Clinical observation and the investigation of the results of pathologic processes have not only shown that this is the case, but have succeeded in locating the position of the nucleus for any given muscle. Though there is some dift'erence of opinion in regard to the exact location of one or two of the nuclei, the tabulation subjoined is approximately correct. Enumerating them from before backward, the nuclei occur in the following order : 1. The sphincter pupillae. 2. The tensor chorioideae (the accommodation nucleus). and the individual does not become aware through sensation, of the presence of a luminous body in the left side of the visual field. 548 TEXT-BOOK OF PHYSIOLOGY. 3. The convergence nucleus, a common nucleus for the conjoint action of the two internal recti muscles. The superior rectus. The inferior rectus. The levator palpebrae. The inferior oblique. Cortical Connections. — The oculo-motor nuclei are in histologic and physiologic relation with the motor area of the cerebrum. Nerve- cells in the cortex give off axons which, entering the pyramidal tract, descend through the internal capsule, and the crus cerebri, from which they cross to the opposite side. The end- tufts arborize around the nuclei of the oculo-motor nerve with the ex- ception of the nucleus for the iris sphincter. Distribution. — After their origin the axons converge to form a com- mon trunk, which emerges from the base of the encephalon, on the inner side of the crus cerebri, in front of the pons Varohi. The nerve then passes forward through the sphenoid fissure into the orbit cavity, where it divides into a superior and an inferior branch. The former is dis- tributed to the superior rectus and the levator palpehrcE muscles; the latter is distributed to the internal and inferior recti and inferior oblique muscles (Fig. 244). From the inferior branch a short bundle of fibers passes to the ciliary or ophthalmic ganglion, where they terminate, arborizing around the ganglion cells. These fibers are smaller in size than those constitut- ing the bulk of the nerve and belong to the system known as the autonomic. These cells give origin to new axons, the ciliary nerves, which enter the eyeball, pass forward between the sclera and chorioid coat, and terminate in the cihary muscle and iris. The ciliary nerves are not portions of the third nerve proper, but periph- FiG. 243. — Diagrammatic View of THE Situation and Relation OF THE Nuclei of Origin of THE Oculo-motor and Path- eticus (Trochlearis) Nerves. The oculo-motor nuclei consist of an anterior nucleus, the Edinger-Westphal nucleus (a and h), and a posterior nucleus; the posterior nucleus has a dor- sal, a ventral, and a mesial portion; the decussation of fibers from the dorsal portion of the posterior nucleus is also shown. The decussation of the fibers of the fourth nerve is also represented.— (£(fiw^er.) THE CRANIAL NERVES. 549 eral sympathetic neurons. As the ciHary ganghon receives filaments from the cavernous plexus of the sympathetic and filaments which become a part of the trigeminal nerve, it is probable that the ciliary nerves contain not only motor, but vaso-motor and sensor fibers. Properties. — Stimulation of the nerve near its exit from the en- cephalon is followed by contraction of the muscles to which it is dis- tributed with the following results, viz. : 1. Diminution in the size of the pupil. 2. Accommodation of the eye for near vision. 3. Elevation of the upper eyelid. 4. Internal deviation and rotation upward and inward of the anterior pole of the eye, combined with a small amount of torsion toward the mesial line, due to preponderating action of the internal rectus and inferior oblique muscles. Division of the nerve experimentally or compres- sion from a pathologic lesion is followed by a relaxation of the muscles, with the following effects, viz. : I. Dilatation of the pupil, the iris responding neither to light nor to efforts of accommoda- tion. Loss of the accommoda- tive power. Fahing of the upper eye- hd (ptosis). 4. External deviation and rotation downward and outward of the anterior pole of the eyeball combined with a small amount of torsion toward the mesial line due to the unopposed action of external rectus and the superior obhque muscles. 5. Double vision or diplopia. The image of the eye of the paralyzed side is projected to the opposite side of the true image and to the upper part of the visual field. Owing to the slight mesial torsion the false image is inchned away from the true image. 6. Immobihty and slight protrusion of the eyeball. Function. — The function of the third nerve is to transmit nerve impulses from the nuclei of origin to all the muscles of the eye except the external rectus and superior oblique and excite them to activity. 2. 3 Fig. 244. — Intra-orbital Portion of the Third Nerve, i. Optic nerve. 2. Third nerve. 3. Superior branch. 4. Inferior branch. 5. Abducens. 6. Trifacial. 7. Ophthalmic branch divided. 8. Nasal branch. 9. Ciliary ganglion. 10. Motor branch to this ganglion from the inferior branch of the third nerve. 11. Sensory fibers. 12. Sympathetic fibers. 13. Ciliary nerves. — (Sappey.) 55° TEXT-BOOK OF PHYSIOLOGY. The majority of the ocular movements, the power of accommoda- tion, the variations in the size of the pupil in accordance with varia- tions in the intensity of the hght, the power of convergence of the visual axes, are all excited by the transmission of nerve impulses by the constituent fibers of the nerve from their related nuclei. This is made evident by the effects which follow stimulation and division of the nerve or lesions of the nuclei themselves. The central nuclei can be excited to activity (i) by nerve impulses descending the motor tract, from the cerebral cortex, (2) by nerve impulses coming through various afferent nerves. This holds true more especially for the sphincter pupillas nucleus. The Iris Reflex or the Pupillary Reflex. — These are terms applied to the variations in the size of the pupil that follow vari- Gasserian GangUon Cil.ary ^< N.ulc.scJ 3rJ Nerac J\/erves Ciliary Ganglion Sympathetic. Postganglionic fibers Superior Cervical Ganglion Vv y~ ThoracicJveroe Pirganglionic Jibers fromSpin al Cord Fig. 245. — Diagram Showing the Structures Involved in the Iris Reflex. ations in the intensity of the light. In the absence of light the pupil 'widely dilates, due largely to the relaxation of the sphincter pupillcB muscle and partly to a contraction of the radiating fibers of the iris which collectively constitute the dilatator pupiUa muscle. With the entrance of light into the eye, the pupil narrows in con- sequence of the contraction of the sphincter pupilloe caused by a stimulation of the peripheral end of the optic nerve, the degree of contraction depending within limits on the intensity of the light. The action is a reflex one and the mechanism involved includes the retina, the optic nerve, the anterior quadrigeminal body, the third nerve, the ciliary nerves (the peripheral sympathetic neurons), and the sphincter pupillae muscle. ( Fig. 245.) In this mechanism the optic nerve is the afferent path, the motor oculi the efferent path, and the anterior quadrigeminal body the intermediate center. These THE CRANIAL NERVES. 551 facts are demonstrated by the entire loss of the reflex which fol- lows division or destruction of any part of this arc. The anterior quadrigeminal body appears to be in relation through its axons and their collateral branches with the sphincter pupUlce nucleus of both sides, inasmuch as stimulation of one retina is followed by narrow- ing of the pupils of both eyes. To this simultaneous contraction of the pupils the term "consensual" has been given. Contraction of both pupils also occurs as an associated movement in the conver- gence of the eyes during accommodation. The dilatation of the pupil is, however, not due exclusively to the relaxation of the sphincter pupillae muscle, but partly to the contraction of the dila- tator pupillcB muscle, which is kept normally in a state of tonic contraction by impulses emanating from a nerve-center in the medulla oblongata. The axons which arise in this center pass down the cord, emerge through the first thoracic nerve, and then ascend to the superior cervical ganglion (see Fig. 245), in which their terminal branches arborize around its nerve-cells. From these cells new axons of the sympathetic system arise which pass successively to the ophthalmic division of the fifth nerve, the nasal nerve, the long ciliar}- nerve and the iris. Experimental research renders it highly probable that the dilatator center is in a state of continuous activity and the dilatator muscle in a state of tonic contraction. Whatever the normal stimulus may be, the center is increased in activity by dyspneic blood, by severe muscle exercise, by emotional excitement, and by stimulation of various sensoiy nerves. That the afferent pathway just alluded to transmits the impulses to the iris is shown by the fact that division in any part of the course is followed by narrowing, stimulation by active dilata- tion of the pupil. The variations in the size of the pupil, though largely a reflex act under the control of the oculo-motor nerve, are nevertheless partly due to the active cooperation of the dilatator nerves and their related muscle. The size of the pupil necessary from moment to moment for the admission of just that amount of light essential to the formation and perception of a distinct image is the result of two nicely adjusted and delicately balanced forces. Wernicke's Pupillary Reaction. — It was stated on page 531 that a modification of the pupillary reaction is observed in some cases of hemianopsia which indicates approximately the seat of lesion. This reaction is present only when the lesion is along the course of the optic tract. In these cases, if a fine ray of light is projected into the eye in such a manner that it falls entirely on the non-responsive side of the retina, there will be an absence of a pupillary response, owing to the break in the reflex arc. If, however, the light be 552 TEXT-BOOK OF PHYSIOLOGY. thrown on the sensitive side of the retina the usual response, a con- traction of the sphincter and a narrowing of the pupil, is at once observed. FOURTH PAIR. THE PATHETICUS. The fourth cranial nerve, the patheticus, consists of peripherally coursing axons which serve to bring the cells from which they arise into relation with the superior obHque muscle. Origin. — The axons of this nerve arise from a group of cells located beneath the aqueduct of Sylvius just posterior to the last nucleus of the third nerve. After emerging from the nu- cleus the nerve-fibers pass down- ward for a short distance, then curve dorsally around the aque- duct of Sylvius, and enter the valve of Vieussens, where they completely decussate with the nerve-fibers of the opposite side. Cortical Connections. — The nucleus of the pathetic nerve is in histologic and physiologic connection with the motor area of the cerebral cortex. Nerve cells in this region give off axons which enter the pyramidal tract and descend through the inter- nal capsule and the crus cerebri, after which they cross to the opposite side. Their end-tufts arborize around the cells of the nuclei already described. Distribution. — After its decussation the nerve-trunk emerges just below the posterior quadrigeminal body, crosses the superior cerebellar peduncle, and winds around the crus cerebri to the anterior border of the pons Varohi. It then enters the orbit cavity through the sphenoid fissure and finally terminates in the superior oblique muscle. In its course the nerve receives filaments from the cavernous plexus of the sympathetic and the ophthalmic division of the trigeminal. Properties. — Stimulation of the nerve-trunk is followed by spas- modic contraction of the superior oblique muscle, the anterior pole of the eyeball being turned downward and outward, combined with slight torsion away from the middle line. Fig. 246. — Distribution of the Patheti- cus. I. Olfactory nerve. II. Optic ner\-es. III. Motor oculi communis. IV. Patheticus, by the side of the ophthalmic branch of the fifth, and passing to the superior oblique muscle. VI. Motor oculi externus. i. Gang- lion of Gasser. 2, 3, 4, 5, 6, 7, 8, 9, 10. Ophthalmic division of the fifth nerve, with its branches. — {Hirsch- jeld.) THE CRANIAL NERVES. 553 Division of the nerve is followed by a relaxation or paralysis of the muscle. In consequence of the now unopposed action of the inferior oblique muscle, the anterior pole of the eyeball is turned upward and inward with shght torsion toward the middle line. The diplopia consequent upon this paralysis is homonymous, the images appearing one above the other. The image of the paralyzed eye is below that of the normal eye and its upper end inclined toward that of the normal eye. Function. — The function of this nerve is to transmit nerve im- pulses to the superior oblique muscle and to excite it to contraction. FIFTH PAIR. THE TRIGEMINAL. The fifth cranial nerve, the trigeminal, consists of both aflferent and efferent axons which for the most part are separate and distinct. The afferent axons constitute by far the major portion, the efferent fibers the minor portion, of the nerve. Origin of the Afferent Axons. The afferent axons have their origin in the mon- axonic cells in the ganglion of Gas- ser, which rests on the apex of the petrous portion of the temporal bone. The cells of this ganglion give origin to a short process which soon di- vides into two branches, one of which passes cen- trally, the other peripherally (Fig. 247). The centrally directed branches collec- tively form the so-called large or sensor root; the peripherally directed branches collectively constitute the three main divisions of the nerve: viz., the ophthalmic, the superior maxillary, and the inferior maxillary. Branches of the carotid plexus of the sym- pathetic enter the nerve in the neighborhood of the ganglion of Gasser and accompany some of its branches to their terminations. Fig. 247. — Scheme of Origin and Constitution of the Trigeminal Nerve, i. Centrally coursing fibers. 2,3, 4. Peripherally coursing fibers of the cells of the ganglion of Gasser. R, N. Nuclei of origin of the efferent fibers. 6. IMotor root. Central terminations of the large root. 554 TEXT-BOOK OF PHYSIOLOGY. Distribution. — i. The Central Branches. — The axons of the large root pass backward into the pons Varolii on its lateral aspect. After entering the pons each axon divides into two branches, one of which passes upward a short distance, the other passes down- ward, descending as far as the second cervical segment. Both branches give off a number of collaterals, some of which terminate in fine end-tufts around nerve-cells in the substantia gelatinosa. 2. The Peripheral Branches. — The peripheral axons emerge from the peripheral end of the ganglion of Gasser in three distinct and separate branches, each of which is distributed to a different region of the face and head. The ophthalmic branch passes forward and subdivides into three large branches, the frontal, the lachrymal, and the nasal. The ulti- mate termination of the branches of these nerves is as follows: viz., the con- junctiva and skin of the upper eyelid, the cornea, the skin of the forehead and the nose, the lachrymal gland and caruncle, and the mucous membrane of the nose (Fig. 248). The superior maxillary branch passes forward through the foramen ro- tundum, crosses the sphe- no-maxillary fossa, enters the infra-orbital canal, and emerges at the infra-orbital foramen. In its course it gives off a number of branches which are distributed as follows : viz., to the integument and conjunctiva of the lower lid, the nose, cheek, and upper lip, the palate, the teeth of the upper jaw, and the alveolar processes (Fig. 249). The inferior maxillary branch passes through the foramen ovale, after which it subdivides into three branches — the auriculo-tem- poral, the lingual, and the inferior dental. The ultimate branches are distributed as follows: viz., the external auditory meatus, the side of the head, the mucous membrane of the mouth, the anterior portion of the tongue, the arches of the palate, the teeth and alveolar process of the lower jaw and the integument of the lower part of the face (Fig. 250). Fig. 248. — Ophthalmic Branch of the Fifth, i. Ganglion of Gasser. 2. Ophthalmic division of the fifth. 3. Lachrymal branch. 4. Frontal branch. 5. E.xternal frontal. 7. Supra-trochlear. 9. External nasal. — (Hirschfeld.) 6. Internal frontal. 8. Nasal branch. 10. Internal nasal. THE CRANIAL NERVES. 555 The afferent axons thus serve to bring into relation the skin, mucous membranes of the head and face, and other sentient struc- tures, with certain sensor end-nuclei in the pons, medulla oblongata, and adjoining structures. Cortical Connections. — The nerve-cells around which the end- tufts of the centrally coursing axons ramify collectively constitute the "sensor end-nuclei" of the trigeminal nerve. From these cells new axons arise which cross the median line, enter the fillet or lemniscus, and ascend directly to the sensor area of the cerebral cortex. Properties. — Irritative pathologic lesions, e. g., pressure by tumors, aneurysms, neuritis, degenerative changes in the ganghon Fig. 249. — I. Superior maxillary nerve. 2, 3, 4, 5. Dental nerves. 6. Spheno- palatine ganglion. 7. Vidian nerve. 8. Large superficial petrosal. 9. Carotid branch of large petrosal. 10. Oculo-motor. 11. Superior cer\'ical ganglion. 12. Carotid branches of this ganglion. 13. Facial. 14. Glosso-pharyngeal. 15. Jacobson's nen'e, and 16, 17, 18, 19, branches to the sympathetic, fenestra rotunda, Eustachian tube. 20. Deep e.xternal petrosal. 21. Deep internal petrosal . — {Hirschjeld . ) cells, or lesions which in any way gradually impair the physical or chemic integrity of the nerve-fibers, give rise to a variety of painful sensations referable to the seat of the lesion or to one or more regions in the peripheral distribution of the nerve. Many of the various forms of trigeminal neuralgia are caused by lesions of this character. Exposure of the dental nerves from caries of the teeth, the presence of minute foreign bodies in the conjunctiva, operative procedures in the nasal chambers, all testify to the extreme sensibility of the nerve. Division of the large root, within the cranium is followed at once by complete abolition of all sensibility in the head and face to which its branches are distributed. The skin and mucous membranes, the eye, nose, or teeth may be experimentally injured without any evi- 5S6 TEXT-BOOK OF PHYSIOLOGY. dences of pain on the part of the animal. Various reflexes, e. g., those of mastication, insahvation, deglutition, the afferent paths of which are formed in part by the fifth nerve, are often seriously im- paired. At the same time the lacrimal secretion diminishes and the pupil contracts. The same results are observed in human beings in w^hom the nerve has been divided for relief from neuralgia. Anes- thesia or a loss of sensibility may also be caused by pathologic lesions of the nerve-trunks or of the sensor end-nuclei. Division of the large root at or near the ganglion of Gasser has not infrequently been followed by an alteration in the nutrition of the eye and nose. In the course of twenty-four hours the eye becomes vascular and inflamed; the cornea becomes opaque; ulceration sets in which may lead to complete destruction of the eyeball. The mucous membrane of the nose becomes swollen, vascular, and liable to hemorrhage on the slightest irritation. The degenerative changes may lead to a complete loss of the sense of smell. These results were formerly attributed to a loss of trophic influence which it was believed the nerve exercised over these structures. Modern experimentation and various surgical procedures have demonstrated that the nutritive disorders are septic in origin, made possible by the anesthetic condi- tion and by the changed vascular supply from division of the vaso- motor fibers which join the nerve at or near the ganglion. Origin of the Efferent Axons. — The efferent axons arise for the most part from nerve-cells located in the gray matter beneath the upper half of the floor of the fourth ventricle. A group of cells known as the superior or accessory nucleus, situated posterior to the corpora cjuadrigemina, give origin to axons which descend and join the axons from the chief motor nucleus (Fig. 247). Distribution. — From their origin the fibers pass forward through the pons and emerge on its lateral aspect, forming the so-called small root of the fifth nerve. This then passes forward beneath the ganglion of Gasser, leaves the cavity of the skull through the foramen ovale, and joins the inferior maxillary division already described. Its axons are ultimately distributed to the muscles of mastication: viz., the masseter, the temporal, the external and internal pterygoids, the mylohyoid, and the anterior portion of the digastric. A few axons are also distributed to the tensor tympani and tensor palati muscles (Fig. 250). The efferent or peripherally coursing axons thus serve to bring the nerve-cells from which they arise into relation with the muscles of mastication. Cortical Connections. — The nuclei of origin of the small root are in histologic and physiologic relation with the lower third of the motor area of the cerebral cortex. Nerve-cells in this region give off axons which enter the pyramidal tract, descend through the in- ternal capsule and the crus cerebri, after which they cross to the THE CRANIAL NERVES. 557 opposite side. Their end-tufts arborize around the cells of nuclei in the medulla oblongata. Properties. — Stimulation of the small root gives rise to convulsive movements of the muscles of mastication. Division of the nerve is followed by a paralysis of these muscles. Contraction or paralysis of Fig. 250. — Inferior Maxillary Branxh of the Trigeminal Nerve, i. Branch to the masseter muscle. 2. Filament of this branch to the temporal muscle. 3. Buccal branch. 4. Branches anastomosing with the facial nerve. 5. Filament from the buccal branch to the temporal muscle. 6. Branches to the e.xternal pterygoid muscle. 7. Middle deep temporal branch. 8. Auriculo-temporal nerve. 9. Temporal branches. 10. Auricular branches. 11. Anastomosis with the facial nerve. 12. Lingual branch. 13. Branch of the small root to the mylo-hyoid muscle. 14. Inferior dental nerve, with its branches (15, 15). 16. Mental branch. 17. Anastomosis of this branch with the facial nerve. — (Hirsch- jeld.) the tensor tympani and tensor palati muscles would also be observed under the same conditions. Functions. — The fifth nerve, by virtue of its transmitting nerve impulses from the periphery to the cerebral cortex, where they evoke sensation, endows all the parts to which it is distributed with sensi- bility; it also endows the muscles of mastication with motihty 558 TEXT-BOOK OF PHYSIOLOGY, Throughrthe relation of its central end-tufts with the motor nuclei in the medulla and pons, it assists in the reflex acts of mastication and insalivation. SIXTH PAIR. THE ABDUCENS. The sixth cranial nerve, the abduccns, consists of peripherally coursing axons which serve to bring the nerve-cells from which they arise into relation with the external rectus muscle. Origin. — The axons arise from a group of cells located in the gray matter beneath the upper half of the floor of the fourth ventricle. It is quite probable that a few fibers in each nerve-trunk come from the nucleus on the opposite side of the middle line. Distribution. — The nerve- fibers pass forward from their origin through the gray and white matter and emerge through the groove between the medulla oblongata and the pons Varolii just external to the anterior pyramid. The nerve then passes through the sphenoid fissure into the orbit cavity, where it is distributed to the external rectus muscle (Fig. 251). In its course the nerve receives filaments from the carotid plexus of the sym- pathetic. Cortical Connections. — The nucleus of the sixth nerve is in histologic and physiologic connection vAih. the motor area of the cerebral cortex. From nerve-cells in this region axons are given off which enter the pyramidal tract, descend through the internal capsule and crus cerebri, after which they cross to the opposite side, w^here their end-tufts arborize around the cells of the nucleus already described. Properties. — Stimulation of the nerve is followed by spasmodic contraction of the external rectus muscle and external deviation of the eyeball. Division of the nerve is followed by paralysis or relaxa- tion of the muscle. As a result of the unopposed action of the internal rectus the anterior pole of the eyeball is turned toward the middle hne (internal strabismus). In consequence of this deviation there is homonymous diplopia. The images are on the same level Fig. 251. — Distribution of the Motor OCULI EXTERNUS OR AbDUCENS. I. Trunk of the motor oculi communis, with its branches (2, 3, 4, 5, 6, 7). 8. Motor oculi externus, passing to the external rectus muscle. 9. Fila- ments of the motor oculi externus anastomosing with the sympathetic. 10. Ciliary nerves. — (Hirschfeld.) THE CRANIAL NERVES. 559 and parallel. The image of the paralyzed eye lies external to that of the normal eye. Function. — The function of this nerve is to transmit nerve im- pulses to the external rectus muscle and excite it to contraction. SEVENTH PAIR. THE FACIAL. The seventh cranial nerve, the facial, consists of peripherally coursing nerve-fibers, which serve to bring the nerve-cells from which they arise into relation with most of the superficial muscles of the head and face. The muscles supplied by this nerve, as stated by the general anatomists, are as follows: The occipito-frontalis, corrugator super- cilii, orbicularis palpebrarum, levator labii superioris, alaeque nasi, zygomatici, the pyramidalis nasi, the compressor nasi, the depressor alae nasi, levator anguli oris, buccinator, orbicularis oris, depressor anguli oris, depressor labii inferioris, the levator menti, the posterior belly of the digastric, the stylo-hyoid, and the platysma myoides. Origin. — The nerve-fibers or axons composing the seventh nerve arise for the most part from a nucleus of large multipolar nerve-cells situated about five milhmeters beneath the upper half of the floor of the fourth ventricle toward the middle line. From this nucleus, which is about four millimeters long, axons emerge which at first pass inward and backward as far as the epen- dyma of the ventricle ; they then turn on themselves, forming an arch that encloses the nucleus of the sixth nerve; they then course down- ward and outAvard, emerging from the pons at its lower border between the olivary and restiform bodies. As the axons approach the floor of the ventricle collateral branches are given oft' which, crossing the median line, arborize around the nerve-cells of the opposite facial nucleus. Clinical observations and histologic investigations, however, render it probable that the libers distributed to the occipito-frontalis, the cor- rugator supercihi, and the upper half of the orbicularis palpebrarum, are derived from the oculo-motor nucleus, and, descending the posterior longitudinal bundle, enter the trunk of the facial as it turns to pass forward through the pons. It is also probable, for similar reasons, that the fibers distributed to the orbicularis oris are derived from the hypoglossal nucleus. Cortical Connections. — The nucleus of the facial nerve is in histologic and physiologic connection with the facial region of the general motor area of the cerebral cortex. From the cells of this region axons descend through the pyramidal tract, the internal cap- sule, and the crus cerebri, beyond wliich they cross to the opposite side and arborize around the cells of the nucleus already described. Distribution. — From its superficial origin the trunk of the nerve passes into the internal auditory meatus beside the auditory nerve. 56o TEXT-BOOK OF PHYSIOLOGY. After passing forward and outward for a short distance through the bone above and between the cochlea and vestibule, the nerve makes a sharp bend, forming the genu facialis, turns backward and enters the aqueduct of Fallopius, the general course of which it follows as far as the stylo-mastoid foramen. After emerging from this foramen Fic. 252. — Superficial Branches of the Facial and the Fifth. — i. Trunk of the facial. 2. Posterior auricular nerve. 3. Branch which it receives from the cervical plexus. 4. Occipital branch. 5, 6. Branches to the muscles of the ear. 7. Digastric branches. 8. Branch to the stylo-hyoid muscle. 9. Superior ter- minal branch. 10. Temporal branches. 11. Frontal branches. 12. Branches to the orbicularis palpebrarum. 13. Nasal or suborbital branches. 14. Buccal branches. 15. Inferior terminal branch. 16. Mental branches. 17. Cervical branches. 18. Superficial temporal nerve (branch of the fifth). 19, 20. Frontal nerves (branches of the fifth). 21, 22, 23, 24, 25, 26, 27. Branches of the fifth. 28, 29, 30, 31, 32. Branches of the cervical nerves. — {Hirschjeld.) the nerve passes downward and forward as far as the parotid gland, within which it terminates by dividing into two main branches, the temporo-facial and the cervico-facial, the ultimate branches of which are distributed as previously stated to the superficial muscles of the head and face (Fig. 252). THE CRANIAL NERVES. 561 The Pars Intermedia or Nerve of Wrisberg. — The facial nerve at the genu, the point where it turns backward to enter the aque- duct of Fallopius, presents a shght enlargement, grayish in color, and in which nerve-cells are contained. This enlargement is known as the geniculate ganglion. The cells of this ganglion, originally bipolar, present single axons which soon divide into centrally and peripherally coursing branches. The former collectively constitute the pars intermedia or nerve of Wrisberg, which, entering and passing through the pons, termi- nates around the sensor end-nucleus of the glosso- pharyngeal nerve ; the latter, the peripherally directed branches, enter the sheath of the facial and accompany it as far as a point about five millimeters above the stylo-mastoid foramen. From its mode of origin the nerve of Wrisberg can not be regarded as an integral part of the facial nerve proper, but is to be regarded as an independent sensor nerve. As to the true function and relation of this nerve there is much conflict of opinion. Branches of the Fa- cial. — In the aqueduct of Fallopius the facial gives off the following branches : the greater and lesser petrosals, the stapedius, and the chorda tympani (Fig. 2 5 3). 1. The greater petrosal nerve is given off near the geniculate ganglion. It then passes forward into the spheno-maxillary fossa and ter- minates in the spheno-palatine ganglion by an arborization of its fibers around the ganglion cells. 2. The lesser petrosal nerve is given off at a point somewhat external to the preceding. It leaves the skull by a small foramen and terminates in the otic ganglion by an arborization of its fibers around the ganglion cells. 3. The stapedius branch leaves the aqueduct of Fallopius somewhat further down by a small foramen, enters the pyramid of the middle ear, and is finally distributed to the stapedius muscle. 4. The chorda tympani is given off from the facial at a point about five millimeters above the stylo-mastoid foramen. It then passes 36 Fig. 253. — Chorda Tympani Nerve, i, 2, 3, 4. Facial nerve passing through the aquae- ductus Fallopii. 5. Ganglioform enlarge- ment. 6. Great petrosal nerve. 7. Spheno- palatine gangHon. 8. Small petrosal nerve. 9. Chorda tympani. 10, 11, 12, 13. Various branches of the facial. 14, 14, 15. Glosso- pharyngeal nerve. — {Hirschjeld.) 562 TEXT-BOOK OF PHYSIOLOGY. upward and forward and enters the tympanum through the iter chordae posterius, crosses the tympanic membrane between the malleus and incus, leaves the tympanum by the iter chordae anterius or canal of Huguier, and finally joins the lingual branch of the fifth. Some of its fibers can be traced to the dorsum of the tongue, others to the submaxillary and sublingual ganglia, where they terminate in tufts around the ganglion cells. Properties. — Electric stimulation of the trunk of the nerve after its emergence from the stylo-mastoid foramen produces convulsive movements in all the muscles to which its branches are distributed. The same results follow stimulation of the intracranial portion of the nerve in an animal recently killed. Irritative pathologic lesions — e. g., tumors, aneurysms, etc. — situated along the course of the nerve or at its nuclear origin, fre- quently give rise to spasmodic movements of the facial muscles which may be tonic or clonic in character. Division of the facial nerve after its emergence from the stylo- mastoid foramen is followed by a complete relaxation or paralysis of the superficial facial muscles. The same result follows compres- sion of the nerve-trunk in any part of its intracranial course. The phenomena presented by an individual suffering from division or compression of the facial nerve, and which collectively constitute facial paralysis, are as follows: a relaxed and immobile condition of the side of the face corresponding to the lesion ; separation of the eye- lids from paralysis of the orbicularis palpebrarum and the unopposed contraction of the levator palpebrae muscles; abohtion of the act of winking; drooping of the angle of the mouth; an escape of saliva from the mouth; contraction of the muscles and distortion of the opposite side of the face; on attempting to laugh or talk the dis- tortion of the face is increased; during mastication the food accu- mulates between the teeth and cheek, from paralysis of the buccina- tor; articulation is impaired from paralysis of the orbicularis oris muscle, the labial sounds especially being imperfectly produced. Properties of the Branches Given off in the Aqueduct of Fallopius. — The great petrosal nerve is in all probabihty composed of efferent fibers (vaso-dilatator and secretor) which leave the pons by way of the nerve of Wrisberg, or pars intermedia, to be distributed around the cells of the spheno-palatine ganglion; for stimulation either of this nerve or of the ganglion is followed by the same results : viz., dilatation of the blood-vessels of, and secretion from, the mucous membrane of the nose, soft palate, upper part of the pharynx, roof of mouth, gums, and upper lip. The small petrosal nerve is also composed of efferent fibers; shortly after leaving the facial it is joined by a small nerve, derived from Jacobson's branch of the glosso-pharyngeal, which is also effer- THE CRANIAL NERVES. 563 ent in function; for stimulation of Jacobson's nerve as well as stimula- tion of the otic ganglion is followed by the same result: viz., dilatation of the blood-vessels of, and secretion from, the mucous membrane of the cheek, lower lip, and gums, and of the parotid and the orbit glands. The stapedius nerve, distributed directly to the stapedius muscle, is motor in function. The Chorda Tympani. — Stimulation of the chorda tympani nerve in the tympanic cavity produces dilatation of the blood-vessels of, and an increased production and discharge of saliva from, the sub- maxillary and subhngual glands. Division of this nerve is followed by a contraction of the blood- vessels and a diminution of the secretion. From these results it is certain that the chorda tympani contains both vaso-dilatator and secre- tor fibers. Nicotin applied to the submaxillary and sublingual gang- lia abolishes the effects of stimulation of the chorda tympani. It does not prevent the same effects when the ganglia themselves are stimulated. It is clear, therefore, that the vaso-dilatator and secretor fibers arborize around the cells of the gangha and are not distributed directly to the gland structures. It is highly probable that the efferent fibers in the chorda tympani emerge from the pons by way of the pars intermedia, or nerve of Wrisberg. Division of the chorda in the tympanum is also followed by a loss of taste in the anterior two-thirds of the tongue. For this and other reasons the chorda tympani has long been regarded as the nerve of taste for this region. The specific physiologic stimulus to the chorda tympani nerve is organic matter in solution acting on the peripheral terminations of the nerve in the mucous membrane of the tongue. The exact pathway for these afferent or gustatory fibers beyond the geniculate ganglion has long been a subject of much discussion. According to some observers these fibers enter the great petrosal nerve, pass forward as far as the spheno-palatine ganglion, then into the superior maxillary division of the trigeminal, and so to the brain. According to others, these fibers pass into the pars intermedia, into the pons, where they terminate around the sensor end-nucleus of the glosso-pharyngeal. The evidence for and against either of these two views is most conflicting and insufficient to justify positive state- ments one way or the other. To the writer the weight of evidence seems to favor the view that the gustatory fibers have their origin in the geniculate ganglion ; that they pass centrally through the pars in- termedia ; that they are similar in function to the glosso-pharyngeal ; and that they are indeed but aberrant branches of this nerve. Functions. — The facial is the motor nerve to the muscles of the face. As these muscles express ideas and emotions the nerve has been termed the nerve of expression. Because of the presence of efferent fibers which leave the main trunk by way of the chorda tympani nerve, it regulates the caliber of the blood vessels of the submaxillary 564 TEXT-BOOK OF PHYSIOLOGY. and sublingual glands and excites the glands to activity. influences hearing by its action on the stapedius muscle. It also EIGHTH PAIR. THE AUDITORY. The eighth cranial nerve, the auditory, consists of the centrally coursing axons of neurons which connect the essential organ of hearing with sensor end-nuclei ,-- 10 in the pons Varolii. This nerve ..-■'' consists of two portions: viz., a cochlear or auditory and a ves- tibular or equilibratory. Origin. — The axons compris- ing the cochlear portion have their origin in the bipolar nerve- cells of the spiral gangHon located in the spiral canal near the base of the osseous lamina spiralis (Fig. 254). From this origin they pass centrally into the cen- tral canal of the modiolus, at the base of which they emerge in well-defined bundles and enter the internal auditory meatus. Dendritic processes from these cells pass peripherally to termi- nate on the ciliated epithelial cells of the organ of Corti. The axons comprising the vestibular portion have their origin in the bipolar nerve-cells of the ganglion of Scarpa located in the internal auditory meatus. From this origin they pass cen- trally in connection with th6 cochlear portion. Dendritic pro- cesses from these cells pass per- ipherally into the internal ear, where they terminate on epithe- lial cells situated on the inner surface of the utricle and saccule and in the ampullae of the semicircular canals. The common trunk of the auditory nerve, consisting of both cochlear and vestibular divisions after emerging from the internal auditory meatus, passes backward, inward, and downward as far Fig. 254. — Origin and Termination OF THE Auditory Nerve. i. Cochlea. 2. Spiral ganglion (Corti). 3. Cochlear nerve. 4. Ventral acoustic nucleus. 5. Lateral acoustic nucleus. 6. Semicircular canals. 7. Ganglion of Scarpa. 8. Vestibular nerve. 9. Dorso-external nucleus (Deiters). 10. Dorso-internal nu- cleus. — (After Moral and Doyon.) THE CRANIAL NERVES. 565 as the lateral aspect of the pons where the two divisions again separate. The cochlear nerve, the external root, passes to the outer side of the restiform body and enters the ventral acoustic nucleus and the lateral acoustic nucleus, around the cells of which its end-tufts arborize. The vestibular nerve, the internal root, passes on the inner side of the restiform body to the dorsal portion of the pons, where, after bifurcating, the end-tufts of the axons arborize around the dorso-internal or chief auditory nucleus and the dorso-external or Deiters' nucleus. Some of the fibers of the vestibular branch descend through the pons and medulla as far as the cuneate nucleus. Cortical Connections. — The cochlear nerve is ultimately con- nected with the cerebral acoustic area, in the temporal lobe of the opposite side through the intermediation of the auditory tract. This tract is complex and involved. In a general way it may be said to consist in part of fibers which come direct from the cochlear branch. After passing through the ventral nucleus and the trapezoid body they cross the median hne, enter the lemniscus or fillet, and finally terminate in the pre- and post-geminal bodies. In their course they give off collateral branches to these various nuclei through which they pass. Other fibers taking their origin from cells in these various nuclei proceed to the cortex where they terminate. Properties. — Stimulation of the cochlear nerve is unattended by either motor or sensor phenomena. Division of the nerve is fol- lowed by a loss of the sense of hearing. Irritative pathologic lesions give rise to sensations of sound of varying character and intensity. Degeneration of the nerve or destruction by tumors, etc., will also be followed by a loss of the sense of hearing. Experimental lesions of the semicircular canals involving a destruction of the physiologic relations of the vestibular nerve are followed by a loss of the coordinating and equilibratory power. Disordered movements, such as rotation to the right or left, somer- saults backward and forward, follow destruction of these canals. Pathologic lesions in the peripheral distribution of the nerve are attended in man by disturbances of equilibrium ; e. g., vertigo, a sense of swaying, pitching, and staggering. Functions. — The function of the cochlear nerve is to convey nerve impulses from its origin to the pons, from which they are transmitted by the auditor\' tract to the acoustic area in the cerebral cortex. The specific physiologic stimulus to the development of these impulses is the impact of atmospheric undulations on the tym- panic membrane, received and transmitted by the chain of bones to the structures of the internal ear, — the organ of Corti, — with which the peripheral terminations of the nerve are connected. The function of the vestibular nerve is the transmission of nerve impulses to the 566 TEXT-BOOK OF PHYSIOLOGY. pons, whence they are transmitted to the cortex of both the cerebrum and cerebelhim and to other centers. The specific physiologic stim- ulus is supposed to be a variation in pressure in the ampullae of the semicircular canals caused by movements of the endolymph induced by changes in the position of the head and body. The impulses carried by the vestibular nerve give rise refiexly to certain adaptive and pro- tective movements by which the equilibrium of the body in both dynamic and static conditions is maintained. NINTH NERVE. THE GLOSSO-PHARYNGEAL. The ninth cranial nerve, the glosso-pharyngeal, consists, as shown by both histologic and experimental methods of research, of both afferent and efferent nerve-fibers, of which the former, however, are by far the more abundant. Near its exit from the cavity of the skull the nerve presents two ganglionic enlargements known as the petrosal and jugular ganglia. Origin of the Afferent Fibers. — The afferent fibers serve to bring certain end-nuclei in the medulla oblongata into anatomic and physiologic relation with portions of the mucous membrane of the tongue, pharynx, and middle ear. The afferent fibers are axons of the monaxonic cells of the petrosal and jugular ganglia. The single axon from each of these cells soon divides into two branches, one of which passes centrally, the other peripherally. The centrally directed branches collectively form the so-called roots, four or five in number, which enter the medulla between the olivary and resti- form bodies. The peripherally directed branches collectively form the two main divisions, from the distribution of which, to the tongue and pharynx, the nerve takes its name. Distribution. — The axons of the centrally directed branches after entering the medulla pass toward its dorsal aspect, where they bifurcate, give off collateral branches, and terminate in fine end- tufts in the immediate neighborhood of two groups of nerve-cells, the sensor end-nuclei. The axons of the peripherally directed branches, after emerging from the base of the skull through the jugular foramen, pass forward and inward under cover of the stylo- pharyngeal muscle; winding around this muscle they divide into terminal branches which are distributed to the mucous membrane of the posterior one-third of the tongue, pharynx, soft palate, uvula, and tonsils (Fig. 257). Origin of the Efferent Fibers. — The efferent fibers serve to bring the nerve-cells from which they arise into connection with a portion of the musculature of the fauces and phar}'nx. These nen-e- cells are located in the lateral portion of the formatio reticularis at some distance below the floor of the fourth ventricle. Thev consti- THE CRANIAL NERVES. 0^7 tute the upper portion of a collection of cells known as the nucleus amhiguus. Distribution. — From this origin the efferent fibers pass dorsally to near the sensor end-nuclei, then turn outward and forward and finally emerge from the medulla in intimate association with the afferent fibers. They are ultimately distributed to the stylo-pharyn- geus, the palato-glossus and to the middle constrictor muscles of the pharynx. In addition to the foregoing eft'erent fibers the glosso- pharyngeal nerve contains at its emergence from the medulla both vaso-motor and secretor fibers. Jacobson's Nerve. — This is a small branch which leaves the glosso-phar}'ngeal at the petrous ganglion. After passing through a small canal in the base of the skull it enters the tympanic cavity, within which it gives off branches to the great and lesser petrosal nerves, to the mucous membrane of the foramen ovale, the foramen rotundum, and to the Eustachian tube. Cortical Connections. — The motor nucleus is doubtless con- nected with the general motor area of the cortex through fibers de- scending in the pyramidal tract. The exact location of the cortical area for the phar}mx is not well determined, but is most likely to be found in the lower part of the general motor area near the termination of the Rolandic fissure. The cortical connections of the afferent tract are unknown. Properties. — Electric stimulation of the glosso-pharyngeal trunk calls forth evidence of pain and contraction of the stylo-pharyngeus and middle constrictor muscles. Division of the nerve abolishes sensibility in the mucous membrane to which it is distributed, impairs the sense of taste in the posterior third of the tongue, and gives rise to paralysis of the above-mentioned muscles. Stimulation of Jacobson's nerve is followed by dilatation of the blood-vessels of, and secretion from, the mucous membrane of the lower lip, cheek, and gums, and from the parotid gland. Division of the nerve is followed by the opposite results. The course of the fibers which give rise to these results is by way of the lesser petrosal to the otic ganglion, around the cells of which the fibers arborize. From the cells of this ganghon non-medullated fibers pass to the blood-vessels and gland cells. Functions. — The afferent fibers of the glosso-pharyngeal trans- mit nerve impulses from the parts to which they are distributed to the cerebral cortex, where they evoke sensations of pain and sensations of taste; they also assist in all probabihty in the performance of certain reflexes connected with deglutition. The efferent fibers trans- mit impulses to muscles, exciting them to activity, and to the otic ganglion, which in turn dilates blood-vessels and excites secretion. 568 TEXT-BOOK OF PHYSIOLOGY. TENTH NERVE. THE PNEUMOGASTRIC OR VAGUS. The tenth cranial nerve, the pneumogastric or vagus, consists, as shown by histologic methods of research, of both afferent and efferent fibers, independent of those derived in its course from adjoin- ing motor or efferent nerves. Near the exit of the nerve from the cavity of the cranium it presents two ganghonic enlargements known respectively as the ganglion of the root (the jugular) and the ganglion of the trunk (the plexiform). Origin of the Afferent Fibers. — The afferent fibers take their origin in the monaxonic cells of the gangha on the root and trunk. The single axon from each of these cells soon divides into two branches, one of which passes centrally, the other peripherally. The centrally directed branches collectively form the so-called roots, ten to fifteen in number, which enter the medulla between the restiform body and the lateral column. The peripherally directed branches collectively form a portion of the common trunk of the nerve. Distribution. — The axons of the centrally directed branches after entering the medulla pass toward its dorsal aspect, where they bifurcate, give off collaterals, and terminate in fine end-tufts in the immediate neighborhood of two groups of nerve-cells, the vagal sensor end-nuclei. The axons of the peripherally directed branches unite to form a portion of the common trunk, which, as it descends the neck and enters the thorax and abdomen, gives off a number of branches which are ultimately distributed to the mucous membrane of the esophagus, larynx, lungs, stomach, and intestine, and also to the heart. The afferent fibers thus serve to bring into anatomic and physiologic relation the mucous membrane of these organs with certain sensor ' end-nuclei in the medulla oblongata. Origin of the Efferent Fibers. — The efferent fibers take their origin from nerve-cells located in the lateral portion of the jormatio reticularis at some distance below the floor of the fourth ventricle. These cells constitute the lower portion of the nucleus amhiguus. Distribution. — From their origin the efferent axons pass dor- sally to near the sensor end-nuclei, then turn outward and forward, and finally emerge from the medulla in close association with the afferent branches. They are ultimately distributed to the levator palati, azygos uvulae, and palato-pharyngus muscles; to the superior and inferior constrictor muscles of the pharynx, and to the muscles of the esophagus; to the muscle-fibers of the stomach and perhaps the intestines; and to the non-striated muscle-fibers of the bronchial tubes. Among the efferent fibers are some which are distributed to the gastric glands and to the pancreas. According to Beevor and Horsley, in the monkey the motor fibers for the levator palati come from the spinal accessory nerve. THE CRANIAL NERVES. 569 The efferent fibers thus serve to bring the nerve-cells from which they arise into anatomic and physiologic connection with a portion of the musculature of the aHmentary canal and its diverticulum, the lung. Communicating Branches. — At or near the ganglia the vagus receives communicating branches from the eleventh nerve, the spi- nal accessor}', the facial, the hypoglossal, and the anterior branches of the two upper cervical nerves. Owing to this manifold origin of the efferent fibers in the trunk and peripheral branches of the vagus, it is, in some instances, difficult, if not impossible, to determine to which of these nerves a given muscle contraction is to be referred. Vagal Branches. — As the vagus passes down the neck it gives off the following main branches (Fig. 255) : 1. The pharyngeal ?terves which, after entering into the formation of the phar}'ngeal plexus, are distributed to the mucous membrane and to the muscles of the pharynx; e. g., superior and inferior constrictors, the levator palati, and the azygos uvulse. 2. The superior laryngeal nerve which, entering the larynx through the thyro-hyoid membrane, is distributed to the mucous mem- brane fining the interior of the larv'nx and to the crico-thyroid muscle. From the superior laryngeal and the main trunk small branches are given oft' which in the rabbit unite to form a single nerve, the so-called depressor nerve. It is distributed to the heart-muscle. Though this anatomic arrangement is not found in man, there are many reasons for believing that analogous fibers are present in the vagus trunk of man and other animals. 3. The inferior laryngeal nerve which is distributed ultimately to all the muscles of the larynx except the crico-thyroid and to the inferior constrictor of the pharynx. 4. The cardiac nerves which, after entering into the formation of the cardiac plexus, are distributed to the heart. 5. The pulmonary nerves distributed to the mucous membrane of the bronchial tubes and their ultimate terminations, the lobules and air-cells, as well as to their non-striated muscle-fibers. 6. The gastric and intestinal nerves, distributed to the mucous mem- brane and muscular walls of the stomach and intestines. Other fibers in all probabiHty pass to the liver, spleen, kidney, and suprarenal bodies. Properties of the Pneumogastric or Vagus Nerve and its Various Branches. — Faradization of the vagus nerve close to the medulla oblongata gives rise to sensations of pain and to contraction of the musculature of a portion of the alimentary tract: viz., the palate, phar}'nx, esophagus, stomach, and possibly of the intestine and of the pulmonary apparatus. Division of the nerve is followed by a loss of sensibihty in the mucous membrane of the ahmentary S70 TEXT-BOOK OF PHYSIOLOGY. tract and of the pulmonary apparatus, together with a loss of motility of the structures above mentioned. Fig. 255. — Distribution of the Pneumogastric. — i. Trunk of the left pneumo- gastric. 2. Ganglion of the trunk. 3. Anastomosis with the spinal accessory. 4. Anastomosis with the subhngual. 5. Pharyngeal branch (the auricular branch is not shown in the figure) . 6. Superior laryngeal branch. 7. External laryngeal nerve. 8. Laryngeal plexus, q, 9. Inferior larj'ngeal branch. 10. Cervical car- diac branch. II. Thoracic cardiac branch. 12, 13. Pulmonary branches. 14. Lin- ,'. gual branch of the fifth. 15. Lower portion of the subhngual. 16. Glosso-pharyn- geal. 17. Spinal accessory. 18,19,20. Spinal nerves. 21. Phrenic nerve. 22,23. Spinal ner\'es. 24, 25, 26, 27, 28, 29, 30. Sympathetic ganglia. — {Hirschjeld.) ■ Stimulation of the trunk of the nerve in different parts of its course produces a variety of results dependent to some extent on the presence of anastomosing branches from adjoining nerves. THE CRANIAL NERVES. 571 The Pharyngeal Nerves. — Faradization of the pharyngeal nerves consisting of both afferent and efferent fibers, gives rise to sensations of pain, contraction of the pharyngeal muscles, and perhaps to vomit- ing. Division of these nerves is followed by a loss of sensibiHty in the parts to which they are distributed and by paralysis of the muscles with a consequent impairment of deglutition. The Superior Laryngeal Nerve. — Faradization of the superior laryngeal nerve gives rise to sensations of pain, and to contraction of the crico-thyroid muscle. Through reflected impulses it causes con- traction of the muscles of deglutition, and of the muscles concerned in the act of coughing; inhibition of the inspirator}' movement and arrest of respiration in the condition of expirator}' standstill, with perhaps a tetanic contraction of the expiratory muscles; and con- traction of the laryngeal muscles with closure of the glottis. Periph- eral stimulation of this nerve — e. g., the contact of foreign particles — gives rise to a similar series of phenomena. Division of these nerves is followed by a loss of sensibility in the laryngeal mucous membrane, paralysis of the crico-thyroid muscle with a consequent lowering of the pitch, and a diminution in the clearness of the voice. In conse- quence of the loss of the sensibiHty there is an inability to perceive the entrance of foreign bodies into the lar}'nx. The Depressor Nerve. — Stimulation of the peripheral end of the depressor nerve is without effect; stimulation of the central end re- tards and even arrests the heart's pulsations and lowers the general blood-pressure. These two effects, though associated, are neverthe- less independent of each other. If the vagus nerves be divided on both sides between the origin of the depressor and the origin of the cardiac nerves, and the former stimulated, there will be a fall of pressure without retardation of the heart. The effect on the heart is attributed to a stimulation of the cardio-inhibitory mechanism in the medulla oblongata. The fall of general blood-pressure was formerly attributed to a sudden dilatation of the splanchnic blood-vessels alone, in conse- quence of a depression of that portion of the general vaso-motor center which maintains through the splanchnic nerves a tonic contraction of their walls. It has been satisfactorily demonstrated that this is not the sole cause ; for after division of the splanchnic nerves, stimulation of the depressor causes a still further fall of from 30 to 40 per cent.' in the general pressure (Porter and Beyer). Evidently, not anyone, but all portions of the vaso-motor center are subject to the effects of depressor stimulation. The Inferior Laryngeal Nerves. — Faradization of the inferior laryngeal nerves produces effects which vary in accordance with the strength of the stimulus, with different animals, and with the same animal at different periods of life. In the adult dog and in man, the 572 TEXT-BOOK OF PHYSIOLOGY. glottis is kept widely open for respiratory purposes by the tonic con- traction of the abductor muscles (the crico-arytenoids) ; for phonatory purposes the glottis is closed and the vocal membranes approximated by the contraction of the adductor muscles. It has been shown that these opposed groups of muscles have independent nerve-supplies; that two sets of fibers in the common trunk can be separated and stimulated independently of each other. Feeble stimulation of the common trunk produces a still further abduction of the vocal cords. With an increase in the strength of the stimulus, however, the reverse obtains: namely, adduction which increases until the glottis is com- pletely closed. Division of the nerves is followed by paralysis of both the phonatory and respiratory muscles, the abductors and adductors, with the result of seriously impairing both phonation and respiration and not infrequently causing death. The fibers of the inferior laryn- geal nerve are derived from the eleventh nerve, the spinal accessory. The Cardiac Nerves. — Faradization of the trunk of the vagus or of the peripheral end of the divided nerve gives rise to a diminution in the frequency and force of the heart's contractions; and if the stim- ulation be sufficiently powerful, completely arrests it in the phase of diastole. To these results the term inhibition is applied. Division of the vagi or of the cardiac branches is follo\Yed by an increase in the number of the contractions from loss of inhibitor influences. The inhibitor fibers of the vagus are generally believed to be derived from the spinal accessory, though this has been questioned. Accord- ing to the recent investigations of Schaternikoiif and Friedenthal, they come direct in the vagus, from a nucleus near the vagal motor nucleus in the medulla, the spinal accessory sending no branches to the heart. In the frog and other batrachia the vagus contains also accelerator or augmentor fibers derived from the sympathetic; hence stimulation, especially if feeble, may increase the heart's action or may only retard, but not arrest, the heart. The Pulmonary Nerves. — The pulmonary nerves, given off from the trunk after its entrance into the thorax, do not lend themselves readily to experimentation. Division of both vagi in the neck above the point of exit of the pulmonary branches is followed by a decrease in the frequency of the respiratory acts, with an increase in their depth. At the same time there is a loss of sensibility of the mucous membrane of the trachea and lungs and a paralysis of non-striated muscle-fibers. Stimulation of the central end of the vagus increases the frequency, but decreases the amplitude, of the respiratory movements. If the stimulation be increased in intensity the respiratory movements in- crease in frequency until the inspiratory muscles pass into the con- dition of tetanus. Feeble stimulation of the vagus not infrequently inhibits the inspiratory movement and increases the expiratory until there is a THE CRANIAL NERVES. 573 complete cessation of movement in the condition of expiratory stand- still. The effect thus produced is similar to, if not identical with, that produced by stimulation of the superior laryngeal nerv^e. This would seem to indicate the presence in the vagus trunk of two sets of afferent fibers coming from the lungs through the pulmonary branches, one of which inhibits inspiration, the other expiration. Faradization of the trunks of the pulmonary branches or stimula- tion of their peripheral terminations in the mucous membrane of the bronchial tubes or alveoli by the inhalation of chemic vapors causes arrest of respiratory movements, a fall of blood-pressure, and a reflex inhibition of the heart (Brodie). Gastric Nerves. — Stimulation of the peripheral end of a divided vagus nerve causes a distinct contraction of the right half of the stomach and secretion from the gastric glands. Division of the nerve abolishes the sensibility of the mucous membrane of the stomach, impairs motihty, and interferes with the secretion of the gastric juice. Similar experimentation on the trunk of the vagus has shown that the nerve excites contraction of the upper part of the small intestine and of the gall-bladder, the secretion of the pancreas, the renal cir- culation, the secretion of urine, etc. Functions. — The afferent fibers transmit nerve impulses from the area of their distribution to the medulla and thence through cortical connections to the sensor cerebral areas, where they evoke sensations. The efferent fibers transmit impulses outward which excite con- traction of the muscles of the esophagus, the stomach, the small intes- tine, and the gall-bladder, and the muscles of the bronchial tubes excite secretion from the glands of the stomach, pancreas, and kidney and exert an inhibitor influence on the activity of the heart. The efferent fibers belong to the autonomic system of nerves and are not connected with the ganglia of the vagus, but with local peripheral ganglia. ELEVENTH PAIR. THE SPINAL ACCESSORY. The eleventh cranial nerve, the spinal accessory, consists of peripherally coursing fibers which bring the nerve-cells from which they arise into relation with separate but functionally related muscles. It consists of two portions, the medullary or bulbar and the spinal. Origin. — The axons comprising the medullary portion arise from a group of nerve-cells in the lower part of the nucleus ambiguus. From this origin the axons pass forward and outward to emerge from the medulla just below and in series with the roots of the vagus nerve. The axons comprising the spinal portion have their origin in nerve-cells in the lateral margin of the anterior horn of the gray matter in the cervical portion of the cord as far down as the fifth 574 TEXT-BOOK OF PHYSIOLOGY. cervical vertebra. From this origin the fibers pass to the surface of the cord to emerge between the ventral and dorsal roots in from six to eight filaments, after which they unite from below upward to form a distinct nerve. This enters the cranial cavity through the foramen magnum, where it joins with the medullary portion to form the common trunk, which then passes forward to emerge from the cranium through the jugular foramen. Distribution. — After emerg- ing from the cranial cavity the nerve soon separates into two branches : 1. An internal or anastomotic branch, consisting chiefly of filaments coming from the medulla oblongata. It soon enters the trunk of the vagus, from which fibers pass to the muscles of the pharynx, to the muscles of the larynx through the inferior laryngeal nerve, and to the heart accord- ing to most authorities. 2. An external branch, consist- ing chiefly of the accessory fibers from the spinal cord. It is distributed to the sterno-cleido-mastoid and trapezius muscles. Cortical Connections. — The nucleus of origin of the medul- lary branch at least is in relation with nerve-cells in the lower third of the general cerebral motor area, the axons of which descend in the pyramidal tract. Properties. — Faradization of the nerve near its origin gives rise to muscle contraction. Destruction of the medullary root is Fig 256. — Spinal Accessory Nerve. I. Trunk of the facial nerve. 2, 2. Glosso - pharyngeal nerv-e. 3, 3. Pneumogastric. 4, 4, 4. Trunk of the spinal accessory. 5. Sublingual nerve. 6. Superior cervical gang- lion. 7, 7. Anastomosis of the first two cervical nerves. 8. Carotid branch of the sympathetic. 9, 10, 11, 12, 13. Branches of the glosso- pharyngeal. 14,15. Branches of the facial. 16. Otic ganglion. 17. Auricular branch of the pneumogas- tric. 18. Anastomosing branch from the spinal accessory to the pneumo- gastric. 19. Anastomosis of the first pair of cervical nerves with the sub- lingual. 20. Anastomosis of the spi- nal accessory with the second pair of cervical nerves. 21. Pharyngeal plexus. 22. Superior laryngeal nerve. 23. External laryngeal nerve. 24. Middle cervical gang- lion. — {Hirschjeld.) THE CRANIAL NERVES. 575 followed by impairment of deglutition and a loss of the power of producing vocal sounds on account of paralysis of the constrictor muscles of the larynx. According to some authorities, there is also an acceleration of the heart's action from a loss of inhibitor influences. Stimulation of the external branch gives rise to contraction of the sterno-cleido-mastoid and trapezius muscles, though division of the branch does not give rise to complete paralysis, as they are sup- plied with motor fibers also from the cervical nerves. In consequence of division of the external branch animals experience extreme short- ness of breath during exercise, from a want of coordination of the muscles of the fore-limbs and the muscles of respiration. Functions. — The spinal accessory nerve transmits nerve impulses outward which influence the movements of deglutition, and the vocal movements of the larynx, which inhibit the action of the heart and which control respiratory movements associated with sustained or prolonged muscle efforts. TWELFTH PAIR. THE HYPOGLOSSAL. The twelfth cranial nerve, the hypoglossal, consists of peripher- ally coursing nerve-fibers which serve to connect the nerve-cells from which they arise with the musculature of the tongue. Origin. — The axons composing the hypoglossal nerve arise from a collection of nerve-cells situated beneath the floor of the fourth ventricle. This nucleus is elongated and extends from the medullary striae downward as far as the lower border of the olivary body. It is located ventro-laterally to the spinal canal. After leaving the cells of the nucleus the axons pass forward and outward toward the surface of the medulla, from which they emerge in ten or twelve small bundles or filaments in the groove between the olivary body and the anterior pyramid. Beyond this point they unite to form a common trunk. Distribution.- — The common trunk thus formed passes out of the cranial cavity through the anterior condyloid foramen. In its course it receives filaments from the first and second cervical nerves, the sympathetic and vagus. It is finally distributed to the intrinsic muscles of the tongue and to the genio-hyo-glossus, hyo-glossus, and stylo-hyoid muscles. Branches derived from the cervical plexus pass to muscles which elevate and depress the hyoid bone. Cortical Connections. — The hypoglossal nerve nuclei are con- nected with nerve-cells in the lower third of the general motor area around the inferior termination of the fissure of Rolando by axons which descend in the pyramidal tract. Properties. — Faradization of the nerve gives rise to convulsive movements of the muscles to which it is distributed. Division of the nerve is followed by a loss of motion and an interference with deglu- 576 TEXT-BOOK OF PHYSIOLOGY. tition, mastication, and articulation, especially in the pronunciation of the consonantal sounds. In hemiplegia, complicated with paraly- sis of the tongue from injury to the hypoglossal tract, the opposite side of the tongue is involved in the paralysis. On protrusion of the tongue the tip is deviated to the paralyzed side, due to the unopposed action of the muscle of the opposite side. Fig. 257. — Distribution or the Hypoglossal Nerve. — i. Root of the fifth nerve. 2. GangHon of Gasser. 3, 4, 5, 6, 7, 9, 10, 12. Branches and anastomoses of the fifth nerve. 11. Submaxillary ganglion. 13. Anterior belly of the digastric muscle. 14. Section of the mylo-hyoid muscle. 15. Glosso-pharyngeal Nerve. 16. Ganglion of Andersch. 17, 18. Branches of the glosso-pharyngeal nerve. 19, 19. Pneumogastric. 20, 21. Gangha of the pneumogastric. 22, 22. Superior laryngeal branch of the pneumogastric. 23. Spinal accessory nerve. 24. Sublin- gual nerve- 25. Descendens noni. 26. Thyro-hyoid branch. 27. Terminal branches. 28. Two branches, one to the gendo-hyo-glossus and the other to the genio-hyoid muscle. — (Sappey.) Function. — The hypoglossal nerve transmits nerve impulses from its center of origin to the intrinsic and extrinsic muscles of the tongue, endowing them with motility. The coordinate activity of these muscles favorably assists mastication, articulation, and deg- lutition. CHAPTER XXII. THE SYMPATHETIC NERVE SYSTEM. The sympathetic nerve system consists of a number of gangHa united one to another by intervening cords of nerve-fibers. These gangHa may for convenience of description be divided into three groups: viz., the vertebral or lateral, the pre-vertebral or collateral, and the peripheral or terminal. The vertebral ganglia are arranged in the form of chains, one on each side of the vertebral column. The number of ganglia in the chain varies in animals of different and in animals of the same species. In man the number varies from 20 to 22. Each chain may be divided into a cervical, a thoracic, a lumbar, a sacral, and a coccygeal portion. The cervical portion is usually described as con- sisting of three gangha — a superior, a middle, and an inferior. This statement is open to question, hov^ever, as the middle one is fre- quently absent and the inferior one is regarded by some anatomists as belonging to the pre-vertebral series. The thoracic portion con- sists of ten or eleven gangha, the lumbar and sacral portions of four each and the coccygeal portion of one, the so-called ganghon impar. The pre-vertebral ganglia are also united in the form of a chain situated in the abdominal cavity. The ganglia constituting this chain are known as the semilunar, the renal, the superior and inferior mesenteric, and hypogastric. The peripheral gangha are in more or less close relation with the tissues and organs in different parts of the body. As members of this group may be mentioned the cihary or ophthalmic, the spheno- palatine, the otic, the submaxillary and the sublingual gangha; the gangUa in walls of the heart, the respiratory organs, the intestines, bladder, etc. The general arrangement of the sympathetic gangha, their inter- connecting cords and branches, is shown in Figs. 258 and 259. Structure of the Ganglia. — Each ganglion consists of a capsule or stroma of connective tissue in which are contained large numbers of nerve-cells, nerve-fibers medullated and non-medullated, and blood-vessels. The nerve-cehs give origin to two or more dendrites, which, perforating a nucleated capsule by which each cell is sur- rounded, branch and rebranch and interlace to form a pericapsular plexus. Each cell gives origin also to an axon, which as it leaves 37 577 578 TEXT-BOOK OF PHYSIOLOGY. Fig. 258. — Cervical and Thoracic Portion of the Sympathetic. — i, i, i. Right pneumogastric. 2. Glosso-pharyngeal. 3. Spinal accessory. 4. Divided trunk of the subungual. 5, 5, 5. Chain of gangha of the sympathetic. 6. Superior cervical ganghon. 7. Branches from this ganglion to the carotid. 8. Nerve of Jacobson. 9. Two filaments from the facial, one to the spheno-palatine and the other! to the otic ganglion. 10. Motor oculi externus. 11. Ophthalmic ganglion, THE SYMPATHETIC NERVE SYSTEM. 579 the cell becomes invested with a sheath continuous with the capsule surrounding the cell-body. It is, however, wanting in a medullary sheath, and hence the nerve presents a gray color. Such a structure, in its entirety, is known as a sympathetic neuron. Structure of the Interconnecting Cords. — The interconnecting cords are composed of non-medullated and medullated nerve-fibers. The former are the axons of cells found in the ganglia more centrally located ; the latter, as will be stated later, are derived from the spinal nerves, from the fibers of which, however, they differ in character, being much smaller and finer. The fibers of the interconnecting cords, as a rule, transmit nerve impulses from the more centrally to the more peripherally located ganglia, and are therefore termed ratni efjerentes. In the vertebral chain some of the cords transmit nerve impulses upward, others downward, others again forward, to the pre-vertebral and peripheral gangha. Among the rami eft'erentes, interconnecting cords, there are some which possess special interest for the physiologist, viz. : 1. The cervical, which connects the thoracic ganglia with the superior cervical ganglion. It is composed mainly of medullated nerve- fibers which are derived originally from the spinal nerves. 2. The great splanchnic nerve, formed by the union of branches from the fifth to the tenth thoracic ganglia. It connects these gangha with the semilunar ganglion. 3. The small splanchnic nerve, formed by the union of branches from the ninth and tenth thoracic gangha. It connects these gangha wdth the solar and renal plexuses. Distribution of the Sympathetic Fibers.— It has been demon- strated by histologic and physiologic methods of investigation that the sympathetic non-meduhated fibers which have their origin in receiving a motor filament from the motor oculi communis and a sensory filament from the nasal branch of the fifth. 12. Spheno-palatine ganglion. 13. Otic gang- lion. 14. Lingual branch of the fifth nerve. 15. Submaxillary ganghon. 16, 17. Superior laryngeal nerve. 18. External laryngeal nerve. 19, 20. Recurrent laryngeal nerve. 21, 22, 23. Anterior branches of the upper four cervical nerves, sending filaments to the superior cervical sympathetic ganglion. 24. Anterior branches of the fifth and sixth cer\'ical nerve, sending filaments to the middle cer\dcal ganglion. 25, 26. Anterior branches of the seventh and eighth cervical and the first dorsal nerves, sending filaments to the inferior cervical ganglion. 27. Middle cervical ganghon. 28. Cord connecting the two gangha. 29. In- ferior cervical ganglion. 30, 31. Filaments connecting this with the middle ganglion. 32. Superior cardiac nerve, t,^. Middle cardiac nerve. 34. Inferior cardiac nerve. 35,35. Cardiac plexus. 36. Ganglion of the cardiac plexus. 37. Nerve following the right coronary artery. 38, 38. Intercostal nerves, with their two filaments of communication with the thoracic ganglia. 39, 40, 41. Great splanchnic nerve. 42. Lesser splanchnic nerve. 43, 43. Solar plexus. 44. Left pneumogastric. 45. Right pneumogastric. 46. Lower end of the phrenic nerve. 47. Section of the right bronchus. 48. Arch of the aorta. 49. Right auricle. 50. Right ventricle. 51,52. Pulmonary artery. 53. Right half of the stomach 54. Section of the diaphragm. — {Sappey.) 58o TEXT-BOOK OF PHYSIOLOGY. Fig. 259. — Lumbar and Sacral Portions of the Sympathetic. — i. Section of the diaphragm. 2. Lower end of the esophagus. 3. Left half of the stomach. 4. Small intestine. 5. Sigmoid flexure of the colon. 6. Rectum. 7. Bladder. 8. Prostate. 9. Lower end of the left pneumogastric. 10. Lower end of the right pneumogastric. 11. Solar plexus. 12. Lower end of the great splanchnic nerve. 13. Lower end of the lesser splanchnic nerve. 14, 14. Last two thoracic ganglia. 15, 15. The four lumbar gangha. 16, 16, 17, 17. Branches from the lumbar ganglia. 18. Superior mesenteric plexus. 19, 21, 22, 23. Aortic lumbar plexus. 20. Inferior mesenteric plexus. 24, 24. Sacral portion of the sympathetic. 25 25, 26, 26, 27, 27. Hypogastric plexus. 28, 29, 30. Tenth, eleventh, and twelfth dorsal nerves. 31, 32, ^2> 34> 35' 3^> 37' 3^' 39- Lumbar and sacral nerves. — (Sappey.) THE SYMPATHETIC NERVE SYSTEM. 581 the cells of the sympathetic ganglia, vertebral, pre-vertebral, and peripheral, are distributed ultimately and directly to but two struc- tures: viz., non-striated muscle and secretor epithelium. Moreover, there is no evidence to warrant the assumption that these structures ever receive nerve impulses directly from the spinal or cranial nerves. All nerve impulses which influence their activities, either in the way of augmentation or inhibition, emanate directly though not origin- ally from the sympathetic ganghon cells. Since non-striated mus- cles are found in the walls of blood-vessels, in the walls of hollow viscera, and around hair-follicles, and since secretor epithelium is found in all glands, there is every reason to believe that the ganglia in some way are associated with vaso-motor and vaso-inhibitor, viscero-motor and viscero-inhibitor, pilo-motor and secretor phe- nomena. The Anatomic Relations of the Sympathetic and Cerebro- spinal Systems. — The sympathetic gangha are connected with the spinal nerves by two branches, one white, the other gray in color, and known respectively as the white and gray rami communicantes. These two rami differ somewhat in their topographic distribution. The white rami are found passing only from those spinal nerves included between the first thoracic and second or third lumbar and their corresponding gangha. The gray rami, on the contrary, are found passing from the ganglia to each of the spinal nerves. In the cervical region, where the gangha do not correspond in number with the cervical nerves, each ganglion gives off two or more gray rami. In man the superior cervical ganghon sends gray rami to the first four cervical nerves; the middle and inferior gangha apparently send gray rami to the fifth and sixth, the seventh and eighth nerves respectively. The white rami are composed of fine meduUated nerve-fibers which arise from nerve- cells situated in the lateral portion of the gray matter in the thoracic and lumbar regions of the spinal cord. From this origin they pass forward into the ventral roots of the spinal nerves, in which they are contained until the spinal nerve formed by the union of the ventral and dorsal roots divides into its anterior and posterior divisions. At this point the fine meduUated nerve-fibers leave the common trunk and pass forward into the cor- responding vertebral ganglion, around the cell-bodies of which some of the fibers at once arborize. Other fibers, however, pass through this ganglion and ascend or descend the cord for a variable distance, and arborize around the cells of more or less distant ganglia; others again pass forward into the pre-vertebral and even the peripheral gangha before they finally terminate. The nerve-cells in the spinal cord are thus brought into relation with the ganglia of all three chains, though for each cell there is but one ganglion terminal, 582 TEXT-BOOK OF PHYSIOLOGY. one cell station, between the spinal cord and the tissues. Though innervated by the spinal cord, these structures receive their nerve impulses, as previously stated, not directly but indirectly through the ganglion cells. The meduUated nerve-fibers coming from the spinal cord are known as pre-ganglionic fibers; the non-medullated fibers, passing from the ganglia, as post- ganglionic fibers. The gray rami are composed of non-medullated nerve-fibers, axons of the cells in the vertebral or lateral gangha. After their emergence from the ganglia they take a backward direction and enter the spinal nerve-trunks, in company with which they pass to the periphery, to be finally distributed to structures in the skin: viz., non-striated muscles of blood-vessels, non-striated muscles of the hair-folhcles and epithehum of glands. They may therefore be regarded as having vaso-motor, pilo-motor, and secretor functions. Afferent Sympathetic Fibers. — ^With the foregoing groups of efferent fibers, the sympathetic nerves, in the thoracic and lumbar regions more especially, contain a number of afferent fibers which when stimulated give rise to sensations of pain or to reflex phe- nomena. The routes by which these afferent fibers reach the spinal cord lead, on the one hand, into and through the gray rami to the ganglia on the posterior roots, where they have their cells of origin; and, on the other hand, into and through the white rami. The number of afferent fibers in any trunk in comparison with the effer- ent is quite small. FUNCTIONS OF THE SYMPATHETIC SYSTEM. The view according to which the sympathetic system is to be regarded as an independent apparatus endowed with functions of its own and in nowise directly dependent for its activities on the spinal cord, is at the present time discarded. Peripheral structures cease to exhibit their characteristic functions after division of the spinal nerves in connection with their related gangha. This does not exclude the possibihty of the sympathetic cell-body, in virtue of the interchanges between it and the blood and lymph by which it is surrounded, maintaining its own nutrition and exerting a favor- able influence over the nutrition of the peripheral tissues to which its efferent branches are distributed. The nerve-tissue in its entirety may be regarded as a single system which may be functionally divided into a nerve system of animal and a nerve system of vegetative life, according as the nerve energies originating in and emanating from the central nervous system are transmitted directly to the skeletal muscles or indirectly, through the intervention of a sympathetic neuron, to visceral muscles and glands. In the former system but one neuron, the spino-periph- THE SYMPATHETIC NERVE SYSTEM. 583 eric, connects the spinal cord proper with the muscle; in the latter system there are two, the spino-ganglionic and the ganglio-peripheric. From the distribution of the post-ganghonic libers it may be in- ferred that the activities of the vascular and visceral muscles, either in the way of augmentation or inhibition, the activities of the muscles of the hair-foUicles, and of the epithehum of glands, are called forth by the ganglia in consequence of the arrival of nerve impulses coming from the spinal cord through the pre-ganghonic fibers. Experimental observations show this to be true. The extent to which these different modes of activity manifest themselves in one or more regions of the body will depend to some extent on the portion of the sympathetic system subjected to experimental procedures. The Functions of the Cervical Portion. — If the sympathetic cord central to the superior cervical ganglion be stimulated with the induced electric current, among the resulting phenomena there Avill be observed dilatation of the pupil, retraction of the nictitating mem- brane in animals possessing it, contraction of the blood-vessels of the skin and mucous membrane in different parts of the head and face, contraction of the blood-vessels of the sahvary glands, increase of secretion from the submaxillary gland, the perspiratory and mucous glands, erection of hairs in different locahties of the head and neck, and in the dog dilatation of the blood-vessels of the lips, gums, and hard palate. If the cervical cord be divided, opposite effects will be observed: viz., contraction of the pupil, dilatation and passive congestion of the blood-vessels, a rise in temperature, and a loss of the power of erecting hairs. Stimulation of the peripheral end causes a disappearance of the latter and a reappearance of the former phenomena. These facts indicate that the cervical portion is efferent in function. The fibers composing it are medullated nerve-fibers derived from the thoracic or dorsal nerves from the first to the fourth. From the several sources the fibers pass via the white rami into the vertebral chain, and thence without interruption to the superior cervical ganglion, in and around the cells of which their end-tufts arborize in their characteristic manner. That the superior cervical ganghon is the cell station between the spinal cord and the peripheral organs is shown by the fact discovered and applied by Langley that the intravenous injection of nicotin or the local appHcation of it to the ganghon itself, impairs the conductivity of the terminals of pre-ganghonic fibers, after which their stimulation has no effect on the ganglion cells, though the latter retain their activity, as shown on direct stimulation. Of the nerve-centers in the spinal cord which through pre-ganglionic fibers influence peripheral structures, some appear to be in a state of constant activity: e. g., the vaso-constrictor centers and the pupillo-dilatator centers. In how far this action is automatic or autochthonic, or reflex, is uncertain. 584 TEXT-BOOK OF PHYSIOLOGY. The Functions of the Thoracic Portion. — The phenomena which follow stimulation of this portion of the sympathetic system resemble in a general way those observed in the head when the cervical portion is stimulated. The situation of the resulting phenomena will vary in accordance with the part the subject of the experiment. For an understanding of the results of experiment the origin and distribution of the following nerve-branches must be kept in view : (a) The cardiac nerves which have their origin in the first thoracic ganglion. From this point they pass by way of the annulus of Vieussens to the inferior cervical ganglion (from which they probably receive additional fibers) and thence to the heart. Stimulation of these nerves gives rise to an increased frequency and an augmentation in the force of the heart-beat. The pre- ganglionic fibers by which these cells are excited to activity emerge from the cord by the first and second thoracic nerves. (b) The splanchnic nerves the roots of which emerge from the fourth to the tenth or eleventh thoracic ganglia. The fibers composing these nerves are for the most part pre-ganglionic and derived from the corresponding spinal nerves. The cell stations of the splanchnic fibers are in the semilunar, superior mesenteric, and renal ganglia. From these ganglia non-medullated post-gang- lionic fibers pass peripherally to the walls of the intestines, the blood-vessels of the intestines, liver, kidneys, spleen, etc. Stimulation of the great splanchnic produces inhibition of the intestinal movements, a marked primary contraction of the intestinal blood-vessels and other viscera, followed by dilatation, coincidently with which there is a primary rise succeeded by a fall of blood-pressure throughout the body. Division of the nerve is followed by dilatation of the intestinal vessels and a fall of blood-pressure. Stimulation of the central end of the divided nerve excites the activity of the general vaso-motor center, as shown by the rise of the general blood-pressure. Stimulation of the smaller splanchnics gives rise to a slight primary contraction of the blood-vessels, soon followed by a marked dilatation. These facts indicate that the splanchnic nerves contain visceral nerves which inhibit intestinal movements, vaso-motor fibers both aug- mentor and inhibitor. The presence of secretory nerves for the intestinal glands is disputed. (c) The cutaneous nerves for the trunk leave the lateral ganglia by the gray rami, enter the thoracic spinal nerves, and pass in com- pany with them to their terminations, to be ultimately distrib- uted to the walls of the blood-vessels, the arrectores pilorum muscles, and the sweat-glands. The pre-ganglionic fibers come from the spinal nerves by the white rami. Their functions are vaso-motor, pilo-motor, and secretor. The cutaneous nerves THE SYMPATHETIC NERVE SYSTEM. 585 for the fore-limbs have their origin from cells in the stellate gang- hon (first dorsal). After a short upward course they enter the trunks of the nerves composing the brachial plexus. The pre-ganglionic fibers come from the white rami of the fourth to the ninth thoracic nerves. After entering the lateral chain they take an upward direction and arborize around the cells of the stellate ganglion. The cutaneous nerves for the hind-limbs are derived from the lower lumbar and the upper sacral ganglia. They also enter the spinal nerves by the gray rami and pass to the blood- vessels and glands of the skin. The pre-ganglionic fibers come from the twelfth thoracic to the third lumbar nerves. In both the brachial and sciatic nerves vaso-motor fibers (constrictors and dilatators) and secretor nerves are present, as shown by experimental methods (see page 345)- The Functions of the Lumbo-sacral Portion. — From the ganglia of the lumbar and sacral regions gray rami enter the lumbar and sacral nerves and accompany them to their distribution. In the lumbar region the vertebral chain contains a number of pre- ganglionic fibers which have descended from the thoracic region as well as fibers which have come into the chain by the white rami from the lumbar nerves themselves. Many of these fibers pass to the inferior mesenteric ganglion, in which they find their cell station. Fibers from the sacral cord pass into the hypogastric plexus. The course and distribution of the individual nerves is complicated and involved. In a general way it may be said that these two regions of the lateral chain send viscero-motor and viscero-inhibitor, vaso-con- strictor and dilator nerves to the pelvic viscera and to the external organs of generation. Their function therefore is to regulate the activities of the viscera as well as the blood-supply in accordance with functional needs. The Functions of the Cephalic Ganglia. — The ganglia situated in the head are usually described in connection with and as con- stituent parts of the cranial nerve system. They, however, bear the same relation to the cranial nerves that the ganglia of the trunk bear to the spinal nerves. They consist of ganglion cells from which post-ganglionic fibers pass to glands, blood-vessels, and non-striated muscles, and to which pre-ganglionic fibers pass from the cranial nerves. Motor and sensor nerves pass through one or more ganglia, though they have no anatomic connection with them. In their structure, distribution, and functions they closely resemble the col- lateral ganglia of the abdominal sympathetic : I. The ciliary or ophthalmic ganglion is situated in the orbital cavity posterior to the eyeball. It is small in size, gray in color, and consists of a connective-tissue stroma containing nerve-cells. From these cells post-ganglionic fibers emerge which, after a 586 TEXT-BOOK OF PHYSIOLOGY. short course forward, penetrate the eyeball and terminate in the circular fibers of the iris and the ciliary muscle. Pre-ganglionic fibers of small size, and similar in their anatomic features to the fibers of the white rami of the spinal nerves, leave the motor oculi by a short root from the inferior division and arborize around the ganglionic cells. Stimulation of the pre-ganglionic fibers gives rise to contraction of the circular fibers of the iris, with a diminution in the size of the pupil, and contraction of the ciliary muscle with accommodation of the eye for near vision. Division of these fibers is followed by the opposite results. Post-ganglionic fibers from the superior cervical gang- lion which come through the cavernous plexus pass through the ciliary ganglion to the blood-vessels of the iris and retina which are vaso-constrictor in function. Sensor fibers from the per- ipheral division of the fifth nerve pass to the cornea and endow it with sensibiHty. 2. The spheno- palatine ganglion is situated in the spheno-maxillary fossa. Its nerve-cells send non-medullated post-ganglionic fibers to the blood-vessels and glands of the mucous membrane of the nasal and oral regions. Stimulation of the ganglion gives rise to dilatation of the blood-vessels and increase of secretion in this entire region. The pre-ganglionic fibers are derived from the seventh or facial nerve by way of the great petrosal. Sensor fibers from the superior maxillary division of the fifth nerve pass through the ganglion to the same regions. 3. The otic ganglion is situated just below the foramen ovale and internal to the third division of the fifth nerve. The post-gang- lionic fibers pass to the parotid gland by w^ay of the auriculo- temporal division of the fifth nerve, and to the blood-vessels of the lower lip, cheek, and gums. The pre-ganglionic fibers are de- rived from the efferent fibers in the glosso-pharyngeal or ninth nerve, by way of Jacobsen's nerve and the small petrosal. Stimu- lation of these nerves in any part of their course gives rise to vascular dilatation and increase of secretion in the region of their distribution. Motor fibers from the small or motor root of the fifth nerve pass through this ganglion to the tensor tym- pani muscle. 4. The submaxillary and sublingual ganglia are situated close to the corresponding glands. Their post-ganglionic fibers pass to the blood-vessels and gland-cells. The pre-ganglionic fibers are derived from the seventh or facial nerve through the chorda tympani branch. Stimulation of the chorda or of the ganglia themselves gives rise to marked dilatation of the blood-vessels and an increased flow of saliva. It therefore contains vaso- dilatator and secretor fibers for these glands. Vaso-constrictor THE SYMPATHETIC NERVE SYSTEM. 587 and a few secretor nerves, it will be recalled, come to these glands from the superior cervical ganglion. Peripheral Ganglia. — Among the peripheral ganglia may be mentioned those in the heart and those in the intestinal walls. The pre-ganglionic fibers are contained in the trunk of the vagus nerve. Stimulation of the peripheral end of the divided vagus gives rise to inhibition of the heart, contraction of the walls of the stomach and intestines, secretion from the gastric and perhaps the pancreatic gland. CHAPTER XXIII. PHONATION; ARTICULATE SPEECH. Phonation, the emission of vocal sounds, is accomplished by the vibration of two elastic membranes which cross the lumen of the larynx antero-posteriorly and which are thrown into vibration by a blast of air from the lungs. Articulate speech is a modification of the voice produced by the teeth and the muscles of the lips^and tongue and employed for the expression of ideas. The larynx, the organ of the voice, is situated in the forepart of the neck, occupying the space between the hyoid bone and the upper extremity of the trachea. In this situation it communicates with the cavity of the pharynx above and the cavity of the trachea below. From its anatomic relations and its internal structure — the interpola- tion of the elastic membranes — the larynx subserves the two widely different yet related functions, respiration and phonation. THE ANATOMY OF THE LARYNX. The larynx consists primarily of a series of cartilages united one with another in such a manner as to form a more or less rigid frame- work, yet possessing at its different joints, a certain amount of motion; and, secondarily, of muscles and nerves which conjointly impart to the cartilages the degree of movement necessary to the performance of the laryngeal functions. It is covered externally by fibrous tissue and lined throughout by mucous membrane con- tinuous with that lining the pharynx and trachea. The larynx presents a superior or pharyngeal and an inferior or tracheal opening. The pharyngeal opening is triangular in shape, the base being directed forward, the apex backward. The plane of this opening in the living subject is almost vertical. The tracheal opening is circular in shape and corresponds in size with the upper ring of the trachea. Viewed from above, the general cavity of the larynx is seen to be partially subdivided by two membranous bands — the vocal bands or cords — which run from before backward in a hori- zontal plane. The space between the bands, the glottis, varies in size and shape from moment to moment in accordance with respira- tory and phonatory necessities. The average width of the glottis, at 588 PHONATION; ARTICULATE SPEECH. 589 its widest part, during quiet respiration is about 13.5 mm. in men and 1 1.5 mm. in women (Semon). With the advent of phonation the vocal membranes are at once approximated, and to such an extent that the glottic opening is reduced to a mere sht. It is then spoken of as the rima glottidis, or chink of the glottis. The space above the vocal bands, the supra-glottic or supra-rimal space, is triangular in shape and extends from the pharyngeal open- ing to the plane of the vocal bands. The mucous membrane lining the walls of this space, presents on either side, just above the vocal bands, a crescentic fold which runs from before backward, and is known as the false vocal band or cord. Be- tween the true and false bands there is a cavity or space prolonged upward and outward for some distance, forming What is known as the ventricle of the larynx. The space below the vocal bands, the infra-glottic or infra-rimal space, is narrow above and elongated from before backward, but wide and circular below, corresponding to the lumen of the trachea. The Laryngeal Cartilages, Articulations, and Ligaments. — The cartilages which compose the framework of the larynx are nine in number, three of which are single: viz., the cricoid, the thyroid, and the epiglottis, while six occur in pairs: viz., the arytenoids, the cornicula laryngis, and the cunei- form. The cricoid cartilage is the foundation cartilage, and affords support to the remaining cartilages and the structures attached to them. In shape it resembles a signet- ring, the broad quadrate portion of which is directed backward, Fig 260. — Longitudinal Section or THE Human Larynx, Show- ing THE Vocal Bands. i. Ventricle of the larynx. 2. Supe- rior vocal cord. 3. Inferior vocal cord. 4. Arytenoid cartilage. 5. Section of the an,'tenoid muscle. 6, 6. Inferior portion of the cavity of the larynx. 7. Section of the posterior portion of the cricoid cartilage. 8. Section of the an- terior portion of the cricoid car- tilage. 9. Superior border of the cricoid cartilage. 10. Section of the thyroid cartilage. 11, 11. Superior portion of the cavity of the larynx. 12, 13. Arytenoid gland. 14, 16. Epiglottis. 15,17. Adipose tissue. 18. Section of the hyoid bone. 19, 19, 20. Trachea. — {Sappey) 59° TEXT-BOOK OF PHYSIOLOGY. while the narrow circular portion is directed forward. It rests upon the upper ring of the trachea, to which it is firmly attached by fibrous tissue. The posterior upper border of the cj^uadrate portion presents on either side an oval convex facet for articulation with the arytenoid cartilage. The long axis of this facet is directed down- ward, outward, and forward. Fig . 2 6 1 . — -Laryngeal Cartilages and Ligaments, Anterior Surface. I. Hyoid bone. 2, 2, 3, 3. Greater and lesser cornua. 4. Thyroid- cartilage. 5. Thyro-hyoid mem- brane. 6. Thyro-hyoid hgaments. 7. Cartilaginous nodule. 8. Cri- coid cartilage. 9. The crico-thyroid membrane. 10. The crico-thyroid ligaments. 11. Trachea. — {Sap- pey.) Fig. 262. — Laryngeal Cartilages and Ligaments. Posterior Sur- face. I, I. Thyroid cartilage. 2. Cricoid cartilage. 3, 3. Arytenoid cartilages. 4, 4. Crico-arytenoid articulations. 5, 5. Crico-thyroid articulations. 6. Union of the cricoid cartilage and of the trachea. 7. Epiglottis. 8. Ligament uniting it to the reentering angle of the thyroid cartilage. — (Sappey.) The thyroid, the largest of the laryngeal cartilages, is composed of two fiat quadrilateral plates, united anteriorly, at an angle of about 90 degrees. Each plate is directed backward and outward and terminates in a free border, which is prolonged upward and downward for some distance, terminating in two processes, the superior and inferior cornua. The upper border of the thyroid is deeply notched in front. The inferior border overlaps laterally the cricoid. PRONATION; ARTICULATE SPEECH. 591 The epiglottis is a leaf-shaped piece of cartilage attached to the thyroid at the median notch. It is firmly united by membranes and ligaments to the thyroid and arytenoid cartilages and to the base of the tongue. The arytenoid cartilages are two in number and symmetric in shape. Each cartilage is a triangular pyramid, the apex of which is re- curved, and directed backward and inward. The base presents three angles — an anterior, an external, and an internal. The anterior angle is long and pointed and projects forward in a horizontal plane. It serves for the attachment of the vocal membranes and is therefore termed the vocal process. The external angle is short, rounded, and prominent, and serves for the attachment of muscles. The internal angle affords a point of insertion for a ligament. The inferior surface of the arytenoid is concave for articulation with the convex surface of the cricoid facet. Its long axis, however, is directed from before backward and almost at right angles to the long axis of the cricoid facet. The cornicula laryngis and the cuneiform cartilages are small ■ nodules of yellow elastic cartilage embedded in a fold of membrane which unites the arytenoid and the epiglottis. They are fragments of a ring of cartilage which in some animals — e. g., anteater — extends between these two cartilages. The crico-thyroid articulation is formed by the apposition of the tip of the inferior cornu of the thyroid cartilage and an articular facet on the side of the cricoid. The joint is provided with a synovial membrane and enclosed by a capsular hgament. The movements permitted at this joint take place around a horizontal axis and consist of an upward and downward movement of both the thyroid and cricoid, combined with a sliding movement of the latter upward and backward. The crico-arytefioid articulation is formed by the apposition of the articulating surfaces of the cricoid and arytenoid cartilages. This joint is provided with a synovial membrane and enclosed by a loose capsular ligament which would permit of an extensive sliding of the arytenoid cartilage downward and outward were it not pre- vented by the posterior crico-arytenoid ligament, which is attached, on the one hand, to the cricoid, and, on the other, to the inner angle of the arytenoid. The movements permitted at this joint are: (i) Rotation of the arytenoid around a vertical axis which lies close to its inner surface. (2) A sliding motion inward and forward with inward rotation of the vocal process, or a sliding motion outward and backward with outward rotation of the vocal process. In either case the process describes an arc of a circle. (3) A sliding movement towards the median line in consequence of which the inner surfaces of the arytenoids are brought almost in contact. 592 TEXT-BOOK OF PHYSIOLOGY. The crico-thyroid membrane is composed mainly of elastic tissue. It may be divided into a mesial and two lateral portions. The mesial portion is well developed, triangular in shape, and unites the contiguous borders of the cricoid and thyroid cartilages. The lateral portion is attached below to the superior border of the cricoid. From this attachment it passes upward and inward under cover of the thyroid. As it ascends it elongates and becomes thinner, and is finally attached anteriorly to the thyroid near the median line, and posteriorly to the vocal process of the arj^tenoid, thus constituting the inferior thyro- arytenoid ligament. It is covered internally by mucous membrane and externally by the internal thyro-arytenoid muscle. The free edge of this ligament forms the basis of the true vocal band. A superior thyro-arytenoid ligament forms the basis of the false vocal band. The thyro-hyoid membrane, composed of elastic tissue, unites the superior border of the thyroid to the hyoid bone. The mucous membrane lining the larynx is thin and pale. As it passes downward it is reflected over the superior thyro-arytenoid ligament, and assists in the formation of the false vocal band; it then passes into and lines the ventricle, after which it is reflected inward over the superior border of the thyro-arytenoid muscle and hgament, and assists in the formation of the true vocal band ; it then returns upon itself and passes downward over the lateral portion of the crico-thyroid membrane into the trachea. The thin, free, reduplicated edge of the mucous membrane con- stitutes the true vocal band. The surface of the mucous membrane is covered by cihated epithehum except in the immediate neighbor- hood of the vocal bands. The vocal bands are attached anteriorly to the thyroid cartilage near the receding angle and posteriorly to the vocal processes of the arytenoid cartilages. They vary in length in the male from 20 to 25 mm. and in the female from 15 to 20 mm. The Muscles of the Larynx. — The muscles which have a direct action on the cartilages of the larynx and determine the position of the vocal bands both for respiratory and phonatory purposes, and which regulate their tension as well, are nine in number and take their names from their points of origin and insertion: viz., two posterior crico-arytenoids, two lateral crico-arytenoids, two thyro-arytenoids, one arytenoid, and two crico-thyroids (Figs. 263 and 264). The posterior crico-arytenoid muscle lies on the posterior surface of the quadrate plate of the cricoid cartilage, on either side of the median line, from which it takes its origin. The fibers of the muscle pass upward and outward and in their course converge to be inserted into the external angle of the arytenoid cartilage. The superior and more horizontally directed fibers rotate the arytenoid PRONATION; ARTICULATE SPEECH. 593 around its vertical axis; the inferior and obliquely directed fibers draw the cartilage downward and inward. As a result of the action of the muscle in its entirety, the vocal process is turned upward and outward, and as the vocal band is carried with it the glottis is widened, a condition necessarv to the free entrance of air into the lungs (Fig. Fig. 263. — Posterior View of the Muscles of the Laryn:?^. i. Posterior crico-arytenoid muscle. 2, 3, 4. Different fasciculi of the arytenoid muscle. 5. Aryteno- epiglottidean muscle. — (Sappey.) 265). Since the contraction of the crico-arytenoid has this result, it is generally spoken of as the abductor or respiratory muscle. The lateral crico-arytenoid muscle arises from the side of the cricoid cartilage. From this point its fibers are directed upward and backward to Fig. 264. — Later.\l View of the Muscles of the Larynx, i. Body of the hyoid bone. 2. Verti- cal section of the thyroid cartilage. 3. Horizontal section of the th}Toid cartilage turned downward to show the deep attachment of the crico- thyroid muscle. 4. Facet of articu- lation of the small cornu of the th)Toid cartilage with the cricoid cartilage. 5. Facet on the cricoid cartilage. 6. Superior attachment of the crico-thyroid muscle. 7. Pos- terior crico-arytenoid muscle. 8, ID. Arytenoid muscle. 9. Thyro- arytenoid muscle. II. Ar}teno- epiglottidean muscle. 12. Middle thyro-hyoid ligament. 13. Lateral thyro-hyoid ligament. — (Sappey.) be inserted into the external process of the arytenoid. Its action is to draw the arytenoid cartilage for- ward and inward, thus approximating and relaxing the vocal band. The thyro-arytenoid muscle arises from the inferior two-thirds of the inner surface of the thyroid cartilage just external to the median line. From this origin the fibers pass backward and outward, 38 594 TEXT-BOOK OF PHYSIOLOGY. to be inserted into the anterior surface and external angle of the arytenoid cartilage. The inner portion of the muscle lies close to and supports, if it does not constitute a part of, the vocal band. The action of the thyro-arytenoid muscle in conjunction with the lateral crico-arytenoid is to rotate the arytenoid cartilage around the vertical axis and to drav^' the vocal process forward and inward, thus carrying the vocal cord toward the median line. When the muscles of the two sides simultaneously contract, the vocal bands are closely approximated and the space between them, the rima vocalis, reduced to a mere slit, one of the conditions essential to phonation (Fig. 266). The arytenoid muscle consists (i) of transversely arranged fibers which arise from and are inserted into the outer surface of the oppo- FlG 265. — Glottis Widely Opened FROM Simultaneous Contraction OF Both Crico-arytenoid Mus- cles, h. Epiglottis. rs. False vocal band. ri. True vocal band. ar. Arytenoid cartilages, a. Space between the arytenoids, c. Cunei- form cartilages, ir. Interarytenoid fold. rap. Aryepiglottic fold. cr. Cartilage rings. — {Mandl.) Fig 266. — Position of the Vocal Bands Due to the Simultaneous Contraction of Both Lateral Crico-arytenoid Muscles and Both Thyro-arytenoid Muscles. h. Epiglottis, rs. False vocal band. ri. True vocal band. or. Space be- tween the arytenoid cartilages, the glottis respiratoria. ar. Arytenoid cartilages, c. Cuneiform cartilages. rap. Aryepiglottic fold. ir. Interary- tenoid io\d.^{Mandl.) site arytenoid cartilages, and (2) of obliquely directed fibers which arise from the outer angle of one arytenoid to be inserted into the apex of the other. In their course they decussate in the median line. The action of this muscle is to approximate the arytenoid cartilages and thus obliterate that portion of the glottis between the vocal processes, the rima respiratoria, and so direct the expiratory blast of air toward and through the rima vocalis. The collective actions of the three foregoing muscles is to close or constrict the glottis, and for this reason they are spoken of as the adductor or phonatory muscles. The crico-thyroid muscle arises from the side and front of the cricoid cartilage and is inserted above into the lower border of the thyroid cartilage. The action of this muscle is to draw up the an- terior part of the cricoid cartilage toward the thyroid, which remains PRONATION; ARTICULATE SPEECH. 595 stationary, and to swing the quadrate plate of the cricoid and the arytenoid cartilages downward and backward. This movement has the result of tensing the vocal bands. The cricoid is at the same time drawn backward by the action of the more longitudinally dis- posed fibers. Nerves of the Larynx. — The nerves which innervate the muscles of the larynx and endow the mucous membrane with sensibihty are derived from the vagus trunk. The superior laryngeal is for the most part sensor and distributed to the mucous membrane, though it contains motor fibers for the crico-thyroid muscle. The inferior laryngeal is purely motor and is distributed to all the muscles with the exception of the crico-thyroid. THE MECHANISM OF PHONATION. Phonation, the production of vocal sounds in the larynx, is the result of the vibration of the vocal bands caused by an expiratory blast of air from the lungs. That a sound may arise it is essential that the glottis be approximately closed and the vocal bands be made more or less tense. The closure of the glottis — the approximation of the vocal pro- cesses and the vocal bands — is accomplished, it will be recalled, by the contraction of the lateral crico-arytenoid, the arytenoid, and the thy ro- arytenoid muscles. The increase in tension is accomphshed by the contraction of the crico-thyroid and the thyro-arytenoid muscles, the former by the backward displacement of the cricoid and arytenoid cartilages, the latter by converting the natural concave edge of the vocal band to a straight hne. The lengthening and tensing of the vocal bands by the crico-thyroid muscle is regarded by some investigators as a coarse means, the approximation of the free edges by the thyro-arytenoid, as a finer means, of adjust- ment for the production of slight changes in the pitch of sounds. The extent to which the glottis is closed and the membranes tensed will depend, however, on the pitch of the sound to be emitted. The appearance presented by the glottis just previous to the emission of a note of medium pitch, as determined by laryngologic examina- tion, is shown in Fig. 267. When the foregoing conditions in the glottis are reahzed, the air stored or collected in the lungs is forced by the contraction of the expiratory muscles, through the narrow space between the bands. As a result of the resistance offered by this narrow outlet and the force of the expiratory muscles the air within the lungs and trachea is subjected to pressure, and as soon as the pressure attains a certain level the vocal bands are thrown into vibrations, which in turn imp; rt to the column of air in the upper air-passages a corresponding s ries of vibrations by 596 TEXT-BOOK OF PHYSIOLOGY. which the laryngeal vibrations arc reinforced. The degree of pres- sure to which the air in the lungs and trachea is subjected was determined by Latour to vary from i6o mm. of water for sounds of moderate, to 940 mm. of water for sounds of highest intensity. With the escape of the air or the separation of the vocal bands the vibra- tion ceases and the sound dies away. The Characteristics of Vocal Sounds. — In common with the sounds produced by all other music instruments, all vocal sounds are characterized by intensity, pitch and quahty, tone or color. The intensity or loudness of a sound depends on the extent or amplitude of the up-and-down vibration or the extent of the excur- sion of the vocal band on either side of the position of equilibrium or rest ; and this in turn depends on the force with which the blast of air strikes the band. The more forceful the blast of air, the larger, other things being equal, will be the primary vibrations of the bands, #r/ ^ Fig. 267. — Position of the Vocal Bands Previous to the Emission OF A Sound, b. Epiglottis, rs. False vocal band. ri. True vocal band. ar. Ary'tenoid cartilages. — (Mandl.) *L_Z Fig. 268. — Position of the Vocal Bands in the Production of Notes of Low Pitch. /. Epiglottis. or. Glottis, ns. False vocal cord. ni. True vocal cord. ar. Arytenoid cartilages. — (Mandl.) and hence the secondary vibrations of the air in the upper air- passages. The pitch of the voice depends on the number of vibrations in a unit of time, a second. This will be conditioned by the length of the bands in vibration or the length and width of the aperture through which the air passes and the degree of tension to which the bands are subjected. In the emission of sounds of highest pitch the tension of the vocal bands and the narrowing of the glottis attain their maxi- mum. In the emission of sounds of lowest pitch the reverse conditions obtain. In passing from the lowest to the highest pitched sounds in the range of the voice peculiar to any one individual, there is a pro- gressive increase in both the tension of the vocal bands and the narrowing of the glottic aperture. In the production of low-pitched notes of men, those due to vibrations lying between 80 and 240 per second, the tension is regulated by the crico- thyroid muscle; the PHONATION; ARTICULATE SPEECH. 597 aperture of the glottis during this time being elliptic in shape and relatively wide (Fig. 268). In the production of notes due to vibrations lying between 240 and 512 vibrations per second, the anterior fibers of the crico-thyroid muscle relax and the thyro-ary- tenoid muscle comes into play; by its action the vocal bands are more closely approximated and the vocal aperture reduced to a hnear slit. In the high-pitched notes emitted by soprano singers the vocal bands are so closely apphed to each other that only a very small portion in front, bounding a small oval aperture, is capable of vibrating (Fig. 269). The difference in the pitch of the voice in men and women is due largely to the greater size and development of the vocal bands in the former than in the latter. The quality of the voice, the timbre or color, depends on the form combined with the intensity and pitch of the vibration. As with sounds produced by music in- struments, the primary or fundamental vibration of the vocal band is compli- cated by the superposition of secondary or partial vibrations (overtones). The form of the vibration will therefore be a resultant of the blending of a number of different vibrations. The quality of the sound produced in the larynx is, however, modified by the resonance of the mouth and nasal cavities; certain of the overtones being reinforced by changes in the shape of the mouth cavity more especially, thus giving to the voice a somewhat different quahty. The Varieties of Voice. — The region of the music scale, comprising all vibrations between 32 and 2048 per second, with which laryngeal sounds are in accord will vary in the two sexes and in dift'erent individuals of the same sex. It is customary to classify voices, especially those of singers, into bass, baritone, tenor, contralto, mezzo-soprano, and soprano, in accordance with the regions of the music scale with which they correspond. Thus the succession of notes characteristic of the bass voice vary in pitch from F, fa', to C , do3, or from 87 to 256 vibrations per second; those of the baritone from A, la, to F', fag, or from 106 to 341 vibrations per second; those of the tenor from C, dOg, to a', kg, or from 128 to 435 vibrations per second; those of the contralto from e, mij, to C", do^, or from 160 to 512 vibrations per second; those of the mezzo-soprano from g, S0I2, Fig. 269. — Glottis Seen WITH THE Laryngo- scope DURING THE EMIS- SION OF High-pitched Sounds, i, 2. Base of the tongue. 3, 4. Epiglot- tis. 5, 6. Pharynx. 7. Arytenoid cartilages. 8. Opening between the true vocal cords. 9. Aryteno- epiglottidean folds. 10. Cartilage of Santorini. 1 1 . Cuneiform cartilage. 12. Superior vocal cords. 13. Inferior \'ocal cords. — (Le Bon.) 598 TEXT-BOOK OF PHYSIOLOGY. to e", mi^, or from 192 to 640 vibrations per second; those of the soprano from b, si2, to g", sol^, or from 240 to 768 vibrations per second. The range of the voice is thus seen to embrace from one and three- quarters to two octaves. Some few individual singers have far ex- ceeded this range, but they are exceptional. Speech is the expression of ideas by means of articulate sounds. These sounds may be divided into vowel and consonant sounds. The vowel sounds, a, e, i, 0, u, are laryngeal sounds modified by the superposition and reinforcement of certain overtones developed in the mouth and pharynx by changes in their shapes. The number of vibrations underlying the production of each vowel sound is a matter of dispute. According to Konig, the sound of a is the result of 940 vibrations; of e, 1880 vibrations; of i, 3760 vibrations; of o, 470 vibrations; of ou, 235 vibrations. Consonant sounds are produced by the more or less complete in- terruption of the vowel sounds during their passage through the organs of speech. These may be divided into: 1. Labials, p, b, m. 2. Labio-dentals, /, v. 3. Linguo-dentals, s, z. 4. Anterior hnguo-palatals, t, d, I, n. 5. Posterior linguo-palatals, k, g, h, y, r. The names of these different groups of consonants indicate the region of the mouth in which they are produced and the means by which the air blast is interrupted. THE NERVE MECHANISM OF THE LARYNX. The nerve mechanism by which the musculature of the larynx is excited to action and coordinated so as to subserve both res- piration and phonation involves the fibers contained in the superior and inferior laryngeal nerves (both branches of the vagus) and their related nerve-centers in the central nerve system. For respiratory purposes it is essential that the lumen of the glottis shall be sufficiently large to permit the entrance and exit of air without hindrance. Laryngoscopic examination of the larynx in the human being shows that during quiet respiration the vocal bands are widely separated and almost stationary, moving but slightly during either inspiration or expiration. At this time, according to the in- vestigations of Semon, the area of the glottis is approximately 160 sq. mm., somewhat less than the area of either the supraglottic or infraglottic regions, which is about 200 sq. mm. This condition of the glottis is maintained by the steady continuous contraction of the posterior crico-arytenoid muscles, the abductors of the vocal bands. PRONATION; ARTICULATE SPEECH. 599 For phonatory purposes it is essential that the respiratory function be temporarily suspended and the vocal bands closely approx- imated. This is accomplished by the contraction of the remaining muscles of the larynx, with the exception of the crico-thyroid, which are collectively known as the adductors of the vocal bands. During phonation the adductor muscles overcome the activity of the abductors. With the cessation of phonation the abductors immedi- ately restore the vocal bands to their former respiratory position. The activities of these two antagonistic groups of muscles are under the control of the central nerve system. The only pathway for the excitatory nerve impulses is through the fibers of the inferior or recurrent laryngeal nerve. The relation of these nerve-fibers both centrally and peripherally, as well as their physiologic action, has been the subject of much experimentation. The results have not always been in accord, owing to the choice of animal, the use of anes- thetics, strength of stimulus, etc. As the outcome of many investigations it is beheved that each muscle group is innervated by its own bundle of nerve-fibers, both of which are contained in the inferior laryngeal, though coming from two separate centers in the medulla oblongata. Russell suc- ceeded in separating the fibers for the abductors from the fibers for the adductors in the inferior laryngeal, and in tracing them to their terminations. So completely was this done that it became possible to produce at will, through stimulation, either abduction or adduction, without contraction of the muscle of opposite function. The laryngeal respiratory center was located by Semon and Horsley, in the cat, in the upper part of the floor of the fourth ven- tricle. Stimulation of this area during etherization was followed by abduction of the vocal bands. The efferent fibers of this center are beheved by some investigators to leave the central nerve system in the spinal accessory nerve, by others in the lower roots of the vagus. From the continuous activity of the abductor muscle, and the stationary position of the vocal bands, it is probable that the medul- lary center is in a state of continuous activity or tonus, the result probably of reflex influences. A cortical representation for laryngeal respiratory movements has been determined by Semon and Horsley in different classes of animals. In the cat especially, stimulation of the border of the olfactory sulcus gives rise to complete abduction of the vocal bands on both sides. The representation is therefore bilateral. The phonatory center was located by the same investigators in the medulla near the ala cinerea and the upper border of the calamus scriptorius. Stimulation of this area was invariably followed by bilateral adduction of the vocal bands and closure of the glottis. A cortical representation for phonatory movements also was 6oo TEXT-BOOK OF PHYSIOLOGY. located in the lower portion of the precentral convolution, near the anterior border. Stimulation of this area gives rise to marked ad- duction of both vocal bands, indicating that the representation is also bilateral. Faradic stimulation of the inferior laryngeal nerve during slight ether anesthetization gives rise to closure of the glottis; the same stimulation, however, during deeper anesthetization gives rise to opening or dilatation of the glottis, a fact indicating that either the adductor muscles or their nerve terminals are depressed by the action of the ether before the muscles and nerves of opposite function. The superior laryngeal nerves contain motor fibers for the crico- thyroid muscles. Stimulation of the nerve gives rise to contraction of the muscle and increased tension of the vocal bands. It is believed that these fibers are derived originally from the efferent fibers of the glosso-pharyngeal nerve. The remaining fibers of the superior laryngeal endow the upper portion of the larynx with extreme sen- sibility which to a certain extent protects the air-passages against the entrance of foreign bodies. Irritation of the terminal filaments of this nerve by particles of food, solid or liquid, gives rise to marked reflex spasm of the adductor muscles and closure of the glottis, fol- lowed by a strong expiration blast of air from the lungs by which the offending particles are removed. Division of this nerve on both sides is followed by a paralysis of the crico-thyroid muscles, a lower- ing of the tension of the vocal bands, and a loss of sensibility of the laryngeal mucous membrane. CHAPTER XXIV. THE SPECIAL SENSES. It is one of the functions of the nerve system to bring the individual into conscious relation with the external world. This is accomphshed in part through the intermediation of afferent nerves, connected peripherally, with highly specialized terminal organs and centrally, with specialized areas in the cerebral cortex. Excitation of the terminal organs by material changes in the environment develops nerve impulses which, transmitted to the cortical areas, evoke sensations. These sensations, differing in character from those vague ill-defined sensations — e. g., fatigue, well-being, discomfort, etc. — caused by material changes occurring within the body, are termed special sensations — e. g., touch; pres- sure ; pain ; temperature; taste; smell; light and its varying quali- ties, intensity, hue, and tint; sound and its var}-ing qualities, intensity, pitch, and timbre. The terminal organs which receive the impress of the external world are the skin, tongue, nose, eye, and ear, and collectively con- stitute the special sense-organs. The physiologic mechanisms which underlie and develop these special sensations are known respectively as the tactile, gustatory, olfactory, optic, and auditory. Each mechanism responds to but a single form of stimulus and to no other. Thus, the stimulus for the skin is mechanic pressure; for the tongue, soluble organic and inorganic matter; for the nose, volatile or gaseous matter; for the eye, ether vibrations; for the ear, atmospheric undulations. These stimuli alone are adequate to the physiologic excitation of the different mechanisms. The factors involved in the production of the sensations include (i) a special physical stimulus; (2) a specialized terminal organ; (3) an afferent nerve pathway; and (4) a specialized receptive sensor cell in the cerebral cortex. Though the resulting sensations in each instance differ widely in their characteristics, it is difficult to present a satisfactory explanation for these differences. If it be assumed that the nerve impulses which ascend the different nerves of special sense are ahke in quality, then it must be admitted that the character of the sensation is the ex- pression of a specialization and organization of the cortical area. If, on the other hand, specialization of the cortex is denied, then there must be admitted a specialization of the peripheral organ — with 601 6o2 TEXT-BOOK OF PHYSIOLOGY. a resulting difference in quality or rapidity of the nerve impulses which would impress or excite the non-specialized cortex in such a way as to call forth the characteristic sensation. It is possible, how- ever, that neither supposition is wholly correct, and that the char- acter of the sensation depends on the construction and adaptation of the entire sense apparatus to the character of the stimulus. Whatever the conditions for their origin and whatever their characteristics, sensations in themselves do not constitute knowledge ; they are but elementary states of consciousness, raw materials out of which the mind elaborates conceptions and forms judgments as to the character of any given object in comparison with former experiences. THE SENSE OF TOUCH. The physiologic mechanism involved in the sense of touch in- cludes the skin and the mucous membrane lining the mouth, the afferent nerves, their cortical connections, and nerve-cells in the cortex of the parietal lobe and the gyrus fornicatus (Figs. 226, 227). Peripheral excitation of this mechanism develops nerve impulses which, transmitted to the cortex, evoke sensations of touch and temperature. To the skin, therefore, is ascribed a touch sense and a temperature sense. Of the touch sensations two kinds may be distinguished: viz., pressure sensations and place sensations. With the contact of an external body there arises the perception not only of the pressure, but also the perception of the place or locality of the contact. In accordance with this, it is customary to attribute to the skin a pressure sense and a location sense. The specific physiologic stimuli to the terminal organs in the skin and oral mucous membrane are mechanic pressure and thermic vibrations. The Skin. — The skin, which constitutes the basis for the sense of touch, covers and closely invests the entire body. It varies in thickness and delicacy in different regions, though its structure is everywhere essentially the same. As the physiologic anatomy of the skin has elsewhere been detailed (page 453), it is only necessary to state here that it is divided into a deep and a superficial layer. The former, known as the derma, consists of an inner layer of rather loose connective tissue and an outer layer of condensed connective tissue. The latter, known as the epidermis, consists of an inner layer of pigment cells and a thick outer layer of epithelial cells. The derma is characterized by the presence of elevations (papillae) which are everywhere extremely abundant. Throughout the derma ramify blood-vessels and nerves. The Peripheral or Terminal Organs. — Between the contact surface and the afferent nerves specialized structures are found THE SENSE OF TOUCH. 603 >^3ri;J^- ^.-:...X^..^-^:.^^:g--0^ which serve as intermediates between the stimulus, on the one hand, and the afferent nerves, on the other hand. By virtue of their struc- ture they are far more irritable than the nerve-fibers and hence respond more quickly to the physiologic stimulus than the nerve- fiber itself. To these specialized organs, found not only in the skin but in other sense-organs as well, the term peripheral or terminal organ is given. It is these structures that are primarily excited to activity by the physiologic stimulus, and that in turn arouse the nerve to activity. Peripheral organs are to be regarded as special modes of termination of afferent nerves and adapted for the impress of a specific stimulus. The peripheral organs of afferent nerves found in the skin and oral mucous membrane present a variety of forms, some of which are as follows: 1. Free Endings. — These are pointed or club-shaped processes, the ultimate terminations of af- erent nerve-fibrils, found in and among epidermic cells. 2. Tactile Cells. — These are oval nucleated bodies found in the deeper layers of the epidermis. They rest upon or are embraced by a cres- centic shaped body, the tactile meniscus, which in turn is directly connected with the nerve-fibril and probably a modification of it (Fig. 270). 3. The Corpuscles of Meissner and Wagner. — In the papillae of the derma, especially in the palm of the hand and in the finger-tips, are found elliptical bodies consisting of a connective- tissue capsule containing a number of tactile discs with which the nerve-fibrils are connected. If the afferent nerve is traced to the capsule, it is found to lose both its neurilemma and medulla, after which the naked fibril penetrates the capsule, breaks up into a number of branches, and after pursuing a more or less spiral course becomes connected with the tactile discs (Fig. 271). 4. Hair Wreaths. — Just below the openings of the sebaceous gland the hair follicles are surrounded by naked axis-cylinder fibrils in the form of a wTeath, which in all probability terminate in the cells of the external root-sheath. These, too, are to be regarded as part of the touch apparatus. 5. Corpuscles 0} Vater or Pacini. — These are oval-shaped structures found along the nerves distributed to the palms of the hands and Fig. 270. — Tactile Cells from Snout OF Pig. a. Tactile cell. m. Tactile disc. «. Nerve-fiber. — {Stirling.) 6o4 TEXT-BOOK OF PHYSIOLOGY. the soles of the feet, on the nerves distributed to the external genital organs, to joints and other structures. They consist of a thick capsule of lamellated connective tissue in the interior of which is a bulb resembling granular protoplasm. The axis- cylinder of the nerve-fiber enters the capsule and becomes con- nected with the bulb (Fig. 272). Other forms of peripheral organs are found in special regions of the skin as well as in different animals. Touch Sense. — The area, stimulation of which evokes sensations of touch, is coextensive with the skin and that limited portion of the mucous membrane lining the mouth. Careful stimulation of the skin by means of a fine stiff bristle has revealed the fact, however, that the touch area is not continuous, but discrete, pre- senting itself under the form of small areas or spots, separated by relatively large areas insensitive to the same agent. Stimulation of these spots always calls forth a sensation of touch. For this reason they are known as "touch spots." The number of such spots in any given area of skin varies considerably. Thus, in the skin of the calf fifteen such spots have been counted in a square centimeter. In the palm of the hand, from forty to fifty have been counted in an area of the same extent. They are also especially abundant in the immediate neighborhood of the hair follicles. The peripheral end-organ associated with the touch spots in the neighborhood of a hair follicle is in all probability the wreath of nerve-fibrils surrounding the follicle. In regions devoid of hairs the end-organ is the Meissner corpuscle, for in the palmar surface of the last phalanx of the index-finger, where the touch sense is quite acute, about 20 corpuscles are present in each square millimeter of surface. The specific stimulus necessary to evoke the sensation of touch is a deformation of the skin; and the greater this is within physiologic limits, the more pronounced is the sensation. Pressure Sense. — The contact of an external body is attended by a certain amount of pressure, which, however, must attain a certain degree before the sensation can be evoked. This is known Fig. 271. — Touch Corpus- cle OF Meissner and Wagner, b. Papilla of cutis, d. Nerve-fiber of touch-corpuscle. e, j. Nerve-fiber in touch- corpuscle, g. Cells of Malpighian layer. — (From Stirling.) THE SENSE OF TOUCH. 605 as the threshold value, or the degree of liminal intensity. Since the sensations are the result of pressure, they are termed pressure sensations, and their intensity may be expressed in terms of pressure. The sensitivity of the skin as determined by the pressure sense varies in different regions of the body and in accordance with the size of the area pressed. Thus, the liminal intensity of a stimulus for an area of nine square millimeters for the skin of the forehead is 0.002 gram; for the flexor aspect of the forearm, 0.003 gram; and for the hips, thigh, and abdomen, 0.005 g^^am; for the palmar surface of the finger, 0.019 gra^i; for the heel, i gram. The delicacy of the sense of touch is measured by the slight increase or decrease in the intensity of the stimulus that v^^ill produce an appreciable change in the intensity of the sensation. Not all changes in the stimulus, however, are attended by a change in the sensation. It has been determined that the latter will change only when the former changes in a definite ratio, which for the volar surface of the third phalanx of the index-finger is as 29 is to 30. Thus, other things being equal, a sensation caused by a given weight will only change with moderate stimulation when one-thirtieth of the weight is either added or subtracted. The ratio of change, how- ever, varies in different regions of the body : thus, for the back of the hand the ratio varies from one-tenth to one-twentieth; for the tongue, one-thirtieth to one-fortieth. The difference of stimulus necessary to evoke a sensation is known as the threshold difference. It seems to be a law not only for the skin, but for other senses as well, that a change in the intensity of a sensation, to an appreciable extent, will occur only when the objective stimulus changes in a definite ratio. This ratio, however, will vary not only in different regions of the skin, in different individuals, but with the sense-organ investigated. Place Sense. — The sensation evoked by stimulation of the skin is always, under normal conditions, referred to the place stimulated. This holds true not only for two or more points near or widely sepa- rated on the same side, but also for corresponding points on opposite sides of the body, even when the stimuli have the same intensity and are simultaneously applied. The cause for this localiz- ing power is to be found in a difference in the quality of the sensation Fig. 272 . — Pacinian Corpuscles, c. Cap- sules, d. Endothelial lining separating the latter, n. Nerve. /. Funicular sheath of nerv-e. m. Central mass. n'. Terminal fiber; and a. Where it splits up into finer fibrils. — {Stirling.) 6o6 TEXT-BOOK OF PHYSIOLOGY. related in some way to the part stimulated. Each cutaneous area is supposed to give to the tactile sensation a quality or local sign by virtue of which the mind is enabled to localize the point of contact. Each cutaneous area which has a local sign of its own is known as a sensory circle, for the reason that the mind does not refer the sensation to a point, but to an area more or less circular in outline. The skin may therefore be regarded as composed of myriads of such circles varying in size in different regions of the body. The delicacy of the localizing power in any part of the skin is determined by testing the power which the part possesses, of distinguishing the sensations produced by the contact of the points of a pair of compasses placed close together. The distance to which the points must be separated in order to evoke two separate recognizable sensations is a measure of the diameter of the sensory circle. Within this circle the two sensations become fused into one sensation. The discriminative sensibihty of different regions as determined by compass points is shown in the following table; the numbers represent the distances at which two sensations are recog- nized : Tip of tongue, i.i Palmar surface of third phalanx of index-finger, 2.2 Red surface of Ups, 4.5 Palmar surface of first phalanx of finger, 5.5 Tip of nose, 6.8 Palm of hand, 8.9 Lower part of forehead, 22.6 Dorsum of hand, 31.6 Dorsum of foot, 40.6 Middle of the back, 67.7 The discriminative sensibility of any portion of the body is a function of its mobility. This is shown by the fact that it increases rapidly from the shoulders to the fingers and from the hips to the toes. The Temperature Sense. — The sensations of heat and cold which are experienced from time to time are caused by changes in the temperature of the skin produced in a variety of ways. As these sensations are specifically different from those of touch, as well as different from each other, it is highly probable that for each sensation there are special nerve-endings distributed throughout the skin. Investigations have shown that all over the skin there are innumerable spots of varying size which if stimulated evoke sensations of heat or cold. Such points are termed heat and cold spots. Each responds to but one kind of stimulus. A warm object applied to a heat spot will evoke a sensation of warmth. It will have no effect on the cold spot. The reverse is also true. Between the cold and heat spots there are areas that are neutral THE SENSE OF TOUCH. 607 insensitive to either heat or cold. The cold spots are more numerous than the heat spots in almost all regions of the body. -'The sensitivity of the skin to temperature changes is ver}' acute, as shown by the fact that even 0.05° C. is readily appreciable. This holds true, however, only when the temperature of the object lies between 27° and 2,^° C. This capability varies in different regions of ''the skin, and depends on the number of heat and cold spots present, the thickness of the epidermis, the thermal conductivity of the object touching it, and the extent to which it is habitually exposed or protected. The physiologic stimulus to the thermic end-organs is the passage nil ■Ji ihii'^^^ lll•....•■••■ '••ili' '--'ii 111' •- ii'ii'i 1111 ji'ji' „.-. n,-: Fig. 273. — Cold and Hot Spots from the Anterior Surface of the Forearm. a. Cold spots, b. Hot spots. The dark parts are the most sensitive, the hatched the medium, the dotted the feebly, and the vacant spaces the non-sensitive. — {Lan- dois and Stirling.) of heat through the skin from the interior of the body to the sur- rounding air. If the radiation is continuous and uniform, the end- organs soon adapt themselves to the temperature of the surrounding air and the sensation of heat, under physiologic conditions, is not evoked. If there is a sudden rise in the external temperature caused by natural or artificial means, which diminishes the radiation, the temperature of the skin will at once rise, the end-organs will be stimulated, and a sensation of warmth developed. If, on the other hand, there is a sudden fall in temperature and an increased radia- tion, the temperature of the skin will fall, the end-organs will be stimulated, and a sensation of cold developed. Experiment also teaches that the intensity of a warm or cold sensation will depend 6o8 TEXT-BOOK OF PHYSIOLOGY. on the existing temperature of the skin, and not upon the absolute temperature of the object. Thus, water at 20° C. will evoke a sensation of heat or cold according as the skin has previously been cooled below or warmed above this temperature. The Muscle Sense. — As a result of the activities of the muscula- ture of the body or even of its individual parts, there arises in con- sciousness a series of sensations, which are termed muscle sensations. These sensations give rise to the perception — 1. Of the direction and duration of both passive (due to external causes) and active movements (due to internal, volitional efforts) which take place without hindrance ; 2. Of the resistance offered to movements by external bodies; and — 3. Of the posture of the body or of its individual parts. As to the seat of the physiologic processes which precede and underHe the development of the sensations two views, at least, may be advanced, viz. : 1. That the processes are central in origin and partake of the nature of a discharge of nerve impulses from the nerve-cells through the motor nerves to the muscles, the entire process being accom- panied by sensation. This is known as the innervation theory. 2. That the processes are peripheral in origin, initiated by stimulation of specialized end-organs in the muscles and tendons which are connected through the intermediation of afferent nerves with nerve-cells in the cerebral cortex. The physiologic mechanism subserving the muscle sense, accord- ing to the second theory, now held by many physiologists, thus in- volves peripheral end-organs, afferent nerves, their cortical connec- tions and nerve-cells in the cerebral cortex at or near the junction of the superior and inferior parietal convolutions. The End-organs. — These are small fusiform structures found in and among the muscle bundles of all the muscles of the body with the exception of the diaphragm and eye muscles. In the muscles of the arm and in the small muscles of the hand they are especially abundant. From their shape they are known as muscle spindles. They vary in length from 2 to 12 mm. and in breadth from 0.15 to 0.4 mm. Each spindle (Fig. 274) consists of a connective-tissue capsule containing from two to ten longitudinally arranged striated muscle fibers of fine diameter. In the middle or equatorial region of these intra-jusal fibers there is frequently found a quantity of non-striated protoplasmic matter. The spindle is supplied with both sensor and motor nerves. The sensor fiber loses its external invest- ments as it approaches the capsule. The naked axis-cylinder then penetrates the capsule, and after dividing several times terminates in a ribbon-hke or spiral manner around the intra-fusal muscle fiber. This ending was described by and is known as Ruffini's "annulo- THE SENSE OF TOUCH. 609 spiral ribbon." The motor nerve also penetrates the capsule and terminates in the polar extremities of the intra-fusal fiber. Sensor end-organs supposed to be connected with the muscle sense are also found in the tendons of muscles. Afferent Nerves. — That muscles are abundantly supplied with afferent nerves has been proved by different methods of investigation. With histologic methods Sherrington has traced afferent fibers from the muscle spindles directly into the spinal nerve ganglia. The con- tractions of muscles from electric stimulation as well as the con- tractions known as muscle cramp, due to unknown agents, give rise to sensations of pain, a fact which indicates the presence in muscles of afferent or sensor nerves. Cortical Area. — Pathologic findings have shown that an im- pairment or a loss of the muscle sense is associated with de- structive lesions of perhaps the superior and inferior parietal Fig. 274. — A Neuro-muscle Spindle of a Cat. (Ruffini.) c. Capsule, pr. e. Primary ending. 5. e. Secondary ending, pi. e. Plate ending. (All these are probably sensor in function.) — {Starling's "Physiology.") convolutions (Fig. 226). In a case reported by Starr the removal of a small tumor in the pia mater situated over the junction of the superior and inferior parietal lobules was followed by a loss of the muscle sense and marked ataxia in the right hand for a period of six weeks, after which recovery took place. These symptoms were attributed to injury of the cortex from unavoidable surgical procedures. The muscle sensations, as stated in foregoing paragraphs, form the basis of the perception not only of the direction and the duration of a body movement and the resistance experienced, but also of the position and the tension of the muscle groups. The latter fact more especially makes it possible for the mind to direct the muscles and to graduate the energy necessary to the accomphshment of a definite purpose. Active Touch. — x^ctive touch or the apphcation of the fingers to the surfaces of external objects implies the cooperation of the skin and the muscles. The sensations which are evoked are combina- 39 6io TEXT-BOOK OF PHYSIOLOGY. tions of contact and muscle sensations. The union of these sensa- tions forms the basis of the perception of hardness, softness, smooth- ness, and roughness of bodies. THE SENSE OF TASTE. The physiologic mechanism involved in the sense of taste includes the tongue, the gustatory nerves (the chorda tympani and the glosso- phar}'ngeal), their cortical connections and nerve-cells in the gray matter of the fourth temporal convolutions. The peripheral excitation of this apparatus gives rise to nerve impulses v^hich transmitted to the brain evoke the sensations of taste. The specific physiologic stimulus is matter, organic and inorganic, in a state of solution. The Tongue. — The tongue consists of both intrinsic and extrinsic muscles, in virtue of which it is susceptible of both a change in shape and position. The movements of the tongue, though not essential to taste, are made use of in the finer discrimination of tastes. The tongue is covered over by mucous membrane continuous with that lining the oral cavity. The dorsum of the tongue presents a series of papillae richly suppHed with blood-vessels and nerves. Of these there are three varieties, the filiform, the fungiform, and the circum vallate (Fig. 275). 1. The filiform papillcB, the most numerous, cover the anterior two -thirds of the tongue; they are conical or filiform in shape and covered with homy epithe- lium which is often prolonged into filamentous tufts. 2. The fungiform papillce, found chiefly at the tip and sides of the tongue, are less numerous but larger than the pre- ceding and of a deep red color. 3. The circumvallate papillce, from eight to ten in number, are situated at the base of the tongue arranged in the form of the letter V. They consist of a central projection surrounded by a wall or circumvallation from which they take their name. The Peripheral End-organs. The Taste-buds. — Embedded in the epithelium covering the mucous membrane not only of the tongue but of the palate and posterior surface of the epiglottis are small ovoid bodies which from their relation to the gustatory nerves Fig. 275. — The Tongue I. Papillae circumval- latae. 2. Papillae fungi formes. THE SENSE OF TASTE. 6ii ^;%!^^V > Fig. are regarded as their peripheral end-organs and known as taste-buds or taste-beakers. Each bud is ovoid in shape (Fig. 276). Its base rests on the tunica propria ; its apex comes up to the epithehum, where it presents a narrow funnel-shaped opening, the taste-pore. The wall of the bud is composed of elongated curved epithelium. The interior contains narrow spindle-shaped neuro-epithelial cells pro- vided at their outer extremity with stiff hair-like filaments which project into the taste-pore. The neuro-epithelial cells are in physiologic relation with the nerves of taste. The terminal branches, after entering the bud at its base, develop fine tufts which come into contact with the cells. That the taste-buds are connected with the nerves of taste is rendered probable from the fact of their degeneration after division of the nerves. The Taste Area.— The taste area, though confined for the most part to the tongue, extends itself in different individuals to the mucous mem- brane of the hard palate, to the anterior sur- face of the soft palate, to the uvula, the anterior and posterior half arches, the tonsils, the posterior wall of the pharynx, and the epiglottis. The Taste Sensations. — The sensations which arise in consequence of impressions made by different substances on the peripheral appara- tus of this area are in so many instances com- binations of taste, touch, temperature, and smell that they are extremely difficult of classification. Nevertheless four primary tastes can be recog- nized: viz., bitter, sweet, acid or sour, salt or sahne. Though the contact of any bitter, sweet, acid, or salt substance with any part of the tongue will, if the substance be present in sufficient quantity or concentration, develop a corresponding sensation, some regions of the tongue are more sensitive and respon- sive than others. Thus, the posterior portion is more sensitive to bitter substances than the anterior; the reverse is true for sweet substances and perhaps for acids and salines. The intensity of the resulting sensation in any given instance will depend on the degree of concentration of the substance, while its massiveness will depend on the area affected. 276. — Taste- bud FROM ClR- cumvallate Papilla of a Child. The oval structure is limited to the epithehum (e) Uning the fur- row, encroach- ing slightly upon the adja- cent connective tissue . (/) ; o, taste-pore through which the taste - cells communicate with the mucous surface. — {After Piersol.) 6i2 TEXT-BOOK OF PHYSIOLOGY. THE SENSE OF SMELL. The physiologic mechanism involved in the sense of smell in- cludes the nasal fossae, the olfactory nerves, the olfactory tracts, and nerve-cells in those areas of the cortex known as the uncinate con- volution and anterior part of the gyrus fornicatus. Peripheral stimu- lation of this mechanism develops nerve impulses which, transmitted to the cortex, evoke the sensations of odor. The specific physiologic stimulus is matter in the gaseous or volatile state. The Nasal Fossae. — The nasal fossae are irregularly shaped cavities separated by a vertical septum formed by the perpendicular plate of the ethmoid bone, the vomer, and the triangular cartilage. The outer wall presents three recesses separated by the projection inward of the turbinated bones. Each fossa opens anteriorly and posteriorly by the anterior and posterior nares, the latter com- municating with the pharynx. Both fossae are lined throughout by mucous membrane. The upper part of the fossa is known as the olfactory, the lower portion as the respiratory region. In the former, the mucous membrane over the septum and superior turbinated bone is somewhat thicker than elsewhere and covered with a neuro- epithelium which constitutes — The Peripheral End-organ.^ — This consists of a basement membrane supporting two kinds of cells, the olfactory and the sustentacular. The olfactory cells are bipolar nerve-cells, the center of which contains a large spheric nucleus. The peripheral pole is cylindric or conic in shape and provided at its extremity with several hair-like processes. The central pole becomes the axon process and passes directly to the olfactory bulb. The sustentacular cells are epithelial in character and, as their name implies, support or sustain the olfactory cells. For the appreciation of odorous particles the air must be drawn through the nasal fossae with a certain degree of velocity. If the particles are widely diffused in the air, they must be drawn not only more quickly but more forcibly into contact with the olfactory hairs, as in the act of sniflfing, the result of short energetic inspira- tions. To many substances the olfactory apparatus is extremely sensitive. Thus, it has been shown that a particle of mercaptan the actual weight of which was calculated to be ^,;^-^,jn„ of a milli- gram gave rise to a distinct sensation. The Olfactory Sensations. — The sensations which arise in consequence of the excitation of the olfactory apparatus are very numerous and their classification is extremely difficult. For this reason it is customary to divide them into two groups: viz., agreeable and disagreeable, in accordance with the feelings they excite in the individual. As the olfactory sensations give rise to feelings rather THE SENSE OF SMELL. 613 than ideas, this sense plays in man a subordinate part in the acquisi- tion of knowledge. In lower animals this sense is employed for the purpose of discovering and securing food, for detecting enemies and friends, and for sexual purposes. In land animals the entire olfac- tory apparatus is well developed and the sense keen ; in some aquatic animals, as the dolphin, whale, and seal, the apparatus is poorly developed and the sense dull. CHAPTER XXV. THE SENSE OF SIGHT. The physiologic mechanism involved in the sense of sight in- cludes the eyeball, the optic nerve, the optic tracts, their cortical connections, and nerve-cells in the cuneus and adjacent gray matter. Peripheral stimulation of this mechanism develops nerve impulses w^hich transmitted to the cortex evoke (i) the sensation of light and its different qualities — colors; (2) the perception of light and color under the form of pictures of external objects; and (3) in connection vi^ith the ocular muscles, the production of muscle sensations by which the size, distance, and direction of objects may be judged. The specific physiologic stimulus to the terminal end-organ, the retina, is the impact of ether vibrations. In general, it may be said that, at least for the same color, the intensity of the objective vibration determines the intensity of the sensation. THE PHYSIOLOGIC ANATOMY OF THE EYEBALL. The eyeball is situated at the fore part of the orbit cavity, and in such a position as to permit of an extensive range of vision. It is loosely held in position by a fibrous membrane, the capsule of Tenon, which is attached, on the one hand, to the eyeball itself, and, on the other, to the walls of the orbit cavity. Thus suspended, the eyeball is susceptible of being moved in any direction by the contraction of the muscles attached to it. The ball is spheroid in shape, measuring about 24 millimeters in its antero-posterior diameter and a little less in its transverse and vertical diameters. When viewed in profile, it is seen to con- sist of the segments of two spheres, of which the posterior is the larger, occupying five-sixths, and the anterior is the smaller, occupy- ing one-sixth of the ball. It is composed of several concentrically arranged membranes enclosing various refracting media essential to vision. The membranes, enumerating them from without inward, are as follows: the sclera and cornea, the chorioid and iris, and the retina. The refracting media are the aqueous humor, the crystal- line lens, and the vitreous humor. The Sclera and Cornea. — The sclera is the thick opaque mem- brane covering the posterior five-sixths of the ball. It is composed 614 THE SENSE OF SIGHT. 615 of layers of connective tissue which are arranged transversely and longitudinally. It is pierced posteriorly by the optic nerve about 3 or 4 millimeters internal to the optic axis. By virtue of its firmness and density the sclera gives form to the eyeball, protects delicate structures enclosed by it, and serves for the attachment of the muscles by which the ball is moved. The cornea is the transparent mem- brane forming the anterior one-sixth of the ball. It is nearly circular in shape, measuring in its horizontal meridian 12 mm., in its vertical meridian 11 mm. The curvature is therefore sharper in the latter than in the former. The radius of curvature of the anterior surface at that central portion ordinarily used in vision is 7.829 mm.; that of the posterior surface about 6 mm. The substance of the cornea is made up of thin layers of delicate transparent fibrils of connective tissue continuous with those found in the sclera. Lymph-spaces are present throughout the cornea, in which are to be found l}TTiph-corpuscles. The anterior surface of the cornea is covered with several layers of nucleated epithelium supported by a structureless membrane, the anterior elastic lamina. The posterior surface also is covered by a layer of epithelium sup- ported by a similar membrane, the membrane of Descemet, which at its periphery becomes continuous with the iris. At the junction of the cornea and sclera there is a circular groove, known as the canal of Schlemm. The Chorioid, Iris, Ciliary Muscle, and Ciliary Processes. — The chorioid is the dark brown membrane which extends forward nearly to the cornea, where it terminates in a series of folds, the cihary processes. Posteriorly, it is pierced by the optic nerve. It is composed largely of blood-vessels, arteries, capillaries, and veins, supported by connective tissue. Externally it is loosely connected to the sclera ; internally it is fined by a layer of hexagonal ceUs con- taining black pigment which, though usually described as a part of the chorioid, is now known to belong, embryologicly and physio- logicly, to the retina. Lying within the outer layer of arteries and veins there is a thick layer of small arterioles and capillaries, known as the chorio-capillaris. The chorioid with its contained blood-vessels bears an important relation to the nutrition and function of the eye. It provides a free supply of lymph and presents a uniform temperature to the retina in contact with it (Fig. 277). The iris is the circular, variously colored membrane in the anterior part of the eye just behind the cornea. It presents a fittle to the nasal side of the center a circular opening, the pupil. The outer or circumferential border is united by connective tissue to the cornea, sclera, and ciliary muscle; the inner border forms the boundary of the pupil. The iris consists of a framework of connective tissue sup- porting blood-vessels, muscle-fibers, and pigmented connective-tissue 6x6 TEXT-BOOK OF PHYSIOLOGY 5^ cells. The anterior surface is covered by a layer of cells continuous with those covering the posterior surface of the cornea. The pos- terior surface is formed by a thin structureless membrane supporting a layer of pigment cells continuous with those lining the chorioid. The color which the iris presents in different individuals depends on the relative amount of pigment in the connective-tissue corpuscles. In blue eyes the pigment is wanting. In gray, brown, and black eyes the pigment is present in progressively increasing amounts. The blood - vessels are connected with those of the chori- oid coat. The muscle- fibers are of the non-striated variety and arranged in two sets, one cir- cularly, the other radially, disposed. The circular fibers are found close to the pupil near the posterior surface of the iris. Contraction of this band of fibers di- minishes, relaxation increases, the size of the pupil. This muscle is known as the sphincter pupilla or sphincter iridis. The radial fibers form a more or less continuous layer in the posterior part of the iris, extending from the margin of the pupil, where they blend with the circular fibers, to the outer border. Contraction of the fibers enlarges the size of the pupil. The muscle is known as the dilatator pupilla. The nerves exciting the circular fibers to action are the ciliary nerves, axons of nerve-cells located in the ciliary or ophthalmic gan- glion. Stimulation Of these fibers gives rise to contraction of the sphincter and diminution in the size of the pupil. The nerves excit- ing the dilatator fibers are axons of nerve-cells located in the superior Fig. 277. — Chorioid Coat of the Eye. — i. Optic nerve. 2, 2, 2, 2, 3, 3, 3, 4. Sclerotic coat divided and turned back to show the chorioid. 5, 5, 5, 5. The cornea, divided into four portions and turned back. 6, 6. Canal of Schlemm. 7. E.xternal surface of the chorioid, traversed by the ciliary nerves and one of the long ciliary arteries. 8. Central vessel into which open the vasa vorticosa. 9, 9, 10, 10. Chorioid zone. 11, 11. Ciliary nerves. 12. Long ciliary artery. 13, 13, 13, 13. Anterior ciliary arteries. 14. Iris. 15, 15. Vas- cular circle of the iris. 16. Pupil. — (Sappey.) THE SENSE OF SIGHT. 617 cervical ganglion. They reach the iris by way of the cervical sympa- thetic, the ophthalmic division of the fifth, and the long ciHary nerve. Stimulation of these nerves is followed by dilatation of the pupil. Both the cihary and superior cervical ganglia are in relation with pre-ganglionic fibers coming from the central nerve system. (See page 551.) The ciliary muscle is a gray circular band about two millimeters in width, consisting of non-striated muscle-fibers. The majority of these fibers pursue a radial or meridional direction. Taking their origin from the junction of the sclera, cornea, and iris, they pass backward to be inserted into the chorioid coat opposite' the ciliary processes. The inner portion of the muscle is interrupted by bundles of fibers which pursue a circular direction. They collectively con- stitute the annular or ring muscle of Muller. The ciliary muscle in Fig. 2 78. — Section through the Ciliary Region of the Human Eye. a. Radi- ating bundles of the ciliary muscle, b. Deeper bundles, c. Circular network. d. Annular muscle of Muller. e. Tendon of ciliary muscle. /. Muscle-fibers on posterior side of the iris. g. Muscles on the cihary border of the same. h. Ligamentum pectinatum. — {After Iwanoff.) common with the circular fibers of the iris receives its nerve-supply direct from the nerve- cells in the cihary ganghon. Contraction of the cihary muscle tenses the chorioid coat, and for this reason it is frequently termed the tensor chorioidecE. The Retina. — The retina is the internal coat of the eye, extending forward almost to the cihary processes, where it terminates in an indented border, known as the ora serrata. In the living condition it is clear, transparent, and pink in color. After death it becomes opaque. The retina is abundantly supplied with blood-vessels, de- rived from the arteria centralis retince, a branch of the ophthalmic, which pierces the optic nerve near the sclera, runs forward in its center, to the retina, in which its terminal branches are distributed. The veins arising from the capillary plexus leave the retina by the same route. 6i8 TEXT-BOOK OF PHYSIOLOGY. In the posterior portion of the retina, at a point corresponding with the axis of vision, there is a small oval area about 2 mm. in its transverse and about 0.8 mm. in its vertical diameter. From the fact that it presents a Pigment-layer (not shown). ycllow appearance,it is known as the macula lutea. This area pre- sents in its center a depression with slop- ing sides, known as the jovea centralis. About 3.5 mm. to the nasal side of the macula is the point of entrance of the optic nerve. The retina is re- markably complex in structure, presenting an appearance when viewed microscopic- ally, something like that represented in Fig. 279, indicating that it is composed of different cellular ele- have been named, from behind Fig. 279. — Vertical Section of — (Schaper.) 2. Layer of rods and cones- 3. External limiting membrane 4. Outer nuclear layer, 5. Outer molecular layer. 6. Inner nuclear layer. 7. Inner molecular layer. 8. Layer of ganglion cells. 9. Layer of nerve-fibers. Human Retina. ments arranged in layers. These forward, as follows : 1. The layer of pigment cells. 2. The layer of rods and cones, or Jacobson's layer. The external limiting membrane. The outer nuclear or granular layer. The outer molecular or reticular layer. The inner nuclear or granular layer. The inner molecular or reticular layer. 8. The layer of gangUon cells. 9. The layer of nerve-fibers. Modern histologic methods of research have made it possible to reduce the retina, exclusive of the pigment cells, to three successive layers of nerve-cells, supported by a highly developed neurogha, forming what has been termed the fibers of Miiller. These nerve- cells are as follows : 1. The visual cells. 2. The bipolar cells. 3. The ganglion cells. THE SENSE OF SIGHT. 619 The relation of these nerve-cells one to another and to the supporting neuroglia tissue and the manner in which they unite to form the above-mentioned layers are schematicly shown in Fig. 280. The pigment layer is composed of hexagonal cells. Though formerly described as forming a part (the inner layer) of the chorioid, these cells belong embryologicly to the retina. From their retinal surface dehcate pigmented processes extend into and between the rods and cones. On expo- sure to light these processes elongate and push themselves between the rods. In the dark they retract and with- draw into the cell-body. The visual cells which form the layer of rods and cones are of two varieties, the rod-shaped and the cone- shaped. The rod-shaped visual cells consist of a straight elongated cylinder extending through the entire thickness of Jacobson's membrane and a fine fiber containing a nucleus, which, after piercing the external limiting membrane, passes into the outer molecular layer, where it terminates in a spheric enlargement. The outer por- tion of the rod is clear and homogeneous, though contain- ing a pigment known as visual purple or rhodopsin ; the inner portion of the rod is slightly granular. The cone - shaped visual cells also consist of two por- tions, a conic portion situated in Jacobson's membrane between the rods, and a fine fiber, containing a nucleus, which, after piercing the external limiting membrane, passes into the outer molecular layer, where it terminates in a fine tuft. The inner portion of the cone is thicker than the rod and rests on the hmiting membrane; the outer portion tapers to a fine point and is known as the cone-style. The cones, as a rule, are shorter than the rods. The proportion of rods to cones varies in different parts of the retina, though there are on Fig 280. — Cross-section of the Retina FROM A Mammal. A. Layer of rods and cones. B. Visual cells (outer gran- ules). C. Outer molecular layer. E. Bipolar cells (inner granules). F. In- ner molecular layer. G. Ganglion cells. H. Layer of nerve-fibers, a. Rods. b. Cones, e. Bipolar rod. f. Bipolar cone. r. Lower ramification of a bi- polar rod. f. Lower ramification of a bipolar cone, g, h, i, j, k. Ganglion cells in various stages, branching from F. X, z. Bipolar contact of rods and cones, t. Miiller's supporting fibers. S. Centrifugal nerve-fibers. — {After Ra- mon y Cajal.) 620 TEXT-BOOK OF PHYSIOLOGY. the average about fourteen rods to one cone. In the macula the rods are almost entirely absent, cones alone being present. The layer of visual cells together with the neuroglia constitute the first three layers of the retina proper. The external limiting mem- •brane is formed by the blending of the ends of neuroglia cells. The bipolar cells consist of a central portion, found in the inner nuclear layer, from which are given off two processes which pass in opposite directions, one toward the visual cells, the other toward the ganglion cells. The former terminate in tufts which arborize around the tufts and spheric enlargements of the visual cells, and assist in the formation of the outer molecular layer; the latter terminate in similar tufts in the inner molecular layer. The ganglion cells are arranged in a single layer, as a rule. They are large and nucleated. From the inner side of each cell there is given off a single axon which passes toward the center of the retina (forming the nerve-fiber layer), where it enters and assists in forming the optic nerve. From the outer side of the ganglion cell dendrites pass into and assist in forming the inner molecular layer. These den- drites come into physiologic relation with those of the inner pro- cesses of the bipolar cells. Horizontally disposed nerve-cells are also present in the outer molecular layer in relation with the visual cells. Spongioblasts or amacrine cells are also present at the border of and in the inner molec- ular layer. From the relation of the ganglion cells, from which the optic nerve- fibers take their origin, to the visual cells and the bipolar cells, the latter may be regarded as the terminal visual organ, the intermediate between the ether vibrations and the ganglion cell. The visual cells are directed toward the chorioid, away from the entering light, dipping into the pigment cells. They, with the pigment layer, are the elements by which the ether vibrations are transformed into ner\'e energy. In the fovea most of the retinal elements are wanting or are reduced in thickness. The cones alone are present. The cone-fibers with their nuclei are directed obliquely upward and outward along the slope of the fovea, to end in tufts which come into physiologic relation with the dendrites of the ganglion cells which at the top of the fovea are generally increased in number (Fig. 281). It is estimated that the optic nerve contains about 500,000 nerve- fibers, and that for each fiber there are about 7 cones, 100 rods, and 7 pigment cells. In accordance with this estimate there would be about 3,500,000 cones, 50,000,000 rods, and 3,500,000 pigment cells. The distance between the centers of two adjacent cones in the fovea is 4 micromillimeters. THE SENSE OF SIGHT. 621 The vitreous humor is the largest of the refracting media and occupies by far the largest portion of the interior of the eyeball. From its position it gives support to the retina. Anteriorly it presents a concavity, in which the crystalline lens is lodged. The vitreous humor consists of water (97 per cent.), organic matter and salts, enclosed in a transparent membrane, the tunica hyaloidea. The mass of the vitre- ous humor is penetrated by a species of connective tissue. The aqueous humor is small in amount in comparison with the vitreous and is found in the space bounded by the cornea, the ciliary body, the suspensory ligament, and the lens. The projection of :^ ®^«e Fig. 281. — Horizontal Section through the Macula and Fovea of a Man Sixty Years Old. The section is not through the exact center of the fovea, for there are only cone visual cells and no remnants of the confluence of the inner granule and ganglion cell layers are present, i. Cones. 2. External limiting membrane. 3. Outer nuclear layer. 4. Henle's fiber layer. 5. Outer molec- ular or reticular layer. 6. Inner nuclear layer. 7. Inner molecular or reticular layer. 8. Layer of ganglion cells. 9. Nerve-fiber layer. — {After Schaper, Stohr's "Histology") the iris into this space partially divides into an anterior and posterior portion or chamber. The aqueous humor is a clear, w^atery, alkaline fluid derived from or secreted by the capillary blood-vessels of the ciliary body. From this origin it passes through the pupil into the anterior chamber. It serves to keep the cornea tense and smooth. The ocular tension partly depends on the presence of this fluid in the eyeball. There is every reason for believing that there is a constant stream of fluid from the blood-vessels into the eye and from the eye through the spaces of Fontana at the base of the iris into the canal of Schlemm, and so into the blood. Any interference with the exit of this fluid rapidly increases the ocular tension. 622 TEXT-BOOK OF PHYSIOLOGY. The lens is the transparent biconvex body situated just behind the iris, in the concavity of the vitreous. The thickness of the lens is 3.6 mm., the diameter about 9 mm. It consists of a transparent capsule containing elongated hexagonal fibers which, having their origin near the anterior central portion of the lens, pass out toward the margin, where they bend around to terminate in a triradiate figure on the opposite side. Chemicly the lens consists of water, a globuhn body (crystalhn), and salts. Fig. 282. — Horizontal Section of the Eyeball. — i. Sclera. 2. Cornea. 3. Chorioid. 4. Iris. 5. Ciliary muscle. 6. Retina. 7. Lens. 8. Suspensory ligament. 9. Canal of Schlemm. 10. Canal of Petit. 11. Optic [nerve. — (Deaver.) The Suspensory Ligament. — The lens is held in position by the suspensory ligament, formed in part by the hyaloid membrane and in part by fibers derived from the ciliary processes. The former be- comes attached to the posterior surface, the latter to the anterior surface of the lens near the equator. The space between the two layers of the ligament is the canal of Petit. The anterior surface of the ligament presents a series of plications conforming to correspond- ing plications on the surface of the ciliary processes. The relations of all the parts entering into the structure of the eye are shown in Fig. 282. THE SENSE OF SIGHT. 623 THE PHYSIOLOGY OF VISION. The Retinal Image. — The general function of the eye is the formation of images of external objects on the free ends of the per- cipient elements of the retina, the rods and cones. The existence of an image on the retina can be readily seen in the excised eye of an albino rabbit, when placed between a lighted candle and the eye of an observer. Its presence in the human eye can be demonstrated with the ophthalmoscope. It is this image, composed of focal points of luminous rays, which stimulates the rods and cones, which is the basis of our sight-perceptions, and out of which the mind con- structs space-relations of external objects. In only two essential respects does the image on the retina differ from the object, aside from the fact that the object has usually three, the image only two, dimensions — viz., in size and relative arrangement of its parts. What- ever the distance, the image is generally smaller than the object; it is also reversed, the upper part of the object becoming the lower part of the image, and the right side of the object the left of the image. The Dioptric Apparatus. — The formation of an image is made possible by the introduction of a complex refracting apparatus con- sisting of the cornea, aqueous humor, lens, and vitreous humor. Without these agencies the ether vibrations would give rise only to a sensation of diffused luminosity. Rays of light emanating from any one point — that is, homocentric rays — arriving at the eye must traverse successively the different refracting media. In their passage from one to the other, they undergo at the surfaces changes in direc- tion before they are finally converged to a focal point. In order to mathematically follow the rays in all their deviations through the media, to determine their focal points and to construct an image, a knowledge of the form of the refracting surfaces, the refractive indices of the different media, and the distances of the surfaces from one another must be known. The following constants are now accepted : The radius of curvature of that portion of each refracting surface used for distinct vision is for the cornea 7.829 mm., for the anterior and posterior surfaces of the lens 10 and 6 mm., respectively. The indices of refraction of the different media are as follows: cornea and aqueous humor, 1.3365; lens, 1. 437 1 ; vitreous body, 1.3365. The distance from the vertex of the cornea to the lens is 3.6 mm.; the thickness of the lens, 3.6 mm.; the distance from the posterior surface of the lens to the retina, 15 mm. As the two surfaces of the cornea are practically parallel, and as the index of refraction of the aqueous humor is the same as that of the cornea, they may be regarded as but one medium. The refracting surfaces may therefore be reduced to the anterior surface of the 624 TEXT-BOOK OF PHYSIOLOGY. cornea, the anterior surface of the lens, and the posterior surface of the lens.* Parallel rays of light entering the eye pass from air, with an index of refraction of 1.00025, ^^^^ the cornea, with an index of refraction of 1.3365. In passing from the rarer into the denser medium they undergo refraction in accordance with the laws of optics and are rendered somewhat convergent. The extent of this first refraction and convergence is sufficiently great to bring parallel rays, if con- tinued, to a focus about 10 mm. behind the retina. This would be the condition in aphakia whether the lens is congenitally absent or has been removed by surgical procedures. Perfect vision, however, requires that the convergence of the light must be great enough to bring the focal point, the image, on the retina. This is accomplished by the introduction of an additional refracting body, the lens. On entering the lens the rays are for the same reason — i. e., the passage from a rarer into a denser medium — again refracted and converged, and if continued would come to a focus about 6.5 mm. behind the retina. On passing from the lens into the vitreous — i. e., from a denser into a rarer medium — the rays are once more converged and to an extent sufficient to focahze them Fig. 283.— Refraction of Homocenteic Rays on the retina (Fig. 283). AND THE Formation of an Image. While it is thus possible to geometricly follow the rays through these media by means of the above-mentioned factors, the procedure is attended with many difficulties. Moreover, as the relations all change when rays enter the eye from objects situated progressively nearer the eye, a separate calculation is necessitated for each distance for the determination of the size of the image. A method by which these difficulties are much reduced was sug- gested by Gauss and developed by Listing. It was demonstrated by Gauss that in every complicated system of refracting media separated by centered spheric surfaces there may be assumed certain ideal or cardinal points, to which the system may be reduced, and which, if their relative position and properties be known, permit of the de- * Strictly speaking, the posterior surface of the cornea is not parallel to the anterior surface, and the index of refraction of the cornea is a triiie greater than that of the aqueous humor, viz., 1.377. But as the increase in the corneal refraction due to a higher index is almost exactly counteracted by a decrease in refraction, due to the higher curvature of the posterior corneal surface, the usual assumptions furnish quite accurate results. THE SENSE OF SIGHT. 625 termination, either by calculation or geometric construction, of the path of the refracted ray, and the position and size of the image in the last medium, of the object in the first. Every dioptric system can be replaced, as Gauss showed, by a single system composed of six cardinal points and six planes per- pendicular to the common axis — e. g., two focal points, two principal points, two nodal points, two focal planes, two principal planes, and two nodal planes. Properties of the Cardinal Points. — The first focal point, F^,in Fig. 284, has the property that every ray wdiich before refraction passes through it, after refraction is parallel to the axis. The second focal point, F^, has the property that every ray which before refraction is parallel to the axis, passes after refraction through it. The second principal point, H^, is the image of the first, H^ ; that is, rays in the first medium which go through the first principal point pass after the last refraction through the second. Planes at right yl )r M, ff,A U ^ ~ ^ Fig. 284. — Diagram showing the Position and Relation of the Cardinal Points. angles to the axis at these points are principal planes. The second principal plane is the image of the first. Every point in the first principal plane has its image after refraction at a corresponding point in the second principal plane at the same distance from the axis and on the same side. The second nodal point, iV,, is the image of the first, N^: a ray which in the first medium is directed to the first nodal point passes after refraction through the second nodal point, and the directions of the rays before and after refraction are parallel to each other. In Fig. 284 let A B represent the axis. The distance of the first focal point, F^, from the first principal plane, H^, is the anterior focal distance. The distance of the posterior focal point, F^, from the second principal plane, H^, is the posterior focal distance. The dis- tance of the first nodal point, N^, from the first focal point is equal to the second focal distance. The distance of the second nodal point, N^, from the posterior focal point is equal to the anterior focal distance. It is evident, therefore, that the distance of the correspond- ing principal and nodal points from each other is equal to the differ- 40 626 TEXT-BOOK OF PHYSIOLOGY. ences between the two focal distances. Also the distance of the two principal points from each other is equal to the distance of the two nodal points from each other. Finally, the focal distances are pro- portional to the refractive indices of the first and last media. Planes passing through the focal points vertically to the axis are known as focal planes. Fig. 285. — Diagram to Find the Image in Last Medium of a Luminous Point IN THE First. From these properties of the cardinal points the position of an image in the last medium of a luminous point in the first may be determined, and the course of a refracted ray in the last medium be constructed if its direction in the first be given according to the fol- lowing rules : I . To find the image in the last medium of a luminous point in the first: Let A (Fig. 285) be this given point. Draw A B parallel to the axis until it meets the second principal plane in B; then B F.^ will be this ray after refraction. Draw a second ray from A to //, //, Fig. 286. — Diagram to Find the Refracted Ray in the Last Medium of a Given Ray in the First Medium. the first nodal point; then draw another ray, D E, from the second nodal point parallel to A C. This will be the refracted ray in the last medium. Where the two refracted rays, BF^ and D E, intersect, the image of A will be ^j.* 2. To find the refracted ray in the last medium of a given ray in the first medium : Let A B (Fig. 286) be the given ray. Continue this * If the point A is infinitely far from the eye, all the rays striking the eye will be parallel to each other. The nodal ray must therefore be drawn, and the point where this nodal ray meets the second focal plane will be the image of ^ = A^, where all rays parallel to the nodal ray will meet. THE SENSE OF SIGHT. 627 ray until it meets the first principal plane in C. Draw C D parallel to the axis. Now assume any point, such as E, in the given ray, and find its image E^ by the Rule i. Then D E^ becomes the course of the refracted ray. The Schematic Eye. — x\ccepting the system of cardinal points. Listing, Bonders, and v. Helmholtz have constructed "schematic" eyes to be substituted for the refracting system of the natural eye. For this purpose it is necessary to make use of the various esti- mates of thp indices of refraction of the different media, of the radii of curvatures of the different refracting surfaces, and of the distances Fig. 287. — Diagram showing the Position of the Cardinal Points in the "Schematic Eye." The continuous lines in the upper half of the figure show their position in the passive emmetropic eye. The dotted lines indicate the change in their position in an eye accommodated for the object A at the distance a from the cornea, or 152 mm. The lower half of the figure shows the formation of a distinct image on the retina of an eye accommodated for the object A at the distance a from the cornea. separating them, to deduce an average eye as a basis for calculation. The most widely accepted attempt is that of v. Helmholtz. The data he assumed are as follows : The refractive index of air = i ; of the cornea and aqueous humor, 1.3365; of the lens, 1.4371; of the vitreous humor, 1.3365; the radius of curvature of the cornea, 7.829 mm.; of the anterior surface of the lens, 10 mm.; of the posterior surface, 6 mm. ; the distance from the apex of the cornea to the ante- rior surface of the lens, 3.6 mm.; thickness of lens, 3.6 mm. From the above-mentioned data v. Helmholtz calculated the position of the cardinal points for the eye as follows (see Fig. 287): The first 628 TEXT-BOOK OF PHYSIOLOGY. focal point is situated 13.745 mm. before the anterior surface of the cornea; the posterior focal point is situated 15.619 mm. behind the posterior surface of the lens; the first principal point, 1.753 mm. behind the cornea; the second principal point, 2.106 mm. behind the cornea; the first and second nodal points, 6.968 and 7.321 mm. behind the apex of the cornea, respectively. The anterior focal distance of this schematic eye, the distance between F^ and H ^, therefore amounts to 15.498 mm., and the posterior focal distance, H^ to F^, to 20.713 mm. When the eye, however, is accommodated for near vision, the relations of the cardinal points are changed and will be as follows, if the point accommodated for, lies 152 mm. from the cornea: Anterior focal distance, 13.990 mm.; posterior focal distance, 18.689 mm. ; distance from cornea of the first and second principal points, 1.858 and 2.257 mm. respectively; distance of the posterior focus, 20.955 mm. from cornea. Given this schematic eye in the accom- modated state, the course of the rays and the determination of the position of an image in the last medium of a luminous point in the first can easily be determined by the rules already given. The Reduced Eye.— As suggested by Listing, this schematic eye may be yet further simplified or reduced to a single Fig. 288.— The Reduced Eye. refracting surface bounded anteriorly by air and posteriorly only by aqueous or vitreous humor. Without introducing any noticeable error in the determination of the size of the retinal image, the anterior principal and the anterior nodal points may be disregarded, owing to the minute- ness of the distances (0.39 mm.) separating the two systems of points. There is thus obtained one principal point and one nodal point, which latter becomes the center of curvature of the single refracting surface. The dimensions of this "reduced" eye are as follows (see Fig. 288). From the anterior surface of the cornea, corresponding to the principal plane H , to the nodal point N, 5.215 mm., from the anterior focal point F^, to the principal plane H, i. e., the anterior focal distance /,' 15.498 mm; from the principal plane H to the posterior focal point Fy, i. g., the posterior focal distance /," 20.713 mm; the index of refraction is 1.3365. There is thus substituted for the natural eye a single refracting surface with a radius of curva- ture, r, of 5.215 mm. In such an eye luminous rays emanating from the anterior focal point are parallel to the axis after refraction in the interior of the eye. Also rays parallel to the axis before refraction unite at the posterior focal point. By means of this reduced eye the construction of the refracted ray, THE SENSE OF SIGHT. 629 the various calculations as to the size of the image, the size of diffusion circles, etc., are greatly facihtated: e. g., In Fig. 289 let A B represent an object. From A homocentric rays fall on the single refracting surface. One of the rays, the nodal ray, falling on the surface perpendicularly, passes unrefracted through the single nodal point, N, to the posterior focal plane. The remain- ing rays, partially represented in the figure, falling on this surface under varying degrees of incidence, undergo corresponding degrees of refraction, by which they form a converging cone of rays which unite at a point situated on the nodal ray. These two - points, A, a, are known as conjugate foci. The same holds true for ho- " ^**«=*»*^ mocentnc rays emanat- Fig. 289. — The Formation of an Image in the ing from B or any other Reduced Eye. point of the object. The Size of the Retinal Image. — The size of the retinal image, /, (in Fig. 289 ab) may now be easily calculated, when the size of the object, O, (in fig. 289 A B) and its distance, D, from the refracting surface with radius of curvature, r, are known, by the following formula : O : I = D -^ r : f" — r. For, as the triangles A N B and a N b are similar, we have A B :ab =fN : N g, or ab ^ — ^^T^"^. Independent of the foregoing method, the size of the retinal image may be calculated if it is remembered that the eye, like any optic system, has a point of such a quality that a ray of light which before entering the eye was directed toward it, after refraction con- tinues as if it came from this point. In other words, there is in the eye a point which allows a ray of light to pass unrefracted. This point, termed the nodal point of the eye, determines the size of the image ; for if a line be drawn from both the upper and lower ends of an object through this nodal point, it is clear that the images of the respective points must lie on these two rays where they intersect the retina. The distance of this nodal point from the retina is 15.498 mm. It is clear, therefore, that the size of the object is to the size of the image, as the distance of the object from the nodal point is to the distance of the nodal point from the retina ; or, in other words, to find the size of the retinal image: multiply the size of the object by 15.5 mm. and divide by the distance of the object from the eye. The Visual Angle. — The angle included between the lines coming from the opposite extremities of an object and crossing at the 630 TEXT-BOOK OF PHYSIOLOGY. nodal point is termed the visual angle. The size of this angle in- creases with the nearness and decreases with the remoteness of an object. The retinal image correspondingly increases or decreases in size. The acuteness of vision depends on the power of the emme- tropic eye to distinguish the smallest retinal image or the smallest distance between two points on the retina. It has been experiment- ally determined that the retina can not distinguish two points unless their images are separated by a distance of 0.004 mm. corresponding to a visual angle of 60 seconds. If the distance is less than this the two sensations fuse into one. The reason assigned for this is, that the distance between the centers of two adjoining cones in the macula is 0.004 rnni- With a visual angle of 60 seconds the two foci fall on separate cones; with a smaller visual angle the two foci fall on and excite but a single cone, and hence there arises the sensation of but a single point. In ophthalmic practice it is customary in testing the acuteness of vision to employ test type of a certain size for specified distances. %:^=^ D=6 D=1S D-60 Fig. 290. — Visual Angle of 5 Minutes. — {After Hansell and Sweet.) Though the entire letter is embraced in an angle of 5 minutes, the strokes are included within an angle of 60 seconds or one minute (Fig. 290). Accommodation. — In a normal or emmetropic eye, homocentric parallel rays of hght (Fig. 291, a, h) after passing through the optic media are converged and brought to a focus on the retina, /. Rays, however, which come from a luminous point situated near the eye, P, and are therefore divergent, passing through the optic media at the same time, are intercepted by the retina before they are focused, and give rise to the formation of diffusion-circles and indistinctness of vision. The reverse is also true. When the eye is adjusted for the refraction and focusing of divergent rays (Fig. 291, P) parallel rays will be brought to a focus before reaching the retina, and, again diverging, will form diffusion-circles. It is evident, there- fore, that it is impossible to simultaneously focus both parallel and divergent rays, and to see distinctly at the same time, two objects which are situated at different distances. The eye must be alternately adjusted first to one object and then to another. The capabihty which the eye possesses of adjusting itself to vision at different distances is termed accommodation. THE SENSE OF SIGHT. t>3i The following table of Listing shows the size of the diffusion- circles formed of objects situated at different distances when the accommodative power is suspended in an emmetropic eye : Distance of Luminous Point. 00 65 m. 25 12 " 6 3 1.500 " 0.750 " 0-375 " 0.188 " 0.094 " 0.088 " Distance of the Focal Point behind the Posterior Surface of the Retina. Diameter of the Diffusion-circle. 0.0 mm. 0.0 mm. 0.005 " O.OOII " 0.012 " 0.0027 " 0.025 " 0.0056 " 0.050 " 0.0112 " O.IOO " 0.0222 " 0.20 " 0.0443 " 0.40 " 0.0825 " 0.80 o.i5i6 " 1.60 " 0.3122 " 3.20 0.5768 " 3-42 " 0.6484 " The normal eye when adjusted for distant vision is in a passive condition, and hence vision of distant objects is unattended with Fig. 291. — The Refraction of Parallel and Divergent Rays in the Emme- tropic Eye in the Passive and in the Active or Accommodated Condition, fatigue. In the act of adjustment, however, for near vision the eye passes into an active state, the result of a muscle effort, the energy of which is proportional to the nearness of the object toward which the eye is directed. From the foregoing table it is evident that between infinity and 65 meters, the diffusion-circles are so sHght that no perceptible accommodative effort is required to ehminate them. From 65 meters to 6 meters the diffusion-circles gradually become larger, though they are yet so faint as to require for their correction an accommodative effort which is scarcely measurable. From 6 meters up to 6 centi- meters, however, a progressive increase in accommodative power is demanded for distinct vision. 632 TEXT-BOOK OF PHYSIOLOGY. Mechanism of Accommodation. — Inasmuch as neither the corneal curvature nor the shape of the eyeball undergoes any change during accommodation, the necessary change, whatever it may be, is to be sought for in the lens. As to the character of the changes in this body, two views are held, based largely on the fact and its interpretation, that images of a luminous point reflected from the anterior surface of the cornea, the anterior and posterior surfaces of the lens, change their relative positions during accommodation. Thus, if in a darkened room a lighted candle be placed in front of and to the side of an individual whose eye is directed to a distant object, an observer placed in the same relative position as the candle will observe three images in the eye, one at the surface of the cornea, two at the pupillary margin (Fig. 292). Of the two latter, one is quite large and situated apparently in front of the third, which is faint, small, and inverted. The middle image Ois reflected from the convex surface of the lens, the last from the concave surface. These images of reflection are known as catoptric images. If now the individual be directed to fix the gaze on a near object, the second image changes its position, , ! advances toward the corneal image and at the a b c same time becomes smaller, a change which, in Fig. 292.— Catop- accordance with the laws of optics, could only be TRIG Images in ^^g ^q ^^^ increase in the convexity of the anterior Upright image surface of the lens. A slight displacement of the of reflection, third image sometimes observed indicates a pos- frotn the cornea. ^{\^\q increase in the convexity of the posterior o. Upright image J tr from the ante- SUrfacC lens. rior surface of According to Helmholtz, during accommoda- verteT^ image' ^^^^ ^^^ entire anterior surface of the lens becomes from the poste- more convex, while at the same time it slightly nor surface of advances, possibly as much as 0.4 mm. in extreme (Helmholtz.') efforts. This change is represented in Fig. 293. According to Tscherning, the increase in convexity of the anterior surface is confined to the central portion, the re- mainder of the surface becoming somewhat flattened. There is, moreover, no evidence that there is any advance of the surface or any increase in the thickness of the lens. A series of new and ingenious experiments lend support to Tscherning's view. The radius of curvature in either case approximates 6 mm. in extreme efforts of accommodation. The increase in convexity naturally in- creases the refracting power. Whichever view is accepted, the nearer the object, — that is, the greater the degree of divergence of the light rays, — the more pro- nounced must be the increase in convexity in order that they may be sufficiently converged and focalized on the retinal surface. Changes in THE SENSE OF SIGHT. 633 the convexity of the lens, either of increase or decrease, are attended by changes in the distinctness of images. Coincident with the lens change, the pupillary margin advances and the pupil itself becomes smaller. By this means an indistinctness of the image is prevented by cutting off the rays which would give rise, owing to the angle at which they fall on the surface, to dift'usion circles, from spheric aberration. The Function of the Ciliary Muscle. — Though it is generally admitted that the increase in the convexity of the lens is caused by the contraction of the ciliary muscle, the exact manner in which this is accomplished is not clearly understood. According to Helmholtz, when the eye is in repose and directed to a distant object the lens is somewhat flattened from a traction exerted by the suspensory liga- ment. When the eye is directed to a near object, the ciliary muscle contracts, thereby relaxing the ligament, as a result of which the lens, by virtue of an inherent elasticity, bulges forward and becomes more convex. In consequence of this latter fact the refracting power is Cornell propei" \Sescemef Jfemir^^jte r— ^>_ --. SpCncterJridu CAssuj (Xiutria Fig. 293. — The Left Half Represents the Eye in a State of Rest. Right Half in State of Accommodation. The proportionally increased. In extreme efforts of accommodation it is believed by some observers that the circularly arranged fibers, the so-called annular muscle, contract and exert a pressure on the periph- ery of the lens and thus aid other mechanisms in relaxing the ligament and in increasing the convexity. This view appears to be supported by the fact that in hypermetropia, where a constant effort is re- quired to obtain a distinct image of even distant objects, the annular muscle becomes very much hypertrophied, thus reinforcing the meridional fibers. In myopia, on the contrary, where the accommo- dative effort is at a minimum, the entire muscle possesses less than its average size and development. According to Tscherning, a different explanation of the action of the cihary muscle must be given. Thus, when it contracts, the antero- internal angle, that portion in close relation with the suspensory ligament, recedes and exerts on the ligament a pressure which in turn exerts a traction on the peripheral portions of the anterior surface of the lens, which produces the deformation observed. At 634 TEXT-BOOK OF PHYSIOLOGY. the same time the postero-external portion of the muscle exerts traction on the chorioid, thus sustaining the vitreous and indirectly the lens. The reason for the flattening of the periphery of the lens from zonular compression and the sharpening of the central convexity is to be found in the fact that the convexity of the more solid central portion, the nucleus, is greater than that of the lens itself. Hence it is easily understood why a zonular traction vv^ould give rise to periph- eral flattening. There is, however, one point which seems difficult to harmonize with Tscherning's view; that is, the fact that during accommodation the lens appears to be sHghtly tremulous, thus showing relaxation, and not increased tension, of the suspensory ligament. Range of Accommodation. — It has been stated that rays of light coming from a luminous point situated at any distance beyond 65 meters are so nearly parallel that no accommodative effort is re- quired for their focalization. So long as the luminous point remains between infinity and 65 meters, the eye, directed toward it, remains completely relaxed. The point at which the object can be distinctly seen without accommodation is termed the far point or the punctum remotum. This for the normal eye is at a distance of 65 meters or beyond.* If the luminous point gradually approaches the eye from a point 65 meters distant, the accommodative power comes into play and gradually increases until it attains its maximum. The nearest point up to which the eye is able to form distinct images of objects is called its near point or punctum proximum. This near point in a healthy boy of twelve years will lie at 2§ inches from the eye, while the same point lies only at 8 inches or 20 cm. in a man of forty years. Of objects which lie nearer than the punctum proximum the eye cannot form distinct images. The distance between the punctum remo- tum and the punctum proximum is termed the range of accommodation. Force of Accommodation. — The increase in curvature of the lens necessary to focalize rays when the eye is directed from the far to the near point necessitates the expenditure of energy on the part of the ciliary muscle. The energy expended in the act of accommo- dation may be measured by a lens, the refracting power of which is such as to enable it to produce the same result — that is, to give the diverging rays coming from the near point, e. g., 20 cm., a parallel direction. A lens, therefore, which has for a near point a focal dis- tance of 20 cm. would be a measure of the force expended, for such a lens placed in front of the crystalline lens, when in a state of repose, would, with the assistance of the latter, bring diverging rays coming * In practical ophthalmic work a point six meters distant is taken as the far point for the reason that the rays at this distance are practically parallel. THE SENSE OF SIGHT. 635 from the near point to a focus on the retina. A lens of this character is said to have a refracting power of 5 dioptrics. Since lenses of the same curvature made from different materials have different refracting powers, it becomes necessary to have, for purposes of comparison, some unit of measurement. The unit now accepted is the refracting power of a glass lens which is sufficient to focalize parallel rays at a distance of 100 cm. or i meter. This amount of refracting power is termed a dioptry. Lenses which would focalize parallel rays at a distance of 50, 20, or 10 cm. are said to have a refractive power of 2, 5, or 10 dioptrics, respectively, obtained by dividing into 100 cm. the focal distance. The refracting power of a biconcave lens is determined by prolonging backward in the direction the parallel rays have come, the rays which have been rendered divergent by the lens. The refracting media of the human eye in repose have collectively a refracting power of about 64 dioptrics, the reciprocal of its focal length. The refracting power of the corneal surface alone is equiva- lent to 42 dioptrics. The crystalline lens could in the schematic eye be replaced by a lens of about 13 dioptrics in front of the eye, as is done after the extraction of a cataract. But owing to its position in a medium denser than air, it has been calculated that its refracting power is about 20 dioptries. The capabiUty of the lens to increase its refraction during accom- modative efforts beyond the 20 dioptries varies considerably at different periods of hfe. At ten years the increase is 14 dioptries, as the near point is 7 cm. ; at thirty years the increase is but 7 diop- tries, as the near point is 14 cm. ; at sixty the increase is but i dioptry, and the near point 100 cm.; at seventy it is zero. From youth to old age, the elasticity of the lens steadily dechnes, and the range of accom- modation diminishes from the recession of the near point. Convergence of the Eyes during Accommodation.— In binocu lar vision of near objects the eyes are turned inward and the optic axis of each — a line passing through the center of the cornea and the center of the eye — turned toward the median line during accom- modation. So long as the eyes are directed toward the far point, 65 meters or beyond, the optic axes are parallel. When the eyes are directed to any point within 65 meters the optic axes are converged, the convergence increasing steadily as the near point is approached. In this way the fovea of each eye is directed to the same point and single vision made possible. Were this not the case, double vision would result. Functions of the Iris. — For purposes of distinct vision it is essen- tail that the quantity of light entering the interior of the eye shall be so adjusted that the formation and subsequent perception of the image shall be sharp and distinct. This is accomplished by the iris, 636 TEXT-BOOK OF PHYSIOLOGY. the circular fibers of which alternately contract and relax with in- creasing and decreasing intensities of the light. The size of the pupil, therefore, through which the light passes, will vary from moment to moment and in accordance with variation in the light intensity. The quantity of light necessary to distinct vision is thus regulated. In the total absence of light the sphincter pupillse muscle is relaxed and the pupil widely dilated. With the appearance of light and an increase in its intensity the muscle again contracts and the pupil progressively narrows. With a given intensity in the light, the sphincter contraction is greater when the hght falls directly into the fovea. Contraction of this muscle also occurs as an associated move- ment in the convergence of the eyes during accommodation and in consensus with the other eye. In addition to this function of the iris, it constitutes, by virtue of the sphincter muscle contraction, an important corrective apparatus. Being non-transparent, it serves as a diaphragm intercepting those rays which would otherwise pass through the peripheral portions of the lens and by spheric aberration give rise to indistinctness of the image. The movements of the iris by which the size of the pupil is determined are caused by the contractions and relaxations of the sphincter piipillcB and dilatator pupiUce muscles. The contraction of the sphincter is entirely reflex and involves those structures necessary to the performance of any reflex act, viz.: a sentient surface, the retina; an afferent nerve, the optic; a central emissive center situated in the gray matter beneath the aqueduct of Sylvius; and an efferent nerve, the motor oculi. The stimulus requisite to the excitation of this mechanism is the impact of light waves or ether vibrations on the rods and cones. According to the intensity of these vibrations will be the resulting contraction of the muscle. The contraction of the dilatator pupillae muscle is determined by the activity of a con- tinuously active nerve-center in the medulla oblongata which trans- mits its nerve impulses through the spinal cord, along the first and second, dorsal nerves to the superior cervical ganglion, and thence to the iris by way of the fifth nerve. (See Fig. 245, page 534.) These two muscles appear to bear an antagonistic relation to each other, for section of the motor oculi is followed by relaxation of the sphincter muscle and dilatation of the pupil. Stimulation of the sympathetic is followed by a more pronounced dilatation. The size of the pupil is the resultant of a balancing of these two forces. OPTIC DEFECTS. Presbyopia. — This is a condition of the eye characterized by a defective or diminished accommodative power. As age advances the lens loses its elasticity and the power to increase its refraction, and vision at the normal reading distance becomes impossible. The near THE SENSE OF SIGHT. 637 point therefore, advances toward the far point, or recedes from the indi- vidual. The range of accommodation is also diminished. At forty years the near point is about 22 cm.; at forty-five years it has receded to 28 cm. This would indicate that the lens in these five years has lost I dioptry of refracting power; at fifty years the near point recedes to 43 cm., and at sixty to 200 cm., indicating a loss in refract- ing power on the part of the lens of 2 and 4 dioptrics respectively. Convex lenses placed before the eyes having a refracting power of 1,2, and 4 dioptrics would in the three instances return the near point to its normal position. At the age of seventy the lens is incapable of any increase during an accommodative eftort. A lens of 4 diop- trics would therefore be required by such a man, for near vision at 10 inches. Myopia. — This is a condition of the eye characterized by an increase in the antero-posterior diameter or a hypernormal refracting power of the lens. The former is the usual condition. Parallel rays of light brought to a focus in front of the retina again diverge, giving Fig. 294. — Myopia. Parallel rays focus at F, cross and form diffu- sion-circles; divergent rays from A focus on the retina. — {Hansell and Sweet.) Fig. 295. — Correction of Myopia BY A Concave Lens.— (iJZ^awse// and Sweet.) rise to diffusion-circles and indistinctness of the image. Divergent rays alone are capable of being focahzed on the retina in its new position. The punctum remotum is always at a definite distance, but approaches the eye as the myopia increases. The near point is usually much nearer the eye than 20 cm. For this reason the condition is termed near sight. The increase in the length of the antero-posterior diameter may range from a fraction of a millimeter up to 10 mm. With an increase of 0.16 mm. the far point is but 200 cm. distant; and with an increase of 3.2 mm. it is but 10 cm. distant. Inasmuch as only divergent rays can be focahzed by the myopic eye normal vision can be restored by the use of a biconcave lens with a diverging power in the first instance of 0.5 dioptry and the second of 10 dioptrics. Hypermetropia. — This is a condition of the eye characterized by decrease of the normal antero-posterior diameter or by a subnormal refracting power of the lens. The former is the usual condition. Parallel rays of light do not, therefore, come to a focus when the 638 TEXT-BOOK OF PHYSIOLOGY. accommodation is suspended. Falling on the retina previous to focalization, they give rise to diffusion-circles and indistinctness of the image. As no object can be seen distinctly no matter how remote, there is no positive far point. The near point is abnormally distant — sometimes as far as 200 cm. For this reason the condition is termed jar sight. A hypermetropic eye w^ithout accommodative effort can focahze only converging rays on the retina. If rays of light vv^ere to come from the retina of such an eye, they would, on emerging, take Tig. 296. — The Hypermetropic Eye. Parallel rays (.4, B) can be focused only at a point behind the eye, as at /; rays of light coming from the retina take, on emerging from the eye, a divergent direction, C, D. K. The negative punctum remotum. a divergent direction, as shown in Fig. 206, dotted line C and D. If these same rays were to be prolonged backward, they would meet at the point K, which is the punctum remotum; and as it is behind the eye, it is termed negative. Since rays coming from the retina take a divergent direction on emerging from the eye, it is evident that only converging rays can be focahzed by a passive hyperme- FiG. 297. — Hypermetropia. Par- allel Rays Focused behind THE Retina. — (Hansell and Sweet.) Fig. 298. — Correction of Hyper- metropia BY A Convex Lens. {Hansell and Sweet.) tropic eye. As there are no convergent rays in nature, it is necessary for distinct vision that all rays, parallel and divergent, shall be given a convergent direction before entering the eye. This is done by placing before the eye convex lenses the converging power of which is proportional to the degree of hypermetropia (Figs. 297, 298). Astigmatism. — This is a condition of the eye characterized by an inequality of curvature of its refracting surfaces in consequence of which not all of a homocentric bundle of rays are brought to the THE SENSE OF SIGHT. 639 same focus. The inequality may be either in the cornea or lens, or both, though usually in the cornea. In the normal cornea the radius of curvature in the vertical meridian is a trifle shorter, 7.6 mm., than that of the horizontal, 7.8 mm., and hence its focal distance is shghtly shorter. The difference, however, in the focal distances is so shght that the error in the forma- tion of the image is scarcely noticeable. A transection of a cone of light coming from the cornea is practically a circle. If, however, the vertical curvature exceeds the normal to any marked extent, the rays passing through this meridian will be more sharply refracted and brought to a focus much sooner than the rays passing through the horizontal meridian. The result will be that the cone of light will be no longer circular, but more or less elliptic. The variations of the shape of this cone are shown in Fig. 299, which represents the appearances presented on cross-section both before and after focaliza- tion of each set of rays. Though the vertical meridian has usually Fig. 299. — Refraction by an Astigmatic Surface. — {Hansell and Sweet.) the sharper curvature, it not infrequently happens that the reverse is true. For the reason that the rays from one point do not all come to the same focus or point, the condition is termed astigmatism. Spheric Aberration. — When the ra}'s of hght which emanate from a point fall upon a spheric lens, they do not after passing through it reunite at one point because of the fact that the more peripheral rays have a shorter focus than the central rays. To this condition the term spheric aberration is given. Spheric aberration can be dem- onstrated in the human eye. That this condition is present to but a slight extent in the nomial eye is due to the presence of the iris, which intercepts those rays which would otherwise pass through the marginal portions of the refracting media. In widely dilated eyes the spheric aberration of the peripheral parts may amount to as much as 4.5 dioptries. . Chromatic Aberration. — When a beam of white light is made to pass through a prism, it is decomposed into the primary colors owing to a difference in the refrangibility of the rays. In passing through the refracting media of the eye the different rays composing 640 TEXT-BOOK OF PHYSIOLOGY. white light also undergo unequal refraction and those rays which give rise to one color are brought to a focus at a point somewhat different from those which give rise to other colors. If the eye is accommodated for one set of rays, it is not for another, and the result is a fringe of colors around the image. This defect in the normal eye is so slight that the mind fails to take cognizance of it. That the eye is incapable of simultaneously focalizing rays of widely different refrangibility, as those which give rise to the blue and red colors, is shown by the following experiment: The eye being directed to a luminous point, a plate of cobalt-glass is placed between the light and the observer close to the eye. This substance has the property of intercepting all rays but the red and the blue and hence these alone will be seen. The center of the image produced will be red and clearly defined, the periphery blue and ill defined. The reason for this is clear. The eye more readily accommodates itself for the red rays, and hence their focal point is distinct. The blue rays, having a higher degree of refrangibility, come to a focus, cross and diverge, and give rise to diffusion-circles. If a biconcave glass be placed before the cobalt, the blue rays can be focahzed on the retina, while the red will fall on the retina without focalization. The image will now be blue and distinct in the center, the periphery red and ill defined. With the removal of the minus glass the reverse condition again obtains. Imperfect Centering. — From a purely physical point of view, the eye is not a perfect optic instrument. In addition to the defects noticed in the foregoing paragraphs, there is yet another, viz.: an imperfect centering of the refracting surfaces. In first-class optic instruments the lenses are centered — that is, their exact centers are situated on the same axis. In viewing an object through such a system the visual line corresponds with the axis of the lens system. This is not the case with the refracting system of the eye. A line passing through the center of the cornea and the center of the eye, the optic axis (O A in Fig. 300), does not pass exactly through the center of the lens and does not fall into the point for most distinct vision, the fovea. This has led to the recognition of other lines the relations of which must be kept in mind in all optic discussions, viz. : 1. The visual axis or visual line {V L), the line connecting the point viewed, the nodal point and the fovea centralis. 2. The line of fixation or line of regard {V C), the line connecting the point viewed with the center of rotation, the latter being situated 6 mm. behind the nodal point of the eye and 9 mm. before the retina. The relations of these lines and certain angles connected with them are shown in Fig. 300. The angle included between the line D D (the major axis of the corneal elhpse) and the visual line is the angle alpha, amounting on the average to 5°. The THE SENSE OF SIGHT. 641 angle included between the optic axis and the line of fixation or regard is the angle gamma, while the angle between the optic axis and the line of vision is the angle beta. In emmetropia the angle alpha is about 5°. In hypermetropia it is greater, amount- ing to 7° or 8°, giving to the eye an appearance of divergence. In myopia it is much smaller — 2° — or in extreme cases may be abolished, the line of vision corresponding with the optic axis or even passing beyond it. The angle gamma is of value in de- termining the actual deviation of the eye in squint. Functions of the Retina. — Of all the layers of the retina, the rods and cones appear to be the most essential to vision. It is only this layer that is capable of receiving the light stimulus and of trans- forming it into some specific form of energy, which in turn arouses Jem^or-aZ S u^ JVhsaZ SuZe. Fig. 300. — Diagram showing the Corneal Axis D D, the Optic Axis O A, the Visual Axis V L, and the Line of Fixation V C; also the Three Angles, in the fibers of the optic nerve the characteristic nerve impulses. A ray of light entering the eye passes entirely through the various layers of the retina, and is arrested only upon reaching the pigmentary epithehum in which the rods and cones are embedded. As to the manner in which the objective stimuli — light and color, so called — are transformed into nerve impulses, but little is known. It is prob- able that the ether vibrations are transformed into heat, which excites the rods and cones. These, acting as highly specialized end organs of the optic nerve, start the impulses on their way to the brain, where the seeing process takes place. As to the relative function of the rods and cones, it has been suggested, from the study of the facts of comparative anatomy, that the rods are impressed only by differ- ences in the intensity of light, while the cones, in addition, are im- pressed by qualitative differences in color. The nerve-fibers them- 41 642 TEXT-BOOK OF PHYSIOLOGY. selves are insensible to the impact of the ether vibrations, and require for their excitation some intermediate form of energy. That this is the case was shown by Bonders, who reflected a beam of Hght on the optic nerve at its entrance without the individual experiencing any sensation of light. This region, occupied only by the optic-nerve fibers and devoid of any special retinal elements, is therefore an insensitive or blind spot. The diameter of this spot is about 1.5 mm., and occupies in the field of vision a space of about 6°. It is situated about 3.5 mm. to the nasal side of the visual axis. Its existence can be demonstrated by the famihar experiment of Mariotte, which con- sists in placing before the eye two objects having the relation to each other as in Fig. 301. With the left eye closed and the right eye directed to the cross, both objects may be visible. But by moving the figure away from or toward the eye, there will be found a distance, about 30 cm., when the circle will be invisible. This occurs when the image falls on the optic nerve at its entrance. The experiment of Purkinje as described in the following paragraph demonstrates also Fig. 301. — Diagram for Observing the Situation of the Blind Spot. — {Helmhollz.) the fact that the sensitive portion of the retina is to be found only in the layer of rods and cones. It is well known that the blood-vessels of the retina are situated in its innermost layers a short distance behind the optic-nerve fibers. Owing to this anatomic arrangement, a portion of the hght coming through the pupil will be intercepted by the vessels and a shadow projected on the layer of rods and cones. Ordinarily, these shadows are not perceived, for the reason that the shaded parts are more sensitive, so that the small amount of hght passing through the vessels produces as strong an impression on this part as does the full amount of hght on the unshaded parts of the retina, and perhaps because the mind has learned to disregard them. But if hght be made to enter the eye obliquely, the position of the shadows will be changed, when at once they become apparent. This can be shown in the following way : If in a darkened room a lighted candle be held several inches to the side and to the front of the eye, and then moved up and down, there will be perceived, apparently in the field of vision, an arbores- cent figure corresponding to the retinal blood-vessels. This is due THE SENSE OF SIGHT. 643 to the falling of the shadows on unusual portions of the layer of rods and cones. Excitability 0} the Retina. — The retina is not equally excitable in all parts of its extent. The maximum degree of sensibility is found in the macula lutea, and especially in its central portion, the fovea. In this region the layers of the retina almost entirely disappear, the layer of rods and cones alone remaining, and in the fovea only the latter are present. That this area is the point 0} most distinct vision is shown by the observation that when the eye is directed to any given point of light, its image always falls in the fovea. Any pathologic change in the fovea is attended by marked indistinctness of vision. The sensibihty of the retina gradually but irregularly diminishes from the macula toward the periphery. This diminution in sensibihty holds true for monochromatic as well as white light. As stated above, the nature of the molecular processes which take place in the retinal tissue, caused on one hand by the light vibrations, and on the other hand developing nerve impulses, is entirely un- known. The discovery of the visual purple in the outer segment of the rods gave promise of some explanation of the process, especially when it was shown to undergo changes when exposed to the action of light. But as the pigment is wanting in the cones, and especially in the fovea, it cannot be considered essential to distinct vision, although that it plays some important role in the visual process is highly probable. It was observed by Van Genderen Stort, that when an animal is kept in darkness some time before death, the cones are long and filiform; but if the animal has been exposed to light, they are short and swollen. It was discovered by Boll that if an animal is kept in darkness an hour or two before death the pigment is massed at the ends of the rods and cones, but after ex- posure to Hght it becomes displaced and extends over and between the rods almost to the external hmiting membrane. These condi- tions are represented in Fig. 302. The Eye a Living Camera. — In its construction, in the arrange- ment of its various parts, and in their mode of action the eye may be compared to a camera ohscura. Though the comparison may not be absolutely exact, yet in a general way it is true that there are many striking points of similarity between them ; e. g., the sclera and chorioid may be compared to the walls of the camera ; the combined refracting media to the single lens, the action of which results in the focusing of the light rays; the retina to the sensitive plate receiving the image formed at the focal point ; the iris to the diaphragm for the regulation of the amount of light to be admitted, and for the partial exclusion of those marginal rays which give rise to spheric aberration; the ciliary muscle to the adjusting screw, by means of which the image is brought to a focus on the sensitive plate, notwithstanding the var}dng distances 644 TEXT-BOOK OF PHYSIOLOGY. of the object from the lens. The presence of the visual purple in the rods of the retina capable of being altered by light makes the com- parison still more striking. Kiihne even succeeded in obtaining a fixed image or an optogram of an external object in a manner similar to that by which an image is fixed on the sensitive plate of a camera. An animal is kept in the dark for about ten minutes in order to permit the retinal pigment to be completely regenerated. The animal, with the eyes covered, is then brought into a room with a single window. While the head is steadily directed to the window, the eye is exposed for several minutes. The eyes are again covered, the animal killed, and the eyes removed by the light of a sodium flame. The retina is then W&^WJ^, ilililtii Fig. 302. — Section of the Retina of a Frog. A. In darkness. B. In light. — {After Van Genderen Start, from Tscherning's "Physiologic Optics.") placed in a 4 per cent, solution of alum. In a short time the image of the window, the optogram, will be fixed (Fig. 303). That portion of the retina corresponding to the image is quite bleached in appear- ance from the action of the light on the pigment. During life the regeneration of the visual purple must take place with extreme rapidity. It is believed to be derived from a pigment secreted by the layer of pigment cells. Binocular Vision. — Though two images are formed, one on each retina, when the eyes are directed to a given object, there results but one sensation. If the direction of either visual axis be changed by pressure on the eyeball, there arise two sensations, and the object appears to be doubled. The reason assigned for this, in the first THE SENSE OF SIGHT. 645 Fig. 303. — Retina of A Rabbit. Opto- gram OF A Win- dow Four Meters Distant, a. Yellow spot, b, b. White streak of nerve- fibers. — (Kuhne.) instance, is that the two images fall into the foveae, two corresponding points; while in the second instance they fall on non-corresponding points. It would appear, therefore, that for the purpose of seeing an object singly when the eyes are directed toward it, the rays eman- ating from it must fall on corresponding parts of the retina. As all portions of the retina are sensitive to light, though in varying degrees, it is not essential that the images always fall in the foveae. The parts of the retinae which correspond physiologicly are shown in Fig. 304. In this figure the retinal area is divided into quadrants by vertical and horizontal lines of separation, as they are termed. If one retina is placed in front of or over the other, it will be found that the quadrants bearing similar letters cover each other. So long as the rays of light, entering the eye, fall on corresponding areas the sensation of but one object arises. If, however, they fall on non- corresponding areas, two sensations arise. Normal binoc- ular vision enlarges very considerably the area of the visual field, permits of a better estimation of the size and distance of objects, enables the mind to form more readily a perception of depth, increases the intensity of sensations and makes sensation more uniform by off- setting retinal rivalry. The Horopter. — When the eyes are in the so-called secondary position, — that is, in a position in which the visual axes are con- verged and directed to a point in front of and in the middle plane of the body, — it will be found on examination that rays of light from a number of other objects enter the eye, pass through the nodal point, and fall on corresponding parts of the two retinae and give rise to but single images. All such points lie, for the hori- zontal line of separation, on a line termed the horopter. The form of this line is that of a circle which passes through the fixation point and the two nodal points. Any object on the horopter will give rise to but a single image. This is shown in Fig. 305, in which the objects I, II, III project their rays into both eyes which fall on corresponding areas. In addition to the horopter for the horizontal line of separation, there is also an horopter for the vertical line of separation. At a Fig. 304. -Corresponding Areas of the Retina. 646 TEXT-BOOK OF PHYSIOLOGY. distance of two meters the vertical horopter is a plane. Within this distance it is concave to the face; beyond this distance it is convex. An object which lies either in front of or behind the fixation point will project its rays on parts of the retinae which do not correspond, and hence give rise to double images. This is evident from examina- tion of Fig. 306. While the eyes are directed to figure 2, of which there is but a single image, the objects B and A give rise to double images, for reasons already given. If the eyes are now directed to B, double images will be formed of 2 and A. At all times, therefore, double images are formed on the retinae the existence of which is scarcely noticed unless the attention is B Fig. 305. — Horopter for the Secondary Position, with Convergence of the Vis- ual Axes. — {Landois.) Fig. 306. — Scheme of Identical and Non- identical Points of the Retina. — (Landois.) directed to them. This is due to the fact that many of the images fall on the peripheral, less sensitive parts of the retinae. At the same time, from a want of accommodation and the formation of diffusion- circles, they are indistinct. For these reasons they are readily neglected. In the primary position of the eyes — that is, a position in which the visual axes are parallel — the horopter is a plane in infinity. In the tertiary position the horopter is a curve of complex form. Movements of the Eyeball. — The almost spheric eyeball lies in the correspondingly shaped cavity of the orbit, like a ball placed in a socket, and is capable of being moved to a considerable extent THE SENSE OF SIGHT. 647 by the six muscles which are attached to it. These muscles are the superior and inferior recti, the external and internal recti, and the superior and inferior obliqui (Fig. 307). The four recti muscles arise from the apex of the orbit cavity, from which point they pass forward to be inserted into the sclera about 7 to 8 mm. from the corneal border. The superior oblique muscle having a similar origin passes forward to the upper and inner angle of the orbit cavity, at which point its tendon passes through a cartilaginous pulley, after which it is reflected backward to be inserted into the superior sur- face of the sclera about 16 mm. behind the corneal border. The inferior oblique muscle arises from the inner and inferior angle of the orbit cavity. It then passes outward, upward, and backward, to be inserted into the upper, posterior ; ' 10 and temporal portion of the sclera about 4 or 5 mm. from the optic nerve entrance. The movements of each eye are referred to three fixed lines or axes, which have their origin at the point of rota- tion of the eyeball, this point lying about 1.7 mm. behind the center of the globe. If the eye looks straight forward in the horizontal plane (the head being erect), the line joining the center of rotation with the object looked at is the line of fixation or line of regard. Around this antero-posterior axis the eye may be regarded as performing its circular rotation or torsion. At right angles to this line, and joining the center of rotation of both eyes, is the horizontal or transverse axis, around which the movements of elevation (up to 34 degrees) and depression (down to 57 degrees) take place. At right angles to both of these lines there is the vertical axis, around which the movements of adduction (toward the nose up to 45 degrees) and abduction (toward the temple up to 42 degrees) occur. The six muscles may be divided into three pairs, each of which has a common axis around which it tends to move the eyeball. But only the common axis of the internal and external recti coincides with one of three axes Fig. 307. — Muscles of the Eye. Tendon or Ligament of Zinn. i. Tendon of Zinn. 2. Ex- ternal rectus divdded. 3. Internal rectus. 4. Inferior rectus. 5. Superior rectus. 6. Superior oblique. 7. Pulley for superior oblique. 8. Inferior oblique, g. Levator palpebrse superioris. 10,10. Its anterior expansion. 11. Optic nerve. — {Sappey.) 648 TEXT-BOOK OF PHYSIOLOGY. before mentioned — namely, with the vertical axis — thus moving the ball only inwardly or outwardly — respectively. The other two pairs, however, have their own axes of action, and their movements of the ball must be therefore analyzed with regard to all the three axes, each of these four muscles producing rotation, elevation, and depres- sion, and abduction or adduction. The superior and inferior recti muscles, forming one pair, move the eye around a horizontal axis which intersects the median plane of the body in front of the eyes at an angle of 63 degrees, and the superior and inferior oblique muscles forming the third pair rotate the globe around a horizontal axis which cuts the median plane of the body behind the eyes at an angle of 39 degrees. Thus it is that each muscle moves the eye as follows, the movement for practical purposes being referred to the cornea: The rectus externus draws the cornea simply to the temporal side, the rectus internus simply to the nose; the superior rectus displaces the cornea upward, sHghtly inward, and turns the upper part toward the nose (medial torsion) ; the inferior rectus moves the cornea downward, shghtly inward, and twists the upper part away from the nose (lateral torsion) ; the superior obhque displaces the cornea downward, slightly outward, and produces medial torsion; while the inferior oblique moves the cornea upward, shghtly outward, and produces lateral tor- sion. These facts show that for certain movements of the eye at least three muscles are necessary (see following table) : Inward and ( Rectus internus. downward, -! Rectus inferior. (. Obliquus superior. Outward and ( Rectus externus. Inward, Rectus internus. Outward, Rectus externus. Upward . ^ I^ectus superior. '^ ' ' ' \ Obliquus inferior. Downward _ / Rectus inferior. , upward, j Rectus superior. '" ' \ Obliquus superior. ' ( Obliquus inferior. Inward attd ( Rectus internus. | Outward and I Rectus externus. upward, -j Rectus superior. ' downward, < Rectus inferior. [ Obliquus inferior. I Obliquus superior. If both eyes have their line of vision in the horizontal plane parallel with each other and with the median plane of the body, they are said to be in the primary position. All other positions are called secondary. Both eyes always move simultaneously, which is called the associated movement of the eyes. There are three forms of asso- ciated movements: (i) movement of both eyes in the same direction; (2) movements of convergence by which the visual lines are con- verged on a point in the middle line of the body; (3) movements of divergence, by which the eyes are brought back from convergence to parallelism, or even to divergence, as in certain stereoscopic exercises. A combination of (i) and (2) or of (i) and (3) takes place for certain positions of the object looked at. Color-perception. — A beam of sunlight passed through a glass prism is decomposed into a series of colors — red, orange, yellow, THE SENSE OF SIGHT. 649 green, blue, and violet — the so-called spectral colors, so well exem- plified in the rainbow. The spectral colors are termed simple colors, because they can not be any further decomposed by a prism. Objectively, the spectral colors consist of very rapid transverse vibra- tions of the ether, from about 400 millions of millions per second for red to about 760 millions of milHons for violet, but subjectively they are sensations caused by the impact of the ether-waves on the per- cipient layer of the retina. It is possible to mix or blend these spectral color-sensations in the eye by stimulating the same area of the retina by different spectral colors, either at the same time or in rapid succession. The following table shows the results of such experiments as performed by v. Helm- holtz (Dk. = dark; Wh. = whitish): Violet. Indigo. Cyan-blue J Bluish- green. Green. Greenish YELLOW. Yellow. Red. Orange. YeUow. Gr.-yellow. Green. Bluish-green. Cyan-blue. Purple. i Dk.-rose. Wh.-rose. Dk.-rose. Wh.-rose. White. Wh.-rose. White. Wh.-green. White. Wh.-green. Wh.-green. White-blue. Water-blue. Bl.-green. Water-blue. Water-blue. Indigo. . . ' White. Wh.-yellow. Wh. -yellow. Green. WTi.-yellow. Gold-yellow Orange. Yellow. Yellow. Gr.-yellow. These are the mixed colors. But it is to be observed that only two new color-sensations can be produced, white and purple, the remain- ing mixed colors already finding their equivalent in the spectrum. White and purple, therefore, are color-sensations which have no objective equivalent in a simple number of ether-vibrations hke the spectral colors. Two spectral colors which by their mixture produce the sensation of white are called complementary colors. Such are red and green- blue, golden yellow and blue, green and violet. The mixture of all the spectral colors produces white again. This is the result of adding two or more color-sensations. Different results are obtained, however, by adding color pigments. Yellow and blue, for example, produce in the eye white, but on the painter's palette green. The colors of nature are usually mixtures of simple colors, as can be shown by spectroscopic analysis or by a synthesis of spectral colors. In all color-sensations we must distinguish three primary qualities : (i) hue; (2) purity or tint; (3) brightness or luminosity. The first quality gives the main name to the color — e. g., red or blue — this de- pending on the spectral color or the mixture of two spectral colors with which it can be matched. The second quality, the tint, depends on the admixture of white with the ground color; and the third quality, brightness, depends on the objective intensity of the light and the subjective sensitiveness of the retina. Color-perception thus far refers 650 TEXT-BOOK OF PHYSIOLOGY. only to the most sensitive part of the retina. At the more peripheral parts of the retina the colors are seen somewhat differently, as is shown by the following table giving the limits up to which the colors are recognized : White. Blue. Red. Green. Externally qo° 80° 65° 50° Internally 60° 55° 50° 40° Superiorly 45° 40° 35° 30° Inferiorly 70° 60° 45° 35° Theories of Color-perception. — The theory of v. Helmholtz, originated by Thomas Young (1807), assumes in its latest form the existence in the human retina of three different kinds of end-organs, each of which is loaded with its own photo-chemical substance capable of being decomposed by a certain color, and thus exciting the fiber of the optic nerve. In the first group these end-organs are loaded \\\\h a red-sensitive substance, which is affected mainly by the red part of the spectrum; the second group has its end-organs provided with a green-sensitive substance, which is mainly excited by the green color ; while the third group is provided with a blue-sensitive substance, this latter being mainly affected and decomposed by the blue-violet portion of the spectrum. All these three different end-organs are present in every part of the most sensitive area of the retina, and are connected by separate nerve-fibers with special parts of the brain, in the cells of which each calls up its separate sensation of red or green or blue. Out of these three primary color-sensations all other color-sensa- tions arise. If a light mainly excites the red- or green- or blue-sensi- tive substance of a retinal area, we term it red, green, or blue, re- spectively. But if two of these photo-chemical substances are stimu- lated simultaneously, quite different sensations arise. Thus simul- taneous stimulation of the red and green substances gives rise to the sensation of yellow, that of red and blue to the sensation of purple, and that of blue and green to the sensation of blue-green. Simul- taneous stimulation of all three substances of a certain area produces the sensation of white. According to this theory, complementary colors are all those which together excite all the three substances. Color-blindness is explained by this theory, on the assumption that two of the photo-chemical substances have become similar or equal in composition to each other. The theory of Hering, brought forward in 1874, has the under- lying assumption that the process of restitution in a nerve-element is capable of exciting a sensation. This theory asserts that there are three visual substances in the retina — a white-black, a red-green, and a yellow-blue visual substance. A destructive process in the white- black substance, such as is induced not only by white light, but also THE SENSE OF SIGHT. 6;i by any other simple or mixed color, produces the sensation of white, while the process of restitution or assimilation in this substance pro- duces the sensation of black. Similarly, red Hght produces dis- assimilation or decomposition in the red-green substance, and this, again, the sensation of red. Green light, however, favors the process of restitution or assimilation in the red-green substances, and thus gives rise to the sensation of green. In the same way the sensation of yellow has its cause in the decomposition of yellow-blue substance induced by yellow light, while the sensation of blue is produced by an assimilative process in the same substance. Simultaneous processes of disassimilation and assimilation in the same visual sub- stance antagonize each other, and consequently produce no color-sen- FiG. 308. — The Lacrimal and Meibomian Glands, and Adjacent Organs of THE Eye. I, I. Inner wall of orbit. 2, 2. Inner portion of orbicularis palpe- brarum. 3, 3. Attachment to circumference of base of orbit. 4. Orifice for transmission of nasal arterj'. 5. Muscle of Horner (tensor tarsi). 6, 6. Mei- bomian glands. 7, 7. Orbital portion of lacrimal gland. 8, 9, 10. Palpebral portion. 11, 11. Mouths of excretory ducts. 12, 13. Lacrimal puncta. — (Sappey.) sation by means of this substance, but only the sensation of white, by reason of decomposition, by both colors, in the white-black substance. Thus, yellow and blue, impinging on the same retinal area, have no effect on the yellow-blue substance, because they are antagonistic in their action on this substance, but only produce the sensation of white, as both yellow and blue decompose the white-black material. Color- blindness is explained by the assumption of the absence of either the red-green or the yellow-blue visual substance in the retina. Accessory Structures. — The eyeball is protected anteriorly by the eyelids and their associated structures, the Meibomian glands, the lacrimal glands, and tears. 652 TEXT-BOOK OF PHYSIOLOGY. The eyelids consist of a central framework of connective tissue supporting muscle tissue (the orbicularis palpebrarum muscle) and glands, and covered externally by skin and internally by a modified skin, the conjunctiva. The free border of each Hd is strengthened by a semilunar plate of dense fibrous tissue, the tarsus. The cuta- neous edge of the lid is bordered vv^ith short stiff hairs. At the inner extremity each eyelid presents a small opening, the punctum lacri- male, the beginning of the lacrimal duct. The two ducts after uniting open into the nasal duct. The Meibomian glands are modified sebaceous glands imbedded in the posterior portion of the lids (Fig. 308). Their ducts open on the free border of the lid. These glands secrete an oleaginous ma- terial resembling sebaceous matter which accumulates along the margin of the lid and prevents the tears from flowing down the cheek. The lacrimal gland is situated at the upper and outer part of the orbit cavity. It consists of a series of compound tubules lined by epithelium. The secretion (the tears) is conducted from the gland to the outer part of the conjunctiva by seven or eight ducts. The lacrimal secretion consists of water and inorganic salts. It is dis- tributed over the corneal surface during the act of winking, thus keeping it moist and free from foreign particles. It eventually passes into the lacrimal ducts and then into the nose. The lacrimal glands receive secretory fibers by way of the fifth nerve and the cervical sympathetic. The secretion can be excited reflexly from stimulation of sensor nerves as well as by emotional states. CHAPTER XXVI. THE SENSE OF HEARING. The physiologic mechanism involved in the sense of hearing in- cludes the ear, the auditory nerve, its cortical connections, and nerve- cells in the cortex of the temporal lobe. Peripheral excitation of this mechanism develops nerve impulses which, transmitted to the cortex, evoke the sensation of sound and its varying qualities — intensity, pitch, and timbre. The specific physiologic stimulus to the terminal organ, the organ of Corti, is the impact of atmospheric undulations of varying energy and rapidity. THE PHYSIOLOGIC ANATOMY OF THE EAR. The ear, the organ of hearing, is lodged vi^ithin the petrous portion of the temporal bone. It may, for convenience of description, be divided into three portions: viz., the external, the middle, and the internal portions (Fig. 309). The external ear consists of the pinna or auricle and the external auditory canal. The pinna is composed of a thin layer of cartilage which presents a series of elevations and depressions. It is attached by fibrous tissue to the outer edge of the auditory canal and covered by a layer of skin continuous with that covering adjacent structures. The general shape of the pinna is concave. Its anterior surface pre- sents, a httle below the center, a deep depression — the concha. The external auditory canal extends from the concha inward for a distance of from 25 to 30 mm. It is directed at first upward, for- ward, inward, and then downward to its termination. It is composed partly of bone and partly of cartilage and lined by a reflection of the skin covering the pinna. At the external portion of the canal the skin contains a number of tubular glands, the ceruminous glands, which resemble in their conformation the perspiratory glands. They secrete cerumen or ear-wax. The middle ear, or tympanum, is an irregularly shaped cavity hollowed out of the temporal bone and situated between the external auditory canal and the internal ear. It is narrow from side to side, though wider above than below. It is relatively long in its antero- posterior and vertical diameters. The upper portion is known as the attic. The middle ear is in communication posteriorly with the 653 654 TEXT-BOOK OF PHYSIOLOGY. mastoid cells, anteriorly with the pharynx through the Eustachian tube. The Eustachian Tube. — The passageway between the tympanic cavity and the naso-pharynx is known from its discoverer as the Eustachian tube. It is composed internally of bone, externally of cartilage, and is lined by mucous membrane covered with ciliated epithelium. Near the middle of its course the tube is contracted, though expanded at either extremity (Fig. 312). It measures about 40 mm. in length. Its general direction from the pharyngeal orifice is outward, backward, and upward at an angle of about 45 degrees. Fig. 309. — The Ear. — i. Pinna, or auricle. 2. Concha. 3. External auditory canal 4. Membrana tympani. 5. Incus. 6. Malleus. 7. Manubrium mallei. 8. Tensor tympani. 9. Tympanic cavity. 10. Eustachian tube. 11. Superior semicircular canal. 12. Posterior semicircular canal. 13. External semicircular canal. 14. Cochlea. 15. Internal auditory canal. 16. Facial nerve. 17. Large petrosal nerve. 18. Vestibular branch of auditory nerve. 19. Cochlear branch. — (Sappey.) The middle ear cavity is separated from the external ear by a membrane — the membrana tympani— and from the internal ear by an osseo-membranous partition which forms a common wall for both cavities. The interior of the cavity is crossed from side to side by a chain of bones and lined by a mucous membrane continuous with that lining the pharynx. The membrana tympani is a thin, translucent, nearly circular membrane, measuring about 10 mm. in diameter, placed at the inner termination of the external auditory canal. It is inclosed in a ring of bone which in the fetal condition can be easily removed, but in THE SENSE OF HEARING. 555 the adult condition can not be removed, owing to its consolidation with the surrounding bone. This membrane consists primarily of a layer of fibrous tissue which is covered externally by a thin layer of skin continuous with that lining the auditory canal, and internally by a thin mucous membrane. The tympanic membrane is placed obliquely at the bottom of the auditory canal, inchning from above and behind downward and forward at an angle of about forty-five degrees. The external surface of this membrane presents a funnel- shaped depression, the sides of which are slightly convex. The Ear-hones. — Running across the tympanic cavity and form- ing an irregular line of joined levers is a chain of bones, which articu- late one with another at their extremities. These bones are known as the malleus, incus, and stapes. The form and arrangement of these bones are shown in Figs. 310, 311. The malleus, or ham- mer bone, consists of a head, neck, and handle, of which the latter is attached to the inner surface of the membrana tympani. The incus or anvil bone presents a concave articular sur- face which receives the head of the malleus. The stapes, or stirrup- bone, articulates exter- FiG. 310. — Tympanic Membrane and the Audi- tory Ossicles (Left) seen from within, i. e., FROM THE Tympanic Cavity'. M. Manu- brium or handle of the malleus. T. Inser- tion of the tensor tympani. h. Head. IF. Long process of the malleus, a. Incus, with the short {K) and the long (/) process. 5. Plate of the stapes. Ax, Ax, is the common axis of rotation of the auditory ossicles. 5'. The pinion-wheel arrangement between the malleus and incus. — (Laudois.) nally with the long pro- cess of the incus, and internally, by its oval base, with the edges of an oval opening, the foramen ovale. The entire chain is partially supported by a ligament attached to the short process of the incus and to the walls of the tympanic cavity. The Tensor Tympani Muscle. — This is a delicate muscle, about 15 mm. in length, situated in a narrow groove just above the Eustachian tube (Fig. 312). It arises from the cartilaginous portion of the Eustachian tube and the adjacent portion of the sphenoid bone. From this origin it passes nearly horizontally backward to the tym- panic cavity; just opposite to the foramen ovale, its tendon bends at 656 TEXT-BOOK OF PHYSIOLOGY. Fig. 311. — Audi- tory Ossicles. — I. Head of malleus. 2. Pro- cessus brevis. 3. Processus graci- lis. 4. Manubri- um. 5. Long pro- cess of incus. 6. Articulation be- tween incus and stapes. 7. Stapes. • — (Sappey.) a right angle over the processus cochleariformis and then passes outward across the tympanic cavity to be inserted into the handle of the malleus near the neck. The stapedius muscle emerges from the cavity of a pyramid of bone v^hich projects from the posterior wall of the tympanum. Its tendon passes forward to be inserted into the neck of the stapes bone near its point of articulation with the incus. The internal ear, or labyrinth, is located within the petrous portion of the temporal bone. It consists of an osseous and a membranous por- tion, the latter contained within the former. The osseous labyrinth is subdivided into vestibule, semicircular canals, and cochlea. The vestibule is a small, triangular-shaped cavity between the semicircular canals and the cochlea. It is separated from the cavity of the middle ear by an osseous partition which pre- sents near its center an oval opening, the foramen ovale. In the living condition this opening is closed by the base of the stapes bone, which is held in position by an annular ligament. The inner wall presents a number of openings for the passage of nerve-fibers (Fig. 313). The semicircular canals are three in number, a superior vertical, an inferior vertical, and a horizontal, each of which opens by two orifices into the cavity of the vestibule, with the ex- ception of the two vertical, which unite at one extremity and then open by a single orifice. Each canal near its vesti- bular orifice is enlarged to almost twice the size of the rest of the canal, forming what is known as the ampulla. The cochlea, the anterior portion of the labyrinth, is a gradually tapering canal, about 35 mm. in length, wound spirally two and a half times around a central bony axis, the modiolus. The cavity of the cochlea is partially subdi- vided into two cavities by a thin spiral plate of bone which projects from the inner wall lamina osseous spiralis. In the natural condition this partition is completed by a connective-tissue membrane, so that the two passages are completely separated from each other. The upper passage or Fig. 312. — M, The Tensor Tympani Muscle — the Eustachian Tube (Left). — {Landois .) known as the THE SENSE OF HEARING. 657 Fig. 313. — Bony Cochlea, i. Ampulla of superior semi- circular canal. 2. Horizontal canal. 3. Junction of supe- rior and posterior semicircu- lar canals. 4. The posterior semicircular canal. 5. Fora- men rotundum. 6. Foramen ovale. 7. Cochlea. scala is in free communication with the vestibule, and is known as the scala vestihuli; the lower passage or scala in the dead condition communicates with the tympanum by means of a round opening, the foramen rotundum, and is therefore known as the scala tympani. In the living condition this opening is completely closed by a mem- brane, a second membrana tympani. Both the scalae vestibuli and tympani communicate at the apex of the cochlea by a small opening, the heli- cotrema. The modiolus, the central bony axis, is perforated from base to apex by a canal for the passage of the auditory nerve-fibers; lateral canals, diverging from the central canal, pass through the osseous lamina spiralis and transmit fibers of the auditory nerve. The interior of the bony laby- rinth is lined by periosteum covered by epithelium and in communication with lymph-spaces at the base of the skull by means of the aqueduct of the vestibule. The membranous labyrinth, lying within the osseous labyrinth, corresponds with it in form, though it is smaller in size. It may be subdivided into vestibule, semi- circular canals, and cochlea (Fig. 314). The vestibular portion consists of two small sacs, the utricle and the saccule, which communicate with each other by means of the two branches of a duct passing through the aqueduct of the vestibule — the ductus endolymphaticus. The semicircular canals communicate with the utricle in the same manner as the bony canals communicate with the vestibule. The saccule communicates with the membranous cochlea by a short canal, the canalis reuniens. The walls of the utricle, saccule, and semicircular canals are composed of connective tissue hned by epithehum. At the points of entrance of the auditory nerve, the maculcB acusticce, in all three structures, the epithehum undergoes a marked change in appearance and structure. It becomes columnar in shape and provided with stiff hair-like processes or threads, which project into the cavity. In the saccule and utricle the hair- like processes are covered by a layer of small crystals of calcium 42 Fig. .314. — I. Utricle. 2. Sac- cule. 3. Vestibular end of cochlea. 4. Canalis reuniens. 5. Membranous cochlea. 6. Membranous semicir- cular canal. — {Potter's "Anatomy.") 658 TEXT-BOOK OF PHYSIOLOGY. Fig carbonate held together by a gelatinous material. The crystals are known as otoliths. The libers of the vestibular nerve, arising from the cells of the ganglion of Scarpa in the internal auditory meatus, send their peri- pherally directed branches through the foramina in the inner wall of the vesti- bule, through the walls of the utricle and semicircular canals near the am- pulla. As the fibers approach the maculas acusticae they subdivide into delicate fibrillae, which ultimately become histologically and physiologi- cally related to the neuro-epithelium. From the relation of the nerve-fibers to the epithelium, the latter must be regarded as the highly specialized terminal organ of the vestibular portion of the auditory nerve. The cochlea is a closed mem- branous tube situated between the osseous lamina spiralis and the outer bony wall. A transection of the entire cochlea shows the relation of the os- seous and membranous portions (Fig. 316). The cochlear tube is triangular in shape. The base is attached to the bony wall, the apex to the edge of osseous lamina spirahs. One side of the tube forms in part the membrane of Reissner, the other side forms in part the basilar membrane. The sides of the cochlea to- ward the scala vestibuli and scala tympani are covered with epithelium. The tri- angular cavity of the cochlear tube is known as the scala media. The inner surface of the cochlear tube is lined by epithelium, which be- comes extraordinarily modi- fied and specialized along the surface of the basilar membrane, to constitute what is known as — The Organ of Corti. — In Fig. 316 this organ is represented as it appears on cross-section of the cochlea. It consists primarily of 315. — Section of Wall of Utricle of the Internal Ear, through macular region, from rabbit, showdng otoliths (o), embedded within granu- lar substance {g). h. Cili- ated cells with processes {p), extending between sustentacu- lar elements {s). m. Base- ment membrane, n. Nerve- fibers within fibrous tissue (/) passing toward hair-cells and becoming non-medullated at basement-membrane. — {After Pier sot.) Scala lympani Fig. Org.Corli mb.basilaris 316. — A Transverse Section of Turn of the Cochlea. THE SENSE OF HEARING. 659 an arch composed of two modified epithelial cells known as the rods or pillars of Corti, which rest below on the basilar membrane, but meet and interlock above ; it consists secondarily of a series of colum- nar epithelial cells provided with hair-like processes which rest upon and are supported by the rods both on the inner and outer aspects of the arch. The space beneath the arch is known as the tunnel. The inner hair cells are not nearly so numerous as the outer hair cells. The epithelial cells external to the outer and inner hair cells are supporting or sustentacular in character. The organ of Corti extends the entire length of the cochlea. The number of rods which, standing side by side, form the inner limb of the arch is estimated at 5600; the number which form the outer hmb is estimated at 3850. The outer, rods are broader than the inner and at some places articulate with two or three inner rods. The upper edges of the rods are flattened, elongated, and project outward, forming a reticulated membrane through the meshes of which the hair-like processes of the cells project. From the connective-tissue thickening on the upper surface of the osseous lamina spirahs there extends outward over the organ of Corti a thin membrane, the memhrana tectoria. The common cavity between the walls of the osseous and membranous labyrinth in the vestibule, the semicircular canals, in the scala vestibuli and scala tympani of the cochlea, is filled with a clear fluid — the perilymph; the common cavity within the walls of the entire membranous labyrinth is also filled with a similar fluid — the endolymph. The hair-like pro- cesses of the epithehal cells covering the maculae acusticae and the rods of Corti are consequently bathed by endolymph. Both fluids are in relation with the subarachnoid lymph-spaces at the base of the brain, the perilymph through the aqueduct of the vestibule, the endo- lymph through the endolymphatic duct. The fibers of the cochlear nerve, arising from the ganglion cells of the spiral gangHofi situated in the osseous lamina spiralis near the modiolus, send their peripheral branches to the saccule and to the organ of Corti. As they approach this structure they lose their medullary sheath and become naked axis-cylinders. The fibers then divide into two parts, of which one passes to the inner hair cells; the other passes between the inner rods and crosses the tunnel between the outer rods to the outer hair cells. The exact method of termina- tion of these fibers in the hair cells is unknown, but doubtless it is both histologic and physiologic. From the relation of the nerve-fibers to the organ of Corti the latter must be regarded as the highly specialized terminal organ of the cochlear division of the auditorv nerve. 66o TEXT-BOOK OF PHYSIOLOGY. THE PHYSIOLOGY OF AUDITION. The general function of the ear is the reception and transmission of atmospheric vibrations from the concha to the percipient elements — the hair cells — of the organ of Corti. The vibratory excitation of these end-organs thus caused, is the basis of auditory perceptions. The atmospheric vibrations are collected by the pinna and concha, conveyed by the auditory canal to the tympanic membrane, trans- mitted by the chain of bones to the labyrinth to pass successively through the perilymph, the membranous walls, the endolymph, to the hair cells. The nerve impulses generated by these vibrations are then transmitted by the cochlear nerve to the auditory centers of the cerebrum, where the sensations of sound are evoked. In order to appreciate the function of the individual structures concerned in this general function there must be kept in mind a few of the character- istics of atmospheric vibrations. Atmospheric Vibrations. — The vibrations of the atmosphere which are the objective causes of the sensations of sound are com- municated to it by the vibrations of elastic bodies such as tuning- forks, rods, strings, membranes, etc. These produce in the air a to-and-fro movement of its particles, resulting in a succession of alternate condensations and rarefactions which are propagated in all directions. The impact of a rhythmic succession of such con- densations on the ear gives rise to musical sounds; the impact of an arrhythmic or irregular succession gives rise to noises. If a writing point attached to a tuning-fork in vibration be placed in contact with a travehng recording surface, each vibration will be recorded in the form of a wave. For this reason atmospheric vibra- tions are generally spoken of as sound-waves. A line drawn hori- zontally through such a curve indicates the position of rest of the fork; the extent of the curve on each side of this line indicates the excursion of the fork or the amplitude of its movement. The sounds which physiologically result from the impact and transmission of the effects of sound-waves, possess intensity, pitch, and quality or tone. The intensity or loudness of a sound depends on the amplitude of the vibration which causes it. The greater the amplitude or swing of the vibrating body, the greater is the energy with which it strikes the ear. The pitch of a sound depends on the number of vibrations which strike the ear in a unit of time — a second. The greater the number, the higher the pitch. Thus while the pitch of the sound caused by the note C, on the first leger line below, of the music scale, corre- sponds to 256 vibrations, the pitch of the sound caused by the note C an octave above, corresponds to 512 vibrations. The lowest rate of THE SENSE OF HEARING. 66i vibration which can produce a distinct sound varies in different individuals from 14 to 18; the liighest rate varies from 35,000 to 40,000 per second. Between these two extremes lies the range of audibihty, which embraces about 11 octaves. Vibrations less than 14 per second can not be perceived as a continuous sound; vibrations beyond 40,000 also fail to be so perceived. In the ascent of the music scale from the lowest to the highest regions there is a gradual increase in the vibration frequency. The quality of a sound depends on the jorm of the vibration. It is this feature which gives rise to those differences in sensations which permit one to distinguish one instrument from another when both are emitting the same note. The form of the sound-wave in any given instance is the resultant of a combination of a fundamental vibration and certain secondary vibrations of subdivisions of the vibrating body. These secondary vibrations give rise to what is known as overtones. By their union with and modification of the fundamental vibration there is produced a special form of vibration which gives rise not to a simple but a composite sensation. It is for this reason that the same note of the piano, the violin, and the human voice varies in quality. The Function of the Pinna and External Auditory Canal. — In those animals possessing movable ears the pinna plays an im- portant part in the collection of sound-waves. In man it is doubtful if it plays a part at all necessar}^ for hearing. Nevertheless an indi- vidual with defective hearing may have the perception of sound increased by placing the pinna at an angle of 90 degrees to the side of the head or by placing the hand behind it. The external auditory canal transmits the sonorous vibrations to the tympanic membrane. From the obliquity of this canal it has been supposed that the vibra- tions, after passing the concha, undergo a series of reflections on their way to the tympanic membrane, which, owing to its inclination, would be struck by them in a much more effective manner. The Function of the Tympanic Membrane. — The function of the tympanic membrane is the reception of the atmospheric vibrations which are transmitted to it. This it does by vibrating in unison with them. The vibrations which the membrane exhibits correspond in amphtude, in frequency, and in form to those of the atmosphere. That this membrane actually reproduces all vibrations within the range of audibility has been experimentally demonstrated. The membrane not being fixed, as far as its tension is concerned, does not possess a fixed fundamental note, like a stationary fixed mem- brane, and is therefore just as well adapted for the reception of one set of vibrations as another. This is made possible by variations in its tension in accordance with the pitch or frequency of the atmos- pheric vibrations. In the absence of vibration the membrane is in 662 TEXT-BOOK OF PHYSIOLOGY. a condition of relaxation; with tlic advent of sound-waves possessing a gradual increase of pitch, as in the ascent of the music scale, the tension of the membrane increases until its maximum is reached at the upper limit of the range of audibility. By this change in tension certain tones become perceptible and distinct, while others become imperceptible and indistinct. The Function of the Tensor Tympani Muscle. — The function of this muscle is, as its name indicates, to change and to fix the tension of the tympanic membrane, so that it can most readily vibrate in unison with vibrations of varying degrees of rapidity. The tendon of this muscle playing around the processus cochleariformis is attached almost at a right angle to the handle of the malleus. Hence as the muscle contracts it exerts its traction from the process and draws the handle of the malleus inward, thus increasing the convexity of the tympanic membrane and at the same time its tension. With the relaxation of the muscle the handle of the malleus passes outward, and the convexity and tension diminish. In the ascent of the music scale, each note corresponding to an increase in vibration frequency, requires for its perception an increase in tension and an increase in the force of the contraction of the tensor muscle. In the descent of the music scale the reverse conditions obtain. The contraction of the muscle is of the nature of a single twitch, and of just sufhcient force and duration to tense the membrane for a given rate of vibration. The contraction of the muscle is excited reflexly. The afferent path is through fibers of the trigeminal nerve distributed to the tym- panic membrane ; the efferent path is through fibers in the small root of the trigeminal. The stimulus is sudden pressure on the tympanic membrane. The more frequently and forcibly the stimulus is applied, the greater is the muscle response. The tensor tympani muscle may therefore be regarded as an accommodative apparatus by which the tympanic membrane is adjusted for the reception of vibrations of varying degrees of frequency. The Function of the Chain of Bones. — The function of the chain of bones is to transmit the effects of the atmospheric vibrations to the fluid of the labyrinth. The manner in which this is accom- plished becomes evident from the relation which the bones of this chain bear to one another and to the tympanic membrane on the one hand and to the fluid of the labyrinth on the other. When pressure is made on the outer surface of the tympanic mem- brane it is at once pushed inward, carrying with it the handle of the malleus, the head at the same time rotating outward around an axis corresponding to its ligamentous attachments. As the handle moves inward a small ledge of bone just below the malleo-incudal joint locks with, and hence pushes inward, the long process of the THE SENSE OF HEARING. 663 incus. Since this process is united at almost a right angle to the stapes bone, the latter is forced toward and into the foramen ovale, thus producing a pressure on the perilymph. With the cessation of the pressure the elastic forces of the membrane and of the hgaments return the handle of the malleus to its former position; by the un- locking of the malleo-incudal joint the entire chain also returns to its former position without exerting undue traction on the basal attachment of the stapes. As the long process of the incus is shorter than the handle of the malleus, and as the movement between them takes place around an axis from before backward, it follows that the excursion of the incus and stapes will be less than that of the malleus, while the force will be greater. Hence as the vibrations are transferred from the tym- panic membrane of large area to the base of the stapes of small area (20 to 1.5), they lose in amphtude but increase in force. Their pres- sure on the perilymph is therefore thirty times greater than on the membrana tympani. In addition to its function as a transmitter of vibrations, the chain of bones serves as a point of attachment for muscles which regulate the tension of the tympanic membrane and the pressure on the labyrinth. The Function of the Stapedius Muscle. — The function of the stapedius muscle is a subject of much discussion. According to Henle, its function is to so adjust the stapes bone that it will be prevented from exerting an undue pressure on the perilymph during the inward excursions of the incus process. According to Toynbee, its function is to press the posterior part of the stapes inward, make it a fixed point, and place the anterior part in such a position that it will vibrate freely and accurately. The Function of the Eustachian Tube.^ — In order that the tym- panic membrane may vibrate freely it is essential that the air pressure on both sides shall be equal at all times. This is made possible by the Eustachian tube. Were it not for this passageway, with each inward swing of the membrane the air in the tympanic cavity would be condensed and its pressure raised, in consequence of which the movement of the membrane would be retarded; with each outw^ard swing, the air would be rarified and its pressure lowered below that of the atmosphere, and in consequence the movement outward would be retarded; the maximum response, therefore, of the membrane to a given vibration could not be attained and the resulting sound would be muffied and indistinct. But as with each vibration of the membrane the air can pass into and out of the tympanum through this tube, inequalities of pressure are prevented and a free vibration peiTuitted. The impairment in the acuteness of hearing which is caused by either a rise or fall of pressure in the middle ear can be shown — 664 TEXT-BOOK OF PHYSIOLOGY. 1. By closing the mouth and nose and then forcing air from the lungs through the Eustachian tube into the tympanum, thus in- creasing the pressure. 2. By closing the mouth and nose and then making an effort of deglutition. As this act is attended by an opening of the phar- yngeal end of the Eustachian tube, the air in the tympanum is partly withdrawn and the pressure lowered. In each instance hearing is impaired. After either experiment the normal con- dition is restored by swallowing with the nasal passages open. The Functions of the Internal Ear. — From the anatomic arrangement of the structures of the internal ear it is evident that if the vibrations of the stapes bone are to reach the peripheral organs — the hair cells — of both the vestibular and cochlear nerves, they must traverse successively the perilymph, the membranous walls, and the endolymph. As the perilymph is incompressible, the inward move- ment of the stapes would be prevented were it not for the elastic character of the membrane closing the foramen rotundum. The pressure wave occasioned by each inward movement of the stapes is transmitted through the scala vestibuli, the helicotrema, the scala tympani, to this membrane, which by virtue of its elasticity is pressed into the tympanic cavity. With the outward movement of the stapes, equilibrium is at once restored. The Functions of the Cochlea. — The cochlea is the portion of the internal ear which is concerned in the perception of tones. The arrangement of the histologic elements of the organ of Corti indicates that they in some way respond to the vibrations of varying frequency and form, and through the development of nerve im- pulses, evoke the sensations of pitch and quahty. The manner in which this is accomphshed is largely a matter of speculation. While many theories have been offered in explanation of the power to distinguish the pitch and the quahty or timbre of a tone, most physiol- ogists prefer that of Helmholtz, who regarded the transverse fibers of the basilar membrane as the elements immediately concerned, and compared them, both in their arrangement and power of sympa- thetic vibration, with the strings of a piano. He said: "If we could so connect every string of a piano with a nerve-fiber that the nerve- fiber would be excited as often as the string vibrated, then, as is actually the case in the ear, every musical note which affected the instrument would excite a series of sensations exactly corresponding to the pendulum-like vibrations into which the original movements of the air can be resolved; and thus the existence of each individual overtone would be exactly perceived, as is actually the case with the ear. The perception of tones of different pitch would, under these circumstances, depend upon different nerve-fibers, and hence would occur quite independently of each other. Microscopic in- THE SENSE OF HEARING. 665 vestigation shows that there are somewhat similar structures in the ear. The free ends of all the nerve-fibers are connected with small elastic particles which we must assume are set into sympathetic vibration by sound-waves." (Stirhng.) The mechanism might be regarded, therefore, somewhat as follows: The sound-waves received by the membrana tympani and transmitted by the chain of bones to the fenestra ovahs produce variable pressures in the fluids of the internal ear; these pressures vsiry in intensity, in number, and in quahty, and correspond with the intensity, pitch, and quahty of the tones. If, therefore, a com- pound wave of pressure be communicated by the base of the stapes, it will be resolved into its constituents by the different transverse fibers of the basilar membrane, each picking out its peculiar portion of the wave and thus stimulating corresponding nerve filaments. Thus different nerve impulses are transmitted to the brain, where they are fused in such a manner as to give rise to a sensation of a particular quahty, but still so imperfectly fused that each constituent, by a strong efi'ort of attention, may be still recognized. The transverse fibers of the basilar membrane vary in length from 0.04125 mm. at the base of the cochlea to 0.495 ^^- ^.t the apex, and, according to Retzius, are about 24,000 in number. As the human ear usually cannot distinguish more than 11,064 tones, it is evident that there is a sufiiicient anatomic basis for this theory. The functions of the semicircular canals have already been stated in connection with the chapter relating to the functions of the cerebellum. CHAPTER XXVII. REPRODUCTION. Reproduction is the process by which a new individual is initiated and developed and the species to which it belongs is preserved. Reproduction is the result of the union and subsequent development of germ- and sperm-cells. These cells are produced and their union accomplished by the cooperation of the reproductive organs charac- teristic of the two sexes. Embryology is a department of anatomic science which has for its object the investigation of the successive stages that the new being passes through during its gradual development prior to birth. THE REPRODUCTIVE ORGANS OF THE FEMALE. The reproductive organs of the female comprise the ovaries, Fallopian tubes, uterus, and vagina (Fig. 317). The Ovaries. — The ovaries are two small, flattened bodies, measuring about 40 mm. in length and 20 in breadth. They are situated in the cavity of the pelvis, one on either side, and embedded in a fold of the peritoneum, known as the broad ligament. A section of the ovary shows that it consists externally of a thin, firm, connective- tissue membrane and internally of a fine connective-tissue stroma, supporting blood-vessels, non-striated muscle-fibers and nerves, and containing in its meshes a very large number of spheric sacs named after their discoverer, de Graaf, the Graafian sacs or follicles. These follicles are very numerous and are present in all portions of the ovary, though they are most abundant toward its peripheral portions. It is estimated that the human ovary contains from 20,000 to 40,000 follicles. The follicles vary considerably in size ; while many are visible to the unaided eye, others require for their detection high powers of the microscope. Although the folHcles are present in the ovary at the time of birth, it is not until the period of puberty that they assume functional activity. From this time on to the catamenial period there is a constant growth and development of these follicles. Each follicle consists of an external investment of fibrous tissue and blood-vessels, and an internal investment of cells, the memhrana granulosa. At the lower portion of this membrane there is an accumulation of cells, the pro- 666 REPRODUCTION. 66: ligerous disc (Fig. 318). The cavity of the foUicle contains a shghtly yellowish, alkaline, albuminous fluid, a transudate in all probability from the blood-vessels. The Graafian follicle is of especial interest, for it is in this structure, and more especially in the proligerous disc, that the true germ- cell or ovum is developed. The ovum is a spheric body measuring about 0.3 mm. in diameter. It consists of a mass of living, protoplasmic material, cytoplasm, a nucleus or germinal vesicle, and a nucleolus or germinal spot. The cytoplasm presents toward its central portion a quantity of granular material, partly fatty in character, the deutoplasm or vitellus. The peripheral portion of the cytoplasm is surrounded by a delicate radially striated border, the zona pellucida or radiata (Fig. 319). ^ ■ijH Fig. 317. — Uterus, Fallopian Tubes amj U\aries; Posterior View. 1, i. Ovaries. 2,2. Fallopian tubes. t„ t,- Fimbriated extremity of the left Fallopian tube seen from its concavity. 4. Opening of the left tube. 5. Fimbriated extremity of the right tube, posterior view. 6, 6. Fimbriae which attach the extremity of each tube to the ovary. 7, 7. Ligaments of the ovar>'. 8, 8, 9, 9. Broad hgament. 10. Uterus. 11. Cervix uteri. 12. Os externum. 13, 13. Vagina. The nucleus consists of a nuclear membrane enclosing contents. The latter consist of an amorphous material in which is embedded a network, some of the threads of which have a strong affinity for certain staining materials, and hence are known as chromatin, while others stain less deeply and are known as achromatin. The Fallopian Tubes. — The Fallopian tubes are about 12 centi- meters in length and extend from the upper angles of the uterus to the ovaries. Each tube is somewhat trumpet-shaped, the narrow portion being close to the uterus, the wide portion close to the ovary. The outer extremity of the tube is expanded and subdivided, and presents a series of processes termed fimbriae, one of which is attached 668 TEXT-BOOK OF PHYSIOLOGY, to the ovary. The tube consists of three coats — an external or serous; a middle or muscular, the fibers of which are arranged longitudinally and transversely; and an internal or mucous. The surface of the mucous coat is covered with a layer of ciliated epithelial cells, the motion of which is toward the uterus. The Uterus. — The uterus is pyriform in shape and divided into It measures, before the first pregnancy, about 7 cm. in length, 5 cm. b ^K> -^ .. f \'^ a body and neck. ■^. ^ V t-^fjT I /' >-' U ■/ in breadth and 2\ cm. in thickness. A frontal section of the uterus shows a central cavity which in the body is triangular in shape, in the neck oval or fusiform (Fig. 320). At the upper angles of the uterus the cavity is contin- uous with the cavity of each Fallopian tube. At the junction of the body and the neck, the cavity presents a constriction, the inter- nal OS. The constric- tion at the end of the neck is known as the external os. The walls of the uterus are extremely thick and composed of non- striated muscle-fibers arranged in a very complicated manner. The interior of the uterus is Hned by mucous membrane covered with cylindric ciliated epithelial cells, the motion of which is toward the external OS. Tubular glands are found in large numbers in the mucous membrane lining the cavity, while racemose glands are found in the mucous membrane lining the neck. Owing to the flattening of the uterus from before backward the walls are almost in contact and the cavitv almost obliterated. t Fig. 31S. — Section of Cortex of Cat's Ovary, Exhibiting Large Graafian Follicles. — a. Peripheral zone of condensed stroma, b. Groups of immature follicles, c. Theca of follicle, d. Membrana granulosa, e. Discus proligerus. /. Zona pellucida. g. Vitellus. h. Germinal vesi- cle, i. Germinal spot. k. Cavity of licjuor fol- liculi. — {After Piersol.) REPRODUCTION. 669 The Vagina. — The vagina is a musculo-membranous canal, from 12 to 18 cm. in length, situated between the rectum and bladder. It extends from the surface of the body to the brim of the pelvis, and embraces at its upper extremity the neck of the uterus. Ovulation. — After the estabhshment of puberty a Graafian follicle develops and ripens or matures periodically, usually every twenty- eight days. During the time of maturation the follicle increases in size, from an augmentation of its fluid contents, and approaches the surface of the ovary, where it forms a projection varying from 6 to 12 mm. in size. When maturation is complete the vesicle rup- ^-dBr ''C^^' r'-^-^^:'^^^^^'^^^^^ Fig. 319.— Ovum of a Cow. — i. Zona pel- lucida. 2. Cytoplasm, vitellus. 3. Nu- cleus, germinal vesicle. 4. Nucleolus, germinal spot. 5. Corona radiata. The radial striation of the zona pellucida can not be seen. — (Siohr.) Fig. 320. — Frontal Section OF THE Uterus, i. Cav- ity of the body. 2, 3. Lateral walls. 4, 4. Cor- nua. 5. Os internum. 6. Cavity of the cervix. 7. Arbor vitae of the cervix. 8. Os externum. 9. Va- gina. — {Sappey.) tures, and the ovum and liquid contents are discharged. The ovum, by a mechanism not fully understood, is received by the fimbriated e-xtremity of the Fallopian tube and enters its cavity. The ovum is then transferred through the tube by the peristaltic contraction of its muscle- fibers and by the action of the cilia of its lining epithelium. The time occupied in the transference of the ovum from the ovary to the interior of the uterus has been estimated to be from four to ten days. Either at the time, or very shortly after, its discharge from the follicle, the ovum, and more especially the nucleus, undergoes a series 670 TEXT-BOOK OF PHYSIOLOGY. of histologic changes which eventuates in an extrusion of a portion of the chromatin material. The extruded portions are known as the polar bodies. The non-extruded portion of the chromatin material is known as the female pronucleus. The succession of changes which the nucleus undergoes is termed maturation. As the nucleus is regarded as the part of the ovum which transmits parental character- istics it is assumed that the extrusion of a portion of the nuclear material is a means by which an excess of inherited substance is prevented. Menstruation. — Menstruation is a periodic discharge of blood and mucus from the surface of the mucous membrane of the uterus, and occurs about every twenty-eight days. The duration of the menstrual period extends over four or five days and the amount of blood discharged varies from 180 c.c. to 200 c.c. Menstruation is usually an accompaniment of ovulation, though the latter process may take place independently of the former. It is characterized by both local and systemic changes. The local changes are most marked in the uterus, the mucous membrane of which increases in thickness from a proliferation of the connective tissue and a hyperemic condi- tion of the blood-vessels. Subsequently to these changes the epithe- lial surface, as well as the more superficial portions of the connective tissue, undergo degeneration and exfoliation, after which the finer blood-vessels rupture and permit of an escape of blood into the uterine cavity. At the end of the menstrual period regenerative changes set in which continue until the normal condition of the mucous membrane is reestablished. The Corpus Luteum. — With the rupture of the Graafian follicle there is an effusion of blood into the follicular cavity which soon coagulates, loses its color and assumes the characteristics of fibrin. The walls of the follicle, which have become thickened from the deposition of a reddish-yellow glutinous substance, now become con- voluted and undergo a still further hypertrophy, until they encroach upon and almost obliterate the follicular cavity. In a few weeks the mass loses its red color and becomes decidedly yellow, when it is known as the corpus luteum. With the continuance of reparative changes this body gradually disappears until at the end of two months nothing remains but a small cicatrix on the surface of the ovary. Such are the changes in the follicle if the ovum has not been im- pregnated. The corpus luteum, after impregnation has taken place, undergoes a much slower development, becomes larger, and continues during the entire period of gestation. The diiJerence between the corpus luteum of the unimpregnated and pregnant condition is expressed in the following table by Dalton: REPRODUCTION. 671 Corpus Luteum of Menstruation. At the end of weeks. One month. Two months. Four months. Six months. Nine months. Corpus Luteum of Pregnancy. central clot reddish three Three-quarters of an inch in diameter convoluted wall pale. I Smaller; convoluted , Larger ; convoluted wall bright wall bright yellow ; clot yellow ; clot still reddish, still reddish. Seven-eighths of an inch in diameter ; convoluted wall bright yellow ; clot perfectly decolorized. Seven-eighths of an inch in diameter ; clot pale and fibrinous; convoluted wall dull yellow. Still as large as at the end of second month ; clot fibrinous ; convoluted wall paler. Half an inch in diameter ; cen- tral clot converted into a radiating cicatrix ; external wall tolerably thick and convoluted, but without any bright yellow color. Reduced to the condition of an insignificant cicatrix. Absent or unnoticeable. Absent. Absent. THE REPRODUCTIVE ORGANS OF THE MALE. The reproductive organs of the male comprise the testicles, vasa deferentia, vesiculae seminales, and penis. The Testicles. — The testicles are oblong glands, about 40 mm. in length, 30 mm. in breadth and 20 mm. in thickness, and contained within the cavity of the scrotum. A section of the testicle (Fig. 321) reveals the presence externally of a dense fibrous membrane, the tunica albuginea, and internally a con- nective - tissue framework consisting mainly of septa, which enter the organ on its posterior aspect at the mediastinum testis, passing inward in a diverging manner. The spaces between the septa are occupied by the true gland substance, the seminiferous tubules. The seminiferous tubules are very numerous, the estimate as to their number varying from 800 to 1000. When unraveled they measure from 30 to 40 cm. in length and 0.3 mm. in diameter. At their peripheral extrem- ities the tubules are very much con- voluted, but as they pass toward the mediastinum testis, the convolutions disappear, and after uniting with one another terminate in from twenty to thirty straight tubes, the vasa recta, which pass through 321. — Diagram of a Ver- tical Section through a Testicle, i. Mediastinum testis. 2, 2. Trabeculae. 3. One of the lobules. 4, 4. Vasa recta. 5. Globus ma- jor of the epididymus. 6. Globus minor. 7. Vas def- erens. — {H olden.) 6/2 TEXT-BOOK OF PHYSIOLOGY. the mediastinum and form the rele testis. At the upper part of the mediastinum the tubules unite to form from nine to thirty small ducts, the vasa efferentia, which soon become very much convoluted. After a short course they unite to form a single tortuous tube, about 7 meters in length and 0.4 mm. in diameter, which descends behind the testicle to its lower border. This tube is known as the epididy- mis. The seminal tubule consists of a basement membrane lined by granular nucleated epithelium. The vas dejerens, the excretory duct of the testicle, is about 60 cm. in length and from 2 to 3 mm. in diameter, and extends upward from the epididymis to the inguinal canal, through which it passes into the abdominal cavity and then to the under surface of the base of the bladder, where it unites with the duct of the vesicula seminalis to form the ejaculatory duct. The vesiculae seminales are two lobulated pyriform bodies, about 40 mm. in length, situated on the under surface of the bladder. Each vesicula seminalis consists of an external fibrous coat, a middle, muscular coat, and an external mucous coat. The mucous coat con- tains a number of small tubu- lar albumin-producing glands which secrete a characteristic fluid. The ejaculatory duct, formed by the union of the vas deferens and the duct of the vesicula semi- nalis, opens into the prostatic portion of the urethra (Fig. 322). The prostate gland is a musculo-glandular mass situated at the posterior extremity of the urethra. It contains a large number of tubules, more or less branched and convoluted, and hned by columnar epithelium. They secrete a fluid which is poured into the urethra at the time of the ejaculation of semen. The penis consists of three parts: the corpus spongiosum below, through which passes the urethra, and the two corpora cavernosa, one on either side and above. The corpus spongiosum terminates anteriorly in a conic-shaped structure, the glans penis; the corpora Fig 322. — Vas Deferens, Vesicula Seminales, and Ejaculatory Ducts. — a. Vas deferens, b. Semi- nal vesicle, c. Ejaculatory duct. d. Termination of the ejaculatory duct. e. Opening of the prostatic utricle. /, g. Veru montanum. /;, /. Pros- tate. — {Liegeois.) REPRODUCTION. 673 cavernosa consist externally of a fibrous investment and internally of erectile tissue. These bodies are abundantly supplied with blood, which after entering their substance by the arteries, passes into sinuses or reservoirs, from which it is carried away by veins. These vessels pass to the dorsum of the penis and unite to form a large vein by which the blood is returned to the general circulation. By virtue of the erectile tissue in the corpora cavernosa the penis becomes erect and rigid when the blood supply is increased. This takes place in response to peripheral stimulation or emotional states, or both combined. When these conditions are established nerve-impulses pass outward through nerves, the nervi erigentes, which have their origin in the lumbar region of the spinal cord, and bring about an active dilatation of the arteries and a relaxation of the non-striated muscle-fibers in the corpora cavernosa. With these events there is a rapid influx of blood and a distention and an erection of the organ. This condition is furthered and maintained by a partial compression of the dorsal vein by the fibrous capsule. Semen.- — The semen is a complex fluid composed of the secretions of the testicles, the vesiculae seminales, the prostatic tubules, and urethral glands. It is grayish-white in color, mucilaginous in con- sistence, characteristic in odor, and somewhat heavier than water. In response to appropriate stimulation the muscle-fibers in the walls of the vasa deferentia, vesiculae seminales, and prostatic tubules contract and discharge their contents into the urethra, from which they are forcibly ejected by the rhythmic contraction of the ejaculatory muscles, the ischio and hidbo cavernosi. The amount of semen dis- charged at each ejaculation varies from i to 5 c.c. Spermatozoa. — The spermatozoa are peculiar morphologic ele- ments which arise within the seminiferous tubules as a result of complex histologic changes in the lining epithelium. An adult sper- matozoon consists of a conoid slightly flattened head, from the pos- terior part of which there projects a short straight rod, provided with a long filamentous tail or cilium and an end-piece (Fig. 2>^'^). The head contains a nucleus of chromatin material. The total length of a spermatozoon varies from 50 to 80 micromillimeters. The char- acteristic physiologic feature of spermatozoa is incessant locomotion when in a suitable medium. So long as they are confined to the vas deferens they are quiescent, but with their advent into the vesicula seminalis and dissemination in its contained fluid, they be- come extremely active and move around with considerable rapidity. The power of locomotion depends on the possession of the tail, which, by lashing the surrounding fluid now in this and now in that direction, propels the head from place to place. The vitality of spermatozoa is such as to enable them to retain their physiologic activities in the uterus for more than eight days. 43 674 TEXT-BOOK OF PHYSIOLOGY. The development of spermatozoa from testicular cells as observed in lower animals indicates that each cell gives rise to four embryonic forms — spermatids — which subsequently develop into adult sperma- tozoa. In this process the primary nuclear chromatin undergoes a division, so that each spermatozoon receives but a fractional amount. The changes by which this condition is brought about are comparable to the changes exhibited by the ovum, and have for their result a reduction in the quantity of hereditary substance to be transmitted. Fecundation. — Fecundation is the union of the spermatozoon (the sperm- cell) with the ovum (the germ-cell) and takes place in the great majority of instances in the Fallopian tube. After the introduction of the spermatozoa into the vagina during the act of copulation, they soon begin to pass upward, into and through, the uterine cavity and out into the Fallopian tube, where they accumulate in large numbers and retain their vitality for some days. The migration is effected by the propelling power of the filamentous tail. From observations made on the behavior of the spermatozoa toward the ovum in lower animals, and on the manner by which their union is effected, the inference may be drawn that a similar procedure takes place in mammals. In lower animals the spermatozoa on approaching an ovum take on increased activity, swimming around it in all directions and apparently seeking a point of entrance. In fish and molluscs the zona pellucida presents a distinct opening, the micropyle, through which the spermatozoon passes. Inasmuch as the mammalian ovum is devoid of such an opening, the mechanism of entrance of the spermatozoon is not clearly understood. Notwithstanding their enormous numbers it is gener- ally believed that but a single spermatozoon effects an entrance into the ovum. With the accomplishment of this, however, the spermatozoon loses its vitality, after which the body and tail dis- appear. The head, which in this instance also is the transmitter of the inherited material, advances to meet and unite with the nucleus of the ovum. A series of histologic changes now arise, which eventuate in the production of a new cell, a parent cell, possessing all the features of cell structure and the physiologic activities and Fig. 32 -Human Spermatozoon. 1 . Front view, 2, side view, of the head. k. Head. m. mid- dle piece. /. Tail. e. Termi- nal filament. — {After Retzius.) REPRODUCTION. 675 characteristics of both ancestral cells. From this parent cell the new being develops through successive division, multiphcation, and differentiation of cells. The Fixation of the Ovum. — If the ovum is to develop into a new being it is essential that it be retained within the cavity of the uterus. This is accomplished by the development of specialized structures on the surface of the uterine mucosa and on the surface of the ovTam. With the fertilization of the ovum, the mucous mem- brane of the uterus takes on an increased growth ; it becomes hyper- trophied and vascular, and develops small elevations known as villi. Inasmuch as this membrane is detached and discharged at the birth of the fetus, it is known as the decidua vera. With the fertilization Fig. 324. — Impregnated Uterus, with Folds of Decidua Growing up Around the Egg. The narrow opening, where the folds approach each other, is seen over the most prominent portion of the egg. — (Dalion.) Fig. 325. — Impregnated Uterus; showing the connection between the villosities of the chorion and the decidual membranes. — (Dalton.) ^ of the ovum, the zona pellucida or radiata also develops villosities, and as it passes from the Fallopian tube into the uterus the villi interdigitate, and its further progress is retarded. (Figs. 324 and 325.) In a short time a portion of the decidua vera grows up on all sides and encloses the ovum. Its retention is thus secured. That portion of the decidua which grows around the ovum is termed the decidua reflexa; while the portion to which the ovum attaches itself is termed the decidua serotina, and is of interest for the reason that it becomes the seat of development of the placenta, the organ by w^hich the fetus is nourished. As development advances the decidua reflexa also increases in size and extent, and about the end of the fourth month comes into contact with the decidua vera, with which it ultimately fuses. 676 TEXT-BOOK OF PHYSIOLOGY. DEVELOPMENT OF FETAL ACCESSORY STRUCTURES. Segmentation of the Ovum. — Shortly after the formation of the parent cell, segmentation of the nucleus and cytoplasm takes place in accordance with karyokinetic methods. The two new cells thus formed undergo a similar division into four, the four into eight, the eight into sixteen, and so on until the space within the zona pellucida is completely filled with a large number of small cells, each possessing the characteristic cell structures. The peripheral cells then arrange themselves in the form of a membrane, and as they are, at the same time, subjected to mutual pressure they assume a polyhedral shape, and give to the membrane a mosaic appearance (Fig. 326). The central cells then undergo hquefac- tion. At some point on the inner surface of the membrane, cells ac- cumulate which by their division and multiplication form a second mem- brane. The two together are known as the external and internal blasto- dermic membranes. Germinal Area. — At about this period there is an accumulation of cells at a certain spot in the sub- stance of the blastodermic membranes which marks the position of the future embryo. This spot, at first circular, soon becomes elongated. A slight indentation now develops into what is known as the primitive trace. Around this area there is a clear space, the area pellucida, which is in turn surrounded by a darker region, the area opaca. The primitive trace soon disappears and the area pellucida becomes guitar-shaped. A second groove, the medullary groove, is now formed, which develops from before backward and becomes the neural medullary canal. Blastodermic Membranes. — The embryo, at this period, con- sists of three layers — viz., the external and the internal blastodermic membranes and a middle membrane formed by a genesis of cells Fig. 326. — Primitive Trace OF THE Embryo, a. Primi- tive trace, b. Area pellucida. c. Area opaca. d. Blastodermic cells, e. Villi beginning to appear on the surface of the zona pellucida. — (Lugois.) REPRODUCTION. 677 from their internal surfaces. These layers are known from without inward as the epiblast, mesoblast, and hypoblast. The epiblast gives rise to the central nerve system, the epidermis and its appendages, and the primitive kidneys. The mesoblast gives rise to the dermis, muscles, bones, nerves, blood-vessels, sympathetic nerve system, connective tissue, the urinary and reproductive apparatus, and the w^alls of the alimentary canal. The hypoblast gives rise to the epithelial hning of the alimentary canal and its glandular appendages, the hver and pancreas, and the epithe- lium of the respiratory tract. Dorsal Laminae. — As develop- ment advances, the true medullary groove deepens, and there arise two longitudinal elevations of the epiblast — the dorsal lamincB, one on either side of [the groove, — which grow up, arch over, and unite so as to form a closed tube, the primitive central nerve system. The Chorda Dorsalis. — Just be- neath the neural canal there arises a group of hypoblastic cells which ar- range themselves in the form of a cylindric rod, which marks out the position of the future bony axis of the body. This rod is known as the chorda dorsalis or notochord. Primitive Vertebrae. — On either side of the neural canal the cells of the mesoblast undergo a longitudinal thickening, which develops and extends around the neural canal and the chorda dorsalis, and forms the arches and bodies of the vertebras. They become divided transversely into segments. The mesoblast now separates into two layers : the external, joining with the epiblast, forms the somatopleura; the internal, joining with the hypoblast, forms the splanchno pleura; the space betw^een them constitutes the pleuro- peritoneal cavity (Fig. 327). Visceral Laminae. — The walls of the pleuro-peritoneal cavity are formed by a downward prolongation of the somatopleura (the visceral lamince), which, as they extend around in front, pinch off a portion of the yolk-sac (formed by the splanchnopleura), which - pp Fig. 327. — Diagram Represent- ing THE Relation of Prim- ary Structures in a Devel- oping Chicken; Vertical Transverse Section. The medullary groove and chorda dorsalis are seen in section; the ahmentary canal pinched off from the yolk-sac is com- pletely closed, a. Amnion. a, c. Amniotic cavity filled with amniotic fluid, pp. Space between amnion and chorion continuous with the pleuro-peritoneal cavity in- side the body. vt. VitelHne membrane, or zona pellucida. ys. Yolk-sac, or umbilical vesicle. — {Foster and Balfour.) 678 TEXT-BOOK OF PHYSIOLOGY. becomes the primitive alimentary canal; the lower portion, remaining outside of the body cavity, forms the umbilical vesicle. The Fetal or Embryonic Membranes. — With the appearance of the visceral laminie two membranes develop in succession, both of which play an important part in the subsequent life of the embryo. These are known as the amnion and the allantois. The amnion is formed by folds of the epiblast and the external layer of the mesoblast rising up in front, behind, and at the sides. These folds gradually extend over the back of the embryo to a certain point where they meet, coalesce, and enclose a cavity known as the amniotic cavity. The membranous partition between the folds is absorbed, after which the outer layer recedes and becomes blended with the primitive enveloping membrane of the ovum and thus Fig. 328 Egg. a Amniotic {Dalton.) Diagram of Fecundated a. Umbilical vesicle. b. cavitv. c. Allantois. — Fig. 329. — Fecundated Egg with Allantois nearly Complete, a. Inner layer of amniotic fold. b. Outer layer of ditto, c. Point where, the amniotic folds come in contact. The allantois is seen penetrating between the outer and inner layers of the amniotic folds. — {Dalton.) assists in the formation of the chorion — the external covering of the embryo. The cavity enclosed by the amnion is at firat quite small, but soon enlarges from the accumulation of a clear, transparent fluid, the amniotic fluid. It gradually increases in amount up to the latter period of gestation, when its volume reaches about one liter. This fluid is derived mainly from the blood, as it contains albumin, sugar, fatty matter, and inorganic salts. Traces of urea indicate that some of its constituents are derived from the embryo itself. The allantois is primarily a pouch or diverticulum which develops from the posterior portion of the alimentary canal. As it develops it enlarges, and in its growth inserts itself between the two layers of the amnion, coming into contact more especially with the external layer. It finally completely surrounds the embryo, after which its edges become fused together (Figs. 328 and 329). REPRODUCTION. 679 The allantois is of especial interest and importance, as it is the means by which the blood of the embryo is brought into relation with the blood of the mother. As it develops, two arteries, the hypogastrics, one from each internal iliac, pass out of the abdominal cavity within the walls of the allantois, and follow it in its course around the embryo. The ultimate branches of these arteries pene- trate the villous processes which develop on the surface of the chorion and which take part in the formation of the placenta. A single large vein emerges from the placenta and returns the blood to the embryo. In its course it winds around the arteries in a spiral manner a number of times. These vessels — the umbilical arteries and vein — are enclosed by the walls of the allantois and amnion, and together constitute the umbilical cord which at the end of gesta- tion is about 60 cm. in length. The Chorion.— The cho- rion, the external investment of the embryo, is formed by the fusion of the primitive egg membrane — the zona pellu- cida — the external layer of the amnion, and the allantois. Very early in development its external surface becomes covered with homogeneous, granular, club-shaped proces- ses, which by continued bud- ding and growth, give to the membrane a shaggy appear- ance. At about the end of the second month these pro- cesses begin to atrophy and disappear from the surface of the chorion, with the exception of that portion which is in contact with the decidua serotina. At this point the processes or villi continue to grow and develop, and insert them- selves more deeply into the mucous membrane. Corresponding processes from the mucous membrane insert themselves between the vilh of the chorion, which by their growth and fusion secure, among other things, the retention of the embryo. The Nutrition of the Embryo. — Coincidently with the develop- ment of the amnion, allantois, and chorion, there arises within the body of the embryo the early forms of many, if not all, of the future viscera. The nutritive material required for their growth is partly contained within the umbilical vesicle lying without the body cavity. That this material may be utihzed, blood-vessels emerge from the body and ramify within the walls of the vesicle. The capillaries to Fig. 330. — Human Embryo and its En- velopes AT THE End of the Third Month. 68o TEXT-BOOK OF PHYSIOLOGY. which these vessels gi\'e rise come into close relation with and absorb the food material, after which it is carried by veins to the heart, by which it is distributed to all parts of the embryo. These vessels are collectively known as the omphalo-mesenteric arteries and veins. This primitive or vitelline circulation is of short duration in mam- mals, as the nutritive material in the vesicle is small in amount and is soon exhausted. In birds, however, it is of primary importance. The main supply of nutritive material, however, is derived from the mother by means of a highly developed and specialized organ — - The Placenta. — Of all the embryonic structures the placenta is the most important. It is formed by the end of the third month, after which it gradually increases in size u p to the end of the eighth imonth, by which time it is fully developed. It then mea- sures from 1 8 to 24 cm. in diameter and weighs from 400 to 600 grams. It is most frequently situ- ated at the upper and back part of the uterine cavity. Though exceed- ingly complex in structure it consists essentially of two portions, a fetal and a maternal. The fetal portion con- sists primarily of those villi on the chorion in relation with the decidua serotina. These structures gradu- ally increase in size and number, and receive the ultimate branches of the umbilical arteries. The maternal portion consists primarily of the decidua serotina. As gestation advances the chorionic villi rapidly increase in size and number, and receive the branches of the umbilical arteries. At the same time the decidua serotina becomes hypertrophied and vascular. With the continued growth and development of these two structures they gradually fuse together and finally become inseparable. In accordance with the needs of the embryo, the decidua serotina and its contained blood- vessels undergo certain histologic changes which result in the forma- tion of large cavities, sinuses, or lakes, into which the blood of the uterine vessels is emptied. Coincidently the villi of the chorion grow 7 /^<5v,- Fig. 331. — Human Embryo, with Amnion and Allantois, in the Third Week. There are as yet no limbs; the embryo and its appendages are surrounded by the tufted chorion. — (Haeckel.) REPRODUCTION. 68i and give off numerous branches, which project themselves in all direc- tions into the blood of uterine sinuses (Figs. 332, 333). As the placenta develops, the structures separating the blood of the mother from that of the child gradually become modified until they are repre- sented by a thin cellular or homogeneous membrane. The conditions now are such as to permit of a free exchange of material between the mother and child. Whether by osmosis or by an act of secretion, the nutritive materials of the maternal blood pass through the intervening membrane into the fetal blood on the one hand, while waste products Fig. 332. — Diagram showing the Relations of the Fetal Membranes. A^n. Amnion. Ch. Chorion. M. Muscle wall of uterus. R. Decidua reflexa. 5. Serotina. V. Decidua vera. Y. Yolk stalk. — {McMurrich.) pass in the reverse direction into the maternal blood on the other hand. Inasmuch as oxygen is absorbed and carbon dioxid exhaled by the same structures, the placenta is to be regarded as both a digestive and a respiratory organ. So long as these exchanges are permitted to take place in a normal manner the nutrition of the embryo is secured. The Fetal Circulation. — The composition of the blood as well as the course it pursues through the heart and vascular apparatus presents peculiarities which have arisen in consequence of the neces- sity of obtaining nutritive material through the placenta and the 682 TEXT-BOOK OF PHYSIOLOGY. almost impervious condition of the pulmonary capillaries. On re- turning from the placenta, the blood in the umbilical vein is relatively rich in nutritive material and scarlet red in color from the presence of oxygen. As it passes into the abdominal cavity a portion of the blood is directed by the ductus venosus into the vena cava, while another portion is emptied into the branches of the portal vein, by which it is distributed to the liver and from which it emerges by the hepatic veins and poured into the vena cava. The blood in the vena cava is thus a mixture of venous blood from the lower extremi- ties and liver, and oxygenated blood from the placenta. After its discharge into the right auricle the blood is directed bv a fold of Amnion Chorion S^^o^ cj 'Compact C layer. c t «• 3 r2 o Cavernous J o I layer. ', Muscularis. 'i Fig. 2)?,2)- — Diagram op Human Placenta at the Close of Pregnancy. — (^Schdper.) Chorionic villi. Internllous spaces. Floating villus. |- Attached ^^lIi. the lining membrane, the Eustachian valve, through an opening in the interauricular septum, the foramen ovale, into the left auricle. It then flows through the auriculo-ventricular opening into the left ventricle, thence into the aorta, and by its branches is distributed to all parts of the body. ^The blood from the head and upper extremities is emptied by the superior vena cava into the right auricle, but as it passes in front of the Eustachian valve, it flows directly into the right ventricle and then into the pulmonary artery. On account of the unexpanded condition of the lungs and the almost impervious condition of the pulmonary capillaries, but a small portion of the blood passes through them, while the larger portion by far passes into the aorta PLATE III. DIAGRAM OF FCETAL CIRCULATION. W Preyer del- REPRODUCTION. 683 directly through a duct, the ductus arteriosus, which enters at a point below the origin of the left carotid and subclavian arteries. A com- parison of the blood distributed to the head and upper extremities, with that distributed to the lower extremities, will show a larger percentage of nutritive material and oxygen in the former than in the latter, a fact which has been offered as an explanation of the more rapid growth of the upper half of the body. As the blood passes through the aorta, a portion is directed from the main current by the hypogas- tric and umbilical arteries to the placenta, where it loses carbon dioxid and gains oxygen, and changes in color from a bluish red to a scarlet red. Parturition. — At the end of gestation — approximately 280 days from the time of conception — a series of changes occur in the uterine structures which lead to an expulsion of the child, the placenta, and decidua vera. To this process in its entirety the term parturition is given. At this time, from causes not clearly defined, the uterine walls begin to exhibit throughout their extent a series of slight con- tractions which are somewhat peristaltic in character; these con- tractions, which gradually increase in frequency and vigor, bring about a dilatation of the internal os and a descent of the membranes into the cervical canal. The pressure exerted by these membranes during the time of the contraction materially assists in the relaxation of the circular fibers and a dilatation of the external os. When the dilatation has so far advanced that the diameter of the external os attains a measure of 7 or 8 cm., the tension of the membranes becomes sufficiently great to lead to their rupture and to a partial escape of the amniotic fluid. With this event, the presenting part of the child, usually the head, descends into, the cervical canal. After a short period of rest the uterine contractions return and rapidly increase in vigor and duration. As a result of the pressure thus exerted from all sides on the body of the child, the head gradually descends into the vagina and finally emerges through the vulva to be followed in a short time by the expulsion of the trunk and limbs, and a discharge of the remaining amniotic fluid. With the expulsion of the child the uterine contractions cease for a period of ten or fifteen minutes, when they again recur, with the result of detaching the placenta and expelling it into the vagina. It is then removed by the co-operative action of the abdominal and perineal muscles. The hemorrhage which would naturally occur with the detachment of the placenta and the laceration of the maternal vessels is prevented by the firm continuous contraction of the uterine walls, by which the vessels are compressed and permanently closed. The Establishment of Inspiration and the Adult Circulation. — After the birth of the child and the detachment of the placenta, there speedily occurs a decrease in the quantity of oxygen and an 684 TEXT-BOOK OF PHYSIOLOGY. increase in the quantity of carbon dioxid in the blood, a condition which causes a discharge of nerve energy from the inspiratory center, a contraction of the inspiratory muscles, an expansion of the thorax, and an inflow of air into the lungs. In the later months of intrauterine life the vascular apparatus undergoes certain anatomic changes which favor the transition from the placental to the adult circulation. Thus the ductus venosus con- tracts, and shunts a larger volume of blood into and through the liver; the Eustachian valve diminishes in size and at the time of birth has almost disappeared; a membranous fold grows upward and backward from the edge of the foramen ovale on the left side; the ductus arteriosus also contracts. With the first inspiration and the expansion of the lungs, the blood which enters the pulmonary artery passes through the pulmonary capillaries in large volume and is returned by the pulmonary veins to the left auricle. The en- trance of the blood into this cavity presses the membranous fold against the margins of the foramen ovale and thus prevents the further flow of blood from the right auricle. The blood entering the right auricle by the inferior vena cava now flows into the right ven- tricle, which is favored by the small size of the Eustachian valve. The foramen ovale is permanently closed at the end of a week or ten days; the ductus arteriosus at the end of four days. The um- bilical vein and ductus venosus, at the end of four or five days, have also become almost impervious from the contraction of their walls. The hypogastric arteries remain open and carry blood to the walls of the bladder. Lactation. — As pregnancy advances the mammary glands in- crease in size, partly from a deposition of fat and connective tissue and partly from a multiplication of the secreting acini. The lining epithelial cells at the same time increase in size, and tow^ard the end of pregnancy begin to exliibit functional activity. At the time of birth, or within a day or so after birth, the acini are filled with a fluid which in its qualitative composition resembles milk and is known as colostrum. It is distinguished from milk more especially in the fact that it contains in large quantity a proteid which coagulates on boiling, and certain inorganic salts which have a laxative effect on the new-born child. Normal lactation and the phenomena which accompany it are fufly established by the end of the second or third day. The composition of milk and the mechanism of its production have been stated in the chapter on Secretion, page 401. Physiologic Activities of the Embryo. — ^During intrauterine life the evolution of structure is accompanied by an evolution of function. The relatively simple and uniform metabolism of the undifferentiated blastodermic membranes gradually increases in REPRODUCTION. 685 complexity and variety, as the individual tissues and organs make their appearance and assume even a slight degree of functional activity. As to the periods at which different organs begin to func- tionate, but Httle is positively known. The primitive heart, in all probability, begins to pulsate very early, as in an embryo from fifteen to eighteen days old and measuring but 2.2 mm. in length, Coste found the amnion, the allantois, the omphalo-mesenteric vessels, and the two primitive aortas developed. In the earlier weeks, all products of metabolism are doubtless elimi- nated by the placental structures; but as metabolism increases in complexity the liver and kidney assume excretory activity. Thus, at the end of the third month the intestine contains a dark, greenish, viscid material — meconium — composed of bile pigments, bile salts, and desquamated epithelium ; the amniotic fluid, as well as the fluid within the bladder, contains urea at the end of the sixth month, indicating the estabhshment of both hepatic and renal activity. Con- tractions of the skeletal muscles of the limbs begin about the fifth month, from which it may be inferred that the mechanism for muscle activity, viz., muscles, efferent nerves, and spinal centers, has become anatomically developed and associated, and capable of coordinate activity. These contractions are, in all probabihty, auto- matic or autochthonic in character due to stimuli arising within the spinal centers. The remaining organs remain more or less inactive. After birth, with the first inspiration and the introduction of food into the ahmentary canal, the physiologic mechanisms which sub- serve general metabolism begin to functionate and in the course of a week are fully estabhshed. At this time the cardiac pulsation averages about 135 a minute; the respiratory movements vary from 30 to 35 a minute, and are diaphragmatic in type; the urine, which was at first scanty, is now abundant and proportional to the food consumed; the digestive glands are elaborating their respective enz}'mes, digestion proceeding as in the adult. The hepatic secre- tion is active and the lower bowel is emptied of its contents; the coordinate activities of the nerve-, muscle-, and gland-mechanisms are entirely reflex in character. Psychic activities are in abeyance by reason of the incomplete development of the cerebral mechanisms. APPENDIX. PHYSIOLOGIC APPARATUS. The study of the physical and physiologic properties of muscles and nerves necessitates the employment of some stimulus which, when applied to either tissue, will call forth a contraction of the muscle, or the develop- ment of a nerve impulse in the nerve. The most convenient stimulus is electricity, for the reason that, with appropriate apparatus, its intensity and duration can be graduated with the utmost nicety. Moreover, it does not destroy the tissues, as do many chemic, physical, and mechanic stimuli. It is therefore necessary that the student should have a practical acquaint- ance with those appliances by means of which elec- tricity is generated, appUed and controlled. The electric cell is an apparatus composed of different elements, which, by virtue of chemic actions taking place among them, generate and conduct elec- tricity. In its simplest form an electric cell consists of two metals — zinc and copper, or carbon, or platinum, etc., immersed in an exciting fluid, usually dilute sul- phuric acid (Fig. 334). The zinc element is the one acted on chemically by the sulphuric acid, and at the expense of which the electricity is maintained. It is kno^vn as the generating element. The copper is the collecting and conducting element. With the immersion of these elements in a solution of H2SO4 a chemic action at once takes place between the zinc and the acid, with the formation of zinc sulphate and the libera- tion of hydrogen, as expressed in the following formula: Zn -f H2SO1 = ZnSO, + H,. The zinc sulphate passes into the solution, while the hydrogen accumulates on the surface of the copper element. As all chemic action is accompanied by the development of electricity, it can be sho\ATi by appropriate means that this is the case at the surface of the zinc. Such a combination is the means of establishing a difference of potential between two points; the point of highest potential bemg the surface of the zinc or the positive element, the point of lowest potential 687 Fig. 334. — An Electric Cell. 688 TEXT-BOOK OF PHYSIOLOGY. being the copper or the negative element. So long as the elements remain unconnected there is no movement of electricity, no current. If the ends of the elements projecting beyond the fluid are connected by a copper wire, a pathway or circuit is estabUshed, and a movement of the electricity takes place. As electricity flows from the pomt of high to the point of low potential, it follows that inside the cell the current flows from the zinc to the copper, and outside the cell from the copper to the zinc. Such a current is termed a continuous, a galvanic or a voltaic cur- rent. Inasmuch as there is a progressive fall in potential between the highest and lowest points, it follows that any two points in the circuit will exhibit a similar difference of potential. For this reason the projecting end of the copper element is at a higher potential than the projecting end of the zinc element. The end of the copper is, therefore, termed the posi- tive, + pole or anode, the end of the zinc the negative, • — pole or kathode. Electric Units. — Owing to the difference of the electric potential in the cell, the electricity leaves the cell under a certain degree of pressure, termed the "electro-motive force." As it passes through the circuit it meets with resistance, the amount of which will depend on the nature of the circuit material, its length, and the area' of its cross-section. In accord- ance with the resistance will depend the quantity of electricity that a given elec- tro-motive force will press through in a unit of time. The strength of the current will therefore not depend entirely on the electro- motive force, but, rather, on the ratio between the electro-motive force and the resistance. For the measurement of electric quantities, a system of imits has been devised. The unit of electro-motive force is the volt; the unit of resistance is the ohm, i. e., the resistance offered by a column of mercury 106.3 cm. long and i sq. mm. in section at 0° C; the unit of quantity is the coulomb; the unit of time is one second. One volt is the electro-motive force which, when steadily appUed, will press through a resistance of one ohm, one coulomb of electricity in one second of time yielding a current strength of one ampere. This relation may be expressed in the following formula. Ohm's law: T -f- FlG. 335. — Two Simple Electric Cells Joined IN Series. C. Copper. Z. Zinc. C (current strength) Electro-motive force (E. M. Resistance (R) F.) . Volt — ^ or Ampere = ^ Ohm In practical work it is often necessary to increase the strength of the current. This is done by uniting two or more cells in series, i. e., uniting the copper of one cell to the zinc of a second, and so on (Fig. 335). If the resistance remains the same the total voltage is that of one cell multi- plied by the number of cells united. PHYSIOLOGIC APPARATUS. The cell as above described cannot maintain a current of constant strength for any length of time, for the following reasons: 1. The sulphuric acid solution, in consequence of its chemic action, soon becomes nothing more than a saturated solution of zinc sulphate, after which its chemic activity ceases. The current, therefore, soon diminishes in strength. 2. The accumulation of hydrogen bubbles on the surface of the copper hinders the passage of the electricity. In a short time they develop a current in the opposite direction, which also tends to weaken the original current. This action is termed polarization of the elements. Cells of this character are not suited for physiologic work, in which constancy in the strength of the current is absolutely necessary. To overcome these disadvantages, cells have been devised which are less violent in action, which prevent polarization, and which main tarn a cur- rent of constant strength for a long period of time. One of the most generally used for physiologic purposes is — The Daniell cell. This consists of a porous cup con- taining a saturated solution of CUSO4, copper sulphate, in which is immersed a copper plate or rod. This combina- tion is placed in a glass vessel containing a solution of H2SO4 (i : 15). In this solution is immersed a roll of sheet zinc (Fig. 336). Each of the plates is provided with a binding screw. When the cell is in action the sulphuric acid at- tacks the zinc, forming zinc sulphate, and liberates hydro- gen; the cup being porous, the hydrogen passes into the copper sulphate solution, where it combines with the sulphuric acid radicle, and liberates metalhc copper. Polarization of the copper is thus prevented. The metallic copper is deposited on the copper plate, which is thus kept bright. The copper sulphate solution is kept at the point of saturation by packing around the copper cylinder a quantity of the crystals of the salt. The sulphuric acid passes back into the porous cup, to take the place of that used. This cell is remarkably constant for these reasons, and well adapted for physiologic as well as other purposes where a current of uniform strength is necessary. The projecting ends of the copper and zinc plates are termed respec- tively the positive pole or anode, and the negative pole or kathode. The electro-motive force of a Daniell cell is practically i volt; but when the two poles are connected by a wire of i ohm resistance, the current strength will be less than i ampere, possibly only 0.7, owing to the resistance offered 44 i-ir -JJAXIELL L KLL. 690 TEXT-BOOK OF PHYSIOLOGY. to the flow of electricity by the fluids between the zinc and the copper. In all measurements, the internal resistance of the cell must be taken into consideration. The Dry Cell. — The commercial dry cell is a convenient source of electricity for general laboratory work. It consists of a cup of zinc, the inner surface of which is covered over with a thick layer of a paste of plaster of Paris, saturated with ammonium chlorid. In the center of the cup there is a rod of carbon. Surrounding this rod and occupying the space between it and the plaster of Paris paste, is a mixture of manganese dioxid and charcoal. The upper surface of the cell is sealed to prevent evapora- tion. The electricity is generated at the surface of the zinc cup by the chemic action of the chlorin which arises from the dissociation of the am- monium chlorid. When the plates are united by a conjunctive wire the current within the cell flows from the zinc (the positive element) to the carbon (the negative element), and without the cell from the carbon (the positive pole) to the zinc (the negative pole) . Leads. — By means of insulated wires attached to the poles of a cell, the electricity may be conducted from the cell and used for exciting or stimulating purpose. As the wires thus become practically prolongations of the plates their ends become the corresponding poles. In experimental work the ends of the wires are provided with special devices, termed — Non-polarizable electrodes. The necessity for the employment of such electrodes arises from the fact that when the ends of the wires from a cell are placed in direct contact with the tissues chemic changes are pro- duced in a short time, which lead to their polarization. As a result, a current opposite in direction to that of the cell is developed, which tends to weaken or neutralize it. This polarization current vitiates the result of many experiments made with highly irritable tissue such as nerve tissue. Whether for stimulating purposes or for the purpose of detecting the exist- ence of electric currents in living tissues, it is essential that the electrodes used shall be non-polarizable. The earliest electrodes of this character were made by du Bois-Reymond and were based on the fact discovered by Regnault that a strip of chemically pure zinc or amalgamated zinc (Matteucci) immersed in a saturated solution of zinc sulphate would not polarize. One form made by du Bois-Reymond is shown in Fig. 337. It Fig. 337. — Non-polarizable Elec- trodes. I. Du Bois-Reymond's. 2. Von Fleischl's. 3. d'Arson- ' val's. PHYSIOLOGIC APPARATUS. 691 consists of a flattened glass tube attached to a universal joint and supported by an insulated brass stand. The lower end of the tube is closed with kaolin or China clay made into a paste with a 0.6 per cent, solution of sodium chlorid. It can be molded into any desired shape. The interior of the tube is partially filled with a saturated solution of sulphate of zinc in which is immersed the strip of amalgamated zinc. To the upper end of the zmc the conducting wire is attached. The V. Fleischl brush electrode is similar to the preceding except that the end of the tube is closed by the brush of a camel's-hair pencil. The d'Arsonval electrode consists of a glass tube containing a silver rod coated with fused silver chlorid. The interior of the tube is filled with normal salt solution 0.6 per cent, and the end closed with a thread or plug of asbestos which is made to project beyond the tube for a short distance. Any one of the these three electrodes is suitable for physiologic experimentation, as their free ends neither corrode the tissues nor develop electric currents. Keys. — Muscle and nerve tissues are con- ductors of electricity. When, therefore, the termmals (the non-polarizable electrodes) of the wires of a cell are placed in contact with either a muscle or a nerve a circuit is made through which a current of electricity flows; when one or both are removed, the circuit is broken and the current ceases. In practical work it is often necessary to keep the elec- trodes in contact with the tissues for a varia- ble length of time. The circuit, however, may be alternately made and broken at will by interposing along the return wire a mechanic contrivance kno^\Tl as a key, of which there are many forms. The du Bois Reymond Friction Key. — This consists of a plate of vulcanite attached to a screw clamp by which it can be fastened to the edge of a table (Fig. 338). The surface of the vulcanite plate carries two rectangular blocks of brass, each of which has two holes drilled through it, for the insertion of wires, which are held in position by small screws. A movable bridge of brass, provided with an ebonite handle, serves to make connection between the blocks. There are two ways of interposing this key in the circuit. 1. As a Simple Key. — For this purpose one of the wires, usually the nega- tive, is carried from the cell to one block and then continued from the second block. When the bridge is dowTi, the circuit is made and the current passes; when it is up, the circuit is broken. 2. As a Short-circuiting Key. — When used for this purpose, the wires of Fig. 338. — Du Bois-Rey- MOND Friction Key. 692 TEXT-BOOK OF PHYSIOLOGY. the cell are carried to the inner holes of each block and then continued from the outer holes to the tissues or to some form of apparatus which it is desired to actuate. When the key is closed, i. e., when the bridge is down, the current on reaching the key, will divide, one portion passing across the bridge and so back to the cell, the other portion passing to the tissue or apparatus. The amount of the cur- rent which is returned to the cell through the short circuit will be proportional to the resistance of the longer circuit. As the latter is usually great in comparison with the former, practically all the current is short-circuited. When the bridge is lowered, therefore, the current is short-circuited; when it is raised, the current flows into the longer circuit through the tissue or apparatus. The Mercury Key. — In this form the connection is established by means of mercury. It consists of a circular block in the center of which there is a cup containing mercury (Fig. 339). At opposite points there are bindmg posts, one of which is provided with a rigid fixed copper rod passing into the mercury; the other is provided with a mova- ble bent rod which may be made to dip into or be with- drawal from the mercury by the ebonite handle. The effect of a constant or galvanic current on a muscle or nerve will depend to some extent on its strength. This may be accurately regulated by means of an apparatus known as— The Rheocord. With this apparatus an electric current may be divided, one portion continuing through a conductor back to the battery, the other portion being sent off through the nerve. The strengths of these two currents are inversely proportional to the resistances of their circuits. A simple form of rheocord (Fig. 340) consists of a long wire arranged for convenience in parallel Imes on a small wooden base and connected at its two ends with binding posts A and B. The resistance of this wire, 1.6 ohms, can be increased by the introduction of small re- sistance coils, between D and B, varying from 5 to 20 ohms. The two binding posts A and B are connected with the positive and negative poles of an electric cell respectively. A simple key is placed in the circuit. From A, a wire passes to one of the electrodes on which the muscle or nerve rests. A second wire passes from the second electrode to a clamp S, by way of the binding post C, which can be fastened to the long wire at any given point. The current, on reaching A, will divide into two branches, one of which will pass along the wire A, B, and thence back to the cell; the other will pass through the nerve and back to S and thence Fig. 339. — A Mercury Key. PHYSIOLOGIC APPARATUS. 693 also to the cell. The amount of current passing through the nerve circuit will be inversely proportional to the resistance of the nerve and directly proportional to the difference of potential between A and S. If S is close to A, the difference of potential is slight. If S is removed from A toward B, the difference of potential is increased and the current sent through the nerve circuit is increased. In many experiments it is necessary to reverse the direction of the cur- rent, in other experiments to de-flecl it, without changing the position of the electrodes. Both these results may be accomplished by the use of — Pohl's commutator. This is a round block of wood with six cups, each of which is in connection with a binding post (Fig. 341). In each of the two cups marked i and 2, + and — , is inserted one end of a copper wire bent at right angles. The other ends of the wires are supported and insulated by a hard -rubber handle.. To the top of each wire is soldered a semicircular copper wire. This arrange- ment permits of a rocking movement, whereby the oppo- site ends of the semicircular wires can be made to dip into cups 3 and 4, and into cups 5 and 6 alternately. Two wires crossed in the middle of the block serve to connect- opposite pairs of cups. When in use, the cups are filled with clean mercury. The method of using the commutator is as follows : I . Asa Current Reverser. — -The positive and negative poles of the electric cell are connected by wires with binding posts i and 2 respectively. A key is interposed in the circuit. Wires are then carried from binding posts 3 and 4 to the electrodes in connection with the muscle or nerve. The rocker of the commutator is so turned that the ends of the semicircular wires dip into cups 3 and 4. The direction of the current will be on the closure of the circuit from i to 3, then from 3 along a wire to and through the tissue and back to 4, and thence to the cell. If the position of the rocker be now reversed so that the opposite ends of the semicircular wires dip into cups 5 and 6, the direction of the current through the tissue will be reversed. The positive current, after entering binding post i, will flow to 5; then along one of the cross wires to 4; then along a wire to and through the tissue and back to 3, along the opposite cross wire to 6, thence to 2 and so back to the cell. Fig 340.— Rheocord. 694 TEXT-BOOK OF PHYSIOLOGY. 2. As a Current Deflector. — When it is desirable to deflect the current to two pairs of electrodes differently situated, wires are carried from binding posts 3 and 4 to one pair, and from 5 and 6 to the other pair. The cross wires are then removed. According to the position of the rocker the current will be deflected to one or the other. The Inductorium. — This is an apparatus designed for the purpose of obtaining single or rapidly succeeding electric currents by induction. Its construction is based on facts discovered by Faraday, some of which are the following: If two circuits, a primary and a secondary, are placed parallel to each other, the former connected with a galvanic cell, the latter with a galvan- ometer, it is found that, at the moment the primary circuit is made, and at the moment it is broken, a current is induced in the secondary circuit, as shown by a momentary deflection of the galvanometer needle. During the continuous flow of the current through the primary circuit there is no Fig. 341. — Pohl's CoiiiiuxATOR. A. Arranged as a current reverser; B, as a cur- rent deflector. evidence of a current in the secondary circuit. The induced current is but of momentary duration. The current flowing through the primary circuit is termed the inducing, the current flowing through the secondary circuit the induced current. The induced current is opposite in direction to that of the inducing current when the circuit is made or closed; it is in the same direction, however, when the circuit is broken or opened. If the circuits are arranged in the form of coils, it is found that, other things being equal, the strength of the induced currents will be proportional to the number of turns in the coils. If the coils are placed at varying distances from each other, the strength of the induced current varies, increasing as the coils are approximated, decreasing as they are separated. Approximation or separation of the coils while the current is flowing through the primary circuit develops an induced current, which disappears, PHYSIOLOGIC APPARATUS. 69s however, the moment the movement of the coil ceases. A sudden increase or decrease in the strength of the inducing current also develops an induced current. When the coils are approximated or the primary current increased in strength, the induced current is opposite in direction to that of the inducing current; with the reverse conditions, the induced current has the same direction . The induced currents have been termed, in honor of their discoverer, Faradic currents. The du Bois-Reymond inductorium, based on the foregoing facts, consists essentially of two coils of insulated copper wire, termed primary and secondary (Fig. 342). The primary coil, R', consists S of thick copper wire wound around a wooden spool attached to a vertical support. The beginning of this coil is at the binding post S", its termination either at binding post P" or S"'. In the course of this primary wire or circuit, there are placed two vertical bars of soft iron, B', con- nected at their bases to form a horseshoe magnet, around the ends of which the wire is coiled, will be explained later. Inside the primar}^ coil there is placed a bimdle of soft iron wires, which, as soon as the circuit is made, become magnetized, with the effect of increasing the action of the inducing current. The secondary coil, R'', consists of a much greater number of turns of a finer copper wire, the ratio bemg about 40 to i, also wound around a spool, having a timnel sufl&ciently large to enable it to slide over the pri- mary. By these means the strength of the induced current is increased. As a result of the construction of the inductorium, the low electro-motive force of the cell is transformed into the high electro-motive force charac- teristic of the induced current. As the number of turns of wire in the secondary coil is to the number in the primary, so are the electro-motive forces in the secondary coil to those m the primary coil. The secondary coil slides along a track, B, which permits it to be Fig. 342. — iNDUCTORiuii OF DU Bois-Reymond. R', Pri- mary, R", secondary spiral. B. Board on which R" moves. I. Scale. -1 . Wires from battery. P', P". Pillars. H. Neef's hammer. B'. Electro-magnet. S'. Binding screw touching the steel spring (H). S" and S'". Binding screws to which to attach \vires where Neef's hammer is not required. The object of this device 696 TEXT-BOOK OF PHYSIOLOGY. moved toward or away from the primary. The distance between the two coils can be measured and the strength of the induced current again re- produced, other things being equal, by means of a centimeter-millimeter scale pasted on the edge of B. The ends of the wire of the secondary coil are fastened to two binding posts to which conducting w^ires provided with hand electrodes can be attached. The inductorium may be used for obtaining either a single current or a series of rapidly repeated induced currents. The Single Induced Current. — On account of its high electro-motive force, its penetrative power, and short duration, the single induced current is a most convenient and suitable form of stimulus for many purposes. In order to obtain such a current, the positive wire of the cell is carried to bindmg post S", and the negative wire either to S"' or P". A key is placed in the primary circuit. The course of the current will then be on the closure of the circuit from the cell to S'^, thence around R' to S'", and so back to the cell; or if the negative wire is connected with P", the course of the current on leaving R' will be through the coils surrounding the two vertical bars B', thence to V", and so back to the cell. If the secondary coil be placed close to the primary and the wires of the secondary brought into contact wdth a muscle, it will be fomid that with both the make and the break of the primary circuit a current is induced in the secondary, as shown by a short quick pulsation of the muscle; but during the time of closure of the circuit, the induced current is wanting, as shown by the quiescent condition of the muscle. It will be apparent, however, from the energy of the contraction that the break induced current is a more efficient stimulus than the make induced current. That this is the case is made evident by removing the secondary to the end of the slidew'ay and then gradually bringing it toward the primary half a centimeter at a time, making and breaking the circuit after each movement until a pulsation of the muscle occurs. It will be fomid to occur first on the break of the circuit. As the secondary approaches the primary a position will be reached when a pulsation occurs on the make as well as on the break of the circuit, though it will be less pronounced. The explanation offered for this difference in the strength of the two induced currents is as follows: With the make of the circuit and the passage of the battery current through the primary coil there is induced in the neighboring and parallel turns of the \vire an extra current opposite in direction to the primary current. This extra or self-induced current antagonizes and prevents the current from attaining its maximum development as quickly as it otherwise would, and therefore its efficiency as an inducer of a current in the secondary is diminished. On the break of the circuit the primary current disappears quickly, arid as there is nothing to retard its disappear- ance its efhciency as an inducer of a current in the secondary coil is not diminished. It is not infrequently stated that the disappearance of the primary current induces in the neighboring coils a break extra current corresponding in direction which assists in the development of the induced current. This is not the case, however, as no break extra current is developed in the inductorium as ordinarily used when actuated by a battery current of moderate strength. As it is not so much the intensity of the current as it is rapid variations in intensity that produce effects, it is readily apparent why the induced current developed at the break of the primary is more effective as a stimulus than the induced current developed at the make of the primary circuit. The quantity of the electricity is however, the same in both cases. PHYSIOLOGIC APPARATUS. 697 If the secondary be pushed further along the slideway until it largely covers the primar}^ coil, a position will be reached when the make induced current equals in its efficiency as a stimulus the break mduced current; and if the secondar}^ be yet further advanced, a position is reached when the make induced current becomes more powerful and efficient than the break induced current, as sho^Mi by the greater contrac- tion of the muscle. This result is explained by the fact that the make extra current is now able of itself to induce a current in the secondary coil, on account of its proximity, which, added to that induced by the batten- current, produces a current, greater than that induced on the break of the circuit.* Rapidly Repeated Induced Currents. — As the single induced current is of extremely short duration, it is inefficient as a stimulus in the conduct of many experiments. It is necessary, therefore, to develop it with a fre- quency that is sufficient to give rise to a summation of effects. The dura- tion of the stimulation may be thus considerably prolonged. This is accomplished by introducing in the primary circuit close to the primary coil an automatic interrupter, usually Neef's modification of Wagner's hammer (Fig. 342). This consists of a vertical post, P', to the top of which is fastened a metallic spring carrying at its opposite end a steel or iron hammer, H, which hangs over, but does not touch, the two vertical bars of soft iron around which the wire of the primary coil is woimd. About the middle of the spring on its upper surface there is a small plate of platmum which is in contact with an adjustable, platinum-tipped screw, S', carried by a plate of brass in connection with binding post S". For the purpose of interrupting the primar}' circuit frequently in a imit of time, and thus developing induced currents in quick succession, the apparatus is arranged in the following way: The positive and negative poles of the electric cell are connected by wires with binding posts P' and P", a key being interposed in the circuit. If the screw S' is in contact with the spring, the current on the closure of the circuit will enter P', pass along the spring to S', thence into and through the primary coil R', to the coils surrounding the vertical bars B', then to P'^, and so back to the cell. As the current passes around the vertical bars, they are magnetized. The magnetization draws down the hammer, and, in so doing, breaks the circuit at the tip of the screw, S'. The vertical bars are at once demagnetized, and the hammer is restored to its original position by the elasticity of the spring. The circuit is thus re-established, the current flows through the coils, the bars are again magnetized, the hammer is drawn down, to be followed by a second break of the circuit. The number of times the circuit is thus made and broken per second will vary with the length of the spring. As each interruption of the primary circuit develops an mduced current, it follows that the latter must succeed each other with a frequency corre- sponding with the frequency of the former. If while the primary circuit is thus being interrupted the wires of the secondary coil be placed in con- * "On certain peculiarities of the inductorium/' Prof. Colin C. Stewart, "Univ. Pa. Medical Bulletin," Feb., 1904. 698 TEXT-BOOK OF PHYSIOLOGY. tact with a muscle, the mduced current will give rise to contractions which will succeed each other so rapidly that they fuse together, producing a spasm or tetanus of the muscle. For this reason these currents are fre- quently spoken of as tetanizing currents, and the procedure as tetanization or Faradization. These currents also increase in strength as the secondary approaches the primary. Helmholtz's Modification of the Inductorium. — With a view of equalizing the strengths of the induced currents, HelmhoUz suggested a device the adoption of which accomphshes this to a certain extent. It consists (Fig. 342) in connecting with a wire binding posts P' and S", and in providing binding post P" with an adjustable screw which can be raised until the spring comes in contact with it, when the hammer is drawn down by the electromagnet B'. This latter arrangement is practically a short- circuiting key by which a portion of the cur- rent is returned to the cell without ever enter- ing the primary coil. The same arrange- ment, though differently lettered, is shown in Fig. 343. By the use of the entire device the changes in the primary coil are made not by making and breaking the primary current, but by alternately long- and short- circuiting the current. "When the short- circuiting key is opened, the full volume of the primary current flows through the pri- mary coil. When the short-circuiting key is closed, most of the current fails to enter the coil, taking the easier path through the key. Some of the current, however, always flows through the coil and is never diverted. The cycle of changes in the electric condition of the primary coil is thus altered for two reasons: "First, we no longer have an alternation between a full primary current and none at all — rather an alternation between a full primary current and a weaker one. The difference in the phases is thus lessened, the extent of the change on making and breaking is lessened, and correspondingly the efficiency of the make and break cur- rents induced in the secondary coil is slightly decreased. "Second, on making the primary current, as in the ordinary coil, the sudden appearance of the primary current is antagonized by the opposing make extra current, with the result that the make induced current is still further reduced; while on break- ing the current the break e.xtra current can now flow through the primary coil across the short-circuiting key. This current, traihng behind the disappearing primary current in the same direction, produces the same effect as if the primary current itself were to disappear slowly. As a result the disappearance of the primary current loses its former efficiency as an inducer of secondary currents, and the break induction current is reduced to about the efficiency of the make. "This so-called 'ecjualizing' of the make and break induced currents is never perfect, if for no other reason, because the make extra current must take the long circuit through the battery, while the break extra current has an easier path through the short-circuiting key, and is thus greater than the make extra current." (C. C. Stewart.) Fig. 343. — Helmholtz's Modifica- tion OF NeEF'S HAMilER. As long as c is not in contact with d, g h remains magnetic; thus c is attracted to d and a secondary circuit, 0, b, c, d, e, is formed; c then springs back again, and thus the process goes on. A new wire is introduced to connect a with /. K. Battery PHYSIOLOGIC APPARATUS. 699 THE GRAPHIC METHOD. The term graphic is applied to a method by which curves or tracings are obtained which represent the extent, duration, and time relations of the movements accompanymg physiologic processes. If these movements can be translated in one direction, they may be recorded in different ways: 1. By attaching the movmg structure — e. g., heart, muscle, etc. — to a delicate lever the free extremity of which is provided with a writmg point. 2. By transmitting the movement through a column of air enclosed in a rubber tube the two ends of which are attached to a metallic capsule, covered by a rubber mem- brane, termed a drum or tam- bour. When the membrane of the first tam- bour is pressed or driven in- ward, the air is ■ forced through the rubber tube into the second tambour and its membrane is pushed out- ward. As soon as the primary pressure is removed, the membranes return to their former condition. If the membrane of the first tambour is drawii outward, the air in the system is rarefied and the membrane of the second tambour is pressed inward. For the purpose of register- ing the movement transmitted by the column of air, tte second tambour is provided with a light lever support- ed by a vertical bearing resting on a small metallic disk. The mem- brane of the first tambour is frequently provided with a button, which is placed over the moving structure. The inward movement of the membrane of the first tambour produces an outward movement of the membrane of the second tambour, indicated, though magnified, by the rise of the free end of the lever. The reverse movement of the membrane is attended by a fall of the lever. The first tambour is termed the receiving, the second the recording tambour (Figs. 344, 345)- Fig. 344. — A Receiving Tambour. Fig. 345. — A Recording T.\iibour. — (Marey.) yoo TEXT-BOOK OF PHYSIOLOGY iiiiiiiiiir''iiiM By enclosing an organ — e. g., kidney, spleen, arm, finger, etc. — in a rigid glass or metal vessel which at one point is in communication with a recording apparatus — e. g., (i) a piston provided with a lever (page 431); or (2) a tambour and lever (page 320); or (3) a mercurial manometer carrying a float and pen (page 305). The space between the part investigated and the vessel is filled with fluid. The varia- tions in volume of the organ cause a displacement of the fluid and give rise to a to-and-fro movement which is taken up and reproduced by the recording apparatus. The writing point may be (i) some form of pen carry- ing ink which records the movement on a white paper surface, or (2) a piece of metal, glass, or paper which records the movement on smoked paper or glass. The Recording Sur- face. — The surface which receives and records the movements of a pen or lever is usually that of a cylinder wliich is covered with glazed jjaper and coated with a thin layer of soot, obtained by passing the cylinder through the flame of a gas burner. The axis of the cylinder is supported by a metal frame- work. If the writing point of the lever be placed against the cylinder and a movement be imparted to it, a portion of the soot is rubbed off, leav- ing a white line behind. If the cyhnder be stationary, the rise and fall of the lever are Such a record shows only the extent of Fig. 346. — Kymograph. (Boruttau's, Pet zold, Leipzig.) recorded as a movement a vertical line. If the cylinder is traveling, however, at a uniform rate, the rise and fall of the lever are recorded in the form of a curve the width of the two arms of which will depend partly on the rapidity of the move- ment of the lever and partly on the rate of movement of the cylinder. The cylinder movement is initiated and maintained by clock-work or by the transmission of power by belting to a system of pulleys m connection with its axis. As the tracing is wave-like in form, the cylinder is frequently spoken of as a kymograph or wave recorder (Fig. 346). From the record thus obtained it is possible to determine not only the PHYSIOLOGIC APPARATUS. 701 -Signal Magnet. extent but also the duration, the form, and the rate of recurrence of any given movement. The Extent of a Movement. — As the lever not only takes up and repro- duces a movement, but at the same time magnifies it, it is essential that the degree of magnification be known, in order to determine the actual extent of the movement. The magnification of the lever is readily deter- mined by dividing the distance between the axis of the lever and its writing point by the distance between the axis and the point of attachment of the structure, and then dividing the height of the tracing by this quotient. The final quotient represents the extent of the movement. The Time Rela- tions of a Movement. — When recorded in the form of a curve, the duration of the ^^^- 247- entire movement, or of any one portion of it, can be determined by means of a time marking or chronographic apparatus, consisting of (i) a small signal magnet provided with a movable armature, to which is attached a writing style; (2) an automatic interrupter; and (3) an electric cell. The Signal Magnet. — The magnet (Fig. 347) is actuated by the electric current made and broken at regular and known intervals by an auto- matically-acting interrupter placed in the circuit. With each make and break of the circuit the armature and style move alternately downward and upward. The excursion of the style can be readily recorded on a travelmg sur- face. The character and num- ber of the interruptions per second will determine the character of the tracing. If they occur in a rhythmic manner, the tracing will be sinusoidal or wave-like in form. If the time of interruption is of short duration as compared with the time of closure of the circuit, the tracing will be a horizontal line with short vertical elevations at regular intervals. The Automatic Interrupter. — The circuit may be interrupted by virbating reeds, tuning-forks, metronomes, etc. A well-kno\Mi form of vibrat- ing reed is sho^^^l in Fig. 348, This consists of a metallic frame carrying a coil of wire in the center of which there is a core of soft iron. To the vertical part of the frame there is fastened the reed, the distal end of which is bent to dip into an adjustable mercury cup. When in circuit the current enters the coil, then flows into and through the frame and the reed to the Fig. 348. — Page's Vibrating Reed. ert's modification.) (Reich- 702 TEXT-BOOK OF PHYSIOLOGY. mercury, and thence back, to the cell. On the closure of the circuit and the magnetization of the iron core the reed is withdrawn from the mercury, the circuit broken, and the core demagnetized. The elasticity of the spring returns it to the mercury, when the circuit is again restored. The reed may be so constructed that it will be raised and lowered 50, 100, or 200 times a second. The armature of the signal magnet undergoes a corre- sponding number of elevations and depressions. If the reed vibrates 100 times in a second, the distance from crest to crest of the wave tracing will represent yl^ of a second. Interrupters of various kinds have been devised which make and break the circuit from i to 250 times a second. Moist Chamber. — In many experiments, it is necessary to keep the nerve or muscle preparation in a uniformly moist atmosphere. To secure Fig. 349. — Moist Chamber. this, a moist chamber is employed. This consists of a hard-rubber plat- form, supported by a piece of brass, which slides up and down a vertical rod, and which can be clamped at any height. By means of a short lever the vertical rod can be turned, carrying the platform from side to side. The rod is secured to a firm iron base. Six double bindmg posts for the attachment of wires pass through the platform. Near the side of the upper surface of the platform there rises a vertical rod, carrying a clamp for holding the femur of a nerve-muscle preparation, as well as a horizontal rod for supporting three pairs of non- polarizable electrodes. A groove around the outer edge of the platform receives a glass shade, which covers the whole. The air of the chamber is kept moist by placing in it pieces of blotting-paper saturated with water. PHYSIOLOGIC APPARATUS. 703 From the under surface of the platform there descends a rod, which, by means of a double bindmg screw, supports a horizontal rod, modified at one end to carry the delicate axis of a Ught stiff recording lever. The end of this lever is pointed, to enable it to write on a smoked glass or paper. Beneath the axis is a strip of brass, carr}-ing a screw, which gives support to the lever until the instant the contraction of the muscle begins. This screw, the after-loading screw, also enables the lever to be placed in a horizontal position. The portion of the lever near the axis is provided with a double hook, the lower portion of which serves for the attach- ment of the weight by which the muscle is counterpoised. In some experiments, as in the registration of a muscle contraction under varying conditions, it is necessary to give the lever mass by attaching weights directly beneath the muscle. This, however, introduces certain errors in the movements of the lever, which somewhat deform what would otherwise be the normal curve. If the weight be attached, not opposite to the muscle attachment, but close to the axis of the lever, the undesirable acceleration of the lever movement, during both contraction and relaxa- tion, is largely prevented. The lever may be a straw, a strip of celluloid or alummium. It should be as light as possible. The writmg point may be made of stiff paper, a piece of tinsel, glass or aluminium. It should have sufficient elasticity to keep it m contact with the cylmder during the excursion of the lever. The writing point should be placed as nearly parallel as possible to the surface of the cylinder. Normal Saline Solution. — To prevent drying and a loss of irrita- bihty the tissue vmder investigation should be kept moist with the normal saline solution (NaCl 0.6 per cent.). This solution very largely prevents either absorption or extraction of water from the tissues and thus retards chemic changes in their composition. Ringer's solution, largely used for the same purpose, is made by saturating 0.65 per cent. NaCl solution with calcium phosphate and then adding 2 c.c. of a i per cent, solution of potassium chlorid to each 100 c.c. The Galvanometer and Capillary Electrometer. — In the detection and investigation of the electric currents of muscles, nerves, and other tissues, the physiologist is limited to the galvanometer and capillary elec- trometer. The prmciple of the galvanometer is based on the fact that an electric current flowing through a wire parallel in direction with a magnetic needle will tend to set the needle at right angles to the direction of the current. The essential requisite of any galvanometer used for physiologic purposes is that it will respond quickly to the influence of extremely weak currents. This is realized by the use of small Hght needles, the adoption of the astatic system, or some similar device by which the directive mflu- ence of the earth's magnetism is eliminated, and the multiplication of the number of turns of the wire in the coils which surround the needle. The tangent galvanometer, or boussole, as constructed by Wiedemann, is the form most frequently employed in physiologic investigations (Fig. 350). It consists primarily of a thick copper cylinder, through which a tunnel has been bored. Within this tunnel is suspended a magnetized ring, just large enough to swing clear of the sides of the chamber. The object of 704 TEXT-BOOK OF PHYSIOLOGY making the magnet ring-shaped is to increase its strength in proportion to its size, and to get rid of the central inactive part. Connected with and passing upward from the magnetized ring through the copper cylinder is an aluminium rod, surmounted by a circular plane mirror. Above the mirror rises a glass tube, which carries on top, on an ebonite support, a little windlass, capable of being centered by three small screws. On the windlass is wound a single filament of silk, which passes down the tube and is attached to the mirror. The magnet can, by this contrivance, be raised or lowered and centered in the copper chamber. Deflections of the mirror from currents of air are prevented by inclosing it with a brass cover provided with a glass window. The coils are placed on each side of the copper chamber, and supported by a rod, on which they slide. By this arrangement they can be approximated until they meet and completely conceal the cy Un- der. By varying the position of the coils the mfluence of the current upon the needle can be increased or diminished. An advantage which this galvan- ometer possesses is the damping of the oscillation of the needle, so that it quickly comes to rest after deflec- tion. This is ac- complished by the development of induction currents in the copper cyl- mder, the direc- tion of which is opposite to that of the movement of the needle. The instrument, therefore, is aperiodic — that 'is to say, when the needle is influenced by a current it moves comparatively slowly until the maximum deflec- tion is reached, when it comes to rest without oscillations. When the circuit is broken the needle swings slowly back to zero, and again comes to rest without oscillations. Inasmuch as the needle is not astatic, it is rendered so by the use of an accessory magnet — the so-called Hauy's bar. This magnet, supported by a rod directed perpendicular to the coils, is placed in the magnetic meridian, horizontal to the needle, with its north pole pointing north. By sliding the magnet toward the needle the directive influence of the earth's magnetism is gradually diminished, and when it is reduced to a minimum the needle acquires its highest degree of instabihty. By means of a pulley Fig. 350. — Wiedemann's Boussole. PHYSIOLOGIC APPARATUS. 70s an angular movement can be imparted to the end of the accessory magnet in the direction of the magnetic meridian, which serves to keep the needle on the zero of the scale. The deflections of the needle are observed by means of an astronomic telescope, above which is placed a scale divided into centimeters and millimeters, and distant from the galvanometer about six or eight feet. As the numbers on the scale are reversed, they will be seen in the mirror in their natural position, and with the deflection of the needle the numbers will appear as if drawn across the mirror. The extent of the deflection is readily determined when the needle comes to rest. The reflecting galvanometer of Sir William Thompson is also used for the same purposes. The Capillary Electrometer. — Notwithstanding the extreme sensi- tiveness of the modem galvanometer, it has been found desirable, in the investigation of many physiologic processes, to possess some means which will respond even more promptly to slight variations in electromo- tive force. This has been realized in the con- struction by Lippmann of the capillary electro- meter. The principle of this apparatus rests upon the fact that the capillary constant or the surface-tension of mer- cury undergoes a change upon the passage of an electric current, in con- sequence of a polariza- tion by hydrogen taking place at its surface. If a capillary glass tube be filled with mercury and its lower end inserted into a solution of sul- phuric acid, and the former connected with the positive and the latter with the negative electrode, it will be observed, upon the passage of the current, that a definite movement of the mercury takes place, in the direction of the nega- tive electrode, in consequence of the diminution of its capillary constant or the tension of its surface in contact with the acid. As a reverse movement follows a cessation of the current, a series of oscillations will follow a rapid making and breaking of the current. If the direction of the current is reversed, the capillary constant is increased and the mercury ascends the tube toward the negative pole. From facts such as these Lippmann con- structed the capillary electrometer, a convenient modification of which Fig. 351. — Von Frey's Capillary Electrometer. 44 7o6 TEXT-BOOK OF PHYSIOLOGY. devised by M. v. Frey, is shown in Fig. 351. This consists of a glass tube, A , forty miUimeters in length, three millimeters in diameter, the lower end of which is drawn out to a fine capillary point. The tube is filled with mercury and its capillary point immersed in a 10 per cent, solution of sulphuric acid. The vessel containing the acid is filled to the extent of several millimeters with mercury also. The mercury in the tube is put in connection with a platinum wire (a), and the acid in the vessel with a second wire (b). When a constant current passes into the apparatus in the direction from b to a the mercury is pushed up the tube, and, upon the breaking of the cur- rent, it may or may not return to the zero-point. For the purpose of measuring in millimeters of mercury the pressure necessary to compensate this change in the capillar}^ constant produced by the electro-motive force of polarization, the apparatus is provided with a pressure-vessel, H, and a manometer, B. This electrometer can be applied to any microscope having a reversible stage. The oscillations of the mercury can then be observed with the microscope provided with an ocular micrometer (Fig. 352). The special advantage of the electrometer is, that it will respond instantly to any variation in the electro-motive force, and indi- cate a difference of potential, according to Lipp- mann's observation, as shght as the roi¥o' °^ ^ Daniell. These rapid oscillations can be recorded by photographic methods. In using either the galvanometer or the elec- trometer for detecting the existence of electric currents or differences of potential in living tissues, it is absolutely essential that non-polarizable electrodes be employed in connection with it Fig. 352. — Capillary Electrometer. R. Mercury in tube ; capillary tube. s. Sulphuric acid. q. Hg. B. Observer. M. Microscope. DISSECTION OF THE HIND-LEG OF THE FROG. Much of our knowledge of the physiologic properties of muscles and nerves has been derived from the study of the muscles and nerves of the cold-blooded animals, especially of the frog, for the reason that in these animals the tissues retain their vitahty under appropriate conditions for a considerable period of time after death or removal from the body. The muscles generally employed for experimental purposes are the gastroc- nemius, the sartorius, the semi-membranosus, the gracilis, and the hyo- glossus. The nerve generally employed is the sciatic. Both muscle and nerve may be studied independently of each other, or they may be studied together, as when in their usual physiologic relation. For this latter pur- pose the gastrocnemius muscle and sciatic nerve are employed, constituting the so-called "nerve-muscle preparation." For these, and many other reasons, the student should familiarize himself with the general anatomy of the frog, and especially with the anatomy of the posterior extremities. PHYSIOLOGIC APPARATUS. 707 Preparation of the Frog. — Destroy the frog by plunging a pin through the skin and soft tissues covering the space between the occipital bone and the first vertebra until the pomt is stopped by the vertebra. Turn the pin toward the head and push it into the brain cavity; move it from side to side and destroy the brain. Pass the pin into the spinal canal and destroy the spinal cord. With a stout pan- of scissors cut off the body behind the fore-Umbs. Remove the viscera and the abdominal walls. Draw the hmd-legs out of the skin. Place the legs on a glass plate, back uppermost, and moisten them freely with normal sahne solution. , ^ ve H.\\/- ec Fig. 353. — Leg Muscles of the Frog. Ventral Surface. — (Ecker.) Fig. 354. — Leg Muscles of the Frog. Dorsal Surface. — (Ecker.) Observe on the outer side of the dorsal surface of the thigh the following muscles (Figs. 353, 354). The triceps femoris (tr), made up of the rectus anticus (ra), the vastus extemus (ve), and the vastus intemus (vi), not seen from behind; on the inner side, the semi-membranosus (sm) and the rectus intemus mmor or gracihs (ri"). Between these two groups, note the biceps femoris (b). Above the thigh observe the gluteus (gl), the ileo- coccygeus (ci), and the pyriformis (p). In the leg observe the gastrocnemius (g) with its tendon (the tendo AchilUs), the tibiahs anticus (ta), and the peroneus (pe). Turn the frog on its back and note the muscles on the ventral surface of the thigh, the rectus intemus major (ri'), and minor (ri"), the adductor magnus (ad"), the sartorius (s), the adductor longus (ad'), and the vastus 7o8 TEXT-BOOK OF PHYSIOLOGY. intemus (vi). In the leg, in addition to those ahready seen from behind, note the tibiahs posticus (tp) and the extensor cruris (ec). Note in the abdominal cavity the three large spinal nerves, the seventh, eighth, and ninth. Dissection of the Sciatic Nerve. — The sciatic nerve is composed of the seventh, eighth, and ninth spinal nerves. After its emergence from the pelvic cavity, it passes down the thigh between the semi-membranosus and the biceps muscles, in company with the femoral blood-vessels. Below the knee it divides into the tibialis and peroneus nerves; the former sending branches into the gastrocnemius. In its course, the sciatic sends branches to the muscles of the entire leg. Carefully separate the biceps and semi-membranosus by tearing the connective tissue uniting them. The sciatic nerve and femoral blood- vessels come into view; with a bent glass rod gently separate the nerve from its surroundings from the knee to the thigh. Begin at the knee. In order to expose the nerve at the pelvis, it will be necessary to divide the pyriformis and the ileo-coccygeus muscles. Care must here be exercised, so as not to injure the nerve which Hes immediately beneath. Lift up the uro-style with the forceps and separate it from the last vertebra. With the scissors cut off the vertebral column above the seventh vertebra. Place the legs on the dorsal surface and then divide the seventh, eighth, and ninth vertebrae lengthwise. With the forceps hft up one lateral half of the vertebrae and free the nerve as far as the knee by dividing con- nective tissue and nerve branches. Be careful not to injure the nerv^e with scissors or forceps. The Nerve-muscle Preparation. — Divide the tendo x\chillis just below its fibro-cartilaginous thickening at the heel, and detach the gastrocnemius up to the knee. Cut through the tibio-fibular bone just below the knee-joint. Cut the femur transversely near its middle and remove the muscles from the lower end, carefully avoiding injury to the nerve. The completed preparation consists of the gastrocnemius muscle, the sciatic nerve, with half of the seventh, eighth, and ninth vertebrae and the lower half of the femur. INDEX. A. Abducens ner\'e, 558 Aberration, chromatic, 639 spheric, 639 Absorption, 221 • by epitheHum of villi, 234 of foods, 231 of lymph, 231 spectra of blood, 257 Accommodation of the eye, 630 convergence of eyes during, 635 force of, 634 mechanism of, 632 range, 634 Action currents of muscles, 94 of nerves, 124 reflex, 134 of medulla oblongata, 497 of spinal cord, 469 Adrenal bodies, 431 Agraphia, 527 Albuminoids, 36 Alcohol, effects of, 143 Alimentary canal, 155 principles, 139 Allantois, 678 Amnion,. 678^ Amylopsin, 205 Amyloses, 25 Animal body, structure of, 19 heat, 401 Ankle clonus, 475 jerk, 475 Aphasia, 526 ataxic, 527 amnesic, 527 Apnea, 394 Arterial circulation, 301 pressure, 316 Arteries, structure and properties of, 309 Articulate speech, 588 Asphyxia, 395 Association centers of cerebrum, 528 Astigmatism, 638 Auditory area, 523 nerve, 564 B. Basal ganglia, 490 Bile, 209 Bile, composition of, 211 mode of secretion, 212 physiologic action, 213 pigments, 212 salts, 211 Blastodermic membranes, 676 Blind spot, 642 Blood, 238 changes in, during respiration, 378 circulation of, 272 coagulation of, 240 chemistry of, 268 extravascular, 269 intravascular, 270 constituents of, 238 corpuscles, 245, 263, 266 defibrinated, 242 general composition of, 267 physical properties of, 239 pressure, 314 causes of, 322 methods of estimation, 316, 318 variations in, 326 quantity of, 267 velocity of, in arteries, 329 of, in capillaries, 331 of, in veins, 332 Burdach, column of, 466 Calorimeter, 406 Capillary blood-vessels, 312 functions of, 312 circulation, 337 electrometer, 689 Capsule, internal, 491 functions of, 501 Carbohydrates, 25 Carbon monoxid hemoglobin, 261 Cardiac cycle, 284 Cardio-accelerator center, 308 Cardio-inhibitor center, 307 Cardio-pulmonary vessels, 276 Caseinogen, 416 Caudate nucleus, 491 Cells, structure of, 43 manifestations of hfe by, 45 Central organs of the nerve system, 456 Cerebellar tract, 405 709 710 INDEX. Cerebellum, 530 functions of, 532 results of experimental lesions, 534 Cerebrum, 502 convolutions of, 504 fissures of, 502 functions of, 510 localization of function in, 513 motor area of the chimpanzee brain, motor area of the human bram, 524 motor area of the monkey's brain, sensor areas of the human bram, 521 sensor areas of the monkey's brain, 515 structure of the gray matter, 507 structure of the white matter, 509 Chemic composition of the body, 24 Chimpanzee brain, motor area of, 521 Cholesterin, 211 Chorda tympanum nerve, 561, 563 Chorion, 679 Chyle, 236 Ciliary movement, 103 muscle, 617 function of, 633 Circulation of blood, 272 forces concerned, 340 Clark's vesicular column, 455 Cochlea, 656 functions of, 664 Colostrum, 418 Commutator, 693 Complemental air, 373 Connective tissues, 51 conjugated proteids, 35 Corpora quadrigemina, 489 functions of, 498 striata, 490 functions of, 499 Corpus luteum, 670 Cranial nerves^ 538 Crura cerebri, 488 functions of, 498 Crystalline lens, 622 D. Daily ration of U. S. soldier, 153 Decidual membrane, 675 Defecation, 219 nerve mechanism of, 219 Deglutition, 172 nerve mechanism of, 179 Demarcation current, 93 Depressor nerve, 309, 571 Dextroses, 26 Diabetes, 425 Diaphragm, 357 Dietaries, 153 Digestion, 154 Dilatator pupillae muscle, 616 Direct cerebellar tract, 465 pyramidal tract, 464 Ductless glands, 427 , Ductus arteriosus, 683 venosus, 688 Dyspnea, 395 E. Electrodes, non-polarizable, 690 Electrotonic alterations in excitabihty of nerves, 126 current, 126 Electro tonus, 125 EncephaJon, 456 Encephalo-spinal fluid, 457 Endocardium, 276 Enterokinose, 208 Epididymis, 672 Epinephrin, 432 Epithelial tissues, functions of, 51 Equilibration, mechanism of, 535 Erepsin, 207 Erythrocytes, 245 Eupnea, 393 Eustachian tube, 654, 663 Excretion, 436 Expiratory forces and muscles, 367 Expired air, composition of, 396 Eye, cardinal points of, 625 dioptric apparatus of, 623 hds of, 652 muscles of, 648 physiologic anatomy of, 614 reduced, 62S schematic, 627 F. Facial nerve, 559 paralysis of, 562 Fallopian tube, 667 Fat, 29 absorption of, 235 digestion of, 207 emulsification of, 31 saponification of, 30 Feces, 218 Fecundation, 674 Fehling's solution, 27 Female organs of reproduction, 666 Fetal circulation, 681 membranes, 676, 678 structures, 676 Fibrin, 34 Fibrinogen, 244 Fillet, 484 INDEX. Follicle, Graafian, 666 Food, 136 animal, 149 cereal, 150 disposition of, 140 heat value of, 144 percentage composition of, 148 principles, 139 quantities required daily, 137 vegetable, 151 Forces aiding the movement of lymph and chyle, 236 Fovea, 61S, 620 Funiculus cuneatus, 4S4 gracilis, 4S4 G. Gall-bladder, 209 Galvanic current, effect of, on nerves, 125 Galvanometer, 703 Gangha, cephalic, 586 Gaseous exchange in lungs, 386 in tissues, 386 Gases of blood, relation of, 379 tension of, 383 Gastric digestion, 179 glands, 182 juice, 185 mode of secretion, 187 physiologic action of, 190 Glossophan'ngeal nerve, 566 Glycogen, 26, 423 Glycogenic function of the liver, 423 Gmelin's test for bile pigments, 212 GoU, columns of, 466 Gowers' antero-lateral tract, 465 Graafian follicle, 666 Graphic method, 699 Green vegetables, 152 H. Hairs, 453 Hearing, sense of, 653 Heart, 272 action of sympathetic nerve on, 305 of vagus nerve on, 305 blood supply, 292 beat, causation, 294 frequency of, 284 course of blood through, 277 cycle of, 284 inhibition of, 305 intracardiac pressure, 287 intraventricular pressure curve, 288 mechanics of, 282 muscle-fibers of, 280 negative pressure of, 291 nerve mechanism of, 301 orifices and valves, 278, 285 Heart, physiologic anatomy of, 272 sounds, 291 synchronism of the two sides, 287 work done by, 341 Heart-muscle, properties of, 297 Heat dissipation, 407 income, 404 relation to work, 410 rigor, 81 Helmholtz's theory of color perception, 650 Hemianopsia, 546 Hemoglobin, 253 absorption spectra, 257 compounds of, 260 Hemoglobinometer, Gowers', 256 Hemometer, v. Fleischl's, 256 Hering's theory of color perception, 650 Horopter, 645 Hypermetropia, 637 Hyperpnea, 394 Hypoglossal nerve, 575 Incus, 655 Induced currents, 696, 697 Inductorium, 695 Insalivation, 161 nerve mechanism of, 168 Inspiration, 364 movements of thorax, 359 muscles, 364 Insula, 507 Intercostal muscles, 357, 358 Internal capsule, 491 functions of, 501 secretion, 427 Intestinal digestion, 198 juice, 201 physiologic action of, 208 movements, 215 nerve mechanism of, 216 Intracardiac pressure, 287 Intrapulmonary pressure, 360 Intrathoracic pressure, 360 Intravascular coagulation, 270 Invertin, 208 Iris, 615 functions of, 635 nerve mechanism of, 550, 636 Iron of the body, 41, 142 Irritabihty of muscles, 72 of nerves, 117 Island of Langerhans, 203 of Reil, 507 Isometric myogram, 83 Isotonic myogram, 79 Isthmus of encephaian, 486 functions of, 492 712 INDEX. Jacobsen's nerve, 567 Joints, 60 classification of, 61 K. Kidney, 440 histology of, 440 Knee-jerk, 475 Kymograph, 700 L. Labyrinth of ear, 656 Lacrimal glands, 636 Lactation, 416, 684 Lacteals, 236 Language, 525 Large intestine, 216 Larynx, 588 nerve mechanism of, 598 structure of, 589 Lateral columns of the spinal cord, 465 Law of contraction, 128 Lemniscus, 484 Lens, crystalhne, 605 Lenticular nucleus, 491 Leukocytes, 263 classification of, 265 Levers, 97 Limbic lobe, 506 Liver, 209, 419 formation of urea in, 426 functions of, 421 production of glycogen, 423 secretion of bile, 422 Localization of functions in cerebrum, 513 Lungs, structure of the, 352 Lymph, 227 absorption of, 231 composition of, 228 functions of, 230 movement of, 236 production of, 228 properties of, 227 Lymph-glands, 224 Lymph-vessels, 222 Lymphocytes, 227, 265 M. Macula lutea, 618 Malleus, 655 Mammary gland, 415 Mastication, 156 Mastication, muscles of, 158 nerve mechanism of, 160 Meats, composition of, 149 Medulla oblongata, 483 reflex activities of, 497 Meibomian glands, 672 Membrana tympani, 654 functions of, 661 Menstruation, 670 Metabohsm on proteid diet, 148 on fat and carbohydrate diet, 148 Methemoglobin, 261 Migration of leukocytes, 338 Milk, 149, 416 composition of, 146, 416 mechanism of secretion, 417 modification of respiratory rhythm, 393 Moist chamber. 702 Mosso's plethysmograph, 336 spygmomanometer, 318 Motor area of chimpanzee brain, 521 of human brain, 522 of monkey brain, 515 oculi nerve, 531 Mouth digestion, 156 Movements of the eyeball, 646 of the intestines, 215 of the lungs, 369 of the stomach, 194 Muscle action currents, 94 contraction, 77 chemic phenomena of, 88 electric phenomena of, 91 graphic record of, 78 modifying influences of, 80 physical phenomena of, 75 rigor mortis, 89 tetanus, 87 thermic phenomena of, 90 electric currents from, 91 electric currents, negative variation of, 93 energy, source of, 89 fatigue, 82 groups, special action of, 96 sense, 608 sound, 88 spindle, 608 stimuli, 73 tissue, 65 chemic composition of, 69 elasticity, 70, 76 histology of, 66, 99 irritability, 72 physical properties of, 70 physiologic properties of, 72 tonicity, 71 Myopia, 637 Myosinogen, 33, 69 Myxedema, 427 INDEX. 713 N. Nerve, abducens, 558 auditory, 564 facial, 559 glossopharyngeal. 566 hypoglossal, 575 impulse, 119 irritability, 117 motor oculi, 547 olfactory, 541 optic, 543 patheticus, 552 pneumogastric, 568 spinal accessory, 573 stimuli, 118 tissue, histology of, 105 trigeminal, 553 Nerve-muscle preparation, 120 Nerve system, functions of, 45S Nerves, chemic composition and meta- bolism of. III classification of, 116 degeneration of, 115 development of, 114 effects of galvanic current on, 125 electric currents of, 121 electric currents of, negative varia- tion of, 122 electric excitation of, 121 electric phenomena of, 121 action currents, 124 diphasic action currents, 124 peripheral endings of, 112 physiologic properties of, 117 pilo-motor, 454 polar stimulation of, 128, 130 relation of, to central nerve system, III stimuli of, 118 Neuron, 105 Nicotin, actions of, 216, 567 Nucleus caudatus, 491 cuneatus, 484 graciUs, 484 lenticularis, 491 Nutrition of the embryo, 679 O. Oculo-motor nerve, 531 Ohm's law, 672 Olein, 30 Olfactory nen^e, 525 Oncograph, 447 Oncometer, 447 Operculum, 507 Ophthalmic ganglion, 585 Optic constants, 623 thalamus, 491 functions of, 500 Optogram, 645 Organ of Corti, 658 Osazones, 29 Ossicles of ear, 656, 660 Otic ganglion, 586 Ovary, 666 Ovulation, 669 Ovum, 667 Oxygen in blood, 381 in tissues, 385 quantity absorbed daily, 391 Oxyhemoglobin, 261 Pacinian corpuscle, 603 Palmitin, 30 Pancreas, 201 Pancreatic juice, 203 physiologic action of, 205 Partial pressure of gases, 380 Parturition, 683 Pathetic nerve, 536 Pepsin, 186 Peptones, 191 Perspiration, 450 Peripheral organs of the nerve system, 1 10 Petrosal nerves, 561, 562 Pettenkofer-Voit respiration apparatus, 388 Pexin, 186 Phagocytosis, 266 Phloridzin diabetes, 426 Phonation, 588 mechanism of, 595 Pilo-motor nerves, 454 Pituitary body, 430 Placenta, 680 Plasma of blood, composition of, 242 Pleura, 359 Pneumatograph, 373 Pneumogastric nerve, 568 Pneumograph, 371 Polar stimulation, 128 of human nerves, 130 Pons varolii, 486 functions of, 492 Portal vein, 224 Postures, 98 Presbyopia, 636 Prosecretion, 204 Proteids, 31 color tests for, 38 Protoplasm, properties of, 46 Ptyalin, 168 Pulmonary vascular apparatus, 339 ventilation, 378 Pulse, 332 frequency, 333 wave, velocity of, 333 714 INDEX. Punctum proximum, 63.). remotum, 634 Pyramidal tracts of spinal cord, 464, 465 R. Reaction of degeneration, 133 Red corpuscles, 245 chemic composition of, 253 function of, 251 life history of, 252 number of, 247 of vertebrated animals, 250 Reduced hemoglobin, 261 Reflex action, 134, 473 laws of, 473 Refractory period of the heart, 300 Regnault's and Reisset's respiration ap- paratus, 390 Relation of gases in the blood, 379 Rennin, 186 Reproduction, 666 Reserve air, 375 Residual air, 375 Respiration, 350 changes in composition of air during, 376 changes in composition of blood, 378 changes in tissues, 384 chemistry of, 375 complemental air, 373 frequency of, 371 mechanism of gaseous exchange, 386 nerve mechanism of, 396 Respiration, total respiratory exchange, 387 volumes of air breathed, 372 Respiratory apparatus, 350 movements, 359 effects of, on arterial pressure, 400 effects of, on the flow of blood through the thoracic vessel, 399 of upper air passages, 370 pressures, 360 quotient, 377, 391 rhythm, 371 sounds, 374 types, 370 Retina, 617 functions of, 641 Retinal image, 623 size of, 629 Rheocord, 692 Rigor mortis 89 Rima glottidis, 589 respiratoria, 594 vocalis, 594 Routes of the absorbed food, 237 Saccharose, 28 Saliva, 164 physiologic action of, 166 Salivary glands, 161 histologic changes in duiing secretion, 165 nerve mechanism of, 170 Sebaceous glands, 438 Sebum, 454 Secretin, 204 Secretion, 411 internal, in Semen, 673 Semicircular canals, 557 Sensor areas of human brain, 521 of monkey brain, 515 Setchenow's center, 477 Sight, sense of, 614 Skeleton, physiology of, 60 Skin, 451 nerve endings in, 603 Smell, sense of, 612 Spectroscope, 258 Speech, 598 Spermatozoa, 673 Spheno-palatine ganglion, 586 Sphygmograph, 334 Sphygmomanometer, 318 Spinal accessory nerve, 573 cord, 459 encephalo-spinal conduction, 479 functions of, 468 as a conductor, 477 as an independent center, 468 nerve fibers of, 463 classification of, 463 reflex actions of, 470 reflex irritability of, 475 relation of spinal nerves to, 466 spino-encephalic conduction, 478 structure of gray matter, 460 structure of white matter, 463 tracts of, 464 Spirometer, 372 Splanchnic nerves, 584 Spleen, 432 functions of, 433 Stanton's sphygmomanometer, 319 Stapes, 655 Starch, digestion of. 167 Starvation, 145 Stearin, 30 Stereognostic area, 524 Stomach, movements of, 194 nerve mechanism of, 197 Suprarenal capsules, 431 Sweat-glands, 452 INDEX. 715 Sympathetic nerve system, 577 cephalic ganglia of, 585 functions of the cervical portion, 583 functions of the lumbo- sacral portions, 585 functions of the thoracic portion, 584 Taste buds, 610 nerve of, 610 sense of, 610 Tears, 6^2 Teeth, 156 Tegmentum, 48S Temperature of body, 402 sense, 606 Tension of gases in blood, 383 tissues, 386 Tensor tympani muscle, 655 functions of, 652 Testicles, 671 Tetanus, 87 Thoracic duct, 227 Thorax, 356 dynamic condition of, 362 mechanic movements of, 359 static condition of, 360 Thyroid gland, 427 functions of, 428 Tidal air, 373 Tongue, 610 Total carbon-dioxid exhaled, 391 oxygen absorbed, 391 respiratory exchange, 387 Touch, sense of, 602 Trachea, 352 Tracts of spinal cord, 465 Trigeminal nerve, 553 Trypsin, 206 Tiirck, column of, 464 Tympanum, 653 U. Umbihcal cord, 679 Upper air-passages, respiratory move- ments of, 370 Urea, 437 seat of formation, 426 Uric acid, 438 Urine, 436 composition of, 437 mechanism of secretion, 444 influence of blood composi- tion, 449 influenceof nerve system,448 relation of blood-pressure to, 445 Urination, 449 Urination, nerve mechanism of, 450 Uterus, 668 Vagus nerve, 568 influence on heart, 305 Valves of heart, 285 Vasa deferentia, 672 Vascular apparatus, 309 nerve mechanism of, 342 glands, 427 Vaso-motor center, 346 nerves, 342 Veins, 313 Velocity of blood, 3 2 8, 332 Venous circulation, 339 Vertebral column, 63 Vesiculae seminales, 672 Villi, 232 functions of, 234 Visceral muscle, 99 functions of, 102 properties of, 100 Vision, 614 accommodation, 630 astigmatism, 638 binocular, 644 color perception, 648 functions of retina, 641 hypermetropia, 637 myopia, 637 presbyopia, 636 Visual angle, 629 Vital capacity of lungs, 373 Vocal bands, 592 sounds, 596 Voice and speech, 596 Volume pulse, 336 W. Walking, 99 Wallerian degeneration, 116 Water, amount of, in the body, 37 Watery vapor in breath, 377 Wernicke's pupillary reaction, 55 i White blood-corpuscles, 263 classification of, 265 function of, 266 migration of, 338 origin of, 266 Wrisberg, nerve of, 561 Yellow spot, 618 Z. Zona pellucida, 676 Zymogen, 168, 186 pepsinogen, 186 ptj'alogen, 168 trv'psinogen, 208 COLUMBIA UNIVERSITY This book is due on the date indicated below, or at the expiration of a definite period after the date of borrowing, as provided by the rules of the Library or by special ar- rangement with the Librarian in charge. DATE BORROWED DATE DUE DATE BORROWED DATE DUE C2S<63a)MSO n QP34 383 1905 -.{ ^: -