Columbia ^nitiersiitp inttjeCitpofi^etoiSorfe ^'^'^ft COLLEGE OF PHYSICIANS AND SURGEONS Reference Library Given by t^x-zv:u-^^^ f'^zsi fjzs TREATISE ON HUMAN PHYSIOLOGY. FOR THE USE OF STUDENTS AND PRACTITIONERS OF MEDICINE. BY HENRY C. CHAPMAN, M.D., PnOFESSOR OF INSTITUTES OF MEDICINE AND MEDICAL JURISPRUDENCE IN JEFFERSON MEDICAL COLLEGE PHILADELPHIA ; CHAIRMAN, BOARD OF CURATORS, ACADEMY OF NATURAL SCIENCES OF PHILA- DELPHIA ; MEMBER OF THE COLLECJE OF PHYSICIANS, OF THE ZOOLOGICAL SOCIETY, PHILADELPHIA ; OF THE AMERICAN PHILOSOPHICAL SOCIETY, AND OF THE AMERICAN PHYSIOLOGICAL SOCIETY. SECOND EDITION. ILLUSTRATED WITH 595 ENGRAVINGS. PHILADELPHIA: LEA BROTHERS & CO 189 9. Entered according to Act of Congress in the year 1899, by LEA BROTHERS & CO., In the C)ffice of the Librarian of Congress at Washington. All riglits reserved. C3G A TO MY WIFE THIS WORK IS AFFECTIOXATELY DEDICATED AS A SMALL ACKNOWLEDGMEXT OF THE IXTEKEST EVIXCED AND ENCOURAGEMENT EXTENDED IN ITS COMPLETION, BY THE AUTHOR. Digitized by the Internet Archive in 2010 with funding from Columbia University Libraries http://www.archive.org/details/treatiseonhumanpOOchap PREFACE TO SECOND EDITION. In submitting a revision of his Treatise on Human Physiology to the profession, the author may say that its fundamental plan remains unchanged, as continued experience in teaching confirms his belief in its adaptation to the needs of both students and prac- titioners, two classes whose demarcation is really artificial. Aside from its plan the book has been recast. The recent ad- vances in our knowledge of Physiology, especially of Physiological Chemistry and of functions of the Xervous System, have necessi- tated the rewriting of a great part of the work and the addition of new illustrations. The author has endeavored to accommodate these important additions without an increase in tlie number of pages, by the most careful condensation and elimination of less important matter, and he trusts that his efforts to make the work more than ever useful as a text-book have not been without V)ene- ficial results. It need hardly be said that the additions made here and there to the bibliography (ahvays obtained from the original sources cpioted) represent but a selected part of the vast Physiological literature that has appeared in the last few years, but it is hoped that no important additions to our knowledge of the subject have been omitted. HEXRY C. CHAPMAX. Philadelphia, April, 1899. PREFACE TO FIRST EDITIOX. To those familiar with the many excellent German, French, and English treatises upon Physiology, it may appear strange that the author should feel it incumbent upon himself to offer one more con- tribution upon such a well-worn theme. The experience, however, of the past eight years, as Professor of the Institutes of Medicine or Physiology in the Jefferson Medical College of Philadelphia, has convinced the author that there is a want felt by students and prac- titioners of medicine for a systematic work, representing the exist- ing state of physiology and its methods of investigation, and based upon comparative and pathological anatomy, clinical medicine, physics, and chemistry, as well as upon experimental research. It is the hope of the author that the present work, embodying essen- tially liis teaching, will not only supply such a want, but will facili- tate and stimulate the study of this most important branch, the institutes, that is to say, the foundation of all rational medicine. The author takes much pleasure in here expressing his acknowl- edgments to Dr. A. P. Brubaker, Demonstrator of Physiology in the Jefferson ]\Iedical College, for the assistance rendered in the performance of the experimental part of the work ; to Arthur E. Brown, Esq., Superintendent of the Zoological Garden, of Philadel- phia, for the many facilities and courtesies extended in the dissec- tion of the rare animals that have died at the Garden, the results of which are frequently made use of in the work, and to Dr. I^awrence Wolff, Demonstrator of Chemistry in the Jefferson Medical College, for the favor of seeing the work through the press. HEXRY C. CHAPMAN. CONTENTS. PAGE Introduction 17-2'; CHAPTER I. GENERAL STRUCTUKE OF THE BODY, PHYSICALLY AND CHEMICALLY. Organs — Tissues — Cells — Pi-oximate Principles of Inorganic Origin — Water — Sodium ("hloride — Potassium Chloride — Cal- cium Phosphate — Calcium Carbonate — Sodium Cai-bouate , 28-i2 CHAPTER II. PROXIMATE PRINCIPLES OF ORGANIC ORIGIN. Carbohydrates — Sugars — Fats ....... -13-56 CHAPTER III. PROXIMATE PRINCIPLES OF THE THIRD CLASS. Proteids — Albuminoids — Amides — Amines — Alcohols — Ferments 57-68 CHAPTER IV. FOOD. Use of Food — Kinds of Food — ^Food Stuffs — Hunger and Thirst — Mixed Diet — Tea and Cofltee — Tobacco— Alcohol— Distilled Liquors — Wine — Malt Lic^uors ...... 69-82 CHAPTER Y. DIGESTION. The Teeth— Mastication— Enamel— Cement— Tooth Pulp- Maxillary Bones and Temporo-maxillary Articulation — In- termaxillary Bone — Muscles of Mastication . . . 83-94 CHAPTER YI. DIGESTION.— ( Continued. ) INSALIYATION AND DEGLlTlTloN. Insalivation — De2;lutition ....... 95-105 10 CONTENTS. CHAPTER VII. DIG ESTION.— ( ttH/(/«(e(/. ) GASTRIC DIGESTION. Functiou of tlie Stomaeli — Experiments on Digestion — Mucous Membrane of Stomach — Gastric Glands — Gastric Juice — Composition of Gastric Juice — Action of Gastric Juice Upon Food lOG- 125 CHAPTER VIII. DIGESTION. — (ro»//»»r'(/.) INTESTINAL DIGESTION. INTESTINAL JUICE. PANCREATIC JUICE. FUNC- TIONS OF LIVER. GLYCOGEN. BILE. FECES. DEFECATION. Intestinal Juice — Pancreatic Juice — Internal Secretion of Pan- creas—The Bile — (Hycogen— The Large Intestine — The Con- tents of the Large Intestine — Defecation — Resume of Diges- tion 126-158 CHAPTER IX. ABSORPTION. Lacteals, Thoracic Duct, etc.— Lymphatic System— Lymph and Chyle— Structure of Villi— Chyle— Venous Absorption — Osmosis — Absorjttion l>y Stomach and Rectum — Conditions favoring Absorpti(m — Resume of Absorption . . . 159-178 CHAPTER X. THE BLOOD, Physical Characters of the Blood — Quantity of Blood in Human Body — Red Corpuscles — Diameter of Red Blood Corpuscles in Vertebrates 17y-190> CHAPTER XI. THE BLO( n).—(nmtinue(L ) White Corpuscles— Structure of Solitary and Lymphatic Glands —Structure of Spleen— Production of White Corpuscles — Thyroid Gland — Internal Secretion of Thyroid Gland —Thy- mus Gland- Blood Plates 191-200 CHAPTER XII. THE ISLOOD.— (rW//////»r-/.) Coagulaticm of the Blood, Theories of 201-207 CHAPTER XIII. T H i; B \A)()D.—{Omtiii iicd. ) Comijosition of tlie Blood— Haemoglobin — Spectrum Analysis- Gases of Blood— Salts of Blood — Composition of Corpuscles -Transfusion 208-22& CONTENTS. 11 GET AFTER XI Y. CIRCL'LATIOX OF THE BLOOD. The Heart — Duration of Movements of Heart .... 230-243 CHAPTEK XY. CIRCrLATION OF THE BLOOD.— (r'o/(//H««rf.) THE HEART. Cardiac Imi)nlse — Cardiograph — \York Done by the Heart — Cause of Sounds of Heart — Conditions Influencing Action of Heart — Cause of Heart's Contraction — Stimuhis to Heait. 244-258 CHAPTER XVI. CTRCULATIOX OF THE BU)0\).—{Oynt!nii,'f1.) THE ARTERIES. Flow of Liquids through Tubes — Elasticity and Contractility of Arteries — Dilatation of Arteries — Sphygmograph . . 259-274 CHAPTER XVII. CIRCULATION OF THE m.OOD.— {Continued.) PRESSURE AND VELOCITY OF THE BLOOD IN THE ARTERIES. Pressure of Liquids — Hydrostatic Paradox — Hydrostatic Bel- lows — Blood Pressure — Hannodynamonieter — Arterial Pres- sure — Aortic Pressure — Kymograph — Blood Pressure in Turtle and Frog — Manometers — Spring Kymograph — Htemodromometer — Stromuhr — Hfemodromograph — Traces of Pressure and Velocity of Blood ..... 275-310 CHAPTER XVIII. CIRCULATION OF THE BLOOD.— (Cr/;«/fHwrf.) THE CAPILLARIES. Structure of Capillaries — Capacity of Capillary System — Phe- nomena of Cajiillary Circulation — Velocity of Blood in Capillaries — Plethysmograph — Pressure of Blood in Capillar- ies — Capillary Force ........ 311-325 CHAPTER XIX. CIRCULATION OF THE mA)0\y.—{Cody, and which the future Avill, no doubt, show to be susceptible of even a wider application than is made of it at present, for the embryo of animals, with the exce])tion of the loAvest, consists of three germinal layers, of which the upper one gives rise to the epidermis and central nervous system, the lower one to th(> epithelium of the alimentary canal and its ap- pendages, the middle one to bone, muscle, vessel, etc. These germinal layers, even at the start, can be readily distinguished, the cells composing them being diflerently affected by physical and chemical agents. Some of the lower animals, for example the hydrozoa, never get beyond this layered stage, the inner layer acting as stomach, the outer as skin. If a tissue in the adult can 'Bernard: Pliysiolofjio Exjierimentale, Umw ii., ]>. 179. Paris, ISoCJ. ^('iivicr: Mcinoires Pour Servir a I'Histoire et a 1' Anatomic des Mollusquez. Paris, 1.S17. Mcnioire sur le (ienre Doi'is, p. 16. INTRODUCTWX. 23 be shown to have been derived from one of these layers in its embrvonic stage its function could almost be predicted. Indeed the whole modern pathological histology is an application of this view\ The older pathologists, like ^lorgagni/ confined themselves to the study of the organs as affected by disease. Bichat,' in investigating the tissues of which the organs are com- posed, created histology ; Schleiden ^ first showed that vegetable tissues consist of cells, and Schwann,* following his lead, applied Schleiden's view to the tissues of animals. The embryologists, Reichert,^ Kolliker,^ Remak,'' etc., then proved that the cells com- posing the tissues were the modified cells of the original mulberry mass of cells into which the Q^g or primitive cell segments. The obvious corollary of these generalizations followed when Virchow,^ Billroth,'' Paget,^" Rindfleisch,'^ etc., shoAved that pathological structures were the still further modified cells composing the tissues of the organ, and that morbid growths were really physiological ones, exhibiting themselves under conditions otherwise than nor- mal ; while with the development of teratology, through the works of Geoffrey St. Hilaire,^^ and others, the explanation of the produc- tion of monsters lusus naturae became possible. That which is pathological at one stage of growth was shown to be physiological at another ; that which is normal in one animal is aljnormal in another. Gradually the strict demarcation between physiology and pathology has been broken do Am, and, with the flision of the two studies, a rational pathology and rational treatment are being slowly developed. Notwithstanding the importance of a knoAvledge of general physics and chemistry, anatomy, embryology, and pathology in the study of the functions of the human body, nevertheless, the study of human physiology is often almost entirely based on experiments made upon living animals : the study of the circulation and respira- tion by means of the graphic method, the making of gastric fistulte, the introduction into the system of an animal of various substances, toxic and narcotic, the removal of various parts of the nervous sys- tem, are examples of the kind of work often exclusively done in physiological laboratories. The student of physiology, however, should not confine himself to the experimental methods, however invaluable and indispensable they may l)e as a means of investigation, but should avail himself also, as far as possible, of the other methods of research just referred to, studying the subject from all the different points of view possible ' De Sedibus Morbonim, 1761. ^ Anatomie (ienerale. 18 Surgical Patholog}-, 1870. " PathologLsche Anat(jmie, 1873. '^HLstoire Generale et Particuliere des Anomalies de 1' organization, 1837. 24 INTRODUCTIOX. and comparing the resnlts obtained by the various methods made use of. As objections are often made to the experimental study of physi- ology, it will not, it is hoped, be considered superfluous if we, for a moment, consider some of the most important of those usually advanced. It is often urged as an objection to a vivisection, that the pain inflicted so disturbs the normal condition that any result as to the function of a part determined in this way is valueless ; the suiferino; entailed vitiatino; anv conclusion as to the healthv function of the part examined. This objection is, of course, not made if anaesthetics are used. There are, however, experiments performed in which it is necessary that the animal should be in the full pos- session of its foculties and which, from the conditions of the inves- tigations, make the use of anaesthetics impossible. As regards such investigations it may be said, without doubt, that animals sufl'er far less from the pain inflicted in a vivisection than man does from a similar wound due to an accident or the knife of the surgeon. This is due to several causes ; the animal is in ignorance of what is going to be done, forgets the operation almost immediately, his nervous organization is less susceptible than tliat of the human being, and his wounds heal up more quickly. The influence of pain, though less in an animal than man, must nevertheless be always taken into consideration. Whenever the vivisection is performed without an anaesthetic, the physiologist ought not to draw any conclusion from the experiment until the animal has had time to recover from the effects of the shock, hemorrliage, etc., and has so far returned to his normal condition that the influence of pain, if any still exists, is so small in amount that it cannot be considered as interfering with the func- tion of the structure examined. It is evident, therefore, that if the physiologist had no higher motive, selfishness would induce him to be as merciful as possible and to eliminate, so far as he is able, pain, as a possible source of fallac}- in his conclusions. The animal, both during and after vivisection, should be treated just as a patient undergoing an operation would be by a wise sur- geon ; the object in both cases being to restore, as rapidly as pos- sible, the physiological conditions — the conditions of health. As an illustration of what has just been said, as regards the amount of permanent disturbance produced in an animal by a vivisection, it may be mentioned that Blondlot's jiointer bitch, in which a gastric fistula had been made, was used, after her recovery, by her master for eight years in the field for hunting purposes, and in the labora- tory for obtaining gastric juice, and that during that period the dog had two litters of pups. The Canadiau, St. ]Martin, on whom the gastric fistula was caused by a gunshot wound, producing far more dangerous effects than the vivisection just referred to, lived to be eighty-four years old, enjoyed good health all his life, married and had children, per- INTRODUCTION. 25 formed the duties of a servant, and Mas during this time frequently of inestimable value to science, as affording Dr. Beaumont and others the rare opportunity of observing gastric digestion in man under the most favorable circumstances. One might as well object that the pain suffered by St. Martin, after the explosion of the gun, vitiated the conclusions drawn by Beaumont, as to object to the conclusions of Blondlot because the making of a gastric fistula in a dog involved the giving of the ani- mal pain. A far more important objection than that just referred to is that, as animals differ very much in their organization, con- clusions drawn from experiments made upon one kind of an animal cannot be applied to another kind ; digestion in a dog, for example, not being: exactlv the same as in a man. It is undoubtedly true that, while frogs, turtles, pigeons, rabbits, dogs, horses, etc., agree anatomically in many respects with each other and man, they disagree to such an extent tliat tlie result of experiments made upon one of these animals is often utterly inap- plicable to the other, and entirely worthless as applied to man. In- deed, the most striking differences in the effect of certain substances are observed even in closely allied animals, varieties of the same species. Thus the black rhinoceros feeds upon the euphorbia, which poisons the white species ; goats and lambs avoid most of the so- lanaceous plants ; the ox and the rabbit will eat belladonna ; the goat, the hemlock ; the horse, aconite. Such differences should be always taken into consideration when the results of a vivisection upon one animal are to be applied to the determination of the function of a structure in another. It must be always proved that the structure and functions compared are homologous. Further, a careful post-mortem examination should be always made after the vivisection, in order to learn exactly what has been done, to show that no structure has been involved which would modify the results except the one examined. It is the neg- lect of such precautions, the indifference to the infliction of pain, the comparing of utterly milike conditions, the absence of the test of post-mortem examination, the want of controlling experiments, and of comparison of the results obtained with the facts of pathol- ogy and comparative anatomy that has brought vivisection into the disrepute in which it is held at the present day by many even edu- cated persons. Crude generalizations, based upon imperfect ex- periments ])erformed upon animals illogically applied to man, have made even medical men doubt altogether of the efficiency of this method, and account for their sympathizing Avith the Avell-meaning, no doubt, but ill-judged efforts to suppress experimental investiga- tion altogether ; and yet if vivisection should be banished from the laboratory, the physiologist would be deprived of his most fertile methods of research. The history of physiology proves not only the importance of vivisection, but its indispensability as a means of present research. Indeed, it is no exaggeration to say that there 26 IXTEODVCTIOX. is not au organ in the animal body Avhose functions have not been learned, in part at least, by vivisections. Let us illustrate this statement by a few examples. Consider the history of the circulation of the blood, and we shall see that every important advance made in a knowledge of the subject was due to a vivisection. Thus, Galen demonstrated by vivisection that the artery contained blood and not air, as its et^^uology would indicate. It was by a vivisection that Harvey proved that the blood flowed from the heart to the periphery through the arteries, and from the periphery back to the heart through the veins. Finally, it was through a vivisection that Malpighi saw, for the first time, the blood actually flowing from the arteries into the veins through the intermediate vessels, the capillaries. One of the most important discoveries ever made in physiology, that of the functions of the roots of the spinal nerves, that the anterior are motor and the posterior are sensory, was demonstrated by Majendie upon a living animal. The influence of the nervous system upon the heart, so far as is known, has been en- tirely learned by the experimental investigations made upon ani- mals by the AVebers, Yon Bezold, Ludwig, Cyon, etc. The beau- tiful investigations of Bernard upon the salivary glands, the l)ancreas, the liver, by means of vivisections, have demonstrated certain peculiarities in reference to the secretion of these organs, that could never have been learned by any other method. By means of vivisection Brown-Sequard showed the influence of the sympathetic nerve in diminishing the calibre of the ])lood vessels, and thence discovered the vasomotor nerves, by which the distri- bution of the l:)lood to the tissues is regulated. It is needless to multiply examples of the imjjortance of vivisection as a means of research, as nearly every chapter in this work will afford such. It must not be forgotten, however, that vivisection is but one means of physiological research, and that however important may be the results obtained by it, the latter, as already mentioned, should be always compared with such facts of comparative anatomy and pathology as have a bearing upon the function investigated, so that so far as possil^le all sources of fallacy may 1)e eliminated. To those fjimiliar with the history of medicine any argument to prove the importance of the study of physiology would be super- fluous. Physiology has always been, and is still, the corner- stone of medicine. The doctrines of Hippocrates, Galen, Syden- ham, Bocrhaave, Hiniter, and Virchow, reflect as a mirror the physiology of the day. It is self-evident that to understand dis- ease and its cure one must first understand health. The study of physiology must precede that of pathology and therapeutics. Hand in hand they advance together, the progress of the one depending ujion that of the other. There is no better illustration of the truth of this view of the dependence of pathology and therapeutics upon physiology than ophthalmic medicine, the most developed and fin- IXTB OD LX'TIOX. 2 7 ished of all Ijrauclies of medicine, whose present perfected condi- tion is entirely due to the comparatively thorough understanding of the structure and function of the healthy eye. On the other hand, diseases, like those of the nervous system, are in a proportionally backward condition owing to the imperfect knowledge of the normal anatomy and physiology of the parts in- volved. Having deiined the subject of physiology, considered the methods by which it is studied, and its importance to 'medicine, it only re- mains now in conclusion to indicate, generally, the order in which the study will be pursued, and here nature ^^'ill be our guide. Our first sensations are those of hunoer and thirst — hence the taking" of food. We "vdll, therefore, after describing the general physical and chemical structure of the body, begin Avitli the study of digestion and absorption, the elaboration of the food into the blood, and its circulation will be then described, the consideration of excretion, animal heat, completing the study of nntrition. But man is more than a vegetable, he feels, thinks, moves. Im- pressions of the outer world made upon his nervous system awaken in him consciousness, the inner world of mind. Through his nervous system man not only becomes aware of the existence of an environment, but adjusts his actions with reference to it. Finally, though the individual perishes in the reproduction of his kind, the race, temporarily at least, survives, hence the study of development. We will begin, therefore, with the study of nutritir)n, consider next the nervous system, concluding with an account of reproduction. CHAPTER I. GENERAL STRUCTURE OF THE BODY, PHYSICALLY AND CHEMICALLY. Before taking up the study of tlio functions, specifically, it will be well to consider, from a general point of view, of what the human body consists, physically and chemically speaking, to obtain some general knowledge of its organization, of which the functions are the living expression. As is known to every one, the human body, like that of a do- mestic animal, is made up of skin, muscles, bone ; of various viscera, such as the heart, lungs, liver, stomach ; of nerves, arteries, etc. The old anatomists busied themselves almost entirely with the description of such organs, their number, size, color, relative posi- tion, etc. This kind of study may be said to have culminated in Cuvier, who, as regards the exactness, extent, and variety of his knowledge, stands without a rival as an anatomist. If, however, any one organ is examined somewhat closely, it will be found to be far from homogeneous. Thus the stomach consists of several tissues, mucous, fibrous, muscular, etc.; the heart, of muscular, connective, adipose, nervous tissue, etc. Such tissues, combined in greater or less proportions, make up the different organs of which the body is composed ; the same tissue, for example, the connective, being found in different organs, just as the substance wood may be applied to making a chair, sofa, bed, or bookcase furnishing a room. The investigation of the tissues, the creation of, histology, is due to the genius of Bichat. If now" any tissue be studied in detail, it (;an be still further resolved into simpler ultimate physical elements or what are commonly called cells, or their modifications. This last analysis was made by Schleiden and Schwann. Through the prog- ress of organic chemistry it has also become possible to state, with tolerable accuracy, of what the body is composed chemically. When the analysis is a proximate one, the result gives such principles as water, common salt, salts of lime ; starch, sugar, fat ; albumin, casein, etc. These principles exist as such in the human body, and are called ])roximate principles, b("'ing the result of a proximate analysis. If now these principles be analyzed, they will be found to consist of hydrogen, oxygen, sodium, chlorine, carbon, nitrogen, phosphorus, etc. In this way it is shown that the human body consists, ultimately, of the ordinary chemical elements. A human being then consists, ultimately, of myriads of cells composed of the ordinary chemical elements. Certain cells form tissues, certain tis- sues act together as organs, and the organs harmoniously working GENERAL STRUCTURE OF THE BODY 29 together constitute a living, healthy man. The chemical elements composing the cells also act in concert, as proximate principles. A resume of the above physical and chemical facts may be seen thrown together synoptically as follows : The Human Body Consists PHYSICALLY of Organs. The organs of tissues. The tissues of cells. The cells of elements. Examples of Cells. 1. Cells floating in a liquid : blood corpuscles, lymph corpuscles. 2. Cells in layers : epidermis, epi- thelium, enamel. 3. Cells in masses : adipose tissue, medulla of hair. 4. Cells imbedded in non-cellular substance : cartilage, bone. 5. Cells forming fusiform bands : unstriated muscular fiber. G. Cells transformed into tubes : capillaries, nerves, dentine. 7. Cells transformed into filaments: fibrous tissue, elastic tissue. A cell may consist, in its wall, of membrane ; in its contents, of liquid and granules ; in its ap- pendages, of filaments. CHEMICALLY of Principles. The principles of elements. Proximate principles. of 1st Class. Water, sodium chloride, calcium phosphate, sodium carbonate, etc. of •2d Class. Starch, sugar, oils, fats. of 3cl Class. Albumin, fibrinogen, hsemoglobin, etc. Ultimate Elements. Oxygen, hydrogen, carbon, nitro- gen, chlorine, phosphorus, sul- phur, calcium, sodium, potas- sium, magnesium, iron, fluor- ine, iodine, silicon. Let us now take up somewhat more in detail what is known of cells and proximate princi])les. A cell may be defined as the ulti- mate elementary living unit, a mass of living matter, varying from the Tj-i-Q mm. to |- mm. (-^ Jg-Q-th to the y^-g-th of an inch) in diameter. It may consist of a cell wall, inclosing cell contents of a liquid, semi-liquid, or granular character. The granules in some cells are united, according to many histologists, by filaments or threads ; the cell contents consisting then of a network. Often among the cell contents can be distinguished a still smaller cell, the nucleus, and, within this, the nucleolus. Sometimes the cell wall is elongated into an appendage, a cilia. Great diflcrence still prevails among histologists, etc., as to the relative importance of the nucleus and nucleolus of the cell contents and cell Avail. According to some observers, the all important element in cell life is the nucleus, Avhile others maintain that it is the cell contents. The cell wall and even the nucleus are regarded by some as the cell contents in a state of retrograde metamorphosis. As we proceed in our studies, it will be seen that there are cells, 30 CELLS. like the blood corpuscles, which have neither nucleus nor cell wall ; Further, there are protoplasmic beings, like the monera, of which the protamoeba (Fig. 1) is an example which, through life, never exhibit either nucleus or cell wall. Such facts prove that in certain cases at least, neither the nu- cleus nor cell wall is an indis- pensable element to the life of cells, and should make physi- ologists cautious in attributing ])Ositive functions to this or that element of a cell. In- deed, it cannot be said that the Protamaba. (H.eckel.) Fig. 2. relative significance of either nucleus, nucleolus, cell wall, or cell centents, is as yet defi- nitely understood. As ex- amples of cells, attention may be called to those lining the uriniferous tubules of the kid- ney, to the cells of the enamel, to those of the epithelium of the mouth (Fig. 2), of the columnar epithelium of the intestine, to the multipolar cell found in nervous tissues, to the ciliated epithelial cells from the pulmonarv mucous Buccal and glandular epithelium, with granular , /T-i. -v\ '' 11 1 matter and oil-globules ; deposited as sediment from membrane (1^ Ig. ■)), to blood human saliva. (Dalton.) Fig. .S. Fig. 4. Columnar ciliated epithelium cells from the human nasal membrane: magnified 300 diameters. (Quain and .Shakpky.) cells (Fig. 4), to unstriated muscular fiber cells. As we take up the differ- ent organs, the cells com- posing their tissues will l)e described more in detail ; Human blood-globules, a. Eed globules, seen flat- wise, h. Red globules, seen edgewise, c. Whit© globule. (Dalton.) GENERAL STUUCTUEE OF THE BODY. 31 so the above example!^ will, therefore, suffice for the pre.sent in giving a general idea of the form of cells. While there is still some doubt as to the exact use of the differ- ent parts of the cells, there is no doubt that the life of the organ- ism resides in the cells composing it. Among other reasons for supjiosing so, may be mentioned the fact that the life of the human being begins as the ovum, a cell, and that the tissues of the em- bryo, out of which are built up the organs of the adult, consist of modified cells, the lineal descendants of this primitive cell or ovum, and inheriting its life characteristics, the life of the organism being the resultant of the lives of the individual cells composing it. The independent life of cells is well seen in some of the lower animals, whose blood corpuscles can be observed actually feeding upon substances artificially introduced into the circulation, and in the embryonic state can be observed dividing and subdividing, and so reproducing themselves. Gland cells, like those of the liver, kidney, etc., in taking from the blood the materials out of which their respective secretions are elaborated, show their independent activities. Pathological processes often present chances for observ- ing this independent cell life, in the wandering of the white and red blood cells out of the vessels, in the rapid proliferation of cells seen in the development of various morbid growths, etc. The pro- tozoa and protophyta, or the simplest of animals and plants, how- ever, offer the most favorable opportunities for observing the life history of cells ; for these simple beings never get beyond the one-cell stage of life, indeed neither tissues nor organs are ever developed in them in the same sense that these are in the higher animals. The entire life cycle of these minute plants and animals can be often fol- lowed under the microscope. The manner in which cells take food, move about, their mode of reproduction — usually through simple di- vision, though sometimes endogenously and by gemmation and conjugation — can be readily observed by an examination of the greenish matter on damp bricks, stones, etc., consisting usually of palmoglea, micrococcus, or the green- ish film-like spirogyra seen covering the ditches and ponds in the neighborhood of the city, and which also usually contain specimens of uni- cellular protozoa paramcecium (Fig. 5), stentor, as w^ell as desmidiaceae, of wdiich Fig. 6 is an example. These re- searches, always interesting to the mere microsco})ist on account of the beauty of the vegetable and activity of the animal forms, have a deep meaning to the philosophical physiologist. For it is reason- able to suppose that the life of man or the higher animals, wdien in the one-cell or ovum stage (Fig. 7), is similar to that of these beings / Paramcecium cainlatuiii a, a. Contractile ^(-■Kll - }i Mouth. (Carpemiu ) 32 CELLS. which pass beyond this uniccllukir stage. Hence, avc may con- clude that the human ovum, or any of the cells descended from it, absorbs and assimilates nutriment, like the unicellular beings just referred to. The segmentation of the egg in the higher animals corresponds also to the division of the cell seen in the reproduction Fig. 6. Fig. TRT^ Pediastrum pertusum. (Carpenter.) Unman ovum, magnified 85 diam. a. Vitelline membrane h. Vitellus. c. Germinative vesicle, d. Germinative spot. (Dalton.) of these minute beings, the manner in which the nucleus divides first into tAvo halves and the cell contents or protoplasm constricts around the new nuclei being essentially the same in both cases ; the only diflFerence Ijeing, as Ave shall see hereafter, that in the former Fig. 8. Division of the yolk of Ascaris. A, B, C (from Kolliker), ovum of Ascaris nigrovenosa ; I) and E, that of Ascaris acuminata (from Bagge). (Quain and Sharpey.) the new cells hold together and are transformed into tissue, in the latter the new cells are scattered, constituting the next generation of cells. This distinction may be seen by comparing the segmenta- tion of ascaris (Fig. 8 ) with the reproduction of protococcus through continued subdivision (Fig. 9). In either case, however, the life of the resultant cells is that inherited by them from the parent cell. The cells resulting from the segmentation of the mammalian ovum or Q^^ are at first very similar, l)ut soon a marked difierence between them can be ob.served. According to the researches of A'^an Bene- den on the rabbit, the diiference is noticeable even in the two first segmentation cells. However this may l)e, the cells soon begin to differ in size, shape, and the manner in which they arc affected by chemical agents. Some dispose themselves so as to form the epi- CELLS. 33 blast, others the hypobhist, and between these two layers a third appears, the mesoblast. The modification of the cells and the fnrther development of these three layers will be considered when we take up the subject of reproduction. It will be seen then that throuo;]i the processes in- cidental to development, cells often lose their originally round form, becoming sometimes flattened or scale-like, and often of a prismatic and columnar shape. Sometimes the cells float free in a liquid, like the blood corpuscles ; or they may arrange themselves in layers, like those of the enamel ; or in masses, as seen in the medulla of hairs. They may be imbedded in a solid non-cellular matrix, as in carti- lage. Cells are sometimes flattened into bands, as in the unstriated Fig. 9. Development of Protococcus pluvialis. (Caepentek.) muscular fiber, or a number are, through the dissolution of their adjacent walls, metamorphosed into tubes, of which the capillaries and dentine are examples, or they may be converted into fibrous tissue. These modifications are shown synoptically arranged in the table giving the physical constituents of the body. The va- rious substances elaborated by cells in diiferent parts of the adult economy will be more appropriately considered as the functions of the organs are taken up. It will be seen that the life of the body is, therefore, the resultant life of the cells composing it ; that the body is a living republic of cells. Let us now return to the chemical composition of the body, or of the cells of which it consists. We have seen that the human body consists of chemical elements acting as proximate principles. A proximate principle may be defined as a principle, simple or compound, which exists and acts as such in the human body. Thus, sodium chloride is a proximate principle. Neither the rare metal sodium, nor the offensive greenish gas chlorine, however, are proximate principles, for they do not exist or act as such in the body. Calcium phosphate is an example of a proximate principle ; but the metal calcium, and the phosphoric acid, not existing or act- ing separately, as calcium and phosphoric acid, in the body, cannot 3 34 GENERAL STRUCTURE OF THE BODY. be reo^arcled as proximate principles. The purely analytical chemist would resolve such proximate principles as fat, albumin, into their ultimate elements, carbon, hydrogen, oxygen, nitrogen, and sidphur respectively. The physiological chemist, however, Avould study these principles without further decomposition, investigating the part that fat and albumin play as such in the economy without re- gard to their ultimate chemical composition. Proximate Principles. Leaving out of consideration for the present the gases, Avhich can be more conveniently treated of under the subject of the blood, the proximate principles can be divided, for convenience of description, into those of inorganic and organic origin, the latter being further subdivided into those in which nitrogen is absent and those in which it is present. Proximate Principles of the First Class, or those of Inorganic Origin. Substances. Where found. Water ...... Universal. Sodium chloride .... Universal, except enamel. Sodium sulphate .... Universal, except milk. Sodium phosphate . . . Universal. Sodium carbonate . . . Blood, saliva, lymph. Potassium chloride . . . Muscles, blood, saliva, gastric juice. Potassium phosphate . . . Universal. Potassium sulphate . . . Bile, gastric juice. Potassium carbonate . . . Bones, lymph. Calcium chloride .... Bones. Calcium fluoride .... Bones, dentine, enamel. Calcium sulphate . . . Blood, feces. Calcium phosphate . . . Universal. Calcium carbonate . . . Bones, teeth, cartilage. Magnesium phosphate . . . Blood, bone, muscle. Iron Blood, bile, feces. Silicic acid Hair, urine. Iodine Thyroid body. As implied in the definition, tlic principk's of this class are in- organic in origin, being found in the rocks forming the crust of the earth, in sea water, springs, etc., and are crystallizable. With the exception of calcium carbonate, of which the otoliths of the ear con- sist, they are combined in the body with the organic principles. This union is so intimate that as the organic principles become effete, and are eliminated, the inorganic substances are cast out with them. Some of these substances play a more important role than others, and are found in greater or less quantities in the economy. Let us consider no^v the most important of these substances, where they occur, and their principal uses. Water, H^O. — In the maintenance of life, none of the proximate principles, Avhether inorganic or organic, surpass in importance WATER. 35 water. When it is learned, liowever, that it constitute.s nearly ()8 per cent, by weight of the whole body, this will no longer be a snb- ject of surprise. In the course of our studies wa shall find that water exists in all parts of the body : in solids, like bone and enamel ; in fluids, like the tears, perspiration, etc. Its uses in the economy are manifold. It gives consistence and general resiliency to the body, pliability to tendons, elasticity to cartilage, resistance to the bones. Various substances, like articles of food and the effete matters, find their way into and out of the body through their solubility in water. The importance of water is at once seen if the system is deprived of it. The tissues become shrivelled and dried up and inflexible, the liquids become thick, inspissated, lose their fluidity. On the other hand, an excess of water gives rise to general del)ility, muscular Aveakness, dropsies, etc. In the living body water exists as " water of composition " — that is, it constitutes an integral part of the tissues. The water is not taken up by the tissues, like a sponge, but really forms a part of its substance, the union l)eing a chemical one. Ql'axtity of Water.' Substance. Enamel Epithelium Teeth Bones Tendons Cartilages . Skin . Liver . Muscles Ligaments . Blood Parts per 1000. 2 \ '. 37 . 100 . 130 . 500 . 550 . 575 . 618 . 725 . 768 . 780 Substance. Milk . Chyle . Bile Urine . Lymph . Saliva . Gastric juice . Perspiration . Tears . Pulmonary vapor Parts per 1000. . 887 . 904 . 905 . 933 . 960 . 983 . 984 . 986 . 990 . 997 The relative amount of water, in the tissues, is regulated by the salts. Thus, when water is added to the blood, the corpuscles be- come swollen, and finally are dissolved away ; but if a strong solu- tion of salt be added instead, the corpuscles lose their water and shrivel up. Most of the water found in the system is taken in as part of the solid and fluid articles of the food. As we shall see hereafter, however, about 300 grammes (4629 grains) are formed in the system throuo-h combustion of hvdroo-en.- The dailv amount of water necessary for the healthy adult is estimated, b}' Dalton,^ at about 2 kil. (4.4 lbs.). This, of course, includes the water en- tering into the solid articles of food. About fifty-two per cent, of the water, after it has played its part in the economy, is dis- charged by the skin and lungs, the rest by the kidneys and with the feces. When, however, the skin is not active, as in the winter 1 Robin et Yerdeil, op. cit. , p. 1 15. 2 Dalton, Phvsiologv, 1882, p. 37. 3 Op. cit., p. 36. 36 GENERAL STBUCTURE OF THE BODY. time, then the kidneys act very freely ; in the summer the reverse is the case. Diuretics favor the one set of emunctories, diaphoretics the other, Bv o;kincino; at the Table it may be seen how universally water is found in the tissues, and its relative amount. Thus, while we find that a thousand parts of pulmonary vapor contain nine hun- dred and ninety -seven parts of water, it Avill be seen there are only two parts of water in a thousand of enamel, and that a substance, like tendon, so different from either of those just mentioned, is half made up of water. The great importance of water in health, and still more in disease, cannot be too much dwelt u})on by the physi- ologist and practising physician. Salts of Sodium. Sodium Chloride, XaCl, — Next to water, common salt is the most important of the inorganic proximate principles, being found, like water, almost universally, even in the ovum. With the exception of the enamel, in which it has not yet been discovered, salt is found in all the solids and fluids of the body. The absolute amount, how- ever, has not yet been determined. The saltish taste of the tears and ]>erspiration is due to the presence of this principle. It is found in the largest proportion in fluids. Quantity of Sodium Chloride/ Substauce. Parts per 1000. Substance. Parts per 1000. Blood 6.04 Saliva .... 1.5 Chyle ..... 5.3 Perspiration . , , 3.4 Lymph , . . .4.1 Urine .... 4.4 Milk 0.8 Feces . . . .3.0 Salt is introduced into the system through the different articles of animal and vegetable food which always contain it ; in addition, salt as such is added to the food of man and the herbivora ; the amount contained in their food not being sufficient for the wants of the economy. Salt, like all other inorganic principles, passes ultimately through the body, and is carried out of it in the urine, feces, perspiration, etc. Recent experiments - have shown that the excretion of sodium chloride does not depend simply on the amount ingested, since in some cases the sodium chloride excreted was much greater for sev- eral days than that taken as food, the excess being supplied by the tissues. The uses of salt in the system are manifold. Disintegration of the red blood corpuscles is prevented through the presence of salt. A solution of sodium chloride having a strength of 0.6 per iK()l)in et Verdeil, op. cit., p. 76. 2 Klein und \'eiTon, Sitzungsbericlite der Wiener Academie ]S[ath.-Phv.s. Klasse, 1807, s. 627. SALTS. 37 cent., the amount in which it is present in the blood, is often called the " physiological salt solution " and is said to be " isotonic " to the red corpuscles since the latter retain their form and coloring matter in the same. The phenomena of osmosis, or the passage of fluids and gases through animal membranes, are greatly modi- lied by the amount of salt present, a solution of salt osmosing through a membrane much less readily than pure water. Absorp- tion is influenced by it. It increases the solubility of albumin ; this substance lieing less quickly coagulated l\v heat in a solution of sodium chloride than in water. From sodium chloride is derived the hydrochloric acid of the gastric juice. Salt is of great use as a condiment, it being imp()ssil)le to support life on food without flavor, however good the latter may be in quantity or (|uality. Nutrition is undoubtedly afl'ected in other ways by salt, as yet not perfectly understood. The experiments of Boussingault ^ upon bullocks, and of Dailly ^ upon sheep, showed what a deleterious ef- fect was produced in their general appearance when these animals were deprived of salt. It is well known how the wild buflalo is found by the salt licks of the Xorthwest, and how the hunter in Southern Africa avails himself of his knowledge of the habits of wild animals collecting near salt springs, to kill his game. Every one is familiar with the fact of how cattle run to any one who will give them salt. It is said that fugitives from justice will often risk capture and their lives to obtain salt. Facts like the above show what a deep-seated want is felt 1)y man and beast alike when de- prived of salt. Sodium Sulphate (Xa.,SO^), connnonly called Glauber salts, is found in the blood and other fluids of the body. It is introduced into the system with food and discharged together with potassium sulphate in the urine in the condition which we shall see hereafter is known as "preformed sulphuric acid." The diarrhoea that sul- phate of sodium gives rise to wlien administered in purgative doses is probably due to the epithelial cells of the intestine being aflected in such a manner by this, as by other laxatives, as to prevent the absorption of water. Sodium phosphate exists in the fluids of the economy, the blood for example, both as monosodium phosphate (XaH.,PO^) and disodium phosphate (Xa^HPO^). These salts are taken into the body as food and are discharged in the feces and urine. The acidity of the urine, as will be shown when that excre- tion is considered, is principally due to the monosodium or ])rimary acid phosphate (XaH.,PO^). The latter osmoses or passes through membranes more readily than the disodium or secondary sodium phosphate. Sodium carbonate (XaCO^) is found in the blood, lymph, saliva, pancreatic, intestinal juices, etc. It is ])roduced within the bodv bv the oxidati(m of organic sodium salts, or is in- troduced with the food. To the existence of this salt the alkalinity ' Chimie Agricole, p. 271. Paris, 1834. 2 Longet : Traite n atoms is the same as that of the oxygen atoms. It may be appropriately mentionetl, also, in this connection, that, according to the numlx-r of carbon atoms present in a glycose, the latter is called a triose (glvcerose), tetrose, hexose (monosaccharides), nonose. Glucose and galactose are usually regarded as l^eing the aldoses of the hexatomic alcohols, sorbite and dulcite, respectively : that is, as having the constitution of an aldehyde alcohol (CHlOH)CHO). Aldehyde is alcohol ^ dehydrogenated and is produced l:»y the aetii ju of oxygen upon alcohol Alcohol. Oxygen. Aldehyde. Water. C^H^O T- b = C,H,0 -f H^O Galactose is f« jund in the brain, combined with proteid in the form of the glucoside - cerebrin. It is produced in the economy through the hydrolytic decomposition of milk sugar, glucose being produced at the same time. Levulose, d-fructose. fruit sugar, foimd in fruits and honey, is produced in the body through the decom- position of cane sugar and is transformed into glucose. Levu- lose, being the ketose of mannite. is therefore a ketone alcohol'^ (COCHpH). The disaccharides, cane sugar, milk sugar, and maltose are. as their name implies, dimultiple sugars, each consisting of C..,H^Ojj, but differing in their atomic arrangement. Saccharose cane sugar is obtained from the cane beet root. We shall see hereafter that cane sugar is converted or inverted into glucose and levulose by the hydrochloric acid of the gastric juice and intestinal ferment. On this account cane sugar, when eaten, becomes indirectly a source of glycogen. Dextrose, d-ghicose. or grape sugar ( C^H^.^O^), is found in the blood and tissues of the body to an extent of about 0.5 per cent. It is derived, as we shall see hereafter, from the digestion of starch, cane sugar, the decomposition of proteid, the dehydration of gly- cogen. A convenient and delicate test for grape sug-ar is the well-known one of Trommer. It is made in the follo^^'ing manner : The suspected liquid is placed in a test-tube ; to this are added one or two drops of sulphate of copj^er ; then the mixture is made distinctly alkaline by the addition of a solu- ' Aldehyde 1 CH3CHO1 being alcohol 1 CH^OH dehvdrogenated. an aldehyde alcohol is a substance containing the groups CHO and OH. characteristic of alde- hydes and alcohol respectively. *A glucoside i? a substance which, in the presence of water and a ferment, yields glucose, etc. Thus for example, Amvgdaliii. Water. Benzoic aldehyde. Hydrocyanic acid. Glucose. C.^H2;XOii-2(H,0) = C\HsO ' - ' Cks' -^ ^CgHiA 'A ketone, a^, for example, acetone (CHjCOCHj ), being characterized by contain- ing the group CO, a ketone alcohol is a substance containing the groups CO and OH, characteristic of a ketone and alcohol. 46 PROXIMATE PRINCIPLES OF ORGANIC ORIGIN. tion of caustic potash. The mixture will become blue, particu- larly if sugar is preseut. Now heat the test-tube till just before boiling point, when, if sugar is present, a reddish precipitate will appear just in the upper part of the tube, and will gradually be seen in the whole liquid. The reaction is due to the cupric oxide being reduced to the condition of a cuprous oxide by the oxidation of the sugar. The solution to be examined should be clear. This can be accomplished by boiling the suspected tissue, finely divided, with water and sulphate of soda and filtering. The organic and coloring matters will be retained, and a clear extract will pass through, the soda not interfering with the test. Maltose and lac- tose respond to Trommer's test. Cane, maple, and beet sugar, however, must be boiled with very weak sulphuric acid to convert them into glucose before the test will be applicable. There are substances in the healthy urine which interfere with the reaction in the reduction of the copper, though sugar be added in considerable quantity. Of course, this does not apply to diabetic urine. Al- buminose, which, as we shall see hereafter, is produced during gas- tric digestion, interferes also with Trommer's test, as noted by Longet, though Dalton j^ointed out first the fact of the products of stomach digestion having this curious effect. With the above qualifications, Trommer's test is very reliable and easily applied. Other tests, such as those of Moore, Barreswil, Maumerie, Bott- ger, Fehling, the fermentation test, and that of torulse, etc., are also used. Lactose, milk sug-ar, so-called on account of it being found in milk, occurs also in the amniotic fluid of the foetus, in the urine in the last days of pregnancy and first days of lactation. Milk sugar is produced in the economy in the mammary glands probably at the expense of glucose, as it does not occur in the blood. According to some chemists it is converted in the system into dextrose and galactose. In all prol)ability, however, it is absorbed as such un- changed. Milk sugar, under the influence of a ferment, readily be- comes lactic acid, which in time causes the souring and clotting of milk, the change taking place in the alimentary canal as well as out of it. The remaining disaccharide, maltose (Cj.,H.,„Oj,), is produced in the economy, together \vith dextrin and glucose, in varying amounts, by the action of the saliva, pancreatic and intestinal juices upon starch, all of the maltose and dextrin being finally transformed, however, into glucose. Sugar is produced within the system as we have seen by the liver, mammary glands, etc. The greater part of the sugar found in the economy is introduced, however, cither in the form of fruit, cane, or milk sugar, or is derived as we just mentioned from starch. SUGAR. -i^ Quantity of Sugar in 100 Parts in Cherries . . . .18.12 Goats' milk . Juice of sugar cane . 18.00 Cows' milk . Apricots . . . .16.48 Indian corn-meal Peaches . . .11.61 Eye flour Pears . . . .11.52 Barley meal . Sweat potatoes . . 10.20 "Wheat flour . Beet roots . . . 8.00 Oatmeal Parsnips . . .4.50 Beef's liver . 5.80 5.20 3.71 3.46 3.04 2.33 2.19 1.79 The exact manner in which sugar is elaborated by plants can not be said as yet to have been definitely established. Recent re- searches ^ render it highly probable, however, that the first stage in the production of sugar by plants consists in the production of formic aldehyde through the reduction of carbonic acid by the action of sunlight upon the chlorophyll of the leaves, the reaction being as folloAvs, Carbonic acid. Formic aklehyde. Oxygen. H CO, = HC.HO + 6, 2 3 ' ,; Xow it is well known that formic aldehyde ^ when produced synthetically in the laboratory can be transformed by appropriate means first into paraformic aldehyde and then into formose, a form of sugar.^ It is quite possible therefore that the formic aldehyde produced in the plant passes through similar stages, becoming ulti- mately perhaps starch or cellulose. With the exception of the i)laccs mentioned sugar does not occur in the economy, being oxidized as rapidly as produced, it passes out of the system as carbon dioxide and water. Glucose. Oxvgen. Carbon dioxide. Water. CaH,,0, -h 120 = 6(C0,) -f 6(HP) Sugar, through its combustion, is therefore one great source of heat. Its uses in this respect will be considered, however, more particularly when the subject of animal heat is taken up. The polysaccharides, or tliird kind of carbohydrates, includes such substances as starch, dextrin, glycogen, etc., and consist chem- ically of some multiple of C^Hj^Og. In the case of starch, this multiple being taken as 3, its chemical composition is expressed by the formula (CgHj^O.).,. Although not crystallizable, starch is far from being an amor- phous powder, it consisting, as found in the potato, for example (Fig. 10), of well marked, laminated granules of definite form. ^Dalton, op. cit., p. 54. ^Eoinke, Berichteder deutschen chemischen Gesellscliaft, 1881, Band 14, s. 2144. Tormie aldehyde beai-s to methyl alcohol the same relation that aldehyde beai-s to alcohol, that is to say it is methyl alcohol dehydrogenated. It is usually ob- tained by the slow combustion of metliyl alcohol brought about by an ignited spiral of platinum wire, the reaction being as follows, Metbvl alcohol. Oxygen. Formic aldehyde. Water. CH,0 + 6 = C'lI.O " 4- H.,0 * Baer, Berichte der deutschen chemischen Gesellschaft, 1870, Band 3, s. 67. 48 PROXIMATE PlilNCIPLES OF ORGANIC ORIGIN. The so-called corpora amylacea found in the brain, and formerly considered as being of the nature of starch, as their name implies are no longer regarded by chemists ^ as carbohydrates. Starch exists abundantly in corn, wheat, oats, rice, potatoes, and indeed in almost all vegetable food. Tapioca, arrowroot, etc., so useful as articles of diet, under certain circumstances, are varieties of starch. Fig. 10. drains of potato starch. Quantity of Starch in 100 Parts in Eice . . 88.65 Peas 37.30 Indian corn . 67.55 Beans 33.00 Barley . 66.43 Flaxseed . 23.40 Oats . . 60.59 Potatoes . 20.00 Rye . . 64.65 Sweet potatoes 16.05 Wheat . 57.88 Chocolate 11.00 Starch may be produced from sugar, and under the influence of solar heat from plants by a process of deoxidation from carbonic acid as shown by the following formula : Carbonic acid. Oxvgen. Starch. Water. eH.CO, — 120 = C,H,„0, + H^O The principle of the development of starch through the deoxida- tion of carbonic acid may be roughly illustrated in the following manner : A bunch of fresh mint being placed within a cylindrical tube containing dilute carbonic acid water standing over the pneu- matic trough is exjiosed to sunlight. Soon the leaves of the mint will be seen covered with minute beads of gas, a small quantity of the latter accumulating at the top of the cylindrical tube. By with- drawing the mint and passing up a few bubbles of nitric oxide, a 1 Hoppe Seyler, 1881, Phj's. Chemie, s. 689. 'Dalton, op. cit., \}. 57. STARCH. 49 dark brown vapor will appear at the top of the tube, proving that the contained gas was oxygen. Starch is insoluble in cold water, but bv boiling the granules are liquefied, and, on cooling, remain fused together as a whitish, oxaline, homogeneous mass. In this condition, it is said to be " hydrated." The most important prop- erty of starch for the physiologist, however, is the readiness with w^hich it is converted into one or more forms of sugar. Thus, if human saliva be added to boiled starch and the mixture be main- tained at a temperature of 100° F., in a short time it will be con- verted into maltose, dextrose, and some little glucose. Starch in its transformation into maltose passes through the in- termediate stages of amylodextrin, erythrodextrin, achrodextrin, and isomaltose, the latter being isomeric with maltose. Maltose, be- ing unabsorbable, is finally converted into glucose, and in this form of sugar appears, as already mentioned, in the blood. Inasmuch as starch is finally transformed into glucose, and as the latter is com- pletely oxidized, starch, like sugar, is a source of energy, indeed a most important one, since one-half of our food, as we shall see, con- sists of starch. Glycogen, or animal starch (CgHj^O.), may be re- garded functionally as so much stored glucose, to be drawn upon by the economy in time of need, glycogen being readily converted by hydration into the more combustible and diffusible glucose, Glycogen. Water. Glucose. C.H^A + HP^C^H^A That such is the case is shown by the fact of the entire disap- pearance of glycogen from the body in starvation, it being trans- formed into glucose to make good the deficiency of the latter in the blood. The significance of glycogen from this point of view is further shown by its conversion into glucose by muscular work. One-half of the glycogen of the body is probably found in muscles, the remaining half in the liver. Indeed, as much as 40 per cent, of the dry solids of the latter organ may consist of glycogen. The glycogen of the economy is derived from the carbohydrates and the glucose of decomposed proteid, 100 parts of the latter yielding 45.08 parts of glucose.^ Glycogen, so far as it is affected by the action of diastatic ferment, does not appear to differ from vegetable starch. Glycuronic acid, or d-glucuronic acid (C^H^^jO.), allied chemically to starch and dextrin, occurs in the urine after the administration of camphor, turpentine, chloral, hydrate, etc., in a state of combination with the latter. It may be obtained by the reduction of saccharic acid with nascent hydrogen. Glycuronic acid, wdiile resembling glucose in reducing alkaline copper solution and in rotating polar- ized light to the right, differs from it in not being fermentable with yeast. Lactic acid, or ethidene lactic acid (CgH^.O.J, is a diatomic, ^ Weintraud u. Laves, Zeitsclirift fiir plivsiolosjisclie Cliemie, 1894, Baud 19, s. 632. 50 PROXIMATE PRINCIPLES OF ORGANIC ORIGIN. monobasic/ oxy-fatty acid. Lactic acid is often called " fermenta- tion lactic acid " on acconnt of being developed throngh the fer- mentation of the carbohydrates, the reaction consisting in the split- ting of the glucose molecule, Glucose. Lactic acid. C H O = 2C H O 6 12 6 3 6 3 A familiar example of such fermentation is the souring of milk, which depends upon the lactic fermentation of milk sugar. Recent experiments render it probable, however, that lactic acid is pro- duced, to a certain extent, at least, from proteid as Avell as from carbohydrates. When absorbed lactic acid appears to be completely oxidized. Lactic acid is inactive to polarized light, it consisting of two acids, right ethidene lactic acid rotating the plane of polariza- tion to the right, left ethidene lactic acid rotating it to the left, the two acids neutralizing each other therefore in this respect. Owing to the fact, however, of the left ethidene lactic acid being destroyed by penicillium glaucum when lactic acid, as such, is al- lowed to stand with that fungus, a means is afforded of obtaining the right ethidene lactic acid alone, or at least in sufficient quantity to rotate the plane of polarization to the right. It is in the latter form that lactic acid, called also sarco and para lactic acid, occurs in the blood muscle and elsewhere in the system. It is this acid to which is due the formation of KII.,POj, which causes the coagula- tion and acidity of muscle when the latter passes into the condition known as rigor mortis. Among the diatomic dibasic acids " that occur in the system may be mentioned oxalic and succinic acids. Oxalic acid (C2ll.,0^) is found in the urine and appears to be derived from the oxalates of the food rather than from the metabolism of the tissues of the body; at least recent observations ^ show that, upon a diet of meat alone or of meat, fat, and sugar, no oxalates are found in the urine. Oxalic acid, in the form of calcium oxalate, gives rise to one form of stone in the bladder and to the urinary sediments arising during acid and also alkaline fermentation. Succinic acid (C^HgOJ, found in the rCH^OH ^ Lactic acid \ CHj is said to be diatomic because it is derived from a diatomic ( COOH r CH.,oii alcohol, propvlglvcol \ i'Yi^ bv the substitution of one atom of oxvgen for two iciLOII atoms of hydrogen, but monobasic, one atom of hydrogen only of the acid being re- placeable by a monad element. 2 Oxalic acid < r 'oQyr is a diatomic acid because it is derived from a diatomic alcohol, glycol, ^ r'H^OIT ^'^ ^^® substitution of two atoms of oxygen for four atoms of hydrogen in the latter, and dibasic, two atoms of the hydrogen of the acid being replaceable by two monadic elements. ''Bunge, Lehrbuch Der Physiologischen und Pathologischen Cliemie, 1894, s. 340. FAT. 51 spleen, th^Toid, and thymns, appears t<3 be derived from proteid putrefaction and alcoholic fermentation. Inosite, though consisting of carbon, hydrogen, and oxygen, and the two latter elements existing in the proportion to form water, is neither a carbohydrate nor an oxy-fatty acid, l»ut a member of the aromatic series, beino- hexa-hvdroxvbenzol (C.H.(OH).). It occurs in the body in the brain, miLscle, liver, lungs, spleen, suprarenal capsules, testicles, and in the vegetable kingdom in beans and un- ripe peas. Xothing is known as to its origin. AVhen introduced into the system inosite appears to be oxidized. Phenol oxybenzol ^ (CgH.OH), commonly called carbohc acid, though an antiseptic itself, is developed normally in the intestine as one of the products of the putrefaction of proteid, probably of tyrosin. Phenol as such, or in the form of the dioxy benzols, pyrocatechin, hydroquinone, appears in the urine, together A\-ith p-cresol, p-ox^-phenyl-acetic, and p-hydrocumaric acids, benzol derivatives, in the form of alka- line ethereal sulphates. Benzoic acid is an interesting member of the aromatic group, since, when introduced into the svstem, it com- bines \^'ith glycocoll to form liip})uric acid, the reaction being as follows : Benzoic acid. Glycocoll. Hippuric acid. Water. C^HX'OOH - XH^CHXOOH = XH(C^H3C0)CHX'00H + H,0 The consideration of t\'rosin, indol, and skatol, will be deferred until the proximate principles of the third class are taken up, as these substances, although aromatic in nature, contain nitrogen. Fat. — Fat is an almost universal constituent of the body ; it is absent, however, in the bones, teeth, the eyelids, and scrotum, elastic and mielastic fibrous tissue. It is always present, even in extreme cases of emaciation, in the orbit, and aroimd the kidneys. Quantity of Fat ix 100 Parts of Tissue.' Sweat .... 0.001 Liver .... 2.4 Saliva . . . .0.02 Muscles . . . .3.3 Lymph .... 0.05 Hair 4.2 Chyle . . . .0.2 Milk 4.3 Mucus .... 0.3 Cortex of brain . . . 8.0 Blood .... 0.4 Medulla . . . .20.0 Cartilage . . . .1.3 Xerves . . . .22.1 Bone .... 1.4 Spinal cord . . . 23 6 Crystalline lens . . 2.0 Adipose tissue . . .82.7 The amount of fat as just shown varies very considerably in the tissues ; thus, while in the sweat, lymph, saliva, etc., there is a mere trace of fat, more than twenty per cent, is found in the nervous system, and over eighty in adipose tissue. The whole amoimt of fat, according to Burdach,^ in the body of a man weighing 80 'Benzol (CgHg) being the so-caUed nucleus and OH the lateral chain. 2 Carpenter, Phvsiology, 1881, p. 88. 'Traite de Phvsiologie, Tome viii., p. 80. Paris, 1857. 52 PBOXIMATE PRIXCIPLES OF ORGJXIC BIG IX. kilograms (176 pounds) was 4 kilograms (8.8 pounds), or 5.2 parts of fat to every 100 of body. Fat exists in the adipose tissue, for example, in the form of vesi- cles which are transparent and contain the oily matters. Fat consists of a mixture of the principle known to chemists as stearin, palmitin, and olein. The first two are solid at the temper- ature of the body, but are held in solution by the olein. They crystallize (Fig. 11) in needle-like forms, assuming a beautiful radi- FlG. 11. stearin crystallized from a warm solution in olein.' UDaltox.) atory or arborescent appearance, where fluid, fatty, oily substances under the microscojie have the appearance of round globules, bright in the center, and dark at the edges. AVith the exception of the pho-pliorized fat of nervous tissues, fat does not exist combined with the other proximate principles, as we found was the case \N-ith the inorganic principles and the sugars ; there is no such mo- lecular union of fat with any principle. There is no difficulty, therefore, in extracting it from the system in a state of purity. Pressure is often the only process needed, the oil Ijeing squeezed out of the interstices of the tissues of the organ containing it. Fats, chemically speaking, are glycerides or ethers of glycerin, that is, glycerin in which three atoms of hydrogen are replaceable by the residues of three molecules of a fatty acid. Thus, for ex- ample, stearin (C^II.(C^^H,.0.,)^), a form of neutral fat is glycerin, fOH ' CjH. ^ OH , in Mhich the three atoms of hvdrogen in the three I OH hydroxyl groups are replaced Ijy the residues of three molecules of stearic acid (C^^H^O.^), thus C3H3 • OC,^U^^O = stearin. FAT. 53 In the case of olein, C,H^(C,,H3,0,),, and palmitin, C,H^(C,,H3P,),, the three atoms of hydrogen in glycerin are repkiced by the residues of three molecules of oleic acidjCj^Hg^.,, and palmitic acid, CjgH3202. Such being the constitution, chemically, of neutral fats, it be- comes intelligible why stearin, for example, in the presence of vapor of water heated to 572° F., takes up water, and splits into glycerin and stearic acid, as follows : Tristearin. Water. Glvcerin. Stearic acid. The action of alkali, soda, for example, upon stearin, is another example of this process, the stearin splitting up into glycerin and stearic acid, the latter combining with the sodium to form sodium stearate or soap, as follows : stearin. Soda. Glycerin. Sodium stearate. 2(C,,H^,„0J + 6NaOH = 2(C3H^03) + GXaC^^H^^^ Saponification, as the splitting of a neutral fat into glycerin and fatty acid is called, whether alkali be present or absent, is brought about in the system by tlie action of the steapsin of the pancreatic juice upon fat. It is a most important function, since the neutral fat is emulsified by the soap so formed, that is, subdivided into mi- nute particles, thereby rendering it absorbable. In a similar man- ner oleic acid, sodium oleate, and other fatty acids and soaps are formed in the system. The odor of the axilla and feet is probably due to the presence of fatty acids. It is an interesting fact that, after feeding an animal with a fatty acid, the chyle will be found to contain a considerable amount of neutral fat, showing that a syn- thesis the reverse of saponification takes place, that is to say, the fatty acid, fed combines with the glycerin of the body, three mole- cules of water being lost to form neutral flit.^ In this connection it may be mentioned that there are other monatomic, monobasic," fatty acids occurring in the body, to be referred to hereafter, such as formic, propionic, butyric, and caproic acids. iMunk, Yirchow Archiv, 1880, Bd. 80, _s._17. 2 A monatomic acid is so called because it is derived from a monatomic alcohol. Acetic acid (C'.^H^O.,), for example, being derived from alcohol (C.JIgO) among other wavs bv oxidation, as follows : Alcohol. Oxygen. Acetic acid. Water. C^HgO 4- 0, = C^HA + H.,0 Acetic acid is a monobasic acid, one atom of hydrogen being replaceable by a monad element, as in the formation of potassium acetate, according to the following reac- tion : Acetic acid. Pota.ssic hydrate. Potassium acetate. Water. C2H,02 + KOH •= KC^HjO., + H,0 What has just been said of acetic acid is applicable to the remaining fatty acids, they all having the constitution chemically of a hydrocarbon group tinited with COoII. Chocolate nut . 49.00 Salmon Sweet alinouds . . 24.28 Cows' milk Indian corn . 8.80 Beans Fowls' eggs . 7.00 Wheat Mackerel . . 6.76 Peas . Calf's liver . 5.58 Oysters Beef's flesh . 5.19 Potatoes 54 PROXIMATE FRINCIPLES OF ORGANIC ORIGIN. Quantity of Fat in 100 Parts of Food.' . 4.85 . 3.70 . 2.50 . 2.10 . 2.10 . 1.51 . 0.11 Tlie fat of the body may 1)0 derived possibly to some extent from the fat of the food. Recent experiments render it improbable, how- ever, that such is the case. Even were it so, more fat is produced in the system than can be accounted for l^y the fat in the food. The experiments of Persoz, Boussino;ault, Thomson, Lawes, Gilbert, and others ujjon geese, ducks, pigs, cows, etc, with reference to tliis point are conclusive. In the case of a cow, for example, under the observa- tion of Voit, it was shown that, of the 2024 grammes (72 ounces) of fat in the milk, only 1658 grammes (59 ounces) could have been derived from the fat of the feed. It is evident, therefore, that the fat obtained in such cases must have been derived from either the carbohydrate or proteid material of the food. It has been proved, however, by experiments made upon dogs,^ for example, fed upon sugar, starch, and fat, that the fat produced could not have been derived from the proteid, but from the carbohydrate material of the food. Further, such facts as the starch of plants becoming oil, of sugar being readily transformed into alcohol and fatty acids, of car- bohydrate principles constituting a part of a fattening diet, there can be no doubt tliat the fat produced in the economy is, under cer- tain circumstances, largely derived from the carl)ohydrates present in the food. On the other hand, it is a matter of every -day obser- vation that animals are best fattened on a feed consisting of proteid as well as of car))oliydrate food stuifs, which renders it probable that fat may l)e derived from proteid, as well as carbohydrate })rin- ciples. Indeed, as shown by Pettenkofer and Voit,'^ so far from the fat produced in the body being proportional to the carbohydrate in- gested, which ought to be the case upon the supposition that fot is derived from the latter, the fat deposited is proportional to the amount of proteid destroyed. Thus, for examjjle, in experiments made upon dogs fed with starch, although the amount of the latter given was much greater in one animal than the other, the amount of flit deposited was nevertheless in each animal about the same, showing that the fat coiikl not have Ijcen derived from tlie starch, but from the proteid destroyed. This becomes intelligible if w^e suppose that the starch, after conversion into sugar in tlie economy, is oxidized and leaves the system as carbon dioxide and water, and ' Pavc'ii, from Dalton, (>]). cit., p. (>'!. 2Riil)iK'r, Zeits. fiii- Biolo^ie, Band 22, 1880, s. 272. ■■'Zeits. fiir Biol()f,^ie, Band ix., s. 435, 1873. Hermann, Phvsiologie, Sechster Band, s. 252, 1881. FAT. 55 that of the proteid of the body decomposed, the non-nitrogenous part is retained within the economy as fat, the nitrogenous elimi- nated as urea. In further confirmation of this view it was also shown by Pettenkofer and Yoit ' that, in the case of dogs fattened upon a meat diet, the fat was derived from the proteid of the food, rather than from that of the body as in the previous experiments, but in the same manner. Apart from experimental evidence, such as that just mentioned, there are a nimiber of general facts which confirm the view that fat may be derived from proteid as, for ex- ample, the fatty degeneration of the tissues, the conversion of dead bodies into adipocere, the development of fats out of peptones, the derivation of fatty acids and substances like acetone (CH.^COCHg) from proteid, that in phosphorus poisoning as the fat increases the albumin diminishes, etc. General considerations and experiments showing then that the fat deposited in the body may be derived from proteid, it may be asked of what use then are the carbohydrate principles always present in fattening diet ; in what way do they contribute toward the production of fat ? Regarding these principles as a source of heat to the economy, their role as a part of fattening diet becomes 2:>erfectly clear, since in being burned they save the fat otherwise derived and which would be drawn upon for the same purpose if they were absent. Hence, the fact of a dog fed on sugar and meat, excreting less urea and getting fatter than when fed on meat alone, of the neg-roes o-ettino- fat durino- the extraction of the sugar from the cane ; of dogs fed on meat and rubol, palm oil, or stearin, get- tino; fat, the suw-ar or oil oiven with the food in these instances sav- ing the fat otherwise produced from the proteid from being biu-ned. The carbohydrate principles evidently then play in the production of fat this secondary role of saving the fat, otherwise produced, from being consumed. If the xiev: of the origin of fat, just referred to, be accepted, it becomes intelligible why individuals become fat whatever they eat, and that if the fat of the body is to be reduced, all Idnds of food must be diminished, as little eaten as possible, to cut off the supply, and plenty of active exercise taken to quicken the circulation aud respiration, and in that way burn off that already deposited. Fat is never discharged from the body in health except in the butter of milk, but is destroyed, burnt, passing away as carbon dioxide and water ; and, therefore, like sugar, being a source of heat and energy : Fat. Oxvgeu. Carbonic acid gas. Water. C„H^,„0, + 0,„ = 57(COJ + 5o(H,p) Fat is useful also as serving to support the organs, like the eye and kidnev. It fills up the spaces between vessels, bones, and muscles, rounding off the trmik and extremities into the graceful curves of the human form. 'Zeits. fiirBiologie, 1869, 1870, 1871. 56 PROXIMATE PRINCIPLES OF ORGANIC ORIGIN. It prevents the loss of heat through its bad conductive power. This function of fat is well shown in the cetacea, of which the whale, dolphin, and jjorpoise are examples. Such animals, being provided with an immense layer of fat just beneath skin, are enabled thereby to retain largely their heat. Cholesterin (CjgH^^O), although consisting of carbon, hydrogen, and oxygen, with the hydrogen in excess and fatty to the touch, appears to have the constitution chemically of a monatomic alcohol (C^pH^gOH). Cholesterin is found in nervous tissue, blood cor- puscles and bile, and will be referred to again in connection w^ith the latter. CHAPTER III. PROXIMATE PRI>XIPLES OF THE THIRD CLASS. This class includes such substances as serum, alljurain, fibrinogen, casein, hemoglobin, mucin, keratin, urea, lecithin, pepsin, etc. They agree mth the principles of the second class in being of or- ganic origin, that is elaborated by organized bodies out of materials derived directly or indirectly from the mineral and vegetable worlds. The ^vater, carbon dioxide, and salts found in the mineral inor- ganic world, constituting the food of plants, with some exceptions, like the fmigi, are converted by the plant through the agency of the sun's light and heat into such principles as starch, sugar, vegetable alVjiunin, fibrin, and casein, etc. The plants in time serve as food for herbivorous animals, which are eaten by the carnivorous ones, while, as we shall soon see, all three, plants, herbivora, and car- nivora, together -svith the inorganic principles, enter into the food of man. It will be seen, therefore, that, so far as the organic principles are concerned in nature, the plant is indispensaljle as preparing the food for the animal ; the former living on carbon dioxide, salts, etc., which would be starvation to the latter. AVhile the organic principles are usually developed in the order indicated, it must be mentioned, however, that chemists have suc- ceeded in artificially preparing some of the principles of the third class, as well as those of the second, from the direct combination of the inorganic elements in the laboratory by purely physico-chemical processes, without invoking in any way the aid of a vital force in the case of either plant (jr animal. The proximate principles of the third class, with some exceptions to be mentioned hereafter, differ, however, from those of the first and second classes in not Ix'ing crystallizaljle. The proximate principles of the third class, however, are distin- guished in a marked degree from those of the first and second in containing nitrogen. This element seems indispensable to the com- position of a body exhibiting life. As is well known, those sub- stances which are xerx changeable, decomposing suddenly, like nitrogen iodide, nitrogen chloride, nitroglycerin, fulminating salts, gunpowder, etc., owe their peculiar properties to the nitrogen they contain. As we proceed in our studies, we shall see that the essence of life is in change. To make use of a- homely simile, nitrogen seems to play the same part in the living body as that by a restless, excitable spirit in the living community ; ever ready himself to be affected 58 PROXIMATE PRINCIPLES OF THE THIRD CLASS. by slight changes and to influence in the same way those around him. Thus an important feature of the nitrogenized proximate princi- ples is the readiness with which they undergo putrefaction — the latter being brought about by the growth and multiplication of a minute protist, the Bacterimn termo (Fig. 12), just as sugar is de- composed into alcohol and carbonic dioxide through the influence of the yeast cell. Fig. 12. Cells of Bacterium termo ; from a putrefying infusion. (Daltox.) The eff^ect of the bacterium cells in inducing putrefaction in this manner, like that of the saccharomyces or yeast cell in producing fermentation, is usually said to be due to catalysis. The word cat- alysis meaning literally to dissolve, break up, while frequently made use of in speaking of those actions in the economy wliich are of this character, is, however, only a word, not an explanation — in fact, merely a convenient way of expressing our ignorance of the phenomena to l)c explained. The susceptibility of these organic principles to change, in and out of the body, is not only due to the nitrogen they contain, but probably to the great number of atoms entering into their compo- sition. It is more natural that haemoglobin (C,.,,.Hj,,2,.N,g^FeS30jj^,), con- sisting of 2010 atoms, should lireak up into its constituent parts on the slightest change taking place in the surrounding conditions, than sodium chloride or water, composed of two or three atoms respectively. It is easier for two or three persons to get along together than 2010, especially Avhen among the latter there are 164 (the nitrogenous atoms) most unstable ones. The organic principles of this class are always combined with the inorganic ones, the union being most intimate, so much so that CELLS. 59 as the first are used up and become eifete, and are cast out of the body, the inorganic principles go with them. Like the principles of the second class, those of the third class are destroyed in the system, never appearing in the excretions in health (with the ex- ception of casein of milk, mucus, epithelium, and epidermis). Being transformed into carbon dioxide, water, urea, etc., through a process of splitting, with subsequent oxidation, they are also a source of heat to the economy like the principles of the second class. It is impossible to offer a classification of the nitrogenous sub- stances occurring in the human body, since the only bond which unites all of them is the nitrogen they contain, whereas the differences depending u])on chemical constitution, mode of deriva- tion, etc., widely separate them. In endeavoring to give some account of these substances, we will consider them successively in groups, associating together such substances as agree in their chem- ical constitution, so far as is known, in their general properties, mode of derivation, etc. From this point of view, inadmissible, perhaps, from a purely chemical standpoint, useful, however, for purpose of description, the proximate principles of third class, those in which nitrogen is present, may be divided into the following groups: proteins, amides, amines, imides, lactic acid, and triatomic al- cohol derivatives, xanthin bodies, benzol derivatives, ferments, etc. It need hardly be added, after what has been already said, that the above groups can not be regarded as physiologically equivalent or placed in the same chemical category, as some of the substances constituting them, as we shall sec hereafter, are derived from the decomposition of protein bodies, some by substitution of residues, others again in a way Avhich is as yet unknown. AVe will begin our study of the proximate principles of the third class with that of the protein group. The protein group of nitrogenous principles constitute the chief mass of the tissues, hence the name from -pcozs'Jco to be preemi- nent. Protein substances, generally speaking, consist of carbon, hydrogen, nitrogen, oxygen, and usually sulphur ; phosphorus iron and copper, being also occasionally present. When heated, })rotein bodies decompose, giving rise to inflammable gases, am- moniacal compounds, carbon dioxide, water, nitrogenized bases, etc., and when thoroughly burned, first to a mass of carbon and then to an ash consisting principally of calcium and magnesium phosphates. In the present state of physiological chemistry it is impossible to classify the protein substances satisfactorily. The following classification, based more especially upon those of Ham- marsten^ and Chittenden,^ will suffice at least for convenience of description. 1 A Text-Book of Plivsioloyical Chomistrv, bv Olof Ilaramarsten, translated bv John A. Mandel, 1893, p. 14. 2 Chittenden, Digestive Proteolysis, Cartwrio-ht Lectures, Medical Eecord, Vol. 45, 1894, p. 449. 60 PROXIMATE PRINCIPLES OF THE THIRD CLASS. Albuminous Bodies ) Globulins or Simple Proteids ( Serum-albumin -^ Lacto-albumiu (^ Myo-albumin / Serum-globulin \ Fibrinogen - Myosin I jSIyo-globulin V, Cell-globulin ' til, .„,:„„+ f Acid-albumin Albuminates | Alkali-albumin Proteoses and Peptones Coagulated Proteids -| Fibrin Protein Substances Combined Proteids Chromo-proteids' ' Glyco-proteids Nueleo-proteids . , Korafin Albuminoids f Korafi! J J':iastin f Hcemoglobin 1 Myohsematin f Mucins \ Mucoids f yielding f Nuclei histon ) nuclein 1 Cell nuclein 1 yielding J Casein L parauuelein ( Vitellin j Collaji V Keuro-keratin The albuminous bodies or simple proteids, while found more es- pecially in the muscles, glands, and blood serum, occur as well in the solids and fluids of the body generally, with the exception of the tears, perspiration, and perhaps urine, in which they are either absent or only found in traces. Quantity of Proteids. 2 Substance. Parts per 1000. Substance. Parts per 1000. Cerebro-spinal fluid 0.9 Chyle . 40.9 Aqueous humor . 1.4 Spinal cord . 74.9 Liquor amnii 7.0 Brain . . 86.3 Intestinal juice 9.5 Liver . . 117.4 Pericardial fluid . 23.6 Muscle . 161.8 Lymph 24.6 Blood . 195.6 Pancreatic juice . 33.3 Middle coat of arterie s . 273.3 Synovia. 39.1 Crystalline lens . . 383.0 Milk .... 39.4 Albuminous bodies consist of carbon, hydrogen, nitrogen, oxygen, sulphur, and occasionally of phosphorus, iron being generally a constituent of their ash. Their percentage composition varies, as follows : Carbon Hydrogen . Nitrogen Oxygen Sulphur Phosphorus 54.5 per cent. 7.3 " " 50.6 - 6.5 - 15.0 -17.6 " 21.50-23.50 " 0.8 - 2.2 " 0.42- 0.85 " The molecular weight of albumin not having been as yet deter- mined, its formula can not be given. That of alkali albuminate is ^ In order to prevent misunderetanding it may be stated that the term ' ' proteid ' ' as suggested by Hoppe Seyler and used by Hammarsten embraces the substances in- cluded above as chrorao- and glyco-proteids. 2 Group Besanez, Lelirbucli der Phy.siologisclien Clieraie, 1878, s. 128. PliOTEIDS. 61 usiiallv accepted as l)eino- approximately C.^Hj^^Xj^SO^, (Lieber- kulin). Although the constitution chemically of albuminous bodies has not yet been established, judging from the products of decomposi- tion', the albumin molecule consists, among other subtances, of such as have a fotty and an aromatic nature. The albimiinous bodies are odorless, tasteless, and usually amorphous. Most of them are colloids, that is, do not diffuse, or if so, but slightly through animal membranes, and have a high osmotic equivalent. They rotate polarized light to the left. The presence of albuminous bodies is determined by precipitation and color tests. Thus, for example, on heating a solution of allnunin to the proper temperature, the latter depending upon the nature of the albumin present, the albimiin will usnallv separate in a solid form as crude " coagulated " albumin. It should be mentioned in this connection that the reaction of the solution containing the albumin must be acid, an alkaline albumin solution not coagulating upon heating, and a neutral one but partly and incompletely. Albuminous bodies are precipitated by the three ordinary mineral acids. Thus, for example, if an albumin solution be allowed to flow gently on nitric acid in a reagent glass, as in the performance of Heller's test, a M'hite opaque ring consisting of pre- cipitated albumin appears where the two liquids meet. Albumi- nous bodies are also precipitated by metallic salts, ferroycanide of potassium in acetic acid solution, alcohol, tannic acid, etc. Albuminous bodies, when heated to the boiling point, give, on the addition of nitric acid, a yellow color known as the xanthoprotein reaction. A solution of mercuric nitrate in nitric nitrous acid known as Millon's reagent, precipitates albumin in solution, giving to it a red color. Tyrosin and other benzol derivatives give the same reaction mth Millon's reagent, contirraing the view that the albumin molecule contains an aromatic group. If caustic soda or potash be added to an albumin solution, and then drop by drop dilute cupric sulphate, the solution becomes just reddish, then reddish violet, and lastly violet blue, the reaction being known as the Biuret test. In testing for albumin, as no one test is characteristic, it is hardly necessary to add that several precipitate and color tests should be made use of. Albumins. — These substances are soluble in water, coagidate by boiling: and on standing with alcohol. Thev are verv rich in sul- phur, containing 1.6 to 2.2 per cent. Serum-albumin, lacto-albu- min, and myo-albumin are found respectively as proteid constitu- ents of blood, ])lasma, milk, and muscle. Serum-albumin usually taken as the tvpe of the albumins, as obtained from the blood of the horse, consists chemically of C53.06, HG.85, N16.04, SI. 80, 022.26.' It is found in the lymph exudations generally as well as in the blood. If a solution of serum-albumin having a neutral or acid reaction 1 Hammarsten, op. cit., p. 62. 62 PROXIMATE PRINCIPLES OE THE THIRD CLASS. be lieated to 70°-75° C. it will coagulate, that is will be precipi- tated in an insoluble form. As it appears, however, that heating at temperatures of 73°, 77° and 84° C. gives three distinct coagu- lations, it is possible that the substance now known as serum-albu- min may really consist of three distinct proteids. An important property of serum-albumin is tliat it is not precipitated by the addition of magnesimn sulphate (MgSO^) to a liquid containing it. Advantage is taken of this to separate serum-albumin from serum- globulin, both of which exist together in the blood-globulins. These albuminous bodies are iusolulile in water, l)ut s<»luble in dilute neu- tral salt solutions. They coagulate by heating. Serum-globulin and fibrinogen are found in blood plasma and lymph. Myosin, the principal proteid constituent of dead muscle, exists in living mus- cle apparently in the form of a promyosin or myosinogen. Myo- globulin, also found in muscle, l^ears to the latter very much the same relation that serum-globulin l^ears to blood plasma. Cell- globulin is found in cells. Serum-globulin, often called para-globulin, as derived from horse's blood, consists chemically of C52.71,H.7.01,Xl5.85,Sl.ll,O28.24.i It is found in the blood, as already mentioned in lymph, and the exudations generally. Serum-globulin in solution is precipitated not only by magnesium sulphate, but also by sodium chloride (NaCl), incompletely, however, by the latter. In neutral or feebly acid solutions, serum-globulin coagulates at a temperature of 75° C Fibrinogen, one of the most important of the globulins as derived from horse's blood, consists chemically of C52.93,II.6.90,N16.66,- S. 1.25,0.22. 26.^ It is found in the liquor sanguinis lymph and at times also in the exudations. Fibrinogen differs from serum-globulin in coagulating at a lower temperature, 5()° to 60° C, and on being as completely precipitated by sodium chloride as by magnesium sulphate. As we shall see hereafter, it is regarded as giving rise to the insolul^le proteid fibrin at the moment of the coagulation of the Ijlood. Albuminates. — Acid albuminate, acid albumin, or syntonin, as it is sometimes called, is produced by the action of diluted hydrochlo- ric acid upon proteid as takes place in the stomach, in the digestion of albuminous food l)y the gastric juice, tlie latter containing hydro- chloric acid. Alkali albuminate is formed by the action of alkali upon albuminous bodies as in the instance of the alkali of the in- testine acting upon proteids. Acid and alkali albuminates are nearly insoluble in water, l)ut are soluble in dilute acid and alkali. Proteoses and Peptones. — Proteoses and albumoses, as they are also called, may l)e regarded as propep tones occurring during the digestion, of albuminous food as intermediary products between al- bumin and ])e]it(me in so far as they are not albuminates. Pep- tones are the final products of the decomposition of albuminous 1 Hammarsten, op. cit., loc. cit. '^ Hammarsten, op. fit., loc. cit. PROTEIDS. 63 bodies, brought about l)y mean? of ferments, or }X)ssibly in other Avays. Proteoses are usually separated from peptones by satura- ting the solution containing them both with ammonium sulphate, the proteoses being precipitated, the peptones remaining in solution. It should be stated, however, that, according to Xeumeister, the deuteroproteose occurring in pepsin digestion is not precipitated by ammonium sulphate.^ Coagulated Proteids. — These bodies, of which fibrin is an exam- ple, are insoluble in water, alcohol, dikite acids and alkalies, salt solutions, V)ut soluble in pepsin, hydrochloric acid, strong acids and alkalies, and alkaline solutions of trypsin. Combined Proteids. — This group of protein substances is more complex than the albuminous bodies or simple proteids just consid- ered. They consist, as their name implies, of proteid combined with non-proteid l^odies, such as coloring matters, carbohydrates, nucleic acid. Chromo-proteids. — These substances consist of proteids combined with a pigment containing iron, such as hemoglobin, the coloring matter of the red lilood corpuscles and its derivatives, to be re- ferred to ag-ain, and histio-hiematin or myo-hi^matin, found espe- cially in the muscle and regarded as existing in two forms, myo- hsematin and oxy-myohiiematin, corresponding to the htemoglobin and oxy-ha?moglobin of the l:)lood. Glyco-proteids. — These are proteids combined with carbohydrates as in mucins, substances foiuid in mucous glands, goblet cells, ce- ment substance, epitheliiun, connective tissue. Mucins are colloidal substances, mucilaginous and thready when in solution. They are insoluble in water, soluble in very weak alkalies, precipitated by acetic acid and yield, when treated ^\\t\\ a mineral acid, a substance capable of reducing a copper oxy -hydrate. The latter property is an important one, since, by means of it, mucins are distinguished from substances closely resembling them in their properties. ^lucin, as derived from the sub-maxillaries, consists, according to Hammars- ten," of C.48.84, H.6.80, X12.;32, S0.84, O.31.20. It may be men- tioned that while mucin agrees in composition with the simple pro- teids in consisting of the same chemical elements it contains less nitrogen and usually less carbon. ^luein substances are usually divided into mucins and mucoids. This classification is, however, an arbitrary one, as there are intermediate substances which make it difficult to define two such groups. Among the so-called mucoids may be mentioned chondro-mucoid found in muscle, the colloid matter of certain tumors, the pseudo-colloid of ovarian cysts ; the two latter Ijcing, however, pathological in nature. Nucleo-proteids. — These substances are foimd in the cells of both the vegetable and animal kingdoms. Thev are characterized more especially by yielding through the action of pepsin, hydrochloric ^ Hammarsten, op. cit., p. 28. ^Op. cit., p. 32. 64 PEOXIMATE PRINCIPLES OF THE THIRD CLASS. acid, phospliorized substances, which, according as they do or do not yield xanthin, are called nucleins or paranucleins. Nuclein occurs as nucleo-histon in the leucocytes of the blood and as the chief constituent of cell nuclei, parauucleiu in casein, yitellin, etc. The supposed importance attached to nucleo-histon as a factor iu the production of the coagulation of the blood will be considered hereafter. Albuminoids. — The substances embraced together as the third class of protein bodies differ so among thcmselyes that they cannot be regarded as a natural group. The albuminoids agree, howeyer, in constituting important parts of the skeleton and being found generally in the economy in an insoluble state and in resisting the action of reagents, particularly of those which dissolye albumins. The albuminoids are deriyed in the economy from the proteids, but do not appear to be couyertible into the latter. Keratin. — This substance is the chief constituent of epidermis, hair, and nails, and in the modified form of neuro-keratiu is found in the brain and the medullary sheath of nerves. As found in the hair keratin consists of carbon, hydrogen, nitrogen, oxygen, and sulphur, being yery rich in the latter. Part of the sulphur, at least, appears to be in a loose state of combination, lead combs becoming black l)v long usage through formation of lead sulphide. Elastin. — This albuminoid is found in the connective tissues and in some cases, as in the ligamentum nuchte, to such an extent as to constitute a special tissue. The elastic tissue in the ligamentum nuchse of the giraffe and elephant is much developed. The liga- mentum nuchffi in the giraffe dissected by the author measured in situ more than 9 feet, 6 feet of which, after removal from the body, contracted to 4 feet. Elastin differs chemically from keratin in containing very little, if any, sulphur. Elastin is very insoluble in boiling water and in most reagents. Collagen. — This substance is the principal constituent of the con- nective tissues and as ossein of the organic substance of bone. It is found also in cartilage, more or less mixed with the substances constituting its chemical basis, the so-called chondrigen. Collagen can be obtained from bones by treating the latter mth hydrochloric acid, which dissolves the earthy matters, and then removing the acid with water. Collagen consists chemicallv, according to Hof- mcister,' of C 50.75, H (5.47, X 17.86, S +'0 24.92. It is in- soluble in water, salt solutions, dilute acids, and alkalies, and is converted by continuous boiling into gelatine. It will be remem- bered that, in addition to the protein bodies just considered, a num- ber of other nitrogenous principles are found in the human economy that cannot be placed in the above category. To the consideration of these let us now turn, premising, however, that, as most of them will be considered again more or less in detail, a passing notice will suffice in tliis connection. ^ Hammarsten, op. cit., p. 37. AMIDES. 65 Amides.^ — Glycocoll, or amido-neetic acid ( C'H ,XH,COOH ), oc- curs iu bile combined with cliolic acid as sodium glycocholate, and in the urine combined with hippuric acid as benzoic acid, and with phenyl acetic acid as plienaceturic acid (Cj^Hj^XO^). The amides, leucin, lysin, tyrosin, aspartic acid, are normal products of the di- gestion of proteids by the trypsin of the pancreatic juice. Leucin, chemically speaking, is amido-caproic acid - ( C.Hj^^XH^ )COOH) ; Ivsin, diamido-caproic acid (C,.H,,(XH.,Y,COOH) ; t_\TOsiu, p-oxy- phenyl-amido-propionic acid (HOCVH^C.HgfXHJCOOH) ; aspartic acid, amido-succinic acid (C.,H3(XH.,)COOH). Taurin, or amido- ethyl-sulphonic acid (XH.,CoH^SO..OH), occui-s in the bile in com- bination with cholic acid as sodium taurocholate. Urea (COX.,HJ, or carbamide, regarded as a diamide, consists of the residue of one molecule of carbon dioxide and two molecules of ammonia in which two atoms of hydrogen are replaced by one of oxygen. Ammonia. Trea. x„ < H. CO -' :C-TT= -(h; ^^h= Amines.' — Auiouo; the amines occurriuo; in the bodv mav be mentioned the amines of the olefines,* cholin and neurin, derivatives of lecithin. Cholin chemically is trimethyl oxy-ethyl ( OTT ammonium hydroxide (CH3).^=X nrr cjj otj ' Xeurin. dif- fering in its chemical composition from cholin in containing one molecule less of water, is trimethyl-viuyl ammonium hydroxide, r OTT (CH3)3=X- ,,p- _ p^ and is a powerful poison. As a matter of general interest it may be mentioned in this connection that pto- maines, basic substances produced from proteid by bacterial putre- faction, are olefine amines, the poisonous ones being called toxines. Thus, for example, putresciu occurring in the urine and feces in cystitis is chemically tetra-methylene-diamin (H.,X(CH.,)^XH,). Cadaverin, found in cholera feces, is penta-methylene-diamin ^ An amide may be regarded as ammonia, in which an atom of hydrogen is re- placed by a residue. Thus, for example, acetamide (C^HjOX ) is ammonia in which an atom of hydrogen is replaced by the residue of acetic acid as follows : Ammonia. Acetamide. rn fc,H30 (h (.h ^ Leucin is regarded by some chemists as being rather iso-butyl-amido-acetic acid. ^An amine or compound ammonia may be regarded as ammonia in which one or more atoms of hydrogen are replaced by one or more alcoholic radicals, such as methyl, ethyl, etc. Thus Ammonia. Ethvlamine. Trietlivlamine. fH (CM, rC,H, N a' H N -^ H • X J CH. 1 11 [h [cm, * defines include such hydrocarbons as ethylene (CoH^), propylene (CjHg). 66 PROXIMATE PRINCIPLES OF THE THIRD CLASS. (H.,N(CH.,).NH.,). Leucomaines, as distino:nisho(l from pto- maines, are the products of protein substance brought al)Out, how- ever, not by micro-organisms, but by the metabolism or the normal exchange of material constantly going on in the economy. Some leucomaines being poisonous in small doses, their accumulation in the system, through imperfect excretion or oxidation, is regarded by many clinicians as a source of disease, of auto-intoxication. Imides. — Of the imide derivatives of the body may be mentioned, creatin and creatinin, and their homolognes, lysatin and lysatinin, ( l^TT derivatives of guanidin, the imide of nrea,^ HX = ^\ xfT^ ' Thus creatin found in the muscles, blood, and urine is methyl guanidin acetic acid, HXC | >-/ptT \pTT r rtion of 1 to 3.55. From such considerations and as confirmed by experience it has been shown that, apart from 1530 grammes (54 oz.) of water drunk as such, life can be best maintained in a state of health on a diet consisting of: water, 559 grammes (19 oz.) derived from the food; proteids, 130 grammes (4.(3 oz.); fats, 100 grammes (3.5 oz.) ; carbo- hydrates, 300 grammes (1 0.5 oz.) ; salts, 20 grammes (0.7 oz.). The proportion in which the proteids, fats, and carl)ohyd rates may re- place each other in a daily diet upon the principles just explained is shown accordino: to different authorities in the followinsr table : Diet of Food Stuffs. Molesebott. Ranke. Voit. At water. Proteid . . loO grammes 100 grammes 118 grammes 125 grammes Fats . . 40 " 100 " 56 " 125 " Carbohydrates 550 " 240 " 500 " 400 " It will be observed that according to Voit the nitroo-enous are to the non-nitrogenous food stuffs in tlie proportion of 1 to 4.7, in the ^ Voit in Hermann, ITandlmcli der Physiologie, Band vi., s. oUO, ISSl. ^Lehmann ( Waoner : Handworterbnclv 1884, ii., s. 18). Frerichs (Archiv f. Anat. und Phys., 1848, s. 4(39). Bidder u. Schmidt (Die WM-dauungsIifte, 1852, s. 348). • o , , ^Die Organische Chemie, 1842. Ann. d. Chemie u. Pliar., xli., 1842; liii., 1845; Iviii., 1840 ; Ixx., 1849 ; Ixxix., 1851. 72 FOOD. daily diet. As our daily food does not actually consist, however, of proteid, carbohydrates, etc., but of bread, meat, and such articles, it becomes as important to determine the quantity and quality of the food Avitli wliich the economy should be supplied in order to maintain a state of health as that of the food stuffs. Indeed, as a matter of fact, the proper proportion in which food stuffs should be present in a normal diet is determined from the nature of the in- gesta, that is the food eaten, and the egesta. As the various kinds of food contain more or less the .different food stuffs it might natu- rally be supposed that it was immaterial whether man lived upon animal or vegetable food. As a matter of fact, as we shall see here- after, proteid food is converted l:)y digestive processes into peptone, whether derived from beef or potatoes, fats and salts are assimilated by the economy, whether supplied by the eating of fish or rice. As vegetable foods are characterized by being rich in carbohydrates and relatively poor in proteids and fats, animal foods in being rich in proteids and fats, and relatively poor in carl)ohydrates, it follows that the economy upon a diet restricted to either one or the other kind of food will receive either too much carbon or too much nitro- o-en. This will become evident from a consideration of the amount of the carbon and nitrogen sup])lied to the economy upon an exclu- sively bread or meat diet in a state of health. Eatio of Carbon to Nitrogen in Excreta. Carbon. Nitrogen. Respiration 248.8 grammes. grammes. Perspiration . 2.6 " " Urine 9.8 " 15.8 " Fa3ces 20.0 " 3.0 " 281.2 18.8 There are found in the excreta 281.8 grammes of carbon and 18.8 grammes of nitrogen, the carbon being to the nitrogen in the proportion of nearly 15 to 1. C =281.2 = 14 9 X= 18.8 •^• Such being the case, it will be seen that, upon a diet restricted to bread, in order that the economy should receive 19 grammes of ni- trogen, 11)44 grammes of bread would have not only to be eaten but assimilated, the svstem then receivino; 30 <»:rammes of carbon to 1 of nitrogen, or twice as much carl)on as necessary. 281.2 grammes of carbon and 18.8 grammes of nitrogen are found in tlie excreta, or 15 C to 1 N. 1944 gr. of bread contain 583 gr. C and 19.4 gr. N, or 30 C to 1 N. 2981 gr. of meat contain 298 gr. C and 89.7 gr. N, or 3 C to 1 N. 990 gr. (2 Ib.s.) of bread contain . C 300 gr. and N 9.9 gr. 337 gr. (I lb.) of meat contain . . C 30 gr. and X 9.9 gr. 1327 gr. of bread and meat contain . C 330 gr. and N 19.8 gr. or C Ki.fJ to N 1. MIXED DIET. 73 On the otlier hand, if the food consists of meat ah)ne, tlicn in order to obtain the necessary 2S1 grammes of carbon as much as 2981 grammes of meat would have to be eaten, the economy receiv- ing then three o-rannnes of carbon to one of nitrogen, the amount of carbon being tlien one-fifth of what it ought to be, relatively to the nitrogen, and the latter in amount absolutely five times too great. If, however, bread and meat be eaten in the proportions given in the table, then the economy will receive for about sixteen grammes of carbon one gramme of nitrogen, the ratio differing a little from that of the excreta, as might be expected, the food of the man con- sisting, as we shall see, of other articles as well as of bread and meat. In the latter case when the carbon and nitrogen of the in- gesta and egesta balance each otlier, and, indeed, the salts and water as well, the economy is then said to be in a state of carbon and nitrogen equilibrium. It should be mentioned, in connection with the example just given of a diet restricted to meat, that, as a matter of fact, life cannot be maintained upon such a diet. As more than 2.2 kilogrammes (4.8 lbs.) of meat must be eaten and digested by a man in 24 hours in order to obtain the 280 grammes of carbon, a task is imposed upon the digestive organs tliat they cannot perform. A man soon succumbs upon a purely meat diet, drawing upon the fat of his own body to supply that which should be present in his food. Even a carnivorous animal, like a dog, whose alimentary apparatus is especially adapted to digest meat, can only be kept alive upon a purely meat diet, when fat and muscular at the begin- ning of the experiment, and when the meat eaten is equal to the -^^ or Jg of the weight of the body, a diet which increases enormously the excretion of urea, a condition far from physiological. On the other hand, if the food consists of fat alone, man or beast will live but a short time, and it is Morthy of mention that on such a diet less urea is excreted than in the starving condition, the albu- minous tissues, the source of the urea, being spared through the oxidation of the fat. If more fat, however, be taken than can be disposed of in this way, as shown by the retention of carbon in the system, then fat is stored up and the albuminous tissues destroyed. The effect of a carbohydrate diet is essentially the same as a fatty one, sugar or transformed starch being, however, more readily oxi- dized than fat, seventeen parts of sugar being equal to ten parts of fat in this respect ; less urea is, therefore, excreted upon a carbo- hydrate diet than upon a fatty one. A certain amount of body fat appears to be also destroyed upon a carbohydrate diet. Of all foods, milk is the one which combines in itself to the greatest extent the proper substances in quantity and quality for the nutrition of the body, and Mere life limited to its earlv periods, it might l)e stated that milk alone would suffice for the maintenance of life ; as the child, however, develops into the adult necessity is felt for other kinds of food as well. All through life, however, milk constitutes a most important article of diet, and can be more relied upon, both in sickness and in health, than any other kind of food. 74 FOOD. While life can not be maintained upon any one article of diet, under certain circumstances the latter may with advantap^e be re- stricted larji^ely, tliough not exclusively to some one kind of food. Thus, for example, certain wild tril)es in South America subsist al- most entirely upon beef. The latter supplies sufficient material for the repair of the tissues, and liberates enough heat to replace the little lost l)y tlie body, the climate being warm, and to supply the energy expended in their daily life. In the arctic regions, however, where the temperature may fall as low as — 72° F. and the body loses heat very rapidly, the food consists principally of oleaginous substances, blubber, fat, etc. These substances in producing, through combustion in the economy, a great quantity of lieat are therefore especially suited as articles of diet. On the other hand, in certain parts of the tropics, wliere the temj^erature may be as high as 140° r.,the body losing but little heat, the staple food, as might be expected from what has just been said, is rice or dates, which produce relatively little heat. In addition to what has already been said in reference to the ex- creta and nutritive value of particular kinds of food, it might also be inferred, from the fact of the teeth of man being of both the carnivorous and herbivorous types and of his alimentary canal be- ing intermediate in character between that of the carnivora and herbivora, that the food should be of a mixed kind. The quantity of food that a man can eat and live is very different, as might be supposed, from that which he should eat. On the one hand, a young Esquimaux is said to have eaten as much as thirty-five pounds of food in twenty-four hours ; on the other that the daily food of Thomas Wood consisted for eighteen years of sixteen ounces of flour made into a pudding with water. Leaving out of consideration such extreme cases, experience has shown that a man in full health and taking active exercise in the open air may sub- sist for a considerable time upon a diet consisting of: meat, 453 grammes (16 ounces) ; bread, 540 grammes (19 ounces) ; butter or fat, 100 grammes (3.5 ounces); water, 1530 grammes (51 ounces). In order, however, that health should be maintained continuously, the above diet should l>e modified so as to contain more bread and meat, and also vegetables and small quantities of coffee, vinegar, and salt, somewhat as in the Daily Ration of the United States Soldier, Bread or flour ...... 22 ounces. Fresh or salt beef 20 " Pork or bacon . . . . . . 12 " Potatoes (three times a week) . . . 16 " Rice 1.6 " Cofifee (or tea 0. 24 oz. ) 1.6 " Sugar ........ 2.4 " Beans 0.64 gill. Vinegar . . . . . . . 0.82 '• Salt 0.16 " HUXGER AXD THIRST. io In concluding this general account of the subject of food, it may be stated that the eifects of cooking food are three : First, to make it more palatable ; second, to utilize it thoroughly ; third, to im- jjrove its digestil)ility. Food which is agreeable to the taste is eaten "vvith more relish ; and, therefore, better digested than if un- palatable. If the food were not cooked, much of it would be unfit to eat and wasted, and even if it could be eaten murh would be un- digested. Hunger and Thirst. — The effects of withholding food entirely or of giving it in too small quantities are seen in cases of starvation and inanition. As an illustration of how life depends upon waste, and of the manner and relative quantities in which the tissues are destroyed to maintain life, the records of death from want of food, solid and liquid, become of interest to the physiologist. For a starving man is living upon himself, and as nature is always eco- nomical in her expenditures, one may feel siu'e that the very best disposition possible under such circumstances is made of the mate- rial available in maintainino; life. In the wastiuo- awav that takes place in these cases we have a guide as to the character of the noiu-ishment that the system would have taken had food been sup- plied from without instead of from within, and can so deduce some conclusions as to the use of food o-enerallv. Shipwrecks, prolonged sieges, imjjrisonments, forced marches, etc., famish the data by which some idea may he obtained of the state of nutrition and of the agonies and horrors in cases of death from starvation. Among the symptoms of starvation mav be men- tioned, first, severe pain in the epigastrium, which usually passes away in a day or so, then an indescribable feeling of weakness, a sort of sinking, in the same parts is experienced. The face be- comes pale and cadaverous, and there is a wild look in the eye. General emaciation follows, an ofFensive odor is noticed about the body, which is covered Avith a brownish secretion. The voice be- comes weak, muscular efibrt is almost impossible, the intelligence can with difficulty only be aroused. Finally death takes place, usually in eight or ten days, often accompanied with mania and convnlsions. On post-mortem examination the most striking fitcts usually noticed are the diminution in the weight of the body, almost entire absence of fat and blood, and the loss in bulk of the most important viscera. The coats of the intestine are so thinned as to be almost transparent, the gall-bladder is distended A\-ith bile, and decomjiosi- tion sets in very rapidly. Death from inanition or insufficient food, though more prolonged than that from actual starvation, is essentially the same process only slower, being characterized by the same symptoms, and the same post-mortem changes. ^lany babies and young children in large cities and even in the country die from inanition — actually starved to death, undoubtedly throngh ignorance in some cases ; bnt in 76 FOOD. others, however, the length of time in death from inanition varying so, and being often so extended, advantage is frequently taken of this to obscure and mask the true cause of death by those interested in escaping from the penalties of their criminal neglect of the cliil- dren placed in their charge. As already observed, one of tlie most prominent symptoms of starvation is the loss of weight. It may be generally stated that when this loss exceeds from twenty to fifty per cent, of the weight of the body, death takes ^^lace. In doves, accord- In cats, accord- ing to Chossat.i ing to Voit.2 . 93.3 97 . 75.0 27 . 71.4 67 . 64.1 17 . 52.0 54 . 44.8 3 . 42.4 18 . 42.3 31 . 39.7 . 34.2 . 33.3 21 . 31.9 26 22.2 18 . 16.7 14 . 10.0 1.9 3 Eelative Loss of Tissue in Starvatiox ix 100 Parts. Fat Blood Spleen ...... Pancreas ..... Liver ...... Heart ...... Intestines ..... Muscles . . . . , Muscular coat of stomach Pharynx and oesophagus Skin" Kidneys ..... Respiratory apparatus . Osseous system .... Ej'es ...... Nervous sj-^stem .... It will be observed from a ghtnce at the results obtained by Cho.ssat and Voit that the ditference in the relative loss of the tissues is very considerable. Tlius the nervous system loses only a little over one per cent., the muscles over forty per cent., while more than ninety per cent, of the fat disappears. Xow it has lieen noticed that in starvation the temperature falls, and most rapidly as deatli approaches ; this is so evident that the immediate cause of death is undoubtedly cold. When it is remem- bered that one of the principal uses of tlie fatty principles is to pro- diu.-e heat throu<>li their combustion, the laroe loss of fat in such cases becomes intelligible, the animal using up its own fat as so much fuel. Inasnnich as no food has been introduced into tlie Ijody there is nothing for the economy to make blood out of, hence the .vlien ordinarily death from starvation ensues. By taking little or no exercise, in passing most of the time in sleep, and residing in a tropical climate, or in a temperate one during the hottest summer months, while the experiment lasts, it is evident that the system needs but little food, the waste of the tissues being reduced to a minimum, and there being but little need for heat production, on account of the high temperature of the surroundings. By living in this way, man can transform himself almost into a cold-blooded or hot-blooded hibernating animal. Under such circumstances he lives upon himself, and continually loses weight. When, as regards this loss of weight, a certain limit is reached, which varies according to the condition, previous mode of life, and peculiarities of the individual, he will certainly die of starvation unless food be taken, death from starvation being only a question of time if the system be deprived of food. There are a number of substances which, although they can not be regarded as foods in the; sense of being essential to health, are, nevertheless, consumed in such large quantities by the majority of mankind that some reference at least should be made to them in this connection. We refer to tea, coffee, tobacco, distilled and fermented liquors. Tea and Coffee. — As the composition of tea and coffee are the same, they may be conveniently studied together. Tea is obtained ALCOHOL. 79 from the leave? of the Tliea chinensis, coffee from tlie Caffea arabica, the tea and coffee phiiits respectively. Tea and coffee, while con- taining food stnffs such as sugar, gum, tannic acid, fats, salts of iron, potash, and soda, owe their peculiar properties to thei'n or caffein. The latter is regarded now as an alkaloid, being chemi- cally trimethyl xantliin (CVH„,X^O., 4- H.,0) which has been re- cently prepared artificially from xanthin. Dimethyl xantliin is the active principle of chocolate. The effects of tea and coffee upon the mind are well known, wakefulness, clearness and activity of thought, disposition for mental or muscular exertion, a sense of ease in respiration, and general comfort. The exhaustion and nerv- ousness often following the excessive use of tea appears to be due to the loss of sleep rather than to any poisonous action of its alka- loid. As regards nutrition, tea and coffee do not appear so much to supply the economy with nutritive material as to promote the trans- formation of that already taken, the exhalation of carbon dioxide being increased.^ As thei'n and caffein exist in tea and coffee only to the amount of 6 per cent, and ^ per cent., respectively, a cup of tea would contain only about 1.2 grammes (20 grains) of thein and a cup of coffee 0.05 grammes (0.7 grain) of caffein, as the remarkable effects of tea and coffee upon the system are not pro- portional, therefore, to the amount of the active principle that they contain, the action of the latter in the economy would appear to resemble that of a ferment, the food and tissue being transformed and carljon dioxide set free as in the various fermentations induced by yeast. Tobacco. — As the employment of tobacco is most extensive in all classes of society, a few words on its effect upon the system in this connection appear appropriate. The active principle of tobacco is a poisonous alkaloid, nicotia, consisting of C\^Hj^X.,. Experiments appear to show that while the use of tobacco increases the elimina- tion of uric and phosphoric acids the feces and urine themselves are diminished, the exhalation of carbon dioxide being but little affected. AMiile the excessive use of tobacco no doubt produces a state of wakefulness, trembling, and nervous excitement, it cannot be denied that when moderately used it is often very beneficial, quieting and soothing the nervous system when exhausted by bodilv and mental effort, and even in ordinarv circumstances producino- a o-eneral tranquillizing effect. Tobacco seems also to promote digestion, stimulating the secre- tion of the gastric juice by reflex action, hence the common custom of smoking a cigar after breakfast or dinner. Alcohol. — Before considering the use of wines, malt liquors, and spirits, it is necessary to learn, if possible, the effects of pure alcohol upon the human body, since this principle is contained in larire or small quantities in all such fluids^ Alcohol chemically consists of CHgCH^OH, and the first question to be investigated is, what Ijc- 1 Smith, Philosophical Transactions, Vol. 149, 1859, p. 681. 80 FOOD. comes of it ^vlien taken into the system ? According to some ex- perimenters, very little alcohol is fonnd in the excretions, 95 per cent, appearing to be oxidized, burnt up ; according toothers, how- ever, alcohol is found in the ventricles of the brain unchanged, and is eliminated by the lungs, skin, and kidneys. It appears, therefore, that alcohol may be consumed in the economy, or excreted as such, or partly oxidized and partly ex- creted. In either case, however, alcohol can be of no benefit to the system, for if it is found as such untransformed in the organs or excreted unchanged, it cannot supply any want, simply passing through the system, and if it is liurnt up it must interfere with the oxidation of other substances, such as fat, etc., which under ordinary circumstances Avould, through combustion, disappear. If the latter view be correct, we have an explanation of hard drinkers becoming often so fat, the alcohol being burnt in preference to their fat, and so allowing their fat to accumulate in the muscles, in the liver, heart, etc., or, what is more likely, the alcohol in some way inter- feres with that splitting of food or tissue that normally precedes its oxidation. Alcohol can never substitute the natural drink of man, water. Many substances which are soluble in the latter are precipitated by the former, and, hence, useless to the system ; further, it does not sujiply any principle to the tissues. Alcohol, in diminishing the amount of urea excreted and the ac- tion of the skin, and in interfering with natural combustion, per- verts the whole nutrition of the body. The active changes and the rapid removal of the effete matters, so characteristic of healthy life, are retarded by alcohol ; hence the susceptibility of the dram drinker to zymotic poisoning and chronic disease. It is well known, also, that less food is taken when alcohol is used, and so alimentation is affected. It is often urged that alcohol " keeps the cold out," but as the cutaneous vessels dilate under the use of alcohol through paralysis of the vaso-constrictor nerves, more blood, and tliercfore more heat, comes to the surface, which instead of be- ing retained within the body as it would otherwise be, escapes, the natural effect of the cold being to contract the vessels and of so keeping the heat in the body. Whether this be the true explana- tion or not, the fact remains the same, that Arctic voyagers keep the cold out far better without the use of alcohol than with it. Finally, in addition to these facts, when it is remembered that many persons preserve their mental and bodily health perfectly without ever touching alcohol, it is difficult to offer a single good physiological reason for the use of alcohol at any time, the body being in health. It must not be forgotten, however, that almost every people, savage or civilized, use alcohol in some form or another. Whether some, as yet unknown, want is supplied to the system by alcohol, or whether it is used merely to drown sorrow or to relieve ennui, is an LIQUORS. 81 undecided question/ Among; civilized jxoplc life is so artificial and man is so liarassed bodily and mentally that, unfortunately, perfect health is far from Ijeing common. Life at times becomes weary, the heart feels oppressed, digestion is sluggish, the circula- tion impeded, muscular languor is present ; then alcohol is useful, for it is a nervo-muscular stimulant. The action of the heart is accelerated, the l)lood flows more rapidly, the heart is relieved, and good results from its use. As a medicine, alcohol is indispensable ; when used for any other purpose, little or nothing can ])e said in its favor. Liquors, Distilled Liquors, Wines, Malt Liquors. — Liquors are prepared by treating dilute alcohol with sugars, ethereal oils, and aromatics. The distilled liquors most commonly used are brandy, whiskey, gin, and rum. They contain, as a rule, a little more than 50 per cent, of alcohol, and hence, when abused, their bad effects. Brandy, the most valuable of them as a medicine, is obtained by the distillation of Avine ; whiskey from rye, wheat, etc.; gin from dif- ferent grains rectified by juniper, and rum from molasses. Brandy, whiskey, and gin diminish the amount of carbon dioxide exhaled, and so interfere with vital processes. Bum, however, increases the carbon dioxide exhaled, and, therefore, is less hurtful in its effects. It has long been known that the rum drinker lives longer than the brandy or gin drinker. Wine, or the fermented juice of the grape, is called full-bodied or light, according to the amount of alcohol jiresent. There is al- ways less alcohol in wines than in the distilled liquors just men- tioned ; thus port, ^Madeira, and sherry contain from 15 to 20 per cent, of alcohol ; claret, sauterne, hock, about 10 to 15 per cent. In countries where the light wines are used by all classes of society, the horrible effects of spirituous liquors are almost unknown, the per cent, of alcohol being so small in light wines. Wine contains, in addition to alcohol, sugar, gluten, and a num- ber of salts, etc. Wine is nutritious in proportion to the amount in which these substances are present. In tlie preparation of many wines, like champagne, the amount of carl>on dioxide is increased ; hence, their great use as diffusible stimulants in those cases where the vital powers demand prompt and active stimulation. Under such circumstances there is no better medicine than champagne. Beer, ale, and porter are made from malted l^arley with the addi- tion of hops, the fluid remaining after se])aration of nitrogenous matters being treated with yeast. All malt licpiors contain alcohol ; about 1 to 4 per cent, in the weaker, and from 6 to 8 per cent, in the stronger kinds. Even as much as 12 per cent, is found in the heavy English beers. ' Important researches have been made recently by Chittenden ( The American Journal of the Medical Sciences, April, 189() ) upon the effect of alcohol upon the various digestive secretions. However valuable, such investigations will not throw any light upon the effect of alcohol upon the system until supplemented by a knowl- edge of the effect of alcohol upon tiie i)rocesses of seci-etion, absorption, etc. 6 82 FOOD. Composition of Fren'ch Beer.' Water 947.00 Alcohol 4.50 Dextrin, glucose, etc. ...... 41.40 Nitrogeuized substances . . . . . 5.26 Mineral salts 1.84 Bitter principle not determined. 1000.00 A most noticeable feature in the composition of French beer as just ji'Iven is the small amount of alcohol, and the very large quantity of glucose, etc. There are also nitrogenized substances, mineral salts, and a bitter prinei])le. Apart from the alcohol they contain, malt liquors are nutritious on account of these carbohydrate and nitrogenized and inorganic principles. They are often of great service to persons who are run down, debilitated, or who are slowly recovering from some exhausting, low type of disease, being taken then as a mediciiw:'. In such cases the small quantity of alcohol in the malt liquor is beneficial, acting as a stimulant, the hops are use- ful as a tonic, and the remaining jjriuciples as food. It will be seen from what has been said of alcohol that the evil resulting from the abuse of liquors of all kinds is proportional to the amount that is present of this principle, that malt liquors and light wines are less injurious than brandy and whiskey, and that beer, ale, etc., containing so many nutritious j)riiu'iples, closely approximate to tiic true idea of a food. Condiments, such as mustard, pepper, and osmazome, the aro- matic matter in roast meat, while not contributing to the repair of the tissue or the liberation of energy, are important adjuncts to fjod, stimulating the nervous system and exciting secretion. Indeed were it not for the flavor imparted to food by such substances it is doubtful whether it would be eaten for any length of time by either man or beast. ' Payen : Suhstances Aliinentaires, ]i. 4()"2. In the origiiiid taljle of Payen, 957 is given, insteiul of 947, probably a typograpiiical error. CHAPTER V. DIGESTION. Ix order that the i'ood shoukl fullill its functions in the economy it must be assimilated, and before that can be accomplished the food must be first di (jested and then absorljed. Digestion should, therefore, be studied first. Under the general term digestion are included several processes : the prehension of food, its mastication and insalivation, deglutition, the changes effected in the food during its passage through the stomach, the small and large intestine, and defecation. Mastication. The chewing of food, or mastication, is effected by the teeth, which, in the adult condition, ifre thirty-two in number, viz., eight incisors, four canines, eight premolars, and twelve molars. A tooth is usually described as having three parts. That jiortion which is seen in the mouth is called the crown. The tapering portion in- serted in the socket, or alveolus of the jaw, is the root or fang, and is held in position by fibrous tissue continuous with the periosteum of the jaw and submucous tissue of the gum. The intermediate constricted part of the tooth between the crown and the fang is known as the neck, the accumulation of fibrous tissue at this posi- tion being called the dental ligament. The incisor or cutting teeth (Fig. 13) four in each jaw, are near- est to the middle line in front of the jaw. They are inserted in their sockets by a single fang. The crown of the tooth is wedge- shaped, and presents a wide, sharp, and chisel-like edge, its lingual or inner surface is concave from above downward. In the upper jaw the central incisors are larger than the lateral ones, whereas, in the lower jaw the lateral are larger than the central ones. The incisors are well adapted to cut and bite the food. The tooth next to the lateral incisors in both jaws is called the canine (Fig. 14), and corresponds to the large tearing and holding tooth in the dog, hence its name. The canine teeth, four in number, are larger than the incisor teeth. The crown is conical and bevelled behind, the fang is longer than in any of the other teeth, and laterally exhibits a slight furrow, as if indicating a tend- ency to subdivide into two. The upper canine or eye teeth are larger and longer than the lower ones. The latter are often called the stomach teeth. The canine teeth assist the incisors in dividing the food. The premolars, two in each jaw (Fig. 15), succeed the canine. 84 DIGESTION. They are shorter and thicker than the latter. The crown is cuboidal, convex externally and internally, and exhibits upon the triturating^ Fig. 13. Fig. 1-1. Canine tixitli of the uiiper jaw. n. Front view. }k Lateral view, .sliowing tlie long fang groovetlou the.side. surface two eminences or cusps, hence their name of bicuspids. The fang is conical and flattened, and deeply Incisor teeth of the upper and lower gloved. The Upper premolars are jaws. «. Front view of t^he upper and larffcr tliauthe lowcr oucs, and their lower middle mci.sors. h. rrontviewof „~. , ,t.,^. the upper and lower lateral incisors. " al V ■ fans:: is more or less subdivided into Lateral viewof theupjjei-and lower mid- " die incisors, showing Ww chisel shape of twO. the crown : a groove is seen niarkiui;- rni 1 i j.1 111 slightly the fang of the lower tooth. 1 hc premolar tccth are succeeded by (QuAiN.) ^1^^ twelve molar or grinding teeth, six 16. in each jaw. The molar tootli (Fig. 16) has a cuboid crown. The trituratino: surface in the upper molars at the four angles is elevated into four tubercles, named from before backwards ; externally and internally, the paracone, metacone, protocone, hypocone, a diagonal ridge, connecting usually the protocone and metacone. In the Fig. 15. lower molars there arc five tuber- j cles or cusps, three on the outer side, the two hypoconulids and [)rotoconulid from before back- \\ards, two on the inner side, the entoconulid and metaconu- lid. Tlic lower molars are in- serted in their .sockets by a pair of conical fangs, the upper ones Firsthicuspid tooth of l)y three fluigs, two external and wli^TSend view; OUG internal, the latter is the showing the latera largest aud o-rOOVcd. The first First molar tooth of groove of the fang and r^ » . the upper and lower the tendency in the U|)- mohir tOOth that IS, the 0116 .laws. Thev are viewed I)er to division. (QUAiN , ■ ^ •. . i • j_i from the outer a.spect. andSHAKPEY.) most antcnorly situated — is the (QuAiNaud sharpey.) TEETH. 85 largest, the third, or the wisdom tooth, the smallest. Often, how- ever, in the savage races of mankind, in the milk teeth of civilized races, in the fossil man, and in the monkey, the last molar is the largest. It is by means of the molar teeth that the food is crushed and ground up. During mastication the external tubercles of the lower molars are opposed to those of the upper ones, and through the lateral motion of the lower jaw inward, the external tubercles pass do^vn the inclined surfaces of the external ones and up those of the in- ternal tubercles of the upper teeth, crushing the substances between them. The teeth are arranged in the jaw somewhat in the form of a curve. In savage races, on account of the prominence of the canine teeth, the curve is rather of an oblong form, and in civilized races the curve is often A^-shaped. The incisor teeth of the upper jaw overlap those of the lower, and the external cusps of the pre- molars and molar teeth close outside those of the lower jaw. It will be also observed that the central incisors of the upper jaw ex- tend over the central and half of the lateral incisors of the lower jaw, whilst the upper lateral incisors come in contact with the outer half of the lower laterals and the anterior half of the lower canines. The canine teeth of the upper jaw extend over half of the lower canines and half of the lower first premolars. The first premolar of the upper jaw is opposed to the half of the first premolar and half of the second premolar of the lower jaw, whilst the second upper premolars impinge upon the posterior half of the second premolar and anterior half of the first molar of the lower jaw. The first molar of the upper jaw is opposed to the posterior two- thirds of the first molar and anterior third of the second molar of the lower jaw. The second upper molar impinges upon the pos- terior third of the second and anterior third of the last molar of the lower jaw. The last molar in the upper jaw is opposed by that part of the third molar in the lower jaw which remains uncovered by the second upper molar. By this disposition it will be seen that no two teeth are opposed to each other only, and that, with the exception of the last molar, each tooth in the upper jaw is opposed to two teeth in the lower one. If a tooth is lost, or even two alternate ones, the remaining teeth will therefore be still useful. If the teeth of man be compared with those of a carnivorous animal, like a lion, or with those of a herbivorous one, like a rhi- noceros, it will be found that in man the teeth are both of the carnivorous and herljivorous kinds, and pretty evenly developed, whereas, in the lion, on the one hand, the teeth are all of the biting, cutting, and tearing character ; while in the rhinoceros, on the other, the largest teeth are of the ffrindins: and crushins: character. On making a longitudinal section of a tooth, of a molar for ex- 86 DIGESTION. ample (Fig. 17), it will be observed that there is a cavity within the crown of the tooth which extends into and throngh the fangs opening by a small apertnre at their apices. This space is the pulp cavity, and contains, in the living tooth, the pulp. The tooth will be also seen, from such a section, to consist of three parts, dentine, or ivory, a yellowish-white Fig. 17. substance bordering the pulp cavity, enamel, a harder and whitish substance capping the crown, cement, a translucent bonv-like laver encrusting the roots. Fig. 18. Section of human molar tooth magnifled. (Owex.) The dentine constitutes the great bulk of the tootli. Chemically it con- sists of about twenty-eight parts of animal matter (tooth cartilage), and seventy-two of earthy salts ; among the latter arc principally found cal- cium ph<)S}>hatc, some calcium car- bonate, and magnesium pliosphate. When examined with the microscope dentine (Fig. 1 8) is seen to consist of an amorphous translucent matrix, in which are iinlx'dded mnnerous canals or tubes, Avhose Avails are distinct from the matrix. These latter are the dental or dentinal tubules, and aver- age in diameter at their commencement y^Q mm. {-^i^-q of an inch). The intermediate space between the adjacent tubules is about three times their diameter. The dental tubules open at their inner ends or beginnings into tlie pulp cavity, outwardly tlicy pass to tlie pe- riphery of the tooth. Tlie tubules run generally in a parallel, but Section of fang, parallel to the dentinal tiibuU's (human canine). Magnified SOO diameters. 1. Cement, with large bone- lacunic and indieation.s of lamellfc. 2. (iranular layer of Purkinje (interglobu- lar spaces). 3. Itcutiual tubules. (Wal- DEYKK.) ENAMEL OF THE TEETH. 87 Fk;. 19. u. I)oiitInt'. }i. Odontoblastic cells. c. Filjcrs. (Tomes.) somewhat wavy course. As they pass outward they become grad- ually narrower, dividing and subdividing, giving off innumerable small branches, Avhich anastomose or end blindly. Some of the terminal l)ran('hes pass into the canalicula of the cement, others into the so-called interglobular spaces, irregular cell-like cavities in the matrix. The Avails of the dental tubules are about as thick as their calibre. In the living tooth the dental tubules are filled with the dental fibers, which are prolongations fr(jm the odontoblastic cells of the pulp (Fig. 19). Tliese den- tal fibers are possil)ly the terminal fila- ments of the nerves supplying the tooth. The contour markings observed in the teeth are due to irregularities in the matrix or intertubular sul)stance. As age advances there is deposited upon the inner surface of the dentine a secondary kind of dentine, known as osteo-dentine, which reseml)les both dentine and bone. This appears to be due to a sort of ossification of the pulp, the effect of which is grad- ually to obliterate the latter and the pulp cavity. Enamel. — The crown of the tooth is covered with the enamel, the hardest of organic substances. It is, however, gradually worn down by protracted use. The enamel is thickest upon that ])art of the tooth most used in trituration, here it exists in several layers ; it is thinnest at the roots, where it gradually disappears. Chemically, enamel consists of about five parts of animal matter, and ninetv-five of earthv constituents, the latter l)eino; mostlv cal- cium phosphate. Microscopically, enamel consists of solid six-sided prisms, the enamel fibers having an average diameter of ^J-q- mm. {-^-^-^-^ of an inch) and a length of ^^^ mm. ( jq^q q^ of an inch). Each prism rests by its inner end upon the den- tine, the outer end being covered with the cuticle of the teeth. Usually there are sev- eral layers of enamel prisms, the outer layer being then covered with the cuticle. The prisms, while arranged in a j)arallel man- ner, do not run in an exactly straight direc- tion, the course beino- rather an undulatinir one. The prisms, when viewed horizontally from their outer ends, present a tessellated appearance (Fig. 20). The so-called cuticle of the teeth, or membrane of Xasmyth, just referred to as cover- ing the outer ends of the enamel prisms or fibers, averages about the gi^ mm. to the ^^Vo ^^i"^- (15^00 ^ the 30^00 «f ^n inch) in thickness. It acts as a protective covering to the enamel. By some histologists the cuticle of the teeth is regarded as a very thin cement. Fig. 20. Section of enamel, higlily magnified, at right angles to the course of its columns ; exhibiting the six-sided char- acter of the latter. (Leidy.) 88 DIGESTION. Cement. — The criista petrosa, or cement, covers the roots of the teeth, beginning at the neck as a thin layer and becoming gradually thicker at the fangs. It adheres very closely to the dentine and to the periosteal lining of the alveoli. Cement differs from bone in its lacuniTe being more variable in their form and size, and their canicula being larger and more numerous. In many animals, like the cat, dog, and hog, the dentine, cement, and enamel are disposed as in man. In the grinding teeth of the herbivora, however, as in those of the elephant, horse, the dentine, enamel, and cement alter- nate with each other in such a way that as the teeth are worn an uneven triturating surface is always maintained. Tooth Pulp. — The pulp of the tooth situated in the pulp cavity is not only the formative organ of the tooth, l)ut the source of its vascular and nervous supply ; the tooth-pulp consisting of cells, blood vessels, nerves, and a small quantity of connective tissue. The cells are most numerous on the surface of the pulp. In this position they are known as odontoblasts and the layers formed by them as the membrana eboris. The odontol)lastic cells exhibit three kinds of processes : Those passing internally into the pulp, others which serve to connect adjacent cells, and those already re- ferred to as being prolonged into the dentinal tubules. The blood vessels pass in and out by the openings in the apex of the tooth, forming beneath the odontoblastic layer a capillary network. The nerves enter by the fang of the tooth and after giving off a few branches form a plexus beneath the odontoblastic layer. The exact manner, however, in Avhich the nerves terminate in the teeth is not known, unless, as already mentioned, the dental fil)ers are of a nervous character. The teeth of the upper jaw are supplied by branches from the superior maxillary nerve, those of the lower by the inferior maxillary. Xo lymphatics, as yet, have been found in the tooth pulp, or in other parts of the teeth. As age advances, the pulp of the tooth diminishes in size through its gradual calcification, the odontoblastic layer atrophies, the connective tissue increases, the capillary net- work disappears, the nerves exhibit a fatty degeneration, and the })ulp ultimately becomes a dried-u]>, insensitive mass. Althougii the pulp may lose entirely its vitality, yet the enamel and dentine may remain serviceable, they appearing to be perfected structures. These are, however, never reproduced when destroyed by wear or decay or by loss of the tooth, -with the rare exception of where a tooth is reproduced for the third time. The way in which the teeth are developed and the manner in which the permanent teeth are preceded by the deciduous or milk .set, will l)e c(»usidered under the subject of reproduction. Maxillary Bones. — Tiie teeth in man and mammalia are confined to the maxillary Ixjues, in which they are imbedded, the bone being moulded so to speak, around the roots of the teeth after these are developed and so forming the sockets. Between the jaw and the MAXILLARY BOXES. 89 tooth there is a space wliich in tlic living tooth is filled up by the alveodental periosteum. Throuoh the elasticity of this root mem- brane the tooth possesses a certain amount of" motion. Were the teeth iramova])ly fixed in their sockets some shock would be felt during mastication. This alveodental periosteum, which passes imperceptibly into the gum and periosteum, consists of connective tissue in which are found nerves and vessels. There is also no sharp line of demarcation between the gum and the mucous mem- brane of the nKjuth on the one hand and the periosteum on the other. Of the maxillary bones the superior, from being immovably ar- ticulated with the other bones of the head, are only passive in mas- tication. The upper teeth, however, offer fixed surfaces, against which those of the lower jaw are brought into a})position. Intermaxillary Bone. — If the inner surface of the superior max- illary bone be examined between the middle line and alveolar mar- gin, in most instances a suture will be readily recognized running downward and outward from the anterior palatine foramen to the outer margin of the second incisor tooth. This suture is interest- ing from several points of view, among others, as indicating in the embryo the distinction existing between the true superior maxillary bones and the intermaxillary bones, the latter being characterized by carrying the incisur teeth. As development advances, however, in man and to a great extent also in monkeys, the superior maxil- laries coalesce to such an extent with the intermaxillaries that the primitive distinction between the bones is almost entirely lost, in some instances the suture itself even disappearing. In the other mammalia, however, the intermaxillaries remain quite distinct from the superior maxillaries and each other, and are readily disarticu- lated. It was this latter circumstance that led Goethe,^ equally great as a poet and naturalist, to look for and discover the inter- maxillary bone in man, so convinced was he that the skull consisted of the same bones in all the mammalia. Temporo-Maxillary Articulation. — The inferior maxillary bone, mandible or lower jaw, consists in the adult of a single piece mov- ably articulated with the temporal bone (Fig. 21). This articula- tion is really a doul)le joint, since there is interposed between the condyle and the glenoid cavity a biconcave oblong piece of fibro- cartilage to the edges of w'hich is attached the capsular ligament. The spaces on either side of the cartilage are lined with synovial membrane, and there is no connection between the two cavities unless the cartilage is perforated. When the jaw is simply de- pressed, the joint acts as a hinge. Through the movement of the condyle on the eminentia articularis, the forward and lateral mo- tions of the jaw are affected. The mechanism of the temporo- maxillary articulation is therefore such as to insure great freedom of motion to the lower jaw. The lateral, forward, and depressing iSamintliche Werke, Band vi., Osteologie, s. 65. 90 DIGESTION. actions of the jaw either succeed each other or are variously com- bined during the mastication of food. If the condyle of the jaw in a carnivorous animal be examined, in a tiger, for example, it will be noticed that its long diameter is transverse, and that the glenoid cavity is grooved, hollowed out, so as to receive it. This disposition is carried out to such an extent in the badger that the lower jaw will remain depressed, interlocked, within the glenoid cavity, even though all the ligaments be cut away. The motion of the lower jaw in many of the carnivora is al- most exclusively of an up and down character, there being little or no lateral motion. In tlie herbivora, however, as in the sheep, rhinoc- eros, etc., it is the lateral motion of the lower jaw that is evident in chewing. In such animals the glenoid cavity is rather shallow and the condyle oblong or ovate. The motion of the jaw in the Fig. 21. Antci'd-posterinr section of the teiujioid-inaxillarv articulation of tlie riglit side. (A. T. .)>;,. (QUAix!) rodentia differs from that observed both in the carnivora and her- bivora, being backward and forward, like that seen in the gnawing action of a rat. This motion is rendered possible in such animals through the long diameter of the condyle and the glenoid cavity having an antero-posterior direction, as in the capybara. The teuiporo-maxillary articulation coml)ines in man, as we have seen, to a great extent, in one joint, the peculiarities just noticed in the temporo-maxillary articulation of the carnivora, herbivora, and rodent types of the mammalia. The various movements of the lower jaw are effected by a number of different muscles : to the consideration of these let us now turn. Muscles of Mastication. — Tliese muscles naturally divide them- selves into two groups, one of which elevates the lowxr jaw, moves it laterally or in an antero-posterior direction ; the other depresses it. Let us study the former group first. MUSCLES OF MASTICATION. 91 Principal Muscles of Mastication. Elevators, etc. Depressorts. Temporal. Masseter. External ) , . -, -r . 1 ^ pteryellies contract, then the hyoid bone will be elevated almost perpendicularly. On the other hand, should the hyoid bone be fixed by its depressor muscles, the loMcr jaw will be slightly depressed if the anterior belly of the digastric muscle acts alone ; should the posterior 1)elly act independently, then the mastoid process will be drawn downward, and with it the back of the head, thereby elevating the upper jaw and opening slightly the mouth. This action of the posterior belly alone, or with the an- terior one acting with it, is no doul)t aided by the deep muscles of the neck. AYhile it is possiljle that the lower jaw can be depressed by the anterior belly of the digastric acting alone, it is most prob- able that the posterior belly acts ^\ ith the anterior one in produc- ing this effect, the muscle acting in the reverse direction of that just referred to producing the movement of the back of the head. This view is confirmed by the fact that in several animals, in the orang, for example, as observed by the author,^ the posterior belly of the digastric muscle is alone present and inserted into the angle of the jaw. That the mouth is to a certain extent opened by the elevation of the upper jaw through the backward motion of the head due to the contraction of the posterior belly of the digastric and of the muscles of the neck, may be shown in various ways. For ex- ample, when the chin is placed upon a table, the lower jaw being then immovable, or when the lower jaw is firmly fixed, as in certain surgical operations, it will be observed that the mouth can be slightly opened, though the lower jaw cannot be depressed. It must be admitted, however, that the movement of the upper jaw in this respect has not much significance, as the opening of the mouth is essentially due to the depression of the lower jaw. Resume. — The eifect of mastication is that the solid food taken into the jnouth is cut and crushed and ground up by the teeth. III. C. Chapman, Proc. Acad, of Nat. Sciences, 1880, p. 101. ^4 DIGESTION. The little pieces that ooze out between the teeth and the cheeks are pushed under the teeth again by the muscular action of the cheeks and lips, while the fragments that escape within the inner side of the teeth are forced back by the tongue. The importance in man of the action of the cheeks, lips, and tongue in mastication is well seen when there is a paralysis of the facial or hypoglossal nerves. In such cases the food accumulates between the cheeks and the teeth, and the want of action of the tongue is seen both in the dif- ficulty of mastication and deglutition. The same effect can be produced by cutting the corresponding nerves in animals.* The thorough mastication of the food insures its further digestion. Indeed, a most fertile source of dyspepsia is the too common oustom of bolting the food. In the latter part of the last century it was shown by Spallanzani " that different kinds of meat when enclosed in perforated tubes and so swallowed, passed through his alimentary canal comparatively undigested. Wlien the meats, how- ever, were first broken up and then placed within the tubes very little undigested matter was found in them when passed by the anus. In gramnivorous birds, like the common fowl, for example, the want of teeth is supplied by pebbles swallowed with the food, the gizzard triturating the food by means of tlie pebbles. Mastication should be kept up until the food is thoroughly ground up. The teeth are so exquisitely sensible to the presence of any hard matter that we are enabled by them to know at once whether the process of mastication is comjjleted. During mastica- tion not only is tlie food thoroughly triturated, but it becomes gradually incorporated with the saliva. To the consideration of the production and effects of this secretion let us now turn. iPanizza, Gaz. Med., 1835, p. 419. ^Fisica Animale et Vegetabile. Venezia, 1782, Tomo secondo, p. 52. CHAPTER VI. DIGESTION.— (Contiiwed.) INSALIVATION AND DEGLUTITION. Fm. Insalivation. The saliva consi.sts of a mixture of the secretion of the parotid, submaxillary, and sublingual glands, usually known as the salivary glands (Fig. 27), and also of the labial, buccal, lingual, molar, and pharyngeal glands. The salivary glands are regarded at present by histologists as being compound tubular rather than racemose or grape-like glands as was formerly sup- posed, the secreting power residing in the cells Avith which the diverticula of the ducts are lined. According to recent researches ' the lumen of the duets appears to be prolonged as a capil- lary network extending be- tween and even into tlic .secreting cells. Ivct us consider now the properties of the saliva se- creted by these different glands 1)€'ginning with the parotid, which is secreted more abundantly than that of the other glands. The parotid saliva as obtained from sali- vary fistula or by introducing a tube directly into the duct of Steno, is an alkaline, clear, watery fluid, the latter property en- abling it to readily mix with and soften the food. The flow of the parotid saliva is most active during mastication, about three times as much saliva being secreted on the ma.sticating side of the mouth as on the ojiposite one. These facts, taken into consider- ation with that of the orifice of the duct of Steno being opposite the second molar tooth, so situated that the saliva at once comes in contact with the food that is being masticated, suggest the view that the function of the parotid saliva is to aid ma.stication. The facts of comparative physiology confirm this conclusion. Thus, in the ruminantia, which chew their food very thoroughly, ' La.sertcin, Pfluger's Archiv, Band o5, 1893, s. 417. The ?. ("ompressiou by the residues of the bohis carried on by the coutraction of the pharynx. E. Contraction of the cesophagus. (Laxdois.) pressure exerted upon the balloons by the bolus of food as it was first shot down by the action of the mylo-hyoid muscles, and, sec- ondly, by the action of the pharynx and (esophagus. In accord- ance with the way the curves were produced, they always presented iDuBoisEeymond's Archiv, 1880, 1881, 1883. 2 New York Medical Journal, 1894. Journal of Experimental Medicine, Vol. II., 1897, p. 453. DEGL UTITIOX. 1 05 two elevations or one elevation with two crests, the first elevation or crest, dne to the rapid, the second to the slow, contraction wave. By such curves Dr. Meltzer determined in his own person, (1) the length of time elapsing between the beginning of deglutition and the moment that the food arrived at the stomach ; (2) the in- terval of time between the Uvo waves of contraction when the bal- loon was in the pharynx ; (3) the time during wliich the food passed through the five contracting segments. The act of deglutition is usually divided, for convenience of description, into three periods, stages, or movements:^ (1) The passage of the bolus from the mouth through the fauces into the pharynx ; (2) from the pharynx into the oesophagus ; (3) from the oesophagus into the stomach. If the description of the process just given is regarded, however, as correct, the division into three move- ments, the limits of which in any case are entirely arbitrary, loses much of its significance and may as well be discarded. While the beginning of deglutition, or the part confined to the mouth, is vol- untarv, the remainder is involuntarv in character, being: due to an impression made upon the mucous membrane of the palate, etc., by the food, Avhich stimulates the center in the medulla, from which emanate the impulses that pass to the muscles involved. Indeed, without solid or liquid food in the pharynx it is impossible to per- form the second act of deglutition ; apparently, tliis is done some- times for three or four times without there beinp; anvthinw to swal- low, but there is really always present, under such circumstances, sufficient saliva to produce the necessary impression. It may be stated in this connection that the different parts of the oesophagus appear to contract independently of each other ^ the propagation of the contraction wave not depending upon the con- tinuity of tissue since one or more segments of the cesophagus mav be removed, and yet the remaining parts will contract in response to the stimulus of impulses passing from the medulla. It is hardly necessary to call attention to the fact that solid and liquid foods can be swallowed in all positions. It is a common feat among jugglers to drink a bottle of wine or a glass of beer while standing on their heads or hands. 1 Majendie, These soutenue a 1' Ecole de Medecine de Pari^, en 1808. Precis Elementaire de Physiologie, Tome ii., p. 59. ^A. Mosso, Moleschott, Untersuchungen, 1878, Band xi., s. 327. Kronecker ii. Meltzer ; Du Bois Eeymond, Archiv, 1881, s. 465. CHAPTER VII, DIGESTION.— (ro;i///,,/«^) GASTRIC DIGESTION. The stomach is a musculo-membranous sac whose walls have on an average a thickness of a little more than two millimeters (a line). When distended it measures laterally about 37.5 centime- ters (15 inches), and antero-posteriorly 12.5 centimeters (5 inches) with a capacity usually of 3 liters (5 pints). The capacity of Fig. 33. Call liladilcT. -- Spleen. - Small iutestiue. J Colon. — Rectum. Digestive apijaraturs of man. (Milnk I^dward.s.) the stomach, however, is often less and sometimes even much greater, varying with the age, sex, and habit of the individual. It is held in position in the upper part of the abdominal cavity by its connection with the oesophagus and the folds of the peritoneum. When empty, the sides of the stomach are usually in contact, and the whole organ presents a flattened appearance. When distended by food, however, the anterior wall of the stomacli becomes superior, and is applied to the diaphragm. This is due to the ends of the MOTIONS OF THE STOMACH. 107 stomach and lesser curvature being comparatively immovable. As the food enters the stomach from the oesophagus, it turns to the left, and, passing into the cardiac end, or greater pouch, thence proceeds along the greater curvature to the pyloric end, returning by the lesser curvature to the cardiac portion, to ])egin the same course over again. Each of these revolutions occupies from about one to three minutes, and are slowest at first, becoming more rapid as digestion advances. The food undergoes, therefore, a sort of churning action, passing from one side of the stomach to the other. Hereby it is thoroughly incorporated with the gastric juice, gradu- ally broken down, liquefied, and finally converted into what is known as the chyme. During the beginning of digestion the pyloric orifice is so firmly closed by the contraction of the circular muscular fiber aided by the circular fold of mucous membrane developed there that no food passes into the duodenum. After the churning movement just described has continued, however, for about a quar- ter of an hour the circular muscular fibers of the pyloric orifice relax. Then the liquid pultaceous part of the food and later the more solid portions and even hard bodies, such as coins, stones, are pushed or forced into the duodenum by the vigorous peristaltic con- tractions of the pyloric jjart of the stomach, the fundus, or cardiac portion, taking little or no part, acting rather as a reservoir. In deed, when digestion is at its height, the cardiac portion of the stomach is quite distinctly separated from the pyloric portion by a " transverse " constricting band, the so-called " sphincter antri pylorici " situated from seven to ten centimeters from the pylorus. The organ then presents an hour-glass form, of which two-fifths consist of the cardiac portion. It is worth mentioning in this con- nection, that this hour-glass form of the stomach, present only in man during digestion, is the form presented in the manatee whether digestion is going on or not ; the author having found in the dis- section of several individuals the stomach ahvays presenting this form, whether it was full of food or empty.^ After the food has been digested and the stomach has been emptied of its contents, which processes are effected within a period of from two to four hours, all the motions just described cease, and do not recommence again until a fresh supply of food is taken. The churning and peristaltic motions of the stomach just described depend upon its muscular fibers assisted by the diaphragm. The muscular coat of the stomach which averages about a millimeter (2V ^^ "^'^ inch) in thickness, consists of three sets of fibers, the longitudinal, circular, and oblique, which are disposed from without inward, in the order just named — that is, the longitudinal fibers are external, the oblique are internal, while the circular fibers lie be- tween the other two. These three sets of fibers are, however, very unequally developed. Thus, the longitudinal fibers are best seen in the lesser curvature ; 'II. C. Chapman, Proc. Acad, of Nat. Sciences, Phila., 1876, p. 452. 108 DIGESTION. the circular fibers are rather indistinct to the left of the cardiac ori- fice, and are most marked at the pyloric, forming then its sphincter muscle ; while the oblique fibers are limited to the cardiac portion of the stomach, passing over it from left to right. It is at the point where these oblique fibers cease that the stomach becomes con- stricted in digestion into the two parts already described. Through the contraction of the longitudinal and circular fibers the food is forced along toward the pylorus, which, through its sphincter muscle, resists at first as we have seen the passage of any food into the small intestines. The cardiac orifice is guarded by the fibers in that situation, as well as by the contraction of the lower part of the oesophagus already referred to. The movement of the food is also due, no doubt, partly to the pressure exerted by the diaphragm and the intestines. The natural stimulus to these motions of the stomach during digestion is the presence of food. The account that we have just given of the movements that the stomach midergoes during digestion in man, is based upon the ex- periments and observations made by Beaumont ^ upon St. Martin supplemented by those recently made upon animals.^' Alexis St. Martin, a voyageur in the service of the American Fur Company, a man about eighteen years of age, of good constitu- tion, robust and healthy, was accidentally wounded by the discharge of a musket on the 6th of June, 1822. The charge, consisting of powder and duck shot, entered the left side posteriorly and ob- liquely, blowing off integument and muscles of the size of a man's hand, fracturing the sixth and seventh ril)s, lacerating the lower portion of the left lobe of the lungs, the diaphragm, and perforating the stomach. Notwithstanding the serious nature of the wounds St. Martin recovered at least so far as concerned his general health. The perforation through the walls of the stomach, hoAvever, re- mained permanently open, having resisted all treatment. This perforation (Fig. 34) was situated three inches to the left of the cardiac portion of the stomach, near the superior termination of the great curvature, and measured about two and a half inches in cir- cumference. The opening was closed under ordinary circumstances by a movable valve formed through a doubling of the coats of the stomach, which had been formed during the progress of the case, and which effectually prevented the escape of food. This valve could be easily depressed, when the interior of the stomach could then be examined. St. Martin, after the recovery of his health, performed all the duties of a common servant — chopping wood, carrying burthens, etc. — married and had several children and enjoyed general good health up to eighty years of age. For a number of years, off and ^ Experiments and Observations on the Gastric Juice, Plattsburgh, 1833. ^Hofmeister and Schiitz, Archiv fiir exper. Path. u. Phar., Band xx., 1886, s. 1. Rossbach, Deutsclies Archiv fiir klinisclie Medecin, Band xlvi., 1890, s. 323. Moritz, Zeitschrift fiir Biologic, Band xxxii., 1895, s. 313. GASTRIC FISTULA. 109 on, St. Martin was under the observation of Beaumont, under strictly physiological conditions. It is this circumstance which makes this case so important in the history of the physiology of di- gestion, the cases of gastric fistula that had hitherto occurred ^ not having afforded much opportunity for the study of gastric diges- tion. It should be mentioned, however, that since the celebrated case of St. Martin interesting cases of gastric fistula, the result of wounds or gastrotomy, have been made use of for purposes of phys- iological investigation among others by Schmidt and Richet, the results of which will be referred to presently. Up to about the middle of the eighteenth century it was still a subject of discussion Fig. 34. Ordinary appearance of the left breast and side, tlie aperture filled with the valve ; the suliject in an erect position. (BEAUMONT.) among physiologists as to whether the action of the stomach in di- gestion was of a chemical or purely mechanical nature. The con- troversy was finally, however, brought to a termination by the dis- covery of Reaumur,- in 1752, that there existed in birds a gastric juice, and that food was softened and partly digested in the stomach of those animals independently of any mechanical action of its walls. Reaumur's experiments consisted in inserting into the stomach of a bird (bustard) a tin tube containing meat, the ends of which were, however, covered with a grating, and permitting the tube to remain a sufficient time in the stomach for the gastric juice to mix with the food ' De Fistula Ventriculi, Eobcrtas Marcus, Berolini, 1835. ^Memoires de 1' Academic des Sciences, 1752, Tome Ixix., p. 461. 110 DIGESTION. and digest it, the walls of the tube resisting any pressure that might be exerted by the "walls of the stomach. In substituting for the tube containing the meat small pieces of sponge, Reaumur was able to collect, by pressing the sponges after they had been rejected, a small quantity of a liquid which gave an acid reaction, and which was the first specimen of a solvent fluid from the stomach ever ob- tained. The next step in advance was made in 1777 by Edward Stevens,^ who employed a juggler, whose habit was to swallow stones, to swallow instead little silver balls, which had previously been filled with diiferent kinds of food, the walls of which, being perforated, permitted the entrance of the gastric juice. After twenty to forty hours these balls M'onld be passed by the anus, and their contents would be found to be more or less digested. From the result of those experiments Stevens concluded that digestion cannot be accounted for by heat, trituration, putrefaction, or even fermentation alone, but l:)y a most powerful humor which is secreted by the tunic of the stomach, and is poured into the cavity of the same. A few years later there appeared the celebrated work of Spal- lauzani,^ in which the observations of Reaumur and Stevens were repeated and confirmed, and extended in a series of experiments made upon quite a number and variety of animals including sev- eral interesting observations made by the author upon himself, some of which have already been alluded to in speaking of the subject of mastication. Spallanzani began his experiment upon himself by first swallowing little linen bags in which the diiferent articles of food, animal or vegetable, were sewn up. These were usually passed by the anus within a period varying from t^venty-three to twenty- four hours, and were found either empty or nearly so, the contents beino; more or less digested, accordino; to the kind of food used and the length of time durino; which thcv had remained within tlie bodv. The necessity of first masticating the food before swallowing it was then demonstrated ; and, in conclusion, a little gastric juice was olitained by vomiting, and the effect of this upon boiled beef tried outside the body, with the result of showing that the beef became pultaceous, and that there was no jjutrefiiction. Spallanzani dis- tinctly recognized a most imjwrtant fact, that the process of diges- tion, beginning in the stomach, is completed in the intestines. In 1803 a woman with a gastric fistula, coming under the care of Dr. Helm,^ in Vienna, that physician profited by the opportunity to make some study of gastric digestion, Init added little of value to what had already been established. In 1824 Front ^ endeavored to show, by analysis, that the acidity of tlie gastric juice in animals was due to hydrochloric acid. Shortly afterward, between 1825 and 1827 simultaneously, ' De Alimentorum Concotione, Thesaura'^ Medicus Smellie, Tomus iii., p. 481. '^FLsica -Vnimak' e Vegetahile, Tomo secundo, Venezia, 1782. ^. Jacob Helm, Zwei krankengeschiten, Vieniic, 1803. 3Iarcus, op. cit., p. 21. * Philosophical Transactions, 1824. GASTRIC JUICE. Ill Leuret and Lassaigne/ Tiedemann and Gmelin ^ made a detailed and extended series of observations npon digestion ; those of the latter being the most elaborate. The experiments were made prin- cipally npon dogs, cats, horses, cows, sheep, birds, reptiles, and fishes, the observations on man being exceptional. In some of the experiments the means of obtaining the gastric juice were the same as those used l)y Kcaumur, etc., already referred to. In many of them, however, another plan was adopted. The animal to be ex- perimented upon after fasting, was made to swallow stones, nails, etc., a few hours afterward the animal was killed, it having been ascertained that such hard substances would excite the stomach to secrete a considerable amount of gastric juice — sufficient in quantity to analyze and experiment with. Notwithstanding the number of animals, experiments performed, and the variety of the observations, nothing definitely was established as to the composition and prop- erties of the gastric juice, to what elements it owed its digestive powers, or exactly what effect it had upon different kinds of food. It will be seen, therefore, from this historical digression that little was positively known of gastric digestion, as it takes place in man, before the observations and experiments of Beaumont were made. Beaumont was the first to observe digestion as it goes on in the healthy human stomach, to describe not only the motions of the latter, but also the manner in which the gastric juice is secreted, its effect upon food, the changes that food undergoes in the stomach, to collect the normal gastric juice in such quantities that it could be analyzed and studied with reference to its effect upon food outside the body, to determine the influence exerted, by temperature, exer- cise, and the nervous system, upon digestion, the length of time that food remains in the stomach, and numerous other interesting facts. Further, it was this remarkable case of St. Martin that first sug- gested to Basso w,^ the Russian naturalist, the making of a per- manent gastric fistula, afterwards also successively performed by Blondlot,^ and frequently resorted to at the present day as a con- venient means of obtaining fresh gastric juice. Let ns turn now to the consideration of the manner in which the gastric juice is produced, its composition, effect upon food, etc., as learned, by means of gastric fistuloe, from the examination of gastric juice obtained by the stomach pump, and from experiments made with artificial gastric juice. During the intervals of digestion the stf)mach is empty, its mucous membrane being simply covered with a very thin, trans- parent, viscid mucus. At this time the reaction of the membrane is either faintly alkaline or neutral. With the introduction of food into the stomach, the membrane at once changes its pale appear- ance, becoming red and turgid from the increased amount of blood. 1 Eecherches pour Servir a 1' Histoire de la Digestion. Paris, 1825. 2 Recherches sur la Digestion. Paris, 1837. "Bulletin de la Societe des I^ aturalistes de Moscow, 1843, Tome xvi., p. 315. *Traite analytique de la digestion, 1843. 112 DIGESTION. Small drops of gastric juice appear as small pellucid points on the surface of the membrane, which has now an acid reaction, and gradually a little stream of gastric juice begins to flow upon the food in the stomach. Beaumont showed most conclusively that food is the natural stimulus to the secretion of the healthy gastric juice. For the exciting impression of food is diffused over the wdiole secreting surface, and the maximum effect is thereby obtained. Local stimulus, however, like that of an India-rubber tube, will ex- cite a flow, and this Beaumont used when a small quantity of gastric juice — an ounce and a half, for example — was required un- mixed with mucus or food. Tlie human gastric juice, which is rarely obtained free from food residues, mucus, and saliva, is a clear or faintly cloudy, almost colorless fluid, having a sour odor and taste, strong acid reaction and low specific gravity 1.001—1.010. As a general rule it con- tains also an admixture of glandular cells or their nuclei ; mucous corjiuscles and more or less changed cylindrical epitheliimi. Composition of Gastric Juice. The first to attempt to analyze the gastric juice was Scopoli, an Italian chemist, in the last century. The gastric juice examined was obtained by Spallanzani from a raven, and, according to Sco- poli, consisted of an animal matter, earthy salts, and what would now be called hydrochloric acid. The gastric juice of St. Martin was examined among others by the late Professor Dunglison, who, in a letter to Beaumont,^ states that it contained free muriatic and acetic acids, phosphates, and muriates, with bases of potassium, sodium, magnesium, and calcium, and an animal matter soluble in cold water, but insoluble in hot. Among the more recent analyses of human gastric juice, that of the woman with a gastric fistula, made by Schmidt, is especially worth of mention. Composition of Human Gastric Juice Holding Saliva. 2 Water 994.400 Pepsin, etc. ....... 3.195 Hydrochloric acid 0.200 Calcium chloride ...... 0.061 Sodium chloride ...... 1.464 Potassium chloride ...... 0.550 Calcium ] Magnesium 'phosphate . . . . . 0.125 Ferrum J Loss 0.005 1000.000 iQp. cit., pp. 7S, SI. ^Annalen tier Chcmie, ]8')4, Band xcii., s. 40. Schmidt p:ivcs as the mean of the two analyses tlie numbers 994.404 for the water, and 1.4()") for tlie sodium chlo- ride. These are probably typograpliical erroi-s, as the other numljere are those given in the table. GASTRIC JUICE. 113 According to this analysis, then liiunan gastric juice consists of water, pepsin, hydrochloric acid, chlorides, and phosphates. It should be mentioned, however, that the organic matter of the gas- tric juice consists not only of pepsin, but of another unformed ferment or enz^-me, the so-called rennin. It would appear also from recent investigation that the amount of hydrochloric acid as given by Schmidt is too small, due jjrol^ably to the gastric juice analyzed by him having been diluted with water or saliva. At least, Richet^ found the hydrochloric acid of the himian gastric juice also obtained from a fistula amounting as the average of eighty observations to 1.7 parts per thousand, the variation being from 0.5 to 3 parts per thousand, an estimate not differing essentially from the later ones of Szabo,^ Ewald,^ and Boas.* It may be men- tioned that the samples of gastric juice analyzed by Szabo was taken from the stomach of a man by means of a stomach piunp, M-ithout the addition of water. The epithelium of the stomach consists of columnar cells, among which occur the so-called goblet, or mucus-secreting cells. The . latter appear to be columnar cells, whose protoplasm has been trans- formed into mucinogen, or mucin, which swells up the cell at its free end, hence its name, as it passes into the cavity of the stomach. With the escape of the mucin, the more or less empty cell resumes the character of the ordinary columnar cell. It has already been mentioned that the gastric juice is secreted by the mucous membrane of the stomach ; let us consider now, so far as is known, the manner of its elaboration. The mucous membrane of the stomach, in the living healthy sub- ject, is of a velvety, pulpy consistence, with an average thickness of about 1.2 millimeters (V=g- of an inch), and in color of a pale pink or reddish appearance, which rapidly changes after death into a brownish hue. The mucous membrane is loosely attached to the submucous coat or the layer of areolar tissue which lies between the mucous coat within and the muscular coat without. It is through the looseness of this attachment that the longitudinal folds into which the membrane is usually thrown are due, and which are effaced when the stomach is distended. The epithelium presents, more particu- larly at the cardiac orifice, a marked contrast as compared with the pavement epitheliimi lining the oesophagus. If the mucous membrane of the stomach be gently washed by allowing a small stream of water to run over it slowly, which will carry off the adhering mucus, and then be examined ^vith a simple lens, little polygonal spaces or depressions "will be noticed in its sur- face, varying in size from ^ to J of a millimeter (o-o"o ^^ T'ff'o ^^ ^^ inch) in diameter. If these depressions or alveoli be ftirther exam- ^ Comptes Eendus, Tome Ixxxiv., p. 450, 1877. ^ Zeit.•")) will be Found resembling those in the pyloric por- tion, but while the upper portion of the tubule is lined with columnar epithelium, the succeeding part or neck is filled rather than lined by large ovoidal or spheroidal granular cells, the so-called parietal" cells. Toward the bottom or fundus of the gland these parietal cells do not form a continuous layer, but are seen scat- tered here and there, and bulging out so as to give the tubule a varicose appearance, the remaining portion of the tubule, except the narrow pas- sage-way in the middle, being occu- pied by finely granular polyhedral angular cells, the so-called central cells, similar, as just mentioned, to those found in the pyloric tubules.^ In the cardiac portion of the stomach, more particularly around the cardiac orifice, the tubules are branched in ' Principal, chief, adelomorphous ( dSv^og, hidden) cells. 2 Ovoid, border, oxyntic ( of w^v, to acidu- late), delomorphous cells. "According to the recent observations of Langendorff and Lasei-stein (Pfliiger's Archiv, 1894, Band Iv., s. 578) the main tube of a gastric tubule, at least those presenting parietal cells, not only extends through- out the length of the tubule as usually described, but gives off lateral branches, ■which ])ass to the parietal cells, and there forms a network on which the cell lies. Gastric gland from liiuuan stomach. 1. Columnar cells. 2. Parietal cells. GASTRIC JUICE. 115 character, the upper part of the tubule dividing into two or three branches, and there usually subdividing again. These cardiac tubules, like simple ones found in the middle zone of the stomach, contain both ovoid and central cells. It will be observed from this brief description that two kinds of glands are found in the human stomach, differing essentially in their structure : pyloric tu- bules, simple and branched, situated in the pyloric part of the stomach, containing columnar and central cells : cardiac tubules, simple and branched, situated in the middle and cardiac parts of the stomach, containing columnar and central cells also. While undoubtedly such a distinction as that just described ex- ists between the gastric glands in man, the exact line of demarca- tion between the two is not as distinct as in certain animals, the dog for example, the diiferent kind of glands passing in man into each other through intermediate forms. Judging from what has been learned of the process of salivary secretion, analogy would lead us to suppose that the gastric juice is secreted in an essentially similar manner, and such would appear to be the case, as shown more particularly by the researches of Heidenhain.^ Thus, if sec- tions of the gastric glands of an animal be examined before the tak- ing of food, the so-called central cells of the cardiac, as well as those of the pyloric glands, will be found pale, finely granular, and not staining readily with aniline or carmine. With the beginning of digestion, however, these cells become swollen, coarsely granular, turbid, and stain more readily with the above reagents ; as diges- tion continues, the coarse, granular, and tm'bid condition and dis- position to stain increase, while at the same time the cells become smaller and shrunken. The only conclusion to be drawn from the changes in these cells is that the readily stainable material, etc., developed during digestion constitutes the antecedent stages, the mother substances, or zymogens of pepsin and rennin, the so-called pepsinogen and renninogen. Inasmuch, however, as the parietal cells of the cardiac portion of the stomach do not exhibit during di- gestion the histological changes observed in the central cells of the cardiac and pyloric glands, only swelling up and projecting some- what externally from the wall of the gland, and from the fact of parietal cells being present in the glands of the stomach of the frog coincidentally with the presence of acid, the pepsin-forming cells being confined almost entirely to the lower part of the oesophagus in that animal, it appears reasonable to attribute to the parietal cells the production of the hydrochloric acid of the gastric juice. If such be the case, however, it is somewhat difficult to understand why, after injecting ferrocyanide of potassium and ferric lactate into the blood of an animal, as in the experiment of Bernard," the pro- duction of Prussian blue should be limited to the surface of the stomach, since if the ovoid cells of the glands actually produce the ' Hermann, Handbuch, Funfter Band, 1S80, s. 141. ^Liquides de 1' Organisme, Tome ii., p. 375. Paris, 1859. 116 DIGESTION. acid the presence of which is necessary for the formation of the salt, the Prussian blue should be visible in the cells of the fundus or their vicinity, as well as upon the surface or mouth of the gland, unless the acid is expelled from the gland as rapidly as produced, which is not improbable. If the above view be accepted as correct then the gastric juice is secreted by only the cardiac tubules, those containing parietal cells producing acid and central cells elaborat- ing the zymogens, the cells of the pyloric tubules elaborating only the latter, and the columnar epithelial cells, mucus. ^ As a confirm- ation of this view it may be mentioned that an infusion of the mu- cous membrane of the pyloric portion of the stomach does not pos- sess digestive properties unless acidulated. It will be recalled also in this connection, that in speaking of the motions of the stomach, at- tention was called to the fact of the cardiac portion of tlie stomach acting as a reservoir for the food, the pyloric portion as the expul- sive part. The significance of this distinction becomes more ap- parent now that it has been shown that digestion is limited to the cardiac part of the stomach. The nature and chemical constitu- tion of pepsin, although it was discovered many years since,^ is still imperfectly understood, it not having been obtained as yet in a suf- ficiently pure state to admit of analysis. It is regarded as being an unformed ferment, an enzyme on account of its characteristic ef- fect upon proteid matter. Like other ferments a small amount of pepsin will convert a large amount of proteid into peptone, the action of the pepsin being retarded like ptyalin by any great excess of the products of digestion. One of the most striking peculiarities of pepsin is that it only acts on acid media and upon albuminous bodies, the latter swelling up, becoming transparent, and then dis- solving under its influence. Hence the gastric juice to be effica- cious contains, as we have seen, both pepsin and hydrochloric acid. It should be mentioned that while hydrochloric acid can be re- placed by certain acids such as lactic, nitric, or jDhosphoric acids, the latter are not so effective. Like other enzymes the action of pepsin is influenced by tempera- ture, the most favorable being about o8°C. (100°F,), while a pro- longed exposure to one of 80 °C. (176°F.) will destroy the enzyme. A solution of pepsin may be obtained relatively pm*e by treat- ing the mucous membrane of the stomach with dilute phosphoric acid and then adding lime water. The resulting precipitate which carries down the pepsin being then dissolved with dilute hydro- chloric acid and the salts removed by dialysis, the non-diffusible pepsin remains in the dialyzer. Rcnnin, derived from zymogen rennin l)y tlie action of an acid and Avhose chemical construction is still unknown, is regarded as being an enzyme on account of the ^According to more recent investigations the changes undergone by the cells during digestion are somewhat different from those described in the text. The re- sults, lu)wever, can be reconciled to a great extent if the diHerent conditions under which tlic cells were examined be taken into consideration. J. N. Langlev, Journal of Physiology, 1880, Vol. II., p. 261. 2 Schwann, Miiller's Archiv, 1836, s. 66. GASTRIC JUICE. 117 property it possesses of coagulating or curdling milk. Some dif- ference of opinion still prevails as to the nature of the process of curdling. Recent researches render it probable, however, that the casein of milk^ is split by rennin into two bodies, one of which, paracasein (cheese), in combining with calcium salts is precipitated as the insoluble curd, while the other, the " whey proteid," remains in solution. There appears to be no doubt that the curdling of milk docs not take place in the absence of calcium salts. There is still some diiference of opinion, however, whether the latter act by combining witli the paracasein to form an insoluble compound, the curd, or whether they influence, in some way, the separating out of the paracasein. Although the chemical nature of rennin is as little understood as that of pepsin, that it is an enzyme is still further shown by the fact that one part will precipitate 800,000 parts of casein.^ It might be supposed that the curdling of milk in the stomach was due to the acid of the gastric juice, since casein is precipitated by lactic acid, developed from lactose by bacteria, as in the souring of milk. Apart, however, from the fact of the casein not being split into curd and whey by the acid but is simply precipitatic as such, curdling will take place even after the gastric juice has been rendered neutral, but will not take place if the latter is boiled, the elevated temperature destroying the enzyme. The advantage of the curdling of milk in the stomach is not apparent, unless it be supposed that its digestion is promoted when in that condition. That such is the case is rendered probable, however, from the fact that the curd is readily digested by the gastric juice, being converted into peptone like other proteids. A comparatively pure solution of rennin may be obtained according to Hammarsten^ in the following way : An infusion of the mucous membrane of the stomach being acidulated with hydrochloric acid, is just neutralized and then shaken with magnesium carbonate until the pepsin is pre- cipitated. The filtrate l)eing precipitated with basic lead acetate is decomposed with very dilute sulphuric acid, and the acid liquid fil- tered and treated with a solution of stearin soap. The rennin is precipitated by the fiitty acids set free, and when the last are placed in water, and removed by shaking with ether, the rennin remains in the watery solution. Hydrochloric Acid of the Gastric Juice. . The hydrochloric acid produced by the parietal cells of the car- diac tubules appears to be derived from the decomposition of the 1 Casein is sometimes called caseinogen, in which case paracasein is named casein. The term caseinogen, if we wish to be consistent in onr nomenclature, should be re- served, liowever, for a mother substance of casein which may yet be shown to exist in the cells of the mammary glands, as pepsinogen, the mother substance of pepsin, exists in the gastric glands. ^ Landois, A Text-book of Human Physiolt)gy. Translated by Stirling, 1891, p. 306. ''Hammareten, op. cit. , p. 184. J. W. Warren, M.D., On the Presence of a Milk- curdling Ferment (Pexin) in the Gastric Mucous Membrane of Vertebrates, Journ. of Exp. Med., Vol. 2, 1897, p. 475. 118 DIGESTION. sodium chlorides of the blood supplied by the food through the action of the primary acid sodium phosphate/ the reaction being as follows : XaCl + XaH^PO^ = HCl + Na^HPO, In confirmation of the above view, it may be mentioned that dur- ing gastric digestion in the dog, while the excretion of chlorides diminishes, the alkalinity of the urine increases, the sodium car- bonate (XaHCOg) to which the latter is due, being the final form assmned bv the sodium liberated in the decomposition of the chlo- rides.' On the supposition that the secondary sodium phosphate (Na.,HPO^) formed according to the above reaction remains in the blood and meets there carbon dioxide and water it becomes intelli- gible how through mutual reaction, the sodium carbonate of the urine may be formed. Thus Na^HPO, + CO^ + H^O = NaH^PO, + NaHC03 As a further proof that the hydrochloric acid of the gastric juice is derived in the manner just mentioned, it may be stated that, ac- cording to recent experiments,^ if a dog be given with his food sodium bromide instead of sodium chloride, more than fifty per cent, of the hydrochloric acid of the gastric juice will be replaced by hydrobromic acid. In this connection it should be stated, how- ever, that when sodium iodine is given instead of sodium chloride the gastric juice contains but little hydroiodic acid. The greater part of the hydrochloric acid present in the gastric juice is regarded as existing in a free state. From the fact, however, that pepsin will convert proteid into acid albumin like hydrochloric acid, though more slowly, as well as for other reasons, it is inferred that part of the hydrochloric acid at least exists in combination with pepsin as a "paired acid," pepsin-hydrochloric acid. The existence of an acid in the free state as in the case of the hydi'ochloric acid of the gastric juice, though a rare occurrence in the animal economy, is not the only one known. Many years since it was observed by Troschel * on a visit to Messina that the salivary glands of the Dolium galia, a gastropodous mollusk, excreted a fluid containing free mineral acids shown afterwards by Boldeker to be hydrochloric and sulphuric acids. Action of Gastric Juice Upon Food. Let us turn now to the consideration of the action of the gastric juice upon the dififerent articles of food as learned either from exper- iments made with the normal secretion obtained from gastric fistulae, with artificial gastric juice, and from an examination of the contents of the stomach. It may be mentioned in this connection that an iMaly, Hermann, Handbuch, 1881, Band v., Zweiter Theil, s. 67. 2E. O. Schoumow-Sumanowski, Archiv fiir exper. Path. u. Pliar., 1894, Band 33, s. 336. ^Neucki u. Sohoumow, Idem, Band 34, 1894, s. 313. *Poggendorff's Annalen, Band 93, s. 614, 1854. ACTION OF GASTRIC JUICE UPON FOOD. 119 artificial gastric juice can be readily prepared by adding a glycerine extract of the mucous membrane of the stomach to a large bulk of 0.3 per cent, hydrochloric acid. When the gastric juice so prepared is used for showing the digestion of proteids and certain albuminoids, to which we shall see its action is limited, the temperature should be maintained at about 37 °C. (100°F.), and the mixture stirred from time to time. When meat is subjected to the action of gastric jnice, whether obtained from a fistula in the stomach or artificially pre- pared, it gradually becomes softer, changes in color, and breaks down into a grumous, pultaceous mass. Under the microscope the muscular fibers, though broken up into small pieces and retaining but little tenacity, are readily recognized through their character- istic strite. The intermuscular connective tissue, the sarcolemma, disappears, however, being completely dissolved out. ^leat is, therefore, not actually dissolved in the stomach, but is rather dis- integrated and converted into a pultaceous liquid, A\hich readily passes into the small intestine. In a similiar manner white of q^^, fibrin, the casein of milk, gelatin, glutin, etc., are broken down, lic|uefied, and converted into a grayish soup-like liquid. The gastric juice, however, not only acts physically upon the albuminous, proteid foods, softening, disintegrat- ing, and liquefying them, but chemically also, transforming them into peptones,^ albumin, becoming alljumin peptone, gelatin, gelatin peptone, etc. The transformation of proteid into peptone by the action of the gastric juice according to the generally accepted - view is essentially as follows : The proteid is first converted by the hy- drochloric acid into acid albumin or syntonin, the latter then, under the influence of the pepsin, takes up water, and splits into two sub- stances, viz., hemialbumose and antialbiunose which passing through intermediate stages finally become hemipeptone and antipeptone, a mixture of the two latter being called amphopeptone. Peptones have hitherto been separated from their antecedents, the so-called albumoses or proteoses ^ by saturating a mixtiu-e containing them both, with ammonium sulphide, it being supposed that all of the pro- teids present would be precipitated except the peptones. As there is good reason however for supposing that certain of these inter- mediate products of proteolytic digestion (deuteroalbumose) are not precipitated, some doubt * still exists as to whether peptones have ever been obtained pure. Further, the only way by which the hemipeptone can be separated from the antipeptone in the ampho- peptone mixture or the final product of peptic digestion depends ' Lehmann, Lehrbuch der Physiologische Chemie, 1853, Band ii. , s. 46. ^ Kiihne, \'erhand Nat. Hist. Med. Vereins, X. F., Band i., Heidelberg, 1876. Neumeister, Lehrbuch der physiologischen Chemie, 1897, s. 2ol. Chittenden, Cartwright Lectures, Medical Eecord, New York, 1891, pp. 485, 516, 545. ^The term proteose is sometimes used as synonymous with albumose, sometimes in a more general sense as including albumoses. From the latter point of view albumose derived from albumin, caseose from casein, etc., would be regarded as proteoses. *Hammarsten, op. cit., p. 28. 120 DIGESTION, upon the fact, as we shall sec hereafter, that while antipeptone re- sists all further digestion, heniipeptone is decomposed through the action of the trypsin of the pancreatic juice into the amido acids leucin and tyrosin. It is obvious however that while this method suffices for the obtaining of antipeptone it necessarily involves the destruction of the heniipeptone. Indeed the existence of the latter peptone is rather an inference from the fact that through the action of trypsin upon amphopeptone two bodies appear, leucin and tyrosin, of which hemijicptone is sup- posed to be the antecedent/ A convenient method of showing the conversion of proteid into peptone by gastric juice and at the same time the necessity of the latter containing both pepsin and dilute hydrochloric acid is as follows : Prepare three cubes of equal size of coagulated white of egg, put one cube into a test-tube containing gastric juice, another into a second tube in which the gastric juice has been boiled that is in a weak solution of hydrochloric acid (0.2 per cent), the pepsin having been destroyed, a third in a tube in which the gastric juice has been neutralized that is in a solution of pe]>sin (0.8 per cent.). After a few hours if the temperature be maintained at about that of the body and the mixture stirred from time to time it will be found that, while the albumin in the gastric juice has been reduced to a grumous condition converted into am- phopeptone, that in the boiled gastric juice or the weak solution of hydrochloric acid has only been transformed into syutonin, and that in the neutralized solution or the solution of pepsin but little if at all modified, some syutonin being formed if the action be prolonged. Peptones from whatever proteids they may be derived, whether al- bumin, fibrin, casein, etc., and, however derived, while differing somewhat from each other in their ultimate composition, are gener- ally characterized by the following properties : They are completely soluble in water and diffuse readily through animal membranes, the latter pro])erty rendering them suscejitible of absorption which the proteids from which they are derived are not. They are precipi- tated from neutral or feebly acid solutions by mercuric chloride, tannic acid, bile acids, and phospho-molybdic acid, but are not pre- cipitated by boiling, by nitric or acetic acids, or potassium ferro- cyanide. They give a red color with Millon's reagent (mercuric nitrate in nitric acid), a yellow color with nitric acid, the xantho- proteic reaction ; a rosy red color with Fehling solution, the biuret reaction. Tliey rotate the plane of polarized light to the left. It has already been mentioned incidentally that the gastric juice acts only upon proteids and albuminoids. Thus, for example, ' It mast be admitted that considerable difference of opinion still prevails as to exactly the manner in which proteid is converted into peptone. Indeed, according to a recent autliority, we know notliini^ certain at the present time concerninu: the essence of pei)tonization. We know not whether peptones are splitting i)roducts of albumin — still less whetlier the splitting products so arising resemble or ditlcr from each other — or whether the peptones arise through a change in the j)osition of the atoms without modification of the size of tiie molecule or througli a taking up of water. Bunge, op. cit., s. 180. ACTION OF GASTRIC JUICE UPON FOOD. 121 while the gastric juice dissolves the albuminous wall of the fat ves- icle, thus setting the fat free, it has no effect upon the fat itself. Gastric juice does not act upon carbohydrates. Any starch, for ex- ample, that may be converted into maltose or dextrose in the stomach is due to the saliva swallowed or possibly to gastric mucus. It was shown many years since ^ and also more recently ^ that cane sugar is converted in the stomach into glucose. This eifect appears to be due, however, not so much to the gastric juice proper as to its hydrochloric acid, since a 0.2 per cent, solution of the latter converts cane sugar into glucose and levulose outside of the body. It is possible also that the cane sugar converted into dextrose in the stomach may l^e due to a soluble enzyme. As the conversion of cane sugar into glucose takes place very slowly in the stomach it is not usually thought that any great amount of glucose is produced in this part of the alimentary canal. The action of the gastric juice in this respect may be, however, more important, at least in man, than is generally supposed, since, as we shall see hereafter, there is still some doubt as to exactly how cane sugar is converted into glucose in the small intestine. Submaxillary mucin and elas- tin are dissolved by the gastric juice, the latter but slowly, however. Neither keratin, or nuclein are dissolved by the gastric juice, hence the cell nucleus is insoluble in the latter. While the membrane of the vegetable cell is not dissolved by the gastric juice, that of the animal cell is, but less readily, in proportion as it approximates in composition to keratin. Oxyheemoglobin, or the coloring matter of the l)lood, is decomposed by the gastric juice into hiematin and acid alljuminate. Hence the blood is changed in the stomach into a dark brown mass. According to the observa- tions of Beaumont, bones were dissolved, to a certain extent at least, by the gastric juice, while water, alcohol, and other fluids^ appeared to be absorbed in the stomach as such or to pass unaflPected into the intestine. It is well known mider certain circumstances that the coats of the stomach itself are unaffected by the action of the gastric juice during life, ])ut are digested after death. It is said that when one of the old alchemists announced that he possessed a universal sol- vent, the question was at once asked in what did he keep it. Natur- ally enough it was asked in the last century of those who held that the gastric juice would dissolve organic substances, why it did not act upon the stomach itself. We have seen, however, that the gastric juice does not digest all kinds of organic food, ])ut that its action is limited rather to particular kinds of it, it having no action upon fat, starch, epidermis, etc. The answer would then appear to be, that the stomach is lined with some substance that the gastric juice does not act upon. According to this idea Ber- ^ Bouchardat et Sandras, Supplement a TAnnuaire de therapeutique, pour 1846, p. 83. 2 Leube, Virchow's Archiv, 1882, Band 88, s. 222. "Qp. dt, p. 97. 122 DIGESTION. narcl ^ held that the lining epithelium of the stomach protected it from the gastric juice, assuming that the epithelium was as con- stantly renewed as destroyed. A confirmation of the view that the epithelium lining of the stomach gives it its immunity from diges- tion during life, is shown by the fact tliat worms, like the thread- worm, ascaris, etc., whose body wall is covered with epithelium, are able to live in the stomach, bathed at times in gastric juice. After the death of the worm, however, from any cause, the mouth or anus being opened, then the gastric juice is able to penetrate within its body and will then act upon the viscera until often nothing will be left of the worm except its outer body wall, which will float about in the stomach, unaifected by the gastric juice. In the same way, if the epithelium of the stomach be loosened from the parts beneath, it will be found undigested in the gastric juice ; as a matter of fact, it is not digested whether living or dead any more than the skin of the ascaris is digested. There is no reason for assuming, then, that during life it is rapidly regenerated because it is constantly being destroyed. After death the epithelium loosening itself from the coats of the stomach, the latter Avill no doubt be attacked by the gastric juice, the epithelium itself remaining unaffected. It must be admitted that this explanation is not entirely satisfactory, being open to objections like all other explanations that have been offered. It presents, however, this advantage, that it does not in- voke the aid of a vital spirit,^ nor of catalysis,^ nor does it attribute to the alkalinity of the blood a preserving power in the stomach that it does not possess in the intestine,^ Ijut depends simply upon the fact as to whether or not epithelium alive or dead is digested by the gastric juice. One of the most interesting facts connected with gastric digestion is the entire absence of putrefaction. It was long since observed ^ that meat does not putrefy, at least for a long time if kept in gastric juice, while the normal secretion itself remains perfectly free from putrefaction even months after withdrawal from the stomach. This effect of the gastric juice is undoubtedly due to its hydrochloric acid, which exerts an anti-fermentative action. If, however, the gastric juice is neutralized, then a fermentation is set up in the stomach whereby lactic and other organic acids are generated. The hydro- chloric acid, like weak mineral acids, acts also as an antiseptic, at least to some extent. Thus the cholera bacillus, varieties of strep- tococcus infecting Avounds, the staphylococcus pyogenes aureus are killed by the gastric juice. Since the hydrochloric acid prevents fermentation with the generation of gases, the nitrogen (72.5 per cent.), carbon dioxide (20.7 per cent.), and hydrogen (0.7 percent.) that are found (Planer) in the stomach "^ are either derived from iPhysiologie Exjierimentale, 1S56, Tome II., p. 404. 2 Hunter, Pliil. Transactions, Londfin, 1772, p. 447. 3Dalt(.n, Pliysi()lo\0,Fe + 2HP - Fe = ^0.,il,s^S>, As a confirmation of the view that a genetic relation cjxists be- tween bilirubin and luematin it may be mentioned that in Amphioxus CHOLESTERIX. 145 and the invertebrata in "which red blood corpuscles do not occur in the blood, bile pigments are not found in the bile, and that the intra- venous injection of haemoglobin or of substances, like water, which disintegrate the red blood corpuscles, increase the bile pigments. Of the iron that separates from the hsematin in the formation of bilirubin the greater part appears to be used again in the reforma- tion of htematin, the remaining part being secreted in the bile. Bilirubin, through oxidation, as in the first stage of Gmelin's test, loses its red color and becomes green, being transformed into bile verdin (C3.,H3j.X^Oj.), the green-colored pigment of the bile. Biliverdin crystallizes somewhat imperfectly from an evaporated solution in glacial acetic acid, is insoluble in water, ether, and chloroform, but is readily soluble in alkaline solutions and alcohol. It frequently constitutes an ingredient of human gall stones. Its presence can not only be determined by Gmelin's test, but by means of spectrum analysis. Both bilirubin aud biliverdin pass as the coloring matters of the bile into the alimentary canal from which they are partly absorbed and partly transformed by putrefactive processes into hydrobilirubin (C32H^^,N^O.), constantly found as one of the coloring matters of the feces, and is probably identical with the urobilin, the urinary pigment. Fig. 42. Cholesterin, from an encysted tumor. (Dalton.) Cholesterin. — Cholesterin (C^-H^^O), so-called on account of its having been first obtained as a solid deposit from the bile, is a con- stant ingredient of that fluid occurring in the proportion of from one to three per cent. Cholesterin is usually regarded as being a monatomic alcohol, its chemical constitution being expressed by the formula CgH^^OH. It is a crystallizable body appearing as thin, colorless, transparent, rhomboidal plates, usually with an ob- 10 146 DIGESTION. long piece cut out of the corner (Fig. 42) when deposited from its ethereal or alcoholic solution. Cholesterin is held in solution in the bile by the bile acids, being insoluble in water and dilute saline fluids. Cholesterin is found in the blood, spleen, nervous system, etc. It differs, therefore, from the bile acids and pigments, in that it is not elaborated by the liver, but is simply separated from the blood by the latter, whence it passes as a constituent of the bile into the alimentary canal, and is excreted in the feces apparently unchanged. The bile contains, in addition to the bile acids, pigments, and cho- lesterin, small quantities of neutral fats, soaps, lecithin, and urea. Among the inorganic constituents of the bile may be mentioned sodium chloride, calcium and magnesium phosphate, and iron. The gases of the bile consist principally of carbon dioxide with a small quantity of nitrogen and traces of oxygen. Functions of the Bile. — It was long since inferred by Haller ^ from the fact of the bile passing into the vipper rather than the lower part of the intestine that it plays some important part in digestion. That such is the case is shown by the fact that in cases of biliary fistula, far less fat is absorbed by the lymphatics of the small intestine than in the normal condition, the bile aiding the pancreatic juice in splitting and emulsifying the fats and promot- ing their subsequent absorption. Indeed, according to some ob- servers, emulsification of the fats does not take place in the absence of the bile." This important function of the bile appears to be due to its bile acids, although the exact manner in which they act in this respect is not, as yet, clearly understood. Bile appears to have also a slight diastatic action. On the other hand, the bile must be regarded as an excretion as well as a secretion, since part, at least, of the bile acids and pigments, the cholesterin and lecithin, are ex- creted in the feces.^ As bile promotes the onward movement of the contents of the alimentary canal, it is usually regarded as being a natural purgative. It is well known that in cases of biliary fistula or occlusion of the bile ducts that when fat or meat is eaten the feces become very offensive, and from this reason it has been inferred that the bile is an antiseptic. While bile undoubtedly retards in some way putrefaction, its action in this respect does not appear to be directly antiseptic, as bile itself outside of the body putrefies rapidly. In conclusion, it may be mentioned that peptic digestion is brought to a standstill in the intestine through the acid chyme of the stomach being neutralized or made alkaline through ad- mixture with the pancreatic juice and the bile, the pepsin being carried down with the precipitate formed by the mixture of chyme and bile and which consists partly of proteids and partly of bile acids. ' Elementa Physiologie, Tomus sextus, p. 615. 2Da.stre, Comptes Rendus, Soc. Biol., 1887, p. 782. 3 See p. 22. GLYCOGEN. 147 Origin and Function of Glycogen. The liver, as might be inferred from its size, possesses other func- tions than that of merely elaborating bile, one of the most impor- tant of which is the production of glycogen. Glycogen {C^^f}^^ is isomeric with starch and dextrin. It differs, however, physically from the latter in that its solution is opalescent, while that of dex- trin is clear, and that the addition of iodine gives to the solution of glycogen a deep brownish-red color, but to that of dextrin a rosy red, and to starch the characteristic blue. The presence of glycogen in the cells of the liver is usually shown by the iodine reaction just referred to, the organ having been removed about twelve hours after a meal and hardened in alcohol. Glycogen is soluble in both hot and cold water, but insoluble in ether and alco- hol, and is one of the few substances in the animal body that de\a- ate the plane of polarization to the right. Glycogen in solution, like other starchy bodies, is readily converted into glucose when boiled, for example, with a dilute mineral acid, or brought in con- tact at the temperature of the body with saliva, pancreatic or intes- tinal juice, or serum. Glycogen becomes glucose also, if simply allowed to remain in the liver after death, or if brought in contact with its tissue after removal from the body, the phenomenon being essentially one of hydration, as shown by the formula filvcogen. Water. Glucose. C;H,„0, + H,0 = C,H,,0, Glycogen can be readily obtained in the following manner : Im- mediately after death, the liver of a well-fed animal is taken out of the body and cut up into small pieces, and coagulated with boiling w^ater. A concentrated decoction is then made of the liver tissue thoroughly ground up, and decolorized with animal charcoal. Strong alcohol being now added, the glycogen will be precipitated as a white powder ; but this is impure, being mixed with a small quantity of glucose, biliary salts, and albuminous matter. The lat- ter can be removed, however, by washing with alcohol, and boiling ■v^dth potassium hydrate. The residue being filtered and dissolved in water, and any albuminous principles still present being removed with acetic acid, the glycogen is reprecipitated with alcohol, and then dried, when it can be kept for a long time, it retaining its properties indefinitely. The quantity of glycogen in the liver may amount in man to as much as ten per cent. — that is to say, assum- ing that the liver in man weighs about 1400 grammes (50 ounces), the glycogen present would be 240 grammes (5 ounces), the amount depending, however, upon the length of time elapsing since the tak- ing of food, and the character of the latter, increasing with diges- tion and diminishing with fasting, and disappearing altogether if no food be taken for four or five days, being more abundant on a vegetable than on an animal diet, and particularly abundant if the food consists largely of carbohydrate matter. When the chemical 148 DIGESTION. composition of glucose and glycogen is compared, and when it is remembered that all of the starch and sugar of the food are trans- formed into glucose during digestion, the above becomes intelligible, on the supposition that the glucose carried by the portal vein to the liver during absorption is converted by and stored up in the liver cells as glycogen, the transformation of the glucose into glycogen being one of dehydration, as shown by the formula : Glucose. Water. Glycogen. C.H^P^ — H^ = C,H^„0, The fact of glycogen being developed on an animal diet as well as on a vegetable one, though in less amoimt, so far from being an objection to the origin of glycogen, as just offered, is a confirmation of it, since it is readily conceivable how nitrogenized matter like glycin may, for example, split uj) in the economy into glucose and urea, as shown by the formula : Glycin. Urea. Glucose. the glucose becoming then glycogen, as when derived from vege- table matter, and the urea being eliminated by the kidneys. That such a transformation of nitrogenized matter actually takes place in the system, at least under certain conditions, appears from the fact that in certain cases of diabetes,^ when the food contained no carbohydrate matter, the glucose increased pari passu with the urea. The above, to a certain extent theoretical, considerations are confirmed by experimental ones. Thus it has been shown by Bernard,^ Pavy,'^ Doch,^ Tscherinow,^ and others that the amount of glycogen in the liver is notably increased within a few hours after the taking of starchy or saccharine articles of food, and that while glycogen is developed on an animal diet, the amount produced is far less than on a vegetable one. Glycerin in- creases the amount of glycogen but it appears to do so only indi- rectly by interfering in some way with its reconversion into glucose by the liver cells. Fat does not influence the production of glycogen. There appears to be no doubt, therefore, that the carbohydrate and nitrogenized principles in part of the food being transformed into glucose are conveyed in the blood of the portal vein to the liver, and that the glucose so derived is, probably by dehydration, converted into glycogen, and, for the time being, at least, is stored up as such in the liver cells. That the glycogen remains, however, only temporarily in the liver, appears from the fact, as shown first by Bernard,*' that in a fasting animal, or in one that has been fed 1 Singer, Med. Chir. Trans., xliii., p. 327. 2 Physiologie Experimentule, p. 159. Paris, 185.5. ^ Nature and Treatment of Diabetes. London, 18G2. *Pflugei-'s Archiv, 1872, Band v., s. 571. ^Virchow's Archiv, 1869, Band xlvii., s. 102. «0p. cit., p. 204. GLYCOGEN. 149 on an exclusively meat diet, that the liver and the blood of the hepatic vein contain glucose, though there is not the slightest trace of it in that of the portal vein, the glycogen stored up in the liver during the intervals of digestion being gradually converted into glucose, and conveyed away by tlie hepatic veins into the general circulation. That the transformation of glycogen into glucose is merely a question of time, is shown by the fact that a decoction made out of a liver taken out of the body of a fasting animal is clear, whereas if it is made out of one taken from an animal fed within a few hours, it is decidedly opalescent through the glycogen it contains not as yet having been transformed into glucose. It is denied by some experimenters that the liver actually con- tains glucose during life. Inasmuch, however, as glucose can be demonstrated in the liver within twenty seconds after the death of the animal from which it has been taken, it can hardly be doubted that such is the case. AYhile there may be a difference of opinion as to whether the liver contains glucose during life, there is no difference of opinion as to its containing glucose after death. In- deed, if all the blood be washed out of the liver by forcing water through the portal vein, the liquid, as it escapes by the hepatic vein, will be found to contain glucose, and this even upward of half an hour after repeated injections. And then, when the presence of glucose can no longer be demonstrated, if the liver be put aside in a warm place for a few hours, glucose can again be obtained, it beino^ a long" time before its o-lveoo-en, the source of the glucose, is exhausted. The conversion of glucose into glycogen, and the storage of the latter in the liver is of advantage to the economy, since the sugar produced during digestion would otherwise accumulate to such an amount in the blood that it would be excreted by the kidneys and therefore wasted. On the other hand, as the sugar of the blood is diminished in amount the loss is made good by the reconversion of the glycogen into glucose and the passage of the latter into the blood. The principal use of glycogen appears, therefore, to depend upon the readiness with which it is developed out of glucose and reconverted into the same, the sugar of the blood being thereby maintained in normal amount. Glycogen occurs not only in the liver but in the muscles, placenta, brain, and other parts of the body as well. The glycogen of muscle is usually regarded as so much stored up carbohydrate material, which can be readily converted into glucose and in being oxidized will liberate energy. As a confirma- tion of this view it may be mentioned that the glycogen of both muscles and liver is rapidly used up by muscular exercise imless food is supplied. In conclusion, it may be pointed out that the transformation of glucose into glycogen, and of glycogen into glucose in the animal, finds an analogy in the vegetable, since, as is well kuo%A'n, the 150 DIGESTION. starch in the leaves of a plant having been converted into sngar, passes down to the roots, where not infrequently it is reconverted into starch. Production of Urea by the Liver. One of the most important functions of the liver, to a consider- able extent at least, is the production of urea. Urea (CH^N^O) is usually regarded as being a carbamide or an amide of carbon diox- NH ide, CO<^TT-? that is, CO.,, in which an atom of oxygen is re- placed by the residues of two molecules of ammonia. Such being its chemical constitution, its production by the liver can be readily accounted for on the supposition that the leucin, tyrosin, and other amides developed in the digestion of proteid food stuiFs are trans- formed into ammonium carbamate, which being carried to the liver is there dehydrated, and becomes urea. Ammonium carbamate. Water. Urea. While there may be some doubt as to whether urea is produced in exactly this way in the liver, recent experiments prove conclu- sively that urea is produced in the liver in some such way. Thus, for example, according to Schroder,^ when blood obtained from a well-fed dog was passed through the blood vessels of the liver of another recently killed dog a noticeable increase in the amount of urea was observed, whereas when the blood used was obtained from a fasting animal there was no increase of urea. It was shown also by the same experimenter that the addition of ammonium carbonate to the blood circulating through the liver increased the amount of urea. This result can be explained by supposing that the ammo- nium carbonate becomes ammonium carbamate and then urea, or urea directly by dehydration, as follows : Ammonium carbonate. Water. Urea. (NHJX'O, — 2Hp = CON^H^ On the other hand it has been shown ^ in cases of animals in wdiich the blood of the portal vein has been made to pass directly into the vena cava without going through the liver at all that car- bamates appear in the blood and that the amount of urea diminishes notably, carbamates not being converted into urea in the absence of the liver. Among its other functions the liver performs the im- portant one of removing and retaining heterogeneous bodies from the blood, or of rendering such as arc of a poisonous nature innox- ious. Thus, for example, while salts of copper are retained by the ^ Archiv fiir exper. Path. u. Pliar., 1882, Band xv., s. 364 ; 1885, Band xix., s. 373. ^Hahn, Pawlow, Massen, and Nencki, Archiv fiir exper. Path. u. Pliar., 1893, Band xxxii., s. 161. THE LARGE INTESTINE. 151 liver, alkaloids such as phenol and cresol, poisonous aromatic sub- stances derived from the putrefaction of proteid food in the intes- tine, are converted into the harmless ethereal or congugate sulphates and which, passing into the general circulation, are excreted by the kidneys. By a similar synthesis, indol and skatol, also putrefactive products, after being converted by oxidation into indoxyl and skatoxyl are transformed by the liver into the corresponding ethereal sulphuric acids, indoxyl-sulphuric acid (indican) and skatoxyl sulphuric acid, and ])ass in that form into the urine. Putrefactive Processes in the Intestines Caused by Micro-organisms. It is well known that various kinds of micro-organisms are in- troduced into the alimentary canal with the food and drink which cause fermentation and putrefaction with the evolution of hydrogen, carbon dioxide, marsh gas,^ sulphuretted hydrogen. Thus, for ex- ample, bacilli occur which, acting upon the carbohydrates, produce acetic, lactic, butyric acids, etc., or upon proteids breaking them up into leuciu, tyrosin, cresol, phenol and its derivatives indol, skatol, fatty acids, etc. Organized ferments, fungi, are present, which ap- pear to transform starch into glucose, cane sugar into glucose and levulose, and split fat into fatty acid and glycerin. It has already been mentioned that many micro-organisms are destroyed by the acid of the gastric juice, and it might be suj^posed, therefore, as the reaction of the intestinal secretions is alkaline, that the small intes- tine would present conditions favorable for fermentation and putre- fliction. Recent observations^ made upon cases of fistula of the ileum in human beings show, however, that upon a mixed diet while acetic and other acids are produced by the bactericidal fermentation of the carbohydrates, the products of the putrefaction of proteid are not developed, putrefaction being prevented from the presence of these acids. In the large intestine the alkali secreted being usually more than sufficient to neutralize the acid derived from the fermen- tation of the carl)ohydrates, the reaction of its contents is alkaline, and such proteid as has escaped digestion and absorption undergoes, therefore, putrefaction. The Large Intestine. This portion of the alimentary canal is so called on account of its relatively large size. It measiu-es usually in length from 1.2 to 1.5 meters (5 to 6 feet), and in diameter from .3.7 to 7.5 centi- ' Marsh ga.s, light carburetted hydrogen or methane (CH4), the only hydrocarbon found in the body, appears to be developed in the intestine from cellulose, according to the following reaction Cellulose. Water. Methane. Carbon dioxide. QH.oOj -I- H/J ==. .3CH, + .SCO^ "Macfadyen, Xencki u. Sieber, Archiv fiir exper. Patli. u. Phar., 1891, Band 28, s. 311. M. Jakowski, Archives Des Sciences Biologiques, St. Petei-sburg, 1892, Tome I., p. 539. 152 DIGESTION. meters (1.5 to 3 inches). The general direction of the large intestine beginning with the csecnm, is from the right iliac fossa upward, then transversely across to the left side of the body ; thence down- ward into the left iliac fossa, finally terminating as the rectum. The small intestine is thus surrounded by the large intestine, the latter being disposed in the form of a horseshoe. The large intestine, like the small, consists essentially of two coats, a mucous, including the submucous, and a muscular. In ad- dition, the large intestine is, to a great ex- FiG. 43. tent, covered with peritoneum, which serves to maintain it in position, and to connect it with certain of the abdominal and pelvic viscera. While the villi and valvuhe con- nivcntes are absent in the large intestine, throughout the whole extent of its mucous membrane there are found tubular and sol- section of the mucms mem- itary glauds which do not differ essentially }irVxhibithfg"the'orifi!'es"o? i" their minutc structure from those of the l^^lSiSg'magnm^"" Small intestine. _ The tubular glands (Fig. 43) of the large intestine are, however, more numerous, longer, and more closely set together than those of the latter, and often are subdivided at their caecal extremities. The mucous membrane of the large intestine is paler, thicker, and more closely adherent to the underlying parts than that of the small intestine. The muscular coat of the large intestine differs consider- ably in certain points from that of the small intestine. Thus, in the colon more particularly, the longitudinal fibers are gathered to- gether in three Avell-marked bands, one of which is anterior, while the other two are latero-posteriorly situated. The large intestine is divided by anatomists into three portions, the cajcum, colon, and rectum, these differing in their size, shape, and the character of their mucous and muscular coats. The most important part, physiologically, of the caecum or caput coli, the widest portion of the large intestine, is the ileo-csecal valve, by means of which the contents of the ileum, after they have passed into the large intestine, are prevented from returning into the small intestine. The small intestine opens into the large intestine by a slit-like aperture (Fig. 44, a e) which lies nearly transverse to the direction of the latter. This aperture is bounded above and below by two semilunar folds or valves which project inward toward the cseciun and colon. At each end of the aperture the two valves or folds run into each other and are then prolonged at each side as a ridge or fr£enum, which gradually fades aAvay. That portion of the valve which looks toward the ileum is covered with villi, and in other respects resembles the mucous membrane of the small intes- tine, while that upon the opposite side of the valve is destitute of villi, and its mucous membrane is like that of the large intestine. Each segment of the valve is covered with mucous membrane, and THE LARGE INTESTINE. 153 Fig. 44. consists of submucous tissue aud muscular fibers, derived fi'om the circular muscular fibers of both the ileum and large intestine. The lono^itudinal muscular fibers of the ileum, however, run con- tinuously into those of the large intestine, taking no part in the formation of the valve, but are stretched across it. The effect of distention of the caecum by its con- tents is that the frsena being put on the stretch, the edges of the valves are brought in apposition, closing the ileo-c»cal aperture so completely that all reflux from the large intestine into the ileum is prevented, but at the same time no hindrance is oifered to the passage of the contents of the ileum into the laro-e intestine. An interest- ing feature about the csecum is its vermiform appendix (Fig. 44, p), a worm-like tube, beginning at its lower end and terminating in a blind extremity, attaining usually about a length of from 7.5 to 15 centimeters (3 to 6 inches), and ha\'ing a diameter aljout the size of a cpiill. The vermiform appendix, so far as is known, has no use in man, but is a very interesting structure as representing in man, in a ru- FiG. 45. View of the Ueo-colic valve from the large intestine. The figure shows the lowest part of the ileum, ;, joining the caecum, c, and the ascending colon, o, which have been opened anteriorly, so as to display the ileo-colic valve ; a, the lower, and e, the upper segment of the valve, p. Vermiform appendix. Caecum of capybara. (From nature.) dimentary condition, tliat which is well developed and performs important functions in many animals. Thus in the horse, tapir, 154 DIGESTION. elephant, rabbit, and beaver, the Cfficiun is very large ; in the capy- bara (Hydrochserus), a species of rodent, the caecnm (Fig. 45, V) measnred 65 centimeters (26 inches) in length, -svhile in a koala (Phascolarctos), a small marsupial, also examined by the author, it attained a length of 125 centimeters (50 inches). Xow, by com- paring the cfecum in the capybara with the vermiform appendix in man, it will be found that the latter corresponds to the blind part of the cseciun, V, in the capybara, while the csecum, or caput coli, in man is homologous with that part of the caecum in the capy- bara communicating with the large in- Fio. 46. testine, I. In other words, the csecum in the animals just mentioned is equal in man to the vermiform appendix and csecum. Further, it will be observed that the crecum of the capybara (Fig. 45) is much longer than the stomach of that animal (Fig. 46), the latter measuring only 25 centimeters (10 inches), while it is needless to state that just the re- verse relation obtains as regards the same parts in man. The significance of stomach of. ai.ybai a. arom nature.) this COUtrast is evidcut CUOUgh whcn the digestion of food in man and the capybara is considered. In the first instance, as we have seen, the action of the stomach is very important ; in the latter instance it is but relatively so, the imperfect digestion of food in the stomach of the capybara being completed in its caecum. In the same manner the cseciun in the tapir, horse, and elephant, etc., supplements the imperfect digestive action of the stomach in these animals. On the other hand, in the giraife, in which there are four well-developed stomachs, the caecum is relatively small. In a word, there is an inverse ratio, both anatomically and physio- logically, between the stomach and the caecum ; when the one is large and active, the other is small and inactive, and vice versa. The conclusion must not, however, be drawn that the caecum in these animals secretes a gastric, or any other digestive juice. The caecum rather appears to be a receptacle where the fluids absorbed by the food in its rapid pas.sage through the alimentary canal have time to produce their digestive effects. The acid reaction often noticed in the caeciun of animals, and sometimes in man, is not due to acid secretion, but, as we have seen, to a kind of lactic or butyric acid fermentation set up in the food, the normal reaction of the secretion of the caecum being alkaline. That the vermiform appendix in man is a rudimentary organ is con- firmed by the fact that it is relatively longer in the embryo than the adult. It is worthy of note that the vermiform appendix is found as in man in all four anthropoid apes, the gorilla, chimpanzee, orang, and gil)bon ; and more remarkable still that it is present in a marsupial, the wombat (Phascolomys). CONTENTS OF LARGE INTESTINE. 155 In addition to what has already been said of the colon, an im- portant feature is its sigmoid flexure, so called from the S-like curve the colon makes just before passing into the rectum. This curva- ture, as we shall see, is the position where the feces are temporarily retained. The large intestine terminates in the rectum, which, while straight in animals in which it was originally described, is far from being such in man. In fact, the rectum in man first passes obliquely downward from left to right, from opposite the left sacro- iliac articulation to the middle line of the sacrum. It then curves forward back of the prostate in the male, and the vagina in the female, and finally passes backward and downward, terminating in the anus. The anus is a dilatable orifice, lined with mucous mem- brane and covered with skin, the skin and mucous membrane be- coming continuous with each other. The margin of the anus and low^er part of the rectum are embraced by the external and internal sphincter muscles, the levators ani and coccygei. These muscles serve to support the bowel, and to close its anal orifice. The in- ternal sphincter muscle consists of the circular fibers only greatly developed. It is situated 2.5 centimeters (1 inch) above the anus, extending over 12 millimeters (about ^ inch) of the intestine, and is about 4 millimeters (2 lines) thick. The rectum, 20 centimeters (about 8 inches) in length, is not sacculated like the rest of the large intestine, the longitudinal mus- cular fibers being scattered over its surface. While the upper part of the rectum is narrow, at the lower part it is dilated into a kind of reservoir just above the anus. The mucous membrane of the rectum is more vascular, thicker, and redder than that of the colon, and moves more freely over the muscular coat. It is thrown into numerous folds, most of which are, however, effaced when the rectum is distended. The Contents of the Large Intestine. — While there is no reason to suppose that anything like true digestion takes place in the large intestine of man, various important changes are effected there by which the undigested residue of the food is transformed into the feces, the most marked changes being in the consistence, color, and odor, and which are gradually developed as it passes from the caecum through the colon into the rectum. As the undigested food passes through the large intestine its liquid portions are being con- stantly absorbed, the feces, therefore, have a much firmer consistence than the contents of the ileum. The large intestine is, therefore, physiologically important, as presenting an extensive absorbing, if not a digestive surface. The absorbing power of the rectum is well known. Indeed, life can be sustained for months by giving nutritious enemata. The color of the feces is of a dariv yellowish-brown, and appears to be due to the presence of stercobilin, the latter being either iden- tical with or a derivative of hydrobilirubin. It is well known that 156 DIGESTION. wlieu the bile is deficient or absent, the stools become lighter or clay -colored. The color of the feces varies also according to the diet. While the cause of the odor of the feces cannot be said to be ex- actly understood, there can be no doubt that it is due to a great ex- tent to the skatol and indol which have escaped absorption, to the decomposition of the bile, and to the secretion of the glands of the colon and rectum. The reaction of the feces is variable, sometimes acid, often alka- line or neutral, depending chiefly upon the kind of food eaten. The entire quantity of feces passed in twenty-four hours upon a mixed diet amounts usually to from 1 20-150 grammes (4-5 ounces), but on a vegetable diet to as much as 383 grammes (11 ounces), which is, as might be expected, the vegetable diet containing so much indigestible matter. When the contents of the large intes- tine are examined microscopically, there will be found a number of undigested substances derived from the vegetable and animal foods. Among other matters, the spiral vessels of vegetables, the cortex of grains, hard vegetable seeds, structures generally consisting largely of cellulose, muscular tissue in various stages of disintegration, tendinous and elastic structure, the organic constituents of bone. The feces chemically may be said to consist of seventy-five parts of water to twenty-five of solid residue. In the latter there have been found among other substances the ammonium-magnesium phos- phate, the magnesium phosphate, salts of sodium, potassium, cal- cium, iron, fatty acids, excretin. The feces contain also mucous pigment and different kinds of micro-organisms, the latter being often present in vast numbers. The large intestine contains in addition to the feces more or less gas, consisting at one time or another of hydrogen, carburetted and sulphuretted hydrogen, carbon dioxide, and nitrogen, which are not infrequently also eliminated by the rectum. These gases are devel- oped, as already mentioned, during the putrefaction of proteid food, most of the nitrogen, however, being derived from the air swallowed with food. Defecation. In health the feces are usually discharged once in twenty-four hours. This rule, however, is far from being invariable, being modified by individual peculiarities. Indeed, there are well authenticated cases of the act of defecation not having been performed during a period of eight years, and even longer, the unabsorbed food apparently having been either rejected by the mouth, or eliminated by the skin or kidneys. On the other hand, there seems to be no reason to doubt that there have been also cases in which the bowels were evacuated as often as twelve times daily, and that for thirty years, and yet without the health being affected.^ 1 Dunglison, Human Physiology, 8th ed., Vol. i., p. 191. Pliiladelphia, 1856. ('hapman, Lectures on the Diseases of Thoracic and Abdominal \'iscera, p. 294. Philadelphia, 1844. RESUME OF DIGESTION. 157 The feces are gradually passed through the contraction of the muscular fibers of the large intestine into the sigmoid flexure of the colon, where they accumulate, and are retained for some time. It is probably the descent of the feces from the sigmoid flexure of the colon that is the immediate cause of the desire to defecate, the action being to a certain extent, as we shall see, under the control of the will. It is often thought that the feces accumulate in the rectima ; the lower part of the rectum, however, in health is almost always empty, though in old persons, or in those of a constipated habits, the feces are often found there. In the act of defecation, the feces first pass from the sigmoid flexure of the colon into the upper constricted part of the rectum, then into the lower portion, the sphincter muscle at first resisting, then giving away, through the inhibition of the nervous centers controlling the sphincter ani, and the fecal mass leaves the body. The action is assisted by the levator ani, which favors the relaxa- tion of the external sphincter, and by the compression of the viscera through the action of the diaphragm and the abdominal muscles. AMien the glottis is closed a point of support is further given to the latter muscles. Resume of Dig^estion. In concluding the subject of digestion, it does not appear to be superfluous to give a brief resume of the different processes of which we have given a somewhat detailed account. The food, after having been taken into the mouth, is masticated, and through the action of the tongue and checks having been col- c? o ci lectcd into a bolus, is then swallowed. The saliva poured into the mouth acts mechanically, aiding mastication and deglutition ; and chemically, in converting some of the starch into maltose, etc. The proteid substances of the food are converted into peptones, and cane sugar to some extent into glucose, by the gastric juice, which has also the effect of dissolving the walls of the fat vesicles, the fat itself thus set free, however, being unaffected by this secre- tion. That part of the starch which has escaped conversion by the saliva either in the mouth or stomach, passes together with the cane sugar unchanged into the small intestine. The intestinal juice supplements the action of the saliva upon starch, of the gastric juice upon proteids and cane sugar. The pancreatic juice converts starch into maltose, proteid into peptone, and splits the fat into fatty acid and glycerin, so rendering it sus- ceptible of emulsion. The bile assists in the emulsifying of fats, and promotes their absorption ; it further retards putrefaction, and in stimulating the peristaltic acid of the intestine acts as. a natural purgative. The conversion of starch into maltose, of albumin into peptone, etc., appears to consist in a hydration of these substances, brought about by the presence of ptyalin, pepsin, etc., entering into the 158 DIGESTION. composition of the saliva, gastric juice, etc., respectively. These enzymes or ferments to which the action of the alimentary secre- tions is due, are elaborated out of the blood, and stored up during the intervals of digestion by the cells of which the glands consist. The ptyalin, pepsin, trypsin, etc., poured out at the moment of secretion, differ somewhat from the principles actually present in the gland during the intervals of digestion, being developed out of the latter at the moment of secretion. That the phenomenon of secretion is not one of mere filtration, is shown by the pressure exerted by the secretion, and that chemical action is going on is made evident through the heat and carbon dioxide developed. The contents of the large intestine consist essentially of the un- digested part of the food, decomposed bile, and of such digested principles as have not been absorbed. As these pass through the large intestine they gradually assume the consistence, color, odor, etc., of the feces. The latter accumulating in the sigmoid flexure of the colon, pass into the rectum and thence out of the body, their expulsion constituting the act of defecation. CHAPTER IX. ABSORPTION. While the digested food in the alimentaiy canal may be said to be inside of the body, using the word in its ordinary acceptation, physiologically it is still outside of it, for if the food simply re- mained in the alimentary canal it would be of no use for nutritive purposes. Indeed, unless the digested food gets into the blood, and is so carried to all parts of the organism, and repairs the waste of its tissues, and supplies the material for the liberation of energy, it might as well not be taken into the system at all. The process by which the digested food passes from the interior of the alimentary canal into the blood, is known as absoq^tion. It is not to be understood, however, that absoi^ption is by any means limited to the alimentary canal, or that the substances of which food consists are the only ones that can be absorbed. We shall soon see that oxygen is absorbed by the blood as it circulates through the lungs, that the skin will take up various substances, and that effusions found under certain circumstances in the cavities of the pleura, pericardium, peritoneum, etc., can be absorbed by these serous surfaces. Inasmuch, however, as we have just seen how the food is digested, our study of absorption will begin with the consideration of the process as it goes on in the alimentary canal. That the ancients were well aware that the human body absorbs, is evident from their writings. Thus Hippocrates,' for example, speaks of " the veins of the stomach and intestine attracting the clearest and most fluid parts of the solid and liquid food." While the ancients were correct in considering: the veins as a means of absorption, it must not be inferred, however, that the course of the circulation was understood by them, it not being learned until modern times that the venous blood from the capil- laries of the stomach and intestine is conveyed by the gastric and mesenteric veins to the portal vein and thence to the liver and from the latter by the hepatic vein and inferior vena cava to the heart. Nothing, however, appears to have been known in ancient times of the lymphatic system. It is well known that in the MTitings of Galen there are preserved vague illusions, like those of Erasistra- tus," " to arteries in the mesentery," " full of milk," and of Hiero- philus ^ to " particular veins ending in certain glands," but the con- text shows that these old anatomists regarded the vessels alluded 1 Opera Omnia, p. 119. Ludg. Batav., 1665. ^Galenus, Opera Omnia, Tomus i., Cap. 5, p. 61. Yenetiis, 1556. 3 Ibid., Cap. 19, p. 141. 160 ABSORPTION. to, which were, no doubt, lymphatics, as niitrieut, and not as ab- sorbent in their function. While it is true that the upper part of the thoracic duct in the horse was described by the Roman anatomist Eustachius ' in 1563, the history of the lymphatic system really begins with Gasparis Aselli's discovery, in 1622, in the dissecting amphitheatre at Pavia, of the lacteals of the small intestine in the dog. Aselli tells us in his work - on the lacteals that, on opening a dog to show some friends the recurrent laryngeal nerves, he was surprised to find in the mesentery, in addition to the arteries and veins, delicate, white lines, which, at first, he thought were nerves. On pricking one of them, ho^s'ever, and seeing a whitish, milk-like fluid escape, he ex- claimed, like Archimedes of old, " Eureka ! " for he felt he had made a great discovery. Aselli further extended his observations to other animals, and found the lacteals in cats, lambs, pigs, cows, and the horse. It was not, however, until 1628, two years after Aselli's death, that the lac- teals were demonstrated in man. For this observation science is indebted to Peiresc, Senator from Aix, who, wishing to know whether Aselli's discovery could be extended to man, permitted the body of a criminal who had been executed to be opened, when the lacteals w^ere found (Fig. 47), the anatomist interested in the post- mortem examination having attended to the feeding of the criminal before execution. Aselli supposed that the lacteals which he had discovered in the mesentery carried the chyle to the liver. This error was corrected by Pecquet,'^ a Frenchman, who showed, in 1649, that in the dog, and afterward in the horse, ox, pig, etc., the mesenteric lymphatics, or lacteals, terminated in a reservoir, the receptaculum chyli, now often called in honor of its discoverer the reservoir of Pecquet ; and further, that this receptaculum was the beginning of the thoracic duct. The functional significance of the forgotten discovery of Eustachius became then for the first time apparent, for it was shown that the lymphatics of the small intestine and thoracic duct oifered a route by which the digested food could be carried from the alimentary canal to the blood in the subclavian vein, and thence to the heart. Two years after the important discovery of the recep- taculum chyli — that is, in 1651 — lymphatics were demonstrated in the liver and other parts of the body by Rudbeck * and Bartho- linus,'^ and their course and connection with each other and the mesenteric lymphatics made out. iQpuse. An:it., Aiitig 13, p. 280. Lud.t?. Batav., 1707. 2 De Laetibus Sine Lacteis Venis, Cap. ix. ^Mediolani, MDCXXVII. ''.Joannis Pecquet!, Diepsei Experimenta Nova Anatomica, Cap. v. and vi., Amst., IGfil. * Olai Kudbeck, Nova Exercitatio Anatomica exhibens ductos hepaticos aquosos vasa glandularum serosa. Clericus & Mangetus, Bibliotheca Anatomica, Tomus ii., p. 029. Genevfe, 1099. 5 Thorns Bartholinic, Anatomia de Lacteis Thoracis et vases Lymphaticis. Hagic Com, 1000. LACTEALS, THORACIC DUCTS, ETC. 161 Fk;. A1 The lymphatic system iu general consists of vessels which, be- ginning as capillary spaces in the skin, mncous membrane, glands, etc., within the tissues, converge toward each other and gradually uniting with larger and larger trunks finally terminate in the sub- clavian veins as the right and left thoracic dncts. The lymjih from the right side of the head and that from the upper extremity passes into the blood of the right subclavian vein, while that from the rest of the body, including the lymph and chyle from the small intestine, is conveyed into the blood of the left subclavian vein by the left thoracic duct (Fig. 47). The lymphatics, in their gen- eral structure, resemljle very closely the veins, consisting, like these vessels, of three coats, an external one, com- posed essentially of white fi- brous tissue ; a middle muscu- lar elastic coat, the elastic muscular fibers being arranged circularly, and an internal epi- thelial layer constituting the internal coat. The lymphatics also contain valves, consisting usually of two semilimar folds. Here and there, along the course of the lymphatics, solid bodies may be seen varying in size between a hemp seed and an almond, which apparently surround the vessels, and through which the contents must pass in their way to the thoracic ducts. These bodies are the lymphatic glands, and are more evident in certain parts of the body than iu others, being well developed, for example, in the cervical, axillary, and inguinal regions. The minute structure and uses of these glands will be described when the elaboration of the blood is considered. The lymphatics not only connect the interstices of the tissues ^^itll the blood, beginning m the one and ending in the other, but they also communicate with the serous cavities. Indeed, the serous cavities, like the peritoneum, pleura, etc., can be regarded morphologically as dilated lymphatic sacs lying ^ between the viscera, these inter- ■a. Laeteals, thoracic duct, etc. a. Intestine, h. Vena cava inferior, c.c. Kight and left subclavian veins, d. Point of opening of thoracic duct into (Daltox. ) left subclavian. ' The Lymphatic Svstem, p. 222. York, 1872. 11 Eecklinghausen, Strieker's Histology. New 162 ABSORPTION. organic spaces representiug on a large scale the minute inter-lacunar spaces, which "sve have just seen often constitute the beginning of a lymphatic. Lymphatics are found very generally throughout the system. According to Sappey/ however, they have never been demonstrated in teeth, hair, nails, etc. Possibly, though, future researches may show that lymphatics exist even in such situations. It is only within recent years that the fluid contained in the lymphatics, or lymph, has been satisfactorily studied. The lymph obtained by experiments made upon animals in the beginning of this century was in too small quantities to admit of thorough analysis, while the human lymph examined was probably abnormal. It was only as recently as 1853 that Colin ^ succeeded in making a fistula in the thoracic duct of the horse, and showed by this method of investigation that large quantities of normal lymph could be ob- tained in a short space of time. Lymph is a transparent, yellowish, alkaline liquid ; the opaline appearance that it sometimes exhibits is due to small particles of fat, while the rosy tint that is often observed in it is caused by the red corpuscles that have passed into it from the blood. When exam- ined under the microscope, lymph is seen to consist of a liquor, and small bodies floating in it, the lymph corpuscles or globules. These measure on an average about -^i^ of a mm. (2-5Vo' ^^ ^" inch) ; they are homogeneous or granular in appearance, and are indistin- guishable, as we shall see, from the white corpuscles of the blood. When we come to study the red blood corpuscles in man and ani- mals, one of the most striking facts to be noted wdll be the great difference in their size. As regards the lymph or white corpuscles, however, it has been shown that their average diameter bears no relation to that of the red corpuscle, being as large, for example, in the musk deer, where the red corpuscle is small, as in man where it is large. Further, the white corpuscle in birds is usually smaller than that of mammals, whereas the red corpuscle of birds is larger than that of the mammal, while in the frog both the white corpuscle and the red are larger than those of the mammal. Like the blood, the lymph coagulates when drawn from the liv- ing body. This is due in both cases to the fibrin which these fluids contain. The lymph clot, however, is less solid than that of the blood, and little or no serum exudes from it. The clot consists not only of fibrin, but of the lymph corpuscles that the lymph carries. Chemically the liquors of the lymph differs, as we shall see, from the liquor of the V)lood (piantitativisly, rather than qualitatively, both these fluids consisting essentially of water, proteid, fibrin, and salts. Usually the lymph contains as much fibrin as the blood, but less proteid. There is more water in the lymph than in the blood, but the amount of salts in both liquids is about the same. 1 Anatomic, tome deuxieme, p. 791. 2Phys. Comp., 1856, Tome ii., p. 100. COMPOSITION OF THE LYMPH. 163 From the fact of these two liquids, the liquors of the lymph and blood, being alike in their chemical composition, it has been inferred that the lymph is nothing but that part of the blood which has es- caped, leaked out, so to speak, from the vascular system into the surrounding tissues, and which is afterward soaked up by the Ijin- phatics. Composition of the Lymph.' Water 95.0 Solids 5.0 Fibrin 0.1 Proteids 4,1 Fat, etc. Traces Extractives 0.3 Salts 0.5 While the question has not yet been definitely settled, it may be mentioned as appropriately here as elsewhere, that according to the researches of Heidenhain^ the formation of lymph cannot be at- tributed to the simple filtration and diffusion of the blood plasma, some kind of secretory action being exerted by the endothelial cells of the walls of the capillaries as well. The gases of the lymph consist principally of carbon dioxide with some nitrogen and traces of oxygen. It has already been mentioned that the red corpuscles often found in the lymph are really red blood corpuscles that have escaped from the capillaries. While it is possible that some of the lymph corpuscles may also be only white blood corpuscles that have passed from the blood with the red ones into the lymph, the lymph corpuscles in general appear to originate in an entirely different manner, there being good reasons for supposing that they are pro- duced in the lymphatic glands, spleen, etc. The consideration of the origin of the lymph, or white corpuscles, and their relation to the red ones and the glands just mentioned, wc will, however, defer until the blood is studied, and pass on to the consideration of the quantity of the lymph, and the causes of its flow through the system. Naturally, from the conditions of the case, the amount of lymph produced can be estimated only approximately. It may be men- tioned, however, that nearly six kilos (13 pounds) of lymph were collected in twenty-four hours from a lymphatic fistula in the arm of a woman by Gubler and Quevenne,^ Various causes have been assigned for the flow of lymph. Of these, some are more impor- tant than others. One of the principal causes of the flow of the lymph is undoubtedly the vis a tergo resulting from the constant passing of the serum of the blood into the lymphatic system, and as the lymph, on account of the valves (Fig, 48) in the vessels, must flow always from the periphery or the radicles of the system , iLandois, op. cit, p. 393. zpfuggr'g Archiv, Band xlix., 1891, s. 209. "Landois, op. cit., p. 394. 164 ABSORPTION. Fi<;. 48. toward the great trunks and blood vessels, each successive addition of serum to the lymphatic system will act as a force propelling for- ward the lymph already there. From the fact that the lymphatics contain unstriped muscular fiber, it is probable that these vessels at times contract upon their contents. This action, however, would appear to be slight, inas- much as the rhythmical contractions of the lymphatics in mam- mals are rarely observed. It should be mentioned in this connec- tion, however, that frogs, toads, lizards, etc., the lymphatics of which are unprovided with valves, possess the so-called lymphatic hearts. The latter are dilated portions of the lymphatics, exhibiting contractility, and which pulsate regularly. The influence of muscular contractions upon the flow of the lymph must not be forgotten, for pres- sure upon the lymphatics from this source will have the same eflect as we shall see it has in accelerating the flow of blood in the veins. From the disposition of the terminal portion of the lymphatic system in the thoracic cavity, it might naturally be inferred that during inspiration, inas- much as all the parts are dilated, that the flow of lymph into the thoracic ducts would be increased, and that, during expiration, as all of the parts are contracted, the lymph will then flow onward into the left subclavian vein, regurgitation being impos- sible through the presence of valves. Experiment has shown that such is in fact the case. With each inspiration the thoracic ducts become dilated through the increased flow of lymph ; at that moment the lymph flows freely from the right thoracic duct into the right subclavian vein. With each expiration the lymph is expelled Avith increased force from the left thoracic duct into the left subclavian vein, and when a fistula is made in that situation the lymph issues as an intermittent jet. Of the difierent causes just given for the flow of the lymph, it would appear that the vis a terr/o and the respiratory movements are the most important, the contractility of the vessels and the pressure of surrounding parts being of secondary importance. Up to this moment, in speaking of the lymphatic system, we have only alluded incidentally to the lymphatics of the small intes- tine, or the lacteals. As these vessels have a special interest for us in connection with the absorption of the digested food, let us study them no\v a little more in detail. The lacteals, or lymphatics of the small intestine, begin in the villi, wliich structures we only alluded to in speaking of the ali- mentary canal, reserving for tlie present moment their more detailed consideration. The villi (Fig. 49) are small processes of the mucous Valves of the lym- phatics. (Sappey.) STRUCTURE OF THE VILLI. 165 membrane of the small intestine, measuring on an average about the Y^^ of a mm. ( Jg of an inch) in length, and al^out the ^-'-j of a mm. {■^^ of an inch) in breadth. They are usually conical, and flattened in form, though sometimes cylindrical, or terminating in an enlarged or clubbed-like extremity. The villi are largest and most numerous in the duodenum and the so-called jejunmn. They are closely set upon the inner surface of the intestine over the val- vule conuiventes, as well as between the same, and give rise to the characteristic velvety appearance of the mucous membrane in this situation. It has been estimated that in the upper part of the small intestine there arc fifty to ninety villi to the square line, their total number amounting to about four millions. The Villi can be well seen by examining a piece of intestine under water mth a simple lens, the mucus having been first removed by gentle washing. When studied with the microscope the villus is seen to consist of a prolongation of the epithelial layer of the mucous membrane of the intestine, enclos- ing a network of blood vessels, the beginning of the lymphatics, or the lacteals, and some plain muscular fibers. These structures are held together and supported l)y lymphoid or retiform tissue, which, Fig. 49. Fig. 50. Villus of man with lacteal and blood vessels injected. (Teichmanx.) Villus of man showing lacteal surrounded by epithelial cells. (Fkey.) at the surface, is condensed into a basement meml^rane, upon which the epithelial cells rest. (Fig. 50.) Up to this time it is doubtful if nerv^es have been demonstrated 166 ABSORPTION. in the villi. It is very pi'obablc, however, that they are present. Each villus usually receives one arterial twig, which, after penetrat- ing it, breaks up into capillaries situated just beneath the basement membrane. The blood is returned usually by one vein. The lym- phatic, or the lacteal, begins in the center of the villus, usually as a single vessel (Fig. 49), with a closed and somewhat expanded ex- tremity. Its caliber is considerably larger than that of the capillary blood vessels surrounding it. The lacteal wdthin the villus, like the lymphatics elsewdiere, is surrounded by a delicate layer of flattened cpitheloid cells (Fig. 50). These are connected with the cells of the basement membrane through those of the lymphoid or connective tissue lying between (Fig. 51). The columnar epithelial cells which cover the villi, and also the surface of the mucous membrane, and which are prolonged into the tubular glands, present a granular appearance with an oval nucleus. They terminate to- ward the basement membrane in a tapering manner, and measure about the 4^o^th of a mm. (-fo^Q o" of an inch) in length. Their free end (Fig. 51), or the surface looking toward the interior of the intestine, consists of a layer of a highly refractive substance, with vertical strise running through it. These strite have been regarded as being either minute canals, or as solid rods. Some of these columnar cells usually contain inucus, and swell up upon the addition of water into the so-called goblet cells which are regarded by some anatomists as the true beginning of the absorbent system. The lymphatic or central lacteal connected with the columnar cells by the lymph chan- nels in the stroma after emerging from the villus passes into the lymphatics of the intestine. These are usually described as consist- ing of two sets, the deep and superficial. The latter pass into the mesentery to the lymphatic glands. The lymphatics coming from the latter, as we have seen, converge toward the reccptacu- lum chyli. During the intervals of digestion the lymphatics of the small in- testine, or tiie lacteals, contain lymph, undistinguishable from that of the lymphatics of the rest of the body. Daring digestion and absorption, however, and more especially when fatty articles have constituted part of the food, the epithelial cells of the villi, and the lymphatics of the small intestine, are then filled Avith the chyle. The chyle is a coagulable, alkaline, opaque, whitish, milky-like fluid, hence the name of the lacteals given to the lymphatics of the small intestine, in which it is found. Diagrammatic representation of the origin of the lacteals in a villus. e. Central lacteal. d. Lymph channels, c. Colum- nar epithelial cells, the attach- ed extremities of which are directly continuous with the lymph channels. COMPOSITION OF THE CHYLE. 167 Composition of the Chyle.' Water 90.5 Solids 9.5 Fibrin 0.1 Proteids 7.0 Fat, etc 1.0 Extractives ] ■, a Salts J The chyle, however, is only the lymph with the ])iT)(lucts of di- gestion added to it, and as the lacteals absorl) princi])ally the fat, the essential difference between the chyle and the lymph is that the former contains a great quantity of fat, the latter usually only a trace. In reference to any analysis of the chyle, it must not l)e for- gotten that its composition \\\\\ differ according to whether the por- tion examined has been taken from the lacteals or the thoracic duct. Indeed, chyle drawn from the thoracic duct is not pure chyle, but chyle mixed with the lymph which has been brought from the ex- tremities to the receptaculum chyli, and thence passed into the thoracic duct. The chyle of the thoracic duct will contain, therefore, less fat and other solid constituents, than that of the lacteals. Further, the amount of flit in the chyle will be variable, depending upon the diet of the man or animal examined. Thus, the chyle of a car- nivorous animal will contain more fat than that of a herbivorous one, the food of the former being richer in fat than that of the latter. At one time it was supposed that the lacteals absorbed exclusively the fatty substances, liut it is now known that they also take up, at least in small quantities, albuminoid and saccharine substances, salts and water. Of the amount of the chyle poured into the thoracic duct, it is impossible to give even an approximate estimate. When examined microscopically, the milky appearance of the chyle is seen to be due to an immense number of very minute fatty granules, which constitute the so-called molecular base of the chyle, and which measure on an average the ^^^ of a mm. (^2^70" ^^ ^^ inch) in diameter. These granules appear to be coated with albumin, which probably prevents their running together and coalescing. The so-called chyle corpuscles found in greater or less number in the chyle, do not differ from those of the lymph or blood, and will be considered again when the latter fluid is studied. What lias Ijcen already stated in reference to the supposed causes of the flow of the lymph will apply equally well to that of the chyle ; but there is one condition, in addition to those already mem- tioned, which appears to influence favorably the flow of the chyle, and so deserves a passing notice. It will be remembered that, in speaking of the structure of the villi, allusion was made to the plain muscular fiber that they contain.' These muscular fibers are dis- persed longitudinally around the lacteal, and their contraction will ' Landols, op. cit., p. 392. 168 ABSORPTION. obviously retract the villus. The eiFect of the action of these mus- cular fibers will then be to force the contents of the lacteal out of the villus into the superficial lymphatics. These muscular fibers have probably, then, some importance in aiding the flow of the chyle toward the thoracic duet. It will be remembered that, up to the time that the lymphatics were discovered, absorption was considered to be effected by the veins only. After the discovery of the lymphatics, however, phys- iologists fell into the opposite error of attributing absorption solely to the lymphatics, denying that the veins took any share in this pro- cess. Indeed, it was not until the present century that it was ex- perimentally demonstrated that the veins as well as the lymphatics absorb. Apart, however, from any experimental evidence, the facts of comparative anatomy alone should have shoAvn that of the two sets of vessels, so far as the absorption of the digested food is con- cerned, the veins play a more important part than the lymphatics. Thus it is well known that in the amphioxus, the lowest of the vertebrata, and in all the invertebrata, the lymphatic system is ab- sent. In these animals, therefore, absorption is carried on solely by veins. Further, while the lymphatic system is present in fishes, batrachia, reptiles, and birds, it is only in the mammalia that it acquires the functional importance that we have ascribed to it. Indeed, according to Bernard,^ the name lacteal cannot be prop- erly applied to the lymphatics of the small intestine in the oviparous vertebrates, since these lymphatics contain always, even during di- gestion, with few exceptions, a clear, transparent lymph instead of chyle, an opaque, whitish fluid, the fat in these animals being taken up, not by the so-called lacteals, Ijut by the portal vein, the greater part of it being thence carried to the renal veins (Jacobsen's system), and so to the vena cava. Inasmuch as absorption is carried on by the veins in the lower animals, we would naturally infer that these vessels must be of great importance in this respect in man and the mammalia. Magendie ^ appears to have ])een the first to show conclusively by experiment that absorption takes place by the blood vessels. Of his many remarkable and accurate experiments, the following may be mentioned : In one experiment the abdomen of a dog that had been well fed some hours previously was opened, and a loop of the intestine drawn out. Ligatures were placed around this loop at a distance of about 37.5 centimeters (15 inches) apart. The lym- phatics arising from this portion of the intestine being all ligated in two places, were divided between the ligatures. Of the five mesenteric arteries and veins passing into the general vascular sys- tem, four were divided and ligated so that the loop of the intestine remained in connection with the rest of the system by only a single vein and artery, even the cellular coat of which was dissected off", ' Physiologie Experimentale, Tome ii., p. 312. 2 Journal de Physiologie, p. 18. Paris, 1821. VENOUS ABSORPTION. 169 so as to remove all doubt of there being a trace of a lymphatic left. Some upas was then introduced into the loop of the intestine prepared in tlie above manner, which was then replaced in the ab- domen, and in a few minutes the characteristic symptoms of poison- ing appeared, showing that the upas had been absorbed Ijy the vein. In another experiment, where the poison was introduced into the foot, the only connection between the limb and the rest of the body was through two quills, introduced into the divided femoral blood vessels, the rest of the parts having been dissected oif. In this case, also, the only possil^le means by which the poison could pass into the general system and make its effects evident was through the circulating blood. The experiments of ]Magendie were soon afterward confirmed by Tiedmann and Gmelin,' Segalas," and by the committee appointed by the Academy of Medicine of Philadelphia to investigate the subject."^ A convenient method of demonstrating venous absorption is to open the abdomen of a frog, withdraw a loop of the intestine, and ligate it in two places, cut away all the mesentery, leaving only a single artery and vein, and introduce a solution of ferrocyanide of potassium into the intestine by an opening made in the latter, re- place the loop within the abdomen, and, after a few minutes, open one of the veins of the foot. On testing the blood for the ferrocy- anide of potassimn by adding tincture of the chloride of iron, the presence of the salt introduced into the intestine will become at once evident, through the formation of Prussian blue, the latter being best demonstrated by adding the perchloride of iron to the serum, the blood having been allowed to stand, or to a clear extract of the blood, made by boiling the latter with a little sodium sulphate and filtering. It is obvious that the only means by which the salt of potassium could pass under such circumstances from the intestine into the general circulation, and thence into the blood of the extremities, was by means of the vein left in the mesentery. As we have seen that by far the greatest part of the food is di- gested in the small intestine, it might be naturally inferred that the water, salts, peptones, sugars, and fat are absorbed by the veins and lymphatics of the small intestine rather than by those of the stom- ach. That such is the case appears to have been shown, at least in animals. Thus, for example, in a dog, in whom a fistula of the duodenum had been established, of the water drunk fully 99 per cent, passed within twenty minutes out of the fistula.* ' Kecherclies sur la route qui prennent divei-ses substances pour passer d' Estomac et du Canal intestinal dans le Sang. Paris, 1821. ^Journal de Physiologie, Tome ii., p. 117. Paris, 1822. ^Philadelphia Journal of the Med. and Phys. Sciences, 1821, Vol. iii., p. 273 ; 1822, Vol. v., p. 327. *3. Von Mering, Therapeutische Monatshefte, Berlin, 1893, s. 201. J. S. Ed- kins, Journal of Phvsiologv, 1892, Vol. xiii., p. 445. Brandl, Zeits. fiir Biologie, 1892, Band 29, s. 277. 170 ABSORPTION. Salts do not appear to be absorbed by the stomach unless intro- duced into the latter in a more concentrated state (o per cent.) than when taken as food. Sugars and peptones appear, however, to be absorbed by the stomach to some extent, especially if the solutions are concentrated (5 per cent.). The absorption of salts, sugars, and peptones by the stomach is much increased if given with alcohol and condiments, such as pepper and mustard. Alcohol itself is readily absorbed by the stomach. As fat to be absorbed must first be emulsified and as that change is only effected in the small intestine, it is evident that fat must pass through the stomach without being absorbed. Apart from the fact that food is rendered fit for absorption largely by digestion in the small intestine, it should be mentioned that ample time is af- forded for its absorption by this part of the alimentary canal, since from nine to twenty-three hours elapse before the food eaten passes out of the small into the large intestine, its passage being retarded by the presence of the villi and valvule conniventes. Experiments made upon animals,^ and observations upon human beings,^ con- firm the view based upon the above considerations, that water, salts, peptones, sugar, and fat are principally absorbed by the small in- testine. In considering the water and salts absorbed by the veins of the small intestine, it must be borne in mind, however, that as part of the water, etc., absorbed is replaced by that excreted by the intestine, the contents of the latter are, therefore, more or less liquid like the chyme. As a proof of the amount of proteid ab- sorbed, it may be mentioned that in a case of fistula of the end of the ileum in a human being, about eighty-five per cent, of tlie pro- teid eaten was absorbed before the latter reached the large intestine. It should be mentioned, in this connection, that while peptones and albumoses are without doubt absorbed by the veins of the stomach and small intestine, they are not found as such in the blood. The only conclusion to be drawn from this fact is that peptones, etc., are converted into serum or blood albumin as they pass through the epithelial cells into the blood. If such be the case then peptones, etc., must, in becoming blood albumin, undergo in the epithelium dehydration and polymerization, the reverse of the processes by which they were produced from proteid, viz., liydration and split- ting. The various carbohydrates appear to be absorbed by the veins of the small intestine in the form of glucose, or glucose and levulose. Thus, starch is converte<' im incii) is preferable, as beinn ficial vasa infereutia. c,c. Larger alveoli, near the peritOUeum, pieuia, ClC, COn- surface. (i, d. Smaller alveoli of the interior, e, e. -gi. i„ „ nnneirlprnKlp pvfpnt Fibrous walls of the alveoli. (Caepenter.) hlhl., LO d COllblueiauiC tJALeiiL, of the adenoid or cytogenous tissue just mentioned, which enters into the formation of the solitary and lymphatic glands, and that these serous sacs communicate by openings or stomata with the lymphatics. The tonsils also appear to consist essentially of nodular masses of lymphoid tissue em- bedded in the submucosa of follicles of the mucous membrane. We have already seen that the lymph differs from the blood quantitatively, rather than qualitatively, and that the chyle is lymph with the products of digestion added to it, more especially of the emulsified fats and oils. The lymph and chyle corpuscles, which are indistinguishaljle from the white (!orpuscles of the blood, seem to consist at first of fatty nuclei, whicli, acquiring an envelope through diffusion in an albuminous fluid, gradually become white corpuscles. In examining the chyle of the lacteals in the villi, in the mesenteric glands, and in the thoracic duct, it was noticed that the so-called molecular base of tlic chyle consisted largely of fatty matter, and that the chyle corpuscles were probably due to an ag- gregation of the minute bodies forming the base of the chyle. It seems probable, therefore, that the chyle corpuscles, or white cor- puscles of the l)lood, are elaborated in the lymphatic glands. In addition to containing white corpuscles, the chyle resembles an early stage of the blood in other respects, thus between the mes- enteric glands and thoracic duct it will coagulate — that is, separate into clot and serum, while the chyle of the thoracic duct exhibits a reddish color. ^Anatomy of the Lymphatic System, 1873. ^Strieker's Histology, p. 215. THE SPLEEX. 195 Spleen. — In examinino; the structure of the spleen one cannot but be impressed with its great similarity to a lymphatic gland. Like the lymphatic gland, the spleen (Fig. 65) consists externally of a fibrous capsule, from which pass inward numerous strands, consti- tuting the so-called trabecuhe, in the meshes of which is contained the splenic pulp. This consists of white blood corpuscles, of red corpuscles in various stages of development or disintegration, of granular matter of a reddish-brown hue, blood crystals, iron, etc. The only difference between the spleen and a lymphatic gland con- sists in the fact that the cells found in the spleen pass directly into the blood. Fig Vertical section of a small superficial portion of the bumaii spleen. Low power. A. Peritonea and fibrous covering, ft. TrabecuUe. c, <■. Malpighian corpuscles, in one of which an artery is .seen cut transversely, in the other longitudinally. (/. Injected arterial twigs, e. Sijleen-pulp (KOLLIKEE.) That the spleen is essentially a lymphatic gland seems confirmed by the fact that when it is small in man or an animal, the lym- phatic glands are large, and vice verm. Xot only is this inverse ratio observed in the same animal but also in different species. Thus, among other instances observed by the author, in the manatee the spleen is very small M^hile the glands are very large, M'hereas, in the sea lion, the reverse obtains. This view of the nature of the spleen is confirmed by the fact that it can be removed from animals with impunity, the lymphatic glands then enlarging and through vicarious action apparently performing its function, and also that the spleen is absent in the lowest of vertebrates, the am- phioxus. On the other hand, with hypertrophy of the spleen, we have, coincidently, disease of the bones indicating the relationship, functionally, between the two. Indeed, recent observations^ render ' Laudenbach, Cent rail )latt fiir Physiologie, 1896, Band ix., s. 1. 196 THE BLOOD. it probable that the spleen produces red blood corpuscles as well as leucocytes which becomes intelligible when it is remembered what has already been said as to the influence of the marrow in hsemato- poiesis. One of the most strikino; peculiarities of the spleen is its great vascularity. Not only does a large quantity of blood flow into the organ, but the distribution is remarkable inasmuch as capillaries in certain parts are absent, the blood of the splenic artery passing then directly into the interstices of the pulp to be taken up by the Fio. m. Front view of tlie right kidney and suprarenal body of a fiill-growu i'cetus. r, V. The renal vein and artery. «. The ureter, a'. The .suprarenal capsule, the letter i,s placed near the .sulcus in which the large veins (;') are seen emerging from the interior of the organ. (Allen Thomson. ) veins, a type of circulation that obtains in the invertebrates. It may be mentioned in this con- nection that the so-called Mal- pighian corpuscles attached to the branches of the splenic artery in the spleen do not appear to differ essentially in their minute structure frle from the fact as we have seen of the liver and pancreas elal)orating internal secretions such as glycogen, urea, and a glycolytic ferment respectively. 1859, s. 61. Gley, Archives de Phvsiologie Normal et Pathologique, 5 Serie, Tome iv., 1892, pp. 135, 311, 664. Christiani, Ibid., 1893, p. 39. Vasale et Generali, Archives Ituliennes, De Biologie, Tomexxv. , 1896, Fas. III., p. 459. 1 Koclier, Bucher, ITorsley, Murray, Howitz referred to by Lauzon, Klinische Yortnige, 1894. ^Chittenden, Science, June, 1897, p. 5. ^ Baumann und Roos, Zeitschrift fiir Phvsiol. Chemle, Band 21, 1896, s. 319, s. 481, Jiand 22, 1896, s. 1. Hutchinson, Journal of Physiology, Vol. 20, 1896, p. 474. * Ewald, Verhandlungen des Congresses fiir innere Medecin, 1896, s. 101. 5 Bernard, Rapport sur les progres et la marche de la Phvsiologie generale en France, 1867, p. <5!>- . . ^ Haller, Elementa Physiologiie, Tomus iii., 1766, p. 400: " Liquorem peculi- arem in ea glandula parari, qui receptns venulis sanguini reddatur, qupe etiam lienis tS: thymi sit utilitas, ipse Ruysciiius .Vutumavit." THE THYMUS GLAXD. 199 The Thymus Gland. — The thymus gland appears in the embryo first as a solid body, but soon becomes a tube closed at both ends and filled with granular matter. From this tube (Fig. 68) there bud out at intervals, on either side, hollow lobular processes, the cavities of which communicate with that of the central axis. The thymus in the adult consists of a series of such oifshoots or lobules united by connective tissue and opening into the central tube, to which, however, there is no outlet. Each lobule (Fig. 69) consists Fig. 60. Section of loi'ulc of thymus. of an external fibrous capsule which sends prolongations into its interior consisting of acini, in the meshes of which are seen the thymus substance. This contains lymph corpuscles, spheroidal granular bodies, and concentric corpuscles. In the expressed thy- mus juice are found corpuscles which are indistinguishable from those of the fluids of the lymphatic glands. The th^^uus gland, in its whole structure, resembles very much a Peyer's patch. The functions of the thymus gland are unknown. It is possible that it elaborates, like other ductless glands, an internal secretion that in some way promotes nutrition, and especially in early life, since it diminishes in size after puberty. The blood contains, as already mentioned, in addition to the red and white corpuscles, other formed elements, the blood plates of Hayem.^ These are minute bodies, though attaining sometimes a size of the ^i^ of a mm. (45V0" ^^ '^° inch) in diameter, circular in form and homogeneous in structure. Much difference of opinion still prevails among histologists as to the nature of the blood plates. 1 Comptes Rendiis, T. 86, p. 58, 1878. 200 THE BLOOD. Some regard them as a distinct, third kind of corpuscle, others as only the nuclei of the disintegrated leucocytes. The latter view is based not only upon morphological grounds but upon the fact of the blood plates containing the same kind of nucleo-albumin ^ as the nucleus of the leucocytes. Apart from contributing nucleo-albu- min to the blood whose significance is speculative and of the sup- posed use in the production of tlie fibrin ferment, the function of the blood plates is entirely unknown. 1 Lilienfeld, Du Bois Eeymond, Archiv fiir Physiologie, 1893, s. 560. CHAPTER XII. THE Bl.OO'D.— {Continued.) One of the most interesting properties of the blood is its power of coagulation, that is of separating into clot and serum. Before coagulation the blood consists of the liquor sanguinis or plasma and the corpuscles ; after coagulation it ^vill be found that the cor- puscles are entangled in a fine network consisting of the meshes of the coaguated fibrin, the two constituting the clot or crassamen- tum, while the proteids, salts, and water remain together as the serum. It is important to notice that the liquor sanguinis, or tlie plasma, is not identical with serum, liquor sanguinis being serum with the addition of fibrinogen, serum liquor sanguinis without fibrinogen. Serum differs also from what are known as serous effusions, which are due to transudations, not to coagulation. Blood. Before coagulation. r Water J Salts 1 Proteid Liquor sauffuini Corpuscles [ Fibrinogen After coagTilation. Serum. I Clot. When the blood is allowed to flow into a tolerably deep, smooth vessel, according to Xasse/ in from about one minute and forty-five seconds to six minutes a gelalanation at all, • but simply a statement of the phenomena to be explained, it is not even a fact, as Ave have seen that the blood coagulates in the living body. In the last century it was generally held that what we call fibrin was produced in some way at the expense of the corpuscles, which run together in coagulation, etc. Petit, Da vies, and Hewson,^ however, held that coagulation was due to some distinct substance independent of either the corpuscles or the serum, and Hewson per- formed several experiments to prove that coagulation was due to the fibrin. For example, Hewson - added a little sodium sulphate to fresh blood, which prevented coagulation. After the mixture had remained standing some time the corpuscles sank to the bottom, the clear fluid which remained on top was then decanted, twice its quantity of water was then added to this, when the fibrin coagulated. On another occasion, this most able observer^ tied the jugular veins at the sternum of a dog just dead, and hung his head over the edge of a table, so the ligatures might be higher than the head. The upper part of the vein became transparent, the red corpuscles sinking ; he then tied the vein, separating the clear from the red part, and let the clear part out, which was fluid, but coagulated soon after. These experiments showed that the coagulation was due to the fibrin, but they did not demonstrate that this fibrin did not come from the corpuscles, which was the view that prevailed at that time. To do this it was necessary to show that the corpuscles were unaffected to coagulation. With reference to determining this point, Johannes Miiller,^ the great Berlin physiologist, in 1832 experimented in the following ways : He added a little solution of sugar to frog's blood, which re- tarded the coagulation, and then filtered the mixture ; the cor- puscles, which are very large, were retained in the filter, and the clear fluid which passed through coagulated. Milller then showed that in blood which was defibrinatcd by whipping, and therefore incoagulable, that the corpuscles were not altered in any appreciable manner ; and further, that when blood to wdiich had been added serum (which separated the corpuscles from each other) was ob- served under the microscope coagulating, the corpuscles were seen to remain intact. Inasmuch as the white stringy substance appearing at the moment 1 Milne Edwards, op. cit., Tome i., p. 119. 2 Works, p. 12. 3 Ibid., p. 32. * Physiology translated by Baly, 1840, Vol. 1st, p. 123. COAGULATION OF THE BLOOD. 205 of coagulation, Avhicli we call filnnu, cviJently does not exist as such in the blood before coagulation, it remains to be determined, if possible, under what form it then does exist. If blood be drawn into a concentrated solution of sodium sulphate to prevent its co- agulation, and sodium chloride be added to the mixture in the pro- portion of ten per cent., a whitish, pasty substance is thrown down, amounting to about 25 parts per lUOO of the blood used, and called by Denis/ who first described it, plasmin, and which, together with serin, constitutes blood albumin. Xow, when plasmin is redis- solved in water, the solution splits into fibrinogen 3 parts, and para- globulin 22 parts, the former coagulating, the latter remaining liquid. It would appear, therefore, that fibrin exists in the blood combined with paraglobulin, as plasmin or some form closely allied to it ; and further, as with the withdrawal of the plasmin from the blood, the latter loses its power of coagulating, the serin remaining liquid, that coagulation of the blood consists, first, in the splitting of albumin into serin and plasmin, and secondly, in the latter splitting into fibrin and paraglobulin, or of the breaking up of al- bumin directly into serin, fibrin, and paraglobulin. On the other hand, the observation, made many years ago by Buchanan,^ that two fluids, like that of hydrocele and ascites, or of ascites and pleurisy, when added together, coagulate, though when separate show no such tendency, has led many to infer that the production of fibrin is rather due to the union of substances in the blood than to the decomposition of the same, as just explained. Indeed, according to Schmidt,^ two such principles actually do exist in the blood, a fibrinoplastic sul)stance, paraglobulin, and a fibri- nogenous one, fibrinogen, whose union brought about by the pres- ence of a ferment at the moment of coagulation constitutes fibrin. Paraglobulin can be readily obtained from the serum of the blood through precipitation by the addition of sodium chloride in excess, and fibrinogen in the same way free from the liquor san- guinis, in which coagulation has been prevented l)y the addition of magnesium sulphate, and the corpuscles have been removed by filtration. Xow, while it is an interesting fact that if paraglobulin in a saline solution be added to eitlier fibrinogen or hydrocele fluid, or if fibrinogen as obtained either from the liquor sanguinis or hydrocele fluid be added in saline solution to serum, fibrin will be produced, it does not necessarily follow that such a union as that of para- globulin and fibrinogen actually takes place in the blood at the moment of coagulation. Indeed, it is yet to be proved that para- globulin exists as such in the clot, seeing that if we obtain it from the serum it must be assumed that it exists in excess partly in the serum and partly in the clot. Again, as under certain circum- ^ Annales des Sciences Xaturelles (iv. ), p. 25. ^Proc. of Glasgow Philos. Soc, 1845. "Du Bois Eevmond, Archiv, 1861, s. 545; 1802, s. 428. Pfliiger's Aa-chiv, 1872, s. 413 ; 1875, s. 291 ; 1876, s. 515. 206 THE BLOOD. stances, parao:lobulin when mixed witli fibrinogen does not produce fibrin, it is still further assumed that the presence of a ferment is necessary to eiFect the union of the two filn'in factors. As a matter of fact, an aqueous extract can be obtained from the serum by co- agulating the latter with alcohol, allowing the mixture to stand, drying and pulverizing the clot, and then, adding water and filter- ing, which, when added to fibrinogen will cause the coagulation of the latter like a ferment. According to Schmidt, such a ferment is derived from the disintegration of the white corpuscles, the latter, as is well known, being always present in sj)ontaneously coagulable fluids and very abundant if the coagulation is marked. It was soon demonstrated, however, that the Schmidt theory of coagulation was untenable, Fredericq/ Hammarsten,^ among others, proving that the clot was due to the coagulation of the fibrinogen in the presence of a ferment, the paraglobulin not entering into the formation of the clot at all. It has been shown, however, in recent years, by Arthus and Pages,^ that if potassium or sodium oxalate be added to freshly drawn blood in sufficient quantities to precipitate its calcium salts, coagulation A\ill be prevented, but that with the addition again of a soluble calcium salt coagulation will take place immediately. The Schmidt-Hammarsten theory has been, therefore, still further modified so as to take into account the influence exerted by the cal- cium salts in the production of coagulation. Thus, according to Pekelharing,^ after the blood has been shed a fibrin ferment is formed through the union of a nucleo-albumin derived from leuco- cytes and blood plates with calcium. At the moment of coagulation the calcium leaves the nucleo-albumin and unites with the fibrinogen or part of it to form an insoluble calcium compound, fibrin. This view is based upon the fact that coagulation will take place if nucleo-albumin, together with calcium salts, be added to fibrinogen solutions, but will not take place if nucleo-albumin or calcium salts be added alone. A still more recent theory, that of Lilienfeld,^ regards the fibrinogen as giving rise under the influence of leuco- nucleiu to thrombosin, which combining Avith calcium forms the fibrin, the leuco-nuclein being derived from a proteid substance, nucleo-histon, obtained from the leucocytes and blood plates. It would appear, therefore, that the phenomena of coagulation is essen- tially that of the union of calcium with fibrinogen, through the influ- ence of a third factor. Either a nucleo-albumin unites with calcium, and the latter then unites with fibrinogen, or a nucleo-albumin develops out of fibrinogen thrombosin, and the latter unites with calcium. It may be added that, according to these theories, blood 1 Hoppe-Seyler : Physiologie Chemie, 1879, s. 416. 2PHii}p,,„ as estimated by Hi'ifner " for dogs' hsemoglobin, be accepted as cor- rect, the molecular weight will be 14001, and therefore very great. The amount of hfemoglo- bin present in a given quantity of Idood can be determined from the amount of iron by coloro- metric methods and by the spectroscope. The iron method is based upon the fact that dry (100° C.) hemoglobin contains 0.42 per cent, of iron. Knowing the amount of the latter in the blood the Hexagonal crystals froni blood of squirrel. 'Med. Chem. Unters., s. 370. ^ Harnmai-sten, op. pit., p. 09. H^MOGLOBIXOMETEB . 215 amount of hsemoglobin can be at once calculated by the following equation : , 100 Fe 100 : 0.42 :: a: : Fe. x equals ---r^ , in which x is the unknown quantity of haemoglobin, Fe the known quantity of iron in the blood, and 0.42 the per cent, of iron in 100 parts of hsemoglobin. To obtain the amount of iron in the blood whose hsemoglobin is to be determined, a known quantity of blood is calcined, the ash is then treated with hydrochloric acid to obtain ferric chloride, which is then transformed into ferrous chloride by boiling with zinc until the liquid is colorless. The liquid being di- luted, the amount of iron in it is determined volumetrically ^ by adding from a burette permanganate of potassium in standard solu- tion until the rose color becomes permanent after agitation, 0.0056 gramme of iron being present for each centimeter of standard solu- tion used. The hsemoglobin, as determined from the quantity of iron, amounts, according to Preyer,- in human blood to about 12.34 per cent. The colorometric method depends upon the comparison of the tint of the blood to be investigated with that of a standard solu- tion. In determiuino- the amount of hajmoirlobin in this wav we make iLse of the hsemoglobinometer of Gowers. This consists (Fig. Fig. 77. A. Pipette bottle for distilled water. P.. Capillary pipette. C. Graduated tube. D. Tube with standard dilution. F. Lancet for pricking the finger. 77) of two glass tubes (D and C) of exactly the same size. Into D are placed 20 cubic mm. of blood diluted with 2000 mm. of water; the strength of the solution is therefore 1 per cent. C is graduated, the scale of 100 degrees extending over a space equal to 1 Sutton, Yolnmetric Analysis, 4th ed., pp. 88, 94. ^Qp. cit., s. 117. 216 THE BLOOD. that in D containing the 1 per cent, dihited blood. The manner of using the apparatus is as follows : Into C are placed 20 cubic mm. of the blood to be examined, which is then diluted until its color is the same as that in D. Suppose, for example, that we have to add to the blood to be investigated placed in C only 30 degrees of water (600 mm.) in order to obtain the same tint of color as that in D, instead of as in the latter case 100 degrees of water (2000 mm.), it follows that the blood in C contains only 30 per cent, of the nor- mal quantity of haemoglobin. Further, if the number of corpuscles in the investigated blood has also been shoAvn to be only 60 per cent, of the normal amount, we have a fraction |^ = i, the nume- rator being the per cent, of the haemoglobin and the denominator the per cent, of corpuscles, giving the average value of each corpus- cle, or half the normal amount. A still more delicate method of determining the amount of haemo- globin is by spectrum analysis. This method is based upon the fact as shown by Preyer ^ that the red, yellow, and first bands of the green of the spectrum can be seen through an 0.8 per cent, solution of haemoglobin and that such a solution can be taken as a standard of comparison. A known amount of the blood whose haemoglobin is to be determined is, therefore, diluted until the same bands are seen with the spectroscope as with the standard solution. That being accomjjlished, the amount of hoemoglobin can be determined by the following equation : X -.k : -.b + c -.h xb = k{b + c) in which X = unknown quantity of hsemoglobin. A-:=per cent, of htemoglobin in solution (0.8). 6 = volume of blood. c= volume of distilled water. Thus suppose, for example, that 2 c.c. of blood required 30 c.c. of water to give an absorption spectrum similar to that of the standard spectrimi, the percentage of which is 0.8 ; then (2 + 30) X = 0.8 — — - ^^ = 12.8 per cent, of oxyhtfimoglobin. To appreciate the manner in which spectrum analysis is applied in the determination of haemoglobin, or in the study of the blood generally, let us endeavor to explain briefly the principles of this method of investigation. As is well known, when sunlight is transmitted through a prism, as in Fig. 78, it is decomposed into the seven colors, violet, indigo, blue, green, yellow, orange, and red. This is called the solar spec- trum. In the early part of this century Fraunhofer described cer- iQp. cit., s. 124. SPECTRUM ANALYSIS. 217 tain lines situated in these colors, and which since then have been knowTi as Fraunhofer's lines (Fig. 79, 7), and which in all prob- ability are due to the presence of certain chemical elements exist- ing in the form of vapor around the sun and which prevent the passage of certain rays emitted by the solar nucleus, it having been demonstrated that a vapor absorbs rays of light having the same Fig. 78. Scheme of a spectroscope for observing the spectmm of blood. A. Tube. S. Slit. r/im. Laver of blood with flame in front of it. P. Prism. JI. Scale. B. Eve of observer looking through a telescope, r r. Spectrum. refrangibility as that which it emits. Tliu~ a liright vellow line in the spectrum, due to incandescent sodimn, will be replaced by a dark one if the liglit from the burning metal be intercepted by the vapor of the same. Since then it has been shown by Brewster, Herschell, and Miiller that various colored solutions prevent the passage of certain of the rays of light, dark bands appearing in the spectrum in tlie place of the rays or colors arrested. In the same manner the inlluence of blood upon the passage of light through it was investigated spectroscopically (Fig. 78), more particularly by Hoppe-Seyler,^ Stokes,- and Sorby,^ and it was shown by these observers that when dilute arterial blood is used two dark bands appear (Fig. 79, 1) between the Fraunhofer lines D and E — that is, in the yellow of the spectrmn, whereas if venous blood is used only one dark band (Fig. 79, 3) appears in the yellow near the line D. Further, it was demonstrated that this difference between arterial and venous blood was solelv due to whether the coloringr matter or the haemoglobin was oxygenated or not, and that the fact of the arterial blood l^eing red or scarlet, and of venous blood being blue or purple, was owing to oxyhtemoglobin being of a red hue and hsemoglobin of a bluish one. That the difference between arterial and venous blood spectroscopically, and as regards color, is due simply to the hcemoglobin being oxvgenated in the former case and I VirchoTT's Archiv, 1862, Band xxiii., s. 446. ^Proc. of Eoval Societv London, 1863, 1864, Vol. xiii., p. .3-55. * Quarterly Journal of Science, 1865, Vol. ii., p. 198. 218 THE BLOOD. unoxygenated in the latter, can be readily demonstrated. Thus, if some reducing agent like ammonium sulphide or an alkaline solu- tion of ferrous sulphate, kept from precipitation by tartaric acid, be added to arterial blood or the M'ashings from a blood clot, the oxy- gen, being loosely combined ^^At\\ haemoglobin, is at once seized with avidity by the reducing agent, the two dark absorption bauds dis- appear, being replaced by the one dark band characteristic of venous blood, and the color changes from red to blue. On the other hand, Avith the exposure of venous blood or a solution of haemoglobin to oxygen, or air containing such, the one dark band will disappear, being replaced by the two dark bands so characteristic of arterial blood, and the color will chano^e from blue to red arain. Fig. 79. Red. Orange. Yellow. Green. w fill C ^/ i ^ WIT I i ll I II 111 y I I l""i '°T « ^ ^ * io il J^ J3 i4- Oxyhsemoglobin and NOo-Hsemoglobin. CO-lIsemoglobin. ! Eeduced Hfemoglobin. Hsematin in acid solu- tion. Hsematin in alkaline solution. Reduced Hoematin. Solar spectrum with P'raunhofer's lines. It will be observed as shown by Fig. 79, that the band situated toward the red end of the spectrum, often called the " a. band," is narrower, darker and more defined than the band toward the green end, the " [i band," the single band of venous blood being called the " y band." It should be mentioned that the situation of these absorption l^ands is often described by stating the wave-lengths of those portions of the spectrum between which the bands are situated. Thus, for example, if the solution made use of in the investigation be one centimeter thick and contain 0.09 per cent, of oxyhsemoglobin, the " a band " is said to ])e situated (Fig. 80) between the wave- length 1 Yo^of o"o *^^ ^ millimet(>r and / -^-^W-^-^ of a millimeter, the " [i band " between / -jof fo-Q of a millimeter and / yof f q-q of a SPECTRUM ANALYSIS. 219 millimeter. To make use of this method, however, the spectroscopes should be provided Avith a scale so disposed as to enable the ob- server to read off directly wave-lengths of any part of the spectrum. According to the amount of oxy haemoglobin present in the blood, or solution of oxyhsemoglobin used, the dark bands will vary in extent. Thus, in a concentrated solution the two bands run into one, there being a general absorption at the blue and red ends of the spectrum, also the light then passing through only the green and red parts. With a still further increase in the strength of the so- FlG. 70 65 60 53 B C D 50 E b 45 G Diagrammatic representation of spectrum of oxyluemoglobin. The wave-lengtlis are indicated in hundred-thousandths of a millimeter by the numbers, the important Fraunhofer lines by the letters, the a band by the dark band to the right of i*, the /3 band by that to the left of ^'. After ROLLETT, in Hermann, Band iv., s. 47, Fig. 5. lution light will be transmitted through only the red portions of the spectrum, lience its red color, as seen by transmitted light. It is hardly necessary to add that the red rays are the last to disappear. The extreme delicacy of spectrum analysis, as applied to the de- termination of the presence of blood, may be appreciated from the fact of the two bands appearing in the spectrum of light trans- mitted through a layer 1 centimeter thick of a solution containing only 1 gramme (15.4 grains) in 10,000 c. cm. (20 pints) of water, or, in round numbers, about 1 grain of haemoglobin in a pint and a third of water. This is an important fact, since, under certain circumstances, in medico-legal cases, for example, the quantity of the suspected substance being exceedingly small, spectrum analysis would he the only means by which it could be determined whether it was Ijlood or not. Indeed, substances already decomposed and putrid, solutions made by washing with water, old stains upon iron, wood, linen that may have lain aside unnoticed for years, can be shown by the spectroscope to contain haemoglobin, and necessarily, therefore, to have been derived from blood, since no other known substance affects light as haemoglobin. Even if the spectrum obtained was that of carbon monoxide, or haemoglobin (acid haematin), characterized by two and one ab- sorption bands respectively (Fig. 79, 2, 4), as in the case of arterial and venous blood, this need be no source of confusion, since the absorption bands of these substances are not situated in exactly the same part of the spectrum as those of arterial and venous blood, and even if a doubt existed as to the exact locality of the bands, there could be none with reference to the presence of 220 THE BLOOD. blood, as it is the hsemoglobiu in each case which is the cause of the appearinjr of the bands. It should be mentioned in this con- nection that spectrum analysis, like all other means at present at our command, enables us only to determine that a substance is blood, but not necessarily human blood. In examining the blood spectroscopically, while the ordinary spectroscope can be used, the microspectroscope will be found more convenient, and especially the form described by Vierordt.^ It may be mentioned here as well as elsewhere that there are several other compounds or derivatives of haemoglobin, many of which have a characteristic spectrum and are of more or less in- terest as well as that of oxyh^emoglobin. Thus, for example, there are substances : methoemoglobin, differing only from oxy- hsemoglobin in that its oxygen is more stable ; hsemochromogen derived from the decomposition of haemoglobin in the absence of oxygen ; luematin on the contrary in the presence of the latter ; hsemotoidin obtained from the haemoglobin of extravasations such as apoplectic clots, corpora lutea, etc. Histio-hsematins, pigments found in the tissue and supposed to be derivative of haemoglobin, of which myohtematin already referred to is an example. H^ma- toporpliyrin or iron-free hsematin obtained through the action of sulphuric acid upon hsematin. Hsemin through the action of hy- drochloric acid upon the same. Hsemin being of especial interest from a medico-legal point of view, its chemical composition, and principal properties and method of obtaining will be briefly noticed. Hffimin as shown by its chemical composition (C.,^H3.Np,HCl) is a htematin hydrochlorate and can be obtained l)y the addition of hydrochloric acid to haemoglobin, 100 parts of the latter yielding about 4 parts of hannin. Hiemin is insohible in alcohol and water, but soluble in acids and alkalies, and can be obtained from a very minute portion of blood by the following method : Triturate the suspected substance with a little common salt and add glacial acetic acid, then warm the mix- ture till bul)bles appear, and then cool it. If the su})!stance, thus treated, contain hfemin, the latter will appear (Fig. 81) as crystals, in tlie form of rhombic tablets disposed sometimes as stars or crosses of a red or brown color. If oxygen be added, the color of the crys- ' Die Quantitative Spectral Analyse in ihrer Anwendiing auf Physiologie. Tubingen, 1876. Fig. 81. Khomliif crystals of luciuin fir hydrochlorate ofhiematiii. GASES OF BLOOD. 221 tals assumes a violet hue, while under the influence of carbon dioxide the crystals lose their transparency. In medico-legal ques- tions where there may be a very small quantity of material to be examined, the presence of haemin crystals will settle the ques- tion as to whether the suspected material is or is not blood. Hence, the importance of the method just given from this point of view. It should be mentioned, however, that the obtaining of hiemin as well as of haemoglobin crystals by whatever method only proves that the material from which they were extracted was l)lood, but not necessarily human blood. In the fact of the oxygen of the blood existing, for the most part, in a state of loose chemical combination with the Inemoglobin lies the explanation of the manner in which blood absorbs or gives off oxygen. Did the oxygen exist simply in a state of solution in the blood then the amount absorbed, or given oif, would depend upon the amount of pressure present. That such is not the case, how- ever, can be shown by exposing venous blood, containing little or no oxygen, to a succession of atmospheres containing increasing quantities of oxygen. At first there is a very rapid absorption of oxygen, but afterward this diminishes or ceases altogether. On the other hand, if arterial blood, containing a considerable quantity of oxygen, be exposed to successively diminishing pressures, at first little oxygen is given ofP, but afterward the escape is sudden and rapid. The amount of oxygen taken up or given off by blood is not, therefore, dependent upon pressure, except so far as the latter influences the passage to or from the plasma, l)ut upon chemical affinity ; the oxygen absorbed or given up by the hemoglobin is therefore a constant (piantity. The amount of oxygen absorbed by dogs' haemoglobin, for example, is 1.59 c. cm. per gramme, the temperature being 0° C, and the barometric pressure TGOmm.,^ one molecule of haemoglobin absorbing one molecule of oxygen. It is generally supposed that the property of absorbing oxygen exhibited by haemoglobin depends upon the iron that it contains, one molecule of oxygen being taken up for each atom of iron in the molecule of haemoglobin. The amount of oxygen that will be absorbed by the blood in any instance can therein be estimated from the amount of iron as Avell as from the hiemoglobin present. It may not be in- appropriate to mention that the oxygen absorbed, or given off by the haemoglobin, has nothing to do with the oxygen entering into its molecular composition, and as already given in its chemical formula. That the haemoglobin is that part of the blood which absorbs and gives up the greatest part of the oxygen there can be no doubt, since, if serum freed of the corpuscles, and therefore of haemoglobin, (the latter constituting 90 per cent, of the former), be experimented with instead of blood, little or no oxygen is absorbed, or given oflP, perhaps ^ per cent, of the entire blood, of which the serum was a ' Hilfner, Zeits. fiir phys. Chemie, Band ii., 1877-78, s. 389. 222 THE BLOOD. part, and that proportional to the pressure. It is, therefore, to their haemoglobin that the red corpuscles owe their function, as we have seen, of being oxygen carriers and, since the hemoglobin at low pressure readily gives up its oxygen, the functional significance of this substance, in respiration, becomes very evident. It may be mentioned in this connection that the carbon dioxide present in the blood is not simply dissolved there, but exists princi- pallv in the form of sodium carbonate and bicarbonate since the absorption and giving up of carbon dioxide by the blood is not de- pendent upon pressure. It is generally hold that these salts are de- composed and the carbon dioxide set free by the haemoglobin of the red blood corpuscles, the latter being supposed to act as an acid. That such is the case, is shown by the fact that more carbon diox- ide can be obtained from blood than from serum, and that after all the carbon dioxide has been extracted from the serum that is possible by the gas pump, two to five per cent, more can be obtained by adding acid. It is quite possible that the acid action of the hfemoglobin, just referred to, may be aided to some extent by the serum-albumin and primary acid phosphate of the blood. According to the recent investigations of Bohr,^ how^ever, it ap- pears that if hremoglobin be exposed to a mixture of oxygen and carbon dioxide, it will absorb carbon dioxide as well as oxygen, the former combining possibly with the globulin and the latter with the hsemochromogen. If such be the case hemoglobin must be re- garded to some extent at least as a carrier of carbon dioxide as well as aiding in the decomposition of the alkaline carbonates and of so setting free carbon dioxide. The small amount of nitrogen that the blood contains appears to exist there in a simple state of solution, the blood absorbing but little less nitrogen than that absorbed by water ; the amount de- pending, at least, within limits upon the law of pressure. The gases of the blood, as has just been incidentally mentioned, can be obtained by subjecting the blood to the mercurial vacuum. For this purpose we make use of Grehant's gas pump. This con- sists (Fig. 82) of a glass reservoir (B), which can be lowered or raised by a rack and pinion, and which communicates by the flex- ible tul)e b with the vertical glass tube c, which is firmly secured to the stand. The vertical tube expands into the oval-shaped dila- tation A, which is continued upward as the narrow tube f, and whose cavity by means of the stopcock R, can be put in communi- cation either with that of the lateral tube h, or of the tube i ter- minating above in the cup C, or cut off from either. The lateral tube h is connected through tubing (h') with the stem e of the bulb D, into which is inserted a flexible tube (1) furnished with a stop- cx)ck (r), for the transference of the blood whose gases are to be determined. Tlic stopcock (R) being in the position 1, Fig. 82 — that is, all communication between the cavity of the vertical tube c ' Skandinavisches Archiv fiir Physiologic, Leipzig, 1891, Band 3, s. 47. GASES OF BLOOD. 223 being completely cut oiF from that of the lateral and terminal tubes h and i, mercury is poured through the reservoir B until it not only rises to the level of the stopcock, but completely fills the reservoir itself The reservoir being then lowered the mercmy will fall in the vertical tube c, a vacuum being produced in consequence Fig. 82. Grehaut-Alverguiat gas pump. above it. If the stopcock he now turned into the position 2 (Fig. 82), the air will pass in from the lateral tube and its appendage into the vertical tube c, and the mercury will foil still lower. The stopcock being now returned into the position 1 (Fig. 82), the reservoir is then elevated, and the mercury with the included air 224 THE BLOOD. Fig. 83. will ascend into the oval dilatation A. The stopcock being now turned into the position 3 (Fig. 82), the air that was just drawn into the vertical tube c from the lateral tube h passes out of the tube i into the atmosphere. The stopcock is then returned to the original position (Fig. 82, 1). By depressing and elevating the reservoir B, and manipulating the stopcock R in the manner just explained, in a very short time a good vacuum is produced in the lateral tube h h' e, and its appendage D. A tube having been in- serted into the artery or vein, the blood to be analyzed is then transferred from the vessel in the living animal to the vacuum in the following manner : A tube (M) of known capacity, say 50 c.c, tapering off at one end (G), and guarded by a stopcock (B) at the other, is filled with mercury by aspiration. The tube is then at the end G put in communication with the blood vessel, by means of a rubber tube readily slipping over the canula previously inserted into the vessel, which is closed by a clip. The stopcock being now opened, and the clip removed, the blood is allowed to flow away for a moment, and then (connection being made by the tubing) into the tube M, driving out of the latter the mercury, which can be received into a convenient receptacle. As soon as the tube is filled with blood, the stopcock being closed, connection is broken with the vessel, and the tube re- versed in position, so that its tapering end G (Fig. 88) may be inserted into the small mercury trough U, previously placed in the large trough N containing ice- water, to retard the coagulation of the blood in the tube. The glass tube is then joined by the end B to the rubber tube I) provided with a stopcock (e) containing boiled distilled water, and previously placed over the tube t (Figs. 82, 83), the latter being furnished with a stopcock (Fig. 82, r) and leading to the vacuum. Both stopcocks (B and r) being now opened, the blood passes from the glass tube (Fig. 83, M) into the vacuum D e (Fig. 82), its place being filled with mercury from the trough ; the stopcocks are then closed. The blood having passed through the tube in the bulb D, gives up its gases readily into the vacuum, the liberation of which is greatly facilitated by surrounding the bulb with water (Fig. 82) at a temperature of about 40° C. (104° F.). As it is also desir- able to keep ])ack the froth and foam arising from the blood as much as possible, the lateral tube e is surrounded by a tin one, through which ice-cold water flows from a reservoir (z), and which effectually accomplishes the object. The gases having been separated from the blood, are next transferred into the vertical tube c, and thence through the terminal one i into a eudiometer, standing over mer- cury in the cup C, by depressing the mercurial reservoir B, and GASES OF BLOOD. 225 turning the stopcock R in the same manner as just explained. The ([uantity of blood from Avhich the gases are obtained will, of course, depend upon the size of the tube transmitting the blood from the vessel to the vacuum, the vessel being clamped as soon as the tube is full of blood. In order to determine the nature and amount of the gases given off from the blood we make use of an eudiometer in the usual way or of a Hem pel's apparatus, wdiich enables us to conveniently trans- fer the mixture of gases successively into a solution of caustic pot- ash and pyrogallic acid, etc., and of so determining by absorption the amount of carbon dioxide and oxygen present, the gas remain- ing over being usually regarded as consisting of nitrogen. The volume of the gas obtained must be reduced, of course, to standard pressure 760 mm. mercury, and standard temperature 0° C, which can be done by the following formula : V = _,.,. ,\ ,\ in which •^ ^ 760 (1 -I- at) Fis the required volume at standard temperature 0° C. and stand- ard pressure 760 mm., T"' the volume at the observed temperature and pressure, h the observed pressure, ]) the tension of the aqueous vapor, a the coefficient of expansion, a constant (.00366), and t the observed temperature. The formula is derived as follows. Firstly, with reference to the correction of the given volume for temperature : l + «/ : 1 : : P : For V=—^- 1 -T- at And secondly, for pressure : V^ V ^ (h—v) V : — — . : : {h—p) : 760 or V= ^^.,;. %( • 1 + at ^ '^ ' 760 (1 + at) As an illustration of the manner of using the formula, let us suppose that 30 c. cm. of nitrogen, or F', were collected at 15° C, 740 mm. barometric pressure, 12.677 mm. being the aqueous ten- sion, then F, or the required volume, would be, at 0° C, and 760 barometric pressure, 27.23 c. cm. 30(740 — 12.677) 30X727.323 21819.690 V^= ^ — = — ~ = ^ 27 ''S c cm 760(1 +.00366X15) 760X1.0549 801724 -'•-^^•'^"^• It will be found on an average that for 100 vol. of blood used there wall be extracted by means of the mercurial pump about 60 vols, of gas, the barometric pressure being 760 mm. (30 cub. in.) and the temperature 0° C. (32° F.), and that the composition of this gas will be according to the kind of blood examined, as follows : Oxygen. CarlJou dioxide. Nitrogen. Arterial blood . . 20 vol. 39 vol. 1 to 2 vol. Venous blood . . 8 to 12 " 46 " 1 to 2 " 15 226 THE BLOOD. The amount of oxygen accords with the fact ah'eady mentioned that 1 gramme of haemoglobin combines with 1.59 c.c. of oxygen, since if it be admitted that 100 c.c. of blood contain lo grammes of haemoglobin, then 100 c.c. of blood should contain 23.85 vols, per cent, of oxygen, the excess of oxygen over that actually found being due to the ftict that the haemoglobin of the blood is not saturated. The proteid material of the plasma of the blood consists of three substances, serum-albumin, paraglobulin, and fibrinogen. The principal properties and reactions of these three proteids having been already noticed, but little remains to be said of them in this connection. Owing to the property ]:)0ssessed by paraglobulin and fibrinogen of being precipitated when Ijlood is saturated with mag- nesium sulphate (^IgSO^), a means is therel:)y offered of separating the serum-albumin from the other two proteids. Serum-albumin exists in human blood to an amount of 45.20 parts per thousand. Although the peptones and proteoses, or the digested proteid food, differs in many respects from serum-albumin, the latter must be derived in the long run from the proteid material of the food. The transformation of peptone, etc., appears to take jjlace, however, not within the alimentary canal, but during absorption, as the peptone, ■etc., passes through the walls of the alimentary canal into the blood. Just as the proteid substances of the food are the sources of the serum-albumin of the blood, so the latter is the source of the pro- teid material of the tissues. It should be mentioned, however, that the tissues do not derive their supply of proteid material directly from the blood, l>ut rather from the lympli l)y which the cells of the tissues are loathed. Paraglobulin exists in human blood to an amount of 31 parts per thousand. It has been stated that there is more paraglobulin in serum than in an equal amount of plasma, the ex- cess of paraglobulin being accounted for on the supposition that it is derived from the substance of the leucocytes disintegrated during coagulation. However this may be, the fact of paraglobulin ex- isting in such an amount in the plasma, renders it probable that, like serum-albumin, it is derived from nitrogenous food and is a considerable source of the proteid material of the tissues. Apart from these meagre statements, and what has been said elsewhere, nothing definite is known either as to the origin or uses of para- globulin. Fibrinogen, the third proteid of the plasma, exists in human blood only in small amounts, from 2-4 parts per thousand. It differs in several respects, as already mentioned, from paraglob- ulin. Apart from the theory already referred of fibrinogen being the source of the fibrin of the blood, nothing is positively known as to its use in the economy, still less as to its origin. The fatty matters that are found in the plasma consist of choles- terin, phosphorized fats, and saponified principles like the marga- rates, oleates, oleic acid existing sometimes in a free state. The fatty sul)stances exist only in small quantities in the blood, and •often depend upon the kind of diet. Thus fatty food increases the SALTS OF THE BLOOD. 227 amount of fat in the blood. The use of these fatty substances in the blood is not exactly understood. The saline materials of the plasma consist of sodium, potassium, and magnesium chlorides, some free soda, of sodium and potassium carlx)nates, of sodium, potassium, and magnesium sulphates, of sodium, potassium, magnesium, and calciimi phosphates ; in a word, three chlorides, free soda, two carbonates, three sulphates, four phosphates. It is possible that these salts do not always exist in the blood in the above form, that arrangement being due perhaps to the difficult and complicated processes incidental to their analysis. It is well known that a considerable quantity of the earthy phos- phates is molecularly united with the fibrin and part of the sodium chloride with the albumin. The natural relation of these salts as well as that of the others must, therefore, to a certain extent, at least, be disarranged in an analysis. The importance of these salts is seen not only in the nutrition of the tissues, the calcium and magnesium phosphates, for example, supplying material for the production of bone, but they are also in- dispensable in maintaining the blood in its proper chemical and physical condition. Thus the alkalinity of the blood is due to its sodium carbonate, while the sodium phosphate dissolves the albumi- nous principles and inorganic matters which are insoluble in pure water. The earthy phosphates are held in solution in the serum through the presence of this salt, and to it is due the fact that so much carbon dioxide is dissolved in the blood. The existence of the corpuscles depends on the presence of sodium chloride and other salts in the serum, which, existing in isotonic amounts absorb any superfluous water, and prevent their disso- lution. According to ^lilne Edwards, the coloring matter of the corpuscles is very soluljle in water, but not so in water to which have been added albimiin and sodium chloride, both of which are found in the serum. While probable, yet it cannot be stated posi- tively that age or sex influences the quantity of these salines. There is no doubt, however, that these principles vary in quantity according to the kind of food. An exclusively animal or vegetable diet will affect the amount of alkaline phosphates respectively. Thus the former are most abundant in the blood of the carnivora, the latter in that of the herbivora. The proportion of the saline principles of the blood is also known to vary in disease ; but the limited data, however, that have been collected are of more interest at present to the pathologist than to the physiologist. One of the most important substances found in the blood is iron. Indeed, when it is deficient the red corpuscles diminish in number. The normal standard is soon regained, however, when iron is adminis- tered. The iron exists in the blood combined with the coloring matter of the corpuscles ; the color of the latter, though, does not depend upon the iron, as was once supposed, for the color M-ill re- main after the iron is removed, while the blood of certain inverte- 228 THE BLOOD. brates like the Limulus (horseshoe crab) is colorless, though iron is present. From the description of the blood just given, it will be seen to consist of water, corpuscles, proteids, inorganic salts, and extractives. If the composition of the corpuscles be now compared with that of the liquor sanguinis, it will be found that the corpuscles contain the phospiiorized fats, the liquor the fatty acids. The potash salts are confined almost entirely to the corpuscles, the soda salts to the liquor ; the latter containing about four times as much soda as the former. All of the iron in the blood is contained in the corpuscles, the greater part of the earthy phosphates, on the contrary, in the liquor. The relative densities, quantity of water, solid matters, proportion of salts in the corpuscles, and liquor sanguinis, are given somewhat in detail in the following table : Blood, in 1000 Parts Each.' Coriniscles, .513. L iquor sangiiinii Density Water 1.0885 , 681.63 1.028 901.51 Solid matters . 318.37 98.49 loooToo lOOOTOO Haematin 15.02 Fibrin 8.06 Globulin . 296.07 Extractives 81.92 Inorganic salts . 7.28 318.37 8.51 98.49 Sodium chloride . 5.546 Potassium chloride 3.679 0.359 Potassium phosphate . 2.343 Potassium sulphate Sodium phosphate Soda . . . 0.132 0.633 0.341 0.281 0.271 1.532 Calcium phosphate Magnesium phosphate Iron .... 0.094 0.060 . undetermined 7.281 0.298 0.218 8.505 In concluding our account of the blood a few words may be said in reference to transfusion, though this subject is usually considered as belonging to therapeutics. About the middle of the seventeenth century experiments were performed which showed that life could be saved in an animal dying from a copious hemorrhage, for ex- ample, by introducing into its vessels fresh blood from an animal of the same species. Application was soon made of this fact in the treatment of human beings, and the wildest enthusiasm was excited, great hopes being entertained that old age could be rejuvenated, etc. Several fatal cases of transfusion, however, occurring, the practice was prohibited in many places by law. It was revived in the early part of this century, and with success. There being a ' Schmidt, in Eanke Physiologic, s. 350. Leipzig, 1875. TRANSFUSION OF THE BLOOD. 229 number of cases on record ^ which would have undoubtedly proved fatal had not transfusion been used. In recent years, however, it has been shown in the case of cer- tain animals, at least the dog and rabbit, for example, that if the serum of the former be introduced into the blood of the latter animal, its blood corpuscles will be disintegrated and the blood rendered laky. This deleterious effect of the serum, together with intravascular clotting, due to the introduction of fibrin ferment, have been assigned as causes of the mortality following transfusion and used as arguments for the discontinuance again of the practice. It has been recommended, therefore, in cases of severe hemorrhage, demanding transfusion, that an isotonic solution of sodium chloride (0.6 per cent.) be introduced instead of blood or serum, which will not injure the corpuscles, but by increasing the bulk and velocity of the circulating fluid and preventing stagnation, will make them more efficacious as oxygen carriers. Having studied the composition and properties of the blood gen- erally, let us now turn to the consideration of its circulation. 1 Berard, Physiologie, Tome iii., p. 219. Paris, 1851. CHAPTER XIV. CIECULATION OF THE BLOOD. The Heart. We have seen that the use of the food is to repair the waste of the tissues, to supply fuel for the production of energy, and that the food is digested, absorbed and gradually elaborated into blood. To supply the wants of the system, to furnish the tissues T\'ith material for their maintenance and repair, to carry away that which has become worn out and effete, the blood must move freely through all parts of the economy. It must circulate. By the cir- culation of the blood is meant that the blood moves in a circle — that is, if we follow its course, for example (Fig. 84), after it passes from the left ventricle of the heart to the aorta we shall see that the blood flows from the aorta into the arteries, thence into the capillaries, from there into the veins, from the latter by the vena cava into the right side of the heart, from tlie right side of the heart through the lungs back to the left side of the heart to the left ventricle, where it started. Usually the passage of the blood from the right auricle of the heart through the lungs and left ventricle is known as the lesser, or pulmonary circulation, while the route from the left ventricle through the arteries, capillaries, and veins to the right auricle is distinguished as the greater or systemic circulation. Using the word circulation in the sense in which it is ordinarily accepted, the terms lesser and greater circulations are not appropriate, and may mislead, inasmuch as we have seen that the blood does not pass directly back from the lungs to the right auricle of the heart, whence it came, but indirectly, first coursiug through the system, and that the blood flo^ving from the left ventricle only returns there after having passed through the luugs. There is, in this sense, then, only one circulation, however conveniently the latter may be divided into the so-called lesser and greater circulations. In another sense, however, there are innimiera1)le circulatious, greater and lesser, since the blood, after leaving the heart (Fig. 84), may go either to the head, or viscera, or extremities before return- ing to the heart. As the motion of the blood is in a circle, it is immaterial at what part of the vascular system we begin its study. We shall see, however, that in exposing any of the great functions of the body, if we follow, as far as practicable, the order in which the facts were actually discovered, and the phenomena generalized by the human mind, that the subject will be presented in the most natural logical TEE HEART. 231 sequence. We will begin, therefore, the study of the circulation of the blood, with the demonstration of the structure and function of the heart. Fkj. 84. Fig. 85. ./■ Lull,- r. a. r. r. a. r. a. I. r. Heart and luugs of man. (>[ilse Edwaeds.) The heart is a hollow pear-shaped muscular organ. It is situated in the thoracic cavity, and lies between the lungs, with which it is connected by the great blood vessels arising from its base (Fig. 85). The heart is loosely enclosed in a sac, the pericardium. This sac, having the form of the heart, and of a bluish-white color, consists of two layers. The external fibrous layer, continuous with the external coat of the great blood vessels, consists of fi- brous tissue, and is a strong, inexten- sible membrane. The internal delicate serous layer does not differ essentially in its general character from that of Diagram of the circulation. 1. Heart. SCrOUS nicmbraue. It SUrrOUuds thc 2. Lungs. S. Head and upper estrenn- Kp^rt closclv adheriuo; tO it and IS thcU ties. 4. Spleen. 5. Intestine. 6. Kiu- J c . r i.\ ney. 7. Lower extremities. 8. Liver, reflected ovcr the Commencement 01 tne ^^*'''™''-^ great blood vessels and thc interior surface of the external fibrous membrane. The cavity of the pericardium contains about a drachm or two of a serous fluid, through the presence of which the opposed internal surfaces of the 232 CIRCULATION OF THE BLOOD. Fir; pericardium glide smoothly over each other, the movements of the heart being thereby facilitated. The pericardium is attached by connective tissue to the pleura on each sicle, and the tendinous center of the diaphragm below. It is not necessary to give a de- tailed, minute description of the disposition of the mus- cular fibers of the heart, Avhich is quite complex, a general account in connec- tion with the present subject being sufficient. The auri- cles, or upper cavities of the heart (Fig, t^ii, d, e), are en- circled by a thin layer of muscular fibers, common to l)oth tliese cavities, and sur- rounding the auricular ap- pendages, the entrance of the vena cava, the coronary and pulmonary veins. Be- neath this superficial layer are the fibers of the deep layer attached to the fibrous rings of the aurieulo- ven- tricular orifices, and dis- posed in an annular and loop-like manner. The muscular fibers of the ventricles, like those of the auricles, are also arranged in two sets, superficial and deep. The superficial fibers (Fig. 86, a, b), which are common to both ventricles, run from base to apex, and at this point pass into the interior of the ventricle in the form of a whorl or spiral, some of the fibers terminating in the columnse carnese and papillary muscles, others returning after a twisting course to the point from which they started. The fibers of the deep set (Fig. 87) surround each ventricle separately, and are disposed in a circular or transverse manner between the external and internal layers of the superficial fibers, and are much better de- veloped in the left ventricle than in the right. Microscopically the muscular substance of the heart consists of transverse striated muscu- Aiiteridi- view ot'lie;ivt. ((Juain.) Fig. 87 Left ventriele of bullock's lar fibers. These fibers, however, differ from ]lS. ''(^^i.)*^ ^*^'p the ordinary fibers of voluntary muscles in several particulars. They are destitute of sarcolemma, much smaller and more granular, not collected into bundles, and are separated by comparatively little connective tissue. The most in- VALVES OF THE HEART, 233 Fir: teresting peculiarity, however, about these libers, is their anasto- mosing or inoscuhition with each other (Fig. 88), which, no doubt, favor the contraction of the heart and the thorough expulsion of the blood from its cavities. If a longitudinal section be carried through the heart from base to apex, its interior will be seen from such a section to consist of four cavities : two auricles, so called from their auricular appendages, and two ventricles ; that the right auri- cle communicates with the venoe cavie and with the right ventricle, and the left auricle with the pulmonary veins and the left ventricle ; there is no com- munication, however, between the two auricles or between the two ventricles ; the rio-ht or venous side of the heart being completely separated from the left or arterial side by the septum of the heart, which is imperforate. In certain mammals, in the dugong (Halicore) and manatee (]\Ianatus) for instance, this distinction of the right from the left side of the heart is to a certain extent visible, even externally, the ventricles at the apex being sep- arated by quite an interval. We have just seen that the heart is covered with the serous layer of the pericardium. It will be ob- served that the interior of the heart is also lined by a thin trans- lucent membrane, the endocardium, which is continuous with the internal coat of the blood vessels and consists of a fibrous elastic and epithelial layer. Just at the point where the auricles pass into the ventricles, the endocardium projects into the cavity of the heart from the wall of the heart on one side, and from the septum on the other. This portion of the endocardium is strengthened by the ad- dition of fibrous tissue. It is these projections that serve to divide the auricles from the ventricles. The interval left between these projections constitutes the auriculo-ventricular orifices. The fibro- elastic tissue in this situation forms a slight ring, to which is at- tached on the right side of the heart the tricuspid valve (Fig. 89, Fig. 91, 5, 5', 5"), three membranous folds, which consist of dou- blino^s of the endocardium thickened bv the included fibrous tissue. By means of these curtains or valves, the auriculo-ventricular orifice can be closed, the edges of the valves being then pressed together (Fig. 91), as we shall see, by the blood, and are kept stretched by the tendinous cords as the sail of a boat is kept stretched against the wind by the sheet line. The chordffi tendinea? are tendinous cords inserted into the valve, and arise either directly from the walls of the ventricle or are con- iluirior. i/^_ fOTIATN.'l (QUAIN.) side of the heart. The mitral valve, however (Fig. 90 and Fig. 91, 6, 6'), by which the left auriculo-ventricular orifice is closed, con- sists of two membranous folds instead of three, as is the case in the tricuspid valve, and is stronger than the latter. It will be observed that the tricuspid and mitral valves open from the auricle to\vard the ventricle, but do not project from the ventricle into the auricle. At the anterior angle of the base of the right ventricle (Fig. 91, 7), may be seen an orifice guarded by three crescentic membanous folds, the semilunar valves. Through this orifice the right ventricle communicates with the pulmonary artery. The semilunar valves consist of doublings of the endocar- dium, strengthened by fibrous tissue. The convex border of each VALVES OF THE HEART. 235 valve is attached to the ed^e of the ring-like orifice of the pulmo- nary artery, the free edge projecting into the latter. Behind each semilunar valve the artery is dilated into a pouch, the sinus of Val- salva. This sinus prevents the valve when open from adhering to the walls of the artery, and enables the blood to get behind each valve and press it down so that the three valves meet (Fig. 91, 7), and so close the orifice, but readily separate when the flow is from Fir:. <.10. The left auricle and ventricle oi)ened and a part of their anterior and left -n-alls removed so as to show their interior. 3/^. The pulmonary artery has heen divided at its commencement so as to show the aorta ; the opening into the left ventricle has been carried a short distance into the aorta between two of the segments of the semilunar valves ; the left part of the auricle with its.appen- dix has been removed. The right auricle has been thrown out of view. (Quaix.) the ventricles toward the great vessels, preventing a reflux from the great vessels back into the ventricle. At the middle of the free border of the semilunar valves may be seen a little nodule of fibrous tissue. These nodules, or corpora Arantii serve as a common central point of contact when the valves are closed. The semilunar valves of the aorta (Fig. 91, 8) do not differ in their structure or function from those of the pulmonary artery, and, like the latter, act when in contact in closing the orifice 236 CIRCULATION OF THE BLOOD. of commuuication between the left ventricle and the aorta. The manner in which the tricuspid and mitral valves act can be readily demonstrated by filling the ventricles with water by means of a funnel introduced into the orifices of the pulmonary artery and aorta ; the water rising up between the walls of the ventricles and the valves will float the valves up until their edges are approxi- mated, so closing the auriculo-ventricular orifices. By pouring water into the pulmonary artery and aorta it will be seen that the water gets in between the wall of the vessel and the valve, into the Fig. 91. View of the base of the ventricular part of the heart, sliowing the relative position of the ar- terial and auriciilo-veatricular orittces. %. The muscular fibers of the ventricles are exposed by the removal of the pericardium, fat, blood vessels, etc.; the pulmouar}- artery and aorta have been removed by a section made immediately beyond the attachment of the semilunar valves, and the auricles have been removed immediatelj" above the auriculo-ventricular orifices. sinus of Valsalva, and so forces the free edges of the semilunar valves toward each other, thus effectually closing the orifices at the mouths of the great vessels. • Such being the general structure of the heart, let us consider now the course that the blood takes in passing through it. In watching the heart beating in a living animal, a mammal, for example, it will be observed that at tlie same moment the right auricle is di- lated by the venous blood flowing from the system through the venae cavse, the left auricle is dilated by the arterial blood flowing into it through the pulmonary veins from the lungs. This syn- chronous dilatation of the auricles is known as the auricular diastole. Suddenly, and succeeding this auricular diastole, or filling up of the auricles, both auricles simultaneously contract, the venous blood passing from the right auricle into the right ventricle, the arterial blood from the left auricle into the left ventricle, regurgitation to any extent into the veuie cavte or pulmonary veins being prevented by the muscular fibers encircling these vessels and the pressure of the blood. This synchronous contraction of the auricles is called the auricular systole. As in the experiment just performed with VALVES OF THE EEABT. 237 the water, so the blood within the ventricles of the heart of the liv- ing animal gets in between the walls of the ventricles and the flaps of the tricuspid and mitral valves and floats the edges of the valves up until the auriculo-ventricular orifices are closed. At this mo- ment, the ventricles Ijeing fully dilated simultaneously contract, with the effect of still more thoroughly approximating the tricus- pid and mitral valves than is the case at the end of the auricular systole, and so of more completely closing the auriculo-ventricular orifices. The papillary muscles contracting at the same time as the walls of the ventricles and acting through the chordae tendinese upon the valves stiffen them and prevent their inversion into the auricles. The synchronous filling up and contraction of the ven- tricles is known as the diastole and systole of the heart, but more properly as the ventricular diastole and ventricular systole. Dur- ine: the ventricular svstole the auricles are receiving blood from the ven£e cavse and the pulmonary veins. Inasmuch as regurgitation backward from the ventricles into the auricles is prevented through the auriculo-ventricular orifices being closed by the approximation of the tricuspid and mitral valves during the ventricular systole, the venous blood passes from the right ventricle through the pulmonary artery to the lungs, and the arterial blood from the left ventricle through the aorta to the system. Immediately after the ventricular systole or contraction of the ventricles follows their relaxation. During this period the heart is in repose. The auriculo-ventricular orifices are again open, the venous and arterial blood that has accumulated in the right and left auricles respectively during the contraction of the ventricles and while the auriculo-ventricular orifices were closed, now flows into the ventricles, Avhile this blood is replaced by the venous blood flowing into the right auricle from the vense cavse, and the arterial blood flowing from the pulmonary veins into the left auricle. Toward the end of the ventricular systole the venous and arterial blood, forced respectively into the pulmonary artery and the aorta, gets in between the walls of the vessels and the semilunar valves in the sinuses of Valsalva, and forces their free edges toward each other as in the experiment just performed with the water. At the end of the ventricular systole, the semilunar valves being closely approximated and the orifices of the great vessels closed, through the elastic recoil of the arteries on their contents, the blood, being unable to regurgitate backward from the pulmonary artery and aorta, is forced on to the lungs and the system. It will be seen from the phenomena just described that, while the right side of the heart containing venous blood is entirely distinct from the left con- taining arterial, nevertheless, the two sides of the heart act as one — the venous blood flowino; into the ri":ht auricle as the arterial blood flows into the left, the synchronous' filling up and emptying of the auricles being followed by the synchronous dilatation and contrac- tion of the ventricles, at the same time the blood forced out of the 238 CIRCULATION OF THE BLOOD. latter passing to the lungs and the system through the pulmonary artery and aorta respectively. The beating of the heart, as we have endeavored to describe it, in an animal, a dog or a rabbit, for example, has been shown to be essentially the same in man, at least so far as comparison has been possible. As might be expected, cases of ectopia cordis are very rare, but there has been a sufficient number of such cases to demonstrate that the manner in which blood flows through the heart in man does not diifer from that of the mammal. While the action of the tricuspid valve and semilunar valves of the pulmonary artery is essentially the same as that of the mitral valve and semilunar valves of the aorta, nevertheless the valves on the right side of the heart do not close their respective orifices as perfectly as those on the left side of the heart, there being some little regurgitation possible back from the pulmonary artery to the right ventricle, and from the right ventricle to the right auricle. The effect of this insufficiency of the valves on the right side of the heart is obviously of advantage ; were it otherwise, an excess of blood driven from the right ventricle through the pulmonary artery to the lungs might rupture those delicate organs. This danger is avoided through the imperfect closure of the pulmonary and the right auriculo-ventricular orifices, since, when resistance is offered by the pulmonary capillaries, the blood will regurgitate backward through the pulmonary artery to the ventricle and thence to the auricle. There is no insufficiency, however, on the left side of the heart, the auriculo-ventricular and aovtic orifices being completely closed by the mitral and semilunar valves respectively. It mil be observed also that the walls of the left ventricle are three or four times as thick as those of the right. This is due, as might have been anticipated, to the fact that the contraction of the left ventricle forces the blood to all parts of the system, whereas the right ven- tricle forces the blood only to the lungs. For the same reason the walls of the auricles are thinner than those of the ventricles, little force being required to drive the blood from the former cavities into the latter. The muscular substance of the heart, like that of muscles gener- ally, is therefore developed according to the amount of muscular force to be expended. As the period which elapses in mammals during a cardiac revo- lution or cycle — that is, the time during which all the cavities of the heart fill and empty themselves — is only about one second, actually 0.8 sec. in man, it is evident that close and careful observa- tion is necessary in order to distinguish the successive phenomena that we have endeavored to describe in the beating heart. It is well, therefore, to begin the study of the action of the heart by observing the phenomena, first, as they present themselves in the lower vertebrates, for example, in frogs, snakes, turtles, and alli- gators. Such animals are not only readily procurable, but are par- DURATION OF MOVEMENTS OF THE HEART. 239 ticularly suitable for the purpose, siuce in them the cardiac revohi- tions succeed each other much more slowly than is the case in mammals, and in the frog especially there is an appreciable interval between the systole of the auricle and that of the ventricle, whereas, in most mammals the systole of the auricle runs so into that of the ventricle that it is impossible to say exactly where the first ends and the second begins, the muscular contraction running as a con- tinuous wave over auricle and ventricle from base to apex. Further, the heart of the frog has only one ventricle, and while there are two such cavities in the heart of the turtle, nevertheless, they communi- cate, the septum being but little developed. In these animals, then, the single ventricle acts like the two ventricles of the mammalian heart, and familiarizes one with the synchronous action of the ventricles when two such cavities are present. Again, these animals oifer through their mode of breathing another advantage, in that the heart will continue beating even after the thorax has been opened, there being no necessity of keeping up artificial respiration. We shall see, however, when we wish to study the action of the heart in mammals, tliat artificial respiration must be maintained, for with the opening of the chest the lungs collapse, respiration ceases, and the circulation stops. Notwithstanding that, in mammals, a cardiac revolution occupies such a small period of time — about one second — nevertheless, the relative parts of the second elapsing during which the auricular and ventricular systole take place and the heart is in repose, have been experimentally determined, as in the horse, for example, by Marey and Chauveau.^ The general results of their observations are embodied in Duration of Movements of Heart ix Horse. Auricular systole. Ventricular systole. Repose. 0.2 sec. 0.4 sec. 0.4 sec. from which it will be observed that the auricular systole lasts two- tenths of a second, the ventricular systole four-tenths of a second, and the repose of the heart four-tenths of a second, one second be- ing supposed to elapse during an entire cardiac revolution. The apparatus necessary for the above determination of the rhythm of the heart's movements as they occur in the horse, as used by Marey, consists essentially of a sound (Fig. 92) to be in- troduced through the jugular vein into the heart of the animal. The sound is divided into two tubes, one of which is a distinct tube, the other being, however, only the space arotnid the tube. The tube terminates at one end in a little elastic bag (r), to be in- serted into the ventricle, and at the other end in a drum provided with a registering lever (Jr). The space surrounding the tube com- municates on the one hand with a similar elastic bag (o) to be inserted into the auricle, and at the other end with a tube passing into a ^Comptes rendus Soc. Biol., Paris, 1861. Comptes rendus Acad. Sciences, Paris, 1862. 240 CIRCULATION OF THE BLOOD. drum provided with a second similar recording lever (/o). The object of the elastic bags o and v is that the successive contractions of the auricle and ventricle in -which they are placed will be trans- mitted through them to the registering levers lo and Iv, and as the auricle contracts before the ventricle it is evident that the lever lo Fk;. !)2. connected with the elastic bag (o) in the auricle will move before the lever (Iv) connected with the bag {v) in the ventricle. If the registering levers are placed in contact with a recording surface (AE) moving at a uniform rate, and if this surface be marked by vertical parallel lines, each intervening space representing the one- tenth of a second, the lengths of time during which the auricular and ventricular systole and the repose of the heart last will be graphically recorded (Fig. 93). The cardiac revolution in this in- stance lasted twelve-tenths seconds. In order to divide the surface of the recording cylinder into a number of spaces each equal to the one-tenth of a second, a vibrat- ing reed (A) and an electro-magnet (B, Fig. 94) are used. The reed clamped under the electro-magnet by one end to a stand (C), the other end dipping into mercury (D), is connected on the one hand with a battery (E), and on the other with another small elec- tro-magnet (F). Such being the disposition, at the moment that the current is made, the electro-magnet (B), being magnetized, will attract the reed, drawing it out of the mercury ; but the current being thereby broken, the electro-magnet being then demagnetized, will cease to attract, and the reed will fall back into the mercury, remaking the current ; the reed will then be again raised, the cur- rent broken, and the reed fall again into the mercury, the number of these alternate elevations and depressions per second depending upon the number of vibrations of the reed in that time. Inas- much, however, as the small electro-magnet (F) is magnetized and THE VIBRATOR. 241 demagnetized iu the same manner as the large one, the bar attached to it and carrying the pen (P) ^\\\\ approach and recede from it syn- chronously with the vibrations of the reed. By placing the pen in Fig. 93. aui-iclo. Tentricle. Tracing the variations of pressure in the right auricle and ventricle, and of the cardiac impulse, in the horse. (To he read from left to right.) (JIarey.) Fig. 94. Vibrator. contact A\'ith the recording cylinder, a trace is obtained in which the equal spaces between the vertical lines made by the marker are 16 242 CIRCULATION OF THE BLOOD. equal to the one-tenth of a second, the reed used vibrating at that rate. By substituting reeds or tuning forks vibrating at the rate of 15, 20, 50, or 100 times a second, we get traces in which the equal spaces represent the corresponding fractional parts of a sec- ond. Usually, there is also a third registering lever (Fig. 90, le) below the ventricular one, connected by tubing M-ith a cardiograph (c), the object of which is to transmit the cardiac impulse caused by the beating up of the heart against the chest. This impulse is shown to be absolutely synchronous with the ventricular beat as recorded by the second lever [h). From the observations of Franck,^ made upon a woman with ectopia cordis, there is no reason to doubt upon the supposition that the cardiac cycle lasts 0.8 seconds, that the duration of the auricular and ventricular systole and the repose of the heart are relatively the same in man as in the horse, as shown in Duration of Movements of Heart in Man. Auricular systole. 0.16 sec. Ventricular systole. 0.32 sec. Repose. 0.32 sec. Inasmuch as it is by the contraction of the ventricles that the blood is driven through the lungs and the system and as the ven- tricles recover themselves, so to speak, during the repose of the heart it might be naturally supposed that when the number of the heartbeats are increased above the normal the duration of the repose of the heart would be shortened rather than that of the ventricular systole. That such is the case appears to have been shown experi- mentally both in man and animals. Thus it has been ascertained in man, by auscultation,- that the period elapsing between the first and the second sound of the heart, or the period corresponding, as Fig. 95. Double myograph. we shall see, to the ventricular systole, varies much less in duration than that of the repose, with a varying heartbeat. Indeed, with a 'Travaux der Lab. de Marey, Tome iii., 1877, p. 311. ^F. C. Donders, Nederlandsch Archief Voor Genees eu Xatuurkunde, Tweede Jaargang, I8G0, p. 139. THE DOUBLE MYOGRAPH. 243 very rapidly beating heart the duration of the repose may be so brief that the contraction of the auricles practically follow that of the ventricles. Experiments made by registering: levers pressed upon the skin overlying an artery in man ^ or upon the exposed heart in animals ' confirm the above conclusions. Thus, for example, with the heart beating in a man at the rate of 47 per minute the ventricular sys- tole lasted 0.34 seconds, the repose 0.93 seconds, whereas with the heart beating at the rate of 128 per minute, the ventricular systole lasted 0.25 seconds, the repose only 0.21 seconds. A convenient method of demonstrating the time elapsing during the contractions of the auricles and the ventricles and the repose of the heart in a living animal, a fi'og or a turtle for example, is by means of the double myograph (Fig. 95). This instrument consists of two levers, to which are attached delicate rods, ending in aluminium plates, which rest upon the auricle and ventricle of the heart of the animal examined. The levers can be shortened or lengthened, their pressure diminished or increased by appropriate mechanical arrangements, and the movements of the auricle and ventricle transmitted l)y them are recorded upon a cylinder moving at a uniform and known rate, by which the time elapsing can be determined. ' E. Thureton, Journal of Auat. and Plivs., Vol. x., 1876, p. 494. 2X. Baxter, Du Bois Eeymond's Archiv, Band, 1878, s. 122. CHAPTER XV. CIECULATION OF THE BhOOJ).— (Continued.) CARDIAC IMPULSE. In examining the heart in a living animal, as described in the last chapter, it Avill be observed that with each ventricular systole the heart, as a whole, moves forward and upward, the apex more particularly beating up against the chest, and so giving rise to what is known as the cardiac impulse. If a finger be placed -svithin the thoracic cavity of a living animal, between the heart and the side of the chest, with every contraction of the ventricle the finger will be pressed against the chest by the apex. Pathological cases, like that of the Viscount ^Montgomery, so graphically described by Harvey,^ have given physiologists the opportunity of showing that the cardiac impulse is produced in men as in animals by the striking of the heart against the chest. In man the cardiac impulse is most distinctly felt in the fifth left intercostal space, about two inches below the left nipple, and one inch to its sternal side. The force and extent to which the cardiac impulse may be perceived varies very much in different individuals, and in the same individual, according to circumstances. Thus, it is more perceptible in emaciated than in fat persons, during expira- tion than in inspiration, in one lying upon the left side than in one lying upon the right, etc. The movement of the heart forward and upward j^roducing the cardiac impulse seems to be due to several causes. Thus, the sudden distention of the great elastic vessels at its base would throw the entire organ forward, the recoil of the ventricles, as they discharge their contents, further aiding the movement. The disposition of the muscular fibers is also such that the heart during its ventricular systole changes its form, bulging somewhat forward, the spiral muscular fibers, at the same time, tilting up the apex. For ordinary purposes the force and extent of the cardiac impulse can be sufficiently well appreciated by the hand. The cardiograph, however, furnishes us M'ith the means of a far more accurate study of the beat of the human heart than that afforded by the sense of touch alone. The cardiograph (Fig. 96) consists of a disk-shaped box, one side of which is formed by an elastic membrane. In the center of the latter is inserted an ivory knob (^1), which is applied to the chest over the place where the cardiac impulse is greatest. The box, or tympanum, communicates by an elastic tube (/) with a second tympanum (6), with which is connected a registering lever ' Exercit. de generat. Animalium, p. loG. London, 1651. THE CARDIOGRAPH. 245 (fZ). It is evident that when the cardiograph is firmly fastened to the chest that the shock of the cardiac impulse will be transmitted to the ivory knob, thence to the first tympanum and through the column of air in the communicating tube to the interior of the second tympanum, and so, by means of the elastic and movable lid of the latter, to the registering lever. If the point of the lever be placed in contact with a cylinder revolving at a uniform rate, we obtain a graphic representation or trace of the heart's impulse (Fig. 97). By such an apparatus variations in the heart's beat, which Fig. 97. Tracing of heart's impulse in man, taken with cardiograph. To be read from left to right. are so slight as to be quite inappreciable by the sense of touch alone, become very perceptible. 'S\lien it is desired to take a cardiographic tracing in a small animal, like a rabbit, guinea-pig, or cat, a very convenient form of cardiograph is that described by Marey^ (Fig. i^'8). The instru- ment, as used by the author, consists of two tambours (a, 6), each of which contains a spring, through which the membrane is kept pro- jected. The two tambours are joined to one another pincer-like, by a hinge, and grasp the cardiac region on each side of the ster- num. A girdle (c) attached by hooks to the tambours passes around the body of the animal, and secures the apparatus firmly. The com- pression of the air in the tambours due to the cardiac impulse is transmitted l)y the tubes (d, e) to a second tambour, to which is at- tached a recording lever, like that represented in Fig, 98. Fig. 99 gives the traces taken by this instrument. It will be remembered that it was by means of the cardiograph iQp. cit., p. 155. 246 CIRCULATION OF THE BLOOD. Fig. 98. and the sound introduced into the heart of the horse that Marey and Chauveau demonstrated experimentally that the cardiac im- pulse is absolutely synchronous with the ventricular systole. What- ever diiference of opinion may exist as to the relative importance of the different causes assigned for the production of the cardiac impulse, there can be no doubt, then, that its immediate cause is the ven- tricular systole. The spiral arrangement of the muscular fibers at the apex of the heart, already alluded to, explains another phenomenon accompanying the ventricular systole, the twisting of the heart. If the apex of the heart be closely watched, it will be noticed that the point twists upon itself from left to right Math the systole, returning to its former position with the diastole. The heart, like a voluntary muscle, which it closely resembles in its substance, also hardens during contraction. This becomes very evident if the organ be grasped by the hand while beating. Like voluntary muscles, the heart also shortens during contraction. This can be demonstrated by quickly cutting the heart out of a living animal, pinuing it down on a board by passing a needle vertically through its base, and then inserting a second needle into the board parallel with the first, so that the apex of the heart just touches the second needle. With each systole it will be seen that the ventricles invariably shorten, the apex dis- tinctly receding from the second needle. If the beating heart be examined in situ there is, on the contrary, an apparent elongation of the heart during its systole. This is due, however, not to any Cardiograiih. (Marey.) Fig. 99. CO. Vk,( Ch. Tracings taken with cardiograph. Co. Guiuea-pig. L. Rabbit. Ch. Cat. (Marey.) elongation of the ventricles, but to the fact that at the moment of the cardiac impulse, which is synchronous with the ventricular systole, the whole heart, as we have seen, is moved forward and CHANGES IN FORM OF THE HEART. 247 protruded ; at this moment the apex is apparently elongated, while, in reality, it is shortened. However carefully the beating heart may be observed, it is, nev- ertheless, impossible, on account of the rapidity of its movements, to obtain a correct idea of the changes it undergoes in the living animal. Owing to this fact, plaster casts ^ (Fig. 100) have been ProjectioB of a dog's heart. Shaded portion indicates ajipearance of diastole ; white portion, of systole. A. Anterior surface. L. Lateral surface. P. Posterior surface. (McKendrick.) made of the distended and contracted heart fixed in that condition at the moment of death, which show, approximately at least, the changes undergone in the form of the heart in a living animal, and reveal the fact that the post-mortem form of the heart is not that of the living animal either in diastole or systole. It must be borne in mind that the changes in the form of the beating heart just de- scribed are such as occur in the opened chest, and necessitating also in the case of the mammal, the maintenance of artificial respiration. While there is no reason to suppose that the changes in the form Fig. 101. 1 ^^vf^Vv/\KA/v^^^MAAAAAANVJ\'A\AMAM/ 1. Cardiographic tracing from a case of ectopia cordis. (Francj'OIS P'ranck.) 2. Cardiographic tracing from the exposed heart of a cat, obtained by placing a light lever on the ventricle. The tuning-fork curve marks 50 vibrations per second. (Landois.) of the heart observed in the unopened chest. Fig. 101, 1, differ es- sentially from those in the opened one. Fig. 101, 2, recent re- searches ^ render it possible that certain minor differences exist in IF. Hesse, Du Bois Eeyraond's Arcliiv(Anatomie), 1880, s. 828. 2 J. B. ITiivcraft, Journal of Physiology, V. xii., 1891, p. 448. J. B. Haycraft & D. R Patel-son, Ebenda, V. xix., 1896, p. 496. 248 - CIRCULATION OF THE BLOOD. the two cases. Thus, for example, it may be supposed that the ven- tricles contract more equably in all diameters, and that there is less flattening of the heart in the antero-posterior direction in the un- opened chest than in the opened one. Work done by the Heart. In mechanics the work done by a machine is usually estimated in kilogramme meters or foot pounds, that is, the number of kilo- grammes or pounds the machine can lift through one meter or foot. In other words, the work done equals the weight multiplied by the height. On the supposition that at each systole of the left ventricle, 180 grammes (6.3 oz.) of blood, the so-called " pulse vol- ume," is ejected into the aorta under a pressure of 3.21 meters (10.2 feet), that being the height to which the blood would rise in a tube placed in the aorta of man,' the left ventricle lifts at each systole 180 grammes of blood, 3.21 meters high, that is, does 578.8 gramme meters of work (180 x 3.21 = 578.8). If the 578.8 grammes be multiplied by 72 on the supposition that the heart beats seventy-two times a minute, and the quotient by (30 and 24 for the hour and day it will be seen that the work done by the left ven- tricle of the heart in twenty-four hours amounts to nearly 60,000 kilogrammeters 578.8 x 72 x 60 x 24 = 59927040 gramme meters. Assuming that the work done by the right ventricle amounts to one-fourth of that done by the left, or 15000 kilogrammeters, the pressure of tlie blood in the pulmonary artery being one-fourth that of the pressure in the aorta, the work done by both ventricles during twenty-four hours would be nearly 75000 kilogrammeters (240 foot tons)." It should be mentioned, however, that the energy put forth by the ventricles of the heart is not only exerted in lift- ing 180 grammes of blood through 3.21 and 0.8 meters, respectively, at each systole, but in imparting to the blood the velocity with which it flows in the aorta and pulmonary artery. Assuming that the velocity in the aorta amounts to 0.5 meter per second, we can make use of the well-known formula T^= s^'Igh in which g is the accelerating force of gravity (9.81 meters per second) to obtain the value of /( or the height through which the 1 80 grammes of blood must be lifted in order to acquire by falling from such height the given velocity. Squaring both sides of the equation V = \^2gh and transposing Ave obtain h = - = — — = 0.0127 meter. g 2 X 9.81 The work done by the left ventricle at each systole will be equal, therefore, to raising 180 grammes of blood 0.0127 meter high, for felling from that height the blood would acquire a velocity of 0.5 ^Haugliton, Animal Mechanics, 1873, p. 137. ^ Kilngrammctci-s are converted into foot pounds by multiplying by 7.233. 1 kilo (2.2 pounds avoird. ) raised 1 meter (3.2 feet) higli = 1 lb. avoird. raised 7.233 high. Foot pounds are converted into foot tons by dividing by 2240. SOUNDS OF THE HEART. 249 meter. As the work done by the left ventricle in this respect is small, amounting in twenty-four hours to only 207.3 kilogramme- ters, it is usually neglected together with that done by the right ventricle, which is necessarily still less, in estimating tlie work done by the heart. We shall see hereafter that, in accordance with the theory of the conservation of energy, that the work of 75000 kilo- grammeters done by the heart in twenty-four hours is transmuted heat. Such being the case, 176263 heat units must l)e applied mechanically by the heart since 1 heat unit so applied will lift 425.5 grammes 1 meter high (176263 X 425.5 = 75000 kilogrammcters). Further, as one gramme of coal when burned yields 8080 heat units, it follows that the heat transformed into work by the heart is equal to that which would be produced by the combustion within the heart of nearly 22 grammes of coal (8080 x 21.8 = 176263). That the heat so transformed into work by the heart is not derived from the combustion of the carbon of its muscular tissue is shown by the fact that if so, the heart, upon the supposition that it weighs al30ut 300 grammes, would be entirely consumed. It may be men- tioned in this connection, though it will be considered hereafter, that as the energy exerted by the heart is expended in overcoming the resistance incidental to the circulation, the energy that disappears in being so applied reappears as heat. If in a living animal the ear be applied to the precordial region, and in man more particularly to the third intercostal space a little to the left of the median line of the chest, accompanying the beat of the heart two successive sounds will be heard, followed by a silence. After a little practice it will be recognized that these two sounds differ from each other in their quality, pitch, and duration. The first sound is a dull, confused one, of a booming character, low in pitch, and lasts longer than either the second sound that follows it or the silence intervening between the second sound and the first one. The second sound as compared with the first one, is a clear sound, well defined, sharp, high in pitch. While, for all practical purposes, it may be said that the second sound immediately follows the first, there is quite an appreciable interval of silence between the second and the first sound, this interval of silence lasting about the same length of time as the second sound. On the supposition that 0.8 second elapses during the period in which the first and second sounds are heard and the silence, the first sound will last 0.32 second, the second sound 0.24 second, the silence 0.24 second. A comparison of the duration of the movements and sounds of the heart shows that the period of 0.32 second during which the first sound is heard is absolutely synchronous with the 0.32 second of the ventricular systole, that the 0.24 second during which the second sound is heard the heart is in repose, and that the silence is syn- chronous partly with the last 0.0.8 second during which the heart is in repose and partly with the 0.16 second of the auricular systole. 250 CIRCULATION OF THE BLOOD. Duration of Movements and Sounds of Heart during 0.8 Second. Ventricular systole. Repose. Auricular sjstole. A __-^— ^~~~-~^ A 0.32 sec. 0.24 sec. + 0.08 sec. + 0.16 sec. V V "^^ — ______ ^ _- — -— ' First sound. Second sound. Silence. From the fact of tlie first sound of the heart being composed of both a valvuhu- and muflfled character it might be naturally supposed that it consists of more than one component and that its production must be due therefore to more than one cause. Such, indeed, has been shown to be the case, the first sound being made up in reality of two sounds, a valvular one caused by the closure of the auriculo- ventricular valves and a muffled one due to the contraction of the muscular fibers of the ventricles. That the first sound is so pro- duced is shown by the fact that it is heard during the period of the ventricular systole during the time that the auriculo-ventric- ular valves close and the muscular fibers contract. That the closure of the auriculo-veutricular valves contributes to the produc- tion of the first sound can be further demonstrated by experiments like those of Chauveau and E'aivre,^ who either modified the first sound or abolished it altogether by preventing the closure of these valves by cutting the chordae tendineje, or introducing a wire ring into the auriculo-veutricular orifices, and by the recent ones of Wintrich ^ who demonstrated by means of a resonator and stetho- scope that the first sound consisted of two components of different pitch. Further, pathology shows that, in man, the character of the first sound is changed if the auriculo-veutricular valves are diseased, and it is well known, also, that in auscultation the first sound is heard with its maximum intensity over these valves, and that it is propa- gated downward along the ventricles to ^vhich they are attached toward the apex. That the muscular contraction of the heart produces a sound, can be demonstrated by the cardiophone (Fig. 102), a distinct sound being heard when the latter is attached to the telephone, and that the sound so produced contributes to the production of the first sound of the heart can be proved by experiments such as those of Ludwig and Dogiel,^ Krehl,* Kasem-Bek,^ in which the valves were made incompetent and the only way of accounting for the sound still . heard was to attribute it to muscular contraction. While some difference of opinion still prevails as to the nature ^ Nouvelle recherches experiraentales sur les Mouvements du Cceur, etc. , p. 30. Paris, 1856. 2 Sitz-berichte der phys. med. soc. zu Erlangen, 1873, s. 1, 1875, s. 51. ^Berichte u. die Verhandl. d. K. Siicksinn, Gessel. der. Wissen. zu Leipzig, 1868, s. 89. < Archiv fur Anat. u. Phys., 1889, s. 253. spfliiger's Archiv, Band xlvii., 1890, s. 53. THE CAEDIOPHOXE. 251 of the sound produced by cardiac or skeletal muscle, it appears to be due to a repetition of the unequal tensions that occur in a muscle during its contraction, rather than of individual contractions, which we shall see hereafter, constitute the condition of tetanus. As has already been observed, the second sound differs from the first in being a clear, well-defined sound, and is essentially of a Fig. 102. Cardiophone. 6. Button to be placed upon heart. W, 11'. 'Wires for attachment to telephone. T. Telephone. valvular character. It is heard during the first three-quarters of the period in which the heart is in repose. Xow, at this moment the semilunar valves of the pulmonary artery and aorta are flapping together through the blood getting in between the valves and the walls of the vessels. The closure of these valves -will account for the second sound of the heart and its simple valvular character. The second sound of the heart can be imitated bv suddenlv closings the aortic valves by a column of water, as was first shown by Rouanet,^ and can be abolished by hooking back the semilunar valves in a living animal, as was first demonstrated by WilUams, and confirmed by the Dublin Committee in their report presented to the meeting of the Briti.^h Association in I806.- We learn also through the changes produced in the character of the second sound of the heart from disease of the semilunar valves, ' J. Eouanet, Analyse Des Bruits Du cceur, These ^'o. 252, Paris, 1832, p. 9. 2 Report of the Sixth Meeting of the British Association for the Advancement of Science, London, 1837, pp. 261, 275. 252 CIRCULATION OF THE BLOOD. and from auscultation that the second sound is heai'd most distinctly opposite the semilunar valves, and is propagated upward along the great vessels to which they are attached. There can be no doubt, then, that the second sound of the heart is caused simply by the closure of the semilunar valves of the pulmonary artery and aorta. It may be mentioned in this connection that when the heart beats more rapidly than usual, the period of silence is shortened rather than the periods during which the two sounds are heard, just as we saw the period of repose of the heart is shortened rather than that of the systole. When it is considered that age, sex, food, exercise, etc., in- fluence the rapidity of the action of the heart, it becomes evident that an intimate sympathy must exist between the circulation and the other great functions of the economy. From time immemo- rial, therefore, the frequency of the heart's action has always been regarded as one of the most important indications of the general health of the system. The practical importance, therefore, of deter- mining, as far as possible, the average beat of the heart in a given time, within the limits of health, must be obvious to every physi- cian. We shall see in the next chapter that with each ventricular systole or cardiac impulse there is an expansion of the arteries due to the blood being forced out of the left ventricle into the aorta. This expansion of the arteries or pulse, which we will consider again in detail, is, for convenience' sake, usually felt and counted instead of the beat of the heart itself, and, other things being equal, the result of such examination can be accepted as a criterion of the condition of the heart and vascular system generally. It will be observed from the Table compiled from the observations of Guy ^ and Milne Edwards,^ that the average number of cardiac beats per minute varies according to the age and sex, and this should always be remembered when the pulse is counted in man. Thus in the foetus, while the number of pulsations per minute is 140 (deter- mined by listening to the foetal heart), at birth the number falls to 136, and that up to the third year of life, while the pulse is still the same in both sexes, it now averages only about 107 beats to the minute. As we pass, however, from infancy to youth, it will be seen that the number of pulsations per minute gradually diminishes, and that at the same period the pulse of the female is a little quicker than that of the male. In adult life the average number of pulsations in the male may be said to be from 70 to 72 per min- ute, and from 6 to 8 beats more in the female. At the approach of old age the pulse becomes a little more frequent, at eighty years of age the number of beats usually being about 80 a minute. As is well known, in animals of different species, but which are closely allied in tlieir general organization, the pulse varies with the size of the animal, l)eing slowest in the largest and fastest in the ' Cyclopa'dia of Anat. andPliys., Vol. iv., p. 181. 2 Pliysiologie, Tome iv., p. 62. Age. FREQUENCY OF HEART'S ACTION. 253 Frequency of Heart's Action. Pulsations per minute. Foetal At birth . 1 year . 2 years . 2 to 7 y ears 8 " 14 14 " 21 21 " 28 28 " 35 35 " 42 42 " 49 49 " 56 56 " 63 63 " 70 70 " 77 Male. I-emale. 140 140 186 136 128 128 107 107 97 98 84 94 76 82 73 80 70 78 68 78 70 77 67 76 68 77 70 78 67 81 71 82 77 " 84 " .smallest auimals. Thus in the horse the number of beats is only 40 to the minute, in the ass about 50, in the sheep from 60 to 80, the clog 100 to 120, in the rabbit 150, and in some of the smallest rodents even 175. The circulation is also more rapid in small in- sects than in large ones, and it has long been a matter of observa- tion that in man the pulse is slower in persons of large stature than in those of small. This connection between the rapidity of the pulse and the size of the animal seems to be a very general one in the animal kingdom, so far as has been observed, and its signifi- cance will become apparent when we study the production of ani- mal heat in the economy, for we shall see then that the rapidity of the circulation is directly correlated with the production of energy, and that, as a general rule, the greatest amount of nervo-muscular activity is exhibited by the smallest auimals of any one order rather than by the largest ones. This dependence of the pulse on the size may to a certain extent explain the difference between the pulse of the young and of the old, and of the sexes as just mentioned. It should be stated, however, that the observations of Volkmann ^ show that youth and sex in themselves, without regard to size, influence the rate of the pulse, for in individuals of equal size the youngest had the quickest pulse, and the pulse of the woman was always quicker than that of the man. It must not be forgotten, however, in counting the pulse that often individuals are met with in perfect health in whom the pulse is extremely rapid, or just the reverse. Thus, according to the late Professor Dunglison,^ the pulse of Sir William Congreve never fell below 128 beats per minute, while, as is well known, on the other hand, tnat of J^s'apoleon I. often did not exceed 40 beats to the min- ^ Die Iltemodynamik, s. 30, 3G. Leipzig, 1850. ^ Human Physiology, 1856, Sth ed., Vol. i., jj. 440. 254 CIRCULATION OF THE BLOOD. ute.^ Haller- refers to cases where the pulse was still slower, being only 23 beats to the minute. As is well known, the action of the heart is also influenced by digestion; according to Milne Edwards,^ there is an increase of from five to ten beats after each meal. On the other hand, pro- longed fasting diminishes the frequency of the pulse from twelve to sixteen beats. According to the same high authority, while vege- table food diminishes the action of the heart animal food increases it, fermented drinks at first diminish then accelerate the movements of the heart. Coffee is, however, in the highest degree a cardiac stimulant. Every one is familiar with the fact that any violent exercise, like running or jumping, increases the action of the heart. As long ago as the early part of the last century it was shown, by the experiments of Bryan Robinson,* that the pulse of a man in the recumbent position being 64 to the minute, was increased to 78 during a slow walk, and still further increased to 100 by walking a league and a-lialf in an hour, and rose as high as 140 to 150 after running as rapidly as possible. It is also well known, from the experiments of Guy,^ that if the number of pulsations on the average be 6G to the minute in a man lying down, the number will be increased to 71 if he sits up, and will be still further increased to 81 if he stands up. After what has just been said in reference to muscular activity increasing the action of the heart, the results of Guy's experiments are just what might have been expected, since muscular force is developed in changing the position of the body and maintaining it in equilibrium. Indeed, it was in this way that many of the older physiologists theoretically explained the acceleration of the heart's beat observed in the change of posture just referred to. It was Guy, however, who first demonstrated, by means of a revolving board which sup- ported the person who was the subject of the experiment and so relieved him of the necessity of supporting himself by muscular exertion, that the variations in the frequency of the heart, according to the position of the body, was dependent upon the quantity of muscular force put forth in maintaining equilibrium in each of the positions. The practical importance of these facts for the physician <;annot be exaggerated, since it is obvious that, in a person suffering with heart disease, it is of the utmost importance that any increase in the action of the heart should be avoided. The greatest caution, under such circumstances, should be advised in the taking of exer- cise ; any sudden or violent effort, like quickly lifting up a trunk, or running rapidly up stairs, should be strictly ])rohibited, the slight acceleration in the heart's beat from such an effort being fre- quently a cause of death in persons affected with heart disease. It is well known that during the day there is a variation in the ^Berard, Physiolofjie, Tome iv., p. 118. ^Elementa Phy^iiologie, Tome ii., p. 250. •' Physiolotjie, Tome iv., p. 79. * A Treatise on tlie Animal Economy, p. 177. lAiblin, 1732. 5 Cycloptedia of Anat. and Pliys., Vol. iv., !>. 188. CONDITIONS INFLUENCING ACTION OF HEART. 200 action of the heart, and for a long time it was supposed that the pulse Avas quicker in the evening than in the morning. According to the older physiologists, "Pulsus nocturnus multo celerior est."' When, however, the action of the heart at evening is considered uninfluenced by food, exercise, etc., it has been found that the pulse at that period of the day is really slower than in the morning, and that the heart is less susceptible to the action of stimulants. This condition is due, no doubt, to muscular fatigue. In sick persons, however, it is otherwise, since at evening there is usually some fever present, and this is accompanied by a quicker pulse. According to INIilne Edwards," while sleep tends to diminish the action of the heart, the number of pulsations at least in man, is not diminished to any extent by that circumstance. In women, and especially children, in that condition, however, there seems to be considerable difference as compared -with the wakeful state. The temperature ot the surrounding atmosphere influences also the rapidity of the action of tlie heart — heat increasing and cold dimin- ishing the number of heart l)eats. De la Roche ^ found that his pulse was increased to 160 beats per minute in an atmosphere of 65.5° C. (150° F.), and it is well known that the pulse is quicker in hot countries than in cold ones. Among the other influences that accelerate or diminish the action of the heart must be mentioned that of respiration. When the manner in which the blood flows through the pulmonic capillaries, and the changes produced in it, have been described, the mutual sympathy existing between the heart and limgs will then be fully ap})reciated. It would be anticipating too much to give a detailed account of this mutual influence at present, but it may be mentioned in this con- nection that the action of the heart may be voluntarily arrested through modifying the conditions of respiration. Thus, for ex- ample, if after a forcible expiration the mouth and nose are closed and then a powerful inspiratory effort is made, the heart may cease to beat. This appears to be due to the extreme dilatation of the heart caused by the venous blood flowing so freely into the right side of the heart as to cause engorgement of the lungs and of the left side. On the other hand if exactly the opposite experiment is tried, that is, if after taking a deep inspiration, and the mouth and nose are closed, a strong expiratory effort is then made, the heart's action may also be arrested. Under these circumstances the heart is contracted, since the flow of the venous blood is interrupted, as shown by the veins of the neck and face swelling up, while the arterial blood is forced out of the compressed lungs into the left ventricle and thence into the arteries. Both of these experiments are dangerous, and should not often be repeated. It is well known that the late Prof. E. F. Weber, of Leipsic, was able, by closing the glottis and at the same time con- ' Keill, Teutamina medico-pliysica, p. 178. London, 1730. 2Physiologie, Tome iv., p. 74. ^xhese, Paris, 1806, p. 33. 256 CIRCULATION OF THE BLOOD. tracting forcibly the chest, to diminish the cardiac beats to three to five a minute, which were unaccompanied with the cardiac impulse or sounds, and with the result, finally, of stopping the action of the heart altogether. On one occasion, having suspended his respira- tion longer than usual. Professor Weber ^ fell into a syncope. This case, concerning the truth of which there can be no question, confirms the statements made by Galen,- and others,'^ that death in certain indi- viduals had been caused by the voluntary suspension of their breath- ing. One of the most interesting and best authenticated cases of the possibility of temporarily arresting the action of the heart was that of Colonel Towhnsend, reported in the early part of the last century by Cheyne.^ This physician relates how Colonel Towhn- send could so arrest the breathing and the beating of his heart that death was simulated. In this condition the pulse could not be felt at the wrist ; there was no cardiac impulse ; a mirror placed in front of the mouth was not tarnished, and, apparently, he was dead. On the occasion reported by Cheyne, Colonel Towhnsend remained in this condition for half an hour ; gradually, hoAvever, the respira- tion and circulation became reestablished. It should be mentioned, however, that Colonel Townhsend died later in the afternoon of the same day that the facts just described occurred. It may be mentioned in this connection as appropriately as else- where that if a Avide glass tube filled with smoke be inserted into one nostril, the other nostril and mouth being closed, that the smoke will move with each beat of the heart. The " cardio-pneu- matic movement," as this movement is called and of which a trac- ing can be obtained by appropriate apparatus, appears to be due to the fact that the heart occupying less space within the thorax when it contracts air will pass into the lungs with each systole and out with each diastole. Having described the motion of the heart and the various influ- ences that modify it it remains now to consider, so far as is known, how the beat of the heart is maintained. When we come to the special study of muscular contractility we shall learn that an ordi- nary voluntary muscle usually contracts in response to a stimulus, the will, emanating in the brain, and transmitted through a nerve to the nmscle. While the heart is a muscular organ, its action differs from that of the ordinary muscle in being involuntary in character. The voluntary muscle, however, not only contracts through the influence of the will or nerve force, but also in response to mechanical, elec- trical or chemical stimuli, and, in this respect, the heart does the same. Thus, if the chest of a living animal be opened, and the heart mechanically irritated by an instrument, a scalpel, for exam- ple, it will be seen to contract like any other muscle stimulated in 1 Milne Edwards, Physiologic, Tome iv., p. 88. ^ffiuvres trad, de Daremberg, Tome i., p. 366. 3Muller's Archiv, 1S51, s. 91. ranc is that part of the artery M^hich ultimately becomes the capillary. AVe have seen that the action of the heart is intermittent THE ARTERIES. 261 in character, each ventricular systole being followed by the diastole, a period of repose during which no blood flow^s into the arterial system from the heart. If, however, a large artery near the heart be opened, it will be observed that the blood flows out of the artery continuously, both during the systole and diastole. With each ven- tricular systole, however, the jet becomes stronger ; the flow in the artery, therefore, is not, like that in the heart, intermittent, but re- mittent. If the artery examined be situated, however, at a distance from the heart, near the periphery, the flow of the blood will be found to be but slightly remittent, indeed almost uniform, while finally, as we shall see in the capillaries, it is entirely so. The flow of the blood, then, as it passes from the heart through the arteries to the capillaries from being intermittent becomes remittent, and finally uniform. It is to the property of elasticity, with which we have seen arteries are endowed, that this transformation of an intermittent motion into a remittent one is due. For, during each ventricular systole, of the blood that is forced into the arteries a part only presses ouAvard the blood already in the arteries, the re- maining part presses outward the walls of the artery. From the moment, however, that the effect of the systole ceases — that is, during the diastole — through its elasticity the walls of the artery recoil on the blood which has distended them, and press it onward (the aortic valves preventing any regurgitation) immediately after the part of the blood that has just preceded — that is, the part forced forward during the systole. There are two successive waves of blood then in the artery, that of the systole and that of the diastole ; they follow each other, however, so rapidly, that ulti- mately they merge into one, the movement of the blood in the capillaries becoming finally uniform. The elasticity of the artery favors, therefore, the onward movement of the blood. Did the arteries consist of rigid tubes the blood would flow through them in the same intermittent manner as it does through the heart. With each ventricular systole blood would flow from the arte- ries into the capillaries in an amount equal to that which flowed from the heart into the aorta, with the diastole of the heart, however, the flow from the arteries would entirely cease. The author is in the habit of demonstrating the difference between the flow of liquids in elastic and rigid tubes by means of the apparatus repre- sented in Fig. 105. This consists of a reservoir (A) containing a colored fluid, and provided with a stopcock (B) by means of which the delivery of the fluid can be regulated. To the stopcock is connected a flexible, but, if possible, a non-elastic tube (C) which is connected with a tin tube (D), the latter bifurcating so that the fluid from the reservoir can pass through the tube G into the tubes E and F, simultaneously. One of these tubes (E) consists of glass, the other (F) of caoutchouc, the former (E) is connected with the tube D by caoutchouc. At their distal ends the tubes D and F are bent downward so that the fluid flowing: from them can 262 CIRCULATION OF THE BLOOD. be conveniently collected in the jars P I. The glass tube, as it terminates, is drawn out so as to simulate the capillary end of an artery, its orifice having a diameter of 2.5 mm. (J^ of an inch). The same effect is accomplished, as regards the caoutchouc tube, by inserting into its distal end a tube of glass of the same length and diameter as that of the distal end of the glass tube. The tubes E F are supported by, and firmly bound to, the table K, which is painted white, so that the colored fluid can be readily seen in the glass tube. The reservoir being filled and the stopcock turned on, the colored fluid passes into the bifurcated tube and thence through the elevation and depression of the lever (G), worked by hand, in an intermit- tent manner, into the rigid glass tube and elastic caoutchouc one. The lever should be uniformly depressed and elevated at the rate of about sixty times to the minute and the fluid watched as it escapes from the tubes. It will be observed, from the reasons Fig. 105. Apparatus to (.Iciuoustratf tlie tiow of a fluid through rigid and elastic tubes. (Marey.) already given, that the flow from the rigid glass tube is absolutely intermittent, with each depression of the lever the flow entirely CL'asing. On the other hand, the flow from the caoutchouc tube is distinctly remittent, the jet not ceasing but only diminishing with the depression of the lever and increasing again with its elevation. It is needless to add that the elevation and depression of the lever represent the opening and closing of the aortic valves, the escape of the fluid from the tubes the flow of blood through the con- stricted arteries toward the capillaries. Tliis exporiraciit not only proves that the elasticity of a tube in- fluences the character of the movement of the fluid flowing through it, but also of the quantity that escapes from it, for if the jars P I be THE ARTERIES. 263 examined, it will be seen that the one collecting the liquid from the elastic tube is almost three times as full as that collecting from the rigid one. During an experiment lasting three minutes, while 2800 c. cm. (3.7 pints) of fluid flowed into the one jar, only 1000 c. cm. (1.7 pints) flowed into the other. This is as might have been expected when it is remembered that an elastic tube is capable of receiving more fluid than a rigid one, for two reasons : first, there is not only the quantity of fluid which, after entering the tube, presses directly onward and which corresponds to the fluid in the rigid tube, but also an additional quantity which presses the walls of the elastic tube outwardly. It is this lateral fluid, so to speak, that follows and adds itself to the part which presses di- rectly onward that converts the intermittent motion into the remit- tent one, and by just so much as the walls of the tube will give to this lateral pressure the amount of fluid entering the elastic tube will be in excess of that entering the rigid one. Second, it being remembered that the principal obstacle to the flow of a liquid through a tube is the friction of its walls, and that the friction is proportional to the square of the velocity of the current, it follows that as the effect of the dilatation of the artery is to diminish the velocity of the current through it, and therefore to diminish the amount of friction according to the square of the velocity of the current, the quantity of fluid delivered from the elastic tube will, therefore, be greater than that from the rigid one. We have seen that the arteries are not only endowed with elastic- ity, but also Tvdth contractility or tonicity, as it was called by Bichat, and it has been shown, experimentally, by Poisseuille,' that the re- coil of the walls of the artery upon the blood that had previously distended it is greater than can be accounted for by the elasticity of the artery alone. Indeed, the tendency of an artery is always to contract, to empty itself of its blood. For this reason difficulty is always experienced in injecting the vessels of an animal immedi- ately after death. If, during life, the calibre of the arteries is about equal to that observed after death, it is because the arteries are during life dis- tended with blood. That the arteries will contract independently of the elasticity or the recoil following upon the distention of its walls through the blood forced into the vessel by the heart can be demonstrated by ligating an artery in two places and in a part of its course where no branches are given off, so as to exclude the influence of the gen- eral circulation, and then opening the artery at a point situated be- tween the ligatures. Under such conditions, although the artery is uninfluenced by the action of the heart, etc., the blood will jet out with force, and the artery will be almost completely emptied. When it is remembered, as we have seen, that in the smallest arte- ries the middle coat consists entirely of muscular fibers, there being ^Journal de Magendie, T. ix., p. 44. 264 CIRCULATION OF THE BLOOD. no elastic tissue present, it becomes evident that the contractiHty, in such cases at least, must be due entirely to the action of the muscu- lar fibers. Hence the distinction clearly made by John Hunter,^ that in the large arteries the recoil of the walls was due almost en- tirely to the elasticity ; in the smallest arteries, on the contrary, to the contractility. The physiological significance of this distinction was also seen. Hunter attributing to the elasticity the conversion of the intermittent action of the heart into the remittent one of the arteiy, to the contractihty the regulating of the calibre of the ar- teries, and, therefore, the supply of the blood to the system. In- asmuch as arteries therefore contract in virtue of their contractility as well as of their elasticity, and as after death the contractility disappears, as might be expected, the amount of contraction is greater in the living artery than the dead one. The contractility of the arteries can be easily demonstrated by the application of various stimuli, mechanical, chemical, electrical, exposure to air, ap- plication of cold, etc. Thus the mere scraping of the walls of an artery or the pricking of a needle Avill cause them to contract. Various chemical substances, such as sulphuric acid, ammonia, alum, and ergot, are among the most powerful stimuli to muscular con- tractility. Indeed, the usefulness of haemostatics in arresting hemorrhage depends upon this property. The smallest arteries readily contract under the influence of both the direct and indirect electrical currents. Simple exposure of the arteries to air suffices to produce a slow but permanent constriction of the vessel. The local application of cold — ice, for example — in stopping bleeding after wounds, is well known to the uneducated, the effect being due to contractility. The stimulus of great heat produces the same result. We have already seen that, through nervous influence, the ar- teries contract. In speaking of the structure of the arteries, it was mentioned that the muscular fibers are supplied by nerves derived from the sympathetic and cerebro-spinal systems. The stimulation by electricity of these vasomotor nerves, as they are called, is fol- lowed by contraction of the arteries they supply, while division or paralysis of these nerves is followed by a dilatation of the vessels. The phenomena of blushing, of sudden pallor in the face, are familiar examples of the influence of the vasomotor nerves in modi- fying the amount of blood in a part ; in the one case the vessels dilating, in the other contracting. When it is remembered that more blood is demanded by an organ at one time than another, a gland when secreting, for example, requiring more arterial blood than when quiescent, it becomes evident that there must be some means in the economy, by which the amount of blood supplying any organ can be varied. It is through the vasomotor filaments that the nervous system modifies the calibre of the arteries, and, in that way, regulates the amount of blood distributed to diflerent iWoiJjs, Vol. iii., p. 194. CONTRACTILITY OF THE ABTEEIE-i. 265 parts of the body. The origin and distribution of tlie vasomotor nerves ^11 be considered in detail hereafter. While it must be admitted that the contractility of the arteries favors somewliat the onward flow of the blood within them, ^-ithont doubt the principal eifect of their contractility is the recriilation of the supply of blood through the modification of their calibre. It should be mentioned, as regards this contractility, that, by what- ever means it is induced, whether the stimuli be mechanical, chem- ical, or electrical, that, unlike ordinary striateG) that there is in the dog, for example, a maximum and a minimum intra-ventricular pressure, amounting to 140 and —50 millimeters of mercury re- spectively.^ The latter being a negative pressure that is lower than that of the atmosphere, the blood will be forced into the heart as we shall see more particularly hereafter. The instrument just re- ferred to by which variations in the intra-ventricular pressure is usually determined, consists essentially (Fig. 135) of two parts, one of which (a) acts as an ordinary manometer, the other as a maximum or minimum manometer according to the position of the valve (v) the part (a) being then clamped. The valve (y) is of a cup and ball variety, and when, as in Fig. 138 permits the passage of the fluid from the heart, but not towards it. Since the ^Fr. (ioltz u. J. Gaule, Pfliif^er's Archiv, Band xvii., 1878, s. 100 ; S. de Jager, Ebenda, Band xxx., 1883, s. 491. MANOMETERS. 295 column of fluid that passes the valve can not return, the mercury will remain at the o^reatest lieio;ht to which it has been elevated, Fig. 136. The maximum manometer of Goltz and Gaule. the instrument then acting as a maximum manometer. By revers- ing the valve the manometer is then converted into a minimum one. Slight variations in the iutra-auricular, ventricular, and aortic pressures can be much better demonstrated, however, by means of Fig. 137. Fig. 138 T^ Diagram to illustrate the essential parts of Hiir- thle's membrane manometer. Curve of pressure in the left ven- tricle of the dog, Hiirthle's mem- brane manometer. (Foster.) Fig. 138 A. Curve of pressure in aorta of dog. (FOSTEK.) membrane manometers than mercurial ones, the inertia of the mer- cury in the latter being too great to be much affected. Among the 296 CIRCULATION OF THE BLOOD. Fig. 139. membrane manometers or tonometers, as they are also called, made use of for this purpose that of Hiirthle ^ is a convenient form. This consists essentially of a very small metal hemispherical drum (Fig. 137, a), the upper end of which is covered with a delicate elastic membrane (e), bearing upon its center a thin metal disc (c?), connected by a short upright (e) with a recording lever (l), the lower end terminating as a tube (6). A catheter filled Avith sodium car- bonate solution having been intro- duced through the jugular vein into the right auricle (^4) or ventricle ( T^), or through the carotid artery into the aorta, and so into the left ventricle, connection is made with the mano- meter, the latter being usually filled wdth the same solution as that in the catheter. Such being the disposition of the apparatus, it is obvious that any variations in the pressure exerted by the heart cavities will be transmitted through the fluid of the catheter and drum to the elastic membrane of the latter, and in turn transmitted thence to the recording lever. It will be ob- served that the curve (Fig. 138 V) of the pressure of the left ventricle in the dog obtained by the Hiirthle mano- meter, as well as that of the right ven- tricle of the horse obtained by a Marey sound (Fig. 93), agree in the following features : the pressure rises at the very beginning of the systole very rapidly, soon reaches a maximum, which is maintained at nearly the same height for some time, that part of the curve constituting the " systolic plateau," then rapidly falls to the line of atmospheric pressure, or even below it, and remains at the base line till the next cardiac beat. It must be mentioned, however, in this connection, that, according to some observers, the production of the so-called " systolic plateau " is due to the friction of the tube, ill-placed canula, etc., the highest point of pressure being naturally peaked, not flattened. By introducing two catheters into the heart of a dog so that the end of one will lie in the ventricle (Fig. 139 V), the end of the other in the aorta (.1), and then connecting the other ends of the catheters with two membrane manometers, the pressure of the ventricle and auricle can be simultaneously recorded. iPfliiger's Archiv, Band xliii., 1888, s. 399. Diagram illustrating the method of recording simultaneously the pressure in the left ventricle and at the root of of the aorta. (Hukthle.) DIFFERENTIA L MANOMETER. 207 An examiuatiou of the two curves (Figs. 138 T'and 138 ^1) shows that at (o), Fig. 138 V, the beginning of the ventricular systole, no effect is produced upon the blood of the aorta, the latter being cut off from the influence of the ventricular pressure by the closing of the aortic valves, A little later, however, as at (1), Fig. 138 J., the aortic valves being now open the effect of the ventricular pres- sure is felt and the pressure in the aorta begins to rise. The sim- ultaneous changes in the pressure of the ventricle and aorta just described can also be demonstrated by means of the differential manometer of Hiirthle^ (Fig. 140). It may be stated as the result of experiments made with different kinds of manometers that the average pressure of the right ventricle is about one-third that of the Fig. 140. ^ '• ) ^) f. - i o 1 ^' ''' di \ 'J- )c^ ^ ^ J.L _„ L -;' .^ J [^^4^ U ti O ir^U V ^ ir o i a T T, Piagram of the diflferential manometer of Hiirthle. (Foster.) T, Ti. The tambours of two membrane manometers, the mouths of the tubes opening into each being shown in section, d, rfj. Central disks of tambours, working on a balance above them, the latter remainiug horizontal a.s long as the pressure in the tambours is equal, but moving upward or downward with any dif- ference in pressure, and, in working against the spring ^ by means of e and ei, moves the lever I. left, and as the pressure of the right auricle is only one-tenth that of the rin-lit ventricle, it would be onlv one-thirtieth that of the lefb ventricle. While the flow of the blood through the arterial system gener- ally is influenced by the length of the vessel, friction, etc., the capillary system, as we shall see, is the constant source of resis- tance. In proportion to the fulness of the capillaries a greater or less obstacle is offered to the flow of the arterial blood. The force that the heart exerts must then vary according to the resistance to be overcome. Arterial pressure is due, therefore, not only to the force exerted by the heart from behind, vis a tcrgo, but to the resistance of- fered by the capillaries in front, vis a frontc. This is readily sllO^^•n by means of the Coats- or Marey'' apparatus, but, as both these methods involve taking the heart out of the animal, and as it is desirable to show the phenomena, the heart being in situ, the author usually makes use of Brubaker's frog manometer (Fig. 141). This consists of a mercurial manometer J/ like that we have used in determining the blood pressure in the rabbit, only that it is smaller. The arterial canula differs, however, from the one used iPfliigers Archiv, Band xlix., 1891, s. 29. 2 Sanderson, Handbook Pliy .biological Laboratory, p. 268. ''Op. cit., p. 70. 298 CIRCULATION OF THE BLOOD, in that experiment. In this instance the end a of a _L-shaped glass tube is inserted into the bulbus arteriosus of the frog, the end h being adjusted to the proximal end of the manometer, while the stem c is connected by the tube d with a funnel e containing a so- lution of sodium carbonate. The funnel corresponds to the pres- sure bottle in the experiment with the rabbit. The frog is secured to a piece of cork, which rests within the stand supporting the manometer ; the stand can be raised or lowered upon the vertical rod ; the latter also supports, by the horizontal rod the funnel. Having first determined the normal blood pressure, it will then be Fig. 141. Brubaker's frotr manometer. observed that as the tube d is compressed, an obstacle being thereby interposed to the flow of blood from the aorta, the pressure will be increased, the mercury rising in the distal limb of the manometer, thus showing that the force which the heart exerts is proportional to the resistance to be overcome. It is hardly necessary to state that the constriction of the tube in the last experiment would represent a capillary obstruction in the living animal. Theory and experiment, therefore, agree in show- ing that the amount of force which the heart usually exerts is far less than the possible force that can be put forth if occasion de- mands it. Assuming that the blood flows through tlie arteries, according to hydraulic laws, we should expect to find the pressure BLOOD PRESSURE IN DIFFERENT ARTERIES. 299 diminishing as we recede from tlie heart to the periphery. Thus, if we watch the colored fluid as it flows from the reservoir (a, Fig. 142) through the liorizontal tube h, it will be observed that the height to which the fluid rises in the vertical tubes c^ and c, in- serted into the horizontal one gradually diminishes as we recede from the first (c^) to the sixth tube (c). In the present experiment, Fig. 142. l)ecrease of pressure in tubes of equal caliber. where the colored fluid rose in the first tube to a height of 27 cm. (10.8 inches) in the sixth to a height of only 9 cm. (3.6 inches), the level of the fluid in the remaining tubes (2, 3, 4, 5) being inter- mediate between these extremes. This difference in the level of the fluid in the vertical tubes is caused by the resistance due to friction which the fluid encounters as it flows from the reservoir through the horizontal tube, and as the resistance encountered at the first tube gradually diminishes as we approach the sixth the height of the fluid or the pressure is proportionally diminished in the tubes as we pass from the reservoir to the outlet. Poisseuille ^ failed with his mercurial manometer to detect any difierence in the blood pressure of arteries situated at different distances from the heart, such as theory indicated should have been found. Indeed, the difference in the blood pressure of two arteries, seen even when one is situated at a considerable distance from the heart, is too slight to be appreciable by the mercurial manometer alone. Volkmaun,^ however, showed by means of the kymograph, that there was a dif- ference of 7 mm. (0.2.S inch) mercury between the blood pressure in the carotid and metatarsal arteries of the dog, the pressure amounting in the first case to 172 mm. (6.8 inches), and in the latter to 165 mm. ['o.Q inches). In the rabbit the difference be- tween the l)lood pressure in the carotid and femoral arteries is only about 5 mm. (i of an inch); in the calf, however, the difference amounts to 26 mm. (1.04 inches). It is not only desirable to determine whether there exists any difference in the ])lood pressure of two arteries like the carotid and metatarsal, but also if the pressure in two arteries like the two ^Op. cit., p. 37. 2 Op. cit., s. 167. 300 CIRCULATION OF THE BLOOD. carotids or the two criirals is equal or different. With tliis object as well as of determining the difference between the pressure in an artery and a vein, the carotid and the jugular vein, for example, we make use of the differential manometer of Bernard ^ (Fig. 143). This consists of a U-shaped glass tube firmly supported upon a stand which carries a graduated scale, and by means of which the Differential manometer of Bernard. tube is filled with mercury to a certain level. The two ends of the U-tube are adapted to lead pipes which are connected with the pres- sure bottle containing the solution of soda, and at e e with arterial canulffi to be inserted into the vessels to be examined. By means of the stopcocks either one or both the vessels can be placed in ' Systeme Nerveux, Tomei., p. 281. THE KYMOGRAPS. 301 communication with the manometer. Suppose, for example, the two ends of the manometer have been inserted by means of the arterial canuls into the carotids of a rabbit. Having opened both stopcocks and removed the clamps from the arteries and allowed the blood to press against the solution of soda, it will be observed that the level of the mercury remains imchanged, showing, there- fore, that the blood pressure in the two arteries is the same. If now one of the stopcocks be closed, at once the mercury will rise in the limb of the tube of the corresponding side, and by doubling the height to which the mercury is elevated, and deducting 1 mm. for Fig. 144. Fick's spring kymograph, a. C-spring. x. Support, d. Eod which communicates the move- ments of the spring to the lever I, and thus to the writing-needle G. c. Leaden tube by which the cayity of the spring is in communication with the artery. every 10 mm. of solution ol sodium carbonate used, the blood pres- sure of the artery on the side v.here the stopcock remained opened is obtained. Admirable an instrument as the kymograph undoubtedly is, and however accurately it fulfils its purpose, it must not be forgotten that the trace recorded on the cylinder is due to the oscillations of the mercury, and, therefore, only indirectly to the pressure of the blood. On account, however, of the inertia of the mercury and the suddenness of the expansion of the artery, the oscillations of the mercury, though caused by the pressure of the blood, are not an ex- act measure of it, since by the time the mercury has risen to its 302 CIRCULATION OF THE BLOOD. highest elevation the artery has collapsed. If the heart is beating very quickly the extent of the oscillations of the mercury is rela- tively too small, and if the interval between the pulsations is pro- longed the excursion of the manometer is too great. The use of the mercurial kymograph is, therefore, limited to the study of the mean pressure and of variations in pressure, such as occur at sufficiently long intervals to prevent the oscillations being mixed up witli those proper to the instrument. In order to study the variations of blood pressure in the exact order in which thoy occur, and as regards their duration and degree, etc., we make use of Fick's spring kymo- graph, which is so constructed that it transmits the movements communicated to it witliout obscuring them by any movement of its own. The instrument (Fig. 144) consists essentially of a hollow C- shaped thin metal spring (a) filled with alcohol and communicat- ing through its proximal end (5) by means of a connecting tube (c) with the pressure bottle containing the solution of the sodium bicarbonate and the arterial cauula. The proximal end of the s^jring being fixed, as the blood pressure increases the spring tends to straighten itself and the distal or free end makes the movements which follow exactly the variations in the arterial tension,^ These Fig. 145. Traces in rabbit taken with Fick's spring kymograph. movements are most exact, the slightest variations in the blood pressure being expressed by them. As they are, however, very small before being recorded, they are enlarged by the lever which is carried by the distal end of the spring. It will be seen from Fig. 145, illustrating a trace of the blood pressure in the carotid artery of the rabbit, taken by the spring kymograph, that the ascent of the lever, due to the expansion of the artery caused by the ventricular systole, is very abrupt, almost vertical, that at the vertex the direction of the trace is horizontal, that the lever in its descent pursues an oblique course at its termination, being also horizontal in direction, and that the dicrotism of the pulse is very evident. Tlie nature of these peculiarities we have already consid- ered in describing the pulse. If we wish to express in millimeters of mercury the absolute blood pressure determined by the spring kymograph, the instrument must first be graduated by comparison ' In some recent forms of Fick's kymograph the memlirane of a small air drum works against a horizontal slip of steel which acts as a spring. VELOCITY OF THE BLOOD. 303 with a mercurial manometer. This is done in the following way : The spring kymograph being so placed that it will write on the re- cording cylinder, its connecting tube in communication with the pressure bottle is adapted to the proximal end of the mercurial manometer. The pressure bottle is first lowered until the solution it contains stands at the same level as that of the mercury in the manometer. The clockwork being put in motion the cylinder re- volves and a trace is taken which will represent the abscissa. The pressure bottle is then raised till the mercury is elevated in the distal limb of the manometer 10 mm. (|- of an inch) higher than in the proximal one, and a second tracing taken, and so on until we have attained a number of tracings parallel with the first one or abscissa, and therefore with each other. The vertical distance between the abscissa, and these lines or the ordinates measured in millimeters expresses then the value of the tracing in millimeters of mercurial pressure. We have already alluded incidentally to the influence of respira- tion in modifying the curve of the blood pressure, and, as we have now seen, how the latter may vary according to the part of the vascu- lar system generally. It is probable, also, that tlie blood pressure de- pends, to a certain extent, upon the size of the animal, the period of life, and general health, cceteris paribus, the blood pressure being greater in larger than in smaller animals, in those of middle age than in very young or very old animals, in strong, healthy than in weak, sickly ones. Inasmuch as the pressure of the blood depends upon the muscular force of the heart, and as the muscular substance of the heart, like all other muscle, is nourished by the blood, it follows that loss of blood in weakening the heart fibers should diminish blood pressure. The experiments of Hales ^ and Colin ^ have shown that such is the case, the blood pressure being diminished in propor- tion to the amount of blood lost. Finally, we shall see that the vasomotor nerves, in modifying the calibre of the vessels, greatly in- fluence the blood vessels. In concluding our account of the arteries, there still remains for consideration the velocity with which the blood flows through them. Physiologists at one time endeavored to determine the velocity of the blood by means of the theorem of Torricelli, assuming that the velocity with which a fluid escapes from a reservoir may be learned from observing the height to which it will flow into a vertical tube connected with the same, the velocity being equal to that which a body would acquire falling in vacuo through a distance equal to the height which the fluid attains in the tube, which is nearly the same as the level of the fluid in the reservoir. Little or no importance, however, can be attached to this manner of determining the veloc- ity of the blood in the arteries, since the cardiac energy is expended in not only imparting a velocity to the blood but in overcoming re- ' Statical Essayn:, Vol. ii., p. 16. London, 1740. 2 Milne Edwards, Physiologie, Tome iv., p. 115. 304 CIRCULATION OF THE BLOOD. sistance, and unless the latter factor is known and be taken into account the velocity obtained by theory will be a gross exaggera- tion. Assuming, according to well-known hydraulic principles that the velocity with which a fluid, in a given time, flows through a tube is equal to the ratio of the efflux to the sectional area of the tube, Hales^ estimated that the blood in the horse flows from the left ventricle into the aorta at the rate of nearly 17 inches in a second, which we will see agrees closely with the velocity recently deter- mined by experiment. Passing by the early attempts to determine the velocity of the blood such as those just mentioned, and which have now only a his- torical interest, let us endeavor to determine, not what the velocity of the blood ought to be in an artery according to theory, but what the velocity actually is in a living animal by experiment. The hsemodromometer (Figs. 146, 147), the instrument invented by Fig. 14G. Fig. 147. Volkmann's hn;iiJoilri)mometer for measuring the rapidity of the arterial circulation. Volkmann" for this purpose, consists of a metallic tube (c), which is united to the two ends of a divided artery, and through which the blood can flow in the same direction as through the vessel itself (Fig. 146). To the metallic tube is attached laterally a U-shaped glass tube (<:?), containing water. By turning stopcocks the metal tube is put in communication with the U-shaped tube in such a way ^Statical Essays, Vol. ii., p. 46. ^ Hfemodynamik, s. 185. THE STEOMUHR. ;305 (Fig. 147) that the blood cannot pass at once as it clid before from the artery through the metal tube to the artery again, but must first pass through the U-shaped tube. The length of this tube being known, and the time it takes for the blood to flow through it being observed, the velocity with which the blood flows through the artery can be determined approximately. There are objections, however, to the use of this instrument, as the blood does not flow through the glass tube as easily as it does through the artery, both on account of the curvature of the tube and of the difference in its substance as compared with that of the artery, and as the blood flows from the proximal end of the artery into the glass tube it drives ahead the water it contains into the distal end, the effect of which is to con- tract the vessels, and so further retard the flow. It is for these reasons, that Volkmann's esti- Fig. 148. mate of the velocity of the blood, for example, in the carotid artery of the horse of 254 milli- meters (10.2 iuches) in a second is too low. By the invention of the stromuhr, in 1857, Ludwig ^ greatly improved Volkmann's method of measuring the velocity of the blood. This instrument, also called the rheometer {;i^oj, to flow, /uzTooi^, a measure), consists (Fig. 148) of two glass bulbs {B, C) of an ovoid shape, and of a known capacity, communicating superiorly by the curved tube and terminating so iuferiorly as to be screwed into the canula? F and G, which are onlv larg-e enough to be inserted into the cut ends of the artery to be examined. The canulse having been ligated, and the vessel previously clamped, by means of the small tube opening into the communicating tube, the bulb C is filled with olive oil up to the mark J/, the bulb B with serum. The small tube is then closed. The clamps having been removed, the blood flows - ~ from the proximal end of the artery by means Ludwig's stromuhr. of the canula F into the bulb C, driving the oil ahead of it through the communicating tube into the bulb B, the serum in the latter being driven out of it through the canula G into the distal end of the artery. So fiir the method of experimenting with the stromuhr is essentially the same as that of the ha?modro- mometer, with these two differences, however, that serum being used instead of water there is less resistance offered to the flow of the blood, and, on account of the shape of the bulbs, a greater quantity of blood can be used, which is also of advantage. The sreat im- provement, however, in Ludwig's instrument, as compared with Volkmann's, consists in this, that by turning the vertical rod H ^ Dogiel, Berichte iiber Die Verhand. Der Kon Sachsischen Gesell. Der Wissen. Zu Leipzig, 1867, s. 200. 20 /^^- 306 CIRCULATION OF THE BLOOD. through 1 80 degrees, by a simple mechanical arrangement, the bulb B now filled with oil communicates through the canula F with the proximal end of the artery, and the bulb C filled with blood com- municates through the canula G with the distal end. The blood still flowing from the proximal end of the artery will now drive the oil out of B into C, and the blood displaced by the oil will pass into the distal end. By turning the rod back again the bulb ( ' ^nll communicate with the canula F, and the bulb B with the canula G. This operation can be repeated several times before the blood coagulates. To illustrate the manner in which the velocity of the blood is determined in a living animal by the stromuhr we will suppose that the instrument has been adapted to the carotid artery of a rabbit. The animal having been firmly secured and the artery exposed and clamped in two places, the clamps being separated by a distance of two inches, about an inch of the intervening vessel is cut out. The stromuhr being attached to the vertical stem of the holder by the horizontal rod and the bulbs having been previously w^armed and their ends screwed into the canul?e which have been inserted into the cut ends of the artery, the bulb C is then filled with oil up to the mark 31, it containing then 5 c. cm., and the bulb B with serum. The clamps are now withdrawn from the artery and the blood from its proximal end will be observed to drive the oil from C into B, the oil displacing the serum in B, which passes into the distal end of the artery. The moment that the blood reaches the level of the mark 31 the movable disk I) is rotated as rapidly as possible through 180 degrees with the effect of putting the bulb B filled with oil in communication with the proximal end of the artery and the bulb C filled with blood in communication with the distal end of the vessel. The blood continuing to flow, the oil is now driven from B into C, the disk being rotated back again the mo- ment that the blood reaches the level of the mark, the bulb (', now filled with oil, communicates as at first with the proximal end of the artery. The experiment may be continued in this way for a minute or more until the blood begins to coagulate. Inasmuch as we learn how often in a given time a definite quantity of oil is dis- placed by tlic blood we learn how. much blood is delivered by the carotid artery in that time. Suppose, for example, that in an ex- periment 5 c. cm. of blood have been delivered by the carotid ar- tery 10 times in 100 seconds — that is, 50 c. cm., then 1 c. cm. of blood has flown from the artery in 2 seconds, or 0.5 c. cm., equal to 500 mm. in 1 second. Dividing this amount by the sectional area of the artery through which it has flown — that is, by 3.14 mm. (1- X 3.14 = 3.14), the diameter of the artery and the can- ula being nearly the same, 2 mm., and the radius, therefore, 1 mm., we get the velocity, nearly 158 mm. (G.3 in.), in 1 second I' = 158.9), the hydraulic principle involved being that the THE H^MODROMOMETEB. 307 velocity equals the ratio of tlic quantity of fluid delivered to the sectional area of the tube. The stromuhr is a most excellent and reliable instrument, as it interferes so little with the circulation, the flow of the l)lood being- only stopped during the instant that the disk is rotated and the blood pressure being little altered by its passage through the instru- ment. This can be sho^^ii by connecting a manometer with the two tubes which are in communication with the bulbs, but which are not seen in the illustration, the tubes being placed in the side of the apparatus not shown in the flgure. Fig. 149. Hfemodromometer of Chauveau and Lortot. Fig. 150. While the stromuhr is admirably adapted to determine the ex- act amount of blood passing through nn artery and the mean ve- locity of the flow, it does not, however, enable us to determine the incessant variations experienced by the blood as regards its velocity. For this object physiologists make use of the ha?modromometer of Chauveau. The construction of this instrument, like the hsema- tachometer of Vierordt,^ is based upon the principle of measuring the velocity of the blood by observing the amount of deviation undergone by a pendulum, the free end of which is suspended in the blood current, the amount of deviation being proportional to the velocity. It is essentially the same kind of instrument as the hydrostatic pendulum used by engineers to measure the velocity of a current of water. Chauveau's htemo- dromometer, invented in 185H. C. Cliapman, Historv of the Discovery of the Circuhition of tlie Blood. Phila., 1884, p. ^A. '^ Claudii Galeni, Opera Omnia, Venetiis, 1556. DISCOVERY OF CIRCULATION OF THE BLOOD. 337 2. The arteries carry blood during life, not air. Galen, A. D. 165.^ 3. The pulmonary circulation. Servetus, 1553." 4. The systemic circulation. Cffisalpinus, 1593.^ 5. The pulmonary and systemic circulations. Harvey, 1628.^ 6. The capillaries. Malpighi, 1G61.^ While it is true that Harvey did not demonstrate the circulation of the blood, never having seen the capillaries, he saw the blood circulating in the mind's eye for he argued that more blood passes through the heart in a given time than can be accounted for by the quantity of the blood in the vessels ; hence the blood must pass and repass through the heart, and in estimating the amount of blood flowing from the left ventricle into the aorta during a short period of time even, the same blood must necessarily be counted over and over again. Again, after noticing the pulsating heart in the snake as it ap- peared after the animal had been opened, Harvey calls attention to the fact that if the vena cava be compressed it gradually empties itself between the point of compression and the heart ; whereas, if the aorta be compressed, it becomes distended between the heart and the point of compression, showing conclusively that the blood in the vena cava flows from the periphery towards the heart, whereas the blood flows in the aorta from the heart towards the periphery. If the great classic of Harvey contained nothing more than the arguments just advanced, they alone would have sufficed to have established the doctrine of the circulation, even though Harvey was obliged to assume, to complete his theory, that the blood passed from the arteries to the veins by anastomosis of ves- sels or by porosities of the flesh and solid parts that are pervious to the blood *" the capillaries not having been then discovered. ' Galenus, Ebenda, cap. 6. 2 Christianismi Eestitutio, MDLIII. ''De Plantis Libri, Florentine, 1583, Lib. 1, Cap. II., Qusestionum Medicaram, Venetiis, lo93, Lib. II. ^Exercitatio anatomica de motu cordis et sanguinis in animalibus, Francofurti, MDCXXVIII. Prelectiones Anatomife Universalis, London, 1880. ^ Opera Omnia, Lug Bat, 1687. ^ "Aut anastomosin vasorum esse, aut porositates, carnis & partium solidarum, pervias sanguini esse." Harvey, Exercitatio, Cap. xi., p. 51. 22 CHAPTER XX. RESPIRATION. We have seen that all vital activity is accompanied by waste, that mental, mnscnlar, and secretory action, and the production of ani- mal heat, involve the development of carbon dioxide, urea, etc. Sncli principles produced through the decomposition of the food and tissues, if retained in the system soon cause death, hence the neces- sity of their being eliminated ; excreted. As the degree of vital activity is conditioned by that of the cell, of fermentation, oxida- tion, etc., and as it is through respiration that oxygen is absorbed, and carbon dioxide exhaled, it is evident that this function is both absorbing and excretory in character, and must constitute a most important part of nutrition. As might be expected, therefore, the absorbing of oxvgcn and elimination of carbon dioxide are not necessarily limited to any part of the body, but may go on in every part of it. Further, while the carbon dioxide excreted is, to a con- siderable extent, due to the combination of the oxygen absorbed with the carbon of the body, there is no reason to suppose that the carbon dioxide excreted at any one moment is produced through the combustion of the oxygen supplied by the air inspired at that moment. On the contrary, the oxygen may have been locked up in the tissues, and supplied, not from the lungs, but from a diifer- ent part of the economy altogether. In fact, an animal will exhale carbon dioxide in an atmosphere of hydrogen. Under such circum- stances, the oxygen of the carbon dioxide must have been absorbed at some previous period. In the widest sense of the term respiration may then be consid- ered as the process by means of whicli oxygen is absorbed by the system, and carbon dioxide is excreted, whatever may be the source of the latter. It is often said that, while animals inhale, plants ex- hale oxygen, and that animal and vegetable life stand, therefore, in a complementary relation to each other. In one sense this is true, since green plants under the influence of solar light decompose car- bon dioxide and water, giving up the oxygen and appropriating the carbon, elaborating the latter into starch, fat, cellulose, etc. Ani- mals, on the other hand, through the absorption of oxygen, burn the carbon of their food produced by plants, and exliale carbon diox- ide. This antithesis between plant and animal life exists, however, only so long as the plant is regarded as the means by which inorganic matter is combined in a form suitable as nutriment for the animal. When, however, the remaining phenomena of plant life are con- sidered, such as the germination of the seed, the expansion of the STRUCTURE OF RESPIRATORY ORGANS. 339 leaf, the butlding and flowering, the movement of the sap, it will be found that all such depend uj^on the absorption of oxygen, and cease when the plant is deprived of it. Respiration, therefore, is as important a function in plant as in animal life. The phenomenon of respiration or breathing in animals is usu- ally associated with the presence of specialized organs, like lungs, gills, etc. Such structures are, however, not indispensable for the performance of this function, since the muscle of a frog, when sep- arated from the animal and drained of its blood, will absorb oxy- gen and excrete carbon dioxide as long as the muscle retains its irritability. There are, indeed, two kinds of respiration, an in- ternal one, taking place in all parts of the body, the tissues giving up to the blood the carbon dioxide generated in them, and absorb- ing oxygen from it, and an external one, the blood giving up to the atmosphere through the lungs or skin its carbon dioxide and re- ceiving oxygen. It is the latter form, or external kind of respira- tion, ordinarily known as breathing, that we propose considering more particularly at present. A respiratory organ consists essentially of a membrane separat- ing tissue or blood, containing carbon dioxide, on the one hand, from the atmosphere, or some other medium containing oxygen, on the other ; the membrane being of such a character as to permit of osmosis. It may be mentioned in this connection that a convenient method of illustrating the osmosis of carbon dioxide and oxygen through a membrane is to immerse a pig's bladder filled with venous blood in a bell-jar of oxygen, the carbon dioxide readily pass- ing through the membrane into the oxy- gen, and the latter in the reverse direction into the venous blood. Whether the animal be aquatic or ter- restrial, simple or complex, the respira- tory organs are only modifications of this simple membranous type of structure, and this will be found to be true, as they ap- pear in the form of skin, gills, tracheie, or lungs. Thus, in many of the lower forms of life, as in the hydrozoa and ac- tinozoa, of which the jelly fish (Fig. 164) and anemone are familiar examples, sim- ply formed animals, in which the diifcr- eutiation of the functions, or the division of labor is not carried to any great extent, respiration is effected by the general cutaneous surface, the skin readily permitting an ex- change between the oxygen dissolved in the sea-water and carbon dioxide developed within their bodies. In many animals such as the Mollusca (Fig. 165), fishes, perenni- FiG. KU. ^-^i^^t^, Jellv fish. 340 EESPIEATION. branchiate batrachia (Fig. 16G), the respiratory organs assume the form of gills, delicate membranons-like structures, whose thin walls readily permit of an osmosis between the oxygen of the sur- roundinof water and the carbon dioxide of the blood. Fig. 165 Fig. Head and gills of mcnobrauchus. Another form of respiration is the tracheal. This is seen in insects, centipedes, etc., and consists of innumerable delicate mem- branous branching tubes or tracheae, ramifying throughout the entire body of the animal, and which, opening externally by lateral apertures, the spiracles or stigmata, permit the entrance of the air. Finally in batrachia, reptiles, birds, and mammals, including man, respiration is effected by the skin and lungs. The action of the skin as a respiratory surface Avill be considered with its other func- tions, and before describing the lungs in man, let us consider a more simple type of lung — that of the frog, for example. The lungs of the frog (Fig. 167) consist of two vascular bladder- like sacs, communicating directly by short bronchi, or rather bron- chial openings, with the larynx. On opening the lung the inner surface (Fig. 168) will be seen to be more or less honeycombed, and the alveoli subdivided into still smaller spaces, or cells. These cells all communicate with the central pulmonary cavity, and are lined with a capillary network intermediate between the arterioles running along the attached borders of the septa and the venules along the free borders. It is evident that a far greater extent of vascular surface is exposed to the air, by this segmented or honey- combed disposition of the inner surface, than if the latter was smooth. If the lungs of the frog be now compared with those of a lizard or turtle, the only noticeable difference is that this segmen- tation of the lung is more marked, while in birds and mammals it is carried to such an extent that each lung consists essentially of an immense number of these honeycombed sacs subdivided into cells, the extent of the vascular space exposed to the air being, therefore, enormously increased. The respiratory organs in man, in the widest sense of the term, include the nares, mouth, pharynx, larynx, trachea, lungs, thorax, and appro])riate muscles. That the nares, not the mouth, constitute the natural entrance for the air to the lungs is shown by the foct that in certain mammals breathing ACTION OF NARES. 341 is accomplished through the nares alone. Thus in the cetacea, of which the whale, dolphin, porpoise, etc., are examples, the soft pal- ate is very much developed and so disposed to embrace the glottis and maintain the cavity of the larynx in communication with the posterior nares, a free passageway, however, being left on either side for the food. Such a disposition of the parts makes it possi- ble for the elephant to use its nose or trunk, pharynx and larynx as a siphon to suck up its drinks and transfer the same to the mouth, at the moment that the latter is open the posterior nares communicating with the glottis only. In the horse, camel, etc., the soft palate is also well developed, and surrounds the large epi- FiG. 167. Fig. 168. Luug of frog, shon'-iug its internal sur face. (Dalton. ) glottis to such an extent as to cut off completely all Respiratory organs of a frog, as scon on their interior COmmUuicatioU bctWCen the surface, a. Hyoiaeau apparatus h. Cartilaginous riug mOUth and the pliarVUX, ex- at the root of the lungs, c. Pulmonary sacs, covered '■ ' n i with vascular ramitications. (Dalton.) CCpt at the momCUt 01 deg- lutition. Indeed, in the horse, if the facial nerves which supply the muscles of the external nares be divided, the animal dies from asphyxia. In describing the structure of the hippopotamus, the author called attention ^ to the fact that when the animal passes under the water, the larynx is so elevated within the pharynx that a continuous passage is offered to the air from the external nares to the lungs, enabling the animal to breathe when almost entirelv submerged. A similar elevation of the larynx is seen in the young kangaroo, and to a certain extent, also, in the human foetus and infant. The ill effects often experienced in breathing through the mouth in a cold, dry atmosphere further prove that the natural entrance to the respiratory tract is the nose, since the air as it passes over the partly ciliated moist and very vascular and warm mucous mem- brane lining the nasal cavities absorbs water, and is elevated to the temperature of the body before entering the lungs. The action of the nares in ordinary breathing is n-ot very apparent, but when the iH. C. Chapman, Proc. Aoad. Nat. Sciences, p. 130. Philadelphia, ISSl. 342 RESPIRATION. breathing becomes labored, then it is very evident. The air having passed the nose and the pharynx, enters the larynx, a triangnlar- like structure surmounting the trachea and consisting of sufficiently Fig. 169. Fig. 170. Human larynx, viewed from above in its ordi- nary post-mortem condition. 5. Vocal mem- branes. 1. Thyroid cartilage. 4. Arytenoid cartilages. 0. Opening of the glottis. The same, with the glottis opened by separa- tion of the vocal cords. 5. Vocal membranes. 1. Thyroid cartilage. 4. Arytenoid cartilages. 0. Opening of the glottis. ( L).iLTOX. ) rigid cartilages to resist atmospheric pressure united by ligaments and movable through muscles. The detailed structure of the larynx we will defer till our account of the voice, considering at present only such of its parts as influence respira- FiG. 171. tion. The larynx is lined with mucous membrane, continuous with that of the pharynx ; the epithelium, hoAvever, ex- cept that covering the vocal cords, is of the ciliated, columnar variety, the move- ment of the cilia being from below, up- ward. If the larynx be viewed from above (Figs. 169, 170), or in section (Fig. 171), it will be observed that it is divided into an upper and lower com- partment by the rima glottidis (0), or the aperture of the glottis, a triangular- like orifice, the sides and base of which are formed by the true vocal cords (Fig. 171) (5, 6) and arytenoid cartilages (4). The vocal cords, or, more properly, the vocal membranes, consist of elastic tissue covered Avith very thin mucous mem- brane, and extending from the thyroid cartilages (Fig. 171, 1 and 2) anteri- orly, to the cricoid (3), and base of the arytenoid cartilages (4) posteriorly. The up])er edges of the vocal membrane extending from the reentering angle of the thyroid carti- View of the vocal membrane. 1. Left half of the thyroid cartilage. 2. Right lialf turned forward and partly cut away. 3. Cricoid carti- lage. 4. .'Vrytenoid cartilages, o. Right half of the vocal membrane, '(i. Upper l)order of the left half. 7. Arytenoid muscle. The upper bor- ders of the V(jcal membrane, e.\- tended between the arytenoid car- tilages and tlie thyroi;li ^^llich the inspired air ultimately passes to the air cells. The air cells, amounting to 725 millions in number/ and representing an area of nearly two hundred square meters (2000 feet), are polyhedral sacs, surrounded by anastomosing elastic fibers, and consist of a fibro-elastic wall, containing, probably, some mus- cular fibers, and lined with a tessellated epithelium. The epithe- lium is more homogeneous and easily demonstrated in the foetus than in the adult. If the primary lobule of the human lung be now compared with the lung of the frog, it will be seen that it rep- resents the entire frog's lung in miniature. The primary lobules of the human lung unite through connective tissue into larger second- ary lobules, and the latter uniting, constitute a lung. The polyhe- dral markings upon the surface of a lung indicate the margins of the secondary lobules, while careful examination will disclose also the outlines of tlie primary lobules composing the secondary ones. Finally, the integration of the primary lobules into the secondary ones, and the latter into lobes, is carried still further into the left lung than in the right, the former consisting of two lobes, the latter of three. While tlie lungs are nourished by the bronchi, it is by means of the pulmonary arteries that the venous blood is carried to them from the right side of the heart and aerated. The pulmonary artery arising, as we have seen, from the right ven- tricle of the heart, soon divides into a rijrht and left l)ranch for either luns:. Following the bronchus and bronchial tubes, the artery divides and subdi- vides, the branches becoming smaller and smaller as they approach the primary lobules (Fig. 17o), until finally they terminate as the pulmonary capillaries. The terminal arterial capillaries sur- round each alveolus or air cell as a vascular circle, which anasto- moses with those of the adjacent alveoli. From these vessels arise a capillary network (Fig. 175), so closely set that the meshes are even smaller than the diameter of the vessels themselves, the latter having usually a diameter of from J^ to 2^^^- of a mm. (2 oV"o ^^ 5 oVo ^^ ^" inch). This network supports the bottom of each air ceil, and the blood that it carries is separated from the air of the cells only by its wall and the extremely delicate epithelial lining of it. The carbon dioxide of the venous blood conveyed to the lungs by the pulmonary artery is thus separated from the oxygen of the air within the air cells brought by the trachea by nothing but the wall of the capillary and epithelium of the air cell. The rapidity with which the osmosis of these gases takes place through such a 1 Landois, op. cit., p. 190. Diagram of two primary lobules of the lungs, magnified. 1. Bronchial tube. 2. A pair of primary lobules connected with tibro-elastic tissue. 3. Intercellular air passages. 4. Air cells. 5. Branches of the pulmonary artery and vein. (Leidy.) 348 RESPIRATION. delicate septum will, therefore, be readily imagined ; the osmosis being still further insured through the great vascularity of the parts, the respiratory surface being thereby continually kept moist, which greatly promotes the exchange of the gases. The full influence of the air upon the blood is further secured in that the capillary plexus is so disposed between the walls of two adjacent air cells that one of its surfaces is exposed to each. It has been estimated^ that a thin layer of blood of 150 square meters (1500 feet) is exposed in the lungs to the air of the air cells, and that this blood, amounting to perhaps 2 liters (3.4 pints), is renewed 10,000 times in twenty-four hours. This estimate is based upon the assumption that the surface of the capillaries is equal to about three-fourths the surface of the air cells. That this is not an exaggeration may be inferred from the fact of an injected lung appearing to consist of nothing but capillaries. From the capillary network surrounding the air cells the pulmonary veins arise, which, uniting wdth each other, gradually form four larger trunks, which finally terminate in the left auricle of ^^^'- ^'^- the heart and convey to it the aerated oxygenated blood to be distributed, as we have seen, by the arterial system to all parts of the body. Having described the pulmonary air cells and blood vessels, the passage by osmosis of the carbon dioxide from the blood into the air cells and of the oxy- gen from the air cells into the blood, let us now consider the means by wliich ^,. ... f , , the air is drawn into the lunffs and Diagrammatic view of i)leiiral sacs. o expelled from them. Tlie heart and lungs are suspended by the great blood vessels in the thoracic cavity. The thorax consists of the sternum ante- riorly, the dorsal vertebra posteriorly, and the ribs laterally. It is covered in above by the cervical muscles and fascia, below by the diaphragm, and laterally, etc., by the intercostal muscles. The thoracic cavity is therefore air-tight. If the lungs be examined in Situ, it will be found that the surface of each lung is covered with a serous membrane continuous with that lining the inner surface of the thorax or tlie pleura. To understand the relations of the pleurse to the lungs and walls of the thorax, let us first conceive the pleura as consisting of two bladders (Fig. 176), and so placed within an empty thorax that the outer wall (c) of each bladder will adhere to the inner surface of the wall of the thorax, the inner walls (r?) of each bladder remaining free. Suppose now that the heart and lungs be inserted between the inner free walls of the two bladders, and that each of the latter be made to adhere to the surface of the lung with which it is in con- 1 Kuss, Physiologic, 1873, p. 338. THE PLEURAL SACS. 349 Diagrammatic view interi)Osed. )f pleural sacs with heart and luugs tact. Such a disposition being made (Fig. 177) the bladders will then represent the two pleurae, the inner walls {d d) the visceral layer, the outer wall (c c) the parietal layers, and the space between the layers the pleural cavities, the spaces between the bladders or the pleura constituting the mediastinal spaces, the narrow septum formed through the union of the two pleurae the mediastinum. In health the opposed sur- faces of the visceral and parietal layers of the pleura are always in con- tact, there being only fluid enough between them to insure their gliding smoothly over each other. Practically, therefore, in normal respiration there is no pleural cavity. This must necessarily be so, since the thorax being an air-tight cage, as it dilates through the action of the inspiratory muscles and recedes from the lungs, the air within the latter will expand and push the lungs after the re- ceding thorax and so keep the visceral layer of the pleura in contact with the parietal one. The air within the lungs becoming rarefied at the same time through expansion, the external denser air will pass through the trachea into the lungs until the pressure of the air within the latter is the same as that of the atmosphere. It will be observed that while it is the force of the inspiratory muscles that dilates the chest, it is the pressure of the air that expands the lungs, and, fur- ther, that inasmuch as the lungs are elastic and therefore otfer a re- sistance to their expansion, the air must overcome this resistance, and hence the pressure exerted by the air within the lungs upon the heart and blood vessels, etc., outside of them must be less than that of the external atmosphere. Thus, suppose, for example, that the pres- sure exerted by the atmosphere as measured by the barometer be 760 mm. of mercury, and that at the end of a quiet inspiration the pressure exerted by the elastic tissue of the lung amounts to 9 mm. of mercury, then the pressure of the air within the lungs, that is, the intra-pulmonary pressure as exerted upon the blood vessels outside of the lungs would amount to 751 mm. of mercury, the latter, or the intra-thoracic pressure, as it is called, being equal to the difference between the intra-])ulmonary and elastic pressures (760 — 9 = 751). It should be mentioned, however, that as the elastic tension exerted by the lungs is proportional to their dis- tention, that is to the depth of the inspiration, the intra-thoracic pressure maybe much less than in the example just given, amount- 350 RESPIRATION. ing to only 720 mm. of mercury ckiring forced inspiration, the elastic tension then being as much as 40 mm. of mercury (760 — 40 = 720). On the other hand as the thorax contracts, and its capacity diminishes, the air within the lungs, exerting now a greater pressure than the air without, will pass out of the lungs, through the trachcffi by which it had just entered the lungs, of course col- lapsing, their elasticity now aiding the expulsion of the air to the same extent as it formerly opposed its entrance. After what has just been said it is obvious that the intra-pulmo- nary j^ressure or the pressure excited by the air within the lungs is, during inspiration, negative, that is, less than that of the atmos- phere, since the external air then passes into the lungs, whereas dur- ing expiration it is positive, or greater than that of the atmosphere since the air then passes out of the lungs. On the other hand the intra-thoracic pressure, or the pressure of the air within the lungs, on the blood vessels, etc., outside the latter will be negative, both during inspiration and expiration, since as long as there is any air in the lungs the pressure exerted by it on the outside of the latter will be more or less neutralized by the pressure exerted by the elastic pulmo- nary tissue. If, however, expiration be forced, as in obstruction of the respiratory passages by violent coughing, for example, the air in the lungs luay be so compressed as to exert a pressure upon the blood vessels outside the lungs as suffices not only to neutralize the elastic tension of the pulmonary tissue, thus rendering the pressure equal to that of the atmosphere, but even to elevate the mercury 80 mm. higher and of so making the intra-thoracic pressure posi- tive, or higher than that of the atmosphere. As a still further proof that the lung is pushed out by the air within it and not pulled out by the receding chest wall it may be mentioned that if a hole be made in the chest the lungs will collapse, however forcible the inspiratory movements of the chest may be, since there is noth- ing to oppose their elastic tension, the atmospheric pressure being exerted equally on both the inner and outer surfaces of the lungs. The action of the thorax and the lungs in respiration was long ago compared by Boyle ^ to a bellows without a valve, but with a bladder within. According to Boyle, who appears to be the first to have comprehended how respiration is accomplished, the air is drawn into the lungs as the thorax expands just as the air was drawn into the bladder as the bellows dilates and expelled from the lungs as the thorax contracts as the air is expelled from the bladder as the bellows contracts. The dilatation of the thoracic cavity and the taking in of the air is known as inspiration, the contraction of the thoracic cav- ity and the giving out of the air expiration, the two acts constitut- ing respiration. Let us consider now a little more in detail tlie means by which this alternate dilatation and contraction of the thoracic cavity caus- ing respiration is eifected. 'Works, Vol. i., London, 1744, p. G4. CHAPTER XXI. EESPIEATION.— (Con/m»ef^) MUSCLES OF RESPIRATION. Reflection iipou the origin and insertion of the various mus- cles acting upon the thorax makes it evident that some of these muscles in contracting will expand the chest, causing inspiration, while the relaxation of these muscles, together with the elasticity of the lungs and the action of certain other muscles, will contract it, causing expiration. The muscles involved in the production of respiration will then natiu'ally divide themselves into two groups, those of inspiration and those of expiration. To the study of these let us now turn. Inspiration Of all the inspiratory muscles the diaphragm is the most impor- tant, since the capacity of the chest is enlarged to a greater extent through its contraction than by that of any other muscle. Indeed, in the male sex at least, as we shall see, gentle breath- Fig. ITS. ing is accomplished almost entirely by the action of the diaphragm. The diaphragm being attached (Fig. 178), to the ensiform cartilage of the sternum, to the carti- lages of the six or seven lower ribs, and often, also, to their osseous portions to the arcuate ligaments and the bodies of the first, second and third lumbar vertebra?, to the invertebral cartilages of the right side, and to the bodies of the first and second lumbar vertebrae, etc., of the left (the crura?) covers in therefore the lower circum- ference of the thorax. From this origin the diaphragm passes upward into the cav- ity of the thorax as a vaulted arch or dome (Fig. 179, B), the cen- tral tendon being the common point of insertion of the muscular fibers wdiicli are of the voluntary character. The diaphragm pre- Interior view of the diaphragm. 1, 2, .3. The three lobes of the central tendon, surrounded by tlie fleshy- fasciculi derived from the inferior margin of the thorax, the crura, 4, .5, and the arcuate ligaments, 6, 7. 8. Aortic orifice. 9. QSsophageal oritice. 10. Quadrate foramen. 11. Psoas muscle. 12. Quadrate lumbar muscle. 352 BESPIRATION. sents several openings through which pass the oesophagus, aorta, vena cava, etc., and is supplied by the phrenic nerve. During the state of repose, as we have just seen, the diaphragm presents the form of a dome or of a vaulted, arched, or curved surface. If the diaphragm, however, be observed during contraction, as can be readily done by opening Fig. 179. largely the abdominal cav- ity of a completely insen- sible living mammal, a cat, dog, or rabbit, for example, it will then be seen that through the contraction of its muscular fibers the curved surface of the dia- phragm assumes more the form of a plane (Fig. 179, A), and that the floor of the thorax descends, the cardiac part more particu- larly from 5 to 40 mm., according to the depth of the inspiration. The effect of the descent of the dia- phragm is, therefore, to en- large in a vertical direction the capacity of the thorax, Diagrammatic sections of the body in inspiration and and tO rarefy thc air within expiration. A. Inspiration. B. Expiration. Tr. Tra- •, rpi , 1 • 1 • chea. St. Sternum. I). Diaphragm. Ah. Abdominal it. 1X16 CXtemal air DCing rHuxLEY." ''"'"^'"^ """^'"^^ ''""''''"' *"' stationary air. ^j^^^^ dcnSCr tliau that withiu the lungs rushes into the latter and proportionally distends them in consequence. The dia- phragm through its contraction acts then as an inspiratory muscle ; it need hardly be added, however, that it is not the diaphragm, but the air, that actually distends the lungs. The author is in the habit of illustrating the action of the diaphragm in respira- tion by the simple apparatus represented in Fig. 180. This con- sists of a bell-jar («), the walls of which correspond to the thorax, and in which are suspended the lungs {LL), the trachea (2) pass- ing through the air-tight fitting cork. The bottom of the jar is closed in air-tight, with India rubber (5) corresponding to the dia- phragm. It is needless to say that there is no such amount of space as (r?) corresponding to the pleural cavity in the human being in a state of health. Such being the disposition of the parts, by pulling down the India rubber (5) the air within the jar will be- come rarefied as indicated by the rise of the mercury in the ma- nometer, the lungs LL will ox])and, and the external air will pass into the latter until the pressure is tlie same as that of the atmos- phere. With the elevation of the India rubber the condition of THE DIAPHEAGM. 353 Diagrammatic view of apparatus to show the action of the diaphragm. the pressure of the air ^vithin and witliout the jar being reversed, the air will pass out of the lungs, the latter collapsing. As the diaphragm descends it pushes downward and forward the abdomi- nal viscera, and as the anterior and lateral walls of the abdomen are extensible, they give way to the pressure so exerted and are protruded. With each inspiration, therefore, the descent of the diaphragm in man becomes perfectly evident through the movement of the abdomen. The action of the diaphragm in producing in- spiration may be readily imi- tated in man and mammal Fig. 180. just dead, by opening the abdomen and pulling the central tendon downward. The external air will rush into the lungs, and often ■\^-ith a distinctly audible sound. While the vertical diameter of the chest is en- larged throuo;h the descent of the diaphragm, neverthe- less, through the attachment of the latter to the sternum and false ribs, during its contraction through the pulling of the sternum and the upper false ribs downward and inward, and the lower ribs upward and in- ward toward the vertebral column, there would be a tendency to diminish, to some extent, the capacity of the thorax. This effect is, however, counteracted by the ribs being elevated at the same time as the diaphragm descends, and through the action of cer- tain muscles, to be described later. The elevation of the ribs is such a constant accompaniment of the descent of the diaphragm that in general terms it may be stated that inspiration is effected by the descent of the one, and the ascent of the other, and this is true, even though the breathing appear entirely diaphragmatic. The ribs (Fig. 181) pass from their articulations with the dorsal vertebrae downward and forward ; they are somewhat twisted in shape and are twelve in number. The upper seven or true ribs are articulated -^rith the sternum ; of the remaining five or false ribs, the eighth, ninth, and tenth are joined to the seventh rib, the last two ribs, viz., the eleventh and twelfth, are unattached anteriorly, and are hence known as floating ribs. As the ribs are elevated they recede from each other, the intercostal spaces, with the exception of possibly the first two, being widened. At the same time they are rotated outward, assuming a more horizontal position, and in tend- ing to straighten themselves become less curved. Through their attachment to the sternum the lower portion of the latter is thrown forward, the flexibility of this part of the thorax being mainly due to the sternal attachment of the ribs beino; cartilao-inous and not 23 354 RESPIRATION. osseous. The effect of this change in the form, position, and direc- tion of the ribs and sternum is to enlarge the capacity of the chest in every direction, vertically through the separation of the ribs, laterally through their rotation outward and straightening, antero- posteriorly, through the movement forward of the sternum. As the external air passes then into the expanding lungs, it is evident that inspiration is produced through the elevation of the ribs as well as through the descent of the diaphragm. The extent of the increase of the capacity of the chest through the elevation of the ribs is greatly influenced by the length, degree of curvature, character of the angles of the ribs, etc. Thus from the ribs being directed obliquely downward and forward when elevated, and as- suming a more horizontal posi- FiG. 181. tion their external ends recede from the posterior wall of the thorax and increase proportion- ally its antero-posterior diam- eter. As the ribs are elevated they remain nearly parallel to each other ; it follows, therefore, that the inspiratory effect pro- duced by this movement of the ribs will be proportional to the length, or, more accurately speaking, to the length of the chord of the arc represented by the curve of the rib. This length, however, varies consid- erably, increasing rapidly from the first to the fifth rib, attain- ing its maximum at the eighth rib, diminishing then progres- sively from the ninth to the twelfth. Other things being equal, it follows, then, that the increase in the antero-posterior diameter of the chest is greater at the level of the seventh to the ninth ribs than at the upper or lower part of the thorax. It is for this reason that during inspiration the inferior portion of the sternum moves so much more forward than the upper portion. The transverse diameter of the chest, on the other hand, is greatly in- fluenced by the amount of the curvature of the ribs, and this varies considerably. Thus the curvature increases from the first to the third ribs, the maximum amount being about that of the sixth ; there is but little difference, however, as regards the curvature of the ribs included between the sixth and ninth. The amount of the curvature can be measured by the versed sine of the arc of the circle represented by the rib, or, what is the same thing, the dis- Front view of the thorax. 1, 2, 3. The three pieces of the sternum. 4, 5. The dorsal vertebrae. 6. The first true rib. 7. Its head. 8. Neck. 9. Tubercle. 10. The seveuth true rib. 11. Costal cartilages. 12. The Hoatiug ribs. 13. Groove for the intercostal blood vessels. ACTION OF THE BIBS. 355 tance from the middle line of the thorax to the most prominent part of it laterally. The angle made by the osseons part of the ribs with their sternal or costal ones, and the length of their car- FiG. 182. Dorsal regiim. Expiration. lu.spiration. Fig. 183. Anterior region of the thorax. Inspiration. Expiration. Fig. 184. Fig. 185. Expiration. Inspiration. tilaginons portions increase from the fonrth to the seventh. Con- sequently, it is in this part of the thorax that the increase of capacity 356 RESPIEA TION. due to the elasticity and flexibility of the cartilage is greatest. The different extent to which the capacity of the thorax is enlarged in its various diameters during inspiration, the influence due to the variation in the length, curvature of the ribs, etc., are shown by the diagrams (Figs. 182, 183, 184, 185) illustrating the admirable and exhaustive "svork of Sibson.^ Let us consider now the muscles which elevate the ribs, and so, together with the action of the dia- phragm, cause inspiration. Muscles of Eespiratiox. Inspiration. Expiration. Ordinary. Diaphragm ..... Internal intercostals, osseous portion. External interco.stals. Internal intercostals, sternal portion. Triangularis sterni. Scaleui ...... Infra costales. Levatores costarum. Auxiliary. Serratus posticus superior . . Oblique. Accessorius ..... Transversal is. Sterno-cleido-mastoid . . . Sacro Lumbalis. Levator anguli scapulte. Trapezius, superior portion. Serratus magnus. Pectorales major, inferior portion. Pectorales minor. These muscles are usually described as consisting of two sets, ordinary or extraordinary, or auxiliary, according as the breathing due to their action is easy or forced. There is, however, no such sharp line of demarcation observable, it being impossible to say just where ordinary easy breathing ends, and forced breathing begins, great difference being observed in this respect within the limits of health, according to individual peculiarities. There are certain muscles, however, such as the external intercostals, scaleni, etc., w^iich intervene in easy inspiration ; these we will consider first, and afterward those coming into play when the breathing is ex- aggerated. That the external intercostal muscles (Fig. 186, 2) are inspiratory in function one would infer from their attachments, and the direction of their fibers. Passing from rib to rib from above downward, and from behind forward, in contracting these muscles, will approximate and elevate the ribs. Experiment justifies this view of the inspiratory function of the external intercostal muscles, since, if they be expo.sed in a living animal Avith each insi^iration, they will be seen in contracting to elevate the ribs. Inasmuch, however, as the general direction of the sternal portion of the inter- nal intercostals is also from above doAvnward, and rather forward than l)ackward, through the change in the curve of the rib, analogy would lead us to suppose tliat their action is the same as that of the 'Phil. Trans., 1846, p. 501. INSPIRA TORY MUSCLES. 60 i external intorcostals, and that they must, therefore, be also regarded as inspiratory in function. This view is confirmed by the observa- tions of Berard/ made upon a man in whom the pectoral muscle was so atrophied as to permit of an experimental investigation of the function of the partly exposed sternal portion of the internal intercostal muscle. When the sternal part of the muscle was stimu- lated, the cartilage of the second rib was elevated, and with it the anterior extremity of the corresponding osseous rib. The scaleni passing obliquely downward from their origin, the transverse processes of the lower six cervical vertebne, to their insertion, the first and second ribs, in acting from their Fig. 186. orisfin during; contraction will elevate these ribs, and indi- rectly the whole thorax. To prove that the scaleni do act in this way it is only neces- sary to sc£ueeze between the fingers the part of the neck including these muscles to feel them contract Avith each inspiration. The movement then experienced, the so- called respiratory pulse of Magendie,- becomes very evident when the superior part of the chest is much di- lated. The action of the scaleni is not only to elevate the ribs, but to fix the first rib as an origin from which the intercostal muscles that elevate the ribs can act. Ordinarily inspiration is also effected by the levatores costariun (Fig. 186) as these muscles, arising from the transverse processes of the twelve dorsal vertebrae, and in- serted fan-like into the upper edges of the ribs between the tu- bercles and the angles in contracting, elevate the ribs. The action of the muscles, which we have just considered, usually suffices to produce easy inspiration. When breathing, however, becomes difficult, labored, or very difficult, then inspiration is aided through the contraction of several muscles, the serratus posticus superior, accessorius, sterno-cleido-mastoid, levator anguli scapulae, superior portion of the trapezius, serratus magnus, and the pectoral muscles. It is not necessary to dwell upon the anatomical disposition of these muscles to prove their importance in labored inspiration. It is evident that the serratus posticus superior passing trom the ^ Physiologic, Tome iii., p. 269. ^Precis elementaire de physiologie, 2(1 ed., Tome ii., p. 323. View of several of the middle dorsal vertebra and ribs, to show the intercostal muscles (A, B). J^. A. P'rom the side. B. From behind. 1, 1. The levatores costarum muscles, short and long. 2. The external intercostal muscles. 3. The internal intercostal layer shown, in the lower of the two spaces repre- sented, by the removal of the external layer, as seen in A in the upper space, in front of the external layer. The deficiency of the internal layer toward the ver- tebral column is shown in B. (After Cloc^uet. ) 358 RESPIRATION. vertebral column to be inserted into the second, third, fourth, and fifth ribs, will, in contracting, elevate the ribs, that the accessorius, extending from the last cervical vertebrae to the angle of the ribs, will produce the same effect. The sterno-cleido-mastoid acts upon the clavicle and sternum, and the levator anguli scapulse, trapezius, and serratus magnus, through the scapula. Finally, the upper ex- tremities being fixed, the pectoral muscles, reversing their action, will elevate the ribs, their force under such circumstances acting upon the thorax instead of from it. The serrati postici inferiores and quadrate lumborum muscles are regarded by some physiologists as aiding the muscles just mentioned in deep inspiration ; according to others, these muscles are expiratory in character. Expiration. Expiration is essentially a passive process, consisting in the re- turn of the thorax to the condition in which it was before inspira- tion. The ascent of the diaphragm, and the descent of the ribs in diminishing the capacity of the thorax, cause the expulsion of the air, or expiration. The relaxation of the inspiratory muscles is, however, accompanied by the contraction of certain muscles which together with the elasticity of the lungs aids in expelling the air from the chest. Inasmuch as the fibers of the osseous portion of the internal intercostal muscles (Fig. 186) pass from rib to rib in exactly the opposite direction as those of the internal intercostal — that is, from above downward, but backward — we would naturally conclude that in contracting they would depress the ribs instead of elevating them, that their function is expiratory instead of inspira- tory. Experiment proves that this view is correct, since, if the osseous portion of the internal intercostal muscles be exposed in a living animal by dissecting off the external ones, they will be found to contract during expiration. This antagonism in the ac- tion of the internal and external intercostal muscles may be illus- trated by a simple mechanical arrangement known as Hamberger's apparatus, though it was really invented by Bernouilli. This con- sists (Fig. 187, A) of two bars (a and h), which are attached on the one hand to a long vertical rod (c) firmly supported, and, on the other hand, to a short one {d). The two bars, tlie long and the short vertical rods, represent respectively the spinal column, two ribs, and a portion of the sternum. The two bars (« and 6) are maintained in the horizontal position by two elastic bands {w z and X y), which are so attached that as they pass from bar to bar they cross each other at nearly right angles. The elastic band {x y) passing from above, downward and forward, represents the external intercostal muscle, the band [w z) passing from above doAvnward, but backward, the osseous portion of the internal intercostal mus- cle. If the band {w z) be removed (Fig. 187, B), there being nothing to oppose the elasticity of the band x y, or the external intercostal muscle, the bars or ribs will be elevated. If the band EXPIRATORY MUSCLES. 359 w z be now replaced, and the band x y removed (Fig. 187, C), then the bars of the ribs will be depressed, there being nothing to oppose the elasticity of the band w z. While the action of the ex- ternal and internal intercostal muscles in respiration, as we have described them, appears to be capable of demonstration in the liv- ing animal and imitated by mechanical contrivances, nevertheless, it must be admitted that the action of these muscles has given rise Fig. 187 Diagram of models illustrating the actiou of the external and internal intercostal muscles. B. Inspiratory elevation. C. Expiratory depression. (Huxley.) to more discussion than that of all the other muscles in the body, and that the most diverse opinions have been offered, and are still held as to their function. Thus, while according to Borelli, Haller, and Cuvier, both the external and internal intercostal muscles are inspiratory, just the opposite opinion, that they are both expiratory was held by Vesalius, Beau and Maissiat Galen. Bartholinus con- sidered the external intercostals to be expiratory, the internal in- spiratory, while Spigelius and Yesling held the external intercos- tals to be inspiratory, the internal expiratory. The external and internal intercostals were regarded at once inspiratory and expira- tory by Mayow and Magendie, while according to Arantius and Cruveilhier, both the internal and external intercostals are passive in inspiration and expiration, performing simply the office of a re- sisting wall in respiration. Whatever view may be held as to the function of the internal intercostal muscles in respiration, there can be no doubt that the triangularis sterni and infracostalis, and possibly, as already men- tioned, the serratus posticus inferior, are expiratory muscles. The triangularis sterni acting from its origin, the ensiform cartilage, the lower border of the sternum, and the lower costal cartilages, in drawing down the cartilages of the second, third, fourth, and fifth ribs must diminish the capacity of the chest. The infracostales produce the same effect, their fibers passing from the inner surface of one rib to the inner surface of the first, second, and third below, their action being from below upward. The muscles that we have just described visually suffice in tranquil expiration ; in difficult or 360 RESPIRATION. labored expiration, iu the acts of blowing, phonation, etc., the mus- cles entering; into the formation of the abdominal walls also conie into play. The general effect of these muscles, viz., the external and internal oblique, transversalis, sacro-lumbalis, etc., is in con- tracting to push up the abdominal viscera and diaphragm into the thorax, diminishing its capacity in the vertical diameter ; these muscles, however, in being attached to the ribs or costal cartilages depress at the same time the ribs and consequently diminish the thorax in its antero-posterior and transverse diameters also. The effect of these muscles is, therefore, to aid powerfully in the expul- sion of the air from the chest in forced expiration, and as their action and that of the diaphragm is more or less voluntary, and at the same time opposed to each other, the intensity and dura- tion of expiration can, to a great extent, be regulated arbitrarily. The importance of this relation is well seen in singing, in performing upon wind instruments, etc., the skill exhibited depending largely upon the nicety with which the contractions of these muscles can be adjusted to each other. We have already seen that the lungs are elastic, and were it not for the pressure exerted upon the inner surface of the lungs by the inspired air the lungs would collapse in virtue of this elasticity, and a considerable space in consequence would be left between the lungs and the chest-wall. The natural tendency of the lungs to contract through their elasticity is well seen when air is allowed to enter the pleural cavities. Under such circumstances as already mentioned the atmospheric pressure being exerted equally on both the inner and outer surfaces of the lungs, there is nothing to oppose their elasticity and the lungs therefore collapse. If one end of a tube be passed into the trachea of an animal just dead, and ligated, and the other end be inserted into a water or mercurial manometer, with the entry of air through an oj)ening made into the pleural cavity the lungs will collapse iu virtue of their elasticity, the level of the liquid in the proximal end of the manometer will be observed to fall, that of the distal end to rise, the difference in the level of the two indi- cating and measuring the amount of elastic force exerted. It was in this way that Carson ^ first showed that the elasticity of the lungs in the calf, sheep, or dog would support a column of water twelve to eighteen inches in height, and in the rabbit six to ten inches, and exert a pressure in man amounting to about half a pound upon the square inch. Finally, the contractility of the bronchi and elasticity of the thoracic walls themselves contribute iu expelling the air from the chest. It is usually considered that in inspiration the upper ribs are elevated before the lower, and in expiration the lower ribs are depressed before the upper, the motion being wave-like from above downward and from below upward. According, however, to the observations of Ransome^ it would appear that the reverse ob- 'Phil. Trans., 1820, p. 29. 2.Stethometer, 1870, p. 37. DIFFERENCE OF BREATHING IN SEXES. 361 tains, the lower ribs in inspiration being elevated first and the upper ones last, and that in expiration it is the upper ribs that are depressed first and the lower ones last. Even if such is the case, it is not inconsistent with the view that the upper part of the chest is moved first in inspiration, the lowest last, since if the scaleni act before the intercostal muscles the upper ribs would be elevated be- fore the lower by the action of the scaleni, even if the lower inter- costal muscles contracted before the upper. It is possible that the difference of opinion in reference to the order in which the ribs are elevated and depressed is due to the action of the intercostal muscles being; considered without reference to the simultaneous action of the other respiratory muscles. While, in a general way, it can be said that inspiration is due to the descent of the diaphragm and the ascent of the ribs, and expiration to the ascent of the diaphragm and descent of the ribs, neverthe- less, there is a noticeable difference, described more particularly by Bean and Maissiat,^ as to the relative importance of the parts played by the diaphragm and the ribs, as observed in the breathing of the two sexes. Thus while in the male sex breathing is accomplished by the diaphragm and the inferior part of the thorax, or the portion Fig. 188. Fig. 189. The changes of the thoracic and abdominal walls of the male during resijiratiou. The same in the female. (Hutchinson.) below the sixth rib, in the female sex it is the superior part of the chest, or that above the seventh rib (Figs. 188, 189), which takes an active part in respiration. It might be supposed that the supe- rior costal type of breathing characteristic of the female is due to iArchive.s generalcs de medecine, 1843, 3d ser., t. xv., p. 397 ; 4th ser., 1843, t. i., p. 265 ; t. ii., p. 257 ; t. iii., p. 249. 362 EESPIEA TION. peculiarities of dress, such as the wearing of corsets, the squeezing of the Avaist, etc., which would interfere with or prevent even the lower part of the chest expanding,^ That this is not the only- cause, however, is proved by the fact that the superior costal t^^e of breathing prevails even in females that have never worn any kind of clothing whatever. That the superior costal type of breathing is of advantage to the female is obvious when one con- siders the extent to which the abdominal viscera and diaphragm are pushed up, as is the case during pregnancy, through the enlarge- ment of the uterus. Under such circumstances, if the breathing of the female was of the inferior costal type and diaphragmatic, like that of the male, inspiration would be difficult and labored. It is also on account of this peculiarity in breathing that women can tolerate with so little inconvenience large accumulations of fluid in the abdominal cavity. While in the adult the diaphragmatic in- ferior costal type of respiration of the male as contrasted with the superior costal type of the female is perfectly evident, the distinction in young children is not noticeable. Indeed, children under about ten years of age breathe almost entirely by the diaphragm. It is not, as a general rule, until near puberty that the distinction in breathing characteristic of the adult sexes becomes apparent. Boerhaave,' however, states that the difiFerence in the types of breathing in the sexes in some cases manifested itself as early as the first year. 1 T. J. Mays, The Therapeutic Gazette, 1887, p. 297. 2 Prselectiones Academiae, Gottingen, 1744, p. 144. CHAPTER XXII. 'RESFIRATIOS.— (Continued.) RESPIRATORY MOVEMENTS AS STUDIED BY THE GRAPHIC METHOD. XoTWiTHSTAXDiXG that the respiratory movements are evident to the eye, and that the respiratory organs can be connected with- out injury with apparatus for recording their movements, it must be admitted that the application of the graphic method to the study of respiration does not give as satisfactory results as is the case in the study of the circulation. Of the instruments devised for the recording of the respiratory movements graphically, the author has found the pneumograph and stethometer to be among the most use- ful. The pneumograph, invented by Marey ^ (Fig. 1 90), consists of an elastic plate A, which is applied to that part of the chest whose Fig. 190. Pneumograph. movements it is desired to study, and firmly secured there by tapes passing around the neck from the edge of the plate and around the chest from the pillars B and C, projecting from the plate. To the lower end of the pillar B is attached a spring (D), the free end of which is so attached that it presses against the elastic membrane covering in the lower surface of an air-drum (E), the latter com- municating through a caoutchouc tube (F), with a recording tam- bour. With the bending of the elastic plate A through the expan- sion of the chest, the pillars B and C recede from each other, the spring D cea.sing at the same time to press on the membrane of the air-drum E. The air within the drum being therefore rarefied, the air from the recording tamljour is drawn into it, and the lever at- tached to the tambour is depressed. AVith the contraction of the chest the elastic plate straightens, the pillars approach each other, the spring presses against the elastic membrane, the air is driven out ' La methode Graphique, p. 542. 364 RESPIRATION. of the drum into the tambour, and the lever is elevated. The de- pression of lever corresponds, therefore, to inspiration, the elevation to expiration. By placing the lever of the recording tambour in contact with the blackened surface of the cylinder moving by clock- FiG. 191. L'pper liue, trace of cbronogiaph. Lower line, trace of respiratory movemeuts. Takeu with pneumograph. Avork, we obtain a trace like that of Fig. 191, representing the breathing of a man set. thirty years. In this trace the distance from a to c represents one respiration ; the part of the trace from a to h, due to the descent of the lever, being inspiratory in origin, that of () to r- due to the Fig. 192. ascent of the lever expira- tory. It will be observed that the inspiratory move- ment, as recorded in its trace, a to h, is extremely abrupt, becoming more gradual at its close, and that the expiratory move- ment (1) to e) is equally ab- rupt at the beginning, but that the gradual movement at the termination is more marked even than in the case of the inspiratory movement. In order to determine accurately the number of respirations in a given time, the length of time of one respiration, the relative duration of one in- spiration and expiration ; the existence of pauses, if any, after inspiration and expiration, it is necessary to make use of some chronographic apparatus, by means of which we can record graphically the time elapsing during which the respiratory move- >retronome. METRONOME. 365 ments are being studied. For this purpose we make use of the metronome in connection with an electro-magnet. The metronome (Fig. 192) is the same as that used by musicians, except that it is con- structed that, with each beat of the pendulum a spring is elevated and depressed, to which are attached two needles, dipping into mercury- cups. This is accomplished by drawing out or pushing in a rod to which the spring carrying the needles is attached, and which, by so doing, brings the spring in contact with the periphery of either one of four wheels having a different number of cogs. The number of movements of the spring will depend, therefore, upon the particular Avheel with whose cogs it is in contact. The four wheels are ro- tated by the axis common to them, and a fifth one, Avhose motion is due to an axis, moved by clockwork, which is regulated by a pen- dulum. With the elevation of the spring the needles are raised out of the mercury in the cups, and with its depression they sink into it again. As the needles are elevated and depressed the cur- rent, passing from the battery through the needles and mercury to the electro-magnet, is made or broken, and the marker connected with the latter synchronously depressed and elevated in the manner already described. In the trace obtained by applying the marker of the electro-magnet to the blackened surface of the revolving cyl- inder as the pendulum beat at the rate of sixty seconds to the min- ute, the distance between two vertical lines represents one second, and as one respiration was performed in three seconds the number of respirations was twenty per minute, the breathing being more rapid than usual, the average number of respirations throughout the day being from fifteen to eighteen per minute. It will be observed from a comparison of the traces (Fig. 191) that the duration of one respiration was three seconds, the inspiratory part lasting one second, the expiratory two seconds, and that the expiratory lasted, therefore, twice as long as the inspiratory effort ; furtlier, that there was no appreciable pause, either after inspiration or expiration, a gradual slowing up of the movement only being noticeable after either. Finally the little undulations of the trace noticeable at the termination of expiration are cardiac in origin. The object of the stethometer is not only to record the respira- tory movements graphically, but to determine also their extent. The instrument consists (Fig. 193) of two parallel bars, the lower ends of which are firmly screwed at right angles into a crossbar so as to form a rigid frame. Through one of the bars passes a slen- der rod (B'), terminating in a convex ivory knob (B). By means of a screw the extent to which the rod and knob are pushed within the frame can be varied as needed and firmly fixed. The opposite bar carries a spring (I), the upper part of which carries a horizontal pin, terminating at one end in an ivory knob, and at the other in a brass disk, the latter being in contact with the tambour (A) attached to the upper part of the bar. The two ivory knobs not only face each other, Isut lie in the same axis. The receiving tambour com- 366 BE8PIEATI0N. municates by means of the tube J M'itli the recording portion of the apparatus, and also through the T-tube with an India-rubber ball, the latter being used to fill both tambours and communicating tube (D). The manner of adapting Fig. 193. the stethometer to the chest \Adll de})end upon the part whose movement it is desired to examine. If, for example, we wish to obtain a graphic representation of the move- ments of the chest in a trans- verse direction, let the in- strument be so applied that the ivory knobs will jjress upon the eighth rib. The knob being firmly fixed, with the expansion of the chest, the rib will press outwardly the knob of the receiving tambour, the air will be driven out of it into the re- cording one, and the lever will be elevated ; with the contraction of the chest the air will return from the re- cording to the receiving tam- bour lever, and the lever will be depressed. With the steth- ometer, therefore, inspiration corresponds to the elevation of, and expiration to the de- scent of the recording lever, just the opposite to what happens, as we have seen, when the pneumograph is used. To obtain a trace representing the enlargement of the chest in an antero-posterior di- rection, the stethometer can be applied so that the ivory knobs are in contact with the manubrium sterni and the third dorsal spine, or the eusiform cartilage and the tenth dorsal spine respectively. Fig. 194 is that of the trace obtained by the stethometer as applied to the seventh ribs in the case of a healthy man, set. 30 years, and is a graphic representation, therefore, of the respiratory movements, in so far as they depend upon the enlargement of the chest in a transverse direction in that particular part of the chest. It is not necessary to dwell upon the peculiarities of the trace recorded by the stethometer. It Avill be observed that the part of the trace from a to h corresponds to the inspiration, that from h to c to expiration, and tliat the relative duration of inspiration to ex- piration is somewhat different from that observed in the trace ob- tained by the pneumograph, the number of respirations being in Recording stethometer. A. Tympanum. B. Ivory knob. B'. Kod which carries the knob opposed to B. C. T-tube, by which A communicates, ou the one hand, with the recording tympanum, on the other with an eUistic bag (D). The purpose of the bag is to enable the observer to vary the quantity of air in the cavity of the tympanum "at will. The tube lead- ing to it can be closed by a clip. (Sanderson.) THE STETHOMETEB. 367 this case eighteen to the minute. On an average the ratio of in- spiration to expiration is as 5 to 6. In order to determine the ex- tent of the enlargement of the chest by the stethometer, the in- strument must be graduated. This can be done either by placing successively between the ivory buttons, rods differing by a known length, and observing the diff'erent levels to which the lever is ele- vated, according to the rod used, the vertical distances between the horizontal lines made by the lever corresponding to a definite in- crease in the distance between the ivory knobs of the particular di- ameter of the chest examined, or by placing directly underneath the ivory knobs a graduated rod, carrying a vertical slide, which can be pushed against the mova}:)le knob, and noticing the different heights to which the recording lever is elevated. In the trace rep- FiG. 194. upper line trace of respiratory movements taken with stethoineter. chronograph. Lower line trace of resented in Fig. 194, the elevation of the lever through the space a to b corresponds to an increase of about 2 mm. {-^^ of an inch) in the lateral diameter of the chest. AVhile in tranquil breathing the increase in the antero-posterior diameter of the thorax may be only one mm. {-^-^ of an inch) in forced breathing, according to Ransome,^ it may amount to as much as 12 to 30 mm. (i to 1.2 inch). It may be mentioned that the movements of the diaphragm can be studied graj^hically in an animal by inserting through the ensi- form cartilage or the abdominal walls a long probe, so that one end will be in contact Avith the diaphragm and the other with a record- ing lever. In describing the circulation it will be remembered that attention was called to the large undulations present in the curve of blood 'Sanderson, Handbook Phys. Lab., p. 302. 368 BESPIBA TION. pressure, and which at that time were simply stated as being, to a certain extent at least, respiratory in origin. In order to study the influence of the respiration upon the circulation, it is essential that a comparison should be made between the curves of blood pressure and respiration taken simultaneously. In the case of man this can be done by applying at the same time the cardiograph and pneumo- graph and comparing the traces so obtained, or in an animal by con- necting a recording tambour with its trachea, and comparing the respiratory trace so obtained with that of the pressure of the blood in its carotid artery, taken in the manner already described. A comparison of the traces of the respiratory movements and the blood pressure in a rabbit (Fig. 195), taken by the latter method, shows Fig. 195. Traces of blood pressure and respiratory movements of rabbit taken simultaneously. Lower trace blood jiressure. Upper trace respiratory movements. that in this case at least the inspiration is almost, if not absolutely, synchronous with the rise of blood pressure and expiration with the fall, the relation between the two naturally suggesting that inspira- tion is the cause of the one, expiration of the other. Nevertheless, reflection makes it clear that respiration on the whole favors the circulation of the blood even though inspiration promotes it to a greater extent than expiration. Let us consider in detail a little why this must be the case. During inspiration, as the chest ex- pands, the air within the lungs becomes rarefied and the external air passes through the trachea from without inward. In doing this, however, the external air has overcome the elasticity of the lungs, the pressure exerted by the air within the lungs upon the intratho- racic vessels will therefore be that of the ordinary atmospheric pres- sure, less the pressure due to the elasticity of the lungs. Suppose, for example, that the pressure exerted by the elasticity be half a pound to the square inch, then the pressure exerted by the air within the lungs upon the great blood vessels or the intrathoracic pressure will be only fourteen and a-half pounds, that of the atmos- phere being fifteen pounds. The effect of this difference of the atmospheric pressure within and without the chest during inspira- tion is tliat a greater quantity of venous blood being forced through the great veins toward the right auricle of the heart and thence through the lungs, a proportionately greater quantity of arterial blood passes, therefore, through the left ventricle into the aorta, the result of which will be to increase the blood pressure. The flow of CIRCULATION AND EESPIRATION. 369 the venous blood from the periphery to the heart being: promoted by inspiration, it might be supposed that the flow of the arterial blood in the reverse direction would be proportionally retarded. It must be remembered, however, that the pressure exerted by the extrathoracic air upon the thin, flaccid Avails of the veins will pro- duce a greater effect than upon the thick, resisting coats of the arteries, and that the pressure of the external air so exerted is not much in excess of the resistance that the heart has to overcome in driving the blood from the ventricle into the arterial system during its systole. During expiration the conditions being the reverse of those obtaining during inspiration the flow of blood through the arteries is favored, since apart from the chest being compressed, the pressure exerted by the intrapulmonary air upon the arteries out- side the lungs becomes greater in proportion as the lungs contract^ their elastic tension diminishing proportionally. On the other hand, the flow of the blood through the veins is not retarded to any great extent during expiration as the veins are somewhat dilated at the moment of the contraction of the lungs, while regurgitation is prevented by the valves. Respiration on the whole, therefore, favors the circulation, since inspiration aids the flow of the venous blood without offering any great obstacle to the arterial flow, while expiration favors the flow of the arterial blood without retarding to any extent the venous flow, and while it is true that in the influence of respiration upon the circulation, inspiration is more important than expiration, nevertheless the difference in the effect of the two Fig. 190. /---ri Comparison of lilood pressure curve with curve of intrathoracic ]ircssnre. To be read from left to riglit. « is tlic lil(i(j(l-prcssure curve, with its rcspiratiiry iniiliilatiniis, the slower heats on the descent bein^ very inarkeil. 6 is the curve of iutrathoracic prc>Miic olitaiued by connecting one limb of a manometer with the pleural cavity. Inspiration begins at /, expiration at e. The intra- thoracic pressure rises very rapidly after the cessation of the inspiratory effort, and then slowly falls as the air issues from the chest ; at the Ijeginning of the inspiratory efiort the fall becomes more rapid. (Foster.) is too small to warrant the conclusion that the large rise and fall in the blood pressure are entirely caused by inspiration, on the one hand, and expiration on the other. Further, in the dog and in the rabbit also, at times, there is no absolute synchronism between the vascular and respiratory rhythms ; in the dog, for example (Fig. 196), the rise in the blood pressure lasting not only to the end of 24 370 RESPIRATION. the inspiration, but during a part of expiration, and the fall in blood pressure lasting not only till the end of expiration, but during a part of inspiration. This want of synchronism between the rhythms, together with the fact that the large undulations character- istic of blood pressure persist even after all respiratory movements have ceased, proves that there must be some influence other than respiration concerned in their production. Thus if an animal, a rabbit, for example, be curarized, in which condition the respiratory nerves cease to act altogether, the heart continues to beat, artificial respiration be maintained and a trace of the blood pressure be taken, a curve like that of Fig. 197 will be obtained. If now the artificial respiration be discontinued the blood pressure rises, and the char- acter of the curve changes ; nevertheless, a rhythmical rise and fall still occur, like that of Fig. 197. The curve so obtained is known as that of Traul)e, from having been first described by that observer. Inasmuch as respiration has entirely ceased, it is evident Fig. 197. l\ A / / l ! I i I i' \\ r- A A A ^ « '"i A A i\ '■'^■ mmmmmwm ; \\ \ \ \j ill V « v\/ i, w ' k V) i! V ^ i M/ V V V H V f. ;*'■ ? 'j Traube's curves. X ./' that the large undulations cannot be due to respiration. The only way of accounting for them is by supposing that they are of vaso- motorial origin, the rhythmic rise and fall in the blood pressure, through the rhythmic constriction of the arteries, being due to a rhythmic stimulus emanating from the vasomotor center of the medulla. This view is confirmed by the following facts : that the phenomena in question are much less marked if the spinal cord be divided l)elow the medulla, and that the undulations persist even after the heart itself be removed, and the circulation be maintained artificially. It is difficult to understand why the vascular rhythm, A B TIFICIAL BESPIRA TION. 171 due to the vasomotor center, should shuulate and be superimposed upon the respiratory rhythm due to the medullary respiratory center, unless throug^h conditions in the evolution of the animal and which we are not familiar with, the two centers in the medulla have been gradually brought to act synchronously. It will be seen, therefore, that while the rise and fall in the blood pressure are in- fluenced by inspiration and expiration, the phenomenon is inde- pendent of respiration, or probably that both are influenced by a common cause. In the study of the circulation and respiration as in the present case it is often necessary to maintain artificial respiration. The form of apparatus that we make use of for this purpose is essen- tially a mercurial pump (Fig. 198), consisting of two cast-iron Fig. 198. Mercurial pump for artificial respiration. cylinders A, B (B not being .seen in Fig. 198), concentrically dis- posed and firmly fixed in a solid frame C. The space between the cylinders contains mercury, through which the bell-jar E covering the internal cylinder B is elevated or depressed by the vertical mo- tion of the rod F connecting it with the wheel G, to the rotation of which the motion of the rod is due. The internal cylinder B opens externally through the two brass nozzles H and I. Each of these nozzles is provided with a valve, which, however, open in 372 BESPIBA TION. opposite directions — that of H from witliout inward, that of I from within outward. As the bell-jar is elevated the air jiasses through H into the internal cylinder, and as Fig. 199. it descends the air passes out of it through I, and thence by means of a tube terminating in a canula to the trachea of the animal whose respiration is to be maintained. The rotation of the wheel G, to which the action of the respiratory pump is due, is eifected by a Backus water motor (K) to which the wheel is con- eauuia. nected by the band I. The Mater supplying the motor is conveyed to it from the hydrant in the laluiratory by the tube M and away from it to the waste- pipe by the tube X. The canula that we use for insertion into the trachea is that of Ludwig, and consists of a tube of glass (Fig. 199) of which the end a, Avhen /)i sitd, faces the lungs and through Mhich the air to be inspired passes, the expired air escaping l)y a small opening. In ordinary tranquil respiration no sound is heard unless the ear be applied directly to the chest, excepting when the mouth is closed and the breathing exclusively nasal, then a soft murmur ac- companies both inspiration and expiration. If the ear, or better, the stethoscope, be successively applied over the trachea and the chest, a very noticeable difference will be observed in the character of the sound heard, as the air passes through these parts both in inspiration and expiration. As might be expected, as the air passes in and out of the trachea, the character of the sound is tubular. In inspiration, the sound, attaining its maximum intensity immediately, maintains it to the close of the act, when it rather suddenly ceases. Immediately, or after a very brief interval, the expiratory sound follows, attaining soon its maximum intensity, but, unlike the in- spiratory sound, rather dying away than ceasing abruptly. As the air passes into the small bronchial tubes and expands the pulmonary air cells it gives rise to a sound difficult of description, and which can only be appreciated by being heard. It is usually described as being of a breezy or vesicular character, and is less intense than the tracheal murmur. The sound gradually increases in intensity from the beginning to the end of inspiration, and ceases rather ab- ruptly. The inspiratory murmur is followed without any interval by the expiratory one, lower in pitch, less intense, and lasting a shorter time. It must be mentioned, however, that the expiratory murmur is frequently absent. Certain modifications of the respira- tory sounds and movements, such as snoring, coughing, sneezing, sighing, ya-s\Tiing, laughing, sobbing, and hiccoughing need only a passing notice, since they are simply exaggerations of either the inspiratory or expiratory movements, or of both. Snoring, a sound too familiar to need description, occurs when the mouth is open, and is due to a vibration or flajiping of the velum palati between NUMBER OF RESPIRATIONS PER MINUTE. 3/3 the two currents of air from the mouth and nose together with a vibration of the air itself. Coughing and sneezing, usually invol- untary acts, consist in a deep inspiration, followed by a convulsive expiration, differing only in degree, the air in the first instance be- ing expelled by the mouth, in the second by both mouth and nares. Sighing and yawning are due to the same cause — want of oxygen in tlie blood — and differ from each other only in the former being voluntary, the latter involuntary. In both these acts a prolonged and deep inspiration is followed by a quick and usually audible ex- piration. Laughing and sobbing, though expressing very different emotions, are produced very much in the same way, and are the result of short, quick, convulsive movements of the diaphragm, which are accompanied by the action of the facial muscles produc- ing those changes in the features so characteristic of joy or sorrow. Laughing and sobbing, like yawning, are, so to speak, catching, or contagious. Hiccough is a purely inspiratory act, and consists in sudden convulsive involuntary contractions of the diaphragm, the glottis constricting spasmodically at the same time ; the well-known sound is due to the air striking against the closed glottis. Hic- cough is frequently caused by partaking too rapidly of dry food or effervescing and alcoholic drinks, and is not an infrec|uent symp- tom of disease. It is obviously of importance that the number of respirations in a given time be determined as accurately as possible. A great dif- ference of opinion, however, has prevailed, in this respect, among physiologists, Haller,^ for example, giviug twenty respirations a minute as the normal number ; Magendie,' fifteen ; Milne Ed- wards,'^ sixteen to twenty-two. This disagreement in the result of a mere matter of observation is due, in some instances, to the num- ber of cases examined having l)een too limited to warrant a general conclusion, and, in others, to infiuences modifying the number of respirations within the limit of health not having been taken into consideration. The importance of examining a great number of cases before drawing any conclusion as to the ayerasc number of respirations per minute is well shown by the observations of Hutchinson.* Of 1887 cases, in 561 the number of respira- tions was found to be twenty per minute ; in 239 cases, sixteen per minute ; in 79 cases, nine to sixteen per minute. Such a dif- ference in the number of respirations, as observed in these three sets of cases, and also of the remaining ones examined, prove that there must be numerous conditions influencing the rapidity of the respiratory movements as we have seen is the case with the pulse. Among these the influence of age is very important, thus, as shown by Quetelet,'' the number of respirations at birth are more ' Elementa Physioloo:i;i', Tomus iii., p. 2S9. ^Precis elementairc de Pliysiologie, Tome iii., p. 337. ^Physiologic, Tome ii., p. 4S0. * Cyclopa?di:i of Aiiiit. and Phys., Vol. iv., Part 2, p. 1085. ^Quetelet, h^ur I'liomnu', etc., 1835, Tome ii., p. 84. of cases. Per minute. Ko. of eases. 79 21 . 129 239 22 143 105 23 . 42 195 24 . 243 74 24 to 40 . 78 561 374 RESPIRATION. Number of Eespirations per Minute. Per minute. 9 to 16 . 16 . . . 17 . . . 18 . . . 19 . . . 20 . . . In a total of these 1887 cases the majority breathed 16 to 24 ; one- third 20 respirations per minute. than double the number at twenty years of age, and from this age upward the number of respirations diminishes. It is evident, there- fore, that the number of respirations per minute, as deduced from the examination of a number of individuals, will depend, cceteris paribus, upon their age ; and we should expect to find young per- sons breathing more rapidly than old ones. It w'ill be readily un- derstood, therefore, why 561 persons, on an average, should be Respirations at Different Ages. minute. Age. 44 At birth. 26 5 years. 20 15 to 20 vears. 19 20 to 25^ " 16 30 " 18 30 to 50 " found to breathe twenty times per minute, and 239 persons only sixteen, if the first set of persons examined are, on an average, younger than the second set. In speaking of the various conditions that modify the number of cardiac beats in a given time, the influence of size was noticed, it being mentioned that the number of cardiac beats in a given time was more numerous in the young and small child, and young and small animal, than in the adult man or large animal. Xow, the same relation that we have just pointed out as existing between youth and the number of respirations in man, will also be found to prevail if large animals are compared with small ones, or if the same animal be compared at different ages. Thus, accord- ing to Milne Edwards,^ Mobile the number of inspirations in the whale is only about four or five in the minute, and in the rhi- noceros, hippopotamus, giraffe, and horse ten to the minute, the number of respirations are thirty-five or more in the same period of time in the rabbit and guinea-pig, while, according to Colin,^ the number of respirations being thirteen to sixteen in the sheep, will be sixteen to seventeen in the lamb ; in the cow, fifteen to eighteen ; in the calf, eighteen to twenty ; in an adult dog, fifteen to eighteen ; in the young dog, eighteen to twenty. The cause of this difference iu the number of respirations, according to the age and ^Physiologic, Tome ii., p. 486. ^ p],yg}yiQgjg (;;;Qjjjpjjj.^ig Tome il., p. 152. WOBK PERFORMED DURING RESPIRATION. 375 size of the animal \<, no doubt, clue, as in the case of the numl^er of cardiac beats, to tlie same cause, that of the vital processes gener- ally beinir more active in small animals than in laroe ones. Sex seems to influence but little the number of respirations, no appreciable diiference being observed in boys or girls ; young men, however, breathe a little more rapidly than young Avomen of the same age. Everyday experience teaches us to what an extent res- piration may be accelerated by nervous excitement and exercise. The influence of muscular exertion is not limited simply to active exercise, the mere change from the recumbent to the sitting posi- tion, or of standing up, will increase the respiratory movements. Thus, Dr. Guy states that lying down the number of his inspira- tions was 13 per minute, while sitting 19, and when standing up 22. As might be expected, during sleep, the number of respirations is diminished, according to Quetelet,^ the diminution being about 1 in 4, or 25 per cent. It will be seen, from what has just been said, that the number of respirations must vary very much wathin the limits of health ; and that, therefore, only an approximately aver- age number can be ascertained. Of 1887 cases examined by Hutch- inson,^ 1731 breathed from 16 to 24 times, and nearly one-third of them 20 times a minute. The average number of respirations we have found to be from 18 to 20 times a minute, and we may add here, incidentally, that during each respiration there are about four heart beats. Mechanical "Work Performed During Respiration. It will be remembered that in describing the circulation, it was es- timated that the mechanical work performed by the heart amounted, in twenty-four hours, to 75,000 kilogrammeters (240 foot tons). AVe shall see hereafter in the investigation of the source of the energy of the body, that it is equally important to determine, as far as possible, the mechanical work performed by the respiratory mus- cles. This may be estimated, at least approximately, in the same way as in the case of the heart by multiplying the weight raised l)y the respiratory muscles l)y the height. It has already been mentioned that owing to the elasticity of the lungs offering a re- sistance to the inspired air distending them, the pressure exerted by the latter against the inner surface of the thorax will be less than that exerted by the external air upon the outer surface of the thorax. It is evident, therefore, that at each inspiration, the chest lifts so much of the weight of the external atmosphere as is not neutralized by a corresponding part of the internal one, the weight raised being directly proportional to the elastic tension of the lungs that is to the depth of the inspiration. Let us suppose that the downward pressure of the atmosphere upon the outer surface of the thorax is 15 pounds upon the square inch and the upward pres- sure of the internal air upon the inner surface 14.8 pounds, or 0.2 »0p. cit., p. 8-<. Hjp. cit., p. 1085. 376 RESPIBA TION. pound less, tlie elastic tension of the lungs amounting to that in easy breathing, and that the chest with an area of 300 square inches is elevated 0.04 of an inch, the Avork done during each inspiration will be 0.2 foot pounds,' and on the supposition that the respirations are on the average 15 per minute, to nearly 2 foot tons - per day. The work done by the diaphragm, if calculated in the same way, will amount to about 2.8 foot tons per day ; that is if it be supposed that its area is 52 square inches, and that in addition to lifting 0.2 pounds of air through 0.2 in. it overcomes about an equal amount of abdominal pressure. Inasmuch, however, as during inspiration the elasticity of the thoracic walls is overcome by the inspiratory muscles, the work done in this respect would amount, if we assume the former to be equal to that of the elasticity of the lungs to an additional 2 foot tons per day.' Neglecting the weight of the sternum and ribs 14 oz. lifted during sleep or when the body is in the recumbent position, the total work done by the inspiratory muscles would amount to nearly 7 foot tons (2177 kilogramme ters) per day and in deep breathing to more than twice as much. The above estimate of the w'ork done is, of course, only an approximate one to be regarded as what may be done by the inspiratory muscles rather than what is done. Inas- much as we have seen that expiration in easy breathing is a passive process, a return to the condition of equilibrium, no work is done by the expiratory muscles. If, however, expiration becomes forced, then the work done may amount to nearly as much as that in inspiration. Breathing Capacity. On account of the importance of ventilation, of estimating the amount of oxygen absorbed, and carbon dioxide exhaled, of de- termining the amount of heat produced in the body, etc., it is nec- essary that the amount of air inspired and expired during respira- tion should be actually measured. For this purpose we make use of the spirometer. The instrument described by Hutchinson,* con- sists (Fig. 200) essentially of a cylindrical vessel (A), containing water, out of which a receiver (B) can be elevated by breathing into it through a tube (C), the height to which the receiver is ele- vated and depressed, as shown by the scale D, indicating the vol- ume of the air expired. In using the spirometer, it should be placed upon a firm, level table, about three feet from the ground. The water tap A¥ then having been turned off, and the air tap T opened, clear, cold Avater is poured through the spout of the cy- lindrical vessel A, until it is full, any excess of water running off by the tap in communication with the air tube. The counterpoising •0.2 X 0.04 X 300 = 2. 4 inch pounds = 0.2 foot pounds = 0.027 kilogiammetei-s. 4820 2 0.2 X 15 X 60 X 24 = ,^.^,- = 2 foot tons = 871 kilogramraeters. ^It mast be admitted, however, that tlie ehisticity of tlie tlioraeie walls lias not been detennined. * ()\u cit., p. Kk;;). SPIROMETER. 377 Fig. 200. Aveiglits being then .■suspended within tlie framework ]M, and over the pnlleys, and the air tap closed, the instrument is ready for an ob.servation. The person wliose breathing capacity is to be deter- mined standing erect with head thrown backward, and loosely attired, applies by the mouth- piece the flexible tube C to his mouth and expires into the spirometer. The air from his lungs passes thence into the tube E, elevating the receiver B, the volume of air expired, expressed in cubic inches, be- ing shown by the number of the scale to which the index connected with the receiver has been elevated. On the other hand, by inhaling through the tube C, the re- ceiver B will descend, the amount of air inspired being indicated by the scale now read, however, in the reverse direction. The volume of air must, however, be corrected for temperature, for the tem- perature of the air will be at once reduced to the tempera- ture of the water in the spi- rometer, to which it has passed, and which is warm or cold ac- cording to the season. Practi- cally the change in the bulk of the air will amount to about ^i^ for every degree Fahr., and the difference should be added or subtracted as the temperature of the room in which is the spirometer is below or above G0°. Suppo.se, for example, 295 cu. in. be breathed into the spirometer, the temperature of the room being 55°, then 2.9 cu. in. should be added to the 295 cu. in., since -^^^ equals ^^-^ of 295, equals 2.95 cu. in. ; on the other hand, if the air be at a temperature of 70°, then 5.9 cu. in. should be subtracted from the 295, since Jjj^^ equals -gL. of 295, equals 5.9 cu. in. The U-shaped tube acts as a gauge, since, as long as the colored fluid that is put into it remains at the same level in its two limbs, the density of the air -svithin and without the receiver is the same, which is necessarily an indispen- sable condition in the working; of the instrument. In order to expel the air from the receiver, and return it to its original posi- tion, the plug M is removed Avith one hand, while the receiver is depressed with the other. The experiments having been con- cluded, and it is desired to empty the water out of the spirometer, Hutchinson's spirometer. 378 BESPIRA TION. it is only necessary to open the water-tap. If a healthy adult breathe easily into the spirometer in the manner indicated, it will be found that usually about 30 cu. in. (489 c. c.) pass into the instrument with each expiration. If now the air be expelled, and tlie receiver returned to its original position, and the air-tap be opened, fresh air will pass freely into the receiver, and, the pressure of the air within and without being the same, the receiver will be elevated by the counterpoisiug weights. Suppose a hundred cubic inches of air have been passed in this way into the receiver, and now a gentle inspiratory effort is made, the receiver will descend, and it will be found that its index has fallen to the number 70 on the scale^ shoM'ing that 30 cu. in. of air have been inspired. By experiment- ing in this way upon a number of persons, it will be found that, (uteris paribus, on the average, that in easy, tranquil breathing about 30 cu. in. of air are taken into the lungs with each inspira- tion, and about 30 cu. in. are given out with each expiration. In reality the expired air is about Jfr *o -^-^ less in volume than the inspired air. This is due, as we shall see, to the fact of the car- bon dioxide excreted being a little less in amount than the oxy- gen absorbed. The 30 cu. in. of air inspired and expired during each respiration are usually known as tlie tidal or ordinary breath- ing air. If now a forcible expiration be made, not only will 30 cu. in. of air pass into the spirometer, as in easy breathing, but as much as 100 additional cu. in. This extra quantity, so to speak, of expired air is not usually changed in respiration, but only when the necessity is felt of more completely renovating the air in the lungs, and is called, therefore, the reserve or supplemental air, and amounts to about 100 cu. in. (1630 c. c). In prolonged expiratory efforts, such as sneezing and blowing, this reserve air is more or less expelled. As the reserve air is vitiated through continually receiving water and carbon dioxide from the blood of the lungs, pearl-divers and others who are in the habit of temporarily arrest- ing their respiration, instinctively first get rid of their reserve air by forcibly expiring several times, and then fill their lungs with fresh air. If the chest be now enlarged by a forcible inspiration instead of an expiration, the spirometer having been suitably ar- ranged, as much as 110 cu. in. can be withdrawn from the instru- ment over and above the 30 cu. in. due to an ordinary inspiration. This constitutes what is known as the complemental air, and usually amounts to 100 cu. in. (1G30 c. c). It is drawn upon whenever an effort is made that demands a temporary arrest of respiration, in blowing, yawning, sneezing, etc., to a certain extent in sleep, when the breathing is deep, at the moment immediately preceding some muscular effort, etc. The complemental air can also be indirectly estimated l)y deductiug the sum of tlie tidal and reserve airs (30 cu. in. plus 100 cu. in.) from the volume of the extreme breathing air, or that which can be expelled from the lungs by the most forcible ex- piration after the most profound inspiration, and which, we shall BREATHING CAPACITY. 379 see in a moment, amounts to 2.'>0 cu. in. ; thus 280 en. in. less l.')0 cu. in. equals 100 eu. in. The capacity of the lungs, and the fact that after death they always contain air, make it evident that the air is never entirely expelled, even by the most powerful expi- ration. A certain quantity of air, therefore, always remains in the lungs. It is known as the residual air, and may be approximately considered as amounting to 1 (330 c. c. (100 cu. in.). The amount of residual air cannot be determined directly since the volume of air within the lungs after an ordinary expiration consists of the sum of the reserve and residual airs. If this, however, can be deter- mined, the deduction from it of the reserve air will give the resid- ual air. It is well known that hydrogen gas when inspired is not absorbed by the blood, and that gases will diffuse into each other until the mixture becomes uniform. Such being the case, let us suppose that 1000 c. c. of hydrogen be inspired and that 100 c. c. of the mixture is shown by analysis to contain 23.5 parts of hy- drogen, the whole mixture will then be 4459 c. c. (23.5 : 100 : : 1000 : X = 4455),^ deducting 1000 c. c. as expired, the remainder 3255 c. c. will be the sum of the reserve and residual volumes from which bv sulitraetinff the reserve volume 1630 c. c. we obtain the residual volume 1625 c. c. (99.6 cubic inches). Assuming the mean capacity of the chest to amount to 312 cu. in., and allowing 100 cu. in. for the heart and great blood vessels, and 100 cu. in. for the pareuchymatic structure of the lungs, there would remain little more than 100 cu. in. for the residual air, wdiicli is the estimate given by Hutchinson. While the method just described gives a sufficiently accurate de- termination of the respiratory capacity, more exact results are ob- tained when the tube of the spirometer communicates with a mask closely fitting to the face of the person experimented upon. The mask is jjrovided with two openings furnished with valves working in opposite directions. Through one of the openings the expired air is expelled, while through the other the air to be inspired passes from the spirometer. A more simple and equally eifective apparatus consists of two ivory tubes which are inserted tightly into the nos- trils and which connect -with a common tube, dividing into two branches ; one of these communicates with the spirometer and trans- mits the air to be breathed, the other allows the expired air to es- cape. Each of the branches is provided with a valve which opens in opposite directions. According, therefore, to wdiich of the ivory tubes is inserted into the nose the air can be either inspired from or expired into the spirometer. We have incidentally alluded, a moment since, to the extreme breathing capacity ; by this is meant the volume of air which can be expelled from the lungs by the most forcible expiration, after the most profound inspiration, or the volume that can be inspired by the most forcible inspiration after the most profound expiration. 'X. Grehant, Journal de FAnatoraie, 1864, p. 523. '380 RESPIRATION. It Avas called by Hutcliinson ^ the vital capacity, as sig:nifyiiig the capacity or volume of air Avhich can only be displaced by living movements, and was determined by this observer to amount in a man of medium height (5 feet 8 inches) to ."3749 c. e. (230 cubic inches), being equal to the sum of the tidal reserve and comple- mental airs. The experiments upon which this conclusion was based were made by means of the spirometer, upon nearly 5000 ])ersons. Hutchinson also showed that the vital capacity is influenced by various conditions. Thus, it was ascertained that, for every inch of height between five and six feet, the extreme breathing capacity is increased eight cubic inches. Tlie position of the body affects the vital capacity. Thus, in one individual while standing erect, it was 260 cubic inches, and when recumbent it Avas 2.")(), a diifer- euce of 30 cubic inches. The vital capacity is influenced, without doubt, by weight, but, as the weight usually increases with the height, it is difficult to separate the effect of one from that of the other. Age has also an influence, the vital capacity increasing up to the thirtieth year of life, and then diminishing to the sixtieth. The vital capacity is also affected by the sex, being greater, as shown by Herbst,^ in the male than in the female. As might be anticipated, any diseased condition affecting the mobility of the tliorax or the dilatability of the lungs, will modify, more or less profoundly, the extreme breathing capacity, hence the importance of the latter as a test of health or disease. Inasmuch as the ex- treme breathing air is made up of the tidal reserve and complemen- tal airs, the latter will be affected by the same conditions as the former. As the effects, however, are less marked than where the whole volume of air is considered, it will be necessary to call further attention to them. When it is remembered that, with each inspira- tion, only about twenty cubic inches of air are introduced, sufficient to fill the trachea and large bronchial tubes, it is evident that there must be some subsidiary force acting in addition to the ordinary respiratory movements of the chest by which the fresh air is brought to the air cells and the vitiated air expelled. The interchange be- tween the fresh air in the upper part of the lungs and the vitiated air in the lower part, is undoulitedly due to the diffusion of the air containing oxygen and carbon dioxide, and which goes on, accord- ing to the law established by Graham,'' that the diffusil)ility of gases is inversely proj)ortional to the square root of their densities — that is, that the diffusion of oxygen is to the diffusion of carbon dioxide as the square root of the density of carbon dioxide, or \/1.529 = 1.237, is to tlie square root of the density of oxygen, or x/lTuTSG = l.OoM, or 1.237 : 1.0514 : : 95 : 81. According to this la\v, then, the lighter gas, the air, with its oxygen, will de- scend more rai)idly than the carbon dioxide, the heavier gas, will iQp. cit, p. lot;:. ^ Meckel's Archiv f. Ansit. n. Phys., p. 3, s. 103, 1828. 'Trans, of Royal Sec Kdinh., Vol. xii., p. 573, 1834. THE ^EROTOXOMETEB. 381 Fig. 201. ascend, 91 parts of oxygen replacing SI parts of carbon dioxide. As this difliision is continnally going on between these gases, tlie air in the pulmonary air cells, where the exchange betw'een the oxygen and carbon dioxide takes place, has a tolerably uniform composition, and the aeration of the blood is far less intermittent in its character than the respiratory movements of the thorax. The passage of the oxygen from the air of the pulmonary air cells into the blood of the pulmonary capillaries, and of carbon dioxide in the reverse direction from the blood into the air, is due to the fact of the tension of the oxygen of the air being higher than that of the blood, and of the tension of the carbon dioxide of the blood be- ing higher than that of the air. Necessarily, therefore, the oxy- gen of the air -within the lungs will pass through the wall of the air cell and capillary into the blood, thence into the red corpuscles, combining, as we have seen, with the haemoglobin of these bodies, while the carbon dioxide will pass in the reverse direction from the blood through the wall of the capil- lary and wall of the air cell into the lungs, and thence out of the body. It is possible that the pulmonary epithe- lium in acting as a secretory surface may also exercise some influence in promoting the absorption of oxygen and elimination of carbon dioxide. On the other hand, the oxygen of the ar- terial blood leaving the haemoglobin will readily diifuse through the capil- lary into the tissues, the tension of the oxygen in the latter being so low as to amount, practically, to nothing, the oxygen combining in some stable form as rapidly as absorbed. While, o\A'ing to the continual production of carbon dioxide in some unknown way in the tissues out of the oxygen al)sorbcd, the tension of the carbon dioxide of the tissues being always higher than that of the blood circulating in their midst, the carbon dioxide will consequently dilFuse in the opposite direction to that of the oxygen, viz., from the tissues through the wall of the capillary into the blood now become venous through deoxidation of most of its haemoglobin. The tension of the gases in the blood is determined by means of the a?rotonometer. This (Fig. 201) consists of a long glass tube A, communicating above by means of the stopcocks B C ^Erotonometer. 382 RESPIRATION. with a tube (i)), bringing the blood, the tension of whose gases is to be determined, and with one [E) leading to the eudiometer for the determination of the gases, and below with a bell-jar ( (t), standing over mercury and with the reservoir of mercury //. The glass tube is first entirely filled with mercury so as to exclude the air, by elevat- ing the reservoir H, and is then surrounded by hot water so as to maintain the temperature of the blood examined at that of the animal from which it was drawn. The glass tube ^i is then filled through the depression of the mercurial reservoir with a mixture consisting of known quantities of nitrogen, oxygen, and carbon dioxide. The blood being allowed to flow from the artery or vein of the animal for a moment out of the tube i), so as to exclude the air, is then diverted into the gas mixture in A. As the blood flows down through the tube into the mercury, the latter is driven up into the bell-jar G, while the tension of its oxygen and carbon dioxide are increased or dimin- ished according to the corresponding tension of the oxygen and carbon dioxide of the gas mixture, as finally determined by the an- alysis of the gases in the eudiometer E, into which the gases are driven by the elevation of the mercurial reservoir. The general re- sults as to the tension of the oxygen and carbon dioxide in the blood as obtained with the sero tonometer by Pfliiger,^ Wolf berg,- Strass- burg,^ Nussbaum,^ are as follows : The tension of oxygen in arte- rial blood (one atmosphere = 760 mm. of mercury) is equal to 29.6 mm. of mercury, corresponding to 3.9 per cent, of atmosphere (760 : 29.6 :: 100 : .r = 3.9), that of carbon dioxide being equal to 21.2 mm., corresponding in amount to 2.8 per cent, of atmosphere. The tension of oxygen in venous blood is 22.04 mm. of mercury, corresponding to 2.9 per cent, of atmosphere, that of carbon dioxide being equal to 41 mm. or 5.4 per cent, of atmosphere. Such being the tension of the gases of the blood, it is obvious that since the tension of the oxygen in the tissues (tension, O.OO) oiFers no resis- tance to that of the oxygen of the arterial blood (tension, 29.6) and as the tension of the carbon dioxide of the arterial blood (tension, 21.2) is less than that of the tissues (tension, o8, possibly), that the oxygen of the arterial blood will pass through the wall of the capillary into the tissues and the carbon dioxide formed in the lat- ter into the blood as follows : Relative Tension of Oxygen and Carbon Dioxide in Arterial Blood and Tissues. Oxygen. CaiOmn dioxide. Tension in arterial blood . . 29.6 mm. Hg 21.2 Wall of capillary .... — f f^ — Tension in tissues .... 0.0 58.2 On the other hand, it has been shown, by catheterizing the kings,^ that although the tension of the carbon dioxide _of the at- ' Pfluger's Arcliiv, Bd. vi., s. 43. ^Baid., Band iv., s. 465. "Ibid., Band vi., s. 65. *lbid., Band vii., s. 296. ^ Pfluger's Archiv, loc. cit. TENSION OF OXYGEN AND CARBON DIOXIDE. -SSo mosphere amounts to only 0.30 mm. of mercury (0.04 per cent, of an atmosphere), tliat of the air of the alveoli, or ceils, may be as much as 29.1 mm. (3.84 per cent, of an atmosphere), and that wliile the tension of the oxygen of the atmosphere is 158.15 mm. (20.8 per cent, of an atmosphere), that of the alveolar air may be reduced to 138 mm. (18.2 per cent, of an atmosphere). If it be admitted that the relative tensions of the gases are such, then the tension of the carbon dioxide of the venous blood (tension 41) being greater than that of the alveolar air (tension 29.1) and the tension of the oxygen of the alveolar air (tension 138) being greater than that of the venous blood (tension 22), tlie carbon dioxide of the venous blood will pass through the wall of the lung into the alveolar air, and the oxygen of the latter into the venous blood, as follows : Relative Tension of Oxygen and Carbon Dioxide in Atmos- phere, Air of Alveoli and Venous Blood of Lungs. Oxygen. Carbon dioxide. Tension in atmo-sphere . . 158.15 mm. 0.30 Tension in air of alveoli . . 138.00 29.10 Wall of lung .... — I 1 — Tension in venous blood . . 22.04 41.04 The amount of the gases and the condition in which they exist in the blood have alreadv been considered. CHAPTEK XXIII. RESPIRATION.— (Continued. ) ABSORPTION OF OXYGEN.— EXHALATION OF CARBON DIOXIDE. Having seen that the essence of respiration consists in the ab- sorption of oxygen, and giving up of carbon dioxide, and the manner in which the air containing these gases is respired, it re- mains for us now to determine as far as possible the amount of oxygen absorbed and carbon dioxide exhaled in a given time. This is one of the most imjiortant problems in experimental physiology, since, as we shall see, the amount of heat and energy liberated in the body will depend upon the amount of oxygen absorbed, and carbon dioxide and Avater exhaled. The amount of oxygen ab- sorbed from, and carbon dioxide exhaled into, a given quantity of air can be determined among other means by the Valentin and Brunner apparatus. Fig. 202. This consists (Fig. 202) of a Woulff's bottle A having a capacity of nearly a liter (61 cu. in.). One of the openings communicates with the moutli-picce B, into which the person expires, the air first passing through pumice-stone and sulphuric acid C so as to dry it. ABSORPTION OF OXYGEN. 385 The middle opening communicates with the set of tubes G H I K. H and I contain phosphorus and baryta for the absorption of the oxygen and carbon dioxide of the expired air, G and K pumice- stone, etc., that of G for the absorption of the watery vapors that may have escaped, the pumice-stone, etc., in C Iv for retaining that taken up by the dry air passing through the baryta solution, and which, if lost, would cause an error in the estimate of the carbon dioxide exhaled, the tubes being weighed before and after the ex- periment. Through the middle opening of the Woulff 's bottle a funnel (D) provided with a stopcock is introduced, the opening being then hermetically closed. The funnel is filled "w-ith a known quantity of mercury. The manner of using the apparatus is as follows : having breathed for say fifteen minutes through the mouth- piece until the air of the WouliF's bottle has been entirely dis- placed by the expired air, the mouth- piece is entirely closed, any external air being further prevented from pass- ing into the AVoulif 's bottle bv the mercury in E acting as a valve, the air-tightness of the apparatus being assured by the rise of the mercury in the tube F, through the contraction of the expired air in A, consequent upon its cooling and the closure of the tube funnel. The stopcock of the funnel being then turned, the mercury passes into the Woullf 's bottle, dis- placing a known quantity of expired air, the latter passing into the set of tubes G H I K, pre\aously adjusted to the middle opening. The weight of the tubes H and I having been previously determined, their increase in w^eight ^dll give, respectively, the amount of oxygen and carbon dioxide al)sorl)ed. Deducting now the amount of oxygen so obtained from the ex- pired air from that contained in an equal quantity of ordinary inspired air, the remainder will be the amount of oxygen retained in the inspiration of such a quantity of air ; on the other hand, deducting the trace of carbon dioxide usually present in the atmosphere from that obtained from the expired air, and the remainder will be the amount of carbon dioxide exhaled into such a quantity of expired air. A much more expeditious method of analysis, however, is that of Hempel.' This consists in passing expired air into a gradu- ^ Neue Methoden fiir Analyse der Gase, von Dr. W. Hempel, Braunschweig, 1880. 25 Hempel apparatus. 386 RESPIRATION. ated burette (Fig. 203 B) filled with mercury, the latter flowing out of the burette as the mercurial reservoir A with which the burette communicates is lowered by means of the wheel work C attached to the solid v^'ooden frame fastened to the table. The sample of gas so obtained reduced to standard temperature and pressure is then driven out of the burette B by elevating the mer- curial reservoir into a Hempel pipette F containing a concentrated solution of soda and after remaining there long enough for the ab- sorption of any carbon dioxide present is driven back into the graduated burette by lowering the mercurial reservoir, the diminu- tion in volume, the latter reduced to standard temperature and pressure, representing the carbon dioxide absorbed. The pipette for the absorption of the carbon dioxide being removed, the bu- rette is connected with one containing pyrogallic acid into which the sample of gas just freed of its carbon dioxide is driven by elevat- ins: the reservoir and in which it is allowed to remain until the oxygen present is absorbed. The sample of gas being then driven back into the graduated burette by lowering the reservoir the diminution in volume, reduced to standard temperature and pres- sure, represents the volume of oxygen absorbed. The ordinary atmospheric air consists in 100 parts of a mechan- ical mixture rather than a chemical combination, of oxygen 20.81, nitrogen 7 9.15,^ and carbon dioxide 0.04 parts. If, however, 100 volumes of expired air be analyzed by either of the two methods just mentioned it will be found that it consists of a mixture of oxygen 16.033, nitrogen 79.587, carbon dioxide 4.38 parts. It will be observed, therefore, that the air in being inspired loses about 4.77 parts oxygen and gains about 4.34 parts of carbon dioxide, the nitrogen remaining practically unchanged in amount. In other words, of a given volume of air breathed about 5 per cent., or J-g^, will represent the oxygen absorbed and nearly the amount of carbon dioxide expired, the oxygen absorbed not being exactly replaced by the carbon dioxide expired, since, as we shall see pres- ently of the oxygen absorbed, part only is expired as carbon dioxide. Let us turn now to the consideration of the amount of the oxygen absorbed and carbon dioxide expired in twenty-four hours and the conditions influencing the same. If it be admitted that during easy breathing about 500 c. c. (30 cubic iuclies) of air is inspired and expired at each respiration, and that the number of respirations throughout the day are, on the average, 15 per minute, the air breathed in 24 hours will be 10,800 liters (381 cubic feet) and the oxygen absorbed will amount to 515.16 liters (18 cubic feet), or 738 grammes, and the carbon dioxide to 468.72 liters (16.6 cubic feet), or 926 grammes, as shown in the following : ' Including argon, 2 per cent. AMOUNT OF AIR INSPIRED. 387 Air Inspired in 24 Hours, etc. 500 c. c. of air inspired at each respiration. 15 respii-ations per minute. 7.5 liters per minute. 60 450 " " hour. 24 10,800 " " day. 10,800 : 100 : : x : 4.77 X = 515.16 liters of oxygen absorbed. 1 liter of oxygen weighs at standard pressure and temperature 1.4298 grammes. 515.16 liters weigh 738 grammes. 10,800 : 100 : : a; : 4.34 X = 468.72 liters of carbon dioxide expired. 1 liter of carbon dioxide weighs 1.966 grammes. 468.72 liters weigh 926 grammes. It might naturally be asked, even if oxygen is absorbed and car- bon dioxide expired in the amounts just stated for a short period of time, does it follow that the total amount of the gases interchanged in the twenty-four hours will be the same as that obtained by the method just given ? That such is the case, however, has been proved by experiments like those of Pettenkofer,^ made with the celebrated respiration apparatus in Munich, large enough to hold a man, and in which the observations extended over a period of twenty-four hours. As might be expected from the nature of the case, the de- termination of the amount of oxygen absorbed and carbon dioxide expired by a human being in a given time must be of an approxi- mate character. AYith animals, however, it is different, and espe- cially in the case of small ones, in which the conditions are very favorable, the determination of the oxygen absorbed, as well as the carbon dioxide expired, can be most accurately determined. The most perfect form of apparatus as yet devised for this purpose is that of Regnault and Reiset." It consists essentially of a receiver filled with air enclosing the animal to be experimented upon, and which communicates on the one hand with a reservoir supplying oxygen as fast as it is consumed during respiration, and on the other with an apparatus for the absorption of the carbon dioxide exhaled. The detailed disposition of the apparatus will be understood from Fig. 204. Within the tubulated bell-jar A, immersed in the cylinder of water B, is placed a little animal, a dog, for example, the subject of the experiment. The animal having been introduced from below, and the opening hermetically closed, the large pipettes G G, filled with a solution of potash or soda of known strength and quantity, and communicating with each other by a caoutchouc tube, absorb the COj exhaled into the air of the jar A, the air being drawn alternately into the pipettes G G through their elevation and depres- 1 Pettenkofer, Ann. Chem. Pharm. Suppl., B. ii., 1862, s. 1. ^Amiales de Chimie et de Physique, 3"°^ ser., Tome xxvi., 1849, p. 441. 388 RESPIRATION. sion by some mechanical arraDgement. According as oxygen is ab- sorbed by the animal, the gas pressure falls in A, and consequently the oxygen of the balloon N, luider the pressure of the calcium chloride solution in P, flows through J/, replacing that lost in A. The object of the gas pipette (( is to enable the observer to draw a small sample of gas out of the chamber for analysis. The temper- ature and pressure of the gas within the chamber, and the amount of oxygen in the chamber at the beginning and the end of the ex- periment, as well as that delivered to the chamber being known. Fig. 204. Regnault and Eciset respiration apparatus. the amount of oxygen absorbed by the animal can be determined, the carbon dioxide expired being equal to the difference in the weight of the soda pipettes before aud after the experiment.^ The advantage of this apparatus is that the animal suffers no inconven- ience from even a prolonged confinement within the chamber, and that the oxygen is furnished as needed, aud the carbon dioxide re- moved as rapidly as produced. The amount of oxygen absorbed and carbon dioxide expired, etc., by a small monkey during a period of five hours, as determined by means of the Regnault and Reiset apparatus, is given in the accompanying Table : 1 For a detailed description of the apparatus and the results obtained by it the reader is referred to Kcsearches upon Kespiration, by H. C. (.'hapman and A. P. Erubaker, Proc. Acad. Nat. Sciences, liS!)l, p. 13. ABSORPTION OF OXYGEN. 389 OxYGENi Absorbed and Carbox Dioxide 'Exhaled, etc., by a Monkey (Cebus Capucinus).' Grammes. Weight of oxygen consumed ..... 13.47 Weight of carbon dioxide produced . . . 16.389 Weight of oxygen contained in tlie carbon dioxide. 11.919 Ratio between the weight of the oxygen contained in the carbon dioxide produced, and the weight of the oxygen consumed ..... 0.884 Weight of oxygen consumed per hour . . . 2.694 Weight of oxygen consumed per liour per kilo- gramme of animal ...... 1.347 Weight of carbon dioxide produced per hour . . 3.277 Weight of carbon dioxide produced per hour per kilogramme of animal . ..... 1.638 The determination of the amount of carbon dioxide expired in a given time is as important as that of the oxygen absorbed since the carbon dioxide containing part of the oxygen absorbed by the sys- tem during some previous period affords the means, therefore, of indirectly estimating the same. In making use of the indirect method of determining the amount of oxygen absorbed by an animal the water exhaled is usually estimated simultaneously with that of the carbon dioxide expired. One of the most accurate forms of apparatus for this purpose is that devised by Voit ' and which is a modified form of the large respiration apparatus of Pettenkofer al- ready referred to. The small respiration apparatus of Voit (Fig. 205) consists of a chamber H in which the subject of the experi- ment, a large dog, for example, is placed ; ^ of a large drum, and pumps worked by a water-wheel for the production of a constant draught of fresh air through the apparatus ; of bottles and tubes containing appropriate materials for the absorption of the "svater and carbon dioxide of the air surrounding the chamber, as well as that from within it ; and of meters for registering the total amount of air that has passed through the chamber, of the fractional part of the same analyzed, and of the air surrounding the chamber analyzed for comparison. The chamber H in which the animal is placed consists of a zinc framework in which solid glass plates are imbedded, a part of Avhich at the front of the chamber is movable and acts as a door. The other two openings present, are for the entrance and exit of the air ventilating the chamber. The air entering by the opening a, seen through the large chamber M, passes by the pipe to the bottom of the chamber, and having traversed the latter, leaves it at its upper portion by the pipe b and passes thence by the pipe d (disconnected with H in Fig. 205) into the large gas meter 18 (Fig. 200), whence having been measured, it is expelled. The constant current of air so passing is drawn out of the tubes d b and chamber H by the ' Chapman and Brnbaker, op. cit., p. 44. ^ Zeitschrift fiir Biologie, 1875, s. 532. 3 In that case the tube (Fig. 205) is connected with the tubeb of the small cham- ber H; when the subject of the experiment is a man, however, it is then connected with the tube b of the larger chamber M. 390 RESPIRATION. rotation of the drum of the gas meter B, whose axis is in connec- tion with that of the overshot water-wheel G, through the teeth of the cog-wheel on the axis of the gas meter interlocking with those of the cog-wheel on the axis of the water-wheel. The water-wheel o fi is kept uniformly rotating through the flow of water from tlic pipe f connected with a small reservoir, tlie latter communicating in turn with that supplying the building, the water emptied by the buckets of the water-wheel passing into a trough is carried away by the waste pipe K. Inasmuch however, as with the water-wheel VOIT'S RESPIRATION APPARATUS. 391 rotating only once a minute and the experiment lasting but six hours over 10,000 liters of air pass through the chamber it_ is obvious that the analysis of such a large volume of air would in- volve a great expenditure of time and labor. This is avoided by divertinjj part of the air, which issues from the chamber, by means of mercurial pumps, from the tube d into the tube .7, terminating in the two branches /" and J' and of determining the amount of carbon dioxide and water in two samples of air. The air from J' passes through the valve v' as the pump is elevated by the crank connected with the axis of the water-wheel and returns through the valve lo' as the pmup is depressed, thence into the short bottles 392 BESPIEA TION. e e containing pumice-stone and sulphuric acid for the absorption of the water, and through the large bottles g containing water and pumice-stone for resaturation, then through the tubes 1 1, containing a solution of baryta, for the absorption of the carbon dioxide, finally escaping by the meter, where it is measured. The air in J" after having passed through a similar set of valves, tubes, etc., escapes by a second meter where it is measured. By this arrange- ment, two samples of air are therefore analyzed, the mean of which represents the amount of carbon dioxide and water in a. given volume of air. As the external air passing into the chamber contains carbon dioxide and water as well as the internal air, the amount of the same must be determined. This is done in exactly the same way as in the case of the internal air, the external air being drawn into a tube by two pumps and passed through a double set of bottles, tubes, and meters similar to those described. The amounts of carbon dioxide and water in a given volume of air surrounding the chamber, having been determined, this is deducted from the carbon dioxide and water in an equal volume of air that has passed simultaneously through the chamber, the difference giving the amount of carbon dioxide and water expired by the animal into a given volume of air. It remains for us now to describe a little more in detail than we have done the manner in which the water and carbon dioxide are determined by means of the absorbing apparatus. The deter- mination of the amount of Mater is very simple. The bottles (e, e, Fig. 206) through which the air from within and without the chamber passes contain, as already stated, pumice-stone and sul- phuric acid, which has a great avidity for water. These being weighed in scales, before and after the experiment, the difference wall give the amount of water in the air from Avithin and without the chamber ; the latter amount, as we have already mentioned, must be then deducted from the former, in order to get the amount of water exhaled by the animal. Water having been absorbed as the air passes through tlic bottles the dried air is resaturated as it passes the bottles (/, the saturated pumice-stone Avithin them giving up the water it contains. Were not the air so resaturated it would take up water from the solution of baryta through Avhich the air next passes, and this must be avoided, as the solution of baryta is used for the absorption of carbon dioxide. The amount of carbon dioxide absorbed is determined by neu- tralizing the baryta solution by oxalic acid before and after the ex- periment, the browning of turmeric paper being used as an indication of the point of neutralization. The method will be made clear by the following example. Suppose, before an experiment with the respiration apparatus, it was ascertained by the means just described that exactly 72.4 c. cm. of oxalic acid neutralized 25 c. cm. of the standard baryta solution, it will be found that at the end of the experiment it requires only 61.8 c. cm. of oxalic acid, or 10.6 c. cm. VOIT'S RESPIRATION APPARATUS. 393 less, to neutralize 25 c. cm. of the baryta solution, drawn out of the tubes by means of a pipette. As the carbon dioxide passes through the latter during the experiment it combines with part of the baryta, and there is, therefore, less baryta to combine with the oxalic acid after the experiment than there was before. Now, as for each milligramme of carbon dioxide that coml:»ines with the baryta dur- ing the experiment there will be 1 c. cm. less of oxalic acid required for neutralization after experiment, it follows that 10.0 milligrammes of carbon dioxide must have been absorbed by the 25 c, cm. of the baryta solution, since it requires 10.6 c. cm. less of oxalic acid for neutralization after the experiment than before. In other words, the baryta before the experiment combined with 72.4 c. cm. of oxalic acid, after the experiment with 61.8 c. cm., because during the experiment it combined with 10.6 milligrammes of carbon dioxide, which arc volumetrically equal to 10.6 c, cm. of oxalic acid. Let us suppose, for example, that by the method just de- scribed the amount of carbon dioxide and water expired by an animal into a given volume of air has been determined, then the total amount of carbon dioxide and water expired by tlie animal at the end of the experiment would be obtained by multiplying the amount of carbon dioxide and Mater in the given volume of air by the ratio of the latter to the volume of air that has passed through the large and the two small meters (internal air) and that still re- mains in the chamber H and the tube 6 d J, and adding up the re- spective quotients. Kesults of Experiment upon a Cat, Obtained with the Voit Kespiration Apparatus. Duration of Experiment, Six Hours. Calculation for Carbon Dioxide and Water. Carbon dio.xide. Water. In 1000 liters of inner air In 1000 liters of outer air . 1.8085 grammes. . 0.5815 " 12.457 grammes. 11.445 Difference . . 1.2270 " 1.012 " In 11600.5 liters of large meter In 66.55 liters chamber and tube In 121.02 3d and 4th meters . . 14.23 " . 0.11 . 0.15 " 11.74 0.07 " 0.12 " Total .... . 14.46 " 11.93 " Calculation foi f Oxygen Absorbed. Before experiment. Weightof animal 3001.3 grms. \ Ingesta . . 0.0 " After exper height of animal . urine -r, . feces Egesta < , ° water carbon dio Total . •iment. . 2987. 80 grms, 0.0 " 0.0 " . 11.93 " xide 14.46 " Total . 3001.3 " . 3014.19 " 3001.30 " The quantity of oxygen absorbed < equals the difference , viz.: 12.89 " Weight of oxygen in carbon dioxide expired l^-^l = 0.81 Weight of oxygen absorbed 12.89 394 RESPIRATION. By substituting for the chamber (iJ) containing the animal one large enough to hold a human being (Fig. 211, M) the carbon dioxide expired by a man in twenty-four hours has been found to amount, upon a mixed diet, to 930 grammes (32.08 ounces), and which contains 253.6 grammes (8.9 ounces) of carbon. The water exhaled by a man in the same period of time cannot, however, be accurately determined by this apparatus, so much of it being pre- cipitated in the chamber, and is estimated, as Ave shall see presently, by another method. The estimate of the amount of carbon dioxide expired by a man in twenty-four hours just given does not differ essentially from that of Andral and Gavarret^ (921 grammes), though greater than that of Edward Smith" (7(30 grammes). The experiments of these observers were made with the object of de- termining only the carbon dioxide exhaled, and the apparatus con- sisted in both instances of a mask closely fitting the face, having two openings provided with valves for the entrance and exit of the air, the carbon dioxide exhaled in the experiments of Andral and Gavarret being determined by means of a solution of potash con- tained in U tubes, and in those of Smith by a solution of potash arranged in numerous layers. The mechanical details of the appa- ratus made use of by these observers, as well as by their predeces- sors, Lavoisier and Seguin, Prout, Davy, Dumas, Allen and Pepys, Scharliug, and others, not being as perfect as those of the Petten- kofer-Voit respiration apparatus, just described, it would be super- fluous to dwell further upon them. In this connection, however, it is proper that some allusion at least be made to the indirect method of determining the amount of carbon dioxide exhaled in a given time, so successfully applied in the case of large animals by Boussingault,^ This method consists of so reo-ulatino; the diet of the animal ex- perimented upon, a horse or cow, for example, that there is no loss of weight during the experiment, and of weighing everything introduced as food, solid and liquid, and all discharged as urine or feces. Know- ing the quantity of carbon entering the body in the food, and leaving it in the urine and feces, the diiFerence between the carbon of the latter and the former (that of the food being in excess) will be the amount of carbon leaving the body by the lungs and skin. As regards the carbon excreted by the skin, it can, for such approxi- mate determinations, be neglected, since, as we shall see, when the skin is considered as a respiratory surface, the carbon dioxide ex- haled does not amount to more than between -Jjj and -^^-^ of the total amount excreted. The amounts of oxygen absorbed and carbon dioxide expired in twenty-four hours, while on the average about what we have stated, are, nevertheless, affected by numerous conditions. Among the most important of these are the rapidity of the respiratory move- ^ Ann. de Chiraie et de Physique, 3me serie, Tome viii., p. 129. 2 Phil. Trans., Vol. 149, 1860, p. 681. ='Mem. de Chimie agricole et de Physiologie, pp. 1-12. Paris, 1854. EXHALATION OF CARBON DIOXIDE. 395 ments, sex, age, food, digestion, exercise, fatigue, sleep, season, tem- perature, period of the day, moisture, atmospheric pressure, nervous system, species, body weight and body surface of animal. Let us consider the influences exerted by the above somewhat in detail. The osmosis of the oxygen of the air and the carbon dioxide of the blood within the pulmonary capillaries not being a sudden action, but a continuous one, the amount of the gases so interchanged will naturally depend on the length of time during which the air re- mains in contact with the respiratory surface ; thus, Vierordt,^ in the experiments performed upon his own person, found that, when he breathed as slowly as possible, 6 per cent, of CO^ was exhaled in each expiration, but that when he breathed as rapidly as possible only 3 per cent, as shown in the following Table : Per cent, of COj in expired air. 5.9 4.3 3.5 3.1 2.9 2.8 No. of expirations per minute. 6 12 24 48 96 150 It does not follow, however, that because the per cent, of carbon dioxide contained in each expiration is greater during slow than in rapid breathing that more carbon dioxide is expired in a given period in the former case than the latter. On the contrary, the reverse obtains, since the small per cent, of carbon dioxide that each ex- piration contains during rapid breathing is more than compensated for by the greater number of expirations. Thus, suppose, for ex- ample, that 250 c. cm. of air are expired six times in a minute, then, as each 100 c. cm. contain 5.9 c. cm. of carbon dioxide : 5.9 X 2.5 X 6, or 88.50 c. cm., will be the amount of carbon di- oxide expired in the given time. On the other hand, if the same quantity of air be expired twelve times in a minute, each expiration will contain only 4.3 per cent, of carbon dioxide, and yet 129 c. cm. of carbon dioxide will be expired in the given time, since 4.3 X 2.5 X 12 equals 129. According to the same authority if an expiration be divided into two equal parts, the first part will contiiin, on an average, 3.72 per cent, of carbon dioxide, the second 5.44 per cent., the air exhaled during the first period of the expira- tion containing less carbon dioxide than that exhaled during the second period. The amount of carbon dioxide exhaled by an in- dividual depends also upon the sex. Thus, it has been shown by Andral and Gavarret ^ that one more gramme of carbon (correspond- ing to 1.85 liters of carbon dioxide) was exhaled per hour by the male than by the female. Indeed, the difference amounted in some instances to even as much as 7 liters. The difference in the weight ' Physiologie des Athmens, p. 102. Karlsruhe, 1845. 2 Op. cit. 396 BESPIBA TION. of the body was not taken into consideration in the observations of Andral and Gavarret. Scharliug,' however, found that more car- bon dioxide was exhaled by the male than the female, even when this was estimated with reference to the body weight. Apart from the greater muscular activity of the male, as compared with the female, being sufficient to account for the difference in the amount of carbon dioxide exhaled by the sexes, other conditions peculiar to the female exert an influence in this respect that must not be overlooked. Thus it was shown by the experiments of Andral and Gavarret," that as long as the menses succeeded each other regularly, the average amount of carbon dioxide exhaled remained about the same, being on the average 11.7 liters per hour, with their cessation the amount increased to about 15 liters, while from 60 to 82 years of age it diminished from 13 to 11 liters. Temporary cessation of the menses whether due to pregnancy or other causes, is also accompanied by an increase of the amount of carbon dioxide exhaled. As is well known, during the first few hours and days after birth, the infant making little or no movement, sleeping most of the time, generates but little heat, and must, therefore, be carefully guarded against changes in the external temperature. At this early period of life the amount of ojygen absorbed and carbon dioxide exhaled must be very small. With the thorough estal)lishment of respira- tion, this amount is increased, and from the fact of the number of respirations being greater in early than in later life, it is probable that the amount of carbon dioxide exhaled, considered with reference to the bodv weight is greater in the infant than in the adult. The necessary data essential for such a comparison are, however, too insuf- ficient to admit of more than the general statement just made. From the observations of Andral and Gavarret ^ based upon the exami- nation of numerous individuals between the ages of 12 and 102 years, we learn that from the age of 12 to 32, there is an absolute increase in the amount of carbon dioxide exhaled, from 32 to 00 years old a slight diminution, and from 60 to 102 'years, a very considerable one. Males. Carbon dioxide exhaled jjer hour. 12 to 16 years of age. 15 liters (915 cubic inches). 17 " 19 " " 20 " 25 " 32 " " 22 " 32 " 60 " " 20 " 63 " 82 " " 15.3 " 102 " " 11 " Wlien these observations are supplemented by those of Schar- ling,* we also learn that the amount of carbon dioxide exhaled in youth, relative to tlie weight of the body, is greater than that in the adult, l)eing in the case of a boy, for example, twice as much 'Ann. de Chimie, Tome viii., 1843, p. 486. ^ (^p p\^ "Op. cit. *0p. cit., p. 129. ABSOBPTIOX OF OXYGEX. 397 as in a man. The results of Scharling's experiments might be in- ferred from those of Andral and Gavarret, since the absolute in- crease in the amount of carbon dioxide exhaled between the period of childhood and adult life is small, as compared with the increase in the weight of the body within the same period. According to Pettenkofer/ more oxygen is absorbed up(jn a ni- trogenous than upon a non-nitrogenous diet, and more upon a non- nitrogenous one than upon a mixed one, the interchange of oxygen and carbon dioxide being, as might be expected, least during fasting, as was shown by the following residts obtained by the above ob- servers. Fasting. Mixed diet. Xon-nitrogenous Nitrogenous diet. diet. Oxvgen . 743 grms, 709 grms. 808 grms. 850 grms. Carbon dioxide 695 '• 912 '• 839 '• 1003 '■' It will be observed that it is only in the ease where no food was taken that the oxygen absorbed is greater than that of the carbon dioxide expired. As regards the influence of the food upon the exhalation of car- bon dioxide, the extended series of experiments performed by Dr, Edward Smith - upon himself and friends, are very conclusive. Food, with reference to the exhalation of carbon dioxide, can be divided, according to Dr. Smith, into two classes, respiratory exci- tants, which increase the exhalation of carbon dioxide, and non- exciters, which diminish it. The excito-respiratory foods include the nitrogenous articles of diet, milk, sugar, rum, beer, stout, the cereals, and |X)tato ; the non-exciters, starch, fat, certain alcoholic compounds, the volatile element of wines and spirits, and coft'ee leaves. The most powerful respiratory excitants are tea and sugar, coffee, rum, milk, cocoa, ales, and chicory come next, then casein and o^luten, and lastlv gelatin and albimiin. The effect of takins: respiratory excitants is soon experienced by the system, the maxi- mum effect being usually attained within an hour ; their action is of a temporary character, and the effect is not proportional to the quantity taken. Certain respiratory excitants, like tea and coffee, cause an exhalation of carbon in excess of that supplied by these foods, while others, like sugar, cause an evolution less in amount than that supplied. In this connection it may l^e mentioned that the soothing influence experienced by persons suffering from de- pression of spirits by drinking tea is probably due to the exhalation of carbon dioxide being increased, an excess of carbon dioxide in the system giving rise to such feelings. According to Dr. Smith, brandy, whiskey, and gin, the volatile elements of alcohol, gin, rum, sherry, and port ^^-ine, when inhaled diminished the quantity of carbon dioxide inhaled, while rum and malt liquors, on the con- 'Sitzungber. d. Konigl. baver Acad. d. WLssen., 1867, s. 255. 2 Ph. Trans., Vol. 14lt, 1860, p. 715. 398 RESPIRATION. trary, increased the exhalation. While the effect of pure alcohol, according to Prout, Horn, and Vierordt,^ is to diminish the exha- lation of carbon dioxide, just the opposite effect is attributed to it by Hervier and St. Leger and Smith. The difference in the result of the effect of alcohol upon the exhalation of carbon dioxide observed by these experimenters may be due to the proportion of carbon di- oxide in the expired air being only considered, and not the absolute quantity exhaled, as was the case in the experiments of Prout, or to the alcohol being administered with or without food, or even to individual peculiarities. It was observed by Lavoisier and Seguin' as long ago as the end of the last century that the absorption of oxygen was increased by digestion, lowering of temperature, and the performance of work — and such has been shown to be the case by the investigation of modern observers, even though the amounts of oxygen obtained by Lavoisier differ both relatively and absolutely from those of the latter. It must always be a source of regret that Lavoisier did not describe the apparatus in which he placed Seguin, and by means of which he obtained the results just given, the genius of Lavoisier being as conspicuously manifested in the disposition of experimen- tal detail, as in the establishment of grand generalizations. In all probability the apparatus used was essentially the same as in the case of the experiments performed upon the guinea-pig with the same object, that of determining the amount of oxygen absorbed and carbon dioxide exhaled in a given time, consisting in that instance of a bell-jar standing over a pneumatic trough, wdthin Avhich the animal was introduced and supported, after being passed up through the water of the trough, the oxygen being introduced as needed, in known quantities, and the carbon dioxide exhaled ab- sorbed by alkali. Recent researches* have shown that from 7 to 34 per cent, more oxygen is absorbed and from 7 to 31 per cent, more carbon dioxide expired during digestion than when fasting. This increase in the gaseous interchange during digestion appears to be due not only to the oxidation of the products of digestion and to the chemical pro- cesses incidental to the latter, but more especially to the activity of the muscular walls of the alimentary canal.* The reverse effect, or the diminution in the exhalation of carbon dioxide in the absence of digestive activity through the depriving one's self, or an animal, of food, was also shown by Yierordt in his own person, by Spallanzani in the case of snails and silk worms, Marchand in frogs, and Bidder and Schmidt on cats.^ That muscular exertion increases the absorption of oxygen and expiration of carbon dioxide, has also been proved by a number of 1 Milne Edwards, Physiologie, Tome ii., p. 536. 2 Mem. del' Acad, des Sciences, 1789, p. .575. »Loewv, Pfliiger s Arcliiv, Band 43, 1888, s. 515. *Zuntzn. Mering, Ebenda, Band 32, 1883, s. 173. ^ Milne Edwards, op. cit., p. 538. ABSORPTION OF OXYGEN. 399 observers. Thus, according to Yierordt/ during moderate exer- cise the carbon dioxide exhaled was increased in amount 19 c. c. (1.197 cubic inches) per minute, while Dr. Smith ^ found that in walking at the rate of three miles an hour, the exhalation of carbon dioxide in one hour was equal to that exhaled during two and three- quarter hours of repose with, and three and one-half hours of re- pose without food, and that the amount of carbon dioxide expired during one hour's work on a tread-wheel was equal to four and one- half hours of rest with and six hours without food. According to Pettenkofer,^ while a man absorbed during rest 867 grammes of oxygen and expired 930 grammes of carbon dioxide, he absorbs during the performance of moderate work, 1006 grammes of oxygen and expires 1134 grammes of carbon dioxide. Hirn^ states, how- ever, as the result of experiments made upon several men that four times as much oxygen is absorbed during work as during rest. The oxygen absorbed and carbon dioxide exhaled is also very much increased by involuntary excitement such as shivering for example, or to a greater extent even by voluntary effort.'' It should be mentioned when muscular exertion is so excessive as to produce fatigue and exhaustion that the gaseous interchange is diminished and the same holds true of severe mental, as well as of bodily work. It has been shown by Speck '^ that the maximum increase of oxygen and carbon dioxide is attained before that of exertion ; that according to the position of the body, the increase for the same amount of work varies, that for a given amount of work the respira- tory activity is greatest during the first part of the period of its performance ; that the greater the increase of carbon dioxide ex- pired, the less is the increase proportionally of oxygen absorbed, so that the carbon dioxide expired may contain more oxygen than is absorbed ; that the quantity of air breathed is so intimately related to the carbon dioxide expired that the latter may be regarded as a measure of respiratory activity. A natural inference from what has just been stated would be that during sleep the oxygen absorbed and carbon dioxide expired would be diminished, and such has been shown experimentally to be the case." According to Smith - the amount of carbon dioxide expired during the night as compared with that expired during the day was in the ratio of 1 to 1.8. In hibernating animals like the marmot, for example, the amount of gaseous interchange is so small that lit- tle or no difference can be detected in the composition of the air in ' C'vclopiedia of Anat. and Pliys., Vol. iv., p. 348. 2 Op. cit., p. 713. 3Lo(._ cit. * Exposition analytique et experimentale de la theorie mecanique de la Chaleur, 3d ed., Tome i., p. 35. ^Marcet, A Contribution to the History of the Respiration of ^lan. London, 1897, p. 43. •■Deutsches Archiv f. klin. Medecin, Band 45, 1889, s. 4()1. 'Milne Edwards, op. cit., Tome ii., p. 528. ^Qp, ^it., p. 693. 400 RESPIRA TION. which the animal has remained for three hours when in this torpid state. Indeed, according to Kegnault and Reiset/ only one-thir- tieth of the usual amount of oxygen is absorbed by the animal when in this condition. The experiments of Vierordt - show that with slight diminution in the external temperature the amount of carbon dioxide exhaled by man is increased about one-sixth. Thus the external tempera- ture being between 3 and 15 degrees C. (37.4° and 59° F.), the absolute amount of carbon dioxide exhaled per minute was 299.33 c. cm. (about 18 inches), while with the external temperature be- tween 16 and 24 degrees the amount exhaled was only 257.81 c. cm. (15 inches). The result of Vierordt's experiments might have been anticipated, since a fall in the external temperature necessitates a greater production of heat, the high temperature of the body being maintained, and this implies a greater absorption of oxygen and consequently a greater exhalation of carbon dioxide. AVhen we come to study the production of animal heat we shall see that one of the most striking contrasts between mammals and birds, as com- pared with remaining animals, is the power the former possess of generating heat to replace that lost through a fall in the external temperature. On the same principle as that just mentioned w^e should expect to find also that more carbon dioxide is exhaled iu winter than in summer, there being a greater demand for the pro- duction of heat in the former case than in the latter. This has been shown to be the case more particularly by the researches of Dr. Edward Smith. '^ Thus the maximum amount of carbon dioxide is exhaled in January, February, and March, the minimum amount in July, August, and part of September ; June and July being months of gradual diminution, October, November, and December of gradual increase. It should be mentioned in this connection, however, that animals, and probably also man, cannot at once adapt themselves as regards their respiration to sudden changes in tem- perature. Thus it was shown many years ago by W. Milne Ed- wards ^ that birds, for example, in w^inter would still consume the same amount of oxygen and exhale the same amount of carbon dioxide as usual, though the external temperature w'as artificially raised to that of summer heat. The inverse ratio existing between the temperature of the environment and the amount of carbon dioxide expired, just referred to, does not, however, always obtain, since Page and others^ have shown that w4iile the expiration of carbon dioxide diminishes with a rise of temperature from 4.4° C. (39.9° F.) to 14.3° C. (57.7° F.), with the attainment of the latter temperature the expiration increases. The effect of variations in the temperature of tlie body upon respiratory activity differs, how- ever, from that of changes in the temperature of the environment, 'Op. fit., p. 411. 2 Op. fit., p. 551. 3()p. cit., p. 703. * De r InlliK'iicc (k's Ajjcns Phvsiques sur la Vie. Paris, 1824, p. 200. 5 Journal of Physiology, Vol.' 2, 1S80, p. 228. JXFLUEXCE OF PSESSUJiE. 401 respiratorv activity being increased l\v a rise and diminished by a fall in the bodily temperature. Thus it has been shown by Colosanti ^ that while g'uinea-pigs absorb per kilogramme per hour 948.17 c. c. of oxygen, the temperature being 37.1° C. (98.7° F.), they absorb as much as 1242.6 c. c, the temperature being 39.7° C. (103.4° F.), and the same results have been obtained by experi- ments- made upon man during the condition of fever. It is well known also that the absorption of oxygen and the expiration of carbon dioxide undergo diurnal variations, the gaseous interchange rising after and falling before meals, the minimum being reached at night, the latter effect being partly due to the fact that more carbon dioxide is expired during sunlight than in darkness. It is well known that the expiration of carbon dioxide is greater in a moist than in a dry atmosphere. Thus, according to Leh- mann,^ rabbits exhaled in a moist air the temperature being 38°C. (100° F.) 352 c. c. (22 cu. in.) of carbon dioxide, while in a dry air at the same temperature they expired only 240 c. c. (15 cu, in.). It has been shown among others by Paul Bert ^ that any increase or diminution in barometric pressure acts upon living beings in in- creasing or diminishing the tension of the oxygen in the air they breathe, and the blood that circulates through their tissues, and that any increase or diminution in atmospheric pressure is unfavor- able to living beings accommodated as they now are, to the present tension of atmospheric oxygen. Indeed, according to this observer, all life perishes in air sufficiently compressed. With a pressure simply of several atmospheres symptoms of narcotic poisoning set in similar to those experienced in breathing an atmosphere contain- ing an excess of carbon dioxide, and due probably to the same cause, namely, an excess of carbon dioxide in the blood. With still higher pressure, 4 of oxygen — that is, 20 atmospheres, and upward — death takes place from asphyxia, accompanied with convulsions, as when caused by a deficiency of oxygen. Precisely the same effect is caused by the gradual diminution of atmospheric pressure. A sudden diminution, however, causes death, probably through the liberation of gases in the blood, which interfere mechanically with its circulation. It might be supposed that an increase or diminution in the den- sity of the air inspired, increasing or diminishing the amount of oxygen absorbed, must sooner or later influence the amoimt of car- bon dioxide exhaled. That such is the case is shown by the ex- periments performed many years ago by Hervier and St. Leger^ in which it was proved that with a slight augmentation of atmospheric pressure, the amount of carbon dioxide exhaled Avas increased. iPfliiger's Archiv, Band 14, 1877, s. 125. ^Fubini and Benedicenti. MoleschoU Untei-sucli. , Baud 14, 1892, s. 623. 3 Physiological ('lieinistrv, 1885, vol. ii.. p. 144. *La Pression Barometrique, 1878, p. 115.S. ^Gazette des hopitaux, 3me serie, 1849, Tome i., p. 374. 26 402 BESPIBA TION. When the pressure, however, exceeds twenty atmospheres the pro- duction of carbon dioxide is diminislied correspondingly to the diminished oxidation, and with still higher pressure it is entirely arrested, oxidation, according to Bert,' as we have seen, ceasing then altogether. With a diminution of atmospheric pressure the amount of carbon dioxide produced is also diminished. The oxygen absorbed and carbon dioxide expired is necessarily influenced by the integrity of the nervous system since the nutritive processes in the tissues, as we shall see hereafter, are governed by the former. Thus division of the motor nerve supplying a muscle reduces the consumption of oxygen 22 per cent., and the production of carbon dioxide 30 per cent., while sectiou of the spinal cord diminishes the absorption by the tissues of oxygen 4 per cent., and the expiration of carbon dioxide 20 per cent., destruction of the cord causing the gaseous exchange to fall to a minimum." In this connection it may be mentioned that the respiratory activity is much greater in hot- blooded than in cold-blooded animals, and that among the former the respiratory activity of birds is higher than that of mammals. Of the same species, cxeteris paribus, the respiratory activity is greater in small than in large animals, the greater consumjjtion of oxygen and production of carbon dioxide being due to the fact that the body surface is greater in relation to the body weight in the former, which entails therefore proportionally a greater loss of heat. Having considered the amounts of oxygen absorbed and carbon dioxide expired, and the various conditions affecting the same, let us study now the ratio in which these gases are interchanged. As the volume of carbon dioxide produced through the combining of carbon with oxygen is equal to the volume of oxygen entering into its formation, it follows if all the oxygen absorbed in inspiration combines with carbon to form carbon dioxide, the volume of the carbon dioxide expired ought to be equal to that of the oxygen inspired. We have just seen, however, that the inspired air loses while in the lungs 4,78 vols, per cent, of oxygen, M'hereas it gains only 4.34 vols, per cent, of carbon dioxide. The ratio of the weight of oxygen contained in the carbon dioxide expired to the weight of the oxygen simultaneously absorbed was called by Pfliiger'^ the "respiratory quotient" and on the above supposi- tion the air respired being estimated in liters woidd be equal to Grammes. Liters. Oxygen 6.205 _ 4. 34 Oxygen 6.834 ~" 4.W 0.907 It will be observed that the respiratory quotient 0.90 is not the ratio of the weight of the oxygen absorbed to the weight of the car- bon dioxide expired, but to the weight of the oxygen in that car- 'Op. c'it., p. ]1.")2. 2Q„i„q„auf|^ Corapt. rend. Soc. Biol., 1884, p. 342. aPHiiger's Archiv, Band 14, 1877, s. 472. RESPIRATORY QUOTIENT. 403 bon dioxide/ Since the latter occupies, however, the same volume as that of the carbon dioxide expired, the respiratory quotient is CO often expressed by the formula ~~ which in the above case 4.34 becomes j-^q =0.907. Inasnuich as of the oxygen absorbed part only is expired in the carbon dioxide, it is evident that part leaves the body in some other form than that of carbon dioxide, and which ex- plains the fact that the volume of the expired air is slightly less than that of the inspired air. In speaking of the composition of the car- bohydrates, it will be remembered that attention was called to the fact of the hydrogen present being in the proportion to form mth the oxygen water. Suppose now that starch, a carbohydrate, be oxidized, the result would be the formation of carbon dioxide and the setting free of the water, the reaction being as follows : C AoO. + O,, = 6(C0 J + 5(H,p) In an animal fed exclusively upon starch the respiratory (quotient will be, therefore, unitv, ~—^- = 1, the volume of carbon dioxide 6(0,) expired being equal to that of oxygen absorbed, all of the latter combining with carbon. If, however, the same animal be fed upon a fat in which the hydrogen is in excess, more than sufficient to form water with the oxygen present, the absorption of oxygen and the oxidation of the fat would result in the formation of carbon diox- ide and the setting free of the water, as in the first case ; but as part of the oxygen absorbed would also combine with that part of the hydrogen in excess to form water, necessarily some of the oxy- gen absorbed would not reappear as carbon dioxide in the expired air, but as water. The reaction would be as follows, supposing olein to be the fat used : C..H,, + SCH^OJ + 0,„„ = 57(CO J + 2{Ilfi;) + 46(H^O) The respiratory quotient on a diet of fat would be, therefore, 57(00^)^0 71, 80(0,) -' If the animal is fed uj)on meat, the respiratory quotient is found to vary from 0.75 to 0.81 (according to the thoroughness with which the meat is digested), since after the urea was separated from the albumin the remainder of the meat would contain an excess of hydrogen, as in the case of fat, hence part of the oxygen absorbed in respiration would not reappear as carbon dioxide but as water, part of the oxygen combining with the carbon to form carbon dioxide and part combining with the hydrogen to form water. These theoretical considerations^ are fully confirmed by the ex- periments of Eegnault and Reiset in which it was shown that in 1 See p. 389. 2 Qp. eit. 404 RESPIRATION. animals fed upon starch the diiference between the weight of the oxygen absorbed and that expired in the carbon dioxide was far less than in the case of animals fed upon fat or meat. On the other hand, in certain kinds of vegetable food, fruits, etc., the oxy- gen present being in excess more than sufficient to form ^vith the hydrogen, water, it is to be expected that more oxygen will be ex- pired in the carbon dioxide than absorbed in inspiration as shown, for example, in the oxidation of tartaric acid C^H^O, -r O3 = 4(C0 J - 3H^0 The respiratory quotient on such a diet would be, therefore, more than unity 8(0)vols. ^ _ The respiratory quotient being the ratio of the oxygen absorbed to the carbon dioxide expired must be affected by the same conditions that we have seen influence the gaseous interchanges and will vary according as the diet is a starvation one, mixed or limited to one particular kind of food. Thus, the respiratory quotient upon a starvation diet is equal to 0.68, upon a non-nitrogenous one 0.75, upon a nitrogenous one 0.90, upon a mixed one 0.94, no work being done and the oxygen absorbed and carl)on dioxide expired, being such as given on page 440. Admitting that the part of the oxygen which is absorbed in inspiration and does not reappear in the carbon dioxide expired, combines with hydrogen to form water within the economy, the quantity so formed and exhaled is small as compared with the Avater taken in as such. Suppose that the hydrogen available for combustion is about 13 grammes (200 grains), the water formed would amount to only 117 grammes (1805 grains), H.O H 1I„0 H 18 : 2 : : 117 : 13 whereas, the water exhaled from the lungs of a man amounts on the average in twenty hours from 400 to 800 grammes^ (6172 to^ 12344 grains). The manner in which the water exhaled by an animal is deter- mined has already been referred to in the descri])tion of the respira- tion apparatus made use of for that purpose. In the case of man,^ however, the water exhaled can be more accurately determined by breathing into a curved tube, terminating in Liebig's bulb, filled "svith sulphuric acid and pumice-stone for the absorption of the water, the latter being estimated Ijy the increase in weight. The amount of water exhaled from the respiratory tract Mill be influenced, as in the case of inert bodies, by the amount of water present in the atmosphere, the temperature, and the pressure. Hence, the dryness of tlie throat and fauces experienced by persons 1 Valentin, Lehrbuch der Physiologie, Band i., s. 527 ; Bunge, Lehrbuch, 1894, s. 272. TEMPERA TUBE OF EXPIRED AIR. 405 Fig. ascendino^ into high altitudes through the loss of water due to the diminished pressure and great cold. The extent of the respiratory surface ^y\\\ influence also the amount of aqueous vapor exhaled. This is well seen in the diminution of the exhalation in old ag'e, as shown by Barral/ the pulmonary cells becoming larger, a less extent of respiratory surface is offered. Finally, the amount of water exhaled is increased by the quan- tity of water taken in as drink, etc., and by the frequency of the respiration. In conclusion, it should be remembered that, if the ordinary con- ditions prevailing be reversed, water may be ab- sorbed by the respiratory surface instead of being- exhaled. The sudden gain in weight frequently observed in individuals who had not partaken of solid or liquid food, often referred to by -writers on physiology," is due, no doubt, to absorption by the lungs of the watery vapor of the atmosphere, rather than to cutaneous absorption, as sometimes sup- posed. The expired air differs from that inspired, not only in having lost oxygen and gained carbon di- oxide and water, but in being warmer. It is due to this fact that the volume of the expired air is about one-ninth greater than that of the inspired air. If, however, both the expired and inspired air be reduced to standard temperature then the volume of the expired air will be found to be less, as already mentioned, than that of the inspired air. According to Grehant,'^ the air being inspired by the nares and having a temperature of 22° C. (71.6° F.), that exhaled by the mouth had a tem- perature of 35° C (95° F.), as determined by a thermometer (Fig. 207, C) placed within the appa- ratus A, through which the air was expired, and which was uninfluenced by the external tempera- ture. When the air was, however, inspired by the mouth, the air expired had a temperature of only 93°. The result of Grehant's observations differ a little from those of Valentin/ previously made. According to the latter observer, the external temperature being at 20° C. {(i^° F.), that of the expired air was 37.2° C. (90° F.). The temperature of the surrounding atmos- phere has an important influence, however, upon that of the expired air ; thus, according to Valentin, in winter the external tempera- ture being — 10° C. (14° F.), that of the expired air was only 29° C. (85° F.). Apparatus for de- termining tempera- ture of expired air. ' Ann. de Cliimie, 1S49, 3me ser., Tome xxv., p. 166. ^Carpenter's Physiology, p. 4U-1. ^Journal tie I'Anat. et de la Phys., Tome i., 1864, p. 546. ' Op. oil. 533. 406 RESPIRATION. Ammonia is undoubtedly exhaled from the lungs, being almost invariably found in the expired air. In fact, it is only absent at certain periods of the day, or during cold weather, as noticed by Richardson,^ In certain conditions of the system, as in cases of ureemic poisoning, the amount of ammonia in the expired air is so great as to become very perceptible to the patient." Considerable difference of opinion has prevailed among physiolo- gists as to whether nitrogen was absorbed or exhaled during respi- ration. The researches of Regnault,^ Boussingault,^ and Barral,^ however, that, in mammals and birds at least, under ordinary cir- cumstances, a small quantity of nitrogen is exhaled in respiration, equal to about one-fiftieth by weight of the oxygen absorbed. The reverse, however, appears to be the case with fishes, according to Humboldt and Provencal,*' nitrogen being absorbed by those animals. According to recent researches " in the case of man no appreciable amount of nitrogen is either absorbed by or given out from the blood during respiration. In speaking of nitrogen, it may be incidentally mentioned that its mixture with oxygen as the air we breathe is obviously of advantage, since, on account of its great diffusibility, the air vitiated with carbon dioxide is readily re- newed during respiration. A small quantity of organic matter, the nature of which is not thoroughly known, but, as we shall see, is, to a great extent, poisonous in character, is constantly present in the expired air. The presence of this organic matter can be shown through the putrefaction of the aqueous products of the expired air when condensed in a cool receiver, or through the putrefaction of a sponge saturated with the vapors exhaled by the lungs. Many articles of food, like onions, garlic, alcohol, sj)irits of tur- pentine, drugs like camphor, musk, asafoetida, when absorbed by the blood and vaporized in the system, are exhaled by the lungs, being readily recognized by their odor in the expired air. That poisonous gases are also exhaled by the lungs is rendered very probable by the experiments of Bernard - and Nysten,^ in which sulphuretted hydrogen and carbon oxide, so fatal when inhaled, were ejected into the veins without bad eflPect, being eliminated by the lungs as ra])idly as they were taken u[) by the venous blood. Many animals in which the respiration is of a feeble character, such as slugs, snails, certain kinds of fish, frogs, etc., continue to live in air from which the oxygen has been removed to a consider- able amount.^" Such, however, is not the case with animals whose respiration is very active, as in man. Any considerable diminution in the amount of oxygen in the surrounding air soon causes death. 'Tlie Cause of tlie ('oagulation of the Blood, p. 360. Ijondon, 1857. ^Lehmann, Pliys. C'liein., Vol. ii., p. 434. Philadelpliia, 1855. ^Op. cit., p. 510. MJhimie Agricole, pj). l-'24. Paris, 1854. 5 Op. cit., p. P29. 6 Milne Edwards, Physiologic, Tome ii., p. 599. 'Marcet, op. cit., p. 27. ^ Substances Toxiques, p. 58. Paris, 1857. ^Recherches de Physiologie, p. 81. ^^Mihie Edwards, Physiologic, Tome ii., p. 020. I EX TIL A no X. 407 Just as a lamp jj^oes out when the air feedino: it does not contain more than about 1 7 per cent, of oxygen, so with the lamp of life its flame too dying; out, respiration soon ceasing, if the amount of oxygen usually present in the atmosphere be diminished ])y ab- sorption, or through dilution with some indifferent gas. In fact, air which has been breathed by man once should not be breatlied again ; such air having lost oxygen and gained carbon, if breathed twice, will give up but little oxygen to his economy. Indeed, as shown by Lavoisier,^ air, having lost about 10 per cent, of oxygen, becomes absolutely irrespirable. Such is found to be the case in certain parts of mines where the air contains only that amount of oxygen. It is well known, also, that birds and mammals will suf- focate in an atmosphere in Avhich the amount of oxygen has been diminished to that extent. Thus, a mouse ^x\\\ die in six minutes, if confined in such an atmosphere, and a sparrow in an hour, if the oxygen be diminished to half that amount, or 5 per cent. It is not, however, the want of oxygen alone that causes death in breath- ing bad air, but the simultaneous increase of carbon as well. The ill effects experienced under such circumstances, such as head- ache, the sense of oppression, and even stupor appear to be due not to the carbon dioxide expired, but to the organic matter which it contains just referred to. This is shown by the fact that an atmos- phere containing 1 per cent, of pure carbon dioxide exerts no de- leterious eflPeet upon the economy, Avhereas an atmosphere contain- ing the same amount of carbon dioxide that has been expired is not only highly injurious, but soon becomes unendurable." As the nature and amount of the organic matter expired to which the deleterious effects of breathing vitiated air is due are unknown, the carbon dioxide expired is taken as a measure of the same. Expe- rience has shown that air fit to breathe should not contain more than 0.07 per cent, of carbon dioxide, and as 468 liters of carbon dioxide are expired in twenty-four hours it is obvious that the latter must be exhaled into 668304 liters of air if that air is to contain only 0.07 per cent, of carbon dioxide. xlit. That is to say, every human being must be supplied with over 27,- 846 liters of air per hour in order that the CO., exhaled into it should not exceed in amount 0.07 per cent. A room having a cubic capacity of 10 meters (352 cubic feet) would contain air enough to supply a human being enclosed within it with oxygen for twenty-four hours, but to prevent vitiation of the air the room would have to have a cubic capacity of 674 meters ' Denxieme, Memoire sur la respiration mem. de Clieniie, T. iv. , p. 22. 2 Pettenkofer, Med. Times and Gazette, 1862, p. 459. co„ Air. CO. 0.07 : 100 : : 1 X = 1128 air. : 1428 : : 168 lit. X = 668301 lit. ai 408 BESPIRATION. (23,724 cubic feet) iu order that at the end of the twenty-four hours the carbon dioxide exhaled into the air M'ould not amount to more than 0.07 per cent. In breathing in the open, where the atmospheric air is out of all proportion to that expired by any one individual, at no moment is any want of fresh air experienced. In our dwellings also, if prop- erly constructed, a due supply of fresh air is maintained by the opening of the windows and doors, and the entrance of the outside air through the cracks, crevices, etc. In churches, theaters, lec- ture-rooms, barracks, prisons, hospitals, etc., however, where large numbers of people are congregated together, the proper supply of fresh air should never be left to chance. Indeed, this is now so well understood that in the ventilation of such buildings as the Chamber of Deputies and many of the hospitals in Paris, in the House of Commons in Loudon, in the Philadelphia Academy of Music, etc., the air is continually renewed by means of fans worked by engines, etc., regard being paid to the fact that the air supplied is in reference not only to the amount of oxygen to be inspired, but also to the carbon dioxide, organic matter, etc., exhaled to be car- ried away, care being taken that the expired air does not mix with that to be inspired, and at the same time that drafts be avoided, the velocity with which the air passes through the chambers not being greater than from two to three feet per second. Internal Respiration. It has already been mentioned that while in external respiration the oxygen of the air passes into the blood and the carbon dioxide of the blood into the air, in internal respiration the oxygen of the blood passes into the tissues and the carbon dioxide of the tissues into the blood. The distinction between external and internal res- piration is, however, a superficial one, since the blood is the means by which the oxygen of the air is indirectly carried to the tissues, and the carbon dioxide produced in the latter conveyed to the air. It should be remembered, however, that the blood, in addition to being the means of transportation of oxygen and carbon dioxide to and fro, as a tissue, consumes oxygen and produces carbon dioxide like other tissues. Thus it is well known that when readily oxi- dizable substances are introduced into the blood and the latter is transfused through the lungs or lung tissues more oxygen is taken up and carbon dioxide given off than by normal blood. There ap- pears to be but little doulit that under ordinary circumstances the tissues give uj> to the blood similarly substances whose complete metamorphosis involves the consumption of oxygen and production of carbon dioxide.' The relative avidity with which the tissues absorb oxygen is shown according to (^uinquaud- in the accompanying table, 100 grammes ' Bohr and IlcnriqiU'Z, Coniptcs Heiidiis, Tome 114, 181)2, p. 14i)(). ^ Comptes Eendus Soc. Biologie, Tome ii., ISUO, p. 28. ABSORPTIOX OF OXYGEN BY TISSUES. 409 of tissue having been snl)niitted in each instance to experiment for a period of three liours at a temperature of 38°C. (100°F.). Absorptiox of Oxygex by Tissues. Muscle . 23 c. c. Spleen . 8 Heart . 21 " Lungs . 7.2 Brain 12 " Adipose tissue 6 Liver 10 •' Bone •5 Kidney . 10 •• Blood . 0.8 Oxygen in being absorbed by the tissues appears to enter into some form of molecuhir combination since its tension in the hitter amounts practically, as already mentioned, to zero. That tlie carbon diox- ide is formed to a great extent, at least, in the tissues, is shown by the fact that the amount of carbon dioxide in the fluids of the cav- ities of the body is greater than that in the l^lood, as shown below, and which can only be accounted for on the supposition that the ■carbon dioxide of tliese fluids passed into them from the tissues, Texsiox of Caebox Dioxide ix Fliids of Body.' Mm. Hg tension. Arterial l)lood 21.28 Peritoneal cavitv ....... 58.50 Acid urine . " 68.00 Cavitv of intestine ....... 58.50 Bile (gall bladder) 50.00 Hydrocele fluid 46.50 Lymph (thoracic duct) ...... 34.00 Tlie carbon dioxide produced in the tissues does not appear to be «ame of animal. Mammalia — Hog, Manatee, Rabbit, Sheep, Goat, Rat, Squirrel, Cat, Panther, Dog, Monkey, Porpoise, Ox, Elephant, Horse, Meptilia — Green snake. Tortoise, Iguana, Alligator, A mphibia — Frog, Pisces — Trout, Eel, Articulata — Beetle, Cockroach, Mollusca — Oyster, Snail, Echinodermata — Star fish. Sea urchin, Sea cucumber. Vermes — Leech, Cn'Jenterata — Anemone, Jelly fish, J'onfera — Sponge, Temperature. 105 (40.3° C.) 104 abdomen, 104 to 100, 104 104 102 102 102 102 102 101 100 liver. 100 99.5 99.5 87 oesophagus, 82.5 69 64 58 51 Observer. Davy. Martine.' Prevost and Du- mas, ^ de la Roche. 3 Davy. Jones. « Davy. 77 surrounding air 76°, 75 " " 74°, Temp, same as sea, 82°, 76.5 surrounding air, 76.25^ 6-10° F. above temp, of sea (66.3°) A^alentin.^ 5-10 " " " (66.7 ) " 6-10 " " " (67.6 ) " " " of air (56. ) Hunter. « Valentin, 5-10 7-10 " " of sea (69.4 ) " " " (72.5 ) Same as sea (68.3° F.) 1 Essays, Medical and Philos., 1740, p. 387. ^Annales de ('him. et de Phys., 2e serie, Tome xxiii., p. 64, 1823. 3 Journal de Physique, Ixxi., p. 298, ISIO. * Investigations, Chem. and Physiol., Smith Contrib., 1856. ^Repertorium fiir Anat. nnd Phys., Vierter Band, s. 859. Bern, 1839. *" Works, ed. by Palmer, Vol. iv., p. 147. London, 1885. WALFERDIX METASTATIC THERMOMETER. 415 As the temperature species, and accordino; differs often in individuals of tl to the biological conditions in- fluencing the animal at the moment of observations, and farther, as the number of observations are compara- tively limited, any results, such as offered in the above resume can only be accepted as giving approximately the average temperature in animals. Of all animals, birds have the highest temperature, that of the chicken, for example, according to Davy ^ being as high as 43° C. (111° F.), a slightly higher temperature, according to Pallas,' even being found in certain small birds. Among mammals the temperature of the rabbit is noteworthy, amounting to 40° C. (105.8° F.). On the other hand the temperature of fishes, with some exceptions, is not usually more than 0.5° C. (0.9° F.) higher than that of the water in which they life, whilst among the invertebrata,^ as in the case of mollusks, star fish, jelly fish, anemone, the excess of the temperature over that of the surrounding medium may be even less, amounting often to no more than 0.2° C. As an exception to the last statement and interesting in this connection may be mentioned the considerable amount of heat developed by bees and ants when swarming. Although a great number of observa- tions have been made, some difference of opinion still prevails as to what constitutes the average normal tem- perature in man. This, however, is readily understood when, as we shall presently see, the temperature of the body not only varies considerably in different situations, but according to numerous circumstances ; among others may be here very appropriately mentioned especially the manner in which the thermometrical observations should be made. It is of the highest importance, not only that the part of the body selected for taking the temperature should be mentioned, but that the ther- mometer used in making the observation should be a standard one. The metastatic thermometer of Walferdin (Fig. 208) is a convenient form of instrument since by means of it a variation of yi^- of a degree. Centigrade, correspond- ing to a millimeter in length of the mercury, can be accurately determined. The instrument, however ex- cellent it may be at the time obtained, should neverthe- less be constantly tested. Further, in using the thermometer it should be so ap- ^ Researches, Phjs. and Anat., p. 186. London, 1839. ^Gavarret, De la Chaleur Prouduite par les Etres Vivants, p. 94. Paris, 1855. 3 Milne Edwards, Physiologie, Tome neuvieme, 186.3, p. 13. le same Fig. 208. w \Vallerdiu's metastatic thermometer. (Laxdois.) 416 ANIMAL HEAT. Fig. 209. plied that the part Avhose temperature is to be determined completely surrounds the bulb of the instrument ; hence, of all parts of the body, the rectum is that which is best adapted for tliermometrical obser- vations, the instrument being inserted to a depth of at least 5 cm. (2 in.). On account, however, of being more convenient, the axilla is frequently made use of in determining the temperature of the human body. It must be remembered in that case then that the temperature is usually ^^-g- to 1 degree lower than that of the rec- tum. The tongue and vagina arc also frequently made use of in taking the temperature. Apart from individual idiosyncrasies the diiference of opinion that prevailed more particularly among the older physiologists with reference to the temperature of man is largely due to neglect of the precautions just referred to. If from the nature of the case, on account of the size of the cavity to be examined, etc., the application of a thermometer is inadmissible, thermo- electric needles are then made use of in determining the temperature. Even greater precautions must be taken than when the observation is made in the usual way on account of the delicacy of the apparatus, as slight a variation as the 47PI7-Q- of a degree having been de- termined by such. Thermo-electric needles (Fig, 209, A f, f A) are usually made of iron and German silver, each needle consisting of iron (f ) and silver (A), soldered together at and near their points, and the two so disposed as to constitute together an element. The iron wires being in the middle, and the silver ones externally, if the latter are connected with each other through a galvanometer (M), a circuit is formed. The deviation of the needle will then indicate the temperature of the part examined through the elec- tricity developed by the contact of the needles Avith the heated surface. The wires are, of course, except where soldered together, carefully isolated, and where held, are covered with silk and var- nish. When the difference in the temperature of two parts of the body is to be determined, the two needles are imbedded in the parts, and the intensity of the current measured and the amount of heat determined, the relation between the deviation of the needle and the amount of heat producing it having been previously experi- mentally determined. This can be accomplished by immersing the needles with delicate thermometers attached, in oil baths Thermo-electric needles. (Landois.) TEMPER ATUEE OF THE HUMAN BODY. 417 cliiFering in temperature, for example, by one dei»:ree C. The deviation of the galvanometer needle will then indicate a diifer- ence in temperature of one degree C Suppose, further, that as measured by the scale, the deviation of the galvanometer needle amounts to 150 mm., then ^-^77 of a decree C. of temperature is indicated by a deviation of 1 mm. of the needle. If absolute temperature be required, then one needle is applied to a surface maintained at a known temperature, and the other to that whose temperature is to be determined, or the known temperature can be gradually reduced until there is no deviation of the needle. The opposite currents being then equal the heat producing them must be equal — that is, the unknown heat is equal to the known. It was by means of such a thermo-electric apparatus that Becquerel,^ and Breschet determined the temperature of the biceps muscle under different external conditions, to be referred to in a moment, and Nobili and ^Melloni - proved that the internal temperature of insects was slightly higher than that of the surrounding atmosphere. Among the most reliable observations that have been made with reference to determining the average temperature of the human body may be mentioned those of Hunter,'^ 37.2° C. (98.9° F.), Daw,' 37.3° C. (99.1° F.), AVunderliclV 37° C. (98.6° F.), Jurgensen,« 37.2° C. The mean of Jurgensen's observations, it will be ob- served, is the same as that of Hunter, a confirmation of the accuracy with which that great physiologist investigated the subject of ani- mal heat as all other biological phenomena. The results of Jurgen- sen's experiments are most important, both on account of their number and the length of time over which they extended. They consisted in reading oif at intervals of five minutes tlie indications of a thermometer permanently retained in the rectum, and extended over three days. The mean obtained by Jurgensen was 37.2° C. (98.9° F.), which we will consider as being the average normal temperature of the human bodv, although variations l)ctween 37° and 38° C. (98.(3° and 100.4° 'F.) may occur within the limits of health. Among the various conditions that modify the normal temperature may be mentioned, in addition to the influence of the part of the body examined, to which we have already incidentally alluded, that exerted l^y age, sex, the time of day, food, muscular and mental work, external temperature, etc. To the consideration of these let us now turn. 1 Ann. des Sciences Xaturelles, 2d sen, 1835, t. iii., p. •2()9. 2 Ann. de Chimie et de Physique, 1S.>1, t. xlviii., p. 208. '^ Works of .John Hunter, ed. bv J. F. Palmer, vol. i., p. 289. London, 1835. Phil. Trans., 1844, p. 61. ^Eesearches, Phvs. and Anat., 18.S9, vol. i., p. 162. 5 Op. cit., s. 92." ^ Deutsche Arch iv klin. Med., Band iii., s. 166. 27 418 ANIMAL HEAT. Age and Sex. According to Andral/ Biirensprung,- and others, the temperature before birth, as well as immediately afterward, is slightly higher than that of the mother ; but as the newborn child possesses but little power of resisting external cold, its temperature soon falls, within two hours, perhaps, from 37.8° to 35.2° C. (100.04° to 95.3° F.). Hence the importance of providing for the infant suf- ficient warmth by suitable means, and to the neglect of which the death in many instances is undoubtedly due. Immediately after birth the temperature of the infant taken in the rectum is between 37.5° and 37.8° C. (99.5° and 100.04° F.), falling after the first bath to 37° C. (98.6° F.) and even lower, while during the next ten days it varies between 37.25° and 37.6° C. (98.9° and 99.6° F.), being notably increased by screaming, etc. During the period in- tervening between early infancy and the age of puberty the tem- perature falls about 0.2° C. (3.6° F.), and from there on till adult life falls about 0.2° C. still more, the normal temperature or 37.2° C. (98.9° F.) being then reached. After sixty years of age the temperature begins to rise again, and at eighty years has again reached that of the newborn child. This rise in temperature in old age is probably due to the diminished circulation of the anaemic skin, since it cannot be supposed that the production of heat has been increased. As a general rule, sex has no appreciable influ- ence upon the temperature of the body. According to Ogle,^ how- ever, the temperature of the female appears to be slightly higher than that of the male. Diurnal Variations. The temperature of the body, like the frequency of the pulse, respiration, and exhalation of carbon dioxide, exhibits periodical variations. From the numerous observations of Davy, Hallmann, Gierse, Biirensprung, Lichteufels, Frohlich, Damrosch, Ogle, Lieb- ermeister, Jurgensen,^ it appears that the temperature of the body increases very quickly from (5 A. M. to 11 A. M., but from that time forward increases more slowly, reaching a maximum between 5 and 6 P. M. About 7 in the evening the temperature begins to fall, reaching the minimum about 5 A. M., tlie diiference being in 24 hours usually about 1° C. (1.8° F.), though it may amount to as much as 2° C. (3.6° F.). Climate seems to influence the time of day at which the maxi- mum and minimum temperatures occur, the minimum being reached, according to Davy, in England by midnight, but in the tropics not before 6 or 7 A. m. iCompt. Rend., T. Ixx., p. 825. 2V. Biirensprung, Arch. f. Anat. u. Phys., 1851, s. 138. 3Kirke's Physiology, 10th ed., p. 255. Phihi., 1881. *Rosentlial, die Physiologic der thierischen Warme in Ilcnuann, op. cit.,Vierter Band, s. 322. VARIATIONS IN TEMPERATURE. 419 Diurnal Variation in Temperature/ A. M. M. P. M. our. Barensprung. i'avy. Ilallmann. Gierse. Jurgensen. 5 .... Cent 36.7 36.6 6 36.68 36.7 36.4 7 36.94* 36.63 36.98 36.7* 36.5* 8 37.16* 36.80* 37.08* 36.8 36.7 9 36.89 36.9 36.8 10 37.26 37.36 37.23 37.0 37.0 11 36.89 37.2 37.2 12 36.87 37.3* 37.3* 1 36.83 37.13 37.3 37.3 2 37.05 37.21 37.50* 37.4 37.4 3 37.15* 37.43 37.4* 37.3* 4 37.17 37.5 37.5 5 37.48 37.05* 37.31 37.43 37.5 37.5 6 36.83 37.29 37.5 37.6 7 37.43 36.50* 37.31* 30.00 37.5* 37.6* 8 .... 37.4 37.7 9 37.02* 37.4 37.5 10 37.29 37.3 37.4 11 36.85 36.72 36.70 36.81 37.2 37.1 12 .... .... 37.1 37.4 1 36.85 36.44 37.0 36.9 2 .... 36.9 36.7 3 36.8 36.7 4 Ast( Brisk .signifies that food was taken. 36.7 36.7 Supposing with Jurgensen, tliat the day temperature begins at 6 A. M. with ;36.4'' C, and ends at 8 p. m. wdth 37.7°, the^ dura- tion of the former with a usually mean temperature of 37. 3°, ex- ceeds the latter with a mean of 3G.9° by four hours, the average temperature for tlie whole dav, being, as already mentioned, about 37.2° C. (98.9° F.). As m^ight be expected, ^Debczyn.ski - finds that persistent night work reve rses the rhythm of the variations of temperature, the thermometer standing highest in the morning (37.8°), instead of in the evening (35.3°). Food. As in the long run the heat, as we shall see, is due to the com- bustion of substances taken into the body as food, it follows that the production of heat is intimately associated with that of nutri- tion. Inasmuch, however, as it is not until the last stage of inani- tion in the starving man or animal that the temperature notably falls, it having been previously maintained in the absence of food through the combustion of the tissues, it is not to be expected that in health the mere taking of food will influence the temperature to any great extent, since the fuel, so to speak, is ordinarily consumed as rapidly as supplied, and when deficient is made up at the expense of the tissues. For example, very hot drinks increase the temperature but little. Suppose, for example, a man weighing (JO kilogrammes (132 pounds) drinks a kilogramme (2.2 pounds) of water at 50° C. 'Landois, op. cit., s. 406. ^ Yirchow u. Hirs?h, Jahresber., 1875, Band i., s. 248. 420 AXniAL HEAT. (122° F.), the temperature of the whole body — supposing it to be o7.2° C. (98.9° F.) aud having the same specific heat as water — would be increased only about 0.2° C. (0.3° F.). It must be re- membered in this instance, as in many others, that the eiFect of taking a hot drink is not so simple as may at first appear, since the circulation being increased by it the loss of heat through evapora- tion will be increased. The one effect neutralizing to a certain ex- tent the other, the full effect of the drink as regards elevation of the temperature is not therefore experienced. Even if the drinks contain specific substances, such as tea, coffee, alcohol, etc., the tem- perature of the body is diminished only two- or three-tenths of a degree C. It is possible that the loss of heat experienced in the taking of alcohol is not only due to the quickened circulation, but to a paralyzing effect exerted upon the vasomotor nerves of the skin, whereby a greater quantity of blood l)eing conveyed to the surface than usual, more heat is consequently given off and so lost. On the other hand, while the effect of cold drinks, etc., is to dimin- ish the temperature of the body, the diminution is also very slight, amounting usually to but a few tenths of a degree C. Thus, ac- cording to Lichteufels and Frolich, AVinternitz, and others,^ drinks at a temperature of 18°, 1(3.3°, and 4.6° C, reduced that of the body in the first two instances within 6 minutes after taking them 0.1°, 0.4°, and in the last in 70 minutes 1.4° C. Further, as in the digestion of solid foods, heat is required to assist the chemico- physical changes, it might be expected that as part of the heat becomes latent, the temperature of the body would be slightly dim- inished temporarily after taking the food, even though the tempera- ture should l)e increased later through further oxidation. That such is the case seems to he shown by the experiments of Vintschgau and Dietl," made upon a dog with gastric fistula, in which the tempera- ture of the food introduced, and which differed but little from that of the body, first fell and then rose. From what has just been said, however, of the compensating power exercised by the economy, whether food be taken or withheld, it would be inferred that the influence exerted by the taking of food upon the daily variations must be very slight, if any. Indeed, the variations in temperature that are observed after meals, as a matter of fact, occur whether food be taken or not. The most, indeed, that can be said is that if a meal be taken late in the day the diminution in temperature, characteristic of that period, is somewhat put off. Indeed, it is not until shortly before death caused by inanition or starvation, for the reasons already given, that the temperature is notably diminished. Muscular, Mental, and Glandular Action. We shall soon see, in our study of muscular action, that at the moment of muscular contraction a considerable amount of heat is set ^ Rosenthal, op. cit. , s. 325. 2Sitz. d. Weiner Acad. Math.-Xatur. u. CI., 2 Abtli, ix., s. ()97, 1870. IXFLUEXCE OF MUSCULAR EXERCISE. 421 free — indeed, probably tlirce-foiirths of the heat developed is pro- duced in the muscles. Thus, according to Davv/ the temperature of the room being 66° F., that of the feet 60°, under the tongue 98°, and of the lu-ine 100° ; after a walk in the open air at 40° the tem- perature of the feet was 96.5° and the urine 101°, that under the tono-ne being unchanged. Indeed, daily observation as well as special experiments teaches us that our ^vhole body is warmed by muscular exercise. Further consideration, however, will show that the body is not as much heated as one would be led to expect from the amount of heat developed under the circumstances, and from the rapiditv with which the temperature of the body foils to the nor- mal with the cessation of the exercise, it is evident that as fast as the heat is developed it is as rapidly radiated away or lost as some other mode of energy. The influence of muscular exercise in ele- vating the temperature of the body is also well seen under certain pathological conditions ; the temperature in tetanus, for example, rising, according to Wunderlich," as high as 44.75° C. (111.2° F.). It should be mentioned, however, that this great rise in temperature can hardlv he attril)utcd entirely to muscular action, since in all probabilitv, at the same time, other influences come into play, such as the action of the vasomotor nerves, which in constricting the vessels of the skin will diminish the usual loss of heat due to radi- ation and evaporation. Xervous-like muscular activity is also accompanied with the pro- duction of heat. Thus, according to Davy,^ during the reading of a work, in England, demanding attention, the temperature of the bodv was increased 0.5° F. Mental effort iu the tropics is accom- panied by a still greater production of heat, amounting, in some instances, to more than 2° F., as in the giving of a lecture, for ex- ample ; in the latter case some of the heat was probably due to the muscular action involved. Lombard* has also determined, by means of delicate thermo-electric apparatus, local increase of tem- perature in the head resulting from mental effort. Schiff"'' has also shown that the action of the nerves, as well as that of the brain, is accompanied with the production of heat. In all in- stances, however, the amount of heat produced, at least that ap- pearing as such, is a small part of the heat produced, as in the case of muscle being converted, as we shall see hereafter, into other modes of energy. Glandular action is also accompanied by the production of heat due to the chemical activity incidental to secretion. Thus, according to Ludwig and Spiess "^^ the temperature of the saliva secreted dur- ing stimulation of the chorda tympani is 1 to 1.5° C. higher than that of the blood of the carotid artery of the same side. AVe have already called attention to the fact of the temperature of the blood 'Phil. Trans., 1844, p. 63. ^Qp. cit., s. 400. ^Pbil. Trans., 1845, p. 443. * Experimental Eesearches on the Regional Temperature of the Head. London, 1879. 3 Archiv de Pliy. Normal et Path., 1870, pp. 5, 198, 323, 421. ^Wien. Sitzb., Band xxv., 1857. 422 ANIMAL HEAT. of the hepatic vehi being higher than that of any other part of the body, due, in part at least, to the size and constant activity of the liver. Surrounding Temperature. Any consideration as to the temperature of man or animal would naturally suggest the influence exerted by that of the surrounding atmosphere, and concerning which there was, at one time, much diflFerence of opinion. So distinguished a teacher as Boerhaave, for example, advocated ^ that neither man nor any animal that breathes by lungs can live in an atmosphere the temperature of which is as high as that of their own bodies and cites ^ in support of this view the experiments performed at his request, by Fahrenheit and Provost, which consisted in placing a sparrow, a cat, and a dog in a sugar- baker's oven, heated to 146° F., and in which it was found they soon died. Notwithstanding the result of these experiments, the great Haller, basing his opinion upon the testimony of Lining Adarason, and other travelers, as to the intense heat that prevailed in certain parts of this country, South Carolina, Senegal, and else- where, hekP in opposition to the view entertained by Boerhaave that man could not only live in an atmosphere 16°, but even 28 °F., higher than that of the blood. About this time important obser- vations bearing upon this question were made by Franklin and Governor Ellis. In a letter dated London, June 17, 1758, in re- ferring to a hot Sunday passed in Philadelphia, in June, 1750, Franklin * recalls tliat, during the day, when the thermometer was at 100° F., in the shade, his body never grew so hot as the air surrounding it, or the inanimate bodies immersed in the same air, and, with his usual acuteness, accounts for the body being kept cool under such circumstances by continual sweating, and by the evaporation of that sweat. Within a month of the same year — that is, in July 17, 1758 — Governor Ellis, in a letter to his brother in London, called atten- tion particularly to the fact that, while in Georgia, a thermometer suspended from under an umbrella which he carried during a walk of one hundred yards registered 105° F., the temperature of his body was only 97°. The letter of Governor Ellis being communi- cated to the Royal Society ^ was thereby at once insured a wide cir- culation ; that of Franklin, though •written first, was not made public, however, till afterward." Shortly after the observation of Ellis, just referred to, it was ascertained l^y Tillet," in experiment- ing with a baker's oven, that the young women in attendance were accustomed to remain in it for a few minutes even when at a tem- ' Pnplectioncs Academicise, Gottingen, 1740, ^'ol. ii., p. 211. ^ Elcmonta Chemiir, Lipste, 1732, Tomus Primus, p. 238. ^Klementii Phvsiologiii?, p. 37. Lausanne, MDCCLX. * Works, Vol. 'iii., p. 301. Phila., 180<). 5]'hil. Trans., 17o9, Part ii., Vol. 1., p. 755. ^.Journal de Physique, 1773, Tome ii., p. 453. 'Mem. de I'Aead. des Sciences, 1764, Tome Ixsxi., p. 188. SURROUNDING TEMPERATURE. 423 peratQve of 126.6° C. (260° F.). In one instance Tillet, anxious for the safety of the woman, requested her to come out, but she as- sured him she felt no inconvenience, and remained in the oven for ten minutes, the latter having a temperature of 137.7° C. (280° F.) ; indeed, on her coming out, beyond the flushing of* the face, there was nothing especially noticeable. While the facts just referred to excited considerable interest at the time, it was not till some years later, however, that any further experiments were performed with the object of ascertaining the effect of heated air upon the tempera- ture of the body. In 1774, the subject, however, was taken up again by Fordyce, who, together with Blagden, Solander, Banks, and others, experimented upon themselves, either in a room heated with flues, and upon the floor of which boiling water was poured, or in rooms heated with flues only. The result of these experi- ments, as descril)ed l)y Blagden,^ may be summed up as follows : In the room containing vapor Fordyce was able to bear for 10 minutes a temperature of 43.3° C. (110° F.), 20 minutes 48.8° C. (120° F.), and for 15 minutes a heat gradually increasing from 53.8° to 54.4° C. (119° to 130° F.). In these experiments, it is said, that the temperature under the tongue and of the urine did not rise higher than 37.7° C. (100° F.), In the room heated with flues onlv, and containing dry air, Fordyce, together with Blagden and Banks in the room, could stand, however, a higher heat than in the former instance, supporting for ten minutes a temperature of 92.2° C. (198° F.). Shortly after these experiments it was ascer- tained by Dobson,- from observations made in the sweating-room of the Liverpool Hospital, that individuals could stand for periods between 10 and 20 minutes a temperature, if the air be dry, of be- tween 94.4° and 106.6° C. (202° and 224° F.). Fordyce, him- self, as mentioned in a subsequent paper by Blagden,^ was able to endure for 8 minutes even as high a temperature as 127° C. (260° F.), the uncomfortable feeling experienced quickly passing away with the breaking out of a profuse sweat. The immunity possessed by persons habitually exposed from time to time to a dry atmosphere, having a temperature even higher than that to which Fordyce, Blagden, etc., were subjected, is undoubtedly due, in a great measure at least, as Franklin supposed, to the cold produced through the evaporation of the cutaneous perspiration and pulmo- nary exhalation. In this way can be explained how the workmen of the sculptor Chantry went into a furnace having a temperature of 171° C. (340° F.), and Chabert, the fire king, into one at be- tween 204° and 315.5° C. (400° and 600° F.). Indeed, the salutary effect, under such circumstances, of keeping the tempera- ture down by evaporation was fully recognized by Fordyce and Blagden,* and proved by them in the following way : Two similar earthen vessels, one containing. water only and the other an equal iPliil. Trans., Vol. Ixv., 1775, Part i.. p. 111. ^ifj^.ni, p. 4(13. 3 Idem, p. 484. *0p. cit., p. 491. 424 ANIMAL HEAT. quantity of water, with a bit of wax, were put upon a piece of wood in the heated room. In an hour and a half the pure water was heated to 60° C. (140° F.), while that containing the wax had acquired a temperature of 66° C. (152° F.), as the wax in melt- ing had formed a film upon the surface of the water, and thereby had prevented evaporation. Further, it was observed that the pure water never came near the boiling point, but if a small quan- tity of oil was dropped into it, as had been done before with the wax, finally the water in both vessels boiled briskly. The effect of sweating in keeping down the bodily temperature is daily seen in the taking of Turkish as compared with Russian baths, an equally high temperature being much better borne in the former, on account of the air being dry, than in the latter, where the air is moist. The profuse perspiration induced through hot baths has long been a matter of comment ; as early as the first half of the last century Le Monnier/ in speaking of the natural hot baths at Baregas, with a temperature in the hottest part of 44.4° C. (112° F.), observes that the sweat poured down from his face after remaining in it 8 minutes, and that after that time he was obliged to leave the bath, with reddened and swollen skin, and greatly increased pulse through violent attacks of vertigo. The conclusion draAvn from the different experiments of Fahrenheit and Provost, Tillot, Fordyce, and Blag- den, etc., that we have just described, was that man could not only exist in an atmosphere having a higher temperature than that of his own body, but that the latter remained unchanged, even when that of the surrounding atmosphere was greatly increased, notwithstand- ing that in an experiment with a dog the temperature was found by Fordyce to increase. It would appear, however, without doubt, from later ol)servations, that with an increase in the temperature of the surrounding air there is an increase in that of the body. Thus, in the experiments made by De la Roche ^ and Berger, it was found that, after remaining 15 minutes in a vapor bath, with a tempera- ture varying between 37.5° and 48.8° C. (99.5° and 119.8° F.), the temperature in the mouth was increased 3.1° C (5.5° F.), while in dry air, but at a temperature of 80° C^ (176° F.), the temperature was increased about 5° C. (9° F.). According to Davy ^ also, who made a great number of observations in different parts of the world, the mean temperature of the body in the tropics is about 1° F. higher than in England. Such a variation has been held by Boileau,^ for example, as abnormal, and as an indication of a slight disturbance in the system due to change of climate, and to which certain delicate persons are liable. The observations of Eydoux ■'' and Souleyet, made during the voyage of the " Bonite," and of Brown-Sequard,*' to the Isle of France, though less in 'Mem. de I'Acad. des Sciences, 1747, Tomelxiv., p. 271. ^Theses de I'ecole de medecine de Paris, 180G, No. 11. Journal de physique, 1776, Tome vii., p. 57. 3Philos. Transact., IS-jO, p. 437. ^Lancet, 1878, p. 413. ^Comp. Kend., 1838, Tome vi., p. 45(5. ^Journal de Physiology, T. ii., p. 554. SURROUNDING TEMPERATURE. 425 number than those of Davy, so far as they go, confirm the result obtained by that reliable observer. Davy^ also showed, from a number of observations, that the mean temperance of the air being 15.5° C. (60° F.), that of the body was 36.7 C. (98.28° F.), whereas, if the temperature of the air rose to 26.6° C. (80° F.), the temperature of the body rose to 37.5° C. (99.67° F.). The temperature of individual portions of the body has been shown to increase with that of the surrounding medium, as well as that of the whole body. In an experiment of Becquerel and Bres- chet,^ for example, where the biceps muscle was surrounded for 1 5 minutes by water at a temperature of 42° C. (107.6° F.), the tem- perature, as determined by their thermo-electric apparatus was in- creased two-tenths of a degree. The rise in temperature, through increase of heat in the surrounding atmosphere, can be well shown in animals. Thus, according to Rosenthal,^ the temperatm'e of a rabbit rose from the normal, 38° C. (104.4° F.) to 45° C. (113° F.), while the external temperature was increased from 32° to 40° C. (89.6° to 104° F.), death taking place at the latter temperature. Essentially the same result was obtained in the experiments of De la Roche and Berger with a guinea-pig. According to these ob- servers, as well as Rosenthal, an increase in the temperature of 6° to 7° C. (10.8° to 12.6° F.) above the normal, however brought about, is fatal to all animals. It would appear from these experi- ments as well as the earlier ones of Provost and Fahrenheit, that large animals bear a high temperature better than small ones, prob- ably Ijecause, in the latter, a greater quantity of heat is produced relatively and more quickly. Thus, in the experiments of Fahren- heit, already referred to, of the three animals placed in the oven the sparrow died in 8 minutes, whereas the dog and the cat survived 28 minutes. According to De la Roche and Berger, a mouse died in 32 minutes, the temperature being increased from 57.5° to 63.7° C. (135° to 146.6° F.), while a guinea-pig survived 1 hour and 25 minutes, the temperature rising from 62 to 80° C. (143.6° to 176° F.); a young ass, however, though weak at the end of the experiment, successfully resisted for nearly three hours a tempera- ture increased from 60° to 75° C. (140° to 167° F.). In the case of man, in certain pathological conditions, as in typhoid and typhus fever, the temperature of the l)ody may rise to 40.5° and 41.1° C. (105° and 106° F.), and yet recovery take place. The highest temperature yet observed in man, and ending in recovery, was in a case of injury to the spine, reported by Dr. J. Teale/ in which the thermometer registered 50° C. (122° F.). The elevation in tem- perature in sunstroke, 40° to 44.4° C. (104° to 112° F.), is also very consideral)le ; in such cases, however, the high temperature is to be attributed, in part at least, not only to the eifect of exposure to the sWs heat, but also to the exercise taken incidental to the 1 Eesearclies, Phvs. and Anat., p. Klo. ^Ann. des .Sciences Xat., 1838, p. 271. "Op. cit., s. 337.' * Lancet, March 6, 1875. 426 AXIMAL HEAT. character of the occupation of those usually attacked, such as field and street laborers, soldiers, etc. Inasmuch, as we have seen, through the free action of the skin, and with proper precautions taken as regards exercise, food, cloth- ing, etc., man can live in an atmosphere the temperature of which is much higher than that of his body, it might naturally be sup- posed that through similar compensating agencies intense cold can be equally well resisted, if not better than intense heat. Such, indeed, experience proves to be the case, the temperature of the body of man, even when exposed to the intense cold of the Arctic regions, is almost the same as in the temperate ones, since the amount of heat generated absolutely, is greater on account of the quantity and quality of food, and relatively so, from the fact of the clothing, etc., being of such a character as to retain the heat produced. In ani- mals the latter protective effect is provided for Ijy their fur, wool, feathers, etc., as the case may be. A glance at the temperature of Arctic animals, as given below, will show how little the temperature of the body in such animals differs from that of animals in temperate regions, though the differ- ence in the temperature of the former, as compared with that of the surrounding atmosphere, mav amount to as much as 76.7° C. (170° F.). Temperature of Arctic Aximals.' Anim al. Temp. of animal. Temp, of air. Difference. Arctic fox . 41.o°C .(106. 7°F.) —25.6° c. 67.1°C. (( . 38.5 —20 6 59.1 a . 37.8 —19.4 57.2 1 ( . 38.5 —29.4 67.9 i i . 37.6 —26.2 63.8 a . 36.6 —23.3 59.9 i i . 37.6 —23.3 60.9 a . 40.3 —20.3 70.7 White hare . 38.3 —29.4 67.7 Fox 1 ( . 37.8 . 41.1 —26.2 —35.6 64.0 76.7 a . 39.4 —32.8 72.2 a . 38.9 —31.7 70.6 u . 38.3 —35.6 73.9 Wolf . 40.5 —32.8 73.3 On account of water Ijeing a better conductor, and having also a greater capacity for heat than air, the temperature of the body will fall more rapidly if exposed to cold water than to air at the same temperature ; hence the great effect of cold baths in the treatment of fevers so much in vogue, particularly in Germany, in late years, and th(; great benefit derived from the application of ice in the treatment of sunstroke. While man and animals can resist the most intense Arctic cold by the agencies just referred to, neverthe- less a far less degree of cold, if suddenly and directly applied to ^Gavarret, op. cit., p. 101. Parry's Journal, p. 130. Philadelphia, 1821. PRODUCTION OF ANIMAL HEAT. 427 the body, will soon prove fetal. Thus, according to Rosenthal,^ animals die if the temperature of their bodies be reduced to 24° C. (75.2° F.), and such is usually the case in man also, as shown by the clinical cases referred to by the same liigh authority ; though, as well known, the temperature in cholera may fall as low as 18.3° C. (64.9° F.). There are some other conditions in addition to those already mentioned which may affect the temperature of the body. Of such are the eff'ects exerted by race, country, labor, sea-sick- ness, and barometrical variations. As such influences are, however, either exceptional or temporary in their character, we will not dwell fiirther upon them, merely mentioning that, according to the late distinguished Professor Dunglison," the temperature of the uterus during labor may rise as high as 41.1° C. (106° F.), that of the vagina at the same time being 40.5° C. (105° F.). Production of Animal Heat. Having considered the temperature of the body, and the various modifying conditions, it now remains to account for the production of this heat, and the manner in which the latter is regulated. Xot- mthstanding that a certain amount of heat is produced through the double decompositions and hydrations continually taking place in the economy,-^ there can be no doubt that, by far the greatest amount of heat produced is due, as Lavoisier supposed, to the slow combustion continually o-oino; on within the body of the animal, caused by the absorption of oxygen, the interchanging of which with carbon dioxide, etc., we ha ye seen, constitutes the essence of respiration. In the paper on the calcination of metals, brought l)efore the Academy of Sciences, in 1775, Lavoisier* had shown that in the decomposition of mercuric oxide by heat the principle (oxygen) so obtained supported both combustion and respiration, whereas, when the same substance was reduced by carbon the principle then obtained (carbon dioxide) supported neither. These fundamental facts having been established, two years later Lavoisier'^ further showed that animals absorb oxygen and exhale carbon dioxide, and during the same year formulated a view on combustion in general in which respiration was regarded as a slow process of combustion, oxygen being absorbed and carbon dioxide and heat given off" just as in the burning of coal. As might have been expected from the methods of investigation so characteristic of the great chemist and physiologist, Lavoisier soon instituted a series of experiments with the view of ascertaining Avhether the amount of carbon dioxide ex- haled and heat produced by an animal in a given time was such as ought to be expected on the supposition that a certain amount of carbon had been burned in the body of the animal, the amount of 'Op. cit., s. 133. 2 piiy^iology, 1856, 8th ed., Vol. i.. p. 6U2. ^D'Arsonval, C'omptes Rendus, Aout 'ioth, 1879. *Mem. de I'Acad. des Sciences, 1775, p. 520. ^gbenda, 1777, p. 183. 428 ANIMAL HEAT. carbon dioxide given off and heat produced ]>y the combustion of a similar amount of carbon outside of the body having been previously determined, and of so establishing the truth of his theory by ex- perimental demonstration. For this purpose, in conjunction with Laplace, he invented the ice calorimeter/ This consisted essentially of three chambers, concentrically disposed ; in the innermost cham- ber was placed the substance mIiosc lieat was to be determined, in the middle one ice, the melting of which was the measure of the heat produced, it having been previously determined how much heat is required to melt a given quantity of ice, wliile in the outer chaml)er ice was also placed in order to shield that in the middle chamber from the external temperature, the melted ice passing out by openings in the two outer chambers provided with stopcocks. Having determined by their experiments the amount of heat that would lie produced Ijy the burning of a pound of carbon Lavoisier and Laplace then placed a guinea-pig in the innermost chamber of their ice calorimeter, so modified as to permit of the free passage of a current of air, so that the respiration of the animal should not be interfered witli, and found that the amount of carbon burned by the guinea-pig while in the calorimeter as deduced from the carbon dioxide expired was only sufficient to account for about nine-tenths of the heat produced as measured by the ice melted. This fact, together with another one observed at the time, namely, that all the oxygen absorbed did not return in the carlion dioxide exhaled, led Lavoisier^ afterward (1785) to the conclusion that of the oxygen inspired part combined with hydrogen to form water and that the heat developed by the combustion of the hydrogen, if added to that due to the combustion of the carbon, would account for the heat produced by an animal, as in tlie experiment with the guinea-pig, just described, and which could not be accounted for by the combustion of the carbon alone. The final conclusion of La- voisier as to the nature of respiration and calorification, leased upon the closest reasoning, observation, and experiments, extending over many years, is best expressed in his own words :^ " Respiration is only a slow combustion of carbon and hydrogen, and which re- sembles in every respect that which goes on in a lighted lamp or candle, and, from this point of view, animals which respire are true combustiljles, which form and consume themselves. In respiration, as in combustion, it is the atmospheric air which furnishes the oxy- gen and caloric,* but, as in respiration, it is the substance itself of the animal ; it is the blood which furnishes the combustible. If animals do not repair hal)itually by food that whicli they lose in ^ Mem. de 1' Acad, des Sciences, 1780, p. 3o5. 2 Hist, de la .Societe Koyale de Medecine, 1787, 508. "Mem. de I'Acud. des Sciences, 1789, p. 570. * To appreciate this passage it must be borne in mind that at tlie date when it wa.s written oxygen was supposed to be composed of oxygen united with caloric, the principle of heat or fire, and that during the formation of carlwn dioxide through the combination of oxygen with carbon the caloric was set free. THE CALORIMETER. 429 respiration, the oil will soon give out in the lamp, and the animal would perish, as a lamp extinguishes itself through want of feeding. The proof of this identity of eifects between respiration and com- bustion is immediately furnished by experiment. In fact, the air which has maintained respiration does not contain any longer, at its exit from the lungs, the same quantity of oxygen ; it contains not only carbonic acid [carbon dioxide] , but, in addition, more water than it contained before inspiration." And now, after a lapse of more than a century, the only essential criticism that can be made upon the views of Lavoisier as to the origin of animal heat, apart from the hypothesis of caloric implied, is that he held that the lungs were the seat of the combustion, whereas it is known that combustion goes on in all parts of the body. But even while holding this view Lavoisier showed his profound appreciation of the nature of the phenomena, since he distinctly states, in one of his communications,^ that possibly the carbon dioxide is not produced, but only exchanged with oxygen in the lungs. However important his generalizations, as to the matter of respiration and animal lieat, nevertheless, dying on the scaffold a victim to the fury of the French Revolution, Lavoisier left his work unfinished. With the view of settling, if possil)le, some of the questions left undetermined by their great chemist, the Paris Academy offered, in 1821, a prize for the best essay on the origin of animal heat. The prize being aAvarded to Depretz, his essay was shortly afterward published,^ that of the unsuccessful competitor, Dulong,'^ not, however, until several years afterward — in fact, after the death of its author. To avoid repetition, we will consider the calorimeters made use of by these experiments and the results ob- tained with them together. The calorimeter of Dulong and Depretz did not differ in prin- ciple essentially from the water calorimeter previously made use of, for the same purpose, by Crawford.* It consisted essentially, like the latter, of two chambers, an inner one, in ^vhich the animal within a willow cage was placed, and an outer one, containing the distilled water, the elevation of whose temperature was taken as the measure of the heat produced by the animal. In the calorim- eter of Crawford, however, while the air of the inner chamber was gradually diminished, and at the end of the experiment was transferred to an eudiometer for analysis, in that of Dulong and Depretz the air in the inner chamber was continually renewed by air from a gasometer, and being transmitted from the inner cham- ber through a spiral tube placed within the water of the outer chamber, passed thence into a water gasometer, where it could be measured and analyzed, the air, in the meantime, as it passed through the spiral tube, giving off the heat (communicated by the ^Mem. del' Acad, des Sciences, 177", P- 191. '^Ann. de Chimie et de Physique, 1824, Tome xxvi., p. 337. ''Ibid., 3ieme serie, 1841, Tome i., p. 440. * Experiments and Observations on Animal Heat. London, 17S8, p. 315. 430 ANIMAL HEAT. animal) to the surrounding water, and so elevating its temperature. The amount of heat produced by the animal, as determined by the elevation of the temperature of the water, is expressed in calories, or heat units, a heat unit being the amount of heat necessary to ele- vate the temperature of a pound of distilled water one degree Cent, or Fahr., according to the thermometer used, or, as is more usually understood at the present day, the amount of heat necessary to ele- vate the temperature of one kilo. (2.2 lbs.) one degree Cent. The amount of heat produced by the animal expressed in heat units while in the calorimeter is then obtained by multiplying the weight of the water by the number of degrees by which the temperature of the water has been increased. Suppose, for example, that the water in the calorimeter weighed 20 kilo., and its temperature had been elevated as shown by the thermometers two degrees Cent,, then 40 calories, or heat units, Avould have l^een produced during Fig. 210. Water calorimeter of Dulong. the experiment by the animal, the latter having neither gained nor lost heat, since, if the animal gained heat, it is evident that all of the heat produced was not given off* to the water, and if it lost heat the latter was not produced during the experiment, but simply ra- diated away from it, as would have been the case with any heated l)ody. In the first case, the heat retained by the animal must be added to the heat as determined by the calorimeter ; and, in the second case, the heat lost by the animal must be subtracted. In making calorimetrical experiments, therefore, the temperature of the animal must be taken at the bes^innine: and the end of the ex- periment. It must be also remembered, however, that the materi- als entering into the composition of the calorimeter, such as copper, iron, brass, etc., absorb heat, even if in less amount than the water, and this heat also expressed in heat units must be added to that absorbed l)y the water. Tliis can be readily estimated, the weight of the materials and their specific heat, or capacity for heat, being ' THE CALOKIMETER. 431 known, the capacity for heat of water being taken as unity. Sup- pose, for simplicity, that the calorimeter is made out of copper, and that it weighs 10 kilo. ; now the specific heat of copper be- ing 0.09 that of water, it is evident that if the 10 kilo, of copper be multiplied by 0.09, the product 0.90, or the water equivalent, when multiplied by the two degrees Cent, equals 1.8, which will be the amount of heat expressed in heat units absorbed by the copper, and which must be added to the 40 heat units already obtained ; or, what is the same thing, if the water equivalent of the copper 0.9, be added to the 20 kilo, of water, and the re- sult 20.9 be multiplied by 2, the quotient will be the same as before — that is, 41.8 heat units produced by the animal. In other words, each kilo, of copper, having 0.09 the capacity of heat of a kilo, of water, 10 kilo, of copper may be regarded as equiva- lent to 0.9 kilo, of water, which, when added to the 20 kilo, of water and multiplied by 2, or the temperature gained, gives 41.8 heat units. It is hardly necessary to add, after what has just been said, that of the other metals usually entering into the construction of the calorimeter the heat absorbed by them, as well as that re- tained or given oif by the animal, which, as we have seen, must be added to or subtracted from the 41.8 heat units, for example, ac- cording as the animal has gained or lost heat during the experi- ment, is determined in exactly the same way as in the case of the copper. As regards obtaining the water equivalent of the animal placed in the calorimeter — that is, its weight multiplied by its specific heat — a difficulty presents itself, since the specific heat of animals has not been absolutely determined. The latter is usu- ally accepted as being 0.8,^ that being the mean specific heat of the tissues so far determined, water being taken as unity. In determiuino: the amomit of heat o-iven off bv an animal in a calorimeter there is another consideration which must not be over- looked, and which is a slight source of error even in the best constructed calorimeters. That is the slight loss of heat due to con- duction and radiation from the instrument, and which cannot be en- tirely prevented. The loss of heat from this cause, however, can be reduced to a very small amount by proper precautions, such as surrounding the calorimeter ^vith down, etc., as was done by Craw- ford, or ])y lowering the temperature of the water in the calorimeter some degrees below that of the surrouuthng atmosphere, the sup- position being that the heat absorbed from the surrounding air dur- ing the first half of the experiment would be radiated back again during the latter half, and that this source of error could, therefore, be neglected, as was admitted in the experiments of Dulong and Depretz. The loss of heat due to radiation, etc., can be also deter- mined experimentally, and can be then taken into account in the final calculation ; or, by self-regulating gas-jets, heat can be sup- ^ Liebermeister, Handburli der Pathologie u. Tlierapie des Fiebers, p. 147. Leipzig, 1875. Kosenthal, Archiv f. Anat., etc., 1878, p. 215. 432 ANIMAL HEAT. plied to restore that which is lost. Further, it is important that the heat should be thoroughly diffused through the water in the calorimeter ; this can be accomplished by the stirrers, as in the ap- paratus of Dulong and Depretz, or by any other suitable mechanical arrangement. The great improvement in the experiments of Du- long and Depretz, however, as compared with those of their prede- cessors, consisted in comparing the expired air with the inspired air, and determining the amount of heat produced and carl)on dioxide ex- haled simultaneously ; whereas, in the experiments of both Lavoisier and Crawford, this was done with the same animal, but at diiferent times. Notwithstanding the great number of experiments per- formed by Dulong and Depretz, and the general acceptance with which their views were received, not much importance can be at- tached to them at the present day on account of the following rea- sons : First. That the temperature of the animal within the calorim- eter was assumed to remain unchanged during the experiment, although Lavoisier had distinctly called attention to the improba- bility of such being the case. Second. Of the amount of carbon dioxide exhaled by the animal being underestimated, part of it be- ing absorbed by the water of the gasometer into which it passes. Third. Of the amount of heat, as deduced from the carbon dioxide exhaled, being also underestimated, both on account of the estimate of Lavoisier of the heat produced by the combustion of carbon and hydrogen obtained with an ice calorimeter, being accepted as the basis of comparison with the heat produced l)y an animal in a water calorimeter, and because the heat-producing power of the carbon and hydrogen burned even, as determined by Lavoisier, is manifestly too low as shown by the later and accurate experiments of Fabre and Silberman ;^ and further, that no account was taken of the heat produced by the burning of the sulphur and phosphorus in the ani- mal economy. Fourth. That the ratio of the carbon to the hydro- gen was erroneously estimated, an important source of error, since far more heat is produced by the combustion of hydrogen than by an equal weight of carbon. Fifth. From the carbon and hydrogen, to whose combustion is the heat principally due, being supposed to exist in the free condition, which they evidently do not. Later investigators have endeavored to utilize the results of Du- long and Depretz in considering them as influenced by the condi- tions just referred to, but as the attempts have been far from satis- factory, it is not necessary to dwell upon them. During late years a number of investigations have been made calorimetrically, with the olyect of determining the heat produced by an animal in a given time. Among these may be mentioned especially those of Senator " upon dogs. The calorimeter used in these experiments was essentially the same as that of Dulong's, the ^Ann. de Chimie et de Physique, 3ieme sen, Tome xxxiv., p. 357; Tome xxxvi., p. 51 ; Tome xxxvii., p. 405. 2 Archiv f. Anat. u. Phys., 1872, s. 1, 1874, s. 18. THE CALORIMETEE. 433 only cliiFerence l)eing that it was usually filled with warm water in order to prevent the animal losing heat. The ventilation of the chamber in Avhich the animal was placed was maintained l)y aspira- tion, the current of air, before entering the calorimeter, being freed from its carbon dioxide by passing it through potash, and the carbon dioxide exhaled into it by the animal being determined after it left it by Pettenkofer's method. In the final estimation of the heat produced by the animal, in addition to that taken up by the calori- meter, the heat absorbed by the air passing through the instrimient was also considered. Senator found, as the mean of his experiments, that a dog fed daily produced 16.5 calories or heat units per hour, with an exhalation during the same time of 4.4 grammes of carbon dioxide, there being produced, as a general rule, 2.5 calories for every kilogramme (2.2 pounds) of weight. In order to obtain the amount of heat produced in twenty-four hours, the 16.5 calories were multiplied l)y 24, l)ut as it is uncertain ^vhether the production of heat is constant, this is hardly admissible. The general conclu- sion to be drawn from the experiments of Senator is, that there i& no constant relation existing between the production of heat and the exhalation of carl)on dioxide, and while during digestion the production of l)oth is increased, in starvation both are diminished. Fig. 211. Calorimeter. The calorimeter (Fig. 211) made use of by the author consists of two copper cylinders concentrically disposed, the outer space a or the space between the cylinders being closed at both ends with copper, the inner space 6, or the space within the cylinder, being closed at one end by copper, and at the other end by an annular door consist- 28 434 ANIMAL HEAT. ing of brass and glass, and which can be hermetically closed by the brass clamps and rubl)er facing soldered to the brass rim internally. The outer chamber a is filled with distilled water by means of a funnel introduced through the opening/, and when full contains 18.1 kilo. (40 lbs.) of water. The inner chamber h, at the end opposite the door, communicates by a stopcock (c/) with the external air, and through the opening h in its roof with a copper spiral, which, after making a dozen turns around the inner cylinder within the water of the outer chamber, terminates in the opening k of the latter. By means of the mercurial pump (already described) the ventilation of the inner chamber can be thorougidy maintained, the air entering the latter through the opening at 2 less grammes of meat, but with 71 more grammes of fat. On the other hand, as Rauke mentions in speaking of the heat produced on a non-nitrogenous diet, of the 150 grammes of fat eaten only 68.5 grammes could have been burned, 81.5 grammes having been deposited in the Ijody. On such a diet, therefore, more than half the flit, if taken with the view of producing heat, would be superfluous. The amount of heat produced upon a mixed diet such as that of Rauke's, as determined from an analysis of the excreta, is some- what less than that ol)tained by multiplying the ditferent amounts of food stuffs contained in such a diet by the number of heat units — we have supposed each gramme of the same would produce when burned in the body, as may be seen from the following calculation : Carbohvdrates 240 grammes X 4.116 = OST.Si calories. Proteids 100 " X 4.937 = 493.70 " Fats 100 " X 9.312 = 838.08 " Total 310 = 2319.62 The difference amounting to about one hundred calories can be to a great extent accounted for, however, when it is remembered that Ilanke assumed that one gramme of proteid, when burned in the body, would jDroduce 4.2(33 instead of 4.937 calories. That the two methods of investigation when properly applied to the same animal will give almost identical results was shown by Rubner,^ l)y an experiment made with a dog in which the heat produced by the animal as determined directly by the calorimeter differed from that as determined indirectly by analysis of the excreta by less than 0.5 per cent. While the heat produced upon a mixed diet was regarded by Ranke," Vierordt,'^ and Yoit,^ respectively, as amounting to 2200, 2497, and 3066 calories, according to the more recent investigations of Danilewsky,-^ 3210 calories are produced upon a mixed diet, moderate work be- ing done and as much as 3780 calories, the work being of a very laborious character. Let us assume, however, with Ranke that the heat liberated by the burning of the food amounts to only 2200 calories, that is, will elevate the temperature of 2200 kilo, of water 1 ° C. or 70 kilo. 31.4° C. (154 poimds 56.5° F.). Such an amount of heat if applied to the heating of a hiunan body weighing 70 kilo. Moidd elevate the temperature 34.1° C. (61.3° 'F.), or 2.1"° C. (4.8° F.) higher, since a human body consisting of only three-fifths water, 42 kilo., and two-fifths tissue, 28 kilo., and the latter having a specific heat, 0.8 that of the water, the 2200 heat units would he applied to heating the equivalent of 64.4 kilo. (146 pounds) of water, instead of 70 kilo. (154 pounds) (28 x 0.8 = 22.4 water ' Zeitschrift fiir Biologie, Band 30, 189:5, s. 13ti. ^Op. cit., s. 207. 3 pl^,^.siologie^ VierteAufl., 1S71, s. 257. * Hermann, Handbuch, Sechster Band, s. 52o. spfliiger's Aixluv, Band 30, 1883, s. 190. 442 . ANIMAL HEAT, 2200 equivalent, 22.4 + 42 = 64.4, -_j^ = 34.1°). In other words the tissue of the human body, from this point of view, bears the same relation to its water as the brass, copper, etc., do to the water of the calorimeter, the human body, in foct, serving as a calorimeter for the determination of the heat produced by foods when l^urned within the body. If, however, the heat produced upon a mixed diet will elevate the temperature of a human being weighing 70 kilo. 34° C. in 24 hours, then at the end of that time the temper- ature of such a person should be about 70° C. (126° F.), and at the end of 4S hours 104° C. (219° F.), instead of 36° C. (98.9° F.), the normal temperature ; as a matter of fact, however, we have seen that the temperature of the human body varies but little. It now remains for us, in conclusion, to endeavor to account for this constant temperature somewhat more in detail than we have already done, and that leads us to the consideration of how the heat produced is expended. Expenditure and Regulation of the Production of Heat. We have seen that there are produced within the human body in twenty-four hours at least 2300 calories, or heat units ; that is, heat enough to raise the temperature of 2300 kilo, of water 1° C, or 23 kilo. 100° C, or from the freezing to the boiling point. It is very evident, therefore, that were such a production of heat kept up, and the heat developed not dissipated, but retained in the body, that the latter in the course of two days, would boil. A little reflec- tion will show, however, that, in addition to the heat given off through radiation and conduction, if the temperature of the body be higher than that of its surroundings, that a certain amount of heat leaves the body in a latent condition, so to speak, locked up in the watery vapor exhaled from the lungs and skin, and from the fact of the solid and liquid food, and the air breathed entering the body at a lower temperature, 15° C. (99° F.), for example, than that of the latter, and leaving it at the same temperature, 37.1° C. (98.9° F.), heat must also be absorbed, and that there must be a still further expenditure of heat in the accomjilishiug of bodily and mental work, since there can be no doubt tliat, whatever be the na- ture of muscular and mental energy, the latter is correlated in some way with heat, the disappearance of the one being coincident with the appearance of the other. Now, from the very nature of the case, the relative amounts of heat expended in the ways mentioned must vary very mucli, according to the character of the climate, of the quantity and (piality of air breathed, of food taken, of the amount of muscular and mental work performed. It is therefore impossible, if for these reasons only, to indicate exactly what be- comes of the heat developed in the body. Further, too much importance must not be attached to any tabular resume of the EXPENDITURE OF HEAT. 443 expenditure of heat, since the data upon which such a resume must be based are, to a certain extent, assumed. It is only of- fered as illustrating in a more detailed way the general observa- tions regarding the expenditure of the heat just made, and as also showing the manner in which a table could be drawn up if all the data had been without cavil experimentally determined. It should be mentioned, however, that this criticism applies only to the rel- ative amounts of expenditure of the heat, the total amount of heat leaving the body being, of course, that produced if the temperature of the body remains constant. A\"e will suppose that the food of a man weighing 70 kilo. (154 pounds) produces in twenty -four hours 2300 calories, or heat units ; that the food of such a man, including the air breathed, be known ; that the specific heat of the food be accepted as l^eing 0.8, and that of the air 0.2() ; that the amount of watery vapor exhaled from the lungs and skin has been determined ; that it be admitted that it requires 582 heat units to vaporize 1 kilo, of water and that the muscular work performed by the man during a day be consid- ered as amounting to 112397 kilogrammeters, that is to say the man lifts 112397 kilo, through one meter (358 tons through one foot), and that the amount of heat necessary to raise the tempera- ture of one kilo, of water 1° C or a heat unit if applied mechan- ically would lift 423 kilo, through one meter (1.3 t(.)ns through one foot), then according to the above data the heat produced will be expended somewhat as follows : Expenditure of Heat. 1.5 kO. (3.3 lbs.) water . . . 34.5 heat units. 1.50 per cent. 1.5 " solid food, raised 23° C. (73°F.) 27.6 " " 1.20 " " 16.0 " (35.2 lbs.) air inspired . . 95.6 " " 4.15 " " 19.0 kil. (41.8 lbs.) 157.7 6.85 0.4 kil. (0.8 lbs.) water ev. froni lungs 232.8 10.12 0.6 " (1.32 lbs.) " •' " skin 384.1 16.70 1.0 kil. (2.2 lbs.) 616.9 26.82 Radiation and conduction . . 1272.6 55.32 External or muscular work . . 252.8 10.99 2300.0 " " 100.00 " " Ratio of muscular work to heat 1 to 9. It will be observed, that of the 2300 heat units produced in twenty-four hours, about 7 per cent, are expended in Avarming the food, including the water and air breathed ; 20 per cent, in evap- orating the water from the lungs and skin ; 55 per cent, in radia- tion and conduction from the general surface of the body, and about 11 per cent., or one-ninth, of the whole heat produced in the per- formance of external or muscular work. Of the bo per cent, of heat that we have supposed is radiated or conducted away, part must be regarded as that heat which we have seen is expended me- chanically in jjerforming the internal work incidental to the circu- 444 ANIMAL HEAT. lation and respiration, bnt which in being transmuted finally into heat aaain, leaves the body in that form rather than as mechanical energy. AVhile 310 numerical estimate can be given, as yet, of the relation existing between heat and nervous energy, there can be no doubt, however, that the latter, like all other kinds of energy, must be developed out of some equivalent form, and leaves the body as such, or as some other mode of motion. That nervous energy is developed out of heat appears very probable from the experiments of Lombard, already referred to, and by which it was shown that, while all mental action was accompanied with the production of heat, that more heat disappeared during deep thought than during reading to one's self, for example, of emotional poetry ; further, it was shown by the same experimenter that more heat disappeared than when the reading was aloud — that is, had a muscular expres- sion, part of the heat produced in the latter case being applied to making the oral or muscular eifort. It is a matter of daily obser- vation that silent grief is deepest, that pent-up emotion finds relief in physical action. This is in accordance with the results of the experiments just mentioned, since the heat that is transformed into emotions or ideas, in the one case, becomes muscular action in the other, and just in proportion as there is more of the one, so there is less of tlie other. Hirn^ endeavored to determine, experimen- tally, the exact quantity of heat expended in the performance of mechanical work by comparing the heat produced within a definite time with the work done, the latter consisting in a man raising his own weight through a given height, the man walking upon the cir- cumference of a tread-wheel rotating in the opposite direction to himself. According to Hirn, a man weighing 75 kilo., during an hour's work upon the tread-wheel placed within the calorimeter, produced 4.">0 heat units, whereas, judging from the amount of oxy- gen absorbed and carbon dioxide exhaled, 500 heat units were pro- duced. What, then, became of the 70 extra heat units? Accord- ing to Hirn, it was at the expense of this amount of heat that the 29,610 kilogrammeters of work were accomplished — that is, of raising; 75 kilo, throug-h nearlv 40(J meters (423x70 = 2-='«^« = 394). On account, however, of the errors incidental to the construction of the apparatus, and of the amount of heat produced as deter- mined from the oxygen absorbed being estimated as too high, the results of Hirn, as just given, cannot be accepted ; nevertheless, the difference between the amount of heat that appeared, as such, and that Av])i(.-li ought to have appeared, can only be accounted for on the supposition that part of the heat produced was expended in the performance of mechanical work, and, as a corollary, it follows that less heat a]ipcars during a muscular contraction, when accom- ' Op. cit., Tome i., p. 35. REGULATION OF TEMPERATURE. 445 panied Avith work, than when without, and which accords with daily experience. Having considered the manner in which animal heat is produced and expended, it remains for us now to account, so far as is possible, for the fact tliat the temperature of a hot-blood animal is maintained nearly constant, notwithstanding the variations in that of its sur- roundings. Among the conditions regulating the production of ani- mal heat may be mentioned the taking of solid and liquid food, the character of the respiration and circulation, the action of the skin, the influence of bodily size. While the amount of heat produced will depend on the quality and quantity of the food, the mere taking of the latter in the form of hot or cold drinks, for example, with the view of increasing or diminishing the general temperature of the body, as is so commonly done, will have, as already mentioned, but little effect. The effect of cold drinks in lowering the general temperature of the body must be also ecjually slight and temporary. On the other hand the effect of a hot drink, as we have seen, may be exactly opposite to what might have been expected, not only through the cooling effect due to the evaporation as in the drinking of hot tea, but on account of the specific substance of which the hot drink consists. Thus, for ex- ample, if hot spirits be taken, while at first a sense of warmth is experienced, with the paralysis of the vasomotor nerves by the al- cohol, a greater quantity of blood flowing to the skin than usual, a proportionally larger quantity of heat will be lost from the general surface, and the effect of the hot drink will be in the long run, there- fore, to lower the temperature of the body rather than to raise it. It has already been mentioned that about 4.1 per cent, of the heat produced is expended in warming the inspired air, and it might naturally be suj)posed that if the respiration be quickened and the amount of air inspired increased, that a proportionally greater quantity of heat would then be expended in warming it. Such Avould appear to be the case, dogs and other animals panting when overheated, since they sweat only in those parts destitute of fur or hair, and the cooling effect of the perspiration being absent, the ex- cess of heat developed is carried away in the expired air. The res- piration when quick, will be more efficient, therefore, in lowering the general temperature of the body than when slow. Hence, also, the rapidity of the breathing in heat dyspnoea, a condition due to the exposure of the body to a high temperature. Under such circum- stances a considerable amount of heat is carried away in the expired air, and the temperature of the body is thereby prevented from rising as high as it would be without such compensatory influence. On account of so much heat being: g-iven off from the skin amountino; through radiation, conduction, and evaporation, to nearly eighty per cent, of the heat produced, any change in the condition of the latter, as regards its structure or the amount of blood circulating through it, etc., will materially influence the general temperature of the body. 446 ANIMAL HEAT. Were the temperature of the skin constant, the amount of heat given oflF or taken up by it would depend simply upon that of the sur- rounding atmosphere, the skin losing heat if the temperature of the iiir was lowered, and gaining heat when that of the air was elevated. As a matter of fact, however, when the body is exposed to a tem- perature cooler than its own, the vessels of the skin contracting, the general surface becomes cooler, the difference between the temper- ature of the body and the surrounding air being diminished, the loss of heat is correspondingly diminished ; on the other hand, when the body is exposed to a higher temperature than its own, the vessels of the skin expanding, the general surface becomes warmer, and a cor- respondingly greater amount of heat is lost. It is a cause frequently of surprise to most persons to learn that, no matter how hot or cold they may feel, the temperature of their body nevertheless remains practically the same. From what has just been said, however, as regards the action of the skin in regulat- ing the temperature of the body, it is obvious that in the cooling of the body through the evaporation from the cutaneous surface, when exposed to a higher external temperature, the greater quan- tity of hot blood then circulating through the cutaneous vessels will, in impressing the sensory nerves, give rise to a general sense of warmth, so that while we feel warmer our body is actually get- ting cooler through the loss of heat involved in the evaporation. On the other hand, when, through the exposure to extreme cold, the cutaneous vessels are diminished in size, the smaller quantity of hot blood circidating through them will give rise to a sense of coolness, so that while we feel cool our body is actually becoming warmer through retention of the heat of the blood within it. The feeling Avarm or cold depends, then, simply upon the relative amounts of blood circulating in the skin. The effect of the successive exposure of the body to cold and heat, as just described, is well seen in the taking of cold baths. While in the bath, the vessels of the skin being contracted, the latter is pale and cold, and the heat is retained, on emerging from the bath the vessels being dilated, the skin is red and warm, and heat is then given oif from the surface. When we come to study the structure of the skin somewhat in detail, we shall see that its adipose tissue, being a bad conductor, prevents any great amount of heat from lacing given oif from the inner parts of the body to the surface, and so lost.' This effect being especially well-marked in those cases where the difference in temperature on both sides of the skin does not amount to more than about 9° C. (16° F.), the significance of tlie good effect of wearing clothing becomes apparent, since under such circumstances the body of a man is surrounded by a layer of air having a temperature of about .'>0° C. (\H^ — H^O = COX^H^ In addition to the facts already offered in favor of the view that urea is produced in the liver, and somewhat in the manner just de- scribed, it may be also mentioned that more urea is found in the liver than in any gland in the body,^ that in acute yellow atrophy ' Zeits. fiir Biolo.oie, Band xr., 1879, s. 122. 2 Hermann, Handbuch, Band vi., 1 Theil, 1881, ss. 189, 192. 3Ptlugei-'s Archiv, Band 46, 1890, s. 552. ^Seejp. 150. ^Centralblatt med. Wiss., 1870, s. 249. 4(38 THE KIDNEYS AND URINE. of the liver the urea of the urine is replaced by leuciu and tyrosin, and that feeding animals with leucin increases the excretion of urea/ Admitting that by far the greatest quantity of urea is produced in the liver, it must be remembered that urea is not only found in the liver, but in many other parts of the system — in the chyle, saliva, blood, serous fluids, etc., and that in starvation in the absence of all food, though the amount of urea is gradually diminished, it is nevertheless present, even to the last. Of course, in such cases, one part of the body being nourished at the expense of another, the nitrogenous tissues, instead of food, supply the materials for the development of urea. That such is the case is shown by an experiment of Schondorif," who observed that while there is no increase of urea in the blood of a fasting dog irrigated through the limbs of a well-fed one, there is a very decided increase of urea in the blood that has passed through the limbs, if the latter be irri- gated through the liver, the blood taking up some substance from the tissues which requires the action of the liver cells to be con- verted into urea. Urea being found under normal circumstances in many parts of the system, and being derived in starvation from the tissues, it is reasonable to suppose that part of the urea is also derived from the latter, even when nitrogenous food is taken, and since leucin and tyrosin are found in the thyroid, thymus, parotid, and submaxillary glands, kidney, liver, and suprarenal capsules, as well as in the pancreas and spleen, analogy would lead us to suppose that they may be antecedents of the urea derived from tissue, as we have supposed them to be of the urea derived from food. In this con- nection it is an interesting fact that M'hile urea is not found in the muscles, spleen, or nervous tissue, creatin (C^H^iN^O^) enters into the composition of muscles to the extent of two per cent., and into that of the spleen and probably of nervous tissue also. Now, since creatin, throvigh dehydration, readily becomes creatinin (C^H^NgO), and the latter through oxidation, urea (CON^H^), it is quite prob- able that creatin may be an antecedent of urea arising out of the disintegration of the muscular tissues, etc., but converted into urea elsewhere. It should be mentioned, however, that the creatin, or rather creatinin, normally found in the urine is not derived from the muscular tissue of the body, but from the food, since it varies in quantity, increasing with a meat diet, but not with exercise, and is absent in starvation. On the supposition that urea, whether derived from food or tissue, is not elaborated by the kidneys, but simply excreted out of the blood brought to them, we might expect to find that the blood of the renal artery contained more urea (0.03 per cent.) than that of the renal vein (0.01 per cent.), but also with the extirpation of the kidneys, or the ligation of the ureters, which has practically the same effect, that the urea Mould accumulate in ' Scliultzen and Nent-ki, Zeit. fiir Biolofjie, 1872. ^Pfliiger's Archiv, Band 54, 1893, s. 420. URIC ACID. 469 the blood. Such indeed has Vjeen found experimentally to be the case, Yoit ^ obtaining- after extirpation of the kidneys in an animal 5.3 grammes of urea, or almost the same amount as Avould have been normally excreted {p.S grammes) in the same time. It may be mentioned that the toxic effects appearing under such circumstances appear to be due not so much to the accumulation of a great quantity of urea as to the retention within the system of other un- defined proteid substances. Uric Acid. — Of the remaining constituents of the urine, uric acid (C5H^X^03) is the most important, it being like urea, one of the forms in which nitrogen leaves the economy. Indeed, in reptiles and birds, uric acid is the principal form in which nitrogen is eliminated. Uric acid existing in the urine in the form of urates, usually as a brownish-yellowish, powdery substance ; ammonium or sodium urate (Fig. 223) may be readily obtained by the decomposition of the same. Thus, if nitric or hydrochloric acid be added to freshly filtered urine in the proportion of about two per cent, by volume, Fig. Fig. 224. Sodium urate from urinary deposit. Uric acid, deposited slowly from urine. and the mixture be allowed to remain at rest, within twenty-four hours uric acid will be deposited as thin crystals on the sides of the vessel. These crystals (Fig. 224) are usually transparent, yellow- ish, rhombic plates, with the angles roimded off, and are frequently collected together in rosette, star-like clusters and spheroidal masses. The crystalline forms of uric acid are, however, very variable, depending upon the concentration of the solution from which they are obtained, the rapidity with which they are formed, and whether they are separated out spontaneously or by the addition of acids to the urine. Uric acid when freed from impurities is a colorless, crystalline powder, tasteless and without odor. If uric acid be 1 Centralblatt med. "Wiss., 1868, p. 468. 470 THE KIDNEYS AND URINE. boiled with nitric acid it dissolves with a yellow color, and with an abundant liberation of gas. If the solution be now evaporated a brilliant red stain is left, which by the addition of aqua ammonia, becomes purple. The presence of uric acid and urates can be readily determined by this procedure, which is usually known as the murexide test. The amount of uric acid in the urine can be determined approximately, at least, by Haycraft's method.^ This consists in making the urine first alkaline ; precipitating with an ammoniacal silver solution, dissolving the precipitate on nitric acid (30 p. c.) and then titrating the solution Math a T---sulpho-cyanide solution, 1 c. c. of the solution corresponding to 0.00168 grammes uric acid. The uric acid excreted in human urine amounts on the average during twenty-four hours upon a mixed diet to about 0.7 grammes (11 grains). The amount eliminated varies considerably, however, with the kind of food taken, O.o grammes (8 grains) upon a non-nitrogenous diet, 2 grammes (31 grains) upon a nitrogenous one, and O.'i grammes (0.3 grains) during starvation, the body sup- plying in the latter case the nitrogenous material. It would ap- pear, therefore, that uric acid like urea is derived from the disinte- gration of nitrogenous food rather than of tissue. Uric acid is not only found in the urine but also in small amounts in the spleen, lungs, heart, pancreas, liver, blood (especially in gout). While uric acid like urea is derived from nitrogenous tissue or food, con- siderable difference of opinion still prevails among chemists as to exactly how or where in the system it is produced. From such facts as that feeding an animal upon uric acid increases the amount of urea excreted, the uric acid, through hydrolysis and oxidation, splitting into urea and carbon dioxide Uric acid. Water. OxTgen. Urea. Carbon dioxide. C^X^H O3 + 2(H,0) + 03 = 2C0N^H^ ^ 3CO^ that in reptiles where oxidation is less rapid than in mammals and in birds when any saving of oxidation is of advantage, urea in the urine is replaced by uric acid, that the molecule of uric acid con- tains the residues of two molecules of urea as shown by the for- mula expressing its chemical constitution NH — CO I I CO C — NHv 1 II ) CO = C,H,N,03 XH — C — NH/ it has been held that uric acid must be regarded as imperfectly oxi- dized urea. On the other hand, it is considered by many chemists that uric acid cannot be an antecedent of urea, being formed by a syn- thesis, possibly of lactic acid and ammonia, in the liver or elsewhere, rather than by the imperfect oxidation of proteid matter. Accord- 1 British MedicalJournal, 1885, p. 1100. HIP PUBIC ACID. All ing to this point of view the relative production of uric acid and urea in different animals depends not upon the extent of oxidation, but on the structure of the uriniferous tubules, the amount of water absorbed, the general physical conditions involved, etc., being better adapted to the excretion of uric acid in one kind of animal and of urea in another. It must be admitted, however, that neither of these ex- planations offers a satisfactory answer as to why the principal nitrog- enous constituent in the urine of reptiles and birds should be uric acid and of mammals urea. In this connection it will be recalled as already mentioned that a number of substances closely allied in chemical constitution to uric acid, such as xanthin, guanin, hypo- xanthin, adenin, etc., are found in small quantities in the urine and which constitute when taken together the so-called xanthin group. Allantoin (C^HgN^g), found in the urine of children within a few days after birth, and in very small quantities in that of the adult in the allantoic fluid (hence its name), is also a derivative of uric acid, being derived by the oxidation of the latter. Hippuric Acid. — Hippuric acid, or benzoyl-amido acetic acid (CgHgNOg), Is owQ 0^ i^Q few important constituents of the urine that is produced in the kidneys themselves, being formed in these organs by the union of benzoic and amido acetic acids (glycin, glycocoll) with dehydration. Benzoic acid. Glvcin. Water. Hippuric acid. C,Hp^ -h C^H.NO^ — H^O = C\H3N03 That such is the origin of hippuric acid within the economy ap- pears from the fact that if arterialized blood containing benzoic acid be passed through the blood vessels of a freshly excised " surviving " dog's kidney, hippuric acid will be found in the perfused blood. On the other hand, as in jaun- diced patients, and in animals Fig. 225. in wdiicli the liver is extirpated, or the ductus communis is li- gated, the benzoic acid admin- istered passes out of the body as such, one w^ould be led to sup- pose that the synthesis with glycin takes place in the liver. It would appear, therefore, that hippuric acid may be pro- duced by the synthesis j ust men- tioned in different parts of the body, more particularly in the dog in the kidney, in the rabbit in the liver, and in man in one or both organs. As a further confirmation of the synthetic origin of hippuric acid, it may be men- tioned that when benzoic acid is taken internally the amount of hip- '=?f\ ^ Hippuric acid. (Lasdois.) 472 THE KIDNEYS AND URINE. puric acid excreted in the urine is increased/ It is also well known that a benzoic acid residue exists in the fodder of ruminants, and which accounts in the above supposition for hippuric acid replacing uric acid in the urine of such animals.^ As hippuric acid is found, however, in the urine of a starving man, or of one upon a meat diet, though in less quantity than when on a vegetable or mixed one, the benzoic acid, like the glycin, must be derived from the dis- integration of proteid materials. Hippuric acid (Fig. 225) crystal- lizes in semi-transparent, four-sided rhombic prisms or columns, or in needles if the crystallization is rapid. The hippuric acid excreted in the urine during twenty-four hours amounts upon a mixed diet to about 0.7 grammes (10.8 grains). If the food consists, however, of fruit, especially plums, it may then amount to as much as 2 grammes QjO grains). Creatinin. — Creatinin (C^H^N.^O), regarded as being the anhydride of creatin (C^HgNgOg), appears in the urine in the form of color- less, shining, monoclinic prisms. The quantity of creatinin excreted in the urine in twenty-four hours amounts on the average to about one gramme. While the amount excreted depends to a great extent upon the quantity of meat eaten, the creatin of the latter being converted into creatinin and eliminated in that form, part is also derived from the proteid of the body, as creatinin is still found in the urine of the starving man even if in diminished amount. Fig. 226. Fig. 227. Creatinin, crystallized from Lot water. (Lehmann.) Calcium oxalate. Iieposited from liealthy urine. Oxalic Acid. — Oxalio acid (CJi.f)^) occurs in the urine in very small amounts (0.02 gramme (0.3 grain) per day) as calcium oxalate which is kept in solution by the acid sodium phosphate. When deposited in the urine in consequence of ammoniacal fermentation, 1 Matschersky, Virchow's Archiv, 1803, s. .528. 2 MeLssner and Shepard, Centralblatt, 1866, Nos. 43 and 4-1. CONJUGATE SULPHATES. 473 calcium oxalate crystallizes (Fig. 227) as regular octohedra or double quadrangular pyramids united base to base. Oxalic acid, as already stated/ appears to be derived from the food, cabbage, spinach, asparagus, apples, grapes, etc., containing it. It should bo mentioned, however, that, according to Hammar- sten,^ oxalic acid has been found in the urine during starvation, and also upon a diet consisting exclusively of flesh and fat, which if the case shows that it may be derived to some extent, at least, from the tissues. Conjugate Sulphates. — The phenol (C,,H,pS0.3H) and cresol (CH^SO.^H^) sulphuric acids, and indoxyl (C^H^NSO j and skatoxyl (CgHj,NSO j) sulphuric acids that occur in small quantities as alkaline salts in the urine are derived as already mentioned ^ from the phenol (CgH.OH) and cresol (C.H.OH) and indol (C,H„N) and skatol (CgH.jN) tliat are produced in the intestines by the putrefaction of pro- teids, and which l)eing carried to the liver, the indol and skatol l)ecom- ing through oxidation indoxyl and skatoxyl, couple with sulphuric Indol. Indoxvl. C3H,N + = C3H,(0H)N acid to form the ethereal or conjugate sulphates and are in that form eliminated by the kidneys. The presence in the urine of potassium indoxyl sulphate, or indican, as it is usually called, can be readily shown by mixing equal volumes of urine and hydrochlo- ric acid and adding two or three drops of a solution of chlorinated lime, whereby oxygen being liberated, the indican is decomposed into indigo blue and potassium acid sulphate. Indican. Indigo blue. Potas.sium acid sulphate. 2C3H^NKSO^ + O^ = C\^H,„N^O, + 2HKS0^ By adding chloroform and shaking the mixture vigorously for some time, the blue coloring matter is dissolved, and after the chlo- roform evaporates remains as a deposit. The amount of indican found in the urine is very small, 0.005-0.02 gr. (0.07-0.3 grains) only being excreted in twenty-four hours. It may be mentioned in this connection, as an interesting fact, that 25 times as much indican occurs in the urine of the horse as in that of man. Aromatic oxyacids, such as paraoxyphenyl acetic acid (C,.HpHC.,H.p.,) and paraoxyphenol-propionic acid (C,.H^OHC3H.02), derived from tyro- sin as intermediate steps in the putrefaction of proteids in the intes- tines, are also found in small quantities in the urine, together with some other organic substances, which have been already referred to in our account of the chemistry of the body. Inorg-anic Constituents of the Urine. — Of these, water is the most important, constituting 95.4 per cent, of the whole urine, 1572 grammes of urine containing 1500 grammes of water. The salts of the urine are taken into the body with the food and pass out of ^P. 50. 2 Op. cit., p. 357. »Pp. 82, 109, 225. 474 THE KIDNEYS AND URINE. it as such in the urine unchanged, or they are produced within the system through oxidation of the sulphur and phosphorus either of the food or tissue, the sulphuric and phosphoric acids combining with bases to form salts. The amount of salts excreted daily in the urine upon a mixed diet varies from 9 to 25 grammes (139 to 386 grains). It is impossible as yet to state exactly the manner in which the chemical elements are combined with each other or the acids with the bases, since the composition of the ash corresponds almost exactly with the direct analysis of the urine. It is for this reason that the amounts of chlorine and sodium, for example, oc- curring in the urine are stated separately in an analysis of the latter rather than as combined as sodium chloride. It is very probable, however, that the sodium, and potassium also, occiu'ring in the urine do exist there as chlorides ; phosphoric acid in combination with sodium and potassium as alkaline, and with calcium and mag- nesium as earthy phosphates ; sulphuric acid with sodium and po- tassium as alkaline sulphates ; uric acid as sodium urate. With the exception of water, sodium chloride constitutes by far the greatest part of the inorganic principles of the urine, as much as from 10 to 15 grammes (154 to 231 grains) being excreted in twenty-four hours. The amount of sodium chloride occurring in the urine de- pending almost entirely upon that contained in the food, the chlo- rine estimated as such will vary therefore proportionally. The phosphoric acid of the urine is excreted principally in the form of potassium and sodium phosphate. The amount of alkaline phosphates excreted in twenty-four hours (2.6 grammes, 45 grains) varies with the kind of food taken, being greater on an animal than on a vegetable diet, the former being richest in soluble phosphates or substances yielding readily phosphoric acid. The earthy phos- phates, calcium and magnesium phosphate, while derived principally from the food, are no doubt formed also within the system through the decomposition of lecithin, nuclein, etc. The earthy phosphates excreted in twenty-four hours amount to about 2.3 grammes (35.5 grains). The alkaline sulphates excreted in the urine amount in twenty-four hours to about 2.5 grammes (40 grains). The sul- phuric acid excreted in the urine is derived from the food only to a very small extent, the greatest part being formed within the body by the burning of the tissues. It is for this reason that the total destruction of body proteid can be estimated from the amount of sulphur eliminated in the urine ' as well as from the nitrogen. The sulphuric acid eliminated is, as regards the nitrogen in the ratio of 1 to 5. Sulphur occurs in the urine not only in the form of sulphates and ethereal sulphates, but also as " neutral sulphur " in which form it is found in cystin and sulphocyanides. In ad- dition to the constituents already mentioned the urine contains 1 Proteid : sulphur :: 100 : 2.2. Proteid = S X 2^5 = 45.-1. FEE.VEXTATIOX OF THE UEIXE. 475 usually traces of nitric and slicic acids, ammonia and iron, carbon dioxide in varying amounts, nitrogen in small quantities (0.8 vol. per cent.) and oxygen in traces. Fermentation of the Urine. — In concludinof our account of the urine, the changes produced in it by standing may be here briefly Fig. 228. Fig. 229. Micrococcus ureje. (Landois. alluded to. It "will be re- membered that the urine, when first passed, is acid, the acidity being due to the acid sodium phosphate. AVithin twelve or twenty-four hours, however, through the devel- opment of a lactic or acetic acid fermentation, Ijrought about by mucus or fungi, uric acid and acid urates are precipitated, and the urine undergoes the so-called " acid fermentation." After a few days this acid fermentation ceases, through the con- version of urea by the addition of water into carbonate of ammonium. Urea. Water. Ammonium carbonate. CON^H^ + 2(ap) = (NHJ„C03 the changes being brought about by the action of the micrococcus urere (Fig. 228). The acid sodium phosphate being then neutralized by the ammo- nium carbonate so formed, the urine becomes alkaline. Ammonium magnesium phosphate. Deposited from healthy urine, during alkaline fermentation. Acid sodium phos. 2NaH PO. Ammon. carb. (^^HJ,C03 Ammon. sodium phos. = 2XaXH,HP0. Carb. dioxide. Water. HO With the alkalinity of the urine, the earthy phosphates, being only soluble in acid flnids, are precipitated, and in combining with the ammonia give rise to the formation of the triple phosphate or ammonium magnesium phosphate (Fig. 229). Magnesium phos. 2MgHP0^ + Ammon. carb. Ammon. mag. phos. (NHJ^CO^ = 2MoXH^P0^ Carb. dioxide. Water. C0„ + H„0 As decomposition goes on, the ammonium carbonate, after satu- rating the elements with which it is capable of uniting, is given oflP free, giving rise to the ammoniacal odor of the urine, and this con- tinues until all of the urea has disappeared. CHAPTER XXVT. THE NEEVOUS SYSTEM. Ix describing the manner in which food is digested, absorbed, and circulated through the economy as Wood, supplying the mate- rial for the repair of the tissues and the production of energy, of the absorption of oxygen, and exhalation of carbon dioxide, water, urea, etc., the influence exerted by the nervous system upon these pro- cesses has only been alluded to, if at all, in an incidental manner. That the phenomena of nutrition are not dependent upon the nerv- ous system, however much it may be influenced by the latter, is shown from the fact that the nutrition of the lower animals, in which the nervous system is but little developed, and of plants, in which, with but few exceptions, so far as is known, it is altogether absent, does not differ from the higher forms of animal life. In- deed, the essential difference between the nutrition of plants, as compared with animals, consists of the deoxidation by plants of the water, carbon dioxide, and ammonia constituting their food, into starch, sugar, fats, albumin, and the storing up of energy, and the oxidation by animals of the latter substances constituting their food, into carbon dioxide, water, and ammonia, and the expenditure of energy. But while such a broad distinction exists between plants and animals, as compared, on the whole, nevertheless, it must not be lost sight of that oxidations, analytical processes, are going on in the economy of plants incidental to the elaboration and circula- tion of the sap, the production of heat, in budding, flowering, etc., and deoxidations, synthetical processes in the economy of animals. Indeed, as has already been mentioned, no sharp line of demarca- tion can be drawn between vegetable and animal life. While nu- trition is not actually dependent upon the nervous system, never- theless every one is, however, conscious of the extent to which it influences nutritive processes. The sudden manner in which diges- tion is brought to a stop by a piece of bad news, the weakness of the heart induced by nervous shock, the sudden blush or pallor due to emotion, are familiar illustrations. The flow of the secre- tions into the alimentary canal in response to food, the rhythmical action of the heart and lungs, though unconsciously brought about, are due equally to the action of the nervous system. The influence of the nervous system upon nutrition has often been compared to that exercised by the rider upon the movements of a horse, the en- ergy being put forth by the latter, but controlled with bit and spur by the former. Man, like other animals, is, however, something more than a mere nutritive machine, becoming conscious, through STRUCTURE OF THE NERVOUS SYSTEM. 477 liis uervoiis system, of an external world. Impressions made upon afferent nerves by heat, light, sound, etc., when conveyed to the sensorium, give rise there to sensations, out of which are developed in still higher centers, emotions, desires, ideas, while voluntary im- pulses are transmitted in the reverse direction by efferent nerves to the muscles. In a word, it is by means of the nervous system that the various nutritive processes that we have studied are brought into relation with each other — are coordinated — that we feel, think, will. Structure of the Nervous System. The nervous system consists morphologically of an association of numerous and independent neurons, that is, of nerve cells and their outgrowths. The nerve cells are confined in a great measure to the cerebro-spinal axis and ganglia ; the outgrowths are found, however, throughout the body. Xerve cells (Fig. 230) are nucle- Fu;. 230. Fig. 231. Nerve cells, from the anterior horn of gray substance of the spinal cord. Neuron with short axon immediately break- ing up into numerous fine filaments, n c. Nerve-cell proper, x. Axon. d. Dendrites. From the cerebellum. (Andeiezen.) ated cells usually more or less ovoid in shape, and differ considerably in size, varying in diameter from the j^ to the ^ of a millimeter (2'"5Vo ^^ sio^ ^^ '"^^ inch). According to recent researches ^ a nerve cell appears to consist of a kind of framework, continuous with the fibrilhe of the nerve fiber, in the meshes of which are contiiined small masses or granules readily stainable with basic aniline dye. Nerve cells occur not only separately, but in many cases are aggre- gated together as ganglia. The latter are generally provided with a thin but strong and closely adherent capsule or sheath continuous with the epineurium or supporting framework of the nerve fibers. 'Nissl, Allgemein Zeits fiir Psychiatrie, Band 52, 1890, s. 1147. 478 THE NERVOUS SYSTEM. Fig. 232. Mhi Neuron with long axon proceeding as an axis cylinder of a nerve fiber, n c. Nerve-cell ])"roper. rf. Dendrites, j-. Axon, d jr. Dendrite sliowing gemmula;. a d "le and Kol- LIKER.) such as is found in the conjunc- tiva ; in each instance the neuri- lemma of the nerve fiber becomes continuous with the capsule en- closing such bodies, the white sub- stance of Schwann remains with- out the latter, the axis-cylinder alone penetrating within. "Rvnprimpnfql in vpi;ticrnfinn qc; sue envelope, e. Axis-cylinder, with its end jLxpeiimtniai inxcsugaiion, as provided at/. (Qualv.) well as morphological considera- tions, proves that the axis-cylinders of the nerve fibers are the avenues by which nervous impulses emanating from the cells of the Vater's or Pacini's corpuscle, a. Stalk. 6. Nerve fiber entering it. a, d. Connective tis- FlG. 239. Fig. 240. \ a. Tactile corpuscle. 6. Xerve. (Qcaix.) Three nerve-end bulbs from the human con- junctiva, treated with acetic acid. Magnified. 300 diameters. (Quaix. ) brain and cord are transmitted as eflPerent impulses to muscles, glands, etc., and by which impressions made upon the skin, sensory 484 THE NERVOUS SYSTEM. organs are transmitted as afferent ones to the cells of the cord and brain. As the neurons of which the nervous system is composed are, however, entirely independent of each other, never absolutely continuous, it must be admitted that even though a nervous im- pulse may pass continuously from the cerebral cortex (Fig. 241, /) to the lumbar enlargement of the cord 4' that arriving there it must pass over a gap, 4' to 5, in order to reach the next neuron, N I, that will in turn carry it on to the foot. Or let us suppose that an impression made upon the skin (Fig. 242, 1) is transmitted Fig. 241. Fig. 242. ATJZ Diagrammatic representation of cerebral and spinal motor cells with axons. 1. Cerebral cell. 2. Axon. .3, 4. Collaterals. 4'. End tufts. 5. Spinal cell. 6. Axon. 7. Limit of spinal cord. jV/. Motor nerve. 8. Muscle. 9. Muscle-end plate. (Raubek. ) Diagrammatic representation of cerebral and spinal sensor.v cells with axons. 1. Skin end tufts. 2. Limit of epidermis. 3. Axon. 4. Common stem. 5. Cell in spinal ganglion. 6. Axon. 7. Limitof sjiinal cord. 8. Ascend- Ingbranch. 9. Descending branch. 10. End tufts. 11. Si)inal cell. 12. Axon. (Raubek.) continuously to a cell 5 in a spinal ganglion and thence to 10 ; on arriving at the latter point it must pass over a gap in order to reach the next neuron, ^Y 11.^ It will be observed tliat there arises from the cell 5 (Fig. 242) in the spinal ganglion one outgrowth or nerve fiber that conducts in two directions towards the nerve cell and away from it, presenting apparcntly'an exceptional disposition to that already described. The study of development shows, how- 1 A. Eauber, Lclirbucli Dcr Anatomic Des Menschen, Zweiter Band, 1S98, s. 270. CHEMICAL COMPOSITION OF NERVOUS TISSUES. 485 ever, that such a nerve fiber consists really of two fibers, afferent and efferent, which have become so closely associated that their original identity is lost. Such cells do not differ, therefore, func- tionally from those in which the outgrowths are situated at different points of the cell. Various explanations have been offered as to how the nervous impulse in the first neuron sets up an impulse in the second one. It has been urged that the neurons may extend their outgrowths until they come in contact temporarily with each other, or that the secondary nervous impulse is developed through a process of induction — or that the tips of the nerve fibrils cause some chemical change in the intervening substance Avhich gives rise to the secondary impulse. It must be admitted, however, that these so-called explanations are merely hypotheses, and that the manner in which nervous impulses are transmitted from neuron to neuron is not as yet understood. Nerve cells, like all cells, have a life his- tory, and as recent researches ^ show, in old age the chromatic substance of the cells diminish while the pigment increases, the cytoplasm becomes vacuolated, the outgro^vths atrophy, and in some instances the entire cell is absorbed. Chemical Composition of the Nervous Tissues. — Less is known of the composition of the nervous tissues than of any other tissues of the body. They appear, however, like the tissues in general, to be composed largely of water, which enters into the constitution of the white matter to the extent of 70 per cent, and into that of the gray to about 75 per cent. Among the solid constituents of the nervous tissues the most important are insoluble albumin and connective tissue, protagon, cholesterin, neurokeratin, nuclein, and mineral bodies.^ Of these substances albumin and connective tissue occur in greater quantity in the gray matter than in the white, the re- maining ones, however, in greater quantity in the white than in the gray. Protagon (C^.^H^^^j^X.POg.), a crystalline substance, consists, according to most chemists, of lecithin and cerebrin. Lecithin ap- pears, as already mentioned,^ to be a triatomic alcohol readily break- ing up into fatty acids, glycero-phosphoric acids, and cholin, the latter giving rise to neurin, Cerebrin resembles lecithin in being a nitrogenous substance, but differs from the latter in not contain- ing phosphorus ; it appears to be a glucoside yielding that form of sugar known as galactose. The cholesterin found in the nervous tissues occurs partly free and partly in chemical combination. Neurokeratin is found in the peripheral nerves as a delicate sheath coverinsT the axis-cvlinder and white substance of Schwann. Nuclein, or the substance of which the nucleus of the nerve cell is composed, appears to be a phosphorized albuminoid. The mineral bodies oc- curring in the nervous tissues consist of the salts of potassium, sodium, magnesium, calcium, and iron. Extractives, such as crea- tin, xanthin, hypoxanthin, moist lactic acid, leucin, uric acid, and urea are found in small quantities. 'Hodge, Journal of Physiology, Vol. xvii., 1894. '^ Hammarsten, op. cit., p. 279. ''See p. 66. CHAPTER XXVII. THE NERVOUS SYSTEM.— (Contiiiued.) BATTERIES. OHMS LAW. INDUCTION APPARATUS. PEN- DULUM MYOGRAPH. LATENT PERIOD. VELOCITY OF CONDUCTION OF NERVOUS IMPULSE. From daily observation we learn that all our actions are the re- sult of motives or stimuli. Impressions made upon the surface of the body and transmitted by nerves to the central nervous system and there giving rise to sensations, are immediately or mediately followed by actions. The impressions made may be so strong, and the corresponding sensation arising so acute, that action instantly follows, as in the sudden involuntary shrinking from a source of pain, or the sensation giving rise to an idea, a longer or shorter time may intervene, during which period the mind has time to reflect as to the course of action, the individual being swayed by this or that idea or motive, the will being so to speak in abeyance. Sooner or later, however, one motive becoming the strongest, voluntary action follows, or, to speak in ordinary language, the will asserts itself, the term will being simply a convenient one, for ex- pressing the fact that action is the result of the strongest motive, the result of the preceding stimulus. The sole difference between these two actions, the involuntary and voluntary, is in the interval of time elapsing between the application of the stimulus and the re- sulting action, and in the stimulus being some external exciting cause other than that of the will, as in the case of a cough, due to a crumb of bread in the larynx, rather than to volition. In addition, however, to the sensations, or ideas, arising within us due to the stimulation of nerves from without inward and of the involuntary or voluntary actions following due to the reflection of the impulses from such stimulation from within outward of which we are all conscious, there are similar actions following the stimu- lation of nerves, of which as long as we are in a state of health w^e are entirely unconscious. 'As illustrations of such actions may be mentioned the flow of the gastric juice in response to the stimulus exerted by food upon the nerves distributed to the stomach, of the dilatation or contraction of the blood vessels brought about through the influence of nervous emotion, of the contraction of the iris in response to light. The phenomena of secretion, like those of sensa- tion, involuntary and voluntary movements, result from the appli- cation of a stimulus to peripheral nerves, which, being transmitted to the nervous centers, is thence reflected to the parts manifesting DANIELVS ELEMENT. 487 the phenomena. That it is by means of the nerves connecting the periphery with the nervous center, and the center with the organs manifesting the phenomena, that the latter are produced becomes at once evident if tlie nerves involved be destroyed, whether by disease, injury, or experiment ; sensation, voluntary movement, se- cretion, etc., at once disappearing. The involuntary muscular con- traction, the result of pain, the voluntary one made in the carrying out of some matured plan, and the flow of a secretion, are equally illustrations of the truth of all nervous action being of this reflex character. In every instance if the phenomenon be traced to its source it will become evident that an action apparently due to an impulse generated from within and transmitted outward is in real- ity due to an impression first made from without and transmitted inward, and then finally reflected outward. That nervous energy, whatever its nature may be, is never generated spontaneously, but must be of this reflex character, some modified preexistent mode of energy, is self-evident, otherwise nerve energy would arise out of nothing. Whatever view may be taken, however, of the origin of ideas, the nature of the will, etc., it will not affect the fact that the irritability of nerves, like that of other tissues, may be called into excitement by appropriate stimuli. While the irritability of a mus- cle, however, shows itself by its contraction, and that of a gland by its secretion, that of the nerve is not manifested by any ordinary visible change in itself, but by some change in the organ to which it is distributed.^ Of the different stimuli, mechanical, chemical, and electrical, available in calling into excitement the property of irritability possessed by nerves, the electrical is by far the most convenient, and since the contraction of a muscle brought about indirectly by the stimulation of the nerve supplying it, is a very striking phenomenon, the muscular contraction may be taken as an evidence and measure of the nervous irritability causing it. As in the stimulation of nerves we shall usually make use of the electricity supplied by a Daniell element, a brief description of the same does not appear superfluous. A single Daniell's element consists (Fig. 243) of a glass vessel S, containing a saturated solution of copper sulphate, in which is immersed a copper cylinder (A), open at both ends and per- forated with holes, and provided with an annular shelf supporting crystals of copper sulphate to replace the solution of the same decom- ^ We shall see presently that the nerve does undergo a change in its electrical condition when excited, but which can only be detected by means of a delicate gal- vanometer, and that possibly heat is also produced. Fig. 243. Daniell's elemeut. (Ganot.) 488 THE NERVOUS SYSTEM. posed during the action of the battery. Within the copper cylinder is a thin porous vessel of unglazed earthenware, containing diluted sulphuric acid, in which is placed a cylinder of amalgamated zinc Z. The positive electricity generated by the action of the acid upon the zinc, passing through the liquid of the battery to the copper cylinder, accumulates at the end of the wire attached by the binding screw to the latter (C), the ware becomes, therefore, the positive pole or elec- trode, though the copper, to which it is attached, from being rela- tively little acted upon, is called the negative or collecting plate ; on the other hand, through the disturbance of the electrical equi- librium the negative electricity developed, passing in the reverse direction from the copper to the zinc, accumulates at the end of the wire attached to the latter (Z), that wire becomes, therefore, the negative pole or electrode ; the zinc, however, from being most acted upon, is called the positive or generating plate. As, how- ever, the effect of the battery is due to the difference of electric potential set up between the metals, the current is rather regarded as being single and as flowdng from the zinc or positive plate through the liquid of the cell to the copper or negative one, thence by the positive pole through the connecting w'ire to the negative pole and so back to the zinc plate. Such being the disposition and action of the parts of a Daniell's element when closed, the hydrogen developed by the action of the dilute acid upon the zinc would be deposited upon the copper plate were it not for the presence of the copper sulphate, which the hydrogen reduces into copper and sulphuric acid, the former being deposited upon the copper plate, and the latter replacing that in the porous cup used up in acting upon the zinc ; the constancy of the battery is thus in- sured for several hours at least, upon which its usefulness for our purpose depends. Did the hydrogen gas generated settle in minute bubbles upon the copper plate, which it otherwise would do in the absence of the solution of copper sulphate, the action of the battery would be interfered with by the polarization of the plate, by which is meant that the hydrogen wdien so deposited not only offers a resistance to the current passing from the zinc to tlie copper, but in generating a counter current in opposition to the latter propor- tionately weakens it. It need hardly be added that if two or more Daniell elements are used, in coupling, the zinc jjlate of one element must be connected with the copper plate of the other by means of a copper ware or stop as in Fig. 245. Among the other forms of batteries often used for physiological purposes may be mentioned those of Bunsen, Smee, Grenet, Leclanche — differing only from the Daniell battery in the character of the metal and liquid used, and their relative arrangement. In describing the action of a Daniell element the electricity generated was spoken of as if flow- ing through the battery to the poles, as one might speak of the flow of water through pipes, just as if there was an actual electrical cur- rent present. As a matter of fact, it is needless to say with refer- ELECTRICITY AS A XERVE STIMULUS. 489 ence to the transmission of electricity, there is no evidence of a transference of particles from place to place as is the case of the flow of water. It will be found, nevertheless, since the molecular changes incidental to the production of electricity are yet unknown, that such a comparison offers an extremely convenient way of pre- senting the essential facts, of representing to the mind in a con- nected way results brought about by changes, the intimate nature of which we know nothing. It might be supposed, at first sight, that the consideration of this subject belongs rather to the domain of physics than to physiology ; as we shall soon learn, however, that the physiologist not only continually uses electricity as a nerve stimulus, but that both nerve and muscle exhibit electrical currents, and offer a resistance to the passage of electricity, etc., it becomes indispensable that a brief account of the principal facts of elec- tricity be offered, sufficient at least to enable the student to under- stand the terms constantly used in the description of the phenomena of general nerve physiology. It is a well-established fact that when two metals are placed in contact, as, for example, zinc with copper or platinum, a disturbance in their electrical condition, or, as it is called by physicists, a dif- ference in potential, ensues, the word potential being used in elec- trical science in the same sense as level or head of water in hydro- dynamics. Xow just as water at a higher level, if it finds a channel, tends to fall to a lower one until equilibrium is established, sim- ilarly if two bodies, or two parts of the same body, have a different potential — that is, are at different electrical levels, so to speak — there will be a tendency to movement from the body having a higher potential to the one with the lower until electrical equili- briiun is established. The agent to which this change, movement, so-called electrical current, is due, is called the electromotive force, and while its nature is unknown, it can be measured by the amount of work performed in the j)assage of a unit of electricity from one position to another, just as the potential energy of water can be measured by the amount of work performed, as in the turning of a water-wheel, etc. Just as the energy exerted in a definite time in raising a weight against gravity may be stored up indefinitely, to be set free again by the falling of the weight, and applied to the performance of mechanical work, so the energy expended in bring- ing up a body against another similarly electrified, and therefore of- fering a resistance like that of gravity, may be temporarily stored up, and with the setting free of the electricity perform work. While, therefore, the principle of electrical measurement must be the same as that of other measurements, the particular standards used Avill not only differ according as statical or dynamical electric- ity is being considered, but as to what shall be accepted as consti- tuting the unit of time, mass, distance, etc. As a matter of fact, with reference to statical electricity, each of two equally charged bodies is said to have a unit of electricity, if when separated by a dis- 490 THE NERVOUS SYSTEM. tance of one centimeter the one will repel the other with a force which will impart in one second a velocity of one centimeter per second to one gramme of matter. As regards the galvanic or cur- rent electricity with which we have, however, more particularly at this moment to do, the unit of electricity is usually accepted as be- ing that quantity of electricity carried in one second by a current of unit strength. The latter, however, is of course arbitrary, but in the sense just used is one such that if a conductor one centimeter long be bent into an arc of one centimeter radius it will exert a force of one dyne, on a unit magnet pole placed at the center. This is called the electro-magnetic unit of current. For convenience' sake, however, in practice a hundred millions of such absolute electro-magnetic units are taken as a unit constituting the so-called volt, and we speak, therefore, of the electro-motive force of a Daniell's cell being equal to 1.079 volts. Furthermore, the elec- tro-mao-netic unit of electro-motive force is that which sends a cur- rent of unit strength through a unit resistance, and, therefore, a unit quantity in a unit time, and this definition brings us now to a consideration of the resistance offered by the conductors in the pas- sage of the electricity and the fixing of some standard for the same. As the unit of resistance must be, of course, an entirely arbitrary one, the standard of resistance ultimately accepted Avill depend upon what is considered most convenient by physicists. As a matter of fact, at the present time, the resistance oifered by a column of mer- cury about 106 cm. long, and 1 square mm. in section at 0° C, is accepted as the unit of resistance commonly known as the interna- tional unit, or one ohm ; or, what is the same thing, the resistance offered by a wire made of an alloy of silver and platinum of defi- nite length and thickness, offering the same resistance as the column of mercury just referred to, is accepted as the unit of resistance, or one ohm. The resistance offered by different bodies to the passage of an electrical current varies very considerably, according to the nature of the body. Metals, being the best conductors, offer the least resistance ; liquids, especially those of a saline character, con- duct, but not so readily as metals. Apart, however, from the con- ductibility of a particular substance, which is constant for that substance, the resistance offered by a conductor is directly propor- tional to its length, and inversely proportional to its cross-section — that is, the longer the conductor the greater the resistance, the thicker the conductor the less the resistance. In the case of a galvanic ele- ment, however, like that of a Daniell's cell, not only must the re- sistance offered by the conducting wires, which may be called the external resistance, be taken into consideration, but also the re- sistance offered by the plates and liquid within the cell, and which may be called the internal resistance. The latter is directly proportional to the distance of the plates from each other, and in- versely proportional to the size of the plates — that is, the larger the plates the less the resistance, the conducting power of the liquid, of THE RESISTANCE BOX. 491 course, being assumed to be constant. In the determination of the electro-motive force, resistance, etc., of nerves it will be found, as we shall see presently, that it is of great advantage to vary by known amounts the resistance offered to the passage of an electrical current. For this purpose we make use of a resistance box, wliicli consists, essentially (Fig. 244), of a series of bobbins (C C) on which are coiled various lengths of standard insulated wire, the latter being so disposed in the box that two ends of the wire of each bobbin (C C) are connected with two brass plates (B B) fitted into the lid of the box, the resistance offered by each coil of wire being indi- cated in ohms on the lid of the box. Suppose, by means of the two binding screws attached to the lid of the box, a current of electric- ity be sent through the coils C C, the resistance encountered will be equal to the total resistance offered by the coils. If, however, the space intervening between the brass plates be plugged up by tight- fitting brass plugs (Fig. 244), so that the brass plates are then con- nected, the current will take the route of least resistance, Fig. 244. passing simply through the brass portion of the lid of the box, from binding screw to binding screw, without traversing the coils at all. It is obvious, therefore, that Eesistauce box. the amount of resistance of- fered to the current passing through the resistance box will depend upon the number of brass plugs taken out. We have just seen that the passage of an electrical current through a galvanic circuit is due to the electro-motive force developed by the element ; and further, that, according to the nature of the circuit, the current meets with more or less resistance. It follows, therefore, as shown by Ohm,^ first from theoretical considerations, and subsequently by experiment, that the strength of the current — that is, the quantity of electricity which, in a unit of time, flows through a given section of the circuit — must be equal to the ratio of the resistance to the electro-motive force. This important result, usually known now as Ohm's law, may be con- E veniently expressed by the equation /= — (1), in which /represents the current strength, Et\\Q electro-motive force, and B the resistance. If in equation {}.) E, or the electro-motive force, is equal to 1 volt, and R, or the resistance, to 1 ohm, then /, or the current strength, will be equal to 1 ampere, and the quantity of electricity delivered per second, 1 coulomb, or per hour, 3000 coulombs (hour ampere). As Ohm's law is a most important one, galvanic batteries being arranged by its means so as to give the greatest amount of electricity possible, we will illustrate its application in this respect by a few examples. ^ Die galvanisclie Kette matliematisch bearbeitet, Berlin, 1827. 492 THE NERVOUS SYSTEM. It -will be remembered that the resistance of a conductor is di- rectly proportional to its length, and inversely proportional to its conductivity and section. If now the length, conductivity, and sec- tion be represented respectively by I, c, and s, then the resistance JR will be equal to ^ ^ • This value of R being substituted in c X s E csE equation (1) we shall obtain 1= — = ^^ (2)- -that is to say, the cs Fig. 2^5. intensity of a current is directly proportional to the section and conductivity of the conductor, but inversely proportional to its length. In the case of a galvanic element, as we have seen, the resistance to be considered is not only that of the conducting wires, but also that of the liquid and plates of the element itself. Call- ing the external resistance, that of the wires, r, and the internal resistance, that of the element, B, we obtain from equation (1) JE I = ^5—; — (o). Xow it is obvious that if anv number of similar K -\- r ^ ■' elements are joined together, say three, as in Fig. 245, there is n times the electro-motive force, but, at the same time, n times the in- ternal resistance, and equation (8) becomes I = ~f^ (4). If, however, the conduct- ing wires be of copper, and short and thick, then the ex- ternal resistance r, in compari- son with R, may be neg- lected, and equation (4) becomes nE E 1 = -~7s = T^ (o) — that is to nR R ^ say, when the internal resistance is great and the external is small, a battery consisting of several elements — three, in this instance — pro- duces no greater eflPect than one element. Suppose, on the other hand, that the conducting wires be very long and thin and the external re- sistance r, therefore, very great, so much so that the internal resist- nE ance R can be neglected in comparison; then /= ^^ — (4) will Galvanic batterv. become / = nE E (6), or as I=- 1= nJ { nR -f r That is to say, when the external resistance is large, and internal resistance small, the intensity within certain limits is very nearly proportional to the number of elements — that is, a battery consisting of three elements produces nearly three times the effect of one clement. Instead of increasing the numljcr of elements, let us now enlarge the plates, say 71, or three times that of a single element (Fig. 240), or join OHM'S LAW. 493 all the copper plates and all the zinc plates together, as in multiple arc and consider what effect will be obtained according to Ohm's law. The electro-motive force under these circumstances, will, of course, remain unchanged — that is, not increased, since it depends upon the nature of the plates and the liquid, and not upon the size of the element, just as the head or force of the water comparable to the electro-motive force is not increased as long as the level remains unchanged, however much the amount of water may be increased, for though there are n times as many Fig. 246. regions, in this case — three, where the electro-motive force acts side by side — they do not assist one another any more than the neighboring vertical columns of water in a reservoir affect the pressure on the exit pipe. Nevertheless, just as in the previous instance, in which the battery was supposed to consist of three elements, there will be a difference in the effect pro- duced according to whether the external or internal resistance is neglected, since although the electro- motive force does remain unchanged, the increase in the size of the plates must be followed by a oaivank element. proportional diminution in their resistance which permits a proportional quantity of electricity to pass through them. Let us first suppose that the external resistance, or r, be so much smaller than the internal or i?, that it can be neglected, and that the plates have been enlarged three n times, then we will obtain E nE from equation J= p -_ (3) J= -v/ = nI{S). That is to say, by enlarging the plates of the element n, or three times (Fig. 246), when the external resistance is small, the intensity is increased corre- spondingly. On the other hand, suppose the internal resistance, or E R, is so small that it can be neglected, then equation /= ^ (3) 771 will become /= — or J= J (9). That is to say, by enlarging the plates of the element n, or three times, when the internal resistance is small the intensity is not increased. Resuming what has just been said, we learn by Ohm's law that if the internal resistance be small, it is of advantage to increase the number of cells ; on the other hand, if the internal resistance be large, while it is of no ad- vantage to increase the number of cells, it is of advantage to enlarge the plates of the cell, nothing, however, being gained by enlarging the plates if the internal resistance be small. It need hardly be added that while the intensity or quantity of electricity flowing through the circuit in a given time remains the same, the density of the current may, however, vary, the latter being inversely as the cross section of the conductor — that is, the less the cross section, the greater the intensity. As, in the stimulation of the nerves by electricity derived from 494 THE NERVOUS SYSTEM. the batteries just described, we ordinarily make use of the induc- tion apparatus, of Du Bois Reymond/ a brief description of that most useful instrument in this connection appears appropriate. As its name implies, it is an apparatus (Fig. 247) by means of which an induced current can be applied to a nerve, and in order that the Fig. 247. Du Bois Reymond's induction apparatus. (La:ndois.) strength of the current may be varied at pleasure, the secondary coil 8, to which the electrodes I L are attached, is placed upon a graduated slide ( Q), so that it can be made to approach or recede from the primary coil P, as near or far as desired. The current Fig. 248. Schema of Du Bois Reymoud's induction apparatus. (Landois.) from the battery B (Figs. 247 and 248), entering the apparatus at the binding screw a, passes up the pillar h and through the German silver spring rf, then through the primary coil P, and the coil F^ returning to the battery by the binding screw p. As the current enters the primary coil P, an induced closing or making current is for the moment developed in the secondary coil /S', and in an oppo- site direction to the primary current. During the passage of the current, however, tlirough the coil P, the iron core within the latter becoming magnetized, the spring d is pulled down from the screw/, the result of which is that, the primary current being interrupted, ' Untersuchungen iiber thierische Electricitat, Zweiter Band, s. 393. Berlin, 1849. DU BOIS REYMOND INDUCTION APPARATUS. 495 there is developed for a moment in the secondary coil S an induced breaking or opening current in the same direction as that of the primary current. As the iron cores within the coil F under these circumstances become demagnetized through the absence of the current, the spring d flies up again ; contact being again made with the screw/, the current passes, as before, through the primary coil, to be again broken with the magnetization of the core within the coil F, and to be again made with the demagnetization of the same, and so on indefinitely. The effect produced by the iron core within the primary spiral is the same as that of the primary spiral itself, since in being magnetized and demagnetized tlu-ough induction by the making and breaking of the primary circuit, the core induces closing and opening currents in the secondary spiral similar to Fig. 249. Iiu Bois Reymond's key. those due to the making and breaking of the current in the primary one. By applying the electrodes I L attached to the secondary coil, to the nerve, the latter will be stimulated by the making and breaking induced currents, and which so rapidly succeed each other that the muscle is soon brought into a state of tetanus. If, how- ever, it is desired to stimulate the nerve by a single induction shock — that is, by one closing and one opening induced current, then the wire of the l^atterv must be attached to the l^indiner screw .S' instead of to a (Fig. 247), a Du Bois Reymond key (Fig. 249) having also been inserted A\itliin the circuit of the primary coil. The key being down, the current will then be short-circuited — that is, will pass 496 THE NERVOUS SYSTEM. directly back to the battery E, since the resistance offered by the key is less than that oifered by the nerve. With the elevation of the key, however (Fig. 249), the current Avill pass through the primary coil p, developing the closing, or making induced current in the secondary coil S as before ; but, as the current through the primary coil is not broken through the fall of the spring, the wire being attached in this experiment to ^' (Fig. 247), there will be no opening or breaking current induced in the secondary coil. The latter is, however, at once developed in the secondary coil by simply depressing the key, the current being then short-circuited again, it returns back to the battery Avithout passing through the primary coil. It ^\\\\ be observed that when the induction appa- ratus is so arranged and used,- that the nerve is stimulated once by the current induced by the closing of the primary circuit, and once by the opening of the same. Suppose, however^ it be desired to stimulate the nerve by only the closing or the opening current? To accomplish this, a second Du Bois Rcymond key (Fig. 250, a) must be also inserted within the circuit of the secondarv coil S, and the two keys worked in the following manner : A^ e will suppose, at the beginning of the experiment, that the key b, within the cir- FiG. 250. stimulation of nerve by closing or opening current. cuit of the primary coil P, is down, and the key a, within that of the secondary coil S, is up, then with the elevation of tlie key h, and the passage of the current from the battery through the primary coil, there will be developed for an instant in the secondary coil an in- duced current, and the nerve will be stimulated by a closing or making single induction shock. The key a should now be de- pressed so that the nerve will not be stimulated by the opening or breaking of the current in the primary coil, due to the depressing of the key 6, and the consequent short-circuiting of the current. The nerve has then been stimulated by the closing of the current only. Supposing the two keys to be both down, let us now elevate the key h ; the secondary current developed in consequence will not influence the nerve as in the preceding experiment, since the key a being down, the secondary current is short-circuited. If, however, now the key a be elevated, and the key b depressed, the secondary SIMPLE FRICTIOX KEY 497 current developed through the breakiug of the primarv current will be transmitted to the nerve, and the latter \\i\\ be stimulated bv the opening or breaking current only. Whether it be desired to stimu- late the nerve by a single induction shock, or many successive ones, or bv the secondary current induced through the making or break- ino- of the primary one, the key should always be used as a short- circuiting one (Fig. 250) rather than as a simple friction key (Fig. 251), since in the latter case muscidar contraction maybe produced Fin. 251. Simple friction key. bv unipolar induction. While no secondary current is induced in S (Fig. 251) by that in the primary, the secondary circuit being broken through the key being open, free static electricity may be given off at the end of the single electrode fL), and transmitted through the nerve to the muscle, the electricity previously acciunu- lated at the end of the electrode being due to the decomposition of the neutral electricity in the secondary coil, induced by that in the primary coil, as takes place in the prime conductor in working the ordinary- electrical machine. If, however, the secondary coil be short-circuited by a Du Bois Reymond key, as in Fig. 250, the key being down, then the secondary circuit being perfectly closed, a secondary current will be developed, and unipolar induction pre- vented, the current passing directly back through the coil, and none passing into the nerve, which, as we have just seen, is not the case, the key being used, as a friction key (Fig. 251), and open. When, however, the short-circuiting key is opened, and the secondary 32 498 THE NERVOUS SYSTEM. circuit is completed by the nerve intervening between the elec- trodes, the circuit being but imperfectly closed, unipolar induction may occur even then, as when the key is used as in Fig. 251. If, however, there be any doubt as to whether the muscular con- traction be due to the stimulus exerted by the nerve excited by the secondary current, or to the unipolar induction shock — that is, the direct transmission of the static electricity through the nerve to the muscle — it can be at once decided by simply dividing the nerve between the lower electrode and the muscle, since, if contraction then ensues, the ends of the nerves being approximated, it must be due to unipolar induction, and not to the nerve, as the division of the nerve does not interfere with the transmission of the electricity, but makes impossible that of the nerve force. It may be mentioned, in this connection, that the surest way to avoid unipolar induction is to put the upper electrode in communication with the earth through the gas or water pipe of the laboratory by a good conductor, and in so leading the free elec- tricity off, prevent it influencing the muscle, and so eifecting the contraction due to nerve excitement, as brought into activity by the secondary current alone. It will be seen, presently, that if a nerve be stimulated first by a closing, and then by an opening induced cur- rent, that the physiological effect due to the latter, as shown by the extent of the muscular contraction, is greater than that due to the Fig. 252.1 Graphic rciiresentation of effect of the extra curreuts on the induction currents. former. Now, it is desirable, under certain circumstances, that the two currents should be equalized as far as possible. To appreciate the manner in which tliis is accomplished, it will be first necessary, however, to explain briefly why the induced opening current is more powerful than the closing one. Inasmuch, as with the closing of the current in the primary coil, there is developed, momentarily, a current in the secondary one, opposite in direction to that of the primary, it might be supposed that, in a similar manner, the indi- 1 Du Bois Keymond, Gesammelte Abhandlunwn, Erster Band, s. 236. Leipzig, 1875. ^ ^ MODIFICATION OF INDUCTION APPARATUS. 499 Fig. 253. vidual coils of the primary current would act inductively on each other. Such ivS found to be experimentally the case, the current so produced, and opposite in direction to that of the inducing current, l)eing known as the inverse extra current. The latter, being oppo- site in direction to that of the inducing current, must weaken it, and it is on account of this retarding influence of the inverse extra current that the closing primary current only gradually attains its maximum intensity, as may be represented graphically (Fig. 252) by the curve line G E, in which the horizontal line T represents the duration of the current. The corresponding closing current, induced in the secondary coil, may in the same manner be repre- sented by the curve I) s h only the ordinate o -s must be drawn be- low the line D J, since the current is in the opposite direction to that inducing it. In a similar manner, at the moment of the open- ing of the primary current, there is developed within the primary coil a direct extra current, so called on account of it being in the same direction as the current inducing it, and therefore intensifying it. But, as there is no arraugement in the ordinary induction appa- ratus by which the primary current is maintained, the direct extra current is suppressed at the opening of the primary current, the latter is therefore suddenly inter- rupted Avhen at its full strength, and may be represented graphically by the perpendicular line E I, and the opening current in the secon- dary coil by the perpendicular / /, it beins; in the same direction as that in the primary, and which, havins: attained its maximum sud- denly, falls off" more gradually, as shown by the curve line / K. From the sudden manner in which the opening current developed in the secondary coil attains its maxi- mum intensity -/ /, as compared with the gradual increase of the closing one D b, it becomes evident why the effect of the stim- ulation by the former current is greater than that by the latter. Such being the case, the induction apparatus being used as just described, let us modify the instrument a little, as done by Helmholtz,^ by connecting the binding screw a (Fig. 253), by means of a wire {w), with the binding screw >S', and lowering the silver spring (d) away from the point of the binding screw, the current will then pass by the connecting wire to directly into the primary coil P without passing first along the spring, and from the primary coil back to the battery by the coils g h ; but with the magnetiza- tion of the core within the latter the spring will be lowered, and ^ Du Bois Keymond, op. cit., s. 231. Helmholtz's modification of induction ap- paratus. 500 THE NERVOUS SYSTEM. the greater part of the current being short-circuited will then pass directly back to the battery by the spring d and pillar m ; the pri- mary current being then weakened, as represented graphically to the extent of the lines A B (Fig. 252), the magnetization of the core within the coils g h (Fig. 253) will not be sufficient to keep the spring do\A'n, the short circuit current will be reopened, and all the current will pass through the primary coil again. The Helm- holtz modification of the induction apparatus being used, as just described, it will be observed that, as the current in the pri- mary coil is never entirely interrupted, the direct extra current developed at the moment of the opening of the primary current within the latter Mill reinforce the primary current, the two cur- rents having the same direction. The partial interruption of the primary current, and the development of the opening secondary current will, therefore, be both gradual, as shown by the curves E 31 and J L, respectively, which is not the case, as we have seen, Fia. 254. The moist chamber, with the nerve-muscle preparation, non-polarizable electrodes, and lever in position ready for an observation. The glass cover is not shown. when the ordinary induction apparatus is used, since the primary current, being entirely interrupted, the direct extra current cannot make this reinforcing effect felt. The opening secondary current ./ L, with Helmholtz's modification, attaining then its maximum intensity, gradually, like that of the closing secondary one D H b, differs but little in its physiological effects from the latter when used as a stimulus. That part of the sciatic nerve supplying the gastrocnemius mus- cle in the frog being the one that we shall make use of in our ex- periments, on account of its length and the readiness with which it NON-POLARIZABLE ELECTRODES. 501 is exposed, it may be mentioned that in preparing the nerve it should be touched as little as possible, and never seized with a pair of forceps, though it must be completely separated from the adja- cent nerves. The gastrocnemius muscle, the contraction of which we take as a measure of the stimulation of the nerve, having been cut through at its insertion the tendo Achillis, must be completely freed up to its origin at the end of the femur ; of the latter enough should be left so that it can be firmly clamped to the bar A (Fig. 254), of the upright B, the tibia and fibula being, however, entirely removed. If the nerve-muscle preparation so prepared and clamped be covered with a glass bell fitting into the rim of the disk D, of ebony or other hard wood a few pieces of wet blotting paper, having been previously placed upon the disk, the nerve and muscle will be prevented from getting dry. The disk is also provided with binding screws for receiving the wires from the secondary coil of the induction apparatus, and from the electrodes E supporting the nerve N. The electrodes should be non-polarizable — that is, elec- trodes which, while transmitting the current from the secondary coil of the induction apparatus, will not generate a current by con- tact with the nerve. Of the different forms of non-polarizable electrodes a convenient one is that consisting of a glass tube (Fig. 254, E), bent and plugged up at one end by a putty made of china clay and 0.75 per cent, solution of sodium chloride, and containing a saturated solution of zinc sulphate, into which is immersed to a depth of about -3 mm. a slip of thoroughly amalgamated zinc. The wires AV AV leadins: to the bindinti; screws are attached to the latter, which is usually sufficiently strong to hold up the electrodes ; if not, the latter can be movably clamped to the upright B, or supported as in Fig. 254, by an electrode bearer S. The glass tube is often closed at its extreme point, the plug of clay being exposed only where the small orifice has been drilled. Through an opening in the disk of the moist chamber the muscle can be attached to a lever (Fig. 254, L), and its contractions made very evident by the eleva- tion of the latter. If the point of the lever be terminated by a brush or pen, by means of the l>lackened cylinder already described, a graphic representation of the muscular contraction can be obtained and preserved for future reference. The lever consists of a thin slip of wood, the portion near the fulcrum being of metal and per- forated or notched to receive the hook attached to the tendon of the muscle, and has usually suspended from it a scale pan con- taining counterpoising weights varying from between 10 to 200 grammes. The moist chamber being so attached to the recording apparatus by means of its upright, that the point of the lever is brought in contact with the blackened surface of the cylinder, the latter is made to rotate for a moment so as to obtain first a base line. The nerve is now stimulated by the induction apparatus, first by a closing and then by an opening shock, without Helmholtz's modification being used, and the cylinder being made to rotate rap- 502 THE NERVOUS SYSTEM. idly it will be observed that the lever is elevated higher in the lat- ter case (Fig. 255) than in the former (Fig. 256), the effect of the opening shock being greater than that of the closing one for the rea- sons already given. Fig. 255. Opening shock. Fig. 256. Fig. 257. closing shock. Curve of tetanus Fig. 258. If, however, the nerve be stimulated by a series of closing and opening shocks the magnetic interruptor of tlie induction apparatus being used, the lever is observed to remain elevated (Fig. 257), the interval between eacb shock being of so short a duration that the lever de- scends but a little distance when it is elevated again. The elevations and depressions of the lever due to the in- dividual contractions of the muscle when so rapidly produced, are, how- ever, soon lost to view, becoming so fused together that they are not, tlicre- fore, apparent in the trace of the muscle curve of tetanus. The slight fall and rise of the lever Ijccome, however, quite evident if the primary current be interrupted, not by the magnetic arrangement (o tA e/' a. sec. Diagram of a muscle curve as drawn on a traveling surface, c. The line described by the point of the lever connected with the muscle, a. The line described by marking lever, ft. The line described by the tuning-fork. The vertical line m marks the moment of stimulation, m', the beginning ; nfl, the maximum ; and iiv^, the end of the contraction of the muscle. (Foster.) to avoid misunderstanding, it may be mentioned in this connection that a distinction is often made between the so-called electrical latent period and the mechanical one just referred to, the former lasting in Whiiijie. the striated muscles of the frog a shorter time (0.002 sec.) than the latter (0.004 sec.).^ If the nerve be stimulated not where it passes ^ W. Biedermann Electrophysiologie, 1895, s. 48. Burdon Sanderson, Central- blatt fiir Physiologic, 1890, — . Tigerstedt, Archiv fiir Anat. u. Phys., 1885, s. 111. VELOCITY OF A XERVOUS IMPULSE. 505 into the muscle, but at some distance from the latter, 2.5 cent. (1 inch), say, as at A (Fig. 261), which can be readily done by simply placing the wires C D of the whippe (the cross piece being left out) in the mercury cups in connection with the binding screws 5 and 6, it will be observed that not only 0.01 sec. (Fig. 262, a b) elapses between the stimulation of the ners-e and the contraction of the muscle, but an additional very small period of time (0.0008 sec, 66', Fig. 262 j inter\'enes, which precedes that of the latent period. The difference in the interval of time elapsing between the stimulation and the contraction in the two cases is e\adently due to the fact that in the case of the nerve being stimulated at A rather than at B, Fig. 261, the impidse must travel through a dis- tance of 2.5 cent. (1 inch) before it reaches the muscle, and as in doing this 0.0008 sec. elapses, it may be inferred that nerve energy is propagated approximately at the rate of 28 meters (91.8 feet) per second. Fig. 262. a 66 Curves illustrating the measurement of the velocity of a nervous impulse. (Diagrammatic.) To be read from left to right, ab. The interval of time elapsing between moment of stimulation and contraction of muscle when nerve stimulated at entrance of latter into muscle, ab'. The interval when nerve stimulated at some distance from muscle, ab. Latent period in both cases. hb'. Interval of time during which nervous impulse travels along nerve to muscle. It is to be understood that the interval of time bb' precedes that of ab, the nerve being stimulated at a. (Foster.) The nerve force is probal)ly, however, transmitted at a slower rate in the nerves of the frog than that just given, since, if a long nerve be stimulated in three different places, near the muscle, mid- way, and above, the curves show that more than double the time elapses during the pas.-^age of the nerve force through the whole nerve than from the middle point to where the nerve passes into muscle.^ While the latent period and the velocity with which nerve force is transmitted, can be determined in the manner just described, a more accurate method is by means of the pendulum myograph. The pendulum myograph (Fig. 263) consists, as its name implies, of a pendulum suspended by a knife edge, working upon a support firmly fixed by a frame imbedded in the wall of the laboratory. The pendulum carries two glass plates, the outer smoked one. A, ser\'ing as a recording surfoce, the inner one, not seen in the figure, as a counterpoise. The plate A, as the pendulum vibrates, pushes aside by its tooth a' the bar e, thereby interrupting the primary current xcdj/ of the induction apparatus, and also a current passing through the small electro-magnet, to which is attached a pen serv- 506 TEE NERVOUS SYSTEM. ing as a marking lever. The pendulum, having reached h' , is held there by a catch similar to that which held it at a before its vibra- tion began. Fig. 263. rendulum myographion. (Foster.) With the interruption of the primary current I (Fig. 264), the nerve is stimulated by the opening shock of the secondary current THE PENDULUM MYOGRAPH. 507 II, transmitted to the electrodes, the moment of stimulation being determined by the moving of the pen acting as a marking lever, due to the simultaneous interrupting of the current passing through the small electro-magnet. The time elapsing is determined, as in the preceding experiment, by the electro-magnetic chronograph /. In using the pendulum myograph the muscle m is attached, as in Fig. 264. Schema for measuring the velocity of the nerve impulse with pendulum myograph. /. Clamp for femur, m. Muscle. N. Nerve; a, near, 6, removed from C, whippe. II. Secondary; I, pri- mary spiral of induction apparatus. B. Battery. 1, 2. Key. 3. Tooth on the smoked plate. (Landois.) the preceding experiment, to a lever ; the latter is, however, in this case much heavier, and is provided with a projecting steel point, which, in being pressed against the smoked plate P, makes the curved line, as the plate is carried past by the vibration of the pen- dulum. To demonstrate the rapidity with which the nerve force is transmitted, we make use of the whippe, as in the preceding experi- ment, throwing the current, by means of the latter, into the nerve at 6, a definite distance from the point first stimulated a. The result, as shown by a tracing (Fig. 265) taken with the pendulum myograph, is the same as when obtained by the cylinder. In order to preserve the tracing on the smoked glass the latter is placed upon sensitive paper and exposed to sunlight. The rate at which nerve force is transmitted has been determined by Helmholtz and Baxt,^ in man as well as in the lower animals. In the case of the motor nerves this was accomplished by applying elec- trodes to the skin over the median nerve at the wrist, elbow, and up- per arm, the arm being firmly surrounded by gypsum, except at the points stimulated. The time elapsing between the application of the electrodes and the muscular contraction, the latter being evinced by the swelling of the muscles of the ball of the thumb against a delicate lever, was greater when the stimulus was applied to the upper arm than at the wrist. The average rate of transmission was deter- mined to be about 33.9 meters (111 feet) per second, varying, how- iMonatsber. d. Berliner Acad., 1807, s. 228; 1870, s. 184. 508 THE NERVOUS SYSTEM. ever, according to the temperature ; being more rapid at a high than at a low one. The rate of transmission of the nerve force in sensory nerves was also determined by Helmholtz ^ in essentially a similar manner. A tactile impression being made successively upon the foot, thigh, and loins, the moment at whicli the sensation is felt is indicated in each instant by a movement of the finger. Now, since the time elapsing during M'hich the impression becomes con- scious perception in the brain, as well as that during which the nerve force is transmitted by the motor nerve to the finger, is the ioij> 5T5. 5'e, of a second. A muscle-curve obtained by means of the pendulum myograph, the nerve being stimulated at a (Fig. 264). To be read from left to right, a indicates the moment at which the induction-shock is sent into the nerve, b the commencement, c the maximum, and d the close of the contraction. The two smaller curves succeeding the larger one are due to oscillations of the lever. Below the muscle-curve is the curve drawn by a tuning-fork making 180 double vibrations a second, each complete curve representing therefore ii,,th <<( a second. It will be observed that the plate of the myograph was travelling more rapidly towanl the close than at the beginning of the contraction, as shown by the greater length of the vibration curves. (Foster.) same in all three cases, the differences observed in the successive observations must be due to the different lengths of the sensory nerves transmitting the impression, the average rate, according to Helmholtz, being about 60 meters (196 feet) per second, modified by the temperature, as in the case of motor nerves. It would appear, however, from recent researches ^ that the rate of conduction of nervous impulses is about the same in sensory as in motor nerves, viz., 35 meters (115 feet) per second. Knowing the rapidity with which nerve force is transmitted through the peripheral nerves, its rate of transmissiou through the spinal cord in man can be inferred from the difference in time elapsing during the passage of a voluntary impulse from the brain through the cord to the upper and to the lower extremity, or in the reverse direction, of an impression made upon the periphery, giv- ing rise in the brain to a sensation. Thus, in the case of the mo- tor fibers of the cord, if the hand be moved first in obedience to the will, and then the foot, it is evident that a longer period will elapse between the application of the stimulu.'^, the will, and the muscular contraction, in the latter case than in the former, since, iPhyso-Ocon Ges. zu Konig.sberg, 1850, Dec. 13. ^Oehl, Archiv italiennes de Biologic, xxi., 3, 1895, p. 401. TBANSMISSION OF NERVE FORCE. 509 in the transmission of the nerve force through the spinal cord to the sciatic nerve, three times the distance has been traversed as in its transmission to the median nerve. In this way it has been shown by Burckhardt ^ that the average rate of transmission of the nerve force through the motor fibers of the cord, is about 10 meters (33 feet) per second, or about one-third of that of the motor fibers of the peripheral nerves. On the supposition that 0.08 sec. elapses during the passage of the nerve force from the brain to the foot, one-half of that time is consumed in its transmission tlirough the cord, and one-half through the nerves. The rate of transmission through the sensory fibers of the cord does not differ very much, however, from tliat of the sensory fibers of the peripheral nerves. Supposing that the distance traversed through the sciatic nerve and cord from the periphery to the sensorium by a sensory impulse be the same as that of the motor impulse just referred to, the time elapsing between the application of the stimulus and the resulting sensation would be about 0.025 sec. As an illustration of the relative slowness with which nerve force is transmitted, it may be mentioned that a whale one hundred feet long would not feel the wound of a harpoon until one second after the weapon was thrust into its tail, and that in response to a volun- tary impulse, about one second would elapse before the tail would be moved, supposing that the nerve force is transmitted in the huge cetacean at the same rate as in man. It should be mentioned, how- ever, in this connection according to Burckhardt, that tactile im- pressions appear to be transmitted much more rapidly through the spinal cord than painful ones, the former at the rate of 42 meters (137 feet), the latter 13 meters (42 feet) per second. The latent period and the velocity with which the nerve force is trans- mitted through the spinal cord being known, it becomes possible to determine approximately at least the time required for the apprehension or perception by the brain of an impression and volition. Thus, supposing the interval of time elapsing between the production of a sound and the hearing of the same has been determined to amount to 0.198 sec, it follows that if we deduct from the latter the time during which the nervous impulse is transmitted through the acoustic nerves, spinal cord, motor nerves and latent period, 0.086 sec, the remainder, 0.112 sec, will be the time required by the brain for perception and volition. Transmission through acoustic nerve . . 0.010 sec. Pei'ception and volition . . . . . 0.112 " Transmission through spinal cord . . . 0.022 " " " motor nerve . . 0.044 " Latent period 0.010 " 0.198 " The interval of time (0.198 sec.) elapsing between the production of a sound and the hearing of the same may be determined among ' Die Physiologische Diagnostik, s. 32, Leipzig, 1875. 510 THE NERVOUS SYSTEM. other methods by means of the apparatus (Fig. 266) in which the clock-work of the Hipp's chrouoscope H, held by an electro-mag- netic anchor is set going through the weaking of the current Klmn2H3Z^ when the latter is short-circuited through Kfia6JZ4. by the tilting up of the board through the electrodes JZ by the falling of the ball, the cause of the sound and which is stopped by the voluntary elevation of the lever h at the instant that the sound is heard. Fig. 2G6. Apparatus for determining the interval elapsing between the production and hearing of a sound. (WuxDT.) The determination of the interval between the production of a light and the seeing of the same can be determined in a similar manner by suitable apparatus. Such determinations, apart from their j^hysiological interest, are also of ])ractical importance to astronomers, it being well known to the latter that considerable difference exists, amounting in some instances to as much as one second, between observation made upon the transit of a star for example, the object being seen by one observer sooner than the other. Indeed, it was such discrepancies that led Hirsch ^ to de- termine, as far as possible, the " reaction time," that is the interval which elapses between the application of the stimulus and the mak- ing of the signal when the sensation is felt, of the rapidity with which impressions are transmitted through the optic and acoustic nerves and perceived by the brain, and of so ascertaining the per- sonal error due to individual peculiarities, and by means of which the observation could be corrected by the personal equation, as it is called. The determination of the rapidity with which nerve force is transmitted is a striking illustration of the advances made in phys- ^BuU. de la Soc. des Sciences nat. de Neufchatel, 1862. RAPIDITY OF NERVE ACTIOX. 511 iology, due to the introduction in its study of physical methods. In the year 1.;ij„Qt ing more directly connected by means of a brass plug. The shunt is provided with two binding screws, to which are attached the t^vo wires from the outer binding screws of the galvanometer and the two electrodes convey- ing the current, a part of which is to be diverted from the galvanometer. The two binding screws of the shunt can be brought into direct connection by turning down a brass bar ; if this be done, the cur- rent from the nerve, for example, will be short-circuited, it passing from one binding screw to the other, back to where it came from, none of the current going to the galvanometer, owing to the re- sistance offered. If, however, the connection between the binding screws be unmade through the raising of the bar, and the i)lug not placed in any of the holes of the shunt, then the current, not be- ing able to pass directly across from one binding screw to the other, will traverse the galvanometer. The coils of the shunt being graduated, however, according to tlie resistance of the galvanometer, by means of the plug, we can vary at will the proportional amount of the current going to the galvanometer to that short-circuited, the amount depending upon the ratio of the resistance of the gal- WIEDEMANN S GALVAyOMETEB. 517 vanometer to that of the shunt. Thus, for example, suppose the plug be inserted into the hole marked 1, then such resistance is oifered in the short circuit that only J^ of the total current goes to the galvanometer, the remaining ^^^ being short-circuited ; if in the hole marked gL, or g-i^, then only yi^ or y-Q^ q, respectively, of the current traverses the galvanometer, the remaining -^-^^, or tVo^O' t»eing short-circuited. Weidemann's galvanometer, consists of a thick cylinder of cop- per (Fig. 275), through which a tunnel is bored, the latter capable of being closed at each end by either a cover with glass front, or bv a solid plug of copper. Within the copper tunnel hangs a mag- netized ring (Fig. -75, A), of such size that it can just swing clear Fig. 275. Wiedemann's galvanometer. of the sides. The object in making the magnet ring-shaped is to make it stronger in proportion to its size, the center, or inactive portion of the magnet, in that form being absent. Connected with, and passing upward from the magnetized ring through a copper tube, is an aluminium rod, terminating in a light frame holding a circular plane mirror, facing east and west (B). In order to prevent currents of air moving the mirror, the latter is inclosed within a cir- cular brass cover (C) having a circular window (W), through which the mirror can be viewed. Above the mirror is screwed a long glass tube (T), at the top of which there is a little windlass, sup- ported by a small piece of ebonite, whose centering on the glass tube is effected by three screws. On the windlass a single fiber of silk is wound, passing through the ebonite and down through the glass tube, by means of which the magnet and mirror are suspended, the frame of the latter being pierced with an eye for the attachment of 518 THE NERVOUS SYSTEM. the platinum hook, to which the end of the silk fiber is looped. The magnetized ring can, by this means, be raised or lowered or centered in the copper chamber, the latter and its attachments being supported by brass columns on a mahogany plate, leyelled by three screws. The coils C C, the turns of which in sensitiye instruments, as in that of the author, may amount to as many as 30,000, and through which is transmitted the electricity exerting a directive in- fluence upon the magnetized ring, are placed upon a sledge, that they can be so approximated as to meet right over the copper cham- ber, and when so disposed completely conceal the latter, as in Fig. 275. Since with the movement of the magnetized ring induced currents are set up in the surrounding copper chamber, opposite in direction to those of the needle, the oscillations of the latter are so diminished that after deflection it comes quickly to rest. The cop- per chamber is, therefore, called the damper, the close fitting of the ring within the latter and the proximity of the coils materially assist- ing in the dampening by it of the oscillations of the ring. Further, in order to render tlie magnetized ring within the copper damper astatic, we make use^ of an accessory magnet (M), a Hauy bar, placed in the magnetic meridian horizontal to the needle, with its north pole pointing north, like that of the magnetized ring, and supported upon a bar (D) directed perpendicularly to the coils, and in a line with their axis. The accessory magnet can slide up and down the bar within its support, the bar being divided into centimeters, for meas- uring the extent of the movement. One end of the magnet being caught between a spring and a screw, and the latter being turned by the pulley P\ the magnet can be moved from its spring end on the other end, forming an angle with the plane of the coils, the angular movement being effected by an experimenter seated at a distance by means of the pulley P-. The galvanometer, being properly located, the accessory magnet, just descriljed, is fixed upon its bar (B) by a clamp to the shelf. The magnet, being first placed at the end of the bar, is then slowly moved down it, the effect being gradually to neutralize the magnetic action of the earth. The moment, however, that the position of neutralization is passed the magnetic ring swings round, carrying the mirror, of course, with it, now facing north and south, so that its opposite poles are placed against the poles of the magnet, the movement involving a full half twist on its fiber. To prevent this, one of the copper plugs should be put in one of the openings of the chamber, by which the movement of the magnetic ring is blocked, the other opening being filled with a glass plug, the movement of the ring can be seen. This twisting tendency being r)bserved, the accessory magnet should be moved back again till the tendency disappears, and the magnetic ring is just sufficiently in- fluenced by the directive action of the earth to be kept in the me- ridian. The instrimtient will then be found to be very sensitive. When botli coils are to be used, they must be connected by carry- 1 Du Bois Keymond, Abhandlungen, s. 370. CAPILLARY ELECTROMETER. 519 Fig. 276. ing a wire from a binding screw of the one to a binding screw of the other, according to the coils used, the remaining free binding screws receiving the wires conveying the current. When both coils enclose the copper chamber the most intense effect is obtained, the recession of coils from the chamber diminishing it. The great advantage of Wiedemann's galvanometer is that by the copper damper the disposition of the coils C, and the accessory magnet M, the magnetized ring is made aperiodic or dead beat^ that is to say, the magnetic ring, when aifected by the current, swings around comparatively slowly, until the maximum deflection is reached, and arriving at this point it rests there without oscilla- tion ; the current being withdrawn, it savings back again to zero, stopping there without further oscillation, a current in the opposite direction being indicated, should it pass the zero. It is highly important in locating the galvanometer that no iron structures whatever should be present in its neighborhood. The instrument may be placed upon a strong wooden shelf fixed to a solid dry wall, or, if the laboratory or lecture- room be upon the ground floor, upon a pillar of concrete, capped with oak, built upon a solid stone foun- dation. In using Wiedemann's gal- vanometer in the laboratory the extent of the deflection of the mag- netized ring is observed by means of an astronomical telescope, and of a scale (Fig. 276), supported by up- right above and at right angles to the long axis of an astronomical telescope, the scale and telescope being placed upon the same table to which the pulley P\ already referred to, is attached, and which ought to be from 6 to 9 feet distant from the galvanometer. The scale being directly opposite the mirror, the reversed numbers of the former will be seen in the latter in their natural position, and with the deflection of the needle the numbers will appear as if drawn across the mirror, the amount of the deflection being indicated by the number seen in the mirror when the needle comes to rest. For lecture purposes, however, the telescope, etc., is not used, a beam from a lime or electric light being received upon a small plane luirror, is thence reflected to the mirror of the galvanometer, and from the latter to a white scale placed at a distance of from 6 to 15 feet, according to the magni- fication desired. In this way the deflection of the magnetic ring can be made evident to a large audience. A very sensitive instrument often made use of in determining the presence of electrical currents in nerves is the capillary elec- trometer of Lippmann. This consists (Fig. 277) of a capillary glass tube (i?) filled from above with mercury and from below with Telescope and scale. 520 THE NERVOUS SYSTEM. Fig. 277. dilute sulphuric acid, and T^-liicli opens by its lower narrow end into a wide glass tube (c) containing mercury (^) and sulphuric acid (s) and conducting wires terminating in non-polarizable electrodes. With the application of the latter to the nerve any electrical current present Avill be at once revealed by the move- ment of the thread of mercury in the direc- tion of the arrow, as observed by the micro- scope, as a very slight difference of electrical potential causes a change in the surface ten- sion of the mercury sulphuric acid meniscus. Inasmuch as in demonstrating the presence of an electrical current in a nerve l)y means of galvanometer, the current is conveyed by the wires passing from the binding screw^ to the nerve, it is obvious that these wires must terminate in non-polarizable electrodes — that is to say, as has been incidentally mentioned, in electrodes that will convey an electrical current already existing in the nerve ex- amined, but will not generate a new one when placed in contact with the latter, since the latter current so generated, extremely weak though it may be in deflecting at once the needle, the galvanometer being so sensitive, might readily be mistaken for the pre-existing current whose presence we wish to demonstrate. In order, however, to understand the manner in which the gen- eration of the current is prevented by the contact of the electrodes with the nerve tissue, it Avill be first necessary to explain what is meant by the polarization of the electrodes, to which the above effect is due. Let us suppose that two platinum electrodes have been immersed in acidulated water, and that the electricity trans- mitted from the battery has decomposed the water, the positive pole being covered with bubbles of oxygen, and the negative with bub- bles of hydrogen. If suddenly, now, the electrodes be disconnected with the battery, and connected with a galvanometer, the direction in which the needle of the latter is deflected will indicate the pres- ence of a current, opposite in direction to that of the battery and weakening the latter, developed through the fact of the nega- tive pole covered with hydrogen becoming positive to the positive pole covered with oxygen, just as in the case of non-constant batteries already referred to. It is the change in the condition of the electrodes which is known as their polarization, and which occurs in a similar manner if a nerve be placed upon two copper wires. We shall see hereafter that when a fresh muscle is con- nected with the galvanometer by copper wires, the deflection of the needle ensuing indicates the presence of a current, but which, on account of the polarization of the electrodes, may be as much due Capillary eloctrumcter. R. Mercury in tube ; eajjillary tube. «. Sulphuric acid. q. Mercury. B. Observer. M. Microscope. (Landois.) HOMOGENEOUS DIVERTING VESSEL. 521 to the generatiou of a current a.< to the presence of a preexisting one. Even perfectly clean platinum electrodes soon become differ- ently affected by contact with organic tissues, and so give rise to difference in electrical tension or electro-motive force. Eegnauld, however, showed in 18-34, that a strip of chemically pure zinc im- mersed in a solution of neutral zinc sulphate, and Matteuci, two years later, that ordinary zinc amalgamated and immersed in a saturated solution of the same, exhibited no polarization. Du Bois Reymond, availing himself of these discoveries, devised non- polarizable electrodes, convenient forms of which, kno^^'n as di- verting vessels and diverting cylinders, are represented in Figs. 278 and 279, and by which no currents are generated when nerve or muscle is placed in contact with the same, A diverting vessel (Fig. 278j consists of a zinc trough (T), containing a saturated Fig. 278. Homogeneous diverting vessel. solution of zinc sulphate, the inner surface of the trough being carefully amalgamated, and the outer surface coated with a layer of black varnish, the object of the latter being to prevent the sul- phate solution coming in contact vd\h any unamalgamated zinc. It mav be mentioned incidentally in this connection that the amalgamating fluid used is that known as Bergot's, prepared by dissolving: at a srentle heat 200 grammes of metallic mercurv in a 1000-gramme mixture consisting by weight of one part of nitric acid to three parts of hydrochloric acid, and adding then 1000 grammes of the latter acid. The fluid should be kept in a cool, dark place, to avoid decomposition. The trough, insulated by a base of vulcanite (V), and provided with a binding screw (K), can be lifted by a handle (R). The insulated cushions (C), called de- riving cushions, are made up of a series of layers of white Swedish 522 TEE NERVOUS SYSTEM. filtering paper, wliicli are stitched together at one end to secure them, and their sides cut perpendicularly with a sharp razor, and soaked in the zinc solution and squeezed so as to get rid of the bubbles of air which would offer resistance to the current. These cushions fill up the cavity of the trough, and project over the lip of the latter, a plate of ebonite (E), and an Indian-rubber band (B) retaining the cushion in this position. Inasmuch, however, as the nerve to be examined, if placed directly upon the deriving cushion would be corroded by the zinc sulphate solution in which the cushion has been soaked, a guard (G) is made, consisting, as already mentioned, of china clay worked up into a soft mass with a 0.5 or 1 per cent, solution of sodium chloride, which when freed of bubbles of air and flattened into a sheet (G) is folded over the Fig. 279. Diverting cyliDclcrs. cushion. A small piece of mica may also be placed upon the clay guard to limit the part to be touched by the tissue. The clay guard not only prevents the corrosion and destruction of the nerve, but through the presence of the salt, the secondary resistance, which would otherwise arise between the liquid conductor and the tissue, and diminish the intensity of the current to be examined is avoided, the salt at the same time being a good conductor. Two diverting vessels being so prepared, a fine silk-covered copper wire is carried from the binding screw (K) of one of the troughs (T) to one side of the Du Bois Reymond key, and another wire from the other trough (T'), not represented, to the other side of the key, wires be- ing also carried from the key K to the binding screws of the gal- vanometer g, as in Fig. 279. Such being the disposition of the diverting vessel, the key and galvanometer, if the key be down, ELECTRICAL CURRENTS OF NERVE. 523 the diverting vessels are short-circuited, but if up, are in commu- nication with the galvanometer. Finally the troughs can be di- rectly connected together by approximating them or indirectly by a closing cushion made out of blotting jjaper saturated in the zinc solution, etc., like the deriving ones. The diverting vessels, key, and galvanometer being so disposed before performing any experi- ment, it ought to be first shown that the diverting vessels are ho- mogeneous or non-polarizable. To do this, the key being down, and the needle of the galvanometer at zero, the two diverting vessels are connected together, and the key opened ; if the needle still re- mains at zero we may be assured that there is no electrical current, that the diverting vessels are homogeneous or non-polarizable. Apart from the fact that the nerve whose electricity is to be ex- amined cannot always be placed between the cushions in the posi- tion desired, it is also often impossible to bring particular points of the nerve in contact with the latter. We frequently, therefore, make use of the non-polarizable electrodes represented in Fig. 279, known as diverting cylinders, which consist of a flattened tube of glass (a) mounted on a universal joint {in I), and supported on a brass upright (A) closed at one end (c) by moistened china clay and filled with the saturated zinc sulphate solution in which is immersed the slip of amalgamated zinc Z. The clay (c) projecting from the end of the tube can be sharpened into a point so that any two parts of the nerve can be touched that is desired. That no polarization occurs when the points of such electrodes are placed in contact with the nerv^e is shown by the absence of the products of electro- lytic action which would otherwise accumulate at the electrodes. Fig. 280. Electrical currents of nerve. Such electrodes are not only serviceable in diverting an electrical current from the nerve to the galvanometer, but can be also used for the purpose of stimulating a nerve by electricity in the same manner as already described. The deriving cushions (Fig. 278), or 524 THE NERVOUS SYSTEM, the diverting cylinders (a), and the key (K) and galvanometer (^r) having been connected as represented in Fig. 279, and a freshly prepared nerve {n) having been placed upon the cushions or in con- tact with the points of the cylinders so that its transverse section or cut end is in contact with one of the cushions or cylinders, and its longitudinal uninjured surface at the equator with the other, with the opening of the key the needle of the galvanometer will at once be deflected, and in a direction which shows that the electrical cur- rent in the nerve passes, as indicated by the arrows (Fig. 280), from the longitudinal surface of the nerve (a) through the galvanometer to the transverse cut surface {x y), the remainder of the circuit be- ing completed by the nerve itself. In this connection it may be mentioned that the galvanometer is not indispensable, if we wish simply to demonstrate the electrical nerve current, as it may be ac- complished by what is known as the physiological rheoscope, which is prepared in the following manner : Upon an insulated glass plate A (Fig. 281) arc placed two pieces of blotting paper (B C) soaked in salt solution, wdiich support two Fig. 281. Physiological rhooscope. albuminous guards (D E), upon which rests the nerve (N) of a nerve-mu.sclc preparation, the cut end of which is in contact with the pad D, the longitudinal surface with the pad E, the muscle (M) being supported by the glass plate F, also insulated. The nerve being so disposed, with the alternate connection and disconnection of the two pieces of blotting paper (B C) by a third piece (G), the muscular contraction that follows in both instances indicates the presence of an electrical current in the nerve passing in the direction of the arrows. Returning now to the case of the nerve Avhen in connection with the galvanometer (Fig. 280), and experimenting a little further by DU BOIS REYMOND'S BOUND COMPENSATOR. 525 changing the position of one or both of the electrodes, it will soon be learned that while the current always passes from the longitudi- nal to the transverse cut surface, the amount of the deflection of the galvanometer needle varies very much according to the position of the electrodes. In certain positions, indeed, as where the electrodes are placed on different sides of the nerves exactly opposite to each other {ah), or on points equidistant from the equator {ef), the needle is not deflected at all, there being no difference of electrical potential at such places. Such was also supposed to be the case with reference to the ends of the nerve. It has been shown, how- ever, bv Du Bois Eeymond and Mendelssohn^ that a current passes through the nerve from transverse section to transverse section, to Avhich the name of " axial stream" has been given by these obser- vers. On the other hand, if one electrode remaining at the cut surface, we move the other along the longitudinal surface toward the equator the deflection of the needle will be increased, the max- imum being reached when the electrodes are at the equator of the longitudinal and transverse surfaces, as in the experiment repre- sented in Fig. 280, ab. Experimentally, in this w^ay, with the galvanometer, it may be learned that all parts of the longitudinal surface of any nerve are positively electrified with reference to the transverse cut surface, and that if any two points (e/) of the longi- tudinal surface, that nearest the equator of the nerve (e) is posi- tively electrified with reference to that more distant (/). That a similar relation exists between the equator of the trans- verse cut surface and its periphery, though not experimentally dem- onstrated, is rendered highly probable from the fact of such a re- lation having been demonstrated in the case of muscles, as we shall see hereafter. Further, by experimenting with different nerves it will be found that the length and thickness of the nerve influence the amount of the electrical current, it being greater in long, thick nerves than in short, slender ones. That an electrical current exists in the nerve during a state of rest, there can be after what has been said, no doubt, whatever the subsequent explanation of the phenomena may be ; but it must be admitted, and the ad- mission is an important one as regards any inference to be here- after drawn as to the relation between nerve electricity and nerve force, that in an uninjured nerve, in which no transverse section has been made, there is no evidence of an electrical current, that is to say, the nerve is isolectric. The electro-motive force of nerve currents such as those just de- scribed can be determined by means of a galvanometer and round compensator (Fig. 282), the principle made use of being essentially the same as that by which a body is weighed. The method con- sists in shunting ofl' by means of the compensator (Fig. 283, III), from the circuit of a standard element, a Daniell cell (D), for ex- ^ Ueber den axialen Nervenstrom, Maurice Mendelssohn, 1885, Archiv f. Anat. und Phys. separat-abdruck. 526 THE NERVOUS SYSTEM. ample, whose electro-motive force is known (1.08 volts), an amount of current sufficient to neutralize or compensate the current deflect- ing the magnet due to the electro-motive force of the nerve N, which is to be determined, just as the unknown weight of a body is learned Fig. 282. Du Bois Reymond's rouud compensator. from the known weight necessary to neutralize or balance it. Let us suppose that the electrical current diverted by the now polari- zable electrodes from the nerve N, the sciatic of the frog, for exam- ple, to the Wiedemann galvanometer G, be sufficient to deflect the magnet to an extent corresponding to 25 divisions of the scale. If ^-(7) XeXff^ Schema for determining electro-motive force by round compensator. now the compensator be turned until the wheel reaches III, part of the current from the Daniell cell will return through IV, II, F, whence it came, and part through III, Pg to the nerve N, and be- RESISTANCE OF NERVE. 527 ing in the reverse direction to the current clue to the nerve the mag- net will be brought back to zero. Such being the case it follows that the electro-motive force of the nerve current is equal to that shunted off from the compensator and neutralizing it, and which amounts, the wheel being at III, to the -^^ of a Daniell or 0.02 volt.^ Recent researches ^ have shown the electro-motive force of the currents in the nerve and spinal tracts of the cat to be 0.01 and 0.04, and in the corresponding parts in the ape 0.005 and 0.29 of a Daniell cell respectively. According to Mendelssohn ^ the electro- motive force of the axial current of the posterior roots of the spinal nerves of frogs — that is, of the current from equator to central or peripheral transverse section amounts respectively to 0.00893 and 0.00767 of a Raoul, that element (copper in copper sulphate solu- tion, and zinc in zinc sulphate) being used instead of a Daniell. As the electrical current of a nerve, after passing through a gal- vanometer, must, in returning to the point from which it started, pass through the nerve, and as induced and constant currents are Fig. 284. Schema for determining the resistance of nerve. frequently thrown into a nerve, the resistance offered by the latter to the passage of an electrical current must also be determined. This is accomplished by essentially the same method as ordinarily made use of in determining the amount of resistance offered by bodies in general to the passage of electricity, and is briefly known as that by the Wheatstone bridge. This method is based upon the 1 For the method of fletermining this, as well as for the constniction and manner of using the compensator, the reader Ls referred to "Researches upon the general physiology of nerve and muscle," Xo. 1, by H. C. Chapman and A. P. Brubaker, Proe. of Acad. Nat. Sciences, Phila., 18§!8, p. 106. 2GotchandHorsley, Phil. Trans., Vol. 182, 1891, pp. 267-526, 3 Op. cit., s. 387. 528 TEE NERVOUS SYSTEM. principle of so disposing the body whose resistance is to be deter- mined, that the cnrrent of electricity traversing it passes through a galvanometer in an opposite direction to that traversing a body whose resistance can be varied, until the current traversing the body exactly neutralizes the former current, as shown bv the gal- vanometer's needle remaining at zero. Such being the case, the unknown resistance is then equal to the known one ; otherwise there would be a deflection of the magnetic needle according as the one body would oifer a greater or less re- sistance to the current than the other. Thus, supposing that the apparatus be arranged as in Fig. 284, then the current from a Daniell's element D, on arriving at A, the end of the long wire A B, or rheocord, splits into two branch currents, one of wdiich will traverse the body X, a nerve, for example, whose resistance is to be determined, and the other the wire A B. Further, the first branch current, on arriving at 0, will divide into two, one of which will pass into the resistance box R, the other into the galvanometer CjT ; the latter current being opposite in direction to that coming from *S', one of the two branch currents into which the current A S divides, the remaining one passing from S to B, and thence back to the Daniell's element. But, as the resistance offered to the cur- rent passing from A toward B can be increased or diminished by the sliding of S from or toward A, all the current returning to the battery when the slider is at A, by varying the position of the slider a point will be reached on the wire, as at S, when the gal- vanometer needle will remain at zero, showing that the current passing down from the nerve from O to the galvanometer is equal and opposite in direction to that passing up from the wire at S. Such being the case, then the resistance offered by the nerve, or x, is to that of the resistance box B, as the part of the wire A S is to the part N B — that is, x: B : : A S : S B. Now, as the resistance B is learned by observing the number of plugs out, and that of A S and SB being also known, the rheocord wire having been previously graduated, the unknown resistance of the nerve, or .r, is given in terms of B, A »S, and S B, as shown by the equation EX AS, SB If A S and ;S' B be constant and equal, then the resistance offered by iV equals that of B, and can be inferred directly from the latter. The method just described of determining the resistance offered by a nerve, for example, to the passage of a current of electricity is at times inconvenient, even quite awkward, on account of the length of the rheocord wire involved. For this reason we make use of the round compensator (Fig. 285) with, however, the acces- sory binding screw O. The principle of determining the resistance, it is needless to add, however, is not at all affected by this modifi- cation for determination of resistance of nerve, the difference be- THE ROUND COMPENSATOR. 529 Fig. 285. tween the long and round rlieocord or compensator being simply in the disposition of detail. Thus, if Fig. 285, a schematic repre- sentation of the round compensator, be compared ^ith that of Fig. 284, the long one, it will be observed that in both instruments the current from the Daniell's element D, on arriving at A splits into two currents, one of which passes to the wheel or slider S, the other to the nerve ; that the current at N divides into two, one of which passes to the galvanometer (l, the other back to the Daniell's ele- ment ; that the current after traversing the nerve divides into two, one of which passes to the gal- vanometer 6r, the other to the resistance box B, and thence back to the Dan- iell's element ; that the two currents, passing in opposite directions through the galvanometer neutral- ize each other. It follows, therefore, that in using the modified round com- pensator we obtain the same proportion as in using the long one, viz.: X : R : : AS : SB, Ry^AS The value of x, or the resistance of the nerve, as obtained by this method, we have determined to be in a portion of the sciatic nerve of the frog, 2 cm. long, 1 cm. broad, and 0.5 mm. thick, when exerted longitudi- nally, twelve million times greater than mercury when taken as unity, and when transversely thirty-two million times greater.^ It may be mentioned in this connection that while the resistance oifered by the human body to the passage of an electrical current is very great in a state of health, it appears to be diminished in certain kinds of disease, so much so in Grave's disease, for example, as to constitute an important diagnostic symptom. Having considered the nerve current and the electro-motive force of the nerve, and the resistance offered by the nerve to the passage ^ Researches upon the General Physiology of Nerve and Muscle, No. 2, by H. C. Chapman and A. P. Brubaker, Proc. Acad. Nat. Sci. Phil., 1888, p. 155. 34 Schema of round compensator, with modification. 530 THE NERVOUS SYSTEM. of electricity, it remains for us now to offer, if possible, some ex- planation of the natural nerve current based upon its physical structure. It is well kno^\Ti that if a solid copper cylinder (Cu, Fig. 286), covered except at its ends by a layer of zinc, Zn, be im- mersed in a conducting fluid like water, that electrical currents are developed, which, as may be shown by the galvanometer, pass from the longitudinal or zinc surface to the transverse copper one, and Fig. 286. Apparatus for the development of electrical currents. that, according as the electrodes are shifted from point to point of its copper and zinc surfaces, these currents become stronger, weaker, or disappear altogether, and that while if the copper be entirely covered by its zinc mantel there is no appreciable electrical current, however the electrodes may be placed. When it is remembered that the ultimate nerve fiber consists histologically of the axis-cylinder surrounded by the white substance of Schwann and neurilemma, it might appear at first sight that one or the other of these two mem- branes bears to each other, or to the axis-cylinder, the same rela- tion electrically that we have seen the outer zinc mantel does to the copper axis of the simple physical apparatus just described. That such, however, is not the case, is proved by the fact that even at the nodes of Ranvier in the spinal nerves, and in the sym- pathetic fibers also, where the white substance of Schwann is absent, nevertheless, electrical currents can be shown to exist, evidently then it cannot be the contact of the substance of Schwann with either the neurilemma or the axis-cylinder that is the cause of the difference in the electrical potential, while the presence of electrical currents in the cord in the absence of the neurilemma equally shows that the contact of that membrane with the axis-cylinder has noth- ing to do, any more than the white substance of Schwann, with the development of such currents. The only conclusion to be drawn ELECTRICAL CURRENTS IN NERVES. 531 from such facts is that of the three parts of which the nerve con- sists, it is the axis-cylinder only which is concerned in the develop- ment of the electrical current, and Avhich confirms the conclusion that we have come to upon other grounds that the axis-cylinder is functionally the most essential part of the ultimate nerve fiber. Among the many theories that have been oifered as explanations of the presence of electrical currents in nerves, it has been held for example that the electrical current developed in a nerve in which a transverse section has been made, is due to the fact that the negatively electrified axis-cylinder is then exposed to the positively electri- fied nutritive fluid surrounding it, since, as we have just seen, the diflerence between the longitudinal and cut surfaces electrically can- not be attributed to the contact of cither neurilemma or substance of Schwann wdth the axis-cylinder. If such be the case, it becomes intelligible why, as we have already mentioned, there is no appreci- able electrical current in the uninjured nerve — that is, in one Avithout a transverse cut section, since under such circumstances the negative axis-cylinder is not exposed to the positive nutritive fluid surround- ing the nerve, just as in the case of the physical apparatus (Fig. 286) there is no electrical current developed as long as the negative copper axis or core is completely enveloped by the positive zinc mantel or hull. As an illustration of the influence of the contact of a surround- ing fluid upon a tissue in the development of an electrical current, it may be here mentioned that if the transverse cut surface of a dried muscle be placed upon the surface of distilled water, that an electrical current will be developed, passing from the longitudinal to the cut surface as soon as the muscle begins to swell through im- bibition of the fluid with which its transverse section is in contact. While the explanation just oflfercd, that of Gruenhageu,^ was consid- FiG. 287. Electromotive double dipolar molecules. ered by that physiologist as satisfactorily explaining the electrical condition of the cut nerve, however plausible it may appear, it must be mentioned that it is not generally accepted by physiologists. Thus, Du Bois Reymond ^ for many years held that the nerve consists 1 Funke, Physiologie, Erster Band, 1876, s. 487. ^ Untersuchungen iiber Thierische Electricitiit, Zweiter Band, s. 323. Berlin, 1849. 532 TEE NERVOUS SYSTEM. not of a homogeneous axis, surrounded by a hull like that of the physical apparatus just described (Fig. 286), but of a series of electro-motive double dipolar molecules, imbedded in an indijfferent and imperfectly conducted medium (Fig. 287), each double molecule consisting of a positive and negative part, the two positive parts placed together within, the two negative parts without, the double mole- cule presenting then a negative surface at the transverse section or cut end, and a positive surface at the longitudinal surface of the nerve. Regarding the double molecule as a minute battery whose positive and negative poles are at the longitudinal and transverse surfaces, respectively, currents will be developed which through the imperfect conductility of the medium will circulate in more or less eccentric lines not only in the immediate neighborhood of each molecule, but at some distance from the latter, from the positive middle surface to the negative ends of the nerve as indicated by the arrows, and giving rise to the deflection of the galvanometer needle, as we have seen is the case when the electrodes are applied to the nerve. Suppose that the nerve does consist according to this hypothesis of molecules, such as just described, it is evident that the electrical current within it is a closed one, the nerve differing in this respect from the zinc-copper apparatus as regards any cur- rent diverted into the galvanometer. In either case the current can only be a partial one, the deflection of the needle indicating the presence of a current, but in no wise the total strength of the current due to the electro-motive force of all the molecules. That the strength of the latter must be much greater than the partial current deflecting the needle is shown by the necessity of using such sensitive galvanometers, and is implied in the overcom- ing of the resistance both of the nerve and the galvanometer cir- cuit, which is considerable. Indeed, were not the total electric strength of the molecules much greater than that Fig. 288. of the partial current, the latter would not be ap- preciated by the galvanometer at all. It is for such reasons that Du Bois Reymond holds that the electro-motive force of the nerve molecules exceeds that producing all other known currents, and is capable, in the highest degree, of producing all the known effects of currents. While there is much to be said in favor of Du Bois lleymond's view of the nerve consisting of electro-motive molecules, it must be admitted that it is difficult to explain on Leyden jar. such a theory the weak currents that are developed by ])lacing the electrodes upon different points of the longitudinal surface, and why currents of any kind are only present in the injured nerve, or one presenting a transverse section. Indeed, this latter fact, equally an objection to the view offered by Gruenhagen, has led pliysiologists, like Hermann,^ to deny alto- ^Handbuch, Zweiter Band, Ei-ster Theil, s. 109. Leipzig, 1879. ELECTRICAL CURRENTS IN NERVES. 533 gether the preoxistciicc of any electrical current in tlie nerve, at- tributing the latter to the death of the transverse cut surface, which, at that moment, becomes negative to the longitudinal surface. On the other hand, according to Radcliife,^ the electrical character of the nerve current is rather static in its nature than voltaic, the nerve being compared on this view to a charged Leyden jar (Fig. 288), the current being simj^ly accidental, and due to the applying of the electrodes of the galvanometer to points having different electrical tensions. After all, however, the difference between static and voltaic or current electricity is not a profound one, being rather one of degree than of kind, since the former is one of high tension, but small in quantity, the latter of low tension, but large in quan- tity ; by tension being meant the tendency of the electricity accu- mulated at the extremities of the electrodes to free itself. 'Dynamics of Xerve and Muscle, p. 24. Lonlon, 1871. CHAPTER XXIX. THE NERVOUS SYSTEM.— (Continued.) CURRENTS OF REST AND OF ACTION. NEGATIVE VARI- ATION. ELECTROTONUS. ELECTROTONIC MODIFICA- TION OF EXCITABILITY. Fig. 289. Whatever view may be held as to the nature and cause of the electrical current present in an injured nerve during rest, there is no difference of opinion as to the fact that it is diminished during activity. The deflection of the galvanometer needle in the latter case is accounted for, however, by Du Bois Eeymond, on the sup- position that the current of rest undergoes during activity a diminu- tion, a " negative variation," while according to Hermann, and most physiologists, it is due to the development of an " action cur- rent," independent of and in a direction opposite to that of the current of rest. That the negative variation or action current con- stitutes an essential feature of nervous action, is shown from the intensity of the one varying with the other, and, as already men- tioned, from the rate at which it travels along the nerve being the same as that at which the nerve impulse itself is propagated. While the current of action or negative variation can be shown by stimu- lating the nerve with a single induction shock the phenom- enon becomes much more evident when the induction apparatus is used with the automatic interrupter, since the shocks thrown into the nerve succeed each other so rapidly that before the gal- vanometer needle can return to its first position, that due to the current of rest, it is again deflected by the nega- tive variation or current of action and consequently re- mains in one position, that due to the latter. Thus, for example, suppose that the transverse section of the nerve N be in contact with one of the diverting electrodes E' (Fig. 289), and the longitudinal surface with the other, and that (^ Disposal of apparatus to show the current action or negative variation. CURRENT OF ACTION. 535 (S^ Disposal of apparatus to show that the current of ac- tion or negative variation is transmitted in both direc- tions. the deflection of the magnetic needle at G, due to the current of rest, amounts to, say C. Such being the case, if now the nerve N be stimulated by the induction apparatus, the deflection of the needle in the reverse direction back towards zero, o indicates either the presence of an " action current " or that the current of rest has been diminished, has undergone a negative variation. If now the experiment be so modified (Fig. 290) that while the nerve is stimu- lated in the middle X, its two ends (c d) are in contact with the electrodes of two galva- nometers {G G'), it will be Fig. 290. observed that there is a cur- rent of action or a diminu- tion in the current of rest (a — 0, 6 — o) of the nerve at both ends, showing that the disturbance in the elec- t r i c a 1 condition of the nerve, whatever its nature may be, is propagated in both directions, from the center or the point of the application of the stimulus : a very important fact, since, if the current of action or the negative variation is intimately associated with that of the de- velopment and propagation of the nerve impulse, it proves that the latter is transmitted from the point of stimulus, both to the central and peripheral ends of the nerve, confirming the view already ad- vanced, that the nerve impulse is transmitted in both directions and that the function of a nerve depends, not upon its intrinsic structure, but whether it terminates in a motor, sensory, or glan- dular organ. By extending our experiments it will be further found that all kinds of nerves, motor, sensory, secretory, exhibit the phenomena of negative variation, the amount of the latter at different points of the nerve depending, however, upon that of the preexisting current of rest. If, however, the latter be absent, there will then be no negative variation though there may be currents of action independent of the latter. Thus, if the diverting electrodes be placed upon two points of the longitudinal surface symmetrically disposed with reference to the equator, the magnetic needle not being then deflected by the nerve current, there can be no diminu- tion of the latter or negative variation. An interesting fact as re- gards the phenomenon of negative variation is, that it cannot only be produced by artificial stimuli, electrical, chemical, thermal, and mechanical, but by natural ones inherent in the nervous system it- self by stimuli from the spinal cord, for example. Thus it is well known that if the sciatic nerve of a living frog be well exposed ^ 536 THE NERVOUS SYSTEM. avoiding, however, the injuring of the blood vessels and the origin of the nerve, and the nerve be cut through at the popliteal space, and the electrodes so disposed that the point of one is in contact with the equator, and the point of the other with the cut surface of the nerve, that with the appearance of the muscular cramps due to the subcutaneous injection of strychnia, the electrical current of the nerve will undergo a negative variation. The significance of this experiment will be better appreciated, however, when the sub- ject of reflex action has been considered ; since the muscular con- traction in strychnia poisoning is due to an impression made upon the skin and transmitted to the spinal cord, and thence reflected by the spinal nerves to the muscles. Fig. 291. Bernstein's differential rheotome. Horizontal view. Negative variation occurs also during the tetanus brought about by the mechanical crushing of a nerve, the destruction of the latter by heat, or when induced by the stimulation of cutaneous branches, as in the case of the sciatic nerve, for example. Recent researches ^ have shown, when electrodes connected with a capillary electrometer are applied to the motor tracts of the spinal cord, spinal nerve roots, or peripheral nerves, that with stimula- tion of the cortical motor areas, the currents of rest present, undergo negative variation, or are neutralized by currents of action. It iGotch & Horsley, Phil. Trans., Vol. 182, 1891, pp. 207-526. BEEXSTEIX'S DIFFERENTIAL RHEOTOME. 537 has already been mentioned that the rapidity at which the nega- tive variation is transmitted is the same as that of the nerve im- pulse itself. This was first determined by Bernstein ^ by means of his differential rheotome (Fig. 291). The principle of this instru- ment (Fig. 292) consists in closing, by C at e, the primary circuit Fig. 292. Schema of Bernstein's differeutial rheotome. N n. Nerve. J. Secondary coil of induction machine. G. Galvanometer, x, ;/. Deflection of needle. E. Battery. C closes primary circuit at e. e closes galvanometer circuit at /. z z. Electrodes in galvanometer circuit. .S'. Cord from motor. (Landois.) stimulating the nerve through .7, and that diverting its current of rest, by c at i, by a wheel, rotating at a known rate, and of so dis- posing the two pairs of electrodes that the stimulating circuit is closed before the diverting one, the interval of time elapsing be- tween the two — that is, the time during which the nerve impulse passes from n to ^" — being determined from the rate at which the wheel is rotating. To explain the manner in which the rapidity of the propagation of the negative variation is determined, in the frog for example, by means of the differential rheotome, we will begin at the moment that the rotating wheel C (Fig. 292) comes in contact with e. At that instant the primary circuit is closed and the nerve being stimulated by / at ?i, the current of action or negative variation will begin at that point and will be transmitted to the other end of the nerve iV, the wheel coming in contact however at that instant through e with i and the galvanometer circuit being then closed, the needle will be deflected in an opposite direction to that due to the current of rest, the latter having undergone negative variation. As the current of action or negative variation is transmitted through the nerve from ' Untei-suchungeii iilier den Erregunsvorgang im Nerven- und Muskel-systeme. Heidelberg, 1871. 538 THE NERVOUS SYSTEM. Fig. 293. the point of application of the stimulus at n to that of the divert- ing electrodes at X, and as the deflection of the galvanometer needle occurs at the moment that the diverting circuit is closed, the rate at which the current of action or negative variation is propagated becomes known since it is transmitted from n to N in the same time that c moves to i, C having first reached e, that is at the rate of 28 meters per second. It was at one time supposed that the current of action or negative variation occurs during the latent period, and during its transmission through the nerve, preceded the nerve im- pulse. It is more probable, however, that the two move- ments accompany each other, as it has been shown that the current of action or negative variation that oc- curs in muscle, accompanies the contraction wave of the latter^ and which corres- ponds to the impulse in the nerve. It will be seen from the disposition of the apparatus represented in Fig. 293 that the current of rest is com- pensated by means of the Daniell cell and rheocord. The galvanometer needle will remain, therefore, at zero until the current of action or negative variation reaches the end of the nerve t, when the needle will be deflected by it, and in the opposite direction to what it would have been deflected by the current of rest had not the latter been Disposal of differential rheotome, etc., for determina- Compensated, lion of rapidity of propagation of the current of action Tlio r»l->ionf nf ca nni-ni-»fin ornegative variation. -LUC OUjetL ui bu ouiiipeii- sating the nerve current in the study of its negative variation by means of the diiferential rheotome is that the movement of the needle should always begin at the same point, viz., zero. It will be noticed, however, that the rheocord — that of Du Bois Reymond — differs in its form from that previously described, though the latter, for the present purpose, might have been just as well used. The rheocord (Fig. 294), con- sists of a long box, at the edge of which are stretched two platinum 1 Burdon Sandei-son, Proceedings of Eoyal Society, 1890. THE RHEOCORD. 539 The rheocord. wires, passing through the connected mercury cups m m, which can be pushed to the other end of the box along the scale graduated in millimeters at the side. When the mercury cups are directly in contact with the brass a, the resistance offered by the Fig. 294. rheocord to the Dauiell's circuit is practically noth- ing as compared ^ith that offered by the nervous cir- cuit, consequently the cur- rent from the Daniell's element simply passes through the rheocord back to the cell, none being di- verted into the nervous cir- cuit. If, however, the mercury cups be pushed away from the brass along the platinum wires, the wires offering a resistance, the amount indicated by the scale, 358 mm. = 1 ohm, and there being no passage for the current from one side of the rheo- cord to the other, except through the parts of the wires lying be- tween the mercury cups and the Ijrass, it follows that a proportional part of the total current from the Dauiell's element is thrown into the nervous circuit. If a greater amount of resistance is needed than that obtained by pushing the mercury cups through the whole length of the platinum wires, then the plugs lettered b, c, d, e, f, g, or numbered, can be drawn out, these being multiples of the resistance offered by the total length of the platinum wires traversed by the mercury cups, the amount of current thrown into the nervous circuit will be then proportionally increased. Thus, for example, if the plug 5, letter g, be M'ithdrawn, then the amount of current thrown into the nerve will be five times as great as when the mercury cups were at the end of the wire, and so proportionally for the remaining plugs. In fact, the rheocord is a form of resistance box, such as already de- scribed. The wheel of the differential rheotome, as has already been men- tioned, is uniformly rotated by the electro-magnetic rotation appara- tus of Helmholtz (Fig. 295, E). The latter consists of four electro- magnets, the two external ones (A' 1') immovable, the two internal ones {UK) movable ; the latter are fixed to the axis by their dis- similar poles, and are supplied by three Daniell's elements, the external ones by one. As the two internal magnets are repelled and attracted by the external ones, the axis is rotated, and with it the wheel, through which it passes, and around which passes the thread from the disk of the rheotome. Although the phenomenon of the negative variation is a momen- tary one its duration has been determined by means of the rheo- 540 THE NERVOUS SYSTEM. tome to amount to 0.0007 second. Such being the case it follows that during the 0.0006 or 0.0007 second that the point a of a Fig. 295. Electro-magnetic rotation .aiiiiaratiis. nerve (Fig. 29G) undergoes its negative variation the intermediate points between a and c will be successively affected in the same WAVES OF NEGATIVE VARIATION. 541 way, the poiut c passing into the condition of negative varia- tion at the end of the 0.0000 or 0.0007 second as the point a passes out of it. The negative variation is propagated, therefore, in the form of a wave, and, being at the rate of 28 meters a second, the wave must be 18 mm. long. That is to say, if the current of Fig. 296. Wave of ucgative variation. action or negative variation travels along the nerve 18 mm. in from 0.0006 to 0.0007 second it will travel 28 meters in 1 second. Further, if it be supposed that while the negative variation travels at the rate of 28 meters a second, that during the same period of time the nerve be stimulated 28 times, then a nerve 28 meters long would exhibit at the end of the second 28 waves of negative varia- tion, each wave being separated by an interval of 1 meter (Fig. 297). isttui: Fig. 297. fS-miL Waves of negative variation. It having been learned by the rheotome that the current of action or negative variation, produced by successive stimuli following each other periodically, is propagated in the form of a wave of definite length and duration, there can be no doubt that the change under- gone by the nerve when in this condition is of a vibratory character. The wave of negative variation or the current of action resembles, therefore, those of water, sound and Hght, with this difference, how- ever, that in the case of the former chemical changes are probably going on in the nerve substance which are absent in the latter, and of which little or nothing is known. It has already been mentioned that uninjured nerves are isolec- tric ; that is, do not exhibit electrical currents. If a normal nerve be stimulated, however, a difference of electrical potential at once ensues, and a current flows in the direction of the arrow (Fig. 298) B to A, the part of the nerve first' traversed by the impulse becom- ing negative electrically to the succeeding parts. The current so 542 TEE NERVOUS SYSTEM. Fig. 298. developed is of but short duration, and is replaced by one flowing in the opposite direction, A to B, the latter being rendered nega- tive by the passage of the nerve im- pulse. The current of action in the uninjured nerve is therefore diphasic in character. It will be observed that the currents of action in the unin- jured nerve, are produced in the same manner as the currents of rest are supposed by Hermann to be produced in the injured ones in so far at least as one part of the nerve is rendered negative to a succeeding part, in the case of the currents of action, by the transmission of the nerve impulse, in that of the currents of rest by injury. It would appear, however, that while the currents of action of the injured as well as of the uninjured nerves are natural physiological currents, the currents of rest are artificial demarcation currents produced by injury and without functional significance. stimulation of uninjured nerve. Elec trodes" at x. Electrotonus.^ Up to the present moment, in exciting the nerve by electrical stimuli we have made use of single or repeated induction shocks, and this not only for convenience' sake, but especially on account of the short duration of induced currents, the object in view being the avoidance of the consideration of the changes undergone by the nerve during the passage of a constant current, and which, had they been present. Mould have rendered the explanation of the changes due to the induced current a more difficult one. Such changes as are induced in the condition of a nerve through the pas- sage of a constant current passing directly to the nerve without the intervention of an induction apparatus can now, however, be con- veniently considered. Let us suppose, then, that N (Fig. 299) represents a nerve, and that through the deviation of the magnets of the galvanometers GG' we learn that the currents of rest are present, passing from the longitudinal surface through the galva- nometers to the transverse cut surfiice of the nerve, through the nerve to the longitudinal surface again in the direction indicated by the arrows. Let now the nerve JVbe stimulated through the non- polarizable electrodes p p' at a point intermediate between its ends, by means of a constant current, say, from a Daniell's element, and which we will hereafter designate as the polarizing current, the de- flection of the galvanometer needles will show that the current passing through the galvanometer G' is increased (r?) constituting ' Du Bois Reymond, Uiitersucliungen iiber thierische Electric! tlit, 1848, Band ii., 8. 289. ELECTROTONUS. 543 Q^-t- /'^ - JV^ the positive phase, the current through G is diminished (c) consti- tuting the negative phase. It is evident, therefore, that the elec- trical condition of the nerve is not only modified temporarily by the momentary stimulus of the constant current, l)ut permanently also during the passage of the current through the nerve in the modi- fication of its electrical condition in the manner just mentioned. It will be observed from an inspection of Fig. 299 that the polarizing current is direct — that is, as it passes through the Fig. 299. nerve from the anode a, or positive pole, to the kathode h, or negative pole, it flows in the same direction as the nerve force itself. Now if it be assumed that the polarizing current de- velops outside of the elec- trodes a h, a new current, the electrotonic current, having the same direction as itself, it is evident that the increasing or dimin- ishing of the currents of rest by the electrotonic current, according as the latter is flowing in the same or in the opposite direction, will account for the difference in the elec- trical condition of the nerve outside of the anode a, and kathode 1:, the former being positively, the latter negatively, electrified. Such being the case, we may call that part of the electrotonic current increasing the current the anelectrotonic, that diminishing the same the katelectro tonic current, indicating the electrical con- ditions of the two currents respectively by the signs plus -f- and minus — . If now the position of the two electrodes a k he. re- versed so that the polarizing current flows through the nerve in the opposite direction to that of the nerve impulse, then the anelectro- tonic current will be developed at p' , the katelectrotonic at p, and the current passing through the galvanometer G will be increased, that through the galvanometer G' diminished. It will be observed, therefore, that the anelectrotonic and katelectrotonic condition just described will depend upon the fiict of the polarizing current pass- ing through the nerve in the direct or reverse direction. In either instance, when the polarizing current is broken the currents of rest previously increased or diminished are for a brief moment dimin- ished or increased. It need hardly be added that the electrotonic 6^ Auelectrotonic and katelectrotonic currents. 544 THE NERVOUS SYSTEM. currents are entirely independent of the currents of rest, the former being present even when the latter are absent. By further experimentation it will be found that the strength of the electro tonic currents depends upon that of the polarizing cur- rent and of the length of the intrapolar portion of the nerve ex- posed to the latter, and of the irritability of the nerve, a dead nerve not exhibiting the electrotonic current. Of the electrotonic currents, the anelectrotonic is of higher po- tential than the katelectrotonic, the electro-motive force of the for- mer amounting to 0.5 of a Daniell, that of the latter to 0.05 T)} The anelectrotonic current differs also from the katelectrotonic cur- rent in attaining its maximum and minimum more slowly. It is an interestino- fact that both the electrotonic currents undergo a negative variation during the passage of an impulse through the nerve. It may be also mentioned in this connection that the with- drawal of the polarizing current gives rise, through the internal polarization set up in the nerve, to " after currents," the latter be- ing positive, that is, in the direction of the polarizing current when the current is strong, and negative when weak. Considerable dif- ference of opinion prevailed at one time among physiologists as to whether electrotonic currents are due to some especial modification of the electro-motive condition of the nerve, which, like the current of action, is transmitted from the point stimulated, through the nerve, from molecule to molecule, or are due to the direct effect of the polarizing current through an escape of the latter, from the electrodes along the extra-polar portions of the nerve. The latter view is, however, the one usually accepted at the present day as best explaining the facts. Fig. 300. At least currents similar to electrotonic ones can be pro- duced when a constant cur- rent is transmitted through a conductor consisting, like a nerve, of three parts, such as is represented in Fig. 300, in which the platinum axis represents the axis- cylinder, the zinc sulphate solution the substance of Schwann, and the clay tube the neurilemma. The leav- ing currents in such a con- ductor, owing to the substance surrounding the axis being a better conductor than the envelope, will pass from the anode into the former, and thence into the axis, and so return by the latter to the kathode. Further, the electrotonic currents so developed re- semble those of a nerve in being entirely dependent upon the polar- ' Du Bois Eeymond, Gesammt. Abliandl. , Band ii. , s. 260. CUi^Tul>Pr and OPT. Direct and crossed pyramidal tracts. AJi and PR. Anterior and posterior roots. AAL nud DAL. Ascend- ing and descending antero-lateral tracts. CT. Cerebellar tract. D. Comma-shaped tract. PMZ. Posterior marginal zone. PEC. Column of Burdach. GC. Column of Goll. The jjarts left white do not undergo degeneration. (Laxdois. ) isted on both sides. It may be mentioned, as confirming the view that the avenues for tactile semsation lie in the posterior columns of the cord, that in the case of Gowers, just mentioned, in which the posterior column was only cedematous, tactile sensibility was unim- paired. While unilateral lesions of the spinal cord, such as those just men- tioned, show that in man at least the paths for the conduction of aU forms of sensory impulses decussate in the cord, clinical and ex- perimental investigations prove that the paths for the impulses from the muscles lie in the columns of Goll (GC, Fig. 324), of the same ' Beitriijfe zur Path. Anat. u. Phvs. der Kiickenmark, 1871 ; Kobner, Deut. Arch. f. klin. Med., Band xix., 1877, s. 190. 574 rUE NERVOUS SYSTEM. Fig. 325. side of the cord. Thus, if the posterior roots be attacked l)y dis- ease, as in locomotor ataxia, or divided experimentally in animals, the secondary degeneration so arising will be ascending, will pro- gress centripctally along the nerve roots to the cord upwards through the so-called Lissauer's zone in Burdach's column [PEC] for a short distance, and passing thence into the columns of Goll {GC), will as- cend on the same side of the cord to the clavate nucleus of the medulla. It is an interesting fact that disease of the columns of Goll is followed by defect of muscular coordination, re- sembling so closely that due to disease of the cerebellum as to admit of no doubt that the impulses determining cerebral coordination pass from the muscles by the columns of Goll to the cla- vate nucleus of the medulla, and thence by relay fibers through the cerebellum to the cortex. If the disposition of the sensory tracts be such as just described, it will be observed that the sensory resemble the motor tracts in that, of the two sensory tracts, one, the sensory, crossesthe middle line of the cord at all levels, the other, the tactile, at the medulla in black, just as, of the two motor tracts, one, the direct pyramidal, crosses the middle line of the cord at all levels, the other, the 'irossed pyramidal tract, at the medulla in block. ^ That such is the case is further shown l)y the fact that division of the columns of Goll in animals is followed by defects of coordination similar to that due to loss of the cerebel- lum. While the function of the direct cerebellar tract (Fig. 324, CT) cannot yet be said to have been demonstrated, the fact of its fibers passing by way of the restiform body to the middle lobe of the cerebellmn and thence by the superior peduncle to the opposite hemi- ' Van Gehuchten, Anatomic Du Systeme Nerveux De L' Homme, Deuxieme Edition, 1897, p. 758. Diagram showing pathway of the sensory impulses. On the left side S S' represent aflferent spinal nerve fibers ; (', an afferent cranial nerve fiber. These fibers terminate near central cells, the neuron S of which cross the middle line and end in the opposite hemi- sphere. (Van Geiiuciitkn.) FUyCTION OF COLUMXS OF COED. 0/0 sphere, render it highly probable at least that they also convey im- pulses from the muscles of the lower part of the trunk, and from between the trunk and the lower limbs, and possibly from the viscera. That the fibers of the direct cerebellar tract are at least centripetal in function, convey impulses from the periphery to the brain, is shown by the fact that secondary degeneration, when arising in this tract, ascends to the medulla. In addition to the fibers, already described, that pass continuously from the posterior roots to the columns of Burdach, to the columns of Goll, the columns of Burdach contain short vertical fibers connecting apparently the gray matter of the pos- terior cornu at different Ijut adjacent levels, which possibly have a commissural or coordinating function. It may be here mentioned that if such be the case it is quite possible that those portions of the anterior columns not containing the efferent fibers of the an- terior roots, may have similiar functions. Of the functions of the remaining tracts of the cord, still undescribcd, the ascending antero- lateral tract (Fig. 324, AAL) of Gowers and the descending antero- lateral tract [DAL), and the so-called comma tract (D) in the column of Burdach, little or nothing is known. That the ascending and descending antero-lateral tracts convey impulses from the periphery to the brain and the brain from the periphery respectively, is shown by the fact that secondary degeneration arising in these tracts pro- gresses centripetally in the former and centrifugally in the latter. It is possible, therefore, that sensory impulses may ascend in part through the ascending antero-lateral tract of Gowers. The de- scending comma tract hardly deserves the name of a tract, extend- ing but a short distance through the cord after section, and consists probably of fibers of the posterior root, which take a descending course after entering the cord. That the spinal cord consists of tracts, such as those just described, is further proved by the man- ner in which the cord develops. Thus it has been shown by Flech- sig ^ that the fibers of the cord get their covering of myelin at dif- ferent periods of development, the fibers having the longest course becoming medullated latest. In conclusion it will be seen from Fig. 324 that there still remain areas of fibers (unshaded) which do not degenerate after section, in- jury, or disease of the cord, and whose functions have not as yet been determined. It must be mentioned in connection with what has been said as to the result of division and disease of different parts of the spinal cord, that, from the fact of the loss of the power of volun- tary motion and sensation being frequently restored, there must ex- ist potentially, so to speak, a vicarious power of interchange of function between different parts of the cord, certain fibers being capable of assuming the transmitting of sensory and motor impulses in addition to their ordinary functions. Although the distribution of the spinal nerves will be found in any treatise on anatomy a brief resume of the same is here offered as illustrating their general * Die Leitungsbahnen ini Gehirn und Riickenmark des Meuschen, 1876. o76 THE NERVOrS SYSTEM. functions. It should be borne in mind that the branches of the spinal nerves, whether anterior or posterior, are in their functions mixed nerves, possessing both motor and sensory properties. The anterior branches of the four upper cervical nerves form the cervical plexus, and the four lower cervical, together with the first dorsal nerve, the bracliial plexus. From the cervical plexus are derived the superficial cervical, great auricular, small occipital, supracla- vicular, and phrenic nerves, and muscular branches ; the brachial plexus supplying mainly the upper extremity, but giving off, also, the supra- and subscapular and thoracic nerves. The posterior branches of the cervical nerves, with the exception of the first, after passing backward from the vertebral canal, divide into external and internal branches, and supply the muscles and integument behind the spinal column, the posterior branch of the first cervical issuing between the arch of the atlas and the vertebral artery, being dis- tributed to the contiguous straight, oblique, and complex muscles. The anterior branches of the dorsal or thoracic nerves, with the exception of the last one, pass outwardly in the intercostal spaces, as the intercostal nerves, the anterior branch of the last dorsal, be- ing situated below the last rib, crosses the quadrate lumbar muscle as it advances between the internal oblique and transverse muscle in a similar manner as an intercostal nerve. In their course the intercostal nerves, as they supply the muscles, give off lateral cutaneous branches, that from the second intercostal or the inter- costo-humeral nerve being an important one, since it extends across the axillary space, running in juxtaposition with the small cuta- neous nerve from the brachial plexus, and supplies the skin on the inner part of the arm. The posterior branches of the dorsal nerves, like those of the spinal nerves generally, after turning backward between the transverse processes of the vertebra?, divide into exter- nal and internal branches, the former supplying the skin contiguous to the angle of the ribs, the longissimus and sacro-lumbar muscles, the latter the skin over the spinous processes of the vertebrae, the multifid and semispinal muscles. The anterior branches of the up- per four lumbar nerves, together with a filament from the last dor- sal nerve, constitute the lumbar plexus, and which, after supplying the psoas and quadrate lumbar muscles, give off the ilio-hypogas- tric, ilio-inguinal, genito-crural, external cutaneous, obturator and anterior crural nerves. The posterior branches of the lumbar nerves pass backward, like those of the dorsal, to supply the longis- simus and sacro-lumbar muscles, and the adjacent skin. The ante- rior branches of the up})er four sacral nerves, together with the fifth and part of the fourth lumbar nerves, form the sacral plexus, from which are derived the filaments supplying the pyriform, internal obturator muscles, etc., the levator and sphincter ani, the superior gluteal, pudic, and great and small sciatic nerves. The sacral, to- gether with the lumbar plexus, give off the nerves supplying the lower extremity. The anterior branch of the fifth sacral, a small SPIXAL NERVES. 577 nerve, emerges from the end of the vertebral canal, and divides into two branches, one of which passes with a filament from the fourth sa- cral to end in the sympathetic, the other joining the coccygeal nerve. While the posterior branches of the upper four sacral nerves pass out of the vertebral canal by the corresponding sacral foramina, the posterior branch of the fifth sacral emerges from the end of the vertebral canal and together with the posterior branch of the coccyg- eal nerve supplies the skin and muscles of the back. The ante- rior branch of the coccygeal nerve also passes out of the end of the vertebral canal, is joined by a branch from the fifth sacral after perfo- rating the coccygeal muscle and the great sacro-sciatic ligament, and terminates in the skin of the buttock. The posterior branch of the coccygeal, like the anterior branch, emerges from the end of the vertebral canal ; its distribution has just been referred to in con- nection with that of the posterior branch of the fifth sacral. 37 CHAPTER XX XL THE NERVOUS SYSTEM.— {Continued.) DIVISION OF LABOR IN ANIMALS AND MAN. REFLEX AUTOMATIC AND NUTRITIVE FUNCTIONS OF SPINAL CORD. One of the most striking differences in the organization of animals is the extent to which the division of labor, physiologically speaking, is carried. Indeed, the lowest forms of life, such as the monera, consisting, as we have seen, of mere masses of protoplasm, are so utterly unorganized as to make it impossible to say whether such beings should be assigned genealogically to the vegetable or animal kingdom. It is true, that among such primitive forms of life there are beings, like the common amoeba, in which there is a slight differentiation of structure, in that not only a nucleus and nucleolus are present, but even an enveloping membrane or cell wall may be developed, and that among the infusoria are also seen forms, like paramcecium, apparently quite organized ; never- theless, even these protozoan animalculse, so much more complex in their structure than the monera, cannot be said to be organized in the same sense that the remaining members of the animal king- dom, or metazoa, are. Even the infusoria, apparently complex as they are in their structure, are morphologically only unicellular, and never passing beyond this primitive one-celled stage ; tissues, and still loss organs, are never developed in them similar to those of which the body of one of the higher animals is made up, since, as we have already seen, the organs in the latter consist of tissues and the tissues of cells, the latter resulting from the division of the primitive cell. Indeed, it is not until we reach in the tree of life the porifera, actinozoa, and hydrozoa, of which the sponge, anemone, and jelly fish, familiar objects at the sea- shore, are examples, that we meet with anything like organization, at least in the true morphological sense of the word — that is to say, of an animal consisting of organs, made uj) of tissues, developed out of cells resulting from the segmentation of a primitive cell, or ovum. Suppose that the structure of one ■of the hydrozoa be considered, as tliat of the common green hydra (Fig. 326), found during the summer in almost every fresh-water Fig. 326. Hydra. (Milne Kdwauds. ) THE HYDRA. 579 Fig. 327. pool, and therefore an object for study accessible to all, it will be found that the animal, about half an inch in length and a line in diameter, is essentially a double-layered tube, closed at one end and open at the other, the latter serving as a mouth and surrounded with delicate tentacles, or feelers, by means of which it seizes its prey, the outer layer, or ectoderm, of the tube, functionating as skin, the inner layer, or endoderm, as a mucous digestive surface. Leaving out of consideration an imperfectly developed neuro- muscular layer or mesoderm intermediate between the ectoderm and endoderm (absent in the protohydra), the hydra may be considered fanctionally as little more than a digestive sac. That the differen- tiation of ectoderm and endoderm is very incomplete, is shown from the fact that if the animal be turned inside out the skin or ectoderm becomes digestive in function, and the digestive surface or endoderm epidermal, just as the mucous membrane of the mouth or anus in man may become skin if everted, or the skin of the same parts mucous membrane if inverted. This is, however, as might have been expected, since, as we shall see hereafter, there can be little doubt but that the ectoderm and endoderm of the hydra are homologous with the epiblast and hypoblast of the em- bryo, or the parts corresponding to the skin and mucous membrane of the adult. Further, that no one part of the hydra differs essentially from any other part, is shown by the well-established fact that if a hydra be cut up into several pieces each piece will live and lead an independent existence and develop into a perfect hydra. While, at first sight, such a result may appear as a very extraordinary one, it be- comes a perfectly natural and intelligible one when it is remembered that all parts of the body of the hydra have essentially the same function, and that there is no in- terdependence between the parts of which it consists. Reproduction by fission, Avhether produced artificially or naturally, is not confined, however, by any means to such low forms of life as the hydra, being observed as well in quite highly organized animals, as among the annelida, of which the ma- rine worms, such as the clam worm (x^ereis pelagica) of our coasts (Fig. 327), etc., are examples. The body of a nereid worm, con- sisting of numerous segments, is naturally very apt to break up into numerous pieces consisting of one or more of the segments, as the animal glides along among the rocks, sand, or seaweed, each piece becoming, under favorable circumstances, a perfect animal. In- Clam worm. Kereis pelagica. 580 THE NERVOUS SYSTEM. deed, at certain seasons of the year there may be seen in certain kinds of these worms (Protnla) at different portions of the body con- strictions indicating the parts where the body will break np, by natural fission, into a progeny of worms. That snch a mode of re- production should take place in an animal as highly organized a& those just mentioned, having a distinct body cavity inclosing a nervous system, alimentary canal, heart, may appear even more extraordinary than the case of the hydra just referred to. It must be borne in mind, however, that in the worm, as in the hydra, there is but little interdependence of parts, each segment having its own nervous ganglion and fractional part, so to speak, of the alimentary canal and vascular tubes running from end to end of the animal. In fact, an annelid may be regarded, inorphologically, as consisting^ of a chain of small annelids (the segments depending but little upon each other, linked together, as it were, for only the time being). A glance now at the organization of a vertebrate animal, or even one of the higher invertebrates, will at once show how profoundly such an animal differs from any of those hitherto mentioned. The brain, as in man, for example, situated in the skull, depending for its ac- tivity upon the blood driven to it by the heart in the thoracic cavity, the rhythmical action of the heart and lungs maintained by nervous influences emanating from the base of the brain, the ali- mentary canal within the abdominal cavity supplying the materials for the nourishment of the brain and other organs, but dependent upon the blood supplied to it by the heart for the elaboration of the alimentary secretions, illustrating sufficiently how intimate is the connection existing between the cranial, thoracic, and abdominal organs, and the impossibility of any one segment of the body con- taining such, living a life entirely independent of the remaining^ ones, as we have just seen is the case in many of the lower animals. This contrast between the lower and higher animals with reference to the extent with which the division of labor is carried on, is well illustrated by the difference between the savage and civilized state of society — and, indeed, the difference is something more than a mere comparison, being of a profound meaning to those who believe that the life of a nation is developed according to law as certainly as that of tlie individuals of which it is composed. In the uncivilized, savage state, each individual is independent of his neighbors as the one segment of the worm may be to that of the other ; his interest not being usually their interest — on the con- trary, often antagonistic — he builds his simple hut, hunts his own game, clothes himself; a birth among his tribe adds to, a death takes away nothing, from his daily life. Under such circumstances there can be no accumulation of wealth and the development inci- dental to it. In the civilized state, on the contrary, the interest of the one is the interest of all, as that of the one organ in the human body is that of the others ; each individual confining himself to one avocation, the latter is advanced to its utmost limits, de])end- ing upon others for that which he does not produce himself, the DIVISION OF LABOR IN ANIMALS. 581 product of his own industry reaches the highest perfection ; and so with the productions of others, and thus the wealth of the nation increases both in variety and amount. Just as with the unciviHzed, as compared with tlie civilized, so with the lower animals as com- pared with the higher ones ; just as the development of a nation depends, not only upon the variety of the interests, but upon the mutual interdependence of the same ; so the life of an animal is high in proportion to the variety of its organs, and the mutual harmonious working of the same. The famous example of the number of persons engaged in the making of nails or pins, and the great number that can, consequently, be so produced, as mentioned by Adam Smith,^ is as applicable as illustrating biological as well as politico-economical laws. The life of a man biologically as well as socially, when compared with that of a sponge, may be summed up in saying that in the former the division of labor is carried, so far as we yet know, to its utmost limits ; in the latter but little, if at all. This division of labor, so characteristic of the higher ani- mals, and which we have illustrated on account of its importance somewhat in detail, is not only well seen in the general organiza- tion of the higher animals, but in the extreme differentiation ex- hibited in their alimentary, vascular, nervous systems, etc., and as it is the functions of the Fig. 328. latter that we are now more particularly con- sidering, it will be well to illustrate the general structure of the nervous system in animals by a few examples before taking up the considera- tion of the subject of the reflex action of the spinal cord of man, the nature of which it is hoped will be made clearer by the preceding introductory than it would have been without it. Of the simplest form of nervous system may be mentioned that of the ascidioida, as seen, for example, in a phalusia, in which the entire nervous system consists (Fig. 328) of a single Nervous system of au T ■ .. • • £o ji-\ ± r ascidiau. A. The mouth. ganglion, receiving or giving otr nlaments irom b The vent. c. The or to the periphery. On touching this worm- fl^f,^^', "• '^^^ """'' like animal, and seeing it contract its body, judging from one's own feelings and actions, we would infer that the animal felt the touch and voluntarily retracted its body, and conclude that the impression made upon the integument was trans- mitted by an afferent centripetal, or sensory nerve, to the ganglion, and there felt, and that the impulse emanating from the latter was transmitted by an efferent, or centrifugal, or motor nerve to the muscle, and there resulted in voluntary motion, the whole action being called a reflex one from the fact of the impression made upon the periphery being first transmitted to the ganglion and thence re- flected back again. If the ganglion be not endowed with sensation 1 An Inquiry into the Nature and Causes of the Wealth of Nations, Vol. i., p. 7. Edinburgh, 1814. 582 THE NERVOUS SYSTEM. aucl volition, then the animal mnst be withont either, since it pos- sesses no other structure of which such qualities can be predicated. Further, if muscular action, in response to stimuli applied to the j^eripherv, is no evidence of cither sensation or volition, then it is impossible to say whether any animal feels, or wills, under any cir- cumstances. If now the nervous system of a starfish be compared "uith that of the ascidian, just mentioned, the only essential diifer- ence presented by the former is that, instead of one ganglion there are five (Fig. 329), which, together with the commissural filaments, constitute a circum-oral ring, from which are given off the nervous filaments supplying the rays. It follows, therefore, that if the ganglion of the ascidian be en- dowed with sensation and volition, then all five ganglia of the starfish are endowed with the same functions, the only diiference between the two being that, in the one, whatever sensation and vo- FiG. 329. Fig. 830. Nervous system of starfish. (Daltox.) Nervous system d ;iiilysia. (Dalton.) lition the animal may be possessed of is concentrated in the single ganglion, Avhcreas, on the other, the sensation and volition are dif- fused among the five ganglia. It is obvious, also, that, on ac- count of the radial symmetry presented by the starfish, it is impos- sible to assign any special function to any one of the ganglia that is not possessed by the others. And, while even in the mollusca, of which the aplysia (Fig. 330), or sea hare, is an example, the supra-cesophageal ganglion (1) is regarded, morphologically, as a brain, there is little reason to suppose that it possesses, exclusively, any very specialized function not shared by the infra-fesophageal (2) one, or that the latter, in turn, differs very much, functionally, from the remaining ganglia (3, 4) distributed through the body, and with Avhich it is connected by a commissural filament as M^ell as with the supra-cesophageal one. It is true also, that the supra- cesophageal ganglion (Fig. 331) of centipedes, insects, etc., is usu- ally spoken of as the brain of such animals, and the ventral chain NERVOUS SYSTEM OF CENTIPEDE. 583 Fig. 331. of gauglia compared to the spinal cord of vertebrates, but, as some of the nerves in insects, for example, supplying the head, are de- rived from the supra-cesophageal ganglion, and others from the infra-cfisophageal ganglion and, as the latter ganglion does not differ essentially from the remaining ones of which the ventral chain consists, it is difficult to see why any one ganglion should be designated as cere- bral and the other as spinal. That there is no such essential diflFerence between the so-called cerebral and spinal ganglion is shoAvn from the fact that, if a worm breaks up into two, through fission, the ganglion that was central in the parent animal be- comes anterior in the new individual, and goes to form its brain. Further, in the case of worms, in- sects, etc., it is questionable Avhether such animals are comparable at all as regards their nervous sys- tems with vertebrated ones, since, as a glance at Fig. 332 will show, while the cerebro-spinal nervous centers of the vertebrate are dorsal, the ganglion chain of the articulate is ventral, and, while the heart is dorsal in the articulate, it is intermediate in the vertebrate between the alimentary canal and the nervous center. In other words, to compare an ar- ticulated wdth a vertebrated animal, with reference to homologizing their nervous systems, one or the other must be placed upside down, and, however the vertebrated animal lie placed, it is obvious that no comparison can be made at all between its nerv- ous system and that of the echinodermatous or mol- luscous type. Such being the case, it would be illogical to apply the results of investigation made upon the nervous system of in- vertebrates to that of vertebrates, the nervous system not being comparable in the two great divisions of the animal kingdom. For this reason, any conclusion as to the functions of the different parts of the nervous system in man, draw^n from the study of the nervous system in animals, must be based upon that of the verte- brates only, more particularly of such classes in which the parts composing the nervous system can, without doubt be homolo- gized. The amphioxus, the low^est of vertebrates, being practic- ally headless, offers, in the structure of its nervous system, little or nothing comparable with the brain of the remaining vertebrates. Unless it be denied that the amphioxus can feel or will, of which there is not the slightest evidence, it necessarily follows that the spinal cord of this primitive vertebrate, at least, is endowed Avith sensation and volition. If such be admitted, and it is difficult to see how the conclusion can be avoided, analogy would lead us to suppose that the spinal cord of the lamprey and myxine, to a cer- tain extent, at least, would possess, also, similar qualities, particu- larly as the sensation and volition exhibited by such animals are Nervous system of centipede. (IlALTOX.) 584 THE NERVOUS SYSTEM. out of all proportion to the amount of brain present. Inasmuch, however, as these marsipo-branchial fishes have a brain, or, at least, the basal ganglia of the brain of the higher vertebrates, it is to be inferred, that with these additional important structures, even if little developed, there would be exhibited corresponding higher fac- ulties than shown 1)y the amphioxus, and such is found to be the Fig. 332. N— \>-. Diagrammatic sections of an articulated invertebrate and vertebrate. 1. Longitudinal section of invertebrate. 2. Longitudinal section of vertebrate. 3. Transverse section of invertebrate. 4. Transverse section of vertebrate. H. Heart. A. Alimentary canal. N. Kervous system. CH. Chorda dorsalis. case, and as we pass from these lowly organized vertebrates through the higher ones, to man, it will be observed that the brain becomes more and more developed both relatively and absolutely with refer- ence to the sj^inal cord, the extremes of the series being represented by man and the amphioxus respectively. Eatio of Brain to Spinal Cord in Vertebrates. Man 33.0 to 1 Mouse 4.0 to 1 Pigeon 3.3 to 1 Triton 0.550 to 1 Lamprej' ....... 0.001 to 1 Amphioxus . . . . , . . 0.0 to 1 Now, as we have seen in general that the higher animals differ from the lower ones in the extent to which the division of labor is carried, the higher grade of life exliibited by the former depending upon the greater differentiation of their organization, the develo])- ment of the brain just alluded to miglit have been anticipated, it being obviously of advantage that certain functions of tlie nervous system would be restricted to the brain, others to the spinal cord, and hence, as we shall see presently, the great development of the intellectual powers in the higlicr animals as comi^arcd with the lower ones. Further, it Avill 1>e found that corresponding with this idea of the division of labor, that while tlic s])inal cord of the lower vertebrates may possess both sensation and ^•()lition, that of the SEAT OF SENSATIOX AXD VOLITIOX. 58o higher ones iu becoming to a considerable extent a conductor of sensory and motor impulses loses such equalities, the seat of the sen- sorium and will being transferred to a higher plane, being gradually elevated, so to speak, in tlie higher animals. Thus, while sensation and volition are diifused through the spinal nervous axis of the low- est vertebrates, it gradually, through the process of development, becomes concentrated in the cranial expansion of that of the higher ones. The theoretical considerations just oifered are fully borne out by experiment as well as by the facts of comparative anatomy. Thus, if a frog be decapitated and a drop of acetic acid be placed upon the skin near the anus ^ the animal keeps changing its posi- tion, and will endeavor to wipe off the acid by means of the foot of the same side of the body to which the acid was applied, and, if the latter be amputated, by means of the opposite foot. Xot infre- quently, also, the author has seen the animal try to remove the acid by one of the upper extremities, both legs having been amputated. Considerable difference of opinion still exists as to whether such an action as that exhibited by a decapitated frog involves sensation and volition, or is to be regarded as a simple reflex action — that is, of an action such that an impression being made upon the skin of an animal and being transmitted by an afferent nerve to the gray matter of the cord, is thence reflected by an efferent nerve to a mus- cle without the animal necessarily feeling anything or making any voluntary effort. It appears to us, however, that a frog with its head on when stimulated by acetic acid gives but little more evi- dence of sensation and volition than with its head off when so stimu- lated, the difterence exhibited between the cases being rather one of degree than of Idnd. Of course, the frog with its head on feels and wills more than with its head off, but it does not follow, in the latter case, that the animal does not feel or will at all. Indeed, if it be denied that the decapitated frog feels and wills, it becomes very questionable whether there is any way at all of positively prov- ing that the frog with its head on feels and wills. Further, if it be affirmed that sensation and volition are restricted to the brain, then the amphioxus must be without either, and that exhibited l)y the lower vertebrates, the frog included, out of proportion to the amount of brain present. It is often urged that, as we know from cases in which the spinal cord has been injured in man, that muscular con- tractions resulting from the tickling of the sole of the foot are per- formed unconsciously, that the muscular action just described as taking place in the decapitated frog is no evidence that the animal either feels or wills. It should be borne in mind, however, that no one ever saw a man with a fractured spine, still less with his head cut off, apply his hand or foot to his anus and wipe away acetic acid placed thereupon, as done liy the decapitated frog, and until this has been observed it can hardly ]:)c said that the cases are par- allel, or that conclusions can be drawn as to the sensation or voli- tion possessed by the spinal cord of the decapitated frog from ob- iPfliiger, Die Sensorisclien Funktionen des Euckeniuarks, 18o3. 5 8 6 THE NEB VO US SYSTEM. servations made upon human beings suffering from injuries of the spine by tickling the soles of the feet. Indeed, the muscular con- tractions following the tickling of the sole of the foot in cases of in- juries of the spine in human beings are very simple in character, similar to those ensuing when the nerve of an amputated limb is stimulated, whether it be that of a man or frog. Such contractions are never coik'dinated with reference to the per- formance of any definite object, and do not suggest in any way the idea that the amputated limb either feels or wills, and the case is not substantially altered by the limb being attached to the body, the only difference being then that the nerve is bent into an affe- rent and efferent arc, the gray matter of the cord connecting the axis-cylinder of the ascending and descending parts of the same. The question may never be settled as to whether the headless frog feels and wills or not, or to what extent sensation and volition may be properties of the spinal cord in the lower vertebrates. Indeed, nothing short of being a frog would give us positive assurance that such an animal possesses consciousness as Professor Huxley ob- served in considering the same point in reference to the crayfish.^ On the supposition, however, that man has gradually developed, and in harmony with the idea that as we pass from the lower to the higher vertebrates through the division of labor, the properties of the spinal cord from being general, become more and more special in character, it is quite possible that many actions wdiich are now performed unconsciously in the higher animals may have been originally accompanied with both sensation and volition in the lower ones, and to a certain extent are still. As a matter of fact, many actions like that of walking, playing upon musical instru- ments, etc., involving at first both sensation and volition, through constant repetition are performed in time unconsciously. Whether this view of all reflex action being originally accompanied with consciousness, but through constant repetition being finally per- formed unconsciously, becoming, as it were, organized within us, a kind of second nature, be accepted or not, there is no doubt that in man, at least, that the seat of sensation and volition is limited to the brain, and that there are many and varied actions going on in the body not involving consciousness at all, and performed entirely by the spinal cord and medulla, to the consideration of which let us now turn. A reflex action (Fig. 333) implies the presence of an afferent or centripetal nerve (A) of the gray matter of the cord ((7), and of eflFerent or centrifugal ones (E E). We make use of these terms in preference to those of sensory and voluntary motor nerves, since many reflex actions like the rhythmical action of the heart and lungs are performed entirely unconsciously without our feeling or willing in the matter at all, while others, involving sensation, as the wink- ing of the eyelids on an object being brought suddenly close to the eyes is entirely involuntary, as we all know from daily experi- 1 The Crayfish, ISSO, p. 89. REFLEX ACTION. 587 enee. In many instances of reflex action, as in cleglntition, walking, conghing, sneezing, tetanns, vomiting, etc., both the aiFerent and efferent nerves involved are cerebro-spinal nerves. In other cases, as in blnshing, etc., while the aflPerent nerves are cerebro-spinal, the eflPerent nerves belong to the sympathetic system. On the otlier hand, the afferent nerves may be derived from the sympathetic, the efferent from the cerebro-spinal system, as in convulsions due to the Fig. 333. Fig. Diagram to illustrate reflex action of medulla. Diagram to illustrate reflex action. presence of intestinal worms, not uncommon in infants. Finally, both afferent and efferent nerves may be sympathetic nerve fibers, as in the production of certain of the intestinal secretions. Whether, however, the afferent and efferent nerves be cerebro-spinal or sym- pathetic in origin, or the phenomena be accompanied with sensation, but without volition, or without either, in each of the instances just referred to, an impression being made upon the periphery and trans- mitted bv an afferent nerve to the g-rav matter of the cord is thence reflected outwardly again to the periphery by an efferent one. Fur- ther, while muscular, glandular, or vascular action may follow an afferent irritation according as the efferent nerve is distributed to muscle, gland, or vessel, as in the instances just given, it is not im- possible that all three effects may be produced simultaneously by a single impulse, as in the case illustrated by Fig. 334. Many of the examples just given being rather illustrations of the reflex action of the medulla than of the spinal cord, their further consideration will be deferred until the afferent and efferent nerves have been described. If the impression made upon the periphery be not a very strong one, usually the reflex action resulting is unilateral — that is to say, is confined to the same side of the body irritated. If, however, the impression be sufficiently strong to pass through the gray matter of the cord and be reflected outwardly, then the reflex action is sym- metrical — that is, the general effect produced on the opposite side of the body is the same as that of the side irritated. As might be expected, if the impression be sufficiently strong to produce the same effect on both sides of the body,- the movements upon the opposite side never surpass in extent those of the side irritated. Further, w^hile the efferent nerve excited is usually on the same plane a& 588 THE NERVOUS SYSTEM. that of the aiFerent one irritated, if the impression be snfficiently strong, the nerves excited are always situated above, and never below, that plane. It should be mentioned, however, in this con- nection in the case of the reflex action of the encephalon the im- pression passes downward to the medulla oblongata. It is also well known that a single weak stimulus, incapable in itself of causing a reflex action, may do so, however, if repeated sufficiently often. The piling up or " summation of the stimuli," as it is called, appears to take place in that part of the spinal cord situated between the terminal twigs of the afferent nerves and the cells. Some difference of opinion exists as to the number of stimuli necessary to elicit a reflex response. It would seem, however, that while 3 feeble stimuli per second will cause reflex action, 16 stimuli per second are much more effective. A certain period of time, the so-called " period of latent stimulation," elapses between the application of a stimulus and the reflex response. In the case of a ])ithed frog, dilute sul- phuric acid being used as the stimulus, and the latent period being the time elapsing between the application of the stimulus to the foot and the withdrawal of the latter, it has been shown that the latent period diminished as the strength of the solution is in- creased. It is also well known that the interval of time elapsing between the application of the stimulus and the response varies within wide limits. Thus in making use of electricity as a stim- ulus it has been shown ^ that the number of stimuli remaining constant, the latent period may vary from 0.05 to 0.4 second. It would appear, of the time elapsing between the application of the stimulus and the reflex response in the frog, that from 0.008 to 0.015 second is applied to the transferring of the impulse from the afferent fiber to the cell in the cord and from the latter to the efferent fiber, the time so consumed being known as " reflex time." ^ Reflex responses are much more readily elicited when the stimulus is applied to the specific end organ of the afferent nerve than to its trunk. Thus the reflex responses following the gentle tickling of the skin are much greater than those due to the stimulation of an exposed cutaneous nerve. It is well known that reflex action is increased by certain substances, and diminished by others. Of the former strychnia is the most powerful ; an animal, a frog, for ex- ample, poisoned with strychnia exliibiting tetanic spasms on the application of tlie slightest stimulus. Of the latter may be men- tioned chloroform, the bromides, etc. That the different parts of the body are intimately connected has been well known from time immemorial to the physician, but it is only within comparatively modern times that it has been recognized that the sympathy, as it was called, undoubtedly existing between the various organs, depends upon reflex action. As the doctrine of sympathy is a very important one from a clinical as well as from a physiological standpoint, it may not appear superfluous to illustrate MVard, Du Bois Reyraonrl Archiv Phys. Abthl., 1880, s. 72. ^ Landois, op. cit., p. 80'.i. liEFLEX ACTION. 589' it a little by a few examples. Thus, for example, the oesophagus having been divided, if the stomach l)e irritated, the salivary glands Avill secrete ; on the other hand, if the lingual nerve be stimulated as by the taking of tobacco, the stomach will secrete. Evidently the impression made upon the stomach in the first case is transmitted to the cord and thence reflected outwardly to the salivary glands, whereas in the second case the impression, being made upon the tongue, is transmitted to the cord and thence reflected to the stomach. Similarly, the irritation due to hemorrhoids modifies the character of the gastric juice to such an extent that digestion becomes impossible, and the ensuing dyspepsia only curable by removal of the hemor- rhoids or the exciting cause. The flow of tears due to some ex- ternal irritation disappears with the loss of sensibility, while photo- phobia, often attributed to irritation of the optical nerve, is in reality due to irritation of the fifth pair of nerves. The fact of disease in one eye often involving loss of the other illustrates the nervous sympathy existing between the two. Xeuralgia of branches of the frontal nerve, due to caries of the teeth, is of frequent occurrence. The irritation, and even inflammation of the abdominal viscera following severe burns is well known to the surgeon. The stop- page of the heart brought about by blows on the epigastrium, the tetanus due to injuries of the thumb and big toe, the paraplegia from disease of the urogenital organs, the development of the mam- mary glands coincident with that of the fcetus are familiar example& of reflex action.^ Fig. 335. The knee-jerk. The well-known " knee-jerk " (Fig. 335) elicited by striking the patellar tendon with the edge of the hand or a percussion hammer, the leg being semi-flexed, is specially interesting as an example of a deep tendon reflex, owing to the fact that it is increased or diminished by diseases, increased, for example, in lateral sclerosis, diminished or lost in locomotor ataxia. 'Brown Sequard, Central Nervous System, p. lo3. Philadelphia, ISfiO. A. P. Brubaker, Reflex Neurose?, American System of Dentistry. 590 THE NERVOUS SYSTEM. Fig. 336. The above are illu.stratious among many that might be offered of the important fact never to be lost sight of, that the exciting causes of many physiological and pathological phenomena are to be sought for, not where the latter are exhibited, but frequently at a remote portion of the body, the impression made upon one organ being transmitted by an afferent nerve to the spinal cord, and thence reflected out- wardly by an efferent one to where the phenomena are exhibited. If the various spinal nerves involved in the production of reflex actions be considered specifically, it Avill be found that just as the osseous spinal column is subdivided into osseous segments, so the spinal cord may be subdivided into nervous ones physiologically at least, the gray matter of which, according to this view, constituting so many reflex centers, and the spinal nerves the afferent and effe- rent nerves to and from the same. A number of such centers appear to have been satisfactorily made out, among which may be mentioned the cilio-spinal center, by which the dilatation of the pupil is effected, situated in the lower part of the cervical and upper part of the dorsal regions of the cord ; it will be considered again in connection with the sympathetic. The sweat and vaso- motor centers, whose influence upon the secretion of sweat and the blood vessels will be treated of hereafter. The ano-spinal center, governing the act of defecation, situated in the lumbar region, the afferent fibers being constituted by the hem- orrhoidal and inferior mesenteric nerves, the efferent by the pudendal plexus, dis- tributed to the sphincter ani muscle. The vesieo-spinal center, both that governing the sphincter vesicae and detrusor urinse, being situated in the lumbar reo;ion of the cord. Two centers are assumed to exist in the cord, one, the automatic center (Fig. 336, A C), maintaining the tonic activity of the sphincter of the bladder, the other a reflex center (/? C) exciting the fibers of the de- trusor uriuffi muscle, the urine-expelling fillers. Such being the disposition, afferent impulses from the sensory center (S) par- alyze the automatic center and excite the reflex center, and so give rise to micturition. If the sensory impulses reach the cerebrum voluntary impulses descend which may aid or inhibit micturition, according as the automatic or reflex centers are stimulated. The center for erection of the penis, lies in the lumbar region of the cord, the af- ferent fibers being the sensory nerves of the penis, the efferent ones the nervi erigentcs. Stimulation of the latter, as we shall see here- OeO Schema of micturition. AC. RC, ('. Automatic, reflex, ami cerebral centers. B. liladiler. S. Sensory center acted un by afferent impulses. (Lanbois. ) BEFLEX ACTION. 591 after, dilates the vessels of the penis. The center for the emission of semen is also situated in the lumbar region, the afferent nerves being the dorsal sensory nerves of the penis ; the efferent, nerve fibers which, emerging with the fourth and fifth lumbar nerves, pass into the sympathetic, and are distributed to the vesiculje semi- nales and vasa differentia, and with the third and fourth sacral nerves pass into the perineal nerves, and are distributed to the accelerator muscle. The center for parturition lies in the lumbar region, the afierent and efferent fibers consisting of part of the uterine plexus. From the fact of the reflex actions being stronger, and of less time elapsing between the application of the stimulus, and the resulting reflex when the spinal cord has been divided, it has been inferred that the encephalic centers exercise a restraining or in- hibitory effect upon the reflex action of the cord. Thus, the spinal cord, being intact in a frog, and the average length of time elapsing between the application of the stimulus and the result- ing reflex effect being determined, it will be observed that if the optic lobes, for example, be stimulated, a greater length of time elapses now than before between the stimulus and the reflex. On the other hand, the spinal cord being divided, less time elapses be- tween the application of the stimulus and the reflex. While such experiments would lead one to conclude that in the frog the optic lobes contain a restraining or inhibitory center, Setschenow ^ center, it must not l^e supposed that the inhibitory influence of the en- cephalon is limited to the optic lobes in man. That there must be complex centers situated probably in the cortex of the brain by Avhich the reflex action of the cord is inhibited, is shown by the manner in which we are able to restrain, for a time at least, the various functions performed by it, such, for example, as keeping the eyelids open when the eyeball is touched, arrest of movement when the skin is tickled, etc. It is held by many physiologists that the spinal cord not only exerts an automatic control over certain viscera, such as the rectum, bladder, etc., as just mentioned, but also over the skeletal muscles as well, maintaining the latter in a state of more or less tonic contraction. Of the facts offered among: others as pro^^ng the existence of a muscle tonus, it has been urged that when a muscle is divided its ends retract. This effect appears to be due, however, not so much to loss of spinal control as to the fact that all muscles are more or less slightly stretched beyond their normal length. It is also well known that if the muscles of a decapitated frog be put on the stretch and the sciatic nerve di- vided the muscles do not elongate, a fact inconsistent Avith the idea of the muscles having been previously maintained in a condition of a tonus by the spinal cord. That a condition of reflex tonus may be brought about, however, is shown l)y the fiict that if the decapi- tated frog be suspended in an abnormal condition it will be 0I3- ^Ueber die Hemmungsmeclianisnuis fiir die Eeflexth;itio-keit des Riifkenmarks, 1863. 592 THE NERVOUS SYSTEM. served that while the leg in whicli the sciatic nerve has been di- vided hangs limp, the sound one is slightly retracted, the weight of tlie limb acting then as a stimulus. It should be mentioned in this connection that while there is no doubt tliat the spinal cord exerts automatic control over certain viscera and blood vessels (vascular tonus), the expression " automatic center " is a misleading one, as the so-called automatic centers differ only from other reflex centers in being stimulated at all times by blood or other stimulus, the or- dinary reflex centers only temporarily. The spinal cord appears also as already mentioned to influence the nutrition of the tissues to which its nerves are distributed, the nutrition of the muscles being controlled by the anterior gray matter, and probably by the motor cells, that of the bones and joints being excited probably through the posterior roots.^ Kiowei-'s Diseases of the Nervous System, Vol. i., 1892, p. 206. CHAPTER XXXII. THE XERYOUS ^YSTE'SL—(Contini'ed.) THE MEDULLARY NERVES. The medulla ohloiiuata, regarded as a center of reflex action, is €ven more important than the spinal cord, on account of its giving origin to ten of the so-called cranial nerves — that is, of the nerves involved in the performance of mastication, insalivation, deglutition, of gastric and intestional digestion, circulation, and respiration — in a word, of the functions of nutrition. In order, however, to appre- ciate the manner in which these nerves conduct afferent and efferent impressions to and from the medulla, the latter acting as a reflex center, it will first be necessary to describe their origin, distribu- tion, and function. From the fact of the medulla being simply the upper expanded portion of the spinal cord one would be led to sup- pose that the ten nerves originating in it would be either motor or sensory in function, and that taken together in pairs from below upward each pair would be comparable to the anterior or motor and posterior or sensory roots of one of the true spinal nerves. As a matter of fact, the roots of the two nerves of any one of the medul- lary pairs, supposing such to exist, do not unite together into a single nerve as in the case of a spinal nerve, but pass on separately to their ultimate distribution as two distinct nerves ; and further, the reflex centers of the medulla oblongata, of which these nerves are the afferent and efferent fibers, are so fused together in man and the higher vertebrates that the primitive disposition of these centers and the relation of the nerves originating m them are no longer ap- parent. In fact, the union is so intimate that it is impossible to say now how many such nerves or roots there were originally, and until that is determined it ^\ill l)e impossible to homologize the medullary ^nth the true spinal nerves. Indeed, until the develop- ment of the cranial nerves in the mammalia has been thorouffhlv worked out by the embryologist, and the relations between the cranial and spinal nerves in some of the lower vertebrates been established by the comparative anatomist, any view yet offered may be considered as based upon little more than speculation.^ Twelve pairs of nerves are given off from the base of the brain. The first two pairs, the olfactory and optic, the special nerves of the sense of smell and sight, are, as we shall see hereafter, morphologically outgrowths of the anterior cerebral vesicle ; the 1 Gegenbaur, Elements of Comparative Anatomy, transl. ]>y F. J. Bell, 1878, p. 515, Gaskell, Journal of Physiology, Vol. x., 1889, p. 153. 38 594 THE NERVOUS SYSTEM. remaiuing ten pairs, however, while apparently arising like the first two pairs from the base of the brain, in reality originate, as already mentioned, from nnclei in the medulla (Fig. 337), hence our reference to them as medullary nerves. Taking them in the order in which they succeed the olfactory and optic nerves, they are as follows (Figs. 338, 339) : The third pair, or motor oculi communis ; fourth pair, or patheticus ; fifth pair, or trigeminal or View of the posterior surface of the medulla, the roof of the fourth ventricle being removed to show the rhomboid sinus clearly. The left lialf uf the fiKure rcjjresents : On. Funiculus cuneatus, and //, funiculus grmilis. O. Obex. ■y). Nucleus of the spinalaceessorv. ji. Nucleus of pneu- niogastric. p + xp. Ala cinera. " H. Ite.stiforni body. A'lr. Nucleus of the hypoglossal. /. Ininiculus teres. (/. Nucleus of the acousticus. m. Striae niedullares. 1,2 and 3. Middle, superior, and inferior cerebellar i>caunc]es respectively. /. Fovea anterior. 4. Eminentia teres (genu nervi facialis). 5. Locus ca^ruleus. The right half of the figure rciiresents t lie nerve nuclei diagrammatically : I'. Motor trigeminal nucleus. V. Median and V", inferior sensory and trigeminal nuclei. I'/. Nucleus of abducens. r//. Facial nucleus. IT//. Posterior median acoustic nucleus. I'///'. Anterior median. VIII". Posterior lateral. VIII'". Anterior lateral acoustic nuclei. IX. Glosso-pharyngeal nucleus. X, XI, and XII. Nuclei of vagus, spinal accessdry, and hyjKj-glossal nerves respect- ively. The Honjan inimerals at the side of the figure, from F to A'//, represent the corresponding nerve roots. (Erb.) View from below of the connection of the principal nerves with the brain. I'. The right olfactorv tract. II. The left optic nerve. IP. The right optic tract ; the left tract is seen passing back into (' and e, the internal and external corjtora geu- ieulata. III. The left oculomotor nerve. IV. The trochlear. V, V. The large roots of the trifacial nerves. + +. The lesser roots, the + of the right side is placed on the Gasserian ganglion. 1, the oplithal- mic ; 2, the superior maxillary; and 3, the inferior maxillary nerves. VI. The left abducent nerve. VII, a, b. The facial and auditory nerves. a, VIII, b. The glosscj-phiiryiigeal, pneumogastric, and spinal accessory nerves. IX. The right liy)Mi-Klossal nerve. C I. The left sulxiccipital or first cervical nerve. trifacial ; sixth pair, or abducens ; seventh pair, or facial ; eighth pair, or auditory, the special nerve of the sense of hearing ; ninth pair, glosso-pharyngeal ; tenth pair, pneumogastric ; eleventh pair, spinal accessory ; twelfth pair, hypo-glossal. The third nerve, or motor oculi communis (Figs. 338 and 339, III), consisting of about 15,000 fibers,^ arises from a series of nuclei (Fig. 340) situated 'Eosenthal, De Numero atqne Mensura Microscop Filn-illarum. Breslaii, 1845. NUCLEI OF THE MEDULLARY NERVES. 595 upon both sides of the middle line of the aqueduct of Sylvius be- neath the corpora quadrigemina, those of the fibers crossing the middle line decussating with those of the opposite side. The nuclei of the third nerve, and those of the fourth and sixth as "well, it may be here mentioned, to avoid repetition, are in rela- FiG. 339. Fig. 3-40. Roots of the cranial nerves. I. First pair ; olfac- tory. II. Second pair ; optic. III. Third pair ; motor ociili communis. IV. Fourth pair; patheticus. V. Fifth pair; nerve of mastication and trifacial. VI. Sixth pair ; motor oculi externus. VII. Facial. VIII. Auditory — Seventh pair. IX. Glosso-pharyngeal. X. Pneumogastric. XI. Spinal accessory — Eighth pair. XII. Xinth pair; sublingual. The numbers 1 to lij refer to branches which will be described hereafter. (HiRSCHFELD.) A partly diagrammatic view of the floor of the aqueduct, looking upward (dorsally ) , nuclei of the third and fourth nerves, and the decussating libers of the latter all shown ; the third nerve nuclei are subdivided into an anterior nucleus, the Edinger-Westphal nucleus (a and 6), and a posterior nucleus ; the posterior nucleus has a dorsal, a ventral, and a mesal portion ; the decussation of the fibers from the dorsal portion of the posterior nucleus of the third nerve is shown. (Edixger.) tion, functionally on the one hand "with axis-cylinders, "svhich arising in the cells of the motor or visual cortex, descend about the knee of the internal capsule, and on the other by the axis-cylinders, which they give rise to, "v\ith the tissues supplied by the ocular nerves. While some difference of opinion still prevails as regards the relative position occupied by the nuclei giving origin to the differ- ent fibers of the third nerve, recent researches ^ render it probable that they are situated from before backwards somewhat in the fol- lowing order (Fig. 341) : J C. K. Mills, The Xervous System and its Diseases, 1898, j). 596 THE NERVOUS SYSTEM. Sphincter iridis, Musciiliis ciliaris, Convergence center, Rectus superior, Rectus internus. Levator palpebra? superioris, Obliquus inferior. Rectus inferior, Obliquus superior, Rectus externus. Fig. 341. 'SV'/i in cter iridis. MhscuIus ciliaris. ^Xr^ r\.(l("iyei-aeiice centre. T\t 1 \J Hnctus superior U.>^::::'- Rectus inlemus'. 0^^~T\ "{■,";9''"' P^'pcbrce superioris KJ^ OblKjuHs inferior. _ Meet us inferior. Obliquus superior. licet us externus Schema of the luielei of the nerves of ocular movemcDt ami of their central and perii)lieral tracts. A'. Right eye. L. Left eye. ('. Chia.sm. Ore. Optic nerve. Of. Optic tract. Q. Pre^eni- inum (anterior quadrigeiuinal body). P. Cortical center for the movement of elevation ot the upper eyelid. M. Cortical center for ocular movement.s. Tii. Course of all the ocular nerves in the cavernous sinus. The names of the different nuclei are printed on the diagram, and the nerve tracts going from these nuclei can be readily traced to where they converge in their course in the cavernous sinus and where they diverge to pass to the various muscles of the eye. The dotted line represents associating and commissural tracts. (Mills.) From this nucleus the fibers pass forward through the cms, emerging at tlie l^ase of the brain from the inner surface of the crura cercl^ri immediately in front of the jions. As the nerve passes through the sphenoidal fissure into the orbit (Fig. 342) it divides into two branches, the superior and smaller branches sup- plying the superior rectus and levator palpebrje superioris muscles, the inferior and larger brancii the internal and inferior recti and THE THIRD XERVE. 597 the superior oblique muscles. The latter or inferior branch gives off also a short, thick filament, which passing into the ophthalmic ganglion of the sympathetic is supposed, as Ave shall see, to pass thence as the short ciliary nerves into the iris, innervating the eir- F^f'- 3-12. cular muscular fibers of the latter. During its course the fibers of the third pair run in common or in juxtaposition witli fibers de- rived from the ophthalmic divis- ion of the fifth pair, and from the cavernous plexus of the sympa- thetic. AVe make use of the ex- pression running in company with, or in juxtaposition with, in preference to that of anastomosis, etc., since the various medullary nerves do not actually receive fibers from or anastomose with each other in the sense that arteries and veins anastomose. The nerves, in fiict, never lose their individuality, but undoubt- edly preserve through the whole extent of their course the char- acteristic functions obtaining at their roots, as in the case of the spinal nerves. Distribun 11 ■! tin' motor oculi communis. 1. Trunk ui Uu- imitur oculi communis. 2. Superior branch. 3. Filaments which this branch sends to the superior rectus and the levator palpebrse superioris. 4. Branch to the internal rectus. 5. Branch to the inferior rectus. 6. Branch to the inferior oblique muscle. 7. Branch to the lenticular ganglion. 8. Motor oculi externus. 9. Filaments of the motor oculi externus anastomosing with the sympathetic. 10. Ciliary nerves. (Hirsch- FELD.) This distinction mu.st be continually borne in mind, for, as we shall see presently, while each of these nerves, at its origin, has a definite function — motor, or sensory — they become, sooner or later, apparently mixed nerves, from the fact of being accompanied by the fibers of the adjacent cranio-medullary nerves. It is in this sense that the third nerve is to be understood as being a motor nerve, any evidences of sensibility being due, not to its intrinsic fibers, but to the extrinsic ones of the fifth pair. That the third nerve is exclusively a motor nerve is shown by the fact of irritation of the root causing contractions of the muscles to which it is dis- tributed, but no pain, while division of the nerve is followed by paralysis of the same.^ Pathological fiicts, like the falling of the upper eyelid, or blepharoptosis, external strabi.smus, immobility of the eye, except outwardly ; inability to rotate the eye on its antero- posterior axis in certain directions ; slight protrusion of the eye- ball ; dilation of the pupil, with some interference with the move- ments of the iris, following disease of the third pair in man, are 1 Mayo, Anatomical and Physiological Commentaries, p. 5. London, 1823. Out- lines of Human Physiology', p. 294. London, 1827. Bernard, Systeme nerveux, Tomeii., p. 204. Paris, 18-58. Chauveau, Journal de phvsiologie, Tome v., p. 274. Paris, 1862. Longet, Phvsiologie, Toraeiii., p. 554." Paris, 1869. 598 THE NERVOUS SYSTEM. Fig. 343. among the proofs that may be offered that the third pair of nerves is in man motor, as we woukl be hxl to snppose it wonkl be, both from its anatomical distribution as well as from the results obtained by vivisection. The Fourth Nerve. The fourth nerve, or patheticus, consisting of about 1200 fibers, arises from a nucleus situated immediately posterior to the nucleus of the third nerve (Fig. 340) and gives origin to the fibers sup- plying the rectus inferior muscle. The fibers so originating cross the middle line of the fourth ventricle and, decussating with those of the opposite side, emerge from the valve of Vieusseus at the base of the brain (Figs. 338 and 339, IV), as comparatively slender filaments at the sides of the pons, and, Avinding around the crura, pass through the sphenoidal fissure (Fig. 343) into the orbit, and supply the superior oblique muscle. Irri- tation of the nerve in a liviuij: animal, at its origin, causes con- traction of the superior oblique muscle, and division of the nerve paralysis of the same.^ In cases where the nerve is diseased in man, paralysis of the superior oblique muscle is observed as well as immobility of the eyeball, so far as rotation is concerned, and, when the eye is moved toward the shoulder, we have double vision, the eye not rotating to maintain the globe in the same relative position. The pathological facts observed in man, as well as the anatomical distribution, confirm the view based upon vivisections, that the fourth nerve is exclusively motor at its origin, any sensibility it may possess further on in its course being due to adjacent filaments from the ophthalmic branches of the fifth pair, or the sympathetic. The Sixth Nerve. The sixth nerve, the abducens, or motor oculi externus, being, like the fourth nerve, distributed to a single muscle, the external rectus, and, therefore, exclusively motor in function, will be consid- ered now, before the fifth nerve, which would, otherwise, be the next in order. The sixth nerve, consisting of about 3000 fibers, arises from a nucleus, situated beneath the eminentia teres, in the middle of the floor of the fourth ventricle (Fig. 337, VI) just pos- ' Longet, op. cit., Tome iii., p. 557. Chauvcau, op. cit., Tome v., p. 275. Bistribnti n ol tlu )i itlit tic ii^ / Olfiftory nerve // Ojticii mcn /// "NT t i iilicum- munib 71 PitlatRUN li} the '^l8), and passes thence through the sphenoidal fissure into the orbit. While in its course the sixth nerve runs in juxtaposition with the filaments derived from the sensitive ophthal- mic branch of the fifth pair, and from the sympathetic through the carotid plexus, and Meckel's ganglion. It is undoubtedly exclu- sively a motor nerve, supplying only the external rectus muscle (Fig. 342, 8). Irritation of the nerve at the root in a living animal causes the latter muscle to contract, but no pain, while division of the nerve is followed bv paralysis of the external rectus and internal strabis- mus,^ the latter lieing also observed in man in cases of disease of the sixth nerve. The third, fourth, and sixth pairs of nerves, taken tosrether, constitute the eiferent or motor nerves in the reflex actions involved in the movements of the pupil and the eyeball in ^^sion, and which will be considered hereafter, the optic nerve and the ophthalmic division of the fifth nerve constituting the afferent or sensory nerves. The Fifth Nerve. The fifth nerve, trifacial, or trigeminus, in arising from the base of the brain by two roots (Fig. 3o8, V -f ), the posterior large and sensory, with ganglion attached, and the anterior small and motor, is usually regarded as especially comparable with a spinal ners-e. For the reasons already given, it is quite as possible, however, that the fibers of the third, fourth, and even of the sixtli nerves may constitute the true motor fibers corresponding to the sensory fibers of the fifth (ophthalmic and superior maxillary) as that the fibers of its small motor root should be so especially regarded, particularly as the latter, as we shall see presently, are distriljuted exclusively in company -s^-ith the fibers of the inferior maxillary branch of the fifth. Of the two roots of which the fifth nerve consists (Fig. 344, J, (r), the larger or sensory root appears, from recent researches," to arise in the Gasserian or semilunar ganglion, situated in the de- pression on the internal portion of the anterior face of the petrous portion of the temporal bone rather than to pass into it, as usually stated. The axis-cvlinders of the cells of the ganglion divide into two branches, of which one set pass towards the brain, decussating with the fibers of the opposite side, as the long root (.7), the other set peripherally as the ophthalmic (*!/), the superior maxillary (X), and the inferior maxillary (i/) nerves. Of the 30,000 fibers pass- ing as the long root (J) towards the brain, some ascending cross the middle line and terminate in the thalamus opticus (C) and sen- sory areas of the cortex (i>) of the opposite hemisphere, others de- scending (i) pass into the cervical region of the spinal cord. The 'Longet, op. cit., Tome iii., p. 560. Cliauvean, op. cit.. Tome v., p. 275. ^S. Eamon y Cayal, Beitrag Zum Studium Der Medulla Oblongata, 1896, s. 1. 600 THE NERVOUS SYSTEM. fibers of the small or motor root ((t) arise from the cells of Uvo centers, a chief motor center (F) situated in the floor of the fourth ventricle and an accessory motor one (TJ) beneath the corpora quad- rigemina, and which are in relation with the cells of the cortex (A, A) of the lower part of the central convolutions of the opposite hemisphere and decussating with those of the opposite side. The two sets of fibers so arising pass together peripherally (G), and, running juxtaposed with the most inferior of the sensory fibers of the long root, constitute the inferior maxillary nerve (ii). The an- FiG. 344. Schema of trigeminal apparatus. A A. Cortical centers for trigeminal motor tracts. B. Cort- ical terminus of the trigeminal sensory tract. ('. Thalamus to which the central trigeminal sen- sory tract may be in large part distributed. I). Accessory (motor) nucleus. £. Descending (mesencephalic) root. F. Chief motor nucleus. G. ]Motor roots. J/. Inferior maxillary nerve. /. Gasserian ganglion. ./. Sensory roots between the (iasserian ganglion and the pons. /»'. Ascending .sensory root. L. Descending (spinal) root. jif. First or ophthalmic division of the trigeminus. JV. Second or superior maxillary division. (Mills.) terior small or motor root, consisting of about 10,000 fibers, passes underneath the ganglion of Gasser, from which it occasionally re- ceives a few filaments, and lying behind the inferior maxillary branch of the large root, passes through the foramen ovale in com- pany with the latter, with which it is finally distributed. It will be observed that while the ophthalmic and superior maxillary branches of the fifth are purely sensory, being derived solely from the large root through the (jasserian ganglion, the inferior maxil- lary branch is both motor and sensory, being derived not only from the ganglion but from the small or motor root as well. THE FIFTH yEEVE. 601 In division of the nerve in a living animal witli the view of de- terminins: its function ' both roots are necessarilv divided, and with the complete loss of sensibility ensuing under such circumstances, there is also observed paralysis of the temporal, masseter, internal and external pterygoid, mylo-hyoid, and anterior belly of the digas- tric muscles, or the muscles of mastication supplied by the fibers of the small root running in the inferior maxillary division of the fifth nerve and of the tensor muscles of the velum palati, and prob- ably of the tensor tympani also. The effect of division of the fifth nerve is very striking in the case of the rabbit, in ^vhich, through the consequent paralysis of the muscles of mastication, the line of contact between the incisor teeth becomes oblique instead of hori- zontal, the incisor teeth being worn away unevenly through the jaw being; drawn to one side bv the action of the active muscles. While it is an extremely difficult operation, if not impossible, to stimulate the small root of the fifth nerve in a living animal, never- theless, there can be little doubt that it is a purely motor nerve in function, since if it be stimulated in an animal just dead, in which the cerebral lobes have been removed, such of the muscles of masti- cation as are supplied by the nerves of the small root (running in the inferior maxillary division of the fifth) at once contract,^ and in the case of old horses, for example, with such force as to break off pieces of the teeth,'^ no such result following stimulation of the large root. The cases of paralysis of the fifth nerve that have been noted in man confirm in the main the results of experiments made upon ani- mals. In all instances where both the large and small roots were involved by the disease, entire loss of sensibility and paralysis of the muscles supplied by the fifth were observed * the only cases in which there was no paralysis of the muscles of mastication, etc., being those in which the small root was unatiected, loss of sensi- bility on the side affected being then only noted. In order to appreciate the results following division of the large root of the fifth nerve in a living animal or disease in man, it will be first necessary to describe briefly the distribution of its principal branches. It has already been mentioned that the large root arising in the ganglion of Gasser passes thence peripherally as the ophthal- mic superior and inferior maxillary nerves. The ophthalmic, the smallest of the three branches of the large root ( Fig. 345, below 3 ), passes through the sphenoidal fissure into the orbit, subdividing into the lachrymal, frontal, and nasal nerves, and gives off during its course to the orbit, fibers to the third, fourth, and sixth nerves, to the tentorium and to the sympa- thetic. The lachrymal nerve supplies the lachrymal gland, con- junctiva, integument of the upper eyelid, and gives off fibers to the orbital branch of the superior maxillary. The frontal ^Bernard, Systeme nerveux, Tome ii. , p. 100. Paris, lSo8. ^Longet, Anat. et Phys. du systeme nerveux, Tome ii., p. lUO. Paris, 1842. ^Chauveau, op. cit., p. -76. *Langet, op. cit., p. 191 ; MilU, op. cit., pp. 890-895. 602 THE NERVOUS SYSTEM. branch divides into the supratrochlear and supraorbital nerves, the former nerve supplies the integument of the forehead and gives oif a long, delicate hlament to the nasal nerve ; the latter, or supra- orbital nerve, passing through the supraorbital foramen, supplies, to a certain extent, the upper eyelid and forehead, the anterior and median portions of the scalp, the mucous membrane of the frontal sinus, and the pericranium covering the frontal and parietal bones. Fig. 345. General plan of the branches of the fifth pair. 1. Lesser root of the fifth pair. 2. Greater root passing forward into the Gasserian ganglion. ;i Placed on the bone above the ophthalmic nerve, ■which is seen dividing into the suin'aorbital, laelirymal, and nasal branches, the latter connected witli tlie u|ilitlKilniic ganglion. 4. I'laced on tlic bone close to the foramen rotundiim, marks the superior maxillary division. 5. Placed on the bone over the foramen ovale, marks the submaxil- lary nerve. (After a sketch by Cuarles Bell. ) %. The nasal branch, before entering the orbit, gives oflP a long fila- ment to the ophthalmic ganglion, and then the long ciliary nerves supplying the ciliary muscle, iris, and cornea ; it then divides into the external nasal, or infra-trochlearis, and the internal nasal, or ethmoidal nerves. The infra-trochlearis nerve supplies the integu- ment of the forehead and nose, the internal surface of the lower eyelid, the lachrymal sac, and caruncula. The internal nasal, or ethmoidal nerve, supplies the mucous membrane of the nose, and partly its integument. The second l)ranch of the fifth nerve, the superior maxillary nerve (Fig. 34(3, 1), passes out of the cranium by the foramen rotundum, and traversing the infraorbital canal emerges by the infraorbital foramen upon the face, giving off palpebral branches to the lower eyelid, nasal branches to the side of the nose, the latter running in common with the nasal branch of the ophthal- SUPERIOR MAXILLARY NERVES. 603 mic and lal)ial Ijranehes to the iutegument and mucous membrane of the upper lip. During its course through the spheno-maxillary fossa the superior maxillary nerve gives off several branches ; the orbital, which, passing into the orbit, gives off, in turn, the temporal and malar nerves, which, emerging by foramina in the malar bones, are distributed to the integument of the temple and side of the forehead, and the integument covering the malar bone respectively, the two posterior dental nerves (Fig. 346), the latter supplying the Fig. 346. / i ^ r-^ . V . -^ "' ^ ^ l? - ^> --Cj ^ - ^*^ Dissection of the superior maxillary nerve and Meckel's ganglion. 1. Superior maxillary nerve. 2. Posterior dental nerves. 3. Inner wall of orbit. 4. Orbital branch (cut). 5. Anterior dental nerve. 6. Meckel's ganglion. 7. Vidian nerve. 8. Sixth nerve. 9. Carotid branch of Vidian. 10. Greater superficial petrosal nerve. 11. Carotid plexus of sympathetic. 12. Lesser superficial petrosal nerve. 13. Superior cervical ganglion of sympathetic. 14. Facial nerve. 15. Interr.al jugular vein. 16. Chorda tympani nerve. 17. Glos.so-pharyngeal nerve. 19. Jacobson's nerve. (From HiRSCHFELD and Le'veille. ) molar and bicuspid teeth, the mucous membrane of the alveolar processes and of the antrum. In the infraorbital canal the anterior dental is given off, constituting, together with the posterior dental, the dental arcade, the anterior dental supplying the canine and incisor teeth, and the mucous membrane of the alveolar processes. The third branch of the fifth nerve, or the inferior maxillary (Fig. 345, 5), passes out of the cranial cavity by the foramen ovale, and after uniting Mith the small or motor root of the fifth, divides into anterior and posterior branches, the anterior branch containing the motor fibers supplying the principal muscles of mastication, and the tensor muscles of the velum palati through the otic ganglion, and derived, as already mentioned, from the small or motor root, the posterior branch containing principally sensory fibers. Among the most important of these may be mentioned the auriculo-temporal, the lingual, and the inferior dental nerves. The auriculo-temporal nerve supplies the integument of the temporal region of the ear, the auditory meatus, the temporo-maxillary articulation, and the parotid gland ; it gives off, also, filaments' that run in common with those of the seventh nerve, or facial. The lingual nerve, distributed to the mucous membrane of the point of the tongue, mouth, gums, sub- 604 THE NERVOUS SYSTEM. lingual gland, submaxillary ganglion, consists, as we shall see^ through a considerable extent of its course, of two distinct nerves, the lingual proper and the chorda tympani, and whose relations will l)e considered presently. The inferior dental nerve, after giv- ing oif the mylo-hyoid nerve, passes through the dental canal in the inferior maxillary bone, and supplying the lower teeth, emerges upon the face at the mental foramen, and, as the mental nerve, supplies the integument of the chin, the lower part of the face, and lower lip, and partly the mucous membrane of the mouth. While, as already mentioned, it is impossible to stimulate directly the large root of the fifth nerve in a living animal, yet, since all of its acces- sible branches, both in man and animals, have been shown to be very sensitive, it might reasonably be inferred that the large root from which all these branches arise is sensory in function, especially W'hen it is remembered that its stimulation in an animal just dead is followed by no contractions of the muscles to which the fifth nerve is distributed. Further, as well known, ^ if the large root be divided in a living animal, entire loss of sensibility on the side of the head affected at once follows, any muscular paralysis ensuing being limited to the parts supplied by the fibers of the small or motor root. The immediate effect of division of the large root is very striking, the cornea, integument, and nuicous meml)rane of the side affected are at once deprived of sensibility, and may be burned, lacerated, or .])ricked without the animal evincing any pain. Loss of general sensibility in the tongue is also observed, though no loss of taste,^ since, as we shall see hereafter, the gustatory properties of the anterior part of the tongue are due to the chorda tympanic fibers of the lingual nerve, and not to those fibers of the lingual proper derived from the inferior maxillary branch of the fifth nerve. The loss of general sensibility, etc., are also observed in paralysis of the fifth nerve occurriup; in human being's. In one of these cases,^ it may be mentioned as a proof of the sensory properties of the large root of the fifth nerve, that an operation was performed Avithout the slightest evidence of pain on the part of the patient. In addition to the loss of sensibility, etc., following division of the large root of tlie fifth nerve, in certain cases inflammation of the eye, ear, and nose have also been observed, the eye on the side af- fected becoming the seat of purulent inflammation ; the cornea, after becoming opacpie, ulcerating, the humors of the eye discharging, and the organ destroyed. Ulcers also appear upon the tongue and lips, and there is a discharge from the mucous membrane of the nose and mouth, and the hearing appears to be affected. The im- pairment in the nutrition of the eye, mouth, etc., following division of the fifth nerve, ai)pears to be due rather to inflannuatory irritation ^Magendie, Journal de Pliy.siologie, Tome iv., pp. 176, 302. Paris, 1824. Ber- nard. Leyons sur la i)livsiologie et la pathologie du Svsteme nerveux, Tome ii., p. 53. Paris, 1.S58. ^SchiftJ Leyons sur la physiologie de la digestion. Tome i., p. 103. Florence, 18()7. Lusanna, Arelii\es de Pliys., Tome ii., p. 27. Paris, 1869. ''Noyes, New York Med. Journal, 1871, Vol. xiv., ]>. 163. THE SEVENTH NERVE. 605 of the nerve than to division of the fiber?^ of the sym]>athetic passing into the Gasserian ganglion Avith eonseqnent vasomotor distnrbance as was formerly snpposed. That the })aralysis of tlie mnscles of mastication incidental to the division of the fifth nerve which inter- feres seriously with the digestion of food may account to some ex- tent for the disturbances of nutrition just mentioned appears to be shoM'n from the fact that the inflammation of the eye, etc., can be j)revented, for some weeks at least, if the animal be artificially fed with good nutritive food. It need hardly be mentioned that the nervous fibers transmitting gustatory, olfactory, and auditory im- pressions are not in any way derived from the large root of the fifth nerve, as once thought, the large root being only a nerve of general sensibility, the small root of motion. The Seventh Nerve. The seventh nerve, the nerve of expression, the facial, or the portio dura of the seventh pair, supposing the latter to include, as in the arrangement of Willis, not only the fibers of the facial pro])er, but those of the auditory, or porto mollis, containing about 4,500 fibers, arises in a fan-shaped manner from a group of cells situated in the grav matter of the floor of the fourth ventricle (Figs. 337, VII; 347; A). Fig. 347. C Schema of the apparatus of the facial nerve. P. Pons. A. Facial nucleus. B. Facial cortico- bulbar tract. C. Cortical center for facial movements. D. Nucleus of the pars intermedia of Wrisberg. E. Descending glossn-pluiryngeal roots. H. Nucleus of the hvpo-glossal nerve. FF. Trunk of the facial nerve, a. (ii'iiiculate ganglion. TTT. Pars interuiedia of Wrisberg and chorda tympaui nerve. M. IMcckel's sphcuo-palatiuc ganglion. O. Otic ganglion, a. Great super- ficial petrosal and Vidian nerves, b. Lesser siq)er. 236. "MilLs, op. cit., pp. 890, 895. *\Y. A. Turner, Journal of Anat. ami Pliys., 1889. Beaver and Ilorsley, Proc. Koyal Society. 5 Gowers, op. cit., Vol. ii., p. 307. ^ The Anatomy of Vertebrates, Vol. iii., p. 150. London, 1868. THE CHORDA TYMPAXI XERVE. 611 Fig. 352. Ill Piagram to illustrate suj>- posed connection of chorda tympani with superior max- illary through facial, great petrosal, and ganglion of Meckel. in man, in reality can be traced through the fibers of the facial as a continuation of the large petrosal, and as the latter nerve is connected through the ganglion of Meckel with the superior max- illarv nerve a pathway evidently exists in these animals by which the impressions made upon the tongue can be transmitted to the latter nerve, and while the chorda tympani nerve has not ])een actually demonstrated in man to be a continu- ation of the large petrosal, as in Fig. 352, both experiments upon animals and patho- logical cases in man lead one, as we shall see, to suppose that such is substantially the case.^ On the other hand, apart from the fact of nerve fibers not anastomosing, there is direct experimental evidence to show that the chorda tympanic fibers do not lose their individuality after joining those of the lingual branch of the inferior maxillary, but pre- serve their functional activity entirely inde- pendent of those of the latter. Thus, if the lingual branch of the inferior maxillarv be divided before it is joined by the chorda tympani, its fibers alone atrophy, with ensu- ing loss of general sensibility of the anterior part of the tongue, whereas, if the chorda tympani nerve be divided before it reaches the lingual its terminal fibers alone atrophy, loss of taste en- suing. Experiment not only shows, however, that the terminal portion of the lingual nerve consists of fibers derived from both the lingual branch of the inferior maxillary, and from the chorda tympani, but that the latter consists of three distinct sets of fibers ; 1st, those endowing the anterior two-thirds of the tono;ue with the sense of taste ; 2d, those modifying the blood vessels of the tongue, vasa dilator nerves ; 3d, those stimulating through the submaxil- lary ganglion the submaxillary and sublingual glands. The chorda tympani nerve, consisting, as it undoubtedly does, then, of sensory, motor, and secretory filjers, it is to be expected that it should have specially different centers of origin, which is in harmony with the view just offered of its motor fibers being derived from the facial, and its sensory fibers from the superior maxillarv nerve through the large petrosal and the ganglion of Meckel. That the chorda tympani nerve does contain at least some fibers derived from the superior maxillary nerve is further shown from the fact that disease of the fifth nerve, removal of the ganglia of Gasser and Meckel in man, is folloMed by the loss of the sense of taste in the anterior two-thirds of the tongue." It must be admitted, however, that it ' Goweis, op. cit., Vol. ii., p. 214 ^Schitt; Leyons sur la Physiologie de Digestion, Tome premier, p. 100. and Turin. Gowers, op. tit.. Vol. ii., p. 21G. Mills, op. cit., p. 094. Florence 612 THE NERVOUS SYSTEM. is held by many physiologists at the present day that the chorda tympani ministers to the sense of taste of the supposition that its fibers are continuous with those of the pars intermedia and that the latter nerye is endowed with gustatory properties because de- rived from the glosso-pharyngeal/ The well-known fact that dis- ease of the facial nerve situated between the origin of the chorda tympani and the geniculate ganglion is accompanied with loss of taste in the anterior part of the tongue - has been cited as a proof that the chorda tympani is continuous with the great petrosal. It is obvious, however, from what has just been said that the fact of disease of the facial involving the sense of taste might be offered equally well as a proof that the chorda tympani is continuous with the pars intermedia. It may be mentioned in this connection that, even if the view- that the chorda tympani is derived from the pars intermedia is not admitted, the fact that the latter unites with the facial in the Fal- lopian canal is not without functional significance, since it is well Fig. 358. Schema of the iiervt'S of the salivary glands. P. Pons. MO. Medulla oblongata. XV. Nerve of Jaeobson. O, SM, IM. Ophthalmic, superior, and inferior maxillary division.s of I', tifth nerve. VII. Seventh nerve. S.iji. Small superticial i)etrosal nerve. I«(/. Vagus. Si/m. Sympathetic. OG. otic, and SO. Submaxillary ganglia. P, >S, L. Parotid, sub-maxillary and sub-lingual glands. T. Tongue. (Laxdois.) known that the facial, after emerging from the stylo-mastoid fora- men, contains sensory fibers, which may account for sensation being more or less restored in certain cases of removal of the Gasserian o-ano-lion. Leaving the further account of the gustatory fibers of the chorda tympani for the present, let us turn now to the consider- ation of those of its fibers that, passing to the submaxillary gang- lion (Fig. 353, SG), constitute, together with the sympathetic fibers 1 Mills, op. cit., p. G86. ^Bernard, Systeme Ncrveux, 1858, Tome ii., p. 122. Sdiiff, op. eit., Tome i., p. 183. Lusanna,- Airhivcs de Physiologie, Tome ii., p. 201. Paris, 1869. Gowers, op. cit., Vol. ii., p. 237. NEEJ^ES OF THE SALIl'ARY GLANDS. 613 accompanying the blood vessels, the efferent fibers involved in the reflex production of saliva by the submaxillary and sub- lingual glands, the lingual glosso-pharyngeal and pnenmogastric nerves, the afferent fibers, the center of the reflex arc being situated in the medulla at the origin of the seventh and ninth cervical nerve. It may be mentioned, in this connection as ap- propriately as elsewhere, that while in the reflex production of saliva by the parotid gland the afferent nerves are the same as in the case of the submaxillary and sublingual nerves ; the ef- ferent nerves involved, in addition to sympathetic fibers, are derived from the otic ganglion, from the facial by the small petrosal, and from the glosso-pharyngeal nerve by the tympani branch of the glosso-pharyngeal or Jacobson's nerve. Fk;. 35-t. 3Incous Mejiibrnne jServe ^ ■^ '"'^ Secretory N Xervi Ceutre\^4 -„ ,'X, j Q^ "~(!^^\_Secretijig CeUs Bloodvessels of Gland Diagram of a salivary gland aud nerves. (La>'dois.) If the submaxillary and sublingual glands be cleanly dissected out, as in a living dog, for example, in which the glands are very accessible, they will be seen to be comparatively at rest, secreting little or no saliva, and their venous blood of a dark hue. If now a drop of vinegar be placed upon the tongue of the animal, at once the arterial twigs enlarge, the blood flows more rapidly, the veins pulsate, the color of their blood becomes scarlet, and the pressure increases, followed by an abundant discharge of limpid, very alka- line saliva, the so-called chorda tympani saliva, containing small quantities of albumin, globulin, mucin. That the phenomena just described are due to impressions transmitted to the medulla by the aflerent sensory fibers of the lingual branch of the inferior maxil- lary and glosso-pharyngeal nerves, and thence reflected back to the submaxillary aud sublingual glands by the efferent secreto-motor fibers of the chorda tympani (Fig. o54), is shown by such fiicts as that, after division of the lingual branch, the secretion of saliva, etc., ceases, but recommences if the central end of the divided nerve be stimulated. On the other hand, if the chorda tympani be divided, 614 THE NEB VO US S YSTEM. tlie vessels supplying the submaxillary and sublingual glands con- tract ; owing to the unopposed action of the sympathetic vaso-con- stricting fibers, the blood flows slowly, is diminished in quantity, and becomes dark, the secretion of saliya diminishes ; the applica- tion of vinegar no longer excites the secretion. That the secretion does not altogether cease after division of the chorda tympani ap- pears to be due to the independent reflex action of the submaxillary ganglion. If now, however, tlie divided chorda tympani be stimu- lated at its distal end, all the former phenomena recur. It may be mentioned, in this connection, though anticipated somewhat, that if the sympathetic plexus surrounding the facial artery be stimulated, the blood vessels of the glands become very much contracted, the lilood flowing more slowly, and darker in color in the veins, and that the saliya then secreted — the so-called sympathetic saliva — is not only diminished in quantity, but contains, in addition to albu- min and mucin, sarcode-like bodies. With division of the sympa- thetic fibers, the secretion of saliva does not altogether cease, a small quantity of the so-called paralytic saliva being secreted, if the tongue be stimulated with induced electricity. The fact that an abundant supply of chorda saliva accompanies increased blood flow, a scanty supply of sympathetic saliva or di- minished one would naturally suggest the idea that the secretion of saliva was simply a vasomotor effect, dependent upon the quantity and pressure of the blood. That such is not the case, however, that the phenomenon depends upon the stimulation of the salivary glands by secretory nerves is shown by the following considerations : That the pressure in the duct is greater than in the artery supply- ing the gland ; that the temperature of the gland rises ; that the amount of carbon dioxide is increased ; that, after the injection of atro[)ine into the gland, stimulation of the chorda tympani will still cause vascular dilatation, though no secretion. Just as there are involved in the production of saliva t\yo sets of nerve fibers, secretory and vaso-dilator, so it is held by many physiologists that there are two kinds of secretory fibers, the secretory fibers proper, whose function it is to regulate the production of water and inorganic salts, and trophic fibers, which cause the forma- tion of the organic constituents of the saliva. While it is pos- sible that such a distinction exists as that of secretory and trophic fibers it cannot be said as yet to have been positively established. In concluding our account of the functions of the facial nerve it remains for us now briefly to call attention to its external branches. Immediately after the nerve passes out of the stylo-mastoid fora- men, as already mentioned, it sends a branch to the glosso-pharyn- geal, upon which, as we shall see, the motor properties of the latter nerve depend. The posterior auricular branch receiving sensory filaments from the cervical plexus supplies the attolens and retra- hens aurem and the posterior portion of the occipito-frontalis muscle THE XIXTH XER VE. 6 1 5 and the adjacent integument. The branches supplying the pos- terior belly of the digastric, stylo-hyoid, and stylo-glossus muscles are important, as these muscles are involved in mastication and deglutition. The temporo-facial branch, as Ave have seen, supplies all the muscles of the upper part of the face. If this branch be paralyzed, the eye remains therefore constantly open, through paralysis of the orbicularis palpebrarum muscle, and may become inflamed in consequence from constant exposure. The frontal por- tion of the occipito-frontalis, attrahens aurem, and the corrugator supercilii are also paralyzed. A striking symptom of paralysis of the facial nerve if these filaments be affected, is inability to corru- gate the brow upon one side, as in frowning. Through paralysis of the muscles that dilate the nostrils olfaction and inspiration are also somewhat interfered with. To appreciate the influence exerted by the facial nerve upon inspiration it may be mentioned that in the horse, where the breathing is entirely nasal, death from suffo- cation very soon takes place if both facial nerves be divided, both nostrils then collapsing and becoming closed with each inspiratory effort.^ The effect of paralysis of the facial nerve is well seen in cases of facial palsy affecting one side, the distortion of the features being due in such cases to the unopposed action of the muscles upon the unaffected side. ^Vhen the paralysis is complete the angle of the mouth is drawn to the sound side, the eye on the affected side is widely opened, even during sleep, the lips are par- alyzed upon one side, the saliva frequently flowing from the corner of the mouth while the food tends to accumulate between the teeth and cheek through paralysis of the buccinator, mastication in con- sequence being materially interfered with. If both facial nerves be paralyzed, mastication becomes very difficult, and the face ex- hibits a peculiarly expressionless appearance. The Ninth Nerve. The next nerve in order, the ninth or glosso-pharyngeal, the con- sideration of the eighth nerve or auditory being deferred for the present, arises in common with the nucleus of the pneumogastric from a column of cells (Fig. 337, IX) deeply situated beneath the lower and outer part of the floor of the fourth ventricle. The nucleus appears to be in relation with axis-cylinders that are supposed to descend from motor cells of the opposite hemisphere, the locality of which is as yet ill-defined, and passing probably near the pyramidal tract cross the middle line to terminate in the medulla. After emerging from the medulla, the fibers of the glosso-pharyngeal proceed forward and outward by a series of five or six roots, contain- ing about 9000 fibers, attached to the surface of the restiform body, the highest being close to the auditory nerve and passes out 1 Bernard, Le^-ons sur la phvsiologie et' la patholuirie du Svstcme Xerveux, Tome ii., p. 308. Paris, 1858. 616 THE NERVOUS SYSTEM. Fir; of the cranial cavity through the jugular forameu (Fig. 355), in company with the pneumogastric and spinal accessory nerves. As the glosso-pharyngeal nerve passes out of the jugular foramen, it expands into the petrous ganglion or ganglion of Audersch from which fine filaments are given oif to the pneumogastric and sympathetic nerves. The o:ano;lion ffives orip^in also to the tympanic or Jacobson's nerve ; the latter, ascending through the canal of the same name in the petrous portion of the temporal bone, expands upon the promontory of the tympanum into a number of Ijranchcs which supply the lin- ing membrane of the tym- panum, the round and oval windows, and tlie Eustachian tube. The tympanic nerve o-ives off also two small branches which pass respec- tively to the large and small ])etrosal nerves and filaments to the sympathetic plexus of the internal carotid artery. From tlie ganglion of Andersch the glosso-pharyngeal nerve descends between the jugular vein and the internal carotid artery to the root of the tongue on the inner side of the stylo- pharyngeus muscle terminating in the muscles and mucous membrane of the pharynx, soft palate, tonsils, the root and m u c o u s membrane of the tongue, including the circum- vallate papillae. During its course the glosso- pharyngeal sends off filaments to the pneumogastric and sym- pathetic, and as already men- tioned, receives filaments from the facial. The glosso-pharyngeal nerve appears from recent researches to consist of three sets of fibers, sensory, gustatory, and motor,^ origi- ' Obei-steiner, op. cit., s. 294, s. -123. The last four cerebral uerves : the facial nerve, the sympathetic and the upper two cervical nerves. 1. Facial nerve. 2. (Jlosso-pharyngeal. 2'. Anastomosis between a branch of the facial and the glosso-pharyngeal. .3. Vagus. 4. Ac- cessory. .5. Hypo-glossal. 6. First cervical ganglion of the sympathetic. 7. First and second cervical nerves. 8. Cavernous jjlexus of the sym- pathetic on the internal carotid artery. 9. Tympanic nerve from the petrous ganglion of the glosso-pharyngeal. 10. Its c o u n e c t i o n with the carotid plexus. 11. Branch to the Eustachian tube. 12, VA. Branches to the oval and round windows of the ear. 14,1.^. Branches joining the small and superficial petrosal nerves. 16. Otic ganglion. 17. Auricular branch from the jugular ganglion and the facial nerve. 18. Anastomosis (if the acii'.-sory with the vagus. 19. AiKistimiosis ol' tlir first cervical nerve with the liypo-glos-ai. -U. Anastomosis of the second cervical nerve with a branch of the accessory. 21. Pharyngeal plexus. 22. Su|ierior laryngeal nerve. 23. Its external branch. 24. .Second cervical ganglion of the sympathetic. (IIirsch- fkld-Sappey.) THE NINTH NERVE. 617 nating in distinct parts of the nucleus of origin in the medulla, some of the motor fibers being derived, however, from the branch of the facial that joins the glosso-pharyngeal nerve at the petrous ganglion. That the glosso-pharyngeal nerve is a sensory nerve, at least at its origin, is shown by the loss of sensibility in the parts to which it is distributed and loss of the sense of taste in the posterior third of the tongue following its division in a living animal or paralysis in man, and that stimulation at the root in a living animal fails to produce muscular contractions. Owing, however, to it containing motor fibers derived as already mentioned from its nucleus, as well as to its connections with the facial, the glosso-pharyngeal un- doubtedly receives motor fibers, to which are due ^ig. 3o6. the muscular contractions following irritation of the glosso-pharyngeal av hen stimulated outside of the cranium, and the difficulty experienced in degluti- tion, if the nerve be divided in an animal, or be paralyzed in man. It has already been men- tioned that the contrac- tions of the muscles in- volved in deglutition fol- lowing; stimulation of the glosso-pharyngeal are re- flex in character, the im- pressions made upon the latter nerve, like those made upon the pala- tine branches of the fifth nerve, being transmitted to the deglutition center in the medulla (Fig. 3o()) and thence reflected through the petrosal nerves to the ganglion of Meckel, and the otic ganglion to the muscles supplied by the latter. It will be seen from the above description that the glosso-pharyn- geal nerve is a sensory nerve, endowing the tongue and pharynx with sensibility, and the posterior third of the tongue, and the an- terior two-thirds as well, with the sense of taste, if the chorda tym- pani be regarded, as already mentioned, as a continuation of the pars intermedia, and the latter a branch of the glosso-pharyngeal. If it be admitted that the glosso-pharyngeal nerve contains specific motor fibers it must be regarded then as a motor as well as a sen- Pecjlufition Centre &ypucj\o^* «chema of the afterent and efferent nerves concerned in deglutition. (Stirling.) 618 THE NERVOUS SYSTEM. soiy nerve, iiidepeudeutly of its connections with the faciah In conclusion it may be mentioned that the glosso-pharyngeal nerve possesses also inhibitory functions, diminisliing or arresting the ac- tion of the cardio-motor, respiratory, and vasomotor centers of the medulla. The Tenth Nerve. The tenth nerve, the pneumogastric, par vagum, or vagus, arises as already mentioned, in common Avith the glosso-pharyngeal from a group of nerve cells situated beneath the lowest part of the floor of the fourth ventricle, giving rise to a promontory on the surface of the latter (Fig. 337, A'). At the point of the calamus scripto- rius, the symmetrically disposed nuclei are in contact at the middle line, but a little higher up are separated by the nuclei, giving origin to the hypo-glossal nerves. From this origin the fibers pass for- ward through the medulla, emerging by twelve or more roots con- taining about 9000 fibers attached to the restiform body in a line below those of the glosso-pharyngeal nerve, and leave the cranial cavity, as already mentioned, in company with the glosso-pharyn- geal, spinal accessory nerves, and the internal jugular vein. In the jugular foramen the pneumogastric nerve presents a well- marked enlargement from one-sixth to one-fourth of an inch in lenp-th, the 2:ang;lion of the root or the iuoular ranolion, from which pass filaments to the facial, and the ganglion of the glosso- pliaryngeal and superior cervical ganglion of the sympathetic. After leaving the cranial cavity the pneumogastric nerve presents another enlargement from half an inch to an inch in length, the ganglion of the trunk, from which filaments pass to the hypo-glossal nerve and occasionally to the arcade formed by the first two cer- vical nerves. Immediately after leaving the cranial cavity the pneu- mogastric nerve receives an important branch from the spinal ac- cessory, and during its course filaments from the first two cervical nerves, and together M'ith fibers from the glosso-pharyngeal, spinal accessory, and sympathetic forms the pharyngeal plexus. That the pneumogastric is exclusively sensory at its origin, whatever may be the functions of its branches, appears to be satisfactorily shown, even though indirectly, by experiments like those of Longet^ made upon horses and dogs just dead, in which stimu- lation of the nerve at its root failed to produce muscular contrac- tions if the nerve was carefully insulated and all its motor con- nections divided. That irritation should be followed by muscular contractions if the latter precaution be not observed, should not ex- cite surprise when it is remembered that the pneumogastric receives motor filaments from at least five sources, viz., the facial, spinal accessory, hypoglossal, and first and second cervical nerves, not to speak of the motor fibers derived from the sympathetic. Any mus- cular contractions ensuing upon irritation of the pneumogastric ' Physiologie, Tomoiii., p. 508. Paris, 1869. THE TEXTH NERVE. 619 must therefore be either reflex in character like many of those of the glosso-pliarvngeal ah-eady referred to, or be attrilnited to the stimu- lation of fibers derived from the motor sources just metitioned. Fig. 357. . 'C f.im\'-. ^^F^' mmw^-^W" i i / >^^y^j^i .1 V: JC^^f, .I^A-/:^' / (U. Distribution of the pneumogastric. 1. Trunk of the left pneumogastric. 2. Ganglion of the trunk. 3. Anastomosis with the spinal accessor}-. 4. Anastomosis with the sublingual. 5. Pharyngeal branch (the auricular branch is not shown in the figure). 6. Superior laryngeal branch. 7. ICxternal laryngeal nerye. 8. Laryngeal plexus. 9, 9. Inferior laryngeal branch. 10. Ceryical cardiac branch. 11. Thoracic cardiac branch. 12, 13. Pulmonary branches. 14. Lingual branch of the fifth, lo. Lower portion of the sublingual. 16. Glosso-pharyugeal. 17. Spinal accessory. 18, 19. 20. Spinal neryes. 21. Phrenic nerye. 22, 23. Spinal ueryes. 24, 25, 26, 27,28,29,30. Sympathetic ganglia. (Hirschfeld.) The most important branches given off by the pneumogastric (Fig. ooT), whose functions Ave shall study seriatim, are as follows : the meningeal, auricular, pharyngeal, superior and inferior laryn- geal, cervical and thoracic, cardiac, anterior and posterior pulmo- nary, oesophageal, and abdominal. (320 THE NEE \ '0 US S \ 'S TEM. The first or mening-eal branch of the pneumogastric uerve is given off from the juguhir ganglion and passes with the vasomotor fibers of the sympatlietic supplying the middle meningeal artery to the occipital and transverse sinnses. It is nsnally regarded as con- sisting of sensory fibers. The auricular, or Arnold's nerve, though containing fibers derived from the facial and glosso-pharyngeal nerves, is usually described as being a In-anch of the pneumogastric nerve, being given off from the ganglion of its trunk. Passing through the temporal bone by the canal of the same name, it is distributed to the external auditory meatus and the mend)rana tympani, endowing those parts with sensi- bility. The jjharyngeal branches are given off from the superior por- tion of the ganglion of the trunk of the pneumogastric nerve, but con- sist largely of filaments derived from the spinal accessory, reinforced, further, during their course, by filaments from the glosso-pharyngeal and superior cervical ganglion of the sympathetic to form the pharyngeal plexus, which supj)lies the nuiscles and mucous mem- brane of the ])harvnx, the motor filaments l)eing derived, as we shall see, from the spinal accessory, and the sensibility being due to the filaments of the pneumogastric proper, and also to those of the pharvngeaH)ranches of the fifth, and of the glosso-pharyngeal. The superior laryngeal nerve arising from the ganglion of the trunk divides into the external and internal branches, the external branch receiving filaments from the inferior laryngeal, and the sympathetic supplies the mucous membrane of the ventricle and crico-thyroid muscles of the larynx, and the inferior constrictor of the pharynx. The internal branch, also receiving filaments from the inferior laryngeal, supplies, like the external branch, the crico-thyroid muscles, and is distributed to the mucous membrane of the epi- glottis, the base of the tongue, the aryteno-epiglottidcan folds, and the mucous mend)rane of the larynx as far down as the true vocal membranes. From the anatomical disposition it might be inferred that the general sensibility of the upper })art of the larynx and the surrounding mucous membrane, as well as the innervation of the crico-thyroid muscle, was due to the superior laryngeal nerve, and experiment shows that such is the case. Thus, stimulation of the suj)erior laryngeal nerves in a living animal gives rise to intense pain, and causes contraction of the crico-thyroid muscle. It is through the exquisite sensil)ility of the upper part of the mucous membrane of the larynx that foreign Ixxlies are prevented from en- tering the air passages ; impressions made by such, being trans- mitted to the medulla, are thence reflected through the inferior larvngeals back to the larynx, bringing al)out a closure of the glottis. Every one is familiar with the fact that if a crund) of bread, etc., fall upon the aryteno-epiglottidcan folds or the edge of the vocal membranes, the sensibility of the parts is such as to ex- cite a convulsive cough, by which the foreign body is dislodged and expelled. The impression conveyed by the superior laryngeal THE INFERIOR LARYNGEAL NERVES. 621 nerve to the cough center of the medulki being reflected thence through the nerves supplying the expiratory muscles of the chest and abdomen, l)y which the coughing is accomplished. That this reflex action is due to the sensibility of the laryngeal mucous mem- brane is shown by the fact that, after division of the superior laryngeal nerve, iun)ressions made upon tlie mucous membrane fail to bring about such action. The superior laryngeals, also, consti- tute the afierent nerves in the reflex mechanism by which, through contraction of the constrictors of the pharynx, the act of deglutition is completed. It is interesting to observe that the impressions made upon the mucous membrane of the larynx, and the surround- ing membrane, and l)y which, through reflex action, deglutition is brought about, cause, at the same time, closure of the glottis, and arrest of respiration, thereby protecting the air-passages against the entrance of food or other foreign bodies. The two inferior or recurrent laryngeal nerves, so called from reascending to the larynx after descending from the pneumogas- tric, diifer slightly in their course on the two sides, that of the left side passing beneath the aorta, that of the right side winding from before backward around the subclavian artery before they as- cend in the groove between the trachea and the oesophagus to the larynx. In other respects, the course and distribution of the two nerves are the same. The curious course taken by the inferior lar- yngeal nerve, Avhether of the right or left side, is due to the fact that, while in the embryonic condition, the larynx and heart are in close proximity ; through the elongation of the neck, incidental to development, the heart and great blood vessels recede from the lar- ynx, and, in so doing, drag down with them the inferior laryngeal nerves, which ])ass, loo])-like, around them. It may be mentioned in this connection, as observed by Owen,' and by the author,- in the individuals dissected by the latter, that in the giraife the infe- rior laryngeal nerves pass directly from the pneumogastric to the larynx, like the superior laryngeals. The significance of this is very evident, for, were the course of the inferior laryngeals in the girafie the same as in man, the nerve, in descending and ascending through so many feet, would, in all probability, be so stretched and tensed as to render it incapable of performing its functions. As the inferior laryngeal nerves ascend they give olf filaments, which join those of the cardiac branches of the pneumogastric filaments to the muscular tissue, and mucous membrane of the upper jiart of the oesophagus, to the mucous membrane and inter-cartilaginous muscular tissue of the trachea, to the inferior constrictor of the pharynx, and, as already mentioned, a branch which joins the su- perior laryngeal, terminating, finally, after penetrating the larynx behind the ])osterior articulation of the cricoid, Avith the thyroid cartilage, in all of the intrinsic muscles of the larynx, except the iQp. cit. Vol. iii., p. 100. ^H. C. Chapman, Proc. Acad. Nat. Sciences, Phil., 1887, p. 37. 622 THE NERVOUS SYSTEM. crico-thyroid, which, it Avill be remenil)cred, is supplied by the su- perior larvng-eal nerve. Direct stimidation of the inferior hirvn- geal nerves proves what one wonkl lie led to expect from their dis- tribution, that thev are principally motor in function, and from the fact, as we shall see hereafter, of division of the spinal accessory being; followed by loss of voice, the respiratory movements of the glottis being, however, unaffected, but that division of the inferior laryngeal nerves not only involves loss of voice, but paralysis of the respiratory movements of the larynx as well — that their motor filaments are derived at least from two different sources, if not more. To anticipate what we shall see more particularly here- after, the muscles of the larynx involved in the production of the voice are the arytenoid, the thyro-arytenoid, and the lateral crico- arytenoid, supplied by the inferior laryngeal nerves and the crico- thyroid, supplied by the superior laryngeal nerves. The pos- terior crico-arytenoid muscles supplied by the inferior laryngeal nerves opening the glottis, are, however, respiratory in function. Now, while in an animal the voice is lost after division of the in- ternal branch of the spinal accessory, nevertheless, the glottis, though not closing on irritation, being still capable of dilatation, respiration is not interfered with. Such being the case, if the in- ferior laryngeal, however, be divided, the glottis is at once mechan- ically closed with each inspiratory effort, and the animal, if young, dies of suffocation. In adults, however, the cartilages of the lar- ynx, being rigid, permit of respiration even after the larynx is para- lyzed. The only inference from these facts is that the libers of the inferior laryngeal that innervate the muscles of phonation are de- rived from the spinal accessory, but that those innervating the res- piratory movements of the glottis are derived from some other source — from the facial, in all probability, or, possibly, from the hypo-glossal, or the cervical nerves that we have seen give off branches to the pneumogastric nerve. Inasmuch, also, as the crico- thyroid muscle is involved in phonation, and as we have seen that the superior laryngeal nerve sup])lying it receives fibers from the inferior laryngeal, in all probability it is the fibers of the latter nerve that influence the crico-thyroid muscle in phonation, other- wise it is difficult to see wdiy the paralysis of the voice following division of the inferior laryngeal nerve should be so complete. It must be admitted, however, that the view just offered of the functions of the laryngeal nerves is not universally accepted. In- deed, considerable difference of opinion still ])revails among phys- iologists as to exactly how the different ])arts of the larynx are innervated. The cervical cardiac branches, two or three in number, arising from the })neumogastric, consist princi])ally, as we shall see, of fibers derived from the sympathetic. The thoracic cardiac branches given off Ixlow the origin of the iuferior laryngeal nerves pass to the cardiac plexus. THE IXNERVATIOX OF THE HEART. 623 The Innervation of the Heart. Intracardiac Centers and Nerves. It is well known that the heart of the lower verteljrates, like the shark, sturgeon, etc., will eontinue beating for many hours after re- moval from the body. The same has been shown to be true also of the heart of rabbits, cats, clogs Avheu proper precautions are taken.^ Such facts show conclusively that the cause of the rhyth- mical beat of the heart, being independent of the central nervous system, must lie within the heart itself. Difference of opinion still prevails, however, as to whether the beat of the heart is due to the heart muscle possessing the power of rhythmical contraction in it- self, or to the heart muscle being periodically stimulated by im- pulses from the intracardiac cells. That the latter is the cause of the rhvthmical beat of the heart appears to be shown from the fact that the contractions are more powerful in those parts of the heart in which the nerve supply is richest. Thus the contractions of the auricle are more powerful than those of the ventricle, those of the base of the ventricle more so than those of the apex, the num- ber of nerve cells being greatest in the auricle, smallest in the ven- tricle. Indeed, in the apex of the ventricle ganglion cells are entirelv absent according to most histologists. It may be also mentioned as confirmatory of the view that the cause of the heart beat is nervous in origin, that while muscarin arrests the contrac- tions of the muscular fibers of the heart it does not exert the same influence upon otlier kinds of either striped or smooth muscle. On the other hand, there can be no doubt that the muscular fibers of the heart respond to stimuli other than nervous, since a slip cut from the ventricle of the heart of a tortoise, when suspended in a moist chamber, will begin beating in a few minutes and continue to beat for more than twenty-four hours. The nerve fibers that are supposed to convey the impulses stimulating the muscular fibers to contract, appear to arise in ganglia situated near the orifice of the superior vena cava, in the septum of the auricles and in the auriculo-ventricular grooves, whence they pass as fine non- medullated fibers to penetrate the walls of the auricles and ventri- cles. The ganglia of the heart, at least in the case of the frog, appear to have antagonistic functions, some of the ganglia, for example, inhibiting the functions of the other. The presence of cardiac ganglia can be readily demonstrated in the heart of the frog, and their functional significance shown by the well-known experiment of Stannius.^ In the frog, as is well known, the two superior venre cava? ('S'lT', Fig. 358) unite before entering the right auricle to form a dilatation — the sinus venosus ('S'T"). It is in the wall of the latter, near the opening of the inferior vena cava, that the first of these ganglia, the ganglion of Remak {R), is situ- ated, the second or the ganglion of Bidder [E), bemg found in the ' Stolnikow, Pawlow, Langendorff in Tlgei-stedt, Lehrbuch Der Physiologie Des Kreblaufes, 1893. ^ Zwei Reilien, Physiologische, Vei-suche, 1851. 624 THE NERVOUS SYSTEM. left auri(•ulo-^'c'ntricular groove, the third ganglion or that of Lud- wig, in the septum between the aurieles. If a ligature be applied between the sinus venosus (aS'T^) and the right auricle (.4, Fig. 359, 1), the heart stops beating and remains in a state of diastole. B.A Fig. 359. I.V.C. Schema of nerve.s of frog's heart. R, Remak's, and B, Bidder's ganglia. .ST. Sinus venosus. A. Auricles. V. Ventricle. BA. Bulbus arteriosus. Vag. Vagi. 59, 2), tlien the inhibitory action of the ganglion of J^udwig being cut off, and there being nothing to counteract the action of the ganglion of Bidder, the ventricle begins to l)eat again. AVhatever the explanation may be of the facts just described, it is evident that the heart possesses an intrinsic nervous mechanism by ^vhich, in response to the stimulus, its fibers arc excited to contract. It may be mentioned in this connection that many of the ganglionic nerve cells of the heart of the frog present not only an axis- cylinder, l)ut a s])iral process as well (Fig. 360, o), of functional interest since the process appears to be derived from the pneumo- gastric nerve and to convey impulses to the nerve cell. Pyriform ganglionic bi- polar nervf-uell from the heart of a frog. m. Sheath. 11. Straight process, o. spi- ral process. CURRENT OF ACTION OF HEART. 625 If non-polarizable electrodes be applied to the surface of the ven- tricle of a frog's heart and connected with a delicate galvanometer, it will be observed that with each ventricular systole the needle of the galvanometer is deflected, returning to rest with each diastole, showing that a change in electrical potential precedes or more prob- ably accompanies the change in form that has l)een described as a car- diac contraction. Further, if one electrode be applied to the base of the heart and the other to the apex it will be foimd that this change in electrical potential, " the current of action," the excita- tion wave travels from base to apex at the rate of from 50 to 150 millimeters per second and preceded according to some observers by a latent period of about 0.08 sec.^ Some difference of opinion still exists as to whether the excitation wave passes along the mus- cular or nervous tissues of the heart. From the fact that the wave travels comparatively slowly, about 90 millimeters per sec- ond or 300 times " less than at the rate at which it would travel if it were transmitted by nervous tissue, it is generally supposed that the wave travels along; the muscular rather than alono- the nervous tissue. That the excitation wave travels along the mus- cular liber is still further shown by the fact that the "block,"^ or the delay that the wave experiences in passing from the auricle to the ventricle, appears to depend upon the relatively few fibers pres- ent in that situation, and that the duration of the "block" is about what it ought to be on the supposition that the wave passes along the muscular fibers connecting the auricles and ventricle. It is well known that, while the heart will contract in response to mechanical and electrical stimuli when sloAvly repeated, it will not contract when the stimuli follow each other too rapidly. Tliis appears to be due to the fact that the heart will not contract secondarily in response to an extra stimulus when applied during the period intervening between the beginning and maximum of its systole, whereas it will contract secondarily when the stimulus is applied during the period intervening between the maximum of one systole and the beginning of the next.^ The period of the cardiac cycle during which the heart refuses to contract in response to a stimulus is called the " refractory period." Since a period exists however in which the heart will contract in response to a stimulus it might be supposed that if the stimulus be rapidly ap- plied during that period, that is during the " non-refractory period," on account of the extra contraction produced with each stimulus, the total number of contractions would be increased. As a matter of fact, however, such is not the ease, as the extra con- 1 Engelmann, 1874, p. 6. ^ The author takes occasion to say that by throwins a beam of light upon the mirror of the galvanometer and reflecting the same upon a screen he has been able to demonstrate the "current of action " of the frog's heart to a large autlience, the ball of light moving pendulum-like with the systole and diastole of the heart. ^Gaskell, Journal of Physiology, ^'ol. iv., p. 95. *Marey, 1876, p. 73. Engelmann, 1895, p. 313. 40 626 THE NERVOUS SYSTEM. traction is followed by a pause, the duration of which, being that of the normal pause plus the interval between the appearance of the extra contraction and what would have been the end of the cardiac cycle in which the extra contraction occurred, the normal number of contractions is maintained. The pause following the extra con- traction induced during the " non-refractory period" is appropri- ately called therefore the " compensatory pause." It follows from Fig. 361. The refractory period and compensatory pause. Curves to be read from left to right. The interruption on the abscissa below each curve indicates the moment at which the ventricle was stimulated. In the curves 1, 2, :!, the ventricle was refractory to the stimulus, the latter being applied during the refractory i)eriod. In the remaining curves an extra contraction and com- pensatory pause are seen, the stimulus having been applied after the refractory period. (Marey. ) what has just been said that a continuous stimulus may produce a rhythmical heart beat, since, the heart contracting only during the *' non-refractory period," each contraction will be followed by a compensatory pause. That the refractory period and compensatory pause are produced inde])endently of the cardiac nerve centers ap- pears to be shown from the fact that both can be obtained when the EXTRA CA RDIA C INHIBITOB Y CENTERS. 627 apex of the ventricle is used in which it is generally supposed, as already mentioned, that nerve centers arc absent. Extracardiac Inhibitory Centers and Nerves. Contrary to what might have been naturally expected from what we have hitherto learned as to the effect of division and stimulation of nerves, division of the pneumogastric nerve in a living animal, so far from arresting the action of the heart, actually increases the rapidity of its pulsations, while electrical stimulation of the pneumo- gastric nerve arrests the heart's action in diastole (Fig. '362), and causes a fall in the blood pressure (Fig. 363). Fig. 'M;± l/\/lAA/W\/l__.../vAAAA. Etfect ol'stimulatii)U of jmk iimogastric nerve upon action of heart in frog. Ill be read from riglit to left. The effect of division of one pneumogastric nerve, however, in a frog or a rabbit, for example, is not by any means as marked as when both nerves have been divided. In the latter case the action of the heart is tremulous, the number of its beats Fig. 363. may be doubled, while the /vA^^'MA/i respiration, from being ^ -^^ . ~^ momentarily accelerated, becomes calm and pro- found, but diminished in frequency. It might natu- rally be supposed that the inhibitory influence of the Effect of cardiac inliibition in rabbit on blood T. f.! n ,1 pressure. Current sent into pneumogastric nerve at a, cardiac nbers Ot tne pneu- shut off at 6. First, there is a rapid fail, and when the mogastric is directly ex- H^a'^to'thenoS.' '''' "'''"''' "''' ''^ '"'"'''"' erted upon the heart. That such, liowever, is not the case, appears from the fact of the latent period — that is, the time elapsing between the application of the stimulus and the inhibitory effect — being very long, nearly one-fifth of a second, instead of one-hundredth of a second, in some cases even two entire beats of the heart intervening before its arrest occur- red, indicating that some resistance must be overcome, the inhibi- tory fibers of the pneumogastric acting upon inhibitory centers in the heart itself. That such is the case is shown by the fact that the action of the heart in the eel and the frog can be arrested by direct stimulation, and that in the mollusca, although no pneumogastric nerve is present, the heart can be- stopped in diastole by direct irritation. Again, if nicotin or curara be subcutaneously injected 628 THE NERVOUS SYSTEM. in small doses into a living animal the heart beats first slower then faster, possibly on acconnt of the extracartliac inhibitory centers of the pnenraogastric (Fig. 364) becoming paralyzed ; if now muscarin or jaborandi be then administered, the heart will be arrested in diastole, the latter sub- Fifi. 364. VaaaJ o extrc-card. inMi. OrsAccelt cceZer.cent. of ■' ' Olil. stances appeanng to act directly npon intracardiac inhibitory centers. On the other hand, if atropia be injected, then neither muscarin nor jaborandi will have any inhibitory effect upon the heart, atropia appearing to par- alyze both the extra- and intracardiac inhibi t o r y centers. Stimulation of t h e ])ncumogastric nerve not only inhibits the heart's action but modifies the latter in many ways. Thus the duration of both tlie systole and diastole are lengthened. The force of the contraction, the input and output of the ventricle are diminished, the diastolic pressure and volume of the blood in the ventricle are in- creased. Tlie contrac- tions of the ventricle do not correspond in number to those of the auricle, the latter being often twice as numerous as the former. A change in elec- trical potential occurs also, the current of rest of the injured auricle of a tortoise heart lead off to a galvanometer exhibiting a marked increase. It may be mentioned in this connection that the act of swallowing temporarily al)olishes the inhibitory action of tlie vagus, the pulse rate l)eing accelerated often -'30 per cent. l)y merely sipping a wineglassful of water. That the influence exerted by the fibers of the pneumogas- tric nerve upon the heart is transmitted centrifugally and is de- pendent upon its motor fi])ers is shown by the fact that if the pneumogastric nerve be divided in a living animal and stimulated Diagrammatic view of tlie nerves influencing tlic action of the lieart. Tlie right half represents the course of tlie inhibitory, and the left the course of the accelerating nerves of the heart ; the arrows showiug the direction in which impressions are conveyed. The ellipse at the up- per extremity of the vagus looking like the section of the nerve is inteiulccl ti> rrprt'sent the vagal nucleus or center. In this diagram tlic iirrves are incorrectly made to cross, instead of i)a,ssiiig lii-hiiid, the aorta. INHIBITORY FIBERS OF VAGUS. 621> at its central end none (if tlie effects such as those just descriljed ensue; stimuhithm of the (Hstal end only slowino; up the action of the heart and causing- a fall in blood pressure ; and that if the stim- ulation be continued too long, so as to exhaust the irritability of the motor fibers, the heart begins to beat again, their inhibitory effect being lost.^ Further, in animals poisoned ^vith curara, which, as is well known, paralyzes the motor nerves, stimulation of the pneu- mogastrie nerve fails to arrest the action of the heart. That the motor fibers of the pneumogastric nerve influencing the heart's ac- tion are derived from the s])inal accessory can be shown by experi- ments like those of Waller," in which after division of the spinal accessory of one side in a living animal, allowing sufficient time to insure disorganization of its fibers, stimulation of the pneumogastric nerve of the corresponding side failed to arrest the action of the heart, the usual effect, however, being observed when the pneumo- gastric nerve was stimulated on the one side in which the s])inal acces- sorv nerve was still intact. It must be mentioned, however, that according to some experimenters, stimulation of the spinal acces- sorv before its union with the pneumogastric nerve, or of its bulbar roots does not inhibit the heart's action and that the method employed l)v AValler just mentioned involves the pulling out of some of the fibers of the pneumogastric nerve. If such be the case it must be admitted that the origin of the inhilMtorv fibers of the vagus are still unknown. The fillers ])assing along the pneumogastric nerve and conveying inhibitory impulses to the heart are usually re- garded as arising from a cardio-inhibitory center (Fig. 364), situ- uated in the medulla oblongata near the nucleus of the hypo-glossal nerve. The cardio-inhibitory center appears to be a tonic center, tiiat is, always acting, division of the pneumogastric nerve being followed as we have seen by quickening of the heart's action. The center seems to be maintained in this state of constant activity re- fiexly through impressions conveyed to it by afferent nerves, since the heart beat is not quickened by division of the pneumogastric if many afferent impulses are cut off, as is the case after division of the spinal cord. It is impossible in the present state of our Icnowledge to offer an entirely satisfactory explanation of the in- hibitory effect of the ]meumogastric nerve upon the heart and of the accompanying fall in blood pressure. A plausible explanation that has been offered is as follows : A stimulus being applied to the central end of the vaso-inhibitory or depressor fibers of the vagus (Fig. 364), the impulse generated, as already mentioned, is not only transmitted to the extracardiac inhibitory centers, whence it is reflected through the cardio-inhibi- tory fibers of the pneumogastric nerve to the heart, slowing or ar- resting the latter, but also which exerts a restraining or inhibitory influence upon the vasomotor center of the medulla, the result of ' Weber, Arcliiv d'Anat. Gen. et cle Physiologie, 1846 ^Gazette Medicate, Sieme serie, Tome xi., p. 420. Pt Paris, 1856. B30 THE NERVOUS SYSTEM. which is that the bh^od pressure sinks through the inhi])ition of the vasomotor nerve fibers supplying the bh>od vessels, and which ema- nate from tliis center. To anticipate a little what will be described more in detail in our consideration of the sympathetic, it maybe men- tioned, with reference to the explanation just offered of the fall in blood pressure, that, under ordinary circumstances, a nervous influ- ence emanates from the vasomotor center in the medulla, and which, being transmitted through the spinal cord, spinal and splanchnic nerves, maintains the l:>lood vessels to which these nerves are dis- tributed in a state of tonic contraction, which keeps up the blood pres- sure. If, however, the vasomotor center of the medulla be paralyzed through the stimulation of the dej^ressor nerve, no such nervous in- fluence being tlien exerted upon the l)lood vessels, the latter dilate, and the blood pressure falls. The result of this is, hoMCver, that the medulla receives less blood, so much passing into the abdominal ves- sels, etc., the consequence of which is, that the extracardiac inhibitory centers of the pneumogastric become less active, and the heart re- sumes its usual activity. That it is to the paralysis of the splanchnic nerve, and consequent dilatation of the great abdominal vessels, that the ftdl in blood pressure induced by stimulation of the depressor nerve is princi])ally due, is shown l)y the fact that if the splanchnic nerves be first divided, and then tlie depressor nerve l)e stimulated, the blood pressure sinks l)ut little more than when the splanchnics are alone divided. That the cardiac branches of the pneumogastric nerves have the same inhil)itory influence upon the heart in man as they have been shown experimentally to have in animals, may be inferred from such pathological ^ cases as those in which the number of heart beats have been knoAvn to be reduced to three or four per minute from the compression exerted upon the nerve by pressing upon glands, tumors, etc. That the inhibitory action of the pneumo- gastric upon the heart can also be exerted in a reflex as well as di- rect manner, is shown by those cases in which there is a sudden stojipage of the heart following blows u})on the epigastrium, es- j)ecially after full meals, draughts of cold water, tlie body being overheated, great emotional excitement, etc., the impression in such cases being transmitted from the general sensory surface to the medulla and thence reflected through the inhibitory fibers of the pneumogastric to the heart. That the ])neumogastric nerve in man contains also special afferent fibers passing from tlie heart as well as efferent ones to it, by which impressions are transmitted to the medulla and thence reflected back to the heart by the inhibitory fibers, appears very probable from what has been shown to be ex- p 'rimentally the case in the rabljit and other animals. Thus, if in the rabbit, the so-called depressor nerve (Fig. 3G4) — that is, the nerve arising partly from the jjueumogastric and partly from the superior laryngeal nerve, be divided and its distal end stimulated, 1 AluUer's Arcliiv, 1841, Heft 3. Jentesche Zeits., 165, s. 384. ACCELERATING FIBERS OF VAGUS. 631 no effect upou the heart is observed ; if, however, the central end of the nerve be stiniuhited, the action of the heart is arrested and the blood ])ressure falls just as if tlie pnenmogastric nerve or the cardio-inhil>itory fibers of the same (corresponding in man to the superior cardiac nerve) be stimulated, the action being evidently a reflex one ; the impression made upon the central end of the de- pressor nerve is transmitted to the medulla and thence reflected back through the cardiac inhibitory fibers of the pneumogastric to the lieart. Extracardiac Accelerator Centers and Nerves. The cardiac fibers of the pneumogastric nerve not only consist of inhibitory or restraining fibers, but also augmentor or acceler- ating ones (Fig. 364). The latter are, however, derived, to a con- siderable extent, also, from fibers, which, descending from the medulla througli the spinal cord, emerge opposite the last cervical and first dorsal ganglia of the sympathetic, which they pass before terminating in the heart. Stimulation of the augmentor nerves not only accelerates the heart's action (Fig. 365), but increases the force of the beat, the Fig. 365. Effect produced by stimulation of peripheral end of the accelerating nerve of the heart. The heart beats quicker. Stimulation begun at 5. (Landois.) output, and the speed of the excitation wave. The accelerating nerves appear to act less powerfully than the inhibitory ones, at least the effect of simultaneous stimulation is inhibition, the amount of the latter being less, however, than when the inhibitory nerves are stimulated alone. Analogy would lead us to suppose that there exists an extracardiac accelerating center, situated probably in the medulla (Fig. 364), which acts upon the heart in a similar manner to that of the extracardiac inhil)itory one. That such a center exists and is tonic in nature, ever acting, appears to be shown by the fact that the pulse rate is lowered by division of the vagi and subsequent bilateral extir]iation of the inferior cer- vical and first thoracic ganglia. It is Mell known that stimulation of the intracardiac nerves by the application of acids to the sur- face of the heart gives rise to reflex actions, such as movements of the limbs, etc. That the impulses are conveyed by the vagi ap- pears to be shown from the fact that such reflexes do not occur if the vagi are divided. The vagi are also supposed by some physi- 632 THE NERVOUS SYSTEM. ologists to convey sensory impnlses to the brain. If snch be the case the sensations cannot be very acnte since in cases like those of the Viscount Montgomery described by Harvey/ where the oppor- tunity was aiforded of feeling directly the heart the individual was entirely unconscious when his heart was touched. Innervation of the Lungs. The pulmonary branches of the pneumogastric nerve are given off as the anterior and posterior branches. The anterior pulmo- nary branches, after sending a few filaments to the trachea, form a plexus wdiich, surrounding the bronchial tubes, is continued to the termination of the latter in the pulmonary air cells. The posterior pulmonary branches, larger and more numerous than the anterior ones, together with fibers derived from the upper three or four thoracic ganglia of the sympathetic, constitute the posterior pul- monary plexus. After giving off fibers to the inferior and pos- terior portion of the trachea, to the muscular tissue and mucous membrane of the middle portion of the oesophagus, to the pos- terior and superior portion of the pericardium, the posterior pul- monary plexus surrounds the bronchial tubes, and, like the anterior one, is continued with the latter to the air cells. The pulmonary branches of the pneumogastric nerve supply the lower part of the trachea, the bronchi, and the lungs, with both sensory and motor fibers, as shown by experiments like those of Longet,^ in which, after division of the pneumogastric nerve in the neck, the mucous membrane of the trachea and bronchus became insensible, while stimulation of its branches caused the muscular fibers of the bron- chus to contract. Respiratory Center and Nerves. The phenomenon of respiration, the principal features of which have been already described, is essentially an involuntary reflex one, involving the nice co5rdination of very complex muscular ac- tion, and depending upon the presence of a respiratory center in relation with afferent and efferent nerves. From the fact that res- piration may continue after removal of all parts of the brain above the level of the bulb, but immediately ceases after the destruction of an area about 5 millimeters wide lying between the nuclei of the pneumogastric and hypo-glossal nerves, in the lower part of the calamus scriptorius it is supposed that the respiratory center, the " u(eud-vital " of Flourens, is situated in the medulla. The res- piratory center appears to consist of two halves symmetrically situated on either side of the middle line, but so intimately con- nected by commissural fibers that the two halves constitute physio- logically but one center. That this is the case is shown by such facts as that the change in the character of the respiration follow- ' Exerc'itationes De (ieneratione Aninmliam, Londini, lO^l, Exer. lii. ^Traite de Pliysiologie, Tome iii., p. 535. AFFERENT BESPIBATORY NERVES. 633 ing division of one pneumogastric nerve, or stimulation of its central end is manifested upon the opposite as well as upon the injured side of the body. On the other hand, if the commissural fibers connecting the two halves of the respiratory center be di- vided, the two halves act separately independently of each other, yet synchronously. Each half of the respiratory center is further supposed by many physiologists to consist physiologically of two centers, inspiratory and expiratory, influencing the inspiratory and expiratory muscles respectively. As the inspiratory center increases the rate of respiration and the expiratory center dimin- ishes it, the inspiratory center is regarded as being acceleratory the expiratory as inhibitory, in nature. Both centers, however, arrest the respiratory movements in the inspiratory and expira- tory phases respectively, if the stimulus be sufficiently power- ful. Of the two centers the accelerating center appears to be the more irrital)le, hence if both centers be stimulated simultane- ously, the effect will be accelerating. While there is no doubt that the respiratory movements are due to impulses arising in the respiratory center and transmitted periodically by efferent nerves to the respiratory muscles, difference of opinion still prevails as to what constitutes exactly the stimulus exciting the respiratory center to action. From the fact that rhythmical respiratory movements still persist even with removal of all parts of the brain above the bulb and after division of the vagi and glosso-pharyngeal nerves, of the spinal cord in the lower cervical region, and posterior roots, it is obvious that the respiratory center is susceptible of being ex- cited by other stimuli than impulses transmitted by afferent nerves. In such exceptional cases and probably in all cases, the stimulus exciting primarily the respiratory center appears to be the blood, ^ the respiratory rhythm being, however, much modified by the influ- ence exerted by the will, the emotions, and various afferent impulses. That the respiratory movements are greatly influenced, if not en- tirely due to the stimulus exerted by the blood is shown by the fact that the number of respirations are increased or diminished, and the rhythm modified in proportion as the blood is freely supplied or cut off, and according to its temperature, and the relative amounts of oxygen or carbon dioxide and products of muscular activity that it contains. That we can voluntarily modify to some extent, at least, our respiratory movements and that the latter are greatly affected by the emotions is familiar to all. Afferent Respiratory Nerves. The afferent respiratory nerves are the pneumogastric and its laryngeal branches, the glosso-pharyngeal, the trigeminus, and the cutaneous nerves generally. AVhile division of the pneumogastric nerve on one side may not afl'ect the respiration, as a general rule iLoewy, Pfluger's Aroliiv, Band xliii., 1889, s. 245, 281. (334 THE NERVOUS SYSTEM. the respiratory movements become slower, deeper, and longer ; these effects being, however, only transient, the respiration soon becomes normal again. If the central end of the divided pnenmogastric be stimulated, the effects following will depend upon the nature of the Fig. 36e a/ Tracing of the respiratory movemeuts of the cat. a. Before, b. After division of both vagi. stimulus. Thus, chemical stimuli excite expiration, mechanical stimuli inspiration, electrical stimuli expiration or inspiration, or both, according to the strength of the current. After section of both pnenmogastric nerves, the respiratory movements become slower, deeper, more powerful (Fig. '](U), 6), the amount of air inspired being, however, the Fig. 367. same, expiration active, with a pause following expiration. Ex])i ration appears to be more readily produced by weak elec- trical stimuli than inspiration, a weak current when applied to the central end of the pnenmo- gastric nerve, both nerves hav- ing been divided, exciting expiration, a strong current in- spiration. tSuch facts as those just men- tioned apj)ear to show that the pneumogastric nerve contains two sets of afferent fibers, one set (CX, Fig. 367) conveying impulses that excite the inspira- tory center [INS), the other set (CX'), conveying impulses that excite the expiratory center (EXP), both sets of fibers origi- nating in the lungs at the pe- riphery of the pneumogastric nerves. From the fact that in- fllation of the lungs appears to cause expiration and collapse inspiration, and that the effects of opening the j)l('Mral cavity or of occluding the bronchus on one side are the same as the following division of one pneumogastric nerve, it is usually held at the present day that the mechanical Schema of the chief respiratory nerves. INS, Inspiratory, and EXP, Expiratory center — motor nerves are in smooth lines. Expiratory motor nerves to abdominal muscles, AB ; to muscles of back, J)(>. Ins])iratory motor nerves. PH. Phrenic to diaphragm, I). INT. Inter- costal nerves. liL. Kccurrent laryngeal. f'X. Pulmonary fibers of vagus that excite inspira- tory center. CX'. Pulmonary fibers that excite expiratory center. CX". I'ibcis ot sii|). laryn- geal thatexcite expiratory (■enter. J.XIf. Fibers of sup. laryngeal that inhiltil the iiisjiiratory center. (Lani)OIS.) COUGH CENTER. 635 Fig. 368. conditions existinf^ at the end of inspiration and expiration consti- tute the stimuli to the same, tlie impulses then generated l)eing transmitted h\ the afferent fibers to the expiratory and inspiratory centers respectively. It should be mentioned, however, that ac- cording to some physiologists at the end of expiration the accumu- lation of carbon dioxide in the air cells excites the afferent fibers that convey impulses to the inspiratory center and so causes in- spiration. It is doubtful, however, whether the carbon dicjxide present in the lungs at the end of expiration exists in sufficient quantity to ex- cite the fibers conveying impulses to the inspiratory center. That the pneumogastric nerves are essential to the proper performance of respiration is shown by the fact that death usually takes place after their division in an animal within from one to six days — re- covery taking place occasionally however through reunion of the divided ends. Stimulation of the central ends of the superior and inferior laryngeal branches of the pneumogastric nerve diminishes or even arrests altogether respira- tion in the expiratory phase. The fibers of the superior laryngeal nerve are exquisitely sensitive, the functional significance of which is well illustrated by those cases in which foreign bodies entering the larynx during deglutition not (jnly arrest inspiration but excite expi- ration and are coughed out. The impulses generated by the pres- ence of foreign bodies in the larynx are conveyed to "a cough center" which appears to be situ- ated in the medulla (Fig. 3(58) whence efferent impulses are transmitted to the expiratory muscles. It may be mentioned in this connection that the cough center receives impulses not only from the larynx, but also from the nose, ear, pharynx, cesophagus, and stomach. The fibers of the glosso -pharyngeal nerve also arrest inspiration, the respiratory center being inhibited through impulses generated by the passage of food during deglutition. That breathing should be suspended during an interval. equal to about that of the three preceding respirations is obviously of great advantage, otherwise the i< Abdom. Muscles J Schema of the aflferent nerves through which coughing may be excited reflexly. The effe- rent nerves are dotted. (Laxdois.) 630 THE NERVOUS SYSTEM. solid and liquid food would be constantly sucked into the larynx when swallowed. Respiration may also be arrested through excitation of the sen- sory fibers of the olfiictory, of the nasal branch of the fifth pair, of the laryngeal and pulmonary branches of the pncumogastric, of the splanchnic, and under certain circumstances of the sciatic and sen- sory nerves in general, though the effect of stimulation of the latter is usually to excite inspiration. On the other hand, stimulation of the cutaneous nerves increases primarily the number and depth of the respirations, though finally arresting respiration in the expira- tory phase. Every one is familiar with the fact that the dashing of cold water in the face, or the first plunge into a cold bath, and the application of a pungent vapor to the nostrils, cause involuntary respiratory efforts. It is well known, also, that the first inspiratory efforts of the newborn child are usually made in response to the stimulation of the cool external air coming in contact with the face, and that impressions on the general surface, such as a slap on the face or upon the buttocks, will frequently excite the child to breathe when otherwise it would not do so. It would appear, therefore, that im- pressions made upon the general sensory surface when transmitted to the medulla will cause, through stimulation of the respiratory center reflexly, inspiratory movements, as well as stimuli trans- mitted through the pneumogastrics. Efferent Respiratory Nerves. The efferent nerves involved in easy breathing are the phrenics, spinal, and pncumogastric nerves. The importance of the phrenic nerves in respiration is shown by the fact tliat after their division, the diaphragm, being paralyzed, is so relaxed, that it is drawn up into the thorax with each ins})iration, and which interferes so with the proper expansion of the lungs that death follows from asphyxia within a few hours. On the other hand, if the spinal cord be divided at the level of the fifth cervical nerve, that is below the origin of the roots of the phrenics, though diaphragmatic breathing continues, costal respiration ceases on account of tlie impulses that pass normally from the respiratory center to the intercostal muscles being then cut off. If the cord be divided however above the origin of the phrenic nerves both diaphragmatic and costal breathing soon cease though respiratory movements of the larynx, face, mouth, and neck may persist. The opening of the glottis, which we have al- ready described as accompanying synchronously inspiration, is due to impulses transmitted from the respiratory center by the fibers of the laryngeal branches of the pncumogastric nerves, particularly by those of the inferior laryngeal. If the pncumogastric be divided above the origin of its laryngeal branches tlirough the paralysis of the muscles of the larynx the vocal membranes become flaccid, the glottis is narrowed, little or no air enters, and respiration soon EFFERENT RESPIRA TOR Y NER VES. 637 ceases. In forced breathing the spinal nerves innervating the extraordinary muscles of respiration, the facial hypo-glossal and spinal accessory nerves, are involved, as well as the nerves just mentioned. The respiratory center is not only connected with the periphery by afferent and efferent nerves but also with the cerebral cortex, as shown by the fact already mentioned that we can modify voluntarily our breathing, at least to some extent. By many physiologists respiratory centers are said to exist in the optic thalami, corpora quadrigemina, pons Varolii, and other situations, as well as in the medulla. If such centers do exist, which is ex- tremely doubtful, they can exert only a secondary influence upon respiration. The cesophageal brandies of the })iu'umogastric given off both above and below the pulmonary ones unite to form the cesophageal plexus, which supplies the muscular tissue and the mucous mem- brane of the lower third of the oesophagus. These branches con- tain both sensory and motor fibers, the latter being probably more numerous, since the mucous membrane cannot be said to be acutely sensitive to heat, cold, or strong irritants. That the motor fibers supplying the oesophagus are derived from the pneumogastric nerve can be shown by experiments like those of Bouchardat and Sandras, ^ Chauveau, ^ Longet, ^ Bernard, * in which, after division of the pneumogastric nerve, the oesophagus was par- alyzed and distended by the food Avhich the animal vainly endeav- ored to swallow. It is still a question, however, from what nerve the motor fibers of the lower third of the oesophagus are derived, since, according to Chauveau, stimulation of the bulbar roots of the spinal accessory, the most prol)able source, do not excite con- tractions of the oesophagus. The abdominal l)ranches of the pneu- mogastric nerve differ somewhat in their course, according as they are distributed to the two sides. That of the left side, situated an- teriorly to the cardiac opening of the stomach, immediately after passing with the tesophagus into the abdominal cavity, gives off numerous branches, some of which are distributed to the muscular walls and mucous membrane of the stomach, while others pass, in company with the sympathetic, along the course of the portal vein to the liver. That of the right side, situated posteriorly, passes through the oesophageal opening of the diaphragm, and, after send- ing a few filaments to the muscular coat and the mucous membrane of the stomach, is distributed to the liver, s])leen, kidneys, supra- renal in com|)any with the sympathetic capsules, the small and large intestine. The gastric branches of the pneumogastric nerves con- sist of motor, secretory, and probably of afferent libers as well. There can be no doubt, also, that stimulation of the pneumogastric nerves causes the stomach to contract, and that the movements of ' Comptes rendus, Tome xxiv., p. 59. Paris, 1847. ^Journal de la jdiysiologie, Tome v., p. 3-42. Paris, 1862. ''Traite de Physioloifie, Tome iii., p. 547. Paris, 1869. *Systeme Nerveux, Tome ii., p. 422. Paris, 1858. 638 THE NERVOUS SYSTEM. the stomach may to a certain extent at least, be reestablished by stimulation of the peripheral extremities of the divided nerves. In- asmuch, however, as several seconds elapse between the application of the stimulus and the contraction, it is probable that the mus- cular contractions of the stomach induced by the stimulation of the pneumoeing due probably to stimuli emanating from Auerbach's plexus, situated betAveen the muscular coats of the intestine and Meissner's plexus in the submucous coat. That the vagi contain secretory fibers is shown by the fact that direct stimulation of the nerves, proper precautions l)eing taken, gives rise to a marked secretion of gastric juice. That the secretion can be also excited indirectly reflexly by afferent impulses trans- mitted from the periphery to the medulla and thence by the secre- tory fibers of the vagi to the stomach is shown by the following considerations. In cases of gastric fistuke in man and animals, it has often been noticed that the placing of food in the mouth or even the sight of food, excited a copious secretion of gastric juice. This was also observed in experiments made upon dogs in which the food, after being taken into the mouth, instead of l:)cing swallowed and entering the stomach, passed by a fistulary opening in the oesophagus out of the body, the food constituting therefore only a " fictitious meal.'" That gastric digestion is profoundly influenced by the pneumogas- tric nerves is further shown by the fact that if they be divided during full digestion in a liying animal in which a gastric fistula has been established, so that the interior of the stomach can be examined, the muscular contractions will be observed^ to cease instantly, the nnicous membrane to become pale and flaccid, the secretion of the gastric juice to l)e arrested, and the organ to have become insensible. It must be mentioned, however, that even when l)oth pneumo- ' Puwlow u. Schuniowii Simiiiiowskaja, Du Bois Keymond Arcliiv, 18'jr), s. 53. 2 Bernard, op. cit. , Tome ii. , p. 422. ABDOMINAL FIBERS OF VAGUS. 639 gastric nerves are divided, if the animal survive the operation, in a day or two digestion may be partly reestablished ^ if the food be finely divided and carefully introduced into the stomach. It is quite possible that the impression due to the presence of food in the stomach and intestines, after reaching the plexus of Meissner, situ- ated in the submucous tissue, and the plexus of Auerbach, lying between the muscular coats is at once reflected back to the stomach without being transmitted to the medulla. Whether the reflex nervous mechanism involved in gastric digestion be such as just mentioned or not, there can be no doubt that digestion in man is very much influenced by the nervous system. Every one is famil- iar with the fact that digestion may be at once stopped by nervous excitement, such as a piece of bad news, etc.; that there exists an intimate sympathy between the brain and the stomach at all times, and it is diliicult to understand by what avenues, other than the abdominal branches of the pneumogastric nerve, impressions are carried to and from these organs. That the abdominal branches of the pneumogastric influence also absorption from the stomach and in- testinal digestion may be inferred from the foct that, after division of the pneumogastric nerves, the absorption of poisons is retarded, if not prevented, and that the most powerful cathartics fail to produce their characteristic purgative effects,^ just as, under similar circumstances, digitalis fails to diminish the action of the heart.^ The branches of the pneumogastric nerves supplying the small and large intestine appear to contain motor fibers, at least stimulation of the pneumograstic nerves causes contraction of the intestine, the stimulus acting, however, as in the case of the stomach, indirectly through the plexuses of Auerbach and Meissner. According to some observers the intestinal nerves contain also inhibitory fibers. It has not yet been established, however, whether the inhibitory fibers pass to the intestine by the pneumogastric or the sympathetic, or by both nerves. In all prol)ability the pneumogastric contains also fibers which excite the intestinal secretion, since it has been es- tablished that stimulation of the pneumogastric after a long latent period causes a flow of the secretion of the pancreas. It is said that division of the pneumogastric nerve through its abdominal branches produces, also, congestion of the liver, renders the bile Avatery, and arrests its glycogenic function. The production of sugar is, how- ever, exaggerated by stimulation of the central ends of the divided nerves. The action is a reflex one, stimulation of the peripheral ends having no effect in this respect. The efferent impulses appear to be transmitted from tlie center, in the medulla, by the sympathetic, rather than by tlie pneumogastric nerve, since division of the latter between the lungs and liver does not affect the production of sugar. ^ ScliiflfJ Lecons sur la physiologie de la digestion, Tome ii., o89. Florence, 1867. Longet, op. cit.. Tome iii., p. 549. 2Brodie,~Phil. Trans., Vol. xiv., p. 104. London, 1814. Eeid, Phys. Anat. and Path. Eesearches. London, 1848. "Wood, American Journal of the Med. Sciences, Vol. Ix., p. 75. Phila., 1870. ^Traube, Gesammelte Beitriige zur Path. u. Physiologie, Bd. i., s. 190. Berlin. 040 THE NERVOUS SYSTEM. The Eleventh Nerve. The spinal accessory or the eleventh nerve (Fig. 355), consisting of from 2000 to 2500 fibers arises by two distinct sets of roots — upper and lower. The upper root or the bulbar portion, originat- ing in a nucleus lying close to the central canal, and continuous with the nucleus of the pneumogastric nerve (Fig. 337, XI), emerges from the side of the medulla below the latter nerve. The lower roots or the spinal portion, originating in the anterior cornu of the cord, curve backward, and, passing through the gray sub- stance and lateral columns of the cord, emerge from the latter as six or eight filaments between the anterior and posterior roots of the first and seventh cervical nerves inclusive. The spinal accessory nerve so formed enters the cranial cavity by the foramen magnum, and leaves the latter by the jugular foramen in company with the pneumogastric and glosso-pharyngeal, and the jugular vein. Dur- ing its course the spinal accessory receives from or gives off some filaments to adjacent nerves. Frequently, as it enters the cranial cavity, it receives filaments from the posterior roots of the first two cervical nerves, to which its recurrent sensibility is due ; occasion- ally also it gives off a filament to the superior ganglion or ganglion of the root of the pneumogastric. It also receives filaments from the anterior branches of the second, third, and fourth cervical nerves. After emerging from the jugular foramen the spinal acces- sory gives off also two branches — internal and external — meriting special notice. The internal branch, consisting principally, if not entirely, of the fibers derived from the medulla, passes to the pneu- mogastric, subdividing as it joins the latter into two small branches, the first of which constitutes a part of the pharyngeal branch of the pneumogastric as already observed ; the second, however, be- comes so intimately united with the pneumogastric nerve that its final distribution cannot be made out by dissection alone, experi- ment only indicating its functional significance, as we shall see pres- ently. The external branch of the spinal accessory, larger than the internal, and derived principally from the fibers of the spinal cord, pass through the posterior portion of the upper third of the sterno-cleido-mastoid muscle, receiving filaments in its course througli the muscle from the second and third cervical nerves, to be finally distributed to the trapezius muscle. That the spinal accessory nerve is essentially motor in function, supplying the muscles just mentioned, can l)e demonstrated experi- mentally by cutting through the occipito-atloid ligaments and stim- ulating the roots of the nerve within the spinal canal by electricity. If, liowever, the filaments arising from the medulla only be stimu- lated contractions of the muscles of the larynx and i)harynx alone ensue, no movements of the sterno-cleido-mastoid or trapezius be- ing observed. On the other hand, if the filaments arising from the spinal cord only be stimulated then the sterno-cleido-mastoid and THE ELEVENTH yERVE. <341 trapezius muscles aloue contract, the laryugeal and pharyngeal mus- cles remaining cpiiescent. Xot only does this striking experiment contirm what the distribution of the spinal accessory would lead us to suppose as to its general motor functions, but it also clearly shows that the muscles of the larynx must be supplied by the spinal acces- c;orv — that is, that the fibers of the recurrent laryngeal nerves sup- plying the muscles of the larynx, except the crico-thyroid, are de- rived not from the pneumogastric but from the spinal accessory nerve/ The spinal accessory nerve appears to be endowed also with a certain amount of dii-ect, apart from the recurrent, sensi- bility already referred to. Whatever sensibility it does possess is, however, due undoubtedly to those filaments derived from the pneumogastric and cervical nerves. In speaking of the functions of the inferior laryngeal branches of the pneumogastric nerve it was mentioned that those nerves consisted of two kinds of fibers, one set influencing the respiratory action of the glottis, another regulating phonation, and that the latter were in reality derived from the internal branch of the spinal accessory. It only remains, therefore, to descril^e the manner in which this can be demonstrated, since the fibers of the inferior laryngeal nerves influencing phona- tion cannot be traced by dissection back to the spinal accessory. Bischoff was the first to demonstrate the influence exerted by the internal branch of the spinal accessory nerve upon the production of the voice by opening in a goat the spinal canal through the occipito-atloid space, and dividing all its roots on both sides, the result being entire extinction of the voice, whatever sound was emitted after the experiment being one which in no wise could be called voice.^ As this method of procedure was however unsuc- cessful in the six preceding experiments, five of which were per- formed upon dogs and one upon the goat, even in the hands of such a skilful anatomist and physiologist as Prof. Bischolf, that intro- duced later and habitually practiced by Bernard is a far more sat- isfactory one. This consists in following by dissection the external or muscular branch of the spinal accessory up to the point where it emerges from the jugular foramen, and where it separates from the internal branch, and then, after seizing the combined trunk between the blades of a forceps, by steady and continuous traction to extract the whole nerve with both its medullary and spinal roots entire ; or to remove the medullary portion with the internal branch aloue, leaving the spinal portion with the external branch intact, in which case the voice is entirely lost ; or to remove the spinal portion with the external branch, leaving the medullary portion with the internal branch intact, in which case the voice is unaffected or in some cases even rendered clearer.^ It is an interesting fact that in a chimpan- zee dissected by Vrolik the internal branch of the spinal accessory 'Bernard, Systeme Xerveux, Tome ii., p. 296. 2 "Qui neutiquam vox appellari potiiit." Bisclioff', Xervi Aeees-sorii Williiiii Anatomia et Physiologie, p. 94. Darrastadii, 1832. ^Bernard, op. cit., Tome ii., p. 29(5. 41 642 THE NEE rOUS SYSTEM. was found passing directly to the larynx instead of to the pueumo- gastric. The usual disposition in this anthropoid appears, however, to be the same as obtains in man, at least such was found to be the case in three individuals dissected by the author. After what has been said of the influence exerted by the pharyngeal branches of the glosso-pharyngeal and of the pharyngeal and inferior laryngeal branches of the pneumogastric in deglutition, and of the inhibitory effects upon the heart by the cardiac fibers of the latter nerve, it is only necessary here to mention again that the motor fibers involved in the perfoi'mance of the above functions are derived from the in- ternal branch of the spinal accessory; at least partly so in the case of deglutition, and entirely so in that of the inhibition of the heart. As to the function of the external or muscular branch of the spinal accessory, it would appear that its action is to excite contraction of the sterno-cleido-mastoid and trapezius muscles, synchronously with the action exerted by the internal branch upon the laryngeal and pharyngeal muscles, the harmonious action of the muscles so brought about being of advantage under certain circumstances. Thus, in prolonged vocal efforts, as in singing, for example, in which, as we shall see, the vocal membranes are put on the stretch, the upper portion of the chest is, at the same time, fixed through the action upon the shoulders, to a certain extent at least, of the sterno-cleido-mastoid and trapezius muscles, and in this way the expulsion of air through the glottis, and upon which the singing depends, can be well regulated. In the same manner, when one makes a muscular effort, the glottis is closed at the same moment that the chest is fixed, respiration being temporarily arrested. The same synchronism in the action of the external and internal branches of the spinal accessory obtain, therefore, in this instance, as in the former. That the external branches of the spinal accessory exert some influence upon the respiratory movement is well seen in ani- mals in which the branches on both sides have been divided, such suffering from shortness of breath after any very great muscular effort, and presenting, also, irregularity in the movements of the anterior extremities, the shortness of breath being apparently due to the want of synchronous action of the sterno-cleido-mastoid and trapezius muscles. The Twelfth Nerve. The twelfth nerve, the hypo-glossal or sublingual, consisting of from 4500 to 5000 fibers, arises from a long column of nerve cells, the lower part of which lies in front of the central canal on each side, the upper part forming a prominence upon the floor of the fourth ventricle (Fig. 337, XII ). Passing thence through the inner part of the olivary body, the fibers emerge as eleven or twelve filaments from the furrow between the anterior pyramid and the olivary body (Fig. 338), which, passing as two distinct bundles through two distinct opanings in the dura mater into the anterior THE TWELFTH XERVE. 643 cond}'loid foramen, unite into a single trunk as they emerge from the cranial cavity. Occasionally, the hypo-glossal nerve, as it passes through the foramen, receives a filament having a ganglion upon it, arising from the postero-lateral portion of the medulla. This gangliouated filament, or posterior root, so to speak, of the hypo- glossal nerve, while exceptionally present in man, is, however, found normally in the dog, cat, rabbit, hog, horse, and calf, and is sensory in function in these animals, the anterior portion of the common trunk corresponding to the hypo-glossal in man, being Fig. 3(59. Distribution of tht suljlingiial ne^^e 1 Root of the tifth nerve. 2. Ganglion of Gasser. 3,4, 5, 6, 7, 9, 10, 12. 15ranchc> and anabtomo^es of the fifth nerve. 11. Submaxillary ganglion. 13. Anterior belly of the digastric mu--cle 1-t '^ettion of the mylo-hyoid muscle. 15. Glosso-pharyn- geal nerve. 16. L+anguon oi Anaerscn. i7. in. Brancties of the glosso-pharyngeal nerve. 19,19. Pneumogastric. 20, 21. Ganglia of the pneumogastric. 22, 22. Superior laryngeal branch of the pneumogastric. 23. Spinal accessory nerve. 24. Sublingual nerve. 2.5. Descendens noni. 26. Thyro-hyoid branch. 27. Terminal branches. 28. Two branches, one to the genio-hyo-glossus, and the other to the genio-hyoid muscle. (Sappey.) motor. After the hypo-glossal passes out of the cranial cavity it gives oif filaments to the sympathetic, to the pneumogastric, to the upper two cervical nerves, and to the lingual branch of the fifth. Descending behind the pneumogastric nerve (Fig. 369) it curves downward and forward to the outer side of the latter, between the internal carotid artery and the jugular vein, and penetrates the genio-hyo-glossal muscle, which it supplies, as also the hyo-glossus, linffualis, sxenio-hvoid, and stvlo-irlossus muscles. 644 THE NERVOUS SYSTEM. The hypo-glossal gives off, also, an important branch, the descen- dens noni, but which, according to the classification of the nerves usually adopted, would be more correctly called the descending^ branch of the twelfth, supplying the sterno-thyroid, sterno-hyoid^ and omo-hyoid muscles, the thyro-hyoid muscle being supplied by the branch of the same name. From the distribution of the hypo- glossal nerve it might naturally be inferred that it is essentially motor in function, any sensibility that it possesses being due to the filaments communicating with the cervical and pneumogastric nerves, and the lingual branch of the fifth. That such is the case is shown by the effect of division of the hypo-glossal in a living animal, and of its paralysis in man. Under such circumstances, through paralysis of the tongue, though the tactile and gustatory senses are not affected, mastication is rendered very difficult, if not impossible, while, through paralysis of the muscles depressing the larynx and hyoid bone, deglutition is made difficult ; in man the power of articulation is lost as well. This is well seen in cases of g-losso- labio-laryngeal paralysis, in which the nuclei of origin in the medulla of the hypo-glossal, as well as the facial, spinal accessory, and glosso-pharyngeal nerves are affected by disease, which involves a gradual and progressive paralysis of the tongue, palate, lips, and laryngeal muscles, rendering articulation, and ultimately deglu- tition, impossible. In cases of hemiplegia the hypo-glossal nerve is usually more or less involved. In such eases the patient protrudes the tongue, the point being deviated to the side atfected with the paralysis, owing^ to the unopposed action of the genio-hyo-glossus muscle of the sound side. That the hypo-glossal nerve is a motor nerve — the motor nerve of the tongue, etc. — is further shown by the effect of stimu- lating the peripheral end of the divided nerve, the tongue, and the muscles to Avhich the nerve is distributed at once contracting. The hypo-glossal nerve, together with the small or motor root of the fifth and the facial nerves, constitutes the efferent fibers, by Avhich the reflex action involved in mastication is accomplished, the lingual branch of the fifth and the glosso-pharyngeal nerves, containing the afferent fibers, the center being situated in the medulla. Having described the distribution and function of the ten ])airs of cranio-mednllary nerves, and having seen that they arise from gray nuclei in the medulla oblongata, it is evident that the medulla consists, not only as we have seen, of fibers passing from the cord to the ganglion of the base of the brain, but may be regarded, also^ as being composed of so many distinct reflex centers, of which the cranio-medunary and spinal nerves constitute tlie afl'erent and effe- rent fibers; the existence in the mcdulhi of about fourteen such cen- ters, probably more, has been estaV>lishe(l. First. That for closing^ the eyelids, the efferent fibers being contained in the optic nerve, and the l)ranches of the fiftli distributed to the conjunctiva and to the skin of the lids, the efl'erent fil)crs in the facial. Second. The REFLEX CEXTEBS OF MEDULLA. 645 center for sneezino-, tlie afferent fibers, being in the olfactory and the fifth nerve, the efferent in the spinal nerves inflneneing expira- tion. Third. The center for conghing, the afferent fillers rising in the ])nenniogastric, the efterent being the same as those last men- tioned. Fourth. The respiratory center, or nrjeud-vital of Flourens. Fifth. The masticatory center. Sixth. The center of insaliva- tion. Seventh, The center of deglutition. Eighth. The cardio- inhibitory centers, the afferent and efferent fibers of which have already been referred to. Ninth. The center for sucking, the af- ferent fibers of which are in the fifth and glosso-pharyngeal nerves, the efferent the facial supplying the lips*. Tenth. The center influencing the act of vomiting, the afferent fibers being in the pneu- mogastric, the efferent in the nerves of expiration. Eleventh. The center of speech — that is, with r(>ference to the movements of the lips, tongue, and larynx. Twelfth. The vasomotor center. Thir- teenth. The center inhibiting the reflex centers of the spinal cord. The medulla oblongata being the seat of the centers receiving the afferent fibers and giving off the efferent ones involved in the per- formance of mastication, insalivation, deglutition, respiration, circu- lation, etc., is, therefore, the great coordinating center of the reflex actions essential to the maintenance of life. Even if all the parts of the brain above the medulla be removed in a living animal, or be undeveloped, as in anencephalous infants, life may yet be main- tained by artificial means, since, if food be introduced into the mouth it ^vill be swallowed, the respiratory and circulatory move- ments will go on in the usual rhythmical manner, the animal or infant will react to impressions made upon the general sensory sur- face, withdrawing its limbs, etc., if pulled or pinched, may even utter a cry, as if in pain, and yet such an animal or human being cannot be said to be really a sentient, still less an intelligent, being, but merely a nutritive reflex mechanism. CHAPTER XXXIII. THE NEEVOUS SYSTE'M.— {Continued.) THE PONS VAROLII. CRURI CEREBRI. CORPORA STRIATA. THALAMI OPTICI. CORPORA aUADRIGEMINA. CEREBELLUM. Whether reflex action of the spinal cord or medulla be accom- panied or not in the lower animals with sensation, volition, con- sciousness, there can be no doubt that the physical seat of what we call feeling, thinking, etc., in man is situated in some part of the brain above the level of the medulla oblongata, since in the absence of such parts one neither feels, thinks, nor wills. Pons Varolii. Just as we have seen that the spinal cord and medulla consist of nervous centers as well as of fibers passing through them to the ganglia at the base of the brain, so the pons Varolii or mesencephalon (Fig. 370, 1) may be regarded as consisting, not only of ascending sensory Fig. 370. ^0 •■■X\ t It f /,.< "^ ^ S^s Diagram of liiimau hrain in transverse vertical section. 1. Tuber annulare. 2,2. Crura cere- bral. 3, 3. Internal capsule. 4, 4. Corona radiata. 5, C. Cerebral ganglia. 7. Corpus callosum. (D ALTON.) and descending motor fibers connecting the cortex Avith the cord^ and of bridging fibers connecting the lateral lobes of the cerebellum — hence its name — but of gray matter performing the functions of a distinct nerv'ous center or centers. That the gray matter or tuber annulare (Fig. 370, 1) is the essential part of the pons CEUBA CE REBEL 647 Varolii is shown by the fact of the bridtiino; fibers of the pons being absent in animals in Avhich the lateral lobes of the cerebellnm are undeveloped as in birds. That tlie tuber annulare, or vesicular matter of the pons Varolii, is that part of the encephalon in the lower mammals in Avhich consciousness first awakens in response to impressions transmitted by the spinal and cranial nerves from the external world appears probable from experiments, such as tliose of Longet,^ Yulpian,- etc., in which, after removal of the whole en- cephalon except the pons, medulla, and cerebellum, sensibility to pain still persisted, the cries emitted by an animal so mutilated not being simply reflex in character, such as are heard in an animal possessing only the medulla already referred to, but as indicating the perception of painful impressions. AVhile it is true that the appreciation of painful and other impressions is not acute, but ob- scure, nevertheless that such an animal is conscious to a certain extent at least, there appears to be little doubt, their condition being apparently similar to patients undergoing a severe surgical oper- ation, but imperfectly under the. influence of an antesthetic, and who, while undoubtedly suffering ])ain at the time, have no recol- lection of it, the impressions due to the operation not being con- veyed to the cerebral hemispheres, and therefore not memorized. Even admitting however that the physical seat of incipient con- sciousness lies, in the lower mammals, in the pons, there is little reason to suppose that the same part of the encephalon in man pos- sesses such a function. Lesions of the pons, at least in man, ap- pear to show that its function is rather of a commissural than of a psychical character. Crura Cerebri. It has alreadv been mentioned that the motor tract beQ-innino- in the cortex of one hemisphere is continued downward through the anterior or inferior portion of the cms cerebri (crusta) to the decus- sating fibers of the medulla, and thence to the antero-lateral columns of the opposite side of the cord ; that the sensory tract beginning on the opposite side of the body crosses the middle line, is continued up- ward through the medulla and posterior or superior portion of the crus cerebri (tegmentum) to terminate in the cortex of the same side. Such being the case, as might be anticipated if botli crura (Fig. 371, 2, 2) are completely divided, sensation and voluntary movement are en- tirely annihilated throughout the body, division of one of the crura involving paralysis of sensation and motion on the opposite side of the body only. The constant tendency to turn toward the side op- posite that of the lesion, the " evolution du manege " of Louget, observed when one cms is imperfectly divided appears to be due to the balance of the muscular action being destroyed through the weakening of the sensori motor apparatus of the opposite side. Division of the crus cerebri involves also paralysis of the oculo- ' Physiologic, Tome iii., p. 306. ^ gyateme Xerveux, p. 542. Paris, 1866. (348 THE NERVOUS SYSTEM. motorius of the same side, and partial paralysis of the facial nerve of the opposite side, and is also followed by contraction of the arteries, a rise in blood pressure, and the loss of power to influence voluntarily the action of the sphincter ani, and the constrictor urethrse. In addition to the motor and sensory fibers just referred to, the crura cerebri contain also fibers passing from the gray mat- ter of the medulla and ])ons to the hemispheres, and of fibers pass- ing forward and backward from the locus niger, or the gray matter separating the crusta from the tegmentum, to the cerebellum, and of fibers passing from the corpora quadrigemina to the cerebellum. The functions of these fibers, so far as known, appear to be com- missural in character. Corpora Striata and Thalami Optici. If the hemispheres of the brain be removed to the level of the corpus callosum, or the bridge of white substance uniting the cere- bral hemispheres, and the fi)rmer be divided and turned aside, the lateral ventricles will be exposed — that is, the two cavities having for their roof the corpus callosum, their floor the fornix, their inner walls the septum lucidum with its enclosed fifth ven- tricle, their outer walls the corpora striata. Each corpus striatum, so called from presenting a striated ap- pearance on section, projects as a half pyriform prominence into the lateral ventricle, constituting, as just said, its outer wall, the largest anterior ])ortion being known as the head ; the narrowest posterior portion the tail, the latter curving backward to the outer side of the thalamus 0])ticus. Each corpus striatum (Fig. 371) consists of two parts, the in- traventricular, or nucleus caudatus (G), and the extraventricular, or nucleus lenticulares (7). The latter consists of three parts separated by white matter, the striae medullares ; the two inner central parts being called the globus pallidus, on account of their pale color, the outer external part the putamen. The caudate and lenticular nuclei are separated by the internal capsule (9) or the diverging fibers of the cms cerebri, to which the corpus striatum owes its name, the external capsule (10) with the clas- trum (11) lying to the outer side of the nucleus lenticularis and close to the insula or island of Reil (5). If now the fornix or floor of the lateral ventricle be removed, a narrow triangular cavity will be exposed, the third ventricle, communicating, on the one hand, with the lateral ventricles by the foramina of jNIonro, and on the other with the fourth ventricle by the iter, the latter passing under the corpora quadrigemina, to be mentioned presently. The floor of the third ventricle is formed from l)eforc backward by the optic conmiissure, iufundibulum, mammillary eminences, posterior l)erforated space, and cerebral crura ; its walls by the thalami optici, situated on the inner side of the crura cerebri, and separated from the corpora striata by the internal capsule and taniia semicircularis. CORPORA SlllIATA ASD THALAMI OFTICI. 049 Each tlialamus opticus consists internally of white matter, ex- ternally of both white and gray matter. The most prominent parts of the thalamus opticus anteriorly, are known as its tuber- cles, posteriorly as the pulvinar. Beneath the latter are situated the corpora geniculata from which arise partially the optic tracts. Fig. 371. Horizontal section of the hemispheres at the level of the cerebral ganglia. 1. Great longitudinal fissure, between frontallobes. 2. Great longitudinal fissure, between occipital lobes. 3. ABterior part of corpus callosum. 4. Fissure of Sylvius. .5. Convolutions of the insula. 6. Caudate nucleus of corpus striatum. 7. Lenticular nucleus of corpus striatum. S. Optic thalamus. 9. Internal ca])sule. 10. External capsule. 11. Claustrum. (Daltox.) One of the best established facts in human or animal cerebral pathology is that a destructive lesion of the corpus striatum, whether produced by disease or experimentally, is followed by a paralysis of motion of the opposite side of the body, sensation re- mained unimpaired. It is true that in some exceptional cases the paralysis is on the same side of the body, but there is no question in such cases as to the paralysis due to the lesion of the corpus striatum being that of motion. It has also been shown that electrical stimulation of the corpus 650 THE NERVOUS SYSTEM. striatum in a living animal, monkeys, clogs, cats, etc., causes a gen- eral unilateral contraction of the muscles of the opposite side of the body, the latter being thrown into a condition of pleurostho- toniis, in Avhich it is bent to the opposite side, the flexor muscles being contracted apparently more than the extensor ones. It is well known also, that in the cetacea — the whale, dolphin — the ele- phant, etc., very muscular animals, the corpora striata are not only absolutely but relatively large and well developed. The facts of pathology, experiment, and comparative anatomy, confirm, there- fore, the view based upon their anatomy that the function of the corpora striata is essentially motor. It has been etjually well established, however, that in man, unless the disorganization of the corpus striatum giving rise to hemi- plegia is situated in the internal capsule the loss of voluntary mo- tion is not persistent. It is obvious, therefore, that the axis-cylin- ders originating in the motor areas of the cortex, traverse, as already mentioned, the internal capsule and that disease of the corpus striatum causes permanent paralysis of motion only so far as it involves the internal capsule. AVhatever, therefore, may be the functions of the corpora striata in the lower animals, these s-anglia can onlv be said to have a motor function in the sense that they are traversed by the motor tracts from the cortex. While lesions of the thalami optici are not of infrequent oc- currence in man, from the fact that the corpora striata and adja- cent parts of the hemispheres are usually involved, conclusions as to the functions of these ganglia, based upon the loss of sensibility, etc., following their destruction, cannot be accepted with the same confidence as in the case of the corpora striata. Nevertheless, if the lesion be limited, as is sometimes the case, to the corpus striatum and the thalamus opticus, and the destruction of these two ganglia is followed by loss of motion and of sensibility on the opposite side of the body, and if it be admitted that the function of the corpus striatum is motor, the conclusion that the thalamus opticus is sen- sory in function becomes then unavoidable. Indeed, it could not be otherwise, since after destruction of the thalamus opticus no other avenue is left by which sensory impressions can be transmit- ted from the general periphery of the body to the cerebral hemi- spheres, except by the posterior third of the posterior segment of the internal capsule or the " sensory crossway." That the thalamus opticus has some sensory function appears to be shown by the fact of its destruction in man being follow^ed by loss of general and special sensibility on the opposite side of the body, tactile sensation being impaired, and hearing and vision in some cases affected.^ It miglit ])e urged, however, that in the case of man whatever sensory functions the thalami optici may be endowed with are only due to some of the axis-cylinders of the sensory tract simply travers- ^ Luys, Reclierc'lies sur le Systerae Xerveux, 1865, p. o38. Cricliton Browne^ West Riding Asylum Reports, Vol. v., p. 227, 1876. Ferrier, op. cit., p. 239. CORPORA STRIATA ASD THALAMI OPTICI. 651 ing it to terminate in the sensory area of tlie cortex. That the paralysis of motion and sensation folloMing lesions of the corpora striata and thalami optici is not due simply to the motor and sensory impulses being normally transmitted through these ganglia from or to the convolutions of the hemispheres, and that after the destruction of these ganglia no avenues are left, therefore, for the transmission of such impulses, is shown by the fact that after re- moval of the cerebral convolutions in a mammal the power of voluntary movement and sensation remains. Thus, for example, in a rabbit the cerebral hemispheres having been removed, while there is nothing observed to indicate that its sensations ever give rise to ideas — that is, that it perceives — nevertheless, it feels even it does not think ; it sees, hears ; if pinched, it cries ; when stirred up, it runs or leaps forward, avoiding with more or less success ob- stacles placed in its path. The animal has undoubtedly possession of its senses, can execute all its bodily movements, but its intelli- gence appears to be gone, at least objects which would have ordi- narily pleased or terrified it make no impression whatever upon it. It must be borne in mind, however, that in any application to be made of such results with the view of elucidating the functions of the basal sranoflia in man, that it does not necessarilv follow that a hu- man being, or even a dog deprived of its cerebral hemispheres, should be in exactly the same mental condition as a rabbit under similar circumstances. On the contrary, there is a good reason for supposing that, as we pass from the lower to the higher mammals, the seat of voluntary motion and sensation is removed to higher and higher levels in the encephalon ; the cerebral convolutions beings more important in this respect in man than in a dog, and the basal ganglia more important in the dog than in the rabV)it, and so on. The most marked contrast in this respect is presented by fishes,^ in which the corpora striata are relatively well developed, the cerebral hemispheres but little so — in fact, the latter are only represented, more particularly in the cartilaginous fishes, by the thin film of nervous matter covering in the cavity or ventricle, of which the corpora striata constitute the floor ; the so-called optic lobes in fishes representing, probably not only the optic lobes of the higher vertebrates, but the thalami optici as well. Undoubtedly a rabbit can do more without its basal ganglia and cerebral convolutions than a dog, and a dog with its basal ganglia but without its hemispheres than a man without the latter. It becomes, therefore, a very difficult matter to say just where sensation begins in man, and still more, where sensation is accompanied or gives rise t(i ideation and volition. It has been suggested that if an impression made upon the pe- riphery must be transmitted to the cerebral convolutions to be thor- oughly appreciated, and that a voluntary impulse developed in re- sponse to such a sensation must emanate in the same, the connections of the basal ganglia through the- corona radiata, with the convolu- ^ L. Edinger, Yorlesungen iiber Den Ban Der Xervosen Centralorgane, 1S9G, s. 72. <)52 THE NERVOUS SYSTEM. tions of the hemispheres, and with each other, offer an avennc for the performance of reflex actions already referred to, Avliich origi- nally being accompanied with both sensation and volition, in time come to be performed withont either. For with the constant rej)- etition of a particular action involving sensation and volition, it is natural to suppose that the circuit traversed might become shorter and shorter, and that impressions which originally reached the cerebral hemisphere before being reflected back, simply passing through the basal ganglia to and fro, gradually take a shorter course, and reaching the thalanuis opticus are at once reflected back through the corpus striatum, short-circuted, so to speak. Optic Lobes. It has already been mentioned that the iter or way by which the third and fourth ventricles communicate with each other, passes underneath the corpora quadrigemina. The latter consist of a white ({uadrate mass more or less divided upon its upper surface by a crucial depression into four eminences, the so-called nates and testes, optic lobes, or quadrigeminal bodies, whence their name. The corpora quadrigemina, or the optic lobes, as we shall hereafter for brevity designate them, are attached laterally to the thalami optici between which they are situated, and also to the geniculate bodies, and therefore indirectly with the optic tracts. Inferiorly they are connected with the cerebellum by the superior peduncles between which is attached the valve of A^ieussens and with the motor columns of the cord by the fibers descending through the pons and embracing the olivary body. The optic lobes are not, however, in man, as their name would imply, the seat of the centers of vision, since the visual path, as we shall see presently, is con- tinued as that part of the optic tract that passes beyond the optic lobes through the posterior limb of tlie internal capsule as the optic expansion or radiation to the cuneus in the occipital lobe. On the other hand, as in many mammals, the occipital lobe is undeveloped, the cerebellum being entirely uncovered, it is obvious that the cen- ter of vision must be situated in such mammals at least in some other part of the brain than the cuneus, the latter being absent. As a further proof that the center of vision is not situated in all animals in the same part of the brain, it may be mentioned, as we shall see presently, that the sense of sight persists in the lower vertebrata even after tlie entire removal of the cerebral hemi- sphere. The optic lobe, as might be expected, constitutes also an important part of the reflex mechanism by which the coordination of the eyeballs and the contraction of the pupil are effected, the ()))tic nerve being the afferent nerve and the oculo-motorius the efferent nerve, tlie reflex centers being situated either in the optic lobe or immediately beneath it. Apart from the anatomical fact that the optic lobes are connected with the motor tracts of the spinal cord, which would, as already remarked, indicate that these OPTIC LOBES. 653 ganglia influence muscular action in some way, it is well known that the optic lobes arc not invariably developed in proportion to the eyes, but, on the contrary, may be quite large, though the eyes and optic tracts be but small, little developed, or even wanting altogether, as, for example, in the myxine or hag fish, and the Apterichthys ctccus among fishes, in the proteus and cecilia among batrachians, and in moles and shrews among mammals, Avhich show that the optic lobes have other functions beside those influ- encing vision. Now, while it has been established that destruction of the optic lobes in animals involves disorders of equilibrium and want of muscular coordination, nevertheless, it must l)e mentioned that a very great difi:erence prevails in this respect according to whether the animal upon which the experiment is performed be a batrachian, bird, or mammal, the optic lobes relatively to the cere- bral hemispheres being so much better developed in the lower than in the higher vertebrates. Thus, for example, a frog with its optic lobes intact, but without its cerebral hemispheres, can coordinate its muscles for the performance of ordinary actions better than a pigeon or a rabbit similarly conditioned, and the latter better than a monkey or man. It may be mentioned, also, in this connection, that the want of coordinating power, etc., following destruction of the optic lobes is not due, as might be supposed, to the blindness entailed, since in the frog, for example, if the e}^s be destroyed, but the optic lobes be left intact, such disorders as those ensuing upon the destruction of these ganglia are not observed. It is well known that if all the encephalic centers above the optic lobes be removed in the frog, gentle stroking of the l)ack excites the animal to croak. The croaking entirely ceasing, however, if the optic lobes be removed, the natural inference is that these ganglia con- tain the reflex centers through which the croaking is produced. As certain plaintive cries emitted by the rabbits cease after removal of the optic lobes, it is possible that a similar reflex center exists in the optic lolies of mammals as well as in those of frogs. Taking this latter fact into consideration, together with that of the circulation and respiration being modified by electrical stimula- tion of the optic lobes, the blood pressure being increased, the heart slowed, the respiration deepened exactly in the same manner as when the sensory nerves are powerfully excited, and that con- tractions of the stomach, intestines, and bladder also follow, it would appear that the optic lobes influence nutrition as well as muscular coordination and vision. The Cerebellum. The cerebellum, constituting about one-eighth of the bulk of the brain, and situated in the posterior fossae of the cranial cavity, consists of two lateral portions, the hemispheres, the anterior rounded eminences of which are known as the amygdalaj, or the tonsils. The hemispheres, though separated behind and below by '654 THE NERVOUS SYSTEM. a wide deep groove, the vallecula or valley, are connected by an in- termediate worm-like ridge, the vermiform process, the portion of the latter situated between the tonsils being called the uvula, while just above the tonsils, and separated from them by a fissure, may be seen the flocculi, or pneumogastric lobules, so called from their vicinity to the nerve of the same name. Each lateral hemi- sphere and vermiform process essentially consists internally of a prismoid trunk of white substance, from which emanate about a dozen broad, thin laminae ; the latter subdividing again into secondary thinner laminae, and the gray substance enfolding them, gives rise to the convolutions and fissures observal^le on the surface of the organ. It has already been mentioned incidentally that the optic lobes -are connected posteriorly with the cerebellum through the superior peduncles of the latter. The fibers of the superior peduncles pass- ing forward and upward to the testes ascend through the crura <;erebri to the thalamus ojTticus and corona radiata, and thence to the frontal temporal and occipital lobes, some of the fibers decus- sating beneath the optic lobes. Inferiorly the superior peduncles are connected with the vermiform process of the cerebellum and with the corpus dentatum, or punch-like layer of gray matter within the white matter of the lateral hemispheres. The middle pedun- cles of the cerebellum constituting, as already mentioned, the trans- verse commissural fibers of the pons Varolii connect the two lateral hemispheres, while the inferior peduncles pass downward into the res- tiform bodies of the medulla, and are collected with the spinal cord. According to most histologists each lateral lobe of the cerebellum is connected with the olivary body of the opposite side, the tract constituting the so-called " cerebro-olivary " system. If the cerebellum be removed in a bird, a pigeon, for example (Fig. 372), though the animal still feels, thinks, wills, it is unable Fig. 372. Pigeon, after removal of the cerebellum. (Dalton.) THE CEBEBELLIM. 655 to stand or flv. If placed upon the back, it is unable to rise. If food be placed within its reach, though it sees it, it cannot pick up the food. Instead of remaining (juiet, it is in a continual state of restlessness and agitation. In a \\ord, though able to make volun- tary movement, the animal has lost the power of coordinating its movements for the performance of a definite object, or of maintain- ing its equilibrium. Its movements highly resemble those of a drunken man. Essentially the same results are obtained if the cerebellum be removed in a mammal. Undoubtedly then, very remarkable disorders, both as regards the maintenance of equi- librium and power of locomotion ensue upon destruction of the cerebellum in mammals and birds, although, as already mentioned, no perceptible change is observable in these respects in the case of frogs, in which the cerebellum has been removed. Differences of opinion still prevail among pathologists as to whether lesions of the cerebellum in man give rise to the same dis- orders as observed in mammals and birds, in which the cerebellum has been removed, and even though it has been held by some phy- siologists that entire absence of the cerebellum, as shown by post- mortem examinations, was not accompanied during life ^vith loss of the power of locomotion, or of the maintenance of equilibrium, nevertheless, it may be questioned whether there is a well-authenti- cated case in which locomotion and ec|uilibrium remained unaf- fected, extensive lesions of the cerebellum existing. Such cases as where there was a congenital absence of the cerebellum, unaccom- panied Mith any disorders of locomotion, etc., being explainable on the supposition that, as in the case of the frog, the function of the cerebellum was performed by other ganglia, probably the optic lobes. On the supposition that the cerebellum is the center for the main- tenance of equilibrium and of muscular coordination, it ought to be best developed in those animals which exhibit such powers in a marked degree, and such we find to be the case. Thus in the shark, for example, in which, of all fish, the muscular system is best developed, and the power of coordination so perfect, as shown, for example, in the manner in which it seizes its prey, the cere- bellmn is larger and more complex in its structure than in any other fish. Among birds, also, the cerebellum is particularly well devel- oped in the carnivorous raptores, in which muscular actions, such as are involved in the swooping down by them upon prey from immense heights, require very nice adjustment of coordination. Among mammals the cerebellum is large ; in the kangaroo, whose peculiar mode of progression necessitates considerable muscular co- ordination, while, in the elephant, in which great nuiscular coordi- nation is demanded, owing to the enormous muscular development, and in the case of the posterior extremities to the absence of the round ligament of the hip-joint, the cerebellum is very large, being equal to one of the hemispheres. . In the anthropoid apes, also, which not nnfrequently assume the semi-erect attitude, the cerebel- 656 THE NERVOUS SYSTEM. lum is larger than iu the remaiuing monkeys. Indeed, in the young chimpanzees and orangs dissected by the anther^ the cerebellum was found so Avell developed as to extend slightly beyond the posterior lobes of the cerebrum, Avhich is not the case in monkeys generally, in adult chimpanzees or orangs and in baboons, macacques, spider- monkeys, etc., the cerebellunj being perfectly covered by the pos- terior lobes of the cerebrum as in man. That the cerebellimi, at least in mammals, birds, and fishes, is concerned in some way in the maintenance of equilibrium and muscular coordination is not only shown by experiment, pathology, and comparative anatomy, but from the fact of the tactile, visual, labyrinthine, and perhaps visceral impressions upon which the maintenance of equilibrium and muscular coordination depend, being transmitted from the periphery through nerves which directly or indirectly terminate in the cerebellum, as we shall now endeavor to show. It has already been mentioned that a frog from which the cerebral hemi- spheres have been removed, but which still preserves its optic lo])cs and cerebellum, retains the power of maintaining its equili- brium and of muscular coordination. If, however, the skin be removed from the hinder legs of such a frog, the animal at once loses this power and falls like a log if the position of its support be changed, the removal of the skin making impossible the trans- mission of those afferent tactile impressions which through some reflex center give rise to those efferent muscular actions requisite for the maintenance of equilibrium. That this reflex center is situated in man in the cerebellum, and that these afferent tactile impressions are transmitted by the posterior columns of the spinal cord, is ren- dered very probable from the fact that sclerosis of these columns causes locomotor ataxia, a disease especially characterized not by a loss of sensibility but of power of coordination, and that the pos- terior columns of the cord through the restiform bodies of the me- dulla terminate in the cerebellum. While visual are not as impor- tant as either tactile or labyrinthine impressions in the maintenance of equilibrium, since the latter almost suffice in the absence of the former, nevertheless they exercise a certain amount of influence. Thus, in cases of locomotor ataxia, for example, equilibrium and coordination are not altogether impossible, even though the tactile impressions be wanting, so long as the labyrinthine and visual im- pressions persist, and in such cases when the transmission of tactile and labyrintliiuc impressions are perfect, the absence of visual ones always entails some slight want in the coordinating power. That such visual impressions are transmitted to the cerebellum, is ren- dered very probable when it is remembered that the optic lobes are connected with the cerebellum both through the superior peduncles and valye of Yieussens. As is well known, remarkal^le disturb- ances of equilibrium ensue if the membranous semicircular canals of the internal car be divided in a bird or mammal, or if they are 'H. C. Cliapman, Proc. Acad, of Xat. Sciences, 1879, p. 68 ; 1880, p. 172. THE CEREBELLUM. 657 diseased as lu ^Meniere's disease iu man, wliieh vary accordiug to the seat of the lesion. Thus, if the horizontal canals be divided in a pigeon, for example, rapid movements of the head in a hori- zontal plane, from side to side, follow, with oscillation of the eye- balls, and a tendency to spin around on a vertical axis is manifested. If, however, the posterior or inferior vertical canals be divided, the head is moved rapidly backward and forward, and the animal tends to turn somersaults backward head over lieels, whereas if the superior vertical canals be divided, the head is moved rapidly forward and backward, and the animal tends to make forward somersaults heels over head. It would appear from the researches of Goltz,^ Mach,' Brewer,-^ and Crum Brown^ among others, that the character of the impressions made upon the vestibular nerves depends upon the degree and relative variations in the pressure exerted by the endolymph upon the ampulhe of the membranous canals, to which, as we shall see hereafter, these nerves are dis- tributed. Such being the case, it is obvious that if the semi- circular canals be divided disturbances of equilibrium must ensue, the natural tension of the endolymph l)eing thereby altered, which will vary according to the particular semicircular canal aifected. It may be mentioned in this connection, that pigeons in which the semicircular canals have been divided on one side in time regain the power of maintaining their equilibrium, but if the canals bo divided on both sides, they never again are able to assume their natural position, the most strange and bizarre attitudes being taken. Whatever may be the natiu-e and mechanism of the labyrinthine impressions, there can be no doubt as to the influence exerted by them in the maintenance of equilibrium, since in their absence the same becomes impossible even though the tactile and visual im- pressions persist. That the membranous semicircular canals and the auditory nerve together constitute an afferent system by which impressions are transmitted to the cerebellum, acting as a reflex coordinating center, appears highly probable when it is remembered that division of the auditory nerve entails disturbances of equi- librium, that the auditory nerve through the restiform bodies is directly connected with the cerebellum, and that a great similarity exists between the effects of destruction of the cerebellum and division of the semicircular canals. Thus, destruction of the anterior por- tion of the middle lobe of the cerebellum, like that of the superior vertical canal, involves displacement of equilibrium fonvard around a horizontal axis, destruction of the posterior part of the median lobe like that of the posterior vertical canal, displacement backward around a horizontal axis, destruction of the lateral lobes of the cerebellum, like that of the horizontal canals, lateral displacement around a vertical axis. The cerebellum appears, therefore, to be the reflex center by which the afferent impressions transmitted by iPfluger's Archiv, 1870. ^^itz. u. der K. Acad, der Wiss., Wien, 1873. 3 Med. .Jahrbucher, Hefti., 1874. *, Journal of Anat. and Phys., May, 1874. 42 6 5 S THE NER VO US SYSTEM. the cutaneous, optic, and acoustic nerves are coordinated with the efferent ones for the maintenance of equilibrium and locomotion. That such reflex actions are accompanied now, or originally at least, with consciousness, and that the cerebellum is that part of the encephalon in which the ideas of space are developed, is ren- dered very probable when it is remembered that many actions in- volving muscular coordination, which are performed now uncon- sciously, w^ere originally accompanied by both sensation and volition, and that the disorders of equilibrium and locomotion following destruction of the cerebellum or of the afferent system leading to it, imply a perversion in the ideas of space relations. From the fact that the loss of coordinating power, etc., following division of the cerebellum in the middle line is only transitory it is usually held that each half of the cerebellum is associated with the medulla and cord of the corresponding side of the body. The rela- tion of the cerebellum to the cerebrum however is a crossed one, each cerebellar hemisphere being connected with the cerebral hemi- sphere of the opposite side of the body. It appears also that the tracts connecting the cerebellum with the medulla, etc., on the one hand, and with the cerebrum on the other, constitute double path- ways, the cerebellum sending as Avell as receiving impulses to and from the different regions with which it is associated. CHAPTER XXXIV. THE NERVOUS QYSTE^L— {Continued.) Fig. 37: THE CEREBRAL HEMISPHERES. The cerebral hemispheres, so called on account of their hemi- spherical form, are two ovoidal masses flattened at their mesial sur- face, where they are separated by the great longitudinal fissure. They consist of gray or vascular and of white or filn'ous nervous tissue. The gray substance, like that of the cerebellum, situated externally and varying between two and three millimeters in thick- ness, sinks at intervals into the white substance to a depth of from ten to twenty-five millimeters, invaginating itself — that is, folds in- ward to return upon itself again, and so gives rise to the convo- luted and fissured surface so characteristic of the brain of man and of many mammals. It is evident that through this convoluted arrangement the hemispheres contain far more gray matter than if they were smooth, ■on the same principle that a pocket hand- kerchief occupies much less room when folded up than when laid out smooth, and that the deeper and more numerous the fis- sures the greater the amount of gray matter present. The gray matter of the convo- lution or cortical layer of the hemispheres, consists of a granular matrix in which are imbedded nerve-cells with their axons, dis- posed in four or more layers (Fig. 373), the latter being distinguished by the character of their nerve cells. Among the most striking of these cells may be mentioned the so-called pyramidal cells, varying in diameter from the ^^^ to :^^ of a millimeter (2-5V0 ^^ eh'S ^^ ^'^ inch), and characterized by their quadrangular base and tail-like extremity, the latter point- ing outwardly. The pyramidal cells are more numerous and larger in the anterior portion of the hemispheres in the convo- lutions of the frontal lobe, for example, the cells of the so-called nuclear layer in the occi])ital and temporal lobes. Certain so-called giant pyramidal cells, attaining a diameter of from the ^^jj- to the yL of a millimeter ( -^i^ to -^^-^ of an inch), i)robably motor in function, like those of the anterior cornu of the spinal cord, are Section of a cerebral convo- lution stained by Golgi's method. 1. Xeuroglia layer. 2. Layer of small cells. " 3. Layer of large pyramidal cells. 4. leaver of 'irregulai cells. (Landois.) 660 THE NERVOUS SYSTEM. also found more particularly in the posterior portion of the frontal lobe in the anterior central convolution, the processes of which ap- pear to be prolonged downward as the axons traversing the antero- lateral columns of the spinal cord and which we have seen are in re- lation with the anterior roots of the spinal nerves, wdiile other cells^ having no processes or axons, are found more especially in the pos- terior part of the hemispheres in the occipital lobe. Although the convolutions or gyri and the fissures or sulci do not run in exactly the same manner in diHerent brains, and are not symmetrically dis- posed even in the two hemispheres of the same brain, nevertheless the general disposition is so constantly the same that the most im- portant of them can be readily recognized and identified, and on account of their supposed functional importance demand at least a brief description. The most striking fissure observable, if the hemi- sphere be viewed laterally, both on account of its depth and con- stancy, it existing not only in man but in all animals whose brain is fissured at all, is the fissure of Sylvius. Beginning as a transverse Fig. 374. Outer surface of the left hemisphere. The regions bouiidi^^il bj' the line ( ) represent the territories over which the branches of the anterior ccixliral urtcry are distributed. The regions bounded by the line ( ) represent the tcrritdries over which the branches of the jiosterior cerebral artery are distributed. /■'. I'rontallobe. 1'. Parietal lobe. O. Occipital lobe. T. Temporo-sjjhenoidal lobe. S. Fissure of Sylvius. ,S'', Horizontal; S", Ascending ramus of tlie same. c. Sulcus centralis or fissure of ItoUuido. A. Anterior central or ascending frontal convolution. B. Posterior central or ascending jiarietal convolution. i'V Superior ; /'"„, Middle, and F^ Inferior frontal convolution. J\, Suporinr, and/^ Inferior frontal sulcus ; f^ Sulcus prse- centralls. P,. Sujierior parietal of postero-jiarietal lobule, viz.: P^, Gyrus supramarginalis ; P'„, (iyrus angularis. ip. Sulcus intraparictalis. cm. Termination of the calloso-margiual fissure. Oj First, Oj Second, O3 third occipital ccuivolutions. pa. Parieto-occipital fissure. 0. Sulcus occipitalis transversus ; o.^, Sulcus occipitalis longitudinalis inferior. 7*,, first; 7'„, second ; T3, third temporo-sphenoidal convolutions. ^,, first ; t^, second temporo-sphenoidal fissures. (After EcKER and DuunT.) THE CEREBRAL HEMISPHERES. 661 furrow on the under side of the brain, it runs thence outward, back- Avard, and upward, separating the temporal [T, Fig. 374) from the frontal lobe {F), and divides on the outer side of the hemisphere into an anterior (.S') and posterior (lood than would be possible if the brain were smooth, becomes evident. Further, ^vhcn it is borne in mind that the brain is enclosed in a bony, unyielding case, and that the amount of blood sent to the brain from the heart must vary with the force of the latter, and that cerebral disturb- ances ensue with any increase or diminution in pressure it might be anticipated that some provision must exist by which a uniform pressure within the cerebral substance is maintained. The latter function appears to be fulfilled by the cerebro-spinal fluid found in the sul)arachnoid cavity of the brain and cord, since if this fluid be withdrawn from a living animal, cerebral disturbances attril)utable to changes in pressure ensue. The cerebro-spinal fluid amounts to at least two ounces, and probably more, and ap- pears to be as ra])idly absorbed as produced, and as it readily passes from the subarachnoid space through the foramen of Magendie or the triangular orifice in the pia mater situated at the inferior angle of the fourth ventricle into the ventricles of the brain or the central canal of the cord, it evidently serves to equalize the pressure in the cranial cavity, merely allowing blood vessels to expand and contract within such limits as do not induce any marked change in the pressure to which the brain substance is usually subjected.^ Tlie entire cncephalon in the adult male brain weighs on an average about fifty ounces, that of the female a little less, about forty-four ounces. On this supposition, the relative weights of the cerebrum, cerebellum, etc., are as follows : ^ ' Mast'iidie, .Journal de Plivsiologio, Tonii' v., p. 27. Paris, 1825. Tome vii., pp. \-m, 1827. 2Quain's Anatomy, 8tli cd., \'ol. ii., \). ijSl. THE CEREBRAL HEMISPHERES. 665 Average weight. Male. Female. Cerebrum .... 43.98 oz. 1244.63 grammes. 38.75 oz. 1096.62 grammes. Cerebellum. 5.25 " 148.57 " 4.76 " 134.70 Pons and medulla . 0.98 " 50.21 " 27.73 11 1.01 " 28.58 Entire enceplialon . 1420.93 44.52 " 1259.90 " Eatio of cerebrum to cerebellum. I'toSi 1 to SI The human brain is absolutely heavier than that of any other animal except the elephant and the cetacea, the brain of the ele- phant usually weighing from 3022.4 to 4528 grammes^ (8 to 10 pounds) or even more, that of the young male elephant which died at the Philadelphia Zoological Gardens having been found by the author to weis-h immediatclv after removal from the skull 4754.4 grammes (10.5 poiuids). The brain of the whale weighs about 2264 grammes (5 pounds);- that of a grampus (Delphinus Risso) as found by the author, 3169.6 grammes (7 pounds). Relatively, however, to the size of the body the brain is larger in certain birds and mammals than in man, as, for example, in the canary bird, field mouse, and ouisitite monkey. With reference, however, to the size of the nerves given off from its base, the brain of man is larger than that of any other animal without exception. In considering the functions of the medulla, pons, cerebellum, and basal ganglia, we have necessarily anticipated somewhat, by a process of exclusion, the functions of the cerebral hemispheres. It only now remains for us to offer the positive evidence bearing upon the questions and confirming the general conclusions already reached by the manner just mentioned. Fig. 377. Pigeou, after removal of the liemispheres. (Dalton.) If the cerebral hemispheres be removed in a pigeon, for example, the animal at once falls into a condition of stupor, its whole ap- pearance being very peculiar and most characteristic (Fig. 377). 1 Cyclopaedia of Anat. Phys., Vol. lii., p. 664. Loud., 18.39-47. 2Rudolphi, Grundriss der Pbysiologie, B. ii., s. 12. Berlin, 1823. QQQ THE NERVOUS SYSTEM. With its head ahiiost buried within the feathers of the neck, with closed eyes, the pigeon stands sufficiently firmly, but without mov- ing, apparently utterly indifferent to its surroundings. From time to time it open its eyes, stretches its neck, or smooths its feathers, but soon again relapses to its former condition of apathy. That the pigeon, however, still feels there can be no doubt. Pinch its neck or one of its toes and a persistent eifort is made to withdraw the part from the grasp. Fire oflP a pistol, the pigeon will open its eyes and turn its head round as if it had heard the report and was looking whence it came. The report of the pistol, however, causes no alarm, for the pigeon makes no effort to escape. While the animal undoubtedly hears and sees, the sensations do not give rise to the usual ideas associated with or developed out of them, the pigeon feels but does not perceive the sensation of sound ; the re- port of the pistol does not give rise to any idea of danger usually associated with the production of sound. In the same way the presence of food, though seen and smelt by the pigeon, does not excite the idea of hunger, the animal making no effort to feed^ starving to death amidst' plenty. That this entire loss of memory, volition and conscious intelligence, following loss of the cerebral hemispheres in a pigeon is not due simply to the effects of shock, hemorrhage, etc., is shown not only by the entirely different effect following destruction of the cerebellum, but that a pigeon from which the cerebral hemispheres have been removed can be kept alive for months by artificial feeding, and, although the effects of shock have long since passed away, nevertheless, the animal never regains its intelligence, remaining ever afterward in this character- istic condition of stupor and apathy. The absence of intelligence that follows the removal of the cerebrum is even more marked in the case of a mammal than in that of the bird. Thus, according to Goltz,^ a dog in which the cerebrum has been removed is reduced to the condition of a mindless machine, conscious sensations, feel- ings, emotions, etc., being all wanting. Although the effects of destruction or compression of the cerebral hemispheres in man, whether due to disease or injury, are not as well established as in the case of birds and mammals through the imperfect localization of the disease, the basal ganglia, etc., being usually involved as well as the cerebral hemispheres ; nevertheless, a sufficient number of cases have been observed by pathologists which show that loss or compression of the cerebral hemispheres in man involves, as in the case of l)irds and mammals, the loss of memory, volition, con- scious intelligence, the nutritive functions, however, remaining un- impaired. Among such cases may be mentioned that of the sailor related by Sir Astley Cooper,^ who, having fallen, probably from the yard-arm, was picked uyt on the deck insensible, practically de- prived of all powers of mind, volition, or sensation, in which con- ^Pfiii.£;er's Arc'liiv, IjuikI xli. 2 Lectures on the PrineipleH and I'raetieeof Siir<,a'rv, p. 18S. PliihKU'lpliia, 1S89. THE CEREBRAL HEMISPHERES. 667 dition he remained for thirteen months, being kept alive all this time bv artificial feeding, the grinding of the teeth and the sucking^ of the lips indicating to his attendants the necessity of giving food and drink. During this period the man lived almost entirely a vegetable existence, the only movements he made, with the excep- tions of the lips, etc., being with the lingers, which he moved to- and-fro to the time of the pulse. In this condition the sailor was seen by Cline, the famous surgeon of the day, who, satisfying him- self that a depression in the skull existed, trephined, and with the happy result that within a short time after the operation the patient ^vas able to get out of bed, talk, and tell where he came from, his mind having been restored through the removal of the pressure exerted by the depressed bone upon the cerebral hemispheres. In general, it may be said that injury or disease of the cerebral hemispheres in man entails disturbance or loss of the intellectual powers, according to the seat and extent of the lesion. Impairment and then loss of memory, weakening and failure of the reasoning powers and of the judgment, invariably follow disease or injury of the cerebral hemispheres, while the facts that under such circum- stances there is no loss of sensation or motor power, and that the vegetative functions also remain unimpaired, as in the case of idiots and the insane, clearly show that the cerebral hemispheres are in- dispensable to the manifestation of the intelligence. On the other hand, the fact already mentioned of animals deprived of their cere- bral hemispheres living for a longer or shorter time when supplied with food, and of human beings being born anencephalous, and yet were kept alive some time, and who sucked and cried like ordinary infants, proves that the cerebral hemispheres are not concerned in the performance of those functions not involving intellection, which have been assigned to other parts of the encephalon. That the in- tellectual powers depend upon the development of the encephalon is also shown by the facts of comparative anatomy, the encephalon of the more intellioent animals beino- much heavier both absolutelv and relatively, with reference to the weight of the body, than that of the less intelligent ones. Thus, in fishes the ratio of the en- cephalon to the body is as 1 to 5,668, in the reptiles as 1 to 1,321, in birds as 1 to 212, in mammals 1 to 189 ^ and in man as 1 to 50, supposing the body of the man to weigh 68.1 kil. (150 pounds) and the brain about 1.37 kil. (3 pounds). Further, the brain of the lowest races of mankind, at least as es- timated from their cranial capacity, is not as heavy as that of the higher and more intellectual ones, the brain of the Australian, for ex- ample, weighing only 1190 grammes (42 oz."),- and correspondingly less bulky. It is also well known that individuals distinguished by ^ Leiiret, Anatomie Comparee du Svsteme Xerveux, pp. 153, 234, 284, 422. Paris, 1839. ^ Davis, Journal of the Acad, of Xat. Stionces, Phila., 1869. Morton, Cranica Americana, p. 253, Pliila., 1839. 668 THE NERVOUS SYSTEM. great intellectual power possessed large, heavy brains. Thus the brain of Abercrombie ^ weighed 1783 grammes (63 oz.), that of Cuvier- 1820 grammes (64.33 oz.). On the other hand, the brain of idiots has been found in some instances to weigh not more than r)66 grammes (20 oz.). It should be mentioned in this connection, however, that the weight of the brain in man depends not only upon race, but on the age, weight, and stature of the individual, and even upon the manner in which the brain is weighed,^ whether as a whole or in parts, with or without the j)ia mater and also in reference to the amount of blood it may contain. It will be observed also from a comparison of the brain of the lower with that of the higher vertebrates, that it is the greater de- velopment of the cerebral hemispheres in the latter to which are due the greater bulk and weight of the encephalon. Thus, as we pass from the brain of the fish (Fig. 378) to that of the reptile (Fig. 379), from the brain of the reptile to that of the bird (Fig. 380), from the latter to the brains of mammals (Fig. 381), includ- ing that of man, one cannot but be impressed with the fact that the cerebral hemispheres become successively more and more developed Fig. 378. Brain of carj). A. Cor- pora striata. B. Optic lobes. C Cerebellum. Fig. 380. Brain of lizard. (I. Cerebral hemispheres. /. Optic lobe.s. 0. Cerebellum. ''. Medulla. d. Spinal cord. Brain of the pigeon. A. Cere- bral hemispheres. B. Optic lobes. C. Cerebellum. until in monkeys (Fig. 382) and man they completely cover the cerebellum. Further, it may also be seen from such a comparison that while the brain in fish, reptiles, birds, and the lower orders of mammals, such as the marsupiala, rodentia (Fig. 381), sirenia, etc., is smooth or nearly so, in the higher orders, including the probos- cidea, cetacea, the ungulata, the carnivora and primates (Figs. 382, 383), it is more or less convoluted. Indeed, so much is this the case that in tlie proboscidea it is particularly convoluted, even more so than in man. In general, it maybe said that the development of ^Edinbursli Med. and .Surg. Journal, LS-i"), Vol. Ixiii., p. 448. 2 " Trois livres onze onces (juatres gros ot demi," is the number given in the ac- count of the autopsv of Cuvier in the Arcliives generales de Medeeine, Tome xxix., p. 144. Paris, 18.32. 3R. Boyd, riiil. Trans. Lond., Vol. I-jI, 18G2, p. 241. THE CEREBRAL HEMISPHERES. 669 the intellectual powers depends not only upon that of the encepli- alon, but more particularly upon that of its cerebral hemispheres, and especially, as affirmed long ago by Erasistratus,^ upon the Fig. 381. Fig. 382. Brain of the rabbit. A. Cere- bral hemispheres. O. Olfactory bulb. C. Cerebellum. Brain of the orang. number and depth of the convolutions of the gray matter of the same. Further, in the savage races of mankind, characterized by a low order of intelligence, the convolutions are not so deep, are Fig. 383. Fig. 384. Cerebrum Fossa svlvia — - Cerebrum. Corp. quadrig. Cerebellum. ' Med. oblong. Brain of human embryo, three months. Cerebellum Med. oblong. Brain of human embrvo, five months less numerous, and are more simply disposed than in the civilized races distinguished by the development of their mental faculties. ^Galenus, De Usu Partium, Lib. 8, Cap. 13. <)70 THE NERVOUS SYSTEM. It is well known that in individuals especially remarkable lor intel- lectual power, as in the case of Gauss/ for example, a distinguished mathematician, the convolutions of the cerebral hemispheres are found to be very numerous and deep, and far from simply arranged. On the other hand, in idiots the convolutions are few, comparatively superficial, and simply disposed. The development of the l)rain also confirms the conclusions based upon the facts of comparative anatomy and ethnology, the transitory stages through which the ftetal brain passes being permanently re- tained in the brains of the lower animals. Thus, at about three weeks of intrauterine life the l)rain of the human foetus resembles that of the adult fish, there being but little difference at this early period in the relative development of the cerebral hemispheres, optic lobes, cerebellum, etc. As development advances the hemi- spheres enlarge and grow backward ; at three months (Fig. 383), though still smooth, they slightly overlap the optic lobes, the latter not having yet divided into the corpora quadrigemina. At about the fifth month (Fig. 384) the cerebral hemispheres in the human foetus overlap the cerebellum, and here and there exhibit a rudi- mentary fissure, though their surface is still almost entirely smooth, as in those of the rodentia. Finally, at about the seventh month, the optic lobes are subdivided into the corpora quadrigemina, while at full term or at birth the convolutions are all formed. The brain of the human foetus, however, at this period, both as regards the number, depth, and simplicity of arrangement of the cerebral convolutions, resembles rather the brain of the chimpanzee than that of the adult man, while the brain of the uneducated child resembles, in similar respects, that of the savage races of mankind rather than that of the civilized ones (Fig. 385) ; a physical correspondence in harmony with their intellectual acquirements. While the facts of experiment, pathology, comparative anatomy, etc., with but few exceptions, and those usually more apparent than real, undoubtedly agree in establishing the view that asso- ciates intellectual power with the development of the cerebral hemispheres, and more })articularly with that of the convolutions, or the gray matter of the same, it must be borne in mind that the quality of the chemical composition of the latter is (piite as im- portant a condition as its mere quantity. It need hardly be added that the exercise of the mental faculties necessitates the connections between the gray or vescular substance of the convolutions and the fibers of the white substance being maintained in their normal condition, just as the action of a mus- cle depends on the position and manner of insertion ; and, above all, upon the free supply of blood and active circulation, both that the materials for the nourishment of the hemispheres and the pro- duction by them of thought, may be supplied in sufficient quantity, and that the effete and worn-out materials incidental to mental ac- ^Quuin, Anatomy, 1878, Vol. ii., pp. 521), 581. THE CEREBRAL HEMISRHERES. 671 tivity may be carried away to the proper emunctories as rapidly as produced. As we have already seen that the different structures of which the encephalon consists, medulla, pons, cerebellum, basal ganglia, cerebral convolutions, etc., have undoubtedly different functions, it is reasonable, therefore, to suppose that the different Fio Cerebrum of man. Lateral view of the right cerebral hemisphere. 1. Fissure of Eolaudo. 2. Ascending frontal convolution, o, Superior ; .3', Middle, and 7, Inferior frontal convolutions. 4. A bridging convolution between the superior and middle frontal convolutions. 5. Ascending parietal fonvolution. (5,8. Supramarginal convolution (S in front points to part of the inferior frontal convolution). 9, 9. Superior temporo-sphenoidal convolution. 10, 11, 12. Convolutions of the island of Reil. or central lobe. 13. Orbital convolutions. 14. Lower extremity of middle temporo-sphenoidal convolutions. 15. Occipital lobe. (From Sappey after Foville") J^. convolutions, or the gray matter of the cerebral hemispheres, have also special faculties or functions. Phrenology has, therefore, a basis worthy of consideration. Phrenology, however, as under- stood by the vulgar, is based upon the untenable assumption that the f >rm of the surface of the brain can be inferred from the ex- ternal configuration of the skull, that any protuberance, or " bump," of the latter is to be taken as an indication of a similar excessive development of the former and the possession of some l)articularly well-developed mental faculty. Apart, however, from the tacts that the skull consists of two tables, and that the outer surjface of the brain is separated from the inner surface of the skull by the dura mater, arachnoid, pia mater, and cerebro-spinal fluid, the latter variable in quantity, the figure of the brain, except in a general way, does not correspond to the figure of the skull. So much so is this the case that in certain animals, as in the elephant, for example, through the enormous development of the frontal sinuses the anterior portion of the skull is no indication of the form of the brain whatever. Further, the surface of the brain is not elevated into l)unips, the convolutions, as we have seen, being formed through the invagination, or dipping down of the gray mat- ter into the white. Even though, then, osseous "bumps" be ever 672 THE NERVOUS SYSTEM. so well developed, there are never any cerebral " bumps " with special functions or faculties corresponding to the osseous ones. Phrenology, as such, nuist be relegated, then, to the charlatan and itinerant showman, Avho amuse their audience by feeling their heads and illustrating their views by showing plaster casts of the heads of Napoleon, Schiller, noted murderers, idiots and the like. Within recent years, however, another kind of phrenologv has been developed and established, more or less satisfactorily based upon entirely different methods of investigation,^ such as exposing the brain in a living animal, and stimulating with a Aveak electrical current a particular convolution, and so determining whether the latter is excitable, and whether its stimulation causes sensory or motor effects ; or, destroying a particular convolution by cutting, corrosion, etc., and observing Avhether the animal is deprived of any of its faculties, and so learning whether the convolution has motor or sensory functions. By such experimental methods it has been established that the convolutions of the brain in animals possesses definite functions, and the same has been shown to be true of the homologous convolutions of the brain in man by experiment, clinical and post-mortem in- vestigation.^ FiCx. 386. The loft hemisphere of the monkey. (Ferrier. ) Thus, electrical irritation of the convolution bordering the fissure of Kolando in the brain of the monkey (Fig. 386, 1, 2, 3, 4, 5, 6, 7, 8, a, b, c, (!) and in man^ (Fig. 387), gives rise to certain well- 'Fritscli and Hitzig, Archiv f. Anat., Physiologie, etc., s. 300, 1870. Ferrier, Functions of the Brain, 1876. Carville and Duret, Archives de Physiologie 2ieme serie, Tome ii., p. 352. Paris, 1875. Dalton, New York Medical" Journal, 1875, p. 225. ^ Hughlings Jackson Ferrier, Localization of Cerebral Disease, p. 42. London, 1879. Gra.sset, Des Localisations dans les Maladies Cerebrales, p. 143. Paris, 1880. Cliarcot, Logons sur les Localisations dans Ics ^laladies du Cerveau, p. 166. Paris, 1878. Kendii, Kevue des Sciences Medicales,. Tome xiii., p. 314. Paris, 1879. Gowers, op. cit., Vol. 2d, p. 15. Mills, op. cit., p. 332. ^Bartholow, American Journal of the Medical Sciences, April, 1874. THE CEBEBBAL HEMISPHERES. 673 defined constant movements of the hands, feet, arms, legs, facial muscles, mouth, and tongue, on the opposite side of the body. Fig. 387. Lateral view of the human brain. Tlie circles and letters have the same significance as those in the brain of the monkey, Fig. 386. (Fereier.) That the muscular contractions induced through electrical stimu- lation of these or other convolutions are not due to an escape or diffusion downward of the electrical current, and so affecting the corpus striatum, etc., is shown, apart from the fact that stimulation by chemical agents produces the same effect, by several consider- ations, among which may be mentioned the feebleness of the current used, the close approximation of the electrodes, the imperfect con- ductivity of the brain substance, the muscular contractions occurring on the opposite side of the body, and not occurring at all when other convolutions were stimulated. That these convolutions are in reality motor centers, constituting the indispensable physical substratum for the volitional, psychical initiation of movements corresponding to those induced by electrical stimulation, the latter acting in the same manner as the stimulus of the will, is further shown by the fact that destruction of these convolutions in the monkey^ by experiment and in man^ by disease causes complete hemiplegia of the opposite side of the body without affecting sensa- tion. On the other hand, destruction in the monkey by experi- iFerrier, Functions of the Brain, 187G, p. -201. ^ Lepine, De la Localisation dans les Maladies C'erebrales, p. 33. Paris, 1875. Glikv, Deutsches Archiv fiir klin. INIed., Dec, 1875. 43 674 THE NERVOUS SYSTEM. ment^ and in man' by disease of certain convolutions, such as the cuneus, visual area, or temporo-sphenoidal convolutions, auditory area (Figs. 388, 389), while not affecting the motor functions entails Fig. 388. \h T Cortical eeuters. Lateral aspect of the liemisiihere. Fig. 389. J r. ^ Cortical centers, ^lesal asjiect of the hemisphere. ^Horslev&Schafer, Phil. Trans., Vol. 179, 1889, p. 1. Beevor et Hoi-sley, Ebend, Vol. 181, 1891, p. 129. 2 Gowers, op. cit., Vol. 2d, pp. 21, 24. THE CEREBRAL HEMISPHERES. 6 (0 Fr A Si/. Motor speech region in tlie left hemisphere. impairment or entire loss of vision or hearing, according as one or l)otli liemispheres are involved. Such observations prove that there are special sensory as well as motor convolutions in the brain of man. The condition of aphasia, whether presented in the usual, or iigraphic, or amnesic form, depending, as, without doubt, it does, upon disease in the region of the posterior extremity of the third left frontal convolution, where the latter abuts on the fissure of Sylvius, and overlaps the island of Reil, is a most convincing argu- ment in favor of the view of the cerebral functions being Fig. 390. localized in the convolutions of the hemispheres. Merely referring incidentally to the researches of Petit,^ Bouil- laud," Dax,^ Broca,* Hugh- lings Jackson,^ etc., upon the subject of aphasia, the detailed consideration of which be- longs rather to the study of clinical medicine and patho- logical anatomy, it may be briefly said that a person presenting the condition of aphasia as ex- hibited in its most usual form is deprived of the faculty of articu- late speech, though such a person comprehends perfectly the mean- ing of words spoken by others ; having a clear idea of language and of the meaning of words, and being able to write perfectly well. In other cases, however, the patient cannot express ideas in writing (agraphia), or cannot remember the words wanted (amnesia); the idea even of language being lost. That the inability to speak exhibited by the person suffering from aphasia, whether simple or combined with the amnesic or agraphic form, is not due to paralysis of the muscles of articulation is shown by the fact that the aphasic individual makes use of these muscles in mastication and deglutition. Though the center for the co(')rdination of the muscles effecting articulation be diseased, since the action of the center of the artic- ulating muscles is bilateral — that is, the center in one hemisphere innervating the muscles of articulation of both sides — there is no difficulty in understanding that such should be the case. "While disease of the center of articulation of the left hemisphere, for the reason just given, does not entail paralysis of the muscles of articulation, it does entail paralysis of articulation or speech, the center for the coordination of the muscles involved in the produc- tion of speech being then affected. When it is remembered, how- ever, that speech is gradually acquired through the constant and 'Recneil d' observations d'anatomie et de cliirurgie, p. 74. Paris, 1766. 2 Archives de M^decine, 1825. ''(Tazette hebdomadaire, A2)ril, 1865. ^Bulletin de la societe anatomique, Tome iv., 1861. 5 London Hospital Kej)orts, Vol. i. 676 THE NERVOUS SYSTEM. Fig. 391. continual association in the mind of sounds or written signs with the corresponding spoken words, that the acquisition of speech, phys- iologically speaking, is the develoi)ment in the brain of an organic nexus between the sound or symbol, and the articulation, it becomes intelligible why if this nexus be broken, that, though the sound be heard and the symbols seen, and the corresponding ideas developed, the words expressing the ideas cannot be uttered, the individual is speechless, because, as Ferrier expresses it,^ the motor part of the sen- sori-motor cohesion, sound-articulation situated in the inferior frontal convolution, is broken. Further, owing to the close proximity of the motor center of the hand and facial muscles (Fig. 391), it is easy to see, therefore, why dextral and facial paralysis are so often present, though not necessarily so in the case of aphasia. At first sight it may appear strange that the center for coordinating the muscles eifectinff articulation should be located exclusively in one hemisphere ; in reality, how- ever, there is nothing more strange in this than that most persons are right-handed. Dextral movement, like articu- late speech, is gradually ac- quired, and there is no more reason to doubt that in the absence of the coordinating centers of articulation of the left hemisphere that of the right could be educated, than that in the absence of the right hand one could learn to use the left. Indeed, it has been found that in left-handed persons suffering with aphasia the in- ferior frontal convolution af- fected is situated in the right instead of the left hemisphere, as is usually the case. The ef- ferent fibers involved in the production of speech pass from the island of Rcil to the knee of the internal ca})sule, thence through the crusta of the left cerebral peduncle, left half of the pons, to the opposite side of the medulla, from whence emerge the nerves supplying the articulating muscles. It may be mentioned in this connection that in cases of ^' word blindness," that is where a person, although seeing Well in most respects, cannot name a let- iQp. cit., p. 274. Schema to illustrate aphasia. V. Visual center. A. Auditory center. 11'. Writing center. Z'. Vo- cal center, v and a afferent filter.s from larynx and ear. SS' S". Afferent fibers from arliculatdry, hand and orbital muscles. */(. /*('. Elicrent tiliers from vocal and writing centers. Dotted lines, fibers connecting centers. (L.\?juois.) PITUITABY BODY. 677 ter or word, the cerebral center involved is situated in the angular gyrus (P'2, Fig. 374), and in cases of "word deafness," where al- though ordinary sounds are heard words are not, the center is situated in the first temporal convolution (Tj, Fig. 374).^ Bv the same methods made use of in determining the functions of the convolutions about the fissure of Rolando, the angular gyrus, the inferior frontal convolution, etc., the functions of the remaining convolutions have been more or less satisfactorily made out, and may be resumed as follows : (Figs. 387, 388, 389.) 1. Postero-parietal lobule : movement of the hind foot, as in walking. 2, 3, 4. Convolutions bounding the fissure of Rolando : move- ments of the arm and leg, as in climbing, swimming, etc. 5. Posterior extremity of the superior frontal convolution : exten- sion forward of the arm and hand. G. Anterior central convolution : supination and flexion of the forearm through action of biceps. 7, 8. Anterior central convolution : elevation and depression of the angle of the mouth, respectively. 9, 10. Inferior or third frontal convolution : movements of the lips and tongue, as in articulation, disease of which causes aphasia. 11. Posterior central convolution : retraction of the angle of the mouth. a, b, c, d. Posterior central convolution : movements of the hand and wrist, as in clinching the fist. 12. Superior and middle frontal convolutions : lateral movements of the head and eyes, elevation of the eyelids, and dilatation of the pupil. 13. Center of sensation. 13'. Occipital lobe, cuneus, supramargiual lobule, angular gyrus: center of vision. 14. Superior temporo-sphenoidal convolution: center of audition. V. Subiculum cornu ammonis : centers of olfaction, gustation, etc. H. Hippocampal region : center of touch. O. Occipital lobes : centers of organic sensations, hunger. F. Frontal lobes : intellectual and reflective powers. Pituitary Body. The pituitary body or hypophysis cerebri is not a single organ as the name would imply, but consists of two distinct lobes which differ histologically, in their mode of origin, and functionally. The anterior or glandular lobe is developed as an invagination of the buccal epithelium. It resembles somewhat in its minute structure the thyroid gland, but differs from the latter in being provided with more or less perfect ducts opening between the dura and pia mater. - It would appear, therefore, that the " internal secretion " which ' Gowers, oj). cit., \n\. "J, ]i. ll"J. 2Haller, Morpliolo.uischcs .Jalirliucli, 18'J6, xxv., s. 31. 678 THE NERVOUS SYSTEM. Fig. 392. The projection tracts joining the cortex with lower nerve centers. Sagittal section, showing the arranKenients of tracts in the internal capsule. A. Tract from the frontal lobe to the pons, thence to the circlielhir licniisjihere of the opposite side. B. ]Motor tract from the central convolutions to the facial nucleus in the pons and to the spinal cord; its decussation is indicated at K. C. Sensory tract from posterior culumns of the cord, through the posterior part of the medulla, pons, crus, and capsule to the jiurielal lobe. I). Visual tract from the optic thalamus (OT) to the occipital lobe. E. Auditory tract from the intergeniculate body, to which a tract jjasses from the "VIII. N. Nucleus (J) to the temporal lobe. F. Sujierior cereii<'llar peduncle. G. Middle cere- bellar peduncle. H. Inferior cereliellar peduncle. CN. Caudate nucleus. CQ. Corpora quadri- gemiua. VT. Fourth ventricle. The numerals refer to the cranial nerves. Fig. IWc Eyes opened. Eyes turned. Mouth opened. Head turned. Tongue. Mouth retracted. Shoulder. Ellmw. Wrist. Fingers. Thumb, inlc. Hi}}. Ankle. Knee Hallux. Toes. Schema of the arrangement of the motor fibers i internal capsula. (Bkkvor and Hoksley.) is elaborated fulfills some function in the economy of the brain. The posterior or infundibular lobe is de- veloped as an outgrowth of the brain. Histologically it consists of nerve cells, neuroglia, closed vesicles lined with epithelial cells containing a colloidal ma- terial. I^ess is known even of the functions of the pos- terior lobe than of the an- terior one. The general course of the tracts connecting the cere- bral convolutions whose functions have just been mentioned with tlie cord are shown in Fig. 392 and the relation of the fibers to each other as they pass through the internal capsule in Fig. o03. The descriptions of SLEEP. 679 the tracts of the special senses will be deferred, however, until the subjects of olfaction, vision, audition, etc., are considered. Sleep. The brain, like every other organ in the body, from time to time must rest, not only that the waste incidental to its functional activity may be repaired, but that its cells or whatever other struc- tural elements concerned in the elaboration of consciousness may not be overtaxed, worn out by constant activity. This need of rest is especially manifest in the case of the brain, for no work is so exhaustinf*; as brain work, and when once the brain is fagged, worn out, nothing is so difficult as to restore it to its natural, healthy activity. This necessity of periods of rest rhythmically alternat- ing with those of activity, is undoubtedly the underlying cause of sleep — however the latter may be brought about and concerning which there still prevails considerable difference of opinion among physiologists. Thus it is held by Sommer ^ that as oxygen appears to be gradually stored up during sleep, as shown by the experi- ments of Pettenkofer, after a time it will have accumulated in such an amount as to accelerate materially the nutritive changes going on in the brain, etc., the effect of which is that awakening occurs. On the other hand, during the waking state this store of oxygen is gradually used up, as shown by increase in the amount of carbon dioxide eliminated, the consequence of which is that exhaustion and general relaxation are experienced, followed by a desire to sleep. According to Pfliiger,^ the combination of this intra-molecular oxy- gen with the carbon of the lirain tissue is so violent as to amount to an explosion, which, taking place at successive intervals, main- tains the brain in a waking condition ; as the stored-up oxygen, however, is gradually used up the explosions diminish in frequency and violence until they cease altogether, and as a consequence sleep follows. A very plausil)le theory of the causation of sleep is that advanced by Dr. Cappie,^ who holds that the molecular activity of the cerebral cells is diminished through less blood being supplied to them by the capillaries, and that consequently the brain occupies less space. But inasmuch as the brain-case must be full, the veins of the pia mater become proportionally distended, the effect of which is that although the absolute quantity of blood, and conse- (][uently the pressure remains the same, the direction of the pres- sure is modified, being less from within and more on the surface of the brain, the latter or the altered direction of the pressure giving rise to sleep. This view is confirmed V)y the researches of Dur- ham,* by whom it was shown that the brain during sleep is in an essentially bloodless condition, that not only the quantity of the blood, but the velocity of its flow is diminished, and also by the iZeits. f. Eat. Med., Band xxxii., s. 214, 1868. s^Arcliiv, 1875, s. 468. 3 The Causation of Sleej), Kdinlmr<;li, 1882. * Guy's Hospital Reports, 3d ser., Vol. vi. 680 THE NERVOUS SYSTEM. observations of Dr. Hughlings Jackson/ who showed by ophthal- moscopic examination that the optic disc during sleep was whiter, the arteries smaller, the veins larger and the adjacent parts of the retina more ana?mic than during the waking state. Among the conditions favoring sleep may be mentioned the ces- sation of stimuli, diminished excitability of the tissues in response to stimuli, and the quality of the blood. The influence exerted by the latter condition is well shown by the well-known experiment of iNlosso,^ in which the blood of a dog- tired out with running; was transfused into that of one who had been resting, the effect being that the dog at once showed signs of fatigue and soon went to sleep. The amount of sleep required is affected by so many conditions, such as age, temperament, habit, mental and physical exhaustion, that it is absurd to lay down any rule upon the subject. In this respect, as in all others physiological, nature is our best guide. The mere fact that some individuals get along with only four or five hours' sleep without their health being aflPected is no argument what- ever that such a small amount of sleep is only required and should suffice for every one. Xo greater mistake is made, and that so often, by students of medicine, physicians, and literary men gener- ally, than to rob themselves of their natural sleep, at the cost of broken-down health and lost spirits, too often never to be regained. It will be observed that up to the present moment, in our expo- sition of the functions of the encephalon, we have endeavored to offer only wliat appears to us to be well-established anatomical and physiological facts, merely mentioning, or not referring at all, to the remaining portions of the encephalon, whose functions have not as yet been made out. It is needless to say, however, that whether or no the different parts of the encephalon and the different convolu- tions of the hemispheres really possess the functions assigned to them, that the phenomenon of consciousness is thereby in no wise explained. Admitting, for example, that the cuneus is the center of vision, and that the exact nature of the molecular changes occur- ring in its cells when the perception of sight is experienced were understood, we would be still unable to understand how the vibra- tions of light falling upon the retina give rise ultimately to visual perceptions — that is, the manner in which a physical impression be- comes a conscious perception. In the present state, at least, of the development of our consciousness it appears impossible even to con- ceive of how the gap between matter and mind, the objective and sub- jective, can ever be bridged over. We can say that the brain is the organ of the mind, even that it converts heat into thought, but, as viewed subjectively, the functions of the brain are synonymous with mental operations. The phenomenon of consciousness must be studied, not only objectively by the physiologist, but subjectively by the psychologist ; nevertheless, too much stress must not be laid upon n^oval I^ondiin Ojilith. IIosp. Keports. 2 1>u"Boi.s Keymond, Arcliiv, 18'J0, s. 89. MATTER AM) MIXD. 681 the distinction of matter and mind, of object and subject, as made by the metaphysician, since the existence of matter or mind, as shown by ultimate analysis, is only an inference. We are conscious of the perceptions of hardness, roundness, Aveight, extension, etc., and we infer the existence of something underlying these qualities, which we call matter, and which produces in us these sensations. We are directly conscious of these perceptions, not of the matter supposed to cause them. The existence of matter being, therefore, an inference from our consciousness, it is impossible to say, not knowiup; auvthinor whatever about its nature, Avhether it is akin to mind or not. On the otlier liand, supjiose that matter does exist, it is certain that the various modes of motion ordinarily known as heat, light, sound, etc., are transformable in us into equivalent modes of consciousness, and we infer from these modes of motion the existence of something, the mind underlying these modes of consciousness, but of whose nature we know just as little as that of the matter, from the effects of which its existence is inferred. The idealist may argue that there is no such thing as matter apart from mind, since material forces are only cognizable as modes of con- sciousness, and the materialist may argue that there is no mind apart from matter, that the modes of consciousness are material, since what exists in us as consciousness is transformable into modes of motion, but it is evident that the forces of the inner are correlated with those of the outer world, the forces of the outer with those of the inner world, that if we begin with mind we end with matter, if with matter we end in mind ; matter and mind being merely sym- bols of the unknown reality underlying both.^ ' Herbert Spencer, First Principles, p. 558. chaptp:r XXXV. THE NERVOUS SYSTEM.— {Continued.) SYMPATHETIC NERVOUS SYSTEM. The sympathetic system of nerves, or the system of organic vegetative life, also known as the trisplanchnic nerve, great inter- costal nerve, etc., consists of a double chain of symmetrically dis- posed ganglia extending the entire length of the vertebral column, which, gradually converging, terminates finally as a single ganglion, the ganglion impar, resting upon the coccyx. While there is no doubt as to the manner in which the double ganglionated cord of which the sympathetic consists ends, it has not as yet been made out exactly how it begins ; the observation of Ribes^ that it begins as it ends, in a ganglion impar situated upon the anterior commu- nicating artery, not having been confirmed by other anatomists. Intercommunicating with the nerves of the cerebro-spinal system, and giving off during its course numerous branches forming intricate plexuses, such as the cardiac, solar, and hypogastric, the sympathetic nerves, as a general rule, follow the course of the great blood ves- sels, entwining the latter as the ivy the oak, to supply the viscera of the great cavities of the body, etc. The nerves of the sympathetic system are usually much smaller, softer, and less distinctly seen than those of the cerebro-spinal sys- tem, present a grayish aspect, and adhere closely, by connective tissue, to contiguous structures. While consisting of medullated nerve fibers, they are largely composed of the pale gray, gelatinous fibers of Eemak, the latter resembling eml)ryonic nerve fibers and the nerve fibers developed in the reunion of nerves. The ganglia of the sympathetic, whether of the ganglionated cord or its branches, do not differ essentially in structure from the ganglia of the pos- terior roots of the spinal nerves, large root of the fifth, trigeminal, glosso-pharyngeal, pneumogastric, etc. They consist of a mass of nerve cells smaller than those of the spinal ganglia, imbedded in a stroma of connective tissue, which is traversed by nerve fillers, the whole being enclosed by a tightly adherent membrane continuous M'ith the sheath of the nerves upon which the ganglia occur, the latter looking like so many grayish-white or reddish-gray swellings or knots. The main ganglia and branches of the sympathetic being situated in the cervical, thoracic, abdominal, and pelvic regions, we may begin in our necessarily brief account of the physiological re- lation of the parts involved with the ganglia of the cervical region, and first with the superior cervical ganglion (Fig. 394). 'Mem. de la Soc. Med. d' Emulation, Tome viii., yi. G06. SYMPA THETIC XEE VO US SYSTEM. Q^'^ Fig. 394. pi ofthe .synipkthetic. 6. SuperioVVervica/yairfflim,'''"--"V'''' ■\"""ng"a'- •^, 5, 5. Chain of Kanglia 8. Nerve of.Iacobson. 9. Two fiJaments tiumlCfJi /^'■»"<-t*^\f'-"m t'^s ganglion to the caroUd mem f?' n f?"^"°"- ^'^- ^^"'"^ oculfexter^^s' "n"' r, iuhfln?,v''' spheno-pafatine and toe other r> sr i 1? '^1 r'*""" '•"•" t^ommunis and a sensor v h n. m ^f„f.?^''''°' "Teiving a motor tila- 1-'. i^plieuo-palatme ganglion. 1.3. Otic eanVlionVaT, ^"^ *'*^ "'"'"='' l>ranch ofthe fifth maxillary ganglion. 16, 17. SunerW far ."^- i - ^'"«''?' I".'""^'* "'"">e fifth nerve 1.5 Si hi Recurrent laryngeal nerm 21 •« f fn". "f L'', "^^'V'- H' K-^'ernal laryngeal nerve io 20 ing ti aments to the superior cervicaT sv4^ Xh '''^"'''r "^ *'',^ "PP^"- fo" cervicafnerves .end! and sixth cervical nerves, sending .^^}^^!:\,^^^, ^^i^'S^^"^^^ 684 THE ' NEE VO US SYSTEM. branches of the seventh and eighth cervical and tlie first dorsal nerves, sending filaments to the inferior cervical ganglion. 27. Middle cervical ganglion. 28. Cord connecting the two ganglia. 29. Inferior cervical ganglion. 30, 31. Filaments connecting this with the middle ganglion. 32. .Snperior cardiac nerve. 33. Middle cardiac nerve. 34. Inferior cardiac nerve. 35, 35. Cardiac plexus. 36. (janglion of the cardiac plexus. 37. Xerve 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 pneu- mogastric. 45. Eight pneumogastric. 4G. Lower end of the jihrenic nerve. 47. Section of the right hronchus. 48. Arch of the aorta. 49. Right auricle. 50. Right ventricle. 51, .52. Pulmonarv artery. 53. Right half of the stomach. 54. .Section of the diaphragm. (Sappey.) The superior or first cervical ganglion, lying upon the rectus major muscle opposite the second and third cervical vertebrae and behind the internal carotid arterv, is connected bv intervening; fila- ments ^vith the upper four spinal nerves — the ganglia of the glosso- pharyngeal, pneumogastric, and the hypo-glossal nerves. In addi- tion to its cord of communication with the second cervical ganglion, the superior cervical gives off an ascending branch, vascular and pharyngeal branches, and the superior cardiac nerve. The ascend- ing branch accompanying the internal carotid artery through the carotid canal divides into two branches, which, subdividing and communicating with each other around the artery^ so form the caro- tid plexus. From the latter are given off filaments to the abducens nerve, and the deep petrosal which passes to the spheno-palatine, or Meckel's ganglion, the latter connected with the spinal system by the superior maxillary and great petrosal nerve. Continuing up- ward around the artery, on reaching the cavernous siiius, the sym- pathetic plexus l^ccomes then the cavernous plexus, an impor- tant one, since it communicates with the semilunar oano-lion and ophthalmic branch of the trigeminal with the ophthalmic ganglion, the latter connected Avith tlie spinal system by the ophthalmic and oculo-motor nerves, and with the oculo-motor and pathetic nerves. From the carotid and cavernous plexuses fine filaments are also given off which entwine themselves around all the branches of the internal carotid artery. The vascular branches of the superior cervical ganglion form plexuses upon the internal carotid artery and its branches. By the plexuses on the internal, maxillary, and facial arteries the syin])athetic communicates with the otic and sub- maxillary ganglia respectively, the otic ganglion being connected with the spinal system by the small petrosal, the submaxillary ganglia by the chorda tympani. The pharyngeal branches, two or three in number, descending to the side of the pharynx, together with branches from the glosso-pharyngeal and pneumogastric nerves, form the pharyngeal plexus, which, as we have already mentioned, supplies the mucous membrane and constrictor muscles of the pliar- ynx. The superior cardiac nerve, derived from the first cervical ganglion and from the cord below it, descends behind the great blood vessels of the neck, and entering the thorax passes on the right side either in front of or behind the subclavian artery, thence along the innominate to tlie l)ack of tlie arch of the aorta, to end in the cardiac plexus. ( )n the left side the nerve follows the carotid artery in its course to the cardiac plexus. CARDIAC XERVES. 685 The superior cardiac nerve commimicates with the pneiimoprastric, aud gives off iilanients to the inferior thyroid artery. The middle, or second cervical ganglion, resting upon the inferior thyroid artery, aud situated opposite the fifth cervical vertebra, is connected with the third cervical ganglion by several branches, and gives off fila- ments to the fifth and sixth spinal nerves, branches which follow the inferior thyroid arteiy to the thyroid body, and the middle car- diac nerve. The latter, as it descends the neck, receives filaments from the superior and inferior cardiac and pneumogastric nerve, and ends in the cardiac plexus. Occasionally the middle cervical ganglion is indistinct, or even absent ; in such cases it appears to be fused "vvith the inferior or third cervical ganglion. The latter, sit- uated behind the vertebral artery and between the transverse pro- cess of the last cervical vertebra and the first rib, gives off, in ad- dition to the branches going to the first thoracic ganglion, branches to the seventh and eighth spinal nerves, to the vertebral artery, and the inferior cardiac nerve, M'liich, after receiving filaments from the middle cardiac and inferior laryngeal nerves, and some- times from the first thoracic ganglion, terminates in the cardiac plexus. Occasionally the inferior cardiac nerve of the left side becomes blended with the middle cardiac nerve. The three cardiac and pneumogastric nerves, together wdth branches from the first thoracic ganglion, form the cardiac plexus. The latter situated behind and beneath the arch of the aorta, gives off branches which, accompanying the coronary arteries, constitute the coronary plexuses. While the cervical portion of the sympathetic consists, as we have seen, of three ganglia, etc., the thoracic portion consists of usu- ally twelve ganglia, resting upon the heads of the ribs and covered by the pleura. The first thoracic ganglion, as already mentioned, is connected with the last cervical, and the last thoracic with the first lumbar, the connecting cord of the latter passing through the diaphragm. Each thoracic ganglion usually gives off two narrow cords, the rami communicantes, which pass to the nearest intercostal nerve. The upper six thoracic ganglia give off, also, branches to the aorta, intercostal blood vessels, and the arsopha- geal and pulmonary plexuses of the pneumogastric nerve. The lower six thoracic ganglia give off, in addition to the branches going to the aorta, branches which go to form the three splanch- nic nerves. The great splanchnic nerve, deriving its roots from the sixth to the tenth thoracic ganglia, inclusive, perforates the cms of the diaphragm, and terminates in the semilunar ganglion. The small splanchnic nerve, deriving its roots from the tenth and eleventh thoracic ganglia, passes through the diaphragm with the preceding nerve, and terminates in the solar plexus. The third splanchnic, sometimes absent, coming from the twelfth thoracic ganglion, pierces the diaphragm, and terminates in the renal plexus, 686 THE SEEVOUS SYSTEM. The solar plexus (Fig. 395), so called on account of the numer- ous filameuts radiating from it, is situated behind the stomach and in front of the aorta and crura of the diaphragm, and surrounding the cceliac and commencement of the superior mesenteric artery, extends to between the suprarenal bodies. It consists of an intri- cate mixture of nerves and ganglia ; among the former may be men- FiG. ?.9o. IS 21 2 Solar plexus. (Hirschfeld.) tioned the great and small splanchnics, as well as filaments from the pneumogastric nerve ; among the latter the semilunar ganglion (Fig. 396), so called on account of its being situated on each side of the plexus, at the side of the coeliac and superior mesenteric arteries. From the solar plexus emanate numerous plexuses, named after the vessels around which the branches entAvine them- selves, as follows : the phrenic, coronary, hepatic, splenic, supra- renal, renal, and spermatic, superior mesenteric, and aortic plexus. The aortic plexus, descending upon the aorta from the solar plexus, of which it is the continuation, after giving off the inferior mesenteric plexus terminates below in the hypogastric plexus. The latter very intricate plexus, situated between the common iliac blood vessels, extends downward as the inferior hypogastric plexus on each side of the rectum, and after receiving branches from the lower lumbar and sacral ganglia, the lower two or three sacral nerves, and the in- ferior mesenteric plexus, gives off the vesico-prostatic, or the vesico- vaginal and uterine plexuses, according to the sex respectively. The lumbar portion of the sympathetic (Fig. 396) consists of four or five ganglia situated at the sides of the vertebne which communi- cate with each other, and with the adjacent lumbar nerves, as in the case of the thoracic ganglia, and give off branches to the aortic and HYPOGASTRIC PLEXUS. 687 1 i;.i n^iviUv four in number, are hvpogastric plexus. .Tl«,-^".l ^"^^ t-e ' ^rf .ive off branches to Jnected likewise ...h "- .^'^^ .uToncUho siugle eoce>-gea the hypogastno plex«^; A ^^^- ^^^„, similar to those otte ganglion ov ganglion ""1« -;; '^ "o svmpa -^ ^^^^.^^ 688 THE NERVOUS SYSTEM. coDsiderable difference of opinion prevailed at one time as to whether the gantrha of the sympathetic were sensitive, there is no doubt on this point at present ; mechanical or chemical irritation of the tho- racic or semilunar ganglia in dogs, calves, and rabbits, having been shown l)y Flourens/ Brachet,- Muller,^ Longet,^ etc., to give rise to pain. The sensibility of the sympathetic, however, is far from acute, being indeed, dull, as compared with that of the cerebro- spinal system. As regards the excitability of the s}nipathetic, it has also been shown by JNIuller,'' Longet,'' and others, thatj stimula- tion of the ganglia, splanchnic nerves, etc., by electricity or chem- ical irritants causes contractions of the muscular coat of the intes- tines. Inasmuch, however, as the muscular coat of the intestines consists of unstriated muscular tissue, the contraction does not immediately follow the stimulation, as in the case of the cerebro- spinal system and striated muscle, and further, the contraction lasts longer, another characteristic of the effect of stimulating unstriated muscular tissue. Since, however, the most important effects follow- ing stimulation of the sympathetic can be obtained, as we shall see presently, by the stimulating of the cerebro-spinal system, and as the ganglia and fibers of the sympathetic lose their properties through atrophy, degeneration, etc., when separated from the cerebro-spinal system, with which Ave have just seen they are in- variably connected, as shown by the ex})eriments of Bernard," Courvoisier,^ etc., it would appear that whatever properties are pos- sessed by the sympathetic are due to its connections with the cere- bro-spinal system. That the sym])athetic system, in fact, is only an appendage of the cerebro-spinal system, is not only shown by the facts just referred to, but also by the very important one in this connection that in the lowest fishes, amphioxus, myxine, the sym- pathetic system is undeveloped or absent, which would not be the case were its presence an indispensable element in the nervous or- ganization of a vertebrate. Up to the beginning of the eighteenth century it may be said that absolutely nothing had been definitely established with regard to the functions of the sympathetic system. In 1712, however, Pourfour du Petit ^ divided the cervical sym- pathetic in a dog, repeating the experiment in 1725, in the presence of Winslow and Senac, and called attention among its consequences to the redness and injected condition of the conjunctiva, the con- tracted condition of the pupil,"' etc. The conclusion drawn by ^ Reclic'irhes experimentale sur les proprietes et les functions du systeme nerveux, p. 230. Paris, 1842. 2 Keclieirlies experimentale sur les functions du svsteme ganglionaire, p. 305. Bruxelles, 1834. ^Mnller, Piiysiology, Vol. i., p. '712. London, 1840. * Physiologic, Tome iii., p. 593. Paris, 1809. ^0\). cit., j). 713. ^Op. cit., p. 595, Systeme Nerveux, Tome ii., p. 568. Paris, 1842. 'Journal de la pliysiologie, Tome v., p. 407. Paris, 1862. * Archiv of Micros. Anat, Band ii., s. 30. • Bonn, 1886. ^Memoires de r Acad, des Sciences, p. 1. Paris, 1827. ^''Due to the unopposed action of tlie tliird pair (jf nerves supplying the circular muscular fibere of tlie iris. VASOMOTOR NERVES. 689 Petit from his experiments and observations was that tlio intercos- tal nerve, as the sympathetic Avas then called, " furnished spirits to the conjunctiva, to the glands, and to the vessels "which are found in these parts, the relaxation of the parts being so evident that there almost always ensues a slight inflammation of the conjunctiva due to the swelling of the vessels ; " that the influence exerted by the sympathetic was propagated from below upward toward the brain, and not from the brain downward, as was often supposed. Notwithstanding the importance of the conclusions correctly drawn from his experiments by Petit with reference to the influence of the sympathetic upon the circulation, nutrition of the eye, etc., nearly a century passed without anything further being added to our knowledge of the functions of the sympathetic. In 1812, however, Dupuy, of Alfort, having removed the superior cervical ganglion in horses, called attention among the effects of the experiment, partic- ularly to the injected condition of the ocular conjunctiva, and to the elevation of temperature in the ears, head, and neck, which were bathed in sweat ; the general conclusion arrived at by Dupuy ' l)eing that the sympathetic exercises a great influence on the nutri- tive functions. A\ hile Petit described the effects of cutting the cervical sympathetic, and Dupuy of removing the superior cervical ganglion, neither of these experimenters offered any definite explana- tion of the hyperemia noted in both cases, nor Dupuy of the rise in temperature 'in the latter one. Indeed, the true explanation of the phenomena at that period would have been impossible, the structure of the arteries not yet being understood. Even though Valentin- had shown, in 18')9, that the arteries contracted in response to stimulation of the nerves distributed to them, it was not admitted that the middle coat of the arteries con- tained muscular fibers until 1840, when such was actually demon- strated to be the case beyond doubt by Henle.^ During the same year, Stilling,^ like Henle, was led to the conclusion that there ex- isted nerves comparable to those distributed to the muscles gener- ally, which act upon the blood vessels, either directly or reflexlv, and which he called " vasomotor nerves." In 1852 Brown- Sequard '" divided the cervical sympathetic on one side in rabbits, and called attention, as Bernard '' had done in the previous year, to the hyperpemia and elevation of temperature, often amounting to as much as 11° F. (6.1° Cent.) on the corresponding side of the head and ear, and for the first time gave the true explanation of the phe- nomena in attributing the rise in temperature of the parts aflected 1. Journal de C'orvisart et Leroux, ISIH, Tome xxxvii., p. 340. Meckel's Archiv, 1818, Band iv., s. 105. ^Dq Functionibus Nervorum Cerebralium ct Nervi Svnipatlietici, p. 153. Bernas 1839. ''Wochenschrift fiir die gesammte Ilcilknnde, lS-10, Xo. 29, s. 329. * Eecherches path, et med. pratkpies sur 1' Irritation. Leipziji-, 1S40. ^The Medical Examiner, New Series, Vol. viii., p. 489. Phila(lel|)liia, August, 1852. ^Comptes rendus de la society de biologic, Tome iii., p. 163. Paris, 1851. 44 690 THE NEB VO US SYSTEM. to the supply of blood being increased through the dilatation of the blood vessels, and by showing that while section of the sympathetic in paralyzing the muscular coats of the arteries permits of their dilatation, electrical stimulation of the central cut end of the sym- pathetic causes their contraction again, and with the latter the restoration of the parts to their normal condition. To Brown- S6quard must be accorded, therefore, the discovery, not exactly of vasomotor nerves, since the existence of such had been previously indicated by Henle and Stilling, but, more especially, of the vaso- constrictor nerves of the cervical sympathetic, and of their mode of action in influencing the calibre of the blood vessels, temperature, etc., of the parts to which the latter are distributed. It should be mentioned, however, injustice to Bernard, that three months after Brown-Sequard's discovery, and without being aware of it, Bernard' offered the same explanation of the experiments performed by him during the previous year (1851), but at that time by him incorrectly, interpreted. The calibre of the veins as well as that of the arteries is regu- lated by vaso-constrictor nerves. Thus, for example, stimulation of the peripheral cut end of the splanchnic nerve causes contraction of the portal vein " and of the sciatic nerve, the femoral artery being ligated, contraction of the superficial veins of the limb.^ The modi- fication in calibre of blood vessels due to the action of vaso-con- strictor nerves can be shown not only by the methods just men- tioned, but also by measuring the amount of blood that flows from a vein before and after stimulation of the vaso-constrictor nerve supplying it, the outflow being much less in the latter than in the former case. Another method also made use of is based upon the fact that stimulation of a vaso-constrictor nerve in contracting the blood vessels of a limb will cause a rise of l)lood pressure in that limb, the general blood pressure remaining however unaltered, as shown by means of a manometer connected with the opposite limb. Contractions of the blood vessels in a limb as due to vasomotor influence can also be studied by means of the plethysmograph of Mosso, already described, the contractions of the vessels being- shown by the diminution in the volume of the limb used, the latter being indicated by the fall of the recording lever. The vaso-constrictor nerves are found not only in the cervical, but also in the thoracic and abdominal portions of the sympathetic, and in the trachial and sciatic plexuses, supplying the upper and lower extremities. While the vaso-constrictor nerves are given off as fibers from the cells of the sympathetic ganglia, the latter are in relation functionally with the axons that pass from the cells situated in the cord at different levels, they being in turn in relation with the axons that descend from cells in the medulla. Hence, division ilbid., 1852, Tome i v., p. 169. 2 Mall, Du P>()is Keyinond Archiv, 1890, s. 57 ; 1892, s. 409. 3Thomp.son, Dii Bois Keyraond Archiv, 1893, .s. 104. VASOMOTOR CENTER. 691 or stimulation of the peripheral eut ends of the medulla cord, or of certain spinal nerves in certain definite regions, is followed by dilata- tions or contractions of the blood vessels, just as if the vaso-con- strictor nerves had themselves been divided or stimulated.^ Thus, for example, while the vaso-constrictor nerves of the head are de- rived from the superior cervical ganglion, they can be traced indi- rectly by their division and electrical stimulation through the cervical cord of the sympathetic to the anterior roots of the first three dorsal spinal nerves, and thence into the anterior columns of the cord. Further, according to Bernard,^ whilst the fibers distributed to the dilating muscular fibers of the iris, thereby causing dilation of the pupil, are derived from the first two dorsal nerves (cilio-spinal center), those distributed and influencing the caKber of the blood vessels are derived from the third dorsal nerve. In the same manner, the vaso-constrictor nerves supplying the blood vessels of the upper extremity, while emanating from the first thoracic ganglion, are, functionally, derived from the spinal cord, passing off from the latter with the anterior roots of the third to the seventh dorsal nerves inclusive, and thence traversing the thoracic portion of the sympathetic and the inferior thoracic ganglion, reach the brachial plexus by the rami communicantes, to be finally distributed with the branches of the plexus, while such of the vaso-constrictor nerves as are derived from the plexus itself are given oiF with the anterior roots of the cervical nerves. The vaso-constrictor nerves supplying the blood vessels of the abdominal viscera, more especially the splanchnic nerves, are largely derived from the dorsal and lumbar portion of the cord ; the latter, together with the sacral portion of the cord, giving oiF fibers which pass through the lumbar and sacral plexuses to the sympathetic, and thence into the lower extremities, supphdng the blood vessels of the latter. Inasmuch, then, as the vaso-constrictor nerves are derived from the spinal cord, traversing more particularly its anterior columns, it might naturally be supposed that all these nerve fibers at some point of the cord, the upper portion most probably, would be brought to a focus, so to speak, and that stimulation of such a por- tion of the cord would cause all of the blood vessels to contract and a corresponding rise in blood pressure and division of the same, a dilatation of the vessels and fall in blood pressure. Such a focus or vasomotor center has indeed been found in animals, not exactly by anatomical demonstration, but by means of successive sections of the cord below upward, and from above downward, and localized in the rabbit, for example, by Owsjani- kow ^ and Dittmar ^ in the floor of the fourth ventricle on either side of the middle line just one millimeter behind the optic lobes and 'Budge and "Waller, Comptes rendus, Tome xxxiii., p. 372. Paris, 1S51. Ludwig and Thiry, Wiener Sitzungsberichte, 1864, Band xlix. II. Abtlieilung, s. 4'21. Vulpian, Leyons snr I'Appareil vaso njoteur, p. 189. Paris, 1875. ^Comptes rendus, Tome iv., p. 383. ^Ludwig's Arbeiten, 1871, s. 210. "Ebenda, 1873, s. 110. 692 THE NERVOUS SYSTEM. extending ab^nt four millimeters toward^ the net of the calamus scriptorius. From this "tonic" center emanate impulses, which transmitted through the anterior columns of the cord and anterior roots of the spinal nerves pass thence to the sympathetic ganglia and vaso-con- strictor nerves, and through the latter maintain the normal calibre of the vessels or the vascular tonus. It has also been established ^ that vaso-constrictor centers exist in the spinal cord, since after section of the cord the tonicity of the vessels beloAV the seat of section is to a certain extent still main- tained. That the sympathetic ganglia contain also vaso-constrictor centers is shown by the fact of the tonicity of the vessels in the limb of a dog being maintained even after removal of a consider- able portion of the spinal cord.- Tlie action of the centers in the cord and sympathetic ganglia i< usually regarded, however, as be- ing of a secondary character to that excited by the principal center in the medulla. Inasmuch as the muscular fibers of the middle coat of the blood vessels are disposed in a circular manner at right angles to the long axis of the vessels, it is not difficult to understand why stimulation of the vaso-constrictor nerves is followed by contraction of the ves- sels — indeed, the disposition of the nervous and muscular fibers being such, it can hardly be conceived how it should be otherwise, and vet, strange as it may appear, as first shown by Bernard,'^ there are also nerves the stimulation of which causes dilatation of the blood vessels instead of contraction, and which may, therefore, be called vaso-dilator nerves ; among such may be mentioned the chorda-tympani, the auriculo-temporal, the nervi-erigentes of the penis ; stimulation of these nerves causing dilatation of the vessels of the tongue,^ of the ear, and of the corpora cavernosa of the penis,^ respectively. Though numerous explanations have been oifered of the manner in which the vaso-dilator nerves act, it must be admit- ted that none of them are satisfactory, and that it is not yet under- stood how their stimulation causes dilatation of the blood vessels. Thus, it has been said that the stimulation of a vaso-dilator nerve causes the vein of the part to contract, and that in consequence an obstacle is oifered to the passage of the blood from the artery to the capillary, which is the cause of the dilatation of the artery. As a matter of fact, however, the vein does not contract, but dilates as much as the artery. It has also been suggested that the stimula- tion of a vaso-dilator nerve excites the activity of the anatomical elements of the part to which the nerve is distributed, the eifect of which in the case of a salivary gland, for example, would be that ^Goltz u. FroiisberfT, Pfliiger's Arcluv, 1874, s. 46:5. 2 Golf/, u. Ewald, Pfliifier's Archiv, 1896, s. .'389. ^Systemc Xcrvoux, Tome ii., p. 144. Pivris, 18.38. Liquides de rOrjj:imisiiie, Tome i., ]>. 'M2. *^'ulpian, op. cit., p. 1.38. •'Eckliard, UiitersiK-hun. ^.Journal de pliy.siologie, Tome iii., p. ITo. Paris, 18G0. CHAPTER XXXVI. THE SKIN AND ITS APPENDAGES. SEBACEOUS MAMMARY AND SUDORIFEROUS GLANDS. PERSPIRATION, TACTILE AND OTHER F0R3IS OF CUTANEOUS SENSATION. Fig. 397. The Skin. The skill or integunient (Fig. 397) constitutes a general protec- tive and sensory covering for the surface of the body. In addition to these important functions in eliminating the sweat, carbon diox- ide, urea, etc., the skin acts also as an excretory organ, supplementing, in this respect, the action of the lungs and kidneys. As we have already seen, the skin, too, in a great measure regulates the production and distribu- tion of heat. To a certain extent, also, the skin acts as an absorbing surface. Further, through special modifications of its sensory structure, the skin min- isters to the sense of touch and other forms of cutaneous sensation. The skin, in addition, then, to being sensory and protective, possesses, as well, ex- cretory, calorilic, alisorbing, and tactile functions. The general appearance of the skin, its extensibility, flexibility, elasticity, and color are sufficiently fa- miliar to all. It may be mentioned in this connection, however, that the color of the skin in the diiferent races of mankind and the varieties of complex- ion observed in different individuals of tlie same race, are due to the amount of pigmentary matter present in the deeper layers of the epidermis and that the color of the true skin, or dermis, is whitisli and semi-transparent, its ap- parent pinkish color being due rather to that of underlying parts and the blood circulating tlirough the latter. The furrows and folds of the skin are caused partly by the muscles and joints and partly by loss of elas- ticity in the skin itself and by the deposition in it of fat. Faint, irregular lines are also observed on most parts of the surface of ^ s Xcili'-al forefinger across two of the ridges the surface, highly magnified. '.1 the of 1. Dermis composed of an intertextiire of bundles of librous tissue. 2. ICpi- dermis. 3. It.s cuticle. 4. Its soft layer. 5. Subcutaneous connective and adipose tissue. (>. Tactile pa- jjillse. 7. Sweat glands. 8. Duet. ii. Spiral jiassagc from the latter tlirough the (-iiidcrmis. 10. Termination of llic iiassage on the summit of ridge. (M:iDY.) THE DERMIS, OB TRUE SKIX. <>^'7 the skin, upon the pahns of the hand and soles of the feet and particularly upon the palmar surface of the last phalanges ; these lines are well marked in the latter situation, being disposed as con- centric curves depending upon the regular arrangement of the underlying papillae of the true skin or dermis. According to Sap- pev,^ the cutaneous surface, on the average in man, is equal to about 1.5 square meters (1(5 S(|uare feet), though in men above the ordi- narv size it may amount to as much as 2 S(|uare meters (21.4 square feet). The significance of such variations physiologically will become apparent presently when we consider the excretory functions of the skin. In harmony with the protective functions of the skin, its thick- ness varies very much in different parts. Thus, where naturally exposed to constant pressure and friction, as on the soles of the feet or the palms of the hands, the skin, as we shall see, is much thicker than that of the face, eyelids, etc. The skin consists of two layers, the dermis and epidermis, special modifications of the latter constituting the hair and nails, the sebaceous, mammary, and sweat glands. The dermis, or true skin, also known as the cutis, vera, corium, etc. (Fig. 397), constituting the deeper layer of the skin, is more or less closely connected to the underlying parts by the connective tissue of the adipose layer of the superficial fascia, or when the adipose layer is absent, by the loose connective tissue to the deeper layer of the fascia or sub- jacent structure, thereby allowing the skin a certain amount of movement backward and forward. The thickness of the adipose layer varies very ranch in different individuals and in different parts of the same individual. Thus while there is no fat beneath the skin of the eyelids, the upper and outer part of the ear, the penis, and the scrotum, a layer about 2 millimeters (J^ of '^i^ inch) in thickness is usually present beneath the skin of the cranium, the nose, the neck, the knee and elbow^, and the dorsum of the hand and foot ; the adipose layer, on an average, in other situa- tions, measuring from 4 to 12 millimeters (^ to | of an inch). In fat persons, however, it may attain a thickness of 25 milli- meters (1 inch) or even more. There is no well-defined line of demarcation between the dermis and the underlying adipose tis- sue, and after separating the two the dermis looks like a coarsely corded network, the meshes being occupied by small round masses of adipose tissue. The dermis consists principally of a dense inter- texture of bundles of fibrous tissue crossing one another at acute angles in different directions, mingled with amorphous matter and some elastic tissue, the latter l)eing most abundant on the front of the body and around the joints. It^ contains also unstriated mus- cular fibers, the erector pili muscle, which, passing downward from the more superficial part of the dermis, are inserted into the hair follicles, and which, when excited to contract through the stimulus 'Anatomie, Tomeiii., p. 5(>-l. Paris, 1877. 698 THE SKIN AND ITS APPENDAGES. of cold, emotions of fear, or electricity, elevate the hairs and so give rise to the condition known as " goose flesh." In consequence of the gradual transition of the dermis into the subjacent tissues, its exact thickness is difticult to estimate. It may be said, however, to be about ^ of a millimeter {-^^ of an inch) thick on the eye- lids, about 1 millimeter (J^ of an inch) on the front of the body, and 3 millimeters (^ of an inch) on the back of the body and the heels, being thickest where the entire skin presents that con- dition. The dermis is thinner in the female than in the male, about half as thick in children as in adults and becomes thinner in old age. At its outer surface the dermis is quite dense, being defined by a more lioraogeneous layer or basement membrane, and projects here and there as small eminences, the papillje, into the deeper layers of the epidermis. The papillae, on which the perfection of the skin as an organ of touch largely depends, they being highly developed where the sense of touch is exquisite, and vice versa, are of two kinds, simple and compound, tlie latter consisting of two, three, or more simple papilhe springing from a common base. The papilhe, composed of a continuation of the fibrous and amorphous structure of the dermis and defined by the basement membrane of the latter, vary in number and size in diiferent parts of the body. They are most numerous and longest in the pahns of the liands and soles of the feet, attaining in these situations a length of from J^ to ^ of a millimeter (the g-i-g- to the j^-^ of an inch), and, being here dis- posed in double rows on the ridges of the dermis, of which they are the continuation, give rise, as already mentioned, to the curved lines so noticeable on the palmar surfaces of the skin of the last phalanges of the fingers and toes. The papilhe are also quite nu- merous on the prepuce, glans penis, nynq)h[e, clitoris, and nipple. In other portions of the body they are less numerous and small, measuring only the -^^ of a millimeter (the -^^^ of an inch). In the face, for example, the papillae are so little developed as to be hardly recognizable. Most of the papilla^ of the palms, fingers, soles, toes, and nipples, especially the compound kind, contain tactile corpus- cles in Avhich, as already mentioned, the cutaneous nerves termi- nate. It will be rememl)ered also that the dio-ital nerves of the fingers and toes appear to terminate in similar shaped, though larger bodies, the Pacinian corj^uscles, situated in the subcutaneous tissue and the nerves suj)])lying tlie skin of tlie glans penis and clitoris in the Krause corpuscles, reseml)ling the tactile and Paci- nian corpuscles, though smaller than either. The dermis with its ])apillie is richly supplied Avith blood vessels and l^anphatics, as well as nerves. Tlie arteries penetrating tlie dermis from beneath end in a capillary network, the latter extending as single loops into the papilhe, Mliile the veins, more numerous and larger than the arteries, terminate in the superficial venous trunks. The lym- phatics already referred to are most numerous on the fore and THE EPIDERMIS. 699 inner part of the body and limbs, being particularly well devel- oped in the palms and soles. The dermis, consisting largely of white fibrous tissue, is by boiling resolved, in a great measure, into gelatine, the ordinary source of glue, hence also its conversion into leather by tanning. The fibrous structure of the dermis, the papilla?, the mouths of hair follicles, etc., may usually be seen in the cut edge and rough surface of a piece of leather. Deprived of its fatty matters, etc., the dermis, when properly thinned, forms also parchment. The epidermis, also knii iiKiiuiiir>. «, a. ('uta- ueous papillte. h. Lndermost and dark- colored layer of oblong vertical epider- mis-cells, f. Mucous or Malpighian layer. redullary sub- stance. 11. Bulb of the hair composed of soft polyhedral cells. 12. Transition of the latter into the cortical substance, medullary substance, and cuticle of the hair. (Leidy.) 706 THE SKIN AND ITS APPENDAGES. upon that of the papilla which the hair bulb tightly encloses or caps. The hairs are continually renewed by constant growth. In some instances, especially after disease, they are cast off or shed, new ones being produced. Permanent baldness is due to atrophy of the papillte, while the sudden blanching of the hair, occurring some- times in a single night, is due to the greater part of the medulla and cortex becoming filled Avith air.^ Chemically, hairs are composed of fats, a gelatine-like substance, albuminous matters, containing a large proportion of sulphur, per- oxide of iron, traces of manganese, silica, sodium, and potassium chlorides, calcium sulphate and phosphate, and magnesium sul- phate.^ With the exception of the palms of the hands and soles of the feet, the jialmar surface of the fingers and toes, the lips, lining of the prepuce and glans penis, hairs cover nearly every part of the surface of the body. The hairs generally project obliquely from the skin, and are regularly disposed, usually in curving lines from particular points. They differ very much as regards their size, fineness, color, form, and number, in diflPerent races, sexes, in- dividuals, and parts of the body. Of the long hairs, attaining sometimes in women a length of 90 cm. (three feet) or more, and a diameter of from the g^^ to ■^^r of a millimeter (y-g^o'o' ^° ^^o" ^^ an inch), the finest are found upon the head. The short, stiff hairs of the nostrils and edges of the eyelids, are from the Jg- to i of a- millimeter {^^-^^ to the y^^ of an inch) in diameter, the fine downy ones from the J^ to gig- of a millimeter (g-oVo ^^ *^^ i2Vo" of an inch). While the fine silken hair of the head in the white race is cylindrical, the crisp hair of the head and beard of the negro is more or less flattened cylindrical. It has been estimated^ that upon a square inch of scalp there are about 1,000 hairs, the num- ber upon the entire head amounting to 120,000. The hairs are elastic, readily electrified by friction, especially in cold, dry weather, and very hygrometric. The latter property is taken advantage of in the making of delicate hygrometers, the hair elongating through the absorption of moisture. The hairs not only serve to protect the general surface, as in shielding the head from excessive cold or heat, but also guard certain orifices, as those of the ears and nose. The eyebrows prevent the perspiration from the forehead running on to the lids, the eyelashes the surface of the conjunctiva from dust, etc. Hair, being a bad conductor of heat, serves also to re- tain that produced within the body. It has already been mentioned that the hairs are quite regularly disposed, and it will be further observed that if a man assume a crouching attitude, with elbows upon the knees, and the chin resting upon the hands, that their general direction u]ion the extremities is oblicpiely downward, a dis- position such, that if the })erson be exposed to wet weather, the rain 'Landois, Yirchow's Arch., 1866, Band xxxv., s. 375. Wilson, Proe. Eoy. Soc. Lond., 1S67, Vol. xv., p. 406. ^Quain's Anatoniv, ^'ol. ii., p. 226. 3 Wilson, Healthy Skin, I). 84. Philadelphia, 1854. SEBA CEO US GL A XDS. 707 ■will l)e drained off, an effect obvionsly (»f advantaresent in the two fluids being so difivrent. The (piantitv of milk secreted in twenty-four hours varies very much, depending upon the c(»ndition of the female, kind of food, etc. Perhaps it may be said that the daily production of milk by the human female amounts to about one liter or nearly a (piart. The gases of human milk have not been investigated ; that of the cow contains in 100 volumes : Nitro- gen, 1.41 ; oxygen, 0.16; carbon dioxide, 0.72. The milk formed at the beginning of lactation — the colostrum — differs from the later in having a higher specific gravity, in be- ing thinner, yellowish in color, and containing many of the milk cells in an entire condition. During the intervals of lactation the mammary glands secrete only a small quantity of viscid mucus. The secretion of milk appears to be influenced if not controlled by the central nervous system through vasomotor or secretory nerves.^ It is well known to obstetricians that the milk of a woman affected by some strong emotion or attacked by disease will not only be altered in quality but even suppressed altogether. The re- sults of experiments made upon animals, though conflicting in some respects, confirm upon the whole the above view, division of the spermatic nerve being usually followed by an increased flow of milk, stimulation by a diminished one. The effect is probably due to vasomotor action, though according to one observer secretory fibers have been traced directly to the cells of the mammary gland. - From the fact, however, that after the severance of all nervous connections milk is still secreted, it may be inferred that the mam- mary gland acts automatically, even though influenced by the cen- tral nervous system. Sudoriferous Glands. The sudoriferous or sweat glands, like the sebaceous and mammary glands, are appendages of the epidermis, beginning about the fifth month of intrauterine life as flask-like involutions of the cells of the illeidenhain in Hermann's Handlnich, Band v., Thl. 1, s. 302. Eolirig, Yir- chow's Archiv, Band 67, 1876, s. llt». Eckhard, Beitnige, IS.'jo, s. 12, 1S77, s. 117. Mironow, Art-hives des Sciences biolooiques, St. Petersburg, Tome iii., 1894, p. 353. ^Arnst^in, Anat. Anzeiger, Band x., 1895, s. 410. 712 THE SKIN AXD ITS APPENDAGES. rete mucosum of the epidermis into the dermis (Fig. 413). As de- velopment advances this solid liask-like rudiment becomes trans- formed into a hollow tube, Avhich, extending itself through the dermis to the subcutaneous adipose tissue, terminates at the one end in a coil, and at the other end as the sweat pore on the surface of the skin, a passage-way in the meantime being formed in the epidermis leading; from the latter into the hollow tube. Each sweat gland, when fully formed, consists of a tube convoluted at its commencement, the secreting portion of a yellowish-red color, spheroidal in form, with an average diameter of 1.2 millimeters (the ^^ of an inch), and pass- ing thence upward, as the sweat duct, in a slightly tortuous manner to the external surface of the dermis. The tube consists of an external pa^'m?i'^L"nVoVrh"Jimau Abrous layer, succecdcd by a basement mem- embrvo at five months; branc, the lattcr Supporting an epithelium of niaguineu 350 diameters. ' t^i ^ . . a. Horny layer of the polyhedral nucleated cells containing granular epidermis, b. Mucous t n • i • * • layer, c. Corium. d. and ycUoWlSh pigment matter. As just men- vet without^ any "ca^'ity* tioned, at the point where the sweat duct ,l°mdTeTK""^ '' '""'" opens on the surface of the dermis a passage- way is continued through the epidermis to the exterior. Where the epidermis is thin the passage-way is straight, but where thick, as in the palms and soles, it takes a spiral course, terminating at the surface in a funnel-shaped orifice. The openings of the sweat ducts may be distinctly seen disposed in a single row on the summits of the ridges of the skin of the palms and soles, if the latter be viewed with a common pocket lens. In other situations, however, they are far less apparent. With the ex- ception of the concave surface of the concha of the ear, the glans penis, the inner layer of the prepuce, and perhaps a few other places, the sweat glans are found in every part of the skin. The number varies, however, very much according to the part of the skin examined. Thus, while according to Krause,^ in the palmar surface of the hand there may be as many as 2,736 sweat glands in 6.7 sq. cm. (1 square inch) of skin, in that of the nates there may be as few as 417 per sq. cm. It is this variation in the number of sweat glands existing in different ])arts of the skin that renders any determination as to their total number, as estimated, for example, by Krause at 2,381,248, so very uncertain. Assuming that the se- creting portion of the coil of each sweat duct, when unravelled, measures 1.5 millimeters (J^r of an inch) in length on the above estimate, if the tubes were placed end to end they would extend a distance of 3.8 kilometers (2^ miles). It should be mentioned, however, with reference to this last estimate, that the length of the excretory portion of the regards the exhalation of watery vapor and carbon dioxide, but that of the kidneys also, and not only with reference to the water but to the urea eliminated as well. Thus, according to Carpenter,^ in one experiment the entire quantity of perspiration for the whole body being in one hour 3,320 grains, (\\ grains of urea, containing 3.0."> X, were obtained. It is not likely, however, that the excretion of urea would have continued during the whole twenty-four hours at such a rate. It should be mentioned in this connection also, ac- cording to Funke,- that through the desquamation of the epidermic scales about 0.7 gramme (1 1 grains) of nitrogen are also daily elim- inated by the skin. According to recent researches the amount of urea excreted in the s^veat is also much increased by muscular work.'* That the sweat, however, contains other substances than those already mentioned is rendered very probal^le from the fact that death soon ensues when the perspiration is suppressed, as, for ex- ample, when the skin is varnished in animals* and also in human beings, as in the celebrated case of the child, who, being covered ^^'ith gold-leaf to personate an angel at the coronation of Leo X., died a few hours afterward.' While death in such cases is no doubt partly due to the imperfect arterialization of the blood and the rapid fall of temperature, the varnish favoring the loss of heat in pro- ducing a cutaneous hyperemia similar to that induced through paralysis of the vasomotor nerves, symptoms like that of uniemic poisoning, tremors, tetanic cramps, movements of rotation, increased reflex excitability, present as well, lead one to suppose that urea and other poisonous substances not yet isolated are retained in the system Avhich are usually carried away in the sweat. That such is the case is shown h\ the fact that if human sweat be injected into the blood of the rabbi t*" the pulse of the latter may be increased from 192 beats per minute to 326, the respiration from 82 to 105, and the temperature raised from 37.2° to 40° C. (99° to 104° F.). Even if it be admitted that the exact cause of death is not yet posi- tively determined there can be no doubt that imperfect action of" the sweat glands must be a source of disease, various matters then accumulating in the system which would otherwise be eliminated. Indeed, too much stress cannot be laid upon the importance of keeping the skin clean — of the free use of Avater. Especially is such the case in tropical climates where the true secret of main- taining one's health lies in attending to the condition of the skin, and where febrile diseases are more successfully treated by active diaphoresis than in any other way. The great importance of daily baths in the maintenance of health cannot be exaggerated, and ap- 'Phy^iol<),£r}-, p. 491. 2 ;^Iolescliott Untei-s., 1858, Band iv., s. 56. '' Argutinsky, Pflnger's Archiv, Band xxxxvi., 1890, s. 552. *Fouicauet, Comptes rendus. Tome vi., p. 369. Paris, 1S:]S. Ibid., 1843, Tome xvi., p. 139. Valentin. Arcliiv f. Physiologie Ileilknnde, 1858, Band ii., s. 433. Bernard, Liqnides de I'Organisme, Tome ii., p. 177. Paris, 1859. ^Laschkewitsch, D\\ Bois Reymond's Arch., 1868, s. 61. ^Rohrig, Jahrb. t'iir Balneologie, 1873, Band i., s. 1. 716 THE SKIN AND ITS APPENDAGES. parently was more appreciated by the ancients than the moderns, as the ruins of the magnificent baths of Caracal la and Diocletian, at Rome, still to this day testify. Noble institutions they were ; the baths or thermae fed by stupendous aqueducts stretching for miles across the Campagna, their perpetual streams of hot and cold water flowing through mouths of solid silver into capacious basins, accom- modating at one time thousands of bathers, and where for the eighth of an English penny the meanest Roman of them all could enjoy the luxury that might have well excited the envy of the kings of Asia/ The secretion of sweat, like other secretions, is influenced by the nervous system, the sweat center or centers, being situated, accord- ing to Luchsinger,^ in the anterior horns of the gray matter of the spinal cord and medulla. From these centers nerve fibers arise, which, passing down the cord, emerge principally with the anterior roots of the third, fourth, and fifth cervical nerves to pass with the brachial plexus to the skin of the upper extremity, and with the anterior roots of the lumbar nerves to supply the lower extremity. The sweat centers may be stimulated directly and reflexly. It is in the latter manner that the sweat centers are excited by muscular exercise, dyspnoea, fear, heat, various substances such as pilocarpin, nicotin, muscarin, and inhibited by cold and atropin. While the sweat nerves emerge from the spinal cord and run in company with the vasomotor nerves, the secretion of sweat is in- dependent of vasomotor influence except in so far as the blood supplies in the long run the materials for the elaboration of the secretion. This is shown by the fact that stimulation of the sci- atic nerve in the cat causes secretion of sweat in the soles of the feet after ligation of the aorta or even after amputation of the limb.^ It is also a matter of daily observation that, although a person may be pale from terror or nausea, sweating may be pro- fuse, and on the other hand, though the skin may be flushed with fever, sweating is absent. That the sweat nerves are true secretory nerves is still furtlier shown by receut histological researches/ their terminal fillers having been followed directly to the secretory cells of the sweat glands. The manner in which the skin regulates the temperature of the body through the radiation, conduction, etc., of the heat produced within it having already been sufficiently considered, it will not be necessary to treat further of the function of the skin in this re- spect. While there can be no doubt that absorption in the lower animals and in many of the higher is to a considerable extent carried on by the skin, frogs, lizards, etc., rapidly gaining in weight when immersed in water, some difference of opinion still prevails among piiysiologists as to what extent the skin in man normally ^ Gibbon, Decline and Fall of the Eoman Empire, Vol. v. , p. 237. London, 1807. ^Pfliiger's Archiv, Band xiii., s. 212; Band xiv., s. 545; Band xv., s. 482; Band xvL, s. 538. '' Goltz, Pfliiger's Archiv, Band xi., 1875, s. 71. Langley, Journal of Physiology, ^'ol. xii., 1891, p. 347. ^Arnstein, Anatomische Anzeiger, Band x., 1895. A B SORPTION B Y SKIX. 7 1 7 acts as an absorbing snrface. It may not appear snpcrflnous, there- fore, if attention bo called to those instances or conditions in which absorption does take place in man by the skin. It is well known, as already mentioned, in speaking of the cause of thirst, that in the case of the shipwrecked sailor the thirst was very much, if not entirely, temporarily relieved by the immersion of the bodv in the sea, or by wearing clothes wet with the same.^ In certain cases also, where the introduction of solid or liquid food by the mouth had become impracticable, immersion of the patient in a bath of tepid milk morning and evening not only relieved the thirst, but for some time maintained life, the weight gained being unaccounted for by the enemata also given.- It has also been shown that not only does the body gain in weight after immersion in a bath through the absorption of the liquid, but that the skin will also absorb cer- tain salts M'hen dissolved in the same. That the skin is permeable by gas is also well known, it having l)een shown by Bichat that if a limb be immersed in a putrid gas the latter will be absorbed by the skin, and by Aubert that the skin absorbs about the -^^ of the oxygen absorbed by the lungs. Admitting, then, that under cer- tain circumstances the skin undoubtedly can absorb, it still remains undetermined to what extent, under normal conditions, it does ab- sorb. Covered, as the skin usually is in man, almost entirely with more or less clothing, it is difficult to comprehend how or what the skin under such circumstances can absorb, the gain in weight of the body through absorption of the watery vapor of the atmosphere sometimes instanced ' being due to the absorption of the vapor by the lungs rather than by the skin. "We have further seen that through the presence of the sebaceous matter the skin is rendered repellant of water, which thereby renders it very insusceptible to the taking up of foreign substances. Indeed, it is very question- able whether such are ever introduced into the system unless the epidermis be disintegrated, the view- sometimes advanced * that sub- tances are absorbed by the sweat ducts being very improbable, since the latter are already filled with sweat, and the movement of the sweat, being from below upward, would tend to wash away foreign substances rather than favor their absorption. It would appear, therefore, as we pass from the lower to the higher animals, that the skin loses its significance as an absorbing surface, becoming essentially protective and excretory in function. Nevertheless, though the absorbing power of the skin in the economy of the higher animals may have been superseded by that of the lungs and alimentary canal, under certain conditions it may even in them act ^ Madden, Experimental Enquirv into the Phvsiologv of Cutaneous Absoi-ption, p. 64. Edinb., 1838. ^Currie, Medical Reports, Vol. i., pp. 308-326. AVatson, Chemical Essays, Vol. iii., p. 100. 3 Lining, Phil. Trans., 1743, p. 49G. Klapp, Inaugural Essay on Cuticular Ab- sorption, p. 30. Philadelphia, 1805. *Auspitz, Wiener med. Jalirb., 1871. Neumann, Wiener med. Wochenschrift, 1871. 718 THE SKIN AND JTS APPENDAGES. vicariously with the same, as no doubt it does, as regards the ex- cretion of water by the kidneys as well as the lungs. Sense of Touch or Locality. The skin acts not only as a general sensory surface through the impressions made upon the epidermis being transmitted thence to the more deeply situated cutaneous nerves, but through its Tactile, Pacinian, and Krause corpuscles, it is endowed with a special modi- fication of sensibility — the tactile sensibility, or the sense of touch, by means of which we not only feel but appreciate to a certain ex- tent the form, size, character or surface, weight, and temperature of objects. While the skin as a whole, therefore, is endowed with a general sensibility more or less acute in different parts of the body, its tactile sensibility, however, is restricted to certain portions of it, and most delicate in those situations where the corpuscles are most abundant. Thus, if the blunt but fine ends of a pair of dividers provided with a graduated bar, or sesthesiometer, be applied to the tip of the tongue — the individual being blindfolded — the two ends of the dividers, though only separated l)y so much as the -^-^ of an inch, will be appreciated as two distinct objects. If, however, the dividers be approximated until they are separated by less than that distance, the two impressions, a moment previous distinctly appre- ciated as such, now fade into one, as if l)ut a single object was touching the tongue. Experimenting in this manner, it was first shown by \Yeber,^ and afterward by Valetin," that the sense of touch varies very much in different parts of the body, being most acute at the tip of the tongue and ends of the fingers ; least so in the back, as shown as follows : Tactile Sensibility.' Both points of dividers Parts of surfaces. felt when separated by these distances. Tip of tongue . . . . . . 0.50 of a line. Palmar surface of third phalanx of fingers 1.00 " " " u u second " " '^ 2.00 " " Dorsal " " third " " " 3.00 " '' Middle of dorsum of tongue . . . 4.00 " " End of the great toe . . . . 5.00 " " Center of hard palate . . . . 6.00 " " Dorsal surface of first phalanx of fingers 7.00 " " " quarter of heads of metacarpal bones 8.00 " " Back of the heel 10.00 " " Dorsum of the hand .... 14.00 '' " '' " foot 18.00 " " Sternum 20.00 " " Five upper dorsal vertebrae . . . 24.00 " " Middle of " " ... 30.00 " " When points of dividers are brought closer than these dis- tances they are felt as one. 1 Warner, Physiologic, Band iii., Zweite Abtli., s. 524. 2 Physiologic, Band ii., s. 558. 3Cari)onter, article Touch, Cyclopaedia of Anat. and Phys., Vol. iv.. Part 2d, p. 11G9. SENSE OF TOUCH OB LOCALITY. "19 The sense of touch, like the other senses, can l)e very much im- proved by attention and practice. Thus, it is said ^ that the female silk throwsters of Bengal can distinguish twenty diiferent degrees of fineness in the unwound cocoons by the touch alone, and that the Indian muslin weaver makes the finest cambric vnth a loom of such simple construction that, if worked by the haiids of a Euro- pean, would turn out but little better than canvas. It is also a well-known fact that those persons who are employed in mints, etc., in the daily haljit of handling coins, detect at once, and with cer- tainty, a light piece. As might be expected, the sense of touch is very much developed in those who have lost the sense of sight, or who have been blind. One of the most remarkable of such cases is that of Giovanni Gonelli, who, at twenty years of age lost his sight, but who, nevertheless, after a lapse of ten years, developed a great talent as a sculptor, modelling such an excellent statue out of clay of Cosmo de Medici from feeling one of marble that the Grand Duke of Tuscany sent him to Rome to make a statue of Pope I"r- ban VIII., which was a very successful one, the likeness being said to be excellent. Stranger still, even a good knowledge of botany and couchology has been acquired through the sense of touch by persons who have been born blind, or who had lost their sight early in life. It is well known, also, as in the case of Baczko," that the blind can learn to distinguish the colors of fabrics by the sense of touch. It is related that Sanderson, the blind professor of mathe- matics at Cambridge, could not only distinguish diiferent medals, but could detect imitations of them often better than professed con- noisseurs, while his appreciation of variations of temperature, it may be mentioned also,^ was so acute that he could tell, through slight modifications in the temperature of the air, when very slight clouds were passing over the sun's disk. It is a familiar fact, also, that the blind learn to read with great facility by passing their fingers over raised letters of about the size of those of a folio Bible. Terrible a calamity as the loss of sight is, it should not be forgotten, as the above examples teach us, what a delicate sense in that of touch we possess if cultivated, and that sources of pleasure and recreation through its development may be offered to those who are born blind, or who have lost their sight later in life. The sense of touch next to that of sight is the most important means bv which we oaiu our knowledo;e of the external world. Indeed our appreciation of the form and qualities of external ob- jects is based almost entirely upon the association of tactile and visual sensations together with those due to the so-called muscular sense. It may be recalled in this connection that the center for touch is usually regarded as being located in the hippocampal re- gion of the cortex. 'Carpenter, op. cit., p. 1177. '^ Eiidolphi, Phvsiologie, Band ii., s. 85. ^Uunglison, Physiology, Vol. i., p. 697. Pliila., 185(5. 720 THE SKIN AND ITS APPENDAGES. Sense of Pressure or Weight. The sense of pressure or of weight is the sense by means of which we appreciate the amount of pressure that is exerted upon the skin. The part of the skin endowed with this sense appears to be es- pecially modified, being character- p,f, 4^4 ized by the presence of the so- ^^^. called "pressure spots" or " pres- .•..,:;.*•" :'••'.*''.•••;*' .'}.'''.'.'. ^^^Q points" (Fig. 414) for the **.. .V '••!.'•; '.'y\<.] .'• y/'-'f:: reception of stimuli. •'-*••)•*•.. :'.''.•::• '"'.' The minimal distance at which ^ b- c two pressure spots, when stimu- Pressu re-spots, a. Middle of the sole of latcd, givC risC tO distiuct SCUSa- the foot. h. Skin of zygoma, c. Skin of the ,. ^. . t/v> , , /> back. (Landois.) tious, varics HI Gitierent parts ot the skin, being in the palm of the hand, for example, from 0.1 to 0.5 mm., on the back from 4 to 6 ram. The smallest perceptible pressure varies, also, according to the lo- cality. Thus a pressure exerted by 0.002 grms. will be appreci- ated if the weight be applied to the forehead, temple, back of the hand, and forearm, 0.005 to 0.015 grms. are felt by the fingers, 0.04 to 0.5 grms. by the chin, abdomen, and nose, 1 gr. by the finger nail.^ Variations are also manifested by the skin in the power of discriminating differences of pressure. Thus, according to Eulen- berg, the forehead, lips, and temples appreciate the difference be- tween 200 and 205 grms, or -^-^ and 300 and 310 grms, or -^-^, the head, fingers, and forearm, the difference between 200 and 220 grms. or Jg- and 200 and 210 grs. or J^. The smallest additional weight appreciated as a difference when added to 1 grm. resting upon the skin is according to Dohrn in the case of the first phalanx of the finger 0.02 grm,, third phalanx 0.49 grm., back of the foot 0,5 grm., palm 1.01 grm,, back 3.8 grms,^ It is a well-known fact that pressure due to a uniform compression such as is exerted upon a finger dipped into mercury, for example, is not felt as such but only at the surface of the level of the fluid. If the weights made use of in experimenting upon the sense of pressure are comparatively heavy ones and the pres- sure has been exerted for some time the sensation produced persists even after removal of the weight as the so-called " after-pressure." Even in the case of light weights being used an interval of time amounting to at least from ^i^ to ■^\-^ of a second must elapse in order to appreciate the difference, the sensations becoming fused Avhen the intervals of application are shorter. Thus it has been shown that when the fingers are pressed against a toothed wheel, the sensation experienced -was a smooth one wdien the teeth touched the skin at the intervals just mentioned, whereas each tooth caused a distinct sensation when the wheel was rotated more slowly. It is also well known that vibrations of strings cease to be distin- ^Anbertu. Kammler, Moleschott Uiitersiiclningcn, Eaml v., 1859, s. 145. ^Landois, op. cit., p. 105:5. SENSE OF PRESSURE OR WEIGHT. 721 guished as such Avhen the rate of vibration exceeds that of 1,600 per second. It has been established l:)y the researches of Weber ^ and Fech- ner - that in the case of the sense of pressure, and as we shall see presently, in that of all kinds of sensation there is a strength of stimulus varying for each sense, the so-called " liminal intensity," which is just powerful enough to awaken sensation. On the other hand, there is also a strength of stimulus, the so-called " maximum of excitation," beyond which no increase of sensation will l)e felt by any further increase of stimulus. There is, therefore, for each sense a " range of sensibility," the range extending between these two limits. It has also been shown that as the strength of the stimulus increases, so also does the sensation, but that the latter in- crease equally when the amount of stimulus necessary to cause a perceptible increase of sensation bears the same ratio to the amount of stimulus already applied. Thus, for example, the eyes being bandaged and the hand extended and supported, if Aveights such as 10, 100, 1000 grammes be successively placed in the hand, it will be found that one-third of the original weight, 3.3 or 33.3 grs., etc., must be always added, according to whichever weight be used in order to appreciate any increase in weight. The fractional increment of the original weight necessary for the discrimination, one-third in the case of weight, is called " the constant pro- portion." The " liminal intensity " and the " constant proportion " being known, the data are given by which the general relation of the sensation to the stimulus can be shown graphically. Suppose, for example, that the sensation under consideration be one of pressure, let the horizontal line o .r, or the abscissa (Fig. 415), be divided into equal parts, 1, 2, 3, 4, to represent equal in- FiG. 415. O / 2 J ^ Graphic illustratioa of reaction of sensation to stimuli. crements of sensation, the zero corresponding to the minimum of sensation, the vertical lines, or the ordinate 0«, lb, '2c, 3d, -ie, the 46 ' Vorlesungen, Band i., Leipzig, s. 133. ^Elemente Der Psjchophysik, Band ii., Leipzig, s, 377. 722 THE SKIN AND ITS APPENDAGES. stimuli, Oa corresponding to the minimum stimulus, say one-fiftieth of a gramnie, each ordinate being equal to the preceding one plus a third of the same, according to the determination of the constant proportional in the case of weight ; it is evident that the difference of length between the line Oa and the lines 16, 2c, 3c?, 4e, indicates the weights that must be used in order that the successive sensa- tions should be equal. As the logarithms of the stimuli increase, however equally, as well as the sensations, when the stimulus is increased in such con- stant proportion it follows that the sensation is not proportional to the stimulus but to the logarithm of the stimulus.^ In other words, if the sensations are as 1, 2, 3, the stimuli are as 10, 100, 1000; 1, 2, 3, being the logarithms respectively of 1, 10, 1000." This so-called Fechner's psycho-physical law of sensation only holds good, however, when the stimuli used are of medium strength, since as we have seen when very light or very heavy weights are used, the increment of pressure necessary for sensation is not a constant proportion of the original stimulus. Muscular Sense. By means of the muscular sense we learn the position of the dif- ferent parts of our bodies, become aware of the density, elasticity, immobility due to the resistance offered by external objects, realize the effort we make when exerting a pressure upon the same, and ap^jreciate the condition of our muscles and the extent of their con- traction. By the muscular sense we learn far more accurately the weight of an object when supported by the hand by muscular effort than when the object simply presses upon the hand, the latter being supported and extended, we not only feel in the first case the pres- sure of the object, but are also conscious of the exertion required to lift and support the weight. It is well known that an individual affected Avith locomotor ataxia, while retaining the sensations of touch, temperature, pain, is unable to coordinate his muscles, and on the other hand, that in certain kinds of nervous diseases, while sen- sation may be impaired or abolished, the power of muscular coordi- nation may be retained. A frog can also coordinate his muscles after entire removal of the skin, and, therefore, in the absence of all cutaneous sensation. It has also been shown by Weber,^ as a gen- eral rule, that while differences in weight are appreciated most acutely by those parts of the skin which are most sensitive to the impressions of touch, as that of the fingers, for example, that, while by the sense of pressure alone a difference in weight of not less than one-eighth can only be determined, by making a muscular ^ W.Wundt, Grundziige Der Physiologischen Psychologie, Band i., 1880, s. 358. 2 A logaritlini of a nniiibcr is the exponent of tlie jjower to which it is necessary to raise a fixed number to pnxhice tlie given nnml)er. Suppose tlie fixed number to be 10, tlie given nvmil)er 100 or 1000, then 2 and o will be the logarithms of 100 and 1000 respectively, since 10^ = 100, lO'' = 1000. ^AVagner, Physiology, Band iii., Zweite Abtli., s. 543. SENSE OF TEMPERATURE. 723 effort, as in lifting, a difference of one-sixteenth can be accurately appreciated. Such considerations as those just mentioned have led many phys- iologists to regard the muscular sense as due to impvdses derived from the muscles, tendons, and joints as well as from the skin. On the other hand, the ataxic symptoms present in certain nervous dis- eases, where sensation is impaired and often referred to as a proof of the existence of a special muscular sense normally, are perfectly well accounted for by other physiologists by the loss of general sensibility. Since the impression made by the foreign bodv, whether it be the ground we tread upon or the child A\e hold in our arms, not being transmitted to the encephalon, in such cases it will not be reflected consciously or otherwise to the appropriate jnuscles whose action enables us to stand securely or grasp firndv, hence our inability to Avalk upon the ground or hold a child in our arms unless we look at the one or the other, the essential reflex action being then effected by the eye and optic nerve instead of the skin and cutaneous nerves. The " constant proportion" for the muscular sense is usually regarded as being yf-g-. Sense of Temperature. By means of the sense of temperature we appreciate the changes in the heat of the skin, the latter being specially modified, pre- senting the so-called " temperature spots" for the reception of im- pulses from hot and cold bodies. The cold (o) and hot (6) spots (Figs. 416, 417) can be mapped out by touching the skin with a Fig. 416. Fig. 417, a 6 m I •.:::: y.v: • • • . ^ ■_*— ^^ :::::::•::: i- ■... ■ Cold- aucl hot-spots from the same part of the-anterior surface of the forearm, a. (.'old-spots. 6. hot-spots. The dark ])arts are the more sensitive, the hatched the medium, the dotted the feeble, and the vacant spaces the non-sensitive. 724 THE SKIN AXD ITS AFFEXDAGES. blunt-i)ointed metal rod previously Avarmed or cooled. The cold points appear to be more numerous than the hot ones. The minimal distance at Avhich the cold spots can be appreciated is, in the case of the forehead, 0.8 mm., and in that of the hot spots 4 to 5 mm. The skin is more sensitive to cold than to heat, that of the left hand greater in this respect than that of the right. The skin varies very much also in regard to its susceptibility to changes in temperature, that of the palm, for example, appreciating a diifereuce of 0.2° C, of the breast 0.4° C, leg 0.6° C, back 0.9° C. In the case of the sense of temperature, as in that of pressure, the " constant propor- tion" is one-third of the original stimulus. It is worthy of mention in this connection that the mucous mem- brane of the alimentary canal, from the oesophagus to the rectum inclusive, is not endowed with the power of discriminating between- differences of temperature. An enema of water cooled down is only appreciated as being cold when the water passes over the skin of the arms. Sense of Pain. It has already been mentioned that difference of opinion still prevails as to whether the sense of pain is due to impulses trans- mitted by special nerves, or to the impulses usually giving rise to pressure, heat and cold being simply exaggerated. Those who hold the former view, argue that the skin is endowed, like other tissues, with general sensibility and when the afferent nerves ministering to the latter are so excited as to affect consciousness, pain results. CHAPTER XXXVII. THE XOSE AND OLFACTION. THE TONGUE AND GUSTATION. Fig. 418. Just as Ave have seen that the skin, in addition to its other functions, acts as a general sensory organ, so we shall soon learn throngli the study of Development, that parts of it being especially modified become very susceptible to certain external impressions, and that such modifications, together with corresponding ones de- veloped in the terminal nerves supplying the parts, constitute special sensory organs, such as the nose, tongue, eye, and ear, and inasmuch as, of such organs, the nose is the most simple in struc- ture, we will begin the consideration of the special senses with the study of Olfaction. Olfaction. The nose, the special organ of the sense of smell, is regarded anatomically as being limited to the pyramidal eminence of the face, extending from the forehead to the upper lip ; physiologically, however, the nose — that is, the organ of olfaction — includes not only the parts just mentioned, con- sisting of the septum, carti- lages, etc., but of the nasal cavities as well ; the mucous membranes lining the latter be- ing endowed not only with general sensibility, as we have seen, but with the special sense of olfaction, its upper half be- ing supplied (Fig. 418) by the olfactory nerve, the special nerve of the sense of smell. The skin of the nose, thin above but thick below, as else- where, is furnished with sudor- iferous and sebaceous glands and hairs ; the hairs are usually small except within the margin of the nostrils, in the latter po- sition, however, they are well developed from all sides, and to a certain extent act like a fine sieve in keeping out dust, etc. The nasal cavities communicating with the exterior, in front, by the anterior nares, and with the jiharynx, behind, by the posterior nares, are lined with a mucous membrane Iiistributiiin of nerves in the nasa! pas.sages. 1. ()lt"aet')ry ganglia, with its nerves. 2. Nasal branch of tilth jiair. 3. .'^pheuo-palatine ganglion. (l).\LTON.) 72(3 XOSE AXD OLFACTION: TONGUE AND GUSTATION. closely applied to the adjacent periosteum and perichondrium, which becomes, at the nostrils, continuous with the skin, at the posterior nares, with the mucous membrane of the pharynx, and at the lachrymo-nasal duct and lachrymal canals with the con- juuctiya. The nasal mucous membrane differs very much in its character according to its situation. Thus on the part lining the so-called " olfactory region," or that coyering the upper part of the septum, the superior and part of the middle turbinated bones is thick, highly yascular, and coyered with a columnar epithelium amidst the cells of which occur peculiar rod-like cells. The latter we shall see presently are the olfactory cells in which the fibers of the olfactory nerye terminate or rather arise just as we haye seen the axis-cylinders iu the anterior roots arise from cells in the cord. On the other hand, the remaining portion of the nasal mucous membrane, the so-called Schneidcrian or pituitary membrane, or the part lining the " respiratory region," that is coyering the lower part of the septum, part of the middle and inferior turbinated bones, is covered with a columnar ciliated epithelium (except within the nostrils where it is squamous), the current due to the cilia be- ing directed towards the pharynx. The nasal mucous membrane is also provided with glands whose secretion keeps the surface moist, a condition essential to the accurate perception of odoriferous im- pressions. The glands of the true olfactory membrane, the so- called Bowman glands, are tubular or mixed glands. The special nerves of the sense of smell or the true olfactory nerves are given off as fifteen to eighteen filaments from the olfac- tory bulb to the olfactory region. The olfactory tract, of which the ganglionic bulb is the expansion, is usually described as the olfac- tory nerve, but improperly, since, as development sho^vs, the olfac- tory tracts are outgrowths of the cerebral hemispheres, their morphological significance masked in man by the excessive de- velopment of the former. The olfactory tracts are two cords or bands, soft and friable, consisting of both white and gray nervous matter, which, passing forward and inward on the under surface of the anterior lobe of the cerebrum to the ethmoid bone, expand at the side of the crusta galli into the olfactory bulbs, from which are given off, as just mentioned, the true olfactory nerves, which, pass- ing through the cribriform foramina of the ethmoid bone, are dis- tributed to the inner and outer walls of the upper parts of the nasal cavities. Each olfactory tract arises apparently by three roots, from the inferior and internal surface of the anterior lobe of the cerebrum in front of the anterior perforated space, the external and internal roots being composed of white matter, the middle of gray, the large proportion of the gray substance, one-third, entering into the composition of the olfactory tract, confirming what has just been said as to the true nature of the latter. AVhile the ante- rior root can be traced into the middle lobe and the middle and internal roots into the anterior lobe, considerable obscurity still OLF ACTIO y. rii prevails as to the deep origin of all three roots. It would appear, however, that the long or external root originates in the island of Reil, the thalamus opticus and the nucleus in the temporo-sphe- noidal lobe in front of the hippocampus, the middle or gray root in the gray substance of the anterior perforated space, the inner root in the gyrus fornicatus. The true olfactory nerves, or the filaments given off from the olfactory bulb, as they descend from the cribri- form plate ramify, and, uniting in a plexiform manner, spread out laterally in brush-like and flattened tufts (Fig. 418). In their minute structure, the olfactory differ from the ordinary cerebral and spinal nerves in being pale and finely granular, in not pos- sessing a substance of Schwann, in adhering to one another, and in presenting oval corpuscles. Their manner of termination is also peculiar, each olfactory fiber appearing to pass into the spindle-shaped bodies (6) interspersed be- tween and among the epithelial cells (a) of the olfactory mem- brane (Fig. 419). These olfactory cells, so-called on account of their Fig. 419. Fig. 420. Cells and terminal nerve-fibers of the olfactory region, highly magnified. 1. From tlie frog. 2. From man. a. Epi- thelial cell, extending deeply into a ramified process, h. Olfactory cells, c. Their peripheral rods. e. Their ex- tremities, seen in 1 to be prolonged into fine hairs. <1. Their central filaments. 3. Olfactory nerve-fibers from the dog. a. The division into tine fibrillae. (Frey after Schultze. ) campal convolution,' in whi localized (Fig. 420), is prov ^ Obersteiner, op. cit. , s. 360. Inner aspect of the right hemisphere, po, position of tlie visual center in the occipital lobe t" of the olfactory center in the uncinate gyrus. (GOWEKS. ) supposed function, present a very characteristic appearance, the cen- tral nucleated portion passing on the one hand internally into a beaded varicose-like thread ((/) ap- parently continuous with the termi- nal olfactory fibril, and, on the other, externally into a rod-like structure (e), which in the frog is prolonged into fine hairs. That the olfactory cells, nerves, bulbs, and tracts, constitute the essential structures, by which external im- pressions are transmitted to the subiculum cornu of the hi])po- ch the sen.se of smell is supposed t<> be ed by the harmonious results of experi- Edinger, op. cit., s. "201. Rauber, op. cit., s. (374. 728 NOSE A ND OLFA CTIOX: TOXG UE AND G USTA TION. ments performed upon animals, of pathological cases observed in man, and of the facts of comparative anatomy. Thus, among the numerous experiments in which the olfactory tracts were divided, and the loss of the sense of smell noticed, may be mentioned those performed upon hunting dogs by Vulpian ^ and Philipaux, in which cases the animals, although deprived of food for thirty-six hours after complete recovery from the effects of the operation failed to find the cooked meat concealed in the corner of the laboratory. That destruc- tion of the olfactory nerves, bulbs, or tracts in man due to disease or injury involves the impairment or loss of the sense of smell is well known to pathologists, a number of such cases having been observed by Schneider, Rolpinck, Eschricht, Fahner, Valentin, Rosenmuller, Ceneti, Pressat,^ Hare,^ Notta,* Ogle,'^ Flint.*' That the olfactory bulbs and nerves are the essential organs of the special sense of smell is still further shown by the fact that they are usually best developed in animals in which the sense of smell is most acute, being better de- veloped, for example, in the mammalia than in the remaining ver- tebrates, while of the former class it is among those orders, as in the carnivora, in which the sense of smell is very acute, that the olfactory region is most developed, in the dog, for example, in which the sense of smell, as well known, is very remarkable. The olfactory nerves, though readily impressed by odorous emanations, are but little affected by ordinary, while the olfactory tracts ap- pear entirely insensible to the latter." That the appreciation of odors or olfaction is due to the material emanations given off by odoriferous substances being carried by the inspired air to the terminal filaments of the olfactory nerves, the olfactory cells, is shown by the manner in which one sniffs the air in order to per- ceive an odor, and from the fact that if the air does not pass through the nostrils, as in occlusion of the posterior nares or in di- vision of the trachea, the sense of smell is abolished. In every case where odorous emanations are i)erceived, the latter must im- pinge upon the olfactory membrane, come in contact, excite the peripheral ends of the olfactory nerves. According to Passy * as small a quantity of musk as the 0.000005 gramme in one liter of air can be appreciated, the amount of oil of peppermint that can be recognized being still smaller, 0.000000005 gramme, while according to Fisher and Penzoldt^ ■^eiroTo^Too" ®^ ^ milligrame of mercaptan in 1 c.cm. of air can be ' Leyons sur la physiologie generale et comparee du systeme nervenx, p. 882, note. Paris, 1866. ^ Cited bv Longet, Anat. et Phvs. du svsteme nerveux, Tome ii., p. 88. Paris, 1842. 'A View of the Structure, etc., of tlie Stomach and Alimentary Organs, p. 145. London, 1S21. * Archives generales de medicine, p. 385. Paris, Avril, 1870. ^ Medico-Chirur. Trans., Lond., 2d ser., Vol. xxxvii., p. 263. ''Flint, Pliysiology, 1874, \o\. v., p. 39. " Magendie, .Journal de piivsiologie, Tome iv., p. 169. Paris, 1824. 8 Comptes Kendus Soc. de Biologic, 1892, p. 84. "Landois, op. cit., p. 1039. THE TONGUE AND GC STATION. 729 detected. Like the sense of touch, and the other special senses, that of smell may be very much developed by practice ; as ex- emplified in the discrimination of the quality of \vine, drugs, etc. It is Avell known that the boy, James Mitchell, who was deaf, dumb, and blind, made use of his sense of smell like a dog to dis- tinguish persons and objects. The sense of smell is, however, far more acute in the lower races of mankind than in the higher ones, to Avhatever extent in the latter it may have been developed by cultivation. Thus it is said that the Mincopies of the Andaman Islands scent the ripeness of the fruits ; that the Peruvian Indians distinguish the different races of mankind l)y scent alone ; that Arabs can smell a fire thirty miles off; that the North American Indians pursue by smell their enemies or their game. However the sense of smell may be developed in man, it is far surpassed in acuteness by that of animals. Every sportsman is aware that odors are recognized by hunting dogs, to which he is entirely insensible. The sense of smell is intimately related to that of taste, so much so, indeed, that if the nose be held, or plugged up, the characteristic taste of certain substances when swallowed, is not appreciated at all, as illustrated in drinking different kinds of wine, it being difficult, usually impossible, to distinguish the same under such circum- stances. Further, it has been observed in those cases in which the sense of smell is lost, that of taste is usually lost also. As a general rule, persons having offensive emanations from the respiratory organs are not aware of such, not appearing to be af- fected by odors passing from within outward through the nostrils. This is due, not so much to the odor being carried by the air ex- pired through the nostrils instead of by that inspired, as to the fact that one becomes in time accustomed to such odors, and ceases to notice them, however fetid they may be. The influence exercised by the nose upon respiration has already been mentioned. We shall see, hereafter, that the nose, also, modi- fies very much the quality of the voice. The Tongue and Gustation. The sense of taste, or gustation, enabling us to appreciate the savor of sapid substances when introduced into the mouth, is due to the susceptibility of the terminal filaments of the chorda tym- pani and glosso-pharyngeal nerves, of being imj)ressed by contact of the same. The influence of the tongue in mastication and deg- lutition, the origin, distribution, and general functions of the chorda tvmpani and glosso-pharyngeal nerves having l)cen considered, it onlv remains for us now to point out the manner in which gusta- tion is performed through the parts just mentioned. That the tono-ue is the or^ran of (gustation there can be no doubt. It would appear, however, from experiments such as those pertormed by 730 NOSE AND OLFACTION; TONGUE AND GUSTATION. Longet ^ and others, in wliicli different parts of the mncous mem- brane are touched with a sponge soaked in a sapid sohition, that the sense of taste, probably in man at least, is limited to the dorsal surface of the tongue, and from the experiments of Canierer," in which solutions were applied through tine glass tubes, more par- ticularly to the circumvallate and fungiform papillae, the parts around the latter not appearing to be impressed by sapid sub- stances. The circumvallate papilla (Fig. 421), so called on ac- count of each papilla being sur- rounded by a trench or fossa, from seven to twelve in num- ber, are disposed in two rows (in the form of a V, the open ano-lc of the latter being: di- rected forwards), on the back part of the tongue. Each papilla is covered by numerous small secondary papilla^, the Vertical sectiou of circumvallate jiapilla, from latter, llOWCVCr, bciuff COU- the calf. 35 diameters. A. The papilla. B. The i i i ,i ji • i i j surrounding wall. The figure shows the nerves of CCalcd by tuC thlCk aud Stratl- the papilla spreading toward the surface, and t* ^ • , i t n-ii r • • ' • ■* tied epithehum, ihe lungi- form papillfe, more numerous than the circumvallate, and readily distinguished during life by their deep red color, while found in the middle and forepart of the dorsum of the tongue, are most numerous and closely set together at the apex and near the borders. Each fungiform papilla, while narrow at its attachment (Fig. 422), at its free extremity is blunt and rounded, and, like toward'the taste-buds^which are imbedded in the ficd epithelium epithelium at the sides ; iu the sulcus on the left the duet of a gland is seen to open. (Engelmann. ) Fig. 422. Surface and seotional view of a fungiform papilla. A. The surface of a fungiform papilla par- tially denuded of the ( pitlielium. (35 diameters.) p. Secondary papilloe. n. Epithelium. B. Section of a fungiform papilla with the blood vessels injected, a. Artery, r. Vein. c. Capillary loops of simple papilhe in the neighborhood, covered by the epithelium. (From KOllikek, after Todd and Bowman. ) the circumvallate })apilhe, is covered with secondary papilhe and epithelium. Imbedded in the epithelium, and more particularly in that of the circumvallate papillse, are found ovoidal flask-shaped ' Pliysioloiiie, Tome iii., p. 52. Paris, 1873. ^Zfitsclirift fiir P.iologie, 1870, Band vi., s. 440. TASTE BUDS. 731 Two taste-buds from the papilla foliata of the rabbit. (450 diameters.) (Esgelma>-s. ) bodies (Fig. 423), having a length of the ^^ of a mm. (g^-g^iy of an inch), and a diameter of the J^ of a mm. (ygVu ^^ ^^^ inch), con- sisting apparently of modified epithelial cells, which, w-ith good reason, are supposed to be the special organs of the sense of taste.' Each ovoid body, sur- rounded by flattened epi- Fig. 423. thelial cells, consists of a cortical and a central part. The former is com- posed of long, flattened, tapering cells, disposed edo;e to edge, and coming to a point at the taste- pore, the latter of spin- dle - shaped taste cells. The latter resemble very closely the olfactory cells ; the distal end of the cell projecting from the orifice of the taste-bud, and the central beaded, varicose end being continuous with the terminal filament of the gustatory nerve. Such being the disposition of the taste cells, it would appear that the ter- minal filaments of the gustatory nerves," of which the fonner are the continuation, are excited by the flow of sapid solutions through the taste-pore into the interior of the taste-bud ; the taste cells being especially susceptible to impressions made by substances in solution, whence the impression is transmitted by the chorda tympani and glosso-pharyngeal nerves to the centers of taste, localized in the subiculum cornu of the hippocampus (Fig. 37o, U), where they are perceived. That the chorda tympani and the glosso-pharyngeal nerves are the special nerves of the sense of taste, the former more particularly for the anterior two-thirds of the tongue, the latter for the posterior third, can be shown, as already mentioned, both by experiments performed upon animals, and by pathological cases observed in man, division or disease of these nerves involving loss of the sense of taste. The glosso-pharyngeal differs from the chorda tympani, however, in this respect, in that it is a nerve of general sensibility, as well as that of taste, the chorda tympani (gustatory fibers) being a nerve of taste alone, the sensory fibers of the lingual ner^^e bearing to the chorda tympani the same relation that the sensory fibers of the glosso-pharyngeal bear to its gustatory ones. It should be mentioned, however, that according to Gowers ^ any gustatory properties that the glosso-pharyngeal possesses is due to fibers derived from the fifth nerve through the otic ganglion, tym- panic plexus, and petrous ganglion. It is generally admitted that all gustatory sensations are made up of four primary sensations, sweet, bitter, acid, and saline. It is iRauber, op. cit., s. 694. ^Edinger op. cit., s. 40. ^Op. cit., Vol. ii., p. 278. 732 NOSE AND OLFACTION ; TONGUE AND GUSTATION. also regarded as probable that there are distinct nerve fibers for the transmission of impulses to special cortical centers, which when re- spectively excited, give rise to the above special sensations. How- ever that may be, it has been shown as a matter of fact,^ that potassium chloride tastes cool and saltish at the anterior part of the tongue, and sweetish at the posterior part ; potassium nitrate cool and piquant at the anterior, and bitter and insipid at the posterior end. Certain substances, like mineral acids, ferric sulphate, jalap, and colocynth, while but little appreciated at the anterior part of the tongue, are appreciated very acutely at the posterior portion. On the other hand, meats, milk, and wines, are equally well appre- ciated at both ends of the tongue. Fig. 424. Filiform papillif. (Qi'ain.) The time which elapses between the a])plication of a sapid sub- stance and the resulting sensation varies with diiferent substances. Thus according to Van Vintschgan " saline substances are tasted most quickly within tlie 0.17 sec, then sweet, acid, and l)itter ones; the latter in the case of (piininc within 0.258 sec. It is well known that the sense of taste is much aided by that of smell, the two sen- ' Lus-tana, Archives de Physiolof^ie, Tome ii., 1869, j). 20S. ^Landois, op. cit., p. 1042. FILIFORM PAPILL.E. 733 sations together giving rise often to that of flavor. The sense of taste is aided also l)y that of sight. Thus, for example, if the eyes be bandaged and red and white wine be rapidly tasted alternately it beeomes impossible in a short time to distinguish one from the other. The most favorable temperature for taste appears to be be- tween 10° and 35° C. (oO" to 95° F.), hot and cold water paralyz- ing taste at least temporarily. The sense of taste like that of smell is susceptible of great improvement. It may be mentioned incidentally that the hliform papillne, the minute conical eminences densely set over the greater part of the dorsum of the tongue and disposed in lines diverging from the raphe, appear to be tactile in function. CHAPTER XXXYIIl. THE EYE AND VISION. The organ of vision includes the optic nerve, the eye and its appendages. The optic nerves — consisting of medunated fibers but without neurilemma, together with some gray nerve fibers — are usually described as arising from the optic chiasma, or commissure. Eegarded, however, as the continuation of the optic tracts, the optic nerves in reality arise, as we have seen, from the optic lobes, thal- FiG. 425. Cortical visual centers on the outer sur- face of the hemisphere. The darker shad- ing indicates the region of the half vision center (the precise limitation of which is not yet known); the lighter shading is that of the supposed higher visual center. (GOWERS.) ami optici, corpora geniculata, cuneal portions of the occipital lobes, and prol)ably also from the angular gyri. The root fibers (438,000 in number)' from these different points of origin, converging, form flat- tened bands, which. Minding obliquely around the under surface of the crura cerebri, pass to the temporal side of one eye and to the nasal side of the other, the decussation of the fibers in the chiasma being therefore incomplete (Fig. 420), at least such is the view held bv most neu- Right homonymous lateral hemianopsia, from lesion of the left visual center of the cortex or left optic tract. A. Dark left nasal half field from blind temijoral half of retina. A'. Dark right tem- ])oral half field from blind nasal half of retina. B. Left eye. B'. Right eye. f, C. Left and right optic nerves, composed of the cross bundles of fibers. /J, I)'. Left and right crossed bundles. JS, E'. Left and right occipital lobes. F, F' . Left and right posterior horns. Ci, G'. Optic radia- tion. //, y/'. optic chiasm. /, /'. Angular gyrus. K. Region of optic thalamus, geniculate body and quadrigcrainal bodies, collcctivelv termed pri- mary optic centers. M, M'. Cuneus. The left ciineus and optic tract are shaded, to show lesion of these parts and the influence of the lesion upon the retina. (Mills.) rologists as explaining best the facts of homonymous lateral hemi- anopsia. Nevertheless, it must be admitted that Kolliker^ and 1 Salzer, Wiener Sitzungsberichte, Band 81, 1880, s. 3. 2 Op. cit., s. 563. THE OPTIC NERVES. 735 other liistologists of authority hohl that the decussation of the fibers in the chiasnui in man is complete. The extent of de- cussation in animals, which is variable, appears to depend upon the amount of separation of the fields of vision. Thus in man and certain mammals, Avhere the eyes are so placed that tliey can both be directed to the same object, the fields of vision overlap and there is incomplete decussation. On the other hand, in the lower mammals, such as the mouse and guinea-pig, birds (with the exception perliaps of owls), reptiles, amphibia, and fishes, in which the fields of vision are distinct and do not over- lap, there is a total decussation. It should be mentioned, how- ever, that the fibers constituting the anterior portion of the chiasma are not derived from the optic tracts, but simply pass from one eye to the other, while the fibers constituting the posterior part — and sometimes wanting — pass from tract to tract without being connected with the eyes. The optic nerves proper, arising from the anterior and outer border of the chiasma, curved in direction and rounded in form, enclosed in a double fibrous sheath, derived from the dura mater and arachnoid, pass into the orbit through the optic foramina, piercing the sclerotic coat of the eye at its posterior, inferior, and internal portions ; the thin, but strong membrane through which the nervous filaments pass into the sclerotic, known as the lamina cribrosa, being partly derived from the sclerotic, and partly from the coverings of the nerve fibers which are lost at this point. At about 5 millimeters (4 of an inch) behind the globe of the eye, the optic nerve receives the central artery and vein of the retina, which, together with a delicate filament from the ophthalmic ganglion, is thence transmitted within the center of the nerve l)y a minute canal, lined with fibrous tissue. That the optic nerves are the special nerves of the sense of sight there can be no doubt, since their injury or division always involves impair- ment or loss of sight. While the optic nerves are the avenues or paths by which the impressions due to the presence of light are transmitted to the cunei and angular gyri, there to become, as we have seen, conscious, intelligent vision, they are, hoMever, abso- lutely insensible to ordinary impressions. Xot only have these nerves been pinched, cut, and cauterized in animals, without the latter evincing any pain, but their insensiliility in man has often been observed also, as in surgical operations, for example, in which the nerves have been exposed. That the optic nerves are especially susceptible to the impressions of the rays of light is still further shown from the fact of their excitation, however caused, always giving rise in consciousness to the idea of liglit — a severe blow on the orbit making one see stars, as often said, the mind having asso- ciated so uniformly the excitement of the optic nerve with the presence of light, that in time it becomes impossible to disassociate the two ; the excitement of the one invariably suggesting the pres- ence of the other. 736 THE EYE AND VISION. The Eyeball. The eyeball, a spheroidal body, partly imbedded in a cushion of fat, protected by the surrounding bony orbit and the eyelids, mois- tened by the lachrymal secretion, and moved by various muscles, is composed of several coats, concentrically disposed, and enclosing several refractive media. Were it not for the fact of the cornea being set in the sclerotic, like a crystal into the rim of the face of a watch, the eyeball would present the form of a spheroid. Owing, however, to the cornea constituting one-tenth of the outer circum- ference of the eye, and to tlie fact just mentioned, the longest diam- eter is in the antero-postcrior direction, as shown by the mean results obtained by Sappey.^ Diameter of Eyeball in Millimeters. Ant. post. Tran.sverse. Vertical. Oblique. Mean of 12 females from 18 to 81 years of age, 23.9 (0.96 inch.) 23.4 23.0 23.8 Mean of 14 jnales from 20 to 79 years of age, 24.6 (0.98 inch.) 23.9 23.2 24.1 It will be observed, from the above, that all the diameters are less in the female than in the male. It may be appropriately men- tioned in this connection, also, that all such measurements should be made as soon as possible after death, within from one to four hours, owino; to the eveball losine; so soon its ncn-mal form and dimensions. The Sclerotic and Cornea. The sclerotic (Fig. 427, 2), the outer protective coat of the eye- ball, covering the posterior five-sixths of the latter, varying in thickness from 1 to | mm. (J^ to the -gig- of an inch), is a dense white, opaque tunic, composed of ordinary connective tissue, mixed with small elastic fibers and a few blood vessels, and yielding, on boiling, gelatine. The cornea, the first of the refractive media, constituting the anterior sixth of the outer circumference of the eyeball, and varying in thickness from 1.1 to ^L i^^™- (o^o to the 3^2 of ^>^ inch), is the transparent projecting tunic (Fig. 427, 3) attached to the periphery of the sclerotic, of which, indeed, it may be regarded as the continuation, consisting, like the latter, of layers of connective tissue, though somewhat modified, l)oth structurally and chemically, since it is transparent, admitting light into the interior of the eye, and yielding chondrine on boiling. The cornea may be described as consisting of three parts : a stratified epithelium anteriorly, con- tinuous W'ith that of the conjunctiva, a middle portion, the cornea proper, continuous witli the sclerotic, consisting of modified connec- tive tissue, posteriorly, of a homogeneous, elastic lamella, covered with epitlielium-like cells, the membrane of Demours or Desceraet, the part of the membrane passing to the anterior surface of the iris, ' Traite d' Anatomie, Tome troisieme, p. 747. Paris, 1877. THE CHOROID. i6i more uoticeable iu the eyes of the sheep and ox than in man, being known as the ligamentum pectinatum iridis. In a state of health in the adult, vessels are n(»t found in the cornea, except at its cir- cumference, where they are disposed in capillary loops, and by Fig. 427. Horizontal section of right eyeball. 1. Optic nerve. 2. Sclerotic coat. 3. Cornea. 4. Canal of Schlemm. 5. Choroid coat. 6. Ciliary muscle. 7. Iris. 8. Crystalline lens. 9. Retina. 10. Hyaloid membrane. 11. Canal of Petit. 12. Vitreous body. 1.3. Aqueous humor. which nutrition is apparently carried on. The ner\-es of the cornea are, however, very numerous, and are derived from the long and short ciliary nerves. Entering the sclerotic, and crossing the choroid, they pass into the cornea, extending almost through to its free surface. The Choroid. Removing the sclerotic in the manner represented in Fig. 428, the second coat of the eyeball from without inward, the choroid with its anterior prolongation, the ciliary muscle will then be ex- posed. The choroid may be regarded essentially as the vascular pigmental tunic of the eyeball. Its inner or pigmental layer constitutes, however, in reality, the outer coat of the retina, being developed, as we shall see hereafter, like the latter from the invagi- nated portion of the optic vesicle. The choroid, varying in thick- ness from the ^ mm. to 1 mm. (j^ to the -^^ of an inch), and covering the eyeball to the same extent as the sclerotic, is connected by its outer surface with the latter tunic by connective tissues, ves- sels, and nerves, the so-called .membrana fusca, and, like the sclerotic, is traversed posteriorly by the optic nerve. The arteries 47 r38 THE EYE AND VISION. of the choroid, the short ciliary, comparatively large after piercing the sclerotic close to the optic nerve, break up into branches, which pass forward and then inward to end in the capillaries, the latter being sometmies known as the tunic of Ruysch. The veins situ- ated externally to the other vessels are very numerousj and, being Fig. 428. Choroid membrane and iris exposed by the removal of the sclerotic and cornea. Twice the natural size. «. One of the segments of the sclerotic thrown back. /. Ciliary muscle, k. Iris, e. One of the ciliary nerves. /. One of the vasa vorticosa or choroidal veins. (Quain.) disposed in curves converging into four trunks, present a peculiar appearance, which has given rise to the name of vasa vorticosa. Among the vessels of the choroid are also found elongated and stellated pigment cells, with branches, which, intercommunicating, constitute a sort of network. The nerves supplying the choroid are derived from the long and short ciliary. The inner surface of the choroid is smooth and is covered with the hexagonal pigmental cells of the retina, which will be considered as the outer layer of that tunic rather than, as formerly, as the inner layer or tapetum nigrum of the choroid for the reason just given. Ciliary Processes. It will be observed from Fig. 428 that the choroid passes forward into the ciliary muscle, the latter in turn passing into the iris, con- stituting, in fact, one continuous layer — the second tunic of the eyeball. If, however, the choroid be viewed from behind, as rep- resented in Fig. 429, in which the eyel)all is supposed to have been divided transversely, it will be seen that the choroid passes forward and posteriorly into the ciliary processes, just as we have seen it passes forward but anteriorly into the ciliary muscle. Or, briefly, the relation of the parts may be expressed by saying that the choroid .splits at its anterior termination into the ciliary muscle CILIARY MUSCLE. 739 Fig. 429. in front, and the ciliary processes behind, the ciliary muscle being continued into the iris, hence the general term of uvea applied to all of these parts by the older anatomists. The ciliary processes or plications, about seventy in number, disposed radially behind the ciliary muscle and the iris, and fitting posteriorly, as we shall see, into corresponding plications of the suspensory ligament of the lens, more particularly into that part of it known as the zone of Zinn, consists of large and small thickenings of the choroid, the small folds alternating, though ir- regularly, with the large ones, the latter measuring about the J^- of an inch in length and the -^^ in dpnth nnd comnOMcd like tlip of the ciliary processes, of which about sev- aeptn, auu COmpUbea lllve Uie euty-one are represented. J^. (Quain.) choroid proper of vessels and pig- ment, the latter, though, being absent in the rounded inner ends. Ciliary processes as seeu from behind. 1. Posterior surface of the iris, with the sphinc- ter muscle of the pupil. 2. Pupil. 3. One Ciliary Muscle. The ciliary muscle (Fig. 428, 6), the continuation anteriorly of the choroid, about 3.1 millimeters (| of an inch) wide, con- sisting of longitudinal and circular fibers, the latter, however, present at the periphery of the iris only, may be regarded as arising from the inner side of the junction of the sclerotic and cornea, close to the canal of Schlemm, and inserted into the choroid opposite the ciliary processes. Such being its disposi- tion, it is evident that, in contracting, the nerves supplying it be- ing the long and short ciliary nerves, it will draw the choroid forward, thereby compressing the vitreous humor and relaxing the suspensory ligament of the crystalline lens, the significance of which action will be better appreciated when the subject of accommodation has been considered. The Iris. The iris (Fig, 428, e), the circular, contractile, and colored mem- brane seen through the transparent cornea, to which the character- istic color of the eye is due, is the muscular diaphragm of the eye, the aperture in its center or pupil permitting and regulating the passage of light into the interior of the eye. The iris, about as thick as the choroid, is attached by its circumferential border to the line of junction of the cornea and sclerotic at the origin of the ciliary muscle, and measures about one-half an inch across, and in a state of rest about the one-fifth of an inch from the circumfer- 740 THE EYE AND VISION. ence to the pupil. The iris consists essentially of a stroma of con- nective tissue and muscular fibers, the latter disposed as a ring around the pupil, constituting the sphincter, and as a rays from the center to the circumference, the dilator muscles of the iris. The pupil, or aperture in the iris regulating the amount of light admitted, varies in size according as the muscular fibers are contracted or relaxed, from the one-twentieth to the one-third of an inch, and during foetal life is closed by a delicate transparent membrane. The iris is supplied by the two long ciliary and anterior ciliary arteries, the latter being derived from the muscular branches of the ophthalmic. The two long ciliary arteries hav- FiG. 430. ing pierced the sclerotic, one on each side of the optic nerve, pass between the latter tunic and the choroid to the ciliary muscle, and each vessel, just before reaching the iris, divides into an upper and lower branch, which, anastomos- ing with the corresponding ves- sels of the opposite side, and with the anterior ciliary arteries, forms a vascular ring, the circulus major of the ciliary muscle, from which small branches are given oif, some of which supply the muscle, M'hile others, converging toward the pupil, form a second vascular circle — the circulus minor ; from the latter capillaries are given oif which terminate in veins. The veins of the iris terminate in the circular venous sinus known as the canal of Schlemm, situated at the junc- tion of the cornea with the scler- otic. The nerves of the iris are the long ciliary, which, as we have already seen, are given off from the nasal branch of the ophthalmic and the short ciliary nerves derived from the ciliary ganglion. The ciliary nerves, after piercing the sclerotic, pass forward on the surface of the choroid, to which tunic they give branches, to the ciliary muscle, in Avhich they form a plexus con- tinued forward into the iris ; they apparently terminate at the pupil in a plexus of uon-medullated fibers. The lenticular or ciliary gan- in. oc. m V. optJi. Diagrammatic representation of the nerves foverniiig the puidl. //. Optic nerve. /. 5) : 1, pig- mentary layer ; 2, columnar layer ; 3, outer nuclear layer ; 4, outer molecular laver ; 5, inner nuclear layer ; 6, inner molecular layer ; 7, ganglionic layer ; and oundary of the third, or outer nuclear layer. The rods exceed the cones in number, the latter amounting to more than three millions, there being usually about four rods to one cone, except at the macula lutea, where cones only are present ; they have an elongated cylindrical form with a diameter of about ^^ of a millimeter {^2'h~oi) of an inch) and a length of Jjj of a millimeter (^^1.^ of an inch). The cones on the other hand, are shorter and thicker, having a diameter of about yi^ of a millimeter (^yg 6 ^^ an inch), bulge out at the inner end or base, and terminate exter- nally by a fine tapering portion. The cones are usually separated by a distance of j^-^ of a millimeter (^^-sVo" ^^^ ^" inch), the inter- vening portion being filled by rods. Through delicate fiber-like prolongations the inner ends of the rods and cones are in relation with the third or outer layer of the retina, the outer nuclear layer, which consists of several strata of clear, oval elliptical nucleated cells from both ends of which delicate fibers are prolonged. These outer cells, presenting marked differ- ences, are of two kinds, known as rod granules and cone cells, ac- cording as they are connected "vvith the rods or cones, respectively. While the outer fibers of the outer nuclear layer are prolonged into the rods and cones, the inner fibers of the same are prolonged into the outer molecular layer ; the latter in turn appears to be in rela- tion through fibrils with the cells of the inner nuclear layer, the latter being in relation with tlie inner molecular layer.^ The seventh layer of the retina from without inward, the ganglionic or layer of nerve cells, consists of a stratum of nerve cells of a sphe- roidal or pyriform figure, which appears to be in relation by fibers on the one hand, with the preceding inner molecular layer, and, on the other, with the fibers of the optic nerve. The latter, constitu- ting the eighth layer of the retina, appears to be bounded by a dis- tinct membrane, the membrana limitans interna, which, however, is not a continuous structure, as its appearance would lead one to sup- pose, but is formed, like that of the membrana limitans externa, by the terminal fibers of the sustenacular or connective tissue frame- work of the retina being united together at this point. From this necessarily brief description of the minute structure of the retina it Avill be seen that the layer of th.e rods and cones, or Jacob's mem- 1 Rauber, op. cit., s. 723. Gehuohten, op. cit. s. 628. 748 THE EYE AND VISION. brane, bounded externally by the pigmentary layer, may be regarded as the termination of the optic nerve fibers. It may be mentioned, in this connection, that, as the rods and cones far exceed the optic nerve fibers in number, it is impossil)]e that each optic nerve fiber should be connected with a rod or cone throughout the retina, though such a relation may exist at the macula lutea. It has already been mentioned that at the macula lutea the rods are absent, the cones only being present ; the latter are, further, nnich longer and nar- rower than elsewhere, especially opposite the fovea. At this por- tion of the retina the various layers of which it consists are also very much thinned. The yellow color of the macula, deepest at the center, is due to a coloring matter diffused through all the layers except that of the cones and tlie outer nuclear layer. It might naturally be»supposed that tlie anterior layer of the retina, that fac- ing the light, would be the sensitive layer — as a matter of fact, of all the layers of the retina, however, that of the rods and cones is most sensitive to light, as can be shown experimentally by so illu- minating the eye that one is able to perceive Fig. 436. the shadows of the vessels of his o^vn retina, which are cast upon the layer of rods and cones. The vessels of the retina, being situ- ated in its anterior layer, necessarily cast their shadows on one of its posterior layers, and the only reason that we do not ordinarily see these shadows is probably that we have be- come so accustomed to them that they no B. A candle placed at the longer attract our attention. If, however, the side of the eye — that is, as !• i • i i i i i • i much to the side of the ceu- source ot light be placcd lu an unusuai posi- B'fnterrMum^fuo'i'; tiou, as iu Fig. 436, thcu thc shadows of the Tiigh'ttre'tritedl/the vcsscls falling ou au uuusual portion of the crystalline leus upon the layer of rods and coucs wiU be perceived, extreme lateral portion of i-iii ii* the eye. CD. Two vessels and wul bc sccu bv ouc looking: at a vcrv of the retina (the size of the , , „ . , •' , ^. „ • , i retina is here greatly exag- (lark surtacc lu a darJc rooui, as it projcctcd fheseTwo vessels "is^seeu as at T>' C , and rcscmbliug cxactlv the vessels JLl"rSc:?i^RK?;^f- of the retina, the picture of the retina so seen being known as the vascular tree of Purkinje. Now it Avas shown by H. Muller,^ that the distance be- tween the anterior layer of the retina, and the layer of rods and cones was about equal to tliat between the retinal vessels and their shadows ; necessarily, tlien, the layer of rods and cones must be sensitive to light. Now, it l)cing remembered that the layer of rods and cones lies next to the pigmental layer, and that the ret- ina, with the exception of the latter layer, is transparent, it follows that a ray of light passes through the retina until it I'caches the pigmental layer wlien it ceases to be light, l)eing transformed into either heat, chemical or nervous force ; the latter exciting the rods and cones, gives rise to an impression which is then transmitted ' Verhaiid. der phy.sik. med. Gcfsellscliaft zu Wurzburg, v., s. 411. VISUAL PURPLE. 749 back to the optic fibers on the anterior surface of the retina, where it is again reflected along tlie optic nerve fibers to the optic lobes, etc. It has been shown more particularly by the researches of Kiihue' that the outer ends of the rods of the retina contain a substance known as " rhodopsin " or "visual purple" and Avhich is appa- rently elaborated out of the retinal epithelium lying l)etween the rods and cones. If an eye after excision or in its natural position be protected from light for a time, and then the light of a lamp or a window, for example, l)e allowed to fall upon it, the retina will show, if examined under red light, the image of the object impressed upon it by the bleaching of the purple. If the retina be further treated with a 4 per cent, solution of alum-potash before the retinal epithelium has had time to obliterate the bleaching effects, the im- age or " optogram " of the external object may be " fixed " as the photographers express it. Even if it be admitted that the chem- ical changes undergone by the visual purple, due to light act as a stimulus to the optic nerve fibers, such changes cannot be essential to vision, since vision is most acute at the yellow spot just where the visual purple is absent, the rods not being present in that situ- ation. INIoreover, vision is fairly distinct in albinos in which the visual purple is absent. Beyond the statement that the rods and cones are excited by the heat or nerve energy, or whatever the form of energy may be into which the light is transformed in the pigmental layer, little can be said as to the special role they play in vision. Such facts, however, as that in the bat, hedge iiog, and mole, nocturnal animals, and night birds, also, the retina consists solely of rods ; whereas, in day-birds, especially in those which live on insects, of brilliant colors, the ret- ina contains a much larger number of cones than the mammalia, would lead one to suppose that the rods are affected by differences in the intensity of the light, the cones by differences in its quality — that is, its color. AVliile there can be no doubt that the fibers of the optic nerve transmit luminous impressions, or their modifica- tions, in the manner described, it can be shown experimentally that the part of the retina where these fibers appear is insensitive to light, and is called, for that reason, the punctum csecum. Thus, if two black points (Fig. 437, A, B), on a piece of paper, separated Fig. 437. A B • • by a distance of two inches, be viewed at a distance of six inches by the right eye, the left eye being closed, the point B Avill be invis- ible, being then opposite the punctum caecum, or blind spot. 1 Centralbl. f. d. med. Wissensch., 1877, s. 19-1. Hermann, op. cit., Bd. 3, 1, 1879, s. 261. 750 THE EYE AND VISION. The Vitreous Humor and Hyaloid Tunic. The vitreous humor, whik' enclosed l)y the retina, does not, how- ever, lie loosely in the cavity of the eyeball, being invested by a delicate membranous capsule, about .^~\-^ of a millimeter (g q^q^q^ of an inch) in thickness — the hyaloid tunic. The latter is thicker in advance of the retina than elsewhere, and, as already mentioned, is impressed by the ciliary processes of the choroid, the zone so formed around the crystalline lens, and well defined by the staining of the processes, being known as the zone of Zinu. Anteriorly the hyaloid tunic splits into two laminae, which, diverging at the border of the crystalline lens, becomes confluent Avith the anterior and posterior surfaces of its capsule, the two laminae adhering at intervals ; if the space between them be inflated, it will assume the appearance of a beaded canal, surrounding the circumference of the lens — the canal of Petit. Such being the disposition of the hyaloid tunic, it is evi- dent that not only does it support the vitreous humor, through in- vesting the latter, but acts also, from what has just been said, as the suspensory ligament of the lens. The vitreous humor, one of the refractor}^ media of the eye, occupying about the posterior two- thirds of the globe, consists of a clear, glassy, gelatinous matter, containing albumin, a mucoid, and mineral bodies. It is divided into compartments by delicate membranous processes, which, given off by the hyaloid tunic, penetrate its substance. The specks that one sees occasionally floating about, as it were, in the field of vision, the so-called muscte volitantes, are due to the shadows cast upon the retina by the connective tissue elements suspended in the vitreous humor. The Crystalline Lens. The crystalline lens (Fig. 427, 8), the most important of the re- fracting media of the eye, transparent and very elastic, is situated in the hyaloid fossa of the vitreous humor, behind the pupil, and is enclosed, as already mentioned, betAveen the laminae of the hyaloid tunic, the latter constituting its suspensory ligament. The crystal- line lens is a double convex lens, the convexity of the posterior surface being greater than that of the anterior. The antero-poste- rior diameter, 6.2 millimeters (J of an inch), is, however, a little less than that of the lateral one, 8.3 millimeters (^ of an inch). With advance in age the convexities diminish, the lens becomes harder and inelastic, which accounts for the gradual diminution in the power of accommodating the eye to distances. If the lens be examined with a low magnifying power, there w^ill be observed on each of its surfaces a star-like Ixxly, nine or sixteen rays of which extend from the center to Avithin about two-thirds of the periphery. The l)ody of the stars and their rays are not of a fibrous character, like the rest of the lens, but consist of a homogeneous substance, which extends between the fibers. The latter are flattened, six- sided prisms, from yig- to -g^g of a millimeter (^-gVs" ^^ 2Tcnr ^^ ^^ THE AQUEOUS HUMOR. 751 inch) In'oad, and from -^i^ to gi^ of a millimeter (yg^oQ- to -q-q\jj- of an inch) thick. Their flat surfaces arc parallel with the surface of the lens, and their direction is from the center, and from the rays of one star to the periphery, where they turn and pass toward those of the other. Chemically, the lens is composed of a globulin, called crystalline, combined with inorganic salts. The crystalline lens is enclosed within a very thin, transparent, elastic membrane, the capsule, which is lined anteriorly with a layer of delicate nucleated cells. The Aqueous Humor. The aqueous humor (Fig. 427, 13), the remaining of the refracting media of the eye, is a colorless, transparent, almost watery fluid, filling the anterior chamber of the eye — that is, the space between the cornea in front and the iris and crystalline lens behind, and the posterior chamber, or the space between the posterior surface of the iris and the lens, supposing that such a place exists, which is very doubtful, and in any case must be very small. That the aqueous humor is secreted possibly by the blood vessels of the iris and ciliary processes, or the internal layer of the cornea, is shown by the rapidity with which it is reproduced after it has been evacuated, as in surgical operations performed upon the eye. The solids of the aqueous humor amount to thirteen per thousand, among which serum globulin and glo1)ulin are found in traces. Intraocular Pressure. The watery fluids filling the cavity of the eye are during life subjected to a pressure, the so-called intraocular pressure. This pressure, depending upon that of the blood pressure of the retina, choroid, etc., must vary with the latter, rising and falling with it. The character of this pressure is determined by pressing upon the eyeball and of so learning whether it is soft, tense, or compressible. CHAPTER XXXIX. PHYSIOLOGICAL OPTICS. Refraction and Accommodation. From the necessarily brief description just given of the eye, it is ajDparent that it resembles essentially in its structure the camera of the photographer, its refractive media being comparable to the lens, the iris to the diaphragm, the choroid to the internal blackened surface, the retina to the sensitive plate, the image of the external object being brought to a focus on the retina or sensitive plate, respectively, through the refraction undergone by the rays of light. In order, however, to understand the manner in which the rays of light are brought to a focus on the retina by the cornea, crystalline lens, etc., it will be necessary to describe briefly the phenomena of refraction or the course that rays of light take in passing through refractive media. Suppose that W W (Fig. 438) represent a mass of water, and C A the direc- FiG. 438. tion of a beam of light pass- ing through the atmosphere L L, the rarer medium, it will be observed that as the ray of light passes through the Avater, the denser me- dium, it is bent toward the perpendicular A F, but that as it passes out of the water into the air again, the rarer medium, it is bent away from the perpendicular. Let now the line C A, repre- senting the direction of the incident beam, be connected with tlie perpendicular B F by the line D E, and the line representing the refracted beam A H, be connected witli the perpendicular by the parallel line G H, and it will be seen that the line G H is three-fourths as long as the line D E ; and further that this ratio of 4 to 3, equal to 1.33G, will be invariably the, same whatever the angle may be that the incident beam C A makes with the surface of the water I K, except it be a right angle, the beam then passing directly through the water without being re- fracted at all. The well-known fact of a stick ajipearing bent when obliquely Refraction of Light. REFRACTION. 753 thrust into water (Fig. 439) or of a coin lying upon tlie bottom of a vessel appearing to be at some distance from the latter (Fig. 440), are familiar illustrations of refraction. Fig. 439. Fig. 440. Illustratioa of refraction. Illustratiou of refraetiou. If, however, with A as a center, and a radius A D, a circle be described, the line D E becoming then trigonometrically the sine of the angle I) A 31, and the line G H the sine of the angle HA X, the law according to which light is refracted as it passes from air through water, may be expressed by saying, that the ratio of the sines of the angles of incidence and of refraction equals | = 1.336 and is constant for the particular substance water, or, briefly, that the index of refraction of water is 1.33. That is to say, if the line D E is 4 inches in length, then H G ^\\\\ be 3 inches, the two being always in the same ratio. If now, for water, crown glass be sub- stituted, it will be found that the sine of the angle of incidence D E is to the sine of the angle of refraction H G not as 4 is to 3, as in the case of air and water, l)ut as 3 to 2 — that is, the index of refrac- tion for the particular substance crown glass equals |- = 1.5. Bearing in mind then, that as the beam of light passes from the air, the rarer medium, through the glass it is bent toward the per- pendicular, but away from it as it passes out of the glass, the denser medium, and that by the index of refraction is meant the ratio of the sines of the angles of incidence and refraction, there will be no diiliculty in compreliending the manner in which the direction of a beam of light is altered in passing through biconvex and biconcave lenses. Let C (Fig. 441), for example, represent a biconvex lens of crown glass in which the radii of curvature are nearly equal — that is to say, the two surfaces or curves of the lens are about equally distant from the centers of the circles of which these curves form parts, and that BE, C G be two luminous rays parallel with the principal axis A D passing through the optical center C of the lens, which fall .upon the lens at the points E and G, respectively. Then, according to the law just enunciated, the 48 754 PHYSIOLOGICAL OPTICS. ray B E being first bent toward the perpendicular, and then away from the perpendicular, and the ray G G being in the same manner bent first toward and then away from the perpendicular, and the ray A G being in the direction of the optical axis, and consequently Effect of bicouvex lens ujMjn rays of light. passing through the lens perpendicularly, and, therefore, unre- fracted, it follows that the three rays, and all others parallel with them, will meet at a point F, known as the principal real focus, and situated in the principal axis of the lens at a distance from the latter (^F H) which will be determined presently, and known as the principal focal distance. The eifect of a biconvex lens is then to bring parallel rays of light to a focus on the side of the lens opposite to the source of light, the amount of convergence depend- ing upon the radius of curvature of the lens and its index of re- fraction, which in this particular case, as w^e have seen, is 1.5. The converse of this is also true, since if the source of light be at the principal focus F, then the divergent rays after leaving the lens will be brought parallel with each other, and with the principal axis. Such being the action of a biconvex lens, it will be seen from a comparison of Fig. 441 with Fig. 442, that the action of a Fig. 442. A*^ 3/ Effect of biconcave lens upon rays of light. biconcave lens is exactly the opposite of a biconvex one, since the rays of light {B E, G G, Fig. 441), after being bent toward their respective perpendiculars and then away from them, according to CONJUGATE FOCI. 755 the law of refraction, will diverge from the princi])al axis A D, instead of converging tOAvard it, and the rays of light B E, C G, and all others parallel with them, will diverge as K L, 31 N, instead of being bronght to a focus, on the side of the lens opposite to that of the light. In the case of a biconcave lens the focus is negative, virtual, that is to say, it is upon the same side of the lens as the light, and its position is found by prolonging backward the rays L K and N 31 until they meet in the principal axis A D. It will be also observed that the converp-ing; ravs L K, N 31 are brought parallel with each other on the same side of the lens as that where the light is now supposed to be. Let us now consider the case in which the luminous object L is beyond the principal focus F (Fig. 443), but so near that all the incident rays L E, L F form a divergent cone, then, according to the law of refraction, the rays, after leaving the lens, will be found to come to a focus at /, and the converse of this will be found to be true, since, if the luminous object be placed at I, the focus will then be at i, hence / and X are conjugate foci. Further, it will be found by experimentation, or by calculation, that if the distance between the luminous object I and the lens be twice the focal distance — that is, twice H F equals H I — then the focus I will be situated on the other side of the lens at the same distance, or twice H F, as at the point A, on the axis A D. If, however, the distance between the lens and the luminous object be less than twice the fo.cal distance, the focus will be situated beyond the point A, and if more than twice the focal distance, then the focus will be situated within the point A — that is, between the point A and the lens. After Coujugate foci of leus. what has just been said, with reference to the manner in which the rays of light are brought to a focus by biconvex lenses, etc., it will be readily seen from Fig. 444 how the image of an object, as of an illuminated arrow, for example, is formed if a biconvex lens be placed between the latter and a screen. It will be observed, however, that the part of the arrow at a being brought to a focus at x, that at h at y, that the image of the arrow is neces- 756 PHYSIOLOGICAL OPTICS. sarily reversed, and that if the luminous object approaches the lens its image recedes and becomes larger, and if it recedes from the lens its image approaches and becomes smaller, and that if the luminous object be situated at twice the focal distance from the lens its image will be of the same size and situated at the same distance from the lens. The distance at which the image is formed l)ehind the lens can be readily calculated in any case by formulse to be found in any standard work on physics. Fig. 444. Fif4. 445. Paths of rays of light through lens with foniiatiou of image. Paths of rays of light witliout lens. It need hardly be added that in the absence of a lens, the rays of light will follow the paths indicated in Fig. 445, and as the light from a will meet at 4 that from b, and the light from 6 at 1 that from rt, no image of the arrow will be formed upon the screen. Having considered now the properties of lenses, let ns apply what has been established of the same to the elucidation of vision, and show how the rays of light, passing successively through the cornea, aqueous humor, crystalline lens, and vitreous humor are finally brought to a focus on the retina. In considering the paths of the rays of light through the refractive media of the eye ])hysicists make use of a normal schematic eye, a standard eye, so to speak, in which certain cardinal points have been established, and by which the course of the rays of light through the eye can be readily constructed, the position of the focus determined, and the size of tlie image estimated. Let ns endeavor, therefore, to explain the method by which the cardinal points are determined. Let M, M^ be two refractive media separated from each other by a spherical surface B C (Fig. 446), constituting what is known op- tically as a simple collecting system, and N the center of curvature — that is, the center of a circle, of which B C forms a part. All the radii drawn from the center N to B C, such as N B, IST x, N Y, being perpendicular rays of light falling in the direction of the radii, must pass unrefracted through N as L D, I^ d', for example, and are called, therefore, lines of direction, while N, the point of inter- section of all such lines, is called the nodal ])oint. The line O A, connecting N, the center of cur\aturc, with the vertex I, and pro- longed in both directions, is known as the optic axis, the plane H E, perpendicular to the optic axis at I, being called the principal plane, and the point I, within the latter, the })rincipal point. Such SIMPLE COLLECTIVE SYSTEM. 757 being prcsuppixscd, it can be shown that all rays jiarallel with each other, and with the optic axis in the medium M, such as f H, p E, falling upon B C, come to a focus at F^ in the second medium, called the second principal focus, or second focal point, the plane S F- P, perpendicular to the optic axis O A, at this point, being the Fig. 440. Simple collective system of refracting media. second focal plane. Of course, the converse of the above is true — that is, rays diverging from F', such as F^ B, F" C, pass into the first medium ])arallel with each other, and with the optic axis. Further, it will lie seen from an inspection of Fig. 446, that rays which are parallel t(^ each other in the first medium, but not paral- lel with the optic axis, such as Q T, U Z, come to a focus in the sec- ond medium in the point D of the second focal plane, where the non- refracted directive ray L D meets the latter, and that rays diverging from D pass through the first medium parallel with each other, but not parallel with the optic axis. It is also evident that all rays, which, in the second medium are parallel with each other, and with the optic axis, such as S B, P C, come to a focus (F^) in the first medium, called the first focal point, or first principal focus, the plane of f F^ p, perpendicular to the optic axis at this point, being known as the first focal plane. Of course, the converse of the above is true, viz., tliat rays diverging from F^ pass through the second medium parallel with each other and with the optic axis. Finally it follows that the radius of the spherical surface X I is equal to the difierence of the distance of the focal points F', F-, from the principal point I — that is, that X I = F' I — F^ I. Such being admitted, it will be seen that an incident ray (Q T) comes to a focus in the second focal plane in the point D, where the non- refracted directive ray L D meets the latter, and that a reversed image | of an external object like an arrow | situated in the first meclium is formed in the second medium at the point where the prolonged ray BF" meets the non-refracted directive ray I'd'. Now did the eye consist simply of two refractive media, separated 758 PHYSIOLOGICAL OPTICS. by a spherical surface, as in the simple collecting system just de- scribed, the construction of the refracted ray and of the image of the object would be essentially the same and equally simple. In- asmuch, however, as the eye consists of four refractive media, cornea, aqueous humor, crystalline lens, and vitreous humor, the cornea and aqueous humor constituting a concavo-convex lens, the crystalline a biconvex lens, and the vitreous humor a concavo-con- vex lens, to apply to the eye what has just been established would involve proceeding from medium to medium, which would be a tedious operation. If, however, the several media are centered, that is, if they have the same optic axis, which is pretty nearly the case in the eye, then, as shown by Gauss,^ the refractive media of such a system may be represented by two imaginary equally strong refractive surfaces (Fig. 447, F P'), the rays falling upon the first system not being refracted, but projected, so to speak, parallel with themselves to the second surface as at x x' , y y' , refraction taking place at the latter just as if that surface alone was present, and that the data required in determining the situa- tion of the tAvo refractive surfaces are the refractive indices of the media, the radii of the refractive surfaces, and the distances of the latter from each other, which can be experimentallv de- termined. Let J/', ]\P, M\ and 31^ (Fig. 447) be four media, System of refractive media liaving the same optic axis. for example, such as the air, aqueous humor, crystalline lens, and vitreous humor ; B C ii spherical surface like the cornea, sep- arating the air from the aqueous humor ; L I the anterior surface of a biconvex lens like the crystalline lens, a spherical surface separating the aqueous humor from the substance of the lens ; and Vv the posterior surface of tlie lens, also a spherical surface, reversely disj)osed, however, with reference to the cornea and an- terior surface of the lens, and separating the substance of the lens from that of the vitreous humor. Such being the relation of the refractive media, and the spherical surfaces separating them, the cardinal points of such a system, six in number, are as follows : two ' Dioptrische Untersuchungen AblKiiid. Giittingcii Gesells., 1841. CABDIXAL FOIXTS. 759 focal points (F' F'-), two principal points (P P'), two nodal points (N N'). Inasmnch as the properties of the two foci F' F-, as re- gards the rays of light diverging from or converging toward them respectively, and of the anterior and posterior focal \Aanesfp, S P, are essentially the same as already described, it Avill not be neces- sary to consider them again in detail in this connection. As re- gards the principal points P P' , they being conjugate foci like LI (Fig. 443), rays of light passing through one point will pass through the other also ; P P' being the principal points, HF and H' F' will be principal planes, and each point of the one plane having a conjugate focus in the otlier, a ray of light passing through a point on one plane will pass through a corresponding point on the other at the same distance from the axis and on the same side, the distance F ' P being the anterior focal length, and the distance F' P' the posterior focal length. In fact, either plane may be re- garded as the image, the other being the object. It will be ob- served that the nodal points X3'' are so disposed that if the incident ray a N were prolonged, it would emerge parallel with the emergent ray N' a' , and vice versa. Such being the position of the cardinal points in the system of refractive media and spherical surfaces rep- resented in Fig. 447, let a 6 be an object, an illuminated arrow, for example, from which rays pass through the above ; its image will be formed at b' a'. That this must be the case can be' at once shown by construction, for the ray af, after cutting the two princi- pal planes in .r.i"', and passing through the posterior focal points F'-, Avill meet the line X' a', emerging from the lens parallel with aX, uniting with the latter at the point a', the same point where the ray « F\ after passing through the anterior focal point and cut- ting the principal planes in i/ 1/' , meets X' a'. In precisely the same manner it can be shown by construction that the point b of the ar- row will be brought to a focus at b'. It need hardly be observed that the image of the arrow will be, of course, reversed. Let us suppose now that the index of refraction for air being taken as unity, that with Listing ^ the index of refraction for the aqueous and vitreous humors has been determined to be equal to 1.3379 (i-P_3.)^ that of the crystalline lens to be 1.4545 (if), the radius of curvature of cornea 8 mm. (t/^ of an inch), the radius of curvature of the anterior surfoee of the crystalline lens 10 mm., that of the posterior surface 6 mm., the distance of the anterior face of the cornea from the anterior surface of the crystalline lens to be equal to 4 mm., the distance from the anterior surface of the lens to the posterior surface, or the thickness of the lens, 4 mm., then by means of appropriate formula?, developed by mathe- matical methods ^ from the relations existing between the radii ' Dioptrik des Auges. Wagner, Physiology, Baudiv. , s. 4ol. 2 Helniholtz, Optique Physiologique, trans, by Javal and Klein, 1867, p. 70. Bonders. On the Anomalies of Accommodation and Kefraction of the Eve, trans, by W. D. Moore, 1864, p. 38. 760 PHYSIOLOGICAL OPTICS. of curvature, the indices of refraction, etc., and the six cardinal points, the exact position of the latter in the human eye can be shown to be as follows : The anterior principal focus 12.8326 mm. in front of the cornea, the posterior principal focus 22. under which distinct vision is possible the more acute the vision, the latter is evidently inversely as the size of the visual angle. The measure of the acuteness of vision in general use among physiolo- gists, based upon this principle is a series of letters, C G B, the thickness of which is one-fifth of their height, and made of such a size that at a distance of twenty feet they subtend an angle of 5 minutes, the acuteness of vision being expressed by the ratio of the distance at which such letters are still distinctly recognized to the distance D, at which they subtend an angle of 5 minutes — that is 762 PHYSIOLOGICAL OPTICS. to say F = ^ • Suppose, for example, that the person whose vision is being tested can recognize a letter at ten feet, then his acuteness of vision will be V = y = y^ = y, that of one whose vision is per- . ^/ 20 feet — that is in whom T = y = ^^ = 1. Practicallv, the smallest Fig. 449. visual angle permitting distinct vision is about 60 seconds, and, corresponding, as it does, to a retinal image of about 2"^^ of a millimeter (g sVir ^^ ^^^ inch), it will just about cover one of the cones of the retina. Two points seen under such a small visual angle would, therefore, appear as one. It has already been mentioned that the cardinal points, by means of which ^\e follow the rays of light as they pass through the media of the eye and determine the position and size of the retinal image, are deduced from the indices of refraction of the aqueous and vitreous humors, lens, radius of curvature of cornea, etc., experimentally determined. In- asmuch as the methods by which the in- dices of refraction of the media of the eye are determined are essentially the same as in the case of water or glass, it need not in this connection be described again. The radius of curvature of the cornea and crystalline, however, being deduced by formulae from the size of their reflected images, and the latter being measured by the ophthalmometer, this instrument merits at least a V)ricf description. The principle upon which the ophthalmom- eter, invented by Helmholtz,^ is constructed is, that if an image of an object a be viewed through two piano-parallel glass plates (Fig. 449) the image, through refraction, will a[)per double, a' ;iiiati.couvex, the sec- tion C a /3 y 5, a concavo-convex lens. (L.VXDOIS.) 766 PHYSIOLOGICAL OPTICS. of light are lironglit to a focus in the eye, and serving in a measure also to elucidate the manner in which the eye is accommodated for diiferent distances, a brief description of these abnormal conditions does not appear superfluous. Let us suppose, for example, that either through elongation of the whole eye or through the con- verging power of the lens being too great, that parallel rays of light are brought to a focus, not on the retina, but in front of it, at B (Fig. 455), circles of diffusion being formed, the image will be in- distinct, blurred. Obviously, in order to see distinctly under such circumstances, the object must be brought closer to the eye, so that the rays of light may be brought to a focus on the retina, hence the eye is said to be short-sighted or myopic. Such a condition can be, however, remedied by placing a suitable concave glass (C) in front of the myopic eye. The rays of light wall then be diverged to such an extent that they will come to a focus upon the retina. Fig. 455. Fig. 450. Myopic t've. Hypermetropic eye. Fig. 457. On the other hand, let us suppose that, owing to the whole eye being too short or through the converging power of the lens being too small, parallel i^ays of light come to a focus behind the ret- ina (Fig. 456 A), circles of diffusion being formed the image will be blurred and indistinct. In order to see distinctly with such an eye the so-called hypermetropic or far- sighted eye, parallel rays of light must converge sufficiently to come to a focus upon the retina. Inas- much, however, as convergent rays of light do not exist in nature, the defect can only be remedied in such an eye, the latter being passive, by placing in front of the eye a suitable c 1, ■ , f ■*! T-v. , convex glass bv which the parallel Schemer .s experiment with Thomsoii'.s ," " | . moditication. ,1. Source of light, j^. Posi- ravs will bc converjjcd Sufficiently tion of retin.a iu regard to the focus c of the '' „ ^ • • i a ray.s entering through two apertures in a tO COUIC tO a toCUS OU thc rctuia. A card, one of which is covered with a colored i -i • • , i i gla.ss 9 in an emmetropic eve. 7/. Position VCry ready and ingCUlOUS nicthod M'^^^J'^rinJ]^ll^T^;:S^t^. for determining whether an eye is enimctroiiie — that is, normal, my- ' In explaining to an audience the manner in wliich astigmatism, myopia, and hyperruetropia, circles of difiiision, etc., are produced tlie autlior lias found the arti- ficial eye of Kuline a very usefid adjunct. A CCOMMODA TION. 767 opic, or hypermetropic consists in placini>' a piece of colored *i^luss g, red, for example, over one of the openings in the card nsed in Scheiner's experiment, as represented in Fig. 457. Supposing the eye to be emmetropic, it is evident that the colored red ray and white ray falling upon the retina at the same spot, but one image, a red one, will be observed. If the eye be myopic, however — that is, the retina is too far back, then through the crossing of the rays of light two images will be seen, a red one below and a white one above. On the other hand, if the eye be hypermetropic the two images will be seen, but the red one will be above, the white one below. Accommodation. In considering the manner in which the rays of light are refracted as they pass through the media of the eye, and the image of an ex- ternal object formed upon the retina, we have supposed heretofore that both the eye and the object were at rest. Every one is familiar with the fact, however, that, notwithstanding that an object may approach or recede from the eye, in either case, at least within cer- tain limits, it is as clearly seen in the first, as in the second po- sition. Such being the case, evidently then the eye must undergo some change, otherwise, as the object approached the eye, the image would recede from the retina, being formed behind it, and as the object receded from the eye the image \vould recede from the retina in the opposite direction, being formed in front of it. Thus, let us suppose that the object being at ^ i^ (Fig. 448), and its image at d c, that the object is moved to H, its focus would then be formed behind the retina at H' , and the condition of the eye would be hypermetropic, as in the case of Scheiner's experiments just de- scribed, unless simultaneously with the movement of the object toward the eye some change was induced in the latter, by which the focus was kept upon the retina at d c. On the other hand, if the object be moved to 31, then the focus would be formed in front of the retina, as at 31' , and the condition of the eye would be myopic, unless simultaneously with the movement of the object from the eye, by some change in the latter, the focus was kept upon the retina at d c. The change undergone by the eye, and by which the image of the object is kept upon the retina, whether the object approaches or recedes, is known as the power of accommodation, and is without doubt due to a change in the shape of the lens ; the latter becoming more convex as the object approaches the eye, less so as the object recedes from it. As the object ap]>roaches the eye, the image tends to recede behind the retina, toward //', but as the lens becomes more convex at the same time, the image tends to ad- vance equally in front of the retina toward 31' , the result of the antagonizing influences being such that the image neither recedes nor advances, but remains upon the retina. On the other hand, as the object recedes from the eye, the image tends to advance in front of 7(38 PHYSIOLOGICAL OPTICS. the retina, toward J/', but as the lens becomes less convex at the same time, the image tends to recede behind the retina, toward H'; the image consequently remains as before upon the retina. Before considering the means by which this change in the shape of the lens is effected, and throuo^h which the eve accommodates it- self to different distances, let ns first show how it can be experi- mentally demonstrated that such a change in the shape of the lens as tliat just described does actually occur during accommodation. With that object let the person whose eye is to be examined be requested to look at some distant object, and while so doing let the light from the flame of a candle (B, Fig. 458) fall upon the eye (C C) at about the angle represented in the figure; if the eye of the observer be situated at E three images will be seen (Fig. 459) ; the first (b) an erect virtual image, due to the reflection of the light from the cornea (b, Fig. 458) to the eye of the observer at E; the Fig. 458. Change in the form of the leus during accomuiodation. second (a) also a virtual erect image due to the reflection of the light from the anterior convex surface of the crystalline lens («) ; the third (c) ; a real reversed image due to the reflection of the light from the posterior concave surface of the crystalline lens formed in the manner represented in Fig. 460. The three images being observed, let now the individual whose eye is being examined look at a near object, and at once the observer at E will notice that, while the position of the images (Fig. 459) a and e due to the reflection of the light of the candle B from the cornea and posterior surface of the lens remains unchanged, that of the image 6 due to the reflection of the light from the anterior sur- face of the lens is very much changed, it Ix'ing now much closer to a, and also that it is smaller than wlien tlie individual w4iose eye is being observed looked at a distant object, which can only be accounted for on the supposition that the anterior surface of the lens increases in convexity, the light falling upon e instead of a PHAKOSCOFE. Ti9 (Fig. 458), and whicli is the case for llio radius of curvature of the anterior surfoce of the lens when the eye is aeconunodated for far objects, being 10 mm., but for near ones <) mm. In performing this experiment the phakoscope of Helmholtz Avill be found a use- ful instrument. It consists (Fig. 461) essentially of a l)lack trian- Fin. 4.-)9. Fi.;. 4(;i. a b (■ ReHeeted iinaKe^^ i" the eye. Real reversed image of comave mirror. Pliakosfope of Jlrliiilinltz. iM( Kp:ndrick.) gular box Avith four openings : the first opening in the base of the triangle supports a needle point, which constitutes the near object ; the second opening, directly op])osite to the first, receives the eye to be observed ; while of the two remaining lateral openings, one containing prisms transmits the light, the other receives the eye of the observer. In using the phakoscope the individnal looks first through tlie window at a distant object, and then at the middle point. It having been shown, then, that the lens becomes more convex — accommodates itself to see near objects — it only remains now to account for this change in the shape of the anterior surface of the lens. It will be remembered, in speaking of the action of the ciliary muscle, it was mentioned that, owing to its disposition with reference to the sclerotic and choroid, that in contracting it would draw the choroid forward, thereby relaxing the suspensory ligament of the lens, the effect of which Avould be that the lens, o\\'ing to its elasticity, would change its shajie. It would appear, therefore, that the change in the convexity of the lens, through which the eye accommodates itself to see near ob- jects, is brought about by the contraction of the ciliary muscle. If such be the case, of which there can be but little doubt, the sense of effort which we experience in looking at near objects must arise from the contraction of the ciliary muscle. Accommodation can 49 770 PHYSIOLOGICAL OPTICS. only take place within a certain range, marked variation being ob- served however in this respect according to individnal pccnliarities. As a rnle, objects sitnated at a distance of 62 meters (200 feet) and beyond to infinity, that is, at the punetnm remotnm or far point, to be seen, do not necessitate accommodation, as the rays of light, coming from snch a distance, being parallel, come to a focns npon the retina ; the nearer, however, the object approaches within this limit the eye, the more accommodating power is exercised, until a point is reached about 12.5 cm. (5 inches) from the eye, the punc- tmn proximum or near point, which if exceeded by the object, can- not be compensated by any further change in the shape of the lens. The accommodation being then strained to its uttermost if the object comes still nearer the eye, the rays of light will not be focussed upon the retina. The range of accommodation of the eye for distance lies then between these two limits, that of the punctum remotum and punctum proximum. The power of accommodation of the eye can be measured by the converging power of a lens, which gives dis- tinct vision of an object placed at the punctum proximum without necessitating any accommodation in the eye — that is, of a lens M'hich brings the diverging rays of light from the punctum proximum to a focus on the retina, just as if they had come parallel from the punctum remotum, for which accommodation is not required in the normal eye. Indeed, that is exactly the effect of the change in the shape of the crystalline lens in accommodation, viz., that of retain- ing on the retina (Fig. 462, r), the focus of the rays of light diverg- ing from t]ie near point p, just as if they came parallel from the far point r r. Fk;. 462. R*^ Condition of Ions in the wnvmaX passive eye and during accniiniiodd/ifm. As the elasticity of the lens diminislies as a result of age and as further it becomes more flattened, the lens gradually loses the power of changing its shape, of becoming more convex as an object ap- proaches the eye, and consequently the punctum proximum recedes further and furtlier from the latter. The diminution in the range PRESBYOPIA. 771 of accommodation so produced is known as presbyopia, which, it Avill be observed, is an anomaly of acommodation, differing there- fore from myopia and hypermetropia, which are anomalies of re- fraction. While the treatment of presbyopia belongs rather to the ophthalmologist than to the physiologist, it may be mentioned that it can be corrected by ])lacing a lens before the eye, such as would give the rays the direction they would have if they came from the normal punctum proximum. Fig. 463. Action of a concave lens in front of the eye, causing parallel rays to enter the eye as if pro- ceeding from a finite point in front of the eye. (Berry.) It may be mentioned also in this connection as regards accom- modation that the myopic differs from the emmetropic eye in that the punctum remotum, or far point, is that point from which di- vergent rays of light come to a focus on the retina, the eye being passive (Fig. 463). While the far point in the myopic eye may be situated at a distance varying from 150 to 300 centimeters (60-120 inches) the punctum proximum, or near point, may be only 10 to 5 centimeters (4 to 2 inches) from the eye, the range of ac- commodation in the myopic eye is therefore limited. On the other hand, in the hypermetropic eye there is no punctum remotum, or far point, since neither divergent nor parallel rays come to a focus in such an eye when non-accommodated or passive. Inasmuch, how- ever, as convergent rays falling upon the eye and directed, say to a point /(Fig. 464), will come to a focus on the retina, when still Fig. 464. Action of a convex lens placed in front of the eye, causing parallel rays to enter the eye, as if directed to a point at a finite distance behind the eye. (Berry.) further refracted by passing through the cornea and crystalline lens that point is often said to .be the punctum remotum, or for pomt, and negative, the converging rays being directed to that point 772 PHYSIOLOGICAL OPTICS. in the same sense as the diverging rays of the myopic eye are di- rected to or appear to come from the punctum remotum, or far point (Fig. 463), which in tliat case is positive. The punctum proximum, or near point, in the hypermetropic eye varies from 20 to 200 cent. (8 to 80 inches). The range of accommodation is, therefore, in- finitely great. The ciliary muscle, by the contraction of which ac- commodation is accomplished, is innervated by nerve fibers that arise, as already mentioned, in the anterior part of the nucleus of the third nerve and pass thence to the eye by the ciliary ganglion and short ciliary nerves. That such is the case is sho^yn by the fact that stimulation of this center is followed by contraction and the accom- modation of the eye to near objects. Accommodation appears to be a voluntary act in response to visual sensations ; at least we are led to accommodate simply by the desire to see distinctly near or far ob- jects. In passing from accommodation for a near object to that for a far one it can hardly be said that we accommodate actively since the action is due simply to the relaxation of the ciliary muscle to the return to a condition more or less of equilibrium. In this re- spect the ciliary muscle diflPers from the iris, the muscle fibers of the latter being influenced, as we have seen, by two sets of nerve fibers, contractor and dilator. It should be mentioned, neverthe- less, that atropin not only paralyzes the accommodation, rendering the eye hypermetropic, but dilates the pupil and that physostigmin renders the eye myopic and contracts the pupil. We shall see presently that in the converging of the axis of the eyes for the pur- pose of viewing near objects as in the accommodating of the eye for the same purpose the pupil contracts, just as we have seen is the case when the eye is exposed to light. This is an instance of what is called an " associated movement," and appears to be due to the fact that the will center, accommodating center, and pupil constrictor center are so intimately connected by nervous ties that when an impulse from the will center stimulates the accommodating center it stimulates at the same the pupil constrictor center. While in the case of most persons, in order to accommodate, the attention must be directed to some near or far object, it is said that by practice the aid of exter- nal objects may be dispensed with, and it is when this is accom- plished that the pupil may appear to contract or dilate voluntarily, the effect being due to accommodation, as just explained. The so-called Argyll Robertson pupil, frequently occurring in locomotor ataxia and progressive i)aralysis of the insane, is a further illustration of the intimate association existing between the voluntary accommodating and pupil constrictor centers. In this condition, Avliile the pupil docs not contract in response to light, a lesion existing in the nervous tie connecting the corpora quadri- gemina and oculo-motor center, it does contract when the eye is accommodated for a near object, the centers causing contraction and accommodation being stimulated simultimeously by the will. In concluding the subjects of refraction and accommodation, it is OPHTHALMOSCOPE. 773 hoped that it will not be deemed sujierfluous if a ])rief account of the ophthalmoscope is oifered by which the fundus of the normal and diseased eye is examined, and through which, in the hands of Bon- ders, Graefe, and others, ophthalmic medicine was revolutionized. Fig. 465. Arrangement for examining the eye of 5. ^ , eye of observer, j-. Source of light. .S", 5, plate of glass directed obliquely, reflecting light into B. The interior of the eye under ordinary circumstances appears dark, since the observer being between the eye to be observed and the source of light intercepts the very rays whose reflection from the interior of the eye would form the image that it is desired to see. Further, the diverging rays from the interior of the eye, con- FiG. 466. OphthalnioscoiH' with convex lens. verging as they pass through its media, are brought to a conjugate focus outside of the eye, which, to be seen, would have to be viewed by the observing eye at a distance so far from the observed eye, 774 PHYSIOLOGICAL OPTICS. that little or nothing could be distinguished. If, hoAvever, the in- terior of the eye be illuminated by light reflected from an obliquely placed glass (Fig, 465), or a concave mirror, the center of which is perforated, and through and behind which the observer can view the eye, then the conjugate focus formed as just described by the rays reflected from the interior of the eye, can be more or less dis- tinctly seen. The image of the retina, entrance of the oj^tic nerve, etc., as viewed by such a mirror as that just described, and constituting the original ophthalmoscope, become, however, much more distinct, if in addition to the mirror the observed eye be viewed through a lens. Suppose the lens used be a convex one (Fig. 466, 6), then the rays of light from the retina A of the obsers'ed eye which would otherwise be brought to a focus rather near the observing eve Fig. 467. j;-« Ophthalmoscope with concave lens. through the converging effect of the lens are l^rought to a focus at B, the image being real, inverted, and magnified. On the other hand, suppose that a concave lens be used, then the rays emanating from Sq (Fig. 467), which would come to a focus at r were it not for the lens, on account of being diverged by tlie latter, are pro- jected back to B, the image being virtual, erect, and more magnified than wlien a convex glass is used. CHAPTER XL. BINOCULAR VISION. SENSATION AND PERCEPTION OF SIGHT. PROTECTIVE APPENDAGES OF THE EYE. Ix describing the manner in wliich vision is eifccted we have liitherto supposed it as being; accomplished by a single eye ; it re- mains for us now to consider how both eyes act in viewing objects, or binocular vision. It might be naturally supposed from seeing an object single, when viewed with one eye, that it would appear double when viewed with both eyes. A little observation will, however, make it clear that with one eye Ave see but one side, so to speak, of an object, the right side, for example, with the right eye, the left side with the left eye, and that in order to obtain a percep- tion of the entire object we must see the two sides of the oljject simultaneously. Thus, for example, wlien we look at a truncated pyramid (Fig. 468, B) placed in the middle line before us, the Fig. 468. / \ _/ \ \ // B / \ / \ / \. Illustrating the piiuciplc of the stereoscope and binocular vision. image falling upon the right eye is such as represented at R, that upon the left eye at L, the perception of the form of B being only obtained when the object is viewed by both eyes simultaneously. When two dissimilar images, one of the one eye, and the other of the other, are thus fused into one perception, the inference by the mind is that the object giving rise to the images is solid. Such, indeed, is the principle of the stereoscope, in Avhich two slightly dissimilar pictures, such as would correspond to the images of two objects as seen by each eye respectively, are by means of mirrors or prisms cast upon the retina so as to give rise to a single perception, that of solidity, or of three dimensions, though each picture has a surface .of but two dimensions. In order, however, that the two retinal images shall be fused into the one mental perception, it is essential that the two images shall fill on corresponding points of the retina, at a a, c c (Fig. 469), otherwise there will be double vision — hence, in viewing an object with both eyes the latter are converged, the angle made by tlie axes of the two eyes being large if the object is near, and small if the latter be distant. 776 BINOCULAR VISION. As it can be shown, however, that the angles a A a and c C c are equal, it follows that the points A C can not lie in a straight line, but in a circle, it being the property of a circle only, that tri- angles erected on the same chord and reaching the periphery have at the latter equal angles. The line joining the points A C (Fig. 469), must, therefore, be a circle of which the chord is equal to the distance between the points of decussation {K K) of the rays of light in the eye. Such a circle is known as the " horopter," and all objects not lying in it are seen double, their images not falling upon corresponding points of the retina. Standing upright, and looking at the distant horizon, the " horopter " would be approximately for normal long-sighted persons, a plane drawn through the feet — that is to say, the ground on which they stand. The eyeball nearly tilling the cavity of the orbit, and resting posteriorly upon a bed or cushion of adipose tissue, is moved by six muscles, the recti superior and in- ferior, externus and internus, and the obliqui superior and inferior. The eifect of these muscles when acting separately is quite apparent from their origin and insertion. The four recti in the order named, arising from the apex of the orbit around the margin of the optic foramen, pass straight forward, piercing the capsule of Tenon or the fibrous membrane surrounding the sclerotic, to be inserted into the latter tunic at about the third or fourth of an inch behind the margin of the cornea, move the eye upward, downward, outward, and inward. The superior oblique muscle, arising from the optic foramen, proceeds toward the internal angle of the orbit and terminates in a round tendon, which, passing- through a fibro-cartilaginous ring or pulley, is thence reflected back- ward and outward to be inserted into the sclerotic between the superior and external recti muscles. Its action is to rotate the eye- ball downward and outward. The inferior oblique muscle arising from the orbital plate of the superior maxillary bone close to the external border of the lachrymal groove passes outward and back- ward between the inferior rectus and the floor of the orbit to be inserted into the external and posterior part of the sclerotic. Its action is to rotate the eyeball upAvard and outward. It can be shown, however, theoretically, as well as by actual observation, that the six muscles whose actions have just been described may be regarded as consisting of three pairs, each of which rotates the eye round a particular axis. Thus the recti superior and inferior rotate the eye up and down round a horizontal axis directed from the upper Diagram to illustrate the horopter. (McKendrick.) LISTING'S LA W. < i i end of the ^nose to the temple; the obli([ui su])orior and inferior obhquely round a horizontal axis directed from the center of the eyeball to the occiput ; the recti internus and externus from side to side round a vertical axis passing through the center of rotation of the eyeball situated a little behind the center of the optic axis, parallel to the median plane of the head, the latter being vertical. The different muscular actions just described may be briefly sum- marized as follows : Action of Ocular Muscles. Number of muscles acting. Oue . . . Two . . . Three Direction. Inward, Outward, Upward, Downward, Inward and upward, Inward aud downward, Outward and upward, Outward and downward. Muscles acting. Internal rectus. External rectus. Superior rectus. Inferior oblique. Inferior rectus. Superior oblique. Internal rectus. Superior rectus. Inferior oblique. Internal rectu.s. Inferior rectus. Superior oblique. External rectus. Superior rectus. Inferior oblique. External rectus. Inferior rectus. Superior oblique. The various movements of the eyeballs, as ju.st described, con- form to a general law, the so-called " Listing's law," which may be briefly described as follows : Let us suppose that the position of the eyeball is the primary one — that is, such in which the head is erect and vertical, and we look straight forward to a distant hori- zon, aud that the visual axes, or the lines from the fixed point of vision to the center of rotation in the vitreous humor, 13.5 mm. from the anterior surface of the cornea, are parallel. Such being the case, it would appear that all movements of the eyel)alls are around either a vertical axis from side to side, or a horizontal axis up aud down, or an oblique axis, the latter situated in the same plane with the other two. In no case, however, does the eyeball rotate around the visual axis itself in a swivel-like movement — that is, such that the pupil would turn around like a wheel, since, if the eye were to so rotate, the rays of light would not fall upon corre- sponding points of the retina.^ It may be also mentioned in this connection that while we can converge or make parallel the visual axes we cannot, at least without assistance of some kind, diverge 1 It should be mentioned, however, that recent researches render it hiijhly prob- able that the views generally prevailing as to the mechanism of the eye movements are not mathematically correct. See an interesting paper on tliat subject by Carl Weiland, Archives of Ophthalmology, Vol. xxvii., No. 1, 1898. 778 SENSATIOX OF SIGHT. them, since, if we do so, tlie rays of light do not fall upon corre- sponding points of the retina. It will be observed, from what has just been said of the action of the ocular muscles, that even in viewing an object with a single eye, that a considerable amount of muscular coordination must take place, since when the eye is moved in any other than the vertical or horizontal meridian three muscles at least must be stimulated, relatively to the amount of inclination of the visual axis needed. Such being the case in single ^•ision, necessarily, then, the amount of muscular coordination required in binocular vision must be much greater. If the eyes of any person be observed, it will be noticed that the two eyes move alike, when the right eye moves to the right so does the left, and to the same extent if the object looked at be distant, if the right eye looks up so does the left, and so in every other direction. Briefly, then, the eyes move in such a manner that the images of an object always fall upon corresponding points of the retina, the essential condition, as we have seen, for the produc- tion of single vision, the movements of the two eyes ceasing to agree Avith each other only when the power of coordination is lost, through disease or by alcoholic or other poisoning. It must be admitted, however, that the nervous mechanism, by which the coordination of the ocular muscles is accomplished, is as yet but imperfectly understood. That is to say, it has not been definitely shown exactly how the centers for the visual paths termi- nating in the occipital cortex and the centers from which arise the third, fourth, and six nerves are connected Mith the will center, supposed to be situated in the frontal lobe, in the front of the pre- central fissure. By movements of the eyes, apart from those of the head, the ex- tent of the field of vision may amount to as much as 200 degrees in the horizontal and 200 degrees in the vertical meridian, that of a single eye being about 145 degrees for the horizontal and 100 de- grees for the vertical meridian. Sensation of Sight. Regarding the sensation of sight as due to the stimulation of the retina by light, observation teaches, as might be supposed, that the intensity and duration of the sensation will vary according to the strength of the luminous vibrations and the length of time during which the latter continue to fall upon the retina. That the in- tensity of the sensation varies with that of the luminous object is a matter of daily experience, a wax candle, for example, appearing brighter than a rushlight. With a little experimentation it becomes soon apparent, however, that the ratio of the sensation to the stimulus is not a simple one, since Avhilc the sensations increase as the luminosity of the object increases, the sensations increase less and less, until finally there is no appreciable increase of sensation, however much the luminosity may be increased — that is to say. DURATION OF SENSATION OF SIGHT. 779 when a light reaches a given brightness it appears so briglit to us that "vve cannot tell when it becomes anv briohter. It is mnch easier, therefore, to distinguish the difference between two feeble lights than the same difference between two bright lights — in fact, if the latter be very bright it becomes then impossible. Thus, for example, while there is no difficulty in distinguishing between the light of a candle and that of a rushlight, it would be impossible to distinguish such a difference between the light of two suns, suppos- ing the light of the one to be in excess of that of the other in the same ratio as that of the candle over that of the rushlight, just as an addition of half an ounce to twenty pounds will not be appre- ciated by the sense of weight. Further, it will be found that if we let the shadows of two rushlights, for example, fall upon white paper, and then move one of the lights away until the shadow ceases to be visible, that in performing the same experiment with two wax candles the candle ^\\\\ have to be moved through the same distance as that of the rushlight before its shadow ceases to be seen, the smallest increment in light in both cases appreciable being in- variable, about the yl^ of the total luminosity made use of. It is also evident that the duration of the sensation is long-er than that of the stimulus, the sensation of sight and the stimulus of light being comparable, in this respect, to a muscular contraction, as induced by a single induction shock. It is for this reason that if two flashes of light follow each other sufficiently quickly, within the one-tenth of a second for a faint light, and the one-thirtieth of a second for a strong one, the two sensations arising are fused into one. Hence, the fact of a luminous point moving rapidly around in a circle giv- ing rise to the sensation of a continuous circle of light, which re- minds one of the production of muscular tetanus. That the dura- tion of the stimulus of light necessary to give rise to the sensation of sight must be very short, is shown from the fact of the electric spark being seen, though the latter is known to last but the 2"'5' o~oVo TTo ^^^ second. When a large portion of the retina is af- fected by light the total sensation experienced is greater in amount than when a small })ortion is so affected, a large piece of Avhite paper, for example, affecting our consciousness more than a small piece. If, however, the surfaces of the papers be equally and uni- formly illuminated, the small piece Avill appear as bright, or white, as the large one, the intensity being the same in both cases. Fiirther, as might be expected, if the images of the two papers be situated upon the retina at sufficient distance apart, the two sensa- tions will be distinct, the relative intensity of the same depending upon the brightness of the objects, while, if the images arc so close to each other that the sensation fuses into one, then the total sensa- tion experienced will be greater than that due to cither one of the images, though not equal to tlie sum of the single sensations. As a general rule, the best eyes fail to distinguish two })nrallc'l white streaks when the distance separating them, as measured from the 780 SENSATIOX OF SIGHT. middle of each, subtends an angle of less than 73 seconds, though some individuals can distinguish objects so close to each other that the distance separating them does not subtend an angle of more than 50 seconds. Xow, as the retinal image corresponding to an angle of 73 seconds would measure in the schematic eye about 0.00536 mm., and that corresponding to an angle of 50 seconds, about 0.00365 mm., and as the average diameter of a retinal cone measures at its widest part about 0.004 mm., it is evident that the visual sensory area has a corresponding physical Ijasis in the retinal anatomical area, which renders it highly probable that there is still another corresponding cerebral or perceptive area. It has already been mentioned that, owing to the unequal re- frangibility of different kinds of light, that white light in passing through a prism is not only refracted, but is decomposed into the seven kinds of light of which white light is composed, viz., violet, indigo, blue, green, yellow, orange, and red, or the colors of the spectrum. In considering, however, the manner in Avhich we be- come conscious of the ditferent colors of which the spectrum is composed, or of any colors or color, we must disabuse ourselves at once of the idea that what we call color exists outside of our own consciousness objectively as such, since what we call color in our- selves subjectively, can be shown experimentally to be due objec- tively to a vibration, an oscillatory movement, a wave of a definite length passing into tlie eye at a certain velocity, all kinds of light being so propagated. In fact, color objectively is to the eye what we shall see pitch in the case of sound is to the ear, the latter de- pending solely upon the number of vil)rations striking the ear in a second. In other words, a wave of a certain length, propagated at a definite rate, in falling upon the retina, gives rise in us to a sensa- tion of a particular color. Thus, the color red is due to the im- pinging upon the retina of a wave about y 5^17 *»f ^^ millimeter (g-gl^oo- of an inch) in length, travelling at such a velocity that about 474,- 439,680,000,000 such waves enter the eye in a second ; the color violet to a wave about o-jQ-g of a millimeter (-^yz1)1) ^^^^^ inch), about 690,000,000,000,000 "such waves entering the eye in a second, the waves giving rise to the violet color being shorter than those to which the red color is due, but following each other into the eye more rapidly than the latter, the waves to which the other colors of the spectrum are due with reference to their length and velocity lying between the extremes just mentioned. The sensation of color depending then upon the successive impulses imparted to the fibers of the optic nerve by waves of different length travelling at different velocities, it is obvious that it would be useless to look into the external world for any attribute or quality that would correspond objectively to what we call in ourselves the sensation of color. In ■other words, the color red of an object is in ourselves, not in the object looking red, because tlie wave giving rise to red is re- flected from the object into our eyes, the remaining waves being SEXSATIOX OF COLOR. ">^I absorbed by tlie object ; similarly surroiiiKling ol^jccts look red when viewed tliroiiirh a red glass, the wave giving rise to red being alone transmitted through the glass to our eye, the remaining waves being absorbed by the glass, and so with all other colors. Our knowledge of color depending then upon the impression made upon the sen- sorium by the waves of light is not absolute, but only relative. In other words, we do not know the light in itself — the thing itself, as Kant^ expressed it — but only by just so much as the light or thing affects our consciousness. The extent to which sen- sation is dependent upon the susceptibility of the organism of being impressed by the external world, is shown by the fact that, not- withstanding the solar spectrum extends beyond the violet in one direction and beyond the red in another, the eye under ordinary circumstances is unconscious of the existence of these extremes, being so organized as not to be affected by the ultra violet or chem- ical rays, or the ultra red or heat rays. Our knowledge being due to sensations arising from impressions made by the environment upon the organism, cannot then be innate, but must have been ulti- mately derived from experience, and therefore relative, as held by Locke.^ After what has just been said, it is evident that no phys- ical or chemical chang-es in the retina will account for our sensation of color, since the cause of the latter lies not in the retina, which is simply an intermediate organ, correlating the physical with the psychical, Init in that part of the cerebrum where the still ])hysical vibration gives rise to sensation. Indeed, the cause of the sensa- tion of color, as might be premised from the present imperfect state of physiological psychology, is not yet understood, although a great number of interesting observations have been made with reference to the effect of fusing colors, of complementary colors, of which a brief account at least in this connection must be given. Though we have spoken of the solar spectrum consisting of seven colors, as a matter of fact, it is made up not only of such, but also of a great number of intermediate tints as well. External nature presents the same tints, and also a number of others like those of purple, brown, gray, etc., which, however, are not present in any part of the spectrum. While such tints are apparently due to dis- tinct simple sensations, it can be shown experimentally that in reality they are compound ones, being obtainable l)y the fusion of two or more color sensations. Thus, purple, which, as just men- tioned, is not present in the spectrum, may be readily produced by the fusion of red and blue, as, for example, by so placing a red and blue wafer and a glass (Fig. 470) that the light will be reflected from the red wafer (R) in the same direction as that coming from the blue wafer (B). In the same way the various tints of nature may be obtained by fusing different colors, sensations with that of Uritiquo of Pure Eeason, trans, by Max Miiller. Second Part, p. ^9. Lon- don, ISSl. 2 Of Human Undei-standing, Locke's Works. Chap, ii., Vol. i. London, 1883. 782 SENSATION OF SIGHT. white or black, different kinds of brown resulting from mixtures of yellow, red, white and black, grays from white and black, as can be shown by making use of a rotating disk, on the surface of which colored sectors are painted, the resulting color being white, for ex- ample, in that of the instance represented in Fig. 471. Experi- FiG. 470. Fig. 471. _^ML ■^ X,ambert's method of studying combinations of colors. Rotating disk of Sir Isaac Xewtiin fur mixing colors. menting in this way, it can be shown that the (juality of a color depends on the wave-length of its constituent waves and on the relative amount of colored and white light falling upon the retina in a given time, a color being saturated when unmixed with white light, as in the case of the colors of the spectrum. As regards the fusion of colors, it is evident, fnnu what has been said of the subject of color, that in mixing red and yelloAV to pro- duce an orange, for example, undistinguishablc from the orange of the spectrum, that the sensation of orange cannot be due to the uniting of the red and yellow waves differing in length from each •other to form an orange wave differing in length from either, but that it is the mixture of the sensation of red and yellow that gives rise to the sensation of orange. In other words, the mixture is psychical, not physical. It is an interesting fact that certain colors, when mixed together in pairs in certain definite proportions, give rise to the sen.sation of white, as, for example, red and blue-green, orange and blue, yellow and indigo-blue, green-yellow and violet ; such colors are said to be complementary colors, since given the color of one of the pairs, say red, all that is necessary or comple- mentary to produce white is the other color of the pair, or green. It can be also experimentally shown, by means of the rotating disk, that the mixture in proper proportions of any three distinct colors of the spectrum arbitrarily selected, but sufficiently far apart, as, for example, red, green and violet, Avill produce white, and that by the further addition of white the sensations of all the other colors can be obtained. In order to avoid any misunderstanding as re- gards the production oi the sensation of white, it should be men- THEORY OF COLOR. 783 tioned that the mixture of red, green, and violet pigments, unless they are perfectly pure, will not produce white ; a mixture of ])ig- ments being totally different from a mixture of sensations of colors, since the color produced l)y the mixing of pigments is due to the light -which has escaped absorjition by the same rather than the color due to a mixture of the colors. For example, the sensations of indigo and gamboge when mixed give rise to the sensation of white, the sensation due to a mixture, however, of indigo and gam- boge pigments is green because the gamboge absorbs the blue, and the indigo absorbs the red and the yellow, while both reflect green. Facts like those just mentioned with reference to the fusion of colors, their complementary relation, the composition of white light, €tc., led the celebrated Young,^ in the beginning of the century, and Helmholtz,^ in recent times, to advocate the view that all of our sensations of color are compounds of three primary color sen- sations, red, green, and violet, and that waves of different lengths give rise to all three of these sensations according to their particular length — that is to say (Fig. 472), the orange wave gives rise to Diagram of three primary color sensations. 1 is the so-called " red," 2 " green," and 3 " violet ' primary color sensation. R, O, Y, etc., represent the red, orange, yellow, etc., color of the spec- trum, and the diagram shows, by the height of the curve in each case, to what extent the several primary color sensations are respectively excited by vibrations of ditferent wave-lengths. (Foster.) much of the first sensation, or red, less of the second, or green, and to little of the third, or violet ; on the other hand, the blue wave gives rise to little of the red sensation, to more of the green, and to much of the violet, etc. The anatomical basis for the above is the assumption that three kinds of nerve fibers exist in the retina, the excitation of which gives rise respectively to the sensations of red, green, and violet — homogeneous light — all three of these so- called fundamental sensations, but with different intensities accord- ing to the length of the wave ; long waves exciting most power- fully the fibers who.se stimulation give rise to the sensation of red, medium waves those causing the sensation of green, short waves those causing the sensation of violet. Accepting pro- visionally the Young-Helmholtz theory of color sensation, it 'Lectuies on Natural Philosophy. London, 1807. ^Op. cit., p. 382. 784 SENSATION OF SIGHT. serves to explain some of the phenomena of color-bliucluess, after- images, etc. AVhile almost all individuals are able to appreciate differences of color, there are some, and the number is far greater than usually supposed, who are unaffected by certain colors, the most common defect being an insensibility to red, blindness to green and violet being rare. Thus, for example, in Daltonism, or blindness to red, so called on account of its having been observed in the celebrated Dalton, the red end of the spectrum appears dark, a red gown lying on a green grass plot, a red cherry among green leaves, are distinguished, not by their color, but by their form, the color of the gown or the fruit appearing to such an eye not red, but green like that of the grass or leaves. Remembering that green is the complementary color to red, and supposing that in a daltonic eye the fibers whose stimulation in an ordinary eye would give rise to the color of red are either absent, diseased, or paralyzed, the phenomenon just referred to can be accounted for. Similarly, if, after a red patch has been looked at steadily for some time until the eye becomes fatigued, a white surface be looked at, a green patch will be seen instead of the red one, the green fibers of the retina, so to speak, being fresh, are susceptible of being excited by the green color (or wave giving rise to it) of the white light re- flected from the paper, the red fibers being, however, exhausted, are no longer susceptible of being excited by the red color (or the wave giving rise to it) of the white light. In the same manner many other negative after-images can be explained, so called as contrasted with positive after-images which are simply due to a sensation, being continued even after the object giving rise to it has been removed from the field of vision. Thus, for example, if the eye be directed momentarily to the sun the image of the latter will be present for some time after, or if a window be looked at for an instant on early M'aking, and the eye then closed, an image of the same with its bright panes and darker sashes will persist for some time. While the Young-Helmholtz theory of color sensation is accepted by many physiologists, another theory has been advanced by Aubert ^ and Hering - among others, the latter of whom maintain that the pri- mary color sensations are white, black, red, yellow, green, and blue, and that these different sensations are due to the changes in the so- called visual substance of the visual apparatus, the changes giving rise to the sensations of black, green, and blue being processes of a constructive-assimilating kind, those giving rise to the sensations of Avhite, red, and yellow, of a destructive-assimilating kind. If Her- ing's view be accepted, then black and white, green and red, blue and yellow, far from being complementary, must be regarded as antagonistic to each other, and the visual substance assumed to be always undergoing changes, never in a state of rest. The limits of this Avork will not permit of further illustration or discussion of 1 Physioloffii- der Netzhaiit, ISGfi. ^Wien. Sitzberich, Lxvi. (1872), Iviii., Ixix., ixx. PERCEPTION OF SIGHT. 785 the relative merits of the Helmholtz and Hering theories of the sensations of color ; it may be pointed out, however, once more, that whether the one or the other theory be accepted, we are not a whit nearer the explanation of the sensation of color, since the transformation of the ultimate physical vibration or wave into the psychical color sensation takes place not in the retina but in the cerebrum. Perception of Sight. It has already been mentioned that as the apparent size of an ob- ject depends upon the visual angle, if two objects, though of different size, subtend with the eye equal angles — that is, if their visual angles are the same — the apparent size of the objects will be the same. The real size of an object is therefore not determined by the sense of sight, the latter only giving rise to the sensation of its apparent size. The estimate of the real size of an object is really an inference based upon its apparent size, but modified by the knowledge of its distance from the eye. In other words, it is not a simple sensation, but a judgment based upon the sensations of touch, as well as those of sight. Knowing the distance of an object from us, we infer from its apparent size its real size ; and con- versely, knowing the size of the object, we infer its distance. Thus, if the image of some well-known object, a man, for example, appear in our field of vision, and we know how far off the man is, we infer his size from that of our retinal image ; and, conversely, knowing the size of the man, if his retinal image be very small, "\ve infer that the man is very fir off. That our estimate of the size of an object is dependent upon the knowledge of its distance from us, is shown from the fact that if we have no means of even approxi- mately estimating the latter it is impossible to obtain any idea of its size. Thus the sun, though about four hundred times the dis- tance of the moon, is apparently of the same size as the latter, but we infer from that very reason that the one body is larger than the other ; did we not know, however, their relative distance from the earth it would be impossible to say which of the two, the sun or the moon, was the larger body. Our estimate of the distance of objects is not only based upon their size, but largely upon the presence of surrounding and intermediate objects, it being difficult to estimate the distance of an object entirely isolated, as in looking at a single distant object at sea. The muscular sensations arising through the contraction of the ocular muscles in converging the visual axis for near objects, and making them parallel for distant ones, aid us very much in forming a correct judgment as to the distance of objects. As with our estimate of the distance of objects, so with that of the idea of solidity, which is essentially an estimate of the distance of the diftcreut parts of an object, the idea being a judgment, a mental combination, of the two dissimilar pictures formed upon the retina, the image of the object as viewed by the 50 786 PERCEPTION OF SOLIDITY, ETC. right eye being, as already mentioned, diiferent from that as viewed by the left eye, the resultant image being seen in relief, and giving rise to the idea of solidity. The fact that we see objects erect, though their images are reversed upon the retina, as already men- tioned, is due to the fact of the sensation of the image derived from the sense of sight being modified by the sensation of the object derived from the sense of touch. The mind associating images situated at the upper and inner part of the retina with the objects giving rise to them but situated below and to the outer side of the eye, and images at the upper and outer part of the retina with objects situated below and to the inner side of the eye, and project- ing outward, the images or the luminous sensation back to the object giving rise to them, finally perceives the objects erect. In the same w^ay, but conversely, wdien a phosphene or luminous image is created by pressing, say on the outer or lower side of the eyeball, the image appears to lie above and to the inner side of the eye. Indeed, the association of the sense of sight with that of touch in obtaining the ideas of the size, distance, solidity, position of ob- jects, etc., is so intimate that w^ere our knowledge of the same derived through the sense of sight alone it would be of the most inexact and unreliable character. That such is the fact has been shown by cases like those of the youth reported by Cheselden,^ who for some time after the sense of sight was given him, he having been born blind, saw everything flat, as in a picture, and supposed that objects when seen touched his eyes, as objects when felt touched his fingers. The newly acquired sense of sight at first rather hindered him in finding his way about the house, which he could do perfectly well by the sense of touch alone. The fact that the youth could not tell of his two pets which was the cat, and which was the dog, by the sense of sight alone, though he could at once distinguish them by feeling them, led him one day to feel the cat and at once look at her, and then setting her down, said, " So puss, I shall know you, another time." AVhat has just been said renders it very probable, as held by Locke,^ that a person born blind, on suddenly obtaining his sight, would be unable by sight alone to distinguish a cube from a sphere — that is, to be able to say w^hich was the sphere, which the cube, for though he knows how the sphere or the cube affects his touch, he has not learned by experience, as yet, that if the cube, etc., affects his touch so and so, it will affect his sight so and so, and enable him by sight alone to distinguish it from the sphere. Since our perception of external objects is elaborated out of the sensations that the retinal images give rise to, it might be supposed that the perception would invariably correspond to the sensation, just as the latter would correspond to the retinal image causing it. As a matter of fact, however, such is not invariably the case, discrepancies arising between the retinal image and the perception, some of cerebral, others of retinal origin, iPhil. Trans., 1728, p. 477. ^Op. cit, Book II., chap, ix., p. 256. PERCEPTION OF SIGHT. 787 the effect of Avhicli is so to modify the perception that the usually reliable judgment as to the size, distance, etc., of objects is per- verted. Thus, for example, the white square (Fig. 478) on the black ground appears larger, and the black square on the white Fig. 473. Fig. 474. Illustration of irradiation. (McKendrick. ) Illusions of size. ground smaller, than it really is, the over-lapping of the white light in either case, or the irradiation, being due, as it were, to retinal or cerebral fibers other than those directly stimulated by the light being thrown into sympathetic vibration. If a white strip be placed between two black ones the inner edges of the former — that is, the edges nearest the black — will appear by contrast whiter than the median portions. In the same manner, the center of a white cross placed upon a black background will often appear shaded, as compared with the remaining parts. The judgment may also be at fault with reference to size, as in Fig. 474, when though the dis- FiG. 475. s Y/ ^ ^7 N C ^ r . / / / / / / / / / / / / / / / / / < ^^ Zoellner's figure, showing an illusion of direction. (McKexdrick.) tance A B is equal to the distance B C, the former appears to be the greater ; or with reference to direction, as in the case of Zoellner's (Fig. 475) lines, which, if looked at obliquely, will give 788 PROTECTIVE APPENDAGES, ETC., OF THE EYE. the impression that the vertical lines, though parallel, converge or diverge, and the oblique lines, though continuous across them, are not exactly opposed to each other. That the above effect is due to an error of judgment, is shown by the fact that by an eifort it may be controlled, the lines being then seen as they really are. If two equal squares be marked, one with vertical, and the other with hori- zontal, alternate dark and light bands, the former will appear broader, and the latter higher than it really is. Short persons should therefore wear dresses horizontally striped if they wish to increase their apparent height, and stout persons avoid wearing longitudinally striped ones. Many other such examples might be given, but the above will sulhce to illustrate the errors of judgment that the sense of siffht alone mav lead one into. Protective Appendages, etc., of the Eye. The eyeljall, with its muscles, etc., is protected by the bony orbit, the outer wall of which is stronger than the inner one, the eye being more exposed to injury from the outer than the inner side ; the inner wall of the orbit projecting, however, considerably beyond the outer wall, the extent of vision is far greater in the outward than in the inner direction. The upper semi-circumference of the orbit and the superciliary ridge is provided with short, stiff hairs, the eye- brows, which serve to protect the eyelids from the perspiration of the forehead, and to shade the eye from excessive light. The eye- lids consist of folds of very thin integument lined by mucous mem- brane, the conjunctiva, the subcutaneous connective tissue being thin, loose, and free from fat, and containing small papilla, and sudoriferous glands. The eyelashes, the short, stiff, curved hairs projecting from the borders of the lids in two or more rows, serve to protect the eye from dust, and, to a certain extent, also, to shade it. The palpebral cartilages, extending from the edges of the lids, which they support, to the margin of the orbit, are small, elongated, semi- lunar plates, attached internally by the tendo-palpebrarum to the lachrymal groove, externally by the external tarsal ligament to the malar bone, and supported by the palpebral ligament. On the pos- terior surface of the tarsal cartilages, lying just beneath the con- junctiva, are found the Meibomian glands, wdiich, in structure, are modified sebaceous glands, whose secretion, an oily fluid, in smear- ing the edges of the eyelids, prevents the overflow of the tears. The eyelids serve to protect the eyeball, their movements constitut- ing, respectively, the opening and closing of the eye, the act of Mdnking favoring the passage of tears over the globe and through the lachrymal canals into the nasal sac ; and hence, when the orbicu- laris palpebrarum is paralyzed, by the contraction of M'hich muscle the eye is closed, the tears do not, as readily as usual, pass into the nose. The eye is principally opened by the raising of the upper eyelid through the contraction of the levator palpebrarum, though it is also opened through the elevation of the upper and depression THE TEARS. 789 of the lower eyelids, respectively, through the action of the plain muscular fibers existing in both eyelids, and which are innervated by the sympathetic, the orbicularis palpebrarum being supplied, as has already been mentioned, by the facial and the levator palpebrae by the third nerve. The eyes are usually kept open, almost involuntarily, though we can close or open them at will ; the action of the orbicularis muscle is, however, to such an extent of a reflex character that if the globe of the eye be touched or irritated, or if the impression of light produces pain, it is then impossible to keep the eye open. It has already been mentioned that the inner surface of the upper and lower eye- lids is lined by a mucous membrane, the conjunctiva. The con- junctiva, continuous with the membrane lining the puncta lach- rymalis, and the lachrymal ducts, is reflected forward from the inner periphery of the lids over the eyeball, that lining the lids being called the palpebral, that covering the eyeball the ocular con- junctiva ; the latter differing, further, in its sclerotic and corneal portions. At the point where the membrane is reflected upon the globe it presents a superior and inferior fold, the former containing numerous glandular follicles and minute lachrymal glands. At the inner canthus there is a vertical fold, the so-called plica semilunaris, w^hich, morphologically, corresponds to the inner and third eyelid, or the nictitating membrane present in many of the lower animals, as in sharks, birds, and some mammals. The caruncula lachrymalis, the reddish, spongy elevation situated at the inner portion of the plica just mentioned, consists of a collection of follicular glands with a few delicate hairs on its surface. The eye is kept continually moist by a thin, watery fluid secreted by the lachrymal gland, which, after being spread over the globe by the movement of the lids and of the eyeball, passes into the lachrymal apparatus, any overflow upon the cheek, constituting the tears, being prevented ordinarily by the secreting of the ]Meibomian glands. The lach- rymal gland, about the size of an almond, ovoid in form, and of a racemose type of structure, is situated at the upper and outer por- tion of the orbit. It presents six to eight ducts, five or six of which open above, and two or three below the outer canthus of the eye. The tears consist largely of water, which amounts to over 90 per cent., the remaining elements being made up of small quantities of epithelium, albumin, sodium chloride, alkaline and earthy phos- phates, mucus, and fat. The actual amount of the lachrymal se- cretion has not been determined. Every one is fiimiliar with the fact that the secretion of tears is very much increased by emotion ; hypersecretion may be also readily induced through reflex action by irritation of the conjunctiva, nasal mucous membrane, muscular effort, laughing, coughing, and sneezing, the efferent nerves Involved being the lachrymal and orbital branches of the fifth nerve, branches of the cervical sympathetic ; the afferent nerves varying according to the exciting cause. The lachrymal apparatus, through which 790 PROTECTIVE APPENDAGES, ETC., OF THE EYE. the tears usually flow into the nose, begins by two little points or orifices, the puncta lachrymale of the eyelids, which leads into the upper and lower lachrymal canals, the latter surrounding the caruncula lachrymalis. Just beyond the caruncula the canals unite and pass then into the lachrymal sac or the upper dilated portion of the nasal duct. The duct being about half an inch in length, fibrous in structure, and lined with ciliated epithelium, empties into the inferior meatus of the nose. Reflux of the tears from the nose to the eye is prevented by the folds of mucous membrane, present in the lachrymal canals, and at the opening of the duct into the nose, acting as valves, the latter one being, in this respect, much more efficient than the former. CHAPTER XLI. PHYSIOLOGICAL ACOUSTICS. Just as we have seen that in order to understand how vision is accomplished, some knowledge of optics is absolutely essential, so for the comprehension of the manner in which the voice is produced and sound is heard, a knowledge of acoustics is equally indispen- sable. Similarly as in the case of vision, attention was continually being called to the distinction between the sensation of sight and the waves of light giving rise to it, so in case of sound the sensation of hearing must be distinguished from the waves of sound giving rise to it, for what constitutes in us subjectively hearing is out of us objectively vibration. Our knowledge of sound is then like that of light, etc., of all knowledge, only relative, depending upon the vibrations and the extent of the susceptibility of the audi- tory apparatus being impressed by the same. Let us consider first, then, how sound is produced in general, and more especially by the larynx, and then turn to the consideration of how it is appreciated by the brain, through the ear and auditory nerve. The sensation of sound, or more properly of musical sound as contrasted with mere noise, is due, as we shall see presently, to the periodic rhythmic vibratory wave-like oscillation of the sounding or sonorous body, being transmitted by an elastic medium, usually the air, to the ear, noise being due to the oscillations being transmitted in an unperiodic, irregular manner. The drawing of the bow across the strings of a violin gives rise in us to what we call music, the shaking of a box containing nails, chisels, files, etc., to noise, the auditory nerve be- ing affected in the one case by oscillations following each other in a regular, orderly sequence, and in the other by irregular, disorderly oscillations following each other in no sequence at all. The effect of noise upon the ear has often been compared to that of flickering light upon the eye, the painful experience in both cases being due to the sudden, abrupt, and irregular stimulation of the auditory and optic nerves respectively. Nevertheless, the difference be- tween noise and sound is not an absolute one, being rather one of degree than of kind, as shown by the noise due to the rattling of a carriage over stones, becoming a musical sound as soon as the oscil- lations become rhythmical and regular in character. Let us en- deavor to explain now, by a few simple illustrations, what is meant by periodical rhythmical vibrations, to which the sensation of sound has just been said to be due. Let us suppose, for example, that a number of persons are standing in a row, one behind the other, each individual's hands restins: against the back of the one in front of 792 PHYSIOLOGICAL ACOUSTICS. liira, and that the individual at the one end of the row be suddenly pushed from behind, forward against the individual standing in front of liim, the latter in turn will be pushed against the individual standing in front of liim, and so through the whole row until the last individual will be pushed forward. Further, let us suppose that the push be not very violent, and that the individual at the one end of the row first pushed forward regains his erect position, and then the second regains his, and so on through the whole row until the last man at the other end of the row regains his position, it is evident that though each individual person may have swayed to and fro, oscillated pendulum-like through a very small fractional part of the distance through which the push has passed, the push itself or the wave may have been transmitted through a long row of individuals, a hundred or more. Conceive the last individual body, the last individual of the row, to be the tympanic membrane of the ear, the intermediate individuals of the row, laminae of air or of any other elastic medium, and we can readily picture to ourselves what is taking place in the air, as the wave giving rise to the sensa- tion of sound passes from the sounding body to the ear. The condi- tions being strictly analogous in both cases, each lamina of air being pushed forward against its neighbor, through the elasticity of the air, after giving up its motion to the next lamina will recoil again, and just as in the case of the individuals in the row, the more rapid the to-and-fro motion of the laminte of the air, the greater the velocity of the push transmitted through the row and of the sound wave through the air. On account of the importance of thoroughly un- derstanding the manner in which the sound is propagated in air, let us consider a little more particularly the case in which it is propagated through a tube of indefinite length. Let A B (Fig. 476) be a tube filled with air, the temperature and pressure being H G Fig. 476. F E D C B 1 P 1 A To illustrate propagation of sound in air. constant, and let us suppose that P be a piston, oscillating rapidly from C to D, then as the piston passes from C to D, it condenses the air in the tube, the condensation, however, not extending at once throughout the whole tube, but on account of the great compressi- bility of the air only to the extent D E. As the piston, however, then passes from D back to C, the air in contact with its anterior face expands and becomes rarefied, and by the time that the piston reaches C the air has become rarefied to an extent (E D) exactly equal, but opposite in direction to that of the previous condensation (I) E). Supposing the tube A B to be divided into equal parts PROPAGATION OF SOUND IN AIR. 793 (D E, E F, EG, GH), etc, it is also evident that by the time the condensation beginning at say E reaches F, due to the forward movement of the piston from C D, condensing D E, that the rarefac- tion beginning at E due to the backward motion of the piston from D to C Avill reach D, and that the forward condensation p] F and backward rarefaction E D are equal and opposite in direction. The condensed and rarefied laminte of air {Y, F, E D), so produced during the forward and backward movements of the piston, consti- tute a wave, a vibration, an undulation, just as the to-and-fro motion of a pendulum constitutes a vibration, the length of the sonorous wave or vibration being the distance traversed by the sound during the complete vibration, or to-and-fro movement of the vibrating body causing it. In France, however, a vibration is considered as being either the to or fro movement, not both, that is to say, each English vibration is equal to two French ones. By a vibra- tion we shall always mean the double vibration e({ual to two single French ones. That is to say, as the piston passes from C to D, the sound travels from D to E, and as the piston passes back from D to C, the sound passes on from E to F. It need hardly be added that the length of the undulations will be less in proportion to the rapidity with which they follow each other, and that though the to- and-fro movements of the individual particles of the air giving rise to the condensations and rarefactions may be very slight, and the undulations long or short, few or many in a given time, the sound wave itself may be transmitted to a great distance. Such being the manner in which a sound wave is propagated in a cylindrical tube, there will be no difficulty in comprehending how sound waves are propagated in an uninclosed medium, if we only conceive each molecule of the vibrating body as acting as the pis- ton in the tube, a series of waves alternately condensed and rare- fied being then generated around each center of vibration, the sound radiating in all directions, like the waves of water spreading out upon the surface from some point of disturbance — the intensity of the same gradually, therefore, in both instances diminishing. That sounding bodies are actually vibrating can be readily demonstrated. In the case of strings it is a mere matter of observation, the vibra- tions being so apparent as to be visible to the naked eye. It will be remembered, also, that we maide use of the traces due to the vi- bration of a reed or tuning fork to determine small intervals of time, and, indeed, by such graphic methods we are accustomed to test the accuracy of our standard tuning forks. Apart, also, from the thrill experienced when a sounding bell is touched, its vibra- tions are made visible indirectly at least by the brisk to-and-fro movement of pith balls placed in contact with it. The vibrations of a sounding glass plate can also be rendered visible, as first shown by the celebrated Chladni ^ by sprinkling sand upon its surface, the sand only remaining at rest upon the part of the plate not in vibra- iDie Akustik, Leipzig, 1802, s. xvi. 794 PHYSIOLOGICAL ACOUSTICS. tion, and disposing itself in characteristic lines according to the shape of the plate and the character of the sound. It has already been mentioned that the vibrations of sonorous bodies can only give rise to the sensation of sound in us by the intervention of an elas- tic medium interposed between the ear and the vibrating body, and vibrating with the latter. While this medium is usually the air, the waves of sound are also transmitted through gases, vaporous liquids, and solids. A diver at the bottom of the water can hear the sound of voices on the bank ; the scratching of a pen at one end of a piece of wood is heard at the other end ; while the earth conducts sound so well that if at night the ear be placed upon the ground the steps of horses or other sounds or noise can be heard at a great distance off. That the waves of sound are not propa- gated in vacuo, as first shown by Hawksbee,^ can be very easily demonstrated by means of an apparatus which consists of an air- pump and receiver standing upon wadding, and a bell, the hammer of which is made to strike by clock-work set going by the raising of a detent passing through the top of the receiver. The bell, etc., having been placed within the receiver, the air from the latter ex- hausted by the pump, and the hammer made to strike, no appreci- able sound will be heard until the air is allowed to pass into the receiver. By allowing hydrogen gas, which is fourteen times lighter than air, to pass into the receiver, and by which the air is rendered very much more attenuated, such a perfect vacuum is obtained that not the slightest sound is heard, even though the ear be placed against the bell itself. The experiment just described is not only a very striking one, as proving that sound is not transmitted in vacuo, or a very attenuated atmosphere, but it illustrates the difference between the cause of sound and the sensation of sound, since, though the hammer may be seen striking the bell and causing it to vibrate, no sound is heard as long as the vacuum is maintained, there being no intermediate medium to transmit the vibrations of the bell to the ear. Sounds, however produced, whether by strings, reeds, tuning forks, bells, plates, etc., are distinguished by their intensity, pitch, and quality, and as these differences in the character of sounds must be thoroughly appreciated in order to understand how the voice is produced, and sounds are heard, let us endeavor, therefore, to explain them now a little in detail. Intensity of Sound. By the intensity of sound is meant the loudness of sound. We hear one sound louder than others because the particles of air set in motion by the sounding body strike the tymj^anic membrane of the ear harder in the one case than another. Just as the force with which a ball strikes a target can be shown on mechanical principles to be proportional to its weight and the square of the velocity with Mhich it is moving, so the force with which the air particles strike 'Phil. Trans., Vol. xxiv., p. 100-4. INTENSITY OF SOUND. 795 the tympanic membrane can be shown to be proportional to the square of the maximum velocity with which it is moving. The intensity of a sound depends, however, on the density of the air in which the sound is generated, and not on that of the air in which it is heard. Thus, while a cannon fired in a valley may be heard at the top of a high mountain above, the same cannon fired at the top of the mountain will not be heard in the valley below, the sound generated in the dense air of the valley being louder than that gen- erated in the rare air on the top of the mountain. The intensity of the sound is also proportional to the square of the amplitude of the vibration, the amplitude being the width of swing, the distance through which the air particle moves to and fro when the sound wave passes it. That such is the case can be readily shown by means of vibrat- ing cords ; for if the latter are long, the oscillations being visible to the eye, it will be seen that the sound becomes feebler in propor- tion as the amplitude of the oscillation decreases. The intensity of sound is modified by the distance of the sonorous body from the ear, varying inversely as the square of the distance ; that is to say, for example, the intensity of the sound of a bell, situated at a dis- tance of 20 yards from the ear, would be only one-fourth of the intensity of the same bell if situated at 10 yards from the ear, or half the distance ; or what is the same thing, the intensity of four bells, situated at a distance of 20 yards, is the same as that of one bell situated at a distance of 10 yards from the ear, supposing, of course, that the bells are all of the same size, and other conditions equal. That the intensity of the sound must diminish in the above ratio — that is, as the square of the distance — will become evident when it is borne in mind that, as the spherical Avaves of sound radiate outward from the center of disturbance toward the periph- ery, the mass of air set in motion must be continually augmented as' the squares of the distance from the center, the areas of circles being to each other as the squares of their radii. The matter affected increasing then as the square of the distance, the intensity of the sound must diminish in the same ratio. If, however, the wave of sound be propagated in a tube, lateral diffusion being pre- vented, as in Fig. 47(5, then the sound can be transmitted through great distances with very little diminution in intensity ; thus Biot found that a person whispering at one end of one of the empty water-pipes of Paris, a tube 3,120 feet in length, could be heard at the other end, and that the firing of a pistol at one end of the tube put out a lighted candle at the other. The intensity of sound is modified by the condition of the atmosphere, sound being better propagated'in calm than in windy weather ; in the latter case, how- ever, sound is better heard when transmitted in the direction of the wind than in the opposite direction. Finally, the intensity of sound is very much increased by the proximity of a sonorous body. Hence, the association of sounding-boxes with strings, as in the case 790 PHYSIOLOGICAL A CO USTICS. of the violin, guitar, etc., the increase in the loudness of the sound being then due to the fact that the box and air Avithin it vil^rate in unison with the strings as we shall endeavor presently to explain. The distance at which sounds are heard, depending upon their in- tensity, may be very great ; thus, it is said that the report of the volcano at St. Vincent was heard at Domerara, 300 miles oflP, and the firine; at Waterloo at Dover.' Pitch of Sound. Sounds are distinguished, as already mentioned, not only by their intensity or loudness, but by their pitch or height. The pitch of a sound can be shown to depend upon the number of vibrations made by a sounding body in a given time — a second, for example — sounds of low pitch being due to the aerial vibrations impinging upon the tympanic membrane following each other slowly, those of high pitch to the aerial vibrations following each other rapidly. Thus, for example, the pitch of the sound of a string four feet in length, sufficiently tensed, and of a given density and thickness vibrating 128 times in a second (Do",Ut^, C^ of piano), is low as compared with that of one two feet in length, vibrat- ^ ing 256 times in a second (Do^,Ut^,C^), or an octavo Fg^zEiq3 .'e.^ In the same way, the pitch of the sound of ^r ^i^ abov an organ-pipe four feet in length due to 128 vibrations per second (Do^t-) is low as compared with that of the sound of one two Fig. 47 Fig. 47i Vibration of string. feet in length, due to 256 vibrations per second (Do^Ut^) or the octave above. It may be mentioned in this con- nection that, while in the case of the string it is the "^ vibrations of the latter (Fig. 477) that give rise to the '"^''""^'p''- aerial vibrations affecting the auditory apparatus, in the case of the organ-pipe it is to the vibrations of the enclosed column of air that the aerial vibrations are due, as the current of air forced by the bellows through the mouth P B of Fig. 478 of the pipe in striking against the upper bevelled lip B, produces a shock, the air issues from the eml)ouchure or space between the lips in an intermittent manner, the pulsations so produced in being trans- mitted to the air enclosed within the ]Mpe in turn .set it into vibra- tion, which causes the sound. It will l:)e observed, also, as might Kianot, Physios, Trans, by Atkinson, p. 175. London, 1870. 2 If the 5th A of the piano he turned to vibrate 440 vibrations per second, in- stead of 426 times a.s a.ssumed in text, then the middle C or Ut=' will vibrate 264 times, and the lowest C 33 times per second. PITCH OF SOUND. 797 Fig. 479. have been anticipated on mechanical principles, that the number of vibrations, both in the case of the strin*.:: and pipe, are inversely as the length, the number of vibrations in both eases being doubled by having the lengths, since, in the latter case, the amount of work to be done being one-half, it can be done in half the time, or double the work can be done in the same time. The distinction between in- tensity or loudness and pitch or height must be carefully borne in mind, being, as just shown, due to entirely diiferent causes ; a sound, therefore, may be a loud one, and yet be low in pitch ; and, on the other hand, a sound may not be a loud one, and yet be high in pitch. In sounding; the long; stringy and long organ-pipe, apart from the intensity of the sound, and from the pitch of the note Do-Ut", 128 vibrations per second, the same, therefore, in both cases, another and very marked difference is ap- preciable, and that by not especi- ally musical ears, viz., the character or quality of the sound. Before considering, however, the quality of sound, or that in which the sound of a violin, for example, differs from that of a piano, and the sound of the latter from the sound of the organ-pipe, or, in general, that which distinguished the sounds of different kinds of musical instruments, let us first endeavor to explain how, by means of the siren, we are able to determine the number of vibrations to which the pitch of a sound is due. The siren — so called on account of its emitting sounds when under water in its original form as invented by Cagniard de la Tour — is a much more simple instrument than that we shall make use of, or the double siren of Helmholtz (Fig. 479). The principle upon which both instruments are con- structed is, however, the same, since the siren of Helmlioltz con- sists of two Dove sirens, the Dove .siren in turn differing from that of Cagniard de la Tour (Fig. 481) in being provided with four series of orifices instead of one. Such being the case, let us begin our description of a double siren with that of a single Dove siren. Suppose, for example, that the lower Dove siren (Fig. 479) be taken apart, it will he seen that the tube B leads into the brass cylinder C, the top of which is closed by a brass 2)late, perforated with four series of holes disposed concentrically, the outermost Helmholtz's double siren. 798 PHYSIOLOGICAL ACOUSTICS. series containing 16, the next 12, the next 10, the next 8 orifices, the latter being opened or closed, respectively, by pressing in or pulling out the keys numbered correspondingly. It will also be seen that the brass disk, receiving in its center the steel axis x, is Fig. 481. Siren of Cagniard de la Tour. Showing oblique opening in siren of C'agniard de la Tour. also perforated with 16, 12, 10, and 8 orifices, disposed concentrically at the same distance from the center, and with the same intervals between them as those on the top of the cylinder C, the only difference be- tween the two sets being that those passing through tlie top of the cylinder C, while oblique in direction (Fig. 480), arc oppositely inclined to those passing also obliquely through the brass disk. The two sets of orifices being so disposed to each other if air be forced by a pair of bellows through the tube B into the cylinder C, the air will issue from the latter not vertically but in side currents, which in impinging against the sides of the orifices of the disk will drive the disk around the axis .v, held upright by means of a steel cap brought down on its upper end. As the disk turns around, its orifices, coming alternately over the orifice of the cylinder C and over the intervening spaces, the continuous current of air passing through the cylinder C is carved into discontinuous puffs, which at first follow each other so slowly that they may be counted. As the motion of the disk, however, increases the puffs of air succeed each other so rapidly that the air links them together as continuous mu- sical notes, whose pitch can then be at once shown to depend upon the number of puffs of air or vibrations, by simply increasing or diminishing the rapidity of the rotation of the disk, the pitch of the note rising or falling accordingly. In order, however, to determine the number of puffs issuing from the orifices in a given time, a sec- ond, for example, they must be recorded. This is accomplished by providing the axis x at its upper part with a screw .s> (Fig. 482) which works into a pair of toothed wheels, the latter rotating as the disk and its axis turn, the number of rotations being indicated by PITCH OF SOUND. 799 the hands on the dial plates (omitted in Fig. 479, but represented in Fig. 481), the hand of one dial plate making an entire revo- lution while that of the other passes over but one division of the graduated circumference. The process of recording can be started or stopped by simply pushing a button, which throws the wheel- work just mentioned into or out of action. In order, now, to show how by means of the siren we determine that the note Do\ emitted by the string or organ-pipe two feet long, is due to the vi- brations following each other at the rate of 25(3 vibrations a second, we force the air from the bellows through the cylinder C, the outer- most series of 1 6 orifices being open until the disk rotates so rapidly that the sound produced by the siren is in unison with that emitted by the string or organ-pipe soiuided at the same time. The sound of the siren and the string or pipe being then in perfect unison, we push the button and so set going the recording mechanism and let the siren sing for just one minute, then instantly stopping the record- ing, we observe by the hands of the dial plate the number of rota- tions the disk d e has made in that time. It will be found that the niunber is just 960 ; dividing this by 60 the quotient, or 16, will be the nimiber of times that the disk has rotated in one second, but since 16 orifices were open in one rotation of the disk 16 puffs of air issued in succession from the siren, and consequently during 16 rotations 256 puffs of air. As the note Do'^, produced by the siren was due to the number of puffs or vibrations of air, and as the note of the siren was in unison with that due to the sounding of the string or pipe, the latter, or Do\ must be also due to the same number of vibrations, viz., 256 vibrations per second. It will be remembered that while the outermost series of orifices, those whicli in the preceding experiment Avere supposed to be open, are 16 in number, the innermost series of orifices are only 8 in number. If the latter now be opened as well as the former by pushing in the key numbered 8, then two sounds will be simultaneously emitted by the siren, one of which, Do\ is due, as before, to the rate of vibration being 256 per second, the other Do" an octave below, the rate being just half, or 128 vibrations per second, the air issuing from 8 orifices during one rotation of the disk, instead of from 16, as in the former case. The innermost and outermost series of orifices being open, then the rate of vibration of the two sounds is as 1 to 2. From what has just been said, it is evident, without further explanation, that if the innermost series of 8 orifices and the next series to it of 10 orifices be open, then the rate of vibration will be as 4 to 5 — that is to say, of the two notes produced by the siren simultaneously, if one be Do', due to 128 vibrations per second, the other note will be Mi- E-, due to 160 vibrations per second, and if the innermost series of 8 orifices and the third series from within outward, that of 12 orifices, be both open, then the rate of vibration of the two sounds will be as 2 to 3 — that is, if Do- be one of the two notes heard simultaneously the other note will be SoP G"', due to 192 vi- 800 PHYSIOLOGICAL ACOUSTICS. bratious per second. It follows, therefore, that if the three inner- most series of orifices, 8, 10, and 12, be open we will obtain the major chord C" E- G^, Do^ Mi" SoP, and if in addition at the same time the outermost series of 1(3 orifices be open C^ E^ G^ C^, which, as produced by the siren, is quite musical. The construction and manner of using a single Dove siren being now understood, there will be no difficulty in comprehending that of Helmholtz, it con- sisting, as already mentioned, of two Dove sirens. It must be men- tioned, however, that the outermost series of orifices in the lower of the two sirens are 18 in number instead of 16, as in the single Dove siren we have just described, and that the orifices in the four series of the upper siren are respectively 9, 12, 15, and 16 in number. If, therefore, we w^ish to obtain by the double siren the major chord C" E- G^ and C^ at the same time, the series of orifices 8, 10 and 12 must be opened in the lower siren, and the series of 16 orifices of the upper siren, the air being allowed, of course, to pass from the bellows through both sirens, the number of rotations of the disks being recorded in the same manner as already described by wheel- work attached to the axis common to the two sirens, and omitted for simplicity in Fig. 479. It will be observed that the double siren is provided with resonance boxes the half of each of which has been removed in the figure, which greatly intensifies the funda- mental sound. The upper siren is also connected with a toothed Avheel and pinion turned by a handle, by which we are enal^led to rotate the cylinder of the upper siren as well as the disk, the handle, etc., being so disposed that if it be turned to the right the orifices in the cylinder and in the disk will then pass over each other more quickly than if the cylinder was at rest, and if in the reverse direc- tion more slowly, the pitch rising in the one case, the puffs suc- ceeding each other then more rapidly, and falling in the other, fol- loAving more slowly. The use of the dial and index underneath the handle will be illustrated hereafter. It is needless to say that by doubling all parts of the siren, etc., as done by Helmholtz,^ that many varied combinations can be introduced, and that the general usefulness of the instrument has thereby been greatly increased. Quality of Sound. Every fundamental tone, whether produced by a string, column of air, reed, etc. — that is, a sound due to the string, for example, vibrat- ing through the whole of its length (Fig. 477), may be accompanied by partial tones or overtones ^ due to the string vibrating through the half, third, fourth, etc., of its length (Fig. 482, (2), (4), (6)), and since the overtones, accompanying and reinforcing the funda- mental tone, due to the sounding of the string of one instrument, 1 On the Sensation of Tone, transl. by A. ,T. Ellis, p. 245. London, 1875. ^By the 1st, 2d, and 3d overtones, etc., will be meant in this chapter, tones due to vibrations wliose rates are twice, three, or four times as rapid as that of the fun- damental tone. QUALITY OF SOUND. 801 are not the same as those of another, or if in part tlie same, are then more or less accentnated, there arises in consequence a difference in the character of the sound as produced by the two instruments, very appreciable, even by unmusical ears, which is called their quality. Thus, for example, the sound of the string of a violin may be as loud as that of the piano, or of that of the vibratino; column of air of the organ-pipe, or of that of the vibrating reed of the oboe, the pitch of the particular note emitted by the four instruments may be the same, the number of vibrations per second to which the note Fk;. 482. Fig. 483. a a a a (1) (2) (3) (4) (5) (6) (1) (2) (3) (4) Formation of nodes and ventral segments. (Tyn'dall. ) Vibrations of tube. (Tyxdall. ) is due being equal in all four instances, and yet no one fails to ap- preciate the difference in the character or the quality of the sound, the overtones reinforcing the fundamental note being different in each instance. Inasmuch, however, as the thorough understanding of the conditions, upon which the quality of soimd depends is not only important, but absolutely essential, in comprehending the man- ner in which the vowels are produced by the larynx, for example, let us endeavor to explain a little more in detail how these partial vibrations, to which the overtones are due, come to be superim- po.sed upon the fundamental one, and how their presence can be de- tected. Let c a (Fig. 483) represent a long India-rubber tube fixed at the one end, and free at the other. By takiug hold of the free 51 802 PHYSIOLOGICAL ACOUSTICS. end, stretching the tube a little, and properly timing the impulses, the tube can be made to swing to and fro, to vibrate as a whole, as represented in Fig. 477. Stop the motion, and now, by a jerk, raise a hump upon the tube, the hump will be observed to run along the tube a b, h c (Fig. 483, (1), (2)), and having reached the fixed end of the tube c, will then run back again, but in the re- verse direction. But just as the latter c b (3) starts at c, let the tube be jerked again, so as to start the hump a b (3) at a, then by the time that the foremost part of the hump beginning at c arrives at b, that beginning at a will also have reached b, the effect of which M'ill be that the point b will remain at rest. For the hump a b (3) in moving on to c must tend to move the point b to the right, and the hump c b moving on to a must tend to move the point b to the left, the consequence of which is, that the point b, in being acted upon by equal and opposite forces, Avill not move at all. Such being the case, the two halves, ab, be of the tube b c, will vibrate as if they were independent of each other (Fig. 483 (4)). The point b at rest is known as the node, the vibrating parts a b, b e as the ventral segments, twice the length of a ventral segment constituting a wave, the latter being made up by both the hump and the depression follow- ing the same. By experimenting a little, it will be soon found that the tube a c (Fig. 482) can be so swung as to form two nodes with three ventral segments (4), or three nodes with four ventral seg- ments (Fig. 482^ (6)), and so on, the tube vibrating in thirds, fourths, etc., of its length, and a little reflection will make it clear that the cause of the formation of the nodes, or points of rest, and of the string in consequence vibrating in its aliquot parts, is pre- cisely the same as that just given in the case of the formation of one node and two ventral segments. Let us now modify the pre- ceding experiment slightly by encircling the tube a c at its cen- ter (Fig. 482, (1)) with the thumb and forefinger of one hand, and, taking hold of the middle of the lower lialf of the tube a b with the other hand, pull it aside. It will be observed that one node is formed, and two ventral or vibrating segments (2), the upper halt of the tube vibrating as well as the lower. Experimenting in this way, but encircling, however, the tube at one-third (3) or one-fourth (5) of its length, and pulling the lower third (3) or lower fourth (5) of the tube away by seizing them, respectively, at their centers, the tubes will be oscillated, so that two nodes with three ventral seg- ments (4). or three nodes with four ventral segments (6), Avill be formed, as the case may be, the vibrations of the string through the space encircled by the thumb and finger, a distance of one inch, acting upon the upper part of the tube exactly as the hand acted when it caused the tube to SAving as a whole. In precisely the same manner, by placing a feather (Fig. 484) upon the center of the stretched violin-string, just as we encircled the tube with the thumb and finger, and drawing a bow across the center of the half of the string instead of pulling it aside with one hand, the FORMA TIOX OF SODFS. 803 string will bo made to vibrate in halves, as shown by the little paper rider being- thrown off. Similarly, by touching the string with a feather at a third (Fig. 485), or a fourth (Fig. 486) of its Fig. 484. Formatiiiu of one node and two ventral segmeuts. (Tyndall.) length, and drawing the bow across the center of the right hand third or fourth of the string the string will vibrate in thirds or fourths, two nodes with three ventral segments, or three nodes with four Fig. 485. Formation of two nodes and three ventral segments. (Tyndall.) ventral segments being formed, as shown by the two or three red paper riders placed upon the vibrating parts being tossed off, and the one or two blue ones remainino; on the string being situated Fig. 480. Formation of tliree nodes and two ventral segments. (Tyndall.) at the nodes, or points of rest. A beautiful way of demonstrat- ing the presence of nodes and ventral segments made use of by the author in addressing a larije audience, is to place a string 804 PHYSIOLOGICAL A CO USTICS. connected at one end with the prong of a tuning fork, and at the other with a peg, by Avhich it can be loosened or tightened in front of the calcium light lantern, an appearance such as that represented in Fig. 487 being presented when the fork is sounded, according Fic. 487. Nodes aud segmeuts of a vibratory string as shown by lantern. to the extent to which the string is tensed. While the string may vibrate as a whole, or in halves, thirds, fourths, fifths, etc., sepa- rately, as we have just shown, as a matter of fact, the string usually in vibrating breaks up, so to speak, into its aliquot parts, the su- }>erimposing of which vibrations upon the fundamental vibration of the string — that is, of the vibration due to the swinging of the Fig. 488. Fig. 489. Resonator of Helniholtz. string, as a whole, gives rise to a resultant vibration, which has been shown to be equal to the al- gebraic sum of all the vibrations,' as represented in Fig. 488 in which the lower curve represents the compound vibration resulting from the blending of the three up- per curves, representing, respec- tively, simple vibrations, whose ratio is as 1, 2, 3. Of course, it must not be supposed that sounds, simple or compound, are due to curves like those depicted in Fig. 488 ; the latter are simply graphic representations of ' Helmholtz, op. cit., p. 4o. Compound waves. (Mi(;RK(iOK Robinson.) OVERTONES. 805 waves of sound, which, as wo have seen, consist of condensations and rarefactions of the air. That the tpne due to the sounding of a string of the piano, such as Do^, vibrating 128 times per sec- ond, is not a simple, but a compound tone, will be appreciated by a trained musician, whose sensitive ear enables him to distinguish some at least of the overtones accompanying the fundamental tone. Any one, however, can convince himself that sucii a tone as that of Do^ sounded by the piano, as elicited by singing the corresponding note, is a compound one, resulting from the blending of the funda- mental tone with overtones, the latter being due to the partial vi- brations of the string, as the former is to the oscillating of the string as a whole, by adapting to his ear in succession each one of the series of nine resonators, of which one is represented in Fig. 489, devised by Helraholtz,' and so constructed as to iutensify the sound of each particular overtone accompanying the fundamental tone, that overtone being then heard alone. Thus, for example, the largest resonator, marked Ut^, being applied to the ear, let the note Ut^ due to 128 vibrations a second be sounded ; the first over- tone or harmonic, or the octave above Ut^, 256 vibrations per sec- ond, will be heard, due to the string vibrating in halves, the sound distinctly heard with the resonator being the same as if the note Ut' had been sounded. Applying the next largest resonator, marked Sol'', to the ear and sounding the Ut^ string on the piano the second overtone, the twelfth above the fundamental, or SoP, will be heard, due to the string vibrating in thirds, the sound heard being the same as if the note Sol'' had been sounded. Adapting in succession the remaining resonators graduallv diminishing in size, and marked respectively Ut* Mi*, SoP Si*"* Ut% Re^ Mi^ the 3d, 4th, 5th, 6th, 7th, 8th, and 9th overtones due to the string or harmonics will be heard vibrating in fourths, fifths, sixths, etc., the sounds heard with the resonators being the same as if the notes Ut* Mi* SoP Si^'* Uf' Re'' Mi'^ had been separately sounded, or as expressed in musical notation as fol- lows, Do^ Ut^ being the fundamental tone : -7^ b^ :*: i^: ^ -(2 i=: ^m Ut2 rt' Sol3 Ut< Mi* Sol* SiM Vt^ Ri- Mi^ It is obvious, therefore, why when the notes Ut^ SoP Ut* are sounded on a musical instrument at the same time with Ut', the re- sulting sound should be harmonious, since these three sounds rein- force respectively the first, second, and third overtones due to the string vibrating in halves, thirds, and fourths respectively. In the same way. Mi* SoP Si'* Ut^ Re' Mi' reinforcing the overtones due M)}.. cit., p. 68. 806 PHYSIOLOGICA L ACQ USTICS. Fig. 490. to tlie string Ut" vibrating in fifths, sixtlis, sevenths, eighths, and ninths, when sounded with Ut^, will also give a harmonious sound. Having described the manner in which partial vibrations are formed, and how in being superimposed upon the fundamental vi- bration a resultant vibration arises, and how the overtones due to the partial vil)rations in being l>lended with the fundamental tone due to the fundamental vibration give rise to a compound tone, it becomes evident without further explanation, that by means of the Helmholtz resonators we can analyze any sound, and demonstrate whether it be a simple or compound one, and, if the latter, what overtones are present, and in this way show on what the quality, timbre, or klangfarbe of the sound depends. Thus, for example, the quality of the sound of the piano, as compared with that of the violin, depends upon the fact that in the case of the latter, when boAved, though the first six overtones or harmonics are present, as in the case of the piano, they are so faintly sounded as to be over- ])Owered by the seventh, eighth, ninth, and tenth overtones. The overtones in the case of an open pipe are not the same as in the case of a closed one ; those of the clarionet differ from those of the oboe, and so through the whole range of orchestral instruments. Inas- much, however, as in addressing a large audience, from the nature of the case, it is impossible for each one in- dividually to make use of the resona- tors and satisfy himself of the existence of overtones upon which the quality of a sound dejiends ; the author is ac- customed to demonstrate the same by means of Koenig's manometric ap- paratus.^ The latter (Fig. 490) con- sists of a frame supporting a number of resonators each of which leads by a narrow India-rubber tul)e into a small chamber, completely divided into two, by an India-rubber partition. The posterior part of the chamber is in communication with the resonator, the anterior part provided with a gas jet with a reservoir containing gas, led thither by an ordinary gas pipe. Each resonator is connected in this way with its own gas chaml:)er and burner, the burners being all placed in a row, one above the other. 0])posite the gas burners is a long mirror with four refiecting sides, at right angles to one another, which can be revolved on an almost perpendicular axis by a toothed w^heel ar- rangement. Turning on the gas, and lighting it as it issues from the Jets in the chambers connected with the resonators, and revolv- ing the mirror, the light reflected from the surfaces of the latter ap- pears as continuous bands. If, however, the air in any one of the ' Kudnl])li Kopiiio-, Qnelqucs Experiences d'Acoustique, p. 73. Paris, 1882. MaiKjmetrie apparatus. (Koenk;.) RESONANCE. 807 resonators be thrown into vibration, then the India-rubber partition of the chamber separating, on the one hand, the air continuous with that of the resonator, and, on the other, the gas, will vibrate, and the gas and flame thrown into agitation, the particular band of light, the corresponding band of light, becoming segmented. Let now a tuning fork Ut^, vibrating 256 times a second, be sounded in front of the apparatus ; at once the flame in connection with the resonator marked Ut^, will become segmented, but the remaining flames will still appear as continuous bands of light, since if the tuning fork be properly bowed the sound produced will be a pure, simple tone, un- accompanied with overtones. Let now, however, the Ut^ Do^ of the piano, or an open organ-])ipe two feet long, giving, therefore, the same fundamental note, be sounded, and immediately some of the remaining bands of light will l)ecome segmented, as well as the one connected with the resonator marked U'^, since the air of the resonators with which they are in connection has been thrown into vibration by the particular overtones present, as, for example, in Fig. 491, a, b, representing respectively the flames due to the fundamental and octave above it. In this way an Fig. 491. optical demonstration can be (yiven of the fact that the quality of the note of a n y musical in.strument depends upon what par- ticular overtones or har- monics accompany the fun- damental, and, as we shall see presently, of the manner in which the vowel sounds are produced by the human , ,,.u,v, ,.i inv, , .un-. voice. As it is important that the manner in which resonators reinforce or intensify sounds should be understood, a brief account of the cause of resonance in general may be as appropriately considered here as elsewhere. It is well known that the velocity with which sound travels in air at the freezing temperature is 1,090 feet in a second, the velocity increasing about two feet for every additional degree of heat Centi- grade (1.8° F.). Let us suppose that the temperature of the sur- rounding atmosphere be ^.0° Cent. (47.3° F.), and that a tuning fork vibrating 256 times per second be sounded ; it is obvious that if, at the end of the second, the sound has reached a distance of 1,101 feet, then each vibration must have been 52 inches long, since 52 multiplied by 256 gives 1,101 feet, and as a vibration or wave of sound consists, as we have seen, of a condensation and rarefaction, the condensation and rarefliction must have been both . just 26 inches in length. That is to say, as the prong of the tuning fork (Fig. 492) moves from A to B, a distance of perhaps the Fumlaiiieutal note. 808 PHYSIOLOGICAL ACOUSTICS. one-twentieth of an inch, it generates the one-half of a sonorous wave, the condensation, the foremost point of which reaches a distance of twenty-six inches, at the same instant that the proDg of the fork reaches B, and as the prong of the fork moves A B Fig. 492. -ZG uiclics ->c V Tuning fork vibrating. ( Ty.vdall. ) back from B to A, the other half of a sonorous wave, is generated, the rarefaction or the part progressing backward toward B, the second condensation progressing forward at the same time toward C. Such being the case, let the tuning fork now be sounded over a jar (Fig. 493), of which the column of air within, from top to bottom, measures just thirteen inches, or '• one-fourth the leng'th of the vibration or ~ <* '^---rr wave due to the sounding of the fork. It follows from what has just been said, ■■*'^^^^-- that during the time the prong of the fork moves from a to 6, the conden- sation, the air which it produces runs from the top of the jar to the bottom, thirteen inches, and from the bottom to the top, thirteen inches, or twenty-six inches in all, the reflected wave reaching the prong of the fork just as the latter reaches 6 ; and similarly, that during the time the prong returns to a from 6, "Q the rarefaction to which it gives rise runs down from the top of the jar to the bottom, and up again, also a distance, in all, of twenty-six inches. The vibrations of the fork being, therefore, perfectly synchronous with the vibrations of the aerial column within the jar, the motion will accumulate in the latter, and spreading out into the room, the sound will be greatly augmented as everyone will appreciate, when the tuning fork is sounded first at some distance from, and then over the mouth of the resonating jar. From what has just been said, it necessarily follows that if Ave sound other tuning forks, vibrating at different rates, the length of the column of air must be varied accordingly if we wish to make use of the latter as a res- onator. It is for this reason that the resonators made use of in Tuning fork vibrating in with jar. QUALITY OF SnUXD. 809 demonstratincr the presence of overtones are of different size, and that the resonators of Koenig's manometric apparatus are so con- structed, that by draAving them out to varying distances, the sound that each resonator will reinforce will then be different. It is on account of its resonating qualities that, in sounding a bell, the latter is often placed near the mouth of a jar, by means of which the intensity of the sound is very much increased. The ancients were well acquainted with the efficacy of such aids in intensifying sound, resonant brass vessels being placed, according to Yitruvius, in their theatres to strengthen the voices of the actors. It is on account of the resonating properties of sound- ing boards, that the latter are associated with musical instruments, and that the stethoscope also has proved in the hands of the clini- cian such an aid in the diagnosis of disease by auscultation. Having shown that sounds are produced by the vibrations of plates, bells, strings, pipes, reeds, membranes, etc., and how the same are distinguished by their intensity, pitch, and quality, let us turn now to the consideration of the larynx, and by means of the principles just established, endeavor to determine what kind of an acoustical instrument the larynx is and how the voice is pro- duced bv it. CHAPTER XLIL THE LARYNX, AND THE PRODUCTION OF THE VOICE AND SPEECH. The larynx, the organ of the voice, situated at tlie top of the trachea and below the root of the tongue and the hyoid bone, con- sists of a framework of cartilages, connected by ligaments, provided with muscles, blood vessels, and nerves, and lined with mucous membrane. The cartilages of the larynx are nine in number, three single and symmetrical pieces, the thyroid, cricoid, and epiglottic, and three pairs, the arytenoid, cornicula laryngis, and cuneiform ; the last two pairs are, however, very small. The thyroid (Fig. 494), Fig. 494. Fig. 495. Bird's-eye view of laryux from above. G E H, the thyroid cartilage, embracing the rings of tlie cricoid, r n X w, and turning upon the axis, X z, which passes tlirough the lower horns. N F, N F, the arytenoid cartilages connected bv the arvt^IU fixed one agaiust the other at the notes F^ 1- ]~1 Witli the do production of the notes fA^ 1 iH , and so on upward tu the eml of the register, the vibrations are due to the vocal membranes alone, the length of tho glottis diminishing, and the cavity of the larynx becoming very small as the pitch of the voice continues rising. These changes undergone by the glottis in the shape and size and in the length and tension of the vocal membranes in the production of low and high notes by the larynx, as observed by Garcia and subsequent investigators, become intelligible Avhen it is remembered, as shown in the last chapter, that the pitch of the note — that is, the number of vibrations per second — rises as the leno;th of tlie strinjr, pipe, or membrane diminishes, or the tension increases, the change in the shape of the glottis and of the tension of the vocal membranes being accomplished by the action of the muscles, as already explained. Thus, men have deeper voices than boys and women, their larynx being larger, and their vocal membranes longer. That the aperture of the glottis is narrowed during the production of sounds any one can convince himself by comparing the time of an ordinary expira- tion with that re(juired for the ])assage of the same quantity of air during a vocal effort, and that the size of the aperture varies with the pitch of the note, from the fact of there being far less air ex- pired during the production of a high note than in that of a low one. That the production of low and high notes is due to varia- tions in the tension of the vocal membranes, as brought about by the action of the thyro-arytenoid and crico-thyroid muscles, is made evident during the passage of the voice from one extreme of the scale to the other by the movement of the thyroid on the cricoid cartilage, which is quite apparent if the tip of tlie finger be placed over the crico-thyroid ligament. As illustrating the nicety and precision with which the tension of the vocal membranes is regu- lated by muscular contraction, let us suppose, with Miiller,^ that the average length of the vocal membrane in man during repose is about -^^'^y of an inch, and during the greatest tension y^\, the dif- ference being, therefore, -^-^\^, or the -I of an inch, and that in the female the corresponding extremes are al)Out -f^\y and -^^^, the difference being -^^q, or the ^ of an inch, and that the natural compass of the voice is about two octaves, or twenty-four semitones. Such being the case, as any cultivated voice can sing ten intervals between the twenty-four semitones, such a voice can produce 240 sounds, necessitating, however, over 240 different states of tension. Inasmuch, however, as the available length of vocal membrane to be tensed is only the i and the | of an inch in the sexes, it follows iQp. cit., Vol. ii., p. 1018. 820 THE LARYNX. that in tlie production of eacli of the 240 sounds the vocal mem- brane must be diminished vohintarily by the j.;^q-q and the ygV-g- of an inch in the case of the male and female sinti;er, respectively, and by considerably less in the case of such phenomenal voices as those of Bastardella, Catalani, Cruvelli, and Patti, for example, with a compass of three octaves, and even more. The remarkable distinct- ness with which certain voices could be heard, like those of the celebrated basso, Lablache, and the late Madame Parepa Rosa, clearly above the sounds of a large chorus and orchestra, is due rather to the absolute accuracy with which the tension of the vocal membranes could be regulated by those great singers, to the purity of their tones rather than to the mere loudness or intensity. It should be mentioned, however, that the singers just referred to were of magnificent physique, as might have been expected, the power of the voice being due to the force with which the air is expelled from the lungs. As the action of tlie diaphragm and abdominal muscles has already been considered, it will be only necessary in this con- nection to recall what has already been said, that the inspiratory and expiratory acts can be so nicely balanced by a skilful singer as to enable him to produce the most delicate tones. It need hardly be added that while sounds may be uttered, and even words spoken during inspiration, that the true and natural voice, and, as we shall see presently, articulate speech are only produced during expiration. While, in childhood, the general character of the voice is the same in both sexes, in the adult condition the male voice differs very much from that of the female, the difference becoming marked at the age of puberty. If castration be performed, therefore, the con- tralto, or soprano, voice of the boy will be retained through life, and such a voice being susceptible of considerable cultivation ad- vantage was cruelly taken of the fact at one time to fill choirs with desirable voices. After the age of puberty, however, the quality of the female voice remains the same, except in gaining strength and extending its compass. At this period, in the case of the male, however, the whole character of the voice changes through the de- velopment of the larynx. While the intensity of the voice in both sexes depends upon the force with which the air is expelled through the larynx, and the range or pitch, bass, tenor, contralto, and soprano, upon the length and tension of the vocal membranes, the quality of any particular individual voice, male or female, depends upon the shape, size, and general make of the larynx, and on the character of the auxiliary resonating cavities. In concluding our account of the production of the voice, a brief description, at least, of the influence exerted by the accessory vocal organs, viz., the trachea, ventricles, superior vocal cords, epiglottis, pharynx, nasal cavities, and mouth, should be offered. The tracliea not only serves to conduct air to the larynx, but through the vibration of its own column of air reinforces the sound produced by the larynx, the vibration being perfectly appreciable if the finger be placed upon the PKODVCTIOX OF FALSETTO VOICE. 821 trachea during a powerful vocal effort. The ventricles probably, also, intensify the sound, the homologous parts being enormously developed in monkeys and apes possessing very loud voices, such as the South American howler (Mycetes), the cliimpanzee, and gorilla. That the superior or false vocal cords and the epiglottis are not essential to the production of the voice, can be shown bv experi- ments like those (»f Longet,^ in which the above parts were removed in animals without the voice being materially affected, and in man those cases in which the epiglottis had been lost through wounds or disease. The pharynx, mouth, and nasal fossfe, acting as resonating cavities, modify, however, very considerably the sounds produced by the vocal membranes. Indeed, in the production of the natural voice their resonance is essential. Thus, Avhile in the production of low notes the velum palati is fixed, and the bucco-pharyngeal and naso-pharyngeal cavities reinforce the laryngeal sounds, in the passage upward to the higher notes these cavities are reduced in size, the isthmus contracting until, with the emission of the highest notes, the nasal fossse is shut off entirely, and the mouth and pharynx alone resound, the tongue at the same time being drawn back into the mouth with its base projecting upward and the tip downward, the capacity of the resounding cavity is still further diminished. Such being the mechanism by Avhich the chest tones or chest register are produced, it is only necessary to add, that if the velum palati lie thrown forward instead of backward, thereby cutting off the mouth from the pharynx, the resonance being then due to the naso-pharyngeal cavity, that we pass from the chest register into that of the head tones or head register.' According to the late Madame Seller,^ however, the head tones are due to the vocal membranes being firmly approximated posteriorly, an oval opening being left with vibrating edges involving only one-half or one-third of the vocal membranes, which gradually contracts as the pitch of the tone rises. As in the case of the head register, so in that of the falsetto or middle register of the female, a difference of opinion still prevails as to the exact manner of its production. Thus, while, according to Fournie,* the falsetto is due to the tongue being pressed strongly backward and the epiglottis forced over the larynx ; according to Seller,' it is due to the thin, fine edges of the vocal membranes alone vibrating. While the distinction between the chest, falsetto, and head registers so fiir as pitch is concerned, is not an absolute one, and while we find that every voice possesses all three registers, nevertheless the chest register almost characterizes male voices and the contralto of the female, the falsetto being the most natural voice of the soprano, though the latter voice is capable iPhysiologie, Tomeii., p. 728. Paris, 1809. ^Fournie, Physiologie de la voix et de la parole, p. 421. Paris, 1866. 3 The Voice in Singing, p. 56. Phila., 18(18. *0p. cit., p. 463. ^Op. cit., p. 56. 822 THE LARYNX. of chest tones, while the head voice is particuhirly well developed in tenors and in the female voice. The falsetto is but little culti- vated at the present day by tenors, and even M'hen it or either of the other two registers is particularly well developed the singer should endeavor to pass as insensibly as possible from one register to another, to give the impression that his voice possesses but one. Speech. While the position of man as the head of the animal kingdom depends upon the development of his intelligence, there can be no question that his superiority over all other animals is, to a great extent, due to his being able to convey his ideas to others by ex- pression, or articulate speech. Speech is made up of syllables articulated or jointed together, the parts of speech called words being formed by the union of one or more syllables, the latter consisting usually of two kind of sounds, vowels and consonants. Speech is voice modulated by the throat, nose, tongue, and lips. Voice may, therefore, exist without speech, and if the production of the voice be restricted to reo-ular vibrations of the vocal mem- branes, it may be said that speech can exist without voice, since, in whispering, the vibrations of the muscular walls of the lips replace those of the vocal membranes, a whisper being, in fact, a very low whistle. Articulate sounds are usually divided by orthoepists into vowels and consonants : vowels being continuous sounds due to the voice alone, but modified by the form of the aperture through which they pass out ; consonants, interrupted sounds due to the in- terruption, more or less, of the voice, and sounded with vowels. This classification is not, however, a very natural one, since the sound of the English i, being a diphthongal sound, cannot be pro- longed like a true vowel (a, o), while certain consonants (1, r, f ) can be pronounced without the current of air being interrupted. The vowel sounds, by which we mean u, o, a, e, are due to the reinforcing of the overtones of the fundamental tone of the larynx by the cavity of the mouth, the changes in the shape of which give rise to so many reso- nators, each of which is adapted to the reinforcing of the particular overtone to which, together with the fundamental tone, the partic- ular vowel is due. The ])resence of overtones coexisting with the fiuidamental tone of the larynx in the emission of vowel sounds, and the determination of what particular overtone accompanies the fundamental tone in the production of any particular vowel, can be shown by the Koenig manometric apparatus described in the last chapter. Thus the vowel sound u is due to the fundamental tone being emitted strong, the cavity of the mouth or the vowel chamber (Fig. o()2, U) being made as deep as possible, by keeping the tongue down at the bottom, and pushing the lips out, the mouth then rein- forcing the fundamental tone of the larynx, and tuned, according to PRODUCTION OF VOWELS. 823 Koenig^ to the pitch of the note ^7|-,, (Fig. ;303), due to 224 vibra- tions per second. The sound o is due to the fundamental note of the hirynx being present, but especially its first octave above being emitted also, and very strong, the cavity of the mouth being en- Section of the parts concerned iu the formation of vowels. Z. l-..^ ^. , „. Epiglottis, fj. Glottis. Ii. Hyoid bone. 1. Thyroid. 2, 3. Cricoid. 4. Arytenoid cartilage. (Laxdois. ) Z. Tongue, p. Soft palate. Ko. of Vib.s., 224, 448, Pitch of vowel Sil larged through the retraction of the lips so as to reinforce the octave, and tuned to the pitch of the note Si\).^, due to 448 vibrations per second. The sound a, like the preceding two vowels, is due to the presence of the fundamental tone of the larynx, but differs Fig. 503. from o in that the funda- mental is accompanied by the double octave above, the orifice of the mouth being so widened that the cavity of the mouth (Fig. 502, ^4) is tuned to the pitch of the note Si\y^ due to 896 vibra- tions per second. In the production of the sound e the cavity of the mouth is still more retracted, reinforcing the third octave above the fundamental, the cavity of the mouth being tuned to the pitch of the note Si\)r, due to 1,792 vibrations per second. As the four vowels u, o, a, e can be produced during one con- tinuous expiration, during which the fundamental and overtones generated by the vocal membranes remain the same, by simply changing the shape of the mouth, it is evident that the production of each individual vowel will depend, as already mentioned, upon which particular octave or overtone is reinforced by the cavity of the mouth, the pitch of the latter depending upon its shape, and that the shape of the mouth remaining unchanged, the correspond- ing vowel will be emitted as long as the expiration blast lasts. 'Quelques: Experiences d' Acoustique, p. 65. Paris, 1882. b5 '^'■b« 890, 1792, :j.')84. (KOESIG.) 824 THE LARYNX. Now while the vowel i agrees with the four vowels just mentioned in being due to the reinforcement of an overtone, the fourth octave accompanying the fundamental by the cavity of the mouth (Fig. 502, 7), which in this instance is tuned to the pitch of the note Si[^y, due to 3,584 vibrations per second, an octave higher than in the case of the vowel e, it diifers from the true vowels in that, the cavity of the mouth remaining the same, if the expiratory blast be prolonged, it does not remain i, but becomes e. The vowels are the only real vocal sounds, it being only on a vowel that a note can be said or sung. Speech, however, is made up not only of vowels, but of consonants — that is, of sounds that are sounded in conjunc- tion with a vowel. While the distinction between vowels and consonants, as already mentioned, is not an absolute one, it may be said that while vowels are due to the vibrations of the vocal mem- branes being modified by the mouth, consonants are due to the expiratory blast being interrupted in various ways in its course through the throat and mouth ; the vibrations of the vocal mem- branes, when essentia], being rather secondary in character. Con- sonants may be divided, according to their manner of production, into two kinds, explosive and continuous, the sound of the explosive consonants being due to the sudden establishment or removal of a particular interruption, that of the continuous consonant to the air rushing continuously through some constriction, for example, ex- plosive consonants are the labials p, b, dentals t, d, and gutturals k, g, p, t, and k, being uttered without the voice, the so-called surds b, d, and g (hard) with the voice sonants — that is, are ac- companied by a vowel sound. In uttering p the lips arc first closed, then the expiratory blast suddenly opening them, the sound is produced. Similarly the sudden interruption of the contact of the tip of the tongue with the hard palate, and of the root of the tongue with tlie soft palate gives rise respectively to the sounds t and k. The continuous consonants are subdivided into aspirates, resonants, and vibratory. In certain cases a brief sound due to the sudden opening of the closed glottis, the so-called spirited lenis, inaugurates a vowel, the vibrations of the vocal membranes immediately following with the production of a true vowel sound. In other cases in uttering a vowel the glottis being open but constricted irregular vibrations produced by friction give rise to the so-called spiritus aspera. The aspirates include the labials f, v, the dentals s, 1, sh, th (hard), z, zh, th (soft), and the gutturals ch, gh. Like the explo- sive consonants, some of the aspirates are uttered without the voice, as f, s, 1, sh, c, h ; some with the voice, as v, z, zh, th, ch. The resonants include the sounds m, n, ng, and the vibratory the sound r, common and guttural. Of the aspirates, f and s are formed through the lips and teeth being brought nearly in contact respec- tively ; th through the placing of the tongue between the two par- tially open rows of teeth ; 1 when the tip of the tongue is placed PRODUCTION OF COXSOXANTS. 825 against the hard pahite, and the air escapes at the sides ; sh through the dorsal surface of the tongue being raised toward the pakiti, the passage-way between the two being thereby narrowed ; ch and gh through the approximation of the root of the tongue to the soft palate. In the production of all of the resonants the vocal mem- branes vibrate and the nasal chambers resonate, the closing of the lips in particular giving rise to m, the contact of the tongue with the hard palate to n, and the approximation of the root of the tongue to the soft palate to ng. The vibratory consonants include the various forms of the sound r, so called on account of being produced by the vibration of the constricted portion of the vocal passage ; thus, the common r is due to the vibrations of the point of the tongue elevated against the hard palate ; the guttural r to vibrations of the uvula or other parts of the walls of the pharynx. The tongue, while an organ of speech, is not essential, since after its loss the faculty of speech, more or less perfect, remains. Finally, while the consonant e is a breathed aspirate, it diifers from all other letters in being formed in the larynx itself, the glottis being nar- rowed enough to produce a wind-rush, but not sufficiently to throw the vocal membranes into vibration, c is redundant, producing the same effect as k or s ; q is equivalent to 1, being used only be- fore the vowel u ; x is the same as ks at the end of a syllable, and z when beginning a word. While the limits of this work will not permit of any further detailed consideration of orthoepy, or of any theory of the origin and growth of language in general, or of that of the language in which this work is written in particular, the above description will suffice as a general account of the production of articulate speech, a factor almost as important as that of intelligence in the develop- ment of civilization. CHAPTER XLIII. THE STRUCTURE OF THE EAR, AND THE SENSATION OF HEARING. The organ of hearing is usually described as consisting of three parts, the external ear, including the pinna or auricle and the ex- ternal auditory meatus, the middle ear or tympanum, and the in- ternal ear, including the labyrinth and the auditory nerve. For convenience, as well as to avoid repetition, the functions of the three parts of the ear will be considered at the same time as that of the description of their structure. The Structure and Functions of the External Ear. The pinna, auricle, or ear, in the ordinary sense of the term — that is, the portion projecting from the head (Fig. 504), with the excep- FiG. 504. Diagram of organ of hearing of left side. 1. The pinna. 2. Bottom of ooncha. 2,2. Meatus externus. o. Tym])amim. Aljuve 3, the chain of o.ssieles. :i ()])euiiig into the ma.stoid cells. 4. P^u.stachiau tube. .1 Meatus internus, containing the facial (uppermost ) and auditory nerves, 6, placed on the vestibule of the labyrinth above the fenestra ovalis. A. Ape.x of the petrou.s l)one. B. Internal carotid artery. C. .Styloid process. 1). Facial nerve, issuing from the stylo-mastoid foramen. E. Mastoid jjrocess. F. Squamous jiart of the bone. (Quaix after Arsoli).) tiou of the lower lobular portion, consists of fibro-cartilage and pre- sents certain prominences, the tragus and antitragus ridges, the helix and antihelix, which, together with their fossse, adapt it to receive the aerial viljrations giving rise when transmitted to the auditory STBCCTUBE OF THE MIDDLE EAR. >^'2~ nerve to the sensation of stmiid. Owing- to the inimolnlity of the ear, through tlie imperfect development of the attoleus, attrahens, and retrahens auri, as well as its intrinsic muscles, the external ear is not as functionally important in man as in the case of the lower animals for the appreciation of the intensity of sound, since persons deprived of it do not experience any sensible change in their power of hearing. That the auricle is, however, of use in enabling us to judge as to the direction of sounds, any one can convince himself by filling the convolutions with wax, or flattening the ear forcibly against the side of the head, when it Avill be found impossible to determine the direction from which the sound comes. Such is also the experience of those persons who have lost the external ear from wounds, etc. Indeed, there can be little doubt that we judge as to the origin and direction of sounds from the fact that the sound waves do not impinge upon the ears alike, and that the intensity of the sound is modified by the manner in which it fiills upon the ex- ternal ear and is reflected from it. Hence, in determining whether a sound proceeds from directly behind or in front of us, we usu- ally incline the head in the direction from which we suppose it to come. The aerial vibrations having been collected by the auricle, are thence transmitted by the external auditory meatus from the concha or the deep concavity within the position of the antihelix and subdivided l)y the helix to the tympanum. The external audi- tory meatus, about an inch aud a quarter in length, is directed in- ward and forward, upward and downward, and is narrowest at its middle portion. It consists of two portions, an iuterfibro-cartilagi- nous one, the prolongation of the auricle, and an inner osseous one, a part of the temporal bone, both portions l>eing lined with skin. The skin of the outer portion is thick and provided with numerous hair, sebaceous and ceruminous glands. The latter, small, round, brownish-yellow bodies imbedded in the subcutaneous tissue, and giving rise to the punctured appearance of the skin, are modified sudoriferous glauds, consisting, like the latter, of a narrow tube coiled upon itself in the form of a ball, and secrete the cerumen or ear-wax. The latter is said to be composed of fiitty and albumi- nous matters of salts of soda and lime, and has a very bitter taste, a property which has been considered of service in preventing insects entering the ear. The cerumen, which probably consists of seba- ceous matter mixed with the proper secretion of the ceruminous glands, lubricates the meatus. The skin of the inner osseous por- tion of the meatus is very thin, destitute of hairs and glands, and at the bottom of the meatus is continued over the tympanic mem- brane as its outer investing layer. The Structure of the Middle Ear. The middle ear, separated from the external ear by the tympanic memlirane, includes tiie tympanum or drum of the ear, the ear bones, with their ligaments, muscles, the mastoid sinuses, aud the Eusta- 828 STRUCTURE OF THE EAR. chian tube. The tympauum, au irregular cavnty in the interior of the petrous portion of the temporal bone, is about half an inch in height and breadth, and perhaps the sixth of an inch from without inward, is closed in front by the tympanic membrane, at the back by the wall of the labyrinth, and opens above and posteriorly into the sinuses and in front into the Eustachian tube. The tympanic membrane separating, as already mentioned, the external auditory meatus from the tympanum, is about two-fifths of an inch in height and breadth, somewhat funnel-shaped in form, and is disposed obliquely, making an angle of 40° with the floor of the meatus. That part of the membrane drawn inward by the tip of the ma- nubrium of the malleus and constituting a central depression is called the umbo. The oblique position of the tympanic membrane is of advantage, since more sound waves fall vertically upon it than if it were placed vertically. The tympanic membrane is inserted by the greater part of its cir- cumference into a groove which, while in the adult is regarded as a portion of the temporal bone, is in reality the only part visible of an originally entirely separate osseous ring, the homologue of the '^ Fig. 505. B C* Bones of the tyiii)i;irimn cil' the left side. A. Malleus. 1. Ldiig or slender process, li. The handle. 4. Sliorl proeess. .l. Head. B. Incus. 1. Body. '1. Short or posterior process. 3. The long process with the orbicular process 4. C. Stajies. 1. Head. 4,5. Crura. 6. Base. I). The three bones in their natural connection, m. Malleus, .vc. incus, x. Stajies. C*. Base of the stapes. tympanic bone of the lower vertebrates, but which in man, instead of remaining distinct as in them, coossifies as development advances witli the tem})oral bone, and grows outwardly as the osseous external auditory meatus, its morphological significance being thereby entirely lost sight of. OSSICLE,^ OF THE MIDDLE EAR. 829 At tlie point Avherc the ring of bone is wanting the tympanic membrane is attached to the bone above, and being less tense in that position even when thrown into folds is distingnished as the mem- brana flaccida. The tympanic membrane, thin and translncent, is composed of a layer of fibrous tissue, the membrana propria, cov- ered externally by the skin of the external auditory meatus, and internally by the mucous membrane of the tympanum, the latter being continuous with that lining the Eustachian tube. The fibrous layer of the tympanum consists of two sets of fibers, of which the greater part radiate from its center, the remaining ones being con- centrically disposed at tlic periphery. The little ear bones (Fig. 505), three in number, the malleus, incus, and stapes, are disposed within the tympanum from before backward in the order named. The malleus, so called on account of its resemblance to a hammer, is suspended vertically from the floor of the tympanum by a slender band of fibers, the suspensory ligament, which passes into its head, the latter articulates through an oval facet covered with cartilage with the body of the incus. The malleus is also connected Avith the tympanic membrane, its tapering, slightly twisted manubrium or handle passing down into the fibrous layer of the latter as far as its center. From the neck of the malleus, or the constricted portion below the head, two processes are given off. The larger process or processus gracilis projecting at right angles and passing into the Glasserian fissure is attached by ligament to the spinous process of the sphenoid bone. The smaller process gives attachment to the tensor tympani muscle, so called on account of its tensing the tympanic membrane and which, arising from the end of the cartilage of the Eustachian tube, and the contiguous surfaces of the sphenoid and temporal bones, passes through a special canal of the latter into the tympanum. The incus or anvil, situated behind and articulated with the malleus as already mentioned, is also sustained in its position by a fibrous band, passing from its short process to the margin of the opening leading into the mastoid cell. The long process of the incus, curved and tapering, descending nearly parallel with the manubrium or handle of the malleus, terminates in the so-called orbicular process, by which it articulates through cartilage with the facet on the head of the stapes, or stirrup. The orbicular process is in reality a distinct bone, being separable from the incus even at birth ; soon after, however, it becomes so ossified with the latter as to be undistinguishable from it. The stapes, or stirrup, situated inwardly between the incus and the foramen ovale of the vestibule, is disposed at right angles to the long process of the incus, the crura — that is, the portion joining its head and its base, lying hori- zontally in the tympanum. By its annular ligament, the margin of the base of the stapes is connected with the border of the fora- men ovale of the vestibule, the pressure of the base of the stapes against the oval window or the perilymph back of it being regu- 830 STRUCTURE OF THE EAR. latecl by the stapeclius muscle, which, arising within the hollow of the pyramid, or the conical eminence projecting from the back part of the tympanum, is inserted into the head of the stirrup. The mastoid sinuses, so called from being situated in the interior of the mastoid portion of the temporal bone, are irregular cavities lined with mucous membrane, which communicate by a large orifice with the upper and back part of the tympanum. The Eustachian tube (Fig. 504, e), al)out an inch and a half long and somewhat trumpet-shaped in form, extends from the front part of the tympa- num obliquely downward, forward, and inward, terminating by an oval orifice in the pharynx on a level with the turbinated bone at the back of the posterior nasal orifice. The Eustachian tube con- sists of two portions, an upper osseous portion situated in the petrous portion of the temporal bone and opening into the tympa- num, and a lower fibro-cartilaginous portion opening into the pharynx, the two portions being united within the angle between the squamous and petrous portions of the temporal bone. It is lined with mucous membrane provided with ciliated epithelium, continuous on the one hand with that of the tympanum, and on the other with that of the pharynx. The existence of such a tube as that just described, putting the cavities of the middle ear in com- munication with that of the pharynx, as well as the presence of a chain of bones connecting the membrana tympani with the oval window of the vestibule, will become intelligible when the develop- ment of the ear is considered. Functions of the Middle Ear. Such being in general the structure and relations of the tympanic membrane, ear bones, Eustachian tube, etc., if the aerial vibrations collected and transmitted by the auricle to the external auditory meatus throw the tympanic membrane into vibration, the vibrations of the latter will in turn be transmitted by the ear bones through the intermediation of the fluids of the vestibule, etc., to the termi- nal filaments of the auditory nerve, and so give rise to the sensation of sound. The importance of the membrana tympani in audition is shown by the fact that the acuteness of hearing is always more or less aflFected in those cases in which the membrane is thickened, per- forated, or destroyed, and that relief is obtained by the wearing of an artificial membrane if the latter can be tolerated. This becomes perfectly intelligible when it is remembered, as shown by Miiller,^ that while aerial vibrations are communicated to solid bodies like the ear bones only with difficulty and Avith considerable diminution in their intensity, they are communicated very readily to the same, a tense membrane like the tympanic membrane intervening, the fact of the membrane being fixed at the periphery, and having air on both sides of it being also most favorable conditions. That mem- • Physiology, Vol. ii., p. 1248. FUXCTIOXS OF THE MIDDLE EAR. 831 branes of as small extent as tliat of tlie m('m])i'ana tympani wlien stretched are readily thrown into vibration, can be shown by ex- periments like those of Savart ^ in which sand strewed over their surface was cast oif, on sonorous vibrations being excited in their vicinity. It is a well-known fact, that membranes vibrate more powerfully, more intensely, when relaxed than when tensed, hence the sensitiveness to all sounds experienced in facial palsy, which is due to the want of innervation of the tensor tympanic muscles by the filaments of the paralyzed facial supplying it. It is also worthy of mention in this connection that the vibrations of the mcmbrana tvmpani are more intense in proportion as tlie latter approaches a vertical position, as accounting to some extent for the appreciation of sounds by musicians, in some of whom the tympanic membrane is almost vertically disposed, whereas in persons with but little car for music the membrane is very oblique in position. It has already been explained that sounds not only differ in their loud- ness or intensity, but in their pitch or number of vibrations per second as well, and since we hear sounds of different pitch, it is obvious, therefore, that there must be some means of tuning — that is, of tightening or relaxing the tympanic membrane, so that the vibrations of the latter shall be the same per second as those to which the particular note or notes heard are due. That is to say, every sonorous aerial wave — that is, a condensation and a rarefac- tion — bending the tympanic membrane once in and once out, the rate of vibration of the membrane must be the same as that of the vibration of the sonorous body causing it, if the particular sound due to the latter is to be heard. That the membrana tympani is relaxed for sounds of low pitch and tensed for those of high pitch, is shown by the insensil)ility to low tones, and marked appreciation to high ones, being proportional to the extent to which the mem- brane is tensed. Thus, if the mouth and nose being closed, we at- tempt to breathe forcibly by expanding the chest, the air within the tympanum becoming rarefied, the tympanic membrane will be forced in by the external air and rendered more tense, the effect of which is that, as Dr. WoUaston - showed, we become deaf to low sounds. A similar deafness to sounds of low pitch is also produced, the nose and mouth being stopped when a strong effort is made to expire, the increased tension of the membrane being due, however, in this instance to the air being forced into the tympanum through the Eustachian tube instead of being sucked out of it and the mem- brane being pushed outwardly. A sudden concussion may produce temporary deafness in either of the al)Ove ways — that is, by forcing air either into or out of the tympanum. It is evident, from the facts just mentioned, that the function of the Eustachian tube is the maintaining of equilibrium between the air within the tympanum and the air without. Hence if the tube 1 Journal de Physiologie, Tome iv., p. 203. Paris, 1824. 2Philos. Trans., Lond., 1820, p. 300. 832 STRUCTURE, OF THE EAR. be closed, which is usually the case, according as the external air becomes denser, as in descending in a diving-glass, or rarer, as in making high mountain ascents, the tympanic membrane will be pushed in or out in either case, will be rendered more tense and pain and deafness experienced, both of which can, however, be usually relieved by the act of swallowing, which, in opening the Eustachian tube, reestablishes the equilibrium between the internal and external pressure. It may be mentioned, in this connection, that the Eustachian tube is opened by the contraction of the tensor palati, levator palati, and the palato-pharyngeus muscles ; the tensor palati, in drawing the hook of the cartilage outward, and the levator palati, in drawing the end of the cartilage upward and inward, en- large and Aviden its pharyngeal orifice, the palato-pharyngeus fixing the cartilage. With the relaxing of the muscles just mentioned, through the elasticity of the cartilage, the tube then closes again almost entirely, a narrow chink alone remaining. Since, while the Eustachian tube is oj^en, the cavity of the tympanum is in commu- nication with that of the pharynx, it follows that if we swallow several times in succession, the nose and mouth being closed, that the air will be gradually drawn from the tympanic cavity, the membrane being rendered tense by the external atmospheric pres- sure, as in the case just mentioned, in which forced inspiratory ef- forts were made, and an insensibility to low sounds experienced. That the tympanic membrane is tensed for high sounds is shown by the fact that in certain individuals,^ whose ordinary limit of ap- preciation was of sounds due to fifteen hundred vibrations per sec- ond by voluntary contraction of the tensor tympani muscle, this was increased, so that sounds could be heard due to 2,500 vibrations per second. There can l>e little doubt, then, that the membrana tympani is relaxed or tensed, according as the sonorous vibrations are low or high in pitch, and that the variations in the tension of the membrane are regulated by the action of the tensor tympani muscle. While there is a great difference in individuals as regards the appreciation of sounds, some persons being insensible to the hum of insects, the chirrup of the sparrow, the squeak of the bat, others to the high sounds of small organ-pipes, or even the highest notes of the piano, there is a limit, nevertheless, to audibility in all, the tympanic membrane failing to link together into a continuous tone vibrations succeeding each other less rapidly than 16 a second, or more so than 38,000 a second. In the former case, we are con- scious only of separate shocks ; in the latter, we are unconscious of sound altogether. The range of audibility lying within the above limits embraces, therefore, about 1 1 octaves, of which about two- thirds, or 7 octaves only, are, however, made use of in music. It is true that we obtain from the lowest C of the piano the note due to 32 vibrations per second, and from the lowest A of the new grand piano that due to 27 vibrations per second, and from a 'Blake, Trans, of the Amer. (Jtological Soc, Vol. v., p. 77. Boston, 1872. RANGE OF MUSICAL SOUNDS. 833 closed organ-pipe 1 G feet long, or an open one 32 feet long, the lowest C, due to 16 vibrations per second, but the latter sound, and that of the lowest C or A of the piano, are so unmusical, so dull and groaning in character, that they are ])ut little used. The deep- est tone made use of in orchestral music being that due to the E string of the double bass, giving 41]- vibrations, the highest that of the D of the piccolo flute, due to 4,752 vibrations per second ; it may be said that practically the range of musical sounds is confined be- tween 40 and 4,000 vibrations per second, the highest C of the piano reaching 4,224 vibrations per second — that is, in round num- bers, as just said, about 7 octaves. Even within such limits the im- mense number and kind of sonorous waves that fall upon the tym- panic membrane while listening to a grand opera as given by the leading artists, together with full choral and grand orchestral ac- companiment, must impress one with the remarkable acoustic prop- erities of the membrana tympani, so small and delicate, and yet so susceptible to such an immense number and variety of sounds. But little imagination is required to picture to one's self, during tlie performance of an opera, the sonorous waves flowing across the auditorium, and breaking upon the drum of the ear like those of the ocean upon some weather-beaten rock or beach, the long waves, from 35 to 12 feet in length proceeding from the deep bass instru- ments and voices of the bassos like billows from the distant sea, the short ones from 30.3 inches in length, like ripples or white caps, from the violins, flutes, and voices of the tenors and sopranos, with intermediate ones of different lengths, and yet all following each other in such orderly mathematical sequence that, amidst such a variety of sounds, we are conscious of nothing but melodious and harmonious tones. From the fact of our being able to appreciate the latter, it is obvious that the tympanic membrane is susceptible of being impressed by simultaneous as well as by successive sounds, and while the limits of this work do not permit of any considera- tion of harmony, discord, of chords, of consonant intervals, or those that give the ear a sense of relief, or dissonant ones that must be resolved, etc., it seems proper to jioint out and illustrate the fact that the vibrations to which harmonious sounds are due are in a definite ratio to each other, and, that, whatever the cause may be, sounds are harmonious in proi)ortion as the ratio between the number of the vibrations giving rise to them is a simple one. The simplest ratio being one to one, two sounds, as produced by the siren, for example, will l)e in perfect union, if the pitch of both be the same. The next simplest ratio being 1 to 2, a harmonious sound will remain, if with the fundamental its first overtone above, or octave, be at the same time given — that is, if with Do^ C^ 256 vibrations per second, Do*, C* 512 vibrations per second be also sounded. The waves, never interfering with each other, will give rise to no discord, and the two sounds blended into one may be continued indefinitely. Proceeding in the same manner, according 53 834 STRUCTURE OF THE EAR. to the simplicitv of the ratio, the next in order will be that of 2 to 3, or C to G — that is, with Do^ C 256 vibrations per second, Sol'' G^ 384 vibrations per second may be sounded ; for there being for every two waves of C three waves of G, there will be a coincidence for every second wave of C and every third wave of G. The next ratio being that of 3 to 4, or C and F, C'^ and F^ Fa\ 341.3 vibrations per second, may be sounded together. Although we have already shown by the siren that the sounding of the notes C E G, together, give rise to the harmonious major chord, nevertheless, according to the law that the smaller the ratio of vibration between diiferent sounds the more perfect the harmony, the combination of C with E — that is, in the ratio of 4 to 5, or, as in the above, of 256 to 320 — is a less pleasing one than that of C to F, in which the ratio is 3 to 4. It is the want of harmony of F with G that excludes it from the cord C E G C ; the cord C F A C is, how- ever, a harmonious one. Continuing the next ratio, that of 6 to 5, or of C to E flat, a minor third, consistently with its ratio, being less simple than that obtaining in the major third, is a less harmo- nious one. Finally, as illustrating a step further the law just enumerated, it may be mentioned, though well known, that the in- terval corresponding to a tone in which the vibrations giving rise to the two notes C" D^, for example, are in the ratio 8 to 9, 256 to 288 is a dissonant one, and that the interval of a semitone C to D flat, in which the ratio ^is 15 to 16, is a very sharp, grating, and dissonant one. About five hundred years before our era^ it was shown by Pythagoras that if a stretched string was so divided into two parts that one was twice the length of the other, and the two parts of the string sounded simultaneously, that the note emitted by the short part was the octave emitted by the long one. Contin- uing to experiment, this celebrated philosopher next showed that if the string be divided in the ratio of 2 to 3 then the interval be- tween the notes emitted would be that of a fifth ; and further, that, according to the ratio in which the string was divided, the remain- ing more or less consonant intervals would be heard, the harmony of the two sounds being proportional to the simplicity of the ratio of the two parts into which the string was divided. 1st, Note, C Lengths of the string, 1 Number of vibrations, 256 288 This important law, the first step made in the physical ex})laua- tion of musical intervals, Pythagoras, however, did not account for, it remaining for later investigators to show that the vibrations of strings are inversely proportional to their length. It has just been mentioned that while the combination of a fundamental tone with its octave, for example, is a consonant, pleasing one, giving ' Montucla, Hist, des Matheraatiques, Paris, An. vii., Tome i., ]>. 114. 2(1. yd. 4th. 3th. Gth. 7th. 8th. D E F G A B c J88 4 320 341 t 384 3 426 _8_ 480 512 CA USE OF BEA TS. 83 5 rise to no discord, tliat of the interval of a tone, or of a semitone, is a dissonant, disagreeable, discordant one. It remains for us now, therefore, to determine, if possible, the physical cause of discord. It will be remembered that in the double siren of Helmholtz there are two series of 12 orifices, each common to both sirens; such be- ing the case, if both these series of orifices are opened and air forced through the instrument, the tM'o sounds produced will be in unison, and will continue so, since the pitch of both will be the same however low or high the sound may be. In describing the double siren attention was also called to "the flict that, by turning the handle of the upper siren the orifices of the wind chest will either meet or retreat from those of its retreating disk, the pitch of the upper siren rising or falling accordingly. But the relation of the rotation of the handle to that of the upper wind chest is such that if the handle be turned through 45 degrees the wind chest turns through 15 degrees, or through the 2V of its circumference, which causes the orifices of the upper wind chest to be closed at exactly the same moment that the 1 2 orifices of the lower wind chest are opened, and vice versa, the effect of which is that the in- tervals between the pufFs of the lower siren — that is, the rarefac- tions of its sonorous waves — Avill be filled up by the puifs or con- densations of the waves of the upper one. But if the condensation of the one set of sonorous waves coincides with the rarefactions of the other set there will he neither condensation nor rarefiiction, upon which all sound depends, the fundamental sounds of the siren will be extinguished through the interference of the two sounds, as it is called, and absolute silence would result were it not for the presence of the overtones of the siren. Rotating, however, the wind chest through 30 degrees, or the -^^ of its circumference, by turning the handle through 90 degrees, the ])uffs or condensa- tions of the sonorous waves of the loAver siren will coincide with those of the upper one, reinforcing the latter ; and as this latter takes place once for each 90 degrees, there will be 4 of these rein- forcings, or beats, as they are called, for every 3G0 degrees, or for one rotation of the handle. The change in the pitch of the sound emitted by the upper siren induced by the rotating of the handle, the pitch of the sound emit- ted by the lower siren remaining the same, gives rise then to beats, of which there will be four for every one rotation of the handle. For a time, however, there may be heard twelve or eight beats ; when such is the case, it is due to the strength of the second or first overtone being sufficient to overpower the fundamental, which vi- brating three times and twice as rapidly as the fundamental, will, of course, give rise to three times, or twice as many beats. It is through the presence of these overtones that, though the tone of the fundamental may swell or sink as the handle is turned, sound is still heard, even though the handle reach the position at which the fundamental sound through interference is extinguished. Beats 836 STRUCTURE OF THE EAR. can be readily produced by tuning forks which are especially suited for this purpose, no overtones being generated if the forks be prop- erly toned. Let us suppose, for example, that of two standard tuning forks Do', each giving 256 vibrations per second, and whose sounds are therefore in unison, one of which be weighted just suffi- ciently to cause it to vibrate a little more slowly than the other, say 255 times. The two sounds then emitted will no longer flow^ on continuously in unison, there being now alternate diminutions and reinforcements of the sounds or beats, and in this particular case one beat per second, which, it will be observed, is exactly the difference between the two rates of vibration of the two forks, 256 and 255. A moment's reflection w-ill make it clear why the beats should occur, and at such a rate. Since the one fork vibrates 256 times in a second, and the other 255 times, it is evident that at the end of the second the wave of the latter fork will be one vibration behind that of the former, and at the end of a half second a half a Avave behind, the one fork having made 128 vibrations, the other Vllh, but at that moment the condensation of the one wave coin- ciding with the rarefaction of the other, the sounds will be extin- guished through their complete interference with each other. From the half of the second onward, however, until the end of the second, the condensations reinforce each other more and more, until at the end of the 256th vibration of the one fork, and the 255th of the other, condensation coincides Avitli condensation, and rarefaction with rarefaction, the full effect of both sounds being then expei*ienced. Similarly, from the half second where the interference is complete backward to the beginning of the second, condensation coincides more and more with condensation, rarefaction with rarefaction, until at the beginning of the second, of course, as at the end, the coinci- dence is complete. Suppose, however, that the two forks vibrate 240 and 234 times a second, then at the end of the first ^ of a sec- ond, one fork will have generated 40 sonorous waves, the other 39, the one wave being one vibration ahead of the other, and therefore, at the end of the -^^ of a second, half a vibration ahead. This in- stant being, however, that at which interference is complete, during Avhich the sound is extinguished, the time elapsing on the one hand between it, or the ^V of the second, and the beginning of the second, and on the other to the end of the ^ of the second, will be charac- terized, as in the preceding case, by a gradual diminution, followed by a gradual augmentation of the sound or one beat ; but as this is repeated in this case six times during the second, there will be six l)eats, which, it will be observed, is exactly the difference between the two rates of the forks, 240 and 234. Experimenting this way with forks, pipes, etc., it can be proved that the number of beats per second is always equal to the difference between the rates of vibration of the two sounds to whose interference they are due. Now it has been shown by Helmholtz that if the beats per second succeed each other less rapidly than 33 per second, the sound is not RESULTANT TONES. 837 disagreeable, but if at that rate, the dissonance becomes then abso- lutely intolerable. As the number of beats per second, however, in- creases, the dissonance diminishes, and when the beats have reached the rate of 132 a second, they disappear and discord vanishes. Beats are therefore the cause of dissonance or discord, and intervals free from them will be harmonious. Thus the fundamental, due, for example, to 256 vibrations per second, Avhen continued with its oc- tave to 512 vibrations is a harmonious one, free from beats, since the difference in the rate of vibration, or 250, is too high to admit of them. The interval of the fifth C and G is still harmonious, the difference in the rate of vibration, 384 — 256 = 128, being also too high. On the other hand, the interval of the fourth C and F due to 341 and 256 vibrations per second respectively, is somewhat dissonant, the difference between the rates of vibration being 59, admitting, therefore of that number of beats below the limits at which discord vanishes ; and the interval of C and E more disso- nant still, the diflPerencc in their rates of vibration being 64, the notes being due to 256 and 320 vibrations per second, respectively. It should be mentioned in this connection, in order to avoid any misconception, that the ]>henomenon of beats is of an entirely dif- ferent nature from that of the resultant tones discovered by Sorge, Tartini, and Helmholtz. That resultant tones should ever have been considered as identical with beats, is not so strange, since the rate of vibration of the first difference tone, or the loudest resultant tones like that of beats, is equal to the difference in the rates of vibrations of the two primary sounds producing them, which led the celebrated Young to regard resultant tones as due to the link- ing together of rapidly recurring beats. That a resultant tone is not made up of beats is shown by the fact that while a resultant tone due to thirty-three vibrations per second is smooth, consonant, musical beats succeeding each other at that rate, as already men- tioned, are most dissonant. In concluding this necessary digression upon the nature of mu- sical intervals, discords, beats, resultant tones, etc., it must be observed that whether they are caused in the manner indicated, or however they may be accounted for physically, hereafter, in any case, no explanation whatever is offered why one rate of vibration should affect us agreeably, and another rate disagreeably — that is, if sounds are harmonious through the absence of discords, why should the presence of the latter give rise in us to a sense of discomfort, dissonance? Nor have we any reason to hope, judging from the past, that the study of mere acoustics will ever throw any light upon our sensations of tone subjectively, or contribute to the prog- ress of music objectively. Indeed, it appears to be generally for- gotten by the cultivators of harmony that the best music was com- posed when acoustics was in its infancy, to this day, the best illustration of theoretical harmony being taken from the works of Mozart, Handel, Haydn, the science of sound having not added one cord or progression that was not known to Bach. 838 STRUCTURE OF THE EAR. llemarkable as are the properties of the tympanic membrane, and essential as it is undoubtedly in normal hearing, when it is remem- bered that it, together v;\i\\ the remaining part of the middle as well as the external ear, is only the intermediate means by which the terminal filaments of the auditory nerve are excited, it becomes intelligible why after the rupture or eyeniibsence of both mem- branes, hearing, though impaired, and appreciation of musical sounds are still possible. The innumerable and diiferent kind of sonorous waves imping- ing upon the tympanic membrane and throwing it into vibration to be appreciated in consciousness as sounds, must be thence con- ducted to the vestibule of the internal ear. This is accomplished by the chain of ear bones stretching across the tympanum from the tympanic membrane to the foramen ovale of the vestibule. The ear bones, while three in number, in point of fact may be regarded physiologically as being equivalent to one long bone, vibrating to and fro with the tymj^anic membrane. That such is the case is not only shown by the manner in which the bones are articulated with each other, but from the fact that in the lower vertebrates the homo- logue of the stapes is a long rod-like bone, passing from the tym- panic membrane to the vestibule, while the homologues of the incus and malleus are not situated Avithin the tympanum, but outside of it, entering into the formation of the lower jaw. Movements of the Ear Bones. The articulation of the malleus and incus is such that w^hile Mith the outward movement of the manubrium of the malleus, the head of the latter moves freely in the joint, Avith the inward movement of the latter the malleus and incus move together as one bone, the lower projecting margins Fig. 506. of their articulating surfaces interlocking together like the teeth of a Bregnet watch key.^ The malleus and incus move freely about an axis (« x, Fig. 50(5) one end of which passes through the anterior ligament of the malleus, the other end through the ligament of the incus. In the case of audition, as in that of vision, the sensation lasts longer than the stimu- lus. Hence, when the interval of time elapsing between two sounds such as that of a pendulum beating seconds is less than the yi^ of a second, the sensations of the two sounds are fused into one sensation. The ear, like the eye, experiences also fatigue. ' Ilelmlioltz, Sensations of Tone, trans, by Ellis, 1875, p. 196. /ffe The ligaments of the ossicles. The figure rep- resents a nearly horizontal section of the tym- panum, carried through the head of the malleus and incus. M. Malleus. /. Incus. /. Articular tooth of incus. Ifja, Anterior and Ifje, External ligament of the malleus. Uj inc. Ligament of the incus. The line ax represents the axis of rota- tion of the two ossicles. (Hensen.) MOVEMENTS OF OSSICLES OF EAR. 839 Thus, for example, when the sound of a tuning fork becomes in- audible to one ear, if the fork be placed to the opposite ear, the sound will be heard distinctly. It is due to the ear becoming fatigued that a person who has been listening for some time to a particular overtone fails to hear the same when the latter is sounded witli its fundamental and the accompanying series of over- tones. The note sounded under such circumstances seems to be poor in quality. Difference of opinion still prevails as to the number of vibrations that must fall upon the ear to give rise to the conscious- ness of sound. According to some from two to five vibrations per second will cause a sensation of sound, a greater number of vibra- tions being, however, necessary, as we have seen, to produce in con- sciousness the sensation of a distinct musical note. In audition, as in the case of the other senses, there is a minimum stimulus necessary for the production of sound. It is said that a pith ball weighing one milligramme (0.0154 grain) falling through 1 mm. (Jg of an inch) upon a glass plate will be heard at a distance of 91 mm. (3.6 inches). The " constant proportion," that is the incre- ment necessary to cause the sensation of sound, is said to be, as in the case of the sensation of touch, temperature, one-third of the original stimulus. In inward movements of the tympanic mem- brane the three ear bones move as one bone around the axis of suspension, the maximum amplitude of the center of the tym- panic membrane being from the -^j to ^ mm., that of the stapes, however, only from the Jg- to J^ mm. That the stapes is pressed against the liquid of the vestibule by the movement of the tympanic membrane and ear bones can be shown experimentally, as by Helmholtz, by fitting a slender glass tube into the semicir- cular canal and filling the vestibule and part of the tube ^\ith water, when, through the forcing of the tympanic membrane in- ward, the water will be seen to rise nearly a millimeter {-^^ of an inch). In outer movements of the tympanic membrane, while ordinarily the articulating processes appear to be retained in apposition by the elastic reaction of the ligament and the stapedial attachment of the incus, in cases where the tympanic membrane is abnormally forced outward the malleus leaves the incus behind, alone complet- ing its outward motion. By this provision of nature the stapes escapes being torn out of the oval Avindow. The movement upon the tympanic membrane and ear bones can be graphically studied and recorded, as by Koenig,^ by attaching a style to the incus or malleus, the tympanic membrane being thrown into vibration by two organ-pipes, and the sound of the latter rein- forced by a resonator. Inasmuch as the distance from the tip of the manubrium, where the aerial waves fall, that is, the point of the application of the pressure to the axis of rotation, is one and a-half times the distance 1 Quelques Experiences d'acoustique, 1882, p. 29. 840 STBUCTURE OF THE EAR. to the long process of tlie incus. Where the effect is produced the amount of movement of the stapes is only two-thirds that of the tip of the manubrium, the force exerted by the stapes is one and a-half times as great as that exerted by the tip of the manubrium. In other words, the parts involved are so disposed as to constitute a lever with unequal arms, the long arm carrying the light weight representing the distance from the maniibrium to the axis of rotation, the short arm carrying the heavy weight the distance from the axis to the stapes. Such being the mechanical relation of the parts it follows that a motion of large amplitude but of little force, such as falls upon the tympanic membrane, becomes a motion of small amplitude but of great force, falling upon the fluid of the vestibule at the oval window. It is in this way that aerial waves, falling upon the tympanic membrane, are transformed into the water waves of the vestibule. Structure of the Internal Ear. The internal ear includes the labyrinth and the auditory nerve. The labyrinth, so-called on account of its highly complex structure, consists of the vestibule, semicircular canals, and cochlea. Though these parts are imbedded in the petrous portion of the temporal bone, their osseous walls are independent of the bony structure of the latter. This is well seen at birth, when the whole labvrinth can Fig. 507. 1, 2, 3. Turns of cochlea. 4. Feuestra rotunda. 5. Fenestra ovalis. 8, 9, 10. Posterior semicir- cular canal. 11. Superior semicircular canal. 12. External or horizontal semicircular canal. _, be readily excavated from the surrounding loose osseous substance. The vestibule, situated between the tympanum and the internal auditory meatus, is a somewhat oval-shaped cavity about 5 millime- ters (I of an inch) in diameter, passing postero-externally into the semicircular canals, and antero-internally into the cochlea, and MEMBILiXO US LAB YPxINTH. 841 communicatintr with the tympanum by the foramen ovale. The semicircidar canals, so-called ou account of theii' form, are three in number and are named from their position superior, posterior, and inferior, or external, the two former being disposed vertically, the latter horizontally. Each semicircular canal expands at one ex- tremity into a bottle-like dilatation, the ampulla, Avhich communi- cates with the vestibule. Of the undilatcd extremities two unite, and then with the remaining one also open into the vestibule. The three semicircular canals thus communicate with the vestibule by five orifices. The vestibule, semicircular canals, and cochlea, as well, are lined throughout with a thin periosteal membrane, which in passing over the foramen ovale and foramen rotundum thereby close these orifices. Within the cavity of this membrane is found a serous-like fluid, the liquor cotungii or perilymph of Breschet, an appropriate name on account of its surrounding the membranous labyrinth also containing a similar fluid, the endolymph of Breschet or lic|Uor of Scarpa. The membranous labyrinth, so called on account of its membranous structure, and receiving the terminal filaments of the internal auditory nerve, floats in the perilymph within the bony labyrinth, with the walls of which it is more or less connected by delicate fibrous bands. The membranous laby- Fic;. 508. rinth, like the osseous, consists of three parts, vestibule, semicircu- lar canals, . and cochlea. The membranous vestibule (Fig. 508), however, is composed of two dis- tinct sacs or pouches, the utriculus (U) and sacculus (S), the former of which, the larger, occupies the hemi-elliptical fossa of the bony vestibule, and gives off three membranous semicircular canals, the latter, the smaller, occupies the hemispherical fossa and gives off through a narrow duct, the membranous cochlea. The sacculus and utriculus, while not communicating directly, do so indirectly through the membranous aqueduct (A) of the vesti- bule, the latter being formed through union of the small ducts pro- ceeding from the sacculus and utriculus, respectively. Adhering to the inner surface of both the utriculus and sacculus, may be seen white, discoidal masses, consisting of minute crystalline particles of calcium carbonate, the so-called otoliths or otoconia. The mem- branous, semicircular canals, about one-third of the diameter of the osseous ones, in the perilymph of which they float, resemble the latter in form and general disposition, being three in number, dis- posed superiorly, vertically, and horizontally, expanding into ampulhe, and communicating with the membranous vestibule by five orifices. The membranous vestibule and semicircular canals, Membranous labyrinth. Cs. Semicircular canals, t'. L'triculus. S. Sacculus. A. A(jue- duct of vestibule. Cr. Ductus reuniens. Co. Cochlea. 842 STRUCTURE OF THE EAR. Fig. 509. consisting of three layers, an outer fibrous, an inner epithelial, and an intermediate niembrana propria, receive, as already mentioned, the terminal filaments of the vestibular branch of the internal audi- tory nerve. The latter divides at the bottom of the internal audi- tory meatus into three branches, the first of which, passing through the pyramidal eminence of the l^ony vestibule at the superior cribri- form spot, is distributed to the utriculus and ampulhe of the superior and inferior or horizontal semicircular canals ; the second, passing through the hemispherical fossa at the middle cribriform spot, is distributed to the sacculus ; and the third through the ampulla of the bony posterior semicircular canal at the inferior cribriform spot, to the ampulla of the membranous posterior semicircular canal. Just in those situations where the nerve fibers penetrate the mem- branous vestibule (macula acustica) and the membranous semicircu- lar canals (crista acustica), their outer or fibrous layer is intimately associated through connective tissue with the bony wall of the vestibule and canals, the perilymph being here absent.' The ul- timate nerve fibers having passed through the membran- ous vestibule and canals, finally terminate in what may be called the auditory epi- thelium, Avhich appears to consist essentially of colum- nar cells intermixed w i t h spindle-shaped ones support- ing long, firm bristles, the auditory hairs (Fig. 509), which penetrate into the en- dolymph and support the oto- liths. The otoliths, otocrania, or ear stones, are small, rhom- bic or octohedral crystals con- sisting of calcium carbonate with traces of other salts and organic matter. The function of the otoliths is very obscure. By some they are regarded as adjuvants, by others as dampers of sound waves. They have also been supposed to aid in some way the appre- ciation of the direction and extent of our movements. Up to the present moment, in order to prevent confusion, we have purposely avoided mentioning, except incidentally, the bony ' M. V. Lenhossek, Beitriige zur Ilistologie des Nervensystems vuid der Sinnes- organe, 1894, s. 1. Diagram of the auditory epitlieliuui, and the mode of termination of tlie nerves of the ampullie. 6. Spindle-shaped cells, each supporting an auditory hair (8). 7. Basal sujjporting cells. .3, 4. Nerve fiber passing through the tunica propria to join the plexus in the epithelium. (M. Schultze.) STRUCTURE OF THE COCHLEA. 843 or membranous cochlea, and yet it will be found that the cochlea, though, at first sight, resembling but little a semicircular canal, consists, like the latter, of a bony tube enclosing and attached to a membranous one, the latter floating in perilymph and containing endolymph. For simplicity sake, k't us, in considering tlie struc- ture of the cochlea, begin by disabusing our minds of it being a coiled tube, and regard it as a straight one, as it is throughout its whole length in birds, and at its commencement in man ; and fur- ther, let us begin our description of its structure by supposing that we are viewing the cochlea at its commencement in transverse section, and endwise, as represented in Fig. 510. Looking at the cochlea Fig. 510. Section through one of the coils of the cochlea, diagrammatic. Mag. ;]0. .ST. Scala tympaDi. .SI'. .Scala vestibuli. CC. CanalLs cochleae. 1. Membrane of Keissuer forming it.s vestibular wall. a. Limbus laminae spiralis, b. Sulcus spiralis. 2. Cochlear nerve. 3. Lamina spiralis, /hc. Mem- brana tectoria. mh. Membrana basilaris. de. Rods of Corti. 4. Ligameutum spirale. from such a point of view, it will be seen to consist of a bony tube, divided by a septum partly bony (lamina o.ssea), partly membranous, into an outer and inner space, the latter communicating through the foramen rotundum M'ith the tympanum, and called, therefore, the scala tyrapani ; the former continuous with the bony cavity of the vestibule, and communicating, therefore, indirectly through the foramen ovale with the tympanum, and called the scala vestibuli. This may be at once .shown by readjusting the cochlear portion of the section that we have just been considering to the remaining portion of the bony labyrinth, and passing bristles througli the foramen rotundum and ovale, supposing the membrane passing across this opening and the stapes be removed. Conceiving, however, that the cochlea be a straight tube, and supposing it to be divided longi- tudinally, it will be found that the bony, membranous partition (Fig. oil) is absent at the end of the cochlea (helicotrema), the end 844 STRUCTUEE OF THE EAR. opposite to the vestibule, the consequence of which is that the bristles just passed through the foramen ovale from the tympanum, if continued onward, after traversing the scala vestibuli, will pass at the end of the cochlea into the scala tympani, and thence, through the foramen lotundum, reach the tympanum. Such being the rela- tions of the scala vestibuli and scala tympani to each other and to the vestibule on the one hand, and to the tympanum on the other, on the supposition that the cochlea is a straight tube, it is obvious Fig. 511. I)iagrammatic view of the relative position of the parts of the ear. EM. External meatus. T.v^r. Tympanic iiiembraue. Ty. Tympanum. ^I. ^lalleus. I. Incus. S. Stapes. li. Round window. (). Oval window. SG. Semicircular canal. U. Utriculus. S. Sacculus. V. Vestibule. SV. Scala vcstibula. ST. Scala tympani. MC. Membranous cochlea. LS. Lamina ossea. E«. Eustachian tube. AN. Auditory nerve. that if the latter be turned two and a-half times upon itself around an axis or modiolus from right to left in the right ear, and the re- verse in the left, the apex being situated downward, forward, and outward, that the above relations will not in any way be essentially changed. From an inspection of Fig. 510, representing the cochlea in transverse section, it will be observed, however, that the mem- branous portion of the septum dividing the interior of the cochlea into the scala vestibuli and scala tympani, and attached to the osseous wall by the ligamentum spirali, consists of two layers, a basilar membrane, and a tectorial membrane, a space intervening between the two, and that just at the point where the tectorial mem- brane is attached to the osseous lamina, which in the coiled tube is, of course, spirally disposed, a third membrane, the membrane of Reissner, passes obliquely across to the outer osseous wall. As a matter of fact, however, as both ends of the cochlea are covered in by membrane, the vestibular scala is separated from the tympanic scala by a membranous tube which is given off by the membranous sacculus (Figs. 508, 511) through the ductus rcuniens just as the membranous semicircular canals are given off by the utriculus, the other end of the membranous cochlear tube being attached by its pointed blind extremity to the wall of the cupola, the latter partly bounding the helico- RODS OF CORTI. 845 trenia. And just as the membrauoiis seniicircular canal, filled with endolymph and floating in perilymph, is attached to the Fig. o12. Fi,. Cr. ' Diagrammatic view of the osseou.s cochlea laid open. 1. Modiolus or ceutrai pillar. 2. Placed on three turns of the lamina spiralis. .3. Scala tympani. 4. Scala vestibuli. wall of the bony semicircu- lar canal, so is the mem- branous cochlea, filled with endolymph and floating in perilymph, attached to the wall of the bony cochlea, the membranous cochlea, however, being spirally dis- posed like the bony cochlea enclosing it (Fig- 512). The membranous cochlea differs, however, from the membranous semicircular canal, not only in being coiled upon itself, but in the highly complex character of the structures lying in the space intervening between the basilar and tectorial membranes, known as the rods of Corti, which receive the terminal filaments of the cochlear branch of the in- ternal auditory nerve. The rods of Corti are stiff", rod-like bodies, dis- posed in two sets, an inner set and an outer set ; the in- ner numbering about 6,0( »0, the outer about 4,500. The inner rods being inclined outwardly, and the outer rods inwardly, the two sets of rods meet at their heads, the space between the rods- basilar membrane — being kno ^m^ LO U, V Scmi-diagramniatic view of part of the basilar mem- brane and tunnel of Corti of the rabbit, from above and the side. Much maguiticd. /. Linibus. Cr. Kx- treniity or crest of limbus witli teeth-like projections. bh. Ba.silar membrane, p. I'erl'oratiou.s lur transmis- sion of nerve fibers -V, which are lepresented at the lower part of the figure, but omitted for the sake of clearness in the upjier. h: l-ilteen of the inner rods of Corti. /li. Their flattened heads seen from above. cr. Nine outer rods of Corti. Ac. Their heads, with the phalangeal processes extendingoutward from them and forming, with the two rows of phalanges, the lamina reticularis. Ir. The fibers of the outer rods are seen to be continued into the striation of the basi- lar membrane, through which the connective tissue fibers and nuclei of the undermost layer are seen. Portions of a few of the basilar processes of the outer hair-cells remain attached to the membrane. (liiAiN und_Sii.\RiM:v. ) -that is, between the latter and the wn as the canal of Corti, The inner 846 STRVCTUliE OF THE EAR. rods support on their inner surfoce one row of epitlielial cells, the inner hair cells, so called on account of their terminating in short, stiff hairs ; the outer rods on their outer surface three or four rows of siruilar cells, though somewhat more elongated than the outer hair cells. The hairs of the latter pass through ring-like structures, the reticulum, attached to the heads of the outer rods. Both the outer and inner hair cells, in all probability, receive, directly or in- directly, the terminal filaments of the cochlear nerve (Fig. 513). The latter, after passing through the foramina of the spiral tract at the bottom of the internal auditory meatus, ascend through the axis of the cochlea, and thence traversing the lamina ossea spiralis perfo- rate the basilar membrane, and so reach, by intermediate filaments, the hair cells. Bearing in mind that the base of the stapes is adher- ent to the periosteum lining the vestibule and covering the foramen ovale ; it is evident that the vibrations of the tympanic membrane, in being transmitted through the ear bones to the perilymph filling the bony labyrinth, will throw into vibration the endolymph filling the membranous labyrinth and the hairs projecting into it, and consec{uently the auditory nerve, regarding, as we do, the hairs as the terminal filaments of the vestibular and cochlear nerves, into which the auditory nerve divides in the meatus, whence the vibra- tions, in being further transmitted, more especially by the fibers of the cochlear nerve, to the temporo-sphenoidal convolutions of the cerebrum, give rise to the sensation and jierception of the sound. With reference to the function of the membrane cover- ing the foramen rotundum, the membrana secondaria, which con- sists on the tympanic side of the mucous membrane, and on the cochlear, of the periosteal layer lining the scala tympani of the cochlea ; while nothing is positively known, in all probability it is pushed outward, as the stapes is pushed inward, which would ob- viously be of advantage in absorbing some, at least, of the super- fluous sonorous wave motion. Such being, in general, the disposi- tion and relation of the parts of which the internal ear is composed, and the manner in Avhich the auditory nerve is distrilmted to it, is thrown into vibration, it is to be expected that such a complexity of structure is correlated with a corresponding differentiation in function. As a matter of fact, however, little has been definitely estaldished as regards the specific functions of the vestibule, semi- circular canals, and cochlea, which is due, no doubt, to any experi- mental investigation being so ditficult on account of the nature of the case, and from the pathological and clinical data on the subject being so meagre and unreliable in character. In the absence of such evidence the facts of comparative anatomy have been appealed to as a means of elucidating the functions of the internal ear. It is w^ell known to anatomists that the organ of hearing exists in the lower animals in a very rudimentary condition ; thus, in certain of the Crustacea, for example, the ear consists of an invagination of the tkin, a cutaneous pit lined with hairs, situated in the basal joint of she internal antennae, which may remain open and contain particles COMPARATIVE ANATOMY OF EAR. 847 of sand, or may be closed and enclose calcareous otoliths. A similar vesicle, lined with ciliated epithelimn, and containing otoliths, is also found in the mollusca situated upon the infra- oesophageal portion of the nervous collar surrounding the alimentary canal. On the supposition that the vesicle just described as occur- ring in the Crustacea and mollusca, and even in lower forms of life, as in the annelida, hydrozoa, etc., is a rudimentary organ of hear- ing, its functions must be limited almost entirely to the appreciation of the intensity or loudness of sounds — at least it is difficult to con- ceive of animals, relativelv so IomIv oriranized, being; affected to anv very great extent by ditference in pitch and quality. If such is the case, and it be admitted that this vesicle, or otocyst of the lower animals, is the homologue of the vestibule of the higher, which the study of the development leads us to suppose, then it follows that the function of the vestibule in man is the appreciation of the in- tensity of sound. In passing from the invertebrata to the verte- brata, and more particularly to the fishes, we find, with the excep- tion of the amphioxus, in which the ear is absent altogether, that the organ of hearing becomes more complex as avc ascend through the successive forms of piscine life. Thus, in the myxine, the ear consists of a vestibule with one semicircular canal ; in the lamprey of a vestibule with two semicircular canals ; and in the teleosts of three with a rudimentary cochlea as well. Xow, Avhile it is evident that it would l)e of advantage to fishes to be able, not only to dis- tiusruish loud from low sounds, but also the direction from which the sounds proceed, the appreciation of melodious and harmonious ones would be of but little use, and since the homology of the semicircular canals of the lower vertebrates with those of the higher ones is un- doubted it is still held by some physiologists that our appreciation of the direction of sounds is connected in some way with these struc- tures. However that may be, experiments upon animals and clinical and pathological observation in man already referred to have shown conclusively that the maintenance of equilibrium depends, to a certain extent, at least, upon the integrity of the semicircular canal. To what extent the inability in maintaining equilibrium in such cases is due to the hearing being impaired, and how much to the transmission of the afferent impressions to the cerebellum being interfered with, upon wliich the maintenance of equilibrium partly depends, is difficult, if not impossible, to determine ex- actly. By a method of exclusion, then, the inference is rather forced upon us, that our sensation of tone dejiends, in some way, upon the cochlea, the structure of which undoubtedly suggests that its function is rather concerned with the appreciation of the quality of sound, a sort of universal resonator, than with that of pitch or intensity. Regarding the rods of Corti, and the hair cells lying upon them, as so many piano keys and strings appropriately tuned, it is obvious that it would analyze sounds, like a series of resonators. The objection offered to the above ingenious view of Helmholtz, that the rods of Corti being absent in the rudimentary cochlea of birds, 848 STRUCTURE OF THE EAR. cannot be essential for the recognition of tones, is not a necessarily fatal one, since, thongh many birds can sing, it does not follow that their sensations and ideas of melody and harmony should be as de- veloped as that of man ; on the contrary, in the absence of a com- plex brain, it is difficult to comprehend how they should have any considerable appreciation of musical sound. A more important objection than that just mentioned is that the length and disposition of the rods of Corti do not vary to the extent that the hypothesis of Helmholtz demands. It has been suggested, therefore, that it is the basilar membrane present in birds as well as mammals that vibrates sympathetically rather than the rods of Corti, the basilar membrane being regarded as consisting of parallel strings of different lengths, tensed radially, but relaxed longitudinally, con- ditions which are consistent with the mechanical theory involved. It would appear, therefore, that the so-called auditory nerve con- sists really of two different nerves, the cochlear nerve, the auditory nerve proper, the pathway for the impulses giving rise to hearing, and the vestibular nerve transmitting the impulses upon which the maintenance of equilibrium depends and possibly those by which we appreciate the direction of sounds. In accordance with this view the cochlear and vestibular nerves, as might be expected, pass by different routes from the periphery to the cortex. The fibers of the cochlear nerve appear to arise from cells in the spiral ganglion and from the anterior auditory nucleus of the cerebellum, and pass thence by the tuljcrclc acusticum and by the strife medullares, into the lemniscus of the opposite side, and so to the posterior quad- rigeminal and internal geniculate bodies of that side into the internal capsule ^ to terminate in the first and second temporal con- volutions of the cortex (Fig. 514). The vestibular nerve lying ventrally to the cochlear nerve passes between the restiform body and the descending root of the fifth nerve to terminate in three distinct nuclei situated in the floor of the fourth ven- tricle and known, respectively, as the chief nucleus, the nucleus of Deiters, and the nucleus of Bechterew. In all probability the fibers of the vestibular nerve terminate in a distinct cortical center, situated in the temporal lobe in the neighborhood of that of the cochlear nerve.^ In conclusion, it must not be forgotten that whatever function be assigned to tlie different parts of the internal ear, that the cause of the sensation of sound, like that of color, is psychical, and, in its subjective aspect, is as little understood in the one case as the other. lEdinger, op. cit., s. 360. Rauber, op. cit., Band ii., s. 830. Obersteiner, op. cit., 8. 412. Fig. 514. Position of the auditory ceutcr in the first tem- jjoral convolution. (Goweks.) CHAPTER XLIV. IRRITABILITY, CONDUCTIVITY, AND CONTRACTILITY OF MUSCLE. Ix consideriug the subject of nervous irritability, it will be re- membered that the contraction of a muscle following stimulation of the nerve supplying it, was taken as an indication and measure of the changes occurring in the latter. The changes undergone by the muscle itself, however, during its contraction remain still to be described. Muscles are of two kinds, striped and unstriped, of which the former will be first studied. Striped muscles, such as the skeletal muscles, heart, diaphragm, etc., consist of fasciculi or bundles of fibers separated by connective tissue, the latter being- prolonged from the outer envelope or perimysium covering the muscle. Each muscular fiber is a more or less cylindrical tube from 3 to 4 cm. (1.2 to 1.6 of an inch) in length, and between ^ and Jj of ^ ^^- (ion ^^^^^ eFo ^^ ^^^ inch^ in diameter, and con- FiG. .J15. /'c - i^ A. Portion of a medium-sized human muscular fiber (magnified nearly SOO diameters). B. Separated bundles of fibrils, equally magnified. ;. o8. Heidelberi?, 1871. 852 IRRITABILITY, ETC., OF MUSCLE. the interpretation of all of the appearances of such a preparation, the same makes very evident the swelling and shortening of the fibers, which is brought out even better if the object be viewed by polarized light. In describing the induction apparatus of Du Bois Reymond, it will be remembered that the secondary coil can be removed as de- sired from the primary and the strength of the stimulus thrown into the nerve or muscle in this way varied. Beginning with a very weak stimulus and gradually increasing the same, the correspond- ing contraction will be found to increase, at first rapidly, then more slowly, until a maximum is reached, then to diminish until contrac- tion finally ceases through the muscle being flitigued from repeated stimulation. If the distance through which the secondary coil be slid along be laid down as the abscissa line and the extent of con- traction as the ordinates, the curve obtained will be the graphic representation of the contraction considered as a function of the stimulus. It should be mentioned, in this connection, that M'hile muscles in the body, where they are on tlie stretch after contraction, return at once to their initial length, out of the body they fail to do so either as completely or as quickly, the rapidity and extent of the return appearing to depend upon the nutrition of the muscle. Sup- pose that instead of varying the electrical stimulus, as in the case just mentioned, we maintain it as constant as possible, but that we place in the little scale pan suspended from the lever attached to the muscle successively 10, 20, 30, 40, and 50 grammes — that is, we gradually increase the weight the muscle has to lift to increase the resistance that it has to overcome. Contrary to what might naturally be expected, the resistance oflPered to the contraction, for a time at least, increases the contraction, then with a continued in- crease of weight, the contraction having reached a maximum, gradually diminishes until finally it ceases altogether. If the Aveio-hts be rerarded as the abscissas and tlie extent of contraction as the ordinates, then the curve obtained will represent the contrac- tion regarded as a function of the resistance. It will be observed, in experimenting with weights, that a stretched muscle reaches quickly its initial length after the extending cause has been re- moved, the elasticity not being very great but j)erfect. Contrary, however, to Avhat miglit have been expected, the extensibility is not diminished during contraction but increased, so that the muscle has to overcome the resistance due to its extensibility before it can raise any weight. Thus, suppose that a muscle be extended a given extent by a weight of say 40 grammes during rest, and tlien that it be unloaded and thrown into a state of tetanus and then again loaded with the same weight, the extension in the latter case will be greater than in the former. It will also be learned, l)y experi- menting with gradually increasing weights, that finally the elonga- tion of the muscle due to its elasticity is exactly compensated by the shortening due to its contraction, such a contractioji of static WOBK DONE BY MUSCLE. equilibrium being reached in the case of the frog, the transverse section being one stjuare centimeter and the weight G92 grammes, and in man the muscles being those of the calf of the leg, and the weight 8 kilogrammes (17.B lti>.). The work done by a muscle, like all work, is estimated by the height through which a weight is raised. Thus, if 5 grammes (77.1 grains) are raised 27 millimeters (1.08 inch) by the muscle of a frog, then 27 x •"), or 135 grammes millimeters (83 grain inch) work is done by such a muscle. By gradually increasing the weights and noting the heights through wliich they are raised, it will be found that the work done gradually increases as the Aveight increases until a maximum is reached, after which there is a gradual diminution until the muscle, as in the former instances, ceases to contract. Tlio fatigue experienced by nnisclc (hiring prolonged Fig. 516. Helmholtz's myophonc. f . Button to be placed on muscle. luLut to tulophone. ir. Wires :or attach- contraction, which sooner or later brings the latter to an end, ap- pears to be due to the accumulation of the waste effete products in- cidental to its activity. Within certain limits such matters are eliminated as rapidly as formed and new materials for the repair of the muscle are at the same time supplied. If, however, the con- tractions follow each other very rapidly, sufficient time is not^ al- loAved for the accomplishing of these processes, and the equilibrium between disassimilation and assimilation is no longer maintained. While the cohesion and irritability of muscle are diminished by fatigue, the elasticity is but little, if at all, affected. The latent period is, however, lengthened. During fatigue the extent of con- 854 IRBITABILITY. ETC., OF MUSCLE. traction is smaller and tlie latter lasts longer than when the muscle is fresh, the return to the initial length is also slower. As might be expected, a muscle is fatigued much sooner when it does work than than when it simply contracts without doing work. If a stetho- scope or myophone (Fig. 5 1(5) l>e applied over a powerfully con- tracting muscle, the biceps, for example, a deep, low tone will be heard, the pitch of which is about 40 vibrations a second, and whicli is, without doubt, due to the successive shortenings which make up a muscular contraction, the latter caused, in all probabil- ity, by 40 nervous impulses being transmitted to the nerve centers along the motor nerves to the muscle. We say that the pitch of this muscular sound or tone is 40 vibrations per second and caused by 40 nervous impulses, because that is the note actually heard, and l)ecause we can produce such a note experimentally out of the body by stimulating the nerve that number of times. It should be mentioned, however, that according to most physi- ologists, the muscular sound heard when the biceps contracts, while due to 40 vibrations per second is really the first overtone or first octave above the fundamental, the latter being due to 20 vibrations per second. If such be the case, then the muscle contracts only 20 times a second, the pitch of the muscular sound produced is 20 vibrations a second, and the nerve is stimulated 20 times a second. AMiether the muscular sound heard be the fundamental note or the octave above, in either case, however, the mechanism of its produc- tion is the same — that is, due to muscular vibration. It will be remembered that in accounting for the first sound of the heart, mus- cular contraction was assigned as one of the causes, and while there is no doubt that it is an clement in the production of the first sound, it must be admitted that it is difficult to understand how the con- traction of the heart, if a simple one, can give rise to a muscular sound, which we have just seen is produced by numerous contrac- tions. Facts of this kind, as Avell as peculiarities in the muscular structure of the heart itself, lead one to suppose that possibly the contraction of the heart during its ventricular systole is rather of a tetanic than simple cliaracter, as is usually supposed. The mus- cle sound or muscle tone due to successive muscular contractions nuist not be confounded with what is unfortunately called muscular tonus or muscular tonicity, by whicli is meant the state of tension due to the muscles in the living body being more or less stretched between their attachments. Sucli being the case, when a muscle is divided transversely it contracts, the two parts receding from each other. The sphincter muscles, however, do not appear to be stretched during repose, but only when they are dilated. On the other hand, by the term muscular tone, as understood more espe- cially by neurologists, is meant the firmness or tone of muscle due to continued nervous excitement emanating from the spinal cord. By some physiologists, however, it is denied that the spinal cord exerts any such tonic influence upon the muscles, and yet it is well MYOSIN. 855 known that a decapitated frog will remain in a sitting posture as long as the spinal cord is intact, but that with its removal the limbs fall apart. Further, the limbs of a decapitated turtle, and, to a certain extent, those of a decapitated rabbit, also retain their firmness, tone, but with the removal of the spinal cord become lax, flaccid. Such facts are incomprehensible unless it be supposed that the muscles are maintained firm, elastic, resilient through the influence of the spinal cord. As the influence exerted hj heat, blood supply, etc., upon the activity of the muscle is essentially the same in the case of muscle as in that of nerve, it will not be necessary to dwell further upon the same in this connection. If living contractile frog's muscle, freed as much as possible from blood, be frozen and then minced and rubbed up in a mortar with four times its weight of snow containing 1 per cent, of sodium chlo- ride, a mixture will be obtained, which at about 0° Cent., can be filtered. The filtrate so obtained, or muscle plasma, at first fluid, becomes, at ordinary temperature, jelly-like, and then se):>arates into a clot and serum, the action, M'hich before coagulation was neutral, or slightly alkaline, now l)eing distinctly acid. The serum contains albumin and extractives ; the clot consists of myosin, a substance intermediate in character between fibrin and globulin. It will be observed as in the case of the fibrin of the blood, that myosin does not exist as such in living contractile muscle, but that it is devel- oped during the coagulation of the same out of some preexisting albuminous element or elements. The myosin so developed from living muscle does not diflcr at all from the myosin obtained by ap- propriate chemical manipulation from dead muscle. Indeed, the passage of a muscle into the condition of rigor mortis, character- ized by loss of its irritability, softness, translucency, extensibility, and elasticity may be regarded as being essentially due to the co- agulation of its muscle plasma, to the development of myosin out of its preexisting albuminous elements. Since living muscle dur- ing its contraction becomes distinctly acid from having been pre- viously faintly alkaline or neutral, from a considerable amount of lactic and sarcolactic acid being set free, as in the condition of rigor mortis, from the fact of the muscle, as in the latter distinc- tion, becoming rigid, it might, at first thought, be supposed that the changes occurring during the contraction of the living muscle arc essentially the same as those occurring in rigor mortis, due to the oxidation of some complex albuminous material elaborated and stored up in the muscle during its periods of repose. That the phenomenon of muscular contraction is not, however, identical with that of rigor mortis, is shown by the important fact that during muscular contraction no myosin is developed, upon the formation of which the phenomenon of rigor mortis depends, and that during contraction the extensibility of the muscle is increased, instead of being diminished, and that it does not lose its translucency. But little is positively known as to the physical and chemical 856 IRRITABILITY. ETC. . OF MUSCLE. changes imdergoue by uiistriatcd muscular fiber during death or contraction ; from what has been established, however, we are led to believe that the processes going on in unstriated muscle fiber dif- fer in degree rather than in kind from those just described as oc- curring in striated muscle. While the limits of this work do not permit of any discussion of general muscular movements which Mould involve a detailed description of the muscles and joints and the consideration of animal mechanics, a brief account of how or- dinary movements are performed does not appear inappropriate in concluding this chapter. The greater part of the skeletal muscles may be regarded as so many sources of power for moving the bones viewed as levers. The levers are of three kinds or orders accord- ing to the relative position of the power, the weight to be moved, and the axis of motion or fulcrum. In a lever of the first kind, as in Fig. 517, A, the power (P) is at one end, the weight (W) at the other, and the fulcrum (F) in the middle. As a familiar ex- A Tllustratiou of lever of fir>;l order. (Kirkes. ) ample of the first kind of lever, occurring in the human body, may may be mentioned the raising of the body from the stooping posture by the action of the hamstring muscles attached to the tuberosity of the ischium (Fig. 517, B). In a lever of the second kind (Fig. 518, A), the power is at one end, the fulcrum at the other, and the weight in the middle. The de])ression of the lower jaw in the opening of the mouth is an illustration of a lever of the second kind (Fig. 518, B), in which the tension of the muscles elevating the jaw represents the weight. In a lever of tlie third kind (Fig. 519, A), while the fulcrum and weight are at either end, the power is in the middle. The flexing of the forearm by the action of the biceps muscle (Fig. 519, B) is an instance of this form of lever in the body. The different movements of the foot offer an illustration of ACTIOX OF MUSCLES AS LEVERS. o< all three kinds of level's : of the first kind when tlie foot is raised and the toe tapped upon the ground, the ankle joint being the ful- FiG. olS. Band Illustration of lever of .second ordiT. ( K irkes.) crnm (Fig. 520, 1); of the second when the body is raised upon the toes, the ground being the fulcrum (Fig. 520, II) ; of the third Fig. 519. Illustration of lever of third order. (Kikkes.) kind, Avhen one dances a weight np and down by moving only the foot, the fulcrum being the ankle-joint (Fig. 520, III). As a gen- FiG. 520. II III Illustration of levers of all three orders. W. Weight of resistance. F. Fulcrum. P.Power. (Ill" -\ ley.) eral rule, in the human body, the poAver is so disposed with refer- ence to the fulcrum, that while a greater range of motion is acquired 858 IRRITABILITY, ETC., OF MUSCLE. the power is diminished. Thus, in the case of the action of the biceps, it is evident that a great amount of force must be put forth to move the forearm, but that a considerable range of movement is obtained through a rehitively slight shortening of the muscular fibers. In the act of standing, as accomplished by muscular action, the body is in a vertical position of equilibrium, a line drawn from the center of gravity of the body falling within the feet placed upon the ground. The head is firmly fixed upon the vertebral column by the cervical muscles pulling from the latter upon the occiput, and the vertebral column itself being fixed by the longissimus dorsi and quadratus lumborum muscles. In the sitting position the head and trunk, together constituting an immovable column, are supported upon the tubera ischii. In the forward posture the line of gravity passes in front, in the backward posture behind, and during the erect posture between, the tubera ischii. In walking, the two legs act alternately, the one leg, the active or supporting leg, carrying the trunk, the other leg being inactive or passive. The act of walking, for convenience of description, may be considered as made up of two acts. Act 1st (Fig. 521) : the active leg being vertical and slightly flexed at the knee, alone supports the center of gravity of the body, Fig. 521. Phases of walking. The thick lines represent the active, the thin the passive, leg. h. The hip- joint. A-, a. Knee. /, h. Ankle, c, d. Heel, m, e. Ball of the tarso-metatarsal joints, z, y. Point of great toe. (Landois.) the passive leg touching the ground with the tip of the great toe (2) only. At this moment the position of the leg corresponds to a right-angle triangle in which the active leg and ground represent the two sides, the passive leg the hypothenuse. Act 2d : the active leg being inclined, moves forward to an oblique position, the trunk moves forward, the active leg being at the same time lengthened that the trunk may remain at the same height. The latter is ac- complished by extension of the knee (3, 4, 5) and the lifting of the heel from the ground (4, 5,), until the foot finally rests upon the ground by the point of the great toe. As the active leg is extended WALKING, RUNNING, ETC. 859 and moves forward the tips of the toes of the passive le^ leave the ground (3), and being slightly flexed at the knee-joint perform a pendulum-like movement (4, 5), the passive foot passing as far in front of the active leg as it was previously behind it. The foot being then placed flat upon the ground, the center of gravity is transferred to what now becomes the active leg, the latter being slightly flexed at the knee and placed vertically. The first act is then repeated, and so on. It will be observed that during walking the trunk leans toward the active leg and inclines somewhat forward, the ef- fect of which is to overcome resistance of the air, and that it slightly rotates on the head of the active femur. Running differs from rapid walking in that at a particular moment, both legs not touch- ing the ground, the body is raised in the air, the necessary impetus being given to the body l>y the forcil>le extension of the active leg. CHAPTER XLV. REPRODUCTION. Spontaneous Generation. Fissiparous, Gemmiparous, and Sexual Generation. At an immensely remote period the earth must have been en- tirely destitute of life, at least the physical conditions of the azoic period of geologists, and the seons preceding it were such as to make the existence of life, as we are acquainted with it, impossible. Whether the nebular hypothesis of the earth having been cast off from the sun be accepted or not, there can be no doubt that at an inconceivably distant period the earth was in a fluid or semi-fluid molten condition, and its temperature so high as to render life im- possible, or even to admit of the union of the chemical elements composing it, the latter existing then separately, as they do in all probability now, in the sun, as shown by spectral analysis. The basalts, prophyries, and lavas entering into the formation of the igneous rocks, the volcanic action constantly going on at the pres- ent day in many parts of the world, the seismic disturbances, the high temperature of mines, etc., not only prove that originally the world was but little else than a ball of fire, but also that the fire, far from being extinguished, is only now restricted to the inner subterraneous regions lying under the crust of the earth. If specu- lation be admitted, we can conceive how with the loss of heat and the lowering of the temperature through the combination of hydro- gen and oxygen the water was formed, and that gradually through the combination of the chemical elements the binary and ternary salts entering into the formation of the rocks constituting the crust of the earth were next produced, and finally, the physical conditions being suitable, that the combination of carbon, hydro- gen, oxygen, nitrogen, and phosphorus or sulphur atoms, resulted in the development of protoplasm, or the simplest kind of life. While it is true that there is no evidence whatever that life now is ever generated otherwise than from preexisting life, soli- tary ta])eworms, maggots, etc., often cited by the uneducated as instances of animals spontaneously generated, offering no exception to the rule, being in reality reproduced, like all life, by preexisting animal life, that the first life appearing upon the face of the earth was, nevertheless, s])ontaneously generated, developed inde- pendently of preexisting life must be admitted, since there was no antecedent life during the azoic period to give rise to it. As to the inconceivability of how spontaneous generation Avas brought about, of how protoplasm, with its remarkable properties, was ever de- SPONTANEOUS GENERATION. 801 veloped through the combination of chemical elements possessing different properties, it may be said that it is just as difficult to comprehend how the combination of acid and base will give rise to a salt exhibiting properties possessed by neither, or how two gases like oxygen and hydrogen in combination produce a liquid, water, different from either. In either case we must suppose that the prop- erties of the substance formed, however remarkable, are the sum of the properties of the elements entering into combination and giving rise to the substance, whatever is true of tlie inorganic in tliis re- spect being true of the organic as well, the question in either case being one of the redistribution of matter and energy only. Admit- ting that life originated spontaneously, there is little reason, how- ever, to hope that the physical conditions which obtained when life first appeared upon the face of the earth can ever be realized ex- perimentally so as to enable one to generate life (h novo. Still it must not be forgotten that what appears impossible to one age becomes perfectly so to a succeeding one. Life having once ap- peared upon the face of the earth, however produced, there is no reason to suppose that it has ever been entirely absent, since catas- trophies, such as volcanic eruptions, earthquakes, floods, climatic changes, etc., which are so destructive to life, are relatively local in action. Further, the first life, out of which all life has since been gradually developed, must have been of the simplest kind ; indeed, so simple as to make it difficult, if not impossible, to say whether such life should be regarded as animal or vegetable, its characters being intermediate between, and partaking of the nature of both plants and animals. The latter, judging from their remains as presented in the Cambrian and Silurian rocks, or such as immediately overlie the azoic strata, were also at first of a simple kind. Thus among the plants and animals living in these early ages of the primary period of geologists may be mentioned seaweeds, jelly fish, coral-making polyps, crinoids, brachiopods, various kinds of mollusca, trilobites, etc. Passing on through the later ages of the primary period, the life becomes more varied and complex ; fishes, ganoids, and sharks, and land plants, pine-like lepidodendrons, and ferns making their ap])ear- ance during the Devonian age, or that of the sandstone, and rc])- tiles in the carboniferous age, or that of the coal period, remark- able also for the richness of its cryptogamous plants. As the ages rolled on, during which the Jura rocks were deposited in SNA-itzer- land, the chalk cliffs in England, the marls in New Jersey, phanerogamous, or flowering plants, palms and trees like those of our own forests, oaks, dogwoods, poplars, beeches, appeared, wliile among the animals that lived during these ages may be mentioned fishes resembling those of the present day, gigantic reptiles, birds, and probably a few marsupial mammals. During the tertiary period that followed, the flowering plants and trees then flourishing resembled closelv those of the forests of the 862 REPRODUCTION. present day, the invertebrate forms of life differed bnt little from those existing now, the fishes and reptiles were similar to those found in our rivers, oceans, and forests ; while herbivorous animals, resembling the tapir, peccary, camel, deer, horse, rhinoceros, and elephant, roamed in herds over the continents, hippopotami wallowed in the streams ; while beasts of prey were also numerous, being represented by animals closely allied to the lion, tiger, hyena, dog, and panther of the present day. During the close of the Tertiary, or, rather, of the post-Tertiary period, the general aspect of tlie world differing but little from that presented by it now, man ap- peared but in a condition of development probably far lower than that of the lowest existing savage, and the process of civilization began. The idea of reproduction is usually associated with that of the difference of sex ; the production of offspring naturally suggesting the idea of two parents. Many plants and animals, however, are reproduced entirely independently of sexual intercourse, by what is known as fission or gemmation ; and as many of the structures of the body are developed by these processes, it is essential that they should be at least briefly illustrated. By the process of fission is meant the division of the single parent organism into two or more parts, each of whicli will become a new being, similar in form, in- heriting the properties of the parent. Reproduction by the process of fission may be observed in many of the lower cryptogamous plants, and among animals in the infusoria, annelida, etc. AVhat Fig. r>22. Fig. 523. Division of blood cells in embryo of stag. (Frey.) interests us in this connection, however, as regards fission is, that the segmentation of the vitellus of the egg, the development of the embryonic blood corpuscles (Fig. 522), the proliferation of the cells constituting morbid growths, etc., are accomplished by this process. On the other hand, by gemmation is understood the reproduction of the new being by a process of budding, as seen in ordinary flower- HydroiJ colony. Eudendrium ramosum. (Gegenbaue. ) FEMALE GENERATIVE ORGANS. 8«J3 ing plants, and among animals in the hydra, actinia, etc., each bud becoming a new animal. In certain cases of gemmiparous repro- duction, however, the buds, instead of being cast oif as produced, remain attached to the parent stock, and so give rise to a colony, as in the hydroids (Fig. 528), each member of Avhich is in commu- nication, directly or indirectly, with each other. Such a mode of reproduction in the humau body is seen in the development of a compound gland (Fig. 524), through the division and subdivision of a simple follicular gland. The reproduction of man and most animals, however, is accomplished by the union of a spermatozoon and an ovum, both male and female generative organs co-exist- ing, however, in the same individual in many inverte- brates. In the tapeworm, for example, which is a hermaphrodite, reproduction is accom- plished even by self-impregnation. The ova and spermatozoa are specialized products of the male and female generative apparatus respectively, which, while elaborated by a process of fission, unlike the products of the latter, must fuse together in order to give rise to a new being, neither spermatozoon nor ovum, by themselves being capable of further development. Further, it will be observed that since, in the production of a new being by sexual generation, the union of the spermatozoSn and ovum is indispensable, the quali- ties of the parents must be transmitted to their offspring. The Itiagrammatic view of devclopnKiit of glands. Fig. 525. Sketch of the uterus and its appendages. 1. Uterus, with its peritoneal covering partially retained. 2. Its fundus. 3. Its neck, with the forepart of the attachment of the vagina removed. 4. Mouth of the uterus. 5. Interior of the vagina. 6. Broad ligament, roniDved on the opposite side. 7. Position of the ovarv behind the broad ligament. 8. lioiiinl huament. ".». Oviduct, or Fallopian tube. 10, Its fimbriated e.\treinitv. 11. Ovary. 12. Ovarian ligament. 13. Process connecting the fimbriated extremity with the ovary. 14. Cut border ot the broad ligament. (WiL.soN.; female generative organs, situated partly Avithin and partly without the pelvis, consist of' the uterus, Fallopian tubes, vagina, ovaries, the external and internal labia, clitoris, etc. The uterus (Fig. 525), 864 REPRODUCTION. or womb, is a pyriform, hollow muscular organ, lying, in the un- impregnated condition, within the pelvis, between the rectum and the bladder, and maintained in position by its attachment to the vagina by the recto- and vesico-uterine peritoneal folds, and the round and broad ligaments. Its upper broad extremity is known as the fundus, or base, the narrow extremity the cervix, or neck, and the intervening portion as the corpus, or body. The uterus is about three inches in length, two inches in breadth, and one inch in thickness. The walls of the uterus consisting of unstriated muscular tissue, being about one-half an inch in thickness, its cavity is but a narrow space. The latter is lined with a thin, soft, smooth, and ciliated mucous membrane of a pale red color, containing numerous tubular glands adhering closely to the underlying muscular tissue, there being no intermediate fibrous or submucous tissue, which becomes continuous with the mucous membrane of the Fallopian tubes and that of the neck of the uterus. The mucous membrane of the latter is of the squamous character, thicker and less soft than that of the body of the uterus, its glands being of the simple follicular kind and secreting a tenacious mucus, the latter in an inspissated condition, ffivin"; rise to the so-called ovula Nal)othi. The uterine mucus, both of the fundus and cervix, is alkaline in reaction. The Fallopian tubes, or the horns of the uterus, are trumpet-shaped tubes about four inches in length, extending from the fundus out- wardly above and beyond the ovary. The outer free extremity opening into the abdominal cavity expands into a funnel-shaped orifice, the pavilion, the margin of which, being fringed with a num- ber of irregular processes, gives rise to its name of fimbriated ex- tremity. One of the largest of these fringed processes, doubled so as to include a furrow, extends along the edge of the broad ligament to be attached to the ovary. The Fallopian tube is lined with ciliated mucous membrane, continuous through its interim or uterine orifice with that of the cavity of the fundus, and disposed in a lon- gitudinal manner or as narrow folds. The tube itself consists of fibrous intermixed with unstriated muscular tissue, loosely invested by peritoneum. The small sac, often absent, attached by a long pedicle close to the fimbriated extremity, is the remains of the duct of ]\Iiiller of the embryo, as we shall see presently. The vagina is a cylindrical canal about four inches in length and an inch and a quarter in breadth (in the virgin adult), extending from the uterus, the neck of which projects into it, to the vulva. The vagina con- sists of three coats, an outer fibro-elastic, a middle unstriated mus- cular, and an inner mucous ; the epithelium of the latter is of the squamous kind, and is provided with numerous minute conical papillae. In the virgin condition the lower orifice or entrance of the vagina is constricted by a crescentic or zone-like fold of the lining of the membrane, the so-called hymen. The latter is usually obliterated by sexual intercourse, childbirth, etc. ; in some instances, GRAAFIAN FOLLICLES AND OVA. 865 however, it is so strong that even impregnation may occur without its being ruptured. Its presence cannot, therefore, be taken as an evidence of virginity, or its absence of the contrary. The inner surface of the anterior and posterior walls of the vagina is rough- ened by folds, the wart-like eminences into which they are divided more particularly at the entrance of the vagina being known as the carunculie myrtiformes. While, as just mentioned, the uterine mucus is alkaline in reaction, that of the vagina is decidedly acid. The two ovaries are compressed ovoid bodies, situated behind the broad ligament and enclosed by a pouch of the latter about an inch from the uterus, to which they are attached by the ovarian liga- ment. The ovary consists of a reddish spongy fibrous stroma, en- closed in a dense fibrous tunic, the tunica albug-inea. AVithin the stroma of the ovary are found numerous vesicular-like bodies, varying from a microscopical size to the fourth of an inch in diameter, the Graafian follicles or vesicles, so-called after Kegnerus de Graaf, their discoverer.^ These vesicles (Fig. 526), which Ovum, Graafian follicle, a. Ovum. b. L>iscus imdiserus. <•. >rembiaiia granulosa. <»37 often described as constitutiDg the so-called deutoplasmic zone as distingnislied from the clearer, more peripheral portion, the proto- plasmic zone. The food, yolk, or deutoplasm exists only in small amount in the human ovum as the latter, being developed within the bodvof the mother and deriving; its nourishment from the blood of the latter, but little is required for the early stages of gro^^•th. In this respect the ovum of the bird diifers markedly from that of the human female, since the bird, being developed outside of the body of the mother, depends entirely upon the food yolk for its growth, hence the great amount present. The nucleus, or germinal vesicle, as it is called, in the ovum discovered in maimnals by Coste/ in 1834, and usually situated near the surface of the egg is a clear, spheroidal vesicle, measuring about the 77V of a milli- meter {^\-^j of an inch) and consists of protoplasm within which is found the nucleolus, macula, or the germinal spot. The latter, dis- covered by AVagner - in 1835, measures about the -^^ of a millimeter (seVo ^^^*^^^) i'^ diameter. It may be mentioned in this connection that there is also found in most mammalian ova in the ])rotoplasm ii peculiar liody, the so-called attraction sphere within which lies ^-^^ ^?^ '^'ft - 'm-^ '"'^I^^M'M Vertical section through the ovarv of a newborn female, a. Ovarium epithelium, h. Egg string, c. Young ova. d. Egg string, with follicles, e. Follicles. /. Mngle follicle. <7. Blood vessel. (Waldeyer.) a single or double centrosome and which appears to initiate the karyokinetic division of the ovum to be presently descril>cd. It is a fact of profound significance that the human ovum, or first cell, from which all the cells composing the body are developed, should be practically undistinguishable, morphologically at least, from the 1 Eecherches sur la generation des Mammiferes par Delpech et Coste. Paris, 1834. ^Miiller, Archiv, 1835. Prodroniiis historiie generatioub. Lips., 1836. 868 EEPRODVCTION. ova of the ordinary mammalia ; that the first or transitory egg-stage through which man passes, should be permanently retained through life in many of the lower plants or animals, such beings never pass- ing beyond the unicellular stage, and that the very lowest, as well as the highest forms begin life in exactly the same way as masses of protoplasm ; the zona pellucida being a secondary formation. The ova are developed from the germinal epithelium (Fig. 528), a covering of the primitive ovary. Through the inward growth of this epithelium into the substance of the ovary, cords of cells {b d) are formed, which become divided into compartments through the encroachment of the fibrous stroma. Of the cells witliin these compartments the largest become ova ; the smallest, the cells of the membrana granulosa of the Graafian follicle (e /), the wall of which is continuous with the stroma. As development advances, fluid accumulates between the growing cells, the follicle assumes the shape of a vesicle, the egg lying eventually to its inner wall. With the ripening of the ovum, the Graafian follicle comes to the surface of the ovary, the wall of which as w^ell as that of the follicle becoming at the same time thinner and thinner, until, finally, they are ruptured, and so permit of the escape of the egg. From the fact of the egg or embryo being found in the Fallopian tube or uterus, except in the unusual case of abdominal pregnancy, it is evident that the Fallopian tube must be so disposed with reference to the Graafian follicle that at the moment of its rupture a tem- porary passage-way is usually formed from one to the other. As a matter of fact, it is not positively known how the egg passes from the Graafian follicle to the Fallopian tube. It may be supposed, however, that the fimbriated extremity affixes itself to the ovary at the moment of rupture of the follicle, or that the egg, dropping into the furrow of the long fimbriated process situated at the edge of the broad lig^ament and attached to the ovary, is transferred bv ciliary action into the orifice of the tube, and thence by the same kind of action through the Fallopian tube into the uterus. The ecrp- havino; arrived in the cavitv of the latter, if not in the mean- time impregnated, sooner or later decomposes and disappears. Be- fore describing, however, the manner in which the ovum is impreg- nated, certain changes undergone by the Graafian follicle and the mucous membrane of the uterus, incidental to the maturation and escape of the ovum from the follicle, M'hether the ovum be impreg- nated or not, must be first considered. Corpus Luteum of Menstruation and Pregnancy. It is impossible to convey by words any idea of tlie extent of the congestion of the internal generative apparatus of the female during the period of the maturation and escape of the ovum from the Graafian follicle. The author can only say that in making post- mortem examinations of females dying while menstruating, he was impressed with the fact that the blood vessels, arteries, capillaries. CORPUS LUTEUM. 800 and veins were distended to an extent never accomplished by an artificial injection, however successfully performed. Such hQuv^ the case (as might be expected) with the rupture of the Graafian follicle, there being quite an abundant hcniorrliage, tlie cavity of the follicle fills with blood. The hitter soon coagulating, as it would do if extravasated elsewhere, the clot remains enclosed within the walls of the follicle (Fig. 529), having no organic connection, however, with the latter, but simply hing loose in the cavity of the follicle, out of Avhich Fk;. 529. it can be readily turned by the handle of a scalpel. The clot, which at this moment is large, soft, and gelatinous, soon begins to eon- tract, and the serum exuded being absorbed by the adjacent parts, it becomes smaller and denser. The coloring matter of the clot at c— the same time undergoing the usual changes incidental to extravasation, and being to a great extent absorbed Avith the serum, a dimi- nution in its color becomes quite perceptible. During this period, about two weeks, the lin- ing membrane of the follicle, which at the oraafian f„iiicie, reeentiv moment of rupture i)resents a smooth, trans- yiM't'^ed (Uiring i.icnstriia- II ■ tliiii, aim filled Willi a lilcHiily parent, vascular aiuiearance, becomes much cuKuium ; shown in \riod it will be found impossible to .separate 870 REPRODUCTION. the yellowish convoluted wall, cither from the ovarian tissue or the central clot, and by the end of two months the whole corpus luteum will be found to be reduced to the condition of a greenish, cicatrix- like spot (Fig. 531), about 6 millimeters (one-fourth of an inch) in Fig. 530. Fig. 531. Iliiiiian (>\ai\ cut open, showing a corpus lutmni, (li\ idcd lougitudinally, three weeks iit'tci mciii.triiation. From a girl, twenty years of age, dead of hsemoptysis. (I.)alton.) Ovary, Kh.iwiiigeorjius luteum, nine weeks after menstruation. From a girl dead of tubercular meningitis. (Dalton.) diameter. At the end of six months the corpus luteum has usually disappeared. It may, however, be sometimes found, though in a very atrophied condition, even seven or eight months after the rup- ture of the follicle. Such, in brief, is the manner in which the corpus luteum of menstruation is developed out of the ruptured Graafian follicle from which the ovum has escaped, at least as ob- served by the author in a number of females dying from natural causes or violent deaths, and which does not differ essentially from the process so admirably described by Dalton.^ As during preg- nancy far more blood flows to the female generative apparatus than during menstruation, it might necessarily be supposed that while the production of the corpus luteum would be essentially the same in both conditions, the corpus luteum, being better nourished, would grow larger and persist longer than the corpus luteum of menstruation. That such is the case there can be no doubt, a cor- pus luteum being present at the end of pregnancy even, and meas- vu'ing as much as half an inch in diameter. While marked differ- ences exist, therefore, between the corpus luteum of menstruation and that of pregnancy, nevertheless, as these differences arc of de- gree, and not of kind, and since the corpus luteum of menstruation during the first three weeks increases in size, but that of pregnancy after the first six months diminishes, it can be readily conceived that at a particular moment the corpus luteum of menstruation might be of the same size as that of pregnancy, and that if the color of the clot and convoluted wall in the two were not well marked, ^ Trans, of the American Med. Assoc., Vol. iv., p, ology, 7th ed., p. 608. Pliila., 1882. 547. Pliila., 1851. Tliysi- MENSTE UA TION. 871 the two corpora lutca might bo undistinguisliablo. At least such has been the experience of the author, in conij)aring numerous cor- pora lutea of menstruation of various ages with those of pregnancy. Further, that the presence or absence of a corpus luteum <'ainiot be accepted as positive evidence of imjiregnation haviug taken phice is shown by the fact that, altliough in several instances in making post-mortem examinations a fletus was removed from the uterus by the author, not a trace of a corpus luteum could be found in either ovary, and, on the other hand, in more than one instance a well- developed corpus luteum being present several months after the last menstruation, there was not the slightest reason to believe that during that period there had been a foetus in the uterus, at least the relatives of the deceased had no object in concealing the fact of im- pregnation, if such had really occurred. Menstruation. Coincident with the maturation and escape of the ovum from the Graafian follicle, the mucous membrane of the uterus undergoes several well-marked changes. Thus, while in the ordinary condi- tions it measures only about 18 millimeters (^^^ of an inch) in thick- ness, at this period it becomes twice or even three times as thick. It is also much softer and more loosely attached to the underlying part than ordinary, being somewhat rugose in character. The glands are very much enlarged, and the surface of the membrane smeared with blood. The latter is due to a kind of disintegration set up in the mucous membrane involving the blood vessels, by which the capillaries are ruptured. The hemorrhage so caused con- stituting the menstrual flow, or the menses, catamenia, etc., appears monthly in the healthy female, and lasts upon the average from four to five days. It appears to be pure arterial blood mixed with desquamated utero-vaginal epithelium ; the amount of the latter would appear from the observations of the author to be greater than usually supposed. The menstrual blood is kept from coagu- lating by the vaginal mucus. As might be expected from the nature of the case, it is impossible to say how much blood is dis- charged during the menstrual period, for, apart from the difficulty experienced in collecting it, women vary very nuich in respect to the amount of blood lost. From 100 "to 200 c.c. (4 to 8 ounces) may be accepted as an approximate estimate of the total flow during the menstrual period. ]\[enstruation is sometimes regarded as the effect of ovulation, the two being so intimately associated. Since menstruation, however, occurs without ovulation in the absence of ovaries, and ovulation without menstruation, it is evident that the two phenomena are not related as cause and effect, but should be considered as the effects of a common cause, the general prepa- ration of the system for impregnation. Indeed, the thickening and shedding of the mucous membrane of the uterus, an(l hemor- rhage during menstruation, differ only in degree, not in kind, from 872 REPRODUCTION. the changes undergone by the mucons membrane dnring pregnancy and ])artiirition, the decidna menstraalis being the forernnner of the decidua graviditatis. That the menstrual flow is the eifect of a deep- lying cause, the fitting of the mucous membrane for tlie reception of the ovum, though not due to the production of the latter, is shown by the constitutional disturbance experienced by the female when the menses first appear, and ever afterward with their monthly reappearance, though then to a less extent. The menses usually appear between the age of thirteen and fifteen years and much earlier in warm climates. At this period, the age of puberty, there is a general development of the body, the limbs become fuller and rounder, hair appears on the mons veneris, the mammary glands enlarge, ova maturate, and the disposition changes. Just before the establishment of the flow, either in the case of its first appear- ance or in after-recurring ones, for about two days a feeling of gen- eral malaise is experienced, particularly a sense of weight and ful- ness in the pelvic organs, the vaginal mucus is increased in amount and becomes rusty in color, and gives rise to the odor so perceptible in certain females, the breasts also enlarge, showing the sympathy existing between the latter and the generative organs. With the establishing of the flow, the disagreeable feelings and uneasiness usually pass aAvay, and by the end of the fourth day, though the time varies, the flow ceases, and the mucous membrane returns to its normal condition. At about forty-five years of age the menses become irregular in their recurrence and usually cease altogether at fifty. The phenomenon of the menses is not restricted to the human female, as is often supposed, the heat or rut of the lower domestic animals, such as that of the mare, cow, bitch, being essen- tially the same process, only recurring at diiferent intervals. In- deed, in monkeys and apes there is a monthly discharge, as in the case of the human female. It is a significant fact that the female of animals, except monkeys, only receive the male during the rut- ting or menstruating period. The Male Generative Apparatus. The male generative apparatus consists of the testicles, the spermatic ducts, the seminal vesicles, prostate and suburethral glands, and the penis. The testicles (Fig. 532), secreting the spermatic fluid, are tAVo glandular bodies suspended by the sper- matic cords Avitliin the scrotum. Tiie latter is essentially a musculo- cutaneous pouch, divided into two recesses by a septum for the re- ception of the two testicles. Each testicle consists of an anterior oval portion of the body, or testis proper, and a posterior elongated portion clas])ing, as it were, the former, the e[)ididymis. The up- per portion of the epididymis is known as the head, or globus major, the lower part as the tail, or globus minor, wliicli, in turning upward upon itself, becomes the spermatic duct. The testes are covered with a dense white fibrous membrane, the tunica albuginea, which MALE GENERATIVE APPARATUS. 873 Fk;. 532 at the back of the testes forms a process, the niediastimim. The Latter, being prolonged as fibrous Ixmds to be inserted into the in- ner surface of the tunica albuginea, serves as a sort of scaffolding to support the delicate glandular substance within. The testicle proper is made up of about two hundred lobules, each lobule in turn consistins: of from one to six seminiferous tubules, of which there are perhaps eight hundred in all. The seminiferous tubules at the narrow end of the lobule assume a straight course, being then known as the vasa recti. The latter entering the mediastinum, constitute together the plexus retiformis, from which emerge about a dozen efferent canals, or vasa efferentia, to pass out to the head of the epididymis. Within the latter these ef- ferent canals form the sper- matic cones, wdiich finally ^ive rise to one convoluted tube, constituting the body and tail of the epididymis, the latter of which, as just mentioned, becomes the sper- matic duct. The spermatic duct passing through the in- guinal canal, leaves the latter -at the internal abdominal ring, and descending backward and do^vnward, passes forward to form, together with the duct of the seminal vesicle, the ejaculatory duct, the latter terminating in the prostatic urethra. The seminifer- ous tubules, about thirty inches in length Avhen unravelled, and the .j-i^ of an inch in diameter, consist of a fibro-membranous wall lined with a delicate layer of soft polyhedra nucleated cells, the sperm cells, which elaborate the spermatic or seminal licjuid, of which about half a drachm is emitted during the orgasm. The latter is a faintly alkaline liquid, slightly heavier than water, becoming jelly-like first, and then hardening after emission. The semen consists chem- ically of 82 per cent, water, serum, albumin, alkali albuminate, nuclein, lecithin, cholesterin, fats, phosphorized fats, alkaline, and earthy phosphates, sulphates, carbonates, nnd chloride, and an odorous body, the so-called "spermatin," the nature of which is unknown. Testicle aud epididymis of the hiiuiaii suliject. (t. Testicle, b. Lobules of the testicle, c. Vasa recta. il. Uete testis. i>. \'asa etfereiitia. /. Cones of the globulus major of the epididymis. ;/. Kpididymis. /i. Vas deferens. /. Vas aberrans. ;«. Branches of the spermatic artery to the testicle and epididymis. ;'. Ramification of the artery upon the testicle and epididymis, n. Deferential artery, p. Ana.stomosis of the deferential with the s])ermatic artery. ( Kol- LIKEK. ) 874 REPRODUCTION. Fig. 533. V^ Physiologically the essential portion of the spermatic fluid, upon which its fecundating powers without doubt depend, are the sper- matozoa that it contains. Indeed, if the seminal liquid be deprived of its spermatozoa, it is rendered entirely inoperative as regards impregnation. The spermatozoa are developed out of the nuclei of the daughter cells of the parent cells, which lie near the outer wall of the seminiferous tubule, the nucleus assuming the form of a spermatozoon, which is set free by the deliquescence of the cell wall enclosing it. The spermatozoa appear first at the age of puberty, and afterAvard till the end, life being found in the semen of healthy men of ninety years of age. The spermatozoa (Fig. 533), measur- ing the 2V of ^ millimeter {-q\-q inch) in length, dis- covered by A-^on Hammen, in 1677, and described by Leeuwenhock, resemble the flagellate animal- cule for which they were first taken. A sperma- tozoon consists of an ovoidal head, measuring ■g^^Q- of a millimeter (g^Vo^ of an inch) containing chromatin and of a filamentary appendage or tail measuring 0.050 mm. (-5 J-jj of an inch) which vibrates with astonishing rapidity. The tail of the spermato- zoon is usually described as consisting of three parts, the middle, main, and end pieces. The middle piece or the thickest part, that nearest the head, is said to contain an axial thread and exhibits a very fine spiral thread running around it. The movements of the spermatozoa are arrested by water and cold, re- tarded by acids, and favored by alkalies. The spermatic fluid, with the spermatozoa, passes from the testicles by the spermatic ducts to the seminal vesicles, wdiere it becomes mixed with the secretion of the latter, the nature and use of which are, how- ever, doubtful, as no secreting glands are found in these vesicles ; its use may be to dilute the mixed spermatic fluid. The spermatic fluid, having ac- cumulated in the seminal vesicles, is thence introduced during coition, still further mixed with the secretion of the prostate gland, of the glands of Cowper, and of the urethra, the use of which is not known, by an ejaculatory efl'ect, into the vagina of the female, the spermatozoa by their vibrating movements passing up into the Fallopian tubes, and even the ovaries, as shown by the development of the ovum in those situations in cases of extra- uterine pregnancy. The spermatozoa have been found moving in the uterus even eight days after emission, the rate of movement being probably from between 1.2 to 3.6 mm. ])er minute. In order that coition should be accomplished, it is essential that the penis should be erect. This is brought about through its blood supply being very much increased by the stimulation of the vaso-dilator Human sperma- tozoiin. h. Head. //*. Middle -piece. I. Tail. e. End- piece. (RETZII'S.) INTERNAL SECRETION OF TESTICLE. 875 fibers of the nervi eri^entes, the later arising probably from the second sacral nerves. The center of erection, sitnated in the cord, can be reflexlj stimulated either by impressions made u])un the ijenital organs or upon tlie mind. Tlie cjacidatory effort is due to the simultaneous contraction of the bulbo urethrie, iscliio-cavernous, and transverse perinaius muscles, due to the reflex stimulation of the ejaculatory center of the spinal cord, situated in the lumbar region. Recent researches ' render it probable that the testicles, in addi- tion to secreting the spermatic fluid, elaborate an " internal secre- tion," spermin,^ having a chemical composition represented by the formula CHj^N^, and which, passing into the blood, increases the mental and physical vigor of the aged, and benefits those afflicted with general prostration and neurasthenia.'^ 1 Brown-Seciuard, Arcliives de Pliysiologie normalc et pathologique, 1889, 92. ^Poehl, Zeitschrift fiir klinische raedecin, Band 2(3, 1S94, s. 13.S. 3Zoth, PHiiger's Arcliiv, Band 62, 1896, s. 335. Preyer, Ibid., s. 379. CHAPTER XLVI. EEPRODUCTION.— (Co/ic/»f^^J.) Impregnation of the Ovum and Development of Embryo. As a matter of fact, nothing is known as to the manner in which the ovum is impregnated in the human female, or of the early stages of the development of the embryo. Since the primitive ova of all animals are more or less alike and the spermatozoa diifer from each other unessentially, it is to be inferred that the process of impreg- nation in the human female is the same as that observed in animals. Further, as the human foetus of about three weeks old (Fig. 534) Fig. 534. Fig. 535. 1,1 Embryo of man. Embryo of rabbit. «. Eye. m. Mid-braiu. o. Ear. r. Spiual marrow, tc. Vertebral column, k. Visceral arches. (Haeckel.) differs but little from that of the rabbit at about ten days (Fig. 535), there can be little doubt that the stages intermediate between that of the e^g and that of three weeks old, through which the human embryo passes, are essentially tlie same as the corresponding stages through wliich the rabbit embryo passes from the stage of the e^^ to that represented in Fig. 535, or the corresponding stages in the development of the dog, hog, etc., or even bird, reptile, or fish. Assuming, then, that the development of man, in the early stages, is the same as that of a rabbit, for example, we will describe, as illustrating the former, the development of the animal ^ up to the period that it begins to diifer from that of man, basing our ac- count of impregnation, however, upon the manner in which that process is said to take place in the Ascaris mcgalocephala,^ a large Avorm found in the alimentary canal of the horse. ^BisclioffJ Entwicklungs Geschichte des K:ininclien-Eies. Braunschweig, 1842. E. Van Jk'neden, La Maturation dc I'tcuf, etc., d'apres des recherches faites cliez le lapin. Bruxolles, 1875. ^ Van Beneden ot Neyt, Nouvelles recherches sur la fecondation et la division mitosique chez I'ascaride megalocephale, Bullet, de I'acad. royalo des sciences de Belgique, 3ser., T. xiv., 1887. MATURATJOX OF OVUM, 'i^ll Either before or immediately after its escape from the Graafian follicle the ovum undergoes a change known as '' maturation," a pro- cess preparatory to, but independent of fertilization. This consists in the extrusion by the germinal vesicles of two minute spherical bodies, the " polar globules " or " directive corpuscles," so-called on account of it being supposed by some embryologists that their presence determinates the pole at which the first segmentation will take place in the event of the ovum being impregnated. The polar globules are formed in the ovum of the Ascaris megalocephala ^ in the following manner : The germinal vesicle approaches the periphery of the vitellus, becomes indistinct in outline, and is transformed into a spindle of fibers, at the equator of wdiich are situated eight chromatin parti- cles (Fig. .)36), The latter shortly separate into two sets, consist- ing of four chromatin particles each (Fig. 5o7). One set of four Fir.. 537 The ovum, with the germinal vesical transformed into a spindle of achromatic fibrils ; from the poles of the spindle other tibrils radiate into the proto- plasm. At the equator of the spindle eight por- tions of chromatin are visible. C.V. Head of a spermatozoon which has previously entered the ovum, and is becoming transformed into the male pronucleus, m. Gelatinous membrane of the ovum. (QuAis.) The chromatin particles are seen separated into two sets. The achromatic tibrils are not shown in this preparation. The ovum is considerably shrunken. (Qcais.) chromatin particles, together with part of the proto})lasm, is extruded into the peri-vitel- line space as the first polar globule (Fig. 538), while the other set of four chromatin particles remains in the vitellus situated upon the equator of the second spindle into which the remainder of the germinal vesicle has been transformed (Fig. .");3J)). Soon two chro- matin particles are extruded from the spindles as the second polar globule (Figs. 540, 541), while the other two chromatin particles remain in the vitellus and constitute, with the remainder of the germinal vesicle, the female pronucleus. The act of impregnation in the rabbit, and in all animals in which impregnation has been observed, consists in the passage of one or more spermatozoa (Fig. 542) through the vitelline membrane of the e^g into the peri-vitel- line space, though one spermatozoon alone normally enters the vitel- 1 Gehuchten Xouvelles observations siir la vesicule gerniinative et les globules polaires de r Ascaris Megalocephale, Anat. Anz., 1887. 878 REPRODUCTION. lus to form the male pronucleus, the union of which with the female pronucleus gives rise to the new being. Fig. 538. Half of the germiual vesicle is extruded into a peri-vitelliue space, and aloug with a portion of the protoplasm is becoming separated oft" from the ovum as a polar globule. The ex- truded half includes four of the chromatin particles ; the other four remain in the ovum. m'. Membrane dividing the polar globule from the ovum. (Quais.) The remainder of the germinal vesicle (after extrusion of the first globule .7') has again become transformed into a spindle of achro- matic fibrils, with the four remaining chromatin particles at the equator of the spindle. (Quain. ) It has also been shown that the head of the spermatozoon, which is the part that is transformed into the male pronucleus, contains only two chromatin particles, the other two having been thrown off in Fig. 540. Fig. 541. The spindle p, now irregularly Y-shajted, is seen approaching the surface of the ovum. I/'. First polar globule, ns. Male pronucleus 'which has become formed from a sperma- tozoon. (QUAIN.) Completion of the process. The second polar globule, g-, is now separated from the ovum ; it containstwoof thechroiuatin particles. Theother two remain in what is left of the germinal vesicle. «3. Which now forms the female pronucleus, ns. Male pronucleus. e,jmk^ ^ip_ ^.[^^ g 7_ 884 BEPROD UCTION. medullary groove (o) deepens, the germ shield (6) and area pel- lucida (c) lose their oval shape and Ijecorae lyre- or sole-shaped^ the area opaca {d), however, reassumes its original round shape. Returning now to the consideration of the embryo as more ad- vanced in development, it will Fig. 557. be seen that not only the me- dullary groove or furrow (Fig. 557) is much deepened, but that the external blastodermic membrane rises up into folds (Irt), which, arching over the dorsal surface of the embryo, coalesce in the middle line and form the amnion, the remain- ing portion of the external blastodermic membrane reced- ing from the amnion proper as the false amniotic folds (/'), until they finally fuse with the inner surface of the chorion. It will also be observed that the middle blastodermic mem- brane or mesoblast has split into two layers (Fig. 558, hf and df), of which hf, the skin fibrous layer, unites with the skin sensory layer h, to form the somato- pleure or the parietes of the body, while the intestinal fibrous layer df, in adhering to the liypoblast dd, forms the splanchno- Diagi'ammatic view of ovum of rabbit to show medullary furrow, amniotic folds, splitting of mesoblast. Fig. 558. In all the figures the letters indicate the same parts, h. Skin sensory layer. ;«)•. Spinal tube. /(/. Skin fibrous layer, w. Primitive vertebra;, ch. Xotoehord. c. Body-cavity {crrloma). df. Intestinal fibrous layer, ilil. Intestinal glandular layer, d. Intestinal cavity, nh. I'mbilical or vitelline vesicle. (Hakckei,. ) pleure, or the fibro-muscular wall of the primitive alimentary canal and umbilical vesicle, the space between the two layers of the meso- blast C becoming eventually the crelom or primitive body cavity, while the internal blastodermic membrane, or the intestinal glandu- DEVELOPMENT OF ORGANS. 885 lar layer d d, giving rise only to the mucous membrane lining the same. An inspection of these different sections will show also that just as the primitive neural canal, or spinal cord, is developed through the medullary groove {inr) being transformed into a tube, which later becomes entirely separated from the external blasto- dermic membrane, the latter giving rise to the epithelium or epi- dermis of the skin, so through the deepening of the furrow (d) in the internal blastodermic membrane the primitive alimentary canal is formed, the uml)ilical vesicle, originally part of the same, being constricted off Ijy the bending downward and inward of the parietes of the body. An inspection of Fig. ooS will also show that as the medullary groove or spinal tube (mr) of the external blastodermic memljrane is formed there is developed within the internal blastodermic memljrane a, rod of cartilage (cA), the notochord, or chorda dorsalis, which represents the axis around which will be developed the bodies of the future vertebrae, the neural canal being finally enclosed by a bony spinal canal, through ossification of that portion of the mesoblast lying above and on either side of the notochord. The embryo of the rabbit consists at this period, then, apart from the enveloping chorion (Fig. 558, E), of two tubes, a neural one above, an alimentary tube below, separated by a rod of cartilage, and enclosed by the walls of the body, the space between the two layers of the mesoblast representing the ccelom, or body cavity. Eesiuning what Ave have just endeavored to describe, it will be seen that through the process of segmentation the vitellus is transformed into a mass of cells, that these cells dispose themselves as three mem- branes or layers, that the three layers give rise to the primitive organs of tlie bodv, out of which the remaining organs are devel- oped, as follows : Membranes and Layers of Embryo and Organ? FROM Them. Developed Membranes. External blasto- dermic membrane or epiblast, Middle blasto- dermic membrane ■{ or mesoblast. Internal blasto- dermic membrane or hypoblast, Skin, sensory, Skin, fibrous, Intestinal fibrou.-, Intestinal oflandulur, Organs. ( Epidermis. ■ Central nervous system. ( Primitive kidneys. ( Dermis. I Peripheral nervous system. <^ Os.>;eous " I Mu.^cular •• " [ Testes. ( Vascular system. I Mesentery. ■{ Wall of alimentary canal I and appeudajres. [ Ovaries. ( Epithelium of alimentary < canal and appendages, i Notochord. 886 EEPEODVCTION. Development of Amnion, AUantois, and Umbilical Vesicle. It has already been mentioned that that portion of the external blastodermic membrane not entering into the formation of the em- bryo rises np into folds (Fig. 559) at the sides, head, and tail ends Fig. 561. a. Umbilical vesicle. 6. Amniotic cavity, c. Allantois. (Daltox.) Fecundated egg, with allan- tois fully formed, a. Umbilical vesicle, b. Amnion, c. Allan- tois. (Daltox.) Fecundated egg, with allantois nearly coinplete. a. Inner lamina of amniotic fold. h. Outer lamina of ditto, c. Point where the am- niotic folds come in contact. The allantois is seen penetrating be- tween the inner and outer laminae of the amniotic folds. (Dalton.) of the latter, and arching over its back, and coalescing in the middle line, form the amnion (a), the remaining peripheral portions of the extensive blastodermic membranes not giving rise to the amnion receding as the false amnion (h) from the trne one (Fig. 5(30), un- til it reaches the inner surface of the chorion, with which it ulti- mately fuses. It will also be seen from Fig. 559, that during the formation of the amnion (6) there buds out as an outgrowth of the posterior portion of the intestine a vesicle, the allantois (c), which, growing outward, gradually extends itself (Fig. 560), around the entire inner surface of the chorion, the cavity of the vesicle being finally ol)literate(l by the fusion of its outer and inner layers (Fig. 561). The chorion, covered with villous processes (Fig. 562, 5 di 2) at this stage will consist, then, from without inward, of the original zona pellucida of the false amnion, tlie allantois. As the allantois develops, blood vessels make their appearance in it, derived from the vessels of the foetus, as we shall see presently, which, in extend- ing into the villous processes of the chorion, serve to convey to the foetus the nutritive material introduced by osmosis from the uterine blood of the mother, the allantois constituting, in fact, the foetal part of the placenta. With the establishing of the allantois, and the consequent nourishing of the fietus by the mother, the um- bilical vesicle (Fig. 562, d s), which, uj) to this time, through its vessels, nourished the same, begins now to diminish in size, and finally disappears altogether. As the human embryo, at the ear- liest period of its existence, so far as observed — that is, from about twelve to fourteen days old — consists, essentially, of the same primi- tive organs and appendages as that of the rabbit, there can be no DEVELOPMENT OF MAMMALIAN EMBRYO. 887 cIonl)t that the still earlier stages of its development, not vet actu- ally seen, are essentially the same as those just described as taking place in the rabbit. Fig. 502. Diagrammatic figures, illustrating the development (if the nianimnlinn embryo and the ftetal membrane. 1. The blastodermic vesicle invested in the zona pclhieida, and showing at its upper pole the embryonic area. 2. Shows the j)inching oft" the embryo from the yolk-sac, and the lor- mation of the "amnion. 3. Further development of amnion, and commencement of allantois. 4. Completion of amnion, and growth of allantois. Chorion gives off villous processes. 5. The allantois has grown all round the vesicle, and gives oil' i)rocesses into the villi which are much hirger than before. The yolk-sac is greatly reduced in size. u. Epiblast of embryo, a'. Kpiblast of non-embryonic part of blastodermic vesicle, al. Allantois. aw. Amnion, ch. Chorion, ch'l. Chorionic villi. inal eolumiL First, the uotochord does not extend entirelv through the head end of the em- 890 BEPEOD UCTION. bryo bnt stops short in a tapering; point at the pituitary fossa. Sec- ond, the mesoblast does not split into the skin fibrous and intestinal fibrous layers. Third, the primordial cranium never exhibits any trace of segmentation into segments or vertebrre. That the embryo skull does, nevertheless, consist of segments of modified vertebrse, though not in the sense held by Goethe,^ the presence of visceral or l)ranchial arches clearly proves, since the latter are morphologically cranial ribs bearing the same relation to diiferent parts of the skull that the thoracic ribs bear to the vertebrae to which they are attached. As the primordial cranium of man, however, shows no trace of such segmentation, gives no evidence of having ever consisted of ver- tebra?, it is evident that the fusion or coalescence of the same must liave taken place at such an early period in the development of the vertebral type that no trace of the primitive segmentation of the skull is ever seen in the transitory condition through which it passes, even in the earliest condition of the embryo. The study of the embryonic or adult skull in man will not enable us, therefore, to determine, even approximately, the number of the primitive vertebrse through the fusion of which it has been developed. The researches of Gegenbaur - go to show, however, that the skull of the shark retains to some extent the primordial type of segmentation, in the fact of there being eight or nine branchial arches, and that the nerves emanating from the brain, excepting the olfactory and optic, bear to the latter the same relation that the spinal nerves bear to the spinal cord. If the latter be the case, and the branchial arches be regarded as homological with so many ribs, then the primitive cranium, in the shark, at least, must have been developed through the coalescence of so many vertebne. Keturning from this brief digression upon the nature of the primordial cranium in man to the Fig. 566. Fig. 567. 1 Visceral arches iu man. thread of development, let us consider what becomes of these branchial arches. The visceral or branchial arches resembling those of fishes, the intervening spaces between them being per- forated by gill-like openings or slits, as in the latter animals, are four in number in man, and symmetrically disposed (Fig. 566),. ' \'iivli()w, Goethe als Xatnrforsclier, 1861, s. 103. ^ Das Kopfskelet der Selachier, 1872. DEVELOPMENT OF SKULL. 891 and are called from before backward the first or mandibular (u), tlie second or liyoid (h), the third or thyro-liyoid (d), the fourth or mh- hyoid (r) arches respectively. Through the fusion at the middle line of the distal ends of the first visceral arches (Fi*r. 560, u), the rudimentary lower jaw (Fig. 567, a) is developed, the permanent jaw being developed by ossification {mi, Fig.j 568) around the cartilages of Meckel (J/), or the rod of cartilage that early a]>pcars within this first arch, the proxi- mal part of the cartilages of jNIeckel not related to the formation of the lower jaw becoming eventually the malleus (w) and incus («') of the middle ear. It may be mentioned in this connection that the stapes is not derived from either the mandibular or hyoid cartilages, being devel- oped as an ossification of the membrane closing the fenestra oval is. In addition to the changes just described, there grows from the root of each of the first or man- dibular arches, forward and inward, a process (Fig. 566, o), the su- perior maxillary, from which are developed the superior maxillary and malar bones, and a pair of cartilaginous rods Avhich ultimately become the pterygoid plate of the sphenoid an, which diverging to enclose the pituitary body unite beneath the anterior end of the primordial cranium to form the septum of the nose. The basis of the cranium consists, therefi)re, at an early i)eriod of development, of cartilage surrounding the notochord, and continuous where the latter ends with the trabecukv cranii, in which the basi occipital, basi sphenoid, and presphenoid bones are develoju'd from three centers of ossification, respectively; the vault of the skull, however, witli the exception of the squamo-occipital — that is, the frontal, parietal, and squamous jiortion of the temporal bones — being developed directly out of membrane, instead of out of cartil- age. During the develoi)nient of tiie su^terior maxillary process from the first or mandibular arch, as just described, there grows downward, between the primitive oH'actory grooves, later, the nos- 2. The zygomatic arch. nia. The mastoid process, tiii. Portiou.s of the h)\verjaw. M. Tlie cartihige of Meckel of the rifjht side, and a small jiart of that of the left side, joining the left cartilage at the symphysis. T. The tym- pauic ring. »(. The malleus. (. The ineus. .«. The stapes. sla. The sta])eilius muscle, s/. The styloid jirocess. p,h, g. The stylo-]ilKuynt;eus, styln-hydid, and stylo-glossus muscles, sti. Stylo-hy(jid lit^ameiit attaclied to the lesser coriiu of the hyoid bouc. //*/. The hyoid boue. th. Thy- roid cartilage." (Quais. ) 892 REPRODUCTION. trilg, the naso-frontal process (Fig. 567, m) or the termination of that ])art of the investment of the head situated beneath the fore- l^rain (v). In this way a large cavity is foi'med, bounded by the naso-frontal process above, the superior maxillary process at the sides, and the primitive lower jaw below, which later, through the inward growth and coalescence of the palatine plates, is subdivided into a mouth below and a nasal cavity above, the latter being fur- ther subdivided into two by the growth of the septum nasi — the congue growing from the inner surface of the center of the first gill arch. The second visceral arches, or hyoid arches (Fig. 566, h), growing downward, and fusing on the middle line, give rise to the lesser cornua of the hyoid bone, the stylo-liyoid ligament (Fig. 568, stl), and styloid process {st). The third visceral arches, the thyro-hyoid (Fig. 566, d), are transformed, through fusion, into the body and greater cornua of the hyoid bone. The fourth visceral arches, or the subhyoid (Fig. 566, r), do not appear to be developed into any particular organ, being situated in that part of the embryo which in the adult becomes the neck, and which is absent in the fnetus. It has just been mentioned that the branchial arches in man resemble those of fish, in that the intervening spaces are per- forated by slit-lilce openings or clefts, through which the water passes by which the vascular gills attat'hed to the arches are bathed and the blood aerated in the latter animals. Apart, however, from Development of the internal ear. (]Iai;< kkl. ) the fact of the branchial arches in man never l)eing fringed with gills, as in the fish, the same present another striking difference, in that these clefts all close up, save the first one, or that intervening between the mandibular and hyoid arches, which persists as the tympano-Eustachian tube — the latter being finally, in the adult, cut off from the exterior by the growing across it of the tympanic mem- brane. Thus, through the transformation of the proximal ends of the first and second visceral arches, and of the cleft between them, the ear bones, meatus, tympanic membrane, tympanum, and Eustachian tube are formed, the external car l)eing developed from the integument near the first and second arches ; the rudimentary internal car through the invagination of that part of the epiblast situated immediately above the upper or proximal ends of the second arch, which, in time closing (Fig. 569, A fl, B h'), becomes a vesi- cle. The latter, the rudimentary vestibule, in giving off succes- DEVELOPMENT OF ALIMENT ARY CANAL. SO 3 Develoiiiiient of the eye. (Remak. ) sivelv the tliree semicircular canals (Fig. 5(39, C, D, E, c, cp, est), and the cochlea (c), originally a straight tube, develops into the internal ear of the adult. It will be remembered, in speaking of functions of the ear, it was mentioned that the transitory stages through whi<'h it passes in its development in man are permanently retained as such in the organ of hearing in the hnver animals. Like the ear, the eye — at least the anterior part of it — appears first as an in- vagination of the epiblast (Fig. 570, A, 3), which in closing up (Fig. 570, B, 2) and separating from the same gives rise to the crys- talline lens (2). On the other hand, through the invagination of the optic cup or vesicle — that is, the peripheral portion of the optic nerve — by the indenting into it of the lens, the inner surface of the cup becomes the retina (4), the outer the tapetum nigrum of the choroid (5), the vitreous humor being developed through the insertion of the mesoblast from below between the lens and the retina. The remaining portions of the eye are also developed out of the mesoblast, through the latter growing around the ball of the eye as a fibrous capsule, Avhich, splitting into an anterior and a pos- terior layer, gives rise to the sclerotic and cornea, and choroid and iris, respectively. Though the brain and spinal cord arc developed out of the epiblast, the cranial nerves, with tlie exception of the olfactory and optic, which are outgrowths of the anterior cerebral vesicle, as well as the spinal nerves and sympathetic, are developed out of the mesoblast. Development of Alimentary Canal and its Appendages. The primitive alimentary canal, like the neural canal, extending as a straight tube from one end of the body to the other, is formed, as already mentioned, through the pinching off of the internal blas- todermic membrane and the intestinal fiV)rous layers of the middle blastodermic membrane covering it, and by the bending inward and downward of the parietes of the body, the upper portion persisting in the adult as the alimentary canal, the lower portion remaining onlv temporarily in the embryo as the umbil- ical vesicle (Fig. 571). At first the alimen- tarv tube is closed at the ends, but as develop- ment proceeds the skin at both its extremities invaginating, deep furrows are formed, which, gradually growing Fig Human embryo, with um- bilical vesicle ; about the fifth week. (Dalton.) 894 BEPRODUCTION. toward the blind ends of the intestinal tube, finally break into the latter, and so give rise to the mouth and anus. Such being the manner in whicii these apertures are formed, it is evident that their lining membrane differs from that of the remaining portion of the alimentarv canal in being developed out of epiblast instead of hypo- blast. The mucous membrane of the mouth being then invaginated skin, the salivary glands, developed through the division and sub- division of its follicular glands, must be regarded as being essentially the same kind of glands as the sudoriparous and sebaceous glands — that is, as epidermal in origin. Hence, also, the fact of the teeth of certain fishes resembling so closely their dermal spines that at the border of the mouth it is difficult to say where the one ends and the other begins. Indeed, teeth are simply calcified mucous membrane, the invaginated oral ejaithelium, giving rise to the enamel, the sub- nmcous papilla below to the dentine, the pulp being made up of a matrix of connective tissue supporting blood vessels and nerve fibers. The alimentary canal does not remain long in the human embryo a simple straight tul)e ; its al^dominal portion soon expands into the stomach, while through the elongation and coiling of the part im- mediately succeeding the latter the small intestine is differentiated from the large one. It has been mentioned that the (glandular structures of the alimentary canal are developed out of the hypo- blast or its lining membrane. This is accomplished through the invagination of the latter into the wall of the alimentary canal, formed, it will be remembered, out of the intestinal fibrous layer of the mesoblast. The simple follicular glands so formed either re- main as such, or, through elongation, become simple tubular glands, or, through segmentation, peptic or racemose glands. The liver and pancreas arise in a similar manner, the only essential difference being that these glands eidarge enormously and recede to a consider- able extent from the alimentary canal, with which they remain, however, through life in communication through their ducts. In the case of the liver, as already mentioned, the cells, like those of the remaining alimentary canal, are hypoblastic in origin, the fi- brous capsule and vessels mesoblastic, the bile ducts beginning as spaces between the cells. Development of the Vascular System. The heart, like the glands just mentioned, is also an appendage of the alimentary canal, but differs from the latter in l)eiug devel- oped only out of the mesoblastic wall of the same. Tiie heart is originally a mass of cells, but, through liquefaction of the latter, or the primitive blood corpuscles, is soon transformed into a muscular sac or tube, which remains for a short time connected by a mesen- tery (Fig. 572, hg) Avith the wall of the alimentary canal, of which it is, as just said, an outgrowth. Coincidently with the develop- ment of the heart, as just described, and in connection with it, there DEVELOPMENT OF THE VASCT'LAR SVSTE^f. 895 appears, apparently tlirough fission of the Inner and outer parts of the intestinal fibrous mesoblastic wall of the alimentary canal, the two primitive aortte and the two primitive cardinal veins, respec- tively. The two primitive aortfe uniting then divide Fk;. ■')7l'. ^gain, the two branches pass- ing along the inner surface of the first visceral arches and, curving around the anterior portion of the alimentary canal, unite anteriorly and pass as one tube into the heart. At first there are but one pair of vas- cular arches encircling the ali- mentary canal ; in time, \vm- ever, five such are developed (Figs. 573-576), three, how- ever, onlv coexisting at one period. The primitive aorta further gives oif lateral branches, of which two, passing to the um- bilical vesicle, are known as the vitelline or omphalo-mes- enteric arteries, while, through the t"\visting of the heart into nu S-like shape, the auricles become uppermost, the ventricles lowermost. Two veins, similarly named, return from the uml)ilical vesicle to the body of the foetus. niagraniniatic transverse section tbrougli the head of an eruliryonie mauiiual. A. Epidermis- plate, m. Medullary tube (braiu-bladder). inr. Wall of the latter. /.' Dermis-plate. .«. Rudinieu- tary skull, c/i. Xotochord. /;. Gill-arch. mjj. Muscle-plate, r. Heart-cavity, anterior part of the body-cavity (rr('/o;;/«). , the permanent arterial stems are represented. The dotted parts disappear. .«. .Sub- .clavian artery, r. Vertebral artery, ax. Axillary artery, c Carotid artery ((-', outer ; c", inner carotid), p. "Pulmonary artery (lung-artery). (Ratuke. ) and pass as a single trunk, the sinus venosus, into the heart. Such being the disposition of the heart and the primitive vessels, it follows that the nutritive material of the umbilical vesicle pasr^es by the 896 REPRODUCTION. Fig. 577. vitelline veins to the heart, and thence throngh the vascnlar arches to the primitive aorta and so to the l)ody generally, the circulation being completed by the vitelline arteries. Neither the heart, aortic trunk, nor vascular arches remain, however, long in the condition in which they have just been described, Tlie heart soon subdivides into a right and left heart through the growtli of a longitudinal septum, and further into auricles and ventricles (Fig. 577) through the growth of transverse septa, the septum between the auricles remaining, liowever, in- complete until after birth, the opening so caused being known as the foramen ovale. Coincidently with the development of the cavities of the heart through the growth of a longitudinal septum in the common arterial trunk, the latter subdivides into aorta and pulmonary artery, tlie aorta finally being dis- posed to the right, the pulmonary artery to the left. Finally through the transformation of the third, fourth, and fifth vascular aortic arches, the first and second having disap- peared, the aorta and its first main branches and the pulmonary artery are developed, the change being brought about through the atrophy or hypertrophy of these arches re- spectively. Thus, for example (Figs. 578— 576), of the left fifth arch (5), the internal half becomes the pulmonary artery (p), the external half the ductus arteriosus, the right fifth arch disappearing,^ The left fourth arch (4) becomes the permanent aorta and gives off the left subclavian artery (.s). The right fourth arch develops into the innominate dividing into the right subclavian and right common carotid, the left common carotid being given oif by the aorta. The third left arch (3) on both sides enters more into the formation of the internal carotid than of the external one, its outer connecting portion, as well as that of the fourth arch, disappearing. With the establishing of the allantois, however, and the dwindl- ing away of the umbilical vesicle, the allantoic or second circula- tion gradually re])laces the vitelline or first one. The allantoic or umbilical veins, (jriginally two in number, appear to be developed as branches of the vitelline veins, which, extending themselves through the allantois, finally pass into the villous processes of the (;horion. Shortly after the apj)earance of the umbilical veins, the right one disappears, and with it the right vitelline vein and that part of the left vitelline outside of the body of the embryo. The mesenteric portion of the latter, or left omphalo-mesenteric vein (Fig, 578, M), enlarges, however, while the remaining portion (O), ' The embiyo is supposed to be lying upon its dorsal surface. Heart and head of an eiu- liryonic dog, from the front. (/. Fore-brain. 6. Eyes. c. Mid-brain, d. Primitive lower jaw. i'. Primitive upper jaw. //'. Gill-arches. ;/. Right auricle. /(. Left auricle. /. Left ventricle. k . Right ventricle. ( BlSCIIOFF. ) DEVELOPMENT OF THE VASCULAR SYSTEM. 807 that returning from the unilMlical vosiolo, atrophies. At the same time the left umbilical vein (Fig. 578, U) becomes very much en- larged, and as it is a branch of the omphalo-mesenteric vein it will, Fig. o7 pearing. J. Jugular vein. S. .Subclavian vein. (Daltox.) Adult condition of venous system. 1. Right auricle of heart. 2. Vena cava superior. 3, 3. Jugular veins. 4, 4. Subclavian veins. 5. Vena cava inferior. 6, 6. Iliac veins. 7. Lumbar veins. 8. Vena azygos major. 9. Vena azygos minor. 10. Superior intercostal vein. (Dalton. ) P^rom the internal part of the latter, that which becomes later the internal iliac arteries, two vessels are given off, which, passing to the allantois, give rise to the umbilical or hypogastric arteries. In the meantime the primitive cardinal veins (Fig. 580, C C ), uniting with the jugular veins (J J), pass into the sinus vcnosus, and so to the heart, there lacing at this period then two superior vense cavie, a disposition which is retained during life in the ele- phant, manatee, rodents, monotremes, and birds. This condition, however, is only a transitory one, since a vessel {Ja, Fig. 580) is given off from the point of union of the left jugular and sub- clavian veins, which, uniting with the corresponding vessel of the right side, forms the superior vena cava (2, Fig. 581), the left primitive superior vena cava almost entirely disappearing, being only represented in the adult by the coronary sinus and a fibrous band descending obliquely on the left auricle. Such being the disposition of the venous system Avith the establishment of the allantois, or, as we shall see presently, of the placenta, the heart in the meantime having become four-chambered, the allantoic DEVELOPMENT OF THE GENITO-URINARY ORGANS. 899 or second circulation will be as follows : The blood returning from the head and upper extremities will pass to the rijrht auricle of the heart by the superior vena cava, thence by the right ventricle and ductus arteriosus to the aorta, and so to the lower extremities, and to the allantois by the umbilical arteries. The latter being nourished by blood that has circulated through the head, etc., will be relatively, therefore, poorly nourished. On the other hand, the blood of the umbilical vein returning directlv from the allantois or placenta laden with nutritive material and oxygen absorbed from the maternal blood will pass with little or no admix- ture from the portal blood into the right auricle, whence guided by the Eustachian valve it will pass through the foramen ovale into the left auricle, thence into the left ventricle, and so by the aorta to the head, lience the fact of the latter being so much better de- veloped than the rest of the body. But little blood passes through the lungs in the foetus, aeration being effected by the placenta ; on the other hand, a very large amount traverses the liver, which may be accounted for on the supposition that the liver acts as a decar- bonizer of the blood, supplementing in this way the want of action of the lungs. At all events, with the establishing of the pulmo- nary respiration, the liver becomes smaller, relatively, while in animals, generally, the lungs and liver are in an inverse ratio as regards size and functional importance. With the replacing of the second or allantoic circulation by the adult pulmonic and systemic circulations the foramen ovale closes, the ductus arteriosus, umbili- cal vein, and umbilical arteries being shrivelled up into cords. The internal portion of the latter remains, however, ])ervious, and persists in the adult as the superior vesical arteries, while the part of the allantois remaining within the body becomes the urinary bladder and urachus. Development of Eespiratory Organs. The respiratory organs may be regarded as appendages of the alimentary canal, since the trachea and oesophagus are originally one and the same tube. As development advances, the trachea separates itself from the cesophagus, the upper portiou becoming the larynx, the lower subdividiug into the two bronchi, the latter, by a process of fission and segmentation, giving rise to the bron- chial tubes and pulmonary lobules. Development of the Genito-urinary Organs. The genito-urinarv organs are so intimatclv associated iu their development that it will be found conv-enient to study them to- gether. In describing the structure of the kidney, it was men- tioned that, however complex in structure the organ may aj)j)ear to be, it consists essentially of a tube, open at oue end, from which are given off diverticula terminating in blind globular-like expausions. 5)00 REPEODVCTION. Such a primitive type of structure is presented tlirough life in the kidneys of the myxinoid fishes, and as a transitory condition in man in the early period of development. The common duct (Fig. o82, ?'•), running from end to end of the body on either side of the notochord, which gives off the primitive nrine Imi;. ">S-. tubes (Fig. '"i'^^, u), is known as the Wolffian duct and appears to be developed out of the skin sensory layer (583, u) by invagina- tion and constriction, precisely as the spinal cord is developed, the duct, however, receding (Fig. 084, /() farther from the general surface of the body than the cord, and terminating in the cloaca or lower portion of the alimentary canal. Coincidently with the development of the Wolffian duct and its diverticula, or the ])rimitive kidneys, there appears in the meso- blast just at that part where the latter splits into the intestinal fibrous layer (Fig. 584, c/), and the skin fibrous layer (// f), the so-called indifferent gland, the cells of which differ in many respects from those of which the latter layers consist, and out of which the germinal epithelium (Fig. 585, g) giving rise to either ova or spermatozoa, as the case may be, ap- pears to be developed. Such a condition of the urinary apparatus does not, however, remain long, there being developed out of the posterior portion of the AVolffian duct near where it passes into the cloaca a secondary duct, the primitive ureter, A\hich gradually o f ;i 'J' li e Primitive kidney human embryo : ii. urine tubes of tlie primitive kidney, ir. Wolffian duct. w'. Upper end of tlie latter (Morgagni'.s hydatid), m. MUllerlan duet, m' . Upper of the latter (Fallopian hy- datid), fi. Hermaphrodite gland, becoming either tes- ticle or ovary. (Koiselt. ) ^IG. 583. yn^n /P ^ ^^^/ 3^ Lj^^v^"" f- j^€^-y=E_:^ y>^ C\ V Fig. r)84. //. Skill sensory l;iyer. n. SpiiKil tulic. n. ijegiiiiiiiij; of tVoiffian body. .'■. Noto- chord. '■. l5ody cavity. /." Intestinal tibrou.s layer, il. Intestinal glandular hiver. (/. Intestinal tube. (IlAiifKKL. } )i. I'riiuitivc spinal cord. /■. Xotocliord. ///.Skin filirous layer, ir. Vertebra-. ./'. Skin sensory layer, riii. Dorsal muscles, hiii. \'eiitral muscles, i/. Mesentery. III. Indiireicnt se.xual ^laiid. le those of the normal nuile or female as due to either hypertrophy or arrest of development, that such modified organs cannot be taken alone as an evidence of sex. Development of Extremities. The limbs first appear as bud-like protuberances from the sides of the body (Fig. 585, e), those giving rise to the upper extremi- ties being developed first. While covered by the outer or skin sensory layer, the limbs are developed more especially out of the deeper or skin fibrous layer, through its cells becoming first carti- lage, with after-ossification of the same. As development advances, the primitive limb-bud recedes from the body, and expanding at its distal extremity, segments the divisio!s. (.Imicolani.; The decidua reflexa, fusing in turn, about the seventh month of pregnancy with the decidua vera,^ it so comes that at the end ot 1 It sh..ukl be mentioncHl, however, that acconling to many f ^brvologi^ts the aecidm retlexa l.oLnns to atrophv about the tilth month of gestation, and being gra(Uially absorbed finally disappears between the sixth and seventh months. RUPTURE OF MEMB RAXES. 909 pregnancy the foetus, suspended from the phu-enta bv the umbilical cord, floats in the amniotic fluid, the enclosing sac of which con- sists of the layers just mentioned. With the rupture of the latter and the escape of tlie water, etc., the child is born, and that life begins which it has been the object of this work to endeavor to describe. INDE A BSOEPTIOX, 159 J\. bv intestines, 170 of oxygen, 383 by stomach, 170 by veins, 1664 Cervical ganglia of sympathetic, 684 Chiasma, 735 Cholalic acid, 143 Cholesterin, 56, 145 Cliolin, 65 Chorda tymjjani nerve, 609, 611 Chorda' tendinea', 2:54 Chorion, 884 villous processes of, 906 Choroid, 737 Chyle, causes of flow of, 167 composition of, 167 coi-pasclcs, 194 molecular base of, 167 Chyme, 107 Cileo-spinal center, 691, 742 Ciliary ganglion, 740 muscle, 739 nerves, 740 processes, 738 Circle of AVillis, 663 Circulation, allantoic, 896 of blood, 230 capillary, in twins, 324 length of time nf entire, 335 portal dcveloi)ment of, 897 Classification of sciences, IS COj condition influencing the production of, 395 formation of, in tissues, 408 Coagulation of blood, 2 Diet, mixed bread and moat, 72 (|uantity of, 71, 74 restricted to carbohydrates, 7'.', to fat, 73 to meat, 73 in troi)ical regions, 74 Digastric muscles, action of, 92 in deglutition, lf>2 Digestion, duration of, 123 influence of exercise upon, 124 intestinal, 126 resume of, 157 I)ioxyacetone, 4-'> Dioxybcnzol, ol Disacchiirides, 45 Discord and harmony, 834 Distilled li(]Uors, 81 Du Bois Kcvmond's kev, 4ii5 Ducts of Miiller, 901 Dulcite, 45 Dulong, calorimeter of, 430 D^'spnoea, 408 EAR, S26 bones of, 828 movements of, 838 comparative anatomy of, 847 development of, 892 external, functions of, 827 internal, S40 middle, functions of, 830 Elasticity of arteries, 2(51 Elastin, 64 Electrotonus in man, 552 secondary, 546 Eleventh nerve, 640 Embryology, relation of physiology to, 22 Enamel, 87 Encephalon, weight of, ()()5 Endosmosis, 171 Endosmotic equivalent, 172 Enzvme, 100 Epiblast, 882 Epidermis, 699 Ejiiglottis, action of, in deglutition, 102 Epithelium of stomacii, 113 of villi, 166 Erythroblasts, 190 p:rythrodextrin, 49, 99 Erythrose, 45 Ethereal sulphuric acid, 67 Ethei-s of glycerin, 52 Ethylene, 66 Kupnica, 408 Excitability and conductivity, 546 I^xcreta, ratio of carbon to nitrogen in, 72 Exosmosis, 171 Expiratory center, 1)1)3 Extra-cardiac accelcratory centei-s, 631 inhibitory center, 628 Extremities, development of, 903 Eye, 734 development of, 893 cardinal points of, 759 protective appendages of. 788 Eyeball, 736 I origm of, 54 use of, 55 i Ficces, 155 I amount of, 156 j composition of, 156 Feces, nitrogen of, 4()4 Fermentation, 58, 68, 99 acid, 50 of urine, 475 alkaline of urine, 475 annufjniacal, 42 Ferments, 67 j amylolytic, 100 organized, 68 unorganized, ()7 Ferratin, 42 Ferric chloride, 42 Ferrous sulphiile, 42 ! Filjere, geminal, 571 j Fibrinogen, 205, 226 coagulation of, 62 Fick and \\'isliccnus, experiment^ of. 465 Fifth nerve, 599 Fn'tus, size and weight of, at diferent ages, 904 Food, 69 conii)osition of, 70 I plastic, 71 l)rinciplcs, 69 (pialitv of, 71 stuHs,"69 uses of, 77 Foot, movements of, 85" Foramen of Majendic, 664 j Formic aldehyde, 47 , Fourth nerve, 598 Franklin, experiments of, 42.5 GALACTOSE, 45 (jalvanometer, 512 Thomson's, 515 Ganglion, l)asal, functions of, 651 ciliary, 740 geniculate, 605 (lastric digestion, aljsence of putn-faction during, 122 juice, acid reaction of, 112 action of food upon, 119 amount of, 123 coni|iosilion of, 112 production of, 118 preparatory action of, 125 !-ecretioii of, 115 s])ecitic gravity of, 112 tidndes, 114 Gastrula, 881 (ieminal libers, 571 Generation appar.itus, female, 864 male, 872 sjjontaneous, 860 tTcniculate ganglion, 605 (Jenitalia, external, development of, 902 (ieno-hvoid nniscle. action of, in degluti- tion, 102 Glands, Eowman's, 726 916 INDEX. Glands, Brunner's, 129 laclirvmal, 788 Lieberkiihn's, 130 lymphatic, 193 mammary, 70!) Meibomian, 788 mucous, 97 parotid, 95 sebaceous, 707 serous, 97 solitary, 193 sublingual, 96 submaxillary, 96 sudoriferous, 711 termination of, 483 Globidin, 1213 Glomeruli, 453 Glosso-labial laryngeal paralysis, 644 Glosso-pharvngeal nerve, 615 Glottis, 81 1" action of, in deglutition, 102 Glucose, 45, 99 Glucoside, 45 Glucuronic acid, 49 Glycerides, 52 Glycerin, 52 aldehyde, 45 ethers of, 52 Glycerose, 44 Glycocholic acid, 143 Glycocol, 51, 66 GlycocoU, 65 Glycogen, 49 functions of, 149 Glycose, 44 (jlycuronic acid, 49, 67 Gmelin's test, 144 Goblet cells, 113 Goll, columns of, 569 Graafian follicles, 865 Graham's law of ditflisibility of gases, 380 Guanidin, ()6 Guanin, 67 Gustation, 730 Gustatory nerves, 731 HJi:MADYNAMOMETEE, 285 Ha-matin, 144, 213 composition of, 220 method of obtaining, 220 Hsematacliometer, 307 Hsematogen, 42 Hjematoidin, 144 Hicmocliromogen, 213 Hsemodromograpli, 308 Ha-modromometer, 304 Haemoglobin, 63, 213 absorption of oxygen by, 221 compcjsition of, 214 method of determining amount of, 216 of ol)taining, 213 molecular weiglit of, 215 ])hysical charactei-s of, 214 Il£ematopoiesis, 190 Hairs, 704 function of, 706 structure of, 705 Hamberger's apparatus, 359 Hard palate, action of, in deglutition, 101 Heart, 231 beat of, influence of age on, 252 of exercise on, 254 of sex on, 252 of temperature on, 255 changes in form of, 247 development of, 895 duration of movements of, in horse, 239 in man, 242 of svstole, methods of determin- ins, 243 flow of blood and contractile force of, 332 frequency of action of, 253 hardening of, 24(5 innervation of, 622, 623 insensibility of, 258 muscular fibers of, 232 nutrition of, 257 sensibility of, 632 shortening of, 246 sounds of, 249 causes of, 250 duration of, 250 fii-st, 249 second, 249 tricaspid valve of, 233 twisting of, 246 work done by the, 248 Heat, animal, production of, 423 determination of production of from analysis of excreta, 440 expenditure of, 442 and mechanical work, 444 production of, by burning food, 438 in diabetes, 465 by human being, 436 tipon mixed diet, 441 by muscle, 439 ratio of, to muscular work, 443 Heller's test, 61 Hemianopsia, 735 Hemispheres, cerebral, 659 Hempel apparatus, 385 Hepatin, 42 Hermaplirodism, 903 Hexatomic alcoliol, 45 Hexose, 45 Hippuric acid, 51, 65, 471 Histology, relation of physiology to, 23 Histio-hicmatin, t)3, 220 Homoiotliermal and poikilothcrmal, 413 Horoi)ter, 77(5 Haughton, Flint, experiments of, 466 Human voice, range of, 815 Hyaloid tunic, 750 Hydrocarbons, 66 Hvdrochloric acid, production of, 118 Hydrolysis, 99 Hydroquinone, 51 INDEX. 01 Hvtlrostatic bellows, 2S1 Ilvpermetropia, Tfili Hypoblast, S82 Hypoglossal muscle, action of, in deglu- tition, 101 nerve, 042 Hypo-xanthin, (i7 TLP:0-C.1:(AL valve. l-)2 1 Imbibition, 173 Imides, (i(> Imido-saivin, (37 xanthin, (57 Impressions, labyrinthine, inHnence of, (;.')7 tactile, inrtuence of, 6o(i visual, influence of, 6oG Indican, lol, 473 Indiffo blue, 473 Indol, ol, 07, lol Indoxyl sulphuric acid, 151 Induction apparatus, 494 Inosite, 44, 51 Insalivation, '.•5 Inspiration, muscles of, 356 Inspiratory center, 033 Interglobular spaces, 87 Intermaxillary bone, 89 Intestinal branches of pneumogastric nerve, 039 digestion, 120 juice, action of, upon food, 132 in animals. 130 in man, 131 Intestine, absorption by, 170 large, 151 contents of, 15S micro-organisms of, 151 mucous membrane of, 152 peristaltic movement of, 120 putrefactive processes of, 151 Intracardiac centers, t)23 inhibitory center, 027 nerves, (523 Intrapulmonary pressure, 349 Intrathoracic pressure, 349 and blood-pressure, 309 Iodine, 42 Iris, 739 functions of, 743 nmscular tibei-s of, 740 Iron, 42 Irradiation, 787 Iso-butyl-amid acetic acid, 05 Iso-dynamic etiuivalent, 71 Iso-maltose, 49 Isotonic solution, 37 KARYOKINESIS, 190 on melosis, 880 Katacrotic pulse, 273 Katelectrotonns, 540 Keratin, (54 Ketone, 45 alcohol, 45 Ketose, 45 Kidneys, primitive, 901 structure of, 450 Knee-jerk, 589 Koenig's manonietric apparatus, 800 Kries's apparatus, 323 Kymogra|)h, Ludwig's, 289 mercurial, 289 spring, 301 T ABYRIXTH, mcmbnmous, 841 1j Ladirymal <;lands, 788 Lactic acid, 44 derivatives, (50 Lacto-albumin, 01 Lactose, 46 Laky l)l..(.d, 213 Landx-rt's method of studying colors, 782 Laryngeal braneriments of, 412 Lenses, bi-concave, 754 lii-convex, 754 Leucin, 05, 138 Leucocytes, 04, 192 Leucomaines, (50 Levden jar, 532 Lieberkiiini's glands, 130 Ligamentum jiectinatum iridis, 736 Lijipmann's capillary electrometer, 520 Liquids, pressure of, 27(5 Litpior sant^ninis, 181 Liipiors, distilled, 81 malt, 81 Liver, 140 production of glycogen by, 147 of urea by, 15(» Lumbar ganglia of sympathetic, 687 Lungs, capacity of, .347 elasticity of, 3(5(» innervatiim of, (532 sui)ply of blood to, .347 tension of gases in, 382 Luxus, 71 Lymph, 194 amount of, 1(53 causes of How of, 1(54 composition of, 10.3 corpuscles, 103, 194 method of obtaining, 1(52 Lymphatic glands, 193 Lymphatics, structure of, 1(51 valv&< of. 1(54 Lysatin, (5(5 Lysjitinin, (50 J^ysin, (55 M ACri.A lutea, 745 Magnesium, 41 018 INDEX. Ma.ant'siiun phospliate of urine, 474 ^lajendie, foramen of, 664 IMalphijj^ian corpuscle, action of, 458 Malt liquors, 81 Maltose, 46, 99 JNIanimalian embryo, development of, 887 Mammary glands, 709 development of, 709 ^Manometer, difierential, 300 frog, 298 maximum, 296 minimum, 296 Marey, experiments of, 240 Mastication, 83 nniscles of, 90 Maxillary hones, 88 Medicine, relation of physiology to, 26 Medulla oblongata, 562 reflex action of, 587 centers of, 644 Medullary nerves, 594 Meibomian glands, 788 Meltzer's experiments, 105 Membrana ebonis, 88 Memlu-anes, rupture of, during labor, 909 Meningeal brani-Jies of tenth nerve, func- tions of, 620 Menstruation, 871 Mesoblast, 882 Methiemoglobin, 220 Methyl alcoiiol, 47 guanidin, (ii't guanidin acetic acid, W) indol, 67 Meti'onome, 365 Micturition, 459 Milk, clotting of, 46 composition of, 710 curdling of, 1 1 7 secretion of, 710 souring of, 50 -sugar, 46 Mitral valve, 234 Molecules, electro-motor, 531 Monobasic acid, 50 Mucin, 63, 99, 113 Mucoids, 63 ciu)ndro, 63 Mucous glands, 97 MuUer, ducts of, 901 Muscle, acidity of, 50 coagulation of, 50 curve, graphic representation of, 508 digastric action of, 92 in deglutition, 102 fatigue of, 853 geno-hvoid, action of, in deglutition, 102 ■ livpoglossal, action of, in deglutition, 'JOI irritability of, 851 as levers, action of, 856 of mastication, 90 mvlo-livoid, action of, in deglutition, "102 ■ Muscle, ocular, 777 papillary, 234 respiratory, wori< done by, 375 reaction of, during contraction, 855 sound, 854 striped, 849 stvlo-glossal, action of, in deglutition, "101 stvlo-hvoid, action of, in deglutition, '102 ' stylo-pharyngeal, action of, in deglu- tition, 102 temporal masseter, 91 tensor palati, action of, in deglutition, 102 termination of, 482 unstriped, 850 work done l)v, 853 Muscular contraction, law of, 551 fibers of heart, 232 sense, 722 Mvlo-hvoid muscle, action of, in degluti- tion, 'l02 Myo-albumin, (U Myo-ha^matin, 63 ^lyopia, 765 Myosin, 855 Myrmecophaga jubata, 96 NASMYTH'S cement, 88 membrane, 87 Needles, astatic, 514 Oereted, 512 Nerves, 481 auditory, 846 cells, 477 ciliary, 740 chorda tympani, 609, 611 functions of, 611 depressor, 630 electrical currents of, 523 electro-motive force of, 525 eleventh, or spinal accessory, 640 branches of, (i40 functions of, 640 origin (if, 640 eflfect of direct current upon, 549 of indirect current upon, 550 excitability of, electrotonic moditiea- tion of, 547 facial, effects of paralysis of, 615 libers, meduUated, 480 non-meduUated, 481 termination of, 482 fifth, 599 nuclei of, origin of, 6(10 roots of, long, 000 short, 600 fourtli, 598 functions of, 599 nucleus of, origin of, 598 gustatory, 731 impidse, raj)iditv of, propagation of, 509 velocity of, propagation of, in frog, 505 INDEX. rno ^"erves, velocity of, ])r()j)afjation of, in motor and sensory, in man, 507 laryngeal, inferior, functions of, G22 maxillary, snjjerior, WW medullary, ')!I4 muscle, preparation of, oOO ninth, or filossopliaryngeal, G15 branches of, (ilfl functions of, (ilT origin of, (ilo olfactory, 72() optic, 735 pneumogastric, hranciics of, intesti- nal, t);iil branches of (I'sophageal, ((37 effects of division of, (53-4 inhibitorv fibers of, origin of, 629 _ resistance of, to electrical current, 529 respirator}', afferent, (133 efferent, ()3() secretory and trophic, ()14 seventh, t)03, ()()5 seventh, functions of, 608 nucleus of, origin of, 605 sixth, 599 spinal, 565 anterior l)ranchcs of, 566 roots ol', functionsof, 567 posterior bi'anches of, 5()() roots of, functions of, 568 ganglion of, 568 recurrent sensil)ility of, 568 sympatlietic, 682 cervical ganglia of, 684 functions of, ()89 influence of, upon nutrition, 695 lumbar ganglia of, 687 structure of, 682 thoracic ganglia of, 685 tenth, or pneumogastric, 618 branches of, ()19 functions of, ()19 origin of, (US third, 594 function of, 597 nuclei of, origin of, 595 situation ot, 59() transmission of, electrical currents through, 546 trifacial or trigeminus, 599 twelfth, or hypoglossal, 642 branches of, 64.'> functions of, 644 origin of, 642 ulnar, application of current over in man, 553 iminjured, currents of action in, 542 vaso-dilator, 691 vaso-motor, 264, 689 constrictor, (')9() reffcx, excitation of, 694 vestibular, functions of, 848 Nervous system, development of, 888 structure of, 477 tissue, chemical composition of, 485 •ing colors, 7^2 Xeurin, 65 Neuroblasts, 479 Neurokeratin, 64 Neuron, 477 Neutral or indifferent point, 548 Newton's methoil of studying col Nintii nerve, ()15 Nitrogen, exhalation of, in air, 40(i imj)ortance of, 57 Nitrogenous j)roximatc principles, 43 Nodal point, 756 Nodes, S02 Non-nitrogenous proximate principles, 44 Nonose, 45 Nose, 725 Notch, dicrotic, 273 predicrotic, 273 Nuclein, ()4 Nucleo-alliumin, 42 Nucleo-hLston, 64 Nussbaum, experiments of, 458 OCULAR muscles, action of, 777 Odont(jblastic cells, 87 Qi>S3 tissues by, 408 amount of, absorlwd by moutli, 389 absorbed in 24 houi-s, 387 Oxy-myoha-matin, (jiZ 920 INDEX. PAIN, sense of, 724 Piilmitic acid, 53 Palmitin, 52 Pancreas, internal secretion of, 130 Pancreatic, fistula, 135 juice, 133 composition of, 135 method of obtaining, 134 production of, 135 Papilla^, 698 circumvallate, 730 fungiform, 730 Papillary muscles, 234 Paracasein, 117 Paraglobulin, 205, 22() Paranuclein, 64 Parotid gland, 95 Pathology, relation of physiology to, 20 Pendulum myograph, 506 Penta methyl diamin, 65 Pepsin, 116 Peptones, 120 Pericardium, 232 Peritoneum, 194 Perspiration, 713 Pettenkofer' s respiration apparatus, 387 test, 143 Phacoscope, 769 Pharnyx, constrictors of, 103 Phenaceturic acid, 65 Phenol, 51 Phenoloxybenzol, 51 Phenyl-acetic acid, 65 Physiological acoustics, 791 optics, 752 Physiology, definition of, 17 method of study, 19 order of study of, 27 relation of, to anatomy, 19 to comparative anatomy, 21 to emijryology, 22 to histology, 23 to medicine, 26 to patliology, 20 to vivisection, 24 Pituitary body, 677 internal secretion of, 677 Placenta, development of, 905 Plasma, 181 Plethvsmograph, 320 Pleura, 194 Pneumogastric nerve, 618 Pneumograpli, 363 Polar globules, or directive corpuscles, 877 Polycrotic pulse, 273 Polysaccharides, 47 Pons Varolii, 646 functions of, 647 structure of, 646 Portal circulation, development of, 897 Porus opticus, 745 Potassium carbonate, 38 cldoride, 38 j)hos])hate of urine, 474 sulphate, 3S Predicrotic iiotcli, 273 Presbyopia, 770 Press sound, 103 Primitive groove, 883 kidneys, 901 streak on axis plate, 883 trace, 882 Principal plane, 75t) points, 756 Pronuclei, conjugation of, 879 Pronucleus, female, 877 male, 878 Propylene, (Ui Protagon, 67 Proteids, classification of, 60 coagulated, 63 combined, 63 chromo-, 63 glyco-, 63 nucleo-, 63 Proteoses, 62 Protococcus, development of, 33 Protophyta, 31 ■ Protozoa, 31 Proximate principles, 28, 33 fii-st class, 34 nitrogenous, 43 non-nitrogenous, 44 organic origin of, 43 third class, 57 Pseudo-colloid, 63 Ptomaines, ()5 Ptyalin, 99 Pulmonary lobules, 346 Pulse, anacrotic, 273 dicrotic, 273 cause of, 273 katacrotic, 273 as modified by disease, 274 polycrotic, 273 production of, 266 tricrotic, 273 volume, 248 wave, rate of propagation of, 272 number of, ])er second, 272 Punctum ciecum, 749 proximum, 770 remotum, 770 Pupil, bilateral reflex, 743 constrictor center, 741 dilator center, 742 Purkinje, experiment of, 748 Putrefaction, 58, ()8 Putrescin, 65 Pyramidal tracts, crossed, 560 direct, 560 Pyrocatechin, 51 REAUMUR, experiments of, 109 Eectum, 155 Eed blood corpuscles, 182 Refraction, 753 index of, 753 Eegnault and Reiset's respiration appa- ratus, 388 Regurgitant venous pulse, 331 INDEX. 921 Renal portal system, 457 Rennin, 116 Reproduction, 860 Resonance, cause of, S()8 Respiration in animals, .'538 artificial, 371 canula used in, 372 in frog, 340 functions of larynx in, :!42 influence of dress upon, 362 inhiV)ition of, 635 internal, 408 in man, 340, 343 muscles of, 351 nasal, 341 number of, conditions influencing, 374 physics of, 348 in plants, 338 in vertebrates, 339 Resj^iratory center, 632 curves, 291 expiration, 358 muscles, work done by, 375 organs, development of, 899 pulse of Majendie, 357 quotient, 402 conditions influencing, 404 upon a fat diet, 40:! upon a meat diet, 403 upon a starcli diet, 403 upon a vegetable diet, 404 Resistance box, 491 Rete mucosum, 700 Retina, 744 cones of, 747 layei"s of, 746 rods of, 747 Retinal image, size of, 762, 780 Rheocord, long, 539 Rheoscope, phvsiological, 524 Ribs, 354 influence of respiration on curvature of, 355 Ritter-Valli law, 556 Rivinus' ducts, 96 Rubner, experiments of, 467 Running, 859 OACCHAROMYC'ES cerevisite, 68 Sacral nerves, 577 Saliva, amount secreted, 101 composition of, 99 secretion of, 9S Salivary diastose, 99 glands, nerves supplving, 612 reflex, 613 Salt solution, physiological, 37 Saponification, 53 Sciences, classification of, 18 Sclerotic, 736 Sebaceous glands, 707 fmu'tions of, 708 Semen, composition of, 873 Semilunar valve, 234 Seminal intensitv, 721 Sense of pressure or weight, 720 Sensory fil)ei-s, 561 organs, termination of, 4S3 Serous glands, 97 Serum albumin, 61, 226 gloljulin, 62 Seventh nerve, f)03, 605 Sight, perception of, 785 sensation of, 778 Silicic acid, 42 Silicon, 42 Sixth nerve, 599 Skatol, 51, 67, 151 Skatoxvl sulphuric acid, 151 Skin, 696 absoq)tion by, 717 cuticle of, 701 dermis of, 697 ei)iderniis of, 699 extent of, 697 general functions of, 69(> strnctiii-e of, 696 papilla- of, 698 rete mucosum of, 700 structure of, 703 Sleep, 679 amount of, 680 causes of, 679 Smell, sense of, acuteness of, 728 Sodium cliloride, 36 of urine, 474 glycocliolate, ^\'^, 142 oleate, 53 plios})liate, 38 of urine, 474 sulphate, 38 taurocliolate, 65, 142 Solar ])lexiis, (iSC. Solitary glands, 193 Somatopieure, 884 Sorbite, 45 Sounds, appreciation of, 832 musical, range of, 833 pitch of, 796 propagation of, 792 quality of, 800 wave, intt'iisity of, 794 Spaces, interglobular, S7 Spectrum analysis, 217 Speech, 822 center of, ()76 influence of tongue in production of, 825 Spermatozoa, 874 Spermatozor>n, maturation of, 878 Sphygmograpii, 267 method of adjusting of natunil pulse, 268 tracings taken by, 269 of artificial pulse, 270 of natural pulse, influence of aire on, 271 Spinal accessory nerve, 640 Spinal cord, 557 automatic functions of, 592 cells of, 559 922 INDEX. Spinal cord, sensorv impulses in pathway of, 572 ■_ effect of division of upon respi- ration, 636 fibers of, 559 general structure of, 558 neuroblasts of, 559 reflex action of, 585 centers of, 591 inhibition of, 591 tactile impulses in, pathway of, 573 nerves, 565 anterior branches of, functions of, 576 posterior branches of, functions of, 576 system, general anatomy of, 579 Spirometer, 377 Splanciinopleure, 884 Spleen, 195 rhythmical contractions of, 196 variations in size of, 196 Spontaneous generation, 860 Squint sound, 103 Stanuius, experiments of, 624 Starch, 48 origin of, 48 Starvation, 75 loss of tissue in, 76 Steapsin, 53, 138 Stearic acid, 52 Stearin, 52 Steno's duct, 95 Stercobilin, 155 Stereoscope, jjrinciples of, 775 Stetliometer, 366 Stethoscope, 809 Stevens, experiments of, 110 Stomach, 106 absor]jtion by, 170 digestion of, after fleatli, 121 epithelium of, 113 muscular hbers of, 107 temperature of, 124 Stromuhr or rheometer, 305 Stylo-glossal muscle, action of, in deglu- tition, 101 Stvlo-hvoid muscle, action of, in degluti- tion, 'l02 Stylo-pharyngeal muscle, action of, in deglutition, 102 Sublingual gland, i)6 Sulimaxillarv gland, i>6 Succinic acid, 50 Sudoriferous glands, 711 development of, 712 number of, 712 Sugar, 47 milk, 46 tests for, 46 Sulphates, alkaline ethereal, 51 conjugate, 151 Sulphuric acid of urine, 474 Superior maxillary nerve, 603 Suprarenal (capsules, 197 Suprarenal capsules, internal secretion of, 197 Sweat, composition of, 713 Sympathetic fibers, distribution of, 683 excitability of, 684, 686 functions of, in man, 694 sensibility of, 684, 686 nervous system, 682 Syntonin, 62 Systolic plateau, 296 IWCTILE sensibility, 719 i Taste cells, 731 pore, 731 Taurocholic acid, 143 Tea, 78 Teal's, secretion of, 789 Teeth, 83 ivoiy, 86 Temperature of animals, 413 average of human body, 417 conditions modifying, 417 constancy of, in blooded animals, 445 effects of atmospheric moisture on, 447 baths upon, 446 clothes upon, 446 size of body on, 447 sense of, 723 Temporal masseter muscles, 91 Temporo-maxillary articulation, 89 Tensor palati muscle, action of, in deglu- tition, 102 Tenth nerve, 618 branches of, auricular, functions of, 620 laryngeal, inferior, functions of, ^ 627 superior, functions of, 620 meningeal, functions of, 620 Test, Biuret, 61 Heller's, 61 xantho-proteic, 61 Testicle, internal secretion of, 875 structure of, 873 Tetanus, curve of, 502 Tetra metliyl diamin, 65 Tetrose, 45 Thalmi optici, effects of lesions of, 650 Thalnuis opticus, 649 Thermo-electric needles, 416 Tliermogenesis, or heat production, 448 Thermo-inhibitorv and accelerator cen- ters, 449 nerves, 449 Thermolysis, or heat dissii)ation, 448 Thermometer, melastatic, 415 Thermotaxis, or heat regulation, 448 Third nerve, 594 Thoracic duct, 161 ganglia of sympathetic, 685 Thyroiodin, 198 Thymus gland, 199 internal secretions of, 199 Thyroid body, 197 internal secretion of, 198 INDEX. 923 Tissues, general structure of, 29 tension of gases in, 382 Tobacco, 79 Tongue, 729 action of, in deglutition, 101 influence of, in production of speech, 82o Tonsils, 194 Tooth pulp, 88 Touch, sense of, 718 Toxincs, 05 Trachea, 344 cilia of, action of, 344 Tniube's curves, 370 Triatoniic alcoiiol derivatives, 06 Tricalcium phosphate, 39 Tricrotic pulse, 273 Tricuspid valve of heart, 233 Trifacial, or trigeniinus nerves, 599 Trimethyl oxyethyl ammonium hydrox- ide, 65 vinyl amnioiiium hydroxide, 05 Triose, 45 Troramer's test, 45 Trypsin, 137 Trvpsinogen, 136 Trvptophan, 138 Twelfth nerve, 642 Tympanic membrane, 829 vibrations of, 831 Tyrosin, 51, 05, 138 UMBIIJCAL vesicle, formation of, 886 Units, electro-magnetic, 489 of resistancee or ohm, 490 Urea, 65, 462 amount of, Davy's method of deter- mining, 463 of nitrogen in Kjeldahl's method of determining, 403 creatin and creatinin as antecedents of, 468 excretion of, conditions influencing, 464 upon difierent diets, 4()4 and exercise, 405 origin of, 467 metiiod of obtaining, 462 production of, iuHuenced by extir- paticjn of kidney, 469 Uric acid, 469 amount of, Ilaycraft's method of de- termining, 470 metiiod of i)l)taining, 469 origin of, 470 Urinary organ, development of, 900 Urine, acid fermentation of, 475 acidity of, 459 alkaline fermentation of, 475 amount of excreted in 24 hours, 474 calcium phosphate of, 474 color of, 459 composition of, 4()2 excretion of, 454 excretion of, influence of blood'pres- sure on, 455 Urine, excretion of, influence of nervous system on, 455 inorganic coastituents of, 474 magnesium ])hosphate of, 474 potassium phosphate of, 474 l)ressure of, in ureter, 455 quantity excreted daily, 460 conditions intiiiencing, 401 sodium chloride of, 474 phosphate of, 474 specific gravity of, 460 sulphuric acid of, 474 Uriniferous tubules, 45] action of, 458 structure of, 452 Urinometer, 4endix, 153 Vestibular nerves, functions of, S48 Vibrator, 240 Villi, 105 epithelium of. KiO Visceral arciies, 890 modiflcation of, 891 Vision, acuteness of, 7t>2 center of, 077 Visual angle. 7(il Vital ca])acity. 3S(» conditions aflecting, 380 Vitellin, 04 Vitelline, formation of, 886 924 IXDEX. Vitellus, se.ffmentation of, 880 Vitreous humor, 7oO Vivisection, relation of physiology to, 24 Vocal membranes, 812 tension of, 819 organs, influence of accessory, 820 Voit's respiration apparatus, 390 Vowels, production of, 823 WALKING, 8.)8 Wandering cells, 191 Water, 35 amount of, exhaled from system, 404 formed in system, 404 equivalent, 435 exhalation of, conditions influencing, 404 Whai-ton's duct, 9.5 Whippe, the, 504 Wliite blood corpuscles, 191 Willis, circle of, 663 Wine, 81 Wolffian bodies, 901 VANTHIX, 64, 67 A. Xantho-proteic test, 61 VEAST, 6S I Young-IIelmlioltz tlie;)ry of color sensations, 784 ZIXX, zone of, 750 Zone of Zinn, 750 Zymogen, 100