^^gijSft|«fKfilH|i:?*M HaXt (f^allege of Agcicultute At (f^ornell DtnioecsUg Cornell University Library QP 36.M36 The human body; a text-book of anatomy, p 3 1924 003 139 692 Cornell University Library The original of tliis book is in tine Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu31 9240031 39692 AMEBIC AN SCIENCE SEHIES. BRIEFER COURSE THE HUMAN BODY A TEXT-BOOK OF ANATOMY, PHT8I0L0QT AND HYGIENE INCLUDING A SPECIAL ACCOUNT OF THE ACTION UPON THE BODY OF ALCOHOL AND OTHER STIMULANTS AND NARCOTICS BY H. NEWELL MARTIN, D.Sc, M.D., M.A., P.E.S. Prcfem/r qf Biology in the Jolvns Hopkins University FOURTH EDITION, REVISED KEW TOEK HENEY HOLT AND COMPANY 1894 COPTRIQHT, 1883, 1884, BY HENEY HOLT & CO. PREFACE This elementary textbook of Physiology has been pre- pared in response to many requests for a textbook framed on the same plan as the "Human Body," but abridged for the use. of students younger, or having less time to give to the surject, than those for whom that book was designed. This demand, and the fact that a second edition of the " Human Body " was called for within twelve months of its publication, have shown me that I was not wrong in believing that the teachers of Elementary Physi- ology in the United States were ready and anxious for a textbook in which the subject was treated from a scientific standpoint, and not presented merely as a set of facts, useful to know, which pupils were to learn by heart like the multiplication table. That some instruction in at least one branch of Natural Science should form a part of the regular educational cur- riculum is now so generally admitted that there is no need to insist upon it. But if this instruction simply means teaching by rote certain facts, no matter how important these facts may be, the proper function of Natural Science in a system of education is missed. Mere training of the memory (no unimportant matter) is otherwise sufiBciently iv PBEFAOE. provided for in the usual school and college course of study: the true use of Natural Science in general education is different. It should prepare the student in another way for the work of subsequent daily life, by training the ob- serving and reasoning faculties. As a department of science, modern Physiology is con- trolled mainly by two leading generalisations — the doctrine of tlie " Conservation of Energy" and that of the " Physio- logical division of labor." I have endeavored in this, as in the larger book, to keep prominent these leading principles ; and, so far as is possible in an elementary book, to exhibit the ascertained facts of Physiology as illustrations of or de- ductions from them. The anatomical and physiological facts which can be described in books of the size of the present, must be pretty much the same in all. Apart from the attempt above men- tioned to make elementary Physiology a more useful edu- cational instrument than it has frequently hitherto been, the present volume differs from most others of its grade in having, as foot-notes or as append ices to the chapters, simple practical directions, assisting a teacher to demonstrate to his class certain fundamental things. The demonstrations and experiments described necessitate the infliction of pain on no animal, and require the death of no creature higher than a frog, except such superfluous kittens, puppies and rats as would be killed in any case, and usually by methods much less merciful than those prescribed in the following pages. The practical directions are, for the most part, reprints from a series of such which I drew up some years ago for a class composed of Baltimore teachers ; those ex- periments which required costly apparatus have, of course, been omitted. The interest which my " Teachers' Class" took in its work, and the good use its members subsequently made of it, have encouraged me to believe that others might be glad of a few hints as to things suitable to show to young students of Physiology. rSEFAOE. V It may be well to anticipate a possible objection. A few persons, some of tliem worthy of respect, assert that no ex- periments on an animal can be shown to a class without hardening the liearts of operator and spectators; even when, in accordance with the dii-ections given in the following pages, the animal is anaesthetised and while in that condi- tion is killed or its brain destroyed. This from an experi- ence of more than fifteen years in the teaching of practical physiology, I know to be not so. So far as the experiments described in the present book are concerned, their effect is most certainly humanizing. Young people are apt to be, not callous, but thoughtless as to the infliction of pain. When they see their teacher take trouble to kill even a frog painlessly, they have brought to their attention in a way si^re to impress them, the fact that the susceptibility of the lower animals to pain is a reality, and its infliction some- thing to be avoided whenever possible. As the question of size is no unimportant one in relation to textbooks designed for junior students with many other subjects to learn, I may be permitted to say that though this volume contains more pages than most of those with which it will have to compete, I believe it is not really lai'ger. The extra pages are due, in part to the above- mentioned appendices to the chapters, and in part to the great number and large size of the figures. My publishers had on hand electrotypes of the figures of the octavo edi- tion, and have been able to utilize them in illustrating this briefer one much better than most textbooks of its scope, without proportionately increasing its price. If I had relied solely on my own judgment the ques- tions at the foot of each page would have been omitted. But it was strongly represented to me by those whose opinion I had reason to value, that such questions were useful in enabling a student to test whether he had mastered his lesson, and that teachei's who disliked such prearranged questions could and would ignore them. I hope that VI PREFACE. the pupils will use the questions and that their teachers will not. Before concluding, I must express my sincere thanks to Miss Frances T. Bauman, who has given me the benefit of her many years' experience as an eminently successful teacher. She kindly read a large portion of the manuscript, and gave me much advice of which I have been glad to avail myself. I have also to acknowledge my indebtedness to Mr. W. H. Howell, Fellow of the Johns Hopkins Uni- versity, who has corrected most of the procf-sheets, and prepared the index. H. Newell Martin. Johns Hopkins University, Augtist 10, 1883. PREFACE TO THE SECOND EDITION. The second edition of this book differs from the first for the most part only in verbal altei-ations or typographical corrections. Chapter XXIII., however, is entirely new, and deals in some detail with the important question of the influence on health of alcohol and various narcotics. H. N. M. March 26, 1884. CONTENTS. CHAPTER I. THE GENESAL STRUCTURE AND ARRANGEMENT OF THE HUMAN BODY. PASS Human Physiology — Hygiene — Anatomy — Histology — Tissues — Organs — Tlie general plan on which the body is constructed — Man is a vertebrate animal — The two chief cavities of the body — The limbs — Man's place among vertebrates— Sum- mary 1 CHAPTER 11. THE MICROSCOPICAL AND CHEMICAL COMPOSITION OF THE BODY. What the tissues are like — Cells and fibres — The physiological division of labor and its results — The chemical composition of the body — Albumens, fats, and carbohydrates 15 CHAPTER ni. THE SKELETON. Bone, cartilage, and connective tissue — Articulations and joints — The bony skeleton — Uses of the mode of structure of the spinal column — Comparison of the skeletons of the upper and lower limbs — Peculiarities of the human skeleton 33 CHAPTER IV. THE STRUCTURE, COMPOSITION, AND HYGIENE OP BONES. Gross structure of bones — The humerus — Why many bones are hollow — Histology of bone — Chemical composition of bone — ^Hygiene of the bony skeleton — Fractures 47 59 viii CONTENTS. CHAPTER V. JOINTS. P Muscles and joints— Structure of tlie hip joint— Ball and socket joints- Hinge joints— Pivot joints— Gliding joints— Disloca- tions — Sprains CHAPTER VI. THE MTJSCLBS. The parts of a muscle — The origin and insertion of muscles — Varieties of muscles — How muscles are controlled — Gross structure of a niuscle — Histology of muscle — Plain muscular tissue — The muscular tissue of the heart — The chemical composition of muscle — Beef tea and meat extracts 67 CHAPTER VII. MOTION AND LOCOMOTION. The special physiology of muscles — Levers in the body — Pulleys in the body — Standing — Walking — Running— Hygiene of the muscles — Exercise 80 CHAPTER VIII. VVHII WE BAT AND BREATHE. How it is that the body can do work — Tlie conservation of en- ergy — Illustrations — Why we need food — Why the body is warm — Tlie influence of starvation upon muscular work and animal heat — Oxidations in the body — The oxygen food of the body — Appendix 93 CHAPTER IX. NDTKITION. The wastes of the body — Receptive and excretory organs— The organs and processes concerned in nutrition 105 CHAPTER X. POODS. Foods as tissue formers — What foods must contain — The special importance of albuminous foods — The dependence of animals CONTENTS. ix pAais on plants — Non-oxidizable foods— Definition of foods — Ali- mentary principles — The nutritive value of various foods — Alcohol — Tea and coffee — Cooking — The advantages of a mixed diet 110 CHAPTER XI. THE DIGESTIVE ORGANS. General arrangement of the alimentary canal — Glands — The mouth — The teeth — Hygiene of the teeth — The tongue — A furred tongue — The salivary glands — The tonsils — The pharynx— The gullet — The stomach — Palpitation of the heart — The small intestine — The large intestine — The liver — The pancreas 128 CHAPTER XII. DIGESTION. The object of digestion — Uses of saliva — Swallowing — The gas- tric juice — Chyme — Chyle — The pancreatic secretion^The bile and its uses — The intestinal secretions — Indigestible sub- stances — Dyspepsia — Appetite — Absorption from the ali- mentary canal — The lacteals — Appendix 153 CHAPTER XIII. BLOOD AND LYMPH. Why we need blood — Histology of blood — The blood corpuscles — Hsemaglobin — the coagulation of blood — Uses of coagu- lation — Blood serum — Blood gases — Summary — Hygienic remarks — Quantity of blood in the body — The lymph — Dialysis — The lymphatic or absorbent vessels — Summary — Appendix 174 CHAPTER XIV. THE ANATOMY OF THE CIECULATOBY OKGANS. The organs of circulation — Functions of the main parts of the vascular system — The pericardium — The heart — The vessels connected with the heart — How the heart is nourished — The valves of the heart — The main arteries of the body — The properties of the arteries — The capillaries— The veins — The course of the blood — The portal circulation — Arterial and venous blood — Appendix 193 X CONTENTS. CHAPTER XV. THE 'WOKKINa 01' THE HEART AND BLOOD VESSELS. FAai: The beat of the heart— Events occurring in each beat— Use of the papillary muscles— Sounds of the heart— Function of the auricles— "Work done daily by the heart— The pulse— Blood- flow in capillaries and veins— Why there is no pulse in these vessels— The muscles of the arteries— Taking cold— Bathing ^Appendix 216 CHAPTER XVI. THE OBJECT AND THE MECHANICS OP EESPIKATION. The object of respiration — The respiratory apparatus — The windpipe— Bronchitis— The lungs — The pleura — Pleurisy — Why the lungs remain expanded — How the air is renewed in the lungs — The respiratory movements — The respiratory sounds — Hygienic remarks— Appendix 233 CHAPTER XVII. THE CHEMISTRY OF RESPIRATION AND VENTILATION. The quantity of air breathed daily — Changes produced in the air by being breathed — Ventilation — When breathed air be- comes unwholesome — How to ventilate — Changes under- gone by the blood in the lungs — Appendix 250 CHAPTER XVIII. THE KIDNEYS AND THE SKIN. General arrangement of the nitrogen-execreting organs — Gross structure of the kidney — Histology of the kidney — The renal secretion— The skin — Hairs— Nails — The sweat glands — The sebaceous glands— Hygiene of the skin — Bathing — Appendix 261 CHAPTER XIX. WHY WE NEED A NERVOUS SYSTEM — ITS ANATOMY. The harmonious co-operation of the organs of the body — Co- ordination—Nerve trunks and nerve centres — The cerebro- spinal centre — The spinal cord— The brain — The cranial nerves— The sympathetic nervous system— The histology of nerve centres and nerve trunks — Appendix 279 CONTENTS. XI CHAPTER XX. TttE OKNERAL PHYSIOLOGY OF THE NEBVOUS SYSTEM. PAQF. The properties of the uurvnus system — Functious of nerve centres and nerve trunks — Siiisory and motor nerves — Classi- fication of nerve centres — Functions of tlie cerebrum — Of the cerebellum — Reflex nerve centres — Automatic nerve centres — Habits — Hygiene of the brain — Appendix 301 CHAPTER XXI. THE SBKSES. Common sensation and special senses— Hunger and thirst — The visual apparatus and its appendages — The globe of the eye — The retina — The blind spot — The formation of images on the retina — Short sight and long sight— Hygiene of the eyes — Hearing — The tympanum — The internal ear — Touch — The localization of skin sensations — The temperature sense —Smell— Taste 314 CHAPTER XXn. VOICE AND SPEECH. The production of voice — The pitch of the voice — Speech — Structure of the larynx — The vocal chords — Range of the human voice — Vowels — Semi-vowels — Consonants 335 CHAPTER XXni. ALCOHOL AND OTHER NARCOTICS. Introductory — Is alcohol a food? — Composition and properties of alcohol — Alcoholic beverages — The direct physiological action of pure alcoliol — Action of diluted alcohol — Absorp- tion of alcohol — Primary effects of a moderate dose of alcohol — Secondary effects of alcohol — Minor diseased con- ditions produced by alcohol — Acute alcoholic diseases — Delirium tremens — Dipsomania — Chronic alcoholic diseases — ^Deteriorations of tissue due to alcohol — Organs impaired or destroyed by alcohol — Moral deterioration produced liy alcohol — Opium and morphia — Chloral — Tobacco 843 THE HUMAN" BODY. CHAPTER I. THE GENERAL STRUCTURE AND ARRANGEMENT OF THE HUMAN BODY. Human Physiology is that department of science which has for its object the discovery and accurate de- scription of the properties and actions of the living healthy human body, and the detection of the uses, or (as physiologists call them) the functions, of its various parts. Physiologists endeavor to find out what the body, as a whole, does while alive, and what each part of it does, and how it does it; also under what conditions the work of the body is best performed; and, in connec- tion with this last aim, to furnish the basis of Hygiene, the science which is concerned with the laws and condi- tions of health. What is human physiology? What is a function? What do physiologists endeavor to discover? What is meant hy Hygiene? 1 2 THE HUMAN BODY. Anatomy. — Clearly, the first step to be taken towards finding out the use and mode of working of each part of the body is to find out what the parts are ; this study is known as Human Anatomy. Examined merely from the exterior, the body is quite a complicated structure : we can all see for ourselves, head and neck, trunk and limbs, and even many smaller but quite distinct parts entering into the formation of these larger ones, as eyes, nose, ears, and mouth ; arm, forearm, and hand ; thigh, leg, and foot. This knowledge of its complexity, which we may all arrive at by looking on the outside of the body, is -Vastly extended when it is dissected and its interior examined ; we then learn that it is made up of many hundreds of diverse parts, each having its own structure, and form, and purpose, but all harmoniously working together in health. Summary. — Anatomy is concerned with the form and structure and connections of the parts of the body. Physiology with the uses of the parts, and the ways in which they work. Hygiene with the conditions of life which promote the health of the body. Microscopic Anatomy or Histology. — When we exam- ine the body from its exterior, we observe that a numuer of different materials enter into its formatior. Hairs, nails, skin, and teeth arc quite different substances ; by feeling through the skin we find harder and softer solid What is human anatomy ? Give illustrations of the complexity of the body in structure? Is its internal structure as varied as its external ? State in a few words the subject matters of the sciences of Human Anatomy, Physiology, and Hygiene. Give examples of the variety of substances entering into the com- position of t'.ie body. What mav we feel through the skin f MIGB08G0PIG ANATOMT OB. SI8T0L0GT. 3 masses under it ; wliile the blood which flows from a cut finger, and the saliva which moistens the mouth, show clearly that liquids exist in the body. If we were to go farther and examine closely, outside and inside, any one part of the body, the hand for in- stance, we should find it made up of quite a number of different materials. On its exterior we see skin and nails ; if the skin were dissected off we should find under it more or less yellowish-white fai j beneath the fat would lie a number of red soft masses, the muscles (answering to what we call the lean of meat) ; under the muscles, again^ would be hard, rigid, whitish bones; at the finger joints, where the ends of different bones lie close together, we should find them covered by still another substance, gristle or cartilage. Finally, binding skin and fat and muscles and bone together, we should discover a tough stringy mate- rial, quite different from all of them, and which, since it unites all the rest, is called connective tissue. If we took any other portion of the body we should arrive at a similar result ; it, too, would be made up of a number of different materials, which materials might, as in the case of the foot, be identical with those found in the hand but ar- ranged together in a different way so as to perform another function (just as wood and nails may be used to budd a house or a bridge, but are put together in a different man- ner in the two cases) ; or we might, as in the eye, find in addition to some materials found in the hand others quite unlike any of them. What different materials do we see on looking at a hand ? What others would be found on dissecting away the skin ? What is the technical name for the lean of meat? What is the technical name of giislle? What is connective tissue ? Are other parts of tlie body besides the hand made up of different substances ? Illustrate by an example ? 4 THE HUMAN BODY. j The branch of anatomy which deals with the charao- i ters of the materials used in the construction of the parts ' of the body is called IdstoJogy, or, since it is mainly carried on with the aid of the microscope, microscopic anatomy. Tissues. ^ — Each of the diSerent primary building ma^ terials which can be distinguished, either with or without the microscope, as entering into the construction of the body, is called a tissue ; we speak, for example, of muscu- lar tissue, fatty tissue, bony tissue, cartilaginous tissue, and so forth ; each tissue has certain properties in which it differs from all the rest, and which it preserves in what- ever part of the body it may be found. It also is charac- terized by certain appearances when examined with a mi- croscope, whicii are the same for the same tissue no matter where it is found. The total number of important tissues is not great ; the variety in structure and use which we find in the parts of the body depends mainly on the diverse ways in whicli the same tissues are combined together, over and over again, in different parts. Organs. — A portion of the body composed of several tissues, and specially fitted for the performance of a par- ticular d uty or function, is called an organ ; thus, the hand is an organ of prehension ; the eye, the organ of sight ; the stomach, an organ of digestion ; and so forth. Summary. — The human body is made up of a limited number of tissues ;* each tissue li,as a characteristic ap- What is histology? Give another name for It. What isatissun? Give examples. How do tissues differ? Are there a large numbei- of important tissues ? How Is the variety in structure of the parts of the body produced? What Is an organ? Give examples. Of what Is the body made up ? * Thevarioua tissues of the body will be considered in more detail snbsequeutly.- the more important are-1. Bony tissue, 2. Cartilaginous tissue. 8. White flbroue TiSStTSS AND ORG Am. S pearance, by which it can be recognized with the micro- scope, and some one or more distinctive properties which fit it for some special use ; thus, it may be very tough, and suited for binding other parts together ; or rigid, and adapted to preserve the shape of the body ; or have the power of changing its length and be useful for moving parts to which its ends are attached. The tissues are variously combined to form the organs of the body, of which there are very many, differing in size, shape, and structure ; some organs contain only a few tis- sues ; others, a great many ; some possess only tissues which are found also in other organs, others contain one or more tissues peculiar to themselves ; but wherever an organ is found, it is constructed and jslaced with reference to the performance of some duty ; the organs are the ma- chines which are found in the factory represented by the body, and the tissues are the materials used in building the machines; or, using another illustration, we may, with Longfellow, compare the body to a dwelling-house ; and then go on to liken the tissues to the brick, stone, mortar, wood, iron, and glass, used in building it ; and the organs to the walls, floors, ceilings, doors, and windows, which, made by combining the primary building materials in different ways, have each a purpose of their own, and all together make the house. How are tissues recogaized ? Give examples of differences in properties of various tissues. How do orgaas differ from one another ? In wliat do all org^ins agree ? Illustrate the relation of organs and tissues to the body as a whole ? connective tissue. 4. Yellow elastic tissue. 5. Glandular tissue, of which there are many varieties. 6, Respiratory tissues. 7. Fatty tissue. 8. Sense-orcanor irritablo tissues. 9. Nervd cell tissue. 10. Nerve fiber tissue. 11. Striped muscular tissue, 12. Uustriped muscular tissue. 13. Epidermic and epithelial tissue. 6 TIIS! HUMAN BODY. The general plan on wMcli the Body is constructed. — "When we desire to gain a general idea of the structural plan of any object we examine, if possible, sections made through it in different directions ; the botanist cuts the stem of the jDlant he is examining lengthwise and cross- wise, and studies the surfaces thus laid bare ; a geologist, investigating the structure of any portion of the earth's crust, endeavors to find exposed surfaces in canons, in railway cuttings, and so forth, where he may see the strata exposed in their natural rrlative positions ; and the archi- tect draws plans which show to his clients sections of the building which he proposes to erect for them ; so, also, the best method of getting a good general idea of the way in which the parts of the human body are put together is to study them as laid bare by cuts made in different direc- tions ; this gives us a general outline and the details may be filled in afterwards. If the whole body were divided from the crown of the head to the lower end of the trunk, and exactly in the middle line, so as to separate it into right and left halves, we should see something like Fig. 1, if we looked at the cut surface of the right half. Such a section shows us, first, that the body fundamentally consists of two tubes or cav- ities, separated by a solid bony partition. The larger cav- ity, I, c, known as the ventral or hcBmal cavity, lies on the front side, and contains tlie greater part of the organs How do we start by preference to gain a knowledge of the struc- tural plan of any mass of matter? Give examples. Apply to the study of human anatomy. What shoula W6 see on examining the cut surface of a human body divided into right and left halves? What organs lie in the haemal cavity? What in the neural? How far does the hsemal cavity extend toward the head ? GENERAL PLAN OP BODY. concerned in keeping up the ■blood flow (organs of circula- tion), in breathing (organs of respiration) and in digesting food (organs of digestion). It does not reach up into the neck, but is entirely confined to the trunk. The smaller cavity, a, a', is tubular in the trunk region, but' passes on through the neck, and widens out in the skull ; it is known as the dorsal or neural cavity, and contains the most important nervous organs, the brain, N', and spinal cord, N. In the partition between the two cavities is a stout bony column, the backbone or spine, e, e, which is made up of a number of short thick bones piled one on the top of another. Man is a vertebrate animal. — The presence of these two chambers with the solid par- tition between them is a prim- ary fact in the anatomy of the body ; it shows that man is a vertebrate animal, that is to say, is a back-boned animal, and belongs to the same great What lies between the haemal and neural cavities? Of what is the spine composed? Fig, 1. — Diagrammatic longitud- inal section of the body, a, the neural tube, with its upper enlarge- ment in the skull cavity at o'; iV, the spinal cord; N', the brain; ee, vertebrae forming the solid parti- tion between the dorsal and vent- ral cavities; b, the pleural, and, c, the abdominal division of the ventral cavity, separated from one another by the diaphragm, d; «, the nasal, and o. the mouth cham- ber, opening behind into the pharynx, from which one tube leads to the lungs, I, and another to the stomach,/; A, the heart; k, a kidney ; 5, the sympathetic nervous chain. From the stomach* /. the intestinal tube leads through the abdominal cavity to the pos- terior opening of the alimentary canal. 8 THE HUMAN BOVT. group as fishes, reptiles, birds, and beasts* : sea ane- mones, clams, and insects are invertebrate animals, and built on quite different plans; sections made through any of them from the head to the opposite end, would show nothing like those two main caYities with a backbone between them which exist in our own bodies. Contents of the two chief cavities of the body. — Exam- ination of Fig. 1 shows that the ventral cavity is entirely closed itself, though some things which lie in it are hollow and communicate with the exterior. On the head we find the nose, i, and the mouth, o, opening on the veiv- tral side ; that is on that surface of the body next which the hajmal cavity lies. The nose chamber joins the mouth chamber at the throat, and from the throat two tubes run down through the neck and enter the ventral cavity. One of these tubes, placed on the ventral side of the other, is the windpipe, and leads to the lungs, Ij the other is the gullet, and leads to the stomach, /. From the stomach, another tube, the intestine, leads to the outside again at the lower or posteriorf end of the trunk. Mouth, throat. What fact in man's anatomy makes him a vertebrate animal? Name some other vertebrate animals. Name some invertebrates. How would sections made through invertebrates differ essentially from similar sections made through a man? Is the ventral cavity open? Uo any smaller cavities in it open on the exterior of the body? What openings do we find on the head? What is the Windpipe? To where does it lead? What is the intes- tine? What parts constitute the alimentary canal? Does this canal lie entirely within the haemal cavity? * Theniain groupem whichanimalsarc.arrangedare— 1. Vei'tebrata, or backboned animals. 2. MoUusca, including snails, slugs, clams, oysters. &c. 3. Arthropoda, including flies, moths, beetles, centipedes, lobsters, spiders, &c. 4. Vermes, includ- ing worms of various kinds. 5. Echinodermata (hedgehog-skinned animals), in- cluding sea urchins, stiir fishes, &c. 6. Ccelenteraia^ the sea-anemones and their allies. 7. The Protozoa ; all microscopic and very simple in structure. t In anatomy the head end of an animal is spoken of as anterior, and the oppo- site end as posterior, no matter what may bf the natural standing position of the creature. TWO CHIEF CAVITIES OF THE BODY. Q gullet, stomach, and intestine, together form the aliment- ary canal, wbicly a^w^see, begins on the head quite aboYe or aitlferioinro^^TneTJventral cavity ; then, at the bot- tom of the neck, enters the ventral cavity and runs on through it, to pass out again posteriorly ; just as a tube might pass quite through a box, in at one end and out at the other, without opening into it at all. In addition to the lungs and the greater part of the alimentary canal, the ventral cavity contains several other things of which we shall have more to say presently ; among the more important of them are, the heart, h ; the kidneys, Tc j the sympathetic nerve centers, s; and several large organs making juices which are conveyed by tubes into the ali- mentary canal and assist in digesting our food. Fig. 3.— a diagrammatic section across the body in the chest region, x, the dorsal tube, which contains the spinal cord; the black mass surrounding it is a vertebra; o, the gullet, a oart of the alimentary canal; A, the heart; sy, sympathetic nervous system; II, lungs; the dotted lines around them are the pleurae; rr, ribs; si, the breastbone. If we examined a section made across the trunk of the body, say about the level of the middle of the chest (Fig. 2), we would find, on the dorsal side, the neural tube, x, cut across, and in it the spinal cord, which is not repre- Name some organs, in addition to parts of the alimentary canal, whicli are found in the ventral cavity. Describe what would be seen on a section made across the body about the middle of the cbest, IQ THE HITMAN BODY. sented in tlie figure. The thick black mass below the neural tube is part of the spinal column ; bounded by this dorsally, by a rib, r, r, on each side, and by the breastbone, st, on the ventral side (below in the figure) is the haemal cavity, containing the lungs, I, I; the heart, h; the gul- let, a; and the sympathetic centers, sy. Fici. 3.— A section across the forearm a short distance below the elbow-joint. R and U, its two piipporting; bones, the radius and ulna; e, the epidermis and d, the dermis, of the ekin; the Tatter is continuous below with bands of connective tissue, 5, which penetrate between and invest the muscles, which are indicated by numbers, n, 71, nerves and vessels. The Limbs. — If, instead of the trunk of the body, our section were made across one of the limbs, we should find no such arrangement of cavities on each side of a bony axis. The limbs have a supporting axis made of one or more bones (as seen at ZJand R, Fig. 3, which represents a section made across the forearm near the elbow joint), but around this axis soft parts, chiefly muscles, are closely packed ; and the whole, like the trunk, is enveloped by skin. The only cavities in the limbs are branching tubes, which are filled during life either with blood, or a watery- looking liquid known as lymph. These tubes, the hlood and lympJi vessels respectively, are not, however, character- istic of the limbs, for they also exist in abundance in head, neck and trunk. How do the limbs differ from the trunk? How is each limb supported? Describe the parts exposed on a cross section of the forearm? "What cavities exist in a limb? What do they contain? Are they found in other parts of the body? MAN'S PLACE AMONG VEBTEBBATE8. H Man's place among Vertebrates, — It must be clear to every one that although man's sti-uctural plan in its broad features, simply indicates that he is a vertebrate animal, yet he is much more like some vertebrates than others. The hair covering more or less of his body, and the organs which produce milk for the nourishment of the infant by its mother, are absent entirely in fishes, reptiles, and birds, but are possessed by ordinary four-footed beasts and by whales, bats, and monkeys. The organs which form milk are the mamtnari/ glands, and all kinds of animals whose females possess them are known as Mammalia *: man is, therefore, a Mammal. In internal structure one of the most important characters of the Mammalia is the pres- ence of a cross-partition, called the midriff or dia- phragm, which separates the hseoial cavity into an an- terior and a posterior division. Tliis partition is shown at d in Fig. I, where it is seen to divide the ventral cavity into an upper and a lower story ; the upper or anterior is the chest or thorax cavity; the lower or posterior, the abdominal cavity. The chest contains the heart, lungs, and most of the gullet ; the abdomen contains the lower In what external characters does the human body differ from that of fishes, reptiles, and birds? Name some animals which agree with mankind in the possession of these cliaracters ? What are the mammary glands? What is meant by Mammalia? To what di- vision of vertebrate animals does man belong? Point out a fact in internal structure in which tlie Mammalia differ from other vertebrates? Where does the diaphragm lie? What is the name of the cavity above it? Wliat is the name of the cavity below it? Name some organs lying in the thorax. Some placed in the abdomen. Some which run through both. * Zoologists classify vertebrate animals in five groups. 1. Pisces, including all true flshca, as sharks, eels, salmons, shad, perch, &c., but excluding the so-called shellfish, as oysters, clams, and lobsters, which are not vertebrates at all. 2. Am- phibia, frogs, toads, newts, salamanders &c. 3. SeplUia, lizards, alligators, turtles, snakes. 4. Aves, birds. 5. Mamm(Uia. 12 TEE EUMAN BODY. end of the gullet (which pierces the diaphragm), the stomach, the intestine, the kidneys, and most of the organs making digestive liquids. The sympathetic nerve Fio. 4. —The tody opened from the front to show the contents of its ventral cavity. Iv,, lungs ; 7i, heart, partly covered by other things ; le, le', right and left liver lobes respectively; ma, stomach; ne, the great omentum, a membrane con- taining fat which hangs down from the posterior border of the stomach and covers the intestines; mi, spleen; zz, diaphragm. ZOOLOGICAL POSITION OF MAN. 13 centers run through, both abdomen and chest, and extend beyond the latter into the neck. The ventral cavity, opened from the front, but with its contents undisturbed, is shown in figure 4. We there see the edge of the diaphragm, z, z ; above this, in the chest, the lungs, lu, lu, and the heart, h ; the latter partly covered by other things. Below the diaphragm is the abdominal cavity, containing in its upper part the liver, le, le'; the stomach, ma ; and the spleen, mi ; hanging down like an apron from the lower border of the stomach is the omen- tum, ne, ne, which lies over and conceals the intestines. Sammary. — Man is a vertebrate animal, because his body presents dorsal and ventral cavities separated from one another by a liai'd partition ; the dorsal cavity con- tains the brain and spinal cord, and reaches into the head; the ventral cavity stops at the bottom of the neck and contains the main organs of circulation, respiration, and digestion. Man belongs to that subdivision of vertebrates known as Mammalia (1) because more or less of his surface is covered by hair ; (3) because of the presence of mammary glands ; (3) because the ventral cavity is completely sep- arated by the diaphragm into thorax and abdomen. That man is intellectually incomparably superior to any other animal, and stands supreme in the world, can Name tlie parts seen when the front wall of a man's trunk is cut away. Describe the relative positions of these parts. On what anatomical grounds do we call man a vertebrate animal? What lies in the dorsal or neural cavity? How far does the upper end of this cavity reach? What organs lie in the ventral cavity? Where does its upper limit lie? Why is man a Mammal? In what is man superior to any other animal? Prom what point of view have anato- mists to regard man's body? What sort of facts do they take into account in assigning man's position among animals? 14 TSE HUMAN BODY. be doubted by no one; still greater is his supremacy when we consider his power of forming conceptions of right and wrong, and his knowledge of moral responsibility. But anatomists have only to deal with man's body as a mate- rial object, and as such they classify it among other ani- mal bodies according to the greater or less resemblances or diiierences which are found between it and them.* * It will be found very useful to accompany the teaching of this chapter with a demonsti-ation on the body of a dead rat, kitten, or puppy. On opening the body the chest and abdominal cavities will be readily shown, and also the main organs in them. Then, on opening the skull, the brain will be seenj and on cutting across the spinal column with strong scissors, the slender soft spinal oord lying in its tube will come into view. CHAPTER II. THE MICROSCOPICAL AND CHEMICAL COMPOSITION OF THE BODY. "What the tissues are like. — Having gained some idea of how the larger parts of the body are arrauged we may next inquire what the tissues, its smallest parts which are combined to make the larger, are like. The simplest tissues are known as cells ; * they are so small that a separated cell can only be seen with the help of a microscope. In a fully formed cell (Fig. 5) we find three parts : (1) a celP body made up of a soft granular substance ; (2) a smaller and less granular cell nucleus imbedded in the cell body; and (3) a tiny dob, the nucleolus, lying in the nucleus. Cells vary much in form and size, though all are very small. A good many, like those represented at b, fig. 5.— Forms float in our blood, and are more or less o'^c^"^ ' "-on^ the rounded. In other places cells are flattened to form thin scales as those in Fig. 6, which represents cells scraped Of what are the larger parts of the body made up? What are the simplest tissues ? What instrument must we employ in order to see them ? Describe the structure of a cell. Describe some differ- ent forms of cells. * So called from an old belief that they were little bags or chambers. Most cells are really solid or semi-solid throughout. U51 16 The human bodt. from the inside of the wall of the abdomen. Elsewhere we find cells elongated, as c, Fig. 5 ; if this goes on to any great extent we get a long slender thread which is called a fiber; but very often fibers are made by a number of cells, all elongating a little and then joining together end to end. Ex- amples of fibers are shown in Figs. 35 and 85. Speaking in general terms, we may say that the whole body con- sists of tiny cells, either rounded and thick, flat and thin, or elongated to form fibers. Just as a -wall is built of distinct bricks or stones, so an organ is made up of a number of cells. All the solid parts of the body are either cells or fibers which have grown from cells, except something which corresponds pretty closely to the mortar which lies betweenwthe bricks of a wall and holds them together. This latter material, known in the body as intercellular substance, is in some places abundant, in others scanty or absent. Wherever found, the intercellular substance is made by the cells which lie imbedded in it ; they pass it out from their surfaces and repair it when necessary, and in this respect it differs very essentially from the mortar- which a mason lays between his bricks. Summary.— Cells are thus at bottom the things which Fig. 6.— Flat cells from the surface of the lining membrane of the abdo- men; a, cell body; fo, nu- cleus; c, nucleoh. What are fibers ? How are they made ? In what respect may an organ be compared to a brick wall ? Wbat corresponds to the mortar of the wall ? What makes the intercellular substance ? How ? State briefly the relationship of its cells to the structure and work- ing of the body. MIVROSCOPIO COMPOSITION OF THE BODY. 17 make up the body and do its work ; their forms and the way they are arranged together determine the form of the organs ; the things which the kinds of cells found in it can do, determine the faculties of each organ. Some cells can make a great deal of hard intercellular substance, and are employed to construct tiie skeleton ; others can change their shape and are used to form the organs which move the body ; others can elaborate peculiar solvent liquids and are used in the organs of digestion ; and so on through all the parts. Anatomy in the long run is a study of the forms which cells and intercellular substances may assume ; and physiology a study of what the cells and in- tercellular substances of the body can do. The physiological division of labor. — In a tribe of wandering savages, living by the chase, we find that each man has no special occupation of his own ; he collects his own food, provides his own shelter, defends himself from wild beasts and liis fellow-men. In a civilized nation, on the contrary, we find that most men have some one par- ticular business : farmers raise crops and cattle ; cooks prepare food ; tailors make clothes ; and policemen and soldiers protect the property and lives of the rest of the community ; in other words, we find a division of labor. Just as the more minute the division of employments in it is^ the more advanced a nation is in civilization, so an animal is higher or lower just as the duties necessary for maintaining its existence are distributed among different What determines the form of an organ 1 What its faculties ? Give examples of the employment of cells with diilerent powei'S to do different things. What is Anatomy really ? What Physiology ? Explain what is meant by the physiological division of labor. In what class of nations is the division most minute ? What decides whelher an animal is higher or lower than another ? 18 THE HUMAN BODY tissues and organs. In the lowest animals every cell is concerned in feeling, and moving, and catching food, and digesting, and breathing ; in higher animals different cells are set apart in different organs for the execution of each of these separate functions. Results of a division of labor. — Proin the division of employments in advanced communities, several important consequences result. In the first place, when every one devotes his time mainly to one kind of work, all kinds of work are better done : the man who always makes boots becomes much more expert than the man who is engaged on other things also : he can not only make more boots in a given time, but he can make better boots ; and so in other cases. In the second place, when various employ- ments are distributed among different persons there arises a necessity for a new kind of industry in order to convey that part of the special produce of any given individual which may be in excess of the needs of himself and his family to others who may want it, and to bring him in return such of their excess production as he may need. The conveyance of food from the country to cities, and of manufactures to agricultural districts, are examples of this sort of labor in civilized communities. Finally, there is developed a necessity for arrangements by which, at any given time, the activity of individuals shall be regu- lated in accordance with the wants of the whole community or of the world at large. This sort of regulation is still What do we find all cells doing in the lowest animals? How do higher animals diif er in this respect ? How does a division of labor influence the quantity of work done by a man? How the quality? Illustrate. What new kinds of employment arise when a division of labor becomes developed in a nation ? Illustrate. MICROSCOPIC COMPOSITION OF TEW BODY 19 very imperfectly carried out even in the most advanced communities, and we accordingly hear from time to time of the orer-production of this or that article ; but it is in part effected through the agency of capitalists who control the activities of many individuals in accordance with what they think to be the quantity of various articles likely to be required from time to time. Exactly similai phenomena result from the division of physiological labor in the human body. Each tissue and organ doing one special work for the whole body, and rely- ing on the others for their aid in turn, every sort of necessary work is better performed ; the tissue or organ, having nothing else to look after, is constructed with reference only to its own particular duty, and is capable of doing it extremely well. This, however, necessitates a distriiuting mechanism by which the excess products, if any, of the various organs, shall be carried to others which require them ; and a regulating mechanism by which the activities of each shall be controlled in accordance with the needs of the whole body at the time being. We accord- ingly find a set of organs, the heart a7id blood-vessels, which carry blood from place to place all over the body, the blood getting in its course something from and giving something to each organ it flows through ; and a set of nervous organs which ramify in every direction and regu- late the activity of all the more important parts. Tlie chemical composition of the body. — If we go be- yond the tissues to seek the ultimate constituents of the body, we must lay aside the microscope, and call in chem- Hnw does the division of duties in it affect the human body? What is the obiecl of the distributing mechanism? What of the regulating ? What are the distributing organs in the body called ? What is the object of the perve organs ? 20 THE HUMAN BODY. istry to our aid, to discover what elements and compounds make up tiie cells and intercellular substance. Elements found in the body.— Of the many elements dis- covered by chemists, only sixteeri. have been found in the healthy human body.* Very few exist in it uncombined. Some oxygen is dissolved in the blood; and that gas is also found, mixed with nitrogen, in the lungs. Chemical compounds existing in the body. — These are so numerous that it would be a long task to enumerate them, but some require mention : they may be divided into organic and inoi-gauic. In a general way we may say that the organic constituents of the body, if all water were separated from them, would burn if put in a fire; and the inorganic components could not be made to burn. Inorganic constituents of the body. — Of the inorganic constituents of the body, water and common salt are the most important; they are found in all the organs and liquids of the body. Phosphate and carbonate of lime are found in large proportions in the bones and teeth; and free hydrochloric acid (spirits of salts or muriatic acid) may always be found in healthy gastric juice, which dis- solves some kinds of food in the stomach. Organic constituents of the body. — All organic con- stituents of the body contain carbon, hydrogen, and How many chemical elements exist in the body? Are most of . them free or combined with others? Name those found free. Into what main groups may be divided the chemical compounds existing in the body? Name some of the chief inorganic compounds helping to build the body. Where are they found in it ? What do all organic substances in the body contain ? * The elements found In the body in health are— carbon, hydrogen, nitrogen, oxygen, sulphur, phosphorus, chlorine, fluorine, silicon, sodium, potassium, Itthlum, calcium, magnesium, iron, and manganese. CnSMICAL COMPOSITION OF THE BODY. 21 oxygen; some contain nitrogen also. There are three chief kinds of them, tIz. : albumens, fats, and carbohydrates. Albuminous or proteid substances. — These are by far the most characteristic organic compounds existing in the body; they are only known as obtained from living beings, having never yet been artificially constructed in the labo- ratory; a good example is found in the white of an egg, which consists chiefly of albumen dissolved in water. All the tissues of the body which have any marked physiolog- ical property contain some albuminous substance, only such things as hairs, nails, and teeth being devoid of them. All albuminous bodies contain nitrogen, carbon, hydrogen, and oxygen; most of them sulphur and phos- phorus in addition. The more important ones found in the body are, (1) Serum alhwmen, which is very like egg albumen, and is found dissolved in the blood; (2) Fibrin, which forms in blood when it clots; (3) Myosin, found in the muscles and "setting" or coagulating after death, when it causes the death stiffening; (4) Casein, found in milk, and forming the main bulk of cheese. Fats belong to the organic compounds in the body which contain no nitrogen; they consist solely of carbon, hydrogen, and oxygen. The chief fats in the body are palmatin, stearin, and olein ; by proper treatment each can be split up into glycerine and a fatty acid; palmitic, stearic, or oleic acid as the case may be. What is found in addition in some of tbem ? How many chief varieties of organic compounds are there in the body ? Name them. Give another name for albuminous substances. Can they be made artificially? Give an example of an albumen. What elements do albumens contain 7 Name the more important albumens of the body ? Where are they found ? What elements do fats contain ? Name the chief fats of the body. Into what may they be decomposed ? 23 THE HUMAN BODY. The carbohydrates also consist entirely of carbon, hydrogen, and oxygen ; they belong to the same class of substances as starch and sugar. The most important car- bohydrato in the body is glycogen, a sort of starch found stored up in the liver and muscles. Glucose or grape sugar also exists in the body; and laciose'or milk sugar is found in milk. What elements do carbohydrates contain ? Name the most im- portant found in the body t Where is glycogen found ? When milk sugar ? CHAPTER III. THE SKELETON. The skeleton * of the human body is composed of three materials : tone, cartilage, and connective tissue. The hones form the main supporting framework of the body, and determine its shape ; they provide levers on • which the muscles moving the body pull, and are arranged so as to surround cavities in which soft, delicate organs, as brain, spinal cord, and heart, may lie in safety. Cartilage finishes off many bones at joints, forming elastic pads with smooth surfaces ; it is also used instead of bones in some parts of the skeleton where considerable flexibility is required. Cartilage affords one of the best tissues of the body for the examination of intercellular substance. A thin slice of it highly magnified. Fig. 7, shows the cartilage cells, a, i, scattered through an almost structureless material. Very young cartilage consists of Of what is the skeleton made up ? What functions do the bones fulfill ? Where is cartilage found ? What are its purposes ? What is seen when a thin slice of cartilage is highly magnified ? Of what does young cartilage consist. * There are two kinds of skele.rcn met with in the animal kingdom ; the external skeleton or exoekeleton, and the Internal skeleton or endoskef-eton. The exoskeleton is made by the skin, either in it or on it ; examples are found in the shells of clams and lobsters ; the scales of fishes and snakes ; the tortoise-shell of turtles ; the feathers of birds; the hair and claws of beasts. In man the exoskeleton is only \v ~^ I !?*M ,^y>r ; i I r^:^ ^^P' Fig. 7.— a thin slice of cartilage highly magnified. of the cartilage, and giyes this the elasticity and flexibility for which it is used in the body. Connective Tissue occurs partly in the form of stout cords — ligaments — which bind different bones together ; or which, called tendons, attach muscles to bones. It also supplements the coarser bony skeleton by a finer one, which extends as a fine network through all the soft parts of the body, making a sort of microscopic skeleton What is a ligament? A tendon? Of wbat are ligaments and tendons composed f Where else do we find connective tissue ? THE BKELBTON. 25 for its cells, and being laid down as a soft packing material, a good deal like raw cotton, in the crevices between different organs, as shown at s, Fig. 3, where it is seen between the muscles of the fore- arm. This tissue is, in fact, so widely spread over the body, from the skin outside to the lining of the alimentary canal within, that if we could employ a solvent which would corrode away all the rest, and leave only the connec- tive tissue, a- very per- fect model of all the organs would be left ; something like a skele- ton leaf, but far more minute in its tracery. Articulations and Joints. — If the pieces forming the hard frame- Por -niiiit purposes ? What would be left if all materials composing the body except its connective tissue were dissolved awa^ ? Vfa- 8;T^'lie bony and cartilaginous skeleton. 26 THE HUMAN BODY. ■work of the body were put together like the beams and planks of a frame house, the whole mass would be rigid and immovable ; we could not raise a hand to the mouth, or put one foot before another. In order to attain mobility the bony skeleton is made np of more than two hundred separate pieces, joined together; the points where they meet are called articulations. An articulation at which a considerable range of movement is permitted is called a joint. The ends of bones which rub over one another in a joint are always covered by a very smooth layer of cartilage. The bony skeleton (Fig. 8) consists of an axial skeleton, supporting head, neck, and trunk, and an aiJpendicular skeleton, supporting the limbs and attaching them to the t^'ink. ^^ ^^^ The Axial Skeleton. — The fundamental portion of this is the backbone, spinal column, or spine, partly seen at e and c. Fig. 8, and represented isolated from the rest of the bones and viewed from the left side in Fig. 9. It forms an axis, on which the rest of tlie body is carried. On the upper end of the vertebral column is the skull, a, b. Fig. 8, and attached by ligaments to the under surface of the skull is the hyoid bone, to which the root of the tongue is fastened. Attached to the sides of part of the spine are the dor- sal ends of the ribs, slender bones which curve round the Wby is the skeleton made up of separate bones ? What are articulations? What is a joint? What covers the end of a bone in a joint ? What are the chief divisions of the bony slieleton ? What parts of the body does the axial skeleton support ? What is the appen- dicular skeleton? What is the fundamental portion of the axial skeleton? What does it bear on its upper end? What is the hyoid bone ? What are the ribs? Where are their ends fixed t PBOTOBAL AROH. a? Bides of the chest and are united in front to the sternum, or Ireastbone, d. Fig. 8. Skull, hyoid bone, vertebral column, ribs, and sternum together form the ; axial skeleton. The appendicular skeleton consists of the pectoral and pelvic girdles, at- taching the limb bones to the axial skeleton ; and of the bones of the limbs themselves. The pectoral arch or girdle consists on each side of a clavicle or collar-bone, u, and a scapula or shoulder-blade, which latter is a fliit, triangular bone, lying on the back of the chest outside the ribs. The clavicle is a slender curved bone like an italic /in form. Its outer end is attached to the scapula, and its inner end to the top of the sternum. It serves to brace out and support the shoulder-joint, and to prevent it from falling downwards and inwards toward the front of the chest. It is absent in beasts which use their fore limbs for walking only, as horses, dogs, and cattle, but is well developed in mon- keys and bats. Fio. 9.— Side view of the spinal colamn. Name the parts which make up the axial skeleton ? Of what main divisions does the appendicular skeleton consist? What hones exist in the pectoral arch ? Where does each lie ? What is its shape ? Name some animals which have no collar bones, and some which have them. 28 TEE HUMAN BODY. The skeleton of the upper limb consists of : (1) The arm bone, or humerus, t, Fig. 8, which extends from the shoulder to the elbow, and meets the scapula at the shoulder-joint ; (3) of two forearm bones, the radius, g, and ulna, f, the radius being on the thumb side ; and (3) of twenty-seven hand bones. Of the hand bones eight, the carpal iones, h, lie in the wrist ; five, the metacarpal hones, i, in the palm of the hand ; and fourteen, the pha- langes, Tc, in the thumb and fingers — two for the thumb, and three for each finger. The pelvic arch or girdle consists of a single bone, the / OS innominatum, s, on each side ; this is firmly fixed at its dorsal end to the lower part of the back-bone, meets its fellow veutrally at the lower end of the abdomen, and bears a deep socket on its outer side, into which the upper end of the thigh-bone fits. The skeleton of the lower limb consists of : (1) The thigh-lone or femur, r, the longest bone in the body, bearing above a hemispherical knob fitting into a hollow on the outside of the os innominatum, with which it forms the hip-joint ; (2) of two bones, tihia and fibula, I and m, in the lower leg, the former on the great toe side ; (3) of How many bones are there In the upper limb? Which of these lies between the elbow and shoulder joints? With what bone does it articulate above? Name the forearm bones. Which of them lies to the outer side when the palm of the hand is turned forward? How many bones are there in the hand? Where are the carpal bones? How many of them are there? The metacarpal bones ; position and number? The phalanges of the hand ; position and number ? How many bones form the pelvic arch? What are they named? To what are their dorsai ends attached? Where do they meet one another ? What bone of the leg forms a joint with the mnommate bone ? What is the first bone in the skeleton of the lower limb ? How does it end above ? With wliat bones does it articulate ? At what joints ? What bones extend from the knee to the ankle joint ? Which of them is on the inner side of the leg ? SKELETON OF FOOT. 29 the knee-cap or patella, q, in front of the knee-joint ; (4) of twenty-six foot bones. Of the foot bones seven, the tarsal bones, n, lie below the ankle-joint ; five, the meta- tarsal bones, a, succeed these in the front half of the sok Fsa Fig. 10.— The last lumbar vertebra and the sacrum seen from the ventral side, Fsa. anterior sacral foramina. of the foot ; and fourteen phalanges, p, are found in the toes ; two in the great toe and three in each of the others. Where is the patella? How many bones are there in each foot? Into what groups are the foot bones classified? Where are the tarsal bones? How many ? The metatarsal ? How many ? The phalanges ? How many ? 30 TSE BUM AN BODY. The vertebral column.— (Fig. 9.) The upper portion of the spine consists of twenty-four separate bones, each called a vertebraj these are piled one above the other, and separated by elastic pads made of cartilage and connective tissue. Seven vertebrae {cervical, C 1-7) are found in the neck ; twelve {dorsal, D 1-12) lie at the back of the chest and carry the ribs ; and five {lumbar, L 1-5) are in the loins. Below the separate vertebrae comes the sacrum, {S 1), which is shown as seen from its ventral aspect in Pig. 10, along with the lowest lumbar vertebra. In childhood the sacrum consists of five distinct vertebrae, but these grow together afterwards, though cross ridges remain indicating the original lines of separation. Succeeding the sacrum and forming the lower end of the spine is the coccyx {Co, 1-4, Fig. 9), a single bone in adults, though consisting of four pieces in children. The structure of a vertebra. — Those vertebrae which remain permanently separate resemble one another in general form, with the exception of the uppermost two. As an example we may take the eleventh from the skull, that is the fourth dorsal vertebra (Figs. 11 and 12). In it we find (1) a thick bony mass, O, rounded on the sides and flattened above and below where it is turned toward its neighbors ; this part is the centrum or body of Of what is the upper portion of the backbone composed? What are the bones forming it culled? What lies between them? How many vertebrae in the neck ? In the chest region? In the loins? Of what parts is the lower portion of the vertebral column com- posed? How many vertebrae form the sacrum? At what period of life are they separate? How is this original separation Indicated on the sacrum of adults? How many vertebrse are united to form the coccyx? What vertebrae differ essentia'.ly in form from the rest? Describe a typical vertebra. A VERTEBRA. 31 the vertebra ; the series of vertebral bodies forms the bony partition (e, e, Fig. 1) already mentioned as existing in tlie trunk between the neural and hsemal cavities. (2) An arch attaclied to the dorsal side of the centrum ; it is the neural arch, A, and with the centrum incloses the neural ring (Fv). The vertebrae being piled one above the other the successive neural rings form the neural tabe, in the Fig. 11. Fig. 12. the end turned from he Fig. 11.— a dorsal vertebra seen from behind, i.e. head. Fig. is. — Two dorsal vertebrae viewed from the left side, and in their natnral relative positions. 6', the body ; A. neura] arch ; Jf^. the neural ring ; Fs, spi- nous process ; Paft. anterior articular proce.«i3 : Pai, posterior articular process : IHy transverse process ; Ft, facet for articulation with the tubercle of a rib ; Fc8^ Fci, articular surfaces on the centrum for articulation with a rib. cavity of which the spinal cord lies. (3) Projecting from the body and arch are several processes ; one reaching out from the dorsal side of the arch is the spinous process; the row of spinous processes which may be felt through the skin along the middle of the back has given the name of spinal column to the whole backbone. What constitutes the hard partition between the dorsal and ventral cavities tif the trunls;? How is the neural tube formed? Why is the spinal column so named V 32 TEE HUMAN BODY. Where the arch joins the centrum it is narrowed to a stalk or 'pedicle, 1%, Fig. 13. When the yertebrEe are placed together in their natural relative positions, apertures {Fi), leading into the neural canal, are left between their nar- rower portions ; through these apertures (called the inter- vertebral foramina) nerves pass out from the spinal cord. The atlas and axis. — The first and second cervical ver- tebra differ considerably from the others. The first, called the atlas (Fig. 13), carries the head ; it has a very Fas Frt Pal Fig. 13. j-ia. 14, Fig. 13.— The'atto*. Fig. 14.— The aa!fe. ^a, body of atlas, i), odontoid pro. cess of axis ; Fas, facet on upper side of atlas with which the skull articulates • and in Fig. 13, anterior articular surface of axis : L, transverse ligament • Frt I'ertebral foramen. > ■ "1 small body and a very large neural ring. A ligament, L, divides the ring into a ventral and a dorsal portion /the spinal cord passes through the latter and a bony peg, D, lies in the former. The peg is the odontoid or tooth-like process. This reaches up from the second cervical or axis vertebra (Fig. 14) and forms a pivot around which the atlas, ^^How are the intervertebral foramina formed? Wliat is their pur- What is the first, cervical vertebra called? Describe its general form _ How is Us neura r ng divided? What iie, in each difSon What IS the second cervical vertebra named? What is the odontoid SPINAL COLUMN. 33 carrying the skull with it, rotates when the head is turned from side to side. On the anterior (upper) surface of the atlas are a pair" of shallow hollows. Fas; into these fit a pair of knobs, found towards the back of the under surface of the skull (Fig. 30), which glide in the hollows during nodding movements of the head. Uses of the mode of structure of the spinal column. — When the backbone is viewed from one side (Fig. 9) it is seen to present four curvatures ; one in the neck, convex ventrally, is followed by a curve in the ojiposite direction in the dorsal region ; in the loins the curvature is again convex ventrally, and opposite the sacrum and coccyx the reverse is the case. These curves add greatly to the springiness of the spine, and prevent the transmission of sudden jars along it.* The compressible elastic pads placed between the centra of the vertebrse promote the same end ; the skull, containing the soft brain (which would be readily injured by mechanical violence) and the spinal cord, contained in the backbone itself, are thus protected from jarring in running, jumping, &c. The compressible pads between the bodies of the verte- brae allow of a certain range of movement between each pair, so that the column as a whole may be bent to a con- How is the skull articulated to the backbone? How many curvatures are there in the backbone? What is their direction? What results from the curvatures of the spinal column? What is the object of the pads between the vertebrae? * Tate a straight but tolerably flexible and elastic bar, as a lath, or, better still, a thin steel rod. Hold it vertical, with one end resting on the floor, and give a smart blow on the upper end ; the jar will be sudden and violent. Now bend the rod and hit it again ; the jar will be much less, as the curved rod yields somewhat to the blow on its top. 3 34 TSE HUMAN BODY. siderable extent in any direction. On the other hand, these pads so limit the movement that no sharp bend can occur at any one point, sucli as might tear or bruise the spinal cord lying in the neural canal. The sacral vertebrae grow together firmly to give a solid support to the pelvic arch, which transmits the weight of all the rest of the body to the lower limbs when we stand. Summary. — The back-bone is rigid enough to sup- port all the rest of the body ; flexible enough to bend considerably in any desired direction, yet not sharply at any one point ; and elastic enough to destroy or greatly diminish any sudden jar or jerk which it may receive. It is one of the most beautiful pieces of mechanism in the body. The ribs are twelve in number on each side (Fig. 15). They are slender curved bones embracing the sides of the chest, and attached at one end to the dorsal vertebrae. Ventrally each rib ends in a costal cartilage ; the carti- lages of the seven upper pairs are directly articulated to the sides of the breast-bone. The eighth, ninth, and tenth cartilages join those of the ribs above them ; the eleventh and twelfth are not attached to the rest of the skeleton at their ventral ends, and are known as the/?-«« ot: floati7ig ribs. How is it that we can bend the backbone? How is the extent of bending at any one point limited? Why? Why do the sacral vertelira3 grow together? State briefly the mechanical properties of the vertebral column. How many ribs are tliere ? What is their shape ? To what are their dorsal ends attached? How dues each rib end ventrally? To what are the costal cartilages of the first seven ribs attached? To wliat the next three costal cartilages? Which are the floating ribs? Why so called? TBE SKULL. 35 Pig. 15.— The ribs of the left side, with the dorsal and two lumbar vertebrae, tne riD cartilagea, and the sternum. The skull (Fig. 16) is composed of tweirb[-e|ght bones : eight of these, forming the cranium, are so arranged as JIow many bones in the skull? 36 THE HUM AN BODY. to surround the brain and protect the ears ; six lie inside the ears ; and the remaining fourteen support the face, Tsp Fig. 16. — A side view of the skull. 0, occipital bone ; 7', temporal • iV,parie' tal ; F, frontal ; S, sphenoid ; Z, malar ; Mx, maxilla ; N, nasal ; i?, ethmoid ; i, lachrymal ; Md. inferior maxilla, surround the mouth and nose, and (with the aid of some of the cranial bones) form the eye-sockets. How many in the cranium? "What purposes do the cranial bones fulfill? How many lie inside the ears? How many bones in thg face? "What parts do the face bones support and protect? CRANIVM. 37 The cranium is a box witli a thick floor (Fig. 1), con- tinuing forwards the partition which in the trunk separates the neural from the haemal cavity. On its under side (Fig. 30) are many small apertures through which nerves and blood-vessels pass in or out, and one larger one, the foramen magnum, through which the spinal cord passes in to join the brain. The cranial bones (Fig. 16) are the following : 1. Tlie occipital bone, 0, unpaired, and having in it the fora- men magnum. It lies at the back of the skull. 2. Tlie frontal ione, F, also unpaired, lies in the forehead. 3. The parietal 1)0716$, Pr, two in number, meet one another above the middle of the crown of the head, and form a great j^art of the roof and sides of the skull. 4. The tem- poral lones, T, one on each side, opposite the temples ; on the exterior of each temporal bone is a large aperture leading into the ear cavity, which is contained in this bone. 5. Tlie sphenoid ione, unpaired, and lying in the middle of the bas&of the skull, but sending out a wing, S, which reaches some way up each side, just in front of the temporal. 6. Tlie ethmoid tone, E, forms the partition be- tween the brain and nose chambers, and part of that be- tween the nose and the eye socket. The facial skeleton. — The majority of the face bones are in pairs, but two are single ; one of these is the loioer jaio lone or mandible, Md, Fig. 16 ; the other is the vomer, "With what is the floor of the cranium continuous? Where does the cranium present holes through it? What are most of these aper- tures for? What is the largest aperture called? What enters the brain case through it? Name the cranial bones. State where each lies. Through which does the foramen magnum pass? Which contains the ear chamber? Which of them are unpaire4? 38 TEE HUMAN BODY. which forms part of the partition between the two nostrils. The paired face bones are : 1. The viaxillcB or upper jaiv-boms, Mx, which carry the upper teeth and form most of the hard palate separating the mouth from the nose. 2. The palate hones, completing the bony palate, and behind which the nostril chambers communicate by the posterior nares (Fig. 20) with the throat cavity, so that air can pass in or out through them in breathing. 3. The malar or cheek-hones, Z. 4. Tlie nasal hones, N, roofing in the upper part of the nose. 5. The lachrymal or tear- bones, L, small and thin, lying between the eye-socket and the nose. 6. The inferior turbinate or spongy hones, which lie inside the nose, one on the outer side of each nostril chamber. The cranial sutures. — All the bones of the skull, except the lower jawbone, are immovably joined together. In the case of most of the cranial bonos this occurs by a dove- tailing, like that used by cabinet-makers. Each bone has its edges notched, and the notches fit accurately into hol- lows on the bone it articulates with ; this kind of articula- tion is called a suture; it is well seen in Fig. 16, between the parietal bone and those in front of, behind, and below it. Comparison of the upper and lower limbs and their supporting arches. The bones of these have already Name the unpau-ed face bones. Where does each lie? Name the paired face bonos. St-ate the position of each in the skull. What bone eavries the lower teeth? Which the upper? What bones form the hard palate? By what openings do the nose chambers communicate with the throat? Behind what bone do these openings lie? What cranial bone is movable? How are most of the cranial bones joined together? Describe a suture? SKELETONS OW LIMBS. p Fio. 17.— The skeleton of the arm and leg. H, the humerus; Cd, its articular head which fits into the glenoid fossa of the scapula; U, the ulna; R, the ra- dius; O, the olecranon; Fe, the femur; P, the patella; M, the fibula; T, the tibia. been enumerated, but certain resemblances and differ- ences between the skeletons of the two limbs (Pig. 17) are worth noting. In general plan it is clear that they 40 THE BUM AN BODT. correspond pretty closely to one another; the pectoral arch answers to the pelvic ; the humerus to the femur ; the radius and ulna are represented by the tibia and fibula J five metacarpal bones correspond to five meta- tarsal, and fourteen phalanges in the digits of the hand ,to fourteen in tlie digits of the foot ; elbow and knee-joints, and wrist and ankle are comparable. There is, however, in the arm no separate bone at the elbow answering to th-e patella at the knee ; but the ulna bears above a bony process, 0, which is in early life a separate bone and represents the patella. There are in the adult carpus eight bones, in the tarsus but seven ; here again we find, however, that originally the astragalus, Ta (Kg. 19), of the tarsus consists of two bones. The elbow-joint bends ventrally and the knee-joint dorsally. When we compare the limbs as a whole greater differ- ences come to light, differences which are related to their different uses. The arms, serving as prehensile organs, have all their parts as movable as is consistent with the requisite strength ; the lower limbs, having to carry all the weight of the body, have their parts more firmly knit together. Accordingly we find the shoulder girdle, G, S Do the upper and Icwer limbs correspond in general plan of struc- ture ? What in the lower limb answers to the pectoral girdle ? What to the humeius ? What bones to those of the forearm ? What to the metacarpiil ? Do the phalanges of the hand and foot agree in number 1 What joints in the leg answer to elbow and wrist ? What bone in the leg is not represented by a separate bone in the arm of adulis? What in the arm corresponds to this leg bone'? Is it ever a separate bone? Which has more bones, hand or foot? How many bones are there in the tarsus in infancy? How many after wards unite to form one? What is the bone formed by this union named? How do elbow and knee joints differ as to the direction in which they bend? Why are the arms made as movable as possible? Why are the lower limb bones more firmly knit? BHOtJLDER AND PSLYIS. 41 Fig. 18, only directly attached to the axial skeleton by the ventral ends of the collar bones, and free to make consid- Pia. 18.— The skeleton of the trunk and the limb arches seen from the front. C clavicle ; 5, ecapula ; Oc, innominate bone attached to the side of the saorum dorsally and meetinET its fellow at the pubic symphysis in the ventral median line. arable movements, as in "shrugging the shoulders." The pelvic girdle, Oc, on the contrary, is firmly and immova- bly attached to the sides of the sacrum. How is the shoulder girdle united to the axial skeleton? Can it move? Give an instance? How is the pelvic attached? Is it movable? 42 ^SM nOMAS BODY. The socket on the outer end of the shoulder-blade, with which the humerus forms the shoulder-joint, is very shal- low, and allows of much freer movement than is permitted by the deeper socket of, the pelvis, into which the top of the thigh bone fits. If we hold one humerus tightly and do not allow it to rotate, we can still move the forearm bones so as to turn the palm of the hand up or down ; no such movement is possible between tibia and fibula. Fig. 19— The bnnes of the toot. Ca, Calcaneum, or heel boue ; Ta, articular surface foi- tibia on the astragalus; Cb, the cuboid bone. In the foot the bones are much less movable than in the hand, and are so arranged as to make a springy arch (Fig. 19) which bears behind on the heel bone, Ca, and in front on the far ends, Os, of the metatarsal bones ; over the crown of the arch at Ta is the surface with which the leg-bones articulate, and on which the weight of the body bears when we stand. Which is deeper, the socket on should ei- -blade for humerus, or on pelvic girdle for femur? Can the foot be turned round so as to bring its sole upwards? Can the hand so as to bring the palm up? Are the hand or the foot bones more movable? How are the foot bone9 arranged? On what points does the arch of the foot bear? On what pait of the ai'ch is the weight of the body borne? PEGVLtAnirtBS OP TSE HUMAN SKELETON. 43 The toes are far less mobile than the fingers, the difference between great toe and thumb being especially marked. The thumb can be made to meet each of the finger-tips, and so the hand can seize and manipulate very small objects, while this power of 02}£OSi'7ig the gj^eat toe to the others is nearly absent in the foot of civilized man. In infants, and in savages who have never worn boots, the great toe is often much more movable, though it never acts so completely like a thumb as it does in most apes, whose feet are used for prehension nearly as much as their hands. Our own toes can by practice be made much more movable than they usually are; persons born without/ hands have learned to write and paint with the toes. ' Peculiarities of the Human Skeleton. — There are some interesting points in the structure of the human skeleton, connected with our power of maintaining the erect posture, and of progressing on the feet so that the hands are left free for grasping. In no other vertebrate is the division of labor between the anterior and posterior limbs carried so far; the highest apes often use the hand in locomotion and the foot for prehension. As characteristic of man's I skeleton we may note: 1. The skull is nearly balanced* on the top of the verte- bral column (Fig. 20) so that but little effort is needed to Are toes or fingers more mobile ? How does the thumb difEer in this respect from the great toe? What reason have we to think that the shoe has produced this effect ? In what animals is the great toe more movable? What power have their feet in consequence? Can we make our toes more movable by practice ? Illustrate. With what facts are the more marked peculiarities of the human skeleton connected? In what living creature is the division of labor between arms and legs carried farthest ? Does the skull of man nearly balance on its support ? * The balance is, however, not quite complete. When any one goes to sleep in an ill-ventilated lecture room he is usuallyawakeued by a sharp jej-k downwardsof 44 ma HUMAN BODY. keep the head erect. In four-footed beasts the sknll, being carried on the front end of a horizontal backbone, needs j special ligaments and considera- f ble muscular efEort to support it ; in apes the skull does not nearly balance on the top of the spine ; its face is much heavier than its back part, while in men the face bones are relatively smaller and the cranium larger. To keep the head erect 'and look things straight in the face " like a man " is far more fatiguing to monkeys, and they cannot maintain that position long. Fis. 20.— The base of the ekull. « mi i - t i „ . Thelowerjawhae been removed. 2. i he human Spmal COlumn, j At the lower part of the figure is . i_i j. j. . ' the hard palate forming the roof when TlCWed irom the iront, IS/ of the mouth and surrounded by i n j. j.i_ ' the upper set of teeth. Above seen to Widen gradually from the this are the paired openings of o ./ the posterior nares and a short neck tO the saCrum, and SO to way above the middle of the fig- ure is the large median /wam«« i3g -(yell fitted to sustain the CTOffnWOT, with the bony convex- "^ .><-.ij. i.^i^v-v. aATc^StftT;ftrS!otTt's weight of the head, upper limbs, ^arT^f^th'e'^kuir'beMnd toe &c.. Carried by it. Its curvatures, ?n's?zi!1oX'';n"frl?oT'tSl which are peculiarly human, add in an ape the portion in front of ,-i t -i • n ^ i.' 'l the occipital condyles would be greatly to its Spring and elasticity; much larger than that behind . , , ■ t , . . -i -in rhem. were it a straight rigid rod the brain, concealed in the skull at its top, would be jarred at every step. How do four-footed beasts differ in this respect? Do apes' skulls balance as well as man's? Wliy not? What is the result of this want of balance? What is observed when the human spinal column is viewed from the front? What is gained by its gradual widening from above down? What feature in our spines is peculiarly human? What benefit results from it? his chin. vigilance the greater weight of the u-tmt ha] The muscles concerned In holding the head erect having relaxes jSieix ilf of the skull exerts ils effect. PEGULIARITIES OF SKELETON. 45 3. The pelvis, to the sides of which the lower limbs are attached, is proportionately very broad in man, so that the balance of the trunk on the legs is not easily upset when the body is bent towards one side. 4. The lower limbs are proportionately very long in man. This makes progression on them more rapid by allowing a longer stride, and also makes it difficult to go on " all fours " except by creeping on the hands and knees. The arms of some a2es_are as long, and of others longer, than their legs. 5. The arched instep and broad sole of the human foot are very characteristic. Most beasts, as horses, walk on the tips of their toes, the hoof being really a veryj)ig nail; others, as bears, place tlie"heel also on tlie ground, but have a much less developed tarsal arch than man. The vaulted human tarsus, made up of a number of small bones, each of which can glide a little over its neighbors, but none of which can move much, is admira- bly calculated to break any jar which might be trans- mitted to the spinal column by the contact of the sole with the ground at each step.* A well arched instep is What feature characterizes the human pelvis? What benefit results from it? Which limbs are longest in man? What ends are gained by the considerable length of the legs? Why do infants crawl on the hands and knees instead of the hands and feet? Which limbs are longest in apes? What structural points in the foot are especially human? What part of the foot do horses put on the ground? Name an animal which puts the heel also on the ground when it walks. How does the bear's tarsal arch differ from man's? What benefit results from the form and structure of the human tarsus? How? Why is a well-arched instep beautiful? * A carriage spring consists of two curved elastic steel bars fastened together at their ends, and -witli their concave sides turned towards one another. The axle of the wheel is attached to the middle of the lower bar, and the weight of the carriage 46 THE HUMAN BODT. therefore rightly considered a beauty; it makes the gait easier and more graceful. bears on the middle of the upper. When the wheel jolts over a stone the jerk is transmitted to the elastic arches, which each flatten a little, and so instead of a sudden jerk a gentle sway is transmitted to the carriage. The tarsal arch of the human foot acts like the upper half of a carnage spring. CHAPTER IV. THE STRUCTUEE, COMPOSITION AND HTUIENE OF BONES. The gross structure of bones. — Although the bones differ very much in shape all are alike in microscopic structure and in chemical composition. When alive they have a bluish-white color, with a pinkish hue when blooci is flowing through them ; they possess considerable flexi- bility and elasticity, which may be best observed in a long slender bone, as a rib.* To get a general idea of the structure of a bone we may select the humerus (Fig. 31). When fresh this is closely invested on its outside by a tough membrane, the '^periosteum, composed of connective tissue and containing many blood-vessels. On its under side new bony tissue is de-l posited as long as the bone is growing thicker, and through-' out life it is concerned in the nourishment of the bone. How do bones differ from one another? In what respects do all bones agree? What is the colorof a living bone? Name some mechan- ical properties of bone. In what bones may such properties be most readily seen? What covers a bone on the exterior? What is it composed of? Does it contain bloodvessels? * The rib of a sheep or a rabbit when thoroughly boiled can be readily scraped clean and preserved, and serves admirably to show the flexibility and elasticity of bone. [47] 48 TEE HUMAN BODY. Fig. 31. — The right humerus, eeea from the front. For description, eee te^t. which dies if it be stripped off.* The periosteum covers the humerus except on its ends {Cp, Tr, CpT) at the shoulder and elbow-joints ; there the bone is covered by a thin layer of gristle or car- tilage. Very early in life the whole humerus consists of cartilage ; this is afterwards absorbed and replaced by bone, leaving only a thin layer of articular cartilage on each end. The bone itself consists of a central nearly cylindrical portion or shaft (extending between the dotted lines X and Z) and two articular ex- tremities. These extremities are enlarged to give a wider What are the functions of the periosteum? Where is the perios- teum absent? Of what does the humerus consist in very early in Ufe? What happens to most of its cartilage afterwards ? Where is some cartilage left? What are the main divisions of the humerus? What is the general form of its shaft ? Why are its ar- ticular extremities large? * Casee have been recorded in which a considerable portion of a bone or even the whole bone has been removed during life, and the periosteum Oeft but slightly in- jured) has formed a new bone in place of the old. STRUCTURE OF BONES. 49 "Mii bearing surface in the joints, and also to provide on which to attach the muscles which move the bone various knobs on the extremities, and the rough patches on the shaft, all mark areas where muscles were fixed. Internal structure. — If the humerus were divided lengthwise we would find that its shaft was hollow ; the space is known as the medullary cavity, and in life is filled with soft fatty marrow. Fig. 32 represents snch a longitudinal section. We see in it that the marrow cavity ends near the articular extremities ; and that in these the bone has a loose, spongy text- ure, except a thin dense layer on the sur- face. In the shaft the compact outer layer is much the thicker, the spongy portion only forming a thin stratum next the medullary cavity.* To the unas- sisted eye the spongy bone appears made up of a trellis-work of thin bony plates which intersect in all directions and sur- round cavities about the size of the space ; the m^ What do the knobs and rough patches on the bone indicate? What should we find on dividing the hu- merus lengthwise? Wliat is its shaft cavity called? What does it contain? Where does the marrow cavity end? What is the texture of the articular extremilies of the bone? How does the shaft differ in structure from the ex- <="* open, a, tremities of the femur? What does the spongy "^^^^ \^^^^ bone look like? lage. humerus marrow bone; c, d, carti- * These facts may readily be demonstrated by sawing in twp lengthwise tbe bones out of a leg o( nmtton, 50 THE HUMAN BODY. head of a small pin. In these spaces there is found dur- ing life a substance known as the red marrow, which is quite diSerent from the yellow fatty marrow of the medul- lary cavity.* Why bones are hollow. — If the bones were solid they would be extremely heavy and unnecessarily strong for the common purposes of life, unless only the same amount of material were used in their construction, and then they would be either loose in texture and easily broken, or, if dense, they would be thin rods and not give sufficient surface for the attachment of muscles. It is a well-known principle in practical mechanics that the same amount of material will bear a greater strain if in the form of a tube than in that of a solid rod of the same length ; hence iron pillars are cast hollow; to fill them up solidly would make them enormously heavier without anything like a propor- tionate increase in strength. Take a glass tube one foot long and a piece of glass rod of the same length and weight; support each at its ends and hang weights on the middle until it breaks; the tube will be found to bear a very much greater strain before yielding. We see an ap- plication of this same method of utilizing a given amount of material to the best advantage for support, in the hol- low stalks of grass, wheat, and barley. Varieties of structure found in different bones, — Bones which, like the humerus and femur, present a shaft and What lies in the cavities of the spongy bone ? Why are most bones hollow ? Which will bear most weight, a tube or a solid rod of the same material, weight, and length ? Give Illustrations. Why are grass stalks hollow ? * Many of tlie bones of birds are thin-walled tubes of dense bone : the central cavity contains air and no marrow, and communicates by tubes with the lungs. Examine the humerus of a pigeon or a rooster. msTozoor of bONR 51 articular extremities, are called long hones; other examples are tibia and fibula, radius and ulna, metacarpal and meta- tarsal bones, and tlie phalanges of fingers and toes. Tab- ular bones form thin plates, like those of the roof of the skull, and the shoulder-blades. Short bones are rounded or angular, and not much longer in one diameter than another ; as the carpal and tarsal (Fig. 19) bones. Irregu- lar hones include all which do not fit well into any of the above classes ; they usually lie in the middle line of the body and are divisible into similar right and left halves ; the vertebrae are good examples. All bones are covered by periosteum except where they enter into the formation of a joint, but in the human body only the long bones possess a medullary cavity con- taining yellow marrow. The rest are filled up by spongy bone, covered by a thin layer of dense, and have red mar- row in their spaces. The liistology ot bone. — The microscope shows that compact bone is only so to the naked eye ; even a hand lens shows minute holes in it; it but difEers from spongy bone in the fact that its cavities are much smaller, and the hard bony plates between them thicker. 11 a thin trans- verse section of the shaft of long bone (Fig. 23) be exam- ined with a microscope magnifying about twenty diameters, even its densest part will be seen to show numerous open- ings which become gradually larger near the medullary What is a long bone? Give examples. A tabular bone? Exam- ples. A short bone? Examples. An irregular bone? Examples. With what is most of the surface of bones covered? Where is the periosteum absent? Wha-t bones contain. yellow marrow? What do the others contain? Does compact bone contain any cavities? How may these be seen ? How does it differ from spongy bone ? What is seen when a thin slice of bone is magnified twenty times? Where do the apertures iu it become larger I 52 THE HUMAN BODY. cavity and Tptiss insensibiy into the spaces of the spongy bone around it. These openings are the cross sections of Fig. 23. — A, a transverse section ot the ulna, natural size ; showing llie medul- lary cavity. B, the more deeply shaded part of A magnifled twenty diameters. tubes known as the Haversian canals, which run all through the bone,, the majority of them in the direction of its long axis, though numerous cross branches unite them. The outermost Haversian canals open on the surface of the bone beneath the periosteum ; from there blood-ves- sels pass in, and, traversing the whole bone in these chan- nels, convey materials for its growth and nourishment. "What are the Haversian canals? Where do the outer ones open? What enterc them? Where do the blood-vessels of a bone run? What do they carry if HISTOLOGY OF BONE. 53 Around each Haversian canal is a series of plates or lamellm, each canal and its lamellae forming an Haversian system ; the entire bone is made up of a number of such systems, with the addition of a few lamellae lying in the corners between them, and some which run around the whole bone on its outer surface. In the «pongy bono the Hayersian canals are very largo, containing r ed nia iTow as well as blood-vessels, and the lamellae around each are few in number. Fio. 24.— A Binall piece of bone, ground very thin and highly magnified. If a bit of bone be still more magnified (Fig. 24) we find that very small cavities lie between the lamellae ; they "What hes around each Haversian canal? What is an Haversian system? Of what does a bone consist in addition to Haversian sys- tems? Are the Haversian canals comparatively large or small in spongy bone? What do the spaces of spongy bone contain in addi- tion to blood-vessels? , „ r^ • . , What spaces lie between the lamellse of an Haversian system? 64 THE HUMAN BODY. are called l acun ce ; from each lacuna radiate many ex- tremely fine tubes, the canalicuU, so that each lacuna with its canaliculi looks something like a small animal with a great many legs. The innermost canaliculi open into the Hayersian canal of the system to which they beloug, and those of various lacunae communicate with one another, so that a set of passages is provided through which liquid which transudes from the blood-vessel in the Haversian canal can ooze all through the bone. I In a living bene a nucleated cell lies in each lacuna. These cells, the hone corpuscles, are the remnants of those which made the bone, all whose hard parts are but in- tercellular substance: a sort of skeleton is made by each cell around itself, and this adheres to the skeletons of the rest, and thus the whole bone is built. Chemical composition of bone. — Apart from the bone corpuscles and the soft contents of the Haversian canals and of the spaces of the cancellated bone, the hard bony substance proper is composed of animal and mineral mat- ters so intimately combined that the smallest distinguish- able bit of bone contains both. The mineral matters give the bone its hardness and stiffness, anu*Iorm about twQ- tiuxd-s of its weight when dried. They may be removed by soaking the bone in diluted muriatic acid,* and the What radiate from the lacuncE? Into what do the innermost canaliculi of an Haversian system open? How is nourishing liquid from the blood carried throughout a bone f What lies in each lacuna of a living bone ? What are the bone corpuscles ? What is the hard part of bone ? How is a whole bone made up ? Of what primary constituents is bone composed ? Is there any fragment of bone that does not contain both ? What qualities do its mineral parts give to a bone ? How much of a dry bone consists of mineral matter ? How may the mineral parts be removed? * Add a couple of ounces of muriatic acid to a pint of water and place a CHEMISTBT OF BONE. 65 animal or organic part of the bone is then left as a tough, flexible mass, retaining perfectly the shape of the original bone. When long boiled in water the greater part of the , animal portion of bone is turned into gelatine and dis- I solved in the water; most of the gelatine which we buy in j the shops is obtained by boiling fresh bones in a closed vessel under a high pressure; the water then gets much hotter than when boiled in the air, and dissolves out the gelatine more quickly; when a shin of beef is used to make soup the bones are put in as well as the softer parts, and the whole is kept boiling for hours so as to get some of the gelatine out of the bones. The animal matter of bone gives it its toughness and flexibility. The earthy portion may be obtained free from the animal by calcining a bone in a bright fire. The residue is a white and very brittle mass, which retains perfectly the shape of the original bone. It is readily powdered and then forms bone ash, which consists chiefly of phosphate and carbonate of calcium; most of the phosphorus of commerce is obtained from it. If the burning be imper- I feet the animal matter is charred but not altogether burnt ' away, and a black mass, known as animal charcoal or "bone black," is left. What then remains behind ? What are its properties? Has it still the shape of llie bone? What happens when a bone is boiled for hours? How is the gelatine of commerce obtained? Why do we use bones in making soup ? What properties does its animal matter confer on bones? How may we get the mineral part of bone free from the animal ? What are its properties when isolated? What is bone ash? From what is phosphorus prepared ? What is animal charcoal ? sheep's rib in the mixture for four or five days, having previously scraped the bone quite clean. It will be found so flexible that a knot may be tied on it; the specimen may be preserved in strong brine or dilute alcohol from year to year for exhibition to a class. 56 TBM HUMAN- BODY. Hygiene of the bony skeleton. — In early life the animal matter of the bones is present in larger proportion than later; hence the bones of children are tougher, more pliable, and not so easily broken. The bones of a young child are tolerably flexible and are capable of being dis- torted by any long-continued strain ; therefore children should never be placed on a bench so higli that the feet haye no support ; if this is frequently done the thigh bones will almost certainly become bent over the edge of the seat by the weight of the lower legs and the feet, and a permanent distortion may be jjroduced. For tlie same reason it is important tliat a child be made to sit straight, when writing or drawing, to avoid the risk of producing a lateral curvature of the spinal column ; and young chil- dren should not bo made t o walk too, early lest they become / bowjjggged, their bones not being rigid enough to bear the weight of the body. How easily the bones yield to prolonged pressure in early life is well illustrated by the distorted feet of Chinese ladies ; and by the extraordinary forms (Fig. 25) which some races produce in their skulls by tying boards or bandages on the heads of the children. A distorted foot, even in the United States, is no uncommon thing in these days of tight boots andliighheels. The la' ter are especially bad, as, "instead of allowing the weight of the body to bear properly directly downwards on the crown of the arch of the instep, they throw it forwards, and violently force the fore part of the foot into the toe of llow do the bones of children differ in composition from those of adults? How in properties? Why should children have a seat allow- ing the feet to be supported? Why should young persons be taught to sit erect while writing? What will happen if young children are encouraged to walli too much? Why? Give instances of the readi- ness with which bones can be distorted in early lite. Why are high- Ueeled boots hurtful? MYQIENB OF BKBLWTOJS. 57 che boot. This not only crushes the toes and leads to deformities, corns, and bunions, but makes the gait stiif, inelastic and ungraceful. FtG. 25.— Skull of a child of the tribe of Chinook Indians (inWaDitiiigthe neigh, burbood of the ("lolnmbia river), distorted by tight bandaging so as to assume the shape considered elegant and fashionable by the tribe. In advanced life the animal matter of the bones is present in deficient amount, and hence they are brittle and easily broken. An infant has its bones but yery imperfectly hardened by mineral matter. Hence the great importance of sup- plying it with food containing phosphate of lime, which is the chief mineral constituent of bone. Of all common articles of diet, milk contains most phosphate of lime s hence one great reason of its value as a food for children. Fracture. — When a bone is broken it is said to he frac- tured ; when it is a clean break the fracture is simple; when the bone is more or less broken up into bits on each side of the break the fracture is comminuted; when the Why are the bones of an old person easily broken? Why should milk form part of a child's diet ? • What is a fracture? A simple fracture? A comminuted fracture / A. compound fracture? 68 THE HUMAN BODY. Boft parts also are lacerated, so that there is an opening from the skin to the broken bone, the fracture is com- poimd. Once a bone is broken the muscles attached to it are apt to pull its ends out of place; hence it requires to be " set," and then kept in position by splints or bandages; this frequently needs much skill and a thorough knowledge of the anatomy of the body. A medical man should be sum- moned at once, as the parts around the break commonly swell very rapidly and make the exact nature of the frac- ture hard to detect, and also the replacement of the dis- placed ends more difficult. Why does a broken bone need "setting"? What is the object of "splints"? Why should skilled assistance be obtained as soon as possible after a bone has been fractured ? Appendix to Chapter IV. When giving lessons on Chapters III and IV, it is very desirable for a teacher to have at hand an articulated human skeleton. This may he purchased for about |40.00 from Henr}' Ward, Rochester, N. Y., and will last for an indefinite number of years. When the school funds do not permit the purchase of a skeleton, one can almost certainly he borrowed from some medical man or medical school for a few days. When there are several public schools in a city it would probably be possible to induce the scliool commissioners to purchase a skeleton to be used by the schools in turn. PLATE I.— THE BONES, JOINTS, AND LIGAMENTS. EXPLANATION OF PLATE L A front view of an adult huraaa skeleton to illustrate the mode in wliicli the bones are connected together at the different joints. For the names of the bones consult the description of figure 8, which commences on page 26. a Ligaments of the Elbow-Joint. 6 The Ligament which is connected to the ventral surfaces of the bodies of the Vertebrae. e Ligament connecting the innominate Bone to the Spine. / Ligament connecting the innominate Bone to the Sacrum. g The Ligaments of the Wrist Joint. h The Membrane which fills up the interval between the two bones of the Fore Arm. I A similar Membrane between the two bones' of the Leg, and, lower dowuj I, ligaments of the Ankle-Joint. k A Membrane which fills up a hole in the Innominate Bone, n Ligaments of the Knee-Joiut. Ligaments of the Toes and Fingers. p Capsular (bag-like) Ligament of the Hip-Joint. q Capsular Ligameut of the tilioulder-Joint. CHAPTEE V, JOINTS. The movements of the hody are brought about by means of soft reddish organs known as the muscles ; the lean of meat is muscle, so every one knows what a dead muscle looks like.* Muscles have the power of shortening with considerable force ; when they do so they pull their ends towards one another and swell out in the middle ; in other words, they become shorter and thicker. With few exceptions the ends of a muscle are attached to separate bones f between which a joint lies, and when the muscle shortens, or, in physiological language, contracts, it pro- duces movement at the joint. The joints and muscles thus form the chief motor apparatuses of the body. What organs produce the movements of the body? What is the technical name of the lean of meat? What power do muscles pos- sess? Wh:it happens when they exert it? To what are the ends of most mnsoles attached? What happens when the muscle contracts? Name the chief motor apparatuses of the body? •In many animals some muscles are much redder than others, and it is then found that the deeper colored are those which are kept most constantly in use ; the leg muscles of a chicken, for example, are redder than those of the wings and breast, and as the coloring matter is turned brown by heat, they form the ' ' dark meat" after cooking ; in birds which fly a great deal the breast muscles (which cluefly move the wings) are also dark. The heart, which is a muscle always at work, is deep red, even in fishes, most of whose muscles are pale. + As an example of a muscle not attached to the skeleton, we may take the artlc- mris oris, which forms a ring around the mouth-opening beneath the skin of the hps ; when it contracts it closes the mouth, or if it contracts more forcioly purses out the lips. The orbiailaris palpebrarum forms a similar ring around the eye o|.eaiQg, and when it contracts closes the eye. 60 TUB HUMAN BODY. Joints. — Articulations which permit of movement by the gliding of one bone over another are called joints ; all are constructed on the same general plan, though the range and direction of movement permitted are different in different Joints. As an example we may take the hip- joint, a section through which is represented in Fig. 36, FiQ. 26.— Section througli the hip-joint. On the outer side of the os innominatum (s, Fig. 8) is a deep hollow, the acetabulum, which receives the upper end of the thigh-bone. The acetabulum is lined by a thin layer of cartilage, with an extremely smooth surface, and its cavity is also deepened by a cartilaginous rim. The upper end of the femur consists of a nearly spherical head, borne on a narrower neck ; this head is covered by car- tilage, and rolls smoothly in the acetabulum like a j^ball in What is a joint? How do joints differ? Describe the hip-joint. EIP-JOINT. 61 a socket. If the hard bones came into direct contact they would be apt to cliip one another when a sudden move- ment was made, especially if the hip-joint were so far bent as to knock the thigh-bone against the rim of the acetabu- lum; the elastic and yielding cartilage forms a protecting cushion between the bones and prevents this. To keep the bones in place and limit the range of movement, ligaments pass from one to the other ; they are composed of connective tissue, are extremely pliable but cannot be stretched, and are very tough and strong. One is the capsular ligament, which forms a bag all round the joint, and another is the round ligament, L. T., Fig. 26, which passes from the rim of the acetabulum to the head of the femur ; from the rim of the socket it passes to tiie center of the acetabulum along a groove in the bone, and then turns out to be fixed to the thigh-bone. Covering the inside of the capsular ligament and con- tinued over the cartilages of the joint is the synovial mem- hram, very thin and composed of a layer of flat cells. This pours out into the joint a very small quantity of synovial liquid, which is somewhat like the white of a raw egg in consistency, and plays the part of the oil moisten- ing those surfaces of a machine which glide over one another ; it lubricates the joint and enables all to run smoothly and with but little friction. In the natural state of the parts the synovial membrane What is the use of the cartilage lining the bones which move over one another in a joint? What is the use of ligaments? Of what are they composed? What are their properties? Name some ligaments of the hip- joint. Where does the capsular ligament lie? Where the round ligament? What membrane lines the joint? Of what is it composed? What does it ponr into the joint? What is synovial liquid lilse? What is its use? Illusirate by an example. 62 THE HUMAN BODY. on the head of the thigh-bone lies close against that lining the acetabulum, so that practically there is no cavity left in the joint. This close contact is not maintained by the ligaments (which are much too loose, and serve mainly to prevent such excessive movement as might roll the femur quite out of its socket), but by the many strong muscles which pass between pelvis and thigh-bone and hold both firmly together. In addition, the pressure of the atmosphere is transmitted by the skin and muscles to the exterior of the air-tight joint, and helps to keep its surfaces together. If all the muscles be cut away from around the hip-joint of a dead body, it is found that the head of the femur is still held in its place by the pressure of the air ; and so firmly that the weight of the whole limb will not draw it out ; but if a hole be pierced into the bottom of the acetabulumj and air be thus let into the joint, then the thigh-bone falls out of place as far as the ligaments will let it. In all joints we find the same essential parts ; bones, articular cartilages, synovial membrane, synovial liquid, and ligaments.* , Ball and socket joints. — Such a joint as that at the hip Is tLere in health any definite space between the bones of the hip joint? What is the cliief use of tlie ligaments? How are the bonet held together? What in addition to muscles helps to keep the bones of the joint in contact? Describe an experiment illustrating the effect of atmospheric pressure in keeping the bones together? "What essential parts are t'ound in aft joints? What is such a joint as the hip- joint called? * The structure of joints can be readily seen in those of a fresh calf's or sheep's foot. The synovial membrane is so thin and so closely adherent to the parts it lines that a microscope is needed for its demonstration ; but all the pther parts are readily made out. BALL AND SOCKET JOINTS. 63 is called a ball and socket joint, and allows of a greater Tariety of m,ovement than any other kind. Through movements taking place at it the thigh can (1) he flexed, that is, bent so that the knee approaches the cliest, and (2) extended or straightened again ; it can (3) be abducted so that the knee is moved away from the middle line of the body, and (4) adduded or brought back again ; by movement at the hip the limb can also (5) be circum- ducted, so that, with kuee and ankle joints held rigid, the whole leg is made to describe a cone, of which the aj)ex is at the hip-joint and the base at the foot ; and finally (6) rotated so that the whole limb can be rolled to and fro a little about its own long axis. All ball and sockets joints allow all these movements to a greater or less extent. Another important ball and socket joint is that be- tween the upper end of the humerus and the hollow {glenoid fossa) near the upper outer corner of the shoulder blade. Tlie glenoid fossa being much shallower than the acetabulum the range of movement possible at the shoulder, is greater than at the hip-joint. Hinge-joints. — In this form the bony cavities and pro- jections are not spherical, but are grooved and ridged so that one bone can glide over the other in one plane only, to and fro, like a door on its hinges. The knee is a hinge-joint ; it can only be bent and straightened, in technical language, flexed and extended. What kind of joints allow of tlie freest movement? What is meant by flexion of the thigh? By extension? By abduction? By adduction? By circumduction? By rotation? What movements do all ball and socket joints permit? What sort of a joint is that at the shoulder? Why is more move- ment possible at it than at the hip-joint? What is a hinge-joint? Give an illustration. Name other hinge-joints 64 THE HUMAN BODY. Between the phalanges of the fingers we find also hinge- joints ; another is found between the lower jaw and the- cranium, allowing us to open and close the mouth. The latter is not, however, a perfect hinge-joint ; it per- mits also of slight lateral movements, and a gliding motion by which the lower jaw can be thrust forward so as to bring the lower range of teeth outside the upper.* Pivot-joints. — In this form one bone rotates about another. A good example is found between the first and sec- ond cervical vertebrae (Figs. 13, 14). The odontoid process of the axis reaches up into the neural arch of the atlas, and, kept in place there by the transverse ligament which does not let it press against the spinal cord, forms a pivot around which the atlas rotates, carrying the skull with it when we turn the head to right or left. A more complicated kind of pivot-joint is found in the forearm. Lay the forearm and hand flat on a table, palm iippermost ; without moving the shoulder-joint at all the hand can then be turned over so that its back is upward. In this movement the radius, which carries the hand, crosses over the ulna. When the palm is turned up {supination) the radius and ulna are jiarallel (Fig. 37, A), and the radius on the outside ; place a finger of the other Is the joint of the lower jaw with thi: skull a perfect hinge joint? What movements can take place at it? What is a pivot- joint? Name an instance from the spinal column. Describe the joint between atlas and axis. What happens to the head when the atlas rotates on the odontoid process of the axis? Where do we find anotlier kind of pivot-joint? Illustrate its action. What happens when we turn the hand so that the palm instead of being up shall be down? How can we observe the relative change in position of radius and ulna while making this movement? * The object of these minor movements is to allow us to chew our foon ; in car- nivova, as cats, which bite, but do not chew, the lower jaw forms a perfect hinge* ^oint with the craiiiu;!}. DISLOCATIONS. 65 hand on it near the wrist, and then turn the hand over ; the lower end of the radius will be found to cross over the ulna and to be on its inner side (Fig. 27, B), when the movement is completed ; in this position the hand is said to be in pronation. The lower end of the hume- rus (Fig. 21) has a large artic- ular surface ; on the inner two- thirds of this, Tr, the ulna fits, and the grooves and ridges of the bones interlocking form a hmge-joint, allowing us only to bend or straighten the elbow- jomt. The radius fits on the rounded outer third, Cpl, and rotates there when the hand is turned over, the nlna form- ing a fixed bar around which it moves. Gliding joints as a rule per- mit of but little movement. Examples are found between the closely-packed bones of the carpus and tarsus (Fig. 19), which slide a little over one another when subjected to pi-essure. Dislocations.— When a bone is displaced at a joint or dislocated, the ligaments are more or less torn and other Fig. 27.— a, arm in gnpination ; B. arm in pronation ; H, humerus ; R. radius ; U ulna. What movement is allowed between ulna and humerus? What between radius and humerus? Around what does the radius rotate when we turn the hand over? Do gliding joints allow free movement? Give instances of gliding joints. What is a dislocation? What parts are injured when a joint ia dislocated? 66 THE HUMAN BODY. surrounding soft parts injured. This generally leads to inflammatioa and swelling, which make it difficult to find out in what directiou the bono has been displaced, and also greatly add to the difficulty of replacing it, or, in sur- gical language, of reducing the dislocatmi. The muscles attached to it are, moreover, apt to pull the dislocated bone more and more out of place. Medical aid should therefore be obtained as soon as possible ; in most cases the reduction of a dislocation can only be attempted with safety by one who knows the forms of the bones and pos- sesses sufficient anatomical knowledge to recognize the direction of the displacement.* A sprain is an injury to a joint, accompanied by strain- ing, twisting, or tearing of the ligaments, but without dis- location of the bones. A sprained joint should get imme- diate and complete rest, continued for weeks if neces- sary ; if there be much swelling or continued pain, medical advice should be obtained. Perhaps a greater number of permanent injuries result from neglected sprains than from broken bones. What results from this injuTy ? What is meant by "reducing a dislocation ?" Why should medical aid be obtained as soon as possi- ble after a joint has been dislociiteil ? What is a sprain ? How should a spniined joint be treated 1 What should be done at once if theie is much swelling or continued pain ? Are neglected sprains apt to lead to permiuient injury ? * Dislocations of the fingers can nsna.ly be reduced by sfrons pulling, aided by a little pressure on the parts of the bones nearest the joint. The reduction of a dis- location of the thumb is much more difficult, and can rarely be accomplished w'.abe out skilled assistance. EXPLANATION W PLATE II. A Tiew of tlie muscles situated on the front surface of the body, seeu in their natural position. It must be uuderstood that beneath tliese muscles manj' others are situated, which cannot be represented in the figure. Muscles of the Face, Head, and Neclc: 1. Muscle of the Forehead. This, together with a muscle at the back of the head, has the power of moving the scalp. 2. Muscle that closes the Eyelids. The muscle that raises the upper eyelid so as to open the eye, is situated within the orbit, and consequently cannot be seen in this figure. 3. 4, 5. Muscles that raise the Upper Lip and angle of the Mouth. 6, 7. Muscles that depress the Lower Lip and angle of the Mouth. By the action of the muscles which raise ihe upper lip, and those that depress the lower lip, the lips are separated. 8. Muscle that draws the Lips together. 9. Muscle of the Temple (Temporal Muscle). 10. Masseter Muscle. 9 and 10 are the two chief muscles of mastication, for when they contract, the movable lower jaw is elevated, so as to crush the food between the teeth in the upper and lower jaws. 11. Muscle that compresses the Nostril. Close to its outer side is a small muscle that dilates the nostril. 12. Muscle that wrinkles the Skin of the Neck, and assists in depressing the lower jaw. 13. Muscle that assists in steadying the Head, and also in moving it from side to side. 14. Muscles that depress the Windpipe and Organ of Voice. The muscles that elevate the same parts are placed beneath the lower jaw, and can- not be seen in the figure. Muscles tliat connect the upper extremity to the trunk. Portions of four of tliese muscles are represented in the figure, viz. : 15. Muscle that elevates the Shoulder. Tr-apezius Muscle. 17. Great Muscle of the Chest, which draws the Arm in front of the Chest (Great Pectoral Muscle). 18. Broad Muscle of the Back, which draws the Arm downwards across the back of the Body (Latissimus Dorsi). 19. Serrated Muscle extends between the Ribs and Shoulder-blade, and draws the shoulder forwards and rotates it, a movement which takes place in *iie elevation of the arm above the head (Serratus magnus). At the lower part of the trunk, on each side, may be seen the large muscle wliich, from the oblique direction of its fibres, is called, 80. Outer Oblique Muscle of the Abdomen. Several muscles lie beneath it. The outline of one of these, 21. Straight Muscle of the Abdomen, may be seen beneath the expanded tendon of insertion of the oblique muscle. These abdominal muscles, by their contraction, possess the power of compressing the contents of the abdomen. Muscles of the upper extremity. 16. Muscle that elevates the Arm (Deltoid Muscle). 32. Biceps or Two-headed Muscle (see also page 70>. 23. Anterior Muscle of the Arm. This and the Biceps are for the purpose of bending the Foi-e-Arm 24. Triceps, or Three-headed Muscle. This counteracts the last two muscles, for it extends the Fore-arm. 85. Muscles that bend the Wrist and Fingers, and pronate the Fore-arm and Hand— that is, turn the Hand with the palm downwards. They are called the Flexor and Pronator Muscles. 26. Muscles that extend the Wrist and Fingers, and supinate the Fore-arm and Hand— that is, turn the Hand with its palm upwards. They are called the Extensor and Supinator Muscles. 27. Muscles that constitute the ball of the Thumb. They move it in different directions. 28. Muscles that move the Little Finger. Muscles which counect the lower extremity to the pelvic bone. Several are represented in the figure. 29. Muscle usually stated to have the power of crossing one Leg over the other, hence called the Tailor's Muscle, or Sartorius; its real action is to assist in bending the knee. 30. Muscles that draw the Thighs together (Adductor Muscles). 31. Muscles that extend or straighten the Leg (Extensor Muscles). The muscles that bend the leg are placed on the back of the thigh, so that they cannot be seen in the figure. Muscles of the leg aud foot: 32. Muscles that bend the Foot upon the Leg, and extend the Toes. 33. Muscles that raise the Heel— these form the prominence of the calf of the Leg. 34. Muscles that turn the Foot outwards. 35. A band of membrane which retains in position the tendons which pass from the leg to the foot. 36. A short muscle which extends the Toes. The muscles wliich turn the foot inwards, so as to counteract the last named muscles, lie beneatli tlie great muscles of the c:\lf, which consequently conceal them. The foot possesses numerous muscles, which act upon the toes, so as to move them about in various direc- tions. These are principally placed on the sole of the foot, so that they cannot be seen in the figure. Only one muscle, 36, which assists in extending the toes, is placed on the back of the foot. PLATE II. —THE SUPEHFICIAL MUSCLES OF THE FRONT OF THE BODY. OHAPTEE VI. THE MUSCLES. The muscles of the human body are more than five hun- dred in number ; they vary very much in size ; from tiny ones not an inch long, in the voice-box, to that on the front of the thigh (39, PI. II.), whicli passes from the pelvis to the tibia, and is eighteen inches or more in length. What- ever their size, muscles present a similar structure and possess the same properties, their various uses depending on the different directions in which they pull, and the different things they pull upon, in addition to their primary function of moving the body the muscles give it roundness and shapeliness ; they also help to enclose cavi- ties, as the abdomen and tlie moutli ; and they hold bones together at joints. The parts of a muscle. — In its commonest form a muscle consists of a red soft central part, called its belly, which tapers towards each end and there passes into one or more dense white cords, made of connective tissue and called tendons; the tendons attach the muscle to • parts of the About how many muscles are there in the body? Between what limits do they difEer in size? In what respects do all muscles resem- ble one another? How are their different uses determined? What functions do muscles fulfill besides moving the body and its parts? Give examples. What is the most usual structure of a muscle? What is the use of tendons ? [67] 68 THE HUMAN BODY. skeleton.* In Pig. 38 ■P:f 16- < Pig. 28.— The muscles on the back of the hand, forearm, and Jower half of the arm, as ex- posed on dissecting away the ekji. are shown some of the muscles of the arm. Their anatomical names we need not trouble about ; but it will be seen that some (8, 11, 13) pass from arm to forearm: others, as 16, 15, 14, 13, 17, 18, start from the forearm bones and pass to the bones of the hands ; near the wrist they end in slender tendons, which are bound down into place by a stout cross band of con- nective tissue. The skin has been dissected away from the back of the middle finger to show the endings of tendons on its pha- langes. The belly of a muscle is its What portion of a muscle is its working part? * The parts of a muscle may readily be seen in that which forms the calf of a frog's leg. Put a teaspoonful of ether in a quart of water, immerse a frog in it, and cover the vessel. In a minute the animal will be quite insensible ; ith head can then be cut off and its spina) cord destroyed by running !l pin along it, without causing the animal any pain. Now make cir- cular cuts through the skin at the top of the thighs and then peel the skin off like a pair of hose : it will come quite easily except about the knee-joint, where it may be necessary to carefully divide one or two tough bands. On the skinned leg many muscles will be observed, and the long slender tendons which run to the toes. The calf muscle will be seen to end below in a strong tendon near the heel. If this be divided, and the muscle turned upwards, it will be found to have at the upper end of its thick rounded "aelly a pair of short ten dons. Tim PARTS OF A MUSCLE. 69 working part ; nerves from the brain or spinal cord enter it, and when its nerve is excited, wlietlier involmitarily or bywliat we call an act of " will," tlie belly contracts; it forcibly changes its shape so as to become shorter and thicker. In so doing it drags on. the tendons, which are passive incxtensible cords and transmit the pull to the parts to which they are attached. The tendons are often quite long, as for example those of many of the muscles moving the fingers (Fig. 28), whose bellies are in the forearm. The belly of the common extensor muscle of the fingers (14, Fig. 28) is seen, for example, to be in the upper half of the forearm, and to end above the wrist in a single tendon which divides up into strips which run along the back of each finger ; the muscles which straighten the thumb, 17, 18 and 19, are . also seen to have long slender tendons. "Where a muscle passes over a joint it is usually reduced to a narrow tendon ; the bulky bellies, if they lay there, would make the joints clumsy and limit their mobility. Some muscles pass over two joints and can produce move- ment at either; the biceps of the arm, fixed above to thai scapula and below to the radius, can ])roduce movement atj either the elbow or the shoulder joint. The shortening of a muscle when it contracts is showij by the movement which it causes ; the thickening may be What enters tlie belly of a muscle? How is the nerve ot a musc'ie excited? Wliat happens when the nerve is excited? What results from the contraction of the belly of a muscle? Are tendons ever long? Describe the common extensor muscle of the fingers and its tendons. Describe the position and length of ten- dons of the muscles which extend the thumb. What happens to a muscle when it passes over a joint? Why? Name a muscle which crosses two joints. At what joints can the biceps muscle of the arm produce movement? How is the shortening of a contracting muscle shown? 70 TEE STTMAJf BODY. seen and felt on the biceps in front of the humerus when the elbow is bent, or in the ball of the thumb when that digit is moved so as to touch the little finger ; when a muscle contracts its belly may also be felt to grow harder. The swelling and hardening of a contracted muscle are daily illustrated when one schoolboy invites another to feel his " biceps." The Origin and Insertion of Muscles. — Almost invaria- bly that part of the skeleton to which one end of a mus- Fio. 29.— The biceps mnacle and the arra-bones, to illustrate how, atider ordi nary circumstances, the elbow joint is flexed when the muscle contracts. cle is fixed is more easily moved than that part on which it pulls by its other tendon ; the less movable attachment is the origin, the other the insertion of the muscle. Tak- ing the biceps of the arm, we find that when the belly of the muscle contracts and pulls on its upper and lower tendons, the result is commonly that only the forearm is moved, the elbow joint being bent as shown in Fig. 29. How may its thickening be recognized? What change besides thiclcening and shortening occurs in the belly of a contracted muscle? Give an example. What is meant by the origin of a muscle? What by the insertion? Give an example. VARlETIEa OF MTTSCLES. 71 The shoulder is so much more firm that it serTOS as a fixed point, and so that end of the biceps is the origin of the muscle, and the radial attachment its insertion. The distincHon is, however, only relative : if the radius were held immovable the muscle would move the shoulder towards the radius, instead of the radius towards the shoulder ; as, for example, in going up a rope " hand over hand. " Varieties of Muscles. — Many muscles have the simple typical form of a belly tapering towards each end, as A, Fig. 30 ; others divide at one end, and are called two-headed, or biceps muscles, i„^J°}i^7^^Tm,": and there are even three-headed or triceps muscles. On the other hand, some muscles have no tendon at all at one end, the belly running right up to the bone to which it is fixed, and some have no tendon at either end. Some- times a tendon runs along the side of a „ muscle, and the fibres of the latter are at- tached to it obliquely {B, Fig. 30) ; such a muscle is called penniform or feather- hke, from a fancied resemblance to the vane of a feather ; or a tendon may run down the middle of the muscle (C), which is then called Upenniform. Sometimes a tendon is found in the mid- dle of the belly as w-^U as at each end (Fig. 31) ; such a cle with a central belly and two terminal ten- dons. B, a penniform muscle; o, a bipenniform muscle. c 31.- gastrlc muscle. Fig. 31.— a di- Is the origin of a muscle under all circumstances its most fixed end? Give an example. Wliat is the simple typical form of a muscle? What is a biceps muscle? What a triceps? Have all muscles tendons at each end? At either end? Describe a penniform muscle. A bipenniform. 72 TEE HUMAN BODY. muscle is called two-bellied or digastric. Eunning along the front of the abdomen, from the pelvis to the chest, on each side of the middle line, is a long muscle, the straight muscle of the abdomen (rectus abdominis) j it is polggastric, consisting of four bellies separated by short tendons. Many muscles are not rounded, but form widCj flat masses, as those which lie beneath the skin on the sides of the abdomen. How the muscles are controlled.— Most of the muscles of the body are paired in a double sense. In the first place, to nearly every one answers a corresponding muscle on the opposite side of the body,* its true mate ; in addi- tion, most are paiitd with, or rather pitted against, an antagonist ; for example, to the biceps muscle (Fig. 29) which lies in, front of the humerus and bends the elbow joint, corresponds the triceps muscle which lies behind the arm bone and extends the elbow; when the biceps contracts tlie triceps relaxes, and vice versa. This orderly working is carried out by means of the Ijrain and spinal cord, which, through the nerves, govern the muscles and regulate their activity. In convulsions these controlling organs are out of gear, and the muscles are excited to con- tract in all sorts of irregular and useless ways ; antagonists pulling against one another at the same moment the "vhole body is made rigid. A digastric. Wliere do we find a polygastric muscle? How is the rectus abdomiuis muscle constituted? Where are flat wide muscles found ? In what two ways are muscles paired ? Give an example of antag- onistic muscles. What happens to the triceps when the biceps con- tracts ? How is tlie orderly worlcing of the muscles guided and con- trolled ? What parts are out of working order in a tit of convulsions ? Why do the limbs often become stifiE in convulsions? * The single muscles cross the middle line and are made up of similar right and left halves; examples aie orbicularis oris and the diaphragm. 'ME GROSS STBUGTURB OF A MUSCLE. 73 The Gross Structure of a Muscle. — Each muscle is an organ composed of several tissues. Its essential constitu- ent is a number of fibres consisting of striped muscular tissue. These are supported and protected by connective tissue; intertwined with blood and lymph vessels, which convey nourishment and carry off waste matters ; and penetrated by nerves which govern their activity. A loose sheath of connective tissue, tJte periniysium, envelopes the whole muscle in a sort of case ; from it partitions run in and sub- divide the belly of the mus- ^ \cle into bundles or /rtscj'cMZi Which run from tendon to tendon, or the whole length of the muscle when it has no tendons. The coarse- ness or fineness of meat de- TipTirl« an tlip siyf nf fin pop I^"- 32.— A emaH bit of muscle com- penas on tne size OI tnese p„^^^ ^j f^,,^ primary fafcicnii. a. nat- fusninnli which mnv hp nral size ; B, the same magnified, showing iclbl/lLLUI, V^ nioil Ulciy ue j^^ secondary fasciculi of which the pri- readily seen in a piece of -"ary are composed. Doiled beef. In good carying, meat Is cut across the fasciculi, or "across the grain," as it is then more easily broken up by the teeth ; the polygonal areas seen on the surface of a slice of beef are cross sections of the fasciculi. The larger fasciculi are subdivided by fine partitions of connective tissue into smaller (Fig. 32), each consisting of a few muscular fibres enveloped in a close Is a muscle an organ or a tissue? Wliat is the chief tissue in it called? What things exist in it besides striped musculav tissue? What IS the use of each? What is-the perimysium? How is a muscle divided into fasciculi? How far do the fasciculi extend? When is meat coarse in texture? Why is beef carved across the grain? Of what are the fasciculi com- posed? 74 THE HUMAN BODY. network of minute blood-vessels. Where a muscle tapers the muscle fibres in the fasciculi are less numerous and when a tendon is formed they disappear alto- gether, leaving only the connective tissue. Histology of Muscle. — The striped mus- cular tissue, which gives the muscle its power of contracting, is found when ex- amined by the microscope to be made up of extremely slender muscular fibres, each about one inch in length, but most of them less than -j^ of an inch across. Each muscalar fibre has externally a tliin slieatli or envelope, tlie sarcolemtna, which envelops tlie contracting part of the fibre. This latter is soft and almost Fio. 33.— A small semi-fluid, and under a microscope is seen giece of muscular , , • i ■ f bre highly mag- to prcscut a Striped appcarauce, as if nifled. At o the -^ '■ ^^ tibre has been crushed and twist- ed so as to tear brighter its conteats, while ^ the tougher ear- colemma, else- where so closely applied to the rest as ro be_ invisible, remains u n t o r a and conspicuous. made up of alternating dimmer and transverse bands (Fig. 33). After death the semi-solid contents of the fibre solidify and death -stiffening is pro- duced ; at the same time the fibre often splits up into a number of very fine threads or fibrillm, which were formerly regarded as true constituents of the living muscular fibre. Plain muscular tissue. — The muscles hitherto spoken of -&■ - Of what is a tendon made ? Of what is striped muscular tissue composed ? Describe the form »nd size of muscular fibres ? What is the sarcolemma? What is the consistency of the con- tractile part of a living muscular fibre? What appearance does it present under the microscope? What is the cause of death stiffenine! What are fibrillse ? *' What do we mean by voluntary muscles ? PLAIN MUSCULAR TISSUE. 75 are all more or less under the control of the will ; we can make them contract or prevent this aa we choose ; they are therefore often called the voluntary muscles.* There are in the body other muscles whose contractions Pia. 34.— The muscular coat of the stomach. m cannot control, and which are hence called involuntary muscles ; they are not attached to the skeleton directly, nor concerned in our ordinary movements, but lie in the What by involuntary? "Which kind is attached to the skeleton? Where do we find the involuntary muscles? * No sharp line can be drawn between voluntary and involuntary muBcles ; the tniiBcIes of respiration are to a certain extent under the control of the will ; any one can draw a long breath when he chooses. But in ordinary quiet breathing we are quite unconscious of their working, and even when we pay heed to it our control of them is limited ; no one can hold his breath long enough to suffocate himself. In- deed, any one of the striped muscles may be thrown into activity, independently of or even against the will, as we see in the "fidgets" of nervousness, and the irre- presBible trembling of extreme terror. Functionally, when we call any muscle vol- ontary, we mean that it may be controlled by the will, b'lt not that it necessarily always is so. Structurally, the heart occupies an intermediate place ; its striped fibres resemble much more those of voluntary than of invo.untary muscles, but its beat is not at all subject to the will ; though, as the exception proving the rule, it may he noted that there is an apparently weU-authenticated ease of a person who coold by an «ct Of will stop his heart. 76 THE HUMAN BODT. Walls of various hollow organs of the body, as the stomach (Fig. 34), the intestines, and the arteries ; by their con. tractions they move things contained in those cavities Like the voluntary muscles, the involuntary consist of contractile elements, with accessory cod- nective tissue, blood-vessels, and nerves ; but- their fibres have a very different appear- ance under the microscope. They are not cross-striped, but are made up of elongated cells united by a small amount of cement- ing material. Each cell (Fig. 35), is flat- tish, and tapers ofE toward its ends ; in its centre is a nucleus with one or two nucle- oli. The cells have the power of shortening in the direction of their long axes. Heart muscle. — The muscular tissue of I e heart is not under the control of the 11 ; it, however, is cross-striped, and more Ice the voluntary than the ordinary in- voluntary muscle, though it differs in some Fia. 93.— TTnstripeii respects from both. muscle-cells. Speaking generally, we may say that the movements necessary for the nutrition of the body are not left for us to look after ourselves, but are carried on by muscles which work involuntarily ; the blood is pumped round by the heart, and food churned up in the What is their function? What are they composed of ? What is seen when a cell from an involuntary muscle is examined with the microscope? Is the heart muscle voluntary? In what respect does it resemble voluntary muscle? What movements of the body does nature not leave to our own control? Give examples. TEE OHEMICAL COMPOSITION OF MUSCLE. 77 stomach and passed along the intestines, whether we think about it or not. The chemical composition of muscle.— Muscle contains about 75 per cent, of water ; and a considerable quantity of salines. Living, resting muscle is alkaline to test paper ; hard-worked or dying muscle is acid. Its chief organic constituents are proteid or albuminous substances (p. 31), and of these the most abundant in a per- fectly fresh muscle is myosin. Soon after death the myosin clots. Dilute acids dissolve myosin and turn it into syntonin, which used to be thought the chief pro- teid of muscle. Beef tea. — When lean meat is heated its myosin is converted into a solid insoluble substance much like the white of a hard-boiled egg. Hence, when a muscle is boiled most of its proteid is coagulated and stays in the meat instead of passing out into the soup. Even if beef be soaked first in cold water this is still the case, as myo- sin is not soluble in water.* It follows that beef tea as ordinarily made contains little but the flavoring matters and salts of the beef, and some gelatin dissolved out from the connective tissue of the muscle. The flavoring matters What propovtion of water does muscle contain? What other in- organic compounds do we tind iu it ? What is the reaction of living muscle 1 How is this changed by work or death ? What are its main organic constituents? Name the most abundant of these. What change occurs in it after death ? What is syntonin ? Wliat happens to the myosin when muscle is lieated ? When we boil meat does its myosin become dissolved in the soup ? Can we get the myosin out of beef by soaking it in cold water ? What things are found in ordinary beef tea ? * To get over this difficulty, various methods of making beef tea have been suggested, in which the chopped meat is soalted an hour or two in strong brine or in very dilute trmriatic acid. In these ways the myosin can be dissolved out at the beef; but the product has such an unpleasant taste that no one is lilsely V) swallpw it, and least of all a sick person. 78 THE HUMAN BODY. make it deceptively taste as if it were a strong solution of the whole meat, whereas, it contains but a small propor- tion of the really nutritious parts, which are chiefly left behind in tasteless shrunken shreds, when the liquor is poured ofE. Some things dissolved out of the meat make beef tea a stimulant to the nervous system and the heart, but its nutritive value is small, and it cannot be relied upon to keep up a sick person's strength for any length of time. Liebig's extract of meat is essentially but a concentrated beef tea; from its stimulating effect it is often useful to persons in feeble health, but other food should be given with it. It contains all the flavoring matters of the meat, and its proper use is for making gravies and flavoring soups ; the erroneousness of the common belief that it is a highly nutritious food cannot be too strongly insisted upon, as sick persons may be starved on it if ignorautly used. Various meat extracts are now prepared by subjecting beef to chemical processes in which it undergoes changes like those experienced in digestion. The myosin is thus made soluble in water and uncoagulable by heat, and a real concentrated meat extract is obtained. Before relying on any one of them for the feeding of an invalid, it would, however, be well to insist on having a statement of its Why does beef tea taste as if all the " strength " of the meat were in it? Where do the chief nutritious parts remain when beef tea is strained off the meat? What is the action of beef tea on the system? What is Liebig's extract of meat ? Why is it sometimes useful to invalids? What should be given them in addition? What is its proper use? Why is it important to know that it is not a nutritious food? How are some other meat extracts made? How is the myosin changed in preparing them? Are they all to be relied on indiscrimi- nately? What should be done before trusting the nutrition iif a feeble person to any one of thew? MEAT EXTRACTS. 79 method of preparation, and then to consult a physician, or some one else who has the requisite knowledge, in order to ascertain if the method is such as might be expected to really attain the end desired. CHAPTER Vn. MOTION AND LOCOMOTION. The special physiology of muscles. — The distinctive prop- erties of muscle are everywhere the siime ; it has tlie power of contracting ; but the uses of difEerent muscles are very varied by reason of the difEerent parts to which they are attached. Some are muscles of respiration, others of swallowing; some bend joints and are called flexors, others straighten them and are called extensors, and so on. The determination of the exact use of any particular muscle is known as its sjjecial physiology, as distinguished from its general physiology, or properties as a muscle, without reference to its use as a muscle in a particular place. We may here consider the special physiology of the muscles concerned in standing and walking. Levers in the body. — In nearly all cases the voluntary muscles carry out their special functions with the co-oper- ation of the skeleton ; most of them are joined to bones at each end and when they contract move the bones, In what respect are all muscles alike? Have all muscles the same uses? Give instances of the employment of muscles for difEerent pur- poses. What is meant by the special physiology of a muscle? What by its general physiology? With what do the voluntary muscles co-operate? To what are the ends of nearly all muscles attached? What happens when a muscle contracts? [80] TUB DIFFERENT KINDS OF LEVERS. 81 and, secondarily, the soft parts attached to these. When muscles move bones the latter are almost invariably to be regarded as levers whose fulcra lie at the joint where the movement takes jilace. Examples of the three forms of levers recognized in mechanics are found in the human body. levers of the first order. — In this form (Pig. 36), the fulcrum or fixed supporting point, F, lies between the weight to be moved and the moving power. The distance F P Jj^ W PiQ. 36.— A lever of the first order. F, fnlcrum ; P, power ; W, reslBtance ci weight. Pi?' from the power to the fulcrum is called the power- arm of the lever, and the distance WF is the weight- arm. When power-arm and weight-arm are equal (as in an ordinary pair of scales), no mechanical advantage is gained ; to lift a pound at W, P must be pressed down with a force greater than a pound ; and the end W will go up just as far as the end P goes down. If PF be longer than WF then a small weight at P will balance a larger one at W, the gain being greater the greater the difference in the length of the arms, but the distance through which W is moved will be less than that through which P moves ; for example, if PF be twice as How are the bones moved by muscles to be re.ararded? Where do the fulcra of these levers lie? How many kinds of levers are found in the body? Describe a lever of the first order. Define power-arm and weight- arm. When is a mechanical advantage gained by such a lever? 6 82 THE HUMAN BODY. long as WF then half a pound at P would balance against a pound at W, and just over half a pound laid on the end P would lift a pound on the end W, but W would only go up half as far as P went down. On the other hand, if the weight-arm were longer than the power-arm there would be a loss in force, but a gain in the distance through which the weight was moyed- Examples of levers of the first order are not numer- ous in the human body. One is found in nodding movements of the head, the fulcrum being where the occipital bone articulates with the atlas (Fig. 20). "When the chin is raised the power is applied to the skull behind the fulcrum by muscles passing from the spinal column F W 'Pia. 37. — A lever of the second order. F, 'f nlcmm ; P, power ; W, weight The arrows indicate the direction in which the forces act. to the back of the head ; the resistance to be overcome is the excess in weight of the part of the head in front of the fulcrum over that behind it, and is not great, as the head is nearly balanced on the top of the spine. To let the chin drop does not necessitate any muscular effort. Levers of the second order. — In this form of lever (Fig. 37), the weight or resistance acts between the ful- crum and the power. The power-arm PF is accordingly What IS lost when power is gained? Are there many levers of the first order in the body? Give an Rxample of one, describing the action. Describe a lever of the second order. LEVEBa IN THE BODY. 83 always longer than the weight-arm, WF, and so a com- paratively weak force can oyercome a considerable resist- ance. There is, however, a loss in rapidity and extent of movement, since it is obvious that when P is raised a certain distance W will be raised less. As an example of this kind of lever we may take the act of standing on the toes. Here tlie foot is the lever, and the fulcrum is where its fore part rests on the ground ; the weight is that of the body, and acts downwards through the ankle joint at Ta, Fig, 19 ; the power is the great muscle of the calf of the leg pulling by its tendon, which is fixed to the end of the heel bone, Ca. Levers of the third order. — la these (Fig. 38), the power is applied between the fulcrum and the weight ; hence the power-arm PF, is always shorter than the p ■ ^ w F FiQ. 38.- A ]ever of the thiid order. F, falcrnm ; P, power ; W, weight. weight-arm, WF. The moving force acts at a mechani- cal disadvantage, but swiftness and range of movement are gained ; this is the form of lever most commonly used in the body. For example, when the forearm is bent up towards the arm the fulcrum is the elbow joint (Fig. 29) ; What is the mec'.iamcal gain in sucVi levers? What is the loss? Give an examnle of employment of a lever of the second order in the body, poii-dng out fulcrum, point of action of the weight, and point of application of the power. Describe a lever of the third order. What is lost and what gained by it? Is it often used in the body? Give an example. 84 Tim HUMAN BODY. the power is apjDlied at the insertion of the biceps muscle into the radius ; the weight is that of the forearm and hand and whatever may be held in the latter, and acts at the centre of gravity of the whole, somewhere on the far side of the point of application of the power. Usually (as in this case), the power-arm is very short, so as to gain speed and extent of movement, the muscles being strong enough to work at a considerable mechanical disadvantage. The limbs are thus also made much more shapely than would be the case were the power applied near or beyond the weight. Pulleys in the body, — Fixed pulleys are used in the body ; they give rise to no loss or gain of power, but serve to change the direction in which certain muscles pull. One of the muscles of the eye- ball, for example, has its origin at the back of the eye-socket, from there it passes to the front and ends, before it reaches the eye-ball, in a long tendon. This tendon passes on to the margin of the frontal bone, which arches over the front of the eye-socket, and there passes through a ring and turns back to the eye-ball. The direction in which the muscle moves the eye is thus quite different from what it would be if the tendon went directly to the eye- ball. Standing. — We only slowly learn to stand in the year or two after birth, and though we finally come to do it without conscious attention, standing always requires the co-operation of many muscles, guided and controlled by Why is the power-arm in the body usually short? What kind of pulley is used in the body? Is any mechanical ad vantage gained from it? What is it used for? Give an example. Is standing a simple process? BTANDINO. 85 tlie nervous system. The influence of the latter is shown by the fall which follows a severe blow on the head, which has fractured no bone and injured no muscle ; " the con- cussion of the brain " stuns the man, and until it has passed off he cannot stand. When we stand erect, with the arms close by the sides and the feet together, the centre of gravity of the whole adult body lies at the articulation between the sacrum and the last lumbar vertebra, and a perpendicular drawn from it will reach the ground between the feet. In any position in which this perpendicular falls within the space bounded by a line drawn close around both feet, we can stand. When the feet are togetlier the area enclosed by this line is small, and a slight sway of the trunk would throw a perpendiculat dropped from the centre of gravity of the body outside it ; the more one foot is in front of the other the greater the sway back or forward which will be compatible with safety, and the greater the lateral distance between the feet the greater the lateral sway which is possible without falling. Consequently, when a man wants to stand very firmly he advances one foot obliquely, so as to increase his base of support both from before back, and from side to side. In consequence of the flexibility of its joints a dead body cannot be balanced on its feet as a statue can. When we stand, the ankle, knee, and hip-joints, if not braced by the muscles, would give way, and the head also Illustrate the influence of the nervous system in connection with standing. Wliere is the centre of gravity of the body when we stand erect? Where does a perpendicular from it reach the ground? Why do we separate the feet wlien we want to stand firmly? Why cannot a dead body be balanced on its feet? What prevents our knee, and hip- joints from bending when we stand? 86 THE HUMAN BODY. fl H fall forward on the chest. But (Fig. 39) muscles, 1, in front of the ankle-joint, and others, I, behind it, both contracting at the same time, keep the joint from yielding ; similarly muscles (3) in front of the knee and hip-joints are opposed by others (II) behind them, and when we stand both con- tract to a certain extent and keep those joints rigid; and the muscles (III), which run from the pelvis to the back of the head similarly pull against others, 3 and 4, which run from the pelvis to the lower end of the breast- bone, and from the upper end of the breastbone to the anterior part of the skull, and their balanced contraction keeps the head erect. Since the degree to which each muscle concerned con- tracts when we stand must be accu- rately adjusted to the contraction of its antagonist on the opposite side of the joint, we may easily compr<5hend why it takes us some time to learn to stand, and why a stunned man, whose muscles have lost guidance from the f^^'rok^'Kffcl^'IS nervous system, falls. behfnd fuTjoimran/by Locomotlou includes all movements their balanced activity e i_i ^ i > -t -i , keep the joints rigid and 01 the body in Space, dependent on the body erect. . -j j i a l its own unaided muscular efforts, such as walking, running, leaping, and swimming. Explain how the different joints concerned are " braced" in stand- ing. "Why does it take a child some time to learn to stand? What is meant in physiology hy locomotion f 1 I Fig. 39.— Diagram illu3- scle WALKma. 87 Walking. — In walking, the body never entirely quits the ground, the heel of the advanced foot reaching this before tl)e toe of the rear foo^ has been raised from it. In each step the advanced leg supports the body, and the foot behind at the beginning of the step propels it. A little attention will enable any one to analyze the act of walking for himself. Stand with the heels to- gether and take a step, commencing with the left foot. The whole body is at first inclined forwards, the movement taking place mainly at the ankle joints. This throws the centre of gravity in front of the base formed by the feet, and a fall would result were not the left foot simul- taneously raised by bending the knee a little, and swung forwards, the toes just clear of the ground and the sole nearly parallel to it. When the step is completed the left knee is straightened and the foot placed on the ground, the heel touching first ; the base is thus extended in the direction of the stride and the fall prevented. Meanwhile the right leg is kept straight but inclined forwards, carry- ing the trunk during the step while the left foot is off the ground; at the same time the right foot is raised, com- mencing with the heel ; when the step of the left leg is completed only the great toe of the right is in contact with the suppoi't. With this toe a push is given which sends the body swinging forward, supported on the left leg, which now in turn is kept rigid except at the ankle joint ; the right knee is immediately afterwards bent and that leg swings forwai'ds, its foot just clear of the ground, as the left did before. The body meanwhile is supported Is the body ever ofE the ground in walking? Dessrihe the act of walking. 88 THE HUMAN BODY. on the left leg alone. When the right leg completes its step its knee is straightened and the foot thus brought, heel first, on the ground ; while it is swinging forwards the left foot is gradually raised, and at the end of the step its great toe alone is on the ground ; with this a push is given as before with that of the right foot, and the left leg then swings forward to make the next step. Walking may, it fact, be briefly described as the act of continually falling forwards and preventing the completion of the fall by thrusting out a leg to meet the ground in front. During each step the body sways a little from side to side, as it is alternately borne by the right and left legs. It also sways up and down a little ; a man standing with his heels together is taller than when one foot is advanced, just as a pair of compasses held erect oa its points is high- er when its legs are together than when they straddled apart ; in that period of each step when the advancing trunk is balanced vertically over one leg, the walker's trunk is more elevated than when the front foot also is on the ground. Women, accordingly, often find that a dress which clears the ground when they are standing sweeps the pavement when they walk. The length of each step is primarily dependent on the length of the legs, though it can be largely controlled by special muscular effort, as we see in a regiment of soldiers, all of whom have been taught to take the same stride, no matter how their legs vary in length. In natural easy walking, little muscular effort is employed to carry the rear leg forward after it has given its push ; it swings on At what part of a step is a man tallest ? Give illustrations. What primarily determines the length of a person's step ? Can this length he controlled ? Illustrate. hyqienb of the muscles. 89 like a pendulum once its foot is raised from the ground. As short pendulums swing faster than long ones the natu- ral step of short-legged peoisle is quicker than that of long-legged. !Runnin;5 differs from walking in several respects. There is a moment when both feet are off the ground ; the toes alone come in contact with it at each step ; and the kuee joint is not straight at the end of the step. In running, when the rear foot is to leave the ground the knee is suddenly straightened, and the ankle-joint extend- ed so as to push the toes forcibly on the sujiport and pow- erfully impel the whole body forwards and upwards. The knee is then considerably flexed and the foot raised some way from the ground, and this occurs before the toes of the front foot reach the support. . The raised leg in each step is forcibly drawn forward by its muscles and not allowed to swing passively as in quiet walking. This increases the rate at which the steps follow one another, and the stride is increased by the sort of one-legged jump that occurs through the jerk given by the straightening knee of the rear leg, just before it leaves the ground. Hygiene of the Muscles. — The healthy working of the muscles is dependent on a healthy state of the body in general ; this is indispensable that they may be sufBciently supplied with proper nourishment, and have their wastes promptly carried away. Hence good food and pure air are necessary for a vigorous muscular system. Muscles also Why do slioTt-legged persons tenrl to take a quicker step than others? How does running differ from walking? Describe the act of run- ning. How is tlie number of steps taken iu a given time increased in running? How is the stride increased? How does the state of general health influence the muscular sys- tem? "Why does an athlete need good food and air? 90 THE HUMAN BODY. should not he exposed to any considerahle continued pressure, since this interferes with the flow of blood and lymph through them which is essential for their nu- trition. Exercise is necessary for the best doTclopment of the muscles. A muscle long left unused diminishes in bulk and degenerates in qtfality, as is well seen when a muscle is paralyzed and remains permanently inactive because of disease of its nerve ; although at first the muscle itself may be perfectly healthy, it alters in a few weeks, and when the nerve is repaired the muscle may in turn be in- capable of activity. The same fact is illustrated by the feeble and wasted state of the muscles of a limb which has been kept motionless in splints for a long time : when the splints are removed it is only after careful and per- sistent exercise that the long idle muscles regain their former size and power. The great muscles of the "brawny arm" of the blacksmith illustrate the converse fact — the growth of muscles when exercised. Exercise, to be useful, must be judicious ; taken to the point of extreme fatigue, day after day, it does harm. When a muscle is woi'ked its substance is used up ; at the same time and afterwards more blood flows to it, and if the exercise is not too violent and the intervals of rest are long enough, the repair and growth will keep pace with or exceed the wasting : but excessive work and too short rest will lead to diminution and enfeeblement of the muscle just as certainly as too little exercise. Few persons can profitably attempt to work hard daily Why should muscles not be exposed to continuous pressure? What happens when a muscle is not used? Illustrate by examples. Why are the muscles of a blacksmith's arm large? When does exercise do harm? Why? Can most persons work hard with both brain and muscle at the same time? VARIETIES OV EXERCISE. 91 with both brain and muscle, but all should regularly use both; choosing which to worh with, and which to simply exercise. The best earthly life, that of the healthy mind in the healthy body, can only so be attained. For persons of arerage physique, engaged in study or business pursuits of a sedentary nature, the minimum of daily exercise should be an amount equivalent to a five-mile walk. Time for Exercise. — Since extra muscular work means extra muscular waste, and should be accompanied by an abundant supply of food materials to the muscles, violent exercise should not be taken after a long fast. Neither should it be taken immediately after a meal ; a great deal of blood is then needed in the digestive organs to provide materials for digesting the food, and this blood cannot be sent off to the muscles without the risk of an attack of indigestion. Strong and hearty young people may take a long walk before breakfast, but others had better wait un- til after eating something before engaging in any kind of hard work. Varieties of Exercise. — In walking and running the muscles chiefly employed are those of the lower limbs and trunk ; these exercises leave the miiscles of the chest and arms imperfectly worked. Bowing is better, since in it nearly all tlie muscles are used. No one exercise em- ploys in proper proportion all the muscles, and gymnasia in which different feats of agility are practiced so as to call different muscles into action have a deservec\ popu- How can the highest development of man, regarded merely as a thinking and moving machine, be attained? Why should we not exercise when fasting? Why not soon after What muscles are chiefly used in walking and running? Which are imperfectly exercised? Why are gymnasia useful? 92 TEE HUMAN BODY. larity. It should be borne in mind, howeyer, that the legs especially need strength; while in the arms delicacy of movement is more important to most persons than great strength; and the fact that gymnastics are usually practised indoors is also a great drawback to their value. Out-of- \ d oor exerc ise in good weather is better than any other, and every one can at least take a walk. The daily ''constitu- tional" is very apt to become wearisome, especially to young persons, and exercise loses half its value if unattended with feelings of mental relaxation and pleasure. Active games, for this reason, have a great value for young and healthy persons; lawn-tennis, base-ball, and cricket are all attended with pleasurable excitement, and are excellent also as ex- ercising many muscles. What is chiefly needed in the muscles of arms and legs respec- tively? Point out conditions under which muscular exercise loses much of its value. Why are athletic games especially useful ? CHAPTER VIII. WHY WE EAT AND BREATHE. How is it that the body can do muscular work? — In the muscles we possess a set of organs capable of moving the body from place to place, of changing the relative positions of its parts, and of lifting external objects: as long as we are alive, more or fewer of our muscles are every moment doing some mechanical work. This fact suggests the question, whore does this power of working come from ? In a few words, the answer is, it comes from the burning of parts of the body itself : in the burning, work-power or energy is set free and some of this is used by the muscles. The conservation of energy.— The different natural forces known to us are not nearly so numerous as the kinds of matter : we all, however, know several of them, as light, heat, electricity, and mechanical work. One of the greatest discoveries of the nineteenth century is that these different natural forces, or forms of energy, can be turned one into another, directly or indirectly : kinds of energy are transmutable, while, so far as we know at pres- What are the functions of the muscles? Are all of our muscles ever at rest at the same time ? What question does the constant activity of our muscles suggest? How may this question be briefly answered ? Name some forms of energy. Can they be turned from one form to another ? 94 TUB HUMAN BODY. ent, kinds of matter are not. We cannot, as tlie alchemists hoped, turn iron or mercury into gold, but we can turn light into heat, and heat into electrical force, or into me- chanical work. When such transformations are made it is always found that a definite amount of one kind of energy disappears to give rise to a certain definite amount of an- other. In other words, it has been discovered that energy cannot be created : if we take a given quantity of heat we can turn some of it into mechanical work ; if we then, turn all this mechanical work back into heat we get again exactly the quantity of heat which disappeared when the mechanical work appeared : and so with all other transformations of energy from one kind to another, and back again. This fact that energy or ivorlc-'power can be turned from one kind into another, and often back again, but never created from nothing or finally destroyed, is known as the law of the conservation of energy. niustrations of the conservation of energy. — In a steam- engine, heat, which is the best known kind of energy, is produced in the furnace ; when the engine is at work all of this energy does not leave it as heat ; some is turned into mechanical work, and the more work the engine does the greater is the difference between the heat generated in the furnace and that leaving the machine. If, however, we used the work to rub two rough surfaces together we could get the heat back, and if (which of course is im- possible in practice) we could avoid all friction between Can matter be transmuted ? What is always found when energy is transformed ? Can man create energy ? Illustrate the fact that energy can be changed in kind but not created. What is meant by the law of the conservation of energy ? Give an illustration of the conservation of energy. TUB CONSERVATION OF MNMBGT. 95 the moving pcarts of the machine, and have all parts of the engine at the end of the experiment exactly at the same temperature as at its beginning, the quantity of heat thus obtained would be exactly equal to the difference between that amount of heat originally generated in the furnace of the engine, and the quantity which had been carried ofE from it to tlie air since its fire was lighted. Having turned some of the heat into mechanical work we could thus turn the work back into heat again, and find it yield exactly the amount which seemed lost. Or we might use the engine to drive an electro-macj'netic machine and so turn part of the heat liberated in its fur- nace, first into mechanical work, and this afterwards into electricity; and if we chose to use the latter with the proper apparatus, as now used for electric lighting, we could turn more or less of it into light; and so have a great part of the energy whicli first became conspicuous as heat in the engine furnace, now manifested in the form of light at some dis- tant point. In fact, starting with a given quantity of one kind of energy, we may by proper contrivances turn all or some of it into one or more other forms ; but if we col- lected all the final forms and retransformed them into the first, we should have exactly the amount of it which had disappeared when the other kinds appeared. Why we need food. — Energy, as we have seen, cannot be created from nothing ; since the body constantly expends energy, it must have a steady supply. This supply comes tJ-ive an example of the transfoi'mation of heat into electrical force. Of electrical force into light. Given a supply of one kind of energy what can we do with it? What would we find if we collected all the final manifestations of energy and turned them back into the original form ? Why must the body have a steady supply of energy ? Where does the supply come from ? 96 THE HUMAN BODY. from the energy libei'ated when parts of the body are turned,, or, as the chemists say, oxidized, just as that used by a locomotive comes from the burning or oxidation of coal or wood in its furnace. In consequence of this constant oxi- dation, which destroys the tissues of the body as coal is destroyed in a furnace, new materials must constantly be supplied to make up for those used for oxidation. These new materials are provided in our food. One chief reason of our needing to eat, is that we may reiilace the parts of the body which have been burned in order to set free the energy which we spend in our muscular movements. Why the body is warm. — As a working steam-engine is warm so are our bodies, because all the energy which is set free when substances are burned in themj is not turned into mechanical work, but some of it appears as heat. This keeping warm is a very important matter, for experi- ment shows that no tissue of the human body works well when cooled down even a few degrees below 98.5° F., which is its natural healthy temperature. Careful experi- ments prove that when a muscle does work it becomes hotter, and we all know that exercise makes us warm. This shows that the oxidation or burning which takes place in a working muscle does not all become turned into mechanical work, but a good share of it appears as heat. What is true of muscle is true of all other organs of the body: when they work, no matter what their kind of work, their substance is oxidized, and some of the energy set free What is the chemical term for 'buriiing? What does food supply? Point out a chief reason for oiir need of eating? Why are our bodies warm ? Why is it important that they should be warm ? How is the temperature of a muscle affected when it works ? Do other organs resemble muscles in this respect? TJSB NEOBSSItr Off foot). Q') by the oxidation appears as heat, assisting to keep the body warm, and at its best -vvorking temperature. A second reason why we need food. — Since the body only works well at a temperature which is higher than that of the air around it (except on a very hot day), and in health always keeps at this temperature, it must lose heat nearly all the time. At night each of us is, in lieaJth, just as warm as in the morning ; and in the morning as when we went to bed ; though we have lost heat to the air during the day, and to the bedclothes at night. In order to keep our bodies at the temperature most suitable to their activity, they must, therefore, generate heat all the time, to com- pensate for the giving of it from them to the outer world. In this necessity of generating heat we find a second reason for the need of food : we require daily to take into our- belves tJiiiigs whicn can be burned (or oxidized) m tiie body, and which in so doing will give off heat. The influence of starvation upon muscular work and animal heat. — When a man is deprived of food the supply of things which can be oxidized in his body is cut off. The tissues and organs are used up and not renewed ; his tem- perature falls, his muscles become weaker and weaker, and at last he dies. The body does not live, and work, and keep warm, by means of a peculiar vital force or energy which inhabits it, but by utilizing the energy set free in it by the oxidation of foods, or of things made in it from foods. If the food supply be cut off, the body first uses up What must we conclude from the fact that our bodies keep at nearly the same temperature all the time? How do we know that they generate heat? Give a reason for taking fond, in addition to its use as a source of eneigy to be spent by the muscles. What happens when a man is starving ? How does the body live, and keep warm, and work? What first happens when the food sup- ply is stopped? 7 98 THE HUMAN BODY any reserye of nutritious matter wliicli may have been stored up in it when the starvation commenced, and as this is expended it becomes weaker and weaker until death supervenes.* How long a man, totally deprived of food, oan keep alive, will depend, partly, on how much reserve material, capable of oxidation, he has stored up in him when the starvation period commences ; but largely, also, on the ex- tent to which he can spare himself muscular work and loss of heat. The breathing movements and beat of the heart must go on, but if the individual lies quiet in bed he need do little or no other muscular work ; and if he is well covered up with blankets, the loss of heat from the body is slight and calls for but little oxidation of the tissues to compensate for it.f Also, a fat person will survive starva- tion longer than a lean one ; during the process his fat is slowly burnt; but so long as it lasts he can supply his mus- cles with something which can be oxidized to yield working power, and lie also, by its burning, can maintain his tem- perature. Fat is, in fact, a sort of reserve fuel, laid up in the body, and a man, in the strict sense of tlie word, can hardly bo said to begin to starve until his fat has nearly all been used up. J Upon wliat does the length of life of a man getting no food de- pend? What expenditures of energy must go on all the time? How does lying in hed diminish the expenditure of energy? Why will a fat man depi-iveil of food live longer than a lean one? When does a fasting man really begin to starue? * When warm-blooded animals are starved their temperature slowly falls; and ■when it comes down to about 77" f. (25° c.) death occurs: the various tissues at that temperature can no longer work so as to maintain life. t Hence Dr. Tanner, and " fasting girls " keep in bed. warmlv covered up, most of the time: the losses of the body in mechanical work and heat are thus reduced to a minimum, and consequently the oxidation of the food reserves stored in the body at the beginning of the fast. t Some warm-blooded animals, as Dears, hibernate; that is, sleep all throiigh OXIDATIONS IN THE BODY. 99 Oxidations in the body. — In the preceding paragraphs oxidation and burning have been used as equivalent phrases : this is in accordance with the teachings of chem- istry. To the chemist a substance is iurned when it is combined with oxygen, whether this combination take place slowly or I'apidly. If the combination occur rapidly the burning or oxidizing mass becomes very hot and also gives ofE light: sncli a rapid and vigorous oxidation is called a com- lustion J no combustions take pi. ice in our bodies. It has, however, been proved that whether the combi- nation of oxygen with an oxidizable, or burnaile, substance takes place rapidly or slowly, at the end of the process ex- actly the same amount of energy will have been set free in each case. When the oxidation occurs in a few seconds the oxidizing mass becomes very hot : when it occurs slowly, in a few days or weeks, the mass will never be very hot, be- cause the heat set free in the process is carried off nearly as fast as it appears. Illustrations of oxidations at a low temperature. — If a piece of magnesium wire be ignited in the air it will become white-hot, flame, and leave at the end of a few What does a chemist mean when he says a substance is hurned ? What is a combustion ? Do combustions occur in our bodies ? Does the quantity of energy liberated by the complete oxidation of any substance vary with the rate of oxidation ? Why is a slowly oxidizing mass of matter not very hot ? Give an instance of the oxidation of the same substance at high and low temperatures. the winter and take no food. They feed well in the warm weather, and are qnita tat at the close of antnmn, when they seek some sheltered place to winter in. This Bhelterand their warm, furry coats make the loss of heat very little: the animal, except for its breathing and the beat of its heart, hardly ever moves during the winter, and even those necessary movements are reduced to the least possible, the breathing and heart-beat being much slower than during the summer. With return of warm weather the creature wakes up again, but is thCB leiin, having burnt up its f»t during its winter sleep. 100 TUB, HUMAN BODY. seconds only a certain amount of incombustible rust or magnesia, which consists of the metal combined with oxy- gen ; under these circumstances it has been burnt or oxid- ized quickly at a high temperature. The heat and light evolved in the process represent the energy which is set free by the metal and oxygen when they combine. We can, however, oxidize the metal in a different way, attend- ed with no evolution of light and no very perceptible rise of temperature If, for instance, we leave it in wet air, it will become gradually turned into magnesia without hav- ing ever been hot to the touch or luminous to the eye. The process then, however, takes days or weeks ; but in this slow oxidation just as much energy is liberated as in the former case, although now all take:, the form of heat ; and instead of being liberated in a short time is spread over a much longer one, as the gradual chemical combi- nation takes place. The slowly oxidizing magnesium is, in consequence, at no moment noticeably hot, since i^ loses its heat to surrounding objects almost as fast as ib generates it. The oxidations occurring in our bodies are of this slow kind. An ounce of arrowroot oxidized in a fire, and in the human body, would liberate exactly as much ener- gy in one case as the other, but the oxidation would take place in a few minutes and at a high temperature in the former, and slowly, at a lower temperature, in the latter. Oxidation in the presence of moisture. — Wet wood or wet coal we know will not burn, or can only be made to do so with difficulty. Other kinds of burning or oxidation are, however, well known, which take place in the pres- How does the rate of oxidation differ in the two cases ? How does the oxidation of arrowroot burned in a fire differ from its oxid» tion in the living body? Can oxidations occur in the presence of moisture ? OXWA TIOJS'S IN THE PRESENCE OF MOISTURE. \0\ ence of moisture. The rusting of iron, for example, is an oxidation or burning of the metal, and takes place faster in damp air than in dry; during the slow rusting in moisture just as much heat is set free as if the same com- pound of iron and oxygen were prepared in a more rapid way. Such experiments throw great light on the oxida- tions which take place in our own bodies. All of them are slow oxidations, which never at any oue moment give «£E a great amount of heat, and all occur in the damp tissues. Summary. (1) Energy can be turned from one form in- to another ; as from heat into meclianical work by a steam- lengine. (2) Our bodies are constantly losing energy, partly in muscular work, and partly as heat lost to surrounding ■objects. (3) Energy cannot be created ; all that can be done is to turn one kind of it into another kind: heat can be turned into mechanical work (as in a locomotive) ; or mechanical work into heat (as by friction) ; or heat into "electricity (as in a thermo-electric machine); and so forth. ((4) Since our bodies spend energy all our life long they must be supplied with it from outside : they can turn into other forms the energy which they receive, but they cannot make it from nothing. (5) The chief .forms of energy which our bodies expend are muscular (;'. e. mechanical) work, and heat. (6) In ordinary machines, as a locomotive, the Give an instance. Does the rate of oxidation or the presence of moisture affect tlic amount of heat liberated ? Of what Icind are tlie oxidations wliicli occur in our bodies ? Give a summary of the contents of this chapter with reference to the following points: (1) The transformation of energy; (3) The loss of energy from the body ; (3) The fact that man cannot create ener- gy but can transmute it ; (4) The fact that otir bodies must be con- stantly supplied with energy from outside ; (5) The chief forms of energy spent by the body ; (6) The source of the energy spent by a Working steam-engine. 102 THE HUMAN BODY. source of the work done and the heat given off is the oxida- tion of coal in a furnace. (7) Chemistry teaches us that just the same amount of energy or work power is given off when an ounce of any given substance is oxidized, wliether the oxidation occurs rapidly or slowly. (8) Chemistry also teaches us that many oxidations, or burning?, occur in the presence of water, and that in them just the same amount of energy is set free as if the oxidation occurred in dry air. (9) In our bodies substances are burnt slowly at a low temperature and in the presence of moisture: in this burn- ing energy is set free which the body uses for performing its necessary work. (10) In the burning which the tissues undergo while they work they are used up and destroyed. (11) To compensate for the destruction of tissue which accompanies and provides the power for every action of the body, material must be taken into it from outside, which will restore or repair the oxidized tissues. (13) Such substances taken into the body from outside are called /oofZs, and the constant oxidation of the body which is necessitated by the performance of the functions essen- tial to life, requires a supply of food from the outer world, if life is to be maintained. (13) The body of a healthy person has in it at any moment a certain reserve of oxid- izable matters, which we may call stored-up food. The most important of these reserve foods is fat. A fat man can accordingly bear starvation longer than a lean one un- der similar circumstances. (7) The amount of energy given off when a substance is oxidized at high or low temperatures; (8) The teachings of cliemistry with reference to oxidations in the presence of moisture ; (9) The con- ditions under wliieh substances are oxidized in our bodies ; (10) The changes which oxidized tissues undergo ; (11) Why we need to talie material from the outer world into our bodies ; (13) What is meant bv food; and why wb need foods ; (13) What are reserve foods. Illustrate. THE OXTGEN FOOD OB THE BODY, 103 The oxygen food of the body. — Hitherto we have only considered the energy-supply of the bcdy from one side ; we have regarded it as dependent on the constant supply of things which can be oxidized. But this is only half the question : if substances are to be oxidized there must be a provision of oxygen to oxidize them. In order that a steam-engine may work and keep warm it is not merely necessary that it have plenty of coal, but it must also have a draught of air through its furnace. Chemistry teaches us that the burning in this case consists in the combination of a gas called oxygen, taken from the air, with other things in the coals: when this combination takes place a great deal of heat is given ofE. The same thing is true of our bodies ; in order that food matters may be burnt in them and enable us to work and keep warm, they must be supplied with oxygen; this they get from the air by breathing. Wc'all know that if his sup- ply of air be cut o£E a man will die in a few minutes. His food is no use to him unless he gets oxygen from the air to combine with it ; while he usually has stored up in his body an excess of food matters which will keep him alive for some time if he gets a supply of oxygon, he has not stored up in him any reserve, or, if any, but a very small one, of oxygen, and so he dies very rapidly if his breathing be prevented. In ordinary language we do not call oxygen a food,but restrict that name to the solids and liquids which we swallow : but inasmuch as it is a material which we must take from the external universe into our bodies in or- Whydoweneed oxygen? What does a working steam-engine need in addition to coal ? What happens in the furnace of an engine? Why do we need to breathe ? What happens if a mans air supply be stopped ? Why does a man die sooner of want of air than of want of food ? Why is oxygen entitled to be called a food ? 104 THE HUMAN BODY. der to keep us alive, oxygen is really a food as much as any of the other substances which we take into our bodies from outside, in order to keep them alive and at work. Suffocation, as death from deficient air supply is named, is really death from oxygen-starvation. Wiat is suffocation? Appendix to Chaptbb VIIL The liberation of energy by oxidation, or burning, at a low tem- perature and in the presence of moisture, is such a fundamental fact in physiology, and its essential agreement with ordinary combustion BO difficult to grasp by most pupils, who naturally associate burning with a high temperature and luminosity, that it is worth while to il- lustrate these facts by a few simple experiments. 1. Buy a coil of magnesium wire, which can be obtained at small cost. Rub it clean with fine emery paper : cut it in two, apply a lighted match to one half and show how it is rapidly consumed with the evolution of light and heat, leaving behind only a white powder, magnesia, which is oxidized magnesium. Put the other half away in a bottle with a few drops of water. After a day or two its surface will be covered by a layer of magnesia; if this be scraped off another will succeed it ; and so on. This experiment shows that oxidation may occur rapidly at a high temperature m a short time, or slowly at a low temperature in a long time, but the ultimate product, in each case, is the same. 3. In relation to a subsequent paragraph (p. 112) the magnesia ob- tained by burning the wire in the air, may be kept, and attempts made to Ignite it: this will serve to show the uselessness of oxidized substances to the body, as sources of energy : they cannot be any more oxidized, and the best thing to do is to get rid of them. 3. G-et a bundle of iron wire : rub it bright with emery or sand paper. Place some in a warm dry bottle by the stove or fireplace. Put the rest In a bottle containing a little water. Next day the first specimen will be found bright, and the second covered with rust. This shows that oxidation may sometimes occur better in the presence of water than in its absence ; and serves as a text for pointing out how oxid!itions occur in the moist tissues of the body. OHAPTEE IX. NUTRITION. The "Wastes of the Body, — A man takes into his body daily seTeral pounds of foods of various kinds, as meats, bread, vegetables, and water, yet lie grows no heavier; it is, therefore, clear that his body must in every twenty-four hours return, on the average, to the outside world about as great a weight of matter as it receives from it. Even in childhood, while growth is taking place and the body be- coming heavier, the gain is never nearly equal to the weight of the foods swallowed. The materials given off daily from the body to the external universe, and compensating more or less accurately for the receipts from the outside world, are its wastes, and are cliiefly things which cannot be burned. Much of the food taken in can be, and is, oxi- dized to enable us to move and keep warm. When burned it is of no further use to us, and would only clog up the various organs, as the ashes and smoke of an engine would soon put its fire out if they were allowed to accumulate in the furnace. The chief wastes of the body are carbon di- oxide gas, water, and a kind of ammonia called urea. Eeceptive and Excretory Organs. — Those organs of the body whose function it is to gather new material from outside for its use are- known as receptive organs. There What, facts make it clear that a man must daily give ofE several pounds weight of matter from his body? Does a child's increase ia weight equal the weight of the food it has eaten? What is meant by the "wastes" of the body? How do most foods differ from wastes in regard to oxidation ? Why must wastes be removed from the body? Name the chief wastes of the body. WJl^t is meant by the receptive organs? [105] 106 THE HUMAN BODY. are two chief sets of these — one to receire oxidizable things, and the other to receive oxygen. The first set is represent- ed by the alimentary canal, consisting of mouth, gullet,* stomach, and intestines. It takes in food and drink. The second set consists of the lutigs, with the air passages lead- ing to them ; their business, as receptive organs, is to absorb oxygen. The organs whose duty it is to get rid of waste materials formed in the body are called excretory organs. The three most important exci-ctory organs are the lungs, the kidneys, and the shin; the lungs pass carbon dioxide gas out to the air, and also water ; the kidneys getnid of urea and water; and the skin, of water and a little urea. The Intermediate Steps between Reception and Ex- cretion. — Between the taking of oxidizable substances into our mouths and oxygen into our lungs, on the one hand, and the return of oxidized matters from our bodies to the surrounding world on the other, a great many intermediate steps take place. The alimentary canal (see Fig. 1) is a tube which runs through the body but nowhere opens into it; so long as food lies in this tube it therefore does not really form a part of the body, and is of no use to it : it resembles coals in the tender of a locomotive, waiting to be transferred to the furnace. In our bodies the furnace is everywhere; wherever there is a living tissue things are What are the functions of the two chief sets? Name those con- cerned in receiving oxidizable things. Those whose business it is to absorb oxygen. What is meant By the excretory organs? Name the most im- portant. What does each get rid of? Why is food in the stomach not really a part of the body? To what may we liken it? Where is the furnace of the body? Why must food be carried all over the body? *Tlje tecJjDical name tor the giUJet is wsophagug. NUTRITION. 107 burned to enable it to work; and the food or fuel must be brought therefore, to every corner of our frames. Digestion. — A great part of our food is solid, and could not of itself get outside of the alimentary canal. To render it available it must be dissolved so that it can soak through the walls of the stomach and intestines. For this purpose we find a set of digestive organs which make solvent juices and pour them on the food which we swallow, and so get it into a liquid state in which it can be absorbed. Circulation. — The solution containing our digested food if it simply soaked through the walls of the alimentary canal, would be of no use to distant parts, as the brain, or the muscles of the limbs. We find, therefore, in the body a set of tubes containing blood, and called blood-vessels: the blood is driven through these, by a pump, the heart. Much of the dissolved food passes into the blood-vessels of the alimentary canal, and from, them is carried by other blood-vessels to every organ, no matter how remote. As the blood flows unceasingly, round and round in its vessels, from part to part, the organs concerned in moving and conveying it are called circulatory organs, and the blood- flow itself is known as the circulation. Absorbents. — Some of the dissolved food is taken up into another set of tubes in the walls of the alimentary canal; these tubes carry it afterwards into the blood-vessels. They are called the absorlents. Why must many foods be dissolved? What is accomplished by the digestive organs? What are the blood-vessels? What enters those of the alimentary canal? How are organs distant from the alimentary canal nourislied? Why are the organs which keep up the blood-flow called circulatory organs? What is meant by the circulation? What are the absorbents? Where do tliey convey the foods which they take up in the walls of the alimentary canal? 108 I^^SM HUMAN BODf Respiration. — The blood in its course flows throngli the lungs. It is necessary not merely that food, hut oxygen also should be carried to every part of the body. As the blood traverses the lungs it picks up oxygen from the air in them; this air is then renewed by taking a fresh breath, and so on. The organs concerned in renewing the air in the lungs are the respiratory orgatis, and the act of renewal is respiration. Assimilation. — As each organ works it oxidizes; some of its substance is broken down by combination with oxygen brought to it by the blood, and is thus converted into burnt waste matter. The blood, as we have seen, brings, how- ever, not merely oxygen, but also food matters in solution. These ooze through the walls of the blood-vessels, and are taken up by the living, tissues and built into new tissues like themselves, to replace the part which has been used up and destroyed. This building and repair of tissues and organs from the dissolved food obtained from the blood is known as assimilation, — in plain English, "a making alike." Each living tissue takes from the blood foods which are not like itself, and builds them up into a form of matter like its own. The converse process, which accompanies all vital action, the breaking down into wastes of a living tissue when it works, is called dissimilation, or "a making unlike." The Relation of the Circulatory Organs and the Absorb- ents to Excretion. — It is as essential to the body that its wastes be carried off from the organs, as that the used-up What must be carried to all parts in addition to food ? Where does the blood get oxygen? What is meant by the respiratory organs? By respiration ? What happens when an organ works ? How are oxidized tissues replaced ?_ What is meant by assimilation ? By dissimilation ? What is needful to each organ in addition to a supply of fresh material ? H^UTItlTJOm 109 Material be replaced by new. Not merely must matter for assimilation be provided, but the -various waste products must be removed. Here iigain tlie blood-vessels and ab- sorbeats come into play. Absorbents are found not only in the walls of the alimentary canal, but all over the body. The wastes of each working tissue are passed out into them, and by them carried into the blood-vessels; these in turn carry the wastes to the lungs, kidneys, and skin, which get rid of them. The blood is thus as important in relation to removing the waste matters of an organ as in regard to supplying it with food and oxygen. Nutrition. — From what has been said above it is clear that tlie nourishment of the body is a very complicated process. It implies — (1) the reception of food from out- side ; (3) the digestion of food ; (3) the absorption of digested food ; (4) the conveyance of absorbed food to all parts by the blood ; (5) the taking up of wastes from the different organs ; (6) the conveyance of these wastes by the blood to excretory organs which pass them out of the body ; (7) the absorption of oxygen in the lungs, and its con- veyance by tlie blood to every organ ; (8) assimilation or the building up of new tissue from materials brought by the blood ; and (9) disassimilation, or the breaking down of working tissues by combination with oxygen. In subsequent chapters we shall have to consider in more detail. Digestion, Circulation, Absorption, Eespira- tion, and Excretion. The sum total of the actions of all the organs concerned in the nourishment of the body is known as the function of nutrition. Where do we find absorbents in addition to those of the alimen- tary canal? What is their function? What part does the blood play in the removal of wastes? Enumerate the processes concerned in the nourishing of the body What is meant by the function of nutrition? CHAPTER X. FOODS. Foods as Tissue Formers. — In the last chapter we have considered foods merely as sources of energy, but they are also required to build up the substance of the body. From birth to manhood we increase in bulk and weight, and that not merely by accumulating water and such sub- stances, but by forming more bone, more muscle, more brain, and so on, from the things which we eat. Even after full growth, when the body ceases to gain weight, the same constructive processes go on; the living tissues are steadily oxidized and broken down as they work, and as constantly reconstructed. Foods are therefore needed, not only to supply the body with work-power by their oxidation, but to supply material from which new living tissue can be constructed. What Foods must Contain. — Most foods serve for both purposes, energy supply and tissue formation; they are built up by the living cells into new tissue before they are oxidized to set energy free. Our food must, therefore, contain such substances as the body can utilize for tissue formation.* The living tissues when analyzed are found What use have foods besides supplying energy to the body? Illustrate from the growth of a child. Why are foods needed for construction after growth has ceased? What purposes do most foods serve? Are they usually oxidized before making tissue? What sort of substances must our food contain? * Whether any food is ever oxidized in the body before being built up into a tissue, as coal is burnt in an engine without ever forming part of the engine, must still be regarded as an open question in phj-siology. The old doctiine that some foods, as starch and sugar, were useful only to set free heat, and others, as albumen and flesh, alone built tissue, must be given up. It seems certain [llOJ THE IMPORTANCE OF PBOTEID FOODS. m to consist mainly of carbon, hydrogen, nitrogen, and oxy- gen, and we might at first suppose that these chemical ele- ments in their uncombined form would serve to nourish us. Experience, however, teaches that this is not the case. Four fifths of the air is nitrogen, but we cannot feed on it; hydrogen gas is of no use as a food; and a lump of char- coal (carbon) might fill the stomach, but would not keep a man from starving. Oxygen can be utilized when taken by the lungs from the air; but all other elements to be of) use as food must be taken, not in their separate state, j but in the form of complex compounds, in which they are chemically combined with other things; as, for example, in starch, and sugar, and fat, and oil, and albuminous sub- stances. The Special Importance of Albuminous or Proteid Foods. — All the active tissues of the body are found to yield on chemical analysis large quantities of proteids. (See p. 21). As the tissvies work this proteid is broken down, and its nitrogen carried off in the form of a peculiar ammoniacal substance, urea; to repair the wasted living tissue new proteids must be laid down in it. So far as we know at present the human body (like that of most animals) is un- able to make proteids out of other things; given one vari- What elements do the tissues yield on analysis ? Can wo feed on these elements in their uncombined state 1 Name one which is absorbed in a free state and used. Whence is it derived ? What organs receive it? Name substauces containing the necessary elements in combination and used as food. What do we find in all the active tissues? What becomes of the nitrogen of working tissues? Explain why proteids are an essential article of diet. that under some conditions sugar and starch may be used in building tissue, though they cannot do it alone; but whether they are under any circumstances ever burnt before making part of a tissue is not certain. On the other hand, there is some reason to suspect that albuminous substances may, when eaten In excess, be oxidized in the body without ever forming part of a hving cell. lis TEE HUMAN BODY. ety of them it can turn it into otlier varieties, but it cannot make proteids from things which are not proteids. Hence these albuminous or proteid substances are an essentia] article of diet. The Limited Constructive Power of the Animal Body.— From what has been said above it is clear that our bodies are, on the whole, destructive rather than constructive in relation to the outer world. They require for their nutri- tion very complex chemical compounds (starch, sugar, fat, proteids), build these up into living tissues, and then oxidize the tissues and return the carbon, hydrogen, and nitrogen, which were received from outside in the form of complicated chemical molecules, to the outer world in the form of much simpler chemical compounds, namely, carbon dioxide, water, and urea. None of these latter substances IS capable of nourishing an animal ; it cannot from them alone build up its tissues or set free energy. How Plants Supply Food for Animala, and Animals Food for Plants. — Since animals are essentially proteid con- sumers, and destroyers also of other complex substances, as starch and sugar, the question naturally suggests itself, How is it, if animals are constantly consuming these things, that the supply of them is kept up? For example, the supply of proteids ; they cannot be made artificially by any process known to us. The answer is, that animals live on the things which plants make, and plants live on Do our bodies on the whole build up or break down rhemical compounds? What class of compounds do they require for their nutrition? What do tliey do with these compounds? What simple compounds docs the body return to the outer world? Can these compounds feed any animal? What facts suggest the question. How is thj supply of pro- teids and other complex foods kept up? How Is the question answered ? NON-OXiniZABLB FOODS. 113 the carbon dioxide and water and ammonia (urea) which animals excrete. As regards our own bodies the question might, indeed, be apparently answered by saying that we get our proteids from the flesh of the other animals which we eat. But, then, we haye to account for the possession of proteids by those animals ; since they cannot make them from urea and carbon dioxide and water any more than we can. The animals whose flesh is used by us as food get their proteids from plants, which arc the great proteid formers of the world; the most carnivorous animal really depends for its most essential foods upon the vegetable kingdom; the fox that devours a hare, in the long run lives on the proteids of the herbs tliat the hare had previously eaten.* Non-Oxidizable Foods.— Besides our oxidizable foods a large number of necessary food materials are not oxidizable, or at least are not oxidized in the body. Typical instances are afforded by water and common salt. The use of these is in great part physical: the water, for instance, dissolves ma- terials in the alimentary canal, and carries the solutions through its walls into the blood and lymph vessels, so that they can be conveyed from place to place; and it permits interchanges by enabling the things it has dissolved to soak through the walls of the vessels. The salines also influence the solubility and chemical interchanges of other things present with them. Fibrinogen, one of the proteids Where does the proteid that a man eats in a piece of beef come from? Explain. What foods are necessary in addilion to oxidizable? Give ex- amples. , What are their physical uses? * Some animals are known which contain chlorophyl, the green coloring matter of plant leaves; and it has recently been proved that these animals, hlie plants, can, when exposed to the action of light, live on the waste products of ulher animals. 214 THE HUMAN BODY. which is carried in the blood all over the body to supply al- buminous material to the tissues, is, for example, insoluble in pure water, but dissolves readily if a small quantity of common salt be present. Besides such uses, the non-oxidiz- able foods have probably others, as what may be called machinery formers. In the lime salts, which give their hardness to the bones and teeth, we have an example of such an employment of them; and to a less extent the same may be true of other tissues. The body is a self -building, and self-repairing machine, and the material for this building and repair, as well as the fuel or oxidizable foods which yield the energy the machine expends, must be supplied in the food. While experience shows us that even for machinery construction oxidizable matters are largely needed, it is nevertheless a gain to replace such substances by non-oxidizable material when possible; just as, if prac- ticable, it would be advantageous to construct an engine out of a substance which would not rust, although other conditions determine the selection of iron for building the - greater part of it. Definition of Foods. — Foods are (1) sulstances which are taken i7ito the alimentary canal, ivhich can he absorbed from it, and after absorption serve to siqiply material for the growth of the body, or for the replacement of matter tvhich has been removed from it; or (2) they are substances which can be oxidized in the body to yield energy for its use; or (3) substances, which by dissolving nutritive or waste Illustrate the use of common salt in helping to keep important substances in solution. Illustrate the employment of non-oxidizable foods in constructing the body. What must foods supply to the body besides fuel? Why? Are oxidizable foods used in machinery construction? Give an example showing the gain of using non- oxidizable matters when possible. Give a definition of foods. • DEFINITION OF FOODS. 115 matters facilitate the transfer of material from the recep- tive organs to the working, and from the working to the excretory. Foods to replace matters which have been oxi- dized must be themselves oxidizable; they are force gener- ators, but may be and generally are also tissue formers: they are nearly always complex organic substances derived from other animals or from plants. Foods to replace matters not oxidized in the body, as water and salt, are force regu- lators, and are for the most part tolerably simple inorganic compounds. Among the force regulators we must, how- ever, include certain foods, which, although oxidized in the body and serving as sources of energy, yet produce effects totally disproportionate to the amount of energy which they thus set free. Their influence as stimulants in exciting cer- tain tissues to activity, or as agents checking the activity of parts, is more marked than their direct action as force gener- ators. As examples, we may take condiments: mustard and pepper are not of much use as sources of energy, although they no doubt yield some when oxidized; we take them for their stimulating effect on the mouth and other parts of the alimentary canal, by which they promote a greater flow of the digestive secretions or an increased appetite for food. Thein, again, the active princi[)le of tea and coffee, is taken for its stimulating effect on the nervous system rather than for the amount of energy which is yielded by its own oxl dation. To the above definition of a food should be added the condition that, neither the substance itself nor any of the What foods must be oxidizable? "Wli at are tliey called? Do they also make tissue? Are they complex or simple? Wliat is their source? What is meant by force regulators? Examples? Are tLey chem- ically complex or simple? What oxidizable foods are included among the force regulators? How is their influence chiefly exbib- ited? Give examples 116 TEE HUMAN BODY. products of its chemical transformation in the hody shall h injurious to the structure or action of any organ; other- wise it would he a poison, not a food. Alimentary Principles. — The substances which in ordi- nary language we call foods are in nearly all cases mixtures of several foodstuffs with substances which are not foods at all. Bread, for example, contains water, salts, gluten (a proteid), some fats, much starch, and a little sugar; all these are true foodstuffs, but mixed with them is a quantity of cellulose (the chief chemical constituent of the walls which surround vegetable cells), and this is not a food, since it is incapable of absorption from the alimentary canal. Chemical examination of all the common articles of diet shows that the actual number of important foodstuffs is but small; they are repeated in various proportions in the different foods we eat, mixed with small quantities of dif- ferent flavoring substances, and so give us a pleasing variety in our meals; but the essential substances are much the same in the fare of the artisan and in the "delicacies of the season." The chief foodstuffs, which are found re- peated in many different foods, are known as " alimentary principles," and the nutritive value of any article of diet depends on the proportion of these foodstuffs which is present, far more than on the various agreeable flavoring matters which cause certain things to be especially sought after, and to have a high market value. Alimentary prin- ciples may be conveniently classified into proteids, albu- minoids, hydrocarbons, carbohydrates, and inorganic bodies. What is a poison? What are ordinary foods? Give an example. Whj' is celhilose not a food? Wliat does chemical examination of ordinary foods show? How do we got variety in our foods? What are " alimentary principles'*? On what does the nutritive value of a food depend? Into w.'iat groups are alimentary principles classified? ALIMENTAET PRINCIPLES. 117 Proteid Alimentary Principles. — Of the nitrogen-contain- ing foodstuifs the most important are proteids: they form an essential part of all diets, and are obtained both from animals and plants. The most common and abundant are myosin and syntoniu, which exist in the lean of all meats; egg albumen; casein, found in milk and cheese; gluten and vegetable casein from various plants. Albuminoid Alimentary Principles. — These also contain nitrogen, biiTcannot entirely replace the proteids as foods; though a man can manage with less proteids when he has some albuminoids in addition. The most impoi'tant is gelatine, which is yielded by the connective tissue and bones of animals when cooked. On the whole the albuminoids are not foods of high value, and the calf's-foot jelly and such compounds often given to invalids have not nearly the nutritive value they are commonly supposed to possess. Hydrocarbons {Fats and Oils). — The most important of these are stearin, pnlmatin, margarin, and olein, which exist in various proportions in animal fats and vegetable oils; the most fluid containing more olein : butter contains a pecu- liar fat known as butyrin. All fats are compounds of glycerine with fatty acids, and, speaking generally, any such substance which is fusible at the temperature of the body will be useful as a food. The stearin of beef and mut- ton fats is not by itself fusible at the body temperature, but is mixed in those foods with so much olein as to be melted What nitrogen-containing substances form an essential article of diet? "Whence are they obtained? Name the most important proteid foods. m , What foods besides proteids contain nitrogen? To what extent can they take the place of proteids? How is gelatin obtained? Should we try to build up an invalid's strength on calf's-foot jelly alone? Give the reasons for your answer. To what group of foods do fats and oils belong? Name the more important What is their chemical composition? Why are some fatty bodies not nutritious ? Give au instance. 118 TEE HUMAN BODY. in the alimentary canal. Beeswax, on the other hand, is a fat which will not melt in the intestines and so passes on unabsorbed, although from its composition it would be use- ful as a food could it be digested. Carbohydrates. — These are mainly of vegetable origin. The most important are starch, found in nearly all vege- table foods; dextrin; gums; grape sugar (found in most fruits) ; and caiie sugar. Sugar of milk and glycogen are alimentary principles of this group derived from animals. All carbohydrates, like the fats, consist of carbon, hydrogen, and oxygen; but the percentage of oxygen in them is much higher than in fa(s. Wlien oxidized they liave therefore less power of combining with additional oxygen than fats, and so are not capable of yielding as much energy to the body. Inorganic Foods. — The most important of these are water; common salt; and the chlorides, phosphates, and sulphates, of potassium, magnesium, and calcium. A suf- ficient quantity of most of tliese subsfances, or of the ma- terial for their formation, exists in all ordinary articles of diet, so that we do not swallow most of them in a separate form. Water and table salt form exceptions to the rule that inorganic bodies are eaten imperceptibly along with other things, since the body loses more of each daily than is usually supplied in that way. It has been maintained that salt as a separate article of diet is an unnecessary luxury, and there seems to be some evidence that certain savage tribes live without more than they get in the meat and vegetables What is the chief source of carbohydrates? Name tlie most im portant. Name carbohydrate foods derived from animals. How do they resemble fats in composition, and iiovv do they differ from them? Can an ounce of starch yield as much energy to the body as an ounce of fat? Give a reason for your answer. Name the more important inorganic foods. Why do we notrequire to eat most of them separately? What Inorganic foods are taken in a separate form ? Why f THE NUTRITIVE VALUE OF DIFFERENT FOODS. 119 which they eat. Such tribes are, however, said to suffer especially from intestiual parasites; and there is no doubt that to many animals as well as most men the absence of salt from their diet is a terrible deprivation. Buffaloes and other creatures are well known to travel miles to reach "saltlicks;" of two sets of oxen, one allowed free access to salt, and the other given none save what existed in its or- dinary food, it was found after a few weeks that those given salt were in much better condition. In man the desire for salt is so great that in regions where it is scarce it is used as money. In some parts of Africa a small quantity of salt will buy a slave, and to say that a man commonly uses salt at his meals is equivalent to stating that he is a luxurious mill- ionaire. In British India, where the poorer natives regard so few things as necessaries of life that it is hard to levy any excise tax, a large part of the revenue is derived from a salt tax, salt being something which even the poorest will buy. As regards Europe, it has been found that youths in the Austrian empire who have fled to the mountains and there led a wild life to avoid the hated military conscription, will, after a time, though able abundantly to supply themselves with other food by hunting, come down to the villages to purchase salt, at the risk of liberty and even of life. The Nutritive Value of Different Foods. — All meats, whether derived from beast, bird, or fish, are highly valu- able foods. They contain abundant albumen, more or less fat, and, when cooked, their connective tissue is in great part turned into gelatin. Fork is tlie least easily digested form of fresh meat, and contains a larger percentage of fat than most. This fat, which, by its oxidation liberates much Give Illustrations of the strenj^th of the desire for salt. Why are meats valuable foods? How does pork differ from other fresh meats? Why is pork not a good form of food for summer? 120 TEE HUMAN BODY. heat, makes it a good food in cold weather for persons with a good digestion. Pigs are especially liable to a parasite, called trichina, which lives in their muscles, and may be transferred thence to man, sometimes causing death. Hence pork should always be thoroughly cooked. Salted meats of all kinds are less digestible and less nutritious than fresh. Milk contains an albuminous substance (casein), also fats (butter), and a sugar, known as sugar of milk, in addition to useful mineral alimentary principles. It will support life longer than any other single food. Cheese consists essen- tially of the casein of milk: it is a very nutritive albuminous food. Eggs contain albumens and fats, and have a high nutritive value: they are more easily digested when cooked soft than hard. Wheat contains more than a tenth of its weight of proteids, more than half its weight of starch, some sugar, and a little fat. The proteid of wheat flour is mainly gluten, which when moistened with water forms a tenacious mass, and this it is to which wheaten bread owes its superiority. When the dough is made, yeast is added to it and causes fermentation by which, among other things, carbon dioxide gas is produced. This gas, im- prisoned in the tenacious dough and expanded by heat dur- ing baking, forms cavities in it, and causes the dough to "rise" and make "light bread," which is not only more pleasant to eat but more easily digested than heavy. Some grains contain a larger percentage of starch, but none have so much gluten as wheat; when bread is made from them Why should pork be well cooked ? How do salted meats differ in value as articles of diet from fresh? Wliat foodstuffs exist in milk? What oue food will support life longest? What is the chii'f aliment- ary principle in cheese? What is the nutritive value of cheese? What makes the value of eggs as foods? Are they moi-e easil\' digested soft or hard boiled? Wiiat foodstuffs exist in wheat? Why is wheaten bread lighter than that made from other grains? ALCOHOL. 121 the carbon dioxide gas escapes so readily from the less tenacious dough that it does not expand the mass properly. Corn contains less proteid, more starch, and more fat than wheat. Rice is poor in proteids but vei-y rich in starch. Peas and leans are rich in proteids and contain about half their weight of starch. Potatoes are a poor food. They coQtain a great deal of water and only about one part of proteids, and fifteen of starch in a hundred parts by weight. Other fresh vegetables, as carrots, turnips, and cabbages, are valuable mainly for the salts they contain ; their weight is chiefly due to water, and they contain but little starch, proteids, or fats. Fruits, like most fresh vegetables, are mainly valuable for their saline constituents, the other food- stuffs in them being only present in small proportion. Some kind of fresh vegetable is, however, a necessary article of diet, as shown by the scurvy which used to prevail among sailors before fresh vegetables or lime-juice were supiDlied to them. Alcohol. — We shall learn later that all drinks containing alcohol are dangerous (Chap. XXIII.), as tending to pro- duce disease, or to make the body less able to resist it, and more dangerous the more alcoliol they contain. For the present we confine ourselves to the question, Has alcohol a just claim to be called a food ? Does it build tissue, or strengthen the muscles, or help to maintain our animal heat ? It may be useful sometimes as a medicine when ordered by a physician, but is it useful to healthy persons who can obtain and digest other foods ? How does corn differ from wheat in composition? What aliment- ary principles are sciirce in rice? Which one is abundant? What do potatoes contain? What is the main useful constituent of most fresh vegetables? Of fruits? How may scurvy be prevented? Why are all alcoholic drinks dangerous? What questions must ibe answered before deciding if alcohol is a true food ? 122 THE HUMAN BODY. Is Alcohol a Tissue-Forming Food ? — To this the answer is certainly no; so far at least as useful tissue is concerned. It often leads to excessive and harmful overgrowth of con- nective tissue and fat, but it does not lead to development of muscle or brain or gland. Is Alcohol a Strengthening Food ? — To this the answer is also no. Alcohol in small doses causes excitement of the brain, and may for a short time cause it and the muscles to overwork or to work when they should be resting: but as it nourishes neither, the final result is bad. The brain and muscle are left in an injured state. As regards the brain, the consequence is often insanity (Chap. XXIII.). As regards the muscles, very careful experiments have been made on soldiers who were given definite tasks to accomplish. The result was that on the days on which they were sup- plied with spirits, they could neither use their muscles as powerfully, nor for as long a time, as on the days when they got no alcoholic drink. Does Alcohol keep up the Heat of the Body ? — To this question, also, the answer is no, though this may seem strange in view of the fact that a drink is often taken " to warm one up." Tlie apparent inconsistency is easily explained. Our feeling of being warm depends on the nerves of the skin (p. 333). We have no nerves which tell us whether heart or muscles or brain are warmer or cooler. These inside parts are always hotter than the skin, and if blood which has been made hot in them fiows in large quantity to the sl^in, we feel warmer because the skin is What is said of alcohol as a tissue-forming food? Is alcohol a strcuglheuing food? How may it lead to overwork? Results? What were the results of experiments made on soldiers as to the action of alcohol on the muscles? Does alcohol maintain the heat of the body? Why does a drink gpmetlujeg make a person feel warmer? TEA AND COFWEB. 123 heated. As alcoholic drinks make more blood flow through the skin, they often make a man feel warmer. But their actual effect upon the temperature of the whole, body is to lower it. The more blood that flows thi'ough the skin, the more heat is given ofE from the body to the air, and the more blood, so cooled, is sent back to the internal organs. The consequence is that alcohol cools the body as a whole, though it may for a short time heat the skin. That a large dose of alcohol leads to excessive loss of heat from the body has been proved by many observations on drunken men, and by experiments on the lower animals. The action of alcohol as an excitant is so much more marked than its efficacy as a source of energy that it is to be regarded as a medicine rather than a true food, and the best plan is to avoid it altogether in health. Tea and Coffee are to be regarded as stimulants rather than nutritive foods. The amount of nourishment in a cup of either is but little. Both have, however, a wonder- ful influence in tranquillizing the nervous system and re- moving the sense of fatigue; and when taken in moderate doses usually leave none of the injurious after-effects of alcohol. Some persons experience wakefulness or a feeling of fulness in the head after taking cofEee, and such should of course avoid it. For relieving fatigue, tea and coffee are far superior to alcohol. Sportsmen out for a long day's shooting find cold tea superior to spirits; military com- manders find a ration of coffee far better than one of whiskey for fat'gued troops; and all arctic explorers have come to a similar conclusion. How is it that alcohol sometimes makes a person feel warmer? How does it cool the body? To what class of foods do tea and coffee belong ? What results do they produce? "Why are they better than alcohol for similar purposes? Give illustrations of the influence of tea and coffee in removing the sensation of fatigue. 124 THE HUMAN BODY. Cooking. — When meat is cooked most of its connective tissue is turned into gelatin, and the whole mass becomes softer and more readily broken up by the teeth. In boil- ing meat it is a good plan to put it first into boiling water which coagulates its surface layer of albumen, and this then keeps in flavoring and other matters which would otherwise pass out into the water. After the first few minutes the cooking should be continued at a lower temperature; meat boiled too fast is hard, tough, and stringy. In roasting or baking meat, the same plan is advisable. Put it close to the fire or in a hot oven for a short time, and then com- plete the cooking m.ore slowly at a lower temperature. The cooking of vegetable foods is of considerable impor- tance. Starch is the chief nutrient matter in most of them, and raw starch is much less easily digested than cooked. When starch is roasted it is turned into a substance known as soluble starch, which is easily dissolved by the digestive liquids, so there is a scientific foundation for the common belief that the crust of a loaf is more digestible than the crumb, and toast than fresh bread. The Oxidizable Matters required daily by the Body. — The necessary quantity of daily food depends upon that of the material used by the body and passed out from it in each twenty-four hours; this varies both in kind and amount with the work done and the organs most used. In children a certain excess is required to furnish material for growth. What happens when meat is cooked ? Why does a good cook first put meat that she is to boil into very hot water ? Why should the boiling be completed at a lower temper- ature? How should meat be baked ? Why is it important to cool? most vegetable foods ? Why is toast more easily digested than fresh bread? What determines the necessary amount of daily food? How does it vary? Why do children require more in proportion to their size than adults ? TUB ADVAMTAGES OF A MIXED DIET. 125 It is impossible to state accurately beforehand just what amount of food any individual will require, but a general idea may be arrived at by taking the average daily losses, by excretion, of a man, as determined by many experiments made on different persons. Such experiments show that a man of average size and doing ordinary work needs rather more than 9|- ounces (274 grams) of carbon to replace his loss of that element ; and about -^-^ of an ounce of nitrogen (20 grams). Some hydrogen is also required, as the body daily loses more water than we take in our food; and this extra amount implies a loss of hydrogen, combined with oxygen in the body to form water. The Advantages of a Mixed Diet, — Since proteid foods contain carbon, nitrogen, and hydrogen, life may be main- tained on them if the necessary salts, water, and oxygen be also supplied; but such a diet would not be economical. Ordinary proteids contain in 100 parts about 52 of carbon and 15 of nitrogen, so a man fed on them alone would get about 3-^ parts of carbon for every 1 of nitrogen. His daily losses are not in this ratio, but about 13.7 parts of carbon to 1 of nitrogen; and to get enough carbon from proteids far more than the necessary amount of nitro- gen must be taken. Of dry proteids 1 pound 2J ounces (527 grams) would yield the necessary carbon, but would contain 2| ounces (79 grams) of nitrogen, or four times more than is necessary to cover the daily losses of that element from the body. Fed on a purely proteid diet a man would, therefore, have to digest a vast quantity to get What is the average daily loss of carbon from the body ? Of nitrogen ? Does a man need hydrogen also in his food ? Why ? On what group of foodstuffs can life be maintained without any others? Why is feeding entirely on albuminous substances not de- sirable ? 126 THE HUMAN BODY. enough carbon, and in eating and absorbing it, and in getting rid of the excess nitrogen (which is useless to him), a great deal of useless labor must be thrust upon the digestive and excretory organs. Were a man to live on bread alone he would force much unnecessary work on his organs. Bread contains little nitrogen in proportion to its carbon, and to get enough nitrogen far more carbon than could he utilized would have to be eaten, digested, and excreted daily. The human race has discovered this fact: men use, where they have a choice, richly proteid substances to supply the nitrogen needed, but derive the carbon mainly from non-nitrogenous foods of the fatty or carbohy- drate kinds, and so avoid excess of either nitrogen or carbon. For instance, lean beef contains about \ of its weight of dry proteid, which proteid contains 15 per cent of nitrogen. Consequently 1 pound 3 ounces of lean meat would supply the nitrogen needed to compensate for a day's losses. But the proteid contains 53 per cent of carbon, so the amount of it in the above weight of fatless meat would be 1070 grains (69 grams) or nearly 2| ounces, leaving 3150 grains (205 grams) or rather more than seven ounces, to be got either from fats or carbohy- drates. The necessary amount would be contained in 3940 grains (256 grams) or about 9 ounces of ordinary fats, or in 7080 grains (460 grams), a little over a pound, of starch; hence either of these with the above quantity of lean meat would form a far better diet both for the purse and the system than meat alone. Explain -why bread by itself would afford a bad diet. Wliy do men use a mixed diet? Explain why lean meat alone would not be a good food. How could the deficient carbon of lean beef be supplied ? TME abvantaqes of a mixed diet. 127 As already pointed out, nearly all common foods contain seNevsi^. foodstuff s. Good butcher's meat, for example, con- tains nearlv half its dry weight of fat : and bread in addition to proteids contains starch, fats, and sugar. In neither of them, however, are the foodstuffs mixed in the physiologically best proportions, and the custom of consuming several of them at each meal, or different ones at different meals dur- ing the day, is not only agreeable to the palate but in a high degree advantageous to the body. The strict vegetarians who do not eat even such substances as eggs, cheese, and milk, but confine themselves to a purely vegetable diet, which is always poor in proteids, take daily far more car- bon than they require, and are to be congratulated on their excellent digestions which are able to stand the strain. Those so-called vegetarians who use eggs, cheese, etc., can of course get on very well, since such substances are extremely rich in proteids, and supply all the nitrogen needed, without the necessity of swallowing the vast bulk of food which must be eaten in order to get it directly from plants. Give illustratious of the fact that most foods contain more than one foodstuflf . Why do we commonly use several foods at one meal? What ele- ment do strict vegetarians take in excess ? How do nominal vegeta- rians get their nitrogen ? CHAPTEE XL THE DIGESTIVE ORGANS. General Arrangement of the Alimentary Canal. — The ali- mentary canal is a tube which runs through the body from the lips to the posterior end of the trunk. It is lined by a soft reddish mucous membrane (easily seen inside the mouth), which is but a redder and moister sort of skin. Outside the mucous membrane are connective tissue and muscular layers, which strengthen the digestive tube and ]nish the swallowed food along it. The mucous membriine is con- structed to absorb dissolved nutritive substances; it soaks them up and passes them into blood or lymph vessels. Im- bedded in this mucous membrane, or lying outside it, are hollow organs called glands; these glands make liquids which alter chemically many substances which we eat, and turn them from things which cannot be absorbed by the mucous membrane into things which can. The whole series of changes which any food material undergoes, between its reception by the mouth and its absorption by the aliment- ary mucous membrane, is spoken of as its digestion. Various foodstuffs undergo different kinds of changes ■What is the alimentary ranal? By what is it liued? What are found outside the mucous membriine of the digestive tube? What are their uses? Witli reference to what object is the alimentary mucous membrane constructed? What does it do with the nutriment it absorbs? What is the function of the glands of the alimentary canal? What is meant by the digestion of a foodstuff? [128] THE KIKDS OP QLAND8. 129 preliminary to absorption, and so we speak of different kinds of digestions; as that of starch, of fats, of albuminous bodies, and so forth. Glands are hollow organs which make or secrete peculiar fluids and pear them out on some free sui-face of the body. They are very widely distributed; we find, for example, digestive glands (of several kinds) opening into the digestive tube, perspiratory glands opening in the skin, tear glands or lachrymal glands pouring out their secretion on the eye- ball. Different glands have their cavities lined by different kinds of cells, and produce different secretions. In general arrangement all glands are built on one or other of two primary structural plans, known as the tubular and the racemose. The Kinds of Glands. — All portions of the body making and pouring forth secretions are not technically called glands. In the peritoneum, which lines the inside of the abdominal cavity (p. 11), we find simply a thin membrane (A, Fig. 40), having on its side nearer the cavity which it surrounds a layer of cells, a, and on its deeper side a net- work of very fine blood-vessels, c, supported by connective tissue, d. Such simple, smooth, secreting surfaces are not common; in most cases an extended area is required to form the necessary amount of secretion, and if this were attained simply by spreading out flat membranes, these, from their number and extent, would be hard to pack con- veniently in the body. Accordingly, in most cases, a large area is obtained by folding the secreting .surface in various Why do we speak of different kinds of digestion? Illustrate. Wliat is agland? Give examples of glands. How do glands difEer? Wliat are the two chief types of glands named? Name and describe a secreting surface which is not technically called a gland. What is gained by folding a secreting surface? 130 mS: HtlMAN noDT, ^^^^^^^_ _{^ -hrm^ ^^^C^ FiQ. 40.— Forms of Glands. A, a simple secreting surface ; a, its epithelium; b, basement membrane ; c, capillaries ; B^ a simple tubular gland ;rU, a secret- ing surface increased by protrusions ; E. a simple racemose gland ; D and (?, compound tubular glands; F, a compound racemose gland. In all but A^ B, and O the capillaries are omitted for the sake of clearness. H, half of a highly devel- oped racemose gland ; c, its main duct. FORMS OF GLANDS. 131 ways so that a wide surface can be packed in a small bulk, just as a Chinese paper lantern when shut up occupies much less space than when extended, although the actual area of the paper in it remains of the same extent. In a few cases the folding takes the form of protrusions into the cavity of the secreting organ, as indicated at 0, Fig. 40, but much more commonly the surface extension is attained in another way, the supporting or lasement memirane, cov- ered by its epithelium, being pitted in or involuted as at B. Such a secreting oi-gan is known as a true glcmd. Forms of Glands. — In some cases the surface involutions are uniform in diameter, or nearly so, throughout {B, Fig. 40). Such glands are known as tubular; examiilcs are found in the lining coat of the stomach (Fig. 48); also in the skin (Fig. 76), where they form the siveat-glands. In other cases the involution swells out at its deeper end and becomes more or less sacculated {E); such glands are named racemose or acinous. The small glands of the skin which form the oily matter poured out on the hairs (p. 273) are of this type. In both kinds the lining cells near the deeper end are commonly different in character from the rest; and around that part of the gland the finest and thinnest walled blood-A'essels form a closer network. These deeper cells form the true secreting tissue of the gland, and the tube lined with different cells, leading from the secreting re- cesses to the surface on which the seci-etion is poured out, and serving merely to drain it off, is known as the duct of the gland. When the duct is undivided the gland is simple; but when, as is more usual, it is branched and each branch ; What is a tubular gland? Examples? A racemose gland? ijlxample? "Where do we find the closest network of blood-vessels "m a gland? Which cells of a gland make its secretion? What is \ iji«ant by the "duct" of a gland? What is a simple glan(J? 132 THE HUMAN BODY. has a true secreting chamber at its end we get a compound gland, tubular {0) or racemose {F, H) as the ease maybe. In many cases the chief duct, in which the smaller ducts unite, is of considerable length, so that the secretion is poured out at some distance from the main mass of the gland. A fully formed gland, H, is thus a complex structure, consisting primarily of a dnct, c, ductules, dd, and secret- ing recesses, ee. The ducts and ductules are lined with cells which are merely protective, and differ in character from the secreting cells which line the deepest parts. The cells lining the ultimate recesses differ ia different glands, and produce different liquids; consequently, though all glands are built on much the same plan, they make very varied secretions, the nature of the secretion of any gland depending on the properties of its cells. The Complexity of the Alimentary Canal. — We may now return to our immediate subject, the alimentary canal. This is not a simple tube, but presents several dilatations on its course; nor is it a comparatively straight tube, as dia- grammatically represented in Pig. 1, but, being much longer than the regions of the body which it traverses, much of it is packed away by being coiled up in the abdominal cavity. Subdivisions of the Alimentary Canal. — The mouth- opening leads into a chamber containing the teeth and tongue, and named the mouth-cJiamler or buccal cavity. This primary dilatation is separated by a constriction (the A compound? How does it happen that the secretion is some- times poured out at a distance from tlie main mass of the gland? Describe a fully developed gland. How is it that glands make such difEerent secretions? On what does the nature of the secretion of a gland depend? How does the alimentary canal differ from a simple uniform tube? Why is a great part of it coiled? Into what does the opening between the lips lead? THE MOUTH CAVITY. 133 isthmus of the fauces') at tlie back of the mouth, from another, the pharynx or throat chamber, which narrows again at the top of the neck into ^(b(]ulht or oesophagus, which runs as a comparatively narrow tube through the thorax, and then, passing through the dia- phragm, dilates in the upper ''^ ' part of the abdominal cavity to form the stomach (see Fig. 1). Beyond the stomach the channel again narrows to form a long and greatly coiled tube, the small intestine, which terminates by opening into the large intestine, which, though shorter is wider, and ends by opening on the exterior. The Mouth Cavity.— (Pig. 41) is bounded in front and Fig. 41.— The mouth, nose and pharynx, with the commencement of on the sides by the lips and the guUet and larynx, as exposed by ■^ . a section, a little to the left of the me- cheeks, below by the tongue, ^K^'^rVillfettt wfnd^Tp'elt h, and above by the palate, f ^peii^k'ol^Enl'fi^-^Jian'LCI; which latter consists of an an- Sb'c^ne' on^te^S^if'^i.e smF^^ terior part, I, supported b} bone and called the hard pal- J ■ 17 J. J 1, the fore part of the cranial cavity; tenor part, I, supported by o,p,g, the turbinate bones of the out- er side of the left nostril chamber. What is the isthmus of the fauces? "Where does the gullet hegin? Through what regions of the body does it pass? "Wliere does the stomach lie? What part of the alimentary canal succeeds tlie stomach? Describe it briefly. How does it end? How does tlie large intestine differ from the small? How does it end? What are the boundaries of the tnouth cavity? Of what parts does the palate consist? 134 THE HUMAN BODY. ate, and a posterior, /, containing no bone, and called the soft palate. The two can readily be distinguished by ap- plying the tip of the tongue to the roof of the mouth and drawing it backwards. The h:ird palate forms the parti- tion between the mouth and nose. The soft palfie arches down at the back of the mouth, hanging like a curtain, between it and the pharynx, as can be seen on holding the mouth open in front of a looking-glass. From the middle of its free border a conical process, the uvula, hangs down. The Teeth. — Immediately within the checks and lips are two semicircles, formed by the borders of the upper and lower jaw-bones, which are covered by the gums, except at interTals along their edges where they contain sockets in which teeth are implanted. During life two sets of teeth are developed : the first or milk set appear soon after birth and are shed during childhood, when the second or permanent set appear. The General Structure of a Tooth. — The teeth differ in minor points from one another, but in all, three parts are distinguishable ;* one, seen in the mouth, and called the crown of the tooth; a second, imbedded in the jaw-bone, and called the root at fang; and between the two, embraced by the edge of the gum, a narrowed portion, the neck or cervix. By differences in their forms and uses the teeth are divided into incisors, canines, bicuspids, and How can we feel the difference between them ? What cavities does the hard palate separate? Where does the soft palate lie? What is the uvula ? What do we tind inside the lips? Where are the gums? What do the margins of the jaw boues contain ? What are the milk teeth? What the permanent ? What parts may we distinguish in every tooth? Into what groups are teeth divided ? Why ? * A number of teeth can be readily obtained from a dentist, and will be found of great use in coBnectioo witli tb'S lesson. UBAHACTEBS OF INDIVIDUAL TEETH. 135 molars, arranged in a definite order in each jaw. Begin- ning at the middle line we meet in each half of each jaw, successively, with two incisors, one canine, and two mo- lars in the milk set; making twenty altogether in the two jaws. The teeth of the permanent set are thirty-two in number, eight in each half of each jaw, viz. — beginning at the middle line — two incisors, one canine, two bicuspids, and three molars. The bicuspids of the permanent set replace the molars of the milk set, while the permanent molars are new teeth added on as the jaw grows, and not substituting any of the milk teeth. The hindmost perma- nent molars are often called the wisdom teeth. Characters of Individual Teeth. — The incisors or cutting Fiai 43. FiQ.45. Pia. 42.— An incisor tooth. Fig. 43.— a canine or eye tooth. Fig. 44. — A bicuspid tooth seen from its outer side; the inner cusp is accord, ingly not visible. Fig. 45.— A molar tooth. teeth (Fig. 42) are adapted for cutting the food. Their crowns are chisel-shaped and have sharp horizontal cutting edges which become worn away by use, so that they are beveled off behind in the upper row and in the opposite Enumerate the milk teeth in order. How many are there alto- gether? Number of permanent teeth? Enumerate in order. What permanent teeth replace the milk molars? What permanent teeth replace no milk teeth? Which are the wisdom teeth? Describe an incisor tgoth, 136 THE HUMAN B0D7 direction in the lower. Each has a single long fang. The canines {dog teeth) (Pig. 43) are somewhat larger than the incisors. Their crowns are thick and somewhat conical, having a central point or cusp on tlio cutting edge. In dogs and cats the canines are very long and pointed, and adapted for seizing and holding prey. The bicuspids or 'premolars (Fig. 44) are rather shorter than the canines and their crowns are cuboidal. Each has two cusps, an outer towards the cheek, and an inner on the side turned towards the interior of the mouth. The molar teeth or grinders (Eig. 45) have large crowns with broad surfaces, on which are four or five projecting tubercles which roughen them and make them better adapted to crush the food. Each- has usually several fangs. The milk teeth differ only in subsidiary points from those of the same names in the per- manent set. The Structure of a Tooth. — If a tooth be broken open a cavity extending through both crown and fang will be found in it. This is filled during life with a soft pulp, con- taining blood-vessels and nerves, and is known as the "pulp cavity." The hard parts of the tooth disposed around the pulp cavity consist of three different tissues. Of these, one immediately surrounds the cavity and makes up most of the bulk of the tooth; \i is. dentine or ivory; covering the dentine on the crown is enamel, the hardest A canine. Kame animals with specially developed canines. For what do they use them? Give another name for a bicuspid tooth. Describe one. Describe a molar tooth. What is the object of the projections on their crowns? How far do the milli teeth differ from the perma- nent in form? What do we find on breaking open a tooth? What is it called? Why? What tissues form the hard parts of 9, tooth? WJiere doeg eugh lie? nraiENE of tee teeth. 137 tissue in the body,* and on the fang the cement, which is a thin layer of bone. The pulp cavity opens below by a narrow apei'ture at the tip of the fang, or at the tip of each fang if the tooth has more than one. Through these openings its blood-vessels and nerves enter. Hygiene of the Teeth. — The teeth should be thoroughly cleansed night and morning, by means of a tooth-brush dipped in tepid water ; once a day soap should be used, or a little very finely powdered chalk sprinkled on the brush. The weak alkali of the soap or chalk is useful. A large proportion of a tooth consists of carbonate of calcium, which readily dissolves in weak acids ; and decomposing food particles lodged between the teeth develop acids, which eat away the tooth slowly but surely. Hence all food particles should be carefully removed from between the teeth ; as this cannot always be effected completely it is important to brush the teeth with alkaline substances which will neutralize and render harmless any acid.f Good manners forbid the public use of a tooth-pick, but on the earliest privacy after a meal a wooden or quill, tooth-pick should be employed systematically and carefully to dislodge all food remnants which may have remained wedged between the teeth. Where is the pulp cavity open ? What things pass through the opening? When and how should the teeth be cleansed? What substance forms a large part of the teeth? In what is this substance soluble? Why should food particles be carefully removed from between the teeth? Why are weak alkaline substances useful in cleaning the teeth? * Enamel will strike fire with flint. t Acid medicines should always be sucked up through a glass tube and swallowed with as little contact as possible with the teeth- After eaph dpgp the BjoutU sliould be thoroughly rinsed with water- 138 THE HUMAN BODT. Once a slight cavity has been formed, the process of decay is apt to go on yery fast ; first, because the ex. it ■^'\^\ Fio. 46.- The upper surface of the tongue. 1, 2, oircumvallate papillse ; 3, fun- giform papillae; 4, filiform papillae; 6, mucous glands. posed deeper layer of the tooth is more easily dissolved tliftU its oatur^ surface; and, scQOod, bcQauge the littl? TBB I'QN&JJR 139 pit forms a lodging-place for bits of food, which, in de- composing, form acids and hasten the corrosion. Small eroded cavities are very apt to be overlooked ; the teeth should, therefore, be thoroughly examined two or three times a year by a dentist. The Tongue (Fig. 46) is a muscular and highly mov- able organ, covered by mucous membrane, and endowed not only with a delicate sense of touch, but with the sense of taste. Its root is attached to the hyoid bone (p. 36). The mucous membrane covering the upper surface of the tongue is roughened by numerous minute elevations or papillcB, of which there are three varieties. The circum- vallate papillm (Fig. 46, 1 and 2) are the largest and fewest, and lie near the root of the tongue, arranged in the form of a V, with its open angle turned towards the lips. The fungiform papillm are rounded masses attached by nar- rower stems. They are found all over the middle and fore part of the upper surface of the tongue, and during life are readily recognized as red dots, more deeply colored than the rest of the mucous membrane. The filiform papill(B are pointed elevations scattered all over the upper surface of the tongue, except near its root. They are on our tongues the smallest and most numerous.* Why is decay of a tooth apt to go on fast once it has commenced? Why sliould the teeth be examined from time to time by a dentist? Briefly describe the tongue. What sensations do we obtain througli it? To what is its root attaclied? What are found on the mucous membrane of the upper surface of the tongue? Of how many varieties? Which are largest and fewest? Where are they found? How are they arranged? Describe tlie fungiform papillae. Where are they found? What do they look like when we examine a person's tongue? Where are the filiform papillce found? What is their form? What papillse on the human tongue are smallest? Most numerous? * The filiform papillae are very large on the tongue of the cat, where they may readily be seen and felt. They are large in nearly all carnivorous animals, 140 TEE HUMAN BODY. What a "Furred Tongue" Indicates. — In health the surface of the tongue is moist, covered by little "fur" and, in childhood, of a red color. In adult life the natural color of the tongue is less red, except around the edges and tip ; a bright red glistening tongue is then usually a symptom of disease. When the digestive organS-are_de- ranged the tongue is commonly covered with a thick yellowish coat, and there is frequently a "bad taste" in. the mouth.* The whole alimentary mucous membrane is in close physiological connection ; and anything disorder- ing the stomach is likely to produce a "furred tongue," which in most cases may be taken as indicating something •wrong with the deeper parts of the digestive tract. The Salivary Glands. — The saliva, which is poured into the mouth and moistens it, is secreted by three pairs of glands, the parotid, the submaxillary, and the sublingual. The parotid glands lie close in front of the ear ; each sends its secretion into the mouth by a duct, which opens inside the cheek opposite the second upper molar tooth. In the disease known as mumps f the parotid glands are inflamed and enlarged. The submaxillary glands lie between the halves of the lower jaw-bone, and their ducts open beneath Describe the surface of a beallhy tongue. How does the tongue of a healthy man differ in apijcarance from that of a healtliy child? When is the tongue apt to be "coated"? What does a furred tongue usually indicate? By what is the saliva secreted ? Where does tlie parotid gland lie? Where does its duct open? What change occurs in the parotid glands during "mumps"? Where are the submaxillary glands? Where do their ducts open? serving to scrape or lick clean bones, etc. Tamed tigers have been known to draw blood by licking the hand of their master. * The fur of the tongue consists of some mucus, a, few cells shed from its surface, and numerous vegetable microscopic organisms belonging to the group of Bacteria. t Technically, parotitis. THE PHARYNX. 141 the tongue. The sublingual glands lie beneath the floor of the mouth behind the submaxillary. i The Fauces is the name given to the passage which/ can be seen at the back of the mouth leading from it' into the pharynx, below the soft palate.* It is bounded above by the soft palate and uvula, below by the root of the tongue, and on the sides by muscles, covered by mucous membrane, which reach from the soft palate to the tongue. The muscles cause elevations known as the pillars of the fauces. Each elevation divides near the tongue, and in the hollow between its divisions lies a tonsil (7, Fig. 46), a soft rounded body about the size of an almond, and con- taining numerous minute glands which form mucus. Enlarged Tonsils. — The tonsils not unfi'cqucutly become enlarged during a cold or sore throaty and then pressing on the Eustachian tube (Chap. XXI), which leads from the throat to the middle ear, keep it closed and produce temporary deafness. Sometimes the enlargement is perma- nent and causes much annoyance. The tonsils can, how- ever, be readily removed without danger, and this is the treatment usually adopted in such cases. The Pharynx or Throat Cavity (Fig. 41). — This portion of the alimentary canal may be described as a conical bag with its broad end turned towards the base of the skull and its other end turned downwards and narrowing into Where do the sublingual glands lie? Wliiit is meant by the fauces? How are they bounded? What are the pillars of the fauces? What is a tonsil? Why is temporary deafness not uncommon when we have a sore throat? What is usually done when the tonsils are permanently enlarged? Briefly describe the pharynx. * Observe for yourself with the help of a looking glass. 142 TBB BVMAN BOUT. the gullet. Its front or ventral wall is imperfect, present- ing apertures which lead into the nose, the mouth, and (through the larynx and windpipe) into the lungs. Except when food is being swallowed the soft palate hangs down between the mouth and pharynx; during deglutition it is raised into a horizontal position, and separates an upper or respiratory portion of the pharynx from the rest. Through this upper part air alone passes,* entering it from the pos- terior ends of the two nostril chambers, while through the lower portion both food and air pass, one on its way to the gullet, h, Fig. 41; the other through the larynx, d, to the windpipe, c; when a morsel of food "goes the wrong way" it takes the latter course. Opening into the upper portion of the pharynx on each side is an Eustachian tube, g. At the root of the tongue, over the opening of the larynx, is a plate of cartilage, the epiglottis, e, which can be seen if the mouth is widely opened and the back of the tongue pressed down by some such thing as the handle of a spoon. Dur- ing swallowing the epiglottis is pressed down like a lid over the opening of the air-tube and helps to keep food from entering it. The pharynx is lined by mucous membrane and has muscles in its walls which, by their contractions, drive the food on. The (Esophagus or Gullet is a tube commencing at the What apertures open into its ventral side? What is tlie usual position of the soft palate? How is tliis position altered during swallowing? What passes through the respiratory division of the pharynx? What things pass through its lower division? What is the destination of each? What is meant by saying a morsel has "gone the wrong way"? Where do the Eustachian tubes open? What is the epiglottis? How may it be seen? What is its use? * During a severe attack of vomiting the soft palate often only acts imper- fectly in closing the passage between gullet and nostrils; hence some of the ejected matter not unfrequently is expelled through the nose. TEE STOMACH. 143 lower termination of the pharynx and which, passing on through the neck and chest, ends below the diaphragm in the stomach. In the neck it lies close behind the windpipe. The Stomach (Eig. 47) is a curved conical bag placed FlQ. «. Fio. 48. Fia. 47.— The stomach, d, lower sai. or the gullet ; a, position of the cardiac aperture : 6, the fundus ; c, the pylorus ; e. the first part of the amali intes- tine ; along o, b, c, the great curvature ; betiveeu the pylorus aiid d, the lesser lorvature. Fig. 48. — A thin section through the gastric mucous membrane, perpendicu- lar to its surface, magnified about 85 diameters, a, a simple peptic gland; 6, a compound peptic gland; c, a mucous gland. transversely in the upper part of the abdominal cavity.* Its larger end is turned to the left and lies close beneath the diaphragm, and opening into its upiier border, through the cardiac orifice at a, is the gullet, d. The narrower right end is continuous at c with the small intestine; the com- munication between the two is the pyloric orifice. The Describe the gullet. Where does it lie in the neck? What is the stomach? Which end of it is larger? Where does this end lie? What opens into it? What is the opening called? What is continuous with the small end of tlie stomach? What is the name of the aperture between the stomach and the small intestine? * The general anatomical arrangement of the stomach, and its connections with the gullet and intestine, may be readily shown on the body of a puppy, kit- ten, or rat, which has been killed by placing it tor five minutes in a small bo2 containing also a sponge soaked with chloroform. 144 THE HUMAN BODY. pyloric end of the stomach is separated from the diaphragm by the liver (see Fig. 4). When moderately distended the stomach is abont twelve inches long, and about four inches across at its widest part, and would contain about three pints. The Glands of the Stomach. — The mucous membrane lining the stomach is seen, when its surface is examined with a common magnifying glass, to be covered with shallow pits. A more powerful microscope shows on the bottom of each one of those pits the openings of several minute tubes, the gastric glands, which lie imbedded in the mu' cous membrane, packed closely, side by side (Fig. 48). These glands secrete the gastric juice. The Muscular Coat of the Stomach lies outside the mu- cous membrane, and is made up (Fig. 34) of plain muscular tissue, whose fibres run in different directions. By its contractions it stirs up the food and mixes it with the gastric juice. Around the pyloric orifice of the stomach is a thick ring of muscle (the pyloric sphincter), which usually is contracted, closing the passage between the stomach and the ommencement of the small intestine. During diges- tion in the stomach the pyloric sphincter relaxes from time to time, and allows food, more or less digested, to pass oe into the intestine. Palpitation of the Heart. — The cardiac end of the stom- ach lies close beneath the diaphragm, and the heart imme- What lies between the right end of the stomacli and the dia- phragm? What is the size of the stomach? What may be seen on examining tlie mucous membrane of the stomach with a hand lens? What does a more powerful magnify- ing instrument show? What is the function of the gastric glands? Describe the muscular coat of the stomach. What is its function? What is the pyloric sphincter? Its function? What happens when the pyloric sphincter relaxes during gastric digestion? THE SMALL INTESTINE. tu < "I ^ f M*. diately aboTe it. Over-distension of the stomach, due to indigestion or flatulency, may press up the diaphragm and interfere with the proper working of the thoracic organs, causing feelings of oppression in the chest, or palpita- tion of the heart. The Small Intestine commences at tlie pylo- rus and ends, after many windings, in the large. It is about twenty feet (six meters) long and about two inches (five centimeters) wide at its gastric end, narrowing to about two thirds of that width at its lower portion. Externally there are no lines of sub- division on the small in- testine, but anatomists ^la. 49.— Diagram of abdominal part of 1 ., -1 J 'u 'i. alimentary canal. C, the cardiac, and P, the arbitrarily describe it as pyloric end of the stomach; D, the duode- . , . - , , . num ; J, I, the convolutions of the small in- COnSlstingOI three parts, testine; CC, the cmcwra with the vermiform . appendix; .40, ascending, TC, transverse, and the first twelve inches HC, descending colon; iJ, the rectum. being the duodenum, the succeeding two fifths of the re- mainder the jejutmm, and the rest the ileum. Why is it that an over-distended stomach sometimes causes palpi- tation of the heart? Where does the small intestine commence? Where does it end? Describe its length and diameter. Of what divisions do anatomists describe it as consisting? 146 THE HUMAN BODY, The Mucous Coat of the Small Intestine. — This is pink, soft, and extremely vascular. It is tliroughout a great por- tion of the length of the tube raised up into permanent transverse folds in the form of crescentic ridges, each fold running transversely for a greater or less way round the in- testine (Fig. 50). These folds are tlie valvulce conniventes. They are first found about two inches from the pylorus, and are most tliickly set and largest in the uppe r half of the je junum , in the lower halfoTwhich they become gradually less conspicuous; they finally dis appe ar altogether about the middb of the ileum. The folds of the mucous membrane Fig. 50. — A portion of the small intestiue opened to show the valvules conni- ventes. serve to greatly increase its surface both for absorption and secretion, and they also delay tlie food in its passage; it collects in the hollows between them, and so is longer ex- posed to the action of the digestive liquids. The Villi. — Examined closely witlitlie eyeor, better, with a hand lens, the mucous membrane of the small intestine is seen not to be smooth but shaggy, being covered everywhere (both over the valvulse conniventes and between tliom) with closely packed minute elevations standing up somewhat like Give the general characteristics of the mucous membi'ane of the small intestine. Wliat are the valvulse conniventes? Where do they commence? Where are they most developed? Where do they cease? What purposes do they subserve? What are the villi? THE VILLI. 147 the "pile" on velvet and known as the villi (Fig. 5]). In structure a villus is somewhat complex. Covering it is a single layer of cells, beneath which the villus may be re- garded as made up of a framework of connective tissue sup- porting the more essential constituents. ISTear the surface is a network of plain muscular tissue. In the centre is an offshoot of the lymphatic or absorbent system, sometimes Fig. 51.— Villi of the small intestine ; magnified about 80 diameters. In the left-hand figure the lacteals, a, 6, c, are filled with white injection ; d. bloodves- sels. In the right-hand figure the lacteals alone are represented, filled with a dark injection. The epithmium covering the villi, and their muscular fibres are omitted. in the form of a single vessel with a closed dilated end, and sometimes as a network formed by two main vessels with cross-branches. During digestion these lymphatics are filled with a milky white liquid absorbed from the intestines, and they are accordingly called the lacteals. They com- municate with larger branches in the outer coats of the in- Describe the structure of a villus, during digestion? Wliat is found in its lymphatics 148 THE HUMAN BODY. testine, and these end in trunks which Join the main lym- phatic system. Finally, in each villus, outside its lacteals and beneath its muscular layer, is a close network of blood- vessels. The Glands of the Small Intesti^^p. — Opening on the surface of the small intestine between the bases of the villi are small glands, the crypts of Lieberkuhn. Each is a simple unbranched tube, lined by a single layer of cells. The Muscular Coat of the Small Intestine lying outside the mucous coat, is composed of plain muscular tissue, dis- posed in two layers: an inner circular, and an outer_longi- tudinal. By their combined and alternating contractions they slowly force the digesting food along the tube. In the duodenum are found in addition minute glands, I the glands of Brunner, which lie outside the mucous membrane, and send their ducts through it to open on its inner surface. The Large Intestine (Fig. 49), forming the final portion of the alimentary canal, is about 5 feet (1.5 meters) long, and varies in diameter from 3|- to 1^ inches (6-4 centi- meters). Anatomists describe it as consisting of the ccecum (cc) with its vermiform appendix, the colon (ac, tc, dc), and the rectum (k). The small intestine does not open into the end of the large but into its side, some distance from its closed upper end; the ca3cum is that part of the large intestine which extends beyond the communication. From it projects the vermiform appendix, a narrow tube not thicker than a cedar pencil, and about 4 inches (10 centi- "Where do we find the crypts of Lieberkuhn? Describe them. Where are the glands of Brunner? Give the dimensions of the large intestine. Of what parts is it made up? How does the small intestine open into it? What is the ciBcum? The vermiform appendix? Its size? THE LIVER. 149 meters) long. The colon commences on the right side of the abdominal caTity where the small intestine communi- cates with the large, runs up for some way on that side {ascending colon), then crosses the middle line {transverse colon) below the stonjach, and turns down {descending colon) on the left side, and there makes an S-shaped bend known as the sigmoid flexure; from this the rechivi proceeds to the opening by which the intestine communicates with the/ exterior. The mucous coat of the large intestine possessesj no Tilli nor valvulee conniventes; it contains numerous closely! set glands much like the crypts of Lieberkiihn of the small( intestine. The Ileo-Colic Valve. — Where the small intestine joins I the large there is a valve formed by two flaps of the mucous membrane sloping down into the colon, and so arranged as , to allow matters to pass readily from the ileum into the large intestine, but not the other way. The Liver. — Besides the secretions formed by the glands imbedded in its walls, the small intestine receives those of two large glands, the liver and pancreas, which lie in the abdominal cavity. The ducts of both open, by a common aperture, into the duodenum about 4 inches (10 centime- ters) from the pylorus. The liver is the largest gland in the body, weighing from 50 to 60 ounces (1400 to 1700 gr.'.ins). It is Describe the colon. What is the sigmoid flexiire? What is the terminal portion of the alimentary canal named? How does the mucous lining of the large intestine differ from, and how does iti-e- semble that of the small ? Where is the ileo-colic valve? How is it formed? What is its function? What large glands pour their secretion into the small in'.estine? Where are they situated? Where do their ducts open? What is the largest gland in the body? What is its weight? Where is it placed? 150 THE HUMAN BODY. situated in the upper part of the abdominal cayity {le, h'. Fig. 4), rather more on the right than on the left side, imme diately below the diaphragm. The liyer is of dark reddish- brown color, and of soft friable texture. The vessels carrying blood to the liver (Fig. 52) are iha 2^ortal vein^p, (p. 20S) and the lieimtic artery; both enter itU a gFoove on its under Fig. 52,— The under surface of the liver. cA, common bile duct; X>c cystic duct; J3/i, hepatic duct; F/, gall-bladder. side, and there also a duct passes out from each half of the organ. The ducts unite to form the hepatic duct, Dh, which meets the cystic duct, Dc, proceeding from the galh Madder, Vf, a pear-shaped sac in which the lite or gall formed by the liver accumulates when food is not being di- gested in the intestine. The common hile duct, Dch, formed Describe the color and texture of the liver. What vessels bring blood to it? Describe the arrangement of its ducts. "What is the gall-bladder? Where does the common bile duct open? THE PANCREAS. 161 by the union of the hepatic and cystic ducts, opens into the duodenum. The Functions of the Liver. — The size of the liver is related to the fact that the organ plays a double function ; on the one hand it is a digestive gland secreting lile; on the other, its cells serve to store up, in the form of a kind of animal starch, called glycogen^ excess of starchy or sugary food absorbed from the intestine during the digestion of a meal, and then to gradually dole this out to the blood for general use by the organs of the body until the next meal is eaten. The Pancreas or Sweetbread * is a compound racemose gland. It is an elongated soft organ of a pinkish-yellow color, lying along the lower border of the stomach. Its right end is embraced by the duodenum which there makes a curve to the left. A duct traverses it and joins the common bile-duct close to its intestinal opening. The pancreas secretes a watery-looking liquid, much like saliva in appearance, which is of great importance in digestion. With what fact is the large size of the liver connected? What are its functions? To wliat group of glands does the pancreas belong? Describe its form and color. Where is it placed? Wbatdoesitsduct unite with? What does its secretion look like? Is it of much value? * Butchers sell two kinds of sweetbread, known as the belly sweetbread and the neck or heart sweetbread. The former is the pancreas; the latter is the thymus^ an organ of doubtful function, found only in young animals, and lying at the bottom of the neck and upper part of the chest in front of the windpipe. CHAPTER XII. DIGESTION. The Object of Digestion. — Some of the foodstuffs which we eat are already ia solution and ready to soak at once into the lymphatics and blood-vessels of the alimentary canal; others, such as a lump of sugar, though not dis- solved when put into the mouth, are readily soluble in the liquids found in the alimentary canal and need no furtlier digestion. In the case of many most important foodstuffs, however, special chemical changes have to be brought about to make them soluble and capable of absorption. The different secretions poured into' the alimentary tube act in various ways upon different foodstuffs, simply dis- solving some and chemically changing others, until at last all are got into a condition in which they can be taken up into the lymph and blood-vessels for transference to distant parts of the body. The Saliva. — The first solvent poured upon the food is the saliva, which, when it meets the food, is a mixture of pure saliva with the mucus secreted by the membrane lining the mouth. This mixed saliva is a colorless, cloudy, feebly alkaline liquid. The Uses of Saliva are mainly physical and mechanical. It keeps the mouth moist and allows us to speak with com- Bxplain the object of digestion. What is the first digestive liquid which the food meets with? How does it differ from pure saliva? Describe mixed saliva. [152] THE USES OF SALIVA. I53 fort ; most young orators know the distress occasioned by the suppression of the salivary secretion through nervous- ness, and the imperfect efficacy under such circumstances of the traditional glass of water placed beside public speakers. The saliva also enables us to swallow dry food; such a thing as a cracker when chewed would give rise merely ±0 a heap of dust, impossible to swallow, were not the mouth cavity kept moist.* The saliva also dissolves such bodies as salt and sugar, when taken into the mouth in a solid form, and enables us to taste them; undissolved substances are not tasted, a fact which any one can verify for himself by Wiping his tongue dry and placing a frag- ment of sugar upon it. No sweetness will be felt until a little moisture has exuded and dissolved part of the sugar. Chemical Action of the Saliva. — In addition to such actions the saliva, however, exerts a chemical one on an important foodstuff. Starch (although it swells up greatly in hot water) is insoluble and could not be absorbed from the alimentary can.tl. The saliva has the power of turning starch into the readily soluble and absorbable grape sugar, the sugar of most fruits, f The starch is made to combine with the elements of water, and the final result is grape sugar. Describe and illustrate the uses of saliva with reference (1) to speech, (2) to swallowing, (3) to dissolving some foods. What foodstuff does saliva act upon chemically? What change is produced by its action? * This fact used to be taken advantage of in the East Indian rice ordeal for the detection of criminals. The gidlty person believing firmly that he cannot swallow the parched rice given him, and sure of detection, is apt to have his salivary glands paralyzed by fear, and so does actually become unable to swal- low the rice; while in those with clear consciences the nervous system, acting normally, excites the usual reflex secretion, and the dry food causes no difficulty of deglutition. t Grape sugar or glucose is now an extensively produced article of commerce, being made for this purpose by the prolonged action of dilute acids upon starchy substances. 154 THE HUMAm BODY. C»H"0" + 2H'0 = 2C"H"0' starch. Water. Grape Sugar. The Influence of Saliva in Promoting Digestion in the Stomach. — So f;ir as chemical changes are concerned the saliva is but of secondary importance in digestion: its main use is to facilitate swallowing. It only changes starch into grape sugar (at least rapidly) when no acid is present, and food passes from the mouth to the stomach where it is mixed with the acid gastric juice, before the saliva has time to do mucli. Indirectly, however, the saliva promotes di- /gestion iu the stomacli. Weak alkalies stimulate the gastric glands to pour forth more abundant secretion,* and the saliva, being alkaline, acts iu this way. This is one reason why food should be well chewed before being swallowed; its taste, and the movements of the jaws, excite a more abundant salivary secretion, and this alkaline saliva, when swallowed, helps to stir the stomach up to work. Swallowing or Deglutition. — A mouthful of solid food is broken up by the teeth and rolled about the mouth by the tongue until it is thoroughly mixed with saliva and made into a soft pasty mass. The muscles of the cheeks keep this from getting between them and the gums.f The mass is finally sent on from the mouth to the stomach by What is the chief use of saliva? Under what circumstances does it change starcli into sujrar? In what portion of the digestive tract is this action of the saliva stopped? "Why? How does the saliva promote digestion in the stomach? Why should food be thoroughly chewed before swallowing? What is the technical term for swallowing? In how many stages does swallowing occur? * Hence the efficacy of a Httte carbonate of soda or apollinaris water taken before meals, in some forms of dyspepsia. t Persons with facial paralysis have from time to time to press out with the finger food which has collected outside the gums, where it can neither bo chewed nor swallowed. DEGLUTITION. 155 the process of deglutition, which occurs in three stages./ The first stage includes the passage from the mouth into the pharynx. The food being collected into a heap on the tongue, the tip of that organ is placed against the front of the hard palate, and then the rest of the tongue is raised from before back, so as to compress the food mass between it and the palate and drive it through the fauces. This much of the act of swallowing is voluntary, or at least is under the control of the will, although it commonly takes place unconsciously. The second stage of deglutition is that in ' which the food passes through the pharynx; it is the most rapid part of its progress, since the pharynx has to be] emptied quickly so as to clear the opening of the air-paS' sages for breathing purposes. The food mass, passing back over the root of the tongue, pushes down the epiglottis ; at the same time the larynx (or voice-box at the top of the windpipe) is raised so as to meet the epiglottis, and thus the passage to the lungs is closed.* The soft palate is, at the same time, moved into a horizontal position, so as to I separate the upper (or respiratory) portion of the pharynx, leading to the nose and the Eustachian tubes (see Fig. 41), from its lower portion, which ends inferiorly in the gullet. Finally the isthmus of the fauces is closed as soon as the food has passed through, by the contraction of the muscles on its sides, and the elevation of the root of the tongue. All passages out of the pharynx except the gullet being thus blocked, when the pharyngeal muscles contract Describe the first stage. What is the second st.age? Which stage is most rapid? Why? How is the passage to the lungs closed while food is passing through the pharynx? How is the passage to the nose blocked? Describe the processes of the second stage of deglutition. * The raising of the larynx during swallowing can be readily felt by placing the finger on its large cartilage forming "Adam's apple" in the neck. i 156 THE HUMAN BOD T the food can only be squeezed into the oesophagus. The muscular movements concerned in this part of deglutition are all excited without the interrention of the will; food touching the mucous membrane of the pharynx produces quite involuntarily the proper action of the swallowing muscles.* Indeed, many persons after having got the mouth completely empty cannot perform the movements of the second stage of deglutition at all. On account of the involuntary nature of the contractions of the pharynx any food which has once entered it must be swallowed; the isthmus of the fauces forms a sort of Rubicon; food that has entered the pharynx must be swallowed, even although the swallower learned immediately that he was taking poi- son. The tJdrd stage of deglutition is that in which the food is passing along the gullet, and is comparatively slow. Even liquid substances do not fall or flow down this tube, but have their passage controlled by its muscular coats, which grip the successive portions swallowed and pass them on. Hence the possibility of performing the appar- ently wonderful feat of drinking a glass of water while standing upon the head, often exhibited by jugglers; peo- ple forgetting that one sees the same thing done every day by horses and other animals which drink with the pharyngeal end of the gullet lower than the stomach. The Gastric Juice. — The food having entered the stom- ach is exposed to the action of the gastric juice, which is a thin colorless or pale yellow liquid of a strongly acid re- action. It contains, beside water and some salts and mu- How are the movements of the second stage of deglutition excited? What is the third stage of deglutition? Is it fast or slow? How is- it that jugglers can drink while standing on the head? Describe the gastric juice. » The process is what is Icnown as a reflex action. See Chap. XX. GASTRIC DIGESTION. 157 cus, free hydrocMoric acid (about .02 per cent.), and a substance cslleA pepsin, which in acid liquids has the power of converting ordinary proteids into closely allied bodies called peptones. It also dissolves solid proteids, changing them at the same time into peptones. Peptones. — Ordinary proteids are typical examples of what are called "colloids;" that is to say, substances which do not readily pass through moist animal membranes; pep- tones are a kind of proteid which does readily pass through such membranes, and are, therefore, capable of absorption from the alimentary canal. (See Dialysis, p. 186.) Gastric Digestion. — In the stomach the onward progress of the food is stayed for some time. The pyloric sphincter remaining contracted closes the aperture leading into the intestine, and the irregularly disposed muscular layers of the stomach keep its semi-liquid contents in constant movement, by which all portions are thoroughly mixed with the secretion of its glands. In the stomach part of the proteid of the food is dissolved and turned into pep- tones. Certain mineral salts (as pho. phate of lime, of which there is always some in bread), which are insoluble in water but soluble in dilute acids, are also dissolved in the stomach. On the other hand, the gastric Juice has no action upon starch, nor does it digest oily substances. By the solution of the white fibrous connective tissues the disintegration of animal foods, commenced by the teeth, is Name its more important constituents. "Wtiat powers does pepsin possess? Wliat are colloids? Give examples. How do peptones differ from otlier proteids? Does food pass on immediately from the stomach to the intestine? How is it kept back? How is it mixed with the gastric juice? What happens to proteid foods in the stomach? Name anotlier substance dissolved iu the stomach. Name foodstuffs which are not changed in the stomach. How are animal foods broken up in the stomach? 158 THE HUMAN BODY. carried much further in the stomach; and the food-mass, mixed with much gastric secretion, becomes reduced to the consistency of a thick soup, usually of a grayisli color. In this state it is called chyme. The Chyme contains, after an ordinary meal, a consid- erable quantity of peptones, which are in great part gradually absorbed into the blood and lymphatic vessels of the gastric mucous membrane and carried ofE, along with other dissolTcd and dialyzable bodies— for example, salts and sugar. After the food has remained in the stomach some time (one and a half to two hours) the chyme begins to be passed on into the intestine in successive portions. The pyloric sphincter relaxes at intervals, and the rest of the stomach, contracting ;t the same moment, injects a quantity of chyme into the duodenum; this is repeated frequently, the larger undigested fragments being at first unable to pass the orifice. At the end of three or four hours after an ordinary meal the stomach is quite emptied, the pyloric sphincter finally relaxing to such an extent as to allow any larger in- digestible massfcs which the gastric juice has not broken down, to be squeezed into the intestine.* The Chyle. — When the chyme passes into the duodenum it finds preparation made for it. The pancreas commences to secrete as soon as food enters the stomach; hence a quantity of its secretion is already accumulated in the intes- tine when the chyme enters. The gall-bladder is distended What is chyme? What things would be found in chyme after an ordinary meal? When does chyme begin to be sent on to the in- testine? How? How soon is the stomach completely emplicd after a meal? What has accumulated in the small intestine when the chyme reaches it ? * Several of the above facts were first obsei'ved on a Canadian trapper^ Alexis St. Martin, who as a result of a gunshot wound had a permanent opening from ths surface of the abdomen to the interior of the stomach. THE PANCBEATIO SECRETION. 159 with bile, secreted since the last meal; the acid chyme stimulating the duodenal mucous membrane causes, through the nervous system, a contraction of the muscular coat of the gall-bladder, and so a gush of bile is poured out on the chyme. From this time on both liver and pancreas continue secreting actively for some liours, and j)our their products into the intestine. The glands of Brunner and the crypts of Lieberkiihn are also set at work. All of these secretions are alkaline, and they suffice very soon to more than neutralize the acidity of the gastric juice, and so to convert the acid chyme into alkaline chyle, which, as found in the intestine after an ordinary meal, contains a great va- riety of things: water, partly swallowed and partly derived from the salivary and other secretions; some undigested proteids; some unchanged starch; oils from the fats eaten; peptones formed in the stomach but not yet absorbed; sal- ines and sugar, which have also escaped complete absorp- tion in the stomach; indigestible substances taken with the food; all mixed with the secretions of the alimentary canal. The Pancreatic Secretion is clear, watery, alkaline, and much like saliva in appearance. The Germans call the pancreas the "abdominal salivary gland." In digestive properties, however, the pancreatic secretion is far more important than the saliva, acting not only on starch but on pi'oteids and fats. On starch it acts like the saliva, but more energetically. It produces changes in proteids simi- lar to those effected in the stomach, but by the agency of a How is an outpouring of iiile on tlie cliyme brouglit about ? Do liver and pancreas ceaae secreting wlien the chyme enters the intes- tine? Wliat other glands are set to work? How is the aoiditj' of the chyme overcome? What is chyle? What does it usually con- tain? Describe the pancreatic secretion. What foodstuffs does it act upon? Describe its action on starch. How does it change proteins? , ' ' - 160 THE HUMAN BODY. different substance, trypsin, which differs from pepsin in acting in an alkaline instead of in an acid medium. On fats it has a double action. To a certain extent it breaks them lip into fatty acids and glycerine.* The fatty acid then combines with some of the alkali present to make a soap, which being soluble in water is capable of absorp- tion, f Glycerine also is soluble in water and capable of absorption. The greater part of the fats is not, how- ever, so broken up, but simply mechanically separated into little droplets which remain suspended in the chyle and give it a whitish color; just as cream-drops are sus- pended in milk, or olive oil in mayonnaise sauce. If oil be shaken up with water, the two cannot be got to mix; immedi- ately the shaking ceases the oil floats up to the top; but if some raw egg be added a creamy mixture is readily formed in which the oil remains for a long time evenly suspended in the watery menstruum. The reason of this is that each oil-droplet becomes surrounded by a delicate pellicle of albumen, and is thus prevented from fusing with its neigh- bors to make large drops which would soon float to the top. Such a mixture is called an emulsion, and the albumen of the pancreatic secretion emulsifies the oils in the chyle, which becomes white (for the same reason as milk is that How does trypsin diflfer from pepsin ? How does pancreatic secre- tiou breali up some fats ? What digestive end is tlms attained 1 How is most of the fat eaten acted upon by the pancreatic secretion ? Why is the chyle while ? How may we mix oil with water ? Ex- plain the process. What is aa emulsion ? What emulsifies the oily matters of the chyle ? * (CijH^60)s [ Os + BHjO = 3 (^CisHa^O j. q^ .^ C^Ha |. q^ 1 Stearin H- 3 Water = 3 Stearic acid + i Glycerine, f Ordinary soap is a compound of a fatty acid with soda, colored and scented by the addition of various substances. Soft soap is a compound of a fatty acid with potash. Both dissolve in water, wbicb the fats from which they fLT& maay will not do- THE BILE. 161 color) because the innumerable tiny oil-drops floating in it reflect all the light which falls on its surface. The Bile. — Human bile when quite fresh is a golden brown liquid. It is alkaline, and besides coloring matters, mineral salts and water, contains the sodium salts of two nitrogenized acids, taurocholic and glycocJiolic, the former predominating in human bile. The TTses of Bile. —Bile has no digestive action upon starch or proteids. It does not break up fats, but to a limited extent emulsifies them when shaken up with them outside the body, though far less perfectly than the pancre- atic secretion. It is even doubtful if this action is exerted in the intestines at all. In many animals, as in man, the bile and pancreatic ducts open together into the duodenum, so that on killing the creature during digestion and finding emulsified fats in the chyle it is impossible to say whether or not the bile had a share in the process. In the rabbit, however, the pancreatic duct opens into the intestine about a foot farther from the stomacli than the bile-duct, and it is found that if a rabbit be killed after being fed with oil, no milky chyle is found down to the point where the pan- creatic duct opens. In this animal therefore the bile alone does not emulsify fats, and since the bile is pretty much the same in rabbits and other mammals it probably does not emulsify fats in them either. From the inertness of bile with respect to most foodstuffs it has been doubted if it is of any digestive use at all, and whether it should not be regarded merely as an excretion, poured into the aliment- Describe fresh human bile. What is its reaction? Name its chief constituents. Name foods on which bile has no influence. How does it act upon fats when sliaken with them? Give a reason for doubt- ing if it emulsifies fats in the intestine. IQ2 THE HUMAN BODY. ary canal to be got rid of. But there are many reasons against such a view. /In the first place, the _enti7^jthe bile into the upper end of the small intestine, where it has to traverse a course of more than twenty feet before ' getting out of the body, makes it probable that bile has some function to fulfill in the intestine. One use is no doubt to assist by its alkalinity in oyercoming the acidity of the chyme, and so to allow the pancreatic secre- ' tion to act upon proteids. Constipation is also apt to occur in cases where the bile-duct is temporarily stopped, so that the bile probably helps to excite the contrac- tions of the muscular coats of the intestines; and it is said that when the bile secretion is deficient putrefaatije_ changes are extremely apt to occur in the intestinal con- tents. Apart from such secondary actions, however, the bile probably has some influence in promoting the absorption of fats. If one end of a very narrow glass tube moistened with water be dipped in oil the latter will not rise in it, or but a short way; but if the tube be moistened with bile instead of water the oil will ascend higher. Again, oil passes through a plug of porous clay kept moist with bile, under a much lower pressure than through one wet with water. Hence bile by moistening the colls lining the intes- tine may facilitate the passage into the villi of oily sub- stances. At any rate, experiment shows that if the bile be prevented from entering the intestine of a dog the animal eats an enormous amount of food compared with that amount which it needed previously; and that of this food Give reasons for believing that bile is not a mere excretion. How does bile aid the digestive power of the pancreas? Point out other uses of bile. Describe experiments ■which tend to prove that bile helps in promoting the absorption of fatty matters from the intes- tine. INTESTINAL DIGMSTION. 163 a great proportion of the fatty part passes out of the ali- , mentary canal unabsorbed. There is no doubt therefore) that the bile somehow aids in the absorption of fats. ( The Succus Entericus or Intestinal Juice consists of the mixed secretions of the glands of Bruiiner and the crypts of Lieberkiihn. It is very difficult to obtain it pure, and hence its digestive action is but imperfectly known. It is alkaline and so helps to overcome the acidity of the chyme and allow the trypsin of the pancreas to act on pro-,' teids, and seems capable itself of dissolving some kinds of proteids and turning them into peptones. Intestinal Digestion. — Having considered separately the digestive actions of the different secretions poured into the small intestine, we may now consider their combined ac- tion. The acid chyme entering the duodenum from the stomach is more than neutralized by the alkaline secretions which it meets in the small intestine; it is made alkaline. This alkalinity allows the pancreatic secretion to finish the I solution and transformation into peptone of proteids which) have escaped conversion in the stomach. The pancreatic secretion also continues that conversion of insoluble starch into soluble and absorbable grape sugar, which had com- menced in the mouth but was checked in the stomach. The bile and pancreatic secretion together emulsify the i fats, with which th«y are thoroughly mixed by the contrac-| tions of the muscular coat of the intestine; they get them into a state of very fine division in the form of microscopic droplets, which are taken up by the cells lining the intes- tine. To a certain extent the fats are also saponified. The What does the succiis entericus consist of? "Why is its digestive action hut little known? Point out some of its uses. Describe the process of intestinal digestion. 164 2'a2? EXIMAN BODY. result of all these processes is a thin, milky looking alka-_ line liquid called chyle.. Indigestible Substances. — With every meal several things are eaten which are not digestible at all. Among them is elastic tissue, forming a part of the connective tissue of all animal foods, and cellulose, which is the chief constit- uent of the cases which envelope the cells of plants. The mucus secreted by the membrane lining the alimentary tract also contains an indigestible substance, mucin. These three materials, together with some water, some undigested foodstufEs, and some excretory substances found in the various secretions poured into tlio alimentary canal, form a residue which collects in the lower end of the large intestine, and is from time to time expelled from the body. Dyspepsia is the common name of a variety of diseased conditions attended with loss of appetite or troublesome digestion. Being often unattended with acute pain, and if it kills at all doing so very slowly, it is pre-eminently suited for treatment by domestic quackery. In reality, however, the immediate cause of the symptoms, and the treatment called for, may vary widely; and the detection of the cause and the choice of the proper remedial agents often call for more than ordinary medical skill. A few of the more common forms of dyspepsia may be mentioned here, with their proximate causes, not in order to enable people to undertake the rash experiment of dosing them- Name some indigestible substances eaten in every ordinary meal. Point out the source of each. What indigestible substance is added in the alimentary canal? What substances are found in tlie lower end of the large intestine? What is meant by dyspepsia? Why is it not a wise thing for people to try to treat it themselves without skilled advice? DTSPMPSIA. 166 selves, but to show how wide a chance there is for any unskilled treatment to miss its end and do more harm than good. Appetite^is primarily due to a condition of the mucous membrane of the stomach, which in health comes on after' a short fast and stimulates its sensory nerves ; and loss of appetite may be due to any of several causes. The stomach may be apathetic and lack its normal sensibility so that the empty condition does not act, as it normally does, as a sufficient excitant. "When food is taken it is a further stimulus and maybe enough; in such cases "ap- petite comes with eating." A bitter before a meal is useful as an appetizer to patients of this sort. On the other hand, the stomach may be too sensitive, and a voracious appetite be felt before a meal, which is replaced by nausea, or even vomiting, as soon as a few mouthfuls have been swallowed ; the extra stimulus of the food then over- ' stimulates the too irritable stomach, just as a draught of mustard and warm water will a healthy one. The proper treatment in such cases is a soothing one.* In states of general debility, when the stomach is too feeble to secrete under any stimulation, the administration of weak acids and artificially prepared pepsin is needed, so as to supply gastric iuice from outside until the improved Describe the symptoms of some chief forms of dyspepsia. * When food is taken it ought to stimulate the sensory gastric nerves, so as ] to excite the reflex centres for the secretory nerves and for the dilatation of | the blood-vessels of the organ; if it does not, the gastric juice will be imper- fectly secreted. In such cases one may stimulate the secretory nerves by weak alkalies (p. 154), as apollinaris water or a little carbonate of soda, before meals; or give drugs, as strychnine, which increase the irritability of reflex nerve-centres. The vascular dilatation may be helped by warm drinks, and this is probably the rationale of the glass of hot water after eating which has! recently been in vogue; the usual cup of hot coffee after dinner is a mor^ agreeable form of the same aid to digestion. 166 TEE HUMAN BODT. digestion strengtliens the stomach up to the point of being able to do its own work. Enough has probably been said to show that dyspepsia is not a disease, but a symptom accompanying many diseased conditions, requiring special knowledge for their 1 treatment. From its nature— depriving the body of its \ proper nourishment— it tends to intensify itself, and so j should never be neglected; a stitch in time saves nine. "— Absorption from the Alimentary Canal— Through its whole extent the mucous membrane lining the digestive tube is traversed by very closely packed tubes of two kinds, the blood and lymph vessels. Matters ready for absorption pass through or between the cells covering the surface of the mucous membrane, and then through the very thin walls of the smallest blood and lymph vessels ; and by these vessels are conveyed to larger channels with thicker walls, which all ultimately lead to the heart. From the heart the digested and absorbed food is distributed to every organ of the body. Absorption from the Mouth, Pharynx, and Gullet is but slight. Some water, some common salt, some sugar, and some grape sugar (made from starch by the action of saliva) are no doubt taken up during tlie processes of chewing and I swallowing. But the time which elapses between taking a mouthful of food and its transference to the stomach is j usually too short to allow the occurrence of any consid- erable absorption. Why should dyspepsia never be neglected? What tubes are found in the mucous membrane of the alimentary canal? How do dissolved foods enter them? Where are the ab- sorbed matters carried? To what parts are they finally distributed? What foodstuffs are partly absorbed in mouth, pharynx, and gullet? Why does not any great amount of absorption take place m those parts? Missing Page EXPLANATION OF PLATE IIL A Genekal View of the Lymphatic or Absoebent System OP Vessels. «, A portion of the small intestine from wliich lacteals or chyle- conveying vessels, d, proceed, their origin within tl)e villi may he seen magnified in fig. 51; /, the duct called thoracic, into which the lacteals open. This duct passes up the back of the chest, and opens into the great veins at g, on the left side of the neck: here the chyle mingles with the venous blood. In the right upper, and lower limbs the superficial lymphatic vessels II II, which lie beneath the skin, are represented. In the left upper and lower limbs the deep lym- phatic vessels which accompany the deep blood-vessels are shown. The lymphatic vessels of the lower limbs join the thoracic duct at the spot where the lacteals open into it: those from the left upper limb and from the left .side of the head and neck open into that duct at the root of the neck. The lymphatics from the right upper limb and from the right side of the head and neck join the great veins at n. mm, enlargements called lymphatic glands, situated in the course of the lymphatic vessels. Tliese vessels convey a fluid called lymph^ which mingles with the blood in the great veins. A fuller account of the lymphatic vessels in general, as distinguished from that section of them known as the lacteals, will he found on p. 188. ABSORPTION FROM THE STOMACH. 167 Absorption from the Stomach is more important. Food stays there a considerable time, and a good deal of the substances mentioned above as being absorbed to a slight degree on their way to the stomach, are taken up to a much greater extent by the mucous membrane of the stomach itself and passed on into the general blood current. In addition, a large proportion of albuminous food is turned in the stomach into peptones, which can be and are readily absorbed by the vessels of the gastric mucous membrane. Absorption from the Small Intestine is by far the most important in bringing nutritive matters into the body. The stomach is an organ rather of digestion than absorp- tion; the small intestine, on the other hand, is specially constructed to absorb. Its valvulse conniventes delay the progress of the food mass which stagnates in the hollows between them; and its innumerable villi, with their blood- vessels and lymphatics (p. 147), reach out, like so many rootlets, into the chyle and take it up. The sugars reaching the small intestine or formed in it are absorbed mainly by the blood- vessels and carried to the liver, where they are turned into glycogen (p. 151), which is heaped up in the liver during digestion, and slowly given out to the blood, as its sugar is used up gradually before the next meal. The peptones passed into the intes- tine from the stomach, or formed in ib by the action of the Why does more absorption take place from the stomach? Name things absorbed from both mouth and stomach?' "What food matters are first absorbed from tlie stomach? Where does the most imporl.int food absorption occur? What structural peculiarities of the small intestine peculiarly fit it for ab- sorbing? . What vessels absorb sugars In the small mtestme? To what organ are these sugars conveyed? What there becomes of them? 138 THE HUMAN BODY. pancreatic secretion, are partly taken up by its lymphatics and partly by its blood-vessels. The emulsified fats main- \\j pass into the lymphatics of the villi, and are carried off jby them. The Lacteals. — The innumerable tiny fat drops drained off by the intestinal lymphatics or lacteals after an ordinary meal make their contents look white and milky, hence the name.* During fasting the lymphatics of the small intestine, like those in other parts of the body (see Chap. XIII.) convey a clear colorless liquid. Absorption from the large Intestine. — In the duo- denum the bulk of food entering from the stomach is increased by the bile and pancreatic secretions poured out on it. Thenceforth absorption overbalances excretion, and the food-mass becomes less and less in bulk to the lower end of the ileum. The contractions of the small intestine drive on its continually diminishing contents, until they reach the ileo-colic valve, through which they are ulti- mately pressed. When the mass enters the large intestine its nutritive portions have been almost entirely absorbed, and it consists chiefly of some water, with the indigestible portions of the food and of the secretions of the alimentary canal. It contains cellulose, elastic tissue, mucin, and somewhat altered bile pigments; commonly some fat if a large quantity has been eaten; and some starch, if raw veg- How are emulsified fats carried off? What are the lacteals? Why so called? Under what conditions do the lacteals not contain milky looking chyle? In what part of the alimentary caual does absorption more than balance the amount of liquid poured out on the food? What are the constituents of the mass passing from the small into the large intestine? What changes does this mass undergo as it passes along the large intestine? * From Latin, lac, milk. ArPENDIX. 169 etables have formed part of the diet. In its progress through the large intestine the food-mass loses still more water, and the digestjon_oi_ataisli and the absorption of fats is continu ed. Finally the residue, with some excre- tory matters added to it in the large intestine, is expelled from the body. APPENDIX TO CHAPTER XII. The digestion and absorption of food are sucli fundamental facts In physiology that a thoroughly intelligent comprehension of them is of great importance; at the same time they are so largely merely chemico-physical phenomena that they are readily illustrated by a few simple experiments. These described below take but little time and cost but little money, while they cannot fail to be of value not merely in interesting a class, but in giving its members a much better idea of the way in which food is digested tlian they can get from merely reading a book. 1. Anatomy of the Alimentary Canal. — Kill a rat by chloroform or drowning. Dissect away the skin from the whole ventral aspect of the body. Note in the neck region the large salivary glands which meet in the middle line: the posterior gland, close to the middle line, rounded and compact, is the submaxillary; on raising it, its duct will be seen passing forwards to the mouth, into which it may be followed by separating the halves of the lower jaw. The large gland, composed of several loosely united lobes, and reaching from the neighborhood of the ear to the submaxillary, is the parotid. Its duct will be found passing forwards over the face to the mouth, near the angle of which it passes in through the cheek muscles. In front of the submaxillary will be found a small gland, the sub- Remove the muscles, etc., covering the larynx and trachea; cut away the front and side walls of the chest and abdomen; remove larynx, trachea, lungs, and heart. The gullet, a slender muscular tube, will now be exposed in the neck; trace it through the chest; note the relative positions of the abdominal viscera as now exposed, before displacing any of them; then turning the liver up out of the way, follow the gullet in the abdomen until it ends in the stomach. 170 THE HUMAN BODY. Note the form of the latter organ; its projection (fundm) to the left of the entry of the gullet; its great and small curmtures; its narrower pyloric portion on the right, from which the small intestine proceeds. Altaclied to the stomach, and hanging down over the other abdominal viscera, notice a thin membrane, the omentum. Follow and unravel the coils of the small intestine, spreading out as far as possible the delicate membrane (mesentery) wbicli slings it. In the mesentery are numerous bands of fat, running in which will be seen blood-vessels and lacteals. The termination of th§ small intestine by opening into the side of the large. Observe the cecum or blind end of the latter, projecting on one side of the point of entry of the small intestine; on the other side follow the large intestine until it ends at the anal aperture, cut- ting away the front of the pelvis to follow its terminal portion (rec- tum). The portion between the caBCum and the rectum is the colon. Spread out the portion of the mesentery lying in the concavity of the first coil (duodenum) of the small intestine; in it will be seen a thin branched glandular mass, Ihe pancreas. Observe the portal vein entering the under side of the liver by several branches. Alongside it will be seen the gall-duct, formed by the union of two main branches, and proceeding, as a slender tube, to open into the duodenum about an inch and a half from the pyloric orifice of the stomach. Note the spleen: an elongated red body lying in the mesentery, behind and to the left of the stomach. Divide the gullet at the top of the neck, and the rectum close to the anus, and severing mesenteric bands, etc., by which intermediate portions of the alimentary canal are fixed, remove the whole tube; then cutting away the mesentery, spread it out at full length, and note the relative length and diameter of its various parts. The whole is seven or eight times as long as the head and trunk of the animal, and the small intestine forms by far the longest part of it. Open the stomach; note that the mucous membrane lining the fun- dus is thin and smooth, and is sharply marked off from the thick corrugated mucous membrane lining the rest of the organ. (This is not the case in the human stomach.) Pass probes through the car- diac orifice into the gullet and through the pyloric mifice into the duodenum. Remove the liver; note its general form. Obtain from your butcher an inch or two of the small intestine of a recently killed calf. Place in 50 per cent, alcohol for twenty, four hours. Then open under water and examine with a hand lens to see the villi. APPENDIX. 171 2. The Action of Saliva on Starch. — Make a thin paste of good arrowroot (wliich is almost pure starch) with boiling water. Let it cool. a. Add two or tbree drops of this starch paste to half a test tube- fill of cold water; next add three or four drops of solution of caustic potash and two or three drops of dilute watery solution of blue vitriol (cupric sulphate). Mix thoroughly and boil over a spirit lamp. No orange-red precipitate will result. This shows that there is no grape sugar in the starch paste. h. Rinse the mouth thoroughly and then collect a small quantity of saliva in a test tube. Dilute with water. Add caustic potash and cupric sulphate solutions as above; mix thoroughly and boil. The mixture will become violet, but give no orange-red precipitate; there- fore there is no grape sugar in saliva. c. Take now three drops of the starch paste and a teaspoonful of saliva,- mix with a half test tubeful of water. Place the mixture in a moderately warm place for five minutes. Then add a few di-ops of the caustic potash and cupric sulphate solutions; mix and boil. An abundant orange or brick red precipitate will be thrown down, prov- ing the presence of grape sugar, which has been produced by the action of the saliva on the starch. 3. Gastric Digestion. — a. Obtain a pig's stomach. Cut it open and wash away its contents with a gentle stream of water. Then dissect off the mucous membrane from its middle part, mince and put aside for a couple of days in three or four ounces of glycerine; The glycerine dissolves the pepsin. Then strain off the glycerine through muslin. 5. Get a butcher to " whip" some fresh drawn blood for you witk a bunch of wire or twigs. The blood fibrin will collect on these (p. 181), and when thoroughly washed with water.forrhs a good proteid for digestion experiments. One lot of it thus obtained and washed may be put aside in 50 per cent, alcohol, and will provide material for digestion experiments for years. c. Add a teaspoonful of muriatic acid to a pint of water. d. Dilute a teaspoonful of the pepsin solution a with two table- spoonfuls of water. Fill a test tube with the mixture; add a few shreds of washed fibrin, and set aside in a warm but not hot place for twenty-four hours. No change will occur, showing that pepsin alone will not dissolve proteids. e. Put some shreds of fibrin in a test tube of the mixture c in a warm place for twenty-four hours. The fibrin will swell up and become translucent, but will not dissolve. This shows that dilute acids will not in a sbort time dissolve proteids. 172 THE HUMAN BODY, f. Half fill a test tube wUb the mixture c, add a teaspoonful of the pepsin solutioc a, and then a few shreds of fibrin. Place in a warm place for twenty-four hours. The fibrin will be more or less completely dissolved at the end of that time. We thus find that pepsin alone and dilute acid alone (at least in a moderate time) will not dissolve proteids, but that acting together they quickly effect a solution. 4. The Action of Bile on Fatty Substances. — a. Shake up some olive oil with water in a test tube. The two liquids soon separate when tlie shaking ceases. b. Obtain an ox gall from the butcher. Cut it open and collect the bile. (The bile of herbivorous animals differs from human bile in being green in color.) Shake up some oil with bile instead of water. A creamy emulsion is formed from which tlie oil only slowly floats up to the top. 5. The Action of the Pancreatic Secretion on Fats. — a. Obtain a pig's pancreas; mince, and extract with about its own bulk of water for two or three hours. Strain off the watery infusion. Add to it half its bulk of oil in a lest tube and shake thoroughly. The oil will be very thoroughly emulsified ; and separate very slowly on standing. 6. Action of Pancreatic Secretion on Starch. — With some of the watery extract of pancreas perform the expei'iraents described above under heading 3; substituting pancreatic extract for saliva. 7. Action of Pancreatic Secretion on Proteids. — a. Obtain a fresh pig's pancreas. Lay aside in a cool place for twenty-four hours. Mince, and extract for two days with twice its bulk of glycerine. Strain off the glycerine extract. b. Dilute the glycerine extract with ten times its bulk of water. Place part of this mixture in a test tube together with some fibrin shreds, and put aside in a, warm place. After twenty-four hours none of the fibrin will have been dissolved. c. To the diluted glycerine extract as above add a teaspoonful of dilute acid (3 e). The fibrin will swell but not dissolve. d. To another portion of the diluted glycerine extract add just sufficient bicarbonate of soda to make it distinctly alkaline, as tested by litmus paper. Then put in some fibrin and set aside in a warm place for a day. The fibrin will be more or less completely dissolved. We thus find that the pancreas affords a substance which, in the presence of weak alkalies.dissolves proteids. The fat-absorbing power of the lymphatics of the small intestine is very readily demonstrable, without giving pain to an animal or any unnecessary destruction of life. In most families superfluous kittens or puppies have to be killed at the time of birth. Feed a kitten or APPENDIX. 173 puppy on rich milk, and three hours after place it in a box or under a bell-jar with a sponge soaked with ether or chloroform. When the animal is completely insensible cut ofE its head, and then rapidly open the abdomen and spread out the mesentery (the thin membrane which slings the small intestine). In it will be seen a beautiful network of lacteal vessels filled with milk-white liquid, some of which can be collected if one of the lacteals be cut open. For comparison a kitten or puppy may be used which has had no food for eiglit or ten hours. The lacteals being then filled with clear, watery -looking lymph, will be Tficognized with difficulty. CHAPTER XIII. BLOOD AND LYMPH. Why we need Blood. — Some very small animals oi simple structure require no blood ; every part catches its own food and gives offi its own wastes to the air or water in which the creature lives. When, however, an animal is larger and more complex, made up of many organs, some of which are far away from the surface of its body, this is impossible; some organs are therefore set apart to catch food, and arrangements made to carry some of this food to the others. In our own bodies many parts lie far away from the stomach and intestines which receive, digest, and absorb our food, and from the lungs which take oxygen gas out of the air we breathe; yet every part, bone and muscle, brain and nerve, skin and gland, needs a steady supply of both of these things to keep it alive. The division of labor, in accordance with which some organs are especially set apart for the purpose of receiving substances from the outside world to build up, nourish, and repair the body, necessitates an arrangement by which the matters received shall be distributed to other parts. This distribution is accomplished by the blood, which flows into every organ from the crown of the head to the sole of the foot. Being pumped round What kind of animals do not need blood? How are their wants supplied and their wastes removed? Why do we find special recep- tive organs In larger animals? Illustrate from the human body. What arrangement is necessitated by the fact that special organs are set apart in the body for receiving food and oxygen? How is the distribution effected? [1741 THE BLOOD. ]75 and round, from place to place, hjtheheari, the blood picks up nourishing things in its course through the walls of the alimentary canal, and oxygen as it flows through the lungs; it then carries them to all other parts of the body. The Removal of Wastes.— The rapidly flowing blood not only conveys a supply of nutritive material for all the organs, but is a sort of sewage stream that drains off their wastes (p. 108), and carries them to the excretory organs, by which they are sent entirely out of the body. The blood is a middleman: on the one hand, between the receiving organs (lungs and alimentary canal) and all th rest; and on the other hand, between the excretory organs and all the others. Each part is thus kept in a well-fed \ and healthy state, though it may lie far distant from all , places where new materials first enter the bod}', and from tliose where refuse and deleterious substances are finally passed from it. The Blood, as every one knows, is a red liquid which is very widely distributed over the body, since it flows from any part of the surface when the sJiin is cut through. There are very few portions of the body into which blood is not carried. One of them is the outer layci' of the skin;* hairs and nails, the hard parts of the teeth and most carti- lugcs also contain no blood; these non-vascular tissues are Where does the blood receive nutritive matters? Oxygen? What does it do with them? What part does the blood play in the removal of wastes? State briefly the functions of the blood with reference to the nutritive processes of the body What is blood? How do we know that it is widely distributed? Name parts into which blood does not flow. How are the non-vas- cular tissues nourished ? * The absence of blood in the superficial layer of the skin may be readily shown; take a fine needle threaded with silk; by taking shallow stitches a pat- tern can be easily embroidered on the palm or back of the band without draw ing a drop of blood. 176 THE HUMAN BODY. nourished by liquid which soaks through the walls of blood-vessels in neighboring parts. The Histology of Blood. — Fresh blood is to the unassisted eye a red opaque liquid showing no sign of being made up of different parts; but when examined by a microscope it is Fig. 63 —Blood-corpuscles. A, magnified about 400 diameters. The red corpuscles have arranged themselves in rouleaux; a,a, colorless corpuscles; B, red coi'puscles more magnified and seen in focus; E^ a red corpuscle slightly out of focus. Near the right-hand top corner is a red corpuscle seen in three- quarter face, and at C one seen edgewise. F,G,H,I, white corpuscles highly magnified. seen to consist of a liquid, the blood-plasma, which has floating in it countless multitudes of closely crowded and extremely minute solid bodies known as Mood-corpuscles, The liquid is colorless and watery-looking; the corpuscles are of two kinds, red and colorless. The red corpuscles are Describe the appearance of fresh drawn blood. "What is seen when a drop is examined with a microscope? Describe the blood- plasma Name the kinds of blood-corpuscles. THE RED CORPUSCLES OF OTHER ANIMALS. 177 by far the most iiumerous and give the blood its color; they art so tiny and so plentiful that about five millions of them are contained in one small drop of blood. They are so closely packed that tlie unaided eye cannot see the spaces between them, and so the whole blood appears uniformly red. The Red Corpuscles of Human Blood (Fig. 53) are cir- cular disks a little hollowed out on each face. Seen singly with a microscope each is not red but pale yellow; it is only when they are crowded in a heap that the mass looks red; a drop of blood spread out very thin on glass, or mixed with a tablespoonful of water, is pale yellow and not red. Soon after blood is drawn most of the red corpuscles cohere side by side in rows, something like piles of coin. The Red Corpuscles of other Animals. — The red corpus- cles of most mammalia resemble those of man in being circular biconcave pale yel- low disks; those of camels / and dromedaries, however, are oval. The blood-cor- puscles of dogs are so like those of man in size ^-^^li that they cannot be ^»- S^-Eel corpuscles of the Frog. readily distinguished; but in most cases the size is suffi- ciently different to enable a safe opinion to be formed. This Which kind is most numerous? Give some idea of their num- ber. Why does the blood look uniformly red to the unaided eye? Describe the form of human, red blood-corpuscles? What is the color of one seen by Itself with a microscope? How may we show that blood looks red only when its corpuscles are crowded close together? How do the red corpuscles become arranged soon after blood is drawn? Describe the corpuscles of most mammalia. How do those of camels and dromedaries difEer from the corpuscles of other mam- mals? Why cannot a dog's blood be easily distinguished from human blood? 178 THE HUMAN BOD T. fact has often been used to further the ends of justice in determining whether spots of blood on the clothes of a suspected murderer were really due to the cause assigned by him. The red blood-corpuscles of birds, reptiles, amphi- bians, and fishes cannot be confounded with those of man, since they are oval and contain a nucleus in the centre such as is not found in our red corpuscles. Haemoglobin. — Each red corpuscle is soft and jelly like. Its chief constituent, besides water, is a substance called hmm'-o-glo'-bin, which has the power of combining with oxygen when in a place where that gas is plentiful, and of giving it off again in a region where oxygen is absent or present only in small quantity. Hence as the blood flows through the lungs, which are constantly supplied with fresh air, its corpuscles take up oxygen, which, as it flows on, is carried by them to distant parts of the body where oxygen is deficient, and there given up to the tissues. This oxygen- carrying is the function of the red corpuscles. Arterial and Venous Blood. — Hemoglobin itself is dark purplish-red in color; haemoglobin combined with oxj'gen is bright scarlet red. Accordingly, the blood which flows to the lungs after giving np its oxygen is dark red in color, and that which, having got a fresh supply of oxygen, flows away from the lungs is bright scarlet. The bright red blood is called arterial and the dark red venous. Can the blond of most mammals be certainly distinguished from human blood? Point out a use which has been made of this fact. How do the red corpuscles of birds, reptiles, and fishes differ from human? Describe tlie consistence of a red corpuscle. What are its chief constituents? Point out an important property of haemoglobin. How does this enable it to receive and distribute oxygen? What is the function of the red corpuscles? What is the color of haemoglobin? What of hoemoglobin com- bined with oxygen? What is the color of blood flowing to the lungs? Why? The color of that flowing from the lungs? Why? What is arterial blood? What venous? THE COAGULATION OF BLOOD. 179 The Colorless Blood Corpuscles are a little larger than the red, but much less numerous (about 1 to 300). As their name implies they contain no coloring matter. Each is a cell with a nucleus, and has the wonderful property of being able to cliange its own shape. Watched with a micro- scope the corpuscle may be seen to alter its form slowly (Fig. 55), or even to creep across the glass. These corpus- cles arc thus little, independently moving cells which live in our blood. Thej^MS or "matter" which collects in an abscess is chiefly made up of colorless blood - corpuscles which have bored through the walls of the smallest blood-voFscls. Their movements are very like those of the microscopic animal named amcela, and are accordingly called amceioid. The Coagulation of Blood. — When blood is first drawn from the living body it is perfectly liquid, flowing in any direction as readily as water. This condition is only tem- porary; in a few minutes the blood becomes viscid and sticky, and comes to resemble a thick red syrup; the viscidity be^ comes more and more marked, until, after the lapse of five or six minutes, the whole mass sets into a jelly which ad- heres to the vessel containing it, so that this may be in- verted without any blood whatever being spilled. This stage is known as that of gelatinization, and is alsoTiot per- How do tlie colorless corpuscles d'ffer from the red in size nnd number? Wbat is each ? Wli-it property does it possess? What is seen when one is watched ivith the help of a microscope? What is pus? Why are the movements of the colorless corpuscles called amoeboid? What is the consistency of fresh drawn blood? What change occurs in it within a few miuutcs? Fig. 55.— a white blood- corpuscle, sketched at suc- cessive intervals of a few seconds to illustrate the chanj^es of foi-m due to its amceboid movements. ! 180 TEE HUMAN BODY. manent. In a few minutes the top of the jelly-Uke mass will be seen to be hollowed or "cupped," and in the con- cavity will be found a small quantity of nearly colorless liquid, the Uood-serum. The jelly next shrinks so as to pull itself loose from the sides and bottom of the vessel con- taining it, and as it shrinks it squeezes out more and more serum. Ultimately we get a solid clot, colored red and smaller in size than the vessel in which the blood coagu- lated, but retaining its form, and floating in a quantity of pale yellow serum. The whole series of changes leading to this result is known as the coagulation or clotting of the blood. Cause of Coagulation. — If a drop of fresh drawn blood be spread out and watched with a powerful microscope, it will be seen that its coagulation is due to the separation of very fine solid threads which run in every direction through the plasma and form a close network entangling all the corpuscles. These threads are composed of an albuminous substance known as fibrin. When they first form, the whole drop is much like a sponge soaked full of water (represented by the serum) and having solid bodies (the corpuscles) in its cavities. After the fibrin threads have been formed they begin to shorten; hence the fibrinous network tends to shrink in every direction, and this shrink- age is greater the longer the clotted blood is kept. At first the threads stick too firmly to the bottom and sides of the What is meant by the stage of gelatinization ? Wliat first follows that stage? What next? What is the final result? What is the whole process called? What is seen on watching a drop of fresh drawn blood with the aid of a good microscope? What are the separated threads composed of? To what may we compare a drop of blood in the first formation of the fibrin threads? What do the threads do after their for- mation? WHIPPED BLOOD. jgl vessel to be pulled away, and thus the first sign of the contraction of the fibrin is seen in the cupping of the sur- face of the gelatinized blood where the threads have no solid attachment, and there the contracting mass presses out from its meshes the first drops of serum. Finally the contraction of the fibrin overcomes its adhesion to the vessel, and the clot pulls itself loose on all sides, pressing out more and more serum. The great majority of the red cor- puscles are held back in the meshes of the fibrin. Whipped Blood. — The essential point in coagulation being the formation of fibrin in the plasma, and blood only forming a certain amount of fibrin,* if this be removed as fast as it forms the remaining blood will not clot. The fibrin may be separated by what is known as " whipping" the blood. For this purpose fresh drawn blood is stirred up vigorously with a bunch of twigs or a bundle of wire, and the sticky fibrin threads as they form adhere to these. If the twigs be then withdrawn a quantity of stringy material will be found attached to them. This is at first colored red by adhering blood-corpuscles, but by washing in water pure fibrin may be obtained perfectly white and in the form of highly elastic threads. The blood from which the fibrin has been in this way removed looks just like ordinary blood, but has lost its power of coagulating spontaneously. Uses of Coagulation. — The living circulating blood in the healthy blood-vessels does not clot ', it contains no solid Why is the first sign of their contraction seen in the cupping ? What is the final result of this contraction ? Why is the clot red ? How can we prevent blood from clotting? How is blood whipped ? What do we find on examining the twigs after whipping blood ? How may we get the pure fibrin ? What are its characters ? How does whipped blood differ from ordinary blood ? * Fibrin is formed from fibrinogen^ a soluble albumen existing in blood-plasma. 182 THE HUMAN BODY. fibrin, but tliis forms in it, sooner or later, wlien the blood gets in any way out of the vessels or if tlic lining of these is injured. By the clotting the mouths of the small vessels opened in a wound are clogged up, and the bleeding, which "Would otherwise go on indefinitely, is stopped. So too, when a surgeon ties an artery, the tight ligatuie crushes or tears its delicate inner surface, and the blood clots where this IS irijurcd. The clot becomes more and more solid, and by the time the ligature is removed has formed a firm plug in the cut end of the artery, which prevents bleeding. Blood Compared with Water. — " Leaving aside its color, we all know that blood is thicker than water; this is true not only in a metaphorical but in a literal sense. In the first place, bulk for bulk, blood is heavier than water; ten toaspoonfuls of blood weigh as much as ten and a half tca- spooufuls of water. Secondly, blood contains in it solid corpuscles and when drawn from the body forms spon- taneously a solid clot, while pure water has no solid bodies floating in it, and can only be made solid by freezing. Thirdly, the blood liquid itself, quite apart from the cor- puscles, is thicker than pure water, because it conlains a great many things dissolved in it; things wliich are of great importance, because they are the foods which the blood is carrying to, and the wastes which it is carrying from, the various organs of the body." The Composition of Blood-Serum. — About one half of I the bulk of fresh blood is corpuscles and the other half When does blood clot? Illustrate the uses of the coagulating propel \y of blood. Conipuve blood with water, (1) as to the weight of equal bulks of the two (specific gravity); (2) ns to its microscopic structure; (3) as to its tendency to solidify ; (4) as to I lie composition of its plasma. Why are the things dissolved in the plasma of great importance? What is the relative proportion of corpuscles rud plasma in blood? TSE COMPOSITION OF BLOOD-SERUM. 183 plasma. What the plasma contains we may learn by ex- amining blood-sernm, which is plasma minus fibrinogen. Blood-serum is very different from water; if we keep on boiling pure water in a saucepan it will all go off in steam and leave nothing behind, but if we try to boil serum we find that we cannot do it; before it gets as hot as boiling water it sets into a stiff, solid mass just like the white of a hard-boiled egg. In fact the serum contains dissolved in it two albumens very like that in the white of an egg, and coagulated in a similar way by boiling. About engirt and a J half pounds of albuminous substances exist in ojie hundred j pounds of blood. Blood-serum also contains considerable quantities of oily and fatty matters, a little sugar, some common salt and carbonate of soda, and small quantities of very many other things, chiefly waste products from the various tissues. VN"ine tenths of the blood-plasma is water. ^' Composition of the Red Corpuscles. — In the fresh moist state these contain a little more than half their weight of water. Nine-tenths of their solid part is haemoglobin ; \they also contain phosphorus and i ron a nd potassium. The Blood Gases. — Ordinary fresh or salt water has a good deal of air dissolved in it, which fishes breathe. Blood also contains a quantity of gases which it gives off when exposed to a vacuum, about sixty p ints of gas to a hundre d ,-;' What may we learn by examining blood-serum? What is blood- serum? What happens when we try to boil blood-serum? Why does it coagulate in heating? What proportion of albumen exists in blood? What things are found in the blood-serum in addition to water? How much water is there in ten pints of blood-plasma? How much solids do ihe red corpuscles contain? What propor- tion of these is haemoglobin? Name other things found in the red corpuscles. What do fishes breathe? What does blood give off when placed in a vacuum? How many pints ot gas for each ten pints of blood ? 184 THE HUMAN BODT. pints of blood. In blood going to the lungs the main gas is carbon dioxide (or carbonic acid), which is a waste product of all the organs of the body. In blood coming from' the lungs the most abundant gas is oxygen. Summary. — "Blood, then, is a very wonderful fluid: wonderful for being made up of colored corpuscles and colorless fluid, wonderful for its fibrin and power of clot- ting, wonderful for the many substances, for the pi'oteids, for the ashes or minerals, for the rest of the things which are locked up in the corpuscles and in the serum. " But you will not wonder at it when you come to see that the blood is the great circulating mai-ket of the body, in which all the things that are wanted by all parts, by the muscles, by the brain, by the skin, by the lungs, liver, and kidneys, are bought and sold. What the -muscle wants it buys from the blood; what it has done with it sells back to the blood; and so with every other organ and part. As long as life lasts this buying and selling is forever going on, and this is why the blood is forever on the move, sweeping restlessly from place to place, bringing to each part the things it wants, and carrying away Ihose with which it has done. When the blood ceases to move, the market is blocked, the buying and selling cease, and all the organs die, starved for tlie lack of the things which they want, choked by the abundance of things for which they have no longer any need." — Foster. Hygienic Remarks. — The blood flowing from any organ will have lost or gained, or gained some things and lost What is the most abundant gas in blood going to the lungs? What in tliat leaving (hose organs? Why may blood be justly called a wonderful fluid? Wliy is its complexity not astonishing? Why is the blood always kept in move- ment during life? What happens when the blood ceases to move? ETOIENIG REMARKS. 185 others, when compared with the blood which entered it. But the losses and gains in particular parts of the bodj are in such small proportion as, with the exception of the blood gases, to elude analysis for the most part; and, the blood from all parts being mixed up in the heart, they balance one another and produce a tolerably constant average. In , health, however, the red corpuscles are present in greater ( proportion to the plasma after a meal than before it. 1 Healthy sleep in proper amount also increases the proportion of red corpuscles, and want of it diminishesjtheir number, as may be recognized in the pallid aspect of a person who has lost several night's rest. Fresh air and plenty of it favors their increase. The proportion of these corpuscles has a great importance, since they serve to carry oxygen, which is necessary for the performance of its functions, all over ', the body. Anwmia is a diseased condition churacterized , by pallor due to deficiency of red blood-corpuscles, and ac- \companied by languor and listlessness. It is not unfrequent in young girls on the verge of womanhood, and in persons overworked and confined within doors. In such cases the \ best remedies are open-air exercise and good food, though imedicincs containing iron are often of great use. The Quantity of Blood in the Body. — The total weight of the blood is about one-thirteenth of that of the whole What would we find on comparing the blood leaving an organ with that which entered it? What losses and gains are most easily detected? How is it that the blood maintains a tolerably uniform average composition ? How does a meal affect the proportion of red corpuscles ? How does sleep ? Illustrate. What is the influence of plenty of fresh air ? Why is the proportion of blood-corpuscles im- portant ? What is ansemia ? What class of persons is apt to suffer from it ? What are the best remedi'js for it ? What is the proportion of the weight of blood to that of the whole body? J 86 TEE HUMAN BODY. body; a man of average size contains about twelve pounds of blood. The Lymph.— The blood lies every where in closed tubes, and consequently does not come into direct contact with any of the cells which make up the body, except those which float in it and those which line the interior of the blood- vessels. At two parts of its course, however, the vessels through which it p.asses have extremely thin walls, and through the walls of these capillaries liquid transudes and bathes the various tissues. The transuded liquid is called lymph j the blood makes lymph, and the lymph dii-ectly nourishes all the tis- sues except those mentioned above, with wliich the blood itself comes in contact. Dialysis. — "When two specimens of water BR—Adi containing dilTercnt matters in solution are s.ra"i «* ^ diaiy- o smg apparatus, separated from one another by a moist animal yqu^s""! ^^l membrane, an interchange of material will ^ moiS^^'^ni^ take place under certain conditions. If A be •°™^™°«- a vessel (Pig. 5G), completely divided vertically by such a membrane, and a solution of common salt in water be placed on the side b, and a solution of sugar in water on the side c, it will be found after a time that some salt has got into c and some sugar into b, although there are no visible pores in the partition. Such an interchange is said to be due to dialysis or osmosis, and if the process were How much blood is there in an average sized man? Wlij' does tlie blood not directly b.itlie most of tlie tissues? "What cells come in contact witli it? Wliat are tlie capillaries? What is lymph? What is the nutritive function of lymph? What liappcns when watery solutions' of different substances are separated by a moist animal menibi'ane? Illustrate. What is such an interchange called? What would be the result at the end of some hours? THE RENEWAL OF THE LTMPR. 187 allowed to go on for some hours the same proportions of salt and sugar would be found in the solutions on each side of the dividing membrane. The Renewal of the Lymph, — Osmotic processes play a great part in tlie nutritive processes of the body. The lymph present in any organ gives up things to the cells there and gets things from them; and so, although it may have originally been tolerably like the liquid part or plasma of the blood, it soon acquires a difEerent chemical composi- tion. Dialysis then commences between the lymph out- side and the blood inside the capillaries, and the latter gives up to the lymph new materials in place of those which it has lost, and takes from it the waste products which it has received from the tissues. When this blood, thus al- terad by exchanges with the lymph, gets again to the stom- ach and intestines, having lost some food materials, it is poorer in these than the richly supplied lymph around their cells, and takes up a supply by dialysis from it. When it reaches the excretory organs it has previously picked up a quantity of waste matters, and loses these by dialysis to the lymph there present, which is specially poor in such mat- ters, since the excretory organs constantly deprive it of them. In consequence of the different wants and wastes of various cells, and of the same cells at difEerent times, the lymph must vary considerably m composition in various organs of the body, and the blood flowing through them will in consequence get and lose different things in differ- How does the lymph in an organ come to differ chemically from the blood plasma which supplied it? What results? What happens when the blood thus changed reaches stomach or intestine ? What wlien it reaches excretory organs ? Why does the lymph vary in composition in difEerent parts of the body ? How does this affect the blood ? 188 THE HUMAN BODY. ent places. But, receiving in its passage through one re- gion what it loses in another, its average composition is kept pretty constant; and, through interchange with it, the average composition of the lymph also. The Lymphatic Vessels or Absorbents. — The blood, on the whole, loses more liquid to the lymph through the cap- illary walls than it receives back at the same time. This de- pends mainly on the fact that the pressure on the blood in- side the vessels is greater than that on the lymph outside, and so a certain amount of filtration of liquid from within out occurs through the vascular wall, in addition to the dialysis. The excess is collected from the various organs of the body into a set of lymphatic vessels, which carry it directly back into some of the larger blood-vessels near where these empty into the heart; and as fast as this on- ward flow of the lymph occurs under pressure from behind, it is renewed in the different organs, fresh liquid filtering through the capillaries to take its place as fast as the old is drained off. Since the lymphatic vessels may be said to take up or absorb the excess of liquid drained from the blood and also the effete matters of the various organs, they are frequently called the absorbents. Lacteals we have already learned to be only another name for the absorbents of the small intestine (p. 147). How is the average composition of tlie blood maintained? How that of the lympli? Give another name for the lymphatic vessels. Does the blood on the whole gain or lose liquid to the lymph as it flows through the cap- illaries 1 Explain why. What becomes ot the excesr of liquid drained off from the blood 1 Where do tl>e lymphatic vessels convey it? What produces the onwiird flow of lymph? How is the lymph thus drained off replaced? Wliy are the lymplmtics called absorbents' \Vbat is meant by tlip lacteals' HiaXOLOGT AND GHEMISTRY OF LYMPH. 189 Histology of Lymph. — Pure lymph is a colorless, watery looking liquid; examined with a microscope it is seen to contain numerous pale corpuscles exactly like those of the blood. It contains none of the red corpuscles. Chemistry of Lymph. —Lymph is not quite so heavy as blood, though heavier than water. It may be described as blood minus its red corpuscles and considerably diluted, but of course in various parts of the body it will contain minute quantities of substances derived from neighboring tissues. Summary. — To sum up: the blood and lymph pro- vide a liquid in which the tissues of the body live; the lymph is derived from the blood, and affords the immedi- ate nourishment of the great majority of the living cells of the body; the excess of it is finally returned to the blood, which indirectly nourishes the cells by keeping up the stock of lymph. The lymph itself moves but slowly, but it is constantly renovated by interchanges with the blood, which is kept in rapid movement by the heart, and which, besides containing a store of new food-matters for the lym ph, absorbs the wastes which the various cells nave poured into the latter. What does lymph look like? What is seen when it i," examined with a microscope? How does lymph differ in density from blood and from water? How may it be briefly described? Wliat docs it contain in various regions of the body? What do the blood and lymph provide? Whence Is the lymph de- rived? Wliat does it afford? Wliat becomes of its excess? How does the blood play a part in nourishing the cells of the body? Which moves faster, lymph or blood? How is the lymph renovated? What keeps the blood in motion? What does tlie blood do b?3ide3 renewing the food-matters in the lymph? 190 THE HUMAN BODY, APPENDIX TO CHAPTER XIII. Many of the main facts pertaining to the structure and composi- tion of blood may be easily demonstrated as follows: 1. Kill a frog witli etlier (note, p. 68); cut off its liead, and collect on a piece of glass a drop of the blood which flows out. Spread out tlie drop so that it forms a thin layer. Hold the glass up against the light, and examine the blood with a hand lens magnifying four orfive diameters. Tlie corpuscles will be readily seen floating in the plasma. 3. Wind tightly a piece of twine around the last joint of a linger; then, taking a needle, prick the skin near the root of the nail. A large drop of blood will exude. Spread it out on a piece of glass and examine, as described above for frog's blood. The corpuscles will be seen floating in the blood liquid, but not so easily as in frog's blood, since those of man are considerably smaller. [3. If a compound microscope is available the form, size, and color of human and frog red blood-corpuscles can be demonstrated; also the tendency of the human to aggregate in rolls, and the color, form, size, and relative number of the colorless corpuscles. As any one possessing a compound microscope is sure to know how to mount a specimen of blood for examination with it, or, if not, to have at hand some treatise on the use of the microscope giving the necessary information, details need not be given here.] 4. Obtaining a large drop of human blood as above described (2) — note: a, that as it flows from the wound it is perfectly liquid; h, that it is red and very opaque; c, spread it out very thin on the glass: note that it then looks yellow when held over a sheet of white paper; d, mix uliiionary artery ; this divides into a branch for each lung ; each branch splits up into minute arteries in its own lung, and these end in the pulmonary capillaries. Prom tlie pulmonary capillaries the blood of each lung is collected into two jndmonary veins, and the four pulmonary veins open into the left auricle. Summary.— One artery, the aorta, arises from the left ventricle. The blood carried out by the aorta comes back by the upper and lower venae cavse to the right auricle; this blood then goes to the right ventricle and is sent thence through the pulmonary artery, which splits up into branches for the lungs. The blood, carried out by the pulmonary artery from the i-ight ventricle of the heart, returns to the left auricle by four pulmonary veins, two from each lung; and then enters the left ventricle and begins its flow again through the aorta. How the Heart is Nourished. — The heart is a very hard- worked organ, and needs an abundant supply of nourish- ment. Its walls are much too thick to allow this to soak in sufficient abundance all through them, from the blood flowing through its cavities; accordingly they are perme- ated by a very close network of capillary blood vessels. These are supplied by the right and left coronary arteries Where do the vense cavse carry it? Where does it pass from the right auricle? What vessel arises from the right ventricle? Into what does the pulmonary artery divide? What happens to each branch? How do the branches finally end? Into what is the blood which flows through the puin-onary capillaries collected? How many pulmonary veins are there? Where do they eurit State briefly the course of the blood flow 200 TBE HUMAN BODY. (Pig, 58), whicli are the two very first branches of the aorta, and the blood from them is collected by the coronary veins and poured by them directly into tlie right auricle. Sp Fig. 59. — The '.eft ventricle and the commencement of the aorta laid open. Mpnit MpL tlie papillary muscles. From their upper ends are seen the chordae tendineffl proceeding to the edges of the flaps of the mitral valve. The opening into the auricle lies between these flaps. At the beginning of the aorta are seen its thie ■ ponch-Jike semilunar valves. What are the coronary arteries J The coronary veins ? AUBIOULO-VENTBICULAB VALVES. 201 The Auriculo-Ventricnlar Valves. — Between each auricle of the heart and the ventricle of the same side are found valyes which allow blood to pass from the auricle to the yentricle, but prevent any flow in the opposite direction. These valves are known as the tricuspid and mitral valves. The mitral valve (Fig. 59) consists of two flaps fixed bj their bases to the margins of the opening between the left auricle and the left ventricle ; their edges hang down into the ventricle when the heart is empty. These edges are not free, but have fixed to them a number of stout connective- tissue cords, the chordm tendinece, which are fixed below to muscular elevations, the papillary muscles, Mpvi and Mpl, on the interior of the ventricle. The cords are long enough to let the valve flaps rise into a horizontal position and so to close the opening between auricle and ventricle, which lies behind the opened aorta, 8p, represented in the figure. The tricuspid valve is like the mitral, but with three flaps instead of two. Semilunar Valves. — These are six in number ; three at \ the mouth of the aorta. Fig. 59, and three, quite like them, at the mouth of the pulmonary artery. Each is a strong crescentic pouch fixed by its more curved border, and with its free edge turned away from the heart. When the valves are in action their free edges meet across the vessel and prevent blood from flowing back into the ventricle. The Course of the Main Arteries of the Body (Fig. 60). — The aorta after leaving the left ventricle makes an arch What is found between each auricle and ventricle? What are they called? Describe the miti-al valve. Where is it placed? What are the chordse tendinese? The papillary muscles? How far will the cords allow the valve flaps to rise? How does the tricuspid valve differ from the mitral? How many semilunar valves are there? Where are they placed' Pescj-jbe them. What is theii use? 202 THB HUMAN BODY. {aA.) with its convexity towards the head. From the heart end of this arch arise the coronary arteries, which carry blood into the walls of the heart. From the convexity of the arch spring the three large trunks : the innomirpate artery ; tlie left common carotid artery (cs) ; and the left subclavian artery {ssi). The innominate soon divides into the right subclavian (sd), and the riglit common carotid (od) Each common carotid runs up the neck on its own side, and divides into branches for the neck, face, scalp, and brain. Each subclavian continues across the arm-pit as the axil- lary artery {a.x), and then runs down to near the elbow as the brachial artery (b). Just above the elbow it divides into the radial and ulnar arteries (r, u,) which supply the fore-arm, and end in small brandies for the hand Beyond its arch the aorta runs back close to the spinal column as the thoracic aoria (A/), which gives off brandies to the walls of the chest and some organs in that cavity. The vessel then passes through the diaphragm, and con- tinues as the abdominal aorta (Aab) to the lower part of the abdomen. The main branches of the abdominal aorta are: (1) the cmliac axis, which divides into branches for the stomach, liver, and spleen; (2) the upper and lower mesen- teric arteries, which supply the intestines with blood; (3) the renal arteries (k), which carry blood to the kidneys. What is meant by the aortic arch? What are its first branches? What branches are given off fmm the vipper side of the aortic arch? Into what vessels does tlie innominate artery divide? To what parts do the common carotid arteries carry l)lood? In wliat does the suliclavian artery terminate? What vessels supply the fore-arm with blood? How do they end? What is the thoracic aorta? The abdominal aorta? Name the chief branches of the abdom- inal aorta. What organs are supplied by the coeliac axis? The mesenteric arteries? The renal arteries? Fig. 60.— The main arteries of the body. Crd and Crs, right and left coronary arteries of the heart, cut short near their origin; Aa, and aA, aortic arch; Ati thoracic aorta; Aab^ abdominal aorta; K^ reual artery; 8d. right, and Ssi, left subclavian; Cd, right, and Cs, left carotid; Ax, axillary artery; B, brachial artery; U, ulnar artery; B, radial artery; Ai, common iliac artery; /. external iliac artery; C, femoral artery; Po, popliteal artery; Ta, anterior, and Tp, pos- terior tibial artery; Pe, peroneal artery. 204 TEB HUMAN BODY. The two trunks into which the posterior end of the ab- dominal aorta divides {Ai) are named the common iliac arteries ; each gives off some branches in the pelvis, and then continues along the thigh as the femoral artery (C); this runs to the knee-joint, behind which it is called the popliteal artery (Pa). The popliteal artery divides into the peroneal {Fe) and tibial (Ta, Tp) arteries, which sup- ply the lower leg and the foot. The Froperties of the Arteries. — Two fundamental facts must be borne in mind in connection with the arteries : First, that they are highly elastic and extensible ; a large artery is, in this respect, much like a piece of rubber tub- ing of the same size. Secmd, the arteries have rings of muscular tissue in their walls, and when the muscle con- tracts the bore of tlie artery (and consequently the amount of blood which flows through it) is diminished. When the muscle relaxes, the bore of the artery is increased, and more blood passes along it to the capillaries in which it ends. The Capillaries. — The smallest arteries pass into the capillaries, which have very thin walls, and form very close networks in nearly all parts of the body ; their immense number compensating for their smaller size. The average diameter of a capillary vessel is so small that only two or three blood-coi-puscles can pass through it abreast, and in many parts the capillaries lie so close together that a pin's lato -what vessels doRS the abdominal aorta ultimately divide? What is the femoral artery derived from? To wliat point does it run? What is the popliteal artery? Into what branches does the popliteal artery divide? What parts do they supply with blood? What main facts are to be borne in mind in connection with the arteries? How is the quantity of blood which an artery will let pass regulated? What is found when the arteries are followed to the ends of their smallest branches? Describe the structure, arrangement and size of the capillaries. THE VEINS. 205 point could not be inserted between two of them, as, for instance, in the deep layers of the skin which can hardly be pricked anywhere with a needle without drawing blood. It is while flowing in tliese delicate tubes that the blood does its nutritive work, the arteries being merely supply- tubes for the capillaries, through whose delicate walls liquid containing nourishment exudes from the blood to bathe the various tissues. Imagine a piece of the finest lace, with all its threads consisting of hollow tubes, and diminished twenty times in size, and you will have some idea of the capillaries. The Veins. — The first veins arise from the capillary net- works in various organs, and like the last arteries are very small. They soon increase in size by union, and so form larger and larger trunks alongside the main artery of the part, but there are many more largo veins Just beneath the skin than there are large arteries. This is especially the case in the limbs, the main veins of which are superficial, and can in many persons be seen as faint blue lines through the skin. Why the large Arteries usually lie deep. — The heart pumps the blood with great force into the arteries, and if an artery is cut very rapid and dangerous bleeding occurs; the veins, if cut, do not bleed nearly so violently as an artery of the same size. Hence it is less dangerous to have a large vein than a large artery close under the skin. Point out a fact illustr.iting the closeness of (he capillaries in many parts of the body. What does the blood do as it flows through the capillaries 1 Where do the first veins arise ? What is their size ? How do they increase in size ? Where do the larger veins lie? In what parts of the body do we especially find large veins close beneath the skin? Why are the large arteries, as a rule, placed deeper than veins of corresponding size ? 206 THE HUMAN BODY The Valves of the Veins. — Except the pulmonary artery and the aorta, which have the semilunar valves, arteries have no valves. Most veins, on the contrary, contain many valves formed by pouches of their lining, which resemble in form the semilunar valves of the aorta and the pulmonary artery. ^'?« ^•'Z^ small portion of the capillary network as seen in tlie fros's web wlien magnifled about 35 diameters, a a small artery feeding the capillaries: v.v small vems carrying blood back from the latter. , c/, c/, =»uai. What arteries have valves? Where are these valves placed? How do veins differ from arteries in regard to the presence of valves m them? rAzrjus OF tee veins. 207 but are turned in the opposite direction, having the edge nearest the heart free and the other fixed. These valves permit blood to flow only towards the heart, for a current in that direction, as in the upper diagram, Pig. 62, presses the valve close against the side of the vessel, and meets with no obstruction from it. Sliould any back-flow be attempted, however, the current closes up the valve and bars its own passage, as indicated in the lower figure. These valves are most numerous in superficial veins and those of muscular parts. Usually _^ the vein is a little dilated opjiosite a valve, and hence in parts where the valves are numerous gets a knotted look. On tying a cord tightly round the fore-arm, so as , , LT^ n • ■ L V. JL Fig. 62— Diagram to lllus- to stop the flow in its subcutaneous trate the mode of action of - ,, . Ti , , • the valves of the veins. 0, the veins and cause their dilatation, capillary, H, the heart end of the points at which valves are placed can be recognized by their swollen appearance. The valves are most frequently found where two veins communi- cate. The Course of the Blood. — From what has been said it is clear that the movement of the blood is a circulation. Starting from any one chamber of the heart it will in time return to it; but to do this it must pass through at least two sets of capillaries; one of these is connected with the In what direction do the valves of tlie veins allow the blood to pass? Make a diagram illustrating the action of the valves. In what veins are the valves most numerous? "Why does a vein with many valves appear knotted? How may we see the dilatations of the veins opposite the valves? Where are the valves of the veins most frequently placed? If we followed the blood course steadily from one chamber of the heart what would we find in time? Through what must blood pass before returning to the chamber of the heart which it leaves? 208 THE HUMAN BODY. aorta, and the other with the pulmonary artery, and in its circuit the blood returns to t'le hea-t twice. Leaving the left side it returns to the right, and leaving the right it returns to the left; and there is no road for it from one side of the heart to the other except through a capillary network. Moreover, it always leaves from a ventricle through an artery, and returns to an auricle through a vein. There is then really only one circulation; but it is not uncommon to speak of two, the flow from the left side ol the heart to the right tlirough most of the body being called the systemic or greater circulation, and from the right to the left through the lungs the. jiulinonary or lesser circulation. But since, after completing either of these alone, the blood is not again at the point from which it started, but is separated frcm it by the septum of the heart, neither is a "circulation" in the proper sense of the word, for a circulation implies that any object at the end of its course is again exactly where it was at the com- mencement. The Portal Circulation. — A certain portion of the blood which leaves the left ventricle of the heart through the aorta has to pass through three sets of capillaries before it can again return there. This is the portion which goes through the stomach and intestines. After traversing the capillaries of those organs it is collected into the portal Through wliat does blood always leave the heart? To what does it return? How many circulationH are there really? What is meant by the systemic circulation? What by the pulmonary? Why is neither a true "circulation" in the pro)3er sense of the word? How many sets of capillaries does some blood pass through in a complete circulation? What portion of the blood is it? What vessel does it enter after traversing the capillaries of the stomach and in- testiues? THE PORTAL OIItOULATION. 209 vein, which enters the liver, and breaking up there into finer and finer branches like an artery, ends in the capillaries of that organ, forming the second set which this blood passes through on its course. From these it is collected by the Jiepatio veins, which pour it into the inferior vena cava which car- ries it to the right auricle, so that it has still to pass through the pulmonary capillaries to get back to the left side of the heart. The portal vein is the only one in the human body which thus like an artery feeds a capillary network, and the flow from the stomach and intestines through the liver to the inferior vena cava, is often spoken of as the portal circulation. Diagram of the Circulation. — Since the two halves of the heart, although placed in proximity in the body, are actually completely separated from one another by an impervious partition, we may con- veniently represent the course of the blood as in the ac- companying diagram (Fig. 63), in which the right and Fig. 63 Diagram of the blood vascular system, show- ing that it forms a single closed circuit with two pumps in it, represented by the right and left halves of the heart, which are separated in the diagram, ra and rv, right auri- cle and ventricle; la and Zv, left auricle and ventricle; ao, aorta; sc, systemic capilla- ries; vc, venae cav£e; pa, pul- monary artery ; pc,pulmonary capillaries; pu, puhnonary veins. Where does this vein carry it? In what does it end? Into what vessels is the blood of the capillaries of the liver collected? Where do they convey it? What chamber of the heart does it first reach? Through what must it pass to get back to the left ventricle? How does the portal vein differ from all others in the body? What is meant by the portal circulation? 210 THE HUMAN BODY. loft halves of the lieart are represented at different points in the vascular system. Such a diagram makes it clear that the heart is really two pumps working side by side, and each engaged in forcing blood to the other. Starting from the left auricle, la, and following the flow, we trace it through the left ventricle, and along the branches of the aorta into the systemic capillaries, sc; thence it passes back through the systemic veins, vc. Beaching the right auricle, ra, it is sent into the right ventricle, rv, and thence through the pulmonary artery, pa, to the lung capillaries, pc, from which the pulmonary veins, pv, carry it to the left auricle, which drives it into the left ventricle, Iv, and this again into the aorta. Arterial and Venous Blood. — The blood when flowing in the pulmonary capillaries gives up carbon dioxide (a waste product which it has gathered in its flow through the other organs) to the air, and receives oxygen from it; since its coloring matter (hsemoglobin) forms a scarlet compound with oxygen, the blood which flows to the left auricle through the pulmonary veins is of a blight red color. This color it maintains until it reaches the sys- temic capillaries, but in these it loses much oxygen to the surrounding tissues, and gains much carbon dioxide from them. But the blood-coloring mutter which has lost its oxygen has a dark purple-black color, and since this unoxidized or " reduced " haemoglobin is now in excess, the Why are we iustificd in diagrammatically representing the heart as made of two sepsiriited pans? Starting from the left am-icle, describe the course of the blood until it returns there. What does the blood give up in the pulmonary capillaries? What does it receive? Why is it bright red when it enters the left auricle? How far in its course does it keep this color? What gases does the blood galu and lose in the systemic capillaries? APPENDIX. 211 blood letiirns to the right auricle of the heart by the vensB cavse of a dark purple-red color. This color it keeps until it reaches the lungs, where the reduced hemo- globin becomes again oxidized. The bright red blood, rich in oxygen and poor in carbon dioxide, is known as "arterial blood," and the dark red as "venous blood;" and it must be borne in mind that the terms haye this peculiar technical meaning, and that the pulmonary veins contain arterial blood, and the pulmonary arteries contain venous blood. The change from arterial to venous takes place in the systemic capillaries, and from venous to arterial in the pulmonary capillaries. What color is the blood when returned to the right auricle? "Why? What is meant by arterial blood? By venous? What veins contain arterial blood? What arteries venous? Where does the cliange from arterial to venous occur? Where that i'nim venous to arterial? APPENDIX TO CHAPTER XTV. 1. In the following directions " dorsal " means the side of the heart naturally turned towards the vertebral column, "ventral" the side next the breast-bone; "right" and "left" refer to the proper rijilit and left of the heart when in its natural position in the body; " an- terior" means more towards the head in the natural position of the parts; and "posterior" the part turned away from the head. 3. Get your butcher to obtain for you a sheep's heart, not cut out of the bag (pericardium), and slill connected with the lungs. Impress upon him that no hole must be punctured in the heart, such as is usually made when a slaughtered sheep is cut up for marlset. 3. Place the heart and lungs on their dorsal sides on a table in their normal relative positions, and with the windpipe directed away from you. Note the loose bag (pericardium) in which the heart lies, and the piece of midrifE {diaphragm) which usually is found attached to its posterior end. t. Carefully dissecting away adherent fat, etc., trace the vessels 212 THE HUMAN BODY. below named until they enter the pericardium. Be very careful not lo cut the veins, which, being thin, collapse when empty, and may be easily overlooked until injured. As each vein is found stuflE it with raw cotton, which makes its dissection much easier. a. The vena cava inferior : find it on the under (iibdominal) side of the diapliragm ; thence follow it until it enters the pericardium, about three Inches further up; to follow it in this part of its course, turn the right lung towards your left and the heart towards your right. The vein just below the diaphragm may be seen to receive several large vessels, the hepatic veins. As it passes through the midriff, two veins from that organ enter it. Between diaphragm iind pericardium the inferior cava receives no brancli; but, lying on its left side, will be seen the lower end of the riglit phrenic nerve, ending below in several branches to the diaphragm. b. Superior vena cava : seek its lower end, entering the pericardium about one inch above the entry of the inferior cava; thence trace it up to the point where it has been cut across; stuff and clean it. c. Between the ends of the two venae cavse will be seen the two right pulmonary veins, proceeding from the lung and entering the pericardium; clean and stuff them. 5. Turn the right lung and the heart back into their natural posi- tions; clear away the loose fat in front of the pericardium, and seek and clean the following vessels in the mass of tissue lying anterior to the heart, and on the ventral side of the windpipe. a. The aorla : immediately on leaving the pericardium this vessel gives off a large brancli; it then arches back and runs down behind the heart and lungs, giving off several branches on its way. b. Tlie pulmonary artery : this will be found imbedded in fat on the dorsal side of the aorta. After a course, outside the pericardium, of about an inch, it ends by dividing into two large branches (right and left pulmonary arteries), which subdivide into smaller vessels as they enter the lungs. c. Observe the thickness and firmness of the arterial walls as compared with those of the veins; they stand out without being stuffed. 6. Notice, on the ventral side of the left pulmonary artery, the left pulmonary veins passing from the lung into the pericardium. 7. Up to this point the dissection may be made before the meeting of the class; on the preparation demonstrate the anatomical facts above noted and tlien proceed as follows: 8. Slit open the pericardiac bag, and note its smooth, moist, glis- tening inner surface, and the similar character of the outer surface of the heart. Cut away the pericardium carefully from the entrances of the various vessels which you have aiieady traced to it. As this APPENDIX. 213 is done, you will notice that inside the pericardium the pulmonary- artery lies on tlie ventral side of the aorta. 9. Note the general form of the heart— that of a cone with its apex turned towards the diaphragm. Very carefully dissect out the entry of the pulmonary veins into the heart. It will probably seem as if the right pulmonary veins and the inferior cava opened into the same portion of the organ, but it will be found subsequently (13. a.) that such is not really the case. Note on the exterior of the organ the follow- ing points: a. Its upper flabby auricular portion into which the veins open, and its denser lower ventricular part. J. Running around the top of the ventricles is a band of fat, an offshoot of which runs obliquely down the front of the heart, passing to the right of its apex, and indicating externally the position of the internal partition or upturn whicli separates the right ventricle, which does not reach the apex of the heart, from the left, which does. c. Note the fleshy " auricular appendages" — one (Jeff) appearing below the pulraonar}' artery; the other (right), between the aorta and superior cava. 10. Dissect away very carefully the collection of fat around the origins of the great arterial trunks and that around the base of the ventricles. In the fat will be found — a. A coronary artery arising from the aorta close to the heart, opposite the right border of the pulmonary artery; it gives off a branch which runs in the groove between right auricle and ventricle, and then nins down the dorsal side of the heart on the ventricles. h. The other coronary artery, considerably larger, arises from the aorta dorsal to the pulmonary artery; its main branch runs along the ventral edge of the ventricular septum. c. Tlie coronary veins and sinus: small coronary veins will be seen accompanying tlie arteries; for the coronary sinus see 11. c. 11. Open the right ventricle by passing the blade of a scalpel through the heart about an inch from the upper border of the ventri- cle, and ou the right of the band of fat marking externally the limits of the ventricles, and noted above (9. b.), and then cut down towards the apex, keeping on the right of this line; cut off the pulmonary artery about an inch above its origin from the heart, and open the right auricle by cutting a bit out of its wall, to the left of the entrances of the venae cavoe. On raising up by its point the wedge- shaped flap cut from the wall of the ventricle, the cavity of the latter will be exposed. a. Pass the handle of a scalpel from the ventricle into the auricle; 214 THE HUMAN BODT. and also from the ventricle into the pulmonary artery, and make out thoroughly the relations of these openings. h. Slit open the auricular appendage ; note the fleshy projections (columns carnecB) on its walls, and the smoothness of tlie rest of the interior of the auricle. Observe the apertures of the venw cava, and note that the pulmonary veins do not open into this auricle. c. Behind or below the entrance of the inferior cava, note the entrance of the coronary sinus; pass a probe through the aperture along the sinus and slit it open ; notice the muscular layer covering it in. 13. Raise up by its apex the flap cut out of the ventricular wall, and if necessary prolong the cuts more towards the base of the ven- tricle until the divisions of the tricuspid iialve come into view. it. Note the columnae carneae on the wall of the ventricle, and the muscular cord (not found in the human heart) stretching across its cavity. Also the prolongation of the ventricular cavity towards the aperture of the pulmonary artery. b. Cut away the right auricle, and examine carefully the tricuspid valve, composed of three membranous flexible flaps, thinning away towards their free edges; proceeding from near tbese edges are strong tendinous cords {diordce tendinem), which are attached at their other ends to muscular elevations {papillary muscles) of the wall of the ventricle. c. Slit up the right ventricle until the origin of the pulmonary artery comes into view. Looking carefully for the flaps of the semi- lunar valves, prolong your cut between two of them so as to open the bit of pulmonary artery still attached to the heart. Spread out the artery and examine the valves. d. Each flap makes, with the wall of the artery, a pouch, opposite which the arterial wall is slightly dilated. The free edge of the valve is turned from the heart, and has in its middle a little nodule (corpus Arantii). 13. Open the left ventricle in a manner similar to that employed for the right. Then open the left auricle by cutting a bit out of its wall above the appendage. Cut the aorta off about half an inch above its origin from the heart. The aperture between left auricle and left ventricle can now be examined ; also the passage from the ventricle into the aorta, and the entry of the pulmonary veins into the auricle ; and the septum between the auricles and that between the ventricles. a. Pass the handle of a scalpel from the ventricle into the auricle; another from the ventricle into the aorta ; and pass also probes into the points of entrance of the pulmonary veins. Observe that no other veins open into this auricle. APPENDIX. 215 5. Slit open the auricular appendage; note the fleshy projections {columnm carnem) on its interior, and the general smoothness of the rest of the inner wall of the auricle. Notice the columnm carnem over the inner surface of the ventricular vpall, also the considerable thickness of the latter, as compared witli that of the right ventricle or of either of the auricles. 6. Carefully raise the wedge-shaped flap of the left ventricle, and cut on towards tlie base of the heart, until the valve (mitrat) between auricle and ventricle is brought into view; one of its two flaps will be seen to lie between the auriculo-ventricular opening and the origin of the aorta. Examine in these flaps their texture, the chordae tendineaB, the columnae carnese, etc., as in the case of tlie right side of the heart (13). d. Examine the semilunar valves at the exit of the aorta; tlien cutting up carefully between two of them, examine the bit of aorta still left attached to the heart, and note tlie valves more carefully as described in 13. d. Note the origins of the coronary arteries in two of the three dilatations {sinuses of Valsalva) of the aortic wall above the semilunar flaps. 14. Examine a piece of aorta. Note that when empty it does not collapse; the thickness of its wall; its extensibility in all directions; its elasticity. 15. Compare with the artery the thin-walled flabby veins which open into the heart. CHAPTER XV. THE WORKING OF THE HEART AND BLOOD-VESSELS. The Beat of the Heart. — It is possible by metliods known to physiologists to open the chest of a living animal, such as a rabbit, made insensible by chloroform, and see its heart at work, alternately contracting and diminishing the cavities within it, and relaxing and exj)anding them. lb is then observed that each beat commences at the mouths of the veins which open into the auricles; and from there runs over the rest of the auricles, and then over the ventricles; the auricles beginning to dilate the moment the ventricles start their contraction. Having finished their contraction, the ventricles begin to dilate, and then for some time neither they nor the auricles are contracting, but the whole heart is expanding. The contraction of any part of the heart is known as its sys'to-le, and the relaxation as its di-as'to-le, and since the two sides of the heart work syn- chronously, the auricles together and the ventricles to- gether, we may describe a whole "cardiac period" or "heart-beat" as made up successively of auricular systole, ventricular systole, and pause. In the pause the heart, if taken between the finger and thumb feels soft and flabby. What is seen when the beating heart of a living animal is exposed ? When do the auricles begin to dilate? What is the state of the heart for a short time after the end of a ventricular contraction? What is meant by the systole of a part of the heart? What by the diastole? Of what does a cardiac period consist? How does the heart feel to the touch during the pause? r216] Events DvumG A (jaUMao perioa 217 but during the systole it, especially in its ventricular por- tion, becomes hard and rigid, and diminished in size so as to force blood out of it. The Cardiac Impulse. — The human heart lies with its 'apex touching the cliest-wall between the fifth and sixth ribs on the left side of tlie breast-bone. At every beat a sort of tap known as the "cardiac impulse," or "apex beat," may be felt by placing the finger at that point. Events occurring within the Heart during a Cardiac Period. — Let us commence just after tlie ead of the ventric- ular systole. At this moment the semilunar valves at the orifices of the aorta and tlie pulmonary artei-y are closed so that no blood can flow back from those vessels. The whole heart, however, is soft and distensible, and yields readily to blood flowing into its auricles from the pulmonary veins and the hollow veins; this blood passes on through the open mitral and tricuspid valves, and fills up the dilating ventri- cles as well as the auricles. As the ventricles fill, back cur- rents are set up along their walls, and carry up the flaps of the auriculo -ventricular valves, so that by the end of the pause they are nearly closed. At this moment the auricles contract; this contraction commences at and narrows the | mouths of the veins so that blood cannot easily flow back from the auricles into them; the flabby and dilating ventri- cles oppose much less resistance, and so the general result is How during the systole?/ How is its bulk cbanged in systole? Where does tbe apex of the heart touch the chest-wall ? What is the cardiac impulse ? What is the position of the semilunar valves just after the end of a ventricular systole? What results from their closure? In what condition is the heart in general ? What parts of it does blood enter ? From what vessels? What cavities does this blood fill ? What hap- pens as the ventricles Inll ? What is the position of the valves at the end of the pause ? Where does the auricular contraction commence ? What is the main result of the auricular contraction ? 318 TEB HUMAN BODY. that the contracting auricles send blood mainly into the ventricles and hardly any back into the veins. The in- creased current into the ventricles produces a greater back current on the sides, which, as the auricles cease their con- traction, and the filled ventricles become tense and press on the blood inside them, completely closes the auriculo-ven- tricular valves. The auricular contraction nowceases, and the ventricu- lar begins. The blood in each ventricle is imprisoned be- tween the auriciilo- ventricular valves behind and the semi- lunar valves in front. The former cannot yield on account of the chordae tendineae fixed to their edges; the semilunar valves, on tlie other hand, can open outwards from tlie ven- tricle and lot the blood pass on; but they are kept tightly shut by the pressure of the blood in the aorta and pulmo- nary artery, just as the lock-gates of a canal are by the pres- sure of the water on them. In order to open the canal-gates water is let in or out of the lock until it stands at the same level on each side of them; but they might be forced open without this by applying sufiBcient power to overcome the higher water pressure on one side. It is in this latter way that the semilunar valves are opened. The contracting ventricle tightens its grip on the blood inside it. As it squeezes harder and harder, at last the pressure on the blood in it becomes greater than the pres- sure exerted on the other side of the valves by the blood in What is llie roiiseqvience of tlie increased flow into the ventricles due to the auricular contraction? What happens when the ventricle begins to contract? Why can- not the imprisoned blood escape back into the auricle? How are the semilunar valves kept closed? Illustrate. How might we force open the gates of a canal lock without bringing the water to the same level on each side? How are the semilunar valves opened? USB OF PAPlLLAttt MUSOLM. 219 the arteries, the valves are forced open, and the blood begins to pass out; the ventricle continues to contract until it has obliterated its cavity and completely emptied itself. Then it commences to relax, and blood to flow back into it from the arteries. This back current, however, catches the pock- ets of the semilunar valves, drives them back, and closes the valve so as to form an impassable barrier, and so the blood which has been forced out of the ventricle is hindered from flowing directly back into it. Use of the Papillary Muscles.— In order that the con- tracting ventricles may not force blood back into the auri- cles, it is essential that the flaps of the mitral and tricuspid valves be held together across the openings which they close, and not pushed back into the auricles. If they were like swinging doors and opened both ways they would be useless ; they must so far resemble an ordi- nary door as only to open in one direction, namely, from the auricle to the ventricle. At the commencement of the ventricular systole this is provided for by the chordae tendin- ese, which are of such a length and so arranged as to keep the valve-flaps shut across the opening, and to maintain their edges in contact. But, as the contracting ventricles shorten, the chordse tendineae would be slackened and the valve-flaps pushed up into the auricle. The little papil- lary muscles prevent this. Shortening as the ventricular systole proceeds, thoy keep the chordae taut and the valves closed. What then happens? How long does the ventricle continue to contract? What then follows? How are the semilunar valves closed? What is essential In order that blood may not be forced back from ventricle to auricle? Illustrate. How is the pushing back of the valve-flaps between auricle and ventricle prevented at the beginning of a ventricular systole? When would the chordae tendineae be slack- ened? What would result? How is the slackening prevented? 220 THE HUMAN BODY. Sounds of the Heart, — If the ear he placed on the chest of another person over the heart region, two distinguisha- ble sounds will be heard during each round of the heart's work. They are known respectively as thejfrs^and second sounds of the heart. The first is of lower pitch and lasts longer than the second and sharper sound; vocally their character may be tolerably imitated by the syllables lub, dup. The cause of the second sound is the closure, or, as one might say, the " clicking up" of the semilunar valves. The first sound takes place during the ventricular sys- tole, and is probably dne to vibrations of the tense ven- tricular wall at that time. In many forms of lieart disease these sounds are modified or cloaked by additional sounds which arise when the cardiac orifices are roughened, or nar- rowed, or dilated, or the valves inefficient. A pliysician often gets important information as to the nature of a heart disease by studying these new or altered sounds. Function of the Auricles. — Tlie ventricles have to do the work of pumping the blood through the blood-vessels. Accordingly their walls are far thicker and more muscular than those of the auricles; and tlie left ventricle, which has to force the blood over most of the body, is stouter than the right, which has only to send blood arc and the compara- tively short pulmonary circuit. The circulation of the blood is, in fact, maintained by the ventricles, and we have to inquire what is the use of the auricles. Not unfre- Whatdo we lienr on listening over tlie heart rcpion of a living per- son's cliest? What are the sounds called? How docs the first differ from the second? What words srive some idea of their character? What is the origin of the second sound? Of the first? What occurs as regards the lieart sounds in many forms of heart disease? What work have the ventricles to do? How do their walls differ from those of the auricles? Which ventricle has the thicker wall? Why? What part of the heart maintains the blood flow? Wons: boifM ST tsu sbaht. 221 quently the heart's action is described as if the auricles first filled with blood, and then contracted and filled the ventricles; and then the yentricles contracted and drove the blood into the arteries. From the account given above, however, it will be seen that the events are not accurately so represented, but that during all the pause the blood flows on through the auricles into the ventricles, which latter are already nearly full when the auricles contract; this contraction merely completes the filling of the ventri- cles, and finishes the closure of the auriculo-ventricular valves. The main use of the auricles is to afford a reservoir into which the veins may empty while the comparatively loug-lasting ventricular contraction is taking place. The Work dona daily by the Heart. — At each beat each ventricle pumps on rather more than six ounces (say four- teen tablespoonfuls) of blood. The elastic aorta and the pulmonary artery are full, and resist the pumping of more liquid into them, just as an elastic bag filled with water could only have more sent into it by force; to get more in. one would have to stretch the bag more. The resistance opposed by these arteries to receiving blood from the heart has been measured in some of the lower animals, and calcu- lations made from them to man. According to these the work which the left ventricle does every day, sending 6^ ounces of blood seventy times a minute into the aorta, is enough to lift one pound 325,584 feet high; and the work done by the right ventricle would lift one pound 108,538 What parts of the heart does the blood enter during the pause? What is the condition of the ventricles as regards fullness at the end of the pause? Wiiat is done by the auricular contraction? What ia the chief use of the auricles? How much blood does each ventricle pump out at every beat? What resists the ventricular emptying? Illustrate. How much work does a man's left ventricle do daily? How much the right? 222 TBt) HUMAN BODY. feet. The work done daily by the Tentricles of the heart together is equal to that required to raise one pound 434,112 feet from the earth's surface, or, what comes to the same thing, more than 193 tons one foot high. If a man weighing 165 pounds climbed up a moui/tain 3644 feet high the muscles of his legs would probably be greatly tired at the end of his journey, and yet in lifting his body that height they would only have done as much work as his heart does every day without fatigue in pump- ing his blood. No doubt the fact that more than half of every round of the heart's activity is taken up by the pause during which its muscles are relaxed and its cavities filling with blood, has a great deal to do with the patient and tireless manner in which it pumps along, minute after minute, hour after hour, and day after day, from birth to death. The Pulse. — When the left ventricle of the heart con- tracts it forces on about six ounces of blood into the aorta, which, with its branches, is already quite full of blood. The elastic arteries are consequently stretched by the extra blood, and the finger laid on one feels it dilating; this dila- tation of an artery following each beat of the heart is called the pulse J it is easiest felt on arteries which lie near the surface of the body, as the radial artery, near the wrist, ^ad the temporal artery, on the brow. The arteries at their ends furthest from the heart lead How much both ventricles together? How high would a man have to climb in order to do as much work by the muscles of his legs as the heart does in a day? How may we account for the fact that the heart does not become fatigued and unable to work? What happens when the left ventricle of the heart contracts? What results in the arteries? What is the pulse? Name arteries or which the pulse is easily felt. TEE PULSE. 223 into capillaries; before the next heart-beat occurs they pass on into these minute vessels as much blood as the aorta re- ceived during the preceding ventricular systole; consequently they shrink again during the pause, just as a piece of rubber tubing with a small hole in it, when overfilled with water, would gradually collapse as the water flowed out of it. The next beat of the heart again overfills and expands the arteries, and so on; at each heart-beat there is a dilatation of the arteries due to the blood sent into them from the ventricle, and between each beat there is a partial collapse of the ar- teries, due to their emptyiug blood into the capillaries. What may be learnt from the Pulse. — The pulse being dependent on the heart's systole, "feeling the pulse" of course primarily gives a convenient means of counting the rate of beat of that organ. To the skilled touch, however, it may tell a great deal more; as, for example, whether it is a readily compressible or "soft pulse," showing that the heart is not keeping the arteries properly filled up with blood, or tense and rigid ("a hard pulse"), indicating that the heart is keeping the arteries excessively filled, and is working too violently, and so on. In healthy adults the pulse rate may vary from sixty-five to seventy-five a minute, the most common rate being seventy-two. In the same in- dividual it is faster when standing than when sitting, and when sitting than when lying down. Any exercise in- Into what do the final arterial branches open? How itmch blood is sent into tlie capillaries during a cardiac period? Wliat change takes place in the "bulk of the arteries during the interval between two ventricular contractions? Illustrate. "What happens in the arteries during each heart-beat? Why? What during each heart pause? Why? How may we conveniently count the rate of heart-beat? What does a soft pulse indicate? A hard pulse? What is the most com- mon pulse rate in health? Within what limits may it vary? How is it influenced by the position of the body? 224 THE HUMAN BODY. creases its rate temporarily and so does excitement; a sick person's pulse should not therefore bo felt when he is ner- vous or excited (as the physician knows when he tries first to get his patient calm and confident). In children the pulse is quicker than in adults, and in old age slower than in middle life. The Flow of the Blood in the Capillaries and Veins. — The blood leaves the heart intermittently and not in a regular stream, a quantity being forced out at each systole of the ventricles; before it reaches the capillaries, however, this rhythmic movement is transformed into a steady fl.ow, as may readily be seen by examining with a microscope thin transparent parts of various animals, as the web of a frog's foot, a bat's wing, or the tail of a small fish. In consequence of the steadiness with which the capillaries supply the veins the flow in these latter is also unaffected directly by each beat of the heart; if a vein be cut the blood wells out uni- formly, while a cut artery spurts out with much more force, and in jets which are more powerful at regular intervals corresponding with the contractions of the ventricles. The Circulation of the Blood as seen in the Frog's Web. — There is no more fascinating or instructive spectacle than the circulation of the blood as seen with the micro- scope in the thin membrane between the toes of a frog's hind limb. Upon focusing beneath the outer layer of the skin a network of minute arteries, veins, and capillaries. How by exercise? "Why should an invalid's pulse not be felt when he is excited? How does nge affect the pul.=e rate? In wha.t manner does the blood leave the heart? How is its flow altered before reaching the capillaries? How may this he observed? Is the flow in the veins rhythmic or steady? Wiiy? How does the bleeding from a cut artery differ from that of a cut vein? "What comes into view on examining a frog's web with a micro- scope? BLOOD FLOW IN THE CAPILLARIES. 225 with the blood flowing through them, comes into yievv (Fig. 61). The arteries, a, are readily recognized by the fact that the flow in them is fastest and from larger to smaller branches. The smallest are seen to end in capillar- ies, which form networks, the channels of which are all nearly equal in size. In the veins arising from the capil- laries the flow is from smaller to larger trunks, and slower than in the arteries, but faster than in the capillaries. Why the Blood flows slowest in the Capillaries. — The reason of the slower flow of the capillaries is that their united area is considerably greater than that of the arteries supplying them, so that the same quantity of blood flowing through them in a given time has a wider channel to flow in and therefore moves more slowly. The area of the veins is smaller than that of all the capillaries, but greater than that of the arteries, and so the rate of movement in them is intermediate. We may picture to ourselves the vascular system as a double cone, widening from the ventricles to the capillaries, and narrowing from the latter to the auricles. Just as water forced in at a narrow end of this would flow quickest there, slowest at the widest part, and quicker again where it passed out the other narrow end, so the blood flows quick in the aorta and hollow veins,* and slow in the capillaries, How may the arteries be recognized? la what are the smallest arteries seen to end? Do the capillaries vary much in size? What is the direction of flow in the veins? How does its rate differ from that in the arteries? From that in the capillaries? "Why does blood flow slowest througli tlie capillaries? Why in the veins quicker than in the capillaries, but slower than in the arteries? How may we picture the vascular system? Illustrate. How do capillaries differ in size from the large arteries? * A good illustration taken from physical geography is aftorded by the Lake of Seneva, in Switzerland. This is supplied at one end by a river which derives its water from the melting glaciers of some of the Alps. From its other end the 226 THE HUMAN BODY. which, though thousands of times smaller than the groat arteries and veins, are millions of times more numerous. The channel through which the blood flows in them is, therefore, when they are all taken together, yery much greater than that to which it is confined in the large arterial and venous trunks. Why there is no Pulse in the Capillaries and Veins.— The heart sends blood into the arteries not steadily but intermittently; each beat forces in some blood, and then comes a pause before the next beat. Accordingly the flow in the larger arteries is not even and continuous, but jerky, as indicated by the pulse. But in the capillaries the flow is quite steady, and yet the capillaries are supplied by the smaller arteries. We have to inquire how this is brought about. The disappearance of the pulse is due to two things, (1) the fact that in the tiny capillaries the blood meets with considerable resistance to its flow, dependent on friction, and (2) that the arteries are A'ery elastic. On account of friction in the capillaries the arteries have difficulty in passing on blood through them; blood there- fore accumulates in the aorta and its large branches and stretches their elastic walls. The stretched arteries press all the time on the blood inside them, and constantly keep squeezing it on into the small arteries and the capillaries; How in number? Is tlie total lilood cliannel greater in arteries or capillaries? In veins or capillaries? Why is tlie blood-flow in tlie great arlevies not steady? Name vessels in which it is steady. To what is the loss of pulse in the capillaries due? What results from friction in the capillaries? What is done by the stretched arteries? water is carried off by the river Rhone. In the comparatively narrow inflowing and outflowing rivers the current is rapid; in the wide bed of tlje lake jt jsmu?!) Blower. ABSENCE OF PULSE IN THE CAPILLARIES . 227 both while the heart is contracting and between two heart- beats. The h6art, in fact, keeps the big elastic arteries over-distended with blood; before they have had time to nearly empty, another systole occurs and fills them up tight again; so all the while the walls of the arteries are stretched and keep pressing on Lhe blood inside them, and steadily forcing it on into the capillaries. Tlie heart keeps the arteries over-full, and the stretched elastic arteries drive the blood through the capillaries. As the arteries are always stretched and always pressing on the blood the cajiillaries receive a steady supply, and the flow through them is uni- form. This even capillary flow passes on a steady blood stream to the veins. * The object of having no pulse in the capillaries is to diminish the danger of their rupture. As we have seen, materials from the blood have to ooze through their walls to nourish the organs of the body, and wastes from the organs to soak back into the blood that they may be carried ofE. Their walls have therefore to be very thin; and if the When? What does the heart do? What happens before the arteries have had lime to empty? Wliat is the condition of the arterial walls all through life? Wliat results from their stretched condition? Wliat keeps the arteries tightly filled? What sends blood through the capillaries? How do the capillaries get a steady blood supply? Wliy do we find a uniform current in the veins? What is gained bjr having no pulse in the capillaries? What must food materials in the iblood do before they can nourish the body? What must the wastes of the organs do? Why must the capillary walls be very thin? * " Every inch of the arterial system may, in fact, be considered as convert- ing a small fraction of the heai-t's jerlc into a steady pressure, and when all these fractions ai'e smnnied up together in the total length of the arterial system no trace of the jerk is left. As the effect of each systole becomes diminished in the smaller vessels liy the causes above mentioned, that of this constant pres- sure becomes more obvious, and gives rise to a steady passage of the fluid from the arteries towards the veins. In this way, in fact, the artei-ies perform the same functions as the air-reservoir of a fire-engine, which converts the jerk- ing impulse given by the pumps into the steady flgw of the delivery hose."- 228 TEE EUMAN BODY. blood were sent into tliem in sudden jets at each beat of the lieart, tliey would run much risk of being torn. The Muscles of the Arteries. — The arteries have rings of plain muscular fibre in- their walls ; when these contract they narrow the artery, and when they relax they allow it to widen under the pressure of the blood in its interior. The vessel then carries more blood to the capillaries of the organ which it supplies. Blusliitig is due to a relaxation of the muscular layer of the arteries of the face and neck, allow- ing more blood to fl.ow to the skin. Why the Arteries have Muscles. — The amount of blood in the body is not sufficient to allow of a full stream of blood through all its organs at one time: the muscular fibres controlling the diameter of the arteries are used to regulate the blood-flow in such a manner that parts hard at work shall get an abundant supply, and parts at rest shall only get just enough to keep them nourished. Usually when one set of organs is at work and its arteries dilated, others are at rest and their arteries contracted. Few persons, for example, feel inclined to do brain-work after a heavy meal; for then a great part of the blood of the whole body is led \ off into the dilated vessels of the digestive organs, and the ' brain gets but a small supply. On the other hand, when the , brain is at work its vessels are dilated, and often the whole head flushed; and when the muscles are exercised, a great portion of the blood of the body is carried off to them; there- What would be apt to happen if blood were sent into them in sudden jets? How are llie muscles of the arteries arranged? What results from their contraction? Prom their relaxation? To what is blushing due? Why cannot all (he organs Iiave a full blood stream through them at the same time? For w)iat purpose are the muscular fibres in the walls of arteries used? What is the usual condition of the arteries of a resting organ? TAKING GOLD. 229 fore, hard thought or violent exercise soon after a meal is very j apt to produce an attack of indigestion by diverting the ' blood from the abdominal or-gans, where it ought to be at/ that time. Young persons whose organs have a super- abundance of energy, enabling them to work under unfa- vorable conditions, are less apt to suffer in such ways than their elders. One sees boys running actively about after eating, when older people feel a desire to sit quiet or even to go to sleep. Taking Cold. — Wlien the skin is chilled its arteries con- tract, as shown by the pallor of the surface. This throws an undue amount of blood into internal parts, whose ves- sels become gorged with blood or "congested," and con- gestion very easily passes into inflammation. Consequently, prolonged exposure of the surface to cold is very apt to be followed by inflammation of parts inside the body, and give rise to a so-called "cold" (which is really an inflam- mation) of the mucous membranes of the head, or throat, or lungs; or of the intestines, causing diarrhoea. In fact, the common summer diarrhoea is far more often due to a chill of the surface leading to intestinal inflam- mation than to the fruits eaten in tliat season, which are so often blamed for it. The best preventive is to^ wear when exposed to sudden changes of temperature, a woollen or at least a cotton garment over the trunk of the Why is it not wise to talte hard exercise or do severe mental work soon after eating? Why do young persons suflfei' less from exercise soon after dinner than do their elders? What happens to its arteries when the skin is chilled? How does this manifest itself? What is its result ou the blood-supply of in- ternal parts? What is congestion? Into what diseased state does it often pass? What diseases are apt to follow a surface chill? What is the most frequent cause of summer diarrhoea? What should be worn when liable to exposure to considerable changes of temperature? 230 TEE HUMAN BODY. body; linen permits any change in the external tempera- ture to act almost at once upon the skin. After an un- aYoidable exposure to cold or wet, the thing to be done is of course to maintain the cutaneous circulation; movement should be persisted in, and a thick dry outer covering put on until warm and dry underclothing can be obtained. In healthy persons, a temporary exposure to cold, as a plunge in a bath, is good, since in them the sudden con- traction of the cutaneous arteries soon passes off, and is succeeded by a dihitation causing a warm healthy glow on the surface. If the bather remain too long in cold water, however, this reaction passes off, and is succeeded by a more persistent chilliness of the surface, which may last all day. The bath should therefore be left before this occurs; but no absolute time can be stated, as the reaction is more marked and lasts longer in strong persons and in those used to cold bathing than in others. Why does linen not form a good inner garment under such circum- Stances? What should be done after unavoidable exposure to cold or wet? Why is a plunge in a cold bath useful to healthy persons? What results if a person remains too long in cold water? When should a cold bath be left? What persons may remain longest with safety in a cold bath? APPENDIX TO CHAPTER XV. 1. A frog may be used to illustrate the beat of the heart. Ana- tomically a frog's heart differs in many respects from that of a mam- mal, but the phenomena of systole and diastole are essentially the same. 2. Etherize a frog as before described. Cut off its head. Check bleeding and destroy its spinal cord by forcing a pointed wooden peg o ng the spinal canal. 3. Laying the animal on its back, carefully divide with scissors the skin along the middle line of the ventral surface for its whole length. Make cross cuts at each end of this longitudinal one and piB out tlie flaps of sUia. APPENDIX. 231 4. Next pick up with forceps the remaining tissues of the ventral wall near its posterior end, and carefully divide tliera longitudinally a rittle on the left side of the middle line; being very careful not to injure either the viscera in the cavity beneath or a large vein {ante- rior abdominal) running along the wall in the middle line. 5. About the point where you see this vein passing from the wall to enter among the viscera of the ventral cavity, youwill come to the bony and cartilaginous tissues of the sternal region. Raise the posterior cartilage in your forceps, make a short transverse cut in front of the vein, and, looking beneath the sternuni, note tlie peri- cardium with the heart lieating inside it. Divide the fibrous bands which pass from the pericardium to the sternum, and with scissors cut away sternum, etc., taking great care not to injure the heart. 6. Push a rod about half an inch in diameter down the animal's throat so as to stretch the parts, and then picking up the pericardium in a pair of forceps, open it and gently cut it away from about the heart; push aside any lobes of the liver which lie on the latter organ. In the heart tlius exposed note — a. Its heat; a regularly alternating contraction {systole) and dila- tation {diastole). b. In consequence of the destruction of the spinal cord compara- tively little blood now flows through the heart, but during the con- traction you will be able to observe tliat tlie ventricular portion, which will be readily recognized, becomes paler; and during dias- tole again becomes deeply colored, getting more or less filled up with blood which shows tlirough its walls. e. Observe that each contraction starts at the auricular end and travels towards the ventricular; this may be more easily seen by- and-by, when the heart begins to beat more slowly. 7. The specimen may be put aside under a bell-jar with a wet sponge, or a piece of flannel soaked in water. If kept from drying the heart will go on beating for hours. 8. To demonstrate the action of tlie valves of the lieart, obtain two uninjured sheep's hearts from a butcher. Remove them from the pericardium, taking care not to injure the vessels. 9. Cutoff the apex of one heart so as to open the ventricles. Then fill up the stumps of the aorta and the pulmonary artery with water. As the water is poured in the semilunar valves will be seen to close up and block the passage to the ventricle, so that the stump of the vessel remains full for some time. The valves rarely act quite per- fectly in a heart removed from the body and treated as above, but they will support the water column quite long enough to illustrate their action. 232 TnS n tTMAN BOD T. 10. Carefully cut the auricles away from the other sheep's heart, taking great care not to injure the ventricles or the auriculo-ventric ular valves. Tlien holding the ventricles, apex down, in one hand, pour water in a stream into them from a pitcher held about a foot above them. As the ventricles (ill, the flaps of the mitral and tricus- pid valves will be seen to float up and close the auriculo-ventricular orifice, illustrating their movement as the ventricle fills during its diastole in the natural working of the heart. 11. The manner in which the elasticity of the arteries and the fric- tion resistance to flow in the capillaries togetlier serve to turn a rhythmic into a steady flow may be readily demonstrated as follows: Take an elastic bag such as is commonly sold with enema appara- tus in drug-stores, and having an entry and exit tube provided with valves In t!ie exit tube place a piece of glass tubing six feet long. Put the entry tube of tlie bag in a basin of water. On pumping, an intermittent flow of water, corresponding to the strolies of the pump, will be obtained from tlie glass tube. Connect a very fine glass nozzle with the end of the long tube; on pumping, less water can be forced through, and the outflow is still rhythmic. ' l3. Replace the glass tube by a rubber tube of the black, highly elastic kind : on pumping we get again a rhythmic outflow. Now connect your narrow nozzle to the end of the rubber tube, and pump : the outflow will be nearly constant, because the rubber tube not being able to empty itself as fast as the water is pumped into it, becomes stretched, and in the interval between two strokes of the pump it keeps on squeezing out the extra water accumulated in it. The longer and more elastic the tube, the quicker and stronger the stroke of the pump, and the naiTower the exit, the more steady will be the outflow. In the body the heart keeps the arteries very tightly stretched all the time, and they keep up accordingly a steady flow into the capillaries. The experiment shows that to get such a steady flow two things are necessary ■ (1) that tlie tubes fed directly by the heart shall be highly elastic, and (3) that there shall be consideraUf resistance to the exit trom their outflow euuo CHAPTER XVI. THE OBJECT AND THE MECHANICS OP RESPIRATION The Object of Respiration. — Blood is renewed, so far as ordinary food materials are concerned, by substances either directly absoi'bed by the blood-vessels of the alimentary canal, or taken up by the lymphatics of the digestive tract and afterwards poured into the blood. But in order that energy may be set free for use by the tissues of the body (Chap. VIII.), oxidations must occur, and the continuance of these vital oxidations depends on a constant supply of oxygen. As their result, waste substances are produced, which are no longer of use to the body, but detrimental to it if present in large quantity. The most abundant of these wastes is carbon dioxide gas. .—— The function of respiration has for its objects (1) to renew the supply of oxygen in the blood, and (3) to get rid of the carbon dioxide produced in the different organs. The Respiratory Apparatus. — This consists primarily of two elastic bags, the lungs, placed in the thorax, filled with air, and communicating by the air-passages with the sur- How is the blood renewed as regards ordinary food matters? What must occur that energy be set free for use by the body ? "What is necessary that the oxidations may continue ? What do the oxida- tions produce? Which is the most abundant waste substance of the body? What are the objects of respiration ? Of what does the respiratory apparatus primarily consist ? [233] 234 TOE EtTMAN Bonr. rounding atmosphere. In the lungs the pulmonary capil- lary blood-vessels form a very close network: through their walls the blood gives off to the air in the lungs carbon dioxide, and takes from this air oxygen. The air in the lungs consequently needs renewal from time to time: other- wise it would no longer have oxygen to give to the blood, and would become so loaded with carbon dioxide as to no longer take that waste product from it. This renewal is effected by the working of a system of muscles, bones, and cartilages whose co-operation brings about that alter- nating expansion and contraction of the chest which we call breathing. When the chest contracts, air depi'ived of its oxygen and polluted with wastes is expelled from the lungs; and when it expands, fresli air, rich in oxygen, and con- taining hardly any carbon dioxide, is taKen into them^ The respiratory organs are, therefore, (1) the lungs; {3) the air-passugcs; (3) the vessels of the pulmonary circula- tion, including the pulmonary artery bringing the blood to the lungs, the pulmonary capillaries carrying it through them, and the pulmonary veins conveying it from them; (4) the muscles, bones, and gristles which are concerned in producing the breathing movements.* The Air-Passages. — Air reaches the pharynx through the nose or mouth (Fig. 1) : on the ventral side of the pharynx What vessels form a close network in the lungs? What takes place through the walls of these vessels? Why must the air in the lungs be renewed? How is the renewal brought about? What ia breathing? What happens when the chest contracts? What when it expands ? Enumerate. the respiratory organs. Through what passages does air reach the pharynx? * To these should be added (5) the nerve centres and nerves which control the muscles of respiration, and which will be subsequently considered (see Chap. XX). TEE AIR-PASSAQES. 235 (Fig. 41) is an aperture through which it passes into the larynx or voice-box (a, Fig. 64), which lies in the upper part of the neck. From the Lirynx air passes on through the windpipe or trachea; this enters the chest, in the upper Fig. 64. Fig. 65. Fig. 64. — The lungs and air-passages seen from the fi'ont. On the left of the figure the pulmonary tissue has been dissected away to show the ramifications ofthe bronchial tubes, a, larynx ; 5, tracliea; d, right bronchus. The left bron- chus is seen entering the root of its lung. Fig. 65. — A small bronchial tube, a, dividing into its terminal branches, c; theso have pouched or sacculated walls and end in the sacculated alveoli, 6. part of which it divides into a right and a left ironchus. Each bronchus enters a hang, and divides in it into a vast number of very small tubes, called the Ironchial tubes. The last and smallest bronchial tubes {a, Fig. 65) open into subdivided elastic sacs, 5, c, with pouched walls. What aperture is found on the ventral side of the pharynx? Where does the larynx lie? Where does the air go from the larynx? Into what does the trachea divide? Where? What are the bronchial tubes? How do the final bronchial tubes terminate? 236 THE E^MAN BODY. Structure of the Windpipe and its Branches. — The trachea, bronchi, and bronchial tubes are lined by mucous membrane, outside of which is a supporting stratum com- posed of connective and plain muscular tissues. Their walls also contain cartilaginous rings or half-rings which keep them open. Below the projection on the throat known as Adam's apple (due to the larynx, see Chap. XXII.) there may readily be felt in thin persons the stifl windpipe pass- ing down to the top of the chest. The Cilia of the Air-Passages. — The mucous membrane of the trachea and its branches, down to almost the smallest, has a layer of ciliated cells on its surface. Each of these cells has on its end turned towards the cavity of the tube a tuft of from twenty to thirty slender threads which are in constant motion; they lash forcibly towards the throat, move gently back again, and then once more violently to- wards the outlet of the air-passage. These moving threads are called cilia. Swaying in the mucus secreted by the membrane which they line, they sweep it on to the throat, where it is coughed or "hawked " up. Imagine a man rowing in a boat at anchor. The sweep of the oars will drive the water back and not the boat forwards. So these little oars, the cilia, being an- chored on the mucous membrane drive on the secretion which bathes its surface. With wliat are the windpipe and its branches lined? What lies 'outside this lininj ' 1 J"" roots of a spinal nerve; 1, anterior (ventral) Assure; 8, poste- rior (dorsal) Assure ; 3, surface groove along the line of attachment of tlie anterior nerve-roots; 4, line of origin of the posterior roots; 5, anterior root niaments or a spinal nerve; 6, posterior root fllamt!nr,C epiglottis; c, the glottis, the lines leading from the letter-point to the free vibrating eilges of tho vocal cords. 6', the ventricles of the larynx: their upper edges, marking them off from the eminences 6. are the false vocal cords. 340 THE HUMAN BODY. are numerous, and are arranged — (1) to pull the arytenoid cartilages towards one another and so narrow the glottis behind; then air forced through the narrowed slit sets the cords vibrating and produces voice. (3) To increase the distance between the arytenoid cartilages behind and the thyroid in front: as the vocal cords are attached to both, this action stretches and tightens them, and so raises the pitch of the voice. (3) To pull the front of the thyroid cartilage nearer the arytenoids and so slacken the cords and lower the pitch of the voice. (4) To separate the arytenoid cartilages, and with them the vocal cords, and thus widen the glottis and allow air to pass through it without pro- ducing voice. The Range of the Human Voice from the lowest note (/ of the unaccented octave) of an ordinary bass to the highest note {g on the thrice-accented octave) of a fairly good soprano is about three octaves: the former note is produced by 88 vibrations per second, the latter by 792. Celebrated singers of course go beyond this limit in each direction : bassos have been known to take a on the grept octave (55 vibrations per second), and Mozart, at Parma, heard a soprano sing a note of the extraordinarily high pitch c on the fifth accented octave (2114 vibrations per second). Vowels are musical tones produced in the larynx and modified by resonance of the air in the pharynx and mouth. To get the broad a sounds, as ah, the mouth is widely opened and the lips drawn back; to get such vowels as State the uses of the muscles of the larynx. What is the ordinary range of the human voice? What notes have celebrated singers taken beyond the ordinary highest and lowest limits? What are vowels? Illustrate the influence of the shape given to the mouth-cavity in the production of different vowels. VOWELS AND CONSONANTS. 341 00 (moor) the lips are protruded and the mouth cavity lengthened. The change in the form of the mouth may be noticed by pronouncing consecutively the vowel-sounds ah, eh, ee, oh, oo. The English i (as in spire) is a diph- thong, consisting of a (pad) followed by e (feet), as may be readily found on attempting to sing a sustained note to the sound i. Semivowels, — In uttering true vowel-sounds the soft palate is raised so as to cut off the air in the nose, which then does not take part in the resonance. For some other sounds (the semivowels or resonants) the initial step is, as in the case of the true vowels, the production of a laryngeal tone; but the soft p;date is not raised, and the mouth-exit is more or less closed by the lips or the tongue; hence the blast partly issues through the nose, and the air there takes part in the vibrations and gives them a special character; this is the case with m, n, and ng. Consonants are sounds produced not mainly by the vocal cords, but by modifications of the expiratory blast on its way through the mouth. The current may be interrupted and the sound changed by the lips {labials, as p and b); or, at or near the teetli, by the tip of the tongue {dentals, as ; and d); or, in the throat, by the i-oot of the tongue and the soft palate {gutturals, as h and g). Consonants may also be classified by the kind of move- ment which gives rise to them. In explosives an interrup- tion to the air-current is suddenly interposed or removed {p, b, t, d, h, g). Other consonants are continuotis {f, s, r) and may be divided into (1) aspirates, when the air Is the long i of English a true vowel ? What is meant by the semivowels ? What are consonants ? How mav they be classified ? 342 THE HUMAN BODY. is made to rush through a narrow aperture, as, for ex- ample, between the lips (/) or the teeth (s) or the tongue and the palate {sh) or the tongue and the teeth {th); (2) resonants or semivowels; (3) vilratories, the different forms of r, due to vibrations of parts bounding a constric- tion put in the way of the air-current on its passage. CHAPTEE XXIII. THE ACTION OF ALCOHOL AND OTHER STIMULANTS AND NARCOTICS UPON THE HUMAN BODY. Introductory. — We have already seen (p. 131) that alcohol is not to be regarded as either a tissue-forming or a force- giving food. By causing a transference of heat from internal parts to the skin, in which the main organs of tlie temperature- sense (p. 333) are located, it produces a temporary feeling that the body is warmer ; but the final result is a loss of animal heat to the air, and a decrease of the temperature of the body as a whole. Experiments made on men under military regimen and discipline have proved that alcohol does not increase the power of sustained muscular work, though it may for a brief time stimulate to unhealthy activity. The relative amount of eneigy liberated in the body for its own use may be very fairly calculated by com- paring the amount of oxygen absorbed by the lungs on one day with the amount absorbed on another. We have learned that on the days when alcohol is taken the oxygen absoibed is not increased. Alcohol seizes some of the oxygen which the foods and tissues would have utilized in its absence ; and what it takes they lose. Most authorities even main- tain that alcohol prevents oxidation, and therefore tissue How does alcohol make one feel warmer? What is the result? What have experiments on soldiers shown as to tlie effect of alcohol on muscular work? How is the absorption of oxygen affected on days when alcohol is taken? What does alcohol do with some of the oxygen? Why do some authorities believe that alcohol directly checks tissue activity? [343] 344 TEE HUMAN BODY. activity, indirectly as well as directly; these experimenters find that it not only takes oxygen from the tissues, but so influences them as to diminish their power of using what it leaves. We may conclude that under ordinary circumstances alcohol is of no use as an energy-yielding food; although, since it is oxidized in the body, it would act as a real food to a starving man; or to a very sick per- son who might be unable for the moment to absorb and digest other substances. As regards tissue-formation, alcohol cannot build up proteid material, since it contains no nitrogen; and proteid material constitutes the essential part of muscular, gland- ular, and nervous tissues. There is even some evidence that alcohol leads to excessive waste of such tissues : several competent observers have found that its use increases the amount of nitrogen waste excreted from the body. The only tissues whose formation alcohol seems sometimes to increase are fatty and connective tissues; and we shall pres- ently learn that in most cases the superabundance of these tissues is deposited in places where it does harm. The study of alcohol as an article of diet leads therefore to the result that (though a physician may find it useful as a medicine in a crisis of disease when the system needs urging to make a special effort) it cannot fairly be regarded as a food when taken by persons in good health and properly nourished. The whip applied to a horse will arouse him to call on What general conclusions may be reached as to the value of alco- hol as a food ? What relation has alcohol to the formation and waste of proteid tissues? Of fatty and connective tissues? When may a physician find alcohol a useful medicine? Illustrate the action of alcohol on the body by comparison with a ■whip used on a horse. ALCOHOL. 345 his reserve force, and perhaps carry himself and his rider safely past some point of special danger; but it does not in any way nourish the horse. As regards the healthy human body alcohol may be compared to a whip: an amount of it not sufficient to cause drunken sleep, temporarily excites various organs; but the consequence is subsequent greater exhaustion. So far we have learned that alcohol as a regular article of diet IS, at least, useless. Were that all, we might regret the annual waste of corn, barley, wheat, and fruits in its production; and think the man foolish who spent his money on it. In such case the matter would be one for moralists and political economists to deal with, and phy- siologists and students of hygiene might leave it alone. Unfortunately, alcoholic drinks are not merely useless but positively hurtful, when taken regularly, even in what is usually called moderation. Alcohol has probably caused in the past, and is certainly causing at present in civilized nations, more disease and death than either bad drainage, bad ventilation, overcrowding, deficient food, overwork, or any other of the conditions prejudicial to health concern- ing which Physiology and Hygiene warn us. The moral degradation and the physical condition of the drunkard speak for themselves; it is therefore the more insidious consequences of alcohol-drinking that we shall mainly describe. Alcohol, when pure, is a transparent colorless liquid, containing the elements carbon, hydrogen, and oxygen (CjHjO); it is lighter than water, and boils at a con- What substances are wasted that alcohol may be prodiiceri? Compare the injury to health resulting from bad drainage, etc. with that produced by alcohol. Describe pure alcohol. 846 THE HUMAN BODY. sideraWj lower temperature; is highly inflammuble, burn- iDg with a bluish flame; and is the essential constituent of all fermented liquors in common use. Alcoholic Beverages include (1) malt liquors, as beer, ale, stout, and porter; (2) cider &tyA perry; (3) wines, as claret, sherry, port, champagne, and catavvba; (4) distilled spirits, as brandy, rum, and whiskey; and their compounds, as gin, cherry brandy, pineapple rum, and so forth; (5) liqueurs, made by adding various flavoring essences to different kinds of spirits. All contain alcohol in greater or less propor- tion, varying from over 70 volumes in the 100 in some kinds of rum to less than 2 in the 100 in "small" beer. The Direct Physiological Action of Pure AlcohoL — Pure alcohol is a very expensive substance, mainly employed in chemical experiments and in the manufacture of certain perfumes and essences. However, some clues to the ac- tion of diluted alcohol on the body may be obtained by a study of its action in tlie concentrated form. Strong alcohol having a great tendency to combine with water, rapidly extracts that substance from any animal organ placed in contact with it; as is shown by the hardening and shrivelling of museum specimens placed in it. Added to raw white of egg it coagulates it, much as if the egg had been boiled: added to fresh blood it acts in a simi- lar manner, coagulating the serum albumen as heat does (p. 183). Pure alcohol placed on the skin evaporates very rapidly, and m so doing abstracts heat (p. 274, note), producing a Of what is alcohol an essential constituent? Classify and name common alcoholic heverages. Within what limits does the quantity of alcohol in them vary? For what purposes is pure alcohol mainly used? What is its ac- tion on animiil organs placed in It? On fresh blood? On the skin when evaporation is permitted? DILUTED ALCOHOL. 347 sensation of coolness. This is succeeded by a feeling of warmth in the part; which also becomes red from temjio- rary paralysis of its blood-vessels, causing them to dilate. If the evaporation be prevented, as by putting a little alco- hol on the skin and covering it with a thimble, the alcohol acts as an irritant; it causes smarting, and finally sets up inflammation. On mucous membranes alcohol acts much as on the skin, but its irritant effect is more marked. Placed on the tongue it causes a feeling of coolness, followed by a hot biting sen- sation, and a red congested condition of thearea with which it came in contact. Introduced into the stomach of a rabbit or dog, where it cannot readily evaporate, strong alcohol causes congestion and inflammation varying in in- tensity with its amount. If the dose is large the animal dies almost instantly, because the powerfully irritated sen- sory nerves of the gastric mucous membi'anes reflexly ex- cite a nerve-centre which stops the heart's beat. Diluted Alcohol docs not produce the above-described direct actions of the pure liquid: this latter taken into the stomach acts as a powerful irritant poison, and generally produces its main effects on the stomach itself. Alcohol in such proportion as it exists in most alcoholic drinks exerts much less local action on the gastric mucous membrane; but it is absorbed and carried in the blood and lymph through the body, and if steadily taken day after day acts upon and When evaporation is prevented? Action on mucous membranes? Illustrate by tongue. By stomach. How does strong alcohol when swallowed sometimes cause sud- den death? How does the action of dilute alcohol differ from that of concen- trated? What results follow its frequent absorption? What condi- tions influence the organs soonest injured? Why are alcoholic dis- eases often not recognized until incurable? 348 THE HUMAN BODY. alters for the worse nearly eyery important organ. The organ first or most seriously attacked varies with the form in which the alcohol is taken, with the amount consumed daily, audwith the constitution of the individual. Prob- ably no one individual ever suffered from all the diseased states produced by alcohol described in the following pages; but habitual drinkers are very apt to experience one or more of them. The diseases produced by alco- hol after absorption into the blood come on so grad- ually (except in the case of obvious drunkards) that the victim rarely perceives them until serious if not irreme- diable damage lias been done: indeed, physicians have only recently come to clearly recognize that men who in com- mon phrase "were never in their lives under the influence of liquor" may nevertheless be drinking enough to do them grave injury. Absorption of Alcohol. — When alcohol (so dilated as not to cause active inflammation of the stomach) is swallowed, i't is quickly absorbed by the capillary blood-vessels of the gastric mucous membrane.* Tliese pass it on to the portal vein, which carries it (p. 208) direct to the liver. Collected from the liver by the hepatic veins it is conveyed through the inferior vena cava to the riglit auricle of the heart. Thence it passes on in the general blood-flow (pp. 198, 199j Can a man wlio drinks but is never drunk be injured by alcohol? By wbat vessels is alcohol first absorbed? To what vessel do they carry it? Describe its further course to the right auricle of the heart. Prom there to the left auricle. * An exception to the rapid absorption of alcohol sometimes occurs when a large quantity o£ raw spirits Is taken. Many eases are recorded where men have for a wager drunk a bottle of whiskey or brandy. The result is often sudden death ; but sometimes no effect is noticed for fifteen or twenty minutes; then there is sudden unconsciousness, passing into stupor, which ends in death. In such cases the large quantity of strong spirits seems temporarily to paralyze the absorbing po.ver of the stomach, PEIMABT EFFECTS OF ALCOHOL. 349 209) to right ventricle, lungs, left anricle, left ventricle, aorta, and by branches of the aorta to the body in general: to the heart-muscle (by the coronary arteries, p. 202), to the brain and spinal cord, to the muscles, to the kidneys, to the skin. "We have to study its action on all these organs. The Primary Effects of a Moderate Dose of Diluted Alco- hol, as a glass of vrliiskey and water, on one unaccustomed to it, are to cause temporary congestion of the stomach; dilatation of blood-vessels of the skin, indicated by the flushed face; a more rapid and forcible beat of the heart;* nervous excitement, exhibited by restlessness and talkative- ness. Then some incoherence of ideas, and often giddi- ness. Finally there is a tendency to sleep. On awaking the- person has some feeling of depression, not much ap- petite, and is in general a little out of sorts for a day. If the dose be larger the stage of giddiness is accompanied by diminution of the sensibility of the skin; and imperfect control over the voluntary muscles, indicated by defective articulation and a staggering gait. The muscles moving the eyeballs cease to work in harmony. Normally they act unconsciously, turning the eyes so that images of objects looked at are focussed on corresponding points of the retinas; and objects are seen single. Soon after the voluntary movements are affected the involuntary regulation of the eye-muscles is impaired, and objects are seen double; the eyeballs being no longer so turned as to bring images on corresponding retinal points. The stora- Name important organs to which the alcohol is ultimately carried in the blood. Describe the primary effects of a moderate dose of dilute alcohol. Of a larger but not fatal dose. •It is doubtful if chemically pure alcohol diluted with water quickens the pulse j most ordinary alcoholic beverages, however, undoubtedly do, 350 rim HUMAN BODY. ach may also be so irritated as to lead to vomiting. Then comes deep drunken sleep; followed by headache, loss of appetite, and prostration similar to, but moi'e marked than, that occurring after the smaller dose. If the alcoholic indulgence be repeated, day after day, some of the above-described primary consequences become less marked; but they give way to more serious functional and structural diseases. The Secondary Effects of Alcohol vary much in inten- lity with the form in which it is taken; also, no doubt, with the constitution of the person taking it, and with the length of time during which he has been drink- ing. We shall consider them in three groups: I. Compa- ratively slight and curable diseased states due to what is commonly considered moderate drinking. II. Severe acute alcoholic diseases. III. Chronic and usually incur- able morbid states, due to steady prolonged drinking; these fall into three main subdivisions: a. General tissue- deterioration; h. Destruction, more or less complete, of cer- tain organs; c. Deterioration of mind and character. I. Minor Diseased Conditions produced by Moderate Drinking. — Of these, alcoholic dyspepsia is the most frequent. A vast number of persons suffer from it without knowing its cause; people who were never drunk in their lives, and consider themselves very temperate. " The symptoms vary, but when slight are something like these: A man (or woman) complains of slight loss of appe- tite, especially in the morning for breakfast; feels languid either on rising or early in the day; retches a little in the What happens if the dose of alcohol be taken day after day? Classify the secondary actions of alcoliol upon the body. Give au account of alcoholic dyspepsia. ACUTE ALOOEOLIC DISEASES. 351 morning, and perhaps brings up a little phlegm only, or may actually vomit; or may be able to take breakfast but feels sick after it. Towards the middle of the morning he is heavy and languid, perhaps, and does not feel easy until he has had a glass of sherry or some spirits, then gets on pretty well, and can eat lunch or dinner. Or if worse, the appetite for both is defective, and there is undue weight or discomfort after meals Now all these symptoms may be due to other causes, but when taken together they are by far most commonly due to al- cohol." * Another frequent result of i-egular "moderate" drinking is tremor, orshakiness of the hands. The hand is unsteady when the arm is folded, and is seen to tremble if it be held out witli the arm extended. This tremor is very marked in the alcoholic disease known as delirhim tremens (p. 353). Even in its simple form it interferes with the performance of any action calling for manual dexterity. The trembling may, in most cases, be stopped for a time by an extra glass; and thus often leads to the acquirement of more serious diseases. We class the above as minor diseased conditions, because in most cases they occur before the will-power is seriously impaired, and abstinence from alcohol is soon followed by recovery. II. Acute Alcoholic Diseases. — A single large dose of alco- Describe alcoliolic tremor. In what disease is it very marked ? What results from even its simple form? How does it often lead to the acquirement of more serious alcoholic disease? Why do we class the dyspepsia and tremor as minor alcoholic dis- eases ? What results from a large dose or repeated small doses of alcohol ? * Dr. Greenfield, in " Alcohol: its Use and Abuse." 352 TBE HUMAN BODY. hoi, or the repetition of small doses at short intervals, ends in a fit of drunkenness. The disgusting appearance of a drunken man, the loath- ing which he excites even in those most attached to him, the loss of control over his actions, which makes him the prey of criminals, or, yet worse, a criminal himself, taken together make a picture to which the physiologist need add nothing. A man not deterred by its contemplation will not be hindered in the indulgence of his appetite by any argument based on injury to his health. Delirium Tremens. — Repeated drunkenness usually ends in an attack of delirium tremens, but this disease is more frequently the result of prolonged drinking which has never culminated in actual drunkenness. It is especially apt to occur in "those who drink hard, but keep from actual loss of consciousness, especially those engaged in hard mental work or subjected to great moral strain or shock ; and, too, those of certain temperaments are pecu- liarly liable to it. It is preceded, usually, by loss of sleep, ideas of persecution or injury, with no foundation in fact, and slight hallucinations, especially at night; the man, meanwhile, in the day looking anxious, slightly excited, nervous and ti-emulous, and perhaps narrating as actual occurrences the hallucinations of the preceding night. Then the senses are partly lost; he sees spectres, horrible and foul creatures about him; has all sorts of painful, terri- fying visions (whence the common name of the 'horrors'); is extremely tremulous, and either excited or lies prostrate, trembling violently on movement, sleepless, anxious, and a prey to spectres and terrors of the imagination." * Undei' wliat conditions may delirium tremens occur? What symptoms usually precede this disease? Describe the con- uitiou of a person sufEering from delirium tremens. * Dr. Greenfield, in " Alcohol; its Use and Abuse." DELIRIUM TliEMENS. 353 Pew persons die in their first attack of delirium tremenSj but lb is nature's unmistakable warning to the tippler; let him not disregard it, unless he is prepared to die without hope in maniacal imaginings so frightful that those around his death-bed can never recall the scene without horror ! Dipsomania is often confounded with delirium tremens, Out though it may lead to that disease it is an essentially different iiathological state. The word properly means a mental disease in which there is periodically an irresistible passion for alcohol; in any form, no matter how distasteful, the dipsomaniac will swallow it with avidity. The disease is sometimes produced by indulgence in drink, bat is more often inherited, especially from parents addicted to alco- holic excess. In the families of such, one child is often epileptic, another idiotic, a third eccentric or perhaps quite mad, and a fourth a dipsomaniac. Wlieu the fit seizes him the dipsomaniac is as irresponsible as a raving madman. His only safeguard against a frightful debauch is to jilace himself under restraint as soon as he perceives the symp- toms which he has learned to recognize as premonitory of his fit of madness. After a time the paroxysm passes off; the patient regains self-control, loses his passion for drink, is greatly ashamed of himself if he has indulged it, and usually behaves in an irreproachable manner for some weeks or months. The sufferers from this frightful disease are entitled to a sympathy to which the common drunkard has no claim. III. Chronic and often Incurable Diseased Conditions produced by Alcohol. — These are apt to be insidious in their What is the proper meaning of the word dipsomania? What dis- eases are apt to be found in the children of parents given to alooliolic exTSS? What should a dipsomaniac do when he feels the fit coming o; ? What happens when the paroxysm passes off? 854 /WS BUMAN BOD Y. approach, and overlooked until they have firmly seated themselves. They include, (a) deterioration of tissue; {b) practical destruction of important organs; {c) mental and moral enfeeblement. («) Deterioration ot Tissue due to Alcohol. — A serious structural change in the body produced by alcoholic excess \a fatty degeneration. The oily matter of the body exists in two forms: first, as adipose or fatty tissue collected under the skin, and in less amount elsewhere, as on the surface of the heart and around the kidneys; second, as minute fat-droplets in the interior of various cells and fibres. Some forms of alcoholic drinks tend to increase the adipose tissue, and may lead to undue accunmlntion of it about the heait, impeding the action of that organ. A more important and frequent result is an increase of fat- droplets in the cells of the liver and the muscular fibres of the heart, the oily matter replacing the natural working substance. A heart which has undergone this change is commonly spoken of by pathologists as a "whiskey heart;" for although fatty degeneration of the heart may occur from other causes, alcoholic indulgence is the most frequent one. Fatty liver or fatty heart is rarely if ever curable; either will ultimately cause death. It is probable that in both cases the fatty degeneration is due to over-stimulation of the organ. Most wines and spirits quicken the beat of the heart, leaving it less time for repair between its strokes. Vyriiy are chronic alcoholic diseases often unnoticed in their curable atages? What main forms do tliey include? In what forms is the oily matter of llie body found? How do some forms of alcohol affect the development of adipose tissue? What may result? How does alcohol produce more serious changes in tUe fatty matter of the body? What is meant by a " whisliey heart"? What is tlie consequence of fatty liver or fatty heart? To what is tlie fat'v degeneraUon in these organs ius? Explain for the heart. ALCOHOLIC DETERIORATION OF TISSUE. 355 Alcohol also increases the breaking down of proteid matter in the body; the liver has much to do in preparing this broken-down proteid for removal by the kidneys, and so gets overworked. Another serious bodily deterioration produced by alco- ho\\?. fibrous degeneration: by this is meant an excessive growth of the connective-tissue, which as we have seen (p. 24) pervades the organs of the body as a fine sup- porting skeleton for the more essential cells. Alcohol- drinking causes this tissue to develop to such an extent as to crush and destroy the cells, especially in the liver and kidneys, which it should protect. So far as the liver is con- cerned, the result is a shrunken, rough mass {hob-nailed liver, or gin-drinker's liver), with hardly any liver-cells left in it. This not only prevents the proper manufacture of bile and glycogen (p. 151), but the contracted liver presses on the branches of the portal vein within it (p. 208)- so as to impede the drainage of .blood from the organs in the abdo- men. As a consequence, an excess of the watery part of the blood oozes into the peritoneal cavity and accumulates, causing abdominal dropsy {ascites). In similar manner the superabundant connective tissue in the kidneys crushes and injures the essential kidney substance, and interferes with the proper function of the oi-gan in excreting nitrogen waste and water. The ultimate consequence is one form of '' Bright's disease" — a very fatal malady, characterized by elimination of albumen in the kidney secretion; retention of proteid wastes in the blood, poisoning the various organs; and accumulation of water in the loose tissue bind- Explain for the liver. What is fibrous degeneration? Describe the results whsn it occurs in the liver. In the Isidneys. What are Ihe characteristics of Bright's disease? 356 THB HUMAN BODY. ing the skin to underlying parts, producing that kind of dropsy known as anasarca. (b) The Organs of the Body most apt to be impaired or destroyod by Alcohol have been in part mentioned in pre- ceding pages. It will, however, be convenient to collect them together, and point out the kind of change produced in each. Probably no tippler ever suffered from all of these diseases, and most of them may develop in persons who are total abstainers; but the organic lesions which are mentioned below are more frequently due to intemperance than to any other cause. A primary action of alcohol after absorption is to cause dilatation of the cutaneous blood-vessels. With occasional alcoholic indulgence this is temporary; with repeated, it be- comes permanent. The Skin is then congested and puffy, and on exposed parts it is seen to have a purplish or red- dish blotched appearance; pimples appear on parts, such as the nose, where the natural circulation is more feeble. The result is the peculiar degraded look of the sot's face. The congestion interferes with the nutrition of the skin; the epidermis (p. 266) is imperfectly nourished and collects in scaly masses, interfering with the proper action of the sweat-glands, thus throwing undue work on the kidneys. When constantly irritated by the direct action of strong alcoholic drinks, the Stomach gradually undergoes lasting changes. Its vessels remain dilated and congested, its connective tissue becomes excessive, its power of secreting gastric juice diminished, and its mucous secretion abnor- mally abundant. The Liver suffers fatty and fibrous degeneration, and is Describe the cousequences of alcoliclic indulgence on the skin. On the stomach. ORG Am INJURED BY ALCOHOL. 357 One of the organs most often and earliest attacked. This we miglit expect, as all the alcohol absorbed from the stom^ ach is cai-ried direct to the liver by tlie portal vein (p. 208). The Heart has its walls at first thickened (Jiypertrophied) and its cavities dilated by the excessive work (p. 354) which alcoholic drinks stimulate it to jicrform. If, as is usually the case, fatty degeneration ensues, tlie organ gradually becomes too feeble to pump the blood around the body, and death results. The walls of the Arteries of drinkers fiequently undergo fatty degeneration; they lose their strength and elasticity, and are liable to rupture, or to the disease known as aneu- rism. The Kidneys are excited to undue activity, in part by the dilatation of their blood-vessels, in part, perhaps, through direct stimulation of their cells by alcohol circu- lating in the blood. Once tlie liver is attacked the nitro- genous waste of the body is not carried to the kidneys in proper form for excretion: some is held back, producing a tendency to gout and rheumatism ; the rest is got rid of by extra kidney effort. The usual result is fibrous degenera- tion of tlie kidneys, causing one kind of Bright's disease. The Lungs, from the congested state of their vessels pro- duced Ly alcoliol, are more subject to the influence of cold, the result being frequent attacks of broncJntis. It has also been recognized of late years that there is a peculiar form of consumption of the lungs wliich is very rapidly fatal, and found only in alcohol-drinkers. On tlie liver? Why is the liver especially apt to be attacked? On the heart? On (he arteries? How docs alcohol affect the kidneys directly? How through the Jiver-disease produced by it? What results? Wliat lung-diseases aro often produced by alcohol? 358 THE HUMAN BODY. The Sense-organs are also affected: their acuteness of per- ception is dulled; and many physicians believe that cata- ract and retinal disease may be produced by drinking. The red inflamed white of the eye of topers is well known. The Brain and Spinal Cord are kept in a chronic state of congestion* and over-excitement. This results at first in in- flammatory disease {delirium tremens); later, in fibrous de- generation, leading to certain forms of paralysis or to epi- lepsy, of which there is one variety well recognized byphy- iiicjans as due to alcohol. (c) Moral Deterioration produced by Alcohol. — One re- sult of a single dose of alcohol is that the control of the Will over the actions and emotions is temporarily enfeebled; the slightly tipsy man laughs and talks loudly, says and does rash things, is enraged or delighted without due cause. If the amount of alcohol be increased, further diminution of will-power is indicated by loss of control over the mus- cles. Excessive habitual use of alcohol results in perma- nent over-excitement of the emotional nature and en- feeblement of the Will; the man's highly emotional state exposes him to special temptation to excesses of all kinds, and his weakened Will decreases the power of resistance: the final outcome is a degraded moral condi- tion. He who was prompt in the performance of duty be Describe the action of alcoliol on tlie sense-organs. On tlie brain an d spinal cord, and the resulting diseases. Describe the moral deterioration produced by alcohol. * " I once had the unusual though unhappy opportunity of observing the same phenomenon in the brain-structure of a man who, in a fit of alcoholic excitement, decapitated himself under the wheel of a railway -carriage, and whose brain was instantaneously evolved from the skull by the crash. The brain itself, entire, was before me within three minutes after death. It exhaled the odor of spirit most distinctly, and its membranes and minute structures were vascular in the ex- treme. It looked as if it had been recently mjected with vermilliou." — Dr. B. W, Ricluirdaon, TUE OPIUM HABIT. 359 gins to shirk that which is irksome; energy gives place to iadifference, truthfulness to lying, integrity to dishonesty; for even with the best intentions in making promises or pledges there is no strength of Will to keep them. In for- feiting the respect of others respect for self is lost and character is overthrown. Meanwhile the passion for drink grows absorbing: no sacrifice is too costly which secures it. Swift and swifter is now the downward progress. A mere sot, the man becomes regardless of every duty, and even in- capacitated for any which momentary shame may make him desire to perform. For such a one there is but one hope — confinement in an asylum where, if not too late, the diseased craving for drink may be gradually overcome, the prostrated Will re- gain its ascendency, and the man at last gain the victory over the Irute. Opium and Morphia. — Opium is a gummy mixture con- taining several active principles, of which the most impor- tant is morphia. The forms in which it is most frequently employed are (1) gum opium, the crude substance, often put up in the form of pills; (2) laudanum, an alcoholic extract of the gum; (3) paregoric, a liquid containing sev- eral substances, of which opium is the most important; (4) morphia and its compounds. The Opium Habit. — Opium is perhaps the most valuable drug at the disposal of the physician. On the other hand, it is one of the most injurious substances used by mankind. It may be that it does not do so much harm in the United States as alcoholic drinks, but only because not so many What is the confirmed drunkard's only hope for cure? What is opium ? In what forms is it most oflen used? Compare the damage done in the United States by indulgence in alcohol and opium. 360 THE HUMAN S0D7. persons have acquired the craTi'tig for it. Used constaTitl_y it is as certainly fatal and the habit is perhaps even harder to break; for it may be indulged more secretly and its effects are not so readily recognized. There is also this to be said: that most inebriates are originally of weak character, wrecking themselves on a rock in full view, through lack of a strong hand at the helm; while many a one of highest gifts and noblest character, who would loathe the low vice of drunkenness, has gone under in the insidious maelstrom spread by opium for its victims. Using the drug at first as prescribed for the relief of suffering, he (or she, for more women than men are addicted to opium excess) is scarcely conscious of danger before being swept on to destruction. Most medical men now fully recognize the danger and only order prolonged use of opium with great caution. Never- theless there are so many persons who habitually use opium that it is important to point out the disastrous results. The Diseased Conditions produced by Regular Use of Opium are fairly uniform. The first phenomenon is deadening of sensibility, accompanied by mental exaltation if the dose be small. This is succeeded by unnatural sleep, disturbed by fantastic dreams. On awaking there is great depression of mind and body: often associated with defective memory, and a feeling that something terrible is about to happen. There is muscular weakness; distaste for food, without actual nausea; an'i an almost irresistible craving for another dose. If the habit be continued further, mental and physical changes occur. Distaste and inaptitude for any kind of Why is opium more disastrous from one point of view? What are the first phenomena following a dose of opium? What is the condition of the person on awaking? What results follow (Continuance of the habit? CHLORAL. 861 exertion; greatly impaired digestion', deficient secretion of bile; sluggishness of the muscles of the intestines, causing constipation. Tlie muscles waste, the skin shrivels, and the person looks prematurely aged. The pulse is quick, the body feverish; the eye dull, except just after the drug has been taken. The final result is failure of the nervous system. Incom- plete paralysis of the lower limbs is followed by a similai state of the muscles of the back. The victim crawls along, bent like an old man. Death finally results from starva- tion, due to complete failure of the digestive orgnns. Morpliia. — When morphia is used, a solution of it is often injected under the skin by a fine syringe. Prolonged use of it in this way is followed by all the symptoms of chronic opium-poisoning above described. The digestive organs are not, however, as soon attacked; but the punctures of the skin repeated for weeks, several times a day, cause in- flammation and ulceration. Danger of administering Opiates to Children. — Children are remarkably sensitive to opium and all preparations con- taining it. Opiates should never he administered to children except ly order of a physician. Many an infant has been poisoned by a few drops of paregoric or of some soothing syrup given by parent or nurse to check diarrhoea or pro- duce sleep. Chloral. — The chloral habit is in this country at present What is the final result? In what do the consequences of injection of morphia beneath the skin resemble and differ from those of opiates taken by the mouth? How are children peculiar as regards opiates? Under what condi- tions only should they be administered to children? "What often re. suits from giving opiates to infants? Compare the frequency of the chlpra} ^nd ppium habits lo thf United States. 362 THE HUMAN BODY more common than the opium habit, and, like it, more fre- quent among women than men. Chloral was, on its discovery a few years ago, heralded as a wonderfully safe and certain promoter of sleep and al- leviator of pain. Medical men have since learned that it is by no means so harmless a drug as they once believed; but :he general public do not seem to have had their eyes opened to its danger. A great many preparations of it have been put on the market, and are sold in drug-stores to all comers. The result is tliat many persons who would hesitate to take opium without medical advice use chloral, believing it harmless. Chloral, taken habitually, is at least as mischievous as opium. It should be forbidden by law to retail it in any form except on the prescription of a physician. The chloral habit is acquired with great ease, and is very hard to break. The first phenomena of chloral disease (cMoralism) are these: The digestion is greatly impaired; the tongue is dry and furred; there is nausea; sometimes vomiting, and a constant feeling of oppression from wind on the stomach. Next, nervous and circulatory disturbances occur. The temper becomes irritable, the Will weak; the hands and logs tremulous; the heart-beat irregular; the face easily flushed. Sleep becomes impossible without use of the drug: when obtained it is troubled, and the person awakes unrested. In later stages the blood is seriously altered. Its color- ing matter is dissolved, and soaks through the walls of the What have medical men lately learned about chloral? Why do so many people take chloral without medical advice? Describe the lirst symptoms of chlonilism. What are the symptoms in more advanced chloralism? What ip the latest stages? THE LOCAL ACTION OF TOBACCO. 363 capillary vessels, causing purplish patches on the skin. Jaundice also frequently occurs. If the chloral-taking be still continued, death results from inipoTerished blood, weakened heart, or paralysis of the nervous system. Not unfrequently chloral-takers un- intentionally commit suicide by indulging in too large a dose. Tobacco contains an active principle, nicotin, which in its pure form is a powerful poison, paralyzing the heart. "When tobacco is smoked some of the nicotin is burned, but there are developed certain acrid vapors which have an irritant action on the mouth and throat. The effects of smoking are thus in part general, due to absorbed nicotin; and in part local, due to irritant matters in the smoke. They vary much with the constitution, habits, and age of the smoker. One general rule at least may be laid down: tobacco is very injurious to young persons wliose physical development is not completed. The Local Action of Tobacco is at first manifested by in- creased flow of saliva. This usually passes off after some practice in smoking; dryness of the mouth follows, and con- sequent thirst, often leading to alcoholic indulgence; and in this, perhaps, lies the greatest danger from tobacco. The habitual smoker usually suffers eventually from what is known to medical men as "smoker's sore-throat." The inflammation often extends to the larynx, injuring the voice and producing a hacking cough, or may spread up How does death from chloral occur? What is nicotin? What other injurious suhstances are found in tobacco-smoke? What general rule may be stated concerning the action of tobacco on tlie human body? Describe the local actions of tobacco. How may tobacco-smoking injure the voice? How the hearing? 364 THE HUMAN BODY. the Eustachian tuhes (p. 330) and impair the hearing. Cigarettes are especially apt to cause these symptoms. Cure is impossible unless smoking be given up. Those who draw the srnoke into their lungs often suffer from chronic inflammation of the bronchial tubes in consequence. The General Action of Tobacco. — Tlie more common effects of absorption of tobacco products are to interfere with development of the red blood-corpuscles, leading to pallor and feebleness; to impair the appetite and weaken digestion; to affect the eyes, rendering the retina less sensitive; to cause palpitation of the heart and enfeeblement of that organ; to induce a lassitude and indisposition to exer- tion that, in view of the heavy odds man has to contend with in the life-struggle, may prove the handicap that causes his failure. If success in life be an aim worth striv- ing for, it is surely unwise to shackle one's self with a habit which cannot promote and may seriously jeopardize it. Describe the general action of tobacco on the body. INDEX. Abdominal aorta, 203 Abdominal cavity, 11 Abdominiil respiration, 346 Abduceuttis nerves, 393 Abduction, 63 Absorbents, 107, 188; relation of to excretion, 108 Absorption, from the month, pharynx and gullet, 166; from the stomach, 167; from tlie small intestine, 167; from the large intestine, 168; of fats, 163 Accommodation, 336 Acetabulum, 60 Acid, glycocliolic, 161; hydro- chloric, 20, 157; oleic, 31; pal- mitic, 21; stearic, 21; tauro- cholio, 161 Acinous glands, 129, 131 Adam's apple, 338 Adduction, 63 Afferent (sensory) nerves, 305 Air, changes produced in by being breathed, 251 ; necessary quantity of for each person, 255 ; quantity of breathed daily, 250; renewal of in the lungs, 240; unwholesome, 354 Air-cells, 237 Air-passages, 234; cilia of, 336 Albumen, egg, 31, 117; serum, 21, 113 Albuminoid alimentary prin- ciples, 117 Albuminous (proteid) substances, 31; action of bile on, 161; of gastric juice on, 157; of pan- creatic secretion on, 159, 173- special importance of as food, 111 Alcohol, 131, 348; absorption of, 348; diseases produced by, 350: IS it a food, 131, 343: mental Alcohol (Continued). and moral deterioration due to, 353, 358 Alimentary canal, 9, 106; absorp- tion from, 166; anatomy of, 169; general arrangement of, 128; sub divisions of, 133 Alimentary principles, 116; al- buminoid, 117; carbohydrate, 118; hydrocarbon, 117; inor- ganic, 118; proteid, 117 Amoeba, 179 Amyloids (see Carbohydrates) Anaimia, 185 Anatomy, human, 3, 17 Anatomy, microscopic (see His, tology) Anatomy, of alimentary canal, 133, 169; of circulatory organs, 192; of ear, 339; of eyeball, 331; of joints, 60; of larynx, 337; of liver, 149: of muscular system, 67; of nervous system, 383, 299; of respiratory organs, 333; of skeleton, 23; of skin, 366; of urinary organs, 361, 278 Animals, classification of, 8 (foot- note) Animal charcoal, 55 ' Animal heat, 96 Ankle joint, 83 Aorta, 198, 312; thoracic, 303; abdominal, 203 Apex beat (cardiac impulse), 317 Apex of heart, 195 Appendicular skeleton, 36 Appetite, cause of, 165 Aqueous humor, 335 Arachnoid, 386 Arch of foot, 43, 45 Areolar tissue, subcutaneous, 268 Arm, skeleton of, 38 Arterial blood, 178, 311 366 INDEX. Arterial pressure, 237 ■Arteries, 195, 202; action of alcohol on, 357; aorta, 198, 212: axillary, 203; brachial, 203; coeliac axis, 303; com- mon iliacs, 304; coronary. 199, 202, 313; femoral, 304; hepatic, 150; left common carotid, 203; left subclavian, 303; mesenteric, 202; peroneal, 204; popliteal, 304; pulmonary, 199, 313; radial, 303, 332; renal, 303, 361 ; right common carotid, 303; right subclavian, 303; temporal, 333; tibial, 304; ulnar, 303 Arteries, course of the main, 201 ; muscles of the, 228: properties of the, 204; why placed deep, 205 Articular cartilage, 36, 48 Articular extremities of bones, 48 Articulations, 35 Arytenoid cartilages, 338 Assimilation, 108 Astragalus, 40 Atlantoaxial articulation, 33 Atlas vertebra, 33 Auditory nerve, 293 Auditory organ, 339 Auricles, 197; function of the,320 Auricular appendages, 213 Auricular contraction, 217 Auriculo-ventrioular orifice, 197 Auriculo-ventricular valves, 301, 317; demonstration of their action, 333 Auscultation' 345 Automatic nerve centres, 307; use of, 309 Axial skeleton, 26 Axillary artery, 202 Axis cylinder of nerves, 296 Axis vertebra, 32 Backbone (see Vertebral column) Ball and socket ioint(enarthrosis), 63 Basement membrane, 131 Base of heart, 195 Bathing, 230, 275; proper time for, 276 Beans, nutritive value of, 121 Beef-tea, 77 Beeswax, 118 Beverages, alcoholic, 346 Biceps muscles, definition of, 71 Biceps muscle, 69, 72 Bicuspids (premolars), 136 Bile, 150, 161; action of in fat absorption, 163, 173; uses of, 161 Bile duct, common (ductus com- munis choledochus), 150, 170 Bi-penniform muscles, 71 Bladder, urinary, 363, 278 Blind spot, 334 Blood, action of oxygen on, de- monstration, 359; arterial and venous, 178, 211; changes un- dergone by in the lungs, 257; circulation of, 307; coagulation of, 179; colorless corpuscles of, 179; compared with water, 183; experiments with, 190; flow of in the capillaries and veins, 324; functions of, 174, 175; gases of, 183; histology of, 176 ; hygiene of, 184; quantity of in tlie body, 185; red corpuscles of,177; whipped (defibrinated), 181 Blood-plasma, 176 Blood-serum, 180, 191; composi- tion of, 182 Blushing, 228 Body, centre of gravity of, 85; chemical composition of, 19; constructive power of, 112; co-operation of the organs of, 379; daily need of foods by, 124; general plan of, 6; levers in the, 80; movements of, 59; oxidations in, 99; oxygen food of, 103; pulleys in, 84; quan- tity of blood in, 185; tempera- ture of, 97; wastes of, 105 Bones, chemical composition of, 54; fractures of, 57; function of, 23; gross structure of, 47; histology of, 51 ; internal struc- ture of, 49; of cranium, 37; of ear, 381, of face, 87; of lower limb, 38; of pectoral arch, 27; INDEX. 367 Bones (Oontinued). of pelvic arch, 38; of upper limb, 88; reason that they are hollow, 50; varieties of, 51 Bone-ash, 55 Bone-black (animal charcoal), 55 Bone corpuscles, 54 Bony skeleton, 26; hygiene of, 56 Brachial artery, 203 Brain, 288; dissection of, 399; hygiene of, 311 Bread, composition of, 116; wheaten, superiority of, 120 Breastbone, 37, 34 Bright's disease, 266 (foot-note) Bronchi, 335 Broncliitis, 337 Brunner, glands of, 148 Buccal cavity (See mouth cavity) Butter, 117 Butyrin, 117 Cabbage, nutritive value of, 131 Caecum, 148, 170 Calcium carbonate, 30, 55 Calcium phosphate, 30, 55, 57 Calcaneum, (heel bone) 43 Calices of kidney, 363, 378 Canaliculi of bone, 54 Cane sugar, 118 Canine teeth, 136 Capillaries, 195, 304; absence of pulse in, 336; circulation in, 234, 335; demonstration of the action of, 333; pulmonary, 199; systemic, 198 Capsular ligament, 61 Carbohydrates (amyloids), 33, 118; kinds of in the body, 32 Carbonate of lime, 30, 55 Carbon dioxide, as a waste pro- duct, 105 ; demonstration of presence of in expired ' air, 259; in the blood, 184; per- centage of in iinwholesome air, 355; quantity of passed from the lungs in a day, 353; useless as a food, 113 Cardiac impulse (apex beat), 317 Cardiac orifice of stomach, 143, 170 ^ Cardiac period, events occurring in a, 317 Carotid arteries, 203 Carpal bones, 28, 51; joints be- tween, 65 Carrots, nutritive value of, 131 Cartilage, articular, 26, 48; cellf of, 33; costal, 34; function of, 33; intervertebral, 30, 33 Casein, 31, 117; vegetable, 117 Cells, 15, 17; air, of lungs, 337; cartilage, 33 ; ciliated, of aii passages, 336; forms of, 15; nerve, 397; plain muscle, 76; structure of, 15 Cellulose, 116, 164 Cement of teeth, 137 Centres, nerve (see Nervecen. tres) Centre of gravity of body, 85 Centrum of vertebrae, 30 Cerebellum, 289; functions of, 306; removal of, 313 Cerebral hemispheres, 389; re- moval of, 313 Cerebro-spinal liquid, 386 Cerebro - spinal nerve system, 384 Cervical enlargement of spinal cord, 387 Cervical vertebrae, 30 Cheese, nutritive value of, 120 Chemical changes in respired air, 251 Chemical composition of albu- mens, 31 ; of bile, 161; of blood- serum, 183; of body, 19; of bone, 54 ; of carbohydrates. 32 of fats, 21; of gastric juice, 156 of lymph, 189; of muscle, 77 of pancreatic secretion, 159; of red corpuscles, 183; of respired air, 253 Chest (see Thorax) Chloral, 361 Chordae tendineae, 301, 314 Choroid, 331 Chyle, 158 Chyme, 158 Cilia, 236; demonstration of ac tion of, 249 Circulation, 107, 207; in capilla- 868 INDEX. Circulation {Continued). riesaud veins, 234; portal, 208; pulmonary, 208; sj-stemic, 208; diagram of, 209 Circulatory organs, 192; relation of to excretion, 108; diagram of, 194 Circumduction, 63 Circumvallate papillae, 139, 334 Clavicle (collar-bone), 37 Clotting of blood (see Coagula- tion) Coagulation of blood, 179; cause of, 180; experiments upon, 190; uses of, 181 Coccyx, 30 Cochlea, 331 Coeliac axis, 202 Coffee, 123 Cold, taking, 229 Collar-bone (clavicle), 27 Colloids, 157 Colon, 149, 170 Colorless blood corpuscles, 179, 190 Columnse carnese, 215 Comminuted fracture of bones, 57 Common bile-duct (ductus com- munis choledochus), 150, 170 Compact bone,49; structure of, 51 Compound fracture of bone, 58 Concha, 330 Condiments as foods, 115 Connective tissue, 24 Conservation of energy, lavr of, 93; illustrations of, 94 Consonants, classification of, 341 Constructive power of the body, 112 Convolutions of the brain, 290 Cooking, 123 Co-ordination, 281 ; centre of, 306 Corium (cutis vera, dermis), 268; papillae of, 270 Corn, nutritive value of, 131 Cornea, 321 Coronary arteries, 199, 203, 213 Coronary sinus, 214 Coronary veins, 300, 313 Corpus Arantii, 314 Corpuscles of blood, 176, 190 Costal cartilage, 34 Costal respiration, 246 Cranial nerves, 290; sutures, 38 Cranium, bunes of, 37 Cricoid cartilage, 338 Crystalline lens, 325 Crypts of IjiGberkilhn, 148 Cuticle (i::pidermis), 366 Death, fromstarvation, 98; from alcohol, 347, 352, 353; from cUoral, 363; from opium or morpliia, 361 Death-stiffening (rigor mortis), 74 Defibrinated blood, 181 [355 Degeneration, fatty, 354; ibrous. Deglutition (see Swallowing) Delirium tremens, 353 Dentine, 136 Dermis (see Corium) Dialysis (osmosic), 186 Diaphragm ;'midrifif), 11, 343; de- monstration of, 348 Diarrhoea, 229 Diet, advantages of a mixed, 135 Digestion, 107, 138; gastric, 157, 171; influence of saliva in, 154; intestinal, 163; object of, 152 Dipsomania, 353 Disassimilation, 108 Diseases due to alcohol, 350; to chloral, 362; to morphia or opi- um, 360; to tobacco, 363 Dislocations, 65; reduction of, 66 Division of labor, physiological, Dorsal (neural) cavity, 7, 31 ; con- tents of, 9, 13 Dorsal vertebrae, 30 Duct of glands, 131 Duct, common bile, 150, 170; cys- tic, 150;hepatic, 150; of parotid '^land, 169; of submaxillary gland, 169 Dura mater, 285 Dyspepsia, 164 Eah, 330 Efferent (motor) nerves, 305 Eggs, nutriiive value of, 130 Egg-album;;n, 31, 117 Eirlitli pair cranial (auditory) nerves, 3 8 INDEX. 369 Elasticity of the arteries, 226, 332; of tlie lungs, 338 Elastic tissue, 164 Elbow joint, 65, 70 Elements found in the body, 30 (foot-note) Eleventh pair cranial (spinal ac- cessory) nerves, 393 Emmetropic eye, 337 Emulsion, 160 Eniimel, 136 Endolymph, 331 Endoskeleton, 33 (foot-note) Energy, 93, 101; chief forms of expended by the body, 101 ; conservation of, 93, 101; liber- ation of by oxidations at low temperature, 104; source of in the body, 95 Epidermis, 266 Epiglottis, 143, 333 Ethmoid bone, 37 Eustachian tube, 141, 330 Excretion and reception, inter- mediate steps between, 106 Excretions, removal of, 108 Excretory organs, 106 Exercise, 90 Exoskeleton, 23 (foot-note) Expiration, 343, 244 Extension at joints, 63 Extensor muscles, 80 External auditory meatus, 330 Extracts of meat, 78 Eye, action of alcohol on, 358; accommodation of, 326; hy- giene of, 828 Eyeball, anatomy of, 321 Eyelashes, 318 Eyelids, 318 Eye-socket, 318 Face, bones of, 37 Facial nerve, 393 Fasciculi of muscles, 73 Fatty acids, 117 Fats (hydrocarbons), 31, 117; ab- sorption of, 162; action of bile on, 161, 173; of gastric juice on, 157; of pancreatic secretion on, 160, 172; as a reserve Fats (Continued). food, 98, 102; emulsifying of, 160, 163; kinds of in body, 31 Fauces, 141; isthmus of the, 133, 155; pillars of the, 141 Femoral artery, 204 Femur, 38 Fibres, 16 ; plain muscle, 76; striped muscle, 74 Fibrillffi, 74 Fibrin, 31, 180 Fibula (peroneal bone), 38, 51 Fifth pair cranial (trigeminal) nerves, 393 Filiform papillae, 139, 334 Flexion at joints, 63 Flexor muscles, 80 Food, amount of required daily, 134; as a force generator, 115; as a foi-ce regulator, 115; as a machinery former, 114; as a tissue former, 110; composi- tion of. 111; cooking of , 133; definition of, 114; inorganic, 118; is alcohol a food, 181, 343; need of, 95, 97; non oxi- dizable, 113; nutritive value of different, 119; special iin- porUmce of albuminous. 111; supply of animal, 112 Food-stufEs (see Alimentary prm- ciples) Foot, skeleton of, 39; peculiari- ties of human, 45 Foramen, intervertebral, 33; magnum, 37; oval, 331 Force-generating foods, 115 Force-regulating foods, 115 Forearm, movements of, 64, 70 Fore limb (see Upper-limb) Fossa, glenoid, 63 Fourtli pair cranial (pathetici) nerves, 393 Fractures of bones, 57 Free (floating) ribs, 34 Frog's web, circulation in, 334 Frontal bone, 37 Fruits, nutritive value of, 131 Fundus of stomach, 170 Fungiform papillae, 139, 334 Purred tongue, 140 370 INDEX. Gall (see Bile) Gall bladder, 150 Games, use of, 92 Ganglia, 284; Gasserian, 292; spinal, 287; sympathetic, 294 Gases of the blood, 183 Gasserian ganglion, 292 Gastric digestion, 157; experi- ments illustrating, 171 Gastric glands, 144 Gastric juice, 144, 156; artificial, 171 Gelatine, 55, 117 Gelatinization, stage of in coagu- lation, 179 Glands, 129; forms of, 131; gas- tric, 144; kinds of, 129; lachrjr- mal, 319; mammary, 11; mei- bomian, 318; of Brunner, 148; of skin, 272; of small intes- tine, 148; salivary, 140, 169 Glenoid fossa, 63 Gliding joints (arthrodia), 65 Glosso-pliaryngeal nerves, 298 Glottis, 385 Glucose (grape sugar), 22, 118; conversion of starch into, 153 Gluten, 117, 120 Glycerine, 21, 117 Glycocholic acid, 161 Glycogen, 22, 118, 151, 167 Grape sugar (see Glucose) Gray nerve fibres, 296 Gullet (see CEsopliagup) Gums, 118, 134 Habits, 309 Hremal cavity (see Ventral cavity) Haemoglobin, 178, 310, 358 Hairs, 270 Hair-follicle, 371 Hand, skeleton of, 28 Hard palate, 188 Haversian canals, 53 Haversian system, 58 Hearing, 329 Heart, 9; action of alcohol on, 349, 857; beat of, 216; cavi- ties of, 197; dissection of, 310; experiments upon, 330; position of, 195; how nour- ished, 199; muscle of, 76; pal- Heart {Gontiniie^. pitation of, 144; sounds of, 220; vessels connected with, 198; work done by daily, 221 Heat of body, source of, 96; in- fluence of starvation upon, 97 Hepatic artery, 150 Hepatic duct, 150 Hepatic veins, 209, 213 Hibernation, 98 (foot-note) High heels, bad effects of, 56 Hilus of kidney, 268, 378 Hind-limb (see Lower-limb) Hinge joints (ginglymi),63 Hip-joint, 28, 60 Histology, definition of, 3; of blood, 176; of bone, 51; of kidneys, 265; of lungs, 387; of lymph, 189; of muscle, 74; of nerve cells, 397; of nerve fibres, 396; of retina, 321; of skin, 266 Hollow veins (see Vense cavae) Human anatomy, definition of, 2, 17 Human physiology, definition of, 1, 2, 17 Humerus, 38, 47 Hunger, 316 Hydrocarbons (see Fats) Hydrochloric acid, 20, 157 Hygiene, definition of, 1, 2; of blood, 184; of bony skeleton, 56; of brain, 311; of eyes, 328; of muscles, 89; of respiration, 245, 354; of skin, 274; of teeth, 137 Hyoid bone, 26 Hypermetropia, 328 Hypoglossal nerves, 293 Ileo-colic valve, 149 Ileum, 145 Iliac arteries, 204 Incisors, 135 Incus (anvil bone), 331 Indigestible substances, 164 Inferior maxillary bone (mandi- ble), 37 Inferior maxillary nerve, 293 Inferior turbinate bone, 38, 333 Innominate artery, 202 - INDEX. 371 Innominate bone (os innomina- tum or pelvic bone), 28, 60 Inorganic constituents of tlie body, 20 Inorganic foods, 118 Insertion of muscles, 70 Inspiration, 243. 244 Intercellular substance, 16, 23 Internal ear (labyrinth), 331 Intervertebral foramina, 33 ; discs, 30, 33 Intestinal digestion, 163 Intestinal juice (succus enteri- cus), 163 Intestines, digestion in, 163; large, 148 (see Large intestine); small, 145 (see Small intestine) Invertebrate animals, character- istics of, 8 Involuntary muscles, 75 Iris, 331 Isthmus of the fauces, 133, 155 Jejunum, 145 Joint, anlile, 83; elbow, 65, 70; hip, 38, 60; knee, 63; shoulder, 43, 63 Joints, 25; ball and socket, 63; general structure of, 60; glid- ing, 65; hinge, 63; pivot, 64; movements at, 63 KiDNETS, 9, 261, 278; action of alcohol on, 355, 357 ; gross anatomy of, 263; histology of, 265; secretion of, 266 Knee-cap (patella), 29 Knee-joint, 63 Labok, physiological division of, Labyrinth (internal ear). 331 Lachrymal apparatus, 319 Lachrymal bones, 38 Lacteals, 147, 168, 188 Lactose (milk sugar), 32, 118 Lacunse of bone, 54 Lamellae of bone, 53 Large intestine, 133, 148; absorp- tion from, 168 Larynx, 235, 337; muscles of, 339 Leg, skeleton of, 28 Levers in the body, 80, 81, 82, 83, 84 Lieberkilhn, crypts of, 148 Liebig's extract of meat, 78 Ligaments, 34, 61; capsular, 61; round, 61 ; transverse, of atlas. 33, 64 Light, action of, on the retina. 833, 335 Limbs, comparison of upper and lower, 38; general structure of, 10 Liver, 149; action of alcohol on, 357; functions of, 151 Localization of skin-sensations, 333 Local sign, 333 Locomotion, 86 Long bones, 51 Long sight (hypermetropia), 328 Lower jaw, bone of, 37; move- ments of, 64 Lower limb, comparison of up- per and, 38; peculiarities of, in man, 45; skeleton of, 28 Lumbar enlargement of spinal cord, 287 Lumbar vertebrae, 30 Lungs, 8, 106, 337; action of al- cohol on, 357; changes under, gone by blood in, 357; de- monstration of the action of, 248; dissection of, 247; elas- ticity of, 338; expansion of, 239 ; quantity of COj passed out from, in a day, 253; quantity of O taken up by, in a day, 253: renewal of air in, 840 Lunula of nails, 371 Lymph, 186; cliemistry of, 189; histology of, 189; renewal of, 187 Lymphatics of small Intestine, 147 Lymphatic vessels (absorbents), 188 Malak bone, 38 Malleus (hammer) bone, 331 Malpighi, pyramids of. 364. 378 Mammalia, definition of, 11, 13 Mammary glands, 11 372 INDEX. Man, as a vertebrate animal, 7 13; place of,among vertebrates, 11, 13 Mandible (inferior maxillary bone), 37 Margarin, 117 Mairo\r, 49, 50; red, 50 Maxilla (superior maxillary bone), 38 Meat extracts, 78 Meats, cooking of, 124; nutritive value of, 119 Medulla oblongata, 289 Medullary cavity of bone, 49, 51 Medullary slieatb of nerves, 296 Meibomian follicles, 318 Membranes of tlie brain and spinal cord, 285 Mesenteric arteries, 202 Meseutery, 170 Mstacarpal bones, 28, 51 Metatarsal bones, 29, 51 Microscopic anatomy (see His- tology) MiflriS (see Diaphragm) Milk, as a food, 57; nutritive value of, 120; sugar (lactose), 22, 118; teeth, 135 Mitral valve, 201, 215 Molar teeth, 136 Moral deterioration due to alco- hol, 361 Morphia, 361 Motor (eflferent) nerves. 305 Motores oculi uerves, 291 Moutli-cavity, 133; absorption from, 166 Movements, at joints, 63; of the body, how effected, 59; in space, 86 Mucin, 164 Mucous coat, small intestine, 146 Mucous membrane, of air-pas- sages, 336; of alimentary canal, 128 Mumps, 140 Muscles, 69, 67; chemical com- position of, 77; contraction of, 69; gross structure of, 73; liis- tology of, 74; how controlled, 72; hygiene of, 89; of arteries, 333; of heart, 76; of larynx, Muscles {Continued). 389; of small intestine, 148; of stomach, 144; origin and in- sertion of, 70; papillary, 201, 214, 219; parts of, 67; rectus abdominis, 72; special physi- ology of, 80; varieties of, 71 Muscular fibres, 74 Muscular tissue, striped, 78; plain, 74 Muscular work, influence of starvation upon, 97; source, 93 Mustard, use of, as a food, 115 Myopia, 327 Myosin, 31, 77, 117 Nails, 271 Narcotics, 348 Nares, posterioi', 38 Nasal bones, 38 Nerves, cranial, 290; kinds of, 294; spinal, 287 Nerves, inferior maxillary, 292; ophthalmic, 292; right phrenic, 212; sciatic, 399; superior max- illary, 293; sympathetic, 294 Nerve-cells, 397 Nerve-centres, 283, 284; classifi- cation of, 805; functions of, 304 Nerve-fibres, afferent and effe- rent, 305; kinds of, 295 Nerve-ganglia, 284 Nerve-trunks, 383; functions of, 304 Nervous system, anatomy of, 282; properties of, 801, 313 Neural arch, SI Neural cavity (see Dorsal cav- ity) Nicotin, 363 Ninth pair cranial (glosso-pha- ryngeal) nerves, 293 Nitrogen-excreting organs, gene- ral arrangement of, 261 Nou-oxidizable foods, 113 Non-vascular tissues, 175 Nucleolus, 15 Nucleus, 15 Nutrition, 109 Nutritive value of different foods, 119 INDEX. 373 Occipital bones, 37: condyles, S3 Odontoid (tooth-like) process of tlie axis, 83, 64 Odorous substances, 338 OSsopliagus (gullet), 8, 133, 143, 169; absorption from, 166 Oils (see Fats) Oil glands (sebaceous - glands), 273 Oleic acid, 21 Oleine, 3t, 117 Olfactory lobes, 289 Olfactory nerves, 390 Omentum, 13, 170 Ophthalmic nerves, 393 Opium, 859 Optic commissures, 291 Optic nerves, 390, 317 Organ, definition of, 4; cifcula- tory, 107, 192, 194; digestive, 107, 128; nitrogen excreting, 261; of hearing, 329; of sight, 317; of smell, 383; of taste, 334, of temperature sense, 333; of touch, 331; receptive and ex- cretory, 105; respiratory, 108, 283 Organic constituents of the body, 30 Organs diseased by alcohol, 856 Origin and insertion of muscles, 70 Os innominatum (see Innominate bone) Osmosis, 186 Oval foramen, 331 'xidations in the body, 99 ■idations, 99, 100 Oxygen, absorption of from the lungs, 358; in the blood, 184; influence of on the color of the blood, 259; quantity of taken up by the lungs in a day, 253 Oxygen food of the body, 103 Oxyhsemoglobin, 258 Palate, 133 Palate bones, 38 Palmitic acid, 31 Palmitin, 31, 117 Palpitation of the heart, 144 Pancreas, 151, 170 Pancreatic secretion, 159; action of on food-stufCs, 160, 172 Papillae of the dermis, 270 Papillse of the tongue, 139 Papillary muscles, 301, 314; use of the, 319 Parietal bones, 37 Parotid gland, 140, 169 Patella (kuee-cap), 29 Pathetic! nerves, 293 Peas, nutritive value of, 131 Pectoral arch or girdle, 37; com- parison of pectoral and pelvic girdles, 38 Pedicle of vetebrse, 33 Pelvic arch or girdle, 38; com- parison of pectoral and pelvic girdles, 38 Pelvis, 38, 45 Pelvis of kidney, 363 Penniform muscles, 71 Pericarditis, 196 Pericardium, 195, 213 Perilymph, 831 Perimysium, 73 Periosteum, 47, 51 Permanent teeth, 135 Peroneal artery, 204 Perspiration, 272 Pepper, use of as a food, 115 Pepsin, 157 Peptones, 157; absorption of, 167 Phalanges of fingers, 28, 51; of toes, 39, 51 Pharynx, 138, 141; absorption from, 166 Phosphate of lime, 20, 55, 57 Phrenic nerve, 313 Physiological division of labor, 17 Physiology, human, definition of, 1, 3, 17 Physiology of muscle, special and general, 80 Pia mater, 385 Pillars of the fauces, 141 Pivot joints, 64 Plain muscular tissue, 74 Plants, as food for animals, 112 374 INDEX. Pleura, 238 Pleurisy, 238 Pneumogastric nerve, 298 Poison, definition of, 116 Polygastrio muscles, 73 Pons varolii, 289 Popliteal artery, 204 Pork, nutritive value of, 119 Portal circulation, 208 Portal vein, 150, 170, 208 Posterior nares, 38 Potatoes, nutritive value of, 121 Premolars (bicuspids), 136 Primitive sheath of nerves, 296 Pronation, 65 Proteid alimentary principles, 117 Proteid substances (see Albumin- ous substances) Psychic nerve centres, 305 Pulleys in the body, 84 Pulmonary artery, 199, 212 Pulmonary circulation, 192, 208 Pulmonary veins, 199, 212 Pulp cavity of tooth, 136 Pulse, 222; disappearance of in capillaries and veins, 226; hard and soft, 223; rate of, 223 Pupil, 381 Pus, 179 Pyloric orifice of stomach, 143, 170 Pyloric sphincter, 144, 157, 158 Pyramids of Malpighi, 264, 278 Rncemose (acinous) glands, 129, 181 Radial artery, 202, 222 Radius, 28, 51 Receptive organs of the body, 105 Reception and excretion, inter- mediate steps betvreen, 106 Rectum, 149, 170 Rectus abdominis muscle, 72 Red blood corpuscles, composi- tion of, 183; function of, 178, 259; of man, 177, 190; of other animals, 177 Red-marrovF, 50 Reduced hsemoglobin, 210 Reducing dislocations, 66 Reflex centres, 808; experiments showing action of, 313; use of, 809 Refracting media of the eye, 325 Renal arteries, 202, 261 Renal secretion (urine), 266 Renal veins, 261 Respiration, 108; abdominal, 246; chemistry of, 250; costal, 246; experiments in, 248, 259; hy~ giene of, 245, 254; object of, 233 Respiratory organs, 108; anat- omy of, 283 Respiratorysounds or murmurs, 245 Retina, 317; histology of, 821 Ribs, 26, 84; action of in respira- tion, 244 Rice, nutritive value of, 121 Right phrenic nerve, 212 Rotation at joints, 63 Round ligament, 61 Running, 89 Saokum, 80, 84 Saliva, 152, chemical action of, 158, 171; influence of in diges- tion, 154; uses of, 152 Salivary glands, 140, 169 Salt, as a constituent of the body, 20, importance of as food, 118 Sarcolemma, 74 Scapula (shoulder-blade), 27, 51 Sciatic nerve, 299 Sclerotic, 821 Sebaceous glands (oil glands), 273 Sebaceous secretion, 274 Secretion, of gastric glands, 144, 156; of glands of small intes- tine, 163; of liidneys, 266; of lachrymal gland, 319; of liver, 150, 161 (see bile); of meibomi- an follicles, 318; of pancreas, 159 (see Pancreatic secretion); of salivary glands, 152 (see Saliva); of sebaceous glands, 274; of sweat glands, 272 Semicircular canals, 331 Semilunar valves, 201, 218; dem- onstration of action of, 281 Semivowels, 841 INDEX. 375 Sensations, 314; common, 315; localization of skin, 333 Senses, special, 316 Sensory (affuient) nerves, 305 Septum of heart, 197, 313 Serum (see Blood-serum) Serum albumen, 21, 113; coagu- lation of, 183, 191 Seventh pair cranial (facial) nerves, 293 Shaft of bones, 48 Short bones, 51 Short sight (myopia), 337 Shoulder girdle(see Pectoral arch) Shoulder ioint, 42, 63 Shower baths, 377 Sight, sensation of, 317; organ of, 317 Sigmoid flexure, 149 Simple fracture of bones, 57 Sinuses of Valsalva, 315 Sixth pair cranial (abducentes) nerves, 292 Skeleton, appendicular, 27; axi- al, 26; composition of, 23; of cranium, 37; of face, 37; of lower limb, 38; of upper limb, 28; peculiarities of human, 43 Skin, 266; action of alcohol on, 356; as a sense-organ, 274; glands of, 272; histology of, 266; hygiene of, 374; sensa. tions, localization of, 333 Skull, 86, 35 ; peculiarities in the position of, 43 Small intestine, 133. 145, 170; absorption from, 167; glands of, 148; lymphatics of, 147; mucous coat of, 146 ; muscular coat of, 148; villi of, 146 Smell, 333 Sounds of the heart, 330 Soiinds, respiratory, 845 Sound waves, action of on the ear, 331 Special physiology of muscles, 80 Speech, 336 Sphenoid bone, 37 Spinal accessory nerves, 893 Spinal cord, 9, 386 ; dissection of, 899 Spinal ganglia, 387 Spinal nerves, 387 Spine (see Vertebral column) Spinous process of verlebrse (neural spine), 31 Spleen, 170 Spongy (cancellated) bone, 49 Sprains, 66 Standing, 84 Stapes (stirrup bone), 331 Starch, 118; action of bile on, 161 ; of gastric juice on, 157; of pancreatic secretion on, 159, 173; of saliva on, 153, 171; sol- uble, 134 Starvation, death from, 98; in- fluence of on muscular work and animal heat, 97 Stearic acid, 81 Stearin, 31, 117 Sternum (breast bone), 37, 34 Stimulants, 115. 132, 343 Stomach, 8 143, 170; absorption from, 167; action of alcohol on, 350, 356; digestion in, 157, 171; glands of, 144; muscular coat of, 144 Striped muscular tissue, 73, 74 Sub-clavian artery, 302 Sublingual gland, 141, 169 Sub-maxillar}' gland, 140, 169 Succus entericus (intestinal juice), 163 Sudoriparous glands (sweat- glands), 131, 272 Suffocation, 104, 253 Sugar, cane, 118; grape (see Grape-sugar) Sugar of milk (lactose), 32, 118 Superior maxillary bone, 38 Superior maxillary nerve, 393 Supination, 64 Swallowing (deglutition), 154; as a reflex action, 309 Sweat, 372 Sweat (sudoriparous) glands, 131, 272 Sweetbread (see Pancreas) Sympathetic nerve centres, 9, 13, '384; ganglia of, 293 Synovial fluid, 61 Synovial meml)rane, 61 Syntonin, 77, 117 376 INDEX. Systemic circulation, 192, 208 Systole of lieart-beat, 216 Tabtjlak bones, 51 Tarsal bones, 29, 51; joints be- tween, 65 Tarsus, benefits of peculiar str\icture of, 45 Taste, 334 Taurocliolic acid, 161 Tea, 123 Tears, 319 Teeth, characteristics of Indi- vidual, 135; general structure of, 134; hygiene of, 137; kinds of, 134 Temperature changes in respired air, 251, 259 Temperature of the body, 96; regulation of, 97; regulation by means of sweat glands, 274 (foot-note) Temperature sense, 333 Temporal artery, 222 Temporal bone, 37 Tendons, 24, 67, 69 Tenth pair cranial (pneumogas- tric) nerves, 293 Thein, 115 Thigh bone (femur), 28 Third pair cranial (motores oculi) nerves, 291 Thirst, 316 Thoracic aorta, 202 Thorax, contents of, 11; dorso- ventral enlargement of, 244; structure of, 242; vertical en- largement of, 242 Thyroid cartilage, 888 Tibia, 28, 51 Tibial artery, 204 Tight lacing, evil effecis of, 247 Tissues, classification of, 4 (foot- note); connective, 24; nerve, 294; non-vascular, 175; plain muscular, 74; striped muscular, 74; subcutaneous areolar, 268: ultimate structure of, 15 Tobacco, 363 Tongue, 139; furred, 140 Tonsils, 141 Touch, 331 Trachea (windpipe), 8, 235; dia section of, 247; structure of, 286 Transverse ligament of the atlas, 32, 64 Triceps muscle, 72 Triceps muscles, definition of, 71 Trichina, 120 Tricuspid valve, 201 , 214 Trigeminal nerves, 292 Trvpsin, 160 Tubular glands, 129, 131 Turbinate bones, 88, 333 Turnips, nutritive valve of, 121 Twelfth pair cranial (hypoglos- sal) nerves, 293 Tympanic membrane, 830 Tympanum, 330 Ulna, 28, 51 Ulnar artery, 202 Unstriped muscle cells, 76 Upper jaw bone, 38 Upper limb, comparison of upper and lower limbs, 38; skeleton of, 28 Urea, 105, 111, 266; useless as food, 112 Ureters, 263, 278 Urethra, 263 Urinary bladder, 263. 278 Urine, "266 Uriniferous tubules, 265 Uvula, 134 Vagi, 293 Valsalva, sinuses of, 215 Valves, auriculo-ventricular, 201, 214, 217, 232; ileocolic, 149; of the heart, demonstration of their action, 231; of the veins, 206; semilunar, 201, 215, 218, 231 Valvulse conniventes, 146 Vascular system, function of the diflferent parts of, 193 Veins, 194, 205; absence of pulse in, 226; circulation in, 224; valves of the, 206 Veins, coronary, 199, 213; he- patic, 209, 212; hollow (venre cavffi), 199, 212; portal, 150, INDEX. 377 Veins (Continued). 170,208; pulmonary, 199, 213; renal, 261 Vegetable casein, 117 Venae cavee (hollow veins), 199, 212 Venous blood, 178, 211 Ventilation, 253; methods of, 256 Ventral (hsemal) cavity, 6; con- tents of, 8, 13 Ventricles, 197 Ventricular contraction, 218 Vermiform appendix, 148 Vertebrse, 30, 51; structure of, 30 Vertebral column, (spine, back- bone), 7, 26, 30, 34; curvatures of, 33; mechanism of, 33; pecu- liarities of human, 44 Vertebrate animals, characteris- tics of, 7; classification of, 11 (foot-note) Vestibule of ear, 331 Villi of small intestine, 146, 170 Visual apparatus, 317 Visual centre, 317 Visual purple, 328 Vitreous humor, 325 Vocal cords, 338 Voice, 335; range of human, 340 Voluntary muscles, 75 (see also foot-note) Vomer, 37 Vowels, 340 Walking, 87 Warm baths, 277 Wastes of the body, 105; removal of, 175 Water, as a constituent of the body, 20; as a food, 113, 118; as a force regulator, 115; as a ■waste product, 105; quantity of lost through the kidneys, 266; through the lungs, 251; through the skin, 273 Wheat, nutritive valve of, 120 Whipped (defibrinated) blood, 181 White blood corpuscles, 179, 190 White nerve fibres, 295 Windpipe (see Trachea) Wisdom teeth, 135 Work, daily, of heart, 221; in- fluence of starvation upon muscular, 97; power of the body to do, 93