UC-NRLF B 3 1ED 3SE AMERICAN SCIENCE SERIES, BRIEFER COURSE THE HUMAN BODY AN ELEMENTARY TEXT-BOOK OF ANATOMY, PHYSIOLOGY 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., F.R.S. Professor of Biology in the Johns Hopkins University THIRD EDITION, REVISED NEW YORK HENRY HOLT AND COMPANY 1889 > BIOLOGY LIBRARY G COPYRIGHT, 1883, 1884, BY HENRY 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 subject, than those for whom that book was designed. This demand^ and the fact that a second edition of the ft 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 sufficiently IV PREFACE. 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 the " 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 appendices 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. PREFACE. V It may be well to anticipate a possible objection. A few persons, some of them worthy of respect, assert that no ex- periments on an animal can be shown to a class without hardening the hearts of operator and spectators; even when, in accordance with the directions 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, nofc 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 sure 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 larger. 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 teachers 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 proof-sheets, and prepared the index. H. NEWELL MABTLKT. JOHNS HOPKINS UNIVERSITY, August 10, 1883. PREFACE TO THE SECOND EDITION. THE second edition of this book differ? from the first for the most part only in verbal alterations 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, 1864. CONTENTS. CHAPTER I. THE GENERAL STRUCTURE AND ARRANGEMENT OF THE HUMAN BODY. PAGE Human Physiology — Hygiene — Anatomy — Histology — Tissues — Organs — The general plau 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 II. THE SfrCROSCOPICAL 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 III. 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 23 CHAPTER IV. THE STRUCTURE, COMPOSITION, AND HYGIENE OF 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 CONTENTS. CHAPTER V. JOINTS. PAGE Muscles and joints — Structure of the hip joint — Ball and socket joints — Hinge joints — Pivot joints — Gliding joints— Disloca- tions— Sprains * 59 CHAPTER VI. THE MUSCLES. The parts of a muscle — The origin and insertion of muscles — Varieties of muscles — How muscles are controlled— Gross structure of a muscle — 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. WHY WE EAT AND BREATHE. How it is that the body can do work — The conservation of en- ergy— Illustrations — Why we need food — Why the body is warm — The influence of starvation upon muscular work and animal heat — Oxidations in the body — The oxygen food of the body — Appendix 93 CHAPTER IX. . NUTRITION. 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 PAGK on plants— Non-oxidizable foods— Definition of foods— All mentary principles — The nutritive value of various foods — Alcobol— Tea and coffee— Cooking— The advantages of a mixed diet 110 CHAPTER XL 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 152 CHAPTER XIII. BLOOD AND LYMPH. Why we need blood— Histology of blood — The blood corpuscles — Hgeniaglobin — 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 OP THE CIRCULATORY ORGANS. 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-1— 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 192 X CONTENTS. CHAPTER XV. THE WORKING OP THE HEART AND BLOOD VESSELS. PAGE 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 OF RESPIRATION. 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 soundj> — Hygienic remarks— Appendix , 233 CHAPTER XVII. THE CHFMISTRY 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-excreting 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 Of 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. THE GENERAL PHYSIOLOGY OF THE NERVOUS SYSTEM. PAGE The properties of the nervous system — Functions of nerve centres and nerve trunks — Sensory and motor nerves — Classi- fication of nerve centres — Functions of the cerehrum — Of the cerebellum — Reflex nerve centres — Automatic nerve centres — Habits — Hygiene of the brain — Appendix 301 CHAPTER XXI. THE SENSES. 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 XXII. 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 XXIII. ALCOHOL AND OTHER STIMULANTS AND NARCOTICS. Introductory — Is alcohol a food? — Composition and properties of alcohol — Alcoholic beverages — The direct physiological action of pure alcohol — 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 by alcohol — Opium and morphia — Chloral — Tobacco 343 THE HUMAN BODY, CHAPTER L 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, j?f 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. T;at is human physiology? What is a function? What do physiologists endeavor to discover? What is meant by 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 en 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 number of different materials enter into its formation. Hairs, nails, skin, and teeth are 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 the body. What may we feel through the skin ? MICROSCOPIC1 ANATOMY OR HISTOLOGY. 3 masses under it ; while 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/^; 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, arid 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 build a house or a bridge, but are put together in a different manner 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 gristle? What is connective tissue? Are other parts of the body besides the hand made up of different substances ? Illustrate by an example? 4 THE HITMAN BODY. The branch of anatomy which deals with the charac- ters of the materials used in the construction of the parts of the body is called histology, or, since it is mainly carried on with the aid of the microscope, microscopic anatomy. Tissues. — Each of the different 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 presents 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, which 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 which 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 duty 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 has a characteristic ap- What is histology? Give another name for it. What is a tissue? Give examples. How do tissues differ? Are there a large number 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 ? * The various tissues of the body will be considered in more detail subsequently: ^ the more important are — 1. Bony tissue. 3. Cartilaginous tissue. 3. White fibroua i TISSUES AND ORGAN'S. 5 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 placed 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 recognized ? Give examples of differences in properties of various tissues. How do organs differ from one another ? In wliat do all organs 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-organ or irritable V.esues. 9. Nerve cell tissue. 10. Nerve fiber tissue. 11. Striped muscular tissue. 12. Unstriped muscular tissue. 13. Epidermic and epithelial tissue. 6 THE HUMAN BODY. The general plan on which, 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 plant 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 relative 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 licemal cavity, lies on the front side, and contains the 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 should we 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 haemal cavity extend toward the head ? GENERAL PLAN OF 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 ? Fia. 1. — Diagrammatic longitud- inal section of the body. «, the neural tube, with its upper enlarge- ment in the skull cavity at a'; N, the spinal cord; N', the brain; ee, vertebrae forming the solid parti* tion between the dorsal and vent- ral cavities; 5, the pleura!, and, e, the abdominal division of the ventral cavity, separated from one another by the diaphragm, 'd; i, the nasal, and o. the mouth cham- ber, opening behind into the pharynx, from which one tube leads to the lungs, /, and another to the stomach,/; A, the heart; k, a kidney ; s, the sympathetic nervous chain. From the stomach, f. the intestinal tube leads through the abdominal cavity to the pos- terior opening of the alimentary canal, 8 THE HUMAN BODY. 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 cavities 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 ven- tral side ; that is on that surface of the body next which the haemal 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, I; the other is the gullet, and leads to the stomach, f. From the stomach, another tube, the intestine, leads to the outside again at the lower or posterior f 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? Do any smaller cavities in it open on the exterior of the body? What openings do we rind 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? * The main groups m which animals arc arranged are— 1. Vertebrata, or backboned animals. 2. Mollusca, 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, star fishes, &c. 6. Cailenterala, 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 be the natural standing position of the creature, TWO CHIEF CAVITIES OF THE BODY. 9 gullet, stomach, and intestine, together form the aliment- ary canal, which, as we see, begins ~on the head quite above or anterior to the ventral 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, k ; 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. 2.— A diagrammatic section across the body in the chest region, x, the dorsal tube, which contains the spinal cord; the l>lack mass surrounding it is a vertebra; a, the gul lot. a. part of the alimentary canal; h, the heart; sy, sympathetic nervous system; II. lungs; the dotted lines around them are the pleurae; rr, ribs; tl, 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, which are found in the ventral cavity. Describe what would he seen on a section oiade across the hody ahout tfte middle of tb$ chest, 10 THE HUMAN BOD7. sented in the 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, sty on the ventral side (below in the figure) is the haemal cavity, containing the lungs, Z, I ; the heart, h; the gul- let, a; and the sympathetic centers, sy. FIG. 3.— A section across the forearm a short distance below the elbow-joint. 1 and 17, its two supporting bones, the radius and ulna; e, the epidermis and d, the dennis, of the skin; the latter is continuous below with bands of connective tissue, «, which penetrate between and invest the muscles, which are indicated by numbers, n, ft, 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 Z7and 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 Uood, or a watery- looking liquid known as lymph. These tubes, the Uood 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 f ound iu otJier par; * ui w« body 2 MAN'S PLACE AMONG VERTEBRATES. \\ Man's place among Vertebrates. — It must be clear to every one that although man's structural 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, arid monkeys. The organs which form milk are the mammary glands, and all kinds of animals whose ' males possess them are known as Mammalia *: man is, therefore, a Mammal. In internal structure one of the nost important characters of the Mammalia is the pres- ence of a cross-partition, called the midriff or die- phragm, which separates the haemal cavity into an an- terior and a posterior division. This partition is shown at d in Fig. 1, 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 tht, 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 characters ? \Vhat 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 the Mammalia differ from other vertebrates? Where does the diaphragm lie? What , is the name of the cavity above it? What 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. — — .to- * Zoologists classify vertebrate animals in five groups. 1. Pisces, including all -"to "| sharks, eels, salmons, shad, perch, &c., but excluding the so-called '"* Meters, which are not vertebrates at all. 2. Am- ]<-i-3 &c. 3. ReptUia, lizards, alligato>-- "••-«-' THE HUMAN BODY. ind of the gullet (which pierces the diaphragm), the itomach, the intestine, the kidneys, and most of the /organs making digestive liquids. The sympathetic nerve (~ 13 no Fro. 4.— The body opened from the front to biipavity. tu. lungs; A, heart, partly covered by o /^..'Aafcrjflbep respectively: ma, stomach; ne, the g4 A ^^ff^h hanes down from the oosf prior 1>1 ja.rc iiiey it Il ^r they COlitUUlf 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, 2, 2 ; 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 amen- tum, ne, ne, which lies over and conceals the intestines. Summary. — Man is a vertebrate animal, because his body presents dorsal and ventral cavities separated from one another by a hard 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 ; (2) 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 the 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 uppti^. limit lie? TV hy is man a Mammal? in what is man superior to iy other animal? From what point of view have anato- mists to regard man's body? What sort of facts do they take iii to account in assigning man's position among animals? 14 THE 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 differences which are found between it and them. * * It will be found very useful to accompany the teaching of this chapter with a demonstration 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 seen, and on cutting across the spinal column with stron£ scissors, the slender soft spinal cord lying in its tutx: 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 arranged 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 cell 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 dot, 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, float in our blood, and are more or less 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 different forms of cells. * So called from an old belief that they were little bags or chambers. Most cells are really solid or semisolid throughout. [15] FiG.'5. — Forms of cells from the body. 16 THE HUMAN BODY. 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 &Jiber; 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 between the 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 ; b, nu- cleus; c, nucleoli. What are fibers ? How are they made ? In what respect may an organ be compared to a brick wall ? What corresponds to the mortar of the wall ? What makes tlie intercellular substance? How ? State briefly the relationship of its cells to the structure and work- ing of the body. MICROSCOPIC COMPOSITION OP 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-mi 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 the 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 his 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 properly 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 ? What its faculties ? Give examples of the employment of cells with different powers 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 whether 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. — From 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 Avith 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 differ 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 THE BODY. 19 very imperfectly carried oufc even in the most advanced communities, and we accordingly hear from time to time of the over-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 similar 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 distributing 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 tTTeneeds of thn whnlfi body at the time being. We accord- mgly find a set of organs, the heart and 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- How does the division of duties in it affect the human body ? What is the object of the distributing mechanism ? What of tha regulating ? What are the distributing organs in the body called ? What is the object of the nerve organs ? 20 THE HUMAN BODY. istry to our aid, to discover what elements and compounds make up the cells and intercellular substance. Elements found in the body. — Of the elements, about seventy in number, known to chemistry, only sixteen exist in the body.* Very few of these exist in it uncombined. Some oxygen is dissolved in the blood ; and it is also found mixed with nitrogen in the lungs. Chemical compounds existing in the body. — These are so numerous that ib would be a long task to enumerate them, but some few require mention : they may be divided into organic and inorganic. 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) exists in the gastric juice, which dissolves some kinds of food in the stomach. Organic constituents of the body. — The organic con- stituents of the body all 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, lithium, e»lciiim, magnesium', iron, and manganese. CHEMICAL COMPOSITION OF TEE BODY. $1 oxygen ; some contain nitrogen also. There a' 3 three chief kinds of them, viz. : 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 labor- atory-) 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 albumen, 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 them ? 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 ? Name the more important albumens of the body. Where are they found ? What elements do fats contain ? Name the chief fats of tne body. Into what may they be decomposed ? 22 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- bohydrate 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 lactose or milk sugar is found in milk. What elements do carbohydrates contain ? Name the most im- portant found in the body ? Where is glycogcn found ? Where milk sugar ? CHAPTER III. THE SKELETON. The skeleton * of the human body is composed of three materials : lone, cartilage, and connective tissue. The bones 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, ~b, 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 skeleton met with in the animal kingdom ; the external skeleton or exoskeleton, and the internal skeleton or endosketeton. The exoskeleton is made by the skin, either in it or on it ; examples are found in the shells of clams anu lobsters : the scales of fishes and snakes ; the tortoise-shell of turtles ; the feathers of bird5*; the hair and claws of beasts. In man the exoskeleton is only Slightly developed, hair, uaiis and teeth belong to it. [23] 24 THE HUMAN BODY, the cells only, but these lay dx^wn around them more and intercellular substance, until at last it forms the main bulk FIG. 7. — A thiu slice of cartilage highly magnified. of the cartilage, and gives 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 what are ligaments and \ tendons composed ? Where else do Wi; nnd connective tissue ? 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, o, succeed these in the front half of the sole Pas Fsa Fia. 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 THE HUMAN BODY. The vertebral column. — (Fig. 9.) The upper portion of the spine consists of twenty-four separate bones, each called a vertebra; 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 Fig. 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, C, 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 called? 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 vertebrae are united to form the coccyx? What vertebrae differ essentially in form from the rest? Describe a typical vertebra. A VERTEBRA. 31 the vertebra ; the series of vertebral bodies forms the bony partition (, 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, vertebral foramen. 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 mtervertcbral foramina formed? What is their pur- pose? What is the first cervical vertebra called? Describe its general form. How is its neural ring divided? What lies in each division? What is the second cervical vertebra named? What is the odontoid process? Around what pivot does the head rotate when the face is XUrnod on either side? SPINAL COLUMN. 33 carrying the skull with it, rotates when the head is turned from side to side. On the {interior (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. 20), vvhich 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 opposite 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 vertebrae 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- bras 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? * Take 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. 34 THE 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, such 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 /ij 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 free v or floating ribs. Flow is it that we can bend the backbone? How is the extent of bending at any one point limited? Why? Why do the sacral vertebrae grow together? State briefly the mechanical properties of the vertebral column. How many ribs are there ? What is their shape ? To what are their dorsal ends attached? How does each rib end ventrally? To what are the costal cartilages of the first seven ribs attached? To what the next three costal cartilages? Which are the floating ribs? Why so called? TEE SKULL. 35 vertebra, The skull (Fig. 16) is composed of twenty-eight bones : these, forming the cranium, are so arranged as How many bones in the skull? 36 THE HUMAN BODY. to surround the brain and protect the ears ; six lie inside the ears ; and the remaining fourteen support the face, Tsp PIG. 16.— A side view of the skull. <9, occipital bone ; T, temporal • TV, parie- tal ; F, frontal ; S. sphenoid ; Z, malar ; MX, maxilla ; 2V, nasal ; Et ethmoid ; L, 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 the face? What parts do the face bones support and protect? CRANIUM. 37 The cranium is a box with 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. 20) 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. The occipital lone, 0, unpaired, and having in it the fora- men magnum. It lies at the back of the skull. 2. The frontal hone, F, also unpaired, lies in the forehead. 3. The parietal bones, Pr, two in number, meet one another above the middle of the crown of the head, and form a great part of the roof and sides of the skull. 4. The tem- poral bones, T, ^ne 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. The sphenoid hone, unpaired, and lying in the middle of the base 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 hone, 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 lower jaw hone 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 unpaired? 38 THE HUMAN BODY. which, forms part of the partition between the two nostrils. The paired face bones are : 1. The maxiUcB or upper jaw-bones, MX, which carry the upper teeth and form most of the hard palate separating the mouth from the nose. 2. The palate bones, 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-bones, Z. 4. TJte nasal bones, 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 bones, 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 bones 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 unpaired face bones. Where does each lie? Name the paired face bones. State the position of each in the skull. What bone carries 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 OF LIMBS. FIG. 17.— The skeleton of the arm and leer. 17, the hnmerus ; Cd, its articu». . head which fits into the glenoid fossa of the scapula ; U, the ulna ; 72, the ra- dius ; 0, the olecranon ; Fe, the femnr ; f, the patella ; M, the fibula ; T the tibia. been enumerated, but certain resemblances and diffei- ences between the skeletons of the two limbs (Fig. 17) are worth noting. In general plan it is clear that they 40 TUE HUMAN BODY. 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 ; five metacarpal bones correspond to fiye metu- tarsal, and fourteen phalanges in the digits of the hand to fourteen in the 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 the 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 (Fig. 19), of the tarsus consists of two bones. The elbow-joint bends ventrally^ud 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, C, 8 Do the upper and lower limbs correspond in general plan of struc- ture ? What in the lower limb answers to the pectoral girdle ? What to tho humerus ? What bones to those of the forearm ? What to the metacarpal ? Do the phalanges of the hand and foot agree in number ? 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 adults? 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 ar« tia lower limb bones more firmly knit? SHOULDER AND PELVIS. 41 Pig. 18, only directly attached to the axial skeleton by the ventral ends of the collar bones, and free to make consid- Fia. 18.— The skeleton of the trunk and the limb arches seen from the front. C. clavicle ; S, scapula ; Oc, innominate bone attached to the side of the saorum dorsally and meeting its fellow at the pubic symphysis in the ventral median line. erable 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 THE HUMAN 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. Cl C? XT SfH FIG. 19.— The bones of the foot. Ca, calcaneum, or heel bone; Ta, articular Btuface for 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 shoulder-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 bones arrans^d? On what points does the arch of the foot bear? On what part of the arch is the weight of the body borne? PECULIARITIES OF 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 opposing the great 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 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 differ in this respect from the great toe? What reason have we to think that tl e 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 ,nd 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 usually awakened by a sharp jerk downwards of 44 THE HUMAN BODY. keep the head erect. In four-footed beasts the skull, being carried on the front end of a horizontal backbone, needs special ligaments and considera- ble muscular effort 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. 2. The human spinal column, when viewed from the front, is of the mouth and surrounded by the upper set of teeth. Above seen to widen gradually from the this are the paired openings of the posterior nares. and a short way above the middle of the fig- ure is the large median foramen magnum, with the bony convex- FIG. 20.— The base of the skull. The lower jaw has been removed. At the lower part of the figure is the hard palate forming the roof neck to the sacrum, and so to be well fitted to sustain the weight of the head, upper limbs, of^ht^kuirbehtd £S &c., carried by it. Its curvatures, which are peculiarly human, add in an ape the portion in front of ,n •, • j i ,• •> the occipital condyies would be greatly to its spring and elasticity; much larger than that behind . -, , • • -\ -\ ji them. 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? Why 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. The muscles concerned In holding the head erect having relaxed their vigilance the greater weight of the front half of ihe skull exerts its effect. PECULIARITIES 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 apes 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 very big nail ; others, as bears, place the heel also on the 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 with 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 BODY. 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 sud- den jerk a gentle sway is transmitted to the carriage. The tarsal arch of the hu- man foot acts like the upper half of a carriage spring. IV. THE STRUCTURE, COMPOSITION AND HYGIENE OF BONES. The gross structure of bones. — Although the bones differ very much in shape all are alike in microscopic structure and in chemical coir _;tion. When alive they have a bluish-white color, with a pinkish hue when blood 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. 21). 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- 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 color of 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. [47J 48 THE HUMAN BODY. Cp FIG. 21.-The from the front, text. r description Tee which dies if it be stripped off.* The periosteum covers the humerus except on its ends (Cp, Tr, Cpl) 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 life? 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? * Cases 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 bearing surface in the joints, and also to provide space on which to attach the muscles which move the bone ; the 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. 22 represents such a longitudinal section. We see in it that the marrow cavity ends near the articular extremities ; and that in these the hone 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 What do the knobs and rough patches on the bone indicate? What should we find on dividing the hu- merus lengthwise? What is its shaft cavity called? What does it contain? Where does the marrow cavity end? What is the texture of the articular extremities of the bone? How FIG. 22.— The humerus does the shaft differ in structure from the ex- cut open, a, marrow tremities of the femur? What does the spongy «Jg5 bone look like? lae. * These facts may readily be demonstrated by sawing in two lengthwise the bones out of a leg of mutton. 50 THE HUMAN BOD7 head of a small pin. In these spaces there is found dur- ing life a substance known as the red marrow, which is quite different 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 the bones of birds are thin walled tubes of dense bone : the centraj cavity contains air and no marrow, and communicatec by tubes with the luiigs. Examine the humerus of a pigeon or a rooster. HISTOLOGY OP BONM. 51 articular extremities, are called long bones ; other examples are tibia and fibula, radius and ulna, metacarpal and meta- tarsal bones, and the 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 andtarsal (Fig. 19) bones. Irregu- lar bones 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 histology oi 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 differs from spongy bone in the fact that its cavities are much smaller, and the hard bony plates between them thicker,, It a thin trans- verse section of the shaft ot 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? What 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 iimes? Where do the apertures in it become larger? THE HUMAN BODY. i cavity and pass insensibly into the spaces ot the spongy bone around it. These openings are the cross sections of Fio. 23.— A, a transverse section oi the ulna, natural size ; showing the medul- lary cavity. B\ the more deeply shaded nart of A magnified 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 enters them? Where do tiie blood-vessels of a bone run? What do they carry n ffiSTOLOGY OP BOflE. 53 Around each Haversian canal is a series of plates or ^ 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 spongy bone the Haversian canals are very large, containing red marrow as well as blood-vessels, and the lamellae around each are few in number. FIG. 24.— A small 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 lamellaB ; they "What lies around each Haversian canal? What is an Haversian system? Of what does a bone consist in addition tc 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? What spaces lie between the lamella} of an Haversian system? 54 THS SUM AN BODY. are called lacuna; from eacli lacuna radiate many ex- tremely fine tubes, the canaliculi, so tnat each, lacuna with its canaliculi looks something like a small animal with a great many legs. The innermost canaliculi open into the Haversian canal of the system to which they belong, 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 ilaversian canal can ooze all .through the bone. In a living bone a nucleated cell lies in each lacuna. These cells, the lone corpuscles, are the remnants of those which made the bone, ail whose hard parts are but in- tercellular substance: a sort of skeleton is made by ea'ch 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 Ilaversian 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, and form about two- thirds of its weight when dried. They may be removed by soaking the bone in diluted muriatic acid.* and the What radiate irom the lacunae? into wnat do the innermost canaliculi of an Haversian system open? How is nourishing liquid from the blood carried throughout a bone? What lies in each lacuna of a living bone? What are the Done corpuscles? What is the hard part of bon^y 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 couole of ounces of Muriacic acid to a pint of water and Dlace CHEMISTRY OF BONE. 55 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« solved in the water ; most of the gelatine which we buy in the shops is obtained by boiling fresh bones in a closed ves- sel 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 m as well as the softer parts, and the whole is kept boiling for hours so as to get some of the gel&tine out of the bones. The animal matter of bone gives it its toughness and flexibility. The earthy portion may be obtained free from the inimal by calcining a bone in a bright fire. The residue is a white and very brittle mass, which retains perfectly the shape of the ordinal 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- fect 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 the 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? rib in the mixture for four or five days, hr.ving previously scraped the bone quite clean. It will be found so flexible that a knot may be tied on it; the specimen mjiy be preserved in strong brine or dilute alcohol from year to year for exhibition to a 56 THE HUMAN SOD 7. 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 high that the feet have 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 produced. For the same reason it is important that a chiP 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 be made to walk too early lest they become bow-legged, 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 and high heels. The latter 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 How 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 walk too much? Why? Give instances of the readi- ness with which bones can be distorted in early life. Whv are high- heeled boots hurtful? HYGIENE OF SKELETON. 57 the boot. This not only crushes the toes and leads to deformities, corns, and bunions, but makes the gait stiff, inelastic and ungraceful. FIG. 25.— Skull of a child of the tribe of Chinook Indian* (inhabiting the neigh- borhood of the Columbia 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 very 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 : hence one great reason of its value as a food for children. Fracture. — When a bone is broken it is said to be/rac- 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 j when the "Why are the bones of an old person easily broken? Why should tnilk form part of a child's diet ? What is a fracture? A supple fracture? A comminuted fracture? A. compound fracture? 68 TEE HUMAN BODY soft parts also are lacerated, so that there is an opening from the skin to the broken bone, the fracture is com- pound. 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 pos- sible 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 be purchased for about $40.00 from Henry 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 cer- tainly be 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 school commissioners to purchase a skeleton to be used by the schools in turn. PLATE I. — THE BOXES, JOINTS, AND LIGAMENTS. EXPLANATION OF PLATE I. A front view of an adult human skeleton to illustrate the mode in which 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. f 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 down, Z, ligaments of the Ankle-Joint. fc A Membrane which fills up a hole hi the Innominate Bone. n Ligaments of the Knee-joint. o o Ligaments of the Toes and Fingers. p Capsular (bag-like) Ligament of the Hip-Joint. q Capsular Ligament of the bhoulder-Joint. CHAPTEE V. JOINTS. The movements of the body 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? What happens when they exert it? To what are the ends of most muscles 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, ar.d as the coloring matter is turned brown by heat, they form the "dark "neat" after cooking ; in birds which fly a great deal the breast muscles (which iefly 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. t As an example of a muscle not attached to the skeleton, we may take the orbic- ularis oris, which forms a ring around the mouth-opening beneath the skin of trie l^pp : when it contracts it closes the mouth, or if it contracts more forcioly purses out the lips. The orbicularis palpebrarum forms a similar ring around the eye opening, andwhen it contracts closes the eye. 60 THE 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. 26. FIG. 26. — Section through 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 ball in What is a joint? How do joints differ? Describe the hip-joint. HIP-JOINT. 61 a socket. If the hard bones came into direct contact they would be apt to chip 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 acctabulr.m to the head of the femur ; from the rim of the socket it passes to the center of the acetajbulum along a groove in the bone, and then turns out to be fixed to the thigh-bone. Covering the inside of the capsular lignment and con- tinued over the cartilages of the joint is the synovial mem- brane, 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 n 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 nsipsulnr lisrn merit 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 like? What is its use? Illustrate by an example. 62 TBS 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 acetabulum, 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 there in health any definite space between the bones of the hip- joint? What is the chief use of the ligaments? How are the bones 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 found in all "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 ?o closely adherent to the parts it lines that a microscope is needed for its demonstration ; but all the other parts are readily made out. BALL AND SOCKET JOINf®. 63 is called a ball and socket joint, and allows of a greater variety of movement than any other kind. Through movements taking place at it the thigh can (1) be flexed, that is, bent so that the knee approaches the chest, 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) adducted or brought back again; by movement at the hip the limb can also (5) be circum- ducted, so that, with knee and ankle joints held rigid, the whole leg is made to describe a cone, of which the apex 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. The 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 the 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 uppermost ; 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 (summation) the radius and ulna are parallel (Fig. 27, A), and the radius on the outside ; place a finger of the other Is the joint of the lower jaw with the 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 another 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 foo<1 ; in car- nivora, as cats, which bite, but do not chew, the lower jaw forms a perfect hinge' joint with, the cranium. 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 tho 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, Ir, the ulna fits, and the grooves and ridges of the bones interlocking form a hinge -joint, allowing us only to bend or straighten the elbow- joint. The radius fits on the rounded outer third, Cpl, and rotates there when the hand is turned over, the ulna form- ing a fixed bar around which it moves. B A n-lirKno- imnfc no a vnln i^ov FlG 27-— A, arm in Bupination ; Witting joints as a rule pei- B arm In pronati0n; a;fiumenw; mit of but little movement. jR'radius; ^ulna' 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 pressure. Dislocations. — When a bone is displaced at a joint or dislocated, the ligaments are more or less torn and other What movement is allowed between ulna and humerus? What between radius and huraerus? 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 is dislocated? 5 66 THE HUMAN BODY. surrounding soft parts injured. This generally leads to inflammation and swelling, which make it difficult to find out in wlnit direction the hono has been displaced, and also greatly add to the difficulty of replacing it, or, in sur- gical language, of reducing the dislocation. 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 cprains than from broken bones. What results from this injury ? What is meant by " reducing a dislocation ?" Why should medical aid be obtained as soon as possi- ble after a joint has been dislocated ? What is a sprain ? How should a sprained joint be treated ? What should be done at once if there is much swelling or continued pain ? Are neglected sprains apt to lead to permanent injury ? * Dislocations of the fingers can usnaily be reduced by strong 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 with- out skilled assistance. EXPLANATION OF PLATE II. A view of the muscles situated on the front surface of the body, seen in their natural position. It must be understood that beneath these muscles many others are situated, which cannot be represented in the figure. Muscles of the Face, Head, and Neck: 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 the 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 that connect the upper extremity to the trunk. Portions of four of these muscles are represented in the figure, viz. : 15. Muscle that elevates the Shoulder. Trapezius 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 the 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 which, from, the oblique direction of its fibres, is called, 20. Outer Oblique Muscle of the Abdomen. Several muscles lie beneatli 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). 22. 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 Fore -Arm 24. Triceps, or Three-headed Muscle. This counteracts the last two muscles, for it extends the Fore-arm. 25. 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 Wrht 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 connect 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 lesr are placed on the back of the thigh, so that they cannot be seen in the figure. Muscles of the leg and 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 which turn the foot inwards, so as to counteract the last named muscles, lie beneath the great muscles of the calf, 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 SUPERFICIAL MUSCLKS OF THE FRONT OF THE BODY. CHAPTER 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 thigli (29, PI. II.), which 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 the mouth ; 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 differ 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 ? [Wl 68 2 HE HUM Ay BOJDT. skeleton.* In Fig. 28 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, 12) 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? FIG. 28.— The muscles on the back of the hand, forearm, and lower half of the arm, as ex- posed on dissecting away the ekm * 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 ; ita head can then be cut off and its spinal cord destroyed by running a 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 ekin 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 belly a pair of short tendons. THE PARTS OF A MUSCLE. 69 working part ; nerves from the brain or spinal cord enter it, and when its nerve is excited, whether involuntarily or by what we call an act of " will," the 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 inextensible 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 the scapula and below to the radius, can produce movement at either the elbow or the shoulder joint. The shortening of a muscle when it contracts is shown by the movement which it causes ; the thickening may be What enters the belly of a muscle? How is the nerve of a muscle excited? What 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 THE HUMAN 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- FIG. 29.— The biceps muscle and the arra-bones, to illustrate how, under 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 thickening 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. VARIETIES OF MUSCLES. 71 The shoulder is so much more firm that it serves as a fixed point, and so that end of the biceps is the origin of the muscle, and the radial attachment its insertion. The distinction 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, and there are even three-headed or fe'SftStal triceps muscles. On the other hand, some muscles have no tendon at all at r 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- like, from a fancied resemblance to the -plQ 37.__A di- vane of a feather ; or a tendon may run gast down the middle of the muscle (C), which is then called bipenniform. Sometimes a tendon is found in the mid- dle of the belly as w^ll as at each end (Fig. 31) ; such a Is the origin of a muscle under all circumstances its most fixed end? Give an example. What 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 bipeiiniform. 72 THE HUMAN BODY. muscle is called two-bellied or* digastric. Banning 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) ; it is polygastric, consisting of four bellies separated by short tendons. Many muscles are not rounded, but form wide, 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 paired 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 5 when the biceps contracts the triceps relaxes, and vice versa. This orderly working is carried out by means of the brain 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 whole body is made rigid. A digastric. Where do we find a polygastric muscle? How is the rectus ubdominis 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 the orderly working of the muscles guided and con- trolled? What parts are out of working order in a fit of convulsions? Why do the limbs often become stiff in convulsions? 'The single mnpcles cross the middle line and are made up of similar right and left halves ; examples are orbicularis oris and the diaphragm. THE GROSS STRUCTURE 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, the perimysium9 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 fasciculi 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- r»PTirl« rm thp >, The oxygen food of the body. — Hitherto w& have only considered the energy-supply of the body from \ne 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 off. 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. We all know that if his sup- ply of air be cut off 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 oxygen, 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- Why do we need 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 man's air supply be stopped ? Why does a man die sooner of want of air than of want of food ? Why is'oxygec 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. What is suffocation? APPENDIX TO CHAPTER VIII. 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 so 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 nritch 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 in a short time, or slowly at a low temperature in a long time, but the ultimate product, in each case, is the same. 2. 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. 8. Get a bundle of iron wire : rub it bright with emery or sand Fiper. Place some in a warm dry bottle by the stove or fireplace, ut 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 oxidations occur in the moist tissues of the body. CHAPTER IX. NUTRITION. The Wastes of the Body. — A man takes into his body daily several 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 chiefly 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. / Receptive 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 off several pounds weight of matter from his body? Does a child's increase in 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. What is meant by the receptive organs? [105] 106 THE HUMAN BODY. are two chief sets of these — one to receive oxidizable things, and the other to receive oxygen. The first set is represent- ed by the alimentary canal, consisting of mouth, gullet * stomachy and intestines. It takes in food and drink. The second set consists of the lungs, 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 excretory organs are the lungs, the kidneys, and the sJcin; the lungs pass carbon dioxide gas out to the air, and also water ; the kidneys get rid 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? ISTame 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? * The technical name for the gullet is cesophagut. 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. AVe 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 absorbents. 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 nourished? Why are the organs which keep up the blood-flow called circulatory organs? What is meant !>y the circulation? What are the ab?jrbents? Where do they convey the foods which they take ; p in the walls of the alimentary canal ? 108 THE HUMAN BODY. Respiration. — The blood in its course flows through the lungs. It is necessary not merely that food, but 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 organs, 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 v supply of fresh material ? NUTRITION. 109 material be replaced by new. Not merely must matter for assimilation be provided, but the various waste products must be removed. Here again the blood-vessels and ab- sorbents 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 the nourishment of the body is a very complicated process. It implies — (1) the. reception, of food from out- side ; (2) 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 the 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, Respira- tion, and Excretion. The sum total of 4he 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 anj* 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 physiology. The old doctrine 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 [HO] THE IMPORTANCE OF PROTEID FOODS. HI 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, 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 tissues 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 we feed on these elements in their uncombined state *? Name one which is absorbed in a free stale and used. Whence is it derived ? What organs receive it? Name substances 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 living cell. 1 1 2 THE HUMAN BOD Y. ety of them it can turn it into other varieties, but it cannot make proteids from things which are not proteids. Hence these albuminous or proteid substances are an essential 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 Animals, 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 chemical compounds? What class of compounds do they require for their nutrition? What do they do with these compounds? What simple compounds does the body return to the outer world? Can these compounds feed any animal? What facts suirgest the question, How is the supply of pro teids nnd other complex foods kept up? How is the question answered? 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 have 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 are 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 that 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 saU. 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. Serum albumen, 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 addition 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, like plants, can, when exposed to the action of light, live on the waste products of other animals:. 114 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 (I) substances which are taken into the alimentary canal, which can be absorbed from it, and after absorption serve to supply material for the growth of the body, or for the -replacement of matter which 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 nou-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-f 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 principle 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 oxi- 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? What are they called? Do they also make tissue? Are they complex or simple? What 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 exhib- ited? Give examples 116 TEE HUMAN BODY. products of its chemical transformation in the "body shall he 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. Why is cellulose not a food? What does chemical examination of ordinary foods show? How do we get variety in our foods? What are "alimentary principles''? On what does the nutritive value of a food depend? Into wLat groups are alimentary principles classified? ALIMENTARY PRINCIPLES. 117 Proteid Alimentary Principles. — Of the nitrogen-contain- ing foodstuffs 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 syntonin, 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, but cannot entirely replace the proteids as foods; though a man can manage with less proteids when he has some albuminoids in addition. The most important 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 calfs-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, palmatin, 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. 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 calfs-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 soms fatty bodies not nutritious? Give an instance. 118 THE 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 cane 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 fats. When oxidized they have 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 these substances, 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 the most im portant. Name carbohydrate foods derived from animals. How do they resemble fats in composition, and how 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 tor your answer. Name the more important inorganic foods. Why do we not require to eat most of them separately? What r.norgaoic foods are taken in a separate form? Why? THE NUTRITIVE VALVE OF DIFFERENT FOODS. 119 which they eat. Such tribes are, however, said to suffer especially from intestinal 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. Pork is the 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 strength 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 THE 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 fresli. 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. Sonic1 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? What foodstuffs exist in milk? What one food will support life longest? What is the chief aliment- ary principle in cheese? What is the nutritive value of cheese? What makes the value of eggs as foods? Are they more easilv digested soft or hard boiled? What foodstuffs exist in wheat? Why is wheaten bread lighter than that made from other grains? ALCOHOL 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 very rich in starch. Peas and leans are rich in proteids and contain about half their weight of starch. Potatoes are a poor food. They contain 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 mainly 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 foodstuffs 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 supplied 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 alcohol 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 scarce 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 be 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 is a stimulant to brain and muscle, and may for a short time excite them to over- work or to work when they should be resting. But as it nourishes neither of them, 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 supplied 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." The apparent inconsistency is easily ex- plained. 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 flows in large quantity to the skin, we feel warmer because the skin is What is said of alcohol as a tissue-forming food? Is alcohol a strengthening 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 sometimes make a person feel warmer? TEA AND COFFEE. 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 decrease it. The more blood that flows through the skin, the more heat is given off 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 a stimulant 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, like alcohol, are stimulant rather than nutritive foods. The amount of nourishment in a cup of either is but little. Both have, however, a wonderful in- fluence in tranquillizing the nervous system and removing the sense of fatigue; and when taken in moderate doses they usually leave none of the injurious after-effects of al- cohol. Some persons, however, experience wakeful ness or a feeling of fulness in the head after taking coffee, 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 commanders find a ration of coffee far better than one of whiskey for fatigued 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 pur- poses? Give illustrations of the influence of tea and coffee in remov- ing 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 more 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 starcli, 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 n good cook first put meat that she is to boil into very hot water? Why should the boiling be completed at a lower tempe- rature? How should meat be baked? Why is it important to cook most vegetable foods? Why is toast more easily digested than fresh bread? What determines the necessary amount of daily food ? Plow does it vary? Why do children require more in proportion to their size than adults? THE ADVANTAGES OF A MIXED DIET. 125 . It is impossible to state accurately beforehand ju\t what amount of food any individual will require, but a genera 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 T77 of an ounce of nitrogen (20 grams). Some hydrogen is also required, as the body daily loses more water than we drink; 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 kept up on them along with the necessary salts, water, and oxy- gen; but such a form of feeding would be anything but eco- nomical. Ordinary proteids contain in 100 parts about 52 of carbon and 15 of nitrogen, so a man fed on them alone would get about 3J 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 so to get enough carbon from proteids far more than the necessary amount of nitro- gen must be taken. Of dry proteids 1 pound 2| 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 ele- ment from the body. Fed on a purely proteid diet a man would, therefore, have to digest a vast quantity to get enough carbon, and in eating and absorbing it, as well as 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 only on albuminous substances not desira- ble? 126 THE HUMAN BODY. in getting rid of the excess nitrogen which is useless to him, a great deal of unnecessary labor would be thrown upon the digestive and excretory organs. Similarly, if a man were to live on bread alone he would throw much un- necessary work on his body. For bread contains but little nitrogen in proportion to its carbon, and so to get enough nitrogen far more carbon than could be utilized would have to be eaten, digested, and excreted daily. Accordingly we find that mankind in general employ a mixed diet when they can get it, using richly proteid sub- stances to supply the nitrogen needed, but deriving the carbon mainly from non-nitrogenous foods of the fatty or carbohydrate kinds, and so avoiding 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 52 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 carbohydrates. 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 bet- ter diet both for the purse and the system than meat alone. As already pointed out, nearly all common foods contain s. Good butcher's meat, for example,contains Explain why bread by itself would afford a bad diet. Why 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? Give illustrations of the fact that most foods contain more than one foodstuff. THE ADVANTAGES OF A MIXED DIET. 127 nearly half its dry weight of fat, and bread besides proteids contains starch, fats, and sugar. In none of them, how- ever, are the foodstuffs mixed in the physiologically best proportions, and the practice of employing several of them at each meal, or different ones at different meals during the day, is thus not only agreeable to the palate but in a high degree advantageous to the body. The strict vegetarians who do not employ even such substances as eggs, cheese, and milk, but confine themselves to a purely vegetable diet, such as is always poor in proteids, daily take 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 ex- tremely rich in proteids, and supply the nitrogen needed, without the necessity of swallowing the vast bulk of food which must be eaten in order to get it from plants directly. 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? CHAPTER 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 push the swallowed food along it. The mucous membrane 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 canal? By what is it liiied? What are found outside the mucous membrane of the digestive tube? What are their uses? With reference to what object is the alimentary mucous membrane constructed? What does iit 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 KINDS OF GLANDS. 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 poar them out on some free surface 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. What is a gland? Give examples of glands. How do glands differ? What are the two chief types of glands named? Name aud describe a secreting surface which is not technically called a gland. What is gained by folding a secreting surface? 130 TEE HUMAN BODY. A B FIG. 40. Forms of Glands. A , a simple secreting surf nee: a, its epithelium; 6, basement membrane; c, capillaries: B, a, simple tubular gland; C', a secret- ing surface increased by protrusions ; £, a simple racemose gland; D and Of, compound tubular glands; F, a compound racemose gland. In all but A and B the capillaries are omitted for the sake of clearness. H, half of » 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 C, Fig. 40, but much more commonly the surface extension is attained in another way, the supporting or "basement membrane, cov- ered by its epithelium, being pitted in or involuted as at B. Such a secreting organ is known as a true gland. 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; examples are found in the lining coat of the stomach (Fig. 48); also in the skin (Fig. 76), where they form the sweat-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-vessels 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 secretion is poured out, and serving meroly 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? Example? Where do we find the closest network of blood-vessels in a gland? Which cells of a gland make its secretion? What is meant by the " duct" of a gland? What is a simple gland? 132 THE HUMAN BODY. has a true secreting chamber at its end we get a compound gland, tubular (G) or racemose (F, H) as the case 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 duct, 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 in 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 Fig. 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-chamber 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 the main mass of the gland? Describe a fully developed gland. How is it that glands make such different 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 bcl ween the lips lead? THE MOUTH CAVITY. 133 h isthmus of tlie fauces) at the back of the mouth, from another, the pharynx or throat chamber, which narrows again at the top of the neck into i\\Q gullet or oesophagus, which runs as a comparatively narrow tube through the thorax, and then, passing through the dia- phragm, dilates in the upper rn- 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. — (Fig. 41) is bounded in front and FIG. 41.— The mouth, nose and pharynx, with the commencement of Oil the Sides by the lips and the gullet and larynx, as exposed by a section, a little to the left of the me- Cheeks, below by the tongue, dian plane of the head. a, vertebral 7 column ; o, gullet ; c, windpipe ; a, *, and above by the palate, which latter consists of an an- terior part, I, supported by bone and called the hard pal- er 8lde of the le£t nostrU chamter' What is the isthmus of the fauces? Where does the gullet begin? Through what regions of the body does it pass? Where does the stomach lie? What part of the alimentary canal succeeds the stomach? Describe it briefly. How does it end? How does the large intestine differ from the small? How does it end? What are the boundaries of the mouth cavity? Of what parts does the palate consist? 134 THE HUMAN BODY. ate, and a posterior, f, containing 110 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 hard palate forms the parti- tion between the mouth and nose. The soft palate 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 cheeks and lips are two semicircles, formed by the borders of the upper and lower jaw-bones, which are covered by the gums, except at intervals 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 or 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 ':eeth 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 find inside the lips ? Where are the gums ? What do the margins of the law bones contain ? What are the inilk teeth ? What the permanent V 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 connection with thio lesson. CHARACTERS 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 ivisdom teeth. Characters of Individual Teeth. — The incisors or cutting FIG. 43. FIG. 44. FIG. 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 tooth. 136 THE HUMAN BODY direction in the lower. Each has a single long fang. The canines (dog teeth) (Fig. 43) are somewhat larger than the incisors. Their crowns are thick and somewhat conical, having a central point or cusp on the cutting edge. Jn 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 lias 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 (Fig. 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; it is dentine or ivory; covering the dentine on the crown is enamel, the hardest A canine. Name 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 milk 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 a tooth? Where does each lie? HYGIENE OF THE 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 aperture 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 each dose the mouth should be thoroughly rinsed with water. 138 THE HUMAN BODY. Once a slight cavity has been formed, the process oi! decay is apt to go on very fast ; first, because the ex- ^ deeper layer of the tooth is more easily dissolved than its natural surface; and, second, because the little THE TONGUE. 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. 26). The mucous membrane covering the upper surface of the tongue is roughened by numerous minute elevations or papilla, of which there are three varieties. The circum- vallate papillcB (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 papillae 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 papillce 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 should the teeth be examined from time to time by a dentist? Briefly describe the tongue. What sensations do we obtain through it? To what is its root attached? 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 the fungiform papillae. Where are they found? What do they look like when we examine a person's tongue? Where are the filiform papillae found? What is their form? What papillae 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 THE 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 sulmaxillary , and the suUingual. 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 \ 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 healthy tongue. How does the tongue of a healthy man differ in appearance from that of a healthy child? When is the tongue apt to be "coated"? "What does a furred tongue usually indicate? By what is the saliva secreted? Where does the paotid 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. TEE PHARYNX. 141 the tongue. The sublingual glands lie beneath the floor of the mouth behind the submaxillary. 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 unfrequently become enlarged during a cold or sore throat, 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? What 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. t * Observe for yourself with the help of a looking glass. 142 THE HUMAN BODY, 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, by 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 the usual position of the soft palate? How is this position altered durjng 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 "gon,e 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. THE 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 (Fig. 47) is a curved conical bag placed FIG. 47. FIG. 48. FIG 47.— The stomach, d, lower end of the gullet ; a, position of the cardiac ept-rture : 6, the fundus ; c, the pylcrus ; «, the first part of the small intes- tine ; along a, 6, c, the great curvature ; between the pylorus and d, the lesser curvature. r'iG. 48. — A thin section through the gastric mucous membrane, perpendicu- lar to its surface, magnified about -25 diameters, a, a simple peptic gland; i>, 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 upper 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 the 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, maybe readily shown on the body of a puppy, kit- ten, or rat, which has been killed by placing it for five minutes in a small box 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 about 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 these pits the openings of several minute tubes, the gastric glands, which lie imbedded in the mu- cous membrane, packed closely, sidrf'-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 commencement 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 on 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 stomach and the dia- phragm? What is the size of the stomach? What may be seen on examining the 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. 145 diately above 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 the pylo- J 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 arbitrarily describe it as FIG. 49.— Diagram of abdominal part of al. C. tlie cardiac, and P, the stomach; D, the duode- num; J, /, the convolutions of the small in- COnSlStlDg Of three parts, testine; CO, the caecum with the vermiform J.-I o 1-1 appendix; AC, ascending, TC, transverse, and the nrst twelve inches DC, descending colon ; jff, the rectum. being the duodenum, the succeeding two fifths of the re- mainder the jejunum, and the rest the ileum. *r 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 throughout 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 the valvulce conniventes. They are first found about two inches from the pylorus, and are most thickly set and largest in the upper half of the jejunum, in the lower half of which they become gradually less conspicuous; they finally disappear altogether about the middle of the ileum. The folds of the mucous membrane FIG. 50. — A portion of the small intestine opened to show the valvulce conni- ventes. serve to greatly increase its surface both for absorption and secretion, and they also delay the 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 with the eye or, 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 them) with closely packed minute elevations standing up somewhat like Give the general characteristics of the mucous membrane of the small intestine. What 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 VILLL 147 the " pile" on velvet and known as the villi (Fig. 51). 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. Near 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. blood ves- sels. In the right-hand figure the lacteals alone are represented, filled with a dark injection. The epithelium 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. What is found in its lymphatics during digestion? 148 THE HUMAN BODY. testine, and these end in trunks which join the main lym- phatic system. Finally, in each yfflusy/ outside its lacteals and beneath its muscular layer, is a close network of blood- vessels. The Glands of the Small Intestine. — Opening on the surface of the small intestine between the bases of the villi are small glands, the crypts of Lieberkulm. 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, 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 2J to 1 J 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 (R). The small intestine does not open into the end of the large but into its side, some distance from its closed upper end; the caecum 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 Lieberkulm? 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 ca3cum? The vermiform appendix? Its size? THE LIVER, 149 meters) long. The colon commences on the right side of the abdominal cavity 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 stomach, and turns down (descending colon) on the left side, and there makes an S-shapcd bend known as the sigmoid flexure; from this the rectum proceeds to the opening by which the intestine communicates with the exterior. The mucous coat of the large intestine possesses no villi nor valvulae conniventes; it contains numerous closely set glands much like the crypts of Lieberkiilm of the small intestine. The Ileo-Colic Valve. — Where the small intestine joins 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 fn the body, weighing from 50 to 60 ounces (1400 to 1700 grams). It is Describe the colon. What is the sigmoid flexure? What is the terminal portion of the alimentary canal named? How does the mucous lining of the large intestine differ from, and how does it re- 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 intestine? 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 cavity (le, le', Fig. 4), rather more on the right than on the left side, imme- diately below the diaphragm. The liver is of dark reddish- brown color, and of soft friable texture. The vessels carrying blood to the liver (Fig. 52) are the portal vein, Vp, (p. 208) and the liepatic artery; both enter it at a groove on its under Dch Lv FIG. 52 —The under surface of the liver, d, rfeht, and s, left lobe; Vh. hepa- 10 vein; Pp, portal vein; Fc, vena cava inferior; Dch. common bile duct; DC cystic duct; Dh, 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 liepatic duct, Dh, which meets the cystic duct, DC, proceeding from the gall- bladder, Vf, a pear-shaped sac in which the bile or gall formed by the liver accumulates when food is not being di- gested in the intestine. The common bile duct, Dch, formed Describe the color and texture of the liver. What vessels brin°- blood to it? Describe the arran«-ement of its ducts. What is the gall-bladder? Where does the common bile duct open? THE PANCREAS. 151 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 bile; 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 pancreMs 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 what group of glands does the pancreas belong? Describe its form and color. Where is it placed? AVhatdoes its duct 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 thyniuSj 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 in 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 further digestion. In the case of many most important foodstuffs, however, special chemical changes hare "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 corn- Explain 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. 153 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 to 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 canal. 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 guilty 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 HUMAfl BODY. C12Hao010 + 2H20 = 2C6H13Ofl Starch. Water. Grape Sugar. The Influence of Saliva in Promoting Digestion in the Stomach. — So far 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 much. Indirectly, however, the saliva promotes di- gestion in the stomach. Weak alkalies stimulate the gastric glands to pour forth more abundant secretion,* and the saliva, being alkaline, acts in 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 starch into sugar? 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 little 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 be chewed nor swallowed. DEGLUTITION. 155 J^ a Mf S/ 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 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 stage? 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. 156 THE HUMAN BODY the food can only be squeezed into the oesophagus. The muscular movements concerned in this part of deglutition are all excited without the intervention 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 third 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, olten 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 sta^e 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 known as a reflex action. See Chap. XX. GASTRIC DIGESTION. 157 cus, free hydrochloric acid (about .02 per cent.), and a substance called 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 phosphate 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 fche solution of the white fibrous connective tissues the .disintegration of animal foodg, commenced by the teeth, is Name its more important constituents. What powers does pepsin What are colloids? Give examples. How do peptones differ from other 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 another substance dissolved in 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 mucli 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 grayish 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 off, along with other dissolved 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 p}Tloric sphincter relaxes at intervals, and the rest of the stomach, contracting ut 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 masses, 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 emptied after a meal? What has accumulated in the small intestine when the chyme reaches it ? * Several of the above facts were first observed on a Canadian trapper, Alexis St. Martin, who as a result of a gunshot wound had a permanent opening from the surface of the abdomen to the interior of the stomach. THE PANCREATIC 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 hours, and pour their products into tbo intestine. The glands of Brunner and the crypts of Lieberkuhn 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 proteids 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 bile on the chyme brought about ? Do liver and pancreas cease secreting when the chyme enters the intes- tine? What other glands are set to work? How is the acidity of the chyme overcome? What is chyle? What does it usually con- • the pancreatic secretion. What foodstuffs does it not it' Describe its action on starch. How does it change proteicte? 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 up 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 bo shaken up with water, the t\vo 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 differ from pepsin ? How does pancreatic secre- tion break up some fats ? What digestive end is thus attained ? How is most of the fat eaten acted upon by the pancreatic secretion ? Why is the chyle white ? How may we mix oil with water ? Ex- plain the process. What is an emulsion ? What emulsifies the oily matters of the chyle ? * = 3 1 Stearin + 3 Water = 3 Stearic acid -f 1 Glycerine. t 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 fat|;er '-' with potash. Both dissolve in water, which the fats from which thev.^" willi.otdo. f! 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 glycoclwlic, the former predominating in human bile. The Uses 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 stomach 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. tfame foods on which bile has no influence. How does it acti upon fats when shaken with them? Give a reason for doubt- it' it emulsifies fats ID the intestine. 162 THE HUMAN BODY. ary canal to be got rid of. But there are many reasons against such a view. In the first place, the entry of the 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 overcoming 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 putrefactive 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 chij kept moist with bile, under a much lower pressure than through one wet with water. Hence bile by moistening the cells 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 t)~ ^ "-'° helps in promoting the absorption of fatty mutters from ftct 2 Uue. * INTESTINAL DIGESTION. 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 Brunner 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 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 fats, with which they 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 snccus entericus consist of? Why is its digestive action but little known? Point out some of its uses. Describe the process of intestinal digestion. 164 THE HUMAN 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 foodstuffs, and some excretory substances found in the various secretions poured into the 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 ./ith 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 the 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? DYSPEPSIA. 165 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 may be 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 juice 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 more agreeable form of the same aid to digestion. 166 THE HUMAN BODY. digestion strengthens 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 treatment. From its nature — depriving the body of its proper nourishment — it tends to intensify itself, and so 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 the processes of chewing and swallowing. But the time which elapses between taking a mouthful of food and its transference to the stomach is 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 in those parts? PLATE III. — A GENERAL VIEW OF THE LYMPHATICS OR ABSORBENTS. That portion of tilt known as the lacteals is seen at d, passing from the small intestine e to the thoracic duct /. EXPLANATION OF PLATE TIL A GENERAL VIEW OF THE LYMPHATIC OR ABSORBENT SYSTEM OP VESSELS. e, A portion of the small intestine from which lacteals or chyle- conveying vessels, d, proceed, their origin within the villi may be seen magnified in fig. 51; /, the duct called thoracic, into which the lacteals open. This duct passes up the hack 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 blooA In the right upper, and lower limbs the superficial lymphatic vessels 1 1 1 1, 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. m m, enlargements called lymphatic glands, situated in the course of the lymphatic vessels. These 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 be 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 valvulae 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 it 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 the stomach? Where does the most important food absorption occur? What structural peculiarities of the small intestine peculiarly fit it for ab- sorbing? What vessels absorb sugars in the small intestine? To what organ are these sugars conveyed? What there becomes of them? 168 THE HUMAN BODY. pancreatic secretion, are partly taken up by its lymphatics and partly by its blood-vessels. The emulsified fats main- ly pass into the lymphatics of the villi, and are carried off by 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 canal 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. APPENDIX. 169 etables have formed part of the diet. In its progress through the large intestine the food-mass loses still more water, and the digestion of starch and the absorption of fats is continued. 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 such 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 ilhistrated 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 than 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 submnxillary, 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- lingual. Remove the muscles, etc., covering the larynx and trachea; cut away the front and side walls of tl.e 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 (fundus) to the left of the entry of the gullet; its great and small curvatures; its narrower pyloric portion on the right, from which the small intestine proceeds. Attached to the stomach, and hanging down over the other abdominal viscera, notice a thin membrane, the amentum. Follow and unravel the coils of the small intestine, spreading out as far as possible the delicate membrane (mesentery) which slings it. In the mesentery are numerous bands of fat, running in which will be seen blood-vessels and lacteals. The termination of the small intestine by opening into the side of the large. Observe the caecum 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 caecum 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, the 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 orifice 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 (which is almost pure starch) with boiling water. Let it cool. a. Add two or three drops of this starch paste to half a test tube- ful 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. b. 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 drops 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. b. Get a butcher to " whip" some fresh drawn blood for you with a bunch of wire or twigs. The blood fibrin will collect on these (p. 181), and when thoroughly washed with water, forms 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 proteid s. 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 short time dissolve proteids. 172 THE HUMAN BODY, f. Half fill a test tube with the mixture c, add a teaspoonful of the pepsin solution 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 the 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 the 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 test 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 experiments described above under heading 2; 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 c). 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 fpr 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 off 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 eight or ten hours. The lacteals being then filled with clear, watery -looking lymph, will be recognized with difficulty. CHAPTEP XIII. BLOOD AND LYMPH, Why we need Biood. — Some very small animals of simple structure require no blood; every part catches its own food and gives off 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 faraway 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 want* 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? [174] ''THE BLOOD. 175 and round, from place to place, by the heart, 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 the 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 body, and from those where refuse and deleterious substances are finally passed from it. The Blood, as every one knows, is a red liquid which is yery widely distributed over the body, since it flows from any part of the surface when the skin is cut through. There are very few portions of the body into which blood is not carried. One of them is the outer layer of the skin;* hairs and nails, the hard parts of the teeth and most carti- lages 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 hand without draw ing a drop of blood, ire THE HUMAN BODY. nourished by liquid which soaks through the wulis 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. 53 —Blood-corpuscles. A, magnified about 400 diameters. The red corpuscles have arranged themselves in rouleaux; a.a, colorless corpuscles; B, red corpuscles 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 blood-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 numerous and give the blood its color; they arc 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 the 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 that they cannot be FlG- ^-Red 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 differ from the corpuscles of other mam- mals? Why cannot a d'>g's blood be easily distinguished from human blood? 178 THE HUMAN BODY. 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 licem' -o-glof -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. — Haemoglobin itself is dark purplish-red in color; haemoglobin combined with oxygen is bright scarlet red. Accordingly, the blood which flows to the lungs after giving up 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 blood 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 the 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 haemoglobin 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 change 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 are thus little, independently moving cells which live in our blood. The pus 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-vessels. Their movements are very like those of the microscopic animal named amw'ba, and are accordingly called amoeboid. 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 also not per- How do the colorless corpuscles differ from the red in size and number? What is each? What property does it possess? What is seen when one is watched with 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 minutes? FIG. 55.— A white blood- corpuscle, sketched at suc- cessive intervals of a few seconds to illustrate the changes of form due to its amoeboid movements. 180 THE HUMAN BODY. manent. In a few minutes the top of the jelly-like 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 Hood-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 ? What 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. 181 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 - 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 , , , i a • L ix FlG- 62.— Diagram to illus- to Stop the nOW in its SUDCUtaneOUS trate the mode of action of ., . , ., . . . the valves of the veins. C, the Veins and Cause their dilatation, capillary, H, the heart end of i-ii the vessel. the points at which valves are placed can be recognized by their swollen appearance. The valves are most frequently found where two veins communi- cate0 The Course of the Blood.— From what has been said it is cloar 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 the 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 SUM AN BODY. aorta, and the other with the pulmonary artery, and in its circuit the blood returns to the heart 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 of the heart to the right through most of the body being called the systemic or greater circulation, and from the right to the left through the lungs the pulmonary 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 what does blood always leave the heart? To what does it return? How many circulation* are there really? What is meant by the systemic circulation? What by the pulmonary? Why is neither a true " circulation" in the proper 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 doec it enter after traversing the capillaries of the stomach and in- testines? TEE PORTAL CIRCULATION. 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 hepatic 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 i\iQ portal circulation. Diagram of the Circulation.— Since the two halves of the heart, although placed in proximity in 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 aur^- cle and ventricle; la and Zv, ., . , ,, , . , left auricle and ventricle; ao, the body, are actually Completely aorta; sc, systemic capilla- ries; vc, venae cavre; pa, pul- Separated from One another by an monary artery ;pc,pulmonary capillaries; pv, pulmonary impervious partition, we may con- veins. veniently represent the course of the blood as in the ac- companying diagram (Fig. 63), in which the right and 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 BOD T. left halves of the heart 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. Reaching the right auricle, ra, it is sent into the right ventricle, rv9 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 (hemoglobin) forms a scarlet compound with oxygen, the blood which flows to the left auricle through the pulmonary veins is of a bright 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 matter 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 justified in diagraumratically representing the heart as made of two separated parts? Starting from the left auricle, 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 gaiu and lose in the ^ jjieiuiv; capillaries? APPENDIX. blood returns to the right auricle of the heart by the venae cavae of a dark purple-red color. This color it keeps until it reaches the lungs, where the reduced haemo- 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 have this peculiar technical meaning, and that the. pulmonary veins contain arterial blood, and the pulmonary arteries contain venous blood. The change~~lfom 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 change from arterial to venous occur? Where that from venous to arterial? APPENDIX TO CHAPTER XIV. 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 right 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 turneJ away from the head. 2. Get your butcher to obtain for you a sheep's heart, not cut out of the bag (pericardium), and still 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 market. 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 midriff (diaphragm) which usually is found attached to its posterior end. 4. Carefully dissecting aw.iv adherent fat, etc.v trace the vessels 212 THE HUMAN BODY. below named until they enter the pericardium. Be very careful not to cut the veins, which, being thin, collapse when empty, and may be easily overlooked until injured. As each vein is found stuff it with raw cotton, which makes its dissection much easier. a. The vena cava inferior : find it on the under (Abdominal) side of the diaphragm ; 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 and pericardium the inferior cava receives no branch; but, lying on its left side, will be seen the lower end of the right 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 aorta : immediately on leaving the pericardium this vessel gives off a large branch; it then arches back and runs down behind the heart and lungs, giving off several branches on its way. 6. The 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 then 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 already traced to it. As this APPENDIX. 213 is done, you will notice that inside the pericardium the pulmonary artery lies on the 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. b. 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 septum which 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 (left) appearing below the pulmonary 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 runs down the dorsal side of the heart on the ventricles. b. 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. The coronary wins and sinus: small coronary veins will be seen accompanying the 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 on the right of the band of fat marking externally the limits of the ventricles, and noted above (9. &.). 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 lieart, and open the right auricle by cutting a bit cut of its wall, to the left of the entrances of the venaa cavse. On raising up by its point the wedge- shaped flap cut ^rom the wall of the ventricle, the cavity of the latter will be exposed. a. Pass the handle of a sca\pei from the ventricle into the auricle; 214 THE HUMAN BODY. » and also from the ventricle into the pulmonary artery, and make out thoroughly the relations of these openings. b. Slit open the auricular appendage; note the fleshy projections (columncB carnece) on it's walls, and the smoothness of the rest of the interior of the auricle. Observe the apertures of the vence caves, 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. 12. 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 valve come into view. a. Note the columns 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 these edges are strong tendinous cords (chorda tendinece), 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 tumed from the heart, and has in its middle a little nodule (corpus Arantiij. 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 puknonary veins. Observe that no other veins open into this auricle. APPENDIX. £15 5. Slit open the auricular appendage; note the fleshy projections (columnce carnece) on its interior, and the general smoothness of the rest of the inner wall of the auricle. Notice the columna carnecs over the inner surface of the ventricular wall, also the considerable thickness of the latter, as compared with that of the right ventricle or of either of the auricles. c. Carefully raise the wedge-shaped flap of the left ventricle, and cut on towards the base of the heart, until the valve (mitral) 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 tendineee, the columnae carnese, etc., as in the case of the right side of the heart (12). d. Examine the semilunar valves at the exit of the aorta; then cutting up carefully between two of them, examine the bit of aorta still left attached to the heart, and note the valves more carefully as described in 12. 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 methods 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 expanding them. It 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 apart 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? [216] EVENTS DURING A CARDIAC PERIOD. 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 chest-wall between the fifth and sixth ribs on the left side of the 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 the end of the ventric- ular systole. At this moment the semilunar valves at the orifices of the aorta and the pulmonary artery 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 (luring the systole? How is its bulk changed in systole? Where does the apex of the heart touch the chest- wall? What 13 the cardiac impulse? Wha'i 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 till? What hap- pens as the ventricles fill? 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? 218 TEE 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 now ceases, and the ventricu- lar begins. The blood in each ventricle is imprisoned be- tween the auriculo-ventricular valves behind and the semi- lunar valves in front. The former cannot yield on account of the chordaB tendineae fixed to their edges; the semilunar valves, on the other hand, can open outwards from the ven- tricle and let 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 sufficient 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 the consequence of the 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? USE OF PAPILLARY MUSCLES. 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- eas, 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 chordae 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, they 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 be 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 the first 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 lul>, 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 due to vibrations of the tense ven- tricular wall at that time. In many forms of heart 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 physician often gets important information as to the nature of a heart disease by studying these new or altered sounds. Function of the Auricles. — The 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 the left ventricle, which has to force the blood over most of the body, is stouter than the right, which has only to send blood around 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 ol^Rie auricles. Not unfre- What do we hear on listening over the heart region of a living per- son's chest? What are the sounds called? How does the first differ from the second? What words give some idea of their character? What is the origin of the second sound? Of the first? What occurs as regards the heart 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? WORK DONE BY THE HEART. 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 ventricles contracted and drove the blood into the arteries. Erom 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 long-lasting ventricular contraction is taking place. The Work done 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 6J ounces of blood seventy times a minute into the aorta, is enough to lift one poundtS$5,584 feet high; and the work done by the right ventricle would lift one pound 108,528 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? What is done by the auricular contraction? What is 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 'THE HUMAN BOLT. feet. The work done daily by the ventricles 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 mountain 2644 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; it is easiest felt on arteries which lie near the surface of the body, as the radial artery, near the wrist, and 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. THE 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 emptying 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 much blood is sent into the capillaries during a cardiac period? What 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 positbn of the body? THE HUMAN BOLT. creases its rate temporarily and so does excitement; a sick person's pulse should not therefore be 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 flow, 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 age affect the pulse rate? In what manner does th-3 blood leave the heart? How is its flow altered before reaching the capillaries? How may this be observed? Is the flow in the veins rhythmic or steady? Why? 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 view (Fig. 61). The arteries, a, are readily recognized by the fact that the flow in them is Jastest 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 £he 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? In 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 through the 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 afforded by the Lake of Geneva, 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 22(5 THE HUMAN BODY. which, though thousands of times smaller than the great 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, very 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 very 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 the total blood channel greater in arteries or capillaries? In veins or capillaries? Why is the blood-flow in the great arteries 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 the lake it is much slower. ABSENCE OF PULSE IN THE CAPILLARIES . 227 both while the heart is contracting and between two heart- beats. The heart, 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 O ? and keep pressing on ihe blood inside them, and steadily forcing it on into the capillaries. The 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 capillaries 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 off. Their walls have therefore to be very thin; and if the When? "What does the heart do? What happens before the arteries have had time to empty? What is the condition of the arterial walls all through life? What results from their stretched condition? What keeps the arteries tightly filled? What sends blood through the capillaries? How do the capillaries get a steady blood supply? Why do we find a uniform current in the veins? What is gained by having no pulse in the capillaries? What must food materials in the blood 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 converting a small fraction of the heart's jerk into a steady pressure, and when all these fractions are summed 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 by 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 arteries 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 flow of *he delivery hose."— HUXLEY. 228 THE HUMAN BODY. blood were sent into them in sudden jets at each beat of the heart, they 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. Blushing is due to a relaxation of the muscular layer of the arteries of the face and neck, allow- ing more blood to flow 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 the muscles of the arteries arranged? What results from their contraction? From their relaxation? To what is blushing due? Why cannot all the organs have a full blood stream through them at the same time? For what purpose are the muscular fibres in the walls of arteries used? What is the usual condition of the arteries of a resting organ? TAKING COLD. 229 fore, hard thought or violent exercise soon after a meal is very apt to produce an attack of indigestion by diverting the blood from the abdominal organs, 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, — When 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 that 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 take hard exercise or do severe mental work soon after eating? Why do young persons suffer 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 on 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 diarrho3a? What should be worn when liable to exposure to considerable changes of temperature? 230 THE HUMAN BODY. body; linen permits any change in the external tempera- ture to act almost at once upon the skin. After an un- avoidable 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 dilatation 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 baih? 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 along 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 pin out the flaps of skin. APPENDIX. 231 4. Next pick up with forceps the remaining tissues of the ventral near its posterior end, and carefully divide them longitudinally a little 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 sternum, note the peri- cardium with the heart beating 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 thus exposed note — a. Its beat; 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 that the 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 through its walls. ' c. 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 the valves of the heart, obtain two uninjured sheep's hearts from a butcher. Remove them from the pericardium, taking care not to injure the vessels. 9. Cut off 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 . THE HUMAN BODY. 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. Then 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 fill, the flaps of the mitral and tricus- pid valves will be seen to float up and cl®=ie 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 together 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 the exit tube place a piece of glass tubing six feet long. Put the entry tube of the bag in a basin of water. On pumping, an intermittent flow of water, corresponding to the strokes of the pump, will be obtained from the 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. 12. Replace th2 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 narrower 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 the tubes fed directly by the heart shall be highly elastic, and (2) that there shall be considerable resistance to the exit from their outflow ends CHAPTER XVI. THE OBJECT AND THE MECHANICS OF RESPIRATION. The Object of Respiration. — Blood is renewed, so far as ordinary food materials are concerned, by substances either directly absorbed 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 (2) 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 THE HUMAN BODY, 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, iind would become so loaded with carbon dioxide as to •40 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 deprived of its oxygen and polluted with wastes is expelled from the lungs; and when it expands, fresh air, rich in oxygen, and con- taining hardly any carbon dioxide, is taken into them. The respiratory organs are, therefore, (1) the lungs; (2) the air-passages; (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 is 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). THE AIR-PASSAGES. 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 larynx 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 front. On the left of the figure the pulmonary tissue has been dissected away to show the ramifications of the bronchial tubes, a, larynx ; 6, trachea; 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,' thes •) have pouched or sacculated walls and end in the sacculated alveoli. 6. * part of which it divides into a right and a left bronchus. Each bronchus enters a lung, and divides in it into & vast number of very small tubes, called the bronchial tubes. The last and smallest bronchial tubes (a, Fig. 65) open into subdivided elastic sacs, ~b, c, with pouched walls. What aperture is found on the ventral side of the pharynx? Where does the larynx He? 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 HUMAN 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 stiff 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 what are the windpipe and its branches lined? What lies outside this lining? What do these walls also contain? What is the use of the cartilages? What is " Adam's apple"? What may be felt below it in front of the neck? What lines the mucous membrane of the windpipe and its sub- divisions? What does each ciliated cell bear on its free end? How do the threads move? What are they called? What is the use of the cilia of the air-passages? Illustrate how they push on the liquid they move in, THE LUNG 8. 237 Bronchitis, or "a cold on the chest," is an inflamma- tion of the membrane lining the bronchial tubes, in con- sequence of which it swells, and secretes an extra amount of mucus. The swelling and secretion tend to close the tabes and interfere with the free passage of air in breathing. The Lungs consist of the bronchial tabes and their ter- minal dilatations, together with blood-vessels, lymphatics, and nerves, all bound firmly together by elastic tissue. The expansions called " air-cells" * at the end of each final branch of a bronchial tube (Fig. 66) are relatively very large, and their surface is still fur- ther increased by the pouches («, V) which project from them. Their walls are highly elastic, and contain a close network of capillary blood-vessels, supplied by the pulmonary artery and emptying into the pulmonary veins. Through the extremely thin lining of the air-cell, and ., . , . *ii £ ii -n • FlG- 66.— Two alveoli of the lung the thin Wall OI the Capillaries highly magnified. 6, 6, the air-cells, . . , or hollow protrusions of the alveo- imbedded. Ill It, OXygen IS au- lus, opening into its central cavity; c, terminal branches of bronchial sorbed by the blood from the tube. air in the air-cell and carbon dioxide given up to It "What is bronchitis? How does an attack of bronchitis interfere with breathing? Of what do the lungs consist? What are the air-cells? How is their surface increased? What do their walls contain? By what are their capillaries filled, and into what do they empty? What inter- change between blood and air occurs in the air-cells of the lungs? * Cell is here used in its primitive sense of a small chamber or cavity (Latin, cellula), and not in its modern histological signification, as one of the distinct pieces of living matter recognized by the microscope as serving to build up the body by their accumulation and co operation. 238 THE HUMAN BODY. has been calculated that if the walls of the air-cells were all spread out flat and placed side by side they would cover an area of 2600 square feet. This great surface, therefore, represents the area of the body by which oxygen is received and carbon dioxide given off. The Pleura. — The exterior of each lung, except where its bronchus and blood-vessels enter it, is covered by a thin elastic serous membrane, the pleura (Fig. 2). This membrane also lines the inside of the chest. Its surface in health is kept moistened by a small quantity of lymph. In consequence of its smoothness and moisture, during the breathing movements the chest wall and lung glide over each other with hardly any friction. Pleurisy is inflammation of the pleura. In its early stages it is usually associated with sharp pain on drawing the breath. Later on a large quantity of lymph is often poured out by the inflamed pleura, filling up the cavity which should be occupied by the lung, and pressing the latter up into a small mass, very inefficient for breathing purposes. The Elasticity of the Lungs. — The lungs are so elastic as to be like a thin india-rubber bag. If we tie a tube tightly into a bronchus and blow in air the lung will dilate, but as soon as we cease blowing and leave the tube open, it will shrink up again. Yet in the chest the lungs always remain so expanded as to completely fill up all the space left for them by the heart and other things contained in the thorax. How is this ? How large is the surface of the body set apart for oxygen recep- tion and carbon dioxide elimination? What is the pleura? What does it cover besides the outer surface of each lung? What is its condition in health? What is its use? What is pleurisy? What symptom usually accompanies its early stages? What happens later? What do the lungs resemble in their elasticity? How ma}T this elasticity be demonstrated? What is the natural condition of the Kings in the Ghent? EXPANSION OF THE L UNGjS. 239 Why the Lungs remain expanded. — We may best under- stand this by considering a thin india-rubber bag, such as a toy balloon. If the neck of the bag is open it collapses. Why ? Because the atmosphere, which pushes on all things near the earth's surface with a pressure of about 15 Ibs. on each square inch (1033 grams on each square cen- timetre), presses equally on the outside and the inside of the bag. These pressures balance one another, and the bag collapses on account of its elastic contractility. We can expand such a bag in two ways. We may blow air into it forcibly, and so make the pressure inside suffi- ciently greater than the opposing aerial pressure outside to overcome the elasticity of the bag. But we can also dis' tend the bag, not by increasing the aerial pressure inside it, but by diminishing that outside it. Suppose (Fig. 67) we tie our rubber bag (d) on the lower end of the tube £, which, like the tube c, passes air-tight through a cork, and then fit the cork tightly into the glass bottle A. The air will then press with its full weight on the inside of the bag through 1) and on the outside of it through c, and the bag will remain collapsed. If now we suck air out through c we diminish its pressure on the outside of the bag without FlG- *?•—: Di^- * gram mustrat- altering the atmospheric pressure on its inside: refa^shlpTof tf will therefore begin to expand, because the Soraxgs in the pressure inside it is no longer counterbalanced by the pres- sure outside. The more air we suck out of c (that is, the more we diminish the atmospheric pressure on the exterior of d) Why does a thin rubber bag collapse when its neck is open? How can we expand such an elastic bag? Describe a model illus- trating the means by which the lungs are kept expanded in the chest- and explain its action? 240 THE HUMAN BODY. the more will the bag expand. Finally, if the rubber bag is distensible enough, when all the air in the bottle is sucked out d will be distended by the push of the air inside it until it completely fills the bottle, whose walls prevent it from going any farther. If now we open c and let in the outside air, the bag will again collapse to its original shrunken dimensions. Application to the Lungs. — The above experiment illus- trates very perfectly how the lungs are kept distended dur- ing life. The chest is an air-tight chamber containing, among other things, the elastic hollow lungs. On the interior of the lungs the weight of the atmosphere presses through the air-passages which lead to them, and answer to the tube b in Fig. 67. Outside the lungs in the thorax there is no air at all, and the uncounterpoised aerial pres- sure inside them overcomes their tendency to shrink, and expands them so as to completely fill all holes and corners of the thoracic chamber not occupied by other organs. If, however, we make a hole in the chest wall and let the air press on the outside of the lungs they collapse at once. How the Air is renewe.d in the Lungs. — Suppose in Fig. S7 that the bottle A has a movable bottom, by pulling down rtrhich its capacity can be increased, and that all air has been sucked out of the bottle through c, which is then closed. The elastic bag will then be distended by the weight of the atmosphere acting upon its interior so as to fill the bottle and press against its sides. If now the movable bottom of A be pulled down so as to make the cavity of the Apply to the lungs the facts illustrated by the model represented in figure 67. Suppose we have a bottle like that in Fig. 67, but with a movable bottom, what would happen when the bottom was pulled down < RENEWAL OF AIR IN LUNGS. 241 bottle larger, the bag would have a larger space to fill. The impediment on its outside being removed the atmospheric pressure on its inside would expand it still further, and the elastic bag would swell out to fill the extra space. As the movable bottom was pulled down, the bag would enlarge and receive fresh air FIG. 08.— The skeleton of the thorax, a, g, vertebral column; &, first rib; c, clavicle ; d, third rib ; i, glenoid fossa. through #. When the bottom was raised again the bag would diminish, and some air be driven out of it through b. It is in quite a similar way that the air is renewed in our lungs by breathing. When we breathe-in, the thoracic cavity is enlarged and air enters the lungs; when we How would the bag inside it be affected? What would the bag receive? What would happen when the bottom was again raised? What happens when we breathe-in? 242 THE HUMAN BODY. breathe-out, the thorax is diminished and air driven out of the lungs. Inspiration and Expiration. — The process of taking air into the lungs is known as inspiration, that of expelling it as expiration. On the average, fifteen to eighteen inspira- tions and expirations occur in each minute. We therefore breathe in and out about once for every four beats of the heart. The Structure of the Thorax. — The thorax is a conical cavity with a rigid supporting skeleton (Fig. 68) formed by the dorsal vertebrae behind, the breast bone in front, and the ribs and rib cartilages on the sides. Between and over these lie muscles, and the whole is covered air-tight by the skin outside and the pleura (p. 238) inside. Above, it is closed by the muscles and other organs of the neck; and below by a movable bottom, the diaphragm. The air-tight chamber thus bounded can be enlarged in all three diame- ters, but especially in the vertical, and in that running from the spinal column to the breastbone (dorso-ventral diameter). The Vertical Enlargement of the Thorax. — This is brought about by the contraction of the diaphragm, which (as may be seen in Fig. 69), is a thin sheet of muscle, with a fibrous membrane in its centre serving as a tendon. In rest the diaphragm is dome-shaped, its concavity being turned towards the abdomen. From the tendon on the crown of What when we breathe-out? What is inspiration? Expiration? How often does each occur in a minute? Compare the rate of respiration and of the heart-beat? What is the form of the thorax? What forms its skeleton? What lie between and over its bones and cartilage? How is it closed air- tight? How is the chest closed above? How below? In what diameters can the chest cavity be enlarged? Describe the diaphragm. THE DIAPHRAGM. 243 the dome, striped muscular fibres radiate, downwards and outwards, in all directions, and are fixed by their inferior ends to the lower ribs, the breast-bone, and the vertebral column. In inspiration (drawing a breath) the muscular FIG. 69.— The lower half of the thorax, with four lumbar vertebrae, showing the diaphragm from above. 1, 2,' 3, central tendon; 4, 5, muscular part. fibres, shortening, flatten the dome and so enlarge the thoracic cavity at the expense of the abdominal. The con- traction of the diaphragm thus greatly increases the size of the thorax chamber by adding to its lowest and widest part. What happens to it during inspiration? What results? 244 THE HUMAN BODY. The Dorso-Ventral Enlargement of the Thorax.— The ribs on the whole slope downwards (Fig. 15) from the vertebral column to the breast-bone, the slope being most marked in the lower ones. During inspiration the breast- bone and the sternal ends of the ribs attached to it are raised by muscles which pull on them, and so the distance between the sternum and the vertebral column is in- creased. That this must be so will readily be seen by examining the diagram Fig 70, where ab represents FIG. 70. — Diagram iiius- the vertebral colunjn, c and d two trating the dorso -ventral in- ., .. . , crease in the diameter of the ribs, and st the sternum. The thorax when the ribs are raised. continuous lines represent the natu- ral position of the ribs at rest in expiration, and the dotted lines the position in inspiration. It is clear that when their lower ends are raised so as to make the bars lie in a more horizontal plane, the sternum is pushed away from the spine, and so the extent of the chest cavity between back-bone and breast-bone is in- creased. Expiration. — Inspiration requires a good deal of muscu- lar effort. When the diaphragm contracts and flattens its dome it has to push down the abdominal viscera on its under side, and to press out the front wall of the abdomen to make room for them. The ribs and breast-bone have also to be pulled up out of their natural position of equilib^ What is the general direction of the ribs? How is it altered! during inspiration? What is the consequence? Illustrate by refer ence to a diagram. Why does inspiration require muscular effort? EXPIRATION. 245 rium. In ordinary expiration, on the contrary, but little if any muscular effort is required. As soon as the muscles which have raised the ribs and sternum relax, these bones return to their natural uncon- strained position; and the elastic abdominal wall presses the abdominal viscera against the under side of the dia- phragm and pushes that organ up again, as soon as its muscular fibres cease contracting. In this way the chest cavity is restored to its original capacity, and the air is sent out of the lungs rather by the elasticity of the parts which were stretched in inspiration, than by any special expiratory muscles. When, however, an expiration is violent (when, for ex- ample, we try to empty our lungs of air as completely as possible, or during a fit of coughing) special expiratory muscles, which pull down the ribs and press up the dia- phragm, are called into action. The Respiratory Sounds. — The entry and exit of air are accompanied by the respiratory sounds or murmurs, which can be heard on applying the ear to the chest wall. The character of these sounds is different and characteristic over the trachea, the larger bronchial tubes, and portions of lung from which large bronchial tubes are absent. They are variously modified in pulmonary affections, and hence the value of auscultation of the lungs in assisting the phy- sician to form a diagnosis. Hygienic Remarks. — Since the diaphragm when it con- How does expiration differ from it in this respect? Explain how the chest is brought hack to its resting position after an inspiration? Give examples of violent expiration? How does it differ from an ordinary expiration in the forces at work for its production? What are the respiratory sounds? Where do their characters differ? Why do physicians study them in lung diseases? 246 THE HUMAN BODY. tracts pushes down the abdominal viscera lying against its under side, these have to make room for themselves by pushing out the soft front of the abdomen, which accord- ingly protrudes when the diaphragm descends. Hence breathing by the diaphragm is indicated on the exterior by FIG. 71. FIG. 71.— Torso of the Statue known as Venus of Milo. FIG. 73. FIG. 72.— Paris Fashion, May, 1880. movements of the abdomen, and is often called ' ' abdominal respiration," as distinguished from breathing by the ribs, called "costal" or "chest breathing." In both sexes the diaphragmatic breathing is the more important, but, as a rule, men and children use the ribs less than adult women. Why does the abdomen protrude during an inspiration? What is meant by abdominal respiration? Why? What is costal respira tion? Which form of breathing is most developed in women? APPENDIX. 247 Since abdomen and chest alternately expand and contract in healthy breathing, anything which impedes their free movement is to be avoided: the tight lacing which used to be thought elegant, and, indeed, is still indulged in by some who think a distorted form beautiful, seriously im- pedes one of the most important functions of the body, leading not only to shortness of breath and an incapacity for muscular exertion, but, as has been proved, in many cases to actual disease. In extreme cases of tight lacing some organs are often directly injured, weals of fibrous tissue being, for example, not unfrequently found developed on the liver from the constant pressure of the lower ribs forced against it by a tight corset. Why should conditions impeding the movement of chest and abdomen be avoided? What is the result of tight lacing? What is of tea found on examining after death the bodies of persons who have practised tight lacing for a long time ? APPENDIX TO CHAPTER XVI. 1. A sheep's lungs with the windpipe attached may be readily ob- tained from a butcher. It is best to secure it and the heart all in one mass, as unless the heart be carefully removed holes are apt to be cut in the lung. 2. Examine the windpipe, and trace it down to its division into the bronchi. In the wall of the windpipe note the horse-shoe-shaped cartilages which keep it open, and which are so arranged that the dorsal aspect of the tube (which lies against the gullet) has no hard parts in it. 3. Trace one bronchus to its lung, and then cutting away the lung tissues follow the branching bronchial tubes through the organ. Note the cartilages in their walls. 4. Carefully divide the other bronchus where it joins the wind- pipe, and lay it and its lung aside. Then slit open the trachea, the bronchus still attached to it and the bronchial tubes. Observe the soft pale-red mucous membrane lining them. 248 THE HUMAN BODY. 5. In the bronchus which has still an uninjured lung attached to it tie air-tight a few inches of glass or other tubing of convenient size. On the end of the glass tube then slip a few inches of rubber tubing. On blowing through the rubber tube the lung will be distended, and as soon as the opening is left free it will collapse; in this way its great extensibility and elasticity will be seen. 6. Blow up the lung moderately, and while it is distended tie a string very tightly around the bit of rubber tubing. This will keep the air from escaping; the distended lung can now be examined at leisure, and its form, lobes, and the smooth moist pleura covering it be better seen than when it is collapsed. 7. To construct the very instructive model depicted in Fig. 67, obtain a wide-necked glass vessel, and a rubber toy balloon. Very carefully untie and open the neck of the balloon, and tie into it tightly a glass rod. Take a cork (one of rubber is best) which fits the neck of the bottle tightly and is perforated by two holes; through one of these holes pass the tube projecting from the neck of the balloon in such way that the collapsed balloon is on the under side of the cork. Through the other hole pass, air-tight, a tube bent as shown in the figure, and on the upper end of tbis slip a few inches of rubber tubing. (Tins can be pinched or tied up at any time, and in that way closed, and so forms a cheap substitute for the stopcock represented in the figure). When the cork is now secured firmly in the bottle the apparatus is ready for use as indicated on p. 239. 8. Substitute a lung for the rubber balloon in the above experi- ment. 9. The action of the diaphragm may be illustrated by substituting for the bottle of § 7 a bell-jar with a wide neck at its upper end. Take a piece of sheet rubber somewhat larger than the bottom of the bell-jar, and tie a button or marble in the centre of it. Lay the rub- ber on the table, with the projection caused by the button down- wards. On it place the bell jar, stretch the rubber moderately tight, turn its edges up around the margin of the bell-jar, and tie very tightly with waxed cord or copper wire. In the neck of the bell- jar place a tight cork with tubes and rubber balloon, as described in § 7. Suck air out of the bottle until the balloon is fairly well ex- panded; then tie the rubber tube. As the air is removed the pressure of the atmosphere on its exterior will cause the rubber sheet to arch up into the cavity of the bell- jar so that it now fairly well represents the diaphragm. The knob caused by the button serves as a handle by which this artificial diaphragm may be pulled down, representing inspiration; as it descends the balloon (lung) enlarges, and air enters it from outside. When the button is let go the artificial diaphragm APPENDIX. 249 ascends, the lung collapses, and air is forced out of it (expiration). Then open the air tube leading into the bell-jar. The lung will col- lapse, and the movements of the diaphragm have no influence upon it. 10. The diaphragm itself may be readily seen on the body of any small animal (rat, kitten, puppy), on removing the abdominal vis- cera. The liver and stomach must be cut away with especial care. a. When the above viscera are removed the vaulted diaphragm will be seen, and through it the pink lungs. b. Seizing some of the folds of peritoneum attached to the dia- phragm, pull it down, imitating its contraction and flattening in in- spiration. The lungs will be seen to follow it closely, expanding to fill the space left by it in its descent. c. Make a free opening into one side of the thorax. The corre- sponding lung will collapse, and be no longer influenced by move- ments of the diaphragm. d. Now open the other side of the chest: its lung also shrinks up; the structure of the diaphragm (its tendinous centre and muscular peripheral regions) can now be better seen, as also the attachment of the pericardium to its thoracic side. 11. The action of the microscopic cilia in driving along the mucus in which they move may be demonstrated as follows: a. Cut off a frog's head and destroy its spinal cord (p. 230) Then cut out its gullet as completely as possible; slit this open and spread it out, inner side up, on a piece of cork or board, and fix it with pins stuck through its edges. b. Prepare a very thin and small shaving of cork. Dissect the skin off one thigh of the animal and wrap a bit of it round the shav- ing of cork, with its underside outwards. c. Place the light mass thus formed on the mucous membrane of the gullet, near its mouth end. The little mass will slowly be moved along to the stomach end of the gullet, and if returned to the mouth end time after time will be swept along in the same direction. This is due to the cilia which line the frog's gullet (they are not present In that of man), and push along to the stomach the mucus bathing them on which the little float swims. d. Place the exposed gullet under a bell- jar with a wet sponge for an hour or two. The mucus secreted by it will be found to have been swept along to the end of it which joins the stomach. CHAPTER XVII. THE CHEMISTRY OF RESPIRATION AND VENTILATION. The Quantity of Air breathed daily. — After an ordi- nary expiration the chest cavity is by no means completely collapsed. At this time the lungs still contain about 200 cubic inches of air. In the next inspiration 30 more cubic inches are taken in, about the same amount sent out at the following expiration, and so on throughout the day. Du- ring quiet breathing the quantity of air in the lungs varies, therefore, with each inspiration and expiration between 230 and 200 cubic inches. At each inspiration something over a pint of fresh air is taken in, and at each expiration about the same amount of vitiated air is expelled. As each of us breathes at least fifteen times a minute, we thus use each minute, and render impure, 15x30— 450 cubic inches (15| pints) of air. In an hour the quantity would be 450 X 60 = 27,000 cubic inches (930 pints), and in twenty-four hours 27,000X24=648,000 cubic inches (22,320 pints) of air, which would weigh about 28. 7 Ibs. We have next to How much air do the lungs contain after an ordinary expiration? How much do they receive at the next inspiration? How much is sent out from them during expiration? Within what limits does the quantity of air in the lungs vary during quiet breathing? What bulk of air is taken in during an inspiration? How often do we breathe? How much air does each one of us render impure every minute? How much in an hour? How many pints in a day? What does this quantity of air weigh? [250] CHANGES IN RESPIEED AIR. 251 see what it is that happens to this vast quantity of air breathed daily by each one of us; what we have taken out of it, and what we have given off to it. The Changes produced in Air by being once breathed. — • These are fourfold — changes in its temperature, in its mois- ture, in its chemical composition, and in its volume. Temperature Changes. — The air taken into the lungs is nearly always cooler than that expired, which has a tem- perature of about 36° C. (97° F.). The temperature of a room is usually about 21° C. (70° F.). The warmer the inspired air, the less the heat which is lost to the body in the breathing process. Changes in Moisture. — Inspired air always contains more or less water vapor, but is rarely saturated — that is, rarely contains so much but it can take up more without showing it as mist; the warmer air is, the more water vapor it re- quires to saturate it. The expired air is nearly saturated for the temperature at which it leaves the body, as is read- ily shown by the vapor deposited when it is slightly cooled, as when a mirror is breathed upon; or by the clouds seen issuing from the nostrils on a frosty day, these being due to the fact that the air as soon as it is cooled cannot hold all the water vapor which it took up when warmed in the body. We therefore conclude that air when breathed gains water vapor and carries it off from the lungs. The quan- tity of water thus removed from the body is about nine ounces each twenty-four hours. Chemical Changes. — The most important changes brought about in the breathed air are those in its chemical What changes are produced in the air on its being once breathed ? How does expired air differ in temperature from inspired? How does expired air differ from inspired in moisture? How much water is evaporated from the lungs daily? 252 THE HUMAN BODY, composition. Pure air when completely dried consists in 100 parts of — By Volume. By Weight. Oxygen 20.8 23 Nitrogen 79.2 77 When breathed once, such air gains rather more than 4 volumes in 100 of carbon dioxide, and loses rather more than 5 of oxygen. More accurately, 100 volumes of ex- pired air, when dried, consist of — Oxygen 15.4 Nitrogen ?L. 2 Carbon dioxide 4.3 The expired air also contains volatile organic substances in quantities too minute for chemical analysis, but readily detected by the nose upon coming into a close room in which a number of persons have been collected. The Quantity of Oxygen taken up by the Lungs in a Day. — We have already seen that the quantity of air breathed in a day is 648,000 cubic inches. This loses 5.4 per cent, of oxygen or 35,000 cubic inches, weighing 12,818 grains (If Ibs.): the body therefore gains this amount of that gas through the lungs daily. The Amount of Carbon Dioxide passed out from the Lungs in a Day. — This being 4.3 per cent, of the total bulk of the air breathed, is 27,864 cubic inches; it weighs 14,105 grains or about 2 Ibs. We thus find that though each breath seems in itself a What is the chemical composition of pure air by volume? By weight? What substances does air gain and lose when once breathed? What is the composition by volume of dried expired air? Wlm'c does dried expired air contain besides oxygen, nitrogen, and carbon dioxide ? What bulk of oxygen does the air breathed in a day lose? What weight? How much oxygen does the body take up daily by means of the lungs? What bulk of carbon dioxide is carried off by breathing in each day? What does it weigh? VENTILATION. 253 very little thing, on calculation it is obvious that the total amount of matter received into the body from the lungs, and that passed out of it by these organs, every day of our lives is considerable. In a year each adult breathes about 10,000 Ibs. of air ; from it he takes 657 Ibs. of oxygen, and to it he gives off 730 Ibs. of carbon dioxide. Changes of Volume in Air once breathed. — If the ex- pired air be measured as it leaves the body its bulk will be found greater than that of the inspired air, since it not only has water vapor added to it, but is expanded in con- sequence of its higher temperature. If, however, it be dried and reduced to the same temperature as the inspired air, its volume will be found diminished, since it has lost 5.4 volumes of oxygen for every 4.3 volumes of carbon dioxide which it has gained. Ventilation. — Since at each breath some oxygen is taken from the air and some carbon dioxide given to it, were the atmosphere around a living man not renewed he would at last be unable to get from the air the oxygen he required; he would die of oxygen starvation or be suffocated, as such a mode of death is called, as surely, though not quite so fast, as if he were put under the receiver of an air-pump and all the air around him removed. Hence the necessity of ventilation to supply fresh air in place of that breathed, and clearly the amount of fresh air requisite must be deter- mined by the number of persons collected in a room: the supply which would be ample for one person would be in- Wliat weight of air is breathed yearly by an adult? How much oxygen is taken from it? How much carbon dioxide is given to it? How does the air expired differ in bulk from inspired? Why? If the expired air be dried and cooled to the temperature of the in- spired, what is found? Why? Why would a man die if the air around him were not renewed? What is suffocation? What is the object of ventilation? 254 THE HUMAN BODY. sufficient for two. Moreover, fires, gas, and lamps all use up the oxygen of the air and give carbon dioxide to it, and hence calculation must be made for them in arranging for the ventilation of a building in which they are to be used. When breathed Air becomes unwholesome. — In order that air be unwholesome to breathe, it is by no means necessary that it shall have lost so much of its oxygen as to make it difficult for the body to get what it wants of that gas. The evil results of insufficient air-supply are rarely directly due to that cause even in the worst ventilated room, for the blood flowing through the lungs can take what oxygen it wants from air containing comparatively little of that gas. The headache and drowsiness which come on from sitting in badly ventilated rooms, and the want of energy and general ill-health which result from permanently living in such, are dependent on a slow poison- ing of the body by the reabsorption of matters eliminated from the lungs in previous respirations. What these are is not accurately known; they doubtless belong to those volatile bodies mentioned above as carried off in small quantities in each breath, since observation shows that the air becomes injurious long before the amount of carbon dioxide in it is sufficient of itself to do any harm. Breath- ing air containing one or two per cent, of that gas produced by ordinary chemical methods does no particular injury, but the breathing of air containing one per cent, of carbon What conditions determine the supply of fresh air which should be provided to a room? Is air ever unwholesome wrhile still capable of supplying the oxygen which the body requires? What results from living in ill- ventilated rooms? Why? Does air once breathed become injuri- ous before the quantity of carbon dioxide in it is poisonous? What percentage of pure carbon dioxide may be present in the air breathed without doing harm? VENTILATION. 255 dioxide produced by respiration is decidedly injurious, because of the other things sent out of the lungs along with it. Carbon dioxide, in any such percentage as is commonly found in a room, is not poisonous, as used to be believed, but as it is tolerably easily estimated in air, while the more dangerous injurious substances evolved in breathing are not, the purity or foulness of the air in a room is usually deter- mined by finding the percentage of carbon dioxide in it; but it must be borne in mind that to mean much this car- bon dioxide must have been produced by breathing; other- wise the amount of it present is no guide to the quantity of the more important poisonous substances present. Of course when a great deal of carbon dioxide is present the air is irrespirable, as for example sometimes at the bottom of wells or brewing- vats. The Quantity of Fresh Air which should be allowed for each Person in a Boom. — In each minute a man breathes out 450 cubic inches of air containing rather more than 4 per cent, of carbon dioxide. This mixed with three times its bulk of pure air would give a little over one cubic foot containing one per cent, of carbon dioxide. Such air is no longer respirable with safety. The result of breath- ing it for an hour or two is headache and drowsiness; of breathing it for weeks or months several hours daily, a What percentage of carbon dioxide produced by breathing shows that the air is unfit for use? Is the proportion of carbon dioxide found ordinarily in a room poisonous? Why is the percentage of carbon dioxide in air usually employed in deciding whether the air is fit to breathe? What must be borne in mind in deciding from the percentage of carbon dioxide in it that air is no longer wholesome? Is air containing much carbon dioxide fit to breathe? Give an example. What bulk of air does a man contaminate with carbon dioxide to the extent of one per cent, in each minute? Is air so contaminated fit to breathe? What are the consequences of breathing it for a few hours? What of breathing it for months? 256 THE HUMAN BODY. lowered tone of the whole body, less power of work, physi- cal or mental, and less power of resisting disease. The ill effects may not show themselves at once, and may accord- ingly be overlooked or considered scientific whims by the careless, but they are there ready to manifest themselves nevertheless. In order to have air to breathe in a fairly pure state every man should have for his own allowance at least about 800 cubic feet of space to begin with, and the arrangements for ventilation should at the very least renew this at the rate of one cubic foot per minute. The nose is, however, the best guide, and it is found that at least five times this supply of fresh air is necessary to keep free from any odor the room inhabited by one adult. If an inhabited room smells " close" to one coming into it from "out of doors," the air in it is unwholesome to breathe for any length of time. How to Ventilate. — Ventilation does not necessarily mean draughts of cold air, as is too often supposed. In warming by indirect radiation it may readily be secured by fixing, in addition to the registers from which the fresh warmed air reaches the room, corresponding openings at the opposite side by which the old air may pass off to make room for the new. An open fire in a room will always keep up a current of air through it, and is one of the most wholesome, though not most economical, methods of warming an apartment. Why are the injurious effects of impure air apt to be ignored? What volume of air should be allowed to each adult? At what rate should it be replenished? What supply of fresh air is needed to keep an inhabited room free from odor? Is it safe to live in a room which " smells close"? How may ventilation be secured in heating by "indirect radia- tion"? What are the advantages and what the disadvantages of an open fire? CHANGES OF BLOOD IN THE L UNGS. 257 Stoves in a room unless constantly supplied with fresh air from without dry its air to an unwholesome extent. If no appliance for providing this supply exists in a room it can usually be got, without a draught, by fixing a board about four inches wide under the lower sash and shutting the window down on it. Fresh air then comes in by the opening between the two sashes and in a current directed upwards, which gradually diffuses itself over the room without being felt as a draught at any one point. In the method of heating by direct radiation the apparatus .em- ployed provides of itself no means of drawing fresh air into a room, as the draught up the chimney of an open fire- place or of a stove does; and therefore special inlet and outlet openings are very necessary. Since, fortunately, few doors and windows fit quite tight, fresh air gets into closed rooms in tolerable abundance for one or two in- habitants. Changes undergone by the Blood in the Lungs. — These are the exact reverse of those exhibited by the breathed air — what the air gains the blood loses, and vice versa. The blood loses heat, and water, and carbon dioxide, in the pul- monary capillaries, and gains oxygen. These gains and losses are accompanied by a change of color from the dark purple which the blood exhibits in the pulmonary artery, to the bright scarlet it possesses in the pulmonary veins. Why the Blood changes its Color as it flows through What are stoves apt to do? Point out a good way of supplying fresh air to a room warmed by a stove? What are especially impor- tant in a room heated by "direct radiation"? Why is it fortunate that doors and windows do not fit air-tight? What is the relationship between the gains and losses of blood in the pulmonary circulation, and the losses and gains of the breathed air? What does the blood lose as it flows through the lungs? What does it gain? What change in the color of the blood accompanies these sains and losses? 258 THE HUMAN BODY. the Pulmonary Capillaries. — The color of the blood depends on its red corpuscles, since pure blood-plasma or blood- serum is colorless or at most a very faint straw yellow. Hence the color change which the blood experiences in circulating through the lungs must be due to some change in its red corpuscles. These consist chiefly of Jicemoglobiri (p. 178), and haemoglobin, as we have learned, is a sub- stance which has the power of absorbing oxygen and form- ing a bright scarlet compound called oxylicemogloUn. This oxyhaemoglobin very easily gives up its oxygen when it is placed under conditions where that gas is scarce: the haemoglobin left behind has a dark purple color. The blood leaving the lungs by the pulmonary veins is bright red because all its haemoglobin has been turned into oxy- haemoglobin. From the left side of the heart it is conveyed by the branches of the aorta to all the organs of the body. These are constantly using oxygen, which is therefore very scarce in them, and as the blood flows through its oxy- haemoglobin is broken up, the oxygen taken away, and dark purple-red haemoglobin left to be conveyed by the veins to the right auricle of the heart. From there it passes to the right ventricle and thence by the pulmonary artery to the lungs, where it again picks up oxygen and Why must the change in color of the blood during its pulmonary circuit be due to a change in its red corpuscles? What is the chief constituent of the red blood-corpuscles? What property does haemo- globin possess with reference to oxygen? What is the color of oxy- haemoglobin? When does oxyhaemoglobin give off its oxygen? What is the color of haemoglobin? Why is the blood in the pulmonary veins bright red? Where is it conveyed? Why is oxygen scanty in most organs of the body? What results as regards the oxy haemoglobin of the blood? What is the color of the blood sent to the right auricle of the heart? What is the subsequent course of this blood until it reaches the lungs? What does it receive in the lungs? How is its color altered in 'those organ bufc are most abundant on the palms of the hands, the soles of the feet, and the brow. Altogether, there are about two and a half millions of them. The perspiration or sweat poured out by the sudoriparous FIG. ?8.— A sweat What is the matrix of a nail? When does the nail grow longer? What is the bed of a nail? How does a nail grow thicker? Which is its thickest part? What is necessary in order that a " cast nail" may be reproduced ? What glands are found in the skin? Describe a sweat gland. Where are the sweat glands most numerous? How many are there on the whole skin? THE PERSPIRATION. 273 glands is a transparent colorless liquid, with a peculiar odor, varying in different races, and in the same individual in different regions of the body. Its quantity in twenty-four hours is subject to great variations, but usually lies between 10,850 and 31,000 grains (or 25 and 71 ounces). The amount is influenced mainly by the surrounding tempera- ture, being greater when this is high; but _ it is also in- creased by other things tending to raise the temperature of the body, as muscular exercise.* The sweat may or may not evaporate as fast as it is secreted; in the former case it is known as insensible, in the latter as sensible per- spiration. By far the most-passes off in the insensible form, drops of sweat only accumulating when the secretion is very profuse, or the surrounding atmosphere is so humid that it does not readily take up more moisture. The perspiration in 1000 partsx contains 990 of water to 10 of solids. Among the latter is, in health, a little urea, some sodium chloride, and otheivsalts. In diseased conditions of the kidneys the urea may be greatly increased, the skin supplementing to a certain extent deficiencies of those organs. The Sebaceous Glands nearly always open into hair fol- licles. They are small compound racemose glands (p. 131). Each presents a duct, opening near the mouth of the hair follicle; when followed back this duct is found to divide into several branches which end in globular expansions. Describe the perspiration. How much is secreted daily? Point out conditions influencing its amount. What is meant by " insensi- ble perspiration"? Under what conditions do we find "sensible perspiration"? What percentage of solids exists in the sweat? What do they contain? When is the proportion, of urea in the perspiration apt to be increased? Where do the sebaceous glands open? To what type of gland do they belong? * In fever the sweat glands are paralyzed, and we find a high temperature of the body with a dry skin. 274 THE HUMAN BODY. The latter are lined by secreting cells. The mouths of the ducts of a pair of sebaceous glands are seen on the sides of the hair follicle in Fig. 77. The Sebaceous Secretion is oily and semi-fluid. In healthy persons it lubricates the hairs and renders them glossy even when no " hair-oil " is used. It is also spread more or less over all the surface of the skin, and makes the cuticle less permeable by water, which in consequence does not readily wet the healthy skin, but runs off it, as "off a duck's back," though to a less marked extent. The Skin as a Sense Organ. — Besides its functions as a protective covering and an excretory organ, the skin is of extreme importance, as being the seat of one of our most important senses — the sense of touch. In this relationship it will be considered later (Chap. XXI). Hygiene of the Skin. — The sebaceous secretion and the solid residue left by evaporating sweat form a solid film over the skin, which tends to choke the mouths of the sweat glands (the so-called "pores" of the skin) and impede their action. Yet these glands, minute though each is, have for their function to separate daily from the body a great amount of water* and some little urea and salines. Hence the importance of personal cleanliness. The whole skin, except that of the scalp, should be washed daily. Women cannot Describe the structure of a sebaceous gland. Describe the sebaceous secretion. Why is the hair of a healthy person, using no hair-oil, glossy? Why does water run off the skin? Enumerate the chief functions of the skin. How are the mouths of the sweat glands apt to be choked up? Point out functions of these glands? How much of the skin should be washed daily? * The sweat glands not merely carry off some water from the body, but serve also to regulate its temperature. When water evaporates from the surface of any object it abstracts heat from that object; and when perspiration evapo- rates from the skin it carries off heat and cools the body. In health, the sweat HYGIENE OF THE SKIN. 275 well wash their hair every day, as it takes so long to dry; but there is no reason why a man should not immerse his head when he takes his bath. Except on parts of the skin especially exposed to contamination, soap should only be used occasionally — say once or twice a week; its employ- ment is quite unnecessary for cleanliness, except on ex- posed parts of the body, if frequent bathing is a habit and the skin be well rubbed afterwards until dry. Soap nearly al- ways contains an excess of alkali, which in itself injures some skins, and, besides, is apt to combine chemically with the sebaceous secretion and carry it too freely away. Persons whose skin is injured by soap, will find in cornmeal a good substitute. No doubt many folk go about in very good health with very little washing; contact with the clothes and other external objects keeps the skin excretions from accumulating to any very great extent. But apart from the duty of personal cleanliness imposed on every one as a member of society in daily intercourse with others, the mere fact that the healthy body can manage to get along under unfavorable conditions is no reason for exposing it to them. A clogged skin throws more work on the lungs and kid- neys than their fair share, and the evil consequences may be experienced any day when something else throws an- other extra strain upon them. Bathing. — One object of bathing is to cleanse the skin; How often should soap be used in the bath? Why is the too fre- quent use of soap not desirable? What is a good substitute for it in cases where soap is injurious to the skin? How does an unclean skin influence internal organs? When are its results apt to show them- selves? glands secrete more vigorously when the body is heated, and so cool it and keep down its temperature. In most fevers the sweat glands are paralyzed; and the abnormally warm body is not cooled by loss of the heat, which in health would have been carried off by the evaporating sweat. 276 THE HUMAN BODY. but it is also useful to strengthen and invigorate the whole frame. For strong healthy persons a cold bath is the best; in severe weather the temperature of the water should be raised to 15° 0. (about 60° F.), at which it still feels quite cool to the surface. The first effect of a cold bath is to contract all the skin-vessels and make the surface pallid. This is soon followed by a reaction, in which the skin becomes red and full of blood, and a glow of warmth is felt in it. The proper time to come out of the bath is while this reaction lasts, and after emersion it should be promoted by a good rub. If the stay in the cold water be too prolonged the state of reaction passes off, the skin again becomes pallid, and the person probably feels cold, uncomfortable, and de- pressed all day: then bathing is injurious instead of bene- ficial; it lowers instead of stimulating the activities of the body. How long one may remain in cold water with benefit, depends greatly on the individual; a vigorous man can bear and set up a healthy reaction after much longer immer- sion than a feeble one; moreover, a person used to cold bathing can with benefit remain in the water longer than one not accustomed to it. Of course, apart from this, the temperature of the water has a great importance. Water which feels cold to the skin may, as shown by the ther- mometer, vary within very wide limits of temperature. The colder it is, the shorter the time which it is wise to remain in it. When to Bathe. — It is perfectly safe to bathe when warm, What ends are obtained by bathing? What sort of a bath should healthy persons take? What is the primary effect of a cold bath on a healthy person? What follows next? When should one leave a cold bath? What happens if one stays too long in a cold bath? Point out conditions which influence the time of remaining with benefit in a cold bath. SHOWER BATHS AND WARM BATHS. 277 provided the skin is not perspiring profusely; the common belief to the contrary notwithstanding. On the other hand, no one should enter a cold bath when feeling chilly, or in a depressed vital condition. It is not wise to take a cold bath immediately after a meal, for the afterglow of the skin tends to draw away too much blood from the digestive organs, which are then actively at work. The best time for a long bath is two or three hours after breakfast; but for a brief daily dip there is no better time than while the body is still warm from bed. Shower Baths abstract less heat from the body than an ordinary cold bath, and at the same time give it a greater stimulus, tending to set up the worm reaction. Hence they are valuable to persons in not very vigorous health. Warm Baths, except occasionally for purposes of clean- liness, are medical remedies, and not proper things for daily use. While promoting the tendency to perspiration (which it is often important to do in disease), they also, if often repeated, lower the general vigor of the body. Persons in feeble health, who cannot stand an ordinary daily cold bath, may diminish the shock to the system by raising the temperature of the water they bathe in to any point at which it still feels cool to the skin. Is it ever safe to bathe while warm? Point out conditions when a cold bath should be avoided. Why is it not wise to take a cool bath soon after a meal? Wliat is the best time for a prolonged cold bath? What the best time for a brief daily dip? Why are shower baths better than immersion baths for persons in enfeebled health? Should healthy persons take daily warmbaths? What is the con- sequence of frequent warm baths? How should persons iii feeble health regulate the temperature of their daily bath? 278 THE HUMAN BODY. APPENDIX TO CHAPTER XVIII. To demonstrate the anatomy of the renal organs proceed as follows: 1. Kill a rat in any merciful way; placing it under a bell-jar with a sponge soaked in ether is a good method. 2. Open the abdomen of the animal, remove its alimentary canal, and cut away (with stout scissors) the ventral portion of the pelvic girdle. The dark-red kidneys will then be easily recognized on each side of the dorsal part of the abdominal cavity, the right one nearer the head than the left. 3. Dissect away neatly the connective tissue, etc., in front of the vertebral column, so as to clean the inferior vena cava and the abdom- inal aorta. Trace out the renal arteries and veins. 4. Find the ureter, a slender tube passing back from the kidney towards the pelvis: it leaves the inner border of the kidney behind the vein and artery; and lying, at first, at some distance from the middle line, converges towards its fellow as it passes back. 5. Follow the ureters back until they reach the urinary bladder; dissect away the tissues around the latter and note its form, etc. 6. Open the bladder; find the apertures of entry of the ureters, and pass bristles through them into those tubes. Note the mucous membrane lining the bladder. 7. Remove one kidney from the body and divide it from its outer to near its inner border; turn the two halves apart (still leaving them connected by the tissues at the inner border), and examine the cut surfaces. 8. Note at the inner border (fiilas) the dilatation (pelvis) of the ureter; the outer, darker, granular cortical portion of the kidney, and the inner, paler, smoother medullary portion; the papilla, formed by •i projection of the medullary substance at the hilus, contained in an expansion (calyx) of the pelvis of the ureter. 9. Obtain a fresh sheep's kidney. Divide it by a section made through it from its outer to its inner border. On the cut surfaces the cortex and medulla will be more readily demonstrated than on the rat's kidney. The pyramids of Malpighi will also be easily seen, and the offshoots of the cortex extending between them. CHAPTER XIX. WHY WE NEED A NERVOUS SYSTEM. ITS ANATOMY. The Harmonious Co-operation of the Organs of the Body. — We have already learned that the body consists of a vast number of cells and fibres, combined to form organs^ and that each kind of cell or fibre and each organ has its own peculiar structure, properties, and uses. Except in so far as the blood, passing from organ to organ, carries mat- ters from one to another, and indirectly enables each organ to act upon the rest, we have as yet seen no means by which all this collection of organs is made to work together, so that each shall not merely look after itself, but regulate its activity in relation to the needs or dangers of other parts of the body. That the organs do co-operate we all know. The lids shut when an object threatens to touch the eye, and (with- out our thinking about it at all) thrust themselves in the way so as to protect the more tender eyuball. When we are using the muscles of the legs vigorously the muscles of respiration hurry their action, and, consequently, oxygen is conveyed more rapidly to the blood for the supply of the working leg muscles, and the carbon dioxide produced in great quantity by these muscles is quickly removed. When the sole of the foot is tickled the muscles of the thigh and Of what is the body made up? How do the various kinds x>f cells, fibres, and organs differ? How does the blood enable each organ to influence the rest? Give an example showing the co-operation of the organs of the body. Give another example. A third. 280 THE I1UHAN BODY. leg, which are not directly interfered with at all, contract and jerk the foot away from its tormentor. Everywhere we find this co-operation among the organs ; and it is only by such co-operation that our oodies are able to continue alive. In ^Esop's fable we are told how the arms and jaws declined to work any longer in providing and grinding food for the lazy stomach, and how they soon came to grief in consequence. We might extend the fable, and go on to state how afterwards the stomach made up its mind to digest and absorb just as much food as it wanted for itself, and not bother about supplying those cantankerous arms and jaws, and the moral would be the same: if the stomach ceased to work for the other parts they soon would cease to be able to send food to it, and so it would itself starve in turn. How a Man differs from a Collection of Living Organs. — Throughout the body, heart, lungs, stomach, intestines, liver, muscles, and skin, all need one another's aid to obtain food and oxygen, to remove wastes, and to avoid dan- gers. This co-operation makes the individual human be- ing ; a mere mass of living organs, arranged together in the. form of man's body, but each acting without reference to the rest, would no more make a man than a mob of strong men would make an army. As in the mob the reckless courage of some, the personal cowardice of others, the uncontrolled ambition of a few, would make the crowd nearly useless for military purposes in spite of the merits of its individual members, so in the body ; if the organs were Is co-operation between its organs general throughout the body? Is it important? Illustrate the importance of co-operation between the parts of the body. For what purposes do the different organs need one another's help? Is the co-operation of organs necessary to make a,n individual human. Illustrate, CO-ORDINATION. 281 not disciplined, controlled, and guided, so as to work to- gether for the good of the whole, death would very soon result. As a matter of fact this is the way in which death almost always does begin. The body is not built like the deacon's "one-boss shay/' to run till every part of it gives out at the same moment. Some important organ ceases to do its part properly; as a consequence the whole complex mechanism is thrown out of gear, and deatn results. Co-ordination means controlling the activities of a num- ber of working things (whether men, or organs, or ma- chines) for the attainment of a definite end. A pro- miscuous and undirected crowd of competent bricklayers, carpenters, hod-carriers, and so forth, would be quite in- competent to build a house. There might be present abundant energy and skill to construct walls and floors and roof; but if each man worked for himself and took no heed of the rest the result would be an odd building, if any at all. Hence the whole work is placed under the control of a master builder, who guides the activities of individ- uals according to the needs of the moment: undirected workmen, if conscientious, would work jufct as hard with- out supervision, but they would work unni healthy body may be regarded as made up -u spme im- portant organ ceases to do its duty? What is meant by co-ordination? Illustrate. How mny the healthy body be regarded when compared with t\ie worknu qerned in building a house? ! 282 THE HUMAN BODY. such a word, i^ ..-epresented by the nervous system, which is in communication with all the other organs, is influenced by the condition and the needs of every part at each mo- ment, and guides the activity of all the others accordingly. Part of this control is exercised consciously and with the co-operation of the "will," but much more is carried on by the nervous system without our knowing anything about it. Nerve-Trunks and Nerve-Centres. — In dissecting the body numerous white cords are found which at first sight might be taken for tendons. That they are something else soon becomes clear, since a great many of them have no connection with muscles, and those which have, usually enter near the middle of the belly of the muscle, instead of being fixed to its ends as most tendons are. These cords are nerve-trunks : followed from the middle line of the body each (Fig. 79) will be found to break up into finer and finer branches, until the subdivisions become too small to be followed without the aid of a microscope. Traced towards the middle of the body the trunk will, in most cases, be found to increase by the union of others with it, and ultimately to join a much larger mass of different structure, from which other similar trunks spring. This mass is nerve-centre. The end of a nerve attached to the centre is, naturally, its central, and the other its distal or peripheral end. What is it in the body which represents the master builder? What are the relations between the nervous system and the other organs of the body ? Is the control of the nervous system always con- ly exercised? How n.ay we recognize that certain white cords found on dissect- •T the be ly -in not tendons? What are they? What is found when •iced towards the outer parts of the body? What a traced m the opposite direction? What is a nerve-centre? .1 by lie peripheral end of a nerve? DIAGRAM OF THE NERVOUS SYSTEM. 283 FIG. r9.-Diagram illustrating the general arrangement of the nervous 284* THE HUMAN BODY. Nerve-centres give origin to nerve-trunks ; these radiate all over the body, branching and becoming smaller and smaller as they proceed from the centre ; finally they end in or among the cells and fibres of the various organs. The general arrangement of the nerve-centres and of the larger nerve-trunks of the body is shown in Fig. 79. The Main Nerve-Centres. — The great majority of the nerve-trunks take their origin from the brain and spinal cord) which together form the great cerebro-spinal centre. Some nerves, however, commence in rounded or oval masses, which vary in size from that of the kernel of an almond down to microscopic dimensions, and which are widely distributed in the body. Each of these smaller centres is called a ganglion. A considerable number of the largest ganglia are united directly to one another by nerve- trunks, and give off nerves especially to blood-vessels and to the organs in the thoracic and abdominal cavities. These ganglia and their branches form the sympathetic nervous system (Figs. 1 and 2), as distinguished from the cerebro- spinal nervous system, consisting of the brain and spinal cord and the nerves proceeding from and to them. The Cerebro-Spinal Centre and its Membranes. — Lying in the skull is the brain, and in the neural canal of the vertebral column the spinal cord or spinal marrow, the two being continuous through the foramen magnum To what do nerve-centres give origin? What becomes of nerve- trunks? From what organs do most nerves arise? What is meant by the cerebro- spinal centre? From what do those nerves arise which are not directly connected with brain and spinal cord? What are the smaller nerve-centres named? What is the sympathetic nervous sys, tern? Where is the brain placed? What organ lies in the neural canal of the backbone? Through what opening do brain and spinal cord unite? THE CEREBRO-SPINAL CENTRE. 285 (Fig. 20) of the occipital bone. This cerebro-spinal centre con- sists of similar right and left halves, incompletely separated by grooves and fissures. Brain and spinal cord are very soft and easily crushed ; accordingly, both are placed in almost com- pletely closed bony cavities, and are also enveloped by mem- branes which give them sup- port. These membranes are three in number. Externally is the dura mater, tough and strong, and composed of con- nective tissue. The innermost enveloping membrane of the cerebro-spinal centre, in imme- diate contact with the proper nervous parts, is. the pia mater, less dense and tough than the dura mater. Covering the out- side of the pia mater is a layer of flat cells ; a similar layer lines the inside of the dura mater, and these two layers are de- scribed as the third membrane •d 9,* Why are brain and spinal cord placed in bony chambers? How many membranes also support them? What is the outside membrane named? What are its mechanical properties? Of what is it composed? Wuut is the pia mater? 286 THE HUMAN BODY. of the cerebro-spinal centre, called the arachnoid. In the space between the two layers of the arachnoid is a small quantity of watery cerebro-spinal liquid. The Spinal Cord (Fig. 80) is nearly cylindrical in form, being, however, a little wider from side to side than dorso- ventrally, and tapering off at its posterior end. Its aver- age diameter is about j inch and its length 17 inches. It weighs 1-J- ounces. There is no marked limit be- Fio. 81.— The spinal cord and nerve-roots. A, a small portion of the cord seen from the ventral side; B, the same seen laterally; C, a cross-section of the cord; Z>, the two roots of a spinal nerve; 1, anterior (ventral) fissure; 2, poste- rior (dorsal) fissure ; 3, surface groove along the line of attachment of the anterior nerve-roots; 4, line of origin of the posterior roots; 5, anterior root filaments of a spinal nerve; 6, posterior root filaments; 6', ganglion of the pos- terior root ; 7, 7'. the first two divisions of the nerve-trunk after its formation by the union of the two roots. What is Hie arachnoid? What is the cerebro-spinal liquid? What is the general form of the spinal cord? Its average diame- ter? Its length? Its weight? How does it connect with the brain? THE SPINAL CORD AND THE SPINAL NERVES. 287 tween the spinal cord and the brain, the one passing gradually into the other. In its course the cord presents two expansions, an upper, 10 (Fig. 80), the cervical en- largement, reaching from the third cervical to the first dorsal vertebrae, and a lower or lumbar enlargement) 9, opposite the last dorsal vertebras. Running along the middle line on both the ventral and the dorsal aspects of the cord are fissures which (C, Fig. 81) nearly divide it into right and left halves. A transverse section, C, shows that the substance of the cord is not alike throughout, but that its white superficial layers envelop a central gray substance arranged somewhat in the form of a capital H. Each half of the gray matter is crescent-shaped, and the, crescents are turned back to back and united across the middle line by the gray com- missure. The Spinal Nerves. — Thirty-one pairs of spinal nerves join the spinal cord in the neural canal of the vertebral column, entering the canal through the inter vertebral fora- mina (p. 32). Each divides in the foramen into a dorsal and ventral portion, known respectively as the posterior and anterior roots of the nerve (6 and 5, Fig. 81), and these are attached to the sides of the cord. On each pos- terior root is a spinal ganglion (6', Fig. 81), placed where What expansions are seen in it? Where is each placed? How are the right and left halves of the cord separated? Is the spinal cord alike all through? What are the colors of its outer and of its inner portions? What is the form of the gray mat- ter of the cord as seen on cross-sections? How are the crescents united? How many spinal nerves are there? What do thoy join? How do they get into the neural canal? Where do they divide? What are the divisions named? To what are they attached? What is found on each posterior root? 288 THE HUMAN BODY. it joins the anterior root to make up the common nerve- trunk. Immediately after its formation by the mixture of fibres from both roots, the trunk begins to divide into branches for the supply of some region of the body. The Brain (Fig. 82) is far larger than the spinal cord and more complex in structure. It weighs on the average about 50 ounces in the adult. The brain consists of three main masses, each with subsidiary parts, following one an- other in series from before back, and respectively known as the fore-brain, mid-brain, and hind-brain. In man the fore-brain, A, weighing about 44 ounces, is much larger than all the rest put together and laps over them. FIG. 82.— Diagram illustrating the general relationships of the parts of the brain. A, fore-brain; 6, mid-brain; B, cerebellum; C, pons Varolii ; D, medulla oblongata; B, C, and D together constitute the hind-brain. What becomes of the common trunk formed by the mixture of the roots? Point out characters in which the brain differs from the spinal cord. What is its weight? Of what main divisions is the brain composed? Which is the largest division? Its weight? THE FORE-BRAIN. 289 It is chiefly formed of two large convoluted musses, sepa- rated from one another by a deep fissure, and known as the cerebral hemispheres. The great size of these is very characteristic of the human brain. Beneath each cere- bral hemisphere is an olfactory lobe (/, Fig. 84), incon- spicuous in man but often larger than the cerebral hemi- spheres, as. in most fishes. The mid brain, #, forms a connecting isthmus between the two other divisions. The hind-brain consists of three main parts: on its dorsal side is the cerebellum, B, Fig. 82; on the under side is the pons Varolii, C, Fig. 82; and behind is the medulla ob- longata, D, Fig. 82, which joins the spinal cord. In nature the main divisions of the brain are not sepa- Cb\ FIG. 83.— The brain from the left side. Cb, the cerebral hemispheres forming the main bulk of the fore-brain; Cbl, the cerebellum; Mo, the medulla oblon- gata; P, the pons Varolii; *, the fissure of Sylvius. By what is the fore-brain chiefly formed? What lies below the cerebral hemispheres? Are the olfactory lobes ever larger than the cerebral hemispheres? What does the mid-brain form? Name the main divisions of the hind-brain? State their relative positions. What part of the brain joins the spinal cord? THE HUMAN BODY. rated so much as has been represented in the diagram for the sake of clearness, but lie close together as represented in Fig. 83; and the mid- brain is entirely covered in on its dorsal side. Nearly everywhere the surface of the brain is folded, the folds, known as the convolutions) being deeper and more numerous in the brain of man than in that of the animals nearest allied to him zoologi- cally. The brain, like the spinal cord, consists of gray and white nervous matter, but somewhat differently arranged; for while the brain, like the cord, contains gray nerve-mat- ter in its interior, a great part of its surface is also covered with it. By the external convolutions of the cerebellum and of the cerebral hemispheres the surface over which this gray substance is spread is very much increased. The Cranial Nerves. — Twelve pairs of nerves leave the skull cavity by apertures in its base; they are known as the cranial nerves. Most of them spring from the under side of the brain, which is represented in Fig. 84. The first pair, or olfactory nerves, are the nerves of smell; they arise from the under sides of the olfactory lobes, /, and pass out through the roof of the nose. The second pair, or optic nerves, II, are the nerves of sight; they spring from the mid-brain, and, under the name of the optic tracts, run down to the under side of the fore-brain, where they unite Is the surface of most of the brain smooth? What are the folds called? How does a man's brain differ, as regards its convolutions, from an ape's? Of what does the brain consist? How does the arrangement of white and gray matter in it differ from that of the spinal cord? How is the surface on which the gray matter is spread increased? How many cranial nerves are there? Where do most of them originate? Name the first pair. Where do they arise? Where do they pass out? Name the second pair. What are the optic tracts? THE CRANIAL NERVES. 291 FIG. 84. — The base of the brain. The cerebral hemispheres are seen over- lapping all the rest. / olfactory lobes; //, optic tract passing to the optic commissure from which the optic nerves proceed; ///. the third nerve or motor oculi; IV, the fourth nerve or patheticus; V, the fifth nerve or trigeminalix; VI. the sixth nerve or abducens; VII, the seventh or facial nerve or portio dura; VIII, the auditory nerve or portio moll is; IX, the ninth or glosso-pharyngeal; X, the tenth or pneumogastric or vagus; XI, the spinal accessory; XII, the hypoglossal; nc/, the first cervical spinal nerve. to form the optic commissure, from which an optic nerve proceeds to each eyeball. All the remaining cranial nerves arise from the hind- brain. The third pair, III., (motores oculi, or movers of the What is the optic commissure? Where does each optic nerve cro? How many pairs of cranial nerves arise from the hind-brain? Name the third pair. What is their distribution? 292 THE HUMAN BODY. are distributed to most of the muscles which move the eyeball and also to that which lifts the upper eyelid. The fourth pair, IV, (pathetiei,) are quite small; each goes to one muscle of the eyeball. The fifth pair of cranial nerves, V, (trigeminals,) re- semble the spinal nerves in having two roots, one of which possesses a ganglion (the Gasserian ganglion}. Beyond the ganglion the two roots form a common trunk which divides into three main branches. The first of these, the ophthalmic, is distributed to the muscles and skin over the forehead and upper eyelid; and also gives branches to the mucous membrane lining the nose, and to the integument over that organ. The second division (superior maxillary nerve) of the trigeminal gives branches to the skin over the temple, to the cheek between the eyebrow and the angle of the mouth, and to the upper teeth; as well as to the mu- cous membrane of the nose, pharynx, soft palate and roof of the mouth. The third division (inferior maxillary] is the largest branch of the trigeminal. It is distributed to the side of the head and the external ear, the lower lip and lower part of the face, the mucous membrane of the mouth and the anterior two thirds of the tongue, the lower teeth, the salivary glands, and the muscles which move the lower jaw in mastication. The sixth pair of cranial nerves, VI, (alducentes,} are distributed each to one muscle of the eyeball on its own side. What is the distribution of the fourth pair? Name the fifth pair of cranial nerves. How do they resemble the spinal nerves? What is the ganglion on one root called? Into how many main branches does the common trunk divide? Name the first branch. State its distribution. The second branch. Its distribu tion. The third main brunch. Its distribution. Name the sixth pair of cranial nerves. Where do they go? NERVOUS SYSTEM. 293 The seventh pair (facial nerves), VII, are distributed to Uiost of the muscles of the face and scalp. The eighth pair (auditory nerves), VIII, are the nerves of hearing, and are distributed to the inner part of the ear. The ninth pair of cranial nerves (glosso-pharyngeal), IX, are distributed chiefly to tongue and pharynx. The tenth pair (pneumogastric nerves or vagi), X, give branches to the pharynx, gullet and stomach, the larynx, windpipe and lungs, and to the heart. The vagi run far- ther through the body than any other cranial nerves. The eleventh pair (spinal accessory nerves), XI, do not arise mainly from the brain, but from the spinal cord by a number of roots attached to its upper portion, between the anterior and posterior roots of the proper spinal nerves. Each enters the skull cavity alongside of the spinal cord and, getting a few filaments from the medulla oblongata, passes out by the same aperture as the glosso-pharyngeal and pneumogastric nerves. Outside the skull the spinal accessory divides into two branches, one of which joins the pneumogastric trunk, while the other is distributed to muscles about the shoulders. The twelfth pair of cranial nerves (hypoglpssi), XII, are distributed mainly to the mtiscles of the tongue. The Sympathetic Nervous System. — The ganglia which form the main centres of the sympathetic nervous system Name the seventh pair of cranial nerves. To what parts are they distributed? What is the eighth pair called? What are their functions? Where do they end ? Name the ninth pair. State their distribution. Name the tenth pair. State their distribution. Name the eleventh pair. Where do they arise? How do they get into the brain-case? With what nerves do they leave the brain- case? State their distribution. Name the twelfth pair of cranial nerves. State their distribution. 294 THE HUMAN BODY. lie in two rows (s, Fig. 1, and sy, Fig,. %), one on each side of the bodies of the vertebrae. Each ganglion is united by a nerve-trunk with the one in front of it and the one behind it, and so two chains are formed reaching from the base of the skull to the coccyx. In the trunk region these chains lie in the ventral cavity, their relative position in which is indicated by the dots sy in the diagrammatic transverse section repre- sented on p,_9 in Fig. 2. Each sympathetic ganglion is united by branches to neighboring spinal nerves, and near the skull to various cranial nerves also; from the ganglia and their uniting corda arise numerous trunks, which in the thorax and abdomen form networks, from which nerves are given off to the or- gans situated in those cavities. Many sympathetic nerves finally end in the walls of the blood-vessels of various or- gans. To the naked eye they are commonly grayer in color than the cerebro-spinal nerves. By means of the junctions between the cranial and spinal nerves and the sympathetic system the brain is enabled to control the parts supplied by the sympathetic system. The Three Kinds of Nerve Tissue. — The microscope shows that.ihe nervous organs contain tissues peculiar to themselves, known as nerve-fibres and nerve-cells. The How are the ganglia of the sympathetic system arranged? How is each united to others? How far through the body d pared previous to the meeting of the class. b. To the class demonstrate the tough dura mater enveloping the brain; then cut it away, noting the processes which it sends between the two cerebral hemispheres and between cerebellum and cerebral hemispheres. Then cut the membrane away. c. Note its glistening inner surface, due to the arachnoid lining it; the pia mater full of blood-vessels and closely attached to the brain; the glistening arachnoid layer covering the exterior of the pia mater. Then put the specimen aside in alcohol for a day or two. This will harden the brain substance. d. When the brain has become somewhat hardened dissect away the pia mater on one side. Show the cerebral hemispheres and their surface convolutions, the cerebellum and its foldings, the medulla oblongata beneath the cerebellum. e. With bone forceps cut away the remainder of the sides and roof of the skull. Then raise the brain in front, and cutting through the vessels, nerves, etc., which attach it to the base of the skull, en- tirely remove it from the skull cavity. On it demonstrate the cere- bral hemispheres (which overlap the cerebellum much less than in man), cerebellum, mid-brain, etc. /. Attached to the base of the brain will be found the stumps of some of the cranial nerves, though most of these will have been en- tirely torn off unless the dissector has some technical skill. The optic commissure, with the optic tracts leading to it and the stumps of the optic nerves leading'from it, will almost certainly be found. g. Make sections across the brain in different directions to see the gray matter spread over most of its surface, and the nodules of gray matter imbedded in its interior. CHAPTEK XX. THE GENERAL PHYSIOLOGY OF THE NERVOUS SYSTEM. The Properties of the Nervous System,— If one's finger unexpectedly touches a very hot object, pain is felt arid the hand is suddenly snatched away ; that is to say, sensation is aroused and certain muscles are caused to contract. If, however, the nerves passing from the arm to the spinal cord have been divided, or if they have been rendered in- capable of activity by disease, no such results follow. Pain is not then felt on touching the hot body nor does any movement of the limb occur ; even more, under such cir- cumstances the strongest effort of the Will of the individual is unable to cause any movement of his hand. If, again, the nerves of the limb have connection with the spinal cord, but parts of the cord are injured higher up, between the brain and the point of junction of the nerves of the arm with the cord, then contact with the hot object may cause the hand to be snatched away, but no pain or other sensation due to the contact will be felt, nor can the will act upon the muscles of the arm, either to make them con- tract or to prevent their contraction. From the compari- son of what happens in such cases (which have been observed again and again upon wounded or diseased persons), with what occurs in the natural condition of things, several im- portant conclusions may be reached: What usually results when a hot object is unexpectedly touched? Under what circumstances clo these results not occur? Can the Will cause movement of the muscles of an arm whose nerves have been cut? When the arm-nerves are intact but the spinal cord is injured near the brain, what happens on touching a hot body? 302 THE HUMAN BODY. 1. The feeling of pain does not reside in the burned part itself; for it is found that applying a hot object to the skin or pinching it arouses no sensation if the nerves between the skin and the nerve-centres be diseased or divided. 2. The hot object when the nerves are intact originates some change which, propagated along the nerves, excites a condition of the nerve-centres accompanied by a feeling, in this particular case a painful one. This is clear from the fact that loss of sensation immediately follows division of the nerves of the limb, but does not immediately follow the injury of any of its other parts. The change propagated along the nerve-trunks and causing them to excite the nerve-centres is called a nervous impulse. 3. When a nerve in the skin is excited it does not direct- ly call forth muscular contractions; for if so, touching the hot object would cause the limb to be moved even when the nerve had been divided high up in the arm, while, as a matter of observation and experiment, we find that no such result follows if the nerve-fibres have been cut in any part of their course from the excited, or, in physiological phrase, the stimulated, part to the spinal marrow. It is- therefore through the nerve-centres that the nervous impulse trans- mitted from the excited part of the slcin is " reflected" or sent lack to act upon the muscles. 4. The preceding fact makes it probable that nerve-fibres How do we know that our feeling of pain does not reside in a burned or pinched part of the skin? What does a touched hot object originate when the nerves are healthy? What is a "nervous impulse"? Does a skin-nerve when excited produce directly a muscular movement? Give reason for your answer. What happens to the nervous impulse transmitted from the excited part of the skin? Is it probable that other nerve-fibres than those arising from the skin are connected with the nerve-centres ? FUNCTIONS OF NERVES AND NERVE-CENTRES. 303 pass from the centre to muscles as well as from the skin to the centre. This is confirmed when we find that if the nerves of the limb be divided the Will is unable to act upon its muscles, showing that these are excited to con- tract through their nerves. That the nerve-fibres con- cerned in arousing sensation and muscular contractions are distinct, is shown also by cases of disease in which the sensibility of the limb is lost while the power of voluntarily moving it remains; and by other cases in which the op- posite is seen, objects touching the hand being felt, while it cannot be moved by the Will. We conclude therefore that certain nerve-fibres when stimulated transmit something (a nervous impulse) to the centres, and that these, when ex- cited by the nervous impulse conveyed to them, may radiate impulses through other nerve-fibres to distant parts, the centre serving as a connecting link between the fibres which carry impulses from without in, and those which convey them from within out. 5. Further we conclude that the spinal cord can act as an intermediary between the fibres carrying in nervous im- pulses and those carrying them out, but that sensations can- not be aroused by impulses reaching the spinal cord only, nor has the Will its seat there ; volition and consciousness are dependent upon states of the brain. This follows from the unconscious movements of the limb which follow stimu- lation of its skin after such injury to the spinal cord as prevents the transmission of nervous impulses farther on; Point out a fact tending to prove that the muscles are normally excited to contraction through their nerves. State facts showing that the nerves of sensation and those governing the muscles are distinct. What purpose does the nerve-centre serve? What further conclusions may we draw from the facts already considered in this chapter? Give reasons for your answer. 304 THE HUMAN BODY. from the absence, in such cases, of sensation in the part whose nerves have been injured; and from the loss of the power of voluntarily causing its muscles to contract. 6. Finally, we conclude that the spinal cord in addition to being a centre for unconscious movements serves also to transmit nervous impulses to and from the brain; this is confirmed by the histological observation that in addition to the nerve-cells, which are the characteristic constituents of nerve-centres, it contains the simply conductive nerve- fibres, many of which pass on to the brain. In other words the spinal cord, besides containing fibres which enter it from, and pass from it to, the skin and muscles, contains many fibres which unite it to other centres. The Functions of Nerve-Centres and Nerve-Trunks, — From what has been stated in the previous paragraphs it is clear that we may distinctly separate the nerve-trunks from the nerve-centres. The fibres serve simply to convey im- pulses either from without to a centre or in the opposite direction, while the centres conduct and do much more. They take heed, some consciously and some unconsciously, of the impulses carried to them by the ingoing nerve-fibres, and then send out impulses along outgoing nerve-fibres; these impulses call into action the proper organs for the safety and well-being of the body in general. The centres do not merely transmit and reflect, they also co-ordinate. Classification of Nerve-Fibres. — The nerve-fibres of the body fall into two great groups corresponding to those 'For what is the spinal cord a centre? What else does it do? How does histology support the belief that the spinal cord is both a nerve-centre and & conductor of nervous impulses? What is the function of nerve-fibres? What is done by nerve- centres in addition to conducting nerve-impulses? Into what main groups may nerve fibres be classified? PSYCHIC NERVE-CENTRES. 305 which carry impulses to the centres and those which carry them out from the centres. The former are called afferent or sensory fibres and the latter efferent or motor. The posterior roots of the spinal nerves contain only afferent, the anterior only efferent, nerve-fibres- Classification of Nerve-Centres,— Nerve-centres are of three kinds: (1) Automatic centres, which; without~Demg~ excited by the action of any sensofyTferve or by the Will^ originate in themselves stimuli for efferent nerves. (2) Re- flex centres, which act quite independently of the Will and of consciousness, but are aroused by the action of a nervous impulse conveyed to them by a sensory nerve, and in turn excite one or more efferent nerves. (3) Conscious or psy- chic centres, whose activity, however aroused, is accom- panied by some kind of mental activity; as feeling, or willing, or reasoning. The Psychic Nerve-Centres lie in the fore-brain, and mainly in the gray matter of its convolutions. If the cere- bral hemispheres of a pigeon be destroyed and all the rest of its body left intact, the animal can still control its muscles so as to execute many movements, but it gives no sign of consciousness. Left to itself it will stand still until it dies; corn and drink placed before it arouse in it no idea of eat- ing; it will die of starvation surrounded by food. Yet it can move all its muscles, and if food is placed in its mouth will swallow it. If its tail be pulled it will walk forward; What fibres are found in the posterior spinal nerve-roots? What in the anterior? Name the main varieties of nerve-centres. What is done by automatic centres? What by reflex? What is the characteristic property of the psychic centres? Where are the psychic nerve-centres located? What may.be ob- served in a pigeon whose cerebral hemispheres have been destroyed? 306 THE HUMAN BODY. if it be put on its back it will get on its feet; if it be thrown into the air it will fly until it strikes against some- thing on which it can alight; if its feathers be ruffled it will smooth them with its bill. The difference between a pigeon in this state and an uninjured pigeon lies in the absence of the power of form- ing ideas or initiating movements. It has no thoughts, no ideas, no Will. We cannot predict what an uninjured pigeon will do under given circumstances: we can say be- forehand what the pigeon with no cerebral hemispheres will do; it is a mere machine or instrument, which can be played upon. In such a pigeon the excitation of any given sensory nerve or nerves excites unconscious nerve-centres which set certain muscles at work, ai;d the result of any one stimulus is always the same invariable movement. The animal exhibits no evidence of possessing any con- sciousness ; it has no desires or emotions ; it is like a piano which while untouched is silent, but when a given key is struck emits always the same note ; so the pigeon without its cerebral hemispheres stays quiet while left to itself, and responds to any one given stimulus always in one invari- able and predicable way. Functions of the Cerebellum. — The cerebellum is the great centre for co-ordinating the muscles of locomotion. Each step we take implies the action of many muscles and many thousands of muscular fibres; the actions of all must be very precisely graded as to amount, and very accurately arranged as to proper sequence./We do not, however, con- sciously think about the muscles to be used in every move- How does such a pigeon differ from an uninjured pigeon? What is the main function of the cerebellum? What is implied in each step that we take? FUNCTIONS OF THE CEREBELLUM. 307 _ment of each step; if we do think at all about our walking ) the cerebral hemispheres simply send a message to the cere- ibelium, and leave it (witH the aid of the spinal cord) to regulate all the details. When we walk without thinking about it, the contact of the foot with the ground stimulates sensory nerves of the sole, which then stimulate the locomotor centres; these centres excite in proper order the nerves which control the muscles; and the co-ordinated action of the muscles produces the next step7~7' A pigeon with its cerebellum—destroyed and all the rest of its nervous system intact stands unsteadily, staggers when it attempts to walk, and flutters uselessly when thrown into the air. But, having its cerebrum, it wills and feels; it does not stand quiet until touched; it initiates movements when left to itself, though it cannot perform them properly. It wills, and feels, and thinks, but cannot co-ordinate the action of its muscles except for some simple movements, regulated by the medulla oblongata or the spinal cord. Automatic Nerve-Centres send out nervous impulses through efferent nerves without waiting to be excited by afferent nerves or by the Will. The most conspicuous are the small nerve-centres buried in the heart, which excite its beat even when it is separated from all the rest of the body. Another automatic centre is that which lies in the medulla oblongata and stimulates the nerves which control the Do we have to think about using each muscle concerned in walk- ing? What happens when we think about our walking? What when we walk without thinking about it ? What do we see in a pigeon whose cerebellum has been destroyed? Does it initiate movements? Does it execute them well? What is its condition as regards willing, feeling, and thinking? What can it not do? What is done by automatic nerve-centres? Give examples of au- tomatic nerve-centres. 308 THE HUMAN BODY. muscles of respiration. When this centre is cut off from all sensory nerves it still acts, and its activity goes on even against the Will. We can voluntarily hold the breath for a short time, but not long enough to kill ourselves by suffo- cation. Although automatic nerve-centres act indepen- dently of impulses carried to them by nerve-trunks, they are nevertheless usually more or less subject to control by them. For example, stimulating the branch of the pneu- mogastric nerve (p. 293) which goes to the automatic heart nerve-centres slows the beat of the organ; and a dash of cold water on the skin makes us draw a deep breath. Reflex Centres are aroused to activity by nervous im- pulses conveyed to them through afferent nerves: they then excite efferent nerves and produce a movement or a secretion. Such nerve-centres do all the routine of the ad- ministrative control of the organs of the body, without troubling the psychic centres. They frequently act with- out the intervention of consciousness at all, and often in spite of the Will. When sugar is placed in the mouth it excites its sensory nerves ; these stimulate a centre from which nerves go to the salivary glands, and these nerves, aroused by the centre, make the gland-cells secrete and pour saliva into the mouth; no effort of the Will can stop this reflex action, so called because a nervous impulse sent to a centre by one set of nerve-fibres is turned back or reflected from it along another set. When a morsel of food enters the pharynx it excites the sensory nerves of the mucous Can a man commit suicide by holding his breath? Are the automatic centres entirely free from control? Illustrate? How are reflex centres excited? What is the consequence of their stimulation? "What sort of work in the body is executed by reflex nerve-centres? Are we always conscious of their action? Can the Will always control them? What happens when sugar is placed on the tongue? Why is it called a _H reflex action"? USES OF AUTOMATIC NER VE- CENTRES. 309 membrane; these arouse a reflex centre of swallowing, which sends out nervous impulses to the swallowing mus- cles, and the food is sent on into the gullet whether we wish it or not. Sneezing when something irritates the mucous membrane of the nose, and coughing where some foreign mass enters the larynx, are other instances of reflex actions. The Use of Automatic and Reflex Centres is to relieve the thinking centres of the vast amount of work which would be thrown upon them if every action of the body each moment had to be planned and willed. Were not the unconscious regulating nerve-centres always at work the mind would be overburdened by the mass of business which it would have to look after every minute. No time would be left for intellectual development if we had to think about and to will each heart-beat, each inspiration and ex- piration, and the swallowing of each mouthful of food. Moreover, during sleep, so necessary for the rest and repair of the psychic centres, the automatic and reflex centres carry on the actions essential for the nutrition of the body and the maintenance of life. If we had to reason concern- ing each beat of the heart and decide if it was time for it to occur and what force it should have, and then to make up our minds whether to will it or not, we could never sleep. Habits are Acquired Reflex Actions, distinguished from primary or those born with us, such as sneezing, coughing, and winking. Every time a nerve-centre acts in a given way it tends to more easily act in that manner again; as a result Give other examples of reflex actions. What is the main use of th<3 automatic and reflex nerve-centres? What would result if the unconscious nerve-centres were not always at work? What are habits? What happens when a nerve-centre acts in a given manner? What is the result? 310 THE HUMAN BODY. many actions which are at first only performed with trouble and thought are after a time executed easily and unconsciously. The act of walking is a good instance; each of us in infancy learned to walk with much pains and care, thinking about each step. But the more we walked the closer became ingrained in the nervous system the connec- tion between the stimulation of nerves in the sole when a foot touched the ground, and the sending out by the reflex nerve-centres with which they were in connection, of impulses to those muscles which had to make the next step. At last the contact of the foot with the ground, stimu- lating some sensory nerves, acts so readily on the " nerve- centres of walking" that the cerebral hemispheres need take no heed about it: we walk ahead while thinking of something else. In other words we have acquired a reflex action not born in us. Other instances will readily come to mind: as the difficulty with which AVC learned to ride, or swim, or skate, thinking about and willing each movement; and the ease with which we do all these things after a little practice. The trained lower nerve-centres then do all the co-ordinating work and the Will has no more need to trouble about the matter. A habit simply means that the unconscious parts of the nervous system have been trained to do certain things under given conditions, and can only be restrained from doing them by a special effort of the con- scious Will. A practised rider will keep his seat uncon- sciously under all ordinary circumstances, and can only fall off his horse by taking some trouble to do so, by will- ing it in fact; an unskilled rider, on the other hand, must exert all his attention to avoid falling. So with what in Illustrate by the act of walking. Give other examples. What does a " formed habit" really mean? Illustrate. EJGIENE OF THE BRAIN. 311 every-day language are called " habits": once we have repeat- ed an action so often that our bodies almost unconsciously do it, it becomes a habit, and needs special exercise of Will to deviate from it. We thus find, in the tendency of the nervous system to go on doing what it has been trained to do, a physiological reason for endeavoring to form good and to avoid bad habits of whatever sort, physiological, business, social, or moral. Every thought, every action, leaves in the nervous system its result for good or ill. The more often we yield to temptation the stronger effort of the Will is required to resist it. The knowledge that every weak yielding degrades our nerve-organs and leaves its trail in the brain, through whose action man is the "para- gon of animals," while every resistance makes less close the bond between the feeling and the act for all future time, ought surely to "give us pause"; on the other hand, every resistance of temptation helps to make subsequent resist- ance easier. Hygiene of the Brain. — The brain, like the muscles, is improved and strengthened by exercise and injured by over- work or idleness; and just as a man may specially develop one set of muscles and neglect the rest until they degenerate, so he may do with his brain; developing one set of intel- lectual faculties and leaving the rest to lie fallow until, at last, he almost loses the power of using them at all. The fierceness of the battle of life nowadays especially tends to produce such lopsided mental development. How often What happens when we have very frequently repeated an action? Point out why it is desirable, even on physiological grounds, to form good habits. How does every thought or act influence the nervous system? What is the consequence of yielding to temptation? What of resisting it? 312 THE HUMAN BODY. does one meet the business man, so absorbed in money- getting that he has lost all power of appreciating any but the lower sensuous pleasures; the intellectual joys of art, science, and literature have no charm for him; he is a mere money-making machine. One, also, not unfrequently meets the scientific man with no appreciation of art or literature; and literary men utterly incapable of sympathy with science. A. good collegiate education in early life, on a broad basis of mathematics, literature, and natural science, is the best security against such deformed mental growth. APPENDIX TO CHAPTER XX. 1. Place a frog on the table: note that it sits up and breathes (as shown by the movements of its throat), and either stays still or jumps around as it pleases; i.e., it has a Will of its own, and its actions cannot be predicted. 2. Etherize two frogs (note, p. 68), removing them from the ether- ized water the moment they become insensible. With strong sharp scissors cut off from one frog (a) all the head in front of the anterior margins of the tympanic membranes: in the other frog (J) remove the head along a line joining the posterior borders of the tympanic membranes. Place both frogs aside on a dish containing a little water for half an hour. The quantity of water should be such that while keeping the frogs moist it will not reach to the wounds. 3. The frog (a) which has lost its cerebral hemispheres, but re- tained its mid brain, cerebellum, and medulla oblongata, will be found after the above-stated time sitting up in a natural position, and breathing. Left to itself it will, however, never walk or jump; it shows no sign of possessing a will. Its heart continues to beat and its respiratory muscles to contract, but left alone it stays where it is. Turned upon its back it will regain its feet; and put into water it will swim: its muscles, and the nerves controlling them, are, there- fore, quite able to act. The animal stays still not because the parts of its body necessary to produce movements are injured, but because it can no longer will a movement. Such a frog shows very well the de- pendence of volition upon the presence of the cerebral hemispheres. APPENDIX. CHAPTER XX. 313 4. The frog (b) will have had its whole brain removed. Its heart will continue to beat, but its breathing movements will cease, be- cause the respiratory centre, which lies in the medulla oblongata, has been cut away. It will also lie down squat, instead of sitting up like a normal frog, because its most important muscle co-ordinating centres have been removed with the mid-brain and cerebellum. Left to itself the animal will, within half an hour of the removal of the head, pull up its hind legs into their natural position, but after this it will make no movement. It has no volition. 5. Such a frog can, however, perform many co-ordinated reflex actions, which may be illustrated as follows: (a) Pinch a toe; it will be pulled away, (b) Soak some blotting-paper in vinegar, and then cut the paper into small pieces about | inch square. Put these bits of paper on different regions of the frog's skin, dipping the ani- mal in clean water after each application, to wash away the vinegar. It will be found that the brainless creature moves its limbs so as to wipe away the acid paper placed on its skin. The frog without its brain has no Will and no consciousness; but its spinal cord when ex- cited by afferent nerves, whose ends the vinegar stimulates, excites in turn efferent nerves which stimulate muscles, whose contrac- tion produces a movement calculated to rub away the irritating object. 6. Now run a stout pin down the frog's neural canal so as to de- stroy its spinal cord. It will be found that no subsequent pinching of the creature or putting of vinegar on its skin causes any movement. Its muscles and nerve-trunks are intact, but the spinal reflex centre, which in the previous experiments was excited by afferent nerves, and then in turn stimulated efferent nerves, is destroyed. The heart continues to beat, on account of the automatic nerve-centres in it; but no voluntary and no reflex actions are exhibited by the animal. 7. The nerve-trunks and the muscles are, however, still active. Turn the frog on its back and carefully expose (p. 299) the origins of the sciatic nerves. On pinching these, the muscles of the leg will be seen to contract. The irritation of the nerve by the pinch starts in it a nervous impulse which travels down the nerve -branches to the muscles. CHAPTEE XXL THE SENSES. Common Sensation and Special Senses. — Changes in many parts of our bodies are accompanied or followed by states of consciousness which we call sensations. All such parts (sensitive parts) are in connection, direct or in- direct, with the brain by sensory nerve-fibres. Since all feel- ing is lost in any region of the body when this connecting path is severed, it is clear that all sensations, whatever their primary exciting cause, are finally dependent on conditions of the brain. Since all nerves lie within the body as circum- scribed by the skin, one might be inclined to suppose that the cause of all sensations would appear to be within our bodies themselves; that the thing felt would be recognized as a modification of some portion of the person feeling. This is the case with regard to many sensations: a headache, tooth- ache, or earache gives us no idea of any external object ; it merely suggests to each one a particular state of a sensitive portion of himself. As regards many sensations this is not so; they suggest to us external causes, to properties of which, and not to states of our bodies, we ascribe them; and so they lead us to the conception of an external universe in which we live. A knife laid on the skin produces changes in it which With what are all sensitive parts of the body in connection ? By what nerve-fibres? How do we know that all sensations finally de- pend on the brain? Why might we suppose that the causes of all sensations would seem to lie within the bocty? Name sensations merely suggesting to us a state of the body itself. What do some other sensations sug- gest to us? Illustrate. COMMON SENSATIONS. 315 lead us to think not of a state of the skin, but of proper- ties of some object outside the skin; we believe we feel a cold heavy hard thing which is not the skin. We have, however, no sensory nerves going into the knife and inform- ing us directly of its condition; what we really feel are the modifications of the body produced by the knife, although we irresistibly think of them as properties of the knife — of some object that is no part of the body. Let now the knife cut through the skin; we feel no more knife, but ex- perience pain, which we think of as a condition of our- selves. We do not say the knife is painful, but that the finger is, and yet we have, so far as sensation goes, as much, reason to call the knife painful as cold. Applied one way it produced local changes in the skin arousing a sensation of cold, and in another local changes causing a sensation of pain. Nevertheless in the one case we speak of the cold as being in the knife, and in the other of the pain as being in the finger. Sensitive parts, such as the surface of the skin, through which we get, or believe we get, information about outer things, are of far more intellectual value to us than sensi- tive parts, such as the subcutaneous tissue into which the knife may cut, which only give us sensations referred to conditions of our own bodies. The former arc called Organs of Special Sense ; the latter are parts endowed with Common Sensation. Common Sensations are quite numerous ; for example, pain, hunger, nausea, thirst, satiety, and fatigue. What is meant by "organs of some special sense"? What by parts endowed with common sensation? Name some common sensations. 316 THE HUMAN BODY. Hunger and Thirst. — These sensations regulate the tak- ing of food. Local conditions play a part in their produc- tion, but general states of the body are also concerned. Hunger in its first stages is due to a condition of the gastric mucous membrane which comes on when the stom- ach has been empty some time; it may then be tempo- rarily stilled by filling the stomach with indigestible sub- stances. But soon the feeling comes back intensified and can only be allayed by the ingestion of nutritive materials; provided these are absorbed and reach the blood their mode of entry is unessential; hunger may be stayed by injections of food into the intestine as completely as by filling the stomach with it. Similarly, thirst maybe temporarily relieved by moisten- ing the throat without swallowing, but then soon returns ; while it may be permanently relieved by water injections into the veins, without wetting the throat at all. Both sensations depend in part on local conditions of sensory nerves, but may be more powerfully excited by poverty of the blood in foods or water ; this deficiency directly stimulates the hunger and thirst centres of the brain. The Special Senses are commonly described as five in number, but there are at least six; namely, sight, hearing, touch, the temperature sense, smell, and taste. To what is the first stage of hunger due? How may it be tempo- rarily stayed? Need food enter the stomach in order to alleviate hunger? How may thirst be temporarily relieved? How permanently without swallowing water? On what do the sensations of hunger and thirst in part depend ? How may they be more powerfully ex- cited? Enumerate the special senses. SIGHT. 317 • The Visual Apparatus consists of nervous tissues immedi- ately concerned in giving rise to sensations, supported, protected, and nourished by other parts. Its essential parts are, (1) the retina, a thin membrane lying in the eyeball and containing microscopic elements which are so acted upon by light as to stimulate (2) the optic nerve; this nerve ends (3) in a part of the brain (visual centre) which when stimu- lated arouses in our consciousness a feeling or sensation of sight. The visual centre may be excited in very many ways, and quite independently of the optic nerve or the retina ; as is frequently seen in delirious persons, in whom inflamma- tion or congestion of the brain excites directly the visual centre and gives rise to visual hallucinations. Usually, however, the cerebral visual centre is only ex- cited through the optic nerve, and the optic nerve only by light acting upon the retina. The eyeball, containing the retina, is so constructed that light can enter it, and so placed and protected in the body that as a general thing no other form of energy can act upon it so as to stimulate the retina. Under exceptional circumstances we may have sight-sensa- tions when no light reaches the eye; anything which stimu- lates the retina, so long as it is connected by the optic nerve with the cerebral visual centre, will cause a sight-sensation. A severe blow on the eye, even in complete darkness, will cause the sensation of a flash of light; the compression of the eyeball excites the retina, the retina excites the optic nerve, Of what does the visual apparatus consist? What are its essen- tial parts? What happens when the visual centre is stimulated? Is it only stimulated by the agency of light? Illustrate. How is the visual centre usually excited? Why is light the form of energy which most of t is it a food, 121, 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, 132 Alimentary principles, 116; al- buminoid, 117; carbohydrate, 118; hydrocarbon, 117"; inor- ganic, 118; proteid, 117 Amoeba, 179 Amyloids (see Carbohydrates) Anaemia, 185 Anatomy, human, 2, 17 Anatomy, microscopic (see His. tology) Anatomy, of alimentary canal, 132, 169; of circulatory organs, 192; of ear, 329; of eyeball, 321; of joints, 60; of larynx, 337; of liver, 149: of muscular system, 67; of nervous system, 282, 299; of respiratory organs, 233; of skeleton, 23; of skin, 266; of uriuaiy organs, 261, 278 Animals, classification of, 8 (foot- note) Animal charcoal, 55 Animal heat, 96 Ankle joint, 83 Aorta, 198, 212; thoracic, 202; abdominal, 202 Apex beat (cardiac impulse), 217 Apex of heart, 195 Appendicular skeleton, 26 Appetite, cause of, 165 Aqueous humor, 325 Arachnoid, 286 Arch of foot, 42. 45 Areolar tissue, subcutaneous, 268 Arm, skeleton of, 28 Arterial blood, 178, 211 366 INDEX. Arterial pressure, 227 Arteries, 195, 202; action of alcohol on, 357; aorta, 198, 212; axillary, 202; brachial, 202; coeliac axis, 202; com- mon iliacs, 204; coronary. 199, 202, 213; femoral, 204, hepatic, 150; left common carotid, 202; left subcluvian, 202; mesenteric, 202; peroueal, 204; popliteal, 204; pulmonary, 199, 212; radial, 202, 222; renal, 202, 261; right common carotid, 202; right subclavian, 202; temporal, 222; tibial, 204; ulimr, 202 Arteries, course of the main, 201; muscles of the, 228: properties of the, 204; why placed deep, 205 Articular cartilage726, 48 Articular extremities of bones, 48 Articulations, 25 Arytenoid cartilages, 338 Assimilation, 108 Astragalus, 40 Atlanto-axial articulation, 32 Atlas vertebra, 32 Auditory nerve, 293 Auditory organ, 329 Auricles, 197; function of the,220 Auricular appendages, 213 Auricular contraction, 217 Auriculo-ventiicular orifice, 197 Auriculo- ventricular valves, 201, 217; demonstration of their action, 232 Auscultation, 245 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 joint(enarthrosis), 62 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, 162, 172; uses of, 161 Bile duct, common (duct us com- munis choledochus), 150, 170 Bi-penniform muscles, 71 Bladder, urinary, 263, 278 Blind spot, 324 Blood, action of oxygen on, de- monstration, 259; arterial and venous, 178, 211; changes un- dergone by in the lungs, 257; circulation of, 207; coagulation of, 179; colorless corpuscles of, 179; compared with water, 182; experiments with, 190; flow of in the capillaries and veins, 224; functions of, 174, 175; gases of, 183; histology of, 176 ; hygiene of, 184; quantity of in the 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, 279; 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, 331, of face, 37; of lower limb, 28; of pectoral arch, 27; INDEX. 367 Bones (Continued). of pelvic arch, 28; of upper limb, 28: 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, 202 Brain, 288; dissection of, 299; hygiene of, 311 Bread, composition of, 116; wheaten. superiority of, 120 Breastbone, 27, 34 Bright's disease, 266 (foot-note) Bronchi, 235 Bronchitis, 237 Brunner, glands of, 148 Buccal cavity (See mouth cavity) Butter, 117 Butyriu, 117 CABBAGE, nutritive value of, 121 Caecum, 148, 170 Calcium carbonate, 20, 55 Calcium phosphate, 20, 55, 57 Calcaneum, (heel bone) 42 Calices of kidney, 263, 278 Canaliculi of bone, 54 Cane suu'ar, 118 Canine teeth, 136 Capillaries, 195, 204; absence of pulse in, 226; circulation in, 224. 225; demonstration of the action of, 232; pulmonary, 199; systemic, 198 Capsular ligament, 61 Carbohydrates (amyloids), 22, 118; kinds of in the body, 22 Carbonate of lime, 20, 55 Carbon dioxide, as -a waste pro- duct, 105 ; demonstration of presence of in expired «,ir, 259; in the blood, 184; p<>r- centage of in unwholesome air, 255; quantity of passed from the lunsrs in a day, 252; useless as a food, 112 Cardiac impulse (apex beat), 217 Cardiac orifice of stomach, 143, 170 Cardiac period, events occurring in a, 217 Carotid arteries, 202 Carpal bones, 28, 51; joints be- tween, 65 Carrots, nutritive value of, 121 Cartilage, articular, 26. 48; cells of, 23; costal, 34; function of, 33; intervertebral, 30. 33 Casein, 21, 117; vegetable, 117 Cells, 15, 17; air, of lungs, 237: cartilage, 23 ; ciliated, of air passages, 236; forms of, 15; nerve, 297; plain muscle, 76; structure of, 15 Cellulose, 116, 164 Cement of teeth, 137 Centres, nerve (see Nerve-cen- tres) Centre of gravity of body, 85 Centrum of vertebrae, 30 Cerebellum, 289; functions of, 306; removal of. 313 Cerebral hemispheres, 289; re- moval of, 812 Cerebro-spinal liquid, 286 Cerebro - spinal nerve system, 284 Cervical enlargement of spinal cord, 287 Cervical vertebrae, 30 Cheese, nutritive value of, 120 Chemical changes in respired air, 251 Chemical composition of albu- mens, 21 ; of bile, 161 ; of blood- serum, 182; of body, 19; of bone, 54; of carbohydrates. 22; of fats, 21 ; of gastric juice, 156; of lymph, 189; of muscle, 77; of pancreatic secretion, 159; of red corpuscles, 183; of respired air, 252 Chest (see Thorax) Chloral, 361 Chordae tendinese, 201, 214 Choroid, 321 Chyle, 158 Chyme. 158 Cilia, 236; demonstration of ac tion of, 249 Circulation, 107, 207; in capilla- 368 INDEX, Circulation (Continued). ries and veins. 224; portal, 208; pulmonary, 208; systeftwc, 208; diagrfflfe of, 209 Circulatory organs, 192; relation of to excretion, 108; diagram of, 194 Circu induction, 63 Circumvallate papillae, 139, 334 Clavicle (collar bone), 27 Clotting of blood (see Coagula- tion) Coagulation of blood, 179; cause of, 180; experimentsunon, 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 Columnae carnese, 215 Comminuted fracture of bones, 57 Common bile-duct (ductus corn- 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, law 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, 121 Cornea, 321 Coronary arteries, 199, 202, 213 Coronary sinus, 214 Coronary veins, 200, 213 Corpus Arantii, 214 Corpuscles of blood, 176, 190 Costal cartilage, 34 Costal respiration, 246 Cranial nerves, 290; sutures, 38 Cranium, bones of, 37 Cricoid cartilage, 338 Crystalline lens, 325 Crypts of Lioberkiihn, 148 Cuticle (epidermis), 266 DEATH, from starvation. 98; from alcohol, 347, 352, 3o3; from chloral, 363; from opium or morphia, 361 Death-stiffening (rigor mortis), 74 Defibrinaied blood, 181 [355 Degeneration, fatty, 354; .abrous, Deglutition (see Swallowing) Delirium tremens, 352 Dentine, 136 Dermis (see Corium) Dir jysis (osmosis), 186 Diaphragm (midriff), 11, 242; de- monstration of, 248 Diarrhoea, 229 Die?, advantages of a mixed, 125 Digestion, 107, 128; 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, 17 Dorsal (neural) cavity, 7, 31 ; con- tents of, 9, 13 Dorsal vertehrae, 30 Duct of glands, 101 Duct, common bile, 150, 170; cys- tic, 150; hepatic, 150; of parotid -land, 169; of submaxillary gland, 169 Dura mater, 285 Dyspepsia, 164 EAR, 330 Efferent (motor) nerves, 305 Eggs, nutritive value of, 120 Egg-albumen, 21, 117 Eighth pair cranial (auditory/ norves, 293 INDEX. 869 Elasticity of the arteries, 226, 232; of the lungs, 238 Elastic tissue, 164 Elbow joint, 65, 70 Elements found in. the bod}T, 20 (foot-note) Eleventh pair cranial (spinal ac- cessory) nerves, 293 Einmetropic eye, 327 Emulsion, 160 Enamel, 136 Endolymph, 331 Endos'keleton, 23 (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, 142, 338 Ethmoid bone, 37 Eustacliian tube, 141, 330 Excretion and reception, inter- mediate steps between, 106 Excretions, removal of, 108 Excretory organs, 106 Exercise, 90 Exoskeletou, 23 (foot-note) Expiration, 242, 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, 328 Eyeball, anatomy of, 321 Eyelashes, 318 Eyelids, 318 Eye-socket, 318 FACE, bones of, 37 Facial nerve, 293 Fasciculi of muscles, 73 Fatty acids. 117 Fats (hydrocarbons), 21, 117; ab- sorption of, 162; action of bile on, 161, 172; 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, 21 Fauces, 141 ; isthmus of the, 133, 155; pillars of the, 141 Femoral artery, 204 Femur, 28 Fibres, 16 ; plain muscle, 76; striped muscle, 74 Fibrillse, 74 Fibrin, 21, 180 Fibula (peroueal bone), 28, 51 Fifth pair cranial (trigeminaI)N. nerves, 292 Filiform papillae, 139, 334 Flexion at joints, 63 Flexor muscles, 80 Food, amount of required daily, 124; as a force generator, 115; as a force regulator, 115; as a machinery former, 114; as a tissue former, 110; composi- tion of, 111; cooking of, 123; definition of, 114; inorganic, 118; is alcohol a food, 121, 343; need of, 95, 97; non oxi- dizable, 113; nutritive value of different, 119; special im- portance of albuminous, 111; supply of animal, 112 Food-stuffs (see Alimentary prin- ciples) Foot, skeleton of. 29; peculiari- ties of human, 45 Fonim^n- intervertebral. 32; magnum, 37; oval, 331 Force-generating foods, 115 Force-regulating foods, 115 Forearm, movements of, 64, 70 Fore limb (see Upper-limb) Fossa, gleuoid, 63 Fourth pair cranial (pathetici) nerves, 292 Fractures of bones, 57 Free (floating) ribs, 34 Frog's web, circulation in, 224 Frontal bone, 37 Fruits, nutritive value of, 121 Fundus of stomach, 170 Fungiform papillae, 139, 334 Furred 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 Gasseriau ganglion., 292 Gastric digestion, 157; experi- ments illustrating, 171 Gastric glands, 144 Gastric juice, 144, 156; artificial, 171 Gelatine, 55, 117 Gelatiiiization, stage of in coagu- lation, 179 Glands. 129; forms of, 131; gas- tric, 144; kinds of, 129; lachry- mal, 319; mammary, 11; mei- bomian, 318; of Bruuuer, 148; of skin, 272; of small intes- tine, 148; salivary, 140, 169 Gleuoid fossa, 63 Gliding joints (arthrodia), 65 Glosso-pharyngeal nerves, 293 Glottis, 335 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 (Esophagus) Gums, 118, 134 HABITS, 309 Haemal cavity (see Ventral cavity) hemoglobin, 178, 210, 258 Hairs, 270 Hair-follicle, 271 Hand, skeleton of, 28 Hard palate, 133 Haversian canals, 52 Haversian system, 53 Hearing, 329 Heart, 9 action of alcohol on, 349, 357; beat of, 216; cavi- ties of, 197; dissection of, 21 wj xperiments upon, 230; position of, ^95; how nour- ished, 199; muscle of, 76; pul- Heart (Continued). pitatiou 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, 212 Hibernation, 98 (foot-note) High heels, bad effects of, 56 Hilus of kidney, 2(53, 278 Hind limb (see Lower limb) Hinge joints (ginglymi),63 Hip-joint, 28, 60 Histology, definition, of, 2; of blood; 176; of bone, 51; of kidneys, 265; of lungs, 237; of lymph, 189; of muscle, 74; of nerve cells, 297; of nerve fibres, 296; of retina, 321; of skin, 266 Hollow veins (see Venae cavse) Human anatomy, definition of, 2, 17 Human physiology, definition of, 1, 2, 17 Humerus, 28, 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, 254; of skin, 274; of teeth, 137 Hyoid bone, 26 Hypermetropia, 328 Hypoglossal nerves, 293 ILEO-COLTC valve, 149 lleum, 145 Iliac arteries, 204 Incisors, 1155 Incus (anvil bone), 331 Indigestible substances, 164 Inferior maxillary bone (mandk ble), 37 Inferior maxillary nerve, 292 Inferior turbimite bone, 38, 333 Innominate artery, 202 INDEX. 371 Innominate bone (os innomina- tum or pelvic bone), 28, 60 Inorganic constituents of the body, 20 Inorganic foods, 118 Insertion of muscles, 70 Inspiration, 242, 244 Intercellular substance, 16, 23 Internal ear (labyrinth), 331 Intervertebral foramina, 32; 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, 321 Isthmus of the fauces, 133, 155 JEJUNUM, 145 Joint, ankle, 83; elbow, 65, 70; hin. 28, 60; knee, 63; shoulder, 42, 63 Joints, 25; ball and socket, 62; general structure of, 60; glid- ing, 65; hinge, 63; pivot, 64; movements at, 63 KIDNEYS, 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 LABOR, physiological division of, Labyrinth (internal ear). 331 Lachrymal apparatus, 319 Lachrymal bones, 38 Lacteals, 147, 168. 188 Lactose (milk sugar), 22, 118 Lacunae of bone, 54 Lamellae of bone, 53 Large intestine, 133, 148; absorp- tion from. 168 Larynx, 235, 337; muscles of, 339 Log, skeleton of, 28 Levers in the body, 80, 81, 82, 83, 84 Lieberkiihn, crypts of, 148 Liebig's extract of meat, 78 Ligaments, 24, 61; capsular, 61; round, 61 ; transverse, of atlas, 32, 64 Light, action of, on the retina, 323, 325 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, 332 Local sign, 332 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, 237; action of al- cohol on, 357; changes under- gone by blood in, 257; de- monstration of the action of, 248; dissection of, 247; elas- ticity of, 238; expansion of, 239 ; quantity of CO2 passed out from, in a day, 252; quantity of O taken up by, in a day, 252; renewal of air in, 240 Luuula of nails, 271 Lymph, 186; chemistry of, 189; histology of, 189; renewal of, 187 Lymphatics of small intestine, 147 Lymphatic vessels (absorbents), 188 MALAR bone, 38 Malleus (hammer) bone, 331 Malpighi, pyramids of, 264. 278 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 Marro./, 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 sheath of nerves, 296 Meibomian follicles, 318 Membranes of the brain and spinal cord, 285 Mesenteric arteries, 202 Mesentery, 170 Metacarpal bones, 28, 51 Metatarsal bones, 29, 51 . Microscopic anatomy (see His- tology) Midriff (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 (efferent) nerves. 305 Motores oculi nerves, 291 Mouth-cavity, 133; absorption from, 166 Movements, at joints, 63; of the body, how effected, 59; in sp;ice, 86 Mucin, 164 Mucous coat, small intestine, 146 Mucous membrane, of air-pas- sages, 236; of alimentary canal, 128 Mumps, 140 Muscles, 59, 67; chemical com- position of, 77; contraction of, 69. gross structure of, 73; his- tology of, 74; how controlled, 72; hygiene of, 89; of arteries, 228; of heart, 76; of larynx, Muscles (Continued). 339; 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, 73; plain, 74 Muscular work, influence of starvation upon, 97; source, 93 Mustard, use of, as a food, 115 Myopia, 327 Myosiu, 21, 77, 117, NAILS, 271 Narcotics, 343 Nares, posterior, 38 Nasal bones, 38 Nerves, cranial, 290; kinds of, 294; spinal, 287 Nerves, inferior maxillary, 292; ophthalmic, 292; right phrenic, 212; sciatic, 299; superior max- illary, 292; sympathetic, 294 Nerve- eel Is, 297 Nerve centres, 282, 284; classifi- cation of, 305; functions of, 304 Nerve-fibres, afferent and effe- rent, 305; kinds of, 295 Nerve-ganglia, 284 Nerve-trunks, 382; functions of, 304 Nervous system, anatomy of, 282; properties of, 301, 312 Neural arch, 31 Neural cavity (see Dorsal cav- ity) Nicotin; 363 Ninth pair cranial (glosso-pha- ryngeal) nerves, 293 Nitrogen-excreting organs, gene- ral arrangement of, 261 Non-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, 33 Odontoid (tooth-like) process of the axis, 32, 64 Odorous substances, 333 (Esophagus (gullet), 8. 133, 142, 169; absorption from, 166 Oils (see Fats) Oil glands (sebaceous - glands), 273 Oleic acid, 21 Oleine, 21, 117 Olfactory lobes, 289 Olfactory nerves, 290 Omentum, 13, 170 Ophthalmic nerves, 292 Opium, 359 Optic commissures, 291 Optic nerves, 290, 317 Organ, definition of, 4; circula- tory, 107, 192, 194; digestive, 107, 123; nitrogen excreting, 261; of hearing, 329; of sight, 317; of smell, 333; of taste, 334, of temperature sense, 333; of touch, 331; receptive and ex- cretory, 105; respiratory, 108, 233 Organic constituents of the body, 20 Organs diseased by alcohol, 356 Origin and insertion of muscles, 70 Osinnominatum (see Innominate bone) Osmosis, 186 Oval foramen, 331 Oxidations in the body, 99 Oxidations, 99, 100 Oxygen, absorption of from the lungs, 258; in the blood, 184; influence of on the color of the blood, 259; quantity of taken up by the lungs in a day, 252 Oxygen food of the body, 103 Oxyha3moglobin, 258 PALATE, 133 Palate bones, 38 Palmitic acid, 21 Palmitin, 21, 117 Palpitation of the heart, 144 Pancreas, 151, 170 Pancreatic secretion, 159; action of on food-stuffs, 160, 172 Papillae of the dermis, 270 Papillae of the tongue, 139 Papillary muscles, 201, 214; use of the, 219 Parietal bones, 37 Parotid gland, 140, 169 Patella (knee-cap), 29 Pathetici nerves, 292 Peas, nutritive value of, 121 Pectoral arch or girdle, 27; com- parison of pectoral and pelvic girdles, 38 Pedicle of vetebrae, 32 Pelvic arch or girdle, 28; com- parison of pectoral and pelvic girdles, 38 Pelvis, 28, 45 Pelvis of kidney, 263 Penniform muscles, 71 Pericarditis, 196 Pericardium, 195, 212 Perilymph, 331 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, 29, 51 Pharynx, 133, 141; absorption from, 166 Phosphate of lime, 20, 55, 57 Phrenic nerve, 212 Physiological division of labor, 17 Physiology, human, definition of, 1, 2, 17 Physiology of muscle, special and general, 80 Pia mater. 285 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, 293 Poison, definition of, 116 Polygastric muscles, 72 POMS varolii, 289 Popliteal artery. 204 Pork, nutritive value of, 119 Portal circulation, 208 Portal vein, 150, I7y, 208 Posterior nares, 38 Potatoes, nutritive value of, 121 Premolars (bi cuspids), 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, 321 Pus, 179 Pyloric orifice of stomach, 143, 170 Pyloric sphincter, 144, 157, 158 Pyramids of Malpigh'i, 264, 278 Racemose (acinous) glands, 129, 131 Radial artery, 202, 222 Radius, 28, 51 Receptive organs of the body, 105 Reception and excretion, inter- mediate steps between, 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 marrow, 50 Reduced haemoglobin, 210 Reducing dislocations, 66 Reflex centres, 308; experiments showing action of, 313; use of, 309 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, 233 Respiratory sounds or murmurs, 245 Retina, 317; histology of, 321 Ribs, 26, 34; action of in respira- tion, 244 Rice, nutritive value of, 121 Right phrenic nerve, 212 Rotation at joints. 63 Round ligament, 61 Running, 89 SACRUM, 30, 34 Saliva, 152, chemical action of, 153, 171; influence of in diges- tion, 15^; uses of, 152 Salivary glands, 140, 169 Salt, as a constituent of the body, 20, importance of as food, 118 Sarcolemma. 74 Scapula (shouldor-blade), 27, 51 Sciatic nerve, 299 Sclerotic, 321 Sebaceous glands (oil glands), 273 Sebaceous secretion, 274 Secretion, of gastric glands, 144, 156; of glands of small intes- tine, 163; of kidneys, 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, 231 Semivowels, 341 INDEX. 375 Sensations, 314; common, 315; localization of skin, 332 Senses, special, 316 Sensory (afferent) nerves, 305 Septum of heart, 197. 213 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), 327 Shoulder gmlle(see Pectoral arch) Shoulder joint. 42, 63 Shower baths, 277 Sight, sensation of, 317; organ of, 317 Sigmoid flexure, 149 Simple fracture of bones, 57 Sinuses of Valsalva, 215 Sixth pair cranial (abducentes) nerves, 292 Skeleton, append icular, 27; axi- al, 26; composition of, 23; of cranium, 37; of face, 37; of lower limb, 28; 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, 274; Vensa. tions, localization of, 332 Skull, 26, 35; peculiarities in the position of, 43 Small intestine, 133. 145, 170; absorpfion 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, 220 Sounds, respiratory, 245 Sound waves, action of on the ear, 331 Special physiology of muscles, 80 Speech, 336 Sphenoid bone, 37 Spinal accessory nerves, 293 Spinal cord, 9, 286; dissection of, 299 Spinal ganglia, 287 Spinal nerves, 287 Spine (see Vertebral column) Spinous process of vertebrae (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, 172; of saliva on, 153, 171; sol- uble. 124 Starvation, death from, 98; in- fluence of on muscular work and animal heat, 97 Stearic acid, 21 Stearin, 21, 117 Sternum (breast bone). 27, 34 Stimulants. 115, 122, 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, 202 Sub lingual gland, 141, 169 Sub-maxillary gland, 140, 169 Succus entericus (intestinal juice). 163 Sudoriparous glands (sweat- glands), 131, 272 Suffocation, 104, 253 Sugar, cane, 118; grape (see Grape-susrar) Sugar of milk (lactose), 22. 118 Superior maxillary bone, 38 Superior rmixillary nerve, 292 Supination, 64 Swallowing (deglutition), 154; as a reflex action, 309 Sweat. 272 Sweat (sudoriparous) glands, 131, 272 Sweetbread (see Pancreas) Sympathetic nerve centres, 9, 12 '284; ganffliaof, 293 Synovial fluid, 61 Sy no vial membrane, 61 Syntonin, 77, 117 376 INDEX. Systemic circulation, 192, 208 Systole of heart-beat, 216 TABULAR bones, 51 Tarsal bones, 29, 51; joints be- tween, 65 Tarsus, benefits of peculiar structure of, 45 Taste. 334 Taurocbolic 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 (pneumpgas- 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, 338 Tibia. 28, 51 Tibial artery, 204 Tight lacing, evil effects 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; dig section of, 247; structure of, 236 Transverse ligament of the atlas, 32, 64 Triceps muscle, 72 Triceps muscles, definition of, 71 Trichina, 120 ' Tricuspid valve, 201, 214 Trigeminal nerves, 292 Trypsin, 160 Tubular glands, 129, 131 Turbinate bones, 38, 333 Turnips, nutritive valve of, 121 Twelfth pair cranial (hypoglos- sal) nerves, 293 Tympanic membrane, 330 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; ileo-colic, 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 different 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 (venae cavse), 199, 212; portal, 150, INDEX. 377 Veins (Continued). 170, 208; pulmonary, 199, 212; renal, 261 Vegetable casein, 117 Venae cavae (hollow veins), 199, 212 Venous blood, 178, 211 Ventilation, 253; methods of, 256 Ventral (haemal) cavity, 6; con- tents of, 8, 13 Ventricles, 197 Ventricular contraction, 218 Vermiform appendix, 148 Vertebrae, 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, 323 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 kidnevs, 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 V v.v RETURN BIOLOGY LIBRARY TO— *> 3503 Life Sciences Bldg. 642-2531 LOAN PERIOD 1 2 3 4 1-MO foTH--MO ^OGRAPH ALL BOOKS MAY BE RECALLED AFTER 7 DAYS Renewed books are subject to immediate recall DUE AS STAMPED BELOW DUE flAY 2 5 1984 Suh'jct to ftecai. immediatelv , _. 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