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AMERICAN SCIENCE SERIES 
 
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 (ix '98) 
 
AMERICAN SCIENCE SERIES BRIEFER COURSE 
 
 THE HUMAN BODY 
 
 e/tf TEXT-BOOK OF ANATOMY, PHYSIOLOGY 
 tAND HYGIENE 
 
 BY 
 
 H. NEWELL MARTIN, D.Sc., M.D., M.A., F.R.S. 
 
 Formerly Professor of Biology in the Johns Hopkins University 
 and of Physiology in the Medical Faculty of the same 
 
 FIFTH EDITION, REVISED 
 WITH PRACTICAL EXERCISES 
 
 BY 
 
 GEORGE WELLS FITZ, M.D. 
 
 Assistant Professor of Physiology and Hygiene in 
 
 Harvard University 
 
 NEW YORK 
 
 HENRY HOLT AND COMPANY 
 1899 
 
(2fP3t> 
 
 Copyright, 1883, 1884, 1898, 
 
 BY 
 
 HENRY HOLT & CO. 
 
PREFACE TO THE FIFTH EDITION. 
 
 Thk revision of this book was undertaken with the idea of 
 bringing it into accord with the later developments of physi- 
 ology, of simplifying the treatment of some parts, of expand- 
 ing that of others, and of enriching the text with additional 
 illustrations. Every effort has been made to avoid injuring 
 those features of Professor Martin's work which have made 
 the book so favorably known. 
 
 The changes in the first nine chapters are largely verbal ; 
 in the tenth and in some succeeding chapters, however, con- 
 siderable alterations and additions have been made ; Chapter 
 XX. has been entirely rewritten, and Chapters XXIII. and 
 an Appendix on Emergencies have been added. The Chap- 
 ter on Narcotics, transferred to the appendix, is retained 
 against the best judgment of the reviser, who believes that 
 the questions involved are ethical and not physiological ; it 
 stands as Professor Martin wrote it, except that the para- 
 graphs on certain drugs have been omitted. 
 
 The directions for demonstrations and experiments have 
 been greatly enlarged and collected into an Appendix. They 
 include the new requirements in Anatomy, Physiology and 
 Hygiene, for admission to Harvard College and the Law- 
 rence Scientific School. It is hoped that teachers will 
 recognize the importance of practical work in physiology as 
 in other sciences. 
 
 iii 
 
iv PREFACE TO THE FIFTH EDITION. 
 
 In accordance with Professor Martin's own judgment, the 
 questions at the foot of the page have been omitted. 
 
 I have been indebted for practical suggestions to Dr. 
 Margaret B. Wilson, of the Normal College, New York City. 
 
 G. W. F 
 
 Cambridge, Mass., 
 August, 1898. 
 
PREFACE TO THE FIRST EDITION. 
 
 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 " Human 
 Bod\ " was called for within twelve months of its publi< - 
 tion, have shown me that I was not wrong in believing that 
 the teachers of Elementary Physiology in the United Stal 
 were readv 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 teach- 
 ing by rote certain facts, no matter how important these 
 facts may be. the proper function of Natural Science in a 
 
 ~tem of education is missed. Mere training of the mem- 
 ory fno unimportant matter . is otherwise sufficiently pro- 
 vided for in the usual school and college course of study : 
 the true use of Natural Science in general education is differ- 
 
vi PREFACE TO THE FIRST EDITION. 
 
 ent. It should prepare the student in another way for the 
 work of subsequent daily life, by training the observing and 
 reasoning faculties. 
 
 As a department of science, modern Physiology is con- 
 trolled mainly by two leading generalizations — 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 de- 
 scribed 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 educa- 
 tional instrument than it has frequently hitherto been, the 
 present volume differs from most others of its grade in hav- 
 ing, as footnotes 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 experiments which 
 require 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 en- 
 couraged me to believe that others might be glad of a few 
 
PREFACE TO THE FIRST EDITION. vn 
 
 hints as to things suitable to show to young student-, of 
 Physiolog) 
 
 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 elass without 
 hardening the hearts of operator and spectators; even when, 
 in accordance with the directions given in the following 
 pages, the animal is anaesthetized and while in that condition 
 is killed or its brain destroyed. This, from an experience of 
 more than fifteen years in the teaching of practical physi- 
 ology. I know to be not so. So far as the experiments de- 
 scribed in the present book are concerned, their effect is most 
 certainly humanizing. Young people are apt to be, not cal- 
 lous, 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 something 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 appen- 
 dices to the chapters, and in part to the great number and 
 large size of the figures. My publishers had on hand electro- 
 types of the figures of the octavo edition, and have been able 
 to utilize them in illustrating this briefer one much better 
 than most textbooks of its scope, without proportionately in- 
 creasing its price. 
 
 If I had relied solely on my own judgment the questions 
 
vin PREFACE TO THE FIRST EDITION. 
 
 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 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 University, who has 
 corrected most of the proof-sheets and prepared the index. 
 
 H. N. M. 
 
 Johns Hopkins University, 
 August 10, 1S83. 
 
CONTENTS. 
 
 CHAPTER I. 
 
 THE GENERAL STRUCTURE AND ARRANGEMENT OF THE HUMAN BODY. 
 
 l AGE 
 
 Human Physiology — Hygiene — Anatomy — Histology — Tissues 
 — Organs — The general plan on which the body is con- 
 structed — Man is a vertebrate animal — Contents of the two 
 chief cavities of the body — The limbs — Man's place among 
 vertebrates — Summary I 
 
 CHAPTER II. 
 
 THE MICROSCOPICAL AND CHEMICAL COMPOSITION OF THE BODY. 
 
 What are the tissues ? — Cells and fibres — The physiological divi- 
 sion of labor and its result- — The chemical composition of 
 the body — Albumens, fats, and carbohydrates 1 1 
 
 CHAPTER III. 
 
 THE SKELETON. 
 
 Rone, cartilage, and connective tissue — Articulations and joints 
 — The bony skeleton — Value of the structural arrangement 
 of the spinal column — Comparison of the skeletons of the 
 upper and lower limbs — Peculiarities of the human skeleton. 17 
 
 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 36 
 
 ix 
 
x 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 46 
 
 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 com- 
 position of muscle — Beef tea and meat extracts 52 
 
 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 64 
 
 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 74 
 
 CHAPTER IX. 
 
 NUTRITION. 
 
 The wastes of the body — Receptive and excretory organs — The 
 organs and processes concerned in nutrition — Digestion — Cir- 
 culation — Respiration 83 
 
CONTENTS. xi 
 
 < IIAPTER X. 
 POODS. 
 
 PAGE 
 
 Foods as tissue formers — What foods must contain — The special 
 importance of albuminous foods — The dependence of animals 
 on plants — Non-oxidizable foods — Definition of foods — Ali- 
 mentary principles — The nutritive value of various foods — 
 Alcohol — Tea and coffee — Cooking — The advantages of a 
 mixed diet 88 
 
 CHAPTER XI. 
 
 THE DIGESTIVE ORGANS. 
 
 General arrangement of the alimentary canal — Glands — The 
 mouth — The teeth — Hygiene of the teeth — The tongue — A 
 furred tongue — The salivary Glands — The tonsils — The 
 pharynx — The gullet — The stomach — Palpitation of the heart 
 — The small intestine — The large intestine — The liver — The 
 pancreas 106 
 
 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 alimen- 
 tary canal — The lymph — The lacteals 131 
 
 CHAPTER XIII. 
 
 BLOOD AND LYMPH. 
 
 Why we need blood — Histology of blood — The blood corpuscles 
 — Haemaglobin — The coagulation of blood — Uses of coagula- 
 tion — Blood serum — Blood gases — Hygienic remarks — Quan- 
 tity of blood in the body — The lymph — Dialysis — The lym- 
 phatic or absorbent vessels 147 
 
 CHAPTER XIV. 
 
 THE ANATOMY OF THE CIRCULATORY ORGANS. 
 
 The organs of circulation — Functions of the circulatory parts of 
 the system — The pericardium — The heart — The vessels con- 
 
xn CONTENTS. 
 
 I-AGE 
 
 nected with the heart — How the heart is nourished — The 
 valves of the heart — The main arteries of the body — The 
 properties of the arteries — The es — The veins — The 
 course of the blood — The portal circulation — Arterial and 
 venous blood 163 
 
 CHAPTER XV. 
 
 THE WORKING OF THE HEART AND EI. GOD VESSELS. 
 
 The beat of the heart — Events occurring in each beat — Use of the 
 papillary muscles — Sounds of the heart — Function of the au- 
 ricles — Work done daily by the heart — Nerves of the heart — 
 The pulse — Blood flow in capillaries and veins — Why there 
 is no pulse in these vessels — The muscles of the arteries — 
 Exposure to cold — Bathing 180 
 
 CHAPTER XVI. 
 
 THE OBJECT AND THE MECHANICS OF RESPIRATION. 
 
 The object of respiration — The respiratory apparatus — The 
 trachea — Bronchitis — The lungs — The pleura? — Pleurisy — 
 Elasticity of the lungs — Inspiration and expiration — Structure 
 and enlargement of thorax — Respiratory sounds — Why the 
 lungs fill with air — The nervous control of respiration — Hy- 
 gienic remarks. 193 
 
 CHAPTER XVII. 
 
 THE CHEMISTRY GF RESPIRATION AND VENTILATION. 
 
 The quantity of air breathed daily — Changes produced in the air 
 by being breathed — Ventilation — When breathed air becomes 
 unwholesome — How to ventilate — Changes undergone by 
 the blood in the lungs 208 
 
 CHAPTER XVIII. 
 
 THE KIDNEYS AND THE SKIN. 
 
 General arrangement of the nitrogen-execreting organs — Gross 
 structure of the kidney — Histology of the kidney — The renal 
 secretion — The skin — Hairs — Nails — The sweat glands — The 
 sebaceous g'.ands — Hygiene of the skin — Bathing 215 
 
CONTENTS. xiii 
 
 CHAPTER XIX. 
 WHY ui NEED A NERVOUS SYSTEM— ITS ANATOMY. 
 
 The harmonious co-operat i<>n of t he organs of the body — Co- 
 ordination — Nerve trunks and nerve centres — The brain and 
 spinal cord and their membranes — The spinal cord — The 
 spinal nerves — The brain — The cranial nerves — The sympa- 
 thetic nervous system — The histology of nerve centres and 
 nerve trunks 230 
 
 CHAPTER XX. 
 
 THE GENERAL PHYSIOLOGY OF THE NERVOUS SYSTEM. 
 
 The properties of the nervous system — Functions of nerve 
 centres and nerve trunks — Sensory and motor nerves — 
 Classification of nerve centres — Functions of the cere- 
 brum — Of the cerebellum — Reflex nerve centres — Auto- 
 matic nerve centres — Habits — Hygiene of the brain 247 
 
 CHAPTER XXI. 
 
 THE SENSES. 
 
 Common sensation and special senses — Hunger and thirst — 
 The visual apparatus and its appendages — Movements 
 of the eyeball — The globe of the eye — The retina — The 
 blind spot — The iris — The formation of images on the 
 retina — Short sight and long sight — Astigmatism — Hy- 
 giene of the eyes — Hearing — The tympanum — The in- 
 ternal ear — Touch — The localization of skin sensations 
 — The muscular sense — Sense of pain — The temperature 
 sense — Smell — Taste 263 
 
 CHAPTER XXII. 
 
 VOICE AND SPEECH. 
 
 The production of voice — The pitch of the voice — Resonance 
 — Speech — Structure of the larynx — The vocal chords — 
 Range of the human voice — Vowels — Semi-vowels — Con- 
 sonants 2S8 
 
xiv CONTENTS. 
 
 CHAPTER XXIII. 
 
 GROWTH AND NUTRITION. 
 
 PACE 
 
 Development — Segmentation — Differentiation — Classification 
 of tissues — Cell nutrition — Trophic nerves — General nu- 
 trition — Internal secretion of glands — Spleen — Thyroid 
 gland — Suprarenal capsules — Pituitary body — Kidney — 
 Pancreas — Health — Disease — Bacteria — Immunity from 
 disease — Toxin — Antitoxin 295 
 
 APPENDIX A. 
 
 EMERGENCIES. 
 
 Gas poisoning — Artificial respiration — Fainting — Sunstroke 
 
 — Convulsions — Alcoholic poisoning — Concussion of 
 brain — Epileptic attacks — Apoplexy — -Common poisons 
 and their antidotes — Bleeding — Bruises and sprains — 
 Burns and scalds — Stings of insects — Snake bite — Foreign 
 body in eye — Contagious diseases — Disinfection 307 
 
 APPENDIX B. 
 
 THE ACTION OF ALCOHOL AND TOBACCO UPON THE 
 HUMAN BODY. 
 
 Introductory — Is alcohol a food ? — Composition and proper- 
 ties of alcohol — Alcoholic beverages — The direct physio- 
 logical action of pure alcohol — Action of diluted alcohol 
 — Absorption of alcohol — Primary effects of a moderate 
 dose of alcohol — Secondary effects of alcohol — Minor 
 diseased conditions produced by alcohol — Acute alco- 
 holic diseases — Delirium tremens — Dipsomania — Chronic 
 alcoholic diseases — Deteriorations of tissue due to alco- 
 hol — Organs impaired or destroyed by alcohol — Moral 
 deterioration produced by alcohol — Tobacco 327 
 
 APPENDIX C. 
 
 DEMONSTRATIONS AND EXPERIMENTS. 
 
 Bones — Muscle — Joints — Levers — Oxidation — Foods — Diges- 
 tive tract — Digestion — Blood — The heart — Heart action 
 
 — Respiratory tract — Respiration — Renal organs — Ner- 
 vous system — Nerve action — Special senses 343 
 
THE HUMAN BODY. 
 
 CHAPTER I. 
 
 THE GENERAL STRUCTURE AND ARRANGEMENT OF THE 
 
 HUMAN BODY. 
 
 Human Physiology is that department of science which 
 has for its object the discovery and accurate description of 
 the properties and actions of the living healthy human body, 
 and the uses, or the functions, of its various parts. Physi- 
 ologists endeavor to find out the work of the body as a 
 whole, and of each of its parts, and the conditions under 
 which this work is best performed. Upon this study is based 
 the science of Hygiene, which is concerned with the laws 
 and conditions of health. 
 
 Anatomy. — Clearly, to discover the use and mode of 
 working of each part of the body we must learn about the 
 parts; this study is Human Anatomy. When the body is 
 examined from without, it is seen to be a complicated struc- 
 ture with its head and neck, trunk and limbs, and the many 
 smaller but distinct parts which enter into the formation of the 
 larger ones, as eyes, nose, ears, and mouth to form the face. 
 Dissected, its complexity is seen to be far greater ; we then 
 learn that it is made up of many hundreds of diverse parts, 
 each having its own form, structure, and purpose, but all 
 working harmoniously together in health. 
 
2 THE HUM Ahl BODY. 
 
 Summary. — Anatomy deals with the form, structure, and 
 connections of the parts of the body ; Physiology with the 
 uses, or functions, of the parts, and the manner of their 
 working ; Hygiene with the conditions of life which promote 
 the health of the body. 
 
 Microscopic Anatomy or Histology. —Examination of 
 the body's surface shows that a number of different materials 
 enter into its formation, such as hair, nails, skin, and teeth. 
 By feeling through the skin, we find harder and softer solid 
 masses beneath ; by piercing it, we find liquid blood. 
 
 A closer examination of any of its parts, as the hand, dis- 
 closes the same variety of materials. We see the skin and 
 nails ; when the skin is dissected off we find yellowish-white 
 fat ; beneath the fat lies a number of soft red masses, the 
 muscles (which correspond to the lean of meat); under the 
 muscles, again, are hard, whitish bones ; the ends of bones 
 which form the joints are covered by still another substance, 
 gristle or cartilage. Finally, binding skin, fat, muscles, and 
 bone together, we discover a tough stringy material, different 
 from all, which is called connective tissue. If we take any 
 other portion of the body, as the foot, we arrive at a similar 
 result ; it, too, is made up of a number of different materials, 
 or tissues, which, though in this case identical with those 
 found in the hand, are arranged 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 differ- 
 ent manner in the two cases | : or we find, as in the eye, 
 some identical and some quite different materials. 
 
 That branch of anatomy which deals with the arrange- 
 ment 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 ,-W/> ORGANS. 3 
 
 Tissues. I'..i< li of the primary building materials which 
 can be recognized, either with or without the mu roscope, as 
 
 entering into the construction of the body, is < ailed a Hssiii 
 we speak, for example, of muscular tissue, fatty tissue, bony 
 tissue, cartilaginous tissue, and so forth ; eat h tissue has cer- 
 tain properties in which it differs from all the rest, and which 
 it preserves in whatever part of the body it may be found 
 It is also, when examined with a microscope, characterized 
 by certain appearances which are always 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 tissues are combined. 
 
 Organs. — Each distinct portion of the body with a spe- / 
 cial use or function is called an organ ; thus, the hand is an 
 organ of prehension ; the eye, the organ of sight ; the stom- 
 ach, 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 appear- 
 ance, by which it can be recognized with the microscope, 
 and one or more distinctive properties which fit it for some 
 special use; thus, it maybe tough, and suited for binding 
 other parts together ; or rigid, and adapted to preserve the 
 shape of the body ; or have the power of contracting and 
 thus of moving parts to which its ends are attached. 
 
 * The various tissues of the body will be considered in more detail 
 in connection with the study of the >pecial organs. The more important 
 are : I. Bony tissue. 2. Cartilaginous tissue. 3. White fibrous con- 
 nective 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 tissues. 9. Nerve cell tissue. 10. Nerve 
 fibre tissue. II. Striped muscular tissue. 12. Unstriped muscular tis- 
 sue. 13. Epidermic and epithelial tissue. 
 
4 THE HUMAN BODY. 
 
 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 tissues ; 
 others, a great many ; some possess only tissues which are 
 found also in other organs, others contain 01 e or more tis- 
 sues 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 machines which are found 
 in the factory represented by the body, and the tissues are 
 the materials used in building the machines ; or, using an- 
 other illustration, we may, with Longfellow, compare the 
 body to a dwelling-house ; and then go on to liken the tis- 
 sues 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. 
 
 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 crosswise, and studies 
 the surfaces thus laid bare ; the 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 ; 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 directions. 
 
 If the whole body is divided into right and left halves, 
 the cut surface of the right half resembles Fig. i. Such a 
 
GENERAL PLAN ( >/ A HODY. 
 
 so tion allows us, lir>t, that the body 
 essentially consists of two main 
 tubes or cavities, separated by a 
 
 solid bony partition. The larger 
 cavity, b, c, known as the ventral 
 cavity, lies on the front side, and 
 contains the organs of circulation, 
 respiration, and digestion. It does 
 not reach into the neck, but is en- 
 tirely 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 con- 
 tains the most important nervous 
 organs, i.e. the brain, X' , and 
 spinal cord, X. In the partition 
 between the two cavities is a stout 
 bony column, the back-bone or 
 spine, e, e, which is made up of a 
 number of short thick bones ar- 
 ranged one on the top of an- 
 other. 
 
 Man is a Vertebrate Animal. — 
 The presence of these two cham- 
 bers with the solid partition be- 
 tween them is a primary fact in 
 the anatomy of the body ; it shows 
 that man is a vertebrate animal, 
 that is, a back-boned animal, and 
 belongs to the same great group as 
 
 Fig. i. — Diagrammatic longitu- 
 dinal section of the body, a, the 
 neural tube, with its upper enlarge- 
 ment in the skull cavity at a' ; A". 
 the spinal cord ; .V, the brain ; ee, 
 vertebrae forming the solid parti- 
 tion between the dorsal and ven- 
 tral cavities ; t>, the pleural, and c, 
 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, f\ //, the heart; k, 
 a kidney ; s, the sympathetic ner- 
 vous chain. From the stomach, f, 
 the intestinal tube leads through 
 the abdominal cavity to the pos- 
 terior opening of the alimentary 
 canal. 
 
6 THE HUM/IN BODY. 
 
 fishes, reptiles, birds, and beasts.* Sea anemones, clams, and 
 insects are invertebrate animals, and sections made through 
 any of them from the head to the opposite end would show 
 nothing like the two main cavities with a back bone between 
 them characteristic of the vertebrates. 
 
 Contents of the Two Chief Cavities of the Body. — Exam- 
 ination of Fig. i shows that the ventral cavity is entirely 
 closed, though some of the organs which lie in it are hollow 
 and communicate with the exterior. On the head we find 
 the nose, /, and the mouth, o, opening on the ventral side, 
 that is, on that surface of the body next which the ventral 
 cavity lies. The nose chamber joins the mouth chamber at 
 the throat, from which 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, /; the other is the gullet, and leads to the stomach, 
 f. From the stomach another tube, the intestine> returns to 
 the outside at the lower or posterior \ end of the trunk. 
 Mouth, throat, gullet, stomach, and intestine together form 
 the alimentary canal, which begins in the head above or an- 
 terior to the ventral cavity, enters this cavity at the bottom 
 of the neck and runs on through it, to pass out again pos- 
 teriorly ; just as a tube might pass through a box, in at one 
 end and out at the other, without opening into it at all. In 
 
 * The main groups in which animals are arranged are : I. Vertebrate*. 
 or back-boned animals. 2. Mollusca, including snails, ^lugs. clams, 
 oysters, etc. 3. Arthropoda. including flics, moth-, beetles, centipedes, 
 lobsters, spiders, etc. 4. Vermes, including worms of various kinds. 5. 
 Eehinodermata (hedgehog-skinned animals), including sea-urchins, star- 
 fishes, etc. 6. Calenteraia, 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 opposite end as posterior, no matter what may be the natural stand- 
 ing position of the creature. 
 
TWO CHIEF CAVITIES OF THE BODY, 7 
 
 addition to the lungs and the greater part of the alimei 
 canal, the ventral t. several other organs, among 
 
 the more important of which arc i | the heart, h ; the 
 
 kidneys, k ,- the sympathetic nerve ^enters, tj and the large di- 
 gestive organs. 
 
 Fig. 2. — A diagrammatic section across the body in the chest region, x, the dqrsal 
 tube, which contains the spinal cord ; the black mass surrounding it is a vertebra ; 
 (i, the gullet, a part of the alimentary canal: h y the heart ; sy. sympathetic nervous 
 system; //, lungs; the dotted lines around them are the pleura: ; rr, ribs ; st, the 
 breastbone. 
 
 If we examine a section made across the trunk of the 
 body, say about the level of the middle of the chest (Tig. 2;, 
 
 Fig. 3. — A section across the forearm a short distance below the elbow-joint. R 
 and £", its two supporting bones, the radius and ulna ; e. the epidermis, and d, the 
 dermis, of the skin ; the latter is continuous below with bands of connective tissue, s, 
 which penetrate between and invest the muscles (i, 2, 3, 4, etc.) ; «, «, nerves and 
 vessels. 
 
 we find on the dorsal side the neural tube, x, and in it the 
 spinal cord, which is not represented in the figure. The 
 part surrounding the neural tube and represented by the 
 
8 THE HUMAN BODY. 
 
 black, star-shaped mass is part of the spinal column. The 
 chest cavity is enclosed by the spinal column, the ribs r, r, 
 and the breastbone si, and contains the lungs, /, /; the 
 heart, h ; the gullet, a ; and the sympathetic centres, sy, sy. 
 
 The Limbs. — If our. section is made across one of the 
 limbs, we find no such arrangement of cavities. Each limb 
 has a supporting axis made of one or more bones (as seen at 
 17 and R, Fig. 3, which represents a section made across the 
 forearm near the elbow joint J, but soft parts, chiefly muscles, 
 are closely packed around this axis, and the whole is en- 
 veloped by skin. 
 
 Man's Place among Vertebrates. — Although man's struc- 
 tural 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 his body, and the organs 
 producing milk for the nourishment of the infant by its 
 mother, are entirely absent in fishes, reptiles, and birds, but 
 are possessed by ordinary four-footed creatures and by whales, 
 bats, and monkeys. The organs which form milk are the 
 mammary glands, and all kinds of animals whose females pos- 
 sess them are known as Mammalia *„• man is, therefore, a 
 Mammal. One of the most important characteristics of the 
 Mammalia is a cross-partition, called the midriff ox di aphragm , 
 (d, Fig. 1 ) which separates the ventral cavity into an anterior 
 and a posterior part; the upper or anterior story is the chest 
 or thoracic cavity; the lower or posterior, the abdominal cavity. 
 The chest contains the heart, lungs, and most of the gullet ; 
 
 * Zoologists classify vertebrate animals in five groups. 1. Pisces, in- 
 cluding all true fishes, as sharks, eels, salmon, shad, perch, etc., but ex- 
 cluding the so-called shellfish, as oysters, clams, and lobsters, which are 
 not vertebrates at all. 2. Amphibia, frogs, toads, newts, salamanders, 
 etc. 3. Reptilia, lizards, alligators, turtles, snakes. 4. Ares, birds. 5. 
 Mammalia. 
 
•. 5 PI VERTEBRATES. 
 
 the abdomen contains the lower end of the gullet (which 
 pierces the diaphragm), the stomach, the intestine, the kid- 
 aeys, and most ot the organs making re liquids. The 
 
 FlG . ..-Diagram showing the position of ^«horacic and abdominaa organs, i, 
 lower border of right lung ; 2 , the same of the left lung ; 3. liver, right . lobe , 4. j*er 
 eft lobe ; 5. susplnsory ligament of the liver ; 6, fundus of gall-bUdder 7 «"£££* 
 stomach I I, fundus of stomach : o. lower border of stomach ; ,o fi ^'tf^ | 
 „, c*cum: 12. vermiform append.x • 13 ***»*•** ~°° '. '*' df" en \n nst colon ; .3. 
 ^transverse colon; £ position of left ■«££«£; Q 7 iTSauB. 
 portion of si -moid colon, corcealed b J; '9« conv°»utton^oi t distended, par: 
 Esr^to f ne e um m ;' ^^^7^^^^ St. covere J bv peritoneum. 
 
io THE HUMAN BODY. 
 
 sympathetic nerve centres 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 Fig. 4. We there see, in the 
 chest, the lungs and the heart, the latter largely covered by 
 the lungs. Below the diaphragm is the abdominal cavity, 
 containing the liver, the stomach, the intestines, and the 
 bladder. 
 
 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 contains 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 
 MammaTia (1) because his body is covered by hair; (2) be- 
 cause of the presence of mammary glands ; ( 3 ) because the 
 ventral cavity is completely separated by the diaphragm into 
 thorax and abdomen. 
 
 That man is intellectually superior to any other animal, and 
 stands supreme in the world, can be doubted by no one, 
 especially when we consider his power of forming concepts of 
 right and wrong, and his feeling of moral responsibility. But 
 anatomists have only to deal with man's body as a material 
 object, and as such they classify it among other animal bodies 
 according to the degree of resemblance found between them. 
 
CHAPTER IT. 
 
 THE MICROSCOPICAL AM> CHEMICAL COMPOSITION 01 
 
 TIIL BODY. 
 
 What are the Tissues? — Having gained some idea of the 
 general arrangement of the larger parts of the body, we may 
 next consider the minute structure of the tissues. The tissues 
 are made up of cells* which are so small that a single one 
 can be seen only with the help of a microscope. A 
 
 a 3 
 
 In a fully formed cell (Fig. 5) we find three f&£ 
 
 parts: (1) a cell body made up of a soft gran- 1 * : ^sf 
 
 ular substance, protoplasm ; ( 2 ) a smaller and C{ H 
 
 less granular cell nucleus embedded in the cell i ,-^M 
 
 body; and (3) a tiny dot, the nucleolus, lying ' *<SP 
 
 in the nucleus. Cells vary much in form and rfJ% 
 
 size, though all are very small. A great many „..,. A 
 
 float in our blood, and are more or less rounded e ^Q$ 
 
 (b). Others are flattened to form thin scales V 
 
 as in Fig. 6, which represents cells scraped p) 
 
 from the peritoneum, the membrane lining the fig. 5.— Forms 
 
 11 r 1 ii r- -ii 1 1 °f ce l' s from the 
 
 wall of the abdomen. Still others are elon- body, 
 gated, as c, Fig. 5. If greatly elongated, the cell become- a 
 slender thread, called a. fibre ; long fibres are often made up of 
 these elongated cells, joined end to end. Examples of fibres 
 are shown in Figs. 35 aid 85. Speaking in general, we may 
 
 * So called from an old belief that they were little bags or chambers. 
 
 Most cells are really solid or semi-solid throughout. 
 
 11 
 
 0& 
 
12 
 
 THE HUMAN BODY. 
 
 say that the whole body consists of_tiny_jcells, either rounded 
 and thick, flat and thin, or elongated to 
 form fibres. 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 fibres which have grown 
 from cells, except something which cor- 
 responds pretty closely to the mortar 
 6^-Flat ceils from which lies between the bricks of a wall 
 
 the surface of the lining r . 
 
 membrane of the abdomen and holds them together. 1 his latter 
 
 (peritoneum) : a, cell-body ; 
 
 b, nucleus ; c, nucleoli. material, known in the body as i nter - 
 cell ular su bs t a we, is in some places abundant, in others scanty 
 or absent. Wherever found, the intercellular substance is 
 made by the cells which lie embedded in it ; they pass it out 
 f from their surfaces and repair it when necessary. 
 
 Summary. — Cells thus essentially make up the body and 
 do its work : their form and arrangement determine the 
 form of the organs ; their activity, the function of the organs. 
 For example, the bone cells have the power of forming the 
 intercellular substance which gives the hardness to the bony 
 skeleton ; the muscle cells are long fibres and by their con- 
 traction move the bones to which they are attached ; the 
 cells embedded in the wall of the stomach secrete the peculiar 
 solvent fluid used in digestion. 
 
 Anatomy may be defined as the study of the forms which cells 
 and intercellular substances assume ; physiology, as the study of 
 the specific activity of the cells. 
 
 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 
 
MICROSCOPICAL COMPOSITION 01 THE BOl 
 
 wild beasts and his fellow men. In a civilized nation, on 
 the contrary, we find thai most men have some one particu 
 lar business: farmers raise crops and cattle; cooks prepare 
 
 food; tailors make clothes; and policemen and soldiers pro- 
 tc< t the property and lives of the rest of the community ; in 
 other words, we find a division of labor. The more minute 
 the division of labor in a nation, the more advan* ed is it in 
 civilization ; so also an animal is higher or lower in propor- 
 tion as the duties necessary for maintaining its existence are 
 distributed among different tissues and organs. The amceba, 
 one of the lowest animals, feels, moves, catches and digests 
 food, and breathes, although it consists of but one cell. 
 Higher animals perform these functions by means of differ- 
 ent cells set apart in special organs. This specialization of 
 function is called differentiation. 
 
 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 be- 
 comes 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. In the second place, 
 when various employments are distributed among different 
 persons, there arises a necessity for a new kind of industry in 
 order to convey the special product of any individual not 
 needed by himself to others who may want it, and to bring 
 him in return such excess production of others 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 
 
M THE HUMAN BODY. 
 
 given time, the activity of individuals shall be regulated in 
 accordance with the wants of the whole community or of the 
 world at large. 
 
 Exactly similar phenomena result from the division of 
 physiological labor in the human body. Each tissue and 
 organ does a special work for the whole body and in turn 
 relies on the others for their aid ; thus every sort of neces- 
 sary work is better performed ; the tissue or organ, since 
 it has 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 all excess products of the various organs 
 shall be carried to others which require them; and a regulat- 
 ing mechanism by which the activities of each shall be con- 
 trolled in accordance with the needs of the whole body. We 
 accordingly find a set of organs, the heart and blood vessels, 
 which circulate the blood so that in its course through the 
 body it gets something from and gives something to each 
 organ through which it flows : and a set of nervous organs 
 which ramify in every direction and regulate the activity of 
 its parts. 
 
 The 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 upon chemistry to 
 discover what elements and compounds make up the cells and 
 intercellular substance. 
 
 Elements found in the Body. — Of the many elements 
 discovered by chemists, only seventeen have been found in 
 the healthy human body.* Very few exist in it uncombined, 
 
 * The elements found in the body in health are carbon, hydrogen, ni- 
 trogen, oxygen, sulphur, phosphorus, chlorine, fluorine, silicon, sodium, 
 potassium, lithium, calcium, magnesium, iron, manganese and iodine. 
 
CHEMICAL COMPOSITION OF THl BODY. 15 
 
 although some oxygen is dissolved in the Mood and is al 
 found, mixed with nitrogen, in the lui 
 
 Chemical Compounds existing in the Body. I i 
 so numerous thai it would be a long task to enumerate them, 
 but some require mention. They may be divided into organic 
 and inorganic. The general distinguishing characteristic of 
 the onstituents of the body is that if dried th( 
 
 would burn in a fire : of the inorganic components, that they 
 could noting made to burn. 
 
 Inorganic Constituents of the Body. — Of the inorgann 
 constituents of the body, water and common sail are the most 
 important ; thcv are found in all the organs and liquids of the 
 body. Phosphate and carbo nate of lime are also found in large 
 proportions in the bones and teeth, annl free hydrochloric 
 acid (muriatic arid; is always found in healthy gastric juice, 
 which dissolves some kinds of food in the stomach. 
 
 Organic Constituents of the Body. — All organic con- 
 stituents of the body contain carbon, hydrogen, and oxygen ; 
 some contain nitrogen also. There are three chief kinds of 
 them, viz., ajbumens, fats, and carbohydrates. 
 
 Albuminous or Proteid Substances. — These are by far 
 the most characteristic organic compounds existing in the 
 body ; they are known only as obtained from living beings, 
 as they have never yet been artificially constructed in the 
 laboratory ; a good example is found in the white of an egg, 
 which consists chiefly of albumen dissolved in water. All 
 the U§sues of the body which have any marked physiological 
 property contain some albuminous substance, only such things 
 as hairs, nails, and teeth being devoid of them. All albumin- 
 ous bodies contain nitrogen, carbon, hydrogen, and oxygen ; 
 most of them sulphur and phosphorus in addition. The more 
 important ones found in the body are, (1) Serum albumin. 
 
AOl 
 
 1 6 THE HUMAN BODY. 
 
 which is very like egg albumin, and is found dissolved in the 
 blood ; (2) Fibrin, which forms in blood when it clots ; ( 3 ) 
 Myosin, which is found in the muscles and which by " setting " 
 or coagulating after death causes the death stiffening ; (4) 
 Casein, which is found in milk, and forms 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 p al mi tin , stearin, 
 and qleiti j by proper chemical treatment each can be split up 
 into glycerine and a fatty_acid, i.e. palmitic, stearic^, or oleic 
 as the case may be. 
 
 The Carbohydrates also consist entirely of carbon, hydro- 
 gen, and oxygen ; they belong to the same class of substances 
 as starch and sugar. The most important carbohydrate found 
 in the body is glycogen, a sort of starch found stored up m 
 the liver and muscles. Glucose or grape sugar also exists in 
 the body ; and lactose or milk sugar is found in milk. 
 
 Cy . f 
 
 ■ 
 
PLATE I.— THR BONES, 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 Fig. 8, which 
 commences on page 20. 
 
 a Ligaments of the Elbow Joint. 
 
 <*> The Ligament which is connected with the ventral surfaces of the bodies of the 
 Vertebrae. 
 
 e Ligament connecting the Innominate Bone to the Spine. 
 / Ligament connecting the Innominate Bone to the Sacrum. 
 
 g The Ligaments of the Wrist Joint. 
 
 h The Membrane which fills up the interval between the two bones of the Fore 
 Arm. 
 
 / A similar Membrane between the two bones of the Leg, and, lower down, /, liga- 
 ments of the Ankle Joint. 
 
 k A Membrane which fills up a hole in the Innominate Bone. 
 
 « Ligaments of the Knee Joint. 
 
 00 Ligaments of the Toes and Fingers. 
 
 / Capsular (bag-like) Ligament of the Hip Joint. 
 
 q Capsular Ligament of the Shoulder Joint. 
 
CHAPTER III. 
 
 THE SKELETON. 
 
 The Skeleton * of the human body is composed of three 
 materials : bone, 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 pull, and they surround cavities in which soft, 
 delicate organs, as brain, spinal cord, and heart, may lie in 
 safety. 
 
 Cartilage caps the ends of bones, forming elastic pads 
 with smooth surfaces for the joints. It is also used instead of 
 bone in some parts of the skeleton where considerable flexi- 
 bility is required, as at the anterior ends of the ribs. Carti- 
 lage affords one of the best tissues of the body for the exami- 
 nation 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 the cells only, but these lay down intercellular sub- 
 stance around them, until at last it forms the main bulk of 
 
 * There are two kinds of skeleton in the animal kingdom : the external 
 skeleton or exoskeleton, and the internal skeleton or endoskeleton. The 
 exoskeleton is made by the skin, either in it or on it ; examples are found in 
 the shells of clams and lobsters; the scales of fishes and snakes ; the tortoise- 
 shell of turtles ; the feathers of birds ; the hair and claws of beasts. In man 
 the exoskeleton is only slightly developed ; hair, nails, and teeth belong to 
 it. 
 
 17 
 
 \ 
 
i8 
 
 THE HUMAN BODY. 
 
 the cartilage, and gives the elasticity and flexibility for which 
 cartilage is used in the body. 
 
 Mtm 
 
 
 ^. 
 
 Mfct 
 
 fc 
 
 «=) 
 
 iemj — — s 
 
 811 
 
 •Vfc -•>&- 
 
 
 wSmMk 
 
 &3£ 
 
 ■ : 
 
 H 
 
 N - ;'■ ■/ ;■• J- v \ v v ; , ■■ X v - ■ ■ :.•■ 
 
 «y 
 
 v 
 
 Fig 7.— A thin slice of cartilage highly magnified. 
 
 Connective Tissue occurs partly in the form of stout cords 
 — ligaments — which bind different bones together, or which, 
 as tendons, attach muscles to bones. It partly supplements 
 the coarser bony skeleton by a fine network which extends 
 through all the soft parts of the body and makes a sort of 
 microscopic skeleton, or supporting meshwork, for its cells. 
 It is laid down as a soft packing material, a good deal like 
 raw cotton, in the crevices between different organs, as shown 
 at s, Fig. 8, between the muscles of the forearm. This tissue 
 is, in fact, so widely spread through the body, from the skin 
 
THE SKELETON. 
 
 *9 
 
 outside to the lining of 
 the alimentary (anal with- 
 in, that it" we could em- 
 ploy a solvent which 
 would remove everything 
 excepl this connective 
 tissue, a very perfect 
 model of all the organs 
 would be left ; something 
 like a skeleton leaf, but far 
 more minute in its tracery. 
 Articulations and 
 Joints. — If the pieces 
 forming the hard frame- 
 work of the body were 
 put together like the 
 beams and planks of a 
 frame house, the whole 
 mass would be rigid and 
 immovable ; we could not 
 raise a hand to the mouth, 
 or put one foot before an- 
 other. In order to attain 
 mobility the bony skeleton 
 is made up of more than 
 two hundred separate 
 pieces, joined together ; 
 the points where they 
 meet are called articula- 
 tions. An articulation 
 in which a considerable 
 range of movement is per- 
 
 Fig. 8. — The bony and cartilaginous skeleton. 
 
20 THE HUMAN BODY. 
 
 mitted is called a joint. The ends of bones which rub against 
 one another in a joint are covered by a smooth layer of carti- 
 lage. 
 
 The Bony Skeleton (Fig. 8) consists of an axial skeleton, 
 supporting head, neck, and trunk, and an appendicular skele- 
 ton, supporting the limbs and attaching them to the trunk. 
 
 The Axial Skeleton. — The fundamental portion of this is 
 the backbotie, spinal column, or spine, partly seen at e and c, 
 Fig. 8, and represented isolated from the rest of the bones 
 and viewed from the left side in Fig. 9. It forms an axis, on 
 which the rest of the body is carried. On the upper end of 
 the vertebral column is the skull, a, b, Fig. 8, and attached 
 by ligaments to the under surface of the skull is the hyoidbone, 
 to which the root of the tongue is fastened. 
 
 Slender bones, called ribs, are attached by their dorsal ends 
 to the sides of part of the spine ; they curve round the sides of 
 the chest and are united in front to the sternum, ox breast-bone, 
 d, Fig. 8. 
 
 Skull, hyoid bone, vertebral column, ribs, and sternum to- 
 gether form the axial skeleton. 
 
 The appendicular skeleton consists of the pectoral and pelvic 
 girdles, attaching the limb bones to the axial skeleton, and 
 of the limb bones themselves. 
 
 The Pectoral Arch or Girdle consists on each side of a 
 collar bone or clavicle, u, and a shoulder blade or scapula. The 
 scapula, Fig. 8, is a flat, triangular bone, lying on the back of 
 the chest outside the ribs. The clavicle is a slender curved 
 bone like an italic f in form. Its outer end is attached to 
 the scapula, and its inner end to the top of the sternum. It 
 serves to support the shoulder joint, and to prevent it from 
 falling backwards or inwards toward the front of the chest. 
 It is absent in creatures which use their fore limbs for walking 
 
PELVIC ARCH SKELETON Oh LOWER LIMB. 
 
 2 I 
 
 only, as horses, dogs, and cattle, but is well developed in 
 
 monkeys and bats. 
 
 The skeleton of the upper limb consists of : (ij 'J 'he arm 
 
 bone or humerus, /, Fig. 8, which extends c , 
 
 from the shoulder to the elbow, and meets 
 
 i 
 
 the scapula at the shoulder joint ; (2) of* 
 
 two forearm bones, the radius, g, and ulna, s 
 
 f, the radius being on the thumb side ; i : 
 
 and (3) of twenty-seven hand bones. Of ' 
 
 the hand bones eight, the carpal bones, h, 
 
 lie in the wrist ; five, the metacarpal bones, 
 
 i, in the palm of the hand ; and fourteen, 
 
 the phalanges, k, in the thumb and fingers 
 
 — two for the thumb, and three for each 
 
 finger. 
 
 The Pelvic Arch or Girdle consists of 
 
 a single bone, the os innominatum, s, on 
 
 each side ; this is firmly fixed at its 
 
 dorsal end to the lower part of the back- 
 
 a, 
 bone, meets its fellow ventrally at the lower 
 
 end of the abdomen, and bears a deep 3 
 socket on its outer side, into which the*' 
 upper end of the thigh bone fits. 
 
 The Skeleton of the Lower Limb con- 
 sists of: (1) The thigh bone ox femur, r, 
 the longest bone in the body, which bears 
 on its upper end a hemispherical knob fit- 
 ting into a hollow on the outside of the 
 os innominatum, to form the hip joint ; 
 (2) of two bones, tibia and fibula, I and m, 
 in the lower leg, the former on the inside ; (3) of the knee cap 
 or patella, q, in front of the knee joint ; (4) of twenty-six foot 
 
 FlG. 9. — Side view of 
 the spinal column. 
 
22 
 
 THE HUMAN BODY. 
 
 bones. Of the foot bones seven, the tarsal bones , n, lie below 
 the ankle joint ; five, the metatarsal bones, o, are anterior to 
 
 ^ 
 
 ~<J 
 
 Fig. io. — The last lumbar vertebra and the sacrum seen from the ventral side. 
 
 these in the front half of the sole of the foot ; and fourteen 
 phala?iges, p, are found in the toes, two in the great toe and 
 three in each of the others. 
 
 The Vertebral Column ("Fig. 9). — The upper portion 
 of the spine consists of twenty-four separate bones, each called 
 a vertebra j these are placed one above the other, and sepa- 
 rated by elastic pads 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 
 
A VERTEBRA. 
 
 *3 
 
 ribs ; and five I lumbar, J. i 5 1 arc in the loins or "small <>f 
 the back." 
 
 Below the separate vertebrae we find the sacrum <-S'i), 
 which is seen in Fig. 10, with the lowest lumbar vertebra. In 
 childhood the sacrum consists of five distinct vertebrae, but 
 these grow together afterwards, though cross ridges remain in- 
 dicating the original lines of separation. Below the sacrum, 
 forming the tip of the spine, is the coccyx (Co 1-4, Fig.9), 
 a single bone in adults, but four bones in children. 
 
 The Structure of a Vertebra. — Those vertebrce which re- 
 main separate resemble one another in general form. As an 
 example we may take the eleventh from the skull, i.e. the 
 fourth dorsal vertebra (Figs, n and 12). 
 
 Fig. 11. Fig. 12. 
 
 FlG. ii.— A dorsal vertebra seen from behind, i.e. the end turned from the head. 
 
 Fig. 12. — Two dorsal vertebrae viewed from the left side, and in their natural rela- 
 tive positions. C, the body ; A , neural arch ; Fv, the neural ring ; Ps, spinous proc- 
 ess ; Pas, anterior articular process; J'ai, posterior articular process; TV, transvt r>e 
 process ; Ft, facet for articulation with the tubercle of a rib ; Fes, Fci, articular sur- 
 faces on the centrum for articulation with a rib. 
 
 In it we find (i) a thick bony mass, C, rounded on the 
 sides and flattened above and below where it faces its neigh- 
 bors, called the cen/rum or body of the vertebra. The series 
 
24 THE HUMAN BODY. 
 
 of vertebral bodies forms the bony partition (e, e, Fig. i) 
 already mentioned as existing in the trunk between the neu- 
 ral and ventral cavities. (2) The arch, A, which is at- 
 tached to the dorsal side of the centrum, is called the neural 
 arch, and with the centrum it forms the neural ring (Fv). By 
 the arrangement of the vertebrae one above the other, the 
 successive neural rings form the neural tube, in the cavity of 
 which the spinal cord lies. (3) Bony processes project from 
 the body and the arch (Figs, n and 12) : these are (a) the 
 spinous process (Ps) which points dorsally and with its fellows 
 forms the ridge of the spine ; (b) the transverse processes (Pt), 
 one on either side, which in the dorsal region support the 
 ribs; and (c) the articular processes (Pas, Pai), four on each 
 vertebra, which form the points of contact with the adjoining 
 vertebrae above and below. 
 
 Where the arch joins the centrum it is narrowed to a stalk 
 ox pedicle, Ii, Fig. 12. When the vertebras are placed to- 
 gether in their natural relative positions, apertures (Pi), w r hich 
 lead into the neural canal, are left between their narrower 
 portions ; through these apertures (called the intervertebral 
 foramina) nerves pass into or out from the spinal cord. 
 
 The Atlas and Axis. — The first and second cervical ver- 
 tebrae, however, differ considerably from the others. The 
 first, called the atlas (Fig. 13), carries the head ; it has a very 
 small body and a very large neural ring. A liganent, 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 
 which rises from the second cervical or axis vertebra (Fig. 14) 
 and forms a pivot around which the atlas, carrying the skull 
 with it, rotates when the head is turned from side to side. 
 On the anterior (upper) surface of the atlas are a pair of shal- 
 
SPIN. II. COLUMN. 
 
 25 
 
 low hollows, Fas. A pair of knobs on the under surface of 
 the skull (Fig. 20) glide in these hollows during nodding 
 movements of the head. 
 
 A a Fas 
 
 Fig. 13. Fig. 14. 
 
 Fig. 13. — The atlas. Fig. 14.— The axis. Aa, body of atlas. Z>, odontoid proc- 
 ess 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; Prevertebral for- 
 amen. 
 
 Value of the Structural Arrangement of the Spinal Col- 
 umn. — 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 in 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.* The elastic cushions 
 (intervertebral disks) placed between the bodies of the verte- 
 brae also aid in protecting the delicate brain and the spinal 
 cord from injury. 
 
 The intervertebral disks allow of a certain range of move- 
 ment between each pair of vertebrae, so that the column as a 
 
 * Take a straight but tolerably flexible and elastic bar, as a lath or, bet- 
 ter 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. 
 
26 THE HUMAN BODY. 
 
 whole may be bent in any direction. On the other hand, 
 these pads and the ligaments so limit the movement that no 
 
 Fig. i 5 .-The ribs of the left side, with the dorsal and two lumbar vertebra, the 
 rib cartilages, and the sternum. 
 
 sharp bend which would compress or injure the spinal cord 
 can occur at any point. 
 
THE SKULL 
 
 27 
 
 The sacral vertebrae are separate in infancy, but grow to- 
 gether firmly to give a solid support to the pelvi* ar< h, whi< h 
 transmits the weight of the body to the lower limbs when we 
 
 stand. 
 
 Tsp 
 
 "ride view of the skull. O, occipital bone : T temporal; Pr parietal; 
 /^frontal: S, sphenoid; Z, malar: Mx, max.lla; iV, nasal; 2T, ethmo.d, Z., lach 
 rymal; .1/^, inferior maxilla. 
 
 Summary. —The backbone is rigid enough to support all 
 the rest of the body ; flexible enough to bend considerably in 
 any desired direction, yet not sharply at any one point ; and 
 
28 THE HUMAN BODY. 
 
 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 twenty-four in number, twelve on each side 
 (Fig. 15). They are slender curved bones which embrace 
 the sides of the chest and are attached at the dorsal end to 
 the dorsal vertebras. Ventrally each rib ends in a costal car- 
 tilage ; the cartilages of the seven upper pairs are directly ar- 
 ticulated to the sides of the breast-bone. The eighth, ninth, 
 and tenth rib cartilages join the cartilages of the ribs above ; 
 the eleventh and twelfth are not attached to the rest of the 
 skeleton at their ventral ends and hence are known as the 
 free or floating ribs. 
 
 The Skull (Fig. 16) is composed of twenty-eight bones: 
 eight of these form the cranium and are arranged to surround 
 the brain and protect the deep parts of the ears ; six lie 
 inside the ears ; and the remaining fourteen support the face, 
 surround the mouth and nose, and (with the aid of some of 
 the cranial bones) form the eye sockets. 
 
 The Cranium is a box whose thick floor (Fig. 1) con- 
 tinues anteriorly the partition which in the trunk separates 
 the neural from the ventral cavity. On its under side (Fig. 
 20) are many small apertures for nerves and blood vessels to 
 pass in or out, and one large opening, the foramen magnum, 
 for the spinal cord. 
 
 The cranial bones (Fig. 16) are the following: 1. The 
 occipital bone, 0, which lies at the back of the skull and has 
 in it the foramen magnum. 2. The frontal bone, F, which 
 forms the forehead. 3. The parietal bones, Pr, two in num- 
 ber, which meet one another above the middle of the crown 
 of the head, and form a large part of the roof and sides of 
 the skull. 4. The temporal bones, T, one on each side, 
 
FACIAL SKELETON— CRASH M. 
 
 which contain the corresponding car cavities. 5. The sphe- 
 noid bone^ which, with the occipital bone. Tonus the base of the 
 skull, and sends <»ut a wing, S, on each side. 6. The ethmoid 
 
 /.'. which forms the partition between the brain and 
 nose chambers, and part of that between 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 bone or mandible, J/d, Fig. 16 ; the other is the vomer, 
 which forms part of the partition between the two nostrils. 
 
 The paired face bones are: 1. The maxilLe or upper jaw 
 nones, Mxy which carry the upper teeth and form most of 
 the hard palate separating the mouth from the nose. 2. The 
 palate bones, which complete the bony palate, and lie in front 
 of the opening (posterior nares) by which the air passes from 
 the nasal chambers into the throat cavity (Fig. 20). 3. The 
 malar or cheek bones, Z. 4. The nasal bones, X, roofing in 
 the upper part of the nose. 5. The lachrymal or tear bones, 
 L, small and thin, 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 jaw bone, are immovably joined together. The 
 edges of most of the cranial bones interlock in a manner 
 similar to the dovetail joint of cabinet-makers. Each bone 
 has notched edges which fit accurately into hollows of the 
 adjacent bone; this kind of articulation (or suture) is well 
 shown in Fig. 16. 
 
 Comparison of the Upper and Lower Limbs and their 
 Supporting Arches. — The bones of the leg and arm have 
 already been enumerated, but certain resemblances and differ- 
 ences between the two (Fig. 17) are worth noting. It is 
 
THE HUM AS BODY. 
 
 clear that thev correspond very closely to one another in 
 general structure : the pectoral arch answers to the pelvic ; 
 
 Fig. 17.— The skeleton of the arm and leg. H, the humerus ; Cd, its articular 
 head which fits into the glenoid fossa of the scapula; l\ the ulna ; R. the radius ; O, 
 the olecranon ; Fe, the femur ; P, the patella ; Fi, the fibula ; T, the tibia. 
 
 the humerus to the femur ; the radius and ulna to the tibia 
 and fibula ; five metacarpal bones correspond to five meta- 
 
SHOULDERS .-INI) mills. 
 
 3i 
 
 tarsal, fourteen phalanges in the digits of the hand to four 
 teen in the digits of the foot ; and elbow and wrist joints, to 
 knee and ankle. There is, however, in the arm do separate 
 
 Fig. 18. — The skeleton of the trunk and the limb arches seen from the front. C, 
 clavicle ; S, scapula ; Or, innominate bone attached to the side of the sacrum dor- 
 sally and meeting its fellow at the pubic symphysis in the ventral median line. 
 
 bone at the elbow answering to the patella at the knee j but the 
 ulna bears a bony process, O, which is in early life a separate 
 bone and may be considered as corresponding to the patella. 
 There are in the adult carpus eight bones, in the tarsus but 
 
32 THE HUMAN BODY. 
 
 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 and the knee joint dorsally. 
 
 When we compare the functions of the limbs greater dif- 
 ferences appear. The arms have their parts light and mova- 
 ble to serve as prehensile organs ; the lower limbs have their 
 parts heavy and firmly knit together to carry the weight of 
 the body. Accordingly we find the shoulder girdle, C, S 
 (Fig. 18), attached to the axial skeleton only by the ventral 
 ends of the collar bones, and hence it is free to make con- 
 siderable movement, as in ''shrugging the shoulders." The 
 pelvic girdle, Oc, on the contrary, is firmly and immovably 
 attached to the sides of the sacrum. 
 
 The socket on the outer end of the shoulder blade, which 
 receives the upper end of the humerus to form the shoulder 
 joint, is very shallow, and allows much freer movement than 
 the deeper socket of the pelvis, into which the top of the 
 femur 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. 
 
 In the foot the bones are much less movable than in the 
 hand, but are so arranged as to make an elastic arch (Fig. 
 19) springing from the rear end of the heel bone, Ca, to the 
 anterior ends, Os, of the metatarsal bones. When we stand, 
 the weight of the body rests on the articular surface (Ta) at 
 the crown of the arch. 
 
 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, so 
 that the hand can seize and manipulate very small objects, 
 
PECULIAR//// S 01 1/1/ HUM/IN SKELETON. 
 
 33 
 
 wnereas this power ol opposing the great toe to tin- others is 
 nearly absent in the foot of civilized man. In infant-, and in 
 savages who have never worn boots, the great toe is often 
 movable, though it never acts so completely like a thumb as 
 
 T;. 
 
 cn 
 
 j 
 
 M5 Tn t'k ** S fLl 3 
 
 Fig. 19.— The bones of the foot. Ca. Calcaneum. or heel bone ; Ta, articular 
 surface for tibia on the astragalus ; Ci>, the cuboid bone. 
 
 it does in most apes, which use their feet for prehension nearly 
 as much as their hands. Our own toes by practice can be 
 made more movable ; persons born without hands have learned 
 to write and paint with the feet. 
 
 Peculiarities of the Human Skeleton. — Our power of main- 
 taining an erect posture and of walking without the aid of the 
 hands gives rise to interesting peculiarities in the structure of 
 the human skeleton. In no other vertebrate is the division of 
 labor between the anterior and posterior limbs carried so far; 
 even 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 keep 
 the head erect. In four-footed beasts the skull is carried on the 
 
 * 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 his chin. Since the muscles concerned in holding the 
 head erect have relaxed their vigilance, the greater weight of the front 
 half of the skull exerts its effect. 
 
34 
 
 THE HUMAN BODY. 
 
 front end of a horizontal backbone, and therefore needs spe- 
 cial ligaments and considerable mus- 
 cular effort to support it ; in apes the 
 skull does not balance on the top of 
 the spine, because the face is much 
 heavier than the brain. Therefore 
 to keep the head erect and look 
 things straight in the face " like a 
 man ' ' is very fatiguing and the po- 
 sition cannot long be maintained. 
 In men, on the contrary, the face 
 bones are relatively smaller and the 
 cranium larger, so that this position 
 
 Fig. 20.— The base of the skull. ° A 
 
 The lower jaw has been removed. j s maintained with ease. 
 At the lower part of the figure is 
 
 TSTL^u^SSSJ^ »■ The human spinal column, 
 Sis a P rr t he 8et paired e ope„i n A g b s 01 „ e f when viewed from the front, is seen 
 
 the posterior nares, and a short . ■ -, •[ i,-\ r . i 1 
 
 way above the middle of the fig- to widen gradually from the neck to 
 
 ure is the large median foramen . _ 
 
 fnagnum, with the bony convex- the sacrum, and is, therefore, well nt- 
 
 ities (or occipital condyles) 
 
 which articulate with the atlas, ted to sustain the weight of the head, 
 
 on its sides. It will be seen that 
 
 the part of the skull behind the upper limbs, etc. Its curvatures, 
 
 occipital condyles is about equal ■ ■ 7 
 
 &SSe%?i^i«t2ni whicb are peculiarly human, add 
 
 the occipital condyles would be ,1 .. i 1 • •. 
 
 much larger than that behind greatly to its spring and elasticity. 
 
 3. The pelvis, to the sides of 
 which the lower limbs are attached, is relatively broad in man, 
 so that the balance of the trunk on the legs is more strongly 
 maintained. 
 
 4. The lower limbs are proportionately much longer than 
 the arms 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 as, and of others 
 longer than, their legs. 
 
PECULIARITIES OF THE HUMAN SKELETON. 35 
 
 5. The arched instep and broad sole <>f the human fool are 
 verj characteristic. Most beasts, as horses, walk on the tips 
 of their tors, and the hoot" is really a very big toe nail; 
 others, as bears, place the heel on the ground to be sun*, but 
 have a less well developed tarsal arch than num. The vaulted 
 
 human tarsus, made up of a number of small bones, ca< h ol 
 whii h ran <_;lide a little over its neighbors, but none of whu h 
 can move much, is admirably calculated to break any jar 
 which might be transmitted to the spinal column by the inter- 
 mittent contact of the sole with the ground.* A well-arched 
 instep is therefore rightly considered beautiful ; it makes the 
 gait easier and more graceful. 
 
 * A carriage spring consists of two curved elastic steel bars fastened to- 
 gether at their ends, with their concave sides turned towards one another. 
 The axle of the wheel is attached to the middle of the lower har, and the 
 weight of the carriage bears on the middle of the upper. When the 
 wheel jolts over a stone the jerk is transmitted to the elastic arches, which 
 are each flattened a little, so that instead of a sudden jerk a gentle sway is 
 transmitted to the carriage. The tarsal arch of the human foot acts like 
 the upper half of a carriage spring. 
 
CHAPTER 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 composition. When alive they have a bluish- 
 white color, with a pinkish hue if blood is flowing through 
 them; they possess considerable flexibility and elasticity; 
 this 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 
 covered by a tough membrane, the periosteum, composed of 
 connective tissue and containing many blood vessels. During 
 the growth of the bone the periosteum deposits new bony 
 tissue upon it and is concerned in its nourishment through- 
 out life. When it is stripped off, the bone dies.f The 
 periosteum covers the humerus except on its ends (Cfi, Tr, 
 CpT) in the shoulder and elbow joints, where the bone is 
 covered by a thin layer of gristle or cartilage. Very early 
 in life the whole humerus consists of cartilage ; this is after- 
 
 * 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. 
 
 •j- 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 
 (left but slightly injured) has formed a new bone in place of the old. 
 
 36 
 
STRUCTURE Oh HONES. 
 
 37 
 
 Traj 
 
 — Em 
 
 
 •V 
 
 .-}>^,N 
 
 '/■fffi Vr> 
 
 /<t 
 
 i>^fe^ 
 
 ^/iV; 
 
 ^ 
 
 ™m 
 
 S4i£e 
 
 Fig. »i.— The right humerus, seen from 
 the front For description, see text. 
 
 Kr* &»££? 
 
 Fig. 22. — The humerus 
 cut open. a, marrow 
 cavity ; 7\ hard bone ; c. 
 spongy bone ; d, carti- 
 lage. 
 
38 THE HUMAN BODY. 
 
 wards absorbed and replaced by bone, leaving only a thin 
 layer of articular cartilage on each end. 
 
 The bone itself consists of an almost cylindrical middle 
 portion or shaft (extending between the dotted lines A' and 
 Z) and two articular extremities. These extremities are en- 
 larged to give a wider 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 mark areas where muscles were 
 fixed. 
 
 Internal Structure. — If the humerus is divided lengthwise, 
 we find that its shaft is 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 that 
 the marrow cavity extends nearly to the articular extremities ; 
 and that in these the bone has a loose, spongy texture, with 
 the exception of a thin dense layer on the surface. In the 
 shaft the compact outer layer is thick, whereas the spongy 
 portion forms only a thin stratum next the medullary cavity.* 
 To the unassisted eye the spongy (cancellated) bone appears 
 made up of a trellis-work of thin bony plates which intersect 
 in all directions and surround pin-head cavities. In these 
 , spaces there is found during life a substance known as the red 
 marrow,j which is quite different from the yellow fatty mar- 
 row of the medullary cavity. 
 
 Why Bones are Hollow. — If the bones were solid and of 
 their present size, they would be extremely heavy J and un- 
 
 * These facts may readily be demonstrated by sawing in two length- 
 wise the bones out of a leg of mutton. 
 
 f The red marrow forms red blood corpuscles. 
 
 % Many of the bones of birds are thin-walled tubes of dense bone : the 
 central cavity contains air and no marrow, and communicates by tubes 
 with the lungs. Examine the humerus of a pigeon or a rooster. 
 
STRUCTURE OF BOM 
 
 necessarily strong for the common purposes of life ; it they 
 were solid and of their present weight, t lid not give 
 
 sufficient surface for the attachment of muscles, and would be 
 easily broken. It is a well-known principle in prat tit al 
 that a tube will bear a greater >train than a solid 
 rod of the same length and amount of material ; hence iron 
 pillars are cast hollow, for it" solid they would be enormously 
 heavier without a proportionate increase in strength, 
 a glass tube and a glass rod each of the same length and 
 _it: support each at its ends and hang weights on the 
 middle until it breaks : the tul e will be found to bear a 
 much greater strain before breaking. We see an application 
 of this same principle in the hollow stalks of grass, wheat, 
 and barley and in the frames of bicycles. 
 
 Varieties of Structure Pound in Different Bones.— Bones 
 which, like the humerus and femur, present a shaft and 
 articular extremities are called Img bones ; other examples 
 are tibia and fibula, radius and ulna, metacarpal and meta- 
 • rs 1 bones, and the phalanges of fingers and toes. Tabular 
 bones form thin plates, like those of the roof of the skull, 
 and the shoulder blades. Short bones are rounded or angular, 
 and not much longer in one diameter than another, as the 
 carpal and tarsal (Fig. 19) bones. Irregular 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 on', 
 long bones possess a medullar}- cavity containing yellow mar- 
 row. The rest are filled up by spongy bone, covered 
 thin layer of ivory bone, and have red marrow in their spaces. 
 
4o 
 
 THE HUMAN BODY. 
 
 The Histology of Bone. — The microscope shows that com- 
 pact bone is really porous, and differs from spongy bone only 
 in the fact that its cavities are much smaller, and the hard 
 bony plates between them thicker. If a thin transverse sec- 
 tion of the shaft of long bone (Fig. 23) is examined with 
 a microscope magnifying about twenty diameters, even its 
 densest part will show numerous openings which become 
 gradually larger near the medullary cavity and pass insensibly 
 into the spaces of the spongy bone around it. These openings 
 
 Fig. 23. — A, a transverse section of the ulna, natural size, showing the medullary 
 cavity. B, the more deeply shaded part of A magnified twenty diameters. 
 
 are the cross-sections of tubes known as the Haversian canals, 
 the majority of which run through the bone in the direction 
 of its lone: axis and are united bv numerous cross branches. The 
 
HISTOL 
 
 4i 
 
 outermost Haversian canals open on the surface of the bone 
 beneath the periosteum, where they receive blood \< 
 which pass through them to convey materials for the bone's 
 growth and nourishment. 
 
 Around each Haversian canal is a series of plates or 
 lamella which, with the canal, form an Haversian system ; the 
 entire bone is made up of a large number of such systems, 
 with the addition of some lamellae which lie in the corners 
 between them, and some which have been formed bv the 
 periosteum on its outer surface. In the spongy bone the 
 Haversian canals are very large, and contain red marrow as 
 well as blood vessels, with only a few lamellae around each. 
 
 Fig. 24. — A small piece of bone, ground very thin and highly magnified. 
 
 If a bit of bone is still more magnified (Fig. 24 we find 
 that very small cavities called lacunae lie between the lamel- 
 lae ; from each lacuna radiate many extremely fine tubes, the 
 canalicult, so that it looks like a small animal with a great 
 many legs. The innermost canaliculi open into the Haver- 
 
42 THE HUMAN BODY. 
 
 sian 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 Haversian canal can ooze through 
 the bone. 
 
 In a living bone a nucleated cell, or bone corpuscle, lies in 
 each lacuna. These are the remnants of those cells which 
 built the bone, by making intercellular substance : each 
 one builds a sort of skeleton around itself which adheres to 
 the skeletons of the others to form the whole bone. 
 
 Chemical Composition of Bone. — Apart from the bone cor- 
 puscles and the soft contents of the Haversian canals and of 
 the spaces of the cancellated bone, the hard bony substance 
 proper is composed of animal and mineral matters so inti- 
 mately combined that the smallest distinguishable bit of bone 
 contains both. The mineral matters give the bone its hard- 
 ness and rigidity, and form about two thirds of its weight 
 when dried. They may be removed by soaking the bone in 
 diluted hydrochloric acid,* and the animal or organic part 
 of the bone is then left as a tough, flexible mass, which retains 
 perfectly the shape of the original bone. 
 
 When the bone is boiled in water, the greater part of the 
 animal portion is turned \nio gelatine (or glue) and is dissolved 
 in the water. Most of the gelatine which we buy in the shops 
 is obtained by boiling fresh bones in a closed vessel under 
 high pressure ; in this way, the water becomes much hotter 
 than when boiled in the air, and dissolves out the gelatine 
 
 * Add a couple of ounces of hydrochloric acid to a pint of water and 
 place a sheep's rib in the mixture for a day or so, after having previously 
 scraped the bone clean, and boiled it to get rid of the fat. It will be 
 found so flexible that a knot may be tied in it ; the specimen may be 
 preserved in strong brine or dilute alcohol from year to year for exhibition 
 to a class. 
 
HYG1ENL OF ski 1 1 ION. 43 
 
 more quickly. When a shin of beef is used to make soup the 
 bones are put in as well as the flesh, and the whole is kept 
 boiling for hours to extract the gelatine. The animal matter 
 of bone gives it toughness and elasticity. 
 
 The earthy portion may be obtained free from the animal 
 by calcining a bone in a bright fire. The residue is a white 
 and very brittle mass, which retains perfectly the shape of 
 
 the original bone. It is readily powdered and then forms 
 bone ash, which consists chiefly of the phosphate and carbon- 
 ate of calcium; most of the phosphorus of commerce is ob- 
 tained from it. If the burning be imperfect the animal matter 
 is charred but not altogether burnt away, and a black mass, 
 known as animal charcoal or " bone black," is left. 
 
 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 toler- 
 ably flexible and are capable of being distorted by a long 
 continued severe strain. For this reason it is important that 
 a child be made to sit straight, when writing or drawing, 
 to avoid the risk of producing a lateral curvature of the spinal 
 column ; and children should not be made to sit up during 
 the first year or to walk too early, as their bones are not 
 rigid enough to bear the weight of the body. The readi- 
 ness with which 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, for, 
 instead of allowing the arch of the foot to support squarely 
 
44 THE HUMAN BODY. 
 
 the weight of the body, they tilt the arch forward and throw 
 the weight upon the toes, which are thereby squeezed into 
 the front of 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 Indians (inhabiting the neighbor- 
 hood 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 grows rapidly and hence needs food containing 
 phosphateof lime, which is the chief mineral constituent of 
 bone. Of all common articles of diet, milk contains most 
 phosphate o f lim e : this is one great reason of its value as a 
 food for children. 
 
 Fracture. — A break in a bone is called a. fracture ; when 
 it is a clean break the fracture is simple; when the bone is 
 more or less broken into bits on each side of the break the 
 fracture is comminuted ; when the soft parts also are lacerated, 
 so that there is an opening from the skin to the broken bone, 
 the fracture is compound. 
 
 If a bone is broken the muscles attached to it tend to pull 
 its ends out of place; hence it requires to be "set," and 
 
HYGIENE OF SKELETON. 45 
 
 then kept in position by splints or bandages ; tins frequently 
 
 needs much skill and a thorough knowledge of the anatom) 
 ot the body. A surgeon should be summoned at once, as the 
 parts around the break ( ommonly swell very rapidly and make 
 the exact nature of the fracture hard to detect, and the re- 
 placment of the displaced ends ciihicult. 
 
CHAPTER A'. 
 
 JOINTS. 
 
 The Movements of the Body are brought about by means 
 of the soft reddish flesh known as the muscles, which are fa- 
 miliar to all in the lean of meat. * Muscles have the power 
 of contracting with considerable force ; they pull their ends 
 toward one another and swell out in the middle (Fig. 29) ; in 
 other words, they become shorter and thicker. With few 
 exceptions, each muscle is attached by its ends to two bones t 
 and overlaps the joint between them. When the muscle 
 shortens, or contracts, it produces movement at the joint. 
 The bones, joints, and muscles thus form the chief motor 
 mechanism of the body. 
 
 Joints. — Articulations which permit of movement by the 
 gliding of one bone on another are called joints; all are con- 
 structed on the same general plan, though the range and 
 
 * In many animals muscles kept most constantly in use are much red- 
 der than others, as, for example, the leg muscles of a chicken, which are 
 redder than those of the wings and breast, and as the coloring matter is 
 turned brown by heat, they form the •• dark meat" after cooking; in 
 birds which fly a great deal the breast muscles (which move the wings) 
 are also dark. The heart, which is a muscle always at work, is deep 
 red. even in fishes, most <>f whose muscles are pale. 
 
 v As an example of a muscle not attached to the skeleton, we may take 
 the orbicularis oris, which forms a ring around the mouth opening, be- 
 neath the ?-kin of the lips : when it contracts it closes the mouth, or if it 
 contracts more forcibly purses out the lips. The orbicularis palpebrarum 
 forms a similar ring around the eye opening, and when it contracts 
 Closes the eye. 
 
 46 
 
HIP JOINTS. 
 
 47 
 
 direction of movement permitted differ in different joints. 
 
 As an example we may take the hip joint. tion of which 
 
 is represented in Fig. 26. 
 
 Section through the hip joint. 
 
 On the outer side of the os innominatum 1 oi\ Fig. 26 | is a 
 deep hollow, the acetabulum, which receives the upper end of 
 the femur. The acetabulum is lined by a thin layer of car- 
 tilage (c) with an extremely smooth surface, and its cavity 
 is also deepened by a cartilaginous rim (r). The upper end 
 of the femur (/ \ consists of a nearly spherical head, borne on 
 a neck ; this head is covered by cartilage, and rolls smoothly 
 in the acetabulum like a ball in a socket. 
 
 Ligaments bind the ends of the bone- together to prevent 
 their displacement ; they are composed of connective tissue, 
 are extremely pliable but cannot be stretched, and are very 
 tough and strong. One is the capsular ligament (c. I. i, which 
 encloses the joint in a bag \ another is the round ligament 
 
48 THE HUMAN BODY. 
 
 (/. /.), Fig. 26, which passes from the rim of the acetabulum 
 along a groove in the bone to the centre of the round head of 
 the femur. 
 
 Covering the inside of the capsular ligament and continued 
 back to the edge of the cartilage of the head of the femur is 
 the very thin synovia/ membrane (j), composed of a layer of 
 flat cells. This pours into the joint a small quantity of synovial 
 liquid, which resembles in consistency the white of a raw egg, 
 and plays the part of oil in a machine by lubricating the joint 
 and enabling it to move smoothly and with little friction. 
 
 In its natural state the synovial membrane lies so that there 
 is practically no cavity left in the joint. The joint surfaces are 
 held in close contact, not by the ligaments (which are much too 
 loose and serve mainly to prevent such excessive movement as 
 might roll the femur 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 atmos- 
 phere is transmitted by the skin and muscles to the exterior of 
 the air-tight joint, and helps to keep its surfaces together. If 
 ail the muscles are 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 so firmly that the weight of the 
 limb will not draw it out ; but if the air is let into the joint by 
 cutting into the cavity, the thigh bone falls as far out of place 
 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 
 
 * The structure of joints can be readily seen in those of a fresh calf's 01 
 sheep's foot. The synovial membrane is so thin and so closely adherent 
 to the parts it lines that a microscope is needed for its demonstration; bui 
 all the other parts are readily made out. 
 
BALL AND SOCKET JOIS 49 
 
 is called a ball and socket joint, and allows a greater variety o( 
 
 movement than any other. The thigh can (i)t> . that 
 
 is, bent so that the knee approaches the chest, and 
 
 tended or straightened again ; it cai o that the 
 
 knee is moved away from the middle line of the body, and 
 
 ■/ducted or brought back again ; the limb can als 
 circumducted, i.e.. with knee and ankle held rigid, the whole 
 _ is swung round to describe a cone, of which the apex is at 
 the hip joint ; and finally 6) rotated, i.e., the whole limb 
 rolled to and fro on its long axis. All ball and socket joints 
 allow tlu^e movements to a greater or less extent. 
 
 Another important ball and socket joint is at the shoulder 
 between the upper end of the humerus and the hollow { glen- 
 oid 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, ox flexed dJ\o\ extended. Between the phalanges 
 of the fingers we find also hinge joints ; another is found be- 
 tween the lower jaw and the cranium, allowing us to open 
 and close the mouth. The latter is not, however, a perfect 
 hinge joint ; it permits also 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. * 
 
 * The object of these minor movements is to allow us our food ; 
 
 in carnivora, as cats, which bite but do not chew, the lower jaw forms a 
 perfect hinge joint with the cranium. 
 
5° 
 
 THE HUMAN BODY. 
 
 JT 
 
 B 
 
 R 
 
 Pivot Joints. — In this form one bone rotates about an- 
 other. 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 
 is kept in place there by the transverse ligament, which does 
 not let it press against the spinal cord. It 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 (supination) : the 
 radius and ulna are parallel. 
 Without moving the shoulder 
 joint at all turn the hand over 
 so that its back is upward (pro- 
 nation): the radius, carrying 
 the hand, crosses over the ulna* 
 (Fig. 27, A). 
 
 The lower end of the hume- 
 rus (Fig. 21) has a large artic- 
 ular surface ; on the inner two 
 thirds of this, Tr, the ulna fits, 
 and the grooves and ridges of 
 the bones interlock to form a 
 B A hinge joint, allowing us only to 
 
 Fig. 27. -A arm in supination; B, 1 j riraicrhtMi the elbow 
 
 arm in pronation. H, humerus; R, L>enCl Or Sliaigllten me eiUOW 
 radius; U. ulna. . . r™ -,■ r, .1 
 
 joint. I he radius nts on the 
 rounded outer third, Cpl, and rotates there when the hand 
 
 U 
 
 * The movements and positions of the bones throughout the forearm 
 and elbow joint may be observed by means of deep pressure with the 
 fingers of the other hand. 
 
A SPRAIN. 5 1 
 
 is turned over, the ulna forming a fixed axis around which it 
 moves. 
 
 Gliding Joints as a rule permit of but little movement. 
 Examples arc found between tin- closely pa< ked bon< 
 the carpus and of the 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 sur- 
 rounding soft parts injured. This generally leads to inflam- 
 mation and swelling, which make it difficult to find out in 
 what direction the bone has been displaced, and also greatly 
 add to the difficulty of replacing it, or, in surgical language, 
 of reducing the dislocation. The muscles attached to it are, 
 moreover, apt to pull the dislocated bone more and more 
 out of place. In most cases the reduction of a dislocation 
 can only be attempted with safety by one who knows the 
 forms of the bones and possesses sufficient anatomical knowl- 
 edge 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, without dislocation 
 of the bones. A sprained joint should as a rule get imme- 
 diate and complete rest, continued for weeks if necessary; if 
 there be much swelling or continued pain, medical advice 
 should be obtained. Perhaps a greater number of permanent 
 injuries result from neglected sprains than from broken bones. 
 
 * Dislocations of the fingers can usually be reduced by strong pulling, 
 aided by a little pressure on the parts of the bones nearest the joint. The 
 reduction of a dislocation of the thumb is much more difficult, and can 
 rarely be accomplished without skilled assistance. 
 
CHAPTER VI. 
 
 THE MUSCLES. 
 
 The Muscles of the human body are more than five_hum: 
 dred in number: they vary much in size, from tiny one- at- 
 tached to the bones of the ear to that on the front of the thigh 
 (29, PI. II), which passes from the pelvis to the tibia and is 
 eighteen inches or more in length. Whatever their size, 
 muscles have a similar structure and the same properties : 
 their variety, forms, and sizes depend on the work they have 
 to do. In addition to their primary function of moving the 
 body the muscles give it roundness and shapeliness ; they also 
 help to enclose cavities, 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 soft red middle part, called its belly , which tapers 
 towards each end, where it passes into one or more dense, white, 
 inelastic cords (tendons), made of connective tissue, which at- 
 tach the muscle to parts of the skeleton.-;' In Fig. 28 are shown 
 
 * 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, im- 
 merse a frog in it, and cover the vessel. In a minute the animal will be 
 quite insensible ; its head can then be cut oft and its spinal cord destroyed 
 by running a pin along it, without causing the animal any pain. Nov/ 
 make circular cuts through the skin at the top of the thighs and then peel 
 the skin off like a pair of hose : it will come quite easily except about the 
 knee joint, where it may be necessary to divide carefully 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 
 
THE PARTS Oh A MUSCLE. 
 
 53 
 
 some of the muscles of the arm. It 
 will be seen that some (i, 2, 3) ] 
 from arm to forearm : others ( 7, 6, 5. 
 4, 8, 9) start from the forearm bones 
 and pass to the bones of the hand ; 
 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 phalanges. 
 
 The belly of a muscle is its work- 
 ing part ; it receives nerves which 
 when excited cause it to contract. 
 In so doing it pulls on the tendons, 
 and they transmit the pull to the 
 parts to which they are attached. 
 
 The tendons are often quite long, 
 as for example that of the common 
 extensor muscles of the fingers (5, 
 Fig. 28), whose belly is in the upper 
 half of the forearm, but whose tendon, 
 dividing above the wrist, is dis- 
 tributed to the joints of the fingers. 
 The muscles which straighten the 
 thumb (8, 9, and 10) are also seen to 
 have long slender tendons. This ar- 
 Fig. 2 8.-The muscles on the rangement makes the limbs light and 
 
 back of the hand, forearm, and 
 
 lower half of the arm, as exposed slender. 
 
 on dissecting away the skin. 
 
 muscle turned upwards, it will be found to have at the upper end of its 
 
 thick rounded belly a pair of short tendons. 
 
54 
 
 THE HUMAN BODY. 
 
 Some muscles pass over two joints and can produce move- 
 ment at either ; the biceps of the arm ; fixed above to the 
 
 Fig. 29. — Back view of the muscles of the trunk 
 Fig. 30. —Front view of the muscles of the trunk. 
 
 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 and hardening 
 may be seen and felt on the biceps in front of the humerus 
 when the elbow is bent, or in the ball of the thumb when it 
 is moved so as to touch the little finger. The swelling and 
 hardening of a contracted muscle are daily illustrated when 
 one schoolboy invites another to feel his "biceps." 
 
VARUTlt S Oh MUSCLIS. 
 
 55 
 
 The Origin and Insertion of Muscles. — That part of the 
 skeleton to which the inner (i.e., nearer the centre of the 
 bod} ) end of the muscle is attached is (ailed its origin ; that 
 to which the outer is attached is called its insertion. Ordi- 
 narily, the origin is the less movable end. This may be seen 
 in the arm, where we find that when the belly of the muscle 
 
 Fig. 31. — The biceps muscle and the arm bones, to illustrate how, under ordinary 
 circumstances, the elbow joint is flexed when the muscle contracts. 
 
 contracts and pulls on its tendons, the result is commonly that 
 only the forearm (insertion) is moved, the elbow joint being 
 bent as shown in Fig. 31 ; the shoulder (origin) is firm and 
 serves as a fixed point. The distinction is, however, only rel- 
 ative : if the radius were held immovable the muscle would 
 move the shoulder toward the radius, instead of the radius 
 toward 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 toward each end, as A, 
 Fig. 32 ; others divide at one end, and are called two-headed 
 or biceps muscles, and some are even three-headed or triceps 
 (back of upper arm). On the other hand, some muscles have 
 no tendon at one end, the belly itself being attached to the 
 
56 
 
 THE HUMAN BODY. 
 
 bone ; a few have no tendon at either end. Sometimes a 
 tendon runs along the side of a muscle, and the fibres of the 
 latter are attached to it obliquely (£, Fig. 
 32); such a muscle is called penniform or 
 featherlike, from a fancied resemblance to 
 the vane of a feather ; or a tendon may run 
 down the middle of the muscle ( C) , which 
 is then called bipenniform. Sometimes a 
 tendon is found in the middle of the belly 
 as well as at each end (Fig. 33); such a 
 Fig. 32. — Diagrams muscle is called hvo-beUied or digastric. 
 
 illustrating, A , typical 
 
 muscle with a central Running along the front of the abdomen, 
 
 belly and two terminal ° ° ' 
 
 £?m° mLscfe ■ cTbi- from the pelvis to the chest, on each side 
 
 penniform muscle. q{ ^ mi(Wle j;^ J g a long musc \^ the 
 
 straight muscle of the abdomen (rectus abdo??i in is); it is poly- 
 gastric, consisting of four bellies separated by short tendons. 
 
 Many muscles are not rounded, but form 
 
 a 
 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, that is, 
 
 they have corresponding muscles upon the 
 
 opposite side.* The muscles are attached to the bones 
 
 in such a way as to cause motion in all directions permitted 
 
 by the joint. Thus some muscles oppose others, as, for 
 
 example, the biceps muscle (Fig. 31), which lies in front 
 
 of the humerus and bends the elbow joint, antagonizes the 
 
 triceps muscle, which lies behind the arm bone and extends the 
 
 elbow ; when the biceps contracts the triceps relaxes, and vice 
 
 versa. This orderly working is carried out by means of the 
 
 * The single muscles cross the middle line and are made up of similar 
 right and left halves; examples are orbicularis oris and the diaphragm. 
 
 Fig. 33. — A digas- 
 tric muscle. 
 
THE GROSS STRUCTURE OF A MUSCLE. 57 
 
 brain and spinal cord, which, through the nerves, govern the 
 muscles and regulate their activity. In convulsions these con- 
 trolling organs are out of gear, and the muscles are excited to 
 
 Fig. 34. — Side view of the muscles of the face and 
 
 contract in all sorts of irregular and useless ways ; antagonists ' 
 pulling against one another at the same moment cause the 
 whole body to become rigid. 
 
 The Gross Structure of a Muscle. — Each muscle is an^ 
 organ composed of several tissues. Its essential constituent is 
 numbers of striped fibres constituting striped muscular tissue. J 
 These are supported and protected by connective tissue, in-/ 
 tertwined with blood and lymph vessels which convey noury 
 
5* 
 
 THE HUMAN BODY. 
 
 ishment and carry off waste matters, and penetrated by 
 nerves which govern their activity. 
 
 A loose sheath of connective tissue, the perimysium, en- 
 velops the whole muscle in a sort of case ; from it partitions 
 
 run in and subdivide the 
 belly of the muscle into 
 bundles ox fasciculi which 
 run from tendon to ten- 
 don, or the whole length 
 of the muscle when it has 
 no tendons. The coarse- 
 
 Fig. 35. — A small bit of muscle composed of .. - 
 
 four primary fasciculi. A, natural size ; E, the neSS Or tmeneSS Ot meat 
 
 same magnified, showing the secondary fasciculi . 
 
 of which the primary are composed. ' depends On the Size of 
 
 these fasciculi, which may be readily seen in a piece of boiled 
 beef. In good carving, meat is cut across the fasciculi, or 
 " across the grain, " as it is then more easily broken up by the 
 teeth ; the polygonal areas seen on the surface of a slice of beef 
 are cross sections of the fasciculi. The larger fasciculi are 
 subdivided by fine partitions of connective tissue into smaller 
 (Fig. 35), each consisting of a few muscular fibres enveloped 
 in a close network of minute blood vessels. Where a muscle 
 tapers the muscle fibres in the fasciculi are less numerous, and 
 when a tendon is formed they disappear altogether, leaving 
 only the connective tissue. 
 
 Histology of Muscle. — The striped ??iuscular tissue, which 
 gives the muscle its power of contracting, is found when ex- 
 amined by the microscope to be made up of extremely slender 
 muscle fibres, each about one inch in length, but most of them 
 less than jfa of an inch across. 
 
 Each muscle fibre has externally a thin sheath or envelope, 
 the sarcolemma, which envelops the contracting part of the 
 
PL41S MUSCULAR TISSUE. 
 
 59 
 
 fibre. This latter is soft and almost semi-fluid ; under a 
 microscope it is seen to present a striped appearance, as if 
 made up of alternating dimmer and brighter 
 transverse bands Fig. j6). After death 
 the contents of the fibre solidify and death- 
 stiffening results ; at the same time the fibre 
 often splits up into a number of very fine 
 threads or fibrilLe, which were formerly re- 
 garded as true constituents of the living mus- 
 cular fibre. 
 
 The contraction of a voluntary muscle, as 
 the calf muscle of the leg of a frog, is very 
 rapid, as the entire twitch, including contrac- 
 tion and relaxation, takes but one tenth of a 
 second. 
 
 F:g. 
 
 -A small 
 
 piece of muscular fi- 
 
 Plam Muscular Tissue. — I he muscles bre highly magni- 
 fied. At a the fibre 
 
 hitherto spoken of are all more or less under has . been crushed 
 
 r and twisted so as to 
 
 the control of the will 
 
 we can make them tear , its u contents, 
 
 while the tougher 
 
 contract or prevent this as we choose; they wher^^ctoseh-ap^ 
 are therefore often called the voluntary mus- [o^be^nlilibi" 1 rS 
 
 . j. ,.,. -iiii i mains untorn and 
 
 cles. I here are in the body other muscles conspicuous. 
 
 * No sharp line can be drawn between voluntary and involuntary mus- 
 he muscles of respiration are to a certain extent under the control of 
 the will: any one can draw a long breath when he chooses. But in ordi- 
 nary quiet breathing we are quite unconscious of their working. an«: 
 when we pay heed to it our control of them is limited; no one can hold 
 his breath long enough to suffocate himself. Indeed, any one of the 
 striped muscles may be thrown into activity, independently or even against 
 the will, a? we see in the •• fidgets" of nervousness, and the irrepressible 
 trembling of extreme terror. Functionally, when we call any muscle 
 voluntary, we mean that it may be controlled by the will, but not that it 
 — arily alv. structurally, the heart occupies an intermedi- 
 
 ate place: its striped fibres resemble much more those of voluntary than 
 voluntary muscles, but its beat is not subject to the will. 
 
60 THE HUMAN BODY. 
 
 whose contractions we cannot control, and which are 
 hence called involuntary muscles ; they are not attached 
 to the skeleton directly, nor concerned in our ordinary 
 movements, but lie in the walls of various hollow organs 
 
 Fig. 37. — The muscular coat of the stomach. 
 
 of the body, as the stomach (Fig. 37), the intestines, and the 
 arteries ; by their contractions they move the contents of 
 those cavities. Like the voluntary muscles, the involun- 
 tary consist of contractile elements, with accessory connective 
 tissue, blood vessels, and nerves ; but they are much shorter 
 and smaller, and their fibres have a very different appearance 
 under the microscope.* They are not cross striped, but are 
 elongated cells united by a small amount of cementing 
 material. Each cell (Fig. 3S) is flattened and tapers off 
 towards its ends ; in its centre is a nucleus with one or two 
 
 * The smooth muscle fibres vary much in size in different organs. 
 An average might be: Length 5^ in. to ^in.; breadth ^Jp in. to 
 T _i_ ¥ in. They are thus seen to be about as lung as the voluntary muscle 
 fibres are broad. 
 
BEEF Tl.i. 
 
 61 
 
 nucleoli. The cells have the power of shortening in the dire* 
 tion of their long axes, but arc very slow in 
 their action. 
 
 Heart Muscle. -The muscular tissue of the 
 
 heart is not under the control of tin- will ; it, 
 however, is cross striped, and more like the 
 voluntary than the ordinary involuntary mus- 
 cle, though it differs from both. The con- 
 traction of the heart muscle is slower than 
 that of voluntary muscles, but more rapid than 
 that of the involuntary muscles. 
 
 Speaking generally, we may say that the 
 movements necessary for the nutrition of the 
 body are not left for us to look after, but 
 aie carried on by muscles which work invol- 
 untarily; the blood is pumped by the heart, 
 and food churned in the stomach and passed m iSe 3 ceFsY(HigSiy 
 along by the intestines, whether we think magm e "' 
 about it or not. 
 
 The Chemical Composition of Muscle. — Muscle contains 
 about 75 per cent, of water and a considerable quantity of 
 salts. Living, resting muscle is alkaline ; hard worked or 
 dying muscle is acid. Its chief organic constituents are 
 proteid or albuminous substances (p. 15), and of these the 
 most abundant in a perfectly fresh muscle is myosin. Soon 
 after death the myosin clots. Dilute acids dissolve myosin 
 and turn it into syntonin, which used to be thought the chief 
 proteid of muscle. 
 
 Beef Tea. — When _ean meat is heated its myosin is 
 converted into a solid insoluble substance much like the 
 white of a hard boiled egg. Hence when a muscle is boiled 
 most of its proteid is coagulated and stays in the meat in- 
 
6 2 THE HUMAN BODY. 
 
 stead of passing out into the water. Even if beef be soaked 
 first in cold water this is still the case, as myosin is not sol- 
 
 Fig. 39. — Fibres from the heart showing the striations and the junctions of the 
 cells. Highly magnified. 
 
 uble in water.* It follows that beef tea as ordinarily made 
 contains little but the flavoring matters and salts of the beef, 
 and some gelatin dissolved out from the connective tissue of 
 the muscle. The flavoring matters make it taste as if it were 
 a strong solution of the whole meat, whereas it contains but 
 a small proportion of the really nutritious parts, which are 
 left behind in tasteless shrunken shreds when the liquor is 
 poured off. Some things dissolved out of the meat make 
 beef tea a stimulant to the nervous system and the heart, but 
 its nutritive value is small, and it cannot be relied upon to 
 keep up a sick person's strength for any length of time. 
 
 * To get over this difficulty, various methods of making beef tea have 
 been suggested, in which the chopped meat is soaked an hour or two in 
 strong brine or in very dilute muriatic acid. In these ways the myosin 
 can be dissolved out of the beef; but the product has such an unpleasant 
 taste that no one is likely to swallow it, and least of all a sick person, 
 
EXFLANATH >X < >F PLATE IT. 
 
 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 Xeck : 
 
 i. Muscle '>f the Forehead. This, together with a muscle at the back of the head, 
 lias the power of moving the scalp. 
 i. Muscle that closes the Eyelids. The muscle that raises the upper eyelid s 
 
 open the eye is situated within the orbit, and consequently cannot be seen in 
 
 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, ana those that depress the lower lip, 
 
 the lips are separated. 
 8. Muscle that draws the Lips together. 
 '. 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 Xeck, 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 ele- 
 vate the same parts are placed beneath the lower jaw, and cannot be seen in 
 the figure. 
 
 Muscles that connect the upper extremity of the trunk. Portions of 
 four of these muscles are represented in the figure, viz. : 
 
 15 Muscle that elevates the Shoulder. Trapezius Muscle. 
 
 17. (ireat Muscle of the Chest, which draws the Arm in front of the Chest t^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, which extends between the Ribs and Shoulder blade, and draws 
 the Shoulder forwards and rotates it, a movement which takes place in the ele- 
 vation of the arm above the head (Serratus magnus). 
 
 At a 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. Cuter Oblique Muscle of the Abdomen. 
 
EXPLANATION OF PLATE II. 
 
 Several muscles lie beneath it. The outline of one of these, 
 
 21. Straight Muscle of the Abdomen, may be seen beneath the expanded tendon of 
 insertion of the oblique muscle. These abdominal muscles, by their contraction, 
 possess the power of compressing the contents of the abdomen. 
 
 Muscles of the upper extremity : 
 
 16. Muscle that elevates the Arm (Deltoid Muscle). 
 
 22. Biceps or Two-headed Muscle (see also page 55). 
 
 23. Anterior Muscle of the Arm. This and the Biceps are for the purpose of bend- 
 ing the Forearm. 
 
 24. Triceps, or Three-headed Muscle. This counteracts the last two muscles, for it 
 extends the Forearm. 
 
 25. Muscles that bend the Wrist and Fingers, and pronate the Forearm and Hand 
 — that is, turn the Hand with the palm downwards. They are called the Flexor 
 and Pronator Muscles. 
 
 26. Muscles that extend the Wrist and Fingers, and supinate the Forearm and Hand 
 — that is, turn the hand with its palm upwards. They are called the Extensor 
 and Supinator Muscles. 
 
 ry. Muscles that constitute the ball of the thumb. They move it in different direc- 
 tions. 
 
 28. Muscles that move the Little Finger. 
 
 Muscles which connect the lower extremity to the pelvic bone : (Sev- 
 eral 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 bend- 
 ing the knee. 
 
 30. Muscles that draw the Thighs together (Adductor Muscles). 
 
 31. Muscles that extend or straighten the Leg (Extensor Muscles). The muscles 
 that bend the Leg are placed on the back of the thigh, so that they cannot be 
 seen in the figure. 
 
 Muscles of the leg 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 fool inwards, so as to counteract the last- 
 named muscles, lie beneath the great muscles of the calf, which conse- 
 quently conceal them. The foot possesses numerous muscles, which act 
 upon the toes, so as to move them about in various directions. These are 
 principally placed on the sole of the foot, so that they cannot be seen in the 
 fio-ure. Only one muscle, 36, which assists in extending the toes, is placed 
 on the back of the foot. 
 
27 -"*'• 
 
 </ 
 
 36 
 
 PLATE II.— THE SUPERFICIAL MUSCLES OF THE FRONT OF THE BODY. 
 
MEAT EXTRACTS. 
 
 Liebig's Extract of Meat is essentially but a concentrated 
 
 beef tea ; from its stimulating eflfa t it is often useful to per- 
 sons in feeble health, but other food should be given with it. 
 It contains all the flavoring matters of the meat, and its 
 proper use is for making gravies and flavoring soups; the 
 erroneousness of the common belief that it is a highly nutri- 
 tious food cannot be too strongly insisted upon, as sick per- 
 sons may be starved on it. 
 
 Various meat extracts are now prepared by subjecting beef 
 to chemical processes in which it undergoes changes like 
 those experienced in digestion. The myosin is thus made 
 soluble in water and uncoagulable by heat, and a real con- 
 centrated meat extract is obtained. Before relying on any 
 one of them for the feeding of an invalid, it would, however, 
 be well to insist on having a statement of its method of 
 preparation, and then to consult a physician, or some one 
 else who has the requisite knowledge, in order to ascertain if 
 the method is such as might be expected to attain the end 
 desired 
 
CHAPTER VII. 
 
 MOTION AND LOCOMOTION. 
 
 The Special Physiology of Muscles. — The distinctive 
 property of muscular tissue (i.e., its power of contraction) is 
 everywhere the same ; but the uses of different muscles are 
 varied by reason of their different positions and mechanical 
 condition. Some are muscles of respiration, others of swal- 
 lowing ; some bend joints and are called flexors, others 
 straighten them and are called extensors, and so on. The 
 determination of the exact use of any particular muscle is 
 known as its special physiology, as distinguished from its gen- 
 eral physiology, or properties as a muscle. We may here 
 consider the special physiology of the muscles concerned in 
 standing and walking. 
 
 Levers in the Body. — In nearly all cases the voluntary 
 muscles perform their work with the co-operation of the 
 skeleton. When muscles move bones the latter are to be 
 regarded as levers whose fulcra lie at the joint where the 
 movement takes place. Examples of the three forms of 
 levers recognized in mechanics are found in the human body. 
 
 Levers of the First Order. — In this form (Fig. 40) the 
 fulcrum or fixed supporting point, F, lies between the weight 
 to be moved and the moving power. The distance PF 
 from the power to the fulcrum is called the power-arm of the 
 lever, and the distance WF is the weight-arm. When 
 
 64 
 
I. I'M.: . 65 
 
 r arm and weight-arm are equal (a>. in an ordinal") 
 of scales) do mechanical advantage is gained; to lift a 
 
 F 
 
 W 
 
 Fig 4^. A lever of the first order. F, fulcrum ; P, power; U', resistance or 
 
 „:it. 
 
 pound at IT. P must lie pressed down with a force slightly 
 greater than a pound ; and the end \V will go up just as far 
 as the end P goes down. If PFbe longer than WF, then a 
 small weight at P will balance a larger one at W, the gain 
 being greater the greater the difference in the length of the 
 arms, but the distance through which W is moved will be 
 han that through which P moves ; for example, if PF is 
 twice as long as WF, then half a pound at P will balance a 
 pound at W, and a little more than half a pound laid on the 
 end P will lift a pound on the end W t but IT will only go 
 up half as far as P goes down. On the other hand, if the 
 weight-arm is longer than the power-arm there will be a loss 
 in force, but a gain in the distance through which the weight 
 is moved. 
 
 An example of levers of the first order is found in nod- 
 ding movements of the head, the fulcrum being where the 
 
 F 
 
 W 
 
 Fig. 41. — A lever of the second order. F, fulcrum ; P y power; W. weight. The 
 arrows indicate the direction in which the forces act. 
 
 occipital bone articulates with the atlas (Fig. 20). When 
 the chin is raised the power is applied to the skull behind 
 
66 THE HUMAN BODY. 
 
 the fulcrum by muscles passing from the spinal column to 
 the back of the head ; the resistance to be overcome is the 
 excess in weight of the part of the head in front of the ful- 
 crum over that behind it. and is not great, as the head is 
 nearly balanced on the top of the spine. To let the chin 
 drop does not necessitate any muscular effort. 
 
 The pull of the triceps to straighten the arm, and of the 
 calf muscles in rising on the toes, are additional examples of 
 the action of levers of the first class ; the fulcrum in each 
 case is at the joint, as it is in all the lever systems of the 
 body. 
 
 Levers of the Second Order. — In this form of lever (Fig. 
 41) the weight or resistance acts between the fulcrum and 
 the power. The power-arm, PF, is accordingly always longer 
 than the weight-arm, WF. and so a comparatively weak 
 force can overcome a considerable resistance. There is, 
 however, a loss in rapidity and extent of movement, since 
 it is obvious that when P is raised a certain distance W will 
 be raised less. Levers of this class are practically unknown 
 in muscular action. 
 
 Levers of the Third Order. — In these (Fig. 42) the 
 power is applied between the fulcrum and the weight ; hence 
 the power-arm, PF } is always shorter than the weight-arm, 
 
 W 
 
 F 
 
 Fig. 42. — A lever of the third order. P, fulcrum ; P, power ; W y weight. 
 
 WF. The moving force acts at a mechanical disadvantage, 
 but swiftness and range of movement are gained. This is the 
 
PULLEYS IN THI BODYSTANDlh <>; 
 
 form of lever mosl commonl) used in the body. For exam 
 pie, when the forearm is bent up towards the arm, the 
 fulcrum is the elbo* joint ( Fig. ^i ); the power is applied at 
 
 the insertion of the biceps mus< le into the radius ; the weight 
 is that of the forearm and hand and whatever may be held in 
 the latter, and acts at the centre of gravity of the whole, 
 somewhere on the far side of the point of application of the 
 power. Usually (as in this case) the power arm is very 
 short, so as to gain speed and extent of movement, the mus- 
 cles being strong enough to work at a considerable me- 
 chanical disadvantage. The limbs are thus also made much 
 more shapely than would be the case were the power applied 
 near or beyond the weight. 
 
 Pulleys in the Body. — Fixed pulleys are used in the 
 body ; they give rise to no loss or gain of power, but serve 
 to change the direction in which certain muscles pull. One 
 of the muscles of the eyeball, for example, has its origin at 
 the back of the eye socket, from there it passes to the front 
 and ends in a long tendon, before it reaches the eyeball. 
 This tendon passes through a ring attached to the margin of 
 the frontal bone, and then turns back to its insertion on the 
 eyeball. The direction in which the muscle moves the eye 
 is thus quite different from what it would be if the tendon 
 went directly to the eyeball. 
 
 Standing. — We slowly learn to stand in the first year after 
 birth, and though we finally come to do it without conscious 
 attention, standing always requires the co-operation of many 
 muscles, guided and controlled by the nervous system. The 
 influence of the latter is shown by the fall following a severe 
 blow on the head, which has fractured no bone and injured 
 no muscle ; "the concussion of the brain " stuns the man, 
 and until it has passed off he cannot stand. 
 
68 THE HUMAN BODY. 
 
 When we stand erect, with the arms close by the sides and 
 the feet together, the centre of gravity of the whole adult body 
 lies at the articulation between the sacrum and the last lumbar 
 vertebra, and a vertical line drawn from it will reach the 
 ground between the feet. In any position in which this vertical 
 falls within the space bounded by a line drawn close around 
 both feet, we can stand. When the feet are together the area 
 enclosed by this line is small, and a slight sway of the trunk 
 will throw the centre of gravity of the body outside it ; the 
 more one foot is in front of the other, the greater the sway 
 back or forward which will be compatible with safety, and the 
 greater the lateral distance between the feet, the greater the 
 lateral sway which is possible without falling. Consequently, 
 when a man wants to stand very firmly he advances one foot 
 obliquely, so as to increase his base of support in both direc- 
 tions. 
 
 In consequence of the flexibility of its joints a dead body 
 cannot be balanced on its feet as a statue can. When we 
 stand, the ankle, knee, and hip joints, if not braced by the 
 muscles, give way, and the head also falls forward on the 
 chest. But (Fig. 43) muscles (1) in front of the ankle joint, 
 and others (I) behind it, by contracting at the same time, 
 keep the joint from yielding ; similarly the contraction of 
 muscles (2) in front of the knee and hip joints, with their an- 
 tagonists (II), make these joints rigid; in like manner, the 
 muscles (III) which run from the pelvis to the back of the head 
 pull against those (3 and 4) which run from the pelvis to the 
 lower end of the breastbone, and from the upper end of the 
 breastbone to the anterior part of the skull, and their bal- 
 anced contraction keeps the head erect. Since the degree 
 to which each muscle concerned contracts when we stand must 
 be accurately adjusted to the contraction of its antagonist 
 
WALKING. 
 
 
 I 
 
 on the opposite side of the joint, we may easily < omprchend 
 u hy it takes us some time to learn to stand, and why a stunned 
 
 man, whose mus< les have lost guidan< e 
 from the nervous system, tails. 
 
 Locomotion includes all movements of 
 the body in space, dependent on its own 
 
 unaided muscular efforts, such as walking, 
 running, leaping, and swimming. 
 
 Walking. — In walking, the heel of the 
 advanced foot reaches the ground before 
 the toe of the rear foot has been raised Ij 
 
 from it. In each step the advanced leg 
 supports the body, and the rear foot 
 propels it. 
 
 A little attention will enable any one 
 to analyze the act of walking for himself. 
 Stand with the heels together and take i III 
 
 a step, commencing with the left foot. The 
 whole body is at first inclined forwards, 
 the movement taking place mainly at 
 the ankle joints. This throws the centre 
 of gravity in front of the base formed by 
 the feet, and a fall would result were 
 not the left foot simultaneously raised by 
 
 n 
 
 Fig. 
 
 -Diagram illus- 
 
 bending the knee a little, and swung for- trating the muscles (drawn 
 
 ° ' ° in thick black lines) 
 
 wards, the toes just clear of the ground and " h , ich , P. ass . Mure . and 
 
 ' J ° behind the joints, and by 
 
 the sole nearly parallel to it. When the £* <£*£* ri ^J 
 step is completed the left knee is straight- tie )0 ye 
 ened and the foot placed on the ground, the heel touching 
 first ; the base is thus extended in the direction of the 
 stride and the fall prevented. Meanwhile the right leg 
 is kept straight but inclined forwards, carrying the trunk 
 
70 THE HUMAN BODY. 
 
 during the step while the left foot is off the ground ; the 
 right foot is now raised, commencing with the heel, and 
 when the step of the left leg is completed, only the great 
 toe of the right is in contact with the support. With 
 this toe a push is given which sends the body swinging for- 
 ward, supported on the left leg, which now in turn is kept 
 rigid except at the ankle joint ; the right knee is immedi- 
 ately bent and that leg swings forwards, its foot just clear of 
 the ground, as the left did before. The body meanwhile is 
 supported on the left leg alone. When the right leg com- 
 pletes its step its knee is straightened and the foot thus 
 brought, heel first, on the ground : while it is swinging for- 
 wards the left heel is gradually raised, and at the end of the 
 step the great toe alone is on the ground ; with this a push is 
 given as was the case with the right foot, and the left leg 
 then swings forward to make the next step. Walking may, 
 in fact, be briefly described as the act of continually falling 
 forward and preventing the completion of the fall by thrust- 
 ing out a leg to meet the ground in front. 
 
 During each step the body sways a little from side to side, 
 as it is alternately borne by the right and left legs. It also 
 sways up and down a little ; a man standing with his heels 
 together is taller than when standing with one foot advanced, 
 just as a pair of compasses held erect on its points is higher 
 when its legs are together than when they are apart. In that 
 period of each step when the advancing trunk is balanced 
 vertically over one leg, the walker's trunk is more elevated 
 than when the front foot also is on the ground. Women, 
 accordingly, often find that a dress which clears the ground 
 when they are standing sweeps the pavement when they 
 walk. 
 
 The length of each step is primarily dependent on the 
 
HYGIENE OF THE MUSCLL 71 
 
 th of the legs, though it can be controlled by muscular 
 effort ; this control we see in a regiment of soldiers, all of 
 
 whom have been taught to take the same stride, no matter 
 how their legs vary in length. In natural easy walking, little 
 muscular effort is employed to carry the rear leg forward 
 
 after it has given its push : it swings on like a pendulum 
 when its foot is clear of the ground. As short pendulums 
 swing faster than long ones the natural step of short-lc. 
 people is quicker than that of long-legged. 
 
 Running differs from walking in several respects. There 
 is a moment when both feet are off the ground; the toes 
 aione come in contact with it at each step ; and the knee 
 joint is not straight at the end of the step. In running. 
 when the rear foot is to leave the ground the knee is sud- 
 denly straightened and the ankle joint extended so as to push 
 the toes forcibly on the ground and powerfully impel the 
 whole body forwards and upwards. The knee is then flexed 
 and the foot raised before the toes of the front foot reach the 
 ground. In each step the raised leg is forcibly drawn for- 
 ward and not allowed to swing passively as in quiet walking. 
 This increases the rate at which the steps lollow one another, 
 and the one-legged jump that occurs through the jerk given 
 by the straightening knee of the rear leg, just before it leaves 
 the ground, increases the distance covered at each step. 
 
 Hygiene of the Muscles. — The healthy working of the 
 muscles is dependent on a healthy state of the body in gen- 
 eral. Hence good food and pure a ir are necessary for a 
 vigorous muscular system. Muscles also should not be ex- 
 posed to any considerable continued pressure, since this in- 
 terferes with the flow of the blood and lymph essential for 
 their nutrition. 
 
 Exercise is necessary for the best development of the 
 
72 THE HUMAN BODY. 
 
 muscles. A muscle long left unus ed diminishes in bulk and 
 degenerates in quality, as is well seen when a muscle is para- 
 lyzed and remains permanently inactive because of injury to 
 its nerve ; although at first the muscle itself may be perfectly 
 healthy, it alters in a few weeks, and when the nerve is re- 
 paired the muscle may be incapable of activity. The same 
 fact is illustrated by the feeble and wasted state of the mus- 
 cles of a limb which has been kept motionless in splints for a 
 long time ; when the splints are removed, it is only after 
 careful and persistent exercise that the long idle muscles 
 regain their former size and power. The great muscles of 
 the "brawny arm*' of the blacksmith illustrate the converse 
 fact — the growth of muscles when exercised. 
 
 Exercise, to be useful, must be judicious ; taken to the 
 point of extreme fatigue, day after day, it may do harm. 
 When a muscle is worked some of its substance is_used_u]2 ; 
 at the same time and afterwards more blood flows to it, and 
 if the exercise is not too violent and the intervals of rest are 
 long enough, the repair and growth will keep pace with or 
 exceed the wasting, but excessive work and too short rest 
 like too little exercise may lead to diminution and enfeeble- 
 rnent of the muscle. 
 
 Few persons can profitably attempt to work hard daily 
 with both brain and muscle, but all should regularly use 
 both, choosing which to work with, and which merely to 
 exercise The best earthly life, that of the healthy mind in 
 the healthy body, can only so be attained. For persons of 
 average physique, engaged in study or business pursuits of a 
 sedentary nature, the minimum of daily exercise should be 
 an amount equivalent to a five or an eight mile walk. 
 
 Time for Exercise. — Since extra muscular work means 
 extra muscular waste, and should be accompanied by an 
 

 <o*» 
 
 VARIETIES 01 EXERCISE. 73 
 
 abundant supply of food materials to the muscles, violent 
 exercise should not. be taken after a long fast. Neither 
 should it be taken Immediately after a meal ; a great deal of 
 
 blood is then needed in the digestive organs to provide ma- 
 terials tor digesting the food, and this blood cannot b<- scut 
 off to the muscles without the risk of an attack of indig< 
 tion. Strong and hearty young people may take a long 
 walk before breakfast, but others should wait until after 
 eating before engaging in any kind of hard work. 
 
 Varieties of Exercise. — In walking and running the mus- 
 cles of the lower limbs and trunk are chiefly used, whereas 
 the muscles of the chest and arms are not. Rowing is better, 
 since in it nearly all the muscles are active. No one exercise 
 employs in proper proportion all the muscles, and gymnasia 
 in which different feats of agility are practised so as to call 
 different muscles into action have a deserved popularity. It 
 should be borne in mind, however, that the legs especially 
 need strength, whereas the arms need delicacy of control 
 rather than great strength. Out-of-door exercise in good 
 weather is better than any other, and every one can at least 
 take a walk. The daily "constitutional" is very apt to 
 become wearisome, especially to young persons, and exer- 
 cise loses half its value if unattended with feelings of mental 
 relaxation and pleasure. Active games, for this reason, 
 have a great value for young and healthy persons ; bicycling, 
 golf, lawn-tennis, baseball, and cricket are all attended with 
 pleasurable excitement, and are excellent as exercising many 
 muscles. Such exercises as make one breathe faster and 
 deeper and increase the rapidity and force of the pulse are 
 excellent for giving exercise to the heart and training the 
 respiratory and circulatory nerve centres. The lungs and 
 chest are also developed thereby. 
 
CHAPTER VIII. 
 WHY WE EAT AND BREATHE. 
 
 How is it that the Body can Do Muscular Work ? — In 
 the muscles we possess a set of organs capable of moving the 
 body from place to place, of changing the relative positions 
 of its parts, and of lifting external objects : as long as we are 
 alive, some of our muscles are at each moment doing me- 
 chanical work. This tact suggests the question, where does 
 this power of working come from ? 
 
 The Conservation of Energy. — The different natural 
 forces known to us are not nearly so numerous as the chemical 
 elements ; we all, however, know several of them, as light, 
 heat, electricity, and mechanical work. One of the greatest 
 discoveries of the nineteenth century is that these different 
 natural forces, or forms of energy, can be turned one into 
 another, directly or indirectly. Kinds of energy are trans- 
 mutable, while, so far as we know at present, kinds of mat- 
 ter are not. We cannot, as the alchemists hoped, turn iron 
 or mercury into gold, but we can turn heat into light, into 
 electrical force, or into mechanical work. When such trans- 
 formations are made it is always found that a definite amount 
 of one kind of energy disappears to give rise to a definite 
 amount of another. In other words, it has been discovered 
 that energy cannot be created. If we take a given quantity 
 of heat we can turn it into mechanical work ; if we then 
 
 74 
 
THE CONSERVATION OF ENERGY, 75 
 
 turn all this mechanical work back into heat w< 
 exactly the quantity of heat which disappeared when the 
 mechanical work appeared, and so with all other transforms 
 turns of energy from one kind to another and ban k again. 
 This fact that energy or work-power can be turned from one 
 kind into another, and of ten back again, but neve) created from 
 nothing or finally destroyed, is known as the law of the con- 
 servation of energy. 
 
 Illustrations of the Conservation of Energy. — In a steam- 
 engine, heat, which is the best known kind of energy, is pro- 
 duced in the furnace. When the engine is at work all of this 
 energy does not leave it as heat ; some is turned into me- 
 chanical work, and the more work the engine does the greater 
 is the difference between the heat generated in the furnace 
 and that leaving the machine. If, however, we use the work 
 to rub two rough surfaces together we can get the heat back, 
 and if (which of course is impossible in practice) * we could 
 avoid all friction between the moving parts of the machine, 
 and have all parts of the engine at the end of the experiment 
 at exactly the same temperature as at the beginning, the 
 quantity of heat obtained plus the quantity which has been 
 carried off from it by the air since its fires were lighted 
 would be exactly equal to the amount of heat originally gen- 
 erated in the furnace of the engine. Having turned some of 
 the heat into mechanical work we could thus turn the work 
 back into heat again, and find it yield exactly the amount 
 which seemed lost. 
 
 Or we might use the engine to drive an electro-magnetic 
 machine and so turn part of the heat liberated in its furnace, 
 
 * The losses of heat through radiation ami the heating of the air. and 
 the losses of mechanical energy by friction between the parts of ma- 
 chines, are great and constantly diminish the supply of force. 
 
76 THE HUMAN BODY. 
 
 first into mechanical work, and this afterwards into elec- 
 tricity; and if we choose to use the latter with the proper 
 apparatus, as now used for electric lighting, we can turn 
 more or less of it into light, and so have a great part of the 
 energy which first became conspicuous as heat in the engine 
 furnace, now manifested in the form of light at some distant 
 point. In theory, starting with a given quantity of one kind 
 of energy, we may turn it into one or more other forms; but 
 if we collect all the final forms and retransfonn them into the 
 first, we shall have exactly the amount of it which disap- 
 peared when the other kinds appeared. 
 
 Why We Need Food. — Energy, as we have seen, cannot 
 be created from nothing ; since the body constantly expends 
 energy, it must have a steady supply. This supply comes 
 from the energy liberated when substances in the body are 
 burned, or, as the chemists say, oxidized, just as that used by a 
 locomotive comes from the burning or oxidation of coal or 
 wood in its furnace. In consequence of this constant oxida- 
 tion, new materials must constantly be supplied to make up 
 for those used for oxidation. These new materials are pro- 
 vided in our food. One chief reason for eating is that we 
 may replace the material which has been burned to set free 
 the energy needed for our muscular efforts. 
 
 Why the Body is Warm. — Keeping warm is a very im- 
 portant matter, for experiment shows that no tissue of the 
 human body works well when cooled down even a few de- 
 grees below 98. 5 F., its natural healthy temperature. Care- 
 ful experiments prove that when a muscle works it becomes 
 hotter, and we all know that exercise makes us warm. This 
 shows that the oxidation which takes place in a working 
 muscle is not all turned into mechanical work, but a good 
 share of it appears as heat. "What is true of muscle is true of 
 
THE Nl CESSI7 Y OF FOOD. 77 
 
 all other organs of the body when the) work. No mattei 
 what their kind of work, material is oxidized, and some of 
 the energy set free b) the oxidation appears as heat, assi 
 Lng to keep the bod) warm and at its best working tempera 
 ture. 
 
 A Second Reason Why We Need Food. — Since the bod) 
 works best at a temperature higher than that of the surround- 
 ing air (except on a very hot day), and in health always 
 keeps at this temperature, it must lose heat nearly all the 
 time. At night each of us is, in health, just as warm as in the 
 morning, and in the morning as when we went to bed, 
 though we have lost heat to the air during the day, and to the 
 bedelothes at night. In order to keep our bodies at the tem- 
 perature most suitable to their aetivity, they must, therefore, 
 generate heat all the time, to compensate for its continued 
 loss. In this necessity of generating heat we find a second 
 reason for taking food. 
 
 The Influence of Starvation upon Muscular Work and 
 Animal Heat. — The body does not live, work, and keep 
 warm by means of any peculiar vital force or energy which 
 inhabits it, but by utilizing the energy set free in it by the 
 oxidation of foods, or of substances made in it from foods. 
 When a man is deprived of food, the supply of material for 
 oxidation is cut off; the body first uses up any reserve of 
 nutritious matter which may have been stored up in it when 
 the starvation commenced, then the tissues are attacked, and 
 as they are burned up the body becomes weaker and weaker 
 until death supervenes.* 
 
 * When warm-blooded animals are starved their temperature slowly 
 falls; and when it conns down to about 77° F. (25" C.) death occurs. The 
 variou> tissues at that temperature can no longer wmk 50 a- to maintain 
 life, 
 
78 THE HUMAN BODY. 
 
 How long a man totally deprived of food can keep alive 
 depends partly on how much reserve material, capable of ox- 
 idation, he has stored up in him when the starvation period 
 commences ; but largely, also, on the extent to which he can 
 avoid muscular work and loss of heat. The breathing move- 
 ments and beat of the heart must go on, but if the individual 
 lies quiet in bed he need do little or no other muscular work ; 
 and if he is well covered up with blankets, the loss of heat 
 from the body is slight and calls for but little oxidation of the 
 tissues to compensate for it.* Also, a healthy fat person will 
 survive starvation longer than a healthy lean one ; during the 
 process his fat is slowly burnt : but so long as it lasts he can 
 supply his muscles with something which can be oxidized to 
 vield working power and maintain his temperature. Fat is, 
 in fact, a sort of reserve fuel, laid up in the body, and one 
 can hardly be said to begin to starve until his fat has nearly 
 all been used up.t 
 
 Oxidations in the Body. — In the preceding paragraphs 
 oxidation and burning have been used as equivalent phrases, 
 in accordance with the teachings of chemistry. To the 
 chemist a substance is burjied when it is combined with 
 
 * Hence Dr. Tanner and "fasting girls" keep in bed, warmly cov- 
 ered up, most of the time. The losses of the body in mechanical work and 
 heat are thus reduced to a minimum, and consequently the oxidation of 
 the food reserves stored in the body at the beginning of the fast. 
 
 -f- Some warm-blooded animals, as bears, hibernate, that is, sleep all 
 through the winter and take no food. They feed well in the warm 
 weather, and are quite fat at the close of autumn, when they seek some 
 sheltered place to winter in. This shelter and their warm, furry coats 
 make the loss of heat very little; the animal, except for its breathing and 
 the beat of its heart, hardly ever moves during the winter, and even those 
 necessary movements are reduced to the fewest possible, the breathing 
 and heart beat being much slower than during the summer. With return 
 of warm weather the creature wakes up again, but is then lean and weak, 
 having burnt up its fat and part of it- muscle during its winter sleep. 
 
OXIDATIONS IN THE BODY. 79 
 
 oxygen, whether this combination takes place slowly or 
 rapidly. If the combination occurs rapidly, the burning or 
 
 Misting mass becomes very hot and also gives off light. 
 Such a rapid and vigorous oxidation is called a combustion; no 
 combustions take place in our bodies. 
 
 It has, however, been proved that whether the combination 
 of oxygen with an oxidizable^ or burnable ^ substance takes place 
 rapidly or slowly, at the end of the process exactly the same 
 amount of energy will have been set free in each case. When 
 the oxidation occurs in a few seconds, the oxidizing mass be- 
 comes very hot ; when it occurs slowly, in a few days or 
 weeks, the mass will never be very hot, because the heat 
 set free in the process is carried off nearly as fast as it 
 appears. 
 
 Illustrations of Oxidations at a Low Temperature. — If a 
 piece of magnesium wire be ignited in the air, it will become 
 white-hot, flame, and leave at the end of a few seconds only a 
 certain amount of incombustible rust or magnesia, which con- 
 sists of the metal combined with oxygen ; under these circum- 
 stances it has been burnt or oxidized quickly at a high 
 temperature. The heat and light evolved in the process rep- 
 resent the energy which is set free by the union of the metal 
 and oxygen. YVe can, however, oxidize the metal in a dif- 
 ferent way. If, for instance, we leave it in damn air. it will 
 be gradually turned into magnesia without having ever been 
 hot to the touch or luminous to the eye. The process then, 
 however, takes days or weeks, but in this slow oxidation just 
 as much energy is liberated as in the former case, although 
 now all takes the form of heat. The slowly oxidizing magne- 
 sium is, in consequence, at no moment noticeably hot, since 
 it loses its heat to surrounding objects as fast as it generates it. 
 The oxidations occurring in our bodies are of this slow kind. 
 
80 THE HUMAN BODY. 
 
 An ounce of arrowroot oxidized in a fire liberates exactly 
 as much energy as if burned in the body, but the oxidation 
 takes place in a shorter time and at a much higher tempera- 
 ture. 
 
 Oxidation in the Presence of Moisture. — Wet wood or 
 wet coal we know will not burn easily, but other kinds of ox- 
 idation which take place in the presence of moisture are well 
 known. The rusting of iron, for example, is an oxidation of 
 the metal, and takes place faster in damp air than in dry; 
 during the slow rusting in moisture just as much heat is set 
 free as if the same compound of iron and oxygen were pre- 
 pared in a more rapid way. Such experiments throw great 
 light on the oxidations which take place in our own bodies. All 
 of them are slow oxidations, which never at any one moment 
 give off a great amount of heat, and all occur in the wet 
 tissues. 
 
 Summary : 
 
 (i) The body is enabled constantly to expend energy in 
 muscular work and in heat only because the law of the con- 
 servation of energy is operative here as elsewhere in nature's 
 dominions. 
 
 (2) This law is: Energy can be transformed from one 
 kind to another, but can never be created from nothing, 
 increased, diminished, nor finally destroyed. 
 
 (3) In accordance with this law the energy expended by 
 the body must have a source. 
 
 (4) Investigations have shown that the source of the body's 
 energy is found in the oxidation of materials. 
 
 (5) Such oxidizable materials are furnished by food, which 
 includes not only that taken into the body at any time, but 
 storage substance, such as fat. 
 
 (6) Rapid and vigorous oxidation is combustion. 
 
THE OXYGEN FOOD OF THE BODY. 81 
 
 (7) The same amount of energy is liberated whether the 
 
 oxidation is slow or rapid. 
 
 (8) In the body oxidation is always relatively slow, and 
 
 takes place in the presence of moisture. 
 
 (9) Hence, by the transformation of energy through oxi- 
 dation in the body of the materials furnished by food, the 
 body is enabled to expend (a) muscular energy, whereby its 
 work, is accomplished; and (/>) heat, whereby its tissues are 
 kept at their best working temperature and the constant outgo 
 of heat compensated. 
 
 The Oxygen Food of the Body. — Hitherto we have con- 
 sidered the energy supply of the body only from one side ; we 
 have regarded it as dependent on the constant supply of 
 oxidizable material. Hut this is only half the question, since 
 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 combi- 
 nation of a gas called oxygen, taken from the air, with carbon 
 and hydrogen 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 the supply of air be cut off, a man will die 
 in a few minutes ; his food is no use to him unless he gets 
 oxygen. While he usually has stored up in his body an ex- 
 cess of food matters, he has litt)e or no reserve of oxygen. In 
 ordinary language we do not call oxygen a food, but restrict 
 that name to the solids and liquids which we swallow j but 
 
82 THE HUMAN BODY. 
 
 inasmuch as it is a material which we must take from the 
 external universe into our bodies to keep us alive, oxygen is 
 really a food. Suffocation, as death from deficient air supply 
 is named, is really death from oxygen starvation. 
 
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 he 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 becoming heavier, 
 the gain is always much less than the weight of the foods 
 swallowed. The materials given off daily from the body, 
 which balance more or less accurately the receipts from the 
 outside world, are its ivas/cs, and are chiefly things which 
 cannot be burned. Much of the food taken in can be, and 
 is, oxidized 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 out its fire if they were allowed to accumulate 
 in the furnace. The chief wastes * of the body are carbon 
 dioxide gas, water, and a substance related to ammonia called 
 urea. 
 
 * Chemically these wastes are : 
 
 Carbon dioxide = CO a 
 Water = H 3 
 
 Urea = CON,H<. 
 
 83 
 
#4 THE HUMAN BODY. 
 
 Receptive and Excretory Organs. — Those organs of the 
 body whose function it is to gather new material from out- 
 side for its use are known as receptive organs. There are 
 two chief sets of these — one to receive oxidizable things, and 
 the other to receive oxygen. The first set is represented by 
 the alimentary canal, consisting of mouth, gullet* stomach, 
 and intestines. It takes in food and drink. The second set 
 consists of the lungs, with the air passages leading 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 skin. The lungs give out carbon dioxide gas and 
 water ; the kidneys get rid of urea and water ; and the skin, 
 of water, common salt and a minute quantity of urea. 
 
 The Intermediate Steps between Reception and Excre- 
 tion. — Between the taking of oxidizable substances into our 
 mouths and oxygen into our lungs, and the return of oxidized 
 matters from our bodies to the surrounding world, a great 
 many intermediate steps take place. The alimentary canal 
 (see Fig. i) is a tube which runs through the body but no- 
 where 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 living tissue, sub- 
 stances are burned to enable it to work. Hence the food or 
 fuel must- be brought 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 
 
 * The technical name for the gullet is oesophagus. 
 
CIRCULATION, RESPIRATION, ETC. 
 
 it available it must be i I so that it can soak thi ■ 
 
 the walls of the stomach and intestines. 1 <>r this purpose 
 we find a set of digestive to make solvent juices and 
 
 pour them upon the food which we swallow, and so get it 
 
 into a liquid state in which it can be absorbed. 
 
 Circulation. — It" the solution containing our digested I 
 simply soaked through the walls of the alimentary canal, it 
 could not reach the distant parts, as the brain or the mi. 
 of the limbs. We find, therefore, in the body a set of tubes 
 containing blood, 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 connecting 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, or lymphatics. 
 
 Respiration. — The blood in its course flows through the 
 lungs. It is necessary not merely that food but oxygen also 
 should be carried to even- part of the body. As the blood 
 traverses the lungs it picks up oxygen from the air in them ; 
 this air is then replaced by taking a fresh breath, and so on. 
 The organs thus concerned 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 ox E 
 brought to it by the blood, and is thus converted into burnt 
 
86 THE HUMAN BODY. 
 
 waste matter. The blood, as we have seen, brings, however, 
 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 them- 
 selves, to replace the part which has been used up and de- 
 stroyed. This building and repair of tissues and organs from 
 the dissolved food obtained from the blood is known as as- 
 similation — in plain English, "a. making alike." Each liv- 
 ing 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 Ab- 
 sorbents to Excretion. — It is essential to the body that its 
 wastes be carried off. Here again the blood vessels and ab- 
 sorbents, or lymphatics, come into play. Lymphatics 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 im- 
 portant for removing the waste matters of an organ as for 
 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 pro- 
 cess. It implies — (i) the reception of food from outside; 
 (2) the digestion of food; (3) the absorption of digested 
 food; (4) the absorption of oxygen in the lungs, and its con- 
 veyance by the blood to every organ ; (5) the conveyance of 
 absorbed food and oxygen to all parts by the blood ; (6) as- 
 similation or the building up of new tissue from materials 
 
NUTRITION, 87 
 
 brought by the blood; (7) disassimilation, or the breaking 
 down of working tissues by combination with oxygen; (8) 
 the taking up of wastes from the different organs ; and (9) the 
 conveyance of these wastes by the blood to excretory oi 
 
 which pass them out of the body. 
 
 In subsequent chapters we shall have to consider in more 
 detail Digestion, Circulation, Absorption, Respiration, and 
 retion . The sum total of the actions of all the organs 
 concerned in the nourishment of the body is known as the 
 function oi nutrition. As will be explained later, some of the 
 food fulfils other purposes than the formation of energy yield- 
 ing material. 
 
CHAPTER X. 
 
 FOOD-. 
 
 Poods 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 not merely 
 by accumulating water and such substances, 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, there are probably some constructive 
 processes going on as the tissues are broken down and recon- 
 structed. 
 
 Foods are therefore needed not only to supply the body 
 with work-power by their oxidation, but to supply material 
 from which tissue can be reconstructed. 
 
 What Foods must Contain. — Most foods serve both for 
 energy supply* and tissue formation : they are probably built 
 up by the living cells into new forms before they are oxidized 
 
 * Whether any food is ever oxidize 1 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 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 reason to 
 suspect that albuminous substances may be oxidized in the body without 
 ever forming part of a living cell. 
 
 88 
 
THE 1MPOR1 i\< I Ok PROTEID FOODS. « s 9 
 
 to set the energ) free. The living tissues when analyzed are 
 found to consist mainl) of carbon, hydrogen, nitrogen, ;in<l 
 oxygen, and we might at first suppose that these chemical ele 
 
 incuts in their UH combined form would serve to nourish us. 
 
 Experience, however, tea< hes that this is not the case. Four 
 
 fifths of the air is nitrogen, but we cannot feed on it ; hydro 
 gen gas is of no use as a food ; and a lump of charcoal (< ar 
 bon) 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 com- 
 plex compounds, in which they are chemically combined with 
 other things ; as, for example, in starch, sugar, fat, oil, and 
 albuminous substances. 
 
 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. 1 5. ) 
 So far as we know at present the human body (like that of 
 most animals) is unable to make proteids out of other things. 
 Given one variety of them it can turn it into other varieties, 
 but it cannot make proteids from things which are not pro- 
 teids. 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 re- 
 lation to the outer world. They require for their nutrition 
 very complex chemical compounds (starch, sugar, fat, pro- 
 teids),* build these up into living tissues, or oxidizable forms, 
 
 * Starch C 6 H,„<>, 
 
 Sugar C 8 H ia O a 
 
 Fat (variable) C sl II, 4O s 
 
 Proteid (variable). C 7 ,.II, : .,N IB 0,.. ; S 
 
90 THE HUMAN BODY. 
 
 then oxidize them and return the carbon, hydrogen, and 
 nitrogen to the outer world in much simpler chemical com- 
 pounds (carbon dioxide, water, and urea). None of these 
 latter substances is capable of nourishing an animal \ it cannot 
 use them to build up its tissues or set energy free. 
 
 How Plants Supply Food for Animals, and Animals 
 Food for Plants. — Since animals cannot utilize the simple sub- 
 stances furnished by nature as food, but must consume com- 
 plex substances, as proteids, fat, and sugar, the question nat- 
 urally suggests itself, How is it that the supply of these is 
 kept up? For example, the supply of proteids, which can- 
 not 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 the carbon dioxide, 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 ani- 
 mals, since they cannot make them from urea, carbon di- 
 oxide, 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 essential food upon 
 the vegetable kingdom ; the fox that devours a hare lives 
 on the proteids of the plants which the hare had previously 
 eaten and built into his own tissues. 
 
 Non-oxidizable Foods. — Besides our oxidizable foods a 
 large number of necessary food materials are not oxidizable, 
 or at least are not oxidized in the body. Typical instances 
 are afforded by water and common salt. The use of these is 
 in great part physical : the water, for instance, dissolves ma- 
 
GENERAL O WSIDERA Tl( )NS OF l< K >/ >s. •> l 
 
 tcnals in the alimentary canal, and carries the solutions 
 through its walls into the Mood and lymph that 
 
 they can be conveyed from place to place; and it permits 
 interchanges by enabling the things it has dissolved to 
 
 through the walls of the vessels. The salines also influence 
 the solubility and chemical interchanges of other things 
 present with them. Fibrinogen) one of the proteids which is 
 carried in the blood all over the body to supply albuminous 
 material to the tissues, is, for example, insoluble in pure 
 water, but dissolves readily if a small quantity of common 
 salt is present. Beside such uses, the non-oxidizable foods 
 have probably other functions : for example, the lime salts 
 give their hardness to the bones and teeth. 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 condi- 
 tions determine the selection of iron for building the greater 
 part of it. 
 
 General onsiderations. — Foods to replace matters which 
 have been oxidized must be themselves oxidizable; they 
 are force generators, but may be and generally are also 
 tissue formers. They are nearly always complex organic sub- 
 stances derived from other animals or from plants. Foods 
 to replace matters not oxidized in the body, as water and 
 salt, are force regulators, and are for the most part fairly 
 simple inorganic compounds. Among the force regulators 
 
92 THE HUMAN BODY. 
 
 we must, however, include certain foods, which, although 
 oxidized in the body and serving as sources of energy, yet 
 produce effects greatly out of proportion to the amount of 
 energy which they thus set free. Their influence as stimu- 
 lants in exciting certain tissues to activity, or as agents check- 
 ing the activity of parts, is more marked than their direct 
 action as force generators, and they may be classed as acces- 
 sory foods. 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 appe- 
 tite for food. Them, again, the active principle of tea and 
 coffee, is taken for its stimulating effect on the nervous sys- 
 tem rather than for the amount of energy which is yielded 
 by its own oxidation. 
 
 To the above consideration of foods should be added the 
 condition that neither the substance itself nor any of the 
 products of its chemical transformation in the body shall be 
 injurious to the structure or action of any organ ; otherwise it 
 is a poison, not a food.* 
 
 Alimentary Principles. — The substances which we call 
 foods are usually mixtures of several foodstuffs with sub- 
 stances which are not foods at all. Bread, for example, con- 
 tains 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 con- 
 stituent of the walls which surround vegetable cells), which 
 
 * This, of course, is true only when the substances are taken in the 
 ordinary moderate or physiological amounts. Many substances become 
 harmful or poisonous if taken in excess, e.g. oxygen, salt, meat, etc. 
 
PROTEID ALIMENTARY PR1NCIPLL <r, 
 
 is not a food, since it is incapable of digestion and absorption 
 from the alimentary (anal. Chemical examination of all the 
 
 common articles of diet shows that the actual number of im- 
 portant foodstuffs is small ; they are repeated in various pro- 
 portions in the different foods we eat, mixed with small 
 quantities of different flavoring substances, and so give us a 
 
 pleasing variety in our meals; hut the essential substances 
 are much the same in the fare of the artisan anu! in the " deli 
 cacies of the season." The chief foodstuffs, which are found 
 repeated in many different foods, are known as "alimentary 
 [rinciples" and the nutritive value of any article of diet de- 
 pends on the amount of these foodstuffs present, far more 
 than on the various agreeable flavoring matters which cause 
 certain things to be sought after and to have a high 
 market value. Alimentary principles may be conveniently 
 classified into proteids, fats, carbohydrates, and inorganic 
 bodies. 
 
 Proteid Alimentary Principles. — Of the nitrogenous food- 
 stuffs 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, found in the lean of all meats, egg albumin, casein 
 of milk and cheese, gluten and vegetable casein from various 
 plants. 
 
 Beside these proteid substances, all of which are apparently 
 able to act as tissue builders, there is a class of nitrogenous 
 substances which do not possess this power though they are 
 oxidized in the body to yield energy. This class is repre- 
 sented by gelatin, derived from connective tissue and bones, 
 and by chondrin, from cartilage. As force producers they 
 have considerable value, but are not nearly as important food 
 for invalids as was at one time supposed. 
 
94 THE HUMAN BODY. 
 
 Necessity of Proteid Food. — Experiments have shown that 
 the excretion of nitrogen (chiefly as urea; in a well-fed 
 animal is equal to the amount of nitrogen taken in with the 
 food.* Th-is balance of income and expenditure is called 
 nitrogenous equilibrium. If the nitrogen of the food is reduced 
 below a certain amount, more nitrogen is excreted than is 
 replaced by the food. This excess of expenditure comes from 
 the fleshy tissues of the animal, which are thus wasted away. 
 All animals thus become flesh-eating (carnivorous) when 
 starving. 
 
 Fats and Oils. — The most important of these are stearin, 
 palmatin, margarin, and olein, which exist in various pro- 
 portions in animal fats and vegetable oils, and butter, which 
 contains a peculiar fat known as butyrin. All fats are com- 
 pounds of glycerin with fatty acids, and, speaking generally, 
 are useful as food if fusible at the temperature of the body. 
 The stearin of beef and mutton fats is not by itself fusible at 
 the body temperature, but as eaten it is mixed with so much 
 olein as to be melted in the alimentary canal. 
 
 Artificial butters, such as margarin, oleomargarin, butter- 
 ine, and cocoa butter, are made of the more easily melted 
 animal or vegetable fats flavored to resemble butter by being 
 churned in butter milk. They are easily digested and pos- 
 sess practically the same nutritive value as butter. 
 
 Fats and oils are rich in carbon and hydrogen, but contain 
 little oxygen. Hence their oxidation liberates much energy. 
 
 Fat. Oxygen. Carbon dioxide. Water. 
 
 C..H-0. -r 145O = 51CO, - 49H O. 
 
 Carbohydrates. — These are mainly of vegetable origin. 
 The most important are starch | found in nearly all vegetable 
 
 * While an animal is growing, the excretion of nitrogen is slightly less 
 than the income owing to its -torage in the growing flesh. 
 
INORGANIC FOODS. 
 
 foods I, dextrin y gums, grape su± • ind in most fruits |, and 
 
 cane sugar. .s - //; r .//- of milk and glycogen i animal Btar< h from 
 the liver) arc alimentary principles of this group derived 
 
 from animals. All carbohydrates, like the fats, consi 
 carbon, hydrogen, and oxygen, but the percentage of 0x3 
 
 in them is much higher than in fats. In feet oxygen is 
 present in just the right proportion to satisfy all the hydro- 
 gen ; hence only carbon remains to be oxidized. They 
 have therefore less power of combining with additional oxy- 
 gen than fats and so are not capable of yielding as much 
 energy to the body. 
 
 Sti;;ar. Oxygen. Carbon dioxide. Water. 
 
 C.H ls O e + 12O = 6C0 2 + 6H 3 0. 
 
 Fuel Values of Food Principles. — The heat produced by 
 the combustion of weighed quantities of food materials has 
 been determined by numerous experimenters, and the average 
 of the results is expressed in the following table : 
 
 Calories. Foot-tons. 
 
 I gram of proteid (dry) 4. 1 6.3 
 
 1 " ' ' fats 9.3 14.2 
 
 1 " "carbohydrates (dry).. 4.1 6.5 
 
 Experiments have further shown that the energy produced 
 in the body (heat, muscular work, etc. ) by the oxidation of 
 the food substances is practically equivalent to that obtained 
 by combustion.* 
 
 * The heat units used by physiologists represent the amount of heat 
 necessary to raise the respective amounts of water one degree Centigrade. 
 1. kilo water i° C. = Caloric = i.o pound water 4" F. 
 
 I. gram " 1° C. = caloric = 0.001 ''4 1' ■ 
 
 0.001 gram " i° C. = micro-calorie = 0.000001 •• •• 4 F. 
 One Calorie is equivalent in mechanical energy to 1. 53 foot-tons. 
 One calorie " " " " " ••0.00153 
 
96 THE HUMAN BODY. 
 
 Inorganic Foods. — The most important of these are water, 
 common salt, and the chlorides, the phosphates and the sul- 
 phates of potassium, magnesium, and calcium. A sufficient 
 quantity of most of these substances, or of the material for 
 their formation, exists in all ordinary articles of diet, so that 
 we do not take 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 
 requires 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 evi- 
 dence that certain savage tribes live without more than they 
 get in the meat and vegetables which they eat. Such tribes 
 are, however, said to suffer 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 ordinary 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 millionaire. 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 tax on salt, which 
 even the poorest will buy. In the Austrian Empire it has 
 been found that youths who have fled to the mountains and 
 there led a wild life to avoid military conscription, will come 
 
NUTRITIVE VALUE OF DIFFERENT FOODS. 97 
 
 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, arc highl) valuable 
 
 foods. They contain abundant albumen, more or less fat, 
 and when rooked, their connective tissue is in great part made 
 soluble by being turned into gelatine. Pork is the least easily 
 digested form of fresh meat, since it contains a larger per 
 centage of fat than most. This fat, which, by its oxidation 
 liberates much heat, makes it a good food in cold weather for 
 persons with a good digestion. Pigs are, however, especially 
 liable to a dangerous parasite, called trichina, which lives in 
 their muscles, and may be transferred to man if the pork is 
 not thoroughly cooked. Salted meats of all kinds are less 
 digestible and less nutritious than fresh. Milk contains an 
 albuminous substance (casein), also fats (butter), and sugar, 
 known as sugar of milk, in addition to useful mineral salts. 
 It will support life longer than any other single food. Cheese 
 consists essentially of the casein of milk, and is a very nutri- 
 tive albuminous food. Eggs contain albumens and fats of 
 high nutritive value, but they are not as easily digested when 
 cooked too long. 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 gives to wheat bread its superiority. When the 
 dough is made, yeast is added to it and causes fermentation 
 by which some of the starch is changed into sugar, then 
 into alcohol and carbon dioxide. If the fermentation is 
 allowed to go too far, the alcohol is changed into acetic 
 and other acids, and sour bread results. The carbon dioxide 
 
9 8 THE HUMsIN BODY. 
 
 imprisoned in the tenacious dough and expanded by heat 
 during baking, forms cavities in it, and causes the dough to 
 "rise" and make "light bread," which is not only more 
 pleasant to eat but more easily digested than heavy. Some 
 grains contain a larger percentage of starch, but less gluten, 
 than wheat ; when bread is made from them 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 and is 
 very nutritious. Rice is poor in proteids, but very rich in 
 starch. Peas and. beans are rich in proteids and contain about 
 half their weight of starch. Potatoes contain a great deal of 
 water and only about two parts of proteids and twenty of 
 starch in a hundred parts by weight, but are rich in useful 
 salts. Other fresh vegetables, as carrots, turnips, and cabbages, 
 as well as fruits, are valuable mainly for the salts they con- 
 tain; their weight is chiefly due to water, and they contain 
 but little starch, proteids, or fats. Some kind of fresh vege- 
 table 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 as a Food. — Evidence goes to show that alcohol 
 in moderate doses is oxidized in the body and yields energy, 
 but cannot build up or restore exhausted tissue. In certain 
 diseases the fact that it requires no digestion and is rapidly 
 absorbed gives it considerable value. The amount of alcohol 
 which can be taken for food, however, is so slight because of 
 its marked stimulating effect that under normal conditions it 
 is practically valueless for food purposes. Its frequent use 
 
 * Scurvy is characterized by swelling and bleeding of the gums, 
 loosening of the teeth, and great weakness ending in death. It was 
 especially frequent among whalers. 
 
TEA AND COFFEE COOKIh 99 
 
 may undoubtedly lead to a serious diminution of vitality, 
 lessened resistance to disease, diminished enduran< e of fatigue, 
 heat, and cold, and to pathological conditions of the vital 
 organs, such as an overgrowth of connective tissue and fat. 
 The consumption of alcohol has so frequently led to wasted 
 opportunities, suffering, and even (rime that it is the part of 
 wisdom to avoid its use. 
 
 Tea and Coffee are to be regarded as stimulants rather than 
 foods. The amount of nourishment in a cup of either is but 
 little. Both have, however, some influence in removing the 
 sense of fatigue, and when occasionally taken in moderate- 
 doses leave as a rule no injurious after-effects. For relieving 
 fatigue, tea and coffee are superior to alcohol, but neither 
 should be used as a substitute for rest and sleep ; in fact it 
 may be questioned whether the habitual use of either is 
 advisable. 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. 
 
 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 boiling 
 meat it is a good plan to put it first into boiling water in 
 order to coagulate the albumen at the surface and thus form 
 a dense coat which keeps flavoring matters and salts from 
 passing into the water. After the first few minutes the cook- 
 ing should be continued at a lower temperature ; meat boiled 
 too fast is hard, tough, and stringy. In roasting or baking 
 meat, it is also advisable to put it close to the fire or in a 
 hot oven for a short time, and then to complete the cooking 
 more slowly. 
 
 The cooking of vegetable foods is of considerable impor- 
 
IOO 
 
 THE HUMAN BODY. 
 
 tance. Starch is the chief nutrient matter in most of them, 
 and raw starch is much less easily digested than cooked 
 since it is enclosed in a thick cell wall of indigestible cellulose 
 which is broken down by cooking. When starch is heated 
 it is turned into a substance known as soluble starch, which is 
 easily dissolved by the digestive liquids ; there is therefore a 
 scientific foundation for the common belief that the crust of 
 
 Fig. 44. — Cells of a raw potato, with starch grains in natural condition. 
 
 a loaf is more digestible than the inside, and toast than fresh 
 bread. 
 
 The Oxidizable Matters Required Daily by the Body. — 
 The amount of food required daily depends upon the quantity 
 of material used up by the body 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. It is impossible to 
 state accurately beforehand just what any individual will 
 require, but a general idea may be arrived at by taking 
 the average daily losses, by excretion, 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 274 grams (9^ ounces) of carbon to 
 
ADVANTAGES OF A MIXED DIET. 101 
 
 replace his loss of that element, and about 20 grams of nitro- 
 gen 1 ,",, of an ounce). Some hydrogen is also required, 
 
 as the bod} daily excretes more water than it receives 
 
 through food and drink ; this extra amount implies a loss of 
 hydrogen, which has combined with oxygen in the body to 
 form water. 
 
 The Advantages of a Mixed Diet. — Since proteid foods 
 contain carbon, nitrogen, and hydrogen, life may be main- 
 tained on them if the necessary salts, water, and oxygen be 
 also supplied \ but such a diet would not he economical. 
 Ordinary proteids contain in 100 parts about 52 of carbon 
 and 15 of nitrogen, so a man fed on them alone would 
 get about 3?, parts of carbon for every 1 of nitrogen. His 
 daily losses are not in this ratio, but about 15 parts of carbon 
 to 1 of nitrogen : therefore to get enough carbon from pro- 
 teids far more than the necessary amount of nitrogen must be 
 taken. Of dry proteids 527 grams (1 pound 2I ounces) 
 would yield the necessary carbon, but would contain 79 
 grams (2! ounces) of nitrogen, or four times more than 
 is necessary to cover the daily losses of that element from the 
 body. Fed on a purely proteid diet a man would, therefore, 
 have to digest a vast quantity to get enough carbon, and in 
 eating and absorbing it, and in getting rid of the excess 
 nitrogen (which is useless to him), a great deal of unnecessary 
 labor would be thrust upon the digestive and excretory 
 organs. Were a man to live on bread alone, he would also 
 force much unnecessary work on his organs. Bread contains 
 little nitrogen in proportion to its carbon, and to get enough 
 nitrogen far more carbon than could be utilized would have 
 to be eaten, digested, and excreted daily. 
 
 The human race has discovered this fact : men use, where 
 they have a choice, richly proteid substances to supply the 
 
102 THE HUMAN BODY. 
 
 nitrogen needed, but derive the carbon mainly from non- 
 nitrogenous foods of the fatty carbohydrate kinds, and so 
 avoid excess of either nitrogen or carbon. For instance, lean 
 beef contains about 25 per cent of drv proteid, and this in 
 turn contains 15 per cent of nitrogen. Consequently 542 
 grams 1 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 
 carbon in the above weight of fatless meat would be 69 grams 
 Tor nearly 2 J ounces J, leaving 205 grams (or rather more 
 than 7 ounces ) to be got either from fats or carbohydrates. 
 The necessary amount is contained in 256 grams (or about 9 
 ounces; of ordinary fats, or in 460 grams | a little over a 
 pound; of starch ; hence either of these with the above quan- 
 tity of lean meat would form a for better diet both for the 
 system and the purse than meat alone. 
 
 As already pointed out, nearly all common foods contain 
 several foodstuffs. Good butcher's meat, for example, con- 
 tains nearly half its dry weight of fat, and bread in addition 
 to proteids contains starch, fats, and sugar. In neither of 
 them, however, are the foodstuffs mixed in the physiologi- 
 cally best proportions, and the custom of consuming several 
 of them at each meal, or different ones at different meals dur- 
 ing the dav, is not only agreeable to the palate but in a high 
 degree advantageous to the body. The strict vegetarians who 
 do not eat even such substances as eggs, cheese, and milk, 
 but confine themselves to a purely vegetable diet, which is 
 always poor in proteids, take daily far more carbon than they 
 require, and are to be congratulated on their excellent diges- 
 tions which are able to stand the strain. Those so-called 
 vegetarians who use eggs, cheese, and other animal substances 
 can of course get on very well, since these are extremely rich 
 
RELATION OF nil I TO WORK. I , 
 
 in proteids, and supply all the nitrog* ii needed, without the 
 aecessity of swallowing the vast bulk <>r i"<>d which must be 
 eaten in order to get it directl) from plants. 
 
 Food Materials.- -The above facts are best shown in the 
 chemical analyses of loud materials. Detailed diet studies 
 have made it possible to construct meals based on the actual 
 nutritive values of different foods, which shall give an ade- 
 quate amount of nutriment to individuals of varying pursuits. 
 
 In the study of the dietaries it has been found that the es- 
 sential points to be observed are the total amount of nitroge- 
 nous material (proteid) and the total fuel value of all the 
 elements. It has been found that the fats and starches are 
 largely interchangeable in the ordinary dietaries, hence their 
 proportions are of less importance. 
 
 Relation of Diet to Work. — It must be remembered that 
 energy is given off in the form of heat, and is used up in the 
 body by the heart (as explained later), and by tissue activity. 
 The external work accomplished by a man under different 
 conditions is shown in the following table, together with the 
 heat equivalents for this work. The amount of work accom- 
 plished is most readily expressed in foot-tons.* 
 
 ESTIMATES OF MECHANICAL WORK DONE BY A MAN IN A DAY. 
 
 Foot-tens Kilogrammetres. Calories of Heat. 
 
 Light work, from 150 to 200 or 46.600 to 62,200 or 109 to 147 
 
 Average " " 300 " 350 " 93.300 •' 108,800 •' 219 " 158 
 
 Hard " " 450 " 500 " 139,900 '• 155,500 •• 329 " 366 
 
 Laborious " " 500 •' 600 " 155,500 " 186,000 " 366 ; - 437 
 
 Protein Fats. , C ^ rb t °" Fuel Value 
 
 hydrates. 
 
 Standard Diet, Atwater 127 gms. 113 gms. 494 gms. 3500 calorie s 
 
 * Each foot-ton represents the effort necessary to raise the equivalent 
 of one ton to a height of one foot. Thi> is equivalent to raising one 
 pound to a height of two thousand feet. A kilogrammetre measures the 
 effort necessary to raise one kilogram (2l lbs.) to a height of one metre- 
 (3| ft-)- 
 
104 
 
 THE HUMAN BODY. 
 
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RELATION OF DIET TO WORK. 105 
 
 In comparing these figures with the number of heat units in 
 Atwater's standard diet it will be noticed that only about 
 one-tenth of the energy value of the food is utilized for ex- 
 ternal work ; the remaining nine-tenths are used up in doing 
 the internal work of the body and in making good the heat 
 losses. It has been estimated that in muscular work only 
 one-third of the energy of the food is converted into mechan- 
 ical work by the muscle, the remaining two-thirds being dis- 
 sipated as heat. 
 
CHAPTER XI. 
 THE DIGESTIVE ORGANS. 
 
 General Arrangement of the Alimentary Canal. — The 
 
 alimentary 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 constructed to ab- 
 sorb dissolved nutritive substances ; it soaks them up and 
 passes them into blood or lymph vessels. Imbedded in this 
 mucous membrane, or lying outside it, are hollow organs 
 called glands ; these glands make liquids which change food 
 substances chemically so that they may be absorbed by the 
 mucous membrane. The whole series of changes which any 
 food material undergoes, between its reception by the mouth 
 and its absorption by the alimentary mucous membrane, is 
 spoken of as its digestion. 
 
 Various foodstuffs undergo different kinds of changes pre- 
 liminary to absorption, and so we speak cf different kinds of 
 digestions ; as that of starch, of fats, of albuminous bodies, 
 and so forth. 
 
 Glands are, ordinarily, hollow organs which make or secrete 
 peculiar fluids and pour them out on some free surface of the 
 
 106 
 
THE KINDS OF GLANDS. 107 
 
 body. They arevery widel) distributed; we find, for exam- 
 ple, digestive glands of several kinds opening into the di- 
 gestive tube, perspiratory glands opening on the skin, 
 lachrymal glands pouring out their se< retion on the eyeball. 
 Different glands have their cavities lined by different kinds 
 of cells, and produce different secretions. In general all 
 glands are built on one or the other of two primary structural 
 plans, known as the tubular and the racemose (Fig. 45). 
 
 The Kinds of Glands. — All portions of the body making 
 and pouring forth secretions are not technically called glands. 
 In the peritoneum, which forms the inside lining of the ab- 
 dominal cavity 1 p. <S |, we find simply a thin membrane (A, 
 Fig. 45 ), having on the side next the cavity which it sur- 
 rounds a layer of cells (a) and on its deeper side a network 
 of very fine blood-vessels (c) supported by connective tissue 
 ('/). This arrangement is also found in the pleurae, the pericar- 
 dium, and the synovial membranes, but is not the most com- 
 mon form of secreting tissue. In most cases the area of the 
 surfaces necessary to secrete the amounts of the various fluids 
 needed would be too great to be packed conveniently in 
 the body by simply spreading out fat membranes. Accord- 
 ingly, in most cases, a large area is obtained by folding the 
 secreting surface in various 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 the same. 
 In a few cases the folding takes the form of protrusions into 
 the cavity of the secreting organ ( C, Fig. 45), but much 
 more commonly the surface extension is attained by pitting or 
 depressing the supporting or basement membrane, covered by 
 it:-, epithelium (B). Such a secreting organ is known as a 
 true gland. 
 
ioS 
 
 THE HUMAN BODY. 
 
 Fig. 45. — Forms of glands. A, a. simple secreting surface; a, its epithelium ; />, 
 basement membrane; c, capillaries ; B, a simple tubular gland ; C. a secreting surface 
 increased by protrusions ; E, a simple racemose gland ; D and G. compound tubular 
 glands ; F, a compound racemose gland. In all but A, />'. and C the capillaries are 
 omitted for the sake of clearness. H, half of a highly developed racemose gland; c t 
 its main duct. 
 
■\Un 01 GLANDS. 109 
 
 Forms of Glands -In some the surface involutions 
 
 arc uniform in diameter, or nearl) so I />'. Fig. 45 ), and are 
 known as tubular ; examples are found in the lining coat of 
 the stomach Fig 57), also in the skin I ig. [09 where 
 they form the sweat-glands. In other cases the involution 
 swells out at its deeper end and becomes more or less saccu- 
 lated 1 A'); such glands are named racemose or acinous. The 
 small glands of the skin which form the oily matter for t he- 
 hairs ( p. 227) 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-\ capillaries) form a closer net- 
 
 work. These deeper cells form the true secreting tissue of 
 the gland, while the tube, lined with different cells, which 
 leads from the secreting recesses to the surface on which the 
 secretion is poured out, serves merely to drain it off and 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 has a true secreting chamber at its end the 
 gland is compound, tubular (G), or racemose ( F, H) as the 
 case may be. In many cases the chief duct, in which the 
 smaller ducts unite, is of considerable length, so that the se- 
 cretion is poured out at some distance from the main mass of 
 the gland. 
 
 A fully formed gland, H, is thus a complex structure, con- 
 sisting primarily ofadi: ductules (dd) and secreting re- 
 cesses (ee). The ducts and ductules are lined with protective 
 cells which differ in character from the secreting cells lining 
 the deepest parts. The cells lining the Ultimate recesses dif- 
 fer in different glands, and produce different liquids; conse- 
 quently, though all glands are built on much the same plan, 
 
no 
 
 THE HUMAN BODY. 
 
 r TL 
 
 they make very varied secretions, according to the properties 
 of their cells. 
 
 The Complexity of the Alimentary Canal. — We may non- 
 return to our immediate subject, the alimentary canal. This 
 
 is not a simple tube, but 
 presents several dilatations in 
 its course; nor is it a com- 
 paratively straight tube, as 
 diagrammatical]}' represented 
 in Fig. i, but, being much 
 longer than the body, much 
 of it is packed away by being 
 coiled up in the abdominal 
 cavity. 
 
 Subdivisions of the Ali- 
 mentary Canal. — The mouth 
 opening leads into a chamber 
 containing the teeth and 
 tongue, named the mouth 
 chamber or buccal cavity. 
 This primary dilatation is 
 separated by a constriction 
 
 Fig. 46 -The mouth, nose, and (Jhe isthmus of the fauces) X. 
 
 pharynx, with the commencement of .1 1 1 r ..u ii_ r 
 
 the gullet and larynx, as exposed by a the back Ot the lllOUth, from 
 
 section, a little to the left of the median -17 
 
 plane of the head, a, vertebral column ; another cavity, the pharynx 
 i, gullet ; <:, windpipe ; d, larynx ; e. 
 
 epiglottis ; y, soft palate; g, opening of or throat chamber, which nar- 
 
 Eustachian tube ; k, tongue ; /, hard 
 
 palate ; m\ the sphenoid bone on the base rOWS a^aill at thetOD of the 
 
 of the skull ; «, the fore part of the era- c x 
 
 nial cavity; o,f,_g, the turbinate bones neck into tne eu // e f or aso . 
 
 of the outer side of the left 
 chamber. 
 
 nostril 
 
 phagus. The latter runs as a 
 comparatively narrow tube through the thorax, and then, 
 passing through the diaphragm, dilates in the upper part of 
 the abdominal cavity to form the stomach (see Fig. i). Be- 
 
THE MOUTH CAVTIY. 
 
 i i r 
 
 vond the stomach the t hannel again narrows to form a long 
 and greatly coiled tube, the small intestine, which terminates 
 
 by opening into the large intestine \ this, though shorter, is 
 wiiler, and ends by opening on the exterior. 
 
 The Mouth Cavity | Figs. 46 and 4 7 . is bounded in front 
 and on the sides by the lips and cheeks, below by the tongue 
 
 '•-■■•»•.■ - ..-..- ■ ■ 
 
 Fin. 47. — 1, soft palate ; 2, its median ridge ; 3, uvula ; 4, anterior, 5, posterior 
 pillar of fauces ; 6, tonsil ; 7, posterior wall of pharynx ; 8, tongue. 
 
 (k), and above by the palate, which consists of an anterior 
 part (/) supported by bone and called the hard palate, and a 
 posterior (_/") containing no bone, and called the soft palate. 
 The two can be distinguished by applying the tip of the 
 tongue to the roof of the mouth and drawing it backwards. 
 The hard palate forms the partition between the mouth and 
 nose. The soft palate arches down at the back of the mouth, 
 
H2 THE HUMAN BODY. 
 
 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 pro- 
 cess, 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, and covered by the gums, except at inter- 
 vals along their edges where teeth are implanted. During 
 life two sets of teeth are developed : the first or milk set ap- 
 pear soon after birth and are shed during childhood, when 
 the second ox 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 ox fang ; and between the two, embraced 
 by the edge of the gum, a narrowed portion, the neck or 
 cervix. By differences in their forms and uses the teeth are 
 divided into incisors, canines, bicuspids , and molars, arranged 
 in a definite order in each jaw. Beginning at the middle 
 line we find in each half of each jaw, successively, two in- 
 cisors, one canine, and two molars in the milk set, making 
 twenty altogether in the two jaws. The teeth of the per- 
 manent 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 as the jaw 
 grows. The last permanent molars are often called the 
 wisdom teeth. 
 
 * A number of teeth can be readily obtained from a dentist, and will 
 be found of great use in connection with this lesson. 
 
CHARACTERS AND STRUCTURE Of TlP.TH. 
 
 " \ 
 
 Characters of Individual Teeth. -The incison or cutting 
 teeth | Fig. 48) arc adapted tor cutting the food. Their 
 cro\vn> are ( hisel shaped and have sharp horizontal cutting 
 edges which become worn away by use, so that they are 
 bevelled off at the back in the upper row and at the front in 
 the lower. Each lias a single long fang. The canines i d>>^ 
 teeth) (Fig. 49) are somewhat larger than the incisors. 
 Their crowns are thick and somewhat conical, having a cen- 
 tral point or cusp on the cutting edge. In dogs and cats the 
 canines are very long and pointed, and adapted for seizing 
 and holding prey. The bicuspids ox premolars (Fig. 50) are 
 
 Fig. 50. 
 
 Fig. 51. 
 
 Fig. 48. Fig. 49. 
 
 Fig. 48. — An incisor tooth. 
 Fig. 49. — A canine or eye tooth. 
 
 Fig. 50. — A bicuspid tuoth seen from its outer side ; the inner cusp is accordingly 
 not visible 
 
 Fig. 51. — A molar tooth. 
 
 rather shorter than the canines and their crowns are cuboidal. 
 Each has two cusps, an outer and an inner. The molar leeth 
 or grinders (Fig. 51 ) have large crowns with broad surfaces, 
 and 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 minor 
 points from those of the same names in the permanent set. 
 
 The Structure of a Tooth. — If a tooth is broken open a 
 cavity extending through both crown and fang will be found 
 in it. This is filled during life w r ith a soft pulp, containing 
 blood-vessels and nerves and known as the "pulp cavity." 
 
U4 
 
 THE HUMAN BODY. 
 
 The hard parts of the tooth disposed around the pulp cavity 
 consist of three different tissues. Of these, one, dentine or 
 ivory, immediately surrounds the cavity and makes up most 
 
 Fig. 52. — Longitudinal section of a molar tooth, k, crown ; n, neck ; _/*, fangs; e, 
 enamel ; </, dentine ; c, cement ; /, pulp cavity. 
 
 of the bulk of the tooth ; covering the dentine on the crown 
 is e?iamel, the hardest 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 
 * Enamel will strike fire with flint. 
 
77// TONGUE. 115 
 
 little very finel) 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 and phosphate of calcium, 
 which readily dissolve in weak a< ids ; de< omposing food par- 
 ticles 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.* (iood manners forbid the public 
 use of a tooth-pick, but on the earliest privacy after a meal a 
 wooden or quill tooth pick, or better dental silk, should be 
 employed systematically and carefully to dislodge all food 
 remnants which may have remained wedged between the 
 teeth. 
 
 Once a slight cavity has been formed, the process of decay 
 is apt to go on very fast ; first, because the exposed deeper 
 layer of the tooth is more easily dissolved than its natural sur- 
 face, and second, because the little pit forms a lodging-place 
 for bits of food, which, in decomposing through the action of 
 bacteria, 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 53) is a muscular and highly movable 
 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. 20). The mucous 
 membrane covering the upper surface of the tongue is rough- 
 
 * Acid medicines should always he sucked through a glass tube and 
 swallowed with as little contact as possible with tin* teeth. After each 
 dose the mouth should be thoroughly rinsed with water. 
 
n6 
 
 THE HUMAN BODY. 
 
 ened by numerous minute elevations or papilla, of which 
 there are three varieties. The circumvallate papilla are the 
 
 Fig. 53. — The upper surface of the tongue., i, 2, circumvallate papillae ; 3, fungi- 
 form papillae ; 4, filiform papillae ; 6, mucous glands. 
 
 largest and fewest, and lie near the root of the tongue, 
 arranged in the form of a V, with its open angle turned to- 
 
WH.il i "FURRED TONGUE" INDICATES. n; 
 
 wards the lips. The fungiform papillce are rounded m. 
 attached by narrower stems. They are found all over tin- 
 middle and tore part of the upper surface of the tongue, and 
 during life are readily recognized as red dots, more deeply 
 
 i olored because more richly supplied with blood than the rest 
 
 of the mucous membrane. The filiform papillce are pointed 
 elevations scattered all over the upper surface of the tongue, 
 e\( ept near its root. On our tongues, they are the smallest 
 and most numerous.* 
 
 What a "Furred Tongue" Indicates. — In health the sur- 
 face of the tongue is moist, covered by little ''fur," and in 
 childhood is 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 deranged the tongue 
 is commonly covered with a thick yellowish coat and there 
 is frequently a " bad taste " in the mouth, t All the parts of 
 the alimentary mucous membrane are in close physiological 
 connection, and anything disordering 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 sublingual, and the submaxillary. 
 
 * The filiform papillce are very large on the tongue of the cat, where 
 they may readily be seen and felt. They are large in nearly all car- 
 onivrous animals, 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 cell- shed from 
 its surface and numerous vegetable microscopic organisms belonging to 
 the group of Bacteria. 
 
n8 THE HUMAN BODY. 
 
 (Fig. 55.) 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 sublingual glands lie under the tongue 
 
 Fig. 55— The salivary glands. One side of the lower jaw has been removed, and 
 the face dissected, in order to show the salivary glands of the right side. 
 
 between the halves of the lower jaw-bone, and their ducts 
 open in the front of the mouth beneath the tongue. The sub- 
 
 * Technically, parotitis. 
 
THE FAUCES THE PHARYNX. i' 
 
 maxillary glands lie beneath the floor of the mouth behind 
 the sublingual near the angle of tin- jaw. 
 
 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 the uvula, below by the root of the toi. 
 and on the sides by muscles, covered by mucous membrane 
 and reaching from the soft palate to the tongue. The mus- 
 cles cause folds known as the pillars ofthefaua . Each fold 
 divides near the tongue, and in the hollow between its divi- 
 sions lies a tonsil | Fig. 53 I, a soft rounded body about the 
 size of an almond containing numerous minute glands which 
 form mucus. 
 
 Enlarged Tonsils. — The tonsils sometimes become en- 
 larged during a cold or sore throat. Occasionally the 
 enlargement is permanent and causes much annoyance. 
 The tonsils can, however, be readily removed without 
 danger, and this is the treatment usually adopted in such 
 cases. 
 
 The Pharynx or Throat Cavity (Fig. 46). — This portion 
 of the alimentary canal may be described as a conical bag 
 with its broad end turned up toward the base of the skull and 
 the other end narrowed into the gullet. Its front or ventral 
 wall is imperfect, presenting 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 swallowing {deglutition | it is raised into a horizontal 
 position, and separates the upper or nasal portion of the 
 pharynx from the rest. Through this upper part only air 
 
 * ( observe for yourself with the help <>f a looking gl 
 
120 THE HUMAN BODY. 
 
 passes,* entering it from the posterior ends of the two nos- 
 tril chambers. Through the lower portion both food and 
 air pass, one on its way to the gullet {p, Fig. 46), 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 the handle of a spoon. 
 During 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 contraction, drive 
 the food on. 
 
 The (Esophagus or Gullet is a tube which commences at 
 the lower termination of the pharynx and, passing on through 
 the neck and chest, ends below the diaphragm in the stom- 
 ach. In the neck it lies close behind the windpipe. 
 
 The Stomach (Fig. 56) is a curved conical elastic bag 
 placed transversely in the upper part of the abdominal cav- 
 ity, f Its larger end is turned to the left and lies close be- 
 neath the diaphragm ; the gullet (</) opens into its upper 
 border, through the cardiac orifice at a. The narrower right 
 end is continuous with the small intestine and communicates 
 
 * During a severe attack of vomiting the soft palate often acts 
 imperfectly in closing the passage between gullet and nostrils ; hence 
 some of the ejected matter not unfrequently is expelled through the nose 
 
 f The general anatomical arrangement of the stomach, and its con- 
 nections with the gullet and intestine, may he readily shown on the body 
 of a puppy, kitten, or rat which has been killed by placing it for five 
 minutes in a small box containing also a sponge soaked with chloroform. 
 
THE STOMACH, 
 
 I 21 
 
 with it through the pyloric orifice (c). The pyloric end oi 
 the stomach is separated from the diaphragm by the liver 
 (see Fig. 4). When moderately distended the stoma* h is 
 about twelve inches long, tour inches a< ross at its widest 
 
 part, and contains about three pints. 
 
 The Glands of the Stomach. — The mucous membrane 
 
 Fig. 56. — The stomach, if, lower end of the gullet ; a, position of the cardiac 
 aperture ; 6, the fundus ; c, the pylorus ; e, the first part of the small intestine ; along 
 k, 6, c, the great curvature ; between the pylorus and d, the lesser curvature. 
 
 Fig. 57. — A thin section through the gastric mucous membrane, perpendicular to 
 its surface, magnified about 25 diameters, a, a simple peptic gland; b, a compound 
 peptic gland ; c, a mucous gland. 
 
 lining the stomach is seen, with a magnifying glass, to be 
 covered with shallow pits. A microscope shows on the bot- 
 tom of each of these pits the openings of several minute tubes, 
 
122 
 
 THE HUMAN BODY. 
 
 fE 
 
 J ,G 
 
 [Mm 
 
 Sub- 
 Mucous 
 coat 
 
 
 
 the gastric glands, which lie imbedded in the mucous mem- 
 brane (Figs. 57 and 58 ) and secrete the gastric Juice. 
 
 The Muscular Coat of 
 the Stomach lies outside 
 the mucous membrane, and 
 is made up (Fig. 34 and 
 Fig. 48^7) of plain muscular 
 tissue, whose fibres run in 
 different directions. By its 
 ^f^-vt^l^ contractions it stirs up the 
 —"■ - >2^H^;"^:-:^^s food and mixes it with the 
 
 gastric juice. Around the 
 I pyloric orifice of the stom- 
 ach is a thick ring of mus- 
 cle (the pyloric sphincter), 
 which usually by contract- 
 ing closes the passage be- 
 tween the stomach and 
 the commencement of the 
 small intestine. During 
 
 digestion in the stomach 
 
 Fig. 58. — Wall of human stomach. E, epi- ° 
 thelium ; G, glands ; Mm, muscularis mucosae, foe pyloric Sphincter re- 
 laxes 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 below, and the heart immediately above, the 
 diaphragm. Over-distension of the stomach by gas (flatu- 
 lence), which is one of the symptoms accompanying indiges- 
 tion, may press up the diaphragm and interfere with the 
 proper working of the thoracic organs, causing feelings of 
 oppression in the chest, or palpitation of the heart. 
 
 I \ 
 
 5 
 
 at 
 
 5 
 
 L 
 
 Serosa 
 
 
SMALL !NTFSTI\r 
 
 I2 3 
 
 The Small Intestine commences at the pylorus and ends, 
 after many windings, in 
 
 the large intestine. It i> 
 about twenty feet 
 meters i long and about 
 two inches I five centi- 
 meters | wide at its gastric 
 end, narrowing to about 
 two thirds o( that width at 
 its lower portion. Kxter- 
 nallv there are no lines of 
 subdivision on the small 
 intestine, but anatomists 
 arbitrarily describe it as 
 consisting of three parts, 
 of which the first ten or 
 twelve in< hes is the duo- 
 denum,* the succeeding 
 two fifths of the remainder 
 the jejunum, and the rest 
 the ileum. 
 
 The MUCOUS Coat Of the Pig. 59— Diagram of abdominal part of ali- 
 mentary canal. C, the cardiac, and P, the 
 Small Intestine is pink, pyloric'endof the stomach; D. the duodenum; 
 
 /. /, the convolutions of the small intestine; CC 
 
 soft, and extremely V as-" the c * cum ^ h / he vermifon " a PP e " dix: ^' c 
 
 ascending, 7 C, transverse, and DL. descending 
 
 cular. Throughout a great cul,jn; * the rectum - 
 portion of the length of the tueb it is raised into permanent 
 folds in the form of crescentic ridges ( Fig. 6oj. These folds 
 (valvulu conniuenies) run transversely for a greater or less 
 distance round the intestine. They are first found about two 
 inches from the pylorus, and are most thickly set and largest 
 
 * Duodenum signifies literally twelve, and is applied here because this 
 portion is about twelve Gngerbrfeadths lung. 
 
124 THE HUMAN BODY. 
 
 in the upper half of the jejunum. In the lower half they 
 become gradually less conspicuous, and finally disappear 
 altogether about the middle of the ileum. The folds of the 
 
 Fig. 60. — A portion of the small intestine opened to show the valvule? conniventes. 
 
 mucous membrane serve greatly to increase its surface both 
 for absorption and secretion, and also to delay the food in its 
 passage ; it collects in the hollows between them, and so is 
 longer exposed 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 to be shaggy and covered everywhere (both over the 
 valvulae conniventes and between them) with closely packed 
 minute elevations standing up somewhat like the "pile" on 
 velvet and known as the villi (Fig. 61). In structure a villus 
 is somewhat complex. Beneath the covering of a single layer 
 of cells the villus consists of a framework of connective 
 tissue supporting 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 
 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 
 are accordingly called the lacteak. They communicate with 
 larger branches in the outer coats of the intestine, which 
 
/'////. GLANDS, ETC., Of SMALL INTESTINE 
 
 125 
 
 unite to form the trunks of the main lymphatic system. 
 Finally, in each villus, outside its Uu teals and beneath its 
 
 muscular layer, is a ( lose network of blood-vessels. 
 
 Fig. 61.— Villi of the small intestine, magnified about 80 diameters. In the left- 
 hand figure the lacteals, a, i, c, are filled with white injection; d. blood-vessels. 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. 
 
 The Glands of the Small Intestine open on the surface 
 of the small intestine between the bases of the villi and are 
 called the crypts of Lieberk'uhn (Fig. 62). 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 produce annular constrictions of the intestine, which 
 slowly travel from the stomach downward, one after another, 
 and thereby force the digesting food along the tube. This 
 movement is called peristalsis. 
 
 The Large Intestine (Fig. 59), forming the final portion 
 
126 
 
 THE HUMAN BODY. 
 
 of the alimentary canal, is about 5 feet (1.5 meters) long, 
 and varies in diameter from 2H01I inches (6-4 centimeters). 
 Anatomists describe it as consisting of the ccecum (cc) with 
 its vermiform appendix, the colon (ac, tc, dc), and the rectum 
 
 A 
 
 Fig. 62. — Vertical section of the intestinal mucous membrane of the rabbit. Two 
 villi are represented, in one of which the dilated lacteal alone is shown, in the other 
 the blood vessels and lacteal are both seen injected, the lacteal white, the blood 
 vessels dark ; a. the lacteal vessels of the villi ; a' , horizontal lacteal, which they join ; 
 f>, capillary blood vessels in one of the villi; c, small artery: d, vein; e, the epithe- 
 lium covering the villi ; g: tubular glands or crypts of Lieberkiihn, some divided down 
 the middle, others cut more irregularly ; i, the submucous layer. A, cross-section of 
 three tubular glands more highly magnified. 
 
 (r). The small intestine opens into the side of the large, 
 some distance from its closed 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 lead pencil, and about 4 inches (10 centi- 
 meters) long. It is a residual structure of considerable 
 importance in some of the lower animals. Its contents are 
 ordinarily the same as those of the caecum. It is therefore 
 frequently the receptacle of grape seeds, etc., which appar- 
 entlv do no harm. It is sometimes the seat of an inflammation 
 
LARGE INTESTINE ILEO 1L VAL\ i 1 ; 
 
 (appendi lue to bacterial activity under favoring con- 
 
 ditions. The colon commences on the right if the 
 
 abdominal cavity where the small intestine < ommuni< ates with 
 the large, runs up for some distance on that side [ascending 
 colon), then the middle line transverse colon) below 
 
 the stomach, and turns down [descending colon) on the left 
 In the lower left side of the abdomen it makes an S-shaped 
 
 Fig. 63. — The ileo-caecal valve, a, ileum ; t>, ascending colon ; c. caecum ; d, junc- 
 tion of the caecum and colon ; e and _/", loose folds of the mucous membrane, forming 
 the ileo-caecal valve ; g, vermiform appendage. 
 
 bend known as the sigmoid flexure ; from this the rectum pro- 
 ceeds 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 numer- 
 ous closely set glands much like the crypts of Lieberkiihn. 
 
 The Ileo-caecal 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 reverse way. 
 
128 
 
 THE HUMAN BODY. 
 
 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 centi- 
 meters 1 from the pylorus. 
 
 The liver is the largest gland in the body, weighing from 
 =;o to 60 ounces (1400 to 1700 grams). It is situated in 
 
 Vf a Lt 
 
 / 
 
 Fig. 64. — The under surface of the liver, d. right, and s, left lobe ; l'h, hepatic 
 vein; l~f>, portal vein; I'c. vena cava inferior: Dch, common bile duct; Dc, cystic duct; 
 Dh % hepatic duct; If. gall bladder. 
 
 the upper part of the abdominal cavity f/e, le ', Fig. 4), 
 rather more on the right than on the left side, immediately 
 below the diaphragm. The liver is of dark reddish-brown 
 color, and of soft friable texture. The vessels carrying 
 blood to the liver (Tig. 64) are the portal vein (Vp), and 
 the hepatic artery ; both enter it at a groove on its under 
 side, where a duct also passes out from each half of the 
 organ. The ducts unite to form the hepatic duct (Dh), 
 
THE LIVER 
 
 129 
 
 which meets the cystic duct | Dc) t proceeding from the gall- 
 bladder ( r/>, a pear-shaped sac in which the bile or gall 
 
 V u 
 
 Fig. 65. — The stomach, pancreas, liver, and duodenum, with part of the rest of the 
 small intestine and the mesentery; the stomach and liver have been turned up so as 
 to expose the pancreas. l\ stomach; D, I)', D", duodenum; L, spleen; /', pancreas; 
 R, right kidney; 7', jejunum; I'/, gal] bladder; A, hepatic duct; c, cystic duct; ch, 
 common bile duct; 1, aorta; 2, an artery (left coronary) of the stomach; 3, hepatic 
 artery; 4, splenic artery; 5, superior mesenteric artery; 6, superior mesenteric vein; 
 7, splenic vein; l'/, portal vein. 
 
 formed by the liver accumulates when food is not being di- 
 gested in the intestine. The common bile duct (Bc/i), formed 
 
130 THE HUM4N BODY. 
 
 by the union of the hepatic and cystic ducts, opens into the 
 duodenum. 
 
 The Functions of the Liver. — The size of the liver sug- 
 gests that it has important functions in the body. It re- 
 ceives all the blood from the stomach and intestines (the 
 portal system). Its cells destroy old red corpuscles. They 
 also take out of the blood excess of sugar and store it up in 
 the form of a kind of animal starch (glycogen), which they 
 later dole out again as sugar when the blood needs it. Ex- 
 periments suggest that the liver cells bring about the final 
 oxidation of nitrogenous materials into urea, in which form 
 they are excreted by the kidneys. 
 
 The Pancreas * 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 drains it and joins the common bile duct close to its 
 intestinal opening. The pancreas secretes a watery-looking 
 liquid, much like saliva in appearance, which is of great 
 importance in digestion. 
 
 * Butchers sell two kinds of sweetbread, known as the belly sweetbread 
 and the neck or heart sweetbread. The former is the pancreas; the 
 latter is the thymus, an organ of doubtful function, found only in young 
 animals, and lying at the bottom of the neck and upper part of the chest 
 in front of the windpipe. 
 
CHAPTER XII. 
 DIGESTION. 
 
 The Object of Digestion. — A few of the foodstuffs which 
 we eat arc in solution and ready to soak at once into the 
 lymphatics and blood vessels of the alimentary canal; others, 
 such as a grain of salt, though not dissolved 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, as milk, special 
 chemical changes have to be brought about to make them 
 capable of absorption. The different secretions poured into 
 the alimentary tube act in various ways upon different food- 
 stuffs, dissolving some and chemically changing others, until 
 at last all are in a condition in which they can be taken up 
 into the lymph and blood-vessels for transference to distant 
 parts of the body. 
 
 Digestive Ferments. — The chemical changes necessary to 
 make the foods absorbable are accomplished almost wholly 
 by the action of various organic ferments, each with a special 
 power adapted to the digestion of a particular foodstuff. 
 P/ya/in, found in saliva, pepsin and rennin in gastric juice, 
 trypsin, a?nylopsin, and sieapsin in the pancreatic juice, and 
 invertin in the intestinal juice, are the most important of 
 these. 
 
 The Saliva, the first solvent poured upon the food, is a 
 mixture of pure saliva from the salivary glands with the 
 
 131 
 
132 THE HUMAN BODY. 
 
 mucus secreted by the membrane lining the mouth. This 
 mixed saliva is a colorless, cloudy, feebly alkaline liquid. 
 
 The Uses of Saliva are mainly physical and mechanical. 
 It keeps the mouth moist and allows us to speak with com- 
 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 further 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 fragment of sugar upon it. 
 
 Chemical Action of the Saliva. — In addition to these phy- 
 sical actions, the saliva effects a chemical change on an im- 
 portant foodstuff, due to the presence of the ferment ptyalin. 
 Starch (although it swells up greatly in hot water) is insoluble 
 and cannot be absorbed from the alimentary canal. Ptyalin 
 adds chemically a portion of water to the starch and thus 
 changes it into the readily soluble and absorbable maltose, a 
 form of sugar. 
 
 2C.H..O.+ 2H.O = 2C.H„0.. 
 
 Starch. Water. Maltose. 
 
 * 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 swallow 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. 
 
SWALLOWING OR DEGLUTITION. 1 33 
 
 The Influence of Saliva in Promoting Digestion in the 
 Stomach. - It changes starch into maltose most rapidly when 
 no acid is present. When the food passes from the mouth to 
 the stomach the saliva's action is retarded l>y the acidity of 
 
 the gastric juice. Indirectly, however, the saliva promotes 
 digestion in the stomach. Weak alkalies stimulate the gastric 
 glands to pour forth more abundant secretion,* and the alka- 
 line saliva 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 the saliva, when swallowed, helps to stimulate 
 the stomach. 
 
 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 it from 
 getting between them and the gums.f The mass is finally sent 
 on from the mouth to the stomach by 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 com- 
 monly takes place unconsciously. The second stage of deglu- 
 tition is that in which the food passes through the pharynx ; 
 
 * Hence the efficacy of a little carbonate of soda or apollinaris water 
 taken before meals, in some forms of dyspepsia. 
 
 | 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. 
 
134 THE HUMAN BODY. 
 
 this 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- 
 passages 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) rises to meet the epiglottis, and thus aids in closing 
 the passage to the lungs.* The soft palate is raised at the 
 same time to close the passage into the nose (see Fig. 46). 
 As the final step the isthmus of the fauces is closed as soon 
 as the food has passed, by the contraction of the muscles on 
 its sides and the elevation of the root of the tongue. As all 
 passages out of the pharynx except the gullet are thus blocked, 
 the pharyngeal muscles, by contracting, can squeeze the food 
 only into the oesophagus. The muscular movements concerned 
 in this part of deglutition are all excited without the interven- 
 tion of the will ; the food, by touching the mucous membrane 
 of the pharynx, produces involuntarily the proper action of 
 the swallowing muscles. f Indeed, many persons after having 
 got the mouth completely empty cannot perform the move- 
 ments of the second stage of deglutition at all. On account 
 of the involuntary nature of the contractions of the pharynx 
 the isthmus of the fauces forms a sort of Rubicon ; food that 
 has entered the pharynx must be swallowed, even though the 
 swallower learns immediately that he is taking poison. The 
 third stage of deglutition is that in which the food is passing 
 along the gullet, and is comparatively slow. Even liquid sub- 
 stances do not fall or flow down this tube, but have their pas- 
 sage more or less controlled by its muscular coats, which grip 
 
 * 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. 
 
 { The process is what is known as a reflex action. See Chap. XX. 
 
GASTRIC JUICE PEPTONES. 135 
 
 the successive portions swallowed and pass them on. Hence 
 the possibility of performing the apparently wonderful feat of 
 drinking a glass of water while standing upon the head : peo- 
 ple forget that one sees the same thing done every day by 
 horses and other animals whit h drink with the pharyngeal end 
 of the gullet lower than the stomach. 
 
 The Gastric Juice.— The food having entered the stomach 
 is exposed to the action of the gastric juice, which is a thin 
 colorless or pale yellow liquid of a strongly acid reaction. It 
 contains, beside water, salts and mucus, free hydrochloric acid 
 (about 0.2 per cent), and a ferment pepsin, which in acid liq- 
 uids has the power of converting ordinary proteids into closely 
 allied substances called peptones. It also dissolves solid pro- 
 teids, 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. 145.) 
 
 The change to peptone is solely for the purpoes of absorp- 
 tion, since peptone is not found in the blood, and when in- 
 troduced acts as a poison. Peptone is chiefly represented in 
 the blood by the blood proteids serum, albumin and serum 
 globulin. This change from the diffusible peptone back to a 
 non-diffusible proteid is supposed to be due to the action of 
 the epithelial cells of the intestine through which the absorp- 
 tion takes place. It is thus seen that the digestion of pro- 
 teids is but a step toward the production of the proteids of 
 the blood, which form the real nitrogenous food of the tissue. 
 
 Gastric Digestion. — In the stomach the onward progress 
 of the food is stayed for some time. The pyloric sphincter 
 
I3 6 THE HUMAN BODY. 
 
 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 secre- 
 tion of its glands. In the stomach, part of the proteid of the 
 food is dissolved and turned into peptones. 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 the solution of the white fibrous con- 
 nective tissues the disintegration of animal foods, commenced 
 by the teeth, is carried much further in the stomach ; and 
 the food mass, mixed with much gastric secretion, becomes 
 reduced to the consistency of a thick soup, usually of a gray- 
 ish color. In this state it is called chyme. 
 
 The Chyme contains, after an ordinary meal, a consid- 
 erable quantity of peptones, which are in part gradually 
 absorbed into the blood and lymphatic vessels of the gastric 
 mucous membrane and carried off, along with other dissolved 
 and dialyzable bodies, e.g. salts and sugar. After the food 
 has remained in the stomach some time (one and a half to 
 two hours) the pyloric sphincter relaxes at intervals to allow 
 the liquefied food to pass on in successive portions into the 
 duodenum. At the end of three or four hours the stomach 
 is ordinarily emptied, as the pyloric sphincter finally relaxes 
 to such an extent as to allow even the large indigestible 
 masses to be squeezed into the intestines.* 
 
 The Chyle. — The pancreas commences to secrete as soon 
 
 * 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 tl e abdomen to the interior of the stomach. 
 
THE PANCREATIC SECRETh 1 37 
 
 as food enters the stoma* h ; hem e a quantity of its sec retion 
 is already accumulated in the intestine when the chyme enters. 
 The gall-bladder is distended with bile, secreted since the 
 last meal. The acid chyme stimulating the duodenal mucous 
 membrane causes a reflex contraction of the muscular coat of 
 the gall-bladder, and a gush of bile is poured out into the 
 chyme. From this time on both liver and pancreas continue 
 secreting actively for some hours, and pour their prodiu ts 
 into the intestine. The glands of the intestine 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. 
 This, as found in the intestine after an ordinary meal, con- 
 tains water, partly swallowed and partly derived from the 
 salivary and other secretions, undigested proteids, some un- 
 changed starch, oils from the fats eaten, peptones formed in 
 the stomach but not yet absorbed, salines and sugar, which 
 have also escaped complete absorption in the stomach, indi- 
 gestible substances taken with the food, together with the 
 secretions of the alimentary canal. 
 
 The Pancreatic Secretion is clear, watery, alkaline, and 
 much like saliva in appearance. The Germans call the pan- 
 creas the "abdominal salivary gland." In digestive prop- 
 erties, however, the pancreatic secretion is far more impor- 
 tant than the saliva, acting not only on starch but on proteids 
 and fats. On starch it acts like the saliva, but more ener- 
 getically because of the presence of the ferment amylopsin. 
 It produces changes in proteids similar to those effected in 
 the stomach, but by the agency of the ferment, trypsin, which 
 differs from pepsin in being able to act in an alkaline, neutral 
 or slightly acid solution. Upon fats the pancreatic juice 
 has a complex effect. Through the action of another fer- 
 
138 THE HUMAN BODY. 
 
 ment, sfeapsin, it splits up a portion of the fats into fatty acids 
 and glycerin. The alkali present unites with the fatty acids 
 to form soap in sufficient quantity to assist in emulsifying 
 such portion of the fats as has not been split up. This pro- 
 cess of changing fats into soaps is known as saponification. 
 As soap and glycerin are soluble in water they are capable of 
 absorption.* The greater part of the fats is not, however, so 
 broken up, but merely mechanically separated into droplets 
 which remain suspended in the chyle and give it a whitish 
 color, just as cream particles are suspended in milk, or olive 
 oil in mayonnaise sauce. If oil is shaken up with water, the 
 two will not mix, but if some raw egg is added a creamy 
 mixture is readily formed in which the oil remains for a long 
 time evenly suspended in the watery menstruum. The rea- 
 son of this is that each oil droplet becomes surrounded by a 
 delicate pellicle of albumen and is thus prevented from fusing 
 with its neighbors 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, making it white because the innumerable tiny oil- 
 drops floating in it reflect all the light which falls on its sur- 
 face. It is probable that fats in this condition of fine divi- 
 sion may be absorbed without further change. 
 
 The saponification of fat, like the peptonizing of proteids, 
 is but a step in the process of getting the fat into the blood. 
 Fat alone is found in the blood ; hence the soap formed is 
 
 *< C ^f'[0,+ 3 H,0 =3( C, ' H "2i-°) + C H;i ' 
 
 I Stearin -f 3 Water = 3 Stearic acid -f- I Glycerin. 
 Ordinary soap is a compound of a fatty acid with soda, colored and 
 scented by the addition of various substances. Soft soap is a compound 
 of a fatty acid with potash. Both dissolve in water, though the fats from 
 which they are made will not. 
 
THE HI I.E. 139 
 
 undoubtedly reconverted into fat by the union of the fatty 
 acids and glycerin. 
 
 The Bile. — Human bile when quite fresh is an alkaline 
 golden-brown liquid. It contains eoloring matters derived 
 from broken down red blood corpuscles, mineral salts, water, 
 and the sodium salts of two nitrogenized acids, (aurocholii 
 and glycocholic, of which the former predominates. 
 
 The Uses of Bile. — Bile has no digestive action upon 
 starch or proteids and does not break up fats. Whether it 
 emulsifies fats has been a matter of much discussion. It has 
 been found by experimentation that if a rabbit is killed after 
 having been fed with oil, no milky chyle is found above the 
 point where the pancreatic duct opens into the intestine, 
 although the bile entered and mixed with the intestinal con- 
 tents a foot a^ove this opening. The bile alone does not, 
 therefore, emulsify fats in the rabbit. In many animals, as 
 in man, the bile and pancreatic ducts open together into the 
 duodenum, so that if an animal is killed during digestion and 
 emulsified fats are found in the chyle, it is impossible to say 
 whether or not the bile had a share in the process of emulsi- 
 fication. As, however, the bile of rabbits is much the same 
 as that of other animals, it has been inferred that the bile 
 does not emulsify fats in the intestine. Some have even 
 gone so far as to say that the inertness of bile with respect to 
 other foodstuffs makes it probable that it has no digestive 
 power at all, but is merely an excretion which is passed out 
 of the body through the alimentary canal. 
 
 There are many facts, however, which militate against this 
 view. The bile enters the upper end of the small intestine 
 at a point which necessitates its traversing more than twenty 
 feet before it can pass from the body. Moreover, a large 
 part of the bile is reabsorbed from the intestinal tract, to be 
 
14° THE HUM4N BODY. 
 
 again secreted by the liver and again reabsorbed. Thus 
 there is a strong supposition in favor of its being intended 
 for special use in the intestinal tract. By its alkalinity it 
 undoubtedly assists in overcoming the acidity of the chyme 
 and so allows the pancreatic secretion to act more strongly. 
 It probably helps to excite the contractions of the muscular 
 coats of the intestines, since constipation often results when 
 the bile duct is temporarily clogged, as it usually is in jaun- 
 dice. It probably also acts as a preservative, for a deficiency 
 of bile secretion is said to lead to putrefaction of the intes- 
 tinal contents. 
 
 There are other facts, moreover, that point to the direct 
 influence of the bile in promoting the absorption of fats. 
 if one end of a very narrow glass tube is moistened with 
 water, oil will rise in it but slightly; if the tube is moistened 
 with bile instead of water, the oil will ascend higher. 
 Again, oil passes through a membrane kept moist with 
 bile under a much lower pressure than through one wet 
 with water. Hence, it is quite possible that bile, by moist- 
 ening the cells lining the intestines, may facilitate the pas- 
 sage of oily substances into the villi and thus promote the 
 absorption of fats. 
 
 Moreover, experiment has shown that if the bile is pre- 
 vented from entering the intestine of a dog he eats much 
 more food than before, and that a great proportion of the 
 fatty part passes out of the alimentary canal unabsorbed. 
 There is no doubt, therefore, that the bile somehow aids in 
 the absorption of fats. 
 
 The Intestinal Juice consists of the mixed secretions ot 
 the crypts of Lieberkiihn and other glands of the intestine. 
 It is very difficult to obtain it pure, and hence its digestive 
 action is imperfectly known. It is alkaline and helps to over- 
 
INTESTINAL DIGESTION. 141 
 
 come the a< idity of the < hyme and to allow the trypsin of the 
 pancreas to ad on proteids. It seems capable itself of dis- 
 solving some kinds of proteids and turning them into pep- 
 tones. 
 
 Intestinal Digestion. — Having ( onsidered separately the 
 digestive actions of the different secretions poured into the 
 small intestine, we may now consider their combined action. 
 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 alka- 
 linity allows the pancreatic secretion to finish the solution 
 and transformation of proteids into peptones. The pancreatic 
 secretion also continues the conversion of starch into maltose. 
 The bile and pancreatic secretion are thoroughly mixed with 
 the fats by the contractions of the intestine, producing an 
 emulsion, which is taken up by the cells lining the intestine. 
 To a certain extent the fats are also saponified. The result 
 of all these processes is a thin, milky alkaline liquid called 
 chyle. 
 
 Indigestible Substances. — With every meal several things 
 are eaten which are not digestible. Among them are elastic 
 tissue, forming a part of the connective tissue of all animal 
 foods, and cellulose, the chief constituent of the cell walls in 
 plants. The mucus secreted by the membrane lining the 
 alimentary tract also contains an indigestible substance, 
 mucin. These three materials, together with water, un- 
 digested foodstuffs, the coloring matter of bile, and other 
 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 rectum. 
 
 The regular daily expulsion of waste matters is of the ut- 
 
142 THE HUMAN BODY. 
 
 most importance from the standpoint of health. If the food 
 contains too little indigestible material there is not sufficient 
 bulk remaining in the large intestine to insure its being 
 moved forward by peristaltic action to the rectum for expul- 
 sion. The waste matters of some foods, as the bran of 
 wheat, the fine beard of oats, by their irritation of the intes- 
 tinal wall lead to a more vigorous peristalsis. Infrequent 
 evacuation permits decomposition through the activity of the 
 hordes of bacteria which infest the large intestine. To the 
 absorption of the products of decomposition from the intes- 
 tine are to be attributed some of the harmful effects of this 
 condition. This is so common a trouble that it is not sur- 
 prising that patent medicines owe their success to the fact 
 that they are chiefly laxative and thus give temporary relief. 
 Exercise, regularity of habit, the use of foods with a large 
 share of waste, such as bread made of graham flour, onions, 
 corn, green peas, fruits, and the drinking of plenty of water, 
 are the best preventatives. 
 
 Dyspepsia is the common name of a variety of diseased 
 conditions attended with loss of appetite or troublesome 
 digestion. The immediate cause of the symptoms and the 
 treatment necessary may vary widely ; 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 themselves, 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 ; loss of appetite 
 
ABSORPTION FROM TUP. ALIMENTARY CANAL. 143 
 
 may be due to any <>f several causes. The stoma* li may be 
 apathetic and lack its normal sensibility so that the empty con- 
 dition does not act as a suffi« ient excitant. If food is taken 
 at such a time it is often a sufficient stimulus, and "appetite 
 comes with eating." A bitter solution 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 replaced by nausea, or even vomiting, as soon as a few 
 mouthfuls have been swallowed ; the extra stimulus of the 
 food overstimulates the too irritable stomach, just as a 
 draught of mustard and warm water overstimulates a healthy 
 one. The proper treatment in such cases should be sooth- 
 ing.* 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 to supply 
 gastric juice until the improved digestion enables the stomach 
 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, which require special knowledge for their treat- 
 ment. Since it deprives the body of its proper nourishment, 
 it tends to intensify itself and should never be neglected. 
 
 Absorption from the Alimentary Canal. — Through its 
 whole extent the mucous membrane lining the digestive tube 
 
 * 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 dila- 
 tation of the blood vessels of the organ ; if it does not, the gastric juice will 
 be imperfectly secreted. In such cases one may stimulate the secretory 
 nerves by weak alkalies (p. 133), 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 uf hot 
 water after eatintr which has been in vogue. 
 
J 44 THE HUMAN BODY. 
 
 is traversed by a very close meshwork of blood and lymph 
 vessels. Matters ready for absorption pass through or be- 
 tween the cells covering the surface of the mucous membrane 
 and then through the very thin walls of the smallest blood 
 and lymph vessels ; by these they are conveyed to the larger 
 channels leading to the heart. From the heart the digested 
 and absorbed food is distributed to every part of the body. 
 
 Absorption from the Mouth, Pharynx, and Gullet is ordi- 
 narily slight. Water, common salt, sugar and grape sugar 
 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 any considerable absorption. 
 
 Absorption from the Stomach. — Food stays in the stomach 
 a considerable time, and it might be supposed that absorbable 
 material would be taken up to a considerable extent by the mu- 
 cous membrane of the stomach and passed on into the general 
 blood current. As a matter of fact, experiments have demon- 
 strated very little absorption in this way. 
 
 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 absorption j 
 the small intestine, on the other hand, is specially constructed 
 to absorb. Its valvulae conniventes delay the progress of the 
 food mass, while its innumerable villi, with their blood vessels 
 and lymphatics (p. 125), reach out, like so many rootlets, 
 into the chyle to take it up. 
 
 The sugars reaching the small intestine or formed in it are 
 absorbed mainly into the blood and carried to the liver, 
 where they are turned into glycogen for storage. The pep- 
 tones passed into the intestine from the stomach, or formed 
 in it by the action of the pancreatic secretion, are taken up 
 
THE LACTEA IS -1)1 A LYSIS. 145 
 
 both by the lymphatics and by the Mood vessels. The emulsi- 
 fied tats pass into the lymphatics of the villi and arc carried 
 by them to the blood. 
 
 The Lacteals. — The innumerable tiny tat drops drained 
 off by the intestinal lymphatics or lacteals after an ordinary 
 meal make their contents look white and milky, heme the 
 name.* During fasting the lymphatics of the small intestine, 
 like those in other parts of the body (see Chap. XIII.) con- 
 vey a clear colorless liquid. 
 
 Dialysis. — When two specimens of water containing differ- 
 ent matters in solution are separated from one another by a moist 
 animal membrane, an interchange of 
 material will take place under certain 
 conditions. If a solution of common 
 salt is placed in an apparatus (Fig. 66) 
 on one side (B) of an animal mem- 
 brane, and a solution of sugar in water 
 on the other side (C), it will be found 
 after a time that some salt has got into 
 
 FlG. 66. — Dialyzing apparatus. 
 
 Caild SOme SU^ar into B, although there A r - animal membrane on end 
 
 ° of tube separating two fluids; 
 
 are no visible pores in the partition, f^ 11 in tube ; c, sugar in 
 and the pressure of the liquid is the 
 
 same on both sides, Such an interchange is said to be due to 
 dialysis or osmosis, and if the process is allowed to go on for 
 some hours the same proportions of salt and sugar will be 
 found in the solutions on each side of the dividing membrane. 
 Substances differ much in the rapidity with which they may 
 be dialyzed. Salts of various kinds ordinarily dialyze much 
 more rapidly than sugar, peptone, etc. Many substances are 
 incapable of dialyzation. Food materials are almost univer- 
 sally found among these, and hence there is the necessity 
 
 * From Latin lac, milk. 
 
1 46 THE HUMAN BODY. 
 
 for digestion, which, by making the foods dialyzable, facili- 
 tates their absorption. Substances which are dialyzable are 
 called crystalloids, those which are not, colloids. 
 
 Absorption from the Large Intestine. — In the duodenum 
 the bulk of food entering from the stomach is increased by 
 the bile and pancreatic secretions. Thenceforth absorption 
 overbalances secretion, and the food mass becomes less and 
 less in bulk to the lower end of the ileum. The contractions 
 of the small intestine push forward its continually diminishing 
 contents, until they reach the ileo-caecal valve, through which 
 they are ultimately pressed. When the mass enters the large 
 intestine its nutritive portions have been almost entirely ab- 
 sorbed, and it consists chiefly of water, with the indigestible 
 portions of the food and the secretions of the alimentary 
 canal. It contains cellulose, elastic tissue, mucus, altered bile 
 pigments, fat if a large quantity has been eaten, and starch 
 if raw vegetables have formed part of the diet. 
 
 In the large intestine there is a considerable absorption of 
 water and of the unabsorbed products of digestion. It is 
 probable that digestion may continue to some degree here. 
 When artificially prepared foods are injected into the rectum 
 in sufficient amounts, the absorption is rapid enough to sus- 
 tain life for several weeks under favorable conditions, although 
 no food is taken into the stomach. 
 
 Finally the residue is expelled from the body. 
 
CHAPTER XIII. 
 
 BLOOD AND LYMPH. 
 
 Why We Need Blood. — 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 
 made up of many organs, some of which are far away from the 
 surface of its body, this is impossible ; some organs are there- 
 fore set apart to catch food, and arrangements made to carry 
 this food to the others. In our own bodies many parts lie far 
 away from the stomach and intestines which receive, digest, 
 and absorb our food, and from the lungs which take oxygen 
 from the air ; yet every part, bone and muscle, brain and 
 nerve, skin and gland, needs a constant supply of these 
 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 minister to the 
 growth and repair of the body and to furnish energy, necessi- 
 tates an arrangement by which the matters received shall be 
 distributed to other parts. The distribution is accomplished 
 by the blood, which goes to every organ from the crown of the 
 head to the sole of the foot. As it flows from part to part, the 
 blood takes nourishment from the alimentary tract and oxygen 
 from the lungs, and gives them out to the parts which need 
 them. 
 
 147 
 
148 THE HUMAN 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. 86), and carries them to the excretory organs, by which 
 they are removed from the body. 
 
 The blood is a middleman, trading between the receiving 
 organs (lungs and alimentary canal) and the tissues of the 
 body, and again between the tissues and the excretory organs. 
 Each part is thus kept supplied with food and freed from 
 wastes, 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 very widely distributed over the body, since it flows from 
 any part of the surface when the skin is cut. There are, how- 
 ever, a few parts into which blood is not carried. The outer 
 layer of the skin,* hairs and nails, the hard parts of the teeth 
 and most cartilages contain no blood : these non-vascular 
 tissues are nourished by liquid which soaks through the walls 
 of blood vessels in neighboring parts. 
 
 The Histology of Blood. — Fresh blood is to the unassisted 
 eyea red opaque liquid showing no sign of being made up of 
 different parts ; but when examined by a microscope it is 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 plasma is color- 
 less and watery -looking ; the corpuscles are of two kinds, red 
 and colorless. The red corpuscles are by far the most numer- 
 ous and give the blood its color ; they are so tiny and so 
 
 * The absence of blood in the superficial layer of the skin may be 
 readily shown : take a fine needle threaded with silk ; by taking -hallow 
 stitches a pattern can be easily embroidered on the palm or back of the 
 hand without drawing a drop oi blood. 
 
PLATE III.— a general view of thb lymphatics ob absorbents. That portion of them 
 known as the lacteal* is seen at d, passing from the small intestine i to the thoracic duct f. 
 
EXPLANATION OF PLATE III. 
 
 A General View of the Lymphatic or Absorbent System 
 
 of Vessels. 
 
 At e is seen 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. 61) ; at/" the thoracic duct, into which the lacteals 
 open. This duct passes up the back of the chest, and opens into the 
 great vein at g, on the left side of the neck : here the chyle mingles with 
 the venous blood. In the right upper and lower limbs the superficial 
 lymphatic vessels / / / /, which lie beneath the skin, are represented. In 
 the left upper and lower limbs the deep lymphatic vessels which accom- 
 pany 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 //. At m m are seen the 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 distin- 
 guished from that section of them known as the lacteaL, will be found on 
 P- *59- 
 
A7:7) BLOi '/» CORPUSCLES. 
 
 149 
 
 plentiful that about five millions of them arc contained in 
 a drop of blood the size of a small pinhead | 1 1 u. nun. . 
 They are so closely packed that the unaided eye cannot see 
 
 
 Fig. 67. — Blood corpuscles. A. magnified about 400 diameters. The red cor- 
 puscles have arranged themselves in rouleaux ; u, a, colorless corpuscles ; B, red 
 corpuscles more magnified and seen in focus ; E, a red corpuscle slightly out of focus. 
 Near the ri.uht-hand top corner is a red corpuscle seen in three-quarter face, and at C 
 one seen edgewise. /•', G, H, /, white corpuscles highly magnified. 
 
 the spaces between them, and so the whole blood appears 
 uniformly red. 
 
 Red Blood Corpuscles. — The red corpuscles of human 
 blood (Fig. 67) are circular disks slightly hollowed out on 
 each face. Seen singly with a microscope each is not 
 red but pale yellow ; a drop of blood spread out very thin on 
 glass, or mixed with a tablespoonful of water, is also pale 
 yellow ; the corpuscles look red only when they are crowded 
 together in a mass. Soon after blood is drawn most of the 
 red corpuscles cohere side by side in rows, something like 
 piles of coin. 
 
*50 
 
 THE HUMAN BODY. 
 
 The red corpuscles of most mammalia resemble those of 
 
 man in being circular bi- 
 concave pale yellow disks; 
 those of camels and drom- 
 edaries, however, are oval. 
 The red blood corpuscles 
 of birds, reptiles, amphib- 
 ians, and fishes are oval 
 
 Fig. 68. — Red corpuscles of the frog. 
 
 and contain a nucleus in the centre such as is not found in 
 human red corpuscles. 
 
 The Origin of the Red Corpuscles. — In adult life the red 
 blood corpuscles are constantly being destroyed and as con- 
 stantly renewed. They are developed in the red marrow of 
 the bones, thrown into the blood current to perform their 
 work of carrying oxygen, and when apparently no longer 
 able to do this work successfully, are destroyed by the 
 liver. 
 
 Haemoglobin. — Each red corpuscle is soft and jelly-like. 
 Its chief constituent, besides water, is a proteid substance 
 containing iron, h&m'o-glo-bin, which has the power of com- 
 bining with oxvgen when in a place where oxygen is plenti- 
 ful, and of giving it off again in a region where it is present 
 in small amount or not at all. This enables the blood to carry 
 oxvgen from the lungs to the active tissues which have used 
 up their supply. 
 
 Haemoglobin itself is dark purplish-red in color ; haemo- 
 globin combined with oxygen is bright scarlet. Accordingly, 
 the blood which flows to the lungs after giving up its oxygen 
 is dark red, but becomes a bright scarlet after having received 
 a fresh supply of oxygen from them. 
 
 The Colorless Blood Corpuscles are a little larger than the 
 red, but much less numerous (about i to 300). As their 
 
THF. COLORLESS BLOOD CORPUSCLES. 
 
 i 51 
 
 name implies, they contain no coloring matter. Each is a 
 
 cell with a nucleus, and lias the won- 
 derful power of changing its shape. 
 Watched with a microscope the cor 
 
 puscles may be seen to alter their 
 form slowly (Fig. 69), or even to 
 creep across the glass. Their move- 
 ments are very like those of the micro- F,G - ,^t a , white bIood 
 
 corpuscle, sketched al succes- 
 
 scopic animal named amoeba, and are »i ve , i , nt ! rv f ls ?l a f l w * 
 
 1 ' to illustrate the chariK' !S "I 
 
 called amoeboid. These 
 
 accordingly 
 
 ban] 
 form due to its amoeboid 
 movements. 
 
 corpuscles are thus little, independently moving cells which 
 live in the liquid of the blood. They apparently have the 
 power of taking into their substance any foreign particles such 
 as broken-down cells, bits of pigment which have been in- 
 jected to test their voracity, and bacteria. These particles 
 they digest by a chemical process not unlike in its results that 
 which takes place in the alimentary tract of higher animals. 
 They have the power of passing through the walls of the cap- 
 illaries and of wandering about through the tissues of the 
 body, literally "seeking what they may devour." Doubtless 
 many disease-producing bacteria which have entered the body 
 either through the lungs or by way of the mouth are success- 
 fully destroyed by the white blood corpuscles. This process 
 is called phagocytosis. 
 
 It is claimed by some that the main explanation of the 
 body's resistance to many kinds of infection (invasion by 
 bacteria) is found in the protection thus afforded by white 
 blood corpuscles, and that the strength of the resistance is in 
 proportion to the vigor of the corpuscles. When the bacte- 
 rial invasion is too great to be handled successfully, the cor- 
 puscles are themselves destroyed by the bacteria. In abscesses 
 we have usually a battleground of these two forces. The in- 
 
152 THE HUMAN BODY. 
 
 vasion of the bacteria through a scratch or cut leads to irrita- 
 tion of the tissues ; this in turn leads to the advance of the 
 army of corpuscles. In the struggle many of the combatants 
 on both sides are destroyed. Many times the corpuscles 
 collect in such numbers that they fill up the tissues and even 
 clog the circulation of the blood, thus shutting off food from 
 themselves and the tissues and contributing to their own de- 
 feat. In the discharge (pus) from such abscesses, white 
 blood corpuscles are found in immense numbers. 
 
 The Coagulation of Blood. — When blood is first drawn 
 from the living body it is perfectly liquid, flowing as readily 
 as water. This condition is only temporary : in a few min- 
 utes the blood becomes sticky and resembles a thick red syrup; 
 the thickening becomes more and more marked, until, after 
 the lapse of five or six minutes, the whole mass is a firm jelly 
 and adheres to the vessel containing it. so that this may be 
 inverted without spilling. This stage is known as that of 
 gelatinization, and is also not permanent. In a few minutes 
 the top of the jelly-like mass will be seen to be hollowed or 
 " cupped," and in the concavity will be found a small quan- 
 tity of nearly colorless liquid, the blood serum. The jelly 
 next shrinks so as to pull itself loose from the sides and bot- 
 tom of the vessel containing 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 co- 
 agulated, 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 freshly drawn blood 
 is studied under the microscope, one will observe beside the 
 red and white blood corpuscles a colorless liquid in which 
 they float. This is the plasma of the blood. Very fine solid 
 
DEFIBRINATED OK WHIPPED BLOOD. 
 
 threads w ill be seen to separate out from the Mood. These 
 quickly run through the plasma in every dire< tion and form a 
 close network entangling the corpuscles. These threads are 
 composed of an albuminous I proteid I substance known as 
 fibrin. When they first form, the whole drop is mu< h like a 
 sponge soaked full of water (represented by the scrum), and 
 having solid bodies (the corpuscles) caught in its meshes. 
 After the fibrin threads have been formed they begin to 
 shorten; hence the fibrinous network tends to shrink in every 
 direction, and this shrinkage is greater the longer the clotted 
 blood is kept. At first the threads stick too firmly to the 
 bottom and sides of the vessel to be pulled away, and thus 
 the first sign of the contraction of the fibrin is seen in the 
 cupping of the surface 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 
 corpuscles are held back in the meshes of the fibrin. 
 
 The clotting of blood takes place only when blood is out- 
 side of the body, and is due to the action of a ferment {fibrin- 
 ferment) upon one of the proteid substances dissolved in the 
 plasma [fibrinogen). This coagulation of the blood resembles 
 closely that of muscle, which is also caused by the action of a 
 ferment. The total amount of fibrin formed is slight (o.2# 
 of the weight of the blood). 
 
 Defibrinated or Whipped Blood. — As the essential point 
 in coagulation is the formation of fibrin in the plasma, and as 
 blood only forms a certain amount of fibrin,* if this is re- 
 
 * Fibrin is formed from fibrinogen, a soluble albumen existing in blood 
 plasma, 
 
154 THE HUMAN BODY. 
 
 moved as fast as it forms the remaining blood will not clot. 
 The fibrin may be separated by what is known as "whipping " 
 the blood. For this purpose freshly drawn blood is stirred 
 vigorously with a bunch of twigs, to which the stickv fibrin 
 threads adhere as they form. If the twigs are withdrawn a 
 quantity of stringy material will be found attached to them. 
 This is at first colored red by adhering blood corpuscles, but 
 if washed in water pure white fibrin may be obtained in the 
 form of highly elastic threads. The blood from which the 
 fibrin has been removed looks like ordinary blood, but has 
 lost its power of coagulating spontaneously. 
 
 Uses of Coagulation. — The living circulating blood in the 
 healthy blood vessels does not clot, because it contains no 
 solid fibrin, but this forms in it when the blood gets out of 
 the heart or blood vessels, or when the lining of these is in- 
 jured. In a wound, the clots close up the mouths of the small 
 vessels which have been opened and stop the bleeding, which 
 might otherwise go on indefinitely. So. too, when a surgeon 
 ties an artery, the tight ligature crushes or tears its delicate 
 inner surface, and causes the blood to clot there. The clot 
 becomes more and more solid, and by the time the ligature is 
 removed is organized into a firm plug which effectually closes 
 the artery. 
 
 The Composition of Blood Serum. — About one half of the 
 bulk of fresh blood is corpuscles and the other half plasma 
 minus the constituents of fibrin. \XYi3t the plasma contains 
 we may learn by examining blood serum, which is plasma 
 minus fibrinogen. 
 
 Blood serum is very different from water : if we keep on 
 boiling pure water in a saucepan it will all go off in steam and 
 leave nothing behind, but if we try to boil serum we find that 
 we cannot do it ; before it gets as hot as boiling water it sets 
 
THE BLOOD GASES. 155 
 
 into a stiff, solid mass just like the white of a hard-boiled < - 
 In fact the scrum contains dissolved in it two albumins very 
 like that in the white of an egg, and coagulated in a similar 
 way by boiling. About eight and a half pounds of albuminous 
 
 substances exist in one hundred pounds of blood. 
 
 Blood serum also contains considerable quantities of oily 
 and fatty matters, a little sugar, some common salt and car- 
 bonate of soda, and small quantities of very many other 
 things, chiefly waste products from the various tissues. Nine 
 tenths of the blood plasma is water. 
 
 Composition of the Red Corpuscles. — In the fresh moist 
 state these contain a little more than half their weight of 
 water. Nine tenths of their solid part is haemoglobin, of 
 which iron is one of the constituents ; they also contain salts 
 of phosphorus and of potassium. 
 
 The Blood Gases. — Ordinary fresh or salt water has a good 
 deal of air dissolved in it; upon this fishes depend for their 
 oxygen. Blood also contains a quantity of gases which it 
 gives off when exposed to a vacuum, about sixty pints of gas 
 to a hundred pints of blood. These gases are, chiefly, oxygen 
 and carbon dioxide. In the lungs the carbon dioxide diffuses 
 out from the plasma of the blood in which it is dissolved into 
 the air contained in the air cells. From this air oxygen dif- 
 fuses into the blood, to be taken up by the haemoglobin of 
 the red blood corpuscles. Hence the blood coming from the 
 lungs is richer in oxygen and poorer in carbon dioxide. In 
 the tissues which have only the carbon dioxide, this gas 
 pushes its way into the blood, while the oxygen of the 
 blood goes out to be used by the tissues; hence the blood re- 
 turning to the heart is richer in carbon dioxide and poorer in 
 oxygen. 
 
 The Blood as a Medium of Exchange. — " Blood, then, is a 
 
156 THE HUMAN BODY. 
 
 very wonderful fluid : wonderful for being made up of colored 
 corpuscles and colorless fluid, wonderful for its fibrin and 
 power of clotting, wonderful for the many substances, for the 
 proteids, for the ashes or minerals, for the rest of the things 
 which are locked up in the corpuscles and in the serum. 
 
 But you will not wonder at it when you come to see that 
 the blood is the great circulating market of the body, in 
 which all the things that are wanted by all parts, by the 
 muscles, by the brain, by the skin, by the lungs, liver, and 
 kidneys, are bought and sold. What the muscle wants it 
 buys from the blood ; what it has done with it sells back to 
 the blood ; and so with every other organ and part. As long 
 as life lasts this buying and selling is forever going on, and 
 this is why the blood is forever on the move, sweeping rest- 
 lessly from place to place, bringing to each part the things it 
 wants, and carrying away those with which it has done. 
 When the blood ceases to move, the market is blocked, the 
 buying and selling cease, and all the organs die, starved for 
 the lack of the things which they want, choked by the abun- 
 dance of things for which they have no longer any need. ' ' — 
 Foster. 
 
 Hygienic Remarks. — The blood flowing from any organ 
 will have lost or gained, or both gained and lost, when com- 
 pared with the blood which entered it. But the losses and 
 gains in particular parts of the body are in such small propor- 
 tion, with the exception of the blood gases, as to elude analy- 
 sis for the most part ; moreover, since the blood from all 
 parts is mixed up in the heart, they balance one another and 
 produce a tolerably constant average. In health, however, 
 the red corpuscles are present in greater proportion after 
 a meal than before. Healthy sleep in proper amount also 
 increases the proportion of red corpuscles, while want of it 
 
THE LYMPH. 157 
 
 diminishes their number, as may be recognized in the pallid 
 aspect of a person who has lost several nights' rest. Fresh air 
 favors their in< reuse. Ancsmia is ;i diseased < ondition < har- 
 acterized by pallor due to deficiem y of red blood corpus* les, 
 and accompanied by languor and listlessness. It is not unfre- 
 quent in young girls on the verge of womanhood, and in per- 
 sons overworked and confined within doors. It must be remem- 
 bered that the oxygen-carrying power of the blood is usually 
 reduced in even greater proportion than the reduction in the 
 number of red corpuscles would indicate. Since thereby the 
 < apacity for effort is correspondingly reduced, it is important 
 for anaemic persons to take only moderate exercise. Fresh 
 air and good food are the best remedies though medicines 
 containing iron are often of great use. 
 
 The Quantity of Blood in the Body. — The total weight of 
 the blood is about one thirteenth that of the whole body; a 
 man of average size contains about twelve pounds of blood. 
 
 The Lymph. — The blood lies everywhere in closed tubes, 
 and consequently does not come into direct contact with any 
 of the body cells, except those which float in it and those 
 which line the interior of the blood vessels. At two points 
 in its course [the capillaries of tissues and capillaries of lungs), 
 however, the vessels through which it passes have extremely 
 thin walls, which permit the plasma to transude and bathe 
 the various tissues. The transuded plasma is called lymph. 
 It oozes through the walls of the capillaries into the spaces 
 between the cells of the tissues and thus becomes the essential 
 means of nourishing the cells of the body. 
 
 The lymph commonly contains all the elements of the body 
 except the red blood corpuscles, though these elements are 
 not found, upon analysis, to be in the same proportions as in 
 the blood itself. 
 
158 THE HUMAN BODY. 
 
 The Renewal of the Lymph. — The lymph present in any 
 organ both gives to and receives from the cells ; and so, al- 
 though it may have originally been like the plasma of the 
 blood, it soon acquires a different chemical composition. 
 The cells take from it food materials to keep up their 
 activity, and give to it the wastes resulting from such activity. 
 
 Fig. 70.— Origin of lymphatics (after Landois\ 5, lymph spaces communicating 
 with lymphatic vessel ;' A , origin of lymphatic by union of lymph spaces; £, E % 
 endothelial rel s forming wall of lymph vessel. 
 
 Thus the lymph becomes progressively poorer in the essential 
 constituents of the plasma and richer in waste matters. The 
 lymph is constantly drained out of the intercellular spaces 
 into the well-defined lymph channels, and slowly finds its way 
 through successive bunches of lymph glands back into the 
 blood. Fresh plasma constantly exudes from the capillaries 
 to take the place of the lymph in the intercellular spaces and 
 
THE LYMPHATIC VESSELS OR ABSORBENTS. 159 
 
 to carry fresh food to the cells, again to be drained off 
 through the lymphatic circulation. The exchanges of oxygen 
 and carbon dioxide are chiefly by diffusion between the tissues 
 and the blood, and do not depend upon the lymph. 
 
 The total amount of lymph passing back again into the 
 blood circulation has been estimated to be equal to the total 
 
 Fig. 71. — Superficial lymphatics and glands. G. Axillary glands. 
 
 bulk of the blood, that is, one thirteenth of the weight of the 
 body. 
 
 In consequence of the different wants and wastes of various 
 cells, and of the same cells at different times, the lymph must 
 vary considerably in composition in various organs of the 
 body. 
 
 The Lymphatic Vessels or Absorbents. — The cells of the 
 body, except the compact layers of epithelium composing 
 surfaces, are rather loosely arranged in the various tissues and 
 
i6o 
 
 THE HUMAN BODY. 
 
 organs. In the irregular branching spaces between the cells, 
 the lymph which has exuded from the capillaries finds a 
 
 Fig. 72. — The lymphatic vessels. The thoracic duct occupies the middle of the 
 figure. It lies upon the spinal column, at the sides of which are seen portions of the 
 ribs (1). a, the receptacle of the chyle ; 6, the trunk of the thoracic duct, opening at 
 c into the junction of the left jugular (/) and subclavian (g) veins as they unite into 
 the left innominate vein, which has been cut across to show the thoracic duct running 
 behind it; d, lymphatic glands placed in the lumbar regions; A, the superior vena 
 cava formed by the junction of the right and left innominate veins. 
 
 temporary abiding place. Leading from these lymph spaces 
 are delicate, thin-walled tubes, which join together to form 
 
LACTEAIS. 
 
 [6i 
 
 larger trunks. In the course of these trunks arc situated knots 
 or beads, called lymph glands, which are filled with cells re- 
 sembling somewhat the white blood corpus* les. 
 These glands are apparently for the purpose of 
 supplying white corpuscles, and also of filter- 
 ing the lymph and destroying, if possible, any 
 foreign materials, such as bacteria, which 
 may have been absorbed from the tissues. 
 The lymph trunks join together to form still 
 larger trunks which finally empty as single 
 trunks, one upon each side of the neck, into 
 the subclavian veins. The walls of the lym- 
 phatic tubes are exceedingly thin and the 
 tubes themselves can only be readily found 
 when they are distended with colored liquid. 
 They are richly supplied with valves which 
 allow the contents to flow only from the tissues 
 toward the heart. 
 
 Since the lymphatic vessels take up or 
 absorb the excess of liquid drained from the 
 blood and also the effete matters of the pey.j 
 various organs, they are frequently called the absorbents. 
 
 Lacteals, about which we have already learned, are the 
 lymphatics of the small intestine (p. 125), but they are 
 larger than the lymphatics of the rest of the system since the 
 absorption into and circulation through them is much greater. 
 The great lymphatic trunk which receives the lymph from 
 the lower limbs and the food materials absorbed from the in- 
 testinal tract is called the thoracic duct and enters the left 
 subclavian vein. 
 
 Histology of Lymph. — Pure lymph is a colorless, watery- 
 looking liquid ; examined with a microscope it is seen to con- 
 
 Fig. 73. — Valves 
 of lymphatics. (Sap- 
 
1 62 THE HUMAN BODY. 
 
 tain numerous pale corpuscles exactly like the white blood 
 corpuscles. These are derived in large part from the blood, 
 but also from the glands through which the lymph comes. 
 
 Chemistry of Lymph. — Lymph is not quite so heavy as 
 blood, though heavier than water. It may be described as 
 blood minus its red corpuscles and considerably diluted, but of 
 course in various parts of the body it contains minute quanti- 
 ties of substances derived from neighboring tissues. 
 
 Summary. — The lymph is a liquid in which the tissues of 
 the body live : it is derived from the blood, and affords the 
 immediate nourishment of the great majority of the living 
 cells of the body ; the excess of it is finally returned tc the 
 blood, which thus indirectly nourishes the cells by keeping 
 up the stock of lymph. The lymph itself moves slowly, but 
 is constantly renovated by the blood. The blood is kept in 
 rapid movement by the heart, and besides containing a store 
 of new food matters for the lymph, absorbs from it the gaseous 
 waste products of the various cells. 
 
CHAPTER XIV. 
 THE ANATOMY OF THE CIRCULATORY ORGANS. 
 
 The Organs of Circulation are the heart and the blood 
 vessels. There are two distinct systems of blood vessels in 
 the body, both connected with the heart ; one system carries 
 blood to, through, and from the lungs, and is known as the 
 pulmonary ; the other guides its flow through all the remain- 
 ing organs, and is known as the systemic. 
 
 General Statement. — During life the pumping of the heart 
 keeps the blood flowing rapidly through the blood vessels ; 
 these paths it never leaves except in cases of disease orinjurv. 
 
 The blood vessels form a continuous system of closed tubes 
 comparable in a certain way to the water mains of a city ; the 
 heart corresponds to the reservoir, the great artery {aorta), 
 with its branches, to the main aqueduct and branch pipes. 
 The course of the blood differs, however, essentially from 
 that of the water supplied to a city, since the blood is carried 
 back to the heart. There is at any instant only a small 
 amount in the heart, but this is steadily replaced by an inflow 
 as fast as it is forced out. 
 
 General Functions of the Parts of the Circulatory Sys- 
 tem. — The blood system is closed * except at two points, one 
 
 * In the spleen only is there a break in the continuity of the blood 
 vessels. The blood escapes from the open ends of the blood vessels, 
 flows through a mesh work of tissue cells, and re-enters the blood vessels 
 at the end of a minute distance. 
 
 163 
 
164 
 
 THE HUMAN BODY. 
 
 on each side of the neck, where lymph vessels pour the excess 
 of lymph back into the veins. Valves at these two points let 
 lymph flow into the blood vessels, but will not allow blood 
 to flow out. Accordingly everything which leaves the blood 
 must do so by oozing through the walls of the blood vessels, 
 and everything which enters it must do the same, ex- 
 cept matters conveyed in by the lymph at the points 
 above mentioned. This interchange through the walls 
 of the vessels takes place only in the capillaries. The 
 capillaries, though far the smallest tubes in the vascular 
 system, are the really important parts. The heart, arter- 
 ....£.,. ies, and veins are merely arrangements for 
 
 keeping the blood flowing through the 
 capillaries. It is while flowing through 
 these and soaking through their walls 
 that the blood does its physiological work. 
 Diagram of the Circulatory Organs. — 
 The general relationship of the heart and 
 blood vessels may be gathered from the 
 
 Tig. 
 
 accompanying diagram (Fig. 74). The 
 heart is essentially a bag with muscular 
 walls, internally divided into four cham- 
 bers (d, g, e,f). The upper two (t/and 
 !S2^ e) receive blood from vessels opening into 
 
 *&Zr^2*S£Ej them known as veins. Thence the blood 
 
 matically represented. .% • • \_ v / 
 
 ' ^ passes on to the remaining chambers (g 
 
 and_/j, which have very muscular walls, and, by forcibly con- 
 tracting, drive the blood out into communicating vessels (i 
 and b) known as arteries. The big arteries divide into 
 smaller, these into still smaller (Plate IV), until the branches 
 become too small to be traced by the unaided eye. The 
 smallest branches are the capillaries, through which the blood 
 
THE POSITION OF THE HEART. 165 
 
 flows into the veins, which in turn < onvey it bat k to the heart. 
 At certain points in the course of the veins valves are placed, 
 n> prevent a back flow. This alternating reception of Mood at 
 owe end of the heart and its ejection from the other occurs in 
 men about seventy times a minute during health. 
 
 The Position of the Heart. — The heart i //, Fig. 4) lies 
 in the chest, immediately above the diaphragm and opposite 
 the lower two thirds of the breast bone. It is conical in form 
 and lies with its base or broader end turned upward and pro- 
 jecting a little to the right of the sternum. Its narrow end or. 
 apex may be felt beating between the cartilages of the fifth and 
 sixth ribs to the left of the sternum. The position of the 
 heart in the body is, therefore, oblique. It does not, how- 
 ever, lie on the left side, as is so commonly believed, but very 
 nearly in the middle line, with the upper part inclined to the 
 right, and the lower (which may be more easily felt beating — 
 hence the common belief) to the left. 
 
 The Pericardium. — The heart is surrounded by a loose 
 conical bag (pericardium) composed of connective tissue and 
 attached by its broad lower part to the upper surface of the 
 diaphragm. The pericardium is lined by a smooth serous 
 membrane like that lining the abdominal cavity, which is con- 
 tinued over the heart itself and adheres closely to it. In the 
 space between the pericardium and the heart is a small quan- 
 tity of liquid which moistens the contiguous surfaces, and 
 thereby diminishes the friction which would otherwise occur 
 during the movements of the heart. 
 
 N >te. — Sometimes, especially in rheumatic fever, the peri- 
 cardium becomes inflamed (pericarditis). In the earlier stages 
 of this inflammation the rubbing surfaces on the outside 
 of the heart and the inside of the pericardium become rough- 
 ened, and their friction produces a sound which can be heard. 
 
1 66 THE HUMAN BODY. 
 
 In later stages great quantities of liquid may accumulate 
 in the pericardium and seriously impede the heart's beat. 
 
 The Cavities of the Heart. — On opening the heart (Fig. 
 74, p. 164) it is found to be divided into completely separate 
 right and left halves by a longitudinal partition (septum) which 
 runs from about the middle of the base to a point a little to 
 the right of the apex. Each of the chambers on the sides of 
 the septum is divided transversely into a thinner basal portion 
 into which veins open (auricle) and a thicker apical portion 
 from which arteries arise (venlricle). The heart cavity thus 
 consists of a right auricle and ventricle and a left auricle 
 and ventricle, each auricle communicating with the ventricle 
 on its own side by an auricula-ventricular orifice. There is 
 no direct communication through the septum between the 
 opposite sides of the heart. To get from one side to the other 
 the blood must leave the heart and pass through a set of 
 capillaries, as may readily be seen by tracing the course of the 
 vessels in Fig. 74. 
 
 The Vessels Connected with the Different Chambers 
 of the Heart. — One big artery, called the aorta, springs from 
 the left ventricle. It runs down to the pelvis, giving off 
 many branches on its way, and then divides into two arteries, 
 one going to each side, which by their branches supply 
 pelvis and legs. 
 
 Its big branches divide into smaller and these into still 
 smaller and spread through the whole body, to muscles, 
 bones, skin, brain, stomach, intestines, liver, kidneys, etc., 
 until they finally end in the systemic capillaries. The sys- 
 temic veins collect the blood from the capillaries of the differ- 
 ent organs, and unite to form the upper and lower hollow veins 
 (the superior and inferior venai cavai). These carry the blood 
 to the right auricle ; thence it enters the right ventricle from 
 
SUMMARY. 
 
 167 
 
 which arises one vessel, the pulmonary artery. The pulmonary 
 
 artery divides into two branches, one for each lung; each 
 branch splits up into minute ,, 
 
 arteries in its own lung, 
 which end in the pulmonary 
 capillaries. From the pul- 
 monary capillaries the 
 blood of each lung is col- 
 lected into two pulmonary 
 veins y which open into the 
 left auricle. 
 
 Summary. — ( )ne artery, 
 the aorta, arises from the 
 left ventricle. The blood 
 carried out by the aorta 
 passes through the capilla- 
 ries in the tissues, returns 
 by the upper and lower 
 venae cavae to the right 
 auricle, goes to the right 
 ventricle, and thence 
 
 1 he pulmonary artery has been cut short 
 
 through the nulmonarv close to its ori s in - *« ri s ht ventricle ; 2, left 
 
 Uiruugll uie pulmonary ven tricle ; 3, root of the pulmonary artery ; 4, 
 nrtprv to thp liino-Q Th^ 4% arch of the aorta; 4". the descending thoracic 
 
 artery 10 me mngs. i ne aorta . 5i part f the right aur i c ie; 6, part of the 
 
 1 1 j . j . i . left auricle ; 7, 7', innominate veins joining to 
 
 DlOOa, Carried by tile pill- form the vena cava superior; 8, inferior vena 
 
 cava ; 9, one of the large hepatic veins ; X, 
 mOliary artery from the placed in the right auriculo-ventncular groove, 
 
 points to the right or posterior coronary artery; 
 right Ventricle Of the heart, X' X, placed in the anterior interventricular 
 
 groove, indicate the left or anterior coronary 
 
 passes through the capil- arterv - 
 
 laries of the lungs, returns to the left auricle by the pul- 
 monary veins, enters the left ventricle, and begins its flow 
 again through the aorta. 
 
 How the Heart is Nourished. — The heart is a hard working 
 organ, and needs an abundant supply of nourishment ; accord- 
 
 Fir,. 75. — Front view of the Heart and 
 Great Vessels. 
 
i68 
 
 THE HUMAN BODY. 
 
 ingly its avails are permeated by a very close network of 
 capillary blood vessels. The blood enters (Fig. 76) through 
 
 Fig. 76. The left ventricle and the commencement of the aorta laid open. Mfm, 
 
 Mf>L the'papillary muscles. From their upper ends are seen the chordae tendinese 
 proceeding to the ed^es of the flaps of the mitral valve. The opening into the 
 auricle lies between these flaps. At the beginning of the aorta are seen its three 
 pouch-like semilunar valves. 
 
 the right and left coronary arteries (the first two branches of 
 the aorta) and leaves by the coronary veins, which carry it 
 to the right auricle. 
 
AURICULO-VENTRICULAR VALX 169 
 
 The Auriculo-Ventricular Valves. Between ca< h auri( le 
 of the heart and the ventricle of the same side are found 
 valves which allow blood to pass from the aurii le to the ven- 
 tricle, but prevent any return. These valves arc known as 
 the tricuspid and mitral valves. The mitral valve | Fig. 76 1 
 
 consists of two flaps fixed by their bases to the margins of 
 the opening between the left auricle and the let ventricle. 
 Their unattached edges hang down into the ventricle when 
 it is being filled and have fixed to them a number of stout 
 connective tissue cords, the chordce tendinece. These in turn 
 are attached to muscular elevations, the papillary muscles 
 (Mpm and J//'/) on the interior of the ventricle. The cords 
 are long enough to let the valve flaps rise into a transverse 
 position and thus to close the opening* between auricle and 
 ventricle. The tricuspid valve is like the mitral, but with 
 three flaps instead of two. 
 
 Semilunar Valves. — These are six in number, three at the 
 mouth of the aorta (Fig. 76), and three at the mouth of the 
 pulmonary artery. Each is a strong crescentic pouch fast- 
 ened by its longer edge, with its free edge turned away from 
 the heart. When the valves are closed, their free edges meet 
 across the vessel and prevent blood from flowing back into 
 the ventricle. 
 
 The Course of the Main Arteries of the Body (Fig. 77). 
 — The aorta after leaving the left ventricle makes an arch 
 (#a) with its convexity towards the head. From the begin- 
 ning of this arch arise the coronary arteries, which carry 
 blood into the walls of the heart. From the convexity of 
 the arch spring three large arterial trunks, the innominate, the 
 left common carotid (or), and the left subclavian (ssi). The 
 
 * This opening lies behind the opened aorta (S/>) and cannot be seen 
 in the figure. 
 
i 70 THE HUM/IN BODY. 
 
 innominate artery soon divides into the right subclavian 
 and the right common carotid (a/). Each common carotid 
 runs up the neck on its own side and divides into branches 
 for the neck. face, scalp and brain. Each subclavian gives 
 off a branch, the vertebral artery, which passes to the b^ain 
 through the transverse processes of the cervical vertebrae 
 (Figs. 13 and 14. p. 25 1. The main branch of the sub- 
 clavian continues across the arm pit as the axillary artery 
 and then runs toward the elbow as the brachial artery 
 (p.). Just above the elbow it divides into the radial and 
 ulnar arteries (k, u), which supply the fore-arm and end in 
 small branches for the hand. 
 
 Beyond its arch the aorta runs close to the spinal column 
 as the thoracic aorta \: . which gives off branches to the 
 walls and some of the organs of the chest. The vessel then 
 passes through the diaphragm, and continues as the abdomi- 
 nal a tb) to the lower part of the abdomen. The main 
 branches of the abdominal aorta are: (1) the catiac axis, 
 which divides into branches for the stomach, liver, and 
 spleen ; (2) the upper and lower mesenteric arteries, which 
 supply the intestines with blood: (3) the renal arteries (k), 
 which supply the kidneys. 
 
 The two trunks into which the posterior end of the ab- 
 dominal aorta divides At 1 are the common iliac arteries. 
 Each gives off branches in the pelvis, and then continues 
 along the thigh as the femoral artery (C ) : this runs to the 
 knee joint, behind which it is called the popliteal artery (Po). 
 The popliteal artery divides into the peroneal (Pe) and tibial 
 
 T:. Tp) arteries, which supply the lower leg and the foot. 
 The Properties of the Arteries. — Two fundamental facts 
 must be borne in mind in connection with the arteries : 
 first, that they are highly elastic and extensible, much like a 
 
PLATE IY.— THE CHIEF ARTERIES AND TEIN8 OF THE BODY. 
 
EXPl W VI [( >\ < >F PLATE IV 
 
 Till ( llRCI l \ PORT? I >RG INS. 
 
 The arteries (except the pulmonary) and the Kit side <>f the luart 
 are colore. 1 red; the veins (excepl the pulmonary) and the right half of 
 the heart blue. ( hi the limbs < >t the left side the arteries are omitted awl 
 only the superficial veins are shown. 
 
 i. Aorta, near its origin from the left ventricle of the heart. 
 
 2. Lower end of aorta. 
 
 3. Iliac artery. 
 
 4. Femoral artery. 
 
 5. Popliteal artery ; the continuation of the femoral which passes behind the 
 
 knee joint. 
 
 6. 7. The main trunks (anterior and posterior tibial arteries into which the pop- 
 
 liteal divides). 
 
 8. Subclavian artery. 
 
 9. Brachial artery. 
 
 10. Radial artery. 
 
 11. Ulnar artery. 
 
 12. Common carotid artery. 
 
 13. Facial artery. 
 
 14. Temporal artery. 
 
 15. Right side of heart, with superior vena cava joining it above, and inferior 
 
 vena cava (16) passing up to it from below. 
 
 17. Innominate vein, formed by the union of subclavian and jugular veins. The 
 
 right and left innominate veins unite to form the superior cava. 
 
 18. Left internal jugular vein. 
 
 19. Axillary vein. 
 
 20. Basilic vein. 
 si. Cephalic vein. 
 
 22. Median vein. 
 
 23. Radial vein. 
 
 24. Ulnar vein. 
 
 25. Median vein. 
 
 26. Iliac vein. 
 
 27. Femoral vein. 
 
 28. Long saphenous vein. 
 
 29. The kidney ; attached to it are seen the renal artery and vein. 
 
 30. Branches of the pulmonary arteries and veins in the lung. 
 
THE MAIN ARTERIES OE THE BODY. 
 
 171 
 
 Fig. 77. — The main arteries of the body. Crd and Crs, right and left coronary ar- 
 teries of the heart, cut short near their origin; An and aA, aortic arch; At, thoracic 
 aorta; Aab, abdominal aorta; A", renal artery; Sd, right, and Ssi, left subclavian; 
 Cd % right, and Cs, left carotid; A.r, axillary artery; />', brachial artery; U. ulnar 
 artery; A', radial artery; A i, common iliac artery; /, external iliac artery; C, femoral 
 artery; J'o, popliteal artery; Ta, anterior, and T/>, posterior tibial artery; flr, peroneal 
 artery. 
 
172 
 
 THE HUMAN BODY. 
 
 piece of rubber tubing of the same size : second, that they 
 have rings of muscular tissue in their walls. When these 
 contract, the bore of the artery, and consequently the amount 
 of blood which flows through it, is diminished. When they 
 relax, the bore of the artery is increased, and more blood 
 passes along it to the capillaries, 
 j The Capillaries. — The smallest arteries (arterioles*) pass 
 
 Fig. 
 
 79- 
 
 Fig. 78. — Diagrammatic representation of a capillary seen from above and in sec- 
 tion. «, the wall of the capillary with. 6, the nuclei; c, nuclei belonging to the 
 connective tissue in which the capillary is supposed to be lying; d, the canal of the 
 capillary. 
 
 Fig. 79. — Transverse section through a small artery and vein. A, artery ; V, vein; 
 e. epithelial lining; tn, middle muscular and elastic coat, thick in the artery, much 
 thinner in the vein; a, outer coat of areolar tissue (magnified 350 diameters). 
 
 into the capillaries, which have very thin walls, and form a 
 close network in all parts of the body. The average diam- 
 
THE VEINS. 173 
 
 etcr of a capillary vessel is so small thai onl) one or two 
 blood corpuscles can pass through it abreast, and in many 
 parts the capillaries lit- so close together that a pin's point 
 cannot be inserted between two of them, as. for example, in 
 the deep layers of the skin, whi< h cannot be pricked without 
 drawing blood. Their immense number, however, mm h 
 more than compensates for their si/e. It is while flowing in 
 these delicate tubes that the blood does its nutritive work, 
 for here only can the Liquid containing nourishment exude 
 from the blood through the thin walls to bathe the various 
 tissues. Imagine a crumpled mass of the finest lace, with all 
 its threads consisting of hollow tubes, and diminished twenty 
 times in size, and you will have some idea of the size and 
 richness of distribution of the capillaries. 
 
 The walls of the capillaries are formed of a single layer of 
 flat cells and are really a continuation of the lining membrane 
 of the arteries, veins, and heart, which thus becomes con- 
 tinuous throughout the circulatory system with the exception 
 of the spleen. 
 
 The Veins. — The smallest veins arise from the capillary 
 network and unite to form larger and larger trunks. One of 
 these usually runs along with the main artery of the part, but 
 there are ordinarily several other large veins just beneath the 
 skin. This is especially the case in the limbs, the main veins 
 of which are superficial, and can in many persons be seen as 
 faint blue lines. The walls of the veins are similar in 
 structure to those of the arteries, except that they are 
 thinner. 
 
 Why the Large Arteries usually lie deep. — The heart 
 pumps the blood with great force into the arteries, and when 
 an artery is cut very rapid and dangerous bleeding occurs ; 
 the veins, if cut, do not bleed nearly so violently as an artery 
 
174 
 
 THE HUMAN BODY. 
 
 of the same size. Hence it is less dangerous to have a large 
 vein than a large artery close under the skin. 
 
 The Valves of the Veins. — Except the pulmonary artery 
 and the aorta, which have the semilunar valves at their origin, 
 
 
 Fig. 80. — A small portion of the capillary network as seen in the frog's web when 
 magnified about 25 diameters, a, a small aitery feeding the capillaries; z', v, smail 
 veins carrying blood back from the latter. 
 
 arteries have no valves. Most veins, on the contrary, con- 
 tain manv valves formed by pouches of their lining, which 
 resemble in form the semilunar valves of the aorta and the 
 pulmonarv artery. These valves permit blood to flow only 
 
THE VALVES OF THE VEINS. 
 
 175 
 
 towards the heart, for a current in thai direction (upper 
 diagram, Fig. 82) presses the valve dose against the side of 
 
 F:c. 3,-Circulation in frog's ^ ^™^A l^^^^i 
 B, tissue of web Lying between the capillar es C ,ceU* oc £ in the other parts 
 £hese are only shown in the right-hand and tower part ot mene , q{ ^^ 
 
 of the field the focus of the microscope lies below the ^P'^rmis^ blood 
 
 epidermic cells-, £ pigment ce Is contracted «.„ par a , -^sibie ; V;. another 
 
 corpuscle (oval in the frog) R^,°« ^fJ^^Se canal of which is smaller than 
 corpuscle squeezing ^ way through a capiUary.Uie can ^ & ^ ^ 
 
 its^wn transverse diameter; H % »~*«^d«2£ • / wSS blood corpuscle. 
 
 corpuscle in capillary seen through the epidermis, /, wmw 
 
Ij6 THE HUMAN BODY. 
 
 the vessel, and meets with no obstruction from it. Should 
 
 any back flow be attempted, however, the current closes up 
 
 A the valve and bars its own passage 
 
 c ' Zlg^J ' h (lower figure). These valves are most 
 
 numerous in superficial veins and those 
 
 D 
 
 of muscular parts. They are found 
 
 u . 
 
 especially where two veins join. 
 Fig. 82.— Diagram to iiius- Usuallv the vein is a little dilated 
 
 trate the mode of action of the 
 
 valves of the veins, c, the capii- pp 0S i te a va lve, and hence in parts 
 
 lary; H, the heart end of the rr ' l 
 
 %esse ' where the valves are numerous has a 
 
 knotted look. On tying a cord tightly round the forearm, 
 so as to stop the flow in its subcutaneous veins and cause their 
 dilatation, the points at which valves are placed can be recog- 
 nized by their swollen appearance. 
 
 The Course of the Blood. — From what has been said it is 
 clear that the movement of the blood is a circulation. Start- 
 ing 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 which is connected with the aorta, and the 
 other with the pulmonary artery. In this 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 There 
 is no road for it from one side of the heart to the other except 
 through a capillar}- 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 the flow from the left side of the heart 
 to the right through most of the body as the systemic or 
 greater circuIatioTi, and of the flow from the right to the left 
 through the mngs as the pulmonary or lesser circulation. But 
 since, after completing either of these, the blood is not again 
 
THE PORTAL CIRCULATION. 
 
 177 
 
 at the point from which it started, but is separated from 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 is at the end of its course where it was at the beginning. 
 
 Fig. 83. — The portal vein and its branches. /, liver, under surface; gb, gall blad- 
 der; st, stomach; s/, spleen;/, pancreas; du, duodenum; ac, ascending colon: c«/, 
 descending colon; a. />, c, d, e, the portal vein and its branches. Portions of the duo- 
 denum and colon have been removed. 
 
 The Portal Circulation. — That portion of the blood which 
 goes through the stomach and intestines has to pass through 
 three sets of capillaries before it can return there. It leaves 
 the left ventricle of the heart through the aorta, traverses the 
 capillaries of the stomach and intestines, is carried by the 
 portal vein into the liver, and here passes through the capil- 
 laries of the portal vein, which in the liver branches like an 
 artery. From these it is collected by the hepatic veins and 
 
178 
 
 THE HUMAN BODY. 
 
 poured into the inferior vena cava, which carries 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. The flow from the 
 stomach and intestines through the liver to the inferior vena 
 cava is often spoken of as the portal circulation. 
 
 Diagram of the Circulation. — Since the two halves of the 
 heart, although placed in proximity in the body, are com- 
 pletely separated from one another 
 by an impervious partition, we may 
 conveniently represent the course of 
 the blood as in the accompanying 
 diagram (Fig. 84), in which the 
 right and 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, 
 each engaged in forcing blood to 
 the other. Starting from the left 
 auricle {la) we trace the flow 
 through the left ventricle, along 
 the branches of the aorta into the 
 
 Fig. 84. — Diagram of the cir- • "ii • / „\ ,u „ 
 
 cuiatory system, showing that it systemic capillaries (sc), thence 
 
 forms a single closed circuit with . . . . , s . 
 
 two pumps in it, represented by through the Systemic Veins (VC) llltO 
 
 the right and left halves of the . . 
 
 heart, which are separated in the right auricle (**#)} thence into 
 
 the diagram, ra and rv, right 
 
 auricle and ventricle; la and iv, the right Ventricle (?'!'), through the 
 
 left auricle and ventricle ; ao, 
 
 aorta ; sc, systemic capillaries : pulmonary artery (pa) to the lung 
 
 vc, venae cavas; />a, pulmonary r J j \i / o 
 
 SsT^/pu'im P otaTve^ cap,lla " capillaries O) along the pulmonary 
 veins (pv) to the left auricle, into the left ventricle (/z/), and 
 again into the aorta. 
 
ARTERIAL ASP I'F.NOUS M.OOD. 179 
 
 Arterial and Venous Blood. The blood when flowing in 
 the pulmonarj capillaries gives up carbon dioxide to the air, 
 and receives oxygen from it. Since its coloring matter 
 (haemoglobin) forms a scarlet compound with oxygen {oxy- 
 hemoglobin », the blood \\hi< h flows to the left auricle through 
 the pulmonary veins is bright red. This color it maintains 
 until it reaches the systemic capillaries, when it loses oxygen 
 and becomes dark purple because of the excess of the darker 
 colored haemoglobin. In the lungs the haemoglobin 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." It must be borne in mind 
 that the terms apply to the character of the blood, and that 
 the pulmonary veins contain arterial blood, and the pulmonary 
 arteries contain venous blood. The change from arterial to 
 venous takes place in the systemic capillaries, and from 
 venous to arterial in the pulmonary capillaries. 
 
CHAPTER XV. 
 THE WORKING OF THE HEART AND BLOOD VESSELS. 
 
 The Beat of the Heart commences as a contraction of the 
 mouths of the veins which open into the auricles. This con- 
 traction runs over the auricles, and is immediately taken up 
 bv the ventricles. The auricles relax the moment the ven- 
 tricles start their contraction. Having finished their contrac- 
 tion, the ventricles begin to dilate, and then for some time 
 neither they nor the auricles contract, but the whole heart ex- 
 pands. The contraction of any part of the heart is known as 
 its svs'to-Ie, and the relaxation as its di-as'lo-le. Since the 
 >ides of the heart work synchronously, the auricles to- 
 gether and the ventricles together, we may describe a whole 
 cardiac period or •' ' heart beat ' ' as made up successively of 
 auricular sys/u/e, ventricular systole, and pause. In the pause 
 the heart is soft and flabby, but during the systole it becomes 
 hard and so diminished in size that the ventricles are entirely 
 emptied. 
 
 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 even- beat a sort of tap 
 known as the cardiac impulse, or apex beat, may be felt by 
 placing the finger at that point. 
 
 i So 
 
EVENTS ni'RING A CARPI. K. PERIOD. 
 
 i. Si 
 
 Fig. 85. — Transverse 
 section through the mid- 
 die of the ventricles of a 
 dog's heart in diastole 
 and in systole. 
 
 Events occurring within the Heart during a Cardiac 
 Period. Lei us commence with the pause at the end of the 
 ventricular systole. At this instant the 
 
 semilunar valves in the orifi< es of the aorta 
 
 and the pulmonary artery are closed so 
 
 that no Mo«>d can flow back from these 
 
 vessels. The whole heart, however, is 
 
 soft and distensible, and readily yields to 
 
 blood flowing into its auricles from the 
 
 pulmonary veins and the venae cavae. 
 
 This blood passes on through the open 
 
 mitral and tricuspid valves, and fills up 
 
 the dilating ventricles as well as the 
 
 auricles. As the ventricles fill, the valve 
 
 flaps float up so that by the end of the 
 
 pause they are nearly closed. At this in- 
 stant the auricles begin to contract at the mouths of the veins 
 and narrow them ; the relaxed ventricles oppose little 
 resistance, and hence the auricles send most of the blood into 
 the ventricles and but little back into the veins. IVhen the 
 auricles cease their contraction, the filled ventricles contract 
 and by their pressure on the blood within, completely close 
 the auriculo-ventricular valves. The blood in each ventricle 
 is now imprisoned between the auriculo-ventricular valves 
 behind and the semilunar valves in front. The former cannot 
 yield on account of the chordae tendineae fixed to their edges; 
 the semilunar valves, on the other hand, can open out- 
 ward from the ventricle and let the blood pass on, but 
 they are kept tightly shut by the pressure of the blood in 
 the aorta and pulmonary artery. The contracting ventricle 
 tightens its grip on the blood. As it squeezes harder and 
 harder, its pressure on the blood becomes greater than the 
 

 THE HUM AS BODY. 
 
 pressure exerted on the other side of the valves by the blood 
 in the aorta, the valves are forced open, and the blood begins 
 to pass out. The ventricle continues to contract until it has 
 
 F:;-. : -' — [ iagt strata the action o( e heart, aur., auri . - I sentri- 
 
 es, iricle contracting, 
 
 valves closed. In B, auricle dilated, 
 ventricle contra t bra - -. . sen ts open. 
 
 complet :ied itself, when it again commences to relax. 
 
 Blood would now flow back into it from the arteries, were it 
 not that this back current instantly catches the pockets of the 
 semilunar valves, carries them back, and closes the valve so 
 as to form an impassable barrier. 
 
 Use of the Papillary Muscles. — In order that the comrad- 
 es may not force blood back into the auricles, it is 
 .rial that the flaps of the mitral and tricuspid valves be 
 held together across the openings which they close, and not 
 be carried back into the auricles. If they were like swinging 
 doors and opened both ways they would be useless : they 
 must so far resemble an ordinary door as only to open in one 
 direction, namely, from the auricle to the ventricle. At the 
 
SOUNDS OF THE HEART. 
 
 commencement of the ventricular systole tins is provided tor 
 by the ( hordse tendineas, whi< h are of such a length and so 
 arranged as to keep the valve flaps shut across the opening, 
 
 and tu maintain their edges in i onta< t. But, as the « ontrai t 
 ing ventricles shorten, the < hordae tendineae would be slack- 
 ened and the valve Haps pushed up into the aurii le, did not 
 the little papillary muscles prevent this. By shortening as 
 the ventricular systole proceeds, they keep the chordae taut 
 and the valves closed. 
 
 Sounds of the Heart. — If the ear is placed on the chest of 
 another person over the heart region, two distinguishable 
 sounds will be heard during each round of the heart's work. 
 They are known respectively as the y?rj/ and second sounds of 
 the heart. The first is of lower pitch, lasts longer and is less 
 sharp than the second. Vocally their character may be toler- 
 ably imitated by the syllables lilb, dup. The cause of the 
 second sound is the closure of the semilunar valves. The first 
 sound takes place during the ventricular systole, and is prob- 
 ably due to vibrations of the tense valve flaps and the ven- 
 tricular wall. In many forms of heart disease these sounds 
 are modified or cloaked by additional sounds due to the 
 roughened, narrowed or dilated cardiac orifices, or to the 
 inefficiency of the valves. 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. Ac- 
 cordingly their walls are far thicker and more muscular than 
 those of the auricles ; 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 comparatively short 
 pulmonary circuit. The circulation of the blood is, in fact, 
 
1 84 THE HUMAN BODY. 
 
 maintained by the ventricles, and one may be led to inquire 
 what is the use of the auricles. During the pause of the heart 
 the blood flows on through the auricles into the ventricles, 
 which are already nearly full when the auricles contract ; this 
 contraction merely completes the filling of the ventricles. 
 The main use of the auricles then is to afford a reservoir into 
 which the veins may empty while the comparatively slow ven- 
 tricular contraction is taking place. 
 
 The Work Done Daily by the Heart. — " The ' work done ' 
 by a contracting muscle is expressed by the height to which a 
 weight is raised. In the case of the heart, the weight raised 
 is the amount of blood contained in the ventricles; the height 
 to which that weight would be raised is the height of intra- 
 ventricular blood-pressure during systole. From these data it 
 is easy to calculate the *' work ' done at each systole, and 
 knowing the pulse-frequency, the average per hour or per day 
 is also known. Admitting for the left ventricle an average 
 discharge of 120 grams, and a systolic pressure of 2 meters, 
 the work done at each contraction will amount to 150 gram- 
 meters : to this amount we may add 50 grammeters as the 
 work done by the right ventricle and by the two auricles, 
 making up a total of 200 grammeters or i kilogrammeter as 
 the work done by the heart at each beat. With a pulse- 
 frequency of 72 per minute this would amount to S64 kgm. 
 per hour, or more than 20,000 kgm. per diem. The whole 
 of this energy is expended in the body, partly in overcoming 
 resistance in the vascular system, and partly transformed into 
 and discharged as heat ; in this form the contractions of the 
 heart yield about ^th of the total daily heat production." — 
 Waller. 
 
 If a man weighing 165 pounds climbs a mountain 2500 
 feet high the muscles of his legs will be tired at the end of 
 
THE NERVES Oi THE HEART. 185 
 
 his journey, and yel in lifting his body thai height they have 
 done onlj as mu< h work as his he-art dor-, ever) day without 
 fatigue in pumping his blood. 
 
 No doubt the fact thai more than half of every round of 
 the heart's a< tivity is taken up by the pause during which its 
 muscles arc 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. 
 
 During the pause between contractions, the heart muscle 
 gets its re>t ; it has been estimated that the heart muscle does 
 active work during only eight hours of the twenty-four and 
 rests during sixteen. When the heart beats more rapidly the 
 period of contraction changes but little, the extra beats en- 
 croaching upon the resting time. In fever, when the heart 
 beat is much more rapid, it has less time to rest and is liable 
 to become exhausted by overwork with insufficient recupera- 
 tion. 
 
 The Nerves of the Heart. — The beat of the heart is due 
 to the contraction of the muscle fibres making up its wall. 
 This contraction is caused by nervous impulses received from 
 nerve centres, as will be explained later. These nerves (in- 
 trinsic heart nerves) are in close connection with the muscle 
 fibres and tend to cause them to contract regularly and some- 
 what rapidly. Their influence is modified by a second set of 
 nerves ( pneumogastric, or vagus ) which tend to make the 
 heart beat more slowly, that is, to inhibit the action of the 
 intrinsic nerves. A third set {accelerator ) have apparently 
 the power of quickening the heart's action. The rate and 
 strength of the beat at any time is due to an involuntary 
 balancing of the influences of the first two sets | and possibly 
 the third) to meet the body's needs. The need of oxygen 
 
1 86 THE HUM AS BODY. 
 
 has the chief influence in modifying the heart's beat, as will 
 be seen under respiration. 
 
 The Pulse. — When the left ventricle of the heart contracts 
 it forces on about 120 grams of blood into the aorta, which, 
 with its branches, is already full of blood. The elastic 
 arteries are consequently stretched by the extra blood. This 
 dilatation of an artery following each beat of the heart is 
 called the pulse. It is best 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. 
 
 Before the next heart beat occurs, the arteries by their 
 elasticity have forced through the capillaries as much blood 
 as the aorta received 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, gradually collapses as the water flows out of it. 
 The next beat of the heart again overfills and expands the 
 arteries, and so on. Thus at each heart beat there is a dila- 
 tation of the arteries due to the blood sent into them from 
 the ventricle, and between each beat there is a partial 
 emptying of the arteries, due to their forcing some of their 
 contents into t lie capillaries. 
 
 What may be learnt from the Pulse. — Since the pulse 
 is dependent on the heart's systole, " feeling the pulse"' gives 
 a convenient means of counting the rate of the heart beat. 
 To the skilled touch, however, it tells much more : as, for 
 example, a readily compressible or "soft pulse " shows that 
 the heart is not keeping the arteries properly filled with blood ; 
 a tense and rigid or " hard pulse'' indicates that the heart is 
 keeping the arteries excessively filled, and is working too vio- 
 lently. In healthy adults the pulse rate varies from sixty-five 
 to seventy-five a minute, the most common rate being seventy- 
 
CIRCULATION OF BLOOD IN FROG'S WEB. 187 
 
 two. In the same individual it is faster when standing than 
 
 when sitting, and when sitting than when lying down. Anv 
 exercise or ext itement increases its rate temporarily. A sit k 
 person's pulse should nol therefore befell when he is nervous 
 or e\< ited. In children the pulse is quit Iter than in adults, 
 and in old age slower than in middle life. 
 
 The Flow of the Blood in the Capillaries and Veins. — 
 The movement of the blood from the heart is intermittent, 
 coinciding with each systole of the ventricles. Before it reaches 
 the capillaries, however, this rhythmic movement is trans- 
 formed into a steady flow, as may readily be seen by examin- 
 ing with a mieroseope thin transparent parts of various animals, 
 e.g. the web of a frog's foot, a bat's wing, or the tail of a 
 small fish. In consequenee of the steadiness with which the 
 capillaries supply the veins the flow in them is also unaffected 
 by the beat of the heart. If a vein is cut the blood wells out 
 uniformly, whereas a cut artery spurts out in powerful jets 
 which correspond 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 in the thin membrane 
 between the toes of a frogs hind limb as seen with the micro- 
 scope. Upon focusing beneath the outer layer of the skin, a 
 network of minute arteries, veins, and capillaries, with the 
 blood flowing through them, comes into view (Figs. 84 and 
 86). The arteries are readily recognized by the fact that the 
 flow in them is fastest and from larger to smaller branches. 
 The smallest end in a capillary network, the channels of which 
 are all nearly equal in size. In the veins arising from the 
 capillaries the flow is from smaller to larger trunks, slower 
 than in the arteries, but faster than in the capillaries. 
 
 The Blood flows most slowly in the Capillaries because 
 
1 88 THE HUMAN BODY. 
 
 their united area is many times greater than tnat 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. The aggregate area of the veins is smaller than that 
 of the capillaries, but greater than that of the arteries ; there- 
 fore the rate of movement in them is intermediate. 
 
 If the aggregate areas of all the branches of the circulatory 
 system were taken, beginning at the origin of the aorta, we 
 should have a double cone, as represented in Fig. 87. Start- 
 ing at the beginning of the aorta we have a tube one inch in 
 diameter, which gradually expands because of the increased 
 
 Fig. B7. — Diagram intended to give an idea of the aggregate sectional diameter of 
 the different parts of the vascular system. A, arteries; C, capillaries; /", veins. 
 (After Schofield.) 
 
 aggregate capacity of the arterial branches until the capillary 
 region is reached. Here there is a sudden expansion to a 
 tube approximately' two feet in diameter. There is now a 
 rapid and then a gradual reduction in size until the tube rep- 
 resenting the venae cavae has a diameter of two inches. Just 
 as water forced in at a narrow end of this tube would flow 
 quickly there, slowly at the widest part, and more quickly 
 again where it passed from the other narrow end, so the blood 
 flows rapidly in the aorta and the venae cavae,* and slowly in 
 * A good illustration taken from physical geography is afforded by 
 
NO PULSE IN CAPILLARIES AND VEINS. 189 
 
 the capillaries, whit h, though thousands of times smaller than 
 the great arteries and veins, arc millions of times more nu- 
 merous. 
 
 Why there is no Pulse in the Capillaries and Veins. — 
 The disappearance of the pulse in the arterioles has two 
 causes, 1 the elasticity of the arteries and 1 2 | the resist 
 an< e offered to it> flow by friction in the smaller 
 
 On account of this friction the larger arteries have diffi- 
 culty in sending blood through them ; it therefore accumu- 
 lates in the aorta and its large branches and stretches their 
 elastic walls. The stretched arteries press constantly on the 
 blood within, and keep squeezing it through the arterioles 
 into the capillaries, both during >ystole and diastole. The 
 heart, in fact, keeps the big elastic arteries over-distended 
 with blood, since before they have had time to lose their 
 grip on the blood within, another systole occurs and fills them 
 up tight again. As the arteries are thus always stretched and 
 always pressing on the blood, the capillaries receive a steady 
 supply and the flow through them is uniform. This even 
 capillary flow passes on a steady blood stream to the veins.* 
 
 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 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. 
 
 * ''Every inch of the arterial system may. in fact, be considered as 
 converting a small fraction of the heart's jerk into a steady pre>.-ure. 
 and when all these fractions are summed up together in the total length 
 of the arterial system no trace of the jerk i- left. As the effect of each 
 systole becomes diminished in the smaller vessels by the causes above 
 mentioned, that of this constant pressure 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 fundi- 
 the air-reservoir of a fire-engine, which converts the jerking impulse 
 fcjiven by the pumps into the -teady flow of the delivery hose." — 
 Huxley. 
 
190 THE HUMAN BODY. 
 
 The Object of having no Pulse in the Capillaries is to 
 diminish the danger of their rupture. As we have seen, liq- 
 uid has to ooze through their walls to nourish the organs of 
 the body, and wastes from the organs must get to the blood 
 that they may be carried oft". Their walls have therefore to 
 be very thin, and if the 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 lace and neck, allowing more blood 
 to flow to the skin. 
 
 Why the Arteries have Muscles. — The amount of blood 
 in the body is not sufficient to allow a full stream of blood 
 through all its organs at one time. The muscular fibres con- 
 trolling 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 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 ar- 
 teries contracted: for example, when the brain is at work, its 
 vessels are dilated and often the whole head flushed ; when 
 the muscles are exercised, a great portion of the blood of the 
 bodv is carried off to them: during digestion, the vessels of 
 the alimentary tract are dilated and absorb a large share of 
 blood. 
 
 This control of the amount of blood which any organ re- 
 ceives is accomplished by nerve control through the branches 
 
EXPOSURE TO COLD. 191 
 
 of the sympathetic syste m upon the mus< le fibres in the walls JLuut, 
 oi the arterioles. These branches are called vaso mo/ot nervi 
 and the control is called vaso-motor action. Contraction of 
 
 the arteriole walls is tfaso constriction^ and relaxation ol walls 
 vaso-dilaiation. Vaso-motor action makes it possible to give 
 
 any organ the amount of blood it needs at any time without 
 calling upon the heart for extra work. 
 
 We can therefore understand how hard thought or violent 
 exercise soon after a meal, by diverting the blood from the 
 abdominal organs, is apt to produce an attack of indigestion. 
 Young per.-ons whose organs have a superabundance of energy, 
 which enables them to work under unfavorable conditions, 
 are less apt to suffer in such ways than their elders. One sees 
 boys running about after eating, when older people feel a 
 desire to sit quiet or even to sleep. 
 
 Exposure to Cold. — Prolonged exposure of the surface to 
 cold is very apt to be followed by a catarrhal condition of the 
 mucous membranes of the nose, throat, lungs, or intestines 
 (diarrhoea). Summer diarrhoea is more often due to a chill 
 of the surface than to the fruits eaten. The best preventive 
 is to wear, when exposed to sudden changes of temperature, a 
 woollen garment* over the trunk of the body ; cotton and 
 linen permit any change in the external temperature to act 
 almost at once upon the skin. After an unavoidable exposure 
 to cold or wet, the thing to be done is of course to maintain 
 the cutaneous circulation; movement should be persisted in, 
 
 * In tropical countries, it is customary for soldiers to wear a flannel 
 band over the abdomen, in addition to other clothing, to prevent chill 
 and consequent diarrhoea. This has come to be known as a cholera belt, 
 since it has been credited with considerable influence in reducing the 
 frequency of severe attacks of diarrhoea, which is one of the most easily 
 recognized symptoms of cholera. 
 
192 THE HUMAN BODY. 
 
 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 contrac- 
 tion of the cutaneous arteries soon passes off, and is succeeded 
 by a dilatation causing a warm healthy glow on the surface. 
 If the bather remains too long in cold water, however, this 
 reaction passes off and is succeeded by a more persistent chil- 
 liness 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. 
 
 It is undoubtedly true, however, that many persons who 
 attempt to take daily cold baths fail to get a warm reaction 
 and are physically depressed rather than stimulated. Others 
 who have a tendency to neuralgia or rheumatism may have 
 these conditions aggravated by such exposure to cold. It is 
 much wiser for these persons to take tepid or warm baths. 
 
CHAPTER XVI. 
 THE OBJECT AND THE MECHANICS OF RESPIRATION. 
 
 The Object of Respiration. — Hlood is renewed, as far as 
 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 after- 
 wards poured into the blood. In order that energy may be 
 set free (Chap. VIII), oxidations must occur, necessitating a 
 constant supply of oxygen. Waste substances are thus pro- 
 duced, which are no longer of use to the body, but detrimen- 
 tal to it if present in large quantity. The most abundant of 
 these wastes is carbon dioxide gas. 
 
 The function of respiration has for its object (i) 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 consists primarily of two elas- 
 tic bags, the hings, placed in a cavity with extensible walls, 
 the thorax. They are filled with air and communicate by air 
 passages with the surrounding atmosphere. In the walls of 
 the lungs the capillary blood vessels form a very close net- 
 work. Through their walls the blood receives oxygen from 
 the air and gives in return carbon dioxide. The air in the 
 lungs consequently needs renewal, since otherwise it would 
 soon have no oxygen to give to the blood, and would become 
 
 193 
 

 194 THE HUM /IN BODY. 
 
 so loaded with carbon dioxide that it could no longer receive 
 it from the blood. This renewal is effected by a system 
 of muscles, bones, and cartilages which co-operate to bring 
 about that alternating expansion and contraction of the chest 
 which we call breathing. When the chest contracts, air 
 poorer in oxygen and richer in carbon dioxide is expelled 
 from the lungs ; when it expands, fresh air, rich in oxygen, 
 and containing hardly any carbon dioxide, is taken into them. 
 
 The respiratory organs are (i) the lungs ; (2) the air pas- 
 sages ; (3) the vessels of the pulmonary circulation, including 
 the pulmonary artery bringing the blood to the lungs, the 
 pulmonary capillaries carrying it through them, and the pul- 
 monary veins conveying it from them ; (4) the muscles, 
 bones, and cartilages 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 
 (Fig. 46) is an aperture through which it passes into the 
 larynx or voice-box (a. Fig. 88), which lies in the upper 
 part of the neck. From the larynx air passes on through the 
 windpipe or trachea, which enters the chest, and in the upper 
 part divides into a right and a left bronchus. Each bronchus 
 enters a lung, and divides in it into a vast number of very small 
 tubes, called the bronchial tubes. The last and smallest bron- 
 chial tubes {[a, Fig. 89) open into subdivided elastic sacs 
 (J>, c) with pouched walls. 
 
 Structure of the Trachea and its Branches. — The trachea, 
 bronchi, and bronchial tubes are lined by mucous membrane, 
 outside of which is a supporting stratum composed of connec- 
 
 * To these should be added (5) the nerve centres and nerves which con- 
 trol the muscles of respiration, and which will be subsequently con- 
 sidered (see Chap. XX). 
 
77//; .-//A' PASSAGES. 
 
 na- 
 
 tive and plain muscular tissues. Their walls also contain 
 incomplete rings of cartilage which keep them open, Below 
 the larynx the stiff windpipe passing down to the top of the 
 chest may readily be felt in thin persons. 
 
 The Cilia of the Air Passages. — The mucous membrane 
 
 Fig. 88. 
 
 Fig. S3 —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 bron- 
 chial tubes, a, larynx ; i\ trachea ; d, right bronchus. The left bronchus is seen en- 
 tering the root of its lung. 
 
 Fig. 89. — A small bronchial tube, a, dividing into its terminal branches, c ; these 
 have pouched or sacculated walls and end in the sacculated alveoli, b. 
 
 of the trachea and its branches, except 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 toward the thro:it, move gently back again, 
 and then once more violently toward the outlet of the air pas- 
 sage. 
 
 These moving threads are called cilia. 
 
 Swaying in the 
 
196 
 
 THE HUM AS BODY. 
 
 mucus secreted by the membrane which they line, they sweep 
 
 it on to the larynx, where it is coughed up. 
 
 Imagine a man rowing in a boat at anchor. The sweep of 
 
 the oars will drive the water back and not the boat forward. 
 So these little oars, the cilia, anchored on 
 the mucous membrane, drive on the secre- 
 tion which bathes its surface. 
 
 Bronchitis, or %, 'acold on the chest," 
 is an inflammation of the membrane lining 
 the bronchial tubes, in consequence of 
 which it swells, and its secretion is changed 
 
 Fig. jo. 
 
 Fig. 01. 
 
 Fig. 90. — The trachea, front, h, hyoid bone; tt' , thyroid cartilage; c, cricoid; e, 
 epiglottis; tr, trachea; b and b', bronchi. 
 Fig. 91. — Ciliated cells from the epithelium. 
 
 in quantity and character. The swelling and secretion tend 
 to close the tubes and interfere with the free passage of air in 
 breathing. 
 
 The Lungs consist of the bronchial tubes and their terminal 
 dilatations, together with blood vessels, lymphatics, and 
 nerves, all bound firmly together by elastic tissue. The ex- 
 pansions called air sacs or alveoli, at the end of each final 
 branch (Figs. 92 and 93), are relatively very large, and 
 their surface is still further increased by the pouches which 
 project from them. Their walls are highly elastic, and con- 
 tain a close network of capillary blood vessels, supplied by the 
 pulmonary artery and emptying into the pulmonary veins. 
 
THE LUNGS. 
 
 197 
 
 Through the extremely thin lining of the air sac, and the 
 thin wall of the capillaries im- ^^g^ — 
 
 bedded in it, oxygen is absorbed 
 by the blood from the air in 
 the air sac and carbon dioxide 
 given up to it. It has been 
 calculated that if the walls of 
 the air cells were spread out flat 
 and placed side by side they 
 would cover an area of 2600 
 square feet. This great sur- 
 face, therefore, represents the 
 area of the body by which 
 
 J J r ig. 91. — I wo alveoli of the lung 
 
 nvvfrpn k rere\vec\ nnH mr hi S n, y magnified. 6, 6, the air cells, 
 
 ox) gen is received ana car- or holl{M}r protrusions of the a iveoi„s, 
 
 1 i- -j_ • ec j opening into its central cavity; c, ter- 
 
 bon dlOXlde given off, and m inal branches of bronchial tube! 
 
 accounts for the rapidity with which the exchange takes 
 
 place. 
 
 The Pleurae. — The exterior of each lung, except where 
 
 its bronchus 
 and blood ves- 
 sels enter it, is 
 covered by a 
 thin elastic ser- 
 ous membrane, 
 the pleura (Fig. 
 2), which close- 
 ly resembles the 
 peritoneum. 
 
 Fig. 93.— Diagram of expansion of end of bronchial tube 'T'hic rn^mK r or>^ 
 
 into air sacs. B, bronchial tube; LB, bronchiole : A , entrance IUS Ilieiliurdlie 
 
 chamber; /, central cavity (infundibulumj; C, L\ alveoli, 1 •< , 
 
 whose walls are covered with capillaries. alSO lines the 
 
 inside of the chest. Its surface in health is kept moist by 
 a small quantity of lymph. In consequence of its smoothness 
 
198 
 
 THE HUMAN BODY. 
 
 and moisture, the lungs glide over the chest wall during the 
 breathing movements with but little friction. 
 
 Pleurisy is inflammation of the pleura. In its early stages 
 
 Fig. 94. — Section of lung with distended blood vessels, highly magnified, c, c, par- 
 titions between alveoli; b, small artery giving off capillaries to alveoli. 
 
 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, taking up space which should be occupied by 
 the lung. 
 
 The Elasticity of the Lungs. — The lungs are as elastic as 
 a thin 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 com- 
 pletely to fill all the space left for them by the heart and 
 other structures contained in the thorax. 
 
 Inspiration and Expiration. — The process of taking air 
 
QUANTITY OF AIR BREATHED. 
 
 199 
 
 into the lungs is known as inspiration^ that of expelling it as 
 expiration. < >n the average, fifteen to eighteen inspirations 
 and expirations occur in each minute. We therefore breathe 
 in and out about once for every four beats of the heart. 
 
 Maximum inspiration. 
 
 Complemental ait 
 
 Ordinary inspiration 
 
 TIDAL AIR 
 
 Ordinary expiration 
 
 Supplemental air 
 
 Maximum expiration 
 Residual air 
 
 2000 
 
 120 
 
 Of 
 
 c.c. cub. in. 
 
 500 c.c.or 30 cub. in. 
 
 5* HI llrfl 
 
 or 
 <:. cub.in. 
 
 1 
 
 •Vital capacity 
 
 1/ 
 
 Capacity of equilibrium 
 
 Fig. 95.— Amounts of air contained by the lungs in various phases of ordinary and 
 of forced respiration. 
 
 Quantity of Air Breathed. — During ordinary quiet res- 
 piration, we inspire and expire about 30 cubic inches, or 
 about one pint, of air ; this is called the tidal air. After an 
 expiration of this amount, we can still expire by effort about 
 100 cubic inches of air ; this is called the supplemental air. 
 There still remains in the lungs about 100 cubic inches of air 
 which cannot be expelled with the most violent effort ; this is 
 the residual air. When breathing quietly, it is possible, after 
 an inspiration of the ordinary 30 cubic inches of air, to in- 
 spire an additional 120 cubic inches ; this is the complemental 
 air. The total amount of air that can be expired after the 
 deepest inspiration possible is called the vital capacity. This 
 varies in different individuals and depends largely on the 
 movability of the chest wall. 
 
:oo 
 
 THE HUMAN BODY. 
 
 The Structure of the Thorax. — The thorax is a conical 
 cavity with a supporting skeleton | Fig. 96 | formed by the 
 
 Fig. q6 — The skeleton of the thorax, a, g, vertebral column ; b, first rib ; <r, clavi- 
 cle ; d, third rib ; i, glenoid fossa. 
 
 il 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 pleurae I p. 197- inside. Above, it is closed by the 
 muscles and other organs of the neck : below bv a movable 
 bottom, the diaphragm. The air-tight chamber thus enclosed 
 can be enlarged in all three diameters, but especially in the 
 vertical, and in the dorso-ventral (running from the spinal col- 
 umn to the breast bone). 
 
 The Vertical Enlargement of the Thorax is brought 
 about by the contraction of the diaphragm Fig. 97), a thin 
 sheet of muscle, with a fibrous membrane in its centre serving 
 
VERTICAL ENLARGEMENT OF THE THORAX, zor 
 
 as a tendon. In rest ihe diaphragm is dome shaped, its con- 
 cavity being turned towards the abdomen. From the tendon 
 on the (Town of the dome, striped muscular fibres radiate, 
 downward and outward, in all directions, and are fixed by 
 their outer ends to the six lower ribs, the breast bone, and 
 tlu- vertebral column. In inspiration the muscular fibres, by 
 shortening, flatten the dome and enlarge the thoracic cavity 
 
 Fig. 97. — The lower half of the thorax, with four lumbar vertebrae, showing the 
 diaphragm from above. 1, 2, 3, central tendon ; 4, 5, muscular part. 
 
 of the diaphragm by adding space to its widest part (Fig. 98). 
 Since the abdominal cavity is surrounded by bony and dense 
 muscular walls, except in front where they are thin and elastic, 
 the downward movement of the diaphragm manifests itself 
 as an outward movement of the front abdominal wall. 
 
202 
 
 THE HUMAN BODY. 
 
 Fig. 98. — Diagram to show the changes in the sternum, diaphragm, and abdominai 
 wall in respiration. A , inspiration ; B, expiration ; 7V, trachea ; St, sternum ; D, 
 diaphragm ; Ab, abdominal wall. The shaded part is to indicate the stationary air. 
 
 The Dorso-Ventral Enlargement of the Thorax. — The 
 
 ribs slope downward (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 at- 
 tached to it are raised by muscles which 
 pull on them, thus increasing the dis- 
 tance between the sternum and the ver- 
 tebral column. That this must be so 
 
 FiG.99 —Diagram illustrating . . 
 
 the dorso ventral increase in thewill readily be seen by examining the 
 
 diameter of the thorax when 
 
 the ribs are raised. diagram Fig. 99, where ^represents 
 
 the vertebral column, c and d two ribs, and st the sterum. 
 
EXPIRATION. 203 
 
 The continuous lines represent the natural position of the 
 ribs al 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 nearly horizontal plane, the 
 sternum is pushed away from the spine, and the extent of the 
 chest cavity between backbone and breast bone is increased. 
 
 Inspiration requires a good deal of muscular 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, shoulders, and breast bone have also to be lifted up 
 and the elasticity of the lungs overcome. 
 
 Expiration. — In ordinary expiration, on the contrary, no 
 muscular effort is required. As soon as the muscles which 
 have raised the ribs and sternum relax, these bones return by 
 their weight and the elasticity of the rib cartilages to their 
 former unconstrained position. The elastic abdominal wall 
 presses the abdominal viscera against the under side of the 
 diaphragm and pushes it 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 and weight of the parts which 
 were stretched and raised in inspiration than by any special 
 expiratory effort. 
 
 When, however, an expiration is violent, as during a sneeze 
 or a fit of coughing, the abdominal muscles act as special 
 expiratory muscles by pulling down the ribs and pressing 
 up the diaphragm. 
 
 The Respiratory Sounds. — The entry and exit of air are 
 accompanied by respiratory sounds or murmurs, which can be 
 heard on applying the ear to the chest wall. These sounds 
 are characteristic over the trachea, the larger bronchial tubes. 
 
204 THE HUMAN BODY. 
 
 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 physician to form a diagnosis. 
 
 Why the Lungs fill with Air may be best understood by 
 considering a pair of bellows, as shown in Fig. ioo. A thin- 
 walled rubber bag (b) is fitted loosely inside the bellows and 
 
 connected with the outside 
 air only through its nozzle 
 (c). It is possible to fill 
 the rubber bag either by 
 blowing air in through the 
 
 Fig. ioo. — Diagram to illustrate the er.trv of , , . . 
 
 air to the lungs" when the thoracic cavity' en- IlOZZle, Or DV Opening the 
 larges, 
 
 bellows. When the rubber 
 bag is filled with air, it is possible to empty it either by 
 closing the bellows or by releasing the handles and allow- 
 ing the weight of the bellows and the elasticity of the bag 
 to force the air out. Whenever the cavity of the bellows is 
 made larger, air enters the rubber bag ; when made smaller, 
 air passes out from the bag. When the bellows are being 
 opened, air enters the cavity; since it is impossible to pull 
 air, this inward movement means that air is being pushed 
 in. When the bellows are being closed the outward move- 
 ment of air indicates similarly that there is a force behind it 
 pushing it out.* 
 
 * It must be remembered that we are at the bottom of a sea of air and 
 that this sea is pressing on all exposed surfaces with a force equal to 
 about 15 lbs. to the square inch of surface, but as it presses equally on 
 all sides of objects, the pressures in opposite directions neutralize each 
 other and we do not notice their presence. As. for example, when we 
 have a piece of thin sheet rubber, it is perfectly flaccid. If, however, 
 we diminish the pressure upon one side by putting the rubber over the 
 mouth and inhaling, the pressure upon the other side, though unchanged, 
 is relatively greater and pushes the membrane in. 
 
THE NERVOUS CONTROL 01 RESPIRATION. 205 
 
 It is thus apparent thai so long as air cannot entei between 
 the walls of the rubber bag and the bellows, the rubber bag 
 will follow the movements of the bellows and be emptied only 
 when the bellows are closed. The chest walls correspond 
 to the bellows and the Lungs to the inner rubber bag. We 
 thus see win- tiie lungs cannot completel) empty themselves 
 during life, since the chest wall is not suffi< iently flexible to 
 close down upon them so far as to obliterate the cavity. If, 
 however, the chest wall becomes punctured, as by a wound, 
 connecting the chest cavity with the external air, the external 
 air pressure, no longer withheld from the lung's surface by 
 the chest wall, presses upon it and neutralizes the pressure 
 of the air within the lung which has kept it expanded; the 
 lung's elasticity then causes it to collapse to a small flaccid 
 mass. 
 
 The Nervous Control of Respiration. — The respiratory 
 movements are produced by contractions of muscles and are 
 controlled by the action of nerves. It has been found that 
 the nervous impulses which give rise to the respiratory move- 
 ments are controlled in part by a nervous centre in the spinal 
 bulb, called the respiratory centre. Its activity seems to de- 
 pend upon the condition of the blood ; when the blood is 
 poor in oxygen and rich in carbon dioxide and other waste 
 matters, this centre, as also the heart centre, becomes active 
 and produces more rapid and deeper contractions of the re- 
 spiratory muscles; when the blood is rich in oxygen and poor 
 in wastes, the centre is more quiescent. During vigorous 
 exercise, oxygen is used up rapidly from the blood and the 
 respiratory centre is kept in a state of greater activity. Dur- 
 ing sleep, oxygen is used up more slowly and the respiratory 
 movements are less frequent. 
 
 Hygienic Remarks. — Since the diaphragm when it con- 
 
2o6 
 
 THE HUMAN BODY. 
 
 tracts pushes down the abdominal viscera lying against its 
 under side, these have to make room for themselves by push- 
 ing out the soft front of the abdomen, which accordingly pro- 
 trudes when the diaphragm descends. Hence breathing by 
 the diaphragm is indicated on the exterior by movements of 
 
 Fig. ioi. — Torso of the Statue 
 known as Venus of Milo. 
 
 Fig. 102. — New York 
 Fashion, 1898. 
 
 the abdomen (Fig. 98) and is often called "abdominal 
 respiration," as distinguished from breathing by the ribs, 
 called " costal "or " chest breathing." As a rule, men and 
 children use the ribs less than adult women. Since abdomen 
 and chest alternately expand and contract in healthy breath- 
 ing, anything which impedes their free movement is to be 
 avoided. The tight lacing which is still indulged in by those 
 who think a distorted form beautiful, seriously impedes one 
 of the most important functions of the body, and leads not 
 
HYGIENIC REMARKS. 207 
 
 only to shortness of breath and an incapacity for muscular 
 exertion, but in many cases to actual deformity or disi 
 
 The abdominal organs are compressed and forced downward, 
 and as a result their attachments are stnt< hed and their 
 functions impeded. In extreme cases of tight lacing some 
 organs are often directly injured ; for example, weals of 
 fibrous tissue are found developed on the liver from the con- 
 stant pressure of the lower ribs forced against it. 
 
 7«*pl 
 
 
CHAPTER XVII. 
 THE CHEMISTRY OF RESPIRATION AND VENTILATION. 
 
 The Quantity of Air breathed daily. — After an ordinary 
 expiration the chest cavity is by no means completely col- 
 lapsed, as the lungs still contain about 200 cubic inches of 
 air. In the next inspiration 30 more cubic inches are taken 
 : the following expiration about the same amount is sent 
 out, and so on throughout the day. During quiet breathing 
 the quantity of air in the lungs varies, therefore, with each 
 as] ration 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 
 a r - expelled. As each of us breathes at least fifteen times a 
 minute, we thus use each minute 15 X 30 = 450 cubic inches 
 157 pints of air. In an hour the quantity is 450 X 60 = 
 27,000 cubic inches ^930 pints), and in twenty-four hours 
 27,000 X 24= 648,000 cubic inches 122.320 pints) of air, 
 which weighs about 28. 7 lbs. We have next to 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 temperature, moisture, volume, 
 and in its chemical composition. 
 
 Changes in Temperature. — The air taken into the lungs 
 is nearly always cooler than that expired, which has a tem- 
 
 20S 
 
CHANGFS IN MOISTURE, 209 
 
 perature of about 36 1 97 F.), The temperature of a room 
 is usuall} about 21 C. (70 F.). The warmer the inspired 
 air, the Less the heat which is lost by the body in the breath- 
 ing pro< ess. 
 
 Changes in Moisture. Inspired air always contains more 
 or loss water vapor, but is rarely saturated — that is, rarely 
 contains all it can take up without showing it as mist. 
 The warmer air is, the water vapor it requires to saturate it. 
 The expired air is nearly saturated at the temperature at 
 which it leaves the body. This is shown by the moisture 
 deposited when it is cooled, as on a mirror, or in the clouds 
 formed by the breath on a frosty day. We therefore con- 
 clude that air when breathed gains water vapor and carries 
 it off from the lungs. The quantity of water thus removed 
 from the body is about nine ounces each tw r enty-four hours. 
 
 Changes in Volume. — If the expired air is 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 consequence of its higher temperature. If, 
 however, it is 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 car- 
 bon dioxide which it has gained. 
 
 Chemical Changes. — The most important changes brought 
 about in the breathed air are those in its chemical composi- 
 tion. 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 
 
210 THE HUMAN BODY. 
 
 5 of oxygen. More accurately, ioo volumes of expired air, 
 when dried, consist of — 
 
 Oxygen 15.4 
 
 Nitrogen 79. 2 
 
 Carbon dioxide 4.3 
 
 The expired air also contains volatile organic substances in 
 quantities too minute for chemical analysis, but readily de- 
 tected 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 (i|- 
 lbs. ). The body therefore gains this amount of oxygen 
 through the lungs daily. 
 
 The Amount of Carbon Dioxide passed Out from the 
 Lungs in a Day is 4. 3 per cent of the total bulk of the air 
 breathed, or 27,864 cubic inches; it weighs 14,105 grains or 
 about 2 lbs. 
 
 We thus find that though each breath seems in itself a very 
 little thing, the total amount of matter received into and 
 passed out of the body through the lungs every day of our 
 lives is considerable. In a year each adult breathes about 
 10,000 lbs. of air; from it he takes 657 lbs. of oxygen, and to 
 it he gives off 730 lbs. of carbon dioxide. 
 
 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 
 
WHEN BREATHED AIR BECOMES UNWHOLESOME. »I1 
 
 the air around him removed. Hence the necessity of ventila- 
 tion to supply fresh air in place of that breathed. Clearly 
 the amount of fresh air requisite must be determined by the 
 number of persons collected in a room. Moreover, since 
 gas and lamps use oxygen and give out carbon dioxide, cal 
 culation must be made for them in arranging for the ventila- 
 tion of a building in which they are to be used. 
 
 When Breathed Air becomes unwholesome. — The evil 
 results of insufficient air supply are not ordinarily directly 
 due to a lack of oxygen, for the blood flowing through the 
 lungs can take the necessary amount of oxygen from air con- 
 taining as little as fifteen or even ten per cent. The head- 
 ache and drowsiness which result from sitting in badly venti- 
 lated rooms, and the lack of energy and general ill-health 
 which accompany permanent living in such conditions, are 
 dependent on a slow poisoning of the body by the reabsorp- 
 tion of matters eliminated from the lungs in previous respi- 
 rations. 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 observa- 
 tion shows that the air becomes injurious long before the 
 reduction of oxygen and the increase of carbon dioxide are 
 sufficient to do any harm. Breathing air which contains 
 one or two per cent of carbon dioxide produced by ordin- 
 ary chemical methods does no injury, but the breathing of 
 air containing one per cent of carbon dioxide produced by 
 respiration is decidedly injurious, because of the organic 
 materials sent out from the lungs at the same time. 
 
 The percentage of carbon dioxide in the air may be readily 
 measured, whereas the more dangerous organic substances con- 
 tained in expired air cannot be. These poisonous materials, 
 however, always bear practically the same relation to the 
 
212 THE HUMAN BODY. 
 
 amount of carbon dioxide ; hence if carbon dioxide is esti- 
 mated, the badness of the air, due to the poisonous factors, 
 may be inferred. It must be remembered, however, that 
 this applies to the carbon dioxide produced by respiration, 
 and not to that produced by the burning of gas or lamps ; 
 hence in rooms lighted by these means allowance must be 
 made, after determining the amount of carbon dioxide, for 
 that which has been produced through their agency. When 
 a very large amount of carbon dioxide is present the air can- 
 not be safely respired, as, for example, at the bottom of wells 
 or in brewing vats. This is due to two factors, the absence 
 of oxygen and the presence of an overwhelming amount of 
 carbon dioxide. 
 
 The Quantity of Fresh Air which should be allowed for 
 each Person in a Room. — A man at rest expires air contain- 
 ing 4$ of carbon dioxide, amounting in one hour to about 
 -| cubic foot. It is agreed by hygienists that 2 parts of 
 respiratory carbon dioxide in 10,000 parts of air are all that 
 are permissible for respiration. Hence air must be introduced 
 into an occupied room in sufficient amount to reduce the re- 
 spiratory impurity of 4^ or 400 parts in 10,000 to 2 parts; 
 therefore there must be added to each breath 200 parts of 
 fresh air, or 3000 cubic feet of air per hour for each indi- 
 vidual. 
 
 Many experiments have shown that there should be an 
 allowance of about 600 cubic feet of space for each man in 
 the room. This permits the requisite change of air without 
 drafts, and insures a chance for the thorough mixing of ex- 
 pired air with the air of the room so that it will not be re- 
 breathed before mixing. 
 
 The nose of a person entering a room from the outside air 
 has been found to be an excellent test of the purity of the air, 
 
//<>//' TO VENTILATE. 
 
 2I 3 
 
 and any odor or sense of i loseness dete* ted in this way sug- 
 that the air contains too much impurity to be breathed 
 with safety. The accompanying tabic shows the relation 
 between the determinations made l>y the sense of smell and 
 the chemical analysis of the amount of carbon dioxide due to 
 respiratory impurity present. 
 
 RELATION OF ORGANIC MATTER TO CARBON DIOXIDE, DK'l I K 
 
 MINED BY ODOR. 
 
 
 Condition of the air of an occupied J '& 
 
 room as determined by the nose. 
 
 Corresponding parts of CO a in 
 10,000 vols, of air due to 
 respiratory impurity 
 
 Total parts of C0 2 in 10,000 
 vols, of air (=-| 4 parts at- 
 mospheric CO s ) 
 
 
 — • - c — 
 ei g B E a 
 
 u.s u (j 
 
 / - - 
 
 : = - 
 
 — u 
 
 '- -- I 
 
 «-> ii i/> 
 
 "■ ■ - - 
 
 v « 3: 
 
 > a 
 
 B se- 
 ll — 
 
 a - 
 
 - U B > 
 
 _ - -. r 
 
 6-5 
 
 IO.5 
 
 13 
 
 How to Ventilate. — Ventilation does not necessarily 
 mean draughts of cold air, as is too often supposed. In 
 warming by indirect radiation, as by furnace or steam pipes in 
 the basement, proper ventilation may readily be secured by 
 arranging openings connected with a chimney, by which the 
 impure air may pass out to make room for the fresh warm air 
 to enter. Since the fresh air is the warmest air of the room 
 it goes immediately to the ceiling and will pass out through 
 any openings it finds there. Hence all outlets should be at 
 the floor level and the inlets for warm air at the ceiling. 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. 
 
 Ordinary stoves in a room contribute little to the ventila- 
 tion, for they take only a small amount of air out of the room 
 through the chimney and bring in as leakage around doors 
 
 v/*-<juUo 
 
214 THE HUMAN BODY. 
 
 and windows only as much as they take out ; hence if these 
 rooms are occupied the air becomes quickly impure. Some 
 stoves are provided with jackets inside of which fresh air may 
 be admitted from outside. If there is no such provision, it 
 is possible to fasten a board three or four inches wide, to fit 
 under the lower sash of a window. Fresh air then enters by 
 the opening between the two sashes at the middle of the 
 window and diffuses through the room, usually without draft. 
 This window should be opened on the windward side of the 
 room so the air will surely enter. The window on the oppo- 
 site side of the room may be opened at the bottom to allow 
 the foul air to pass out. In this way the change of air in the 
 room may be made continuous. Since, fortunately, few doors 
 and windows fit quite tight, fresh air gets into closed rooms 
 in tolerable abundance for one or two occupants. 
 
 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, water, and carbon dioxide, 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 of the oxyhemoglobin 
 in the pulmonary veins. 
 
 o 
 v 
 
 
CHAPTER XVIII. 
 
 THE KIDNEYS AND THE SKIN. 
 
 General Arrangement of the Nitrogen-excreting Organs. 
 — These organs are (i) the kidneys, the glands which secrete 
 the urine; (2) the ureters or ducts of the kidneys, which 
 carry the secretion to (3) the urinary bladder, a reservoir in 
 which it accumulates and from which it is expelled from time 
 to time through (4) the urethra, an exit tube. The general 
 arrangement of these parts, as seen from behind, is shown in 
 Fig. 103. The kidneys (A 5 ) lie at the back of the abdominal 
 cavity, opposite the upper lumbar vertebrae, one on each side 
 of the middle line. Each is a firm mass, with a convex outer 
 and a concave inner border, and its upper end a little larger 
 than the lower. From the abdominal aorta (A) a renal 
 artery (Ar) enters the inner border of each kidney, to break 
 up within it into finer branches, ultimately ending in capil- 
 laries. These unite to form the renal veins ( J'r), one of 
 w r hich leaves each kidney and opens into the inferior vena 
 cava ( Vc). From the concave border of each kidney proceeds 
 also the ureter (t 7 "), a slender tube opening below into the 
 bladder ( Vu) near its lower end. From the bladder proceeds 
 the urethra (Ua}. The channel of each ureter passes very 
 obliquely through the wall of the bladder; accordingly if the 
 
 215 
 
2l6 
 
 THE HUMAN BODY. 
 
 Fig. 103. — The renal organs, viewed from behind. R, right kidnev. A, aorta; At 
 right renal artery; / V. inferior vena cava; IV, right renal vein; L~, right ureter; I V 
 bladder; l~a, commencement of urethra. 
 
WAV (li Rl 01 I Hi K1DNB YS, 217 
 
 pressure in the bladder rises above that of the liquid in the 
 ureter the walls of the oblique passage arc pres ed together 
 and it is closed. Usually the Madder (which contains mus- 
 cular tissue in its walls) is relaxed, and the urine flows readily 
 into it from the ureters. Since the passage of the urethra is 
 kept closed by elastic tissue around the upper end, the urine 
 accumulates in the bladder. When the bladder contra* ts and 
 presses on its 1 ontents the ureters are 1 losed in the way above 
 indicated, the elasticity of the fibres closing the urethral 
 exit from the bladder is overcome, and the liquid is forced 
 out. 
 
 The Gross Structure of the Kidneys. — When a section is 
 made through a kidney from its outer to its inner border 
 (Fig. 104) it is seen that a deep fissure, the hilus, leads into 
 it. In the hilus the ureter widens out to form the pelvis 0/ 
 the kidney, which breaks up into a number of smaller divisions, 
 the cups or calices. The cut surface of the kidney proper is 
 seen to consist of two distinct parts, an outer or cortical por- 
 tion, and an inner or medullary. The medullary portion is 
 less red and more glistening, is finely striated in a radial 
 direction, and does not consist of one continuous mass, but 
 of a number of conical portions, the pyramids of Malpighi 
 (2'). Each of these pyramids is separated from its neighbors 
 by a prolongation (*) of the cortical substance. This, how- 
 ever, does not reach to the apex of the pyramid, which pro- 
 jects, as the papilla, into a calyx of the ureter. At its outer 
 end each pyramid separates into smaller portions (2"), sep- 
 arated by thin layers of cortex and gradually spreading every- 
 where into it. The cortical substance is redder and more 
 granular-looking than the medullary. It forms everywhere 
 the outer layer of the organ, besides dipping in between the 
 pyramids in the manner above described. 
 
21 
 
 THE HUMAN BODY. 
 
 The renal artery divides in the hilus into branches (5) which 
 run into the kidney substance between the pyramids, giving 
 
 
 Fig. 1-4. — Section through the right kidney from its outer to its inner border, i. 
 cortex : 2, medulla: 2'. pyramid of Maipighi ; 2". pyramid of Ferrein : ~. small 
 branches of the renal artery entering between the pyramids : A, a branch of the renal 
 the pelvis of the kidney ; I', ureter ; C. a 
 
 off a few twigs to them, and end finally in a much closer 
 vascular network in the cortex. 
 
 The Minute Structure of the Kidneys. — The kidneys are 
 compound tubular glands, composed of branched microscopic 
 
THE RENAL si CRETION. 
 
 2 l<) 
 
 urtniferous tubules y lined by a single layer of se< reting cells 
 • I g. 105), supported by conne< - 
 tive tissue, and supplied with 
 blood vessels, nerves, and lym- 
 phatics. Each of the final 
 branches of each tubule ends in 
 a dilatation which contains a 
 knot of blood vessels! Fig. 106), 
 through whose walls water and 
 salts enter the tubule. As the 
 water trickles along the tubules, 
 their cells take the urea from 
 the blood in the capillaries 
 wrapped closely around them 
 (Fig. 105). The tubules unite 
 in the pyramids to form larger 
 ducts, which pour the secretion 
 
 . . ... tuft; in nature it forms a close invest- 
 
 llltO the CallCeS OI the pelvis OI ment around each vessel of glomerulus; 
 
 A, space in capsule; d, neck of capsule; 
 the ureter, which then COnveYS /ft firet convoluted portion of an urin- 
 
 iferous tubule ; o, granular epithelial 
 it tO the bladder. cells ; A, bast- ment membrane. 
 
 The Renal Secretion is a watery, acid solution of urea and 
 inorganic salts. These solids amount to 4 per cent of the 
 total secretion and give the solution an average specific grav- 
 ity of 1.022. The urine excreted in twenty-four hours con- 
 tains : urea, 35 gms. (i| oz.) ; inorganic salts (chiefly sodium, 
 potassium, ammonia, calcium, and magnesium), i6\ gms. 
 (J oz.) j and water, 1400 gms. (3 pints). 
 
 The urea, which is secreted by the kidneys and was formerly 
 supposed to be formed there, is made by the liver as a final 
 oxidation of nitrogenous materials which have been turned into 
 the blood by the tissues. As the chief organs for the excre- 
 tion of this nitrogenous waste, the kidneys arc among the 
 
 Fig. 105. — Diagram of a kidney k.\'>- 
 merulus and the commencement <if an 
 uriniferous tubule a, afferent blood 
 vessel pushing in the wall, tc, of a 
 Malpighian capsule and ending in the 
 capillary tuft from which the vein e 
 issues; c, involuted epithelium; for 
 the sake of distinctness it is repre- 
 sented as a wrapping for the whole 
 
220 
 
 THE HUM. -IS BODY. 
 
 most important of the body. Any defect in their healthy 
 activity leads to serious trouble, due to the accumulation of 
 nitrogenous wastes in the body. 
 
 The Skill, which covers the whole exterior of the body, 
 consists everywhere of two distinct layers, an outer, the cuticle 
 
 vt at 
 
 Fig. 106. — Circulation in the kidney, ai. small brancli of renal artery giving off the 
 branch va, which enters glomerulus, issues as ve. and then breaks up into capillaries, 
 which after surrounding the tubule find their way by v into zr£, branch of the renal 
 vein ; >//. capillaries around tubules in parts of the cortical substance where there are 
 no glomeruli. 
 
 or epidermis, * and an inner, the dermis. Hairs and naUs are 
 excessively developed parts of the epidermis. 
 
 The Epidermis I Fig. 107) consists of cells, arranged in 
 manv lavers and united by a small amount of cementing sub- 
 stance. The deepest layer is composed of elongated or 
 columnar cells, set with their long axes perpendicular to the 
 dermis beneath. It is succeeded by several strata of roundish 
 cells (£), which in the outer layers become more and more 
 
 * A blister is due to the accumulation of liquid between layers of the 
 epidermis. 
 
THE i rim rmis. 
 
 2 2 I 
 
 Rattened in a plane parallel to the surface. The outermost 
 epidermi< stratum is composed of many layers of much 
 
 I 
 
 x — a 
 
 Fig. 107. — A section through the epidermis, somewhat diagrammatic, highly mag- 
 nified. Below is seen a papilla of the dermis, with its artery,/, and veins, eg ; «t the 
 horny layer of the epidermis; b, the rete muscosum nr Malpighian layer; d. the layer 
 of columnar epidermic cells in immediate contact with the dermis; //, the duct of a 
 sweat gland. 
 
 flattened cells from which the nuclei, conspicuous in the 
 deeper layers, have disappeared. These superficial cells are 
 dead, and are constantly being shed from the surface of the 
 
222 
 
 THE HUM AS BODY. 
 
 body. Their place is taken by new cells, formed in the 
 
 deeper layers, pushed up to the sur- 
 face and flattened in their progress. 
 The change in the form of the cells as 
 they travel outward is accompanied 
 by chemical changes : they finally 
 constitute a semi - transparent dry 
 horny stratum (a), distinct from a 
 deeper, more opaque, and softer layer 
 (b and d ) of the epidermis. 
 
 The material which is peeled off 
 the skin on rubbing it with a rough 
 
 Fig. 108. — Magnified view _ 
 
 of the epidermis, showing towel alter a warm bath, consists ol 
 
 mouths of the sweat glands. 
 
 dead outer scales of the horny stratum 
 of the epidermis. 
 
 Nerves penetrate the deeper layers of the epidermis, but 
 no blood vessels enter it. The epidermis is also penetrated 
 by the ducts of sweat glands, which have their mouths along 
 the ridges (Fig. ioSi. and by the hairs. In dark races the 
 color is due to a pigment contained chiefly in the deeper 
 cells of the epidermis. 
 
 The Dermis, or True Skin (Fig. 109). consists of a close 
 felt-work of connective tissue, which becomes wider meshed 
 below and passes gradually into the subcutaneous areolar 
 tissue. In texture it is much like damp raw cotton, and 
 loosely attaches the skin to parts beneath. In tanning, the 
 dermis is turned into leather, its connective tissue forming an 
 insoluble and tough compound with the tannin of the oak- 
 bark employed. Wherever there are hairs bundles of plain 
 muscular tissue are found in the dermis ; it contains also a 
 close network of capillary blood vessels, and numerous lym- 
 phatics and nerves. In shaving, as long as the razor keeps 
 
THE PAPILLA OF THE DERMIS. 
 
 «3 
 
 in the epidermis there is no bleeding ; bul a deeper cut 
 
 shows at once the presence of blood vessels in the true skin. 
 
 Fig ioq. -Diagram to show the structure of the skin., E.c epidermis corneous 
 part; is.™, epidermis, Malpighian part; D.c, connective tissue of dermis; /•P a P> 11 f> 
 S sweat gland, the coils of the tube cut across or lengthwise; d, its duct, /, tat, v, 
 blood vessels; », nerve; t.c, tactile corpuscle. 
 
 The Papillae of the Dermis.— The outer surface of the 
 dermis is almost everywhere raised into minute elevations, 
 
224 
 
 THE HUMAN BODY. 
 
 called papilla, on which the epidermis is molded, so that its 
 deep side presents pits corresponding to the projections of 
 the dermis. In Fig. 108 are shown papillae of the dermis 
 containing a knot of blood-vessels, supplied by small arte- 
 ries and having the blood carried off from them by little 
 veins. Other papillae contain no capillary loops, but, in- 
 stead, special organs connected with nerve-fibres [tactile cor- 
 puscles'), and concerned in the sense of touch. On the 
 palm of the hand the dermic papillae are especially well 
 
 Fig. no. — Section of the skin, showing the hair follicles, sebaceous glands, and 
 the muscles of the hair, <t, epidermis; &, dermis; c, muscles of the hair follicLs; d, 
 sebaceous glands. 
 
 developed, as they are in most parts where the sense of 
 touch is acute, and are arranged in rows. The epidermis 
 fills up the hollows between the papillae of the same row, but 
 dips down between adjacent rows, and thus produces the 
 finer epidermic ridges.* On the thumbs and finger tips, 
 these ridges, finely dotted by the mouths of the sweat ducts, 
 assume more or less definite patterns. These patterns, which 
 are different in each person, persist throughout life and are 
 used for personal identification. The wrinkles of old per- 
 sons are due to the absorption of subcutaneous fat and of 
 
 * The more marked furrows on the palm, the so-called "lines of life" 
 of the gypsy's palmistry, have a different origin. 
 
HAIRS 4ND \.i//S. 225 
 
 other soft parts beneath the skin, which docs no1 shrink to 
 the same extent and is therefore thrown into folds. 
 
 Hairs, longer or shorter, are found all over the surface of 
 the body, except in a few regions, as the palms of tin- hands 
 and the soles ^( the feet. A hair is a slender thread of epi- 
 dermis, developed on a special dermic papilla placed at the 
 bottom of a depression, formed by a pitting-in of the dermis. 
 The depression is known as the hair follicle. The part of 
 the hair buried in the follicle is called its root, and is sn< - 
 ceeded by a stem, which (in uncut hairs) tapers off to a. point. 
 Each hair is made up of a number of epidermic cells, 
 arranged together to form a fibre. * 
 
 Nails. — A nail is a part of the epidermis, with its horny 
 stratum greatly developed. The back part of the nail fits 
 into a furrow of the dermis, and is called its root. The visible- 
 part consists of a body, attached to the dermis beneath ( which 
 forms the bed of the nail), and of a free edge. Near the root 
 is a little area, whiter than the rest of the nail, called the 
 lunula. The whiteness is due in part to the greater opaque- 
 ness of the nail there, and partly to the less vascular eharacter 
 of its bed, whieh when seen through the nail causes its junk 
 color. 
 
 The portion of the dermis on which the nail is formed is 
 called its matrix. At the root of the nail is a groove, in which 
 by the addition of new cells the nail grows in length. The 
 part of the matrix lying beneath the body of the nail, called 
 its bed, is highly vascular. New cells formed on its bed and 
 added to its under surface cause the nail to increase in thick- 
 ness, as it is pushed forward by the new growth at its root. 
 
 * The hairs of different races often present characterise differences. 
 The white races have cylindrical hair, whereas negroes have flattened or 
 ribboidike hair, hence its tendency to curl. 
 
226 
 
 THE HUMAN BODY. 
 
 The free end of a nail is therefore its thickest part. If a 
 nail is "cast" in consequence of an injury, or torn off, a 
 new one is produced, provided the matrix is not destroyed. 
 
 The Glands of the Skin are of two kinds, siveat and oil 
 glands. 
 
 The Sweat Glands Figs. 1 08 and in arc microscopic 
 tubes which reach from the surface of the skin to the subcu- 
 taneous areolar tissue ; there the tube often branches, and is 
 coiled up into a little knot, intertwined 
 with blood capillaries. These glands are 
 found all over the skin, but are most 
 abundant on the palms of the hands, the 
 soles of the feet, and the brow. Alto- 
 gether, there are about two and a half 
 millions of them. 
 
 The perspiration or sweat poured out by 
 these glands is a transparent colorless 
 liquid, with a peculiar odor, varying in 
 different races, and in different regions of 
 the body. Its quantity in twenty-four 
 hours is subject to great variations, but 
 v sweat lMa jj v ]j es between 700 and 2000 grams 
 
 The amount is 
 
 gland, d, horny layer 
 
 cuticle; r. Malpighian , j nnnrpO 
 
 layer; b. dermis. The C or 2 3 anQ Z 1 OUnCeSJ 
 
 fmbedded he in ^he ^ub^u- influenced mainly by the surrounding tem- 
 
 taneous fat, are seen be- . . . . . , . , 
 
 low the dermis. perature, being greater when this is high ; 
 
 but it is also increased by other conditions tending to raise 
 the temperature of the body, as muscular exercise.* The 
 * The secretion of perspiration is greatly increased during muscular 
 exercise and is closely related to the heat control of the body, for during 
 muscular exercise much more heat is produced in the body. By the evap- 
 \ oration of this extra amount of perspiration a large share of the heat is 
 
 \ removed, keeping the body temperature at the normal point (98' 4 F. ). 
 
 \ In fever, the sweat glands do not act ; as a result the skin is ordinarily 
 
 ' drv and less heat is lost. 
 
THl- si BM :EOl S < .LANDS. 227 
 
 sweat may or may not evaporate as fast as it is sei reted ; in 
 the former case it is known as insensible t in the latter as sen- 
 sible perspiration. By far the most passes off in the insensible 
 form ; drops of sweat accumulate onl) when the secretion is 
 very profuse, or the surrounding atmosphere so humid that it 
 dues not readily take up more moisture. The perspiration 
 in 1000 parts contains 990 of water to 10 of solids. Among 
 the latter is, in health, a little urea, some sodium chloride 
 and other salts. In diseased conditions of the kidneys, when 
 they are not able to excrete all the urea of the blood, it col- 
 lects in the blood and is excreted by the skin in greater 
 amount than ordinarily. By causing profuse perspiration 
 under such conditions, a considerable amount of urea can thus 
 be eliminated from the system to supplement the impaired 
 action of the kidneys. 
 
 The Sebaceous Glands usually open into hair follicles (Fig. 
 no). They are small compound racemose glands (p. 107). 
 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, lined by 
 secreting cells. The mouth of the ducts discharges into the 
 hair follicle. 
 
 The Sebaceous Secretion is oily and semi-fluid. In healthy 
 persons it lubricates the hair and renders it glossy. It is also 
 spread more or less over all the surface of the skin, and makes 
 it oily and less permeable by water. 
 
 The Skin as a Sense Organ. — Besides its functions as a 
 protective covering and an excretory organ, the skin is of ex- 
 treme importance, as being the seat of the dermal senses. 
 (Chap. XXI.) 
 
 Hygiene of the Skin. — The sebaceous secretion and the 
 
22$ THE HUMAN BODY. ■ 
 
 solid residue left by evaporating sweat form a film on the 
 skin. Hence the importance of personal cleanliness. Ex- 
 posed parts of the body except the scalp should be 
 washed daily with good soap. The entire body should be 
 washed with warm water and soap at least on e or twice a 
 week. If the skin becomes dry from too frequent bathing, 
 the oil should be restored by use of vaseline, tallow or other 
 emollient. Xo doubt many persons go about in very good 
 health with very little washing: contact with the clothes and 
 other external objects keeos the skin excretions from accu- 
 mulating to any very great extent. But apart from the duty of 
 personal cleanliness imposed on every one in daily intercourse 
 with others, the greater immunity from infectious diseases 
 afforded by cleanliness should be an important inducement. 
 Undoubtedly the habit of washing the hands before eating is 
 a most effective preventive measure. 
 
 Bathing. — One object of bathing is to cleanse the skin ; 
 another, to strengthen and invigorate the whole frame. For 
 some strong healthy persons a cold bath may be the best; but 
 in severe weather the temperature of the water should be raised 
 to 15 C. about 6o~ 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. The proper time 
 to come out of the bath is while this reaction lasts, and it 
 should be promoted by a good rubbing. If the stay in the 
 cold water is too prolonged, the state of reaction passes off, the 
 skin again becomes pallid, and the person feels cold, uncom- 
 fortable, and depressed all day. Such bathing is injurious in- 
 stead of beneficial, since it lowers instead of stimulating the 
 activities of the body. How long one may remain in cold 
 
BATHING. 229 
 
 sea water with benefit depends greatly on the individual ; a 
 vigorous man can bear and set up a healthy reaction after ten 
 or twenty minutes' immersion, whereas a feeble person may be 
 exhausted by one minute's exposure. Of course, apart from 
 tins, the temperature of the water is of great importance. 
 Water which feels cold to the skin may 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. — [t is perfectly safe to bathe when warm, 
 in spite of the common belief. No one should enter a cold 
 bath when feeling chilly, when in a depressed vital condition, 
 or immediately after a meal. The best time for a long cold 
 bath is two or three hours after breakfast or the mid-day meal. 
 For a brief daily dip there is no better time than on rising in 
 the morning. 
 
 Shower Baths are coming into general use because of their 
 convenience and economy of water. They may be supplied 
 with warm or cold water and are effective for both cleanli- 
 ness and stimulation. The cold shower is far better than the 
 cold plunge, since it stimulates both by the coolness of the 
 water and the force with which it comes against the skin. At 
 the same time it does not chill the body nor lead to depres- 
 sion by abstracting a large amount of heat. 
 
 Prolonged Warm Baths, except occasionally for purposes 
 of cleanliness, are medical remedies, and not proper for daily 
 use. While promoting the tendency to perspiration (often 
 important in disease), they also, if often repeated, lower the 
 general vigor of the body. 
 
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 matters from one to 
 another, and indirectly enables each organ to act upon the 
 rest, we have not as yet studied the 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 the others. 
 
 That the organs do co-operate we all know. When an 
 object threatens to touch the eye, the lids involuntarily shut. 
 When we are using the muscles of the le°:s vi^orouslv the 
 muscles of respiration hurry their action, that oxygen may be 
 conveyed more rapidly to the blood for the supply of the 
 working leg muscles, and that the wastes produced by them 
 may be quickly removed. When the sole of the foot is 
 tickled the muscles of the thigh and leg, which are not 
 directly interfered with at all, contract and jerk the foot away 
 from its tormentor. Everywhere among the organs we find 
 this co-operation through which our bodies are enabled to 
 continue alive. In .Esop's fable we are told how the arms 
 
 230 
 
A COLLECTION OF LIVING ORGANS. 231 
 
 and jaws declined to work any longer in providing and 
 grinding food for the lazy stoma* h, and how they so< n came 
 to grief in consequence. We might extend the fable, and 
 
 tell 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. 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 dangers. 
 This co-operation makes the individual human being. 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. 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 pur- 
 poses in spite of the merits of its individual members. In 
 the body, if the organs were not disciplined, controlled, and 
 guided, so as to work together 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-hoss 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 death 
 results. 
 
 Co-ordination means controlling and combining the activ- 
 ities of a number of working units (whether men, organs, or 
 
232 THE HUMAN BODY. 
 
 machines) for the attainment of a definite end. A promiscuous 
 and undirected crowd of competent bricklayers, carpenters, 
 hod-carriers, and so forth, would be quite incompetent to 
 build a house. There might be present abundant energy and 
 skill to construct walls, 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 individuals according to the needs 
 of the moment. The healthy body may be regarded as made 
 up of a number of conscientious workers, the organs, who are 
 concerned in building it and keeping it in repair, each one 
 acting so as to co-operate with the rest for the attainment of 
 the common end. The master builder is represented 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 moment, and guides the activity of all accordingly. 
 Part of this control is exercised consciously, but much more 
 is carried on 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. If 
 followed from the middle line of the body (Fig. 112) each 
 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. TraGed 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 
 
DIAGRAM OF THE NERVOL'S SYSTl 2 53 
 
 Fig. us.— Diagram illustrating the general arrangement of the nervous system. 
 
234 THE HUMAN BODY. 
 
 mass of different structure (spinal cord, or brain). The inner 
 end of a nerve is its proximal, and the other its distal or 
 peripheral end. 
 
 Nerve trunks radiate all over the body, branching and 
 becoming smaller and smaller as they proceed ; they end in 
 or among the cells and fibres of the various organs. The 
 general arrangement is shown in Fig. 112. 
 
 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 cerebrospinal 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 gan- 
 glion. 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 dis- 
 tinguished from the cerebro-spinal nervous system, consisting 
 of the brain and spinal cord and the nerves proceeding from 
 and to them.* 
 
 The Brain, Spinal Cord and their Membranes. — The 
 brain lies in the skull and is continuous through \hz foramen 
 magnum (Fig. 2c) of the occipital bone with the spinal cord, 
 which lies in the vertebral column, and should be considered 
 as a part of the brain. Both the brain and the spinal cord are 
 incompletely separated by grooves and fissures into similar 
 right and left halves. They are very soft and easily crushed, 
 
 * The name "sympathetic nervous system" is largely a misnomer, 
 since it is a part of the general nervous system and works in direct con- 
 nection with it. 
 
THE SPINAL CORD. 
 
 235 
 
 and are accordingly placed in 
 almost completely i losed bon) 
 cavities, and enveloped by mem- 
 branes which give them support. 
 These membranes arc three in 
 number. The external covering, 
 the dura mater i is tough, strong, 
 and composed of connective tissue. 
 The innermost membrane in im- 
 mediate contact with the brain 
 and cord, the pia mater, is less 
 dense and tough than the dura 
 mater. A layer of flat cells covers 
 the outside of the pia, and a similar 
 layer lines the inside of the dura; 
 these two layers form the third 
 membrane, the arachnoid. In 
 the space between the two layers 
 of the arachnoid is a small quan- 
 tity of watery cerebrospinal liquid. 
 The Spinal Cord (Fig. 113) is 
 nearly cylindrical in form, al- 
 though a little wider laterally 
 than dorso-ventrally, and taper- 
 ing off at its posterior end. Its 
 
 Fig. 111. — Diagrammatic view from before 
 of the spinal cord and medulla oblongata, in- 
 cluding the roots of the spinal and some of the 
 cranial nerves, and on one side the gangliated 
 chain of the sympathetic. The spinal nerves are 
 enumerated in order on the right side of the 
 figure. Br, brachial plexus ; Cr. anterior crural, 
 O, obturator, and Sc, great sciatic nerves, coming 
 off fiom lumbo-sacral plexus ; x, x , rilum ter- 
 minate ; a, b, c, superior, middle, and inferior 
 cervical ganglia of the sympathetic, the last 
 united with the first thoracic, d \ </ ■' , the eleventh 
 thoracic ganglion ; /, the twelfth thoracic (or first 
 lumbar) ; below ss, the chain of sacral ganglia. 
 
 f /n\v 
 
 " 
 
 Sc 
 
-3 6 
 
 THE HUMAN BODY. 
 
 average diameter is about |- inch and its length 1 7 inches. 
 It weighs i\ ounces. There is no marked limit between the 
 spinal cord and the brain, the one passing gradually into the 
 other. In its course the cord presents two expansions, an 
 upper (¥ig. 113), the cervical enlargement, reaching from 
 the third cervical to the first dorsal vertebrae, and a 
 lower or lumbar enlargement, opposite the last dorsal 
 vertebrae. 
 
 F;g. 114 — 1 - -yinal cord and nerve roots. A, a small portion of the cord 
 seen from the ventral side ; Z>, the same seen laterally ; C, a cross-section of the cord ; 
 D. the two roots of a spinal nerve ; i, anterior (ventral* fissure: 2. posterior (dorsal) 
 
 - gi 've along the line of attachment of the anterior nerve re - 
 
 line of origin of the posterior roots ; 5, anterior root filaments of a spinal nerve ; 
 6. posterior root filaments ; 6', ganglion of the posterior root ; 7. 7'. the first two 
 . :ns of the nerve trur.-. - formation by the union of the two roots. 
 
 Running along the middle line on both the ventral and the 
 dorsal aspects of the cord are fissures which (C, Fig. 114) 
 nearly divide it into right and left halves. 
 
 A transverse section (Fig. 115) shows that the substance of 
 
THE SPINAL NERVES. 2 37 
 
 the cord is not alike throughout, but thai its while superfi< ial 
 layers envelop a < entral gray substance < ontaining nerve cells 
 
 Fig. 115.— A thin transverse section of half the spinal cord magnified about to di- 
 ameters. 1, anterior fissure ; 2, posterior fissure; 3, central canal ; 8, pia mater 
 enveloping the cord ; 6, 7, bands of pia mater penetrating the cord and supporting 
 its nerve elements ; 9, a posterior root ; 10, bundles of an anterior root ; a , />, c, a, e, 
 groups of nerve cells in the gray matter. 
 
 arranged somewhat in the form of a capital H. The crescent- 
 shaped halves of the gray matter are turned back to back and 
 united across the middle line by the gray commissure. 
 
 The white portion of the spinal cord surrounding the cen- 
 tral gray matter is composed almost entirely of nerve fibres 
 with their sheaths. These pass up and down the cord in well- 
 defined tracts. 
 
 The Spinal Nerves. — Thirty-one pairs of spinal nerves 
 
2 3 8 
 
 THE HUMAK BODY. 
 
 join the spinal cord in the neural canal of the vertebral col- 
 umn, entering the canal through the intervertebral foramina 
 (Fig. 113). Each divides in the foramen into a dorsal and 
 ventral portion, known respectively as the posterior and an- 
 terior roots of the nerve (6 and 5, Fig. 114), which are at- 
 tached to the sides of the cord. On each posterior root is a 
 spinal ganglion (6', Fig. 114), placed where 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. 116) 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 
 
 Fig. 116. — Diagram illustrating the general relationships of the parts of the brain. 
 A , fore-brain ; i>, mid-brain: i?, cerebellum ; C, pons Varolii ; D, medulla oblon- 
 gata ; 2>, C, and D together constitute the hind-brain. 
 
 masses, each with subsidiary parts, following one another in 
 series from before back, and respectively known as the fore- 
 
THE BRAIN. 
 
 239 
 
 brain, mid-brain t and hind-brain.* In man the fore brain (A), 
 weighing about 44 oun< es, is mm h larger than all the rest 
 
 put together and overlaps them. It is tunned < hidly of two 
 
 large convoluted mass^, separated from one another by a 
 deep fissure, and known as the cerebral hemispheres. The 
 i^reat size of these is very characteristic of the human brain in 
 contrast to the lower animals, beneath each cerebral hemi- 
 sphere is an olfactory lobe [I, Fig. 118), inconspii nous in man, 
 but in animals often larger than the cerebral hemispheres, as in 
 most fishes. The mid-brain (<£) forms a connecting isthmus 
 
 Cb 
 
 Fig. 117. — The brain from the left side. Cb, the cerebral hemispheres forming the 
 main iulk of the fore-brain ; Col, the cerebellum ; Mo, the medulla oblongata ; /', the 
 pons Varolii ; *, the fissure of Sylvius. 
 
 between the two other divisions. The hind-brain consists of 
 three main parts ; on its dorsal side the cerebellum (B, Fig. 
 116), on the under side the pons Varolii {C, Fig. 116), and 
 
 * The terms arise from the relative positions of the three hollow nodules 
 in the embryonic central nervous tract, which later develop to form the>e 
 portion- of the adult brain. 
 
24° THE HUMAN BODY. 
 
 behind the medulla oblongata ( D, Fig. 116), which joins the 
 spinal cord. 
 
 In nature the main divisions of the brain are not separated 
 as has been represented in the diagram for the sake of clear- 
 ness, but lie close together with the mid-brain entirely covered 
 on its dorsal side (Fig. 117). Nearly everywhere the surface 
 of the brain is laid in folds, known as the convolutions, which are 
 deeper and more numerous in man than in any of the animals. 
 
 The brain, like the spinal cord, consists of gray and white 
 nervous matter, but somewhat differently arranged, since in 
 addition to containing gray nerve matter in its interior, a 
 great part of the brain's surface is also covered with it. By 
 the numerous convolutions of the cerebellum and of the cere- 
 bral 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, and are known as the 
 cranial nerves. Most of them spring from the under side of 
 the brain, which is represented in Fig. 118. The first pair, 
 or olfactory nerves (I), 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 optic tracts, run down to the under side of 
 the fore-brain, where they unite 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, or motor nerves of the eye (III), are distributed 
 to three of the muscles which move the eyeball, and also to 
 the muscle which lifts the upper eyelid. 
 
 The fourth pair (IV) are quite small; each goes to one 
 muscle of the eyeball. 
 
THE CRANIAL NF.RVFS. 
 
 241 
 
 The fifth pair or trigeminals ( I') resemble the spinal nerves 
 in having two roots, one of which po 1 a ganglion (the 
 Gasserian ganglion'). Beyond the ganglion the two roots 
 
 Fig. 118. — The base of the brain. The cerebral hemispheres are seen overlapping 
 all the rest. /, olfactory lobes ; //, optic tract passing to the optic commissure from 
 which the optic nerves proceed ; ///, the third nerve or viator oculi ; Il\ the fourth 
 nerve or patheticus ; I ■', the fifth nerve or trigemi ualis ; / '/, the sixth nerve or 
 abducens : V//, the seventh or facial nerve or portio dura; l'1/I, the auditory 
 nerve or port io mollis : /.Y, the ninth or glosso-pharyngeal : X, the tenth or pneu- 
 mogastric or vagus ; XI, the spinal accessory ; A'//, the hypoglossal ; ncl, the first 
 cervical spinal nerve. 
 
 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 
 
242 THE HUMAN BODY. 
 
 integument over that organ. The second division, the supe- 
 rior maxillary nerve, gives branches to the skin over the 
 temple, to the cheek between the eyebrow and the angle of 
 the mouth, to the upper teeth, and to the mucous membrane 
 of the nose, pharynx, soft palate and roof of the mouth. The 
 third division, the inferior maxillary, is the largest branch of 
 the trigeminal. It is distributed to the side of the head, the 
 external ear, the lower lip, the lower part of the face, the 
 mucous membrane of the mouth, 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 (VI) are distributed each to one muscle of 
 the eyeball on its own side. 
 
 The seventh pair, or facial nerves (VII), are distributed 
 to most of the muscles of the face and scalp. 
 
 The eighth pair, or auditory nerves (VIII), are the nerves of 
 hearing, and are distributed to the inner part of the ear. 
 
 The ninth pair, or glossopharyngeal nerves (IX), are dis- 
 tributed chiefly to tongue and pharynx. 
 
 The tenth pair, pneumogastric nerves or vagi (X), give 
 branches to the pharynx, gullet, stomach, larynx, windpipe, 
 lungs, and heart. The vagi run farther through the body 
 than any other cranial nerves. 
 
 The eleventh pair, or 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, gets a few 
 filaments from the medulla oblongata, and passes out by the 
 same aperture as the glossopharyngeal and pneumogastric 
 nerves. Outside the skull the spinal accessory divides 
 into two branches, one of which joins the pneumogastric 
 
THE SYMPATHETIC NERVOUS SYSTEM. 243 
 
 trunk, while tV other is distributed to muscles about the 
 
 shoulders. 
 
 The twelfth Pair, or hypoglossal nerves (XII), arc distrib- 
 uted mainly to the muscles of the tongue. 
 
 The Sympathetic Nervous System. — The ganglia which 
 form the main centres of the sympathetic nervous system lie 
 in two rows | Fig. 113), one on each side of the bodies of 
 the vertebrae. Each ganglion is united by a nerve trunk with 
 the one anterior and the one posterior to it. Two chains are 
 thus formed reaching from the base of the skull to the coccyx 
 and lying in the ventral cavity (Fig. 2). 
 
 Each ganglion is united by short branches to neighboring 
 spinal nerves, and near the skull to various cranial nerves also. 
 From the ganglia and their uniting cords arise numerous 
 trunks, forming networks in the thorax and abdomen, from 
 which nerves are given off to the organs situated in those 
 cavities. Many sympathetic nerves finally end in the walls 
 of the blood vessels of various organs. 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 controls the 
 parts supplied by this system. 
 
 Nerve Tissue. — The microscope shows that the nervous 
 organs contain structures peculiar to themselves, known as 
 nerve fibres and nerve cells. The cells are found only in the 
 brain, cord and ganglia, whereas the fibres, of which there 
 are two main varieties known as the white and the gray, are 
 found throughout the nervous system. The white variety 
 predominates in the cerebro-spinal nerves and in the white 
 substance of the brain and cord ; the gray, in the sympathetic 
 trunks and the gray portions of the brain and cord. 
 
244 
 
 THE HUMAN BODY. 
 
 White Nerve Fibres consist of extremely delicate threads, 
 about -g-jyVo i ncn in diameter, but frequently of a length pro- 
 portionally very great. If a perfectly fresh white nerve fibre 
 is examined with the microscope it presents the appearance 
 of a homogeneous glassy thread. Soon, however, it acquirer 
 a characteristic double border (Fig. 119), from the coagula- 
 
 FiG. 1 to. — To illustrate the 
 fresh: n, node. B, nerve fibre 
 by dark lines : n.c, nucleus ; / 
 highly magnified: in, medulla; 
 axis cylinder : n.x, surrounded 
 show n.c, nucleus with fine line 
 fine connective tissue, c : n.c', 
 fibre deprived of its neurilemm 
 rounding the axis cylinder, n x 
 
 structure of nerve fibres. A, nerve fibre examined 
 with axis cylinder shaded, and medulla represented 
 granular cell substance near the nucleus. C, more 
 n, node. D, nerve treated with reagents to show the 
 by medulla, ;//. E, nerve treated with reagents to 
 over it representing the neurilemma, and outside this 
 nucleus lying in the fine connective tissue. F, nerve 
 a showing medulla broken up into fragments, in, sur- 
 
 tion of a portion of its substance, as a result of which three 
 layers are brought into view. Outside is a thin transparent 
 envelope called the primitive sheath or neurilemma ; inside 
 
GRAY NERVE FIBRES. 245 
 
 tin's is a fatt) substance, forming the medullary sheath (the 
 coagulation of \\hi< h gives the fibre its double border 
 the centre is a core, the axis cylinder^ which is the essential 
 part of the fibre, since near its ending the primitive and 
 medullary sheaths are frequently absent. At intervals of 
 about gij inch along the fibre arc found nuclei. In the course 
 (A a nerve trunk its fibres rarely divide; when a branch is 
 given off sonic fibres merely separate from the rest, much as 
 a skein of silk might be separated at one end into smaller 
 bundles containing fewer threads. The white matter of the 
 spinal cord, brain, and nerve trunks consists largely of med- 
 ullated nerve fibres, whereas the gray matter of the cord and 
 brain consists largely of nerve cells. 
 
 Gray Nerve Fibres have no medullary sheath, and consist 
 merely of an axis cylinder and primitive sheath. Gray fibres 
 are especially abundant in the sympathetic trunks, and are 
 the only ones found in the olfactory nerve. 
 
 Nerve Cells. — In the ganglia lying in the course of nerves 
 and in the gray matter of the spinal cord and the brain are 
 found large nucleated and branched cells connected with the 
 nerve fibres, and called ganglion or nerve cells. They differ 
 in size, shape, and number of branches, but present fairly 
 characteristic appearances. 
 
 The cell substance is granular and contains a large, round 
 nucleus with a central spot called the nucleolus. There are 
 usually several branches which subdivide to form tree-like 
 forms. One branch, however, does not divide, but forms 
 the nerve fibre, axis cylinder or neuron, which finds its way 
 out to other parts of the nervous system. 
 
 It was formerly supposed that the nerve cells were con- 
 nected with each other by means of their branches and axis 
 cylinders, but it has recently been shown that each nerve cell 
 
246 THE HUMAN BODY. 
 
 with its branches and axis cylinder forms an anatomical unit 
 and that the nutrition of the branches and axis cylinder 
 depends entirely upon their connection with the nerve cell. 
 
 Fig. 120. — A lar^e nerve cell from the anterior horn of the spinal cord. », nucleus; 
 n', small body, called the nucleolus, inside the nucleus ; /, branched processes ; n./>, 
 unbranched process continued into the axis cylinder of a motor nerve fibre. 
 
 If the nerve fibre becomes injured, the end of the fibre 
 beyond the point of injury dies and is replaced by a new 
 fibre which grows out from the cell. 
 
 The Structure of Nerve Centres. — The nerve cells repre- 
 sent the active part of the nervous tissue. Since they are 
 grouped in special localities of the body, such as the ganglia, 
 spinal cord and brain, these are called nerve centres. This is 
 especially true of the brain and spinal cord, which constitute 
 the central nervous system. The nerve centres consist of 
 
 white and gray nerve fibres, of nerve cells, and of connec- 
 tive tissue and blood vessels, arranged together in different 
 ways in different centres. 
 
CHAPTER XX. 
 
 TIIF GENERA] PHYSIOLOGY OF I III. NERVOl - SYSTEM. 
 
 Nature of Nervous Impulse. — A nervous impulse has so 
 little direct manifestation that it has been impossible to de- 
 termine its true nature. It shows itself mainly in muscular 
 contraction, glandular activity, etc. It is transmitted with 
 such great rapidity through the nerves (one hundred feet per 
 second ) that it is difficult to suppose that it is a mechanical 
 or chemical process; at the same time it is so much slower 
 than an electric current that it is probably not at all related 
 to it. It is thought to be a molecular change of some kind 
 passed along the axis cylinder. 
 
 If a nerve is cut, and an electric current is sent through it, 
 the contraction of the muscle attached to it shows that a ner- 
 vous impulse has passed along the nerve. If a drop of acid 
 or of a strong salt solution is placed on the end of the nerve, 
 the same result is reached. Under natural conditions, how- 
 ever, nervous impulses do not arise in nerve fibres, but in 
 nerve cells or in special structures connected with the ends 
 of nerves, as the sense organs. Experiments have shown 
 that a nerve fibre merely conducts the nervous impulse, but 
 has no share in its formation or modification. 
 
 The strength of the nervous impulse judged from a mechan- 
 ical standpoint is infinitely less than the energy which is dis- 
 charged in muscle or gland as a result of its action; it bears 
 
 247 
 
248 THE HUMAN BODY. 
 
 very much the relation to the muscular energy which the 
 force required to pull the trigger of a gun bears to that devel- 
 oped by the explosion of the powder. The discovery that 
 nerve cells are not continuous with each other by means of 
 their fibres, but that each cell and its branches, including the 
 axis cylinder, forms a distinct unit, complicates the problem 
 of the real nature of the nervous impulse. Anatomically 
 the path from the skin through the nerve trunks to the 
 spinal cord and thence up to the cortex of the brain is made 
 up of a number of these units. The impulse which travels 
 from the end of the finger to the cortex of the brain to excite 
 consciou . ness must either leap from one unit to another in this 
 chain in order to bring its message to consciousness, or the 
 nervous impulse of one cell must when transmitted along its 
 axis cylinder (neuron) be able to stimulate the next ceil to 
 discharge a similar impulse along its neuron until the final 
 stage is reached and a change in consciousness produced. If 
 the latter supposition is true, the cells act as relays, and we 
 have what maybe called a relay system. 
 
 Nerve Action. — When the large nerve trunk which passes 
 down the thigh is cut across, an animal loses the power of 
 movement in the muscles of the leg. It is also unconscious 
 of pinching or pricking of the skin of the leg; in fact, it is 
 possible to mutilate its leg to any extent without giving rise 
 to pain. If, however, the distal end of the cut nerve is 
 pinched or an electric shock is sent through it, the muscles 
 contract. If the proximal end of the cut nerve is pinched or 
 an electric shock is sent through it, the animal shows signs of 
 pain. 
 
 The nerve trunks transmit to muscles stimuli which cause them 
 to contract {motor stimuli). 
 
 Sensations do not lie hi the exterior parts 0/ the body. 
 
NFRIT AC1 
 
 249 
 
 A - ■ trunks transmit stimuli which give rise to sensation) 
 for example > sensations of pain [sensory .stimuli). 
 
 as, 
 
 Fig. 121. Illustrating the functions of the spinal nerves. Divided at a.— Irritated 
 at 1 : pain. Irritated at 2: muscular contraction. 
 
 When the anterior nerve roots of spinal nerves are cut, all 
 power of motion is lost in the muscles with which they are 
 connected. In this case, however, the animal feels perfectly 
 
 2\ 
 
 Fig. 122. — Illustrating the functions of the roots of the spinal nerves, a, anterior 
 root; /, posterior root Divided at a. — Irritated at 1 : no result. Irritated at 2 : con- 
 traction of muscles supplied with fibres from the root. Divided at />. Irritated at 
 
 3 : no result. Irritated at 4 : pain produced. 
 
 the stimulation of the skin to which the nerve trunks are dis- 
 tributed. If the distal ends of these nerves are stimulated 
 electrically, it causes contraction of the muscles. When 
 the proximal ends are stimulated electrically, there is no 
 effect. 
 
 The nerves which transmit the motor stimuli pass through the 
 anterior roots of the spinal nerves. 
 
 Motor nerves carry stimuli outward from the central part of 
 the nervous system {efferent nerves}. 
 
250 THE HUMAN BODY. 
 
 When the posterior roots are cut and the anterior are in- 
 tact, the power of motion in the limb is not affected, but all 
 sensation is lost. If the distal ends are stimulated electrically 
 or pinched there is no effect, but when the proximal ends are 
 stimulated pain is manifested. 
 
 The nerves which transmit the sensory stimuli pass through 
 the posterior roots of the spinal nerves. 
 
 Sensory nerves carry stimuli from the outside of the body 
 toward the central part of the nervous system (afferent nerves). 
 
 It has also been found that when an animal has been tired 
 out, as a bird by flying, the nerve cells in the anterior part 
 of the gray matter of the cord, with which the nerves of the 
 fatigued muscles are connected, show distinct changes in their 
 microscopic structure. These changes have been interpreted 
 to mean fatigue of the nerve cells. When these cells are de- 
 stroyed, the power of motion is lost in the connected muscles. 
 
 The motor nerve cells which cause the contractions of the 
 ??iuscles with which they are connected by nerves lie in the an- 
 terior cornua of the spinal cord. 
 
 When the ganglia of the dorsal roots of the spinal nerves 
 are destroyed, sensation is lost in the parts connected by 
 fibres with the cells lying in the destroyed region. 
 
 Sensory cells lie in the ganglia of the dorsal roots of the 
 spinal nerves. 
 
 When the upper part of the spinal cord is injured, all sen- 
 sation and voluntary motion are lost in the legs and lower 
 trunk ; the individual becomes unconscious of the entire lower 
 part of his body. If the sole of the foot is then tickled with 
 a feather or quill, or a hot object applied to it, the foot is 
 jerked away by the muscles of the leg, showing that the power 
 of motion is in itself intact. 
 
 The motor nerve cells of the cord are not capable of starting 
 
NERVE ACTION. 
 
 251 
 
 voluntary contractions t but depend upon stimuli from other 
 
 Cells . 
 
 They may be stimulated by strong sensory stimuli from the 
 periphery to produce protective movements (reflex action). 
 
 The seat of sensation docs not lie in the spinal cord. 
 
 When the gray matter in certain localities of the cortex of 
 the brain is removed, ]>ower of voluntary motion is lost for 
 certain muscles. When the nerve cells lying in the same 
 
 Fig. 123. — Diagram of outer surface of left cerebral hemisphere to illustrate the 
 localization of functions. The motor area is shaded in vertical and transverse lines : 
 Sy, fissure of Sylvius ; an, angular gyrus or convolution ; Ro, fissure of Rolando ; Fv, 
 frontal lobe ; Pa, parietal lobe ; Te , temporal lobe. Only a very few of the more im- 
 portant fissures are indicated. 
 
 localities of the brain are stimulated, muscular movements are 
 caused in the group of muscles that was paralyzed by the re- 
 moval of the cells. The removal of cortical gray matter near 
 the fissure of Rolando (Fig. 123) in the left side of the brain, 
 for example, gives rise to paralysis of the right leg muscles ; 
 the stimulation of cells in the same region causes contraction 
 of the same muscles. 
 
252 THE HUMAN BODY. 
 
 The motor cells which cause voluntary muscular movements 
 are seated in the cortex of the brain. 
 
 Definite areas of the brain correspond to certain muscular 
 groups, as leg, arm, and tongue (localization of functions). 
 
 The motor arras of each side of the brain correspond with 
 muscular groups upon the opposite side of the body* 
 
 Afferent Nerves. — All sensory nerves are afferent nerves, 
 but not all afferent nerves are sensory, since many nerves 
 bring impulses inward to the central nervous system which 
 do not result in sensation ; anion? these are the afferent nerves 
 from the heart, muscles, and viscera. 
 
 Efferent Nerves. — Motor nerve impulses have their most 
 tangible manifestations in muscular contractions (musculo- 
 molor), but these do not constitute the most important of the 
 outgoing stimuli transmitted by the efferent nerves, since they 
 are also concerned in controlling the heart (car dio -motor) , the 
 secretion of glands (secreto-motor) , intestinal movements (vis- 
 cero-motor) , changes in blood vessels (vaso-molor) , and cellular 
 activity in general (trophic r). 
 
 In addition, efferent nerves have a distinctly different func- 
 tion. The vagus, for example, tends to retard or inhibit the 
 action of the heart, and the vaso-dilator nerves are supposed 
 to diminish the stimulation of the vaso-constrictors when they 
 cause a dilatation of blood vessels. This action is called 
 inhibition, and the nerves, inhibitory nerves. Since these in- 
 hibitory results are due to nervous stimuli sent out from the 
 
 * This is true in general, but it is claimed that either side of the brain 
 can control both sides of the body, though it does not have to do so 
 under normal conditions. 
 
 -f- Trophic nerves are tin >se which are supposed to stimulate nutritive 
 changes in the cell itself, that is. to bring about in the cell those changes 
 which keep it in good working order. The existence of such nerves has 
 not been demonstrated, but is inferred, 
 
RELATION BF.TIVF.F.N SENSATION AND MOTION. 
 
 centra! nervous system, the nerves which carry them are 
 efferent nerves. 
 
 Relation between Sensation and Motion. — When a hot 
 iron is applied to the skin, muscles contract so as to remove 
 the threatened part from danger. As we have seen, this takes 
 place even when the spinal cord is injured, provided that the 
 point of injury is above the place where lie the sensory and 
 
 Nerve cells with intermingling branches, not continuous between cells 
 
 Afferent Nerve Fiber" 4 
 
 Sensory 
 Epithelinm 
 
 \ Efferent Nerve Fiber 
 
 Muscle 
 
 Fig. 124. — Diagram of reflex arc. (After Colton.) 
 
 motor cells directly concerned. This movement is very quick, 
 taking only .06 to .08 Sec. Experiments have shown con- 
 clusively that the nerve cells (sensory and motor) concerned 
 in this action are located in the gray matter of the cord. 
 Since the motion immediately follows the stimulation without 
 the intervention of consciousness, it is said to be " reflected " 
 and the process is called a spinal reflex. 
 
 If the irritation of the skin is so slight that it does not give 
 rise to a reflex withdrawal, it may excite consciousness and 
 
2 54 
 
 THE HUMAN BODY. 
 
 individual. 
 
 Cortex cerebri 
 
 Under these 
 
 Spinal bulb and cord 3 
 
 the consequent desire for withdrawal on the part of the 
 
 circumstances the least time 
 required for the move- 
 ment is much greater, 
 averaging .15 Sec, since 
 the impulse has to be 
 transmitted to the brain 
 and a much greater num- 
 ber of cells have to act. 
 This process is known as a 
 voluntary reaction . 
 
 Functions of the Spinal 
 
 F:~. ::=. — V '."n tar y reaction. 1, epithelium ; p AT ,J wr ■l 
 
 2. afferent nerve fibre ; 3, spinal sensory cell ; vOiQ.. >> C na\e Seen 
 
 4, afferent tract ; 5. cortial sensory cell; 6. com- , , . . 
 
 raissural fibre ; 7, cortical motor cell ; 8, efferent that the Spinal COrd Con- 
 tract ; 9, spinal motor cell ; 10, efferent nerve 
 
 fibre; n, muscle. tains (i) cells which have 
 
 the power of producing muscular contractions, (2) cells 
 which receive sensory impulses from the nerve endings, 
 as in the skin, and (3) nerve fibres which connect these 
 cells with the periphery and with other cells in the upper 
 part of the spinal cord and the brain. Many experi- 
 ments on animals with the spinal cord intact but with the 
 brain destroyed show that they are able to make complicated 
 reflex movements which are in general of a protective nature. 
 As we study the normal individual we see that many of the 
 sudden movements made are of the nature of the spinal reflex, 
 since they are done so quickly that the individual cannot 
 inhibit them, as winking. We thus see that the cord acts 
 (1) as a motor centre, either in response to stimulation from 
 cells in the brain, or, reflexly, in response to sensory stimuli 
 in the periphery, and (2) as a conductor of nervous impulses 
 from the periphery to the brain, and the reverse. 
 
 The motor and sensory fibres which pass up the cord to 
 
FUNCTION OF THE SPINAL BULB. 255 
 
 the brain cross from one side to Ihe other. Thus the right 
 side of the body is in general controlled by the left side of 
 the brain and via ■ a. The sensory fibres cross shortly 
 after entering the cord in the dorsal root. The motor fibres 
 cross mainly in the upper part of the cord, where they may 
 be recognized as interlacing bundles. These motor and sen 
 sory fibres find their way through the length of the spinal 
 cord in fairly well defined columns or tra< ts outside of the 
 gray matter. 
 
 Functions of the Spinal Bulb 1 ''Medulla Oblongata >. — The 
 spinal cord at its upper part, just before its union with the 
 brain, expands and opens out, exposing the gray matter on 
 its dorsal side. This expansion of the cord is called the 
 spinal bu/l> or medulla oblongata. Experiments have shown 
 that nerve cells in the spinal bulb include among others those 
 which have direct control of the heart beat and of respira- 
 tion. These centres have been described as automatic, but 
 it is probably not true that they are automatic in the sense 
 that they initiate the muscular contractions of the heart or 
 respiratory muscles without any stimulus coming to them. 
 They are doubtless reflex centres and are stimulated from 
 without, probably by the condition of the blood. When the 
 spinal bulb is injured death results from the cessation of the 
 heart action and of breathing. Hence it is one of the vital 
 centres of the nervous system. 
 
 Functions of the Ganglia of the Brain. — In the base of 
 the brain, covered over by the cerebral hemispheres, lie 
 isolated patches of gray matter known as the basal ganglia. 
 The functions of these are not well understood since experi- 
 mental evidence is more or less contradictory, owing to the 
 difficulty of performing experiments without injuring adjacent 
 nerve fibres. 
 
256 THE HUMAN BODY. 
 
 Functions of the Cerebrum. — When the cerebral hemi- 
 spheres of a pigeon are destroyed and the rest of the body is 
 in a normal condition, the animal can still control its muscles 
 so as to execute many movements, but gives no sign of con- 
 sciousness. Left to itself it will stand still until it dies ; corn 
 and drink placed before it arouse in it no idea of eating ; it 
 will die of starvation surrounded by food. Yet it can move 
 all of its muscles, and if food is placed in its mouth will swal- 
 If its tail is pulled it will walk forward ; if it is put 
 on its back it will get on its feet ; if it is thrown into the air 
 it v. ill fly until it strikes against something on which it can 
 alight : if its feathers are ruffled it will smooth them with its 
 bill. 
 
 The difference between a pigeon in state and an un- 
 
 injured pigeon lies in the absence of the power of forming 
 ideas or of initiating movements. It has no thoughts, no ideas, 
 no will. We cannot predict what an uninjured pigeon will 
 do under varying conditio: can predict what the pig- 
 
 eon with no cerebral hemispheres will do : it is a mere ma- 
 chine or instrument, which can be played upon. In such a 
 pigeon the excitation of any given sensor}' nerve excites 
 reflexly the nerve centres of the spinal cord and brain, 
 which cause certain muscles to contract, resulting in the 
 same invariable movement. The pigeon exhibits no evi- 
 dence of possessing consciousness : it has no desires or emo- 
 tions ; it s:ays quiet while left to itself, and reacts reflexly 
 when any stimulus is given to it, and always in an unvarying 
 manner. 
 
 In human beings, accidental injury to parts of the brain 
 and disease have made it possible to study the associated 
 losses of power. This evidence confirms the inferences I 
 upon experiments on the lower animals, and shows that in the 
 
BRAIN LOCALIZATION, 257 
 
 human brain the functions arc- distributed in much the same 
 way as in dogs and pigeons. All actions directed by volun- 
 tary attention thus find their origin in the nerve I ells of the 
 ( erebrum. 
 
 Brain Localization. — As we have seen, certain portions of 
 the < ortex of the (erebrum are associated with definite move- 
 ments of the limbs, etc. These motor areas have been 
 mapped out with so great clearness that in a number of cases 
 of paralysis due to brain tumor the surgeon has confidently 
 cut into the brain in a definite spot and located the trouble. 
 Kxperiments show, however, that the movements which are 
 caused by stimulation of the cells in these areas are complex 
 movements, such as scratching or picking up objects, involv- 
 ing a large number of muscles which are definitely controlled 
 to accomplish a certain end. 
 
 Since the motor cells in the spinal cord act upon single 
 fibres of muscles, there are doubtless intermediate motor cen- 
 tres standing between the cells of the cortex of the brain and 
 the immediate motor cells of the cord which have the power 
 of controlling large numbers of spinal motor cells and unify- 
 ing their work. 
 
 This mechanism is somewhat similar to that existing in a 
 factory. The individual workmen correspond to the spinal 
 motor cells ; the foremen who oversee the work of these men 
 correspond to the intermediate cells ; and the superintendent 
 who has charge of the foremen, and hence of the whole es- 
 tablishment, corresponds to the cells of the brain. 
 
 The centres of the brain associated with the sense organs, 
 as seeing and hearing, are pretty definitely localized, but 
 those which have to do with intellectual processes, as mem- 
 ory, reasoning, and association, have not been definitely 
 localized. Doubtless they have no definite localization, since 
 
258 THE HUMAN BODY. 
 
 each process probably involves one phase of the activity of 
 many groups of brain cells. 
 
 Inter/central Fibres. — It is easy to see that the various 
 processes which thus call into play large numbers of brain 
 cells necessitate nerve fibres to connect the cells of different 
 parts of the cortex. These fibres are called intercefrfral or 
 commissural fibres and take their paths between the brain 
 cells, without passing out of the cranium. 
 
 Functions of the Cerebellum. — When the cerebellum is 
 removed from animals they stand and walk unsteadily, stag- 
 gering and fluttering with many useless movements. The 
 muscles tend to contract in a less purposeful way and with less 
 vigor. The manifestations permit little of definite inference 
 except this, that the cerebellum is concerned to some degree 
 with the co-ordination of muscular contractions. It is a large 
 organ, and it is to be inferred that it has important functions ; 
 their definite values, however, are not yet well determined. 
 
 Modes of Nervous Reaction. — The simplest mode of re- 
 action is a spinal reflex, such as the instant withdrawal of the 
 hand upon coming into contact with a hot stove. The re- 
 sponse is immediate, always the same, preceded by no con- 
 ception of the movement to be made and by no conscious 
 memory of the means of making it. The sensory stimuli pass 
 up the afferent nerve to the sensory cells, which in turn in- 
 fluence other cells until finally certain motor cells are selected 
 and stimulated to send impulses down the efferent nerves 
 which result in a complicated but co-ordinated contraction of 
 a number of muscles, producing a protective movement. A 
 voluntary reaction is more complicated. When a bright ball is 
 held before a child, the light waves enter the eye, are trans- 
 lated in the retina into nervous impulses which travel along 
 the afferent nerves to the optic sensory centre of the brain. 
 
THE USE ()/ REFLEX CENTRES. 259 
 
 The cells of this centre communicate with appropriate « entres 
 through intercentral tra< ts and a desire for the ball results. 
 Motor centres are then stimulated, beginning probably with 
 the arm group of the cortex and ending with the motor cells 
 in the Spinal cord. These latter cells, thus selected and uni- 
 fied in their action by the higher motor centres, stimulate the 
 muscle fibres to produce by their contractions the definite 
 movements which give possession of the ball. This mode of 
 action cannot be predicted, involves consciousness, and may 
 even permit considerable delay between the stimulation and 
 the response, as in the case of one whose desire to visit 
 Europe, aroused by books of travel, finds motor completion 
 only after the lapse of years. 
 
 The line between reflex and voluntary reaction cannot be 
 sharply drawn in ordinary activity. Voluntary reactions tend 
 through constant repetition to have reflex characteristics in 
 that the motor response follows directly upon the sensory 
 stimuli, as in walking. The cells, at first directed by con- 
 sciousness, have become trained to do their work without its 
 supervision, but doubtless the same motor cells are involved 
 as in a corresponding voluntary reaction. 
 
 The Use of Reflex Centres is to relieve the thinking cen- 
 tres of the vast amount of work which would be thrown upon 
 them if every action of the body had to be planned and willed 
 at each moment. 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. No 
 time would be left for intellectual development if we had to 
 think about and to will each heart beat, each inspiration and 
 expiration, and the swallowing of each mouthful of food. 
 Sleep would be impossible, and life as we know it could not 
 be maintained. 
 
2 Go THE HUMAN BODY. 
 
 Habits.— Every time a nerve cell acts in a given way, it 
 becomes easier for it to repeat the action : as a result 
 many actions which are at first performed only with trouble 
 and thought are 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 more the nervous system became 
 trained to adapt the muscular movement to the guidance of the 
 nerve impulses from the sole of the foot. At last the contact of 
 the foot with the ground, stimulating some sensory nerves, acts 
 so readily on the " nerve centres of walking " that conscious- 
 ness need take no heed about it : we walk ahead while think- 
 ing of something else. Other instances will readily come 
 to mind, as the difficulty with which we learned to ride, swim, 
 or -skate, when obliged to think about and will each move- 
 ment, and the ease with which we do all these after a little 
 practice. The trained nerve centres then do all the co-ordi- 
 nating work and consciousness 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. 
 
 We thus find, in the tendency of the nervous system to go 
 on doing what it has been trained to do, a physiological rea- 
 son for endeavoring to form good and to avoid bad habits of 
 every sort. Every thought, every action, leaves in the ner- 
 vous system its result for good or ill. The more often we 
 yield to temptation the stronger the effort required to resist 
 it, whereas every resistance of temptation helps to make sub- 
 sequent resistance easier. 
 
 Growth of the Brain. — The nervous system in the human 
 being grows more slowly than any other part of the body, for 
 while the nerve cells are complete in number in childhood, 
 
HYGIENE OF THE BRAIN. 261 
 
 yet their bran< lies and 1 onsequently iheir means nf 1 1 mini - 
 
 eating with other cells are not fully developed until much 
 
 later, even as late as the t\\nit\ fifth or thirtieth year of life. 
 
 As we have seen, the power of the nervous system to 1 0- 
 ordinate the activities of the body depends very Largely upon 
 the number and extenf of these bran< hes. In this lies, in part, 
 
 the explanation of the slowness with which the mental power 
 of the child develops and the fact that ripe judgment, which is 
 the final test of nerve action, is found only in the mature man 
 or woman. Much of the precocity which is not rare in child- 
 hood is due simply to an exceptional memory, and does not 
 mean real intellectual force. 
 
 Hygiene of the Brain. — The brain, like the muscles, is 
 improved and strengthened by exercise and injured by over- 
 work or idleness. A man may especially develop one set of 
 intellectual faculties and leave the rest to lie fallow until, at last, 
 he almost loses the power of using them at all. The fierce- 
 ness of the battle of life especially tends to produce a one-sided 
 mental development. The business man, for example, be- 
 comes only too frequently so absorbed in money-getting that 
 he loses the intellectual joys of art, science, and literature, and 
 becomes a mere money-making machine. The scientific man 
 has often no appreciation of art or literature, and the literary 
 man is utterly incapable of sympathy with science. A good 
 collegiate education in early life, on a broad basis of mathe- 
 matics, literature, and natural science, is the best security 
 against such deformed mental growth. 
 
 Besides exercise, the greatest need for the healthy develop- 
 ment of the brain is sufficient sleep. The infant sleeps 15 
 to 20 hours, the young child 12 to 14, and the boy of 
 high-school age should get 9 to 10 hours of sleep. Those 
 who are using the brain require more sleep than those who 
 
262 THE HUMAN BODY. 
 
 are doing muscular work, and no student can safely sleep less 
 than nine hours. 
 
 In order that the brain may keep in its best working order, 
 it must work with ease and pleasure. Probably no condition 
 is so important in keeping the nervous system in a healthy 
 state as enjoyment of work and cheerfulness in daily life. 
 Plavs and games which give the keenest enjoyment, especially 
 if involving physical activity, are of the utmost importance 
 for the well-being of this master tissue of the body. 
 
CHAPTER XXI. 
 
 THK 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 (sens/: 
 parts) are in connection, direct or indirect, with the brain by 
 sensory nerve fibres. Since all feeling 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 circumscribed 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 sensa- 
 tions : headache, toothache, 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 external causes, and we 
 ascribe the sensations to the external objects as their properties. 
 Thus they lead us to the conception of an external universe in 
 which we live. A knife laid on the skin produces changes in 
 the skin which lead us to think that we feel a cold heavy hard 
 thing which is not the skin. We have, however, no sensory 
 nerves going into the knife and informing us directly of its 
 
 263 
 
264 THE HUMAN BODY. 
 
 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. If, however, the knife cuts 
 through the skin, we cease to feel the knife and experience 
 pain, which we think of as a condition of ourselves. We do 
 not sav 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. 
 
 Those sensitive parts, such as the surface of the skin, through 
 which we get information about the outer world are of far 
 more intellectual value to us than such parts, as the subcutane- 
 ous tissue, which give us sensations referred only to conditions 
 of our own bodies. The former are called organs of special 
 sense ; the latter possess common sensation. 
 
 Common Sensations are numerous, as, for example, pain, 
 hunger, nausea, thirst, satiety, and fatigue. 
 
 Hunger and Thirst regulate the taking of food. Local 
 conditions play a part in their production, 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 stomach has 
 been empty some time. It may be temporarily stilled by 
 filling the stomach with indigestible substances, but soon the 
 feeling comes back intensified and can be allayed only by the 
 ingestion of nutritive materials. Provided that these are 
 absorbed and reach the blood their mode of entry is not 
 essential ; hunger may be stayed by injections of food into 
 the intestine as completely as by filling the stomach with it. 
 
77//:" risen APPARATUS. 265 
 
 Similarly, thirst may be temporarily relieved b) moistening 
 file throat without swallowing, but soon returns; whereas it 
 may be permanently relieved b) water inj« tions into the veins, 
 without wetting the throat at all. 
 
 Both sensations depend in part on local conditions of 
 sensory nerves, but especially on the poverty of the blood in 
 foods or water, which leads to changes in nerve < ells. It has 
 even been inferred that there are hunger and thirst centres of 
 the brain which are thus stimulated. 
 
 The Special Senses are commonly described as five in 
 number, sight, hearing, touch, smell, and taste, but to these 
 we must add several others. 
 
 The Visual Apparatus consists of nervous tissues immedi- 
 ately concerned in giving rise to sensations, supported, pro- 
 tected, and nourished by other parts. Its essential parts are 
 (1) the retina, a thin membrane lying in the eyeball and con- 
 taining microscopic elements which are so acted upon by 
 light as to stimulate (2) the optic nerve; this nerve ends in (3) 
 the visual centre of the brain, which when stimulated 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 of the retina, as is 
 frequently seen in delirious persons, in whom inflammation or 
 congestion of the brain excites directly the visual centre and 
 gives rise to visual hallucinations. 
 
 Usually, however, the cerebral visual centre is excited only 
 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- 
 
266 THE HUMAN BODY. 
 
 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, 
 the optic nerve the visual nerve centre, and the result is a 
 sight sensation.* 
 
 The Eye Socket. — The eyeball is lodged in a bony cavity. 
 the orbit, open in front. Each orbit is a pyramidal chamber 
 containing connective tissue, blood vessels, nerves, and much 
 fat. The fat forms a soft cushion on which the back of the 
 eyeball rolls. 
 
 The Eyelids are folds of skin, strengthened by cartilage 
 
 * The fact that sight sensations may be aroused quite independently of 
 all light acting upon the eye is paralleled by similar phenomena in re- 
 gard to other senses, and is of fundamental psychological and metaphys- 
 ical importance. That a blow on the closed eye gives rise to a vivid 
 light sensation, even in the absence of all actual light, proves that our 
 sensation of light is quite a different thing from light itself. The visual 
 sensory apparatus, it is true, is so constructed and protected that of all 
 the forces of nature, light is the one which far more frequently stimulates 
 it. But as regards the peculiarity in the quality of the sensation which 
 leads us to classify it as" a visual sensation," that peculiarity has nothing 
 to do with any property of light. The visual nerve centre when stimu- 
 lated causes a sight sensation, whether it has been excited by light, by a 
 blow, or by electricity. Similarly the auditory brain centre gives us a 
 sound sensation when stimulated by actual external sound waves, by 
 a blow on the ear, or by disease of the auditory organ. One kind of 
 energy, light, excites more often than any other the visual nerve appa- 
 ratus; another, sound, the auditory nerve apparatus; a third, pressure, the 
 touch nerve organs. Hence we come to associate light with visual sen- 
 sations and to think of it as something like our sight feelings; to imagine 
 sound as something like our auditory sensations; and so forth. As a 
 matter of fact both light and sound are merely movements of ether or air; 
 it is our own stimulated nerve centres which produce visual and 
 auditory sensations; the ethereal or aerial vibrations merely act as 
 the stimuli which give rise to nervous impulses in the nervous apparatus. 
 
THE LACHRYMAL APPARATUS. 
 
 267 
 
 LQ 
 
 and moved by muscles. Opening along the edge of 
 eyelid are from twenty to thirty minute glands, called the 
 Meibomian follicles. Their secretion is sometimes abnormally 
 
 abundant, and then appears as a yellowish matter along the 
 edges of the eyelids, which often dries in the night and 
 causes the lids to be glued together in the morning. The 
 eyelashes are curved hairs, arranged in one or two rows along 
 each lid. They help to keep dust from falling into the eye, 
 and, when the lids are nearly closed, protect it from a daz- 
 zling light. 
 
 The Lachrymal Apparatus consists of a tear gland in each 
 orbit, of ducts which carry its secre- 
 tion to the upper eyelid, and of 
 canals by which this, unless exces- 
 sive, is carried off from the front of 
 the eve without running down over LD 
 the face. The lachrymal or tear 
 gland, about the size of an almond. Fig. 126. From view of left 
 
 * eye. with eyelid partly removed 
 
 lies in the upper and outer corner of to show lachrymal gland, l.g, 
 
 rr and lachrymal duct, L.D. 
 
 the orbit. It is a compound race- 
 mose gland, from which twelve or fourteen ducts run and open 
 on the inner surface of the upper eyelid at its outer corner. 
 The secretion spreads evenly over the exposed part of the eye 
 by the movements of winking, and keeps it moist. It is drained 
 off by two lachrymal canals, one of which opens by a small pore 
 on an elevation, or papilla, near the inner end of the margin 
 of each eyelid. The aperture of the lower canal can be readily 
 seen by examining its papilla in front of a looking glass. The 
 canals run inward and open into the lachrymal sac. which lies 
 just outside the nose, in a hollow where the lachrymal and 
 superior maxillary bones (Z and J/.v. Fig. 16) meet. From 
 this sac the nasal duel proceeds and opens into the nose 
 
268 
 
 THE HUMAN BODY. 
 
 chamber below the interior turbinate bone (q, Fig. 46, 
 p. no). 
 
 Tears are constantly being secreted, but ordinarily in such 
 quantity as to be drained off into the nose, from which they 
 flow into the pharynx and are swallowed. When the lachry- 
 mal duct is stopped up, however, their continual presence 
 makes itself unpleasantly felt, and may need the aid of a 
 surgeon to clear the passage. In weeping the secretion is 
 increased, and then not only more of it enters the nose, but 
 some flows down the cheeks. The frequent swallowing move- 
 ments of a crying child are due to the collection of tears in 
 the pharynx. 
 
 Movements of the Eyeball. — Six muscles connect the eye- 
 ball with the wall of the cavity containing the eye. Four of 
 
 A B 
 
 Fig. 127. — A, the muscles of the right eyeball viewed from above ; />, the muscles 
 of the left eyeball viewed from the outer side ; S.R, superior retcus ; In/ R, inferior 
 rectus ; £.R, external rectus ; S.Ob, superior oblique ; Inf. Ob, inferior oblique; 
 77, the optic nerves ; ch, their crossing or chiasma ; ///, the third cranial nerve. 
 
 these are attached around the entrance of the optic nerve at 
 the back of the socket and extend forward, to be inserted into 
 the eyeball near the edge of the transparent front part (cornea). 
 These are called the recti, or straight, muscles (Fig. 8&, b), 
 and are further named according to their position, externa/, 
 
THE EYEBALL. 269 
 
 internal) superior y and inferior. F.a« h mus< le when < ontrai t- 
 ing rotates the eye toward itself. Two muscles, the oblique ^ 
 arc atta< hed to the sides of the orbit and inserted into the 
 c\ eball behind the recti. 
 
 The motions of the eye produced by these muscles are 
 chiefly from right to Left and up and down. A combination 
 of these two motions permits the eye to be turned in any di- 
 rection. The eves are so controlled through the nerves stim- 
 ulating the muscles, that the axial lines of the globes of the 
 eyes converge to pass through whatever object is looked at : 
 hence the axes of the eyes arc parallel to each other only when 
 one looks at a distant object. 
 
 The Globe of the Eye is on the whole spheroidal, but con- 
 sists of segments of two spheres (Fig. 128). A portion of a 
 sphere of small radius forms its anterior transparent part, anil 
 is set upon the front of its posterior segment, which is part of 
 a larger sphere. In general terms it may be described as con- 
 sisting of three coals and three refracting media. 
 
 The outer coat (1 and 3, Fig. 128) consists of the sclerotic 
 and the cornea. The cornea is transparent and is situated in 
 front ; the sclerotic is opaque and white and covers the back, 
 sides and a part of the front of the globe, where it is seen 
 between the eyelids as the white of the eye. Both are com- 
 posed of dense connective tissue and are tough and strong. 
 
 The second coat consists of the choroid (9, 10) and the 
 iris (14). The choroid consists mainly of blood vessels sup- 
 ported by loose connective tissue, which in its inner layers 
 contains many dark brown or black pigment granules.* 
 Towards the front of the eyeball, where it begins to diminish 
 in diameter, the choroid separates from the sclerotic and turns 
 
 * In pink-eyed rabbits and occasionally in human l>eings this pigment 
 ir- absent. 
 
7° 
 
 THE HUMAN BODY. 
 
 in to form the iris, the colored part of the eye which is seen 
 through the cornea. In the centre of the iris is a circular 
 dark aperture, the pupil, through which light reaches the 
 interior of the eyeball. 
 
 Fig. 128. — The left eyeball in horizontal section from before back, t, sclerotic; 2, 
 junction of sclerotic and cornea ; 3, cornea ; 4, 5, conjunctiva ; 6, posterior elastic layer 
 of cornea; 7, ciliary muscle; 10, choroid; n, 13, ciliary processes; 14, iris; 15, retina; 
 16, optic nerve ; 17, artery entering retina in optic nerve ; 18, fovea centralis ; 19, region 
 where sensory part of retina ends ; 22, suspensory ligament ; 23 is placed in the canal of 
 Petit, and the line from 25 points to it; 24, the anterior part of the hyaloid membrane ; 
 26, 27, 28, are placed on the lens ; 28 points to the line of attachment around it of the 
 suspensory ligament ; 29, vitreous humor; 30, anterior chamber of aqueous humor; 31, 
 posterior chamber of aqueous humor. 
 
 The third or innermost coat, the retina (15), "is the essential 
 part of the eye, since in it the light produces those changes 
 that give rise to nervous impulses in the optic nerve. It lines 
 the posterior half of the eyeball. 
 
 The Microscopic Structure of the Retina is very com- 
 plex ; although but ^ inch in thickness it presents ten dis- 
 tinct layers. 
 
THE RET IN A. 
 
 271 
 
 Beginning (Fig. 129) with its front or inner side we find 
 the interned limiting membrane (1), a thin structureless layer; 
 
 wf lu 
 
 Fig. 129. — A section through the retina from its anterior or inner surface ( i ) in contact 
 with the hyaloid membrane, to its outer (to) in contact with the choroid, i. internal 
 limiting membrane ; 2, nerve-fibre layer: 3, nerve cell layer; 4. inner molecular layer ; 
 5, inner granular layer; 6, outer molecular layer; 7. outer granular layer; 8, external 
 limiting membrane ; 9, rod and cone layer ; 10, pigment cell layer. 
 
 the nerve fibre layer (2), formed by radiating fibres of the 
 optic nerve ; the nerve cell layer (3); the inner molecular layer 
 (4), consisting partly of very fine nerve fibrils, and largely of 
 
72 
 
 THE HUMAN BODY, 
 
 connective tissue: the inner granular layer (5), composed of 
 nucleated cells : the outer molecular layer (6). thinner than the 
 inner; the - >anular layer (7), composed of thick and 
 
 thin fibres on each of which is a conspicuous nucleus with a 
 nucleolus : the thin external lijniting membrane (8), perforated 
 by apertures through which the rods and cones (9) of the 
 ninth laver join the fibres of the seventh ; and outside of all, 
 next the choroid, the pigmentary layer (10). The nerve fibres 
 are believed to be continuous with the rods and cones. 
 Light entering the eve passes through the transparent retina 
 until it reaches and excites the rods and cones which stimu- 
 late the nerves. 
 
 The Blind Spot. — Where the optic nerve enters the retina 
 it forms a small elevation (Fig. 130), from which nerve fibres 
 
 Fig. 130.— The right retina as it would be seen if the front part of the eyeball with the 
 lens and vitreous humor were removed. The white disk to the right marks the entry of 
 the optic nerve (biind spoti; the lines radiating from this are the retinal arteries and 
 veins. The small central dark patch is the yellow spot, the region of most acute vision. 
 
 radiate. This elevation possesses neither rods nor cones and 
 is blind, as may be readily demonstrated. Close the left eye 
 
THE IRIS. 
 
 and look steadily with the right at the cross (Fig. 131), 
 holding the page vertically in front of the face, and moving 
 
 Fig. 131. 
 
 it alternately from and toward yon. When the book is about 
 ten inches from the eye the white disk entirely diappears from 
 view because its image then falls on the part of the retina 
 where the optic nerve enters. 
 
 Light consists of vibrations in an ether which pervades 
 space. An object which sets up no waves in the ether does not 
 excite the visual nervous apparatus, and appears black ; an 
 object which sets up ethereal vibrations capable of exciting the 
 rods and cones of the retina appears white or colored. The 
 ethereal vibrations enter the eye through the cornea, pass 
 on through the pupil and lens to stimulate the retina. 
 
 The Iris. — In the front portion of the eye behind the 
 transparent cornea, and floating in the aqueous humor, lies 
 a colored curtain (the iris) which forms a circle, with a hole 
 (the pupil) in its centre. The iris has muscular fibres which 
 enable it to make the pupil larger or smaller according as the 
 light is faint or bright. All the light which goes to the retina 
 must pass through the pupil, and the brightness of the images 
 on the retina is dependent upon the number of rays which 
 find their way through ; hence a large opening gives brighter 
 images than a small one. The iris by its adjustment of the 
 
274 
 
 THE HUMAN BODY. 
 
 size of the pupil thus reflexly controls the amount of light 
 and keeps the retina from injury by excess. It has another 
 function : when we look at near objects the pupil becomes 
 smaller than when we look at distant objects.* The iris thus 
 acts as the diaphragm of a camera, since it is possible to form 
 a sharp image of a near object only with a small bundle of 
 rays. 
 
 When there is little light, as at twilight, the pupils are large 
 and the eye cannot make distinct images, even of distant ob- 
 jects ; hence everything seems blurred. 
 
 The Refracting Surfaces of the Eye are three in number : 
 i the anterior surface of the cornea, (2) the anterior sur- 
 face of the crystalline lens, and (3) the posterior surface of 
 the crystalline lens (Fig 128). These surfaces act together 
 like a convex lens, to bend the rays of light which pass 
 through them (Fig. 132), so that all those which start from 
 
 Fig. 132. — Illustrating the formation behind a convex lens of a diminished and in- 
 verted image of an object placed m front of it. 
 
 one point of an external object meet again in a focus on one 
 point of the retina. In this way small and inverted images of 
 the objects at which we look are formed on the retina, and 
 stimulate its rods and cones. 
 
 * This change of pupil can be readily seen in another's eye by pressing 
 the hand over it for a moment or two and then removing the hand. 
 
ACCOM Mi ~)DA TION. 275 
 
 Accommodation. — In the healthy eyeball the crystalline 
 lens is controlled by muscles which change its convexity, 
 
 making it greater when we look at near, and less when we 
 look at distant, objects. Standing at a window behind a lace 
 curtain we can look at the curtain and sec its threads plainly, 
 but while so doing we sec houses on the other side of the 
 street indistinctly, because the convexity of the lens is such 
 
 Fig. 133. — Section of front part of eyeball showing the change in the form of the lens 
 when near and distant objects are looked at. a, c, l>, cornea ; A , lens when near object 
 is looked at ; />', lens when distant object is looked at. 
 
 as to focus light on the retina from the near object, and not 
 from the distant. We can, however, "focus" on the houses 
 over the way and see them plainly ; but then we no longer 
 see the curtain distinctly, because the lens has changed its 
 form to focus light from the far object on the retina. The 
 eye relaxes to focus on distant objects, and a muscular effort 
 is necessary to increase the convexity of the lens, i.e. accom- 
 modate, for near objects. 
 
 Short Sight and Long Sight. — In the normal eye the range 
 of accommodation is very great, making it possible to focus 
 on objects infinitely distant or only six or eight inches 
 from the eye. In the natural healthy eye parallel rays of 
 light meet on the retina when the muscles controlling 
 the crvstalline lens are relaxed and the lens is at its flattest 
 
276 
 
 THE HUMAN BODY. 
 
 (A, Fig. 134). Such eyes are emmetropic or normal. In some 
 eyes the eyeball is elongated and when not accommodated 
 
 parallel rays meet in front 
 of the retina (B). Persons 
 with such eyes cannot see 
 distant objects distinctly 
 without the aid of diverg- 
 ing (concave) spectacles ; 
 they are myopic or short- 
 sighted. In others, the eye- 
 ball is flattened, and when 
 not accommodated parallel 
 rays are brought to a 
 focus behind the retina 
 (C). To see even distant 
 objects, such persons must 
 therefore use muscular 
 
 effort to increase the con- 
 tropic ( A), a mvopic {B\. and a hvperme- • „_, „ (-.1 1 
 
 tropica-, eye. verging power of the lens ; 
 
 and when objects are near they cannot bring the rays pro- 
 ceeding from them to a focus soon enough. To get distinct 
 retinal images of near objects, they therefore need converging 
 (convex) spectacles. Such eyes are called hypermetropic or 
 far-sighted. 
 
 Astigmatism. — The refracting surfaces of the eye acting 
 together are equivalent in refracting power to a single, spher- 
 ical surface of fairly short curvature. Frequently, however, 
 the result is not the same as would be given by a perfect 
 spherical surface, owing to inequalities in the curvature of the 
 eye. In one direction the curvature may be greater than 
 that at right angles to it. This tendency to a cylindrical 
 form is called astigmatism. It interferes with the formation 
 
 Fig. 134. — Diagram illustrating the path 
 of parallel rays after entering an emme- 
 
HYGIENE OF THE EYES. 
 
 -77 
 
 of perfect images and sometimes leads to serious eye strain in 
 the effort to better the vision. Astigmatism may be de- 
 tected by lo iking at black lines radiating from a point or at 
 
 Fig. 135. — Lines for the detection of astigmatism. 
 
 fine black concentric circles. Portions of the lines or circles 
 appear gray and others black ; the gray portions are out of 
 focus. This defect is corrected by proper cylindrical glasses 
 which equalize the curvatures of the eye. 
 
 Hygiene of the Eyes. — Since the healthy eye is so con- 
 structed that when it is not accommodated it forms images of 
 distant objects on the retina, muscular effort is required to see 
 near objects, and fatigue results if the effort is long con- 
 tinued. 
 
 In a hypermetropic eye still more effort is needed to see 
 near objects, and this results in greater muscular fatigue. 
 Hvpermetropic persons can often read well for a while, but 
 then complain that they can no longer see distinctly. This 
 kind of weak sight should always lead to examination of the 
 eves by an oculist; otherwise severe headaches may result and 
 the eyes be injured. 
 
 Children sometimes have hypermetropic eyes, and should 
 be at once provided with suitable glasses. In old age another 
 kind of far-sightedness {presbyopia) is common, due to stiff- 
 
278 
 
 THE HUMAN BODY. 
 
 ness of the crystalline lens, which cannot become convex 
 enough during accommodation to focus the images of near 
 objects on the retina. 
 
 Short-sighted eyes appear to be more common now than 
 formerly, especially in those who use the eyes constantly at 
 short range. Myopia is rare among those who live mainly 
 out of doors. It is not so apt to lead to permanent injury 
 
 Fig. 136.— Semi-diagrammatic section through the right ear. .1/. concha ; G, external 
 auditory meatus : T. tympanic or drum membrane : P, middle ear : o, oval foramen : 
 r, round foramen. Extending from 7' to o is seen the chain of tvmpanic bones. R, 
 Eustachian tube. /', B, S, bony labyrinth: / '. vestibule; B, semicircular canal: S, 
 cochlea. S. I, /', membranous semicircular canal and vestibule. A, auditory nerve di- 
 viding into branches for vestibule, semicircular canal, and cochlea. 
 
 of the eye as hypermetropia, but the effort to see dis- 
 tinctly any but near objects is apt to produce headaches 
 and other symptoms of nervous exhaustion. Eye strain 
 frequently shows itself in headaches and general nervous 
 symptoms which do not appear to be associated with the 
 eyes. They are, however, relieved when the eyes are cor- 
 
HI. -1 RING— THE EAR. 
 
 279 
 
 rected by glasses. The general health also reacts upon 
 the eyes and tends to exaggerate the nervous effects of eye 
 
 strain. 
 
 Hearing. — The ear | Fig. 136 l ( onsists of three portions, 
 known respectively as the external ear, the middle ear, and the 
 
 internal ear or labyrinth. The latter is the essential hearing 
 organ sinee it contains the ends of the auditory nerve fibres. 
 
 The External Ear consists of the expansion ( M), seen on 
 the exterior of the head, called the concha, and a passage 
 leading in from it, the external auditory meatus (G). This pass- 
 age is closed at its inner end by the tympanic membrane ox drum 
 /' 1. It is lined by a prolongation of the skin, through which 
 numerous small glands, secreting the wax of the ear, open. 
 
 The Middle Ear, or drum chamber of the ear (Fig. 137 
 and P, Fig. 136), is 
 an irregular cavity in 
 the temporal bone, 
 closed externally by 
 the drum membrane. 
 From its inner side 
 the Eustachian tube 
 (R, Fig. 136) pro- 
 ceeds and opens into 
 the pharynx. This 
 tube allows air from 
 the throat to enter the 
 cavity, and serves to 
 
 Keep equal tne atniOS- K IG ,37 — The middle ear and its bones, considerably 
 , . magnified G, the inner end of the external auditory 
 
 pheriC pressure On meatus, closed internally by the conical tympanic mem- 
 brane ; Z.. the malleus, or hammer-bone : H , the incus, 
 ach. side Of the drum or anvil-bone ; J>, the stapes, or stirrup-bone. 
 
 membrane.* Three small bones (Fig. 137) stretch across 
 * Frequently the inflammation of sore throat extends into the Eusta- 
 
280 THE HUMAN BODY. 
 
 the cavity from the drum membrane to the labyrinth ; they 
 transmit the vibrations of the membrane, produced by sound 
 waves in the external air, to the liquid of the labyrinth. The 
 outmost bone is the hammer or malleus ; the inmost, the stirrup 
 or stapes ; and the middle bone, the anvil or incus. 
 
 The Internal Ear, or Labyrinth, consists primarily of 
 chambers and tubes hollowed out in the temporal bone. 
 The middle chamber, called the vestibule ( V, Fig. 135), has 
 an opening, the oval foramen (0), in its outer side, into which 
 the inner end of the stapes fits. Behind, the vestibule opens 
 into three semicircular canals (one of which is shown at B, 
 Fig. 135), and in front into a spirally coiled tube (-5"), the 
 cochlea. In these bony chambers and tubes lie membranous 
 chambers and tubes, in which the fibres of the auditory nerve 
 (A, Fig. 135) end. All the labyrinth chamber outside these 
 membranous parts is occupied by a watery liquid, known as 
 perilymph. The membranous chambers are filled with a sim- 
 ilar liquid, the endolymph. 
 
 The cochlea consists essentially of a tube coiled upon itself 
 something like a snail shell. Partitions running through the 
 length of the tube divide it into three cavities (Fig. 138), 
 the middle and triangular-shaped cavity, which contains the 
 auditory nerve terminals, and two side cavities. Each cavity 
 is filled with endolymph. The membrane which divides the 
 tube into nearly equal parts is called the basilar membrane. 
 This supports the structure known as the organ of Corti in 
 which the nerve terminals end (Fig. 138). The rods and 
 cells which form the organ of Corti are continued with the 
 basilar membrane throughout the length of the cochlea. The 
 
 chian tube and closes it. The air in the cavity of the middle ear is then 
 absorbed and permits the external air to press the drum in, producing 
 m ore or less deafness. 
 
THl- COCHLEA. 
 
 2 8 i 
 
 organ of Corti and the basilar membrane form a series of 
 vibrating cords with corresponding nerve apparatus for re- 
 ceiving vibrations transmitted from the bones of the ear 
 
 Fig. 13S. — Diagram of a section of a coil of the cochlea. CC, canal of the cochlea ; 
 mR, its upper wall ; Sc I ', the part of the bony cavity above the canal of the cochlea ; 
 Sc.T, the part below it; O.C, the organ of Corti on the basilar membrane; A.N, 
 branch of auditory nerve in the central column of the spiral ; <i , connective tissue cush- 
 ion to which the basilar membrane is attached; b, the bony wails: m.t. a membrane 
 lying over the organ of Corti ; l.s, the spiral ledge projecting from the axis. 
 
 through the endolymph of the ear and for transforming them 
 into nervous impulses. The vibrating cords of the basilar 
 membrane are so arranged that they can respond to vibrations 
 
282 THE HUMAN BODY. 
 
 varying in rapidity from 30 to about 20,000 per second. 
 Each portion of the membrane has its own rate of vibration 
 and is set in motion by vibrations of the same rate trans- 
 mitted to it from the external air. Any vibrations in the en- 
 dolymph will pick out the portions of the basilar membrane 
 with corresponding vibrations and thus selectively create ner- 
 vous impulses in the corresponding nerve terminals in the 
 organ of Corti. These impulses transmitted to the auditory 
 centre give rise to sensations which we recognize as sounds. 
 
 Sound. — The sensation which we know as sound is origi- 
 nated by oscillations produced in the air by vibrating bodies, 
 such as a piano string or an organ pipe. A musical lone is 
 caused by a regular succession of such oscillations. Loud- 
 ness depends upon the extent, pitch upon the rapidity of 
 vibration ; slow vibrations give rise to deep, rapid vibra- 
 tions to shrill, tones. A 16-inch organ pipe and the lowest 
 string of the piano give about $$ vibrations to the second, 
 their octave 66, and so on, doubling for each octave. A 
 pure tone is of one pitch throughout, but each vibrating body 
 gives out a complex sound made up of the vibration as a 
 whole (fundamental tone), together with vibrations of parts 
 of itself (overtones^). The quality which enables us to dis- 
 tinguish between a piano and a violin, an organ or the human 
 voice, depends upon the richness and character of these over- 
 tones. It is called color, or timbre. 
 
 The Semicircular Canals are associated with the sense of 
 equilibrium. 
 
 Nerves are distributed to the ends of the semicircular 
 canals and terminate in cells with hairs (Fig. 139). These 
 hairs project into the endolvmph of the cavity. They 
 are arranged so that when an individual is standing one 
 canal of each ear is horizontal, the second is vertical 
 
SKIN OR DERMAL SENSF.S. 
 
 2*3 
 
 antero-posteriorly, and the third is in the vertical plane 
 
 at right angles to the second. 
 Motion in any direi tion 
 gives rise to a movement of 
 endolymph through the hairs 
 of the cells, just as water in a 
 bucket which is suddenly 
 rotated moves along the 
 inner surface of the bucket. 
 This causes pressure upon the 
 hairs and leads to the trans- 
 mission of nervous impulses 
 which in turn give rise to . , ,. 
 
 tic 139.— Diagram of epithelium in ner- 
 the Sensation Of movement vous region of ampullaofa semicircular canal. 
 
 and equilibrium. Persistent dizziness has frequently led to 
 diagnoses of disease in this region. 
 
 Skin or Dermal Senses. — Many sensory nerves end in the 
 skin through which we get several kinds of sensation. When 
 a pencil point is pressed against the skin, we have a sense ot 
 touch and of pressure ; when pressed very strongly, a sense of 
 pain. When the point is pressed very lightly upon various 
 points an occasional cold point is discovered. When a warm 
 point is applied the sense of warmth is distinct and strong at 
 certain points in the skin and weak at others. Each special 
 sensation is probably due to a special nerve ending and nerve, 
 capable of translating the stimuli (whether change of tem- 
 perature, pressure, etc.) into nervous impulses which give rise 
 in the brain to the corresponding sensation.* 
 
 By combinations of these sensations we get the charac- 
 
 *This is a marked illustration of the fact that nerves transmit special 
 kinds of nervous impulses or have specific energy [specific energy of 
 nerves). 
 
284 THE HUMAN BODY. 
 
 teristics of the objects that we touch, of hardness, softness, 
 smoothness, roughness, heat or cold, size, if the object is 
 small enough to be received as a unit, and number, if several 
 objects are applied to the skin at once, provided they are not 
 too near together. 
 
 The Localization of Skin Sensations. — When the eyes are 
 closed and a point of the skin is touched we can with some 
 accuracy indicate the region stimulated ; because, although 
 tactile feelings are alike in general characters, they differ in 
 something {local sign) besides intensity by which we can dis- 
 tinguish them as originated on certain parts of the skin. 
 The fineness of the localizing power varies widely in different 
 skin regions, and is measured by observing the least distance 
 which must separate two objects (as the blunted points of a 
 pair of compasses) in order that they may be felt as two. 
 The following table illustrates some of the differences ob- 
 served : 
 
 Tongue-tip 1. 1 mm. (.04 inch) 
 
 Palm side of last phalanx of finger 2.2 mm. (.08 inch) 
 
 Red part of lips 4.4 mm. (. 16 inch) 
 
 Tip of nose 6.6 mm. (.24 inch) 
 
 Back of second phalanx of finger .'. n.o mm. (.44 inch) 
 
 Heel 22.0 mm. (.88 inch) 
 
 Back of hand 30.8 mm. (1.23 inches) 
 
 Forearm 39.6 mm. (1.58 inches) 
 
 Sternum 44.0 mm. (1.76 inches) 
 
 Back of neck 52.8 mm. (2. 1 1 inches) 
 
 Middle of back 66.0 mm. (2.64 inches) 
 
 It is supposed that the variations in discriminating power 
 are dependent upon the richness of distribution of the tactile 
 nerve ends, and that one or more untouched terminals must 
 lie between those on which the compass points rest in order 
 that two points may be distinguished. 
 
THE MUSCULAR Si 
 
 285 
 
 The Muscular Sense. — Movements of the limbs are a< com- 
 panied by a sensation of effort, which is proportional to the 
 
 Fig. 140. — Section of skin showing two papillae of the dermis and some of the deeper 
 cells of the epidermis, a, papilla containing bluod vessels; b, papilla containing a 
 tactile corpuscle. / : </, medullated nerve fibres goingto the corpuscle : at/", optical cross- 
 sections of the fibres are seen as they wind round the outside of the corpuscle ; the 
 general transverse direction of the connective tissue bundles of the capsule of the 
 corpuscle is shown. 
 
 energy expended and enables one to estimate the weight of 
 the object moved and the direction of movement. These 
 sensations have been called the muscular sense. They have 
 been attributed to many causes and are now supposed to be 
 due to a complex of nervous impulses received from joints, 
 muscles, tendons, skin, etc. They give, in addition to sense 
 of effort and of direction of movement, a sense of the position 
 of the limbs. The muscular sense is exceedingly important as 
 a subconscious guide to muscular control. 
 
 Pain may be described as a general sensation, since it has 
 no special locality or peculiarity of manifestation. In general 
 it is a danger signal to prevent injury, and guide to the way of 
 health. While abnormal conditions in all tissues and organs 
 may give rise to pain, the skin is far more sensitive than the 
 deeper structures. Experiments suggest that there may be 
 
2 86 
 
 THE HUMAN BODY. 
 
 special pain nerves, although their special terminal structure 
 has not been identified. 
 
 Smell. — The endings of the olfactory nerves are spread in 
 the mucous membrane of the upper parts of the nasal cavities. 
 
 The olfactory cells are distributed 
 between the cells of the mucous 
 membrane (Fig. 141) and send 
 fine filaments out to the surface. 
 I , yy They are scattered over the upper 
 kiYL ano - lower turbinate bones (0, p, 
 Fig. 46) (which are expansions 
 of the ethmoid on the outer wall 
 of the nostril chamber), the 
 opposite part of the partition 
 between the nares and that part 
 of the roof of the nose (n, Fig. 
 46) which separates it from the 
 cranial cavity. 
 
 Odorous Substances, the stim- 
 uli of the olfactory apparatus, are 
 -Ceils from the olfactory rdinarilv gaseous. Thev fre- 
 
 1, from the frog. 2, from - D 
 
 man ; a, columnar cell, with its branched ^,, 1£iT - 1 i-l,- 0/ «• ■, <~.w-^»-fiill-i- mkan 
 
 deep process :r. so-called oltactory cell: q uentl > aCt pOWerfull) « hen 
 
 c, its narrow outer process: d, its • n _«_:* 
 
 slender central process 3, gray nerve present ID very small quantity, 
 
 fibres of the olt'actorv nerve, seen di- . r . . 
 
 vidinginto fine peripheral branches at a. A gram Or two 01 mUSK kept m a 
 
 room will give the air in it an odor for years, and yet at the end 
 will hardly have diminished in weight. While some gases or 
 vapors have this powerful influence upon the olfactory organ, 
 others, as pure air, do not stimulate it at all.* 
 
 TasLe. — The organ of taste is the mucous membrane on 
 
 * In ordinary breathing, the air passes through the lower part of the 
 nose and therefore does not reach the olfactory surface. In ••sniffing," 
 the air is passed directly over this surface. 
 
 Fig 
 
 epithelium. 
 
TASTE. 287 
 
 the upper side of the tongue, and possibly on the soft palate 
 and fauces. The mucous membrane of the tongue presents 
 innumerable elevations or papillae (l'ig. 53) of three kinds 
 (p. 116). The filiform papillae are organs of touch, for the 
 tongue has the sense of touch as well as of taste. The cir- 
 c umvallate and fungiform papillae contain the endings of 
 branches of the glossopharyngeal and trigeminal nerves (pp. 
 241, 242 ), which, when excited by bodies in solution, 
 stimulate the taste centres in the brain. 
 
 Many so-called tastes (flavors) are really smells ; odorif- 
 erous particles of substances which are being eaten reach the 
 nose through the posterior nares and arouse smell sensations 
 which, since they accompany the presence of objects in the 
 mouth, we take for tastes. Such is the case with most spices, 
 since when the nasal chambers are closed by a cold in the 
 head or by pinching the nose, the so-called " taste " of spices 
 is not perceived, but only a certain pungency due to stimula- 
 tion of nerves of common sensation in the tongue. 
 
CHAPTER XXII. 
 VOICE AND SPEECH. 
 
 Voice consists of sounds produced by the vibrations of two 
 elastic folds called the vocal cords. These cords lie in the 
 larynx, which is situated between the pharynx and the wind- 
 pipe, and is a portion of the air passage specially modified to 
 form a voice organ. 
 
 The vocal cords project into the larynx so that only a nar- 
 row slit, the glottis, is left between them. When they are put 
 in a certain position the air driven through the glottis sets 
 them vibrating and they give rise to sounds. The stronger 
 the blast the louder the voice. 
 
 The pitc/i of the voice is primarily dependent on the size of 
 the larynx. The longer the vocal cords are, the lower is the 
 pitch of the voice. Children, in whom the larynx is small, 
 have shrill voices ; and for the same reason a woman's voice 
 is usually higher pitched than a man's. About sixteen or 
 seventeen years of age a boy's larynx grows very fast, and 
 his voice becomes about an octave deeper in tone. 
 
 While every one's voice has a certain natural pitch which 
 leads us to call it soprano, tenor, bass, and so forth, this pitch 
 can be modified within limits, so that we each can sing a 
 number of notes. This variety is due to the action of muscles 
 in the larynx which alter the tension of the vocal cords. 
 
 288 
 
RESONANCE SPEECH. 
 
 The more tightly they are strefc hed the higher pit< hed is the 
 tone which they emit. 
 
 Resonance. — Although musical instruments depend prima- 
 rily upon vibrating bodies, yet the volume and quality of their 
 tones are largely determined by resonaru e chambers, as in the 
 cornet and organ, or by sounding boards, as in the piano and 
 violin. When a tuning fork is held in the fingers and tapped 
 it gives a very low tone. When, however, it is touched to a 
 hollow box open at one end and so constructed that the air 
 column contained in it will vibrate in unison with the tuning 
 fork, the volume and purity of the sound are enormously in- 
 creased. 
 
 The pharynx, mouth and nose cavities act as a resonance 
 chamber for the vibrations of the vocal cords, picking out and 
 reinforcing the tones to which the air contained in them cor- 
 mds in rate of vibration. When the vocal cords vibrate 
 they set the air in vibration. The sound is made louder and 
 changed in character by this selective emphasis on fundamen- 
 tal tones and overtones. 
 
 Speech. — By movements of throat, soft palate, tongue, 
 cheeks, and lips, the size and form of the resonance chamber 
 are varied, and with them the tone of voice. By movements 
 of tongue, lips, and palate, the air current, and therefore the 
 sound, is interrupted from time to time, or the air is forced 
 through a narrow passage in the mouth, giving rise to sounds 
 in addition to those originated by the vocal cords. The 
 primitive feeble monotonous tone due to the vibration of the 
 vocal cords is thus reinforced and altered in throat and 
 mouth, and voice is developed into articulate speech. 
 
 The Larnyx consists of a framework of nine cartilages, mov- 
 ably articulated together, and having muscles attached to them 
 by whose contractions their relative positions are altered. 
 
290 
 
 THE HUMAN BODY. 
 
 These cartilages form a tube, continuous with the windpipe 
 and lined by mucous membrane. At one level the vocal 
 
 Fig. 142. — The more important cartilages of the larynx from behind, t, thyroid ; Cs, 
 its superior, and Ci, its interior, horn of the right side : **, cricoid cartilage : t, aryte- 
 noid cartilage : Pv, the comer to which the posterior end of a vocal cord is attached ; 
 Pm, corner on which the muscles which approximate or separate the^vocal cords are in- 
 serted ; co, cartilage of Santorini. 
 
 cords, also covered with mucous membrane, project into the 
 tube, leaving for the passage of air only the narrow slit of the 
 glottis. 
 
 The largest cartilage of the larnyx (/, Fig. 142) is the 
 thyroid. It is placed in front and consists of right and left 
 halves which meet at an angle in front, but separate behind 
 so as to enclose a V-shaped space. The front of the thyroid 
 cartilage causes the prominence in the neck known as Adam's 
 apple. The epiglottis, not represented in the figure, is at- 
 tached to the top of the thyroid cartilage and overhangs the 
 entry from pharynx to larynx. It may be seen, covered 
 by mucous membrane, projecting at the root of the tongue, if 
 
THE VOCAL CORDS— LARYNGEAL MUSCLES. 201 
 
 the mouth is held open before a mirror, and the tongue held 
 down, it is represented as seen from behind at a, Fig. 143. 
 The cricoid cartilage (**, Fig. 142) has the form of a signet- 
 ring, with its broad part turned toward the ba< k of the throat, 
 and placed in the lower part of the opening between the 
 halves of the thyroid. The two arytenoid cartilages (t, Fig. 
 142) are placed on the top of the wide posterior part of the 
 cricoid; each is pyramidal in form. The remaining laryn- 
 geal cartilages are of less importance. 
 
 The Vocal Cords, which are rather projecting pads of elas- 
 tic tissue than cords in the ordinary sense of the word, pro- 
 ceed, one from each arytenoid cartilage behind, to the angle 
 where the halves of the thyroid meet in front. When open, 
 as in quiet breathing, the glottis (c, Fig. 143) is narrow in 
 front and wider behind, and since air driven through the 
 opening does not then set the margins of the cords in vibra- 
 tion, no sound is produced. 
 
 The Muscles of the Larynx. — The laryngeal muscles are 
 numerous. One set of muscles pulls the arytenoid cartilages 
 towards one another and thus narrows the glottis behind ; air 
 forced through the narrowed slit causes vibration of the cords 
 and produces voice. Another set stretches and tightens the 
 vocal cords by pulling the arytenoid cartilages backward, and 
 thereby raises the pitch of the voice. A third set pulls the 
 front of the thyroid cartilage nearer the arytenoids and so 
 slackens the cords and lowers the pitch of the voice. A 
 fourth set separates the arytenoid cartilages, and with them 
 the vocal cords, and thus widens the glottis and allows air to 
 pass through it without producing voice. 
 
 The Range of the Human Voice from the lowest note (/ 
 of the unaccented octave) of an ordinary bass to the highest 
 note (g on the thrice accented octave) of a fairly good so- 
 
292 
 
 THE HUMAN BODY. 
 
 prano is about three octaves : the former note is produced by 
 88 vibrations per second the latter by 792. Celebrated 
 
 Fig. 143 — The larynx viewed from its pharyngeal opening. The back wall of the 
 pharynx has been divided and its edges (n) turned aside, i, body of hyoid ; 2, its 
 small, and 3, its great, horns; 4, upper and lower horns of thyroid cartilage; 5, mucous 
 membrane of front of pharynx, covering the back of the cricoid cartilage ; 6, upper 
 end of gullet ; 7, windpipe, lying in front of the gullet ; 8. eminence caused by carti- 
 lage of Santorini ; 9, eminence caused by cartilage of Wrisberg — both lie in, 10, the 
 aryteno-epiglottidean fold of mucous membrane, surrounding the opening {adit us 
 laryngis) from pharynx to larynx; a, projecting tip of epiglottis; c, the glottis — the 
 lines leading from the letter point to the free vibrating edges of the vocal cords ; b\ 
 the ventricles of the larynxt— heir upper edges, marking them off from the eminences 
 b, are the false vocal cords. 
 
 singers of course go beyond this limit in each direction : 
 basses have been known to take a on the great octave (55 
 vibrations per second), and Mozart, at Parma, heard a soprano 
 
VOWELS ./v/> ( ( WSONANTS. 
 
 sing .1 note of the extraordinarily high pitch c on the fifth 
 accented octave (2 114 vibrations per second). 
 
 Vowels. ire musical tones produced in the larynx and mod 
 ified by resonance of the air in the pharynx and mouth. To 
 gel the broad a sounds, as ah, the mouth is widel) opened 
 and the lips drawn back. Such vowels as 00 (moor) arc pro- 
 duced by protruding the lips and lengthening the mouth cav- 
 ity. The change in the form of the mouth may be noticed by 
 pronouncing consecutively the vowel sounds <///, eh, ee, oh, 00., 
 The English i (as in spire) is a diphthong, ('insisting of a 
 (pad) followed by e (feet), as may be readily found on at- 
 tempting to sing a sustained note to the sound i. 
 
 Semivowels.— In uttering true vowel sounds the soft palate- 
 is raised so as to shut off the resonance of the nasal cavity. 
 For sumo other sounds (the semivowels or resonants 1 the initial 
 step is, as in the case of the true vowels, the production of a 
 laryngeal tone ; but the soft palate is not raised, and the 
 mouth exit is more or less closed by the lips or the tongue ; 
 hence the blast issues partly through the nose, which by its 
 resonance gives them a special character, as in the case of m, 
 n, and ng. 
 
 Consonants are sounds produced not mainly by the vocal 
 cords, but by modifications of the expiratory blast on its way 
 through the mouth. The current may be interrupted and the 
 sound changed by the lips (labials, as/ and b); or, at or near 
 the teeth, by the tip of the tongue (denials, as /and d); or, 
 in the throat, by the root of the tongue and the soft palate 
 {gutturals, as /' and g). 
 
 Consonants may also be classified by the kind of move- 
 ment which gives rise to them. In explosives an interruption 
 to the air current is suddenly interposed or removed 1 p, b, t, 
 d, £, g)- Other consonants are conluiuuus (/" s, r) and may 
 
294 THE HUMAN BODY. 
 
 be divided into (ij aspirates, when the air is made, to rush 
 through a narrow aperture, as, for example, between the lips 
 (/ ), the teeth (s), the tongue and the palate i's/ij, or the 
 tongue and the teeth {th)\ (2) resonan/s or semivowels; (3; 
 libratories, the different forms of r, due to vibrations of parts 
 bounding a constriction put in the way of the air current on 
 its passage. 
 
CHAPTER XXIII. 
 
 GROWTH AND NUTRITION. 
 
 Development. — The human body, like the bodies of all 
 animals, begins life as a single cell. This single cell divides 
 to form two. these in turn form four, and so the process of 
 division (segmentation) continues until there is a mulberry- 
 like mass of cells which do not appear to differ one from 
 another and which occupy about the same space as the 
 original cell (Fig. 144). From this time on the continued 
 
 Fig. 144.— A, an ovum; B to £, successive stages in its segmentation until the 
 morula, F, is produced ; a, cell sac ; b, cell contents ; c, nucleus. 
 
 increase in number is accompanied by an increase in bulk. 
 The cells no longer follow the same course of growth, but 
 groups of cells develop peculiarities of their own, according 
 
 295 
 
296 THE HUMAN BODY. 
 
 to a process known as d ition. Ultimately three lay- 
 
 are formed. Each of these layers continues differen- 
 tia: _ ith the result that from one layer the skin and the 
 central nervous system are developed ; from another the mus- 
 cular and bony system : and from the third the alimentary 
 tract. 
 
 The tissues resulting from this differentiation may be 
 roughly classified in the following manner : 
 
 1 ■ Undifferentiated tissues. These are composed of 
 cells with no special development, retaining much of the 
 form and properties of rudimentary cells. Lymph corpuscles 
 and some of the white blood corpuscles belong to this cl ss 
 
 : 1 Supporting tiss ies 3 including cartilage, bone, and 
 connective tissue. 
 
 Nutritive tissues, including those cells which have to 
 
 do with the reception and preparation of food, the secretion 
 
 gestive fluids, and the :ion of waste matter- as, for 
 
 the cells of the stomach, intestines, lungs, kidney. 
 
 and skin, and the glands of the alimentary tract. 
 
 4 borage tiss s 3 resented by the liver cells and 
 
 such connective tissue cells as become loaded with fat. 
 : Irritable tissues, as the - se organs. 
 
 o-ordinating and automatic tiss s 3 as the nerve 
 
 cells. 
 
 Motor tissue?, represented by ciliated and muscle 
 
 cells. 
 
 (8) Conductive tissues, as nerve fibr - 
 
 Protective tissues, including the epithelial lining of 
 the cavities of the body, the epidermis, hairs, nails, and the 
 enamel of the teeth. 
 
 : I Reproductive tissues, by which the ovum with ts 
 power of developing into a new individual is produced. 
 
CELL NUTRITION. 297 
 
 The cells making up the various tissues of the body have 
 characteristic forms and powers. Cells with like dowi 
 
 gether with supporting cells, arc grouped into ma 
 (alU-d organs. These organs are placed in such positions as 
 will inter. ere least with the activity of the body as a whole, 
 and will best subserve, by their special activities, its welfare. 
 The fun tions of any organ are the sum of the functions of 
 the cells composing it. These eells may all have the same 
 work to do, as in muscle, or may have different work, as in 
 the glands of the stomach, some cells of which se< rete pepsin, 
 others hydrochloric acid, while both secrete water. 
 
 Cell Nutrition. — Kadi cell has work to do for the body 
 as a whole ; it has also to look after its own well-being in 
 order to be able to do its work. This means that each cell 
 of the bodies of the higher animals must take food materials 
 in the form of serum albumin or globulin, sugar, oxygen, etc., 
 must combine them into a compound which is capable of 
 ready oxidation for the liberation of energy, must then be 
 prepared to liberate this energy under the stimulation of nerve 
 impulses, must direct the energy into useful channels, and 
 get rid of the waste products of oxidation. It must appro- 
 priate substance and build it up into its own protoplasm for 
 growth or repair. That these changes in cells may be con- 
 siderable is shown by Fig. 145. 
 
 All the activities of the cell are stimulated and controlled 
 by impulses received through connected nerves. The nervous 
 impulses which have to do with the nutrition, growth, and 
 general condition of the cell itself are supposed to be distinct 
 from the impulses which stimulate the cell to work for the 
 body as a whole, and have even been supposed to be trans- 
 mitted to the cell through special nerves (trophic nerves). 
 The cell may thus be considered an individual member 
 
298 
 
 THE HUMAN BODY. 
 
 of a community with certain duties and privileges of its 
 own. 
 
 Fig. 145 — Serous glands, a, rabbit's pancreas " loaded " (resting) ; c, " discharged " 
 (active) (observed in the living animal) (Kiihne and Lea), b, loaded ; d, discharged, 
 alveolus of parotid (fresh preparations) (Langley). 
 
 General Nutrition. — We have seen that the cells making 
 up the body have work to do both for themselves and for the 
 other cells of the body, thus forming a vast army with one 
 general plan of campaign. While we have definite knowl- 
 edge of many of the general conditions under which the 
 cells work, and of their contributions to the human economy, 
 yet there is much which we do not know. When the body 
 is deprived for a considerable time of certain salts and acids, 
 it becomes weak and diseased (scurvy), but we do not know 
 in what the efficacy of the acids and salts consists. We can 
 only infer that they influence the cells and enable them to do 
 their work better. Again, up to a certain point an increase 
 of exercise for the cells of the body means an increase of 
 power, and apparently their full power is not reached unless 
 this opportunity for practice and exercise is given them. 
 When thus exercised they become larger as well as more 
 effective. Other tissues than those exercised also feel the 
 stimulus. This is especially true of the exercise of the mus- 
 
ANIMAL HEAT— HEAT CONTROL. 299 
 
 cles, which seems able, by making indirect demands upon the 
 other cells <>f the body, to bring about the full development 
 of all. Even the passive tissues, such as hone and tendon, 
 are influenced through muscular exercise. 
 
 Animal Heat. — Cellular a< tivity produces energy in forms 
 useful to the body, including heat. We have seen that a 
 certain amount of heat is necessary, since all the tissues of the 
 body work best at a temperature of 39 C. (98 .5 F. ). It 
 is easily demonstrated that under normal conditions the tem- 
 perature of the body remains constant at this optimal temper- 
 ature throughout life. 
 
 Muscular activity furnishes far more heat than any other 
 form of activity in the body. It has been found by experi- 
 ment that of the potential energy set free in the oxidation of 
 material in the muscles two thirds appear as heat, whereas only 
 one third does work as muscular energy. Heat is, therefore, 
 developed in proportion to the amount of muscular work 
 done, and in hard work a much larger amount of heat is pro- 
 duced than is necessary to maintain the body temperature. 
 This excess of heat becomes a waste product which must be 
 got rid of in order to prevent a rise in body temperature 
 (fever). 
 
 Heat Control. — A definite mechanism for the control of 
 the heat loss exists in the body to insure the maintenance of 
 the best temperature. The heat is carried by the blood from 
 the heat-producing centres, muscles, glands, etc., to all parts 
 of the body, including exposed inactive tissues, such as the 
 skin, lungs, ears, nose, fingers and toes. The presence of an 
 excess of heat reflexly stimulates the blood vessels of the skin 
 to dilate and the perspiratory glands to secrete. The result 
 is that a large mass of blood is thrown into contact with the 
 cooler surface of the body, which is being still further cooled 
 
3oo THE HUMAN BODY. 
 
 by the evaporation of the moisture. The blood rapidly loses 
 its heat and goes back to the interior parts of the body 
 cooler, again to take up the heat, carry it to the surface and 
 get rid of it. An increased amount of heat is also got rid of 
 by the lungs during the more rapid breathing accompanying 
 severe work. 
 
 During rest a reverse process takes place. The blood ves- 
 sels of the skin reflexly contract, keeping the blood within 
 the interior of the body, which is now protected from heat 
 loss by a thick layer of skin and fat. This process of vaso- 
 motor control has been likened to the taking off and putting 
 on of an overcoat. Cold blooded animals are without this 
 mechanism and have a variable temperature, dependent upon 
 that of the medium in which they are. In summer a frog 
 may have a temperature of ioo° F. , in winter of 33 or 
 
 Fever. — In the condition known as fever, the temperature 
 of the body is raised above the normal. This is thought to 
 be due in most cases to the following factors : first, reduction 
 in the amount of perspiration which ordinarily accompanies 
 fever (dry skin /, hence diminished heat loss through its 
 evaporation ; second, increased production of heat by un- 
 usual activity and consequent heat formation in the tissues ; 
 and third, disarrangement of the heat-controlling nerve 
 mechanism. 
 
 Fever is not primarily a disease, but a symptom of several 
 diseases, and depends upon varying factors rather than upon 
 any particular set of conditions. 
 
 Internal Secretion of Glands. — We have seen that some 
 glands secrete fluids which they carry through ducts to sur- 
 faces more or less remote from themselves. There are certain 
 glands of the body, as the spleen, the thyroid gland, etc., 
 
1NTF.RN.-H. SECRETION Of GLANDS, 301 
 
 which have no du< ts and whose onl) conne< tion with the 
 of the bod} is b) means of the blood passing in through the 
 artery and out through the vein; hence their secretion must 
 be given to the bio "1 to be < arried to th< of the body 
 
 (internal secretion). This makes it very diffii wit to determine 
 the ival fun< tions of these organs experimentally, since large 
 amounts of blood pass through them in twenty-four hours, and 
 substances, even if given off in considerable quantities in their 
 secretions, are so greatly dilwted as to escape detection. 
 
 The spleen is sitwated in the left side of the abdominal cav- 
 ity wnder the eleventh rib. It is a large mass of cellular tisswe 
 sw| (ported by a framework of connective tisswe, into which 
 the blood escapes from the open ends of the blood vessels in 
 its passage through it. In malaria and in certain blood 
 diseases associated with a large increase of white blood cor- 
 puscles the spleen becomes greatly enlarged. Apart from its 
 function of giving off white blood corpuscles, little is known 
 of the spleen, as it can be removed without serious results. 
 
 The thyroid gland, which lies on either side and below the 
 larynx ; the thymus gland, which is found near the thyroid ; 
 the suprarenal capsule, the small gland lying above each 
 kidney ; and the pituitary body, a very small gland lying at 
 the base of the brain, are other examples of ductless glands. 
 
 That these last named glands have important functions is 
 shown by cases of disease and by experiments made on ani- 
 mals in which the glands were removed. When the thyroid 
 gland is removed from the body, the tissues become more or 
 less gelatinous, the animal weakens and soon dies. When 
 the secreting cells of the thyroid gland are destroyed in man 
 by disease, a similar condition of the tissues follows. If the 
 thyroid glands from pig or sheep are then eaten, the tissues 
 again recover their character and strength is regained, show- 
 
3 C2 THE HUMAN BODY. 
 
 ing a definite relation between the abnormal condition of the 
 tissues and the secretion of the glands. 
 
 Removal of the suprarenal capsules leads quickly to death. 
 Disease of the capsules is associated with muscular weakness 
 and pigmentation or bronzing of the skin. Experiments have 
 shown that the secretion of these capsules is undoubtedly 
 closely associated with the vaso-motor control of blood vessels. 
 
 Removal of the pituitary body leads also to rapid death, 
 with symptoms somewhat resembling the removal of the 
 thyroid gland. Disease of the pituitary body in man is asso- 
 ciated with a curious condition of enlargement of the bones 
 of the body {giantism'). 
 
 Experiments have shown that the kidney, beside its func- 
 tion of the external secretion (excretion) of urine from the 
 blood, acts apparently as a ductless gland. When three 
 quarters of the secreting substances of the two kidneys have 
 been removed (one half of one kidney and the whole of the 
 other), the secretion of urine is carried on adequately, but the 
 animal, in spite of a voracious appetite, rapidly wastes away 
 and dies, showing that the kidney must contribute to the 
 blood substances essential to health. 
 
 Removal of the pancreas or disease affecting certain of its 
 cells leads to a secretion of sugar from the kidney (diabetes) 
 and to a rapid wasting of the body and final death. 
 
 Experiments have shown that an animal cannot survive the 
 removal of the liver, although the entire secretion of the bile 
 may be poured out on the surface of the body through a fistula 
 and lost without serious harm. This shows that its internal 
 secretion is also of extreme importance. 
 
 The essential result of interference with the internal secre- 
 tions of the glands seems to be a profound disturbance of 
 nutrition, which, though it assumes various aspects, is distinctly 
 
HEALTH DISEASE, 303 
 
 related to the power of the cells in assimilating and utilizing 
 
 food material and in performing their work. 
 
 Health. -We have seen that the < ells of the body act as 
 
 individuals in the work of the body, and that their efforts are 
 controlled by the nervous system, in order that a balanced 
 effort toward the one end of maintaining the body's effective 
 power may be obtained. We may therefore define health as 
 that condition in which the work of each cell of the body is 
 perfectly done through the proper co-ordination and balance 
 of all. 
 
 Disease thus becomes a condition in which the working 
 power of cells in a part of the body is reduced or lost or the 
 balance destroyed.* Tissue cells are hindered in their work 
 or even destroyed by certain minute unicellular parasitic 
 plants called bacteria. Some of these have the power of de- 
 veloping in the body, interfering with its balance, and 
 directly destroying the cells of the tissues. They also develop 
 poisonous substances through their own activity (pto- 
 maines),! which, when carried away by the blood, may 
 overwhelm the vital powers and finally produce death. 
 
 Immunity from Disease. — Certain diseases are commu- 
 nicated from individual to individual and are classed as 
 contagious and probably bacterial, though this has not been 
 demonstrated in the case of all. The most common are scar- 
 let fever, diphtheria, smallpox, typhoid fever, yellow fever, 
 cholera, plague, and tuberculosis (consumption). In some 
 of these diseases, as measles, mumps, and scarlet fever, one 
 
 * Some diseases are not thoroughly understood and cannot be classified 
 in this way. Most diseases, however, come within the two cl 
 named. 
 
 f These disease-producing bacteria may be grown on certain sub- 
 stance- as Ixmillon. gelatin, potato, etc. When thus cultivated they give 
 ri- to substances among the most pui^onou- known. 
 
304 THE HUMAN BODY. 
 
 attack ordinarily protects against a second attack and the 
 individual thus protected is said to be immune to them. 
 
 It has been recently shown by experiments that when the 
 blood of an animal which has recently had the disease is in- 
 jected into the blood of another animal, it will give the latter 
 immunity, even when the disease germs are inoculated directly 
 into its tissues. This has been applied in certain diseases, 
 notably diphtheria, in the following manner : — The poisonous 
 substance {toxin) developed in cultures of diphtheria bacilli, 
 and carefully filtered to remove all living bacilli, is injected 
 into a horse in successive doses, each one so small that it is 
 not fatal. After weeks or months of continuous dosing, the 
 horse is apparently perfectly well and vigorous. The serum 
 of its blood when injected into the subcutaneous lymph spaces 
 and thence absorbed into the blood of a man is capable of 
 making all the tissues of the body unfriendly to the diphtheria 
 bacilli, and of protecting the individual entirely from their 
 ravages. More than this, it may even be capable, under 
 favorable circumstances, of destroying bacilli which have 
 already a foothold and have produced the symptoms of diph- 
 theria. It is inferred that a new substance {antitoxin) has 
 been formed in the blood. The production of the antitoxin 
 is thus apparently a distinct reaction of the body to the stim- 
 ulus of the toxin in such a way as to neutralize its bad effect, 
 provided that the vitality of the tissues has not been already 
 too far lowered by an overwhelming amount of toxin. 
 
 The immunity gained by a previous attack of the disease is 
 in like manner probably due to the antitoxin developed in the 
 body as a reaction to the toxin of the disease. Since vacci- 
 nation protects against smallpox, it is probable that cowpox 
 (vaccinia) is a modified form of smallpox. 
 
 The immunity of scarlet fever, smallpox and yellow fever 
 
IMMUNITY FROM DISE 1SE. 3°5 
 
 may last for years or even for life, whereas that of diphtheria 
 is for a few weeks onl) ; of tuberculosis none has been dis- 
 covered. Whether this difference is due to the tact that the 
 antitoxin is produced by the body only during the present e of 
 the toxin | i.e. during the disease ) and that the duration of the 
 immunity depends upon the rapidity with which the antitoxin 
 i^ eliminated from the body, or that the formation of the anti- 
 toxin by the ti>sues continues, after being once started by 
 the toxin, for periods which vary in different diseases, has 
 not been determined. It is probable that the power of the 
 tissues to develop the proteetive substances is limited and is 
 perfect only in a few diseases. It may be possible, however, 
 eventually, by the use of animals for the development of anti- 
 toxins or for the modification of disease-producing bacilli, to 
 stamp out contagious diseases by giving immunity, as has 
 been done in the case of smallpox. 
 
APPENDIX A. 
 
 EMERGENCIES. 
 
 SUFFOCATION. 
 
 Suffocation — Gas Poisoning. — In cases where a person is 
 deprived of oxygen, the vital powers may become so much 
 depressed that life appears extinct. This may be due to in- 
 terference with the act of breathing; to the presence of gas, 
 as carbon dioxide or illuminating gas, in such quantities as 
 to displace the oxygen : to submersion in water : or to en- 
 closure in a small space from which the oxygen is readily 
 used up in the regular process of breathing and cannot be 
 renewed. Ordinarily suffocation is complicated with poison- 
 ing by gases.* 
 
 tfment : — Remove the patient into the fresh air. Dash 
 cold water into the face, slap the chest and tickle the nose. 
 Hold ammonia under the nostrils or take the tongue in a dry 
 handkerchief and every four seconds draw it out with moder- 
 ate force. If these measures fail to re-establish breathing, 
 artificial respiration must be immediately undertaken. 
 
 Artificial Respiration is used in all cases of suffocation 
 and drowning in which natural respiratory movements have 
 
 * Illuminating gas contains the very poisonous ga.s. carbon monoxide, 
 which unites with the haemoglobin of the blood to displace the oxygen in 
 the red corpuscles. 
 
 307 
 
3° S EMERGENCIES. 
 
 ceased. If an individual lias been under water, the lungs 
 are naturally filled with water and should be at once emptied. 
 Turn him on his face, clasp your hands under the lower 
 chest and raise him from the ground : the pressure upon 
 the lower chest will compres> the lungs and tend to empty 
 them of water. Repeat two or three times, taking care not 
 to injure the face by rough handling. Do not, however, 
 delay artificial respiration in the attempt to remove all of the 
 water. 
 
 Wipe out the mouth and throat. Turn the patient over on 
 his back with something under his back and shoulders so that 
 the head will rest well back. Pass a pin through the tip of 
 the tongue. Draw the tongue out from the mouth ; pass a 
 string around it back of the pin, cross it over the chin and 
 tie it behind the head so that the tongue will be held for- 
 ward and will not close the air passage into the larynx.* 
 Loosen the clothing, and, if wet, cover it with dry. 
 
 Place yourself at the head of the patient, grasp his fore- 
 arms near the elbow and carry them upward so that they lie 
 parallel at each side of his head (Fig. 146;. Let them rest 
 there for a moment : notice that air enters through the nose 
 and mouth. Then carry the arms back and press them upon 
 the chest | Fig. 147) : notice that air is expired. Repeat 
 this regularly every three or four seconds. 
 
 After five or ten minutes of artificial respiration, it may be 
 best, if in winter, to remove the patient to a warm place. 
 During the time of removal continue, if possible, artificial 
 respiration and especially rhythmic pressure in the region of 
 the heart every one or two seconds, since this may tend to 
 
 * This is necessary only when no one else is present to hold the 
 tongue. If two are present, friction upon the limbs should also be em- 
 ployed. 
 
SUFFOCATION. 
 
 3°9 
 
 keep tlu- blood in circulation and carry aerated blood from 
 the lungs to the tissues. 
 
 Fig. 146.— Showing position for inspiration. 
 
 Fig. 147. — Showing position for expiration. 
 
 Hot water applied to the heart stimulates its action, and 
 an electric battery, one pole of the induction coil applied to 
 
3 1 o EMERGENCIES. 
 
 the back of the neck and the other to the region of the dia- 
 phragm, may also be useful for this purpose. 
 
 Warm water may be injected into the rectum, ioo~ F., to 
 aid in restoring the heat of the body. Hot cloths, hot water 
 bottles, hot bricks, etc., should also be applied externally as 
 soon as possible, but burns should be avoided. 
 
 Stimulants may be given by the mouth if the patient is able 
 to swallow ; if not and the heart is still beating, they will, if 
 given in the rectum, be absorbed and carried by the blood to 
 the respiratory and cardiac centres. 
 
 Artificial respiration should be continued for one or two 
 hours if necessary, as there is always hope if the pulse or 
 heart beat can be detected. After treatment, avoid shock by 
 keeping the patient quiet in bed and use stimulants as freely 
 as needed. Persons have been saved after being under water 
 as long as twelve to fifteen minutes. 
 
 Choking. — Solid objects too large to be swallowed or ac- 
 cidentally caught in the larynx lead by their presence to reflex 
 spasms of the epiglottis and closure of the respiratory tract. 
 The result is a more or less complete but usually temporary 
 suffocation. Distress and violent coughing are prominent 
 symptoms. 
 
 Treatment : — Strike the patient strongly with the flat of 
 the hand on the back. Lay him on a bed or chairs with the 
 head and upper part of the chest hanging over. Let him 
 take a full breath and then make sudden pressure on the back 
 as he expires. In a child, raising by the feet may aid in dis- 
 lodging the object. If ineffective, do not waste time, but 
 pass the finger down the throat, taking the precaution to in- 
 sert a folded handkerchief between the teeth to avoid being 
 bitten. An ordinary finger is long enough to reach to the 
 larynx, and the object may be felt and removed. An emetic 
 
UNCi WSCIOUSNESS. 3 1 1 
 
 of mustard water is sometimes effective if the object has not 
 passed too far. Avoid exhaustion of patient in the attempts 
 at removal, since objet ts which can pass through the oesoph- 
 agus by the larynx will do no harm if they are assisted in 
 their passage by masses of food with large waste, as potato and 
 turnip. 
 
 At times children are taken suddenly with croup, the symp- 
 toms of which resemble those of choking. (live the child 
 warm water or, better, a teaspoonful of syrup of ipecac, and 
 repeat until vomiting occurs. Apply hot water, ice, or mus- 
 tard plasters to the throat. Send for the doctor. 
 
 UNCONSCIOUSNESS. 
 
 Symptoms and Treatment. — Unconsciousness may be 
 caused by so many conditions that it is well to examine a 
 person who is unconscious to determine the cause, if it is not 
 known. The general treatment for unconsciousness maV be 
 begun while the examination is being made. 
 
 Send for a physician. 
 
 Place the patient on his back. Loosen the clothing about 
 throat and chest. Give him plenty of fresh air, and if the 
 breathing has ceased while the pulse is still felt, apply arti- 
 ficial respiration. Do not give stimulants if the face is flushed 
 or if the pulse is strong, since they increase the heart's action 
 and, in case of ruptured blood vessels in the brain, the bleed- 
 ing and consequent injury of the brain tissue. If the temper- 
 ature of the body is raised, apply wet cloths or ice. Note if 
 there is fracture of bones, including ribs, collar bone, and 
 skull. Run the fingers down the spinous processes of the 
 vertebrae and note if they are uniformly distributed in a 
 
3 1 2 EMERGENCIES. 
 
 straight line. Open the eyes and see if the pupils are dilated, 
 contracted or equal in size. Note odor of breath. 
 
 Unconsciousness may be due to (a) narcosis by ether, 
 chloroform, opium, morphine, chloral, aconite, etc., the 
 treatment of which is given under Poisons, below ; (b) faint- 
 ing; (c) sunstroke; (d) convulsions; (e) alcohol poisoning; 
 (_/") concussion of brain ; (g) epileptic attack; {h) apoplexy. 
 
 Fainting. — The pulse is found weak, the face pale. 
 
 Treatment : — Place patient upon his back, with the head 
 and chest lower than the rest of the body. If there is vom- 
 iting, place him upon his side. Apply smelling salts, or give 
 ammonia, strong coffee, brandy or whiskey. Insure plenty 
 of fresh air by fanning, and avoid excitement. 
 
 Sunstroke. — When working on a hot sunny day, or on 
 warm days when the air is full of moisture, persons are some- 
 times overcome with the heat, having headache, weakness, 
 and difficulty of vision. The individual quickly becomes un- 
 conscious, and may even fall so as to be injured. The body 
 is usually hot to the touch, the skin dry, the face flushed, the 
 pulse full and rapid, but there may be coldness, pallor, and 
 weak pulse. Twitchings of the body may also be noticed. 
 
 Treatment : — Reduce the heat of the body as rapidly as 
 possible by throwing cold water over the patient and applying 
 ice to the head. Strip the body and wrap it in a sheet kept 
 wet by frequent applications of water. Continue until con- 
 sciousness is regained or the temperature of the body is 
 lowered. Do not send the patient to his home or to a hos- 
 pital until after the treatment has been begun. If the patient 
 does not exhibit symptoms of high temperature, but shows 
 pallor of face and weak pulse, do not use cold applications, 
 but give rest, quiet, food and stimulants in cautious amounts. 
 
Uh i h )l SNliSS. 
 
 Convulsions.— Children may have these atta< k> as a result 
 of disorders of the stoma* h, or of fever. 
 
 Treatment : — Keep the child from injuring himself. Put him 
 into .1 warm bath or wrap him in a blanket dipped into hot 
 water. Keep the head cool 1>\ applying cold water or ice. 
 If the convulsions continue, give an emetic, as a teaspoonful 
 of syrup of ipecac, if the child can swallow. Assist vomiting 
 by thrusting the finger down the throat or by using a feather. 
 ( rive injection of soap and warm water, as the seat of irritation 
 may be in the lower bowel. 
 
 Alcoholic Poisoning — Drunkenness. — The pulse is full or, 
 later, weak. The breathing is natural, the pupils of eyes of 
 equal size, and when the eye is touched the eyelid will close 
 immediately. The patient can usually be roused to speak. 
 Alcoholic odor in the breath is always present, but is not an 
 infallible symptom. The diagnosis of intoxication should not 
 be made unless it is an absolutely clear case, since many per- 
 sons have died from apoplexy or head injury when they were 
 supposed to be drunk. 
 
 Treatment : — If the patient has not already vomited, turn 
 him on his face and raise him with clasped hands under the 
 abdomen. If not effective, give an emetic of mustard water. 
 If there are symptoms of collapse, as cold skin and feeble 
 pulse, apply heat and give stimulants, as ammonia, coffee, 
 or strychnia. 
 
 Concussion of Brain.- — Unconsciousness may be due to a 
 blow on the head which produces temporary unconsciousness, 
 or gives rise to compression of the brain by fracture of the 
 skull or by bleeding due to laceration of brain tissue. The 
 symptoms are more or less similar to those of apoplexy. 
 Bleeding from the ear shows that there has been a fracture of 
 the base of the skull. 
 
3 14 EMERGESClES. 
 
 Treatment • — Keep the patient in a cool quiet place, with 
 the head slightly raised. Avoid strong light and all excite- 
 ment. Loosen the clothing. If the body is cold, apply heat. 
 Do not give stimulants unless the pulse is very weak. 
 
 Epileptic Attacks may come on suddenly or gradually 
 with symptoms which the patient recognizes. Loss of con- 
 sciousness may be accompanied by a peculiar cry, sudden 
 pallor of the face, and more or less stiffening of the body. 
 The tongue is sometimes bitten and the eyes have a peculiar 
 upward rolling motion. An attack usually lasts for a minute or 
 two only, but several attacks may follow each other rapid'.y. 
 
 Treatment: — Keep patient from injuring himself, but do 
 not struggle with him. Allow him to lie flat, and put a piece 
 of folded cloth between the teeth to prevent biting of the 
 
 _ :e. The muscular contractions if prolonged give lis 
 exhaustion and lameness, but these may be lessened by putting 
 the patient into a bath of warm water. After the attack put 
 him to bed and if nece-sary use stimulants in small quantities, 
 attacks are seldom serious, and it is usually unneces- 
 sary to do anything except prevent bodily in; 
 
 Apoplexy is due to bleeding from a ruptured blood v- 
 in the brain and consequent pressure of the blood upon the 
 brain tissue. The nerve cells or nerve fibres when pre 
 upon cease to perform their functions and more or less un- 
 consciousness and paralysis result. The face is flushed, the 
 pupils of the eyes more or less dilated and perhaps unequal 
 in size, the breathing slow, irregular, and noisy, the cheeks 
 puffed out and drawn in with the air movement, and the 
 pulse slow and full. There may be also convulsions and 
 vomiting. An important symptom is one-sided paralysis. 
 Notice whether the face is drawn to one side away from the 
 paralvzed side) or the head kept on one side. 
 
POISONS. 3 1 5 
 
 Treatment : —Keep the patient absolutely quiet, lying down, 
 
 the head moderately raised. Apply < old water or ice to the 
 head. If the patient can swallow, give castor oil or a dose 
 of salts. The bowels may be emptied by giving injection of 
 soap and warm water. Do not give stimulants. 
 
 POISONS. 
 
 General Treatment : 
 
 i ) Send for the nearest doctor 
 
 2) Empty the stomach by the use of 
 
 a) Emetics to produce vomiting : 
 
 Tickle throat with finger or feather. 
 
 Mustard water, tablespoonful to tumbler of 
 tepid water. 
 
 Salt water, tablespoonful to tumbler of tepid 
 water. 
 
 Zinc sulphate, 20 to 30 grains to half a tumbler 
 of tepid water. 
 
 Copper sulphate, 10 grains to 2 ounces of warm 
 water. 
 
 Ipecac, 30 grains of powder or 2 tablespoonfuls 
 of the wine or the syrup of ipecac. 
 
 Cauiiim : Emetics are valueless when taken 
 after substances which produce anaesthesia of 
 throat and stomach and after powerful cor- 
 rosives (as opium, morphine, carbolic acid, 
 aconite, cocaine, strong acids and alkalies), 
 have had time to act. 
 t>) Stomach tube. Use any rubber tube two feet or 
 
 more in length by one half inch diameter. In 
 
 introducing it, avoid the larynx and get the 
 
$16 EMERGENCIES. 
 
 patient to make swallowing movements. Meas- 
 ure on the tube the distance trom the stomach 
 to the mouth with the head thrown back, and 
 insert only enough of the tube to reach the 
 stomach, so as to avoid perforation in case of 
 corrosion. Pour water through a funnel into 
 the tube ; then drop the end of the tube and 
 press upon the abdomen to force out the con- 
 tents of the stomach. This may be repeated 
 and neutralizing substances introduced, alkalies 
 for acids, acids for alkalies. 
 
 3) Give antidotes : 
 
 a) Chemical (which destroy the power of the poison). 
 
 (See Special Poisons.) 
 b~) Physiological (which neutralize the constitutional 
 
 effects of the poison ; for example, stimulants). 
 
 4) Give diluents (which dilute and hence weaken the power 
 
 of corrosives, water, milk or any harmless fluid). 
 
 5) Give demulcents (which tend to coat over the poisons, 
 
 or furnish a protective coating to the stomach, or by 
 their coagulation entangle the poison; for example, 
 milk, white of egg, boiled starch, mucilage, boiled 
 slippery elm bark). These are particularly valuable 
 in the case of corrosive and irritant poisons 
 Constitutional Treatment : 
 
 1) Stimulants (which increase the power of the heart and 
 overcome weakness and depression): 
 Aromatic spirits of ammonia or water of ammonia, 
 
 tablespoonful in half glass of water ; frequent small 
 
 doses. 
 Alcohol, one or two teaspoonfuls in two ounces of 
 
 water, or twice as much whiskey or brandy. 
 
COMMON POISONS AND THEIR ANTIDOTES. 317 
 
 Coffee, in strong solution. 
 
 Vapor of ether inhaled or one teaspoonful in cold 
 
 water. 
 Tincture of nux vomica, five to ten drops in water ; 
 
 or strychnia J,, to ,.'„ grain. 
 Stimulants arc not absorbed from the stomach if 
 
 there is much corrosive action, as in the case 01 
 
 strong acids and alkalies ; they may then be given 
 
 by the rectum. 
 
 2) External heat (of special value in depression). 
 
 Apply warm blankets, hot water bottles, hot bricks, 
 
 etc. 
 Caution : In case of more or less complete loss of 
 consciousness, apply nothing hot enough to burn. 
 
 3) Friction (to aid depressed circulation). 
 
 Rub toward the heart in order to aid the venous re- 
 turn. Keep the patient in a horizontal position, 
 or, in case of profound depression, with the head 
 and chest lower than the rest of the body. Sud- 
 den raising of the head should always be avoided. 
 
 COMMON POISONS AND THEIR ANTIDOTES. 
 
 Irritant Poisons (more or less corrosive) : 
 
 Arsenic (paris green, Fowler's solution, arsenious acid, 
 some vermin killers). 
 
 Precipitated oxide of iron, made by precipitating any 
 solution of iron with ammonia, washing soda or any 
 strong alkali in solution. Wash precipitate with 
 water through a cloth. Give two or three tablespoon- 
 
3i8 EMERGENCIES. 
 
 fuls. If the iron precipitate cannot be obtained 
 immediately, give moistened plaster of wall which will 
 mix with the poison and serve to protect the stomach. 
 Wash out stomach. 
 Phosphorus (matches, Rough on Rats). 
 Emetics: magnesia, plaster from wall. 
 Empty stomach. 
 
 Caution: Do not give oily substances as milk, etc. 
 Corrosive sublimate (mercuric bichloride, bug poison). 
 
 White of egg ; emetics. Wash out stomach. 
 Iodine (tincture). 
 Starch (boiled). 
 Lead (paints, hair dyes). 
 
 Sulphates (Epsom salts, Glauber's salts, alum), emetics, 
 etc. 
 Cantharides (Spanish fly, irritant liniments). 
 Demulcents, diluents, camphor, and opium. 
 Caution: Avoid fat or oil. 
 Corrosives : 
 
 Acids [sulphuric acid = oil of vitriol (H 2 S0 4 ); hydrochloric 
 acid — muriatic acid (HO); nitric acid (HN0 3 )] . 
 Water, dilute alkalies, lime water, soap solution, tooth 
 powder, chalk or plaster of wall, followed by demul- 
 cents. Wash out stomach. 
 Carbolic acid. 
 
 Water, sulphates (Glauber's or Epsom salts) or alum. 
 Roll patient to prevent corrosive action. Wash out 
 stomach. 
 Oxalic acid. 
 
 Lime or chalk. Stimulants as needed. Wash out 
 stomach. 
 Alkalies [caustic soda = sodium hydroxide (NaOH); caustic 
 
COMMOS POISONS AND THEIR ANTIDOTES. 3*9 
 
 potash = potassium hydroxide I K< >H): ammonia = am- 
 monium hydroxide (NH 4 OH)]. 
 
 Dilute acid, vinegar, bard cider, lemon or orange 
 juice, followed by demulcents. 
 Narcotics : 
 
 Opium (laudanum, paregoric, morphine, black drops, 
 McMunn's elixir, soothing syrups, cholera mixtures, 
 Dover's powder). 
 
 Solution potassium permanganate, ioto 15 grains in half 
 a glass of water. Wash out stomach. Tannic acid, 
 strong hot coffee, strychnia, fo to T V grain. 
 Electric battery. Keep awake by non-exhausting 
 means. Perform artificial respiration and maintain 
 body temperature. 
 
 In opium poisoning a distinguishing symptom is 
 pin-head contraction of the pupils of the eyes. 
 Chloral hydrate (chloral, knock-out drops). 
 
 Treatmen tsame as for opium. 
 Aconite. 
 
 Wash out stomach. Stimulants, as coffee, ammonia, 
 
 alcohol. 
 Tobacco (snuff). 
 
 Tea or coffee, vinegar, and stimulants. Heat and 
 friction. 
 Ether and chloroform. 
 
 Lower head and chest. Use artificial respiration. 
 Stimulants, especially ammonia, nux vomica or 
 strychnia. 
 Nux vomica (strychnia). 
 
 Vapor of ether or chloroform, to control the spasms. 
 Bromide of potassium or sodium (20 to 30 grains), 
 
3*0 EMERGENCIES. 
 
 chloral (20 grains) or morphine (£ to ± grain). Give 
 in rectum if patient cannot swallow. 
 
 FIRST AID TO THE INJURED. 
 
 Dislocations. — When the end of a bone slips out of its 
 joint, it is said to be dislocated. Owing to the arrangement 
 of ligaments, dislocation is associated with more or less tear- 
 ing of the capsular and reinforcing ligaments and bleeding 
 from the ruptured vessels, followed by swelling and discolora- 
 tion. The swelling of the joint is apt to be so great that it is 
 wise to restore the bone as soon as possible. Compare it 
 with its corresponding joint and attempt to restore it 10 its 
 place ; if successful apply a bandage, handkerchief or cloth 
 in such a way as to keep the joint in place. It is well if the 
 joint is accessible, as the ankle, elbow, etc.. to apply a wad 
 of cloth or other soft elastic material (compress) around the 
 joint and then wind a bandage tightly over it to prevent 
 swelling. 
 
 Fractures. — A fracture or break of a bone may usually be 
 recognized by movement of the pieces or by crepitus when the 
 broken ends are nibbed together. The pieces of bone should 
 be brought as nearly as possible into their proper positions 
 and held there by splints. Sticks, umbrellas, canes, pillows 
 or folded sheets may be fastened with cords or bandages 
 along the sides of the limb to stiffen it and hold it in position. 
 To move such a patient it is necessary to put him on a board, 
 shutter or other object so that he can lie at full length and be 
 carried without jarring. An arm may be put into a sling 
 passed around the neck. A broken leg may be bound to the 
 sound one, taking care to draw the foot of the broken leg out 
 to the full length of the sound one. 
 
FIRST .UP TO THE INJURED. 
 
 321 
 
 Bleeding. — Either arteries or veins may be cut and the 
 blood thus permitted to escape. Arterial Mood is recognized 
 by its spurting. Venous bleeding is usually a slow oozing. 
 
 In case an artery is injured, it is not sufficient to apply a 
 bandage over the point of injury, but the artery must be 
 compressed at some point where it lies over a bone so that 
 the pressure may be sufficient to (lose it against the blood 
 pressure. Pressure may be applied by means of a pad of 
 
 Fig. 148. — Compression of artery in leg. 
 
 FlG. 149. — Compression of femoral 
 artery. 
 
 cloth, a smooth stone or other object bound tightly over the 
 spot. The chief points of pressure for arteries are as follows : 
 1) behind the knees; 21 the inner side of the thigh (Fig. 
 148) ; 3) the inner border of the biceps muscle in the upper 
 arm (Fig. 149). 
 
 For bleeding from veins and ordinary slight cuts, a light 
 pressure by a pad over the point of injury is sufficient. 
 
322 EMERGENCIES. 
 
 Bleeding from the nose suggests trouble with the mucous 
 membrane lining the nasal cavity, and if habitual should re- 
 ceive the attention of a physician. Profuse bleeding may 
 necessitate the application of dilute solutions of tannin or 
 alum ; if these are not successful, the nose should be plugged 
 by a physician. 
 
 Bleeding from the lungs and stomach occurs at times, but 
 is seldom fatal. Rest and quiet are essential. 
 
 Bruises and Sprains. — Apply hot water or rub vigorously 
 with fingers. 
 
 Antiseptic Treatment of Wounds. — " Catching cold " in 
 a wound means the entrance of bacteria and consequent in- 
 flammation. After carefully washing the hands with soap 
 and hot water, wash the wound thoroughly with a solution of 
 carbolic acid (3$), a solution of corrosive sublimate (1 to 
 1000), or a solution of formalin (1 to 40). If you do not 
 have these, use strong alcohol, whiskey, brandy or boiled 
 water. Then bring the edges of the wound together, hold 
 in place by a compress of baked clean cloth, and bind tightly 
 with a bandage. If treated in this way, the wound will ordi- 
 narily heal " by first intention," and need not be disturbed. 
 
 Burns and Scalds. — If slight, apply a paste of cooking 
 soda or alum. If extensive, apply Carron oil (equal parts 
 lime water and linseed oil). When a burn covers a quarter 
 of the surface of the body, it should be regarded as very 
 serious, possibly fatal, and a physician should be summoned 
 immediately. Apply vaseline, Carron oil, etc., or put into 
 bath tub with warm water to which a cup or two of salt has 
 been added. Keep the water at a temperature of 90 ° to 
 ioo° F. Watch the strength carefully and give stimulants, as 
 strychnia, coffee, alcohol, ammonia, etc., as needed.* 
 
 * When a person's clothing takes fire, roll him in wet cloths, woollen 
 
I/RST AID TO THE INJURED. 323 
 
 Pain. — Apply heat, as hot water bottle, etc., or mustard 
 
 plaster. 
 
 Stings of Insects. — Apply ammonia or soda. 
 
 Snake Bite. — I ><> not give large amounts of alcohol. Suck 
 out the poison or cauterize the wound immediately, or tie a 
 string tightly around the limb above the point of injure to 
 prevent carrying the poison into the system. Use stimulants, 
 as ammonia, coffee, alcohol, if necessary. 
 
 Poisoning by Canned Foods, Ice Cream, Salads, etc. — 
 Give an emetic, and castor oil to clear out bowels. 
 
 Foreign Body in Eye. — Take a small pencil or stick and 
 press upon the middle of the upper part of the eyelid, at the 
 same time raising the lid by means of the eyelashes with the 
 other hand. Press down the cartilage of the lid until its 
 edge swings below and exposes the inner surface. Find the 
 object and remove by making a soft moistened point of a 
 handkerchief. When no assistance can be obtained avoid 
 rubbing the eye, grasp the eyelashes and hold away from the 
 eye to permit the tears to wash the object from beneath. 
 One or two drops of a 2^ solution of cocaine may be put 
 into the eye to allay the pain after the object is removed or 
 the pain of an object which cannot be removed. Persistent 
 aching and redness of one eye usually means irritation by a 
 foreign body. 
 
 Frost Bite. — When a part of the body is frozen it should 
 be rubbed with melting snow, ice or ice water. As soon as 
 the blood returns apply cracked ice to reduce the reaction. 
 
 clothing, rug or carpet, or put out the fire with water, sand, ashes or 
 other non-burnable material. If nothing is at hand, pull off burning 
 clothing or roll him over and over to crush out the flume. When in a 
 burning building where the smoke is thick, keep the head near the floor. 
 If no escape is possible, get upon the outside of the window-sill and close 
 the window. 
 
324 EMERGENCIES. 
 
 Contagious Diseases. — Since contagious diseases are all 
 probably due to bacteria, washing serves to remove them from 
 the person, and hence aids to avoid infection. When one 
 comes in contact with a sick person he should touch him 
 only with the hands and then wash them with warm water and 
 soap immediately afterward, to avoid contaminating door 
 knobs and articles of furniture which others are liable to 
 touch. It is better to try to avoid all diseases, even whooping 
 cough, measles and mumps, since they are never without 
 possibilities of danger. 
 
 Tuberculosis (consumption ) must be considered as one of 
 the contagious diseases and should be guarded against by 
 isolation or rigid cleanliness, including the destruction of all 
 sputum by burning or with strong antiseptics. 
 
 A person who has a contagious disease should be immedi- 
 ately isolated from every one except a nurse, and the nurse 
 should also be isolated. All articles of food or clothing 
 coming from the room should be burned or disinfected. 
 
 Most contagious diseases are acquired by transferring the 
 bacteria from objects on which they have been deposited to 
 the mouth, by taking infected food, as milk or water, or by 
 inhaling them as dust. All suspicious food and water should 
 be well cooked or boiled before it is used. 
 
 Disinfection. — All unnecessary articles of furniture, dra- 
 peries, cushions, etc., should be removed from a room to be 
 occupied by a person with a contagious disease. Articles of 
 furniture and clothing which have come in contact with the 
 patient directly or indirectly should be either destroyed by 
 burning, or disinfected by boiling, or soaking thoroughly in 
 a strong antiseptic solution, such as carbolic acid or formalin. 
 The room should be disinfected by the fumes of formalde- 
 hyde generated from a solution of formalin (one liter of 
 
FIRST AID TO THE INJUR/:/). 325 
 
 formalin to 1000 cubic feet of air space). Windows and 
 
 doors should be tightly closed and sealed. 
 
 Disinfectant Solutions: 
 
 Milk of lime — one part of fresh lime to five parts of water. 
 Stir before using. This may be used for discharges in 
 typhoid, cholera, etc., and should be mixed with them 
 in sufficient amount to make them strongly alkaline. 
 After standing a half hour they may be thrown into 
 privy or sewer. Whitewashing with a freshly made 
 solution is an effective treatment for nearly all forms of 
 bacteria. 
 Chloride of lime — one pound to two and one half gallons 
 
 of water. This may be used for excreta. 
 Fumigation by sulphur is comparatively valueless. Sun- 
 light is effective for surface disinfection only. Ventila- 
 tion cannot remove all disease germs. Dusting and 
 beating of garments merely serve to scatter the germs 
 and endanger the individual who does the beating. 
 
APPENDIX B. 
 
 THE ACTION OF ALCOHOL AND TOBACCO UPON THE. 
 
 HUMAN BODY. 
 
 Introductory. — We have already seen (p. 98) that alcohol 
 is not to be regarded as either a tissue-forming or a force- 
 giving food. 
 
 By causing a transference of heat from internal parts to 
 the skin, in which the main organs of the temperature sense 
 (p. 283) are located, it produces a temporary feeling that the 
 body is warmer ; but the final result is a loss of animal heat 
 to the air, and a decrease of the temperature of the body as a 
 whole. Experiments made on men under military regimen 
 and discipline have proved that alcohol does not increase the 
 power of sustained muscular work, though it may for a brief 
 time stimulate to unhealthy activity. The relative amount of 
 energy liberated in the body for its own use may be very (airly 
 calculated by comparing the amount of oxygen absorbed by 
 the lungs on one day with the amount absorbed on another. 
 We have learned that on the days when alcohol is taken the 
 oxygen absorbed is not increased. Alcohol seizes some of 
 the oxygen which the foods and tissues would have utilized in 
 its absence; and what it takes they lose. Most authorities 
 even maintain that alcohol prevents oxidation, and therefore 
 tissue activity, indirectly as well as directly ; these experi- 
 
 3 2 7 
 
328 ALCOHOL AND TOBACCO. 
 
 menters find that it not only takes oxygen from the tissues, 
 but so influences them as to diminish their power of using 
 what it leaves. AVe may conclude that under ordinary cir- 
 cumstances alcohol is of no use as an energy-yielding food ; 
 although, since it is oxidized in the body, it would act as a 
 real food to a starving man ; or to a very sick person who 
 might be unable for the moment to absorb and digest other 
 substances. 
 
 As regards tissue-formation, alcohol cannot build up proteid 
 material, since it contains no nitrogen : and proteid material 
 constitutes the essential part of muscular, glandular, and 
 nervous tissues. There is even some evidence that alcohol 
 leads to excessive waste of such tissues : several competent 
 observers have found that its use increases the amount of 
 nitrogen waste excreted from the body. The only tissues 
 whose formation alcohol seems sometimes to increase are 
 fatty and connective tissues ; and we shall presently learn that 
 in most cases the superabundance of these tissues is deposited 
 in places where it does harm. 
 
 The study of alcohol as an article of diet leads therefore to 
 the result that (though a physician may find it useful as a 
 medicine in a crisis of disease when the system needs urging 
 to make a special effort) it cannot fairly be regarded as a food 
 when taken by persons in good health and properly nourished. 
 
 The whip applied to a horse will arouse him to call on his 
 reserve force, and perhaps carry himself and his rider safely 
 past some point of special danger; but it does not in anyway 
 nourish the horse. As regards the healthy human body 
 alcohol may be compared to a whip : an amount of it not 
 sufficient to cause drunken sleep, temporarily excites various 
 organs ; but the consequence is subsequent greater exhaustion. 
 
 So far we have learned that alcohol as a regular article of 
 
ALCOHOLIC BEVERAGES. 329 
 
 diet is, at least, useless. Were that all, we mighl regret the 
 
 annual waste of corn, barley, wheat, and fruits in its produc- 
 tion, and think the man foolish who spent his money on it. 
 In such case the matter would be one for moralists and 
 political economists to deal with, and physiologists and 
 students of hygiene might leave it alone. Unfortunately, 
 alcoholic drinks are not merely useless but positively hurtful, 
 when taken regularly, even in what is usually called modera- 
 tion. Alcohol has probably caused in the past, and is 
 certainly causing at present in civilized nations, more disease 
 and death than either bad drainage, bad ventilation, over- 
 crowding, deficient food, overwork, or any other of the con- 
 ditions prejudicial to health concerning which Physiology and 
 Hygiene warn us. The moral degradation and the physical 
 condition of the drunkard speak for themselves ; it is there- 
 fore the more insidious consequences of alcohol-drinking that 
 we shall mainly describe. 
 
 Alcohol, when pure, is a transparent colorless liquid, con- 
 taining the elements carbon, hydrogen, and oxygen (C 2 H 6 0); 
 it is lighter than water, and boils at a considerably lower 
 temperature ; is highly inflammable, burning with a bluish 
 flame ; and is the essential constituent of all fermented liquors 
 in common use. 
 
 Alcoholic Beverages include (1) ma// liquors, as beer, ale, 
 stout, and porter; (2) cider and perry j (3) wines, as claret, 
 sherry, port, champagne, and catawba ; (4) distilled spiri/s, as 
 brandy, rum, and whiskey ; and their compounds, as gin, 
 cherry brandy, pineapple rum, and so forth ; (5) Uqueurs, 
 made by adding various flavoring essences to different kinds 
 of spirits. All contain alcohol in greater or less proportion, 
 varying from over 70 volumes in the 100 in some kinds of 
 rum to less than 2 in the 100 in " small " beer. 
 
33° ALCOHOL AND TOBACCO. 
 
 The Direct Physiological Action of Pure Alcohol. — Pure 
 alcohol is a very expensive substance, mainly employed in 
 chemical experiments and in the manufacture of certain per- 
 fumes and essences. However, some clues to the action of 
 diluted alcohol on the body may be obtained by a study of its 
 action in the concentrated form. 
 
 Strong alcohol having a great tendency to combine with 
 water, rapidly extracts that substance from any animal organ 
 placed in contact with it ; as is shown by the hardening and 
 shrivelling of museum specimens placed in it. 
 
 Added to raw white of egg it coagulates it, much as if the 
 egg had been boiled : added to fresh blood it acts in a simi- 
 lar manner, coagulating the serum albumin as heat does 
 
 (P- 155). 
 
 Pure alcohol placed on the skin evaporates very rapidly, 
 
 and in so doing abstracts heat (p. 226, note), producing a 
 sensation of coolness. This is succeeded by a feeling of 
 warmth in the part, which also becomes red from temporary 
 paralysis of its blood vessels, causing them to dilate. If the 
 evaporation be prevented, as by putting a little alcohol on 
 the skin and covering it with a thimble, the alcohol acts as 
 an irritant ; it causes smarting, and finally sets up inflamma- 
 tion. 
 
 On mucous membranes alcohol acts much as on the skin, 
 but its irritant effect is more marked. Placed on the tongue 
 it causes a feeling of coolness, followed by a hot, biting sen- 
 sation, and a red congested condition of the area with which 
 it came in contact. Introduced into the stomach of a rabbit 
 or dog, where it cannot readily evaporate, strong alcohol 
 causes congestion and inflammation varying in intensity with 
 its amount. If the dose is large the animal dies almost 
 instantly, because the powerfully irritated sensory nerves of 
 
DILUTED ALCOHOL -ABSORPTION OF ALCOHOL 331 
 
 the gastric mucous membranes reflexly excite a nerve centre 
 
 which stops the heart's beat. 
 
 Diluted Alcohol docs not produce the above-des< ribed 
 
 direct actions of the pure Liquid : this latter taken into the 
 stomach acts as a powerful irritant poison, and generally 
 produces its main effects on the stomach itself. Alcohol in 
 such proportion as it exists in most alcoholic drinks exerts 
 much less local action on the gastric mucous membrane ; but 
 it is absorbed and carried in the blood and lymph through 
 the body, and if steadily taken day after day acts upon and 
 alters for the worse nearly every important organ. The 
 organ first or most seriously attacked varies with the form in 
 which the alcohol is taken, with the amount consumed daily, 
 and with the constitution of the individual. Probably no 
 one individual ever suffered from all the diseased states 
 produced by alcohol described in the following pages ; but 
 habitual drinkers are very apt to experience one or more of 
 them. The diseases produced by alcohol after absorption 
 into the blood come on so gradually (except in the case of 
 obvious drunkards) that the victim rarely perceives them 
 until serious if not irremediable damage has been done: 
 indeed, physicians have only recently come to clearly 
 recognize that men who in common phrase "were never in 
 their lives under the influence of liquor" may nevertheless 
 be drinking enough to do them grave injury. 
 
 Absorption of Alcohol. — When alcohol (so diluted as not 
 to cause active inflammation of the stomach) is swallowed, it 
 is quickly absorbed by the capillary blood vessels of the 
 gastric mucous membrane.* These pass it on to the portal 
 
 * An exception to the rapid absorption of alcohol sometimes occurs 
 when a large quantity of raw spirits is taken. Many cases are recorded 
 where men have for a wager drunk a bottle of whiskey or brandy. The. 
 
33 2 ALCOHOL AND TOBACCO. 
 
 vein, which carries it (p. 177) direct to the liver. Collected 
 from the liver by the hepatic veins, it is conveyed through 
 the inferior vena cava to the right auricle of the heart. 
 Thence it passes on in the general blood flow (pp. 167, 168, 
 177) to right ventricle, lungs, left auricle, left ventricle, 
 aorta, and by branches of the aorta to the body in general : 
 to the heart muscle (by the coronary arteries, p. 169), to the 
 brain and spinal cord, to the muscles, to the kidneys, to the 
 skin. We have to study its action on all these organs. 
 
 The Primary Effects of a Moderate Dose of Diluted 
 Alcohol, as a glass of whiskey and water, on one unaccustomed 
 to it, are to cause temporary congestion of the stomach ; 
 dilatation of blood vessels of the skin, indicated by the 
 flushed face; a more rapid and forcible beat of the heart \ * 
 nervous excitement, exhibited by restlessness and talkative- 
 ness. Then some incoherence of ideas, and often giddiness. 
 Finally there is a tendency to sleep. On awaking the person 
 has some feeling of depression, not much appetite, and is in 
 general a little out of sorts for a day. 
 
 If the dose be larger the stage of giddiness is accompanied 
 by diminution of the sensibility of the skin, and imperfect 
 control over the voluntary muscles, indicated by defective 
 articulation and a staggering gait. The muscles moving the 
 eyeballs cease to work in harmony. Normally they act 
 unconsciously, turning the eyes so that images of objects 
 looked at are focused on corresponding points of the retinas, 
 and objects are seen single. Soon after the voluntary move- 
 result is often sudden death, but sometimes no effect is noticed for fifteen 
 or twenty minutes ; then there is a sudden unconsciousness, passing into 
 stupor, which ends in death. In such cases the large quantity of strong 
 spirits seems temporarily to paralyze the absorbing power of the stomach. 
 
 *It is doubtful if chemically pure alcohol diluted with water quickens 
 the pulse ; most ordinary alcoholic beverages, however, undoubtedly do. 
 
SECONDARY EFFECTS OF ALCOHOL. 333 
 
 ments arc affected the involuntary regulation of the eye- 
 muscles is impaired, and objects are seen double, the eye- 
 balls being no longer so turned as to bring images on 
 corresponding retinal points. The stomach may also be so 
 
 irritated as to lead to vomiting. Then comes deep drunken 
 sleep ; followed by headache, loss of appetite, and prostration 
 similar to, but more marked than, that occurring after the 
 smaller dose 
 
 If the alcoholic indulgence be repeated, day after day, 
 some of the above-described primary consequences become 
 less marked ; but they give way to more serious functional 
 and structural diseases. 
 
 The Secondary Effects of Alcohol vary much in intensity 
 with the form in which it is taken ; also, no doubt, with the 
 constitution of the person taking it, and with the length of 
 time during which he has been drinking. We shall consider 
 them in three groups : I. Comparatively slight and curable 
 diseased states due to what is commonly considered moderate 
 drinking. II. Severe acute alcoholic diseases. III. Chronic 
 and usually incurable morbid states, due to steady, prolonged 
 drinking ; these fall into three main subdivisions : a. Gen- 
 eral tissue deterioration ; b. Destruction, more or less com- 
 plete, of certain organs ; c. Deterioration of mind and 
 character. 
 
 I. Minor Diseased Conditions produced by Moderate 
 Drinking. — Of these, alcoholic dyspepsia is the most frequent. 
 A vast number of persons suffer from it without knowing its 
 cause, people who were never drunk in their lives, and con- 
 sider themselves very temperate. " The symptoms vary, but 
 when slight are something like these : A man (or woman) 
 complains of slight loss of appetite, especially in the morning 
 for breakfast; feels languid either on rising or early in the 
 
334 ALCOHOL AND TOBACCO. 
 
 day ; retches a little in the morning, and perhaps brings up a 
 little phlegm only, or may actually vomit ; or may be able to 
 take breakfast, but feels sick after it. Towards the middle of 
 the morning he is heavy and languid, perhaps, and does not 
 feel easy until he has had a glass of sherry or some spirits ; 
 then gets on pretty well, and can eat lunch or dinner. Or 
 if worse, the appetite for both is defective, and there is 
 undue weight or discomfort after meals. . . . Now all 
 these symptoms may be due to other causes, but when taken 
 together they are by far most commonly due to alcohol." * 
 
 Another frequent result of regular "moderate" drinking 
 is tremor, or shakiness of the hands. The hand is unsteady 
 when the arm is folded, and is seen to tremble if it be held 
 out with the arm extended. This tremor is very marked in 
 the alcoholic disease known as delirium tremens (p. 335). 
 Even in its simple form it interferes with the performance 
 of any action calling for manual dexterity. The trembling 
 may, in most cases, be stopped for a time by an extra glass ; 
 and thus often leads to the acquirement of more serious 
 diseases. 
 
 We class the above as minor diseased conditions, because 
 in most cases they occur before the will power is seriously 
 impaired, and abstinence from alcohol is soon followed by 
 recovery. 
 
 II. Acute Alcoholic Diseases. — A single large dose of 
 alcohol, or the repetition of small doses at short intervals, 
 ends in a fit of drunkenness. 
 
 The disgusting appearance of a drunken man, the loathing 
 
 which he excites even in those most attached to him, the loss 
 
 of control over his actions, which makes him the prey of 
 
 criminals, or, yet worse, a criminal himself, taken together 
 
 * Dr. Greenfield, in "Alcohol : its Use and Abuse." 
 
DELIRIUM IRHMF.NS-niPS0M.-1NM. 335 
 
 make a picture to which the physiologist need add nothing. 
 A man not deterred by its contemplation will not be hindered 
 in the indulgence of his appetite by any argument based on 
 injury to his health. 
 
 Delirium Tremens. — Repeated drunkenness usually ends 
 in an attack of delirium tremens, but this disease is more 
 frequently the result of prolonged drinking which has never 
 culminated in actual drunkenness. It is especially apt to 
 occur in " those who drink hard, but keep from actual loss of 
 consciousness, especially those engaged in hard mental work 
 or subjected to great moral strain or shock ; and, too, those 
 of certain temperaments are peculiarly liable to it. It is 
 preceded, usually, by loss of sleep, ideas of persecution or 
 injury, with no foundation in fact, and slight hallucinations, 
 especially at night ; the man, meanwhile, in the day looking 
 anxious, slightly excited, nervous and tremulous, and perhaps 
 narrating as actual occurrences the hallucinations of the pre- 
 ceding night. Then the senses are partly lost ; he sees spec- 
 tres, horrible and foul creatures about him ; has all sorts of 
 painful, terrifying visions (whence the common name of the 
 1 horrors ' ); is extremely tremulous, and either excited or lies 
 prostrate, trembling violently on movement, sleepless, anx- 
 ious, and a prey to spectres and terrors of the imagina- 
 tion." * 
 
 Few persons die in their first attack of delirium tremens, 
 but it is nature's unmistakable warning to the tippler; let 
 him not disregard it, unless he is prepared to die without 
 hope in maniacal imaginings so frightful that those around 
 his death-bed can never recall the scene without horror ! 
 
 Dipsomania is often confounded with delirium tremens ; 
 but though it may lead to that disease it is an essentially 
 * Dr. Greenfield, in "Alcohol : its Use and Abuse." 
 
3S 6 ALCOHOL AND TOBACCO. 
 
 different pathological state. The word properly means a 
 mental disease in which there is periodically an irresistible 
 passion for alcohol ; in any form, no matter how distasteful, 
 the dipsomaniac will swallow it with avidity. The disease 
 is sometimes produced by indulgence in drink, but is more 
 often inherited, especially from parents addicted to alcoholic 
 excess. In the families of such, one child is often epileptic, 
 another idiotic, a third eccentric or perhaps quite mad, and 
 a fourth a dipsomaniac. When the fit seizes him the dipso- 
 maniac is as irresponsible as a raving madman. His only 
 safeguard against a frightful debauch is to place himself 
 under restraint as soon as he perceives the symptoms which 
 he has learned to recognize as premonitory of his fit of mad- 
 ness. After a time the paroxysm passes off; the patient 
 regains self-control, loses his passion for drink, is greatly 
 ashamed of himself if he has indulged it, and usually behaves 
 in an irreproachable manner for some weeks or months. 
 
 The sufferers from this frightful disease are entitled to a 
 sympathy to which the common drunkard has no claim. 
 
 III. Chronic and often Incurable Diseased Conditions 
 produced by Alcohol. — These are apt to be insidious in their 
 approach, and overlooked until they have firmly seated 
 themselves. They include (a) deterioration of tissue ; (3) 
 practical destruction of important organs ; (c) mental and 
 moral enfeeblement. 
 
 (a) Deterioration of Tissue due to Alcohol. — A serious 
 structural change in the body produced by alcoholic excess 
 is fatty degeneration. The oily matter of the body exists in 
 two forms : first, as adipose or fatty tissue collected under 
 the skin, and in less amount elsewhere, as on the surface of 
 the heart and around the kidneys ; second, as minute fat- 
 droplets in the interior of various cells and fibres. Some 
 
DISEASED CONDITIONS PRODUCED HY ALCOHOL. 337 
 
 forms of alcoholic drinks tend to increase the adipose tissue, 
 
 and may lead to undue accumulation of it about the heart, 
 impeding the action of that organ. A more important and 
 frequent result is an increase of fat -droplets in the cells of 
 the liver and the muscular fibres of the heart, the oily matter 
 replacing the natural working substance. A heart which has 
 undergone this change is commonly spoken of by patholo- 
 gists as a " whiskey heart "; for although fatty degeneration 
 of the heart may occur from other causes, alcoholic indub 
 gence is the most frequent one. Fatty liver or fatty heart is 
 rarely if ever curable ; either will ultimately cause death. It 
 is probable that in both cases the fatty degeneration is due 
 to over-stimulation of the organ. Most wines and spirits 
 quicken the beat of the heart, leaving it less time for repair 
 between its strokes. Alcohol also increases the breaking 
 down of proteid matter in the body ; the liver has much to 
 do in preparing this broken-down proteid for removal by the 
 kidneys, and so gets overworked. 
 
 Another serious bodily deterioration produced by alcohol 
 is fibrous degeneration : by this is meant an excessive growth 
 of the connective tissue, which, as we have seen (p. 18), per- 
 vades the organs of the body as a fine supporting skeleton for 
 the more essential cells. Alcohol-drinking causes this tissue 
 to develop to such an extent as to crush and destroy the 
 cells, especially in the liver and kidneys, which it should 
 protect. So far as the liver is concerned, the result is a 
 shrunken, rough mass {hob-nailed liver , or gin-drinker'' s liver), 
 with hardly any liver cells left in it. This not only prevents 
 the proper manufacture of bile and glycogen (p. 130), but 
 the contracted liver presses on the branches of the portal vein 
 within it (p. 177) so as to impede the drainage of blood from 
 the organs in the abdomen. As a consequence, an excess of 
 
33 8 ALCOHOL AND TOBACCO. 
 
 the watery part of the blood oozes into the peritoneal cavity 
 and accumulates, causing abdominal dropsy (asci/es). In simi- 
 lar manner the superabundant connective tissue in the kid- 
 neys crushes and injures the essential kidney substance, and 
 interferes with the proper function of the organ in excreting 
 nitrogen waste and water. The ultimate consequence is one 
 form of " Bright's disease " — a very fatal malady, character- 
 ized by elimination of albumen in the kidney secretion ; 
 retention of proteid wastes in the blood, poisoning the vari- 
 ous organs ; and accumulation of water in the loose tissue 
 binding the skin to underlying parts, producing that kind of 
 dropsy known as anasarca. 
 
 (6) The Organs of the Body most apt to be impaired or 
 destroyed by Alcohol have been in part mentioned in pre- 
 ceding pages. It will, however, be convenient to collect 
 them together and point out the kind of change produced in 
 each. Probably no tippler ever suffered from all of these 
 diseases, and most of them may develop in persons who are 
 total abstainers ; but the organic lesions which are mentioned 
 below are more frequently due to intemperance than to any 
 other cause. 
 
 A primary action of alcohol after absorption is to cause 
 dilatation of the cutaneous blood vessels. With occasional 
 alcoholic indulgence this is temporary j with repeated, it be- 
 comes permanent. The Skin is then congested and puffy, 
 and on exposed parts it is seen to have a purplish or reddish 
 blotched appearance ; pimples appear on parts, such as the 
 nose, where the natural circulation is more feeble. The result 
 is the peculiar degraded look of the sot's face. The conges- 
 tion interferes with the nutrition of the skin ; the epidermis 
 (p. 200) is imperfectly nourished and collects in scaly masses, 
 
OkGANS injured by ALCOHOL 339 
 
 interfering with the proper action of the sweat glands, thus 
 throwing undue work on the kidn< 
 
 When constantly irritated by the direct action of strong 
 alcoholic drinks, the Stomach gradually undergoes lasting 
 changes. Its vessels remain dilated and congested, its con- 
 nective tissue becomes excessive, its power of secreting gas- 
 trie juice diminished, and its mucous secretion abnormally 
 abundant. 
 
 The Liver suffers fatty and fibrous degeneration, and is 
 one of the organs most often and earliest attacked. This we 
 might expect, as all the alcohol absorbed from the stomach is 
 carried direct to the liver by the portal vein (p. 177). 
 
 The Heart has its walls at first thickened (hypertrophied) 
 and its cavities dilated by the excessive work (p. 337) which 
 alcoholic drinks stimulate it to perform. If, as is usually the 
 case, fatty degeneration ensues, the organ gradually becomes 
 too feeble to pump the blood around the body, and death 
 results. 
 
 The walls of the Arteries of drinkers frequently undergo 
 fatty degeneration ; they lose their strength and elasticity, 
 and are liable to rupture, or to the disease known as aneu- 
 rism. 
 
 The Kidneys are excited to undue activity, in part by the 
 dilatation of their blood vessels, in part, perhaps, through 
 direct stimulation of their cells by alcohol circulating in the 
 blood. Once the liver is attacked the nitrogenous waste of 
 the body is not carried to the kidneys in proper form for 
 excretion : some is held back, producing a tendency to gout 
 and rheumatism; the rest is got rid of by extra kidney effort. 
 The usual result is fibrous degeneration of the kidneys, caus- 
 ing one kind of Bright's disease. 
 
 The Lungs, from the congested state of their vessels pro- 
 
340 ALCOHOL AND TOBACCO. 
 
 duced by alcohol, are more subject to the influence of cold, 
 the result being frequent attacks of bronchitis. It has also 
 been recognized of late years that there is a peculiar form of 
 consumption of the lungs which is very rapidly fatal, and 
 found only in alcohol-drinkers. 
 
 The Sense Organs are also affected ; their acuteness of per- 
 ception is dulled, and many physicians believe that cataract 
 and retinal disease may be produced by drinking. The red 
 inflamed white of the eye of topers is well known. 
 
 The Brain and Spinal Cord are kept in a chronic state of 
 congestion* and over-excitement. This results at first in 
 inflammatorv disease {delirium tremens) ; later, in fibrous 
 degeneration, leading to certain forms of paralysis or to epi- 
 lepsy, of which there is one variety well recognized by phy- 
 sicians as due to alcohol. 
 
 (c) Moral Deterioration produced by Alcohol. — One 
 result of a single dose of alcohol is that the control of the 
 Will over the actions and emotions is temporarily enfeebled : 
 the slightly tipsy man laughs and talks loudly, says and 
 does rash things, is enraged or delighted without due cause. 
 If the amount of alcohol be increased, further diminution 
 of will-power is indicated by loss of control over the mus- 
 cles. Excessive habitual use of alcohol results in per- 
 manent over-excitement of the emotional nature and en- 
 feeblement of the Will ; the man's highly emotional state 
 
 * -I once had the unusual though unhappy opportunity of observing 
 the same phenomenon in the brain structure of a man who, in a fit of 
 alcoholic excitement, decapitated himself under the wheel of a railway- 
 carriage, and whose brain was instantaneously evolved from the skull by 
 the crash. The brain itself, entire, was before me within three minutes 
 after death. It exhaled the odor of spirit most distinctly, and its mem- 
 branes and minute structures were vascular in the extreme. It looked 
 as if it had been recently injected with vermillion." — Dr. B. IV. 
 Richardson. 
 
LOCAL ACTION OF TOBAa.o. 34 I 
 
 exposes him to special temptation to excesses of all kinds, 
 
 and his weakened Will decreases the power of resist- 
 ance : the final outcome is a degraded moral condition. 
 He who was prompt in the performance of duty begins 
 to shirk that which is irksome; energy gives place to indiffer- 
 ence, truthfulness to lying, integrity to dishonesty ; for even 
 with the best intentions in making promises or pledges there- 
 is no strength of Will to keep them. In forfeiting the respect 
 of others respect for self is lost and character is overthrown. 
 Meanwhile the passion for drink grows absorbing: no sacri- 
 fice is too costly which secures it. Swift and swifter is now 
 the downward progress. A mere sot, the man becomes 
 regardless of every duty, and even incapacitated for any 
 which momentary shame may make him desire to perform. 
 
 For such a one there is but one hope — confinement in an 
 asylum where, if not too late, the diseased craving for drink 
 may be gradually overcome, the prostrated Will regain its 
 ascendency, and the man at last gain the victory over the 
 brute. 
 
 Tobacco contains an active principle, nicotin, which in its 
 pure form is a powerful poison, paralyzing the heart. When 
 tobacco is smoked some of the nicotin is burned, but there 
 are developed certain acrid vapors which have an irritant 
 action on the mouth and throat. The effects of smoking are 
 thus in part general, due to absorbed nicotin ; and in part 
 local, due to irritant matters in the smoke. They vary much 
 with the constitution, habits, and age of the smoker. One 
 general rule at least may be laid down : tobacco is very injuri- 
 ous to young persons whose physical development is not com- 
 pleted. 
 
 The Local Action of Tobacco is at first manifested by 
 increased flow of saliva. This usually passes off after some 
 
342 ALCOHOL AND TOBACCO. 
 
 practice in smoking ; dryness of the mouth follows, and con- 
 sequent thirst, often leading to alcoholic indulgence ; and in 
 this, perhaps, lies the greatest danger from tobacco. The 
 habitual smoker usually suffers eventually from what is known 
 to medical men as "smoker's sore-throat." The inflamma- 
 tion often extends to the larynx, injuring the voice and pro- 
 ducing a hacking cough, or may spread up the Eustachian 
 tubes (p. 2 79 J and impair the hearing. Cigarettes are espe- 
 cially apt to cause these symptoms. Cure is impossible 
 unless smoking be given up. Those who draw the smoke 
 into their lungs often suffer from chronic inflammation of the 
 bronchial tubes in consequence. 
 
 The General Action of Tobacco. — The more common 
 effects of absorption of tobacco products are to interfere with 
 development of the red blood-corpuscles, leading to pallor 
 and feebleness ; to impair the appetite and weaken digestion; 
 to affect the eyes, rendering the retina less sensitive ; to 
 cause palpitation of the heart and enfeeblement of that 
 organ ; to induce a lassitude and indisposition to exertion 
 that, in view of the heavy odds man has to contend with in 
 the life-struggle, may prove the handicap that causes his fail- 
 ure. If success in life be an aim worth striving for, it is 
 surely unwise to shackle one's self with a habit which cannot 
 promote and may seriously jeopardize it. 
 
APPENDIX C. 
 
 DEMONSTRATIONS AND EXPERIMENTS.* 
 
 BONES. 
 
 Materials : Hind leg of sheep sawed lengthwise through the 
 joints. Pieces of fresh ivory bone (thin bones 
 such as are found in the legs of fowl will an- 
 swer). Pieces of dry ivory bone. 
 Reagents : Hydrochloric acid (HO) and ammonia. 
 Apparatus : Balance with metric weights from i centigram to 
 25 or 50 grams. The balance may be a small 
 hand balance carefully adjusted. 
 Human skeleton (such as may be purchased for 
 
 525 or S30). 
 Microscope. 
 
 Dissection or Demonstrations : 
 
 To be done preferably by pupils working together in pairs with speci- 
 men. 
 
 1) Structure of a long bone. 
 
 a) Position and arrangement of dense (ivory) and 
 
 cancellated bone. 
 
 b) Medullary canal. 
 
 c) Joint ends with epiphyses. 
 
 d) Articular cartilage. 
 
 * The practical work is planned to include that given in the Outline of 
 Requirements in Anatomy, Physiology and Hygiene for Admission to 
 Harvard College and the Laurence Scientific School. 
 
 343 
 
344 DEMONSTRATIONS AND EXPERIMENTS. 
 
 e) Periosteum. 
 
 f) Red and yellow bone marrow. 
 
 g) Microscopic structure of bone. 
 2) Composition of bone. 
 
 a) Boil a piece of fresh bone in water to extract 
 
 gelatin. 
 
 b) Burn a piece of fresh bone to destroy animal matter. 
 
 c) Put piece of fresh bone into solution, one part 
 
 hydrochloric acid, four parts water (let stand 
 one or two days and if necessary change the 
 solution) to remove mineral matter. 
 Experiments : 
 
 1. Proportions of water and solid in fresh bone. Break 
 piece in small fragments, weigh, dry in a current of 
 warm air to constant weight and determine loss. 
 2a. Proportions of animal and mineral matter in dry bone. 
 Weigh, burn on a piece of sheet iron over live coals 
 or on a piece of platinum foil over Bunsen burner and 
 weigh. 
 2b. Second method. Weigh, dissolve in 10$ hydrochloric 
 
 acid, dry to constant weight and determine loss. 
 Note. — Demonstrate the presence of mineral matter in the solution by 
 precipitating it with ammonia. 
 
 JOINTS. 
 
 Materials : Split joint of sheep. 
 Apparatus : Microscope. 
 Dissection or Demonstrations : 
 
 a) Capsular and reinforcing ligament. 
 
 b) Synovial membrane. 
 
 c) Synovial fluid. 
 
 d) Articular cartilage. 
 
 e) Functions of ligaments. 
 
MUSCLE. 345 
 
 MUSCLE. 
 
 Material ■ A frog. 
 
 A >licc of meat cut across the grain (a low cut of 
 
 the leg including the bone). 
 Normal silt solution, made by dissolving *\\ gms. 
 of dried table salt in i liter of water. 
 Dissection or Demonstrations : 
 
 i) Uncover muscles in frog's leg. Note 
 
 a) Outlines of muscles. 
 
 b) Tendon attachments. 
 
 c) Relations of muscles to joints. 
 
 2) In piece of beef, note 
 
 0) Muscle bundles. 
 
 b) Connective tissue boundaries of muscles and bun- 
 
 dles. 
 
 c) Surface or intermuscular tendon, if present. 
 
 3) Prepare muscle fibre by plunging a freshly killed frog 
 
 into water at 55 C. (131 F.) and allowing it to 
 
 cool. 
 
 a) Tease muscle with needles in normal salt solu- 
 
 tion. 
 
 b) Examine under microscope. 
 
 Experiment : Proportions of water and solid in muscle. (De- 
 termine as in bone (1). 
 
 MUSCLE ACTION. 
 
 Materials : Calf muscle of leg of frog with sciatic nerve 
 attached (nerve-muscle preparation). 
 
 Apparatus : Induction coil, battery and wires. A small coil 
 such as is used by physicians will answer the 
 purpose. 
 Recording apparatus (Fig. 150). 
 
346 
 
 DEMONSTRATIONS AND EXPERIMENTS. 
 
LEVERS. 347 
 
 Experiments (or Demonstrations) : 
 What results follow 
 
 a) Single electrical shock through nerve? 
 
 b) Single electrical shock through muscle? 
 
 c) Rapid succession of shocks through nerve? "Tet- 
 
 anus. ' ' 
 Demonstrations : 
 
 i) Contraction curve. 
 2) Curve of fatigue. 
 
 a) Regular stimulation at intervals of one second. 
 
 b) Tetanus. 
 Directions : 
 
 For the contraction curve, the smoked glass should be 
 moved so that the distance between the rise and fall of 
 the writing point will be one or two inches. 
 
 For the curve of fatigue, the smoked glass should be moved 
 between each contraction just enough to allow the next 
 contraction to make its own record. For tetanus, a 
 slow, continuous movement is necessary. The rapid in- 
 terruption of the current necessary for tetanus can easily 
 be accomplished by tapping the end of one wire on a 
 piece of tin connected with the other, if no key is 
 available. 
 
 LEVERS. 
 
 The leverage conditions in the body may best be studied 
 by means of an apparatus arranged to represent the action 
 in several joints (Fig. 151). 
 Apparatus : Lever apparatus. 
 Problems to be experimentally solved with the lever apparatus. 
 
 1) Apparatus arranged to represent action of biceps. 
 
 a) How much force must the biceps exert to hold a 
 
348 DEMONSTRATIONS AND EXPERIMENTS. 
 
 T 
 
 i 
 r 
 i 
 i 
 
 A 
 
 * 
 
 A 
 
 Fig. 151. — Lever apparatus for studying the mechanics of muscles, bones, and 
 joints — shown as arranged for the study of forces in the calf muscles and ankle joint. 
 The larger figure shows two connected bars, 1 and 3 : (1) represents either the bones 
 of leg or upper arm, and (3) those of the foot or arm. Another view of the joint 
 is shown in smaller figure. A brass sleeve (2) having at its lower end the joint with 
 the brass cross-arm (^) slips easily on the rod (1) and forms a part of it. The joint 
 pressure is measured by the spring scale (4) which resists the pressure of arm (3) upon 
 the hinge and sleeve. The spring scale labelled " calf " represents the calf muscle, 
 the biceps muscle, or the triceps muscle, and measures the force each is made to exert 
 according as it is attached as represented or in the position of one or the other of the 
 dotted lines. The pull may be made greater or less by moving the upper attachment 
 up or down the rod (1). The spring scale (<:) measuris the effective force of the calf 
 muscles in the position shown and may be changed to (/>') and ( T) for measuring the 
 effective forces of the biceps and triceps muscles of the arm respectively. 
 
LEVERS. 349 
 
 pound weight in the hand when the elbow forms 
 a right angle and the forearm is horizontal? 
 b) How much is the pressure in the joint under the 
 same conditions ? 
 
 2) Apparatus arranged to represent action of triceps. 
 
 a) How much force must the triceps exert to make 
 
 the hand push one pound ? 
 //) How much is the pressure at the elbow joint ? 
 
 3) Apparatus arranged to represent action of muscles of 
 
 calf of leg. 
 a) When a person of 150 lbs.* weight is stand- 
 ing on one foot, how much force must the 
 calf muscles exert to raise the heel from the 
 floor? 
 i) How much is the pressure in the ankle joint ? 
 Problems to be solved arithmetically. Each pupil should use 
 his own weight and make the necessary measurements on 
 himself or on a skeleton. 
 
 1. a) How much force do the calf muscles exert in rais- 
 
 ing the heel from the floor when standing on 
 one foot ? 
 b) How much is the pressure in the ankle joint? 
 
 2. a) How much is the muscle pull through the patella 
 
 to raise the body from a kneeling posture (the 
 
 whole weight on one leg) ? 
 b) How much is the pressure in the knee joint ? 
 3. a) How much does the biceps pull when, by flexing 
 
 the forearm, 50 lbs. are raised in the palm of 
 
 hand? 
 b) How much is the pressure in the elbow joint ? 
 
 * Use 1.5 lbs. on balance to represent the 150 lbs. 
 
35° DEMONSTRATIONS AND EXPERIMENTS. 
 
 OXIDATION. 
 
 Materials : Magnesium tape. 
 Fine emery paper. 
 Fine iron wire. 
 Oxygen. 
 Sulphur. 
 Demonstrations or Experiments ; 
 
 i ) Rub magnesium tape clean with emery paper. Cut off 
 two pieces. 
 
 a) Apply a lighted match to one ; note manifesta- 
 
 tions of energy and changes (magnesia) in 
 magnesium. 
 
 b) Place the other in a bottle with a few drops 
 
 of water ; examine in a day or so, and com- 
 pare with i) a. 
 
 2) Attempt to burn magnesia obtained from 1) a. 
 
 3) Rub the iron wire bright with emery paper. 
 
 a ) Place some in a warm dry bottle by the stove. 
 b ) Place some in a bottle containing a little water, 
 
 and in a day or so compare results with those 
 
 from 3) (7. 
 
 4) Melt a drop of sulphur on end of iron wire. Ignite 
 
 and plunge into a bottle of oxygen. 
 
 a') Note manifestations of energy. 
 
 b~) Note changes in iron and compare with 3) b. 
 
 FOODS. 
 
 Materials : Starch. Dextrin. Glucose. Fat. Sweet Oil. 
 
 Egg albumin. Cut white of egg repeatedly with 
 scissors, shake with 20 parts water and filter. 
 
FOODS. 35i 
 
 Meat juice. 1 11>. meat finely < hopped, soaked for 
 
 12 hours in four parts of water and filtered. 
 
 Peptone, freshly prepared by digesting fibrin or 
 egg albumin in an artifn ial gastric juice. 
 
 Reagents, etc. : A< etic ac id (strong vinegar). Nit- 
 ric acid. Hydrochloric acid. Ammonia. Sodic 
 hydrate. Sodic carbonate. Cupric sulphate. 
 
 Thick starch paste, made by boiling ordinary corn 
 starch. 
 
 Acid or alkali albumin, made by heating egg albu- 
 min with 5$ hydrochloric acid or with weak 
 sodic hydrate solution. 
 
 Milk. 
 
 Tests for Food Constituents * 
 
 1) Starch and dextrin, dry or (better) in solution with a 
 
 watery solution of iodine — change of color. This 
 test is most conveniently made with drops of the solu- 
 tions on a white plate. 
 
 2) Glucose, maltose or lactose solution in test tube with 
 
 half inch strong solution caustic soda and one or two 
 drops of dilute solution sulphate of copper ; shake and 
 boil — color or colored precipitate. (Trommer's test. ) 
 
 3) Fat. 
 
 a) With 1 per cent solution of osmicacid — color; or 
 
 b) By dissolving in ether and allowing to evaporate 
 
 on glass — grease spot. 
 
 4) Egg albumin or serum albumin in dilute solution. 
 
 a) Heat in test tube — opacity or precipitate ; or 
 
 b) In contact with strong nitric acid poured care- 
 
 * These tests cover the experimental work needed as a preliminary for 
 digestive experiments. The schedule will be found convenient for re- 
 cording results. 
 
35 2 
 
 DEMONSTRATIONS AND EXPERIMENTS. 
 
 fully and slowly down side of test tube — color 
 or precipitate. 
 
 5) Proteid. 
 
 a) Boil with strong nitric acid (color) ; cool and 
 
 make alkaline with ammonia — color or colored 
 precipitate (Xanthoproteic test), or 
 
 b) With strong sodic hydrate solution and one or 
 
 two drops very dilute copper sulphate — color 
 (biuret test). 
 
 6) Peptone. Biuret test — color. 
 
 FOOD MATERIALS. 
 
 Tests. 
 
 Heat 
 
 Iodine 
 
 Trommer 
 
 Xanthoproteic 
 
 Biuret 
 
 Ether 
 
 Starch. 
 
 Dextrin. 
 
 Glucose. 
 
 Fat. 
 
 Albumin. 
 
 Meat 
 Juice. 
 
 
 
 
 
 
 Peptone. 
 
 NOTE. — Students may be tested by giving them mixtures of solutions 
 or other food substances to be tested for fat, sugar, proteid, starch, etc. 
 They should be led to study the foodstuffs, as cabbage, beets, fruits, etc., 
 to determine their constituents.* They should also be encouraged to find 
 out the effects of cooking and to report to the class results of experiments 
 at home. The water in which food substances have been boiled may 
 also be studied. 
 
 Demonstrations : 
 
 1) Effect on thick starch paste of 
 
 a) Saliva, a few drops. 
 
 b) Pancreatic extract, a few drops of solution. 
 
 * Cellulose is not easily demonstrated as a food constituent. It may be 
 sometimes shown under the microscope after soaking thin sections of the 
 substances for a few minutes in a strong watery solution of iodine, washing 
 with water, transferring to dilute sulphuric acid (2 parts acid to 1 part 
 water by volume); mount the sections on the slide in acid solution and 
 examine. If successful, the cellulose is left blue. 
 
FOODS. 353 
 
 2) Kitc< t of neutralizing the acid or alkali albumin by 
 
 addition of weak sodic hydrate solution or by the 
 addition of weak acid solution. Color with litmus 
 solution in order to determine neutral point. 
 
 3) Typical emulsions under a microscope: 
 
 a) Milk. 
 
 /') Oil which has been shaken with solution of pan- 
 creatic extract of bile. 
 Experiments ; Typical foodstuffs. 
 
 1) Milk. 
 
 a) Determine specific gravity with hydrometer. 
 
 b) Determine reaction by adding a few drops of lit- 
 
 mus solution. 
 
 c) 1) Warm milk in small beaker, add drop by drop 
 
 a dilute solution of acetic acid, constantly 
 stirring, until precipitation (casein and fat); 
 filter; test filtrate by Trommer's test (lac- 
 tose). 
 2) Dry residue by squeezing it in the fingers, add 
 to a small portion of it an equal amount of 
 ether, allow it to stand a few minutes, put a 
 drop of the ether from it upon a watch glass 
 and allow to evaporate (fat) ; remove ether 
 from the residue and test latter by the Xan- 
 thoproteic test. 
 
 2) Flour. Moisten one teaspoonful of flour and tie the 
 
 dough in a piece of muslin. Knead thor- 
 oughly, first in a small vessel containing 
 water, saving the w r ater, and, second, in 
 running water until the water is no longer 
 colored. 
 a) Determine what was washed out of dough. 
 
354 DEMONSTRATIONS AND EXPERIMENTS. 
 
 b) Examine the residue (crude glutin) in muslin ; 
 observe tenacity ; determine the class of food 
 materials to which it belongs. 
 Note. — Other food stuffs may be examined with profit. 
 
 ANATOMY OF DIGESTIVE TRACT. 
 
 Materials: Sound and diseased natural teeth obtained from a 
 dentist. 
 
 Dilute hydrochloric acid. 
 
 Rat or cat. 
 
 Chloroform. 
 
 An inch or two of the small intestine of a recently 
 killed calf. 
 
 50$ solution of alcohol 
 
 Normal salt solution. 
 
 Hand magnifier. 
 Demonstration : 
 
 1) After having soaked the sound teeth in warm water for 
 
 one or two days and then sawed them in two with a 
 fine fret or scroll saw, examine the structure. 
 
 2) Demonstrate the excavations of teeth by decay. 
 
 3) Test the effect of an acid, as dilute hydrochloric or 
 
 vinegar, upon teeth. 
 Dissection : Kill a rat or cat by chloroform. 
 
 1) Dissect away the skin from the whole ventral aspect of 
 the body and note the large salivary glands in the neck 
 region : 
 
 a) The posterior gland (submaxillary), rounded 
 and compact, close to the middle line. Raise 
 the submaxillary, and thereby expose its duct, 
 which passes forward to the mouth, into which 
 
DIGESTIVE TRACT. 355 
 
 it may be followed by separating the halves 
 of the lower jaw. 
 
 b) The large gland, composed of several loosely 
 
 united lobes (parotid), which reaches from 
 the neighborhood of the ear to the submaxil- 
 lary. Note the duct of the parotid \\hi<h 
 passes forward over the face to the mouth, 
 near the angle of which it passes in through 
 the cheek muscles. 
 
 c) A small gland in front of the submaxillary (sub- 
 
 lingual). 
 
 2) Remove the muscles, etc., covering the larynx and 
 
 trachea ; cut away the front and side walls of the 
 chest and abdomen ; remove larynx, trachea, lungs, 
 and heart. 
 
 a) Note the gullet, a slender muscular tube in the 
 
 neck, and trace it through the chest. 
 
 b) Sketch the relative positions of the abdominal 
 
 viscera before displacing any of them. 
 
 3) Turn the liver out of the way and follow the gullet in 
 
 the abdomen until it ends in the stomach. 
 
 a) Note the form of the stomach ; 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. 
 
 b) Notice a thin membrane (the omentum) attached 
 
 to the stomach, and hanging down over the 
 other abdominal viscera. 
 
 4) Follow and unravel the coils of the small intestine, 
 
 spreading out as far as possible the delicate membrane 
 
35 6 DEMONSTRATIONS AND EXPERIMENTS. 
 
 (mesentery ) which suspends it from the upper dor- 
 sal part of the abdominal cavity. 
 
 a > Note blood vessels and lacteals running in the 
 numerous bands of fat in the mesentery. (The 
 lacteals are best seen in a cat killed three or 
 four hours after a meal of rich milk. ) 
 51 Open into the side of the large intestine opposite junc- 
 tion with small. 
 
 a j Note the termination of the small intestine (ileo- 
 cecal valve). 
 bj Observe the caecum or blind end of the large 
 intestine, projecting on one side of the point 
 of entry of the small. (Note position of the 
 vermiform appendix in the human body.) 
 
 c) Follow the large intestine until it ends at the 
 
 anal aperture, cutting away the front of the 
 pelvis to follow its terminal portion (rectum). 
 
 d ) Xote the colon, the portion between the caecum 
 
 and the rectum. 
 6) Spread out the portion of the mesentery lying in the 
 
 concavity of the first coil (duodenum) of the small 
 
 intestine, and note 
 
 a) The pancreas, a thin branched glandular mass. 
 
 b | The portal vein entering the under side of the 
 liver by several branches. 
 
 Cj Near it the gall duct, formed by the union of two 
 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. 
 
 d) The spleen, an elongated red body lying behind 
 
 and to the left of the stomach. 
 
 e) The portal veins ; trace them to the liver. 
 
DIGESTION, 35 7 
 
 7) Divide the gullet at the top of the neck, and the rectum 
 
 close to the anus, and severing atta< hments, remove 
 
 the whole tube ; then cut away the mesentery and 
 
 spread it out at full length. 
 
 a) Note the relative length and diameter of its 
 
 various parts and determine the ratio of its 
 
 length to the body length. 
 
 8) Open the stomach along its greater curvature. 
 
 a) Note the thin smooth mucous membrane which 
 lines the fundus, 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.) 
 
 3) Examine under water the surface of the lining 
 membrane with a hand lens. 
 
 9) Remove the liver. 
 
 a) Note its general form. 
 
 3) Scrape its cut surface and examine cells in normal 
 salt solution under microscope. 
 
 10) Cut out piece of the intestine (or that of calf), wash 
 
 inner surface gently with normal salt solution and 
 examine in solution with a hand lens. Or 
 
 11) Place a piece of small intestine or that of calf in 50^ 
 
 alcohol for twenty-four hours. Then open and 
 examine the villi under water with a hand lens. 
 
 DIGESTION. 
 
 Materials: Blood fibrin. This can be obtained by stirring 
 fresh blood. Dried fibrin may be used for diges- 
 tion experiments, or 
 Egg albumin, coagulated. Stir white of egg into 
 
35 8 DEMONSTRATIONS AND EXPERIMENTS. 
 
 boiling water acidulated with vinegar or acetic 
 acid. 
 Meat juice. 
 
 Bile of pig or other animal obtained from butcher. 
 Glycerole pepsin. Buy of druggist or collect by 
 taking the middle portion of fresh stomach of 
 pig, scraping off the mucous membrane, adding 
 glycerin, and allowing to stand several days, 
 stirring occasionally. Use a few drops for each 
 experiment. 
 Pancreatic extract. Purchase of druggist or pre- 
 pare from fresh pancreas, by grinding thoroughly 
 with sand in a mortar, a | Add water to one 
 half and filter through cloth, for amylolytic fer- 
 ment, b \ Add three or four volumes of glycer- 
 in to the remainder and allow to stand several 
 days, for proteolytic ferment. 
 Saliva. Collect by chewing paraffin or a piece of 
 
 rubber, and filter, 
 o. 2 per cent solution of hydrochloric acid. Add 
 6.5 c.c. commercial hydrochloric acid to 1 liter 
 of distilled water. 
 Apparatus: Water bath for holding test tubes in digestion ex- 
 periments. An oblong deep tin pan, contain- 
 ing a wire test tube rack, nearly filled with 
 water and heated by a Bunsen burner, lamp or 
 alcohol lamp will answer. Temperature should 
 be kept at 99'' F. ($8° C. . 
 Thermometer. Those with scales on stem or in 
 
 glass tubes to be preferred. 
 Test tube racks. Wire racks with a capacity for 
 three dozen test tubes are useful in water bath. 
 
DIGESTION. 359 
 
 Wooden test tube racks with holes and pins 
 
 should be supplied to the tables. 
 Dialyzer (Fig. 66, p. 145). '1'his may be made 
 
 from a section of a lamp chimney, one end 
 
 being covered with bladder, intestine, or moist 
 
 parchment paper. 
 Funnels. For students' use, they should be two 
 
 inches in diameter j for preparing material, six 
 
 or eight inches. 
 Test tubes. A dozen six-inch test tubes for each 
 
 student. 
 Beakers. Nests of three beakers of from four to 
 
 six ounce capacity. 
 Filter papers. Three inches in diameter is a 
 
 convenient size. A few of six or eight inches 
 
 diameter will be needed. 
 Litmus rubbed up in boiling water and filtered. 
 Demonstrations : 
 
 1) Penetration of animal membrane (dialyzer) by crystal- 
 
 loids (sugar, salt) and peptone. 
 
 2) Non-penetration of animal membrane (dialyzer) by 
 
 colloids (starch, albumin) except peptone. 
 Experiments : * Use a test tube for each experiment. Iden- 
 tify them by slipping bits of paper con- 
 
 * The digestion ordinarily requires a number of hours, and it may be 
 best to prepare the solutions, put them in the water bath, and leave them 
 until the next day for examination. The digestion of starch and of 
 fibrin if shaken every few minutes is so rapid that it may be possible to 
 get the proper reactions after a few minutes for starch and after half an 
 hour for fibrin. If the laboratory section extends for two hours, as it 
 should during the digestion work, the digestions may be sufficiently 
 completed at the end of that time for all the characteristic tests. It is 
 best under these circumstances to have the pupils prepare test tubes 
 first then have the demonstrations and experiments which can be accom- 
 
360 DEMONSTRATIONS AND EXPERIMENTS. 
 
 taining names of students and contents in 
 the open end. Place the test tubes for 
 all digestion experiments in that portion 
 of the water bath reserved for each stu- 
 dent. It is best to use small amounts of 
 substances for digestion, and fill the test 
 tubes about two thirds full of solution. 
 Two or three drops of the solution of 
 pepsin and of pancreatic extract are suffi- 
 cient. Shake frequently. 
 
 1. a) Effect of saliva on starch (38 C). 
 
 b) " " proteid ( 3 8°C.). 
 
 c) " " fat (38 °C). 
 
 d) Influence of temperature f about i8°C. and 6o°C). 
 
 2. a) Effect of pepsin on boiled fibrin (38° C). 
 
 b) " o.2# HC1 " " " 
 
 c) " pepsin and 0.2^ HC1 on boiled fibrin 
 (38° C). 
 
 d) Influence of temperature (about i8°C. and 6o°C.) 
 
 on action of pepsin and 0.2^ HC1 on boiled 
 fibrin. 
 
 e) Test product of gastric digestion {2,0) for peptones 
 
 by means of biuret test. 
 
 3. a\ Effect of pancreatic extract on starch. 
 
 b) " " " fibrin or egg albumin. 
 
 plished immediately, to be followed by the examination of digestion 
 products toward the end of the exercise. Students sufficiently inter- 
 ested and with plenty of time to do quantitative work, may deter- 
 mine the relative rapidity of digestion by artificial gastric juice and by 
 pancreatic extract, by taking weighed amounts of fibrin, exposing them 
 to digestion for a certain length of time, carefully wishing and reweigh- 
 ing the fibrin to determine the amount digested. Expt-rimc-nts may also 
 be made upon, the time taken to digest raw and cooked starchy foods,, 
 etc.. etc. 
 
STRUCTURE AND COMPOSITION OF HI.OOD. 361 
 
 c) Influence of acidity and alkalinity on action of pan- 
 
 creatic extra* t. 
 
 d) Effect of shaking oil with pancreatic extract. 
 
 e) tl " boiling fat or oil with caustic soda or cans- 
 tic potash. (Test result by shaking a few drops 
 with water. ) 
 
 4. Influence of bile on absorption of fats. 
 
 a) Moisten a filter paper stretched across top of a 
 funnel with bile and put on paper a teaspoonful 
 of oil. Moisten another filter paper similarly 
 placed with water and apply the same amount 
 of oil. Note comparative rapidity of penetra- 
 tion. 
 
 STRUCTURE AND COMPOSITION OF BLOOD. 
 
 Materials : Frog. 
 Ether. 
 Blood clot. 
 Defibrinated blood. 
 Blood serum. 
 Apparatus : Hand magnifier. 
 
 Microscope with powers, up to 450. 
 Bundle of twigs or wire. 
 Two fruit jars. 
 Demonstrations : 
 
 1) Put a frog in a solution of one teaspoonful of ether to a 
 quart of water, and cover the vessel for a minute or 
 two. Remove the frog, cut off its head and collect 
 on a piece of glass a drop of the blood which flows 
 out. Spread out the drop so that it forms a thin 
 layer and hold the glass up against the light. 
 
362 DEMONSTRATIONS AND EXPERIMENTS. 
 
 a) Examine the blood with a hand magnifier and a 
 microscope, noting form, size, color, and 
 relative numbers of red and white corpuscles. 
 
 2) Wind tightly a piece of twine around the last joint of a 
 
 finger ; then, taking a needle, prick the skin of the 
 side of the finger. A large drop of blood will exude. 
 Spread it out on a piece of glass under a cover glass. 
 
 a) Examine with hand magnifier. 
 
 b) Examine with microscope and demonstrate 
 
 1) Form, size, and color of human as compared 
 
 with frog red blood corpuscles. 
 
 2) Form of aggregation of human blood cor- 
 
 puscles. 
 
 3) Color, form, size, and relative number of 
 
 white blood corpuscles. 
 
 3) Obtain a large drop of human blood as above (2) de- 
 
 scribed. Note 
 
 a) Physical characteristics (color, opacity, etc. ) when 
 
 it flows from wound. 
 
 b) Apparent change of color when it is spread very 
 
 thin on the glass and held over a sheet of white 
 paper. 
 
 c) Color, when mixed with a teaspoonful or more of 
 
 water in a wine glass. 
 
 4) Place another large drop of human blood, obtained as 
 
 above, on a clean glass plate. To prevent drying up 
 cover by inverting over the drop a wine glass whose 
 interior has been moistened with water. 
 
 a) In four or five minutes remove the wine glass and 
 
 note the condition of the blood. 
 
 b) Replace the moist wine glass and in half an hour 
 
 examine again. 
 
AH ATOMY OF THE HEART. 363 
 
 5) Collect Mood at butcher's in a glass jar ; set aside until 
 
 the blood clots and carry it home with the least 
 possible shaking. Observe the clot and scrum next 
 day j carefully collect latter. 
 
 6) Collect blood in the pail and beat it vigorously with the 
 
 twigs for three or four minutes. 
 
 a) Note quantity of stringy elastic material (fibrin) 
 
 collected on the twigs. 
 
 b) Wash the twigs thoroughly with water and observe 
 
 color of fibrin. 
 
 7) Take some of the serum from specimen 5. 
 
 a) Note physical characteristics. 
 
 b) Heat it in a test tube. 
 
 c) Add nitric acid to some in test tube. 
 
 8) Place a small quantity of whipped blood (6) on a piece 
 
 of platinum foil. Heat. 
 
 a) Note that after the drop dries it blackens, showing 
 
 that it contains much organic matter. 
 
 b) Continue heating until this is burned away ; 
 
 examine the residue of white ash, consisting of 
 the mineral constituents of the blood. 
 
 ANATOMY OF THE HEART. 
 
 Materials: Sheep's heart, not cut out of the pericardium, 
 
 severed from the lungs, nor punctured. 
 Dissection * or Demonstration : 
 
 1) Place the heart and lungs on their dorsal side upon a 
 table in their normal relative positions, with the wind- 
 pipe turned away. 
 
 * The dissection may be made before the meeting of the class and the 
 anatomical facts through 3) c demonstrated upon the preparation. 
 
;64 DEMONSTRATIONS AND EXPERIMENTS. 
 
 a) Note the pericardium and the piece of diaphragm 
 
 which is usually found attached to its posterior 
 end. 
 
 b) Inflate lungs and note relations of heart. 
 
 2) Carefully dissect away adherent fat, etc. , without cutting 
 
 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. 
 
 a) Note the vena cava inferior on the under (abdom- 
 
 inal) side of the diaphragm; thence follow it 
 until it enters the pericardium. 
 
 b) Observe the hepatic and other veins which the 
 
 vena cava inferior receives from the liver, spleen, 
 kidneys, and diaphragm. 
 
 c) Observe the right phrenic nerve lying on the left 
 
 side of the inferior vena cava and ending below 
 in several branches to the diaphragm. 
 
 d) Find the lower end of the superior vena cava, 
 
 which enters 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. 
 e) Notice between the ends of the two venae cavae the 
 right pulmonary veins proceeding from the lung 
 and entering the pericardium. 
 
 3) Turn the right lung and the heart back to their natural 
 
 position ; clear away the loose fat in front of the 
 pericardium ; seek and clean the following vessels in 
 the mass of tissue lying anterior to the heart and on 
 the ventral side of the windpipe. Note 
 
 a) The aorta : its arch and branches. 
 
 b) The pulmonary artery imbedded in fat on the 
 
ANATOMY OF THE HEART. 
 
 dorsal side <>f the aorta ; note < ourse and follow 
 branches into lungs. 
 
 Note.- Observe the thickness and firmness of the 
 arterial walls as compared with those of the veins. 
 
 c) The left pulmonary veins on the ventral side of 
 
 the left pulmonary artery, passing from the lung 
 into the pericardium. 
 
 4) Slit open the pericardial sac, and note 
 
 a*) Its smooth, moist, glistening inner surface, and 
 the similar character of the outer surface of the 
 heart. 
 
 b~) The character and amount of pericardial fluid. 
 
 5) Cut away the pericardium carefully from the various 
 
 vessels at the base, and note 
 
 a) While this is being done, that inside the pericar- 
 
 dium the pulmonary artery lies on the ventral 
 side of the aorta. 
 
 b) The general form and position of the heart. 
 
 6) Carefully dissect out the entrance 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 auricle, but it will be found subse- 
 quently (13) that such is not really the case. Note 
 on the exterior the following points : 
 a) The flabby auricle (left) into which the veins 
 open and its companion (right) between the 
 aorta and the superior vena cava. 
 
 d) A band of fat running around the top of the ven- 
 
 tricles ; an offshoot from it runs obliquely down 
 the front of the heart, passes to the right of its 
 apex and indicates externally the position of 
 the internal partition or septum, which sepa- 
 
3^0 DEMONSTRATIONS AND EXPERIMENTS. 
 
 rates the right ventricle (which does not reach 
 the apex of the heart) from the left. 
 
 7) Dissect away carefully the collections of fat around 
 
 origins of the great arterial trunks and around the 
 base of the ventricles. In the fat will be found 
 
 a) A coronary artery rising from the aorta close to 
 
 the heart, opposite the right border of the pul- 
 monary artery ; it gives off a branch which runs 
 in the groove between the right auricle and 
 ventricle, then runs down the dorsal side of 
 the heart. 
 
 b) The other coronary artery, considerably larger, 
 
 rising from the aorta dorsal to the pulmonary 
 artery ; its main branch runs along the ventral 
 edge of the ventricular septum. 
 
 c) The coronary veins accompanying the arteries. 
 
 8) Open the right ventricle by passing the blade of a scal- 
 
 pel through its wall about one inch from the upper 
 border of the ventricle and on the right of a band of 
 fat which marks the external partition between the 
 ventricle (see 6, b) ; cut down towards the apex. 
 Make a corresponding cut through the wall of the same 
 ventricle on its other side. Raise point of wedge- 
 shaped flap and expose cavity. Cut off the pulmon- 
 ary artery about an inch above its origin and open 
 the right auricle by cutting apiece out of its wall at 
 the left of the venae cavse. 
 
 a) Pass the handle of a scalpel from the ventricle 
 
 into the auricle, and also from the ventricle 
 into the pulmonary artery ; study out the rela- 
 tions of these openings. 
 
 b) Slit open the auricle ; note the fleshy projections 
 
ANATOMY OF THE HEART. Z ( >1 
 
 (column* came*) on its walls, and the 
 smoothness of the interior surface of the auri- 
 cle. Observe the apertures of the venae cavae, 
 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. 
 
 d) Pass a probe through the aperture along the sinus 
 
 and slit it open ; notice the muscular layer 
 covering it in. 
 9 ) Raise by its apex the flap cut out of the ventricular 
 wall, and if necessary prolong the cuts toward the 
 base' of the ventricle until the divisions of the tricus- 
 pid valve come into view, and note 
 
 a) The column* earner on the wall of the ven- 
 
 tricle, and the muscular cord (not found in the 
 human heart) stretching across its cavity. 
 
 b) The prolongation of the ventricular cavity towards 
 
 the aperture of the pulmonary artery. 
 10) Cut away the right auricle. 
 
 a) Examine carefully the triscupid valve, composed 
 of three membranous flexible flaps, thinning 
 away towards their free edges; proceeding 
 from near these edges are strong tendinous 
 cords (chord* tendine*), which are attached 
 at their other ends to muscular elevations (pap- 
 illary muscles) of the wall of the ventricle, 
 n) Slit up the right ventricle until the origin of the pul- 
 monary artery comes into view. Looking carefully 
 for the flaps of the semilunar valves, prolong the cut 
 between two of them so as to open the bit of pulmon- 
 
368 DEMONSTRATIONS AND EXPERIMENTS. 
 
 ary artery still attached to the heart. Spread out the 
 artery. 
 
 a) Examine the valves. 
 
 b) Observe the pouch made by each flap and the 
 
 slightly dilated wall of the artery behind it. 
 
 c) Note that the free edge of the valve is turned from 
 
 the heart, and has in its middle a little nodule 
 (corpus Arantii). 
 
 12) 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. Cut the aorta off 
 about half an inch above its origin from the heart, 
 and note 
 
 a) The aperture between left auricle and left ventri- 
 
 cle. 
 
 b) The passage from the ventricle into the aorta. 
 
 c) The entry of the pulmonary veins into the auricle. 
 
 d ) The septum between the auricles and that between 
 
 the ventricles. 
 
 13) Pass the handle of a scalpel from the ventricle into the 
 
 auricle ; another from the ventricle into the aorta ; 
 also pass probes into the points of entrance of the 
 pulmonary veins. 
 
 14) Slit open the left auricle and note 
 
 a) The columnae carneae, and the smoothness of the 
 
 inner wall. 
 
 b) The columnae carneae of the ventricle, also the 
 
 considerable thickness of the wall as compared 
 with that of the right ventricle or of either of 
 the auricles. 
 
 15) Carefully raise the wedge-shaped flap of the left ven- 
 
 tricle, and cut toward the base of the heart, until 
 
HEART ACTION. 3 r> 9 
 
 the valve (mitral) between auricle and ventricle is 
 brought into view. 
 
 a) Note that one of its two Haps lies between the 
 
 auriculo-ventricular opening and the origin of 
 the aorta. 
 
 b) Examine in these flaps their texture, the chordae 
 
 tendineae, the columnse carneae, etc. 
 c) Examine the semilunar valves at the exit of the 
 aorta. 
 1 6) Slit the aorta carefully between two of these valves. 
 
 a) Examine the bit of aorta still left attached to the 
 
 heart and note the thickness of its wall, its 
 extensibility in all directions, its elasticity and 
 firmness. 
 
 b) Note the valves. 
 
 c) Note the origins of the coronary arteries in two 
 
 of the three dilatations of the aortic wall above 
 the semilunar flaps. 
 
 d) Compare the artery with the veins which open 
 
 into the heart. 
 
 HEART ACTION. 
 
 Jfa/en'als : Frogs.* 
 
 Ether. 
 
 Two sheep's hearts. 
 Apparatus : A piece of sheet cork or of thin board with a 
 half-inch hole cut in it. 
 
 Microscope. 
 
 Caliper rule. 
 
 * Anatomically a frog's heart differs in many respects from that of a 
 mammal but the phenomena of systole and diastole are essentially the 
 
370 
 
 DEMONSTRATIONS AND EXPERIMENTS. 
 
 Recording apparatus, similar to that used for 
 muscle. 
 
 Fig. 150. — Diagram of Marey tambour apparatus for recording curves, a, the 
 rubber membrane coinciding with the movements of the membrane of the trans- 
 mitting apparatus ; b y tambour ; c, smoked glass plate. 
 
 Fig. 151.— Diagram of cardiograph, «, cup; <5, knob; c, spring; d, rubber mem- 
 brane. 
 
 Cardiograph. 
 
 Marey tambour. 
 
 Circulation apparatus made from bulb syringe, 
 
 such as may be obtained at the drug store. 
 Manometer. 
 
HEART ACTION. 
 
 37i 
 
 u 
 
 ^§^ 
 
 Fig. 152. — Manometer. 
 
 Several feet of glass tubing. 
 
 Glass nozzle (glass tubing drawn out in flame). 
 
 Scalpel. 
 
 A piece of sheet lead such as comes in tea chests. 
 
 Scissors. 
 
 Forceps. 
 
 Rod, \ inch diameter (a small test tube). 
 
 Glass window (a circular piece of glass i-t inches 
 in diameter, cemented into a short tin tube). 
 
 Graduate. 
 
 Two basins. 
 Demonstrations : 
 
 1) Take a medium-sized frog. Wrap it carefully in a damp 
 cloth and then in tea lead so that one foot is outside 
 the lead. Fasten it to perforated sheet cork or board 
 
37 2 DEMONSTRATIONS AND EXPERIMENTS. 
 
 and pin or tie toes so that the web of foot is spread 
 over hole. Clamp in place on microscope stage. 
 Focus carefully on web. Note 
 
 a) Movement of blood corpuscles. 
 
 b) Blood vessels in which blood is passing toward 
 
 finer branches (arteries). 
 
 c) Smallest vessels through which blood is passing 
 
 (capillaries). 
 
 d) Vessels in which blood is passing from small 
 
 branches to large trunks (veins). 
 
 e) Rapidity of movement of red blood corpuscles and 
 
 position in blood stream Also bending of red 
 blood corpuscles at arterial branches. 
 /) Movement of white blood corpuscles and their 
 
 position in blood stream. 
 g) Intermission of blood flow (?) and coincidence 
 with heart beat. 
 2) Cut the medulla oblongata of an etherized frog by nick- 
 ing with the point of scalpel at right angles to the 
 length of the body in the line joining posterior mar- 
 gins of the ear disks. Introduce a blunt wire and 
 destroy the brain * and spinal cord. Run a pointed 
 match into the cut to prevent bleeding. 
 
 Lay the animal on its back, and 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 cut and pin out the 
 flaps of skin. 
 
 Next pick up with forceps the remaining tissues of 
 the ventral wall near its posterior end, and divide 
 them longitudinally a little on the left side of the 
 * The frog is in this way painlessly killed. 
 
HI ART ACTION. 373 
 
 middle Line, being very careful not to injure cither 
 the viscera in the cavity beneath or a large vein (an- 
 terior abdominal) running along the wall in the mid- 
 dle line. 
 
 About the point where the vein passes from the 
 wall to enter among the viscera of the ventral cavity 
 are the bony and cartilaginous tissues of the sternal 
 region. Raise the posterior cartilage with the for- 
 ceps, make a short transverse cut in front of the vein, 
 and, looking beneath the sternum, note the pericar- 
 dium with the heart beating inside. 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. 
 
 Push a rod of about half an inch in diameter down 
 the throat so as to stretch the parts ; then picking up 
 the pericardium with the forceps, open it and gently 
 cut it away. 
 a) Note the parts of heart : 
 
 1) Ventricle, single in case of frog. 
 
 2) Auricles, right and left. 
 
 3) Bulbus arteriosus on front aspect of heart. 
 
 4) Sinus venosus under the heart, seen by gent- 
 
 ly raising the apex. 
 
 5) Two aortas. 
 
 6) Pulmonary veins and venae cavae. 
 
 b) Note systole and diastole of heart. 
 
 c) Changes of color and size of its parts. 
 
 d) Determine the order of contraction of the dif- 
 
 ferent parts. 
 e) Put aside under a bell -jar with a wet sponge, or a 
 
374 DEMONSTRATIONS AND EXPERIMENTS. 
 
 piece of flannel soaked in water. Note duration 
 of heart beat. 
 
 3) To demonstrate the action of the valves of the heart, 
 
 carefully remove a sheep's heart from the pericar- 
 dium. 
 
 a) Aortic valve. 
 
 1) Cut off aorta one inch above valves. Tie 
 
 into it a piece of glass tubing, down which 
 pour water. Note the efficiency of the 
 valves. 
 
 2) Tie a piece of glass tubing into one pulmonary 
 
 vein and tie off the other. Fill the tubing 
 with water. Squeeze ventricles with hand 
 and note results. 
 
 b) Mitral valve. 
 
 1) Tie into the left auricle a glass window and 
 watch appearance of mitral valve as ven- 
 tricle is squeezed and relaxed. 
 
 c) Mitral and tricuspid valves. 
 
 1) Carefully cut the auricles away from another 
 sheep's heart, taking great care not to in- 
 jure the ventricles or the auriculo-ven- 
 tricular valves. Then holding the ventri- 
 cles, apex down, in one hand, pour water 
 in a stream into them from a pitcher held 
 about a foot above. Note the movement 
 of the mitral and tricuspid valves. 
 
 4) Take bulb syringe and fit the outflow tube to receive 
 
 either a piece of glass tubing about two feet long or 
 apiece of pure gum rubber tubing (one inch " sap " 
 tubing); also prepare nozzle with a hole about ^ inch 
 in diameter which can be fitted to the distal end of 
 
HEART /tCTlON. 375 
 
 either glass or rubber tube. A basin of water and 
 another basin into which to receive the discharge are 
 needed. 
 
 a) Put aspirating end of bulb syringe in a basin of 
 
 water ; fill syringe ; attach glass tube ; squeeze 
 and release bulb regularly every two seconds. 
 Note character of outflow and measure amount 
 for i o or 20 seconds.* 
 
 b) Attach nozzle to end of glass tube ; pump regu- 
 
 larly as before and note character of outflow ; 
 measure outflow. 
 
 c) Remove glass tube and attach rubber tube. Pump 
 
 as before, noticing character of outflow, and 
 measure the outflow for same period. 
 
 d) Attach nozzle to rubber tube and test as in b). 
 
 e) Determine factors contributing to uniform flow. 
 /) Connect a manometer with the arterial side of the 
 
 apparatus and measure pressures developed in a, 
 b, c, and d. 
 g) Determine the relation of the internal pressure to 
 the size of the rubber tube in d (the flow may 
 be conveniently stopped for these measure- 
 ments). 
 h) Attach a large tube to nozzle (to represent vein) 
 in d and connect another manometer to it. 
 Compare pressures. 
 5) Record human pulse curve by pressing knob of cardio- 
 graph (Fig. 151) on carotid artery at side of larynx 
 by means of a band around neck. Connect this 
 with a Marey tambour (Fig. 150) on recording appa- 
 
 * Attempt should be made to squeeze the bulb with the same force 
 throughout these experiments. 
 
37 6 DEMONSTRATIONS AND EXPERIMENTS. 
 
 ratus and move the smoked glass* over the writing 
 point to separate the records. 
 
 a) Note the general form of curve. 
 
 b) Note the dicrotic wave. 
 
 c) Interpret curve in relation to size of arter\. 
 
 ANATOMY OF THE RESPIRATORY TRACT. 
 
 Materials: Sheep's lungs with windpipe and heart attached, 
 to prevent puncturing of lungs through careless 
 removal of heart. 
 Rat or kitten. 
 Frog. 
 
 Chloroform. 
 Normal salt solution. 
 Apparatus: A few inches of glass and of rubber tubing about 
 \ inch diameter. 
 Some small object, as apiece of cork or rubber. 
 Microscope. 
 Dissection or Demonstration: 
 
 i) Examine the windpipe of the sheep and trace its division 
 into the bronchi. 
 
 a) Notice in its wall the horseshoe-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. 
 2) Slip a rubber tube on the end of the glass tube and in- 
 sert the other end of the glass tube into the trachea; 
 tie firmly ; blow out lungs and tie rubber tube to 
 keep distended. Note 
 a) The extensibility and elasticity of the lungs. 
 
 * The record may be "fixed" by flowing the plate with dilute shellac 
 varnish and letting it dry. 
 
An ATOMY Oh' THE RESPIRATORY TRACT. 37 7 
 
 b) The size and form the lungs assume when dis- 
 
 tended. 
 
 c) The spat e for the heart. 
 
 d) The concavity of the lower (diaphragm) surface 
 
 of the distended lungs. 
 e) The lobes. 
 /) The pleural membrane. 
 
 3) Trace one bronchus to its lung. 
 
 a) Cut through the lung tissue and follow the branch- 
 
 ing bronchi through the lung. 
 
 b) Note the cartilage rings in their walls. 
 
 c) Note mucous membrane lining tubes. 
 
 d) Wash surface with normal salt solution; gently 
 scrape with scalpel and examine scrapings, under 
 microscope. 
 
 4) Remove from a chloroformed rat or kitten the abdominal 
 
 viscera, cutting away the liver and stomach with 
 
 especial care. 
 
 a) Examine the vaulted diaphragm and through it 
 
 the lungs. 
 
 5) Seize some of the folds of the peritoneum attached to the 
 
 diaphragm and pull it down, imitating its contraction 
 
 and flattening in inspiration. 
 
 a) Observe corresponding movements of lungs. 
 
 6) Make a free opening into one side of the thorax. 
 
 a) Note behavior of lung. 
 
 7) Open the other side of the chest. 
 
 a) Note result upon the lung. 
 
 b) Observe the structure of the diaphragm (its ten- 
 
 dinous centre and muscular periphery) and also 
 the attachment of the pericardium to its thoracic 
 side. 
 
37^ MONSTRATIONS AND EXPERIMENTS. 
 
 8) Place a recently killed frog on its back. Fasten lower 
 
 jaw wide open. 
 
 a) Place small object on roof of mouth near nose. 
 
 Note movement. 
 
 b) Examine scraping from roof of mouth in normal 
 
 salt solution under microscope. 
 
 9) Remove as much of oesophagus as possible ; split it 
 
 open and pin out. 
 
 a) Place small object upon it near mouth end ; note 
 
 behavior. 
 
 b) Set aside under moist glass ; note position of 
 
 mucus on surface at end of a half-hour.* 
 
 RESPIRATION. 
 
 Materials: Wood shaving. 
 Lime water. 
 Hydrochloric acid. 
 
 Blood clot, defibrinated blood or piece of liver. 
 Lungs of cat or rat. 
 Apparatus : Thermometer. 
 
 Mirror. 
 
 Wide -mouthed bottle. 
 
 Test tube. 
 
 Glass tubes. 
 
 Rubber tubing. 
 
 Bell-jar of two quarts' capacity. 
 
 Sheet rubber. 
 
 Pinchcock. 
 
 * Cilia are present in the respiratory passages, but not in the oesoph- 
 agus of man. 
 
RFSPIRATION. 379 
 
 Rubber stopper with double perforations, to fit 
 
 bell -jar. 
 Two pieces of glass tubing, one bent, to fit per- 
 forations of stopper. 
 Water* valve respiration apparatus for carbon 
 dioxide. 
 Experiments and Demonstrations: 
 i ) Note the effect of breathing 
 
 a) On the bulb of a thermometer. 
 
 b) On a mirror, knife blade or other polished metallic 
 
 surface. 
 
 2) Burn a shaving in a wide-mouthed bottle of air and 
 
 close tightly. 
 
 a) Pour lime water into the bottle and shake. Note 
 
 result (carbonate of lime). 
 
 b) Pour a few drops of hydrochloric acid into a) and 
 
 note result. 
 
 c) Blow breath through a tube into a solution of lime 
 
 water. 
 
 d) Add hydrochloric acid as in b). 
 
 e) Demonstrate by means of the water-valve respira- 
 
 tion apparatus (Fig. 153) the relative amounts of 
 carbon dioxide in atmospheric air and in expired 
 air, by partly filling bottles with lime water and 
 breathing through them. 
 
 3) Blow breath through a weak solution of lime water 
 
 colored with phenol phthalein.* 
 
 4) Cut open blood clot or piece of liver. 
 
 a) Compare freshly cut surface with surface exposed 
 to air. 
 * Phenolphthalein is pink in alkaline solutions, colorless in acid. 
 
3 8o 
 
 DEMONSTRATIONS AND EXPERIMENTS. 
 
 b) Place freshly cut piece of blood clot or liver into 
 
 a bottle containing oxygen. Or 
 b') Shake defibrinated blood in bottle containing 
 oxygen. Note result (oxyhemoglobin^. 
 
 ^^~*~(( (.(.(({ 
 
 L 
 
 1 
 
 C 
 
 Fig. 153. — Apparatus to demonstrate carbon dioxide in expired air. a, inspiration ; 
 b, expiration. 
 
 5 Connect manometer by a piece of rubber tubing with a 
 piece of glass tubing in the mouth ; place also in the 
 mouth a short piece of tubing \ to \ inch diameter. 
 
 a) Breathe as ordinarily ; note changes in pressure as 
 
 shown by manometer. 
 
 b) Breathe quickly ; note changes as above. 
 
 6) Substitute for glass tubing in 5) a glass tube drawn 
 
 out to a point. 
 
 a) Breathe as ordinarily ; note pressures. 
 
 b) Breathe strongly ; note pressures. 
 
 7) Connect the distant end of the rubber tubing from the 
 
 tube in the mouth to the Marey tambour and record 
 the curves made by the writing point. 
 
RESPIRATION. 
 
 38i 
 
 8) Illustrate the action of the diaphragm by substituting 
 for the chest wall a bell-jar of two quarts' capacity 
 (Fig. 154). Tie the lungs of a cat or a rat on a long 
 
 piece of glass tubing which is then passed up from 
 
 d 
 
 Fig. 154— Breathing apparatus, a, lungs of cat; i, rubber diaphragm; c, bowl ; 
 d, pinchcock. 
 
 beneath through one of the perforations in the stop- 
 per. Seat the stopper firmly in the mouth of bell-jar. 
 Stretch a piece of heavy pure gum sheet rubber over 
 the larger end of the bell-jar and tie it firmly in 
 position. Press the rubber membrane down on the 
 top of a bowl and close the rubber tube at the end of 
 the bent glass tube with a pinchcock. 
 
 a) To represent inspiration, lift the bell-jar from the 
 
 bowl, allowing the rubber membrane to flatten. 
 
 b) To represent expiration press the membrane on the 
 
 bowl. 
 
 c) To represent the effect of a puncture of the chest 
 
 wall, open the bent tube, when the jar is lifted 
 from the bowl. 
 
382 DEMONSTRATIONS AND EXPERIMENTS. 
 
 RENAL ORGANS. 
 
 Materials : 
 
 Rat. 
 
 Chloroform. 
 Fresh sheep's kidney. 
 Apparatus : 
 
 Sponge. 
 Bell jar. 
 Stout scissors. 
 Bristles. 
 Dissection or Demonstrations : 
 
 Kill a rat by placing it under a bell-jar with a sponge 
 soaked in chloroform. 
 
 i) Open the abdomen, remove the alimentary canal, 
 and cut away with stout scissors the ventral 
 portion of the pelvic girdle. Note the dark red 
 kidneys on each side of the dorsal part of the 
 abdominal cavity, the right one nearer the head 
 than the left. 
 
 2) Dissect away the connective tissue, etc., in front 
 
 of the vertebral column, so as to clean the in- 
 ferior vena cava and the abdominal aorta. 
 
 a) Trace out the renal arteries and veins. 
 
 b) Find the ureter, a slender tube passing 
 
 posteriorly from the kidney, and trace 
 it to the bladder. 
 
 3) Dissect away the tissues around the urinary blad- 
 
 der. Note its form, etc. 
 
 4) Open the bladder. 
 
 a) Find the orifices of the ureters, and pass 
 bristles through them. 
 
ANATOMY OF THE NERVOUS SYSTEM. 383 
 
 b) Note the mucous membrane lining the blad- 
 der, 
 
 5) Remove one kidney from the body and divide it 
 
 from its outer nearly to its inner border; turn 
 the two halves apart. Examine the cut surfaces 
 and note 
 
 a) At the inner border the dilatation of the 
 
 ureter. 
 
 b) The outer cortical portion of the kidney. 
 
 c) The medullary portion. 
 
 d) The papillae. 
 
 6) Obtain a fresh sheep's kidney. Divide it from its 
 
 outer to its inner border, and demonstrate 
 
 a) On the cut surfaces the cortex and me- 
 
 dulla. 
 
 b) The pyramids of Malpighi and the off- 
 
 shoots of the cortex extending between 
 them. 
 
 ANATOMY OF THE NERVOUS SYSTEM. 
 Materials : 
 
 Frog. 
 Ether. 
 
 Fresh calf's or sheep's head. 
 Alcohol. 
 Apparatus : 
 
 Stout scissors. 
 Bone forceps. 
 Dissection or Demonstrations : 
 
 Kill a frog with ether ; open its abdomen and remove 
 the viscera. 
 a) Note at the back of the abdominal cavity a bundle 
 
384 DEMONSTRATIONS AND EXPERIMENTS. 
 
 of white cords (nerve trunks) passing to each 
 
 IPC 
 
 b) Trace the sciatic nerve into which they unite and 
 dissect it along its course until it ends in fine 
 branches in the hind leg. 
 
 2) With stout scissors cut very carefully bit by bit the 
 
 bodies of the vertebrae (which will be seen projecting 
 in the middle line at the back of the abdominal 
 cavity) until the neural canal is laid open and the 
 spinal cord exposed. Note 
 
 a) The origin of the nerves from the spinal cord. 
 
 b) Their division into anterior and posterior (ventral 
 
 and dorsal) roots before they join the cord. 
 
 c) The ganglionic enlargements on the posterior 
 
 roots. 
 
 3) Turn the frog upon its abdomen and remove the skin 
 
 arid muscles on the dorsal side of the spinal column. 
 AYith great care cut away the upper two thirds of the 
 neural arches of the vertebrae. Then remove the 
 upper half of the skull cavity. Gently raise the brain 
 and spinal cord, divide the nerves which spring from 
 them and lift out the whole cerebro-spinal system 
 and place it in alcohol for twenty-four hours. * 
 Note 
 
 a) The origin of nerves from both brain and cord.f 
 
 b) The union of the brain and cord, etc. 
 
 4) Dissect away the skin and muscles covering the 
 
 * The specimen may be hardened and preserved in a solution — forma- 
 lin, 2 parts; alcohol, 20 parts; water. 78 parts. 
 
 f A frog's brain differs in many important points from that of a mam- 
 mal, as in the very small cerebellum, the comparatively small cerebral 
 hemispheres, the comparatively large mid-brain and the absence of con- 
 volutions. 
 
ANATOMY OF THE NERVOUS SYSTEM. 3 8 5 
 
 cranium of a calfs ... sheep's head. Then with a 
 small saw verycarefull) divide the bones inacircular 
 dire, tion, so as to < »t off the crown of the head. Next 
 carefully remove the loosened bones of the top of the 
 
 skull, tearing them away from the dura mater lining 
 
 them. 
 
 a) Demonstrate the tough dura mater enveloping the 
 
 brain. 
 
 b) Cut it away and note the processes which it sends 
 
 between the two cerebral hemispheres and be- 
 tween the cerebellum and the cerebral hemi- 
 spheres. 
 
 c) Cut the membrane away and note 
 
 i) Its glistening inner surface, due to the 
 arachnoid membrane lining it. 
 
 2) The pia mater full of blood vessels and 
 
 closely attached to the brain. 
 
 3) The glistening arachnoid layer covering the 
 
 exterior of the pia mater. 
 d) Put the specimen aside in the hardening solution 
 for a day or two. When the brain has become 
 somewhat hardened dissect away the pia mater 
 on one side and show 
 
 1) The cerebral hemispheres and their surface 
 
 convolutions. 
 
 2) The cerebellum and its foldings. 
 
 3) The medulla oblongata beneath the cerebel- 
 
 lum. 
 e) With bone forceps cut away the remainder of the 
 sides and roof of the skull. Find 
 
 1) Nerves to eyes. 
 
 2) Nerves to nose. 
 
3 86 DEMONSTRATIONS AND EXPERIMENTS. 
 
 f) Raise the brain in front and cut through the ves- 
 sels, nerves, etc. , which attach it to the base of 
 the skull cavity: remove it from the skull 
 cavity. 
 
 i) The cerebral hemispheres, which overlap the 
 cerebellum much less than in man. 
 
 2) Cerebellum. 
 
 3) Mid-brain, etc. 
 
 4) Stumps of the cranial nerves attached to the 
 
 base of the brain.* 
 
 5) Optic commissure, with the optic tracts 
 
 leading to it. 
 
 6) Stumps of the optic nerves leading from it. 
 g) Make sections across the brain in different direc- 
 tions and note 
 
 1) Gray matter spread over most of its surface. 
 
 2) The nodules of gray matter imbedded in its 
 
 interior. 
 
 NERVE ACTION. 
 
 Materials: Frog. 
 
 Blotting paper. 
 
 Vinegar. 
 Apparatus : Stout scissors. 
 
 Feather. 
 
 Bone forceps. 
 
 Blunt wire. 
 Demonstrations or Experiments: 
 
 1) Feign a blow at a person's eye after having told him 
 that he is not to be actually struck. 
 
 * Most of these will have been torn off unless the dissector has some 
 technical skill. 
 
NERVE ACTION. 
 
 2) a) Count a boy's pulse and breathing while he is sitting 
 
 quietly. 
 b) Let him run a hundred yards at full speed, and 
 immediately count pulse and breathing movements. 
 ( lompare results. 
 
 3) Tickle the inside of the nose with a feather. 
 
 4) Place a live frog on a table and note its movements and 
 
 reactions to varying conditions : 
 
 a) Breathing. 
 
 b) Winking. 
 
 c) Jumping, etc. 
 Voluntary Rear lion (Chain Reaction): 
 
 5) Divide the class into two equal groups so arranged in 
 
 series that a signal may be passed from one to another 
 of each group by touching hands. Let some one give a 
 signal by touching the hand of each of the first members 
 of the two series. As soon as the pressure is felt, let 
 them transmit it to the next and so on until finally 
 the last members of the series press on the hands of 
 the instructor, who decides which signal came first.* 
 
 a) Chain reaction with eyes shut. 
 
 b) Chain reaction by one series with eyes shut, other 
 
 series looking on. 
 
 c) Conditions in b) reversed. 
 Reflex Reaction : 
 
 6) Prepare a frogf by destroying its brain as soon as it is 
 
 under the influence of ether. 
 
 * To record roughly the time of a single reaction or of a chain reac- 
 tion, the inventive teacher can use a pendulum beating seconds and a 
 recording apparatus such as w.is used for cardiograph tracing-, with a 
 Marey tambour to transmit the signal. 
 
 \ This is best done an hour or two before the experiment. 
 
388 DEMONSTRATIONS AND EXPERIMENTS. 
 
 a) Note reactions of frog 
 
 i) When toe is pinched. 
 
 2) When small bits of blotting paper soaked in 
 vinegar are put one by one on different re- 
 gions of its skin. (Dip the animal in clean 
 water after each application to wash away 
 the vinegar.) 
 
 b) Destroy its spinal cord by running a blunt wire 
 
 down the neural canal. Repeat a) and compare 
 results. 
 
 c) Turn frog (b ) on its back and carefully expose the 
 
 origins of the sciatic nerves. Pinch these and 
 note result. 
 
 SPECIAL SENSES. 
 
 DERMAL SENSES. 
 
 Apparatus: Drawing compasses (any form, not too sharp, 
 may be used). 
 Scale graduated to millimeters. 
 Vessel of cold water. 
 Vessel of lukewarm water. 
 Vessel of hot water. 
 Forceps. 
 Experiments (two students workitig together) : 
 
 1) Take a straight piece of hair in forceps and, by ascer- 
 taining the greatest length which will give rise to a 
 sensation of pressure, determine the relative sensitive- 
 ness of 
 
 a) Palm. 
 
 b) Back of hand. 
 
 c) Forehead. 
 
SPECIAL SENSES. 
 
 2) What is the least distance that the two points of the 
 
 compasses may be separated and still be recognized 
 as two when applied to 
 
 a) Finger tip ? 
 
 b) Back of hand ? 
 
 c) Back of neck ? 
 
 3) a) What sensations are caused by the light pressure of 
 
 a pencil point on the back of the hand? 
 /') Are the cold points constant in their position ? (Test 
 from day to day.) 
 
 4) Temperature sense. 
 
 a) Put a finger of the right hand into warm water and 
 
 a finger of the left hand into cold water. Note 
 the immediate sensations and the change in 
 sensations after the fingers have remained some 
 time in the water. 
 
 b) Withdraw the fingers and plunge both immediately 
 
 into the vessel containing lukewarm water. 
 Compare the sensations of the two fingers. 
 
 TASTE AND SMELL.* 
 
 Materials : Onion. Dilute ammonia f one drop of 
 
 Sugar. strong ammonia in a glass 
 
 Salt. of water). 
 
 Dilute Vinegar. Cabbage. 
 
 Carrot. Quinine. 
 
 Experiments (two students working together) : 
 
 1) Eliminate odor by holding the nose and determine 
 
 * Care should be taken not to exhaust the sense organs by over-stim- 
 ulation. 
 
39° DEMONSTRATIONS AND EXPERIMENTS. 
 
 a) Which of these materials have odor. 
 
 b) Which have taste. Classify them. 
 
 c) Where " taste " is located in the mouth. 
 
 HEARING. 
 
 Apparatus ; Tuning fork and resonance chamber. 
 
 Stretched wire or catgut (violin). 
 
 Violin bow. 
 Deinonstrations and experiments : 
 i. Sound dependent on vibration. 
 
 2. Pitch* " " rapidity of vibration. 
 
 3. Volume " " extent of vibration. 
 
 4. " " " resonance. 
 
 5. Test of acuteness of hearing with watch at varying dis- 
 
 tances from ear. 
 
 6. Test the sense of direction by hearing, 
 
 a) Using both ears and closing eyes. 
 
 b) Using one ear " " " . 
 
 VISION. 
 
 Materials : Fresh eye of white rabbit, calf or sheep. 
 Apparatus : Cards with two parallel fine black lines £ m.m. 
 apart. 
 Cards for blind spot (spots 2 in. apart). 
 Worsteds for color test (Milton Bradley). One 
 skein of each of the standard prismatic colors 
 with their tints and shades will supply a large 
 class if cut up into small hanks. 
 
 * Pitch may be graphically demonstrated by means of a manometric 
 flame and a revolving mirror, using the voice or a cornet for the produc- 
 tion of tones. 
 
VISION. 19* 
 
 Color top with color disks (Milton Bradley). 
 Prism. A small glass prism, 6o° angles. 
 Photographic camera. Any photographh cam< 
 
 which has a ground glass will answer. 
 Spectac le lenses, < oncave and < onvex. 
 Candle. 
 
 Screen, a piece of cardboard placed in a vertical 
 position on base. 
 Demonstrations : 
 
 i) Remove eye from the socket of a freshly killed rabbit. 
 Point eye toward a window and note 
 
 a) Image of window on retina. 
 
 b) Size and inversion of image. 
 
 2) Demonstrate formation of image by a lens. Use a 
 camera with ground glass, or an ordinary magnifying 
 glass, and receive image on paper. 
 
 3 Demonstrate effect of diaphragms on brightness and 
 sharpness of image. 
 
 4) Analyze white light by means of a prism, throwing 
 
 spectrum on white paper. 
 
 5) Mix colors by means of color top. 
 
 a) Black with white in different proportions (grays). 
 
 b) Various colors with white (tints). 
 
 c) " " " black (shades). 
 r /) << " " each other. 
 
 6) Test color blindness by giving to pupil a set of the 
 
 standard colors and their tints and shades ; hold up 
 color and ask for the selection of all pieces resem- 
 bling it. 
 
 7) Use lenses and lighted candle for the formation of 
 
 actual images. 
 
39 2 DEMONSTRATIONS AND EXPERIMENTS. 
 
 a) Near sightedness. Arrange screen just behind 
 
 the focus of lens (image on screen somewhat 
 blurred). Place concave spectacle lens in front 
 of magnifying glass and note result. 
 
 b) Far sightedness. Arrange screen just in front of 
 
 the focus of lens (image on screen somewhat 
 blurred). Place convex spectacle lens in front 
 of magnifying glass and note result. 
 8) Indicate by means of diagrams 
 
 a) Corresponding parts of retinae. 
 
 b) How size and distance of objects are estimated. 
 Experiments : 
 
 i) Sharpness of vision. 
 
 What is the farthest distance at which the two parallel 
 lines on card can be seen as two (using one eye) 
 
 a) When card is held in line of vision ? 
 
 b) When card is held 20 away from line of vision ? 
 
 2) Changes in iris. 
 
 a) Sit facing a window ; cover one eye with hand for 
 
 one minute. Quickly uncover eye and note 
 changes in pupil by means of a mirror. 
 
 b) Observe eye of companion in a uniformly lighted 
 
 room or out of doors, and compare the size of 
 pupil when looking at a distant object with that 
 when looking at an object six inches away. 
 
 3) Blind spot. 
 
 What is the distance at which the right hand spot on 
 card disappears when one looks at the left spot with 
 right eye, holding the card so that the spots are 
 on the same level ? 
 
 (Draw a diagram of an eye and locate the axis of 
 vision, blind spot, lens, iris, cornea, retina.) 
 
VISION. 39 3 
 
 4) Accommodation: Determine the range of accommoda- 
 
 tion in your own eye. 
 
 5) Binocular vision. 
 
 a) Hold two pencils vertically in front of the ey< 
 
 one at a distant e of one foot, the other at two 
 feet. When looking at either one what is the 
 appearance of the other, and why? Show by 
 diagram. 
 
 b) Under what conditions do you see " single " when 
 
 using both eyes ? 
 
 6) What are the movements of the eyeballs in changing 
 
 from far to near vision ? 
 
 7) Test visual judgment of 
 
 a) The sizes of disks of different colors (black, white, 
 
 red, etc.) but of the same size. 
 
 b) The lengths of vertical and horizontal lines of the 
 
 same length. 
 
 c) The two halves of a line, one of which is crossed 
 
 by several short lines. 
 
INDEX. 
 
 Abdominal aorta, 170 
 
 Abdominal cavity, B, 10 
 
 Abdominal respiration, 206 
 
 Abduction, 49 
 
 Absorbents, 85, 159, 161 ; rela- 
 tion of, to excretion, 86 
 
 Absorption, from the mouth, 
 pharynx and gullet, 144 ; 1 
 from the stomach, 144 ; from ' 
 the small intestine, 144; from 
 the large intestine, 146 ; of 
 fats, 139 
 
 Accommodation, 276 
 
 Acetabulum, 47 
 
 Acid, acetic, 97; glycocholic, 
 139; hydrochloric, 15, 135; 
 oleic, iS; palmitic, 16; stearic, 
 16; taurocholic, 139 
 
 Acinous glands, 107, 109 
 
 Adam's apple, 290 
 
 Afferent (sensory) nerves, 250, 
 252 
 
 Air, changes produced in, by 
 being breathed, 209; neces- 
 sary quantity of, for each per- 
 son, 212; quantity of, breathed 
 daily, 199, 20S; renewal of, in 
 the lungs, 204; unwholesome, 
 212; why the lungs fill with, 
 204. 
 
 Air-passages, 195; cilia of, 195 
 
 Air-sacs, 197 
 
 Albumin, egg, 15, 93; serum, 
 
 15 
 Albuminous (proteid) sub- 
 stances, 15; action of bile on, 
 139; of gastric juice on, 135; 
 of pancreatic secretion on, 
 137; special importance of, as 
 food, 89 
 
 Alcohol, 98; as a food, 98 
 
 Alimentary canal, 6, ^4; ab-. 
 sorption from, 143; anatomy 
 of, no; general arrangement 
 of, 106; subdivisions of, no 
 
 Alimentary principles, 93; car- 
 bohydrate, 94; hydrocarbon, 
 94; inorganic, 95; proteid, 93 
 
 Alveoli (see Air-sacs) 
 
 Amoeba, 151 
 
 Amyloids (see Carbohydrates) 
 
 Amylopsin, 131 
 
 Anaemia, 157 
 
 Anatomy, human, 1, 2, 12 
 
 Anatomy, microscopic (see 
 Histology) 
 
 Anatomy, of alimentary canal, 
 no; of circulatory organs, 
 163; of ear, 279; of eyeball, 
 269; of joints, 46; of larynx, 
 289; of liver, 12S; of muscular 
 system, 52; of nervous sys- 
 tem, 230; of respiratory or- 
 gans, 193; of skeleton, 17; of 
 skin, 222; of urinary organs, 
 251 
 
 Animals, classification of, 6 
 (foot-note) • 
 
 Animal charcoal, 43 
 
 Animal heat, 76 
 
 Ankle joint, 33, 49 
 
 Antitoxin, 302 
 
 Anvil (incus) bone, 280 
 
 Aorta, 163, 166; thoracic, 170; 
 abdominal, 170 
 
 Apex beat (cardiac impulsed, 
 1 So 
 
 Apex of heart, 165 
 
 Appendicular skeleton, 20 
 
 Appetite, cause of, 142 
 
 395 
 
39 6 
 
 INDEX. 
 
 Aqueous humor, 273 
 
 Arachnoid, 235 
 
 Arch of foot, 32, 35 
 
 Areolar tissue, subcutaneous, 
 222 
 
 Arm, skeleton of, 21 
 
 Arterial blood, 150, 179 
 
 Arterial pressure, 189 
 
 Arteries, 164, 169 ; aorta, 166 ; 
 axillary, 170 ; brachial, 170 ; 
 coeliac axis, 170 ; common 
 iliacs, 170; coronary, 168, 169; 
 femoral, 170 ; hepatic, 128 ; 
 innominate, 169 ; left com- 
 mon carotid, 169 ; left sub- 
 clavian, 169; mesenteric, 170; 
 peroneal, 170; popliteal, 170; 
 pulmonary, 167 ; radial, 170, 
 186; renal, 170,215,218; right 
 common carotid, 170 ; right 
 subclavian, 170 ; temporal, 
 1S6 ; tibial, 170 ; ulnar, 170 ; 
 vertebral, 170 
 
 Arteries, course of the main, 
 169; muscles of the, 190 ; 
 properties of the, 170 ; why 
 placed deep, 173 
 
 Arterioles, 172 
 
 Articular cartilage, 20, 38 
 
 Articular extremities of bones, 
 38 
 
 Articulations, 19 
 
 Arytenoid cartilages, 291 
 
 Assimilation, S5, 86 
 
 Astigmatism, 276 
 
 Astragalus, 32 
 
 Atlanto-axial articulation, 24 
 
 Atlas vertebra, 24 
 
 Auditory nerve, 242 
 
 Auricles, 166 ; function of the, 
 
 183 
 Auricular contraction, 181 
 Auriculo-ventricular orifice, 166 
 Auriculo - ventricular valves, 
 
 169, 181 
 Auscultation, 204 
 Automatic nerve centres, 255 
 Axial skeleton, 20 
 Axillary artery, 170 
 Axis cylinder (neuron) of 
 
 nerves, 245 
 Axis vertebra, 24 
 
 Backbone (sec Vertebral col- 
 ' umn) 
 
 Bacteria, 301 
 
 Ball and socket joint (enarthro- 
 sis), 48 
 
 Basement membrane, 109 
 
 Base of heart, 165 
 
 Bathing, 192, 22S ; proper time 
 for, 229 
 
 Baths, shower, 229 ; warm, 
 229 
 
 Beans, nutritive value of, 98 
 
 Beef-tea, 61 
 
 Biceps muscles, definition of, 
 52, 55 56 
 
 Bicuspids (premolars), 112 
 
 Bile, 129, 139 ; action of, in fat 
 absorption, 139 ; uses of, 139 
 
 Bile duct, common (ductus com- 
 munis choledochus), 129 
 
 Bi-penniform muscles, 56 
 
 Bladder, urinary, 215 
 
 Blind spot, 272 
 
 Blister, 220 
 
 Blood, arterial and venous, 150, 
 179 ; changes undergone by, 
 in the lungs, 214 ; circulation 
 of, 176 ; coagulation of, 152 ; 
 colorless corpuscles of, 150 ; 
 flow of, in the capillaries and 
 veins, 187 ; functions of, 147, 
 148 ; gases of, 155 ; histology 
 of, 148 ; as a medium of ex- 
 change, 155; hygiene of, 156; 
 quantity of, in the body, 
 157 ; red corpuscles of, 149; 
 whipped (defibrinated), 153 
 
 Blood-plasma, 148, 152 
 
 Blood-serum, 152 ; composition 
 of, 154 
 
 Blushing, 190 
 
 Body, centre of gravity of, 68; 
 chemical composition of, 14; 
 constructive power of, 89 ; 
 co-operation of the organs of, 
 230 ; daily need of foods by, 
 100; general plan of, 4; levers 
 in the, 64; movements of, 46; 
 oxidations in, 78 ; oxygen 
 food of, 81 ; pulleys in, 67 ; 
 quantity of blood in, 157; 
 resistance of body to infec- 
 
INPf X. 
 
 397 
 
 tion, l?l ; temperature of, 77; 
 
 wastes "i . - |. 
 
 Bones, chemical composition 
 
 of, 42; fractures <>f, 44 ; func- 
 tion of, 17; gross structure 
 of, 36 ; histology of, 4° '. in- 
 ternal structure of, 38 ; of 
 cranium, 28 ; of ear, 329 ; of 
 face, 2() ; of lower limb, 21 ; 
 of pectoral arch, 20; of pelvic 
 arch, 21 ; of upper limb, 21 ; 
 reason that they are hollow, 
 38; varieties of, 39 
 
 Bone-ash, 43 
 
 Bone-black (animal charcoal), 
 
 43 
 Bone corpuscles, 42 
 Bony skeleton, 20; hygiene of, 
 
 43' 
 Brachial artery, 170 
 Brain, 234, 2S3; growth of, 261; 
 
 hygiene of, 261 ; localization, 
 
 257 
 
 Bread, composition of, 92; 
 wheaten, superiority of,97 
 
 Breastbone, 20, 28 
 
 Bronchi, 195 
 
 Bronchitis, 196 
 
 Buccal cavity (see Mouth cav- 
 ity) 
 
 Butter, 94 
 
 Butyrin, 94 
 
 Cabbage, nutritive value of, 
 98 
 
 Caecum, 126 
 
 Calcaneum (heel bone), 32 
 
 Calcium carbonate, 15, 43 
 
 Calcium phosphate, 15, 43, 44, 
 96 
 
 Calices of kidney, 217 
 
 Canaliculi of bone, 41 
 
 Cane sugar, 95 
 
 Canine teeth, 112 
 
 Capillaries, 164, 172; absence ot 
 pulse in, 189; circulation in, 
 187. 188; pulmonary, 169; sys- 
 temic, 166 
 
 Capsular ligament, 47 
 
 Carbohydrates (amyloids), 16, 
 94; kinds of, in the body, 16 
 
 Carbonate of lime, 15, 43 
 
 Carbon dioxide, as a waste 
 produi t, B3; in the blood, 155: 
 percentage of, in unwhole- 
 some air, 211, 213; quantity 
 
 of, passed from the lungs in 
 a day, 210; useless as a food, 
 00 
 
 :iac impulse (apex beat), 
 I So 
 Cardiac orifice of stomach, 121 
 Cardiac period, events occur- 
 ring in a, 181 
 Cardio-motor nerves, 252 
 Carotid arteries, 169, 170 
 Carpal bones, 21, 39; joints be- 
 tween, 51 
 Carrots, nutritive value of, 98 
 Cartilage, articular, 20, 38; cells 
 of, 17; costal, 28; function of, 
 25; intervertebral, 22, 25 
 Casein, 16, 93; vegetable, 93 
 Cells, 11, 12; air, of lungs, 197; 
 cartilage, 17; ciliated, of air 
 passages, 195; forms of. 11; 
 nerve, 245; plain muscle, 60; 
 structure of, 11 
 Cellulose, 92, 141 
 Cement of teeth, 114 
 Centre of gravity of body, 63 
 Centres, nerve (see Nerve-cen- 
 tres) 
 Centres, reflex, use of, 259 
 Centrum of vertebrae, 23 
 Cerebellum, 239; functions of, 
 
 258 
 
 Cerebral hemispheres, 239 
 
 Cerebro-spinal liquid, 235 
 
 Cerebrum, 256 
 
 Cervical enlargement of spinal 
 cord, 236 
 
 Cervical vertebrae, 22 
 
 Cheese, nutritive value of, 97 
 
 Chemical changes in respired 
 air, 209 
 
 Chemical composition of albu- 
 mens, 15; of bile, 139; of 
 blood-serum, 154; of body, 
 14; of bone. 42; of carbohy- 
 drates, 16; of fats, 16; of gas- 
 tric juice, 135; of lymph, 162; 
 of muscle, 61 ; of pancreatic 
 secretion, 137; of red cor- 
 
39« 
 
 INDEX. 
 
 puscles, 149; of respired air, 
 209 
 
 Chest (see Thorax ) 
 
 Chondrin, 93 
 
 Chordae tendineae, 169 
 
 Choroid, 269 
 
 Chyle. 136, 141 
 
 Chyme, 136 
 
 Cilia, 195 
 
 Circulation, 85, 176; in capilla- 
 ries and veins, 187; portal, 
 177; pulmonary, 176; sys- 
 temic, 176; diagram of, 17S 
 
 Circulatory organs, 163; rela- 
 tion of, to excretion, S6; dia- 
 gram of, 164 
 
 Circulatory system, function of 
 the different parts of the, 163 
 
 Circumduction, 49 
 
 Circumvallate papillae, 116 
 
 Clavicle (collar-bone), 20 
 
 Clotting of blood (see Coagula- 
 tion) 
 
 Coagulation of blood, 152; cause 
 of, 152; uses of, 154 
 
 Coccyx, 23 
 
 Cochlea, 2S0 
 
 Cceliac axis, 170 
 
 Coffee, 99 
 
 Cold, exposure to, 191 
 
 Collar-bone (clavicle), 20 
 
 Colloids, 135, 146 
 
 Colon, 126 
 
 Colorless blood corpuscles, 150 
 
 Comminuted fracture of bones, 
 44 
 
 Common bile-duct (ductus com- 
 munis choledochus, 129 
 
 Compact bone, 3S; structure of, 
 
 39 
 Complemental air, 199 
 Compound fracture of bone, 44 
 Concha, 279 
 
 Condiments as foods, 92 
 Conductive tissues, 296 
 Connective tissue, 18 
 Conservation of energy, law of, 
 
 74: illustrations of, 75 
 Consonants, classification of, 
 
 293 
 Constructive power of the body, 
 89 
 
 Convolutions of the brain, 240 
 Cooking, 99 
 
 Co-ordinating tissues, 296 
 Co-ordination, 231; centre of, 
 
 253 
 Cord, spinal, functions of, 
 
 254 
 Corn, nutritive value of, 98 
 Cornea, 269 
 
 Coronary arteries, 168, 169 
 Coronary veins, 168 
 Corpuscles of blood, 148 
 Corti, organ of, 280 
 Costal cartilage, 28 
 Costal respiration, 206 
 Cranial nerves, 240; sutures, 
 
 29 
 Cranium, bones of, 28 
 Cricoid cartilage, 291 
 Crypts of Lieberklihn, 125 
 Crystalline lens, 274 
 Crystalloids, 146 
 Cuticle (epidermis), 220 
 
 Death, from starvation, 78 
 Death-stiffening (rigor mortis), 
 
 59 
 
 Defibrinated blood, 153 
 
 Deglutition (see Swallowing) 
 
 Dentine, 114 
 
 Dermal senses, 283 
 
 Dermis, 222; papillae of, 223 
 
 Development of the body, 295 
 
 Dextrin, 94 
 
 Diabetes, 300 
 
 Dialysis (osmosis), 145 
 
 Diaphragm (midriff), 8, 200 
 
 Diarrhoea, 191 
 
 Diastole of heart beat, 1S0 
 
 Diet, advantages of a mixed, 
 101, 108; relation of diet to 
 work, 104 
 
 Dietaries, standard, 104 
 
 Differentiation of tissues, 296 
 
 Digastric muscle, 56 
 
 Digestion, 84, 106; gastric, 35; 
 influence of saliva in, 133; in- 
 testinal, 1S1; object of, 131 
 
 Diphtheria, inoculation in, 302 
 
 Disassimilation, S6 
 
 Disease, definition of, 301; im- 
 munity from, 302 
 
INDEX. 
 
 399 
 
 Dislocations, $l\ reduction of, 
 
 Division of labor, physiologi- 
 cal, 1 1 
 
 Dorsal (neural) cavity, 51 con- 
 tents Of, 5, i° 
 
 Dorsal vertebra-. 22 
 
 Duct of glands, 109 
 
 Du<t, common bile, 129; cystic, 
 129; hepatic, 128; of parotid 
 gland, 119; of submaxillary 
 gland, 119 
 
 Duodenum, 123, 130 
 
 Dura mater, 235 
 
 1 >\ spepsia, 142 
 
 Ear, 329 
 
 Efferent (motor) nerves, 250, 
 
 252 
 Egg-albumin, 15, 93 
 Eggs, nutritive value of, 97 
 Eighth pair cranial (auditory) 
 
 nerves. 242 
 Elasticity of the arteries, 188, 
 
 1S9; of the lungs, 19S 
 Elastic tissue, 141 
 Elbow joint, 50. 55 
 Elements found in the body, 14 
 
 (foot-note) 
 Eleventh pair cranial (spinal 
 
 accessory) nerves, 242 
 Emmetropic eye, 276 
 Emulsion, 138 
 Enamel, 114 
 Endolymph, 2S0 
 Endoskeleton, 17 (foot-note) 
 Energy, 74, So; chief forms of, 
 expended by the body, 80; 
 conservation of, 74, 80; source 
 of, in the body, 7° 
 Epidermis, 220 
 Epiglottis, 120. 290 
 Equilibrium, nitrogenous, 94 
 Equilibrium, sense of, 282 
 Ethmoid bone, 29 
 Eustachian tube, 120,279 
 Excretion and reception, inter- 
 mediate steps between, 84 
 Excretions, removal of, 86 
 Excretory organs, 84 
 Exercise. 72; effect of, 298 
 Exoskeleton, 17 (foot note) 
 
 Expiration, 198, 203 
 Extension at joints, 
 
 Extensor mus< les, '>4 
 
 External auditory meatus, V) 
 
 External ear, 27<> 
 
 I.xtracts of meat, 63 
 
 accommodation of, globe 
 'of, 269; hygiene of, 277; re- 
 fracting substances of, 274 
 
 Eyeball, anatomy of, 209 
 
 Eyelashes, 267 
 
 Eyelids, 266 
 Eye-socket, 266 
 
 Face, bones of, 29 
 
 Facial nerve, 242 
 
 Fasciculi of muscles, 58 
 
 Fats (hvdrocarbons), 16, 94; ab- 
 sorption of, 190; action of 
 bile on, 134; of gastric juice 
 on, 135; of pancreatic secre- 
 tion on, 13S; as a reserve 
 food, 78, 81; emulsifying of 
 138, 141 ; kinds of, in body, 16 
 
 Fattv acids, 94 
 
 Fauces, 119; isthmus of the, 
 no, 134; pillars of the, 119 
 
 Femoral artery, 170 
 
 Femur. 21, 47 
 
 Fibres, 11; plain muscle, 59". 
 striped muscle, 5S; nerve, 
 
 243 
 
 Fibrillar, 59 
 
 Fibrin, 16, 153 
 
 Fibrinogen, 91, 153 
 
 Fibula (peroneal bone), 21, 39 
 
 Fifth pair cranial (trigeminal) 
 nerves, 241 
 
 Filiform papillae, 117 
 
 Flatulence, 122 
 
 Flexion at joints, 49 
 
 Flexor muscles, 64 
 
 Food, accessory, 92; amount of, 
 required daily, 100; analyses, 
 103 ; as a force generator, 
 91; as a force regulator, 91 ; 
 as a machinery former, 91; 
 as a tissue former, S3; com- 
 position of, SS; cooking of. 
 99; inorganic, 95; alcohol as a 
 food, 98; need of, 76, 77: n uI >- 
 oxidizable, 90; nutritive val- 
 
400 
 
 INDEX. 
 
 ue of different, 96; necessity 
 of proteid, 93; special impor- 
 tance of albuminous, 89; sup- 
 ply of animal, 90 
 
 Food principles, fuel values of, 
 95 
 
 Foodstuffs (see Alimentary 
 principles) 
 
 Foot, skeleton of, 22; peculiari- 
 ties of human, 35 
 
 Foramen, intervertebral, 24; 
 magnum, 28, 234; oval, 280 
 
 Force-generating foods, 91 
 
 Force-regulating foods, 91 
 
 Forearm, movements of, 50, 55 
 
 Fore-limb (see Upper-limb) 
 
 Fossa, glenoid, 49 
 
 Fourth pair cranial (pathetici) 
 nerves, 240 
 
 Fractures of bones, 44 
 
 Free (floating) ribs, 2S 
 
 Frog's web, circulation in, 187 
 
 Frontal bone, 2S 
 
 Fruits, nutritive value of, 9S 
 
 Fuel values of food principles, 
 95 
 
 Fundamental tone, 2S2 
 
 Fungiform papillae, 116 
 
 Furred tongue, 117 
 
 Gall (see Bile) 
 
 Gall bladder, 129 
 
 Games, use of, 73 
 
 Ganglia, 234, 255 ; Gasserian, 
 241; spinal, 238; sympathetic, 
 243 
 
 Gases of the blood, 155 
 
 Gasserian ganglion, 241 
 
 Gastric digestion, 135 
 
 Gastric glands, 121 
 
 Gastric juice, 121, 135 
 
 Gelatine, 42, 93 
 
 Gelatinization, stage of, in co- 
 agulation, 152 
 
 Giantism, 300 
 
 Glands, 106; forms of, 109; gas- 
 tric, 121; internal secretion 
 of, 299: kinds of, 107; lachry- 
 mal, 107; lymph, 161; mam- 
 mary, 8; Meibomian, 267; of 
 skin, 226; of small intestine, 
 125; salivary, 119 
 
 Glenoid fossa, 49 
 Gliding joints (arthrodia), 51 
 Glosso-pharyngeal nerves, 242 
 Glottis, 288 
 
 Glucose (grape sugar), 16, 94; 
 conversion of starch into, 132 
 Gluten, 93, 97 
 Glycerine, 16, 94 
 Glycocholic acid, 139 
 Glycogen, 16, 95, 130, 144 
 Grape sugar (see Glucose) 
 Gray nerve fibres, 245 
 Gullet (see (Esophagus) 
 Gums, 94, 112 
 
 Habits, 260 
 
 Haemal cavity (see Ventral cav- 
 ity) 
 
 Haemoglobin, 150, 179, 214 
 
 Hair-follicle, 235 
 
 Hairs, 225 
 
 Hand, skeleton of, 21 
 
 Hard palate, m 
 
 Haversian canals, 40 
 
 Haversian system, 41 
 
 Health, definition of, 301 
 
 Hearing, 279 
 
 Heart, 7; beat of, 180; cavities 
 of, 166; dissection of, 178; 
 position of, 165; how nour- 
 ished, 167; muscle of, 61; 
 nerves of, 185; palpitation of, 
 122; sounds of, 183; vessels 
 connected with, 166; work 
 done by daily, 184 
 
 Heat of body, source of, 76; in- 
 fluence of starvation upon, 
 77 
 
 Heat units, 95 
 
 Hepatic artery, 128 
 
 Hepatic duct, 128 
 
 Hepatic veins, 177 
 
 Hibernation, 7S (foot-note) 
 
 High heels, bad effects of, 43 
 
 Hilus of kidney, 217 
 
 Hind limb (see Lower limb) 
 
 Hinge joints (ginglymi), 49 
 
 Hip-joint, 21, 46 
 
 Histology, definition of, 2; of 
 blood, 148; of bone, 40; of 
 kidneys, 218; of lungs, 197; of 
 lymph, 161; of muscle, 58; of 
 
INDEX. 
 
 40 1 
 
 nerve cells, 245; of nerve 
 fibres, 244; of retina, 270; of 
 skin, 220 
 Hollow veins (see Vetue cava) 
 Human anatomy, definition of, 
 
 I, 8. 12 
 Human physiology, definition 
 
 of, 1, 2, 12 
 Humerus, 21, 36 
 Hunger, 264 
 
 Hydrocarbons (see Fats) 
 Hydrochloric acid, 15, 135 
 Hygiene, definition of, 1, 2; of 
 blood, 156; of bony skeleton, 
 43; of brain, 261 ; of eyes, 277; 
 of muscles, 71; of respiration, 
 205; of skin, 227; of teeth, 114 
 Hyoid bone, 20, 115 
 Hypermetropia, 276 
 Hypermetropic eye, 276 
 Hypoglossal nerves, 243 
 
 Ileo-ccecal valve, 127 
 
 Ileum, 123 
 
 Iliac arteries, 170 
 
 Immunity from disease, 302 
 
 Impulse, nature of nervous, 247 
 
 Incisors, 112 
 
 Incus (anvil bone), 280 
 
 Indigestible substances, 141 
 
 Infection, resistance of body to, 
 
 151 
 
 Inferior maxillary bone (mandi- 
 ble). 29 
 
 Inferior maxillary nerve, 242 
 
 Inferor turbinate bone, 29 
 
 Innominate artery, 169 
 
 Innominate bone (os innomina- 
 tum or pelvic bone), 21, 47 
 
 Inoculation in diphtheria, 302 
 
 Inorganic constituents of the 
 body, 15 
 
 Inorganic foods, 95 
 
 Insertion of muscles, 55 
 
 Inspiration, 198, 203 
 
 Intercellular substance, 12, 17 
 
 Intercentral fibres, 258 
 
 Internal ear (labyrinth), 279, 2S0 
 
 Internal secretion of glands, 
 299 
 
 Intervertebral foramina, 24; 
 disks, 25 
 
 Intestinal digestion, 141 
 
 Intestinal juice (succus enteri- 
 cus), 140 
 
 Intestines, digestion in, 141: 
 large, 125 (see Large intes- 
 tine); small, 123 (see Small 
 intestine) 
 
 Invertebrate animals, charac- 
 teristics of, 6 
 
 Invertin, 131 
 
 Involuntary muscles, 60 
 
 Iris, 269, 273 
 
 Irritable tissues, 296 
 
 Isthmus of the fauces, no, 
 134 
 
 Jejunum, 123 
 
 Joint, ankle, 22; elbow, 50, 55; 
 hip, 21, 47; knee, 49, shoul- 
 der, 32, 49 
 
 Joints, 19; ball and socket, 4-; 
 general structure of, 46 ; glid- 
 ing, 5i: hinge, 49; pivot, 50; 
 movements at, 44 
 
 Kidneys, 7, 215, 300; gross an- 
 atomy of, 217; histology of, 
 21S; secretion of, 219 
 
 Knee-cap (patella) 21 
 
 Knee-joint, 49 
 
 Labor, physiological division 
 of, 12 
 
 Labyrinth (internal ear), 2S0 
 
 Lachrymal apparatus, 267 
 
 Lachrymal bones, 29 
 
 Lachrymal glands, 107 
 
 Lacteals, 124, 145, 161 
 
 Lactose (milk sugarj, 16, 95 
 
 Lacunae of bone, 41 
 
 Lamellae of bone, 41 
 
 Large intestine, in, 125; ab- 
 sorption from, 146 
 
 Larynx, 195, 289; muscles of, 
 291 
 
 Leg, skeleton of, 21 
 
 Levers in the body, 64 
 
 Lieberkiihn, crypts of, 125 
 
 Liebig's extract of meat, 63 
 
 Ligaments, 18, 47; capsular, 47; 
 round, 47; transverse, of 
 atlas, 24, 50 
 
402 
 
 INDEX. 
 
 Light, action of, on the retina, 
 
 273 
 
 Limbs, comparison of upper 
 and lower, 29; general struc- 
 ture of, S 
 
 Liver, 127; functions of, 130 
 
 Localization of sensations of 
 brain, 257 
 
 Locomotion, 69 
 
 Long bones, 39 
 
 Long sight (hypermetropia), 
 
 275 
 
 Lower jaw, bone of, 29; move- 
 ments of, 49 
 
 Lower limb, comparison of up- 
 per and, 29; peculiarities of, 
 in man, 34; skeleton of, 21 
 
 Lumbar enlargement of spinal 
 cord, 236 
 
 Lumbar vertebrae, 22 
 
 Lungs, 6, S4, 196; changes un- 
 dergone by blood in, 214; 
 elasticity of, 198; quantity of 
 C0 2 passed out from, in a 
 day, 210; quantity of O taken 
 up by, in a day, 210; renewal 
 of air in, 19S; why they fill 
 with air, 204 
 
 Lunula of nails, 225 
 
 Lymph, 157; chemistry of, 162; 
 histologv of, 161; renewal of, 
 153 
 
 Lymphatics of small intestine, 
 
 124 
 
 Lymphatic vessels (absorbents), 
 
 159 
 
 Magnesium phosphate, 96 
 
 Malar bone, 29 
 
 Malleus (hammer) bone, 2S0 
 
 Malpighi, pyramids of, 217 
 
 Maltose, 132 
 
 Mammalia, definition of, 8, 10 
 
 Mammary glands, 8 
 
 Man, as a vertebrate animal, 5, 
 10; place of, among verte- 
 brates, 8, 10 
 
 Mandible (inferior maxillary 
 bone), 29 
 
 Margarin, 94 
 
 Marrow, 38, 39; red, 3S; yellow, 
 39 
 
 Matrix, 225 
 
 Maxilla (superior maxillary 
 
 bone), 29 
 Maxillary nerve, inferior, 242; 
 
 superior, 242 
 Meat extracts, 63 
 Meats, cooking of, 99; nutritive 
 
 value of, 97 
 Medulla oblongata, 240, 255 
 Medullary cavity of bone, 38, 
 
 40 
 Medullary sheath of nerves, 
 
 245 
 
 Meibomian follicles, 267 
 
 Membranes of the brain and 
 spinal cord, 234 
 
 Mesenteric arteries, 170 
 
 Metacarpal bones, 21, 39 
 
 Metatarsal bones, 22, 39 
 
 Microscopic anatomy (see His- 
 tology) 
 
 Middle ear, 279 
 
 Midriff (see Diaphragm) 
 
 Milk, as a food, 44; nutritive 
 value of, 97; sugar (lactose), 
 16, 95; teeth, 112 
 
 Mitral valve. 169 
 
 Molar teeth. 112 
 
 Motor (efferent) nerves, 250, 
 252 
 
 Motor stimuli, 21S 
 
 Motor tissues, 296 
 
 Mouth cavity, no, in; absorp- 
 tion from, 144 
 
 Movements, at joints, 49; of 
 eyeball, 26S; of the body, how 
 effected, 46; in space, 69 
 
 Mucin, 141 
 
 Mucous coat, small intestine, 
 123 
 
 Mucous membrane, of air-pas- 
 sages, 195; of alimentary 
 canal, 106 
 
 Mumps, 119 
 
 Muscles, 46, 52; chemical com- 
 position of, 61 ; contraction 
 of, 54; gross structure of, 57; 
 histology of, 5S; how con- 
 trolled, 56; hygiene of, 71; of 
 arteries, 190; of heart, 61; of 
 larynx, 291; of small intes- 
 tine, 125; of stomach, 123; 
 
INPI X. 
 
 403 
 
 origin and insertion of, 55; 
 papillary, K >. 1 - 1 ; parts of, 
 52; rectus abdominis, 5<>; spe- 
 cial physiology of, 64; varie- 
 ties of, '55 
 
 M us< alar fibres. 
 
 M uscular sense. 
 
 Muscular tissue, striped, 57; 
 plain, 59 
 
 Muscular work, influence ol 
 starvation Upon, 77; source, 
 
 74 
 
 Musculo- motor nerves, 252 
 Mustard, use of, as a food, 92 
 Myopia, 276 
 M yopic eye, 276 
 Myosin, 16, 61, 93 
 
 Nails, 225 
 
 Nares, posterior, 29 
 
 Nasal bones, 29 
 
 Nerve action, 24S 
 
 Nerves, cranial, 240; kinds of, 
 243; spinal, 237 
 
 Nerves, heart, 1S5; inferior 
 maxillary, 242; ophthalmic, 
 241; superior maxillary, 242; 
 sympathetic, 243; trophic, 297 
 
 Nerve-cells, 245 
 
 Nerve-centres, 232, 234, 246 
 
 Nerve-fibres, afferent and effer- 
 ent, 250; kinds of, 243 
 
 Nerve-ganglia, 234 
 
 Nerve-trunks, 232 
 
 Nervous control of respiration, 
 205 
 
 Nervous impulses, nature of, 
 
 247 
 
 Nervous system, anatomy of, 
 230 
 
 Neural arch, 24 
 
 Neural cavity (see Dorsal cav- 
 ity) 
 
 Neurilemma of nerve fibre, 244 
 
 Neuron of axis cylinder, 245, 
 248 
 
 Ninth pair cranial (glosso-pha- 
 ryngeal) nerves, 242 
 
 Nitrogen-excreting organs, 
 general arrangement of, 215 
 
 Nitrogenous equilibrium, 94 
 
 Non-oxidizable foods, 90 
 
 Non-vascular tissues, 148 
 
 Nucleolus, II 
 
 N U< li'US I 1 
 
 Nut rit ion. B6; of cells, 2<>7 
 
 N utritive tissues. 
 
 Nutritive value of differen 
 
 foods, <)<> 
 
 Occiiti \i bones, 28 
 
 Odontoid (tooth -like) process of 
 
 the axis, 29, 50 
 Odorous substances, 286 
 QEsophagus (gullet), 6, no, 120; 
 
 absorption from, 144 
 
 Oil glands (sebaceous glands), 
 227 
 
 Oils (see Fats) 
 
 Oleic acid, 16 
 
 Oleine, 16, 94 
 
 Olfactory lobes, 239 
 
 Olfactory nerves, 240 
 
 Ophthalmic nerves, 241 
 
 Optic commissures, 240 
 
 Optic nerves, 240, 265 
 
 Organ, definition of, 3; circula- 
 tory, 85, 163, 164; digestive, 
 85, 106; nitrogen-excreting, 
 215; of hearing, 279; of sight, 
 265, of smell, 2S6; of taste, 
 286; of temperature sense, 
 2S3; of touch, 283; receptive 
 and excretory, 84; respira- 
 tory, S5, 193 
 
 Organ of Corti, 280 
 
 Organic constituents of the 
 body, 15 
 
 Organic matter, relation of, to 
 carbon dioxide determined 
 by odor, 213 
 
 Origin and insertion of muscles, 
 
 55, 
 
 Os innominatum (see Innomi- 
 nate bone) 
 
 Osmosis, 145 
 
 Oval foramen, 280 
 
 Overtones, 282 
 
 Oxidations, 78, 79 
 
 Oxidations in the body, 78 
 
 Oxygen absorption of, from the 
 lungs, 179 214; in the blood, 
 155; influence of, on the color 
 of the blood, 214; quantity 
 
404 
 
 INDEX. 
 
 of, taken up by the lungs in a 
 
 day, 210 
 Oxygen food of the body. Si 
 Oxyhemoglobin, 179, 214 
 
 Pain, sensations of, 249, 2^5 
 
 Palate, in 
 
 Palate bones, 29 
 
 Palmatin, 16, 94 
 
 Palmitic acid. 16 
 
 Palpitation of the heart, 122 
 
 Pancreas, 12S, 130, 300 
 
 Pancreatic secretion, 137; ac- 
 tion of, on foodstuffs, 13S 
 
 Papillae of the dermis, 223 
 
 Papillae of the tongue, 116 
 
 Papillary muscles, 169; use of 
 the, 181 
 
 Parietal bones, 28 
 
 Parotid gland, 119 
 
 Patella (knee-capi, 21 
 
 Peas, nutritive value of, 9S 
 
 Pectoral arch or girdle, 20; 
 comparison of pectoral and 
 pelvic girdles. 30 
 
 Pedicle of vertebrae, 24 
 
 Pelvic arch or girdle, 21; com- 
 parison of pectoral and pel- 
 vic girdles, 32 
 
 Pelvis. 21, 34 
 
 Pelvis of kidney, 217 
 
 Penniform muscles, 56 
 
 Pepper, use of, as a food, 92 
 
 Pepsin, 131, 135 
 
 Peptones, 135: absorption of, 
 
 144 
 Pericarditis, 165 
 Pericardium, 165 
 Perilymph, 280 
 Perimysium, 58 
 Periosteum, 36, 39 
 Peristalsis, 125 
 Peritoneum, 109 
 Permanent teeth, 112 
 Peroneal artery, 170 
 Perspiration, 226 
 Phagocytosis, 151 
 Phalanges of fingers, 21, 39; of 
 
 toes, 22, 39 
 Pharynx, no, 119; absorption 
 
 from, 144 
 Phosphate of lime, 15, 43, 44 
 
 Physiological division of labor, 
 
 12 
 Physiology, human, definition 
 
 of, 1, 2, 12 
 Physiology of muscle, special 
 
 and general, 6,4 
 Pia mater, 235 
 Pillars of the fauces, 119 
 Pitch, 2?2. 2SS 
 Pituitary body, 300 
 Pivot joints, 50 
 Plain muscular tissue, 59 
 Plants, as food for animals. 90 
 Pleura, 197 
 Pleurisy, 187 
 
 Pneumogastric nerves, 1S5, 242 
 Poison, definition of, 92 
 Polygastric muscles, 56 
 Pons Varolii, 239 
 Popliteal artery, 170 
 Pork, nutritive value of, 97 
 Portal circulation, 177 
 Portal vein, 12S, 177 
 Posterior nares, 29 
 Potassium phosphate, 96 
 Potatoes, nutritive value of, 9S 
 Premolars (bicuspids), 112 
 Presbyopia, 27S 
 
 Primitive sheath of nerves, 244 
 Pronation, 50 
 Protective tissues, 296 
 Proteid alimentary principles, 
 
 93 
 
 Proteid food, necessity of, 93 
 
 Proteid substances (see Albu- 
 minous substances) 
 
 Ptomaines. 301 
 
 Ptyalin, 131 
 
 Pulleys in the body, 67 
 
 Pulmonary artery, 167 
 
 Pulmonary circulation, 163, 176 
 
 Pulmonary veins. 167 
 
 Pulp cavity of tooth, 113 
 
 Pulse, 1S6 ; disappearance of, 
 in capillaries and veins, 1S9 ; 
 hard and soft, 1S6 ; rate of, 
 1 86 
 
 Pupil, 270. 273 
 
 Pus, 152 
 
 Pyloric orifice of stomach, 121 
 
 Pyloric sphincter, 122 
 
 Pyramids of Malpighi, 217 
 
IND/ V. 
 
 4o5 
 
 R \. 1 icosi (acinous) glands, 107, 
 
 ioq 
 Radial artery, 17", 186 
 
 ins, 21, 
 
 Reaction, modes of nervous, 
 
 258 ; voluntary, 2^4 
 Re< eption and excretion, inter- 
 mediate steps between, 84 
 
 Receptive organs of thebodv, 
 
 B4 
 
 Rectum, 1 26 
 
 Rectus abdominis muscle, 56 
 Red blood corpuscles, composi- 
 tion of, 155; function of, 150; 
 of man, 149 ; of other ani- 
 mals, 150 
 Red marrow, 38 
 Reducing dislocations, 51 
 Reflex action, 251 ; spinal, 254 
 Reflex centres, 259 ; use of, 
 
 259 
 Refracting media of the eye, 
 
 269, 274 
 
 Renal arteries, 170, 215, 218 
 
 Renal secretion (urine), 219 
 
 Renal veins, 215 
 
 Rennin, 131 
 
 Reproductive tissues, 88 
 
 Residual air, 199 
 
 Resonance, 289 
 
 Respiration, 85; abdominal, 206; 
 chemistry of, 209; costal, 206; 
 hygiene of, 205, 212; nervous 
 control of, 205; object of, 193 
 
 Respiratory centre, 205 
 
 Respiratory organs, 85, 194 ; 
 anatomy of, 193 
 
 Respiratory sounds or mur- 
 murs, 203 
 
 Retina, 265; histology of, 270 
 
 Ribs, 20, 2S; action of, in respi- 
 ration, 201 
 
 Rice, nutritive value of, 98 
 
 Rotation at joints, 49 
 
 Round ligament, 47 
 
 Running, 71 
 
 Sacrum, 23, 25 
 
 Saliva, 131; chemical action of, 
 
 132; influence of, in digestion, 
 
 133; uses of, 132 
 Salivary glands, 119 
 
 Salt, as a constituent of the 
 body, 1 ; ; importance of, 
 
 food, 96 
 Saponification, 138 
 Sarcolemma, 58 
 
 Scapula (shoulder-blade), 20, 39 
 
 Sclerotic, 209 
 
 Scurvy, 98 
 
 Sebaceous glands (oil gland^i, 
 
 227 
 Sebaceous secretion, 227 
 Secretion, internal, of glands, 
 109; of gastric glands, 122, 
 135; of glands of small intes- 
 tine, 140; of kidneys, 219; of 
 lachrymal gland, 267 ; of 
 liver, 128, 139 (see Bile); of 
 Meibomian follicles, 267 ; of 
 pancreas, 137 (see Pancreatic 
 secretion); of salivary glands, 
 131 (see Saliva); of sebaceous 
 glands, 227; of sweat glands, 
 226 
 
 Secreto-motor nerves, 252 
 
 Segmentation, 295 
 
 Semicircular canals, 280 
 
 Semilunar valves, 168, 181, 2S2; 
 demonstration of action of, 
 
 Semivowels, 293 
 
 Sensation and motion, relation 
 between. 253 
 
 Sensations, 248; common, 264; 
 localization of skin, 2S4 
 
 Sense, muscular, 285 
 
 Senses, special, 263; common, 
 264; dermal, 283 
 
 Sensory (afferent) nerves, 250 
 
 Sensory stimuli, 249 
 
 Septum of heart, 166 
 
 Serous membrane, 165 
 
 Serum (see Blood-serum) 
 
 Serum albumin, 15; coagula- 
 tion of, 155 
 
 Seventh pair cranial (facial) 
 nerves, 242 
 
 Shaft of bones, 38 
 
 Short bones, 39 
 
 Short sight (myopia), 275 
 
 Shoulder girdle (see Pectoral 
 arch ) 
 
 Shoulder joint, 32, 49 
 
 Shower baths, 229 
 
406 
 
 INDEX. 
 
 Sight, sensation of, 265; organ 
 of, 265 
 
 Sigmoid flexure, 127 
 
 Simple fracture of bones, 44 
 
 Sixth pair cranial (abducentes) 
 nerves, 242 
 
 Skeleton, appendicular, 20; axi- 
 al, 20; composition of, 17; of 
 cranium, 28; of face, 29; of 
 lower limb, 21; of upper 
 limb, 21; peculiarities of 
 human, 33 
 
 Skin, 220; as a sense-organ, 
 227; glands of, 226; histology 
 of, 220; hygiene of, 227 
 
 Skull, 20, 28; peculiarities in 
 the position of, 33 
 
 Sleep, 156 
 
 Small intestine, ill, 123; ab- 
 sorption from, 144; glands 
 of, 125; lymphatics of, 124; 
 mucous coat of, 123; muscu- 
 lar coat of, 125; villi of, 
 124 
 
 Smell, 2S6 
 
 Soft palate, in 
 
 Sound, 282 
 
 Sounds of the heart, 183 
 
 Sounds, respiratory, 203 
 
 Sound waves, action of, on the 
 ear, 280 
 
 Special physiology of muscles, 
 
 64 
 Speech, 289 
 Sphenoid bone, 29 
 Spinal accessory nerves, 242 
 Spinal cord, 7, 235; functions 
 
 of, 254 
 Spinal ganglia, 243 
 Spinal nerves, 237 
 Spinal reflex, 254 
 Spine (see Vertebral column) 
 Spinous process of vertebrae 
 
 (neural spine), 24 
 Spleen, 163, 299 
 Spongy (cancellated) bone, 38 
 Sprains, 51 
 Standing, 67 
 
 Stapes (stirrup bone), 280 
 Starch, 99; action of bile on, 
 
 139; of gastric juice on, 136; 
 
 of pancreatic secretion on, 
 
 137; of saliva on, 133; solu- 
 ble, 100 
 
 Starvation, death from, 78; in- 
 fluence of, on muscular work 
 and animal heat, 77 
 
 Steapsin, 131, 138 
 
 Stearic acid, 16 
 
 Stearin, 16, 94 
 
 Sternum (breast-bone), 20 
 
 Stimulants, 92 
 
 Stomach, 6, no, 121; absorp- 
 tion from, 144; digestion in, 
 X 35I glands of, 121 ; muscular 
 coat of, 122 
 
 Storage tissues, 296 
 
 Striped muscular tissue, 57, 58 
 
 Sub-clavian artery, 169 
 
 Sub-lingual gland, 119 
 
 Sub-maxillary gland, 119 
 
 Suffocation, 82,210 
 
 Sugar, cane, 95; grape (see 
 Grape sugar) 
 
 Sugar of milk (lactose), 16, 95 
 
 Superior maxillary bone, 29 
 
 Superior maxillary nerve, 242 
 
 Supination, 50 
 
 Supplemental air, 199 
 
 Supporting tissues, 296 
 
 Suprarenal capsule 
 
 Swallowing (deglutition), 120, 
 
 133 
 Sweat, 226 
 Sweat (sudoriparous) glands, 
 
 109, 226 
 Sweetbread (see Pancreas) 
 Sympathetic nerve centres, 7, 
 
 10, 243; ganglia of, 243 
 Synovial fluid, 48 
 Synovial membrane, 48 
 Syntonin, 61, 93 
 Systemic circulation, 163, 176 
 Systole of heart-beat, 180 
 
 Tabular bones, 39 
 
 Tarsal bones, 22, 39; joints be- 
 tween, 51 
 
 Tarsus, benefits of peculiar 
 structure of, 35 
 
 Taste, 286 
 
 Taurocholic acid, 139 
 
 Tea, 99 
 
 Tears, 267 
 
lNPr:x. 
 
 407 
 
 Teeth, characteristics of Indi- 
 vidual, 112; genera] structure 
 of, 113; hygiene of, 114: kinds 
 of, 113 
 
 Temperature- changes In re- 
 spired air, - 
 Temperature of the body, 76; 
 regulation of, 77; regulation 
 by means of sweat glands, 
 226 (foot note) 
 Temperature sense, 283 
 Temporal artery, 186 
 Temporal bone, 28 
 Tendons. iS, 52, 53 
 Tenth pair cranial (pneumogas- 
 
 tric) nerves, 242 
 Thein, 92 
 
 Thigh bone (femur), 21 
 Third pair cranial (motores 
 
 oculi) nerves, 242 
 Thirst, 264 
 Thoracic aorta, 170 
 Thoracic duct, 161 
 Thorax, contents of, 8; dorso- 
 ventral enlargement of, 201; 
 structure of, 200; vertical en- 
 largement of, 200 
 Thyroid cartilage, 290 
 Thyroid glands, 299, 300 
 Tibia, SI, 29 
 Tibial artery, 170 
 Tidal air, 199 
 Tight lacing, evil effects of, 
 
 206 
 Timbre, 2S2 
 
 Tissues, classification of, 3 
 (foot-note); connective, 18; 
 differentiation of , 296; nerve, 
 243; non-vascular, 14S; plain 
 muscular. 59; striped muscu- 
 lar, 57; subcutaneous areolar, 
 222; ultimate structure of, II 
 Tone, 2S2; fundamental, 282 
 Tongue, 115; furred, 117 
 Tonsils, 119 
 Touch, 283 
 Toxin, 302 
 Trachea (windpipe), 6, 195; 
 
 structure of, 195 
 Transverse ligament of the at- 
 las, 25, 50 
 Triceps muscle, 56 
 
 Triceps muscles, definition of, 
 
 55 
 Trichina, 97 
 
 Tricuspid valve, 169 
 Trigeminal nerves, 241 
 Trophic nerves, 252, 297 
 Trypsin, 137 
 Tubular glands, 107, 109 
 Turbinate bones, 29 
 Turnips, nutritive value of, 98 
 Twelfth pair cranial (hypoglos- 
 sal) nerves, 243 
 Tympanic membrane, 279 
 
 Ulna, si, 39 
 
 Ulnar artery, 170 
 
 Undifferentiated tissues, 118 
 
 Units, heat, 118 
 
 Unstriped muscle cells, 60 
 
 Upper jaw bone, 29 
 
 Upper limb, comparison of up- 
 per and lower limbs, 29; skel- 
 ton of, 21 
 
 Urea, 83, 219; useless as food : 
 96 
 
 Ureters, 215 
 
 Urethra, 215 
 
 Urinary bladder, 215 
 
 Urine, 219 
 
 Uriniferous tubules, 219 
 
 Uvula, 112 
 
 Vaccinia (cowpox), 303 
 
 Vagi, 242 
 
 Valves, auriculo -ventricular, 
 169, 181; ileo-coecal, 127; of 
 the veins, 174; semilunar, 169, 
 
 1S1 
 Valvulae conniventes, 123 
 Vaso-motor nerves, 252 
 Veins, 164, 173; absence of 
 
 pulse in, 1S9: circulation in, 
 
 1S6; valves of the, 177 
 Veins, coronary, 168; hepatic, 
 
 177; hollow (venae cavae), 166; 
 
 portal, 12S, 177; pulmonary, 
 
 167; renal, 215 
 Vegetable casein, 93 
 Venae cavae (hollow veins), 166 
 Venous blood, 150. 179 
 Ventilation, 210; methods of, 
 
 213 
 
4o8 
 
 INDEX. 
 
 Ventral (haemal) cavity, 5; con- 
 tents of, 5, 7, 10 
 Ventricles, 166 
 Ventricular contraction, 181 
 Vermiform appendix, 126 
 Vertebrae, 23, 34; structure of, 
 
 23 
 
 Vertebral column (spine, back- 
 bone), 5. 20, 22, 27;curvatures 
 of, 25; mechanism of, 25; pe- 
 culiarities of human, 34 
 
 Vertebrate animals, character- 
 istics of, 6; classification of, 8 
 (foot-note) 
 
 Vestibule of ear, 280 
 
 Villi of small intestine, 124 
 
 Viscero-motor nerves, 252 
 
 Visual apparatus, 265 
 
 Visual centre, 265 
 
 Vital capacity, 199 
 
 Vitreous humor, 270 
 
 Vocal cords, 288, 291 
 
 Voice, 288; range of human, 
 291 
 
 Voluntary muscles, 59 (see also 
 foot-note) 
 
 Voluntary reaction, 254 
 
 Vomer, 29 
 
 Vowels, 293 
 
 Walking, 69 
 
 Warm baths, 229 
 
 Wastes of the body, 83; removal 
 of, 141, 148 
 
 Water, as a constituent of the 
 body, 15; as a food, 90, 95; 
 as a force regulator, 91; as a 
 waste product, 83; quantity 
 of, lost through the kidneys, 
 219; through the lungs, 209; 
 through the skin, 227 
 
 Wheat, nutritive value of, 97 
 
 Whipped (defibrinated) blood, 
 
 153 
 
 White blood corpuscles, 150 
 
 White nerve fibres, 244 
 
 Windpipe (see Trachea) 
 
 Wisdom teeth, 112 
 
 Woollen garments, 191 
 
 Work, daily, of heart, 184; esti- 
 mates of daily mechanical, 
 104; influence of starvation 
 upon muscular, 77; power of 
 the body to do, 74; relation of 
 diet to, 104 
 

 
 
 
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