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Las diagrammas suivants iliustrant la mAthoda. 1 2 3 1 2 3 4 5 6 1.0 36 ■ 2.0 Hi Hi I 2.2 1.8 MICROCOPY RESOLUTION TEST CHART NATIONAL BUREAU OF STANDARDS STANDARD REFERENCE MATERIAL 1010a (ANSI -Id ISO TEST CHART No. 2) «p -m FUNDAMENTALS OF HUMAN PHYSIOLOGY FUNDAMENTAL.S OF HUMAI PHYSIOLOGY BY R. G. PEARCE, B.A., M.D., Director of Medical Research Laboratory. Lakeside Hospital, Cleveland. Ohio; Formerly Assistant Professor of Physiology. University of Illinoia, Chicaxo. Illinois. AND J. J. R. MACLEOD, M.B., D.P.H., PiOfcssor of Physiology in the University of Toronto. Toronto. Canada: Formerly Professor of Physiology. Western Reserve University. Cleveland, Ohio. SECOM) EJJITIUX ST. LOUIS V. MOSBY COMPANY 1918 Copyright, 1916, 1918, by C. V. Mosby Company Prtnaf C. V. Uotby Company St. Lovi* PREFACE TO FIRST EDITION. The object kept in view in the preparation of the present vol- ume has been to give an elementary, yet comprehensive, review of the various facts and theories wliich go to form the modern science of human physiology. It is hoped that such a volume will be of use, not only to college students who may desire, for the sake of the knowledge itself, to learn something of the work- ings of the human body, but also to those who must know some physiology before they can properly proceed to study other sciences, such as pharmacology and hygiene. Although similar in scope with the sister volume designed primarily for the use of dental students, considerable altera- tions have been made so as to substitute, for those parts of the subject with which the dental student roust have a special ac- quaintance, matters of more general interest. Thus, much less space is devoted to the subjects of salivary secretion and dontal caries, while on the other hand more attention has been given to a brief description of the structure of the more important organs and tissues, and to other general facts of anatomy. The physiological action of few of the better known drugs has also been indicated, and the chapters dealing with the physiology of the central nervous system have been somewhat simplified. In the first two cliaptei-s some of the essential facts bearing on the application of the laws of physical chemistry to life pro- cesses are discussed, and since a general knowledge of these laws is assumed, it is advised that students who may be unfamil- iar with them should consult some text in general chemistry. The authors desire to thank Prof. T. Wingate Todd and Mr. P. M. Spurney for their kind assistance in the preparation of the diagrams. The authors are also deeply indebted to Dr. Paul G. Hanzlik for his advice in connection with the adaptation of the book for the use of students of pharmacy. R. Q. Pearce. J. J. R. Macleod. (oi^l5 PREFACE TO SECOND EDITION. Tlio sliort tinu- t'lapsin*! hctwcoii the first edition ami the second t-dition iiav Mot lU'ccssitatcd any material chancres in the text. Numerons small eri-ors l-av "ven corroetcd and an ap- pendix containing notes on pubKe and personal hygiene has ])een addy Cavities— The Skeleton— The Bones of the Trunk -T^e L.imbs —The Articuladons 17 Chapter I THE PHYSICO-CHEMICAL BASIS OF LIFE. The Chemical Basis of Animal Tissues— Water— Proteins— Lipoids —Carbohydrates— The Influence of Physico-Chemical Laws on Physiological Processes — Properties of Crystalloids — Osmotic Phenomena in Cells— Reactions of Body Fluids— Colloids— Gen- eral Nature of Enzymes or Ferments , 33 Chapter III. THE MUSCULAR SYSTEM. The General Properties of Mascular Tissues — Contractility — Irritability— The Simple Muscular Contraction— Tetanic Con- traction—Effect of Load— Elaatlcity of Muscle — Chemical Changes Accompanying Contraction— Rigor Mortis 48 Chapter IV. THE BLOOD. Introduction— Physical Properties— The CorpuscleE— Erythrocytes -Hsemoglobln— Enumeration of Blood Corpus"'es— The Cigin of the Erythrocytes— The White Cells— Leuco.ytes— Lympho- cytes— Estimation of the White Cells— Function of the Leuco- eytPR— The Blood Platelets— The Blood Plasma 51 vii VIU CONTENTS. Chafteb v. THE BLOOD. Page The Defensive Mechanism o/ the Blood — Coagulation of the Blood — Antibodies in the Blood — The Process of Inflammation — Toxins — Antitoxins — Ehrlich's Side Chain Theory of Immunity — Anaphylaxis — Phagocytosis — Opsonins — Vaccines — Serum Di- agnosis 5S Chapter VI. THE LYMPH. Lymph Formation — Lymphagogues — Lymph Reabsorption — The Movement of Lymph 66 Chapter VII. THE CIRCULATORY SYSTEM. Introduction — Anatomical Considerations — The Heart — The Blood Vessels — Physiological Properties of Heart Muscle — Character of Cardiac Contraction — The Sequence of the Heart Beat — The Action of Inorganic Salts on the Heart Beat — The Vascular Mechanism of the Heart — Definition of Terms — Events of the Cardiac Cycle — The Heart Sounds — Diseases of the Cardiac Valves 70 Chapter VIII. THE CIRCULATION. The Blood Flow Through the Vessels — The Part the Heart Plays— The Part the Arteries Play — Arterial Blood Pressure — Factors Which Maange in Lungs 104 Chapter X. THE RESPIRATION. The Nervous Control of the Respiration— Reflex Respiratory Move- ments-Chemical Control of Respiration — The Effect of Changes in the Respired Air on the Respiration— Mountain Sickness— Ventilation— The Voice — Mechanism of the Voice — Speech 121 Chafteb XI. ANIMAL HEAT AND FEVER. Animal Heat— Normal Temperature — Factors Concerned in Main- taining the Body Temperature — Regulation of Body Tempera- ture — Fever — Antipyretics 132 Chapter XII. DIGESTION. Necessity and General Nature of Digestion— The Alimentary Canal —Anatomical ConBlderations- Blood Supply of the Alimentary Canal— The Mouth— The Teeth— The Salivary Gland*— The Pharynx— The Stomach— The Small Intestines— The Large In- testines — The Liver and the Pancreas - 138 CONTENTS. Chapter XIII. DIGESTION. Page Digestion in the Mouth— Salivary Secretion— The Nerve Supply of the Salivary Glands — The Reflex Nervous Control of Salivary Secretion— General Functions of Saliva— The Hygiene of the Mouth — Tartar Forn^-.tion and Salivary Calculi— Mastication — Deglutition or Swallowing— The Act of Vomiting 150 Chapter XIV. DIGESTION: IN THE STOMACH. The Secretion of Gastric Juice — The Active Constituents of Gastric Juice — The Movements of the Stomach — The Open- ing of the Pyloric Sphincter — Rate of Discharge of Food from the Stomach 163 Chaiteb XV. DIGESTION: IN THE INTESTINE. Secretion of Bile and Pancreatic Juice — Functions and Composi- tion of Pancreatic Juice and Bile — Chemical Changes Produced by Intestinal Digestion — Bacterial Digestion In the Intestine — Products of Bacterial Digestion — Protection of Mucous Mem- brane of Intestine Against Autodigestion— Movements of the Intestines — Action of Cathartics — The Absorption of Food — R(>8um<^ of .Vrtions of Digestive Enzymes 174 Chapter XVI. METABOLISM: ENERGY BALANCE. Introductory — General and Special Metabolism — Energy Balance — Caloric Value of Foods — Basal Heat Production— Influence of Food, Muscular Work, Atmosphere, and Size of Body 18fi Chapter XVII. METABOLISM: THE MATERIAL BALANCE OF THE BODY. Starvation — Normal Metabolism — Nitrogen Balance — Protein Spar- ers — The Irreducible Protein Minimum — Varying Nutritive Values of DIft'erent Proteins 194 ■M CONTENTS. XI ClIAPTEE XVIII. THE SCIENCE OP DIETETICS. Page The Proper Amount ot Nitrogen— Chittenden's Experiments— The Most Suitable Diet for Efficiency— Chemical Composition of the Common Foodstuffs 202 Chapter XIX. SPECIAL METABOLISM. Metabolism of Proteins— Urea— Ammonia— Creatlnin—Purin Bodies — Relative Importance of Proteins, Fats and Carbohydrates in Metabolism 211 Chapter XX. SPECIAL METABOLISM. Metabolism of Fats — Metabolism of Carbohydrates — Metabolism of Inorganir Salts — Vitamines 218 Chapter XXI. THE DUCTLESS GLANDS. Introduction — Thyroid and Parathyroid Glands — Adrenal Glands — Pituitary Gland— Spleen— Thymus Gland 227 Chapter XXII. THE FLUID EXCRETIONS. The Excretion of Urine— Composition of Urine— Organic Constitu- ents — Urea — Ammonia — Creatlnin — Uric Acid — Inorganic Con- stituents—Abnormal Constituents— The Organs of Excretion — The Blood Supply of the Kidney— Nature of Urine Excretion Micturition — Drugs which act on the Kidney — The Secretions of the Skin— The Sweat Glands— The Sebaceous Glands— The Mammary Glands 239 zu CONTENTS. Chapteb XXIII. THE NERVOUS SYSTEM. Page The Functions and Structure of the Nervous System — Fundamental Elements of the Reflex Arc — Integration of the Nervous Sys- tem 251 Chapteb XXIV. THE NERVOUS SYSTEM. Reflex Action — The Nerve Structures Involved in the Reflexes of the Higher Animals — The Receptors of Pain, Touch, Tempera- ture — Local Anesthesia and Analgesia — The Afferent Fiber — Choice of Paths on Entering Spinal Cord — The Nerve Center — Thn Efferent Neurone — Types of Reflexes — Spinal Shod; — The Essential Characteristics of Reflex Action — Muscular Tone and Reciprocal Action of Muscles — Symptoms Due to Lesions Affecting the Reflexes 256 CUAFTES XXV. THE NERVOUS SYSTEM. The Brain Stem — The General Course and Functions of the Cranial Nerves — Tlie Brain — Influence of the Brain on the Reflex Func- tions of the Spinal Cord — Functions of the Cerebrum — Cerebral Localization — Experimental and Clinical Observations — The Sensory Centers — The Mental Process — Aphasia — The Cerebel- lum—Relationship to Body Equilibrium — The Semicircular Canals — The Sympathetic Nervous System — General Character- istics — The Course of Some of the Most Important Pathways — Action of Drugs on the Central Nervous System 26i' Chapter XXVI. THE SPECIAL SENSES: VISION. Optical Apparatus of the Eye— Formation of Retinal Image- Changes in the Eye During Accommodation from Near Vision — The Function of the Pupil — Imperfections in the Optical System of the Eye — Long and Short-Sightedness- Astigma- tism, etc—The Sensory Apparatus of the Eye — The Functions of the Retina— Blind Spot— Fovea Centralis— The Movements of the Eyeballs— Diplopia— Judgments of Vision— Color Vision — Color Blindness 285 CONTENTS. xin Chapter XXVII. THE SPECIAL SENSES. Page Hearing— The Cochlea— How Sound Waves are Transmitted to this by Tympanic Membrane and Auditory Ossicles — Causes of Deafness — Taste — Nature of Receptors for Taste — The Location of the Four Fundamental Taste Sensations — Rela- tionship Between Chemical Structure and Taste— Association Between Taste, Common Sensation of Touch, and Smell — Action of Certain Drupe on Taste — Smell — Nature of the Re- ceptors of Smell (the Olfactory Epithelium) — Nature of Stimulus 297 CU^U'TEB XXVIII. REPRODUCTION. Fertilization — The Accessory Phenomena of Reproduction in Man — Female Organs — Male Organs — Impregnation — Ovulation — Pregnancy — Birth 306 Pig, 1. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. ILLUSTRATIONS. Page Diagram of a cell 20 Types of epithelial cells 21 Types of epithelial ceils 22 Connective tissue cells from a chick embryo 23 Fibers from ligamentum nuchae of the ox 23 Segment of a transversely ground section from the shaft of a long bone 24 Fat cells treated with alcohol 25 Cell from smooth muscle of intestine; cross section of smooth muscle of Intestine 25 Voluntary muscle fiber 25 Large-sized nerve cell with processes 26 The thoracic and abdominal cavities 28 The human skeleton 29 Dlalyser 39 Thoma-Zeiss Hsemocytome.er 63 White blood-corpuscles from man 55 Position of the heart In the thorax 71 Diagram of the heart and large vessels 72 Diagram of the valves of the heart 73 Cross section of small artery and vein 74 Arterioles and capillaries from the human brain 75 Dissection of heart to show aurlculo-ventrlcular bundle 78 Diagram showing relative pressure in auricle, vestricle and aorta 80 Diagram of experiment to show how a pulse comes to disap- pear when fluid flows through an elastic tube when there is resistance to the outflow 85 Apparatus for measuring the arterial blood pressure in man. . . 87 Section of cat's lung 92 Effect of stimulating vagus and sympathetic nerves on a frog's heart 94 Diagram of structure of lungs showing larynx, bronchi, bron- chioles and alveoli Ill The position of the lungs in the thorax 113 llering's apparatus for demonstrating the action of the respira- tory pump 114 Diagram to show movement of diaphragm during respiration. . 115 xiv ■■M ILLUSTRATIONS. XV Fig. 31. 32. 33. 34. 35. 36. 37. 38. 39. 40. 41. 42. 43. 44. 45. 46. 47. 48. 49. 50. 51. 52. 53. 54. 55. 56. 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. Page Position to be adopted for tffecting aitiflcial respiration 118 Diagram of laryngoscope "^ Position of tlie glottis preliminary to the utterance of sound. . . 128 Position of open glottis *28 The position of the tongue and lips during the utterance of the letters indicated Diagram of the alimentary tube and its appendages II Scheme of a longitudinal section through a human tooth 148 Section from the human maxillary gland 14* The stomach and duodenum opened 146 The mucosa of the stomach 146 Longitudinal section of duodenum near pyloric end 148 The microscopic structure of the liver 149 Cells of parotid glai:d showing zymogen granules 150 The nerve supply of the submaxillary gland 151 The changes which take place in the position of the root of the tongue, the soft palate, the epiglottis and the larynx during the second stage of swallowing 158 Diagrams of outline and position of stomach as Indicated by skiagrams taken on man in the erect position at Intervals after swallow ing food 164 Diagram of stomach showing miniature stomach separated from main stomach by a double layer of mucous membrane. 165 Diagram of the time it takes for a capsule containing bismuth to reach the various parts of the large intestine 184 Diagram of AtwaterBenedict respiratory calorimeter 189 The thyroid gland 229 Cretin, 19 years old 230 Case of myxoedema 231 Median sagittal section through pituitary of monkey 235 Before and after onset of acromegalic symptoms 236 The situation, direction, forms, and supports of the kidney 243 Longitudinal section through the kidney 244 Diagram of urinary system 247 Schema of simple reflex arc 252 Diagram of nervous system of segmented invertebrate 254 Diagram of section of spinal cord showing tracts 259 Under aspect of human brain 269 Vertical transverse section of human brain 270 Cortical centers in man 275 The semicircular canals of the ear 282 Formation of Image on retina 287 Section through the anterior portion of the eye 288 XVI ILIiL'STRATlONS. Pig. Page 67. A, spherical aberration ; B, chromatic aberration 291 68. Errors in refraction 292 69. Semidiagrammatic section through the right ear 298 70. Tympanum of right side with the auditory ossicles in place 300 71. Schema to show the course of the taste fibers from tongue to brain 302 COLOR PLATES. Plate I. Diagram of circulation Facing 76 Plate II. Dietetic chart Facing 207 Plate III. Diagram of the uriniferous tubules, the arteries, and veins of the kidney Facing 244 Plate IV. The simplest reflex arc in the spinal cord Facing 257 Plate V. Reflex arc through the spinal cord, in which an inter- mediary neurone exists between the afferent and efferent ne^ rones Facing 259 Plate VI. Course of the pyramidal fibers from the cerebral cor- tex to the spinal cord Facing 260 Plate VII. Diagram of the dorsal aspect of the medulla and pons Facing 272 Plate VIII. Diagrammatic view of the organ of Corti Facing 297 FUNDAIENTALS OF HUMAN PHYSIOLOGY. / CHAPTER I. THE STRUCTURAL BASIS OF THE BODY. The Scope of Physiology. — Physiology is the study of the plienomena of living things, just as anatomy or morphology is a study of their structure. The study of anatomy is most logically pursued by starting with tlie simplest organisms and gradually proceeding through the more complex forms until man is reached. Except for certain fundamental functions, sueli as nutrition, which are common to all cells, this method is not the most suitable one to pursue in physiology, because in the low- est organisms all of the functions are crowded together in a lim- ited number of cells — indeed, it may be in one single cell. It is easier to study a function when it is performed by a tissue or organ that has been set apart for this particular purpose than when it is performed by cells that do many other things. Another reason for p.iying more attention to the functions of higher rather than lower animals is that the knowledge which wc iu(iuire may be more directly applicable in explaining the functions of man, and therefore in enabling us more readily to detect and rectify any abnormalities. During the embryonic development of one of the higher ani- mals, a single cell, the ovum, produces numerous other cells, which become more and more collected into groups, in many of which the cells undergo very marked changes in shape and structure, or produce materials, such as the skeleton or teeth, which show no cell structure whatsoever. Thus we have formed the tissues and organs, each having some particular function of 17 18 THE PHYSIOIXXIICAL SYSTEMS. its own, although certain functions remain which are common to all. In other words, as the organism becomes more and more complex, there comes to be a division of labor on the part of the cells that comprise it. The conditions are exactly like those which obtain in the development of a community of men. In primeval communities there is little division of labor; every indi- vidual makes his own clothes, hunts his own food, manufactures and uses his own implements of war; but as civilization begins to appear, certain individuals specialize as hunters and fighters, otlicrs as makers of clothing, others as artisans. Although, in its first stages, this division of labor may be far from absolute, for every meiiiiicr of the community must still fight and take part in the building of his hut, yet it soon tends to become more and more so, until, as in the civil! /ed communities of this twentieth century of ours, specialization has become the order of the day. A good example of a one-celled animal is the amoeba, which is often found floating in stagnant water, and which consists of nothing more than a mass of tissue, or protoplasm, as it is called, and yet this apparently simple structure can move from place to place, it can pick up and incorporate with its own substance par- ticles of food with which it comes in contact, it can store up as granules certain of these foodstuffs, and get rid of others that it does not require ; it grows as a result of this incorporation, until at last it splits in two and each half repeats the cycle. In other words, this single cell shows all of the so-called attributes of life : movement, digestion and assimilation of food, growth and repro- duction. No one of these properties is necessarily confined to living structures alone, for some perfectly inanimate bodies may exhibit one or other of them, yet when all occur together, we consider the structure to be living. In the higher animals, these functions are performed by the so-called systems, sucU as the digestive, the circulatory, the res- piratory, tlie excretory, the motor, the nervous and the reproduc- tive, each system being composed of certain organs and tissues which are designed for the special purpose of can-ying out some particular function or functions. One function, nowever, is com- mon to all of the organs and tissues, namely, that of nutrition. I FUNDAMENTALS OF HUMAN PHYSIOLOGY. 19 I S I I 3 which includes the process by which the digested food is built up into the protoplasm of the cells, or assimilation, and that by which the resulting substances are broken down again, or disas- similation. It is by these processes that the energy of life is set free; the energy by which the tissues perform their functions, and which appears as body heat. Every cell in the animal body is therefore a seat of energy production, and at the same time each is a machine for converting this energy into some definite form of work. In this regard the animal machine differs from a steam engine, in which energy liberation occurs in the furnace, and conversion of this energy to movement occurs in the pis- tons. The furnace and the machinery of the animal body are located jiTthe tissue cells, and the digestive, circulatory, respira- tory ^nd excretory systems are provided for the purpose of transporting, to and from the living cells, the fuel (i. e., the food), along with the oxygen to burn it and the pases produced by its combustion. These processes of assimilation and disas- similation constitute the study of metabolism, the practical side of which is included in the science of nutrition. The Structural Basis of the Body. As has been indicated above, the structural and physiological unit of the body is the cell, and the structure and function of any organ depends on the nature of the cells which compose it. The general characteristics of the cells present important sim- ilarities, whether it be a cell wliich forms th" -^e organism as in the case of the ama?ba or a cell which 'i infinites- imal part of a higher organism. A cell ma> .e defined as a small mass of protoplasm having a nucleu.s, and in general, wc ma.y regard protoplasm as any material which is endowed with life. It is the physical basis of life, and is not any specific sub- stance. The protoplasm of the muscle cell is, for example, quite different from that of the nerve cell. Indeed in any single cell there are at least two kinds of protoplasm — one composing the nucleus and the other, the cytoplasm. The nucleus is general^' oval or spherical and lies near the center of the cytoplasm, 20 THE EI'ITHELIAI. TISSUES. which forms the outer protoplasmic mass. The cytoplasm sur- rounds the nucleus and is more homogenous than the nucleus. There are often granules and small vacuoles in it which rep- resent stages in the metabolism of the cell. By multiplication and differentiation, the simple cell is finally represented in tlie body in a number of different forms. These \'acuulcs. Chriimatin network. i.initt liflw' »k. Nuclear flu'u]. Nuc.ear membrane. - *. Ctll-niemlirane. -. . Kxophi'sm. -,-.-■:- Spongioplasm. H>ul(>pl:isin. Niiclenliis. Cliromatiii net knot. Cetitriisiime. rt-ntr'xpliere. Forei),'?: inrlosiires. Metaplasm. ••'is 1 — DiMsriMtn of a cell. (Bohni, D;.vi(Ioft and Huber. ) compose the elemental tissues of the body, the epithelial, the founrctivp, the muscular and the nervous tissue. We might also classify the blood and the lytnph, as fundamental tissue. The Epithelial Tissue.— This consists almost entirely of cells with a very small amount of intercellular substance which holds the cells together. This tissue cover s the internal and external free surfaces of the body, as the external layers of the skin, raucous membranes of the moutli, the alimentary canal, the in- ternal surfaces of the body cavities and the secreting eel's along the duet.s of the various glands of the body. Because of its wide distribution and function, we find many varieties of epi- FUNDAMENTALS OF HUMAN PHYSlOrx^GY. 21 thelial cells. Pigs. 2 and 3 illustrate some of the varieties of this tissue. 1/ mims. HM-.I (til. Peiir ihiitti Paiiment ails, Inleruilial cells. \y. 2.— T.vi,os of ..pitholial lolls. (Hill's Histology.) A, SiniDlf coUiinnHr rolls from intestin.. ; B, Ciliated epitlielium from trachea ; C, Epitl.olial cells from bladder. The Connective Tissue.— This group of tissues, iu whieh are iiioluded the Imiies, eartilages and tendons, serves as a support- ing framework for the nin.seular, nervous and glandular organ.. Its function i.s,-nliivl>- one of support. The eonnective tissue cells are made up of two elements, i. e., cells and intercellular 22 THE MUSCULAR TISSUES. substance. The intercellular substance is produced by the con- nective tissue cells and exists in many varieties throughout the body. In places it forms an elastic coat of fibrous material, as in the walls of the blood vessels; it is sometimes dense and PaitmcttI cell. Pcar-shaptd all. Iiilerslilial cell. ^ ( 'ortteum or r". tutriiy layer. Striiinm luiutum. Strtiium granutosum. ■JS] — Miilpighuin or germ- inal layer. Flgr. 3, — Tyi)es of epithelial cells. (Hill's Histology.) A, Section of blad- der epithelium: B, Section of epidermis of sl' "f " Ininsvoisoly Broutul section from the shaft of a : (BOhiii '1 FUNDAMENTALS OF HUMAN PHYSIOLOGY. 25 as the sarcolemma. This variety of muscle (Fig. 9) receives its name of striated from the fact that in microscopic prepara- tion its fibrils show a remarkable cross striation, the significance of whicli i not known. Connerlive-tissur cdl. Nuclru^ nl jatrrlt. -IB, ,. — K;i( .cll.s ;is thoy iippcar in sections treatprt with aU-ohol. ■> .mlic.l 'lissolM-s th.. fat. (Hiir.s Histology.) Nucleu .-t Nucleus >»rtfpy vtin. 1MB. 8-<<. C.ll from .smooth mum-le of intesti.u. ; h. Cross .soctiot. of smooth miLscle of intestine. (Hill's Histology.) smooin Satcolmma. SarcoslyUs the smooth snrrolt-mnia. (Hill's HistoloKy.) T'.^ Nervous Tissues.— Nerve tissue is composed of nerve colls and fibei's ai-ising from the nerve cell. Such a structure IS kiujwii lis a iinn-oiir. The neurone is imbedded and sup- ported by coiii.ective tissue, the neuroglia. The long fibers aris- 26 rjlE GBOS.S iSTRlJCTlTRES OP THE BODY. ing from the nerve cells receive their nourishment from the cell. These may be very long; for example, the nerve cells from whicli the nerves in our hands or feet arise, are located some- where in the spinal cord (see Fig. 10). The long process run- linithlike Irlndfndrnn Uain dendrite. .— Si rmda-y dendrite — Basal dendrite. . . Neurnxis mlh roUalrr.ih. Fig. 10.— Lurge-slzt'ii nerve till with processes. (BOliin and IJavidoff.) 1 1 ing out from the cell is known as an axonc, and the shorter more branching process, the dendrite. The Gross Structures of the Body. From the fundamental tissues the various jiarts and organs of the body are developed, just as the various buildings which form a city are built ovit of the same varieties of building ma- terial. The description of the various individual organs of the FUNDAMENTALS OF HUMAN PHYSIOUXJY. 27 botly will be found in the appropriate chapters. At present we will concern ourselves with a brief consideration of the gross architecture of the body. The Skin. — The body is everywhere covered by the skin. This tissue is built of an outer layer of epithelial tissue and an inner one of connective tissue. The hairs and nails are mod- ifications of epithelial tissue. In the connective tissues are found the blood vessels and nerves which supply the skin. The Subcutaneous Tissue.— Just beneath the skin is a layer composed of connective tissue. In jome places this binds the skin directly to the bones and in others it separates the skin from the miiscles. The subcutaneous fat is found in this layer and is called adipose tissue. The subcutaneous tissue is usually spoken of as fascia. The Muscles.— The skin and the superficial fascia form a pro- tective covering for the muscles, bones and internal organs. The muscles comprise the lean meat of the body and are formed by a mass of muscle cells which have been described above. The muscle bundles are held together by connective tissue, in which are found the blood vessels and the nerves which supply the muscles. The attach ments of the muscles to the bones are known as tne origin and. the insertion of the muscles. The insertion usually refers to the attachment of the muscle on the bone which has the greatest freedom of movement when the muscle con- tracts The covering of the boue is composed of a fibrous con- nective tissue, called the periostei-m. To this the muscles are attached, either directly or indin-ctly, by means of a tough band called A^tendpn. Whenever a mnsele"~contracts, the points of attachment ai ight closer together. The Body ( .s.— The tr - ': has two conipartments which are fillet.' with uie various organs composing the viscera. The ii££er chamber is called the t horac ic cavity and holds the heart and the lings; the lower chamber, which is separated from the upper by a sheet of muscle called the diaphragm, is the^- d^minal ctivity. This contains, mainly, the viscera concerned in the digestion and absorption of food, and the organs of ex- cretion. 28 THE BODY CAVITIES. Cut end of 1st rib Veaiebral roluniii ill tliiinix ItiKlit inarfin of area nf heart KiBhl dome nf diaphraKin Orifice in dla- pliracm fur inferior vena cava Orifice In dia phracm for esophagus* I'illars of diaplirai;m Vertpliral cciliiiim in abdoMicn 4th rih tdinwine under pleural linlnc rieural cavity Left margin nf area of iieart rut end of 5th rib Left dome of diaphragm Orifipe for aorta In diaphragm I'eritonoal cavity I'eivic caritjr / ^ Vie. 11— The thoracic and abdominal cavities. (From a preparation by T. Wingate Todd.) The viscera are directly or indirectly attached to the posterior surfaces of the thoracic and abdominal cavities by means of sheets of connective tissue (caHed mesenteries) in which are found the blood vessels and the nerves that supply the viscera (see Fig. 11). The figures give the general idea of the structure and the position of the various viscera. The cranial cavity is formed by the bones of the skull, and is the receptacle for the brain. Tiie cranial cavity is extended by means of a large opening in the base of the skull into the canal formed by th.« .sjiinous processt>s of the verteltral column. This canal contains tiic spinal coi'd. The Skeleton.— The bones and cartilar's of the bodyjorm the 'Tli« pliutogiaph makes it appear to the right of Its true position. FUNDAMENTALS OP HUMAN PHYSIOIXX3Y. 29 lliiiiicriiH Fihula Tibia Frontal Imne Malar bone Superior niasilla Mandible Verlfbral i-nluinn (cervical) Claiiclo Siernnni KillH Vertebral column (lumbar) 0.S innonilnatum Carpus Mi'tacariius riialanjtcs of flUKcrs fatella u , . ^^^ ^^K. Tardus Metatarsus I'balanges of toes Fiit. 12. The human «keleton. (Irom a photouraph by T. WIngate Todd.) skeleton, whieli is the structural foundation for the soft tissues. We will eonsider it in three divisions: the skull, the trunk, and the limb.s. 30 THE SKELETON. The Bones op the Skull.— The sk ull i.s composed of the bones of the cranium and the face. The cranium is the bony ca.se which protects the brain. It is formed by the union at their edges of several flat-shaped bones, and it is attached to the ver- tebral column in such a way that the spinal canal terminates in the large opening in the base of the skull called the foramen magnum (see Fig. 12). It is through this opening that' the .spinal cord leaves the skull. There are numerous other openings in the base of the skull for the entrance and exit of blood ves- sels and nerves. The nasal and upper and lower jaw bones make the framework for the face. The lower jaw is the onlv unpaired bone in the face. The Bones op the Trunk.— T he spinal colum n is composed of thirty-four or thirty-five irregular-shaped bones, or verte- brae, bound together by ligaments and separated from one~an- other by cartilagenous discs. The upper seven of the vertebra, forming the neck, are joined in a manner which permits of a relatively large degree of motion. These are the cervical ver- tebne. The next twelve vertebra; are the thoracic, and to them the ribs are attached. They have a fairly restricted degree of motion. Below are five larger vertebras forming the lumba r poi-- tion of the column. When the body is bent forward or side- wise, the greatest degree of motion occurs in the joints between the lumbar vertebrae. The rest of the bones forming the ver- tebral column are more or less fused together tg^ form the sa- crum,^onsisting of five bones, and the coccy x, wjth four or five bones representing "the tail of lower animals. The posterior portion of each vertebra consists of an arch of bone. This forms the spinal canal in which the spinal cord lies. The spinal nerves emerge between the bones of the vertebrae along the whole length of the column. There are twelve pairs of ribs. The upper ones are small but they increase progressively in length from above down until the seventh, below which they gradually decrease again. The upper six pairs are attached in front by means of cartilage to the sternum or breast bone. The next four p^irs terminate in 1 FUNDAMENTALS OP HUMAN PHYSIOIXWY. 31 front in a cartilage connecting them with the pair directly above. The two lower pairs are attached only to the vertebrs, and are called the false or floating ribs. The bones of tliejsboulder^rdle are pair ed. The large wing- shaped bone on the lateral posterior surface of the shoulder is the scapula and the smaller bone in front and attached to the breast bone is the clavicle or shoulder bone. The shoulder gir- dle furnishes support for the upper limbs. Tlie bones forming the pelvic or hip girdle are also paired. The individual bones are fused together, however, and appear to form a right and left bone usually called the innomiiiate. The pelvic arch forms the floor of the body cavity and it fur- nishes the support for the lower limbs. The liiMBS.— The upper and lower limbs are more or less alike, inasmuch a^ both contain analogous bones. The bone of the upper arm is the humerus; the lower arm contains two long bones, th« ulna and the radius. There are eight bone .^ in the wrist caUed jLbe. caii)als. The hand bones are the five m_eta- (•ari)a|s, and the fourteen phalanges compose the finger bones. In the lower limb we have the femur or thigh bone, the tibia a'li.Uli.e fibala, the bones of the lower leg. The ankle "^is made up of seven irregular shaped cuboid bones known as the tar- sals. The foot contains five metatarsa ls and the fourteen pha- IflTiges, the bones of the toes. A close stuiy of the figures of the skeleton will give a much better idea of the structure of the skeleton than can be had from a description. Articui.atio2;s.— The union of one bone with another is known as an articulation, of which there are several varieties in the body. When the bones are connected in a manner so that they are immovable, as in the bones of the cranium and hip the union is known as a suture. An articulation allowing some movement of the bones is caUed a joint. The joints in the ver- tebral column allow only a limited amount of motion, whereas the joints of the limbs allow a large amount of motion. In the hip and shoulder we have what is known as a bjU and socket jomk Here the upper end of the limb bones are rounded and 32 .\RTICrr,.\TIONS. fit into a socket of the shoulder or liip bone, allowing a wide range of movement. At the elbow and knee there is aliinge joint which allows the lower segment of the limb to be fl_exed or extended on the upper one in one plane only. This form of joint connects the bones of the fingers and toes. The bones of the wrist and the ankle form a gliding joint, and are capable of little movement. The articulating surfaces of the joints aie covered with a smooth inembrane (synovial), which is bathed with a small amount of fluid which serves to lubricate the joint. The joints are held together by means of ligaments formed from toufeh fibrous tissue. When this connection is torn, with- out a displacement of the bones, the injury is called a sprain, and when the bones are actually displaced, there is a dislocation of the joint. " " ' — ciiAPTKR rr. TIIK PIIYSU'O-CIIK.MlCAr. HASIS OP LIFE. With the object of ascertaining to v.' ..t extent the known laws of physics and chemistry can explain the fundamental processes that are common to all cells, we must make ourselves familiar first of all, with the chemical and physical nature of the constitu- ents of the cell, and secondly, with the physico-chemical laws which govern the reactions that take place between these con- stituents. The same laws will control the reactions which take place in the juices secreted by cells; for example, in the blood and in secretions such as tlie saliva. The Chemical Basis of Animal Tissues.-Certain substances are found m every living cell and in approximately e.|ual quan- tities; hence these may be considered the primary constituents of protoplasm. In general they consist of the proteins, lipoids, in- organic salts, water, and probably the carbohydrates. Protoplast - IS the substance composed of these primary constituents By its activity the protopla.sm produces the secondary constituents of" tlie cell, which are not the same in all cells, and which include the granules of -gment or other material, the masses of glycogen the globules ox fat or the vesicles of fluid which are found em- bedded in the protoplasm. By whatever process we attempt to isolate its constituents, we of course kdl the cell, . that we can never learn by analysis what may have been the real manner of union of these substances in the living condition. All we can find out is the nature of the building material after the structure (the cell) into which it is built has been pulled to pieces. If the chemical process by which we disintegrate the cell is a very energetic one, for example, com- bustion, we always find the elements, carbon, hydrogen, nitrogen oxygen, sulphur, phosphorus, sodium, pot.iSsium, calcium, chlo- 33 34 TIIK CHEMICAL BASIS OP THE CEU-. ■i rine, and usually traces of other elements, such as iodine, iron, etc. If the decomposition be less complete, definite chemical compounds are obtained, namely, wate r, proteins, lipoids, car- bohydrates, and the phosphates and chlorides of sodium, potas- sium and calcium. We shall proceed to consider briefly the main characteristics of each of these substances and their place in the animal economy. Water. — This is the principal constituent of active living organisms, and is the vehicle in which the absorbed foodstuffs and the excretory products are dissolved. It may be sai'l Jndee 1 that protoplasm is essentially an aqueous solution, in which other substances of vast complexity are suspended. Water, on account of its very unique physical and chemical properties, is of prime importance in all physiological reactions. These properties are : its chemical inactivity at body temperatures; its great jsolv ent j power (it is the '>?st ki.\,,-n universal solvent) ; its specific heat, f or capacity of ab&^ -bing heat ; and, depending on this, the large amount of heat which it takes to change water into a vapor — latent heat of steam. Tjiese last mentioned properties are made use of in the higher animals for regulating the body temperature. Of great importance in the maintenance of the chemical bal- ance of the body are the electric phenomena which attend the solution of certain substances in water. These will be discussed later in connection with ionization. Water has also a very great surface tension. It is this property which determines the height to which water will rise in plants and in the soil, and which no doubt plays a role in the processes of absorption going on in various parts of the animal body. Proteins.- -The great importance of prote ins in aiiimal life is attested by the fact that they are absolutely indispensable in- gredients of food. An animal fed on food containing no protein will die nearly as soon as if food had been withheld altogether. Proteins are complex bodies composed of carbon^ hydrogen, oxy- gen, nitrogen, and, in nearly all cases, sulphur. Some may con- tain in addition phosphorus, iron, iodine, or certain other elements. The proportions in which the above elements are found in different proteins do not vary so much as the differences FUNDAMENTALS OF HUMAN PHYSIOLOGY. 35 in the chemical behavior of the proU-iiis would lead us to expect. In general the percontHge composition by weight is; Carbon 53 per cent Hydrogen 7 per cent Oxygen 22 per cent Nitrogen 16 per cent Sulphur 1 to 2 per cent The essential differences in the structure of the molecules of different proteins have been brought to Mght by studies of the products obtained by partially splitting up the molecule. We are able to do this by subjecting protein to the action of super- heated steam, or by boiling with acids or alkalies in various con- centrations, or by the action of the ferments of digestive juices or by bacteria. The cleavage produced by ferments or bacteria i8_ much more discriminate than that brought about by strong chemical reagents; that is to say, the chemical groupings are not so roughly torn asunder by the biological as by the chemical agencies. At first the proteins break up into compounds still possessing many of the features of the protein molecule. These are the proteoses and peptones, which consist of aggregates of smaller molecules, capable of being further resolved into simple crystal- line substances. These have been called the building stones of the protein molecule, and although they differ from one another in many re .^^ects, they have one feature in common, namely, that each consists of an organic acid having one or more of its hydro- gen atoms substituted by the radicle, NH,. Such substances are palled amino bodice, or nmhw acids. For example7the formula of acetic acid is CH.COOH. If for one of the H atoms there is sub- stituted the NIL group, we have CII,NII,COOH, which is araino- acetic acid, or glycocoll. That the large and complex protein molecule is really built up out of these amino bodies has been very conclusively shown by Emil Fischer, who succeeded in causing two or more of them to become united to form a body called a polypeptid. When several amino bodies were thus synthesized, the polypeptid was found to 36 MPOIDS. possess many of the properties of peptones, which we have just stated are the earliest deeoniposition products of protein. Pi-oteins differ from one another, not oidy in the nature of the amino bodies of which tliey are composed (although certain of these are common to all proteins), but also in the manner in which the amino bodies are linked together. We shall see the practical value of knowing what are the amino bodies in a given protein when we come to the sub.iect of dietetics (.see p. 202). The proteins of the cell are classified into two groups. The first includes the simple proteins, such as egg and serum albumin ; and the second, the compound proteins, from which non-protein groups can be split off. L1P01D.S. — These include all the substances composing a cell which are soluble in fat solvents. Besides fats and fatty acid.s. the most important of these substances are lecithin and choles- terol. Lecithin is widely distributed in the animal body, and is very important in the metabolism and in the physical structure of the cell. It consists chemically of glj^erine, fatty acid, phosphoric acid, and a nitrogenous base called cholin. Cholesterol is another widely distributed lipoid. It is not in reality a fatty body, but rather resembles the terpenes. Lecithin and cholesterol are abundant in brain tissue, in the envelopes of erythrocytes, and in bile. The fats exist mainly as secondary constituents of the cell, being deposited in very large amounts in certain of the connective tissue cells of the body, in bone marrow and in the omental tis- sues. Chemically, the tissue fats are of three kinds: olein, pal- mitin, and stearin, each having a distinctive melting point. They are compounds of the tri-valent alcohol, glycerine, and one of the higher fatty acids, oleic, palmitic, or stearic acid. Besides those that are present in the animal tissues, fats made up of glycerine combined with various lower members of the fatty acid series occur in such .secretions as milk. In order to understand the influence which fats have on general metabolism, it is important to remember that they differ from the carbohydrates in contain- H FUNDAMENTALS ().• Uuivi 'HYSIOUKJY. 37 iiig a very low percentage of oxygen and a relatively high per- centage of hydrogen and carbon. Thus, the empirical formula of palmitin is CsiHggOe or C3H,(C,eH3iO,)3, that of dextrose CeH.jOg. and of protein C.oH^jNjAjS. The Carbohydrates arc also mainly secondary cell constitu- ents, although it is becoming more and more evident that they are also necessary as primary constituents. In general they may be defined chemically as consisting of the elements C, H, and O, the latter two being present in the molecule in the same propor- tion as in water; thus, the formula for dextrose is CeHjoOg. The basic carbohydrates arc the simple sugars or monosac- chnrides, such as grape sugar or dextrose. When two molecules of monosaccharide become fused together with the elimination of a molecule of water (thus giving the formula CijHjjO,,), a secondary sugar or disaccharide results. Cane sugar, lactose (or milk sugar) and maltose (or malt sugar) are examples. If sev- eral HBgiisaccharide molecules similarly fuse together, polysac- charides having the formula (CaHmOs)^ are formed. These in- clude the dextrines or gums, glycogen or animal starch, the ordi- nary starches, and cellulose. Since so many molecules are fused together, it is not to be wondered at that there should be so many varieties of each of these classes of polysaccharides, for, as in the case of proteins, not only may the actual "building stones" of the molecule be different, but they may be built together in very diverse ways. The polysaccharides may be hydrolyzed (i. e., caused to take up water and split up) into disaccharides, and these into monosaccharides by boiling with acids or by tlie action of diastatio and inversive fcnucnts (sw p. 47). The following formulte illustrate these facts: 1. CgHijOo^^ a monosaccharide (dextrose). a disaccharide (cane sugar) composed ofi -H..0. 2. C.,H,,0„= C«H„0«+C,II.,0„ 3. (CbHilOJ/i = a polysaccharide (starch) composed of: n C.HijOe — n H„0 where n signifies that an indefinite namber of molecules are involved in the reaction. 38 PHYSIOO-CHEMICAL LAWS. The Influence of Physico-Chemical Laws on Physiological Processes. Having learned of wliat materials the cell is composed, we may proceed to entiiiire into the chemical and physical reactions by which" it performs its functions. The cell, either of plants or of animals, may be considered as a chemical laboratory, in which are constantly going on reactions, that are guided, as to their direction and scope, by the physical conditions under which they occur. A study of the material outcome of these reactions constitutes the science of metabolism, to which special chapters are devoted further on. At present, liowever, we must briefly e.\amine the pliysico-chemical conditions existing in the cell which may give the directive influence to the reactions. "Why should certain cells, like those which line the intestine, absorb digested food and pass it on to the blood, whilst others, like those of tb" kidney, pick up the effete products from the blood and excrete them into the urine! We must ascertain whether these are proces.ses depending on pjirely pbi'sicQ-chemical causes.or whether they are a function of the living protoplasm itself, a vital action, as we may call it. In general it may be said that the aim of most investigations of the activities of cells is to find a physico-chemical explanation for them, and it is one of the achievements of modern physiology that some should have been thus explainable. A large number, however, do not permit of such an explanatioai, and this has induced certain investigators to believe that there are some animal functions which are stri>..;y vital and can never be accounted for on a physical basis. The "physical" and the "vital schools" of phy.siologists are there- fore always witli us. From the standpoint of physical chemistry, the cell may l)o considered as a collection of two classes of chemical substances, called crystalloids and colloids, dissolved in water, or in the lip- oids, or in each other, and surrounded by a membrane which is permeable towards certain substances but not towards others {s.^iiiperineable, jis it is railed). On a larger scale, the same gen- eral conditions exist in all of the animal fluids, such as the blood. FUNDAMENTALS OK HUMAN rilYSIOLOGY. 39 the lymph, the secretions and the excretions. We may therefore study the above laws with a view to applying them to both cells and body fluids. Properties of Crystalloids. — As their name implies, these form crystals under suitable conditions. When present in solu- tion they diffuse quickly throughout the solution, and can readily Kig. 13. — Dialyser made of tube of imichment paper Huspended in a vessel of distnied water. The fluid to be dialysed is placed in the tube, and the distilled water must be frequently changed. pass through membranes^ such as a piece of parehniciit, placed between the solution containing tliom and another solution. This process is called dialysis, and the apparatus used for observing it, a dialyser (see Fig. K{). Dialy sis tljffcrs from filtration, the latter process consisting in the pass..ge of fluids, and the sub- stances dissolved in them, through more or less pervious mem- branes as a result of differences of pressure on the two sides of the membrane. If instead of using a simple membrane, such as parchment, we choose one which does not permit the crystalloid itself to diffuse, but permits the .solvent to do so — a semipermeable membrane, as it is called, — a very interesting property of dis- solved crystalloids comes to light, namely, their tendency to oc- cupy more room in the solvent, tb"t is. to cause dilution by at- tracting the solvent through the membrane. Cell membranes are semipermeable, but they are too small niul delicate for most ex- perimental purposes. For this purpose we use an artificial mem- brane coniposed of a precipitate of copper ferrocyanide sup- ported in the pores of an unglazed clay vessel. If a solution of 40 EI-KCTKOIATKS crystalloid— say, cane sugar— be placed in such a semipermeable membrane and this then submerged in water, it will be found that the cane sugar solution quickly increases in volume, or if expansion be impossible, a remarkably high pressure will be developed. This is called osmotic pressure, and it is a measure of the tendency of dissolved crystalloids to expand in the solvent. It has been found that the laws which govern osmotic pressure are identical with tho.se governing tlie behavior of gases. There- fore, osmotic pressure ought t.. be proportional to the number of molecules of dissolved crystalloid. This is the case for the sugars, but It IS not so for the saline crystalloids, such as the alkaline chlorides, niti-ates, etc., for these cause a greater asmotic pres- sure than we should expect from their molecular weights. Why IS this? -The answer is revealed by observing the behavior of the two classes of crystalloids towards the electric current. So- lutions of sugars or urea do not conduct the current any better than water, whereas solutions of saline crystalloids conduct very readily. The former are therefore called non-chctrolytes and the latter electrolytes. It has been found that the reason for this IS that molecules of electrolytes when they are dissolved break into parts called "ions," each ion being charged with electricity of a certain sign, i. e., positive or negative. When- ever an electric current is passed through the solution, the ions hitherto distributed throughout the solution in pairs carrving electrical charges of opposite signs, now line themselves up so that the ions with one kind of charge form a chain across the solution along which that kind of electricity readilv passes, and m so doing carries the ions with it. This splitting of electrolytes into ions is called dissociation or romzation. The ions which carry a charge of positive elec- tricity and which therefore travel towards the kathode or nega- tivejjoie (.since unlike ..hrtriciti,^ attract each oth.-r) are called kathxons, and the negatively charged ions that travel to the anode nnms Ilvdrogen and the metallic elements belong to the group of kathions; oxygen, the halogens and all acid groups, to the anions. These facts may be more clearly understood from the following equations : m fi;ndament.\i,s of JICMAN IMIVSIOI.OGY. 41 In water, or in a solution of a non-electrolyte, molecules of HjO or non-electrolyte may be represented as existing thus: H2O H,0 H3O H,0 H,0 H,0 H,0 In a solution of an electrolyte, the molecules split into ions thus: Na^ CI- Na^ CI" Na* Cl" Na* CI- Na* CI" Na* Cl- Na* CI- Na* CI- Na* Cl- When an electric current passes through a solution of au electrolyte, the ions arrange themselves thus : Kathode- Anode* Na* Na* Na* CI- CI- Cl- Na* Na* Na* CI- CI- Cl" Na* Na* Na* CI" Ch Cl- To return to osmotic pressure, the ions influence this as if they vm-e molecules, so that when we dissolve, say, sodium chloride in water, the osmotic pressure is almost twice what it should be because every molecule has split into two ions. Osmotic Phenomena in Oells.-Over and over again we shall have to refer to these physico-chemical processes in explaining physiological phenomena. For the present it may make matters clearer if we consider how osmosis explains the behavior of cells when suspended in different solutions. The cell wall acts as a semipermeable membrane. Thus, if we examine red blood cor- puscles suspended in diffei-.-it saline solutions under the micro- scope, we shall observe tha Lhey shrink or crenate when the solu- tions are strong, and expand and become globular in shape when these are weak. TUc shrinkage is due to .liffusion of water out of the corpuscle and the swelling, to its diffusion in; that is to say, in the former case the osmotic pressure of the surrounding fluid ,s greater tlmn that of the corpuscular contents and vice I X 42 REACTION OP BODY FLUIDS. versa in the latter case. In this way we have a simple and con- venient method of comparing the relative osmotic pressure of dif- ferent solutions. When the solution has a higher pressure, it is called hypertonic; when less, hypotonic; when the same, isotonic. It is evident that the body fluids must always be isotonic with the cell contents, and that we must be careful never to introduce fluids into the blood vessels that are not isotonic with the blood. A one per cent solution of common salt is almost isotonic with blood, and is accordingly used for intravenous or subcutaneous injections, or for washing out body cavities or surfaces lined with delicate menibi-anes, such as the conjunctiva or nares. Such a solution is generally called a physiological or normal salt solu- tion. Reaction of Body Fluida.— Closely dependent upon these properties of ionization are the reactions which determine the acidity and alkalinity of the body fluids. When we speak of the degree of acidity or alkalinity of a solution in chemistry, we mean the amount of alkali or acid, respectively, which it is nec- essary to add in order that the solution may become neutral to- wards an indicator, such as litnuis. This titrable reaction is how- ever a very different thing from the real strength of the acid or alkali ; for example, we may have solutions of lactic and hydro- chloric acids that require the same amount of alkali to neutral- ize them, but the hydrochloric acid solution will have much more powerful acid properties (attack other substances, taste more acid, act much more powerfully as an antiseptic, etc.). The rea- son for the difference is the degree of ionization ; the strong acids ionize much more completely than the weak. As a result of this ionization, each molecule of the acid splits into H-ions and an ion composed of the remainder. To ascertain the real acidity tec must therefore measure the concentration of H-ions. (These considerations also apply in the case of alkalies, only in this case OH-ions determine the degree of alkalinity.) This can be done accurately by measuring the speed at which certain chemical processes proceed, that depend on the concentration of H-ions. The conversion of cane sugar into invert sugar is a good process to employ for measuring the speed of reaction. FUNDAMENTALS OF HUMAN PHYSIOLOGY. 43 But even this refinement in technique does not enable us to measure the H-ion concentration— for now we must use this ex- pression when speaking of acidity or alkalinity— of such impor- tant fluids as blood and saliva, in which there is an extremely low H-ion concentration. If either of these fluids be placed on litmus papers, the red litmus turns blue, but all that this signifies is that the litmus is a stronger acid than those present in blood or saliva, so that it Jccomposes the bases with which they were combined and changes the color. If we employ phenolphthalein, which is a much feebler acid, tlien blood serum reacts neutral and saliva often acid. Methods have been devised to estimate the hydrogen-ion con- centration in the various fluids of the body. The details of this cannot be given here. Before leaving this subject, it is important to point out that the blood has an H-ion concentration which is practically the same as that of water, i. e., is as nearly neutral as it could be. Jj. also has the power of maintaining this neutrality practically con- stant even when large amounts of acid or alkali are added to it. Although saliva and some other body fluids are not so nearly neutral as blood, yet they can also lock away much acid or alkali without materially changing the H-ion concentration. This property is due to the fact that the body fluids contain such salts as phosphates and carbonates, which exist as neutral and acid salts, and can change from the one state to the other witho^t greatly altering the H-ion concentration, and yet, in so changing, cjinJock away or liberate H- or OH-ions. This has been called the "buffer" action, and is a most important factor in maintain- ing constant the neutrality of the animal body. OolloidB.— These are substances which do not diffuse through membranes when they are dissolved. Thus if blood serum be placed in a dialyser which is surrounded by distilled water, all the crystalloids will diffu.se out of it, leaving the colloids, which consist mainly of proteins. The physical reason for this failure to diffuse is the large size of the molecules, in comparison with file small size of those of the crystalloids. By causing a beam of light to pass through a colloidal solution and holding a micro- 44 COLLOIDS. J i scope at right angles to this beam, the colloidal particles become evident, just as particles of dust become evident in a beam of daylight in a darkened room. Filters can be made of unglazed porcelain impregnated with gelatin in which the pores are so very minute that colloids can not pass through them, though water and inorganic salts do so. When blood serum is filtered through such a filter, the filtrate contains no trace of protein. The colloidal molecules can very readily be caused to fuse together, thus forming aggregates "of molecules which become so large that they either confer an opacity on the solution or actually form a precipitate. A property of colloids which is closely related to the above is that of adsorpti on. This means thejtendency for dissolved sub- stances to become condensed or concentrated at the surface of colloidal molecules. An example is the well known action of charcoal when shaken with colored solutions. It removes the pig- ment by adsorbing it. Adsorption is due to surface tension, which is the tension created at the surface between a solid and a liquid, or between a liquid and a gas. It is in virtue of surface tension that a raindrop a.ssumes a more or less spherical shape. Since colloids exist as particles, there must be an enormous num- ber of surfaces throughout the solution, that is, an enormous sur- face tension. Now many substances, when in solution, have the power of decreasing the surface tension, and in doing so it has been found that they accumulate at the surface, that is to say, in a colloidal solution, at the surface of the colloidal molecules. The practical application of thi.s is that it helps to explain the physical chemistry of the cell, the protoplasm of which is a col- loidal solution cont-aining among other things proteins and lipoids. The lipoids depress the surface tension and therefore collect on the surface of tlie cell and form its supposed mem- brane, whilst the proteins exist in colloidal solution inside. It is possibly by their solvent action on lipoids that ether and chloro- form so disturb the condition of the nerve cells as to cause anes- thesia. A knowledge of colloidal chemistry is coming to be of great importance in physiology. PUNDAMENTAIiS OP HUMAN PHYPIOLOOY. 45 Oeneral Nature of Enzymes or Ferments. To decompose proteins, fats or carbohydrates into simple mole- cules in the laboratory necessitates the use of powerful chemical or physico-chemical agencies. Thus, to decompose the protein molecule into amino bodies ro(juires strong mineral acid and a liigh temperature. In the animal body similar processes occur readily at a comparatively low temperature and without the use of strong chemicals in the ordinary sense. The agencies which bring this about are the enzymes or ferments. These are all col- loidal substances (see p. 4;}), so that they are rendihf desfroifid by heat and are precipitated by the same reagents as proteins. They are capable of acting in extremely small quantities. Thus, a few drops of saliva can convert large quantities of starch solu- tion into sugar. During the action, the enzymes do not them- selves undergo any permanent change, for even after they have been acting for a long time, they can still go on doing their work if fresh material be supplied upon which to act. These proper- ties are explained by the fact that they act catalytically, just as the oxides of nitrogen do in tlie manufacture of sulphuric acid. That is to say, they do not really contribute anything to a chemi- cal reaction, but merely serve as accelerators of reactions, which however would occur, though very slowly, in their absence. Thus, to take our example of starch again, if this were left for several yeai's in the presence of water, it would take up some of the water and split into s-< ,^J /, . FUNDAMENTALS OF HUMAN PHYSIOLOGY. 55 The Whit© Blood Cells.— In_m»rma]^ human blood there are about ten thousand cells in a cubic millimeter of blood, or about onejo^verj; five hundred red cells. In many ways they resemble the unicellular amoeba, for like it they have the power of making indetendeal movement by extending tiny processes called pseu- dopodia in one direction and by retracting them in another. By virtue of this peculiar movement they are able to flow, as it were, between the^ endothelial cells of the capillaries and find their way into the tissue spaces. There are a number of forms of white cells differing from each other in size, in the character of their nucleus, and in the granules they contain. In general, they are classified in two main groups on morphological grounds, viz., leucocytes and lymphocytes. vW;^ vW^:) \^M^::\ VM/ H'^^-O v^^y Fiff. 15.— White blood-corijusclt's frotn man. (HiU's Histology.) Small mononuclear. Large mononuclear. Polynuilrar. The leucocytes are the most numerous and compose about 65 per cent of the total white cells. They are characterized by a lobed nucleus, the parts of which are connected by strands of chromatin material. To this class belong several sub-groups. The m^t^important of these are the cc"s known as polymorpho- ""^l^»_''J^"Co<'yt^- They comprise abcut 96 per cent of the leucocytes. Others are known as cqsijiophiles, since they have granules which have a marked aflfinity for acid stains. The lymphocytes, the second variety, are so-culled, since they are supposed to be formed in the lymph glands of the body. They possess a single large round nucleus surrounded by a clear layer of protoplasm. There are two sub-groups in this class: the large momnuclcur lymphocytes, which contain a rather abun- dant cytoplasm about the nucleus, and the small mononuclear lymphocytes, in which the amount of cytoplasm is very small. 56 THE BLOOD PLASMA. 1 11 I The former comprise about 4 per cent, and the latter about 30 per cent, of the white cells. Estimation of the White Cells.— The number of white cells found in the blood is estimated by the same principle that is em- j)loyed in the counting of the red cells (see p. 52). In certain diseases their number may vary greatly. The number is also in- creased after meals. A marked increase over normal is known as a leucocytosis. The Function op the Leucocytes.— In acute infections, as ill appendicitis, pneumonia, and localized or general septic con- ditions in whicli pus is formed, there is usually a great increase in the number of the polymorphonuclear leucocytes. In more cl n-onic i nfections, as in tuberculosis, tlie lymphocytes afe^Found in greater number. IiUhe parasitic diseases of animal origin, as tapeworm and hookworm, in some skin diseases, and in scarlet fever, thejeosinophile leucocytes are more abundant. In the disease leucocytha;mia the lymphocytes may be present in such great numbers that they impede the movement of blood by in- creasing its viscosity or thickness. The above observations sug- gest that leucocytes play an important role in the protection of the body from infective processes. This function will be rlis- cussed later. Another important function they may have is the preparation of the peculiar proteins which are found in the blood plasma. The_Blood Platelets.— These bodies are smaller than the erythrocytes, and number about 300,000 in a ibic millimeter of bloiod. When blood is shed they disintegrate very rapidly, and set free a substance which plays a part in the coagulation of the blood. Little is known concerning their chemical constitution or their physiological function. The Blood Plasma. The blood plasma is a very complex fluid containing all the va- ried substances associated with the function of the blood. Water composes 90 per cent of the plasma. The plasma proteins consti- tute the largest solid constituent (7 per cent), andTncTude serum FUNDAMENTALS OF HUMAN PHYSIOLOGY. 57 globulin, serum albumin, and fibrinogen. There are a number of bodies wHicH contain nitrogen which are not proteins. These may be grouped into two classes; the first, represented by the IHino acids and other nitrogenous bodies derived from the pro- tein of the food and from which the tissue cells are built^and the second group, represented by waste materials given oflf by the tissue cells. These include substances such as urea, uric acid, creatinine and ammonia. The njon-->itrogenous organic bodies arc dextrose, of which 0.1 per cent is p. jscnt in normal plasma, and a small (luantitj of fat. About 1 per cent of inorganic sa[ts is found, the cliief of which is sodium chloride, which constitutes 60 per cent of the a.sh. Sodium carbonate is foujid in a little Iphs •legree. Besides these two we find small amounts of potassium, sodium and calcium chlorides and phosphates. An important group of substances known as liormones are excreted into the plasma by some of the glands of the body, and affect the meta holism of the tissues in a specific manner. Another group of bodies, the antito.\ins, complcme.nt.s, and opsonins (.see p. 61), are found in the blood. These are concerned in the protection of the body against infective organisms. .^ \y CHAPTER V. THE BLOOD (Cont'd). The Defensive Mechanisms of the Blood. The Coagulation of the Blood.— Whenever a blood vessel is slightly cut, the blood, which at first comes very freely, soon ceases to flow because of the formation of a plug or clot of blood at the site of the injury. The process uy which the blood spon- taneously formr the plug in the injured vessel is known as coagu- lation, or clot formation. It protects the body from fatal liem- orrhage in case of an ordinary wound. A clot is a semi-solid mass, which on microscopical examination is seen to consist oTa mShwork of fibrils holding the blood corpuscles in their inter- spaces. If blood is collected in a basin and whipped with some twigs while it is clotting, the fibrils will collect on the twigs in stringy masses, and the blood will remain fluid. The stringy material is called fibrin . Obviously, fibrin cannot exist in the blood stream, else the blood would form a clot within the blood vessels ; it is formed only when occasion demands, such as an in- jury to the~T)lood vessel. There are a number of experiments which explain the process of coagulation. Thus, if blood is prevented from clotting by cooling it to 0.° Centigrade, and is then mixed with a saturated solution of salt, a white precipitate forms, which may be filtered off and dissolved in 0.1 per cent salt water. This solution may be made to clot by the addition of a very little blood from which the fibrin has been removed. In other words, we have prepared a substance which under proper conditions forms the fibrin of the clot. This sub- stance is called fibrinogen, since it is the precursor of fibrin. Again, if blood be treated Avith sodium oxalate, it will not clot unless calcium salts be added in amount sufficient to precipitate completely all the oxalate and leave some in excess. In other 68 FUNDAMENTALS OF HUMAN PnYSIOUXJY. 59 7 words, th e presenc e of a soluble calcium salt is necessary in order to haye^tHfi Wood clot. Defibrinated blood will, however, cause the clotting of pure fibrinogen solutions even though all the cal- cium be removed from both solutions. In order to explain the above facts, we must assume that three substances are present in solution in t'Ke'^ood: fibrinogen, cal- cium salts, and another substance, which has been called fhrom- bogcn. Under the proper conditions, thrombogen will combine with calcium salts to form thrombin, which in turn unites with fibrinogen to form fibrin, which is the substance forming the franiewort of the clot. The reason wTiy the blood does not clot within the bIr)od ves- sels is not definitely known. It is probablothat the blood con- tains a substance which prevents the combinatioi of thrombogen with calcium salts, and which we call a nti-thro7nbin. Whenever a blood vessel is injured, the tissues and the Wood platelets liber- ate a lipoid body called kcphalin, which unites with the anti- thrombin and thus allows the formation of thrombin to take place at the site of the wound. The whole process may be graphically shown in the following schema : Anti-thrombin + kephalin = inactive anti-thrombin. ) Thrombogen + calcium salts = thrombin. Thrombin -f fibrinogen = fibrin. Fibrin + corpuscles = clot. Because calcium salts are necessary to the coagulation of the blood, the administration of calcium lactate has been exten- sively used as a means to arrest ha?morrhages or to increase the coagulation power of the blood. It is doubtful, however, if the calcium content of the blood ever sinks below that required for clot formation. Normal horse serum has also been recommended on empirical grounds in various conditions in which the coag- ulation power of the blood is deficient, as in the severe anemias or following operations in which it is difficult to arrest hieni- orrhage. Antibodies in the Blood.— The coagulation of the blood is only one of the measures which are developed in the blood for the 60 THE DEFENSIVE MECHANISM OF THE BLOOD. protection of the animal. No less important in this regard are ^he-destruction and removal of toxic and injurious substances fromthe body. All the infectious diseases are caused by the agency of micro- organisms. The greater number of these are microscopic plants known as bacteria and fungi ; some, however, are unicellular ani- mals known as protozoa. It is especially against the bacteria that a method of defense exists in the body ; the protozoal diseases, on the other hand— such as syphilis, malaria, sleepmg sickness and those caused by amoeba in the mouth and alimentary tract— find relatively little resistance offered to their growth in the bo dy, and their destruction therefore must be for the most part brought aljiout by drugs. — The Process of Inflammation, which in a general way is known by the eoiiunon symptoms of fever, pain, swelling and redness, is a sign of an increased activity on the part of the tis- .sues in an effort to destroy some foreign body which is poisonous to the cells. ]\Iicroscopieal examination of a section of inflamed tissue will show that the bkwd vessels are dilated, and that the tissue spaces are infiltrated with leucocytes. It suggests that the blood elements must have a very important part in the process. The study of this function of the body is one of the most inter- esting chapters of physiolog .l science, and includes the ques- tions of immunity from disease and the cure of infectious pro- cesses. ]Many pathogenic organisms can be cultivated on artificial media and the products of their metabolism can then be studied. It has been found that they may be di^ded into two groups: the ojic group producing the soluble poisons, or true toxins, which are excreted from the cell; and the other producing toxic sub- stances, the endo-toxins, which are not excreted from the cefl. We wiTI first take up the manner in which the body deals with the toxins. Toxins.— If a culture of diphtheria or tetanus bacilli be fil- tered through a porcelain filter, the bodies of the bacilli are re- moved and the filtrate contains the soluble toxic principles which the bacilli have produced and excreted into the nutrient fluid. FUNDAMENTALS OF HUMAN FIIYSIOLOOY. 61 Injections of a small amount of this filtrate into an animal will produce the same symptoms as are produced when a pure culture of the bacilli is injected. Each bacillus produces a specific kind of toxin. Diphtheria toxin acts primarily on the vascular sys- tem ; tetanus toxin, on the central nervous system. The chemical nature of the toxin molecule is unknown, since it has been impos- sible to separate it in pure form. It is probably closely related to the protein molecule, and on the other hand resembles the tVrinents in many of its actions (see p. 45). A peculiarity in the action of the toxins is that a relatively long period elapses betv'vi jn the injection of the toxin and the reaction of the body, whereas in the case of the alkaloids or vegetable poisons, the re- action appears very quickly. Antitonn.— In spite of the very poisonous character of the toxin molecule, the body is provided w'H a means of defense iigainst it, and is able to make itself still x, rther immune to the action of the toxin. Thus, if somewhat less than the fatal dose of diphtheria or tetanus toxin be injected into the body, certain symptoms will follow, and the animal will react to the toxin in such a way that a subsequent injection can be made larger with- out proving fatal. If successively increasing doses are given, the animal after some weeks will be able to withstand very large .loses of the tosh^. In other words, t he bod y develops an im- munity towards the toxic agent; it produces 'an "antibody which neutralizes the poison of the loxiu. To this body we give the name of antitoxin. Since these antibodies are found in solution in the blood, it is possible to withdraw the blood from such an immune animal, and inject it into a non-immune animal, thus rendering the latter immune to the toxin. It is this principle that is used in the preparation of diphtheria and tetanus anti- toxins. The exact nature of the combination of the toxin and the antitoxin cannot be learned from chemical studies, but Ehrlich has given to the phenomenon a biological explanation based on the various known reactions of the bodies. EhrUch'g Side Chain ThepT3_ot Immunity.— Briefly summar- ized Ehrlich 's theory is as fnllmvs: ~Each toxi:: molceule is made up of a central nucleus of chemical radicles similar to those ) V 62 THE SID/ IAIN T!IEuRV. found in organic compounds To t i. main body of this mole- cule are attached ayeast two ■ laer rai' Ic', or side chains. One of these has a great affinity foi' eovi.nu < henical constituents of the tissues of susceptible animals, and unit. -• the toxin molecule to the tissue cell. This chain is known as the hnptophore group. The other side chain, the fojvphore group, > rts th» injurious effect upon the tissue after the haptophore group has joined the toxin to the cell. For example, tetanus toxin owes its eflfect to the fact that nervous tissue contains a chemical substance which unites readily with the haptophore group of the tetanus toxin, and also substances that are readily attacked b} the toxophore group of the toxin. The antitoxins ai-^ supposed V< act by com- bining with the haptophore group, thus preventing the toxin from uniting with the cell// According to this theory the formation of antitoxins may be accounted for as follows : When a receptor, as ,ve may ierm the portion of the cell which unites withTthe haptoph. re groups, is united to the toxin, the cell endeavors to adapt itself to the loss of this radicle by the production of another similar one. Since the general rule of nature is to respond to an action with an over- i-eaction, many more receptors are made than are actually needed to unite with the haptophore groups of the toxin present. The re- ceptors produced in such great number break away fcom the parent cell. These accordingly are stored up in the hi kkI, and whenever any of the particular toxin for which they ar adapted is present in the circulation, they unite with it and thus prevent the toxin from uniting with the tissue cells. A body v leh pos- sesses a store of such antibodies is said therefoi to be immune. Toxins are not the only substances which will protiu specific antibodies. This property is a general characteris- <>i ..roteins Any substance producing an antib(4y is known a,, u ant^n For example, if Jiuman blood be injected into a rabbi' ad at several days some of the rabbit's blood serum is mixe with .. man blood serum, a precipitate will form, whereas th, lood oi a B2™Sl rabbit will produce no such pr^crpTtate. Th, lirstln- jection of human blood serves to stimulate the rabbit cell? t- ^M -^miAi^ FlM'VMkn r\r.s of ih'man 'ir.(HiY. 63 form soil, substaiif." w ich prec'pitatf anv hu m birjo<3 sub- soquently a.Jdod. The i action is speci; tor (.lood . any other species of aniinai u !1 not be i.recii at.^d blood ,om a rabbit sensitized with hum, n blo«» .-red, the heart's a. tion weakened, and ' -oath iiii,' interf.re.^ wit. This on.iition is known as anaphy.,,cti shock. Th.-j-. action is ;i . ■,= r.ti on.' for proteins and is specifi for ach protein used. 1 j.uenom. o.. is *^xplained by'assum in that tl .. firat injection, while pr. ing the bodies which we reitir. '1 .. ibov as precipitin:,, also ^ luces an excess of a f . r- uieri- hi.h is able hr, ak iown the foreign protein very qui 'y " *f' ■ "0" Jecti.. takes plaee.s. The product s of iroket protf moll uIp. a.s ''i< y are f.roduced in the 1 A, poise ous NT I H lH.,r nd :odu the phenomenon a! ' .•- scribe not excrete ..oisonous toxin into the surrounding 'n, but they eaus. dis- asc by directly attaeking the f - 64 ()PS(»NINS. ,1 ! ^1 1 to ingest pathogenic bacteria and to destroy them. The exact function of the different varieties of white cells in the blood is not definitely known. //In active inflammatory processes the poly- morphonuclear leucocytes are by far the most numerous ^n the otiief hand, in cases of chronic infection, as in tuberculosis the number of lymphocytes is increased.// Some of the forms of wh:*e cells do not take an active part in the ingestion of bacteria, and therefore cannot directly destroy them. Yet, in the defense of the organism, they take a part which is no less important than that of the phagocj'te. In very simple forms of life the cells of the alimentary tract both ingest and digest the food material. In higher forms the cells of the alimentary tract secrete the fluids which digest the food. In the one case the digestion is intra-cellular, and in the latter, extra-cellular. In the same way we find the blood leu- cocytes able both to destroy and to digest "substances by intra- cellular action, and also sharing with other cells of the body the power to secrete substances into the blood plasma which have the power of destroying the organisms or toxic material. Opsonins.— Normal blood serum has a very strong destruc- tive influence on most species of bacteria, whether they arej)atho- genic or not. This ability is not possessed to the same extent by the blood plasma. The difference is explained by the fact that in Jhe process of coagulation the white blood cells are broken 'l*'^-" f ?** liberate their bactericidal bodies. Extracts made of leucocytes have this same effect, but the reaction is much more rapid in the presence of blood plasma or serum. The co-oper- ation on the part of the plasma or serum is explained by the presence of some substance in solution which ent^bles the_leu- cocytes to attack the bacteria more readily. TliaT some^sucli substances also aid in the phagocytic action of the leucocytes is indicated by the fact that the white cells ingest bacteria much more quickly in blood serum than in normal saline solution. These substances are known as opsonins^ and are char- acteristic for each individual organism wlifch. atimulaies their P':94ycti9n. At the beginning of an infective process, in which the phagocytosis is very active, each leucocyte may be able to at- FUNDAMENTALS OF IIITMAN PHYSIOI^OGV. ^ tack only one or two bacteria; later in the disease, however, when the opsonic pow. r has been increased for the infective agent the leucocytes may be able to ingest a much larger number without injury to themselves. The_opsonic index is a figure expressing ^liilfliL^! ^^^""'nber of pathogenic organisms of a certain kind Jhat a normal leucocyte can ingest in serum, to that~wfiich the s ame leu cocyte can ingest in the presence of tTiTiFnim of a patient -vho is suffering from the infective agent. A high op- ««5iqi5^ex therefore indicate s a relative immunity or hiiTiiirst- •'"ice tojthe disease in question. Vaccines.— The bactericidal power of tl leucocytes for many l.aeteria_can be greatly increased by the injection of dead bac- l(-ria into the body. This fact is made use of in the prepara- tion of bacterial vaccines, which consist of suspensions of dead baetena m physiologic salt solutions. Great care and skill must be used in the preparation of these vaccines, which should b*' used onl3 as a therapeutic agent when bacteriologic examina- tion has demonstrated the infecting organism. The failure of vaccines vo produce the desired effect, in many cases, may be because the infecting bacteria produce antibodies which in turn neutralize tliose produced by the body to protect it from the toxic action of the bacteria in question. In recent years inoc- ulations with typlioid vaccine have been extensively and sue- .•.-ssfully used in various armies as a prophylac-e measure Serum Diagnosis.— The determination of the presence of spe- nhc antibodies in tiie bmly lias been made a diagnostic metho.l -M tlie ease of .some diseases. For example, in typhoid fever, the blood .soon acquires the ability to inhibit the movement of the typIioid bacillus. This phenomenon is the basis of the Widal test »,or typhoid. ~" The serum diagnosis of syphilis, known as the Wassermann tost, depends on the production of antibodies in the svphilitic blood, which, under the proper conditions, will bring about the •lestriietion of blood corpuscles. n;ii a I <^ CHAPTER VI. THE LYMPH. The blood circulates in closed tubules, so that the nourishment which is supplied the tissues and the effete products which re- sult from their activity must pass through the walls of the ves- sels. The fluid which is transuded from the capillaries and which surrounds the cells of the tissues is known as the lymph and serves as the medium of exchange between the cells and the blood plasma. It is the middleman of exchange between the blood and the tissues. Lymph is a slightly yellow transparent fluid, closely resembling the blood plasma from which it is derived. To aid in' returning the lymph to the blood, there is provided a special systen- of vessels called the lymphatics, which are very thin- walled japillary tubules lined with endothelial cells. These tu- bules lead to larger ones which, after passing through a ! -r^ph gland along their course, finally empty into a large vein-li^ . es- sel, the thoracic duct, lying alongside of the oesophagus in the thorax, and emptying into the left subclavian vein. A smaller lymphatic vessel, the right thoracic duct, empties into the right subclavian vein. The lymph obtained from the thoracic duct by means of a fine tube inserted into the vessel varies somewhat in nature. After a meal the fluid is like milk, beeau.se of the presence of droplets of fat which have been absorbed from tiie intestines. The lymphatics of the viscera appear as white lines in the mesentery and on thi.s account are called lacteals. The lymph which is collected during a fast is very much like the blood plasma. Its specific gravity is less than that of blood, since it contains less protein material, but on t'le other hand its salt content is the same and it clots in much the same manner as blood. On microscopic examination there are found many colorless corpuscles, identical with those present in blood. Sume of these corpuscles are formed within the lympli r>6 FUNDAMENTALS OP JIUMAX PTIYSIOLOOY. 67 glands through which the lymph vessels pass on their way to the subclavian vein. Lymph Formation.— Many physiologists have attempted to discover the precise mcehanism by which the plasma passes through the capillary walls into the lymph spaces, but the com plete knowledge of the process is not yet at hand. The relatively high blood pressure within the capillaries provides filtration pressure by which a fluid might be filtered through the capillary- walls, and there is no doubt that such a process does occur, as, for example, after the capillary pressure has been increased by con- striction of the veins by a bandage, etc. Filtration, however, cannot explain all the known phenomena of lymph formation Osmosi sjp. 40) also plays a_part as follows: fhe~tissues"use up the nutritional elements brought to them by the lymph. The diffusion pressure of the substances in the lymph is now reduced so that it becomes less than that present in the blood. Therefore substances within the blood must pass out through the capillary walls into the lymph, thus keeping the concentration of the fluid more or less constant. The waste products of the tissue pass into the lymph and, by increasing the molecular concentration of the lymph, draw water from the blood. Again, the breaking down of the large protein molecules into smaller ones, in the processes of tissue metabolism, will cause the molecular concentration of the tissues to rise, increasing the osmotic pressure. This causes water to be abstracted r, n the lymph, which in turn draws on the blood for water. Lymphagoguet nere are certain substances which affect the rate of lymph formation in a very peculiar way. These are •Nill.'d lymphagogiios, and includ." ,".xtrac(s from iiumv shfimsh leech extract, peptones, etc. When such substances are injected into the blood of an animal, there follows a great increase in the rate of lymph formation and lymph flow. Indeed some people are very susooi>tible to this action, and eating shellfish, oysters and some fruits will cause their tissues to become swollen be- cause of an increased lymph formation. How these substances can effect the change by altering the physico-chemical constitu- tion of the blood plasma is not clear. Some investigators believe 68 THE LYMPH. I that they have a stimulating action on the endothelial cells lining the capillaries and thus produce an actual secretion of lymph. It is more probable, however, that they poison these cells in a way which increases their permeability and thus permits a freer filtration of lympli from the blood plasma. There are other facts nevertheless which support the th«ory of an actual secreting mechanism within tlie cells of the capillary walls, but they are too technical to consider here. //They suggest that although the physico-chemical laws of diffusion, osmosis, filtrationjetcT, play the most important role in lymph formation, the cells of the capillary walls may themselves have an active part in the pro- cess. //~ Lymph Reabsorption.— Within the tissue spaces, and within the ceils of the tissues, changes are continually taking place which alter the character of the lympli. Oxygen and food substances are removed from the lymph by the tissue cells, and waste sub- stances, the result of the tissue metabolism, are added to it. In the case of oxygen and carbon dioxide, the exchange is so reg- ulated as to keep constant the supply of these bodies in the lymph. The loss of any substance is quickly compensated for by the addition of new material from the blood. The solid waste matter excreted by the cell can also find its way directly from the cell through the lymph and into the blood plasma. //lt_LS probable that during periods of rest or of slight actiyity~the '^^^^'*ii'** ^^'^ "^ ^'^^'^ importance in the exchange of the lymph. lTow?fer,' wlien the exudation of Jymph becomeslncreased. as .iiiring exercise or following the use of some lympiiagogue, or when there are substances in the lymph which the capillaries cannot absorb into the blood, thejiimphfltics become very im- portant in helping to remove the excess of lymph formed.y/ ~ The Hovement of the Lymph,— The mechanism By which the lymph of the tissues is collected by the capillaries of the lymph- atic system is not understood any better than the mechanism of lymph formation, but no doubt the same laws apply to both pro- cesses. The movement of the lymph along the lymphatic vessels is possible becau.se of the presence of valves along the course of the vessels. if FUNDAMENTALS OF HUMAN Pll /.SIOI-OGY. 69 // The j)rocess_of lymph absorption is rather slow except when it i s aidgd by t h ft maa sagfi^jroduced by the movements of the sur- roundingjiarts,//The rapid action of poisons, or drugs intro- duced by a hypodermic syringe, is due to their absorption from the intra-cellular or lymph spaces directly into the blood. Col- ored solutions as india ink are absorbed by the lymphatics, and by using a substance like this it is possible to trace the lymphat- ics of a portion of the body. Micro-organisms, such as the strep- tococcus, which causes one of the familiar forms of what is known as blood poisoning, are taken up by the lymphatics, and it is easy to trace the channels traversed by the organism by the in- named lymphatic walls which appear as red lines under the skin. Since all these vessels pass through a lympha tic gland on their way to the subclavian vein, thMe_glauds are often very much swollen, and may even be destroyed as the result of the infection. It is probable that one of the functions of the lymph gland is to catch and render non-toxic, poisons which are being carried into the circulation by way of the lymphatics. One of the most dreaded diseases, carcinoma, is carried by the lymphatic system to other parts of the body. For this reason we most often see the metastatic growths of cancer in the region of the lymph glands which have caught the straying cancer cell and have been infect- ed by it. ^/The increased exudation of lymph in the tissues which occurs in inflammatory conditions is no doubt of great advantage to the ) tissues, since, by this means, a greater supply of nourishment is ( provided for the repair of the damaged cells, and the defensive / substances (antibodies, etc.) are brought into play. )l K CHAPTER VII. THE CIRCULATORY SYSTEM. Introduction.— The circulatory system provides for the trans- portation of blood through the tissues, thus enabling each indi- vidual cell to obtain nourishment and to rid itself of the waste products of its activity. The system includes the heart, the blood vessels, and the lymphatics. From a mechanical standpoint, we may say that the heart con- sists of a pair of pumps; each pump consisting of two parts, an upper chamber, the auricle, and the lower one, the ventricle. Thin, membranous valves , called auriculo-ventricular, separate the upper and lower chambers and prevent the Blood from flow- ing back into the auricle when the ventricle contracts. Connect- ed with the ventricles are the arteries, which conduct the blood away from the heart, to which it is returned by the great veins leading into the auricles. At the point where the arteries emerge from the heart are cup-shaped valves, called semilunar, which prevent the passage of blood from the arteries into the ventricles while the latter are relaxing. Anatomical Considerations. The heart is suspended at its base by the large arteries, and lies practically free in a sac of tough fibrous ti.s.«uc called the pericardium. On each side are the lungs, with the diaphragm below, the chest wall in front, and the oesophagus behind (P'ig. 16). The sarfaco of the lioavt and the interior of the pericardial sac are bathed with a serous fluid, the pericardial fluid. The muscular fibers forming the walls of the four cham- bers of the heart are arranged so tluit th;'ir contraction dimin- ishes the size of the cavities and empties the heart of blood. From the study of the embryonic heart, and from comparative 70 FUNDAMENTALS OF HUMAN PHYSIOUJOY. 71 studies in the lower animals, we know that the heart has de- veloped from a single tube, the division of the auricles and the ventricles being a rather late stage in the development of the mammalian heart. The fact that the two auricles beat synchro- nouriy, followed by the contraction of the two ventricles, is signi- ficant oftEe development of the auricles from the proximal, and Fig. 16. — The position of the lienrt in tiie thorax. (T. Wingrate Todd.) of the ventricles from the distal end of the primitive ardiac tube. The fibers of the auricles run transversely, beginning and end- ing in the fibrous tissue which separates the auricles from the ventricles. The musculature of the ventricles is somewhat hard- er to trace. There are layers that run transversely around the ventricles, and also layers which describe more or less of a spiral course from the base of the ventricles to the apex and then are reflected back in transverse layers, until they finally end in the papillary muscles, which are connected with fibrinous threads, the chordae tendineae, to the edge of the auriculo-ventricular valves. When the ventricles contract, this arrangement of muscular H II ill 72 ! !i i: THE HEART. fibera causes the apex aud the base of the heart to approach one another, and the transverse section is changed from an ellipse to a circle The base of the heart, hung as it is to the large vessels m the thorax, appears to be fixed, and one would expect that the Aroh ot Aorta Suparior V«na Cava Left Folmonary Vein I«ft Anriole Pulmonary Artery Sea>i~Luna Valvea Left Ventricle Right Ventricle" Pis. 17.-DlaKram of the heart and the large vessels. apex is the part which moves up and down. This is not the ease tZTV? V^T ^^ ^^P^"™^'^*' ^«d is explained by the fact' that the blood, when ,t is forced from the ventricle during the %:^^v\'^;^^ FUNDAMENTALS OP HUMAN PHYSIOLOGY. 73 cardiac contraction, exerts its force on the apex as well as ou the blood m the arte/ies. This serves to fix the apex in the vertical position and to bring the base of the ventricles downwards during their contraction. In some individuals there is a visible pulsation at about the level of the fifth rib on the left side This IS called the_apexbeat, and is causedLJaLthe^roUUoa of the a£exinthe transverse diameter and by the sudden change of the ventricle from asoft flabby _condition into a firm one . . .^ ■»■"=• '^> riifni. ana t< , lert coronary artery O wall nt ri<»hf o„j u V.Z^ZT^• '• ^"'^ "' '""'• -^"^ '' °' '^" -nrHcTo^'V/roTs'tr^Jarf. The walls of the auricles are relatively thin, as they are not required to do heavy work. Tho ventricular muscles, on the other hand, are well developed, that of the left ventricle being very strong and adapted to the heavy work it must perform. The valves guarding the opening between the auricles and ventricles are composed of thin membran:;. of fibrous tissue, cov- ered with endothelial cells similar to the lining of the heart and he blood ves..ek fFig. 18). In acute rheumatism and tonsil- itis, the enuofhehai covering of the interior of the heart and of the valves IS often inflamed, and permanent changes may take place which injure the valves and produce what is known as val- vular disease ot the heart. The chords tendineie connect the ■! , i 74 THE BL(X)D VESSELS. free margins of the valves with the papillary muscles, which arise from the musculature of the ventricle like little knobs of tissue. This arrangement prevents the valves from being everted into the auricle during the contraction of the ventricle. The valves on the left side consist of two flaps and are called the mitral i;alvcs; those on the right side have three flaps and hen"ce~are called tricuspid valves. The valves guarding the arterial orifices consist of three cup-shaped membranes and are known as the snn Umar valv es, because of their crescent-shape when they are c'losecT WTicnever the pressure in the arteries is greater than that in tlie ventricles, these valves are tightly closed, and prevent any blood entering the ventricle from the arteries. The Blood Vessels.— The blood vessels are divided into three classes: The ar teries, which carry the blood aivay from the heart; the ly^ijiTTwliich carry the blood hack to the heart, and the capillaries, which connect the arterie.s and the veins. They ■Mt^^- (li^ifs n';^;,;;^^)^"''"" '"' """' "■■""■^ ^""' ^•'" -*• ""•^'•^: >■■ vom. iii-o Jill tiihu ir stnictiiies, lined with a delicate coat of endo- thelial ells. The walls of the arteries are relativ.•l^• much stronger, uul are made up of lay<-rs of fibrous and ela.stic tissue and layer: of smooth muscle fibers (see Fig. 19). The elastic ti.ssue plays a very important part in the circulation of the hlood, as its tendency to .stretch makes the arteries le.ss liable to be ruptured by any increase in pressure of the blood, and thev can adapt themselves to any sudden change in the amount of FUNDAMENTALS OP HUMAN' PHYSIOUKJY, 75 blood which is forced into them. The contraction of the muscle found in the arterial walls lessens the size of the lumen. The importance of .such an action will be shown later. As the ar- teries branch, the walls become thinner, although the muscular coat is found in the very terminal brandies of the arteries, which are called the arterioles, and" 'fro m which the capillaries FiK. 20. — Arterioles and capillaries from t.ie human brain. Magnilied 300 times. /, Small artery; 2. Transition ve.sse! ; .1. Coarser capillaries; <. Kincr capillaries; a. Structureless membrane still v ith some nuclei, repre.wntatlve of the tunica adventitial b. Xuclel of the n.usrular fiber-cells; r. Nuclei within the small artery, perhaps appertaining to an endothelium; d. Nuclei in the transition vessels. (Gray's Anatomy.) ''^"^- The walls of the capillaries consist of a single layer of epithelial cells, which being very thin, thus allows for the dif- fusion of the various elements of the blood into the lymph or uice versa. The lymph is contained in special vessels called lymphatics. DiiTusion also occurs between the tissues and the lymph and blood. ft f 76 I'ROI'EKTIES OP HEART MUSCLE. Tlie veins have, in general, the same structure as the arteries Their lumen is relatively larger and their walls much thinner than those of the arteries. As will be seen from the accompanying diagram (Plate I) the blood pumped from the two sides of the heart circulates throii^ two distinct and separate systems of blood vessefsr Prom the right ventricle the blood goes through the pulmonary artery to the lungs and is returned to the left auricle by the pulmonarv veins, then to the left ventricle, whe: "e it is sent over the body through the aorta and its branches, to the capillaries imbedded in the tissues. From these it is returned through the veins to the venae cava;, which discharge it into the right auricle. //Wemay say, therefore, that the circulatory .-stem consists of two circles of tubing interposed in which are two force pumps, the valves of which are so disposed as to allow ^he bloo^ to flow in one direc- tion only.// The Physiologic Properties of Hea»t Muscle. The Character of Garlic Contraction.-Thc c^ntracdon of our volunt_arj muscles is not djie.to h single stimulus sent from tlie brain through the nerves, but rather to a series oj such stim- uli, which produce a more or less continued or tonic co^^ion of the niu.scl.-. If tms :vere not the case, our movements would be very quick ai,d jerky similar to these made by a person suf- fering with St. \itus dance. Injhe case of the heart muscle however, eic-h beat consists of a single complete muscular' con- traction, and it is ii.ipossible to produce a tonic or continued^con- traction in the 'icart such as can be produced in voluntary mus- cle by .-ipid successive stimuli. Another peculiarity of heart muscle is that each time it contracts it dots so with all thQ f^cc that It has at the moment. Skeletal muscle contracts wi'th grat- er or less intensity according to the strength of the stimulus it receives. Heart muscle, and in a lesser degree some otlier muscles, such as those of the intestinal tract and spleen, have the power of making automatic rhythmic coiitraetion.s which follow each other in a definite se(iuence. This phenomennn in the case of cardiac I'lalf I l>iMKi:iiii of Cii iiihuiiKi 'I'll (Vina- ciWir). It. A. ( liKht :iiiriilil. /' I Mit'T.vi. I'.W ( iiuliiuiiiury vein. iidi. /. i .1.1. mill />..!. t usiiMiliiiK iind ilc-iicmlin; hi'nii. \ isitni and ImhIv UMHiTMlh i. /' r i smiill blacU wssfls aii' tin- azynns \.iii> Ml. .1(1 i-iiiiilalis as folliiws: I'.r. ilKlit Vftitt i. Ic). I'. A. (iniliiiunaiy ' ;■ n aii>i(|. ,, /,.!'. (l,.fi v.iitiiil.M. ""' I I II \. and H. (oiipilasifs of |iiii:,il Min. hliii*. I,i. divert. The FUNDAMENTALS OP HUMAN PHYSIOIXXIY. 77 muscle IS not dependent on the influence of the nerves, as can be shown by the fact that the heart removed from the body will con- tinue to beat for some time if it is properly nourished by perfus- ing blood through it under pressure. The cause of this prop- orty of automaticity is still unsettled, and there have been some very interesting discussions and arguments among physiologists concerning it. Some believe that the heart muscle has this prop- erty inherent in itself, and that it originates the impulse which causes the contraction of the heart; while others think that there are present in the heart-muscle cells of a nervous character whose special function it is to originate the beat. Experimental facts can be found in support of either theory, but the question is still in dispute. Heart muscle differs from other muscle in that each fiber consists of a single cell containing striated protoplasm It may quite well be that this kind of muscle possesses some char- acteristics usually ascribed to nervous tissue, and that it does originate the stimuli which produce automatic movements The Sequence of the Heart Beat.-Inspection of the beating heart of a recently killed turtle or frog shows that the heart beat begins by a contraction in the large veins where they join the auricles. From these vessels the beat spreads, as it were to the auricles and then to the ventricles, beginning at the ba'se and '•■uling at the apex. It has been determined that the auricles p.)8.sess the power of making rhythmical contractions to a greater • iogree than do the ventricles, and that the contraction of the ventricle is dependent upon stimuli arising in the auricle For this reason the auricles have been called the pacemaker of the hearty The auricles are completely separated from the ventricles In- a firm sheet of connective tissue save by a thin band of mus- cular tissue in one locality, known as the auriculo-ventriculur ^'''J}i^L^L}hl.l"!'^k^of His, This tissue is responsible for the conduction to the ventricle of the stimulus arising in the auricle nt each heart beat. Disease of the Bundle of His produces changes in the rate of the ventricular contraction which may be .letected by alteration in the regularity and reduction in the rate of the heart beat. Such a condition is known as heart- itlock. if ii«' 78 THE SEQl'EN'CE f)F THE HEART BKAT. It is of interest to kno-v that there has been quite an advance recently in the knowledge of the conduction of the cardiac im- pulse from the auricles on to tlic ventricles. It has been known for a long time that wl.,-ii a muscle contracts, a small but delinite electric current is set up between the relaxed and the contract- ing portions of the muscles. New methods of detecting and re- Hgr .l-lMs.s....tioM :.f h,..„. t„ s(„.w a,ni..uN..v..ntric-ulHr ..undle (Keith)- t, the beg.nn.ng of the bundu... k„own as the A-V node; Z. the bundle dlv ding .no wo branches; i the branch running on the righl side of ,i,e inte vln tn.ular s.ptum. (From Howell's Physiology.) inier\en- eofding the .iirectioii of the flow of such currents p.'oduced in the he.irt in man have shown tliat cases of heart block ^i-e by no -•: pans lar... The instrnme.it used for this purpose is a highly sensitized galvanoimt.r, and the tracings are known as dectvo- cardiograms. By this metJ.od it can be shown that in certain eases of heart diseH*- the auricles beat twice to the ventricles once, or again tliat tlie auricles may beat v.-ry fast while the ventricles are beating very irregularly and slowlv. The Action of Inorganic Salts on the Heart Beat.— A ver' interesting theory has recently be-n advanced concerning tlie cause of the Lean beat. It will be re,„..,„b..red that the blood contains salts of sodium, potassium and alcium in solution If these salts are replaced by other no.i-poison..us salts in the same '•oncentration as th. s,dts removed. f> h.-art will not beat if FUNDAMENTALS np HUMAN PHYSIOLOGY. 79 the heart IS perfused with a solution of sr,lium chloride alone the beat becomes very weak and finally stops. If however a small amount of calcium and potassium salts is added to the sodium chloride solution, the heart will again begin to beat, but it stops after a while in a state of relaxation, or diastole, if calcium chloride 18 removed from the solution, or in systole, or contrac- tion, if the potassium salts are removed. These experiments sug- gest that the salts of the blood offer a solution to the problem of the cause of the heart beat, the potassium favoring relaxation and the calcium contraction. If the proper balance of these salts IS present in the blood, it is conceivable that a regular se -stole during which the blood is actually leaving the ventricles. Ihe^enod of relaxation and rest of the cardiac muscles is called diastoe The cardi.c cycle i,.cludos the time of .systole and dias tole of the heart. // The Events of the Cardiac Cycle.-During diastole the blood H<.w.s in a .st..anipletely eJose them Ven- tricular systole .. r b,gi,.s. Tk- H.^,1 valves prownt the pass- age of blood bm>k into the auricles, a.ul the «.tire force of the ventricles is expended in forcing tl... hloo«l mt thromrh the ar- terial openings. Whenever the prensure in tke ventricles exceeds that ifl th. arteries, the ^^milunar valv.^ op.n anu rnmain open till th*. force of the ventricle falls belo»- tW pressure of bl«od in the arteries. .T'he time between the closti^ of t*,.- auricuio-ven- tricrlar valves and the opening of the mmiibmmr valves ,s called the period of getting up power, -r the pre-sphygmic pcrioci/{Fig. I 11 r Fls. 22.-DiaKram showing r-lativo ,.„.ssu... in .uncle, ventricle and norta. It is obvious that when the blood is leaving the ventricles the pressure must be j.-ss in the arteries than in the heart Each v.-n tricle pours out more blood into its artery than can pass through the capillaries in the same unit of time, and hence the arterial walls are stivtelie.l and tli.. I.I.mmI is put under their eln.stic ten- FUNDAMENTAI,S OP HUMAN PHYSIOIXXIV. gj sion At the moment the ventricles exert less pressure than does he e ast.c reco, of the arteries on the blood, the semilunar ^at: are closed tightly by backward eddying currents in the arte ies ZuZ" T""'' '"^ "*"™ '' ^^°«^ "'t« '^^ ventricle" The blood, having attained a certain momentum during the second after the ventricle cea-ses to exert pressure on it th„« nm XT Tr;!^' f-T^ -T^ j"/beyo„r;:.r;:i :; valves This momentum being lost, the blood, by the oressure which the stretched elastic wall of the arter UeKerts o??. e .lood, IS forced back on to the semilunar valves and i. to the na faHy relaxed base of the aorta. The blood, beil g t us p eve " '■d from returning to the heart, must continue to flow on into the capillaries, and tU. onward flow never ceases, because tin x cardiac systole occurs before the arteries ha^e c Zd texer all , high and^or V,l n the second sou>.,l is a short-pau^e It ha b. .• T. *'.'"7'^ Pmmentally that^ho first soLd is .aus^,!^ t^f ^ :^;:: a-.d sudden t.n.sion of the auriculo-ventricular valves at tr- ...ent of ..aru,ac s^.tole, an moment the blood is forced back on them, following ventricular systole.// This sound is also sub- ject to variations in heart di.sease, especially in disease of the valves themselves, in which case becau.se of roughening they may offer resistance to the outrush of blood from the ventricles, or by not closing tightly, allow the pa.ssage of blood in the wrong direc- tion. In either case the sound is changed in character and is a u.seful diagnostic sign. By using these heart sounds as signals of the events occurring within the heart, it is possible to calculate the time relations of the various pha.scs of the cardiac cycle. The heart in the ordinary individual beats about seventy times a minute, so that we may say that tlie cardiac cycle is completed in about eight-tenths of a second. Hy.stole of the auricles lakes about one-t(>nth of a second systole of the ventricle thi-ee-tenths of a second, and diastole about five-tenths of a second. Diseases of Cardiac Valves.-lf the mitral valve is diseased, the blood may be retarded from flowing from the auricle into the ventricle. This condition is called mitral stenosis. If the valves cannot close tightly and thereby permit the blood to regurgitate into the auricle during ventricular .sy.stole. the condition is called nntral i»suffifie„n,. Disea.sc of the semilunar valves is likewi.se divided into aortic .s/oio.s/.s an.l insufficiency, depending on the character of the functional diange in the valves. / ^ CHAPTER VIII. THE CIRCULATION (Cont'd). The Blood Plow Through the Vessels. Introduction.— A clearer idea of the principles governing the circulation of blood through the vessels can be had if the laws governing the flow of water in a city water system are called to mind. For example, a water-works system is arranged by means of either special pumps or a standpipe, to furnish a stream of water at a constant rate and pressure into the city water mains The water is first forced into one large pipe and from this de- livered to the consumer by means of much smaller pipes By simple mathematical calculation it can be shown that the total cross-section area of the smaller pipes is many times that of the main pipe; for the sake of argument, let us sav 800 times great- er. Therefore the average rate of flow of water in the smaller pipes must be 800 times less than in the main pipe, providing all the outlets are open. However, if only one-half of the distribut- ing pipes are in use, the flow of water would be only 400 times less than m the main pipe, and the resistance offered by the walls of the pipes to the flowing water is also halved. Thus the same amount of water is delivered in the same unit of time but under twice the pressure, since only one-half of the force used to deliv- er the water through all the pipes is used in delivering it through one half of them. In other words, it takes X force to overcome the resistance offered by Y, therefore X equals Y. When X re mains constant and Y is halved, then X— Y 2 e(|uals X/2 leav n.g X/2 as a remainder. To bring it home, there is les^ water delivered from the garden hose and it has far less pres.sure be- hind ,t when all the ,».ighbors are al.so using the water, than there is when only a few outlets an» in use. Likewise if the amount and the pressure of water in the main pipe are varied by changing the force of th.. pumps or the level of water in the Ilia 84 THE BI/XID PLOW THROUGH THE VESSELS. ilM standpipe, the amount and prc-ssure of water delivered are also varied in the same direction. The pumps and the standpipe correspond to the heart and the large arteries, the distributing pipes to the smaller arteries and capillaries. With these ideas in mind let us consider the part the heart and blood vessels play in maintaining the circulation. The Part the Heart Plays.— At each systole 60 to 90 c. c. of blood are forced into the aorta. Cardiac systole lasts ubout 0.3 of a seconii, the diastole 0.5 second. Therefore the heart is rest- ing about 60 per cent of the time. By experiment it has been demonstrated that the left ventricle forces the blood out into the aorta with a pressure equivalent to the weight of a column of mercury from 160 to ino mm. in height. The heart alone, how- ever, actually propf .a j,c Mood through the arteries for only the time of its systole; t'aring the diastole, as already explained, the blood would cease to flow entirely if it were not for the part which the large arteries play in maintaining the circulation The Part the Arteries Play.— If 100 c. c. of water are forced in 0.3 second into an ordinary metal pipe at intervals of 0.8 of a second, 100 c. c. must flow out from the opposite end in 0.3 sec- ond ; during 0.5 second no water will be flowing in the tube. Let us now replace the metal tube with an elastic rubber tube, the end of which is fitted with a nozzle filled with glass beads. Now if 100 c. c. of water are forced into the tube in 0.3 second, the rubber tube expands because the beads retard the free outflow of water and thus make it impossible for 100 c. c. of water to pass through them in the time allotted. After t!.o water ceases to flow into the tube, the water stored up in the expanded portion con- tinues to flow ouL through the beads because of the elastic recoil of the rubJjer. If the resistance offered to the water and the expansile force of the tube be properly ad.iuste1, a constant stream of water may be obtained irom the outlet, in spite of the faet th*t an intermittent foree i.s supplying thv water (Fig 93) The intermittent stream of the arteries is changed into the constant rtream in the veins by a .somewhat similar process The walls of .he arteries are composed in part of a layer of strong elastic fussue, and this expands to a greater or less degree at each FUNDAMENTALS OK HUMAN Pll YSIOUKSY. 85 heart beat. The resistance which the arteries and the capillarieg offer to the flow of blood prevents the passage of the entire sys- tolic output of the heart into the veins during the actual ven- tricular contraction. It is, therefore, necessary that the large arteries expand in order to make room for the blood. '/K part of the energy of ihc heart beat is stored up in the elastic coats of the arteries, and after closure of the semilunar valves, which guard the ventricular orifice, the blood in the distended arteries is forced on through the capillaries by the pressure, pf the ar- terial walls.// Arterial Blood PrcMure.— P>om tlic foregoing description we see that there ar^everal factors which contribute to the main- KiB. 23.— KiaKiiim «r .xii.rtmc-iit lo show how a pulse (produced by com- piessiiiar the bulb B) comes to disappear when Huid flows through an elastic lub.^ (f) when there is resistance (a) to the outflow. A, basin of water- H. bulb syringe; C and fc', stop cocks; D. rigid tube; F, elastic tube; O bulb fllled with sponge. toiianoo of a constant stream of blood through the capillaries: vi/., tht_£'uinping action of the heart, the resistance of the ar- tfiioles aiiTcapiliaries, the elastic recoil of the blood vessels, and the amount of blood itself.//That the velocity and the pressure of thelbloo.l (lopoiid on those factors "■ s fir.,t of all dcmonstrcted ill 17.'^2 by R.'v. S:ci)h.'ii Jlales, who .1 a book published in that year report.-^ having experimentally determined the blood pres- Hure in tlio femoral artery o' horse. lie found that the pres- sure was sufficient to raise t..e blood in a tube seven feet above the level of the heart, and he also observed that each beat of the lieart and each respiratory movement affected the pressure of the blood. /The pressure exerted by the blood on the vessel wall at the height of the .nvstole of the ventricle is known as the systolic blood pressure, and that exerted by the elastic recoil of the 86 ARTERIAL BLOOD PRESSURE. f 'i m ] arteries on the blood during the diastole of the heart is known as the dtastolic blood pressure.. The average between these two pressures is called the average 'or mean arterial blood pressure. Since Hales' experiment better apparatus has been devised to measure the blood pressure in animals under different conditions. Determinations of the pressure existing in different portions of the vascular system show that there is a steady decrease of pressure of the blood from the aorta to the entrance of the vena cava into the nghi auricle. It thus happens that the blood is al- ways flowing from a place of higher pressure to one of lower pressure. Methyls whi, h are of much practical importance in the diag- nosis of vascular diseases hHve boen devised to determine the Mood pressure in n.ar. The principle of tJiese metho.ls consists m laeasunng the pressure required to shut off oi.ipletcly the blood supply in an artery. This i.s accomplished by placing a rubber sac encased in a leather i.aiul about the arm (Fig 24) Hy means of tubing Ms sae is conneetcd with a mercury gauee and an air pump. When .l.e sac -s pumped up with air. the ves- sels in the arm are compimsej. and when the blood can no longer force Its way under the obstruction, the pulse at the wrist disap- pears and at this moment the height of the m.^rcury in the gauge .s measured. This represent.s the systolic blood pressure. If de- sired, a similar measurement may be made in the arteries of the leg. To measure the diastolic pt( .ssure is more difficult. The method depends on the experimentally determined fact that when the pul.% wave produced in the arteries by each systole of the heart IS of greatest anjditude, the pressure in the air sac or compress- ing band equals the lowest pressure present in the vessel between the pulses. Recently improvements have been made in the method of judg- ing the point of obliteration of the artery, and also the point of maximum pulsation, by listening to the sounds produced at each pulse wave when the artery is being compres.sed. The 'vstolic blood pressure in the artery of the arm In healthy 1 KUNUAMKNTAI-S OF IIIMAN I'UY.snHxKjy. 87 young men varies from 110 to 130 mm. of mercury when it is determined in the sitting posture. When a person is lying down the pressure is a little less, and after hard exercise a little higher. The blood pressure under ordinary conditions is relatively con- stant, and is dependent on a deliputt- adju-stnient of the relation- sliip existing between the force of tli.- heart, th.- iiinoiuit of blood Fie 24. — Apiiaratu.s for tiuasuriiiK the arterial blood pressure In man. The pressure In the curt Ih raised by means of the syringe until the pulse can no loni,. r be felt at the wrist. This pressure is read off on the mercury manometer (systolic pressure). puiiii)ed at each bcit. tl:e resistance which the walls of the blood vessels offer to the flow of the blood, the size of the vascular sys- tem, and the amount of blood in the body./ Since the amount of l)i(..Hl in the body is relatively constant, we may say that the factors which change are the heart and the blood vessels. How lii 1 78 1 2.5 MICROCOPY RESOLUTION TEST CHART NATIONAL BUREAU OF STANDARDS STANDARD REFERENCE MATERIAL 1010a (ANSI and ISO TEST CHART No. 2) 88 ARTERIAL BIi(M)D PRESSURE. !1 ii ii .1 these factors influence the blood pressure may be seen if we again compare the system to the city water supply. Factors Which Maintain B'ood Pressure.— When the most water is being pumped into the mains, then the water has the greatest velocity and pressure. Likewise, when the heart is pumping most blood into the aorta, the velocity and the pressure of blood in the vessels are the greatest. If the amount of water remains constant, a uniform outflow through all the outlet tubes will be maintained, but if the number of outlet tubes be dimin- ished, then more water will have to Aow, per minute of time, through the remaining tubes; hence the velocity and the pres- sure must be increased. The same conditions are present in the body. A narrowing of the arterioles throughout the body or in some extensive vascular area, causes the pressure and the velocity of the blood to be in- creased in the remaining vessels, provided, of course, the heart beat is unchanged. A dilation of the arterioles, on the other hand, results in a fall of pressure and a decrease in the velocity of the blood. In tlie same way also an increase or decrease in the action of the heart will result in an increase or decrease in the pressure and velocity of the blood. The dependence of these two factors, i. e., the heart and the vascular system, on the maintenance of the normal blood pres- sure, is seen in the fact tliat, with a fast heart and dilated blood vessels, the blood pressure may be exactly the same as when the heart is beating very slowly but the arterioles are all constricted. /fitja apparent, therefore, that the velocity of the blood in the vessels is dependent on the pressure of the blood and the extent of the vascular area at the time in question.;/ The Velocity of the Blood.— By the velocity of the flow of blood we mean the actual time it takes for a particle of blood to pass between two points. If the rate were uniform throughout the vascular area, we could compute the time which a particle of blood would take to pass through the circulator> system. This is not the case, however, for the flow of blood is much swifter in the aorta than in the smaller vessels, and liere again our analogy between the circulatory system and the city water system applies. f4l FUNDAMENTAUS 1>F IH'MAN PHYSIOLOGY. 89 Just as the combined cross area of the small pipes leading from the main pipe of the water system is great <'r by many times than the area of the main pipe, so it has be<*n estimated that the total cross section of the capillaries of the body is 800 times larger than that of the aorta. ;t has been estimated that the rate of blood flow in the aorta is about 320 mm. per second. /The average rate of flo\ir in the capil- laries nuist then be 800 times less than that in the aorta, or 0,4 mm. per second.// As the length of a capillary has been estimated to be about 0.5 mm., the blood takes about a second to pass through them into the veins. This has been verified by micro- scopic examination of the blood flow in the capillaries. The velocity of the blood must be altered whenever the size of the vascular area is changed, and since during a cardiac cycle exactly the same amount of blood is delivered into the right auricle as the left ventricle forces out into the aorta, it follows that the same amount must pass through the vascular area of the body in the same time.// In otlier words, the_amount_o|_blpod which flo ws in a given series of blood vessels in a given time is in- dcpiendcnt of tTie size of the blood Vessels./'' The Return of the Blood to the Heart.— We must now con- sider the nature of the force which propels the blood, and study what changes take place in the movement of the blootl during its passage through the vessels. The blood is expelled from the loft ventricle with consider- able force and at a high velocity. On its way through the body much of the energy given out by the contraction of the heart is used to overcome the resistance offered by the walls of the ves- sels and the capillaries. In consoquence of this, the velocity and the pressure of the blood on the sides of the vessels are much re- duced. The blood is collected from the capillaries by the veins, and since the volume of the veins is less than tlie volume of the capil- laries its velocity is nuich increased. /^he relatively large caliber of the veins, however, offers little resistance to the flow of blood, and the energy remaining from that imparted to the bloo-'' ^ Relation of the Sympathetic and Vagtu Nerves to the Heart. — The antagonistic action existing between the cardiac fibers of the sympathetic and vagus nerves allows the heart to respond (juickly to any need that the body may demand of it. These demands are made through the brain, by various afferent or sen- sory nerves. This is brought about in the following way : The Cardiac Center. — In the medulla, the hind part of the brain, there is a collection of nerve cells from which the cardiac branches of the vagus arise. Near by also are located the cells from which the sympathetic nerves of the heart arise. Both of these nerve centers, for by this term are known the imr^ortant cell stations of the brain, ai'e supplied by extensive connections with afferent or sensory fibers coming from all parts of the body, the brain and even the heart. The centers become more or less active in response to impulses reaching them along the sensory fibers. The Cardiac Depressor Nerves. — One of the most important of the different cardiac nerves is that known as tha^ardiac depres- sor. It has its beginnings in filaments lying in the left ventricle and in the aorta, and runs to the medulla in the vagus trunk in inosTinammals, or as a separate nerve in the rabbit. The normal stimulus to the depressor nerve is a high blood pressure^in the ventricles and aorta. The stimulus, thus set up, acts through the vagus center and the vagus nerve, and slows the heart. It also acts on the vasomotor center md causes the bloo d vess els to dilate. Both changes produce a fall in the blood pressure. /The vagus nerve, besides the afferent vagus fibers, carries afferent or sensory nerves to the vagus center. This can be demonstrated by cutting one vagus and stimulating the central end, i. e., the end running to the brain. A marked slowing of the heart usually 96 NERVOUS CONTROL OP BLOOD VESSELS. Mli results. By acting through the vagus center and nerves, or through th(! sympathetic center and nerves, most of the sensory nerves of the lody, if stimulated, can produce a reflex slowing or quickening of the heart beat. One cannot, however, always predict exactly what result will be obtained. The stimulation of the fifth nerve in the nasal cavity or in the mouth always causes a reflex slowing of the heart. Stimulation of the laryngeal nerve and the nerves of the peritoneum have a similar effect. It ip also of interest to note that the act of swallowing will often cause a decrease in the rate of the heart through reflex vagus action. The relation of the blood pressure to the rai- of the heart has been noted in connection with the cardiac depressor nerve (p. 95). //Anything which produces an increase in the julse rate, other conditions being equal, will cause an increase in the blood pressure, and this acts reflexly to bring about a slowing of the heart. The reverse of this is likewise true. In this quick- ening or slowing of the heart, the vagi and the sympathetic nerves always act. //in the adult the normal rate of the heart varies between 68 and 76 per minute. In children the rate is a little faster, and in infants it may be normally 130 r r more. The Nervous Control of the Blood Vessels. During muscular activity the metabolism of the body may be increased five or six times, as can be judged from the amount of carbon dioxide given off by the lungs. Since this increase is due to the activity of the muscles, it is necessary that these obtain a greater supply of oxygen, and that they be able to rid them- selves of the carbon dioxide which is a waste product of their activity. //Rvpt^^^nth fir o''g <^" reauires an increased blood supply when it becomes active, so that blood has to be diverted from the inactive to the active tissues, and the least important activities of the bofiy have to be subordinated to the one which is most needed at the time in question^/ This a .iion is brought about partly by the central nervous jystem, acting through its afferent and efferent nerves on the musculature of the blood vessels of FUNDAMENTALS OP HUMAN PnYSIOLOOY. 97 the body, and partly by means of chemical substances which are produced at an early stage of the activity itself. The Vaiomotor Nerves. — It was discovered in the middle of the past century by the French physiologist, Claude Bernard, that^Bection of the cervical sympathetic nerve in the neck of the rabbit causes a marked dilation of the blood vessels of the ear, and that during stimulation of the nerve with an electric cur- rent, the blood vessels become very small, and the ear conse- quently colder. //This experiment shows that the nervous system plays an important role in the control of the flow of blood through the tissues, and from it many important truths about the nervous control of the blood vessels may be deduced. If cutting a nerve will cause the blood vessels to dilate, and stimulating the same nerve with an electric current will cause the vessels to coiistri''' to much less than their normal size, it follows that the blood vessels must be normally held in a state half way between ex- treme dilation and constriction bv stimuli received from the nervous system. The nerve fibers which carry the stimuli, be- cause of their power of producing constriction of the blood ves- sels, are known as vasoconstrict or nerve fiber s. They are com- parable in action to the accelerator nerves to the heart, since stim- ulation of either type of nerve tends to produce an increase in the blood j^ressurCj the one by quickening the lieart rate and the other by constricting the blood vessels and increasing the resist- ance to the flow of blood. The presence of the vasoconstrictor fibers in the sympathetic nerves is easily shown by the fact that stimulation of these nerves to aiiy part of the body produces a marked diminution in the size of the part to which the nerves are connected. At the same time there is an increase in the general blood pressure, because the freedom of outflow of blood from the arterial system is some- what reduced. Tlie large jitryes which supply the jimbs also contain vasoconstrictor nerves. These are derived from fibers coming from the ganglia of the sympathetic chain in the thorax and abdomen and joining with the roots of the spinal nerves in order that the fibers may be distributed along with the cerebro- spinal nerves to the part in question (see p. 282). 98 VASOMOTOR NERVES. ir 1 > The vasomotor nerves to the kidney and the abdominal viscera are for the most part supplied by the lower thoracic nerves. These symgathetic fibers are ccanbined and enter the abdomen in what are known as the splanchnic nerves, which terminate about nerve cells in. a ganglion behind the stomach, which is called the *£M'7"-^T ganglion of the solar plexus. Vasodilator Nerves. — There is another class of cilerent nerve fibers to the arteries, which are known as thyvasodila tor nerve s When stimulated they bring about a dilatation of the arte- rioles, and allow a greater amount of blood to pass through the vessels.^/ V asodilat or nerve fibers are found in all the spinal nerves, and they run to the blood vessels along with the nerve trunks supplying the various organs. Unlike the vasoconstrictor nerves, they do not seem to be continually exerting an influence or tonic action on the blood vessels. Because their action is hard to elicit, not so much is known of their normal functions as is known of the vasoconstrictor nerves. In some iier s, however, r t hey pr edominate and their action is easily setii. Such is the case i n the chorda tympani^ a nerve coming from the seventh cranial nerve and supplying the submaxillary gland with fibers, which when stimulated bring about an increase in the flow of saliva and marked dilatation of the blood vessels of the gland (see p. 151). The arterioles normally may be sup- posed to be held in a state midway between dilatation and con- traction. Stimulation of the vasodilator nervt s probably in- hibits the tonic action of the vasoconstrictor nerves, and the mus- cles of the vessels are extended by the force of the arterial blood pressure. ( After section of the sciatic nerve, the constrictor fibers soon*] [die, and the dilator fibers, which live for a time, may be shown I to be present by the fact that the volume of the leg increases | J when the nerve is stimulated. ' Vasomotor Reflexes. — In the same manner as the heart i.s influenced by afferent stimuli reaching cardiac centers from peri- pheral parts of the body, we find//afferent stimuli affecting the size of the blood vessels reflexly by way of the vasomotor center — located in the medulla near the vagus center — and the vaso- ■V FUNDAMENTALS OP HT'VAN PHYSIOLOGY. 99 il -^ m"*.. nerves// Some of the afferent impulsca cause dilation of the blood vessels, while other-: cause constriction. Perhaps the most important of the sense y nerves, which, when stimulated, produce a dilation of the blood vessels, is the cardiac depressor, which we mentioned in connection with the afferent nerves of the hei'Tt. It will be remembered that this nerve has sensory endings in the left ventricle and in the aorta, and that these are stimulated when the blond pressure in the arterial system reaches too great a height for the safety of the individual. The stimuli originating in '^e sensory ' ings of this nerve are carried to the cardiac center and are ti. transmitteu to the heart through the vagus nerves./' Be.videp the slowing of the heart which is thus produced, there alsc ..<;'*ur8 a dilation of the peripheral iressels brought 'l :nt by tl. - action of the stimuli on the vasomotor center. /JO' ■ is easily demonstrated by electrically stimulating the cardiac depressor nerve after both vagi have been cut in the neck and the reflex vagus action thus removed. The fall of blood pressure which is obtained under these conditions is due to an inhibition of the constrictor center and a stimula- tion of the dilator center of the vasomotor nerves. The stimulation of many of the afferent or sensory nerves of the body is followed by a change in the blood pressure. Just what this change may be it is often impossible to predict. Strong sensory stimuli of short duration may produce a marked rise in blood pressure, the constrictor center being the most affected. On the other hand, if the stimuli are very strong or continued over a long period of time, the constrictor nerves may become exhausted, as it were, resulting in a dilation of the arteries and a fall in the general blood pressure. Like phenomena are often seen following fright, pain, grief, and excitement. The patient becomes suddenly pale, dizzy, and may faint, losing conscious- ness entirely. This is due to a fall in the arterial blood pressure produced by a temporary inhibition of the vasoconstrictor nerves and perhaps also bj slowing of the heart, due to vagus stimula- tion. If the person be standing, the blood naturally flows to the vessels of the abdominal viscera and dependent portions of the body, and the brain is thereby rendered bloodless. The treat- 100 EFFECTS OF GRAVITY ON BLOOD FLOW. ii ment of these casesis to elevate the feet and abdomen and _to lo wer t he head. - In case the depression of the blood pressure slowly develops because of the gradual onset of fatigue ia the vasomotor and other nervous centers, a condition known aajsurgical shock super- venes. The tr eatment of this condition domands plenty of air, stimulants, saline or blood transfusion, and measures to main- tain the body temperature. // The Presgtire Effects of Gravity on the Blood Flow vary according to the posture of the body. In the upright position the blood vessels of the feet support a column of blood of rela- tively great height, but when the individual is lying down this ceases to be the case. // In spite of this, by means of the delicate adjustments which the nervous system can bring about in the heart and the blood vessels, there is little difference in the pres- sure of the blood in the arteries in any position which the person may assume.// The blood vessels and nerves soon lose this power if it is not continuously exercised. This is illustrated in patients who have been confined to their beds for a time. If they try to walk or to stand up suddenly, they become very dizzy and may faint, which means that the blood has left the vessels of the brain and is gathered by the force of gravity in the vessels of the dependent parts of the body. "With a normal vasomotor mechanism, the vessels of the feet and viscera would quickly constrict to such an extent that the blood pressure would remain at its normal height in the vessels of the brain. The fact that stimulation of sensory nerves by the gross meth- ods of the laboratory results in very profound changes in the blood pressure and in the velocity of the circulation of the blood, suggests that normally the vasomotor and cardiac nerves play an important role in the proper distribution of blood in the various parts of the body. It may be supposed that normally the nerves of the vascular system function to control the blood flow through the various organs according to their respective needs. Whenever the work of an organ is increased, the blood flow like- wise is augmented in the part, while in the rest of the body the blood flow is diminished to a greater or less extent. The blood fm FUNDAMENTALS OP HUMAN I'lIYSlOLOGY. 101 supply is continually changing according to the call of the vari- ous tissues for blood ; now the muscles, now the digestive organs, now the brain demand more blood, and this is supplied in the proper amount by the nervous system commanding some arte- rioles to dilate and others to constrict. Haemorrhage. — The action of the vasomotor mechanism is beautifully shown in tlie case of haemorrhage. As blood is with- drawn, the vasomotor nerves are stimulated by the falling pres- sure in the brain.// This brings about a more powerful tonic con- striction of the vessels through the action of vasoconstrictor nerves; the vascular area becomes smaller and smaller in size, and less blood is required to maintain the blood pressure. Be- cause of this mechanism a relatively large amount of blood can bo lost without affecting the general blood pressure. The Regulation of the Blood Supply by Chemical Stimuli.— Tlic caliber of the blood vessels may be influenced by other means than through their nervous mechanism. Acids in very small concentrations cause a vascular dilatation. For example, lactic acid and carbonic acid, both of which are formed during muscu- lar work, may produce a local dilatation of the blood vessels, the plienomenon thus constituting an automatic mechanism for deliv- ering more blood to a part when it is needed. On the other hand, the secretion of the adrenal and of a portion of the pituitary ^land (see p. 2.'{:}) i)r()(lucos a constriction of the vessels and thus tends to maintain the normal blood pressure. Recently it has been shown that during periods of excitement and sensory pain the amount of the adrenal secretions may be increased and the arterial blood pressure raised as a result of general vasocon- striction (p. 97). Because of its vasoconstricting properties, extract of the adrenal glands ("adrenalin" or " epitifphrin") is used in local aiia-sthetics, as in cocain solution, to prevent bleeding and to minimize the absorption of the cocain into the general circulation. Asphyxia. — Whenever the amount of oxygen which the blood must supply to the tissues falls below the minimum amount re- quired, a condition known as asphyxia develops. If the nervous centers are intact, any int upon administration, produce a marked fall in the blood pressure which is due to the peri- pheral dilatation of the blood vessels. This is a direct action on the muscles and does not involve the nervous system. The use of an extract of the adrenal glands, commercially known as adrenalin_or^qpinephrin, as an astringent in case of hajmorrhage is^ue to its action on the muscles of the arterioles. The intra- venous injection of adrenalin is followed by an increase in the blood pressure brought about by the general constriction of the peripheral blood vessels. This action is made use of in the treat- ment of urticaria, a disease commonly known as hives, in which there is a dilatation of the blood vessels of the skin. / CHAPTER IX. :'$, ^. THE RESPIRATION. Oxygen is one of the essential substances required by every living organism, in the cells of which it combines with the carbon to form carbon dioxide, and with hydrogen to form water. All the phenomena accompanying the supply and utilization of oxy- gen and the excretion of carbon dioxide are included under the subject of respiration. In the simplest forms of life the excliange of oxygen and car- bon dioxide gas occurs directly with the air, but in more complex organisms this sort of exchange is impossible, since practically none of the cells composing the organism is in direct communi- cation with the air. Some sort of respiratory apparatus becomes necessary, so that each cell may be supplied with oxygen and have its carbon dioxiie removed. In tlie higher animals this is accomplished through the agency of the blood, which is well adapted to transport the oxygen and carbon dioxide, first because it contains chemical bodies with which the gases can unite, and secondly because it comes in close contact with the tissue cells in the peripheral portions of the body, and with the atmospheric air in the capillaries of the lungs. /The study of the respiratory function therefore includes the mechanism of the gas exchange between the tissues and the blood, or internal respiration, and also that between the lungs and the blood, or external respiration. Internal Respiration. The energy which the body expends in the performance of the functions of life, including the heat which is required to main- tain the body temperature, is produced in the cellular chemical reactions, in which the oxygen of the air combines with the 104 FUNDAMENTALS OB' HUMAN PHYSIOLOGY. 105 hydrogen and carbon of the foodstuffs to form water and carbon dioxide gas. Oxidation in the Tissues. — The actual mechanism which unites the oxygen with the carbon and hydrogen of the food- stuffs within the tissue cells, is not entirely known. In spite of the fact that the processes of combustion of hydrocarbon matter outside the body yield the same end products as the oxidations taking place within it, the two processes are not strictly analo- gous. An important point of difference lies in the fact that the ^intraceUular materials — fats, proteins, and carbohydrates — are oxidize(i_with relatively great rapidity at low temperatures (98.4*), wher eas th e same reactions outside the body require a very high temperature. // Let us take as an example the cell of the yeast plant, in which there is a substance, under the influence of which, the sugar molecule becomes split up, at a temperature below that of tlie body, to produce carbon dioxide and water. Himilar substances are/present in the tissue cells of plants and aninials; they are the ferments or enzymes J( see j). 4.")), and tliey hs catalytic agents. The function ofthese bodies is to incre the velocity of many chemical reactions which otherwise proceed so slowly that they may be said in some cases not to exist. A class of these substances is present within the tissue cells, which at the demand of the tissues control the extent and the velocity of the union of oxygen with the hydrocarbons of the food. Such en- zymes are known as oxidases. "What evidence have we, however, that tliis oxidation takes place within the tissues and not within tlie blood itself? It is ponceivable that the substances that are to be oxidized are col- lected from the tissues by the blood, and that the oxygen combines with them in this fluid. It is quite possible that some oxidation takes place in the blood, for it is essentially a tissue and has a metabolism of its own, but this is not true for the oxidation which concerns the tissues, since this takes place in the tissues themselves, as can be shown by the following fact : The blood of a frog may be replaced with saline solution in which oxygen is dissolved under pressure, without killing the animal. It is 106 OXIDATION IN THE TISSUES. hardly conceivable that oxidation similar to that occurring with- in the body can take place in a solution of sodium chloride. Relation op Oxidative Process to Activity. — Under ordinary conditions the blood has a supply of food and oxygen sufficient for the needs of the body. An excess of eithor does not intensify the oxidative process. An animal will give off the same amount of carbon dioxide in an atmosphere of pure oxygen as it will under ordinary conditions. //This fact indicates that the oxida- tive processes are governed not by the supply of food or oxygen, but rather by the actual needs of the tissues.//A muscle freshly removed from the body may be made to contract, and will give off carbon dioxide for some time in the entire absence of oxygen in the surrounding medium. Another feature of this experiment is that for a time after the muscle has ceased to contract, it will produce heat and take up a large amount of oxygen. Indeed ythe maximal intake of oxygen and output of heat often occurs after the actual period of work./7ln this respect the muscle can be likened to a storage battery which is charged by the actual expenditure of energy and delivers quickly the energy stored up when the circuit is closed. If the volume intake of oxygen and output of carbon dioxide is measured, it will be found that the amounts are greatly increased during periods of tissue activ- ity. Experiments have demonstrated that a muscle at full work will use up its own volume of oxygen in ten minutes. To supply such an amount of oxygen requires a very high degree of effi- ciency on the part of the distributing agent, the blood. Physical Laws Governing Solution op Gases. — A brief re- view of the physical laws governing the solution of gases in water will help us materially to understand the mecha- ism of the trans- portation of oxygen and carbon dioxide by the blood and the respiratory mechanism in general. Gases differ from solid and fluid materials in that the parti- cles which compose them repel more than they attract each other, thus permitting the gas to diffuse throughout the atmos- phere. The repelling force exerted by the molecules of gas on the walls of the container produce the phenomena of gaseous F'!!**"*'^- ^* follows, therefore, thatUhe pressure which a gas i i FUNDAMENTAIiS OP HUMAN PI1YSK)1X)0Y. 107 exerts varies with the numbe r of m olecules of the gas present in the atmospherevY The various gases diffuse out into space until this diffusion pressure is balanced by the force of gravity. The weight of a substance is the force which gravity exerts on it. The weight of a gas would therefore be an indication of the diffusion pressure of the gas in the atmosphere, and also indi- rectly of the number of molecules of gas present. The weight of a gas or the pressure of the jjas on the earth's surface is measured by an instrument called a barometer, in which the atmosphere is balanced against a long column of mercury, and the weight expressed in the number of millimeters of mercury which the atmosphere will support. At sea level and at 15.5° Centigrade, the pressure whi**^ the atmosphere exerts on the surface of any fluid is sufficient to support the weight of a col- umn of mercury 760 millimeters in height. The solubility of a gas in a fluid is measured by the number of cubic centimeters of gas which one cubic centimeter of fluid will dissolve under standard conditions of temperature and pressure. Such a figure is known as the coefficient of solubility. For ex- ample, pure carbon dioxide gas under standard conditions of temperature and pressure (760 mm. pressure and 15.5 degrees Cent.) will dissolve to the amount of one c. c. in one c. c. of water. Under like conditions only 0.04 c. c. of oxygen will be dissolved. The coefficient of solubility of carbon dioxide is therefore 1.0 and of oxygen 0.04. The amount of gas which will go into solution in water depends on three factors : the temperature of the water, the solubility of the gas in water, and the pressure which the gas exerts on the surface of the water. As a rule, the higher the temperature of the water, the less gas will go into solution, or in other words, the solubility of a gas varies inversely with the temperature. // If, in place of having pure gases over a fluid, a mixture of several gases be present, then we find the solubility of each of the gases varying directly with the pressure it exerts on the sur- face of the fluid. Suppose that in place of exposing a cubic centi- meter of water to oxygen at 760 mm. pre.ssure, we expose it to oxygen at a pressure of 152 mm. mercury, which is the normal 108 HEMOGLOBIN. pressure of oxygen in the air {V5 of an atmosphere) it would absorb V5 of .04 c. c. or .008 c. c. of oxygen. The presence of other gases does not enter into consideration, for according to /VDalton-Henry's law, when two or more gases are mixed together, each of them produces the same pressure as if it separately occu- pied the entire space and the other gases were absent. //When the fluid has taken up all the gas it can, an equilibrium becomes es- tablished between the gas in the atmosphere and the gas within the fluid. The pressure which the gas in the fluid exerts on the gas in the atmosphere is known as the tension of the gas, and equals the pressure of the gas in the outside atmosphere to which it is exposed. This can be easily measured. Since the pressure of the oxygen in the air in the lungs is less than that in the outside atmosphere, it is apparent that if the blood should carry the same amount of oxygen as water does, the amount would be very small indeed., Analysis of the amount of oxygen in arterial blood shows tliat it contains 40 times the amount per c. c. that water can dissolve under like conditions.// For example, let us imagine human blood to be water. It would carry then only 1/40 of the volume of oxygen that it does, and the tissues of the body would need a vascular system the size of an elephant's in order to obtain as much oxygen as normally is supplied by the blood. Therefore it is obvious that the laws for simple solutions can apply only in a slight degree to the gases ill the blood. They would account at the most for only 0.7 per cent of the total oxygeii and 2 per cent of the carbon dioxide found in the blood. H«moglobin.-^T,lic extraordinary ability of the blood to carry oxygen and carbon dioxide lies in tlie presence of sub- stances capable of chemically uniting with and storing up large amounts of the gases. The iron-containing protein substance called hffimoglobin, found in the red blood cells, carries the o xyge n, and t^e alkalies and proteins of the blood carry most of the carbon dioxide. Analysis of samples of arterial and venous blood gives the following average figures, which represent the volumes of the gas found in one hundred volumes of blood. PUNDAMENTAIiS OF ITt^MAN PHYSIOLOGY. 109 CO, Nitrogen 40 1-2 45-50 1-2 Oxygen 100 vol. arterial blood contains 20 100 vol. venous blood contains 10-12 The small amount of nitrogen present in the blood in spite of the large percentage found in the atmosphere (4/5 of the baro- metric pressure being due to nitrogen) is due to the absence of anj' chemical body within the blood plasma which will unite with nitrogen. //Of jhc 20 volumes per cent of oxygen found in arterial blood only 0.7 per cent is in solution in the plasma. // The Mechanism of the Respiratory Exchange.— The oxygen in the alveoli or air passages of the lungs comprises about 14 to 15 per cent of the total air, and exerts on the cells of the respira- tory epithelium a pressure of about 100 mm. mercury, more or less. Venous blood when it reaches the lungs contains about 50 per cent less oxygen than does arterial blood, and can take up from 6 to 8 c. c. of oxygen for every one hundred c. c. of blood. Hemoglobin solutions are almost completely saturated with oxy- gen at pressures of oxygen much less than 100 mm. of mercury. There are, therefore, very favorable conditions in the kngs for ha'moglobin to take up oxygen from the air. It must be under- stood, however, that the hsmoglobin does not obtain oxygen di- rectly from the air. The hemoglobin is held in the blood corpus- cles which are floating in the blood plasma. Between the plasma and the air in the lungs lie two thin membranes, the capillary wall and the wall lining the ali' sip of the lung. The oxygen must first be dissolved by the fluid in the lung epithelium; from this the cells of the capillary walls take oxygen, and the plasma in turn takes the oxygen from the capillary cells. The plasma loses the oxygen thus obtained because the hajmoglobin is very greedy for oxygen. There is accordingly a difference in the oxygen pressure in the plasma of the capillaries of the lungs sufficient to account for the absorption of oxygen by the htemoglobin of the blood. The blood leaving the lungs is delivered into the left heart, from which it is distributed over the body. Since oxidation takes place within the tissue cells, oxygen is being continually called for, and the lymph surrounding the cells must continually gain a fresh supply of oxygen from the plasma of the bloud. This re- 110 THE EXCHANGE OP CARBON DIOXIDE. duces the tension of oxygen in the plasma and causes an evolution of oxygen from the oxyhsemoglobin, which is taken up by the plasma to be passed on to the lymph and then on to the cell. There is thus a descending scale of pressure or tension of oxygen from the air of the lungs, where its pressure may amount to 100 mm. of mercury, until it reaches the tissue elements, where the pressure may be considered zero. Zander ordinary conditions the circulation is fast enough to prohibit the complete reduction of the oxyluemoglobin. In case it is not, or in case the oxygen sup- ply is short, the phenomena of asphyxia develop //see p. 101). Effect of Carbon Dioxide on OxYHiEMooLOBiN. — As a result of the oxidative changes which take place within the cells, carbon dioxide is produced, and the tension of this gas rises in the tis- sues. It will be remembered in the discussion of the dissociation of oxyhaemoglobin, that theeffect of increased tensions of carbon dioxide is to increase the rate of reduction of oxyhaemoglobin into oxygen and haemoglobin. Since there is a high tension of car- bon dioxide present in the tissues and at the site of the capil- laries, the effect on the reduction of oxyhaemoglobin is very marked, and has a great influence on the rate at which oxygen is supplied to the tissues. Just as there is a descending pressure of oxygen from the air in the lungs to the cell, so is there a de- crease in pressure from the carbon dioxide in the cells to the air of the lungs. This gas therefore passes through the lymph to the plasma and out of the plasma through the pulmonary epithelium by the simple process of diffusion. The Exchange op Carbon Dioxiqe. — Analysis of venous blood shows that 100 c. c. contains about 45 to 50 c. c. of carbon diox- ide, and t^at the gas exerts a pressure or tension of about 40 mm. mercury, which is equal to about five per cent of an atmosphere. Now water will dissolve under these conditions about 2V^ c. c. of carbon dioxide per 100 c. c. This would leave the most of the carbon dioxide of the blood unaccounted for, in case the blood has the same solvent power for the gas that water has. The rest of the carbon dioxide therefore must be accounted for as being in chemical combination with the constituents of the plasma and corpuscles. Th e major jart is probably held^ in^ the form of FUNDAMENTALS OP HUMAN PnYSIOI/XlY. Ill sodium carbonate and bicarbonate, the remainder being combined with the proteins of the plasma and the red corpuscles. The most satisfactory explanation of the manner in which carbon dioxide is dissociated from the above mentioned compounds in the blood, is that there are substances in the plasma, such as the blood pro- teins, which act as weak acids, and gradually drive off the carbon dioxide when, as in the air in the lungs, its escape is rendered easy by a lowered carbon dioxide pressure outside the plasma. The External Respiration. Anatomical Considerations. — The constant call of the tissues for oxygen and the formation of the waste gas, carbon dioxide, demand a mechanism by which the blood can continually renew its supply of oxygen and excrete its excess of carbon dioxide. This exchange, as we have seen, is effected in the lungs, which are built up in the following way : The nasal and oral cavities lead to the pharynx, from which Fig. 27. — Diagram of structure of lungs showing larynx, bronchi, bron- chioles and alveoli. open two tubes: one posterior, the te^ophagus, going to the ali- mentary tract, and the other, anterior the trachea, going to the lungs (Fig. 27). At the beginning of the trachea is placed the larynx, or the voice box, the opening of which is guarded by a flap of tissue, the epiglottis. Within the larynx are the vocal cords. The trachea, or windpipe, is a relatively large tube, about four and one-half inches long, which, after its entrance into the 112 THE LUNGS. thorax, divides into two tubes, the bronchi, each of which subdi- vides again and again, the branches gradually growing smaller until they are mere twigs, and are known as bronchioles, or small bronchi. The lumen of the trachea iind bronchi is maintained patent by cartilage plates, which are imbedded in the walls of the tubes. The bronchioles, however, have no such plates, their walls being composed of fibrous and elastic tissue, in which is a layer of smooth muscle. The whole system of tubes is lined with a layer of ciliated epithelium. (See Fig. 25, p. 92.) The bronchioles terminate in wide air sacs or cavities, the in- fundibuli, from the walls of which extend numerous minute cavi- ties, the alveoli. The wlls of the alveoli are very thin but strong, and are composed of a layer of elastic tissue lined with a single layer of flattened epithelium. It is estimated that the epi- thelial surfaces of the alveoli, if they were spread out on a flat surface, would cover about 1,000 square feet. Such a large area exposed to the air of the lungs offers the best of facilities for the rapid exchange of the respiratory gases, and in fact the walls of the alveoli are the true respiratory membrane of tne lung, for through them the exchange of gases between the air and the blood takes place. Below the epithelial colls of the alveoli lie the capillaries of the pulmonary artery in a regular meshwork; so numerous, indeed, are they that each individual erythrocyte is able to come in close contact with the air in the alveolus, separ- ated only therefrom by the lining of the alveolus, the wall of the artery, and the plasma of the blood. This arrangement makes possible the rapid exchange of ga.sos which must take place with- in the lungs. The two lungs in company with tlie heart occupy the thoracic cavity, which is bounded above and on the sides by the ribs and their attached tissues, and below by the diaphragm, a muscular sheet of tis.sue which divides the body cavity into a thoracic and an abdominal portion (Fig. 28). The lungs are suspended at their roots, which are composed of the trachea and tlie pulmonary blood vessels, and they lie free in the thoracic cavity in close ap- position with the walls of the thorax. Covering the outside of the lungs and the inside of the thoracic cavity, which is in con- FUNDAMENTALS OP HUMAN PIIVSIOU)OY. 113 tact with the lungs, is a thin endothelial membrane known as the pleura, the surface of which is kept moist by a secretion of lymph. This smooth membrane allows the surface of the lungs to move easily over the inner surface of the thorax during the changes in the size of the cavity which accompany the respiratory movements. Mechanism of Breathing. — Normal breathing has the object of bringing about a constant renewal of air in the lungs, and it is effected by movements of the thorax and diaphragm. When- ever the cavity of the thorax is enlarged, as in the act of inspira- tion, the lungs must increa.se . \ size to fill the space, and air is Fig. 28. — The position of the lungs in tlie thorax. (T. Wingate Todd.) pushed into the respiratory tubules and the air sacs by the pres- sure of the outside atmosphere. At expiration the reverse takes place, and the air is expelled. A very good conception of the mechanism by which this is brought about may be had by refer- ence to Pig. 29. Any increase in size of tlie bottle, a.s by pulling down the bottom rubber membrane, will cause air to expand the rubber sacs coming in by the tube passing through tKe cork of the bottle. When the size of the cavity is decreased by releasing the 114 MECHANISM OP BREATHING. membrane, the reverse takes place and air is expelled from the rubber sacs. With every inspiration the thorax is increased in size in all diameters, from above downwards by the contraction of the diaphragm, and in the transverse diameter by the movement of the ribs. The Pakt Played by the Diaphragm.— The diaphragm is a circular sheet of muscle which divides the body cavity into two compartments, the upper being the thorax, the lower the abdom- fis Fiff 29 — Heiings apparatus for demonstratlner the action of the respira- tory pump. The thorax is represented by a bottle, the diaphragm by a sheet of rubber forming its bottom, the trachea by a tube passing through h. cork, and the lungs by two thin rubber bags. A thin piece of rubber tubing crosses the bottle. This represents the heart. The action of the diaphragm pumps air In and out of the lungs and water through the heart. The lungs and heart are thin rubber bags. (From Baird and Co.'s catalogue.) inal cavity. In the upper compartment are the lungs and heart with the accompanying blood vessels and air passages. The ab- dominal cavity contains the digestive organs and glands, as the iivev, kidneys, spleen and reproductive organs The peripheral iR FUNDAMENTALS OP HUMAN PHYSIOLOGY. 115 edges of the diaphragm are attached to the lumbar vertebrse at the back, to the lower border of the ribs on the sides, and to the tip of the sternum in front. The muscular fibers rudiate to- wards the center and end in a tendinous sheet of tissue called the central tendon of the diaphragm. When these fibers are relaxed, the diaphragm is pushed up into the thoracic cavity, forming a dome-shaped arch. This is caused by the pressure of the abdomi nal organs, supported by the muscular walls of the abdomen, on its lower surface, a suction pressure on the upper surface of the diaphragm being maintained by the natural tendency of the lungs to contract. The central tendon is pulled downwards and the arched dome is flattened on contraction of the diaphragm, Fljf. SO. — Diagram to show movenirtit of diu|)lii'iiii:m durinK respiration: I, expiration; H, normal Inspiration; HI, forced Inspiration. tluis increasing the siz*' of the thoracic cavity (Fig. 30). An- other resiilt of the lowering of the diaphragm is the slight pro- trusion of the abdomen due to the pressure exerted on the vis- cera. This type of breathing is therefore known as abdominal or diaphragmatic breathing. 116 MECHANISM OP BREATHING. it TiiE Part Played by the Thorax.— The action of cert'in muscles attached to the ribs also produces an enlargement of the thoracic cavity. Each pair of corresponding ribs, which are ar- ticulated posteriorly with the vertebral column and anteriorly with the sternum, forms a ring directed obliquely from behind forwards and downwards. Any muscles whose action would bring about a raising of the anterior ends of the ribs, would therefore lessen the oblique position and increase the distance be- tween each pair of ribs, and also add to the antero-posterior diameter of the thorax. Each rib increases in length from above downwards, and as the ribs are raised, the lower longer rib occupies the place previously held by its shorter neighbor. This movement therefore causes the dome or apex of the thorax to become more flat and broad. And also the lower ribs are so articulated with the spinal column that they exhibit an up- ward rotary movement, which resembles that made by a bucket handle, and which increases the lateral or transverse diameter of the thorax. The muscles which are responsible for the inspiratory eleva- tion of the ribs are mainly the external intercostals, aidf J by other muscles of the thorax, some of which are called into "se only when very powerful respiratory movements are necessaiy. Normal expiration is almost entirely a passive act. The re- coil of the stretched elastic tissue of the lungs, after the in- spiratory muscles have ceased to act, returns the diaphragm and thoracic cage to the expiratory position. This is aided somewhat by the actions of the internal intercostal muscles which lower the ribs. By increasing the size of the thoracic cavity, inspiration causes a corresponding increase in volume of the thoracic organs, viz., the lungs and the vascular structures, because th<» *horax is a closed cavity, and whenever it expands it must eit> .1 produce a vacuum between the organs which fill it and its own walls, or the volume of the organs must increase. It is the latter process which mainly occurs, the result being that air is pushed into the lungs by the atmospheric pressure whenever the thoracic cavity is increased in size. The Movements op the Lungs.— The changes produced in FUNDAMENTALS OP HUMAN PHYSIOUXiy. 117 the size of the thoracic cavity and the lungs during normal res- piration or in disease, are easily determined by noting the sounds which are produced by tapping or percussing with the fingers the thoracic walls during inspiration and expiration. A low-pitched resonant sound is elicited over the lungs containing air, whereas a high-pitched non-resonant or tympanitic hollow sound is heard over the solid viscera and abdominal organs. In disease when changes take place in the substance of the lungs, as in tubercu- losis, pneumonia, etc., alterations occur in the tone elicited on percussion. These alterations are of gi-eat diagnostic import- ance. In pleurisy, a condition in which the pleural surfaces are roughened, a friction rub or vibration, produced by the rubbing of the roughened surfa. <"< of the pleura of the lungs on that of the thorax, may be detected by placing the ear over the affected area. The pain following a broken rib is caused by the irritation of the pleural membrane by the broken edge of the rib. It is al- leviated by making the ribs immcable by tightly strapping the thorax with adhesive plaster over the region of the pain. RrsPiBATORY Sounds. — Accompanying inspiration a rustling sound, described as a vesicular sound, may be heard over most of the lung area. It is produced by the dilatation of the alveoli and fine bronchi. Over the larger air passages a high, sharper tone is heard, called bronchial breathing. In diseases in which the alveoli are destroyed and the lungs are filled with fluid, etc., the bronchial breath sounds replace the vesicular sounds. Variations occur in the respiratory movements under various emotional and physical conditions. Any foreign or irritating body within the air passages will cause a cough. This consists in a forced expiration, during the first portion of which the glot- tis is closed. The irritating substance is likely to be expelled by the sudden opening of the glottis. The presence of irritating substances in the nasal cavity gives rise to sneezing, a sudden and noisy expiration through the nat pI passages preceded by a rapid and deep inspiration. In crying, inspirations are short and spasmodic, followed by prolonged expirations, whereas laaghing is quite the reverse. Yawning, the expression of drowsiness or ennui, consists in long deep inspirations followed by a short ei- ilii 118 ARTIFICIAL, RESI'IRATION. piration. Hiccoughing is due to spasmodic contractions of the diaphragm, the peculiar sound being due to sudden closure of the glottis. Artificial Respiration. — In cases of suspended respiration in human beings caused by drowning, excess of anaesthesia, or other injury, artificial respiration is often necessary to restore normal breathing. The most efficient of those methods is described by Schafcr, and is known as Sehafer's method (Fig. 31). He de- scribes the method as follows: It consists of laying the subject in the prone posture, preferably on the ground, with a thick folded garment underneath the chest and epigastrium. The operator puts himself athwart or at the side of the subject, facing Fig. 31. — Pusiliuii to be adopted for effecting artiflcial nsplration. (Schafer.) his head (Fig. 31) and phiccs his hands on each side ovor the lower part of the back (lower ribs). He then slowly throws the weight of his body forward to bear upon his own arms, and thus presses upon the thorax of the subject and forces the air out of the lungs. This being effected, he gradually relaxes the pressure by bringing his own body up again to a more erect position, but without moving his hands. These movements are repeated reg- ularly at a rate of twelve to fifteen per minute until normal res- piration begins. Volumes of Air Respired. — At each inspiration the lungs take in about 500 e. c. of air, which is given out again at expiration. B'UNDAMENTALS OF HUMAN PHYSIOLOGY. 119 This is kiiowu as the tidul air. After tlie completion of the ordi- nary inspiration, it is possible by a forced inspiration to take 1500 c. c. more air into the lungs. This amount is known as the complemental air. Likewise after a normal expiration about 1500 c. c. more air can be expelled from the lungs. This is known as the supplemental air. In spite of forced expiration there will still remain within the lung about 1000 c. c. of air which fills the alveoli and air tubes, known as the residual air. This air remains in the air spaces after the forced expiration because the lungs cannot relax to their fullest extent, being held open by the suc- tion pressure of the thorax. In other words, the thoracic cavity is larger in the expiratory position by 1000 c. c. than the lungs are. That this is the case is shown by the immediate contraction of the lungs into a small volume when the thorax is opened, for then the atmospheric pressure becomes equalized on the out- side and inside of the lungs, and the elastic tissue contracts and forces out the residual air. From this it is obvious that the elas- tic recoil of the stretched lungs must always tend to pull the organ away from the chest wall and thus create a negative or suc- tion pressure within the thoracic cavity. Anything which de- stroys this relation makes breathing impossible, because the lungs are no longer held against the chest walls. It is for this reason that wounds in the chest are very dangerous. The trachea, bronchi, etc., require quite a little air to fill them, so that only a part of the tidal air reaches the alveoli. In other words, it is only a portion of the air we expire that comes in contact wiih the respiratory epithelium and undergoes any iiange in composition. It is estimated that about 140 c. c. represents the actual vol- ume of the air tubes. This leaves 360 c. c. of air which reaches the alveoli. This amount is used to dilute the 1000 c. c. of residual air and 1500 c. c. of supplemental air already in the alveoli. In fact the function of breathing may be said to con- sist in continually diluting the alveolar air with a quantity of fresh air in order that its composition may remain more or less I'onstant. The inspired or atmospheric iiir is a mixture of oxygen, car- hi 120 GASEOUS EXCHANGE IN LUNGS. CO, 0.04 bon dioxide and nitrogen, and is relatively constant utider ordi- nary conditions. The expired air varies somewhat according to the rate and depth of respiration. The following table gives the average percentage composition of inspired and expired air: Nitrogen Oxygen Inspired air 79 20.96 Expired air 79+ 16.02 4.38 The above analysis shows that there is a marked difference be- tween the inspired and the expired air. It shows us further that of the oxygen taken up by the blood, only part appears again combined with carbon in the gas COj. The retention of oxygen is due to the oxidation of substances which do not appear in the expired gases. This subject is fully discussed under the head of respiratory quotient in the c'apter on metabolism (p. 194). Mechanism of Oaseous Exchange in Lungs. — We have seen that in the blood the pressure or tension of the oxygen is greater, whereas that of the CO, is less than in the tissues. These rela- tions will account for the gas exchange which occurs between the blood and tissues, if we apply the physical law of the diffusion of gases, which states that two gases under different pressures and separated by a membrane through which they may pass free- ly, will mix with each other until the tensions on both sides of the membrane are equal. Before this law can be applied to explain the exchange of gases between the blood and air within the lungs, we must prove that the tension of the oxygen is less, and of the COj greater in the venous blood than in the alveolar air. A consideration of these problems is included under the subject of external respiration. ^Fl J CHAPTER X. THE RESPIRATION (Cont'd). Nervous Control of Respiration. — Under normal conditions we breathe from 14 to 18 times a minute. According to the de- mand of the tissues for oxygen, we breathe fast or slow, but the respirations are rhythmic in time and under like conditions are equal in volume. The respiratory movements, unlike those of the heart, are initiated by impulses transmitted to the respira- tory muscles from the central nervous system. These arise from the so-called respiratory centers in the medulla oblongata (p. 268). Anatomically these centers cannot be sharply localized, but destruction of the portion of the medulla in which they exist causes an immediate cessation of respiratory movements. The centers are connected with the diaphragm by the phrenic nerves, and to the muscles of the ribs, larynx and nares by spinal or cranial nerves. Like all other nerve centers, the respiratory center is influenced by afferent impulses, the chief ones of which come from the lungs by way of the vagus, but there are many others. In fact all the sensory nerves of the body, as well as the higher centers of the brain, are able to influ- ence the respiratory center. Disease of the phrenic nerves causes paralysis of the diaphragm, and impairs the ventilation of the lungs. Likewise paralysis involving the spinal cord be- low the exit of the phrenic nerves may paralyze the nerves of the thoracic muscles, and throw the whole work of respiration on the diaphragm. If the vagus nerves of a dog or cat are cut in the neck, the respiration becomes deeper and slower, yet the volume of air re- spired per minute is not greatly altered. This change is due to the elimination of stimuli normally coming from the lungs by way of the vagi to the respiratory center, which serve to control the depth of respiration. It can be experimentally demonstrated 121 ii 122 CIIEMICAI, CO.NTRor- OK RKl^l'lRATION. that the collapse of the alveoli of the lungs which occurs at the end of normal expiration, and the stretching of the alveolar walls which occurs at the end of normal inspiration, cause stimuli to be passed along the vagi to the center, and that these stimuli bring on the next phase of respiration. The breaking of the connection between the lungs and the alveoli destroys this influence and the respirations become deep and slow. In the absence of the vagi, the higher centers assume partial control of the regulation of the respiratory movements. If they also are destroyed, however, breathing becomes inade(iuate to maintain life, although the center itself is still able to keep up a modified, rhythmic respiration. Reflex Respiratory Movements. — The cutaneous nerves, es- pecially those of the face and abdomen, have a marked influence on respiration. These can be excited by heat or cold or pain ; for instance, a cold bath will cause a deepening or (juickening of the respiration. Another example is found in the forced ex piratory effort made on inhalation of acid or sharp smelling sub- stances, which not only affect the olfactory nerves, but also the sensitive endings of the fifth nerve in the nasal mucous mem- brane. Chemical Control of Respiration. — In spite of this very effec- tive method of nervous control of the respiration, there is an- other no less important means of respiratory control, which de- pends on the ability of chemical substances in the blood to stim- ulate the respiratory center. The substances which most readily affect the center are acids, such as carbon dioxide (which in solu- tion forms a weak acid,) and lactic acid, which is formed under certain conditions in the body. Lack of oxygen, if it be consid- erable, also causes tlio center to show marked signs of activity. In the introductory chapter the physico-chemical properties of the blood and tissue fluids were discus.sed. It will be recalled that these are practically neutral fluids, that is, they show an al- most exact balance in the number of hydrogen and hydroxyl ions, a condition which determines the neutrality of a fluid. Any increase in the amount of carbon dioxide in the blood would form proportionately more carbonic acid, which yields hydrogen ions, and thus tend to destroy the neutral balance of the blood. This FUNDAMENTALS OF UfMAN PlIVSIOUHJY. 123 increase in the hydrogen ion concentration in the blood is suffi- cient to stimulate the respiratory center and augment the rate and depth of respiration in order to expel the carbon dioxide and thus reduce the acidity of the blood. All acids which yield hydrogen ions in solution have this effect on respiration when they are injected into the blood. Lactic acid, which is formed when the oxygen supply to the tissues is diminished or inade- quate, is perhaps the most important factor coming into play in the stimulation of the respiratory center which occurs during exercise. The carbon dioxide tension of the blood during exer- cise may be actually decreased owing to the increased ventilation of the lungs as a result of the presence of lactic acid in the blood. The increase in breathing due to lack of oxygen is not nearly so easily elicited as that caused by excess of acids. In fact, the percentage of oxygen may be diminished to about one-half of that found in the atmosphere before breathing is markedly af- fected. In disturbances of the gaseous exchange of the lungs, the re- spiratory center attempts to compensate for the change by in- creasing the number and the depth of the respirations. If the gas exchange be markedly insufficient, the breathing becomes very much exaggerated, and practically all possible respiratory muscles are called into play. This is the case during an attack of asthma, in which the muscles of the arms and abdomen are used by the patient in his efforts to obtain enough air. Difficult breathing of this kind is known as dyspnoea. If the gas exchange is very insufficient, the phenomenon of asphyxia sets in. The control of the respiration, therefore, may be said to be two-fold, dependent not only on the nerve supply of the respira- tory center from the afferent sensory and cerebral nerves, but iilso on the chemical constitution of the blotxl, which stimulates the center directly. Each factor plays an important part in the control of the respiratory movements. The bronchial muscles are supplied through the vagi with nerve fibers which produce dilatation and constriction of the bronchi. Just what the normal conditions are which call for the action of these nerves is not known. It is generally thought that 124 VENTILATION. I asthma is caused by the constriction of the bronchioles by spasm of the bronchial muscles. Atropin, a drug which paralyzes cer- tain nerves, is of therapeutic use in this disease, since it paralyzes the nerve endings in the bronchial muscleu. Adrenalin is also sometimes of use. The Effect of Changes in the Respired Air on the Respiration. A very slight increase in the percentage of carbon dioxide in the alveolar air is accompanied by a very marked quickening of re- spiration. On the other hand, the carbon dlox'ie content of the atmosphere may be increased to about one per cent without em- barrassing the respiratory function, except during muscular work, and it is only at concentrations of carbon dioxide of three or four per cent of an atmosphere that the respiratory function is seriously impaired. The reason for this is that the inspired air becomes greatly diluted before it reaches the alveoli, so that a slight increase — up to one per cent of carbon dioxide — in the atmosphere only quickens and deepens the respiration sufficient- ly to maintain the pressure of carbon dioxide at its normal level ill the alveoli. An increase in the oxygen pressure has no such effect. In fact pure oxygen has scarcely any influence on the rate of breathing in the normal man. In persons suffering with heart failure or diseases in which the respiratory function of the lungs is im- paired, however, the presence of a high concentration of oxygen in the alveoli may make it possible for the oxygen-starved ^ Dod to obtain enough of this gas to saturate it and thus improve the general condition. The reason for these effects of oxygen is that under normal conditions the pressure of oxygen in the atmos- phere is more than sufficient to saturate the haemoglobin of the blood, so that an increase in the oxygen pressure will add only a small amount more of oxygen to that dissolved in the plasma al- ready. On the other hand, the oxygen pressure in the atmos- phere may be reduced to less than half that found at sea level without destroying life. This brings up the interesting question of mountain sickness. Mountain Sickness.— At an altitude of 5,000 meters (about 16,000 feet) the air is reduced to a little over half an atmos- FUNDAMENTALS OF HUMAN PHYSIOLOGY. 125 phere, and the oxygen tension is therefore only about eleven per cent of an atmosphere in place of twenty per cent. Therefore, in order to supply the needed oxygen, respiration must become more rapid. This, however, by washing out the carbon dioxide, serves to reduce the tension of carbon dioxide in the alveoli and blood to such an extent that the action of this gas on the re- spiratory center is weakened, and breathing may be very slow or cease for a time, producing a condition known as apnea. The lack of oxygen weakens the heart, the slightest miiscular move- ments are accomplished with diflBculty, and the individual suf- fers from nausea, vertigo, b>iadache and general weakness. After living for some time at such altitudes a person becomes accus- tomed to the rarity of the atmosphere and in some manner is able to compensate for the lessened oxygen in the air. Ventilation. — The disagreeable odor of a crowded room and the symptoms which accompany it are well known and are usual- ly attributed to the rebreathing of air. In support of this the historical incident of the Black Hole of Calcutta, in which many people perished from lack of air, is often cited. "We have already seen that atmospheres up to one per cent of carbon dioxide, or containing less than half of the normal percentage of oxygen, can be respired with no ill effects. But the percentage of carbon dioxide in the worst ventilated room does not, as a rule, rise above five-tenths per cent, or at most over one per cent, of an atmos- phere. That this amount affects our body metabolism is impos- sible, since the carbon dioxide in the alveolar air is kept at a constant level of from five to six per cent by the control which the respiratory center exercises on the respiratory movements. Moreover perfectly normal respiration can take place in a room where the oxygen content is so low that a match will not burn. Because of these facts it was suggested at one time that a toxic substance might be present in the expired air, but this has not been confirmed by subsequent investigators. In spite of the fact that there is a normal percentage of oxygen and carbon dioxide, a room miy be unbearably close if it is too warm and the air is saturattid with moisture. So long as the body can radiate its heat quickly into the atmosphere, the room does not feel stuffy, but 126 VENTILATION. when evaporation is slow, because of saturation of the air, and heat is no longer given off quickly by the body, the individuals in the room become very uncomfortable. An electric fan, which distributes the air evenly over the room and thus quickens the removal of the warm moist air immediately surrounding the body, adds much to the comfort of the person. In addition to insisting upon fresh air in public offices and private houses, it is necessary that the ventilating engineer should pay heed to something besides the percentage of oxygen and carbon dioxide in the room. He should also direct his efforts towards cooling and increasing the circulation of the air that surrounds the bodies of the individuals, by setting the air in motion by means of fans. The conditions of temperature, the moisture, and the windless atmosphere found in public rooms and homes diminish the heat loss of the body and thus the heat production, which means that the activity of the occupants must be less. A reasonable tem- perature with a relatively low percentage of moisture, and ordi- nary care in providing fresh air, will maintain the proper hy- gienic conditions of a room. The temperature of the blood exerts an influence on the respiratory centers, which is reflected in the rate and depth of the respiration. The increased respiratory rate observed in fever may be reduced by any measures which reduce the tem- perature of the blood. If this be a-lvisable, cool b?"hs, per- fusions and the antipyretic drugs are of value. There are a number of drugs which affect the respiratory system either by direct action on the respiratory organs or by influencing the nervous mechanism concerned in respiration. The drugs which produce a sensation of nausea are often used to increase the bronchial secretions. As was shown on p. 61, the mechanism depends on the reflex stimulation, through the vomiting center, of secretory fibers of the nerves going to the bronchi. The use of ammonium chloride in cough syrups to increase and liquefy the secretions is purely empirical. A number of drugs depress the respiratory center, such as the opium series. For this rea- son they are used extensively in cough syrups. Any drug which PTTND.\MENTAI•• 132 FUNDAMENTALS (»K HUMAN rUYSIOLOOV. 133 haves more or less like a cold-blooded animal for some time im- mediately following birth, during which period it must there- fore be carefully protected from cooling, for, if its temperature be allowed to fall to any considerable extent, it is not likely to survive. It takes several months before the heat regulating mechanism becomes so developed that the infant can withstand any considerable degree of cold. Factors Concerned in Maintaining the Body Temperature. — Tlie body temperature is a balance between heat production and heat loss. Heat is produced by combustion of the organic food- stuffs in the muscles, the amount which each foodstuff thus pro- duces being the same as when it is burned outside the body, except in the case of protein, when allowance must be made for the incomplete combustion of this substance in the animal body (sfo p. 187). The muscles are therefore the furnaces of the ani- mal body, the fuel being the organic foodstuffs. Heat is lost from the body mainly from the skin, but partly also from the lungs and in excreta. Heat loss from the skin is brought about by the utilization of several physical processes, namely: (1) by conduction along objects which are in contact with the skin or through the air; (2) by convection, that is, by being carried away in currents of air which move about the body; (3) by radi- ation; (4) by evaporation of sweat. This last is the means by wliich most heat can be lost, because it takes a large amount of latent heat to vaporize the sweat (see p. 34). Heat loss from the lungs is mainly due to vaporization of water, with which the expired air is saturated. A small amount is also absorbed in warming the air itself. The heat lost in the urine and faeces is almost negligible. The Regulation of the Body Temperature.— It is plain that a very sensitive regulatory mechanism nuist exist in order that the production and loss of heat may be so adjusted as to keep the body temperature practically constant. When heat loss becomes excessive, then must heat production be increased to maintain the balance, and vice versa when heat loss is slight. The conditions are to a certain extent comparable with those obtaining in a house heated by a furnaee and radiators and provided with a 134 ANIMAL HEAT AND FEVER. thermo-regulator, which, being activated by the temperature of the rooms, acts on the furnace so as to raise or lower its rate of combustion. In the animal body the thermo-regulator is the nervous sys- tem. Whenever the temperature of the blood changes from the normal, a n erve cen ter C8lled_the thernwsenic becomes acted on with the result that it transmits impulses to the muscles, which, by incroasing or diminishing their tone (see p. 265), cause a greater or a less heat production. But the center does more than the thermo-regulator of a house, for it controls the agencies of heat loss. Thus, when the blood temperature tends to rise, the thermogenic center causes more heat to be lost from the skin and lungs in the following ways: (1) It acts on the blood vessels of the skin, causing them to dilate so that more blood is brought to the surface of the body to be cooled off. (2) It excites the sweat glands, so that more heat has to be utilized to evaporate the sweat. (3) It quickens the respirations, so that more air has to be warmed and saturated with moisture. The degree to which these cooling processes are used varies in different animals. Thus in the dog, since there are no sweat glands over the surface of the body (they are confined to the pads of the paws), increase in the respiration is the chief method of cooling, hence the panting on warm days. In the case of man, civilization has stepped in to assist the reflex control of heat loss, as by the choice of clothing and the artificial heating of rooms. Desirable though this voluntary control of heat loss from the l)ody may be, there can be little doubt that it is often overdone to the detriment of good health. Living in overheated rooms during the cooler months of the year suppresses to a very low degree tlie heat loss from the body and thereby lowers the tone and heat production of the muscular system. The food is thereby incompletely metabolized and is stored away as fat ; the superficial capillaries are constricted and the skin becomes bloodless. But it is not looks alone that suffer, but health as well, for, by having so little to do, the heat-regulat- ing mechanism gets out of gear so that when it is required to act, as when the person goes outside, it may not do so promptly PUNDAMKXTAli!5 OF HUMAN PHYiSl()lA)GY. 135 enough, with the result that the body temperature falls some- what, and catarrhs, etc., are the result. There can be little doubt that much of the benefit of open-air sleeping is due to the con- stant stimulation of the metabolic processes which it causes. The importance of the evaporation of sweat in bringing about loss of heat in man partly explains why climate should have so important an influence on his well-being. It is not so much the temperature of the air, as its relative humidity, that is of impor- tance; that is, the degree, expressed in percentage, to which the air is saturated with moisture at the tei"perature of observation. Thus, a relative humidity of 75 per ci t at 15° C. means that the air contains 75 per cent of the total aaount of moisture which it would contain if it were saturated with moisture at a tempera- ture of 15° C. A high relative humidity at a high temperature makes it impossible for much sweat to be evaporated, with the result that the body cannot cool properly, and the body tempera- ture is likely to rise unless muscular activity be reduced to a minimum. This explains why it is impossible to do much muscu- lar work in hot humid atmospheres. On the other hand, if the relative humidity is low, the temperature may rise to an extraor- dinary degree (even above that of the body itself) without caus- ing fever, provided always that the body is not so covered with clothing that evaporation of sweat is impossible. At low temperatures of the air, relative humidity has an effect which is exactly opposite to that which it has at high tempera- tures, for now it affects, not the evaporation of sweat, but the heat conductivity of the air itself. Cold moist air conducts away heat much more rapidly than cold dry air. Hence, a tem- perature many degrees below zero on the dry plains of the West may be much more tolerable to man than a much higher tem- perature along the shores of the Great Lakes. Fever. — Any rise of temperature above the normal limits constitutes fever. When of slight degree, as it is in many semi- acute diseases, its detection demands frequent observation, so as to allow for the normal diurnal variation of the body tempera- ture. For example, if the temperature were recorded in the morning in such a patient, a slight degree of fever niiijht quite 136 ANIMAL HEAT AND FEVEB. easily be missed, because at this time the normal temperature is low. In acute infectious diseases, the afternoon temperature may rise to 106° P. or 41° C, or even above this, without prov- ing fatal. A temperature of 113° F. or 45° C. has been observed, but lasting for only a short time. Fever is always higher in in- fants and young children than in adults. As to the causes of fever, two possibilities exist: either (1) that heat production has been increased, or (2) that heat loss has been diminished, or, of course, both factors may operate simul- taneously. To go into this unsolved problem is unnecessary here ; suffice it to say that there can be no doubt that disturbance in the thermogenic center is the underlying cause of fever, and that it is the avenues of heat loss by the skin rather than the sources of heat supply in the muscles that are first of all acted on. The cold sensation down the back, the shivering, the goose skin, are the familiar initial symptoms of fever, and when the fever comes to an end, excessive sweating sets in and this, in part at least, explains the fall in temperature. Increased combustion in the muscles no doubt occurs during the height of the fever and accounts for the great wasting, but that this is not the only cause of the rise in temperature is evidenced by the fact that severe muscular exercise does not in itself cause fever, even although there may be much more combustion going on in the body (see p. 191). Certain drugs called antipyretics lower the temperature in fever. The most important of these are acetanilide, salicylates (aspirin), phenacetin, and quinine. The first three mentioned act on the thermogenic center, whereas quinine sejms to act directly on the combustion processes in the muscles. The body temperature is raised by cocaine and by the toxic products of bacterial growth. Even cultures which have been attenuated by keeping them for some time at high temperatures have this effect, and it is believed by many that fever is of the nature of a protective mechanism to destroy or attenuate the invading bacteria. There is bacteriological as well as clinical support for this view, thus, certain pathogenic organisms (such a.s the strep- tococcus of erysipelas) cannot live at a temperature above 41° C, FUNDAMFNTALS OF HUMAN rHYSIOUXiY. 137 and cholera patients are much more likely to survive if the dis- ease be accompanied by a moderate degree of fever. Heat stroke, or sun stroke, is due to an increase in body tem- perature that is above the limits of safety. When sweating and the other processes by which heat is lost from the body are act- ing properly it is remarkable how high an air temperature may be borne without danger; for example, in dry air a man can sit for some minutes in an oven at 100" C. while his dinner cooks beside him (Leonard Hill). But if anything should interfere with heat loss, or if heat production be excessive, as during mus- cular exercise, there is always danger of heat stroke. Free move- ment of the air is probably the most important way for safe- guarding against deficient heat loss. It is almost certainly on account of the absence of such air movement, coupled with a high relative humidity, that discomfort is experienced in hot, stuffy atmospheres, for the faulty heat loss causes a slight rise in body temperature. This slight degree of hyperpyrexia low- ers the resistance of the organism to infection. J CHAPTER XII. DIGESTION. Necessity and General Nature of Digestion: The Alimentary Canal. The never-ceasing process of combustion that goes on in tlie animal body, as well as the constant wear and tear of the tissues, makes it necessary that the supply of fuel and of building mate- rial be frequently renewed. For this purpose food is taken. This food is composed of fats and carbohydrates, which are mainly fuel materials, of inorganic salts and water, which are neces- sary to repair the worn tissues, and of proteins, which are both fuel and repair materials, and are therefore the most important of the organic foodstuffs. The blood transports the foodstuffs from the digestive canal to the tissues. In the digestive canal the foodstuffs are digested by hydrolyzing enzymes (see p. 46), which are furnished partly in the secretions of the digestive glands and partly from the numerous micro-organisms that swarm in the intestinal contents. The enzymes, as we have seen, are very discriminative in their action, for not only is the enzyme for protein without action on u fat or carbohydrate, but each of the different stages in protein break-down retiuires its own pe- culiar enzyme. It becomes necessary therefore that the enzymes be mixed with the food in proper sequence, and to render this possible the digestive canal is found to be divided into special compartments, such as the moutli, the stomach, the small intes- tines, etc., each provided with its own assortment of enzymes and with some mechanism by which the food, when it has been sufficiently digested, can be passed on to the next stage. Such correlation between the different stages of digestion necessitates the existence, in the different levels of the gastro- intestinal tract, of mechanisms which are specially developed to 138 FUNDAMENTALS OP HUMAN PHYSKlUWY. 139 bring about the right secretion at the right time. These mech- anisms are of two essentially different types, a ncri-ous reflex control, and a chemical or "hormone" control. The nervous con- trol is exercised through a nerve center, which is called into ac- tivity by afferent stimuli proceeding from sensory nerve endings or receptors (see p. 256) that are especially sensitized so as to be stimulated by some property of food (its taste or smell, or its consistency or chemical nature). This type of control exists where prompt response of the glandular secretion is impor- tant, as in the mouth and in the early .stages of digestion in the stomach. The hormone control consists in the action directly on the gland cells of substances which have b-en absorbed into tlie blood from the mucous membrane of the gastrointestinal tract. The production of these substances depends upon the nature of the contents of the digestive tube. This is a more .sluggish proc- ess of control than the nervous, but it is sufficient for the cor relation of most of the digestive functions. These considerations point the way to the scheme which we must adopt in studying the process of digestion ; we must explain how each digestive juice comes to be secreted, what action it has on the foodstuffs, aiad what it is, after each stage in digestion is completed, that controls the movement onward of the food to the next stage. And when we have followed each foodstuff to its last stage in digestion, we may then proceed to study the means by which the digested foodstuffs are absorbed into the cir- culating fluids, and in what form they are carried to the tissues. On account of the varying nature of their food we find that the digestive system differs considerably in different groups of animals. In the omnivora, such as man. the digestive canal be- gins with the mouth cavity, ii- which the f(K)d is broken up me- chanically and is mi.xed witli the saliva in sufficient amount to render it capable of being swallowed. The saliva, by containing starch-splitting ferment, also initiates the digestive process. The food is then carried by wrv of the o-sophagus to the stomach, in the near or cardiac eno ^f which it eollect.s and becomes gradually permeated by the acid gastric juice. It is then caught up, portion by portion, by the peristaltic waves of the m 140 THE AUMENTABY CANAL. further or pyloric end of the stomach and, after being thor- oughly broken down by this movement and partially digested by the pepsin of gastric juice, is passed on in portions into the duodenum, where it meets with the secretions of the pancreas and liver. These secretions, actinp along with auxiliary juices secreted by the intestine itself, ultimately bring most of it into a state suitable for absorption. What the digestive juices leave unacted on bacteria attack, especially in the cfficum, so that by the time the food has gained the large intestine it has been di- gested as far as it can be. In its further slow movement along the large intestine the process of absorption of water proceeds rapidly. Disturbances in tlio digestive process may be due not only to possible inadequacy in the secretion of one or other of the diges- tive juices, but also to disturbances in the movements of the digestive canal. Such disturbances will not only prevent the forward movement of the food at the proper time, but, by failing to agitate the food, they will prevent its thorough admixture with the digestive juices, so that the enzymes which these con- tain will not become properly mixed with the food. The Alimentary Canal. Anatomical Considerations.— The alimentary canal or tract may be considered as an involuted portion of the skin, whose function is to prepare and to absorb material for the nourish- ment of tlie body. The canal forms a tube which communicates with the exterior at tlie mouth and the anal opening. It is lined throughout with mucous membrane composed of epithelial tissue overlying a submucous coat of loose connective tissue. The outer coats ai-e made up of fibrous connective tissue and circular and longitudinal layers of smooth muscles. Imbedded in th: conts are many blood .^ssels, lymphatics and nerves Numerous ghu.ds which pour their digestive juices directly into the canal ar«> also found in tlie walls of the canal ; good exam- ples of those are the gastric or stomach glands. Other glands, too large to be imbedded in the walls, are connected with the canal by means of ducts, through which the glandular secre- FUNDAMENTALS OP HUMAN PHYSIOLOGY. 141 tions find their way. The salivary glands, the pancreas and the liver are examples of this type. The total length of the canal is about 28 feet ; the great length being possible since the tube is greatly coiled in the abdominal cavity. The canal is finictioiially and .structurallv divided into MlrVARV GLANDS LARGE ! \ INTESTINE SMALL INTESTINE ANUS FIs. SC— Tiiagiain of fh.- alimentary tiilit- and iis niipendages (After Testut.) several organs, viz. : tlif mouth, oesophagus, stomach, small and large intestines, and rectum. The mouth contains the teeth and the tongue. The mouth posteriorly opens into the pharvnx which also communicates above with the nasal passages. The pharynx, below the leve of the mouth terminates at the opening 142 THE AMMENTARY CANAL. of two tubes, the respiratory opening or larynx anteriorly, and the oesophageal, posteriorly. The oesophagus passes through the thorax, penetrates the diaphragm, and then terminates in a di- lated sac, the stomaeh. The stomach at its lower pole or pyloric region narrows and is continued as a greatly coiled and long tube, the small intestines, which in turn leads into a larger and shorter tul)e, the large intestines. This finally terminates in the rectum or lower bowel and emerges to the exterior through the anal orifice. The Blood Supply of the Alimentary Canal.— The stomach and the intestines are attached to the posterior body wall by means of a sheet of ti.ssue called a mesentery, in which are found the blood vessels, lymphatics and nerves which supply the ali- mentary canal. The arterial blood supply is derived from ves- sels coming directly from the descending aorta. The branches of these finally end in a capillary network in the walls of the intestinal canal. The venous blood which emerges from this capillary network is collected by the veins of the mesentery, which lead to the large vessel going to the liver, the portal vein.' This vein, on entering the liver, breaks up into a capillary system which is continued into the liver veins; these empty into the vena cava at the level of the diaphragm. The liver also re- ceives arterial blood through the hepatic artery, which is a branch of the aorta. The vagus (the tenth cranial nerve) which courses through the neck and the thorax finally ends in the abdomen, and along with the sympathetic nerve fibers, contained in the splanchnic nerves, innervates the intestinal canal and accessory glands. The Mouth.— The cavity of the mouth is bounded in front and on the sides by the lips, and the cheeks, above by the pal- ate, and below by tissues of the lower jaw. The cavity contains the tongue and teeth. The tongue is a thick muscular organ covered with mucous membrane which is endowed with both tactile and taste sensibility. Its function is to mix and roll the food between the teeth, and to aid in the production of speech. In health it is moist and of a red color. In disease it may be covered with a thick fur caused by profuse bacterial growth. FUNDAMENTALS OP HUMAN PHYSIoriOOY. 143 The Teeth are found implanted on the borders of the upper and lower jaw bones. The bones are covered with a tissue, known as the gum, which encircles the lower portion of each -F.H.imtl. 'Pulp tavity VtntiH. -~—~Crmfnlum. Kig. 37.— Schenif of a loiisltiulltiiil Rertl,.,, IhiouKli a human tooth. In the ennnifl a,v se,.,> tho ■•|ln,* of Iletzlus." (Mills HlHtoloKy. after Bf.hm and DavldofT. ) tooth. Two sets of teeth an- lungs and the posterior is the oeso- Cardiac OririLC T.sophaRiis ; Fundus — Great Curvature Ductus Communit Cholcdochus ^ Duct of WIrsOng Duodenum Fig- sn.— Th.. .st..mach and rtu-Mlrnuni „,» nr.I. (Ru.ha.ian, Anatomy.) phagus which, passing through the .u-.k an.l chest, end* below he diaphragm in the stomach. Th. inner or muco-is raom- Drane of the oesophagus is lim,l with epithelial tissue which con- tains many small glands. The outer coat of the tube contain, muscular and fibrous connective tissue. llje Stomach— The stomach is an expanded ^ac-like portion BP1 146 THE ALIMENTARY CANAL. of the alimentary canal. The end joining the oesophagus is known as the cardiac portion, and that joining the small intes- tines, the pyloric portion of the stomach. The entir-^ inner surface of the stomach is lined with a thick mucous membrane, which is crowded with the opening of glands, the secretion of which constitutes the gastric juice. These glands are simple tubular structures which are closely packed side by side in the Fig. 40. — The mucosa of the stomach. (Gray's Anatomy.) mucous membrane. TJie glands at the cardiac portion differ a little from those in the pyloric region. It is generally thought that the cardiac glands are responsible for the secretion of the hydrochloric acid and the pyloric glands for the pepsin which is found in the gastric juice. The muscular coats of the stomach number three. The inner FUNDAMENTALS OP HUMAN PHYSIOLOGY. 147 coat is made up of strips of muscle which run more or less ob- li. 'lex. for when dr. food is sliown to a fasting animal, salivati<. is marked, but may cause tio secretion when it i.s offered 1 a \\,l\- fed animal It is possilile in this .ase, liowever, that there may be inhibition of the glandular activities on ; count of the pres- ence of fo-d pro^luets in the blood. Perluips he mo«! interesting fact of all is hat even a fasting ami will aft- r . i me lai' 'o salivate if he i)e repeatedly sliown fo< which ises a secre* but which he is not permitted to gr The M»tise - inmctu- ately established again, however, if >.ime fooortant 1- ict of tasting (see iti' ^ tiiany . als seem to be lim- i the a Kali which is present ■ra it also contains a certain "!' alin, which can (juickly con- Fi VDAMENTAI.S OP IHTMAV PIlYsIOFXKJV. 155 V f . Joke ■'tarclies nto dcxtriiu- n maltose. Evcii when this a« I is r pr<. unced. liowe\ for it varies considerably in iifff-rii iiidivi. ils — it caniioi .loct-ed to any extent in tlw mouth cavity, part, )n aceount ot 'he liort tii"- food remains liert tnd partly bee ise many sfarei es. as in hi aits, are takci more r less in a raw state. In .son. animal such as the doR. the suiiva has no diistatic actimi v liatevr; .\ hough there can therefore be little diastatic din^t-stion in ili .,w<' . a good deal may go on in the stoma, h. for tli<' - i thai , vailowed along with the food does not -Poi stroyed by gastrie juice until some thirty n, nites nfte ».d has ga, d the stomach. id its i>reparation for mail Although ma.stieaiu)n tli swallowing are undoubted th * , another exi.sts which i gestion; this is the .^tiiiii id, for foods with a fla ■ posterior nares. Such hut it serves as th. ,i(l< of the gastrie ji; a whole materially is always more or h H-tions of the mouth cav- "^' L niportince for proper taste iierve endings, ' iii '^iractory nerve in the itid '<>• .tly gratifi<'S the appetite, stimulus m set agoing tiie secretion any relish for food, digestion as V . for this reason unpalatable food ligestible. Recent investigations point to another function of the saliva. Pepsin, a ferment v hich is important in the digestion of the proteins and whieh found in th. juice .secreted t y the glands of the stomach, - . jy absorbed by starch when in he col- loidal state as i' II. rally eaten. In this condition the fer- ment is not free . act upon tli. proteins an. I dig^'stion is de- layed. If the salivii be a lowed to partially digest the starch into sugar before tli. food i afhes the stomacii, the colloidal state is changed by the action of \h" f.tyalin of the saliva, and ab- sorption rt!int sulv-ct (.f re.ioar<'l! in r-'cent vears. H IS f, rtam that because of im| .tp,.r care, conditions aris.- in the mouth which lea.1 So the .lee;. ,f the teeth aud to more serious 156 TABTAR FORMATION. interference to the health in general. The prevention of such processes depends on keeping the mouth clean. For this pur- pose we have the mechanical cleaning of the teeth with a brush, and the use of various dental powders and pastes. These act mostly in a mechanical manner. Numerous mouth washes are also prescribed on account of their cleansing, neutralizing and antiseptic properties. When the reaction of the saliva is acid to litmus an alkaline mouth wash is required, whereas in other conditions, an astringent acid wash is prescribed. Tartar Formation and Salivary Calculi.— Under certain con- ditions a precipitate, varying in color from pale yellow to almost black, collects on the teeth, particularly on the lower incisors and molars. This precipitate is called tartar, and it may be either hard (as on the incisors) or soft (as on the molars). Its chemical composition varies considerably, as is shown in the two following analyses: I II Water and organic matter 32.24 per cent 31.48 per cent Magnesium pliosphate 0.98 per cent 4.91 per cent Calcium pliosphate 63.08 per cent 72.73 per cent Calcium carbonate 3.7 percent (Talbot) The organic matter consists of epithelial scales, other extran- eous matter and leptothrix chains. The place and manner of deposition shows clearly that the tartar is largely derived from the saliva, the chemical explanation of the precipitation being probably as follows : Saliva, as it is produced in the gland, con- tains calcium bicarbonate, which is soluble in water, and is pre- vented from changing into the insoluble carbonate by the pres- ence of free carbon dioxide in solution. When the saliva is dis- charged into the mouth somo of the carbon dioxide escapes from it so that the bicarbonate changes to carbonate and becomes pre- cipitated. The precipitate carries down with it phosphates as well as any organic debris or mico-organisms that may be present. The precipitation of calcium carbonate may even take place in the salivary ducts (Wharton's), thus forming salivary calculi. PirNDAMENTAI.S OF HUMAN PHYSIOLOGY. 157 which may reach the size of a pea or larger. Such calculi may contain as much as 3.8 per cent of organic matter, the remainder being largely calcium carbonate. The following table gives the composition of three such calculi : I II ni Calcium carbonate 81.2 per cent 79.4 per cent 80.7 per cent Calcium phosphate 4.1 per cent B.O per cent 4.2 per cent Magnesium phosphate ... % present Organic matter and other soluble solids 13.3 per cent 13.3 per cent 13.4 per cent ^^ter 1.3 per cent 2.3 per cent 1.7 per cent (Ttibot) Maatication.— By the movements of the lower jaw on the upper, the two rows of teeth come together so as to serve for bit- ing or crushing the food. The resulting comminution of the food forms tile fii-st step in digestion. The up and down motion of the lower jaw results in biting by the incisors, and after the mouthful has been taken, the side to side movements enable the grinding teeth to cru.sh and break it up into fragments of the proper size for swallowing. The most suitable size of the mouth- ful is about five cubic centimeters, but this varies greatly with liabit. / 'ter mastication, the mass weighs from 3.2 to 6.5 gram, about one-fourth of this weight being due to saliva. The food is now a semi-fluid mush containing particles which are usually less than 2 millimeters in diameter. Some, however, may measure 7 and even 12 millimeters. Determination of the proper degree of fineness of the food is a function of the tongue, gums and cheeks, for which purpose the mucous membrane covering them is supplied with very sensitive touch nerve endings (see p. 256). The sensitiveness of the tongue, etc., in this regard explains why an object which can scarcely be felt by the fingers seems to be quite large in the mouth. If some particles of food that are too large for swallow- ing happen to be carried backward in the mouth, the tongue re- turns them for further mastication. The saliva assists in mastication in .several ways: (1) by dis- solving some of the food constituents; (2) by partially digesting , 158 MASTICATION. some of the starch; (3) by softening the mass of food so that it is more readily crushed ; (4) by covering the bolus with mucus so as to make it more readily transferable from place to place. The secretion of saliva is therefore stimulated by the chewing movements, and its composition varies according to the nature of the food (p. l,-)2). I?) some animals, such as the cat and dog. iMSr. ir..— The ewed. Deglutition or Swallowing.— After bej»g masticated the fowj is rolled up by the tongue, acting against tae palate, into a boliw. and this, after being lubricated by saliva, is moved by elevation of the front of the tongue, towards the back of the mouth. About this time a slight inspiratory contraction «f the dia- phragm occurs—the socalkJ respiration of swallwiny—and the mylohyoid muscle of the floor of the mouth quwkly con- tracts with the consequence that the bolus passes between the pillars of the fauces into the pharynx. This marks the beginning of the sfcoiul stage, the first event of whir-h is tiiat the bolus, by stimulating sensory nerve endings, acts on nerve centers situated in the medulla oblongata so as to cause a coordinated series of movements of the muscles of the pharynx and larynx and an in- hibition for a moment of the respiration (p. 121). The movements alter the shape of the pharynx and of the various openings into it in such a manner as to compel the bolus of food to pass into the esophagus: (see Fig. 4")) tlius. (1) the soft palate becomes ek'vated and the posterior wall of the pharynx bulges forward so as to shut off the posterior imres, (2) the posterior pillars of the fauces approxinuite so as to shut off the mouth cavity, and (3) in about a tenth of a second after the mylonyoic' has con- tracted, the larynx is pulled upwards and forward-s under the root of the tongue, which by being drawn backwards becomes banked up over the laryngeal opening. This pulling up of the larynx brings the opening into it near to the lower half of the dorsal side of the epiglottis, but the ui)per half of this structur* projects beyond and serves as a ledge to guide the bolus saftly past this critical part of its course. (4) To further safeguard 160 DEGLUTITION. any entry of food into the air passages, the laryngeal opening is narrowed by approximation of the true and false vocal cords. The force which propels the bolus, so far, is mainly the con- traction of the mylohyoid, assisted by the movements of the root of the tongue. When it has reached the lower end of the pharynx, however, the bolus readily falls into the oesophagus, which has become dilated on account of a retlex inhibition of thJ constrictor muscles of its upper end. This so-called second stage of swallowing is therefore a complex coordinated movement ini- tiated by afferent stimuli and involving reciprocal action of various groups of muscles: inhibition of the respiratory muscles and of those that constrict the opsophagus, and stimulation of those that elevate the palate, the root of the tongue and the larynx. It is purely an involuntary process. The last stage of fJcfjUdition consists in the passage of the swallowed food along the o'sophagus. The way in which this is done depends very much on the physical consistence of the food. A solid bolus, that more or less fills the oesophagus, excites a typical peristaltic wave, which is characterized by a dilatation of the oesophagus immediately in front of, and a constriction over and behind the bolus. This wave travels down the esopha- gus at such a rate that it reaches the cardiac sphincter in about five or six seconds. On arriving hero the cardiac sphincter, oi-dmarily contracted, relaxes for a moment so that the bolus passes into the stomach. The peristaltic wave travels much more rapidly in the upper portion of the oesophagus than lower down because of differences in the nature of the muscular coat, this being of the striated variety above, and of the non-striated, be- low. The purpose of more rapid movement in the upper portion IS no doubt that the bolus may be hurried past the regions, where, by distending the opsophagus, it might interfere with the function of neighboring structures, such as the heart. The peris- taltic wave of the opsophagus, unlike that of the intestines (see p. 181), is transmitted by nerves, namely, by the .esophageal branches of the vagus, one of the most important of the nerves ariN'ng directly from the brain. If these be severed, but the mus- cular coat left intact, tlie wsophagus becomes dilated above the PUND.\MENTAI,S OF HUMAN PHYSIOLOGY. 161 level of the section and contracted below, and no peristaltic wave can pass along it; on tlie other hand, the muscular coat may be severed (by crushing, etc.) but the peristaltic wave will jump the breach, provided no damage lias been done to the nerves. The propagation of the wave by nerves indicates that the sec- ond and third stages of deglutition must be rehearsed, as it were, in the nerve centers from which arise the fibers to the pharynx and the different levels of the oesophagus. The afferent stimuli which initiate this process arise, not as might be expected, in the oesophagus itself, but in the pharynx, and they are carried to the brain by the fifth, superior laryngeal and vagus nerves; thus, a foreign body placed directly in the oesophagus does not begin to move until the pharynx is stimuhited, as by touching it. The Act of Vomiting. — This is usually preceded by a feeling of sickness or nausea and is initiated by a very active secretion of saliva. The saliva, mixed with air, accumulates to a consider- able extent at the lower end of the oesophagus and thus distends it. A forced inspiration is now made, during the first stage of which the glottis is open so that the air enters the lungs, but later the glottis closes so that the in- spired air is sucked into the oesophagus, which, already somewhat distended by saliva, now becomes markedly so. The abdominal muscles then contract so as to compress the stomach against the diaphragm and, simultaneously, the cardiac sphincter lelaxes, the head is held foiward and the contents of the stomach are ejected through the previously distended oesophagus. The compression of the stomach by the contracting abdominal mus- cles is assisted by an actual contraction of the' stomach itself, as has been clearly demonstrated by the X-ray method. After the contents of the stomach itself have been evacuated, the |)yloric sphincter may also relax and thus permit the contents (bile, etc.) of the duodenum to be vomited. The act of vomiting 's controlled by a center located in the medulla, and the afferent fibers to this center may come from many different regions of the body. Perhaps the most potent of them come from the sensory nerve endings of the fauces and pharynx. This explains the tendency to vomit when the mucosa 162 DEGLUTITION. of this region is mechanically stimulated. Other afferent im- pulses come from the mucosa of the stomach itself, and these are stimulated by swallowing certain drugs called emetics, import- ant among which are strong salt solution, mustard water, zinc sulphate, etc. When some poisonous substance has been swal- lowed, the immediate treatment is to give one of these emetics and thus cause the poison to be vomited. Certain other emetics, particularly apomorphine, act on the vomiting center of the brain itself, and can therefore act when given subcutaneously with a hypodermic syringe. Afferent vomiting impulses also arise from the abdominal vi.scera, thus explaining the vomiting which occurs in strangulated hernia, and in other irritative lesions involving this region. // CHAPTER XIV. DIGESTION (Cont'd). Digestion in the Stomach. The Secretion of Gastric Juice. — After passing the cardiac sphincter, the food collects in the fundus of the stomach. When it is solid in consistency it becomes disposed in definite layers, the first swallowed near the mucosa, the last swallowed in the center. When, as is usual in man, the food is more or less fluid, it collects in the most dependent part of the body of the stomach and the Layer formation is less evident (see Fig. 46). Within a few minutes of the entry of the first portion of food, the glands of the gastric mucosa begin to secrete their digestive juices. The immediate exciting cause of this secretion is not the contact of food with the mucosa — although this acts later — but is a ner- vous stimulus transmitted to the stomach through the vagus nerve* and coming from a nerve center situated in the medulla. The activities of this gastric center are called into operation by afferent impulsrs in the nerves that terminate in the taste buds and olfactory i, 'Ihelium. The process of gastric secretion is therefore initiated in the moutli, and the stimulus tliat is re- sponsible for it is the good taste and the flavor of the food. Just as in the case of tlie salivary glands, the food, in order to excite the secretion, need not actually enter the mouth, for a psychologi- cal stimulus may also act on the gastric center. Thus, the sight or smell of savory food, or even the hearing of s""nc sound that is known by experience to be associated with the gratification of the appetite can call it forth. These important facts were first of all revealed by observations through a gastric fistula (arti- ficial opening) in the case of a boy who, because of stricture of the cesophagus, was unable to take food by the mouth. This lAtter the vagi are cut, this secretion of gastric Juice does not occur. 163 164 niOKSTION IN THE STOMACH. boy had to be fed through tlie gastric fistuls;, but it was noticed that when he was allowed to chew food foi vhich he had a relish and then spit it out, gastric secretion occurred. This observa- tion suggested to Pavlov the establishment of analogous condi- tions in dogs, with the modification that, besides the fistula in the stomach, another was made in the oesophagus. The animal could therefore swallow interminably without ever becoming satisfied, because the food escaped by the oesophageal fistula. I-ig. 4fi.— I.iaKiams ,.f outliiio and position of stomach as indioatoU by skia- Btams taken on man In the erect position at Intervals after swallowing food Impregnated with bismuth subnitrate. A, moderately full; B. practically empty. The clear space at the upper end of the stomach is due to gas. and It will be noticed that this "stomach bladder" lies close to the heart (T Wingate Todd.) Nevertheless the gastric juice flowed abundantly, provided thii "sham feeding" was with appetizing food. Stones, bread, acid or irritating substances, although they might cause much saliva to be seorett^d and swallowed (see p. If),'?^, had no influence whatso- ever on the flow of gastric juice. The only adequate stimulus was gratification of the appetite. FUNDAMENTALS OF HUMAN I'llYSIOLOCiY. 165 In passing, it may be well to call attention to the practical importance of these observations in connection with the feeding of debilitated persons; by frei|iient feeding with appetizing fwd the nutritional condition is likely to improve much more rapidly than by occasional stuffing with uncongenial mixtures, however rich these may be in calories and nitrogen. The secretion is therefore well named the appitilc jidcr, and it lasts sometimes for nearly two hours after sham feeding has been discontinued. Yet this is only about one-half as long as the time during which gastric .juice is secreted when the food is ac- A^^ Vie. 47. — DiiiRrani of stuiiiiU'li showiiiK iiiiniatuif stomiu'li (N) sopiiiutod from the main stomach ( l') by a double layer of muious numbrune. A. A. Is the opening of the pouch on the abdominal wall. (Pavlov.) tually permitted to enter the stomach. In order to investigate the cause of the conHnucd secretion, it was neces.sary to devise some means by which the ga.stric juice could be collected, un- mixed with food, while nornml digestion was in progress. As there is no duct, the only means by which this could be done was by isolating a portion of the stomach as a pouch with an opening exteriorly through which the secretions collecting in it could be removed. An operation for making such a pouch, or "miniature stomach," as it is called, without injuring any of the nerves of ^WB" 166 l)10E.STI()N IN THE STOMACH. the .stomach lias bctMi di-viscd by Pavlov (.see Fig. 47). By sim- ultaneously collecting the secretions from the main stomach and the miniature stomach after sham feeding, it was found that they ran strictly parallel with each other, in amount as well as in strength of secretion. The secretion in the miniature stomach therefore accurately mirrors the secretion occurring in the main stomach, and so permits us to study this during the actual diges- tion of food. By introducing food directly into the main stomach through a fistula, it was found, by observations on the secretions from the miniature stomach, that very little secretion occurred until after some time, provided of course that precautions had been taken, as by experimenting on a sleeping animal, not to excite the appe- tite juice. There was found to be great discrimination in the nature of the adequate stimulus for this local secretion ; mechani- cal stimulation of the gastric mucosa, contact with alkaline fluids, such as saliva, or with white of egg, failed to produce any secre- tion ; water had a slight effect, milk still more, whereas a marked secretion occurred when a decoction of meat or meat extract, or a solution containing the half-digested products of peptic diges- tion (such as Witte's peptone) was placed in the main stomach. It was further observed, when meat was directly placed in the stomach, that the juice which collected in the pouch increased, both in quantity and in strength, after the first hour, and that it continued to flow even after four hours, thus indicating that the primary stimulus had come from the extractives in the meat, furth.-r stimulation being due to the proteose and peptones liberated as the protein of the meat became digested. This local stimulation is independent of the medullary nerve center that controls secretion of the appetite juice, for it still oc- curred after botli vagi had been divided or even after destruc- tion of the sympathetic nerve plexuses in the abdomen. It might, however, still be a nervous reflex involving the local nerve struc- tures (plexus of Aucrbach'i in the walls of the stomach, although this is not so probable as tliat it is dependent upon some chemical excitation of the gland cells by substances appearing in the blood as a re^mlt of absorption from the stomach. This "hormone" FUNDAMENTALS OF HUMAN I'llYSlOHJGY. 167 (see p. 227) is not mcnly absorbed food, for no gastric secretion occurred when solutions of meat extract, or of peptone were in- jected intravenously. It must therefore be some substauce which is absorbed into the blood from the mucous membrane of the stomach, and which is produced in this as a result of the action of the gastric contents on its cells. In confirmation of this view it has been shown that boiled extracts of the mucous membrane of the pyloric region of the stomach (made with water or weak acid or solutions of peptone or dextrin) cause some gastric juice to be secreted when they are injected in small quantities every ten minutes into a vein, similar injections of the extracting fluids themselves being without effect. We are now provided with the necessary facts from which to draw a completed account of the mechanism of gastric secretion. The satisfaction of taking food causes appetite juice to flow and this soon digests some of the protein. The products of this diges- tion, along with the extractive substances of the food, after some time (which is probably quite short in the case of man), gain the pylorus, where they act on the mucosa to produce some hormone, which becomes absorbed into the blood and stimulates further secretion of the juice. As digestion proceeds juice therefore con- tinues to be secreted. The appetite juice sets the process agoing; it initiates gastric digestion. The Active Constituents of Gastric Juice. — When there is no food in the stomach, a certain amount of mucous secretion is present in it, and most of the gland cells are filled with zymo- gen granules (see p. 151). An extract (made with glycerine) of the mucosa in this resting condition exhibits no digestive powers; but if the mucosa be first of all macerated with weak hydrochloric acid, the extract becomes highly active, because it contains large amounts of the proteolytic ferment pepsin. Other cells in the stomach produce the necessary hydrochloric acid. It may be concluded, therefore, that during the process of secre- tion the zymogen granules are activated by hydrochloric acid and converted to pepsin. In conformity with this, it has been found that the secretion of a pouch of stomach pre pared from the pyloric region possesses no digestive activity, 168 niOESTION IN THE STOMACH. since in this region no hydrochloric acid is secreted. The activa- tion of the zymogen can also be accomplished by tissue extracts and by the products of micro-organismal growth. Because- of such growth in the stomach contents, it is often found, in dis eased conditions in which there is no acid secretion, tliat active pepsin, nevertheless, is present. Accompanying the pepsin, if indeed not identical with it, the gastric juice contains the milk- curdling ferment, rennin. It also contains a fat-splitting fer- i/ient, lipase, whose activities are, however, limited to emulf-ified fats. The most remarkable constituent of the gastric secretion is hydrochloric acid, which in some animals, such as the dou'. mav attain a percentage of 0.6, being usually about 0.4 in the . ase of mt^ii. It is derived from the parietal cells of the glands in the cardiac region of the stomach, none being present in the secre- tion of the pyloric region, where there are no parietal cells. The source of the acid is of course the blood, for although this i.? practically neutral, yet it contains, on the one hand, substances such as sodium bicarbonate which readily yield hydrogen ions, and on the other, chlorides which, by dissociation, make chlorine ic.is readily available. Although it is thus possible, in the light of modern physico-chemical teaching, to formulate an equation for the reaction, yet we are at a loss to explain why just at this particular place (i. e., in the gland cells of the stomach) in the .niimal body, and nowhere else, the CI- and H-ions should be picked out of the blood and secreted as HCl. Little as we know about the cause and mechanism of tiic secre- tion of hydrochloric acid, we do know something regarding its value and use in the process of di(jfs(ion, and in general we may state that this is partly regulatory and partly digestive. It is regulatory in that it serves as the exciting cau^e of subse<)uent events in the digestive process, and digestive not only in that it actually assists in the break-down of protein, but also because it may cause a certain amount of acil hydrolysis of sugar after enough has been secreted so that some is free. Its action on protein is, however, the most important, for it initiates pro- teolytic break-down by produciiig so-calUnl acid-protein on ^m^a Fl'MlAMENTALS (»F HIMAN I'IIYSIOlA»«Y. 16l» which the pepsin — itself also dependent, us we have seen, on a preliminary activation by acid — th^n unfolds its action. As the protein becomes progressively broken down, the proteose and peptone which are produced absorb still more of the acid, so that it is some considerable time after gastric digestion has started before any acid is allowed to exist in the free state. It is only after there is some free acid that it can hydrolyse sugars or perform another important function, namely, act as an un*ii>''ptic. In this regard, however, it must be renisembered that it i> ot.i , towards certain organisms tliat such antiseptic action is i&i'Hyot!, Tor there may be bacteria in the gastric contents evei. ij. ert...'>. if excessive secretion of hydrocliifric acid. The und u icd tf;iiilency for intestinal putrofuction to increase when the> .. IS J. ui^ticient •iccretiou of hydrochloric acid is probably de- pendent more upon the delay in digestion ^'^hich this occasions, than upon any specific antiseptic power c" hydrochloric acid. During the time that elapses before a sufHcioncy of hydrochloric acid has accumulated to perform this function, bacterial fermen- tation occurs in the stomach contents. Carboliydrates are broken down by this process, at first into simple ungai-s and then into lactic acid, which may come to be present in considerable amount before the fermentation process is terminated. For these reasons we find that there is relatively much more lactic acid detectable in the gastric content? removed by the stomach tube at an early stage in gastric digestion than later. The so-called acid albumin which results from the action of tli<> acid, becomes attacked by the pepsin, which still further breaks it down into so-called proteose and peptones, which do not coagulate by heat and which become progressively mom dif- fusible through animal membranes. Although pepsin is capable of carrying the digestive process far beyond the stage of pep- t .nes, this does not occur in the comparatively short time (about s,ix hours) during which the food remains in the stomach. Slight as is this action of pepsin in the stomach, it nevertheless appears to be of eonsiderable importance for the subsequent digestion of protein by the other proteolytic ferments, trypsin and erepsin (see p. 178), which operate in the small intestine. Thus, a given f^^^TT'^^ET -r--.l^ 170 DIGESTION IN THE STOMACH. amount of blood serum becomes digested much farther in a given time by a given amount of trypsin if it receives a prelim- inary digestion by means of pepsin, than when it is acted on by trypsin alone, and erepsin will cause no digestion of most pro- teins unless these are first of all acted on by either pepsin or trypsin. But peptic digestion is not essential for life, for sev- eral cases are now on record in which individuals have thrived after the stomach has been removed. The milk curdling action of gastric juice is due partly to the hydrochloric acid and partly to pepsin. Curiously enough the curdled milk undergoes little further change until It reaches tlie small intestine. The lipase in ga.-'tric juice can act only on emulsified fat and ill a neutral or alkaline reaction. Fat digestion cannot therefore be an important gastric process. It has been supposed that there is a certain specific adaptation between the chemical nature of the food and the amount and strength of the gnstrie secretion. For example, it has been found, by observations on the gastric juice flowing from a minia- ture .stomach (see Fig. 47). that feeding with bread causes a maximal secretion during the first hour, whereas with an equiva- lent amount of flesh the maximum oceura during the first and second hours, and with milk it is delayed till the third or fourth. In proteolytic power the bread juice is much the strongest of the three, but it contains a lower percentage of acid than the others. The Movements of the Stomach.— Solid food after being swallowed accumulates in the body of the stomach, where on ac- count of an absence of movements it is not uniformly acted on by the gastric juice, its outer layers only becoming digested. In the case of man, however, some of the food, because of its semi-fluid nature, passes beyond the so-called transverse band and into the pyloric region, in which waves of ontraction make their appearance. Starting very faintly at tliis point, these waves travel towards the pylorus and become graitric contents, as we have just seen, must attain a cer- tain degree before it becomes an adecjuate stimulus for the open- ing of the pyloric sphincter, and consecjuently the rate at which tht different foodstuffs leave the stomach is to a large extent proportional to their power of combination with the acid. Pro- teins combine with large amounts of acid, so that their initial di.Sf}iHrge is delayed and before any further discharge occurs. Whi>n fats are mixed wjtli other foods, they materially delay the disehargi' Thes*' etfects are no doubt due in part to tli-; iniiibit(try influence which fats have on gastric secretion; and in part to the ]il>eration of futtv acid in the luodenum by the action of pancreatic lipase. This fatty acid mm FUNDAMENTALS OP HUMAN PHYSIOUKJY. CT3 seems to be liberated so (juickly that it is not immediatelv- neu- tralized by alkali. Water alone begins to leave the stomach almost immediately after it is taken, because in this case the sphiaeter opens before an acid reaction has been acquired, and remains open on account of there being no acid in the duodenum to cflfect its closure. Water does not remain for a sufficient time in the stomach to excite any gastric secretion, and consecjucntly it readily car- ries infection into the intestine. The discharjje of raw egg al- bumin is peculiar. Like water it begins to pms the pylorus im- mediately after ingestion, its reaction inr some <'me being alka- line; it becomes acid later, so that the itwchargc becomes inter- mittent because of the duodenal reflex. The wmsistency of food itself does not affect tlie rate of discharpp unle« hard particles are present in it, when a marked retardation oerurs. It is well known that the gastric contents are but slowly dis- charged into the duodenum when there is excessive gas accu- mulation in the stomach. This is due to the atony of the stomach which accompanies pathological gas acm»anlation. y CHAPTER XV. DIGESTION (Cont'd). Ii^Mtinai Oifestion Tlie Movements of the Intestines: Absorption. The Secretion of Ifie and Pawtreatic Juice.— Besides caus- ing reflex closure of the pyloric sphincter, the contact of the chyme, which is the name given to the senii-digested food as it leaves the sti iiaeh, with the duodenal mucosa inaugurates the processes uf inte«*inal digestion by exciting th(- secretion of bile aod pancreatic jawe Neither of these juices is secreted into the intestine during iiawting; but both begin to tiow very soon afte^r takinte fi»od, ani i»ey gradually increase in amount tt*r abc. t tiir<>e BMors, and then rai)idl\ decline The Me ax fimr, conies mainly from the gasU Waiider m whicti it has la'cimniittted dur- ing fastinc. When tte gall niadder supply uas been (exhausted, tie bile cones directly from the liver witiiout entering the gall bfadder. Tins direct aeerenon becomes more and more marked as digestion proceeds. Bile is partly an excretory prodact of the liver, and is thus being 'tonstanxly secreted into the bdr ducts. On account of its value as a digestive fluid it is not, however, allowed to run to waste, but is stored up in the gall bladui ;• until foosent from biood plaoma. It is present in much greater concenti'ation in ex- tracts of the intestinal mucosa than in the succus entericus, so that, like the inverting enzymes, it possibly displays its action while the protein is being absorbed as proteoses and peptones. It serves as the last barrier against the entry into the blood of protein in any other form than as a mixture of amino acids. Less completely digested protein is poisonous when added to the blood (p. 63). fv^»r"''3r2f- ^'^MP i-*:. FUNDAMENTALS OF HUMAV PHY-SIOLOGY. 179 Most of the food is now in a suitable condition for absorption. Before we proceed to study the nature of this process, however, there are one or two furtlier digestive changes that we must con- sider. The Digestive Function of Intestinal Bacteria.— On account of the antiseptic action of free Hydrochloric acid, there is, ordi- narily, no bacterial growth in t!ie stomach, but the neutraliza- tion of acid by the pancreatic juice and bile in the intestine pro- vides a perfect medium for such growth. The extent and nature of the bacterial growth varies very greatly according to the na- ture of the diet. There can be no doubt that the micro-organisms are a valuable aid to digestion in the case of most animals, especially of those whose diet includes cellulose Indeed, in such animals as the herbivora special provision i.s made to encourage bacterial growth by the great length of the large intestine, for without bacteria, digestion of cellulose is impossible. Thus if newly-hatched chicks be fed with sterilized grain they succumb in about tno weeks, but if a small amount of the excrement of tlie fowl be mixed with the grain, they thrive as ordinarily. On the other hand, if the food contains no cellulose, animals may develop and grow with sterile intestinal contents; thus guinea pigs have been ro moved from the uterus unJer aseptic conditions and kept in a sterile place on sterilized milk and have thrived and grown cus normal guinea pigs. The organisms in the intestine of man are probably much more useful than harmful. No doubt they arp parasites, but they are useful parasites; they work for their liv- ing, not only by assisting when necessary lu the digestion of food but also by destroying certain substances which, if absorbed, would have a toxic action on the host. Thus cholin, a substance produced by the digestion of lecithin, is distinctly poisonous, but it really never gets into the blood because the bacteria destroy it. In the case of man bacterial digestion occurs in both the small and the large intestines, and there are varieties of bacteria capa- ble of acting on all the foodstuffs. They may break up the sugars into lactic acid or even further so as to form CO^ and 11. It has been claimed that this formation of lactic acid in the intestine is LifS I^kI 180 INTESTINAL DIGESTION. of benefit to the health of man because when it occurs other bac- teria which are more harmful than useful become destroyed. To encourage this growth of lactic acid bacteria, it has been recom- nxeuded that large quantities of sour milk should be taken. It is undoubtedly true that such treatment is of benefit in many per- sons who suffer from excessive intestinal putrefaction, but that such treatment should prolong the life of ( herwise healthy ituli- viduals is visionary. As in herbivora, there are also bacteria in man which break up cellulose, producing methane and CO,. After diets containing much vegetable matter, therefore, a large amount of gas is likely to accumulate in the intestines. Prom fats, the intestinal bacteria produce lower fatty acids, which tend to cause the contents in the lower portion of the small in- testiiif^s to become acid in reaction. Although capable of hy'irolyzing native protein from the very start, bacteria act most readily on protein that has been partially diji^'sted by the proteolytic enzymes of the stomach and intes- tines. The products of this action are more or less characteristic because of the peculiar manner in which the aromatic groups of the protein molecule are attacked, producing from it such sub- stances as phenol, skatol, indol, etc., to which tlie characteristic odor of the faeces is due. When protein has been adequately di- gested in the stomach, it is so rapidly acted on by the trypsin (and erepsin) of the small gut and is so quickly absorbed that bacteria have no chance to act on it. When protein has been in- adequately digested in the ston-.acii. however, the trypsin fails to digest it quickly enough, s( that bacterial putrefaction sets in which may be (|uite marked in the small intestine, although much more so in the colon. Even wlien they do not find a suitable sub- .strate in the footl, the bacteria attack the proteins of the intes- tinal secretions themselves, which accounts for the well-known occurrence of this process during starvation. The Immunity of the Walls of the Digestive Organs Toward the Enzymes Which Act within Them.— The immunity of the mucosa of the stomach and intestin^.j seems ' j be due in main to the presence in the cells of the mucosa of anti-enzymes, that is, of substances which can inhibit the action of the various enzymes iD'^iHd FUNDAMENTALS OP HUMAN PHYf lOIiOOY. 181 (antipepsin, antitrypsin, etc.). As we should expect, very .strong anti-enzymes can be prepared from tapeworms and other intes- tinal worms. It is by virtue of possessing these, that the worms are not digested. The immunity of the gland cells and ducts, as of the pancreas, to the proteolytic enzymes which they produce is possibly to be explained in another way, namely, by tlie ex- istence of the enzyme as an inactive precursor (c. g., trypsino- gen) until after the secretion has been carried to a rogioii whose walls contain the specific anti-botly. A certain degree of im- munity to the destructive action of the intestinal bacteria on the mucous membrane may be conferred by the mucin, which is quite abundant, at least in the empty .stomach and in the large intes- tine. The relatively poor growtli of bacteria which occurs on inoculating fa'cal matter in culture media —although many bac- teria can be seen by microscopic examination to be present — is probably to be explained by their having been killed by the mucin. The Movements of the Intestines. The Movements of the Small Intestine have two functions : (1) to macerate and mix up the food and (2) to move it along to- wards the lower ei.d of the gut. These two functions are sub- served by two different types of movement, the so-called pendular and the peristaltic. The pcndtdar movements are rendered evi- dent by allowing the intestine to float out in a bath of isotonic saline (p. 42), when the various loops sway from side to side like a pendulum. By closer examination it can be seen that the move- ments arc produced by faint waves of contraction of both muscu- lar coats, wliich sweep with considerable rapidity along the gut. When the waves arrive at a part of the intestine containing any solid substance, they become accentuated, and this becomes most marked at the middle of the solid mass of food, thus tending, on account of the contraction of the circular fibers, to divide the mass into two. Tlieso movements are therefore sometimes called segmenting movements. Their function is evidently to break up the food masses and thus mix the food with the digestive juices. This can be very well shown in skiagram shadows of the ab- 1.0 I.I 2.5 12.2 2.0 t.8 MICROCOPY RESOLUTION TEST CHART NATIONAL BUREAU OF STANDARDS STANDARD REFERENCE MATERIAL 1010a (ANSI and ISO TEST CHART No. 2) 182 INTESTINAL DIGESTION. domen some time after taking food mixed with bismuth. A column of food can be seen to divide into several segments, each of which in a few seconds breaks into two, the neighboring halves then joining together, and the process repeating itslf. Two varieties of peristaltic waves are usually described, both of which are characterized by a marked constriction preceded by a distinct dilatation of the gut, which may extend for a consid- erable distance down it (two feet). The one variety of wave travels slowly (i^ cm. per minute), and has the function of car- rying along the food; the other travels very rapidly (peristaltic rush), and is evidently for the purpose of hurrying along irri- tating substances. Besides being set up by the presence of food in the intestine, these waves may be influenced through the nervous system ; stim- ulation of the vagus excites them, whereas stimulation of the sympathetic brings about a marked inhibition, in which the whole gut becomes profoundly relaxed with the exception of the ileo- colic sphincter, which contracts. This influence of the splanch- nic iray be excited reflexly, as by pain or fear. The Movements of the Large Intestine are more difficult to study than those of the small intestine. They vary considerably in different animals, as indeed is to be expected when we remember that the function of this part of the alimentary tract depends upon the nature of the food. In herbivora, for example, food may lie in the capacious caecum for days, and even in carnivora, in which this part of the gut is rudimentary, it may remain for twenty-four hours. In man the conditions seem to be intermedi- ate between those in the herbivora and carnivora, and the move- ments are believed to be as follows: As the semi-fluid food en- ters the caecum through the ileo-cajcal valve and collects in the caecum and proximal colon, it excites the occurrence of waves o^ constriction, which start probably about the hepatic flexure and travel in a central direction towards the caecum, into which the food is thus forced back. Occasionally the arrival of the wave at the ctecum starts a true peristaltic wave, which travels distally, getting feebler as it proceeds, and which may carry some of the contents into the FUNDAMENTALS OP HUMAN PHYSIOLOGY. 183 transverse colon. Here the contents assume more or less of the consistency of faces, and more powerful peristaltic waves make their appearances so that the solid masses are carried on towards the rectum. These waves are sufficiently energetic to keep the descending? colon comparatively empty, and the faecal massea gradually accumulate in the sigmoid flexure and rectum until evacuated by the act of de*" 'cation. The act of defecation is accomplished by the simultaneous peristaltic contraction of the rectum and the opening of the in- ternal sphincter of the anus. Cathartics are medicines which aecelemte or bring about a passage of the intestinal contents along the alimentary tract and cause the emptying of the bowel. They produce this effect either by directly exciting and accel- erating the intestinal peristalsis, or indirectly, by lessening the nonnal absorption or increasing the secretions of the intestinal glands, and so keeping the contents of the intestine fluid and voluminous. Examination of the accompanying diagram (Fig. 48) will show how long food takes to pass along the various parts of the gastro- intestinal tract. The Absorption of Food. As has been explained, the whole object of digestion is to break up the large molecules of which food is composed into smaller ones so that they can be absorbed into the blood or lymph which circulates in the mucous membrane of the intestines. Except un- der unusual circumstances, no absorption occurs until the small intestine is reacheu. Here sugars are absorbed into the blood as dextrose, anri i ccins as amino acids, whilst fats are ab- sorbed into the 1:, h.\tic vessels, as fatty acids and glycerine. These substances are absorbed in solution, which would lead us to expect that, because of the water absorbed along with them, the contents of the small intestine would be more solid at its lower than at its upper end; but this is not the case, for the digestive juices which have been secreted nake up for the loss of water. It is in the large intestine that the water is finally absorbed. 184 THE ABSORPTION OF POOD. il lial Attempts have been made to explain the mechanism of ah sor-.tion in terms of the known laws of filtration, osmosis, surface tc ion, and imbibition, but little further progress has been made than to establish the fact that although these processes may play a rolp, they are not alone re- sponsible. Thus, if blood serum be placed in an isolated loop of intestine, it will become entirely absorbed, even altliough identical in all the above properties witli the blood of the animal. That osmosis does have some influence, however, is evi- denced by the well-known effect of a strong saline soaition in the int<>stino; it attracts water from the blood, thus di- luting the intestinal contents and stim- ulating peristaltic contractions. It is in this way that saline catliartics act. Kcgarding tlie absorption of fats, it is now definitely known that these are first of all split into fatty acid and gly- cerine by the action of the lipase of pan- Diagram of time croatic juicc. The fatty acid then unites It takes for a capsule con- •*! n i- ^ j. taininB bismuth to reach "'"" "'kail to torm a soap, or With bile the various parts of the salts lo form a soluble coiiipouiid. In ei- large Intestine. ., ^, ,. , , „ tlicr case, the dis.solvcd fatty acid i)asses into the intestinal epithelium, into which is also absorbed the glycerine, the two re-uniting after their absorption so as to form neutral fat again. The neutral fat then passes into the central lacteal of the villus, whence it is transported by the abdominal lymphatics to the thoracic duct, which discharges it into the subclavian vein on the left side of the root of the neck. Hunficr scnsatious coincide with stomach contractions, but these difTer from those which occur during digestion. Thirst is due to dryness of the throat. It is temporarily relieved by moistening the throat, but unless li(iuid is swallowed permanent thirst develops because tin tissues become dry. Fig. 4S. Resume of Actions of Digestive Eiujnnes. Secbetion Saliva . Gastric juice., Pancreatic }ui"e . . . . Bile Tntcstijial juice . . . . Baitrria Enzyme ob Adjuvant Agency Ptyalln Alkalies . . . . Pepsin HCl. Lipase Trypslnogen Lipase Amylopsiii Alkali . . . . Action Bile salts Alkali Converts boiled starch into maltose. Favors action of ptyalln. (1) Converts metaproteins (acid albu- min, etc.) into proteoses and pep- tones. (2) Clots milk. (1) Produces metaproteins. (2) Acts as antiseptic. (3) Stops action of ptyalln. Acts on emulsified fats. Inactive until acted on by enterokinase. Splits neutral fat into fatty acid and glycerine. Converts all 3tarches into maltose. (1) Helps to neutralize HCl of chyme. (2) Combines with fatty acid to form soaps. (1) Augment the action of lipase and and amylopsin. (2) Precipitate pepsin and peptones in chyme. (3) Combine with fatty acids. (1) Helps to neutralize HCl of chyme. (2) Combines with fatty a' Id to form soaps. Converts trypslnogen into trypsin, which splits proteins into amino bodies. Converts caseinogen and peptones into simple amino bodies. One for each dlsaccharide, splitting them into monosaccharides. (Both the last two enzymes are more plentiful in the epithelium than Acting on in the intestinal Juice.) carbohydrates (1) Digest cellulose. (2) Split monosaccharides into lactic Acting on and lower acids. fats Split higher, into lower fatty acids. Acting on proteins . . . . ^P^'^ ^^ aromatic groups, as phenol, cresol, etc. i (Besides these "peclflc actions, bacteria I may perform many of the diges- I (ivc fuucliuus of the juices.) E^nterokinase. Erepsin .... Inverting enzymes . .. CHAPTER XVI. METABOLISM. The Energy Balance. Introdnctoiy. — The object of digestion, as we have seen, is to render the food capable of absorption into the circulatory fluids, the blood and lymph. The absorbed food products are then transported to the various organs and tissues of the body, where they may be either used or stored away against future requirements. After being used, certain substances are produced as waste products, and these pass back into the blood to be car- ried to the organs of excretion, hy which they are expelled from the body. By comparison of the amount of these excretory -prod ucts with that of the constituents of food, we can tell how much of the latter has been retained in the body, or lost from it. This constitutes the subject of general metabolism. On the other hand, we may direct our attention, not to the balance between intake and output, but to the chemical changes through which each foodstuff must pass between its absorption and excretion. This is the subject of special metabolism. In the one case we content ourselves with a comparison of the raw material which is acquired and the finished product which is produced by the animal ft.ctory ; in the other, we seek to learn something of the particular changes to which each crude product is subjected be- fore it can be used for the purpose of driving the machinery of life or of repairing the worn out parts of the body. In drawing up such a balance sheet of general metabolism, we must select for comparison substances which are common do both intake and output. In general the intake comprises, besides oxy- gen, the proteins, fats and carbohydrates, and the output, carbon dioxide, water and the various nitrogenous constituents of urine. This dissimilarity in chemical structure between the substances ingested and those excreted limits us, in balancing the one 186 FUNDAMENTALS OF HUMAN PHYSIOIiOOY. 187 against the other, to a comparison of the smallest fragments into which each can be broken. Such fragments are the ele- ments, and of these carbon and nitrogen alone can be measured with accuracy in both intake and output. From the balance sheets of intake and output of carbon and nitrogen, and from information obtained by observing the ratio between the amounts of oxygen consumed by the animal and of carbonic acid (C0:() excreted, we can draw far-reaching conclusions regarding the relative amounts of protein, fat and carbohydrate which have participated in the metabolism. As has already been stated, the essential nature of the meta- bolic process in animals is one of oxidation, that is, one by which large unstable molecules are broken down to those that are simple and stable. During this process of kataholism, as it is called, the potential energy locked away in the large mole- cules becomes liberated as actual or kinetic energy, which takes the form of movement and heat. It therefore becomes of im- portance to compare the actual energy which an animal ex- pends in a given time with the energy which has meanwhile been rendered available by metabolism. This is called the energy balance. We shall first of all consider this and then proceed to examine somewhat more in detail the material hal- ance of the body. Energy Balance. The unit of energy is the large calorie (uritteii ('.), which is the iiinount of heat required to raise the temperature of one kilogranmie of water through one dejfree (Centigrade) of temperature.* We can determine the caloric value by allov.-- iiig a measured (luantity of a substance to burn in comprcssod oxygen in a steel bomb which is placed in a known volume of water at a certain temperature. Whenever combustion is com- pleted, we ascertain the increase in temperature of the water in degrees (Centigrade), and multiply this by the volume of water iThe distinction between a calorie and a degree of temperature must b« clearly undersluuU. The former expresses quantity of actual heat energy ; the latter merely tells us the Intensity at which the heat energy Is belns given out. 188 THE ENERQT BALANCE. in liters. Measured in such a calorimeter, as this apparatus is called, it has been found that the number of calories liberated by burning one gram of each of the proximate principles of food is as follows : Carbohydrates l^'""^ ^^ Sugar 4.0 Protein 5.0 Fat 9.3 The same number of calories will be liberated at whatever rate the combustion proceeds, provided it results in the same end products. When a substance, such as sugar or fat, is burned in the presence of oxygen, it yields carbon dioxide and water, which are also the end products of the metabolism of these foodstuffs in the animal body; therefore, when a gram of ougar or fat is rapidly burned in a calorimeter, it releases the same amount of energy as when it is slowly oxidized in the animal body. But the case is different for proteins, because these yield less com- pletely oxidized end products in the animal body than they yield when burned in oxygen; so that, to ascertain the physiological energy value of protein, we must deduct from its physical heat value (calories) the physical heat value of the incompletely ox- idized end products of its metabolism. It is obvious that we can compute the total available energy of our diet by multiply- ing the quantity of each foodstuff by its caloric value. In order to measure the energy which is actually liberated in the animal body, we must also use a calorimeter, but of some- what different construction from that used by the chemist, for we have to provide for long continued observations and for an uninterrupted supply of oxygen to the animal. Animal calor- imeters are also usually provided with means for the measure- ment of the amounts of carbon dioxide (and water) discharged and of oxygen absorbed by tlie animal during the observation. Such respiration calorimeters have been made for all sorts of ani- mals, the most perfect for use on man having been constructed in America (see Fig. 49). As illustrating the extreme accuracy of even the largest of these, it is interesting to note that the act- ual heat given out when a definite amount of alcohol or ether is FUNDAMENTALS OP HUMAN PHYSIOLOGY. 189 burned in one of them exactly corresponds to the amount as meas- ured by the smaller bomb calorimeter. All of the energy liber- ated in the body does not, however, take the form of heat. A variable amount appears as mechanical work, so that to measure in calories all of the energy which an animal expends, one must add to the actual calories given out, the caloric equivalent of Pig. 49. — Diagram of Atwater-Benodict Respiration Calorimeter. As the animal uses up the Oj, the total volume of air shrinks. This shrinkage Is Indi- cated by the meter, and a corresponding amount of Oj Is delivered from the weighed Oj-cylinder. The Increase in weight of bottles II and III gives the CO2. the muscular work whicli has been performed by the animal during the period of observation. This can be measured by means of an ergometer, a calorie corresponding to 425 kilo- grammeters* of work. That it has been possible to striVe an accurate balance between the intake and the output of t.icrgy of the animal body, is one of the achievements of modern experi- mental biology. It can be done in the case of the human ani- 2 A kllogrammeter is the product of the load in kilograms multiplied by the distance in meters through which It is lifted. 190 THE ENERGY BALANCE. mal ; thus, a man doing work on a bicycle ergometer in the Bene- dict calorimeter gave out as actual heat, 4,833 C, and did work equalling 602 C, giving a total of 5,435 C. By drawing up a balance sheet of his intake and output of food material during this period, it was found that the man had consumed an amount capable of yielding 5,459 C, which may be considered as ex- actly balancing the actual output. Having thus satisfied ourselves as to the extreme accuracy of the method for measuring energy output, we shall now consider some of the conditions which control it. To study these we must first of all determine the basal heat production, that is, the smaU- est energy output which is compatible with health. This is as- certained by allowing the man to sleep in the calorimeter and then measuring his calorie output while he is still resting in bed in the morning, and fifteen hours after the last meal. "When the results thus obtained on a number of individuals are calcu- lated so as to represent the calorie output per kilogram of body weight in each case, it will be found that 1 C. per kilo per hour is discharged. That is to say, the total energy expenditure in 24 hours in a man of 70 kilos, which is a good average weight will be 70 X 24 = 1,680 0. ' "When food is taken f heat production rises, the increase over the basal heat production amounting, for an ordinary diet, to about ten per cent. Besides being the ultimate source of all the body heat, food is therefore a direct stimulant of heat production. This specific dynamic action, as it is called, is not, however, the same for all groups of foodstuffs, being greatest for proteins and least for carbohydrates Thus, if a starving animal is given an amount of protein which is equal in caloric value to the calorie output during starvation, the calorie output will increase by 30 per cent, whereas with carbohydrates it will increase only by 6 per cent. Evidently, then, protein liberates much free heat during its assimilation in the animal body; it burns with a hot- ter flame than fats or carbohydrates, although, as in the case of fats, at least, before it is completely burnt, it may not yield so much energy. This peculiar property of proteins accounts for their well-known heating qualities. It explains why protein com- FUNDAMENTALS OP HUMAN PHYSIOLOGY. 191 poses so Icrge a proportion of the diet of peoples living in cold regions, and why it is cut down in the diet of those who dwell near the tropics. Individuals maintained on a low protein diet may suffer intensely from the cold. If we add to the basal heat production of 1,680 C. another 168 C. (or 10 per cent) on account of food, the total 1,848 C. nevertheless falls far short of that which we know must be liber- ated when we calculate the available energy of the diet. What becomes of the extra fuel? The answer is that it is used for muscular work. Thus it has been found that if the observed person, instead of lying down in the calorimeter, is made to sit in a chair, the heat production is raised by 8 per cent, or if he performs such movements as would be necessary for ordinary work (writing at a desk) , it may rise 29 per cent, that is to say, to 90 C. per hour. Allowing 8 hours for sleep and 16 hours for work, we can thus account for 2,168 C, the remaining 300 odd C. which is required to bring the total to that which we know, from statistical tables of the diets of such workers, to b the actual daily expenditure, being due to the exercise of walking. If the exercise be more strenuous, still more calories will be ex- pended; thus, to ascend a hill of 1,650 feet at the rate of 2.7 miles an hour require 407 extra calories. Field workers may expend, in 24 hours, almost twice as many calories as those en- gaged in sedentary occupations. Another factor which controls the energy output is the cool- ing influence of the atmosphere. When this is marked, more heat must be liberated in order to maintain the body temperature (see p. 132). In other words, the necessary heat loss must be compensated by an increased heat production, just as we must burn more coal to keep the house at a given temperature on a cold, than on a warm, day. This adjustment of energy liberation to the rate of cooling at the surface of the body explains, among other things, why it should be that small animals give out much more energy, per unit of body weight, than those that are larger. The small animal has relatively the greater surface area, just as two cubes of equal weight when brought together have a com- bined weight which is double that of either cube, but a surface 192 THE ENERGY nALANCE. area which is less than double (two surfaces having been brought together). Greater tendency to surface cooling explains why small animals should so much more quickly succumb to cold than those that are larger, and why slim persons should feel the cold more keenly than those that are stout. Other things, such as diet, external temperature, etc., being the same, it is therefore surface area and not budij weight which determines the energy production, a fact which is clearly dem- onstrated by finding that the calorie output for different animals is constant when it is calculated for each square meter of sur- face. Thus, a horse produces only 14.5 C. per kg. of body weight in 24 hours, whereas a mouse produces 452 C, but if we calculate according to square meter of surface the dif- ferences practically vanish. These facts, however, do not apply when the differences in size are due to age. This has been most strikingly demonstrated in the case of man, for it has been found that the calorie requirement per unit of surface is very distinctly greater in the early yea-s of life than later. Thus, tak- ing the discharge of carbon Cvox- .3 as a criterion of the energy discharge, the following it'sults have been obtained from indi viduals sitting down : Carbon dioxide discharged, per Arerage age Average weight Hiiuare meter of surface 'yeaw) (kilograms) and hour (grams) \Mates 9 2/3 28 29.9 12 1/2 34 26.5 16 1/2 51 23.5 19 1/2 60 21.8 26 68 18.5 36 68 16.9 46 77 16.3 68 85 Females 14.2 8 22 26.6 12 36 20.1 16 49 16.0 17 2/3 64 14.8 30 64 ie.s 46 «7 17.8 )*• PUNPA MENTALS OP H MAN I'llYSlOLOT.Y. 193 This table shows us cleiiriy -at over and above the greater combustion necessary on account of their relatively greater sur- face, chikh-^n re<|uire calories for growth. They mur* be fed more liberally than adults, otherwise they starve. The table further shows that boys must be more liberally fed than girls of equal age and body weight, probably because of their greater restlessness. It is on account of these greater food requirements that childre?! are the first to die in famine. Recent work has shown that the above conclusions are not strictly warranted by the facts, for tl -e appear to >-> other factors than surface and mass of the body affecting t energy requirement of the growing organism. CHAPTER XVII. METABOLISM (Cont'd). The Material Balance of the Body. We must distinguish between the balances of the organic and the inorganic foodstuffs. From a study of the former we shall gain information regarding the sources of the energy production whose behavior under various conditions we have just studied. From a study of the inorganic balance, although we shall learn nothing regarding energy exchange — for such substances can yield no energy — we shall become acquainted with several facts of extreme importance in the maintenance of nutrition and growth. To draw up a balance sheet of organic intake and output re- quires an accurate chemical analysis of the food and of the excreta (urine and expired air). Furnished with such analyses we proceed to ascertain the total amount of nitrogen and carbon in the excreta in a given time and to calculate, from the known percentage of nitrogen in protein, how much protein must have undergone metabolism. We then compute how much carbon this quantity of protein would account for, and we deduct this from the total carbon excretion. The remainder of carbon must have come from the metabolism of fats and carbohydrates, and al- though we cannot tell exactly its source, yet we can arrive at a close approximation by observing the respiratory quotient (R. Q.), which is the ratio of the volume of carbon dioxide exhaled CO, to that of oxygen retained by the body in a given time, i. e., 0, When carbohydrates are the only foodstuff undergoing metabol- ism, the quotient is one, that is to say, the CO, excretion and O, intake are equal in volume. The reason for this is that a molecule of carbohydrate consists of C along with H and in the same 194 FUNDAMENTALS OF HUMAN PIIYSIOIXKIY. 195 proportions as they exist in water ; therefore oxygen is required to oxidize the C, but not the H, and, since eciuiniolocular quan- tities of all gases occupy equal volumes (at the same tempera- ture and pressure), the volume of CO2 produced e(iuals the vol- ume of C required to produce it. The conditions are other- wise in the case of fats and proteins, for besides C these mole- cules contain an excess of H, so that O is required to oxidize some of the H, as well as all of the C. A greater volume of Oj is therefore absorbed du 'ng their combustion than the volume of COj that is produced, and R. Q. is about 0.7. By observing this quotient, therefore, we can approximately determine the source from which the non-protein carbon excretion is derived. Having in the above manner computed how much of each of the proximate principles has undergone metabolism, we next pro- ceed to compare intake and output with a view to finding whether there is an equilibrium between the two, or whether re- tention 01- loss is occurring. Starvation. — In order to furnish us with a standard condition with which we may compare others, we will first of all study the metabolism during starvation. When an animal is starved, it has to live on its own tissues, but in doing so, it saves its protein so that the excretion of nitrogen falls after a few days to a low level, the energy requirements being meanwhile supplied, as much as possible, from stored carbohydrate and fat. Although always small in comparison with fat, the stores of carbohydrate vary considerably in different animals. They are much larger in man and the herbivora than in the carnivora. During the first few days of starvation it is common, in the herbivora, to find that the excretion of nitrogen is actually greater than it was before starvation, because the custom has become established in the metabolism of these animals of using carbohydrates as the main fuel material, so that when this fuel is withheld, as in starvation, proteins are used more than before and the nitrogen excretion becomes greater. We may say that the herbivorous animal has become carnivorous. The same thing may occur in man when the previous diet was largely carbohydrate. During the greater part of starvation, however, most of the 196 STARVATION. energy required lo maintain life is derived from fat, as little as possible being derived from protein. This type of metabolism lasts until all the available resources of fat have become ex- hausted, when a more extensive metabolism of protein sets in with the consequence that the nitrogen excretion rises. This is really the harbinger of death— it is often called the pmnortal rise in nitrogen excretion. It means that all the ordinary fuel of the animal economy has been used up, and that it has become necessary to burn the very tissues themselves in order to obtain sufficient energy to maintain life. Working capital being all exhausted, an attempt is made to keep things going for a little longer time by liquidation of permanent assets. But these assets, as represented by protein, are of little real value in yielding the desired energy because, as we have seen, only 4.1 calories are available against 9.3, obtainable from fats. These facts explain why during starvation a fat man excretes daily less nitrogen than a lean man, and why the fat man can stand the starvation for a longer time. Not only is there this general saving of protein during star- vation, but there is also a discriminate utilization of what has to be used by the different organs according to their relative activities. This is very clearly shown by comparison of the loss of weight which each organ undergoes during starvation. The heart and brain, whicli must be active if life is to be maintained, lose only about 3 per cent of their original weight, whereas the voluntary muscles, the liver and the spleen lose 31, 54 and 67 per cent, respectively. No doubt some of this loss is to be ac- counted for as due to the disappearance of fat, but a sufficient remainder represents protein to make it plain that there must have been a mobilization of this substance from tissues where it was not absolutely necessary, such as the liver and voluntary muscles, to organs, such as the heart, in which energy transfor- mation is sine qua non of life. The vital organs live at the ex- pense of those whose functions are accessory. When we compare the excretion of carbon dioxide from day to day during starvation, it will be found to remain practically constant, wlien calculated for each kilogram of body weight. The FUNDAMENTALS DP Hl'MAN I'lIYSIOLUOY. 197 same is true for tlie calorie output. Certain unusual substances such as creatin also make their appearance in the urine, and there is an increase in the excretion of ammonia, indicating that larger quantities of free acid are being set free in the organism. Starvation ends in death in an adult man in somewhat over four weeks, but much sooner in children, because of their more active metabolism. At the time of death the body weight may be reduced by 50 per cent. The body temperature does not change until within a few days of death, when it begins to fall, and it is undoubtedly true that if means be taken to prevent cool- ing of the animal at this stage, life will be prolonged. Normal Metabolism. — Apart from the practical importance of knowing something about the behavior of an animal during starvation, sucli knowledge is of great value since it furnishes a standard with which to compare the metabolism of animals under normal conditions. Taking again the nitrogen balance as indi- cating the extent of protein wear and tear in the body, let us consider first of all the conditions under which equilibrium may be regained. It would be quite natural to suppose that if an amount of protein containing the same amount of nitrogen as is excreted during starvation were given to a starving animal, the intake and output of nitrogen would balance. We are led to make this assumption because wc know that any business bal- ance sheet showing an excess of expenditure over income could be met by such an adjustment. But it is a very different matter with the nitrogen balance sheet of the body; for, if we give the starving animal just enough protein to cover the nitrogen loss, we shall cause the excretion to rise to a total which is practically (n|ual to the starvation amount plus all that we have given as food, and although by daily giving this amount of protein there may be a slight decline in the excretion, it will never come near to being the same as that of the intake. Such feeding will pro- long life for a few days only. To strike equilibrium we must give an amount of protein whose nitrogen content is at least two and one-half times that of the starvation level. For a few days following the establishment of this more liberal diet, the nitrogen excrctiun will bo far i: ex- 198 NORMAL METABOLISM. cess of the income, but it will gradually decline until it corre- sponds to the intake. Having once gained an equilibrium, we may raise its level by gradually increasing the protein intake. During this progressive raising of the protein intake, it will be found, at least in the carnivora (eat and dog), that for a day or so immediately following each increase in protein intake, a certain amount of nitrogen is retained by the body. The ex- cretion of nitrogen, in other words, does not immediately be- come adjusted so as to correspond to the intake. The amount of nitrogen thus retained is too great to be accounted as a re- tention of disintegration products of protein; it must there- fore be due to an actual building up of new protein tissue, that is, growth of muscles. Such results undoubtedly obtain in the cat, and less mark- edly in the dog. In man and the herbivorous animals, this is not the case, for in these we can never give a sufficiency of pro- tein alone to maintain nitrogen equilibrium; there will always be an excess of excretion over intake. But indeed it scarcely re- quires any experiment to prove this, for it is self-evident when we consider that there are only 400 C. in a pound of lean meat, and there are few who could eat more than 4 pounds a day, an amount which however would only furnish about half of the' re- quired calories. A person fed exclusively on flesh is therefore being partly starved, although he may Ihink that he is eating abundantly and be quite comfortable and active. This fact has a practical application in the so-called Banting cure for obesity, which consists essentially in limiting the diet to flesh and green vegetables, allowing only a very small quota of carbohydrates or fats. Protein Sparers.— Very different results are obtained when carbohydrates or fals are freely given with the protein. Nitrogen Ciiuilibrium can then be regained on very much less protein ; so we speak of fats and carbohydrates as being "protein sparers." Carbohydrates are much better protein sparers than fats; indeed they are so efficient in this regard that it is now believed that carbohydrates are essential for life, so that when the food con- tains no carbohydrates, a part of the carbon of protein is FUNDAMENTALS OK HUMAN PUYSIOIjOOY. 199 converted into this substance. This important truth is supported by evidence derived from other tields of investigation (e. g., the behavior of diabetic patients, where the power to use carbohy- drates is much depressed). The marked protein-sparing action of carbohydrates is illustrated in another way, namely, by the fact that we can greatly diminish the protein break-down during starvation by giving carbohydrates. In this way we can indeed reduce the daily nitrogen excretion to about one-third what it is in complete starvation. The Protein Minimum.— In the case of man living on an average diet, although the daily nitrogen excretion is about 15 grams, it can be lowered to about 6 grams, provided that, in place of the protein that has been removed from the diet, enough carbohydrate is given to bring the total calories up to the normal daily requirement. If an excess of carbohydrate over these energy requirements be given, the protein may be still further reduced and yet equilibrium main- tained. To do this, however, it is not the amount of carbohy- drate alone that determines the ease with which the irreducible protein minimum can be reached ; the kind of protein itself makes a very great difference. This has been very beautifully shown by one investigator, who first of all determined his nitrogen ex- cretion while living on nothing but starch and sugar, and then proceeded to see how little of differnt kinds of protein he had to take in order to bring himself into nitrogenous equilibrium. He found that he had to take the following amounts: 30 gm. meat protein, 31 gm. milk protein, 34 gm. rice protein, 38 gm. potato protein, 54 gm. bean protein, 76 gm. bread protein, and 102 gm. Indian corn protein. The organism is evidently able to satisfy its protein demands when it takes meat protein much more readily than with vegetable proteins. To understand why proteins should vary so much in their nutritive value, we must examine their ultimate structure very closely. When the protein molecule is disintegrated, as by diges- tion, it yields a great number of nitrogen-containing acids, the amino acids, a? well as several bases and aromatic substances The mest impo.. int of these acids are glyciu. alanin, serin, valin, 200 N(»UMA[. METAB(JL18M. leucin, prolin, aspartic and glutamic acids, the bases being lysin, histidin and arginin and the aromatic bodies, phenylalanin, tyro- sin and tryptophan. These substances constitute the available "units" or "building stones" of protein molecules, but in no two proteins are the materials used exactly in the same propor- tions, some proteins having a preponderance of one or more and an absence of others, just as in a row of houses there may be no two that are exactly alike, although for all of them the same building materials were available. Albumin and globulin are the most important proteins of blood and tissues, so that the food must contain the necessary units for their construction. If it fails in this regard, even to the extent of lacking only one of them, the organism will either be unable to construct that pro- tein, and will therefore suffer from partial starvation, or it will have to construct for itself this missing unit, a process which it can accomplish for some but not all of the units. It is therefore apparent that those proteins are most valu- able as foods that contain in array of units which can be reunited to form all the varieties of protein entering into the structure of the body proteins. Naturally, the protein which most nearly meets the requirement is meat protein, so that we are not sur- prised to find that less of it than of any other protein has to be taken to gain nitrogen equilibrium. Casein, the protein of milk, although it does not contain one of the most important units, namely, glycin, is almost as good as meat protein, because the organism is itself able to manufacture glycin. When, on the contrary, proteins (such as zein from corn) are given, in which certain units are missing, starvation inevitably ensues. But it does not do so if the missing units, (which in the case of zein is tryptophan) are added to the diet. These most important facts have been ascertained by experi- ments carried out in New Haven by Osborne and Mendel. Young albino rats, just weaned, were fed on a basal diet con- sisting of the sugar, fat and salts of milk to which was added the protein whose nutrition value it was desired to study. The rats were weighed from day to day, and the results plotted as a curve— the curve of growth. A gradually rising curve FUNDAMENTALS Of HllMAN PHYSIOUMJV. 201 was obtained when casein or the albumin of milk or eggs, or the edestin of hemp seed, or the glutenin of wheat was fed, but this was not the case with the gliadin of wheat or, as above mentioned, with zein of corn. It will be seen, there- fore, that of the two proteins in wheat one, glutenin, contains all the necessary units for building up the growing tissues, but that in the other protein, gliadin, some essential unit is absent ; by analysis this was found to be lysin. By adding lysin to gliadin a normal curve of growth resulted, thus showing that this was really the missing unit. The result was made even more spectacular by feeding a batch of young rats >u gliadin alone, 80 that they remained undeveloped and stunted, and then adding lysin to their diet, when they very (juickly made up for lost time, and soon reached, if not quite, yet almost as good a development as their more fortunate brothers who had been fed on glutenin or casein from the first. The animal economy itself can therefore produce certain of the amino bodies — thus, as we have seen, it can produce glycin — this power being much more developed, in the case of herbivor- ous, as compared with carnivorous animals. In the vegetable food on which oxen live, several of the prominent amino bodies of muscle protein are missing, but they are constructed in the organism by altering the arrangement of the molecules of those amino bodies which are present, so that a protein is built up which is very like that present in the tissue of the carnivorous animals. Even in the case of the herbivora, however, there are limitations to the power of forming new amino bodies. Trypto- phan, for example, cannot be formed in this way. CHAPTER XVIII. THE SCIENCE OF DIETETICS. In order that a proper assortment of amino bodies may be assured in the diet, protein is taken in excess of the quan- tity necessary to repair the tissues. It has been thought by some that the surplus thus taken by the average indi- vidual is much more than need be, and that an unnecessary strain is thus thrown on the organs which have to dispose of the excess. It has been claimed by the adherents of this view that many of the obscure symptoms — headaches, muscular and back pains, sleepiness, etc. — that city folk are liable to suffer from, are due to the presence in the blood of unnecessary by-products of ex- cessive protein metabolism. Such opinions seemed to receive very weighty indorsement some years ago when Chittenden pub- lished a long series of observations showing that men in various callings in life, could perform their daily work quite satisfac- torily and apparently maintain their health after reducing the protein of their diets to less than half of the usual amount. No direct benefit could be claimed for this reduction except that some of the men believed that they felt better and fitter and more inclined for work, an improvement which admits of no quantitative measurement because of the psychological elements involved. Although these observations were conducted with all the care and accuracy of the highly trained scientist, they have been considered quite iuade(iuate to justify the claim that man takes too much protein. The observations have, neverthe- less, been of immense value in compelling a careful review of the evidence that the proportion of protein which habit has pre- scribed as being the proper one for us to take, is really the most suitable for our daily needs. There are, however, differences in the protein content of the diet according to the race and envirnnment. This has been as- 202 FUNDAMENTALS OP HUMAN PllYsjlOLOGY. 203 certained by compiling the stardard diet for a community, that is, measuring the exact quantities of protein and carbohydrate in the diets which the people are accustomed to live on, and aver- aging the results. One remarkable outcome of such statistical work has been to show that for peoples living under approxi- mately the same conditions as regards climate and amount of daily muscular work, the average daily requirement of calorics, carbon and nitrogen works out pretty much the same, although there may be some diversity in the proportions of protein and carbohydrate. The following table shows this: Type of individuals. Protein Pat Carbo. Total Cal. C N gm. gm. gm. gm. gm. Average workman in Germany, 20 years age. 118 56 500 3,045 328 18.8 German soldier in the field 151 46 522 3,190 340 24 British soldier in peace... 133 115 429 3,400 21.3 Russian soldier in war (Man- churian campaign) .... 187 27 775 4,900 30 Professional man 100 100 240 2.324 230 16 Such figures can be compiled with tolerable accuracy because the diet is under control. It is of course more diflRcult to collect suflSciently accurate data regarding the diets of civilians, but it is safe to say that the average city dweller in temperate zones derives his daily requirement of 15 gm. nitrogf'n in 95 gm. of protein, which also yields 60 gm. of the required 2oU gm. car- bon. This deficit he might supply either from fats or carbohy- drates, the actual proportion depending on availability and price. It should be particularly noted that the proportion of protein is very much increased whenever strenuous muscular work has to be performed. Now the question is, do such statistical studies substantiate Chittenden's claim that the protein which we are accustomed to consume could profitably be reduced! They cer- tainly do not. Let us for a moment consider the health condition and physical development of communities such as the Bengalis of Lower Bengal, who live largely on rice and take only a little less in the way of protein than the amount Chittenden would 204 DIETETICS. have us take. Their body weight, chest measurement and muscular development are distinctly inferior to those of the natives of Eastern Bengal, who, nevertheless, belong to the same race as the lower Bengalis, but differ from them in taking more protein in their food. Not only this, but the lower Bengalis are in every sense of the word half starved, and are very prone to disease, especially of the kidneys, the very type of disease to which we are told excessive protein consumption must predispose. Dia- betes is also very prevalent amongst these people, probably be- cause of the enormous quantities of sugar-yielding food (car- boiiydrates) which they are compelled to eat in order to pro- vide sufficii .it calories for life. Mentally, they are a very in ferior race. This, then, is an experiment on a much grander scale than Chittenden's, ond what of the results? It is for- tunate that most of Chittenden's subjects "through force of circumstances" have returned to their old dietetic habits. p]xactly concordant results have been obtained when attempts have been made to reduce the protein in the dietaries of public institutions such as prisons, alms houses, etc. There has invari- ably been a distinct increase in the sick list, especially of such diseases as pneumonia, tuberculosis, etc. And if we seek for evidence of an opposite nature, we do not find that excessive protein ingestion is fraught with any evil consequences to the community. Thus the Eskimo takes five times more protein than the Bengali and two and one-half times more than the European, yet he is peculiarly free from "uric acid" disea.ses; and his physical endurance and his power of withstanding cold are ex- traordinary. There are a great many secondary factors, such as availability, taste, etc., that determine the average diet of a community, but the main determining factors are instinct and experience. In the struggle for supremacy of one race over another, we may assume that adequacy of diet has been a determining factor, and that the average which is taken usually represents that which conduces to the greatest efficiency. We have dealt at some length on these questions because of their great practical importance, and because they show us that FUNDAMENTALS OF HUMAN PHYSIOLCKJY. 205 ill the matter of the protein content of our diet, as in tliat of all other animal functions, there comes into play the principle of the "factor of safety." We have two lungs, although it is . nuti'itive values of the food must be considered, and the old adage should never be forgotten, that "one man's food is an- other man's poison." Very practical conclusions may be drawn from these observa- tions regarding the most suitable diet for the city dweller. It is evident that v/e are now-a-days .in possession of a sufficient 206 DIETETICS. amount of scientific information regarding both the daily require- ments of the body and the ability of the various foodstuflEa to fulfill these requirements, to compute, from the market prices of foods, how much it should take per diem for an individual, or a family of individuals, to live healthfully and economically. The day will surely come when, through the medium of schools and the press, everyone will know what we may call the fundamentals of dietetics, namely: (1) that a man of sedentary occupation (the ordinary city clerk) requires daily 2,600 calories, and t laboring man, at least 3,000 calories. (2) That at least 5 per cent of the calories should be provided in protein food of animal origin (m«»ats, milk) with 10 per cent or more as other protein (bread, Ov.tmeal, etc.). To enable the housewife to purvey the necessary food to meet these requirements, she must therefore become familiar with the caloric value and the percentage of protein in the different classes of protein foods, and of the caloric values of other great staples of diet. Canned foods will no doubt some day have printed on the label : "This can contains calories, of which per cent are in proteins of grade " And this is no Utopian idea; it is practical common sense. The adoption of such a scheme is far more likely to be the solution of the problem of the high cost of living than anything else, for, indeed, it is not so much the high cost of living as it is the cost of high living that troubles us. We demand business efficiency in our manufac- turing organizations, and yet we are inclined to ridicule as un- practical any attempts at nutritive efficiency in the animal organ- ization which is o.xr own body. Not only the principles of dietetics, but the details as well are now so thoroughly under- stood that their application in the feeding of the masses is only a matter of education. Dietarj- impostures of the meanest de- scription, often hiding behind a "bluff" of scientific knowledge, are of course the most serious enemies we shall have to face in spreading the knowledge. It will be the duty of physicians, of pharmacists, and of the educated classes to offset this commercial brigandage by spreading the gospel of food efficiency. As illustrating the food efficiency, in relationship to cost we I •e- to of a ie id i.v m i. jr al I" -" 3(1 -III .'ill rill Ti) Sii :iii iilii \ 170. S60 1SS5 34 10 1 3TT IliJO i:;ii5 on 310 11 SO I l«70l ii;2oi 'Mil ' ' ^^ f ' ■ j 1 Mi OBBi Ul r =- - ^ 1 1 ^^ ^^ "™ — — ! 'J- 1^ 1 1 in. 1 1 Wli.il.' milk Skim milk. t'i<:iiii. I (..'lll-CSl'. liiHier. Av.r.in.' miiltnii I iMW ) I AVlTil^r |Mllk I I^IW ) |l'"ish — lliiiiiiili'i' ( law). Hmi'imi. \\li.-,it liriMi .V.sli .111(1 ivaipr. rnitiiii 111 l.sl (Jualitv CZl ('MllMlh.vdMlIc l!i(C. I'Kiliiii 111 :.'ii(l (.iuiilily. l--al. Cal.iiicK. I'l.Ue It lljclctlc ctiait. sIlllHiliir lli.' nil , , iilai;,|. ai|!..!l!!t.>^ ,.f (It,- \:,tf>:tK lii.iximat.' piiiicliilcs I iiHliialcd h.v llic sha.l.Mi ai.a.sl and llir .alinirs i iiali- ralol In led I yielded hy liiiiiiiiiK I II. .if llie , ormiK.iicr f IsliilTs Tli. nii'ii- li.rs Id III., left repres.iil llie cal.irir values and tlie names |„ the liKlit, llie f(i(id ill (lUeNtioii. m^mrn FUNDAMENTALS OF HUMAN PHYPIOIiOGY. 207 may take. the following table from the menu of a well-known restaurant company: Cost Calories Calories Cost In cents Total % in for 5 cents in cents per portion protein per 1000 calories Bread 5 933 12 933 5 Apple pie 5 343 5 337 15 Boston pork and beans 15 868 12 276 18 Ham sandwich ... 5 212 20 198 30 Corn beef hash... 15 538 14 170 30 Beef stew 15 641 25 199 32 Club sandwich ... 25 438 20 82 61 Sliced pineapple ..5 36 8 36 138 Mayonnaise 20 53 16 13 35 (Lu9k) The above table is not by any means from a cheap restaurant. By economy and judicious purchasing it is possible even in New York to purchase, for 8 cents, 1,000 calories having the proper proportion of protein, so that a working man may easily cover his dietetic requirements for 25 cents a day, exclusive of the cost of cooking. All he spends above this is for personal taste and relish. Chemistry of the Commoner Foodstuffs. The accompanying diagram (Plate II) indicates the composi- tion of some of tlie commoner foods and is self-explanatory. There are cei-tain foodstuffs concerning which a little more detail may however be advisable. Wheat Flour, besides a large amount of starch, contains two proteins, glutcnin and gliadin. When the flour is mixed with water and then kneaded, it forms dough, because the proteins cliange into a sticky substance called gluten. As dough the flour is not a suitable food, because the digestive juices cannot pene- trate it. To render it digestible the dough must be made porous and this is accomplished by causing bubbles of carbon dioxide gas to develop in it, either by mixing it with baking powder which is composed of a bicarbonate and an organic acid (tar- mm 208 DIETETICS. taric) or by keeping it in a wr-rm place with yeast, which fer- ments the sugar that is present. The sugar is developed from the starch by the action of the diastase (see p. 154) present in the yeast. When the yeast has been allowed to act for some time, or if baking powder was used, when the gas formation has ceased, suit- able portions (loaves) of dough are placed in the oven. The heat causes the inclosed bubbles of gas to expand so that the whole mass becomes aerated and further increase of temperature acts on the proteins and starches on the surface coagulating the for- mer and converting the latter into dextrins. The crust is thus formed. Brown bread is made from wheat from which all the husk has not been removed. There are two possible advantages of this over white bread, namely, the husks act as a mild laxative and they seem to contain traces of vitamines (see p. 224). Other Cereals. — These include maize or Indian corn, oatmeal and rice, and differ from wheat in that their proteins do not form gluten when mixed with water. They cannot therefore be formed into bread unless they be mixed with some wheat flour. They are relatively rich in ash, and maize contains a large proportion of fat. When rice composes a large proportion of the diet, as is the case in tropical countries, the unpolished variety should be used to supply the vitamines. When the diet is a mixed one, however, danger of an insufficiency of vitamines cannot exist. As has been already explained, the protein of cereals is not of first qual- ity, because it does not contain all of the amino acids (building stones) of tissue proteins. Milk and Milk Preparations.— Whole milk is as nearly as possible a perfect food, for its protein is of the first <|uality and it contains a sufficiency of fats and carbohydrates for the growth of the tissues. Where muscular exercise must also be performed, carbohydrates should be added to the milk, and this is best ac- complished by the use of cereals. Milk is an economical food, for one quart nearly equals in nutritive value a pound of steak or eight or nine eggs, and is easily digested and assimulated, but somewhat constipating. The chief protein of milk is caseinogen (phosphoprotein) and is cliaraetorized by l)eing pix'cipitated wam^mmm .J Pt'NDAMENTAI.S OF IIVMAX I'lIYsIOfAHiY. 209 by weak .icids and by the action of gastric juice. When milk som-s some of the milk sugar, or lactose, becomes converted by bacterial action into lactic acid and this precipitates caseinogen. When an extract of the nnicous membrane of the stomach is added to milk and the mixture kept warm, the clot which forms is called casein. By separating the casein and allowing it to stand for some time ferments, derived from moulds and bacteria, act on it to produce cheese. The cheese, besides casein, contains much fat and mineral matter. Cheddar cheese is especially rich in fat. Cheese is a very concentrated article of diet and when taken in moderation is thoroughly digested and assimilated. Cream consists of the milk fats with some of the constituents of milk. It is the most easily assimilated of all the fats and is hence very nutritious. When sweetened, flavored an I rozen it forms ice cream, which should not be regarded, as it usually is, as a luxury, but as a highly nutritious food. It should not there- fore surprise the indulgent parent when a child refuses food after visiting the corner pharmacy. On standing, cream ripens (undergoes change due to bacterial growth), and the fat can be made to separate as buffer. There is no foodstuff that con- tains jnore calories than butter, and it also contains certain vi- tamines. The fluid from which the butter separates, butfer- milk, contains practically no fat and is acid to the taste because of bacterial action on the lactose producing lactic acid. Its in- fluence on the nature of bacterial growth in the intestines has already been referred to. Eggs. — The only point we need emphasize is the much greater percentage of fat substances (lipoids) in the yolk than in the white. One dozen eggs equals in food value two pounds of meat. Eggs are therefore more costly than milk. '^eats. — The building stones of the protein molecule of meat, lor reasons which arc obvious, are more nearly identical with tliose of the tissues of man than are those of any other food. The carbohydrate is however insufficient in amount, for which rea- son we take potatoes with meat. The flavors of different meats depend largely on the extractive sub.stances which they contain. These include creatin and purin substances. Wlieii a decoction ■ L..ML mm 210 DIETETICS. of meat is evaporated to small bulk, after precipitating all of the protein, tneat extract is prepared, which, like coffee or tea, has no nutritive value but acts as a mild stimulant (caffein and thein are chemically very closely related to the purin bodies of meat extract). Clear soups are mainly dilute solutions of meat ex- tractives, but in beef tea, if properly made, there is much meat protein. Other Foods and Condiments.— Although green vegetables and salads consist very largely of water, they are very important articles of diet, because they contain cellulose, which serves to increase the bulk of the intestinal contents— to serve as ballast, as it were— and prev constipation by keeping the intestinal musculature active. Some vegetables, such as spinach, are especially important since they contain iron. Salads have a further importance because of the oil taken with them. The rel- ishes and the condiment flavors are by no means insignificant adjuncts of diet, for they give the relisli to food without whicli digestion is likely to be inefficient. This most important prop- erty of diet has been sufficiently insisted upon elsewhere. CHAPTER XIX. SPECIAL METABOLISM. But wc must now return to the more theoretical aspects of our subject. "We will proceed to trace out very briefly the interme- diary stages in metabolism through which proteins, fats and car- bohydrates have to pass in order to yield the energy required to drive the animal machine and to supply material with which to repair the broken-down tissues. Metabolism of Proteina.— We must follow the amino acids after their absorption into the blood until they ultimately reap- pear, the nitrogen among the nitrogenous constituents of urine and the carbon as part of the carbon dioxide of expired air. In order to do this it is necessary for us to bocome familiar with the nature and source of the urinary substances xvhich contain nitroge7i, and to consider some of the most important chemical relationships of these substances, so that we may understand how they become formed in tlie body. Tiie substances in question are : urea, ammonia, creatinin, the purin bodies, and undetermined nitrogenous substances. Urea and ammonia may be considered together. Urea and Ammonia. — There is no doubt that it is as ammonia tliat the nitrogen of the amino acids is set free in the organism. The free ammonia would, however, be highly poisonous, so that it immediately becomes combined with acid substances to form harmless neutral salts. The acid which is ordinarily used for thi'; purpi 'arbonic, of which there is always plenty in the blood and . juices. T'v :!mmonium carbonat'^ thus formed becomes changed into urea \jj removal of tiie elements of water from the molecule, thus: OH ONH, NH, NH, / / / / 2NH3 + CO = CO — H,0 \ \ OH ONH, Ammonia Carbonic Ammonium acid carboiialu 211 NH, / " CO — ILO = CO \ \ ONH, Ammonium earbaniate NH, Urea ■H 212 METABOLISM OP PROTEINS. The conversion of ammonium carbonate occurs largely in the liver. Our evidence for this is: (1) If solutions containing ammonium carbonate be made to circulate through an excised liver, urea is formed. (2) If this organ be seriously damaged, either experimentally or by disease, less urea and more ammonia appear in the urine. We see therefore that urea is formed in order to prevent the poisonous action of ammonia. But the am- monia may be more usefully employed; instead of being com- bined with carbonic acid in order that it may be got rid of, it may be employed to neutralize, and thus render harmless, any other acids that make their appearance. Thus, it may be em- ployed to neutralize th 2 acids which sometimes result during the metabolism of fat, as in the disease diabetes; or the lactic acid that appears in the muscles during strenuous muscular exercise ; or the acids produced on account of inadequate oxygenation. Taking acids by the mouth has a similar effect; thus the am- monia excretion rises after drinking .solutions containing weak mineral acids. Ammonia is, of course, not the only alkali which is available in the organism for the purpose of neutralizing acids. The fixed alkalies, sodium and potassium, are also used. Thus, when we greatly increase the proportion of these, as by taking alkaline drinks, or by eating vegetable foods, the ammonia excretion diminishes. Urea is an inert substance, capable of uniting with acids to form unstable salts (urea nitrate and oxalate), and like other amino acids, being decomposed by nitrous acid so as to yield free nitrogen. This latter reaction is used for the quantitative estimation of urea, the evolved nitrogen being proportional to the amount of urea, thus : / CO + 2 IINO„ -= 2 CO, -f 2 N, -I- 2 H,0 Certain bacteria are capable of causing urea to take up 2 mole- cules of water so as to form ammonium carbonate, a process FUNDAMENTALS OF HUMAN PIIYs^IOLOGY. 213 really the reverse of that which occurs in the organism and rep- resented by the above formula;. This change occurs in urine and accounts for the ammoniacal odor which develops when this fluid is allowed to stand. Creatinin. — This is very closely related to creatin, which is the most abundant extractive substance in muscle, and which yields urea when it is boiled with weak alkali. These chemical facts would lead us to expect that some relationship must exist be- tween the creatin of muscle and the creatinin and urea of urine, but, so far, it has been impossible to show what this relationship is. One very important fact has, however, been brought to light, namely, that creatin makes its appearance in the urine when carbohydrate substances are not being oxidi/ed in the body, as in starvation, and in the disease diabetes. This is one reason for the growing belief that carbohydrates are something more than iiitTt' energy materials (see p. 216). The excretion of creatinin is so remarkably independent of the amount of prot«'in in the food that it is believed to represent more especially the end prod- uct of the protein break-down of the tissues themselves, in con- trast to urea, which partly represents the cast-off nitrogen of the pi'otcin of the food. PuBiN Bodies. — These are of particular interest because they include uric acid, about which more nonsense has been written tlian about any other product of animal metabolism. The so- called uric acid diathesis is very largely a medical myth— a cloak for ignorance. TJric acid is the end oxidation product of the purin bodies, which include the hypoxanthin and xanthin of muscle and their amino derivatives, the adenin and guanin of nuclein. These relationships are seen in the following formula;: Oxv nnrins of muscle f Hypoxanthin CJI^N.O Oxy purins ot muscle j ^^^^^^^.^^ C,H,N,0, Amino purins of nuclein. . (adenin ;.-^^"^nm? ( Guanin CsH^N.ONII Uric acid CsH.NA There are therefore two sources for uric acid in the animal 214 PROTEIN METABOLISM. body, namely, the muscles and the nuclei of the cells. This ex- plains why the uric acid excretion increases after strenuous mus- cular work, and why it is much above the normal when cellular break-down is very excessive, as in the disease called leucocythe- mia, in which there is an excess of leucocytes in the blood (see p. 55). Anotlicr source of uric acid is the food when it con- tains either muscle (flesh) or glands (sweetbreads), for a large proportion (about half) of the ingested purins do not become destroyed in their passage through the organism, but become oxidized to uric acid, which is excreted in the urine. This is called the exogenous in contrast to purin produced in the tissues, which is called endogenous. There is only a trace of uric acid in the urine of manmials, but in birds and reptiles most of the nitrogen is present in this form. The reason is tliat in the.se animals it is important to have semi- solid, instead of fluid excreta, so that tlie urea which results from protein metabolism becomes converted into uric acid, which, either free or as salts, is relatively insoluble. Uric acid is chemi- cally a diureide, that is to say, it consists of two urea molecules linked together by a cliain of carbon atoms. The chain of carbon atoms is furnished by substances not unlike lactic acid and the synthesis occurs in the liver. If this organ be removed from the circulation in birds, such as geese, in which the operation is comparatively easy, a very large part of the uric acid in the urine becomes replaced by ammonium lactate. The relative insolubility of uric acid and its salts, which we have already referred to, makes it apt to become precipitated in urine, especially on standing. It forms the orange reddish de- posit, so frequently observed in summer, when on account of per- spiration the urine does not contain as much water as usual. Such deposits do not therefore indicate that there is an excess of uric acid in the blood, but merely that enough water is not being excreted to dissolve the usual amount of urates. Sometimes the urate becomes deposited in the joint cartilages, particularly in those of the great toe, causing local swelling and redness and great pain. This is gout, and it may be most effectually treated by drinking large quantities of alkaline fluids, and eliminating FUNDAMENTALS l»F IIL'MAN I'llYsIOLOGY. 215 from the dietary such foodstuffs as meats and sweetbreads, which yield exogenous purins. As we have said, there is no reason to Ix'lieve that any othor diseases other than gout are due to an excess of uric acid in the blood. Besides the above there arc traces of other nitrogenous sub- stances in the urine, such as: 1. Hippuric acid, which, as its name signifies, is very abun- dant in the urine of the horse and other herbivora, and which is the excretory product of the aromatic substances which the food of these animals contains. 2. Cystin, an amino acid containing sulphur. 3. Pigments and mucin. The exact significance of the end products of nitrogenous met- nbolimi has been very beautifully demonstrated by Folin, of Harvard. The observations were made on several men who lived for some days on a diet rich in protein (but containing no purin- containing foodstuffs), and then on one which was very poor in protein. The problem was to see liow each of the nitrogenous constituents behaved during the two periods, both absolutely and in relation to the total amount of nitrogen excreted. In or- der to show the latter relationship the results are given, as in the following table, not as urea, etc., but as urea-nitrogen, etc. : On the protein-rich On the protein- diet poor diet Quantity of urine 1170 c. c. 385 c. c. Total nitrogen 16.8 gm. 3.6 gm. Urea-nitrogen 14.7 gm. (87.5) 2.2 gm. (61.7) Ammonia-nitrogen 0.49 gm. (3.0) 0.42 gm. (11.3) Uric-acid-nit rogen 0.18 gm. (1.1) 0.09 gm. (2.5) Creatinin-nitrogen 0.58 gm. (3.6) 0.60 gm. (17.2) Undetermined nitrogen. 0.85 gm. (4.9) 0.27 gm. (7.3) The figures in parentheses represent the percentage which the nitroj^n of each substance furnishes of the total amount of nitro- gen excreted. It will be seen that urea decreases on the poor diet relatively more than total nitrogen, thus indicating that it comes partly from proteins in the food (exogenous) and partly 216 l'R()TKI.\ MtTAUitLlSM. from the organism itself (endogenous). Tliis result leads us to infer that most of the amino substances of protein foods which are not required as building stones for the tissues arc broken down so as to yield ammonia, which is excreted as exogenous urea ni the urine, but that the amino acids that are really appropri- ated by the tissues, although they may also produce some urea (endogenous), cause other end-products to l)c formed. The most important of these endogenous bodies is evidently crcatinin, for as will be seen from the above table, this substance is excreted in' the same absolute amount during both the starvation and the protein-rich periods. Direct evidence that this conclusion is correct has been ob- tained by examination of the blood and muscles for amino bodies ammonia and urea. The results have shown that the amino acids absorbed from the intestine are carried through the liver into the systemic blood, which transports them to the muscles where those that are not required fof building up the tissues are broken down into ammonia and jwcarbonaceous residue, which IS then burned just exactly as if it wcro carbohydrate or fat The useless ammonia becomes converted into urea in the manner already described, either in the nuiscles themselves, or by being earned to the liver, which, as we have seen, possesses to a verv •-'^h degree the power of producing urea. The Relative Importance of Proteins, Pats and Carbohy- drates m Metabolism.-The metabolism of fats and carbohy- drates, with regard both to their importance as builders of living tissues and the type of their metabolism, is very different from that of proteins. That carbohydrates and fats are less impor- tant m the animal economy than proteins is evidenced by the fact that we can live perfectly well on protein food alone but not on either of the others. This does not, however, justify us m concluding that carbohydrates and fats are merely materials which are oxidized by the tissues for the purpose of producing energy, fuel as it were, and which can be dispensed with Thev are more than this, for no cell, in however starved a condition it may be, is entirely free from either of them, thus indicating that they must have been protluced out of protein itself Pro- FUN'DAMKSTALS OK III'MAN I'IlYsH>li«KJY. 217 trills arc no doubt the most important ingredients of cells, but fats and carbohydrates are indispensable also. As reserve materials, striking differences exist among the tliree foodstuffs. Proteins are of little value in this regard for, as we have seen, very little, if any, can become laid down in the tissues when excess is taken as food; on the contrary, all that is not required is tlirown out of the body, and when the food sup- ply is cut off, as in starvation, t' protein is spared as much as possible (see p. 10.')). Caihohydrates arc very readily depos- ited as a .starch-like substance, called glycogen, and this reserve is the first to be called on, not only in starvation, but alrjo when muscular work is performed. It may be considered as the most iiinuediately available material for combustion in the organism, but the limits of its storage arc restricted in man to some hun- dreds of grams, which, as we have seen, soon become used up in starvation. Fat is pre-eminently the storage material, and the supply may serve in man to furnish, along with a little pro- tein, onojigh fuel for several weeks' existence. The relative importance of the tlnee foodstuffs is shown in the extent to which each is used in the melabolism during muscular exercise. When there is an abundant store of glycogen, the energy is entirely derived from this source ; when there is little glycogen but much fat, it is fat that is burned, and when neither of these is abundant but much protein is being taken with the food, """ the animal is reduced to living on its own tissues, as in starvation, it is protein. In other words, the type of metabolism occurring during muscular work is the same as that which imme- diately preceded it; the only change is in the extent of the com- bustion, not ir Uie nature of the fuel employed. i i/ CHAPTER XX. SPECIAL METABOLISM (Cont'd). Metabolum of Pats. — Fats are absorbed by the lacteals and discharged into the blood of the left subclavian vein through the thoracic duct. They are carried to various parts of the body and gain entry into the cells, in the protoplasm of y hich they become deposited. This process occurs extensively in the sub- cutaneous connective tissues, between the muscles, and retropcri- toneally around the kidney (the suet). The fat which is thus deposited possesses more or less the same qualities as the fat of the food. Thus, when the only fat taken over a long period of time is one with a - ry low melting-point, such as oil, the fat deposited in t'l tissues is likely to be oily in character, whereas it is stiff after I'eeding with a high melting-point fat, such as mutton fat. This similarity between the tissue fat and that of the food becomes very striking when the animal has been sub- jected to a preliminary period of starvation and then fed for some weeks with a large excess of the particular fat and as little carbohydrate and protein as possible. /Fat in the food is of course not the only source of the fat in the tissues. It is algo !2Fi?^'^ .2HI. o^c^J'^^ohydrates, a fact which is well known to farmers, who fatten their stock by feeding them with maize and other starchy grains, and to physicians, who reduce their corpulent patients by restricting carbohydrate foods. The fat thus deposited has the chemical characteristics of the fat which is peculiar to that animal. It is almost certain that there is ordi- "*'"ilO.?.l?™?tioii 0^ fat out of protein in the higher animair)( The fat thus deposited in the tissues may remain for a long time, but ultimately it is again taken up by the blood and car- ried to whatever sictiye tissue requires it as fuel. Before being thus burnt, it sjjlits into glycerine and fat acid (see p. 178). The fat acid po.ssibly undergoes some preliminary change in the 218 FUNDAMENTALS OP UUMAN niYSl(Jl> fat nioleeuli' to hv cDinposcd (see p. 36) becomes oxidized (burnt), not all at once but piece by piece, two carbon atoms being split off at a time. If the fat acid chain originally contained an even number of carbon atoms, the oxidation process might stop short when there are yet four carbon atoms in the chain, thus producing oxybutyria acid (CH3CHOHCH2COOH). This imperfect metabolism of fat oc curs in severe cases of diabetes and often causes death. It also iK'curs in carbohydrate starvation, and indicates, more clearly than any thing else, that e\ en carbohydrates are essential for life. Metabolism of Carbohydrates. — It will be remembered that these include the starches and the sugars, and that during diges- tion they are all hydrolyzed to dextrose or la;vulose, as which they are absorbed into the blood of the portal vein. This ab- sorption is rapid, so that a striking increase in the percentage of sugar occurs in the blood of the portal vein shortly after the food has been taken. Most of this excess of sugar does not imme- diately gain entry to the blood of the systemic circulation, how- ever, because it is retained by the liver. For this purpose the liver cells convert the sugar into the starch-like substance, glyco- gen, which becomes deposited in their protoplasm as irregular colloidal masses, which stain with iodine and carmine. The liver does not manage in this way to remove all of the excess of sugar from the portal blood, so that, even in a healthy animal, there ^ a distinct postprandial increase of sugar, or hyperglycsemia, as it is called, in the systemic blood. If too much sugar passes the liver it causes so marked a postprandial hyperglycaemia that some sugar escapes into the urine, thus causing glycosuria. This is one of the early symptoms of diabetes, and its occurrence furnishes us with a warning that less carbohydrates should be given in the food. If the warning be heeded, the severer form of the disease will very probably be staved off. The glycogen deposited in the liver stays there until the per- pentage of sugar in the systemic blood begins to fall below the normal level (which in man is about 0.1 per cent), when it becomes reconverted into sugar, which is added to the blood. 220 METAH(tI,I8M (tP CAUnoiIYDRATES. The reason why the sugar in the systemic blood tends to fall is that the tissues, especially the muscles, are using it up as fuel. If so much sugar is taken that the storage capacity of the liver is overstepped, the excess of sugar is carried by the systemic blood to the tissues, where much of it may be changed into fat. The glycogenic function of the liver, as the above process is called, is analogous to the starch-forming function of many plants, such as potatoes. Of the sugar whicli is formed in the green leaves of these plants, some is immediately used for build- ing up other substances, the remainder being converted into starch, which becomes deposited in the roots, etc., until it is required (as during the second year's growth), when it is grad- ually reconverted into sugar. Besides carbohydrates it is known that proteins form glyco- gen ; fats, however, cannot form it. In severe castas of diabetes It is therefore usual to find that although carbohydrate foods are entirely withlield, dextrose continues to be eliminated in the urine. It may come partly from the protein of the food and partly from that of the tissues. The adjustment between the rate at which the glycogen of the liver becomes converted into dextrose and the percentage of sugar in the systemic blood is effected partly through the nervous system and partly by means of substances called chemical mes- sengers of hormones (.see p. 227) .secreted into the blood from the ductless glands, such as the pancreas and the adrenals. The very first symptoms of diabetes, which we have seen to consist in an excessive postprandial rise in the systemic blood-sugar and a consequent glycosuria, must therefore be due to defects in one or other of these regulatory mechanisms. It is therefore of great interest to know tliat glycosuria can be induced in the lower animals by stimulation of the nerves of the liver or by interfer- ing with the function of the pancreas or the adrenal glands. The nerves of the liver may be stimulated either directly or through a nerve center located in the niedulhi oblongata (.see p. 258). Complete removal of the pancreas is followed in a few hours by a very acute form of diabetes, which is invariably fatal in a few weeLs, whatever the treatment may be. Injection of extract PUNDAMEXTAI-S OP HUMAN PHYSIOLOGY. 221 of the adrenal gland (adrenalin) causes a transient hyperglycte- niia and glycosuria. These laboratory discoveries have in their turn caused clinical investigators to pay close attention to the nature of the causes of diabetes. It has been found, as a result, that oft-repeated overstimulation of the nervous system — nerve straiii, as it is ,.;,1],.,1 — jrreatly pres of poly- liedral cells with no colloid material. The functions of the two glands are probably essentially dif- ferent, the thyroid having to do with the general nutrition of the KiK. 5". — Thf Uiyroiil jrlaiul. (ijiay's AiitiUmiy, afttr Spalteliolz. ) animal, and the parathyroid with the condition of the nervous system. They lie so close together, however, that it is very diffi- pult tn .study their separate functions. The importance of the glands is indicated by the relatively largo blood supply. 230 TIIK l)Crn.K,-S (ifjAM)S. When the tloroid is not properly developed in eliildreii, the condition is known as cnlitiism (Fig. 51). Tlie eliild fails to grow in height, although its bones may thicken. The cranial bones soon fuse together, so that the growth of the brain is hin- /'f'^V'"!'"'^'"- '" ^''■'"■'' "'''• '^'''-' "^-'Ou'iit with thyroid cxt.act w.s started too late to be of benefit. (Patient of Dr. S. J. Webster ) dered and the mental powers fail to develop. The chiM becomes uhotic, and although it may live for years, it will remain, even nt thirty years of age, a stunted, pot-bellied, ugly creature with the intelligence of an infant. The cause of this failure to de- FUNDAMENTALS OF HUMAN l'II¥.S10L(XiY. 231 velop is undoubtedly bound up in some way with the deficiency of the thyroid, for if the cretin be given the extract of this gland, its condition will immediately improve, and indeed, if taken early enough, it may quickly make up for lost time and grow both physically and mentally as it ought to. Atrophy of the thyroid gland in older persons causes myxcr- ,lnndema ; B. Same after seven months'" treatment. (TiffersteOt.) tic, being most commonly seen in women. The skin is dry and often of a yellowish color, the hair falls out, the subcutaneous tissues grow excessively, so that the hands, the feet and the face become large and puffy, and the speech indistinct, because of the thickening of the lips. The metabolism also becomes very slug- gish, so that the intake of food and the excretion of nitrogen in the urine become diminished, and the temperature subnormal. If unchecked, mental symptoms become apparent, first of all, a dulling of the intellect with sleepiness and lethargy, a ^ later, muscular twitchings and tremors. Just as in cretinism, so in «■■ Tin: TiivijDii* (ir.wh. niyxoedeiiia, adiniiiistratioii of tliyroid extract c-aus.-s these symp- toms to disappear, so tliat in a nioiitli or so the patient may have returned to his or her normal condition, to maintain which, how- ever, tlie thyroid extract must continue to be given. Wlien the gland is removed surgically, either in lower animals or in man, very acute symptoms ending in death usually super- vene. These include a peculiar form of muscular tremor called tetany, passing into actual convulsions, which, by involving the respiratory muscles, ultimately cause dyspnoea and death. It is, however, probable that these nervous symptoms are due to the unavoidable removal of the parathyroid glands. The tetany i^ removed by giving caUium salts. These conditions associated with deficiency of the thyroid are grouped togetliei- as hypofhu- roidism. Even in healthy individuals thyroid extract taken by mouth excites a more active metabolism, and may cause increased heart activity. One result of this increased metabolism is disappear- ance of subcutaneous fat and increased appetite, thus rendering the administration of moderate doses of thyroid extract a not uncommon method of treatment for obesity. Such treatment should never be attempted except under the control of a physi- cian, for it is very easy to take too nuicii of the extract and cause palpitation and nervous excitement. When the thyroid (and parathyroid) glands become exccss- 'vely active in man, the condition is called hyperthyroidism, and the symptoms are very like those above described as produced by taking thyroid extract. To he exact, they a.e palpitation, wasting of the muscles and conse-iuent weakness, extreme ner- vousness and protrusion of the eyeballs. On account of this last mentioned symptom the condition is usually called exophthalmic goitre. This acute and often fatal disease is to be distinguished from chronic goitre, in which there are very few general symp toms, but great enlargement of the iliyi. :,i gland, indeed an v. largement which may be so pronounced as pra^^tically to obliter- ate the neck and sometimes so compiv^s the trachea as to inter- fere with breathing. The easr.s ot chroni- jjoitre occur in the same districts in which the cxophtiiaimic varietv is common, these FlNDA'Ml.NTAI.^ - H' 111 MAN I'll YSI()l,-. \..ch gland is vfUowi-sh in color, and is seen, on microscopic examination to be composed of a medullary and a cortical portion. The medulla consists of irregular collections of cells containing granules wliich stain deeply brown with chromic acid and are therefore called chromophile granules. Similar chromophile granules may e.xist in other parts of the body. The great splanchnic nerve, which it will be remembered arises from the sympathetic chain ill the thorax (.see p. '2S2). makes very intimate connection witli tlie adrenal medulla, for which reason and because of the fact tliat it is developed from the same embryonic tissue as the sym- pathetic system of nerves, the medulla of the adrenal gland is lielieved to be closely bound up with the functions of the sympa- thetic nervous system. The cortex is composed of rows of col- iiniiiiir cells which do not contain chrrnnophile granules. Small thoufjh they be, the adrenal glands are cs.sential to life, for their leinoval causes extreme muscular weakness and a fall in blood pressure followed by death within twenty-four hours. When they are the seat of disease (tuberculous), symptoms of extreme muscular prostration, accompanied by vomiting and a peculiar bronzing of the skin, set in and grow steadily worse until at last the patient succumbs. This is called Addison's disease. The most striking proof of tlieir importance is obtained by \n- jocting an extract of the nieiUiUa of the adrenal gland into a vein. It causes au iiamediate rise in blood pressure, which is 234 THE ADUENAL GLANDS. more or less proportional to tlie strength of the extract. The rise is accompanied by a slowing of the heart, due to the reflex stimulation of the vagus centre excited by the rising blood pres- sure. When this reflex slowing is rendered impossible by cutting the vagi, the rise in blood pressure following the injection may be enormous. The active substance in the extract is called adren- alin, suprarcnin, adrcnin or cpincphrin. It is a comparatively simple chemical body, having the formula: (IIO)C (IIO)C CH (J— CII ( on ) CII,,— NHCII,, CH CH and existing in two varieties wliich differ from one another ac- cording to the direction toward which the plane of polarized light is rotated. The variety rotating to the left is, by many times, stronger in its physiological actions than tliat which rotates to the right. Tlie discovery of its chemical structure has made it possible for chenii.sts to prepare suprarenin synthetically, and also to prepare a .series of related substances having less marked though similar properties. These are closely related to certain of the bodies which appear during the putrefaction of meat. By cai-eful studies of the action of the suprarenin, or related substances, it lias been found that the rise in blood pressure, above referred to, is duo to stimulation of tlie muscle fibers in the walls of the blood vessels. It is on this account that a weak solution of suprarenin is used to stoj) hemorrhage, as after removing polypi from the nose, or in bleeding from tlie gums, as after tooth ex- traction. The muscle of arteries is by no means the only struc- ture on which adrenalin acts; indeed it stimulates every structure which is capable of being stimulated by the symi)athetic nervous system (.see p. 282). Thus, it causes the pupil to dilate, saliva to be .s«'creted (p. 1.")1). the inovciiieiits of tlie intestine to be in- hibited (p. 182), wherea.s it has no action on the blood vessels FUNDAMENTAf.S OF HUMAN I'llYfcilOLOGY. 235 of the lungs or brain, which do not possess vasomotor nervrs. This similarity between the results which follow suprarenin in- jection and stimulation of the sympathetic system is particularly significant when we call to mind the fact that the medulla of the adrenal gland is developed from the same embryonic tissue as the sympathetic system. The clotting power of the blood is diminished after injections of suprarenin. The Pituitary Gland. — This occupies the Sella Turcica of the base of the cranium and is composed of three portions or lobes. The anterior lobe consists of large epithelial cells and is really Kig. 53.— Mediiiii SiiKittitl si'ctluii thioiiKli pituitary of nioiikoy ; somidia- trrammatlr ( HiitiiiK) : nt disturbance, and extracts of it when injected intraven- , do not have any characteristic effects. It becomes very ! ' I enlarged in certain diseases, namely: (1) in leucocythe- a form of ana-mia, which is characterized by a great increase III llie leucocytes of the blood (.see p. .'».")) ; (2) in tyi)hoi two salts : a neutral or diurate of sodium (CsHaN^OaNaj) and the biurate or acid urate of sodium (CjHjN^OjHNa). The biurates are neutral in reaction and con- stitute the urates normally found in the blood and urine. They exist in two isomeric forms (o and the 6). The b is more solu- ble than the a form. It may be that the deposition of urate tar- tar on the teeth, and the deposits of urates in the joints of a pa- tient suffering with gout, are due to the change of the 6 form into the less soluble a type. There are a number of other nitrogenous bodies in the urine which are included in the item of unclassified nitrogen in the above analysis. The most important of these is urinary indican, which is derived from the indol produced in the intestines by the action of bacteria on the amino acid tryptophane. The yellow color of the urine is produced by a pigment called urochronu', which is believed to be derived from the pigments in the blood. The Inorqanic Constituents op the Urine. — The urinary salts are chiefly the chlorides, sulphates and phosphates of so- dium, potassium, calcium and magnesium. The potassium and sodium salts are found in greatest abundance, since they form tiic main inorganic constituent of the food, and moreover the trrcater portion of the salts of the heavier metals, as calcium, iron, bismuth, mercury, etc., is excreted by tlie intestines. There is very little retention of salts by the body except during the for- mation of bone, so that the amount of the inorganic constituents of urine varies from day to day with the diet. The chlorides are formed for the most part from tlie inorganic chlorides of the food ; the phosphates and the sulpliates are derived from the sul- phur and phosphorus of the nucleo-protein molecules. If the urine is neutral or alkaline in reaction, there is apt to be a de- 242 THE ORGANS OF EXCRETION. posit of calcium or magnesium phosphate. This will dissolve when the urine is rendered faintly acid. Abnormal Constitient.s op the Urine. — Many of the sub- stances found in the blood occur in minute traces in the urine. When any of these bodies are increased to an unusual amount in the urine, they become what we may term pathological con- stituents. The bodies most commonly affected arc the proteins and sugars. The finding of a protein, such as albumin, in more than the faintest trace, is an indication of nephritis or Bright's disease. The presence of albumin may be detected by heating in a test tube a slightly acidulated sample of urine. Normal urine contains the faintest trace of the blood sugar dextrose, but in abnormal conditions, as in the disease diabetex or after a meal rich in sugars, a large amount of dextrose ap- pears in the urine as a result of an increase in the sugar of the blood. The condition probably represents the inability of the tissues to make use of their carbohydrate food in the proper man- ner, and the kidney therefore excretes the sugar as if it were a waste material. The Kidneys. Lying upon the posterior wall of the abdominal cavity at the level of the lower ribs and on each side of the vertebral col- umn are the kidneys, the organs of urine excretion. Each kidney is of the nature of a tubular gland of a very complex structure, anatomically adapted to bring a large amount of blood at a high pressure in clo.se relation with the excreting epithelial cells which line the walls of the gland tubules. The tubules empty into a pouch-shaped sac on the inner edge of the kidney, the pelvis of the kidney, and this is connected with the urinary bladder by means of a small tube, the ureter. The urinifrrous tubules may be divided into the excretory portion and the collecting portion. The tubules arise in the outer part of the kidney, in the region called the cortex, as a body called the Malpighian corpuscle. This corpuscle cnnsist.s of the dilated end of a tubule which is invaginated to form a PUNDAMENT.\J.S OP HUMAN IMIYSIOLOGY. 243 eup-sliapod vessel, within the cup of whicli lies a tuft of cap- illaries. The capillaries compose the structure known as the TIRMINAl MUT Of PHOtTkTC VCIN ORIGIN or DUCTUS CHOLIDOCHU* ritKOUS CAMUtC rcLvisop KIDNCV MIGHT (KIIMaTIC VCIN tcrr • PCHMATie ARTcnV AND VCIN CllULO- PIGNOUS tUGPCRITONCilt LAMINA Fig. Ha. — The situation, diifction. foinis (Clay's .\iiatoniy, after Sopiuy.) Miul sui)iH)it.>! ot tile kidney. glomerulus, and the tuhular part is known as the capsule of liowinan. From Bowman's capsule a short neck leads into what is known as the convoluted tubule, which is a very tortuous vessel lined v/ith large epithelial cells. This structure lies in the cortex of the kidney and is nourislied by the blood which has already been through the glomerular capillaries. A loop of the tubule leads down into the center or medullary portion of the kidney and back again to the cortex, where the cortex again becomes very tortuous, and finally empties, in company with many other siinilar vessels, into a common collecting tubule, which leads to the pelvis of the kidney. 244 THE KIDNEYS. The Blood Supply op the Kidney is very large compared with that of the other organs of the same size. The renal arteries come from the aorta and distribute their blood directly to the Figr. 56. — Longitudinal . tion through the kidney: 1, Cortex; 1', me- dullary rays; 1". labyrini 2. medulla; 2', papillary portion of medulla; 2", boundary layer of medulla; 3, transverse section of tubules In the boundary layer; 4, fat of r.-nal sinus; 5, artery; •. transverse medullary rays; A. branch of renal artery; C. renal calyx; U, ureter (after Tyson and Henle). glomeruli and the inner medullary portions of the kidney. The vessels of the glomerulus are collected into an afferent vein, which again breaks up into capillaries to supply the remaining struc- tures of the cortical portions of the kidney (Plate III). The Nerves op the Kidney. — The kidney is very richly sup- plied with vasomotor nerve fibers, which are carried to it in the splanchnic nerves. Whether there are nerve fibers in either the vagus or splanchnic nerves which have a secretory influence on the kidney cells, is at present an unsettled question. The Nature of Urine Excretion.— In spite of repeated at- tempts to explain the nature of urine excretion, there remain I'lati'III IiiiiKiMin 111' ilic 111 iniri!'.>iis luliiili^s iikI lilt vi-iiis I Mile) <>( 'li.' Ui.liH.N. I IpI.-itU ), 111.- .ii-t.-iit-s I i.mI ) rUNDAMENTAI-S Of If M. ^ PHYSIOLOGY. 245 i illy understood. The her or ii3 than the function of lood. Many ound in the ire found in many steps in th. process which iw not constituents of V e urine ure f or " d b; kidney, and are j esent in the b, hkJ p. la. T the kidney is to n^ ;iove th ^ substances irom tht bodies re prtrsent n the i loi 1 plas? \ which are no urine, md again >i.'mc of the urina / constituents far grtater corjcen t : ati^ ■ a the uririe than in the blood plasma. To explain These fac -, -udwig, a famous physiologist of tho innt'teenth c-.-ntury. formulated what is known as the mechanical th.'ory f nr..Me excrn..) Impressed by the peculia: relatio' ship of B. wman's oaf«ule and the glomerular cap 'laries, lie fludt i that t]\>' ^i ilpiRhiaii corpuscle is a filtti g ai.nar wnici separates, n .lilute solution, a portion of all the ifu r Mibstances of tl bUK)d. ' '>e absence of such diffus Ktances as sugar m iH.rmal i e and its presence in the a relativelv lartre aiiuiunt, h. lieved to be due to th al the epith. ..ani of 'he tubules to reabsorb these subs' the dtltrtt; irine. .ik-wiso, the high concentration mtr...'pnou bodies, such as urea, he explainc ' y . ' water thf> gh t. * tub '"s into the blood. 1. u t cory Ludtt • de?"onstrated that the urine * lirectly witl< ■ ^d flow and the blood press. aoy. In othe -rds. the greater the supply of blood and tiie greater its pixssi. e, the more rapidly will the ' atery solution of the urine be filtered from the blood. He wa it able, how ever to bring any satisfactory proof of the re; '.s- on of water or other substances by the epithelium of ti rinary tubuh-^. Indeed, most experiments show that this docs not occur. It is impossible to explain all the facts of urinary xcretion by simple physical laws. For example, urea and dixu-se are both found in the blood and both obey the same physico clu 'oi-al laws; nevertheless the one is excreted in the urine and the otli.r is retained in the blood. Furthermor wl; are injected into the blood, they are -xeiet^ i but do not appear in t- ose of other irts <■*' That an increase in the prc-sur. f biooii has a very marked accelerating effect on thi lib ire IS &> sorption or; this ion varied if the kid- n certain pignienis by tho kidney cells, ■te body. Ill ihe leiieii vessels excretion of urine. 246 THE KIDNEYS. is not necessarily evidence that the increased blood supply is the cause of the excretion. That other factors are concerned is demon- strated by the action of drugs which cause an increase in renal ex- cretion. For example, digitalis, a drug stimulating the circulatory apparatus, causes a marked diuresis in cases of a weak heart where the pressure has been totally inadequate to maintain a urine excretion, but has little or no action on the normal kidney. On the other hand, sodium sulphate injected into the blood causes a diuresis without marked change in rate of blood flow or blood pressure by direct stimulation of the renal epithelium. In almost every case, moreover, an increase in the excretion of urine is followed by an increase in the amount of oxygen used up by the kidney. It is a general law that every increase in cell activity is accompanied by an increase in the amount of oxygen used by the organ, and the increased blood flow accompanying most forms of diuresis is readily explained on the basis of the physiological need of the tissue for water and oxygen. If physi- cal laws were sufficient to explain all the phenomena of excre- tion, there would be no need for oxygen in increased amounts during periods of increased urine formation. A conception of the actual amount of work which the cells must do to excrete the urine may be obtained by comparing the osmotic pressure of the urine with that of the blood. The osmotic pressure of the blood is only half that of the urine, and for each one thousand cubic centimeters excreted, it is sufficient to call for the expenditure, on the part of the renal cells, of a force capable of lifting a pound through one thousand feet. We may conclude that the nature of the excretory mechanism cannot be explained by the physico-chemical laws as we now know them, i. e., the phenomena of osmosis, filtration, absorption, etc., but rather that it must be duo to a vital action on the part of the renal cells. It is this vital function of the cells which enables them to remove one substance from the blood and to leave another which is identically the same so far as physico-chemical properties are concerned. Micturition.— The urine discharged from the collecting tubules of the kidney into the pelvis, is carried to the urinary FUNDAMENTALS OK HUMAN IMIYSIOUKjY. 247 bladder through the ureters (Fiff. T)?). Tlie muscular coats of the ureter have a movement similar to that of the digestive canal and by peristaltic waves force the urine down through the ureter into the bladder. The urine thus collected by the bladder is retained for a time and is at intervals ejected through the urethra by the act of micturition. This consists of strong contraction of the bladder walls, ogether with the contraction of the diaphrag- matic and abdominal muscles, the effect of which is to reduce the Vf.n,% <n„ .-.., .vM.-x ar- ,„ .1... spinal ror.I. . Aft-r Kollikw. ) II... .,l1..,H„t l>I..T IN tl,.. ,,,.st,.,i.,r r.,nt (M. l.lM.k. Kiv,-s .,(T .■„lla...n.ls whi.h ■ ml .,.v s.VM„|,.,s an,„,Hl ,1,.. .-lis of ,|,.. ,„;..n..r i,„,m ,!„ r.-.l), II,.. axons .. wlH.I. f,.,n, ,1m. ..|T..,..n. .il...,s ..f ,h.. ant.-nor roots. ,,■;.„» II.,wells ^BPB FtTNDAMKNTM.S '>F IIIMAN I'll YSIoI.or.Y. 257 l)Ut it is over 60 mm. for the skin of the had; of the neck. The temperature receptors are still more definitely located in areas, some being specialized for heat and others for cold. These so- called heat and cold spots are most frequent on the portions of the body that are covered by clothing, for example, the skin of the thorax, than on those that are exposed, for example, the face. They are fairly frequent on the skin of the dorsum of the hand, where their existence can be very easily demonstrated by slowly drawing a pencil gently over the skin. At certain places the point of He pencil feels hot, at ■ f^ie ■ cold, and in others it cau.ses no temperature sensation w' "wn .b.:llar tract. (After Htiwell. ) Plate IV'. Other collatt'rals run to int.iiiiediary cells, which then communicati' with tlic anterior horn cells (Plate V). The Nervk Center and Intermediarv N'KruoNBs. — When the entering nfivc impulse travels by a eoUati'ral to an anterior liorn cell, wf havt- the simplest type of reflex action, namely, one involving a r«e>'pt^)r, n sensory nerve fiber, the posterior ro;als. The affer«»iit impulse when it en- '•n llio cord is more likely to travel u{) the posterior coJmmns and then, as already outlined, to the cerebrum, where it is trans- mitted to the large pyramidal nerve celb of the grey matter. From the pvramidai cells -spnag tht fibers of the piirumidtd fnicta, which, as they {»uss dtm-ttward through tlfe whit* wattiT of the cerebrum, erowd closer ana ehiser togetlier until, ls>- the time the basal ganglia are rt^ehed <^«ic thalamus on the inside, and corpus striatuin on the outside), they form a narrow bun- dle, which occupies the middle portion of the strip of white matter lyine between 'feese gangliii. This white matter w ••all.'d the nilininl nipsi- ■ (Fig. (ili). and it is of very gr^at clinical interest because. "*-ing in the ne.ghborhood of a large artery i branch of miiidle ct-rebral), which saoietimes bursts iji elderly people, it is apt to become torn iip by extravasated blood, thus destroying the pyramidal fibei-s m^ eassing paraly- sis. This is what occurs in apopl-xn Below tite iiternal c.ipsule the tibers run into the crura cerebri, tten into the peas, thence into the medulla (^ilongata. in the frwt of which rh#?- form u dis- tinct bulging called the pyramid; heia-e their name [iiraaiidal fibers (see Fig. 61 1. In the lower portion of the medulla, a most interesting thing occurs, namely, three-fourths of the fibers f-ross to the oppo- site side, thus constrtuting th(> "^-r«.v.vH//Vm <>/ tht jii/fdnwls f Plate VF 1. Tli.'s.- croHw-ii fibers run down ni the lateral coluuuis of the spimil cord as tIic crossed i)yrami«ial tracts. The i)yra- midal fibers which do not cross in the medulla form the direct pyramidal tracts of the cord, and tlie\ gradually cro.ss in the cord itself. The pyramidal fibers end by synapsis around the cells of the anterior horn, .so that all fibers from the cerebrum ultimately cross to the opposite side before they reach the anterior horn cells, for which reason it happens that a lesion involving the pyramidal tiaet anywhere above the decussation, such as a haemorrhage in the internal capsule above referred to, always causes paralysis of the opposite sidt of the body (hemiplegia). These facts regarding the course of the pyramidal fibers have been ascertained by microscopic examination of sections from '-^ r,*- ■aWB* wm^ it? ^///;-^ |.|l|,, VI •i.llls. i<< llM |.> I.lllli'l.ll lil"l- ri'iMI ll I-. I.|:il ...r!.-X <'< III' .|„,,;il ,,,r.; . /. Iil"is 111 nurl.i .■!■ .1:111.1! 1,. 'MS, ;. lil.i'is uln.-l, i|.. ti.ii ■ n.s- Ih 111.' lll...|lllla (.111. .1 liVlallll.t .i tl:i. 1 1 , ■" -I lil"'"^ "' ""^'' '" Ml. ilulia i.i,.ss.il |..\ n.ini.l.il li;ii I I I .^1"' H.iw.ll.l zvsa^ "^^r^^ FI'NDAMENT.VLS <)F HUMAN IMIYSIOI/MiY. 261 ; various levels of the spinal cord some time after destruction of tlie Rolandic area of tlie oereltrum (see p. '275^ The pyramidal fibers are degenerated and they occupy the areas indicated in Fig. 60. Since the degeneration occurs below the destruction, it is called descending degeneration, in contradistinction to as- cending degeneration, which we saw to follow section of the posterior roots between their ganglia and tlie cord (see p. '2r)8). To sum tip, the sensory impulse on entering the spinal cord by the posterior root, by traversing a collateral, may take the shortest possible pathway to the efferent nerve cell of the an- terior horn, or it may avoid this and travel up the posterior columns of the cord to the medulla, thence by the fillet to the cerebral cortex of the opposite side, and thence down the pyra- midal tracts to the anterior horn cells. In this long cerebral route there arc at least three places where the impulse must pa.ss by means of a .synapsis from nerve fibers on to nerve cells, and then along the nerve fibers arising from these. These three places are: (1) in the medulla. (2) in the cerebral cortex, (3) in the anterior horn. This long cerebral route, a?- it is called, is by tio n.eans the only one along which afferent impulses may travel to the brain. Some may be carried by collaterals to certain cells of the grey matter of the cord, and from these cells fibers may run up the cord to the ceiebellum or les.ser brain. These cerebellar tracts are located in the lateral columns of the cord outside the crossed pyramidal tracts (see Fig. 60). Tliey do not degenerate when the posterior roots are cut, but do so after section of the cord itself (this distinguishing them from the fibers in tlie posterior columns). The impulses which they transmit to the cerebellum have to do with certain subconscious sensations concerned ii' the maintenance of the tone of tlie muscles. There are also certain patinvays in the white matter of tlie cord which trans- mit descending impulses from the cerebellum. The main bundles of ascending and descending fibers in rlu' spinal cord an- fharted in Fig. 60. wliieh slioui.l be earetuUy studied. The Kffekknt Fiber oh Nel:k« _^-^i FUNDAMENTALS UF HUMAN niYslOLOGY. 263 ill the paralyzed region, the Urst to do so being the protective reflexes, of which the flexion reflex is the type. The flexion reflex is elicited by any stimulus wliieh would cause pain in an animal capable of feeling. Such stimuli are called nocuous and the reflex response is always of such a nature — usually flexion— as to cause the injured part to be removed from further damage. The return of the flexion reflex is soon followed by that of the fcnec jerk, which is elicited by tapping the patellar tendon after putting it on the stretch by passively bending the knee joint. Somewhat later in many animals (e.g., dog) the scratch reflex appears, so-called because it consists of a scratching movement of the hind leg in response to mechanical irritation of the flank of the animal. It is a reflex of very great interest because it illustrates to what a remarkable degree the spinal cord, unaided by the brain, is capable of bringing about complicated and purposeful co-ordinated movement. Later still, in the lower animals, practically all the reflex movements which a normal aninxal exhibits may reappear. When the cord becomes severed in man, as by spinal fracture, spinal shock is extremely profound, and in order to keep the patient alive great care must be taken, on account of the incon- tinence of urine, to prevent infection of the bladder and kidneys and to protect the skin from ulceration (bed sores). Even in such cases, however, many of the reflexes recover in the para- lyzed regions, but the recovery is slow and the limbs invariably atrophy. It is particularly important to note that the time of re- appearance of the reflexes bears a relationship to the degree of d.vclopment of the cerebral hemispheres, thus r;Midering it evi- dent that spinal shock is due to a break in the nerve paths which lead to and from 'lie brain. The higher the animal, the more frequently do al flex acts involve a cerebral path Instead of taking the short tuts available through the collaterals (see p. 2'>4 From usage, as it were, the cerebral paths become so well developed that when they are suddenly severed, the reflex action becomes impossible until the entering afferent impulse has learned to use the hitherto unused short cuts available through collaterals. When completely recovered from spinal shock, an 264 RKFI.EX ACTION. ! animal, say a dog, in so far as voluntary njovement is con- cerned, is entirely paralyzed in all portions of the body below the level of the section of the cord. It cannot voluntarily move the aflfected parts, it cannot walk, it fools no pain or any other sensation below the lesion, and yet when appropriately stimu- lated, the paralyzed limbs may rofloxly undergo various, often very complicated movements. The Essential Characteristics of Reflex Action.— As studied on a perfectly recovered spinal dog these are as follows: 1. For a certnin interval nftor applying the stimulus there is no resi)onso, the duration of this "latent period" depending partly on the tiature of the leflex (sliort in the protective re- flexes, loiirr ill the s( ratch reflex) and partly on the strength of the stinmlus. 2. The response may porsist for some time after lit Jitimulus is removed (after vsponse). 3. The degree of the resp>i;ise is roughly proportional to the strength of tlie stimulus, except in certain of the protective re- flexes, suth are the ganglia found in the cochlea and internal au. ^ tus (Scarpa's ganglion). The ganglia of the ninth ai.' icves are situated along the course of the nerves. • mate position of the various ganglia will be best lean.cv. , consultation of the accompanying diagram (Plate VII). In the brain stem there are three sensory or afferent nuclei, a long, combined one for the ninth, tenth and eleventh nerves, ex- tending practically from the upper to the lower limits of the medulla, one for the eighth in the center of the pons, and a very long one for the fifth, extending from near the upper limit of the pons down into the spinal cord. The motor or efferent nuclei for the third, fourth, sixth and twelfth nerves are com- posed of cells shaped like those of the anterior horn of the spinal cord. They lie near the middle line and extend throughout the whole lengtli of medulla and pons. The motor nuclei of tlie fifth, seventh, ninth, tenth and eleventh lie outside the above. The Brain. — The first question Avhich naturally arises is, wliat influence does the brain have on the reflex movements pro- duced through the spinal cord? Thp.se influences may be sum marized as follows: 1. The brain enables the animal to will that a partici.' ir movement shall or shall not take place, irrespective of the stimu- lation of spinal reflexes. Much of this iTifluence of the brain is of course voluntaiy in nature, but some of it is subconscious or involuntary. In general it may be said that the cerebrum, through the pyramidal trarts, usually exercises a damping or I VIII Mx.X riate VII — I iiiiKiain if thf (liiisii 1 as il 111' tli^ in the tlooi- of tln' fiiviitli vi'iilrn tifi-vfs. (Afti'i' ShiiriiiKlnn. ) Ic with till- iiiiclii •rtillla .inil iHiiis sliiiwIiiK if ciri^'iii (if till- iiMiiiMl liuinbond "ii the li'ft cif the i liKht. The judutifli'S of the I iiifiiior). :iif sliowii rut m' The linKiiiir iiv M ui'Ici all .I.h.mI rril III all' 1. the ii'olor lOielluin- lilue and imiiihi leil on the I'lioi). M. (Miiihllei. anil /. iia iniidiineinina. Thi lho\i niH'lei are nl lUise IHi •sent on lioth siiles. PrXOA MENTALS OF UTMAN I'llYSlOLOT.Y. 273 inhibitory influence on the spinal reflexes. It is for this reason that the reflex response to a certain stimulus is usually much more pronounced in a spinal, as compared with a normal animal. For example, it is impossible to bring about the scratch reflex in many normal dogs, whereas it is always present in spinal animals. In man this restraining influence of the pyramidal tracts on spinal reflexes is very evident in the case of knee-jerk, which, it will be remembered, is the extension of the leg which occurs whon the stretched patellar tendon is tapped. Ordinarily the kick is modtiate in I.|rr»'e, but in patients whose pyramidal tracts are disoised. as v> spastic paraplegia, it becomes very pronounced. 2. The 1 lin, beinK t\w \iuk station for the projicient wnsations (\). 28.')!, sight, li. ing and smell, adds greatly to the number of affen-nt p.iS'.w^-s by which reflex actions can be excited. 3. Since in higher aiiima travel through the brain i \> more or less involved in the n i degree of co-ordination than th, the muscular response. For i impulses reach the cerebellum, is to strengthen some impulses more perfect movement results. 4. The animal becomes conscious place of application of tlie sensory degree to which it has moved its muse The Functions of the Ce. Tlic complicated movements, such as scratch reflex, which we have seen that a out in the paralyzed region after shock more and more numerous and complica are left in connection with the spinal c higher up in the cerebrospinal axis V.- more capable does the part of the aii v., all'trent impulses usually any nerve centers becom tions, so tliat a much higli II in a spinal animal atteuiis pie. some of these afferent ^e 111 iction, as we shall see, weak " others, so that a ..f the nature and It M'. biit of the * i in the ill carry p, -rt'd awrtv. become HH Tiie b%liei t'l^s Hut is to !K iht sec u is inaii' the below the *^;«T5 '- ^4 274 THE CERT.ilAL I HJALIZATION. come to peform complicated niovements. The important centers in the medulla, pons and mesencephalon add their influ< ice to those of the spinal cord itself, so that integration becomes more comprehensive. If the cut is made above the level of the pons, in other words, if the cerebral hemispheres alone be discon- nected from the rest of the cerebrospinal axis — decerebratioii, as it is called — we obtain an animal possessing all the reflex actions that are necessary for its bare existence, although it is of course incapable of feeling or, if the ^asal ganglion he also destroyed, of seeing or hearing. It becomt- a mere au^ iton: it breathes, the blood circulation is normal, it cr.n walk run or swim, it swallows food if the reflex a<*t of swuUowing be stimulated by placing the food in the mouth, hv.' it has not the sense to take food itself even when ■"« is place., uear it. All the mental procesf's are absent; it ha^ xio memory, no volition, no likes and dislikes. By seeing that it takes food, it has been possible to keep such a decerebrated dog alive for eighteen months, and the lower we descend in the animal scale, the easier it becomes to perform the operation and to keep the animal alive. In higher animals, such as monkeys, however, life is impossible without the cerebrum, thus supporting the conclusion, which we have already drawn (see p. 255), that the cerebrum oomes to be a necessary part of every reflex action in the higher animals. Cerebral Localuation. — The various functio s of the cere- brum are located in different portions of it. This localization of cerebral functions has been very extensively studied during recent years, partly by experimental work on the higher mam- malia and partly by clinical studies on man. Careful observa- tions are made of the behavior of the various functions of the animal either after removal or destruction of a portion of the cerebrum, or during its stimulation by the electric current. Im- portant additions to our knowledge of cerebral localization are also being made by correlating the symptoms observed in insane persons with the lesions which are revealed 1 / post-mortem examination. It has been found that there are roughly three areas on the cerebrum with distinct and separate functions (Fig. 63). FUNDAMENTALS OF HUMAN PHTSIOUXIT. 275 I, In the portions of the cerebrum hich lie in front of the ascending frontal convolutions — prefrontal region — ere located the centers of the intellect (thought, ideation, memory, etc.). This part of tlie cerebrum is accordingly by far the best de- veloped in man; it if much '.ess so in the apes and monkeys, becomes insignificant ;n the dog, and still more so in the rabbit. It has been destroyed by accident in man with the result that all the higher mental powers vanished. Fig 63. Cortical centers in man. of the three shaded areas bordering on the Rolandic fissure («oJ.), the most anterior is the precentral associationa! area, the middle one is the motor area (the position of the body areas are indicated on It), and the most posterior Is the sensory area, to the cells of which the fillet fibers proceed. The centers for seeing and hearing are also shown. The unshaded portion In front of the Rolandic area Is the pr -ential ; the portions behind, the parietal and temperosphenoidal. II. The next portion includes roughly the region of the cerebrum bordering upon the Rolandic fissure (i. e., the ascend- ing frontal and ascending parietal convolutions). Here are located *;he highest centers for the movements of the various parts of the body. Microscopic examination of the grey matter reveals the presence of large triangular nerve cells, which com- municate by synapses (sec p. 2rj2) with the afferent fibers that carry the sensory impulses, whose course from the posterior 276 THE CERKHRAIi LOCAUZATION. spinal roots we liave already traced (p. 258). From each of these cells au efferent fiber runs to join the pyramidal tract (p. 260), and thus connect witli the anterior horn cells of the spinal cord. In the Rolandic area, as it is called, is therefore situated the cerebral link in tlie chain of neurones (see p. 261) through which the ordinary movements of the body take place. Such movements may be set agoing, either by stimulation of the Rolandic nerve cells thro ..h afferent fibers — a pure reflex — or by impulses coming to them from the centers of volition situated in the prefrontal convolutions. Or, again, the nerve cell, at the same time that it receives a sensory impulse coming up from the spinal cord, may receive one from the prefrontal convolu- tions which may either interdict or greatly modify the reflex response. Every possible muscular group in the body has a center of its own in the Rolandic area, the determination of the exact location of these centers being one of the achievements of modern medical science. Thus, if we stimulate with a finely graded electric stimulus, say, the center of the thumb, it will be found that the thumb undergoes a slow, purposeful, co-ordi- nated movement; and so on for every other center. Or, if in- stead of stimulating, we cut away one of the centers and allow the animal to recover from the immediate effects of the opera- tion, it will be found that all the more finely co-ordinated move- ments of the corresponding part of the body have disappeared, although gross reflex movements may be possible, because the spinal reflexes are still intact. If the entire Rolandic area on one side is removed, the muscles of the opposite side of the body, except those of the trunk, become completely paralyzed for some time, after which, however, particularly in the case of young animals, tlie paralysis becomes recovered from, thus in- dicating that some other poi-tions of the brain have assumed the function of the destroyed centers. If the stimulus is a very strong one, the movements do not remain confined to the cor- responding muscle group, but they spread on to neighboring groups until ultimately the whole extremity or perhaps even all the muscles of that side of the body are involved. FUNDAMENTALS OP HUMAN PUYSIC- -.i. 277 These experimental results find their exact counterpart in clinical experience. Thus when some center becomes irritatml by pressure on it of some tumor growing in the mombranos of the brain (meningeal tumor), or by a piece of bone, as in do- pressed fracture of the skull, or by blood clot, convulsive at- tacks (known as Jacksonian epilepsy) arc common. The first sign of such an attack is usually some peculiar sensation (aura) aflfccting the part of the body wliieh corresponds to the irritated area; the muscles of this part begin to twitch and more mviscles are involved, until ultimately all those of the cor- responding half of the body become contracted. Tliere is, how- ever, no loss of consciousness, as there is in true epilepsy. The evident cause of these symptoms has clearly indicated the proper treatment for such cases, namely, surgical removal of the cause of irritation. For this purpose a very careful study is first of all made of tlie exact group of muscles in which tlu' convulsions originate ; the location of the area on the cerebrum is thus ascertained and a trephine liole is made in tlic correspond- ing part of the cranium and through this h^le the tumor or blood clot is removed. III. These so-called motor areas are of course also scnsonj areas in the sense that the afferent stimuli which come up from the spinal cord run to them. They arc really sensori-motor centers. For some of the more highly specialized piojicient sensations, siioh as vision and liearing (see p. 28.")), there are, however, special centers. These, along with an extensive field of associational or junctional grey matter, constitute the third main division of the cerebral cortex and occupy the greater part of the parietal, the temporosphenoidal and the occipital lobes. The visual is the most definite of these centers. Thus if the occipital lobe be removed or destroyed by disease on one side, the corresponding half of each retina becomes blind. It is by studying the exact nature of the involvement of vision in sucli cases that the pliyslcian is able to locate the position of a tumor, etc. The center for hearing is in the temporosphenoidal lobe, but its location is not very definite. 278 THE MENTAL PROCESS. !l ! It will be seen, however, that the visual and auditory centers take up but a small part of this third division of the cerebrum, the most of it being occupied by associational areas. The nerve cells of these areas do not, like those of the motor and sensory centers, send fibers which run as pyramidal or optic fibers to some lower nerve center, but only to other cerebral centers, which they serve to link together. They are specialized to serve as junction points for all the receiving and discharging centers of the cerebrum, so that all actions may be properly correlated or integrated. These junctional centei-s thus perform the great function of adapting every action of the entire animal to some definite purpose. Together with the nerve cells in the prefrontal areas, the associational cells represent the highest development of cerebral integration, so that we find the areas in which they lie becoming more and more pronounced, the higher we ascend the animal scale. The Mental Process. — The impression received by the visual center when a young animal looks for the first time at, say a bell, becomes stored away in nerve cells lying in or close to that center, and when Ihe bell is moved sound memories are likewise stored in the auditory center. At first these remain as isolated memory impressions and the animal is unable to associate tlie sight with the sound of the bell But later, with repetition, the visual and the auditory centers become linked together, through nerve cells and fibers which occupy the associational areas, so that the invocation of one memory is followed by association with others. It is evident that the intricacy of this interlace- ment of different centers will, in large part, determine the in- tellectual development of the animal, and the possibility of his learning to judge of all the consecjuences that must follow every impression which he receives or every act which he performs. In man these associational areas are very poorly developed at the time of birth, so that the human infant can perform but a few acts for itself. Kverythiiig has to be learned, and the learning process goes hand in hand with development of the associational areas, which proceeds through many years. On the other hant^ most of the lower animals are born with the associational areas FUNDAMENTALS OK HUMAN PUYSIOLOtiY. 27» already laid down and capable of very little further increase, so that, although much more able than the human infant tfii fend for itself at birth, the lower animal does not afterwardii develop mentally to the same extent. The practical application of these facts concerning the func- tions of different areas of the cerebrum is in the study of mental diseases. To serve as an example we may take aphasia. This means inability to interpret sights or sounds or to express the thoughts in language. In the former variety — called sensory aphasia— the patient can see or hear perfectly well, but fails to recognize that he has seen or heard the object before. He fails to recognize a printed word (word blindness) or to in- terpret it when spoken (word deafness). The lesion responsible for this condition is located in the associational areas and not in the centers themselves. In the other variety, called motor aphasia, the patient understands the meaning of sounds or sights, of spoken or written words, but is unable to express his thoughts or impressions in language. The lesion in this case in- volves some of the centers concerned in the higher control of the muscles which are used in speech, and very commonly it is situated in the left side of the cerebrum. In all three forms of aphasia there is more or less decrease in the mental powers. Cerebellum. The afferent impulses set up by stimulation of the nerves of the skin in a spinal animal, and due therefore to changes in the environment, after entering the spinal cord travel to the various centers in the cord. Although complicated movements may result (e.g., the scratch reflex), there is an entire absence of the power of maintaining bodily equilibrium, and the animal cannot stand because the muscles are not kept in the degree of tone which is necessary to keep the joints properly stiffened. A similar inability to maintain the center of gravity of the body results from removal of the cerebellum, or small brain, which it will be remembered is situated dorsal to the medulla and pons, with which it is connected by three peduncles. The cerebellum uisists of two lateral hemiiphercs and a median 280 TIIK CKKKUKMJM. lobe called the vermis. The remarkable infolding of the grey matter which composes its surface, and the large number of nuclei which lie embedded in its central white matter are stru( - tural peculiarities of the cerebellum. The immediate results of removal of the cerebellum consist in extreme restlessness and inco-ordination of movements. The animal is constantly throwing itself about in so violent a man- ner that unless controlled it may dash itself to death. Gradually the excitement gets less, until after several weeks all that is noticed is that there is a condition of muscular weakness and tremor, and difficulty in maintaining the body equilibrium. Quite similar symptoms occur when the cerebellum is diseased in man (as by the growth of a tumor), the condition being called cerebellar ataxia, and being characterized by the uncer- tain gait which is like that of a drunken man. These observations indicate tliat the function of the cerebtUum is to harmonize the actions of the various nuiscular groups, so that any disturbance in the center of gravity of the body may be subconsciously rectified by appropriate action of tlie various muscular groups. It evidently represents the nerve center hav- ing supreme control over other nerve centers, so that these may not bring about such movements as would disturb the cquili- brimn of the animal. In order that the cerebellum may perform this function it must, however, be informed of two things. In the first place, it must know the existing state of contraction of the nniscles and the tightness of the various tendons that pull upon the joints, and in the second, it must know the exact position of the center of gravity of the body. Information of the condition of the muscles and tendons is supplied through the nerves of muscle sense, which run in every muscle nerve and are connected in the muscles with peculiar sensory nerve terminations called muscle spindles. When the muscles contract, or the tendons are put on the stretch, these spindles are c pressed and sensory or afferent stimuli pass up the nei es of muscle sense, enter the cord by th-. pos Fl'NDAMKNTAI.S OF JUMAN I'll YSIOLOtiV. 281 terior roots and reach the cerebellum by way of the lateral col- iiiniis (see p. 261). Information regarding the center of gravity of the body is supplied through the vestibular division of the eighth nerve, which, it will be recalled, is connected with the semicircular can- als and vestibule. In these structures are membranous tubes or sacs containing a sensory organ (called the crista or macula acoustica), which consist.s essentially of groups of columnar cells furnished with very fine hair-like processes at their free ends and connected at the other end with tiie fibers of the eighth nerve. The hair-like processes float in the fluid whioh is con- tained in the membranous canals or sacs. This fluid does not, however, completely fill these structures, so that it moves when- ever the head is moved. Tliis niovemeiit ^ifects he hair-like processes and thus sets up nerve impulses which are carried to the cerebellum. To make the hair cells of tliis receiving apparatus capable of responding to every possible movement c^i the head, it is, ' nvever, evident that there nuist be some definite arrangement the tubes. This is provided for in the disposition of the semi- circular canals in three planes, namely, a horizontal and two vertical (Fig. 64). Taken together tlie three canals form a struc- ture which looks somewhat like a chair, the horizontal canals being the seat of the chair and the two vertical canals joining together to form its back and arms. The back of each chair is directed inwards so that they are back to back. At one end of each canal is a swelling, the ampulla, in which the sensory nerve apparatus above described is located. It is evident that when the head is moved in any direction the fluid in some of these canals will be set in motion. It is this movement of the fluid which stimulates the hair cells. That this is really the function of the semicircular canals is proved by the fact that if they are irritated or destroyed, gravfl disturbances occur in the bodily movements. This is what occurs in Meniere's disease, in which attacks of giddiness, often severe enough to cause the patient to fall, and accompanied by extreme nausea, are the chief symp- toms, the lesion being a chronic inflammation involving the . 282 THE SYMPATHETIC NERVOUS SYSTEM. semicircular canals. It is believed by some that the constant movements of the fluid in the semicircular canals is the cause of sea sickness. The unusual nature of these movements causes Vie. 64 — The seiniiircular laiiiiUs of the ear, showing their atrangeiiieiit In the three planes of space. (From Howell's Physiology.) confusion in the impressions transmitted to the cerebellum from the canals, but after a while the cerebellum may become accus- tomed to them and the sea sickness passes away. The Sympathetic Nervous System. Along with the vagus and one or two less prominent cere- brospinal nerves, the sympathetic constitutes the autonomic nervmis system, so-called because it has to do with the innerva- tion of automatically acting structures, such as the viscera, the glands and the blood vessels. The characteristic structural fea- ture of the nerves of this system is that they are connected with nerve ganglia located outside the central nervous system. In these ganglia the nerve fibers run to nerve cells, around which they form synapses, thus permitting the nerve impulse to pass on to the cell, which then transmits it to its destination along its FUN1)AMENTAI-S UP HUMAN I'llYSIOLOOY. 283 own axon (soe p. 253). Before arriving at the RanRlion in which the synapsis is formed, the fibers are called pregan- glionic; after they leave, they are called postganglionic. A preganglionic fiber may run through several ganglia before it becomes changed to a postganglionic fiber. In the case of the vagus and other cerebral autonomic nerves, the ganglia are often situated, as in the heart (see p. 92), at the end of the nerve, but in the case of the sympathetic itself, they are more numerous, and are mainly situated at the sides of the vertebral column, where, together with the connecting fibers, they form a chain — the sympathetic chain — which can easily be seen on opening the thorax and displacing the heart and lungs. Two fine branches connect each of the spinal nerves with the corresponding sympathetic ganglion. It is through one of these branches that the sympathetic chain receives its fibers from the spinal cord. Through the other, fibers run from the ganglion to the spinal nerve. Some of the sympathetic ganglia are situated at a distance from the spinal cord; the ganglia which compose the solar and hypogastric plexuses are examples. In the thorax, the uppermost ganglion is very large and is called the stellate ganglion. Its postganglionic fibers constitute the vasomotor nerves of the blood vessels of the anterior ex- tremity, and the sympathetic fibers to the heart. Some pregan- glionic fibers run through the stellate ganglion to pass up the neck as the cervical sympathetic, their cell station being in the superior cervical ganglion. They act on the pupil (dilating it), on the salivary glands (causing vasoconstriction and stimulating glandular changes), and on the blood vessels of the head, face and mucosa of the inside of the mouth. From about the fifth dorsal vertebra downwards, branches run from the sympathetic chain on each side to become collected into a large nerve called the great splanchnic, which passes down by the pillars of the diaphragm into the abdomen and runs to the ganglia of the coeliac plexus. This nerve supplies all of the blood vessels of the intestines and other abdominal viscera. Its action on these vessels has already been described (see p. 97). It also carries nerve impulses for the control of the move- 284 THE SYMPATHETIC NERVOUS SYSTEM. ments of the stomach and intestines and for some of the digestive glands. In the abdomen the sympathetic chain gives off branches, which form the pelvic nerves and supply the blood vessels of the lower extremity. It is important to note that the connections between the sympathetic system and the cerebrospinal axis are limited to the spinal nerve roots between the second thoracic and the second lumbar. The results which follow stimulation of the sympathetic system are exactly like those which are pro- duced by injections of adrenalin (sec p. 23.'?). Depending partly on their mode of origin from the central nervous system and partly on the manner in which various drugs act on them, the autonomic system of nerves has been divided into: (1) sympathetic. (2) parasympathetic, and (3) enteric. The sympathetic include all fibers that arise from the thoracic portion of the spinal cord. Their endings are stimulated by adrenalin and paralyzed by ergotoxin. The parasynip-ithetic in- clude the fibers arising along with the cranial and pelvic nerves. They are stimiilated by pilocarpin and niuscarin and paralyzed by atropin. The vagus nerve to the heart is an example. The enteric constitute the extensive plexuses of nerves already de- scribed as present between the coats of the stomach and intes- tines. They have a regulatory function over the movements of these viscera, r-id they react toward drugs much like the para- sympathetics. Nicotin is a drug which acts on the s ?i;ipses, and therefore affects all fibers of the autonomic system, although its action is relatively feeble in the case of the enteric group. '^CIIAPTKR XXVI. THE SPECIAL SENSES. The sensory nerve terminations, or afferent receptors, that are scattered over the skin are affected by stimuli which come in actual contact with the surface of the body. In order that the stimuli transmitted from a distance, such as those of light, sound and smell, or the projicient^nsations as they are called, may be appreciated by the liervous'system, specifically designed or- gans, called the organs of special sense, are required. Those organs collect the stimuli in such a way as to cause them to act effectively on receptors which have been especially adapted to react to them. Although not really a projicient sensation, taste is conven- iently considired along with the above. Vision. Ligh t is due to vibration of the ethereal particles that oc- cupy spa7e.~TTie vibrations occur at right angles to the rays of light, and these travel at high velocity in straight lines from the source of the light. The rate of vibration of the rays is not always the same, and on this difference depends the color of the light, red ligh t vibrating much slower, and its waves being accordingly much longer, than those of violet light. The termi- nations of the optic nerve, the retina, have been specially developed to receive the light waves. But in order that a comprehensive picture of everything that is to be seen may bo projected on the retina, an ogtjcal apparatus, consisting of the cornea aod lens, is situated i.n front of it. The retina and the optical apparatus are built into a globe— the eyebal l— which, piyotjng on the attachment of the optic nerve, can be so moved that images from different parts of the field of vision may be 286 ir ••/ / t /-I /i r /", . .■>». 286 VISION. i; \ focused in turn on the retina. These niovements are eflfected by the so-called ocular muscles. There are, therefore, t hree fu nctions involved in the act of s^/ ] seeing: (1) That of the retin a, in reacting to light. (2) That of ) the cornea, jtc., in focusing the light. (3) That of the ocular 1 muscle s, in moving the eyeball. The Optical Apparatus of the Eye. It will readily be seen that th§_eye is constructed on much the same principle as a photographic camera, the retina being like the sensitive plate. There is, however, an important .dif- ference in the manner by which objects at varying distances are brought to a focus on the sensitive surface in these two cases: in the camera, it is done by adjusting the distance between the iens and the focusing screen; in the eye, it is doue by varying the convexity of the lens. In order to understand how the optical apparatus works, it is necessary to know something about the refraction of light. When a ray of light passes from one medium to another, it be- comes bent or refracted. When it passes from air to water or glass, for example, it becomes refracted so that the angle which the refracted ray makes with the perpendicular to the surface is less than that of the entering ray. In other words, the ray becomes bent towards the perpendicular. The greater the dif- ference in density between the two medic, the -» pater is the difference between the two angles. A figure ex the ratio between these two angles is called the index t ,. action. If the ray of light leaves the denser medium by a surface which is parallel with that by which it entered (as in passing through a pane of glass), it will be refracted back to its old direction, but if, as in a prism, it leaves the denser medium by a surface which forms an angle with that by which it entered, the original refraction will be exaggerated. If two prisms be placed with their broad ends together, parallel rays of light coming from a certain direction will be bent so that, on leaving the pri.sms, they meet somewhere behind them. Two prisms so arranged are virtually the same as a biconvex lens. It is plain that the PLTXOAMF.NTAtiS OP IM'MAN IMIYSlo focusing power of such a lens will depend i.= its index of refraction, and, secondly, the cm faces. A considerable part of the actual refr; a n which enter the eye is accomplished at tin -ved the cornea, a smaller degree of refraction King ' lens itself. The reason for this is that ' le rt'fra from air to cornea is much greater than IL it b*r\v. and the humors of the eye in which the If? i^ » humors and the cornea having very iiiiich the indices. The entering rays are, thei e, r' places in the eye, namely, at the anteri*., surfa< and on passing through the lens. 'iinj^ firat ..f it *ur )f rh*- rays ■'♦" ■ f. of : 'U- iii'iex vhe l*ns ...\,-ri r'i,.stj :'. e two 'It - (>rn. I Fig. 65. — Formation of iningo on letiiiii. 0..1. is ttie optic axis. Accommodation of the Eye for Near Vision. — When the eye is at rest, its optical sys*-^m is of such a strength that parallel rays, i. e., rays that are reflected from objects at a distance, are brought to a focus exactly on the retina. The picture thus formed is, however, upside down for the same reason that it is so on the screen of a camera (Fig. 6.")). When the object looked at is so near that the rays reflected from it are divergent when they enter the eye, it becomes necessary, if the image is still to be focused on the retina, that some adjustment take place in the optical system of the eye. This could happen in one of two ways, either by lengthening the distance between the lens and the retina (the method used in a camera), or by in- creasing the convexity of the lens. The former process cannot 288 VISION. occur in the eye, but the second is rendered possible by bulging of the anterior surface of the lens. There are several ways by which this bulging of the lens can bo proven to occur. Thus, if the eye of a person who is looking at some distant object be inspected from the side of the head, that is to say, in profile, it is easy to note the exact position of the iris, which, with t)ie pupil in its center, hangs as a circular curtain just in front of the lens (Fig. 66). If the person is now told to regard some Fig. 66. — Sottioii thiimgh tlio anterior piirtioii of tlie tyc : C, the cornea; /. the iris (note the circular muscular fibers cut across at the margin) ; L, the lens ; Ci, the ciliary process ; S, the suspensory ligament ; Sri, the scler- otlo or outer protective coat of the eye. (From a preparation hy P. M, Spur- ney. ) object held close to him, it will be seen that the iri.s is pushed forward nearer to the cornea. That this is really due to a bulg- ing of the anterior surface of the lens can be shown by placing a candle to one side and a little in front of the head and then, from the other side, viewing the images of the candle flame which arc cast on the eye. It will be seen that one image occurs at the anterior surface of the cornea, and another, less distinct, at the anterior surface of the lens. This image from the lens Kisn- .I.S IIK IIIMXN I'llVMltMHiV. 289 will be seen to , /e forward — that is to say, closer to the image at the cornea — ..'.icii the person shifts his gaze from a distant to a near object. By using optical apparatus for measuring the size of the images, the degree to which the convexity of the lens has increased, as a result of the bulging, can be accurately measured. This change in the convexity of the lens depends on the fact that it is composed of a ball of transparent elastic material, which is kept more or less flattened antero-posteriorly because of its being slung in a capsule which compresses it. The edges of the capsule are attached to a fine ligament (the suspensory liga- ment), which runs backwards and outwards to become inserted into the ciliary processes (Fig. 66). These processi>s exist as thickenings of the anterior portion of the choroid, or pigment coat of the eye, and they can be moved forwards by the action of a small fan-shaped nuiscle, called the ciliary muscle, which at its narrow end originates in the corneo-scleral junction, and runs back to be attached, by its wide end, to the ciliary i)ro- cesses. When this nuiscle is at rest, the ciliary processes lie at such a distance from the edges of the lens that the suspensory ligament is •.<.■ on the stretch. When the ciliary muscle con- tracts, it .luii'- ti ..ilinry processes forward, thus slackening the su.speirvi y .igaiiei.l ii id removing the tension on the capsule of the lenr wilh the v siil' that the latter bulges because of its elasticity. 'Ti; : ' !l.tv «>!' i le lens to become accommodated for near visio i iviids, •:!! 'iefore, first, on the elasticity of the lens, and seitu .!!/. un ii action of the ciliary muscle.|^Inter- ference with cj *;= r i' 'i .-^ renders accommodation faulty. For example, the lens, along with the other elastic tissues of the body [e. g., the arteries (p. 8G)], becomes less elastic in oh' age, thus accounting for the "long-sightedness" (or presbyopia) which ordinarily develops at this time. Paralysis of the ciliary muscle produces the same effect in even more marked degree, which explains the utter inability to brinp ^^bout any accommo- dation after treating the eye with atropi. which is given for this purpose before testing the vision in order to find out the strength of lenses required to correct for errors in refraction. 1^ 290 THE FUNCTION OF THE PUPIL. The Function of the Pupil. — Every optical instrument con- tains a so-called diaphragm, which is a black curtain having a central aperture whose diameter can be altered to any required size. The object of this is to prevent all unnecessary rays of light from entering the optical instrument, thus materially in- creasing the distinctness of the image. In the eye, this function is performed by the iris with the pupil in its center. The size of the pupil is altered by the action of two sets of muscle fibers in the iris. One of these runs in a circular manner around the inner edge of the iris; by contracting it causes constriction of the pupil, an event which occurs, along with the bulging of the lens, during accommodation for near vision. The other layer of fibers runs in a radial manner, and by contracting causes dila- tation of the pupil. This occurs in partial darkness, or when the )eye is at rest (although not during sleep). |The circular fibe rs pre supplied by th e third nerve, and the radial fiber s by the s ympathetic . iaBiiiiiini;itif view of the oiBiiti of Corti (Toslul): /*. l);isil:ir imiiiliraiic ; .1. II, iimor mid outiT nxls of Corti: (>', W, 6," hair cells; 7, 7', NUppoiiiiiK tills. I I'miii Iliiwt'H's I'liysioloKy. ) «■ ^m CHAPTPm XXVII. THE SPECIAL SENSES (Cont'd). Hearing. Like light, sound travels in waves, but not as transverse waves of the ether that fills space, but as longitudinal waves of con- densation and rarefaction of the atmosphere itself. The magni- tude of these waves is much greater and their rate of trans- mission much slower than the waves of light; therefore we see the flash of a gun long before we hear its sound. The several qualities of sound, such as pitch, loudness and quality or timber, depend respectively on the frequency, the magnitude and the contour of the waves. Sound waves are not appreciated by the ordinary nerve receptors but only by those of the cochlear division of the eighth nerve. These are connected, in the cochlea of the internal ear, with a highly specialized receptor capable of converting the sound waves into nerve impulse?. The cochlea consists of a bony tube wound two and one-half times as a spiral around a central column, up the -enter of which runs the end of the cochlear nerve. A loi.^ tudinal section of the cochlea (Fig. 69), tlierefore shows us this spiral tube in sec- tion at several ploces, and it is noticed that there projects into it from the central column a ledge of bone having a C-shaped free margin. From the lower lip of the C, a membrane called the basilar membrane, stretches across the tube, which it thus divides into two canals, of which the upper is again divided into two by another membrane running from the upper surface of tlie bony ledge. The basilar membrane is a very important part of the mechan- ism for reacting to sound waves. Resting on it is a peculiar struc- ture called the organ of Covti (Plate VIII), which in transverse sections of the cochlear canal is seen to be composed of two rows of long epithelial cells set up on end like the rafters of a roof, 297 208 HEARING. with shortor "hair" cells leaning up against them, particularly on the side away from the central column. The sound waves which act on the basilar membrane are transmitted to the fluid which fills the uppermost of the three divisions of the cochlear tube (see Fig. 69) through a membiane covering an oval shaped opening (the oval window) in the bony partition separating the internal from the middle ear. After reaching the apex of the cochlea they pass through a small aperture in the basilar membrane into the Fig 6» SemidiaBiammHtic sfotion through the right ear (Czermak) ; G, external auditory meatus; T. membrana tympani ; P, tympanic cavity or middle ear with the auditory ossicles stretching across it and the Eustachian tube (B) entering -It; o, oval ve Indow : r, round window; B, semicircular canals; S, :ochlea : Vt, upper canal of cochlea; Pt, lower canal of cochlea. (From Howell's Ph jlogy.) lowest canal, down which they travel to lose themselves against the membrane covering another opening (the round window) sit- uated near the oval window in the same partition of bone. As they pass along these canals the waves cause the basilar mem- brane to move or vibrate. The vibration affects the cells of the organ of Corti, and so sets up nerve impulses which are trans- mitted to tlie cochlear nerve by means of ner^^e fibers which con- nect with each of the main cells of the Organ. A fine membrane FIJNDAMENTAI-S OF IltlMAN IMIYSIOUHIY. 299 the top of the hair cells, and by rub membrane augments (called tectorial) rests bing on them when they move, action of the basilar membrane. We must now consider how the sound waves are brought from the outside to the oval window. The pinna of the ear col- lects the sound waves from the outside and directs them into the external auditory cnnal, at the inner end of which they strike the drum of the ear or tympanic membrane. This membrane is stretched loosely in an oblique direction across the canal, and is composed partly of fibers which radiate to the edge of the membrane from the handle of the malleus, a process of one of the auditory ossicles, to which it is attached. Because of these properties, the tympanic membrane, unlike an ordinary drum, is capable of vibrating to a great variety of notes, and the vibrations cause the handle of the malleus to move in and out. Between the tympanic membrane and the cochlea is the middle ear, or tympanum, consisting of a cavity across which stretches the auditory ossicles composed of three small bones, the malleus, the incus and the stapes. Besides the long process or handle already described, the malleus consists of a rounded head sit- uated above and forming a saddle-shaped articulation with the head of the incus and a short process which runs from just be- low the head to the anterior wall of the tympanum. The incus is somewhat like a bicuspid tooth, the malleus articulating with the crown, and having two fangs, a short one passing backward and a long one vertically downwards. This process, at its lower end, suddenly bends inwards to form a ball and socket joint with a stirrup-shaped bone (the stapes), the foot piece of which is oval in shape and fits into the oval window already mentioned. The ossicles act together as a bent lever, the axis of rotation passing through the short process of the malleus in front and the short process of the incus behind. If perpendiculars be drawn from this axis to the tips of the handle of the malleus and the long process of the incus, it will be found that the latter is only two thirds Ihe length of the former (Fig. 70). The amplitude of movement at the stappH will therefore be only two-thirds of that at the center of the tympanic membrane, but one and one- •.mo llEAKINO. half times stronger. The inerease in force with which the movements of the tympanic membrane arc conveyed to the oval window is still further magnified by the fact that the latter is only one-twentieth the size of the former. It is by these move- ments at the oval window that waves arc set up in the fluid occupying the uppermost membranous tube of the cochlea and thus acting on the basilar membrane. The tympanic cavity or Kig. TO. Tyiniiamini of lislit side witli the auditoiy os-sieles in idace (Mor- ris) : 1, incus (like bicuspid tooth) with one process (J) attached to wall of tympanum and the other running downwards to articulate at 9 and 8, the .stapes: n, head of malleus attached to tympanic membrane. (From How- ell's Physiology.) tympanum across which the chain of ossicles stretches is kept at atmospheric pressure by the Euslaeliinn tube, which connects it with the posterior nares. Deafness may be due to the futlowiny causes: 1. Rupture of the tympanic membrane. 2. Ankylosis or stiffening of the joints between the ossicles nsF^'ac*'^few« !Ai' .-a&v. PIJNOAMKNTAI.S OF HUMAN IMIYSIOIAKIV. 301 the „..^ .... ligaments which hokl thoin iii place iii me tympanic cavity. Flexibility of the joints between the osHicles prevents sudden jars at the oval window, for the joint between the mal- leus and incus, being saddle-shaped, unlocks whenever abnormal or excessive movements are transmitted to the malleus. 3. Blocking of the Kustachian tube. Tlis is quite com- monly a result of adenoids or it may be due simply to a catarrh of the tube. The result of the block is that the pressure on the tympanic cavity falls below that of the atmosphere because of absorption of oxygen into the blood, and the tympanic mem- brane bulges inwards and becomes stretched so that it cannot vibrate properly to the sound waves. The deafness in this case is easily removed by reopening the Eustachian tube by forcing air into it. This can be done by attaching a large syringe bulb to one nostril, closing the other nostril, and while t'-o putient is swallowing a mouthful of water, suddenly compressinj? ♦'.e bulb. The auditory distress which is experienced by a person on going into compressed air (as into a caisson) is also due to dis- turbance in the tympanic pressure, for it takes a few moments before this reaches that on the outside. Blowing the nose usually removes the distress. In all these conditions, the patient hears perfectly when a tuning fork is applied to the skull or teeth. This is because the sound vibrations are then transmitted to the cochlea through the bones of the head. When the cochlea is diseased, however, the tuning fork cannot be heard either when it is sounded in the air or when it is applied to the skull or teeth. The Sense of Taste. Scattered over the mucous menibraiie of the tongue and buccal cavity, and extending back into the pharynx and even into the larynx, are the receptors of Utstc, or taste buds. They are most numerous in the grooves around the circumvallate papillae at the root of the tongue, and in the fungiform papillae. Each taste bud is composed of a mass of fusiform cells packed like a barrel filled with staves. The staves in the center project as hairs beyond those on the outside, and it is evidently by action 302 TASTE. on these hairs that certain dissolved substances set up a stimulus of taste. This stimulus is then conveyed by fine nerve fibers which arborize around the taste cells, to the chorda tympani and lingual nerves in the anterior portion of the tongue and the glossopharyngeal in the posterior part. Through these nerves the sensations are carried to the combined afferent nucleus of the fifth and ninth nerves in the medulla oblongata (see Fig. 71). .tunLuun ^^Vnw. Fig. 71. — Schema to show the course of the taste fibers from tongue to brain (Cushing). The dotted lines represent the course as indicated by Cush- Ing's observationa. The full blacli lines indicate another path by which the impulses may reach the brain. (From Howell's Physloloify- ) Substances cannot be tasted unless they are in solution, thus, quinine powder is tasteless. One of the functions of saliva is to bring substances into solution in order that they may be tasted. There ai-e four fundamental taste sensations: sweet, saline, bitter and sour or acid. The ability to distinguish each of these tastes is not evenly distributed over the tongue, but occurs in definite areas. These can be mapped out by applying solutions, FtlNDAMFNTALS OF HUMAN PHYS10IXW3Y. 303 possessing one or another of these (lualities, by means of a fine camel-hair brush, to different portions of the tongue previously dried somewhat with a towel. Bitter taste is absent from all parts of the tongue except the base, hence a mouthful of a weak solution of quinine sulphate has practically no taste until it is swallowed, when however it tastes intensely bitter. Sweet and sour tastes are most acute at the tip and sides of the tongue. Saline taste is more evenly distributed. This location of taste sensations is not a hard and fast one, for neighboring taste buds in, say, the bitter area at the root of the tongue may appreciate different tastes; thus, if a solution containing quinine and sugar be applied to one papilla, it may taste sweet, whereas when applied to a neighboring one, it tastes bitter. With weak solutions one taste may neutralize another; thus the addition of a small amount of salt to a weak sugar solu- tion may remove its sweet taste. This neutralization of one taste by another does not occur when the solutions are stronger ; thus a mixture of acid and sugar, as in lemonade, causes stimu- lation of both "acid" and "sweet" taste buds. The stimula- tion of one kind of taste bud may cause other taste buds to be- come more acutely sensitive, which explains the sweetish taste of water after washing out the mouth with a solution of salt. Attempts have been made to correlate the chemical structure of organic substances with the taste which they excite, but with little success. Thus pure proteins have very little taste, whereas half-digested protein is intensely bitter ; on the other hand, the pure amino acids, which form a large proportion of the de- composition products in such a digest, are sweet. In the case of acids and alkalies, however, it has been established that the acid taste is due to the H-ion and the alkaline to the OH-ion. Some acids, such as acetic, taste more acid than we should expect from their degree of dissociation into H-ions. This is because of their power of penetration into the cells of the taste buds. When platinum terminals from a battery are applied to the tongue, the positive pole tastes alkaline and the negative acid, because OH-ions accumulate at the former and H-ions at the latter. TriE Association of Taste, Touch and Smell.— The four 304 TASTE. fundamental tastes do not nearly represent all the tastes and flavors with which we are familiar. The relish of an appetizing meal, the pi(iuancy of condiments, the bouquet of a fine wine, would remain unappreciated were there no other nerve I'eceptors than those described above. Two other types of nerve receptors are involved, namely, (1) those of common sensation, as in the case of acids, which add an astringent character to the sour taste, and (2) those of smell, as in wines and flavored foods. The importance of the sense of smell in "tasting" explains the loss of this ability d" ' ' nasal catarrh or cold in the head. Under such condition' . , pic and an onion may taste alike. Certain drugs wheu • ^..«ed to the tongue affect taste sensa- tions in different degrees. Thus cocaine first of all paralyzes the receptors of common sensation so that pain is no longer felt and an acid loses all of its astringent qualities and merely tastes sour. A little later the bitter taste also disappears, then salt, then sour, but the saline taste remains even after the cocaine has developed its full effect. Another interesting drug acting on the taste sensations, is a substance present in the leaves of Gymncma sylvestre. When these leaves are chewed, the sweet and bitter tastes are absent, t'.. e of acid and of salt and ordi- nary sensation (astringency, etc.) being, however, unaffected. The Sense of Smell. In man the sense of smell is very feeble when compared with that of the lower animals, and it is of very unequal development in different individuals. It is, moreover, readily fatigued, as is the experience of every one who has been compelled to live in stuffy rooms. The receptors are repn.onted by the coluianar epithelium of the superior and middle turbinate bones and the adjacent parts of the nasal septum. This epithelium is composed of large columnar cells, each cell being connected with a nerve fiber which is one of the branches of a fusiform bipolar nerve cell lying im- mediately beneath the epithelium. The second branch of each nerve cell inins through the cribiform plate to join the olfactory bulb. After making connections with nerve cells here, the path- '■"•wvf^m FUNDAMENTALS OP HUMAN Pll /SIOLOGY. 305 way is continued along the olfactory tract to the hippocampal region of the brain. As we would expect, this portion of the brain is highly developed in those animals having a very acute sense of smell. The olfactory epithelium is kept constantly moist with fluid, a!id substances cannot be smelled unless the odorous particles which they give off become dissolved in this fluid. These odor- ous particles diffuse into the upper nares from the air currents which, with each respiration, are passing backwards and for- wards along the lower nasal passages. There is no actual move- ment of air over the olfactory epithelium. Nature op Stimulus. — It is impossible to state just exactly what it is that emanates from an odorous body to excite the ol- factory sense. All we can say is that it does not require to be present in more than the merest trace in the air in order to un- fold its action. Thus even in the case of man, with his undevel- oped sense of smell, 0.000,000,000,04 of a gramme of mercaptan. suspended in a liter of air, can be smelled, and in the case of the dog, the dilution may no doubt be many thousand times greater. The sense of smell is the most important of the projicient sensa- tions in certain aquatic animals, and is very closely associated with the sexual functions of the animal. Just as in the case of taste, certain substances owe their peculiar odors to simultane- ous stimulation of the olfactory epithelium and the receptors of common sensation. Thus the pungency of acids, of ammonia, chlorine, etc., is due to stimulation of the endings of the fifth nerve. Attempts have been made to classify odors, as has been done for tastes, but with no success. CHAPTER XXVIII. REPRODUCTION. The most important function of an animal's life is the produc- tion of a new individual which in all peculiarities of function and structure is essentially like the parent. The fundamental prob- lems of the process of reproduction which are of physiological importance, are those of fertilization and heredity. Fertiliza- tion consists in the union of two parent cells to produce a new cell which is endowed with the power of growth and subdivision. Heredity refers to the phenomenon which directs the cell thus fertilized to develop into an individual like its parents. Since up to the present time most of our knowledge of these processes is based on anatomical data, we will discuss them very briefly and will pay more attention to what we may term the accessory phenomena of reproduction, which are of more practi- cal interest at present. Reproduction in the unicellular animals is a simple process. The parent cell divides exactly in halves and two daughter cells are produced. In the multicellular animals this type of repro- duction is impossible and the process is delegated to a portion of the animal's body known as the reproductive system. This system in man includes the specialized tissues which produce the cells or eggs from which the new individual develops, and the accessory organs which are concerned in providing favorable conditions for the development of these cells. Fertilixation.— A » ry simple type of fertilization is seen in unicellular animals, which ordinarily reproduce by simple divi- sion. After a series of simple divisions the cell becomes unable to develop more cells until after it has united with another cell to form one large cell. This process is termed conjugation. In higher forms, the development of the egg is always preceded by the phenomenon of fertilization, which is somewhat similar to 306 J FUNDAMENTALS OF HUMAN PHYSIOLOGY. 307 that of conjugation in lower forms. In this process, cells of two types are concerned, the male, or sperm cell, or spermatozoon, and the female cell or ovani. The spermatozoon has tlic ability to move and to penetrate tlie ovum. The nuclear elements of both cells unite to form a new nucleus, which is then capable of undergoing a long series of subdivisions. In changes which pre- cede fertilization, the nuclear material originally present in both male and female cells is reduced, and when the cells fuse, the re- sulting nucleus contains a normal quantity of nuclear material. The Accessory Phenomena zt Reproduction in Man. — The beginning of the active sexual life in man is between the ages of fourteen and sixteen, and is called tlie age of puberty. In both boys and girls the whole body shows a marked develop- ment at this time. The growth of hair on the pubic regions and arm pits, and on the face of boys, the deepening of the male voice, and the development of the breasts in the female, are all accompanying phenomena of the development of puberty. In females this age is marked by the onset of menstruation, which consists of a periodic flow of mucus and blood from the uterus. The flow lasts from four to five days, and recurs with great regu- larity about every four weeks. In males fully formed seminal fluid, containing live sperm cells, appears. The Female Organs of Reproduction. — These are the ovaries, oviducts, uterus and the vagina. The ovaries are paired bodies lying in the lower part of the abdominal cavity and held in posi- tion by the broad ligament. The cells from which the ova de- velop are imbedded in the fibrous tissue of the ovary. A number of these cells, better developed than their fellows, and surrounded by a layer of cells, which form a sort of follicle, lie near the sur- face of the ovary. These are the Graafiayi follicles, in which the ova develop till they are ripe, when they are extruded into the abdominal cavity by rupture of the follicle. In very close appo- sition to the ovaries is a tube, the oviduct, which leads to the uterus. The outer end of this tube is fimbriated, and it is fur- nished with cilia, the movements of which cause currents in the fluids of the abdominal cavity, and which direct the ova dis- charged from the follicle into the oviduct. The uterus is a pear- 308 REPRODUCTION. 1 shaped organ with muscular walls. It is about 7 cm. in length and consists of an upper dilated portion, called the fundus, and a lower constricted portion, called the cervix. The cervix opens by a small aperture into the vagina, which is a membranous cana about 10 cm. long extending to the vaginal outlet at the external genitalia. The Male Organs of Generation are the testicles, vas deferens, seminal vesicles, the penis, the prostate gland, and a number of small glands along the urethra. The testicles consist of two parts, a portion of which is cellular and is concerned in the development of the spermatozoa; and a portion called the epididymis, containing the lower portion of the very long and convoluted duct, the vas deferens. This duct connects the testicles with the seminal vesicles, which he at the. base of the bladder and in close relation to the prostate gland. The seminal vesicles are united by a short duct with the urethra, which is the outlet for the excretions of both the kidney and the testicles. The spermatozoa are developed in the testicles and find their way to the seminal vesicles through the vas deferens. On their way they become mixed with a number of fluid secretions, the chief of which are derived from the seminal vesicles of the pros- tate gland and of the glands of Cowper. The resulting mixture is the seminal fluid. Impregnation.~The seminal fluid containing the spermatozoa is deposited in the vagina during coitus. Attracted by the acid reaction oi the secretions of the uterus or under an unknown in- fluence, the spermatozoa soon enter the uterine cavity through its opening into the vagina, and find their way to the oviduct, where they remain waiting for the ovum to appear. Ovulation.— At about the time of a menstrual period an ovum is discharged from a ripened Graafian follicle and finds its way into the oviduct by way of the fimbriated extremity of the tube, down which it is conducted to the uterus. It is a debated ques- tion as to what the exact relation between menstruation and ovu- lation may be. Whether ovulation precedes or follows menstrua- W ;1 PUNDAMENTAI^ OP HUMAN PHYSIOLOGY. 309 tion is not known, but the weight of evidence favors the belief that menstruation serves to prepare the uterine walls for the reception of the fertilized ovum should one be discharged. In animals there are periods, called the rutting period, during which impregnation of the ovum with the spermatozoon is pos- sible. Preceding this period there occurs a swelling of the exter- nal genitalia and some discharge of mucus. This period probably corresponds to the menstrual period in woman, for there is much evidence to show that impregnation occurs most freciuently fol- lowing the menses. Menstruation ceases during pregnancy and is generally absent during the period of lactation. It ceases altogether between the ages of about forty-five and fifty. After this time, which is known as the climacteric period, a woman is no longer capable of bearing children. The union of the spermatozoon and the ovum usually occurs in the oviduct. If the ovum is not fertilized it is cast off. If it is fertilized, a considerable thickening of the uterine mucous membrane takes place from the proliferation of its cells. When the ovum reaches the uterus, it becomes imbedded in the mucous membrane of the fundus of the uterus. This mucous membrane is very vascular and soon becomes fused with the out«r layer of the ovum. . Pregnancy.— At first the ovum receives its nourishment directly from the mucous membrane of the uterus, but as the ovum develops and becomes what we term an embryo, the part lying next to the uterine mucosa becomes very vascular ; a similar process takes place in the ute.me mucosa directly in contact with the embryo. By this process the placenta is formed, the organ through which the embryo obtains nourishment from the mother. The vascular system of the embryo is, however, entirely sepa- rate from the maternal vessels, and the blood of the mother never directly enters the em!'-: .. The interchange between the two must be effected through tlie cells covering the vessels of the uterine and foetal portions of tlie placenta. In other words, the embryo may be said to live a parasitic yet entirely independent life, since through its placental vessels it exchanges its effete 310 BIRTH. products for the oxygon and noiirisluneiit contained in the motlier's blood. Birth. — While the ovum is being developed into a human being by division of the original cell of the fertilized ovum, the uterus becomes very much enlarged, and its walls increase in size by the growth of muscular tissue. At the end of approximately 280 days from the date of impregnation of the ovum, the devel- ojiment is complete and birth takes place. This consists in the expulsion of the fci'tus l)y mu.scula'' contractions of the uterus. Directly the child is born, the placenta begins to separate from the uterine wall and is soon expelled. The child deprived of its placental nourishment must now begin an independent life. It must take in its own oxygen and give off carbon dioxide by its respiratory organs. It nui take its food through the alimentary canal, and e.\crete its waste products through its kidneys. APPENDIX. Notes on PubUc and Personal Hygiene. The study of hygiene is closely associated with the study of physiology. Until recent years the teachings of hygiene benig built upon speculative knowledge, were very enipincal, but with the development of bacteriology and the awakenmg of public interest in the general welfare, there has arisen a hy- giene built upon biologic laws. The problems of hygiene are to determine what conditions may alter the normal activity of the bodv and to devise measures to remedy unfavorable condi- tions Old age is the one natural death. Hygiene is the sci- ence which seeks to place in our hands a weapon for tiie de- fense of the body against the many conditions which may shorten life or reduce its working efficiency. Unfortunately only the briefest review of the fundamental considerations ot the science is possible here. In general we may classify the agencies which interfere with the health of the bodv into those which are due to some inher- ent defect in the body mechanism, those due to abuse of the body and those depending upon an unfavorable environment. The study of the first of these clas.ses is delegated to the science of medicine, and the latter two classes to the science of per- sonal and public hygiene. ^ ^ , , The farmer, possessing his private water and food supply and sv.stem of sewage disposal, and being somewhat removed from 'communication with other people, has few problems of public health. Tt is when families assemble in villages and cities where thev must share the general utilities in common and where thev are brought into close contact with each other that the problems of public hygiene arise. Pure air, food and water and a satisfactory manner of disposal of the waste ma- 311 312 APPENDIX. terials of the body and the home, as well as the prevention of communicable diseases, are the problems with which the guardians of the public health have been primarily concerned. Today the principles of public and private hygiene are based upon definite quantitative and qualitative knowledge. All arts, crafts and sciences contribute towards making life easier, longer, and more worth while. A healthy body and mind de- pend very much upon a good environment. To provide the best environment is the function of hygiene. The Public Health. We shall, first of all, consider the means by which the public health is controlled. The problems to be faced are as follows : General administration, control of conuuunieable diseases, child hygiene, general sanitation, industrial hygiene, water and fowl supplies. The administration of public health is di- vided into federal, state, and local supervision. The local au- thorities are naturally the most important and have the most varied duties. These include the supervision of food and wa- ter supplies, sewage disposal, the sanitation of public and pri- vate buildings, the establishment and enforcement of quaran- tine and the supervision of the care of infectious diseases, the distribution of vaccines and antitovins, the laboratory diag- nosis of communicable diseases, the care of the sick poor, and child welfare. The state authorities have an advisory super- vision over local authorities, and deal with all questions involv- ing intercommunity life. In rural districts they take over many of the functions which are in the hands of the local a\i- thorities in the larger districts. They maintain a bureau of vital statistics based upon reports of the local authorities. They ■ administer the laws relating to foods and drugs, and maintain laboratories for determining the purity of the various foods, drugs, etc., and for the diagnosis of communicable diseases. The establishment and the administration of sanatoria for "-.e care and treatment of such diseases as tuberculosis are als under state control. The federal authorities serve the state in APPENDIX. 313 much the same capacity as the state boards £ rve the local or- ganizations. All matters of ir^erstate or national bearing are under their supervision. They administer the national quar- antine laws and care for the health of the marine service. They have charge of the enforcement of the national food and drug laws, which relate to interstate coi.iinerce. The government maintains laboratories in which problems of hygiene are in- vestigated. Another important branch of the service is the compilation into national reports of the vital statistics received from the various states. The supervision of the health of dis- tricts where federal work is being done is also their duty. Ex- amples of this arc found in the sanitary Avork done in the Phil- ippines and in the canal zone at Panama. We may now examine into the naiurc of the problems with which the Public Health Administration has to deal. Communicable Diseases are those which are transmitted from person to person or from an animal to a person. Modern science has demonstrated that such diseases are cai" d by defi- nite and specific organisms (bacteria and proto: a;, many of which have been isolated and the manner of their transmission from ho.st to host determined. In many diseases, although the causative organism has not been isolated, its existence is in- ferred and the manner of its transmissi-^ surmised from the character istics of the disease. It has al- ) been established that infectious diseases never arise spouianeously, but that the causative organism is always derived from a previous case of the disease. The mere presence of the organism does not, how- ever, always produce the disease. Indeed disease-producin(/ organisms are often present in a person who shows no symp. toms of the disease because of immunity towards it, but such an individual may serve as a carrier and transmit the disease germs to people who are not immune, with disastrous results. Thus we find all degrees of severity in the diseases produced by pathogenic organisms, and the most severe symptoms often accompany the disease in one person infected by the same or- ganism which in another produces scarcely any effect. We must .'W-r, , 314 APPENDIX. conclude, therefore, that the spread and the continuance of dis- ease is possible, first, '■. those who carry the germ without showing any symptoms ; second, by those who show symptoms that are so mild or so typical as to prevent recognition by ex- perienced observers; third, by individuals during the stage of incubation of the disease; and fourth, by persons suffering from the fully developed disease. The actual transmission of disease is accomplished in a num- ber of wavs. The causative germ may be shed oflE in the ex- creta of a patient, as in typhoid fever; in the secretions of the respiratory tract, as in diphtheria and scark' ' -er; m the sputum, as in pulmonary tuberculosis; or fro^( <'>—-, as in the case of venereal diseases and smallpox. When the germs exist in a free state in the blood, they may be transmitted by blood- sucking insects, as, for example, the transmission of the ma- laria parasite by the mosquito. Material carrying the germs may be conveyed from person to person by direct contact. This, no doubt, is the chief method the greatest number of infections being probably brought about bv the introduction of the germs into the mouth and respira- torv passages by the fingers or by food and drink. The public drinking cup, the dirty lavatory, careless spitting and cough- ing in public places, and the almost universal practice of touching the li'>s with the fingers contribute largely to the transmission of disease. The necessary toilet procedures, the handkerchief, dirtv hands-are all souu-es of dancer, not only to the individual, but to other people as well. Only absolute cleanliness can protect from contact infection. Formerlv it was thought that articles used by a diseased in- dividual might retain their infectious nature for some time following use. This is now thought to be rather an uncommon means of infection, direct or indirect contact soon after the organism has been released being the much more usual. Articles of food and drink v-^=lily act as vehicles of infection. Milk, because it acts s an a.tmirable medium for the growth of most organisms an-i also l.ccausc of the possibility < ' its be- *} ,-M APPENDIX. 315 ing infected during handling, is especially liable to carry dis- ease-producing organisms. Water is readily polluted by ex- creta and thus scatters infection, but the air is probably unim- portant in this regard, for expii«>d air does not in itself con- tain germs. It is only when it is Inden with droplets of ex- creta derived from the respiratory membranes, or when the air is filled with dust, that air-transmission of disease n>ay oc- c»ir. Malaria, yellow fever, and several other diseases arc transmitted by the bites of mosiiuitos «nd other insects. Flies may carry infectious material on tncir legs and this material they may carry to articles of food upon which they alight. Animals sufferinK with hydronhobia may transmit the disease germs by biting a person. In the nmnagement and the prevention of the spread of dis- ease, there are several procedures which appfy more or less generallv. First, all cases of infectious nature should be re- ported to the health authorities. This is required by law in most communities. The necessity for this depends on the fact that most persons arc apt to be careless about the health of other persons, and will not, unless required by law, adopt proper precautions to avoid the spread of any infectious dis- ease with which they may be afflicted. When the case is re- ported, the health authorities should see to it that the patient is cared for in such a manner as not to endanger others. This is accomplished by the use of such measures as isolation, quar- antine, disinfecti(m, vaccination and the destruction of vermin, mosquitos, etc. The value of isolating a patient with pu infectious disease rests upon the fact that the disinfect imi of the discharges can- not otherwise be guaranteed, nor persons who might visit the sick room be prevented from coming in contact with infectious agencies. Quarantine is only a more complete isolation of the patient. Isolation refers to thf nurse and patient; quarantine refers to the premises and all persons within the premises. Disinfection is the act of destroying the disease-producing i'.^atMt: .m^ii 316 APPENDIX. organisms which exist in infectious material. In diseases, such as diphtheria, pneumonia, influenza, colds, scarlet fever, tuber- culosis, etc., which are spread by the discharges of the nose and mouth, or by the excreta, the greatest care should be exer- cised to burn all the discharges and all objects which may con- tain them, or to chemically destroy the infectious organisms. In former times it was always customary to disinfect all the rooms and premises where infectious diseases had been housed. At present it is thought to be more efficacious to destroy or to disinfect everything used by the patient immediately after use, and to take extreme care in the method of disposal of all excreta. The nurse is also warned to be scrupulously clean and to be especially careful to wash her hands after touching the patient or any object which may be contaminated. Vaccination is another means of preventing disease. The principles underlying the process are discussed in this book (page 65). Typhoid fever and smallpox are examples of dis- eases in which, as a prophylactic measure, vaccination is of the greatest value. The fact that certain varieties of mosquitos carry the or- ganisms of yellow fever and malaria makes it incumbent upon a community to destroy these insects. The flea, which infests rats, may bite a person and infect him with the organism of plague. Rats are, therefore, dangerous and should be de- stroyed. The following is a list of the more important infectious dis- eases, with a brief note as to their causative organism and the prophylactic measures which are used for their prevention. The classification is based upon that pjiven by Rosenau in Pre- ventive Medicine and Hygiene, 1015, in which the diseases are grouped according to practical sanitary considerations. Diseases Spread Largely Through the Secretions .vnd Dib- CIIAROES OP THE NoSE, MoUTH AND TlIROAT. Diphtheria is an infectious disease affecting the mucous mem- brane of the throat or nose and producing severe constitutional APPEINDIX. 317 symptom.. The causative organism is the Bacillus diphtheriae S can be artificially cultivated (on nutritive media, such Isl^od serum, etc.) from secretions of the throat of a pat.n or from a carrier. The bacillus is then recognized ^y bacterio- lo. oal and n.icroscopical exa.nination. It is invariably trans- uU^d bv contact. An antitoxin has been discovered which rves bo"th as a curative agent in the sick and as a preventive n asure in people exposed to the disease. The antitoxin should be "ed in all such cases. Infection is possible as long as diph- ?her a organisms are present in the secretions of the throat Scarlet Fever is an acute febrile infection characterized by a sore throat, diffuse scarlet rash, and a high fever. After a f V davs of fever the superficial layer of the skin desquamate o peel Many degrees of virulence of the disease occur bu al cases are ec.ually infective and capable of producing the severest sy.nptoms in another. The causative organism is not known The hvgienic measures are isolation, inmiediate disin- f t^n of all secretions and of all articles used by the patient Measles is an acute febrile disease characterized by skm eruptions and inflammation of the eyes, nose, and J^^V^^'^^^^ passages. The causative organism is unknown. It is generally considered an unimpoitant disease, but it ranks with scarle fever as a cause of death in children. It is very contagious, and earlv re<.»gnition is necessary for prophylactic success Preven- tive^neasures are similar to those employed ^"^^J^^/^^/' _,. Whooping Cough is an infectious disease of childhood Ihe infective virus exists in the secretions of the throat, and it is eonnnunicable from the earliest symptoms. As a cause of in- fant mortality, especially during the first two J'««»:« ^fj' ^'J* is sndlv underrated by the laity. A much more strict isolation of children with the disease should be established. Lobar Pneumonia is an acute infection, though not generally considered a highly contagious disease. It is one of the chief los of death in early as well a. in late life. One of its causativ organisms is the pneumococcus. It is transniittcd by eonta t and ,nanv persons without the disease harbor the organism m their 318 APPENDIX. secretions. A lowered bodily resistance predisposes the indi- vidual to attack. All secretions from a case should be care- fully disinfected. Cerebrospinal Fever is a disease of the brain and spinal cord caused by the meningococcus. It is probably trans .rred by the secretions of the nose and throat. As in the case of the pneumococcus, many healthy people carry the germ. A serum having both prophylactic and curative qualities has been dis- covered. Tuberculosis is a disease produced by the tubercle bacillus. It is the most common infectious disease and the chief problem of the public h^-alth service. All degrees of infection occur, this being dependent upon the state of health of the individual and the severity of the infection. Children are highly susceptible, and should not be allowed in the same house with a case of the dip' . Its control consists in avoiding infection and in main- s' ..J the general health. This 's accomplished by the disin- 1 of all excreta from the patient, which is possible only ■< . .he co-operation of the patient, who must be taught to care for himself and to avoid infecting others. Pure air and food and rest are the curative measures of the disease. Other diseases of this group art influenza, common colds, mumps, etc. These are all infectious, but unfortunately no measures have been devised by health authorities to control their spread. It is to be hoped that the public will become ac- quainted with the fact that colds and influenza are infectious and highly contagious diseases. The person who shows grit in going to work with a bad cold or with influenza may do his neighbor harm and his employer no good, because he spreads an infection which lessens the working capacity of all who may contract the disease. DlSE.\SES L.\RGELY SPRE.\D TlIROUGII EXCRET.\. Typhoid Pever is the principal disease which is spread through the discharges of the alimentary tract and the kidneys. It is among the cummonest of the infectious diseases, and to APPENDIX. 319 prevent its spread is one of the most stn-ious problems of sanita- tion Everv ease arises from a-iothei ease, and infection is transmitted" in so many different ways that it is diffieult to con- trol People who have had the disease may act as earners ot the organism for years after recovery. One mode of trans- mission is contact. The nnrse or patient with the smalles amonnt of infected nrine or feces on the hand is a potential danger, for the disease is as easy to transmit from one person to another as is diphtheria or scarlet fever. Water is also a highly important mode of transmission. Water is infected by excreta containing the organism, which is named the Bacillus typhosus. Examples of epidemics spread by the water system are verv numerous. Milk is anof.ier important source of in- fect ion "because it is handled by many persons who may have typhoid germs. Likewise, flies carrying excreta on the legs and infecting meat and vegetables, shellfish and ice, all may serve as carriers. Fortunately there has recently been developed a vaccine which protects the individual from the disease. Its use has practically removed the incidence of typhoid fever m armies and its more general use is urged in domestic life. The control of tvphoid is shnilar to that of other infectious dis- eases All excreta should be disinfected before going into the city drains, and the patient should be isolated. Prophylactic measures in the community include care of sewage disposal and a pure water and food supply. Other diseases of this group are cholera, hookwoi-m, and the dysenteric diseases. Their prevention lies in personal cleanli- ii'ess and caie of disposal of the excreta. DiSKASKS Sl'KKAO BV InSKCTS .\NI) VkRMIN. The malaria parasite is transferred from man to man by the AnoplH-l.'s mos.iuito. The disea.s.> is best controlled by the suppres.sion of the mosquito and by careful screeni-..g of ma- larial patients. Yellow Fever is also a mos(iuito-borne disease ; and its con- trol is simiiar l«» that employed in inalaria. 320 APPENDIX. Plague is a disease caused by the Bacillus pestis, which is transmitted 'y the bite of the rat flea. Diseases for Which There are Specific or Special Measures. Smallpox.— This disease, caused by an unknown organism and formerly one of the dreaded diseases, is now capable of complete control by the use of general vaccination. The crus- ades against vaccination have no reasonable excuse, and those who start them are a menace to society. The danger and in- convenience of vaccination are verj jlight when compared with those of the disease from which the individual is protected. Hydrophobia is also caused by an unknown organism, and is usually transmitted by the bite of a dog. It is by no means an uncommon disease in America. To avoid danger of infection the best rule to follow is to take extreme care when handling a sick dog so as to prevent any saliva from coming in contact with the skin; In suspected cases, the dog should be isolated and afterwards killed if definite symptoms of rabies develop. People suspected of being exposed to the disease should rece' 'e the Pasteur treatment. Venereal Diseases are unfortunately one of the major prob- lems of the health officer and of public health. The difficulty in controlling them is the fact t .n they are considered dis- graces, and are, therefore, kept secret by the individual. The two chief diseases are syphilis, a disease caused by a protozoon, the Treponema pallidum, and gonorrhea produced by the gono- coccus. The transmission of venereal disease is, as a rule, by venereal contact. Other modes of transmission are, however, not uncommon, so that no one is safe. In the case of syphilis there can be no doubt that many innocent persons become in- fected with the disease, fcr it can be transmitted by contact, as is shown by the infection starting on the lips and fingers of innocent people. The registration of cases of venereal disease, the cli)sing of public houses, the supervision of the disinfection of dishes in eating houses, the abolishment of the common APPENDIX. 321 drinking cup, and the education of the young people in regard to the danger of venereal disease, are methods of control. The foregoing list by no means includes all of the infectious diseases which are of importance in connection with the pub- lic health. For a complete discussion of the subject the reader is referred to works on hygiene and medicine. Sanitation and Industrial Hygiene. The environment and the character of the homes in which people live have much to do with their health and happiness. Bad dwelling conditions and unclean habits predispose the in- dividual to disease. Unfortunately the sanitary conditions of manv of the homes that are now occupied are not capable ot improvement, nor is it possible to change people's habits be- cause when onee these are formed, it is almost impossible to l)reak awav from them. The one hope of sanitary workers lies in the education of young people in the ways of cleanliness and thrift, and in the building of sanitary dwellings ni the future. The lack of light and air in houses and tenement buildings, the lack of space for children to play out of doors, the dirty and sometime' filthy dooryards and homes, all predispose the children of the poor to disease. Under the topic of personal hygiene this question will be discussed further. 'iTnder the head of sanitation may be placed a number of health problems commonly called nuisances. These include the disposal of waste materials, the control of vermin and insects, and a number of miscellaneous items, as spitting, air contam- ination with smoke, obnoxious odors from trades, etc. Sewage Disposal.—Human excreta are always regarded as m- fpctious and must be dealt with accordingly. This requires that the «>xcreta be promptly removed under conditions which will prevent contact with individuals or insects, or the pollu- tion of water supplies. Where a. municipal sewerage system is established, the wastes are carried away in closed sewers to a place removed from possible danger to the community. In rural districts and even in small towns the ordinary privy ^ 322 AITFNDIX. found almost universally is most unsanitary, and is a constant menace to the health of the people. Insects usually can gain access to the vaults, and the seepage of water may contaminate wells in the vicinity. Privies should be constructed according to the directions furnished by the United States Department of Agriculture (Farmers' Bulletin 463). Reform in this re- gard cannot be too strongly v njed upon people not having the use of proper sewerage systeni.^. The use of cesspools for private sewage disposal purposes may be made very satisfactory. Two types are recognized : the tight and the leaching cesspool. The tight cesspool must be used in all places where there is danger of water pollution. The leaching cesspool is very successful where the soil is sandy and thus acts as a natural filter. The Disposal of Other Wastes Such as Garbage, Ashes, Paper, etc.— As a rule these do not bear upon the public health and should be dealt with by the public service department. How- ever, they may indirectly bear upon health. For example, gar- bage, manure and dead animals attract and offer breeding places for flies and vermin. These, as mentioned above, may serve to carry infection. It should be the duty of health au- thorities to see that such wastes are disposed of in a manner to prevent unnecessary nuisance to the householders and to pre- vent the breeding of flies, rats, and other vermin. The question of fly suppression is at present in the public mind. No doubt flies act as carriers of infection and they should therefore be suppressed. The fly swatting campaign con- ducted by cities is commendable, but attention should also be paid to the prompt removal of manure and waste material, or to their protection against flies. These precautions alone will soon result in a great decrea.se in the number of flies. Ever since Laveran did his masterly work upon the life history of the organism which causes malaria, the presence of the mosquito has been tabooed. We now know that malaria and yellow fever are transmitted from person to person in no other way than through the bite of certain mosquitos. APPENDIX. 323 WheTievor either one of these diseases threatens a eonnuunity, it becomes the dutv of the health authorities to suppress the mosquito. The ordinary mosquito (Culex punffeus) found in Northern comnumities is supposedly harmless. It may he dis- tinguished bv the faet that when rostius or biting its body is parallel with th'^ resting uirface, whereas the malaria mos- quito, Anopheles, forms iu. aente ,• nglc to the resting surface. The measures taken t . drstn.y the mosquito are: first, to drain all low-lying lands where water stands during the hot season ; secondly, to remove all receptacles which may contain water; cesspools, rain barrels, and cisterns which cannot be drained should be sci'eened; thirdly, the stric. screening of all cases of malaria and yellow fever. Spitting should be prohibited on the grounds of decency and because it may spread disease. Smoke, dust and unpleasant odors may become nuisances and thus come under the control of the health !)oards. Many cities have ordinances governing these items. IXDl'STKI-VL IIVGIKNK. While it is almost impossible to change the habits of mem- bers of a househohl, it is possible by law to govern the con- ditions under which people may woi-k for others. This is known as industrial hygiene. There has been n. branch of the science that has made greMer strides than this one. The work- ing conditions of millions have been improved and many lives thus saved. Factoi'ies are now built with the idea of the com- fort of the employee in mind, and the dangerous and hazard- ous trades have been made more safe by the introduction of safety devices on every machine on which this is possible. Dust, which in the older days predisposed many workmen to lung'trouble, has been eliminated by the in.stallation and use of suction blowers. The modern employer finds that attention to these details and to light, ventilation, and cleanliness save money in the long run. In many factories medical examination 324 APPENDIX. of all workers is compulsory, and many incipient diseases are thus detected and corrected. Child-labor is gradually becom- ing a thing of the past in most states. Hours of labor are shorter, in some cases too short for the best results. In some trades the workers handle materials which are poi- sonous or injurious to the health. Diseases produced under these conditions are known as industrial diseases. The most common of these are poisoning by phosphorus, arsenic, lead, brass, and mercurv. State inspection of factories engaged m the manufacture of articles in which such dangerous materials are used, has lessened the incidence of these disenses. C'aisson disease or "bends," which develc s in laborers work- ing in atmospheres of increased air ^i^ssure, is another example of an occupational disease. The trouble is entirely eliminated bv very gradually reducing the air pressure sur- rounding the laborers while they are returning to normal at- mospheric air pressure. Child Hygiene The protection of the health of children from birth up through school age is termed child hygiene. The facts that twenty -five per cent of all deaths occur before the age of five, and that the majority of these occur before the age of two, emphasize the importance of child hygiene. In practically all cities there have been established institutions for the care of infants and for the instruction of mothers in such questions of child welfare as feeding, etc., for it is known that the chief cause of infant mortality is the ignorant treatment given babies by their mothers. Only education can remedy this. The health of school children is also quickly coming under the supervision of competent doctors and nurses. The poorly ven- tilated and overheated stuffy rooms found in many homes, the crowding in the homes of the poor, insufficient and dirty food, irregular and improper feeding, the over-dressing of the in- fant in warm weather and even in cold weather, and the use of drugs and pacifiers, are the predisposing causes of most of APPENDIX. ^25 the diseases of infancy. The encouragement given to mothers to nurse their babies, the inspection and teaching of home hy- giene by visiting nurses, the improved milk supply, and the timely articles in papers on child hygiene, have done much to reduce mortality in cities. The instruction in domestic science given by the public school is a most promising work. The medical inspection of school children by which defects of the nose, throat, eyes, teeth and ears and other physical de- ficiencies are detected, the establishment of playgrounds, the proper ventilation and sanitation of the school buildings, and the care in preventing the spread of the communicable diseases, have contril)uted much to child welfare. Food Supplies. The piotection of the public from impure food supplies is an important function cxf the public health service. In general this activity is directed towards preventing the possibility of contamination of foods, or other articles for human consump- tion, with infectious matter of insects, or the sale of diseased meat and decomposed food material. The inspection of cattle before slaughter and the examination of the carcass after slaughter by competent veterinarians is necessary. Such in- spection is re(|uired by the United States law for all meat that is to be shipped from one state to another. Meat for local co.i- sumption is subject to only state laws, which unfortunately, in many instances, are inadeciuate. Among the diseases whii may be transmitted from animals to man through eating im- properly cooked and diseased moat, are tuberculosis, tri- chinosis (a disease caused by a small worm often present in pork), tapeworm, and hoof and mouth disease. Since milk is used so largely as an article of diet for infants and young children, ♦he importance of a pure supply cannot be overestimated. A pure milk supply depends upon several fac- tors. The cows which produce it must be healthy; the milk- man must be clean and free from disease ; the milk must have a 326 APPENDIX. 'm required food value and must not be adulterated; and it must be delivered to the consumer in clean receptacles and within a short time after milking. These many provisions, coupled with the fact that milk is most readily infected by microorganisms, make the problem of a strictly hygienic milk supply a difficult one. The inspection and the laws governing dairies have im- proved the mfuner of c(.llecting milk, and the process known as pasteurization, which frees milk from microorganisms, as well ;":s the improved methods for distribution, have made the milk supply of cities very good in late years. In country districts, however, there is still much that should be done. The farmer Avith a small milk route, who keeps his cows in dirty stables, and who in milking collects almos* \s much dirt in the pail as he does milk, needs to be educated. Water Supplies. Since diseases are often water-borne, great care must be taken in choosing the source of a water supply, and in prevent- ing the water from being contaminated before it reaches the consumers. The most dangerous contamination of water sup- plies is from sewage and human excreta, other sources being from animals and from tiie disposal of the water of houaes and factories. A bacteriological test is the most delicate indicator of the purity of water. This consists in estimating the total number of bacteria in a measured quantity of water and in de- termining whether or not the Bacillus coli (Colon Bacillus), an organism always picsent in the excreta of man and animals, is present. If the colon bacillus is present, it is presumptive evi- dence that the water is cf th( pa-'-nts. Later it th< iividv himself who cares for his bod It is herelt.re she aty of ery one to know ai 1 to Hiply he lav f heal' to his ehildi and to himself. - ifh phvsi< >gical tin ct ions is nutrition, < cretion, nervous ai i muscular letivii , and rejiroduction require spe- cial hygienic control whic . tn be successfully applied only after (ii< fundampntaK of i)h\ siology are understood. A few of the ii.or' uts'andiiu' ' trienic aspects of the subjecl may now be coush red. The Hy Tie^e of Nutrition. — In the chapter on dietc. ,cs (i- src 202) the lod value •; 'he various foodstuffs and the ca iric lequircments of the »d> are h\ '• liscussed. Mention wi iiiadf here of a few of th«' pract hygienic points concern the coii>umpti"' of food. The -'aloric .eeds «> the Itody are best determined e jwrfecti' norm 1 appetite The person who.se bod' is ,er- f^et runii. ic or^ci and \ ho has the proper regai ir e ^v- gienii aws, insti 'ively chouses a balanced ration iicieiii Iff ] undereating are commoi. only ^eased or perverted tastes. A> age ad- e made to deteiinine whether or not the proper numl»er oi ies are being taken. If readjustment of the 'liet ir sueh <■ -.es should cause no im- nroveiueiit, a p! siciau .^iiouM lie ''onsulted. The use of • ketl loods da:' s from early times. Cooking usually makes iiM.d iii<. ■ ppet ing, as wnl as more digestible, and it kills all t1 p-.(;isitps ai«d <' >ease germs. On the other ,ik1, poor cook ,na.." *hv rood indigestible. "A good ook .saves dodo is ji I adage. In thfso busy tiiiit M ,i»st everyone eats too fast, and the teeth are little used Uieir most important fimction, that of niasticatioii Faddists who would have food over-masticated err on the side of wisdom. Reference has been made to the effect of appetite upon the secretion of the appetite gastric juice I page 163). The chewinir of food allows the organs of taste full time to appreciate the food so that the secretion of the appetite-juice is fully stimulated. It has been taught that the drinking of water at meals is not hygienic Experience and experiment .show this to be false, for a moderate amount of v nter drunk durii .' a meal is bene- ficial to proper assimilatioi water in excess, or the ti' food and so make the j) of con se, unwise. Tht amounts is perhapr bar purine bodies (caiTein stimulating to the ner\ stance, known as tanui either beverasre is takeu jurwms : insults may follow. havinL' asi iii'paired digest these oe.erages. The use of alcoholic beverage ficial to health. Tn moderate !i any ill effects on the body, but Tl ice-cold \^ ta • *>- 1 a ff' 'f >-ess, -■*". J \ . rv "rv.Mts V 011< s^ tet should iier of uiiiiecessary an bene- | lints they may not produe danger of habit-formatioi 330 APPENDIX. and the disense and misery which the abuse of alcohol brings, are sufficient arguments that total abstinence is best of all. The effects of tobacco on the human body are so complicated that many statements regarding its use are unreliable. The majority of investigators of the question are convinced that it does not work great h;.vin upon grown men who use it mod- erately. On the other Land, there is a uniform concensus of opinion that the use of it in excess m- in growing boys is abso- lutely harmful. The Hygiene of Excretion.—Physiology teaches us that the organs of excretion are the lungs, kidneys, bowels, and skin. In the perfectly normal individual, the excretory processes must keep pace with the ingestion of water and food materials. Anything which disturbs this delicate balance is harmful. The care of the excretory organs is, therefore, an important part of private hygiene. In the metabolic processes which are continually taking place within the l)ody, end-products are formed, which must be promptly excreted or they become poisons. An example of such poisonous action is the effect which high concentrations of carbon dioxide have upon the tissues .her. respiration be- comes embarrassed; another is the production of the disease gout, when the kidneys fail to excrete uric acid. The healthy body is able to take care of the nornml end-products of the body's metabolism, but when the excretory organs are over- burdened with i)oisons which are more or less foreign to the body, a disturbance of excretion takes place, and the poisons collect and injuie the tissues. The poisons resulting from the decomposing food nwitcrial in the intestinal tract, due to the failure of the bowels to e\ Hcuate the refuse nuiterial promptly, so that bacteria flourish therein, and the absorption of toxins produced by pathogenic bacteria in local abscesses, such as are often found in the gums and tonsils, are Avithout doubt the (•ause (»f many chronic diseases of the heart and kidneys. In some cases bacteria themselves also enter the blood from the APPENDIX. 331 aliiuentarv tract or from abscesses and produce a general sys- temic infection, or locate in some particular spot of the body, there causing local inflammatory changes. Recent work indi- cates that many cases of chronic rheumatism of the joints and muscular pains of obscure origin are produced in this manner. These facts teach us that extreme care must be observed in order that the organs of excretion may do their work properly so as not to become overburdened by poisonous materials^ I'roper care of the teeth and the gums by careful washing and cleaning, the inspection of the teeth by a competent dentist at reasonable intervals of time, the avoidance of colds and all sorts of infections, free elimination of the waste products ot digesti.)n bv the bowels, the excretion of a proper amount of urine living in an atmosphere of good air, and the cleanliness of the person and surroundings-all are of importance in pro- moting good health. One of the commonest ills of mankind, and one which pre- disposes the bodv to the inroads of serious diseases is consti- pation. The foods which are eaten today lack the rough coarse fibers which the foods of our ancestors contained. Our diet is bland, soft and concentrated, so that peristalsis of the in- testines is scarcelv necessary to complete the process of diges- tion of manv articles of the diet, with the natural result that the intestinal muscle fails to develop properly, and peristalsis when it is re(iuired is not strong enough to force the waste materials along and out of the body. Regular meals, rest for some time after them, and the habit of going to the stool at a regular time each day, preferably after the first large meal of the day when peristalsis is most active, the eating of coarse foods and taking of sufficient exercise will prevent constipa- ticm in most cases. If f-.e condition becomes an established habit, laxatives may be necessary, but since these are apt to make the condition more chrmiic, they should be avoided whenever possi])le. Massage of the abdomen, exercises calcu- lated to strengthen the abdominal muscles, and the use of a 332 APPENDIX. lower seji abdomen 1 the closet so that the thighs will support the •ing defecation, are other curative measures. The importance of the fact that most people do not drink enough water is not appreciated. The soluble toxins and waste materials of the body's metabolism are excreted by the kidneys in solution in water. Diluted solutions of poisons have a much less injurious action upon protoplasm than concen- trated ones, and theiCfore a concenl rated urine, if it contains harmful substances, is more apt to damage the kidney than a diluted uriiu. The beneficial action of water in removing poisons from the body is illustrated by the improvement which occurs in people with severe infections, such as typhoid fever, after drinking large (|uantities of water and after a free urine secretion. Although much water is lost by the body through the skin and lungs, such water carries little or none of the impurities of the body. It is the kidneys which excrete these substances, and enough water should be taken to insure an excretion of from 1200 to 1500 c.c. of urine each day. As has just been stated, the skin is not an important organ of excretion, although a large amount of water is lost through the sweat p Hu'^ in the course of a day. The chief functions of the skin ■•>■<■ \ .-otection and regulation of the temperature of the body. 'I'l- latter function is hampered by the wearing of tightly woven clothes, which prevent air from circulating freely about the body. Personal cleanliness need not be em- phasized here. If decency did not demand it, health would, for infection lies in dirt Bathing is not alone for the pur- pose of cleanliness, for in the bath the pores of the skin are opened up, the cutaneous circulation is increased and the general well-being of the body improved. A cold bath in the morning toughens the body against changes of temperature and raises its resistance to infectious organisms. It does this by bracing up the circulating system and stimulating meta- bolism. APPENDIX. 333 Ventilation.— The jrenerai principles of vcntaaiion have been discussed on page 125. There are some practical consid- erations that aiP iiiiport.»mt. The problems of ventilating and of heatinsf a huildinjr are closely related. Ventilating wstems must be devised to secune a coMitant renewal and gentle movement of the air with the least possible loss of heat in the winter- and the .aintenju»c5 of a eowfortable temperature dur- ing til*- summer. Duriuc coH weather the temperature of a room should not exceed «8° F . and the air at this tempera- ture should cfwtain about fortr per cent of the moisture it will hold whep saturatetl. To .^cure the proper amount of iuf««turp rwiui'^ t'"«^ '^ relatively large amount of water be ..va|»«rated. Moisture can be add«d by plaetng pans of water on radiators, or by the use of one of the niunerous varieties of air n»»«t.e!iers which are on the market. A warm dry air is very irritating and produces iutianiimation of the nasal mejnbranes. Much of the discomfort which is experienced in a ^ose room is occasi(med by the lack of air currents. Tightly woven clothes, coupled with stagnant air, prevent evanoration of the sweat, so that overheating of the body occurs. A fan to keep the air in motion and loosely woven underclothing will make a stuffy room comfortable. Air in the poorly ventilated rooms seldom has enough carbon dioxide in it to be harmful, and the oxygen content can sink to a point where a match will no longer burn in it, without causing much bodily dis- comfort, provided the air is not too warm and humid and is kept in motion. We are, therefore, forced to believe that .systems which are aimed solely at renewing the air in order that the gaseous content be kept normal, i-.re not getting at the real center of the problem of ventilation. The fear of drafts has been one of the chief obstacles in the proper ventilation of buildings. Gentle drafts .n-e tiol "njur ous ; on the contrary, they are often beneficial and a necessity for good ventilation. Of course, a strong draft r^t cool uir 334 APPENDIX. bloAvi.ig directly against a person may be harmful by causing unequal stimulation of the heat regulating mechanism, and thus may lower the vitality to such a point that the organisms which produce a cold and which are omnipresent can obtain a foothold and grow on the exposed mucous surfaces. Ex- posure to cold in the open, in persons accustomed to changes of temperature, does not produce a cold. One of the great drawbacks to the methods of heating which are used at pres- ent is that thev maintain a constant temperature in the room and do not allow the body to adapt itself to changes when these are encountered. Such exposure then produces a con- gestion of the ves.sels of the nose and throat, and conse- quently a favorable condition for the growth of bacteria. Once established, a cold may be a very troublesome thing to cure. The hot foot bath, hot drinks and a good purge when one feels the cold coming on, will often cut the attack short. The Hygiene of the Nervous System.— There has been an alarming increase in the occurrence of nervous and mental diseases during the past decade. A very important contrib- uting factor to this increase, no doubt, lies in the greater ex- penditure of nervous energy required of people than in former years. The responsibilities of modern business, professional iiiid social life are much greater than they were in the past. ^Foreover, the great development of mechanical labor-saving devices has lessened the need of physical exertion and allowed more time for mental pursuits. A close investigation of the causes for mental breakdown and nervous prostration reveals the fact that it is not alone overwork and worry which bring about the condition, but that an imp"i"taiit contributing factor is the failure of indi- viduals to obey th- simple laws of hygiene. Physical man if entirely neglected does not remain strong, but soor wears out. Many people are attempting to place, as it were, a racing motor upon a worn-out running gear. The mind may be ever so brilliant, but without a healthy body to house it, it is worth little. APPENDIX. 335 There lUst cvev be a lialance between mental and physical activities, and if the proper eiinilibrium is maintained, mental overwork cannot occur. The man with nervous prostration is usually suffering from poor digestion and a rapid, weak heart. If these are corrected, his nervous symptoms often disappear. No hard and fast rule can be given in regard to the amount of mental and physical work and rest a person sliould have. Each must decide this for himself, and in de- ciding should consider the health as of equal importance to wo)-k or pleasure. INfental rest nnd relaxation are as neces- sary as physical rest. Changes from the regular occupation provide a vacation suited to the needs of many individuals; thus, a man engaged in physical work might take his vaca- tion impi-oving his mind, while a professional or business man might benefit most by spending his spare time working in the open. If the elements of sleep, rest, play, nutrition and work are ])ropei'l>- blended, no one need fear a mental or physical breakdoAvn. The greater mental activities of recent years have added to the use of the eyes. When a person is engaged in out-of-door work or in work which does not demand the close attention of the eyes, the muscles of accommodation are little used, but in work such as reading and prolonged near work, eye strain is likely to occur. Especially is this true if the eye has some optical defect. If vision is not distinct and the eyes tire (|uickly, they should be examined by an expert. The researches of lighting engineers have determined that the best method of artificial lighting for general purposes is by the use of ceiling lights. For close work dully shaded lights about nineteen inches above the work and of sufficient intensity to reflect light equal in power to that of eight can- dles from each square foot of white surface to be illuminated are considered best. The Hygiene of the Muscular System.— Bodily activity is as necessary for the well being of an individual as is proper nu- 886 APPENDIX. trition, excretion, or a normal nervous system. In no other way are all the activities of the body so greatly stimulated as by muscular exercise, for it increases the oxidative changes of the body, helps the flow of blood through the organs and the tissues', and by stimulating the heat regulating mechan- ism makes the body better able to adapt itself to changing conditions of temperature. Properly regulated muscular ex- ercise also increases the muscular strength cf the heart, and the depth and rate of respiration. The latter is very impor- tant in stimulating the lymph flow. Muscular activity is so necessary to the health of the in- dividual that any tendency to neglect it is regrettable. Auto- mobile riding seems to be taking the place of exercise in many cases, and the habit of walking is not indulged in to the ex- tent it should be. The great interest in sports which has been awakened in late years is a good sign, but far too few are able to take advantages of the opportunities these offer. Walk- ing is the one great exercise open to all, and it is as good a form of exercise as any if properly engaged in. The brisk walk, with shoulders thrown back, respirations deepened, and the arms swinging, brings every muscle of the body more or less into play. Moreover, walking can be engaored in every day in the year, whereas golf, tennis and other forms of exer- cise can be taken only at intervals. INDEX. Abducens or sixth nerve. 271 Aberration, chromatic. 291 spherical. 291 Absorption. 183 Accelerator nerves of heart. 9i Accommodation. 287 mechanism, 289 pupil In, 290 Acidity. 42 of gastric juice. 168 Acromegaly. 236 Addison's disease and adrenals, 23- Adrenalin, 234 Adrenals (suprarenal capsules). 232 Adsorption, 44 Afferent nerve paths, 257 Albumin, 36 Albuminuria, 242 Alimentary canal, anatomy of. 140 Amino bodies. 35 Amoeba. 18 Ammonia. 211 In urine, 240 Amylopsln, 177 Anesthesia. 257 Analgesia. 257 Anaphylaxis. 263 Animal heat. 132 Antibodies In b'ood. 59 Antlenzymes, 47. 180 Antipyretics. 136 Antlthrombln. 59 Antitoxin, 61 Apex beat of heart, 73 Aphasia, 279 Appetite, 154, 1C3 Arterial blood pressure. 85 Articulations, 37 Asphyxia. 101 Assimilation {see Metabolism) Association areas of cerebrum. 278 fibers of cerebrum. 278 Associative memory, 279 Asthma, 123 Astigmatism, 292 Atmosphere and metabolism. 191 Auditory areas of cerebrum. 278 Auditory ossicles. 299 Augmentor nerves of heart. 93 Auricle, function of. 167 Anrlculo-ventrlcular valves. 74 Auscultation of lungs. 117 Autonomic nervous system, Mi Bar.eria digestion, 169, 179 Beat of heart, 72, 76 Beef tea, 209 Berl-Berl. 224 Bile, 174 . Binocular Msion. 295 ; Bladder, urinary, 247 Blind spot, 294 Blood, 51 coagulation of, 58 functions of, 51 Rases of, 108 microscopic characters of, 51 pliysical properties of, 51 pUtts, 56 plasma, 56 Blood corpuscles, 51 enumeration of, 52 source of, 54 887 % r'?rrK 338 INDEX. Blood flow, rate of, 90 Blood presBure, 85 Blood vessels, anatctny of, 74 nervous control of, 97 Body cavities, 27 Body fat. source of, 218 Brain, 268 Bread, 207 Breathing, mechaniBm of. 113 Brighfs disease, 242 Bundle of His, 77 Butter, 208 Calcium, 223 Calcium salts and coagulation of Uood, 59 Calorimeter, 189 Calorie, 188 Capacity of lungs, 118 Carbodydrates, 37 food values of. 188 metabolism of, 116 relative metabolic Importance, 216 Carbon dioxide: effect of oxy haemoglobin, 110 mechanism of exchange, 110 production of, 104 Cardiac cycle, events of, 79 Cardiac muscle, 76 Cardiac depressor nerve, 95 Centers, vascular-nervous, 95 Cerebellum, 279 Cereals, 208 Cen brum, 273 funrHon of. in modifying re- flex-^H. 278 loralizatiou in, 275 relation to receptor system, 275 sensory areas, 277 Cheese, 209 Chemical componltlon of body. 33 Chemistry, of bile, 176 of foods, 207 of gastric juice, 167 of pancreatic juice, 174 of urine, 239 Childbirth. 310 Cholesterol, 36 Chordw tendinete, 74 Chyme, 171 Ciliary muscle, 299 Circulation, 83 diagram of, 70 influence of arteries, 84; of drugs. 101; of gravity, 100; of hsemorrhage, 194; of ner- vous system, 92 ; of respiratory movements, 92 renal. 244 pulmonary, 91 time of, 90 venous, 89 Circulatory system, anatomy, 70 Circumvallate papllte, 301 Clothing, 134 Climate, effect of temperature, 135 Coagulation of blood, 58 Cocaine, 103 Colloids, 43 Complemental air, 119 Condiments, 210 Cones of retina, 293 Connective tissue. 21 Consciousness. 27S Consonants. 130 rontractlon of muscle. 48 tetanic contraction, 49 Co-ordination, function of cerebel- lum, 279 Cord, spinal, 257 Cords, vocal, 127 Cornea, 288 Corpora quadrigeuiiua, 269 Corpuscles of blood, 52 INDEX. :\:v.) i Cortl. organ of. 297 Coughing. 117 Cranial nerves. 271 Creatlnln, 240 Cretinism. 230 Cream. 209 Crying. 217 Crystalloids, ^.9 Cystine, 215 Deglutition. 159 Dendrite, 253 Determination of blood pressure. 86 Diabetes, 220 Dialysis. 39 Diaphragm, relation to breathing, 114 Diastole of heart. 80 Diastolic blood pressure, 8f> Dietetics. 202 Diet, suitability of, 205 fundamentals of, 206 Digestion: bacterial-intestine, 179 of cellulose, 179 necesb' '. 138 in intescie, 174, 179 In mouth, 150 in stomach. 163 object of. 138 resume of digestive ferments. 185 Direct pyramidal tract. 260 Disaccharides. 37 Diuretics. 248 Ductless glands. 227 Dyspnea. 123 Efferent nerve paths. 261 Eggs. 209 Electrolytes. 40 Energy balance (sre Metabolism) Enterokinase. 177 Enzymes. 45 Epithelial tissue. 20 Erepsin, 178 Erythrocytes. 52 Eustachian tube. 300 Excreta, endogenous and exogen- ous, 215 Excretion, from lungs. 111 renal. 239 Exercise, muscular, and metabol- ism, 217 Exogenous excreta, 215 Expiration, 212 Expired air, composition of, 119 Expectorants, 126 Eye (« INDEX. Obc8it>, treatment of, 198 Oculomotor nerve, 271 Opsonins, 64 Optical defects. 291 Optic tlialaml, 259 Organ of Cortl, 297 Osmosis, 40 Osmotic pressure, SO Oviduct, 307 Ovulation, 30b Ovum, 307 Oxidase. lf»5 Oxidation, In tissues. 105 as source of animal heat, 106 Oxyf?en, absorption of. by blood, 108 Oxyhffimoglobln, effect of CO, on. 110 Pain, 257 Pancreatic juice. 174 composition of, 177 Pancreatic secretin 175 Pancreatic secretion, control of, 174 Paralysis, 267 Parathyroids. 228 Pepsin, 167 Pepsinogen. 167 Peptone, 35 Peristalsis. 182 Perspiration. 248 Phagocytosis. 64 Physico-chemical laws, 38 Pituitary body, 235 Platelets, or plaques, of blood, 56 Plasma, blood, 56 Pons Varolii. 258 Postsphygmlc period, 80 Precipitins, 62 Pregnancy, 309 Presbyopia, 292 Pressure, arterial, 86 intrathoracic, 115 osmotic. 40 Presphygmic period. 80 Properties of body, physical and physiological. 33 Proteins, jaemlcal composition of. 34 compound. 35 Insoluble. 36 Irr ^ ;i'ci re minimum, 199 iiuii"ivfc :;:••." of, 197 relk- vP uetr.hcilc Importance of, ^ t! requ^ : ;tit ; f I' 'Jy for, 203 simp ..2 sparers of, 198 Proteose. 04 Protoplasm, composition of, 33 primary constituents of, 33 secondary constituents of, 34 Puberty, 307 Pulmonary circulation, 92 Pulse, use of. In diagnosis, 91 tracings, 91 wave, 224 Purin bodies, 213 Pyloric sphincter, control of, 171 Pylorus, 170 Pyramidal tracts, 260 Ran-e of voice, 129 Rate of blood flow, 90 of body fluids. 43 Reason, faculty of. 279 Reciprocal inhibition. 26f Rereptors. 62. 255 Rt.. blood corpuscles. 52 Reflex animal, characteristics of. compared with normal, 263 Reflex arcs, 252 Reflex action. 264 Reflex paths, 256 Reflex time. 262 INDEX. ;u:^ i Reflexes, function of apinal cord in. 262 typea of. 262 Uenal secretion, 242 Reproduction, sexual, 306 Reproductory organs, accessory : female. 307 male, 308 Residual air, 119 Respiration, 104 artificial, 118 control of, 123 external. 111 interna!. 104 r-. jves of, 2.?2 vo.ume of air in, 120 Respiratory center, 121 exchange, 109 movements, 115 organs, 172 quotient, 119, 194 reflex, 121 sounds, 117 Rickets, 223 Rolando, Assure of, 275 Roots of spinal nerves. 258 Saliva, function of, 154 tartar formation, 156 Salivary g'ands, 39 secretion of. 150 Scratch reflex. 263 Salt hunger, 223 Sea sickness, 282 Sebaceous glands, 249 Secretin, gastric, 166 pancreatic, 174 Secretion: control of, 139 gastric, control of, 164 milk, 250 pancreatic, control of. 174 salivary, control of, 154 sebaceous, 240 Secretory process: hormone control of, 139 nervo'.is control of, 139 Semicircular canals, bony. 281 Semilunar ganglion, 98 S«ml?unar valve? 73 Semipermeable membrane, 39 Sensory areas of cortex. 27 ! Serum diagnosis, 65 Shivering. 136 Shock, 100 Sight, 285 Skin, function of. :i48 Skeleton. 29 Smell, 303 Sneezing, 117 Solutions, Isotonic, 42 hypertonic, 42 hypotonic, 42 Sound, loudness of, 12i) Sounds of heart, 81 Special senses, 285 Specific dynamic action oi loocis, 190 Tartar, 156 Taste. 302 Taste-buds, 302 Tectorial membrane, 298 Temperature of body, 132 Temperature, effect of, on mus- cular contraction, 133 Temperature sensation zero, 257 Temperature sense, 257 Temperature, bodily, regulation uf. 133 Tetany, 231 Thorax, contents of, 113 movements of. In respiration. 113 Thrombin. 59 Thrombogen 69 Thymus, 238 Thyroid gland, 229 344 INDEX. Tidal air, 118 Touch, sensatioDB of, 256 Toxins, bacterial, 60 Toxophores, 62 Trypsin, 74 Trypsinogen, 177 Urea, 211, 240 Uric acid, 213, 240 Urinary organs, 242 Urinary salts, nitrogen, 211 Urine, ammonia, 211 excretion of, 239 nature of excretory process, 243 Vaccines, 66 Vagus nerve, action of, on heart, 93 Valves of heart, 73, 82 Varicose vlens, 90 Vasoconstrictor nerves, 98 Vasodilator center, 95 Vasodilator nerves, 98 Vasomotor torn, 101 Veins, blood in, 89 Velocity of blood, 88 Ventilation, 175 Vision, 285 color, 296 stereoscopic, 296 Visual defects, 290 treatment of, 291 Vital capacity, 119 Vilamines, 224 Vocal cords, false, 126 relation of, to pitch, 127 Voice, 126 Vomiting, 161 Vowels, 129 Water, proportion of, in bcJy, 34 physiological pr0pert;e8 of, 34 Wheat flour, 207 White blood-corpuscles, 55 Xanthin bodies, 213 Yawning, 117