HX64089339 QP34 .R21 A manual of human ph RECAP Columtiia ®nibersiitp intfieCitpofi^clogorfe COLLEGE OF PHYSICIANS AND SURGEONS Reference Library- Given by Frederic S. Lee, Columbia College, New York- PLATE I. A, upper bone of sternum ; B, B, two first ribs: C, C, second pair of ribs ; D.D, right and left lungs; E, lower end of sternum : F F, right and left halves of the diaphragm in sections : the right half separating the right lung from the liver, the left half separating the left lung from the broad cardiac end of the stomach; G, G, eighth pair of ribs; K, K, ninth pair of ribs. Sauntiets' Mcio SiS Stties A MANUAL OF HUMAN PHYSIOLOGY PREPARED WITH SPECIAL REFERENCE TO STUDENTS OF MEDICINE BY JOSEPH H. RAYMOND, A.M., M.D., PROFESSOR OF PHYSIOLOGY AND HYGIENE IN THE LONG ISLAND COLLEGE HOSPITAL, AND DIRECTOR OF PHYSIOLOGY IN THE HOAGLAND LABORATORY. WITH 102 ILLUSTRATIONS IN TEXT AND 4 FULL-PAGE COLORED PLATES. PHILADELPHIA W. B. SAUNDERS 925 Walnut Street. 1894. B^fJ^lGAWIjaRAKi Copyright, 1894, by W. B. SAUNDERS. ELEOTROTYPED BY PRESS OF WESTOOTT 8. THOMSON, PHILADA. W. B. SAUNDERS. PHILADA. PREFACE The author's experience of twenty years as a teacher of Physiology to medical students has brought him to the conclusion that in the short time allotted to the study of physiology in medical schools students can assimilate only the main facts and principles of this branch of medicine, which lies at the very foundation of a sound knowledge of the healing art; and that even if there were time to investigate the more recondite and abstruse parts of the subject, such an investigation would be profitless during this formative period. In his teaching the author has kept this thought constantly in mind, and in this manual has endeavored to put into a concrete and available form the results of his experience. SEPTKMnKR, 1894. Digitized by the Internet Archive in 2010 with funding from Columbia University Libraries http://www.archive.org/details/manualofhumanphyOOraym CONTENTS. PAGE Introduction 17 I. Physiologicai, Chemistry 25 Inorganic Ingredients, 27 ; Carbohydrates, 41 ; Fats and Allied Substances, 53; Proteids, 57; Food, 82. II. NuTRiTivK Functions 92 1. Digestion, 92: (A) Mouth, 95; (B) Stomach, 103; (C) Intes- tinal, 118. 2. Absorption, 131 : Structure of Villi, 131 ; Lymph, 133; Chyle, 134; Absorption of Fats, 135. Blood, 136: Physical Proper- ties, 136; Color, 137; Reaction, 137; Odor, 137; Taste, 137; Quantity, 137; Distribution, 137; Temperature, 138; Micro- scopical Structure, 138; Red Corpuscles, 138; Number of Corpuscles, 139; Color of Red Corpuscles, 139; Structure of Red Corpuscles, 139; Development of Red Corpuscles, 140; Destruction of Red Corpuscles, 140; Function of Red Cor- puscles, 140; White Blood Corpuscles, 141 ; Composition of White Corpuscles, 142; F'unclion of White Corpuscles, 142; Plaques, 142; Composition of Plasma, 143; Coagulation, 143; Causes of Coagulation, 145 ; Gases in the Blood, 147. 3. Respiration, 149: The Nose, 149; Mouth Breathing, 150; The Trachea, 151 ; The Bronchii, 152; The Lungs, 152; The Thorax, 153; Inspiratory Movements, 154; Expiratory Move- ments, 155 ; Movements of Glottis, 156 ; Capacity of the Lungs, '57; Vital Capacity, 158; Frequency of Respiration, 158; Cause of Resjiiration, 158 ; Types of Respiration, 158; Chem- istry of Respiration, 159; Expired Air, 160 ; Ventilation, 161; Changes in the Blood due to Respiration, 163 ; Internal Respiration, 163. 7 CONTENTS. 4. Vital Heat, 164: Warm-blooded Animals, 165; Homoiothermal Animals, 165; Poikilothermal Animals, 165; Heat-unit, 166; ■ Sources of Heat, 166 ; Temperature of Different Parts of P>ody, 167; Temperature at Different Ages, 167; Daily Variations in Temperature, 168; Instances of High and Low Temperature, 168; Regulation of Temperature, 169. 5. Circulation of the Blood, 170: The Heart, 170; Right Auricle, 1 70; Right Ventricle, 170; Left Auricle, 171 ; Left Ventricle, 172; Cardiac Valves, 172; Pulmonary Valves, 173; Mitral Valve, 173; Aortic Valve, 174; The Arteries, 174; The Ca- pillaries, 174; The Veins, 175 ; Circulation of the Blood, 175 ; Cardiac Movements, 176; Movements of Blood during Systole and Diastole, 177; Shortening of the Heart, 180 ; Cardiac Impulse, 180; Papillary Muscles, 181 ; Cardiac Sounds, 1S2; Characteristics of Cardiac Sounds, 182; Causes of Cardiac Sounds, 182; Circulation in the Arteries, 183; Internal Fric- tion, 184; Arterial Pressure, 185 ; Rate of Flow in Veins, 185 ; Pulse- wave, 186; Circulation in the Capillaries, 187; Circula- tion in the Veins, 187 ; Compression of the Veins, 188; Aspira- tion of the Thorax, 188; Force of Gravity, 188. 6. Lymphatic System, 189: Lymphatic Vessels, 189; Lymphatic Glands, 190. 7. Ductless Gla7ids, 191 : The Spleen, 192; Functions of the Spleen, 192; Thymus Gland, 193; Thyroid Gland, 194; Su- prarenal Capsules, 194; Pituitary Body, 194. 8. The Skin, 195: Corium, 195; Epidermis, 196; Perspiratory Gland, 196; Office of Perspiration, 199; Sebaceous Gland, 199; Composition of Sebum, 200; Cerumen, 200; Hairs and Nails, 200 ; Functions of Skin, 200 ; Protection, 201 ; Excretion, 201 ; Sensation, 202 ; Respiration, 203 ; Regulation of Temperature, 203 ; Care of the Skin, 203 ; Baths, 204. 9. The Kidtieys, 204 : Urine, 207 ; Water, 209 ; Urea, 209 ; Source of Urea, 209; From Proteids of Food, 209; From Proteids of Tissue, 210; From Proteids of Blood and Lymph, 210; Uric acid, 211 ; Source of Uric Acid, 212; Hippuric Acid, 212; Creatinin, 212; Inorganic Constituents of Urine, 212; Coloring-matter of Urine, 214; Mucus of Urine, 214; Gases of Urine, 214. PAGE CONTENTS. 9 PAGE III. Nekvous Functions ^'5 General Considerations, 215. Termination of Ne,-ve-fibres, 220 : Corpuscles of Tacini, 221 ; Tactile Corpuscles, 221 ; End-bulbs, 221. Chemistry of Nervous Matter, 22\. Fjtndions of Ne)-ve- celis and Nerve-fibres, 221. Classification of Nerve-centres, 221: Conscious, 222; Reflex, 222; Automatic, 222; Relay, 222; Junction, 222. Classification of Nerve-fibres, 222. Efferent Nerves, 223: Motor, 224; Vaso-motor, 224; Secre- tory, 224; Trophic, 224; Inhibitory, 224. Afferent Ne>-ves, 224 : Sensory, 225 ; Nerves of Special Sense, 225 ; Thermic, 225 ; Excito-r'eflex, 225 ; Inhibitory, 225. Intcrccntral Nerves, 225.' Nen'estimuli, 226: Classification, 227; General, 227; Special, 227. General Arrangement of Nervous System, 227 : Certhro-spinal System, 22T. Spinal Cord, 228; Enlargement, 228; Fissures, 228; Section of Spinal Cord, 230; Minute Struc- ture,' 230; Tracts in the Cord, 231 ; Gray Matter, 232; Nerves, 233; Functions of Nerves, 233; Recurrent Sensibility, 233; Ganglia, 234 ; Connection of Nerve-roots with the Cord, 234 ; Conductor of Impulses, 235 ; Methods of Examination, 235 ; Conducting-paths, 236; Nerve-centres, 237; Reflex Action, 237. Special Centres, 240 : Musculo-tonic, 240; Respiratory, 240 ; Cardio-accelerator, 241 ; Vasomotor, 241 ; Sudorific, 24I ; Cilio-spinal, 241 ; Genilo-spinal, 241 ; Ano-spinal, 241 ; Vesico- spinal, 243; Trophic, 245; Various, 245. The Brain, 246: Weight, 246; Gray Matter, 246; White Matter, 246. Medulla Oblongata, 247: Fissures, 248; Funiculi, 248; Functions, 249; Nerve-centres, 249; Reflex Centres, 249; Control on Deglutition, 249; Control on Vomiting, 249; Cen- tral Vomiting, 250; Rumination, 250; Automatic Centres, 250; Respiratory Centre, 251; Resistance Theory of Respiration, 251; Asphyxia, 252; (l) Dyspnrea, 253; (2) Convulsion, 253; (3) Exhaustion, 253; (4) Inspiratory Spasm, 253; Cardio-inhib- itory Centre, 254; Vasomotor Centre, 254; Depressor Nerve- fibres, 255. Pons Varolii, 21^: Functions, 256. CerebellufU, 2^6: Functions, 257. Cerebrum, 258. Fissures, 259 : Fissure of Sylvius, 260; Fissure of Rolando, 261 ; Parieto-occiiiital Fis- sure, 261. Lobes of Cerebrum, 262: Frontal Lobe, 262 ; Pa- rietal Lobe, 263; Occipital Lobe, 263; Temiwro-sphenoiflal Lobe, 263; Central I-obe on Island of Reil, 263. Crura Cerebri, 263. Basal Ganglia, 264 : Corpora Striata, 264; Optic lO CONTENTS. PAGE Tlialami, 264; Tubercula, or Corpora Quadrigemina, 264. Mi- croscopical Structure of Hemispheres, 265: Gray Matter, 265; White Matter, 2^"]. Functions of the Cerebrtcm, 268; Mem- ory, 270; Reason, 270; Judgment, 270. Cerebral Localization, 271 : Centre for Motion, 272; Centre for Speech, 273; Sen- sory Areas, 273 ; Auditory Centre, 274 ; Optic Centre, 274 ; Olfactory Centre, 274 ; Functions of Corpora Quadrigemina, 274; Functions of Corpora Striata and Optic Thaiami, 274. Cranial Nerves, 275 : Olfactory Nerve, 276 ; Optic nerve, 277; Motor-oculi Nerve, 278; Trigeminus Nerve, 281; Ab- ducens Nerve, 289 ; Facial Nerve, 290 ; Auditory Nerve, 292 ; Glosso-pharyngeal Nerve, 293 ; Pneumogastric Nerve, 293 ; Spinal Accessory Nerve, 297 ; Hypoglossal Nerve, 298. The Senses, 299 : General Sensibility, 299 ; Sense of Tojich, 299 ; Sense of Pressure, 300 ; Sense of Temperature, 300 ; Sense of Pain, 300; Sense of Smell, 301 ; Sense of Taste, 303 : Conditions of Sense of Taste, 305 ; Sense of Sight, 306 : Sclerotic Coat of Eye, 306 ; Cornea, 307 ; Choroid, 307 ; Iris, 307 ; Cil- iary Muscle, 308; Retina, 309; Layers of Retina, 309; An- terior and Posterior Chambers of Eye, 310; Vitreous Body, 311 ; Crystalline Lens, 311; Suspensory Ligament, 312; Ar- terial Supply of Eye, 312; Physiology of Vision, 312; Accom- modation, 315 ; Phakoscope of Helmholtz, 317 ; Emmetropia, 318; Ametropia, 318; Myopia, 318; Hypermetropia, 319; Presbyopia, 319; Astigmatism, 319; Functions of Retina, 319; Movements of Eyeball, 321 ; Appendages of Eye, 321 ; Lachrymal Apparatus, 321 ; Meibomian Glands, 323. Sense of Hearing, 323: External Ear, 323; Middle Ear, 324; In- ternal Ear, 325; Vestibule, 326; Semicircular Canals, 326, 328; Cochlea, 326; Organ of Corti, 327; Mechanism of Hearing, 328; Eustachian Tube, 331. Sympathetic Nervous System, 331 : Sympathetic Ganglia and Nerves, 333; Functions of the Sympathetic, 334. IV. The Reproductive Functions 336 Reproductive Organs, 336. Genital Oigans of Male, 336 : Testes, 336; Spermatozoa, 336; Vas Deferens and Vesicula Seminalis, 339. Genital Organs of Female, 339 : Ovary, 339; Parovarium, 342 ; Ovum, 342 ; Fallopian Tubes, 343 ; Uterus, 345. Ovulation, 345 ; Menstruation, 347 : Composition of Menses, 348 ; Cause CONTENTS. II of Menstruation, 349; Relation between Menstruation and Ovulation, 350; Formation ol" Corpus Luteum, 351 ; Matura- tion of the Ovum, 351 ; Method of Fertilization, 354; Mem- branes of the Embryo, 358; Amnion, 358; Yolk-sac, 359; Allantois, 359; Chorion, 360; Placenta, 360. Circulation in the Embryo, 362 : Vitelline Circulation, 362 ; Placental or Foetal Circulation, 362; Changes in the Circulation at Birth, 365. LIST OF ILLUSTRATIONS. FIG. PAGE 1. Partial or Green-stick Fracture 38 2. Bone Tied in Knot 39 3. Starch-grains 43 4. Diagram showing Proportion of P^ood-stufis 86 5. Stomach and AHmentary Canal 93 6. Salivary Glands 98 7. Muscular Coat of Pharynx and (Esophagus loi 8. Cardiac Glands 105 9. Left Breast and Side, sliowing perA^ratioii of walls of stomach of Alexis St. Martin io6 10. Portion of Wall of Stomach, showing valvula.' conniventes ... 119 11. Vertical Section of Duodenum 120 12. Section of L&, grape-sugar, diabetic sugar) (CgHigOg) is normally found in the blood, chyle, lymph, and in very small amount in the urine. In the disease known as " dia- betes, mellitus" the quantity of dextrose in the blood and urine is very much increased. It is a substance of much interest, as it is in the form of dextrose that the carbohy- drates of the food find their way into the blood. In its pure state dextrose is colorless and readily crystallizes ; it is soluble in cold water, more so in hot water. It is dextro-rotatory, whence it derives its name. Dextrose reduces metallic oxides, a property which is made use of in determining its presence and in measuring its quan- tity. Tests based on this are Trommer's, Fehling's, Moore's, and others. Fermentations of Dextrose. — Dextrose undergoes vari- ous fermentations: (i) Alcoholic; (2) Lactic; and (3) Butyric. I. Alcoholic Fermentation. — In alcoholic fermentation, under the influence of yeast, the dextrose is decomposed and ethyl alcohol and carbonic.anhydride are produced CA RB OH YDRA TES. 49 (CgHigOg ^ 2C2HgO + 2CO2). This process is at the height of its activity when the temperature is 25° C. ; when above 45° C. or below 5° C. it ceases. When sugar is present in the solution to the extent of more than 15 per cent., the process of fermentation will be arrested, by the alcohol produced, before all the sugar has been decomposed. 2. Lactic Ferine ntatioii. — When milk sours, the sugar which it contains is converted into lactic acid, constitut- ing the lactic fermentation (CgHj.^Og = 2C3Hg03). This fermentation is not confined to milk-sugar, but may occur also with dextrose. This change is brought about by the presence of specific micro-organisms. It is stated that there exists also in the mucous membrane of the stomach an enzyme which can change lactose, and possibly dextrose, into lactic acid. 3. Butyric Fermentation. — When the lactic fermenta- tion is continued for some time, it is liable to pass into the butyric. This change is due to the action of a fer- ment (organized) upon the lactic acid. In the change hydrogen and carbonic anhydride are given off (2C3Hg03 = C3H7.COOH.+ 2C02H- 2H2). The optimum (most favorable) temperature for the lactic and butyric fermen- tations is from 35° C. to 40° C. When the diet consists largely of carbohydrates, both these fermentations may occur in the alimentary canal. LcBviilose (left-rotating sugar, fruit-sugar, or mucin- sugar) (CgHjjOg) is found in many fruits and in honey, and is said to occur occasionally in urine. It is not crystallizable. When cane-sugar is treated with dilute mineral acids, it is decomposed into equal parts of dextrose and laevulose. Cane-sugar has a dextro- rotatory action on polarized light, but when changed by 4 50 HUMAN PHYSIOLOGY. the acid the solution becomes laevo-rotatory, and the cane-sugar is said to be " inverted ;" hence the mixture of dextrose and laevulose is sometimes spoken of as " in- vert-sugar." As will be seen in the consideration of cane-sugar, " inversion " takes place in the alimentary- canal. Although in many respects laevulose is very similar to dextrose, still its action on polarized light serves to distinguish the two. Galactose (CgHj^Og). — When lactose is boiled with dilute mineral acids it is changed into dextrose and galactose : QaH^Pn + HP = CgHi A + CeHj A Lactose. Dextrose. Galactose. W hiosit, or muscle-sugar (CgHjaOg + 2H2O), has been found in the muscles, lungs, liver, spleen, kidneys, and brain, and pathologically in urine. It occurs also in beans and grape-juice. Because of its sweet taste and its chemi- cal composition it has been regarded as a carbohydrate, but as it has no rotatory action on polarized light, does not reduce metallic salts, and does not undergo the alcoholic fermentation, it is now regarded as belonging to the benzol series, and not as being a carbohydrate. Its ability to undergo lactic fermentation is very doubtful, 3. Cane-sugar Group. Saccharose, or cane-sugar (C12H22O11). — This sugar is not found in the human body, but it nevertheless plays an important part in the food of man. It occurs in the sugar-cane and in some other plants. It does not reduce metallic salts, it is soluble in water, it is dextro-rotatory, and it does not undergo alcoholic, but does readily un- dergo lactic, fermentation in presence of sour milk to CARB OH YD R A TES. 5 I which zinc oxide is added to fix the acid as formed. One of the interesting facts connected with saccharose is its property of " inversion," which, as we have seen, consists in its decomposition into equal parts of dextrose and laevulose, and to this mixture the name of " invert- sugar" has been given. This change is represented chemically as follows : C12H22O11 + H2O — CgHiaOg + CgHjgOg, Cane-sugar. Water. Dextrose. Lsevulose. and may be produced by the action of acid, as has been described under " Lsevulose." It takes place also in the small intestine under the influence of an enzyme of the intestinal juice — namely, invcrtiii. This enzyme exists also in yeast, where it has the same power as in the intestinal juice. Cane-sugar cannot be taken up as such by the blood, and when injected into an animal it is eliminated un- altered in the urine. When taken in as food it is absorbed, not as cane-sugar, but as invert-sugar, into which it has been changed. This inversion is most pro- nounced in the small intestine ; it is claimed that it may take place also in the stomach, and that there exists in the gastric juice an enzyme which has this power. Maltose (CjaHgaOu + HjO). — In considering malto- dextrin it was stated that starch-paste, under the in- fluence of diastase, passes into maltodextrin, and, if the action be continued, into maltose. When starch-paste or glycogen is treated with .saliva, malto.se is the principal sugar formed ; prolonged treatment with pancreatic juice will produce, beside the maltose, some dextrose. Al- though pancreatic juice, on the one hand, acts in this manner, still the tissue of the small inte.stine or an ex- tract of it has but slight action on the paste. On the 52 HUMAN PHYSIOLOGY. other hand, the pancreatic juice rapidly changes maltose into dextrose. Maltose, like cane-sugar, injected into the blood is eliminated as maltose in the urine. From this fact it would appear that maltose is not absorbed as such in the intestine, but as dextrose ; and it would further appear that, inasmuch as the tissue of the intes- tine has this converting" power, the change from maltose into dextrose occurs while the process of absorption is actually taking place, and not before. The action of pancreatic juice on starch in the intestine will be further discussed in the consideration of the ferments of this fluid Maltose is soluble in water, but it is less soluble in alcohol than dextrose. It is crystallizable, dextro-rota- tory, and reduces metallic salts. Maltose is distinguished from dextrose (i) by the difference in its rotatory power on polarized light, that of maltose being greater ; (2) by maltose having a less reducing power, as when boiled with Fehling's solution only two-thirds as much cuprous oxide is separated out with maltose as with dextrose ; (3) by Barfoed's reagent, which, consisting of a solution of cupric acetate in water to which acetic acid has been added, is reduced by dextrose, but not by maltose. Lactose (milk-sugar, sugar of milk) (C12H22O11 -f- HgO) is found only in milk, although it has been said to occur in the urine of lying-in women and in sucklings. It is crystallizable, less soluble in water than dextrose, and insoluble in alcohol. It is dextro-rotatory, its power in this respect being the same as that of dextrose. It does not reduce Barfoed's reagent. As above noted in speak- ing of galactose, lactose is changed into equal parts of sugar and dextrose by boiling it with dilute mineral acids. FATTY ACIDS, ETC. 53 Lactose by itself does not undergo alcoholic fermenta- tion with yeast, but an alcoholic fermentation does take place in milk, as when mare's milk is used for the prepa- ration of kumyss and kephir. This fermentation is due to special ferments, the nature of which is not fully un- derstood. In Russia kephir ferment may be purchased. Lactose readily undergoes the lactic fermentation. It is this change which takes place in the souring of milk due to the action of a ferment. The character of the change in the case of lactose is the same as described in dextrose and saccharose. Lactose injected into the blood is eliminated by the urine, as are saccharose and malt- ose, and like them must therefore be changed in the alimentary canal during the process of absorption. This conversion, which is probably into dextrose and galac- tose, takes place, as in the case of maltose, while the sugar is passing through the walls of the intestines. C. Fatty Acids, Fats, and Allied Substances. Formic Acid. — This acid has been obtained from the spleen, thymus gland, pancreas, muscles, brain, blood, and urine. Acetic Acid. — Fermentation of the food in the stomach may produce acetic acid. It has been found in normal and in diabetic urine. Acetone. — Diabetic urine yields acetone on distilla- tion ; it is this substance which gives the ethereal odor to such urine. The blood of persons suffering from diabetes has also been found to contain it, and to its presence has been attributed the fatal coma which comes on in some cases of this disease. Acetone has been found also in the urine of healthy children, and 54 HUMAN PHYSIOLOGY. it has been stated that it has been detected in their breath. Propionic Acid. — This acid is found in perspiration, in fermenting diabetic urine, and it has been found also in the contents of the stomach and in normal urine. Normal Butyric Acid is found in perspiration, in the contents of the large intestines, in the faeces, and in urine. It occurs also during lactic fermentation. Isobutyric Acid occurs in faeces, and is one of the products of the putrefaction of proteids. Caproic and Caprylic Acids are constituents of the perspiration, and, with Capric Acid, are found also in butter. Neutral Fats are palmitin, stearin, and olcin. They are regarded by chemists as compounds of glycerin and the respective fatty acid. Thus the acid of palmitin is palmitic ; that of stearin, stearic ; and that of olein, oleic. They are characterized by being insoluble in water, slightly soluble in alcohol, and very soluble in ether and chloroform. All fats are mixtures of the three vari- eties, the difference in the consistency of any given fat depending upon the proportion in which the neutral fats are present. Thus in the more solid fats, such as suet, stearin predominates, while in the fluid fats it is olein which is in excess. There is a difference also in the proportions of these substances in the fats of different animals. Human fat and that of carnivorous animals contain palmitin in excess over stearin and olein, while in that of the herbivora stearin predominates, and in that of fishes, olein. Source of Fat in the Huniari Body. — Human fat is derived from the fats, the carbohydrates, and the proteids of the food. In fatty meats, nuts, eggs, milk, and other FATTY ACIDS, ETC. 55 food more or less fat exists as a constituent, and un- doubtedly contributes to the formation of the fat of the body. Food containing starch and sugar is also fatten- ing in its nature, and persons who have an excess of fat are placed upon a diet containing a minimum of these ingredients. Herbivorous animals — the cow, for instance — rely entirely upon vegetable food for their support, and it is the carbohydrates which this contains that are converted into the fat of their milk or that which covers their muscles. That proteid food will also produce fat is shown by the amount of the latter which carnivorous animals put on. Offices of Fat. — The offices which fat subserves in the human body are manifold : (i) It protects the underlying parts from injury, as in the palm of the hand and the sole of the foot ; (2) it serves as a lubricator, as in the seba- ceous matter poured out upon the skin, which keeps it soft and pliable ; (3) it acts as a non-conductor of heat, aiding in the retention within the body of the vital heat, which would otherwise be lost so rapidly as to produce injur- ious results ; (4) it serves as a reservoir when the sup- ply of food is cut off or diminished ; thus in wasting diseases the fat deposited in various parts of the body is absorbed and contributes to its nutrition ; (5) it is a source of energy and of heat through its oxidation. Important properties of fats, besides those already mentioned, which deserve special consideration, are two — that of forming a soap and that of forming an emul- sion. Saponification. — Fats are said to be saponifiable ; that is, capable of being converted into a soap. If a fat be heated with a caustic alkali under pressure, it splits up into glycerin, and a fatty acid which unites with the $6 HUMAN PHYSIOLOGY. alkali, the compound being a soap. Thus, if palmitin be the fat selected and the alkali be sodium, the palmitic acid, uniting with the sodium, would form sodium pal- mitate, a soap. If potassium were the alkali, the product would be potassium palmitate ; similarly, stearin would form a stearate, and olein an oleate. The sodium soaps are hard, and those of potassium are soft. In the dis- cussion of intestinal digestion it will be seen that the process of saponification takes place in the small intes- tine, and that the soap there formed aids in the import- ant functions of that portion of the alimentary canal, Emulsification. — Besides being saponifiable, fats are also emulsifiable — capable of forming an emiJlsion. If oil and water be poured into a test-tube, they will at once separate, the oil floating on the water. If the mouth of the tube be closed by the thumb and the tube firmly shaken, the oil and water will form a milky mix- ture, but will separate again when the agitation ceases ; if a small amount of an alkali be added and the tube be again shaken, the separation will not take place as before, but the milky appearance will continue for some con- siderable time. If a drop of the mixture be placed under the microscope, it will be found that the oil-globules have been broken up into an exceedingly fine state of subdi- vision, some of the particles being too small to measure even with a very high magnifying power. This more or less permanent subdivision and suspension of the oil-glob- ules constitutes an emulsion. The change is not a chem- ical one, but is purely physical. A similar process takes place in the small intestine during intestinal digestion, and is a necessary preliminary to the absorption of fat. Lactic Acid is found in the alimentary canal, especially when large quantities of carbohydrates have been in- PRO TEWS. 57 gested. It occurs also in muscles, and has been said to exist in the nerve-cells of the brain. It has already been mentioned as the product of lactic fermentation. Sarcolactic Acid occurs in blood and in muscles ; to the latter it gives their acid reaction. Cholesterin. — Chemically, this substance is an alcohol, the only one found free in the human body. It occurs in the bile, in the blood, in white nervous matter, and in the crystalline lens. It is a constituent also of the yolk of ^ZZ^ of wheat, Indian corn, peas, and beans. It has some characteristics of the fats, such as insolubility in water and solubility in ether and chloroform, but it is not saponifiable, and is in other most important respects un- like them. It is classified here more for purposes of con- venience than for any affinity with other members of the class. D. Proteids. These ingredients compose the principal parts of the muscles, the glands, and the nervous tissues, and of the solids of the blood they are the most important. Their percentage composition is as follows : Carbon . . . .50.-55. Hydrogen . . 6.9- 7.3 Nitrogen . . .15.-18. Oxygen . . .20. -23.5 Sulphur 0.3- 2. When proteids are burned, there is found in the ash a certain quantity of salts — from the ignition of egg-albu- min, for instance, chlorides of sodium and potassium result, and salts of calcium, magnesium, and iron in small quantities. It is still undecided whether these salts are integral parts of proteids or impurities. Reactions of Proteids. — The presence or absence of proteids is determined by certain reactions, three of which are given : 58 HUMAN PHYSIOLOGY. Xanthoproteic Reaction. — When proteids are heated with strong nitric acid, they turn yellow, the color be- coming deep orange on the addition of ammonia, caustic soda, or potash. Millo7i's Reaction. — Proteids when heated with Millon's reagent give a white precipitate which becomes brick- red on cooling. This reagent is prepared by dissolving mercury in nitric acid and adding water. The precipi- tate which forms is allowed to settle, and the fluid is the reagent. Very small amounts of proteids give the red color without the precipitate. Piotrowski s Reaction. — When a proteid is mixed with an excess of concentrated solution of sodium hydrate and one or two drops of a dilute solution of cupric sul- phate, a violet color is produced which becomes deeper on boiling. Classification. — The proteids are classified as follows : XT ^- ii_ • f Egg-albumin. I. Native albumms \ c I berum-albumm. Acid-albumin. Syntonin. Alkali-albumin. Casein. Crystallin. Vitellin. Paraglobulin. 3. Globulins \ Serum-globulin. Fibrinogen. Myosin. Globin. 4. Albumoses. 8. Intermediate products. 5. Peptones. 7. Enzymes. 9. Waste products. 6. Albuminoids. 10. Coloring matters. 2. Derived albumins P ROTE IDS. 59 1. Native Albumins. Native albumins are found in the solids and fluids of the body. They are soluble in water, and are coagu- lated by heat at from 65° to 73° C, coagulation taking place more readily if dilute acetic acid be present. They are not precipitated by alkaline carbonates, by chloride of sodium, the solution of neutral salts in general, or by dilute acids. Egg- Albumin. — As its name implies, egg-albumin is obtained from the white of egg. If much of it be taken in the food or if it be injected into the blood, part of it appears in the urine. When shaken with ether it is pre- cipitated. Nitric acid, heat, and the prolonged action of alcohol coagulate egg-albumin, and mercuric chloride, nitrate of silver, and lead acetate precipitate it, forming insoluble compounds. Serum- Albumin. — Serum-albumin occurs in the blood, in lymph, in chyle, in milk, and in some pathological fluids. When albumin is found in the urine it is- gener- ally serum-albumin. Serum-albumin differs from egg- albumin in not readily being coagulated by alcohol or precipitated by ether, and in not appearing in the urine when injected into the blood. 2. Derived Albumins. The members of this group are sometimes spoken of as " albuminates." They are insoluble in distilled water and in dilute neutral saline solutions, but are soluble in acids and alkalies. Their solutions are not coagulated by boiling. Acid- Albumin. — When a solution of either of the native albumins is treated with a dilute acid — hydrochloric acid, 60 HUMAN PHYSIOLOGY. for instance — it is converted into acid-albumin. In this conversion it undergoes important changes. Its solution is not coagulated by heat, and when it is neutralized the proteid is precipitated. The conversion from the native to the acid-albumin is gradual, and is hastened by heat, care being taken that the temperature is not sufficiently high to coagulate it. Globulins are likewise converted into acid-albumins by the same means, but more readily, while coagulated proteids or iibrin require the acid to be concentrated. Each proteid produces its own special acid-albumin, although the difference between them is very slight. Syntonin. — Syntonin is the special acid-albumin which results from the action of acids on myosin — the globulin which occurs in muscles. It is of special interest as be- ing the acid-albumin formed in the stomach during the digestion of muscular tissue. It is soluble in lime-water, and this solution is partially coagulated by boiling ; it is insoluble in acid sodium phosphate (NaHgPOJ, while other acid-albumins are soluble. It differs from alkali- albumin in that when acid sodium phosphate is present and an alkali is added it does not pass into solution until the whole of the acid phosphate salt has been converted into the neutral phosphate (NagHPO^), while alkali-albu- min is soluble before this change takes place. Alkali- Albumin. — If a native albumin be treated with a dilute alkali in the manner described in the treatment with a dilute acid, it will be converted into alkali- albumin, as in the former instance when an acid was used it was changed into acid-albumin. The alkali-albu- min, like the acid-albumin, is not coagulated by heat; when neutralized the proteid is precipitated, and the precipitate, which is insoluble in water and in neutral PRO TEWS- 6 1 solution of sodium chloride, is dissolved by dilute acids or alkalies. Some writers have regarded acid- and alkali-albumin as differing from each other only in that in the one case the proteid is united with an acid, and in the other case with a base ; but more recent investigations seem to show that, though closely related, they are in reality distinct, and that what was said of the product of the action of acids on proteids is probably true of that of alkalies — namely, that each proteid yields its own product, although as yet they cannot well be distinguished. Acid- albumin can be converted into alkali-albumin by strong alkalies, but alkali-albumin cannot be changed into acid- albumin by the action of acids. In 1838, Mulder de- scribed a substance which he called "protein." This designation is now abandoned. It has been suggested that what he called " protein " might have been alkali- albumin. Casein exists in human milk in from 0.18 to 1.90 per cent., the mean being 0.63 per cent., and in that of the cow in from 1.17 to 7.40 per cent, 3.01 per cent, being the mean. This derived albumin occurs only in milk. It has been suggested that this physiological ingredient should be called " caseinogen," and that the term " case- in" should be restricted to the curd formed when milk coagulates under the influence of rennin, the ferment in rennet. Inasmuch as we speak of " fibrinogen " and " fibrin," the former before and the latter after coagula- tion, the suggestion is well worthy of consideration as tending to simplification. Casein is precipitated by acids and by rennet at 40° C, and it contains 0.847 P^^ cent. of phosphorus. When pure it is a fine snow-white powder insoluble in water, but is soluble in alkalies, 62 HUMAN PHYSIOLOGY. carbonates and phosphates of the alkahes, hme- and baryta-water. As has already been stated, casein clots under the in- fluence of the enzyme rennin, but alkali-albumin, which has been regarded by some as identical with casein, does not. Milk from which casein has been removed by pre- cipitation still contains a small amount of a coagulable proteid — lactalbuniin — very similar to serum-albumin, but not identical. Upon the surface of milk exposed for some time to a temperature above 50° C. a pellicle forms, which is stated by some chemists to be casein, by others lactalbumin. This formation takes place more rapidly if a stream of air be blown over the surface of the milk. What has been said of casein applies especially to that obtained from cow's milk. The differences between cow's milk and human milk, so far as regards casein, are as follows : I. Human milk, when it clots at all with ren- nin, does so less firmly than cow's milk ; 2. Acids very imperfectly precipitate the casein from human milk : to do this completely magnesium sulphate must be used to the point of saturation; 3. The casein of human milk is less soluble in water than that of cow's milk. 3. Globulins. Globulins are insoluble in distilled water, but are solu- able in dilute saline solutions, as, for instance, i per cent, sodium chloride, in very dilute acids and alkalies. If the saline solutions be saturated, the globulins will be precipitated. If the acid or the alkali be not dilute, but strong, the globulins will be converted into acid-albu- min or into alkali-albumin. PROTEIDS. 63 Crystallin (globulin) is the globulin of the crystalline lens. Vitellin is the proteid of the yolk of eggs. An identi- cal globulin has been obtained from vegetable proto- plasm. In the Q.^%, vitellin is associated with lecithin, and indeed up to the present time vitellin has never been obtained free from lecithin. It has been said to occur in the chyle and in the amniotic fluid. Paraglobjilin {?,Qx\xvc\-^<:kivX\Vi\ fibrino-plastin ; serum- casein) exists in blood-plasma to the amount of from 2 to 4 per cent., and also in lymph, in chyle, and in serous fluids like the fluid in hydrocele. In urine there has been found a globulin which is apparently identical with paraglobulin. Fibrinogen. — The plasma of blood contains fibrinogen, as do also chyle and serous fluids. Like paraglobulin, it is contained in the fluid of hydrocele. It is of great physiological interest, as the clotting of blood consists in the conversion of fibrinogen into fibrin. For purposes of study fibrin is usually obtained by whipping blood with twigs or with wires. The material that clings to these is fibrin, together with some of the white and red corpuscles of the blood, which are entangled in the meshes of the fibrin. When washed in water the red coloring-matter is washed out and the fibrin is colorless. Fibrin is insoluble in water and in dilute saline solutions. In dilute acids — as, for instance, hydrochloric acid — it swells up and becomes transparent. If it be left in the acid for a long time or if the temperature be raised to 40° C, it is changed into acid-albumin. Myosin. — When a muscle passes into the condition known as rigor mortis or " cadaveric rigidity," this change is due to a coagulation or clotting of the material of 64 HUMAN PHYSIOLOGY. which the muscle consists, the clot being myosin. It has been suggested that this substance should, before coagulation, be called "myosinogen," and after coagula- tion "myosin," just as "fibrinogen" and "fibrin" are spoken of. It will be remembered that an acid acting on myosin converts it into syntonin. Globin. — When exposed to the air for a sufficient time haemoglobin, the red coloring-matter of the blood, decomposes, and globin is one of the products. Globin is very slightly soluble in dilute acids, alkalies, and solu- tions of sodium chloride, but is converted into acid- and alkali-albumin by strong acids and alkalies respectively. 4. Albumoses. If a proteid be acted upon by pepsin in the presence of 0.2 per cent, of hydrochloric acid, a portion of it is- changed into an acid-albumin. Some writers regard this as syntonin, but the tendency at the present time is to apply the name of " syntonin " only to that partic- ular acid-albumin formed by the action of acid on myosin. It has also been spoken of as " parapeptone," but the two are not identical, as is evident from the fact that parapeptone is incapable of being converted into peptone by the action of pepsin. Subsequently, if the action of the pepsin be continued, this acid-albumin disappears and parapeptone and albumoses are produced. Still later in the process these albumoses are changed into peptones. If instead of pepsin and hydrochloric acid the proteid be treated with trypsin, one of the enzymes of pancreatic juice, and a 0.25 per cent, solution of sodium carbonate, alkali-albumin is formed, and later albumoses, which are changed into peptones, some of which still later are con- PROTEIDS. 65 verted into leucin and tyrosin. The albumoses, then, are intermediate products in the conversion of proteids into peptones. The theory of Kiihne is that in the diges- tion of a proteid two albumoses are formed, anti-albu- mose and hemi-albumose. Anti-albumose is practically not distinguished from acid-albumin or syntonin ; the further action of the digestive ferment converts it into antipeptone. Hemi-albumose is identical with what has been called " propeptone." It occurs occasionally in the urine, and is found also in the marrow of bones and in cerebro- spinal fluid. Under the further influence of the ferment it passes into hemipeptone. Hemi-albumose is regarded by some writers as being composed of four forms of albumose : i, protalbumose ; 2, deutero-albumose ; 3, hetero-albumose ; 4, dysalbumose ; but this is not yet determined. This subject is further discussed in treat- ing of Digestion. Albumoses have of late assumed a position of great importance, for the reason that they have been found to possess peculiar properties which were never before sus- pected. The poison of the cobra, regarded as the most virulent of animal poisons, is an albumose. When cer- tain albumoses are injected into the blood its coagula- bility may be destroyed and death may result. This action was formerly attributed to peptones, but it is now believed to be due to the albumoses in the peptones. Immunity from certain diseases has been brought about by the protective influence of certain albumoses which have been produced by the action of the germs of those diseases, so that in this group of substances there is a variety of members, some beneficial and some poisonous. Albumoses also occur in plants, as wheat and the papaw. 66 HUMAN PHYSIOLOGY. 5. Peptones. In no part of physiological chemistry has more valu- able work been done than in the study of this group of physiological ingredients, one important result being to show that what have been described as peptones are in reality mixtures of albumoses and peptones. True peptones are very soluble in water, and are not precipitated by boiling nitric acid, by acetic acid, or by potassium ferrocyanide. They are, however, precip- itated from neutral or feebly-acid solutions by mercuric chloride, tannic acid, bile-acids, and phospho-tungstic acid. They give Millon's and the Biuret reaction, are very diffusible, and are laevo-rotatory. In stating that peptones are very diffusible it must also be stated that this is true when they are compared with other proteids, but when the comparison is made with crystalline sub- stances, such as sodium chloride, peptones are not very diffusible. As has already been seen, antipeptone is the peptone which results from the action of the digestive ferments — pepsin or trypsin — on anti-albumose, and hemipeptone is that which results from their action on hemi-albumose. The latter yields leucin and tyrosin with the further action of trypsin ; the former does not, though the action of the ferment be prolonged. E. Albuminoids. The albuminoids resemble the proteids in their com- position ; some of them contain no sulphur. They are neither crystallizable nor diffusible. Mucin. — Mucus, the product of mucous glands, owes its peculiar ropy consistency to the ingredient mucin. ALBUMINOIDS. 67 Mucin contains carbon, hydrogen, nitrogen, and oxygen, but no sulphur. It is derived from the proteids, and exhibits Millon's and the Xanthoproteic reactions. When treated with mineral acids an acid-albumin is formed, and at the same time there is produced a carbohydrate which may yield, when treated with acid, a reducing sugar. On account of these two products which result from the action of an acid on mucin, it has been regarded by some, although probably incorrectly, as a mixture of a proteid and a carbohydrate. It has been assumed that the mucin of different fluids is the same substance, but that it is slightly modified in each instance. This has not been proved ; indeed, the weight of evidence rather favors the view that there are several mucins, differing in certain particulars. Mucin is an ingredient of bile, but is not found in that fluid while it is still in the liver. It is added to the bile while in the gall-bladder, and is secreted by the lining membrane thereof Mucin dissolves in water and is precipitated by acetic acid and by alcohol. Gelatin. — When connective tissues are boiled in water for a considerable time, especially in a Papin digester, they yield a substance which is called " gelatin." It has been assumed that there is in bone a substance which has been named " ossein," and that in the ordinary connec- tive tissues there is another substance called " collagen ;" moreover, that the gelatin is not an original constituent of the tissues, but is the product of these two substances after the boiling. This assumption has much to sustain it, for if tendons be treated with trypsin, everything will be dissolved but the collagen, and if bones be treated with cold dilute acid, the salts will be dissolved and the ossein will remain. These two substances — collag^en 68 HUMAN PHYSIOLOGY. and ossein — are insoluble in water, in saline solutions, in cold dilute acids, and in alkalies. If, however, they be boiled in water for a long time, they are changed into gelatin, which when it cools forms a jelly or " gela- tinizes." When this gelatin is dry it forms a transparent brittle substance which is familiar as glue or as the gelatin used in food. Gelatin is insoluble in cold water, but swells up in it, and, when the water is warmed, dissolves. It is precipitated by tannic acid and mercuric chloride, but not by acids, by alum, nor by the salts of silver, iron, copper, or lead. Its percentage composition is carbon, 50.76 ; hydrogen, 7.15 ; oxygen, 23.21 ; nitrogen, 18.32 ; sulphur, 0.5. The sulphur is believed to be due to impurities, and is not regarded as a constituent of pure gelatin. By compar- ing this analysis with that of the proteids the difference will be seen. If collagen be boiled in water for a longer period than is sufficient to convert it into gelatin, the latter will be converted into gelatin-peptones. This same change takes place if gelatin be treated with pepsin in presence of an acid or with trypsin, and the same conversion takes place in the stomach. Gelatin-peptones are more solu- ble than gelatin, and are diffusible. It will be remem- bered that in noting the action of the enzymes, pepsin and trypsin, upon proteids, albumoses were formed as intermediate products before the final formation of pep- tones. Likewise, when gelatin is changed into gelatin- peptones there are intermediate products, to which the name of" gelatoses" has been given. Gelatin is digested and absorbed in man and is a valuable food-stuff, but does not supply the tissues with nitrogen, as its nitrogen cannot be built up into that of a proteid. ALBUMINOIDS. 69 Chondrin. — As gelatin is looked upon as a product of the prolonged boiling in water of collagen and ossein, so chondrin is regarded as resulting from a similar treat- ment of " chondrigen," the matrix of hyaline cartilage. Chondrigen is insoluble in water, but when boiled in a Papin digester it is dissolved gradually and is trans- formed into chondrin, which gelatinizes on cooling. The percentage composition of chondrin is carbon, 50.9; hydrogen, 7.1; nitrogen, 14.9; oxygen, 29; sul- phur, 0.4. It is precipitated by acetic acid, which does not redissolve the precipitate. Mineral acids in small amounts produce a precipitate which dissolves in excess of the acids. Chondrin is also precipitated by alum and by the salts of silver, iron, and lead. There is some evidence showing that chondrin is a mixture of mucin and gelatin, but this combination is not conclusively determined. Elastin. — This substance is an ingredient of elastic tis- sue, as, for instance, the ligamentum nuchae. Its per- centage composition is carbon, 55.6 ; hydrogen, 'j.'j ; nitro- gen, 17.7; oxygen, 21.1 ; it does not contain sulphur, Elastin is soluble only when boiled in strong alkalies at 100° C. If boiled with sulphuric acid at 100° C.,it is not only dissolved, but is also decomposed, yielding from 30 to 40 per cent, of leucin and 0.25 per cent, of tyrosin. Elastin is digested under the influence of pepsin in an acid, and trypsin in an alkaline medium, but it is doubtful whether elastin passes into the stage of peptone, but rather does not go beyond the intermediate stage of what may be termed " elastoses." Keratin. — This substance is found in all horny tissues, such as hair, nails, and epidermis. Its percentage com- position is carbon, 52.5; hydrogen, 7; nitrogen, 17; JO HUMAN PHYSIOLOGY. oxygen, 25 ; sulphur, 5. Keratin is dissolved by alka- lies, and the sulphur forms sulphides of the metals. It is unaffected by the action of pepsin or trypsin. F. Enzymes. There are two classes of enzymes or ferments : (i) or- ganized ferments, of which yeast is an example, and (2) unorganized or soluble ferments, of which pepsin is an example. It has been proposed to limit the term " fer- ment " to the organized class, and to denominate the changes which its members cause in substances upon which they act as " fermentation," while to the soluble or iinoj'ganized class to apply the name of " enzyme," and to give to the process for which its members are responsible the term "zymolysis." There will here be discussed only the unorganized ferments or enzymes. Some of the enzymes on analysis have been found to be , very similar in their composition to the proteids, although containing less carbon. This similarity is shown in the percentage composition of trypsin. The unorganized enzymes are soluble in water and in glycerin, and are precipitated by an excess of absolute alcohol, but are not diffusible. Minute quantities of unorganized en- zymes under proper conditions will bring about zymo- lytic changes in considerable quantities of the substances upon which they act, apparently without diminishing. The conditions under which they act vary for each enzyme, but as a rule high temperatures destroy and low temperatures inhibit, while for each there is a tem- perature at which its action is the most pronounced ; this is called the " optimum " temperature. Thus for pepsin the optimum temperature is from 35° to 40° C, while below 1° C. its action ceases, as it does also at ENZYMES. 71 70° C, while boiling permanently destroys it. It has been determined, however, that when perfectly dry the enzymes may be heated to 160° C. without destroying their power. An interesting fact also connected with the enzymes is, that when they have produced a considerable amount of their product their action is diminished, and that if this new product accumulates still more, the zymolytic action of the enzymes may be brought to an end, although their power to act would still be present if these products were removed. In some instances the enzyme is not the direct product of the cells, but the cells form what is termed a " zymogen," which is afterv/ard converted into the enzyme. Each zymogen is named from the enzyme which it produces : thus the zymogen of trypsin is " trypsinogen," that of pepsin is " pepsinogen," etc. It is an interesting and valuable fact that chloroform in- hibits the action of the organized ferments, but does not interfere with that of the unorganized. As it is very im- portant to have a clear idea of the meaning of certain terms which occur repeatedly in the discussion of the enzymes and their action, these terms will here be de- fined — namely : Amylolytic Enzyme. — The conversion of starch into sugar is an amylolytic change, and an enzyme which has the power of producing this change is an amylolytic enzyme. Diastatic or Diastasic Ensymc. — There exists in barley an enzyme, diastase, which has the power of changing starch into sugar ; the change itself, and also the en- zyme, are spoken of as diastatic or diastasic. It will be seen, therefore, that amylolytic, diastatic, and diastasic are synonymous. 72 HUMAN PHYSIOLOGY. ' Proteolytic Enzyme. — The conversion of a proteid into a peptone is a proteolytic change, and any enzyme which causes it is a proteolytic enzyme. Hydrolytic Enzyme. — It is now generally accepted that in the conversion of starch into sugar and of proteids into peptones the change consists in the assumption of a molecule of water; thus, Starch. Water. Sugar. This change is called " hydrolysis," and the action is said to be hydrolytic. Both amylolytic and proteolytic changes are hydrolytic. Indeed, there are reasons for believing that the enzymes produce their action in every instance by causing the substances upon which they act to unite with water. Ptyalin. — This enzyme is found in saliva, and is one of its important constituents. It is an intere.sting fact that from many of the tissues and fluids of the body a similar enzyme may be obtained. This is especially marked in the pig. When ptyalin is obtained from saliva it is a white powder which dissolves in water and converts starch into maltose. This action mark- edly takes place in solutions that are neutral. So far as known, ptyalin is formed directly by the cells, and there is no intermediate stage of a zymogen. If such a substance should be discovered, it would, by analogy, be called " ptyalinogen." Ptyalin is an amylolytic enzyme, but acts only on cooked starch. Amylopsin. — This substance is also an amylolytic en- zyme, and acts on both cooked and raw starch. Its action is more rapid than that of ptyalin, and further it ENZYMES. 73 changes the maltose into dextrose, in which form sugar is absorbed during the digestive process. Pepsin. — This substance is the enzyme of the gastric juice, and is proteolytic in its action. There exists for pepsin a true zymogen, pepsinogen, which is formed by the cells of the gastric glands, and under the influence of the hydrochloric acid of the gastric juice the pepsin- ogen becomes pepsin. Pepsin exerts its proteolytic action only in the presence of an acid, of which, for experi- mental purposes, hydrochloric acid, 0.2 per cent., is the best. Trypsin. — This substance is the proteolytic enzyme of pancreatic juice. Considerable study has been made of trypsin, its composition being given as follows : carbon, 47.22 to 48.09 ; hydrogen, 7.15 to 7.44; nitrogen, 12.59 to 13.41 ; sulphur, 1.73 to 1.86. Trypsin acts most promptly in the presence of an alkali, but it will act also in neutral solutions or even when 0.012 per cent, of hydrochloric acid is present ; but its action ceases when free hydrochloric acid is present to the amount of o. i per cent. In connection with this enzyme it is interesting to note that the contents of the small intestine, into which the pancreatic juice is discharged, are not invariable in their reaction. Sometimes they are alkaline, at other times neutral, and they may even be acid. When this acidity exists in the upper part of the small intestine, it is due to the hydrochloric acid produced by the stomach, but when it is found elsewhere it is attributable to lactic or butyric acid formed as a result of fermentation of the carbohydrates of the food. It is claimed that a small amount of lactic acid, less than 0.05 per cent., is an aid to the proteolytic action of trypsin, but that more than 74 HUMAN PHYSIOLOGY. this percentage puts a stop to the process. Trypsin has its zymogen, which is called " trypsinogen." Pialyn (Steapsin). — This enzyme is sometimes spoken of as the " fat-splitting ferment," because its action is to decompose the neutral fats, the result being a fatty acid and glycerin. The optimum temperature for the action of pialyn is 40° C, and the most favorable reaction is a slightly alkaline one. Rennin. — In cheese-making the casein of milk is co- agulated by rennet, which is an infusion in brine of the fourth stomach of the calf This coagulating property of rennet is due to an enzyme to which has been given the names of " rennet ferment," " milk-curdling ferment," and " rennin." Rennin may be extracted from the mucous membrane of the stomach of most animals, including man. The zymogen of rennin is denominated " ren- ninogen." Fibrin-ferment. — The clotting of blood is due to the change of its fibrinogen into fibrin under the influence of an enzyme, fibrin-ferment. The theory that this clot- ting is produced by the breaking down of the white cor- puscles seems to be the most reasonable one at the pres- ent time. In the consideration of the coagulation of the blood this subject will again be referred to. Muscle-ensynie. — The clotting of the plasma of muscle is attributed to this enzyme, which is regarded as dis- tinct from fibrin-ferment. It is sometimes spoken of as " myosin-ferment." G. Intermediate Products. There exists in the body a class of substances which, after they are formed by the tissues, perform some office in the economy of the body, but what this office is, exactly, INTERMEDIATE PRODUCTS. 75 is not understood. These substances are not permanent, but undergo changes into other forms, and are therefore known as " intermediate products " or " by-products." Sodium GlycocJiolate (CagH^jNOgNa) is one of the in- gredients of the bile of man, of the ox, and of other animals, only traces of it being found in the carnivora, some authorities claiming it to be absent. This salt con- sists of glycocholic acid united with sodium. Glycocholic acid is composed of glycin and cholalic acid, and is some- times found in the urine in jaundice. Sodium Taurocliolate {C26H45NS07Na) and sodium glycocholate are known as the " bile-salts." Sodium taurocholate, which is composed of taurocholic acid and sodium, exists in both human and ox bile. In the bile of carnivora it exists without the glycocholate. Tauro- cholic acid is composed of taurin and cholalic acid. Cholalic acid or cholic acid, which is produced by the decomposition of the bile-acids, is formed in the small intestine, and still more abundantly in the large intestine. Taurocholic acid precipitates ordinary proteids from their solutions, but has no such action on peptones. When the contents of the stomach, therefore, enter the small intestine, the proteids are thrown down and the enzymes can act upon them more readily, while the peptones are absorbed. This acid is said also to possess antiseptic properties to a marked degree. Petterikofer s Test for Bile-acids. — This test consists in the production of a cherry-red color, which changes to a purple, when a few drops of a 20 per cent, solution of cane-sugar are added to a solution of bile-acids or the biliary^ salts and followed by concentrated sulphuric acid. Other substances, such as morphine and salicylic acid, will give the same color reactions, so that to exclude them 'j6 HUMAN PHYSIOLOGY. it is necessary to evaporate to dryness the fluid to be ex- amined, to extract with absolute alcohol, and to precip- itate by the addition of ether in excess. To this precip- itate, when dissolved in water, the test may be applied as already indicated. Lecithin (C44H9QNPO9). — This ingredient is sometimes known as " phosphorized fat." It is a constituent of the red and white blood-corpuscles, of the bile, brain, nerves, semen, and pus. It occurs also in yeast and in other vegetable cells, in the yolk of ^^%, and in milk. Cerebrin (Cj^NggNOg). — This substance is found in the brain, in nerves, and in pus-corpuscles. Protagon (CigoHgogNgPOgg). — This substance is also found in the brain. It is still undecided whether pro- tagon is an independent substance or is a mixture of lecithin and cerebrin, although evidence is accumulating which indicates that it is not a mixture. H. Waste Products. This class includes substances which are the result of the disintegrative changes that occur in the tissues of the body and in the food. After being formed they are eliminated, being of no use. Krcatin (QHgNgOg). — This substance is one of the characteristic ingredients of the muscles, and in the metabolism of these tissues ultimately becomes con- verted into urea. Kreatin occurs also in nervous tissues. It is not a constituent of urine, although it is sometimes so regarded. When found in this fluid it has doubtless been produced from kreatinin by the methods used to obtain it from the urine. Kreatin readily becomes con- verted into kreatinin by giving up a molecule of water. Kreatinin (C^H^NgO). — A comparison of the formulae WASTE PRODUCTS. 7/ of kreatin and kreatinin shows that the latter is a de- hydrated form of the former. Kreatinin readily unites with water, forming kreatin ; it exists in the urine in pro- portions which vary according to the amount of proteids eaten — from 0.5 to 4.9 grammes per diem. Urea ((NH2)2CO) is the principal waste product in the urine of mammals, although it occurs in small amounts in that of birds, especially when they are fed on meat., In the urine of man it is present to the amount of 2.5 to 3.2 per cent, 30 grammes on an average being daily excreted. In blood it occurs in the proportion of 0.025 per cent., and it may also be obtained from lymph, per- spiration, and from the liver. Urea is soluble in water and alcohol, but insoluble in anhydrous ether. Under the influence of bacteria, urea undergoes alkaline fer- mentation, in which two molecules of water are taken up and carbonate of ammonia is formed. This change is expressed by the formula (NH2)2CO -f 2H2O = (NHJ^CO^ Urea. Water. Carbonate of ammonia. The source of urea is from the kreatin of muscular tissue, and the liver is, in all probability, the organ in which take place the transformations that result in its production, so that when this organ is diseased there is likely to be a diminished amount of urea excreted. Uric Acid (C5H4N4O3) is found in small quantities in human urine, only from 0.2 to i gramme being daily ex- creted. This acid is, however, abundant in the urine of birds and of reptiles. It is found constantly in the spleen, and it has been found also in the lungs, the heart, the pancreas, the brain, and the liver. The calculi which 78 HUMAN PHYSIOLOGY. form in the urinary organs frequently consist of uric acid or of salts formed from it. The so-called " concretions " which form in the joints of persons suffering from gout are composed of uric acid. The principal salts into the formation of which uric acid enters are sodium, potas- sium, and ammonium urates. In the production of urea uric acid is regarded as one of the steps. QH.NA + H,0 + O = QH^NA + (NH2),CO Uric acid. Water. Oxygen. Alloxan. Urea. Hippiiric Acid (C9H9NO3). — This ingredient of human urine is excreted to the amount of but from o.i to i.O gramme per diem. It is much more abundant in horses and in other herbivora. Leiicin (C6Hm(NH2)O.OH) occurs in the pancreas, spleen, thymus, thyroid, salivary glands, and liver. It is sometimes found in urine, especially in certain diseases of the liver, such as acute yellow atrophy. Leucin occurs also in the bulbs, tubers, and seeds of some plants. It is found in the small intestine during the digestion of proteids. Tyrosin (CgHj^NOg). — This is an ingredient of the pan- creas and pancreatic juice and of the .spleen. Tyrosin is intimately associated with leucin, being found with it dur- ing the pancreatic digestion of proteids ; also in urine during diseases of the liver, and in plants. Indol (CgH^N) occurs in the faeces, and is one of the ingredients which gives them their peculiar odor. Indol is a product of the decomposition of proteids which occurs in the intestines. Skatol (C9H9N) occurs in the faeces with indol, and it contributes to produce the faecal odor. COL O RING-MA TTERS. 79 I. Coloring-matters. HcBmoglobin (Reduced Haemoglobin) (CgugHggoNjj^FeSj- O179). — Haemoglobin with oxyhaemoglobin gives the characteristic color to the bipod. In the blood of an asphyxiated animal the coloring-matter is almost entirely haemoglobin ; in venous b-lood it is both haemoglobin and oxyhaemoglobin, while in arterial blood the oxyhaemo- globin is in excess. It is probable that there are various haemoglobins, as this ingredient obtained from the blood of different animals varies in important particulars. The percentage composition of that of the dog is as follows : carbon, 53.85 ; hydrogen, 7.32 ; nitrogen, 16.17; sulphur, 0.390; iron, 0.430 ; oxygen, 21.84. The great physio- logical interest which attaches to this substance is due to its affinity for, and the readiness with which it gives up, oxygen. Oxyhcemoglobin is a compound of one molecule of oxygen and one molecule of haemoglobin. The power of haemoglobin to take up oxygen depends upon the iron it contains. When oxyhaemoglobin is treated with acids or with strong alkalies it is decomposed, the products being a proteid, globin, and haematin. This change takes place in extravasated blood and also during diges- tion. Haematin may be found in the faeces, especially after a meat diet. If to dried blood a crystal of common salt be added, and on this be dropped glacial acetic acid, and heat be then applied, there form crystals which are called " haemin crystals." Chemically speaking, they are chloride of haematin. Carbon-monoxide Hcsmoglobin. — A union of one mole- cule of haemoglobin and one of carbon monoxide pro- duces the coloring-matter carbon-monoxide haemoglobin. 8o HUMAN PHYSIOLOGY. If a current of carbon monoxide be passed through a so- lution of oxyhaemoglobin, the gas will displace the oxy- gen and carbon-monoxide haemoglobin will be formed. An important difference is to be noted in the behavior of this gas as compared with oxygen : while oxygen is easily replaced, carbon monoxide is not. Carbon mon- oxide is the gas formed when combustion is incomplete, such as is produced by the charcoal furnace used in France for suicidal purposes ; the charcoal fumes when inhaled in sufficient quantity produce fatal results. The combinations of haemoglobin with oxygen, carbon mon- oxide, and other gases are definite compounds, each of which crystallizes in its own characteristic form and has its own spectrum. Bilirubin (C16HJ8N2O3). — The bile of man and of carnivora owes its ' golden-red color to bilirubin. This coloring-matter is insoluble in water, but is very soluble in solutions that are alkaline. Bilirubin is identical with what was formerly called " haematoidin," a coloring-mat- ter found in old blood-clots, in corpora lutea, and some- times in urine. Biliverdin (CigHigNjOJ, which is the coloring-matter of the bile of herbivora, is characterized by its bright- green color. Its formula shows that it is oxidized bili- rubin, and when the golden-red bile of carnivora is ex- posed to the air it becomes green, its bilirubin having been changed into biliverdin. Any oxidizing agent pro- duces the same effect, and on this fact are based tests for the presence of the bile-pigment. Gmelin's test is as follows : Nitric acid, which contains nitrous acid, is poured into a test-tube, and upon it is poured the fluid sus- pected of containing the coloring-matter, care being taken .not to mix the two, but to permit the fluid to float on the COL ORING- MA TTERS. 8 1 acid. If the bile-pigments be present, colored rings appear where the two fluids join, the ring nearest the acid being yellow, and those above being red, violet, blue, and green. This test is sufficiently delicate to detect the presence of i part of bilirubin in 70,000 parts of the solvent. Hydrobilirubin {Q^^^f^^ is another coloring-matter in the bile, and exists also in faeces, in which it has been described as " stercobilin." The identity of hydrobili- rubin and urobilin, a coloring-matter of the urine, may now be regarded as established. It gives to the urine a red or reddish-yellow color, and is especially abundant in highly-colored urine, as in fevers. One authority at least believes that the urobilin of normal urine and that of pathological urine have certain essential points of difference. All these bile-pigments are regarded as being derived from haemoglobin, and the liver-cells are probably the structures endowed with the power of their formation. Urochrome. — This coloring-matter of the urine is re- garded by some as distinct from, and by others as iden- tical with, urobilin. Melanins. — There is a group of substances to which the name melanins might well be given, as its members differ somewhat from one another. In general this group comprises the black or dark pigments, as in the choroid, the skin, etc. Fiiscin is the melanin of the cell-substance and pro- cesses of the retinal epithelium. Urinary melanin is the name given to the coloring- matter of the dark-brown or black urine of persons suffering with melanotic tumors ; that is, tumors which are dark-colored from containing- a melanin. 82 HUMAN PHYSIOLOGY. Lutein is the yellow pigment of the corpus luteum. Serum-lutein is the pigment which gives the yellowish color to the serum of blood. This fluid may sometimes owe part of its color to bile-pigments. FOOD. The human body is constantly wasting. In a single day this waste is estimated to be at least eight pounds. If this loss were not compensated for, death would result from starvation, the length of time necessary to produce this fatal result depending much on circumstances. In one instance, in which one hundred and fifty persons in 1816 were wrecked on the "Medusa," after being thirteen days without food either solid or liquid all were dead but fifteen. It is, however, to be said that in this case there was not only absence of food, but as an addi- tional factor in hastening the result there was also ex- posure to the elements. It may be said, in general, that death will supervene when the body has lost four-tenths of its weight. To supply the waste of the body and to maintain it in its physiological condition food is taken. There is a process of oxidation taking place in the body in which the oxygen taken in by the lung oxidizes some of the fats, carbohydrates, and proteids, and as a result there are formed carbon dioxide, water, and urea; that is, complex substances are broken up into simpler forms and energy is produced. Besides this, the body is constantly the seat of certain activities, as movements of the muscles, the production of vital heat, and nervous activity, and for this food is also required. Food, tJien, may be defined as material taken into the body to repair FOOD. 83 the zvaste of tissues and to produce energy. Foods are made up of food-stuffs and otlier substances associated with them, which latter, being indigestible, are of no value either for purposes of nutrition or for the genera- tion of energy. Foodstuffs are divided into four classes, and they have already been discussed in treating of the physiological ingredients. The classes of food-stuffs are : 1. Inorganic, including water and salts. 2. Carbohydrates. 3. Fats or oils. 4. Proteids. I. Inorganic Food-stuffs. — Water is, as has been pointed out, one of the most important ingredients of the body, and is therefore one of the most essential of the food- stuffs. It is the solvent of many of the constituents of the food and the salts, and by its softening action on the dry parts aids in the processes by which they are masti- cated and swallowed. It is important to remember that water should be free from such impurities as render it harmful. Thus, if it be too " hard " — that is, contains too much lime — there is liability to the production of gastric or intestinal derangements ; if it contain the germs of disease, sickness may follow its use. It is by drinking water infected with the germs of cholera or of typhoid fever that these diseases are often produced. To avoid this danger, when there is any doubt as to the purity of the water it should be boiled. In one family known to the writer no water that has not been boiled has been drunk for many months. The impression that boiled water is unpalatable is erroneous. But boiling the water will be of no avail in avoiding the danger of infection if impure ice be used 84 HUMAN PHYSIOLOGY. in connection with it. Nothing is more clearly settled than that freezing does not destroy all disease-producing germs. The typhoid-fever epidemic which occurred in 1885 at Plymouth, Pa., where, of a population of 8000, 1 153 persons were stricken with the disease, 1 14 of them dying, is a striking instance of the vitality of the typhoid germs. The drinking-water of Plymouth became con- taminated from the faeces of a patient having typhoid fever, although these faeces had been frozen for a long time during the winter months. Laboratory experiments have demonstrated that the germs of this disease may be frozen for more than one hundred days and still retain their vitality. The writer investigated an epidemic of dysentery in which the disease was traced to ice used in drinking- water. The ice had been cut from a pond in which during the summer hogs wallowed, and in which they deposited their excreta. When melted this ice had a most offensive odor. Other instances might be given show- ing the danger from the use of impure ice, but the one cited will suffice. Fortunately, there is now furnished for use in many of our cities artificial ice, which, if properly prepared, is free from all contamination. In this process of manufacturing ice the water is not only boiled, but is distilled, and when ready for freezing is absolutely pure. With boiled water and artificial ice all danger of infection through these channels may surely be prevented. Salts. — The list of salts taken in with the food has already been given, the most important being sodium chloride, calcium phosphate, and the alkaline carbonates and phosphates. The offices which these salts perform in the economy of the body vary. By some of them the solubility of certain ingredients is made possible, as FOOD. 85 is the globulin in the blood by virtue of the presence of sodium chloride. Salts are stimulants also to the glands, causing the latter to secrete more actively ; thus the di- gestive fluids are more abundantly poured out when the food is properly;salted, and the kidneys more completely perform their functions under the stimulation of the salts. 2. Carbohydrates. — These food-stuffs, in the form of starch and sugar, are especially abundant in vegetable foods and in milk, and less so in animal foods. 3. Fats or Oils. — These food-stuffs are found in milk, in butter, in cheese, in the fatty tissues of meat, and also in some vegetables, such as nuts. The following table shows the amount in some of the ordinary foods : Meat 5 to 10 per cent. Milk 3 to 4 " Eggs 12 Cheese 8 to 30 " Butter 85 to 90 " " 4. Pkoteids. — This class contains some of the most valuable of the food-stuffs. The importance of this cla.ss is readily under.stood when it is recalled that the principal ingredients of the blood and the muscles are supplied by the protcids of the food. This is the only class who.se members contain nitrogen, and it has there- fore been sometimes .spoken of as the " nitrogenous ' class. The albuminoids contain nitrogen also, but this class has little nutritive value, except gelatin, which is valuable, but, as has already been .stated, its nitro- gen is not available for the tissues. The proteids are represented in eggs by albumin, in milk by casein, in 86 HUMA N PH YSIOL O G Y. meat by myosin, in peas and in beans by legumin, and in the cereals by gluten. The amount of proteids varies in different foods ; thus there is in Meat .... Milk .... Peas and beans Grains (flour) Bread . . . Potatoes . . 15 to 23 per cent. 3 to 4 " 23 to 27 " 8 to II " 6 to 9 " I to 4 " The following diagram (Fig. 4) shows the amount of the principal food-stuffs in some of the more generally used foods : Proteids. Fats. Carbohydrates. Water. Explanation. Human milk Cow's milk , m 6 87i, 1 slllllllllll^M — 'SS=^SrE^=?^=^S=:=^==2=£:3:^ ^^^^^^^^^i^ 3t ■?-Ni 86 ■ ;illll^sfl e==^==^eSSe=^SS5S =-^.^£r=£r^=:?^:Z=^?5^ Fish... Leguminous fruits. Potatoes 7 fig 15 20l 2 j5 ae 6 i 5S S6 Bread | Fig. 4. — Diagram showing the proportion of the principal food-stuffs in a few typical comestibles. Tlie numbers indicate percentages. Salts and indigestible materials omitted. (After Yeo.) From the above consideration of the food-stuffs it is seen that they are in most respects the same as the tis- FOOD. 87 sues of the body ; yet it would be erroneous to infer that the fats and the proteids of the food go directly into the tissues as such, and take the place of the fats and proteids which are wasted. There are many intermediate steps, some of which are known and will be discussed, and others of which we are entirely ignorant. Experience has abundantly demonstrated that in order to maintain the body at its physiological standard, representatives from all these four classes of food-stuffs must be sup- plied. If man be deprived of water, death speedily re- sults ; it comes as surely, though not so quickly, if fats or carbohydrates or proteids be cut off from the food- supply. Indeed, a man may be starved to death by with- holding the salts. Whenever, therefore, it is found that life can be main- tained physiologically for a long period of time on any diet, it is certain that this diet contains representatives of all the classes enumerated. Thus, milk, which is the sole food of young children — among some of the Eskimos to the sixth year of life — is found on analysis to con- tain such representatives, the inorganic class being rep- resented by water and salts, the carbohydrates by milk- sugar, the fats by butter, and the proteids by casein and some albumin. It is not, howev^er, sufficient that each class should be represented, but the proportions of the ingredients must be proper. It is possible that any given food may have the requisite constituents, but may have too much of one and too little of another. It has been determined that the daily waste of the body is 4500 grains of carbon and 300 grains of nitrogen, or 15 to I, so that in the food the nitrogen should be to the carbon as i is to 15. In the table given above it is seen that in the proteids 88 HUMAN PHYSIOLOGY. there are three times as much carbon as nitrogen, so that should proteids only be supplied to the body there would have to be given an enormous amount of nitrogenous food in order to supply enough of the carbonaceous. The effect of this excess of nitrogenous food would be to injure the digestive and eliminating organs. Imag- ine, for instance, the effect upon the digestive apparatus if man's exclusive diet were potatoes. It will be seen by the table that in potatoes there are 2 per cent, of proteids and 20.75 P^^ cent, of carbohydrates. There- fore, to obtain enough proteids from potatoes to sustain life it would be necessary to eat daily at least ten pounds, or thirty good-sized potatoes. In some parts of the world this has been put into practice, the effect being to distend the stomach and to derange digestion to a harm- ful degree. If the diet were exclusively of meat, then in order to supply the body with the necessary amount of car- bonaceous material a very large quantity of meat would be required, and to meet this requirement there would be taken in an excess of nitrogenous constituents, thus placing a serious burden on the eliminating organs to get rid of them. Experience demonstrates that a mix- ture of foods is the true physiological method of supply- ing the wants of the human body: from meat is obtained the proteids necessary for nutrition ; from the potato is derived the starch ; and from butter is secured the fat. Experience shows also that a higher standard of effi- ciency is maintained by a variety of food, a change being made from one kind of meat to another and from one vegetable to another, always, however, giving the body the food-stuffs in the proper quantities to supply its demands. FOOD. 89 There are individuals who believe that meat-eating is not only unnecessary to, but that it tends also to degrade, man ; they consequently confine themselves to vegetable diet : this exclusive dietary practice is called " vegeta- rianism." It is true that vegetables contain all the phys- iological ingredients necessary for nutrition, but, as above noted in the case of potatoes, the proportion is not such as will subserve the best interests of the body, and phys- iologists have decried the system as being irrational. The following extract from a letter of Dr. Alanus, a veg- etarian, published in the Medical and Surgical Reporter, gives his experience in this matter : " Having lived for a long time as a vegetarian without feeling any better or worse than formerly with mixed food, I made one day the disagreeable discovery that my arteries began to show signs of atheromatous degenera- tion. Particularly in the temporal and radial arteries this morbid process was unmistakable. Being still under forty, I could not interpret this symptom as a manifesta- tion of old age, and being, furthermore, not addicted to drink, I was utterly unable to explain the matter. I turned it over and over in my mind without finding a solution of the enigma. I, however, found the explana- tion quite accidentally in a work of that excellent ph}-- sician. Dr. E. Monin of Paris. The following is the verbal translation of the passage in question : ' In order to continue the criticism of vegetarianism we must not ignore the work of the late lamented Gubler on the in- fluence, of a vegetable diet on the chalky degeneration of the arteries. Vegetable food, richer in mineral salts than that of animal origin, introduces more mineral salts into the blood. Raymond has observed numerous cases of atheroma in a monastery of vegetarian friars, amongst 90 HUMAN PHYSIOLOGY. Others that of the prior, a man scarcely thirty-two years old, whose arteries were already considerably indurated. The naval surgeon, Treille, has seen numerous cases of atheromatous degeneration in Bombay and Calcutta, where many people live exclusively on rice. A vegeta- ble diet, therefore, ruins the blood-vessels and makes one prematurely old, if it is true that a man is as old as his arteries. It must produce at the same time tartar, the senile arch of the cornea, and phosphaturia.' Having, unfortunately, seen these newest results of medical in- vestigation confirmed by my own case, I have, as a matter of course, returned to a mixed diet. I can no longer consider purely vegetable food as the normal diet of man, but only as a curative method which is of the greatest service in various morbid states. Some patients may follow this diet for weeks and months, but it is not adapted for everybody's continued use. It is the same as with the starvation cure, which cures some patients, but is not fit to be used continually by the healthy. I have become richer by one experience, which has shown me that a single brutal fact can knock down the most beautiful theoretical structure." Another factor to determine the nutritive value of any food is its digestibility. The chemical analysis of cheese would place it high among the foods, but experience shows that its constitution is such as not readily to per- mit the action of the digestive fluids, and its availability as a food is therefore low. In regard to meats, it may be said that veal is not of such nutritive value as beef Indeed, to many persons it seems almost poisonous. It is certainly much less digestible than beef or mutton, though more digestible when roasted. FOOD. 91 In conclusion, then, the following table is given as showing a simple daily diet for an adult : Butter or fat 100 grammes. Meat 453 Bread 540 Water 1530 " With this diet life could doubtless be maintained for a long time, but for reasons already given it should be varied. II. NUTRITIVE FUNCTIONS. I. Digestion. Having considered the composition of the body and food, there may now be taken up the study of the nutri- tive functions. As has already been noted, the body is constantly pro- ducing energy and undergoing ivaste, both of which re- quire the taking of food. But food is absolutely of no use to the body until it reaches the blood and by this fluid is conveyed to the tissues. So long as the food re- mains within the alimentary canal it is as much outside the body, so far as nutrition is concerned, as if it had never been taken inside. To be of any service the food must enter the blood, and it does this by being absorbed. In some forms of animal life the food is of such a nature that it readily and without further change under- goes absorption ; that is, passes through the walls of the absorbing vessels. In other forms of animal life this is not the case : in the latter form of animals, unless cer- tain changes take place, the food passes out of the ali- mentary canal as waste material, without having con- tributed to the nutrition of the body in the slightest degree. Unless, therefore, some provision were made to obviate this, such animals would die of starvation. The provision which has been made consists in the presence of certain organs whose duty is to change the form of the food-substances from that in which they will not, into that in which they will, be absorbed. Sub- stances that are not in a condition to be absorbed — that is, will not pass through animal membranes — are said to be " non-diffusible ;" those that are in a condition to pass 92 DIGESTION. 93 through are said to be " diffusible." The above change, then, consists mainly in the alteration from a non-diffusi- ble to a diffusible state. The only exception to this rule is that of the fats, which are otherwise prepared. It is this change (its preparation for absorption) which con- stitutes food-digestion, and the organs concerned in bringing about these necessary changes in the food are the digestive organs. Manifestly, these organs will be simple or be complex according to the amount of change which it is necessary to bring about in the food in order that absorption may take place. Thus, if the food on which an animal relies for its sustentation be already in a diffusible form, no change will be needed, and the ani- mal will therefore have no digestive organs. If the req- uisite change be a slight one, the number of the digestive organs will be few and their structure will be simple. But if the food be varied in its composition, and largely made up of non-diffusible food-stuffs, then the digestive apparatu.s — that is, the group of organs concerned in diges- tion — will be complex. Such is the character of the food of man, and, consequently, p,j, such is the character of his digestive apparatus (Fig. 5). 5. — I. Stomach; 2-4. Small intes- tine : 5. Caecum : 6 Vermiform ap- pendix ; 7, 8, 9. Colon ; 10. Sigmoid flexure; 11. Rectum; 12. Spleen. 94 HUMAN PHYSIOLOGY. The human digestive apparatus consists of the ali- mentary canal and the other digestive organs, which, although outside, still communicate with this canal by- ducts through which their secretion is poured. The ali- mentary canal consists of the mouth, the oesophagus, the stomach, and the small intestine. The digestive organs which are outside, but discharge their secretion into, this canal are the salivary glands, the liver, and the pancreas. The digestive process is subdivided into three parts : (A) That which takes place in the mouth — mouth digestion ; (B) that which takes place in the stomach — stomach or gastric digestion ; and (C) that which takes place in the small intestine — intestinal digestion. For- merly, when digestion was spoken of it was always stomach digestion which was referred to, because it was supposed that the entire process took place in that organ, and when digestion was impaired the rem- edies which physicians employed were directed to the stomach alone. There is, unfortunately, too much of this kind of practice even now, but the study of phys- iology has taught that indigestion may be due quite as much to the improper performance of mouth and intestinal digestion as to that which takes place in the stomach, and unless this be recognized many cases will unsuccess- fully be treated. When food is taken into the mouth it has, presumably, been as fully prepared as possible by the removal of those portions which are of no nutritive value. No one eats the husks of corn, the shells of nuts, the gristle of meat, or similar substances, because experience has shown that they are of little or of no nutritive value and that their digestion is practically impossible. Such extraneous MOUTH DIGESTION. 95 matters, therefore, are removed, and the food is further prepared, provided this preparation be necessary, by the process of cooking. In the form, then, in which the food is taken in it is as fully prepared as it can be out- side the body. Whatever remains to be done in order that the food may be prepared for absorption must be effected after it enters the alimentary canal. Some of the ingredients of human food are already in a diffusible form — that is, in a condition to be absorbed by the blood-vessels of the alimentary canal — and there- fore they need to undergo no change. Such ingredients are water, salts, and dextrose, and were they the only constituents of the food, no digestive organs would be needed ; but, as already seen, this is not the fact. The greater part of the food is in a non-diffusible form, and must be converted into a diffusible form before it can be absorbed. The first step in this conversion is that which takes place in the mouth. A. Mouth Digestion. When food enters the mouth it consists of a mixture of various food-stuffs. In order that the changes which these food-.stuffs undergo may be traced thoroughly, let it be supposed that representatives of all classes of food- stuffs are present — namely, (i) inorganic, salts and water; (2) carbohydrates, starch and sugar; {■^)fats, or oils; and (4) proteids. The water and salts are absorbed directly by the blood, for the most part from the stomach, although there is doubtless some absorption in the mouth. If the food remained in the mouth a longer time than it usually docs, more of these ingredients would there be absorbed, but the duration of time is so short that the amount ab- 96 HUMAN PHYSIOLOGY. sorbed cannot be very great. All the food of a fluid nature, no matter what classes of food-stuffs it comprises, passes immediately from the mouth into the pharynx, and thence through the oesophagus into the stomach. Such food undergoes no chemical changes whatever dur- ing this time ; thus, milk, chocolate, and beverages of various kinds are unchanged in this part of digestion. If, however, fluids be taken into the mouth when it contains solid food, the latter will be softened by them, and the two will be mixed, and will come under the influence of the agents concerned in carrying on mouth digestion. These agents are the teeth and the salivary glands. Mastication. — The chewing of the food, or mastication, is performed by the teeth, of which there are two sets. The first set of teeth, which are known as " temporary," " deciduous," or " milk-teeth," and which exist during early childhood, are twenty in number, and the second or permanent set, which begin to take the place of the first set at about the sixth year of life, remain to a greater or lesser extent until old age. The latter set is composed of thirty- two teeth — four incisors, two canines, four bicus- pids, and six molars — in each jaw. The incisors, or cutting teeth, are adapted to bite the food ; the molar teeth, or grinders, are adapted to grind the food, while the canines and bicuspids in man aid the incisors and molars. In the carnivora, the canines — or " tushes " as they are called — are very long and pointed, and are admirably adapted to pierce the body of their prey, even to the vitals, thus killing and subsequently tearing the ani- mal preparatory to feeding upon it. The herbivora need no such aggressive weapons, and in them the molars are so constructed as to grind the food, their teeth resem- bling the grindstones of the miller. The teeth of man MOUTH DIGESTION. 97 have characters which resemble those of both car- nivora and herbivora, and from this fact it may be inferred that it was designed that man should have a mixed diet. The function of the teeth in man is to thoroughly sub- divide and comminute the food ; and this function is an essential part of the process of digestion. As will be seen later, during digestion certain fluids are poured into the alimentary canal to contribute their part toward the process. These fluids cannot act properly on large, com- pact masses of food. While their action is not entirely that of solution, still, in order to fulfil perfectly their oflice they must come in direct contact with every por- tion of the food. This contact is the more essential be- cause the given time in which to act is not unlimited, and if the process be not completed within the allotted time, digestion will be performed incompletely. When the chemist desires to dissolve a substance quickly and com- pletely, he first thoroughly pulverizes it in a mortar. Likewise, in digestion one of the most important steps is this process of comminution or mastication. If masti- cation be insufficiently performed, the succeeding steps in the process of digestion are seriously interfered with, and indigestion or dyspepsia results. Insufficient mastication is one of the commonest causes of indigestion, and many dyspeptics are drugged with remedies prescribed to overcome some fancied trouble in the stomach when they should be sent to a dentist. De- fective mastication may be due to various causes. The teeth may be so decayed as to expose sensitive surfaces, and when food which is at all hard is taken into the mouth, the discomfort, or sometimes the pain, caused their possessor in chewing it makes the performance of 98 HUMAN PHYSIOLOGY. the act incomplete, and the food is swallowed half masti- cated ; or the eater may be in too great a hurry and not give enough time to this important act. Whatever the cause, the result is the same ; therefore too much atten- tion cannot be given to this process, which is so simple as often to be overlooked. Insalivation. — Coincident with mastication is the act of insalivation or the incorporation of saliva with the food. Saliva is the secretion of the salivary glands (Fig. 6), which comprise the parotid, submaxillary, and sublin- gual ; and their products, to- gether with that of the mu- cous glands of the mouth, form the saliva. The sali- vary glands are known as " compound racemose ;" they are made of lobes, and these, again, of lobules which end Fig. 6. — Dissection of the Side of the Face, showing the salivary glands (after Yeo) : m alvCOll. ThcSC glands arC a, sublingual gland; b, submaxillary ^f ^^^ kinds : OUC is Called gland, with its duct opening on the floor of the mouth beneath the tongue at '' mUCOUS," bcCaUSC itS CcUs d: ..parotidgland and Us duct, which ^^^^^^^ ^ ^^j^ of which UlU- opens on the inner side oi the cheek. cin is a constituent, and the other is called " serous," because the product of its cells is more watery in its nature, or is called " albuminous," because it contains serum-albumin. The sublingual gland is of the mucous kind, the parotid gland is of the albu- minous, while the submaxillary gland is of a mixed cha- racter, its secretion being both mucous and serous, the alveoli of the serous kind being more numerous. The mucous glands of the mouth — " buccal," as they are MOUTH DIGESTION. 99 called — secrete mucus only, their office being to moisten the mouth when mastication is not going on. Mucus from the buccal glands mixes also with the products of the salivary glands. Saliva is an alkaline fluid with a specific gravity of 1004, and is secreted to the amount of i^ litres daily. It is occasionally acid a few hours after a meal, and may be slightly acid between midnight and morn- ing. The greatest acidity is observed two or three hours after breakfast and four or five hours after dinner. Saliva is composed of 99.5 per cent, of water and 0.05 per cent, of solids. Of the solids, one-half is inorganic, the salts being principally sodium chloride, calcium carbonate, and calcium phosphate. It is these latter two salts which accumulate on the teeth, forming the " tartar." They likewise occasionally form "salivary calculi" in the in- terior of the salivary glands or their ducts, and require removal by the surgeon. Another salt — which, how- ever, is not invariably present in the saliva — is potassium sulphocyanide, which has, so far as known, no physiolog- ical importance. The remaining constituents of the saliva are mucin, serum-albumin, serum-globulin, ptyalin, and some carbon dioxide in solution. Examined under the microscope, there are seen epithelial scales from the mucous membrane of the mouth, and leucocytes, prob- ably from the tonsils and elsewhere, described usually as " salivary corpuscles." Bacteria and portions of food are commonly found in saliva, but they are not constituent parts, but rather impurities. Office of Saliva. — The office of saliva is twofold: (i) chemical ; and (2) mechanical. The Clieinical Action of Hn)nan Sali^'a is due to the enzyme ptyalin, which has already been described. This lOO HUMAN PHYSIOLOGY. enzyme is found in the parotid gland of new-born children, but not in the submaxillary gland, and it is not found as an ingredient of the saliva of animals other than man. It will be recalled that ptyalin has the power of changing hydrated starch into dextrin and maltose. If the action of the ptyalin be long continued, some of the maltose becomes dextrose ; but as the time required to accom- plish this change is longer than the ptyalin continues to act during ordinary digestion, this change probably takes place only occasionally. Ptyalin has no action on raw starch. It will be seen, therefore, that the contribution which the chemical action of saliva makes to the process of digestion is not very great, and yet it is not wholly to be ignored. Mechanical Office of Saliva. — The principal office of saliva is undoubtedly mechanical. While the teeth are thoroughly comminuting the food, they are at the same time working saliva into the interstices which they make between the particles of the food. This process not only facilitates the chemical action of the ptyalin, but it tends also to keep the particles separated, so that when the food reaches the stomach the gastric juice may the more readily permeate it and produce its characteristic action. Saliva aids also in softening the food, thus enabling the process of deglutition, or swallowing, more easily to be performed. The secretion of the mucous glands of the mouth is of special importance in this act, the consistency of the mucus secreted being "ropy" and possessing great lubricating properties. Saliva is intimately connected with the sense of taste. Only soluble substances are sapid ; that is, excite the sense of taste. Insoluble sub- stances have no taste. It is for this reason, among others, that calomel is such an excellent cathartic for children ; MOUTH DIGESTION. lOI being insoluble, it is tasteless, and they readily swallow it. Soluble substances not already in a state of solution are dissolved by the saliva, and in this condition excite the sense of taste. When in a febrile or other state, in which the secretion of saliva is greatly diminished, de- glutition is difficult and the sense of taste is markedly deteriorated. A portion of the food having been thoroughly mas- ticated and insalivated, it is collected by the tongue and cheeks into a small mass known as the " aUment- ary bolus," which now undergoes the process of de- glutition. Deglutitio?i, or the act of swallowing, consists in the passage of the food from the mouth, through the pharynx and oesopha- gus (Fig. 7) to the stomach. Deg- lutition is divided into three stages or steps. In the first stage the ali- mentary bolus is carried by the tongue back into the pharynx; as the bolus passes over the soft palate it receives a coating of the very viscid secretion of the mucous glands, which are here situated. This first step is purely voluntaiy, entirely under the control of the Fig. 7.— Muscular coat of the HI I r 1 i_ Pharynx and (Esophagus , and may be performed or not as desired. After the bolus, however, reaches the phar- ynx, it passes from the control of the will. If one were informed at this stage of the act that the bolus contained the most virulent poison, it could not be rejected, but he would be compelled to swallow it. In this, the second stage, the bolus passes through the pharynx, under the 102 HUMAN PHYSIOLOGY. influence of the constrictor muscles, into the oesophagus. The tongue is drawn backward, the isthmus of the fauces is contracted, and the soft palate, the larynx, and the pharynx are elevated, so that the entrance of food into either the posterior nares or the larynx is pre- vented ; the constrictor muscles then contracting, the food is carried through the pharynx into the oesoph- agus. It was formerly thought that the function of the epi- glottis was to prevent the entrance of food into the lar- ynx, and its relations would seem to justify such a view, but observation shows that this view is not true. In the first place, this organ is present only in mammals, and is absent in other vertebrates, although the process of deg- lutition is performed as well in the former as in the latter. Then, too, a dog whose epiglottis has been excised ex- periences no difficulty in swallowing either solids or liquids. The elevation of the larynx and the backward drawing of the tongue are alone sufficient to protect the glottis from the entrance of food. From the pharynx the food passes into the oesophagus, and through the latter into the stomach ; this constitutes the third stage, which is also involuntary in its character, and which is brought about by the successive contrac- tions of the muscular coat of the oesophagus. In the act of rumination, which is characteristic of the rumi- nants, and in vomiting, there is a reversal of this action, so that the contents of the stomach are carried to the pharynx. In deglutition the food does not pass through the oesophagus by virtue of the force of gravity. This is shown by the fact that deglutition may be performed as successfully when an individual is standing on his head STOMACH DIGESTION. IO3 as when he is on his feet, and many animals, such as the horse and dog, always perform the act in opposition to gravity. This act is brought about by a series of mus- cular contractions which begin in the mouth and end at the stomach. During deglutition the ptyalin continues its action on the starch ; other than this action no chem- ical change takes place in the food while it is passing through the oesophagus. The mucous membrane of this canal furnishes a mucus which has no digestive action, but is simply a lubricant. B. Stomach Digestion. The food, having reached the stomach, now undergoes stomach or gastric digestion. The stomach in the human adult is about 35 centimetres in length and 12 in width, and when distended it may contain 3 litres. Coats of tJic Stomach. — The stomach is composed of four coats: serous, muscular, submucous, and mucous. The serous coat is a reflection of the peritoneum. The sub- mucous coat, which contains the nerves and blood-vessels, is of special interest as giving to the mucous coat great mobility and as permitting it to form folds, called " rugae," when the cavity is empty. This structure is in striking contrast with the anatomical structure of the uterus, in which organ, the submucous coat being absent and the mucous lying directly upon the muscular coat, there is a total want of mobility in the membrane. Aside from this statement neither the serous nor the submucous coat has any special physiological interest. The muscular coat is composed of three layers : longitudinal, circular, and oblique. The lous^itudiiial layer is made up of fibres continuous with similar fibres of the oesophagus, and is 104 HUMAN PHYSIOLOGY. most external — that is, immediately beneath the peri- toneum. These fibres radiate from the oesophageal or cardiac orifice, and are especially abundant in the region of the greater and lesser curvatures. They extend to the intestine, where they form a layer of the muscular coat of that organ. The circular layer is situated inter- nal to the longitudinal, and, as the name implies, its fibres encircle the stomach — that is, are in general at right angles to the longitudinal axis of the stomach. At the pyloric orifice of the stomach, where the duo- denum begins, these circular fibres are aggregated in such number as to receive the name of " pyloric muscle." Their projection into the interior of the organ at this location with its covering of mucous membrane con- • stitutes the pyloric valve. The oblique layer is found especially at the cardiac extremity of the stomach. The mucous coat, or mucous membrane, is soft and velvety. Near the cardiac orifice the membrane is about i^ millimetres in thickness, and near the pylorus 2 milli- metres, while in general between these two points its thickness is about i millimetre. Its surface is composed of columnar epithelium, which secretes the mucus found in the stomach in the intervals of digestion, this mucus being a constituent of the gastric juice. In the mucous membrane, and forming a part of it, are two sets of glands, the " pyloric " glands, so called from their abundance in the pyloric portion of the stomach, and the "cardiac" glands (Fig. 8), which are so called because of their occurrence in the cardiac region. The ducts of both sets are lined by columnar epithelium continuous with that covering the mucous membrane. In the tubes of the pyloric glands are granular cells called " chief cells." The same kind of cells is found in STOMACH DIGESTION. 105 the tubes of the cardiac glands, and beneath these cells — that is, between them and the basement membrane — are, besides, larger cells, which are ovoid in shape and which Fig. 8. — Cardiac Glands. Diagram showing the Relation of the Ultimate Twigs of the Blood-vessels, K and A, and of the absorbent radicals, L, to the glands of the stomach, and the different kinds of epithelium — namely, above, cylindrical cells ; small pale cells in the lumen, outside which are the dark ovoid cells. are known as " parietal cells." These cells cause the base- ment membrane against which they lie to bulge out. The chief cells are regarded as producing the pepsin- ogen which is converted into the pepsin of the gastric juice, and the parietal cells as producing the hydro- chloric acid. The vascularity of the stomach is very great. In the intervals of digestion the mucous mem- brane is of a pale pinkish color, while during active di- gestion its color is a bright red. This change in color is due to the greatly increased amount of blood present in the blood-vessels of the or^an at this time. I06 HUMAN PHYSIOLOGY. Prior to 1822 the process of stomach digestion was little understood. During that year Alexis St. Martin, a Canadian boatman, was so injured by the accidental discharge of a gun that when the wound healed there remained in his side a permanent opening (nearly 2)^ centimetres in diameter), which com- municated with the cavity of the stomach (Fig. 9). Fig q— left Dreist and Sidt ^<.lcct posi- Dr.Beaumont, thc surgcon tion) showing perforation of the walls of . ^ ^^ ^^^ ^^^ the stomach of Alexis St. Martin. o ' subsequently others, car- ried on a series of experiments and observations extend- ing through years, and the present knowledge of stomach digestion is largely based upon this remarkable case. During the intervals of digestion the mucous mem- brane of the stomach is pale in color, and is covered with a transparent and viscid mucus which is neutral or alka- line in reaction. This mucus is the product of the epi- thelium of the mucous membrane. After food has en- tered the stomach drops of gastric juice appear at the mouths of the glands. Quantity of Gastric Juice. — The amount of gastric juice daily secreted is difficult of determination, and it is not surprising that authorities should differ so much on this point. Dr. Beaumont estimated it to be 180 grammes in the case of St. Martin, while others place it as high as 7 litres, or one-tenth of the weight of the body. The gastric juice is never in large quantity in the stomach at any one time. It is secreted gradually by the glands, is STOMACH DIGESTION. 10/ poured out into the cavity of the stomach, where it per- meates the food, is passed on into the small intestine, where it is absorbed by the blood-vessels, and is then returned to the circulation, from which its constituents were derived. It has the following properties : it is clear, slightly yellowish in color, and strongly acid. Its specific gravity is from looi to loio. Composition of Hiiniaii Gastric Juice mixed zvith Saliva. — As can readily be understood, it is impossible to obtain gastric juice unmixed with particles of food or saliva or other foreign substances, hence an accurate analysis can- not be given. The analysis of Schmidt of gastric juice from a women having a gastric fistula is as follows : Percentages. Water 99.4400 Organic substances (pepsin, peptones, and rennin) -3195 Free hydrochloric acid .0200 Calcium chloride 0061 Sodium " . . • .1464 Potassium " -OS 50 Calcium | Magnesium V phosphates 0125 Ferrum J Loss 0005 100.0000 The constituents of the gastric juice of any special physiological interest arc hydrochloric acid, pepsin, and rennin. It was at one time a matter of dispute whether the acidity of this fluid was due to hydrochloric or to lactic acid, but there is now a unanimity of opinion that it is the former. If lactic acid be present, it is probably Io8 HUMAN PHYSIOLOGY. due to lactic fermentation which has taken place in the carbohydrates of the food when these are in excess. This fermentation may go on to the formation of acetic and butyric acids, these changes being doubtless due to the presence of micro-organisms. Hydrochloric Acid. — The amount of free hydrochloric acid in human gastric juice varies from 0.05 to 0.3 per cent. Several of the best authorities give the average as between 0.2 and 0.3 per cent. Pepsin. — The " chief" cells of both the cardiac and the pyloric glands, during the intervals of digestion, produce the zymogen pepsinogen, which has no digestive action upon proteids. The parietal cells produce hydrochloric acid, the action of which upon the pepsinogen converts the latter into pepsin. This acid is formed from the chlorides which are brought to the glands by the blood. The action of pepsin upon proteids in presence of hy- drochloric acid has already been studied. To recapit- ulate : The proteid is first converted into acid-albumin, or syntonin (some authorities, it will be remembered, limit the term "syntonin" to that particular acid-albumin which is produced from myosin), which passes into al- bumose, and this into peptone or peptone with some albumose. Renniji. — There is in human gastric juice another en- zyme, rennin, which is produced from renninogen, a zymogen which, like pepsinogen, is the product of the " chief" cells of the gastric glands. It is interesting to note in this connection that some observers have found that this enzyme was absent from the gastric juice in carcinoma of the stomach, atrophy of its mucous membrane, and in some cases of gastric catarrh. It will be remembered that rennin coagulates the casein of milk. In the gastric STOMACH DIGESTION. IO9 digestion of this important food the coagulation of the casein is a prehminary step. Mothers are sometimes frightened when their children, seemingly in perfect health, vomit curdled milk, but this curdling of milk is a normal process, and the only abnormality consists in its regurgitation, which is usually due to over-feeding. As matter of secondary interest there is some evidence that in gastric juice there is a lactic-acid ferment which changes the lactose of milk into lactic acid ; another ferment which converts cane-sugar into glucose; and still another, a fat-splitting one, which breaks up fats into glycerin and fatty acids, but the amount of these materials changed in the stomach is not very great. Gastric juice does not change starch. The albuminoids are, some of them, as has been seen, converted into peptones, but they have little nutritive value. The one which is more than any other looked upon as contributing to nutrition is gelatin. But gelatin is not available directly for the growth and repair of tis- sues. It has an " albumin-sparing " action. Much less flesh is required by an animal if fat be taken with the flesh, this being spoken of as the " albumin-sparing " action of fat. The same is true of gelatin. Gelatin forms urea, and when present in the food in large amount the kidneys are excited to increased action. Chyme. — The mixture of food and gastric juice is called " chyme." Chyme is not a mixture having a con- stant composition : it varies according to the articles of food ingested. There are, in addition to the presence of pepsin and hydrochloric acid, two other requisites for normal diges- tion. The temperature must be favorable, and this is found in the stomach where the thermometer indicates 38° C ; I lO HUMAN PHYSIOL OGY. the other requisite is the muscular movements of the stomach. Muscular Movements of Stomach. — In the empty con- dition of the stomach the direction of the greater curva- ture is downward and that of the lesser curvature up- ward ; but as food enters and begins to fill this organ, it rises upward in such a manner that when filled the greater curvature is forward and the lesser curvature backward. From the time that food enters the cavity of the stomach until it has all passed out the muscular coat of the stom- ach is in action. The walls are in contact except where separated by food, and are constantly rubbing against each other, or against that which separates them, with a rotatory motion. The masses of food are by this means broken up and the gastric juice is incorporated with them. In the stomach of the cow it is not unusual to find balls of considerable size, made up of hair which the animal has licked from her hide and swallowed. These balls are perfectly spherical, and are undoubtedly formed by this rotatory or churning motion of the muscular coats of the stomach. There is, besides this, a movement which car- ries the food toward the pyloric orifice, and which is known as " vermicular" or "peristaltic." If any portion of the food as it reaches this part of the stomach be sufficiently liquid, the pyloric muscle relaxes and per- mits it to pass through into the duodenum ; otherwise it is carried back, and is again brought under the influence of the rotatory movements of the stomach. While during the greater part of stomach digestion the pyloric muscle keeps the pylorus closed, only relaxing to permit the prepared material to pass, at the close of the act it remains so relaxed that solid particles can pass into the duodenum without difficulty. STOMACH DIGESTION. 1 1 1 Self -digestion of Stomach. — One of the interesting and still unexplained physiological enigmas is : Why does not the stomach, which is proteid in its nature, undergo self-digestion during life ? It is known that when death takes place during the period of active stomach diges- tion erosion of the mucous membrane, and even perfora- tion of the wall of the stomach, may occur. As this takes place at the most dependent portion, where the gas- tric juice naturally gravitates, the explanation is simple. But if this self-digestion can occur after death, why^ not during life ? No satisfactory answer to this question has yet been given, although many theories have been ad- vanced. Results of Stomach Digestion. — The following, then, are the results of stomach digestion : The proteids are con- verted into peptones ; in the case of milk the proteid casein is first coagulated, and then changed into peptone. Starch is not changed by the gastric juice, though the action of the ptyalin, which commenced in the mouth and was continued in the oesophagus, does not cease in the stomach until the food becomes so acid as to prevent the further action of the enzyme. Some of the carbohydrates may, as has been seen, undergo the lactic fermentation. If fat be present in the food in the free state, as in oil, it is made more fluid by the heat of the stomach ; if it be in the form of adipose tissue, in which the fat is en- closed in sacs, forming the adipose vesicles, these sacs, being proteid in their nature, are acted upon by the gas- tric juice as are other proteids, and the fat is set free, when it is acted upon in the same manner as the free fat just referred to. Some of the fat may be split up into glycerin and fatty acids, but the greater part passes on into the duodenum. 1 1 2 HUMAN PHYSIOL OGY. The stomach contains gases which in the dog have been found to be nitrogen, oxygen, and carbon dioxide. The hydrochloric acid that is normally present in gas- tric juice prevents the formation of gases from fermen- tative changes in the food. The stomach-gases are at- tributable to the air incorporated with the food in the mouth, and to the saliva, in which, as we have seen, carbon dioxide exists in solution. It is also probable that there is some escape of gases from the intestine into the stomach. Duration of Stomach Digestion. — The duration of stom- ach digestion is variable, and depends upon several cir- cumstances, among which is the composition of the stomach-contents. Some kinds of food remain in the stomach longer than others. Stomach digestion may in general be said to be from one and a half to five and a half hours, according to the nature of the food. The following table contains a list of some of the sub- stances with which Dr. Beaumont experimented, and the length of time they remained in the stomach : Kind of Food. Time. Pig's feet and tripe i hour. Salmon i Milk 2 hours. Potatoes, roasted 2 Roast turkey 2>^ " Soft-boiled eggs 2>^ " Beefsteak, broiled 2% " . Hard-boiled eggs 3 Potatoes, boiled SH " Pork, boiled 4)4 " roast . . . 5/i " STOMACH DIGESTION. 1 1 3 The above table, and others of hke nature, are to be very cautiously made use of in determining the digest- ibihty of the different foods. The observations here re- corded simply indicate the length of time the respective articles remained in the stomach, and nothing more. Sub- stances are digested vj\\Qn they are in condition to be ab- sorbed, and not until then. Whenever any portion of the food is rendered sufficiently liquid, it is liable to pass out from the stomach, although there are other factors than this liquid character of the food. If two different articles of food were in the stomach at the same time, one might pass out from that organ into the small in- testine in one hour, while the other might remain in the stomach two hours. From this fact alone one would not be justified in assuming that the one substance v/as twice as digestible as the other, for the former might not at the time it left the stomach have been prepared for absorption, but might require several hours for such a change after it reached the small intestine ; while the latter, although it remained in the stomach an hour after the former had left it, might at the time it left the stom- ach have been in a condition to pass at once into the blood. The practical use of tables showing the length of time that different substances remain in the stomach seems to be to determine of what the food should consist when this organ is unable to perform its function in a normal manner and it is considered wise to lighten its labors as much as possible. For this purpose such food should be selected as will remain in the stomach but a short time, even though it pass out in an undigested state, for, as will hereafter be seen, the peptonizing func- tion is as well carried on in the small intestine as in the 8 I 1 4 HUMAN PH YSIOL OGY. stomach, and in a disabled condition of the latter organ the former will supplement it. In the dog so thoroughly may digestion be performed by the intestines alone, with- out the aid of the stomach, that this latter organ has been almost completely removed, yet the animal has been kept alive in excellent health and strength. The proper foods under these circumstances are those that are liquid when ingested or are readily liquefied in the stomach. As above stated, the length of time that food remains in the stomach is not determined by its consistency alone. One of the important factors is the amount of hydrochloric acid present; thus when this acid is rel- atively great it seems to act as an irritant, and the pyloric muscle relaxes more readily than when the amount is less. Some light has been thrown on this question of the duration of stomach digestion by the application of methods of obtaining and examining the contents of the stomach for diagnostic purposes. To ascertain how far the digestive process is interfered with, " trial " meals are given. The stomach is evacuated by means of a soft-rubber stomach-pipe after a proper time, and in- spection shows how far the process of digestion has advanced. Ewald's " trial " meal consists of one water- roll weighing 35 grammes and a cup of tea or 300 or 400 cc. of water. After this food has been two and a half hours in the stomach that organ will be found empty; in one case the food had disappeared after one hour. Riegel's " trial " meal consists of a cup of broth, 400 grammes ; beef, 60 grammes ; and bread, 50 grammes. After seven hours the stomach will be found empty. Artificial Gastric Juice. — In addition to the observa- STOMACH DIGESTION. 1 1 5 tions of Beaumont and others upon cases of gastric fistula, many experiments have been made with an arti- ficial gastric juice made by extracting the pepsin from the mucous membrane of the stomach of the pig with glycerin, and adding to this glycerin-extract 0.2 per cent, of hydrochloric acid. The results of these experiments are, however, not to be regarded as identical with those that take place in the stomach of a living human being. The factors in the problem are many, and some of them are still undetermined, as, for instance, the action of the gastric juice on the different proteids. Effects of Alcohol on Digestion. — Much has been written on the effects of alcoholic and other beverages upon di- gestion, and the testimony is very conflicting. Thus one authority states that the action of pepsin is retarded tem- porarily by the presence of alcohol, but after the latter is absorbed, which occurs very rapidly, there is an increased flow of very active gastric juice; another says that alco- hol retards, and even prevents, digestion ; while a third maintains that it aids digestion from the beginning of its entrance into the stomach. The fact probably is that in each of these opinions there is some truth, and that the effects of alcohol vary according to the conditions present. The first principle which may be laid down is that alco- hol, under ordinary circumstances, is not needed to aid digestion, but it is to be regarded as an agent which, under the direction of the physician, may be employed to assist him in the treatment of diseased conditions. About 95 per cent, of the alcohol taken into the body is oxidized, carbon-dioxide and water resulting. To this extent it serves to produce heat, and whenever, therefore, the supply of food is insufficient, alcohol is of value in preventing so far as possible the using up of the tissues 1 1 6 HUMAN PHYSIO LOG Y. of the body. The above statement is true if an amount not exceeding two ounces be taken daily, but when an abundance of food can be obtained the use of alcohol offers no advantages. Alcohol in small doses excites the nervous system, and if this stimulation be kept up harm must result, for after the stimulation there is a de- pressing reaction. The action of alcohol on the vascular system is to excite the latter and to increase the circula- tion of the blood ; thus in a given time both nerves and muscles are supplied with more blood. It is this action which produces the sense of warmth when alcohol has been taken, but this warmth is purely subjective, the thermometer showing that alcohol, even in moderate amount, actually lowers the temperature. The blood- vessels of the skin dilate under the influence of alcohol, and there is a loss of heat by radiation from the blood. The pulse is smaller and is increased in rate, while its strength is diminished, showing action upon the heart. One who has made a special study of the action of alco- hol upon the nervous system says that it seems to in- duce progressive paralysis, the judgment being affected first, although the imagination and emotions may be more than usually active ; the motor centres and speech are next affected, then the cerebellum, then the spinal cord ; and finally, if the quantity taken be large, death may result. An instructive lesson may be obtained by observing the effect of alcohol upon animal tissues immersed in it. It is known that such tissues are dried up and shrivelled ; in the same way, although to a very much less degree, the proteids of the cells of the mucous membrane are affected in the form of coagulation when alcohol is taken into the empty stomach in concentration, as in whiskey S TO MA CH DICES TION. 1 1 7 or in brandy. When diluted the action of alcohol is less pronounced. When the stomach contains food the lia- bility of injury is less, as then the alcohol is diluted by the liquids, and, if there be proteids in the food, some of these are coagulated, the mucous membrane thus being doubly protected. The frequent imbibing of spirituous liquors on an empty stomach, as practised by so many, is the most injurious form of alcohol-taking. Not only are the nervous and vascular systems affected, but a catarrhal condition of the digestive organs is also pro- duced. If the alcohol contain impurities, such as fusel oil, its action is still more harmful. Before leaving the process of stomach digestion it may be well to call attention to the fact that the hydrochloric acid of the gastric juice has a germicide action on some of the pathogenic bacteria. This action, on the one hand, is not true of all pathogenic bacteria, for those which produce tuberculosis and anthrax are not destroyed by gastric juice ; on the other hand, the cholera spirillum, the germ of Asiatic cholera, is destroyed in normal gas- tric juice. Experiments have demonstrated this fact, and also that if a solution of soda be injected into the stom- ach, the vitality of this micro-organism is not destroyed. It is therefore of the utmost importance, during the prevalence of cholera, to keep the digestive organs in normal condition. Anything which tends to produce a catarrhal condition of the stomach, as alcohol in excess, will be likely to increase the alkaline mucus, and thus make the conditions favorable should the spirilla find their way into the stomach in solid or in liquid food. It is probably by interfering with normal digestion, inhibit- ing the production of hydrochloric acid, that fear con- duces toward the spread of this disease. Dr. Beaumont Il8 HUMAN PHYSIOLOGY. in the case of St. Martin observed that when his temper was irritated the secretion of gastric juice was greatly interfered with or even suspended. Unusual fatigue and a condition of fever would produce the same results. It is a matter of common experience that fear, worry, anger, the receipt of unexpected news, either joyous or sorrow- ful, will oftentimes seriously interrupt gastric digestion. Therefore at all times the endeavor should be to keep the mind, during the period of digestion at least, free from these disturbing agencies. The acidity of gastric juice, even in comparative health, is not always the same : it may be in excess or it may be deficient. In the latter condition, the antifermentative action of the acid being diminished, there occurs fer- mentation of the carbohydrates, and lactic, acetic, and butyric acids appear, together with hydrogen and other gases. These acids and gases give rise to heartburn, waterbrash, and other conditions indicative of disordered digestion. C. Intestinal Digestion. The small intestine, in which intestinal digestion takes place, is about 22 feet long, extending from the stomach to the ileo-cscal valve, where it passes into the large in- testine. Coats of the Intestiiie. — Like the stomach, the small in- testine is composed of four coats : i, serous ; 2, muscular; 3, submucous ; 4, mucous. It is divided into three por- tions : [a), duodenum ; {b), jejunum ; {c), ileum. As in the stomach, the two coats which have physiological interest are the muscular and the mucoiis. The muscular coat is made up of two layers : an external or longitudinal and an inner or circular. INTESTIA'AL DIGESTION'. 119 Intestine, laid open to show the valvulae conniventes (Brinton). VahndcB Conniventes. — The mucous coat of the intestine is covered by a single layer of columnar epithelium. It is arranged in folds to which the name "valvulae f^.^^^'^"'- conniventes " has been given (Fig. lo). These folds, which begin about i centimetres below the py- lorus, are present through- Fig. lo.-Portion of the Wall of the Small out the length of the small intestine, excepting in the lower part of the ileum. They are more abundant in the upper half of the intestine, where they have been counted to the number of six hundred, than in the lower half, where only two hundred and fifty have been found. These folds are arranged around the interior of the in- testine at right angles to its long axis. They do not completely encircle it like a ring, but vary in length, some extending two-thirds and others only one-third the distance around. The widest of them is not more than half an inch in width, projecting into the calibre of the intestine to this extent. Each fold is mucous membrane, and between these reduplications of mucous membrane is connective tissue, which so binds the folds together that even in the condition of distention the valvulae con- niventes are not obliterated, as is the case with the rugae of the stomach. By means of these foldings the extent of the mucous membrane is greatly increased over what it would be did it simply line the intestine. Villi. — Projecting from the mucous membrane includ- ing the valvulae conniventes are the "villi" (Fig. ii), which are so numerous as to give to it a velvety appear- ance. These villi are prominences, some triangular, some 1 20 HUMAN PHYSIOLOGY. WPiE'"f:|-''l#--Wife^^^ are intimately connected \ ^■^Jip^lijl-iigplljl^^^ the process of absorption, i^^P-"^:^ conical, and some filiform in shape, and in length are about i mm., and in width at their base about one-fourth their length. They are most nu- merous in the duodenum and the jejunum, although present throughout the whole extent of the small intestine. It has been estimated that there are no less than five millions of these villi in an intestine. They with and their further description will therefore be deferred until that subject is discussed. Bmnner's Glands. — In the submucous coat of the upper part of the duodenum, and, to a less extent, in that of the lower part and in the begin- K.y ning of the jejunum,, are certain glands known as the " glands Fm. xi.-verticai Section of Duode- ^^ grunner," or the duodenal num, snowing villi (a) ; crypts ol Lieberkuhn(/;),andBrunner's glands glauds. ThcSC are raCCmOSe (c) in the submucosa (j), with ducts , , • -i ^ ^i • ^i {d): muscuiaris mucosa (;«), and glands. Similar to thosc lu the circular muscular coat (/), (Scho- oeSOphagUS aud alsO tO tllC lobules of a salivary gland. They discharge through ducts which open upon the surface of the mucous membrane of the intestine. Their secretion is mucus having a slightly alkaline reaction, but it has never been successfully obtained so pure as to admit of its being analyzed. These glands are so few in number, cornparatively, that their product cannot INTESTINAL DIGESTION. 121 be very abundant nor very important in its action upon the food, although a ferment has been described as one of its constituents which has the power of conv^erting maltose into glucose. The secretion of these glands, together with that of the follicles of Lieberkiihn, con- stitutes the intestinal juice. These glands are inflamed and ulcerate whenever the body is burned to any great extent. Follicles of Lieberkiihn. — The follicles or crypts of Lieberkuhn, which are found throughout the entire length of the small intestine, are tubular glands in the mucous membrane, and not beneath it, as is the case with the glands of Brunner. Their lining is a layer of colum- nar epithelium. Besides these tubular glands there are solitary glands scattered throughout the mucous mem- brane of the intestine, and agminated glands, commonly known as " Peyer's patches," which number about twenty- five, and which are most numerous in the ileum. These glands have no excretory ducts, but they produce a secre- tion which probably oozes through the walls of the glands and contributes something to the intestinal juice. In typhoid fever Peyer's patches become inflamed and often undergo ulceration. Intestinal Juice. — The intestinal juice, "succus en- tericus," is the product of all the glands, but the follicles of Lieberkuhn, being vastly more numerous, contribute by far the greater part of this fluid. It is an alkaline secretion having a specific gravity of loio, and contain- ing about 95 per cent, of water, salts, and at least one ferment, invertin. As to the presence of other ferments there is doubt. Action of Intestinal Juice. — The action of intestinal juice upon the food has not been thoroughly determined. 122 HUMAN PHYSIOLOGY. The property which it possesses in the most marked degree is that of changing cane-sugar into invert- sugar, which, as will be remembered, is a mixture of Isevulose and dextrose. This inversion is due to the fer- ment invertin. The intestinal juice also converts starch. Fig. 12. — Section of Lobule of a Rabbit's Liver, in which the blood and bile-capillaries have been injected (after Cadiat) : a, intralobular vein; (5, interlobular veins; c, biliary canals beginning in fine capillaries. both raw and cooked, into sugar. Maltose is changed into glucose, and the viscid secretion of Peyer's patches brings about the latter change very quickly. The neutral INTESTINAL DIGESTION. 123 fats are not decomposed by intestinal juice, but this fluid, by virtue of its alkalinity, does emulsify them. Its action on proteids is not determined, some experimenters report- ing that it possesses proteolytic powers, others denying it. From the above considerations the intestinal juice may be regarded as possessing some digestive action upon the food-stuffs, the most marked of which action is its power of inversion. It is not an abundant secre- tion, and perhaps its most important office is to lubricate the mucous membrane of the small intestine. The Bile. — The bile is one of the products of the cells Fig. 13. — The Liver: i, right lobe ; 2, left lobe; 3, posterior border; 4, anterior bor- der; 5, lobus quadratus ; 6, lobus Spigelii ; 7, lobus caudatiis; 8, 9, longitudinal fis- sure; 10, transverse fissure; 11, portal vein; 12, hepatic artery; 13, ductus com- munis choledochus; 14, gall-badder fissure; 15, inferior vena cava ; 16, hepatic vein; 17, round ligament ; 18, suspensory or broad ligament. of the liver, and as it is secreted it passes into the gall- bladder through the hepatic and cystic ducts, where it is stored until needed at the time of intestinal digestion. Bile when discharged from the gall-bladder is a viscid fluid, having in man a golden-brown color, a specific gravity of 124 HUMAN PHYSIOLOGY. 1018, and an alkaline reaction. Its viscidity is due to mucus, which is not present when the bile leaves the liver, but which is added to it while it is stored in the Qu y^(' o ' rounded by Bowman's capsule; 2, con- fomiS a loOp, and rC-entCrS striclion, or neck ; 3, proximal convoluted tubule; 4, spiral tubule; 5, descending limb of Henle's loop; 6, Henle's loop; 7 and 8, ascending limb of Henle's loop ; 9, wavy part of ascending limb of Henle's loop; 10, irregular tubule; 11, distal con- voluted tubule; 12, first part of collecting tube; 13 and 14, straight part of collecting pighiaU CapSule Or Cap- tube; 15, excretory duct of Bellini. g^j^ ^^ BoWmaU. This complicated structure may, perhaps, be traced more easily in the opposite direction. Beginning with the Malpighian capsule in the cortical portion, there is the cortical portion, again becomes convoluted, and finally terminates in a spherical body, the Mai- KIDNE YS. 207 next the convoluted tubule, which, as it passes into the medullary portion, becomes straight and is known as the "descending limb of Henle's loop." This bends on itself, forming the ascending limb, likewise straight, passes back into the cortex, becomes convoluted, and enters a straight collecting tube which opens at the apex of a pyramid. The Malpighian capsule is lined by a layer of squa- mous epithelium which is reflected over the glomerulus it contains. Between these two layers of cells there is a cavity continuous with the uriniferous tubule. The tubule throughout its entire length is lined by epithelium, which, however, varies in character in different portions. The renal artery enters the kidney at its hilum, and its branches, after pursuing a pe- culiar course, terminate in af- ferent vessels, each of which penetrates the wall of a Mal- pighian capsule, forming the glomerulus. The vessels com- ing from the capsules — efferent vessels — pass out through their walls and form a venous plexus around the uriniferous tubules, ultimately taking part in the formation of the renal vein, which emerges from the kidney at the hilum and discharges into the inferior vena cava. Urine. — The function of the kidney is to form the urine, which is a yellow or amber-colored fluid, acid in reaction, and having a specific gravity of about 1020 in the adult ; in the new-born child, of about 1005. The quantity of Fig. 40.— Bowman's Capsule and Glomerulus (after Landois) : a, vas afferens ; e, vas efferens ; c, capil- lary network of the cortex; k, en- dothelial structure of the capsule; h, origin of convoluted tubule. 208 HUMAN PHYSIOLOGY. urine voided in twenty-four hours is about 1 500 grammes. Water constitutes 95.2 per cent, and the solids 4.8 per cent., of which 2.2 per cent., nearly one-half, is urea. The following table shows the composition of urine : Percentages. 96.0 2.0 •OS .04 .II 1-5 Daily amount. 1450. grammes. 30. 0.75 " 0.75 " 1.5 " 3- " 7-5 " 3. " Water .... Urea .... Uric acid . . Hippuric acid Creatinin . . Phosphates ^ Chlorides > Sulphates J Mucus and other in- gredients 3 The general characteristics of the urine and its com- position are subject to considerable variation in a condi- tion of health. It may, when its specific gravity is low (1002), be almost colorless, while when concentrated its color will be a reddish-brown. Its reaction, although generally acid, may be alkaline, as at the beginning of digestion, or its acidity may be increased, as during the afternoon or the night. The kind of food also affects the reaction. Thus in the carnivora the urine is acid, while in the herbivora it is alkaline. If vegetables be fed to a carnivorous animal and flesh to an herbivorous, the reaction of the urine will be the opposite to that of the urine when each is consuming its normal food The feeding of flesh to the herbivorous animal is practically accomplished by giving it no food, under which circum- stances it lives upon its own tissues. The acidity of urine is usually attributed to acid sodium phosphate, KIDNE YS. 209 but several organic acids or organic salts are probably involved.* Water. — The amount of water excreted daily is on an average 1450 grammes, and constitutes 96 per cent, of the urine. It is separated from the blood by the epi- thelial cells covering the glomerulus, and not by fil- tration due to blood-pressure. It is true that as blood- pressure in the glomerulus increases the amount of water eliminated also increases, but this is not due to the sim- ple increase of pressure, but is due to the fact that with increased pressure more blood flows through the glom- erulus ; consequently there is more material from which the cells can separate water. Urea. — Of all the ingredients of the urine, urea is the most important. It represents to a great extent the nitrogenous waste of the tissues. The amount of urea daily excreted is in the male about 30 grammes ; it is less in the female. The actual amount eliminated in children is less, but, proportional to the weight of the body, the child excretes more urea than does the adult. Source of Urea. — The ingredient urea is not formed by the kidney: it exists in the blood when this fluid reaches the kidney, and this organ separates it from the blood. The separation is brought about by the epithelium of those portions of the uriniferous tubules about which is entwined the venous plexus already referred to ; that is, the convoluted tubules and the ascending limb of Henle's loop. The source of urea is threefold: i,the proteids of the food; 2, the proteids of the tissues; and 3, the pro- teids of the blood and lymph. I . Urea from the Proteids of the Food. — The greater the amount of proteids absorbed, the greater is the amount of urea excreted. Thus if large quantities of H 2 I O HUMAN PHYSIOL OGY. meat be eaten, the amount of urea in the urine will be very large, whereas if food without nitrogen in its com- position be taken, the urea will be present in a minimum amount. It might be thought that the increased amount of urea excreted under these circumstances is derived from the tissues, but it appears in so short a time (an hour or two) that this cannot be the case. In discussing intes- tinal digestion it was stated that when an excess of pro- teid food was taken the overplus of the peptones was changed into leucin and tyrosin by the action of the trypsin. These two substan'ces are absorbed by the blood-vessels and carried by the portal vein to the liver, where they are probably converted into urea. There is no direct proof of this conversion, but the hypothesis is a reasonable one, for so far as is known the liver is the only gland which contains urea, and, further, it has been shown that when leucin is fed to animals it reappears as urea. 2. Urea from the Proteids of the Tissues. — The muscles contain creatin to the amount of from 0.2 to 0.4 per cent. Creatin is recognized as a substance intermediate between proteids and urea, and it exists also in the brain and ner- vous system generally, in the spleen, and in various glands. Creatin in all probability is one of the sources of urea, but where the conversion takes place is un- known ; possibly it is accomplished by the epithelium of the tubules of the kidney. 3. Urea from the Proteids of the Blood and Lymph. — All the proteids present in the blood and lymph do not become integral parts of the tissues, so that there is a certain amount of the proteids constantly circulating. The circulating proteids are not permanent, but, like other proteids, undergo conversion into urea. It is not to be assumed from this statement of the origin of urea that KIDNE YS. 211 the proteids are converted directly into that substance. It has ah'eady been seen that there are some intermediate stages — for example, leucin, tyrosin, and creatin — and there are doubtless others of which nothing is known. Uric Acid. — Besides being an ingredient of the urine, uric acid has also been detected in the spleen, the heart, the liver, and the brain. In the blood it is also present, especially in gout. In the urine the amount of uric acid under ordinary circumstances does not exceed 0.75 grammes per diem. The amount will be still less if the diet be vegetable, but if it be ani- mal and abundant the quantity may be as much as 2 grammes. It is less in attacks of gout, during which the quantity in the blood is increased. In febrile conditions the amount is also increased. Uric acid is not free in the urine, but is combined with sodium, ammonium, potassium, calcium, and magnesium to form urates, the Fig. 41. — Uric Acid and Urates (Fiiiike). sodium and ammonium urates being the most abundant. Under ordinary circumstances it remains in combination, 212 HUMAN PHYSIOLOGY. but when the urine is very acid it appears in the form of crystals (Fig. 41). So2irce of Uric Acid. — Uric acid is regarded by some writers as being an intermediate product in the forma- tion of urea. These believe that the process of oxidation of the nitrogenous materials has for some reason, as from an insufficient supply of oxygen, been arrested before the stage of urea is reached ; but this theory of the formation of uric acid has not been substantiated. From the evi- dence now at our disposal it must be regarded as one of the final products of oxidation, as is the case with urea. There is some evidence that uric acid is formed in the spleen of man, the quantity eliminated being in- creased when the spleen is enlarged, and being dimin- ished when this organ is reduced in size. There is no reliable evidence that the human liver produces this acid, although it is doubtless formed in the liver of birds. Hippiiric acid, another ingredient of urine, is excreted in about the same amount as uric acid. A vegetable diet, especially of fruits, may increase this excretion to 2 grammes daily. Hippuric acid has also been found in perspiration and in blood. Creatinin. — As shown by the table, creatinin is ex- creted daily to the amount of 1.5 grammes. It is con- sidered as being formed from creatin, and is spoken of as the anhydride of creatin. Creatin, it will be remem- bered, is a constituent of muscles especially, although it is found also in nervous tissue. As would be expected from its derivation, the quantity in urine will be increased under a diet of flesh. Inorganic Constituents of Urine. — The inorganic con- stituents of urine are principally phosphates, chlorides, and sulphates. The phosphates especially worthy of KIDNE YS. 213 mention are those of sodium, both neutral and acid. To the latter is attributed the acidity of the urine. The Fig. 42. — Calcium Phosphate (Laache). phosphates of the urine are derived from the phosphates of the food, and there is no foundation for the theory that Fig. 43.— Triple Phosphates and Ammonium Urate (Laache). they are increased by mental exertion and represent the waste of nerve-tissue. The amount of phosphates ex- 214 HUMAN PHYSIOLOGY. creted is increased in fevers and in diseases of the bones, and is diminished during pregnancy. The chlorides are mainly represented by the chloride of sodium, and, as they are derived from the food, the amount eliminated depends upon the amount in the food. In pneumonia the amount of chlorides is diminished. The sulphates in the urine are principally salts of potassium and sodium, which are derived from the food, but they differ in this respect from the phosphates and chlorides, that while the latter exist in the food in the same form as in the urine, the sulphates are derived principally from the proteids, of which sulphur is a constituent, while the sulphates of the food contribute but little. Coloring-matter of the Urine. — The coloring-matter of the urine is not ordinarily abundant. It probably does not consist of one substance alone, but of several, the best known of which is urobilin. Some writers, how- ever, hold that normal urine contains but one pigment, to which the name " urochrome " has been given. " Uro- erythrin " is the name given to the coloring-matter in pink urinary deposits and to the highly- colored urine present in rheumatism, and " urinary melanin " to that found in the dark-brown or black urine of persons suf- fering from melanotic tumors, the color of which is very dark, due to the presence of melanin. Mucus. — The urine contains mucus, derived from the various passages through which it passes, which under normal conditions has no decomposing action on the urea. Gases of the Urine. — Oxygen, nitrogen, and carbon dioxide are present in the urine, the latter gas being the most abundant, the quantity being increased after active muscular exertion. III. NERVOUS FUNCTIONS. I. General Considerations. There is a most intimate relationship existing be- tween the different organs of the body — so intimate, indeed, that not one of the whole number can be said to be entirely independent. Many illustrations of this dependency might be given, but one will suffice. The respirations of an individual at rest are not far from sixteen per minute, and the pulsations of the radial artery are, in the same condition, about seventy. If, now, he exercise violently — running around the block, for instance — the respirations will be found to have greatly increased, amounting perhaps to. thirty per minute, while at the same time the pulsations of the artery will have reached one hundred and twenty per minute. Is this change from the quiescent condition a mere coincidence, or is there a reason for it ? If the latter, how has the change been brought about ? During a resting condition the muscles of the body do not make much demand upon the blood, and with the heart beating seventy times per minute the muscles, as well as the other tissues, are receiving all the material they need for the performance of their functions. The sixteen respirations a minute are also sufficient to supply the blood with all the oxygen required and to remove from it the necessary amount of carbon dioxide. When, however, the muscles are called upon for the increased exertion above referred to, they must have a greater sup- ply of the necessary materials, to furnish which a larger amount of blood must be sent to them. Then, too, as a 215 2l6 HUMAN PHYSIOLOGY. result of the extra work, more muscular tissue is wasted, and the waste must be taken away rapidly to the organs whose duty it is to eliminate it. To send the larger sup- ply of blood the heart must beat faster, and to provide the increased oxygen and to remove the additional car- bon dioxide the respiratory movements must be more rapid. The muscles of the body have not the power within themselves to increase their activity, but when acted upon properly from without they have. Neither has the heart-muscle the power to beat more quickly until stimulated thereto by some influence outside itself. Equally powerless are the agencies which produce the respiratory movements. These outside influences, by which the muscles contract and by which the heart and the respiratory apparatus act in harmony, are derived from the nervous system, a collection of organs one of whose functions is to cause the different organs to act harmoniously. The effect of a want of harmony under the circumstances just supposed would be most disastrous. If the nervous force were not at command to make the muscles respond when their increased action was desired, there would be a condition of paralysis, or if, when the muscles attempted to perform this added task, the heart should fail to respond, the effort would be fruitless, and equally unavailing would be the attempt if at the crucial moment the lungs and other respiratory organs should be unresponsive. As was said, many illustrations of the interdependence of the organs might be given, but a little reflection will suggest them almost ad infinitum. The simplest movements that are made require for their performance the conjoint action of several, often many, muscles, and were it not for the exciting and con- trolling power of the nervous system, instead of the har- NERVOUS FUNCTIONS. 21/ mony which is everywhere and at all times apparent there would result the utmost confusion. In what has been said thus far reference has been had only to the individual, as if he were alone on the face of the earth and interested only in himself; but there are other human beings with whom he is constantly brought into relation, and a world of other animate objects as well as an infinite amount of inanimate matter. This relation- ship is also accomplished through the nervous system, principally by means of the special senses. It will, therefore, be seen that the nervous functions are those which bring the different organs of the body into har- monious relations with one another, and, in addition, bring the individual, through the special senses, sight, hearing, etc., into relation with the world outside him. The nervous system is made up of collections of nervous tissue, which is composed of two kinds of matter — cel- lular or vesicular, and fibrous. Cellular or vesicular nerz'ous matter is found in the ex- ternal portions of the brain, the internal portions of the spinal cord, and in ganglia generally, a ganglion being a collection of nerve-cells. Such a collection of nerve-cells is also .spoken of as a " nerve-centre," being so called for the reason that it is composed of nerve-cells or vesicles (Fig. 44). From its grayish color it is also known as gray nervous matter, and, because of its ashy appear- ance, as cineritious nervous matter. When examined under the microscope it is seen to be made up of nerve- cells or ganglion-corpuscles, which are the characteristic elements, together with nerve-fibres and blood-vessels, all imbedded in neuroglia, a form of connective tissue. Nerve-cells vary in size, from 10 m.mm. in the sympa- thetic ganglia to 135 m.mm. in the anterior cornua of the 2l8 HUMAN PHYSIOLOGY. spinal cord. These bodies vary also somewhat in shape, some being spherical and others ovoid, while still others are exceedingly angular. They possess very prominent nuclei and nucleoli, and they have processes varying in number and giving rise to a nomenclature by which they are distinguished. Cells with one process or pole are Fig. 44. — Multipolar Nerve-cells : a, from the anterior gray column of the spinal cord of the dog-fish Ij'ing on a texture of fibrils, c\ b, prolongation from cells ; d, nerve- fibres cut across (Cadiat). unipolar ; with two poles, bipolar ; with three or more poles, multipolar. Sometimes cells are found having no process ; to such the term apolar has been given. It is doubtful, however, whether there are such cells, except as the result of accident by which a process has been broken off In the spinal ganglia unipolar cells exist, while in the cord cells are found the number of whose processes is as many as eight. Frequently the processes may be seen to be branched, the branches themselves subdividing again and again. Often, however, one pro- cess may be traced for a considerable distance from the nerve-cell in which it originated without any branch NERVOUS FUNCTIONS. 219 being discovered. Such a process is continuous with the axis-cyHnder of a nerve-fibre, and is therefore called the " axis-cylinder prolonga- tion." The branched pro- cesses disappear in the nerv- ous tissue : they probably con- nect with processes from other nerve-cells. Fibrous nervous matter, which is the material com- posing nerve-fibres, is of two kinds : (i) medullated, and (2) non-medullated. {\) Medullated fibres, which are called also " white fibres " by reason of their color, make up the white por- tion of the brain and the spinal cord, and, with few exceptions, the cerebro-spinal nerves — namely, those having their origin in the brain and spinal cord. A medullated fibre is composed of the axis-cylinder, the most central portion, the white substance of Schwann, which envelops it, and the primitive sheath, sometimes called " neurilemma," a delicate external membrane (Fig. 45). Of all these .structures the axis-cylinder is the most important ; indeed, it is an essential, as without it the nerve could not perform its functions. The neurilemma and the white substance are not always present in all portions of a medullated nerve. At the. commencement and at the termination they arc absent. The size of the medullated fibres is very variable. In the gray sub.stance of the spinal cord they may be found, Fig. 45. — A, three medullated nerve- fibres, the medullary sheath of which is stained dark with osmic acid ; N, nodes of Ranvier ; B, two non-med- ullated nerve-fibres, with nuclei in the primitive sheath. 220 HUMAN PHYSIOLOGY. having a diameter of 2 m.mm., while in the peripheral nerves this may be as much as 18 m.mm. (2) Non-medidlated fibres, which are known also as " gray and gelatinous fibres " and " fibres of Remak," compose the olfactory nerve and the sympathetic nerves, and are also found elsewhere. As their name implies, they have none of the medullary or white substance of Schwann. They are composed of fibrillae within a sheath, the former being the axis-cylinder, the latter the neu- rilemma. Scattered along the fibre between these two structures are nuclei. Termination of Nerve-fibres. — Nerve-fibres terminate in various ways. In voluntary muscles they terminate in end-plates, fibres from which, doubtless representing the axis-cylinders, are connected with the contractile tissue of the muscular fibres. In involuntary muscular Fig. 46. — Drawing from a Section of Injected Fig. 47. — End-bulb from Human Skin, showing three papillje, the central one containing a tactile corpuscle (ci), connected with a meduUated nerve, and that at each side (c) occupied by vessels (Cadiat). Conjunctiva, treated-with osmic acid, showing cells of core (Long- worth) : a, nerve-fibre ; b, nucleus of sheath; c, nerve-fibre within core ; d, cells of core. tissue the nerve-fibres form a plexus from which are given off smaller fibres that are ultimately distributed to NERVOUS FUNCTIONS. 221 the nucleoli. In glands the nerve-fibres end in secreting cells; in the skin some terminate in the hair-follicles and others in the epithelium. Besides these nerve-fibres there are three kinds of corpuscles in and beneath the skin with which nerves are connected — namely : ( i) TJic corpuscles of Pacini, which are constantly found in the subcutaneous tissue of the palms of the hands and the soles of the feet, and are sometimes found also in other situations, such as the dorsal surface of the hands and feet, and the nipples ; (2) TJie tactile corpuscles (Fig. 46), which are present in about one in four of the papillae of the skin of the third phalanx of the index finger, are found also in other papillae, but not in such great proportion. As a rule they are most abundant on the plantar surface of the feet; (3) The end-bulbs (Fig. 47), which occur in the con- junctiva, the mouth, the tongue, the glans penis, and the clitoris. Chemistry of Nervous Matter. — The chemical com- position of nervous matter is by no means thoroughly understood. Among its constituents are cholesterin, lecithin, cerebrin, protagon, and neuro-keratin. Functions of Nerve-cells and Nerve-fibres. — The nerve-cells receive and generate impulses, while nerve- fibres have the power only to conduct the impulses. Classification of Nerve-centres. — A collection of nerve-cells, whether it be large or small, is a nerve-centre or ganglion. In such a centre there are, besides the cells, blood-vessels, nerve-fibres, and neuroglia, but the cells are the characteristic element upon which the function of a centre depends. These centres may be divided into (i) conscious; (2) reflex; (3) automatic; (4) relay; and (5) junction. 222 HUMAN PHYSIOLOGY. Conscious nerve-centres are located in the brain. In them the sensation of pain is produced, and out from them go the impulses which result in voluntary move- ments. Reflex Nen>e-centres. — The gray matter of the spinal cord is an admirable example of a purely reflex centre. Impressions reaching it by the sensory roots of the spinal nerves excite impulses which travel out along motor nerves to muscles, and cause them to contract. In this there is no consciousness ; indeed, in an animal that is decapitated the same action takes place. Reflex centres are found also in the brain. Automatic nerve-cejitres do not require to be excited to action by impulses coming to them through afferent nerves, as is the case with the reflex centres, but they send out impulses without such excitation. The cardio- inhibitory centre in the medulla oblongata, in which cen- tre originate the impulses that have already been spoken of as being sent to the heart through the pneumogastric, is one of these. Relay Nerve-centres. — When a feeble impulse reaches a relay centre, that centre is excited, and from it may go out very powerful impulses, just as a feeble current of electricity may bring into play a local battery which will have much greater power than the current which brought it into action. Junction nerve-centres are those which are so con- nected with other centres that an impulse exciting one may also excite the other, and thus impulses may be sent to several regions of the body. Classification of Nerve-fibres. — Nerve-fibres con- duct impulses from within outward and from without inward. Whether it is the function of a given nerve NERVOUS FUNCTIONS. 223 to do the one or the other does not depend upon anything in the nerve itself, but upon its relations; and there is every reason to believe that were it pos- sible to separate a nerve from its anatomical connections and attach it to different structures, it would be just as capable of acting in its new relations as it did in the old; just as a copper wire will equally well carry a current of electricity to ring a bell or to supply a motor or to turn a hand on a dial : the result depends not upon the wire, but upon the mechanism with which it is in connection. Studying nerves, then, as they are actually found in the body, it will be found that there are some which carry impulses outward from nerve-centres; these are efferent nerves. Inasmuch as the impulse is going away from the centre, they are also called " centrifugal nerves ;" those which carry impulses from the periphery to the centres are called " afferent " or " centripetal nerves ;" while a third class comprise those which connect nerve-centres with one another, and are called " intercentral nerves." Bflterent nerves were formerly spoken of as motor nerves, and indeed even now some writers use the terms efferent and motor as synonyms. All motor nerves are efferent, for they carry impulses outward, but all efferent nerves are not motor nerves. A nerve which carries an impulse to a muscle, and thus brings about motion, is properly called a " motor nerve ;" but one that conducts an impulse to a gland, the result of which is the activity of its cells and the production of a secretion, is improp- erly named a motor nerve, although it is unquestionably an efferent nerve. Secretory is a much more expressive name. Efferent nerves maybe divided as follows: (i) 224 HUMAN PHYSIOLOGY. motor; (2) vaso-motor; (3) secretory ; (4) trophic ; and (5) inhibitory. Motor nerves terminate in muscles, and convey to them impulses which cause and regulate their contraction. Vaso-motor nerves, although distributed to the muscu- lar tissue of blood-vessels, and thus act as motor nerves, regulate the amount of blood supplied to a part, and it seems wise to separate them from the purely motor nerves and put them in a class by themselves. Secretory Nerves. — The impulses which these nerves carry to glands bring about their secretion. The chorda tympani is a striking example. Trophic nerves are supposed by some to govern the nutrition of the structures to which they are distributed entirely independently of the regulation of the blood- supply. It is still a mooted question whether such nerves exist. The subject will be again discussed in the consideration of the functions of the fifth pair of cranial nerves. Efferent inhibitory nerves carry outward impulses which restrain or inhibit the action of the organs to which they are distributed. The pneumogastric, so far as the heart is concerned, is such a nerve. Without its restraining influence the heart would beat much faster. Afferent nerves in some physiological works are called " sensory nerves," but there is the same impro- priety in using these terms synonymously as in the case of efferent and motor nerves. All sensory nerves are afferent, but all afferent nerves are not sensory. Affer- ent nerves may be divided as follows, although the dis- tinction is by no means so well marked as in the efferent nerves: (i) sensory; (2) nerves of special sense; (3) thermic nerves ; (4) excito-reflex ; and (5) inhibitory. NERVOUS FUNCTIONS. 225 (i) Sensory Ncn lUARv Pnocesc RCULAR SINUS CAAAL or pcm Fig. 65. — Section of Eyeball. ball. In the anterior part the membrane is absent and its place is occupied by the cornea. Cornea. — This structure is the most prominent portion of the eyeball, and by virtue of its transparency the iris can be seen through it. Choroid. — Internal to the sclerotic is the choroid, a vascular membrane containing pigment. Its ante- rior portion is thickened, forming the ciliary body, the inner parts of which consist of folds, the ciliary proc- esses. Iris. — The iris is a muscular curtain behind the cornea, the fibres being both circular and radiating (Fig. 66). In the centre is an opening, the pupil, around which, on the posterior surface of the iris, are arranged the circular fibres forming the sphincter pupillae, which receives its nervous supply from the motor oculi through the ciliary 3o8 HU3IAN PHYSIOLOGY. ganglion. The muscular fibres which form the dilator pupillae are arranged in a radiating direction from the circumference to the margin of the pupil, where they blend with the fibres of the sphincter. These fibres are supplied with sympa- thetic nerves from the ciliary ganglion. It is the iris that gives to the eye its character- istic color, which varies in dif- ferent persons according to the amount and the arrangement of the pigment, the latter being more abundant and more dis- seminated in dark than in light eyes. Fig. 66. — Choroid Membrane and Iris, exposed by the removal of the sclerotic and cornea : a, one of the segments of the sclerotic thrown back ; l>, ciliary muscle ; c, iris ; e, one of the ciliary nerves ; /, one of the vasa vorticosa or choroidal veins (Quain). Fig. 67. — Diagrammatic Section of Retina, showing the relation of the different layers in the posterior part of the fundus (not the macula lutea) (Schultze): I, nerve-fibre layer in which the retinal vessels run next to the vitreous humor ; 2, layer of nerve-cells ; 3, internal granular layer; 4, internal nuclear layer; 5, external granular layer ; 6, external nuclear layer ; 7, rods and cones with their extremities imbedded in the epithelial cells; 8, pigmented epithelium lying next to the choroid coat. Ciliary Muscle. — Between the sclerotic and choroid, anteriorly, is the ciliary muscle, a band about 3 mm. NERVOUS FUNCTIONS. 3O9 broad, composed of radiating and circular unstriped fibres. Retina. — The retina is the most internal of the tunics of the eye, and it is the portion which receives the rays of light. In the centre of the retina is the macula lutea, or yellow spot of Sommering, and at its centre is a depres- sion, the fovea centralis (Fig. 67). At a distance of about 2.5 mm. internal to the macula lutea is the optic disk, the entrance of the optic nerve. As at this point vision is absent, it is also called the "blind spot." Through its centre passes the central artery of the retina. The structure of the retina is very complex, being made up of ten layers : (i) Meinbrana liinitans interna, the most internal layer. (2) Fibrous layer, composed of nerve-fibres of the optic nerve. (3) Vesicular layer, consisting of large ganglionic nerve- cells, one process from each of which passes into the fibrous layer, and which is regarded as connecting with a nerve- fibre, while from the other end of the cell goes off another process (in some more than one), which passes into the fourth layer. (4) Inner molecular or granular layer, so called from its granular appearance, consists of minute fibres which are believed to connect with the adjoining layer. (5) Inner nuclear layer, containing oval nuclei be- lieved to be bipolar nerve-cells, one process of which passes into the inner molecular layer, and which is regarded by some as connecting, through this, with the ganglion-cells of the third layer: the other process passes into the sixth layer, and is believed to connect with the rods and cones. Besides the oval nuclei this layer contains other cells. 3IO HUMAN PHYSIOLOGY. (6) Otiier molecular layer, containing minute fibres and stellate cells, regarded as ganglion-cells. (7) Outer nuclear layer, consisting of oval nucleated cells of two varieties ; one variety, called " rod-granules," con- nects with the rods of the ninth layer, and the other, called " cone-granules," connects with the cones of that layer. (8) Membrana limitans externa is the next layer. (9) Jacob's membrane, or layer of rods and cones, is com- posed of rods and cones, the former solid bodies arranged perpendicularly to the surface, each of which is made up of an outer and an inner part joined together. The outer part presents a striated appearance, and is composed of disks, one upon another. The inner part connects with a rod-granule of the seventh layer. The cones, which are not so numerous as the rods, are conical in shape, their bases lying in the membrana limitans externa. They possess also an inner and an outer portion, the former being likewise striated, but the latter is more bulging. (10) Pigmentary layer, consisting of a single layer of pigmented cells, was formerly regarded as belonging to the choroid. The retina at the macula lutea differs in structure from that just described, inasmuch as the nerve-fibres of the second layer do not form a continuous layer; the third layer is composed of several strata of cells instead of one stratum ; there are only cones, no rods, and in the seventh layer there are only cone-granules. At the fovea centralis are to be found only the cones, the outer nuclear layer, and a thin inner molecular layer. Anterior and Posterior Chambers. — The anterior cham- ber is the space between the cornea and the iris, while the NERVOUS FUNCTIONS. 3II posterior chamber is the space between the peripheral part of the iris, the suspensory hgament, and the cihary processes. The latter is very much smaller than it was formerly supposed to be ; indeed, it hardly deserves the name of " chamber." Both these .spaces are filled with aqueous humor, an alkaline fluid, 96.7 per cent, of which is water and o.i sodium chloride. Vitreous Body. — This body is composed of transpa- rent, jelly-like material, called also " vitreous humor," which is enclosed by the hyaloid membrane. In the Fig. 68. — Fundus of an Eye containing little pigment, choroidal vessels visible (Wecker). anterior portion, which is depressed, this membrane is wanting, and in the depression is the crystalline lens. The margin of the hyaloid membrane is attached to the margin of the lens, and it is called the "suspensory lig- ament." • Crystalline Lens. — The lens is transparent and doubly convex, being more convex on the posterior than on the 312 HUMAN PHYSIOLOGY. anterior surface. It is situated behind the pupil, between the aqueous humor and the vitreous body, and is sup- ported by these structures and the suspensory hgament. It is contained in its capsule, which is also transparent and highly elastic. The capsule is in contact with the border of the iris, but not with the rest of the structure, and the small space thus left is the posterior chamber. Suspefisory Ligament. — This ligament is a portion of the hyaloid membrane which encloses the vitreous body, and is situated between that body and the ciliary pro- cesses. It aids in supporting the lens. Arterial Supply to the Eye. — The vessels which supply blood to the eye are the ciliary arteries and the arteria cen- tralis retinae (Figs. 68, 69). The nervous supply has already been considered. Physiology of Vision. — The eye has very aptly been compared to a photo- graphic camera, the trans- parent structure through which pass the rays of light representing the lenses, and the retina rep- resenting the sensitive plate on which the image is received, while the pig- mented choroid coat is the representative of the lamp- black with which the photographer darkens the interior of the camera-box to prevent any reflected light striking the plate and interfering with the sharpness of the pic- ture. In the camera, in order to bring to a focus upon the plate the rays of light coming from objects at differ- ent distances, the photographer uses a focusing screw, Fig. 69. — Normal Optic Disk of the Left Eye (after Jaeger). NERVOUS FUNCTIONS. 313 by which the lens may be moved nearer to or farther from the object he wishes to photograph ; and in order that clear images may be obtained by the eye it is neces- sary to accomplish the same result, for when the eye is focused for near objects those at a distance are blurred, and vice versa. This fact may readily be demonstrated by looking through a piece of mosquito-netting at the windows of a house on the opposite side of a street. When the threads of the net can be seen distinctly the bars of the window will be indistinct, and when the bars of the window are clear and distinct, then the threads are blurred. In the optical apparatus of the eye there is no provision for altering the position of the lenses, but there is one which answers the same purpose, and which is called " accommodation." In connection with every camera there is an arrangement of openings or diaphragms by which a greater or lesser amount of light may be admitted according to circumstances. In the eye the iris serves a similar purpose. In many cameras it is necessary to have a number of such dia- phragms, each having openings of different sizes, but some are provided with a single one, the size of whose opening can be altered ; this is called an " iris dia- phragm," and is a rude contrivance compared with the natural iris from which it derives its name, and which by means of its muscular fibres can alter in a moment the size of the pupil. Rays of light coming from an object, in order to pro- duce a distinct image of that object, must be brought to a focus upon the retina. If the media through which the light from an object passes to reach the retina were all of the same density as the air, and were also plane surfaces, an impression would be produced, but there 314 HUMAN PHYSIOLOGY. would be no distinct image. Actually, before such rays do reach the retina, they must pass through certain media which, by reason of both density and shape. Fig. 70. — Principal Focus of a Convex Lens. The parallel rays, a, b, c, d, are re- fracted by the lens so as to unite at the point F, on the axis, P ; the ray, P, under- goes no refraction. F is the principal focus. refract them and bring them to a focus, thus producing a sharp and distinct image of the object looked at. These media are the cornea, the aqueous humor, the crystalline lens, and the vitreous body. The cornea by its density and convex shape refracts the rays falling upon it, but, as its anterior and posterior surfaces are parallel, the cornea and the aqueous humor may be considered together as one medium, the posterior surface of which, that of the aqueous humor covering the convex crystalline lens, is concave. The anterior convex surface of the cornea and the concave posterior surface of the aqueous humor act as a con- cavo-convex lens, so that there are in reality but three media: i, cornea and aqueous humor; 2, crystalline lens; and 3, vitreous body. The optical axis of the eye passes through the centre of the cornea, directly back- ward through all these media until it terminates in the fovea centralis of the retina. Rays of light falling upon the cornea are refracted and made convergent, and this effect is increased by the lens, so that when the rays reach the NERVOUS FUNCTIONS. 315 retina they are brought to a focus. If the entire optical apparatus of the eye were rigid and immovable, it would be necessary, in order to obtain a clear image of an object, either for the individual to approach or to recede from the object, or to cause the object to do the same with reference to him, for only parallel rays — namely, rays coming from objects at a distance of 10 metres or more — are brought to a focus in the normal eye unless some change is brought about in the refractive media. If an object be within that distance, the rays of light coming from it are brought to a focus by altering the shape of the crystalline lens ; this is accommodation. Acco7nniodation. — As already stated, the optical appa- ratus of the eye is .in a state of rest when it is looking at objects more than 10 metres away; thus to see the stars, although millions of kilometres distant, no effort is Fig. 71.— Diagram showing the Changes in the Lens during Accommodation. The cih'ary muscle on the right is supposed to be passive, as in looking at distant objects : the suspensory ligament, L, is therefore tight, and compresses the anterior surface of the lens, W, so as to flatten it. On the left the ciliary muscle, M, is contracting, so as to relax the ligament, which allows the lens to become more convex. This contraction occurs when looking at near objects. required ; but if it be desired to see objects within that distance, there is a change in the refractive media until a point so close to the eye is reached that no amount of effort will enable them to be seen. The point at which objects cease to be seen distinctly is called the " near 3i6 HUMAN PHYSIOLOGY. point," and it is, for a normal or emmetropic eye, about 12 cm., although it is not the same in all persons. The accommodation of the eye is brought about especially by the change in the shape of the crystalline lens ; thus in looking at near objects the eye becomes more convex. This accommodation is accomplished in the following manner : The lens is a very elastic struc- ture, which is kept in a less convex condition when far Fig. 72. Fig, 73. Fig. 72. — Diagram showing three reflections of a candle : i, from the anterior surface of cornea ; 2, from the anterior surface of lens ; 3, from the posterior surface of lens. For further explanation see text. The experiment is best performed by employing an instrument invented by Helmholtz, termed a.j>hakoscope. Fig. 73.^Phakoscope of Helmholtz : a.t B B' are two prisms, by which the light of a candle is concentrated on the eye of the person experimented with; A is the aperture for the eye of the observer. The observer notices three double images, as in Fig. 72, reflected from the eye under examination when the eye is fixed upon a distant object; the position of the images having been noticed, the eye is then made to focus a near object, such as a reed pushed up ; the images from the anterior surfaces of the lens will be observed to move toward each other, in consequence of the lens becoming more convex. objects are looked at than its elasticity would cause it to assume were it allowed free play ; but the lens is enclosed in a capsule to which the suspensory ligament NERVOUS FUNCTIONS. 317 is attached, and the tension of this Hgament is such as to pull upon the anterior portion of the capsule and flatten it, at the same time flattening the anterior sur- face of the contained lens. But when a near object is to be looked at, the ciliary muscle contracts, and as its fixed point is at the junction of the cornea and sclerotic, this contraction draws the ciliary processes forward and relaxes the suspensory ligament, thus removing the influence which tends to flatten the lens and permits the latter by its elasticity to become more convex. The act is a voluntary one, the nervous supply for which is furnished to the ciliary muscle by the motor oculi through the ciliary nerves. At the same time that this muscular action is taking place the pupil becomes smaller and the eyes converge. Pliakoscope of Hcbnholtz. — The above explanation of the mechanism of accommodation is attributable to Helmholtz, who, to demonstrate it, has devised an ap- paratus called a " phakoscope " (Fig. 73), but it may also be demonstrated in the following manner : If a candle-flame be held at one side of the eye of a person who is looking at a distant object, and an observer look at the other side, he will see three images of the flame, the brightest and most distinct being an erect image which is formed by the anterior surface of the cornea. Besides this image there is a second image, which is also erect, but which is less distinct and larger; this image is formed at the anterior surface of the lens. A third image is also seen, which is inverted and also indistinct; this image is formed at the posterior surface of the lens, which, being concave forward, acts like a concave mirror and inverts the image. If the person then look at a near object, the second image becomes 3l8 HUMAN PHYSIOLOGY. brighter and smaller, and at the same time approaches the first, while the first image undergoes no change, and the third a change so slight as not to be perceptible (Fig. 72). This proves that in accommodating the eye for near objects the change which takes place is an increase in the convexity of the anterior surface of the crystalline lens. The same may be shown by looking at the eye from the side, when in accommodation the iris may be seen to move forward, being pushed in that direction b}^ the anterior surface of the lens with which it is in contact. Emnietropia is a condition of the eye in which the principal focus falls exactly upon the layer of rods and cones of the retina when the accommodation is relaxed, or, as it is expressed, when the eye is in a state of accom- modative rest. This is another way of saying that in this condition of the eye parallel rays are focused on the retina. An emmetropic eye is a normal eye. Ametropia. — Whenever the permanent condition of an eye is not as described above it is one of ametropia. Of this condition there are several varieties. Myopia. — A myopic eye is one that is abnormally elongated, and some authorities regard an increased convexity of the lens as constituting an essential part of this condition. The retina is so far from the lens that parallel rays are focused in front of it, and, crossing, do not form distinct images on the retina, the images being blurred. To correct this, concave glasses are used, which cause these rays to diverge as they enter the eye, and by adjusting the concavity to the amount of myopia parallel rays are thus brought to a focus on the retina as they are in the emmetropic eye without glasses. A myopic eye is commonly said to be a " near-sighted " one. NERVOUS FUNCTIONS. 319 Hypcrmetropia. — In this condition the eye is shorter than normal, and the retina is too near the lens, so that parallel rays are brought to a focus behind the retina and indistinct vision is produced, as in the myopic eye. In the endeavor to overcome this defect the ciliary muscle is liable to overstrain in order to converge the rays to a focus upon the retina, and the constant effort is painful and injurious. The condition is corrected by the use of convex glasses. Presbyopia, which is sometimes called " old sight," sometimes " long sight," is the condition of the eye seen in elderly people. In this condition it is difficult to see near objects, although the vision for those at a distance is unaffected. It is usually attributed to a lessened elas- ticity of the lens, though the ciliary muscle is also less strong, and some writers state that it depends on dimi- nution of the convexity of the cornea. To aid in correct- ing it convex glasses are used. Astigmatism. — In this condition the cornea is usually at fault, its curvature being greater in one meridian than in another, and consequently the rays of light from an object are not all brought to the same focus, and the image, therefore, is not distinct. For the correction of astigmatism glasses are worn which are segments of a cylinder — that is, curved in but one direction — and which are known as " cylindrical " glasses. The crystalline lens may also be at fault in astigmatism. Functions of the Retina. — As odors excite the olfactory apparatus and savors excite the gustatory, so does light excite the retina. As neither odors nor savors reach the brain, where smell and taste are produced, but only the nerve-impulses which they excite and which the olfac- tory and gustatory nerves transmit, so when the light- waves fall upon the retina they go no farther ; but the 320 HUMAN PHYSIOLOGY. nerve-impulses which they there excite are carried to the brain by the optic nerve and produce the sensation called " light." Thus it is that a blow upon the eye or an injury to the optic nerve produces in the brain the impression of a flash of light, although the room in which the blow or injury was received may be absolutely dark. That the optic nerve is itself insensitive to light is shown by the fact that at the point where it enters the eye, forming the optic disk, is the " blind spot," at which there is an entire absence of sight. This fact may be demonstrated in the following simple way : Look with the right eye at the round black spot here printed, closing the left eye, and holding the book six inches from it. The spot and the cross can both be seen. Now carry the book away from the face farther and farther, still looking at the spot. A point will be reached where the cross will all at once disappear, and when this occurs the light from the cross falls upon the optic disk. If the book be carried still farther, the cross will again come in sight. There is no doubt but that the portion of the retina which reacts to the stimulus of light is the layer of rods and cones, and of this layer the cones are especially sen- sitive. This is shown by the fact that the macula lutea (yellow spot) is the portion of the retina which is the most sensitive, and here there are no nerve-fibres, but rods and cones, and in the fovea centralis, which is the most sen- sitive portion of the macula, only cones are found. How the retina converts the impressions that light-waves pro- duce upon it into nerve-impulses is still an unsettled question. One theory is that the light produces chem- NERVOUS FUNCTIONS. 321 ical changes in the retina, the result of which is to stim- ulate the nerve-fibres; another theory is that there are thermic influences produced by the light which have the same effect ; while a third theory regards the pigment- cells of the retina as in some way connected with the phenomena. Movements of the Eyeball. — The eyeball is moved by muscles which have already, to some extent, been consid- ered in connection with the functions of the cranial nerves. The arrows in Fig. 74 indicate the direction in which the different muscles act. Thus it will be seen that the in- *-4 4-<: Fig. 74. — Movements of the Eyeballs: i, inferior oblique; 2, superior rectus; 3, ex- ternal rectus; 4, internal rectus; 5, superior oblique; 6, inferior rectus. ternal rectus rotates the eye inward ; the external rectus, outward ; the superior rectus, upward and inward ; the in- ferior rectus, downward and inward ; the superior oblique, downward and outward ; the inferior oblique, upward and outward. By a combination of two of these muscles various other movements are produced; thus the superior rectus and inferior oblique, acting together, rotate the eyeball vertically upward, while the inferior rectus and superior oblique jointly rotate it vertically downward. Appendages of the Eye. — Lachrymal Apparatus. — To 21 322 HUMAN PHYSIOLOGY. Fig. 75. — Muscles of the Eye: i, the palpebral elevator; 2, the trochlear muscle; 3, the pulley through which the tendon of insertion plays; 4, superior rectus muscle; 5, inferior rectus muscle; 6, external rectus muscle; 7, 8, its two points of origin; 9, interval through which pass the oculo-molor and abducens nerves; 10, inferior oblique muscle ; 11, optic nerve ; 12, cut surface of the malar process of the superior maxillary bone ; 13, the nasal notch ; A, the eyeball. keep the conjunctiva (the mucous membrane covering the anterior segment of the sclerotic and the cornea) moist and in normal condition is the function of the tears. They are secreted by the lachrymal gland, a compound racemose gland lodged in a de- pression at the upper and outer portion of the orbit (Fig. 'jG). Its ducts, about seven in number, open on the upper and outer half of the conjunctiva near its reflec- tion on the eyeball. At the edge FxG. 76.-1, canaliculus; 2, lach- of thc uppcr and lowcr cyclids, rymai sac; 3, nasal duct; 4, at their inucr cxtrcmitics, are plica semilunaris ; 5, caruncula . , , , 1 • \ lachryraaiis. opcnmgs (puncta lachrymauaj NERVOUS FUNCTIONS. 323 Fig. 77. — I, lachrymal gland; 2, its ducts; 3, punctum lachrymale ; a. conjunctiva ; 4, Meibomian glands. into which the tears pass after performing their func- tion. These openings are the beginnings of the can- ahcuh, which open into the lachrymal sac, or the dilated upper extremity of the nasal duct, which dis- charges at the inferior meatus of the nose, the opening here being partially closed by a fold of mucous membrane, the valve of Hasner. Meibomian Glands. — On the posterior surface of the eyelids, beneath the con- junctiva, are the Meibomian glands (Fig. yy), thirty in number on the upper and fewer on the lower lid. Their ducts open on the edges of the lids, and their secretion prevents the adhesion of the lids and the tears from running over them on to the cheeks. 5. Sense of Hearing. — The ear, the organ of hearing, is divided into three parts, external, middle, and internal, the latter being essential, while the others are accessory (Fig. 78). The external ear consists of the pinna or auricle and the external auditory canal or meatus. The office of the pinna is to collect the sound-waves and direct them to the canal, which they traverse to reach the membrana tympani. In some animals, such as the horse, the auri- cles are very important, enabling the animal to detect the direction from which sounds come, and they are cap- able of considerable movement; but in man they are not so important, although when the hearing is defect- ive they arc of assistance. That they are not essential to 324 HUMAN PHYSIOLOGY. hearing is shown by the fact that when removed hearing is not affected, and also by the fact that in birds, where they are absent, the sense of hearing is well marked. Fig. 78. — Semi-diagrammatic Section through the Right Ear (Czermak) : G, external auditory meatus; T, membrana tympani ; P, tympanic cavity : o, fenestra ovalis ; r, fenestra rotunda ; B, semicircular canal ; S, cochlea ; Vt, scala vestibuli ; Pt, scala tympani. The middle ear, tympanum, or tympanic cavity, is sepa- rated from the meatus by the membrana tympani. It is a cavity in the petrous portion of the temporal bone, is filled with air, and is in communi- cation with the pharynx by means of the Eustachian tube. It is lined with mu- cous membrane covered with ciliated epithelium. In the tympanic cavity are the ossicles (Fig. 79), a Fig. 79.-Ossicles of the Right Ear. chaiu of bonCS which COtt- lOeaiUeabr process NERVOUS FUNCTIONS. 325 nect the membrana tympani with the labyrinth or inter- nal ear. These bones are the malleus, the incus, and the stapes, otherwise known as the hammer, the anvil, and the stirrup, so called from their resemblance to these objects. The internal car, or labyrintJi, consists of three parts, the vestibule, the semicircular canals, and the cochlea. Fig. 80. — View of the Interior of the Left Labyrinth ; the bony wall of the labyrinth is removed superiorly and externally: i, fovea semielliptica; 2, fovea hemispherica ; 3, common opening of the superior and posterior semicircular canals; 4, opening of the aqueduct of the vestibule; 5, the superior, 6, the posterior, and 7, the external, semicircular canals ; 8, spiral tube of the cochlea (scala tympani) ; 9, opening of the aqueduct of the cochlea ; 10, placed on the lamina spiralis in the scala vestibuli (Sommering). CANALI*; REUNIENS Fig. 81. — Diagram of the Membranous Labyrinth (Gray). The.se arc cavities in the temporal bone which com- municate with the tympanum through the fenestra ovalis and fenestra rotunda, and with the internal auditory 326 HUMAN PHYSIOLOGY. meatus, through which runs the auditory nerve, the nerve of hearing. These cavities form the osseous laby- rinth. Within these is the membranous labyrinth, which contains the endolymph, while between the osseous and membranous labyrinths is a fluid, the perilymph. Vestibule. — The vestibule is a common cavity with which all the other portions of the labyrinth are in com- munication. On its inner wall are openings through which filaments of the auditory nerve enter; on its outer wall is the fenestra ovalis, an opening closed by the base of the stapes ; posteriorly the semicircular canals com- municate by five openings, and anteriorly is the opening of communication with the scala vestibuli of the cochlea. The membranous portion of the vestibule consists of two sacs, the utricle and the saccule, in the walls of which nerve-filaments are distributed, and within are the otoliths, two small bodies consisting of grains of car- bonate of lime. Semicircular Canals. — These canals are three in num- ber. The superior semicircular canal is vertical and at right angles to the posterior surface of the petrous por- tion of the temporal bone ; the posterior is also vertical, but is parallel with the surface of the bone, while the external or horizontal is directed outward and back- ward. The arrangement of these canals is such that each one is at right angles with the other two. Cochlea. — This structure resembles somewhat a snail- shell (Fig. 82). In its central portion is the axis, modi- olus, or columella, around which winds a spiral canal divided into two parts by a partition partly bony and partly membranous. The bony portion is the lamina spiralis, and the membranous portion is the membrana basilaris, while the lower canal is the scala tympani. NERVOUS FUNCTIONS. 327 The upper canal is subdivided by the membrane of Reissner, the larger part of the canal being the scala vestibuli, and the smaller the scala media, also called " canal of the cochlea." In the latter canal, covered over Fig. 82. — The Bony and Membranous Cochlea laid open : st , scala tympani ; sxi, scala vestibuli ; cc, scala media or ductus cochlearis ; h, lamina spiralis ossea ; h, helicotrema, or opening con- necting the scalse tympani and vestib- uli. Fig. 83. — Section through one of the Coils of the Cochlea (diagrammatic) : ST, scala tympani ; SV, scala vestibuli ; CC, canalis cochleae or canalis membranaceus ; R, membrane of Reissner; A',?, lamina spira- lis ossea ; Us, limbus lamina spiralis ; ji', sulcus spiralis; nc, cochlear nerve;^i-, gan- glion spirale; /, membrana tectoria (below the membrana tectoria is the lamina retic- ularis) ; b, membrana basilaris ; Co, rods ofCorti; /jr/, ligamentum spirale (Quain). by the membrana tectoria, is the organ of Corti, which is to the sense of hearing what the retina is to the sense of sight. Organ of Corti. — This structure is located on the membrana basilaris, and extends throughout the length of the cochlea, winding with it. It is composed of cells whose arrangement has been likened to the keyboard of a piano. The two central cells, which are rod-like, are the inner and outer rods of Corti. They form an angle with each other, being separated at the base and meeting above, leaving a space between them, the zona arcuata. As there are rows of these rods, this space forms a 328 HUMAN PHYSIOLOGY. tunnel extending the entire length of the cochlea. The number of the inner rods has been estimated at six thousand, and of the outer at four thousand five hun- dred. At the sides of these rods are rows of cells which are in communication with the terminal filaments of the auditory nerve. On the tops of these cells are hair- like processes, or cilia, covered by a delicate membrane with perforations, through which pass the cilia of the outer hair-cells. The membrana tectoria covers all these structures. Meclianisni of Hearing. — The membrana tympani is made to vibrate by the impulse of the sound-waves which reach it; through the ossicles these vibrations are communicated to the internal ear, the base of the stapes at its every movement sending a wave through the perilymph. This wave passes up the scala vestibuli from the fenestra ovalis, which the base of the stirrup closes, to the top of the cochlea, and comes down the scala tympani to the fenestra rotunda, in its course pass- ing over and under the membranous labyrinth filled with endolymph, through which fluid the vibrations are com- municated to the terminal filaments of the auditory nerve. It is supposed that these waves in the endo- lymph of the membranous vestibule cause the otoliths to come in contact with the nerve-filaments and to stim- ulate them. The nerves ending in the semicircular canals are believed to preside over the maintenance of the equilibrium of the body, and not to be connected with hearing. This will be referred to later. The cochlear division of the auditory nerve sends into the modiolus of the cochlea branches that pass in between the plates of the lamina spiralis, where they form a plexus in which are ganglion-cells, from which the nerve-filaments pass NERVOUS FUNCTIONS. 329 to the organ of Corti, terminating, it is believed, in the hair-cells. The waves already referred to as being set in motion through the endolymph pass over and under these cells, with which the nerve-filaments are connected, and cause the basilar membrane on which they rest to vibrate. This motion is communicated to the outer rods of Corti, which in turn pass it to the hairs of the special auditory cells through the medium of the perforated membrane, and from there it passes to the nerves. Here it is con- verted into impulses which are transmitted to the brain, where sound is produced. It has been supposed that the rods of Corti are so arranged as to vibrate with particular tones, one rod for each tone, but it is doubtful whether such a differentiation can be made out in the auditory apparatus. The rods are not present in the ears of birds, and there is no reason to believe that birds cannot appreciate musical tones. In the basilar membrane there are fibres enough to respond to all the notes that can be appreciated ; that is, from thirty-three waves to thirty-eight thousand waves in a second. It is more probable that the rods simply act as levers to communicate the vibrations of the fibres of the basilar membrane to the terminal nerve-filaments in the auditory cells. Just how one is able to distingui.sh the differences in the intensity (loudness), pitch, and quality of sounds is not understood. The explanation most generally ac- cepted at the present time, as to pitch at least, is that as, when a tone is sung over the strings of a piano, certain strings are set in vibration sympathetically, so in the basilar membrane, where, as in the piano, there are fibres of different length, these respond to different tones, and 330 HUMAN PHYSIOLOGY. that in connection with each tone there is a separate filament of the auditory nerve, so that if the note be a high one a certain fibre is set in vibration, and the nerve- filament in communication with it transmits an impulse to certain cells in the brain, which when excited give the impression of a high tone, and so with other tones and other nerve-cells. The introduction of the telephone and a study of its mechanism have led some writers to question the expla- nations which are generally accepted of the mechanism of hearing, and to suggest that as the single telephone wire transmits the complex sounds produced by an orchestra to a distance where they are reproduced in all their variety of intensity, pitch, and quality, so " the cochlea does not act on the principle of sympathetic vibration, but that the hairs of all its auditory cells vibrate to every tone, just as the drum of the ear does ; that there is no analysis of complex vibration in the cochlea or elsewhere in the peripheral mechanism of the ear ; that the hair-cells transform sound-vibrations into nerve-vibrations similar in frequency and amplitude to the sound-vibrations ; that simple and complex vibra- tions of nerve-molecules arrive in the sensory cells of the brain, and there produce, not sound again of course, but the sensations of sound, the nature of which depends not upon the stimulation of different sensory cells, but on the frequency, the amplitude, and the form of the vibrations coming into the cells, probably through all the fibres of the auditory nerve." This explanation has been put forth by Prof. William Rutherford under the title of the " Telephone Theory of the Sense of Hearing." Although sound-waves for the most part are trans- mitted to the internal ear through the tympanum, they NERVOUS FUNCTIONS. 331 may also be transmitted through the bones of the head. Thus vibrating bodies— a tuning-fork, for example— may be placed on the top of the head and the sound will be heard, or it may be held between the teeth with the same result. This fact is made use of in the audiphone, a fan- like device held in the teeth by the deaf If the essential portions of the auditory apparatus be so diseased as to cause deafness, no such device as the audiphone will be of any use. Eustachian Tube.— To permit the membrana tympani to respond properly to the sound-waves that reach it, the pressure of the atmosphere must be the same on both sides, and as the external pressure is subject to constant changes, a provision for a similar change on the tym- panic side is essential. This is accomplished by the Eustachian tube, the channel of connection between the tympanic cavity and the pharynx. The pharyngeal orifice of this tube is closed except during sv/allowing, at which time it is opened. If it were always open the sound of one's own voice would be so loud as to be ex- tremely disagreeable. Semicircular Canals. — These structures have probably no connection with hearing, nor are they designed to distinguish the direction from which sound-waves come, as when diseased the hearing is in no wise affected, but under these circumstances there is a feeling of giddiness and the movements of the body are uncertain. If one of them be cut, the head of the animal experimented upon is violently moved to and fro in the plane of the canal which was divided, and it walks in an unsteady manner. The canals are therefore regarded as being connected with the maintenance of equilibrium. Sympathetic Nervous System. — The sympathetic ner- 332 HUMAN PHYSIOLOGY. Fig. 84. — Diagrammatic view of the Sympathetic Cord of the Right Side, showing its connections with the prin- cipal cerebro-spinal nerves and the main prseaortic plexuses. (Reduced from Quain's Anatomy.) Cerebro-spinal Nerves. — VI., a por- tion of the sixth cranial as it passes through the cavernous sinus, receiving two twigs from the carotid plexus of the sympathetic nerve ; O, ophthalmic ganglion connected by a twig with the carotid plexus; M, connection of the spheno-palatine ganglion by the Vidian nerve with the carotid plexus ; C, cervi- cal plexus ; Br, brachial plexus ; D 6, sixth intercostal nerve ; D 12, twelfth ; L 3, third lumbar nerve; S i, first sac- ral nerve ; S 3, third ; S s, fifth ; Cr, anterior crural nerve ; Cr, great sciatic ; p7i, vagus in the lower part of the neck ; r, recurrent nerve winding round the subclavian artery. Sympathetic Cord. — c, superior cer- vical ganglion ; c' , second, or middle ; c" , inferior ; from each of these ganglia cardiac nerves (all deep on this side) are seen descending to the cardiac plexus ; d i, placed immediately below the first dorsal sympathetic ganglion ; I d 6, \% opposite the sixth ; / 1, first lumbar ganglion ; c g, the terminal or coccygeal ganglion. Prceaortic and Visceral Plexuses. — //, pharyngeal, and, lower down, lar- yngeal plexus ; pi, post, pulmonary plexus spreading from the vagus on the back of the right bronchus ; ca, on the aorta, the cardiac plexus, toward which, in addition to the cardiac nerve from the three cervical sympathetic ganglia, other branches are seen descending from the vagus and recurrent nerves ; CO, right or posterior and co' , left or anterior coronary plexus ; o, oesophageal plexus in long meshes on the gullet ; sp, great splanchnic nerve formed by branches from the fifth, sixth, seventh, eighth, and ninth dorsal ganglia; +, small splanchnic from the ninth and tenth: + -\-, smallest or third splanchnic from the eleventh ; the first and second of these are shown joining the solar plexus, so: the third descending to the renal plexus, re : connecting branches between the solar plexus and the vagi are also represented ; pn' , above the place where the right vagus passes to the lower or posterior surface of the stomach ; pn" , the left distributed on the anterior or upper surface of the cardiac portion of the organ : from the solar NERVOUS FUNCTIONS. 333 vous system consists of ganglia and nerves (Fig. 84). The four ganglia which some writers describe as sympathetic ganglia of the head, have been described in connection with the trigeminus. Sympathetic Ganglia and Nerves. — From the base of the skull to the end of the spinal column there is on each side of the latter a chain of ganglia (twenty-four in number) which are connected in a series by nervous matter, each being spoken of as a ganglionic cord. At the coccyx these cords unite in one ganglion, the gan- glion impar, and they are called " lateral," " vertebral," or " vaso-motor " ganglia. Besides these ganglia there are three gangliated plexuses — the cardiac in the thoracic cavity, the solar in the a"bdominal, and the hypogastric in the pelvic cavity. These are spoken of as " collateral " ganglia. There are besides ganglia in the viscera, as, for instance, in the heart; these are terminal ganglia. The ganglia on the posterior roots of spinal nerves are also regarded as belonging to the sympathetic system. The sympathetic ganglia differ in no important par- ticular from the ganglia already described. The nerve- cells are small, and are to a considerable extent unipolar. The nervous matter which connects the ganglia consists of both white and gray nerve-fibres. The ganglia are plexus large branches are seen surrounding the arteries of the cosliac axis, and descend- ing to }ns, the sup. mesenteric plexus : opposite to this is an indication of the supra- renal plexus; below re (the renal plexus), the spermatic plexus is also indicated; ao, on the front of the aorta, marks the aortic plexus, formed by nerves descending from the solar and sup. mesenteric plexuses and from the lumbar ganglia; ml, the inf. mesenteric plexus surrounding the corresponding artery ; hy, hypogastric plexus placed between the common iliac vessels, connected above with the aortic plexus, receiving nerves from the lower lumbar ganglia, and dividing below into the right and left pelvic or inf. hypogastric plexuses ; //, the right pelvic plexus ; from this the nerves descending are joined by those from the plexus on the sup. hemorrhoidal vessels, mi' , by ner\'es from the sacral ganglia, and by visceral nerves from the third and fourth sacral spinal nerves, and there are thus formed the rectal, vesical, and other plexuses, which ramify upon the viscera, as toward ir, and v, the rectum and bladder. 334 HUMAN PHYSIOLOGY. also intimately connected with the cerebro-spinal nerves by both white and gray fibres. The white fibres which pass fi-om the spinal nerves to the ganglia are con- tinuous with the white fibres just described in the branches of communication between the ganglia. The gray fibres pass fi-om the ganglia to the spinal nerves. The most recent writers are inclined to regard the cerebro-spinal and sympathetic systems not as distinct, but as parts of one great whole, and the intimate rela- tionship between the two is strongly confirmatory of this view. The history of the development of both is the same : the vaso-motor nerves, which are called " sympa- thetic," have their real origin in the cord and medulla, and, so far as known, the ganglia of the sympathetic do not respond reflexly to stimuli, as they would be expected to do if they were independent centres. Functions of the Sympathetic. — The efferent fibres of the sympathetic are distributed to the muscles of the vascular system as vaso-motor fibres ; that is, vaso-con- strictor and cardio-accelerator, and vaso-dilator and car- dio-inhibitory. The vaso-constrictor and cardio-inhib- itory nerves pass out from the spinal cord by the anterior roots of the spinal nerves from the second dorsal to the second lumbar, and pass to the lateral ganglia of the sympathetic. They are at this time medullated fibres, but in the ganglia they become non-medullated, and also increase in number, and go to their various points of distribution. The cardio-accelerator fibres pass into the stellate inferior cervical ganglion, where they lose their medullary sheath, and leave it as non-medullated fibres, to be distributed to the heart. The vaso-dilator or vaso- inhibitory nerves are doubtless as numerous as the vaso- constrictor, but far less is known of them. The nervi NERVOUS FUNCTIONS. 335 erigentes which pass to the hypogastric plexus, the chorda tympani, and the small petrosal nerve are illus- trations of this class of inhibitory fibres, as is also the cardio-vagus, the inhibitory nerve of the heart. These nerve-fibres have no connection with the lateral ganglia, but they pass on to the collateral or terminal ganglia. The sympathetic efferent fibres are also distributed to the muscles of the viscera, and are viscero-motor and viscero-inhibitory. The fibres which supply innervation to the muscles of the lower portion of the oesophagus, the stomach, and the intestines, by virtue of which they perform their peristaltic movements, are of this character. The viscero-inhibitory are but little understood. In addi- tion to these there are also glandular nerves which are distributed to secreting organs : of these little is known except as to the parotid, submaxillary, and lachrymal glands. The functions of the sympathetic ganglia are, so far as known, threefold : i, to change the medullated into non-medullated fibres ; 2, to divide the fibres into a large number of filaments ; and 3, to exercise a trophic or nutritive influence on the distal portions of the nerves, and possibly on the structures to which they are distrib- uted. The centres in the cord with which the sympa- thetic nerves are connected are Clark's vesicular column, Stilling's sacral nucleus, which is in that part of the cord corresponding to the second and third segments of the sacrum, and a third in the neighborhood of the vagal nucleus, that is, the portion of the medulla in which the vagus nerve has its origin. IV. REPRODUCTIVE FUNCTIONS. The reproductive functions are those concerned in the perpetuation of the species. In the lower forms of ani- mal life, where the individual consists of a single cell, this process of reproduction is very simple, consisting of the division of the cell into two, each of which has the same power of dividing to form new individuals in the same manner as itself was formed. This is asexual reproduction. In the higher animals the reproduction is sexual ; that is, it requires the union of two elements pro- duced in the organs of two individuals, the male and the female, neither of which can accomplish the process alone. I. Reproductive Organs. These organs, which are also called the genital or generative organs, are in the male the testes, each with its duct, the vas deferens, and the reservoir, the vesicula seminalis, and the penis ; and in the female, the ovaries, Fallopian tubes, uterus, and vagina. Genital Organs of the Male. — Testes. — The testes, or testicles (Fig. 85), two in number, are situated in the scrotum. They are composed of lobules, the number of which in each testis is variously estimated at from two hundred and fifty to four hundred. In each lobule are convoluted seminiferous tubules, tubuli seminiferi, varying in number from one to three. Spermatozoa. — In the interior of the testes are several layers of epithelial cells which, from the fact that they form the essential part of the semen, are called " sem- inal cells." At the time of puberty some of these cells, mother-cells, undergo division, producing thereby a 336 REPRODUCIIVE FUNCTIONS. 337 Fig. 85.— Testicle and Epididymis of the Human Subject: a, testicle ; b, lobules of the testicle ; c, vasa recta ; d, rete testis ; c, vasa efferentia ; f, cones of the globus major of the epididymis ; g, epididymis ; h, vas deferens ; i, vas aberrans ; in, branches of the spermatic artery to the testicle and epididymis; n, ramification of the artery upon the testicle and epididymis ; o, deferential artery ; /, anastomosis of the deferential with the spermatic artery (KiiUiker). Fk;. 86.— Section ol the 'I'ubull bcminiferi of a Rat (Schafer) : a, tubuli in which the spermatozoa are not fully developed; i^, spermatozoa more developed; f, spermatozoa still more developed. 22 338 HUMAN PHYSIOLOGY. number of smaller cells. These daughter-cells are called " spermatoblasts," and it is these cells that are changed into the spermatozoa which are the fecundat- ing elements of the semen. Each spermatozoon con- sists of a head, a body, and a tail. These terms do not indicate any special organ- ization, but are used simply for purposes of description, as we speak of the head of an arrow. The spermatozoa of different animals vary in size, although their general appearance is much the same. The human sperma- tozoon is about 0.055 mm. long (Fig. 87, a), while that of menobranchus is 0.57 mm. (Fig. ^j , c). These structures are endowed with the power of locomotion, due to the vibratory motion of their Fig. 87,-Spermatozoa : a, human ; /,. of ^^ils or fiagclla, by which , of menobranchus (magnified they Can travcl for a Consid- erable distance in the gen- erative passages of the female. The seminiferous tubules terminate at the apices of the lobules in the vasa recta (straight tubes), about thirty in number. In the mediastinum these tubes form a net- work, the rete testis, the vessels of which end in the vasa efferentia, about fifteen in number. These vessels connect the testicles with the epididymis, the continua- tion of which is the vas deferens. the rat ; 480 times). REPRODUCTIVE FUNCTIONS. 339 Vas Deferens and Vesienla Seniina/is. — The vas deferens may be regarded as the excretory duct of the testis (Fig. 88). It terminates at the base of the bladder, where it unites with the duct of the vesicula seminahs to form the ejaculatory duct, which discharges into the prostatic portion of the urethra. The spermatozoa traverse the following vessels after leaving the seminiferous tubules : vasa recta, rete testis, epididymis, and vas deferens. The mucous mem- brane lining each of these chan- nels adds its secretion as the spermatozoa pass along, until the vesicula seminalis is reached, which acts as a reservoir for the semen. The lining of the vasa recta and the rete testis is a single layer of flattened epi- thelium ; that of the vasa effer- entia, the epididymis, and the vas deferens is columnar and ciliated. The spermatozoa, up to the time that they reach the seminal vesicles, display but little of their characteri-stic motion. This is probably due to the fact that they are more or less agglutinated, but in these reservoirs there is formed a considerable quantity of secretion which dilutes the semen, and at this time the oscillatory motions of the spermatozoa become very marked. Genital Organs of the Female. — Ovary. — The ovaries (I''igs. 89, 90, 91J, two in number, are analogues of the IG. 88. — Posterior View of the Fundus of the Bladder : i, peri- toneum extending as far down as the transverse line ; 2, ureters ; 3, deferent canals; 4, seminal vesicle of the left side ; 5, right seminal vesicle dissected so as to show its tubular character ; 6, dnct of the seminal vesicle, joining the deferent canal to form, 7, the ejaculatory duct ; 8, prostate; 9, membranous por- tion of the urethra. 340 HUMAN PHYSIOLOGY. testicles. They are situated in the posterior part of the broad Hgament, one on each side of the uterus. The human ovar}- weighs about 8 grammes, and consists of stroma and Graafian vesicles or follicles. The stroma is made up of spindle-shaped cells, which are regarded by some authorities as non-striated muscle-cells, and by others as connective-tissue cells, together with connective tissue. The outer layer of the ovary, formerly called Fig. 89. — Section of the Ovary of a Cat, enlarged six times (Schron) : i, outer covering and free border of the ovary (epithelium and albuginea) ; i', attached border ; 2, vas- cular zone, or medullary substance ; 3, parenchymatous zone, or cortical substance ; 4, blood-vessels ; 5, Graafian follicles in their earliest stages, lying near the surface; 6, 7, S, more advanced follicles, imbedded more deeply in the stroma ; 9, an almost mature follicle, containing the ovTim in its deepest part ; 9', a follicle from which the ovum has accidentally escaped; 10, corpns luteum. "tunica albuginea," is now regarded as condensed stroma. The covering of the ovary is a single layer of columnar cells, the germinal epithelium of Waldeyer. This is quite different in appearance and structure from the peritoneum, which is covered hy flattened endothelium. The Graafian vesicles are sacs in the ovarian stroma var}'ing in size according to the period of their develop- ment. The wall of a vesicle is called the " membrana REPRODUCTIVE FUNCTIONS. 341 propria," and is made up of two layers — an external layer of capillary blood-vessels, the tunica vasculosa, and an internal or fibrous layer, the tunica fibrosa. The latter is lined with granular cells arranged somewhat in the form of a membrane, making the membrana or tunica granulosa. At one part of this membrane the cells are accumulated, forming the discus or cumulus proligerus, Fig. 90. — Part of the same section as represented in Fig. 89, more highly enlarged (Schron) : i, small Graafian follicles near the surface ; 2, fibrous stroma ; 3, 3', less fibrous, more superficial stroma ; 4, blood-vessels ; 5, a follicle still further advanced ; 6, one or two more deeply placed ; 7, one further developed, enclosed by a prolonga- tion of the fibrous stroma; 8, part of the largest follicle; a, membrana granulosa; b, discus proligerus ; c, ovum ;