SINCE the issue of the first volume of the Saunders Question=Cotnpends, OVER 265,000 COPIES of these unrivalled publications have been sold. This enormous sale is indisputable evidence of the value of these self-helps to students and physicians. SAUNDERS' QUESTION-COMPENDS. No. t. ESSENTIALS OF PHYSIOLOGY PREPARED ESPECIALLY FOR STUDENTS OF MEDICINE BY SIDNEY P. BUDGETT, M.D. 1 1 Professor of Physiology in the Medical Department of Washington University, St. Louis. Second Edition, Thoroughly Revised BY HAVEN EMERSON, A.M., M.D. i "t Physiology in Columbia University (College of Physicians and Surgeons), New York. x ARRANGED WITH QUESTIONS FOLLOWING EACH CHAPTER ILLUSTRATED PHILADELPHIA AND LONDON . B. SAUNDERS COMPANY 1906 '''..CQf '* ; -S^fciip, iele(Jtrt>ty]?ed', print?d, and copyrighted November, 1901. Reprinted October, 1902. Revised, reprinted, and recopyrighted August, 1905. COPYRIGHT, 1905, BY W. B. SAUNDERS & COMPANY. Reprinted August, 1906. PRESS OF W. B. SAUNDERS COMPANY PHILADELPHIA PREFACE TO THE SECOND EDITION. Tin: present revision has given opportunity to add a short summary of the adaptations of the blood in health and disease to foreign substances introduced into the body. A somewhat fuller treatment of the subject of human lactation and of the functions of the red and white blood-cells and of the blood as a tissue has seemed advisable. No change in the scope of the book JIMS l>een attempted. HAVEN EMERSON. Ni:\v YORK. '723*3 PREFACE. THESE abbreviated lecture notes are intended for the use of students in conjunction with a text-book, and not as a substitute for a larger work. Conse- quently, no attempt has been made fully to illustrate this book. The questions introduced at the end of eaeh chapter are not exhaustive, but may, it is hoped, if carefully considered, be found useful as an aid to thinking over what has been read. CONTENTS. CHAPTER I. PAOE Protoplasm, Blood, and Lymph 11 CHAPTER II. The Circulation of the Blood 39 CHAPTER III. Respiration 63 CHAPTER IV. Digestion ...... 77 CHAPTER V. Metalx>lism and Nutrition 105 CHAPTER VI. Excretion 127 CHAPTER VII. Animal Heat 141 CHAPTER VIII. Muscle and Nerve 147 CHAPTER IX. The Nervous System . . . 160 CHAPTER X. The Special Senses .210 Index .229 PHYSIOLOGY. CHAPTER I. PROTOPLASM, BLOOD, AND LYMPH. PROTOPLASM. PHYSIOLOGY is the science of the functions of living matter, as distinguished from the science of the form of living matter, or Morphology. The two groups <>f living matter are plants and animals, which are distin- guished physiologically bv the following essential differ- ence : The plant is able by the aid of solar energy to con- .-trnei its protoplasm from inorganic matter, t. e., water, carbon dioxid, and inorganic salts. The animal cell is unable to form protcid material from inorganic mate- rial. The animal cell has feeble powers <>!' synthesis and i> characterized chiefly by its power to break down organic material into simpler compounds. The animal cell must make its protoplasm largely of organic com- pounds alreadv formed. Living protoplasm, or bioplasm, is composed of a fine network of fibrilhe in which the more fluid portion of the protoplasm is contained. Protoplasm is impo-- >ible .if exact analysis since its life is destroyed by treatment with chemical reagents. It contains a large 11 12 \ : fj PROTOPLASM, BLOOD, AND LYMPH. st->i< v:f pme'itiai c.ie;;r\ ; it is unstable; and has the following propei -ties : iri liability, contractility, con- ductivity, nutrition, or assimilation, including processes of construction and destruction, and repro- duction. By irritability is meant that property of proto- plasm by virtue of which it is able to respond to a stimulus, which may be the normal nerve-impulse probably consisting in the transmission of a physical rather than a chemical change along a nerve fiber or an artificial stimulus, mechanical, thermal, chemical, or electrical. The response consists of a chemical change in the protoplasm, accompanied by the produc- tion of heat or visible motion or both, and often to a degree far in excess of the energy applied as a stimulus. Contractility is the property by virtue of which protoplasm is able to change its shape; the simplest instance being the ameboid movement of the white blood-cells. Conductivity is the property by virtue of which protoplasm is able to transmit an impulse from one part to another of its substance, as instanced in the passage of a nerve impulse. By nutrition we mean the power of converting dead food material into living substance. By reproduction we mean the power of each cell, or organism, to perpetuate its kind by the formation of new individuals. The tissues of the human body consist of cells and intercellular substance, the latter being of simpler material than the protoplasm of the cells, manufactured by the cells, and lacking the characteristics of living matter. On analysis, dead protoplasm is found to consist of water, inorganic salts, proteids, nucleoproteids, carbohy- 1'KOTEJDS. 13 (1 rates, fats, lecithin, cholesterin, and various simpler substances. Whether, and to what extent, these are, in the living condition, chemically combined with one an- other is not known. Proteids are highly complex bodies of unknown composition, made up of carbon, oxygen, hydrogen, nitrogen, sulphur, and sometimes phosphorus, in the fol- lowing proportions by weight: Carbon, 51 to 55% ; Oxygen, 20 to 24% ; Nitrogen, 15 to 17% ; Hydro- gen, 6.8 to 7.3% ; and Sulphur, 0.3 to 5%. A single proteid molecule may perhaps contain as many as 2000 atoms; the molecular weight of egg-albumen being possibly as high as 14,000. Native proteids are coagu- lated by boiling; they are precipitated by alcohol, by the salts of the heavy metals, and by mineral acids, and are coagulated by prolonged treatment with alcohol; they are nondialv/able. The table on the following page gives the solubility of several native proteids, proteoses, and peptones. Nucleoproteids are the most abundant proteids found in the cell protoplasm. They are compounds of a proteid and nuclein, nuclein itself being a com- pound of a proteid and nucleic acid, while nucleic acid may be split into phosphoric acid and nucleic bases, Mich as adenin, guanin, etc. Carbohydrates are composed of carbon, hydrogen, and oxygen, the two latter being present in the propor- tions to form water; they are simpler than the proteids, though some of the polysaccharids appear to be very complicated in structure : The carbohydrates may be divided into three groups, as follows : Monosaccharids, e. H g |l II I f i II 11 II 1 1 co cc y CD CC 1 M 1 1 GO GO B GO B B GO O C "/I O cc 7) o 1 SOLUBILITY. GO GO GO GO GO GO GO o P NaCl SOLUTION. g g g g 1* g g 5 ce GO ^ S o ^ loco 00 Saturated. 22 >- HH w h- GO co ,Jg- B B B B B O o -vi co co co cc co > i H ' ^ o O O O Saturated + acid. tT 1 hH 1 1 h- 1 1 f 1 I GO g 3 B B B B O g co cc co co cc j " & O (NH 4 ) 2 S0 4 . Saturated Sol. t 1 1 1 hH GO GO GO GO B B B O O O cc co co II PROTEIDS. 15 The stereochemical formulae of many sugars are kno\\ n, Kmil Fischer having, in the laboratory, syn- thesized a greater number than are known to exist in nature. The monosaccharids are aldehyds or ketones of hexatomic alcohols, and are known as aldoses and ketoses ; for instance, dextrose is the aldehyd of the alcohol sorbite ; levulose, or fruit-sugar, is the ketone of the alcohol inannite. The stereoelieniical formula for Grape-sugar (d-Glu- cose, or Dextrose) is as follows : H II OH H I I I I CH 2 OH - C C-C C COH I I I I OH OH H OH For Fruit-sugar (d-Levulose) : H H OH I I I CH 2 OH C C C CO CH a OH I I I OH OH H In the formula for dextrose, it will be notieed that there are a number of possible different arrangements of the four intermediate ( 1 II.()II groups; for instance, We may transpose the II and the OH in the last group, thus : H H OH OH I I I I CH,OH-C C C- C COH I I I I OH OH H H and we have d-Mannose, another sugar of the aldose group. It would be possible for sixteen different al- doses to exist, each with the formula CH,OH.(CHOH) r < '< >Il ; of these, twelve are known. Like other aide- 16 PROTOPLASM, BLOOD, AND LYMPH. hyds, they act as reducing agents, upon which property depend Trommer's and Fehl ing's tests. A series of these glycoses has been investigated, be- ginning with Triose ; in the triose group there are two possible isomers, only one, Glycerose, being known. The series is as follows : Trioses, C 3 H,.O 3 . 2 possible isomers. Tetroses, C 4 H 8 O 4 . 4 " Pentoses, C 5 H 10 O 5 . 8 " " Hexoses, C 6 H 12 O 6 . 16 t( " Heptoses, C 7 H U O 7 . 32 Octoses, C 8 H 16 O 8 . 64 Nonoses, C 9 H 18 O 9 . 128 Only those containing three carbon atoms, or a multiple of three, namely, members of the triose, hexose, and nonose groups, are assimilable to more than a trifling extent ; the others, when absorbed from the alimentary canal, being excreted unchanged by the kidneys. Of the disaccharids, the three following are of in- terest : Cane-sugar, Malt-sugar, and Milk-sugar. Cane- sugar can, by hydrolysis (see below), be converted into one molecule of dextrose and one molecule of levulose ; Malt-sugar, or Maltose, into two molecules of dextrose ; and Milk-sugar, or Lactose, into one molecule of dex- trose, and one molecule of galactose, another member of the hexose group. Of the polysaccharids, starch, the dextrins, glyco- gen, and cellulose are familiar instances ; the formula for each being (C 6 H 10 O 5 ) n . Fats are the ethereal salts of glycerin and fatty acids ; animal fats usually being mixtures of the thre' fats: METABOLISM. 17 I'alinitin, C.H.^CjgH^O.,),. Melting-point, 45 C. Stearin, ( ' j I (< \ J I,' ()J 3 . " 53-66 C. Olein, CX^H^),. -5C. The melting-point of a mixed fat depends on the rela- tive proportions of the mixture. Human fat contains from $1 c /o to 80^ olein, and is liquid at body-temper- ature. Lecithin is a complicated nitrogen- and phosphorus- containing fat, found in all cells, and more especially in the nervous system. Cholesterin, C^H^OH, is also found in the nervous system ; it is a constituent of all cells, especially blood- cells, and is present in the bile. It is a monatomic alcohol. Of special importance, amongst the inorganic salts of protoplasm, are the phosphates and chlorids of po- ta-sium, sodium, and calcium. Iron is also present, and is an indispensable constituent of the red blood- cell. The sum of the chemical exchanges occurring in liv- ing tissue is known as Metabolism. The process of building up living tissues, or assimilation, may be spoken of as Anabolism and is constructive or syn- thetic. Destructive or analytic processes are summed up in the term Katabolism. There is never complete < < ation of these processes even during rest of tissues or cells. Equilibrium is only obtained by constant eliange; the constant destruction which goes on within the cell demands an equally continuous supply of new material, which in the case of the proteids must be -iipplied as such from without. Hence the name proteids, or material "of first importance." Since oxidation is one of the chemical changes in- 2 18 PROTOPLASM, BLOOD, AND LYMPH. eluded under metabolism, a continuous supply of oxy- gen is another necessity. One of the chief products of oxidation is carbon dioxid ; this, and other waste products arising from katabolic changes, must be re- moved from the cell as fast as they are formed, as their accumulation is injurious to the bioplasm, and destruc- tive of its irritability. Another characteristic katabolic change is Hydrolysis, which consists in the hydration and splitting-up of a comparatively complex substance into two or more simpler bodies ; for instance : (C 6 H 10 5 ) n + nH 2 = nC 6 H 12 6 . Glycogen Water Dextrose Amongst the anabolic or synthetic changes there occurs the opposite of hydrolysis namely, one consist- ing of the building of two or more comparatively simple bodies into one complex substance, accompanied by dehydration ; for instance : nC 6 H 12 6 = (C 6 H 10 5 ) n + nH 2 Dextrose Glycogen Water. This is called dehydrolysis. After the food has been absorbed by the walls of the alimentary canal, it is still far out of the reach of the majority of the cells of the body ; the same is true of the oxygen that is absorbed from the air spaces of the lungs ; the cells would thus starve to death but for the intervention of the Blood, which, as it passes through the vessels of the alimentary canal, takes up the food, and on its way through the pulmonary vessels, takes up oxygen, carrying these to all parts of the body. The blood is, however, inclosed in a system of tubes, so that only those cells which line the vessels can obtain their nourishment directly from the blood. THE BLOOD. 19 Through tin- walls of the smaller vessels, there filters out a li(jiiid, closely resembling the blood plasma, called Lymph. In it, held in solution, are the neces- sary food-stiitls, and into it as it lies in the lymph- spaces, which intervene between the cells of the various tissues, there diffuses, from the blood-vessels, oxygen ; BO i hat the cells are thus supplied with both food and oxygen, through the lymph, by the blood. At the same time the waste products of cell metabolism pass from the cells into the lymph, and thus to the blood, by which they are carried to the various organs whose i unction it is to excrete them. The blood thus plays the part of both purveyor and scavenger. It also serves to equalize the temperature of the different parts of the body. THE BLOOD. The blood consists of cells and plasma. In that of man, the cells form about 48^ ; in that of women and children, rather less. The cells are of two varieties the red cells, or erythrocytes ; and the white cells, or leukocytes. Of the latter, there are several different ff ammonia from the proteid molecules. The Ducleoproteid found in the liquid part of the blood after it is shed perhaps originates from the leukocytes after the blood leaves the vessels, and may not lc a normal constituent of the plasma. Ferments arc present in small quantities only; a diantatie fennent is one which converts starch into sugar; a glycolytic fi'i'inent splits up sugar; a stcatolytic ferment splits up fats. * The three proteids of blood plasma differ in their solubility, as is set forth in Table I. They also differ in the temperature at which they coagulate. Serum- all >umin coagulates at three different temperatures: the first portion at 72 to 75 C. ; the second at 77 to 78 C. ; and the third at 83 to 86 C. Serum- globulin coagulates at 75 G. ; Fibrinogen, at 56 C. ; and Nucleoproteid, at 65 C. Coagulation. A highly important characteristic of blood is its power of clotting when shed; were it not ibr this, fatal hemorrhage might result from a very trifling wound. In the class of patients known as " bleeders" this is the case; their blood is lacking in the power of clotting. The term hemophilia is applied to this condition. From three to six minutes after human blood leaves the blood-vessel, if conditions be favorable, it becomes syrupy in consistence, and later forms a jelly which con- traets and expresses a clear yellow liquid the Serum. This change depends upon the appearance, in the plasma, of innumerable fine fibrils, which are distributed through- out the whole mass of blood in the form of a close mesh- work. In the interstices of this the blood-cells are en- tangled, so that they form a part of the clot, though not an indispensable part, for plasma may be caused to clot 22 PROTOPLASM, BLOOD, AND LYMPH. after the complete removal of the cells, in which case the clot is a light yellow, transparent jelly. The fibrils, on the formation of which clotting de- pends, consist of an almost insoluble proteid which is called Fibrin. If the blood, as it is shed, be collected in a vessel and whipped with a bundle of twigs, the fibrin fibrils adhere, as fast as they are formed, to the whipper, and may thus be removed from the blood. The blood thus defibrinated remains liquid indefinitely, and, by its appearance, cannot be distinguished from normal blood. If the fibrin collected in this way be washed free from the few blood-cells which are held between its fibrils, it is found to be a stringy, elastic substance, and gray in color. In composition, serum is similar to plasma, save that it contains no fibrinogen ; in addition, it contains a fer- ment of which mention will be made below. We see, then, that fibrinogen disappears during the clotting of blood. Further, if fibrinogen be removed before the blood has had time to clot, clotting Avill be entirely prevented ; thus fibrinogen is necessary to the clotting of blood. The clotting of blood depends upon the conversion of fibrinogen into fibrin. The next question is, What is the cause of this conversion ? The clotting of blood may be prevented by the addition of a certain quantity of a salt, such as magnesium sulphate, the amount added being insufficient to precipitate the proteids of the plasma. Blood so treated is known as salted blood, and from it, by allowing the blood-cells to settle, can be ob- tained salted plasma, which remains liquid. Now, if to salted plasma there be added a small quantity of blood-serum, or a small quantity of an extract made from a blood clotythe salted plasma clots ; its fibrinogen is converted into fibrin. The small quantity of serum CLOTTING OF BLOOD. 23 which is necessary indicates that the process may de- ]'iid upon the action of a ferment, or enzyme. Enzymes. The following are some of the charac- teristics of enzymes, or ferments, a class of bodies of whose nature we are ignorant, their analysis having, so far, proved impossible, owing to the difficulty of sepa- rating them from impurities, and of obtaining them in sufficient quantities. Their activity does not exhaust or use them up ; con- sequently A minute quantity of enzyme may cause the fermen- tation of an indefinite amount of fermentable material. The accumulation of the products of fermentation interferes with their continued action. Their action is retarded by cold. There is an optimum temperature, at which an en- zyme acts most rapidly : the optimum for those found in the human body is about 40 C. They are destroyed by boiling, though in a dry con- dition they may be heated to a temperature of 100 C. without injury. The activity of many enzymes is dependent on the reaction of the solution in which they are present, a neutral or slightly alkaline reaction being,most favor- able in the majority of cases ; pepsin, however, requires a slightly acid reaction. The chemical change resulting from their action is usually one of hydrolysis. (See page 18.) Maltase, however, while its characteristic action is the conversion of maltose (malt-sugar), by hydrolysis, into dextrose, can, if added to a strong solution of dextrose, convert a -mall portion of the latter into maltose. It is possible that other enzymes are capable of this reversed zymolysis, and that this affords an explanation of the hindering of an accumulation of the products of fermentation. 24 PROTOPLASM, 'BLOOD, AND LYMPH. Finely divided platinum, paladium, and iridum, be- have, in some respects, as do enzymes ; for instance, they may, by hydrolysis, invert cane-sugar that is, convert it into equal parts of dextrose and levulose. In the decomposition of H 2 O 2 , platinum appears to act by contact, and not by entering into the reaction. We know no more of the method of action of fer- ments than we know of their composition ; amongst other explanations that have been suggested are the fol- lowing ; according to one of these theories, the enzyme unites with the fermentable material to form an unstable compound which readily breaks down into the original enzyme, and substances which are simpler and more stable than the original fermentable material, e.g.: (1) Malt-sugar -f Enzyme + HZ^ Substance x. (2) Substance x = Enzyme -f Grape-sugar -f Grape-sugar. According to another hypothesis, the enzyme is in a state of molecular movement, which is, by contact, im- parted to the fermentable material, renders it unstable, or increases its instability, and thus causes it to break down into simpler and more stable substances. The susceptibility of any substance to the action of a given enzyme depends upon its molecular structure. To return to the clotting of the blood, there are other indications that the process is one of zymolysis. For instance, serum that has been boiled is no longer capable of causing salted blood or solutions of pure fibrinogen to clot ; again, clotting is retarded by cold, and hastened by keeping the blood at or a little above body-temperature. It is supposed that clotting is in- deed caused by an enzyme, to which the name of fibrin= ferment has been given. This ferment probably origin- ates, on the shedding of blood, from the union of a nucleoproteid, derived from the white blood-cells, with CLOTTING OF BLOOD. 25 calcium. Clotting may be prevented by the addition of any substance e. g., potassium oxalate or soap which will cause the precipitation of the soluble calcium of the plasma. It seems that contact with any foreign >urface causes the white blood-cells to excrete nucleo- protcid into the plasma, with the subsequent formation of fibrin-ferment; for if blood be drawn directly into oil through an oiled cannula, the formation of fibrin- frrment is very much delayed, apparently because the leukocytes are protected from the injury to which, but for the oiling of the cannula and receptacle, they would have been subjected. The prevention of coagulation by cooling the blood to C. also depends, in part, upon conservation of the leukocytes. The clotting of blood may, for the time being, be j in-vented by the intravascular injection of albumoses, or of a very small quantity of nucleoproteid ; the in- jection of larger amounts of nucleoproteid causes extensive intravascular clotting. The lungs in some unknown way lessen the tendency of the blood that circulates through them to coagulate, while the liver exerts an influence in the opposite direction. Transfusion. After severe hemorrhage it is some- times necessary to increase the bulk of the patient's blood by the injection of some liquid, and the choice of this liquid is important. Since defibrinated blood always contains fibrin-ferment, it is inadvisable to in- ject the blood of another person, even if that person is known to be perfectly healthy, and the blood has been whipped to prevent its coagulation; the fibrin-ferment contained in it may cause intravascular clotting of the n innant of the patient's own blood. The injection of blood taken from some other animal is objectionable for the same reason, and possesses another disadvantage 26 PROTOPLASM, BLOOD, AND LYMPH. namely, that the blood of one species may destroy the cells in the blood of another species with which it is mixed ; this is known as the globulicidal action. The direct transfusion of blood from the vessel of one patient into the vessel of another is dangerous, in that the leukocytes may be injured as they pass through the connecting cannula, and thus, nucleoproteid being set free, fibrin-ferment may be formed and coagulation be caused. In consequence of the difficulties and dangers of using defibrinated blood or direct transfusion of blood from one human to another recourse is usually had to infusions of solutions of inorganic salts, subcu- taneously or intravenously. A fluid for such purposes should be a perfect solution, isotonic with the blood ; i. e., the equivalent of an 0.85 % solution of sodium chlorid, sterile, and heated to body temperature. Calcium, potassium, and sodium salts should be used in about the following proportions to have an infusion fluid of most efficiency: Calcium chlorid, 0.026%; Potassium chlorid, 0.035 %; Sodium chlorid, 0.75%. After hemorrhage an infusion of a saline solution promptly fills the place of the bulk of blood plasma lost, and the regeneration of red blood-cells usually follows rapidly. Osmotic Pressure. Osmosis is not precisely understood, but the following explanation of the phenomenon, though not free from objections, may be of service. When a substance is dissolved in a liquid, it behaves as though it were a gas ; its molecules are in constant motion. The outermost layer of liquid acts as a limit- ing membrane, against which the molecules of the sub- stance in solution are continually striking ; the result of these impacts is a constant outward pressure, just as the molecules of a gas inclosed in a vessel are continu- OSMOTIC PRESSURE. 27 nllv striking against the inner surface of the vessel and suhjeetinir it to a pressure. In each case, the pressure i- proportional to the number of molecules contained in the one case, in a given quantity of liquid ; in the other, in a given space. The larger the number of molecules, the greater the pressure. Let a vessel containing water be divided into two compartments by a loosely stretched membrane of such a nature that water can easily pass through it, while it is entirely impermeable by albumin. If, now, some albumin be introduced into one of the compartments, a (Fig. 1), and be dissolved, its molecules will wander in all directions through the solution, and many of them striking against the membrane, will press it through the water, and cause it to bulge into compartment b (Fig. 2). This is possible only where the membrane is permeable by water. The albumin solution will have increased in bulk, owing to the passage of water through the mem- brane. When the membrane has become taut, the passage of water from b into a will not cease, for the albumin molecules are not only striking against the membrane, but against every part of the limiting layer of the solu- tion in a, including that forming the upper surface of the liquid. The tendency will be, then, to force this >urface layer upward, and since no such tendency exists in 1) (for the water in 6 contains no substance in solu- tion j, water will continue to pass from 6 into , and the level of the liquid in a will rise, while that of the water in b will sink (Fig. 3). This will go on until all the water has been absorbed by the albumin solution, or until the difference between the levels of the two liquids represents a hydrostatic pressure equal to the osmotic pressure of the albumin solution, at which point equi- librium will be established. A much more convenient 28 PEOTOPLASM, BLOOD, AND LYMPH. - /- t 3. 4 I OSMOTIC PRESSURE. 29 \ L C. indicates an osmotic pressure of 9,437 mm. of mercury. If, then, we find the freezing-point of a solution to be, for example, 0.02 C., its osmotic pres- sure must be 9437 X 0.02 = = 188 mm. Hg. In order to make solutions of two different sub- -tances, which shall be isotonic with one another, each MI! stance must be dissolved in proportion to its molec- ular weight, and each solution made up, by the addi- tion of water, to the same bulk. For instance, take one gram-molecule of Cane-sugar, C^H^O^ that is, ' 1- grams (a gram-molecule is the molecular weight of a Mihstance expressed in grams), dissolve it in water, and add water until the solution measures 1 liter. A solution of Grape-sugar, C 6 H 12 O 6 , to be isotpnic with the above solution of cane-sugar, must be made in the same way, with one gram-molecule, 180 grams, of grape- sugar. The freezing-point of each will be 1.8 C. ; the nsmotic pressure, 9437 Xl.8 == 16,986 mm. Hg. In the case of an equimolecular solution of an elec- tiolvte, however, the freezing-point would be lower, and the osmotic pressure higher. An electrolyte is a >ul stance a certain proportion of whose molecules undergo di-- ociation when it is dissolved ; for instance, Sodium Chlorid is, to a certain extent, dissociated, on solution, into Na and Cl ions, each ion behaving, as far 30 PROTOPLASM, BLOOD, AND LYMPH. as osmotic pressure is concerned, as though it were a molecule. In the case of a salt like Mercuric Chloric!, the molecules which become dissociated split up into three ions, Hg, Cl, and Cl, so that the freezing-point will be depressed still further, and the osmotic pressure will be still higher, than in the case of an equimolecular solution of a nonelectrolyte. Solutions of an electro- lyte are capable of conducting electricity ; solutions of nonelectrolytes are nonconductors. If solutions of two different substances be separated from one another by a membrane which is impermeable by each of these substances, but permeable by water, water will pass through the membrane toward the solution possessing the higher osmotic pressure. This w r ill continue until, by the dilution of the one, and con- centration of the other, the osmotic pressures of the two have been equalized ; that is, provided the two liquids be kept at the same level, in order to exclude the effect of hydrostatic pressure. If solutions of two different substances be separated from one another by a membrane which is impermeable by one of them, slightly permeable by the other, and readily permeable by water, the result may be compli- cated. As an example, let us take two solutions, a and 6, separated by a membrane which is impermeable by the substance dissolved in a, slightly permeable by the substance dissolved in b, and readily permeable by water. If the osmotic pressure of a be greater than that of 6, water will pass from b to a, but not so rapidly as it would do if b were pure water ; for the osmotic pressure of 6 will retard its loss of water, since the majority of the molecules in b will, on reaching the membrane, strike against it and rebound ; a few will, however, pass through into a, and the final result, if the experiment be sufficiently long continued, will be the complete absorption of 6 by a. ERYTHROCYTES. 31 If, at the beginning of the experiment, the osmotic piv-sure of l> he greater than that of a, although the final result will be the same as in the last case con- sidered, water will at first pass from a to 6, for more I mil is exerted by b. Since, however, the osmotic pn-sure of b will be continually reduced, not only by dilution, but also by the slow diffusion of its dissolved substanee into a, and at the same time the osmotic pressure of (i will continually increase, owing to loss of water and gain of the substance which diffuses into it t'miu b, a time must come when the two solutions are isotonic with one another, and the passage of water through the membrane will momentarily cease. The -ult-tanee dissolved in b will, however, continue to diffuse through the membrane into a; this will raise the osmotic pressure of a above that of 6, and water will now begin to pass in the direction of a. The final re-ult will, as above, be the complete absorption of b by a. Erythrocytes. The chemical composition of the iv 1 cells is about as follows : Water 90.0%. Hemoglobin 36.0%. Proteids 3.2%. Lecithin and cholesterin 0.2%. Inorganic salts 0.6^. While amongst the inorganic salts of plasma and lymph the sodium salts predominate, in the cells potassium silts are the more abundant. Hemoglobin is a compound proteid, which may be split up into a globulin and a pigment, Hemochromogen. Both these substances, apparently owing to the fact that tin y contain iron, possess a marked affinity for oxygen, with which they unite to form unstable compounds; in the one case Oxy hemoglobin, in the other, Hematin. Hemoglobin, Hb, and Oxyhemoglobin, HbCXj, are both 32 PROTOPLASM, BLOOD, AND LYMPH. crystalline, and soluble in water. Oxyhemoglobin is scarlet in color, and is accountable for the color of arte- i rial blood, venous blood being dark purple owing to the reduction of much of the hemoglobin. Hemoglobin also possesses an affinity for Carbon monoxid, with i which it unites to form Carbon-monoxid hemoglobin, HbCO, a compound which is more stable than HbO 2 . j This is why the inhalation of coal-gas is dangerous ; ; the carbon monoxid contained in coal-gas combines with the hemoglobin, and thus prevents its union with oxy- gen. Hemoglobin forms a still more stable compound with nitric oxid. If oxyhemoglobin be treated with an i oxidizing agent, it is converted into Methemoylobin, which contains the same amount of oxygen as does oxyhemoglobin, but the union is a firmer one. Methem- oglobin is brown in color. Each of these pigments shows, in dilute solution, a characteristic spectrum. Oxyhemoglobin shows two absorption bands between the Frauenhofer lines D and E, the band toward the red end of the spectrum being the narrower and darker of the two. Reduced hemoglobin shows one band, be- tween the lines D and E, which is broader and less well-defined than the absorption bands of oxyhemoglo- bin. By means of photography, another absorption band, still more characteristic of blood pigment, may be shown between the Frauenhofer lines G and II this is known as Soret's band. Leukocytes, or white blood-cells, are composed about as follows : Water, 88.5 C f ; proteids and nucleo proteids, 9 ^ ; and small quantities of lecithin, choles- terin, fats, inorganic salts, etc. The leukocytes are, as we have seen, concerned in the clotting of blood ; the blood platelets also probably take part in the formation of fibrin-ferment. The leu- kocytes possess the power of changing their shape (ame- ADAPTATION OF BLOOD. 33 boid vemcnt), and in this way escape through the walls of the capillary blood-vessels (diapedesis) and wander through the tissue spaces ; this process is greatly accelerated by the presence of an irritant, the leukocytes collecting in large numbers in an inflamed area, and being directed thither by chemotropism. If a small tube filled with a culture of bacteria be introduced under the skin, the chemical products of bacterial ac- tivity will diffuse through the open end of the tube into the lymph-spaces; on coming in contact with the leu- kocyte-, they influence them in such a manner that the leukocytes are caused to move in the direction from which the bacterial products approach them. It is sup- po-cd that the leukocytes either ingest the bacteria ( phagocytosis), or secrete some substance which inhibits their growth and activity; the leukocytes of the frog have been shown to do both, In this way the white blood-cells may afford protection against the inroads of bacteria, .and assist in maintaining the health of the Individual. The functions of the leukocytes are : 1. To protect the body against pathogenic bacteria (phagocytic and bactericidal action). _. To aid in the absorption of fats from the intestine. >. To aid in the absorption of peptones from the in- testine. 4. To take part in the process of blood-coagulation. : >. To help maintain the normal composition of the blood plasma as to proteids. ADAPTATION OF BLOOD. Kmler the description of blood and its functions should be included the chemical defenses of the l.dv against injury and disease. C 1 lotting of blood is a great protection against injury. The acid gastric juice is de- 3 34 PROTOPLASM, BLOOD, AND LYMPH. structive to most bacteria introduced in the food. But in addition to these means of assisting in the protection of the body, there is a power of adaptation to meet the harmful agencies which may enter the blood stream, possessed by the blood plasma, and capable of great development and apparently of innumerable variations. The presence of these substances in the plasma is due chiefly to the activity of the endothelial cells lining the heart cavities and the blood vessels, and of the red and white blood-cells. Bacteriolysins are soluble proteids of the blood plasma, destroyed by heating to 55 C., capable of de- stroying various kinds of bacteria. Hemolysins are similar substances which are able to destroy the red blood-cells of another species. The increase of bacteriolysins in the blood may be accomplished by the injection of increasing but non- fatal doses of bacteria or their products into the circu- lation. The hemolytic power of blood may be developed to greater than normal degree in a similar manner. On analysis by experimental methods it is found that the bacteriolysin or hemolysin consists of two sub- stances, called the immune body and the complement. The bacteria or cell destroying substances of the blood cannot act upon their objects of attack without an in- termediary substance, a substance, as it were, with two chemical affinities, the immune body which is found to be specific for each bacteriolysin or hemolysin which is developed, and when the action has taken place the immune body is considered to be united to the bacterial product on one side and the blood complement upon the other. A further property of the blood is a power of agglu- tinating or clumping and rendering immobile the bac- THE LYMPH. 35 teria which it mav be called upon to attack. This property also, though present at all times, is capable of development and increase, as is seen in the course of various diseases; as, for example, in typhoid fever, where the specific agglutinins or the patient's blood are so developed as to show a clumping of typhoid bac- teria when the patient's serum and a culture of typhoid bacteria are brought together. Coincident with the increase of hemolytic power de- veloped by injecting the blood of one species of animal into another species, there are developed specific pre- cipitins. If the serum is taken from a rabbit which ha- for a period of weeks had small subcutaneous doses of human blood serum, and is added to human blood -tri i in, a precipitate will occur, which will not take place when such adapted rabbit serum is added to the blood of any other animal, except that of the anthro- poid apes. This is the so-called Biological test for the source of a suspected blood. THE LYMPH. Lymph is formed by the filtration of plasma through the walls of the capillaries into the lymph-spaces, which lie outside the capillaries and between the cells of the various tissues. Its composition is, however, not pre- ci.-ely the same as that of the plasma, owing to the fact that the proteids do not pass through the capillary wall a- readily as do the other constituents of the plasma. The capillaries of different parts of the body differ in their permeability, those of the liver being the most permeable, those of the lower limbs the least so; con- Bequently, the lymph formed in different parts differs in composition ; that formed in the liver may contain protcid.- to the extent of 6^ ; that formed in the legs, about 3(3 PROTOPLASM, BLOOD, AND LYMPH. The force concerned in causing the filtration of the plasma into the lymph-spaces in other words, in the formation of the lymph is the intracapillary blood pressure. To this force are opposed the following : the slight resistance offered by the capillary wall to the passage through it of water and inorganic salts ; the much more effective resistance which is opposed to the passage of proteids ; and the osmotic pressure which is exerted by that portion of the proteids which does not pass through the wall, but remains within the capil- laries. This portion is usually the larger. Proteids form about 8 ^ of the plasma, and exert an osmotic pressure of about 30 mm. of mercury ; the lymph con- tains about 3 th. The negative pressure in the great veins at the base of the neck acting upon the opening of the tho- racic duct at its venous junction. 7th. The effect of contraction and relaxation of the skeletal, and visceral musculature. QUESTIONS FOR CHAPTER I. What is the physiological difference between plants and ani- mal- '. J Name the properties of a living cell. What is the source of the potential energy which is contained in food? In what respect does bioplasm resemble dynamite? Why is it impossible to convert fat and carbohydrate into pro- tein! ? Why is hydrolysis accompanied by the liberation pf heat ? Why are native proteids divided into two classes? How may native proteids be removed from a solution which also ">i it a ins proteoses and peptones, without removing the two latter? What proportion of a blood clot consists of fibrin ? How does hemoglobin differ from other proteids? Ho\\ may albumins be separated from globulins? Give the functions of the blood as a whole, and of the red cells and leukocytes independently. What are some of the changes which occur in blood when it ia boiled? What are the effects of removing all the inorganic salts from blood? 38 PROTOPLASM, BLOOD, AND LYMPH. Does the "salting" of blood prevent the formation of fibrin- ferment, or does it prevent its activity ? Does'the addition of fibrin-ferment to defibrinated blood cause it to clot ? How may defibrinated blood be caused to clot ? If the coagulation of blood be prevented by rapidly cooling it to C., and keeping it at this temperature until most of the cells have settled, and if the upper and lower layers of plasma be sep- arated and warmed, which will coagulate first ? By what different methods may fibrinogen be removed from the blood, without at the same time removing the other proteids? What effect has the addition of defibrinated blood on a solution of pure fibrinogen? What is the effect of introducing a foreign body into the blood- vessels ? What are the agencies which may be brought into activity to resist the harmful effect of foreign substances in the blood stream ? Why does the dilution of salted blood cause it to clot? Why does packing a wound with gauze hasten clotting ? How may we determine whether a given reaction is caused by an enzyme? Is lymph a product of the lymphatic glands ? What is the difference between lymph and serum ? What are the important constituents of lymph ? Why does serum remain liquid at C. ? How may the osmotic pressure of plasma be reduced ? Why should distilled water not be injected into the blood-ves- sels? Why does an organ that is removed from the body quickly lose its irritability? The osmotic pressure of the. plasma is due chiefly to the inor- ganic salts which are present in small quantity. Why, then, are the proteids of greater importance in relation to the exchange of water between the plasma and lymph ? Does a \% solution of maltose or a \% solution of dextrose possess the higher osmotic pressure ? Why ? CHAPTER II. THE CIRCULATION OF THE BLOOD. The Heart. The blood is inclosed in a system of < la-tic tubes, the blood-vessels, a portion of which has 1) n developed into a muscular pump, the heart, which |Mscsses the power of rhythmic contraction and relaxa- tion. As the heart relaxes, blood flows into it from the veins ; as it contracts, blood is forced out into the arteries. The direction in which the blood flows through the heart is determined by the valves, which open toward the arteries only. The heart is divided into two halves, the right heart and the left ; shortly after birth an opening which connects the cavities of the two hearts closes, leaving them with no communication. Each half pos- -< --eg two chambers, an auricle and a ventricle; the muscular wall of the ventricle being much thicker, in each case, than that of the auricle, and the wall of the left ventricle much thicker than that of the fight. This arrangement corresponds with the amount of work done by the walls of the different chambers. The blood* pumped out by the right ventricle enters the pulmonary artery, and is distributed through its branches to the capillaries of the lungs, where it is arterialized ; thence it flows through the pulmonary veins to the left heart, by which it is forced out into the aorta. The elastic wall of the aorta, always in a state of distention, forces the blood onward through the smaller arteries, through the capillaries, and through the veins, back to the right 39 40 THE CIRCULATION OF THE BLOOD. heart. The distention of the aorta is due to the fact that it requires more force to quicken the flow of blood through the small arterioles and capillaries than it does to stretch the aorta and larger arteries. Thus the elas- ticity of the aorta and larger arteries lessens the work which is required of the heart. Between the right auricle and ventricle is placed the tricuspid valve ; between the right ventricle and pul- monary artery, and at the root of the latter, is the pul- monary set of semilunar valves. The mitral valve is set between the left auricle and ventricle, while the aortic set of semilunar valves, at the root of the aorta, separates this vessel from the left ventricle. The Heart Cycle. The cardiac beat is initiated by a contraction of the muscular libers in the walls of the large veins close to the auricles. The contraction spreads to, and sweeps over, the auricular musculature, driving the contents of the auricles into the ventricles, and constitut- ing the auricular systole. This merely completes the nil- ing of the ventricle, in which, previous to the systole of the auricle, blood has accumulated by inflow, through the latter, from the veins. The auricular systole lasts but 0.1 of a second, and is followed by the systole of the ventricles. Were it not for the auricles, the flow of blood from the veins into the heart would be checked during the ventricular systole ; as it is, the auricles not only assist in the filling of the ventricles, but constitute a time-saving reservoir which is of special value when the heart rhythm is rapid. As the ventricles fill, the free edges of the auriculo- ventricular valves are carried upward and approach one another, their complete closure being effected by the rise of pressure within the ventricles, at the begin- ning of ventricular systole. The intraventricular pressure rises rapidly as the systole proceeds, the back- THE HEART. 41 flow of blood into the auricles being prevented by the tricuspid and mitral valves, which are held in place by their tendinous cords ; while the outflow into the arteries is, for the moment, prevented by the semilnnar valves, which are kept closed by the higher pressures in the pulmonary artery and aorta. As soon, however, as the pressure within the ventricle rises, in the one case, higher than that in the pulmonary artery, in the other, above that in the aorta, the semilunar valves must open .as the blood is ejected by the ventricles into the arteries. The ventricles probably never completely empty themselves, and they are far from doing so when the heart is beating slowly. Then follows the ventri- cular diastole, or period of relaxation and rest, at the 'gi nning of which the pressure within the ventricle falls below that in the aorta, the semilunar valves being closed in consequence. A short interval elapses before the intraventricular pressure falls below that within the auricle, and until this point is reached the auriculo- ventricular valves must, of course, remain closed. The whole series of events just described occurs simultaneously in the right and left hearts, and constitutes a heart cycle. When the heart beats with average frequency, that is, seventy-two times a min- ute, each cycle lasts about 0.8 of a second, and may be tabulated as in Table 2 (p. 42). It will be noticed that while the auricular systole lasts 0.1 of a second, and the diastole 0.7, the systole of the ventricle occupies 0.3, and its diastole 0.5 of a second, the ventricular cycle beginning 0.1 of a second later than that of the auricle, and lasting to the end of the first tenth of a second in the succeeding auricular cycle. When the frequency of the heart-beat is in- creased, each cycle is, of course, shortened, this reduc- tion being: accomplished, for the most part, at the 42 THE CIRCULATION OF THE BLOOD. 4- 4- t . t t rf t 4.4. a, -0 C ^ THE HEART. 43 < 'Xpcnse of the diastole, the systole of the ventricle lasting almost as long :ls usual. The behavior of the valves depends upon the rela- tive height of the pressure on either side of them ; the auriculo-ventricular valves, for instance, remain closed as long as tin- pressure within the ventricle is higher than that in the auricle; when the pressure within the auricle rises above that in the ventricle, they open, and remain so until the intraventricular pressure again predominates. In the same way, the semilunar valves are kept closed by an arterial pressure that is greater than the intraventricular pressure, and give way when the ventricular rises above the arterial. It will be noticed that both sets of valves are, for two short pi-rinds, closed at the same time. The rate at which the heart beats is governed by the << ntral nervous system, which, in this respect, exerts it- emu rol chiefly over the auricles, the auricular rhythm s< 1 1 i iiii t he pace for the ventricles. The auricular stimu- lu- is probably transmitted, not by nerve-fibers, but by the contraction of a few muscle-fibers connecting the auricles with the ventricles. If the auricles are caused t<> -top beating by the stimulation of the pneumogastric urrve, the ventricles, after a brief pause, begin to beat with a much slower rhythm of their own. Although the central nervous system controls the heart-beat, it is by no means essential to its continuance, a- may be shown by removing the heart from the body, when, if properly supplied with oxygenated blood, it may go on beating for hours. The cardiac muscle itself seems to possess an inherent power of rhythmic contraction, for even small isolated pieces of the ven- tricle which appear to contain no nerve-cells will beat rhythmically if supplied with arterial blood* Heart Sounds. If the ear be placed against the 44 THE CIRCULATION OF THE BLOOD. chest-wall, two sounds are heard each time the heart beats. The first accompanies the ventricular systole, and is more prolonged than the second, which is diastolic (see Table 2). The first sound, which seems to be compound, is probably produced in part by the contraction of the ventricle, and in part by the vibration of the auriculo- ventricular valves on closure. Each ventricle takes part in the production of the first sound. Disease of either of the auriculo-ventricular valves produces a change in the valvular element of the sound, which, in the case of mitral abnormality, is best appreciated by placing the ear, or stethoscope, over the fifth left inter- costal space, at the point where the apex-beat of the left ventricle may be seen or felt ; evidence of tricuspid error being best heard just to the right of the sternum, at about the same level. The second sound occurs at the beginning of the ven- tricular diastole, and is due to the vibration of the semilunar valves at, or just after, their closure. Th aortic sound is most clearly heard at the point where the second right costal cartilage joins the sternum ; while the closure of the pulmonary semilunar valve is most distinct over the second left intercostal space, close to the sternum. It is, however, impossible to distin- guish between the normal aortic and pulmonary sounds, though an abnormality in one set may be located in tin way. If the rate at which the blood flows through vessel of different size be compared, it will be seen that th larger the vessel, the greater the speed. In the ao the blood flows most rapidly, for the sectional area o this vessel is smaller than the united sectional area of its branches, consequently the blood, having less room, must flow more quickly. The rate of flow is inversely proportional to the width of bed. The united sectional THE HEART. 45 area of the systemic capillaries has been estimated to be a> iiiiidi as SOU times that of the aorta; in this dis- trict, then, the stream is sluggish. As the blood flows from the capillaries into the small veins, the width of bed decrease's, and the stream quickens; in large veins the rate will approach, but never equal, that in the aorta. The velocity of the circulation, as a whole, of co ii r>- iiim-ases or decreases with a change in the rate and strength of the heart-beat. .. Blood Pressure. The blood as it flows through the ve-sels is under constant pressure. This pressure is the product of the propelling force exerted by the heart, and the resistance offered to the flow by hydraulic friction. During the diastole of the ventricle, the flow is kept up \>\- the elastic and overfilled aorta and larger arteries. As li(|iiid flows through, a tube, friction exists between it- particles; and the nearer the wall of the tube, the greater the friction ; therefore, if we compare the flow of liquid through a large tube with its flow through a number of small tubes, the united sectional area of which is equal to the sectional area of the large tube, we shall find that it meets with much more resistance iu the small ones; for a much larger proportion of the liquid will flow in the neighborhood of the tube-wall, and the friction will be greater. The blood, then, will meet with most resistance on passing through the innu- merable arterioles and capillaries, into which the larger arteries divide; this is usually spoken of as the per- ipheral resistance. The overcoming of this periph- eral resistance uses up most of the heart force, and, by the time the blood reaches the veins, it flows under but little pressure, which, however, suffices to carry it as far as the right heart. The fall in pressure js-continuous from the beginning of the aorta to^the ending of the veins, for friction comes into play along the whole route, 46 THE CIRCULATION OF THE BLOOD. though in the larger vessels it is but slight. In the arteries the fall is a gradual one, but it becomes abrupt in the arteriole and capillary district, while in the veins the pressure again decreases slowly. The blood pressure is variable, especially that in the arteries. As there are two factors in the production of the blood pressure, so there are two main causes con- cerned in bringing about its variation ; namely, (a) a change in the propelling force, the heart-beat, and (b) a change in the peripheral resistance. A third cause consists in an alteration of the capacity of the vessels, more especially of the large veins. An increase in the rate and strength of the heart-beat naturally raises the pressure in the arteries and capillaries, and since the heart transfers blood from the veins into the arteries, the pressure in the large veins must under these cir- cumstances be lowered. When the activity of the heart is depressed, the resulting changes in blood pressure are the opposite of those just enumerated. While elastic tissue is a characteristic feature in the walls of the large arteries, in the arterioles muscular tissue predominates, and gives to these small vessels the important property of varying their caliber. With a change in their size, the resistance which they offer to the blood flow also varies ; a wide-spread constriction of the arterioles re- sulting in a marked rise in arterial pressure, Avhile a great fall accompanies their general relaxation, for the blood, under these circumstances, flows more readily from the arteries into the capillaries. The highest possible arterial pressure is attained by a general con- striction of the arterioles, accompanied by a strong and rapid heart-beat. A very low pressure will result from a general dilatation of the arterioles and a slow, weak heart-beat ; if at the same time the walls of the large veins and of the branches of the portal vein relax, the NERVOUS CONTROL. 47 hloud will tend t<> stagnate in these veins, and, since little blond will reach the heart, but little can be pumped into the arteries, in which the pressure will tall to a dangerous extent. Nervous Control. The heart is controlled by the central nervous system, through two sets of nerves ; one Bet, arising from the Cardio-inhibitory Center, lessens its activity ; the other, carrying impulses from the Accelera- tor or Augmentor Center, quickens and strengthens the beat. The eardio-inhibitory nerve-fibers reach the heart through the pneumogastric, and probably exert their in- fluence over the heart muscle, not directly, but through the mediation of nerve-cells which are situated in the wall of the organ. On division of both pneumogastric nerves, in the neck, the heart beats more rapidly, for the controlling influence of the center is thus cut off. If the end of the peripheral .portion of one of these divided nerves be stimulated with electric shocks, the heart-beat will become slow, or, if the current be strong, will stop for a short, time. The auricles may, in this way, l>e prevented from beating for an hour or more if the stimulation be kept up; but the ventricles, after a short pause, begin to beat at a slower rate than before. The diastole is very much prolonged, and, of course, uives time for the accumulation within the heart of more blood than usual between beats ; the ventricle thus dilated fails to empty itself ; indeed, to such an extent i.> thi- the case that a slowly beating heart may, at the end of its systole, contain more blood than it usually contains at the beginning of the contraction. This residual blood will, in the succeeding diastole, retard the inflow from the veins, and, in consequence, less blood will enter the heart in a given time, and the pres- sure in the large veins will rise. Since less blood enters the heart in a given time, less will be pumped out into 48 THE CIRCULATION OF THE BLOOD. the arteries, and the arterial pressure falls. Although the output of the ventricle is decreased, the contraction volume that is, the amount forced out by a single con- traction is increased. To repeat, then, a slow heart- beat results in a dilatation of the ventricle and a rise of venous pressure, a lessened output, and a fall of arterial pressure. The cardio=inhibitory center is situated in the spinal bulb, and is bilateral. It is continually active, and this tone may be increased or decreased in a variety of ways ; for instance, a rise of arterial pressure increases its activity, the importance of this fact being apparent, for any abnormal rise of pressure will tend to bring about its own fall by lessening the output of the heart, through stimulation of this center. The center is not only affected by the pressure at which the blood flows through the neighboring vessels, but it is also sensitive to its chemical composition ; if the blood becomes unusually venous, the center is stimulated. A reflex slowing of the heart may be caused by the stimulation of various sensory nerves ; for instance, the nasal branch of the trifacial, as on the inhalation of chlo form or ammonia vapor into the nostrils. A reflex event is one which is produced by the passage of an afferent nerve-impulse from the periphery to a center, the center responding by the dispatch of an efferent (outward) impulse which brings about the even be it the contraction of a muscle, secretion by a gland or inhibition of the heart. A reflex slowing of th heart is readily caused by stimulating the afferem nerve-fibers of the pneuniogastric ; these fibers normally carry afferent impulses from the lungs, heart, liver, stomach, etc., to the spinal bulb, but not all of them necessarily reach the cardio-inhibitory center. During expiration the heart beats slowly, owing to afferent NERVOUS CONTROL. 49 impulses from the lungs, which, on reaching the bulb, alVect the center either directly or through the interven- tion f the emotions. The cardio=augmentor center is probably also situ- ated in the spinal bulb; the nerve-fibers arising from it descend the spinal cord as far as the upper end of the thoracic region, where they probably end, but make physiologic connection in the gray matter with nerve- cells whose fibers pass out through the upper thoracic ventral nerve-roots; in the dog, through the second and third. They join the sympathetic chain, and probably end in the ganglion stellaturn, where a second cell station intervenes, the fibers originating from the ganglion cells passing to the heart muscles. This last of nerve-libers come under the head ot what are known a- post-ganglionic fibers of the sympathetic -\Met mentioned, the pre-ganglionic sympathetic fibers, which, originating from cells situated in the gray matter of the >|inal cord, end in sympathetic ganglia. The nervous chain which connects the spinal cord with in- voluntary tissue, such as plain muscle, cardiac muscle, and glandular epithelium, usually, if not always, con- sists of two links pre-gangl ionic and post-ganglionic nerve-fibers. If the augmentor center possesses tone, 50 THE CIRCULATION OF THE BLOOD. that is, is continuously active, as seems probable, its influence over the heart-beat is not so marked as that of the inhibitory center. The stimulation of the augmentor nerves increases the strength of both the auricular and the ventricular contraction, the output of the venticle is increased, the venous pressure is lowered, and the arterial pressure raised. During muscular exercise the augmentor center is stimulated by the chemical waste products of muscular metabolism, which proceeds more rapidly during activity than during rest. A rise of body- temperature also directly stimu- lates the center. A reflex quickening of the heart may be provoked by the stimulation of almost any nerve-trunk, but is usually followed by slowing, owing to the simultaneous or subsequent stimulation of the inhibitory center through the same channel. As is well known, the heart-beat may be quickened by the emotions. Nervous control is not the only cause of variation in the strength of the heart-beat; the quantity and quality of the coronary blood supply also exert an in- fluence. The effect of an alteration in the amount of blood supplied to the heart is much more marked in regard to strength than frequency. The ventricle beats more strongly when its coronary blood supply is in- creased. A high arterial blood pressure is favorable to a strong heart-beat, unless the ventricle becomes dilated in consequence, in which case the coronary cir- culation is retarded. A moderately high pressure also increases the force of the heart-beat, owing to the fact that muscles work to better advantage against a certain amount of resistance. The quality of the blood is im- portant, especially in regard to the amount of oxygen contained. The variation of the peripheral resistance is also NERVOUS CONTROL. 51 under the control of the central nervous system. There exi-ts in the spinal bull) a center, known as the vaso- constrictor center, which exerts an influence over the muscular walls of the vessels, most evident in the ca.-e of the arterioles. As in the case of the cardie-inhibi- tory center, the activity of this center is continuous, and its tone is variable. Like the inhibitory center, it acts as a regulatory mechanism whereby the blond pressure is kept fairly constant. If the arte- rial pressure falls, this center becomes more active, and brings about a constriction of the arterioles, thus rais- ing the peripheral resistance, and with it the arterial blood pressure. It is also stimulated by a venous con- dition of the blood, the arterial pressure rising to a Teat height during dyspnea, in spite of the simulta- neous inhibition of the heart. Its activity is reduced by certain drugs, such as chloroform, ether, alcohol, etc. It may be indirectly stimulated through almost any afferent nerve; for instance, the application of cold to the skin, by stimulating the cutaneous nerves, and thus indirectly influencing the constrictor center, brings about a reflex paling of the skin. On the other hand, the application of warmth causes a reflex dilatation of the cutaneous vessels, by inhibiting the constrictor liter. One afferent nerve which transmits impulses fmiu the heart to the spinal bulb, and is known as the depressor nerve, is of special importance through its relation to this center, and consequent influence on the IVM illation of the blood pressure. When the arterial piv ure rise,s unduly, the intracardiac pressure inu.-t ri.-c, and in so doing stimulates the endings of the ,r nerve; this results in the passage through the nerve of impulses which, on reaching the bulb, inhibit the constrictor center. The activity of the center being reduced, the arterioles are allowed to 52 THE CIRCULATION OF THE BLOOD. dilate, the peripheral resistance is lessened, and the arterial pressure falls. The depressor nerve thus serves as a safeguard against any undue rise of arterial pressure, and affords the heart protection against over- work. As in the case of the centers which regulate the heart-beat, this center also may be influenced by the emotions ; for example, blushing is due to its inhi- bition by nerve impulses descending from the brain. The control exercised over the vessels by the con- strictor center is specialized, for although it maintains a general vascular tone, it does not, as a rule, cause marked contraction of all the arterioles at the same time ; if the vessels of the skin be unusually constricted, those of the viscera are allowed to dilate, and vice versa. This arrangement insures a more even blood pressure than would otherwise exist. The course of the constrictor nerve=fibers resem- bles, to a certain extent, that followed by the cardio- augmentors. The nerve-fibers originating in the center pass down the spinal cord, to end in the gray matter at different levels of the thoracic and upper lumbar regions. The ends of the fibers make physiologic con- nection with nerve-cells whose axons, usually of small caliber, pass out through the anterior spinal nerve-roots to enter the sympathetic system as pre-ganglionic fibers. They end in one or other of the sympathetic ganglia in contact relations with cells whose axons, post-ganglionic fibers, usually nonmedullated, are distributed to the arterioles in almost every part of the body. The post- ganglionic fibers which innervate the vessels of the skin reach their destination by passing through a gra ramus communicans to the spinal nerve supplying the cutaneous area in question (Fig. 4.) ; those for the visceral arterioles do not reenter a spinal nerve, but reach the viscera through the sympathetic (Fig. 5) ^*JK-V twAf V Fig. 4. Q/rVvt-vx^ b -rCp >KcU. U -/"' Fig. 5. NKIIVOUS CONTROL. 55 The pre-ganglionic fibers for the head pass up the cervical sympathetic and end in the superior cervical sympathetic ganglion (Fig. 4). Since all the vasoconstrictor fibers originating from the center pass down the spinal cord to the thoracic region, division of the cord in the cervical region must he followed by a great fall of blood pressure, for all the vessels in the body dilate; if, however, the animal be kept alive, the vascular tone will, after a time, gradually reappear, depending apparently on an increased irritability of the spinal cord, the cells from which the pre-ganglionic fibers originate acting as vicarious constrictor centers. If, now, the thoracic cord is destroyed, the vascular tone again disappears for a time, but is partly reestablished either through the influence of the sympathetic ganglion cells from which the post-ganglionic fibers spring, or owing to the independent contraction of the muscular wall of the vessels. Some veins have been shown to possess a supply of vasoconstrictor nerves; for example, the portal veins. Since the administration of chloroform or ether tends to paralyze the vasomotor center, it is very important that an anesthetized patient be kept in a horizontal po- Hiion, lor, otherwise, the blood will accumulate in the relaxed abdominal veins, and will, by force of gravity, be prevented from reaching the heart. Scattered through the different regions of the spinal cord and bulb are vasodilator nerve-centers, whose cells o-ive olT'axons which, for the most part, follow the same course as the pre-ganglionic vasoconstrictors; no chief vasodilator center has been proved to exist in the bulb. The existence of vasodilator fibers in a mixed nerve-trunk may be demonM rated by special methods of stimulation ; there are, however, some nerves which 56 THE CIRCULATION OF THE BLOOD. contain vasodilators unmixed with vasoconstrictors. The chorda tympani nerve is one of these,* and trans- mits to the sublingual and submaxillary glands vaso- dilator fibers which leave the bulb in the seventh cranial nerve. On stimulation of this nerve, the arterioles in the glands dilate, and the blood flows through them more rapidly than before. The pre-gangl ionic fibers of the chorda tympani end in contact with submaxillary and sublingual ganglion cells, from which post-gangli- onic fibers are distributed to the arterioles. The post- ganglionic vasoconstrictor fibers for the arterioles of these glands come from the superior cervical sympa- thetic ganglion by way of the carotid plexus. During the activity of an organ its blood supply is increased, the maximum supply being afforded by the dilatation of its own arterioles, the constriction of the arterioles in other parts of the body, and a strong and rapid heart-beat. The Pulse. If the blood flow through an artery be compared with that through a vein, a marked difference will be observed ; the flow through the artery is remittent, that through the vein is constant ; the artery pulsates, the vein does not. The arterial pulse consists in a rhythmic enlargement and subsequent shrinkage of the vessel due to slight variations in arterial blood pressure. The enlargement is caused by the sudden rise of pressure which follows the ventricular systole. As the ventricle forces out its contents the aortic pressure is raised ; this rise is rapidly transmitted throughout the arterial system, the vessel-wall of each succeeding portion expanding as it is reached by the wave of heightened pressure. The slight delay in the transmission of the pulse to the more distant arteries may be readily appreciated by simultaneously feeling the carotid, and the radial pulse. Were the arteries rigid tubes, the THE PULSE. 57 transmission of the pulse would be instantaneous ; and, as it is, the higher the pressure already existing in the arteries, the more rapidly the pulse travels; for when the pressure is high, the vessel-wall, already tightly stretched, is less capable of further expansion than when the pressure is low. When the pressure is high, the pulse will, for the same reason, be small. A large pulse occurs when the heart-beat is strong and the pressure , owing to peripheral dilatation of the arte- rioles, is comparatively low. The small pulse of high pressure is hard, or incompressible ; that is, it will be more- difficult to flatten the artery with the finger than when the pressure is low, a low pressure pulse being s.ii't and compressible. A small, hard pulse indicates high blood pressure; a large, soft pulse indicates low pressure and strong heart-beat; a small, soft pulse indicates a weak heart-beat and low pressure. The blood flows through the capillaries and veins in a e. >nstant stream, the pulse having been extinguished by the resistance offered by the arterioles. As before -i a ted, it requires less force to stretch the elastic arteries than to quicken the flow past the peripheral resistance, consequently each time the ventricle contracts, the quantity of blood ejected is for the moment -'accommo- dated in the arteries. The heart-force thus transmitted to and stored in the arterial wall is during diastole a^ain transferred to the blood stream, the arteries being allowed the period of a whole heart cycle for emptying into the capillaries the quantity of blood which they receive during one systole. In case the arterioles of a limited area be dilated, the general arterial pressure remaining high, a pulse will appear in the small veins of this area, and the blood entering the veins will be arterial in color, for, owing to the quickening of the Mono! stream, a smaller proportion of the oxy hemo- globin will be reduced. 58 THE CIRCULATION OF THE BLOOD. If tlie form of the pulse=wa ve be recorded, it is found to consist in the sudden rapid expansion of the vessel, or sudden rise of pressure within the vessel, followed by a more gradual decrease in size or fall of pressure, the fall being slightly irregular owing to the occurrence of minor pressure waves. These latter are more prominent when the arterial tension is comparatively low and the heart-beat strong. The most marked of these secondary waves is known as the dicrotic wave ; it originates in the aorta immediately after the closure of the aortic valve, and is transmitted through the arteries in the wake of the main pulse-wave. It is probably caused by the closure of the valves. The arterial blood pressure rises and falls slightly as a result of respiration. The reason for this is that enlargement of the thorax tends, not only to cause the inspiration of air, but also to aspirate blood into the intrathoracic veins and heart ; while on collapse of the chest during expiration, the entrance of blood is less favored, and during forcible expiration is retarded. Consequently, the right heart receives and pumps during inspiration more, and during expiration less, blood into the pulmonary vessels. At the beginning of inspiration there is a slight delay in the reception by the left heart of the surplus blood, for the lungs on inflation accommodate more blood than before, and thus even reduce the amount reaching the left heart. On the other hand, just at the beginning of expiration the supply of blood to the left heart is still further increased, for the excess of blood contained by the inflated lungs, on their collapse, passes to the left heart. The effect, then, of the respiratory movements of the thorax is that the left heart also, after a slight delay, receives and pumps more blood during inspiration, and thus raises the arterial pressure ; while, during expira- THE PULSE. 59 tion, alter a momentarily increased supply, it receives and pumps less blood, and the arterial pressure falls. Venous Circulation. The blood in the veins flows under very low pressure, for most of the heart-force has been used up in carrying it past the peripheral resist- ance. Its flow, however, receives material assistance through the contraction of the skeletal and visceral musculature, and through the aspiration of the thorax. When a muscle contracts, it compresses the veins in its neighborhood, and, since they are provided with valves, helps to press the blood onward toward the heart. Forcible expiration of course retards the passage of blood into the thorax. The pressure in the distal veins does not fluctuate ; is highest at the capillaries, and decreases as the heart is approached. At the upper border of the thorax the Lrreat veins in the neck show a variation in pressure due to the greater ease of emptying during inspiratory increase of thoracic negative pressure. On expiration the veins are seen to fill and on inspiration to empty, giving the appearance of a pulse to this respiratory variation of pressure. For about an inch and a half above the thorax the suction effect of the intrathoracic neu.uive pressure is so great as to cause an intravenous negative pressure of a slight degree, usually only during inspiration. A true venous pulse may occur under two condi- tions physiologically. If a gland such as the submax- illary is stimulated vigorously to increased activity the freedom of the capillary path through the gland is so great, >wing to capillary dilatation, that the arterial pulse i< communicated through the capillaries and ap- pear- in the veins leaving the gland. Owing to the absence of valves at the entrance of the venae ca\;e into the rijrht auricle the auricular systole causes a re- 60 THE CIRCULATION OF THE BLOOD. gurgitation of blood into the veins, and a resulting venous pulse perceptible for a distance, which depends upon the force of cardiac contraction, and the varying pressure in the great veins, and may often be seen high in the neck in the external jugular vein. QUESTIONS FOR CHAPTER II. What determines the moment at which the cardiac valve open and closes ? "Why are the auriculo-ventricular and semilunar valves neve] open at the same time ? Does blood enter or leave the ventricle in the interval betwee the first and second heart-sounds ? Does blood enter or leave the ventricle in the interval betweei the second and first sounds? If the auriculo-ventricular valves be insufficient, during wha period of the heart cycle will blood escape from the ventricle into the auricle ? If the aortic valve be insufficient, during what period of the cycle will blood flow back from the aorta into the ventricle? Of what accompanying event should we make use in distin- guishing the first from the second heart-sound ? If while the force which propels liquid through a tube remains constant the resistance be varied, how is the expenditure of the pro- pelling force modified ? Why is the pressure in the aorta higher than that in the small arteries? Which travels most rapidly, the pulse or the blood stream ? When the pulse is large, what is the condition of the arterioles? When the heart is beating strongly, how can you determine the extent of vascular tone? What sort of pulse accompanies dyspnea ? Why should the dicrotism of the pulse be exaggerated when the peripheral resistance is low ? What different circumstances tend to the production of a capil- lary pulse ? How does it happen that not only the auricle, but the ventricle QUESTIONS. 61 ill-.. brats more slowly during increased activity of the inhibitory center? What is the result of inhibiting the cardio-inhibitory center? Why should division of both pueumogastric nerves lower the pressure in the large veins? In what respect would the regulation of the blood pressure be modified by destruction of the cardio-inhibitory center? Why should compression of the aorta cause the heart to beat more slowly? Through what two channels may one organ influence another? How is tin- blood-flow through the small vessels affected by loss of arterial elasticity? What imiM>rtance do you attach to the position of a patient dur- ing chloroform or ether anesthesia? ( 'o m pa re the effects on blood pressure of the division of the spinal cord in the cervical and in the lumbar regions. How many neurones are concerned in the control exercised by the constrictor center over a single arteriole? How can it be determined whether the control exercised by a center is continuous? How does bleeding modify vascular tone? How does indirect differ from direct stimulation of a center? What conditions of the circulatory system may lead to fainting? Of what importance is the iutracapillary blood pressure? It all the nerves of a limb have been divided, would it be pos- sible, by causing the muscles of this limb to perform work, to in- tluenee the heart-beat ? How does severe hemorrhage cause dilution of the blood? How does a rise of arterial pressure tend to concentrate the blood? HO\N does the concentration of the blood tend toward a rise of blood pressure? What nervous meclianism opposes these two tendencies? In what particulars is the existence of the vasoconstrictor center a MM nve of economy to the body? What different vascular conditions may lead to a paling of the fare ' What class of vessels is the seat of every important alteration in the composition of the blood ? 62 THE CIRCULATION OF THE BLOOD. In what organ is lymph most rapidly formed ? In the absence of the vasoconstrictor center, how could the blood supply of a given organ be modified according to its needs ? In what respect would the regulation of the blood pressure be interfered with by division of both depressor nerves? Would the division of the cervical sympathetic nerve have any effect on the color of the face ? Would you class the vasodilators as vasomotor nerves ? Is constant standing or walking the more productive of varicose veins ? How can we afford the greatest voluntary assistance to the en- trance of venous blood into the heart ? Why does putting a cold object, such as a key, down the back tend to stop epistaxis ? How are the low T er limbs affected by compression of the iliac veins? How would you expect the size of the heart to vary during dyspnea ? What effect on intrathoracic pressure has the systole of the ven- tricles ? If the heart be emptied of blood and be caused to beat, which of the heart-sounds will be heard ? How do you know that the slow rate of blood-flow through the capillary district is due to the width of bed and not to resistance? Explain the occurrence of a venous pulse. CHAPTER III. RESPIRATION, Tin-: function of the lungs consists in the exposure <>i' i In- blood to the air, whereby an exchange of gases between the air and the blood is rendered possible. This exposure is, however, totally ineffective, the lungs valueless, unless their alveoli are constantly ventilated. The ventilation of the lungs is accomplished by the n-piratory muscles, which by their contraction bring about variation in the capacity of the thorax, and con- sequently in that of the lungs. The inner surface of the lnnealeni, levatores costarum, serrati postici superiores, external intereostals, and intercartilaginous portion of the internal intereostals, which all take part in raising the ribs, and thus increasing the lateral and antero- 63 64 RESPIRATION. posterior diameters. These diameters of the chest are increased by raising the ribs, owing to the obliquity of the costo vertebral hinge. Quiet expiration is accom-i plished, without the aid of muscular contraction, by the elastic recoil of parts which are distorted during inspi- ration, such as the costal cartilages, the abdominal wall, and the lungs, and by the weight of the ribs, sternumj thoracic muscles, etc. In forced expiration, the dia- phragm is pushed upward by the abdominal viscera* | through the contraction of the abdominal muscles, while the ribs are drawn downward by the contraction of the triangulares sterni, interosseous portion of the internal intercostals, etc. Even when the inspiratory muscles are at rest, there exists, between the layers of the pleurae, a negative pressure ; that is, a pressure less than atmospheric pres- sure. This is due to the fact that a certain amount of the atmospheric pressure is consumed in holding tin lung in contact with the chest-wall, the remainder be exerted, through the lung, against the inner surface oi the thorax and the outer surface of the heart an( vessels. The lungs are not large enough to fill th thoracic cavity unless they are inflated, and their infla tion requires a small amount of force. If the inter pleural pressure be measured Avhen the respiratory mus cles are quiescent, or after death, it will be found to b about 754 mm. of mercury, or about 6 mm. Hg les than atmospheric pressure ; a negative pressure, then, 01 6 mm. Hg. At the end of a forcible inspiration the interpleural pressure may fall as low as 730 mm. Hg, for the lungs are further inflated and, of course, offer more resistance to the inflating force the atmospheric pressure. The interpleural pressure is always lower than the intrapulmonary pressure, though during forci- ble expiration it may rise above atmospheric pressure, NEGATIVE PRESSURE. 65 If the < -hot-wall be pierced, so that air can enter the interplenral space, the outer as well as the inner surface it' the lung being now exposed to the full atmospheric piv lire, the lung, owing to its own elasticity, will promptly collapse. If both sides of the thorax be perforated, respiration must cease, for, since the elasticity of the lungs will resist the entrance of air, through the trachea, into themselves, an enlargement of the chest will onlv result in the entrance of air into the inter- pleiiral .-paces. The importance of the interpleural negative pressure, in respect to the flow of blood through the vein- into the "chest, has been already mentioned. The outer surface of the heart and large intrathoracic vessels U Mibjected, when the thorax is at rest, to a pie me of only 754 mm. Hg, while the veins which lie outside the chest are exposed to the full atmospheric pie me 700 mm. Hg ; it is evident, then, that blood will be forced from points where the veins are more, to a point where they are less, compressed. Inspiration will further this tendency; expiration will lessen it, and, if forcible, will prevent the entrance of blood. 1 1 opi ration may seem to assume one of two types, diaphragmatic or costal, but under normal conditions of lodv movements both the diaphragm arid the tho- racie muscles enter into every respiratory movement. I'o-iiinu of the body, clothing, or habit may modify the normal freedom of respiratory movement, and it i> .-en that women usually breathe more costally than diaphragrnatically, and that the reverse is true with men. In < inbles coughing, save that part of the air is expelled through the nose, and may be excited by stimulation of the nasal branch of the fifth cranial nerve, or through the c licet of a bright light on the retina. The reflex ga>p which is excited by entering cold water is familiar to all. During swallowing, respiration is stopped by inhibit ion of the respiratory center through the glosso- pharyngeal nerve, the pharyngeal terminations of which arc -t imnlated by the substance swallowed, thus affording a mechanism which prevents the inhalation of food into the trachea. The center may also be inhibited on the introduction of irritating gases into the nasal fossae, the terminations of the fifth cranial nerve being thus stimulated; the same effect may be produced by the inhalation of licjuid. As is well known, the emotions have a marked influence over the depth and rate of respiration, and may cause its temporary arrest. The 74 RESPIRATION. respiratory center is also under the control of the will, though it cannot be thus inhibited indefinitely. When the proper arterialization of the blood is pre- vented, hyperpnea, or increased depth and frequency of respiration, ensues ; if this does not result in the access of oxygen to the required extent, or in the removal of the surplus carbon dioxid, or both, there follows more exaggerated breathing, dyspnea, in which forcibl expiration predominates. If the struggle still prov ineffectual, convulsions intervene, giving place exhaustion, a few long-drawn inspirations, and death Apnea, or temporary cessation of breathing, may induced by rapid artificial respiration ; this, in the normal animal, is not due to overoxygenation of the blood, for the blood will take up little more oxygen than usual when pure oxygen is breathed, and the same condition is produced if hydrogen be used for inflating the lungs. It is caused by the effect produced on the respiratory center through the afferent fibers of the vagus, the pulmonary terminations of which are stimu- lated by the rapidly repeated distention and collapse of the lungs. If both vagi have previously been divided, it is more difficult to induce apnea, and impossible by the use of hydrogen ; in this case, it is probably due to a better arterialization of the blood, which, after division of the vagi, has become defective. QUESTIONS FOR CHAPTER III. If a cannula which is connected with a mercury manometer be thrust through the chest-wall without injuring the lung, in which direction will the mercury move ? Under what circumstances will the movement of the mercury be greatest ? Is the interpleural pressure ever positive ? nlMSTIONS. 75 What force resists the expansion of the thorax when tin- glottis is rl.tsed? Does the elasticity of the lungs aid in, or oppose, inspiration? H<>\\ is the color of the face affected by a. fit of coughing, and \\hat is the mechanism concerned? Why is it impossible to voluntarily empty the lungs? What force causes air to enter the lungs during inspiration? Is it possible for a contraction of the diaphragm to cause e.xpi- rat ion ? What \\onld be the result of replacing the blood by serum? What causes a newly born animal to breathe? What causes the reduction of oxy hemoglobin in the systemic capillaries? Ho\\ is it that blood leaving an active organ may in color resemble arterial blood ? What are the direct and indirect effects of lack of oxygen ? 1 iocs the blood undergo purification on its passage through the heart ? Why is it dangerous to breathe coal-gas? Is the color of venous blood due to the presence of an excess of ear'uoii dioxid? (Jive the causation and describe the occurrence of dyspnea. The spectra of oxyhemoglobin and carl>on monoxid hemoglobin an- \ery similar. How can these two substances l>e most readily distinguished from each other? Which of the effects of destroying the spinal bulbxire immedi- ately fatal? What is the effect of separating the two halves of the medulla by a median incision? M\ plain the result of introducing a foreign body into the larynx. How is this effect modified after division of the spinal cord at the le\. 1 of the seventh cervical nerves? Of what importance is the stimulation of the medullary centers by the \\aste products of muscular activity ? How does biting the lip stop sneezing? Why are the lungs lass well protected after division of the glos- sopharyn.ueal nerves? Why is it dangerous to divide the laryngeal nerves? 76 RESPIRATION. Curari paralyzes the skeletal muscles. How does it cause death? Why is paralysis of the expiratory less injurious than that of the inspiratory muscles ? Why is ventilation necessary ? How does the contraction of the bronchial muscles affect respi- ration ? Why is the respiratory quotient of a herbivorous animal mod fied by starvation ? CHAPTER IV. DIGESTION* DIGESTION consists in the physical and chemical al- tcration of food, the resulting products being, as a rule, IIHMV easily absorbed, and in some cases more readily a iinilated, than the food-stuffs as they are originally taken. In order that it may be absorbed, food must be soluble, though it is possible, but highly improbable, that fats form an exception to this rule. Much of our food is taken in a form that requires mechanical subdivision ; this is accomplished by the teeth and tongue, and by the movements of the stomach. The soluble portion of the food that happens to betaken in solid form for instance, cane-sugar is readily dis- solved in the saliva or gastric juice, but insoluble food- -t i ill's must of necessity undergo some change in com- position, and this is brought about by the various en- zymes, or ferments, which are secreted by the x glands of the alimentary canal, or by bacteria which are constantly pi (-nit in the intestine. Our food consists of a mixture of various substances, tin- most important of which are proteids, albuminoids, carbohydrates, fats, water, and inorganic salts. Pro- trid< arc essential, though taken alone they form neither a suitable nor economic diet. In discussing the diges- tion of these food-stuffs it will be well to treat them Separately. Digestion of Carbohydrates. On introduction of the food into the mouth it is subjected to the 77 78 DIGESTION. influence of the saliva, with Avhich it is mixed by movements of the tongue and lower jaw. Here begins the solution of those food-stuffs which are soluble in water. That part of digestion which consists of chemical change also begins in the case of cooked starch and the dextrins. Uncooked starch is insoluble ; it exists in the form of granules covered with envelopes of cellulose, which is also insoluble, and which, though it belongs to the starch group of carbohydrates, is not at- tacked by the enzymes of the alimentary canal ; it passes unchanged through the mouth and stomach into the in- testine, where a part of it is acted on by bacteria. The cooking of starch breaks open the cellulose envelopes, and the starch, rendered partly soluble, is set free. There is contained in saliva an enzyme, ptyalin, which is manu- factured by the salivary glands, and which is amyloly tic ; that is, it brings about the hydrolysis of starch. By this ferment starch is converted into soluble starch or ahiylo- dextrin. The soluble starch is further split up into dex- trin and malt-sugar ; the dextrin thus formed also under- goes hydrolysis, being converted into a simpler form of dextrin and maltose. The final product is maltose, but before the series of reactions ends there probably are a number of different dextrins formed ; each one, in turn, being split up with the formation of a simpler dextrin and malt-sugar. The formula (C g H 10 O 5 ) n is used to represent each member of the starch group. Supposing, for the sake of simplicity, that the true formula for soluble starch is (C 6 H 10 O 5 ) 30 , as has been stated, then the series of changes which occur may be represented by the fol- lowing equations : (1) 3 (C 6 H 10 5 ) 30 + H 2 = (C 6 H 10 5 ) 28 + C H H n O n . Sol. Starch Dextrin Maltose (2) (C 6 H 10 5 ) 28 + H 2 = (C 6 H 10 5 ) 26 + C 12 H 22 U . Dextrin Dextrin Maltose DIGESTION OF CARBC > 1 1 VI U i ATES. 7!) (:) (C 6 H 10 5 ) 26 + H a O = (C 6 H I0 5 ) 24 + C^Ou. I '.-x triii Dexlriu Maltose an into the intestine. The pancreatic juice contains an cn/ynie, amylopsin, which closely resembles pytalin in it> action, and may be identical with it. Not only does the amylopsin convert the dextrins and cooked March which may have escaped salivary digestion into maltose 1 , but it also brings about the same changes in 80 DIGESTION. any raw starch that has been liberated from its cellulose covering through the action of bacteria. Probably none of the starch or dextrin which enters the intestine is absorbed before undergoing digestion, for amylopsin acts rapidly and powerfully, but it is possible for both these substances to be absorbed as such in the large in- testine. So far, then, we have found that starch is con- verted by digestion into maltose, a sugar which, although capable of being absorbed, is of no value as such to the organism ; if it enters the blood as maltose, it is ex- creted by the kidneys. Yet it is very unusual to find maltose in the urine, for the maltose which happens to be absorbed by the epithelial cells which line the stom- ach and intestines is converted, before it reaches the blood, probably by the action of an enzyme contained within the cells, into dextrose. This change also occurs : within the stomach under the influence of hydrochloric acid, one molecule of maltose being, by hydrolysis, con-^1 verted into two molecules of dextrose. The succus en- tericus, or intestinal juice, contains an enzyme, invertin, which brings about the same change. Cane=sugar is acted on by neither pytalin nor amylopsin ; like mal- tose, it is of no value to the body until it has been di- gested, though it may be absorbed. After eating very large quantities of cane-sugar a very small amount may be found in the urine, but the majority is hydrolyzed before or during absorption ; the change occurs either in the stomach through the action of hydrochloric acid, in the intestines under the influence of invertin, or dur- ing its passage through the epithelial cells. The nature of the change is as follows : C 12 H 22 lt + H 2 = C 6 H 12 6 + C 6 H 12 6 . Cane-sugar Dextrose Levulose Both dextrose and levulose are assimilable ; that is, they can be utilized by the bioplasm. Lactose, or milk- DIGESTION OF CARBOHYDRATES. 81 sugar, is another disaccharid which is acted on in the same way in the intestine, but not in the stomach ; the change is as follows : C l2 H 22 O n + H 2 = C 6 H 12 6 + C 6 H 13 6 . Milk-sugar Dextrose Galactose Not all the dextrose which is taken with the food or is formed during digestion reaches the blood; a variable <|iiantity becomes the prey of bacteria. This may occur in the mouth, if the sugar is retained between the teeth; in the stomach, during the period when there is no free hydrochloric acid present; or in the intestines, which constantly contain bacteria. The main result of this bacterial decomposition is the formation of lactic acid. The lactic acid bacillus not only acts on sugar, but at- tacks starch and the dextrins also, probably first con- verting these into dextrose, and the dextrose into lactic acid. The destruction of the enamel of the teeth is due to the formation of lactic acid in this way. The lactic acid may be partly converted into butyric acid by the fiirt her action of bacteria. Another product of the de- composition of carbohydrates by bacteria in the intestines is alcohol, which is formed in small quantities only. This is, of course, absorbed together with the lactic acid, and oxidized in the system. The succus entericus, or intestinal juice, which is secreted by the simple glands of the intestinal mucous membrane, exerts a very feeble diastatic action, slowly converting starch into sugar; it also inverts cane-sugar into dextrose and levulose ; con- verts maltose into dextrose, and lactose into dextrose and galactose. Much of the cellulose escapes bacterial decomposition and appears in the feces. The starch and dextrins which on introduction into the large intestine may be absorbed without previous change are evidently digested on their way through the epithelium, for they do not appear in the blood. 82 DIGESTION. TABLE 3. DIGESTION OF STARCH. ymph and blood Cellulose Starch a. b. raw cooked Marsh-gas, etc. a. b. c. t Maltose J b. Gastric epi- tlielium (abgorbe(1) Sol. starch a. h. Dextrins a. b. -^-Dextrose.... Intestinal epithelium Maltose-^ a. -^-(absorbed). Lactic acid, butyric acid, alcohol, etc. (absorbed) -^-Dextrose.. 4~ ..ympli and blood DIGESTION OF PROTEIDS. 83 Iii Table 3 the double dotted line represents the pylo- ru> ; above these lines are shown the changes undergone by starch and its products in the stomach, the change beginning, however, in the mouth. Below these lines an- -riven the changes which occur in the intestines. The different agencies through which these reactions are effected are mentioned above, in the text. Digestion of Proteids. Proceeding to the digestion of another group of food-stuffs, namely, the proteids, we have tn do with substances the majority of which are 1 1 in re complex than even starch. Of their structural formulae we have no knowledge. As their name in- dicates, they are the most important of the food-stuffs, without a supply of which life cannot be supported for any considerable time. Their chief characteristics have been already mentioned. Uncooked proteids and those which are not rendered insoluble by heat may, if given in the solid form, be dissolved in the saliva. Saliva, however, contains no prote< >\yt\c enzyme ; it is incapable of bringing about any chemical change in the proteids, which, conse- quently, suffer no digestion before they reach the stomach, though they may, if long retained within the mouth, for instance, between the teeth, undergo bac- terial decomposition. Although, like soluble starch, the soluble native proteids may, to a certain extent, be absorbed from the intestine without first undergoing digestion, the absoqrtion of the products of proteid digestion goes on much more rapidly ; coagulated pro- teids are altogether incapable of being absorbed until they have been converted into a soluble form. Our knowledge of the changes which proteids undergo during digestion is even less exact than in the case of carbo- hyd rates, but it seems highly probable that here, too, we have a series of hydrolytic reactions, the original mole- 84 DIGESTION. cule of native proteid being hydrated and split up into simpler and more stable substances. In support of this view it may be mentioned that the same products result from the treatment of proteids with hydrolyzing agents, such as boiling mineral acids or superheated steam. On entering the stomach, proteids are subjected toi the influence of the gastric juice, the important constit- uents of which are pepsin, hydrochloric acid Q.2f c , renuin, water, and inorganic salts. The first recognizable step in the digestion of the native proteids is their conversion into a form which, unless first precipitated by neutralization, is uncoagu- lable by heat. For example, egg-albumen is converted by pepsin (the proteolytic enzyme of gastric juice) and hydrochloric acid, or more slowly by the action of hydrochloric acid alone, into an album inate acid albumin. If a digestion which contains albuminate be neutralized, a precipitate is formed which consists of albuminate, and is called a neutralization precipi- tate ; if an excess of alkali be added, the albuminate redissolves, as an alkali albumin. Albumin that has been coagulated by boiling is by pepsin and hydro- chloric acid converted into soluble albuminate, but the change is less rapid than in the case of soluble albumins. All the native proteids may be acted on in this way. As gastric digestion progresses, the albuminates are con- verted into proteoses, and these into peptones. The solubility of the proteid increases as it passes from one form to the next ; at the same time, its power of dif- fusing through animal membranes increases. Native proteids and albuminates are nondialyzable ; proteoses are very slightly dialyzable, peptones distinctly so, though they pass through membranes much more slowly than do the simpler crystalloids. This probably de- pends upon the large size of the proteid molecule. DIGESTION OF PROTEIDS. 85 Pepsin is incapable of causing proteolysis in neutral or alkaline solution ; it requires the presence of an acid, hydrochloric acid being the most favorable to its action. It is quickly destroyed by alkalies, and acts less rapidly when neutral salts, such as sodium chlorid, are present. Peptones are the final products of gastric digestion, In it thcv may undergo further change on reaching the intestines, where they are acted on by the pancreatic juice. The pancreas secretes a proteolytic enzyme, trypsin, the action of which is very similar to that of pepsin. Unlike pepsin, it is destroyed by hydrochloric aei<>iling milk renders it rather less readily digestible ; in the case of cow's milk, however, this effect is somewhat neutralized by the fact that in this condition it curdles iu small flocculi instead of in large masses, so that it is more thoroughly exposed to the action of the gastric jui f native ) 1 proteid / i i Indol, Ski ttol, Phenol, etc. / a. -^ s eces. t (small quantity) 92 DIGESTION, are absorbed in quantity by the epithelial cells which line the intestines. Peptones are, however, not found in the blood under ordinary circumstances, and if they reach the blood, are at once excreted (provided the blood pressure is not too much depressed) by the kid- neys. It appears that the epithelial cells, having taken up the peptones, reconvert them by synthesis into native proteids, and discharge them in this condition into the lymph, from which they pass into the blood-capillaries. The work done by the digestive juices might, at first sight, appear to be labor spent in vain, for the peptones so formed must be reconverted into albumins or globulins by the epithelial cells, and this entails the expenditure of a large amount of energy ; further, it has been shown that soluble native proteids may be absorbed without undergoing digestion. We must, however, remember that peptones are more readily absorbed than undigested proteids, and that coagulated proteids are incapable of absorption until they have been rendered soluble by di- gestion. Again, gelatin, egg-albumen, casein, and sev- eral other forms of soluble proteids are nonassimilable, and if injected directly into the circulation are excreted by the kidneys. These substances must undergo some change in constitution before they can be utilized as food by the cells of the body. The epithelial cells which line the intestines evidently possess the power of bringing about this rearrangement of the molecule of egg-albumen, provided it has not been rendered insoluble by cooking, but it is possible that the change is more readily effected after digestion has occurred ; it may be easier for the epithelial cell to construct serum albumin out of egg- albumen peptones than out of the native unchanged egg-albumen. The gastric digestion of proteids is, on the whole, favored by the use of small quantities of alcohol. It is DIGESTION OF FAT. 93 true that the presence of alcohol somewhat retards the action <>t' pepsin, but alcohol taken in small quantities is rapidly absorbed from the stomach. It stimulates the gastric glands to more rapid secretion of the gastric juice, and in this way, at least in cases where the pro- cess is less active than normal, hastens digestion. Not all the proteid of the food is digested and ab- sorbed; a variable amount, especially of the vegetable proteid, is excreted with the feces. Digestion of Fat. Fats are digested neither in the mouth nor in the stomach, but in the latter may, to a HI mil extent, undergo bacterial decomposition. In the intestine they are emulsified. Fats which contain some live fatty acid may be emulsified by the soap which is formed by the union of this fatty acid with sodium, the latter being derived from the sodium carbonate of the pancreatic juice and bile. Neutral fats, which contain no tree fatty acid, are also emulsified in the intestine, but not quite so readily, for in this case, before emulsification can take place, some of the fat must be split up with the liberation of fatty acid, which, with sodium, forms soap. The splitting of the fat is caused by an enzyme of the pancreatic juice, called steapsin, or pialyn. The change produced is hydrolytic, one molecule of fait being hy- dra ted and split up with the formation of one molecule of glycerin and three molecules of fatty acid ; for example : C 3 H 5 (C 18 H 35 2 ) 3 + 3H,0 = CjHjCOH), + 3C 17 H ?5 CO 2 H. Stearin Glycerin Stearic Acid It is probable that all the fat which is absorbed is first split up in this way ; some of the fatty acid set free is combined as soap, and by emulsifying the rest of the fat, hastens its digestion, for in this way the fat is more completely exposed to the action of the steapsin ; an- 94 DIGESTION. other portion is probably absorbed by the epithelium as fatty acid. Fatty acids are insoluble in water, but in the intestine they are held in solution by the presence of bile salts, sodium glycocholate and sodium tauro- cholate : the favorable influence exerted by bile on the digestion of fat probably depends on this property. Some of the fatty acid may be absorbed as soap. It is highly improbable that fat is absorbed without under- going digestion, as has been supposed. The fatty acid which is absorbed is, by the epithelial cells, recombined with glycerin to form fat ; the absorbed soap is combined in the same way, the sodium being first split off and united with some other acid radicle. Even if fatty acid be administered in the absence of glycerin, it may be converted into fat in the epithelial cells, which in this case appear to manufacture the glycerin. In the absence of bile, the absorption of fat is defective, much of it undergoing bacterial decomposition into fatty acids in the large intestine and being excreted in the feces. TABLE 5. DIGESTION OF FAT IN THE INTESTINE. Fat Glycerin- Fatty acid -> . + Na 2 C0 3 = Soapi- H 2 + C0 2 Intestinal epithelium Fat Lymph The fat which passes from the intestinal epithelial cells into the lymph-spaces of the villi does not enter 1 The soap first formed causes the emulsification of the remain- ing fat. BILE. 95 the blood-capillaries, but passes through the lymphatic vessels into the thoracic duct, and so reaches the subcla- vian vein, where it is mixed with the blood. The solu- ble constituents of the food, on the other hand, pass from the lymph-spaces of the villi into the blood-capil- laries, for the percentage of sugar and proteids in the lymph which reaches the thoracic duct is very little in- creased during absorption. Sugars and proteids may be absorbed in the stomach to a certain extent, but in the intestine conditions are much more favorable to ab- sorption. Water is not absorbed from the stomach, but passes on into the intestines ; it is absorbed most rapidly in the ileum aud large intestine. Bile. The chief constituents of bile, as secreted by the liver, are water, bile salts, inorganic salts, pigments, cholesterin, lecithin, and soaps. To these, as the bile passes through the ducts, and during its stay within the gall-bladder, is added mucin. The bile salts are sodium glycocholate and sodium taurocholate; in human bile the former predominates. They are present in bile to the extent of about 7.5 c / . They are largely reabsorbed, but in the intestine a portion of these salts may be hydrolyzed through the action of bacteria, as follows : C 2 H 43 6 -f H 2 = C 24 H 40 5 + CH 2 .NH 2 .C0 2 H (ilyL-ucholic Acid Cholic Acid Glycocol C 26 H 43 6 + H.,0 = C 24 H 40 5 + C 2 H 4 NH 2 S0 2 OH Tanrocholic Acid Cholic Acid Taurin The taurin, glycocol, and part of the cholic acid formed ' are absorbed. The bile salts are useful in holding in solution cholesterin and lecithin, and appear to be used more than once, possibly over aud over again. It has already been mentioned that they exert an important influence on the absorption of fat. The bile pigments, bilirubiu and biliverdiu, originate from the hemoglobin, 96 DIGESTION. :: of broken-down red blood-cells ; they contain, howeve no iron, this being split off and retained in the liver, where the bile pigments are formed. The iron so | retained may be used in the synthesis of new hemo- globin. A certain amount of bile pigment seems to be reabsorbed from the intestine, to be again excreted. Most of the pigment is reduced by the action of the free hydrogen in the intestine, or, through putrefaction, to hydrobilirubin, some of which is absorbed and I eliminated by the kidneys ; in the urine it is called | urobilin. Movements Concerned in Digestion. Secretion of the Digestive Juices. Mastication is performed by movements of the lower jaw, the muscles concerned being innervated through the inferior maxillary brand: of the fifth cranial nerve. The food is kept betweer the teeth by movements of the tongue and contractior of the muscles of the cheeks. The food is thus no1 only ground up, but is mixed with the saliva. Tl latter is secreted by three pairs of glands, the parotid submaxillary, and sublingual glands ; and to a smalle extent by the glands of the oral mucous membrane The activity of the salivary glands is controlled by the central nervous system, the salivary centers bein situated in the spinal bulb. Two sets of secreto nerves, cranial and sympathetic, are distributed to eac gland. The cranial nerve-fibers (pre-ganglionic) whic innervate the parotid leave the bulb in the ninth craui nerve and probably end in the otic ganglion in contact relations with nerve-cells whose axons (post-ganglionic) reach the parotid through the auriculotemporal branch of the trifacial. The cranial fibers which control the ] submaxillary and sublingual glands emerge from the bulb in the facial nerve, and, by way of the chorda tympani, reach the submaxillary and sublingual ganglia. MOVEMENTS CONCERNED IN DIGESTION. 97 In these ganglia they end, and make physiologic con- in ct ion with cells whose post-gangl ionic fibers are dis- tributed to the gland-cells. Post-ganglionic sympathetic nerve-fibers from the superior cervical sympathetic ganglion are supplied to each of these glands. The cranial secretory fibers are accompanied by vasodilator fibers ; the sympathetic, by vasoconstrictors. Artificial stimulation of the chorda tympani produces a result which differs widely from the effect of stimula- ting the cervical sympathetic. In the former case, the submaxillary gland secretes abundant watery saliva ; in the latter case, the secretion is thick and scanty. Stimulation of the chorda tympani of course increases the blood supply of the gland, and thus renders a copious secretion possible, but the variation of the 1)1 ood supply probably does not account altogether for the difference in the two results. The normal secretion of saliva is a reflex event. It is readily initiated by stimulation of the terminations of the afferent nerves of the oral mucous membrane by food or other sub- stances placed in the mouth, weak acids forming a particularly effective stimulus. Reflex secretion of saliva is not brought about through the sympathetic nerve-fibers, but only through the cranial fibers. The si li vary centers are not under the control of the will, but by thinking of food we may cause the dispatch of involuntary nerve impulses from the brain to the salivary centers, and thus indirectly bring about a flow of saliva. These centers may be not only excited through the emotions, as by the sight or smell of food, but they may also be inhibited, as by fear or nervous worry. Reflex secretion of saliva may result from simulation of afferent nerves in parts of the body other than the mouth; irritation of the gastric mucous membrane may cause it, a flow of saliva usually pre- 7 98 DIGESTION ceding vomiting. Irritation of the uterus may also be effective, the early stages of pregnancy often being accompanied by profuse secretion of saliva. After division of the chorda tympani there follows a slow continuous secretion of saliva by the submaxillary gland ; this is called paralytic secretion, and probably results from a local stimulation of the group of nerve- cells in the gland which form the submaxillary ganglion. How the stimulus originates is unknown, and it may be that the activity of the nerve-cells is increased by the cessation of inhibitory impulses, which normally are perhaps transmitted to them through the chorda tympani. The administration of atropin causes dry ness of the mouth, by paralyzing the terminations of the post-ganglionic fibers of the cranial nerve supply ; the sympathetic fibers are not affected. Pilocarpin provokes secretion, apparently by stimulating the terminations of the same fibers. The food, after being masticated and mixed with the saliva, is swallowed. Only the first of the movements which play a part in deglutition are voluntary. If the mouth be empty of anything that could be swallowed, including saliva, it is impossible to voluntarily provoke all the swallowing movements. They are for the most part purely reflex, and are excited through the afferent nerves of the soft palate, of the back of the tongue, and of the fauces, which are stimulated by the contact of food, or any other substance, with the mucous membrane covering these parts. The first part of the action, which may be accomplished voluntarily, con- sists in the approximation of the tip of the tongue to the hard palate, followed by a raising of the floor of the mouth and tongue by the contraction of the mylo- hyoid muscles. This forces the food back through the fauces into the pharynx ; in the case of liquid no further MOVEMENTS CONCERNED IN DIGESTION. 99 muscular action is necessary to carry it as far as the lower end of the esophagus; nevertheless, the contrac- tion of several muscles, in regular sequence, follows. As the food enters the pharynx, it is prevented from passing upward into the nasal pharynx by the contrac- tion of the levatores palati and superior constrictors of the pharynx, which occurs even before the food touches the soft palate ; its entrance into the larynx is prevented I > 'X DlfcSTIX>K '/' ' 101 denal mucous membrane caused by the acid chyme. The rhyme then will be mixed with, and neutralized by, the alkaline bile and pancreatic juice; the pepsin will be rapidly destroyed by the trypsin and sodium car- Inmate, and the partly digested proteids precipitated by the bile salts. The secretion of pancreatic juice is not entirely dependent on the central nervous system ; there exist local ganglia which govern the activity of this gland. The secretion of bile seems to be influenced im >re or less by the absorbed products of gastric digestion. I )uring starvation the intestines are pale and motionless, l)i it after the taking of food they become flushed with blood and exhibit movements of two kinds, rhythmic and peristaltic. The rhythmic or pendular movement (insists of a swaying of the intestinal loops occasioned by the contraction of both the longitudinal and circular nials of muscle, constriction being but little in evidence. The wave of contraction passes over the intestines, from above downward, from twenty to fifty times as rapidly as the peristaltic contractions. The rhythmic move- ments are of muscular, the peristaltic of nervous, origin. As in the case of the stomach, the vagus supplies the intestine with both motor and inhibitory nerve-fibers ; tin sympathetic supplies chiefly inhibitor} 7 fibers. These nerves appear, however, to exert only a regulatory influ- ence over the intestinal movements, for after the division of all the extrinsic nerves, peristalsis may continue or he- mine exaggerated ; the nerve-cells of Auerbach's plexus pn >1 >ablv constitute a local mechanism by which peristalsis is <( tordinated. The movement consists of a constriction which travels from the duodenum downward at the rate of alxwt 1 mm. per second, and is preceded by a wave of relaxation ; the latter, of course, increases the ease with which the contents of the intestine are pressed onward by the constriction following in its wake. If a K)2 .DIGESTION. local stimulus be applied to the mucous membrane of the intestine, a constriction appears above the point stimulated, while for some distance below, the muscles are inhibited and relax. The large intestine shows similar peristaltic move- ments, which begin at the ileocecal valve, and are prop- agated in the direction of the rectum, but do not reach it. The feces accumulate in the sigmoid flexure. The descending colon, rectum, and anus receive two sets of nerve-fibers, one, coming through the sympathetic, from the lumbar region of the cord (the pre-ganglionic fibers ending in the inferior mesenteric ganglia), the other, from the sacral portion of the cord through the nervi erigentes, the pre-ganglionic fibers of this set ending in small ganglia near the part innervated. The first set are for the most part motor, the latter inhibitory. Ordinarily the rectum is empty, and is only thrown into reflex peristalsis by the entrance of feces from above ; defecation may be delayed by the contraction of the internal and external sphincters of the anus, the former consisting of involuntary, the latter of voluntary, mus- cle. The filling of the rectum gives rise to a desire to defecate, which may or may not be resisted ; if the former, the contraction of the external sphincter is voluntarily strengthened ; if the latter, the emptying of the rectum is assisted by a contraction of the abdominal muscles and inhibition of the external sphincter, the internal sphincter being at the same time reflexly inhib- ited. If by injury to the spinal cord voluntary nerve impulses are prevented from reaching the centers in the lumbar region, defecation becomes purely reflex, and may be carried on without the aid of the will. If the lumbar portion of the cord be destroyed, the reflex mechanism is put out of existence, and fecal inconti- nence results. QUESTIONS. 103 Vomiting is a reflex action which usually results from irritation of the gastric mucous membrane, and is preceded by a feeling of nausea. It may also be excited in a variety of other ways ; for instance, mechan- ical irritation of the pharynx, intestinal obstruction, irritation of the uterus, as in pregnancy, and through the emotions. It is brought about mainly by strong contractions of the diaphragm and abdominal muscles, with simultaneous closure of the glottis. The stomach is thus compressed and its contents ejected through the esophagus, the cardiac sphincter being meantime relaxed. 1 he walls of the stomach take some part in the expul- sion of the food, but unassisted are ineffective. Vomit- ing is controlled by a center situated in the medulla. QUESTIONS FOR CHAPTER IV. What foods actually require digestion before they can be ab- sorbed? Does proteid undergo any preparation for absorption in the month? If raw starch and saliva be mixed, will the digestion of the former be assisted by boiling the mixture? If starch paste be acidified with HC1, the addition of what sub- stance will enable saliva to digest the starch? If starch and saliva be mixed, and a drop of the mixture be ti->trd at intervals with iodin solution, why does the color reaction vary? What step in digestion which is of more importance than the salivary digestion of starch is carried on in the mouth? Why is it well to wash the teeth after each meal ? What secretion possesses the widest range of digestive power? Can you readily arrange the digestive secretions in the order of their relative importance ? How is digestion affected by removal of the stomach ? In what respect is digestion most interfered with by removal of the pancreas ? 104 DIGESTION. Which of the following substances are of equal value as food, whether they be injected directly into the blood stream or intro- duced into the alimentary canal : dextrose, cane-sugar, soluble starch, lactose, egg-albumen, peptones, raw serum albumin, cooked serum albumin, levulose ? Supposing that pyloric and duodenal fistulse have been estab- lished, so that there is no communication between the stomach and intestines, the animal may be fed through the mouth, or by intro- ducing food and water directly into the duodenum. Which method of feeding will prove the more satisfactory ? What effect on digestion has the existence of a biliary fistula? How does fat reach the blood stream ? How is digestion modified by the absence of hydrochloric acid from the gastric juice ? What constituents of food require no digestion ? What different factors play a part in determining the reaction of the intestinal contents? If a small quantity of egg-albumen be absorbed from the intes- tines without having undergone digestion, how is it that it does not appear in the urine ? Under what circumstances does glycerin appear in the intes- tines? How does dextrin differ from starch in its physical properties? Where and how is bread and butter digested ? Why is it impossible to swallow six times in rapid succession without placing something in the mouth ? Have the emotions any influence over digestion ? and is the effect of all emotions the same ? Why should the addition of horn shavings, which are indigest- ible, enable a rabbit to live on a milk diet ? How is it that proteid food does not result in peptone poison- ing? What becomes of the hemoglobin of the red cells which break down? If soluble starch is absorbed from the intestine, why does it not appear in the blood ? What evidence of constipation may be shown by the urine? What instances of synthesis in the body can you mention ? CHAPTER V. METABOLISM AND NUTRITION* THE food, after digestion and absorption, reaches the lymph-spaces of the gastric and intestinal mucous mem- hranes. The proteids and carbohydrates pass, for the niitst part, from the lymph into the blood-capillaries, and are carried through the portal vessels to the liver ; tin- flit, on the other hand, reaches the subclavian vein through the lymphatic vessels. During the absorption of fat, the lymph which passes through the lymphatic vessels of the mesentery, or lacteals, resembles milk in appearance, and is called chyle. As we have seen, the carbohydrates reach the blood ehiefly in the form of dextrose. If during absorption samples of blood be taken from the portal and hepatic veins and compared, it will be found that the hepatic Mood contains the smaller percentage of sugar. Evi- dently, then, during absorption sugar disappears from the blood as it passes through the liver. If the liver of a well-fed animal be examined with the microscope, the liver-cells will be seen to contain an opalescent sub- stance, which lies in that portion of the cell adjacent to the blood-capillary. On treatment with iodin, this sub- stance gives a port-wine color reaction, resembling that niven with iodin by erythrodextrin. It is a carbohy- drate with the formula (C r H 10 O 5 ) n , the molecule being smaller than that of starch ; according to observations made on the freezing-point of its solutions, it may be represented as (C 6 H 10 O 5 ) 10 . Like starch, glycogen is 105 106 METABOLISM AND NUTRITION. nondialyzable ; unlike starch, it is readily soluble. On starvation, glycogen rapidly disappears from the liver. If through the vessels of an excised, glycogen-free liver there be kept up an artificial flow of blood which con- tains dextrose, the percentage of sugar in the blood diminishes, and glycogen appears in the liver-cells. The conversion of sugar into glycogeu is synthetic, and con- sists in the following reaction : 10C 6 H 12 6 = (C 6 H 10 5 ) 10 + 10H 2 0; Dextrose Glycogeu that is, if we may take the above formula to represent glycogen. Not all the sugar which reaches the liver is converted into glycogen ; a large proportion passes through the liver unchanged and is distributed, through the arteries, to the system in general. Sugar is rapidly taken up from the lymph by the muscles ; a certain amount being converted by them into and stored as gly- cogeu. Taken collectively, the muscles may contain as much glycogen as is found in the liver, but in muscle the percentage is smaller. Some of the sugar taken up by the muscles may perhaps at once, without undergoing previous elaboration, be utilized as a source of energy, being burnt up with the formation of carbon dioxid and water ; it is probable, however, that an active muscle which uses an excess of sugar does not carry the oxida- tion of this excess beyond the formation of lactic acid, C 3 H 6 O 3 , and that this lactic acid is completely oxidized elsewhere. Exercise reduces the amount of glycogen held in muscle, but that other substances may afford a supply of energy for muscular work is shown by the fact that a muscle may perform work after all its glyco- gen has disappeared. If a muscle is paralyzed by divi- sion of its nerve supply, an accumulation of glycogen goes on within it for several days. Other portions of GLYCOSURIA. 107 the sugar received by a muscle may, within it, be com- bined with some other substance, for instance, proteid, or it may be con verted into and stored as fat. During starvation, when all the glycogen has disappeared from the liver and muscles, and when the body's store of fat has been used up, the blood still contains sugar which can only have originated from the proteids of the body, fin- sugar continues to be used by the tissues and yet does not disappear. Glycogen itself may be formed by the liver on a purely proteid diet, and this is not sur- prising, for proteids appear to contain a carbohydrate radicle in their constitution. It is probable that the liver having stored the carbohydrate excess which it re- ceives during absorption, as glycogen, reconverts this -tmv into sugar as it is needed by the rest of the body. That the liver can convert glycogeu into sugar is cer- tain, for it may be caused to do so by the stimulation < iling the liver immediately after the death of an ani- mal, possibly owing to the destruction of a ferment which may be contained within the cells and be answer- aide for the conversion. Again, by injuring the floor <>t' the. fourth ventricle, the liver may be carfsed to dis- charge its glycogen as sugar; whether the result is dm- to interference with the circulation of blood through the liver, or whether there exists in the bull) a definite center which regulates the metabolism of the liver-cells, is uncertain. In consequence of this change the blood will, for the time being, contain an excess of sugar, which t he kidneys at once begin to excrete, giving rise to Glyco- suria. This they do whenever sugar accumulates in the l)lM>d beyond the normal amount 0.1 to 0.2^. The appearance of sugar in the urine does not, therefore, indi- cate an abnormality of the kidneys, but merely that they 108 METABOLISM AND NUTRITION. are discharging their normal function in removing from the blood an excess of sugar, for the occurrence of which they are not answerable. Sugar may accumulate in the blood from a variety of causes ; the simplest cause is the taking of abundant carbohydrate food, but it is not easy in this way to produce glycosuria (sugar in the urine). Disease of the pancreas often, its removal always, causes glycosuria, but this has nothing to do with the digestive function of the pancreatic juice, nor, apparently, with those cells of the pancreas which pro- duce this secretion. It seems probable that the groups of epithelioid cells which are known as Langerhans's bodies play an important part in regard to metabolism in general. Pancreatic diabetes continues in the ab- sence of carbohydrate food, and even during starvation ; the sugar in this latter case must originate from the break-down of proteids. Carbohydrate food increases pancreatic glycosuria. In the normal condition the pancreas evidently regulates the proteid and carbohy- drate metabolism of other organs, but whether through the manufacture of some substance which is carried to them by the lymph and blood, or in some other way, is unknown. In the absence of this pancreatic influence, either more proteid than usual is converted into sugar or less sugar is used by the tissues ; at the same time gly- cogen disappears from the liver. The liver can, how- ever, if provided with levulose, convert this form of sugar into glycogen, and the levulose administered does not increase the glycosuria, but is utilized in the body. Fat, after absorption, does not pass through the liver before entering the general circulation. There is no doubt that not all the fat of the food can, on reaching the cells of the body, be simply stored in the form in which it was taken, for the fat of different animals varies in composition. Human fat contains a larger PROTEID METABOLISM. 109 proportion of olein than does mutton or beef fat. If mutton or beef fat is to be stored, the excess of, for instance, stearin must be either split up and rearranged in the form of olein, or oxidized and excreted. Under certain conditions, however, some foreign fat may be stored in the adipose tissues of an animal, but this is unusual. Not all the fat stored in the body is derived from the fat of a food; a small proportion may be formed from sugar or glycogen, and probably more from proteid. It is the opinion of some investigators that ;il most all the fat of the food is oxidized by the cells as it reaches them, and that very little is stored as fat. Fat affords a large amount of energy to the system, which may be utilized in performing mechanical work, clu-inical work in the way of synthesis, and in main- taining the temperature of the body. The final prod- ucts of its oxidation are carbon dioxid and water. The waste products of proteid metabolism also in- clude water and carbon dioxid, but there are formed, in addition, nitrogenous substances, the chief of which is urea. It is not to be supposed that the proteid metab- olUm which goes on within the cells, results in the direct decomposition of proteid into urea, carbon djoxid, and water, for in the muscles which contain the larger pro- jx>rtion of body proteids, and in which proteid metab- oli>m goes on continually, little or no urea is to be found. That this absence of urea is not due to its rapid removal from the muscle by the lymph and blood lias been proved by keeping up an artificial circulation through the vessels of a dog's hind limbs, the bleen to contain two urea groups united with a central chain of C.C.CO: NH C=O 0=C C NIL I II >c=o NH C-NH X 112 METABOLISM AND NUTRITION. Through oxidation and hydrolysis, uric acid may be decomposed, with the formation of two molecules of urea and one of oxalic acid. If urea be administered to a bird, it is converted by the liver into uric acid ; on the other hand, uric acid administered to a mammal is de- composed by the liver with the formation of urea. Th amount of uric acid found in human urine is variable there is usually one part of uric acid to about thirty-iiv parts of urea, but the ratio varies with the nature of the food. The amount of uric acid is increased by nuclec proteid food, though nuclein does not seem to be diges and absorbed to more than a small extent. It has bee stated above that nuclein may be split up, with the for mation of xanthin bases, which are closely related to uric acid. In leukemia, a pathologic condition in which the number of leukocytes in the blood is largely in creased, the excretion of uric acid is also increased, per haps owing to the break-down of leukocytes in unusu numbers, and the liberation of their nucleoproteid, whic is then converted into uric acid. Not all the uric aci formed in the body may be expected to appear, as such, in the excretions, for much of it is probably convertec into urea ; the uric acid of the urine has perhaps reachec the kidneys without passing through the liver. Hippuric acid is a nitrogenous waste product whidj appears in human urine in small quantities only ; it more abundant in the urine of the herbivora, and, in th( case of man, may be increased by eating vegetables more especially fruits, which contain aromatic substances that are oxidized in the body, with the formation of ben zoic acid. Hippuric acid appears in the urine, to a cer tain extent, even during starvation, and cannot therefore be entirely derived from food ; aromatic compounds must originate in small quantities from the metabolism of proteids, and be converted into benzoic acid. The HIPPURIC ACID. 113 benzole acid, whether it be formed from food or from body proteids, is combined by the kidney with glycocol to form hippuric acid, and thus excreted. It appears, then, that urea is not an immediate prod- uct of proteid metabolism, but that intermediate sub- stances are formed, such as creatin, ammonium salts, ]>< tssibly amido-acids, etc. It is certain that glycocol may be formed in the body, for the administration of ben- zole acid results in the appearance of hippuric acid in the urine. As in the case of the nitrogenous, so in the case of the carbonaceous half of proteid, decomposition into the final waste products, carbon dioxid and water, is not immediate. Indeed, after a meal consisting of proteids, the excretion as urea of an amount of nitrogen corre- sponding to that administered is accomplished earlier than the excretion of the amount of carbon and hydro- gen contained in the proteid. This indicates that the proteid is split into a nitrogenous and a nonnitrogenous part, the latter being perhaps transformed into glycogen, dextrose, or fat before it is utilized by the cells. It is known that these substances may be formed from pro- teid food, as has been stated above. It seems probable that fats and carbohydrates never form part of the bio- plasm, but are held closely in contact with it within the cells, and utilized by it as a source of energy. Some of the proteid food is undoubtedly transformed into the living proteid of bioplasm, but it is unlikely that it all undergoes this process before being oxidized. In all likelihood, the fats, the carbohydrates, and most of the proteid, after entering the cell, suffer decomposition without ever becoming a part of bioplasm. Some of their decomposition products may subsequently undergo synthesis ; for example, sugar may in this way be trans- formed into fat. The proteid of bioplasm, or, as it is called, tissue proteid, may be supposed to break down 8 114 METABOLISM AND NUTRITION. but slowly ; at the rate, it has been estimated, of about 1 1 ism in the cells of the spinal cord. Monkeys survive the operation longer; they also show muscular tremors, and myxedema may follow. Myxedema is a condition associated in man with atrophy of the thyroid ; the symptoms are an overgrowth of the subcutaneous con- nective tissue, muscular weakness, sometimes spasms, and mental failure. The congenital form is known as cretinism, the child being idiotic and deformed. In man the removal of the thyroid is sometimes followed by myxedema, this variety being known as operative myxedema, or cachexia strumipriva. The symptoms may l>e relieved by injecting an extract made from the thyroid of some other animal into a vein or under the skin, or even by the administration of raw thyroid with the food. The normal thyroid evidently produces a snl (stance, or substances, which enter the lymph and blood, are carried throughout the system, and take effect more especially on the central nervous system. In the absence of these substances, the metabolism of the nerve- eel Is becomes abnormal, but may be rectified by the administration of thyroid extract. The overgrowth of subcutaneous connective tissue is also due to abnormal metabolism. The thyroid produces an iodin compound, known as iodothyrin, or thyroiodin, which appears to be one of the substances answerable for thyroid influence, tor this product is, on injection, effective in relieving the symptoms of myxedema. It is possible that this irland also possesses the power of neutralizing poisonous 116 METABOLISM AND NUTEITION. products of normal metabolism. The irritability of the cardie-inhibitory and depressor nerves is reduced by the removal of the thyroid, and increased by the injection of iodothyrin, which tends also to lessen the irritability of the vasoconstrictors. The removal of the pituitary body is, in dogs, fol- lowed by symptoms very similar to those seen on removal of the thyroid. In man, however, disease of the pituitary body is not accompanied by myxedema, but by an overgrowth of the bones of the face and limbs ; a condition named . acromegaly. Injection of extracts made from the posterior lobe into the vessels causes strengthening of the heart-beat and constriction of the arteries, apparently influencing directly the mus- cular coats of the vessels. In dogs the removal of both adrenal bodies, or supra- renal capsules, is more quickly fatal than is the removal of either the thyroid or the pituitary body. The symp- toms which precede death are extreme muscular weak- ness, weak heart-beat, and loss of vascular tone. In man a condition known as Addison's disease is asso- ciated with abnormality of the adrenals. The symp- toms are similar to, but less acute than, those following the removal of the bodies ; in addition, there occurs a peculiar bronzing of the skin, and sometimes of the mucous membranes. Dogs die too soon for this symp- tom to develop, but in rabbits, which survive the oper- ation longer, pigmentation of the skin has occurred. Very marked eifects are produced in normal animals by the intra vascular injection of adrenal extracts. Mus- cular contraction is unusually prolonged, an effect resem- bling that of veratrin. The cardie-inhibitory center is strongly stimulated, the auricle ceases to contract, and the ventricle beats slowly ; nevertheless the arterial blood pressure rises, owing to a direct stimulation of the NUTRITION. 117 art orioles. This effect is transitory but energetic; if the vagi have been previously divided, the pressure rises to a uTeat height. Extracts made from the cortical por- tion of the gland are inert; the active principle is to be obtained from the medullary portion only. A substance, epinephrin, which has been isolated from the extract, produces, on injection, the characteristic effects, and is evidently one of the active principles of the gland, though perhaps not the only one. We may conclude, then, that the adrenal body elaborates epinephrin, and perhaps other substances, which pass into the circulation and art on muscular tissue skeletal, cardiac, and vascular in such a manner that its tone is increased ; in other words, they hasten muscular metabolism, perhaps more especially in regard to the oxidation of carbohydrates. In the absence of this influence the muscles lose their tone. NUTRITION. The body is constantly liberating energy supplied by the food, in which it has been stored by the plant ; the ultimate source of this energy being the light and heat of the sun. The question to be discussecj, is, whether the different food-stuffs are of equal importance, and whether they are all necessary to the maintenance of life. It may be mentioned, in the first place, that di- gestion goes on more readily on a mixed diet. In all experiments on nutrition it is necessary to keep an ex- aet account of the amount and quality of both the food and the excreta. In this connection it is usually suffi- cient, as far as the proteids are concerned, to estimate the amount of nitrogen excreted in the urine and feces. Proteids contain, by weight, from 15^ to 17 % nitro- gen ; consequently, the appearance of 1 gram of nitro- gen in the excreta indicates the decomposition of about 118 METABOLISM AND NUTKITION. 6.25 grams of proteid. If the nitrogen excreted exactly equals the amount taken in the food, the animal is said to be in a condition of nitrogenous equilibrium. If the excreta contain less nitrogen than was taken in the food, nitrogen has been stored in the body ; that is, proteid has been laid up. If more nitrogen appears in the excreta than was contained in the food, the excess must have been derived from the break-down of an un- usual amount of body proteids. Even if nitrogenous equilibrium is maintained, the weight of the body may not remain constant, for carbon equilibrium does not always accompany an equilibrium in nitrogen. Carbon is contained in all classes of food-stuif, and while a condition of nitrogenous equilibrium exists, glycogen or fat may be stored up even on a purely proteid diet, leading to a deficit in the carbon excreted. On the other hand, fat or glycogen may be used up, and thus lead to the excretion of an excess of carbon, without interfering with the maintenance of nitrogenous equilib- rium. It is therefore necessary, in making experiments on the relative value or the fate of the food-stuffs, to estimate not only the nitrogen, but also the carbon of the food and excreta. During starvation metabolism does not cease, but goes on entirely at the expense of the carbohydrates, fats, and proteids of the body. After using up a certain proportion of this store, the animal dies; the period which lapses before death depending largely on the condition of the animal when starvation began. A lean animal will usually withstand the loss of about 0.4 of its body-weight ; one that is fat may live until its weight has been reduced by 0.5 ; an adult human being may live for three weeks without food if supplied with water ; children die in a few days, after losing about 0.25 of their weight, Fat disappears rapidly during NUTRITION. 119 starvation ; the proteids, as long as fat is being utilized, diminish very slowly. When most of the fat has been cni i snmed the body falls back upon its store of pro- teids, and the excretion of urea is suddenly increased beyond that of the preceding period. While the fat la-ts, the proteids are not used to any extent as a source of energy for the maintenance of temperature or i'or muscular work ; but when the supply of fat has been exhausted, they must be so used; and even before this Man-e is reached, proteid must be decomposed in the for- mation of sugar, which never disappears from the blood. A- starvation progresses metabolism diminishes, and tin- loss of weight grows less from day to day. The greatest loss in weight is sustained by the adipose tissue ; then come the muscles ; next the liver, spleen, etc., and, lastly, the heart and central nervous system, which suffer almost no loss, for they live at the expense f the other tissues. It might be supposed that a daily supply of proteid food, equal in quantity to the amount of tissue proteid which is broken down per diem during starvation, would suffice to keep an animal in a condition of nitrogenous equilibrium, but this is far from being the case. This depends uptpi the fact that proteid metabolism within the cells is stimulated by the reception of proteid food ; the larger the quantity of proteid food which reaches the tissues, the more rapidly does proteid metabolism go on, and, as a result of this, the cells are capable of using practically all the proteid which is supplied to them. In one classic ex- periment a dog, during starvation, was found to con- sume his store of muscle at the rate of 165 grams per diem; at the same time he was burning up 95 grams of fat. When given 500 grams of lean meat, the nitrogen in his urine showed that 599 grams were de- composed ; that is, that he had used lip 99 grams of 120 METABOLISM AND NUTRITION. muscle in addition to what he had received. At the same time 47 grams of fat were oxidized. In one day of starvation the animal had lost in weight 260 grams ; the administration of 500 grams of meat only reduced this loss to 146 grams. On gradually increasing the amount of proteid food, from day to day, it was not until 1500 grams of meat were given that loss of weight was pre- vented ; at this point nitrogenous equilibrium was es- tablished, and 4 grams of fat were stored up. In- creasing the amount of proteid food still further did not lead to an appreciable storing up of proteid tissue ; in fact, when 2500 grams were given, 2512 grams were decomposed, a loss of muscle to the extent of 1 2 grams. Fat was, however, stored up to the extent of 57 grams. Thus, if kept on a purely proteid diet an animal must, in order to maintain nitrogenous equilibrium, receive a certain amount of food ; if more than this be given, it does not lead to the storing-up of the excess, for the cells become spendthrift and burn up all the proteid that they receive, in this way maintaining nitrogenous equilibrium at a higher level. Proteid metabolism may, however, be reduced by a mixed diet. In the case of the animal which required 1 500 grams of meat for the maintenance of nitrogenous equilibrium, an addition of 150 grams of fat to this amount of meat resulted in the building-up of tissue to the extent of 26 grams. Further than this, if 150 grams of the fat was given, the amount of proteid neces- sary was much less ; under these circumstances the allow- ance of meat was reduced to 800 grams without the ap- pearance of an excess of nitrogen in the urine. There- fore, a mixed diet is the more economic, for proteid is the most expensive of foods ; it is better physiologi- cally, for digestion is much less likely to become dis- ordered. Carbohydrates are even more effective than NUTRITION. 121 fats in the reduction of proteid metabolism ; gelatin serves this purpose better than either. If, then, it is desired to reduce proteid metabolism as far as possible, in order that there may be a building-up of tissue pro- teid, of muscle, for example, it is best to give but a moderate amount of proteid, with a good proportion of one of the other foods, or, better still, a mixture of all the others. A mixture of the other foods, no matter hu\\ abundant the diet, will not, in the absence of pro- lei* 1 food, serve to maintain nitrogenous equilibrium; life will be prolonged, but death from proteid starvation is inevitable. There is a difference of opinion as to the relative pro- portions in which the food-stuffs should be combined to form an ideal diet. The following is the diet recom- mended by Voit, and is intended for a man of 70 kilo- grams : Proteid, 118 grams. Fat, 56 grams. Carbohydrates, 500 grams. This diet is supposed to consist of both animal and vegetable food, and, consequently, cannot be expected to be absorbed in toto, for vegetable food is /I ess readily digested than meat, owing chiefly to the cellulose cover- ing. In order to calculate the amount of energy supplied to the body by a given diet, we must know the combustion equivalent of each food-stuff; this is determined by burning the substance in question, and measuring the ln-at given off. In the case of fats and carbohyd rates, the same amount of energy is liberated within the body as when the substance is burned outside the Inxly, for the oxidation is in each case complete, the final products of combustion being carbon dioxid and water. Not all the energy contained in proteids is set free within the 122 METABOLISM AND NUTRITION. body, for the end-products of proteid metabolism are, in the main, carbon dioxid, water, and, instead of nitrogen, urea, which is capable of undergoing oxidation and liberating energy. Besides urea, other oxidizable sub- stances are formed in small quantities, and we must de- duct the energy thus lost to the body from that intro- duced in proteid. The potential energy of a substance is expressed in calories. A calorie is the amount of heat required to raise the temperature of 1 gram of water by 1 C. The potential energy available to the body from 1 gram of proteid is 4100 calories ; from 1 gram of fat 9300 calories ; and from 1 gram of carbohydrate, 4100 calories. Adopting Voit's diet, as given above, the available energy will be : Proteid, 118 grams X 4100 . . 483,800 Fat, 56 grams X 9300 520,800 Carbohydrate, 500 grams X 4100 . 2,050,000 3,054,600 calories. This represents a diet suitable for a man doing ordinary work ; increased labor entails the necessity of a larger food supply. As muscular work is performed almost entirely at the expense of the nonnitrogenous foods, it would seem rational to vary the diet by increasing the proportion of these when more work is to be done ; ex- perience has shown, however, that it is better to give more proteid also. The metabolism of the nonnitrog- enous foods is also increased by exposure of the body to cold ; that of proteids is not affected to an appreciable extent. The combustion equivalent of fat is higher than that of the other foods, and dwellers in cold cli- mates are said to have a craving for fatty food, but there is no proof that fat is more readily used by the muscles in keeping up the temperature of the body. Inorganic salts form as essential a part of the diet as NUTRITION. 123 the foods which supply energy to the body. It has been shown that an animal fed on food from which the inor- ganic salts have been, as far as possible, removed dies Sooner than similar animals which are starved. Inor- ganic salts are necessary for the neutralization of acids funned during metabolism ; for instance, sulphuric acid, which originates from the oxidation of the sulphur con- tained in the proteid molecule. It is true that this may, to a certain extent, be neutralized by ammonia, also split off from proteid. This is by no means the only use of the inorganic salts, and, of course, neutral salts, such as sodium chlorid, are not used in this way. Amongst the uses of the inorganic salts in the body may be mentioned the following : they maintain the alkalinity of the blood and lymph, which is of the utmost importance, for an acid reaction rapidly destroys the irritability of bioplasm; they are of importance in regard to the osmotic pressure of the liquids and cells <>f the body ; their presence is necessary to the solution of the globulins; from sodium chlorid is derived the clilorin for the formation of hydrochloric acid in the gastric glands; sodium chlorid, potassium salts, and soluble calcium salts are necessary to the activity of the heart ; calcium salts are concerned in the clotting of blood, and so on. It would appear that the inorganic salts of the food must, to a certain extent, be in combi- nation with organic substances, such as proteid; other- wise, they do not fulfill all that is required of them. A vegetable diet contains an excess of potassium salts, and seems to necessitate a supply of sodium chlorid, for the potassium salts react to some extent with the sodium chlorid of the blood, forming potassium chlorid and, for instance, sodium phosphate; this loss of sodium chlorid to the blood must be made good by its addition to the food. A supply of calcium for the building-up of 124 METABOLISM AND NUTRITION. bone is needed especially by growing children, and this want is particularly well supplied by milk, which con- tains an abundance of calcium. Iron is another sub- stance which is needed, chiefly in relation to the forma- tion of hemoglobin ; this is supplied in combination with nucleo-albumins in the food, but inorganic salts of iron may be absorbed. A diet consisting entirely of milk is unsuitable for any but infants, for it contains an insuffi- cient quantity of iron. The infant contains within its tissues a store of iron which is slowly used up during the period of suckling ; if confined to a milk diet beyond the usual time, it becomes anemic. Water supplies no energy to the body, but is indis- pensable, for in its absence metabolism is impossible. It serves as a solvent for both food and excreta ; in the re- moval of the latter, large quantities of water are elimi- nated, and must be replaced. The evaporation of sweat is a most important means of resisting the effect of a high temperature. QUESTIONS FOR CHAPTER V. During the absorption of carbohydrates, in which set of blood- vessels is the percentage of sugar the highest? How may glycogen be most readily caused to disappear from the muscles ? Would you expect to cause glycosuria by puncturing the med ulla of an animal which had for some time been fed on fat ? Is the appearance of sugar in the urine a necessarily serious symptom ? May it occur in health ? How is the percentage of sugar in the body increased after death ? How may we determine whether a certain substance is formed by a particular organ ? Compare the work done by the liver on a proteid diet witli thai done on a carbohydrate diet. QUESTIONS. 125 1'nder \\liat circumstances would you expect an accumulation of urea in the blood ? 1'nder what circumstances would you expect the urea of the urine to be replaced by ammonium salts? Does sleep cause a variation in the rate of nitrogenous or non- 11 it r< tt'iious metabolism ? Does all the urea which appears in the urine originate from the break-down of tissue proteids? From what nitrogenous substances may urea be formed by the liver? Can a molecule of urea be formed from one molecule of glycocol ? "What are the waste products of muscular metabolism? Which is the more nutritious, soup made by boiling meat or the insoluble residue? "Which is the more palatable? Why? What changes occur in the composition of a calf's urine when it is weaned? Is the formation of fat from sugar a synthetic or an analytic process? Mention instances of synthesis and analysis which occur during metabolism. Wliat different factors prevent an accumulation of sugar in the blood? What is meant by internal secretion ? Distinguish between internal and external secretion. What is the physiologic treatment of myxedema? x Compare the effect of injecting epinephrin into the vessels of two animals, one of which is normal, the spinal cord of the other having In eu previously divided at the level of the seventh cervical nerves. By what operative procedure may we insure the highest blood pressure on the injection of epinephrin? Is the percentage of ammonia in the urine increased by the administration of ammonium carbonate? How may it be increased ? How may muscular exercise be caused to increase the excretion of urea? If an animal receives no nitrogenous food, does nitrogen dis- appear from the urine? 126 METABOLISM AND NUTRITION. What organ receives, in proportion to its size, the smallest arte- rial blood supply? Do all the end-products of hepatic metabolism enter the bile- ducts ? Do the amounts of urea and uric acid in the urine always vary together ? What is the surest means of increasing proteid metabolism? If an animal be kept in a condition of nitrogenous equilibrium, does its weight necessarily remain constant ? Can an animal gain in weight when in a condition of carbon equilibrium ? Is it possible, by giving a large quantity of proteid food, to cause the appearance of proteid in the urine? What is the final effect of an abundant diet containing an in- sufficient amount of proteid? Supposing that an animal is receiving a daily allowance of 200 grams of proteid food, and that it excretes 30 grams of nitrogen, and 60 grams of carbon, what are we to conclude? If an animal, on a diet of 200 grams of proteid, excretes 40 grams of nitrogen, and 120 grams of carbon, what are we to con- clude? Under what circumstances will moderate muscular exercise cause a deficit of nitrogen in the urine? Why does the administration of a mineral acid reduce the pro- portion of nitrogen which is excreted in the form of urea? Under these circumstances, how is this nitrogen excreted ? To what kind of diet is the addition of sodium chlorid of most importance ? During starvation the heart loses but little weight. Is the rate of cardiac metabolism slow as compared with that of skeletal muscle ? In choosing a diet for a child which is deprived of milk, to what inorganic constituent should special attention be paid ? What are the limitations to the use of milk as the sole article of diet? CHAPTER VI. EXCRETION. THE waste products of metabolism, carbon clioxid, water, urea, and other substances in smaller quantities, the water and inorganic salts that are absorbed from the alimentary canal, and other material which, though al>H>rbed, undergoes no chemical change in the body, are all excreted through various channels. Carbon dioxid is, in the main, excreted by the lungs, but is also elim- inated, to a much less extent, in various secretions, such as the sweat, saliva, etc. Only a small proportion of the water which is excreted has originated in the eniirsc of metabolism ; most of it represents that which was taken through the mouth. It is excreted by the glands of the alimentary canal ; most of this, however, is reabsorbed. It is also excreted by the lacrimal lauds, and, in much larger quantities, by thfc respira- tory mucous membranes, sweat glands, and kidneys. Urea is found in traces in the saliva, bile, intestinal juice, and milk, but by far the majority is excreted in the urine. The Urine. The chief constituents of the urine are water, urea, uric acid, hippuric acid, xanthin bases, creat- i u iu, conjugated sulphates, and inorganic salts. The origin of these substances has been already discussed. A 1 >< >ut 30 grams of urea is excreted per diem, the amount varying with proteid metabolism. The amount of uric aeid is also variable, the average being about 0.8 gram ; 127 128 EXCRETION. it depends more upon the quality than the quantity of the food, and probably upon the extent of cell destruction ; it is increased by exercise, and diminished by rest. Free uric acid is not found in fresh urine ; it is excreted in the form of the more soluble urates ; on standing, these may be converted into free acid, which is precipi- tated ; this occurs most readily in acid urine, and is due to the reaction of the urates with the acid phosphates. The xanthin bases include xanthin, hypoxanthin, guanin, adenin, etc.; they are closely related to uric acid, which may be formed from them in the body. About 0.1 gram xanthin bases is excreted per diem. The crea- tinin of the urine is derived chiefly from the creatin of the food, and varies with the amount so taken, the aver- age excretion being about 1 gram per diem. Hippuric acid occurs in the urine to the extent of about 0.7 gram per diem, and varies with the amount of vegetable food eaten. The conjugated sulphates have been mentioned in speaking of proteid putrefaction in the large intes- tine ; conditions which favor the growth and activity of bacteria in the intestines increase the amount of these substances in the urine, while rendering the contents of the intestines antiseptic prevents their appearance. The urinary pigments are derived directly or indirectly from hemoglobin. Not the whole of the inorganic constit- uents of the urine are derived directly from the food ; for instance, sulphuric acid and phosphoric acid are formed in the metabolism of proteids, the sulphates of the urine originating, for the most part, in this way, the phosphates to a less extent. Besides sulphates and phosphates, there are present carbonates and, in larger quantity, chlorids. Sodium, potassium, magnesium, and calcium are present ; the relative quantity of each is indicated by the order in which they are mentioned ; they are, of course, combined as salts. THE SECRETION OF URINE. 129 The acidity of the urine is not due to the presence of five acid, but to the acid phosphates. Both acid and alkaline phosphates are present in the urine, the former predominating. The degree of acidity depends upon several factors ; in the main, it represents the balance l)ct \\een the available bases taken in the food, and the acids produced in metabolism. The secretion of the acid gastric juice usually decreases the acidity of the urine secreted during gastric digestion, but this effect may be neutralized by the secretion of the alkaline saliva, bile and pancreatic juice. Vegetable food contains, in addition to alkalies, salts of organic acids, which, on oxidation, are converted into carbonates, and may be used in neutralizing the acids formed during metabolism ; vegetable food, therefore, reduces the acidity of the urine ; from animal food, on the other hand, the amount of acid formed exceeds the available bases, and the excess is neutralized by the conversion of alkaline into acid phosphates. The specific gravity varies from 1015 to 1025, and depends chiefly upon the amount of liquid absorbed by the alimentary canal, and the amount excreted through other channels. The amount of food consumed will, of course, influence the quantity of solids excreted. In making observations on the specific grav- ity of the urine, it is best to collect and mix the whole amount passed in twenty-four hours, beginning with an empty bladder. The amount varies from 1200 to 1700 c.c. The secretion of urine depends chiefly upon the blood supply of the kidney. The kidney receives this supply, through the short renal artery, from the aorta ; the pres- sure in the first set of capillaries those forming the irlomerulus being, in consequence of this arrangement, high. The pressure in the capillaries of the kidney varies, of course, with the strength and rate of the heart- 9 130 EXCRETION. beat; it also varies with the condition of the arterioles in other parts of the body, and, in addition, with the state of its own arterioles. The kidney will receive the most abundant supply of blood when the heart-beat is strong, the vessels of other parts constricted, and the local arterioles dilated. Under these circumstances the amount of urine secreted will be abundant. In cold weather the cutaneous vessels are constricted and more blood flows through the abdominal organs, including the kidney ; in cold weather, therefore, more urine will be secreted than when it is warm, for in the latter condi- tion the kidney receives less blood, the skin more, and the blood is concentrated by the free secretion of sweat. The kidney vessels are controlled by the central ner- vous system, through both vasoconstrictor and vaso= dilator nerves which leave the spinal cord in the lower thoracic nerves, enter the sympathetic, and pass through the splanchnic to the solar ganglia, where they probably .end in contact with cells whose nonmedullated axons (post-ganglionic fibers) pass along the renal artery to the kidney. A division of these nerves results in a dilatation of the renal arterioles and an increased flow of urine ; their stimulation ordinarily causes vasocon- striction and lessened secretion, but if stimulated with slowly repeated induction shocks, the action of the vaso- dilators is called into play. A division of the spinal cord in the upper thoracic region or division of both splanchnics leads to the dilatation of so many vessels that the general blood pressure is reduced to a point at which the dilatation of the kidney arterioles cannot result in an increased flow of blood through the kidney. The existence of a double set of capillaries in the kid- ney offers an unusually high resistance, and, to over- come this, a comparatively high blood pressure is necessary. THE SECRETION OF URINE. 131 We not consist only in that offered by the membrane to the passage of water and salts, for the proteids, owing to the osmotic pressure which they exert, tend to retain water and to prevent its escape from the serum. The proteids of plasma exert an osmotic pressure of from 25 to ;}() mm. of mercury ; this, then, must be added to the r< >i stance which is offered by the membrane to filtration of water and salts. Thus, to cause filtration a some- what greater force is needed, and it has been found that the secretion of urine ceases when the blood pressure falls below 40 mm. of mercury ; it also ceases when the pressure in the capsule has been raised to within 40 or 50 mm. Hg of that in the capillaries. The urine as it leaves the kidney is a very different liquid from any that could result from the mere filtra- tion of blood plasma ; if, then, filtration goes on into 132 EXCRETION the capsule, this filtrate must be greatly modified as it passes through the tubule toward the pelvis of the kid- ney. This undoubtedly takes place, for the more rap- idly the urine passes through the tubules, the less it is modified, and the more it resembles the plasma in com- position and reaction. When it traverses the tubules more slowly, time is given for its concentration, appar- ently by the absorption of water. If water is absorbed from the glomerular filtrate by the cells which line the tubule, they perform an immense quantity of work, for the osmotic pressure of the urine is much greater than that of the blood plasma. In one case the osmotic pressure of the urine of a cat which had been deprived of water was greater than that of its blood plasma by 498 meters of water ; and the tubule cells, in transfer- ring water from urine of this density to the blood plasma, must have exerted a tremendous force. The cells of which the convoluted tubules are formed are much more highly developed than those which line the capsule, and we may expect them to be more specialized in function. It seems probable that uric acid is excreted in this portion of the tubule ; experiment has proved that such is the case in birds. With regard to the ex- cretion of the more soluble urea, we have no knowledge as to whether it occurs in the capsule or tubules ; we might expect that it would accompany the inorganic salts and water through the wall of the capsule. The urine as it leaves the capsule is alkaline in reaction, re- sembling the plasma in this respect ; on its passage through the tubules it becomes acid, either through the addition of acid phosphates or the removal of alkalies. Temporary ligation of the renal artery prevents the secretion of urine not only during the period of occlu- sion, but for some little time after the circulation is re- established. Some take this as proof that filtration is THE SECRETION OF URINE. 133 not answerable for the glomerular secretion. It is easy to see how this might incapacitate the tubule cells for the performance of work, but why it should put a stop to filtration is obscure; the glomerular epithelium is in some way rendered less permeable. That the epithelium of some part of the mechanism is injured, is evidenced by the appearance of albumin in the urine that is subse- quently first secreted. Diuretics are substances which increase the flow of urine ; one class, known as saline diuretics, do this by bringing about hydremic plethora, and by causing a dilatation of the renal arterioles. Amongst the saline diuretics are sodium chlorid, urea, dextrose, sodium ace- tate, and many others. On injecting any of these into the blood, the first effect is a rise in the osmotic pressure of the plasma, the rise being proportionate to the result- ing increase in molecular concentration. This increase of osmotic pressure causes the absorption of water from the lymph-spaces, and the blood will be diluted ; we shall have a condition of hydremic plethora. The bulk of the blood being thus increased, the pressure within the vessels is raised, consequently the filtration of urine will be hastened. Even when the condition of plethora has disappeared diuresis may continue, for tKe renal arte- rioles remain dilated for some time. That the saline diuretics do not act through stimulation of the epithe- lium is proved by the fact that they produce no diuresis if, on their administration, an increased blood supply to the kidney is prevented. The dilatation of the renal arterioles is caused by a direct action of these diuretics either on the walls of the vessels or on the peripheral nervous mechanism. The existence of secretory nerve- fibers for the kidney has not been proved. The urine is carried from the kidney to the bladder through the ureter, its passage being aided by rhythmic 134 EXCRETION. contractions which sweep down the ureter every twenty seconds or so. These appear to be of muscular origin, since they may continue, after isolation, in the portions of the ureter which contain no nerve-cells. The ureter, on reaching the bladder, runs for a short distance obliquely through the bladder-wall ; a valve is thus formed which prevents the backflow of urine from the bladder into the ureter, for a rise of pressure in the former will compress this portion of the latter. Micturition. When the bladder contains no urine, its muscular walls are in a state of slight tonic contrac- tion ; as urine enters, the muscles relax slightly, and, provided the urine is not introduced too rapidly, allow an accumulation of about 250 c.c. ; when this point has been reached, rhythmic contractions appear and increase in force as distention goes on. The exit of the urine into the urethra is prevented by the elasticity of the neck of the bladder and of the surrounding parts, and, almost surely, by a reflex tonic contraction of the cir- cular coat of muscle at this point. As the bladder fills a desire to urinate is felt. The emptying of the bladder may perhaps be instituted by a voluntary inhibition of the center which exerts a tonic control over the circular layer of muscle surrounding the neck of the bladder ; at the same time, a voluntary contraction of the abdo- minal muscles raises the intravesical pressure, and assists in the expulsion of the urine. The chief factor in expelling the urine is, however, the reflex contraction of the muscular wall of the bladder itself. The exit of urine may be prevented or retarded by a voluntary contraction of the perineal muscles. After division of the spinal cord in the thoracic region, micturition may be carried on reflexly by centers situated in the lumbar cord. The bladder is innervated through two sets of nerves ; one set, leaving the lumbar SECRETION OF SWEAT. 135 region, enters the sympathetic, and, reaching the in- ferior mesenteric ganglia, is here connected with gan- glion cells from which originate post-ganglion ic fibers; these are distributed to the bladder through the hypo- irnstric nerve and plexus. Stimulation of these nerves excites weak contractions of the bladder- wall, but M.metimes the result is an inhibition of these muscles. The other set of fibers leaves the cord in the sacral nerves, and, without entering the sympathetic, reaches the hyj>ogastric plexus through the nervi erigentes. These fibers end in small ganglia, situated in or near the bladder-wall^ where they come into contact relations with the cells whose axons form the post-ganglion ic link in this chain. These nerves, when stimulated, cause strong contractions of the bladder and expulsion of the urine. If the lumbar region of the spinal cord is destroyed, all nervous control over the bladder is lost, but, in the dog, the bladder empties itself at irregu- lar intervals, a stimulus being afforded to the muscle by the stretching which results from distention ; in man, the urine accumulates in the bladder to a certain extent, and, after this, as the urine enters from the ureters, the excess drains off through the urethra. Secretion of Sweat. The sweat is a' watery fluid containing but a small percentage of solid matter. Sodium chlorid forms the chief solid constituent ; there are also present other salts, fatty acids, and traces of urea. The sweat is ordinarily acid in reaction ; but if abundant, is neutral or alkaline. In uremia the amount of urea is sometimes much increased. The amount of sweat secreted naturally varies considerably, being much greater in warm than in cold weather. Ordinarily, the sweat evaporates as fast as it reaches the surface ; this is called invisible or insensible perspiration. The amount of insensible perspiration depends upon the 136 EXCRETION. condition of the surrounding atmosphere ; if the air be moist, less of the sweat will evaporate and the skin will be visibly damp ; if the air be dry and warm, evaporation will go on more rapidly and the skin may appear dry, though the secretion may in reality be more abundant. When the skin is flushed, the secre- tion of sweat is usually, but not necessarily, increased. An abundant supply of blood to the sweat glands favors, but does not provoke, their activity, which is controlled by definite secretory nerves. These nerve-fibers leave the thoracic and upper lumbar regions of the spinal cord, and end in the ganglia of the lateral sympathetic chain ; the post-ganglionic fibers, which arise from cells in these ganglia, pass through the gray rami to the various spinal nerve-trunks, and are distributed, through the cutaneous branches of these, to the sweat glands. The course is similar to that followed by the vasocon- strictors. The pre-ganglionic sweat nerves for the skin of the face and head end in the superior cervical sympathetic ganglion. It is not known whether there exists in the medulla a chief sweat center to which the spinal sweat centers are subordinate. As is well known, sweat may be secreted as a result of the emotions ; in such cases the spinal centers are stimulated by invol- untary nerve impulses descending from the brain ; they cannot be voluntarily controlled. The secretion of sweat is ordinarily a reflex event arising from the stimulation of afferent cutaneous nerves, as by the application of heat. That it is not a result of the direct stimulation of the glands by heat is shown by the fact that exposure to heat, after the division of the nerves of a part, does not cause sweating of the paralyzed area. At the same time, the impossibility of provoking the secretion by increasing the blood supply is demon- strated, for, owing to the division of the vasoconstrictors, THE SECRETION OF MILK. 137 the skin will be flashed, yet it will remain dry. On the other hand, stimulation of the peripheral end of the divided nerve, although it will bring about a paling of the skin, through the stimulation of the vasoconstrictors, will cause sweating of the part by exciting the sweat nerves. The result of stimulating the renal nerves has an entirely different effect on the secretion of urine. The sweat centers may be directly stimulated by a rise in the temperature of the blood, or by venous blood. Atropin prevents the secretion of sweat by paralyzing the terminations of the secretory nerves ; pilocarpin causes sweating by stimulating either the terminations of these nerves or the gland cells them- selves ; it possibly acts in both ways. Strychnin causes secretion by its action on the spinal cord ; nicotin acts chiefly on the centers, but to a certain extent on the peripheral mechanism. The sebaceous glands of the skin have not been shown to be controlled through the nerves. The sebum excreted by these glands consists of the debris which results from the degeneration of the epithelial cells of the glands themselves. It is an oily liquid made up of fats, fatty acids, cholesterin, proteid, , salts, and water. The ill effects of coating the skin with varnish are not due to interference with excretion through the cuta- neous glands, but to the resulting dilatation of the cuta- neous vessels and consequent loss of heat. The Secretion of Milk. Unlike the sebaceous and sweat glands, to which it is nearly related, the mam- mary gland is only occasionally active ; in the male, with very infrequent exceptions, never. That the activity of this gland may, to a certain extent, be in- fluenced by the nervous system is proved by the fre- quent instances of the cessation or modification of lae- 138 EXCRETION. tation as a result of emotions or nervous disorder. There is, however, little or no experimental evidence from which we can gain an insight into the mechanism. Milk consists chiefly of water, holding in solution pro- teids, carbohydrates, and inorganic salts ; and in sus- pension, globules of fat. The chief proteid, or nucleo- albumin, is caseinogen ; in addition, there are smaller quantities of albumin and globulin. Lactose is the chief carbohydrate, and occurs in larger amount than the caseinogen. The fat consists of stearin, palmitin, olein, and smaller quantities of other fats. The inor- ganic constituents, with the exception of iron, closely correspond, in the proportion which they bear to one another, to those of the new-born animal. The average proportions of the constituents of nor- mal human milk and cows' milk are as follows : HUMAN. Cows'. Fat 4. % 4. % Sugar 7. % 4.5 % Proteids .... 1.5^ 3.5 % Salts 0.2^ 0.75% Water 87. 3 # 87.25^ Before lactation begins the alveoli of the gland en- large, the epithelium thickens, and the cells multiply. There appear within the cells, more particularly near their free border, granules and fat droplets which are extruded into the alveoli. At the beginning of lacta- tion for a day or two the secretion varies from that which follows, in having numerous degenerated cells, a lower percentage of fat and sugar, and almost four times as much proteid. The effect of this early secre- tion, which is called colostrum, is to cause a free evacuation of the bowels of the nursing child. Colos- trum is lacking in caseinogen, in spite of its high pro- teid percentage. The normal physiological stimulus to the activity of QUESTIONS. 139 the n-land cells is (he emptying of the ducts, and al- though iij) to a certain point the secretion is continuous without external stimulus, when the alveoli and ducts arc distended secretion is inhibited reflex ly or directly liv the high pressure in the ducts, to be resumed, and at a very rapid rate, when the child nurses. The ac- tivity of the gland varies with the physical stimulus of the sucking child. The amount varies under normal conditions from 10 to 1(5 ounces a day in the first week of lactation, to 30 to 40 ounces a day in the ninth month of lactation. In an average nursing period of ten to twenty min- utes, the amount obtained from a single breast varies from about one ounce in the first week to six ounces in the sixth week and later. Lactation usually ceases promptly when nursing is discontinued, but the appli- cation of pressure and cold, and the use of atropin and saline cathartics hasten the cessation of the glandu- lar activity, and the process of involution in the gland. The proteids of the diet if in excess increase the pro- teid caseinogen of the milk, also the fat and possibly the sugar. Lack of exercise will have the same effect as excessive proteid diet. The percentage />f fats, car- bohydrates, and proteids in the milk can be easily diminished by a free fluid diet. QUESTIONS FOR CHAPTER VI. What are the most prominent differences between the composi- tion of the blood plasma and that of the urine? What readily diffusible sul>stance is found in the blood, but not in the urine? What nondiffusible substance, when it is introduced into the blood, appears in the urine? Carefully compare the effect of dividing the renal nerves, with that of stimulating them, (a) in regard to the renal blood supply, and (6) with respect to the secretion of urine? 140 EXCRETION. Make a similar comparison of the effects of dividing and stimu- lating the sciatic nerve on the blood supply and activity of the sweat glands of the leg ? Compare the nature of the control exercised by the nervous sys- tem, on the one hand, over the secretion of urine, on the other, over the secretion of sweat ? Under what circumstances may the quantity of urine in health fall considerably below the average ? What effect have the seasons on the specific gravity of the urine ? How do you collect twenty-four hours' urine ? Why does the injection of a large quantity of normal saline so- lution into the vessels cause diuresis ? Supposing that the sodium chlorid of the plasma were incapable of passing from the glomerulus into the capsule, would the blood pressure required for the filtration of water be greater or less than the normal ? How do you account for the fact that the urine is, in respect to inorganic constituents, more concentrated than the plasma ? Would you expect the reaction of the urine to vary with its specific gravity ? Why ? What effect has the administration of alkalies on the relations existing between different nitrogenous compounds of the urine ? What is the simplest method of producing diuresis ? Which of the normal constituents of the blood plasma, when present in excess, cause diuresis ? How would the secretion of urine be affected by increasing the percentage of proteids in the blood plasma ? How may the reaction of the urine be caused to resemble that of the blood ? How does starvation modify the urine of the herbivora ? What relation exists between the amount of blood supplied to the kidney and the reaction of the urine ? How may we determine whether a drug which exerts an influ- ence over the secretion of sweat acts upon the sweat centers or on the peripheral mechanism ? How may we determine whether, on application of heat to the skin, the sweat glands are stimulated directly or reflexly ? What are the reasons for the intermittent function of the mam- mary glands? Describe the normal course of lactation. CHAPTER VII. ANIMAL HEAT. THE temperature of the body depends upon the liber- ation, in the form of heat, of the potential energy in- troduced in food. This is set free, not only from the food that has been absorbed and assimilated, but to a l-ss extent from the food as it undergoes digestion in the alimentary canal. The larger proportion of heat is produced in the muscles, the process being under the control of the central nervous system. Next to the muscles in heat production come the glands, more especially the liver. In order that the temperature may remain constant, as it does within very narrow limits, exactly the same amount of heat must be liberated within the body as is given off from the surface and lost in the excreta. If the production of heat fails to keep pace with the loss, the temperature sinks ; if the pro- duction of heat is more rapid than the loss, the tempera- turc goes up. Both production and loss are very vari- al>le, but in the normal condition the one keeps pace with the other. In fever, if the temperature remains constant, the same is true ; but in this case the adjust- ment fails during the rise of temperature. If a cold-blooded, or poikilothermic, animal is ex- posed to cold, its temperature sinks to that of its sur- roundings ; on exposure to heat its temperature rises. Wurm-blooded, or homoiothermic, animals behave quite otherwise ; for instance, a dog was placed in a chamber 141 142 ANIMAL HEAT. the temperature of which was 91 C. ( 130 F.) ; the first effect was a slight rise in the dog's tempera- ture. The metabolism of the muscles is governed by the central nervous system, and the cells of the nervous system are subjected to afferent impulses coming from the periphery ; for instance, from the skin. If cold be applied to the skin, it stimulates certain afferent nerves, which in turn transmit impulses to the central nervous ; system, and cause the dispatch of efferent nerve im- pulses which hasten the chemical changes within the muscles ; more material is oxidized within the muscle, and more heat is produced. If the cold be at all in- tense, the increased metabolism of the muscle will find visible expression in shivering, which consists of weak incoordinated contractions. The value of shivering is apparent. At the same time there occurs a reflex con- striction of the cutaneous arterioles, brought about by the stimulation of the vasoconstrictor center through the afferent nerves of the skin. In consequence of this con- striction, less blood will flow through the superficial vessels, and the loss of heat will be much less than it would be were more blood brought near the surface. The animal will feel cold, owing to the cooling of the surface and peripheral terminations of the sensory nerves, which carry impulses toward the brain, but its temper- ature may, in reality, be a little higher than usual. Amongst the afferent nerves of the skin are two sets of fibers whose peripheral terminations are so specialized that they are stimulated by slight changes of tempera- ture. One set is stimulated by cooling, and transmits impulses which, on reaching the brain, give rise to a sen- sation of cold ; they are unaffected by warmth. The other set is stimulated by a rise of temperature, the re- suiting sensation being one of heat. Whether the reflex THEKMOGENIC CENTERS. 1 I:: effects of changes of temperature are produced through the-e nerves is uncertain, but highly probable. The metabolism of the muscles is controlled by nerve- cells H mated in the spinal cord, and these have been called thermogenic centers; there is no reason to sup- pose that these cells are other than the ordinary motor nerve cells which govern the contraction of the muscles. They do not appear, in the absence of higher centers, to afford a mechanism which, on exposure to cold, suffices for the regulation of the temperature, through increased production of heat; for the animal whose spinal cord IIMS been divided in the cervical region behaves as a cold-blooded animal ; its metabolism is depressed by ex- po i ire to cold, increased by exposure to heat. The activity of the thermogenic centers of the cord appeal's to be regulated by centers situated in some higher portion of the central nervous system, these latter centers being influenced by the afferent impulses which are inaugurated by changes in the temperature of the surroundings. A warm-blooded animal may be exposed to great heat and yet maintain a constant body-temperature. This is due, not so much to a lessened production of heat, as to an increased loss of heat from the surface. The application of warmth to the skin brings about a reflex dilatation of the cutaneous vessels ; the skin flushes, more blood being brought near to the surface. If, however, the temperature of the surrounding atmosphere be much greater than that of the body, the effect of this event, taken by itself, would be a rise of body-temperature, for heat would be transmitted from the air to the blood. This, in the normal condition, does not happen, unless the heat be intense or the exposure l>e prolonged. We have already seen that the application of heat to the skin causes a reflex secretion of sweat ; in the evapo- 144 ANIMAL HEAT. ration of this sweat, a large quantity of heat is absorbed from the blood and carried off, as latent heat, in the re- sulting watery vapor. This is the most potent factor in preventing a rise of body-temperature on exposure to a warm atmosphere. It will be readily understood that the cooling of the skin in this way will be materially in- fluenced by the state of the surrounding air. If the air be dry, evaporation will be favored ; if moist, retarded. The effect of a hot bath is to raise the temperature of the body, for water is a much better conductor than air, and if warmer than the blood, will rapidly give up heat to the latter ; at the same time, evaporation from the ' immersed skin will be prevented. A bath in water at 45 C. would soon prove fatal, w r hile exposure to dry air at 125 C. might be borne with impunity for the same length of time. The first effect of a warm bath is a slight rise of body-temperature ; after the bath is over there is a slight fall, but a return to normal soon follows. Although a cold bath abstracts much heat from the body, the metabolism is so stirred up that the first effect may be a slight rise of body-temperature ; if the bath be prolonged, a slight fall may result, but on leaving the water the temperature rises a little above normal. An animal which possesses much subcutaneous fat is better protected from a loss of heat than one that is lean. The involuntary regulation of the body-temperature may be voluntarily assisted by the donning or doffing of clothing, and by taking or abstaining from exercise. The average axillary temperature is about 37.1(98.8 a F.). Small daily variations occur, the temperature being ' lowest between midnight and early morning, highest in the late afternoon ; the effect of a meal is to slightly raise the temperature. If a warm-blooded animal is exposed to such intense cold that the height- ened metabolism cannot keep pace with the great loss QUESTIONS. 145 from the surface, the temperature, after the preliminary rise, gradually sinks ; unconsciousness supervenes, and is followed by death. The hibernating animals with- stand the fall of body-temperature, which may go almost as far as C., without ill effects. Metabolism pru- < < < ds at a minimal rate ; the heart-beat is weak and in- fre<|iient; respiration is depressed and irregular, and the respiratory exchange almost ceases. The respiratory <|iii>tient sinks, for oxygen may be stored in the body; the animal may, in this way, gain slightly in weight, ('old-blooded animals may be frozen solid, and by gradual thawing be resuscitated; a snail has been re- < lured to a temperature of 1 20 C. without succumbing. In this case metabolism, of course, ceases; life becomes latent. Changes of temperature affect proteid metabolism verv little ; the increased production of heat which c -n. -nes on exposure to cold is accomplished at the ex- pense of the non nitrogenous foods. A warm-blooded animal poisoned with curari reacts to changes of temperature as though it were cold blooded. Curari paralyzes the terminations of the motor nerve-fibers, and thus deprives the Central nerv- ous system of its control over the chief thermogenic tissue of the body. QUESTIONS FOR CHAPTER VII. If heat is being continually produced within the body, why does not the temperature of the body continually rise? What nervous centers are concerned in regulating the loss of heat? Does the activity of these centers usually vary in the same direc- tion? In what respects is the regulation of body-temperature affected by a division of the afferent cutaneous nerves ? 10 146 ANIMAL HEAT. After this operation, will an animal better withstand exposure to heat or cold ? Compare the effect on the regulation of body-temperature which results from division of the ventral spinal nerve-roots with that which follows division of the sympathetic rami communicantes. In the former case, what reflex which normally follows exposure to cold will be prevented, while in the latter case it persists ? What cold and heat reflexes will be rendered impossible in each case ? In very hot weather, will the administration of atropin tend to raise or lower the body-temperature ? Can we by means of the clinical thermometer determine the rate of heat production or heat loss ? Under what circumstances may the temperature of the body rise, while the production of heat remains constant ? Does a fall of body-temperature always depend on lessened heat production ? The sensation of warmth which on a cold day results from drink- ing alcohol is due to the warming of the skin by an increase in the cutaneous circulation, the activity of the constrictor center being depressed by the alcohol. What is the effect on the temperature of the body as a whole ? CHAPTER VIII. MUSCLE AND NERVE. THE physiology of muscle and nerve is best and most profitably studied in the laboratory ; only a mere outline of the subject need be given here. The general properties of skeletal, cardiac, and plain muscle are the same, but display minor differences. Skeletal muscles may be controlled by the will, but are also subject to reflex influences. The contraction of cardiac muscle is independent of, but regulated by, the nervous system. Plain muscle, with the exception of the ciliary muscle, is beyond the control of the will ; its contraction is ordinarily reflex, but if it be deprived of nervous influence, it may develop an independent tone. The ease with which chemical changes may be set going within normal muscle renders it irritable ; that is, it is capable of responding to a stimulus. Cardiac muscle is more irritable than plain muscle; plain muscle than skel- etal. Muscle responds to mechanical, thermal, chemical, and electrical stimuli, and to the normal nerve impulse the nature of which has not been determined. In order that the application of a force may act as a stimulus it must be of sufficient intensity and duration, and must not be too gradual. On the application of a stimulus, a mus- cle shortens and thickens without changing its bulk ; this is called contraction. That muscle is directly irri- table may be shown by paralyzing the terminations of 147 148 MUSCLE AND NERVE. its motor nerve with curari ; in this condition it is still responsive to a stimulus. Muscle is 'extensible, but does not stretch in propor- tion to the force applied; as the elongation is increased, the extensibility becomes less and less. On cessation of stretching, or other distortion, muscle, by virtue of its elasticity, resumes its normal shape. When a muscle is stimulated it contracts, but there is a momentary delay in the appearance of the mechan- ical change ; this is known as the latent period of mus- cle. When the stimulation is direct, the latent period amounts to about 0.004 second ; if the muscle be indi- rectly stimulated, by applying the excitant to its nerve, the latent period is prolonged to about 0.007 second, the extra delay being due to the motor end-plate ; in addition to this, the time which elapses between the stimulation of a nerve and the beginning of the mechan- ical response of the muscle will be influenced by the length of nerve over which the nerve impulse has to travel. The average rate of transmission of the nerve impulse is about 50 meters per second. The contrac- tion produced by a single induction shock lasts about 0.1 second, but varies with the resistance offered and with the condition of the muscle. The contraction of plain muscle is very much more prolonged. The con- traction of muscle may be divided into the period of shortening and the period of relaxation, the former being of somewhat less duration than the latter. The con- traction of a muscle-fiber is not confined to the point stimulated, but sweeps over the whole fiber, as a wave, with a velocity of, in human muscle, about 10 meters per second. The extent of shortening varies with the condition of the muscle, the strength of stimulus, the weight lifted, FATIGUE. 149 the way in which the weight is applied, etc. Other conditions remaining the same, the degree of shortening is less in a fatigued than in a fresh muscle ; the short- ening occurs rather more slowly ; the relaxation is very much prolonged. Fatigue depends on several factors ; it is due in part to the consumption of the store of energy-containing material, in part to the accumulation of waste products. The motor nerve-ending is more sensitive to fatigue than the muscle itself. The cells of the central nervous system concerned in producing muscular contraction are also subject to fatigue. Con- traction is much prolonged by veratrin and by adrenal extract. If, beginning with a current too weak to pro- voke contraction, successive single induction shocks of gradually increasing strength be passed through a mus- cle, a point will be reached where a just visible contrac- tion results ; this is known as a minimal stimulus. On further increasing the strength of stimulus, the extent of shortening will go on increasing up to a certain j)oint, when the maximal contraction of which the muscle is capable will have been reached. Further increase of stimulus will not increase the extent of shortening. If, however, the muscle be stimulated at short intervals, with a stimulus that is just sufficient to cause a maxi- mal contraction when the muscle is fresh, until it shows signs of fatigue, a further increase in the strength of the stimulus may now provoke a contraction equal to that of the fresh muscle. Cardiac muscle responds to even a minimal stimulus with a maximal contraction. If a muscle be caused to lift a load, any addition of weight will reduce the height to which the load is lifted, though it does not necessarily diminish the amount of work done. The work accomplished is the product of 150 MUSCLE AND NERVE. the load by the height to which it is raised. If the muscle contracts without lifting a load, no external work is done ; the energy resulting from the chemical change, upon which contraction depends, is all liberated as heat. If so great a resistance is opposed to the active muscle that it cannot shorten, no work is done, the energy set free all appearing in the form of heat. When the muscle is working to best advantage, not more than one-fourth of the energy set free is converted into work, and it is quite possible that even this one-fourth is first set free as heat which, by causing the anisotropic fibrillse to absorb water, brings about their shortening. The efficiency of all three kinds of muscle is greatest when they contract against a certain amount of resistance. The term isometric contraction is applied to a muscle contraction made when the muscle is so fixed at both ends that it cannot shorten during contraction. The term isotonic contraction is applied to a muscle contraction made under such conditions that the tension of the muscle remains constant throughout the contrac- tion. So far we have considered only the single contraction, or twitch, of muscle. In the body it is comparatively seldom that a muscle contracts for so short a period as 0.1 second ; usually the contraction is more prolonged, and probably consists in the fusion of a number of sin- gle contractions, which are provoked by successive stim- uli following each other so rapidly that time is not allowed for relaxation. If the voluntary contraction of muscle be graphically recorded, the tracing shows a slight rhythmic oscillation at the rate of about 10 to 12 per second, which appears to depend on the dispatch, by motor nerve-cells of the cord, of successive nerve im- pulses following each other at this rate. A similar form of contraction may be caused by artificial stimula- tion of muscle with rapidly repeated induction shocks. IRRITABILITY. 151 When the stimuli arc so rapidly repeated that a graphic record shows no undulations, the contraction is spoken of as complete tetanus ; if time is allowed for a partial relaxation between contractions, it is an incomplete tetanus. The breaking induction shock, when a submaximal stimulus is used, is more effective than the making shock; this depends on the induction apparatus. When the voltaic, constant, or battery current is used, closing the circuit (or making the current) is more effective than opening the circuit (or breaking the current). This de- I tends upon changes in the irritability of the muscle, or nerve, as the case may be, produced by the passage of the current. The irritability of the muscle or nerve is raised at, and in the neighborhood of, the negative elec- trode, or kathode ; it is lowered at the anode and in its neighborhood. It is supposed that a sudden rise of irri- ta I lility serves as a stimulus. When the current is made, the irritability of the muscle is suddenly raised in the neighborhood of the kathode, the muscle is stimulated at this point, and a contraction instituted which travels along the muscle; the anodal end remains relaxed until this wave of contraction reaches it. The "muscle as a whole then relaxes, though the kathodal end maintains a slight degree of shortening. This continues as long as the current flows evenly ; when it is broken, the irri- tability of the anodal end, which had been depressed below the normal, suddenly rises to normal or a little above it, and, if the current be of sufficient intensity, a contraction will originate at this point. If the current be weak, no contraction will result, for the anodal stim- ulus is not so effective as the kathodal. The relative efficiency of kathodal and anodal stimuli may bear some relation to the fact that, in the case of the former, the rise of irritability is from normal upward, while, in that of the latter, it is a return to normal from a point Mow 152 MUSCLE AND NERVE. it. If the current does not flow evenly, but rises or falls in intensity, there are corresponding changes of irritability in the muscle, and these may act as stimuli. If a nerve which is connected with a muscle is stim- ulated by a constant current, the contraction of the muscle will depend upon the direction in which the current flows, and upon its intensity. What happens is shown in the following table, which illustrates the so-called law of contraction. If, when a current is passed through a nerve, the anode is nearest the muscle, it is called an ascending current ; if the kathode is next the muscle, a descending current. PFLUGER'S LAW. CUKEENT : Weak ASCENDING DESCENDING make C C break C C make C C C break C Medium Strong The results of stimulation with weak and medium intensity of current may be understood from what has already been said, but, in the case of strong stimulation, further explanation is needed. The passage of a con- stant current not only modifies the irritability of a nerve, it also changes its conductivity, or power of transmitting the nerve impulse. With weak and me-_ dium currents, the change in conductivity is not suffi- cient to modify the result ; but with strong currents, the eifect is pronounced. While a strong current flows through the nerve, the conductivity is reduced, not only in the area between the electrodes, but for a short dis- tance on either side of them, and just after the current ceases to flow the anodal end fails to transmit the im- CONDUCTIVITY. 153 pulse, With a strong ascending or descending current tin- nerve is stimulated on making the current at the kathode; on breaking, at the anode. With an ascend- ing current, however, while the impulse starting at the anode easily reaches the muscle, the impulse which re- sults from making the current, and starts from the kathode, is by the lessened conductivity prevented from passing along the nerve, and no contraction ensues. ( )n the other hand, with a descending current we get a making contraction, for the impulse starts from the kathode which is near the muscle, while the impulse provoked by the anodal stimulus fails to traverse the anodal area of depressed conductivity, and we get no breaking contraction. The condition induced in a nerve by the passage of a constant current is known as elec- trotonus ; that at the anodal end, anelectrotonus ; at the kathodal end, katelectrotonus. In order to stimulate a nerve in the intact body, one electrode is usually placed over the course of the nerve, the other on some indiffer- ent part of the body, at, perhaps, some distance from the first. Under these circumstances, we cannot expect to obtain a demonstration of the law of contraction just described, for the current, instead of being confined to the nerve, will pass obliquely through it : if the anode be over the nerve, in a sheaf of diverging lines ; if the kathode be over the nerve, in converging lines. In the former case the anelectrotonic area will be narrower than the katelectrotonic area ; in the latter case the con- ditions will be reversed. Where the lines of force are the more concentrated, the current will be denser and its effects more pronounced. With a weak current, therefore, a contraction of the muscle (which is inner- vated by this nerve) will be most readily excited by the stronger of the two forms of stimulus, the making, when the area of katelectrotonus is concentrated by placing the kathode over the nerve. With an intensity 154 MUSCLE AND NERVE. of current only just sufficient to give this result, no contraction can be obtained on breaking the current if the kathode is over the nerve ; no contraction occurs at the make or break when the anode is over the nerve. If we now increase the strength of the current little by little, and use first one electrode and then the other with each rise in intensity, we shall reach a point at which, in addition to the result already obtained, we get making and breaking contractions when the anode is over the nerve. Of these, only the breaking con- traction results from true anodal stimulation ; the mak- ing contraction results from stimulation of the nerve in the katelectrotonic area. The katelectro tonic area is more diffuse than the anelectrotonic when the anode is over the nerve, but the greater efficiency of the katho- dal stimulus equalizes the effects of the make and break. The strength of the current must be still fur- ther increased before we can obtain a breaking con- traction with the kathode over the nerve, for with this arrangement the area of anelectrotonus is more diffuse, j The results thus obtained will have appeared as fol- lows : LAW OF UNIPOLAR STIMULATION. CURRENT. ELECTRODE OVER NERVE. CONTRACTION ON : ABBREVIATION. Minimal .... kathode closing circuit KCC. Medium kathode anode closing circuit closing circuit KCC. ACC anode opening circuit AOC. Strong ..... kathode anode closing circuit closing circuit KCC. ACC. anode kathode opening circuit opening circuit AOC. KOC. The formula for this normal sequence of reactions is CONDUCTIVITY. 155 usually written thus, KCC, ACC, AOC, KOC, and indicates the order in which these events occur with increasing strength of current. KCC means kathodal closing contraction; AOC, anodal opening contraction, etc., closing the circuit being synonymous with making the current ; opening the circuit, with breaking the current. When the nerves of a muscle are degenerat- ing, the reaction, for some reason, varies from the normal, the anodal closing contraction being obtained with a weaker current than the kathodal closing con- traction ; this is known as the reaction of degeneration, and affords a means of diagnosis. Another important means of determining the condition of a muscle de- pends upon the fact that after the degeneration of its nerves, a muscle no longer responds to the induced current, while its irritability to the constant current rises above the normal. Its irritability should be compared with that of the corresponding muscle on the opposite side of the body. If the nerve fails to regen- erate, the muscle, in time, undergoes complete atrophy. When a muscle or nerve is injured at a certain point, the electric potential at this point is lo>vered ; the injured portion becomes negative as compared with the uninjured portion. If the injured and uninjured parts be connected by means of a conductor, a wire, for example, a current will flow through the conductor IVmii the uninjured, or positive, to the injured, or negative, pole of the muscle. This is called the cur- rent of rest, or demarcation current. When a nerve has been divided and is dropped back into the wound, the surrounding lymph may serve to connect the in- jured with the uninjured portion of the nerve, a cur- rent will l)e set up, and the nerve may l>e stimulated ; this must be taken into account in experimenting upon divided nerves. Not only is an injured part of nerve or muscle elec- 156 MUSCLE AND NERVE. trically negative to uninjured parts, but active parts are negative as compared with resting parts ; consequently when an uninjured portion of muscle or nerve becomes active, the difference of potential between this point and an injured point will be lessened, and, if the two points are connected by a conductor, the demarcation current will be, for the moment, weakened; this weak- ening of the demarcation current is called the negative variation. Every nerve-fiber is an outgrowth from, or a process of, a nerve-cell. A nerve-cell usually has several pro- cesses ; one, the axis-cylinder process, or axon, becomes a nerve-fiber ; the others branch freely and are usually very much shorter than the axon ; they are called den= drites, or protoplasmic processes. A nerve-cell with its processes constitutes a neurone. Each process is dependent for its existence upon connection with the parent nerve-cell ; if a nerve-fiber be divided, the por- tion that is cut off from the cell invariably dies ; re- generation can only occur through the growth of that portion of the axon which remains in connection with the nerve-cell. Division of the axon produces secon- dary effects on the cell itself; the cell-body shows signs of degeneration which, if regeneration of the axon does not occur, usually becomes complete. If conditions are favorable to regeneration and the axon grows out to, and makes physiologic connection with, the muscle, the cell recovers. The nerve-cells of the posterior spinal root ganglia are originally bipolar ; they give off but two processes. Later, these two processes unite for a short distance, rendering the cell-body unipolar. Each process be- comes a medullated nerve-fiber ; one, distributed to peripheral structures, functions as a dendrite ; the other enters the spinal cord and is undoubtedly an axon. These cells suffer less from a division of their processes CONDUCTIVITY. 157 than is tin rase with the cells of the spinal cord which uive oil' eil'erent fibers. Xcrve-cells dispatch impulses through their axons ; they are excited by stimulation of their dend rites. A nerve-fiber, if stimulated midway in its course, trans- mits impulses in both directions, but a visible result occurs at one end only. In the case of an efferent nerve-fiber, a motor fiber, for example, the only appreciable result is muscular contraction (except that, by means of a galvanometer, an action current may be slmwn to travel along the nerve in both directions) ; no change appears to be caused in the motor cell by the entrance of the impulse. In the case of an afferent nerve-fiber, stimulated midway between the periphery and the spinal cord, the visible result is brought about by the central discharge of the impulse in the spinal cord ; no effect can be shown to occur at the periphery. When an impulse travels along a nerve-fiber, it spreads into any branches that are given off; the result of this is that if one branch of a motor nerve-fiber be stimu- lated near its muscular termination, the impulse which I >asses up the fiber toward the spinal cord will spread into any branch that happens to be given off at a higher level, and traveling down this, may cause the contraction of another muscle-fiber. This is called a pseudo=reflex. It is probable that a similar event may occur on the stimulation of the central termination of an afferent nerve-fiber within the spinal cord ; the im- pulse passing back along the fiber may spread through a collateral branch which is given off from a point nearer to the parent cell, and stimulate other nerve-cells in the neighborhood of which this collateral ends. (See Pig. 7.) Nerve-fibers do not seem to be susceptible of fatigue ; they may be stimulated for many hours without loss of irritability or conductivity; their terminations, how- 158 MUSCLE AND NERVE. ever, are readily fatigued. The conductivity of a nerve-fiber may be temporarily suppressed by freezing, or by pressure, or by exposure to ether vapor, etc. ; also, as we have seen, by the passage of a constant current. If a nerve be crushed, its conductivity at this point is destroyed. If a nerve be divided and the two ends brought together, an impulse cannot be trans- mitted across the gap, continuity of the axis-cylinder being necessary to conduction. The Chemical Composition of Muscle. Muscle consists of the following constituents: water, 75^ ; proteids, including paramyosinogen, myosinogen, and albumin, 20 ^ ; fats, glycogen, phosphoearnic acid, and inorganic salts, in small quantities; and waste products of muscular metabolism, such as kreatin, xanthin bases, sarcolactic acid, etc. Mammalian muscle, when its blood supply is shut off, very soon loses its irritability, and before long goes ! into rigor mortis. In this condition it is less elastic ' and less extensible, and, if no resistance be offered, it shortens ; like that of contracting muscle, its reaction becomes slightly acid. The rigidity depends upon the precipitation or coagulation of paramyosinogen and myo- sinogen, these being converted into insoluble myosin. If perfectly fresh muscle be frozen, and subjected to pressure, there may be expressed from it a liquid of syrupy consistence called muscle plasma. If kept cold, the plasma remains liquid, but if warmed, it clots ; from the clot separates a serum, of which the reaction is acid. The clot consists of myosin ; the serum con- tains albumin. The proteids of muscle may be ex- tracted by means of a 10% solution of ammonium chlorid, or a 5 % solution of magnesium sulphate ; on dilution, the extract clots, especially if it be kept warm. If before clotting occurs the extract be heated, the different proteids will be found to coagulate at different QUESTIONS. 159 temperatures. Paramyosinogen, a globulin, precipi- tates by heat at 47 C. ; myosinogen, a proteid with many of the characters of a globulin, at 56 C 1 .; myo- globulin, at 6*3 C. ; albumin, similar to serum albu- min, at about 73 C. The last two occur in quite -mall amounts. If a living muscle is heated gradually, its vitality is entirely lost, with its loss of irritability, when it has readied a temperature sufficient to coagu- late the proteid of the lowest coagulation temperature ; namely, the paramyosinogen at 47 C. QUESTIONS FOR CHAPTER VIII. Is the contraction of muscle dependent on katabolic or anabolic changes? What is meant by the conductivity of muscle? In order to produce complete tetanus, why is the frequency of Mi in illation that is required less in the case of a fatigued than in the case of a fresh muscle? If an isolated muscle has been fatigued by continued stimula- tion, why does washing out its vessels with normal salt solution tend toward the recovery of its irritability ? Do the irritability and conductivity of a nerve-fiber always vary in the same direction ? What is the effect of treating a muscle with the extract made from a fatigued muscle? If on passing a constant current through a muscle the intensity of the current be suddenly raised, at which electrode will contrac- tion begin ? On stimulating a nerve-trunk in the intact body with the con- stant current, by the application of which electrode may we expect to >ncceed with the weakest current? ' If in this respect the response is abnormal, what are we to conclude? If a muscle fails to respond to the induced current, but ia h.v] u>rirritable to the constant current, what must we conclude? If a nerve has been divided, how can we determine when its Regeneration is complete? What causes an extremity to " go to sleep " ? CHAPTER IX. THE NERVOUS SYSTEM. The spinal cord, in the grouping of its nerve-cells and in its relation to the tissues of the different parts of the body, shows a segmental arrangement, though each segment is intimately connected with the rest of the central nervous system. From each segment arises a pair of spinal nerves, through which relations with a particular segment of the body are established ; there is, however, an over- lapping of the innervation of a particular body seg- ment, so that a given muscle receives nerve-fibers from two or three segments of the cord ; this is especially the case with the muscles of the limbs. In conse- quence of this arrangement, a lesion which is strictly confined to one segment of the cord never deprives any one muscle of its nerve supply. Each spinal nerve is connected with the cord by two roots, a ventral, or anterior, and a dorsal, or posterior, root, and each of these, where it joins the cord, is di- vided into several small rootlets, which are shown in figure 6. If the anterior nerve=root be divided, as at a, degeneration of the peripheral portion of the root occurs, and many nerve-fibers will be found to degen- erate in the common nerve-trunk as far as its termina- tions in the muscles and sympathetic system. The fibers of the anterior root arise from cells which are situated in the gray matter of the cord, at the level of 160 11 "isw. 6 and 7. 162 THE NERVOUS SYSTEM. each fiber's exit. The portion of the anterior root which remains in continuity with the cord does not degenerate at once, for it has not been separated from its parent cell as is the case with the portion peripheral to the lesion. Division of the posterior spinal nerve-root at a point between the root ganglion and the cord, as at 6, figure 6, leads to degeneration of the rootlets which are left in connection with the cord, and degeneration of the pos- terior root-fibers may be traced within the cord, up- ward as far as the spinal bulb, downward for a short distance* only. No degeneration occurs peripheral to the lesion, for the posterior root-fibers are the axons of posterior root-ganglion cells, and only that part of a fiber which is cut off from its parent ganglion cell is destroyed. If the posterior root=ganglion is removed or crushed, the resulting degeneration destroys not only the nerve-fibers which have grown from the ganglion into the spinal cord, but those also which are distrib- uted to' the periphery through the spinal nerve-trunk. Division of the spinal nerve=trunk at a point periph- eral to the root-ganglion causes degeneration, peripheral to the lesion, of all its fibers ; central to the lesion, of none. Figure 7 shows the cell connection of the fibers of both roots. It will be noticed that the peripheral pro- cess of one posterior root-ganglion cell is represented as turning aside into the anterior nerve-root, instead of accompanying its fellows down the spinal nerve-trunk. The fibers which follow this course are distributed to the membranes of the cord, etc. If the nerve-roots be divided as shown in figure 8, and the peripheral cut end of the anterior root be stimulated at , there will result a contraction of the muscle Mj to which some of the fibers of this nerve are Figs. 8 and 9. 164 THE NERVOUS SYSTEM. distributed. This result will not be prevented by pre- vious destruction of the posterior root-ganglion, and degeneration of the posterior root-fibers. The anterior root contains motor nerve-fibers which are the axons of spinal cells. Stimulation of the central cut end of the anterior nerve-root, at b y produces no visible effect, for the resulting nerve impulses are evidently unable to spread to other neurones within the cord, though they probably reach the motor cells whose axons are stimu- lated. On stimulation of the central cut end of the posterior nerve=root, at c, there may occur a reflex contraction of the muscle IT, and, if the spinal cord be intact and connected with the brain, sensation. The nerve impulses excited in the posterior root-fibers enter the cord and are transmitted by the ascending branches of these fibers toward the brain, and by their collateral branches (Fig. 7) to the motor cells of the gray matter. The motor cells are thus stimulated, and dispatch impulses through the anterior root to the muscles which they innervate. Stimulation of the peripheral cut end of the posterior root, at d, produces, as far as can be determined, no result. Impulses will reach the peri- pheral terminations of the posterior root-fibers in, for instance, the skin; but, even if the impulse actually reaches the structures in which the fiber ends, no eifect seems to be produced. The fibers of the anterior nerve-roots are efferent ; they transmit impulses from the cord to the periphery. The fibers of the posterior nerve-roots are afferent; they transmit impulses from the periphery to the spinal cord. An afferent neurone and an efferent neurone together constitute the simplest form of reflex arc. A more elaborate form of reflex arc, including three neurones, is shown in figure 9. As will be seen, this THE SPINAL CORD. 165 form allows a more widespread reflex, through the stimulation of a greater number of motor cells. The axons of the central, or mediate, cells do not leave the central nervous system, but ascend and descend the mrd, thus bringing different levels into communication with one another. Some cross the median line and afford a basis for crossed reflexes ; neurones of this class are called com miss urn I. The stimulation of the anterior root may give rise to sensation or to reflexes, for, as has been mentioned above, some of the posterior root-fibers bend back toward the cord through the anterior root (Fig. 7) ; this is called recurrent sensibility. In some of the lower animals, for instance, the fish, reflexes may be carried on by one segment of the cord after it has been isolated from the rest. As a general rule, the reflex irritability of the spinal cord is in- creased by excluding the impulses which normally descend from the brain. In the spinal animal that is, one whose cord, or the greater portion of it, has been separated from the brain it is easier to predict the kind of reflex that will be evoked by a given stimulus. If a spinal dog be held in the vertical 'position, the stretching of the skin of the pendent legs will give rise to a reflex raising of these. A minimal stimulus applied to the skin will provoke reflex contraction of muscles on the same side of the body ; if the intensity of the stimulus be raised, the reflex may spread to the opposite side also. Reflexes spread tailward more readily than head ward ; it is more difficult to cause reflex movement of the foreleg by stimulation of the skin of the hinder part of the body than to cause move- ments of the hind limb by stimulating anteriorly. It is impossible to cause reflex simultaneous contraction of antagonistic muscles ; if the flexors of a limb con- 166 THE NERVOUS SYSTEM. tract, the extensors relax, and vice versa. The relaxa- tion is due to an inhibition of the motor cells which control the antagonistic muscles. The skeletal muscles possess a tone which is of reflex origin ; they are kept in a state of slight tonic contraction by weak motor impulses which continually reach them from the spinal centers, the activity of these centers resulting from the constant arrival of afferent nerve impulses from the periphery. If the motor cells be inhibited by impulses coming to them from the brain, or from a contracting antagonistic muscle through afferent nerves, their ac- tivity is lessened and the muscle which they govern is allowed to relax ; its tone disappears. The division of its nerve supply puts an end to the tone of a muscle, as may be readily understood. During sleep muscular tone disappears. When a muscle loses its tone, it also loses what is known as myotatic irritability, which consists in the power of a muscle, when stretched, to respond to a mechanical stimulus. The knee=jerk which is evoked by tapping the patellar tendon when the extensor muscles are put on the stretch depends on myotatic irritability ; it is not a true reflex, but is a response to the direct mechanical stimulation of the extensors, by the sudden extra tension resulting from the tap on the tendon. Although it is not a reflex contraction, it is, nevertheless, dependent on the ex- istence of reflex muscular tone; an injury to the reflex arc, upon the integrity of which muscular tone depends, abolishes the knee-jerk ; this is the case in tabes dor- salis, in which the posterior nerve-roots are affected. The knee-jerk also disappears when injury is done to the lumbar region of the cord, wherein lie the motor cells concerned. On the other hand, a lesion situated above this region may, by preventing cerebral inhibi- tion from reaching these cells, render them more irri- THE SYMPATHETIC SYSTEM. 1G7 table than in the normal condition, and result in exag- geration of the knee-jerk. The extent or absence of myotatic irritability is, consequently, a symptom of diagnostic import. The condition of the reflexes innervated by different portions of the spinal cord is of givat assistance in determining the position of a lesion; as instances, the following may be mentioned: the scapular reflex, controlled by the fifth cervical to the first thoracic segments; palmar reflex, seventh cervical to first thoracic; epigastric reflex, fourth to seventh thoracic ; abdominal reflex, seventh to eleventh thoracic ; crenmsteric reflex, first to third lumbar ; knee-jerk, second to fourth lumbar; gluteal reflex, fourth and fifth lumbar ; plantar reflex, first and second sacral ; Achilles tendon reflex, third to fifth sacral. These centers become hyperirritable when, by injury to the pyramidal tracts, the control exercised by the brain is eliminated, though, in man, complete division of the cord is followed by depression of the centers situated below the lesion. The reflexes are abolished by degeneration of the spinal centers which control them ; the muscles concerned show the reaction of degeneration, are hyper- irri table to the constant current, lose their irritability to the induced current, and finally atrophy. The Sympathetic System. In the thoracic and upper lumbar regions many of the nerve-fibers of the anterior and posterior spinal nerve-roots do not pass out to the periphery through the corresponding nerve-trunk, 1m t enter the sympathetic system through the white rami communicantes. The efferent fibers which follow this course probably originate from a group of small nerve-cells which in these regions of the cord are situ- ated in the dorsolateral portion of the anterior horn, the group being known as the intarmedio-lateral. These efferent fibers are medullated, like the other fibers of 168 THE NERVOUS SYSTEM. the anterior root, but are smaller than the rest. They all end in one or other of the sympathetic ganglia, and are called pre=ganglionic sympathetic fibers. The sympathetic system includes two chains of lateral, or vertebral, ganglia ; and collateral, or prevertebral, gan- glia which are found in the solar plexus, mesenteric plexus, and, smaller ones, in close proximity to the viscera. The pre-ganglionic sympathetic fibers which are con- cerned in the innervation of the vessels, glands, or musculature of the abdominal and thoracic viscera, pass through the lateral sympathetic chain, to end in one of the prevertebral ganglia. Here they make physiologic connection with sympathetic nerve-cells, the relation being one of contact. From the ganglion cells are given off the post=ganglionic fibers, usually nonmedullated, which reach the tissue concerned (Fig. 5). The pre-ganglionic sympathetic fibers which are con- cerned in the innervation of the vessels of the skeletal muscles or in the innervation of the vessels, plain muscle, and glands of the skin, end in one or other of the ganglia of the lateral chain. The corresponding post-ganglionic fibers, which originate here, pass, by way of the gray rami communicantes, into the spinal nerves and thus reach the periphery (Fig. 4). The posterior root-fibers which enter the sympathetic system are distributed to the viscera (Fig. 10), and form one of the channels through which afferent impulses pass from the viscera to the central nervous system. Afferent impulses are also carried from the heart, lungs, liver, stomach, etc., by the pneumogastric nerve to the medulla, and from the pelvic viscera by the second, third, and fourth sacral nerves to the spinal cord. The pain resulting from disease of the viscera is often referred by the patient to a definite area of the Fig. 10. The course of an afferent sympathetic fiber. 170 THE NERVOUS SYSTEM. skin; this area being that which is supplied with afferent fibers by the same dorsal spinal nerve-root which transmits afferent impulses from the viscus in question. Even in the case of the skin, with which we are so familiar, it is only through past experience that we are able to localize the point of origin of a given cutaneous sensation. It would seem that the afferent nerve-fibers which enter the cord through a given nerve-root, whether they be cutaneous or visceral, make very similar connections within the central nervous system. Thus we are very apt to be misled into confusing the sensation resulting from an unusual visceral irritation with those which arise from stimula- tion of an area whose afferent fibers may discharge their impulses at much the same point within the cord, and do so more frequently. Not only does this con- fusion of sensations exist; even the reflexes which may be excited by stimulation of a given cutaneous area are intensified by irritation of the viscus whose afferent fibers enter through the same nerve-root. Whatever the destination of an efferent pre-gangli- onic sympathetic nerve-fiber, it leaves the spinal cord in the thoracic or upper lumbar region, and originates from a cell situated in the cord at the level where it emerges. These pre-ganglionic fibers all end in sym- pathetic ganglia, and the post-ganglionic fibers, which originate from the ganglion cells, are all distributed to cells (plain muscle, of the vessels, viscera, and skin, cardiac muscle, and gland cells) the activity of which is involuntary. The sympathetic system supplies nerve-fibers of various function; as, vasoconstrictors and vasodilators, of wide distribution ; viscero-motor fibers, for the spleen, uterus and Fallopian tubes, intes- tines, etc.; cardio-augmentors ; viscero-inhibitory fibers, such as those supplied to the stomach and intestines; Till; SYMPATHETIC SYSTEM. 171 pupillo- dilators ; secretory fibers for the salivary, lacri- nial, and sweat glands, and for the small glands of the oral, nasal, and pharyngeal mucous membranes; pilo- inotors, which control the plain muscle of the skin and bring about the erection of the hair and the condition known as goose-skin. The arrangement of two other sets of peripheral nerve-fibers, one set emerging from the central nervous >vstom in certain cranial nerves, the other, in the (second) third (and fourth) sacral nerves, resembles that of the sympathetic nerve-fibers. These fibers, also, are dis- tributed to gland cells, cardiac and plain muscle-fibers. Each set consists of pre-gangl ionic and post-gangl ionic fibers. The fibers included in the cranial set vary in function. They are : pupillo-constrictors and fibers of visual accommodation, in the third cranial nerve ; in the seventh and ninth cranial nerves, secretory fibers for the salivary glands, and glands of the lips and check, and vasodilators for the salivary glands, tongue, soft palate, and floor of the mouth ; in the tenth and eleventh cranial nerves, viscero-motors for the esopha- gus, stomach, small intestines, ascending and horizontal eolkiu at the time of application, and upon the rapidity with which the lowering of the temperature is brought about. The endings of cold-nerves may also be stimu- lated by the application of heat, but the resulting sen- sation is one of cold. The endings of cold-nerves are more numerous than those of heat-nerves ; the endings of pain-nerves, more numerous than those of either of the other varieties. Many of the afferent nerve-fibers which are distrib- uted to the skeletal muscles end in muscle spindles, which consist of several muscle-fibers inclosed in a connective-tissue covering, within which the nerve- til MTS ramify upon the muscle. When a muscle con- tracts or is stretched, these nerve-endings are stimulated, impulses are transmitted to the central nervous system and give rise to sensations which are described as muscle sense. By means of these impressions, we form an idea of the force and extent of the contraction of our muscles, and of the resistance opposed to their con- traction ; the pressure nerves of the skin are also im- portant in this respect. The afferent nerves of the viscera are concerned, for ,f tin- most part, in reflexes of which we are unconscious; it is seldom that we experience visceral sensations ; operations upon the normal abdominal viscera are pain- less ; yet under certain circumstances these nerves may transmit impulses which excite intense pain. As was stated alve,the central axons of the posterior spinal root-ganglion cells, on entering the cord, divide into ascending and descending branches. The former are the longer, but vary in length. Both branches finally end in the gray matter, some ascending as far as the medulla ; both give off collaterals (Fig. 7), which also end in the gray matter. The course of these fibers is in the posterior, or dorsal, columns of white matter, 174 THE NERVOUS SYSTEM. each of which is subdivided into a dorsomedian and a dorsolateral tract (Figs. 11, 12). The fibers ascend at first in the dorsolateral tract, but, in the case of those of the lumbar nerves which reach the medulla, they later- pass over into the dorsomedian tract, and thus reach the dorsomedian nucleus, or nucleus gracilis of the medulla, where they end. The dorsolateral tract, when it reaches the medulla, consists chiefly of fibers which carry impulses from the upper extremities ; these fibers end in the dorsolateral nucleus, or nucleus cuneatus. These two nuclei serve as cell stations for the forward- ing of impulses to the cerebellum and to the cerebrum, in response to impulses received from the periphery. They contain nerve-cells whose axons follow several different paths ; some, the internal arcuate fibers, curve ventral ward, cross the median line, and ascend in the fillet, or lemniscus, on the opposite side, toward the cerebrum (Fig. 11). Probably, only the minority of these reach the cortex ; many of them end at lower levels in, for instance, the optic thalamus and corpora quadrigemina. The optic thalamus seems to afford another cell station on the way to the cerebral cortex. In the internal cap- sule the ascending fibers are found in the posterior portion of the dorsal limb. The dorsal nuclei are connected with the cerebellum, through the restiform body, by two sets of fibers ; one set, arising from the cells of these nuclei, passes directly into the restiform body on the same side ; another set, the external arcuate fibers, follows the same course as the internal arcuates until, the median line having been crossed, they reach the surface, and, passing in front of the pyramid, enter the restiform body, and so, the cere- bellum. The fibers which thus reach the cerebellum carry impulses to the roof nuclei and cortex of the inferior vermis. It is highly probable that impulses Fig. 11. 176 THE NERVOUS SYSTEM. which are concerned in muscle=sense ascend the cord and reach the cerebellum and cerebrum over the paths just described; there is some evidence that the im- pulses concerned in tactile sensibility, pressure sense, also follow this course. If the posterior nerve-roots be divided, the degen- eration of fibers within the cord is confined to those in the dorsal columns. Division of the cord itself is fol- lowed by the degeneration of not only the dorsal column ln/v\A~ Fig. 12. The ascending and descending tracts of the spinal cord, in cross-section. fibers which have entered below the point of lesion, but of fibers situated in other tracts. Figure 9 shows central cells whose axons ascend and descend the cord for short distances, in that part of the white matter which is adjacent to the gray. Many of these will be divided in making a transverse section of the cord, and degeneration will occur in that portion of the fiber which is separated from its parent cell ; in those which have grown from below upward, and are divided, de- Fig. 13. Serial sections showing the course and connections of the direct cere- bellar tract. (The upper .section is disproportionately reduced.) 12 178 THE NERVOUS SYSTEM. generation will occur above the lesion ; those which have grown downward, and are divided, will degenerate below the lesion. In addition to these, fibers of much greater length will be found to degenerate both above and below the point of section. One distinctly marked ascending tract, or tract of fibers which degenerate above the point of section, is the direct cerebellar tract (Figs. 12 and 13). The fibers which constitute this tract originate from a group of cells which persists throughout the thoracic cord, and is known as the column of Clarke, or the vesicular cyl- inder. The group lies at the base of the posterior horn of gray matter, and toward its median border. In the neighborhood of these cells many of the dorsal column collaterals end, and thus bring the group under the influence of the afferent impulses which enter through the posterior roots. The direct cerebellar tract ascends the cord without undergoing decussation and enters the cerebellum through the restiform body, its fibers ending chiefly in the cortex of the vermis, partly on the same, partly on the opposite side. What afferent impulses are carried by this tract is uncertain. It must be re- membered that impulses which reach the cerebellum may cause the dispatch of cerebellar impulses to the cerebrum, for the two are intimately connected through the superior cerebellar peduncle, or brachium conjunc- tivum (Fig. 13). Another ascending tract is that of Gowers, or the anterolateral ascending tract (Figs. 12, 14). Its fibers originate from cells situated in the gray matter, on the same and on the opposite side of the cord ; they pass for the most part into the cerebellum, some ascending as far as the level of the inferior corpus quadrigeminum, and then curving downward into the vermis ; others entering the cerebellum through the restiform body. WucV. "ig. 14. Serial sections showing the course and connections of the anterolateral ascending tract. (Upper section disproportionately reduced.) 180 THE NERVOUS SYSTEM. Mixed with these fibers are some which do not enter the cerebellum, but end in the corpora quadrigeminj and optic thalamus. This tract appears to convey im- pulses concerned in temperature sensations and pain. Destruction of the ventrolateral portion of the spinal cord on one side leads to loss of the perception of pain- ful stimuli, of heat and cold, when these are applied to the skin on the opposite side of the body below the lesion. Of the cranial nerves, the first, second, fifth, both divisions of the eighth, the ninth, and tenth contain afferent nerve-fibers. In the case of the fifth, eighth, ninth, and tenth, these afferent fibers behave much as do the afferent fibers which enter the cord ; on entering the medulla they divide into ascending and descending branches, the latter being, however, the longer ; from these, collateral branches are given off. The afferent fibers of the tenth cranial nerve, vagus or pneumogastric, have a wide distribution and carry impulses from the heart, lungs, pharynx, larynx, trachea, esophagus, stomach, intestines, liver, pancreas, and spleen. These fibers, on entering the medulla, divide into short ascending branches which end in the nucleus alae cinereae, and long descending branches which form the tractus solitarius, or solitary bundle. These give off many collaterals which end amongst cells, that are scattered along this tract and form the nucleus of the solitary bundle. The axons of the cells of these two nuclei follow a course similar to that of the internal arcuate fibers which originate from the cells of the gracile and cuneate nuclei. They curve through the retictilar formation to the median line, cross it, and ascend in the opposite fillet ; some fibers, however, enter the posterior longitudinal bundle, and ascend in this toward the brain (Fig. 15). The further course of the fibers which Fie. 15. The afferent fibers of tbe niiiih and tenth cruuiul nerves. 182 THE NERVOUS SYSTEM. enter the fillet is the same as that already described (Fig. 11). These fibers, before they decussate, give off collaterals which end in the reticular formation, and may be supposed to influence the cells of the cardio- inhibitory, respiratory, and vasoconstrictor centers which are situated in this neighborhood. The ninth cranial nerve, or glossopharyngeal, con- tains afferent fibers which carry impulses from the tongue, pharynx, Eustachian tube, etc. Its central con- nections are much the same as those of the pneumogas- tric (Fig. 15). The cochlear, or auditory division of the eighth cranial nerve, consists of afferent fibers which are dis- tributed to the cochlea, and carry auditory impulses. These fibers are the axons of the bipolar cells of the spiral ganglion; in the medulla they end in two nuclei, the ventral and dorsal cochlear nuclei. The axons from the cells which form these nuclei pass through the tra- pezium and striae acusticse, as shown in figure 16, to the superior olive on the opposite side ; some, however, end in the superior olive on the same side. Many of the fibers end in the olive ; others pass through it and ascend, with the axons of olivary cells, in the lateral fillet. The fibers of the lateral fillet end on the same side in the inferior corpus quadrigeminum, in the medial gen- iculate body, and a few in the superior corpus quad- rigeminum ; and on the opposite side, in the inferior corpus quadrigeminum. From the geniculate body im- pulses are forwarded to the cerebrum ; the corpora quad- rigemina probably act as centers through which sounds may bring about reflex movements of the head and eyes. The auditory impulses pass chiefly to the opposite side of the brain, but it will be seen from the diagram (Fig. 16) that there are several means of communication with the same side of the brain. Fig. 16. The cochlear nerve. 184 THE NERVOUS SYSTEM. The vestibular division of the eighth cranial nerve consists of afferent fibers which arise from the vesti- bular ganglion cells. The peripheral processes of these bipolar cells end in the vestibule and semicircular canals. This nerve carries afferent impulses, by means of which we are informed of movements of the head or of the body as a whole, and which assist in the reflex and voluntary maintenance of equilibrium. On entering the medulla at the lower border of the pons, they end, for the most part, in four nuclei namely, the superior, lateral, and medial vestibular nuclei, and the nucleus of the descending, or spinal, vestibular root. Some fibers pass directly into the cerebellum. The axons of the vestibular nuclear cells follow several different routes ; axons from each nucleus enter, and ascend in the median fillet and posterior longitudinal bundle, mainly on the opposite side ; from the lateral and superior nuclei fibers also pass into the cerebellum, while others descend the cord ; both these sets probably play a part in reflex equilibration (Fig. 17). The fifth cranial nerve, trigeminus or trifacial, con- tains afferent fibers which carry impulses from the skin of the face, from the conjunctiva, and from the mucous membranes of the nose and mouth. Some of the fibers distributed to the tongue may cany impulses which result in sensations of taste. The afferent fibers of the trigeminus originate from cells situated in the Gasserian ganglion. On entering the pons they divide into very short ascending branches which end in the chief trige= minal nucleus, and very long descending branches, the spinal root, whose collaterals end amongst the cells of the substantia gelatinosa which forms the nucleus of the spinal root. The axons which arise in these nuclei give off collaterals in the reticular formation, and probably AFFERENT NERVE-FIBERS. 185 ascend in the median fillet on the opposite side of the median line (Fig. 18). The second cranial, or optic, nerve differs entirely in its method of development from the other afferent nerves that we have considered ; it may, however, be described with them. It consists chiefly of afferent fibers which are the axons of retinal ganglion cells. Light which falls upon the retina does not stimulate these cells directly, but takes effect upon the rods and coin's of the outer layer. Between the rod and cone cells and the ganglion cells, mediate the bipolar neurones of the retina. The axons of the retinal ganglion cells enter the optic nerve, and pass along it to the optic chiasma ; here the fibers from the nasal half of the retina, and some of those which originate from the cells in the macula lutea, decussate, and enter the opposite optic tract; the fibers from the temporal half of the retina do not cross, but proceed through the optic tract on the same side toward the brain. The optic tract, then, contains fibers from the temporal half of the homonymous retina, fibers from the maculae luteae of both eyes, and fibers from the nasal half of the contralateral ret inn. These fibers reach and end in the external geni- culate body, the pulvinar, and the anterior corpus quad- rigeminum. Axons originating from the cells of these bodies transmit impulses through the optic radiation to the occipital cortex, which constitutes the visual area of the brain. The anterior corpus quadrigeminum forms a center through which visual reflexes are probably inaugurated ; fibers originate here which decussate and descend through the posterior longitudinal bundle into the spinal cord, giving off, on their way, collaterals which terminate in the motor nuclei of the nerves which innervate the muscles of the eye. They very probably Fig. 17. The vestibular nerve. Fig. 18. The afferent fibers of the fifth cranial nerve. 188 THE NERVOUS SYSTEM. also bring about reflex turning of the head in response to visual stimuli (Fig. 19). The first cranial, or olfactory, nerve consists of the axons of cells situated in the olfactory mucous mem- brane of the nose ; the dendrites of these cells reach the surface ; their axons pass through the cribriform plate of the ethmoid bone, and enter the olfactory bulb. The axons end here, in the olfactory glomerali, in con- tact with the dendrites of the mitral cells, whose axons form the second link in the chain which transmits olfactory impulses toward the brain. The mitral cell axons run in two directions ; one set enters the anterior commissure, and, passing through it, reaches, on the one hand, the opposite olfactory bulb, on the other, the opposite hippocampus. Of the other set, the majority of fibers pass through the lateral olfactory gyrus to the uncus, where they end. The fibers of the medial root end in the trigonum, where they make cell connections which bring them into communication with other parts of the olfactory area. From the cells of the uncus, in contact with which the fibers of the lateral root end, axons pass to the hippocampus. The hippocampal neurones, in turn, make, through the fornix, manifold connections, some of which are shown in figure 20. Some of the fibers end in the nucleus habenulse, whence neurones descend through Meynert's retroflexed bundle ; others end in the corpus mammillare, and make con- nections with neurones whose axons divide into two branches, one ascending to the anterior nucleus of the optic thalamus, the other descending. Sensory Cortical Areas. Certain areas of the cor- tex cerebri are closely associated with sensation, and it is to these areas that impulses provocative of sensation are carried. Destruction of the left occipital lobe leads to blindness of the left half of each retina ; destruction of Fig. 19. The optic nerve. 190 THE NERVOUS SYSTEM. the right occipital lobe causes blindness of the right half of each retina. The cortical area lying on either side of the calcarine fissure is probably concerned in re- ception of impulses from the macula lutea, or area of most distinct vision, of each eye. Figure 21 shows the visual and other sensory areas of the cortex, those for cutaneous sensibility being, however, of doubtful location. Descending Tracts of the Spinal Cord. Hav- ing considered the channels through which afferent nerve impulses are carried from the periphery to the brain, there remain for description the connections between higher centers and the peripheral efferent neurones. After transverse sections of the spinal cord, degeneration of certain nerve-fibers occurs below the lesion ; these degenerated fibers are, of course, the pro- cesses of cells which are situated at various levels above the lesion. There are many cells in the gray matter of the cord whose axons enter the white columns, and ascend or descend, for comparatively short dis- tances, to end in the gray matter at different levels ; on their way through the white matter they give off col- laterals which also enter and end in the gray matter (Fig. 9). In addition to these, there are fibers which descend into the cord from higher levels. Two such tracts have already been mentioned namely, the fibers which descend from the vestibular nuclei (Fig. 17), and those which descend in the posterior longitudinal bundle from the superior corpus quadrigeminum (Fig. 19). Both these sets of fibers descend through the ventrolateral columns of the cord, and give off collat- erals to the gray matter. Fibers also descend, in all probability, from the cerebellum, though these may be interrupted by cell stations in the inferior olives, or in the pons. There is no doubt that the cerebellum, Fig. 20. Olfactory connections. 192 THE NERVOUS SYSTEM. either directly or indirectly, exerts an influence over the motor neurones of the cord, for its removal results in marked interference with the coordination of move- ments and the maintenance of equilibrium. Another set of fibers descends from the red nucleus into the opposite half of the spinal cord, and is found just medial to the direct cerebellar tract. Two descending tracts, with the course and function of which we are better acquainted, are the direct and crossed pyramidal tracts. It is perhaps better to call them the ventral and lateral pyramidal tracts (Fig. 12). They originate chiefly from cells which are situated in what are known as the motor areas of the cortex. It has been found that the stimulation of certain areas of the cortex cerebri results in the contraction of certain groups of muscles. Figure 22 shows the dis- tribution of these areas. In these areas are large pyramidal cells, so called on account of their shape, whose axons pass through the corona radiata to the internal capsule, of which they form the knee and anterior two-thirds of the pos- terior limb (Fig. 23). The arrangement of the pyra- midal fibers in the internal capsule shows a certain correspondence to that of the motor areas from which they originate ; most anteriorly are situated the fibers from the motor area for the eyes, then come those for the head, and these are followed in order by those for the tongue and mouth, shoulder, elbow, wrist, fingers, trunk, hip, knee, toes. The arrangement of these fibers in definite groups according to their origin per- sists throughout their course, though even in the internal capsule there is some admixture. The pyramidal fibers pass down through the middle portion of the crusta of the cerebral peduncle, and through the ventral portion of the pons, into the medulla, where they form the DESCENDING TRACTS OF THE SPINAL CORD. 193 pyramid from which their name is derived. At the ln\\cr cud of the medulla the majority of the fibers cross, in the pyramidal decussation, into the lateral pyramidal tract on the opposite side, and, descending the cord, end at successive levels in the gray matter near Clarke's column. The stimulation of the motor cells of the 'anterior horn must therefore entail the mediation of an intervening neurone, which perhaps stimulates several motor cells. Not all the pyramidal fibers decussate in the medulla; a few pass into the lateral pyramidal tract of the same side, some descend in the homonymous ventral pyramidal tract. The fibers of the ventral pyramidal tract decussate at various levels of the cord and end in the gray matter of the opposite half. The fibers which, without crossing, de- scend the lateral pyramidal tract end in the gray matter on the same side of the cord. By far the majority of the pyramidal fibers, then, cross in the medulla; of the remainder, the majority cross before they end ; only a ie\v end without crossing the median line. Each half of the brain controls muscles on the opposite side of the body. As the pyramidal tracts descend the cord they gradually diminish in bulk, for fibers leatfe them at each succeeding level to end in the gray matter. The ventral pyramidal tract disappears before reaching the lumbar region. It is important to note that movement is not the only result of stimulating a given cortical area. If carefully localized stimulation be applied to the motor area for one set of muscles, the antagonists of this set relax ; for example, stimulation of an area of flexion causes contraction of the flexor muscles concerned and simultaneous relaxation of the extensors which are an- tagonistic to them. The cortex can therefore both pro- voke and inhibit muscular contraction. Evidence of 13 Fig. 21. Sensory areas of the cortex cerebri. Fig. 22. Motor areas of the cortex cerebrL 196 THE NERVOUS SYSTEM. the removal of this cortical inhibition is seen on division of the pyramids : the spinal centers, released from con- trol, respond more readily than usual to the afferent impulses which reach them from the periphery, and reflex muscular tone is exaggerated. Some of the motor fibers of the internal capsule, which, on reaching the cerebral peduncle, lie medial to the fibers of the pyramidal tract, end in the motor nuclei of the cranial nerves ; as is shown in figures 24 and 25. In addition, it appears that fibers descend through the median fillet, to end in the nuclei of the seventh and twelfth nerves. Motor Cranial Nerves. The third cranial nerve, oculomotor, arises from a nucleus which consists of several cell-groups situated in the floor of the Sylvian aqueduct, at the level of the superior corpora quadri- gemina. The most anteriorly situated cells of this nucleus appear to be concerned in accommodation ; the next, in constriction of the pupil ; those innervat- ing the muscles of the eyeball namely, the inferior, superior, and internal recti, and the inferior oblique muscles and the levator palpebrse being situated more posteriorly. Some axons of the third nerve decussate before their exit, but the majority do not (Fig. 24). The fourth cranial nerve, or trochlear nerve, arises from a group of nerve-cells which occupy much the same position as the nucleus of the third nerve, but are situated rather more posteriorly. The axons of these cells descend for a short distance before entering the velum, in which they cross to the opposite side, and emerge as the fourth nerve. This nerve innervates the superior oblique muscle of the eyeball (Fig. 24). The smaller root of the fifth cranial nerve arises from two nuclei, the chief of which is situated in the Fig. 23. Origin and course of the ventral and lateral pyramidal tracts. 198 THE NERVOUS SYSTEM. dorsal portion of the pons ; the other nucleus, that of the descending root, consists of a group of cells which are scattered over a narrow area, from the chief nucleus, forward, to the level of the corpora quadrigemina. The axons of these cells join the lower branch of the tri- geminus, and innervate the muscles of mastication. Cortical fibers, chiefly from the opposite hemisphere, probably reach the motor nucleus of the fifth nerve (Fig. 24). The fibers of the sixth cranial nerve, or abducens, arise from a nucleus which is situated in the dorso- medial portion of the pons in the floor of the fourth ventricle. This nerve innervates the external rectus muscle of the eyeball. Cortical fibers reach this nucleus, chiefly from the opposite hemisphere (Fig. 24). This nucleus is brought under the influence of the superior corpus quadrigeminum through the posterior longi- tudinal bundle (Fig. 19). The same is true of the nucleus of the third nerve. The seventh cranial, or facial nerve, arises from a nucleus situated ventrolaterally from that of the sixth nerve, and extending further posteriorly. The axons pass dorsomedially, and run for a short distance an- teriorly beneath the floor of the fourth ventricle ; they arch over the nucleus of the sixth nerve, and emerge ventrally from the lower border of the pons. This nerve is distributed to the muscles of the face. Corti- cal fibers, chiefly from the opposite side, reach this nucleus ; descending fibers of the median fillet also probably reach it (Fig. 24). The motor fibers of the ninth cranial, or glosso- pharyngeal nerve, originate from the nucleus ambiguus, which lies in the reticular formation dorsal to the in- ferior olive. Its axons proceed dorsomedially, turn, and emerge in company with the afferent fibers of the Fig. 24. The efferent fibers of the third, fourth, fifth, sixth, and seventh cra- nial nerves. 200 THE NERVOUS SYSTEM. nerve. The motor fibers of this nerve are distributed to the middle constrictor muscle of the pharynx, and to the stylopharyngeus. This nucleus probably receives cortical fibers, mainly from the opposite side (Fig. 25). The motor fibers of the tenth cranial nerve, vagus, or pneumogastric, also arise from the nucleus ambiguus, and its central connections are the same (Fig. 25). Its motor fibers are distributed to pharynx and esophagus, larynx, bronchial muscles, stomach, and intestines. It also contains cardio-inhibitory fibers, and secretory fibers for the gastric glands and pancreas. It is doubtful whether the cranial portion of the eleventh nerve, which also originates from the nucleus ambiguus, belongs in reality to this nerve or to the vagus, which it joins. The spinal portion originates from cells situated in the lateral horn of the cervical region, from the level of the first to the fifth or sixth cervical nerve. The spinal portion innervates the sternocleidomastoid and trapezius muscles. The nuclei of this nerve receive fibers from the opposite half of the brain, and possibly a few from the same side (Fig. 25). The twelfth cranial, or hypoglossal nerve, is the motor nerve for the tongue, and arises from a nucleus which lies close to the median line in the dorsal part of the medulla ; the upper end of this group of nerve-cells is just beneath the floor of the fourth ventricle ; lower down, it is ventral to the central canal. It receives fibers from the cortex cerebri, chiefly from the opposite side, and some descending fibers from the median fillet (Fig. 25). Fig. 25. The efferent fibers of the ninth, tenth, eleventh, and twelfth cranial nerves. 202 THE NERVOUS SYSTEM. THE CEREBRUM* The cerebral hemispheres are concerned in sensation, consciousness, memory, intelligence, and volition. The destruction of a sensory area leads to loss of the sen- sation with which the area had to do ; for instance, re- moval of the two occipital lobes results in complete blindness, though the eyes are uninjured. The pupils, however, continue to contract when light falls on either retina ; the reflex arc concerned includes the rod and cone cells and the bipolar cells of the retina, the retinal ganglion cells and their axons, neurones of the anterior corpus quadrigeminum, and those of the third nerve which innervate the constrictor pupillse. An injury to either of the links in this chain will, of course, put an end to the light-reflex. Destruction of a motor area results in paralysis of the muscles which were innervated by this portion of the cortex. There may, in time, be some recovery of move- ment, especially in young patients, but the finer move- ments, such as those of the hand, are permanently lost. The paralyzed muscles may be caused to contract re- flexly. Destruction of a sensory area e. f which is 1.0, into the cornea, the refractive index of which is 1.37, its radius of curvature being 7.8 mm. Very little refraction occurs at the posterior -urf'ace of the cornea, since the refractive index of the aqueous humor (1.33) differs but little from that of the cornea. The refractive index of the lens is 1.43, the radius of curvature of its anterior surface being, when the eiliary muscle is at rest, 10 mm.; here, again, the refraction is considerable. The rays a re again refracted at the posterior surface of the lens, the radius of curv- ature of this surface being 6 mm.; here the rays pass into the vitreous humor, the refractive index of which is the same as that of the aqueous humor (1.33). Tliis complex system of media and refracting sur- faces may, however, be represented by what is known as the reduced eye, which consists of one medium with an index of refraction about the same as that of the aqueous and vitreous humors, bounded by one surface with a radius of curvature of 5.1 mm. The refraction Buffered by a ray of light on entering such an eye, would be equal to the total refraction suffered, on its way to the retina, by a ray forming the same angle with the principal axis of the normal eye. This imaginary refracting surface lies between the cornea and the lens. Tin- nodal point of the 'reduced eye that is, the center of curvature of its refracting surface is situated 0.47 nun. in front of the posterior surface of the lens, and, of course, on the principal axis. Such a reduced eye represents the normal eye only when the ciliary muscle is at rest. The refracting surface of a reduced eye that shall accurately represent the refraction that occurs in the normal eye when the ciliary muscle is contracted must have a greater curvature. Rays of light the 212 THE SPECIAL SENSES. course of which is parallel to the principal axis are re- fracted to meet, at the posterior principal focus, on the principal axis ; when the ciliary muscle is at rest, the posterior principal focus falls upon the retina. The an- terior principal focus lies 12.9 mm. in front of the cor- nea, on the principal axis ; rays which emanate from this point are, within the eye, rendered parallel to the principal axis. The cardinal points of the system are the anterior and posterior principal foci, the nodal point, and the principal point, the latter being the point where the optic axis cuts the refracting surface of the reduced eye, and being situated in the aqueous humor 2.2 mm. behind the anterior surface of the cornea. Rays of light which fall perpendicularly upon the refracting surface of the reduced eye suffer no refrac- tion, but pass on through the nodal point to the retina. Consequently, a ray of light emanating from a point above the principal axis, and falling perpendicular to the refracting surface, will reach the retina at a point below the principal axis ; a ray coming from a point situated below the principal axis will strike the retina above it. Light stimulates certain structures in the retina, and, as a result, nerve impulses are transmitted to the brain, there giving rise to sensations. By experience we learn to associate sensations resulting from stimulation of the lower part of the retina with light emanating from a point situated above the optic axis; sensations resulting from stimulation of the upper part of the retina, with light coming from a source situated below the optic axis; the same is true of stimulation of the lateral portions of the retina the resulting sensations are associated with points on the opposite side of the axis. The formation of an image on the retina is shown in figure 26. With the exception of the principal ray, VISION. 213 winch falls perpendicularly upon the refracting surface of the reduced eye (this surface is represented in the figure by a broken line), the diverging rays which are reflected from a given point of the surface of an opaque object, and which enter the eye, are refracted to meet the principal ray upon the retina, and form here an image of the point from which they were reflected. In like manner, there are formed images of other equidis- tant points of the object at the points where their prin- cipal rays strike the retina. In this way an image of Fig. 26. Formation of an image on the retipa. the whole object may be formed; it is, of course, inverted. When the ciliary muscle of the eye is at rest, rays of light which diverge from a point near the eye are not, by the time they reach the retina, brought to a focus ; consequently, they form, instead of a sharp image, a diffusion circle. In order that a sharp image of a near object may be formed on the retina, the focal distance of the eye must be shortened. This is known as accommodation, and is accomplished by the contrac- 214 THE SPECIAL SENSES. tion of the ciliary muscle. When this muscle is at rest, the lens is flattened by the tension to which the suspensory ligament and capsule are subjected owing to intraocular pressure. When the ciliary muscle con- tracts, it stretches the elastic choroid coat, and pulls forward its anterior margin, to which is attached the suspensory ligament. The suspensory ligament and capsule being thus slackened, and the pressure on the inclosed lens being reduced, the anterior surface of the elastic lens bulges forward, its curvature is increased, and, with the curvature, the power of refraction. The image of an object which is near the eye may thus be formed upon the retina. The normal eye cannot, how- ever, be accommodated for objects which lie within 10 or 12 centimeters of the cornea. This is known as the near-point of distinct vision. Since parallel rays are brought to a focus upon the retina of the resting eye, the far-point of vision is at an infinite distance. Accommodation is accompanied by constriction of the pupil, and by convergence of the optic axes of the two eyes ; to a certain extent the latter may, by prac- tice, be dissociated from the two former. The motor impulses concerned in causing these events reach the eye through the third nerve ; pre-ganglionic fibers which carry motor impulses to the ciliary muscle and constrictor pupillse end in the ciliary ganglion, and make connection here with cells whose post-ganglionic fibers are distributed to these structures. Although the ciliary muscle is of the unstriped variety, it is under the control of the will, and the eye may, by practice, be accommodated for short distances without fixing the attention upon near objects. No direct voluntary con- trol can be exercised over the size of the pupil, but it may be indirectly varied through voluntary contraction or relaxation of the ciliary muscle, with which its MYOPIA. 215 movements are associated. Light, when it falls on cither retina, onuses n-tiex constriction of both pupils; the afferent impulses concerned being probably carried to the anterior corpus quadrigeminum, whence impulses are dispatched to the nuclei of the third cranial nerves. The size of the pupil is also influenced by pupillo-dila- tor fibers, which leave the spinal cord in the second thoracic nerve and enter the sympathetic chain to end in the superior cervical sympathetic ganglion. Con- nection is here made with nerve-cells whose axons form post-ganglionic fibers that pass through the cavernous plexus to the Gasserian ganglion, and thence with the ophthalmic division of the fifth nerve to the eye, reach- ing the latter through the long ciliary nerves. The pupillo-dilator center is probably situated in close prox- imity to the nucleus of the third nerve, and appears to exert a tonic influence, for division of the cervical sympathetic is followed by constriction of the pupil. Dilatation of the pupil accompanies relaxation of the ciliary muscle; it may be caused reflexly by stimula- tion of afferent nerves, as, for instance, by tickling the palm of the hand, or by applying a painful stimulus to the back of the neck ; it is influenced by the emotions. It is probable that dilatation depends upon contraction of radially disposed cells of the iris, but whether or no these cells are plain muscle-cells, is uncertain. Both accommodation and the size of the pupil are affected by certain drugs ; atropin, for example, paralyzes the terminations of the motor nerve-fibers of the ciliary and constrictor muscles, and probably stimulates the fibers which cause dilatation ; physostigmin, on the other hand, stimulates the terminations of these nerves, and paralyzes the dilators. Myopia, or short sight, depends upon the fact that the posterior principal focus falls in front of, instead of 216 THE SPECIAL SENSES. upon, the retina. In the hypermetropic, or long-sighted eye, the posterior principal focus lies behind the retina. The former condition usually results from the antero- posterior diameter of the eye being abnormally great ; the most frequent cause of hypermetropia is an abnor- mally small anteroposterior diameter of the eyeball. The hypermetropic eye has, when the ciliary muscle is at rest, neither near- nor far-point of distinct vision, for rays which come from even an infinite distance are not brought to a focus by the time they reach the retina, and still more is this the case with those emanating from objects which are near the eye ; the condition may, however, be compensated to a certain extent by accom- modation, but the near-point of vision is always further from the eye than the normal. The near-point of dis- tinct vision of the myopic eye is nearer to the eye than that of the emmetropic or normal eye, consequently a larger image of a small object may be formed on the retina of a myopic eye, and small objects may thus be seen more distinctly by a short-sighted individual than by one whose vision is normal. The far-point of dis- tinct vision of the myopic eye is at a comparatively short distance, for only the divergent rays which fall upon the cornea can be focused upon the retina ; paral- lel rays are brought to a focus before reaching it. As age advances, the power of accommodation is impaired, through weakness of the ciliary muscle and lessening of the elasticity of the lens, the condition being known as presbyopia; the near-point of distinct vision grad- ually recedes from the eye, but there is no interference with the vision of distant objects. Astigmatism is an irregularity of vision which is usually dependent on differences in the curvature of the cornea. In the commonest form the curvature of the cor- nea is greater in the vertical than in the horizontal mer- ASTIGMATISM. 217 idian, and, as a result of this, the rays which, diverging from a given point, fall upon the vertical meridian of the cornea, are brought to a. focus earlier than those which fall upon the horizontal meridian. Consequently, when the eye is so accommodated that the anterior of these two foci falls upon the retina, the image formed will be, instead of a point, a horizontal line ; if the pos- terior focus falls upon the retina, the image will be a vertical line (Fig. 27). Almost every eye is more or less astigmatic, and none are free from defects. One constant defect consists in spheric aberration, which depends upon the fact that rays falling upon the periph- Fig. 27. Illustrating astigmatism. ery of the lens are more refracted, and Brought to a focus earlier, than those which fall nearer to the prin- cipal point. This effect is, however, to a certain extent, neutralized by the curvature and index of refraction of the peripheral portion being less than is the case with the more central portion of the lens. The iris, too, forms a diaphragm which prevents light from falling on the periphery of the lens, and this is of special impor- tance in the case of the more divergent rays which reach the eye from near objects ; as we have seen, the iris contracts when near objects are viewed. Chromatic aberration is caused by dispersion due to the unequal refrangibility of rays of different wave-length ; those of 218 THE SPECIAL SENSES. shorter wave-length, e. g., the violet rays, are more refracted than those of greater wave-length, e. g., the red rays. Under ordinary circumstances, neither spheric nor chromatic aberration interferes with distinct vision. Color Vision. White light on analysis is found to consist of a mixture of rays of varying wave-length. When light falls upon the retina, the resulting sensa- tion varies with the wave-length of its component rays. According to the Young-Helmholtz theory, there are in the retina three substances, all of which are to a certain extent acted upon by any ray of light, whatever its wave- length ; but the readiness with which each substance reacts to diiferent rays varies. For instance, rays the wave-length of which is in the neighborhood of 0.000675 mm. aifect one substance more than the other two, and give rise to a sensation of red ; rays of about 0.000525 mm. wave-length produce the greatest effect on the second substance, and give rise to a sensation of green ; rays of 0.000430 mm. wave-length cause the greatest change in the third substance, and result in a sensation of violet. A sensation of yellow results from the simultaneous production of red and green sensations in certain proportion ; a sensation of orange is produced by slightly increasing the red sensation and lessening the green. Thus a host of different color sensations may be produced by the fusion of the primary sensa- tions in varying proportions. The sensation of white results from the fusion of all three primary sensations in definite proportions; this is what occurs when ordi- nary daylight falls upon the retina, but to produce this result it is not necessary that all the rays of the visible spectrum should enter the eye. Any two rays which between them excite all three color sensations in the right proportion, will give rise to a sensation of white ; for instance, a ray of the wave-length 0.000564 mm., COLOR VISION. 219 when it alone roaches the retina, causes a sensation of greenish-yellow l>y acting about equally on the visual substances concerned in red and green sensations ; if to this ray be added one of the wave-length 0.000433 nun. which by itself causes a sensation of violet by acting to about the same extent on the third substance, a sensation of white will result. Every ray situated toward one end of the spectrum has its complementary ray, found toward the opposite end, combination with which gives rise to a sensation of white. Rays near the middle of the spectrum which give rise to a sensation of green require to be combined with rays from both ends of the spectrum in order to cause a sensation of white. A sensation of black is caused by the absence of any stimulus. There are certain facts in color vision which cannot be satisfactorily explained on this theory, and in consequence several others have been advanced ; to all these there are, however, objections. According to the theory of Hering, there are six pri- mary color sensations, depending on anabolic or katabo- lic changes in three visual substances. In one of these substances katabolic changes may be excited by the rays of any part of the visible spectrum, and a sensation of white results; in the absence of light, anabolic changes predominate, and give rise to a sensation of blackness. Another substance is caused to break down by the rays of greater wave-length, giving rise to a sensation of red, while it is rapidly built up tinder the influence of the rays of medium length, with a resulting sensation of green. The third substance suffers katabolic changes under the influence of rays which thus produce sensa- tions of yellow, and undergoes constructive changes when exposed to the rays of shorter wave-length which thus produce a sensation of blue. When rays of all wave- lengths fall upon the retina, the metabolism of only the 220 THE SPECIAL SENSES. f i white-black " substance is affected ; the other two sub- stances remain in equilibrium. Orange sensations result from the simultaneous break-down of the red-green and yellow-blue substances, violet sensations from the simul- taneous building up of yellow-blue and break-down of red-green substance. Color-blindness appears to depend upon the exist- ence in the retina of the individual of but two visual substances. As a rule, those who are color-blind fail to distinguish between red and green ; this may be explained on the Young-Helmholtz theory, by supposing either the " red substance " or the " green substance " to be absent from the retina ; on Hering's theory by the absence of the " red-green substance. 77 When light falls upon the retina, it affects both the pigment epithelial cells of the outer layer, and the rods and cones ; visual sensation depends upon stimulation of the latter elements, and it results whatever be the nature of the stimulus. Pressure when applied to the eyeball affords mechanical stimulation of the retina, and a visual sensation follows. If in the dark sudden pres- sure be applied to the nasal side of the eyeball, the resulting sensation resembles that produced by a flash of light occurring on the opposite side of the visual axis, and to the subject it appears to be the consequence of such an event taking place outside the body. If the experiment is made in the light, the impression of a dim blue disc is given. The retina may also be stimulated electrically, with the production of visual sensations. Different parts of the retina are not equally sensi- tive to light, and a variation in the quality of light affects them differently. We can most accurately dis- tinguish between closely adjacent points when their im- ages fall upon the yellow spot, or macula lutea; in this respect acuteness of vision gradually diminishes as the THE RETINA. 001 periphery of the retina is approached. The same is true in respect to color vision ; the extreme periphery of the retina is color-blind. On the other hand, the macula lutea is not the part of the retina that is most sen- sitive to dim illumination. Rods are absent from the macula lutea, cones only being present ; as the periph- ery is approached, the number of rods increases, the number of cones diminishes, and before the border is reached the cones disappear. It seems probable that the cones are chiefly concerned in acute vision and in color vision, while the rods minister to the perception of luminosity without, perhaps, affording a means for the appreciation of color. The rods contain a substance, visual purple, which is absent from the cones, and it may be owing to the presence of this substance that the rods are most readily stimulated by rays of light of short wave-length, for it is by these that visual purple is most rapidly bleached. Visual purple is rendered colorless by exposure to light, but during the process an intermediate substance, a pigment called visual yellow, is formed. On exclusion of light, visual purple again slowly appears in the rods, but not in the absence of the layer of pigment epithelium, which evidently ex- erts an influence on its formation. The optic disc, that part of the retina where the fibers of the optic nerve leave the eye, is devoid of rods and cones, and is blind. Of this defect we are unconscious, until it is pointed out to us that, with but one eye open, the image of an object which falls upon this area is unseen. The image of an object never falls simultaneously upon the blind spots of both eyes. When light falls upon the retina, the effect on con- sciousness varies with the intensity of the light, with the duration of the exposure, with the size of the retinal area illuminated, and with the condition of the retina. 222 THE SPECIAL SENSES. The excitability of the retina is reduced by exposure to light ; it becomes fatigued, and visual sensations are less intense ; this probably also depends upon fatigue of the central visual mechanism. In order to excite visual sensation, light must be of certain intensity, this intensity varying with the part of the retina upon which it falls. We cannot distinguish between the different intensity of two lights, unless one be brighter than the other by one-hundredth part, and, consequently, the brighter the lights, the more difficult it is to appreciate their different value. A flash of light may appear less bright than a somewhat weaker light that lasts longer. A small light may appear less luminous than a larger one which is in reality of less intensity. Since the sen- sation outlasts the stimulus by a short period, a rapid succession of stimuli of very short duration gives rise to a continuous sensation. The survival of a visual sensation after the stimulus has ceased is known as a positive after=image. Negative after-images are fatigue phenomena ; for instance, if after fixing the eye for a few moments upon a red object it is turned to a white surface, there appears a greenish image of this object ; this is explained by assuming that in the area of the retina upon which the rays from the red object fell the visual substance upon which the red rays take most effect has been used up or rendered inexcitable to' a greater extent than either the green or the violet per- ceiving elements ; consequently, when the whole retina is subsequently exposed to white light, which excites all three primary sensations, the two which have not been fatigued will predominate, and we experience a sensation of greenish-blue. The color of a negative after-image is always complementary to that of its original. When two objects the colors of which are comple- mentary to one another are placed in contact, the color EXTRINSIC MUSCLES. 223 of each, more particularly along the adjacent edges, appears to IK- intensified. This may be explained by assuming that stimulation of any retinal area causes Hmnltaneous changes to occur in neighboring areas; by some, these induced changes are supposed to be similar to those occurring in the stimulated area; by others, they are considered to be of an opposite nature. A white object on a dark field looks larger than it does on a white field ; this is called irradiation, and depends upon the failure of the eye to bring all the rays to a proper focus, the size of the retinal image being slightly increased through the formation of diffu- sion circles instead of points. To each eyeball are attached three pairs of muscles, the two members of each pair being antagonistic to eaeli other. The movements of the two eyes are asso- ciated in such a way that their visual axes are kept parallel to each other when directed toward distant ob- jects. During accommodation the visual axes con- verge. In what is known as the primary position of the eyes, the visual axes are parallel, and, the head being erect, are directed toward a distant point at their own level. The center of rotation of the eyeball lies . 13.54 mm. behind the anterior surface of the cornea on the optic axis. The optic axis docs not exactly corre- spond to the visual axis, but cuts the retina on the inner side of, and slightly above, the macula lutea. Dotation of the eyes from the primary position to the right is caused by contraction of the right external rec- I tus muscle and left internal rectus ; horizontal converg- ence is caused by contraction of the two internal recti. Upward rotation is brought about by the simultaneous contraction of the superior recti and inferior oblique I muscles ; downward rotation, by the simultaneous con- traction of the inferior recti and superior oblique 224 THE SPECIAL SENSES. muscles. More than two muscles must act upon each eye in order to bring about oblique upward or down- ward movement; this is accompanied by more or less wheel movement, or rotation on the optic axis. The voluntary contraction of one muscle is accompanied by inhibition of its antagonist. As long as, through the associated movements of the two eyes, the visual axes are directed toward the same point, an image of this point will fall upon the macula lutea of each eye, and will give rise to a single sensa- tion. The maculae luteae are not the only areas of the retinae simultaneous stimulation of which gives rise to a single sensation ; each retinal area, with the exception of those near the nasal edges of the retinae, has a corre= sponding area in the opposite retina. When the two retinal images of an object fall upon corresponding or identical areas, the object appears single ; when the im- ages fall upon areas which do not correspond, the object appears to be double. Slight asymmetry in the position of images falling upon peripheral areas of the retinae does not so readily cause diplopia (double vision) as does the asymmetric arrangement of images on the maculae luteae. We first learn to interpret our visual sensations through comparison with sensations provoked through other channels. Our visual judgment of the size of an object is formed by comparing the sensation which it excites with those produced by other objects with which we are familiar, and if the object be large, by the angle through which the eye must be moved in order to cover its surface. The movements of the eye are estimated partly through the intensity of the effort expended in causing the contraction of the ocular muscles, and partly through the muscular sensation resulting from their contraction. The distance of an object may be much HEARING. 225 more accurately determined by using both eyes than by ii.-ing only one ; in the case of a near object, the degrees of accommodation and of convergence are important aids to judgment of distance. It is difficult to form an idea of the shape of an unfamiliar solid object by m rans of one eye, but since, when both eyes are used, it is viewed from two points, the retinal images differ slightly, and we are enabled to appreciate its depth. HEARING. Sound-waves that enter the external auditory meatus cause vibration of the tympanic membrane, and are transmitted through the chain of ossicles, which vibrate as a whole, to the perilymph of the internal ear. The vibration of the perilymph is transmitted to the endo- lymph of the membranous labyrinth, and in some way takes effect on the terminations of the nerve-fibers of the auditory branch of the eighth cranial nerve. Pressure on the two sides of the tympanic membrane is equalized by the communication which exists between the middle ear and the pharynx by means of the Eustachian tube ; uneven pressure would interfere with the vibration of the membrane. The vibrations which give rise to a musical sound are rhythmic ; a noise results from arhythmic vibrations. Sounds vary in intensity, or loudncss, in pitch, and in quality. Intensity depends upon the amplitude of the vibration ; pitch, upon the rate of vibration. A single sound emitted by a musical instrument is usually not simple, but compound, and this depends upon the ad- mixture of overtones with the fundamental tone. The same note produced by different instruments differs in quality, owing to variation in the number and intensity of accompanying overtones. When two sounds occur 15 226 THE SPECIAL SENSES. simultaneously, the vibrations upon which they depend do not reach the ear separately, but are fused, and form a compound wave ; nevertheless, we are capable of analyzing a complex sound. The ear probably contains a system of resonators, which, like the strings of a harp or other instrument, are caused to vibrate when sub- jected to the influence of sound-waves, each resonator responding to a tone of definite pitch. The basilar membrane of the cochlea, with its thousands of radial fibers of different lengths, perhaps serves as a system of resonators in the analysis of sounds, the vibration of each fiber being communicated, through the organ of Corti, to a particular nerve-fiber of the auditory nerve. Our aural judgments are much less exact than our visual judgments, and even by the use of both ears it. is difficult to determine whence a sound reaches us. This is especially true of sounds which emanate from a point in the median vertical plane. It is less difficult to locate sounds whose source of origin is lateral to the head, for, in this case, the intensity, and perhaps the quality of the sound, as it reaches the two ears varies. SMELL. The true olfactory mucous membrane is very limited in extent, and is confined to that portion of the nasal mucous membrane which covers the medial surface of the superior turbinated bone, and the corresponding area of the septum. Here are situated cells which give off the fibers which constitute the olfactory nerve, and end in the olfactory bulb. The air as it is inspired does not pass over this area, but gases and particles of odorous substances which enter the nose reach the olfactory mucous membrane by diffusion. Odorous substances may excite a sensation of smell when intro- QUESTIONS. 227 duced into the nostrils in solution in normal saline, but not in distilled water, which probably injures the olfac- tory cells. TASTE. Not the whole of the oral mucous membrane is sen- sitive to sapid substances ; the taste organs are confined to the back, the tip, and the edges of the tongue, and to the palate and the pillars of the fauces ; their distri- bution, however, varies considerably in different indi- viduals. The taste-buds, which are found on the sides of the circumvallate papilla?, and on the fungi form papilla?, are supposed to serve as end-organs of taste, but probably there are others. The back of the tongue is most sensitive to bitter substances ; the tip and sides, to sweet substances. The other tastes are acid and salt ; flavors are appreciated by the olfactory cells, and are not true tastes. Nerve-fibers which are concerned in taste are supplied to the back of the tongue by the glossopharyngeal nerve, and to the anterior two-thirds by the lingual, but the path by which these fibers enter the medulla is uncertain. QUESTIONS FOR CHAPTER X. Can parallel and divergent rays of light which happen to fall upon the eye be simultaneously focused on the retina? During accommodation, where are parallel rays brought to a focus ? What sort of lens must be used for the correction of myopia? What sort of lens is needed after removal of the lens from the eye? To what extent is vision interfered with by the application of atropin ? How do we know that light does not stimulate the fibers of the optic nerve ? 228 THE SPECIAL SENSES. Why, when accommodation is relaxed, does a near object appear to be double ? Why is vi'sion indistinct when the eye is immersed in water ? Why do hypermetropic eves tire more readily than myopic eyes? What effect on the eye has division of the cervical sympathetic nerve ? When the internal rectus muscle of one eye is paralyzed, the eyeball will be rotated outward, owing to the unresisted tonic contraction of the external rectus. Why, under these circum- stances, should turning the opposite eye outward cause the injured eye to return to the primary position ? Why does the application of pressure to one side of the eyeball cause diplopia ? If sound-waves reach the retina, why do they not result in visual sensation ? INDEX. ABDUCENS, 198 Aberration, 217 Absorption of cane-sugar, 80 of egg-albumen, 92 of fat, 94 of native proteids, 83, 95 of peptones, 90, 91 of starch, 80 of water, 95 Accelerator center, 47, 49 Accessory nerve, 71, 171, 200 Accommodation, 196, 213, 214, 223 Achroodextrin, 79 Acid albumin, 84 amido-, 85, 111, 112 benzoic, 112 butyric, 81 carbamic, 110 fatty, 93, 94 hippuric, 112, 128 hydrochloric, 79, 80, 84, 87 lactic, 81, 94, 106, 110 phosphocarnic, 69, 158 phosphoric, 128 sulphuric, 123, 128 uric, 111,127, 128, 132 Acromegaly, 116 Action current, 156 Addison's disease, 116 Adrenal bodies, 116 extract, 149 Afferent nerve-fibers, 164 After-image, 222 Agglutinating property of blood, 34 Albumin, 14, 159 coagulation temperature of, 21 Albuminate, 84 Albuminoids, 89 Albumoses, 14, 25, 85 Alcohol, 51,81,92 Alexia, 204 Alkali albumin, 84, 92 Alkalinity of blood, 20, 123 Amido-acids, 85, 95, 111, 112 Ammonia, 21,48, 123 Ammonium salts, 110, 111 Amylopsin, 79 Anabolism, 17 Anaerobic contraction, 69 Anemia, 124 ' Animal heat, 141 Antagonistic muscles, inhibi- tion of, 166, 193, 224 Anterolateral ascending tract, 178, 205 Aorta, 44, 45 Apesthesia, 204 Aphasia, 204, 205 Apnea, 74 Aqueous humor, 210 Arcuate fibers, 174 Areas, association, 204 auditory, 204 motor cortical, 192, 202 retinal, 224 229 230 INDEX. Areas, sensory cortical, 188, 202 visual, 185, 202 Arterialization of blood, 67 Arteries, blood-flow in, 56 blood-pressure in, 46, 48, 50, 51 Arterioles, 46 direct stimulation of, 116 innervation of, 52 Asphyxia, 74 Aspiration, thoracic, 58, 59 Assimilation, 113 Association areas, 204 fibers, 205 Astigmatism, 215 Atropin, 98, 137, 139, 215 Auditory area, 204 nerve, 182, 226 Auerbach's plexus, 101, 172 Augmentor center, 47, 49, 50 nerve, course of, 49 Autonomic nerve-fibers, 171 BACTERIA, 33, 78, 81, 83, 87, 95 Bacteriolysins, 34 Baths, 144 Benzoic acid, 112 Bile, 87, 94, 95 pigments, 95 salts, 94, 95 Biological test for source of suspected blood, 35 Bioplasm, 11 Bladder, gall-, 100 urinary, 134 Blindness, 188, 202 Blood, 19 adaptation of, 33 agglutinating property of, 34 alkalinity of, 20, 123 biological test for, 35 circulation of, 39 coagulation of, 21 color of, 32 defibrinated, 22, 25, 26 functions of, 19 reaction of, 21, 123 Blood, salted, 22 venosity of, 48 Blood-cells, 19 red, 19,31 functions of, 20 white, 19,24,32, 112 functions of, 33 Blood-flow, arterial, 56 capillary, 45, 56 Blood-plasma, 20 dextrose in, 108 Blood-platelets, 19, 32 Blood-pressure, arterial, 46, 48, 50,51 influence of respiration on, 58 intracapillary, 36 intravenous negative, 59 respiratory variation of, 59 regulation of, 48, 51, 52 Blood-supply, coronary, 50 during activity, 56, 69 Brachium conjunctivum, 178, 206 Bundle, Meynert's, retroflexed, 188 posterior longitudinal, 180, 184, 185, 198 solitary, 180 Burdaclvs tract, 174 Butyric acid, 81 CALCIUM, 25, 123 Calorie, 122 Cane-sugar, 13, 16 digestion of, 80 in urine, 80 Capillaries, blood-flow in, 45, 56 blood-pressure in, 36, 131 exchange of gases in, 68 permeability of, 35 renal, 129 Capsule, internal, 192, 196, 203 Carbamic acid, 110 Carbohydrates, 13 bacterial decomposition of, 81,87 digestion of, 77, 83 INDEX. 231 Carbohydrates, potential en- cr<;y of, 122 Carbon dioxid, 69 elimination of, 68, 127 in blood, 68 equilibrium, 118 monoxid, 32 hemoglobin, 32 Cardinal points, 212 Cardio-accelerator center, 47, 49 Cardio-augmentor center, 47, 49 Cardio-inhibitory center, 47- 51, 116 Casein, 89, 138 Caseinogen, 89, 138 Cellulose, 16, 78, 81, 88, 121 Cerebellum, 174, 178, 190, 205 Cerebral hemispheres, removal of, 194, 203 Cerebrum, 202 Chemotropism, 33 Chloroform, 48, 51, 55 Cholesterin, 17, 31, 32, 95, 137 Cholic acid, 95 Chorda tympani, 55, 56, 97 Chromatic aberration, 217 Chyle, 105 Ciliary muscle, 211, 213, 214 nerves, 215 Clarke's column, 178, 193 Coal-gas poisoning, 32 Cochlea, 226 Cochlear nerve, 182 Cold, influence on circulation, 51, 130, 142 on metabolism, 122, 142 on renal secretion, 130 on respiration, 73, 145 on vasoconstrictor center, 51, 130, 142 Cold-blooded animals, 141 Cold-nerves, 140 Collagen, 90 Collaterals, 157, 164 Color-blindness, 219 Color-vision, 218-220 Colostrum, 138 Complement, 34 Conductivity of muscle, 148 of nerve, 152, 157, 158 Cones, retinal, 185, 221 Conjugated sulphates, 87, 128 Constipation, 88 Constrictor center. See Vaso- constrictor center. Contraction, 148 isometric, 150 isotonic, 150 law of, 152 Pfliiger's, 152 maximal, 149 tetanic, 151 voluntary, 150 Contrast, 223 Convergence, 214, 223 Coordination, 203, 204, 206 Cornea, 210 Coronary blood-supply, 50 Corpora geniculata, 182, 185 quadrigemina, 174, 178, ivJ. 190, 198, 202 Corpus callosum, 205 marnillare, 188 restiforme, 174,178 Cortex cerebri, association areas of, 204 inhibition by, 193 motor areas of, 192, 202 sensory areas of, 188, 202 Coughing, 73 Cranial nerves, eighth, 182, 188, 226 eleventh, 71, 171,200 fifth, 48, 73, 96, 99, 184, 196 first, 188 fourth, 196 ninth, 49, 96,99, 171, 180, 182, 198, 227 second, 185 seventh, 56, 171,198 sixth, 198 tenth, 43, 47, 48, 72, 74, 99, 171, 180, 200 232 INDEX. Cranial nerves, third, 171, 196, 202, 214 twelfth, 200 Creatin, 111, 112, 128, 158 Creatinin, 111, 128 Cretinism, 115 Cristse ampullares, 207 Curari, 145, 148 Current, action, 156 constant, 151, 167 demarcation, 155 induced, 151, 167 Cycle, cardiac, 40, 42 DEAFNESS, 204 Decussation, pyramidal, 193 sensory, 174 Defecation, 102 Degeneration of nerve-fibers, 156 of spinal nerve-roots, 176, 178 reaction of, 155, 167 Deglutition, 49, 98 influence of, on respiration, 73,99 Dehydrolysis, 18, 106 Demarcation current, 155 Depressor nerve, 51, 116 Dextrin, 16, 17 Dextrose, 13, 15, 18 formation of, from proteid, 107, 109, 119 metabolism of, 105 Diabetes mellitus, 107, 108 pancreatic, 108 Diapedesis, 33 Diaphragm, 63 Dicrotic pulse, 58 Diet, carbohydrate, 67, 120 fatty, 122 ideal, 121 influence of, on respiratory quotient, 67 milk, 88, 124, 138 mixed, 120 vegetable, 112, 123, 129 Digestion, 77 of albuminoids, 90 of carbohydrates, 77, 82 of fat, 93 of nucleoproteids, 88 of proteids, 83,91 Diplopia, 224 Diuretics, 133 Dyspnea, 71, 74 cardiac, 72 hemorrhagic, 71 influence on cardio-inhibi- tory center, 48 on vasoconstrictor center, 51 CO 2 -, 72 O-, 72 EAR, 225 Efferent nerve-fibers, 164 Egg-albumen, 92 Elasticity of aorta, 39 of lungs, 65 of muscle, 148 Elastin, 90 Electrolytes, 29 Electrotonus, 153 Emmetropia, 216 Emotions, influence of, on heart, 49 on movements of stomach, 100 on respiration, 73 on secretion of milk, 138 on secretion of saliva, 97 Emulsification, 93 Enamel, destruction of, 81 Energy, 117, 121, 141 Enzymes, characteristics of, 23 Epinephrin, 117 Equilibrium, 184, 192, 205, 207 carbon, 118 nitrogenous, 118, 120 Erythrocytes, 19, 31 functions of, 20 Erythrodextrin, 79 Esophagus, 99 INDEX. 233 Evaporation of sweat, 135, 143 Excretion, 127 Exercise, influence of, on heart- beat, 50 on metabolism, 106, 113, 122, 128 on respiration, 72 on respiratory quotient, 67 Extracts, adrenal, 117, 149 Eye, reduced, 211 muscles of, 196, 198, 223, 224 FACIAL nerve, 56, 171, 198 Fallopian tubes, 170 Fat, 16 digestion of, 93 in milk, 138 metabolism of, 107, 108, 118 potential energy of, 122 Fatigue of muscle, 149 of nerve, 158 of retina, 222 Fatty acids, 93,94 diet, 122 Feces, 87, 102 Ferments, characteristics of, 23 Fever, 141 Fibrin, 22 Fibrin-ferment, 24, 25, 32 Fibrinogen, 22 coagulation temperature of, 21 solubility of, 14 Fillet, 174, 180, 184 descending fibers of, 198, 200 lateral, 182 Filtration of urine, 131, 133 Fornix, 188 Freezing- point, depression of, 29 Fruit-sugar, 15 GANGLION, Gasserian, 184, 215 posterior root, 156, 162 spiral, 182 Ganglion, superior cervical sympathetic, 52, 56, 97, 137, 215 sympathetic, 168 Gastric juice, 84 secretion of, 99 Gelatin, 90, 121 Geniculate bodies, 182,185 Globulicidal action, 26 Glossopharyngeal nerve, 49, 73, 99, 182, 198, 227 Glycerin, 93 Glycocol, 95, 111, 113 Glycogen, 16, 105, 112, 118 Glycoses, 16 Glycosuria, 107 Goll's tract, 174 Gowers' tract, 178 Gram-molecule, 29 Grape-sugar, 13, 15 HEARING, 225 Heart, 39 acceleration of, 47, 49 beat, 40 contraction-volume of, 47 cycle, 40, 42 dilatation of, 47, 50 during starvation, 119 frequency, 41, 43 influence of blood on, 50 of blood-pressure on, 50 inhibition of, 48 innervation of, 43, 47, 48 output of, 47, 50 residual blood in, 47 sounds, 43, 44 valves of, 39-43, 58 Heat, animal, 139 influence of, on circulation, 141 loss of, 139, 141 production, 139 Heat-nerves, 140, 172 Hematin, 31 Hemispheres, cerebral, removal of, 202, 203 234 INDEX. Hemochromogen, 31 Hemoglobin, 31, 68, 95 Hemolysins, 34 Hemophilia, 21 Hibernation, 145 Hippocampus, 188 Hippuric acid, 112, 128 Hydremic plethora, 133 Hydrochloric acid, 79, 84, 87 action of, on carbohy- drates, 80 Hydrolysis, 18, 78, 84, 93 Hypermetropia, 216 Hyperpnea, 19 Hypoglossal nerve, 200 IMMUNE body, 34 Indol, 87 Induced current, 151 Inhibition, cortical, 193 of antagonistic muscles, 166, 193, 224 of the heart, 48 Inorganic salts in diet, 122 uses of, 123 Insensible perspiration, 135 Internal capsule, 174, 192 secretion, 108, 114 Interpleural pressure, 64 Intestinal epithelium, 80, 81, 92,94 juice, 80, 81 movements, 101 Intracapillary pressure, 36 Invertin, 80 lodin, 79 lodothyrin, 115 Ions, 29 Iron in food, 124 in hemoglobin, 31, 96 in milk, 138 Irradiation, 223 Irritability, 12 influence of constant current on, 151 myotatic, 166 Isomaltose, 79 Isometric contraction of mus- cle, 150 Isotonic contraction of muscle, 150 solutions, 29 KATABOLISM, 17 Keratin, 90 Kidneys, excretion of sugar by, 107 removal of, 110 secretion by, 129 Knee-jerk, 166 Kreatin, 111, 112, 128, 158 Kreatinin, 111, 128 LACRIMAL glands, innervation of, 171 Lactation, 137 Lactic acid, 81, 94, 106, 110 Lactose, 16, 80, 138 Language, 204 Laryngeal nerves, 73, 99 Lecithin, 17,31,32,95 Lemniscus, 174, 180, 184, 198, 200 Lens, 210 Leucin, 85, 111 Leukemia, 112 Leukocytes, 19, 25, 32, 112 Levulose, 15, 80, 108 Light-reflex, 202 Lingual nerve, 227 Liver, capillaries of, 35 disease of, 111 formation of conjugated sul- phates by, 87 of urea by, 110 glycogenic function of, 105 removal of, 110 Locomotor ataxia, 204 Lungs, collapse of, 58, 65, 72 function of, 63 inflation of, 58, 64, 72 influence of, on coagulation, 25 ixnr.x. 235 Lungs, ventilation of, 63 Lymph, 19, 35, 51) factors which control flow of, 36 Lymphatic circulation, 105 MACULA acustica, 207 lutea, 185, 193, 220 Maltase, 23 Maltose, 16, 78 Malt-sugar, 16, 78 Mastication, 77, 96 muscles of, 198 Metabolism, 17 abnormal, 108, 115, 116 acids formed in, 122, 128 carbohydrate, 105 during starvation, 118 muscular, 106, 108, 114, 142 of fat, 108 proteid, 109, 119 Methemoglobin, 32 Micturition, 134 Milk, composition of, 138 curdling of, 89 diet, 88, 124, 138 secretion of, 137 Milk-sugar, 15, 80, 138 Motor cortical areas, 192 Mucin, 95 Muscle, 147 cardiac, 147, 149 ciliary, 211 composition of, 158 contraction of, 148, 150 elasticity of, 148 extensibility of, 148 injury to, 155 irritability of, 147, 151 isometric contraction of, 150 isotonic contraction of, 150 latent period of, 148 plain, 147 Muscles, inspiratory, 63, 70 of eyeball, 196, 198, 223 of mastication, 198 Muscle-sense, 173, 176, 204 Muscle-spindles, 173 Muscular metabolism, 106, 108, 114, 142 tone, 117, 147,167 exaggeration of, 196 work, 122 influence of, on heart-beat, 50 on metabolism, 106 on respiration, 72 on respiratory quotient, 67 Myoglobulin, 159 Myopia, 215 Myosin, 158 Myosinogen, 159 Myotatic irritability, 166 Myxedema, 115 NEGATIVE variation, 156 Nerve-fibers, 156 Nerve-impulse, 148 Nerve-roots, 160 division of, 204 Nerves, afferent, 164, 172 afferent visceral, 173 cold-, 142, 172 conductivity of, 152, 158 cutaneous, 152, 157 efferent, 164.' heat-, 142, 172 muscle-sense, 173 pain, 172 post-ganglionic, 49, 168 pre-ganglionic, 49, 168 pressure, 172 regeneration of, 156 sympathetic, 167, 174 Nervous system, 160 during starvation, 119 Neurone, 156 Nitrogenous equilibrium, 118, 120 Normal salt solution, 26 Nuclein, 13,88, 111 Nucleo-albumin, 88, 138 236 INDEX. Nucleoproteids, 12, 21, 25, 88, 111 Nucleus alae cinerese, 180 ambiguus, 198 cochlear, 182 cuneatus, 174 Deiters', 206 gracilis, 174 habenuke, 188 vestibular, 182, 190, 206, 207 Nutrition, 117 OCCIPITAL lobe, 188 Oculomotor nerve, 196 (Esophagus, 97. See Esoph- agus. Olein, 17, 109, 138 Olfactory nerve, 188, 226 Olive, inferior, 190 superior, 182 Optic disc, 221 nerve, 184 thalamus, 168, 188, 206 Osmosis, 26, 131 Oxalic acid, 112 Oxygen in blood, 67 Oxyhemoglobin, 68, 69, 70 PAIN, 180 referred, 168 Palmitin, 17, 138 Pancreas, disease of, 108 removal of, 108 Pancreatic diabetes, 108 digestion of carbohydrates, 79 of fat, 93 of proteids, 84 Paralysis, 106, 203 Paralytic secretion, 98 Paramyosinogen, 159 Pepsin, 84 Peptones, 14, 84, 90, 100 Peripheral resistance, 45, 50, 51 Peristalsis, 100, 101, 171 Permeability of capillary wall, 35 of membranes, 27, 30 of renal epithelium, 131, 133 Pfliiger's law of contraction, 152 Phagocytosis, 33 Phenol, 87 Phosphates in urine, 128, 129 Phosphocarnic acid, 70, 158 Phosphoric acid, 128 Phrenic nerve, 71 Physiology, definition of, 11 Physostigmin, 215 Pialyn, 93 Pigments, bile, 95 urinary, 128 Pilocarpin, 98, 137 Pilomo tor nerve-fibers, 171 Pituitary body, 116 Plain muscle, 147 Plasma, 20 dextrose in ,J.08 Pneumogastric nerve, 43, 47, 48,72,74,99, 171,180,200 Portal circulation, 105 vein, dilatation of, 46 innervation of, 55 Posterior longitudinal bundle, 180, 184, 185, 190, 198 Post-ganglionic nerve-fibers, 49, 168 Precipitins, 35 Pre-ganglionic nerve-fibers, 49, 168 Presbyopia, 206 Pressure, arterial, 45, 48 atmospheric, 63 blood, 45 intravenous negative, 59 respiratory variation of, 59 interpleural, 64 intracapillary, 36 intrapulmonary, 64 negative, 64 osmotic, 26, 36, 131 partial, 67 Pressure-sense, 176 INDKX. 237 Progression, 205 Proteid metabolism, 109, 119 Proteids, absorption of, 83, 90, 91, 95 bacterial decomposition of, 87 characteristics of, 13 composition of, 13 digestion of, 83 formation of dextrose from, 107, 108, 118 of fat from, 109 of glycogen from, 107 in urine, 133 osmotic pressure of, 131 solubility of, 14, 123 tissue, 113 Proteoses, 14, 84, 90 Protoplasm, 11 assimilation of, 12 conductivity of, 12 contractility of, 12 irritability of, 12 nutrition of, 12 reproduction of, 12 Pseudo-nuclein, 88 Pseudo-reflex, 157 Ptyalin, 78 Pulse, 56 dicrotic, 58 form of, 57 variation of, 57 venous, 59 Puncture diabetes, 107 Pupil, constriction of, 196, 214 dilatation of, 215 reflexes of, 202 Pupillo-dilator fibers, 171 Pyramidal cells, 192 decussaj,ion, 193 tracts, 192, 193 Pyramids, decussation of, 193 section of, 196 KAMI communicantes, 167 Reaction, influence of, on pep- sin, 85 Reaction, influence of, on ptyalin, 79 on rennin, 89 of blood-plasma, 21, 123 of degeneration, 155, 167 of sweat, 135 of urine, 129, 132 Recurrent sensibility, 165 Red blood-cells, 19, 31 functions of, 20 nucleus, 192, 206 Reduced eye, 211 Referred pain, 168 Reflex action, 48 arc, 164 centers, 167 pseudo-, 157 Reflexes, 165 special, 167 tendon, 166 Refraction, 210 Regeneration of nerve-fibers, 156 Renal nerves, 130 secretion, 129 tubules, 132 vessels, 129 Rennin, 89 Residual air, 66 blood, 47 Respiration, external, 66 influence of blood-pressure on, 58, 65 of exercise on, 72 of venous blood on, 71 internal, 68 types of, 65 Respiratory capacity, 66 center, 70 muscles, 63 3uotient, 66 lythm, 70 surface, 66 volumes, 65 Restiform body, 174, 178 Retina, 210, 212, 220 Retinal areas, 224 cones, 185, 221 238 INDEX. Retinal ganglion-cells, 185 rods, 185, 221 Rhythm, cardiac, 143 intestinal, 101 of ureters, 134 respiratory, 70 Rigor mortis, 158 Rods of retina, 185, 221 SACRAL nerves, 171 Saline diuretics, 133 Saliva, 78, 83, 96 secretion of, 96, 98 Salivary glands, 96 innervatioii of , 171 Sebaceous glands, 137 Secretion, internal, 108, 114 of bile, 114 of gastric juice, 99 of milk, 137 of pancreatic juice, 100 of saliva, 96, 98 of sweat, 136 of urine, 129 paralytic, 98 Secretory nerves, gastric, 99 pancreatic, 100 salivary, 96, 97 sweat, 136 Semicircular canals, 205, 207 Serum, 21 globulicidal action of, 26 Serum-albumin, 14 coagulation temperature of, 21 solubility of, 14 Serum-globulin, 14 coagulation temperature of, 21 solubility of, 14 Shivering, 142 Short sight, 215 Skatol, 87 Smell, 226 Sneezing, 73 Soap, 93 Solubility of proteids, 14, 123 Sound, 225 Special senses, 210 Spectra, 31 Speech center, 204, 205 Spheric aberration, 217 Spinal animal, 165 cord, 160 division of, 55, 71, 131 nerve-roots, 160 Spleen, innervation of, 170 Starch, 13, 16, 78 Starvation, 67, 107, 108, 118, 120, 121 Steapsin, 93 Stearin, 17, 93, 109, 138 Stereochemical formulse, 15 Stimulation, unipolar, law of, 154 Stimuli, 12, 147, 151 minimal, 149 Stomach, innervation of, 100, 170 Striae acusticae, 182 Strychnin, 137 Substantia gelatinosa, 184 Succus entericus, 80, 81, 87 Sulphuric acid, 123, 128 Superior cervical sympathetic ganglion, 52, 56, 97, 137, 215 Sweat, 134 Sweat-gland, innervation of, 171 Sympathetic ganglia, 49, 52, 168 nerve-fibers, 167-171 system, 167 TABES, 204 Taste, 227 Taurin, 95 Temperature, axillary, 144 coagulation, 21, 159 influence on cardio-augmen- tor center, 50 on respiration, 72 regulation of, 141 Temperature-sense, 180 239 Test, biological, for suspected blood, :i") Tetanus, 151 Thalamus, optic, 174, 188, 206 Thermogenic centers, 143 Thyroid, 115 influence of, on circulation, 115 Thyroiodin, 115 Tissue proteid, 113 Tone, exaggeration of, 116 of cardio-augmentor center, 49 of cardio-inhibitory center, 48 of plain muscle, 147 of skeletal muscle, 117, 166 of vasoconstrictor center, 51 vascular, 52, 55. 116 Tracts, ariterolateral ascend- ing, 178, 204 ascending spinal, 173 descending spinal, 176, 190 direct cerebellar, 178, 205 dorsolateral, 174, 205 dorsomedian, 174, 205 pyramidal, 176, 192, 193 Transfusion, 25 Trapezium, 182 Trochlear nerve, 196 Trypsin, 85 Tympanum, 225 Tyrosin, 85, 111 UNCUS, 188 Unipolar stimulation, law of, 154 Urari, 145, 148 Urea, 122 amount of, 127 excretion of, 132, 135 formation of, 109, 111 Uremia, 135 Ureter, 133 Uric acid, 111, 128 amount of, 127 excretion of, 132 Urine, albumin in, 133 amount of, 129 cane-sugar in, 80 composition of, 127 concentration of, 132 dextrose in, 107 filtration of, 131, 133 maltose in, 80 peptones in, 92 reaction of, 129, 132 specific gravity of, 129 urea in, 110 Urobilin, 96 Uterus, innervation of, 170 VAGUS nerve, 43, 47, 48, 72, 74, 99, 117, 171, 180, 200 Valves, cardiac, 39, 41, 43, 44, 58 of veins, 59 Vasoconstrictor center, 51, 107 influence of afferent nerves on, 51 of blood on, 51 of blood-pressure on, 51 of depressor nerve on, 51 of drugs on, 51, 55 of emotions on, 52 tone of, 51' nerve-fibers, course of, 52, 55, 97 cutaneous, 136 renal, 130 Vasodilator centers, 55 nerve-fibers, 55, 97 renal, 131 Vegetable diet, 112, 123, 129 Veins, blood-flow in, 45, 56, 57, 59 blood-pressure in, 45, 47, 4%, 50,59 capacity of, 47 innervation of, 55 portal, 55 pulse in, 57 valves of, 59 240 INDEX. Velocity of blood-flow, 44 Venosity of blood, influence of, on cardio-inhibitory center, 48 on respiratory center, 71 on vasoconstrictor cen- ter, 51 Venous blood, 68 circulation, 59 pulse, 59 Veratrin, 149 Vermis, 174, 178, 206 Vertigo, 208 Vestibular nerve, 182, 184, 205 Viscero-inhibitory nerve-fibers of stomach, 100, 170 Visceromotor nerve-fibers of stomach, 100, 170 Vision, 210 color, 218, 221 Visual area, 185 judgment, 224 Visual purple, 221 reflexes, 185 Vitreous humor, 210 Vomiting, 103 WARMTH, influence of, on res- piratory center, 72 on vasoconstrictor center, 51 Waste products, 18 excretion of, 127 of muscular metabolism., 50, 72 Water, absorption of, 95 excretion of, 127, 135 in diet, 124 Work, 149 and diet, 122 XANTHIN, 13, 88, 112, 158 SAUNDERS' BOOKS Pathology, Physiology Histology, Embryology and Bacteriology W. B. SAUNDERS COMPANY 925 Walnut Street Philadelphia 9. Henrietta Street Covent Garden, London LITERARY SUPERIORITY E excellent judgment displayed in the publications of the house at the ery beginning of its career, and the success of the modern business methods employed by it, at once attracted the attention of leading men in the profession, and many of the most prominent writers of America offered their books for publication. Thus, there were p/oduced in rapid succession a number of works that immediately placed the house in the front rank. One need only cite such instances as Keen's five volume work on Surgery, Kelly and Noble's Gynecology and Alxlominal Surgery, Fowler's Surgery, Ashton's Gynecology, Moynihan's works on Abdominal Operations and on Gallstones, Sahli, Kinnicutt, and Potter's Diagnostic Methods, Stengel's Path- ology, Hir-t's Obstetrics, Anders' Practice, DaCosta's Surgery, Church and Peterson's Nervous and Mental Diseases, and the International Text- Book of Surgery, edited by Warren and Gould. These books have made for them- selves a place among the best works on their several subjects. A Complete Catalogue of Our Publications will be Sent upon Request SAUNDERS' BOOKS ON American Text-Book of Pathology American Text>Book of Pathology. Edited by LUDVIG HEKTOEN, M. D., Professor of Pathology, Rush Medical College, in affiliation with the University of Chicago ; and DAVID RIES- MAN, M. D., Professor of Clinical Medicine, Philadelphia Poly- clinic. Handsome imperial octavo, 1245 P a g es > 443 illustrations, 66 in colors. Cloth, $7.50 net ; Sheep or Half Morocco, $9.00 net. SUMPTUOUSLY ILLUSTRATED The present work is the most representative treatise on the subject that has appeared in English. It furnishes practitioners and students with a compre- hensive textbook on the essential principles and facts in General Pathology and Pathologic Anatomy, with especial emphasis on the relations of the latter to practical medicine. The pictorial feature of the work forms a complete atlas of pathologic anatomy and histology. Quarterly Medical Journal, Sheffield, England " As to the illustrations, we can only say that whilst all of them are good, most of them are really beautiful, and for them alone the book is worth having. Both colored and plain, they are distributed so profusely as to add very largely to the interest of the reader and to help the student." McConnelFs Pathology A Manual of Pathology. By GUTHRIE MCCONNELL, M.D., Pathologist to the Skin and Cancer Hospital, St. Louis. i2mo of 523 pages, with 170 illustrations. Flexible leather, $2.50 net. RECENTLY ISSUED Dr. McConnell has discussed his subject wi h a clearness and precision of style that render the work of great assistance to both student and practitioner. The illustrations, many of them original, have been introduced for their prac- tical value. PATHOLOGY. Well/-' Chemical Pathology Chemical Pathology. By H. GIDEON WELLS, PH.D., M.D., Assistant Professor of Pathology in the University of Chicago. Octavo of 549 pages. Cloth, $3.25 net; Half Mo- rocco, $4.75 net. RECENTLY ISSUED Dr. Wells discusses in the introductory chapter the chemistry and physics of the animal cell, giving the essential facts of the composition of protends, and of ionization, diffusion, osmotic pressure, etc., and the relation of these facts to celluhr activities. Special. chapter are devoted to Diabetes and to f '> ic acid Metabolism and Gout. Wm. H. Welch. M. D., Professor of Pathology, Johns Hopkins University. "The work fills a real need in the English literature of a very important subject. I shall be glad to recommend it." McFarlandV Pathology A Text-Book of Pathology. By JOSEPH MCFARLAND, M.D., Professor of Pathology and Bacteriology in the Medico- Chirurgical College of Philadelphia. Octavo of 818 pages, with 350 illustrations, many in colors. Cloth, $5.00 net; Half Mo- rocco, $6.50 net. RECENTLY ISSUED-BEAUTIFULLY ILLUSTRATED Unlike most works on pathology, this work treats the subject, not from the professor's point of view, but 'from that of the student. American Medicine " We feel confident in saying no other recent treatise, not encyclopedic in character on any subject, contains so much direct and correlated information on the branch with which it deals." SAUNDERS? BOOKS ON Diirck and Hektoen's General Pathologic Histology Atlas and Epitome of General Pathologic Histology. By PR. DR. H. DURCK, of Munich. Edited, with additions, by LUDVIG HEKTOEN, M. D., Professor of Pathology, Rush Medical College, Chicago. With 172 colored figures on 77 lithographic plates, 36 text-figures, many in colors, and 353 pages of text. In Saunders' Atlas Series. Cloth, $5.00 net. RECENTLY ISSUED This new atlas gives the accepted views in regard to the significance of pathologic processes, conflicting theories having been omitted. All the illus- trations have been made from original specimens, in many cases as high as twenty-six colors having been required. W. T. Councilman, M.D., Professor of Pathologic Anatomy, Harvard University. " I have seen no plates which impress me as so truly representing histologic appear- ances as do these. The book is a valuable one." Howell's Physiology 1 A Text=Book of Physiology. By WILLIAM H. HOWELL, PH. D., M. D., Professor of Physiology in the Johns Hopkins University, Baltimore, Md. Octavo of 915 pages, with 275 illustrations. Cloth, $4.00 net. JUST READY THE NEW (2d) EDITION Dr. Howell has had many years of experience as a teacher of physiology in several of the leading medical schools, and is therefore exceedingly well fitted to write a text-book on this subject. Main emphasis has been laid upon those facts and views which will be directly helpful in the practical branches of medicine. At the same time, however, sufficient consideration has been given to the experimental side of the science. The London Lancet PATHOLOGY. Stengel's Text-Book of Pathology New (5th) Edition Recently Issued A Text-Book of Pathology. By ALFRED STENGEL, M. D., Professor of Clinical Medicine in the University of Pennsylvania. Octavo volume of 979 pages, with 400 text-illustrations, many in colors, and 7 full-page colored plates. Cloth, $5.00 net ; Half Morocco, $6.50 net. WITH 400 TEXT-CUTS, MANY IN COLORS, AND 7 COLORED PLATES In this work the practical application of pathologic facts to clinical medi- cine is considered more fully than is customary in works on pathology. In this edition the section dealing with General Pathology has been most extensively revised, several of the important chapters having been piactically rewritten. A very useful addition is an Appendix treating of the technic of pathologic methods, giving briefly the most important methods at present in use for the study of pathology, including, however, only those methods capable of giving satisfactory results. PERSONAL AND PRESS OPINIONS William H. Welch, M. D., Professor of Pathology, Johns Hopkins University, Baltimore, Md. " I consider the work abreast of modern pathcrlogy, and useful to both students and practitioners. It presents in a concise and well-considered form the essential facts of general and special pathologic anatomy, with more than usual emphasis upon pathologic physiology. Ludvig Hektoen, M. D., Professor of Pathology, Rush Medical College, Chicago. " I regard it as the most serviceable text-book for students on this subject yet written by an American author." The Lancet, London " This volume is intended to present the subject of pathology in as practical a form as possible, and more especially from the point of view of the ' clinical pathologist.' Thee subjects have been faithfully carried out, and a valuable text-book is the result. We can most favorably recommend it to our readers as a thoroughly practical work on clinical pathology. SAUNDERS' BOOKS ON GET Am orison THE NEW THE BEST nmeriCan STANDARD Illustrated Dictionary Recently Issued The New (4th) Edition* The American Illustrated Medical Dictionary. A new and complete dictionary of the terms used in Medicine, Surgery, Dentistry, Pharmacy, Chemistry, and kindred branches; with over 100 new and elaborate tables and many handsome illustra- tions. By W. A. NEWMAN BORLAND, M. D., Editor of "The American Pocket Medical Dictionary." Large octavo, nearly 850 pages, bound in full flexible leather. Price, $4.50 net; with thumb index, $5.00 net. Gives a Maximum Amount of Matter in a Minimum Space, and at the Lowest Possible Cost WITH 2000 NEW TERMS The immediate success of this work is due to the special features that distinguish it from other books of its kind. It gives a maximum of matter in a minimum space and at the lowest possible cost. Though it is practi- cally unabridged, yet by the use of thin bible paper and flexible morocco binding it is only i^ inches thick. In this new edition the book has been thoroughly revised, and upward of two thousand new terms have been added, thus bringing the book absolutely up to date. The book con- tains hundreds of terms not to be found in any other dictionary, over 100 original tables, and many handsome illustrations. PERSONAL OPINIONS Howard A. Kelly, M. D., Professor of Gynecology, Johns Hopkins University, Baltimore. " Dr. Borland's dictionary is admirable. It is so well gotten up and of such conve- nient size. No errors have been found in my use of it." J. Collins Warren, M.D., Professor of Surgery, Harvard Medical School. "I regard it as! a valuable aid to my medical literary work. It is very complete and of convenient size to handle comfortably. I use it in preference to any other." EMBRYOLOGY. Heisler's Text-Book qf Embryology Recently Issued The New (3d) Edition A Text-Book of Embryology. By JOHN C. HEISLER, M.D., Professor of Anatomy in the Medico-Chirurgical College, Phila- delphia. Octavo volume of 435 pages, with 212 illustrations, 32 of them in colors. Cloth, $3.00 net. WITH 212 ILLUSTRATIONS. 32 IN COLORS The fact of embryology having acquired in recent years such great interest in connection with the teaching and with the proper comprehension of human anatomy, it is of first importance to the student of medicine that a concise and yet sufficiently full text-book upon the subject be available. The new edition of this work represents all the latest advances recently made in the science of embryology. Many portions have been entirely rewritten, and a great deal of new and important matter added. A number of new illustrations have also been prepared which will prove valuable. Heisler's Embryology has become a standard work. PERSONAL AND PRESS OPINIONS G. Carl Huber. M. D.. Professor of Histology and Embryology, University of Michigan. Ann Arbor. " I find the second edition of 'A Text-Book of Embryology ' by Dr. Heisler an improv.- ment on the first. The figures added increase greatly the value of the work. I am again recommending it to our students." William Wathen, M.D., Professor of Obstetrics, Abdominal Surgery, and Gynecology, and Dean, Kentucky School of Medicine, Louisville, Ky. " It is systematic, scientific, full of simplicity, and just such a work as a medical student will be able to comprehend." Birmingham Medical Review. England " We can most confidently recommend Dr. Heisler's book to the student of biology or medicine for his careful study, if his aim be to acquire a sound and practical acquaintance with the subject of embryology." SAUNDERS' BOOKS ON Mallory and Wright's Pathologic Technique Recently Issued Third Edition, Enlarged Pathologic Technique. A Practical Manual for Workers in Pathologic Histology, including Directions for the Performance )f Autopsies and for Clinical Diagnosis by Laboratory Methods By FRANK B. MALLORY, M. D., Associate Professor of Pathology, harvard University; and JAMES H. WRIGHT, M. D., Director of he Clinico-Pathologic Laboratories, Massachusetts General Hos- >ital. Octavo of 469 pages, with 138 illustrations. Cloth, $3.00 net. WITH CHAPTERS ON POST-MORTEM TECHNIQUE AND AUTOPSIES In revising the book for the new edition the authors have kept in view the leeds of the laboratory worker, whether student, practitioner, or pathologist, or a practical manual of histologic and bacteriologic methods in the study of >athologic material. Many parts have been rewritten, many new methods lave been added, and the number of illustrations has been considerably ncreased. Among the many changes and additions may be mentioned the .mplification of the description of the Parasite of Actinomycosis and the nsertion of descriptions of the Bacillus of Bubonic Plague, of the Parasite of tfycetoma, and Wright's methods for the cultivation of Anaerobic Bacteria, fhere have also been added new staining methods for elastic tissue by Veigert, for bone by Schmorl, and for connective tissue by Mallory. PERSONAL AND PRESS OPINIONS Yilliam H. Welch, M.D., Professor of Pathology, Johns Hopkins University, Baltimore, Md. " I have been looking forward to the publication of this book, and I am glad to say that find it a most useful laboratory and post-mortem guide, full of practical information and veil up to date." ioston Medical and Surgical Journal " This manual, since its first appearance, has been recognized as the standard guide in >athological technique, and has become well-nigh indispensable to the laboratory worker." HISTOLOGY. Bohm, Davidoff, and Huber's Histology A Text-Book of Human Histology. Including Microscopic Technic. By DR. A. A. BOHM and DR. M. VON DAVIDOFF, of Munich, and G. CARL HUBER, M. D., Professor of Histology and Embryology in the University of Michigan, Ann Arbor. Handsome octavo of 528 pages, with 377 beautiful original illus- trations. Flexible cloth, $3.50 net. RECENTLY ISSUED SECOND REVISED EDITION The work of Drs. Bohm and Davidoff is well known in the German edi- tion, and has been considered one of the most practically useful books on the subject of Human Histology. This American edition has been in great part rewritten and very much enlarged by Dr. Huber, who has also added over one hundred original illustrations. Dr. Huber's extensive additions have rendered the work the most complete students' text-book on Histology in existence. DrewV Invertebrate Zoology A Laboratory Manual of Invertebrate Zoology. By GILMAN A. DREW, PH.D., Professor of Biology at the Univer- sity of Maine. With the aid of Members of the Zoological Staff of Instructors at the Marine Biological Laboratory, Woods Holl, Mass. i2mo of 200 pages. Cloth, $1.25 net. RECENTLY ISSUED The subject is presented in a logical way, and the type study has been followed, as this method has been the prevailing one for many years. Prof. Ellison A. Smyth, Jr., Virginia Polytechnic Institute 10 SAUNDERS' BOOKS ON McFarland f s Pathogenic Bacteria The New(5th)Edition, Revised A Text-Book upon the Pathogenic Bacteria. By JOSEPH MCFARLAND, M. D., Professor of Pathology and Bacteriology in the Medico-Chirurgical College of Philadelphia ; Pathologist to the Medico-Chirurgical Hospital, Philadelphia, etc. Octavo volume of 647 pages, finely illustrated. Cloth, $3.50 net. RECENTLY ISSUED This book gives a concise account of the technical procedures necessary in the study of bacteriology, a brief description of the life-history of the import- ant pathogenic bacteria, and sufficient description of the pathologic lesions accompanying the micro-organism al invasions to give an idea of the origin of symptoms and the causes of death. The illustrations are mainly reproductions of the best the world affords, and are beautifully and accurately executed. The Lancet, London " It is excellently adapted for practitioners and medical students, for whom it is avowedly written. . . . The descriptions given are accurate and readable." Hill's Histology and Organog'raphy A Manual of Histology and Organography. By CHARLES HILL, M. D., Professor of Histology and Embryology, North- western University, Chicago. i2mo of 463 pages, with 313 illustrations. Flexible leather, $2.00 net. RECENTLY ISSUED Dr. Hill's fifteen years' experience as a teacher of histology has enabled him to present a work characterized by clearness and brevity of style and a BACTERIOLOGY AND PATHOLOGY. II Eyre's Bacteriologic Technique The Elements of Bacteriologic Technique. A Laboratory Guide for the Medical, Dental, and Technical Student. By J. W. H. EYRE, M. D., F. R. S. Edin., Bacteriologist to Guy's Hospital, London, and Lecturer on Bacteriology, Medical and Dental Schools, etc. Octavo, 375 pages, with 170 illustrations. Cloth, $2.50 net. This book presents, concisely yet clearly, the various methods at present in use for the study of bacteria, and elucidates such points in their life-his- tories as are debatable or still undetermined. The illustrations are numerous and practical. Medical News, New York "Of the many laboratory guides constantly being issued, this book is undoubtedly the best that has reached us." Warren's Pathology and Therapeutics Surgical Pathology and Therapeutics. By JOHN COLLINS WARREN, M. D., LL.D., F. R. C. S. (Hon.), Professor of Surgery, Harvard Medical School. Octavo, 873 pages, 136 relief and lithographic illustrations, 33 in colors. With an Appendix on Scientific Aids to Surgical Diagnosis, and a series of articles on Regional Bacteriology. Cloth, $5.00 net; Sheep or Half Mo- rocco, $6.50 net. SECOND EDITION. WITH AN APPENDIX In the second edition of this book all the important changes have been embodied in a new Appendix. In addition to an enumeration of the scientific aids to surgical diagnosis there is presented a series of sections on regional bacteriology, in which are given a description of the flora of the affected part, and the general principles of treating the affections they produce. Roswell Park. M. D.. In the Harvard Graduate Magazine. " I think it is the most creditable book on surgical pathology, and the most beautiful medi- cal illustration of the bookmakers' art that has ever been issued from the American press." 12 SAUNDERS' BOOKS ON Diirck arid Hektoen's Special Pathologic Histology Atlas and Epitome of Special Pathologic Histology. By DR. H. DURCK, of Munich. Edited, with additions, by LUDVIG HEKTOEN, M. D., Professor of Pathology, Rush Medical College, Chicago. In two parts. Part I. Circulatory, Respira- tory, and Gastro-intestinal Tracts. 120 colored figures on 62 plates, and 158 pages of text. Part II. Liver, Urinary and Sexual Organs, Nervous System, Skin, Muscles, and Bones. 123 colored figures on 60 plates, and 192 pages of text. Per part : Cloth, $3.00 net. In Saunders* Hand-Atlas Series. The great value of these plates is that they represent in the exact colors the effect of the stains, which is of such great importance for the differentia- tion of tissue. The text portion of the book is admirable. William H. Welch, M. D., Professor of Pathology, Johns Hopkins University, Baltimore. " I consider Diirck's 'Atlas of Special Pathologic Histology/ edited by Hektoen, a very useful book for students and others. The plates are admirable." Sobotta arid Huber's Human Histology Atlas and Epitome of Human Histology and Microscopic Anatomy. By PRIVATDOCENT DR. J. SOBOTTA, of Wurzburg. Edited, with additions, by G. CARL HUBER, M. D., Professor of Histology and Embryology, and Director of the Histological Laboratory, University of Michigan, Ann Arbor. With 214 colored figures on 80 plates, 68 text-illustrations, and 248 pages of text. Cloth, $4.50 net. In Saunders* Hand- Atlas Series. Lewellys F. Barker, M. D., Professor of the Principles and Practice of Medicine, Johns Hopkins University. "I congratulate you upon the appearance of this volume. The illustrations are certainly very fine, and Dr. Huber has made important contributions to the text. The book should have a large sale." PHYSIOLOGY. 13 American Text- Book of Physiology American Text-Book of Physiology. In two volumes. Edited by WILLIAM H. HOWELL, PH. D., M. D., Professor of Physiology in the Johns Hopkins University, Baltimore, Md. Two royal octavo volumes of about 600 pages each, fully illus- trated. Per volume : Cloth, $3.00 net ; Sheep or Half Morocco, #4-25 net. SECOND EDITION, REVISED AND ENLARGED Even in the short time that has elapsed since the first edition of this work there has been much progress in Physiology, and in this edition the book has been thoroughly revised to keep p.ice with this progress. The chapter upon the Central Nervous System has been entirely rewritten. A section on Physical Chemistry forms a valuable addition, since these views are taking a large part in current discussion in physiologic and medical literature. The Medical News " The work will stand as a work of reference on physiology. To him who desires to know the status of modern physiology, who expects to obtain suggestions as to further physiologic inquiry, we know of none in English which so eminently meets such a demand." Stewart's Physiology A Manual of Physiology, with Practical Exercises. For Students and Practitioners. By G. N. STEWART, M. A., M. D., D. Sc., Professor of Physiology in the University of Chicago. Octavo volume of 911 pages, with 395 text-illustra- tions and colored plates. Cloth, #4.00 net. RECENTLY ISSUED NEW (5th) EDITION This work is written in a plain and attractive style that renders it particu- larly suited to the needs of students. The systematic portion is so treated that it can be used independently of the practical exercises, which constitute an important feature of the book. In the present edition a considerable amount of m-w matter has been added, especially to the chapters on Blood, Digestion, and the Central Nervous System. Philadelphia Medical Journal " Those familiar with the attainments of Prof. Stewart as an original investigator, as a teacher and a writer, need no assurance that in this volume he has presented in a tere, concise, accurate manner the essential and best established facts of physiology in a most attractive manner." 14 SAUNDERS' fOOJfS ON Levy and Klemperer's Clinical Bacteriology The Elements of Clinical Bacteriology. By DRS. ERNST LEVY and FELIX KLEMPERER, of the University of Strasburg- Translated and edited by AUGUSTUS A. ESHNER, M. D., Pro- fessor of Clinical Medicine, Philadelphia Polyclinic. Octavo volume of 440 pages, fully illustrated. Cloth, $2.50 net. Lehmann, Neumann, and Weaver's Bacteriology Atlas and Epitome of Bacteriology : INCLUDING A TEXT- BOOK OF SPECIAL BACTERIOLOGIC DIAGNOSIS. By PROF. DR. K. B. LEHMANN and DR. R. O. NEUMANN, of Wiirzburg. From the Second Revised and Enlarged German Edition. Edited, with additions, by G. H. WEAVER, M. D., Assistant Professor of Pathology and Bacteriology, Rush Medical College, Chicago. In two parts. Part I. 632 colored figures on 69 lithographic plates. Part II. 511 pages of text, illustrated. Per part: Cloth, $2.50 net. In Saunders' Hand-Atlas Series. Lewis' Anatomy and Physiology Anatomy and Physiology for Nurses. By LEROY LEWIS, M. D. , Surgeon to and Lecturer on Anatomy and Physi- ology for Nurses at the Lewis Hospital, Bay City, Michigan. i2mo of 317 pages, with 146 illustrations. Cloth, $1.75 net, RECENTLY ISSUED Nurses Journal of the Pacific Coast " It is not in any sense rudimentary, but comprehensive in its treatment of the subjects in hand." PATHOLOGY, BACTERIOLOGY, AND PHYSIOLOGY. 15 Tumors Second Revised Edition PATHOLOGY AND SURGICAL TREATMENT OF TUMORS. By NICHOLAS SENN, M. D., PH. D., LL.D., Professor of Surgery, Rush Medical Col- lege, Chicago. Handsome octavo, 718 pages, with 478 engravings, including 12 full-page colored plates. Cloth, #5.00 net ; Sheep or Half Morocco, $6.50 net. " The most exhaustive of any recent book in English on this subject. It is well illustrated, and will doubtless remain as the principal monograph on the subject in our language for some years." Journat of the American Medical Association. Stoney's Bacteriology and Technic BACTERIOLOGY AND SURGICAL TECHNIC FOR NURSES. BY EMILY M. A. STONEY, Superintendent of the Training School for Nurses at the Carney Hospital, South Boston, Mass. Revised by FREDERIC R. GRIF- FITH, M.D., Surgeon, New York. I2mo of 278 pages, profusely illus- trated. Cloth, $1.50 net. " These subjects are treated most accurately and up to date, without the super- fluous reading which is so often employed. . . . Nurses will find this book of the greatest value." The Trained Nurse and Hospital Review. Clarkson's Histology A TEXT-BOOK OF HISTOLOGY. Descriptive and Practical. For the Use of Students. By ARTHUR CLARKSON, M. B., C. M. Edin., for- merly Demonstrator of Physiology in the Owen's College, Manchester, England. Octavo, 554 pages, with 174 colored original illustrations. Cloth, $4.00 net. " The volume in the hands of students will greatly aid in the comprehension of a subject which in most instances is found rather difficult. . . . The work must be con- sidered a valuable addition to the list of available text-bboks, and is to be highly recommended." New York Medical Journal. Gorham's Bacteriology A LABORATORY COURSE IN BACTERIOLOGY. For the Use of Medical, Agricultural, and Industrial Students. By FREDERIC P. GORHAM, A. M., Associate Professor of Biology in Brown University, Providence, R. I., etc. I2mo of 192 pages, with 97 illustrations. Cloth, $1.25 net. " One of the best students' laboratory guides to the study of bacteriology on the market. . . . The technic is thoroughly modern and amply sufficient for all practical purposes." American Journal of the Medical Sciences. . Recently Issued Raymond s Physiology New od) Edition HUMAN PHYSIOLOGY. By JOSEPH H. RAYMOND A. M.. M. D .Pro- fessor of Physiology and Hygiene, Long Island College Hospital, New York. Octavo of 685 pages, with 444 illustrations. Cloth, $3. 'O net. "The book is well gotten up and well printed, and may be regarded as a trust- worthy guide for the student and a useful work of reference for the genera practi- tioner. The illustrations are numerous and are well executed.' - The Lancet, London. 16 BACTERIOLOGY, PHYSIOLOGY, AND HISTOLOGY. Ball's Bacteriology Recently Issued Fifth Edition, Revised ESSENTIALS OF BACTERIOLOGY : being a concise and systematic intro- duction to the Study of Micro-organisms. By M. V. BALL, M. D., late Bacteriologist to St. Agnes' Hospital, Philadelphia. I2mo of 236 pages, with 96 illustrations, some in colors, and 5 plates. Cloth, $1.00 net. In Saunders 1 Question- Compend Series. " The technic with regard to media, staining, mounting, and the like is culled from the latest authoritative works." 77ia Medical Times, New York. Budgett's Physiology ESSENTIALS OF PHYSIOLOGY. Prepared especially for Students of Medicine, and arranged with questions following each chapter. By SIDNEY P. BUDGETT, M. D., Professor of Physiology, Medical Depart- ment of Washington University, St. Louis. i6mo volume of 245 pages, finely illustrated with many full-page half-tones. Cloth, $1.00 net. In Saunders'' Question- Compend Series. " He has an excellent conception of his subject ... It is one of the most satisfac- tory books of this c\a.^. University of Pennsylvania Medical Bulletin. Recently Issued Leroy s Histology New (3d) Edition ESSENTIALS OF HISTOLOGY. By Louis LEROY, M. D., Professor of Histology and Pathology, Vanderbilt University, Nashville, Tennessee. I2mo, 275 pages, with 92 original illustrations. Cloth, $i.co net. In Saunders 1 Question- Compend Series. " The work in its present form stands as a model of what a student's aid should be ; and we unhesitatingly say that the practitioner as well would find a glance through the book of lasting benefit "The Medical World, Philadelphia. Bastin's Botany LABORATORY EXERCISES IN BOTANY. By the late EDSON S. BASTIN, M. A. Octavo, 536 pages, with 87 plates. Cloth, $2.00 net. Barton and Wells' Medical Thesaurus A THESAURUS OF MEDICAL WORDS AND PHRASES. By WILFRED M. BARTON, M. D., Assistant Professor of Materia Medica and Therapeu- tics ; and WALTER A. WELLS, M. D., Demonstrator of Laryngology, Georgetown University, Washington, D. C. I2mo, 534 pages. Flexible leather, $2.50 net. . Fifth Edition, Revised American Pocket Dictionary Recently issued AMERICAN POCKET MEDICAL DICTIONARY. Edited by W. A. NEWMAN DORLAND, M. D., Assistant Obstetrician to the Hospital ot the University of Pennsylvania. Containing the pronunciation and < nition of the principal words used in medicine and kindred sciences, with 64 extensive tables. Handsomely bound in flexible leather, with gold edges, $1.00 net; with patent thumb index, $1.25 net. " I can recommend it to our students without reserve." J. H. HOLLAND, M. D,, of the Jefferson Medical College, Philadelphia. 14 DAY USE RETURN TO DESK FROM WHICH BORROWED This book is due on the last date stamped below, or on the date to which renewed. Renewed books are subject to immediate recall. MOV 5 1S5S OTTOTW DQT191960 '-,- DEC Ifi 19 Rn UL.U J- O V 9 MAR'^O^e? OCT 31 1964 ^^ General Library University of California R*rlralv LD 21-100m-6,'56 (B9311slO)476 '