COLUMBIA LIBRARIES OFFSjTE HEALTH SCIENCES STANDARD HX64098575 QP41.Se81885 Topical synopsis of hUEmhbmum^ ' / / __ J I >^^fe, . ,<2^>-' Digitized by the Internet Archive in 2010 with funding from Columbia University Libraries http://www.archive.org/details/topicalsynopsisoOOsewa A TOPICAL SYNOPSIS OF LECTURES ON ANIMAL PHYSIOLOGY. BY HENRY SEWALL, PH. D„ PROFESSOR OF PHYSIOLOGY IN THE UNIVERSITY OF MICHIGAN. SECOND EDITION REVISED. ANN akbor: THE REGISTER PRINTING AND PUBLISHING HOUSE, 1885. aT'4 / AUTHOR'S NOTE TO THE FIRST EDITION, This skeleton of a course of lectures on physiology has been -prepared at intervals, with the sole object of helping students to fix the attention upon the main facts of the subject. The topics have served simply as points of departure in the lecture room, and no effort has been made to render the " Synopsis " clear to any for whom the spaces between the paragraphs have not already been filled in. The author has been burdened with no^desire for origin- ality, and for good reasons the admirable text-books of Professor Martin and of Dr. Foster, especially the latter, hgve frequently been followed in l»oth order ,and substance in the preparation of these notes. I. THE OBJECT OF PHYSIOLOGY AND THE:F0NCTI0NS OF LIVING MATTER. Pliysiology is the study of the chemistry and physics of the liviug body. Physiologically, Life is the smu of the functions of matter called Protoplasm. Protoplasm is made up of the elements C, H, O, N, traces of P and S; some inorganic salts. Contains much water and probably residues of proteids, fats and carbohydrates. To make protoplasm needs building material and building energy. In the animal both are supplied by the food and oxygen taken in. In the green plant sunlight supplies building energy. Living protoplasm is continually wasting. In the animal the waste matter contains less potential energy than the food; the energy difference is the vital force of the animal. The general functions of all protoplasm are exhibited by the simplest living thing, as an amceba, or ivhiie blood corpuscle. These functions are: Contraciiliiy. SpontaneUy. Irriiabiliiy. Conductivity. Co-or dined ion. Assimilation. This leads to Growth by Intussusception. Growth stops when the weight of egesta equals that of in<: enliven. The cortical and medullary por- tions of the opened kidney; the papilbe. The pyramids of Malpighi and of Ferrein. MICROSCOPIC STKUCTURE OF THE KIDXEY. The uriniferous tubules; the Malpighian corpuscles; the loops of Henle; the convoluted and collecting parts of the tubules. The lining cells peculiar to the different parts of the tubules. The blood supply of the kidney; the f/loiuei-uh'. THE URINE. The quantity secreted in 24 hours varies from 40 to 60 fluid ounces. The complementary activity of skin and kidneys. The color, reaction and specific gravity of urine. The variation of color and specific gravity. THE AMOUNT AND COMPOSITION OF URINE PASSED BY A MEDIUM SIZED MAN IN TWENTY-FOUR HOURS. (Foster's Physiology.) Water 1,500.000 grammes Total solids 72.000 grammes Urea 33.180 grammes Chlorine 7.000 grammes Uric acid 555 grammes Ammonia 770 grammes Hippuric acid. . .I:(X) grammes Potassium 2.500 grammes Pigment fats,&c 10.000 grammes Sodium 11,090 grammes Sulphuric acid. . 2.012 grammes Calcimii 260 grammes Phosphoric acid 3. Ki-l grammes Magnesium 207 grammes —64— The ash of urine is nearly the same as the inorganic mat- ter directly determined. The general nature and origin of the various substances found in the urine. THE SECRETORY MECHANISM. The uriniferous tubule consists of two parts, each of which probably serves special purposes. The thin-walled capsules round the glomeruli probably allow rapid filtration of water and salts through them, while the cells lining the tubules proper have no doubt the function of active secretion. IN^FLUEIN^CES DETEEMINING THE AMOUNT OF THE SECRE- TION. Increased flow of blood to the kidney, bringing about a high blood-pressure in the glomeruli, increases the amount of urine secreted. This may follow general rise of blood-press- ure or local dilatation of the renal arteries. The effect of cold in constricting the vessels of the skin is to raise general blood-pressure. Complementary action of skin and kidiieys. Dilution of the blood increases the secretion. Stoppage of the secretion after section of the spinal cord. .THE SECRETORY EPITHELIUM OF THE TUBULES. It is probable that the cells lining the tubules have the power of active secretion independent of blood-flow. The passage of indigo-carmine through the renal cells. The injection of urea or urates excites the flow of urine. The process of secretion as studied in the kidney of an amphibian. The distinction between selection by the kidney cells of urea from the blood and the manufacture of it by them from certain antecedents. The evidences as to the part played by the kidney cells in the elimination of urea. The physiology of micturition. —(55— DEM0N8T11ATIOXS. The secretion as collected from the ureter; the efiPect of Ijlood-pressure upon the rate of secretion. The effect of dilution of the blood and of the addition of urea to it, upon the rate of secretion. XIII. THE PHYSIOLOGY OF SECRETION. All the phenomena of secretion probably depend in the end for their occurrence on the physicfd laws of difPusion and filtration. The nature of the laws regulating the diffusion and filtra- tion of fluids and gases. Simple application of the laws of diffusion in the living body. The production of diarrhoea by the j)reseuce of mag- nesium salts in the intestine. The interchange of matter between the lymph and the blood and the relation of the animal cell to the process. The gas exchange in the lungs. Secretion is not simply a process of diffusion and filtration through dead membranes. The diff'usion membrane of secre- tion is (illve. In the simplest form of true secretion certain substances are selected by and passed through the secreting membrane. But most secreted fluids contain specific matters which have been produced by the vital activity of secretory cells. The typical secretory animal membrane : ( 1 ) the secretory cell; (2) the basement membrane; (3) the capillary network. The modification of the typical secretory membrane into glands. Various forms of glands: tubular aiid racemose glands. The parts of a gland: the duct; the acinus or alveolus. The circulation in glandular tissue. Enzyni. Mucous and (iJhiuiiiiious glands. THE PHENOMENA OF SECRETION AS DETERMINED IN THE SUB-MAXILLARY GLAND. The nerve supply of the gland, and the processes of normal secretion. -68- THE CHEMICAL C0:NSTITUTI0N" OF SALIVA. The proportions of water, salts, and organic matters. The relative diffusibility of the constituents. The specific bodies of the secretion. THE cha:nges produced in the sub-maxillary GLAI^D BY STIMULATIJ^G THE PERIPHERAL END OF THE CHORDA TYMPANl NERVE. The dilation of the blood vessels; the venous pulse and red blood in the veins. Yaso-dilator nerves. The volume of fluid continuously secreted may exceed that of the gland; the fluid could therefore not have been all stored in the resting gland, but must have come from the blood dur- ing the stimulation. The saliva is not simply filtered from the blood, for the secretion still goes on when the pressure of saliva within the duct exceeds that of the blood in the artery of the gland. Fibres of the cliorda iympani must control the secretory activity of the gland cells; for, after poisoning with atropin, stimulation of the choi-rtal circulation, from which the circulation in the hepatic arteries and capillaries is distinct. The division of the liver substance into lobules. Glisson's capsule and the three interlobular vessels, the he- patic artery, the portal vein and the bile duct, inclosed by it. The intra-lobular, the sub-lobular and the hepatic veins. —88— The hepatic cells; granular polyhedral bodies often contain- ing globules of fat and masses of glycogen. The histological changes of the hepatic cells during diges_ tion. The origin of the bile ducts between the liver cells. CONSTRUCTIVE METABOLISM OF THE BODY. THE PART PLAYED BY THE LIVER IK THE HISTORY OF GLYCOGEN. The liver is preeminently the organ of those chemical changes in the body which do not involve the formation or disintegration of permanent tissues. Glycogen may be found in considerable quantity in the liver cells of normal animals; it may also be extracted in small amounts from probably any living tissue. When food is withheld from an animal the quantity of gly- cogen in its liver begins immediately to diminish, and finally probably completely disappears. If food be again given, the accumulation of glycogen in the liver proceeds rapidly till it has reached its former amount. Carbohydrate foods are particularly favorable to the laying up of glycogen by the liver. The glycogen is no doubt constructed by the activity of the liver cells out of the food matter coming from the digestive tract. When the liver is removed from the body and allowed to lie in a warm place, after a time it is found that the glycogen has disappeared and that sugar has been produced in its place. If the liver be boiled while quite fresh, it is found to contain much glycogen but little or no sugar. When the liver is re- moved from the body its store of glycogen is turned into sugar by the action of a ferment, probably produced within the liver cells. It is probable that the glycogenetic function of the liver consists in the storage within the liver cells of the carbohy- drate moieties of the food matter in the comparatively insolu- —89- ble form of glycogen. Under normal conditions this glycogen is transformed into soluble sugar at a certain definite rate, tlie sugar passing into the general circulation for the supply of the tissues. Through this function of the liver, both tlie overloading of the tissues with carbohydrate matter at the time of feeding and their suffering for want of it in time of hunger, are prevented. DIABETES. Temporary diabetes may be artificially j)roduced in an animal. If a well-fed rabbit be punctured in the vaso-motor region of the medulla the flow of the urine will be increased and in one to two hours it will contain considerable sugar, which after a day or two will have disappeared again. If the animal be previously starved so that the liver contains little or no glycogen, the ui-ine after the operation will contain little or no sugar. The sugar found, then, has come from stored-uj) glycogen. The obscurity of the cause of this diabetes. Mild and severe forms of natui'al diabetes and the relation of the nature of the food-supply to them. FORMATION OE FAT IX THE BODY. The fluctuation in the quantity of fat in the body. Histological changes in the connective tissue corpuscle which is being converted into a fat cell. Fatty degeneration of proteid containing tissues. The ripening of cheese. The fat of the body may be produced from the metabolism of food matters other than fat. A greater quantity of fat may appear in the milk of a cow than was contained in the food of the animal. The amount of wax produced by bees far exceeds that of the fat found in the saccharine food of the creatures. It has l)een shown, in one instance, that for every 100 i)arts of fat in the food of a fattening pig, 472 parts were laid up as fat in the body. Proteid foods as a source of fat. —90— The fat of the living body consists of certain average pro- portions of tri-olein, tri-palmitin and tri-stearin, which are unaltered by the variation of the proportions of those sub- stances in the food; therefore the fat of the body is not sim- ply that of the food stored up unchanged. The chemical changes by means of which carbohydrates and proteids may give rise to fats, THE STRUCTURE AND SECRETIOlSr OF THE MAMMARY GLANDS. Each human mammary gland is comj)osed of a number of distinct lobes which are bound together by connective tissue containing much fat. Each lobe is farther divided into smaller and smaller lobules. The ductules of neighboring acini unite, and the ducts, from 15 to 20 in number, of the various lobes thus formed open separately upon the nipple. The ducts are dilated near their external openings so as to form small milk reservoirs. The ducts and the terminal acini are lined by short columnar epithelium. Fresh milk is alkaline in reaction but may become acid while yet in the gland duct. Its chemical constituents are, — water; casein, serum albumin; fats; milk sugar; potassium phosphate, calcium phosphate, potassium chloride, magnesium phosphate. The fatty globules forming the emulsion are surrounded by albuminous envelopes. Colosh'iiDi differs from ordinary milk in being deficient in casein and proportionately rich in albumin. Milk sugar is readily changed by fermentation into lactic acid, which then causes coagulation of the casein. The protoplasm of the mammary gland cell probably forms all the organic constituents of the milk. Histological changes in the gland cells during lactation. The fats of milk are increased by proteid feeding and the amount of milk sugar is not dependent on the carbohydrates eaten. — ill— The ferment secreted 1)y the stomach glands -wliich coagu- lates casein. THE STRUCTURK AND PHYSIOLOGY OF THIC SPLEEN. The structure of the spleen is much like that of a lym- phatic gland. The organ consists of a reticular framework of bands of (>lastic tissue, in the interspaces of which rests the red-brown spleen pulp which consists of a network of branched connectiA^e tissue corpuscles, through the interstices of which oozes blood in which are for nd red corpuscles appar- ently undergoing destructive metamorphosis. The trabecular substance of the spleen contains much plain muscular tissue. The outer connective tissue coat of the smaller arteries is frequently dilated into small spheroidal bodies which have the structure of lymph follicles, the so-called MaJj)i(j/tiaii cor- puscles. The spleen may be extirpated without danger to the life of the animal. After such an operation there seems to be an increase in the size of the lymphatic glands and in the activity of the medulla of bones. The spleen increases in size up to about the fifth hour of digestion, and then diminishes again. The amount of blood passing through the spleen is proba- bly regulated by the action of the muscle fibres found in the trabecular tissue of the organ. Rhythmic contractions of the spleen. The spleen is probably a seat of the formation of white cor- puscles and destruction of red corpuscles of the blood. The peculiar "spleen corpuscles" which contain fragments of red blood disks. The pulp of the spleen is very rich in so-called extractive matters. THE ORIGIN OF UREA. The living tissues are continually being wasted and restored, and the nitrogen of the wastes is nearly all contained in the urea excreted. —92— Muscular tissue contains kreatin, uric acid and other crys- talline nitrogenous bodies, but no urea. THE EELATIOI^ OF THE KIDJS^EYS TO THE EOEMATIOI^ OF UREA. It is probable that the nitrogenous crystalline substances of the muscle are waste products of the tissue and in part antecedents of urea. There is some reason to believe that the cells of the renal tubules may effect the conversion into urea of certain antece- dents of the latter which are found in the blood. THE RELATION OF PAI^CREATIC DIGESTION AND OF THE LIVER TO THE FORMATIOJT OF UREA. The pancreatic digestion of proteids may give rise in the intestine to considerable amounts of leucin and tyrosin. Leucin injected into the alimentary canal reappears as urea in the urine. The liver always contains urea in its substance. It is not improbable that the liver cells turn into urea the leucin produced by excessive proteid digestion in the intestine. The possible chemical process by which the liver forms urea from leucin, as indicated by the results which follow the ingestion of sarcosin. Increase of proteid in the food increases the amount of urea excreted. It is probable that the amount of leucin and tyrosin formed in pancreatic digestion is proportional to the excess of proteid in the food. Uric acid, though less oxidized than urea, is probably not an antecedent of the latter. Uric acid replaces the urea in the excrement of birds. The chemical functions of the liver which are indicated in the elimination of hippuric acid. STATISTICAL STUDY OF NUTRITION. The proportion in which the various tissues exist in the body. The relative diminution of the tissues during starva- tion. -93— The history o£ nitrogen excretion in the urine of a starving animal. Lnxvfi consumpi ion. The study of the changes taking place in the body by a comparison of the substances entering it with those coming out of it. The effect of nitrogenous foods on the chemical [)r()cesses of the body. Niivogcn equiUhrinin. The Banting system of dietetics. The effects of fatty, of carbohydrate food, and of gelatine. The functions of these foods as force regulators. The effects of salts in the food. It is probable that the urea excreted has at least two differ- ent sources; arising in pretty definite quantities from the nitr(^genous tissues, and also coming in fluctuating quantities from the decomposition of proteid matter which never forms part of the general tissues. The dietetic value of the various food stuffs. THE NATURE OF THE PROCESSES WHICH GIVE RISE TO THE BODILY ENERGY. The amount of energy evolved by the body is represented by the difference between the chemical potentials of the food and the waste matter, and is wholly unaffected by the manner in which this degradation is brought about. In every change of matter in the body by which molecules are made more unstable, energy is absorbed; in every change in which the reverse takes place, energy is evolved. The energy set free in the body all reappears either as heat or mechanical energy. Those movements of the body which involve friction are attended with a loss of heat. The difference between the mechanical energy of the blood in the aorta and in the ven;e cavrP must be represented by an equivalent of heat, produced by friction in the blood-vessels. The heat lost by radiation, conduction and evaporation owes its origin to chemical changes in the body. 12 ^94— tpie energy supply of the Body. The amount of energy stored up in tlie various food matters may be determined in heat units when tliey are completely burned. The direct oxidation of the following. Gives rise to dried at 100° Centigrade: Gram, degree, Met.-Kilo. 1 gram Beef-fat 9069 3841 1 gram Arrowroot 3912 1657 1 gram Beef-muscle purified with ether. , 5103 2161 1 gram Urea 2206 934 Supposing that all the nitrogen of proteid food goes out as urea, 1 gram of dry proteid, such as dried beef-muscle, would give rise to about one-third gram of urea, hence : Gram, degree, Met.-Kilo. 1 gram Proteid 5103 2161 Less I3 gram Urea 735 331 Available energy of 1 gram of Proteid. . 4368 1850 (Foster's Physiology.) ' THE SOUllCE OF ENERGY OF MUSCULAR WORK. It was the belief of Liebig that the non-nitiogenous, or "respiratory," foods were oxidized in the body to maintain its temperature, while the nitrogenous, or "plastic," foods went to form the living tissues, and that the functional changes of the latter gave rise to the nitrogen of the egesta. It is probable that muscular labor does not involve the destruction of the nitrogenous part of the muscle molecule. The amount of nitrogen excreted is not increased by muscular work. The experiments of Parkes, of Fick and Wislicenus. The experiments of Flint. The amount of carbonic acid excreted is immediately and greatly increased by muscular work. The experiments of Pettenkof er and Voit comparing the oxidations of the body while in a state of rest and at work. —95— Tho oxidations of tlic l)o(ly o(;cur in the tissiK^s and not in tlui l)loo(l or the. liinj^s. These, oxidations firi^ not immediately dependent upon the respiration. Excess ol; carbonic acid given off during tlie day and of oxygen absorbed in the nigiit. The muscle molecule ])robfd)ly consists of an essential nitrogenous ]X)rtion capable of adding to itself certain com- bustible non-nitrogenous matters, which latter, during func- tional activity, are oxidized and give rise to free energy. ANIMAL HICAT. The energy diiference between the food and waste matters all reappears as heat in a resting animal. During work, the oxidations of the body and the heat produced are increased. The muscles, glands and central nervous tissues are the chief seats of heat prodviction in the body. The mechanical energy of the circulating blood finally reappears as heat. The body temperature of different animals. Cold-blooded and warm-blooded animals. The temperature of hibernating animals. I'he difference between the temperatures of different i^arts of the body and the variation of temperature in the same part. The blood coming fr6m the liver is the Avarmest in the body. The blood as a heat distributer. THE MAINTENANCE OF A CONSTANT BODY TEMPER- xiTURE. THE REGULATION OF THE LOSS OK HEAT. The loss of heat through various channels is calculated as follows : In warming I'seces and urine 2.5 p. c. In warming expired air 5.2 p. c In evaporating the water of respiration. 14.7 p. c. In conduction, radiation and evaporation by the sl\in 77.5 p. c. —96— The means by wliicli the loss of heat through the lungs and skin is controlled. The reflex excitement of the organs through which heat is lost to the body. Temperature nerves. The perfection of this regulation as shown by the high temperatures which can be borne in a dry atmosphere. In some hair-covered animals the chief loss of heat is by means of the lungs and mouth. The function of the non-conducting layer of subcutaneous fat. THE REGULATION OF HEAT PRODUCTION. The oxidations in the body of a warm-blooded animal are increased by a low surrounding temperature; those of a cold- blooded animal are decreased. This increased production of heat in warm-blooded animals is probably the result of a reflex action in which the activity of a thermogenic nerve-centre is involved. A curarized ani- mal, or one whose spinal cord has been divided, shows, like a cold-blooded creature, diminished oxidations when the sur- rounding temperature is lowered. The action of the thermogenic centre increases the chemi- cal changes of the tissues, leading to an excessive absorption of oxygen and evolution of carbonic acid. It has been made certain that the loss of heat from the body is under nervous control, chiefly through means of, 1, the vaso-motor centres; 2, the sweat centres; 3, the respira- tory centres. It has been made highly probable that the production of heat is under the nervous control of centres which cause, 1, an increase of heat production; 2, a diminution of heat pro- duction. That is, there are probably heat producing and heat inhibitory nerve-centres. THE INFLUENCE OF THE NERVOUS SYSTEM ON THE NUTRITIVE PROCESSES OF THE BODY. Many obscure facts point to a nervous regulation of the nutritive processes of the body, but in no instance has such —97— an action been proven. Inflammation of the cornea which follows section of the trigeminal nerve. Pneumonia which succeeds division of the vagi. It is at present safest to consider that the liefilthy nutrition of a part depends upon the Hn)ii total of its physiological actions rather than on the influence exerted by a special " trophic " nerve. DEMONSTRATION. Extraction of glycogen from the fresh liver, and the con- version, by the liver ferment, of glycogen into sugar. XVII. THE SPINAL CORD. STRUCTURE OF THE SPINAL CORD AND ACCESSOIJV PARTS. The spinal C(H'd is closely invested by the vascular y>/Vf iiififn; which gives rise to the connective tissue frame-work of the cord. Outside the pin iiiafcr is the (irddnioid membrane, and between the two sheets of tissue is foimd the cereV)ro-spinal Huid. The functions of the cerebro-spinal fluid. Surrounding the parts just described is a dense membrane, the diird vinfci-, which is, at points, attached to the wall of the neural canal. The spinal cord is held in position by the spinal nerves entering it, and by ligaments passing fn mi the ^jk^ wo/^t to the (hu-a Dudo-. The cervical and lumbar enlargements of the cord. The caiida equiiui and the fihim iermimde. Each spinal nerve divides into two branches, the anterior and jDosterior spinal roots, just after entering the neural canal. All the sensory fibres of the spinal nerves enter the cord by the posterior roots; all the motor fibres leave the cord by the ((.idei'ior roots. Each posterior root bears a ganglion near the point of its juncture with the anterior root. The function of the ganglion of the posterior nerve-root. The spinal cord is divided longitudinally on its anteritn- side by a broad shallow groove, the diderioi- tncdian fissure. Posteriorly the cord is similarly divided by a deeper and nar- rower posterior median fissure, which is filled by a sheet of infiected connective tissue. The two sets of spinal nerve- roots enter the cord along tolerably definite lines, the Udend —100— fissures. As marked out by these fissures, the cord may be considered to be made up of a pair of anferioi; a pair of laf- eral, and a pair of posterior- cohimns. The posterior columns have further indicated on their surface a narrow posterior median cohimn. The central canal of the spinal cord, lined by cuboidal cil- iated epithelium. Running through the cord is a core of gray matter which has a double crescent shape in cross-section. The nervous matter of the white substance of the cord is composed of meduUated nerve fibres ; that of the gray sub- stance is made of nerve cells and nerve fibres chiefly without the fatty sheath. The variation in form and mass of the gray matter in dif- ferent parts of the cord. The gelatinous substance in the pos- terior cornua. The shape and distribution of the nerve cells and the con- nection of nerves with them. The anterior white commissure and the gray commissures. Most, if not all, the nerve fibres reaching the spinal cord, sooner or later enter its gray substance. The nervous elements of the cord are intimately bound and supported by a connective tissue frame-work. The neuroglia. THE SPINAL CORD AS A CENTRE FOR REFLEX ACTIONS. The spinal cord contains nervous centres capable of send- ing out nervous discharges which may stir up complicated, co-ordinated, and adaptive movements. These movements are never initiated in the cord, but are brought about by impulses reaching the cord from without ; that is, they are not spontaneous, but reflex in character. The stimulation of the terminal organs of the afferent nerves is much better adapted for arousing reflexes than the direct stimulation of a nerve trunk. The nerve cell requires time to cause an efferent nervous clischiirgo after having received an impulse from an afferent nerve. The retlex nerve cell is readily excited to action by a succession of distinct impulses reaching it, l)ut rarely by a single one. Extremely feeble stimuli when summated in the s[)inal cord may produce powerful effects. Examples. The inhibition of a reflex action may be occasioned by the strong stimulation of any afferent nerve, or by the influence of nerve centres in the brain or spinal cord other than the reflex centre. The physiological nature of "shock." The spinal cord has no power of leariiitifj to adapt its activ- ities to new conditions. In a certain sense the spinal cord may be looked on as a servant of the centres of intelligence which has learned, under their instruction, to carry out alone certain oft repeated actions. There is no evidence of the spinal cord possessing a con- scious intelligence. THE SPINAL CORD AS A COLLECTION OF AUTOMATIC CENTRES. One of the functions of the spinal cord, probably, is to act nearly independently by means of special centres whose duty it is to preserve the organic welfare of the body, and whose powers in part are, no doubt, automatic. The nervous control of the sijhincter muscles of the body; the sexual centres; muscular tonicity; subsidiary vaso-motor centres. The peculiar movements of a mammal with divided spinal cord. THE PATHS OF CONDUCTION IN THE SPINAL CORD. AVe usually have conscious sensation of the impulses reach- ing the spinal cord; in such cases the impulses must be trans- mitted to the brain. —102— We cannot suppose that all the nerve fibres entering tli6 cord are individually represented by fibres passing to the brain in that organ, for the number of nerve fibres in the spinal cord is not great enough to admit of this. In such a case, also, the shape of the spinal cord would be that of an inverted cone. We may suppose that the fibres, or most of them, from the periphery on the one hand, and from the brain on the other, are connected with certain nerve centres in the gray matter of the spinal cord by whose mediation impulses reaching the cord from many different sources may be sent out of it by a single channel, or conversely. In this sense the nerve centres of the cord act as relay stations for the transmission of im- pulses reaching them from any quarter. The segmental distribution of the gray matter in the cord. The area of gray matter in a cross section of the cord rises and falls with the sectional area of the nerve fibres entering the cord at that level. It has been attempted to determine the anatomical and physiological grouping of the nerve fibres of the spinal cord, (1) by a study of the direction in which cut fibres degenerate; (2) by the different periods at which various collections of the fibres assume the medullary sheath; (3) by pathological data; (4) by observation of the results following physiologi- cal experiment. All impulses, whether sensory or motor, passing between the brain and the body at large, cross the middle line and end in the side opposite to that in which they originated. The decussation occurs at the level of, and below the pons varolii. Sensory impulses probably cross to the opposite side lower down in the spinal cord than do the volitional impulses. Volitional impulses cross most largely in the medulla and travel along the cord in the lateral and anterior columns, and enter the nervous centres of the anterior cornua of the gray matter of the cord, whence they emerge in the anterior spinal — lo;-;— roots. Volitional fil)res which have not already crossed to the opposite side in the medulla prol)al)ly i)ass down the cord in the anterior column on the same side as that on which they originate, nntil they cross the middle line and then enter the lateral column of the opposite side. Sensory impulses reaching the cord enter the ])()sterior cor- nua of its gray matter or its posterior white columns, and soon crossing, })roceed to the brain chieily in the lateral col- umns. Tracts of degeneration in the spinal cord accom[)anying various forms of paralysis. The most marked i-esults of lateral hemi-section of the spinal cord is a paralysis of voluntary motion and hyperes- thesia on the same side below the injury, Avith a loss of sen- sation on the opposite sitle; ]jrobal)ly neither of these effects is complete. The functions, sensory and motor, wliich are abolished by a hemi-section of the cord may be gradually recovered with- out reunion of the divided parts. Purely tactual and painful sensory impulses probably pass through the cord along different paths. The phenomena of analgesia. The gray matter of the cord can no doubt conduct in any direction the impulses which reach it. DEMONSTRATIONS. Comparison of the retiex action obtained by stimulating the skin and a nerve trunk of a beheaded frog. The purposeful character of retiex actions. The summation of stimuli in the spinal cord. The inhibition of refle:? action in a frog, (a) through the strong stimulation of an afferent nerve; ("ft^through stimula^ tion of the optic lobes, XYIIl. THE BRAIN. THE MEDULLA OBLONGATA. The inednlla l)esides being the pathway of the nerve fibres connecting the brain and spinal cord, contains a number of automatic and reflex nerve centres which especially preside over the "organic " functions of the body. Among the nerve centres are included, — a respiratory centre ; a cardio-inhibitory centre ; a diabetic centre ; a vaso-motor centre ; centre of deglu- tition; centre of reflex secretion of saliva; a vomiting centre; centre of movements for oesophagus and stomach; and prob- ably centres for the co-ordination of movements of the body. The medullary centres, though capable of independent action, are no doubt normally under the influence of other similar centres in higher parts of the brain. THE CHANGES PRODUCED IN AN ANIMAL BY THE REMOVAL OF ITS CEREBRUM. A frog or a pigeon bears well the extirpation of the cere- brum, but a mammal sooner or later succumbs to such an operation. The loss of the cerebrum involves the loss of spontaneous movement; an animal without that organ stirs only in answer to a stimulus. With the loss of its cerebrum an animal appears to lose its faculty of iiercepiion and the power of iormingjiHlgmenis The deterioration of the animal is in its psychical powers. The aspects of a frog and of a pigeon after removal of the cerebral lobes are nearly normal. Food is not voluntarily taken, tlunigh it is swallowed when placed in the mouth. No sign of fear can be aroused. The animal exhi))its no fur- ther evidence of the possession of free will. —106— The most complex co-ordinated movements may still be carried out. The balancing and swimming of a frog, and the flight of a pigeon whose cerebral hemispheres have been re- moved. Such an animal appears to retain its normal sensa- tions. A frog deprived of its cerebrum avoids obstacles in leaping. The same general results follow the destruction of the cere- brum in a mammal. A rabbit or a rat so treated ceases to notice food. Its gaze is attracted by a moving light, and it may utter plaintive cries and leap on being stimulated. Its sensations are preserved but its perceptions are lost. THE LOCALIZATION OF FUNCTION IN THE CEREBRUM. THE STRUCTURE OF THE CEREBRUM. The interior of the cerebral hemispheres is chiefly com- posed of masses of nerve fibres which terminate in the cortex. The nerve cells of the cerebrum are contained in the cortical substance, a thin sheet of gray matter which overlies the con- voluted surface of the hemispheres. In general the cerebrum may be considered to be the seat of thought, of conciousness, and of will power. It is not certain whether the manifold functions of the cere- bral cortex are separately localized in the various convolutions, or whether the whole brain is to be regarded as a complicated machine in which the activity of one part involves that of all the rest. The effect of gradual removal of a pigeon's brain is a gradual loss of psychical power in the animal. In certain pathological conditions, as in the disease aphasia, there is strong suggestion of a localization of function in the cortex. The limited^anastomosis of the blood-vessels of the cortex is suggestive of localization. There may be produced in an animal definite movements or signs of sensation, as a result of the electrical stimulation of —107— well defined areas of the cerebral convolutions. Mechanical or chemical stimulation of the cortex is not followed by positive results. The different results following^ stimulation of the coi'tex in the various stages of mori)hia narcosis. Removal of a "motor" area of the cortex is said by some to be followed by a loss of \'oluiita)-y control over the muscles for- merly excited by the stimulation of that area. Removal of a "sensory" area is said in like manner to involve a loss of the appropriate sensations. The results supporting the theory of localization, as ob- tained in the exi)eriments of Fritsch and Hitzig, of Ferrier and of Munk. The nature of the i)henomena l)r()ught out by artificial stimulation of the cortex, and of those which follow the extir- pation of various areas. There is a gradual recovery from the motor paralysis or loss of sensation which follows removal of a limited area of the cortex. In this recovery the function of the lost part has not been assumed by any definite homologous area in another part of the brain. Extensive lesions of the brain have been suffered by men without permanent motor or sensory disturbance. According to the experiments of Goltz, there is no distinct localization of function in the cerebral cortex; but a gradual loss of psychical power, of sensation, and of definite volun- tary motion, follows extirpation of an}' part of the cerebral convolutions in the dog, and these disturbances are more ex- tensive and less readily recovered from, the more widespread the lesion. After suffering such an operation an animal responds in a reflex manner to stimuli much more readily than usual. Exaggeration of the " tendon reflex " in motor paralysis. Parts of the brain below the cerebrum are no doubt capalile of carrying out independently complicated activities in which simple sensations are involved. —108— The difference between psyclioses and neuroses. Cerebral " reaction time." THE CORPORA STRIATA AND THE OPTIC THALAMI. The so-called "basal ganglia " are masses of gray tissue con- taining many nerve cells. Most of tlie fibres of the crura cerebri pass into the basal ganglia before proceeding to the cortex of the brain. The anterior fibres of the peduncles enter the corpora striata, and the posterior fibres join the optic thai- ami, before continuing into the cerebral substance. The nerve fibres which enter the basal ganglia are no doubt largely con- nected with nerve cells found there. When a lesion involves both the corpus striatum and optic thalamus of one side, there is loss of voluntary motion and of sensation on the opposite side of the body, without necessary impairment of intellectual faculties. It is probable that the basal ganglia act as sets of relay sta- tions which mediate between the cerebral cortex and nervous centres in lower parts of the brain and spinal cord. There is some reason to believe that the corpora striata are chiefly concerned in the modification of volitional impulses passing to it from the cerebral convolutions; and that the optic thalami receive the sensory impulses before they proceed to the surface of the brain. Injury to the optic thalami is followed by blindness or im- perfection of vision. THE CORPORA QUADRIGEMINA. These bodies correspond to the corpora bigemina, or optic lobes, of the frog and pigeon. The nervous centres for the co-ordination of the movement of the eyeballs with the contraction of the pupils lie in or below the anterior half of the corpora quadrigemina. The manner in which the actions of these centres are asso- ciated; when the visual axes are converged the pupils contract, when the axes becomes parallel the pupils dilate. —109— Movements of the opposite eye are brought about by the stimulation of the corpora t[uadrigemina on one side. Extiri)ation of the corpora quadrigemina, or of the optic lobes, on one side produces blindness in the opposite eye. The seat of visual sensations appears to be in the corpora quaih'igemina, but visual perceptions are lost when the cere- bral cortex is destroyed. Other physiological functions, as that of respiration, prob- ably are regulated by special centres situated in the corpora quadrigemina. THE CEREBELLUM. The structure of the cerebellum and the manner of its association with the rest of the brain. The chief function of the cerebellum is to serve as a col- lection of nerve centres whose action maintains the equilib- rium of the body and co-ordinates its movements. Lesions of the cerebellum artificially produced are followed by unsteadiness of gait, and when a large amount of nervous substance is lo3t complete failure of co-ordination is the re suit. Lateral lesions produce more effect than those established in the median line. Extensive asymmetrical injury of the cerebellum, as of sec- tion of the middle peduncle on one side, produces remarkable forced movements of the animal, together with a peculiar roll- ing back and forth of the eyes. Section of one of the crura cerebri is also follow^ed by forced movements, as also are injuries of the corpora striata and optic thalami, or even of the cerebral cortex alone. The passage of a galvanic current through the back part of the head produces a sensation of giddiness and a rolling motion of the eyes. There is no reason to believe that the cerebellum is con- nected with the sexual functions. The special sexual centres appear to be situated in the lumbar region of the spinal cord. 14 — no— The cerebellum is probably capable of learning to carry out reilexly new and complicated purposive actions. The functions of the infant's brain. General consideration of the relation of the activities of the various parts of the central nervous system. THE SEMI-CmCULAR CANALS AND THEIR RELATION TO THE MAINTENANCE OF THE EQUILIBRIUM OF THE BODY. THE STEUCTURE OF THE SEMI-CIRCULAR CA^TALS. The planes of the three membranous canals lie approxi- mately in the three dimensions of space. The ampullar enlargement of each canal and the modified termination o£ the filaments of the auditory nerve within it. The cavity of each canal communicates with that of the utricle. The whole membranous labyrinth is filled with endolympli. THE EFFECT OF CUTTING THE SEMI-CIECULAR CANALS IN A PIGEON. When one of the semi-circular canals of a pigeon is divid- ed, remarkable disturbances of equilibrium immediately fol- low. When one of the horizontal canals is cut, the head moves from side to side; when one of the vertical canals is operated on, the movement is up and down. These disturb- ances of equilibrium become more marked when a number of canals is divided, and the animal places its head in unusual positions with respect to the body. Gradual recovery takes place if but one or two canals be injured. Injury of the semi-circular canals of the mammal is fol- lowed by the same general results as in the case of the pigeon. These results are not due to partial muscular paralysis, nor probp,bly to unusual auditory sensations. — 1 1 1 — THE SENb;: OF EQUILIBRIUM. The maintenance of the equilibrium of the body requires the co-ordinated activity of comi)licated nerve-muscular mechanisms. The afPerent impulses which determine the action of this motor apparatus may arrive from differei.'j sources. The body must know its })ositioii in reference to surround- ing objects in order to maintain its equilibrium. Such a knowledge of the body's position may be attained through visual sensations, facfilc sensations, and ui iiscular fiensations, But it has been shown that a person may be conscious of a change of position without the excitement of any of the fore- going sensations. The impulses which bring this information are supposed by some to arise in the sepai-circular canals. It is possible that movements of the body may cause a change of jjressure of the endolymph within the semi-circular canals upon the nervous mechanisms there, the intensity of excite- ment in each ampulla depending upon the direction of the movement. The truth of this hypothesis is not established. The various means by which vertigo may be produced. THE CRURA CEREBRI AND PONS VAROLII. These bodies contain considerable gray matter, but the chief functions we can ascribe to them are those in which they serve as connecting links between different parts of the central nervous system. Marked disturbance of equilibrium follows injury of either the crura cerebri or the pons varolii. THE BLOOD SUPPLY OF THE BRAIN. The amount of blood supplied to the brain is, in proportion to the size of the organ, probably small. AVhen the brain is exposed it is found to undergo rhythmic alterations of volume, occasioned by the heart beats and re- spiratory movements. During its periods of activity the brain appears to receive more blood than when at rest. —112— Owing to the rigid cranial envelope sudden variations of the amount of blood in the brain subject its substance to such changes of pressure as may affect the consciousness. The blood supply of the brain is no doubt under elaborate vaso-motor regulation. DEMONSTEATIONS. The phenomena exhibited by a pigeon and by a frog after removal of the cerebral hemispheres. The phenomena of "forced movements." The effects following'^section of the semi-circular canals in the pigeon and the frog. <, XIX. THE EYE AND SIGHT. The anatomical mechanis^m whose excitement gives rise to a simple sensation consists of ( 1 ) a peripheral " sense organ,' ( 2 ) an afferent nerve, ( 3 ) a central nerve-cell organ. It is only the activity of the central organ which directly affects consciousness. It is often difficnlt to determine in which part of the sense apparatus the disturbance which gives rise to a sensation originates. The difference between physical and physiological "light." The sensitiAJ^eness of the retina to certain ether vibrations. Specific nerve energy. The difference between simple sensations and judgments. THE STRUCTURE OF THE EYE AND PARTS NEAR IT. The small third eyelid which represents the nictitating membrane of som^ animals. The perforated lachrymal papillse. The lachrymal gland. The Meibomian glands. The action of the accessory glandular and muscular mechan- isms of the eye. The reflex secretions from the lachrymal glands, and the aid rendered by winking movements to the emptying of the lachrymal canals. The six muscles for the movement of the eyeball. The eyeball. The oblique entrance of the optic nerve. The sclerotic coat and cornea continuous with it. The radius of cui'vature of the cornea is smaller than that of the remaining sui'face of the ej^eball. The choroid coat; its blood-vessels, pigment-cells, and ciliary processes. The iris; its inner cii*- cular and outer radial plain muscle fibres; its vessels, nerves and pigment. The ciliary muscles. The crystcdline lens; its —114— suspmsoi-fj 1i(/(nnenl. The sheet of tissue known as the "sus- pensory ligament" is attached at its inner edge to the anterior surface of the lens, and at its outer edge to the inner surface of the ciliary processes. The vitreous humour and hyaloid membrane. The aqueous humour. The anterior and 2^os- terior chambers of the aqueous humour. The ca/nal of Schlemm. The retina; the ora serrata; the macula lutea and fovea centralis; the blood-vessels of the optic nerve and their distribution in the retina. Commencing at its anterior surface there may be recognized in the 1mm an retina ten distinct layers; (l)Membrana liml- tans interna; (2) layer of nerve fibres; (3) layer of nerve cells; (4) inner molecular layer; (5) inner nuclear layer; (6) outer molecular layer; (7) outer nuclear layer; (8) membrana limitans externa; (9) layer of rods and cones; (10) layer of tessellated, pigment-holding cells. The macula lutea, or yellow spot, is free from blood-vessels except at its margin. The blood-vessels of the retina ramify in the nerve fibre layer, and their capillaries do not extend outward beyond the inner nuclear layer. The fovea centralis contains only the retinal cones, the rods being there absent. The optical advantages accruing to the fovea centralis as the spot of distinct vision from the absence of blood-vessels, and of the inner retinal layers in it. The pigment-free part of the choroid which forms the tapetum in some animals. THE EYE AS AN OPTICAL INSTRUMENT. When a ray of light falls on the retina we become conscious of a sensation of light. In order that we may become aware of the form of a dis- tant object, an image of it must be thrown upon the retina. The laws determining the formation of images in an ordin- ary camera. The camera obscura. The eye is a camera made up of a dark chamber to which —115— the liglit is admitted through a diai)hragra, the iris; tAVo refracting media, tiie cornea and crystalline lens, intercept the light before its entrance into the retinal chamber. The refracting power of a lens depends (a) upon the cur- vature of its surface, (/>) upon the refracting power of its substance. The foci of all the refracting media of the eye fall up(jn an 02)tic axis which meets the retina a little above and inside of the fovea centralis. We may calculate the path of all oblique rays entering the eye by assuming that they meet the optical axis at a "nodal" point and leave the axis in a direction parallel to the first from a second nodal point. The nodal j)oiuts are near together on the optical axis within the lens. Primary and secondary optical axes. The refraction of a ray of light entering the eye occurs chiefly at the anterior surface of the cornea and at the anterior and posterior surfaces of the lens. The inversion of the retinal image. The spatial projection of retinal impressions. When the head is plunged under water the refraction by the cornea is nearly done away with; hence the marked com- pensatory curvature of the fish's lens. The anterior and posterior surfaces of the cornea being . nearly parallel, they may be regarded as one. The refractive powers of the aqueous and vitreous humours are nearly the same as that of the cornea, we may regard the refracting surfaces of the lens as three, the anterior surface of the cornea, the anterior and posterior surfaces of the lens. It is calculated that the focus of the refracting media of the eye lies, for parallel rays, 14647 mm. behind the poster- ior surface of the lens and 22.647 mm. behind the anterior surface of the cornea. The reason why the pupil of an observed eye appears dark. Albinos. Principle of the ojythahnoscope. The luminous eyes of some nocturnal animals. —US- ACCOMMODATION. The focal distance at which a distinct image of an object may be formed by light passing through a refracting surface, the refractive index remaining the same, depends, (a) upon the curvature of the surface, (6) on the angle which the entering rays form with it. In order that an image which is thrown upon a certain fixed plane may remain distinct when one of those factors is changed, the other factor must under- go a compensatory change. If this accommodation is not brought about, the image is replaced by a series of blurred "diffusion circles." Accommodation in the human eye as illustrated by " Schei- ner's experiment." The near limit of distinct vision. In the normal or emmefropic eye, the near limit is at a dis- tance of ten to twelve centimetres; the far limit may be regarded as at an infinite distance. In the short sighted or myopic eye the near liiiiit is brought within five to six centi- metres distance of the cornea and the far limit at a variable but not considerable distance. In the far sighted or hyper- metropic eye, the near limit of distinct vision is some dis- tance away, and a far limit does not exist. In the three cases, an image formed by rays parallel to the optical axis falls respectively on the retina, before it and behind it. The pres- byopic eyes of old people. The structural or physiological peculiarities which occasion- these various defects. THE APPARATUS OF ACCOMMODATIOK While at rest, the eye is accommodated for objects at an extreme distance. In accommodating for near objects two movements may be observed in the eye, (1) a narrowing of the pupil, (2) a change in the curvature of the anterior surface of the lens by which it becomes more convex. In its normal condition the lens is an elastic body whose curved surfaces are somewhat flattened by the pressure of the —117 inclosing suspensory ligament which is kept stretched by its attachment to tlie choroid. When the ciliary muscles con- tract, the choroid is pulled forward and the suspensory liga- ment is slackened, thus allowing the anterior surface of the lens to bulge outward. Proof that accommodation is accomplished by change in curvature of the anterior surface of thedens. THE MOVEMEXTS OF THE PUPIL. The pupil is contracted when light falls upon the retina, but is dilated in the dark. It is contracted when we accom- modate for near objects, but it is dilated when we accommo- date for distant ones. It is contracted when the optical axes converge and dilated when they become i^arallel. The contraction of the pupil is an active movement ; it is not certain whether dilation of the pupil is due to the condi- tion of radial muscle fibres or to simple inhibition of the activity of the circular muscles. The condition of the eye during sleep. These movements of the pupil are the result of reflex and associated actions. When the movement is brought about by light falling upon the retina, the optic nerve is the afferent nerve of the reflex apparatus; the third or oculo-motor nerve is the efferent nerve whose excitement causes contraction, and the sj^mpathetic is the eft'erent dilator nerve. There is union between the reflex centres for movement of the pupils; for subjecting one eye to changes of illumination produces movement of tlie opposite pupil. The action of drugs upon the pupil, as of atropin or physo- stigmin, is probably wholly local. ADYAXTAGES AXD DEFECTS OF THE EYE AS AX OPTI- CAL APPARATUS. Owing to its accommodating power the place of formation of all images in the eye is at the principal focus. The theoretically perfect defining power of the eye in the region of the fovea centralis. IS —118— When light passes through a spherical lens it can throw a well (lehned image of larger dimensions upon a curved sur- face, like that of the retina, than upon a plane surface. The special defects of the myopic, hypermytropic and pres- byopic eye. The s])herical abcrrcdion due to the form of the lens is probably insignihcant in comparison with other optical defects of the eye. The refractive power of the lens varies in dif- ferent parts of it. The most obvious use of the iris is to diminish spherical aberration by cutting off circumferential rays. The refracting surfaces of the eye are not perfect sections of a sphere, but are often more convex along one meridian than another. Hence, lines having different directions can- not all be brought simultaneously to a focus on the retina. This leads to a defect known as astigmatism.. Illustrations of astigmatism. Methods of determining the cJiromatic aherTation of the eye. Eutopic phenomenon. — Floating particles in the vitreous humour, the musca' volitantes. Imperfections in the lens. Tears on the cornea. The observation of the margin of the pupil. The luminosity and the floating colored clouds of the retina. The refracting surfaces of the eye are not centred on the optic axis. SENSATIONS OF VISION. The education of the senses. The part of the retina which is directly excited by light is the posterior layer of rods and cones. The optic nerve itself is unirritable towards light. The blind s])ot. The shadows of the retinal blood-vessels seen as Purldnje's figures. The amount of energy contained in a luminous wave may be exceedingly small. — llil - The movement of pigment in the retinal epithelium under under the influence of Kg] it. The retinal pigments ^\ liicli are altered by light. Bt)th rods and cones are pi'obably directly irritated b ;• light; in certain animals the first and in others the second of these elements seems to be absent. It has been conjf ctured that rods serve chiefly to give mere sensation of light, while the cones are adapted to permit of distinctness of vision. The demcmstration of the yellow pigment of the macula lutea. Perception of the rods and cones of one's own retina. The alternate spontaneous blindness of the two eyes. Temporary blindness produced by pressure on the bulb. THE RELATION OF THE DURATION AND STRENGTH OF THE STIMULUS TO THE SENSATION. Subjective and objective light. The sensation produced by a momentary flash of light has a much longer duration than the stimulus itself; when single flashes follow each other sufficiently rapidly the separate sen- sations are fused. The intervals between the flashes must be smaller the stronger the light, in order that the separate sen- sations may he completely fused. The duration of the "after image" is longer the stronger the light which caused the sen- sation. "Positive" tnd "negative" after-images. Instantaneous photography. Apparent motion produced by the fusion of sensations from momentary stimuli. The intensity of sensation varies with the intensity of illu- mination ; but the relation of the variation of the intensities is not a simple one. Weber's law. The increase of stimulus which is necessary to produce the smallest increase of sensation bears always the same proportion to the whole intensity of the stimulus which has already been applied. Practical application of this law. —120— THE DISTINCTION AND FUSION OF SIMULTANEOUS SEN- SATIONS. Two objects appear as one if brought near enongli together. In order to appear as two objects, the distance between their images on the retina must not be less than the diameter of a single retina cone. In the human eye objects thrown thus near together in the fovea of the retina may still be distin- guished apart. Toward the periphery of the retina the dis- tinction is not nearly as fine. Green. and blue light, in the order named, each permit of finer definition than white light, while red light is least advantageous. Cause of the broken outline of fine lines which are drawn close together. The distinction between cerebral and retinal visual areas. The number of cones in the retina is much greater than that of the fibres in the optic nerve. COLOR SENSATIONS. Besides the sensations of white and black, we may attain certain sensations of color, the quality of each of which is determined by the wave length of the incident light. The spectral colors are red, orange, yellow, green, blue, violet. The fusion of blue and red produces another simple color, purple, not found in the spectrum. The physical cause of color. All the hues of nature may be imitated by the proper fusion of the primary color sensations with each other or with white or black. The origin of browns, and olive-greens. Various methods and the resiilts of mixing simple color sensations. The cause of the difference between the sensation obtained by the mixture of two colors on the retina and that derived from the mixture of the pigments themselves. A cplor is said to be more or less saturated according as it contains less or more of white light. No color is abso- lutely saturated. — 121 - Every color which is suHicieiitly ilhiiiiinated appears white. 8timuhition of a considerable retinal area is necessary to excite a sensation of color; very small colored objects appear black. Color sensation produced by electric stimulation of the eye. Gray is a mixture of white and black. Complementary colors are those which, when mixed on the retina, produce the sensation of white light. The following are comjjlementary colors; — Red and green- blue; orange and cyan-blue; yellow and ultramarine-blue; greenish-yellow and violet; green and purple. Any three colors, situated in the spectrum as far apart as possible, may, in proper proportions, together produce white ; by varying the proportions, all of the other spectral colors may be derived from the three primary colors. The Hcring theory of color sensation. The Young-HelmhoJfz theory of colour sensation. The difference of sensitiveness of the retina to different colors. In a waning light the red sensations disappear first and the blue last; hence, red objects first become dark. COLORED AFTER-IMAGES. The sensation of light lasting longer than the stimulus, an object may still be seen for a time after its removal from the field of vision; such sensations are known as affo'-inuiges. The after-image is at first positive, or of the same brightness and color as the stimulus; soon it becomes negoHre, or of brightness and color complementary to the original stimulus. Successive Coufrasf. The greater saturation of a color by contrast. Colors whose infl^^ence is mutually aiding or de- teriorating. The conditions of the retina upon which depend the bright- ness or darkness of an after-image. Explanation of changes in after-images as a result of re- tinal fatigue. The successive fading of the colors of an after-image. The intrinsic light of the retina. —122— SIMULTANEOUS CONTRAST. Light aiul dark surfaces appear respectively brighter and darker when viewed together. The phenomena of colored shadows. When a piece of gray paper is laid on a colored ground and covered with tissue paper, the gray slip aj^pears to have a color complementary to that of the surface. The comparison of strips of black paper respectively seen through and reflected by colored glass plates. The phenomena of simultaneous contrast occur as if every colored image which falls upon the retina rendered the neigh- boring parts of the retina more irritable toward the comple- mentary color. The physiological basis of taste in color. COLOR BLINDNESS. Home persons are incapable of acquiring certain color sen- sations. The most common form of the defect is that of "red- blindness." To persons suffering from it, the colors rose-red and bluish-green are identical. They distinguish in the spec- trum but two colors, calling them yellow and blue; under the yellow they include the red, orange, yellow and green, and blue and violet are called blue. About 5 p. c. of the population are affected to some degree with red-blindness. Temporary color-blindness induced by wearing colored glasses, and by the ingestion of santonin. A rarer form of color-blindness is said to occur in which the sensation of red is preserved, but that of green is lost. Color-blindness on the periphery of the retina. Methods of testing for color-blindness. A^ISUAL PERCEPTIONS. The mind derives ideas from simple visual sensations; sen- sations give rise to visual perceptions. In most of our visual ideas we take little account of simple —123— sensations, but use directly the complex jnch/menis founded on them. The psychical eifects produced by viewin<2; a landscai)e through differently colored gbisse.s. The perception of the positions of objects. The localiza- tion of objects by vision is a subjective process. The images of objects are inverted on the retina. MODIFIED PERCEPTIONS. Irradiation: bright objects appear larger than dark ones of the same size. Illustrations. The blind spot is not perceived chiefly because no sensation is aroused by it. The retina itself gives rise in the dark to luminous sensa- tions. Intrinsic colored images of the retina. Lights produced by pressure on the eyeball. Effect of stimulating the eye or optic ner\'e. Visual judgments of size. The only method of determin- ing the relative size of objects is the comparison of the mag- nitude of their images thrown upon the retina ; our estimation of their real size depends upon the distance from the eye at which they are believed to be situated. This distance seems greater when sulidivided by intervening objects and when seen obscurely ; the apparent size of the moon in mid-sky and on the horizon; comparison of the lengths of two equal lines, one of which is subdivided and the other not; the greater apparent size of objects in a fog. The appreciation of differ- ence of size by contrast. Judgments of the magnitude of angles. VISION WITH TWO EYES. In general, the reason why an object viewed with two eyes appears single is that the image of each point on it falls upon "corresponding" or "identical" areas of the two retinas. Points on the inner side of one retina have their correspond- ing points on homologous parts of the outer side of the other. —124— MOVEMENTS OF THE EYEBALL. The orbit and the eyeball form a ball and socket joint, the centre of rotation being 1.8 mm. behind the centre of the eye. The reflex fixation of external objects which keeps the eye- balls at rest when the head is moved. The "primary" and "secondary" positions of the eye. The position of the resting eye. The rotation of the eye around its visual axis when the latter is changed from a primary to an oblique position. The muscles of the eyeball and the movements brought about by their action. The co-ordination of the movements of the eyeball. The double images that result when the co-ordination centre fails to act. Apparent rotation of toothed wheels brought about by the rinsing motion. False judgments of motion. THE IIOEOPTER. Distinct vision of objects can be had only when the images of their parts fall upon corresponding points of the two retinas. In any given position of the visual axes such corre- sponding points are projected outward upon some definite line or surface, and this line or area of distinct vision is known as the horopter. The horopter changes its form or position with changes of direction of the visual axes. When standing erect and looking toward the horizon the horopter is upon the ground before the eyes. The precautions necessary in walk- ing upon a hillside, or upon a level while looking through a prism. THE JUDGMENTS THAT ARISE FROM BINOCULAR VISION. By means of the movements of the two eyeballs and the images falling upon corresponding point of the two retinas, —125— we are enabled to form certain judgments concerning the form, size, and distance of objects. Illustrations of the judgments concerning size and distance as depending on the " muscular sense " of innervation of the eye-muscles. The idea of perspective aroused by the shading and color- ing of objects. When a solid object is viewed the images falling upon the two retinas cannot be identical; they, however, do not give rise to double vision, but are fused in the cerebrum so as to give the perception of single solid objects. The shading of an object largely assists in the formation of a judgment of its solidity. Applications of the stereoscope. The telestereoscope. The psychical influence of the use of two eyes. When two different colors or white and black are viewed at the same time, each by one eye, there is not a fusion of color in the sensation but an alternate mastery of one and the other. DEMONSTRATIONS. Scheiner's experiment. Observation of the movements of the pupil. Astigmatism. The blind spot. Purkiuje's figures. The mixture of colors upon a rotating disk. Complementary colors. After-images. Tests for color-blindness. The yellow spot. Irradiation. Simultaneous contrast. Judgments of distance. Judgments of motion. The stereoscope. The telestereoscope. XX. THE EAR AND HEARING. THE STRUCTURE OF THE EAR. The organ of hearing may be considered to be made up of three parts; -an external ear, composed of the pinna and auditory meatus, the latter being separated by the tympanic membrane from the middle ear or tympanum. The tympanum contains the auditory ossicles, malleus, incus and stapes, and its cavity opens upon the upper wall of the pharynx by means of the Eustachian tube; an infernal ear, consisting of a membranous labyrinth, to which the auditory nerve is dis- tributed, which is contained within a bony labyrinth ; the two labyrinths are filled with fluid known respectively as the endolymph and the peril ymj^h. The division of the bony labyrinth into vestibule, semi-circular canals and cochlea. The fenestra rotunda and fenestra oralis are placed in the bony wall separating the tympanum respectively from the scala tympani of the cochlea, and from the vestibule. The membranous vestibule is composed of two sacs, the saccule and utricle, whose cavities are indirectly united. The mem- branous semi-circular canals spring from the utricle, and the cavity of the saccule is continuous with that of the mem- branous canal of the cochlea. The auditory hair-cells upon the maculse of the vestibular sacs and on the cristse of the ampullse of the semi-circular canals. The otoliths within the sacs and ampullae. The microscopic structure of the membranous cochlea and of the organ of Corti contained in it. THE SPECIAL FUNCTIONS OF THE PARTS OF THE ACOUSTIC APPARATUS. THE PIXNA OK EXTERNAL EAR. The modification of the concha in different animals. Its purpose is to collect the waves of sound from the external air. —128— The use of the pinna by animals in determining the direc- tion of sound. THE MEMBRAI^A TYMPAiq"!. The curved surface and funnel-shape of the tympanic membrane. This membrane is easily set vibrating by air waves, and has no fundamental note of its own. Its peculiar shape adapts it for transmitting motions of great amplitude and small energy as motions of small amplitude and great energy. The movements of the auditory ossicles. The ossicles form a sort of compound lever by which the oscillations of the tympanic membrane are exactly transferred to the mem- brane of the fenestra ovalis, but with diminished amplitude and correspondingly increased force. The mean extent of the excursions of the tip of the malleus is probably near 1-28 mm. The excursions of the stapes are only f as great, but are 1^ times as energetic. The tensor tympani muscle serves by its contraction to pre- vent the tympanic membrane being pushed out too far. The laxator tympani muscle probably by its contraction causes the ear-drum to move outward. The stapedius muscle probably acts to prevent the stapes being driven too far into the fenestra ovale. THE EUSTACHIAN TUBE. This channel connecting the middle ear and the pharynx serves to keep the pressure within the tympanic cavity equal to that of the atmosphere. The tube is probably only opened during the act of swallowing. THE GENERATION OF AUDITORY SENSATIONS. THE MEMBEANOUS LABYRINTH. The filaments of the auditory nerve end in the maculae and cristse of the internal ear and in the basilar membrane of the cochlea. It is supposed that vibrations of the endolymph set —129— these end-organs in corresponding motion, tlius mechanically stimulating the auditory nerve. The distinction between physical and physiological sound. Graphic representaticm of air waves. The transmission of sound through the bones of the skull ; hearing without a tympanic membrane. Sounds may be divided into musical tones which are caused by rhythmic or periodic vibrations of the air, and noises which are due to non-periodic vibrations. Sounds are distinguished by the three characters of loud- ness, pitch and qiialitij. The physical peculiarities implied in these terms. The physical range of audible tones. Each musical note is made up of a fundamental tone, which determines the pitch, with which a greater or less number of overtones are combined, the latter determining the quality of the note. The manner in which the partial tones are produced together with the fundamental tone. It is the varied predom- inance of different partials which causes the dift'erence of quality in the notes of various musical instruments. The composite air-waves formed by the fusion of partial vibrations. . Nearly every body capable of periodic vibration has a fun- damental tone of its own. The tympanic membrane has no particular fundamental tone. The simple arithmetical relations of the vibration rates of the tones of a musical chord. The production of musical tones and notes upon the siren. Sympathetic vibrations. The analysis and synthesis of musical tones. The high fundamental tone of the external auditory meatus. There is reason to think that the organ of Corti may be regarded as a musical instrument capable of responding by sympathetic vibration to all audible tones. The physiological basis of the musical sense. —1 Bo- lt has been supposed that the auditory hairs upon, and the otoliths near, the macula? and crist?e of the labyrinth are con- cerned in the reproduction of irregular vibrations known as noises. The simplest aural apparatus known is a mere sac whose walls are set with hair-cells, and whose cavity is filled with fluid containing otoliths. When single sounds are repeated with sufficient rapidity, they fuse into a continuous tone whose pitch is determined by the rate at which the single sounds succeed each other. Tones produced by vibrations recurring less than 30 times a second are not heard. The upper limit of auditory sensation is reached when vibrations recur 38,000 times per second. The variation of this limit with the loudness of sound and with the individual. The power of distinguishing pitch differs much in different parts of the scale. The fineness of musical appreciation of quality and pitch. The subjective nature of sound. Individual differences in the appreciation of tones. AUDITORY JUDGMENTS. Any stimulation of the auditory nervous apparatus is inter- preted as dae to sound waves. From the loudness, quality, and pitch of sounds, we for m judgments as to their origin, direction and distance. The nature of ventriloquism. XXI. THE ORGAN AND SENSE OF SMELL. The cavity of the nose on each side of the nasal septum is divided functionally into a lower respiratory and upper olfac- tory chamber. The olfactory mucous membrane, to which the olfactory nerve is distributed, lines the upper and middle turbinated parts of the fossae and the upper part of the sep- tum. The ciliated epithelium and mucous glands of the respiratory chambers of the nose. The termination of the nerve fibres in the olfactory cells of the upper chamber. THE ORIGIN OF SENSATIONS OF SMELL. Odorous particles are carried by diffusion into the olfactory chamber of the nose, or drawn into it by active inhalation. Odorous bodies must come into contact with the olfactory mucous membrane in order to produce a sensation, and the particles must not be in liquid form. Filling the nose with an odorous liquid causes no sensation of smell. "When sev*- eral odors are simultaneously inhaled, the peculiarity of each may be distinguished. Localization of an odor by the sense of smell is very im- perfect. The sensation requires some time to develop itself after application of the stimulus, and may last for a considerable time. Certain pungent substances, as ammonia, give rise to sensa- tions through the nose which are not those of smell proper; are probably due to stimulation of the fifth nerve. There may be sensations of smell of purely subjective origin. XXII. THE ORGAN AND SENSE OF TASTE. The glossopharyngeal and the lingual nerves are the special nerves of taste. The modified termination of the gustatory nerves in the mucous membrane of the tongue and palate. Many sensations which we are accustomed to distinguish as those of taste are really sensations of smell. Sapid substances may be classified as sweet, sour, saline and bitter. They act in solution as chemical stimuli. Sensations of taste may arise from mechanical or electrical stimulation of the gustatory apparatus. XXIII. GENERAL SENSIBILITY AND SENSATIONS OF TOUCH. The distribution and modified terminations of sensory nerves. We possess a certain faculty of general sensibility which gives rise to a consciousness of irritation in the body without enabling us to localize the stimulus or distinguish its nature. Such are the sensations due to irritation of a nerve trunk or of the viscera. Such sensations readily merge into those of pain. The more special sensations of feeling are those derived from touch, temperature and muscular activity. TACTILE SENSATIONS. SENSATIONS OF PRESSURE. The smallest difference which can be distinguished between two unequal weights laid upon the skin is proportional to the magnitude of the weights. When separate sensations of contact succeed each other with sufficient rapidity they become fused. Not all parts of the skin are equally sensible to variations or pressure. Sensations of contact are present when the intensity of the pressure is varied, and fade away when it becomes constant. A cold body is judged to be heavier than a warm one of equal weight. There is reason to believe that there exist tactual nerves distinct from those of general sensibility. TACTILE PERCEPTIONS AND JUDGMENTS. Sensations of contact are referred generally to definite localities on the skin. The erroneous judgments that arise — 13fi— from the irritation of the nerves of an amputated limb. Mistaken judgments arising when a marble is rolled between the tips of two crossed fingers. The power localizing contact upon the skin is not the same in all parts. The division of the skin into tactual areas. The power of localization is most marked upon the tip of the tongue and the palmar surface of the finger, and least marked upon the forearm, sternum, and back. The fineness of tactile perception is greatly increased by- exercise. THE TEMPERATURE SENSE. Bodies warmer or colder than the skin when in contact with it give rise to sensations of heat or cold. The erroneous judg- ments that may arise from artificially rendering the two hands of different temperatures. The range of finest distinction of temperature is included between limits which lie near the body temperature. Not all parts are equally sensitive to variations of tempera- ture. There are probably special afferent temperature nerves which are irritated by variations of temperature. There is reason to believe that the sensation of heat, cold, and pressure, respectively, are aroused through the excitement of different sensory nerves. THE MUSCULAR SENSE. We commonly estimate the weight *of bodies by observing the intensity of muscular exertion necessary to lift them. Muscular sensations are probably peripheral in origin. The effects following diminution of tactile and muscular sensibility in locomotor ataocy. Judgments which arise from the muscular sense. INDEX. PAGE. I.— The object of physiology and the functions of living matter 5 II.— The nature of physiological laws 6 III.— The lymph and blood 7 Coagulation of blood 8 Causes of coagulation 8 Chemistry of "blood 10 History of blood corpuscles 10 IV.— The chemistry of animal tissues 11 Proteids 12 Fats and carbohydrates 13 Physiological metabolites 14 v.— Epii helium, connective tissue and the skeleton 15 Joints and bony levers •. 17 VI.— The contractile tissues 18 Ciliated cells and classification of muscle 18 Electrical phenomena 23 Chemistry of muscle 24 Physiology of unstriated muscle 26 VII.— Nervous tissues 27 Histology of nerves 27 Classification and physiology of nerves 28 Electrotonus ; 29 viii.— Reflex action 30 Inhibition 32 IX.— The circulation of the blood , 35 Structure of the organs of circulation 35 Physiology of the heart 37 Hydraulics of the circulation 44 Vaso-motor regulation 47 Circulation of lymph 49 X.— The respiration 53 Structure of the organs, and the movements of respiration 53 Capacity of the lungs, and changes of air iniespiration. 55 Changes of the blood in the lungs 56 Nerves of respiration and action of the respiratory centre 57 XL— The skin and its appendages 61 xn. — The kidneys and their secretion 63 xni. — Physiology of secretion 67 XIV. — Foods and force-regulators 71 XV. — Digestion 73 The saliva 73 Deglutition ■: 74 The stomach and gastric juice 75 Changes of food in the intestine 79 XVI.— Nutrition 87 The liver and the history of glycogen 88 Diabetes and fat-formation 89 The spleen, and the origin of urea .' 91 Animal heat 95 XVII.— The spinal cord 99 The cord as a reflex centre 100 Paths of conduction in the cord 101 XVIII.— The brain 105 Changes produced in ananimal by extirpation of the cerebrum 105 Localization of function in the cerebrum 106 ('orpora striata, optic thalami and corpora quadrigemiua 108 The cerebellum. .r 109 The semicircular canals and equilibrium 110 XIX. — The eye and sight 113 The eye as an optical instrument 114 Accommodatii n 116 Movements of the pupil - 117 "Visual sensations 118 Color sensations 120 Visual perctptions 122 XX.— The ear and hearing 127 Functions of the component parts of the ear 127 Auditory sensations 128 XXI. — Theorgan and sense of smell 131 XXII.— The organ and sense of taste 133 xxni.— Sensations from the skin 135 General sensation 135 The muscular sense 136 :^-4