lumbar autonomic) also produces secretions of saliva. The amount is relatively small, is thick and turbid and contains many solids. At the same time the glands become pale, thus indicating that vascular constriction has occurred. It can be shown that secre- tion is not dependent upon the blood-pressure in the glands, since if the blood supply is cut off the glands will still secrete if its nerves are stimulated. In the above illustration, physiologists call the first set of fibers which produces the large supply of thin, watery secretion and the influx of blood secretory nerve fibers, whereas they call the other set which causes the formation of organic constituents of secretion trophic, since it influences the metabolism of the cells.3 Glands of the Stomach. — The food after being moistened through the saliva is swallowed and is next acted upon by the glands in the stomach. The mucous membrane of the stomach as a whole contains secreting epithelial cells grouped into small glands distributed throughout the mucous membrane. If the membrane as a whole is examined, minute depressions, just visible to the naked eye, are seen, the so-called gastric pits. These are the openings of the glands. The glands at the pyloric end (junction with intestine) have a different structure from those at the fundic end (junction with small intestines) of the stomach, the details of which need not be entered into. The glands in the fundus have two kinds of secreting cells: the central or peptic cells, and the cells of the border, the parietal cells. The peptic cells are contained only in the glands of the pyloric part of the stomach. The peptic cells of the pyloric and fundic glands furnish apparently two digestive enzymes, pepsin and rennin; the parietal cells secrete hydrochloric acid. Until recently the nerve supply of the stomach glands was in doubt. It is now known that their action is controlled by reflex arcs as in the case of the glands just considered. Special secretory nerves are pres- 3 The saliva as a digestive fluid acts mainly upon the starch. It con- tains an active enzyme, ptyalin. Ptyalin acts readily upon boiled starch, converting it into sugar and dextrin. In addition to its digestive function, the saliva moistens the food and makes it suitable for swallowing, and the mucin acts as a kind of lubricator.
12 178 PSYCHOLOGY 12 178 PSYCHOLOGY ent. This is shown quite clearly in the phenomena which occur when a gastric fistula is made; at the same time the oesophagus is divided halfway up to the neck, and subsequently made to open out upon the skin surface, When the animal is fed the food drops out again through the now external oesophageal opening. The food thus never reaches the stomach. When an animal thus pre- pared is made to chew and swallow food (sham feeding) a marked secretion of gastric juice appears some five to six minutes later. This proves very definitely the existence of a reflex arc system. It has been shown further that these glands show conditioned re- flexes (habit influence) similar to those exhibited in the case of the salivary glands. The secretory fibers to the stomach belong to the vagus (pre-ganglionic fibers). The experiments described above upon dogs have also been made upon human beings where a surgical operation for disease has made such an arrangement necessary. These conditioned reflexes play an important role in the course of digestion.
Pancreas. — After the food leaves the stomach it enters the small intestine. The upper ten inches of the small intestine is known as the duodenum. In the duodenum the contents of the alimentary tract are next subjected to the action of the secre- tions from the pancreas. The main duct of the pancreatic gland (duct of Wirsung) opens directly into the duodenum together with the common bile duct. The pancreas is a compound tubular gland like the salivary gland. The gland as a whole is long and irregular in shape. It is 12 or 13 em. long and weighs from 66 to 102, grams. The gland is under definite neural control, the post- ganglionic fibers coming directly from the cceliac ' plexus. The origin of the pre-ganglionic fibers is not so clear. Pavlow claims that the mechanical or electrical stimulation of the vagus or splanchnic gives a marked flow of pancreatic juice. As in the case of the other glands studied, conditioned reflexes may be operative in the pancreas, although the evidence is not so sure. Secretion seems to begin the moment food enters the stomach, which must be due to a neural impulse transmitted through the afferent nerves of the cerebro-spinal system and then out through the vagus to the coeliac plexus (sympathetic) and thence over the ORGANS OF RESPONSE 179 post-ganglionic neurones to the gland. It is possible that the gland may be stirred to activity also by the action of a hormone, although this is contested. Starling states that the normal method of arousing the pancreatic secretion is not through reflex arcs, but by chemical action; the acid of the gastric juice, upon reach- ing the duodenum, produces secretin. This in turn is absorbed by the blood, carried to the pancreas and stimulates this organ to activity (hormone action). It is said that the secretion brought about by nervous reflexes and by the action of the secretin are different. The former is thick, opalescent, rich in enzymes and protein, but poor" in alkalides; the trypsin is secreted in active form. The secretion is stopped by atropin and started by pilocar- pin. The chemical secretion is thin and watery, contains few enzymes, and is rich in alkalides. The trypsin appears in inactive form. The secretion is not affected by atropin. The digestive action of the pancreatic secretion depends upon its three en- zymes, trypsin, diastase and lipase. Besides the glandular secre- tion pouring into the small intestine through the pancreatic duct, other secretions arise in this region from the small tubular glands which exist in the mucous membrane of the intestine itself.
This region of the intestine is the place where the most active absorptions of the products of digestion (carbohydrates, fats, proteins) take place.
The Liver. — At the same time that the contents of the ali- mentary tract are acted upon by the pancreas, they are also acted upon by secretions from the liver. As has been pointed out, the opening of the duct (bile) from the pancreas is common to the liver. This gland is really a gigantic structure, weighing close to 1600 grams. The HVCT is an organ receiving the very highest respect of the physiologists. It seems to be a laboratory for very complex chemical operations. The preparation of the bile, which is stored in a gall bladder and then injected into the duodenum, is probably only a secondary function. Post-gan- glionic neurones end in the liver and probably also afferent fibers belonging to the cerebro-spinal system. The formation of bile is not activated by the mere presence of foodstuffs in the gastro- intestinal tube, that is, the presence of food in the stomach does 180 PSYCHOLOGY 180 PSYCHOLOGY not arouse a neural impulse which excttes the liver cells to increased secretion. The alimentary substances must be absorbed into the blood; they are passed by it through the portal vein and thus reach the liver, exciting it to secrete bile. A protein meal at the end of thirty minutes produces a marked increase in bile secretion, which reaches its maximum after four hours. A meal of fat similarly produces the secretion of bile. Carbohydrates produce only a slight secretion. Apparently the liver is also induced to secrete bile by an increased flow of blood. Interrup- tion of the blood stream arrests its secretion.
From our standpoint the most interesting phenomenon con- nected with the liver is its power to convert the sugars into gly- cogen and to store it against a time of need. The function of glycogen and its formation is touched upon on page 219.
The Kidney and Skin as Excretory Organs. — The main function of the kidneys is to purge the blood from the products of katabolic processes. Its excretory activity, then, must stand in intimate relation with the composition of the blood. Two theories are held as regards the formation of urine which the kidneys secrete. It is held (1) that the urine is formed by the simple physical process of filtration and diffusion, since certain structures in the kidney (glomeruli) seem to be favorable organs for such a process. The theory holds that the water is. filtered through them from the blood, carrying with it both the inorganic salts and the specific elements (urea, etc.) of the secretion. (2) The other view holds that the water and inorganic salts are pro- duced by filtration in the glomeruli, but that the urea and related bodies are eliminated through the activity of certain epithelial cells found in the convoluted tubes of the kidneys. Physiologists are somewhat divided in their adherence to these views, although the majority seem to side with the second. The kidneys receive a rich supply of nerve fibers, but their reflex function and connec- tions are not well understood. There is some evidence that the secretion of urine is controlled through chemical stimuli (hormones).
The urine, which is very complex in its structure, is secreted continuously and carried to the bladder through the ureters, and ORGANS OF RESPONSE 181 is ejected from time to time from the bladder through the urethra by the act of micturition.
The excretory glands of the skin are the sweat glands and seba- ceous glands; the former are particularly abundant in the palms of the hand and the soles of the feet (Fig. 6). There are probably two millions in the whole cutaneous surface. The secretory cells lie in the deep tissues of the skin. The duct is composed of smooth muscle cells. It opens upon the surface of the skin in pores. The average quantity of sweat eliminated in twenty-four hours may amount to two or three liters-. The existence of secre- tory fibers running to the sweat glands has been definitely shown ( post-ganglionic neurones ).
The sebaceous glands are found on cutaneous surfaces asso- ciated with the hair. They secrete an oily semi-liquid material. It is supposed that this secretion serves to protect the hairs from becoming too brittle and too easily permeated with moisture. The oiling of the skin which occurs by their action prevents an undue loss of heat from evaporation of the sweat. Similar glands are present in the sex organs.
B. DUCTLESS GLANDS (INTERNAL SECRETION).
Within recent years the ductless glands have become increas- ingly a subject of physiological experimentation. Many of the results which have been obtained throw light upon problems in behavior. The closest contact between this field and objective psychology is in the realm of emotional behavior.
The study of emotions has always been backward in psychol- ogy, mainly because the psychologist could not get any way of envisaging them. Observation shows that the human organism does not always act in the same dead level way that he would presumably act if only the organized reflex pathways belong- ing to the central nervous system were functioning. Man goes about his daily duties with a varying amount of what, in a slangy way, has been called "pep," and what has speculatively been called "drive" by scientific men. "Drive" is not a satisfactory word, because it seems to add something to the organism which comes in from the outside, whereas the term "pep" belongs pe- culiarly to the organism. The term "libido" has been used by 182 PSYCHOLOGY 182 PSYCHOLOGY the Freudians in a somewhat similar way? but always with defi- nite sex implications. This term likewise for psychological use is not very satisfactory, however well it may work in psycho- pathology. The main facts which can be obtained by observation seem to center around the following: (1) The human being seems at times to work at a higher level of energy than at other times (page 198); (2) at times the individual works with a persistency far beyond that ordinarily displayed; (3) the individual seems totally unable to accomplish his1 daily duties, execute his stable habits; we speak of him as being excited, flighty, or else depressed. These are not meant as characterizations of the various emo- tional types or states. Attention is called to them merely to show that the organic tone changes from time to time, and that the individual displays an increase or decrease in emotional tone. It is thought that a study of the endocrine glands may help us to understand these factors. The following chapter takes up emotional response in detail.
The Endocrine or Ductless Glands. — The endocrine glands differ from the duct glands which we have just considered in that they have no external outlet. The material which they manufacture js absorbed into the blood stream and carried to other organs. The active materials secreted by ductless glands have been termed hormones, which means etymologically ' ' I stir up." A good many of the hormones, though, inhibit action, so that certain authors prefer a different terminology. The term hormone as first used (by Starling) really meant any substance produced by cells in one part of the body and carried by the blood stream to more distant parts. According to this usage, there are a great many hormones not secreted by ductless glands, such as water, urea, glucose and inorganic salts. It seems better then to drop the term hormone and adopt the new term used by Schafer, autacoid substance, or simply autacoid.. An autacoid is a specific organic substance formed by the cells' of one organ and passed from it into the circulatory fluid to produce effect upon other organs similar to those produced % drugs (the in- ternal secretions of the endocrine glands apparently act like drugs). Further there are excitatory autacoids and those which ORGANS OF RESPONSE 183 restrain or produce inhibition, inhibitory autacoids. The former would come under the definition of a hormone, and the latter Schafer designates by a new word, chalone. The nature of auta- coidal action is not well understood. We know that the active material is not injured by prolonged boiling. In general the autacoids have not been isolated. One, however, has been iso- lated and appears in crystalline form, adrenin. Two or three others may possibly have been isolated, for example, thyroxin. We know that they have an effect upon the sympathetic nerve centers, a direct effect upon smooth muscle and upon the secre- tion of other glands.
The Chief Endocrine Glands. — We may divide the endocrine glands into three principal divisions: (1) The thyroid apparatus, which consists of the two thyroids and the four small para- thyroids, two on each side. (2) The suprarenal apparatus; and (3) the pituitary apparatus. There are several other glands which unquestionably secrete autacoid substances, as the pineal gland, the sex glands, the pancreas and the alimentary mucous membrane.
The Thyroid Glands. — Fig. 54 gives one view of the thyroid apparatus. It consists of the two lobes of the thyroid situated on either side of the larynx and windpipe, and of the connecting lobe (not shown), and of a superior and inferior parathyroid on each side. The superior parathyroid is in close contact with the thyroid and sometimes imbedded in it. The inferior parathyroid may lie in contact (ventral aspect) or be removed to a greater or less distance. Occasionally accessory thyroids, quite small in number, may occur. The thyroid is an organ made up of small closed vesicles; each vesicle is lined with epithelial cells. The vesicles are generally filled with a viscid fluid ' ' colloid. ' ' There are very numerous blood-vessels, the thyroids being among the most vascular organs of the body. The gland is innervated by the sympathetic (thoracico-lumbar) and by the vagus (pre-gan- glionic). The nerves are distributed both to the blood-vessels and directly to the secreting cells (epithelium). The colloid is insoluble in alcohol, water or ether. It doubtless contains the active principle and probably serves as a storehouse from which 184 PSYCHOLOGY the organism from time to time draws out a» needed supply. The colloid of the human thyroid appears always to contain iodine.
The parathyroids are very small, about 6 mm. in length, 3 to 4 mm. broad. Each parathyroid is a mass of epithelium-like cells. These are arranged in strands with numerous capillaries Fio. 54. — 1, (Esophagus; 2, trachea; 3, inferior laryngeal nerve; 4, inferior thyroid artery; 5, inferior parathyroid; 6, thyroid (lateral lobe); 7, vagus nerve; 8, superior para- thyroid; 12, pharynx. (Morris's Human Anatomy.) P. Blakiston's Son & Co.
running between or around them. These glands contain some plain muscle fibers. Small vesicles are also present containing colloid material. The innervation is the same as the thyroid, the nerves ending both on the cells and on the blood-vessels.
Effect of Removal of the Parathyroids. — If the four small parathyroids are removed, the animal usually dies within a few days or 'at most in a few weeks. For the first day or two, the only symptom is loss of appetite. The reflexes then become exalted, and later cramp-like contractions occur and eventually convul- ORGANS OF RESPONSE 185 sive fits. The body temperature may rise two or three degrees during the fit. The paroxysms are accompanied by rapid gasp- ing respiration, sometimes by vomiting and diarrhea. The pic- ture as a whole is sometimes called tetany (tetania parathyreo- priva, not to be confused with normal tetanic contraction, page 165). It is assumed that the parathyroids yield an autacoid of a restraining type which tends to prevent overexertion or dis- charge of nerve cells. Besides these apparent neural effects, there is a widespread effect on metabolism which can be noted in the few cases where the animal survives the operation for some length of time. In the young animal the calcification of the teeth is delayed, the skeletal bones remain smaller than in the controls. There is thus some reason for believing that the parathyroids furnish a second autacoid which is able to influence calcium metabolism.
It has been found that the bad effects of removal of the para- thyroid can be partly relieved by the injection of the extract of parathyroid. Extract of pituitary is also said to keep the organ- ism alive. But so far a satisfactory way of keeping the animal alive for any considerable length of time has not been found. We shall see that the reverse is true when the thyroid is removed and the parathyroids are left intact.
Removal of the Thyroid. — -In removing the thyroid, at least two of the parathyroids must be left intact. The results of the removal of the thyroid, or^ of spontaneous atrophy of that organ, are most clearly marked in young animals. The following symp- toms appear: The growth, of the body as a whole, and especially of the skeleton, is arrested-^ the development of the generative organs is delayed; the integument is swollen, the skin remains dry and the hair thin; in the young human the face is pale and puffy and the abdomen is swollen; the f ontanelles remain open; deaf -mutism is common; there is an arrest of the development of the cells in the cerebral cortex: This is the typical picture of cretinism. In the thyroid atrophy of the adult human (myx- oedenia) a similar picture is presented. There is thickening and swelling of the integument, drying of the skin, falling out of the 186 PSYCHOLOGY 186 PSYCHOLOGY hair, low body temperature and a general impairment of sensi- bility; the level of behavior is low; metabolism is diminished; there is a considerable deposition of fat with a diminution of sex function, and an increased tolerance for sugar. Myxoedema may be produced when goitrous tumors (the tumor destroying the secreting cells) are removed. This is called post-operative myx- cedema (cachexia strumipriva). This may show itself in a few days or months or even years after the operation. Unless the parathyroids are removed with the thyroid, symptoms of tetany do not appear.
It is interesting to note that the above symptoms, whether due to atrophy or to surgical removal of the gland, may be made to disappear or be allayed by the administration of thyroid sub- stance, either hypodermically or by the mouth. Persons can be completely restored to health and kept normal by eating the thyroid substance. If the treatment is omitted the symptoms again appear. The effects are therefore due to the absence of an autacoid that actively influences metabolism.
Effect of Excess of Thyroid Secretion. — The effect of a too great amount of the thyroid autacoid can be tested by administer- ing thyroid extract by injection or by the mouth. The immediate results of intravenous injection are slight. When given by the mouth, there is a lowering of blood-pressure, rapid pulse, with some irregularity, nervous excitability, flushing of the skin, in- creased perspiration and increase of nitrogen metabolism. If the feeding is long continued, the body fat is diminished and glycosuria may appear. In extreme cases there may be dilatation of the pupil, great excitement, sleepiness, and tremors of the limbs. In short, we have the symptoms which appear in exoph- thalmic goitre, where there is an enlarged gland (with no de- struction of tissue) with a great oversecretion of the thyroid autacoid.
Exophthalmic goitre is more common in women than in men, a fact which may be related to the enlargement of the gland when the female reaches puberty and during pregnancy.
The antacoid of the thyroid has never been isolated with cer- ORGANS OF RESPONSE 187 tainty.4 Its production seems to be promoted, however, by the administration of iodides. It seems directly to increase the excit- ability of the nerve cells. It is probable that more than one autacoid is secreted, since some of the results seem to show that it restrains the activity of certain other organs, such as the pitu- itary gland. If this is true, we would have at least two autacoids given into the blood stream — one inhibitory in character, affect- ing certain organs; the other exciting in character, affecting cer- tain other organs.
The thyroid exerts great influence upon the generative organs. In the young thyrodectomized subject the generative glands are but imperfectly and slowly developed, sexual infantilism being the rule. It also has some effect upon the liver and pancreas and upon the adrenals, acting as a direct stimulus to the suprarenal capsules, causing them to yield adrenin to the blood in larger quantities. Attention has already been called to the fact that it serves to inhibit the growth of the pituitary body. When the thyroid is removed, the pituitary body becomes much enlarged and increases its secretion.
The Adrenal Apparatus. — The secretions from the suprarenal 4 Plummer states that the thyroid secretions determine the amount of energy that any given cell within the body can produce on stimulation either from within or without. Kendall claims to have isolated the compound, the ultimate analysis of which is C, 22.74; H, 1.72; O, 8.21; N, 2.38; I, 65,10. He calls the active constituent "thyroxin." One-third of 1 m.g. of this sub- stance increases the metabolic rate of a one-hundred-and-fifty pound indi- vidual 1 per cent. If the basal metabolic rate of an individual of this weight is 30 per cent, below normal (hypoactive thyroid) the administration of 10 m.g. will raise the rate to normal. By the administration of greater amounts of this substance the basal metabolic rate may be raised to a figure just as high as is compatible with life. As the metabolic rate is raised, the fundamental changes noted in the text occur, such as pulse rate increase, pulse pressure increase, utilization of body sugar. Fats and proteins will be used up in greater amounts than normal. The carbon dioxide output will l)e increased, as will the oxygen consumption, and there will be an increase in nitrogen elimination. Administration of " thyroxin " will relieve sub- normal activity of tissues; i.e., myxoedema will disappear. If by the administration' of "thyroxin" the metabolic rate is carried high enough, a condi- tion like that found in hyperthyroidism will result.
188 PSYCHOLOGY capsules or adrenals have a profound effect Upon many of the tis- sues of the body. Attention was early directed to the adrenals because of their connection with Addison 's disease.
The adrenals, which are closely attached to the kidneys, con- sist of two parts: (1) cortex, and (2) medulla which in man are anatomically joined, but which in some animals are completely separated (fish).
The (1) cortex of the adrenal is composed of epithelium-like cells arranged in columns. There are a number of lipoid gran- ules, yellowish in color. The (2) adrenal medulla is composed of cells which have a different form and structure from those of the cortex. It is described as a solid cell mass permeated by capillaries and venous spaces somewhat similar to liver tissue. The cell protoplasm contains a number of granules and -imparts a yellowish-brown color to the medulla When the adrenals are fixed in any solution containing chromic acid salts. Oftentimes there are a number of accessory glands which have a similar structure to the medulla (paraganglia or chromaffine).
The suprarenals are richly supplied with nerves and blood- vessels. The blood supply to these glands is greater than that of any other organ in the body (except the pituitary body). The nerve supply is also rich. No less than thirty-three small bundles approach it (post-ganglionic neurones from the cceliac, phrenic and renal plexuses and from the splanchnic). The nerves enter the adrenal cortex supplying both the blood-vessels and its secret- ing cells, but the great majority pass into the adrenal medulla.
Little is known regarding the functions of the cortex. It may partly prepare the material with which the medulla works. Some authors suggest that there is a close connection between the de- velopment of the sex organs and the adrenal cortex.
Function of the Adrenal Medulla.— In animals death fol- lows the removal of both glands. There is little disturbance noted at first, but at the end of a few days the animal becomes lively and begins to manifest signs of muscular weakness and incoordination. The body temperature becomes lowered, weak- ness becomes extreme, pulse feeble and blood-pressure low. Since death always follows the removal of the adrenals, experimental rgery even in pathological cases is not resorted to in the human Addison 's disease, however, seems to be due to a degen- eration of the adrenal gland (usually tubercular). This disease ORGANS OF RESPONSE 189 is characterized by languor, general debility, weakness and loss of tone of the skeletal, vascular and visceral musculature. The heart action is feeble; there is a loss of appetite and a disturb- ance of the digestive tract with extreme emaciation. The bronz- ing of the skin is the most striking characteristic of Addison's disease. The disease is nearly always fatal, but the life of a patient suffering from it may be prolonged for some years.
So far it has been found to be impossible to secure beneficial results in Addison's disease, or in the case of animals whose adrenals have been removed, by the administration of supra- renal extract. Nothing seems to take the place of the internal secretion of the gland. Nor has it been found possible to get an implanted adrenal to grow.