added. This action is caused by the presence of a special ferment, amylopsin. 2d. Upon albumin. The albuminous bodies are changed by the juice into, first, an alkali albumin, and then into peptone. The albumin does not swell up, as is the case in gastric digestion, but is gradually corroded and dissolved. This change is due to the presence of the ferment, trypsin. Long-continued action of trypsin converts the peptones into two crystalline bodies, leucin and tyrosin. 3d. Upon fats. The most striking action of the pancreatic juice is the emulsification of the fats or their subdivision into minute particles of microscopic size. This change takes place rapidly and depends upon the alkalinity of the fluid and the quantity of albumin present, combined with the intestinal movements. The neutral fats are also decomposed into their corresponding fatty acids and glycerin ; the acids thus set free unite with the alkaline bases present in the intestine and form soaps. This decomposition of the neutral fats is caused by the ferment, steapsin. 4th. Upon cane sugar the juice also exerts a special influence, converting it readily into glucose.

The total quantity of this fluid secreted in twenty-four hours has not been accurately determined; it varies from one to two pounds; it is poured out most abundantly an hour after meals.

The Bile has an important influence in the elaboration of the food and its preparation for absorption. It is a golden-brown, viscid fluid, having a neutral or alkaline reaction and a specific gravity of 1.020.

The biliary salts, sodium glycocholate and taurocholate, are characteristic ingredients, and are formed in the liver by the process of secretion, from materials furnished by the blood. It is probable that they are derived from the nitrogenized compounds, though the stages in the process are unknown. They are reabsorbed from the small intestine to play some ulterior part in nutrition.

Cholesterin is a product of waste taken up by the blood from the nervous tissues and excreted by the liver. It crystallizes in the form of rhombic

plates, which are quite transparent. When retained within the blood, it gives rise to the condition of cholesteræmia, attended with severe nervous symptoms. It is given off in the feces under the form of stercorin.

The coloring matters which give the tints to the bile are biliverdin and bilirubin, and are probably derived from the coloring matter of the blood. Their presence in any fluid can be recognized by adding to it nitric acid containing nitrous acid, when a play of colors is observed, beginning with green, blue, violet, red, and yellow.

The Bile is both a secretion and an excretion; it is constantly being formed and discharged by the hepatic ducts into the gall bladder, in which it is stored up, during the intervals of digestion. As soon as food enters the intestines it is poured out abundantly by the contraction of the walls of the gall bladder.

The amount secreted in 24 hours is about 21⁄2 pounds.

Functions of the Bile.—(1) It assists in the emulsification of the fats and promotes their absorption. (2) It tends to prevent putrefactive changes in the food. (3) It stimulates the secretions of the intestinal glands, and excites the normal peristaltic movement of the bowels.

The digested food, the chyme, is a grayish, pultaceous mass, but as it passes through the intestines it becomes yellow, from admixture with the bile. It is propelled onward by vermicular motion, by the contraction of the circular and longitudinal muscular fibers.

As the Digested Food passes through the intestines, the nutritious matters are absorbed into the blood, and the residue enters the large intestine.

The Feces consist chiefly of indigestible matters, excretin, stercorin, and salts, varying in amount from 4 to 7 ozs. in 24 hours.

Defecation is the voluntary act of extruding the feces from the body, accomplished by a relaxation of the sphincter muscle, the contraction of the walls of the rectum, assisted by the abdominal muscles.

The Gases contained in the stomach and small intestine are oxygen, nitrogen, hydrogen, and carbonic acid. In the large intestine, carbonic acid, sulphuretted and carburetted hydrogen. They are introduced with the food, and also developed by chemical changes in the alimentary canal. They distend the intestines, aid capillary circulation, and tend to prevent pressure.

ABSORPTION.

The term absorption is applied to the passage or transference of material into the blood from the tissues, from the serous cavities, and from the mucous surfaces of the body. The most important of these surfaces, especially in its relation to the formation of the blood, is the mucous surface of the alimentary canal; for it is from this organ that new materials are derived which maintain the quality and quantity of the blood. The absorption of materials from the interstices of the tissues is to be regarded rather as a return to the blood of liquid nutritive material which has escaped from the blood-vessels for nutritive purposes, and which, if not returned, would lead to an accumulation of such fluid and the development of dropsical conditions.

The anatomical mechanisms involved in the absorptive process are, primarily, the lymph spaces, the lymph capillaries and blood capillaries; secondarily, the lymphatic vessels and larger blood-vessels.

Lymph Spaces, Lymph Capillaries, Blood Capillaries.-Everywhere throughout the body, in the intervals of connective tissue bundles, and in the interstices of the several structures of which an organ is composed, are found spaces of irregular shape and size, determined largely by the nature of the organ in which they are found, which have been termed lymph spaces or lacuna, from the fact that during the living condition they are continually receiving the lymph which has escaped from the bloodvessels throughout the body. In addition to the connective tissue lymph spaces, various observers have described special lymph spaces in the testicle, kidney, liver, thymus gland, and spleen; in all secreting glands between the basement membrane and blood-vessels; around blood-vessels (perivascular spaces) and around nerves. The serous cavities of the body, peritoneal, pleural, pericardial, etc., may also be regarded as lymph spaces, which are in direct communication by open mouths or stomata with the lymphatic capillaries. This method of communication is not only true of serous membranes, but to some extent also of mucous membranes. The cylindrical sheaths and endothelial cells surrounding the brain, spinal cord, and nerves can also be looked upon as lymph spaces in connection with lymph capillaries.

The lymphatic capillaries, in which the lymphatic vessels proper take their origin, are arranged in the form of plexuses of quite irregular shape. In most situations they are intimately interwoven with the blood-vessels, from which, however, they can be readily distinguished by their larger