The Creation of God, Jacob Hartmann [e manga reader TXT] 📗

Action of pancreatic juice. (1) It acts on starch raw and boiled with great energy, rapidly converting it into grape sugar. (2) On proteids (meats) it also exercises a solvent action, so far similar to that of gastric juice that by it the proteids are converted into peptones. (3) On fats pancreatic juice has a twofold action: it emulsifies them, and it splits up neutral fats into their respective acids and glycerine.

Thus pancreatic juice is remarkable for the power it possesses of acting on all food-stuffs—on starch, fats, and proteids.

Succus entericus (intestinal juice). The precise action of this is not known. It has been said to act upon starch, to convert proteids into peptones, and to emulsify fats. On the other hand, each of these actions has been denied.

The portal system of veins. The portal vein, or vena porta, collects the blood from the stomach, intestines, pancreas, and spleen; and carries it to the liver, from which the bile is secreted; ramifying after the manner of an artery in the substance of the liver and conveying to the capillaries of that organ the blood collected in the main trunk. This blood, together with that of the hepatic artery, after having served for the secretion of the bile and the nourishment of the liver, is withdrawn from that organ by the hepatic veins, and carried by them into the vena cava inferior.

Digestion begins at the mouth. Food is masticated by the movement of the lower jaw, broken into small pieces, moistened by the saliva, and starchy substances are converted into sugar. No change takes place during the rapid transit through the æsophagus.

In the stomach the proteids are acted upon by the gastric juice and converted into peptones. Fats remain unchanged, and sugars are not acted upon. While these changes are proceeding, the thick grayish liquid, or chyme, formed by the imperfectly dissolved food, is from time to time ejected through the pylorus, accompanied even by large morsels of solid less digested matter. This may occur within a few minutes of food having been token, but the larger escape from the stomach probably does not begin till from one to two and lasts from four to five hours after the meal, becoming more rapid towards the end, such pieces as most resist the gastric juice being the last to leave the stomach. Substances can be absorbed from the cavity of the stomach into the circulation. The presumption is, that the diffusible sugars and peptones pass by osmosis direct into the capillaries, and so into the gastric veins.

In the small intestines the semi-digested food, or chyme, as it passes the biliary orifice causes a gush of bile, and at the same time the pancreatic juice which flows freely into the intestine at the taking of the meal, is secreted again with renewed vigor, when the gastric digestion is completed. The conversion of starch into sugar, which may have languished in the stomach, is resumed with great activity by the pancreatic juice. The pancreatic juice emulsifies fats, and also splits them into their respective fatty acids and glycerine, and the bile is able to a certain extent to saponify the free fatty acids. It also appears that the slight emulsifying power of the bile is much increased by the presence of soap; and as a matter of fact, the bile and pancreatic juice do largely emulsify the contents of the small intestines, so that the grayish turbid chyme is changed into a creamy-looking fluid, which has been called chyle. These products as they are formed pass into the lacteals or the portal blood-vessels.

Through the large intestine pass off indigestible or undigested constituents of the meal, and the gases generated.

Absorption takes place from the stomach, and occurs along the course of the small and large intestines, especially of water. The largest and most important part of the digested material passes away from the canal during the transit of food along the small intestines, partly into the lacteals, partly into the portal vein.

Digestion being, broadly speaking, the conversion of non-diffusible proteids and starch into highly diffusible peptones and sugar, and the emulsifying, or division into minute particles, of various fats, it is natural to suppose that the diffusible peptones and sugars pass by osmosis into the blood-vessels, and that the emulsified fats pass into the lacteals. That the great mass of the fat which enters the body from the intestines passes through the lacteals, there can be no doubt; and there is but little doubt that a considerable quantity of peptone and sugar does pass into the portal blood.

Chyle is a white milky-looking fluid, which after its escape coagulates, forming a not very firm clot. The nature of the coagulation seems to be exactly the same as that of blood.

Lymph seems to be blood minus red corpuscles, and chyle is lymph plus a very large quantity of minutely divided fats.

It has been calculated that a quantity equal to that of the whole blood may pass through the thoracic duct in twenty-four hours, and of this it is supposed that about half comes from food through the lacteals, the remainder from the body at large; but these calculations are based on uncertain data.

Entrance of chyle into the lacteals. The lacteals begin at a club-shaped lymphatic space lying in the center of the villus, and connected with the smaller lymphatic spaces of the adenoid tissue around it; it opens below into the submucous lymphatic plexus from which the lacteals spring.

The thoracic duct is the common trunk which receives the absorbents from both the lower limbs, from the abdominal viscera, from the walls of the abdomen, from the left side of the thorax, left lung, left side of the heart, and left upper limbs, and from the left side of the head and neck. It is from fifteen to eighteen inches long in the adult, and extends from the second lumbar vertebra to the root of the neck. At the last dorsal vertebra there is usually a dilation of the duct, of variable size, which is called the receptaculum chyli, and is the common place of junction of the lymphatics of the lower limbs and the trunks of the lacteal vessels. There are two sets of absorbent vessels—the lacteals, which convey the chyle from the alimentary canal to the thoracic duct; and the lymphatics, which take up the lymph from all the other parts of the body and return it into the venous system. There is a right lymphatic duct, about a quarter to a half inch in length, which receives the lymph from the absorbents of the right upper limb, the right side of the head and neck, the right side of the chest, the right lung and the right half of the heart, and the upper surface of the liver. The thoracic duct terminates on the outer side of the internal jugular vein, in the angle formed by the union of that vein with the subclavian, and the subclavian empties itself in the superior vena cava.

Lymphatics and lacteals are furnished with valves serving the same office as those of