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b. Intestinal Digestion.—By this is meant the other digestive processes which go on in the intestine under the action of the secretion of Lieberkühn’s follicles—the succus entericus. This is a yellowish, often opalescent, strongly alkaline fluid. The alkalinity is due to the presence of sodium carbonate. It contains a small amount of protein, shed epithelial cells, &c. The secretion of some 170 c.c in 24 hours has been observed in a short loop of human intestine by H. S. Hamburger and E. Hekma, but it is almost impossible to get a measure of the actual amount of secretion from the whole gut. Most of the ferments are present in very small amount in the intestinal juice. They seem to be actually within the epithelial lining of the intestine, for extracts made from the intestinal mucous membrane are richer in ferments than the secretion.

5. Bile.—This fluid, in all probability, has little direct action in ordinary digestion, although it contains substances which act indirectly. The bile salts act as solvents for fats and fatty acids, and as activators of pancreatic lipase. The salts also serve to keep cholestrin in solution. Bile is to be looked upon rather as the excretion, the result of the hepatic metabolism, than as a digestive juice. Various workers have shown that when the bile is prevented from entering the intestine owing to a fistula having been made, the animal or patient may continue to enjoy good health, thus proving that this fluid is not essential to any of the digestive processes which normally take place.

1. Salivary Glands.—The secretion from the various glands is generally evoked by nervous impulses, through the secretory