24 Feeds and Feeding. 



is here directed to its function in the digestion and absorption of 

 the fats of foods. 



Bile, the product of the liver, is a clear, greenish or golden col- 

 ored fluid, alkaline in reaction, and extremely bitter in taste. The 

 bile furnishes the alkalies which are necessary for the conversion 

 of the fats of the food into soaps, that is, for changing them from 

 an unabsorbable into a readily absorbable condition. It is of such 

 nature that it readily forms an emulsion with fats, and in this form 

 the latter present a very large surface for the action of the steapsin 

 of the pancreatic juice. The process of the decomposition of the fats 

 into fatty acids and glycerin is greatly hastened by this means. In 

 the presence of bile the fatty acids take on alkali and form soaps, 

 which are soluble in water and can be absorbed into the walls of the 

 intestine. After performing this important function the bile is not 

 wholly excreted with the contents of the intestine, but is in part 

 taken up by the circulation and again utilized. According to Colin, 

 the liver of the horse secretes over 13 lbs., of the ox 5.7 lbs., and of 

 the sheep 0.75 lb. of bile during each 24 hours. 



36. The intestinal secretion. — The first portion of the small in- 

 testine secretes no fluids except possibly water, but into it are 

 poured the pancreatic juice and the bile, as already described. Fur- 

 ther on, the small intestine secretes its own digestive fluid contain- 

 ing several enzymes, the most important of which are erepsin and 

 the invertases. 



Erepsin is an enzyme of great digesting power which attacks and 

 still further splits or cleaves those proteoses and peptones which 

 have escaped such action by trypsin, likewise converting them into 

 amino acids, the ultimate digestion products of the proteins. 



The invertases, sucrase, maltase, and lactase, are enzymes which 

 convert cane-, malt-, and milk-sugars into the more simple glucose- 

 like sugars. 



Thus into the small intestine are poured the complex bile; the 

 three digestive enzymes from the pancreas — trypsin, amylopsiu, and 

 steapsin ; and finally erepsin and the invertases from its own walls. 

 Water is also freely poured into the small intestine from its walls. 



While in the small intestine, the food, which has been masticated 

 in the mouth and partially digested in the stomach, is acted on by 

 all the various fluids above described. That part of the food which 

 thus far has escaped digestion is now vigorously and variously at- 

 tacked, so that under ordinary conditions little that is useful is 

 lost. The larger portion of all the digested material is absorbed 



