THE DIGESTION OF FOOD 113 



165. Digestion in intestines. — It appears, then, that in 

 the intestines protein digestion must be completed with 

 the cleavage of peptones into the simpler amiilo acids, 

 the larger part of the starch transformed to sugar and the 

 digestion of the fats wholly accomplished or mainly so. 

 As a matter of fact, the partial solution in the stomach of 

 the proteins and the swelling of the undissolved part to a 

 gelatinous mass may be considered as a preparation of the 

 food for intestinal digestion, for through these changes 

 the proteins present a larger surface to the attack of 

 trypsin and other intestinal enzyms and digestion pro- 

 ceeds more promptly than would be the case with the 

 freshly ingested food. Moreover, the compounds in the 

 chyme, especially the acid, indirectly react on the liver 

 and pancreas, and cause an abundant flow of digestive 

 fluids from these glands. 



166. Digestive fluids act together. — ^As soon as the 

 chyme mixes with the bile and pancreatic juice, the mass 

 is changed from an acid to an alkaline condition. This 

 seems to be essential to the effective operation of the 

 pancreatic ferments. While the pancreatic juice will 

 carry on digestion by itself, this is not satisfactory in the 

 absence of bile, one reason for this being that when the 

 latter is not permitted to enter the small intestine, the 

 digestion of fats is very imperfect. It seems essential that 

 these two liquids act together. The bile aids in rendering 

 the digesting mass alkaline, contributes to the formation 

 and solution of the fatty acids and soaps, and in these 

 ways promotes the activity of the pancreas enzyms. 



167. Action of intestinal juices. — ^The juices that flow 

 from the small glands in the intestinal walls appear essen- 

 tially to supplement the work of the bile and pan- 

 creatic juice. In the first place, they probably contain a 



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