HOW ANIMALS DIGEST. 



93 



animals has no other office, so far as we know, than to 

 moisten the food for swallowing. 



Taking Man as an example, let us note the main facts 

 in the process. During mastication, by which the relative 

 surface is increased, the food is mixed with saliva, which 

 moistens the food, 48 and turns a small part of the starch into 

 grape-sugar. Passed into the stomach, the food meets the 

 gastric juice. This is acid, and, first, stops the action of 

 the saliva ; secondly, by means of the pepsin which it con- 

 tains, and the acid, it dissolves the albumen, fibrin, and such 

 constituents of the food. This solution of albuminoids 

 is called a peptone, and is especially distinguished from 

 other such solutions by its diffusibility i. e., the ease with 

 which it passes through a membrane. Some of these pep- 

 tones, with the sugars of the food, whether original or the 

 product of the action of the saliva, are absorbed from the 

 stomach. The food, while in the stomach, is kept in con- 

 tinual motion, and, after a time, is discharged in gushes 

 into the intestine. The name chyme is given to the pulpy 

 mass of food in the stomach. 49 In the intestine the chyme 

 meets three fluids bile, pancreatic juice, and intestinal 

 juice. All of these are alkaline, and at once give the acid 

 chyme an alkaline reaction. This change permits the 

 action of the saliva to recom- 

 mence, which is aided by the 

 pancreatic and intestinal juices. 

 The pancreatic juice has much 

 more important functions. It 

 changes albuminoid food into 

 peptones, and probably breaks 

 up the fats into very small par- 

 ticles, which are suspended in 



the fluid chyle. This forms an FIG. 59. chyle corpuscles, x BOO. 

 emulsion, like milk, and causes the chyle to appear whit- 

 ish. The bile has important functions, but little under- 



