THE DIGESTION OF FOOD 109 



glycerin, but, in conjunction with the bile, also effects 

 their emulsification, this latter result being aided, doubt- 

 less, by the soaps which are formed from a union of the 

 fatty acids and the alkaline bases (mostly sodium) in 

 the bile. The cleavage of the fats is due to an enzym to 

 which the name of steapsin is given, also called "lipase." 

 (See Par. 128.) 



156. Amylopsin. — ^We have seen that starch is acted 

 upon to a small extent by the saliva, and that this action 

 is not prolonged in the stomach beyond the time when the 

 stomach contents become fully acidified. Starch diges- 

 tion is therefore carried on mainly in the intestines, 

 chiefly, if not wholly, by a diastatic ferment in the pan- 

 creatic juice which has the power of hydrolyzmg the 

 starch mostly into maltose. This pancreatic diastase, 

 called amylopsin by some authors, is not found in the 

 digestive tract of young animals as abundantly during 

 the period of milk-feeding as after vegetable foods are 

 taken, for milk does not require the action of a diastatic 

 ferment. The presence of bile is very favorable to the 

 action of amylopsin. (See Par. 128.) 



157. Intestinal juices. — ^Mention has been made of 

 juices that are secreted by small glands distributed in 

 the walls of the small intestine. These are quite impor- 

 tant factors in digestion, as they supplement the action 

 of the ferments of the pancreatic juice. It appears to be 

 shown that an enzym, erepsin, is found in these juices 

 that is unable to act upon any of the native proteins 

 except casein, but has the power of decomposing proteoses 

 and peptones into simpler compounds, particularly the 

 amino-acids. These secretions contain, also, the ferments 

 that hydrolize sucrose, maltose, and lactose into dextrose. 

 It is held also that trypsin does not exist as such in the 



