INTESTINAL DIGESTION 205 



mere nervous irritation by the acid because it is possible 

 to make an extract from the duodenal lining of one 

 animal (treating it with acid) and to inject this extract 

 into the blood of a second animal which, thereupon, se- 

 cretes pancreatic juice. Secretin is an example of 

 what we call a hormone, a product added to the blood 

 in one place but having its important effects elsewhere. 



The juice which flows from the duct of the pancreas 

 plays a large part in digestion. It is customary to say 

 that it contains three enzymes. One of these is a 

 diastase or amylase .closely resembling the ptyalin of 

 the saliva. Under its influence starch may be digested 

 from its original condition or the work may be taken 

 up in the dextrin stages and carried forward. The 

 consequences are practically the same as though the 

 saliva had resumed its action after the interruption 

 suffered in the stomach. 



The pancreatic juice contains also a lipase, an enzyme 

 adapted to act on fat. Under its influence fats undergo 

 cleavage with the formation of fatty acids and glycerin. 

 At an early stage in the intestinal digestion of fats 

 emulsification, that is, fine subdivision, takes place. 

 This is favorable to digestion, as we have already pointed 

 out, but is not to be confused with digestion itself. 

 There is the possibility in the intestine, not existing in 

 the stomach, that the fatty acids formed may combine 

 with alkali. This is the reaction known as saponifica- 

 tion or soap formation. It has proved very difficult 

 to say how far it usually goes on. 



Tryptic Digestion. Pancreatic juice, as it comes from 

 the gland, may or may not have the power to continue 

 the digestion of proteins. If it does not have this power 

 at the outset it is destined to acquire it after mixing with 

 the bile and the intestinal juice. These secretions are 

 said to be capable of activating the pancreatic juice. 

 The protein-splitting enzyme of active pancreatic juice 

 is known as trypsin. It carries along the transformation 

 begun by pepsin. 



