THE JUICES POURED OUT UPON THE FOOD. 75 



logical importance of those already well known, has given us 

 a new insight into the importance of the small intestine in 

 the great problem of alimentation. The following is a list 

 of these chemical substances, together with a brief indication 

 of their physiological functions, which are discussed in greater 

 detail later. 



Proteinase. This ferment is found in the secretion and 

 mucous membrane of the duodenum and originates from 

 the glands of BRUNNER, found in this section of the intestine. 

 It seems to be identical with the acid-proteinase of the 

 stomach, as it acts best in an acid medium. It is evident 

 that some opportunity is given this ferment to aid in the 

 digestion of proteins. But as compared with the activity of 

 the stomach, or pancreas, that of the duodenum is probably 

 only small. 



Protease (erepsin) is one of the most important ferments 

 found in the intestinal juice. This ferment, discovered by 

 COHNHEIM, has no action upon "native" proteins except 

 casein, but has the power of splitting proteoses and pep- 

 tones into a number of simpler substances (mono- and 

 diamino acids, ammonia, etc.) which are similar to those 

 formed through the action of either acid- or alkali-pro- 

 teinase on proteins. Protease must therefore not be con- 

 founded with the proteolytic ferments of either the stomach 

 or pancreas. The presence of this ferment in human in- 

 testinal juice has been proved by HAMBURGER and HEKMA. 



Lipase (steapsin). It is ordinarily stated that lipase does 

 not occur in the intestinal juice or in the mucosa. The 

 experiments of KASTLE and LOEVENHART indicate, however, 

 that it is found in all portions of the mucosa of the small 

 intestine in sufficient amounts to be of the greatest impor- 

 tance in the absorption of fats. The lipase of the intestine 

 is identical with that of the pancreas and pancreatic juice, 

 and, like the latter, splits fats into fatty acid and alcohol. 



Amylase is found in the small intestine and is secreted 

 in sufficient amounts to play an important role in the absorp- 



