THE CHEMISTRY OF DIGESTION 423 



which becomes active only when converted into pepsin or trypsin 

 by some activating agent. It has been shown that the conversion 

 of trypsinogen to trypsin occurs only when the pancreatic juice is 

 poured into the small intestine, and that it is brought about 

 through a constituent of the succus entericus, enterokinase. This 

 substance is believed to be an enzym having the sole function of 

 activating trypsinogen to trypsin. The conversion of pepsinogen 

 to pepsin is a similar activation, but whether it is carried on by 

 an enzym, gastric kinase, or by the hydrochloric acid of gastric 

 juice, cannot be said at the present time. 



