332 STUDIES IN ADVANCED PHYSIOLO'GY 



juice several other substances which it is not yet possible to 

 secure in a pure form, but the presence of which can be 

 easily demonstrated by the actions which they exert. One 

 of these is the ferment called "rennet," a ferment which 

 coagulates milk. Traces of mucin also are present. 



a. Pepsin. The principal ingredient of gastric juice 

 is the ferment called "pepsin." This is an organic com- 

 pound of an albuminous nature, possessing almost all the 

 characteristics of ordinary peptones. It has the property 

 of digesting albumens and albuminoids, transforming the 

 albumens into soluble peptones and the albuminoids into 

 dialyzable gelatin. It is able to effect these changes, how- 

 ever, only in an acid solution, which explains the presence 

 of the free hydrochloric acid in the stomach. In fact, it is 

 possible that the pepsin and the acid may in conjunction, 

 as a pepsin-acid, effect these changes. 



The change from the non-dialyzable and sometimes solid 

 proteids to the liquid and dialyzable peptones is, however, 

 not a direct one. As in the case of the conversion of sugar 

 into maltose by the ptyalin so here there are between the 

 beginning proteids and the final peptones a number of 

 intermediate stages designated as acid albumens and pro- 

 teoses. By the experiments of Kiihne and Chittenden quite 

 a number of these intermediate products have been deter- 

 mined and studied, and these experimenters have worked 

 out a table showing the stages through which the proteids 

 pass toward the final peptones. However, in an elementary 

 text-book these changes are too intricate to be dwelt upon, 

 the significant fact being that a large part of the proteids 

 of the stomach are converted by the continued action of the 

 gastric juice into peptones, while the intermediate stages 

 and any proteids not affected by the gastric digestion are 

 passed into the intestine and there their change into pep- 

 tones is completed by the action of the pancreatic juice. 



. It must not be understood that a proteid is merely a 

 solid albumen and a peptone a liquid albumen. The vital 



