108 NATURE OF PROTEOLYTIC FERMENTS 



because the whole organ has become similarly dis- 

 harmonious. 



The fact that the animal organism replies to the 

 invasion of disharmonious substances which, either 

 taking their origin from the metabolism of certain 

 cells of its organs, or being normal constituents of 

 the cells, pass directly into the blood plasma by 

 means of specifically directed ferments, is of the 

 greatest importance to physiology as well as to 

 pathology. 



Up to the present we have only been able to dis- 

 tinguish three different proteolytic ferments, namely,, 

 pepsin, trypsin, and erepsin. In addition to these, 

 we may perhaps reckon as proteolytic the ferments of 

 rennet, and of fibrin. Strictly speaking, erepsin must 

 be excluded, because it is principally directed against 

 the products of decomposition of albumen. Our 

 experience of the defensive ferments induces the 

 supposition that trypsin, for instance, is not uniform 

 in its nature. Of course, it may be possible that 

 there are ferments which, just as a master-key can 

 open various kinds of locks, are able to decompose 

 very different substrates, when these belong to the 

 same type of compound. But it is more likely that, 

 in trypsin, ferments of different kinds are combined, 

 and that in the blood the different components each 

 act separately. 



The defensive ferments are, as we have already 



