48 AGRICULTURAL BACTERIOLOGY. 



cause of the fermentations. We should have simply learned 

 that instead of producing the fermentation by a direct metabo- 

 lism or the direct result of their growth, they do it by secret- 

 ing an enzyme which itself produces the chemical change 

 characterizing the fermentation. 



Now this conclusion as to the agency of enzymes in the 

 action of organized ferments is not simply a theoretical one, 

 but one which has been demonstrated by actual observation. 

 It has been shown in recent years that a number of the fer- 

 mentations which were formerly classed as organized are pro- 

 duced directly by enzymes, which enzymes have been pro- 

 duced by living bacteria. For example, there is a class of 

 bacteria which has the power of curdling milk without ren- 

 dering it acid, an action very similar to that of rennet. It 

 has been demonstrated that this curdling is due to an en- 

 zyme secreted by the bacteria and that this enzyme is quite 

 similar to rennet. It may be wholly separated from the bac- 

 teria cells and preserved in the form of a powder, somewhat 

 in the same way that rennet can be separated from the stomach 

 of a young mammal. It will curdle milk as quickly as the 

 rennet. Further, these same bacteria produce a second enzyme 

 which has the power of digesting the curdled milk, and this 

 second ferment is similar to that secreted by the pancreas of a 

 mammal. Numerous other examples might be given, but 

 these are enough to illustrate the fact that some fermentative 

 processes, though fundamentally due to microorganisms, are 

 directly the result of the action of enzymes. It has even 

 been claimed in recent years that the alcoholic fermentation is 

 thus produced. Buchner, by subjecting the yeast cell to high 

 pressure, has separated from the cells a liquid substance which 

 contains no living cells, but which is capable of producing the 

 alcoholic fermentation. He has claimed that this contains an 

 enzyme, named by him zymase, which has been produced by 

 the yeast cell and is the direct cause of the fermentation of the 



