FERMENTATION. 47 



A very long list of such enzymes can now be given, each with 

 its power of producing definite actions upon certain fermentable 

 substances. For example, the following enzymes have been 

 recognized as acting upon starches, sugars and cellulose com- 

 pounds : Trehalase, lactase, inulase, pectase, cytase, carubinase, 

 while zymase, oxydase, invertase, and maltase act on glycerides. 

 The list might be easily extended. Each of these enzymes is 

 the product of the activity of some living plant or animal cell, 

 and each has the active^ power of producing chemical changes 

 of a katabolic (decomposition) nature in certain definite ferment- 

 able substances. 



The fact that plant cells so commonly produce these en- 

 zymes as the result of their active growth led naturally to the 

 question whether the various so-called organized ferments 

 might not act in the same way, and produce their fermenta- 

 tions through the action of enzymes which they secrete. This 

 suggestion was a natural one, for the power of producing en- 

 zymes seems a very common one in the cell activities of higher 

 plants. Is it not likely then, that the same power may be 

 possessed by the lower plants as well, and if so, may not the 

 action of the organized ferments be explained by supposing 

 them to secrete enzymes whose direct action produces the fer- 

 mentative change? If this were the case the difference be- 

 tween the organized and unorganized ferments would in con- 

 siderable degree disappear. The so-called organized ferments 

 would then act in just the same way as the unorganized fer- 

 ments, the difference being simply in the source of the enzymes. 



But although this \vould reduce the two processes to a com- 

 mon ground it would not in the slightest degree affect the 

 close relation of the microorganisms to the process of fermen- 

 tation. It would only place their agency one step further back. 

 If it is true that bacteria produce enzymes and the enzymes 

 directly cause the chemical changes, it still follows that the 

 organized ferments, the bacteria and yeasts, are after all the 



