32 THE NATURE OF THE ACTIVITIES OF MICROORGANISMS. 



the grain, etc. The larger part of the enzymes listed above are 

 secreted by certain plants. The power to secrete enzymes is thus 

 quite a common property of plant cells. Indeed, it is becoming 

 evident that many so-called life processes are produced directly 

 by enzymes secreted by animals and plants. Now, the action 

 produced by the enzyme trypsin, secreted by the digestive glands of 

 animals, is very similar, if not identical, with the action produced 

 by certain of the bacteria when growing and acting upon proteid 

 food. It is a natural question to ask if it may not be true that 

 the bacteria secrete an enzyme similar to trypsin, and that their 

 action upon their food is really a digestion due to the enzyme which 

 they secrete. Are not both cases properly called digestion? If 

 we can find such an enzyme in a solution where these bacteria have 

 been growing for a time, it would follow that they must have secreted 

 it and that their action upon the proteid food is due directly to the 

 enzyme. This question will at once broaden into a second one, 

 and we shall be forced to ask whether the action on all organized 

 ferments may not be explained by supposing the living bacteria 

 or yeasts to secrete an enzyme whose direct action is responsible 

 for the fermentative change. If this be the case, the distinction 

 between the organized and unorganized ferments disappears. 

 The so-called organized ferments would then act in exactly the 

 same way as the unorganized, the difference being simply that 

 in the one case the enzyme is secreted by the active cells of larger 

 animals and plants, and in the other by the active cells of bacteria 

 and yeasts. 



Now this conclusion is not simply a theoretical one, but it has 

 been demonstrated to be true for at least a considerable portion of 

 the organized fermentations. In the first place, it has been shown 

 that the power of secreting enzymes is a common one among fungi; 

 common molds are known to secrete enzymes of much the same 

 nature as digestive enzymes. They soften up proteid substances, 

 in order, apparently, that they may absorb them. In other words, 

 they "digest" them for their own use. When, in pursuance of this 

 idea, we study carefully the various fermentations at first regarded 

 as belonging to the class of organized ferments, we find, in some cases, 



