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, 
