ORGANIZED AND UNORGANIZED FERMENTS. 33 
that the living bacterial cells do secrete an enzyme that actually 
produces the chemical change in the fermented body. For example; 
there is a class of bacteria that has the power of curdling miik 
without rendering it acid, an action very similar to that of the 
enzyme rennin (rennet), secreted by the stomach glands of calves. 
But since the curdling of milk by bacteria was produced by living 
organisms that grow and multiply during the process, it was regarded 
as one of the class of organized fermentations, and was so identified. 
But it has been demonstrated that this curdling is due to an enzyme 
secreted by the bacteria, and that this enzyme is quite similar to 
rennet. It may be entirely separated from the bacteria 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 calf. 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. 
Many other examples of the same nature might be mentioned. 
The general processes of putrefaction and decay are produced, it is 
true, by the destructive agency of microorganisms, but directly, to a 
great extent at least, by the enzymes secreted by the bacteria. But 
while many of the organized fermentations are thus explained, 
some have not been brought so easily into this category, since it has 
been difficult to prove that they do really produce an enzyme. The 
longest known fermentation of all, the alcoholic fermentation of 
sugar by yeast, did not for a long time disclose any enzyme, even 
though careful search was made for one. But, thinking that per- 
haps in this case the yeast cell produced the enzyme but did 
not excrete it, retaining it in its own body, Buchner devised a 
method of crushing the yeast cell and squeezing out the inclosed 
juice. Upon doing this he obtained a liquid containing no living 
matter, but capable of producing the alcoholic fermentation in a 
normal manner. The liquid evidently contained an enzyme which 
had thus been pressed out of the yeast cell. This enzyme has been 
named zymase. It would seem from this that the yeast cell is a 
little chemical laboratory that manufactures an enzyme and then 
