36 FERMENTATION, PUTREFACTION, AND DECAY 
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 
normalmanner ‘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 
takes inside of itself the sugar which the enzyme ferments, after 
which the cell ejects the products of fermentation, alcohol, and car- 
bon dioxid. 
There are still, however, some fermentations concerning which 
it has been impossible as yet to prove the formation of an enzyme. 
The lactic acid bacteria have the power of fermenting milk-sugar 
and producing lactic acid from it. Careful search has been made, 
for an enzyme with but partial success. It is very probable that 
here, too, the enzyme may be produced and that it is not secreted 
from the bacterial cell. Should this eventually prove to be true, it 
would apparently reduce all types of fermentation to the one of 
enzyme action. This would not reduce in the slightest degree the 
importance of the microdrganisms in the matter. It would still 
be the fact that this large class of chemical changes is brought 
about by the life activities of living organisms, but we would under- 
stand that they perform their action by first secreting enzymes and 
that the enzymes are the direct agents for bringing about the fer- 
mentative changes. 
It is desirable to notice also that even if we accept the enzyme 
conception of fermentations we are no nearer a satisfactory under- 
standing of the real nature of the phenomenon. For over fifty 
years science has been trying to explain these mysterious changes 
