34 THE NATURE OF THE ACTIVITIES OF MICROORGANISMS. 
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 microorganisms 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 understand that 
they perform their action by first secreting enzymes and that the 
enzymes are the direct agents for bringing about the fermentative 
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 
in fermentable bodies. At one time it was thought that they were 
purely chemical processes; but this has been disproved by showing 
that living organisms are necessary to their production. Pasteur 
thought they were due to "life without oxygen," claiming that the 
living germ required oxygen for its life, that if it did not find plenty 
of free oxygen, it would take atoms of this element out of the sugar 
molecules or other fermentable body, and that the withdrawal of this 
oxygen caused the molecule to fall to pieces. This theory has also 
been abandoned. The theory that all living fermenting agents se- 
crete a chemical enzyme appears to stand the test of experiment, but 
it explains little, for we do not know what enzymes are and we have 
absolutely no knowledge of how they act. Are they wholly lifeless 
chemical bodies or are they semiliving, as some would say ? What- 
ever they are, they are still as great mysteries as the fermentations 
