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 



