44 AGRICULTURAL BACTERIOLOGY. 



These discoveries led to a sharp separation of fermenting 

 substances into two different classes. On the one hand were 

 those which, like yeast, w r ere produced by organisms and were 

 called organized ferments, and on the other those which con- 

 tained no organisms and were called unorganized ferments. 

 These latter ferments later received the name of enzymes, which 

 name is now in most common use. 



During the last twenty years there has been a gradual 

 breaking down of the distinction between the two classes, 

 which is leading toward the conclusion that the two types of 

 fermentation may be fundamentally one. This conclusion is 

 greatly modifying our attitude toward quite a number of fer- 

 mentations of importance to agriculture, which have been pre- 

 viously attributed to bacteria. 



THEORIES AS TO THE NATURE OF FERMENTATION. 



From the beginning of the modern study of fermentation 

 various explanations have been given as to the actual manner 

 in which the fermentation is caused. The action of cnzvmes 

 has from the beginning been regarded as a purely chemical phe- 

 nomenon. But the organic fermentations have received several 

 different explanations. Early in the century Kutzig first ad- 

 vanced the theory that such fermentations were physiological 

 processes resulting from the life processes of the fermenting 

 organisms. But this view of the phenomenon was combated 

 by Liebig who regarded the organic fermentations as purely 

 chemical phenomena. His conception was that fermentable 

 bodies consisted of molecules in a condition of unstable equili- 

 brium which naturally broke to pieces under the stimulus of 

 the presence of a little albuminous matter. 



Liebig's preeminent position as a chemist lent a weight to 

 this theory, which supported it in the face of facts, until Pasteur 

 succeeded in establishing conclusively the relation of the phe- 

 nomena to the growth of living organisms. But Pasteur's 



