FERMENTATION. 39 



CHAPTER II. 



0* 



FERMENTATION. 



ALTHOUGH the chemical actions of bacteria are widely varied 

 there are some points in which they all agree. They com- 

 monly result in decomposition. They begin slowly and, as the 

 bacteria increase in numbers, they continue with increasing 

 activity. They result in the disappearance of certain chemical 

 compounds and the appearance of new ones, accompanying 

 the growth of the bacteria. All belong to a type of chemical 

 change which is called fermentation. 



Our understanding of the relation of bacteria to fermenta- 

 tive processes has been greatly modified in the last few years 

 as the result of the study of the method by which the fermen- 

 tations are produced. We have noticed that some of the new 

 substances produced by bacterial life are excretions, but that 

 others do not seem to be the result of the metabolism, 

 never having entered into the bodies of the bacteria. How 

 are the latter changes produced ? The answer to this question 

 involves the whole problem of fermentations as it has been 

 developed in the nineteenth century. Some aspects of the 

 question are so intimately connected with our subject that a 

 brief review of the phenomena of fermentation must be here 

 given. 



We must notice at the outset the extreme significance of fer- 

 mentation in agriculture. It is not easy to define fermentative 

 processes in a manner beyond criticism. In general they are 

 progressive chemical changes taking place under the influence 

 of certain organic substances which are present in very small 

 quantity in the fermenting mass. The nature of the chemical 



