76 FEEMENTS AND MICRO -PAKASITES, 



The causal connection between micro-organisms and 

 fermentation and putrefaction is definitely demonstrated 

 by tbe investigations to which we have referred. It 

 was found that organisms were present in all putrefying 

 and fermenting substances; the same organisms were 

 shown to be widely distributed in our surroundings ; 

 it was demonstrated that without these organisms no 

 fermentation or putrefaction occurred even when the 

 fermentescible substances were left otherwise unaltered, 

 the entrance of the organisms being alone prevented,, 

 and that these changes only occurred when living germs 

 had been introduced by contact with the impure 

 surroundings. 



Modeof action But there remained the further question, viz., in what 

 cells in the way the action of these organisms on the fermentescible 

 substances was to be explained ; and the further experi- 

 ments and researches with reference to the etiology of 

 the process of fermentation were made with the view 

 of ascertaining whether fermentation and putrefaction 

 were to be regarded as a vital process, as a manifestation 

 of the life and activity of the causal organisms, and 

 what were the intimate changes that took place. 



Even shortly after Schwann's discovery definite views 

 were formed as to the mode of action of the organisms. 

 Schwann himself asserted that the fermentative process 

 went on pari passu with the growth of the yeast, and 

 that fermentation occurred by the yeast plant with- 

 drawing from the nutritive substratum certain materials 

 necessary for its growth, and at the same time inducing 

 the formation of alcohol from the elements which 

 were of no use for nutrition. The contemporaries of 

 Schwann expressed views which were similar but on 

 the whole more speculative, and not sufficiently based 

 on experiment. The vitalistic theory was in reality first 

 elaborated by Pasteur. It is true that Pasteur did not 

 succeed in finding at first a suitable explanation of the 

 process of fermentation, or one which was permanently 

 adopted; on the contrary, his teaching has undergone 

 most important modifications in the course of time, and 

 as the result of further experiments and better know- 



