GRADUAL DEVELOPMENT OF THE GERM THEORY. 79 



most necessary condition of fermentation ; lie looked on 

 it as practically an indispensable condition for every 

 fermentation, and formulated his views by saying that 

 fermentation occurred as soon as any living cell was 

 compelled to grow in the absence of oxygen, and that 

 wherever fermentation was found there also the oxygen 

 was deficient. More especially in the case of the 

 alcoholic fermentation Pasteur assumed that the yeast 

 cells, owing to the deficiency of oxygen, took it from the 

 sugar molecule, and thus caused the latter to break up. 



Numerous later investigations have shown that 

 Pasteur's results are only in part correct; the majority of 

 fermentative organisms can, it is true, live and grow with- 

 out free oxygen, and it is especially those organisms which 

 can exist without oxygen which possess the property of 

 exciting fermentation. But, and in this the more recent 

 views differ somewhat from Pasteur's, these organisms 

 are as a rule also able to thrive when oxygen is admitted, 

 destruction or hampering of their development by 

 oxygen only rarely happens, and the vegetative life and 

 the fermentative action of the most typical fermentative 

 organisms occurs most actively in the presence of 

 oxygen. 



Pasteur's view as to the more exact manner in which 

 decomposition of the fermentescible materials by the 

 micro-organisms takes place has not, therefore, held its 

 ground, and other investigators have only as yet been 

 able to suggest more or less probable hypotheses as to 

 the nature of the physiological process of fermentation, 

 and none of these views can be looked on as free from 

 objection. (Compare the remarks in the fourth part.) 

 But the numerous experiments which have been under- 

 taken as proof of the one or the other hypothesis have 

 always shown that the most intimate relations exist 

 between the living micro-organisms and the ferment- 

 ations, and that fermentation must undoubtedly be 

 looked on as a physiological act of the micro-organisms. 

 In favour of this view we have, besides the numerous 

 experiments of Schwann and his followers, the fact that ^ 

 the intensity of the fermentation runs parallel with the yeast cells 



