STUDIES IN FERMENTATION 79 



forms will thrive and produce different effects. 

 Frequently one change follows another, the ordi- 

 nary aerobic organisms using up the available 

 oxygen in the material, and thus creating a condi- 

 tion in which the anaerobes may take their turn. 



Some organisms, as Pasteur found in the case 

 of common yeast of beer and wine and some species 

 of molds, may live either with or without free 

 oxygen. In any case they need oxygen for their 

 life, and if they cannot secure it directly they take 

 it out of some of the compounds in which it is 

 chemically combined. Pasteur found that the 

 ordinary yeast of beer, if given abundant oxygen, 

 would grow rapidly, but would produce very little 

 alcohol. If its supply of oxygen were limited, it 

 would ferment much more of the sugar into alcohol 

 and carbon dioxide. By being forced to wrest 

 away its oxygen from sugar it becomes thereby a 

 ferment. Fermentation depends, therefore, in his 

 view, on the capacity of an organism to live with- 

 out air. 



What is called putrefaction was proven by Pas- 

 teur to be essentially like the phenomena which 

 had been described as fermentations, only it is pro- 

 duced, as a rule, by different kinds of organisms 

 and gives rise to different products. What we com- 



