ALCOHOLIC FERMENTS. 117 



of fermentation constitute a group of living beings, whose 

 function as ferments is directly " a necessary consequence of 

 life without air, of life without free oxygen "; and further, that 

 such a fermentation can also take place in a pure sugar solu- 

 tion. He maintains that the reason why Brefeld could not 

 get yeast to develop in a moist chamber in an atmosphere of 

 carbonic acid, was because he was working with old yeast-cells, 

 whilst it is only possible for yeast to multiply in the absence 

 of free oxygen when the cells are very young. The minute 

 quantity of free oxygen which is present in the liquid to 

 which the yeast is added " rejuvenates the cells and makes 

 it possible for them to again resume the power to bud, to 

 preserve life, and to carry on their multiplication without 

 access of air." 



Hence Pasteur makes a distinction between two classes 

 of organisms : aerobic, those which cannot live without the 

 presence of free air ; and anaerobic, those which can exist in 

 the absence of air. According to his view, these latter 

 constitute " ferments in the true sense of the word." 



It would be incorrect to assume that the presence of 

 alcohol and carbonic acid amongst the products of a fermen- 

 tation unconditionally presupposes the influence of "organisms 

 of alcoholic fermentation in the true sense of the term." 

 The researches of Lechartier and Bellamy, which were 

 subsequently extended by Pasteur, showed, namely, that 

 when grapes, oranges, and other fruits on which no yeast^cells 

 were present, were preserved in vessels filled with carbonic 

 acid, a development of alcohol and carbonic acid took place. 

 " The fermentative character is consequently not a condition 

 of the existence of yeast ; the fermentative power is not 

 peculiar to cells of a special nature, is no fixed structural 

 characteristic, but is a property which is dependent upon 

 external conditions and upon the mode of nutrition of the 

 organism." 



" In short, fermentation is a very general phenomenon. 

 It is life without air, life without free oxygen; or more 



