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LOUIS PASTEUK 



although with less activity, and under these circumstances 

 its fermentative character will be most marked; under these 

 circumstances, moreover, we shall find the greatest dispro- 

 portion, all other conditions being the same, between the 

 weight of yeast formed and the weight of sugar decomposed. 

 Lastly, if free oxygen occurs in varying quantities, the 

 ferment-power of the yeast may pass through all the degrees 

 comprehended between the two extreme limits of which 

 we have just spoken. It seems to us that we could not 

 have a better proof of the direct relation that fermentation 

 bears to life, carried on in the absence of free oxygen, 

 or with a quantity of that gas insufficient for all the acts 

 of nutrition and assimilation. 



Another equally striking proof of the truth of this theory 

 is the fact previously demonstrated that the ordinary moulds 

 assume the character of a ferment when compelled to live 

 without air, or with quantities of air too scant to permit of 

 their organs having around them as much of that element 

 as is necessary for their life as aerobian plants. Ferments, 

 therefore, only possess in a higher degree a character which 

 belongs to many common moulds, if not to all, and which 

 they share, probably, more or less, with all living cells, 

 namely the power of living either an aerobian or anaerobian 

 life, according to the conditions under which they are 

 placed. 



It may be readily understood how, in their state of 

 aerobian life, the alcoholic ferments have failed to attract 

 attention. These ferments are only cultivated out of con- 

 tract with air, at the bottom of liquids which soon become 

 saturated with carbonic acid gas. Air is only present in 

 the earlier developments of their germs, and without at- 

 tracting the attention of the operator, whilst in their state 

 of anaerobian growth their life and action are of pro- 

 longed duration. We must have recourse to special ex- 

 perimental apparatus to enable us to demonstrate the mode 

 of life of alcoholic ferments under the influence of free 

 oxygen ; it is their state of existence apart from air, in the 

 depths of liquids, that attracts all our attention. The results 

 of their action are, however, marvellous, if we regard 

 the products resulting from them, in the important in- 



