260 STUDIES ON rERMENTATIOX. 



entirely, or cause it to develop in a saccharine medium de- 

 prived of free oxygen, it will multiply just as if air were 

 present, althougli with less activity, and under these circum- 

 stances its fermentative character will be most marked ; under 

 these circumstances, moreover, we shall find the greatest dis- 

 proportion, 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 com- 

 prehended 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, demonstrated in Chapter IV., 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, there- 

 fore, only possess in a higher degree a character which belongs 

 to many common moulds, if not to all, and which they share, 

 probablj'', more or less, with all living cells, namely the power 

 of living either an aerobian or anaerobian life, according to 

 the conditions under which the}' are placed. 



It may be readily understood how, in their state of aerobian 

 life, the alcoholic ferments have failed to attract attention. 

 Those ferments are only cultivated out of contact with air, 

 at the bottom of liquids which soon become saturated with 

 carbonic acid gas. Air is only present in the earlier develop- 

 ments of their germs, and without attracting the attention 

 of the operator, whilst in their state of anaerobian growth 



expressed as .^ ._, := 3'1." Jules Eaulin, Etudes chimiques sur la vegeta- 

 tion. Eecherches sur le developpement d'une mucedinee dans tin milieu 

 artificiel, p. 192, Paris, 1870. We have seen, iu the case of yeast, that 

 this ratio may be as low as y. 



I 



