THEORY OF FERMENTATION 297 



The proportions were I of yeast to 76 of fermented 

 sugar in the first case, and I of yeast to 89 of fermented 

 sugar in the second. 



From these facts the following consequences may be de- 

 duced: 



1. The fermentable liquid (flask B), which since it had 

 been in contact with air, necessarily held air in solution, 

 although not to the point of saturation, inasmuch as it had 

 been once boiled to free it from all foreign germs, furnished 

 a weight of yeast sensibly greater than that yielded by the 

 liquid which contained no air at all (flask A) or, at least, 

 which could only have contained an exceedingly minute 

 quantity. 



2. This same slightly aerated fermentable liquid fer- 

 mented much more rapidly than the other. In eight or ten 

 days it contained no more sugar; while the other, after 

 twenty days, still contained an appreciable quantity. 



Is this last fact to be explained by the greater quantity 

 of yeast formed in B? By no means. At first, when the 

 air has access to the liquid, much yeast is formed and little 

 sugar disappears, as we shall prove immediately; never- 

 theless the yeast formed in contact with the air is more 

 active than the other. Fermentation is correlative first to 

 the development of the globules, and then to the continued 

 life of those globules once formed. The more oxygen these 

 last globules have at their disposal during their formation, 

 the more vigorous, transparent, and turgescent, and, as a 

 consequence of this last quality, the more active they are 

 in decomposing sugar. We shall hereafter revert to these 

 facts. 



3. In the airless flask the proportion of yeast to sugar was 

 fo ; it was only ^ in the flask which had air at first. 



The proportion that the weight of yeast bears to the weight 

 of the sugar is, therefore, variable, and this variation de- 

 pends, to a certain extent, upon the presence of air and the 

 possibility of oxygen being absorbed by the yeast. We 

 shall presently show that yeast possesses the power of 

 absorbing that gas and emitting carbonic acid, like ordinary 

 fungi, that even oxygen may be reckoned amongst the num- 

 ber of food-stuffs that may be assimilated by this plant, and 



