244 STUDIES ON FERMENTATION. 



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 ; nevertheless 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, trans- 

 parent, and turgescent, and, as a consequence of this last 

 quality, the more active they are in decomposing sugar. We 

 shall revert hereafter to these facts. 



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

 ■g'-y ; it was only y'^ in the flask which had air at first. 



The proportion that the weight of yeast formed bears to the 

 weight of the sugar is, therefore, variable, and this variation 

 depends, 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 number of food-stuffs that 

 may be assimilated by this plant, and that this fixation of 

 oxygen in yeast, as well as the oxidations resulting from it, 

 have the most marked effect on the life of yeast, on the multi- 

 plication of its cells, and on their activity as ferments acting 

 upon sugar, whether immediately or afterwards, apart from 

 supplies of oxygen or air. 



In the preceding experiment, conducted without the presence 

 of air, there is one circumstance particularly worthy of notice. 

 This experiment succeeds, that is to say, the yeast sown in the 

 medium deprived of oxygen develops, only when this yeast 

 is in a state of great vigour. We have already explained the 

 meaning of this last expression. But we wish now to cull 

 attention to a very evident fact in connection with this point. 

 We impregnate a fermentable liquid ; yeast develops and 

 fermentation appears. This lasts for several days and then 

 ceases. Let us suppose that, from the day when fermentation 



