STUDIES ON FERMENTATION. 247 



nated more or less with oxygen. The yeast immediately seizes 

 upon this gas and acquires a state of freshness and activity, which 

 permits it to live afterwards out of contact with air, and to act as 

 a ferment. Thus, in ordinary brewery practice, we find the yeast 

 already formed in abundance even before the earliest external 

 signs of fermentation have made their appearance. In this first 

 phase of its existence, yeast lives chiefly like an ordinary fungus. 



From the same circumstances it is clear that the brewer's 

 fermentations may, speaking quite strictly, last for an indefinite 

 time, in consequence of the unceasing supply of fresh wort, and 

 from the fact, moreover, that the exterior air is constantly being 

 introduced during the work, and that the air contained in the 

 fresh worts keeps up the vital activity of the yeast, as the act of 

 breathing keeps up the vigour and life of cells in all living 

 beings. If the air could not renew itself in any way, the vital 

 activity which the cells originally received, under its influence, 

 would become more and more exhausted, and the fermentation 

 eventually come to an end. 



We may recount one of the results obtained in other experi- 

 ments similar to the last, in which, however, we employed j^east 

 which was still older than that used for our experiment with 

 flask A (Fig. 60), and moreover took still greater precautions to 

 prevent the presence of air. Instead of leaving the flask, as 

 well as the dish, to cool slowly, after having expelled all air by 

 boiling, we permitted the liquid in the dish to continue boiling 

 whilst the flask was being cooled by artificial means ; the end of 

 the escape tube was then taken out of the still boiling dish and 

 plunged into the mercury trough. In impregnating the liquid, 

 instead of employing the contents of tlie small cylindrical funnel 

 whilst still in a state of fermentation, we waited until this was 

 finished. Under these conditions, fermentation was still going 

 on in our flask, after a lapse of three months. We stopped it 

 and found that 0-255 gramme (3-9 grains) of yeast had been 

 formed, and that 45 grammes (693 grains) of sugar had 

 fermented, the ratio between the weights of yeast and sugar 



0*255 1 



being thus = . In this experiment the yeast de- 



45 176 



