1889.] 



on Yeast. 



577 



has proved that, in its absence, the yeast will, when denied free access 

 of atmospheric oxygen, and when fermentation has once started, 

 decompose a portion of itself in order to obtain the necessary elements 

 to maintain its vitality. But given the necessary excess of carbo- 

 hydrate, and assuming that in two or more flasks undergoing alcoholic 



fermentation the conditions of culture are the same with respect to 

 temperature, pressure, food, and amount of ferment added, it follows 

 that the rate of evolution of carbonic anhydride becomes a measure 

 of the fermentative activity of the fungus respectively producing it. 

 I have here an apparatus devised to effect this measurement. It will 

 be seen to be extremely simple in its working, but I find that it gives 

 results of surprising constancy. 



As introductory to the working of this apparatus, I will ask your 

 permission to repeat the well-known experiment which proves that 

 carbonic anhydride is one of the resulting products of alcoholic 

 fermentation. [Experiment shown.] 



The two flasks which I have here, contain (represented in the 

 diagram) equal (xuantities of the same sugar solution and of the 



