518 



BIOLOGY OF THE MICRO-ORGANISMS. 



Yeast ashes. 



certain quantities from yeast by extraction with ice- 

 water (with regard to this point see below). In like 

 manner, besides cellulose, we find gum-like bodies, 

 glycerine, succinic acid, &c., which are also carbonaceous 

 and non-nitrogenous materials ; usually, however, these 

 substances occur in too small quantities to exert any 

 marked influence on the relation between proteid and 

 cellulose. 



Of the several analyses of the ashes of yeast, the 

 following results seem the most trustworthy (Mit- 

 scherlich) : 



Potash 



Phosphoric acid 



Calcium 



Magnesia 

 Silicic acid 



Ashes of Yeast. 

 High Fermentation. 

 38'8 per cent. . 

 53-9 



i-o 



6-0 

 Traces 



Ashes of Yeast. 

 Low Fermentation. 

 . . . 28'3 per cent. 

 ... 59-4 

 ... 4-3 

 81 



The ashes are therefore chiefly distinguished from 

 those of the mould fungi by the much larger quantity 

 of phosphoric acid present, this difference corresponding 

 entirely to the larger amount of albumen. 



Nutrient 

 materials. 



2. The Nutrient Materials of the Budding Fungi. 



In investigating the mode of nutrition and the nutrient 

 materials of the yeast fungi, it is necessary to note that 

 these terms are not identical with fermentation and 

 fermentescible materials. Fermentation runs its course 

 to a certain extent independently of the nutrition of the 

 yeast ; it is not a necessary part of the tissue change of 

 the cells, but only forms an extension and complication 

 of the same, which it is better to disregard for the present 

 in attempting to ascertain the nature of the necessary 

 nutrient materials, a*nd the mode in which they are 

 used up by the yeast cells. This separation of the two 

 processes has only been properly carried out in the more 

 recent experiments, while on the other hand former 

 investigators always linked fermentation and the growth 

 of yeast together. The more recent investigations made 



