304 LOUIS PASTEUR 



the yeast and that of the fermented sugar -^ 2 1 ' T -=-^ T , which 

 is considerably higher than the preceding ones. 



We may still further increase this ratio by making our 

 estimation as soon as possible after the impregnation, or 

 the addition of the ferment. It will be readily understood 

 why yeast, which is composed of cells that bud and sub- 

 sequently detach themselves from one another, soon forms 

 a deposit at the bottom of the vessels. In consequence 

 of this habit of growth, the cells constantly covering each 

 other prevents the lower layers from having access to 

 the oxygen held in solution in the liquid, which is ab- 

 sorbed by the upper ones. Hence, these which are covered 

 and deprived of this gas act on the sugar without de- 

 riving any vital benefit from the oxygen a circumstance 

 which must tend to diminish the ratio of which we are 

 speaking. Once more repeating the preceding experiment, 

 but stopping it as soon as we think that the weight of 

 yeast formed may be determined by the balance (we find 

 that this may be done twenty-four hours after impregna- 

 tion with an inappreciable quantity of yeast), in this case 

 the ratio between the weights of yeast and sugar is 

 llr. ?98 8 y uKr = f This is the highest ratio we have been 

 able to obtain. 



Under these conditions the fermentation of sugar is 

 extremely languid: the ratio obtained is very nearly the 

 same that ordinary fungoid growths would give. The car- 

 bonic acid evolved is principally formed by the decom- 

 positions which result from the assimilation of atmospheric 

 oxygen. The yeast, therefore, lives and performs its func- 

 tions after the manner of ordinary fungi: so far it is 

 no longer a ferment, so to say; moreover, we might expect 

 to find it to cease to be a ferment at all if we could 

 only surround each cell separately with all the air that it 

 required. This is what the preceding phenomena teach 

 us; we shall have occasion to compare them later on with 

 others which relate to the vital action exercised on yeast 

 by the sugar of milk. 



We may here be permitted to make a digression. 



In his work on fermentations, which 'M. Schutzenberger 

 has recently published, the author criticises the deductions 





