136 MICRO-ORGANISMS AND FERMENTATION. 



to decompose a large amount of sugar within a short time ; 

 thus, the activity or energy is expressed by the amount of 

 sugar fermented in unit time, and determined as the proportion 

 between the weight of decomposed sugar on one hand, and the 

 weight of yeast and time elapsed on the other. If the fermented 

 sugar is termed S, the amount of yeast, I, and the duration of 

 the fermentation, t, then, according to PASTEUR, the fermenta- 



Of 



tive power = , and the activity or energy = . But the activity 

 I it y 



of the yeast-cell is continuous, and the quantity expressed by -, 



l 



therefore represents the amount of sugar fermented for the 

 total number of time units during which the fermentation 

 lasted. Therefore the duration must necessarily be taken into 

 account in comparisons made for the purpose of determining 

 the fermentative power of yeast (pouvoir du ferment) ; for the 

 duration decides the results of the experiment according to 

 which PASTEUR determines the fermentative power, and upon 

 which he builds up his theory ; but as he does not reckon with 

 the time elapsed, it follows that his determinations must be 

 incorrect, annihilating the foundation of the theory. Thus, 

 PASTEUR'S " power of the ferment " and " activity " of the 

 yeast in reality amount to one and the same thing. 



In PASTEUR'S experiments, however, the real determinations 

 of time which were requisite for establishing the total power of 

 the ferment could not be made, because the amount of sugar 

 upon which the yeast had to react was too small. When 

 BROWN carried out a fermentation according to PASTEUR'S 

 experiments, with a supply of air, until the original amount of 

 sugar had been fermented, and when he then added fresh 

 amounts of sugar, the yeast was able to ferment three times as 

 much sugar as there was originally present, without any 

 increase of weight of the yeast taking place. It also deserves 

 notice that PASTEUR used cane-sugar, which had previously to 

 be inverted ; this inversion, which does not depend on the 

 fermentative function, could only take place slowly under the 

 conditions of PASTEUR'S experiments, and he ought to have 

 allowed for the time taken in inversion. 



BROWN also points out the fact that none of PASTEUR'S 



