252 STUDIES ON FERMENTATION. 



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. Schiitzenberger has 

 recently published, the author criticises the deductions that we 

 have drawn from the preceding experiments, and combats the 

 explanation which we have given of the phenomena of fermen- 

 tation.* It is an easy matter to show the weak point of M. 

 Schiitzenberger's reasoning. We determined the power of the 

 ferment by the relation of the weight of sugar decomposed to 

 the weight of yeast produced. M. Schiitzenberger asserts that 

 in doing this we lay down a doubtful hypothesis, and he thinks 

 that this power, which he terms fermentative energy, may be 

 estimated more correctly by the quantity of sugar decomposed 

 by the unit-weight of yeast in unit-time ; moreover, since our 

 experiments show that yeast is very vigorous when it has a 

 sufficient supply of oxj^gen, and that, in such a case, it can 

 decompose much sugar in a little time, M. Schiitzenberger con- 

 cludes that it must then have great power as a ferment, even 

 greater than it has when it performs its functions without the aid 

 of air, since under this condition it decomposes sugar very slowly. 

 In short, he is disposed to draw from our observations the very 

 opposite conclusion to that which we arrived at. 



M. Schiitzenberger has failed to notice that the power of a 

 ferment is independent of the time during which it performs its 

 functions. We placed a trace of yeast in one litre of saccharine 

 wort ; it propagated, and all the sugar was decomposed. Now, 

 whether the chemical action involved in this decomposition of 

 sugar had required for its completion one day, or one month, or 

 one year, such a factor was of no more importance in this matter 

 than the mechanical labour required to raise a ton of materials 

 from the ground to the top of a house would be affected by the 



* [International Science Series, vol. xx., pp. 179-182. London, 1876. — 

 D. C. E.] 



