330 STUDIES ON FERMENTATION. 



adopted. "\Ye have little doubt that his pupils could tell us that 

 Liebig did not even employ that instrument without which any 

 exact study of fermentation is not merely difficult but well-nigh 

 impossible. AVe ourselves, for the reasons mentioned, did not 

 obtain a simple alcoholic fermentation any more than Liebig 

 did. In that particular experiment, the details of which we 

 gave in our Memoir of 1860, we obtained lactic and alcoholic 

 fermentation together ; an appreciable quantity of lactic acid 

 formed and arrested the propagation of the lactic and alcoholic 

 ferments, so that more than half of the sugar remained in the 

 liquid without fermenting. This, however, in no way detracted 

 from the correctness of the conclusion which we deduced 

 from the experiment, and from other similar ones ; it might 

 even be said that, from a general and philosophical point of 

 view — which is the only one of interest here — the result was 

 doubly satisfactory, inasmvich as we demonstrated that mineral 

 media were adapted to the simultaneous development of several 

 organized ferments, instead of only one. The fortuitous asso- 

 ciation of different ferments could not invalidate the conclusion 

 that all the nitrogen of the cells of the alcoholic and lactic fer- 

 ments was derived from the nitrogen in the ammoniacal salts, 

 and that all the carbon of those ferments was taken from the 

 sugar, since, in the medium employed in our experiment, the 

 sugar was the only substance that contained carbon. Liebig 

 carefully abstained from noticing this fact, which would have 

 been fatal to the very groundwork of his criticisms, and thought 

 that he w^as keeping up the appearance of a grave contradiction 

 by arguing that we had never obtained a simple alcoholic fer- 

 mentation. It would be unprofitable to dwell longer upon the 

 subject of the difficulties which the propagation of yeast in a 

 saccharine mineral medium formerly presented. As a matter 

 of fact, the progress of our studies has imparted to the question 

 an aspect very different from that which it formerly wore ; it 

 was this circumstance which emboldened us to offer, in our 

 reply to Liebig before the Academy of Sciences in 1871, to 

 prepare, in a saccharine mineral medium, in the presence of a 



