374 LOUIS PASTEUR 



mineral medium by the albuminous matters that they intro- 

 duce into it. It is interesting to peruse, in our Memoir of 

 1860, certain facts of the same kind relating to fermentation 

 by means of albumens that of the blood for example, from 

 which, we may mention incidentally, we were led to infer the 

 existence of several distinct albumens in the serum, a con- 

 clusion which, since then, has been confirmed by various 

 observers, notably by M. Bechamp. Now, in his experiments 

 on fermentation in sweetened water, with yeast-ash and a 

 salt of ammonia, there is no doubt that Liebig had failed to 

 avoid those difficulties which are entailed by the spontaneous 

 growth of other organisms than yeast. Moreover, it is pos- 

 sible that, to have established the certainty of this result, 

 Liebig should have had recourse to a closer microscopical 

 observation than from certain passages in his Memoir he 

 seems to have adopted. We 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. We ourselves, for the rea- 

 sons mentioned, did not obtain a simple alcoholic fermenta- 

 tion 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 appre- 

 ciable quantity of lactic acid formed and arrested the propa- 

 gation of the lactic and alcoholic ferments, so that more 

 than half of the sugar remained in the liquid without fer- 

 menting. This, however, in no way detracted from the cor- 

 rectness of the conclusion which we deduced from the ex- 

 periment, 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 satis- 

 factory, inasmuch as we demonstrated that mineral media 

 were adapted to the simultaneous development of several 

 organized ferments instead of only one. The fortuitous asso- 

 cation of different ferments could not invalidate the conclu- 

 sion that all the nitrogen of the cells of the alcoholic and lac- 

 tic ferments was derived from the nitrogen in the ammonia- 

 cal salts, and that all the carbon of those ferments was taken 

 from the sugar, since, in the medium employed in our exper- 

 iment, the sugar was the only substance that contained car- 



