DISCUSSION WITH LIEBIG 131 



be cultivated and transferred from medium to medium 

 with its specific properties. The other theory denies 

 this fertile specificity, since it admits again in 1869, 

 as we have just seen, that the cells of the yeast can 

 separate "the elements of sugar or of other organic 

 molecules." 



These two memoirs of Liebig were translated and 

 published in 1871 in the Annales de chimie et de physique. 

 I cannot surmise what procured for them the honor of 

 this exhumation. Pasteur was taken by surprise, and 

 replied in the Comptes-rendus de I'Academie. The war 

 of 1870 had just ended, and his soul was embittered. 

 He did not consider at all in these memoirs the special 

 pleading, or dissertation, on origins and causes. He 

 went straight to the facts. Liebig had had the impru- 

 dence to gainsay some of those facts which troubled him. 

 He would not have it, for example, that the yeast could 

 develop, live and produce fermentation in a medium 

 containing only sugar, mineral salts and ammonia, as 

 the exclusive source of nitrogen. The last dress given 

 to his theory demanded in addition to these, as I have 

 emphasized above, a previously elaborated albuminous 

 compound. 



In this respect I find it very difficult to come to terms 

 with Liebig. While he was on the scent of philosophical 

 explanations, he could just as well have admitted that 

 the yeast itself manufactured in its own tissues the 

 albuminoid substance of which it had need. I do not 

 see wherein this conception stood in the way of the final 

 development of his theory. But he had his idea, which 

 the experiments of Pasteur contradicted. He, therefore, 

 had repeated this experiment of fermentation in a mineral 

 medium and had not succeeded, because it is difficult, 

 and had concluded that Pasteur was deceived. 



He denied, furthermore, that Mycoderma aceti was the 



