132 PASTEUR: THE HISTORY OF A MIND 



agent of acetification in the German vinegar works; 

 "for," he said, "on a wood shaving which had been 

 used for 25 years in a large vinegar factory in Munich, 

 there was no trace of mycoderma visible, even under the 

 microscope." 



In the presence of these denials, Pasteur had recourse 

 anew to the tactics which had proved so successful with 

 Pouchet, Joly and Musset. He demanded that Liebig 

 present himself, in company with him, before a com- 

 mission of the Academy of Sciences, which should be 

 charged with the duty of pronouncing between them, and 

 in the presence of which Pasteur offered in the first place 

 to prepare, in an exclusively mineral medium, as much 

 yeast of beer as Liebig could reasonably demand; in 

 the second place he promised to show to the commis- 

 sion, and to Liebig himself, the acetifying mycoderma 

 on all the beech shavings of the factory in Munich. 



The challenge was urgent. Pasteur would not have 

 been in position to give it at the time of his studies in 

 1860 on alcoholic fermentation. His cultures of yeast 

 in a mineral medium were at that time too poor and too 

 uncertain, but since he had begun his studies on beer, 

 to which we shall soon refer, and had found yeasts ac- 

 commodating themselves to these mediocre culture con- 

 ditions, he was sure of his facts. Liebig did not accept 

 the challenge. He only remained a little melancholy. 



I have as proof of this a letter in which he states the 

 somewhat fallacious idea, that by going into the subject 

 thoroughly enough, Pasteur and he would have ended by 

 discovering and understanding each other. "I have 

 often thought," he wrote me in 1872, "in my long prac- 

 tical career and at my age (69 years), how much pains 

 and how many researches are necessary to probe to the 

 depths a rather complicated phenomenon. The greatest 

 difficulty comes from the fact that we are too much ac- 



