62 PASTEUR: THE HISTORY OF A MIND 



budding, and probably acting on sugar only as a result of 

 their growth." 



It was only a phrase. Schwann had brought argu- 

 ments and made experiments. He had shown in the 

 first place that, contrary to what Gay-Lussac had said, 

 oxygen was not sufficient to start a fermentation. When 

 heated air was admitted to sugared must, the sugar re- 

 mained intact, and no yeast was produced. But the 

 oxygen in the air had not been touched. That which was 

 lacking was a something contained in the air, which the heat 

 had destroyed. Schwann says clearly that this some- 

 thing is a germ; he even says it is a vegetable germ, 

 basing this statement upon the fact that he has found 

 the yeast sensitive to arsenic, like many vegetables, and 

 not to nux vomica, which is deadly to many animals. 

 He found the yeast in the precipitate of fermented bever- 

 ages ; he assured himself that the fermentation begins only 

 when the yeast is present, and is arrested when the 

 yeast ceases to multiply. He recognized the existence 

 of a very close relation between the reproduction of the 

 yeast and the fermentation, and in closing, he expresses 

 the opinion that the plant nourishes itself on the sugar 

 and rejects in the form of alcohol everything that it 

 cannot use. 



Almost word for word this is a statement of our 

 present ideas. So perfectly do we agree with it that 

 we ask ourselves why the contemporaries of Schwann 

 were not able to hear his voice. The reason is very 

 simple: they had then* prejudices as we surely have ours. 

 They also loved new ideas less than we; they demanded 

 proofs before accepting new ideas, and it is unfortunate 

 that those of Schwann had not the desired clearness. 

 The very short memoir, in which they were set forth, 

 was given out as a preliminary communication, but 

 this was not followed by any more detailed publication. 



