TRANSFORMATION OF ONE SPECIES INTO ANOTHER 193 



On sweetened wine or must of beer, exposed in a 

 shallow porcelain basin, he sowed some mycoderma which 

 formed a pellicle on the surface. He then submerged 

 this pellicle, thoroughly shaking the liquid in order to 

 dislocate and moisten all parts of it. Then he introduced 

 the whole into a flask which he filled completely full and 

 which he closed with a stopper to which was attached a 

 tube, the opposite end of which opened under water 

 so as to allow no contact of air with the liquid. In this 

 closed flask he saw a true fermentation take place, which 

 he attributed to the transformation of the mycoderma 

 cells into yeast. 



At Clermont, where Pasteur did me the honor of 

 working in my laboratory, we repeated this experiment 

 several times, and as I was naturally more intransigent 

 than he, being his pupil, I refused to yield to this proof, 

 and I objected to the possible presence of globules 

 of yeast derived from the air, from the water, or from 

 the flasks before or after the filling, in spite of the pre- 

 cautions taken to avoid it. Pasteur resisted because, 

 in his mind, this fact was related to other ideas which 

 we shall encounter soon, and which are relative to the 

 general theory of fermentation. The experiment, further- 

 more, sometimes succeeded with a clearness which made 

 it convincing and closed my mouth. In short, Pastuer 

 had reported his conviction in Paris, and it reappears 

 several times in his Notes of 1872 and 1873 before the 

 Academy of Sciences. 



If I recall this fact, it is because Pasteur loved to cite 

 it himself as an example of the ease with which the 

 least preconceived idea leads even the most alert observer 

 into error. Thus it is that he has taken pains to re- 

 count how he discovered his self-deception. It is in- 

 teresting to see his mind at work in one of the thousand 

 details of his scientific life. 



