214 PASTEUR: THE HISTORY OF A MIND , v 



instruct it, perhaps even give rise to some new ideas 

 there, but it is sterile for those who have taken part in it. 

 A savant is not the routine man of the study; he is the 

 man of the laboratory. 



VII 

 ORIGIN OF THE YEASTS OF WINE 



Pasteur had entered into his own domain in the dis- 

 cussion of a part of the posthumous work of Bernard. 

 He wished to elucidate a question which he had had 

 at heart since the beginning of his studies on alcoholic 

 fermentation, to which he has returned many times, 

 but which he has not completely solved, because it is 

 difficult. That is the question of the origin of yeasts. 



In his Etudes sur la bi&re, he had very much enlarged 

 the conclusions of his first memoir of 1862, published 

 in the Bulletin de la sodete chimique, and had shown 

 that there existed a great number of yeasts, different 

 not only in form, but also in their physiological prop- 

 erties and in the various tastes which they communicate 

 to the liquids which they ferment. But whence come 

 these numerous yeasts? Are they special vegetative 

 forms of a microscopic plant other than the yeast, and 

 known under another name? And if so, what is this 

 plant? or rather, what are the different plants which 

 give birth to the different yeasts? If, on the contrary 

 these yeasts have no other form of reproduction than 

 that with which we are familiar, how, in nature, do they 

 pass the winter and the periods during which there are 

 no sugary solutions to ferment? Experiment teaches, 

 as a matter of fact, that, when dried and exposed to the 

 air, the various yeasts rapidly lose their vitality. 



