PASTEUR: LACTIC FERMENTATION 67 



and as it was defended with energy and talent, it ended 

 by triumphing. Taught in all the books, accepted as 

 true in all the works published on fermentation, it had 

 become almost a dogma, that is to say, what in science is 

 the most difficult to overturn. We may attack facts by 

 showing that they are inexact, experiments by testing 

 their conclusions; but what can we do against a doctrine 

 to some extent philosophic, resting for the most part on 

 argumentation, an argumentation so voluminous that 

 one can demolish certain parts of it without weakening 

 the rest, and which is based on that half mystical con- 

 ception of an imparted movement? 



This detailed exposition was necessary in order 

 to show the state of the question at the time Pasteur 

 approached it, and to understand the nature of the means 

 which he employed to solve it. We shall now be able 

 to go on more quickly: we have reached the level ground. 



V 

 PASTEUR: LACTIC FERMENTATION 



The point which I wish to make clear in the beginning 

 is this: if Pasteur immediately made decided progress in 

 his studies it is because he approached them with another 

 guiding idea than his contemporaries. 



In his memoirs, especially in the introduction to his 

 Memoire sur la fermentation lactique,^ it is easy to find 

 what guided him, but it must be a little more developed. 

 Its origin is an observation made during the study of the 

 rotary power. In many of the industrial fermentations, 

 we meet, as a secondary product, amyl alcohol, a sub- 

 stance endowed with rotary power and capable, further- 



1 Ann. de ch. et de phys., 3'' serie, t. LII. Paris, 1858, p. 404. 



