130 PASTEUR: THE HISTORY OF A MIND 



When the yeast ceases to grow, "the union between the 

 constituent parts of its cell-contents is destroyed, and it 

 is through the movement that goes on there that the 

 cells of the yeast cause a derangement, or a separation, of 

 the elements of the sugar, or of other organic molecules." 

 And behold how, even in the sciences, that is to say 

 where one is dealing only with facts, one can always 

 many the Grand Turk and the Republic of Venice. 

 Liebig made a concession of words on condition that 

 his opponent would make to him a concession of facts. 

 "I grant you," he said, "that this is a vital phenomenon 

 taking place in a living organism, provided you grant 

 me that it is of a chemical order. If you do not make 

 this concession, I shall always have the right to say 

 that you have not looked into the question far enough, 

 that you have been arrested before a closed door which 

 I am trying to open." The curious thing is that, fun- 

 damentally, he was right; that the term vital phenom- 

 enon which Pasteur resolved upon, was in no sense 

 more exact than Liebig's phrase molecular disintegration 

 (d'ebranlement moleculaire) ; that, furthermore, all phe- 

 nomena of nutrition within the cell are reduced neces- 

 sarily to chemical phenomena. But the value of a 

 theory lies not in the words which express it, all of which 

 are necessarily somewhat vague; otherwise, absolute 

 truth and clearness would be reached on a question, and 

 we shall never arrive at that. The value of a theory 

 depends upon the direction which it gives to research. 

 If Liebig was perhaps right in affirming that within 

 the cell, in the deep roots of the vital act, his theory and 

 that of Pasteur were blended, one is astonished to see 

 him ignore or forget that they are essentially distinct 

 from the point of view of research and progress. The 

 one theory affirms the specificity of the act of fermenta- 

 tion and incarnates it in a living organism, which can 



