128 PASTEUR: THE HISTORY OF A MIND 



unsuitable as food for even the least exacting micro- 

 organism; but it is sufficient, and if one scrapes with the 

 point of a knife the surface of these beech shavings, which 

 seem so sound and clean, he finds there a transparent 

 pellicle formed of cells entirely similar to those in the 

 Orleans casks. The manufacture of vinegar is then 

 everywhere due to bacterial action. 



Ill 

 DISCUSSION WITH LIEBIG 



This conclusion was not calculated to please Liebig, 

 who was defeated on his own ground, and on a question 

 w^here the close analogy between the industrial results 

 and those furnished by platinum black seemed to rule 

 out all physiological action. An old champion such as 

 he could not yield without fighting, and he retaliated 

 with two memoirs, the one On fermentation and the source 

 of muscular energy, 1 read before the Royal Academy of 

 Sciences of Munich in 1868 and 1869, the other 2 in- 

 serted in the Proceedings of the Bavarian Academy in 

 1869. Both demonstrate how difficult it is for even 

 the most eminent scientific man to adapt himself in his 

 old age to new ideas, when they run contrary to the 

 current of those in which he has passed his life. Experi- 

 ence and erudition are then a restraint: one must shed 

 his old skin and abstract himself from all that he has 

 learned. 



As the title of the first of these memoirs indicates, 

 Liebig enlarged the scope of the debate and returned 

 to the question of alcoholic fermentation in search of 



1 Ann. de ch. et de phys., t. XXIII, 4", se. p. 5. 



2 Ib., p. 149. 



