ACETIC FEEMENTATION. 85 



require, and he did not yet know all the precau- 

 tions indicated later on, which were indispensable to 

 success. Though in his original memoir of 1860 

 Pasteur had pointed out the difficulties of his experi- 

 ment, these difficulties existed nevertheless. Liebig 

 took hold of them with skill, exaggerated them ; saw, 

 so to speak, nothing but them ; and declared that the 

 results announced never could have been obtained. 

 But in 1871 the fundamental experiment of Pasteur, 

 on the life of yeast in a sweetened mineral medium, 

 had become a trifle for him. He knew exactly how 

 to form media deprived of all foreign germs, how to 

 prepare pure yeast, and how to prevent the introduc- 

 tion of new germs, which could develop in the liquids 

 and hinder the life of the yeast. 



* Choose,' said he to Liebig, ' from the members 

 of the Academy one or several, and ask them to de- 

 cide between you and me. I am ready to prepare 

 before you and before them, in a sweetened mineral 

 medium, as much yeast as you can reasonably ask for, 

 and with substances provided by yourself.' 



Liebig's second objection had reference to acetic 

 fermentation. The process of acetification known as 

 that of * beech shavings ' is widely practised in Germany 

 and even in France. It consists in causing alcohol 

 diluted with water and with the addition of some 

 millicmes of acetic acid to trickle slowly into barrels 

 or vats filled with shavings of beech, either massed 



