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pursued the following method : Into groups of 

 stationary barrels they poured a mixture of 

 two-thirds ripened vinegar and one-third 

 wine. On the surface of this mixture there 

 was formed a thin film, of which no one knew 

 the composition, but which was necessary in 

 order to obtain a prompt and thorough acetifi- 

 cation, or transformation into vinegar. The 

 manufacturers took great care of this film, for, 

 if it was dislodged or if it sank to the bottom 

 of the barrels, the whole operation had to be 

 done over. What was this film which, in order 

 to work well, required a current of fresh air 

 that was furnished by drilling an opening in 

 the barrels a little above the level of the liquid? 

 Pasteur worked for nearly a year on this prob- 

 lem, and he proved that acetification was caused 

 by a microbe which, living on the surface of the 

 liquid, obtained oxygen from the air and trans- 

 ferred a part of it to the liquid below, which 

 in this way was oxidised. He gave this microbe 

 the name of mycoderma aceti, or mycoderm 

 of vinegar. This ferment is endowed with 



