82 LOUIS PASTEUR. 



that the vinegar is formed by the action of the myco- 

 dermic film on its surface, we can understand at once 

 that the mycoderm and the little eels continually 

 carry on a struggle for existence, since both of these 

 living things the one animal the other vegetable 

 imperiously demand the same aliment, oxygen. They 

 live, moreover, in the same superficial layers, a circum- 

 stance which gives rise to very curious phenomena. 

 When, for one reason or another, the film of myco- 

 derm is not formed, or when there is any delay in 

 its production, the little eels invade in such great 

 numbers the upper layers of the liquid that they 

 absorb all the oxygen. The little plant has in conse- 

 quence great difficulty in developing itself or even in 

 beginning its life. Eeciprocally, when the work of 

 acetification is active, and when the mycoderm has 

 occupied the upper layers, it gradually drives away 

 the eels, which take refuge, not deep down, where 

 they would perish, but against the moist sides of the 

 barrel or the vat. There they form a thick whitish 

 scum all in motion. It is a very curious spectacle. 

 Here their enemy, the mycoderm, can no longer 

 injure them to the same extent, since they are sur- 

 rounded with air ; and here they wait with impatience 

 tor the moment when they can again take their place 

 in the liquid, and, in their turn, fight against the 

 mycoderm. In Pasteur's process, where the vats are 

 very often cleansed, it is easy to keep them free from 



