ACETIC FERMENTATION. 81 



Prior to Pasteur's investigations, the ignorance re- 

 garding these organisms was such that they were 

 actually considered necessary to the production of the 

 vinegar ; whereas they are, on the contrary, most inimi- 

 cal to it, and must, if possible, be got rid of. This is, 

 moreover, rendered desirable by the repugnance which 

 is naturally felt to using a liquid denied by the presence 

 of such animalcules a repugnance which becomes 

 almost insurmountable to anyone who has once seen 

 through a microscope the swarms contained in a drop 

 of vinegar. The mischief wrought by these little 

 beings in the manufacture of vinegar results from the 

 fact that they require air to live. The effect can 

 easily be perceived by filling to the brim a bottle of 

 vinegar, corking it, and then comparing it with a 

 similar bottle half filled with the same vinegar, and left 

 uncorked in contact with the air. In the first bottle, 

 the motions of the eel-like creatures become gradually 

 slower, until after a few days they cease to multiply 

 and fall lifeless to the bottom of the vessel. In the 

 second bottle, on the contrary, they continue to swarm 

 and move about. This need of oxygen is further de- 

 monstrated by the fact that, if the vinegar reaches a 

 certain depth in the bottle, life is suspended in the 

 lower parts, and the little eel-like organisms, in order 

 to breathe more freely, form a crawling zone in the 

 upper layers of the liquid. 



Connecting these observations with the other fact 



