72 LOUIS PASTEUR. 



be acidulated by small quantities of pure acetic acid, 

 one actually sees the mycoderm developing, and the 

 alcohol transforming itself into acetic acid. It is 

 not possible to demonstrate in a more convincing 

 manner that the albuminoid matters of the wine are 

 not in this case the acetic ferment. These albuminoid 

 matters, however, contribute to the acetic fermenta- 

 tion, but only as being an aliment to the mycoderma 

 aceti, and notably a nitrogenous aliment. The true 

 and only ferment of vinegar is the little fungus; it 

 is the great agent of the phenomenon; it, indeed, 

 accomplishes all. 



Is there not a great charm in seeing an obscure 

 subject clearly illuminated by facts well understood 

 and well interpreted ? If in a bottle containing wine 

 and air and raised to a temperature of 50 or 60 

 the wine never turns sour, it is because the germs 

 of the mycoderma aceti, which the wine and the 

 air hold in suspension, are deprived of all vitality 

 by the heat. Placed, however, in contact with ordi- 

 nary air, this once-heated wine can turn sour ; because, 

 though the germs of the mycoderma aceti contained 

 at first in the wine are killed, this is not the case 

 with those derived from the surrounding air. Pure 

 alcoholised water never turns sour, even in contact 

 with ordinary air, and with whatever germs this air 

 may carry, or that may be found in the dust of the 

 vessels which receive it. The reason is that these 



