66 LOUIS PASTEUR. 



ACETIC FERMENTATION. 



THE MANUFACTURE OF VINEGAR. 



SOON afterwards Pasteur came upon a most curious 

 illustration of the ' fixation ' of atmospheric oxygen by 

 a microscopic organism the transformation of wine 

 into vinegar. As its name indicates, vinegar is 

 nothing else than wine turned sour. Everybody 

 has remarked that wine, left to itself, in circum- 

 stances which occur daily, is frequently transformed 

 into vinegar. This is noticed more particularly 

 when bottles, having been uncorked, are left in a 

 half- empty condition. Sometimes, however, wine 

 turns sour even in corked bottles. In this case 

 we may be sure that the bottles have been standing 

 upright, and that corks more or less defective have 

 permitted the air to penetrate into the wine. The 

 presence of air, in fact, is indispensable to the chemical 

 act of transforming wine into vinegar. How does this 

 air intervene ? And what is the little microscopic 

 creature which, in conjunction with the air, becomes 

 the agent of this fermentation ? 



