ACETIC FERMENTATION. 69 



in contact with the air, without the least acetifica- 

 tion. In this difference between natural wine and pure 

 water alcoholised, and exposed to contact with air, we 

 touch upon a vital point in the phenomena of fermen- 

 tation. The celebrated theory of Liebig, which Pas- 

 teur was destined to overthrow, might be thus summed 

 up : If pure alcoholised water cannot become sour in 

 contact with air, as is the case with wine, it is because 

 the pure alcoholised water lacks the albuminoid sub- 

 stance which exists in the wine in a state of chemical 

 alteration, and which is a ferment capable of causing 

 the oxygen of the air to combine with the alcohol. 

 And the proof, according to Liebig, that things act 

 rigorously thus is, that if you add to the mixture of 

 water and alcohol a little flour, or a little meat-juice, 

 or even a minute quantity of any vegetable juice, 

 the acetic fermentation arises, as if by compulsion. 

 In other words, by the addition of a small quantity 

 of any nitrogenised substance in process of alteration, 

 you cause the union of the oxygen of the air with the 

 alcohol. 



There is doubtless always in the wine, when it 

 turns sour, a necessary intermediary, producing the 

 fixation of the oxygen of the air ; since in no circum- 

 stances can pure alcohol, diluted to any degree what- 

 ever with pure water, transform itself into vinegar. 

 But this necessary intermediary is not, as the German 

 theory would have it, a dead albuminoid substance ; 



