114 LOUIS PASTEUR. 



jurious alterations, Pasteur, always obedient to a pre- 

 conceived idea, while carefully controlling it with the 

 utmost rigour of the experimental method, asked him- 

 self whether the diseases of wine did not proceed from 

 organised ferments, from little microscopic vegeta- 

 tions ? In the observed alterations, he thought, there 

 must be some influences at work foreign to the normal 

 composition of the wine. 



This hypothesis was verified. In his hands the in- 

 jurious modifications suffered by wines were shown to 

 be correlative with the presence and the multiplication 

 of microscopic vegetations. Such growths alter the 

 wine, either by subtracting from it what they need for 

 their nourishment, or, and principally, by forming new 

 products which are the effect of the multiplication of 

 these parasites in the mass of the wine. 



Everyone knows what is meant by acid nine, 

 sharp ii'ine, sour ivine. The former experiments of 

 Pasteur had clearly shown that no wine can become 

 acid, sharp can, in a word, become vinegar without 

 the presence of a little microscopic fungus known by 

 the name of mycoderma aceti. This little plant is the 

 necessary agent in the condensation of the oxygen of 

 the air, and its fixation on the alcohol of the wine. 

 Chaptal, who published a volume on the art of wine- 

 making, knew of the existence of these mycoderm 

 flowers ; but to his eyes they were only ' elementary 

 forms of vegetation,' which had no influence whatever 





