METHODS IN THE MANUFACTURE OF VINEGAR 123 



air when microbes do not intervene; but the acetifica- 

 tion in the German process is very rapid. It is true 

 that it was not immediately plain just where the micro- 

 organisms could intervene in this mass of shavings, which 

 always remain unchanged, but there was something 

 which resembled it in the factory of Orleans, a village 

 which, for a long time, has had a merited reputation for 

 its vinegars. 



There they carry on operations in casks lying on end 

 in piles and filled about two-thirds full of a mixture of 

 unfermented vinegar and fermented wine. Now, on the 

 surface of the liquid, in the casks which behave properly, 

 there is a fragile pellicle which the vinegar-maker takes 

 great pains not to disturb and not to submerge, because 

 he considers it a precious ally. Experience having taught 

 him that it needs air, he has opened for it a large window 

 in the top end of the cask, above the surface of the liquid. 

 He watches this pellicle and cares for it. As long as it 

 remains spread over the surface of the liquid, all goes 

 well; if it is broken and falls in fragments, all is lost. 

 It is then necessary to produce a new one; and some- 

 times, God knows, with how much trouble, expense and 

 groping about ! A blast of heat, a blast of cold, may sud- 

 denly interrupt all manufacture. 



What then is this pellicle which is so precious and so 

 delicate? Pasteur had been asking himself this question 

 for a long time, but he only felt himself ripe for the study 

 of this question after he had carried out his studies on 

 the nutrition of micro-organisms and on the spontaneous 

 generations which we have reviewed. He was hence- 

 forth armed and equipped, and less than a year sufficed 

 him to make on this subject one of those researches a la 

 Lavoisier, which immediately become classic because of 

 their fullness, their elegance and their simplicity. 



