METHODS IN THE MANUFACTURE OP 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 some- 

 thing which resembled it in the factory of Orleans, a 

 village which, for a long time, has had a merited reputa- 

 tion 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 

 fermented vinegar and unfermented 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 sometimes, God knows, with how much trouble, 

 expense and groping about ! A blast of heat, a blast of 

 cold, may suddenly 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 d, la 

 Lavoisier, which immediately become classic because of 

 their fullness, their elegance and their simplicity. 



