48 LOUIS PASTEUR. 



liquor ? Up to a certain point it might be maintained 

 that the dissolved matters which had heen in contact 

 with the oxygen of the air had been thrown into mole- 

 cular motion, that this motion had been communicated 

 to the fermentable matter, and that the deposit of the 

 pretended organised ferment was but an accident 

 one of the physical changes or one of the precipitates 

 so frequently observed in the modifications of albumi- 

 noid matters. In the observation of Cagniard-Latour 

 and of Schwann as to the life of the yeast, Liebig 

 saw nothing more. ' One cannot deny,' said he, ' the 

 organisation of the yeast or its multiplication by bud- 

 ing, but these living cells are always associated with 

 other dead cells in process of molecular alteration. 

 It is these molecular motions which communicate 

 themselves to the molecules of the sugar, break them 

 up, and cause them to ferment.' 



The arguments of Liebig derived great strength 

 from the belief which was shared by all chemists 

 that the cells of yeast perish during fermentation 

 and form lactate of ammonia. On examining this 

 assertion, Pasteur found that not only was there ro 

 ammonia formed during alcoholic fermentation, but 

 that even if ammonia were added it disappeared, en 

 tering into the formation of new yeast cells. Was not 

 this a proof of the potency of the organised ferment ? 



Tormented, however, by the idea that, notwith- 

 standing all these facts, the reasonings of Liebig 



