52 LOUIS PASTEUR. 



which, they are sown is suitable for their nourishment, 

 they will multiply to infinity ; but the character most 

 essential to be observed is, that they may be sown in a 

 liquid which contains only ammonia and crystallisable 

 substances, together with the fermentable substances, 

 sugar, lactic acid, gum, &c. The butyric fermentation 

 manifests itself as these little organisms multiply. 

 Their weight sensibly increases, though it is always 

 minute in comparison with the quantity of butyric 

 acid produced ; this is found to be the case in all 

 other fermentations. 



This experiment no doubt resembles those made 

 with the alcoholic and lactic ferments. But it is dis- 

 tinguished from them by one circumstance eminently 

 worthy of attention. The butyric ferment, by its 

 motions and by its mode of generation, furnishes the 

 irrefutable proof of its organisation and of its life. 

 This ferment, moreover, presented to Pasteur a new 

 and unexpected peculiarity. The vibrios live and 

 multiply without the smallest supply of air or of free 

 oxygen. Not only, indeed, do they live without air, 

 but the air destroys them and arrests the fermentation 

 which they initiate. If a current of pure carbonic 

 acid is made to pass into the liquid where they are 

 multiplying, their life and reproduction do not appear 

 to be at all affected by it. If, on the contrary, instead 

 of the current of carbonic acid we employ one of 

 atmospheric air for only one or two hours, the vibrios 



