54 PASTEUR 



studies of fermentations, from 1857 to 1859, 

 and notably those of alcoholic fermentation. 

 It was here also that he was destined to dis- 

 cover a phenomenon which overthrew all ac- 

 cepted ideas regarding the essential conditions 

 of animal life. No one had questioned that 

 oxygen was a necessity to all animals without 

 exception. Pasteur proceeded to prove that for 

 certain species it was fatal, and that they died 

 at its contact. While examining under the mi- 

 croscope a tiny drop of butyric fermentation, 

 placed between two very thin sheets of glass, 

 Pasteur observed that the bacteria krjown as 

 the vibrion, which produce this fermentation, 

 were very lively at the centre and furthest from 

 the air, but that those near the border line be- 

 came inert. What was he to conclude from 

 this phenomenon, which contradicted all obser- 

 vations that he had previously made of various 

 infusions, in which the animalcula left the 

 centre of the drop in order to draw near to the 

 margin which supplied them with more oxy- 

 gen? Was it possible that there were animal 



