96 LOUIS PASTEUR. 



stove heated to 100 degrees. As it was urged, how- 

 ever, that certain organisms could resist this tempera- 

 ture, M. Pouchet heated the hay from 200 to 300 

 degrees, or to any temperature that might be 

 desired. 



Pasteur came to disturb the triumph of M. 

 Pouchet. 



In a lecture which he gave at the Sorbonne in 

 1864, before a large assembly composed of savants, 

 philosophers, ladies, priests, and novelists Alexandre 

 Dumas was in the first row all showing eager interest 

 in the problems to be dealt with in the lecture, 

 Pasteur thus criticised the experiment of Pouchet: 

 ' This experiment is irreproachable, but irreproachable 

 only on those points which have attracted the atten- 

 tion of its author. I will demonstrate before you that 

 there is a cause of error which M. Pouchet has not 

 perceived, which he has not in the least suspected, 

 which no one before him suspected, but which 

 renders his experiment as completely illusory as 

 that of Van Helmont's pot of dirty linen. I will 

 show you where the mice got in. I will prove to 

 you, in short, that it is the mercury which carries the 

 germs into the vessels, or, rather, not to go beyond 

 the demonstrated fact, the dust which is suspended in 

 the air.' 



To render visible this floating dust, Pasteur caused 

 the hall to be darkened, and pierced the obscurity by a 



