SPONTANEOUS GENERATION 325 



the flame. In this way we charge our seven-and-twenty 

 flasks with clean vivifying mountain air. 



We place the fifty flasks, with their necks open, over 

 a kitchen stove, in a temperature varying from 50 to 90 

 Fahr., and in three days find twenty-one out of the 

 twenty-three flasks opened on the hayloft invaded by 

 organisms two only of the group remaining free from 

 them. After three weeks' exposure to precisely the same 

 conditions, not one of the twenty-seven flasks opened in 

 free air had given way. No germ from the kitchen air 

 had ascended the narrow necks, the flasks being shaped 

 to produce this result. They are still in the Alps, as 

 clear, I doubt not, and as free from life as they were 

 when sent off from London. 1 



What is my colleague's conclusion from the experi- 

 ment before us? Twenty -seven putrescible infusions, first 

 in vacuo, and afterward supplied with the most invigorat- 

 ing air, have shown no sign of putrefaction or of life. 

 And as to the others, I almost shrink from asking him 

 whether the hayloft has rendered them spontaneously 

 generative. Is not the inference here imperative that it 

 is not the air of the loft which is connected through a 

 constantly open door with the general atmosphere but 

 something contained in the air, that has produced the 

 effects observed? What is this something? A sunbeam 

 entering through a chink in the roof or wall, and travers- 

 ing the air of the loft, would show it to be laden with 

 suspended dust particles. Indeed the dust is distinctly 

 visible in the diffused daylight. Can it have been the 

 origin of the observed life? If so, are we not bound by 

 all antecedent experience to regard these fruitful particles 



1 An actual experiment made at the Bel Alp is here described. 



