IN THE AIR THERE ARE LIVING GERMS 



99 



days. Did the genetic power then wait for the disappear- 

 ance of this swan's neck in order to manifest itself? 

 WTiat is your explanation worth in the presence of this: 

 the curves of the neck, remaining moist at the moment 

 when the fire was extinguished, washed in its passage the 

 air which traversed them in a thin thread? In the 

 beginning when the entrance of the air was rapid, the 

 purifying action of this washing was doubled by that of 



Fig. 12. Swan-neck flask used by Pasteur in his study of spontaneous 



generation. 



the liquid, still hot and able to destroy the germs which 

 came in contact with it. Later, the wet walls of the 

 neck have held fast the germs of the air as they have 

 passed through the narrow opening. The proof of this 

 is that if you shake the flask in such a way as to introduce 

 into the curve of the neck a little drop of the infusion, 

 having previously closed the open end so that nothing 

 new will enter, this drop becomes clouded, and if you 

 then mix this drop with the rest of the liquid, the latter 



