XI PHENOMENA OF ORGANIC NATURE 387 



But not content with explaining the experiments 

 of others, M. Pasteur went to work to satisfy himself 

 completely. He said to himself : " If my view is 

 right, and if, in point of fact, all these appearances 

 of spontaneous generation are altogether due to the 

 falling of minute germs suspended in the atmo- 

 sphere, why, I ought not only to be able to show 

 the germs, but I ought to be able to catch 

 and sow them, and produce the resulting organ- 

 isms." He, accordingly, constructed a very in- 

 genious apparatus to enable him to accomplish the 

 trapping of the " germ dust " in the air. He fixed 

 in the window of his room a glass tube, in the 

 centre of which he had placed a ball of gun-cotton, 

 which, as you all know, is ordinary cotton- wool, 

 which, from having been steeped in strong acid, is 

 converted into a substance of great explosive power. 

 It is also soluble in alcohol and ether. One end 

 of the glass tube was, of course, open to the ex- 

 ternal air ; and at the other end of it he placed an 

 aspirator, a contrivance for causing a current cf 

 the external air to pass through the tube. He 

 kept this apparatus going for four-and-twenty 

 hours, and then removed the dusted gun-cotton, 

 and dissolved it in alcohol and ether. He then 

 allowed this to stand for a few hours, and the re- 

 sult was, that a very fine dust was gradually de- 

 posited at the bottom of it. That dust, on being 

 transferred to the stage of a microscope, was found 

 to contain an enormous number of starch grains. 



