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 of 
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, 
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: 
a 
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; 
” 
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, 
cag 
