76 ORIGINATION OF LIVING BEINGS. 



supplied with the large quantity that had so puzzled 

 him. 



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 spon- 

 taneous generation are altogether due to the falling of 

 minute germs suspended in the atmosphere, — 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 organisms." He, accordingly, constructed 

 a very ingenious apparatus to enable him to accomplish 

 this trapping of this " 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 solu- 

 ble in alcohol and ether. One end of the glass tube 

 Avas, of course, open to the external 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 his apparatus going for four-and- 

 twenty hours, and then removed the dusted gun-cot- 

 ton, and dissolved it in alcohol and ether. He then al- 

 lowed this to stand for a few hours, and the result was, 

 that a very fine dust was gradually deposited at the 

 bottom of it. That dust, on being transferred to the 

 stage of a microscope, was found to contain an enor- 

 mous number of starch grains. You know that the 

 materials of our food and the greater portion of plants 

 are composed of starch, and we are constantly making 

 use of it in a variety of ways, so that there is always 



