ORIGINATION OF LIVING BEINGS 61 



if, in point of fact, all these appearances of spontaneous 

 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 con- 

 verted 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 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 this apparatus going for four-and-twenty 

 hours, and then removed the dusted gun-cotton, and dis- 

 solved it in alcohol and ether. He then allowed 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 enormous 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 a quantity of it suspended in the air. It 

 is these starch grains which form many of those bright 

 specks that we see dancing in a ray of light sometimes. 

 But besides these, M. Pasteur found also an immense 

 aumber of other organic substances such as spores of fungi, 

 which had been floating about in the air and had got caged 

 In this way. 



He went farther, and said to himself, " If these really 

 are the things that give rise to the appearance of spon 

 taneous generation, I ought to be able to take a ball of 

 this dusted gun-cotton and put it into one of my vessels, 

 containing that boiled infusion which has been kept away 

 from the air, and in which no infusoria are at present 

 developed, and then, if I am right, the introduction of this 

 gun-cotton will give rise to organisms/' 



Accordingly, he took one of these vessels of infusion, 

 which had been kept eighteen months, without the least 

 appearance of life, and by a most ingenious contrivance, 



