ORIGINATION OF LIVING BEINGS. 77 



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 be- 

 sides these, M. Pasteur found also an immense number 

 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 spontaneous 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 in- 

 fusoria 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 infu- 

 sion, which had been kept eighteen months, without 

 the least appearance of life, and by a most ingenious 

 contrivance, he managed to break it open and intro- 

 duce such a ball of gun-cotton, without allowing the 

 infusion or the cotton ball to come into contact with 

 any air but that which had been subjected to a red 

 heat, and in twenty-four hours he had the satisfaction 

 of finding all the indications of what had been hitherto 

 called spontaneous generation. He had succeeded in 

 catching the germs and developing organisms in the 

 way he had anticipated. 



It now struck him that the truth of his conclusions 

 might be demonstrated without all the apparatus he 

 had employed. ^To do this, he took some decaying 

 animal or vegetable substance, such as urine, which is 

 an extremely decomposable substance, or the juice of 



