x.] BIOGENESIS AND ABIOGENESIS. 235 



falling vertically out of the air, the fluid, which has 

 remained clear and desert for months, becomes, in a 

 few days, turbid and full of life. 



These experiments have been repeated over and over 

 again by independent observers with entire success ; and 

 there is one very simple mode of seeing the facts for 

 oneself, which I may as well describe. 



Prepare a solution (much used by M. Pasteur, and 

 often called " Pasteur's solution") composed of water 

 with tartrate of ammonia, sugar, and yeast-ash dissolved 

 therein. 1 Divide it into three portions in as many 

 flasks ; boil all three for a quarter of an hour ; and, 

 while the steam is passing out, stop the neck of one 

 with a large plug of cotton-wool, so that this also may 

 be thoroughly steamed. Now set the flasks aside to cool, 

 and, when their contents are cold, add to one of the 

 open ones a drop of filtered infusion of hay which has 

 stood for twenty-four hours, and is consequently full of 

 the active and excessively minute organisms known as 

 Bacteria. In a couple of days of ordinary warm weather 

 the contents of this flask will be milky from the enormous 

 multiplication of Bacteria. The other flask, open and 

 exposed to the air, will, sooner or later, become milky 

 with Bacteria, and patches of mould may appear in 

 it ; while the liquid in the flask, the neck of which 

 is plugged with cotton-wool, will remain clear for an 

 indefinite time. I have sought in vain for any ex- 

 planation of these facts, except the obvious one, that 

 the air contains germs competent to give rise to 

 Bacteria, such as those with which the first solution 

 has been knowingly and purposely inoculated, and to 

 the mould-Fungi. And I have not yet been able to 

 meet with any advocate of Abiogenesis who seriously 



1 Infusion of hay treated in the same way yields similar results ; but as it 

 contains organic matter, the argument which follows cannot be based upon it. 



