VIII BIOGENESIS AND ABIOGENESIS 251 



if, after the contained fluid has been carefully 

 boiled, the tube is heated sufficiently to destroy 

 any germs which may be present in the air which 

 enters as the fluid cools, the apparatus may be 

 left to itself for any time and no life will appear 

 in the fluid. The reason is plain. Although there 

 is free communication between the atmosphere 

 laden with germs and the germless air in the flask, 

 contact between the two takes place only in the 

 tube ; and as the germs cannot fall upwards, and 

 there are no currents, they never reach the interior 

 of the flask. But if the tube be broken short off 

 where it proceeds from the flask, and free access 

 be thus given to germs 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 one's self, 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.^ Divide it into three 

 portions in as many flasks; boil all three for a 



^ Infusion of hay treated in the same way yields similar 

 results ; but as it contains organic matter, the argument wliich 

 follows cannot be based upon it. 



