BIOGENESIS AND ABIOGENESIS 73 



deprived of all germs. The discussion on this sub- 

 ject became so active that the French Academy 

 of Sciences in 1860 offered a prize for the solution 

 of the matter. It was then that Pasteur came Pasteur 

 upon the scene and made the classical experiments 

 which will always be associated with his name. 

 First of all he showed, as Spallanzani had done 

 before him, that infusions in which life would have 

 appeared if they had not been sterilised, or if after 

 sterilisation they had been left exposed to the air, 

 would if boiled sufficiently long in closed vessels 

 remain permanently without any signs of life. 

 Then it was argued that this was because the fluid 

 was deprived of fresh air. To this Pasteur retorted 

 by the further experiment of filtering the air which 

 was admitted to the sterilised fluid through a wad 

 of cotton-wool. He even showed that if the flask 

 in which the sterilised fluid was placed had a long 

 neck bent into a zig-zag shape the contents re- 

 mained untainted by life. The explanation of all 

 these things is very simple, now that we know it. 

 The air all around us is full of minute organisms, 

 such as bacteria, which are capable of growing and 

 multiplying with enormous rapidity in various in- 

 fusions, such, for example, as beef-tea, and by their 

 growth of causing the putrefaction of the fluid in 

 question. Hence in all such fluids which have 

 been exposed to the air there are these small 



