ORIGIN OF LOWEST ORGANISMS. 101 



a short neck, and to this, the access of germs and 

 organic particles is freely permitted till the fluid has 

 become cool, and then the neck of the flask is 

 hermetically sealed ; whilst the last (C) is sealed 

 during ebullition, after all air has been expelled. 

 Now, if Pasteur's theory of fermentation, and the 

 prevalent notions concerning the universal distribution 

 of " germs " throughout the atmosphere were true, it 

 might be expected that the fluid in B would always 

 rapidly change ; that that in A would always remain 

 pure ; and that the fluid in C would, similarly, un- 

 dergo no alteration. The facts, however, are quite the 

 reverse : if a strong turnip infusion be employed, the 

 fluid in A will almost always remain unchanged ; that 

 in B will sometimes rapidly change, and at other times 

 will remain quite pure ; whilst that in C will almost 

 invariably become turbid in from two to six days. 

 But, even if it were not the case that some fluids, 

 different from those used by M. Pasteur, will almost 

 invariably undergo change in bent-neck vessels, M. 

 Pasteur's explanation of the cause of the preservation 

 would have been altogether upset by the fact that 

 some of tJie very fluids wJiicJi remain pure in tlie bent- 

 neck apparatus will become foetid if shut up in vacua. It 

 is, therefore, of course useless to talk of a particular 

 boiled fluid having been saved from putrefaction on 

 the ground that the living atmospheric germs (whose 

 presence is supposed to be necessary for the initiation 

 of such a process) have been altogether filtered from 



