ORIGIN OF LOWEST ORGANISMS. 43 



being filtered, prevented from gaining access to the 

 fluid. 



If germs derived from the air are the sole causes of 

 putrefaction, then, surely, deprivation from air ought 

 to be just as efficacious as any process of filtration of 

 air more especially when the filtration or the depri- 

 vation have a common starting point. And the mode 

 of procedure, in both cases, is precisely the same up to 

 a certain point. A fluid is boiled for a short time 

 in order to kill the germs which may be within the 

 flask, and to expel its previously contained air. At 

 a certain stage of the ebullition, this may be arrested, 

 if we have to do with a bent-neck flask, or one 

 whose neck is plugged with cotton-wool, and no 

 change, it is said, will subsequently take place in the 

 contained fluid, because the air which enters is, by 

 either of these means, filtered from its germs. But 

 if, whilst ebullition continued, the neck of the flask 

 had been hermetically sealed so as altogether to 

 prevent the re-ingress of air and if the fluid, thus 

 contained in vacua, would nevertheless undergo fer- 

 mentation, obviously the former explanation must be 

 altogether shelved. 



In the face of M. Pasteur's explanations, and those of 

 Professor Huxley, these frequent positive results with 

 fluids contained in vacua are absolutely contradictory. 

 There may naturally arise, therefore, a very grave doubt 

 as to the validity of the explanation adduced by M. 

 Pasteur, and adopted by Professor Huxley and others. 



