ORIGIN OF LOWEST ORGANISMS. 93 



quate to account for the occasional preservation of 

 boiled fluids in bent- neck flasks. They show that the 

 preservation, far from being universal, is only occa- 

 sional, and that preservation or non-preservation of 

 different fluids is almost wholly dependent upon their 

 nature. They lend no countenance, moreover, to 

 his particular theory, that fermentation cannot be 

 initiated without the agency of living ferments, they 

 are, on the contrary, wholly opposed to this restriction. 

 The plug of cotton-wool, or the narrow and bent tube 

 may, it is true, protect the boiled fluid from subse- 

 quent contact with living " germs" ; but that the fluids 

 do not undergo change on account of such deprivation 

 cannot be safely affirmed, when the same means 

 would also filter from the fluid some of the multi- 

 tudinous particles of organic matter (dead), which the 

 air undoubtedly contains, and which may act as 

 ferments. It must be remembered that the main 

 object of M. Pasteur's investigation was to determine 

 whether fermentation took place under the agency of 

 mere dead nitrogenous matter, as Liebig and others 

 affirm ; or whether it is only initiated by living 

 organisms, as he himself supposes. Obviously, there- 

 fore, the same filtration which purified the air from 

 any living organisms w r ould filter from it its ni- 

 trogenous particles, which are the other possible 

 ferments : so that no conclusion could be drawn 

 from such experiments, more favourable to the one 

 than to the other of these hypotheses. All that 



