ORIGIN OF LO WES T OR GA NISMS. 2 1 



known which when alone are not decomposed by cer- 

 tain agents, but which are attacked, when they exist 

 in contact with other bodies incapable of resisting 

 the influence of these agents. Thus platinum alone 

 does not dissolve in nitric acid, but when allied with 

 silver, it is easily dissolved ;-pure copper is not dis- 

 solved by sulphuric acid, but it does dissolve in this 

 when it is allied with zinc, &c. According to M. 

 Liebig it is the same with ferments and fermentable 

 substances ; sugar, which does not change when it is 

 quite alone, changes that is to say ferments when 

 it is in contact with a nitrogenous substance under- 

 going change, that is, with a ferment." 



Thus, in accordance with this latter view, living 

 ferments are not needed mere dead, organic or nitro- 

 genous matter suffices to initiate the processes in 

 question.* Those who hold this opinion may or may 

 not believe that organisms are capable of arising 

 de novo ;"\ though there can be little doubt that a 



* Those who hold this opinion do not of course deny that 

 living ferments can initiate fermentations. Every-day expe- 

 rience convinces them of the truth of this. They merely affirm 

 that the intervention of vital action is not essential : they look 

 upon fermentation as a purely chemical process, and believe that 

 even in those cases where fermentation is initiated by living 

 organisms (such as beer-yeast), these although living act che- 

 mically upon the matter which undergoes fermentation. 



t They may not believe this, because they may be unaware of 

 the fact of the invariable association of some organisms with 

 some kinds of fermentations, and may consequently have never 

 concerned themselves with the evidence bearing upon this part 

 of the question. (See Gerhardt, loc. tit,} 



