1 68 The Theory of Atmospheric Germs. [April, 



The positive proposition ' omne vivum e vivo'' is asserted by 

 all the evidence of visible nature, and by microscopic research, 

 to those confines beyond which human powers cannot reach. 

 That there is an exception to the seemingly universal law 

 in the case of those organisms which are invisible it must 

 be the duty of those who embrace the theory of spontaneous 

 generation to prove, or else to tolerate becomingly the 

 scepticism of others. It behoves us seriously to weigh the 

 only real objection to the reception of the germ theory — 

 the resistance to the destructive agency of heat, and to 

 inquire as to the effects of other physical agencies which 

 may contribute to a solution of the question. It is not by 

 the results of a single method of investigation that this 

 question is to be judged, but rather by the collective evidence 

 of many methods. 



Heat is not the only destructive agency which may be 

 employed in the inquiry : others, fraught with much valuable 

 teaching, may be put in force, though these have been 

 apparently in the recent controversies entirely ignored. 

 Such are the evidences derived from the destructive in- 

 fluences of chemical and of poisonous agents. It has been 

 known from time immemorial that the addition of certain 

 compounds prevents both putrefaction and fermentation. 

 The belief being that these processes were essentially 

 chemical, it was naturally probable that the agents which 

 suppressed them should be susceptible of a chemical classifi- 

 cation : but the infinite variety and opposite properties of 

 the various agents precluded this classification. If the 

 processes were, as asserted, those of oxidation, it would 

 surely be not unreasonable to expect that the agents which 

 arrest them should also arrest oxidation ; but common ex- 

 perience taught an absolutely contrary lesson— that oxidising 

 agents were the most efficient in arresting the processes. 

 Again, on the chemical theory there ought to be some quanti- 

 tative relation between the amount of a chemical agent 

 employed and the degree of its influence; but the fact is 

 that an agent present in such feeble quantity as to be capable 

 of no appreciable chemical effect on a mass of putrescible 

 material is yet capable of stopping all putrefaction. Further- 

 more, agents, such as carbolic acid, which are proved to 

 exert no influence whatever on processes purely chemical, are 

 among the most efficient of all means for preventing putre- 

 faction and fermentation. 



A large series of observations shows, on the other hand, 

 that the agents arresting these processes exert their in- 

 fluence precisely in so far as they are poisonous agents to low 



