482 INDUCTION. 



chemical actions which constitute life), and the con- 

 sequent is death, either of the whole organism, or of 

 some portion of it ; let us compare with these cases 

 other cases, as much resembling them as possible, but 

 in which that effect is not produced. And, first of 

 all, " many insoluble basic salts of arsenious acid are 

 known not to be poisonous. The substance called 

 alkargen, discovered by Bunsen, which contains a 

 very large quantity of arsenic, and approaches very 

 closely in composition to the organic arsenious com- 

 pounds found in the body, has not the slightest 

 injurious action upon the organism." Now when 

 these substances are brought into contact with the 

 tissues in any way, they do not combine with them ; 

 they do not arrest their progress to decomposition. 

 As far, therefore, as these instances go, it appears 

 that when the effect is absent, it is by reason of the 

 absence of that antecedent which we had already good 

 ground for considering as the proximate cause. 



But the rigorous conditions of the Method of 

 Difference are not yet satisfied ; for we cannot be 

 sure that these unpoisonous bodies agree with the 

 poisonous substances in every property, except the 

 particular one, of entering into a difficultly decom- 

 posable compound with the animal tissues. To render 

 the method strictly applicable, we need an instance, 

 not of a different substance, but of one of the very 

 same substances, under circumstances which would 

 prevent it from forming, with the tissues, the sort of 

 compound in question ; and then, if death does not 

 follow, our case is made out. Now such instances 

 are afforded by the antidotes to these poisons. For 

 example, in case of poisoning by arsenious acid, if 

 hydrated peroxide of iron is administered, the destruc- 

 tive agency is instantly checked. Now this peroxide 



