292 INDUCTION. 



CHAPTER IX. 



MISCELLANEOUS EXAMPLES OF THE FOUK METHODS. 



§ 1. I SHALL select, as a first example, an interesting speculation of one 

 of the most eminent of theoretical chemists. Baron Liebig. The object in 

 view is to ascertain the immediate cause of the death produced by metal- 

 lic poisons. 



Arsenious acid, and the salts of lead, bismuth, copper, and mercury, if 

 introduced into the animal organism, except in the smallest doses, destroy 

 life. These facts have long been known, as insulated truths of the lowest 

 order of generalization ; but it was reserved for Liebig, by an apt employ- 

 ment of the first two of our methods of experimental inquiry, to connect 

 these truths together by a higher induction, pointing out what property, 

 common to all these deleterious substances, is the really operating cause of 

 their fatal effect. 



When solutions of these substances are placed in sufiiciently close con- 

 tact with many animal products, albumen, milk, muscular fibre, and animal 

 membranes, the acid or salt leaves the water in which it was dissolved, 

 and enters into combination with the animal substance, which substance, 

 after being thus acted upon, is found to have lost its tendency to sponta- 

 neous decomposition, or putrefaction. 



Observation also shows, in cases whei'e death has been produced by 

 these poisons, that the parts of the body with which the poisonous sub- 

 stances have been brought into contact, do not afterward putrefy. 



And, finally, when the poison has been supplied in too small a quantity 

 to destroy life, eschars are produced, that is, certain superficial portions of 

 the tissues ai'e destroyed, which are afterward thrown off by the reparative 

 process taking place in the healthy parts. 



These three sets of instances admit of being treated according to the 

 Method of Agreement. In all of them the metallic compounds are 

 brought into contact with the substances which compose the human or ani- 

 mal body ; and the instances do not seem to agree in any other circum- 

 stance. The remaining antecedents are as different, and even opposite, as 

 they could possibly be made; for in some the animal substances exposed 

 to the action of the poisons are in a state of life, in others only in a state 

 of organization, in others not even in that. And what is the result which 

 follows in all the cases ? The conversion of the animal substance (by com- 

 bination with the poison) into a chemical compound, held together by so 

 powerful a force as to resist the subsequent action of the ordinary causes 

 of decomposition. Now, organic life (the necessary condition of sensitive 

 life) consisting in a continual state of decomposition and recomposition of 

 the different organs and tissues, whatever incapacitates them for this de- 

 composition destroys life. And thus the proximate cause of the death pro- 

 duced by this description of poisons is ascertained, as far as the Method 

 of Agreement can ascertain it. 



Let us now bring our conclusion to the test of the Method of Difference. 

 Setting out from the cases already mentioned, in which the antecedent is 

 the pi'esence of substances forming with the tissues a compound incapable 



