466 INDUCTION. 



lasts longer, and putrefaction sets in later and proceeds more 

 slowly. 



Both these propositions had to he proved hy experiment ; 

 and for the experiments which prove them, science is also in- 

 debted to Dr. Brown- Sequard. The former of the two that 

 paralysed muscles have greater irritability than healthy 

 muscles he ascertained in various ways, but most decisively 

 by " comparing the duration of irritability in a paralysed 

 muscle and in the corresponding healthy one of the opposite 

 side, while they are both submitted to the same excitation." 

 He " often found in experimenting in that way, that the para- 

 lysed muscle remained irritable twice, three times, or even four 

 times as long as the healthy one/' This is a case of induction 

 by the Method of Difference. The two limbs, being those of 

 the same animal, were presumed to differ in no circumstance 

 material to the case except the paralysis, to the presence and 

 absence of which, therefore, the difference in the muscular 

 irritability was to be attributed. This assumption of complete 

 resemblance in all material circumstances save one, evidently 

 could not be safely made in any one pair of experiments, be- 

 cause the two legs of any given animal might be accidentally 

 in very different pathological conditions ; but if, besides taking 

 pains to avoid any such difference, the experiment was re- 

 peated sufficiently often in different animals to exclude the 

 supposition that any abnormal circumstance could be present 

 in them all, the conditions of the Method of Difference were 

 adequately secured. 



In the same manner in which Dr. Brown- Sequard proved 

 that paralysed muscles have greater irritability, he also proved 

 the correlative proposition respecting cadaveric rigidity and 

 putrefaction. Having, by section of the roots of the sciatic 

 nerve, and again of a lateral half of the spinal cord, produced 

 paralysis in one hind leg of an animal while the other re- 

 mained healthy, he found that not only did muscular irritability 

 last much longer in the paralysed limb, but rigidity set in 

 later and ended later, and putrefaction began later and was 

 less rapid than on the healthy side. This is a common case 



