ON MUSCULAR IRRITABILITY. 163 



more obvious as we proceed to review the interesting experiments which 

 clear the ground. It will be well to bear in mind the conditions necessary 

 to a successful experiment, as the bearing of the after remarks wiU be more 

 apparent. 



1. The source of irritability, viz. the blood, must be cut off from two sym- 

 metrical limbs of the same animal. 



2. The possibility of nervous supply must be cut off in one limb and 

 retained in the other. 



Three animals (in all respects similar) so situated must be taken. 



One must be placed under conditions which enable the limb with the nerve 

 intact to remain in a flaccid, uncontrolled state, equivalent to the condi- 

 tion of volitional paralysis ; another must be caused to maintain continuous 

 control over the limb, without the induction of motor acts ; the third to 

 exercise the Hmb and contract the muscles. 



These conditions being achieved, we have to note in which of these cases 

 rigor mortis of the limb supplied with nerve sets in earlier than in the other 

 limb deprived of both nerve and blood. This will furnish us with the com- 

 parative rate at which the irritability is exhausted in limbs so situated. 



The next question is, whether such an experimental combination is pos- 

 sible. 



At the very threshold an insurmountable obstacle meets us in the tase of 

 ■warm-blooded animals ; for in them to cut off the supply of blood is to induce 

 immediate paralysis, which is rapidly succeeded by the condition of rigor 

 mortis. This is weU illustrated in the effect of deligation of the abdominal 

 aorta. Diu-ing the early stages of the paralysis thus induced in the hind 

 extremities, both the nerves and muscles are susceptible to the stimulus of 

 galvanism, and sensation is likewise perfect. Why, therefore, is it that 

 volition is unable to influence these limbs ? The same, and similar experi- 

 ments upon cold-bloods enable me to answer this question. I find that if, in 

 these creatures, the cii'culation be cut off from a limb in which the nerve is 

 still allowed to remain, the paralysis is not immediate — in fact, does not come 

 on for a period of from one to three hours, the frog during this interval being 

 able to xise the limb ; but at length we get the same condition of complete 

 paralysis which obtains at once in the warm-bloods. The following experi- 

 ment will Ulustrate this : — 



August 11, 6 P.M. 1866. — ^A large frog was taken and thoroughly ether- 

 ized. The arteiy supplying one of the hind limbs was taken up and tied, 

 and then cut below the ligature. The hgature was applied to prevent 

 general bleeding. The nerve was then raised up out of the way, and the 

 whole of the structui-es of the thigh were cut through to the bone, leaving 

 the nerve intact. The skin was then brought together with sutures. In 

 rather over an hour the frog began to respire, and I found he possessed 

 sensibility in the Kmb, and was also able to move it a Little. 10 p.m. The 

 frog seemed to have complete control over the partially amputated limb in 

 all those muscles still possessing bony connexions. 8 a.m. Aug. 12. The 

 limb was found to be completely paralyzed, but quite flaccid. It possessed 

 very little irritability — quite a marked difference in this respect between the 

 two Umbs. The limb is now dragged after the body at full length. Its 

 sensation api^ears ferfect. 4 p.m. The paralyzed limb is now void of all 

 in-itcdnlity, as tested by galvanism. It is, hotuever, still flaccid, and the sen- 

 sibility to pain normal. 9 a.m. Aug. 13. The paralyzed limb is now in a 

 state of riyor, and there is an entire absence of sensation. 



In this case, as in others of the kind, we observe there is a gradual dimi- 



m2 



