THEIE NATURE AND EFFECTS. 27 



was ligatured and the other was poisoned, when the 

 cord was excited by a current the stimulus had to he 

 transmitted to the non-poisoned leg through the trunk 

 of the nerve which was unaffected, whereas on the 

 gther leg it had to overcome the resistance induced by 

 the paralysing poison. There is no need to suppose a 

 special effect of the poison on the ends of the motor 

 nerves ; the different lengths of the trunks affected 



would account for a considerable difference. To this 



• 



we have also to add the paralysing effect on muscle, 

 which, though not so great as on the nerve, is yet not 

 unimportant, and would tell on the same side. 



Moreover, it does not necessarily follow that because 

 a nerve to which poison has had access conveys elec- 

 trical stimuli in a very imperfect manner, or not at all, 

 therefore tliat the effect of that poison has been to 

 paralyse the nerve. It is unfortunate that the only test 

 we have of the vitality of a nerve is its power of causing 

 contraction in a muscle when irritated by electricity or 

 mechanically. It would be going too far to say, there- 

 fore, that because a nerve did not transmit such rude 

 stimuli it was dead ; and even if the animal loses the 

 power of withdrawing a limb that is being painfully 

 stimulated, the break in the power of conducting im- 

 pressions or stimuli may be in any part of the nervous 

 chain necessarily called into requisition in such an 

 action. 



A poison that produces death by totally different 



