58 ON THE NATURE AND ACTION OF THE 



motor and vaso-motor nerves and on the functions of the cord. 

 The reflex centres, through which irritation of the fifth nerve 

 acts, remain unaffected after the reflex function of the cord is 

 nearly gone ; and even then the power of voluntary motion 

 still exists. 



The eff"ect of the poison upon the respiratory and vaso-motor 

 nerves will be considered under the heads of respiration and 

 circulation. 



Action of Cohra-poisoyi on Motor Nerves. 



As the contraction of a muscle, on irritation of the motor 

 nerve supplying it, is the index by which we judge of the 

 irritability of the nerve itself, the paralysing effect of cobra- 

 poison upon muscle renders the exact determination of its 

 action upon motor nerves much more difficult than in the case 

 of such a poison as curare, which leaves the muscular 

 irritability intact. For the failure of a muscle to contract on 

 irritation of its motor nerve can be due only to paralysis of the 

 motor nerve in the case of curare ; but in poisoning by cobra- 

 venom it may be due to enfeeblement of the muscles, as well 

 as paralysis of the nerve. But if we find instances in which 

 the muscles still retain their irritability almost unaltered, and 

 respond readily to direct stimulation after tliey ha\ e ceased to 

 contract on irritation of their motor nerve, we are justified in 

 saying that the nerve is paralysed; and such is the case in 

 Experiment XLI. 



In Experiment XXV this action on the ends of motor nerves 

 is all the more evident from the paralysis being most complete 

 in the part where the poison was introduced. At this part, it 

 was brought, in a concentrated state, into contact with the ends 

 of the motor nerves, while the other parts of the body received 

 it after dilution with the blood ; and in them the paralysis was 

 much less marked. 



The paralysis of the hind legs, so often noticed in experi- 

 ments, appears to be due, at least in considerable measure, to 

 the local action of the poison on the ends of the motor nerves 

 of the legs, as the injection or bite is often made on the flank 

 or thigh. 



