CHAPTEE II 



ELECTRIC RESPONSE 



Conditions for obtaining electric response Method of injury Current of 

 injury Injured end, cuproid: uninjured, zincoid Current of response 

 in nerve from more excited to less excited Difficulties of present nomen- 

 clature Electric recorder Two types of response, positive and negative 

 Universal applicability of electric mode of response Electric response 

 a measure of physiological activity Electric response in plants. 



UNLIKE muscle, a length of nerve, when mechanically 

 or electrically excited, does not undergo any visible 

 change. That it is thrown into an excitatory state, and 

 that it conducts the excitatory disturbance, is shown 

 however by the contraction produced in an attached 

 piece of muscle, which serves as an indicator. 



But the excitatory effect produced in the nerve by 

 stimulus can also be detected by an electrical method. 

 If an isolated piece of nerve be taken and two contacts 

 be made on its surface by means of non-polarisable 

 electrodes at A and B, connection being made with a 

 galvanometer, no current will be observed, as both A 

 and B are in the same physico-chemical condition. 

 The two points, that is to say, are iso-electric. 



If now the nerve be excited by stimulus, similar 

 disturbances will be evoked at both A and B. If, 

 further, these disturbances, reaching A and B almost 

 simultaneously, cause any electrical change, then, 



