ELECTRIC RESPONSE 9 



effect produced at A, the existing difference of 

 potential may thus be reduced, with a consequent 

 diminution of the current of injury. During stimula- 

 tion, therefore, a nerve exhibits a negative variation. 

 We may express this in a different way by saying 

 that a ' current of action ' was produced in response 

 to stimulus, and acted in an opposite direction to 

 the current of injury (fig. 2, b). The action current 

 in the nerve is from the relatively more excited to the 

 relatively less excited. 



Difficulties of present nomenclature. We shall deal 

 later with a method by which a responsive current of action 

 is obtained without any antecedent current of injury. ' Nega- 

 tive variation ' has then no meaning. Or, again, a current of 

 injury may sometimes undergo a change of direction (see note, 

 p. 12). In view of these considerations it is necessary to 

 have at our disposal other forms of expression by which the 

 direction of the current of response can still be designated. 

 Keeping in touch with the old phraseology, we might then 

 call a current ' negative ' that flowed from the more excited 

 to the less excited. Or, bearing in mind the fact that an 

 uninjured contact acts as the zinc in a voltaic couple, we 

 might call it ' zincoid,' and the injured contact * cuproid.' 

 Stimulation of the uninjured end, approximating it to the 

 condition of the injured, might then be said to induce a 

 cuproid change. 



The electric change produced in a normal nerve by stimu- 

 lation may therefore be expressed by saying that there has been 

 a negative variation, or that there was a current of action 

 from the more excited to the less excited, or that stimulation 

 has produced a cuproid change. 



The excitation, or molecular disturbance, produced 

 by a stimulus has thus a concomitant electrical expres^ 



