RESPONSE IN METALS 89 



From these experiments it will be seen how in one 

 identical piece of wire the responsive current flows now 

 in one direction and then 

 in the other, in absolute 



conformity with theoretical . 



considerations. A B LJ 



Method of exaltation.-A * "^ST " 



Still more Striking COrrobora- The contact Bis made more excitable 



f i -, by chemical stimulant (Na 2 C!O 3 ). 



tlOn OI these reSUltS may, The current of response is towards 



T . -, n , the more excitable B. 



however, be obtained by the 



converse process of relative exaltation of the respon- 

 siveness of one contact. This may be accomplished 

 by touching one contact, say B, with a reagent which 

 like Na 2 C0 3 exalts the electric excitability. On stimu- 

 lation of the wire, the current of response is towards the 

 more excitable B (fig. 53). 



I give four records (fig. 54) which will clearly 

 exhibit the responses as obtained by the methods of 

 relative depression or exaltation. In (a) B is touched 

 with the excitant Na 2 C0 3 , a permanent current flows 

 from A to B, response to stimulus is in the same direc- 

 tion as the permanent current (positive variation). 

 In (b) B is touched with a trace of the depressant 

 oxalic acid, the permanent current is in the same 

 direction as before, but the current of response is in 

 the opposite direction (negative variation). In (c) B 

 is touched with dilute KHO, the response is exhibited 

 by a positive variation. In (d) B is touched with strong 

 KHO, the response is now exhibited by a negative 

 variation. The last two results, apparently anomalous, 

 are due to the fact, which will be demonstrated later, 



