Page:Collected Physical Papers.djvu/303

Rh dilute NaCl solution at A and B), one contact, say A, is touched with a few drops of very dilute Na2CO3, which is an exciting agent. The electric excitability of A will now be found to be greater than that of B as demonstrated by the upsetting of the previous balance, the resultant current being now towards the more excitable A.

Similarly, when A is depressed by a trace of oxalic acid, the electric excitability of A is less than that of B, the resultant deflection being now downwards (current of response towards the relatively more responsive B). It is to be remembered that in all cases the resultant current of response in the wire is towards the more excitable point.

An interesting line of investigation rendered possible by a modification of method of balance described above is to compare the relative excitability induced by various chemical reagents, the influence of different strengths of the same reagent, and the modification of the effect by the duration of application. We may thus compare the effect of the reagent in relation to the normal effect of water or dilute NaCl solution. There is again an extremely delicate method of comparison of the