Page:Collected Physical Papers.djvu/308

288 conditions the electric variation at the two points continuously balance each other, and there is no resultant effect.

When one point is acted on by a chemical reagent, not only is its electric excitability changed, but its time relations—its latent period, the time-rate of its acquiring the maximum electric variation, and the recovery from the effect of stimulus—become also modified. Using the block method, we may place a drop of excitant Na$2$CO$3$ on A and depressant KBr on B. On simultaneous vibration of A and B, the A effect being relatively much stronger than B effect, the resultant is an upward deflection. But on moving the balancing clamp away from A (thus decreasing the stimulation intensity of A and increasing that of B) we can find a point where the A effect is equal and opposite to the B effect. But owing to change of time relations, simultaneous vibration of A and B no longer gives a continuous balance; we obtain instead a diphasic variation. The diphasic curve thus obtained is exactly the same as the resultant curve deduced from the algebraic summation of the A and B curves obtained separately.

Continuous Transformation from Positive to Negative through an Intermediate Diphasic Response.—In the following record, fig. 74, I succeeded in obtaining a continuous transformation from positive to negative due to induced changes in the relative sensitiveness of the two contacts. I found that traces of after-effect due to application of Na$2$CO$3$, even after it is washed off, remain for a time, the increased sensitiveness conferred disappearing gradually. Again, if we apply Na$2$CO$3$ solution to a fresh point, the sensitiveness gradually increases. There is another interesting point, viz., that the begin-