along from the other end towards N, the wire being mechanically stimulated during the test. The galvanometer spot remains quiescent as long as the exploring Contact is over normal areas. But soon as it touches the zone on which is impressed the invisible image of physico-chemical change, the differential effect of stimulus at once reveals it by producing a vigorous movement of the galvanometer spot. At N1 there was no movement, but there was an upward movement of response when the explorer came over "Carbonate." As the explorer passed on to N2 there was a cessation of movement, but when it reached the area marked "Oxalic" there was a vigorous movement downwards (fig. 3).
Interference Effects.
I have already described case of interference in the galvanometrie effect when the two points A and B in similar molecular conditions are simultaneously acted on by the same mechanical stimulus. Under these 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—will also be modified. Using the block method, we may place a drop of excitant Na2CO3 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 would be an upward deection. But on shifting the balancing clamp away from A (thus decreasing the stimulation intensity of A and increasing that of B) we may 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 will no longer give a continuous balance; instead we obtain a diphasie variation. The diphasie 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. 4, I succeeded in obtaining a continuous transformation from positive to negative phase by continuous change in the relative sensitiveness of the two contacts. I found that traces of after effect due to application of Na2CO3, even after it is Washed off, remain for a time, the increased sensitiveness conferred disappearing gradually. Again, if we apply Na2CO3 solution to a fresh point, the sensitiveness gradually increases. There is another interesting point, viz., that the beginning of response is earlier when the application of Na2CO3 is fresh. In the experiment whose record is given, the Wire is held at one end, and successive uniform vibrations imparted to the wire as a Whole at inter-
