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124 induced by the current, which assisted the propagation of the excitatory disturbance in a selected direction. On the cessation of this inducing force, there may be a rebound and a temporary reversal of previous molecular arrangement, with concomitant reversal of the conductivity variation. The immediate after-effect of a current flowing in a particular direction on conductivity is likely to be a transient change, the sign of which would be opposite to that of the direct effect. The after-effect of a heterodromous current may thus be a temporary depression, that of a homodromous current, a temporary enhancement of conductivity.

47.—Direct and after-effect of heterodromous and homodromous currents. First two records, N, N, normal. ↓, enhanced transmission under heterodromous current; ⇣ arrest of conduction as an after-effect of heterodromous current. Next record ↑ shows arrest under homodromous current. Last record ⇡ shows enhancement of conduction greater than normal, as an after-effect of homodromous current. (Dotted arrow indicates the after-effect on cessation of a given current. ↑ homodromous and ↓ heterodromous current).

Experiment 43.—This inference will be found fully justified in the following experiment:— The first two responses are normal, after which the heterodromous current