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Rh of depressed excitability. In spite of this the resulting response is enhanced (Fig. 50). The enhancement of conduction under heterodromous current is, in reality, much greater than is indicated in the record. Similarly, under homodromous current the depression of conduction in the nerve may be so great as to cause even an abolition of response, in spite of the enhanced excitability of the muscle (Fig. 51). The actual effects of current on conductivity are, thus, far in excess of what are indicated in the records.

On the cessation of a current there is induced in the plant-tissue a transient conductivity change of opposite sign to that induced by the direct current (cf. Expt. 43). The same I find lo be the case as regards the after-effect of current on conductivity change in animal nerve. Of this I only give a typical experiment of the direct and after-effect of homodromous current on salt-tetanus.

Experiment 46.—In this experiment sufficient length of time was allowed to elapse after the application of the salt

51.—Direct and after-etfect of homodromous current. Transmitted excitation (salt-tetanus T,) arrested under homodromous current denoted by up-pointing arrow; on cessation of current represented by dotted line there is a transient enhancement above the normal.