gave rise to an enhanced response. The depressing after-
effect of a heterodromous current rendered the next re-
sponse ineffective.' The following record taken during the
passage of the homodromous current exhibited an abolition
of response due to induced depression of conductivity.
Finally, the after-effect of the homodromous current is seen
to be a response larger than the normal (Fig. 47). These
experiments show that the after-effect of cessation of a
current iu a given direction is a transient conductivity
variation, of which the sign is opposite to that induced by
the continuation of the current.
PART IT — INFLUENCE OF DIRECTION OF ELECTRIC CURRENT ON CONDUCTION OF EXCITATION IN ANIMAL NERVE.
I shall now take up the question whether an electric current induced any selective variation of conductivity in the animal nerve, similar to that induced iu the conduct- ing tissue of the plant.
THE METHOD OF EXPERIMENT.
In the experiments which I am about to describe, arrangements were specially made so that (1) the excita- tion had not to traverse the polar region, and (2) the point of stimulation was at a relatively great distance from either pole. The fulfilment of the latter condition ensured the point of stimulation being placed at the neutral region.
In the choice of experimental specimens I was fortu- nate enough to secure frogs of unusually large size, locally known as " golden frogs " {Rami tigrina). A preparation was made of the spine, the attached nerve, the muscle and the tendon. The electrodes for constant current were applied at the extreme ends, on the spine and on the
