494 Prof. J. C. Bose. Influence of Electric 



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. 



Experiment 3. — This inference will be found fully justified in the following 

 experiment : — The first two responses are normal, after which the hetero- 

 dromous current gave rise to an enhanced response. The depressing after- 

 effect of a heterodromous current rendered the next response ineffective. 

 The following record taken during the passage of the homodromous current 

 exhibited an abolition of response due to induced depression of con- 

 ductivity. Finally, the after-effect of the homodromous current is seen 

 to be a response larger than the normal (fig. 4). These experiments show 



Fig. 4. — 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.) 



that the after-effect of cessation of a current in a given direction is a 

 transient conductivity variation, of which the sign is opposite to that 

 induced by the continuation of the current. 



