502 



Prof. J. C. Bose. Influence of Electric 



by increasing the length, of the conducting path, i.e. by taking greater length 

 of nerve for transmission of excitation. The result is seen in the second 

 column of Table VII. It will now be understood how, by shortening the 

 length of nerve, the normal effect may undergo a reversal. I shall in the 

 following Table denote the change of conductivity of nerve by C„ that of 

 the excitability of muscle, by E OT . 



Table VII. — Eeversal of Normal Effect by Shortening the Length of Nerve. 



Length of 

 nerve. 



Direction of 

 Current. 



Conductivity of nerve versus 

 excitability of muscle. 



Resulting response. 



2. Short 



Heterodromous 



Homodromous 



Enhanced C„ > Depressed E,„ 

 Depressed C„ > Enhanced E OT 



Enhanced C„ < Depressed E OT 

 Depressed C„ < Enhanced ~E m 



Enhanced response. 

 Depressed response. 



Depressed response. 

 Enhanced response. 



Heterodromous 



Homodromous 





I shall now give experimental verification of the truth of the inferences 

 that have been outlined above. 



Experiment 7. — We have seen that, when the nerve is stimulated in the 

 middle or indifferent region, the transmitted effect is normal. From the 

 above we see that this normal effect will persist, as long as the nerve-tract is 

 of sufficient length; and that the effect will undergo an apparent reversal 

 when it is very much shortened. This is fully borne out by results of 

 numerous experiments. For example, the length of nerve in a preparation 

 was 90 mm. "When stimulus was applied near the spine (length of trans- 

 mission = 90 mm.), the transmitted effect was found to be normal, i.e. 

 enhanced response under heterodromous, and depressed response under 

 homodromous current. The transmitted effect remained normal as the 

 stimulator was gradually moved towards the muscle, thus reducing the 

 length of transmission. A critical length was now found below which the 

 effects underwent a reversal. This was the case when the length of the 

 nerve was reduced to 15 mm., the reversed effects being an enhanced 

 response under homodromous, and a depressed response under heterodromous 

 current. These are due, as explained before, to the induced variation of 

 excitability of muscle, which now became the predominant factor. The very 

 great influence exerted by the direction of current on conductivity of nerve is 

 forcibly brought to our mind by the fact that under normal conditions it 

 completely overpowers the opposing effect of change of excitability in the 

 muscle. 



