148 



ELECTRO-PHYSIOLO* ;Y 



CHAP. 





induction apparatus being included in the circuit, when the finally 

 retarding influence of the extrapolar anelectrotonus upon the rate 

 of conductivity appeared on repeating the four twitches. This 

 occurred in fact without exception : apart from the influence of 

 duration of closure (as already mentioned), the value of this 

 retardation at each cross-section of the nerve was creator in 



O 



proportion with its proximity to the positive pole of the polarising 

 current. If this result can hardly be regarded as surprising 



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FIG. 186. Influence of electrotonus upon conductivity in nerve, (v. Bezold.) 



since it agrees perfectly with the reaction of excitability at the 

 single points of the extrapolar tract of the nerve as described 

 above, v. Bezold's further observations are at first sight very 

 remarkable. He finds a similar reaction of conductivity when 

 the polarising current at c is descending, the myopolar tract of 

 the nerve being therefore in katelectrotonus. In view of the 

 contrast expressed in all other relations between anelectrotonic 

 and katelectrotonic alterations of the nerve, we should a priori 

 expect the contrary, i.e. acceleration of conductivity, or no 

 alteration. The fact is, however, less surprising when it is 

 remembered that v. Bezold employed very strong constant 

 currents, and prolonged the closure for thirteen minutes. Under 

 these circumstances the polar katelectrotonus of the muscle is 

 also expressed as a pronounced depression of excitability and of 



