

INTRODUCTION. 101 



circuit the nerve-current which appears in the piece of nerve con- 

 cerned passes more easily along- the constantly closed external arc 

 of connection than through the nerve substance ; hence the earlier 

 occurrence of "-what appear to be break-excitations on opening 

 the battery circuit. 



A similar explanation, it may be remarked, holds for the fact, 

 also discovered by Hering and me, that with a 'like' exciting 

 current excitation appears earlier when the current is closed and 

 opened in the nerve-circuit. For in this case also we have a nerve 

 with a stronger current in the parts concerned, since there is no 

 opportunity for the current to discharge itself through an external 

 arc of small resistance, and so fall off in strength from internal 

 polarisation. Closure in the nerve-circuit of a like current thus 

 causes alteration from a higher ordinate than closure in the main 

 circuit. The former is therefore more operative, that is to say 

 weaker exciting currents can excite the nerve, because they find it 

 so to speak more strongly electrotonised, and therefore in a more 

 excitable condition. 



I have had little experience of the excitatory effects of like 

 currents, as I observed scarcely any break-excitations at all with 

 the current strengths used by me. I shall therefore refrain from, 

 discussing- this subject. Bering's explanation is as follows : 

 * On closure in the main circuit the nerve-current previously 

 passing into the electrode applied to the surface of the nerve is only 

 reinforced by the arrival of the battery-current. But if the nerve- 

 circuit is closed after the main circuit,, the nerve- and battery- 

 currents are closed at the same moment, and hence the effect of 

 closure will be greater in the latter case. Similarly, the two 

 currents disappear simultaneously on opening in the nerve-circuit/ 



Although, as already said, this subject must be left undiscussed, 

 I nevertheless believe with regard to the effects of closure that my 

 experiments 1 , which have lately been confirmed and extended by 

 Hermann 2 , show that the rise of a current from zero to a consider- 

 able height has far less excitatory effect than even a very slight 

 rise beginning, not at zero, but at a definite positive height. 

 Hence, if Hering's assumption were correct, closure in the nerve- 

 circuit would be less operative than closure in the main circuit, 

 which, however, is not the case. 



It should be noted that all these phenomena appear constantly 



1 Pfluger's Archiv, xxviii. p. 144. 



2 Ibid. xxx. pp. ii and 12. 



