12 CHANGES OF EXCITABILITY IN NERVES 



Hermann found a diminution in the influence of an intrapolar 

 stimulus at the positive pole of an ascending- current ; with weak 

 currents, on the contrary, he obtained a reinforcement. 



Particulars as to the strength of the polarising current, as well 

 as with regard to the distance between its electrodes and those 

 of the test-current, are, it is true, wanting in Hermann's paper; 

 but the facts disclosed by him do nevertheless tell against Pfliiger's 

 theory, and cannot be explained in accordance with it, unless one 

 assumes that the intrapolar test-electrodes were not near enough 

 to the respective poles to lie in the anelectrotonic tract when the 

 currents were weak ; and, similarly, that with strong currents the 

 anelectrotonus had extended to their position, although they lay 

 tolerably near the negative pole. Obviously this cannot be decided 

 without new experiments, at least so long as we have no detailed 

 particulars on which to found conclusions. 



Shortly after Hermann, Bernstein 1 took up this question. He 

 employed maximal induction-shocks, and by their means investi- 

 gated the change of excitability in the tract lying between the 

 polarising current and the muscle. He moved the test-electrodes 

 as close as possible to the nearest electrode of the polarising 

 current ; the distance between the electrodes of the latter being, 

 on the other hand, considerable, namely 25 nim. The strength of 

 the current was great, ranging from 4 Daniells with a derivation 

 circuit of 10,000 rheochord units, up to 6 Groves without deri- 

 vation. He sums up the result of his experiments thus ' When 

 a constant current is passing along a nerve, the liberation of 

 excitation is impeded at the positive pole, so that weak stimuli 

 exercise less influence than under normal circumstances ; but the 

 maximum of the excitation elicited by powerful stimuli is greater. 

 At the negative pole, on the other hand, the liberation of excitation 

 is facilitated, so that weak stimuli have greater effect ; but the 

 maximum of excitation which can be liberated by strong stimuli 

 is less.' 



By a closer sifting of his results Bernstein endeavoured to show 

 their accordance with Pfliiger's theory, and expressly declared that 

 they were no way in antagonism with its chief points, but rather 

 served to confirm it. 



Hermann 2 soon came forward in opposition to Bernstein. He 

 had repeated Bernstein's experiments without succeeding in" con- 



1 Bernstein, Afchiv fur die gesammte Physiologic, viii, 1874, pp. 40-60. 



2 Hermann, Archiv fur die ges. Physiologic, viii, 1874, pp. 258-275. 



