544 ADDENDUM. 



circuit very rapidly indeed (according to Hermann by derivation 

 (Abgleichung) through the envelope) the latter retains its charge 

 under the same conditions for a considerable time. That this is 

 actually the case, Hermann has shown by a separate series of 

 experiments, in which he investigated with the galvanometer 

 the state of polarisation of various polarisable arrangements 

 (voltameter, Wollaston's points, wire model and living nerve) at 

 various periods after the opening of a polarising current led through 

 them, the result being that the nerve and wire model contrasted 

 with the others in respect of the rapidity of their de polarisation. 



In the introduction to his paper the subject is treated mathe- 

 matically : it is shown that on the hypothesis that a living nerve 

 possesses as regards polarisation the properties of the ' Kernleiter? 

 the result of Fleischl's experiment must be as it actually is J . 



If the ' Kernleiter' theory could be accepted as proved, the ex- 

 planation might be regarded as satisfactory. But for the present 

 a serious difficulty exists, in the fact that the extrapolar currents 

 which are regarded as the characteristic phenomena of 'electro- 

 tonus ' in the sense in which the word was first used by du Bois- 

 Reymond, do not, as they ought to do if they are directly dependent 

 on physical polarisation between the sheath and core of the nerve 

 fibres, appear at the instant that the polarising current is closed. 

 Not long ago an experiment was made by Helmholtz for the pur- 

 pose of proving this 2 . It consisted in comparing the time which 

 elapses when an excitatory wave is propagated through two nerve 

 channels, of which one is an undivided nerve, the other consists of 

 two nerves a and b of which the ends are opposed to each other in 

 such a way that when a current of short duration is led through 

 a where it is not in contact with b, b is excited by the electrotonus 

 induced in the applied part of a. It being found that if the whole 

 length of the channel of conduction was the same, the time lost in 

 transmission was the same, it was concluded by Helmholtz that the 

 rate of propagation of electrotonus did not materially differ from 

 that of excitation. It has now been, so far as can be seen, conclu- 

 sively proved by a new series of experiments conducted by Prof. 

 Bernstein 3 with his repeating rheotome, that the electrotonic effect 



1 The answer which is expected from Prof. Fleischl has not yet appeared. Editor, 

 April, 1887. 



" Helmholtz, < Monatsberichte der Berl. Acad.' 15 Juli, 1885. 



3 J. Bernstein, Ueber das Entstehen u. Verschwinden der electrotonischen 

 Strome im Nerven, ' Archiv. f. Anat. u. Physiol.' 1886, p. 197. 



