ELECTROMOTIVE ACTION IN NERVE 281 



i.e. more than 165 m. Further experiments undertaken with 

 Hermann's fall rheotome on Tschirjew's principle showed beyond 

 doubt that the anelectrotonic depression of excitability is present 

 at a point of the nerve 1 mm. distant, at the moment of closing 

 the polarising current. The same must be assumed for the 

 katelectrotonic rise of excitability, as well as for the galvanic 

 expression of electrotonus. These experiments imply that the 

 alterations are not propagated, like excitation, as a wave from 

 section to section, but begin simultaneously at all points, at 

 closure of the polarising current. These diametrically opposite 

 opinions have not yet been reconciled, but it must be admitted 

 that the last experiments of Hermann and his pupils are open 

 to no well-founded objection, while the results of Bernstein's 

 rheotome experiment are not, for reasons stated above, perfectly 

 free from ambiguity. 



2. In Non-medullated Nerve 



A series of facts which are of great importance for the recog- 

 nition of the true nature and characteristics of the electrotonic 

 alterations in medullated nerve may be observed on certain non- 

 living (dead) conductors of a particular kind, and also upon 

 non-medullated nerve. As regards the latter, it has already been 

 pointed out that the appearance of the true, typical, extrapolar 

 electrotonus is correlated with certain structural peculiarities of 

 medullated nerve - fibres, more particularly the presence and 

 integrity of the medullary sheath. This point must now be 

 examined in detail. Among the few suitable objects of experi- 

 ment we have in addition to the olfactory nerve of the pike, as 

 first employed by Kuhne, and the unfortunately over-susceptible 

 nerves of the crayfish (lobster) claw in the larger examples of 

 our native species of Anodonta, long unbranched non-medullated 

 nerves, which extend from the two anterior to the posterior 

 ganglia, and present a high capacity of resistance (Biedermann). 

 As regards the electromotive properties of these fine nerve-fibres 

 (which, if taken together, are not nearly as thick as the frog's 

 sciatic), it has already been stated that the demarcation current 

 is unusually vigorous, as in the pike's olfactorius. 



If it is led off with unpolarisable electrodes to a sensitive 

 galvanometer, while a battery current of 12 Dan. is passed into 



