554 



NERVE 



succeeds an initial slight diminution. 1 It is thus extremely doubtful 

 whether the observations of Biedermann can be taken to indicate a 

 separation between "physical" and "physiological" electromotive 

 factors ; if susceptibility to change through the action of ether is to be 

 taken as a crucial test, then we must regard the whole effect as 

 physiological. 



The character of the nerve. — The non-medullated nerves of Anodon, 

 Eledone, and Octopus, are readily excited by the passage of a galvanic 

 current, and an electrical excitatory response is propagated at each 

 closure of such a current along the nerve. The electrical response 

 evidently differs in its time relations from that present in medullated 

 nerve, since a single closing excitation causes an obvious galvano- 

 metric deflection in a distant portion of the nerve ; it is thus far 

 more prolonged than in the case of medullated nerve. It is, how- 

 ever, of the same general character, the proximal surface contact 

 becomes galvanometrically negative to the more distant contact on the 

 cross section. 



This initial excitatory effect on closing a polarising current has the 

 same sign whatever the direction of the current, but the subsequent 

 electrical changes differ in accordance as the extrapolar region is anodic 

 or cathodic. On the anodic side it is quickly succeeded and over- 

 powered by an electrical change of opposite sign, the anodic extrapolar 

 electrotonic current ; on the cathodic side it is, according to Biedermann, 

 unaltered, being neither augmented nor diminished. 2 If the galvanometer 

 contacts are both placed on the surface, so that the resting difference 

 and the excitatory electrical response produce but very slight galvano- 

 metric effects, then the appearance of the anelectrotonic change and 

 the absence of the catelectrotonic one become very conspicuous. As the 

 galvanometric contacts approach the polarising ones, the anelectrotonic 

 change increases in intensity, although such increase is small when 

 compared with the similar augmentation in medullated nerve. The 

 amount of the effect also increases with that of the polarising 

 current, but a maximum is soon reached, and further increase of 

 polarising intensity does not cause any perceptible augmentation. The 

 structure of non-medullated nerves is not favourable for electrolytic 

 spread, and this factor is therefore reduced to comparatively small 

 proportions. Biedermann thus concludes that the physiological reaction 

 of the tissue at the anode is the chief if not the sole source of the 

 anodic electrotonic current in such nerves. The change spreads with 

 diminishing intensity into the anodic extrapolar region. 



These facts have not been confirmed by Boruttau. In the non- 

 medullated nerves of large Cephalopoda, Octopus and Eledone moschatus, 

 Boruttau observed both anelectrotonic and catelectrotonic extrapolar 

 currents. Thus in Octopus the anelectrotonic effect gave a galvano- 

 metric deflection of 64, the catelectrotonic one of 49, and, on increasing 

 the intensity of the polarising current, the effects were anelectrotonic 95, 

 catelectrotonic 70, when 18 mm. of nerve intervened between polarising 

 and galvanometric contacts. 3 Further, both effects showed the excitatory 



1 Waller, " Proc. Physiol. Soc," Journ. Physiol., Cambridge and London, 1896, 

 vol. xix. 



2 Biedermann, " Elektrophysiologie," 1895, S. 685; Sitzwwjsb. d. k. Akad. d. 

 Wissensch., Wien, Bd. xciii. Abth. 3. 



J Boruttau, Arch. f. d. gcs. Physiol.. Bonn, 1897, Bd. lxvi. S. 285. 



