INFLUENCE OF ANESTHETICS. 553 



only physical phenomena are those due to current escape. The distinc- 

 tion has, however, some practical value, since it brings into prominence 

 other aspects of electrotonic phenomena, which are at any rate not so 

 obviously associated with electrolysis as the preceding. The first of 

 these is that due to the comparison of the extrapolar effects in normal 

 and in etherised nerve respectively. 



It has been already stated that the cathodic and anodic electrotonic 

 effects differ in their time relations. In a normal nerve, with extra- 

 polar leads at 1 cm. distance from those of the polarising current, it 

 is notable that the anodic electrotonic effect of a prolonged closure 

 (several seconds) is far larger than the cathodic one, as judged by 

 the galvanometric deflection. 1 Thus in one of Biedermann's ex- 

 periments the anodic effect gave a deflection of 46, the cathodic only 

 25 ; on increasing the intensity of the polarising currents, the anodic 

 gave 96, the cathodic 60. The nerve was now etherised ; it gave no 

 excitatory electrical response, and the deflections were, anodic 24, 

 cathodic 24, with the first intensity of polarising current ; anodic 68, 

 cathodic 66, with the second one. The inequality between the anodic 

 and cathodic electrotonic effects thus disappear in etherised nerve ; but 

 it will be observed that both effects are still present although 

 excitability and conductivity are in abeyance. The explanation given by 

 Biedermann is that in the etherised nerve the condition of electrotonus 

 during closure is a true expression of the polar electrolytic changes, 

 but that in normal nerve, owing to physiological response, a further 

 concomitant effect occurs. This is especially prominent on the anodic 

 side, and spreads from the pole in diminishing amount through the extra- 

 polar region ; since it produces electromotive changes of similar sign to 

 those of the anodic electrolytic change, the total anodic extrapolar 

 effect is thus augmented. In the etherised nerve the production of 

 this physiological response is in abeyance, hence the total anodic effect 

 is diminished, and is now nearly equal to the cathodic one. In support 

 of this, he states that etherised nerve shows little or no electrotonic 

 effect at some distance from the polarised region, whilst the normal 

 nerve shows at the same distance the anelectrotonic current due 

 to the physiological response. The anodic electrotonic changes 

 observed during closure in a normal sciatic nerve, within 1 cm. 

 of the polarising current, are thus regarded as the sum of electrolytic 

 spread, and of a physiological response of the nerve at the anode, 

 rendering all parts at or near this galvanometrically positive to 

 those more remote ; this response subsides when the polarising current 

 is broken. The basis of the response is a reaction corresponding with 

 an assimilation process in Hering's sense ; it is present in diminishing 

 amount through the anodic extrapolar region, and corresponds with 

 greater functional capacity, i.e. galvanometric positivity, of the tissue. 



Further support for this view is afforded by other facts to be 

 referred to ; it must, however, be noted that Waller has found that 

 both the cathodic and the anodic electrotonic effects and their ex- 

 citatory diminution are influenced by all those agencies which affect the 

 electrical response of nerve. Thus ether and C0 2 may abolish both 

 electrotonic effects, the abolition being succeeded by secondary augmenta- 

 tion. When the gases are weak, an augmenting effect immediately 



1 Biedermann, " Elektrophy siologie, " S. 696; Sitzunysb. d. k. Akad. d. Wissensch., 

 Wien, 1888, Bd. xcvii. Abth. 3, S. 84. 



