552 



NER VE. 



point proximal to the pole is galvanometrically negative to the more 

 distal one, these being opposed in direction to the anelectrotonic current. 

 A similar line of argument applies to the cathodic extrapolar region. 

 In this case the excitatory electrical change gains in galvanometric 

 value as it travels from the cathode, and thus brief currents traverse 

 the nerve from the more distal to the proximal contacts, i.e. in the 

 opposite direction to the cathodic electrotonic current (see Fig. 289). 

 By means of rheotome observations, Hermann has conclusively demon- 

 strated the existence of these changes in the propagated electrical 

 response of cooled nerves. 1 Experiments with the capillary electrometer 

 have confirmed and extended this demonstration. It appears that the 

 single electrical diphasic response of an uninjured nerve, having the 

 character shown in Fig. 270 (I. or III.), is completely altered when the 

 proximal contact, i.e. that nearest the seat of excitation, is rendered 

 persistently positive to the distal one by extrapolar electrotonus. 2 The 

 record under these circumstances is like that produced when the distal 

 contact lies on a warmed or injured region (Fig. 270, II, IV.). 

 If the polarisation is of opposite sign, the descending limb of the 

 electrometer curve becomes more extensive as compared with the 



Polarising current 



Fig. 289. — The upper portion represents the anodic extrapolar effects. 

 The excitatory electrical change is more pronounced under the 

 contact (2), nearer the anode than under the distal contact (1). 

 The lower portion represents the cathodic effect, the electrical 

 change due to excitation being more pronounced at (1) than at (2). 



ascending one. Hence relative positivity is associated with greater 

 functional capacity of the tissue, so that, when this is aroused, the 

 state of excitation is of large amount ; relative negativity is associated 

 with diminished functional capacity. 



Influence of anaesthetics. — The natural tendency to regard the 

 changes of electrotonus as states of electrolytic polarisation has been 

 strongly resented by some investigators, and particularly by Biedermann, 

 who differentiates between the " physical " (electrolytic) and the 

 " physiological " factors concerned in the production of the phenomena. 3 

 The theoretical value of the distinction is most certainly open to 

 question, since the electrolytic phenomena displayed by a living nerve 

 are admitted by all to be dependent upon its molecular condition, and 

 as this is one thing during the living and another during the dead state, 

 they must be logically regarded as physiological. In this sense, the 



Hermann, Arch. f. d. ges. Physiol.. Bonn, 1872, Bd. vi. S. 359 ; 1873, Bd. vii. S. 349 ; 

 Bd. x. S. 215 ; 1875, Bd. xii. S. 157. 



2 Gotch and Burch, Proc. Roy. Soc. London, 1898, vol. lxiii. p. 300. 



3 Biedermann, " Elektrophysiologie," S. 694. 



