Response of Nerve investigated ivith Electrometer. 307 



Nerve during passage of a Polarising Current of such direction 

 that the Proximal Electrometer Contact is positive to the Distal One. 



(a) Fresh nerve prepared with electrometer contacts on surface 

 and cross-section. The proximal contact is in this case positive to 

 the distal owing to the resting difference ; this is increased by the 

 anodic extrapolar effect of a polarising current as in arrangement A 

 (fig. 2). Each single stimulus of the plexus causes a very marked 

 displacement of the meniscus plainly visible to the eye. The photo- 

 graphic record is of the character shown in fig. I (v). The initial 

 rise is succeeded by a pronounced and prolonged effect of similar 

 sign : it indicates that the prolonged change present in the un- 

 polarised nerve and figured in fig. 1 (ii) is increased. 



(6) Fresh nerve uninjured with both electrometer contacts 

 upon the surface. There is no difference of potential between the 

 contacts, but during polarisation the anodic extrapolar effect in 

 arrangement A and the cathodic extrapolar effect in arrangement 

 C are such that the proximal electrometer contact is positive to the 

 distal. This is particularly the case with arrangement A owing to 

 the nearer proximity of the contact to the polarised region. 



The persistent extrapolar state is indicated by a downward move- 

 ment of the meniscus which reaches a certain level and is raised by 

 suitable alteration of pressure to the middle of the optical field. 

 Each single stimulus applied to the plexus, although in the unpolarised 

 nerve not followed by any displacement visible to the eye, produces 

 now a visible change. The records show that the initial rise is 

 still present, but that it is succeeded by a prolonged effect of similar 

 character to that obtained in fresh nerve with the distal contact upon 

 the cross-section. The curve given in fig. 1 (vii) shows its form. 



(c) Nerve kept in 0*6 per cent. NaCl. It has been already 

 stated that after twenty- four hours, the excised nerve gives no 

 difference of potential when the electrometer contacts are placed 

 upon cross-section and surface. 



Polarisation may be produced of such character that the proximal 

 electrometer contact (i.e., that nearest the seat of excitation) is posi- 

 tive to the distal one, by arrangement A or C, as in the case of unin- 

 jured nerve. The effect caused by the single stimulus of the plexus 

 is modified in the same way as in the previous class of observations. 

 Instead of the spike which characterises the unpolarised nerve, the 

 records show that the initial rise is followed by a prolonged effect of 

 the form shown in fig. 1 (ix). As in the case of the uninjured nerve, 

 this is more pronounced when the arrangement is that given in A 

 than that of C (fig. 2) for the reason previously referred to. 



If the kept nerve is subjected to a fresh cross -section, then the 

 results of polarisation of this character resemble those described 

 under (a) as occurring in the fresh nerve with a cross-section. 



