308 Prof. F. Gotch and Mr. G. J. Burch. Electrical 



Nerve during passage of a Polarising Current of such direction that 

 the Proximal Electrometer Contact is negative to the Distal One. 



(a) Fresh nerve with electrometer contacts upon surface and 

 cross-section. The arrangement made use of is that given in fig. 2, 

 B, and the resting demarcation difference is now largely diminished 

 or entirely overpowered by the polarisation extrapolar effect in the 

 cathodic region. The single excitation of the plexus rarely produces 

 any visible movement of the meniscus, and the record upon the plate 

 is found to be of the character indicated in fig. 1 (vi) . It is evident 

 that this differs from both the unpolarised nerve, fig. 1 (ii), and the 

 nerve in the state of opposite polarisation, fig. 1 (v), by the circum- 

 stance that the early part of the effect now takes the form of a small 

 spike, and that the terminal prolonged portion forming the tail is 

 reduced to very small proportions. The curve thus indicates that 

 the proximal contact becomes first negative and then positive in 

 rapid succession, whilst the prolonged effect no longer masks the 

 second positive change as in the other instances just referred to. 



(6) Fresh nerve uninjured, with contacts both upon the surface. 

 Polarisation effects resulting in relative negativity of the contact 

 proximal to the seat of excitation may be attained by either an 

 arrangement like that given in fig. 2 B, or one like that of D. In 

 the first case the electrometer contacts are in the cathodic extrapolar 

 region; in the second case they lie in the anodic extrapolar region. 



With either arrangement a single stimulus applied to the plexus 

 produces no alteration in the level of the meniscus visible to the eye, 

 but each plate when developed shows a record of the type indicated 

 in fig. 1 (viii) ; the form of the photographed excursion is that of a 

 very small spike the two limbs of which follow each other in rapid 

 succession. The spike is sometimes, especially with arrangement D, 

 followed by a curved prolongation dipping for a short distance 

 below the resting level, but in no case has an effect in this direction 

 been obtained at all comparable with that already referred to as 

 producing the negative tail daring the oppositely directed polarisation. 



(c) Nerve kept in O6 per cent. NaCJ. Polarisation producing 

 relative negativity of the electrometer contact proximal to the seat 

 of excitation can be attained by either of the two arrangements, B or 

 D (fig. 2). When present, a single excitation causes no visible dis- 

 placement of the meniscus, but the photographic records show that 

 there is an abrupt up-and-down excursion of the type indicated in 

 fig. 1 (x). When compared with that produced in the unpolarised 

 nerve, fig. 1 (iii) 5 the form of the spike is seen to be one in whicli 

 the ascending and descending limbs are more closely approximated, 

 and a slight dip below the resting level follows the completion of 

 the excursion. 



