ELECTROMOTIVE ACTION IX NERVE 



267 



points -of the nerve lying on the kathodic side (ke) become more 

 negative, all points on the anodic side (Ae) more positive than 

 before. These alterations are, however, unequal in degree at different 

 points, being greater in the vicinity of the electrodes, and less at 

 a distance from them. If the positive increment from A-e is 

 represented by lines, the height of which expresses the increase, 

 and if the heads of these lines are joined together, the resulting 

 curve represents the alterations of potential occurring at the 

 respective points. The alterations on the kathodic side may be 

 similarly expressed, only here the ordinates must be drawn down- 

 wards from the nerve as abscissa, to show that the potential on 

 this side is negative. The two parts of the curve represent the 

 state of the extrapolar regions. As a matter of fact we do not 



A K 



r 



FIG. 204. 



know the reaction of the intrapolar tract, because it is impossible 

 (on technical grounds) to investigate this area. We can only 

 presume that the alterations of potential there are such as are 

 expressed by the connecting line i. These curves do not of 

 course represent actual magnitudes of potential, at given extra- 

 polar points, they merely express the general fact that there is a 

 diminution from the poles outwards. 



Since the nerve to be examined is usually bounded by two 

 cross-sections, and is thus cib initio electromotive, there must, 

 with a suitable lead-off, be interference between the demarca- 

 tion current and the electrotonic increment, which is of course 

 always in the same direction as the polarising current. This pro- 

 duces at one end of the nerve a negative, at the other a positive 

 variation of the longitudinal- transverse current, lasting as long as 

 the closure of the polarising battery current (Fig. 204). If 

 the electrodes are shifted from the cut end towards the centre, 

 there will obviously be deflections in the galvanometer, on either 

 side of the tract traversed by the current, in the direction of the 

 polarising current. And this will equally be the case when the 



