PHENOMENA OF MUSCLE AND NERVE. 313 



the polarising 1 current, and that it is connected with the actual pro- 

 duction of two oppositely polarised axial regions ; that, on the 

 other hand, with one-sided polarisation the extrapolar after-current 

 is in the same direction as the polarising- current. The first con- 

 dition is present when a platinum wire is immersed in sulphate of 

 zinc solution or weak sulphuric acid, and the polarising- current is 

 led in at two points in the fluid ; the second occurs when a 

 copper wire is immersed in weak sulphuric acid, and the current is 

 led in at two points in the fluid, also when a platinum wire is 

 similarly immersed, and one leading--in electrode is connected directly 

 with the wire 1 . 



These two main facts were supported by the new experiments. 

 In addition, however, the following- facts were ascertained : 



(i) With platinum wire in zinc sulphate solution lig-ht mag-nets 

 show an extrapolar after-current which is exclusively on both 

 sides, provided the polarising current is of moderate strength ; when 

 stronger currents are used, this current is preceded, on. the anodal 

 side, by a rapid + effect, in consequence of which the prevailing 

 after-current appears to be much weaker here than on the 

 kathodal side, where no such previous effect appears. When very 

 strong currents are used the + effect on the anodal side may quite 

 overpower the one. 



(a) With platinum wire in weak sulphuric acid the extrapolar 

 after-current generally remains even with the strongest 

 currents. The arrangements for this experiment in which a fluid, 

 other than zinc sulphate, is employed, have been most advantage- 

 ously modified so as to do away with the tubes bound round with 

 membrane (see Pfliiger, ' Archiv,' vi. p. 319). The side openings of 

 the experiment tube having been filled to the brim with zinc 

 sulphate solution, were closed by elastic tubing caps into which 

 glass plugs were fitted ; into the four side openings used for leading 

 in and off, amalgamated zinc wires instead of glass plugs were 

 introduced and fixed. The main tube was now turned through 1 80 

 so that the side tubes pointed downwards, and the zinc solution was 

 poured out of the tube, the side tubes alone remaining full ; the 

 fluid to be experimented with was now injected or aspirated into the 

 tube : it was thus brought above the zinc without disturbance of 

 any kind. 



(3) With a very thin envelope of fluid surrounding the platinum 



1 See the method of experiment as described in Pfliiger, ' Archiv,' vol. vi. p. 312, 319. 



