PHENOMENA OF MUSCLE AND NERVE. 317 



therefore, depend upon the extent to which the former can spread 

 into these regions. It is evident that this state of affairs must be at 

 a minimum for the distance in which the extrapolar polarisation is at 

 its maximum. The maximal polarised regions in themselves will 

 have no idiopolar-currents, but only currents between one another, 

 which, if led off, would be in character, just as two pieces of 

 metal in fluid give a considerable bipolar-current. Mere observa- 

 tion readily shows that when the fluid cylinder is large, the depo- 

 sition of zinc on the one side, and the development of gas on the 

 other, spreads, even with moderate strength of current, far out into 

 the extrapolar regions, whereas, on the other hand, in the intra- 

 polar region both are invisible quite close to the electrodes, provided 

 that this region be not very long. There can be no doubt 

 that where the ions are visible the maximum of polarisation has been 

 reached, and that this maximum may stretch still further out. But 

 on account of the good conduction of the core, the bipolar-current 

 must spread in the fluid beyond the region of maximal polarisa- 

 tion, the effect of which is that the surfaces of potential proceeding 

 from the maximal polarised portions, independent of ihe decreasing 

 tension due to the proper polarisation of the parts superficial to the 

 core, run almost concentrically along the core, and in consequence 

 the idiopolar-Guirent of the extrapolar region must be almost or 

 quite concealed. As a matter of fact I have never succeeded, after 

 numberless experiments with tubes i| metre long, and with the 

 finest wire core, in ascertaining a * turning-point ' in the extrapolar 

 region, although such a point certainly must theoretically exist. The 

 bipolar-current, when it is present, spreads so far into the extra- 

 polar region that on reaching a position where the idiopolar 

 current alone might occur, the polarisation effects have dwindled 

 almost to nothing. (See Pfliiger, * Archiv,' vol. vii. p. 317.) 



It is quite otherwise in the case of very thin envelopes of fluid. 

 In the first place, the fall of polarisation effect is here much steeper, 

 since the intensity of the lines of current entering the core must 

 decrease much more rapidly in proportion to their distance from the 

 led-through region, this more rapid decrease being due to the much 

 more marked inequalities in their length. In the second place, 

 a greater resistance is offered to the passage of the bipolar currents, 

 and moreover, the conditions are not favourable for their extrapolar 

 spread. In this case, too, the distribution of tension upon the 

 surface of the thin fluid envelope must be a true expression of 

 the distribution upon the core itself. So then here the idiopolar 



