1912.] The Process of Excitation in Nerve and Muscle. 521 



of Hill's treatment of Nernst's hypothesis. Hill introduced into the 

 equations the distance between the membranes, as of course he was obliged 

 to do when dealing with currents of long duration. From his equations 

 the effect of an alteration of this distance can be foreseen. Xow if, as I 

 have suggested, the postulation of transverse membranes is proved untenable 

 by the known facts of the localisation of the excitatory process, we must, 

 at first sight, suppose that the effective distance between the membranes is 

 really the distance between the electrodes placed on the surface membrane 

 of the cell. But Lapicque has shown, and some unpublished experiments 

 of my own completely confirm his results, that the constants of the curve 

 relating current strength to current duration, which should be changed 

 by an alteration of the distance between the membranes, are not changed 

 when the distance between the exciting electrodes is varied by a large 

 amount. This point needs to be cleared up, but further discussion of it at 

 the present time would serve no useful purpose. 



Apparently, then, the hypothesis requires a sheath membrane impermeable 

 to certain ions. What evidence is there to support or to defeat such a 

 supposition ? Work on the osmotic phenomena of cells is not wholly 

 convincing on this point. For example, that of Overton* on the perme- 

 ability of muscle fibres certainly gives evidence of the presence of 

 membranes only slightly permeable to simple ions, but the location of such 

 membranes is rather a matter of general probability than of demonstration. 

 The bulk of the evidence which really bears upon our problem comes from 

 work on the electric phenomena of the excitable tissues. Ostwaldf seems 

 to have been the first to suggest that the presence of membranes permeable 

 only to certain ions might be the determining factor in producing differences 

 in the concentration of ions within and without the excitable cell : such 

 differences of potential might be the source of the electric phenomena 

 observed. Cybulskij also pointed out that the electric phenomena of 

 injured excitable cells would result, if there were normally a permanent 

 difference of potential between the inside and the outside of the cell. More 

 recently he has returned to the problem,§ and, though postulating also 

 additional sources of electromotive force, still gives to the existence of the 

 permanent polarisation at a surface membrane the chief part in the electro- 

 motive phenomena. He constructs, in fact, with an artificial semi-permeable 

 membrane a model polarised cell, which yields just such electromotive 



* Overton, ' Arch. f. d. ges. Physiol.,' 1902, vol. 92, p. 115. 



t Ostwald, ' Zeitschr. f. physik. Chemie,' 1890, vol. 6, p. 71. 



\ Cybulski, ' Bullet, internal, de lAcad. des Sciences de C'racovie,' 1898, p. 231. 



§ Cybulski, 'Arch, internat. de Physiol.,' 1912, vol. 11, p. 418. 



