1902.] On the Injury Current in Mammalian Nerve. 



283 



exhibiting an actual rise, so that the highest value of the injury 

 current is only attained when the nerve has lain for some time upon 

 the electrodes. Several observers* have noted the initial rise, and 

 explanations have been offered which accord with the generally held 

 " alteration " theory of the nerve current. In face, however, of facts 

 recently brought forward in a series of papers by one of us,t it is 

 difficult to accept the prevailing theory as satisfactory. The attempt 

 was therefore made to study this particular phase of the injury 

 current from the point of view set forth in the papers alluded to. 

 That view, which may be called the " concentration cell " theory of 

 the injury current, is based upon the hypothesis of the core-model 

 structure of nerve, % and lays stress on certain pre-existing peculiarities 

 of constitution. These may briefly be described as (a) a separation of 

 the solutions of electrolytes of the nerve into internal and external 

 solutions by a membrane which permits only imperfect diffusion to 

 take place between them ; (/>) a difference in the quantitative distribu 

 tion of electrolytes in the solutions, the internal one being of small 

 volume, but of great concentration and high specific conductivity. 

 Such a difference between the solutions must give rise on' rupture of 

 the membrane, as by section or other injury, to diffusion processes, 

 and consequently to differences of potential. 



If such electrical differences as are found in the phenomenon of the 

 injury current arise from the source indicated, they should be capable 

 of modification in just the same manner that a process of diffusion can 

 be modified. The value of a diffusion process depends primarily upon 

 the concentration ratio of the two solutions in contact, and may be 

 increased by diluting the weaker solution. In the experiments already 

 reported upon,§ the extreme case of this dilution was exemplified by 

 immersing the nerve for a short time in water ; the result was an 

 increase of the injury current due to the enhanced value of the diffu- 

 sion process. 



In relation to the experiments recorded here, it may be said that the 

 temperature of the solutions, or the fact of any difference of tempera- 

 ture existing between them, is hardly less important than the concen- 

 tration. In frog's nerve, the solutions are already approximately at 

 the temperature of the laboratory. But with mammalian nerve the 

 case is very different. Eemoved immediately after death, such a 

 nerve has a temperature presumably not far removed from that of the 



* Waller, " Croonian Lecture," ' Phil. Trans.,' London, 1896. 



f J. S. Macdonald, " The Source of the Demarcation Current considered as a 

 Concentration Cell," ' Proc. Eoy. Soc' vol. 67, p. 315, &c, 1900, &c. ; " The Injury 

 Current of JSerre. The Key to its Physical Structure," 'The Thompson Yates 

 Laboratories' Eoports,' vol. 4, part 2, 1902, pp. 213—350. 



X G-ninhagen, ' Xonigsberger Med. Jahrb.,' vol. 4, p. 199; Strong, 'Journal of 

 Physiology,' vol. 25, p. 427 ; Boruttau, ' Pfliiger's Archiv,' vol. 63, p. 154, &c, &c. 



§ J. S. Macdonald, ' The Thompson Yates Laboratories' Report,' loc. cit. 



