I08 ANIMAL ELECTRICITY. — LECTURE V. 



may add, vary with variations in that state. Bad 

 nerves give bad currents, and that is specially the 

 case at this season of the year (February) when 

 nerves are at their worst. 



There can be, I think, little doubt that these 

 extrapolar currents are an effect of electrolytic 

 polarisation. This interpretation, which was origin- 

 ated by Matteucci, elaborated by Hermann, and 

 more recently by Boruttau, has completely displaced 

 the original interpretation of du Bois-Reymond, who 

 discovered the facts — so completely indeed that I think 

 its consideration could only complicate the question 

 to us ; if you are curious in the matter, you will find 

 it argued at length in the '' Thierische Elektricitat," 

 vol. ii., p. 289 to 389. 



Nerve, made up of medullated fibres, is an 

 electrolyte, or rather a pair of electrolytes. Each 

 fibre consists essentially of a central grey core sur- 

 rounded by a sheath of white matter. And from 

 the fact that nerve composed of such fibres is the 

 only^ tissue of the body that exhibits the extrapolar 

 currents just described, we may conclude that the 

 electrolytic interface is the surface of separation be- 

 tween grey axis and white sheath. 



The electrolytic effects are as follows : current 

 entering the nerve by the anode, traverses the w^hite 

 sheath to the grey core ; at the interface between 



' Subject however to some reservation, as indicated in the note to Lecture IV., 

 p. 98. 



