THE PHYSICAL STRUCTURE OF THE NERVE 
The pre-existing structures of the nerve are such as to primarily determine the fact that 
local injury is productive of an injury current : and this is true whether the differential 
distribution of electrolytes giving rise to it is (i) also pre-existent, or (2) the result of 
chemical change, a secondary consequence of injury. 
To explain fully the intended meaning of this statement it is necessary to briefly 
consider the nature and arrangement of materials in the nerve from a purely physical 
point of view. It is not, and never has been considered, sufficient to dwell solely 
upon details of histological structure, and to read into them an appropriate physical 
meaning, and it is at the present date more obvious than ever that this is not the 
primary method of examination. The data of primary importance are provided by a 
knowledge of the manner in which the structures of the nerve behave, when the 
electrolytes contained in solution in them are set in movement by a source of electro- 
motive force ; or it might also be said by the manner in which the electrolytes, when 
diffusing, give rise to a source of electromotive force. 
From such a point of view an intimate acquaintance is necessary with : — 
(<-7) The conductivity of the nerve. 
(J?) Secondary features of its conductivity, such as the polarization phe- 
nomena, 
(r) The injury current. 
The consideration of the last aid to knowledge, the injury current, is, although 
held to be the most important, abandoned in this section as begging the question set 
in the research. 
The facts which have been determined by purely physical methods of examina- 
tion are contained in the statement that the nerve behaves as a core model, and that 
a core model is always a complex conductor composed of materials of at least two 
different specific conductivities, arranged cylindrically, the one surrounding the other. 
Practically it has always been found necessary to place in the core of the core model 
a material of higher specific conductivity than that of which the mantle is composed, 
and this fact may be used as an argument that the core of the nerve fibre is of higher 
specific conductivity than its sheath (it being universally acknowledged that the 
comparison between core model and nerve trunk can, without fallacy, be used as if 
in reality a comparison between the core model and nerve fibre). 
