THE INJURY CURRENT OF NERVE 
345 
There is one ' pre-existent structure ' of the nerve which necessarily plays an 
important part, namely, the barrier (or barriers) which previously to the occurrence 
of 1 injury ' had maintained separate and distinct from one another the different 
structures of the nerve. 
There is another ' pre-existent structure ' also of undoubted importance in 
determining the value and direction of the phenomenon, namely, the solution which 
bathes the outer surfaces of the nerve fibres. 
The value of this last factor has been studied in this paper, and it has in this 
research been definitely proved to have a value which is only and completely given 
to it by the fact that it is a solution of electrolytes : a value which may be altered in 
a precise and quantitative manner by modifications of the electrolytes which it 
contains ; these modifications adding to it, subtracting from it, and even reversing it. 
The strength of the solution, as it exists upon the nerve removed from a living 
animal or immediately after death (before the stoppage of the circulation has had 
time to lead to local modifications in the lymph), is that of the ordinary ' normal 
saline' solution; that is to say it is 'entirely pre-existent:' modifications occurring 
later are only sources of error in the estimation of its importance. 
The remaining structure upon which the injury current depends, the ' internal 
solution ' of the nerve, as necessarily owes all its importance and value to the fact 
that it is a solution of electrolytes ; and it is, as such, capable of modification by the 
addition or subtraction of electrolytes. 
The decision as to its ' pre-existent ' or ' newly acquired ' importance, as deter- 
mining the value of the injury current, lies entirely in the answer to this question. 
Are the electrolytes in this solution, which render its value (as a solution) different from 
that of the external ' normal saline, pre-existent ; or are they newly contributed by chemical 
change, the secondary consequence of injury ? 
It is considered that this question is best approached in the following way. 
A study of the polarization phenomena of nerve has led to an appreciation 
of the fact, that the greater part of the conductivity of the nerve is due to the 
internal solutions of the axis cylinders. 
If this greater conductivity means a greater specific conductivity of these solutions, 
then the injury current is explained in terms entirely of pre-existent structures. If it 
does not, but means a greater volume of ' normal saline ' solution within the axis 
cylinder than outside of it in the nerve trunk, then the axis cylinder solutions form by 
far the greatest mass of conducting structure in the nerve. 
Changes in the specific conductivity of this mass, such as would follow the 
addition of electrolytes by chemical change affecting each unit of it, and subsequent 
to injury, must necessarily add considerably to the general conductivity of the nerve. 
