THE INJURY CURRENT OF NERVE 
257 
In the first place, it is apparently obvious that the resistance of the longer 
stretches of nerve examined, as obtained from the Wheatstone bridge method, was 
also the actual resistance encountered by the nerve's own current when led through 
the outer path to the cross section, and so back through the nerve. Also, that a 
variation in the nerve's own current produced by the insertion of resistance in the 
outer path did not produce any effect upon this resistance. A reference to experi- 
ment A will show that the value for this resistance used in the calculations was the 
same, and led to the same satisfactory result, when the resistance in the whole circuit 
was varied from 135,000 ohms to 335,000 ohms; and when, therefore, the new 
current was in one case three times as great almost as in the other. 
This longitudinal resistance apparently remains constant when the current 
traversing it is greatly varied, which would not be the case if any very large fraction 
of the resistance was due to polarization, and if, as is supposed, the polarization 
increased largely with the current. 
This is a fact of considerable interest since, in dealing with the general problem 
of the electromotive phenomena of the nerve, it is necessary to know the nature and 
quantity of the electrolytes present in the nerve. The first guide to such knowledge 
is provided by measurements of electrical conductivity, and if these measurements 
are once acknowledged to be misleading by reason of special conditions present, then 
the main source of information is rendered valueless. 
Measurements of electrical conductivity of nerve can be undertaken, by deter- 
mining the resistance of a cut piece of nerve from cross section to cross section, in 
which it would seem that the error introduced by polarization would be absent, if it 
be assumed that all the polarization phenomena are due to the fact that stream lines 
pass from one constituent structure of the nerve fibre to another. For in this method 
of examination, when all the parallel constituent structures are traversed by stream 
lines parallel to them, this cannot occur, except as a negligible error due to artificially 
produced bends in the course of nerve fibres. 
It is possible that even to such measurements exceptions may be taken, since 
there is some reason to fear the presence of a true ' longitudinal polarization,' the 
outcome of circumstances of physical structure not understood. 
It is noteworthy, therefore, that in the measurements given above there is no 
reason to consider such a complication : so that the errors due to polarization are so 
small as to be negligible, and do not interfere with a practical use of these measure- 
ments as the basis of calculation. 
The confidence obtained from such results has led to the institution of the 
measurements of conductivity in the next section, and their use as guides to the 
quantity of electrolytes contained in solution in the nerve, and, therefore, as assisting 
to form an opinion of the quantity of matter upon which all the electromotive 
phenomena of nerve depend. 
