THE INJURY CURRENT OF NERVE 343 
Let us, as a concession, admit that one-half of the space is so taken up. 
In the nerve bundle only one-third of the space is taken up by the axis cylinders 
of the nerve fibres. This figure was found by the examination of an enlarged 
microphotograph of a cross section of a fasciculus of nerve fibres.* 
On this computation only one-sixth of the total cross section of the nerve 
consists of cross sections of axis cyclinders. 
Let us, as a further concession, admit that the axis cylinders form one-fifth of 
the total bulk of the nerve. 
Therefore ', we find ourselves to have come to the opinion that structures occupying only 
one-fifth of the bulk of the nerve account for nine-tenths of its electrical conductivity. 
The amount of water in the nerve is not more than two-thirds of its weight. 
All the electrolytes which can conduct an electrical current are in solution in this 
water. 
Let us suppose the water to be uniformly distributed throughout the nerve 
trunk, to be all free to take electrolytes into solution, and admit that two-thirds of 
the mass of the axis cylinders consists of solutions of electrolytes. 
Then it follows that solutions occupying only two-fifteenths — 
21 2 , 
— x or ths 
3 5 15 
of the total bulk of the nerve account for nine-tenths of its conductivity. 
Truly, although the total conductivity of the nerve is small, the specific conduc- 
tivity of these solutions in the axis cylinders ot the nerve must be very great. 
The specific conductivity of nerve =50 ... (Hg. x io~ s ). 
50 x = +5 
10 
The specific conductivity of solutions occupying only 2-l5ths of the space, and 
accounting for a conductivity of 45 is equal to 
4 x -i or 340 (approx.) 
That is to say, upon this computation, that the solutions of the axis cylinder have a 
conductivity as great as that of a 2* 6 grammes per cent, solution of KCl. 
These figures are large. They are not so large as an admission of any, even 
of the necessary, imagination might have made them. They are too small to explain 
the facts of the previous section, but even in this form they are large enough to 
provide a basis for criticism of the ' apparently ' concentrated solutions of the axis 
cylinder. 
* This figure was determined by the examination of a square area of the drawing in B'ohm Davidoff and Huber ; p. 143. 
