THE CURRENT OF INJURY 
The statements subsequently made are all based upon observations taken from 
experiments upon mammalian nerve, which offers several advantages for the purposes 
of this enquiry. 
In the first place, mammalian nerve can be obtained in comparatively long 
stretches, and in the case of the phrenic or the vagus nerves in long stretches free from 
branches and, therefore, from undesirable accessory cross sections. The phrenic 
nerve, in addition, offers the advantage of containing only medullated fibres of 
uniform size and relative value of axis cylinder and myelin ; it is, however, not easy 
to remove as neatly from its pleural covering as are nerves placed in a bed of loose 
areolar tissue, and on this account, although at first made use of, it has been for the 
present abandoned. 
Certain mammalian nerves, such as the vagus of the dog, although for many 
reasons preferable, suffer from the disadvantage of exhibiting a relatively small 
difference of potential between the longitudinal surface and the cross section. It is in 
such cases naturally more difficult to form a correct opinion of the real distribution 
of potential upon the surface of the nerve. 
This apparent disadvantage is, however, discounted by the comparatively small 
resistance of mammalian nerve in general, as contrasted with the relatively minute 
sciatic nerve of the frog. The resistance in the nerve being small, a slight potential 
difference gives rise to an appreciable current through the galvanometer, and com- 
pensation and determination of potential difference is in this manner rendered far 
more exact. The disadvantage has also in the present case been of no interest since 
an extremely sensitive galvanometer (Thompson pattern, Muirhead and Company) of 
50,000 ohms, resistance has been used throughout the whole series of experiments. 
The differences of potential measured in the case of the vagus nerve recently 
removed from the dog were rarely as great as - oio volt, averaging about "007 volt. 
In the case of the sciatic nerve of the dog and cat the potential differences obtained are 
much greater, and are greater than the potential difference ordinarily obtained from the 
sciatic nerve of the frog. The frequent examples given subsequently in this paper 
will be found fully to bear out this statement. Consequently, it is easy in the case 
of the mammalian sciatic nerve, dealing with a low resistance and a large difference of 
potential, to measure accurately the comparatively large currents which are found and 
to compensate the potential differences with ease. The results of a typical examina- 
tion of a sciatic nerve are given in Experiment I. 
c 
