REPLACEMENT OF THE EXTERNAL SOLUTION OF THE 
NERVE BY WATER 
Experiments on Normal, Abnormal, and Degenerated Nerve 
In the last section it was stated that the main characteristic of nerve of interest 
from the point of view of the injury current was the presence of ' membranes,' 
which confine the important structures of the nerve cell processes from too familiar 
contact with the surrounding lymph. Such an arrangement is by no means peculiar 
to nerve, but seems to be the common property, in varying degree, of every cellular 
structure. The peculiar characteristic of nerve is the longitudinally unbroken con- 
tinuity of its constituent parts, and their arrangement side by side in the nerve trunk 
in parallel tubular compartments. In a sense this peculiarity is shared with muscle; 
but in that case there is a secondary transverse segmentation which is not obvious in 
nerve, and also the limits of the peculiarity are there narrowed by the incomparably 
shorter length of the muscle fibres. 
If it is believed that the internal solution of electrolytes found within cells in 
general is not the same as that which is found bathing their external surface, then 
the case of the nerve cell process of the nerve trunk offers itself as the most suitable 
for the testing of this opinion. For such a difference must give rise upon rupture 
of the membranes to diffusion processes, and consequently to differences of potential ; 
and the prolonged surface of the nerve cell process obviously offers the best case for 
the examination of these electrical differences. 
If such electrical differences as are found in the phenomenon of the injury current 
are to be totally explained in this way, they should be capable of modification in a 
manner entirely the same as that which would be expected from a process of diffusion. 
The value of a diffusion process depends upon the ratio between the concentration 
of the two solutions in contact, between which diffusion is taking place, and it can be 
greatly increased by diminishing the concentration of the weaker solution. Let us, 
therefore, reduce the concentration of the external solution of the nerve trunk to a 
minimum, the value of the diffusion process consequent upon rupture of the 'mem- 
branes ' (which confine the internal solution) should be greatly enhanced, and with 
this there should also occur a great increase in the injury current. 
Such a modification of the conditions of the nerve trunk is easily obtained by 
immersing it in water. For there is no reason to doubt that the primary effect of such 
an immersion is the extreme dilution of the external solution ; although, as a later 
consequence, a dilution of the internal solution must also inevitably occur. This 
differential modification of external and internal solution is the usual result of 
immersion in solutions, and is a fact continually taken advantage of in the impregnation 
