350 The Structure and Function of Nerve Fibres. 
word “excitation,” as affording a complete explanation of the origin of one of the 
most interesting physical phenomena of nerve—the injury-current. This phe- 
nomenon I carefully examined. The evidence and the arguments which had 
been previously made use of to associate this phenomenon with secondary con- 
sequences of injury were, as I found and explained, quite inconclusive. These 
arguments also were misleading, since their tendency was to detract from the 
interest taken in that most important feature of the nerve, its physical structure. 
They tended, for example, to separate this “injury-current” as a functional 
occurrence, from the facts of the electrical conductivity of nerve, in which I was 
certain lay the key to its meaning. I therefore planned the steps of my investiga- 
tion on the assumption that this phenomenon was dependent upon facts entirely 
similar to those upon which the electrical conductivity was confessedly dependent, 
that is to say, upon the number, character, and arrangement of the electrolytes 
permanently present in the nerve. None of the relations elicited by me in the 
course of this investigation led me at any moment to doubt the truth of this 
conception. I was, however, compelled, at its close, to admit that these 
electrolytes were present in a more liberated condition in the neighbourhood 
of the injury than elsewhere. The word excitation, however, which might then 
have been conceivably introduced into the statement of this fact, involved so 
many conceptions foreign to my meaning, and possessing no relation to the facts 
discovered, that I carefully avoided—-or rather resisted—its introduction. The 
fact made clear from the results of this investigation, that there were more 
electrolytes in motion at the site of injury than in other parts of the nerve, ran a 
great risk of being accepted as a proof that new electrolytes (simple waste 
products) were being freshly formed there as a consequence of some localised 
chemical change. 
Now the facts are different, the actual nature of the electrolytes concerned 
has been in great measure determined. They have been definitely found to 
be of the kind suspected by me—inorganic salts, permanent constituents of the 
axis-cylinder. It is therefore possible to speak of this portion of the axis- 
cylinder in very definite terms. It is a portion containing a concentrated aqueous 
solution of a potassium salt, and some partially coagulated proteid, and in these 
conditions it is unlike other portions of the axis-cylinder. One is therefore in a 
position clearly to face questions asked with the object of seeking to link its 
existence, and the consequences of its existence, in terms of nerve-function. 
Personally, I would arrange the facts in these terms. The factor in this 
condition of importance to the remainder of the nerve-fibre is the presence of so 
much potassium salt. The existence of so much potassium salt in a state of simple 
solution is the consequence of a violent stimulation. The consequences involved 
by the presence of this salt are (1) the invasion of neighbouring portions of the 
fibre by salt diffusing from this point, and (2) a resultant alteration in the 
electrical potential of points in the axis-cylinder. The direct consequence of 
the entrance of potassium salt, properly belonging to another portion of the fibre, 
is some secondary coagulation. The direct consequence of the alteration in 
potential is to render inexcitable the immediately neighbouring portion of the 
axis-cylinder, and to render more excitable more distant regions. 
