
1905. | The Structure and Function of Nerve Fibres. 325 
osmotic-pressure experiments as were mine. Macallum’s conclusions, 
however, are entirely in the opposite direction. He has come to the 
conclusion that, except in certain limited spots, there are practically no 
electrolytes present in the axis-cylinder of the nerve-fibre. This finding 
is, indeed, not only opposed to the teaching of osmotic-pressure experiments, 
but also to that of all the very numerous series of experiments in which the 
peculiarities of the electrical conductivity of nerves have been studied. His 
conclusion is based upon the fact that the reagent used has only pre- 
cipitated potassium salts at certain points—nodes of Ranvier, and certain 
indefinitely placed intermediate points—which taken together probably do 
not represent more than one-hundredth part of the total length of the nerve- 
fibres. 
The pith of this contribution is the fact that I have to record a series 
of observations, which have amply served to substantiate my original 
conclusion and to refute Macallum’s. These observations show that it is 
true that a solution of inorganic salts, neutral salts, is present at every site 
of injury to a nerve-fibre of a strength not to be found in the same way 
in other parts of the fibre. Such a solution can be observed at any and 
every point of a nerve-fibre by the simple resort of injuring that part of 
the fibre. The evidence upon which this statement is based is histological 
in character, and has been obtained by two methods of observation. The 
first method has been the examination of nerve-fibres in a dye,® neutral red, 
extremely insoluble in, and therefore precipitated by, neutral inorganic 
salts. The second method has been the use of Macallum’s own reagent. 
I will begin by considering the appearances to be observed in the nerve- 
fibre, when examined in solutions of neutral red. 
Neutral red stains the nerve-fibre a uniform piuk colour, sometimes an 
orange-yellow. Presumably these slight differences mark slight modifica- 
tions in the relative amount of acid and alkaline salts present, as the dye 
is a very sensitive indicator. In addition to this uniform staining of the 
fibre, certain points are peculiarly affected by the dye: (1) the sites of 
injury ; (2) some of the nodes of Ranvier; (3) and certain granules which 
form first in the situations already given, but which finally spread from 
thence, involving very considerable stretches of the nerve-fibre. At these 
special points there is a very intense collection of the stain ; under certain 
conditions red, under other conditions yellow. Apparently, therefore, the 
sites of injury may be slightly acid (acid salts) or slightly alkaline (alkaline 
salts). Whether slightly acid or slightly alkaline, it is in both cases 
possible to prove, under the microscope, the presence of the injury-current. 
There can, therefore, be no longer any room for the contention that this 
