324 . Prof. J. S. Macdonald. [Apr 
for instances in which the value of the cell was reversed, and found them, 
the general conclusion arrived at remained as before. The hypothesis being 
correct, the value of the internal solution was ten times greater than that of 
the decinormal solution (lymph) found bathing the outer surface of the 
nerve. | 
This conclusion necessarily brought me up against the facts of osmotic 
pressure. I therefore studied the alterations in volume of the nerve conse- 
quent upon alterations in the strength of the external solution,? and failed to 
find in them any support for the idea that there was an extraordinarily con- 
centrated solution within the nerve-fibre. Obviously, as such experiments at 
once show, the osmotic pressure exerted by the internal solution of the nerve 
is similar to that of the decinormal solution found upon its surface. Still, 
believing that the conductivity of the internal solution was of a higher order 
than that of the external solution, and that the injury-current was in reality 
produced by a diffusion process between the two solutions, I was, however, 
forced to the conclusion that the major part of the inorganic salts within the 
nerve-fibre were arranged there in some special manner.’ It was necessary to 
assume that the salts only possessed the osmotic pressure due to their real 
quantity, and were only capable of taking part in processes of diffusion in this 
real quantity, at the actual site of injury. It was not possible to consider 
that they were elsewhere in a state of ordinary chemical union, since they 
played their proper part in the conductivity of the nerve. In my imagination 
they were arranged along hypothetical surfaces, the surfaces of the fibrils, in 
such a way that they were free to move along these surfaces, but not at right 
angles to them. Subsequent microscopical experience has convinced me of 
the artificial character of these neuro-fibrils, and I am now logically driven to 
consider the concealed salts as present upon the surfaces of particles existing 
in the colloidal solucion of the axis-cylinder. | 
Within recent years Macallum, of Toronto, has considerably extended the 
methods available for the direct observation of the chemical constituents 
packed away within the minute and enclosed cellular elements of the 
tissues, and has placed at our dispcsal a number of reactions which can be 
watched beneath high powers of the microscope. In his own hands and 
in the hands of others who have adopted them these methods have already 
led to the collection of a mass of most interesting data. Most recent of 
these methods has been one for the detection of potassium salts.7 Using 
this method—precipitation with cobalt nitrite, and: subsequent blackening 
of the precipitate by the addition of ammonium sulphide—Macallum has 
carefully examined the case of the nerve-fibre. His observations have led 
him to certain conclusions as much opposed to the evidence obtained from 
