334 Prof. J. 8. Macdonald. [Apr. 17, 
has been exhausted in the endeavour to discover almost every conceivable 
kind of product of change other than this one, which has now been discovered. 
The acid products expected from a consideration of the apparently analogous 
case of muscle-injury have been shown in the course of this research to be 
definitely not present. There is no longer any reason to consider their 
existence as probable, since the fact has now been recorded that the site of 
injury may be neutral, and even alkaline, ata time when the process of injury 
is most effective in the production of its consequence, the injury-current. So 
far, therefore, there is no reason to consider the existence of any process 
of chemical change. 
Again, when attention is paid to the extraordinary series of exciting causes, 
which can be used to provoke this change, further doubt must be thrown upon 
the suggestion that it is the result of a definite chemical reaction. The 
similarity in consequence of the application of slight modifications of 
temperature in both directions of the scale, of slight mechanical interference, 
of acids and alkalies, of other chemical reagents having apparently no common 
basis of chemical action, clearly indicates the improbable nature of the 
statement that the energy thus disclosed has been previously locked up in 
some form of chemical combination. ‘The indications are therefore such as to 
demand a search for some physical bond between these salts and the 
remaining constituents of the axis-cylinder removable by a great variety of 
circumstances. 
Our attention once directed to the physical conditions present within the 
axis-cylinder, it is seen that the most remarkable condition present is the yet 
imperfectly understood condition of proteid material in a state of colloid 
solution. The facts of the case, therefore, so far as they have been elicited, 
may be accepted as an indication that this state of colloid solution is in some 
way a possible store of potential energy. If this is so, then the state of more 
perfect colloid solution should rationally be expected to function as a more 
ample store than any state of less perfect solution. It therefore becomes a 
matter of importance to inquire whether any diminution in the perfection of 
the colloid solution of the axis-cylinder, any tendency towards coagulation, 
has been observed in the region of the nerve-fibre in which this redistribution 
of energy has been found. 
It is at this point that my observations of the staining effects of neutral- 
red and toluidin-blue come to the assistance of those made with the aid of 
Macallum’s reagent. They may be accepted as evidence of the deposition of 
colloid material (gel.) as granules of visible dimensions, upon the surfaces 
of which the dyes are precipitated from the solutions of inorganic salts 
surrounding them. In medullated nerve therefore a colloid solution is found, 
