330 Prof. J. S. Macdonald. [Apr. 17, 
(1) A suddenly produced change at the injured segment resulting in the 
local liberation of inorganic salts into a new state of simple aqueous solution. 
(2) A transmitted effect observed in the neighbouring portion of the axis- 
cylinder, probably involving an alteration of the colloidal state of the 
solution; for such I take to be the teaching of my attempts to obtain 
spherical granules instead of crystalline precipitates with neutral-red. 
(3) Evidence obtained from an observation of the granules, that even the 
injury-current is on some occasions brought to an abrupt termination by the 
complete disappearance of its source, the electrolytes being again suddenly 
replaced in the concealed position, or condition, from whence they have 
come; and thus the conclusion that change is therefore even in this case 
sometimes a reversible one. 
Let us then suppose that in all these events we have a modified 
representation of the process of excitation and its consequences upon 
neighbouring segments of the fibre; a reversible change during which 
electrolytes are set free into a state of simple solution, and are then recovered 
from this state back into their original condition. Here truly there is the 
appearance and the withdrawal of a source of energy, a relay placed at every 
point of the nerve to ensure the continuous propagation of the excited state. 
Inorganic salts are set free to move ; they move ever so little ; the next segment 
of the fibre is chargedias a consequence (let us say negatively); the colloidal 
state of the fibre is thus changed from its condition of equilibrium; as a 
result a setting free of electrolytes at this new point and the propagation of 
the process; in the meantime the communication of the negative charge to the 
onward segment has left the original segment positively charged, the state of 
colloidal equilibrium is thereby reproduced, and the last involved segment is 
brought to a condition of rest. The idea of such a progressive fall from and 
return to a condition of colloidal equilibrium has already been advanced in 
explanation of this phenomenon, the novelty is an introduction of a new 
source of energy with the justification of actual observation. 
The manner in which I have been able to associate the collections of 
potassium salts observed by Macallum with the process of injury—and 
possibly with excitation—in the case of the nerve-fibre, must necessarily 
have some bearing upon the collections found by him in the other excitable 
tissue examined, the muscle-fibre. In the muscle-fibre he has depicted the 
presence of strong solutions of potassium salts in one only of the two sets of 
alternately-arranged discs of which each fibril is composed. In this case, also, 
attention must be drawn to the fact that here we have a picture of alternately- 
arranged regions of high and low osmotic pressure. Is it not possible that in 
this case also we have a picture, not of a resting, but of an excited tissue ? 
