332 Prof. J. 8S. Macdonald. [Apr. 17, 
indeed enchained there, and are thus unable to exert an osmotic pressure, or 
by diffusing away, give rise to electrical phenomena. To explain, in the 
presence of such an hypothesis, diffusion processes consequent upon injury, it 
seems necessary to invent a phenomenon really secondary to injury and 
involving new conditions of the fibrillar structure. The invention of such a 
phenomenon is as culpable as the invention of a chemical change, and the 
necessity for doing so is equivalent to the necessity of abandoning this 
supposition.” 
Obviously the main difference between the state of the evidence then and 
now is, that a distinction of the kind suggested between the condition of the 
inorganic salts at the “cut end” and their condition at remaining portions of 
the nerve-fibre has been actually observed. It follows, therefore, ‘that the 
original hypothesis, temporarily rendered absurd by the necessity for such an 
assumption, is now remarkably strengthened by the conversion of the 
assumption into a fact. | 
There is, however, another difference of importance, which may well be 
dealt with at once before proceeding to a consideration of the main point. In 
doing so it may be necessary to anticipate conclusions arrived at more logically 
at a later stage. This difference is that, in the statement quoted above, the 
fibrille are mentioned as veritable units of structure of the nerve-fibre ; 
whereas in the preceding part of this present communication they have been 
neglected, and the axis-cylinder has been dealt with as if it were a 
homogeneous colloid solution. This change of opinion is considered justified 
by the following facts. My personal acquaintance with the microscopical 
appearances of nerve-fibres has since then largely increased. Whilst 
cultivating it in pursuit of the present histological investigation I have used 
dyes suitable for a revelation of neuro-fibrils. I have, however, never seen 
these neuro-fibrils, except under such circumstances as demanded their 
criticism as possible artefacts, as for example after the use of fixatives, or in 
short stretches of nerve-fibres obviously suffering from the results of 
excitation. Yet the only peculiarity marking the use of these dyes in this 
investigation has been the fact, that they have been for the most part 
presented to the fibres in solutions of such salts as were least likely—as 
previous observations had shown—to destroy the “living state” of the 
fibres. 
In place of these neuro-fibrils, however, the granules spoken of have made 
an absolutely constant appearance. Such granules I have observed forming 
at the cut ends of the fibres, but also in portions of the fibres remote from 
positions of injury. Such granules may, even in portions of intact fibres, be 
observed to increase and again to diminish in size. They may be seen at any 
