2 74 
THOMPSON YATES LABORATORIES REPORT 
of tissue with dyes for purposes of histological research. In such researches the 
artifice of immersion is freely used to remove some impregnating solution from the 
external surface, and to leave it within the internal solutions of the cellular elements 
of the tissue. It is an occurrence, however, which does not require for its confirm- 
ation such evidence as this, if it be granted* that the limiting surfaces of cell, as shewn 
by the osmotic pressure exerted by the solutions in them during immersion in water, 
are barriers which limit the extent to which diffusion can take place through them. 
For it at once follows that it is easier to remove particles in solution outside the 
barrier, than those which are protected by such obstacles to their removal. Moreover, 
this differential modification by immersion in water is seen to be the converse of a 
modification of which no one will deny the actuality, namely, the easier access of an 
impregnating solution to the external solutions of the nerve than to the axis cylinders 
of its nerve fibres. 
Granted that an immersion in water affects first the external solution, the modi- 
fication in the injury current produced by such an artifice is of great interest. 
Immersion in water always very sensibly increases the injury current of nerve. The result 
of the experiment is entirely in agreement with the anticipation, which foresaw such a 
result following upon the dilution of the external solution ; and in so far as it is a 
confirmation of this, it may itself be used to strengthen the evidence in favour of the 
great importance of the core model structure of the nerve. 
Nor is this the limit to the interest of the information which can be obtained from 
such experiments. There is no circumstance under which nerve shews an injury 
current, that the current is not increased by an immersion in water. But further, 
whereas nerve can be placed in, what is ordinarily considered, such a debilitated con- 
dition that it shews no injury current, it sometimes happens that even then an immersion 
in water will evoke from it an injury current as great as that which can be obtained by 
the same artifice trom the most ' vigorous ' nerve. These latter conditions are, in fact, 
such as to justifiably provoke the following statement : — Even when all the solutions in 
the nerve, external and internal, have been brought by processes of diffusion to a common 
level, then an immersion in water is of itself productive of such a new difference in concen- 
tration of the external and internal solution as to reproduce, and to reproduce to its full extent, 
the phenomenon of the injury current. This statement is based, as will be seen, upon the 
examination ot the injury current of degenerated nerve. Such a nerve removed from 
the body and provided with a new cross section may shew no injury current, and yet 
an immersion in water may reveal a current as great as that obtainable from a healthy 
nerve taken from the same animal and subjected to the same artifice. 
In such a nerve there is reason to believe that the tubular limiting ' membranes ' 
are yet intact, their contents, on the other hand, are gravely altered. There is still, 
in such a nerve cell, substance limited by the neurilemma : although the cell substance 
* See Preliminary communication, Proceedings Royal Society. J. S. Macdonald, vol. lxvii, 315-320. 
