336 Prof. J. 8. Macdonald. [Apr. 17, 
colloid solutions containing electrolytes, as, for instance, the conductivity of 
lymph, and, indeed, of nerve itself. Before this objection can be dealt with, 
another corollary must, however, be considered. Viewed from this hypo- 
thesis, colloid solutions must be considered as in a peculiar condition, which 
we may call “pseudo-polarisation,” when placed at a different potential in 
different parts of their continuity—as during the transmission of an electrical 
current. A colloid solution placed as a conductor in the path of an electrical 
current should ossess a graduated series of states of perfection dostributed 
throughout its length. The extreme case of degradation would be found at 
one end of the solution. At this point, therefore, a large quantity of 
electrolytes would enter the state of simple aqueous solution, thus diminishing 
the resistance. Diminution of resistance at, this point would, however, alter 
the distribution of potential, and the neighbouring portion of the solution 
would in its turn enter the same, or nearly the same, extreme condition of 
degradation. The resistance of the solution would in this way become 
increased at one electrode, diminished in the neighbourhood of the other ; 
and in only one point, which from analogy to the case of nerve (probably 
very exact analogy) might be called “the indifferent point,’ would the 
colloid solution retain its original state of perfection. Thus the measure- 
ment of electrical conductivity, even by rapidly alternating currents, might 
provide a very false estimate of the distribution of electrolytes within a 
colloid solution in its original condition of homogeneous equilibrium. The 
hypothesis, therefore, is not at once rendered impossible by these measure- 
ments. 
The possibility of such a “pseudo-polarisation” is not drawn from the 
imagination. Examining under the microscope nerve-fibres staining with 
neutral-red and toluidin-blue, I have observed regions of the axis-cylinder 
affected in just this way. Such regions, which are not those directly affected 
by diffusion inwards from the source of the injury-current, but are more 
distant regions, carrying the current arising from the injury-current source, 
are beset with stained granules, arranged very regularly within the axis- 
cylinder, varying in number and in size in a very definite way. Wherever 
the number of the granules counted across the axis-cylinder is large, the size 
of each individual granule is small; wherever the number is small, the size is 
great. Further, the number, and therefore the size, varies in a very definite 
manner along the region affected. So struck was I at first with the possible 
relation between the appearances observed and the passage of an electrical 
current, and so affected by the observation that these appearances occurred 
in regions of the fibre not directly involved by the injury, that I associated 
them with the possible transit of an action-current ; now, however, I should 
