— tale 
1905. | The Structure and Function of Nerve Fibres. 341 
consider briefly the relation existing between some of the physical and functional 
changes produced by the action of a polarising current. ‘‘ Pseudo-polarisation,” 
unlike true polarisation, is fully developed within a very short time from the 
institution of the current. The time required being that taken by the colloid 
solution in responding to a difference of potential. At the kathode desolution 
has occurred, and the corresponding rise in local osmotic pressure. At the anode 
the contrary change has taken place, and the osmotic pressure has fallen. At 
some point intermediate between the poles the normal state is maintained. At 
the moment of current closure, the osmotic pressure at the kathode is relatively 
much greater than the osmotic pressure at a point immediately beyond the kathode 
than it will ever be again during the continuance of the current, the difference 
being due to a distinction between the conditions present at the moment of 
establishment of diffusion, and those present after a steady condition of diffusion 
has begun. The negative ion being the faster, this is the only moment when the 
point beyond the kathode is negative to the kathode itself. At this moment, 
therefore, this negativity, due primarily to the initiation of diffusion, produces an 
excitation in the extrapolar region, and thus causes the travelling nervous impulse 
characteristic of current closure. 
In an extremely excitable nerve it might be expected that the wave of 
positivity, and therefore of lowered osmotic pressure following in the wake of 
this transmitted process, might provide an opportunity for a new and almost 
equally sudden diffusion from the kathode, and therefore for a repetition of 
the travelling excitation. In such a case a series of excitations might be started 
from the kathode, and give rise to a tetanic response of the motor organ. . There 
is no difficulty in the way of providing a complete explanation for the kathodal 
phenomena occurring at the moment of current closure. The ease with which 
this can be done, however, entails some discussion as to the reasons which deter- 
mine the absence of a transmitted positive “inhibitory state” starting from the 
anode, travelling along the nerve with a wake of negativity behind it. If the fall 
of osmotic pressure at the anode was as great as the rise of pressure at the 
kathode, then the use of the same hypothesis would indicate the necessity for such 
an occurrence. ‘The fall of osmotic pressure at the anode is, however, in fact, less 
than the rise at the kathode, and this is determined by the following consideration, 
In the state of normal equilibrium of the colloid solution, the amount of 
inorganic salt present, in a state in which it can exert an osmotic pressure, is 
comparatively small. The concentration of the salt solution at this time is about 
that of a decinormal solution. When complete coagulation of the colloid has 
taken place, there is reason for believing that the concentration is very much 
greater, being somewhere about ten times as great. A fall of pressure below the 
normal never involves any great relative difference of pressure, a rise of pressure, 
however, may entail comparatively great relative differences. This distinction 
would seem sufficient to explain the comparative insignificance, and even the 
complete absence, of the transmission of an “inhibitory nervous impulse” starting 
from the anode. 
When considering the functional changes observed during the time of closure of 
the current, it is necessary to reckon two sets of physical conditions. The one set, 
