342 Prof. J. 8S. Macdonald. [Apr. 17, 
determined by true polarisation, taking place on the surfaces of the partially 
permeable sheath of the nerve-fibre, that is, at the nodes of Ranvier. The other 
set, determined by ‘“ pseudo-polarisation.” There is a certain similarity between 
the effects of these two conditions occurring at each pole. Their consequences are 
added together in the production of the anelectrotonic and katelectrotonic arrange- 
ments of differences of potential. The two factors, however, have different time 
relations, the effects of true polarisation gradually increasing, the consequences of 
“‘pseudo-polarisation” being most marked to begin with, and subsequently 
declining. The polar conditions due to true polarisation are sufficiently well 
understood. Here it is only necessary to dwell upon the polar conditions due 
to “ pseudo-polarisation.” 
During the early stages of current closure, the condition of ‘‘ pseudo- 
polarisation” gives rise to an increased osmotic pressure in the region of the 
kathode, a diminished osmotic pressure in the region of the anode. The partially 
permeable membrane of the nerve-sheath is more permeable to the negative anion 
than to the positive kation. An increase in osmotic pressure will therefore lead 
to the separation of diffusing ions in the line of this sheath. The diffusion is in 
this case outwards, and the faster negative ion therefore communicates its 
negative charge to the parts outside this sheath, that is to say, to the surface 
of the nerve. ach point in the kathodal extrapolar region nearer to the kathode 
is therefore more negative than more distal points. The condition due to true 
polarisation is therefore reinforced. At the anode, the region initially of 
diminished osmotic pressure, diffusion is inwards, and the external surface of 
the nerve possesses the charge of the more slowly diffusing positive kation. 
Here, then, the condition of anelectrotonus, due to true polarisation, is rein- 
forced. From reasons given above, the addition at the anode is much smaller 
than the addition at the kathode. The anelectrotonic condition is therefore at 
first smaller in magnitude than the katelectrotonic condition, both also at first 
increase in magnitude with the increase of true polarisation. The condition due 
to “pseudo-polarisation ” is, however, undergoing a diminution with lapse of time, 
possibly at once accounting for the subsequent serious fall in the value of 
katelectrotonic condition. To explain this, it is necessary to spend a few moments 
with the details of the condition of “ pseudo-polarisation.” 
The essence of the condition of “ pseudo-polarisation ” is the arrangement of the 
colloid particles of the axis-cylinder in a series of graduated sizes between the 
poles. The particles (aggregates of molecules) at the anode are smaller than those 
occurring in normal stretches of the nerve, those at the kathode are bigger and 
less numerous. The immediate consequence of this arrangement is the motion 
of inorganic salts in large quantity in the kathodal region, in small quantity at 
the anodal region. This, however, is a condition which cannot remain as per- 
manently as the cause of its original appearance. The salts diffuse, and finally 
their distribution must, at least, become far more uniform, and that, too, before 
the essential condition of “ pseudo-polarisation ” has been removed. The electrical 
consequences of the differential distribution of osmotic pressure inaugurated by 
“‘ pseudo-polarisation ” are therefore evanescent. 
The functional changes of excitability at the poles are primarily dependent upon 
