1888 - 89 .] Mr G. N. Stewart on Electrotonic Variation. 237 
however, is ascending, and the action stream will appear as a 
negative variation of it. 
These are the considerations which led me to expect that a 
positive variation, if it existed, would he found with strong currents 
upon the anodic side, hut not upon the side of the cathode. It 
was not overlooked that the ordinary electrotonic negative varia- 
tion might he so large as to reverse the action current. Still it 
was hoped that, even in this case, indications might he found in 
the curve of the stimulation effect to show that the expected true 
action current was really in play. 
Method of the Investigation. 
The first one or two observations were made without compensat- 
ing the electrotonic currents. They, indeed, give the same general 
results as when compensation was used. But it was obvious that it 
would not do to accept a positive variation on the evidence of an 
uncompensated anodic current. For it would he necessary to show 
Fig. 2. — A, B, C, D are electrodes ; I, stimulating electrodes ; G, galvano- 
meter ; P, P', Polil’s commutators; Com., compensator; Bat., polarising 
battery ; K, cell connected with commutator ; F, is a paraffin double key by 
which the polarising and galvanometer circuits were closed at the same time. 
that the apparent positive variation was not analogous to that which 
the intrapolar current undergoes when the nerve is stimulated, the 
so-called “ charge of resistance effect.” It was found that after 
compensation the positive variation continued in undiminished or 
scarcely diminished amount. Hay more, over-compensation did not 
abolish, nor begin to abolish it. Fig. 2 shows the arrangement 
