28 
Transactions of the Boyal Society of South Africa. 
observations, is incapable of giving precise information as to the seat of the 
changes producing the positive effects. 
As mentioned above my experiments with the string galvanometer 
support Waller's findings. The initial change may appear as a positive 
deflection, but I agree with Gotch in so far as the initial deflection is con- 
cerned, that its cause is relative predominance of occurrences at the distal 
contact, not indeed because of greater activity here but on account of the 
slower development of the changes. 
If it is true that the positive variation depends for its appearance on 
difference in time relations between the changes under the two electrodes, 
we would expect that conditions which slow the processes would suffice to 
convert a negative into a positive deflection, and this is, as a matter of 
fact, the case. 
Fig. 3. 
Superposed curves obtained from nerves shortly after preparation. Curve a at room 
temperature, Curve b after the cross-section has been cooled with cold Kinger's solution. 
The action current has been changed by cooling from a negative to a positive deflection. 
The curves show both phases of the positive after-variation and the persisting positive 
change. 
Fig. 3 represents two records obtained from nerves which had been 
kept in Ringer's solution for two hours after preparation. 
The curves are superposed with the zero lines coincident. Curve a 
shows the usual negative deflection during stimulation followed by the 
after-variation. Curve b gives the response obtained after the cross-section 
had been cooled by cold Einger's solution. The deflection during stimula- 
tion is now positive. 
This result justifies us in applying the method of explanation put 
forward for uninjured nerve, also to the case where the current is led 
off from longitudinal surface and cross-section, and where the demarcation 
current has diminished in amount through lapse of time. 
