32 
Transactions of the Royal Society of South Africa. 
nerves, where the demarcation current is large as in fig. 1, the persisting 
change has a value of about 5 x 10"^ volt, while the first element gives a 
change of about 8 x lO"^ volt. When the demarcation current has dis- 
appeared the second element is no longer perceptible. It would appear 
that tetanisation increases the demarcation current when the latter is 
present. 
It is evident that another view of this persisting change might be 
adopted, and the positive after-variation described as large at first and 
leaving behind it a wake of less amount and longer duration. The dis- 
appearance of the persisting change would then be correlated less with 
diminution of the demarcation current than with the accompanying 
development of the second phase and its wake. 
We may exclude the possibility that the persisting positive change is 
caused by Anelectrotonus, which depends on the electrolytic polarisability 
of nerve. The tetanising current used is a weak one, being of minimal or 
slightly above the minimal strength required to stimulate the nerve. 
Conclusions. 
The action current recorded from fresh isolated nerve on tetanisation 
when the leading off electrodes are placed on longitudinal surface and 
cross-section is monophasic, or if diphasic, the second phase is very 
slightly developed. The individual responses to the tetanic shocks are 
superposed on the deflection. 
When the demarcation current has diminished in value the action 
current is diphasic. Either phase may predominate in the record, de- 
pending on two factors — electromotive force and rate of change at 
the two electrodes. 
The after-effect is compounded of two parts : (1) a variation opposite 
in direction to the action current and monophasic or diphasic according 
to the condition of the tissue under the distal electrode, and (2) a per- 
sisting positive variation, probably to be ascribed to increase in the 
demarcation current caused by tetanisation. 
