Positive Electrical Variation in Isolated Nerve. 29 
So far we have been chiefly considering the initial variation. With 
regard to the after-variation most observers have followed Hering in 
attributing it to a process occurring in the uninjured portion of the 
nerve and affecting the electrode in contact with the longitudinal surface. 
Strong support has been afforded to that view by Garten's " work. 
Gotch takes the view that positive after-variation, when it occurs, is 
usually due to the presence of a tail or wake of the change under the 
distal electrode, which is permitted to affect the instrument by some 
circumstance which diminishes the capacity of the tissue under the 
proximal contact. He mentions, however, that under other conditions 
positive after-effects may be developed as appears from the experiments 
of Hering and Head. As regards the cause and seat of such after-effects 
Gotch offers no opinion, and his criticism of Waller's conclusions refers 
only to the initial change. 
Cremer, f writing before the publication of Garten's observations, 
declared that it was not possible upon the evidence so far adduced to 
decide whether the positive after-effect is due to the proximal electrode 
becoming more positive or to the distal electrode becoming more negative. 
He was of opinion that the positive effect only appears when the demarca- 
tion current is no longer of its full normal value and waves of negativity 
can force their way to the second electrode. Further, even conceding that 
the positive after-effects are conditioned solely by changes at the proximal 
electrode, it does not follow that the process is opposed to that which 
gives rise to negative change. There is the possibility that a negative 
change may persist corresponding to the tonic contraction of muscles, 
and that a temporary interruption of this may produce the positive after- 
effect. 
With regard to this view of Oremer's, I would point out that I have 
obtained large positive after-effects from nerves immediately after removal 
from the body, when the demarcation current produced by the cross- 
section must be at its height. 
The typical persisting effect which I have obtained after tetanisation 
is positive, while we would expect on Cremer's theory that it should, 
after a short positive deflection, be negative. 
If fig. 1 is referred to it will be observed that the after-effect consists 
of a fall and rise of the curve, that is to say a positive variation, lasting for 
4 to 5 sec, and after this the curve runs parallel to and below the zero 
line. The interruption of the curve is due to the introduction of a 
control deflection. It may be many minutes before the zero is regained. 
In curve a of fig. 3 the after-effect is diphasic, a positive variation 
being followed by a negative, and the diphasic variation lasts for 
about 5 sec. 
* hoc. cit, t Nagel's Handbuch, Bd. 4, H. 2, s. 903. 
