Positive Electrical Variation in Isolated Nerve. 
27 
portion of the nerve. The tissae at the cross-section is not able, owing to 
the injury, to develop perceptibly the condition of excitation. The result 
is that the action current appears as a large upward deflection — the nega- 
tive variation — with the separate deflections superposed. 
After preservation for some hours in Einger's fluid, the effects of the 
injury diminish, as evidenced by the decreased demarcation current, and 
the region at the cross-section develops excitation to some extent. The 
negative deflection is now less, as the influence of the second phase of the 
action current becomes evident. 
When the interval between preparation and experiment is lengthened, 
the action current frequently shows itself as a positive variation. In cases 
where this occurs the demarcation current has subsided to a large extent. 
The nerve, however, in the neighbourhood of the cross-section is still in an 
altered condition, and I think we may look upon the positive variation as 
evidence that the response to the induction shocks is here slower than in 
the remainder of the nerve, and therefore exercises a greater influence 
upon the galvanometer. 
This is in agreement with the explanation put forward by Waller in so 
far as that observer distinguished by experiment between this positive 
variation and fixed anelectrotonus. Waller points out that the variation is 
particularly sensitive to the action of drugs, differing in that respect from 
exclusively physical electrotonus. 
He contrasts the positive deflection with the usual negative deflection 
as regards its increase with increasing strength of stimulation. The nega- 
tive deflection exhibits staircase ascent with a stimulus that is increasing 
step by step, while the reverse is true of the positive variation, which 
diminishes as the stimulus is increased, and may ultimately give place to 
a positive variation. 
Waller does not commit himself on the question as to whether or not 
the appearance of positive or negative action current may depend upon 
different rates of development of the two states, and considers that the 
positive variation must be admitted to rank as a true action current, but 
on the whole he inclines to the view that positive deflection and positive 
after-deflection are of the same genus and to be interpreted as the sign of a 
physiologico-chemical assimilation consequent upon previous dissimilation. 
This is not in accordance with the view put forward in this paper. 
Waller's results have been submitted to criticism by Gotch.'" This 
observer, who used the capillary electrometer, did not find positive change 
as the initial effect of stimulation in any of his experiments, and is of 
opinion that Waller's results are all effects due to the development of 
relative negativity of the tissue under the distal contact. Gotch points out 
that the method used by Waller, unless extended to comprise rheotome 
* Schafer's Text-book of Physiology, vol. ii., p. 540. 
