Positive Electrical Variation in Isolated Nerve. 
31 
sign of a wake of the change under the distal electrode in Gotch's sense, 
coming to light when the process giving the after-effect is suppressed by 
cold, or it may be due to after-effect at the distal electrode. Some results 
that I have obtained seem to indicate that cooling the distal electrode 
favours negative after-effect. Fig. 4 is an example of this. Curve a is 
taken from a preparation which had been preserved for some hours in 
Einger's solution and no fresh section made. Curve was recorded after 
cooling the tissue under the distal electrode. 
In some records taken from nerves at a considerable interval after 
preparation the negative phase of the after-effect is predominant, so that the 
curve shows practically only upward deflection at the close of stimulation 
and the zero line is regained in about 4 sec. This is so in fig. 5, recorded 
after 20 hours' preservation in Einger's solution. Here both phases are 
Fia. 5. 
Response from nerves 20 hours after preparation, without fresh section. The action 
current is positive, and the second phase of the after- variation is predominant. 
doubtless present, but for some reason the second predominates, and it is 
of importance to observe that its duration is similar to that of the first 
phase when alone evident, and of the whole after-variation when both 
phases are apparent on the curve. This figure gives a response of the 
type described by Waller as the fifth member of his series, and with regard 
to which he states that " it was far less frequently and assuredly observed, 
and I do not know whether in order of development it should be placed 
before or after the response positive followed by positive." 
It appears to me that we are able to distinguish two elements in the 
electrical changes which follow excitation, one of which is associated with 
the brief process which occurs in the part or parts of the nerve that have 
previously been in the condition of excitation, and is evidenced by one or 
both phases of the positive after variation, and another which shows itself 
as a persisting positive change, lasting for several minutes after the first 
short-lived process has terminated. This second intimately depends on 
the presence and amount of the demarcation current. In the case of fresh 
