228 
THOMPSON YATES LABORATORIES REPORT 
In the accompanying figure the two darkly-shaded records (i and 2) are two diphasic records of 
not very different character. The first is the outcome of one change, affecting two points in succession, at 
an interval of onset of - ooi second, and lasting at each point for '004." 
The second is the result of two such changes passing the same two points with an interval between 
them of - ooi ." 
It is obvious that in the second two out of the four phases actually occurring are entirely unrep- 
resented in the record, since occurring at the same time and being equal and of opposite sign they are 
completely eliminated from it. The actual record, although the result of two nervous impulses, let us say, passing 
at an interval of -oo\, is exactly the same as the iecord would be of one nervous impulse passing along the nerve if its 
passage was observed by placing electrodes upon two points separated by double the distance which divides the two 
points arbitrarily chosen. 
To emphasize the statement, it is interesting by an examination of fig. 2 to convince oneself that the 
passage of ten nervous impulses at the rate of one thousand per second, or of one thousand nervous im- 
pulses at the same rate, and even if each in succession produced at every point its appropriate electrical 
change might in a record give rise to a diphasic variation. In this extreme case the diphasic record could 
hardly be interpreted as due to the occurrence of only one electrical change at each point. 
Such considerations hold good for ever)' experimental record taken as the observed effect of two or 
more successive stimuli, and vitiate, in a very great number of cases, conclusions drawn in their neglect. 
When many successive stimuli are used, as in faradisation, and when imperfect recording instruments add 
further fallacies to the record, as in galvanometric observations, it is impossible to base any conclusion of 
even suggestive interest upon such records. It ma}' even be reasonably said that such criticism applied 
to diphasic and multiplied diphasic records obtained by the observation of two points in the continuity of 
the nerve, may be transferred to records of' negative variations,' taken from the longitudinal surface and 
cross section. Confidence is only implicitly placed in such records when it is imagined that electrical 
change only occurs at the point on the longitudinal surface, and that the real change is, therefore, mono- 
phasic. This is, however, far from being the truth, for even exactly-taken records of such single 
negative variations are triphasic : and no one can satisfactorily declare what the nature of the real phases 
occurring at either point was, which has resulted in this triphasic record. 
