re
rendered approximately equal. The records of A and B were at first taken
separately (fig. 66, _a_). It will be noticed that the maximum
deflection of A was attained relatively much earlier than that of B.
The resultant curve R' was obtained by summation.

[Illustration: FIG. 66.--DIPHASIC VARIATION
(_a_) Records of A and B obtained separately. R' is the resultant by
algebraical summation. (_b_) Diphasic record obtained by
simultaneous stimulation of A and B.]

After taking the records of A and B separately, a record of resultant
effect R due to simultaneous vibration of A and B was next taken. It
gave the curious two-phased response--positive effect followed by
negative after-vibration, practically similar to the resultant curve R'
(fig. 66, _b_).

The positive portion of the curve is due to A effect and the negative to
B. If by any means, say by either increasing the amplitude of vibration
of A or increasing its sensitiveness, the response of A is very greatly
enhanced, then the positive effect would be predominant and the negative
effect would become inconspicuous. When the two constituent responses
are of the same order of magnitude, we shall have a positive response
followed by a negative after-vibration; the first twitch will belong to
the one which responds earlier. If the response of A is very much
reduced, then the positive effect will be reduced to a mere twitch and
the negative effect will become predominant.

I give a series of records, fig. 67, in which these three principal
types are well exhibited, the two contacts having been rendered
unequally excitable by solutions of the two reagents KBr and
Na_2CO_3. A and B were vibrated simultaneously and records taken.
(_a_) First, the relative response of B (downward) is increased by
increasing its amplitude of vibration. The amplitude of vibration of A
was throughout maintained constant. The negative or downward response is
now very conspicuous, there being only a mere preliminary indication of
the positive effect. (_b_) The amplitude of vibration of B is now
slightly reduced, and we obtain the diphasic effect. (_c_) The intensity
of vibration of B is diminished still further, and the negative effect
is seen reduced to a slight downward after-vibration, the positive
up-curve being now very prominent (fig. 67).

[Illustration: FIG. 67.--NEGATIVE, DIPHASIC, AND POSITIVE RESULTANT
RESPONSE]

#Continuous transformation from negative to positive