286 Transactions of the Boyal Society of South Africa. 
the secondary coil of an inductorium, were applied with their wicks about 
2 mm. apart on the dorsal surface at the left lateral margin. The right 
and left leading off non-polarizable electrodes were placed, the left at the 
mid-point of the transverse diameter of the ventricle on the dorsal surface, 
where it remained during the experiment, and the right electrode was at 
first placed about 2*6 mm. from the point of stimulation on the line 
between that point and the left electrode, that is to say, on the transverse 
diameter of the ventricle. The right and left electrodes were 25 mm. 
apart. The ventricle was stimulated by a break induction shock, and the 
response recorded photographically on moving sensitized paper with a 
magnification of 660 diameters. The right electrode was then shifted by 
about 2*6 mm. along the transverse diameter towards the left electrode and 
another record taken, and the process was repeated, the right electrode 
being moved each time by as nearly as possible an equal distance towards 
the right margin, passing the left electrode at the middle point and being 
finally placed on the right margin at a point 50 mm. distant from its first 
position. In this way a series of records is obtained in which the 
variations under the right and left electrodes (what may be termed the 
right and left variations) are separated from each other by varying time 
intervals, the right variation at first leading, and after the crossing of the 
electrodes, the left variation leading. 
Curve 1 commences with a downward deflection followed by an upward 
deflection. The curve then falls slightly and a plateau with small irregu- 
larities follows. The plateau is terminated by a sharp upward deflection, 
after which the curve falls to and beyond the zero line, being interrupted 
on its descent by a notch. After regaining the zero line the curve runs 
horizontally until it terminates in a slow descent and return. I have 
lettered the peaks Q^, B^, Qi, Bi, and T. is the preliminary positive 
deflection of the right variation, i?,. and the plateau indicates its succeed- 
ing negative portion, ft is the preliminary positive deflection of the left 
variation. Bi indicates the peak of its negative deflection, which is here 
followed by an increase of negativity giving the downward summit. The 
horizontal part of the curve is due to the compensation of the two varia- 
tions, and the direction of variation T indicates that the right variation 
commences to decline before the left. 
As the time interval between the variations is reduced the plateau 
shortens, and then the amplitude of the deflections is cut down. In 
curve 10 the left variation has begun to lead, and in record 19 we have 
a curve similar but of opposite direction to curve 1. As the variations 
change their time relations when the electrodes cross at the mid-point, 
the series of records shows that the terminal variation T changes from 
a downward to an upward deflection. In the later records this terminal 
variation is a complex presenting both downward and upward deflections. 
