612 
PHYSIOLOGY 
In computer-simulated plots of ventricular acti- 
vation in animals 2* v^^ith Purkinje fibers pene- 
trating as we propose in animals of this cate- 
gory, enough asynchrony of activation between 
endocardium and epicardium exists to generate 
such a front. 
Indeed, this might account for the apparent 
lability in contour of QRS in the same horse 
from beat to beat or among different individual 
cattle. In the horse (Figure 2) QRS in the Y 
axis electrocardiogram may vary from a QS to a 
qrS pattern. Possibly QRS in the former pattern 
arises from accelerated conduction over Pur- 
kinje fibers permitting complete cancellation of 
fronts during free-wall activity; while, in the 
latter case, Purkinje fiber conduction may be 
slowed and sufficient asynchrony results to gen- 
erate a R-wave. 
With respect to the electrocardiogram being 
"blind" to ventricular disease, animals in group 
II propose a particular problem. Since most of 
the ventricular mass in individuals of those 
cranial 
Figure 2. — Schematic drawings of cross-sections through the human and canine torso. R = right side, L = left 
side, D = dorsal side, and V = ventral side. Black cones are constructed from points on the torso where 
unipolarly-recording electrodes are placed to the face of the ventricle they "see." Criss-crossing arrows con- 
nect cross-sections of the torsos which contain cross-sections of the heart that appear analogous. 
