40 Mr Mines, On Pulsus alternans. 
while in order to give adequate expression to the possibilities of 
Gaskell’s hypothesis we must subdivide v, thus v=v'+v”. Then 
the series of beats will run 
V—v, V—v"’, Vv’, Veu", Ge. cccccccceees (2). 
Series (1) then expresses only the special case of (2) in which 
v or v’=0. 
Clearly, whenever v' is greater or less than v’, as will happen 
in most cases, there will be alternation in the extent to which the 
ventricle contracts and so alternation in the pulse wave, if the 
circulation is intact. 
But while the relative force of contraction of the ventricle 
in the beats V—v' and V—v" as registered by the suspension 
method or by the pulse wave, will depend chiefly on the relative 
amounts of tissue in v’ and v”, the apex beat (which is due largely 
to a twisting of the ventricles) and the electrocardiogram (which 
is affected by the path of the excitation wave in the musculature) 
will depend in even greater measure on the positions of the 
portions of muscle v' and v’. Therefore, when v' is greater than 
vy’, the pulse wave corresponding to V—v" will be greater than 
that corresponding to V—v’, while the apex beat corresponding to 
V—v" may be either greater or less than that corresponding to 
V-—v'. This may be made clearer by taking an extreme case. 
Supposing that v' represents a fairly large area of muscle in the 
posterior wall of the ventricles while »” represents a much smaller 
area in the anterior walls. The radial pulse wave produced by 
V—v' will be greater than that due to V—v’, but the apex beat 
may easily be greater for V—v' than for V—v’. Thus the larger 
apex beats will fall in the odd series, the larger pulse waves in 
the even series. 
Similarly with respect to the electrocardiogram. The failure of 
excitation in a small region near the apex is likely to produce greater 
modification of the detectable electric variation of the whole heart, 
than is the failure of a larger amount of muscle nearer the base. 
In those cases where v =v", the pulse waves or the suspension 
record may show no alternation, while the apex beats or the electric 
variations, or both, give clear evidence of alternation. 
Such cases are of peculiar interest ; although absolute equality 
of v' and v’’ will be extremely rare, an approximation to this con- 
dition is encountered fairly often, so that while the beats of the 
ventricle are apparently only very slightly if at all different in 
size, the electrogram exhibits marked alternation. It was through 
finding several cases of this kind in the frog’s heart that my interest 
in the subject was aroused*. 
* T have already published examples in this Journal. See Vol. xvi. Plate vit. 
Figs. 8, 9, 10. 
