Mi Mines, On Pulsus alternans. 41 
It is possible to interpret such curves as these on the assump- 
tion that the path followed by the excitation wave in the ventricle 
was different in the odd and in the even series of excitations. The 
mechanical record, unlike the electrical, takes no count of the order 
in which the various regions of the ventricle become excited. 
It is interesting to note that this condition, for which I have 
proposed the name pulsus alternans celatus, is frequently followed 
by marked mechanical alternation. An instance of this has been 
shown*. Comparison of curves (b) and (c)* illustrates once more 
the fact discovered by Gaskell, that when the odd series gets 
smaller the even series gets larger. Evidently this means that 
a portion of the tissue which was contracting with the odd series 
goes over to the even series or vice versa. To do so, it has only to 
miss one beat or to take up one extra excitation. 
Windle (1910) in fig. 7 of his paper gives a curve which illus- 
trates the same point. 
From what has been said, it is clear that an extra-systole of 
the musculature as a whole, whether provoked by an idio- 
ventricular excitation or by an artificial stimulus, will be expected 
to influence very materially the distribution of the tissue v’ and v” 
between the odd and the even series. Exactly what etfect the 
extra-systole will produce will depend on the moment of its 
arrival. Theoretically it may be expected sometimes to reduce 
and sometimes to increase the extent of the alternation, depending 
on the phase in which it arrives. But it will generally produce 
one or the other effect, for it is only for a short period in each 
complete cycle of two beats that v’ and v” are both refractory. 
Supposing at a certain instant v’ is refractory and v” is not. At 
the beat about to arrive v” would respond. But if at this mstant 
an extra-systole occurs, v” will give a premature response and will 
then miss either one or two natural excitations, depending on the 
exact time relations of the extra-systole and the natural excitations. 
Ifit missesone only it will be transferred from one series to the other. 
These conclusions are precisely in accord with Windle’s observa- 
tions: that extra-systoles have a profound effect on the course of 
pulsus alternans, but sometimes in the direction of increasing and 
sometimes reducing the alternation. 
Postscript. Since the above was written my attention has 
been drawn to another paper by Hering (Zeitschr. f. exper. Pathol. 
u. Therap. 1909, vit. p. 363). On p. 372, Hering put forward a 
view which is practically identical with that advocated in the 
present paper. He did not, however, recognise that this view 
was implicit in Gaskell’s original statement. 
Nov. 13, 1912. 
* loc. cit. Fig. 11. 
