557 
The then following sinusimpulse reaches the ventricle towards the 
close of the diastole and may, therefore, be followed by a small 
ventricular systole. This small ventricular systole now yields a short 
refractory stage. Therefore the next auricular systole can be followed 
again by a ventricular systole, which, on account of the short 
durations of the preceding pause, is again small and short. For this 
reason the next auricular systole can again be followed by a ven- 
tricular systole. Thus by a single induction shock the halved rhythm 
of the ventricle is changed into the normal rhythm of twice the 
rapidity. 
Figs. 1 and 2 show us that we are able to change the halved 
rhythm into the normal one by means of a single induction shock. 
Now the question arises why the ventricle does not take up the 
normal rhythm spontaneously. From the fact that the halved rhythm 
can be changed into the normal, it, indeed, appears that the meta- 
bolic condition of the ventricular muscle enables the ventricle to 
beat with a double frequency. Still the ventricle persists in its halved 
rhythm, unless we administer a stimulus at the right moment. The 
cause must be looked for in the magnitude and the long duration 
of the ventricular systoles of the halved rhythm. Every second 
sinusimpulse rebounds on this prolonged refractory stage; the ven- 
tricle is caught in the halved rhythm and can escape from it only, 
when through: an extra stimulus a small ventricular systole is evoked 
directly or indirectly. 
When, however, the ventricle has been pulsating for some time 
in the halved rhythm, the ventricle gradually discards the residual 
refractory stage under the influence of the many prolonged ventri- 
cular pauses, so that the total refractory stage is shortened after 
all. In this way the normal ventricular rhythm may yet return 
spontaneously. This is illustrated in Fig. 3. 
Fig. 3. 
The curves of this figure originate from the same frog’s heart’ 
which procured the curves of fig. 2. 
36 
Proceedings Royal Acad. Amsterdam. Vol XXIII. 
