556 
rhythm. We can change this halved rhythm again into the normal 
rhythm of twice thé rapidity, by eliciting a small ventricular systole. 
This happens in Fig. 1 *)- 
At the downward deflection of the signal an auricular extra- 
systole was evoked, after which the excitation reached the ventricle 
during the- refractory “stage. Consequently the rhythm of the ven- 
tricle did not change here. However, at the upward deflection of 
the signal the stimulus was repeated towards the end of the pause. 
Now the auricles are. refractory, but the ventricle responds to the 
stimulus with an extrasystole. After this the periodic sinusimpulse 
reaches the ventricle towards the end of the diastole, so that a 
decreased systole of the ventricle ensues. This is accompanied by 
a short refractory stage so that also the subsequent sinusimpulse 
again results in a ventricular systole. In this way every sinusimpulse 
may be followed by a ventricular systole. 
Fig. 2 shows the suspension curves of a frog’s heart, 10 minutes 
after bleeding. The stimulating electrode is at the auricles. At the 
first downward deflection of the signal the auricles receive a closing 
shock, which results in an extrasystole of the auricles, followed by 
a compensatory pause. 
It is evident that the ventricular rhythm is influenced only in 
this way that the next systole of tne ventricle appears somewhat earlier. 
When, however, at the upward deflection of the signal the auri- 
cles receive the opening induction shock at an earlier moment of 
the auricular period, the result is quite different. After the thus 
excited extrasystole of the auricles, coinciding with the commence- 
ment of the ventricular systole, the excitation reaches the ventricle 
still in the latter’s refractory stage. 
After the compensatory pause of the auricles the next auricular 
systole is followed again by a ventricular systole. Thus arises 
an extrapause of the ventricle, followed by an enlarged and broad- 
ened systole. Of this the refractory stage is prolonged, so that the 
next auricular systole cannot be followed by a ventricular systole. 
Again a prolonged ventricular pause arises, which is again followed 
by an enlarged systole of the ventricle. 
Thus the ventricle is caught in the halved rhythm by only one 
stimulus administered to the auricles. At the second downward 
deflection of the signal the auricles receive a closing shock towards 
the close of the pause, which evokes an extrasystole of these 
chambers. After this the next ventricular systole commences earlier. 
1) Between fig. 5 of the previous publication and fig. 1 of this paper two 
ventricular systoles have not been reproduced. 
