1597 
extra-systole of the ventricle by an extra-stimulation (the stimulation 
that I applied three systoles earlier, and that took place at an earlier 
moment of the heart-period, evidently reached the auricle during 
its refractory stage). The strongly increased postcompensatory systole 
fixes the rhythm of the ventricle in the halved one. At 2 I applied 
an extra-stimulation at the end of the diastole, which caused a 
rather large extra-systole without compensatory pause. If on the 
contrary I apply the extra-stimulation at 3 earlier, a smaller extra- 
systole follows, so that the normal rhythm is restored. During the 
26 systole of this restored normal rhythm I convert this in the 
usual way again into the halved one. The 4" systole of this rhythm 
yet partially is to be seen at Fig. 10. At L the normal rhythm 
is not restored, at 2 it is indeed. After what has been said before 
this is obvious. At 3 I cause an extra-pause withont ventricle extra- 
systole, but I prevent the return of the halved rhythm (as at 1 of 
Fig. 9) by stimulating again in this extra-pause at 4; by doing so 
I make a new extra-systole occur, which is smaller than the post- 
compensatory one would have become. For this reason and likewise 
because it comes earlier the normal rhythm is retained. The next- 
following impulse, coming from the auricle, consequently reaches 
the ventricle later after this extra-systole, than it would have arrived 
after the post-compensatory systole, if I had omitted the stimulation. 
A place may still be given in this series to Fig. 11. In this heart 
(eurvesheet 104) ventricle-bigeminy occurred half an hour after the 
poisoning. After a few minutes I convert at 1 of Fig. 11 this 
bigeminy into the normal rhythm by an induction-stroke at the end 
of the pause between 2 groups. The proportions under which this 
conversion is brought about, are not so simple here. 
The extra systole comes here in the place of the first systole of 
a bigeminusgroup. But now the systole, following after the extra- 
systole, is wider than the second systole of a group, and has 
consequently a greater periodical refractory-stage. Consequently we 
should not expect after it another systole with a short interval. Yet 
this happens, the normal rhythm is even promptly restored. We 
find the cause of this phenomenon in modifications of the a—v- 
interval. A little measurement teaches us namely, that the a—v- 
interval of the systole, succeeding the extra-systole is considerably 
abbreviated namely about */, second. The slight lengthening of the 
duration of the ventricle-systole by no means counter-balances 
this abbreviation of the a—v-interval, so that the auricle-systole, 
succeeding this ventricle-systole, can easily be followed by a new 
ventricle-systole. 
