1593 
Two groups previously I had applied an extra-stimulation a little 
later; the extra-systole is now larger, but the next systole is still 
larger, apparently, because the preceding a-v-interval has been 
lengthened, and consequently the systole occurs later (vide fig. 4). 
A more accurate mensuration shows us that in reality this systole 
begins at a later moment. This fact especially also counteracts 
the occurrence of the normal rhythm. 
When now the restored normal rhythm of fig. 4 has passed again 
into the halved rhythm, I execute here after the 6 systole of the 
halved rhythm a second method of converting from the halved rhythm 
into the normal one (vide fig. 5). 
Fig. 5. 
I deseribed already previously, how the halved rhythm can be 
converted into the normal one by an extra-stimulation at the end 
of the diastole. I had then to apply the extra-stimulation at a 
special moment of the diastole to make the conversion succeed. So I 
applied, also with this heart, in Fig. 1 (at QO) the extra-stimulation 
towards the end of the diastole. If I had applied the extra-stimu- 
lation at an earlier moment of the diastole, it would either have 
had no effect, and consequently have permitted the halved rhythm to 
continue undisturbed, or it would have produced a still smaller 
extra-systole. The next impulse however would then, after this 
smaller extra-systole, have produced later a systole which would 
for this reason have become too large to let the normal rhythm 
continue. If I had on the contrary applied the extra-stimulation 
later, the extra-systole itself would have proved to be larger, and 
would have become too large for the restoration of the normal 
rhythm. The halved rhythm would have continued (Vide fig. 8) or 
heart-bigeminy might have occurred as in Fig. 3. 
It is therefore obvious, why I had to irritate the ventricle exactly 
at a special moment in order to obtain restoration of the normal rhythm. 
TIGERSTEDT, STRÖMBERG and ENGrimMann could also bring about a 
twice as strong frequency of the pulsations by an extra-stimulation 
during the diastole in their experiments on the sinus venosus and 
