550 
direction. This excitation encounters in the auricles the periodic 
sinusimpulse, so that both excitations are annihilated and no prema- 
ture ventricular systole can follow. After the extrapause of the ven- 
tricle, thus originating, the following systole of the ventricle is 
extended and broadened. Now because this systole engenders a 
prolonged refractory stage of the ventricle, the ventricle is caught 
in the halved-rhythm'). It is evident that the previously described 
experiments succeed only when the extra stimulus affects the auri- 
culoventricular groove at a special moment. 
If that moment coincides with the moment at which the periodic sinus- 
impulse enters the auricles, the experiment will succeed. Success will 
even be achieved when the extra stimulus is applied somewhat later 
or earlier. In fig. 4 e.g. at the second upward deflection of the signal, 
it was applied shortly after the /-deflection, therefore shortly after 
the periodic impulse had entered the auricles from the sinus venosus. 
In fig. 6 the experiment succeeded twice through extra stimuli 
which were applied shortly before the /-deflection in the auricu- 
loventricular groove. At the first upward deflection of the signal the 
extra stimulus was applied on the peak of the negative 7-deflection, 
i.e. still before the P-deflection would be registered *). The excitation 
then traverses the auricles in a retrograde direction and encounters 
the periodic sinusimpulse in the vicinity of the sinus venosus. The 
P-deflection, which otherwise would have revealed itself directly 
after the close of the 7-defleetion, does not appear now. The auri- 
cular systole is somewhat premature in this case and may still just 
be seen in the suspension curve in the last part of the ventricular 
diastole. It is obvious that this auricular systole is chiefly owing to 
the extra stimulus. 
At the second upward deflection of the signal the stimulus was 
applied a little before the peak of the 7-deflection. The result is similar 
to that with the previous stimulus viz. an extrapause of the ventricle. 
If the extra stimulus is applied much later or earlier than the 
moment at which the sinus impulse enters the auricles, no extrapause 
of the ventricle will follow. If later the extra stimulus will affect 
the ventricle after the refractory stage and an extrasystole of the 
ventricle will ensue, followed by a compensatory pause. This is 
illustrated in fig. 3, in the lower curves at the second upward 
deflection of the signal. 
1) These transpositions of rhythm in the bled frog’s heart will be discussed in 
the following communication. 
2) In the electrogram-curve we see the P-deflections appear directly after the 
close of the 7'-deflectiuns. 
