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that the next sinusimpulse reaches the ventricle again during the 
refractory stage. Owing to this the next pause of the ventricle is 
again prolonged with the ordinary consequences. In this way the 
ventricular halved-rhythm is brought about artificially. 
At the second deflection of the signal again an extrasystole of the 
auricles is evoked in the beginning of a ventricular systole. Because 
hereafter the excitation reaches the ventricle during the refractory 
stage, the halved rhythm of course continues. 
At the third deflection of the signal, however, an extrasystole of 
the auricles is evoked after the termination of a ventricular systole. 
After this the excitation reaches the ventricle towards the end of 
the pause so that a premature ventricular systole follows. Now because 
this ventricular systole is premature, the next sinusimpulse reaches 
the ventricle after the close of the refractory stage, so that a small 
systole of the ventricle can follow. This systole is small on account 
of the short duration of the preceding pause and therefore causes 
a short refractory stage. For this reason also the following sinus- 
impulse is again responded to by a ventricular systole, which also 
is a small one again. In this way the normal rhythm of the ventricle 
is restored. 
In the above we have given some instances of changes of rhythm 
in the bled frog’s heart. We could enforce at will any given rhythm 
upon the ventricle by evoking one ventricular systole of a certain 
magnitude and duration. 
