544 
ment of -a ventricular systole. After the evoked extrasystole 
of the auricles the excitation reached the ventricle after the refractory 
stage, so that a premature ventricular systole ensued. When, how- 
ever, at the next upward deflection of the signal the stimulus is 
repeated at the commencement of the postcompensatory systole, the 
excitation after the extra auricular systole thus evoked, readily 
reaches the ventricle during the refractory stage. Now an extrapause 
of the ventricle follows. In this way it is easy to repeat the ex- 
periment during every following ventricular systole, which is broad- 
ened every time. At last it is even unnecessary to stimulate the 
auricles at the commencement of the ventricular systole, the last 
stimulus being given about the middle of the ventricular systole 
without diminishing the suecess of the experiment. This, indeed, is 
easily understood, if we look more carefully at the ventricular 
systoles of this artificial halved ventricular rhythm. We then observe 
that after the compensatory pause the postcompensatory systole is 
broader than the preceding ventricular systoles, and that every sue- 
ceeding systole surpasses its predecessor in broadness. We see then 
that the contractility of the ventricular muscle increases after every 
lengthened ventricular pause. This restoration of the ventricular 
muscle in the artificial halved rhythm involves an increase in dura- 
tion of the refractory stage from systole to systole. This is why 
ultimately the stimulus can be administered to the auricles later in 
the ventricular period, without interfering with the suecess of the 
experiment. After the last stimulus the ventricle resumes again the 
normal rhythm. *) 
In the second place we can lengthen the refractory stage of the 
ventricle by poisons, namely digitalis, veratrin, antiarin or barium- 
chloride and, by doing so, ensure success of our experiment. The 
curves of Fig. 2 refer to a frog’s heart that had been poisoned 
with bariumchloride. At every upward deflection of the signal the 
auricles receive an opening induction shock at the commencement 
of a ventricular systole. Every time there appears an extrasystole 
of the auricles and every time after this the excitation reaches the 
ventricle during the refractory stage, so that extrapauses of the ventricle 
originate, which are not preceded by premature ventricular systoles *). 
1) After poisoning with veratrin, digitalis, antiarin or barium-chloride, the halved 
rhythm of the ventricle can persist after one or more extra-pauses of the ventricle, 
without stimulating the heart any more. This also occurs after bleeding the non- 
poisoned frog’s heart. (See fig. 5). 
2) In a later stage of this intoxication the ventricle maintains its pulsation in 
the halved rhythm after such an artificial extrapause. 
