Physiology. — “On the Artificial Extra-pause of the Ventricle 
of the Frog's Heart.’ By Dr. S. pr Borr. (Communicated by 
Prof. W. EINTHOVEN). 
(Communicated at the meeting of June 26, 1920). 
DastrE and LANGENDORFE were the first to show that sometimes 
after applying an artificial stimulus to the auricles of the frog’s heart, 
a prolonged ventricular pause arises, which is not initiated by an 
extrasystole of the ventricle. ENGELMANN was in position to corroborate 
this experiment and to elucidate it. He pointed out that the experiment 
succeeds only when the stimulus is given to the auricles at the 
commencement of the ventricular systole, after which an extrasystole 
of the auricles will ensue. After this the excitation proceeds to the 
ventricle and reaches it before the close of the refractory stage, so 
that no ventricular systole follows. Only after the compensatory 
pause which succeeds the extrasystole of the auricles do the auricles 
and the ventricles resume their normal rhythm. This experiment, 
however, seldom succeeds. It is instanced in fig. 1. At 1 the auricles 
were given an induction shock *) at the commencement of the ven- 
tricular systole. After the auricular extrasystole evoked by this shock 
the excitation reached the ventricle during the refractory stage, so 
that no systole of this chamber arose. 
Not before the end of the compensatory pause of the auricles did 
an auricular systole arise again, followed by a ventricular systole. 
I have now been more successful in this experiment, by lengthen- 
ing the duration of the refractory stage of the ventricle. Then 
the excitation after the artificial extrasystole of the auricles will 
with greater certainty reach the ventricle still in the refractory 
stage. This lengthening of the refractory stage of the ventricle may 
be effected in different ways. First of all we know ever since 
LANGENDORFF wrote, that the duration of the posteompensatory sys- 
tole has increased. I now found that during the postcompensatory 
systole also the duration of the refractory stage has increased. It 
1) In all figures the closing of the primary circuit was indicated by a downward 
deflection of the signal. At the opening of the primary circuit an upward deflection 
of the signal was effected. In figs. 1, 2, 3, 4, and 6 the closing stimuli were shut 
off and consequently they did not reach the heart. 
