Physiology. — “On Artificial and Spontaneous Changes of Rhythm 
in the Bled Frog's Heart’. By Dr. S. pr Boer. (Communicated 
by Prof. W. EINTHOVEN). 
(Communicated at the meeting of June 26, 1920). 
When a frog’s heart has been deprived of blood and suspended, 
the rhythm of the ventricle is sometimes reduced to a halved rhythm, 
a phenomenon that may also be observed in the intact circulation 
of the blood after poisoning with veratrin, digitalis, antiarin or 
bariumchloride. 
The cause lies in the fact that under these conditions the duration 
of the refractory stage of the ventricle increases. This increase of 
the duration of the refractory stage is to be ascribed to a disturbance 
of the metabolic equipoise, so that at the commencement of every 
ventricular systole the ventricular muscle is not fully restored. What 
is still left over of the refractory stage we call the residual refractory 
stage. In every systole the periodic refractory stage is added to this, 
as a result of the contraction of the ventricular muscle. Consequently 
when the metabolic equipoise has been disturbed, the total refractory 
stage consists of the two components mentioned just now. It is clear 
that the disturbance of the metabolic equipoise after poisoning with 
veratrin, digitalis, antiarin and bariumchloride is caused by a reinforced 
energy of the ventricular muscle. After bleeding, however, this 
anomaly arises from the inadequate anabolic processes. 
As soon as the refractory stage lasts longer than a sinusperiod, 
the normal rhythm of the ventricle passes into a halved rhythm. 
(This may happen suddenly or more gradually along the path of 
group-formation) *). 
Before the halved rhythm reveals itself spontaneously, we can 
halve the rhythm of the ventricle artificially, as appears from the 
following considerations : 
the duration of the total refractory stage . 
We eall — - J 5 the relative 
the duration of a sinusperiod 
duration of the refractory stage. 
') A more extensive discussion of this question has been given by me in Archives 
Néerl. de Physiologie tome J (1917) pp. 534 —538. 
