537 
of the auricles. When after this the excitation reaches the ventricle 
before the middle of the diastole, the refractory stage of the ventricle 
VS 
Lot mes An | 
LLLLLLLE LLL LLLLLLLLELLNLLLLLELLELLE LL 
Fig. °s. 
has just come to a close. Consequently the ventricle begins to 
fibrillate while the auricles revert to pulsating in the normal rhythm. 
At 4 a renewed shock is administered to the auricles after a post- 
compensatory systole as early as possible in the excitable period. 
Again a brief fibrillation of the ventricle ensues after the auricular 
extrasystole. 
The above experiments afford sufficient evidence to assert that the 
ventricle begins to fibrillate when an excitation reaches this chamber 
directly after the conclusion of the refractory stage. Lf, however, an 
excitation reaches the ventricle later, an ordinary premature systole 
is originated. 
It appears, then, that experimentally the ventricle can be made 
to fibrillate through an excitation, by a single shock to the auricles 
directly after the conclusion of the refractory stage. After the 
auricular extrasystole thus excited, the excitation proceeds to the 
ventricle and makes it fibrillate, when at least it reaches the ventricle 
directly after the conclusion of the refractory stage. If the excitation 
reaches the ventricle too early, te. during the refractory stage, an 
extra-pause of the ventricle will ensue, because the excitation rebounds 
on the still non-excitable ventricle. If however the excitation comes 
too late, a premature ventricular systole will appear. It is evident 
that the success of the experiment depends on the three following 
factors : 
|. on the moment at which the auricles are stimulated. Since the 
excitation reaches the ventricle almost always too late, it is desirable 
to stimulate the auricles as early as possible in the excitable period. 
2. on the time of conduction from the point at which the auricles 
are stimulated to the ventricle. 
