COLD HEART-STIMULATION OF AUfJCLE AND SINUS. 591 



auricular systole must occur before the ventricle contracts 

 again. But if the stimulation fall just at the time when the 



Fig. 178 



Stimulation of Auricle (minimal). 



abscissa is reached, or rather before this point, a ventricular 

 contraction may exceptionally be produced with a short latency, 

 and the auricular induced contraction succeeds it. 



Auricular Stimulation — Maximal. 



The same features are to be observed as in the last section, 

 except that there is no refractory period (Fig. 179). 



Stimulation in all phases of the ventricular cycle usually 

 causes a reduplicated auricular and ventricular beat. Should 

 the stimulation fall before the ventricular maximum is attained, 

 the auricular reduplication precedes the ventricular in the 

 ordinary way, but should the stimulation fall after the ventri- 

 cular maximum, the auricular reduplication is exceptionally 

 synchronous with, or subsequent to, the ventricular; usually 

 however, the induced ventricular beat precedes in ordinary 

 rhythm the induced ventricular. 



Stimulation of the Venoiis Sinus — Minimal. 



A refractory period may be present on minimal stimulation, 

 nearly up to the maximum of ventricular systole. Thereafter 

 reduplication results. A strictly minimal stimulation may origin- 

 ate a reduplication at any period of the beat having a long 

 latency, that is to say, the ventricular reduplication is preceded 

 by the auricular induced contraction (Fig. 180). Thus stimula- 

 tion applied just before the ventricular relaxation is completed, 

 instead of having an instantaneous ventricular and auricular 



