HEATED HEART-STIMULATION OF VENOUS SINUS. 595 



but occasionally causes an instantaneous reduplication of both 

 auricular and ventricular beats. 



A reduplicated ventricular beat is of the ch^lracter already 

 described. * 



Stimulation of the Venous Sinus — Minimal Stimuli, 



The venous sinus in its general absence of a refractory phase 

 shows a resemblance to the ventricle, but it may manifest the 

 same exception in exhibiting it. 



When this occasional refractory period is present it may exist 

 during active systole, and up to its maximum. It is excep- 

 tionally present in cases which as a rule show no refractory 

 period. 



Stimulation falling before the maximum of systole (Fig. 184, 

 a ventricular tracing alone given) causes a reduplication which 



Fig. 184. 



Stimulation of Venous Sinus (minimal). 



is preceded by an auricular contraction, whilst stimulation fall- 

 ing immediately after maximum of systole causes reduplication, 

 which may be preceded by an auricular pulsation, or may 

 occasion an induced systole, auricle and ventricle contracting at 

 the same time. 



The most perfect reduplicated beat occurs when stimulation 

 falls at the end of systole. 



Venous Sinus — Maximal Stimulation. 



Occasionally a stimulation of maximum strength falling at 

 the commencement of the ventricular systole causes an appa- 

 rent omission of the following pulsation ; but this result is not 

 so frequent as in the case of the normal heart. Usually a dis- 

 tinct reduplication occurs at whatever time in the cycle stimu- 

 lation falls (Fig. 185). 



2 Q 2 



