NORMAL HEART-STIMULATION OF VENOUS SINUS. 



587 



Stimulation of the venous sinus by a minimal shock is usually- 

 potent to produce some effect or other at every stage of ven- 

 tricular activity (Fig. 173, &). 



Stimulation at the instant of commencement of ventricular 

 systole usually causes omission of the following sequential beat 

 of both auricle and ventricle. 



This period may occasionally be slightly prolonged into 

 systole. 



Stimulation of the sinus at all other periods of ventricular 

 activity causes a reduplication of the systole. This induced 

 ventricular systole is preceded by an induced auricular systole, 

 and therefore has the prolonged latency before referred to. 



Stimulation falling at the commencement of ventricular 

 systole may cause auricular reduplication with ventricular 

 omission (Fig. 171, a). 



In consequence of the long latency, we find all ventricular 

 curves separated by a distinct interval from (their) reduplica- 

 tions. 



Stimulation of Venous Sinus — Maximal. 



The period during which stimulation causes .ventricular 

 omission is well marked, and in some cases extends into the 



Fiff. 174. 



Btiiniilation of Venous Sinus (maximal), a, normal rbythm; h and c, 

 "**■ stimulations all effective. 



