474 



Drs. T. L. Brunton and T. Cash. 



Stimulation of the Venous Sinus — Minimal Stimuli , 



With minimal stimulation of the venous sinus there is no refractory 

 period except occasionally for an instant at the maximum of auricular 

 systole. Reduplication occurs at all phases of the ventricular systole. 

 Length of latency depends upon whether the stimulation induces an 

 auricular contraction or not. If the auricular systole follows the 

 stimulus, then the ventricular latency must be long (fig. 24). 



Fig. 2 k 



Stimulation of Venous Sinus (minimal). 



It is longer if stimulation falls at the commencement of ventricular 

 systole, because at that phase, until the auricle has contracted, no 

 ventricular reduplication occurs. Occasionally, though rarely, and 

 that after the maximum of ventricular contraction, auricular redupli- 

 cation follows, or is synchronous with the ventricular systole, and then 

 latency is invariably short. Reduplication with prolonged latency, 

 probably from auricular reduplication, is well seen in the appended 

 tracing (fig. 25). 



Fig. 25. 



Stimulation of Venous Sinus (minimal). 



The stimulation at the end of relaxation in one case causes redupli- 

 cation of auricle, coinciding with that of the ventricle. 



The tracing illustrates the rule that when the sinus is stimulated 

 no refractory period is observed as regards the ventricular redupli- 

 cation. 



Venous Sinus — Maximal Stimulation. 



There is no insensitive period as far as regards the ventricle. During 

 all phases of the systole stimulation causes a reduplication of the 



