STRYCHNIA-STIMULATION OF VENOUS SINUS. 599 



The latencies are invariably long when the auricle is so 

 stimulated that its induced beat is a normal one and precedes 

 the induced ventricular systole in its normal rhythm. 



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 maxi- 

 mum auricular systole. Eeduplication 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. 190). 



Fig. 190. 



f 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 con- 

 traction, auricular reduplication follows, or is synchronous with 

 the ventricular systole, and then latency is invariably short. 

 Eeduplication with prolonged latency, probably from auricular 

 reduplication, is well seen in the appended tracing (Fig. 191). 



Fig. 191 



Stimxilation of Yenoua Sinus (minimal). 



