On Electrical Stimulation of the Frog's Heart, 467 



reached. Stimulation before the maximum of systole has longer latency 

 than stimulation at the maximum. 



Auric u I ar S timulation — Minimal. 



A refractory period is obviously present, but it is not of so great 

 length as in the case of ventricular stimulation. It may be said to 

 extend usually through the maximum of auricular systole (fig. 12), 

 and even up to near the maximum of ventricular systole ; occa- 

 sionally it exists only just at its commencement. 



Fig. 12. 



Stimulation of Auricle (minimal) . 



As regards the reduplication, we find that as in the case of the 

 normal heart, a long latency prevails, because an induced auricular 

 systole must occur before the ventricle contracts again. But if the 

 stimulation fall just at the time when the abscissa is reached, or 

 rather before this point, a ventricular contraction may exceptionally 

 be produced with a short latency, and the auricular induced contrac- 

 tion 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. 13). 



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 re- 

 duplication precedes the ventricular in the ordinary way, but should 

 the stimulation fall, after the ventricular maximum, the auricular 

 reduplication is exceptionally synchronous with, or subsequent to, 

 the ventricular : usually, however, the induced ventricular beat pre- 

 cedes in ordinary rhythm the induced ventricular. 



Stimulation of the Venous 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 originate a reduplica- 

 tion at any period of the beat having a long latency, that is to say, 



vol. xxxv. 2 I 



