600 ELECTRICAL STIMULATION OF THE FROG'S HEART. 



The stimulation at the end of relaxation in one case causes 

 reduplication of the auricle, coinciding with that of the 

 ventricle. 



The tracing illustrates the rule that when the sinus is stimu- 

 lated no refractory period is observed as regards the ventricular 

 reduplication. 



Venous Sinus — Maximal Stimulation. 



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

 During all phases of the systole stimulation causes a reduplica- 

 tion of the ventricular beat (Fig. 192). Inhibition of the ventri- 

 cular systole has not been found in many of the hearts 

 examined, though it occasionally occurs. 



Fig. 192. 



Stimulation of Venous Sinus (maximal). 



Should the exciting shock fall at such a time as to cause an 

 instantaneous auricular systole, we find this systole is nearly 

 synchronous with that of the ventricle, and that the latter has 

 a short latency, but should the shock fall so that the auricle 

 responds by a genuine contraction, the ventricular reduplication 

 follows with a long latency. 



Inhibition of the ventricular with reduplication of the auri- 

 cular beat may result occasionally from stimulation of the 

 venous sinus. 



Appendix A. Cooled Heart. 



The construction of a simple piece of apparatus has enabled 

 us to obtain curves much more striking than those which 

 appeared in the foregoing paper, as they represent a far greater 

 variation of temperature. 



