On Electrical Stimulation of the Frog's Heart. 461 



Stimulation falling after the maximum of ventricular systole may 

 cause an induced auricular contraction, but this is nearly synchronous 

 with, or even subsequent to, the induced ventricular contraction 

 (fig. 4, a and b, and fig. 3, c). 



Fig. 4. 



a. b. 

 Stimulation of Ventricle (maximal). 



Sometimes reduplication of the ventricular beat may occur without 

 reduplication of the ventricular (fig. 3, c). 



These results may be possibly due, in part at least, to direct stimu- 

 lation of the auricle itself by the strong current used to stimulate 

 the ventricle. 



Stimulation of the Auricle — Minimal. 



When minimal stimuli are applied to the auricle, there is occa- 

 sionally a refractory period, extending from the beginning to the 

 maximum of auricular systole. When the stimulus is applied at the 

 maximum of auricular systole, or just after it, it sometimes produces 

 an omission, or, as we may term it, an apparent inhibition of the 

 next auricular and ventricular systoles (fig. 5, b). Stimulation falling 

 after this point and occasionally on it, will cause a reduplication of 

 auricular and ventricular contractions to occur which may have a 

 latency of as much as 1*25 seconds. 



Fig. 5. 



