On Electrical Stimulation of the Frog's Heart. 457 



The temperature of the room in which the experiments were con- 

 ducted was 67° to 70° F. The frog employed was, on all occasions, 

 the Rana temporaria. 



Stimulation of the Ventricle — Minimal. 



On stimulating the ventricle with a single induction shock of 

 minimal potency we find — 



(1.) That between the commencement of the ventricular systole up 

 to or nearly up to its maximum there is a refractory period (fig. l r 



Fig. 1. 



C: 



Stimulation of Ventricle (minimal) . 



a and b, stimulation in different phases of refractory period. 

 <?, stimulation after refractory period has passed, showing different 

 forms of reduplication. 



a and &) during which stimulation applied to the ventricle has no 

 effect whatever on that beat of the heart, or the one succeeding it, nor 

 is the auricle in anywise affected. 



(2.) That after the refractory period has elapsed stimulation 

 causes a reduplication of the beat (fig. 1, c). 



(3.) The latency of this reduplicated beat becomes distinctly 

 shorter as the systole passes into the diastole. Thus supposing the 

 value of a single cardiac systole to be V'S, stimulation falling just at 

 the maximum of a beat will cause a reduplicated beat with a latency 

 of *33. When the stimulation occurs half way down the curve of 

 relaxation, the latency is '18^or '2, and when applied at the instant 

 before the abscissae would have been reached the latency is only *13. 



