590 



ELECTRICAL STIMULATION OF THE FROG S HEART. 



Ventricular Stimulation — Maximal. 



Stimulation sometimes causes omission when applied at the 

 very commencement of systole. All stimulation thereafter 

 applied causes a reduplication of the ventricular systole, with a 

 latency that becomes shorter the later the stimulation is 

 applied. If auricular reduplication occurs it is always sequen- 

 tial to ventricular (Fig. 177, a). Stimulation at the maximum 

 of systole may cause a blending with the reduplicated beat 

 closely resembliDg one prolonged systole (Fig. 177, h). The 

 induced beat is most perfect when stimulation falls, just as the 

 abscissa is reached. Stimulation before the maximum of 

 systole has longer latency than stimulation at the maximum. 



Fig. 177. 



Stimulation of the Ventricle (maximal). 



Auricular Stimulation — 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. 178), and even up to near the maximum of ventri- 

 cular systole ; occasionally it exists only just at its commence- 

 ment. 



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

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



