On Electrical Stimulation of the Frog's Heart. 471 



Fig. 18. 



Stimulation of Venous Sinus (minimal). 



an auricular contraction, whilst stimulation falling immediately after 

 maximum of systole causes reduplication, which may be preceded by 

 an auricular pulsation, or may occasion an induced systole, auricle 

 and ventricle contracting at the same time. 



The most perfect reduplicated beat occurs when stimulation falls at 

 the end of systole. 



Venous Sinus — Maximal Stimulation. 



Occasionally a stimulation of maximum strength falling at the 

 commencement of the ventricular systole causes an apparent omission 

 of the following pulsation ; but this result is not so frequent as in the 

 case of the normal heart. Usually a distinct reduplication occurs at 

 whatever time in the cycle stimulation falls (fig. 19). 



Fie. 19. 



Stimulation of Venous Sinus (maximal) . 



The reduplication is at all times, except in the last stage of systole, 

 preceded by an auricular contraction. 



The auricular induced contraction appears to follow stimulation 

 more rapidly than in the case of the normal heart. Therefore the 

 induced ventricular contraction (fig. 19, ventricular tracing alone 

 given) which follows the auricular has a shorter latency than is 

 normally the case. The heating process having been carried so far 

 that a rapid cardiac rhythm with imperfect systole has resulted, it is 

 often found that there is an indifference to stimulation in the so-called 

 refractory period, or even in all phases of the cardiac cycle alternating 

 with the usual sensibility. 



On the Effect of Strychnia upon the Frog's Heart. 



The apparatus used in this series of experiments was identical with 

 that employed in the investigation of stimuli applied to the frog's 

 heart. The frog was killed by the brain being destroyed, and a small 



