614 ELECTRICAL STIMULATION OF THE FROG'S HEART. 



in which reduplication occurs at once on stimulation, and ven- 

 tricular reduplication succeeds or occurs occasionally (stimulation 

 at the end of auricular relaxation) in 0*5", followed by ventricle. 



Fig. 207. 



Stimulatioa of Venous Sinus (maximal). 



Appendix C. Action of Strychnia on the Frog's Heart. 



In order to test the correctness of the conclusion that 

 strychnia lengthens the refractory period, we placed frogs in 

 which the medulla and cord only existed on the cardiograph. 

 The effects of stimulation were then observed, and subsequently 

 a small dose of strychnia was injected into the dorsal lymph 

 sac ; as soon as the resulting spasm was well developed, stimu- 

 lation was again applied, the strength of stimulation and the 

 position of the electrodes remaining constant. 



Thus in Fig. 208 P2, a frog's heart, in which active circulation 

 was present, showed a refractory period through about one-half of 

 the maximal maintenance of systole. In 3', after the injection, 

 of a small dose of strychnia into the dorsal lymph sac, distinct 

 spasm was present, and in 5' Fig. P^ was taken, which showed 

 that the refractory period had become prolonged, until relaxa- 

 tion of the ventricle had commenced. 



It may happen that stronger stimulation before the maximum 

 of systole is reached, causes an auricular beat, which precedes 



