On Electrical Stimulation of the Frog's Heart. 487 



Stimulation of Yenous Sinus (maximal). 



reduplication succeeds or occurs occasionally (stimulation at the end 

 of auricular relaxation) in "5", followed by ventricle. 



Appendix C. Strychnia on 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, stimulation was again applied, the strength of stimu- 

 lation and the position of the electrodes remaining constant. 



Thus, in fig. P 2 , a frog's heart, in which active circulation was 

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



Stimulation of Ventricle. 

 1. Before injection of strychnia. 2. After injection of strychnia. 



