580 ELECTEICAL STIMULATION OF THE FROG's HEART. 



(5) The ventricular reduplication is often associated with a 

 reduplication of the auricular beat, but in no case has the latter 

 its commencement before the former. It is usually, in fact 

 distinctly later (Fig. 166, a). 



It is to be noted that, minimal stimulation applied to the 

 ventricle during its refractory period produces no effect on the 

 auricle. 



Fm. 166. 



Stimulation of Yentricle (minimal). Tracing shows long pause after reduplica- 

 tion. The two opening stimulations occur after maximum of systole has 



Fig. 167. — Time- Writer, marking seconds. Applicable to all tracings in the 

 paper, except those in the Appendices. 



We may divide each ventricular cycle into three parts, the 

 first reaching from the commencement of systole nearly up to 

 its maximum, the second from nearly the maximum of the 

 systole to its end, and the third embracing the whole diastolic 

 period from the end of one systole to the beginning of another 

 {vide diagram A) except when the stimulation falls immediately 



A. 



Fig. 168. — Diagram A shows the division of the ventricular cycle into three 

 parts. — 1. Refractory period. 2. Sensitive period. 3. Accelerative period. 



