594 ELECTRICAL STIMULATION OF THE FROG'S HEART. 



duration, and therefore the reduplication falls outside the systole 

 during which stimulation occurs, the latency being actually 

 shorter, however, than in the unheated heart. 



Ventricular Stimulation — Maximal Stimuli. 



When stimuli of maximal intensity are applied to the ven- 

 tricle of the heated heart, we notice (Fig. 183) : — 



(1) That there is no refractory period; (2) Stimuli at the 

 commencement of the ventricular systole may cause omission 

 of the succeeding beat; (3) Eeduplication occurs at all phases, 

 and has the same characteristics as in minimal stimulation ; 



(4) Latencies follow the same rule as in minimal stimulation ; 



(5) The reduplicated beat is most perfect when stimulation 

 falls— 



I. At the very commencement of systole. 

 II. At its termination. 



The value of any beat and its reduplication, with the time 

 intervening and of the succeeding pause, was about equal to 

 two normal cardiac cycles. Occasionally a double reduplication,, 

 or a series of contractions, resulted from a single stimulation. 



Auricular Stimulation — Minimal Stimuli. 



There is apparently no refractory period. All stimuli cause 

 reduplication, and in all cases induced auricular systole pre- 

 cedes an induced ventricular systole. This occurs even in 

 advanced auricular diastole, when occasionally in the normal 

 heart a simultaneous auricular and ventricular systole results. 



Auricular Stimulation — Maximal Stimuli. 



There is no refractory period. Stimulation just after the 

 auricular maximum has been passed frequently causes an 

 apparent omission of the following beat. 



Stimulation before the maximum of the ventricular systole 

 causes an induced ventricular beat preceded by an auricular 

 contraction. 



After the maximum, stimulation usually has the same effect. 



