470 



Drs. T. L. Brunton and T. Cash. 



Ventricular Stimulation — Maximal stimuli. 



When stimuli of maximal intensity are applied to the ventricle of 

 the heated heart, we notice (fig. 17) : — 



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

 mencement of the ventricular systole may cause omission of the 

 succeeding beat ; (3) Reduplication 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 inter- 

 vening 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 precedes 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, but 

 occasionally causes an instantaneous reduplication of both auricular 

 and ventricular beats. 



A reduplicated ventricular beat is of the character already described. 



Stimulation of the Venous Sinus — Minimal Stimuli. 



The venous sinus in its general absence of a refractory phase 

 shows a resemblance to the ventricle, but it may manifest the same 

 exception in exhibiting it. 



When this occasional refractory period is present it may exist 

 during active systole, and up to its maximum. It is exceptionally 

 present in cases which as a rule show no refractory period. 



Stimulation falling before the maximum of systole (fig. 18, a ventri- 

 cular tracing alone given) causes a reduplication which is preceded by 



