582 ELECTRICAL STIMULATION OF THE FROG's HEART. 



In most cases this systole was apparently no higher than 

 normal, and consequently we cannot with plausibility regard it 

 as a case of superposition of two systoles. 



In some cases the time within which this pause may be pro- 

 duced is strictly limited to the point indicated ; in others, how- 

 ever, it may extend some little distance towards the maximum 

 of systole, though it never reaches this. In other words, it 

 may encroach upon the refractory period which we have men- 

 tioned when speaking of minimal stimuli, although it never 

 extends through the whole of it. 



This phase may occasionally, though rarely, be absent. Its 

 place is then taken by reduplication, or very rarely by insensi- 

 bility to stimulation, as in the refractory period. 



Keduplication with maximal stimuli occurs during all times 

 of the cycle, except at the very commencement of the systole. 



A very considerable latency is to be observed in cases where 

 stimulation falls early in the systole. The latency, when this 

 is the position of the shock, is usually 0*5' or even more, and 

 occasionally where stimulation is coincident with the earliest 

 possible attempt at systole, nearly the whole beat may lapse 

 before reduplication. 



The latency is greatest when the stimulus is applied at the 

 commencement of the ventricular systole (with the exception 

 of its very beginning), and it gradually decreases towards the 

 end of systole, at which time it is at a minimum. During the 

 diastole the latency seems to remain constantly the same as at 

 the end of systole. The later in the phase of ventricular 

 activity the reduplicated systole commences the more perfect 

 is it. 



In all the points already mentioned our results agree with 

 those of Marey. 



Stimulation of the ventricle falling before or at the maximum 

 of ventricular systole, ix., during the refractory period of a 

 minimal stimulation, frequently causes a reduplication of the 

 auricular systole which holds the same relation to the induced 

 ventricular beat that the auricular contraction normally holds 

 to the ventricular. 



Stimulation falling after the maximum of ventricular systole 



