NORMAL HEAllT-STIMULATION OF VENTRICLE. 581 



after the end of the refractory period. In all these points our 

 results agree with those already obtained by Marey.* 



Stimulation applied to the ventricle during the first period 

 has no effect whatever either in accelerating the occurrence of 

 the second beat, or altering the length of the subsequent 

 pauses. This constitutes the refractory period. 



Stimulation applied during the second period causes redupli- 

 cation of the systole, the next systole succeeding with a con- 

 stantly diminishing latency up to the end of the period. When 

 the stimulation is applied in this period, the two systoles being 

 more or less united, there is no distinct pause between them, 

 but the diastolic pause succeeding the second occupies very 

 nearly the interval of time corresponding to two normal dia- 

 stolic pauses. In this second period the heart is more sensitive 

 to the action of minimal stimuli than in the first period. In 

 the third period, that of acceleration, stimulus applied to the 

 ventricle hastens the advent of the succeeding systole, and the 

 latent period is very short, being nearly equal throughout its 

 whole extent to the latency at the end of the second period. The 

 sensibility of the heart to stimuli is scarcely so great in this 

 period as in the second. 



The length of the diastolic pause succeeding the accelerated 

 systole is longer than normal, the increase in length being nearly 

 equal to the amount of acceleration. 



Stimulation of the Ventricle — Maximal. 



When stimuli of maximal potency are applied to the 

 ventricle between the maximum auricular systole and the com- 

 mencement of ventricular systole, the ventricular systole im- 

 mediately following the stimulus is rarely slightly higher than 

 normal, and the diastolic pause succeeding it is excessively 

 long — so long, indeed, as to be nearly, if not quite, equal to the 

 time which would, as a rule, be occupied by two diastoles, so 

 that the time occupied by the systole and diastole after stimu- 

 lation applied at this period of the heart's cycle, is equal to the 

 time usually occupied by one systole and two diastolic pauses. 



• Op. ciL, p. 72. 



