EXCITABILITY CYCLE OF MAMMALIAN AURICLE

Abstract

A reinvestigation was made of the cyclical variations in excitability known to occur in the heart. A comparison was made of the auricular and ventricular excitability cycle. The phenomena of excitation were essentially the same in the 2 tissues. The auricle has a slightly lower threshold than does the ventricle under the conditions described. Recovery of excitability following a beat is not a smoothly progressive process but reveals oscillatory changes which create dips or periods of relative supernormality during the cycle. All phenomena of the refractory period, latencies, dips, etc., are shorter in duration and less conspicuous than in the ventricle. A post-refractory period of slight supernormality was observed more frequently in the auricle than in the ventricle. As in the ventricle the length of the absolute refractory period depends upon the duration and strength of the stimulating pulse.