A wave is described occurring in the venous pulse of man late in the diastolic period. This wave is a diastolic wave, since in an increase in length of the cardiac cycle it follows the h wave at its regular interval and becomes separated from the a wave of the next cardiac cycle. There is no wave on the venous pulse in man which can be referred to a contraction of the region of the great veins or sinus region of the heart.
The h wave is a normal occurrence in the venous pulse curve from man and the dog. It occurs, according to the experience in this work, in all normal individuals in which the heart rate is sufficiently slow to prevent its obliteration by the a wave. The x wave, while not infrequent, is not always present in man even when the cardiac cycle is of sufficient length to prevent its obliteration by the a wave. This wave has not been observed in the dog.
There is no wave on the venous pulse curve of the dog that can be referred to a contraction of the sinus region of the heart. Extra-systoles from stimulation of the venous region of the dog's heart produce no contraction of this region sufficiently pronounced to be recorded on a venous pulse tracing. After an interval of from 0.07 to 0.I second, representing the interval of veno-auricular conduction plus the latent period of the auricle, the auricle contracts. Extrasystoles from stimulation of the right auricle show, after an interval following the stimulus much shorter than that noted above and representing the latent period of the auricle, an a wave followed by ventricular systole after the usual a-c interval. It would seem probable that the sinus region of the heart, while capable of irritability, conductivity and rhythmicity (Erlanger and Blackman (I6)), does not normally manifest contractility.