Not enough investigations have been made of the rate of the pulse during sleep under various conditions. Klewitz [Footnote: Klewitz: Deutsch. Arch. f. klin. Med. 1913, cxii, 38.] found that the average pulse rate of normal individuals while awake and active was 74 per minute, but while asleep the average fell to 59 per minute. He found also that if a state of perfect rest could be obtained during the waking period, the pulse rate was slowed. This is also true in cases of compensated cardiac lesions, but it was not true in decompensated hearts. He found that irregularities such as extrasystoles and organic tachycardia did not disappear during sleep, whereas functional tachycardia did. It is well known that high blood pressure slows the pulse rate; that low blood pressure generally increases the pulse rate, and that arteriosclerosis, or the gradual aging of the arteries, slows the pulse, except when the cardiac degeneration of old age makes the heart again more irritable and more rapid. The rapid heart in hyperthyroidism is also well understood. It is not so frequently noted that hypersecretion of the thyroid may cause a rapid heart without any other tangible or discoverable thyroid symptom or symptoms of hyperthyroidism. Bile in the blood almost always slows the pulse. INTERPRETATION OF TRACINGS The interpretation of the arterial tracing shows that the nearly vertical tip-stroke is due to the sudden rise of blood pressure caused by the contraction of the ventricles. The long and irregular down-stroke means a gradual fall of the blood pressure. The first upward rise in this gradual decline is due to the secondary contraction and expansion of the artery; in other words, a tidal wave. The second upward rise in the decline is called the recoil, or the dicrotic wave, and is due to the sudden closure of the aortic valves and the recoil of the blood wave. The interpretation of the jugular tracing, or phlebogram as the vein tracing may be termed, shows the apex of the rise to be due to the contraction of the auricle. The short downward curve from the apex means relaxation of the auricle. The second lesser rise, called the carotid wave, is believed to be due to the impact of the sudden expansion of the carotid artery. The drop of the wave tracing after this cartoid rise is due to the auricular diastole. The immediate following second rise not so high as that of the auricular contraction is known as the ventricular wave, and corresponds to the dicrotic wave in the radial. The next lesser decline shows ventricular diastole, or the heart rest. A tracing of the jugular vein shows the activity of the right side of the heart. The tracing of the carotid and radial shows the activity of the left side of the heart. After normal tracings have been carefully taken and studied by the clinician or a laboratory assistant, abnormalities in these readings are readily shown graphically. Especially characteristic are tracings of