We have spoken of the heart thus far as a single organ; it is actually two hearts side by side, and these would work just as well if they were at a distance instead of being built into one organ. There has probably been more misunderstanding of the heart by people in general than of any of the other parts of the body. This is because from the earliest times the heart has been looked upon as the seat of the affections, and so powers and properties have been attributed to it to which it is not at all entitled. As we tried to make perfectly clear in a former chapter all intelligence and all feelings are located in the brain; the heart cannot possibly take any more active part in these than can the stomach, liver, kidneys or any of the other parts of the body which are concerned with the maintaining of the tissues in good working order. Probably no one really knows how it came about originally that the heart was endowed with these peculiar gifts. It is true that in time of strong emotion there are changes in the activity of the heart which we can perceive. These occur because the heart is under the same kind of nervous control as are the smooth muscles and glands, and shares with them in the disturbances which accompany emotion; but the real seat of these emotions is, of course, the brain. As a matter of fact the heart is nothing but a muscular pump whose sole function is to keep the blood in motion. From what has already been said it is clear that the heart cannot relax its activity for more than an instant without disastrous results; the pressing need of the tissues for oxygen requires that the blood be kept moving. If there were any other way in which the needs of the cells could be supplied except through the movement of the blood, the heart could be dispensed with perfectly well. We have emphasized this about the heart because it is much easier to understand its working if one thinks of it simply as a pumping organ than if one is attributing to it mystic functions connected with our higher emotions. [Illustration: DIAGRAM SHOWING THE RELATION OF THE TWO HALVES OF THE HEART _ra_ and _rv_, right auricle and ventricle; _la_ and _lv_, left auricle and ventricle; _ao_, aorta; _vc_, venæ cavæ; _pa_, pulmonary artery; _pc_, pulmonary capillaries; _pv_, pulmonary vein. (Martin’s “Human Body.”)]