equalized throughout the arterial system, and there is no more pulse. The advantage of this is that the blood flows through the capillaries in a steady stream and not in a series of jerks. This, in fact, is the chief, but not the only, benefit we derive from having elastic arteries. Since the heart operates as an intermittent pump, it is evident that unless the arteries were elastic and so could take up the shock, the blood would have to pass through the capillaries in a series of jerks, exactly corresponding with the beats of the heart. There is abundant proof, which we shall return to in a moment, that to have the blood move through the capillaries in this jerky fashion would be disastrous. Before taking that up, however, we wish to show that by having elastic arteries the actual work of the heart is less than it would be if the arteries were stiff. The reason is really very simple. As was stated a few pages back, the heart is actually emptying itself only during three-eighths of every beat. If the arteries were stiff tubes, and therefore not able to take up any of the blood within themselves, exactly as much would have to pass out through the capillaries during this three-eighths of the beat as was pumped in by the heart. In other words, if the heart were pumping five quarts a minute, five quarts would have to pass through the capillaries in three-eighths of the minute instead of having the whole minute in which to do it. Since the arteries are actually elastic, they are able, by stretching a little more, to make room for part of the blood and so spread the time of its passage through the capillaries out over the whole time instead of confining it just to the period when the ventricle is contracting. Evidently it would take more work to pump five quarts of blood through the capillaries in three-eighths of a minute than in a whole minute.