Doctors no longer forbid patients with heart disease to take exercise, but set them at carefully planned exercise in the open air, particularly walking and hill-climbing; at the same time feeding them well, so as to assist nature in building up and strengthening the heart muscle until it can overcome the defect. In this way, they may live, with reasonable care, ten, fifteen, or twenty years--often, in fact, until they die of something else. Don't worry about your heart if it should happen to palpitate, or take a "hop-skip-and-jump" occasionally. You will never get real heart disease until you have had some fever or serious illness, which leaves you short of breath for a long time afterward. Danger to the Heart through the Nervous System. The other chief way in which the heart may be affected is through the nervous system. Being the great supply pump for the entire body, it is, of course, connected most thoroughly and elaborately by nerve wires with the brain and, through it, with every other organ in the body. So delicately is it geared,--set on such a hair-trigger, as it were,--that it not only beats faster when work is done anywhere in the body, but begins to hurry in anticipation of work to be done anywhere. You all know how your heart throbs and beats like a hammer and goes pit-a-pat when you are just expecting to do something important,--for instance, to speak a piece or strike a fast ball,--or even when you are greatly excited watching somebody else do something, as in the finish of a close race. Two-thirds of the starts and jumps and throbbings that the heart makes, are due to excitement, or nervous overstrain, or the fact that your dinner is not digesting properly; and they don't indicate anything serious at all, but are simply useful danger signals to you that something is not just right. In work and in athletics for instance, this rapid and uncomfortably vigorous action of the heart is one of nature's best checks and guides. When your heart begins to throb and plunge uncomfortably, you should slow up until it begins to quiet down again, and you will seldom get into serious trouble. The next time you try the same feat, you will probably find that you can go a little farther, or faster, without making it throb. Indeed, getting into training is very largely getting the heart built up and educated, so that you can run or play, or wrestle hard without overtaxing it. Whatever you can do within the limits of your heart is safe, wholesome, and invigorating; whatever goes beyond this, is dangerous and likely to be injurious. [Illustration: ROWING IS A SPLENDID EXERCISE FOR HEART AND LUNGS]