It is a common saying that we do not fully value a thing until we lose it. We often value the love and worth of a friend when he has been taken from us by death, more than when he was with us in the flesh; it is only when we have left school or college that we understand the greatness of our opportunity of education, which has gone forever; and it is the sick and the ailing who realize the value of good health. We are so used to vigorous health that we take it for granted.（1） The organs of our body work so smoothly that we scarcely know we have lungs and liver, heart and stomach. But when any of these get upset and give us pain and sickness, we learn by bitter experience what an unspeakable blessing it is to be well,
（2）It is therefore wise and necessary to learn in time, before we have lost out health, that it can be kept only by knowing and observing the laws of health. Nature's laws cannot be ignored with impunity. In the long run they will avenge themselves on us if we forget them, even if they do not do so at once. At first we may not feel the result of excesses and unhealthy habits; but we certainly shall some day. （3）Many a man who in middle age finds himself a confirmed invalid has to curse the follies of his youth: but his remorse is vain, for Nature never forgives breaches of the laws of health.
（4） Loss of health makes us miserable, and a burden to ourselves and our friends. It cripples our efforts, so that we cannot accomplish many of the good and great things we might have done. It spoils our life. What must we do to keep our health?
We must be moderate in eating and drinking, and wise in the choice of plain, wholesome simple food. Gluttony has killed thousands, and strong drink tens of thousands. （5） We must, when young, get plenty of sleep, which is “nature's sweet restorer” (恢复剂), and not try to bum the candle at both ends. We must live as much as possible in the open air and keep our rooms well ventilated. We must get sufficient and regular physical exercise; and keep our bodies clean. And we must avoid bad habits and secret sins as we avoid the devil, and keep our thoughts clean and our bodies pure. Our ideal must be the second mind in the sound body.
