and sickness； we learn by bitter experience what an unspeakable blessing it is to be well。
It is therefore wise and necessary to learn in time； before we have lost our health； that it can be kept only by knowing and observing the laws of health。 Nature’s laws cannot be ignored with impunity3。 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。 “The mills of God grind slowly； but they grind exceedingly small。” 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； flor Nature never forgives breaches of the laws of health—“physical sins”； as Huxley called them。
Loss of health makes us miserable； and a burden to ourselves and our friends。 It cripples our efforts； so that we cannot acplish 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； wholesome4 simple food。 Cluttony has killed thousands； and strong drink tens of thousands。 We must； when young； get plenty of sleep。 which is “nattlre’s sweet restorer”； and not try to burn the candle at both ends。 We must live as much as possible in the open air and keep our rooms well ventilated5。 We must get sufficient and regular physical exercise； and keep our bo