When one's body is kept rested, nature is constantly throwing off germs of disease, constantly working, and working most actively, to protect the body from anything that would interfere with its perfect health. When one's body is not rested, nature works just as hard, but the tired body--through its various forms of tension that impede the circulation, prevent the healthy absorption of food and oxygen, and clog the way so that impurities cannot be carried off--interferes with nature's work and thus makes it impossible for her to keep the machine well oiled. When we are tired, the very fact of being tired makes us more tired, unless we rest properly. A great deal--it seems to me more than one-half--of the fatigue in the world comes from the need of an intelligent understanding of how to keep rested. The more that lack of intelligence is allowed to grow, the worse it is going to be for the health of the nation. We have less of that plain common sense than our grandfathers and grandmothers. They had less than their fathers and mothers. We need more than our ancestors, because life is more complicated now, than it was then. We can get more if we will, because there is more real understanding of the science of hygiene than our fathers and mothers had before us. Our need now is to use _practically_ the information which a few individuals are able to give us, and especially to teach such practical use to our children. Let us find out how we would actually go to work to keep rested, and take the information of plain common sense and use it. To keep rested we must not overwork our body inside or outside. We must keep it in an equilibrium of action and rest. We overwork our body inside when we eat the wrong food and when we eat too much or not enough of the right food, for then the stomach has more than its share of work to do, and as the effort to do it well robs the brain and the whole nervous system, so, of course, the rest of the body has not its rightful supply of energy and the natural result is great fatigue. We overwork our body inside when we do not give it its due amount of fresh air. The blood needs the oxygen to supply itself and the nerves and muscles with power to do their work. When the oxygen is not supplied to the blood, the machinery of the body has to work with so much less power than really belongs to it, that there is great strain in the effort to do its work properly, and the effect is, of course, fatigue.