I speak advisedly when I say "other than food." Air is largely a food. It is the most thoroughly alive thing we take into the body. Every breath carries in millions of microbes, many of which are assimilated. The odors from earth, grass, tree, flower, plant, and from cooking foods are foods in themselves; they are minute particles of the substances from which they come, and are often so attenuated that they pass directly from the lungs into the blood, and are assimilated without digestion. And the atmosphere is permeated with the One Original Substance, which is life itself. Consciously recognize this whenever you think of your breathing, and think that you are breathing in life; you really are, and conscious recognition helps the process. See to it that you do not breathe air containing poisonous gases, and that you do not rebreathe the air which has been used by yourself or others. That is all there is to the matter of breathing correctly. Keep your spine straight and your chest flexible, and breathe pure air, recognizing with thankfulness the fact that you breathe in the Eternal Life. That is not difficult; and beyond these things give little thought to your breathing except to thank God that you have learned how to do it perfectly. CHAPTER XV. SLEEP. Vital power is renewed in sleep. Every living thing sleeps; men, animals, reptiles, fish, and insects sleep, and even plants have regular periods of slumber. And this is because it is in sleep that we come into such contact with the Principle of Life in nature that our own lives may be renewed. It is in sleep that the brain of man is recharged with vital energy, and the Principle of Health within him is given new strength. It is of the first importance, then, that we should sleep in a natural, normal, and perfectly healthy manner.