The wonderful nervous relaxation induced by neutral baths is an excellent substitute for sleep in case of sleeplessness, and often induces sleep as well. Neutral baths are now used not only in cases of insomnia and extreme nervous irritability, but also in cases of acute mania. When sleep occurs in a neutral bath, it is particularly restful. A physician who often sleeps in the bath tub expresses this fact by saying that "he sleeps faster" there than in bed. Sleep may also be induced by monotonous sound, or lack of sound, or the monotonous holding of the attention. Keeping awake is due to continued change and interruption or arrest of the attention. Exercise taken in the afternoon will often promote sleep at night in those who find sleep difficult. Slow, deep, rhythmic breathing is useful when wakeful, partly as a substitute for sleep, partly as an inducer of sleep. Sleep is Nature's great rejuvenator, and the health-seeker should avail himself of it to the full. Our sleep should not only be sufficient in duration but also in intensity, and should be regular. [Sidenote: Hours of Sleep] The number of hours of sleep generally needed varies with circumstances. The average is seven to nine. In general one should sleep when sleepy and not try to sleep more. Growing children require more sleep than grown-ups. Parents often foolishly sacrifice their children's sleep by compelling them to rise early for farm "chores," or in order to sell papers, or for other "useful" purposes. [Sidenote: Eating before Retiring] One's best sleep is with the stomach empty. It is true that food puts one to sleep at first, by diverting blood from the head; but it disturbs sleep later. Water, unless it induces bladder-action during the night, or even fruit, may be taken without injury before retiring. If one goes to bed with an empty stomach, he can often get along well with six or seven hours' sleep, but if he goes to bed soon after a hearty meal, he usually needs from eight to ten hours' sleep. [Sidenote: Place of Sleep] It has already been pointed out that sleeping outdoors is more restful than sleeping indoors. [Sidenote: Pillows] A pillow is not a necessity if one sleeps lying prone with one arm extended above the head and the leg opposite drawn up. This sleeping attitude can easily be reversed to the opposite side. It has one advantage over pillow-sleeping, that of not tending to round shoulders. This prone position is often used now for infants, but is seldom enjoyed by adults. [Sidenote: Type of Bed] A modern "hard" bed is far preferable to the old-fashioned soft (and hot) feather bed. [Sidenote: Character of Thoughts]