CHIEFLY PHYSIOLOGICAL.
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greater the necessity for sleep; just as with a steamer, the greater the number of revolutions its engine makes, the more imperative is the demand, for fuel.” * These statements justify and explain the instinctive demand for sleep. They also show why it is that infants require more sleep than children, and children than middle-age folk, and middle- age folk than old people. Infants must have sleep for repair and rapid growth; children, for repair and moderate growth; middle-age folk, for repair without growth; and old people, only for the minimum of repair. Girls, between the ages of fourteen and eighteen, must have sleep, not only for repair and growth, like hoys, but for the additional task of constructing, or, more properly speaking, of developing and perfecting then, a reproductive system, — the engine within an engine. The bearing of this physiological fact upon education is obvious. Work of the school is work of the brain. Work of the brain eats the brain away. Sleep is the chance
* Sleep and its Derangements, pp. 9, 10, 13.