Although the human body was conceived by him still as “the clay cottage” of the mind, yet he wanted us to understand “how necessary _Health_ is to our business and happiness, and how requisite a strong constitution, able to endure hardship and fatigue” (7: p. 2). So he began his treatise with the physical care of the child. A simple, rigorous life was his ideal, and so he prescribed the following rules for children: Plenty of open air, of exercise, and of sleep; plain diet, no wine or strong drink, and very little or no drugs; not too warm or straight clothing; the head and feet especially to be kept cold, and the feet to be accustomed by exposure to wetness. Locke studied medicine, and once practiced it with much success. And the hygienic rules above cited, which were the result of his own experience and experimentation, introduced almost a revolution in the physical bringing up of children. We see how subsequent writers, like Rousseau and Kant, reflect his thoughts. His ideas of mental training rest on his theory of the mind. According to him, the mind of a new-born child is a _tabula rasa_: there is nothing innate in it; experience is what makes a mind. Every sensation one receives or every act one does, however small and insignificant it may seem, leaves some impression upon it, and contributes not only to the constitution of its content, but also to the formation of a definite tendency. He recognized the important rôle played by the unconscious or automatic part of the mind in our actual life, which is nothing more than an aggregate or a system of various habits. Volition has but little power against it; it works more “constantly and with greater facility than reason, which, when we have most need of it, is seldom fairly consulted and more rarely obeyed” (7: p. 91). Habit formation is, therefore, the great thing in education. The significance of any act of a child, of any educational process, is to be measured only by what kind of habit it is likely to lead to.