The idea that the body may be preserved in a healthy state longer by sparing it——_i.e._, by inactivity——is an error which springs from a false and mechanical conception of life. It is just as foolish to imagine that health depends on the abundance and excellence of food, for without the power of assimilating the food taken, nourishment of whatever kind does more harm than good; all real strength develops from activity alone. § 56. Physical education, according as it relates to the repairing, the muscular, or the emotional activities, is divided into (1) diatetics, (2) gymnastics, (3) sexual education. In the direct activity of life these all interact with each other, but for our purposes we are obliged to speak of them as if they worked independently. Moreover, in the development of the human being, they come into maturity of development in a certain order: nutrition, muscular growth, sexual maturity. But Pedagogics can treat of these only as they are found in the infant, the child, and the youth; for with the arrival of mature life, education is over. FIRST CHAPTER. _Diatetics._ § 57. By diatetics we mean the art of repairing the constant waste of the system, and, in childhood, of also building it up to its full form and size. Since in reality each organism has its own way of doing this, the diatetical practice must vary somewhat with sex, age, temperament, occupation, and circumstances. The science of Pedagogics has then, in this department, only to enunciate general principles. If we go into details, we fall into triviality. Nothing can be of more importance for the whole life than the way in which the physical education is managed in the very first stages of development. So generally is this fact accepted, that almost every nation has its own distinct system, which has been carefully elaborated. Many of these systems, no doubt, are characterized by gross errors, and widely differ as to time, place, and character, and yet they all have a justification for their peculiar form. § 58. The best food for the infant in the first months of its life is its mother's milk. The employment of another nurse, if a general custom, as in France, is highly objectionable, since with the milk the child is likely to imbibe to some extent his physical and ethical nature. The milk of an animal can never supply the place to a child of that of its own mother. In Walter Scott's story of _The Fair Maid of Perth_, Eachim is represented as timorous by nature, having been nourished by a white doe after the death of his mother. § 59. When the teeth make their appearance, it is a sign that the child is ready for solid food; and yet, till the second teeth appear, light, half-solid food and vegetables should constitute the principal part of the diet.