higher kinetic equivalent, into enthusiasm for science, art, and philosophy, for humanity, for the ideal, for God.
With the approach of this unique period, at about eleven or twelve in girls, and thirteen or fourteen in boys, there occurs an acceleration in physical growth which reaches its height at twelve and thirteen in girls, and at fourteen or fifteen in boys, and then rapidly slows up, but is more prolonged in boys than in girls. There is a retardation at eighteen or nineteen, and thereafter little increase. On account of the girls' relative precocity of growth, there is a period during which they are taller and heavier than boys of the same age. For height this lasts from eleven or twelve to fourteen or later. The various parts and tissues of the body do not grow with equal and constant pace, but the energy of growth drives hither and thither. Boys grow stout most slowly while they are growing tall fastest, i.e., from April to August; and they grow tall most slowly while they are growing stout fastest, i.e., from August to December. Perverse or defective nutrition tends to retard growth, to delay the characteristic growth periods and to reduce the final size attained, as well as to produce criminality or moral arrest and reversion. Excessive functional activity has the same tendency, likewise disease and sexual precocity. The skeleton takes a prominent part in the increased growth of adolescence, especially the hips and chest. The circumference of the chest, which shows little increase from ten to twelve years, thereafter develops rapidly, reaching a maximum of growth at fifteen, but continuing to nineteen. Lung capacity, the most trustworthy index of vitality, likewise increases to a marked degree, especially from twelve to fourteen in girls and from fourteen to sixteen in boys. With deeper breathing is associated better oxidation of the blood, greater endurance, power to resist disease, and intensity of life. According to Oppenheim, the muscular tissue grows faster during adolescence than any other tissue, unless it be fat in girls. This rapid growth of bone and muscle does not proceed symmetrically. Sometimes the muscles grow more slowly than the bones to which they are attached, which causes growing pains. Sometimes the reverse is the case, causing loose-jointedness. Again, the larger and more fundamental muscles take precedence of the smaller and accessory muscles in growth at early adolescence. It is little wonder if, with all this disproportionate growth, the adolescent is awkward and clumsy.
