The growth-impulse can operate to mature the body only as the foods that will further growth and build tissue, both bone and muscle, are supplied for the use of the body in its growth. The kind of food is therefore as vital a need as the amount, particularly during the years of physical formation. Not only strength and health during growth but later too are effected by proper growth-diet.

Overrestriction of diet undernourishes the body, leaves it undeveloped and open to disease. Maladjustment of diet produces malnutrition that causes malformation or malfunctioning of the body which may last throughout life. Selection of proper food and thorough mastication result in nutrition.

During physical development all constitutions are delicate, so easily harmed. To grow physically and into mature health with high resistance to disease requires science-guided care in childhood and youth, also during disease.

An ice-bag applied to a child's head during fevers may make its body-temperature subnormal for life.

Reenforcing a delicate child's diet by feeding 1-2 T cream in mid-afternoon, as is desirable, may disorder digestion if rest is not enforced for 1-2 hours afterwards.

Adult-treatment of childhood and youth, like adult-diet, may not only do injury at the time but so weaken the constitution as to undermine later health.

Starving a child in illness may injure its intestines, while such treatment in adult-illness may be desirable. Sunshine, so important in plant-growth, is a powerful agency in tissue-building of children in need of much tissue-repair, as is a tuberculous child. But sun treatment (heliotherapy) for adults is not so assuredly advisable.

Exercise, as well as food, is necessary to growth and to bodily habits of health. But such competitive sports as may strain the heart, as can football, may injure growing boys.