A report on national vitality, prepared many years ago by a governmental commission,1 pointed out that whatever diminishes poverty or increases the physical means of welfare has the improvement of health as one of its first and most evident effects. Therefore an important method of maintaining vital efficiency is to conserve natural resources—land, raw materials, forests and water. Only in this way can food, clothing, shelter and the other means of maintaining life be obtained. Conversely, the conservation of health will tend in several ways to the conservation of wealth. First, the more vigorous and long lived the race, the better utilization can it make of its natural resources. The labor power of such a race is greater, more intense, more intelligent and more inventive.
In considering such problems of conservation as they affect human life, one usually thinks far more of mortality than of morbidity. The latter, however,