SKELETAL growth terminates with the attainment of sexual maturity and is a function of physiologic age rather than of chronologic age. In this series of studies, nitrogen was chosen as an indispensable component of active protoplasmic tissue and calcium as an essential element of the skeletal system, and their balances were determined under a variety of circumstances. In the period of growth that precedes sexual maturity, the factors—dietary, infectious and hormonal—that affect one of these tends in a general way to exert a similar effect on the other. After puberty, it might be anticipated that the fate of these two items would differ; the need for the storage of calcium is passing, the sharp acceleration of growth in height changing to a decelerating phase synchronously with the attainment of sexual maturity, but considerable growth involving the storage of nitrogen will be involved in the development of the sexual apparatus,