In the original cell division a cell gives up a part of itself in order to go on growing. The principle of separation, as basic in growth and development, is manifest in that original biological phenomenon. The same principle of separation is operative in the birth process. Physiological differentiation and integration have proceeded to a point which allows the infant to function as a new living unity, and separation from the mother is necessary if the new functioning aggregate of cells which we call a baby is to go on living. Just as the orig­ inal cell would die if it did not undergo division, so the in­ fant would die if it were not divided from the mother. This is the end of one phase of growth with its more exclusive biological characteristics, and the beginning of a different phase that brings into operation new factors and new in­ fluences, and new functions emerge in both the infant and in the adults concerned with his birth.