IT HAS become almost a custom for the pediatrician to introduce the subject of adolescence with an apology to the internist for a seeming intrusion into his field. Yet, if the justification for the existence of pediatrics as a specialty rests at all on its concern with the problems of growth and development, there would seem little need for any attempt to defend his interest in this period. It will be evident from Dr. Stuart's discussion that the processes of growth in this period can be understood only by ignoring chronologic age and thinking in terms of physiologic age; a concept which involves ideally a continuous record of a person, the gradual acquiring of which may have taken twelve to fourteen years of a pediatrician's supervision. To interrupt such an experience abruptly at some arbitrarily chosen year may be to terminate the study at the very peak of a curve,