A physician offers practical, plainspoken guidance for boys and young men on bodily development, sexual hygiene, and the habits that conserve physical and mental energy. He explains basic physiology and puberty, describes how life begins and how to care for oneself during adolescence, and addresses night emissions, self-abuse, and remedies to stop harmful practices while warning against medical charlatans. The author also gives vocational counsel to help readers recognize aptitudes and fit themselves to careers, and discusses how environment and disease can erode brain power and vitality, emphasizing prevention and early instruction to promote long-term health and effectiveness.