The second stage of a boy's physical development, the early adolescent stage--twelve to fifteen years--is the physiological. Puberty marks its advent, although the exact sign of its arrival is hard to determine. It has been easy to discover it in a girl's life, but it still remains a matter of some guessing in a boy. _A recent work of Dr. Crompton states that the kinking of the hair upon the pubic bone is a sure sign of the beginning of the period_. Some physical directors have found this a satisfactory sign, and have made this the basis of a graded work with boys. It is in this period, then, that the boy should learn something of the anatomy and physiology of the male sexual organs. The third stage of sex instruction for boys is during the later adolescent period--at least over fifteen years--and this should be pathological. A free discussion of the so-called social evil and the forms of venereal disease would certainly educate the boys to a proper conception of the entire subject. All questions should be discussed in ordinary language and business-like style. =Sources of Knowledge for Sex Instruction= 1. THE BIOLOGICAL PERIOD (UNDER TWELVE YEARS). --A Frank Talk with Boys and Girls About Their Birth (Free). --A Straight Talk with Boys About Their Birth and Early Boyhood (Free). Chapman.--How Shall I Tell My Child? (.25). Muncie.--Four Epochs of Life (Chapters 7-12) ($1.50). Thresher.--Story of Life for Little Children (Free). --When and How to Tell Children. (Oregon State Board of Health.) 2. THE PHYSIOLOGICAL PERIOD (TWELVE TO FIFTEEN YEARS). Hall.--From Youth Into Manhood (.50). How My Uncle, the Doctor, Instructed Me in Matters of Sex (.10). Lowry.--Truths (.50). --The Secret of Strength (Social Hygiene Society of Portland, Oregon) (Free). --Virility and Physical Development (Social Hygiene Society of Portland, Oregon) (Free). --Address the Secretary of the Social Hygiene Society, 311 Young Men's Christian Association Building, Portland, Oregon. 3. THE PATHOLOGICAL PERIOD (OVER FIFTEEN YEARS). Educational Pamphlets, Nos. 1 and 6 (American Society of Sanitary and Moral Prophylaxis) (.10 each). --Four Sex Lies (Oregon State Board of Health) (Free). Hall.--From Youth Into Manhood (Chapter on Sexual Hygiene) (.50). Health and the Hygiene of Sex (.10). The Young Man's Problem (.10). =A Word of Caution=