If there were no other reasons for sex-instruction, I believe that it would be worth while to teach such hygienic knowledge of self and sex as would guard young people against harmful habits and unhealthful care of their sexual mechanisms; and which, moreover, would guide them across the threshold of adolescence with some helpful understanding of the significance of the metamorphosis. Many men and women suffer from injured, if not ruined, health because they did not know, especially between ten and fourteen years, the laws of personal sex-hygiene, which concern health in ways not involving sexual relationship. Many boys and some girls are injured both physically and mentally by the habit of masturbation. Numerous girls are injured physically and many mentally because they have not learned in advance the nature and hygiene of menstruation. Many boys are injured both in mind and character because they have no scientific guidance which helps them understand themselves during the stormy transition from youth into manhood. Moreover, there are certain simple hygienic commands that children under twelve should receive from parents and teachers. In all these lines the bearings of personal hygienic instruction are so obvious that we need not at this time stop to consider in more detail this first reason or problem for sex-instruction of young people. Sec. 7. _Second Problem for Sex-instruction: Social Diseases_ [Sidenote: Recent publicity regarding vice and disease.] During the past decade the general public has received some astounding revelations concerning the enormous extent of illicit sexual promiscuity, which is immorality according to our commonly accepted code of morals. Along with the evidence as to the existence of widespread promiscuity, has come the still more alarming information from the medical profession that sexual promiscuity commonly distributes the germs of the two highly infectious and exceedingly destructive diseases, syphilis and gonorrhea, known in medical science as venereal or social. When these are acquired by individuals guilty of sexual promiscuity, they seriously and often fatally affect the victim; but of far greater social-hygienic importance is the medical evidence that they are very often transmitted to persons innocent of any transgression of the moral law, especially to wives and children. The medical revelations concerning the relation of sexual immorality to the plague of social diseases, has come from certain eminent physicians, notably the late Dr. Prince A. Morrow. His translation of Fournier's "Syphilis and Marriage" (1881), his own "Social Diseases and Marriage" (1904), and several of his pamphlets published by the American Society of Sanitary and Moral Prophylaxis, have been authoritative statements of conditions as the medical world sees them. [Sidenote: Social diseases and immorality.]