The less power we have to operate by control of the congenital factors, the more necessary shall we feel it to be to minimise the dangers threatening the child by influencing its environment. It is true that in this department, as in others, there is much diversity of opinion regarding the limits of educability. Some contend that we can mould the child like wax, a view which prevailed especially during the "period of enlightenment" in the eighteenth century; others maintain that organic development is predetermined at the time of procreation, and that subsequent influences can have no effect. Although we must be careful not to overestimate the power of education, it would be no less erroneous to assume that development is inalterably predetermined at the time of procreation. This applies to the efficacy of educational influences in general, and to educational influences affecting the sexual life in particular. The following consideration must be given due weight. The power of the educator is limited, not merely by the child's hereditary dispositions, but also by the nature of its environment. Rudolf Lehmann, in his work on Education and the Educator (_Erziehung und Erzieher_), rightly points out that Rousseau, in his _Emile_, when discussing the problems of education, neglects too much the influences of environment. If we wish our reasoning to furnish us with results of practical value, and not to remain confined to the purely theoretical plane, we must give due weight to this consideration. This applies with equal force to the matter of sexual education. We know that the sexual impulse may be excited by innumerable external stimuli. Such stimuli are continuously in operation, and the best educator has no power to exclude their influence. The mere association of the child with persons of the opposite sex provides such stimuli. But a separation of the sexes will not do away with them, as is proved, not only by the homosexual manifestations of the undifferentiated sexual impulse, but also by those that arise transiently, at any rate, when the members of one sex are completely segregated from those of the other--as in boarding-schools, on board ship, and in prisons. The educator cannot even count on being at all times able to safeguard the child from the sight of sexual acts. In the country, but also in the town, children have opportunities for this; not only when the members of a large family sleep in a single room, and the children can watch their parents and others in the act of sexual intercourse; but in various other ways. The mere kissing of affianced lovers must in this sense be regarded as a sexual act, and how is it possible so to bring up a child that it will never have an opportunity of seeing anything of the kind? If we go further, and recognise that through the association of ideas such a sexual stimulus may arise from witnessing the coupling of animals--of dogs, for