The higher the character of a function and the wider its relations, the more serious and the more numerous are the dangers to which it is exposed. A physiologist remarks, ‘In youth the affinity of the tissues for vital stimuli seems to be greater when the development is less complete.’ That which the strong adult may endure with comparative impunity destroys the growing youth, whose nature, from the very necessities of development, possesses a keener sensitiveness to all vital stimuli. This important remark is true of mental as well as physical youth, and applies with especial force to the prevention of the dangers of premature sexual development. More care is needed to secure healthy, strengthening influences for the early life of sex than for any other more simply physical function. * * * * * In the preceding considerations, the faculty of sex has been regarded chiefly in its individual aspect, and the principles laid down by means of which the largest amount of health and strength can be secured for each individual. But this half-view is entirely insufficient in considering those physiological peculiarities of the function of sex, which must determine the true aim of education. There are two other physiological facts to be considered--viz., the Duality of Sex, and its Results. The power we are now considering enters into a different category from all other physical functions, as being, _first_, the faculty of two, not of one only, and, _second_, as resulting in parentage. Directly a physical function is the property of two, it belongs to a different class from those faculties which regard solely the individual. That very fact gives it a stamp, which requires that the relations of the two factors should be considered. No faculty can be regarded in the light of simple self-indulgence, which requires two for its proper exercise. The consideration of such faculty in its imperfect condition as belonging to one-half only is an essentially false view. It is unscientific, therefore, to regard this exceptional faculty simply as a limited individual function, as we regard the other powers of the human body. Its inevitable relations to man, to woman, and to the race must always stand forth as a prominent fact in determining the aim of education. If this be so, the moral education of youth, with the necessary physiological guidance given to their sexual powers, must always be influenced by a consideration of these two inevitable physiological facts--viz., duality and parentage, and the training of young men and women, should mould them into true relations towards each other and towards offspring.