At a slightly later period, the public-school age, there emerges the tendency, in addition to onanism, for promiscuous practices, usually of a homogenic nature. A further stage of sex-education must now be opened out, namely the principle that physical sex expression must be the expression only of love. The problem now becomes necessarily more acute, but there is this element which tends to lessen the difficulties of the instructor's task. The individual is always interested about himself; he is naturally egotistical. The youth will gladly listen to what can be told him of his own nature. He must be shown the immense superiority of mind both over the emotional and physical natures. This may involve a slight dethronement of the public school appreciation of sport. So long as it is slight such a dethronement will be a reform in itself. The boy in his middle teens must be taught that man is greater in his mental than in his physical activity; he must be reminded that he is inferior to many animals on the physical level. The application of this doctrine to sex is that sex-expression for the purpose of physical curiosity or excitement is a denial of the monopoly of love, which belongs to the emotional and mental capacities. The young man and the girl, who has left school, will be ready to receive the whole standard of sex-morality as has been outlined in this manual. The chief trouble now becomes over-sentimentality, the tendency to develop emotionally at the expense of the mind. And it becomes, therefore, essential to remind the pupil that where there are continual passing and promiscuous sexual or love affairs, the mind is being shut out from its natural functions. To be attracted sexually towards any pretty girl, to develop sexual relations with different women from week to week, is simply a form of mental unbalance. The emotions are in the saddle. For directly the mind begins to operate there is introduced the element of permanency and constancy. The deepest and most real pleasures only begin in the realm of mentality. The man who hears music only to beat time or remember a catchy tune is shut out of the immense joy of the intellectual love of music. So the young man who lives in a fever of hot-house sexuality, of absorbing intrigues in the dance-room, or the morbid atmosphere of the street corner, is shut out of all the exquisite joys of love. He does not know this, any more than the irreligious man knows what he loses through an absence of the spiritual sense. But he must be told.