This process cannot, however, be carried out to an unlimited extent any more than can the conversion of heat into mechanical work in our machines. A certain amount of direct sexual satisfaction is for most organizations indispensable, and the renunciation of this individually varying amount is punished by manifestations which we are compelled to regard as morbid. The process of sublimation, under the influence of civilization, leads both to sexual perversions and to psycho-neuroses. These two conditions are closely related, as Freud views the process of their development; they stand to each other as positive and negative, sexual perversions being the positive pole and psycho-neuroses the negative. It often happens, he remarks, that a brother may be sexually perverse, while his sister, with a weaker sexual temperament, is a neurotic whose symptoms are a transformation of her brother's perversion; while in many families the men are immoral, the women pure and refined but highly nervous. In the case of women who have no defect of sexual impulse there is yet the same pressure of civilized morality pushing them into neurotic states. It is a terribly serious injustice, Freud remarks, that the civilized standard of sexual life is the same for all persons, because though some, by their organization, may easily accept it, for others it involves the most difficult psychic sacrifices. The unmarried girl, who has become nervously weak, cannot be advised to seek relief in marriage, for she must be strong in order to "bear" marriage, while we urge a man on no account to marry a girl who is not strong. The married woman who has experienced the deceptions of marriage has usually no way of relief left but by abandoning her virtue. "The more strenuously she has been educated, and the more completely she has been subjected to the demands of civilization, the more she fears this way of escape, and in the conflict between her desires and her sense of duty, she also seeks refuge--in neurosis. Nothing protects her virtue so surely as disease." Taking a still wider view of the influence of the narrow "civilized" conception of sexual morality on women, Freud finds that it is not limited to the production of neurotic conditions; it affects the whole intellectual aptitude of women. Their education denies them any occupation with sexual problems, although such problems are so full of interest to them, for it inculcates the ancient prejudice that any curiosity in such matters is unwomanly and a proof of wicked inclinations. They are thus terrified from thinking, and knowledge is deprived of worth. The prohibition to think extends, automatically and inevitably, far beyond the sexual sphere. "I do not believe," Freud concludes, "that there is any opposition between intellectual