Of the two parties in this conflict—the instinctive {73} impulse and the repressive force—the first, according to Freud, is wholly the product of the sex instinct. This instinct is conceived of as being much more active and potent in the infant and child than had been suspected by any previous investigator. The normal sexual interest and activity as manifested in the adult are developed out of the sexual impulse of the child by a regular series of modifications, which appear to be regarded as due partly to a process of natural development and partly to the influence of external repressive forces. In the infant the instinct is egocentric and the object of its interest is the individual’s own body; with the increase of the mental field consequent on enlarging experience the instinctive activity is externalized, and its object of interest changes so that the child acquires a specific inclination towards other individuals without distinction of sex; finally, as a last stage of development the instinctive inclination is localized to members of the opposite sex. This series of transformations is regarded as normal by Freud, and as essential to the appearance of the “normal” adult type. The evolution of this series is sensitive to interference by outside influences, and any disturbance of it either by way of anticipation or delay will have profound effects upon the ultimate character and temperament of the subject. The psychical energy of an instinct so important as that of sex is very great, and is not dissipated by the forces of repression brought to bear upon it, but transformed into activities ostensibly quite different and directed into channels having no obvious connection with their source. It is a fundamental characteristic of the mind to be able to accept these substitutes for the actual indulgence of the instinct, and to enjoy a symbolical gratification in manifestations which have no overt sexual significance. When development proceeds normally the {74} surplus energy of the sex instinct finds an outlet in activities of social value—æsthetic, poetic, altruistic; when development is interfered with the outflow of energy is apt to result in definite disease of the mind or in peculiarities of character scarcely to be distinguished therefrom.