Such processes as these, viz., inflammatory stimuli originating in the external genital organs, or developmental stimuli proceeding from the testicles, may lead to the practice of masturbation without having directly affected the child's consciousness. Just as in the pithed frog, if we stimulate one foot with acetic acid, the other foot scratches the irritated area, so a child may, with his hands or in some other way, scratch itching regions of the body, and, above all, of the external genital organs, without its being necessary for us to assume that he is fully conscious of what he is doing. Further, as we have already pointed out, such masturbation may or may not be preceded by a reflex erection. And just as the boy soon learns that itching is relieved by scratching, so also he learns that by means of artificial stimulation he may induce sensations of a voluptuous character. It is the same with the little girl, in whom sensations occur in the genital organs, due in some cases to developmental, and in others to pathological stimuli (skin eruptions are an instance of the latter kind), and these lead to manipulations of the genital organs. In contradistinction to the cases just described, in which the child has learned spontaneously to practise artificial stimulation of his genital organs, are the cases in which seduction by others is the cause of masturbation. Nurses sometimes touch, stroke, and stimulate the external genital organs of the children entrusted to their care--boys and girls alike--either to keep them quiet, or for the gratification of their own lustful feelings. In this way the child, who in the case of all agreeable sensations has a natural desire for their repetition, is gradually led to imitate the manipulations which have given rise to the voluptuous sensations, and is thus seduced to the practice of masturbation.