Thus we see that all our methods of investigation exhibit extensive lacunae, and further, that they are all in many respects fallacious; we shall therefore endeavour to supplement each by the others, in order to arrive at results which shall be as free from error as possible. Thus guided, we learn that sexual incidents occur in childhood far more frequently than is usually supposed. So common are they, that they cannot possibly escape the notice of any practising physician or educationalist who pays attention to the question, provided, of course, that he enjoys the confidence of the parents. These latter have often been aware of such sexual manifestations in their children for a long time, but a false shame has prevented them from asking the advice of the physician. They have been afraid lest he should regard the child as intellectually or morally deficient, or as the offspring of a degenerate family. In addition, we have to take into account self-deception on the part of the parents, who, indeed, often deceive themselves willingly, saying to themselves that the matter is of no importance, and that the symptoms will disappear spontaneously. Having given this brief account of the terminology to be employed and of the methods of investigation, I propose to sketch no less briefly the history of the subject. Casual references to the sexual life of the child are to be found even in the older scientific literature. In the latter half of the eighteenth century, and at the beginning of the nineteenth, interest in the subject became more general. Two works, in especial, published almost simultaneously, attracted the attention of physicians and educationalists. One of these, Rousseau's _Emile_, discusses the proper conduct of parents and elders in relation to the awakening sexual life, and what they should do in order to delay that awakening as much as possible. The other, the celebrated work of Tissot, depicts the dangers of masturbation, but deals chiefly with persons who have attained sexual maturity. None the less, in consequence of this book, much attention was directed to the sexual life of the child. Earlier works on masturbation, such as that of Sarganeck, for instance, had not succeeded in arousing any enduring interest in this question. But Rousseau's and Tissot's books induced a large number of physicians and educationalists to occupy themselves in this province of study. Thus at this early day many authorities were led to advocate the sexual enlightenment of children, in order to guide them in the avoidance of the dangers of the sexual life. An excellent historical and critical study of this movement, written by Thalhofer, has recently been published.[4] Among the educationalists who took part in it may be mentioned Basedow, Salzmann, Campe, and Niemeyer. The modern movement in favour of sexual enlightenment originated chiefly in the endeavour to prevent the diffusion of venereal diseases; but the earlier movement, occurring at a