where one of them predominates the other is proportionately less pronounced. At one end of the series stand those extreme cases of whom one can say: These people would have fallen ill whatever happened, whatever they experienced, however merciful life had been to them, because of their anomalous Libido-development. At the other end stand cases which call forth the opposite verdict—they would undoubtedly have escaped illness if life had not put such and such burdens upon them. In the intermediate cases in the series, more or less of the disposing factor (the sexual constitution) is combined with less or more of the injurious impositions of life. Their sexual constitution would not have brought about their neurosis if they had not gone through such and such experiences, and life’s vicissitudes would not have worked traumatically upon them if the Libido had been otherwise constituted. In this series I can perhaps admit a certain preponderance in the effect of the predisposing factor, but this admission again depends upon where you draw the line in marking the boundaries of nervousness. I shall now suggest to you that we should call series such as these _complemental series_, and will inform you beforehand that we shall find occasion to establish others of this kind. The tenacity with which the Libido holds to particular channels and particular objects, the ‘_adhesiveness_’ of the Libido, so to say, seems to be an independent factor, varying in individuals, the determining conditions of which are completely unknown to us, but the importance of which in the ætiology of the neuroses we shall certainly no longer underestimate. At the same time we should not overestimate the close relation between the two things. A similar ‘adhesiveness’ of the Libido occurs—from unknown causes—in normal people under numerous conditions, and is found as a decisive factor in those persons who in a certain sense are the extreme opposite of neurotics—namely, perverted persons. It was known before the time of psycho-analysis that in the anamnesis of such persons a very early impression, relating to an abnormal instinct-tendency or object-choice, is frequently discovered, to which the Libido of that person henceforth remains attached for life (Binet). It is often hard to say what has enabled this impression to exert such an intense power of attraction upon the Libido. I will describe a case of this kind observed by myself. A man to whom the genitals and all the other attractions in a woman now mean nothing can be roused to irresistible sexual excitation only by a shoe-clad foot of a certain shape; he can remember an event in his sixth year which determined this fixation of Libido. He was sitting upon a stool by the side of his governess who was to give him an English lesson. She was a plain, elderly, shrivelled old maid, with watery blue eyes and a snub nose, and on this day she had hurt her foot and had it therefore stretched out on