The theory which we had attempted to construct in the _Studien_ remained, as I have said, very incomplete; and in particular we had scarcely touched upon the problem of ætiology, upon the question of the ground in which the pathogenic process takes root. I now learned from my rapidly increasing experience that it was not _any_ kind of emotional excitation that was in action behind the phenomena of the neurosis but regularly one of a sexual nature, whether it was a current sexual conflict or the effect of earlier sexual experiences. I was not prepared for this conclusion and my expectations played no part in it, for I had begun my investigation of neurotics quite unsuspectingly. While I was writing my “History of the Psycho-Analytic Movement” in 1914, there recurred to my mind some remarks that had been made to me by Breuer, Charcot and Chrobak, which might have led me to this discovery earlier. But at the time I heard them I did not understand what these authorities meant; indeed they had told me more than they knew themselves or were prepared to defend. What I heard from them lay dormant and passive within me, until the chance of my cathartic experiments brought it out as an apparently original discovery. Nor was I then aware that in deriving hysteria from sexuality, I was going back to the very beginnings of medicine and following up a thought of Plato’s. It was not until later that I learnt this from an essay by Havelock Ellis. Under the influence of my surprising discovery, I now took a momentous step. I went beyond the domain of hysteria and began to investigate the sexual life of the so-called neurasthenics who used to visit me in numbers during my consultation hours. This experiment cost me, it is true, my popularity as a doctor, but it brought me convictions which today, almost thirty years later, have lost none of their force. There was a great deal of equivocation and mystery-making to be overcome, but once that had been done, it turned out that in all of these patients grave abuses of the sexual function were present. Considering how extremely widespread are these abuses on the one hand and neurasthenia on the other, a frequent coincidence between the two would not have proved much; but there was more in it than that one bald fact. Closer observation suggested to me that it was possible to pick out from the confused jumble of clinical pictures covered by the name of neurasthenia two fundamentally different types, which might appear in any degree of mixture but which were nevertheless to be observed in their pure forms. In the one type the central phenomenon was the anxiety attack with its equivalents, rudimentary forms and chronic surrogate symptoms; I consequently gave it the name of _anxiety neurosis_, and limited the term _neurasthenia_ to the other type. Now it was easy to establish the fact that each of these types have a different abnormality of sexual life as its corresponding ætiological factor: in the former case _coitus