Thoroughgoing and painstaking dissection of the human soul, such as has been practiced by Freud for nearly a quarter of a century and by many followers of his theories in the past decade, revealed to him a number of unmistakable facts from the developmental history of the individual which forced him to postulate his very radical and revolutionary theories of the sexual instinct in man. Recent behavior studies in the higher anthropoids have likewise revealed very interesting facts concerning the sexual instinct of these animals. Freud was led to make certain assertions from his painfully acquired experience, such as the unfailing sexual agency in the causation of neurotic manifestations, and that his experience of many years has as yet shown no exception to this rule, which quite naturally provoked a good deal of bitter and fanatic criticism not only from lay people but from experienced physicians. The cause for this lies in the nature of the thing itself, that much tabooed subject of sexuality. Unfortunately, as Hitschmann[6] says, physicians in their personal relations to the sexual life have not been given any preference over the rest of the children of men and many of them stand under the ban of that combination of prudery and lust which governs the attitude of most cultivated people in sexual matters. Especially unsavory appears to most people Freud's theory of infantile sexuality, a subject which has heretofore been looked upon chiefly from a moralistic standpoint, and was spoken of by others merely as odd or as a frightful example of precocious depravity. It is somewhat strange that of all the frightful depravities, if we wish to call it so--inherent in man, of the marked criminalistic components universally present in man which psychoanalytic studies have revealed--the sex depravity should have provoked the most fanatic attacks. Indeed to those who are accustomed to look at man with the psychoanalytic eye, Rochefoucauld's incisive statement does not at all sound strange. He said, "I have never seen the soul of a bad man; but I had a glimpse at the soul of a good man; I was shocked." I therefore crave the indulgence of those of you who are not familiar with psychoanalytic literature for what I am about to quote briefly from Freud's theories on the sexual instinct in man.