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The following notes are intended to call attention to two regions on the borderline of psycho-analysis and biology, where the methods of the one science may throw light on the problems of the other. My best thanks are due to my friend, Dr. F. O. Stohr, for continual opportunity to consult psycho-analytic literature.
Freud, in the now classical Three Contributions to the Theory of Sex (second English edition, Washington, 1920, p. 50), distinguishes three phases of masturbatory activity in the development of sexual life. One of these occurs during the nursing period, the second at about the fourth year, and the third at puberty. It has long been known that the onrush of sexual development constituting puberty is associated with a maximum in the rate of bodily growth and the two are probably correlated physiologically.
Recent work1 on the rate of growth in man and other mammals has shown that there are three periods when the rate is at a maximum, and that in man these are: (1) just after birth; (2) between the third and the fifth years; and (3) about puberty. It seems therefore that each of the three phases distinguished by Freud is associated with a maximum in the growth rate. We can hardly doubt that some underlying physiological relation exists between them.
In that highly speculative and daring work, Beyond the Pleasure Principle, Freud has postulated two classes of instincts— life instincts associated with sexuality, and death instincts associated with the ego. In his discussion of the latter he suggests that the sadistic element in sexuality is derived from a masochistic death instinct, belonging to