is allowed.” (W.  Heape, “The ‘Sexual Season’ of Mammals,” Quarterly Journal of Microscopical Science, vol. xliv, Part I, 1900.  Estrus has since been fully discussed in Marshall’s Physiology of Reproduction.) This description clearly brings out the fundamentally vascular character of the process I have termed “tumescence”; it must be added, however, that in man the nervous elements in the process tend to become more conspicuous, and more or less obliterate these primitive limitations of sexual desire. (See “Sexual Periodicity” in the first volume of these Studies.)

Moll subsequently restated his position with reference to my somewhat different analysis of the sexual impulse, still maintaining his original view ("Analyse des Geschlechtstriebes,” Medizinische Klinik, Nos. 12 and 13, 1905; also Geschlecht und Gesellschaft, vol. ii, Nos. 9 and 10).  Numa Praetorius (Jahrbuch fuer Sexeuelle Zwischenstufen, 1904, p. 592) accepts contrectation, tumescence, and detumescence as all being stages in the same process, contrectation, which he defines as the sexual craving for a definite individual, coming first.  Robert Mueller (Sexualbiologie, 1907, p. 37) criticises Moll much in the same sense as I have done and considers that contrectation and detumescence cannot be separated, but are two expressions of the same impulse; so also Max Katte, “Die Praeliminarien des Geschlechtsaktes,” Zeitschrift fuer Sexualwissenschaft, Oct., 1908, and G. Saint-Paul, L’Homosexualite et les Types Homosexuels, 1910, p. 390.

While I regard Moll’s analysis as a valuable contribution to the elucidation of the sexual impulse, I must repeat that I cannot regard it as final or completely adequate.  As I understand the process, contrectation is an incident in the development of tumescence, an extremely important incident indeed, but not an absolutely fundamental and primitive part of it.  It is equally an incident, highly important though not primitive and fundamental, of detumescence.  Contrectation, from first to last; furnishes the best conditions for the exercise of the sexual process, but it is not an absolutely essential part of the process and in the early stages of zooelogical development it had no existence at all.  Tumescence and detumescence are alike fundamental, primitive, and essential; in resting the sexual impulse on these necessarily connected processes we are basing ourselves on the solid bedrock of nature.

Moreover, of the two processes, tumescence, which in time comes first, is by far the most important, and nearly the whole of sexual psychology is rooted in it.  To assert, with Moll, that the sexual process may be analyzed into contrectation and detumescence alone is to omit the most essential part of the process.  It is much the same as to analyze the mechanism of a gun into probable contact with the hand, and a more or less independent