sexual instinct is continuous during the time of sexual life, but it varies in intensity. Under physiological conditions it is never intermittent (periodical), as in animals. In men it manifests an organic variation of intensity in consonance with the collection and expenditure of semen; in women the increase of sexual desire coincides with the process of ovulation, and in such a way that libido sexualis is greater after the menstrual period.
Sexual instinct—as emotion, idea, and impulse—is a function of the cerebral cortex. Thus far no definite region of the cortex has been proved to be exclusively the seat of sexual sensations and impulses.[1]
Owing to the close relations which exist between the sexual instinct and the olfactory sense, it is to be presumed that the sexual and olfactory centres lie close together in the cerebral cortex. The development of the sexual life has its beginning in the organic sensations which arise from the developing reproductive glands. These excite the attention of the individual. Readings and the experiences of every-day life (which, unfortunately, to-day are too early and too frequently suggestive) convert these notions into clear ideas. These become accentuated by organic sensations which are pleasurable. With this accentuation of erotic ideas by lustful feelings, an impulse to induce these (sexual desire) is developed.
Thus there is established a mutual dependence between the cerebral cortex (as the place of origin of sensations and ideas) and the reproductive organs. The latter, by reason of physiological processes (hyperæmia, secretion of semen, ovulation), give rise to sexual ideas, images, and impulses.
The cerebral cortex, by means of apperceived or reproduced sensual ideas, reacts on the reproductive organs, inducing hyperæmia, secretion of semen, erection, ejaculation. This results by means of centres for vasomotor innervation and ejaculation, which are situated in the lumbar portion of the cord and lie close together. Both are reflex centres.
The erection-centre (Goltz, Eckhard) is an intermediate station placed between the brain and the genital apparatus. The nervous paths which connect it with the brain probably run through the pedunculi cerebri and the pons. This centre may be excited by central (psychical and organic) stimuli, by direct irritation of the nerve-tract in the pedunculis cerebri, pons, or cervical portion of the cord, as well as by peripheral irritation of the sensory nerves (penis, clitoris, and annexa). It is not directly subordinated to the will.
The excitation of this centre is conveyed to the corpora cavernosa by means of nerves (nervi erigentes—Eckhard) running in the first three sacral nerves.
The action of the nervi erigentes, which renders erection possible,- ↑ The olfactory centre is presumed by Ferrier (“Functions of the Brain”) to be in the region of the gyrus uncinatus. Zuckerkandl (“Ueber das Riechcentrum,” 1887), from researches in comparative anatomy, concludes that the olfactory centre has its seat in Ammon’s horn.
