The experiment of Goltz, according to whom, when (in dogs) the lumbar portion of the cord is severed, erection is more easily induced, shows that the erection-centre is also subject to inhibitory influences from the brain.
In men the fact that the will and emotions (fear of unsuccessful coitus, surprise inter actum sexualem, etc.) may inhibit the occurrence of erection, and cause it, when present, to disappear, also indicates this.
The duration of erection is dependent upon the duration of its exciting causes (sensory stimuli), the absence of inhibitory influences, the nervous energy of the centre, and the early or late occurrence of ejaculation (v. infra).
The central and highest portion of the sexual mechanism is the cerebral cortex. It is justifiable to presume that there is a definite region of the cortex (cerebral centre) which gives rise to sexual feelings, ideas, and impulses, and is the place of origin of the psycho-somatic processes which we designate as sexual life, sexual instinct, and sexual desire. This centre is excitable to both central and peripheral stimuli.
Central stimuli, in the form of organic excitation, may be due to diseases of the cerebral cortex. Physiologically they consist of psychical stimuli (memory and sensory perceptions).
Under physiological conditions these stimuli are essentially visual perceptions and memory-pictures (i.e., lascivious stories) and also tactile impressions (touch, pressure of the hand, kiss, etc.).
Within physiological limits auditory and olfactory perceptions certainly play but a very subordinate rôle. Under pathological conditions (v. infra) the latter have a very decided influence in inducing sexual excitement.
Among animals the influence of olfactory perceptions on the sexual sense is unmistakable. Althaus (“Beiträge zur Physiol. und Pathol. des Olfactorius.” Archiv für Psych., xii, H 1) declares that the sense of smell is important with reference to the reproduction of the species. He shows that animals of opposite sexes are drawn to each other by means of olfactory perceptions, and that almost all animals, at the time of rutting, emit a very strong odor from their genitals. An experiment by Schiff is confirmatory of this. He extirpated the olfactory nerves in puppies, and found that, as the animals grew, the male was unable to distinguish the female. On the other hand, an experiment by Mantegazza (“Hygiene of Love”), who removed the eyes of rabbits and found that the defect constituted no obstacle to procreation, shows how important in animals the olfactory sense is for the vita sexualis.
It is also remarkable that many animals (musk-ox, civet-cat, beaver) possess glands on their sexual organs, which secrete materials having a very strong odor.
Althaus also shows that in man there are certain relations existing between the olfactory and sexual senses. He mentions Cloquet (“Osphrésiologie,” Paris, 1826), who calls attention to the sensual pleasure excited by the odors of flowers, and tells how Richelieu lived in an atmosphere loaded with the heaviest perfumes, in order to excite his sexual functions.