Thus, by the inhibitory action of the brain, the tonus of the centre of erection preserves the equilibrium, and it requires longer preparations and more intense excitations than is ordinarily furnished in social intercourse to evoke erections, necessary for the performance of the sexual act. When cerebral inhibition is removed, as in sleep, erections are facilitated. On the other hand, when the inhibitory influences are increased, as in a state of intense mental occupation or of depressing emotion, as fear of inability to consummate the act, or fear of detection, or at the loss of the object of one’s affections, or in cases of extreme modesty or disgust, etc., erections may be prevented or entirely arrested. Hence the normal accomplishment of the sex-act requires complete absence of doubts, apprehensions, of any anxiety whatever, and want of confidence in one’s own power. Otherwise the inhibitory influences will prevent a perfect erection. _Centre of ejaculation._—The centre of ejaculation has its seat in the level of the fourth lumbar vertebra. In a state of perfect health, the excitability of this centre is much lower than that of erection. Hence it requires more intense stimuli and longer preparation to produce an ejaculation than an erection. The best stimulus for this centre is the tender, soft, warm vaginal mucosa, when rubbing against the glans and the skin of the penis. _Orgasmus._—The complicated reflex nerve phenomena taking place in a complete and perfect male sexual act may be described as follows: At the first voluptuous thrill of a physical pleasurable sensation, and at the first tactile excitation of the sensual organs, the cerebral centre of inhibition is at once paralyzed and its influence is removed. The centre of erection has now opportunity for the full display of its vasodilatory influences. The tonus of the genital vessels is removed, and an increased amount of blood flows into the arteries and caverns so as to render the penis stone hard. Through the increased blood supply and under the greatly increased nervous tension, the genital glands, the testicles, seminal vesicles, and prostate secrete an increased amount of their respective fluids. These secretions pour into the urethral bulb and distend the same. The excitations, radiating from this distension, serve to stimulate the centre of ejaculation, and the contractions of the muscles bulbo-cavernosus and accelerator urinae take place. The result of these contractions is the phenomenon of ejaculation. Simultaneously with the ejaculation, the nervous tension, which was increased to the highest degree through the excitations of the different organs, is also removed. This explosion of the nervous tension during the crisis produces the pleasurable sensations which are known under the name orgasm[E] (from the Greek word ὀργᾶν, to swell with lust).