Erections may finally be evoked by the stimulation of the peripheral nerves at the genitals as on the glans and on the skin of the penis. Especially the prostatic urethra and the colliculus are recognized as the most sensitive area, the focal point of the nervous impressions on the genital system. Pressure of the metal sound on the prostate or its cauterization, tumors, calculi and inflammations, e. c., gonorrhoea, may often excite erections. The prostatic mucous membrane is supposed to be the seat of the pleasurable sensations. During any kind of sexual activity, the prostatic area is intensely congested, and its nerves are in a high state of tension. Excitations at the neighboring parts of the genital organs, as evoked by hemorrhoids, stone in the bladder, full bladder, worms or full rectum, may also produce erections. The peripheral excitations of the genitals are transmitted to the central nervous system, i. e., the centres in the pons and in the medulla, by reflex action. From these centres the stimulus is conveyed to the centres of erection in the lumbar region. If the individual is in a state of unconsciousness as in sleep, the stimulus at the periphery takes the direct road to the centre of erection. The excitation of this centre is then carried by the way of the nervi erigentes to the corpora cavernosa. _Centre of inhibition._—All the nervous elements, the cerebral centre of voluptas or sex-desire, the spinal centre of erection, and the nerves at the periphery, not only at the genitals, but the nerve endings of the skin through the entire body, work in perfect harmony. Hence a man in full vigor of virility would have vigorous erections at the slightest touch or even sight of a comely woman. Given our present mode of life, with the ubiquitous opportunities for such sights at all times, normal healthy men would have to walk around on the streets in a state of permanent priapism, but for the cerebral centre of inhibition. The influence emanating from this inhibitory centre works upon the spinal centre to prevent erection. When the influence of this centre is removed, erection is facilitated. When the spinal cord of a dog is severed in the lumbar region, the irritation of the genitals more readily provokes erection. With the removal of the inhibitory influence during sleep, the least excitation of the genitals causes vigorous erections. When the stimulation of the inhibitory centre is unusually increased, as in neurasthenics and other nervous disorders, erections fail to appear, when they are most desired.