The duration of erection depends on the duration of its causes, and the early or late occurrence of the orgasm; and the degree of pleasure, on the condition of the nervous system, and the agreeable-ness of the sexual mate. Among physiological conditions which stimulate the erection-center are visual preceptions (sight of a naked woman), memory pictures (a lascivious story), and tactile impressions (kissing a woman, or feeling her breasts or other portions of her body).

Auditory and olfactory perceptions have also been said to exercise a certain degree of influence; but, outside of those animals which it is well known are attracted to each other by the odor of the genitals, during rutting season, the sexual part which smell plays with man, notwithstanding the great importance attached to it by certain writers, is, in my view, a very subordinate one.1