According to Hensen, the direct stimulation of the sexual impulse proceeds by way of the dorsal nerve of the (penis or) clitoris; he assumes, however, that certain states of the reproductive glands are able to induce an increase in the irritability of the centres connected with the aforesaid nerves. In women it certainly appears that particular states of the ovary have a stimulating or inhibiting influence respectively on sexual excitement, so that we might ascribe to the ovaries the rôle of a regulator of the sexual impulse. The processes that occur in the ovary at the time of the ripening and rupture of the graafian follicle, and the resulting tension of the follicular wall, induce by stimulation of the ovarian nerves an increased sensibility of the central zones, and produce in a menstruating female a condition of increased sexual excitability, so that slight stimuli will give rise to a powerful orgasm more readily than would otherwise be the case, when the reflex irritability of the centre is less pronounced and the sexual impulse is consequently less intense. Still more than during these ordinary menstrual processes may this stimulation be effective at the time of the menarche, when the changes in the ovary occur for the first time and with the greatest intensity, so that at this time the individual may be especially susceptible to sexual stimulation.

At such times of sexual excitement, very slight external peripheral stimuli, in the form either of tactile stimulation of the sensory nerves of the skin and the external genital organs, or of stimulation of the imaginative and perceptive faculties of the brain, suffice to induce a powerful increase of the sexual impulse; whereas at other times, at which no particular sexual excitement exists, much stronger stimuli are needed to produce such an effect. Thus the sexual impulse in women is more readily and more powerfully increased in proportion as the central organ is in a condition of temporarily enhanced excitability in consequence of the condition of the ovaries.

The gratification of this impulse, the act of copulation, produces the specific sensation of sexual pleasure; in the female this is effected chiefly by friction of the glans clitoridis, the organ when erect projecting downwards at a right angle, and pressing upon the intromitted penis—the friction of the glans produces powerful mechanical stimulation of the numerous plexuses of sensory nerve fibres, which terminate in the genital corpuscles of Krause. In woman, then, we find in the ovary the place of origin and the means of regulation of the sexual impulse, and in the clitoris we find the seat of the specific sensation of sexual pleasure.

In the poorer classes of society, an increase of the sexual impulse occurs in women chiefly in consequence of bad example and of unfavorable domestic conditions, such as lead to persons of opposite sexes sleeping in the same bed, and also in consequence of the abuse of alcohol. In the well-to-do classes, it is the perusal of modern equivocal romances, visits to theatres, balls, and evening parties, and, speaking generally, idleness combined with luxurious living, that serve to stimulate the sexual impulse in woman.

A certain dependence of the sexual impulse upon seasonal variations appears to exist also in the human species. At any rate in certain months of the year, a definite increase in the number of conceptions continues to recur, which indicates that during these months a larger number of sexually mature individuals is engaged in the discharge of sexual functions. Rosenstadt regards this as the manifestation of a “physiological custom,” immanent in the physical constitution of civilized man, and inherited by him from his animal ancestors. He explains it in the following terms: “Primitive man inherited from his mammalian forefathers the peculiarity of reproducing his kind only during a certain definite period, the period of heat or rut. After humanity had entered upon this period, copulation was effected en masse, as was easy in view of the primitive community of sexual intercourse before the origin of marriage. In the course of his progress toward civilization, however, man began to reproduce his kind indifferently throughout the entire year; but the original “physiological custom,” in accordance with which reproduction occurred at definite seasons only, did not disappear, and persists, indeed, to a certain extent even to the present day as a survival of earlier mammalian life, and manifests itself in the annual recurrence in certain months of an increase in the number of conceptions. The analogy in structure and function between the genital organs of the human species and those of other mammals (the female anthropoid apes do not merely exhibit from time to time a period of heat, but are subject to a more or less regular menstruation), which for the most part reproduce their kind only at certain definite periods, leads to the conclusion that in the human species also the sexual impulse may originally have awakened only at a particular season of the year, and that the persistence of this physiological custom in man, in spite of the fact that sexual intercourse occurs all through the year, and notwithstanding that the conditions necessary to awaken the sexual impulse are actually perennial, must be ascribed to inheritance.”

This view, which is maintained also by other gynecologists, finds support in Kulischer’s assumption, based upon ethnological investigations, according to which coupling in primitive man took place only at certain seasons, namely, at spring and at harvest-time. In support of this view, which was held also by von Hellwald, Kulischer refers to a number of actual and symbolical practices among different races, which make the assumption extremely probable.

Sexual desire in women, the sexual impulse, outlasts the proper sexual life, and manifests itself even after the cessation of menstruation, when the possibility of conception has passed away; it appears, therefore, to have no necessary connection with the function of ovulation.

This is indicated by the always respectable number of women who enter upon marriage even after the climacteric age. Thus the percentage of brides who were more than 45 years of age was: In Prussia, 2.58 per cent.; in England, 1.38 per cent.; in Sweden, 1.53 per cent.; in Ireland, 0.31 per cent. Of quite peculiar interest are the figures relating to elderly women who marry men considerably younger than themselves. Thus we learn from the tables of Routh that in the space of 10 years in Ireland:

Women between the ages of 46 and 55 years married
Men below the age of 17 in1 instance.
Men between the ages of 17 and 25 in35 instances.
Men between the ages of 26 and 35 in145 instances.
Men between the ages of 36 and 45 in227 instances.
And women of ages greater than 55 years married
Men below the age of 17 in1 instance.
Men between the ages of 17 and 25 in3 instances.
Men between the ages of 26 and 35 in12 instances.
Men between the ages of 36 and 45 in15 instances.
Men between the ages of 46 and 55 in52 instances.

In England during the year 1855 the age of the bride exceeded the climacteric age in 778 instances. The brides were: