I. Of the central or peripherally aroused perceptions.
II. Of the pleasurable sensations associated with these.
Hence arises the impulse to sexual satisfaction (libido sexualis). This impulse becomes stronger in proportion as cerebral excitement, consequent on appropriate perceptions and the working of the imagination, strengthens the intensity of these pleasurable sensations. If the conditions are favorable to the performance of the sexual act by means of which satisfaction is attained, the continually increasing impulse finds expression in action; in other circumstances, inhibitory perceptions intervene, sexual excitement diminishes, the activity of the centre for erection is inhibited, and the sexual act itself is prevented. In the case of civilized humanity the ready action of such perceptions for the inhibition of the sexual impulse is necessary and decisive. On the strength of the impulsive perceptions the constitution and various organic processes have an important influence; on the strength of the inhibitory perceptions, education and the cultivation of self-control are powerfully operative.
In addition to mental influences, all forms of local irritation of the sensory nerves of the female genital organs and adjacent parts, by internal processes or external friction, serve to increase the strength of the sexual impulse. Among internal processes which stimulate the erectile centre by centripetal impulses must be included, the stimulus of the enlarged graafian follicle, stasis in various vascular areas of the genital organs in consequence of a sedentary mode of life, abdominal plethora from excessive consumption of food and stimulating drinks, and habitual constipation. External friction may be in the form of intentional manipulation, but it may be due to certain bodily attitudes or to the arrangement of the clothing.
In normally constituted individuals, the sexual impulse is by no means constant in its intensity. Apart from the temporary indifference resulting from sexual gratification, and apart from the decline in the impulse that occurs after prolonged continence, ensuing after a certain reactionary intensity of desire has been happily overcome, the mode of life has a very great influence. The town-dweller, who is continually reminded of sexual matters, and continually solicited to sexual intercourse, is in any case more subject than the countryman to sexual excitement. A sedentary and sheltered mode of life, a chiefly animal diet, the free use of alcohol and of spices, and the like, have a stimulating action on the sexual life. In the female, the sexual impulse is stronger just after menstruation. In neuropathic women this increase of excitement may occur to a pathological degree. Not infrequently also in the climacteric period, women are subject to sexual excitement due to pruritus, especially in those neuropathically predisposed. Magnan reports the case of a lady who was subject to matutinal accesses of intense erethismus genitalis. The same author writes of a young lady who since puberty had been subject to continually increasing sexual impulse, which she gratified by masturbation. Gradually it came to pass that the sight of a good-looking man produced violent sexual excitement, and on these occasions, since she felt herself unable to answer for her own conduct, she used to lock herself up in her bedroom till the storm had passed away. Ultimately she surrendered herself to any available man in order to obtain rest from her torturing desires, but neither intercourse nor onanism gave her relief, so that she was finally sent to an asylum.
As regards pathological increase of the sexual impulse, hyperæsthesia sexualis, the constitution of the individual is, according to von Krafft-Ebing (Psychopathia Sexualis), of great importance. He writes: “With a neuropathic constitution, a pathological increase of sexual desire is often associated, and such individuals bear for the greater part of their life the heavy burden of this constitutionally anomalous sexual impulse. The intensity of the sexual impulse may be such as to amount to an organic compulsion, and the freedom of the will may thus be seriously imperilled. Non-satisfaction of this desire may induce a true sexual heat (like that of lower animals), or a mental state characterized by sensations of anxiety, in which the individual yields to the impulse, and his responsibility for his action is most questionable. Should the person so affected not give way to his desire, he runs the danger, by this enforced abstinence, of injuring his nervous system by the induction of neurasthenia, or of seriously aggravating neurasthenia that already exists.
“Excessive sexual desire may arise either from peripheral or from central causes. The former variety is less common. Such cases as do occur, may arise from pruritus of the genitals, from eczema, or from substances which by their remote local action stimulate sexual desire, such for instance as cantharides.
“Sexual excitement of central origin is common in those suffering from congenital neuropathic predisposition, in hysterical subjects, and in states of mental exaltation. In such cases, when the cerebral cortex, including the psychosexual centre, is in a state of hyperæsthesia (abnormal excitability of the imagination, facilitated association of ideas), not only optical and tactile sensations, but also auditory and olfactory impressions, will arouse lascivious perceptions.
“Sexual hyperæsthesia may be continuous, with exacerbations, or intermittent, and even periodic. In the last case, according to von Krafft-Ebing, it is either an independent cerebral neurosis, or else a partial manifestation of a general condition of mental excitement (mania, dementia paralytica, dementia senilis, etc.).”
Erotogenic zones, the stimulation of which leads to an increase in the intensity of the sexual impulse and of sexual sensibility, are in woman first of all and principally the clitoris, which indeed is said to be the only zone of this nature in the virgin state (an opinion held by von Krafft-Ebing and others, but certainly most improbable); next to this comes the whole of the external genitals, and especially the parts covered with hair; also the vagina by friction and inter coitum; finally the nipple and its areola when stimulated by titillation—an increase of the excitability of this region appears to result from suckling.