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.