With opportunity for the natural satisfaction of the sexual instinct, every expression of it that does not correspond with the purpose of nature,—_i.e._, propagation,—must be regarded as perverse. The perverse sexual acts resulting from paræsthesia are of the greatest importance clinically, socially, and forensically; and, therefore, they must here receive careful consideration; all æsthetic and polite disgust must be overcome. Perversion of the sexual instinct, as will be seen from what follows, is not to be confounded with perversity in the sexual act; since the latter may be induced by conditions which are not psychopathology. The concrete perverse act, monstrous as it may be, is not decisive. In order to differentiate between disease (perversion) and vice (perversity), one must investigate the whole personality of the individual and the original impulse leading to the perverse act. Therein will be found the key of diagnosis (_v. infra_). Paræsthesia may occur in combination with hyperæsthesia. This association seems to be frequent clinically. Sexual acts are then confidently to be expected. The perverse direction of sexual activity may be toward sexual satisfaction with the opposite or the same sex. Thus two great groups of perversions of the sexual life may be distinguished. _1. Sexual Inclination toward Persons of the Opposite Sex, with Perverse Activity of the Instinct._ 1. _Association of Active Cruelty and Violence with Lust_—_Sadism._[40]—That lust and cruelty frequently occur together is a fact that has long been recognized and not infrequently observed. Writers of all kinds have called attention to this phenomenon.[41] The not infrequent cases where individuals of very excitable sexual natures bite or scratch the companion in intercourse fall within physiological limits.[42] The older authors have called attention to the relation between lust and cruelty. Blumröder (“Ueber Irresein,” Leipzig, 1836, p. 51) saw a man who had several wounds bitten into the pectoral muscle, which a woman, in great sexual excitement, had given him at the acme of lustful feeling during coitus. Blumröder (“Ueber Lust und Schmerz,” Friedreich’s _Magazin für Seelenkunde_, 1830, ii, 5) calls especial attention to the psychological connection between lust and murder. In relation to this, he especially refers to the Indian myths of Siva and Durga (Death and Lust); to human sacrifice with sensual mysteries; and to sexual instinct at puberty with a lustful impulse to suicide, with whipping, pinching, and pricking of the genitals, in the blind impulse to satisfy sexual desire. Lombroso (“Verzeni e Agnoletti,” Rome, 1874) also cites numerous examples of the occurrence of a desire to murder with greatly increased lust.