That cruelty and sexual impulse are most intimately connected is beyond doubt taught by the history of civilization, but in the explanation of this connection no one has gone beyond the accentuation of the aggressive factors of the libido. The aggression which is mixed with the sexual impulse is according to some authors a remnant of cannibalistic lust, a participation on the part of the domination apparatus (Bemächtigungsapparatus), which served also for the gratification of the great wants of the other, ontogenetically the older impulse.[21] It has also been claimed that every pain contains in itself the possibility of a pleasurable sensation. Let us be satisfied with the impression that the explanation of this perversion is by no means satisfactory and that it is possible that many psychic efforts unite themselves into one effect. The most striking peculiarity of this perversion lies in the fact that its active and passive forms are regularly encountered together in the same person. He who experiences pleasure by causing pain to others in sexual relations is also able to experience the pain emanating from sexual relations as pleasure. A sadist is simultaneously a masochist, though either the active or the passive side of the perversion may be more strongly developed and thus represent his preponderate sexual activity.[22] We thus see that certain perverted propensities regularly appear in _contrasting pairs_, a thing which, in view of the material to be produced later, must claim great theoretical value. It is furthermore clear that the existence of the contrast, sadism and masochism, can not readily be attributed to the mixture of aggression. On the other hand one may be tempted to connect such simultaneously existing contrasts with the united contrast of male and female in bisexuality, the significance of which is reduced in psychoanalysis to the contrast of activity and passivity. 3. GENERAL STATEMENTS APPLICABLE TO ALL PERVERSIONS