Even when we have eliminated all these forms of auto-erotic activity, however refined, in which the subject takes a voluntary part, we have still left unexplored an important portion of the auto-erotic field, a portion which many people are alone inclined to consider normal: sexual orgasm during sleep. That under conditions of sexual abstinence in healthy individuals there must inevitably be some auto-erotic manifestations during waking life, a careful study of the facts compels us to believe. There can be no doubt, also, that, under the same conditions, the occurrence of the complete orgasm during sleep with, in men, seminal emissions, is altogether normal. Even Zeus himself, as Pausanias has recorded, was liable to such accidents: a statement which, at all events, shows that to the Greek mind there was nothing derogatory in such an occurrence.[231] The Jews, however, regarded it as an impurity,[232] and the same idea was transmitted to the Christian church and embodied in the word _pollutio_, by which the phenomenon was designated in ecclesiastical phraseology.[233] According to Billuart and other theologians, pollution in sleep is not sin, unless voluntarily caused; if, however, it begins in sleep, and is completed in the half-waking state, with a sense of pleasure, it is a venial sin. But it seems allowable to permit a nocturnal pollution to complete itself on awaking, if it occurs without intention; and St. Thomas even says "_Si pollutio placeat ut naturæ exoneratio vel alleviatio peccatum non creditur_."