With the recognition that homosexuality in youth may be due to an as yet undifferentiated sexual impulse, homosexuality in mature age to a retarded development on a congenital basis, and homosexuality in sold age to a return to the attitude of youth, the area of spurious or "pseudo" homosexuality seems to me to be very much restricted. Most, perhaps all, authorities still accept the reality of this spurious homosexuality in heterosexual persons. But they enter into no details concerning it, and they bring forward no minutely observed cases in which it occurred. Hirschfeld, in discussing the diagnosis of homosexuality and seeking to distinguish genuine from spurious inverts,[134] enumerates three classes of the latter: (1) those who practise homosexuality for purposes of gain, more especially male prostitutes and blackmailers; (2) persons who, from motives of pity, good nature, friendship, etc., allow themselves to be the objects of homosexual desire; (3) normal persons who, when excluded from the society of the opposite sex, as in schools, barracks, on board ship, or in prison, have sexual relations with persons of their own sex. Now Hirschfeld clearly realizes that the mere sexual act is no proof of the direction of the sexual impulse; it may be rendered possible by mechanical irritation (as by the stimulation of a full bladder) and in women without any stimulation at all; such cases can have little psychological significance. Moreover, he seems to admit that some subdivisions of his first class are true inverts. He further mentions that some 75 per cent. of the individuals included in these classes are between 15 and 25 years of age, that is to say, that they have scarcely emerged from the period when we have reason to believe that, in a large number of individuals at all events, the sexual impulse is not yet definitely differentiated; so that neither its homosexual nor its heterosexual tendencies can properly be regarded as spurious.