It has been remarked by Professor Wilhelm Ostwald that the problem of homosexuality is a problem left over to us by the Middle Ages, which for five hundred years dealt with inverts as it dealt with heretics and witches. To regard the matter thus is to emphasize its social and humanitarian interest rather than its biological and psychological significance. It is no doubt this human interest of the question of inversion, rather than its scientific importance, great as the latter is, which is mainly responsible for the remarkable activity with which the study of homosexuality has been carried on during recent years.