In 1896 the most comprehensive book so far written on the subject in England was published in French by Mr. André Raffalovich (in Lacassagne's _Bibliothèque de Criminologie_), _Uranisme et Unisexualité_. This book dealt chiefly with congenital inversion, publishing no new cases, but revealing a wide knowledge of the matter. Raffalovich put forward many just and sagacious reflections on the nature and treatment of inversion, and the attitude of society toward perverted sexuality. The historical portions of the book, which are of special interest, deal largely with the remarkable prevalence of inversion in England, neglected by previous investigators. Raffalovich, whose attitude is, on the whole, philosophical rather than scientific, regards congenital inversion as a large and inevitable factor in human life, but, taking the Catholic standpoint, he condemns all sexuality, either heterosexual or homosexual, and urges the invert to restrain the physical manifestations of his instinct and to aim at an ideal of chastity. On the whole, it may be said that the book is the work of a thinker who has reached his own results in his own way, and those results bear an imprint of originality and freedom from tradition. In recent years no one has so largely contributed to place our knowledge of sexual inversion on a broad and accurate basis as Dr. Magnus Hirschfeld of Berlin, who possesses an unequalled acquaintance with the phenomena of homosexuality in all their aspects. He has studied the matter exhaustively in Germany and to some extent in other countries also; he has received the histories of a thousand inverts; he is said to have met over ten thousand homosexual persons. As editor of the _Jahrbuch für sexuelle Zwischenstufen_, which he established in 1899, and author of various important monographs--more especially on transitional psychic and physical stages between masculinity and femininity--Hirschfeld had already contributed greatly to the progress of investigation in this field before the appearance in 1914 of his great work, _Die Homosexualität des Mannes und des Weibes_. This is not only the largest but the most precise, detailed, and comprehensive--even the most condensed--work which has yet appeared on the subject. It is, indeed, an encyclopedia of homosexuality. For such a task Hirschfeld had been prepared by many years of strenuous activity as a physician, an investigator, a medico-legal expert before the courts, and his position as president of the _Wissenschaftlich-humanitären Komitee_ which is concerned with the defense of the interests of the homosexual in Germany. In Hirschfeld's book the pathological conception of inversion has entirely disappeared; homosexuality is regarded as primarily a biological phenomenon of universal extension, and secondarily as a social phenomenon of serious importance. There is no attempt to invent new theories; the main value of Hirschfeld's work lies, indeed, in