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 fuer 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 Homosexualitaet 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-humanitaeren 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.