[105] Ulrichs, in his _Argonauticus_, in 1869, estimated the number as only 25,000, but admitted that this was probably a decided underestimate. Bloch (_Die Prostitution_, Bd. i, p. 792) has found reason to believe that in Cologne in the fifteenth century the percentage was nearly as high as Hirschfeld finds it today. A few years earlier Bloch had believed (_Beiträge_, part i, p. 215, 1902) that Hirschfeld's estimate of 2 per cent, was "sheer nonsense." [106] Hirschfeld mentions the case of two men, artists, one of them married, who were intimate friends for a great many years before each discovered that the other was an invert. [107] See articles by Numa Praetorius and Fernan, maintaining that homosexuality is at least as frequent in France (_Sexual-Probleme_, March and December, 1909). [108] Dr. Laupts, _L'Homosexualité_, 1910, pp. 413, 420. [109] Näcke, _Zeitschrift für Sexualwissenschaft_, 1908, Heft 6. [110] It is a fact significant of the French attitude toward homosexuality that the psychologist, Dr. Saint-Paul, when writing a book on this subject, though in a completely normal and correct manner, thought it desirable to adopt a pseudonym. [111] A well-informed series of papers dealing with English homosexuality generally, and especially with London (L. Pavia, "Die männliche Homosexualität in England," _Vierteljahrsberichte des wissenschaftlich-humanitären Komitees_, 1909-1911) will be found instructive even by those who are familiar with London. And see also Hirschfeld, _Die Homosexualität_, ch. xxvi. Much information of historical nature concerning homosexuality in England will be found in Eugen Dühren (Iwan Bloch), _Das Geschlechtsleben in England_. [112] This: is doubtless the reason why so many English inverts establish themselves outside England. Paris, Florence, Nice, Naples, Cairo, and other places, are said to swarm with homosexual Englishmen. CHAPTER II. THE STUDY OF SEXUAL INVERSION. Westphal--Hössli--Casper--Ulrichs--Krafft-Ebing--Moll--Féré--Kiernan-- Lydston--Raffalovich--Edward Carpenter--Hirschfeld.