Seventy-five years ago, the Nazis ransacked the offices of German sex-researcher and gay-rights activist Magnus Hirschfeld, seizing hundreds of books that were burned in a towering pyre four days later. To mark the day Tuesday, Berlin dedicated a stretch of the Spree river to Hirschfeld, while the city's Charite hospital opened a new exhibition of his work called "Sex Burns." The tributes to Hirschfeld are "a clear acknowledgment for gays that a persecution has taken place and that reparation is necessary," said Alexander Zinn, head of Germany's Lesbian and Gay Association, at the dedication ceremony. "That is a first step in the right direction" Nazi Germany declared homosexuality an aberration that threatened the German race and convicted some 50,000 homosexuals as criminals. An estimated 10,000 to 15,000 homosexuals, mostly men, were deported to concentration camps, where few survived.