Supplemented by "The Restoration", a biography of Ulrichs by Magnus Hirschfeld from a chapter in his The Homosexuality of Men and Women. Hirschfeld reported his visit to Persichetti in 1909.
Also, by Karl Heinrich Ulrichs, "Vindex" (The Vindicator, 1864) and "Critical Arrows" (1879), the first and last books collectively titled Research on The Riddle of Man-Manly Love.
The pieces complement each other. Persichetti and Hirschfeld talk about Ulrichs' life and work. The first and last of Ulrichs 12 books, "Vindex" and "Critical Arrows" illuminate Ulrichs' first attempt at literary activism, and his final activist work sum up his previous 11 books.