https://digital.katalog.queersearch.org/s/katalog/item/43550, “Vita Sexualis: Karl Ulrichs and the Origins of Sexual Science”, https://digital.katalog.queersearch.org/s/katalog/item/47928, QueerSearch, accessed 28. April 2025, https://digital.katalog.queersearch.org/s/katalog/item/26405