South Africa's epidemic of venereal syphilis in the 1930s and 40s

Mercury for the treatment of syphilis was applied topically in the form of ammoniated or salicylated mercury ointments.
Mercury for the treatment of syphilis was applied topically in the form of ammoniated or salicylated mercury ointments. 
The photograph of patients applying "blue ointment" to each other was taken at Rietfontein Hospital, Johannesburg, circa 1911. Image source: Adler C. Rietfontein Hospital. Adler Mus Bull. 1985; 11(1):15-20