The most common treatment of syphilis - from the first outbreaks in the 19th century to the early years of the 20th century was mercury given in various forms - pills, ointments, steam baths or even enemas.
Mercury was the remedy of choice for syphilis in Protestant Europe. Paracelsus (1493-1541) formulated mercury as an ointment because he recognised the toxicity and risk of poisoning when administrating mercury as an elixir. Mercury was already being used in Western Europe to treat skin diseases [...]
The mercury, or ‘blue mass’, pills shown in the print were popular from the 17th to 19th century and used mercury in its elemental form or compound form, usually mercurous chloride (also known as calomel). The first effective treatment for syphilis, Salvarsan, was only found in 1910 — five years after the causative bacterium was identified by Fritz Schaudinn (a zoologist) and Erich Hoffmann (a dermatologist).
Mercury is of course highly toxic, so the "cure" was quite often worse that the disease itself. But was the mercury completely inefficient and the whole therapy akin to drinking holy water or having sex with virgin, or was there a shade of chance, that it would actually work and cure the disease?