Syphilis
Historic use of mercury

As a form of chemotherapy, elemental mercury had been used to treat skin diseases in Europe as early as 1363. As syphilis spread, preparations of mercury were among the first medicines used to combat it. Mercury is in fact highly anti-microbial: by the 16th century it was sometimes found to be sufficient to halt development of the disease when applied to ulcers as an inunction or when inhaled as a suffumigation. It was also treated by ingestion of mercury compounds. Once the disease had gained a strong foothold, however, the amounts and forms of mercury necessary to control its development exceeded the human body's ability to tolerate it, and the treatment became worse and more lethal than the disease. Nevertheless, medically directed mercury poisoning became widespread through the 17th, 18th, and 19th centuries in Europe, North America, and India. Mercury salts such as mercury (II) chloride were still in prominent medical use as late as 1916, and considered effective and worthwhile treatments.
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