Mercury is pretty neat stuff. The shiny silvery liquid has fascinated humans for millennia (there's evidence people used it as early as 1500 BC) and will undoubtedly continue to fascinate far into the future when shape-shifting Robert Patrick clones overtake the planet. How could something so awesome not be good for you?
That was the thinking for centuries, when Mercury was used to treat pretty much anything and everything. Scraped your knee? Just rub a little mercury on it. Having some problems with regularity? Forget fiber, time to get some mercury up in there! If you lived more than 100 years ago, you simply weren't considered healthy if you weren't leaking silver from at least one orifice.
Mercury, as we now know, is toxic as hell. Symptoms of mercury poisoning include chest pains, heart and lung problems, coughing, tremors, violent muscle spasms, psychotic reactions, delirium, hallucinations, suicidal tendencies, restless spleen syndrome, testicular twisting and anal implosion. OK, we just made the last few up, but they barely looked out of place on that horror show list of symptoms did they?
It's a testament to just how cool a substance Mercury is that people kept trying to cure shit with it for 1,000 years after everybody who ingested it dropped dead. "Yes my Lord, I'm afraid another member of your court has perished. The autopsy showed it was Silver Liver Syndrome. Not even the gallons of wicked-awesome Mercury we fed him could bring him back to health."
There was a silver lining, though, as it helped to fight the spread of STDs. Mercury was used as a cure for syphilis and to its credit, the "cure" usually resulted in one less person with syphilis in the world. It's generally believed Mozart was poisoned by mercury-based syphilis cures, which contradicts the film Amadeus in which he was killed by writing too much music somehow.