For centuries people with maladies of any kind could look forward to a good dose of mercury, as the medical establishment had pretty much concluded that shiny things were good for people. This shipwreck made them think again.
In 1810, a Spanish ship got caught in a storm near Cadiz. Fortunately for the sailors onboard, a Brtish naval ship was nearby. The HMS Triumph sent out its longboats to help the vessel -- but also to help itself to the cargo of the ship. Unfortunately for the sailors on the Triumph, the Spanish ship was headed for South Africa, and it contained vast stores of mercury. Mercury is used to extract gold from gold mines -- some old mines still have high levels of mercury and are a danger to hikers and explorers who venture inside.
The mercury had been held in leather bags. In the Spanish vessel, those bags were stored in closed-off areas; on the Triumph, they were stored in the sailor's living quarters. It wasn't long before people started feeling ill effects. Sailors started salivating constantly and copiously -- a sign of mercury poisoning. Their gums became inflamed. They'd lose consciousness. While the men only sickened, every animal on the ship, including a canary, died. Even the cockroaches died. Eventually, the ship had to be purged of all the mercury that it couldn't store away from people.
This was odd. While doctors knew that too much mercury could do harm (as could too much of any other medicine), it never occurred to anyone that just being near mercury was dangerous. At first, experts who heard of the case thought that the problem was a strange reaction between the mercury and the leather. It was another 13 years before a Dr William Burnett read about an experiment done by Michael Faraday, during which Faraday found that mercury emitted vapour. Perhaps this vapour was not so good for people, Burnett posited.
It would be at least another 50 years before the scientific establishment considered that mercury in general wasn't good for people. Sometimes it takes a while to change a set idea. But the incident of the HMS Triumph at least got the ball rolling.