3: Germs in Surgery

Laugh or cry (take your pick), but up until the late 19th century, doctors didn't really see the need to wash their hands before picking up a scalpel.

The result? A lot of gangrene. Most early-19th century doctors tended to attribute contagion to "bad air" and blamed disease on imbalances of the "four humors" (that's blood, phlegm, yellow bile and black bile, in case you weren't familiar).

"Germ theory" (the revolutionary idea that germs cause disease) had been around for a while, but it wasn't till Louis Pasteur got behind it in the 1860s that people started listening. It took a while, but doctors like Joseph Lister eventually connected the dots and realized that hospitals and doctors had the potential to pass on life-threatening germs to patients.

Lister went on to pioneer the idea of actually cleaning wounds and using disinfectant. Remember him next time you reach for the Purell.

For more medical disasters, check out our Top 10 Cures That Didn't Work
Ever wonder how long a germ can live? The folks at How Stuff Works know.