Germ TheoryFrom Reddit user theworldgotme:
The jump from the Miasma theory to modern Germ theory was fairly incredible. Great minds of the nineteenth century essentially created modern medicine from scratch.
Reddit user Tmg05:
In the mid 1800s, high maternal mortality rates for mothers giving birth at hospitals resulted in Vienna Hospital tasking Hungarian physician Ignaz Semmelweis with finding out why.
Semmelweis realized it was due to cross contamination and urged doctors to start washing their hands. At the time, there was such critical backlash from the medical community that Semmelweis slipped into depression and died from what appeared to be dementia.