Before Louis Pasteur (in France) and Robert Koch (in Germany) came along with their germ theories of disease, people thought that infection was caused by various kinds of “bad air.” The new theories (introduced around 1870) proposed that infection was caused by tiny invisible living organisms (“germs”). To many this seemed hard to believe (“Tiny invisible invaders in my body? Right. And my granny's the Queen of England.”) Even when the theory was accepted, it wasn't clear how it related to surgical practices. Over thirty years, surgeons gradually figured out that the first step in reducing the inflammation, pus, rotting flesh, and death after a surgery was making sure the surgical area was clean and germ-free.