One of history’s greatest medical discoveries happened by accident.
What and who?

Question

Accepted Answer

Penicillin — Alexander Fleming, 1928. He returned from holiday to find mould killing bacteria on a forgotten petri dish. — The mould was Penicillium notatum. Mass production took another 15 years. Fleming warned repeatedly about overuse; nobody listened.

One of history’s greatest medical discoveries happened by accident. What and who?