Alexander Fleming was a biologist and pharmacologist by trade, but his most famous discovery was accidental and changed medicine forever. Which substance did he identify and isolate?

Alexander Fleming discovered penicillin after carelessly leaving a culture plate out in his lab before going on holiday. He came back to find that mold had grown - the mold that would end up being the world's first true antibiotic.

Asked by Kiera Hart · Last updated 4 years ago · 8.8M views