The myth

One miraculous day, mould spores drifted through an open window in the laboratory of Alexander Fleming, and settled on a petri dish of bacteria. The bacteria died; Fleming had accidentally discovered antibiotics. ��

The “truth”

Divine intervention, or at least the redundancy of scientific method, is clearly implied in this story’s popularity. Fleming was searching for a so-called “magic bullet” against infection. In 1922 he sneezed on to a culture dish, and subsequently noticed that bacteria didn’t form in the spots of his mucus. He’d discovered lysozyme, a kind of natural antiseptic.

In 1928, Fleming returned to work from a fortnight’s holiday to discover that bacteria he’d been culturing had died in contact with a fast-growing mould. He identified this as a species of Penicillium and began to explore its properties, which were only fully realised later by other researchers from a related field.

The contaminant certainly didn’t float through the windows, which were fixed shut; more likely, it came from a mycology lab in the same building. Its discovery was not “luck” – it was research. Fleming kept his workspace in creative disorder deliberately to promote serendipity, which has always played a part in scientific advance.