Scottish scientist Alexander Fleming's desk was often littered with small glass dishes filled with bacteria cultures scraped from boils, abscesses, and infections. Fleming allowed the cultures to sit around for weeks, hoping something interesting would turn up.
One day, he decided to clean the bacteria-filled dishes and dumped them into a tub of disinfectant. He soon noticed a dish in the tub, which was still above the surface of the water and cleaning agent. As he did, Fleming suddenly saw a dab of fungus on one side of the dish, which had killed the bacteria. The fungus turned out to be a rare strain of penicillium that had drifted onto the dish from an open window.
Fleming began testing the fungus and found that it killed deadly bacteria, yet was harmless to human tissue. However, he was unable to produce it in any significant quantity and didn’t believe it would be effective in treating disease, but he wrote up the findings in a paper he presented to the scientific community. A decade later, another team of scientists followed up on his lead. Using more sophisticated techniques, they were able to successfully produce one of the most life-saving drugs in modern medicine.