The Mold on the Petri Dish

There was a stack of petri dishes on a bench in a London laboratory, and one of them had gone wrong. Alexander Fleming had left for a holiday in August of nineteen twenty-eight, and when he returned in September the lab was exactly as messy as he had left it. He was known for not being tidy. Dishes piled up. He would look at the failed ones before washing them — a habit, a small ritual of forensic curiosity — and on this particular morning, one dish stopped him. A mold had grown on it. Colonies of staphylococcus bacteria surrounded the mold on all sides. But directly around the mold, for a visible radius, the bacterial colonies had been destroyed. He could have washed it. That was the most natural thing to do with a contaminated plate. The mold was Penicillium notatum, likely drifted up from a mycology lab on the floor below, an accident of the building's air currents and open windows.