In 1928, while studying influenza, Fleming noticed that mould had developed accidentally on a set of culture dishes being used to grow the staphylococci germ. The mould had created a bacteria-free circle around itself. Fleming experimented further and named the active substance penicillin. It was two other scientists however, Australian Howard Florey and Ernst Chain, a refugee from Nazi Germany, who developed penicillin further so that it could be produced as a drug. At first supplies of penicillin were very limited, but by the 1940s it was being mass-produced by the American drugs industry.