Then in 1928 he made the observations which were eventually to make him famous and which are often claimed as the major discovery in medical science in the 20th-c. Fleming had left a culture dish of staphylococci uncovered, and by accident it became contaminated with an airborne mould. He noticed that the bacteria were killed in areas surrounding the mould, which he identified as Penicillium notatum. He cultured the mould in broth and confirmed that a chemical from it (which he named penicillin) was bactericidal and did not injure white blood cells (a pointer to its lack of toxicity). He saw it as a possibly useful local antiseptic. However, the chemical methods of the time were inadequate to allow concentrated penicillin to be obtained; it is easily destroyed and present only in traces in a culture broth. That success came through work in the Second World War by a team led by Florey, and Fleming had no real part in the later work and was cool in his attitude to it.
The widespread use of penicillin from the 1940s onwards made a vast change in the treatment of many infections; it also led to a successful search for other antibiotics, and it made Fleming a nearlegendary figure, partly because of a wartime need for national heroes. The legend portrayed him as lucky and diffident; both were exaggerations, since his discovery was a part of his systematic work and good observation and he fully enjoyed his retrospective fame.
See also the Chronology of major events in science.
David Millar, Ian Millar, John Millar, Margaret Millar 1996, 2002
