This inventor of penicillin was born at Lochfield near Darvel in Ayrshire, Scotland on 6 August, 1881. He attended Louden Moor School, Darvel School, and Kilmarnock Academy before moving to London where he attended the Polytechnic.

Following four years spent in a shipping office, he enrolled at St Mary's Medical School, London University.

On qualifying with distinction in 1906, he began work as a research assistant under Sir Almroth Wright, a pioneer in vaccine therapy, also of St Mary's.

He gained an MB, BS(London) with Gold Medal in 1908, and became a lecturer at St Mary's until 1914. Signing up for the war effort (1914) he obtained the position of captain in the Army Medical Corps, before returning to St Mary's in 1918.

By 1928, he was elected Professor of the School. He was elected Fellow of the Royal Society in 1943 and knighted in 1944. Then in 1948, was elected Emeritus Professor of Bacteriology, University of London.

It was in 1928 while working on the influenza virus, Fleming observed that mould had developed accidentally on a staphylococcus culture plate and that the mould had created a bacteria-free circle around itself. He was inspired to further experiment and he found that this mould culture prevented growth of staphylococci. He named the active substance penicillin.