Scottish bacteriologist Alexander Fleming is best known for his 1928 discovery of the bacteria-fighting antibiotic penicillin, widely regarded as one of the greatest medical discoveries of the twentieth century. Before penicillin, the few drugs that were available to fight bacterial disease were inefficient and highly toxic to the human body. Fleming's discovery won him the 1945 Nobel Prize for medicine jointly with Ernst Chain and Baron Howard W. Florey.

Fleming's early life was rustic. He was born in a farmhouse in Lochfield, Ayrshire, Scotland, the third of four children by Hugh Fleming, a farmer, and his second wife, Grace (Morton) Fleming. He had two stepbrothers and two stepsisters from Hugh Fleming's first marriage. His father died when Fleming was seven and his mother and oldest stepbrother, Thomas, were left to manage the farm.

The natural intelligence Fleming possessed became evident even though his early education was basic. He first attended...