The Scottish bacteriologist Sir Alexander Fleming (1881-1955) is best known for his discovery of penicillin, which has been hailed as "the greatest contribution medical science ever made to humanity."

Alexander Fleming was born on Aug. 6, 1881, at Lochfield, Ayrshire, one of the eight children of Hugh Fleming, a farmer. Nature, which he considered his first and best teacher, developed his power of observation and taught him to apply his powers of reasoning to what he observed and to act in accordance with his observations. Like many Scots who were forced to leave their native land for better career opportunities, Fleming, at the age of 13, left for London, where he lived with his brothers. He attended lectures at the Polytechnic School and worked for 4 years in a shipping office. In 1901 an uncle left Fleming a legacy that enabled him to study medicine, and he entered St. Mary's Hospital Medical School...