To more colorful colleagues, the bristle-haired Scottish microbe hunter working in a cluttered laboratory at London's St. Mary's Hospital seemed downright dull. But he was nothing if not dogged. He was 47 years old, and he had spent 20 years trying to find something to kill the microbes that cause infections in man, especially in wounds. To no avail; he found a substance in human tears that killed some germs, but not the important ones.
It seemed just another minor setback when, on a September morning in 1928, Dr. Alexander Fleming looked at a little glass dish in which he had been...