From the time of Hippocrates to that of Louis Pasteur, the medical profession relied on plausible but almost wholly mistaken ideas about the causes of and best treatments for infectious illness. Bleeding, purging, and mysterious nostrums remained staple remedies, and surgeons, often wearing filthy butcher's aprons, blithely spread infection from patient to patient. Then between 1879 and 1900 came the germ revolution. After two decades of scientific virtuosity, outstanding feats of intellectual courage, bitter personal rivalries, and a large dose of good fortune, doctors came to realize...