William Jenner, British physician, 1873.

UNITED KINGDOM - JUNE 28: Chromolithographed caricature by Spy, subtitled �Physic�. Sir William Jenner (1815-1898) established the difference between typhus and typhoid fevers in 1851. Typhoid fever is contracted from food or water contaminated by Salmonella typhi; typhus is spread by lice. Doctors had previously diagnosed both conditions as �continued fever�. Jenner�s discovery had important implications for the treatment of both diseases. He was a professor at University College, London, from 1848 to 1879, became physician-in-ordinary to Queen Victoria in 1862, and to the Prince of Wales the following year. From the magazine �Vanity Fair�. (Photo by SSPL/Getty Images)