Van Leeuwenhoek was the first to observe microscopic organisms, using simple single-lensed microscopes of his own design.[1] 1729–1799 Lazzaro Spallanzani Italian Proved that bacteria did not arise due to spontaneous generation by developing a sealed, sterile broth medium.[2][3] 1749–1823 Edward Jenner English Developed vaccination techniques against smallpox.[2] 1818–1865 Ignaz Semmelweis Hungarian Demonstrated that doctors washing their hands with chlorine solutoin significantly reduced mortality of women giving birth in the hospital setting.[4] 1853–1938 Hans Christian Gram Danish Developed the Gram stain used to identify and classify bacteria.[2] 1845–1922 Charles Lavaran French 1907 Nobel Prize in Physiology or Medicine for discovering the causative agents of malaria and trypanosomiasis.[2] 1827–1912 Joseph Lister English Introduced sterilisation techniques to surgery.[2][5] 1822–1895 Louis Pasteur French Seminal discoveries in vaccination, food safety, and microbial fermentatoion.