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| 1882 |
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| Robert Koch (1843–1910) described the etiology of the tubercle bacillus. This discovery led him (1884) to state Koch's postulates, a method of isolating microorganisms and proving that they are specific causes, not merely concomitants, of disease. | 1 |
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| 1883 |
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| Ilia I. Mechnikov (1845–1916) described the action of phagocytic cells in transparent starfish larvae. His discovery led to a general explanation of local inflammation. | 2 |
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| 1883 |
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| Edouard van Beneden (1845–1901) described how the chromosomes are derived in equal numbers from the conjugating germ cells. This led to the discovery of reduction division in the formation of the gametes. | 3 |
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| 1887 |
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| Svante A. Arrhenius (1859–1927) announced his theory of electrolytic dissociation, according to which most of the molecules of an electrolyte are immediately dissociated into two ions when dissolved. | 4 |
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| 1888–91 |
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| Wilhelm Roux (1850–1924) destroyed half of the two-cell stage of a frog's embryo (1888). The remaining cell developed into half an embryo. In 1891 Hans Driesch (1867–1941), working with sea urchin embryos, got results contradictory to Roux's. This drew attention to the relative roles of the internal and external environments on the development of cells. | 5 |
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| 1890 |
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| Emil von Behring (1854–1917) and Shíbasaburo Kitasato (1856–1931) demonstrated that the serum of immunized rabbits neutralized the toxin of tetanus. This discovery opened the possibility that disease could be prevented through the stimulation of specific antibody production. | 6 |
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| 1892 |
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| August Weismann (1834–1914) described in Das Keimplasma his theory of the continuity of the germ plasm and a scheme for the unfolding of a particulate hereditary pattern in embryogenesis. | 7 |
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| 1893 |
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| Theobald Smith (1859–1934), in “Investigations into the Nature, Causation and Prevention of Southern Cattle Fever,” demonstrated that parasites could act as vectors of disease. | 8 |
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| 1895 |
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| Wilhelm K. Röntgen (1845–1923) discovered x-rays and immediately realized that his discovery had a practical application in medicine. | 9 |
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| 1897 |
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| Eduard Buchner (1860–1917) discovered that zymase, a cell-free yeast extract, caused fermentation, thus resolving a long-standing controversy over “vital” and “inorganic” ferments. | 10 |
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| 1900 |
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| Hugo de Vries (1848–1935), Carl Correns (1864–1933), and Erich Tschermak (1871–1962) independently rediscovered the 1865 work of Gregor Mendel while searching the literature to confirm their own experimental results. | 11 |
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| 1903 |
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| Walter S. Sutton (1876–1916) pointed out that the Mendelian ratios could be explained by the cytological behavior of the chromosomes. | 12 |
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