Avery, Oswald T. (Theodore)(1877–1955) bacteriologist; born in Halifax, Nova Scotia, Canada. He came to New York City (NYC) in 1887 when his clergyman father began missionary work in the Bowery. He practiced medicine in NYC (1904–07), became a bacteriologist at Hoagland Laboratory, Brooklyn (1907–13), then joined the Rockefeller Institute (1913–48). His career-long studies of the pneumococcus bacterium included the immunological classification of this organism (1917). His discovery that this bacterium's immunospecific substances were polysaccharide capsular type-specific antigens was a breakthrough in the developing science of immunochemistry. His subsequent pneumococcal research, summarized in 1944, indicated that the agent that transforms nonvirulent strains to virulent was DNA, thus demonstrating that DNA is the chemical basis of heredity.