Viruses In 1898 Martinus Beijerinck (1851–1931) discovered the tobacco mosaic virus, and first described viruses as being distinct from other microbes. These entities, which straddle the realms of living and nonliving chemistry, are composed of nucleic acids often coated with protein molecules. When Wendell Meredith Stanley (1904–1971) crystallized the same virus in 1935, he helped push further toward the view that the processes of life were in fact chemical and physical processes, governed by the same laws that hold sway in the nonliving world. Alfred Day Hershey (1908–1997) and Martha Cowles Chase (1930– ) used bacteriophages (viruses that infect bacteria) to help establish that DNA is the carrier of genetic information. Meanwhile, viral diseases like AIDS have posed a challenge to medicine, as drugs like antibiotics do not harm viruses. The development of polio vaccines by Jonas Salk (1914–1995) and Albert Bruce Sabin (1906–1993) in the 1950s were an important victory over a viral disease.