In 1952, American geneticist and bacteriologist Alfred D. Hershey (1908–1997) and American geneticist Martha C. Chase (also known as Martha Epstein; 1927–2003) further carried out experiments to prove that DNA was the true carrier of genetic material—not protein. By tagging certain bacteriophages (a virus that infects and replicates within a bacteria) with radioactive isotopes, they were able to follow the effects, noting when certain radioactive elements entered or did not enter the bacteria. This showed that protein was not infecting the bacteria, but DNA from the virus’s nucleus.