A landmark experiment done in 1952 which showed that DNA is the hereditary material. The experiment, done by Martha Hershey and Alfred Chase, involved allowing a bacteriophage which contained DNA labeled with 32P (an isotope of phosphorus) and a protein labeled with 35S (an isotope of sulfur) to attach to some bacteria. When the bacteriophages were later removed, they found that it was the 32P (and thus the DNA) that had entered the bacterial cells rather than the 35S (indicating the protein).