Alfred Day Hershey (1908-1997) was an American Nobel Prize-winning bacteriologist and geneticist. He began performing experiments with bacteriophages with Italian-American Salvador Luria and German Max Delbruck in 1940, and observed that when two different strains of bacteriophage have infected the same bacteria, the two viruses may exchange genetic information. All were awards the Nobel Prize in Physiology or Medicine in 1969 for their discovery on the replication of viruses and their genetic structure.