(January 28, 1909 - February 11, 1972) A Canadian-American geneticist. He received his MD from McGill University in 1932, at the age of 23. Working with Oswald Avery and Maclyn McCarty, MacLeod showed that changes in the form or function of bacteria are caused by changes in DNA. The Avery-McCarty-MacLeod experiment was vital in the discovery that genetic material is contained in DNA, not in protein. Later in life, MacLeod became involved in health issues related to the Second World War, such as the microbial diseases typhus fever, malaria, and pneumonia, which posed serious threats to military personnel.