Colin Munro MacLeod (1909-1972), Canadian-US geneticist. MacLeod was born and educated in Canada, later working in the USA. He is most famous for the part he played in the research known as the Avery-MacLeod-McCarty experiment in the early 1940s. This work demonstrated that DNA (deoxyribonucleic acid) was the transforming principle in the bacterial extracts that could cause benign bacterial strains to turn into the more virulent strains. Although MacLeod and his fellow researchers did not receive a Nobel Prize, this is considered one of the fundamental discoveries in genetics. Signed photograph, circa 1940.