He was also a founder member of the British Society for Immunology alongside John H. Humphrey, Bob White, and Robin Coombs. Mitchison discovered the transference of transplantation immunity by sensitised cells, thereby providing evidence relating transplantation immunity to hypersensitivity reactions of the 'delayed' type. He devised a method for revealing mixtures of cells of different genotypes in vivo and used it to be equal first in demonstrating that the 'radiation recovery factor' is a graft of living cells and not a humoral agent. He carried out the most exact quantitative analysis of tolerance hitherto attempted in a cellular system and proved that persistence of tolerance depends on persistence of antigen. Mitchison was elected a Fellow of the Royal Society (FRS) in 1967. He is also a foreign member of the National Academy of Sciences, USA. He holds an Honorary Doctorate from the Weizmann Institute and won the Novartis Prize in Basic Immunology. In honor of its Founding Director, the Deutsches Rheuma-Forschungszentrum Berlin (DRFZ), a Leibniz Institute, annually awards the Avrion Mitchison Prize to young scientists contributing significantly to understanding and treating rheumatic diseases. Donated by the Ernst Schering Foundation until 2018, the prize is now awarded by the DRFZ. The prize money is 3.000 Euros. Antietam Creek  Antietam Creek is a  tributary of the Potomac River located in south central Pennsylvania and western Maryland in the United States, a region known as the Hagerstown Valley. The creek became famous as a focal point of the Battle of Antietam during the American Civil War. The creek is formed in Franklin County, Pennsylvania, at the confluence of the West and East Branches of Antietam Creek, about south of Waynesboro, Pennsylvania. Welty's Mill Bridge crosses the East Branch of Little Antietam at Washington Township in Franklin County, Pennsylvania. The stream runs for about upon its entering Washington County, Maryland. The course proceeds southward in a meandering pattern, and the creek empties into the Potomac south of Sharpsburg about upstream of Washington. The watershed area is and includes parts of Franklin County (106 mi2) and Washington County (185 mi2). Major tributaries in Pennsylvania include the East and West Branches, Red Run and Falls Creek. Major tributaries in Maryland include Little Antietam Creek, Beaver Creek, and Marsh Run.