John Macleod (physiologist)

John James Rickard Macleod (September 6, 1876 – March 16, 1935) was a Scottish physician and physiologist. He is best known for being awarded the Nobel Prize in Physiology or Medicine in 1923 for the discovery of insulin.

Macleod was born in Cluny, Scotland, and educated at Aberdeen Grammar School and the University of Aberdeen, where he graduated with honors in medicine in 1898. After postgraduate studies, he moved to the United States, teaching physiology at Western Reserve University in Cleveland, Ohio. In 1918, he became Professor of Physiology at the University of Toronto in Canada.

At the University of Toronto, Macleod directed research into carbohydrate metabolism, including investigations on diabetes. He provided laboratory space and equipment, and delegated the work to Frederick Banting and Charles Best to isolate the anti-diabetic internal secretion from the pancreas. James Collip joined the team later to purify the extract, making it suitable for human trials.

While Banting and Best are typically credited with the discovery of insulin, Macleod's role was critical in guiding, supporting, and providing resources to the research team. He also played a significant role in preparing the insulin extract for clinical use.

Although the Nobel Prize was awarded jointly to Banting and Macleod, Banting felt that Best should have been recognized. He subsequently shared his portion of the prize money with Best. Macleod shared his prize money with Collip.

Macleod returned to Scotland in 1928 as Regius Professor of Physiology at the University of Aberdeen, where he continued his research and teaching until his death in 1935. His research interests also included studies on asphyxia and anoxia, and he authored several books on physiology and medicine. His contributions significantly advanced our understanding of carbohydrate metabolism and the treatment of diabetes.