John James Rickard Macleod was a Scottish biochemist and physiologist. An accomplished researcher in carbohydrate metabolism in his own right, his ground-breaking collaborative work with Frederick Banting ultimately led to a shared Nobel Prize in Physiology or Medicine for the discovery of insulin. This accomplishment saved the lives of countless people living with diabetes.

Born on September 6th, 1876 in Clunie, Perthshire, MacLeod was the son of clergyman Rev. Robert Macleod. Macleod’s first official encounter with the scientific world came when he enrolled to study medicine at the University of Aberdeen where he subsequently obtained his PhD in 1898. He was then awarded a fellowship to study biochemistry at the University of Leipzig in Germany. In 1903, Macleod emigrated to the U.S. and was appointed Professor of Physiology at the Western Reserve University in Cleaveland, Ohio. He eventually made his way to Canada as a sessional lecturer of physiology at McGill University in Montreal and was later elected Professor of Physiology and Associate Dean of Medicine at the University of Toronto. In Toronto, he studied a wide array of medical topics, including Mycobacterium tuberculosis, electroshock and creatinine metabolism, as well as brain-blood circulation.

It was not until 1905 that he became interested in carbohydrate metabolism, publishing approximately 37 papers on the topic and 12 papers on glycosuria, the excretion of glucose into urine commonly seen in patients living with diabetes. In 1920, Frederick Banting, a medical doctor with a deep interest in diabetes, approached Macleod with the idea of treating the condition with a pancreas secretion he had hypothesized would regulate glucose levels. Macleod introduced Banting to one of his own students, Charles Best, and the two conducted experiments to isolate pancreatic extracts from dogs during the summer Macleod was on holiday in Scotland. Banting and Best subsequently isolated a pancreatic secretion from one dog that successfully lowered blood sugar levels in another dog living with diabetes having gone through surgical removal of the pancreas. This secretion came to be known as insulin.

Knowing the importance of experimental trials and repetitions, Macleod consequently dedicated his whole laboratory to insulin research and brought James Collip, a biochemist, to purify the extract and prepare insulin in a more pure, stable form. In January 1922, the team performed the first successful clinical trial on a 14-year-old patient living with diabetes named Leonard Thompson. This drew huge public interest and was viewed almost as a miracle. In February of the same year, the discovery was made public, patented and sold to the University of Toronto for one dollar, while the financial proceeds of the patent were given to the British Medical Research Council for the Encouragement of Research. In 1923, Banting and Macleod received the Nobel Prize in Physiology or Medicine for their discovery of insulin. Banting subsequently shared his prize money with Best whilst Macleod shared his with Collip as a way of demonstrating the joint effort that went into this discovery.

For all of his accomplishments in physiology, Macleod was elected a Fellow of the Royal Society of Canada in 1919, the Royal Society in London in 1923, and the Royal College of Physicians in London in 1930. Macleod returned to Aberdeen University in his later years and became the Dean of the University of Aberdeen Medical Faculty. In his spare time, he enjoyed golfing, painting, and motorcycling. Macleod remained active while battling arthritis towards his later years. He died on March 16th, 1935 in Aberdeen, Scotland.

— Written by Nargol Ghazian