James Macleod, the Scottish physiologist who is most known for his work on carbohydrate metabolism and insulin, was born on September 6, 1876 in Cluny, Scotland. He was the son of Reverend Robert Macleod. After his family moved to Aberdeen he attended Aberdeen Grammar School and then Marischal College of the University of Aberdeen to study medicine. In 1898 he obtained his medical degree with honors and was awarded the Anderson Traveling Fellowship. That year he published his first paper which was on the phosphorus content of muscle.

Macleod worked for a year at the Institute for Physiology at the University of Leipzig, Germany. The following year he was made demonstrator of Physiology at the London Hospital Medical School, and in 1902 was given the position of Lecturer in Biochemistry at the same school. That same year he was granted the McKinnon Research Studentship of the Royal Society until 1903 when appointed Professor of Physiology at the Western Reserve University at Cleveland, Ohio. In 1905 Macleod first became interested in carbohydrate metabolism especially in patients with the disease diabetes. He published thirty-seven papers on carbohydrate metabolism and an additional twelve papers on the experimentally produced glycosuria. He published a textbook on diabetes mellitus, the most common form of diabetes, which is the result of the body's failure to process the sugar glucose. When glucose can not be correctly stored and used, the level of glucose with the bloodstream rise, which cause serious complications. Diabetes mellitus was fatal during this time period.

During the winter session of 1916, Macleod was Professor of Physiology at McGill University, Montreal. In 1918 he was elected Professor of Physiology at the University of Toronto, Canada along with Director of the Physiological Laboratory and Associate Dean of the Faculty of Medicine. It was that this university that he did his work with insulin. Macleod and his research team found that the pancreas secretes insulin, which regulates the amount of glucose in the body's cells. Research revealed diabetes mellitus to be a failure of the pancreas to produce insulin. Frederick Banting, a Canadian surgeon came to Macleod in 1921 and asked for help in isolating insulin. He gave Banting laboratory access, dogs for experiment subject and medical student Charles Best as an assistant. Banting and Best performed a series of experiments, surgically changing the dog's pancreas. They extracted the insulin producing cells and then removed the insulin from these cells. They injected the insulin into the dog that was now artificially made diabetic. Observations showed that the injections controlled glucose levels in the dogs. Macleod and Canadian biochemist James Bertram Collip worked with Banting and Best to refine methods of removing and purifying insulin. In 1922, Banting and Best injected their insulin into a fourteen year old diabetic boy, which successfully treated his condition. Macleod publicly announced their discovery in February of 1922 and the patent for manufacturing of the pancreatic extract was approved. All financial proceeds of the patent went to the British Medical Research Council and the discoverers were given no payment. Banting and Macleod were jointly awarded the 1923 Nobel Prize for physiology or medicine. They both shared the prize money with Best and Collip.

Macleod was appointed Regius Professor of Physiology at the University of Aberdeen in 1928 and he held that position along with Consultant Physiologist to the Rowett Institute for Animal Nutrition until his death. Throughout his life, Macleod wrote eleven books and monographs. In 1932 he returned to his research and work on the possibility that the central nervous system plays a role in the cause of hyperglycemia. After experimenting on rabbits, Macleod concluded that stimulation of gluconeogenesis in the liver occurred via the parasympathetic nervous system. He also did work on air sickness, purine bases and electric shock. James Macleod died March 16, 1935.

Other important life facts
1919 - Fellow of the Royal Society of Canada
1921 to 1923 - President of the American Physiological Society
1923 - Fellow of Royal Society of London
1925 to 1926 - President of the Royal Canadian Institute
1930 - Fellow of the Royal College of Physicians, London
1932 - Fellow of the Royal Society of Edinburgh