Macleod was born in
Clunie, near
Dunkeld in
Perthshire. Soon after he was born, his father Robert Macleod, a
minister of the
Free Church, was transferred to
Aberdeen, where John attended
Aberdeen Grammar School and enrolled in the study of medicine at the
University of Aberdeen. In 1910, he delivered a lecture on various forms of experimental diabetes and their significance for
diabetes mellitus at the joint meeting of the section on Pharmacology and Therapeutics and the section on Pathology and Physiology of the
American Medical Association. In 1916, he was a Professor of Physiology at
McGill University in
Montreal, Canada. After the
First World War, he went on to teach physiology at the
University of Toronto, where he became director of the physiology lab and an assistant to the dean of the medical faculty. He researched various topics in physiology and biochemistry, among which were the
chemism of
Mycobacterium tuberculosis,
electroshocks,
creatinine metabolism and blood circulation in the brain. In 1905 he became interested in carbohydrate metabolism and
diabetes, publishing a series of scientific papers and several monographs on the subject from then on. Additionally, Macleod was a popular lecturer and an influential contributor to the development of the six-year course in medicine at the University of Toronto.
Frederick Banting and the discovery of insulin At the end of 1920, Macleod was approached by Frederick Banting, a young Canadian physician who had the idea of curing diabetes using an extract from a
pancreas whose functioning had been disrupted. Macleod was not enthusiastic, because (unlike Banting) he knew about unsuccessful experiments in this direction by other researchers. He thought it more likely that the
nervous system had a crucial role in regulating blood
glucose concentration. Even though Banting had virtually no experience of physiology, he managed to convince Macleod to lend him laboratory space during a holiday in Scotland that summer. While Macleod was away, Banting and Best achieved a breakthrough: they isolated an internal secretion of the pancreas and succeeded in reducing the blood sugar level of another dog, whose pancreas had been surgically removed. Macleod who was "desperate to snatch victory from the jaws of defeat" stepped in and finished the presentation. From Banting's viewpoint, "this was a brazen coup by Macleod to rob him of the credit for having discovered insulin – and to rub salt into the wound, it had been done in front of the most eminent doctors in the field". Their discovery was first published in the February 1922 issue of
The Journal of Laboratory and Clinical Medicine. Macleod declined co-authorship because he considered it Banting's and Best's work. Despite their success, there remained the issue of how to get enough pancreas extract to continue the experiments. Together, the three researchers developed alcohol extraction, which proved to be far more efficient than other methods. This convinced Macleod to divert the whole laboratory to insulin research and to bring in the biochemist
James Collip to help with purifying the extract. The first
human clinical trial was unsuccessful. Banting was insufficiently qualified to participate and felt sidelined. By the winter of 1922, he was certain that all Macleod's colleagues were conspiring against him. There was a reported physical altercation between Banting and Collip, as Banting saw Collip's breakthrough on alcohol purification as a threat, while Collip was reluctant to share the details. Collip threatened to leave because of the strained atmosphere but the encouragement of others who saw the potential of their research prevented escalation of the conflict.
Later years Macleod returned to Scotland in 1928 to become
Regius Professor of Physiology at the University of Aberdeen (in succession to his former teacher,
John Alexander MacWilliam who retired in 1927) and later Dean of the University of Aberdeen Medical Faculty. Between 1929 and 1933 he was also a member of the Medical Research Council. Macleod did not continue to work on insulin, but he remained active as a researcher, lecturer and author. His last major contribution was a proof that the
central nervous system does have an important role in maintaining carbohydrate metabolism balance, as was his original hypothesis. His theory about conversion of
fats into carbohydrates remained unproven, despite his provision of several indirect proofs. despite which he remained active almost until his death. In 1933 he made a lecture tour of the US, and in 1934 he published the 7th edition of his book
Physiology and Biochemistry in Modern Medicine. ==Works==