A medical triumph of the twentieth century, insulin’s discovery in 1922 is universally celebrated. For children and adults with Type 1 diabetes, a diagnosis that had once meant slow death became a manageable condition within months.
One of the most intense and bitter conflicts in science history lies behind this historic triumph.
There was only one person at the center of the storm: Dr. John James Rickard Macleod. Macleod, a world-renowned Scottish physiologist and head of the Department of Physiology at the University of Toronto, provided laboratory space, scientific direction, and institutional authority that enabled the research.
A heated debate over scientific credit, academic hierarchy, and personal ego erupted as the Nobel Committee awarded the 1923 Nobel Prize in Physiology or Medicine jointly to Frederick Banting and Macleod.
Macleod’s story is one of brilliant science and explosive conflict, followed by a long, difficult road to historical vindication.
Physiology: The Path of a Brilliant Mind
John Macleod was a respected figure in international medicine long before Frederick Banting ever walked into his office with an idea.
His father was a clergyman, and Macleod was born in Cluny, Scotland, in 1876. After graduating from the University of Aberdeen with highest honors, he pursued advanced research in physiology and biochemistry at the Institute for Physiology in Leipzig, Germany.
In his research, Macleod was fascinated by the process of how food is converted into energy in the human body. The author of dozens of rigorous scientific papers and authoritative textbooks on carbohydrate metabolism and carbohydrate regulation in the bloodstream, he became a worldwide expert in the field of carbohydrate metabolism and carbohydrate regulation in the bloodstream.
Macleod’s appointment as Professor and Head of the Physiology Department at the University of Toronto followed fifteen years as a professor at Western Reserve University in Cleveland, Ohio.
By equipping its laboratories with state-of-the-art analytical tools, he transformed the department into a modern, research-oriented organization. Students and staff were held to high standards of scientific evidence by him because he had a sharp, analytical mind.
Macleod meets Banting in the fateful meeting
A mysterious orthopedic surgeon named Frederick Banting requested a meeting with Macleod in November 1920.
Banting was not trained in research or biochemistry, and he had no background in endocrine studies. Macleod was presented with a rough handwritten hypothesis: when one tied off the pancreatic ducts in living dogs, the digestive tissue would degenerate, leaving the hormone-producing cells intact.
There were valid scientific reasons for Macleod’s initial skepticism. Over the last thirty years, dozens of highly experienced researchers have attempted similar experiments around the world. There were many technical hurdles and toxic complications that prevented most of them from succeeding.
In a gentle manner, he pointed out to Banting that his knowledge of the existing medical literature was superficial. Additionally, he pointed out that the surgical approach he proposed was not entirely new.
Banting, however, was recognized for his relentless effort and obsessive determination by Macleod. The medical implications would be enormous if Banting’s approach was successful. Macleod knew this well.
During 1921, Macleod granted Banting the following:
- At the University of Toronto, there is an unused laboratory room on the top floor.
- For surgical procedures, ten dogs were used as experimental subjects.
- During his undergraduate education, Charles Best learned how to measure blood sugar levels.
During his days instructing Banting and Best on experimental design, surgical protocols, and chemical methods required to accurately measure blood glucose levels, Macleod spent days preparing for his planned summer research sabbatical in Scotland.
The Breakthrough and Macleod’s Crucial Guidance
During Macleod’s stay in Scotland, Banting and Best conducted their famous summer experiments in the sweltering attic. An extract derived from degenerated pancreatic tissue successfully lowered the blood sugar of a diabetic dog by the end of July 1921.
The return of Macleod to Toronto in 1921 was not merely a matter of taking over or sitting back. While the young men had proved the concept, their crude extract was far too impure and dangerous for human consumption. He carefully examined their preliminary data, insisted on rigorous control experiments, and realized that they had proven the concept, but they had not proven it was safe for humans to consume.
Immediately, MacLeod reallocated his department’s resources to scale up the project:
1. Bring in James Collip
In addition to Macleod, Dr. James Collip, a highly skilled biochemist on sabbatical, was recruited to be part of the team. For the extraction to be purified, Collip had to calculate the exact concentration of chemical alcohol. It was done to prevent abscesses and toxic fevers from developing in human patients after injection.
2. Establishing a rigorous experimental process
Macleod switched the lab’s focus from surgical duct ligation — which yielded small amounts of insulin extract — to extracting insulin directly from fetal or adult cattle’s pancreas obtained from local slaughterhouses. Large-scale production was made possible by this single decision.
3. Identifying the hormone.
Macleod suggested changing the substance’s name from Banting and Best’s informal name “isletin” to insulin, derived from the Latin word insula, meaning island, to conform to international scientific naming standards.
MacLeod’s strategic direction allowed the team to move from animal experiments to human clinical trials in less than six months. The insulin era began in January 1922, when 14-year-old Leonard Thompson was saved at Toronto General Hospital.
Putting an end to a bitter feud
The scientific world celebrated the breakthrough, but the laboratory atmosphere inside the University of Toronto deteriorated into open hostility.
There are vast differences in personality, background, and academic culture at the root of the conflict:
- Banting was a hot-tempered, informal person, suspicious of authority, and protective of his original ideas. Macleod, he felt, was an armchair academic who had not participated physically in the summer lab. The time had come for him to claim glory.
- A formal and aristocratic Scottish professor, MacLeod spoke precisely. The editorial “we” refers to the collective efforts of Macleod’s department when making public presentations or writing press releases.
Macleod’s repeated use of “our research” and “we discovered” sounded to Banting like a senior administrator taking credit from two young researchers.
There was a rapid escalation of tension. Taking credit for Macleod’s idea was accused by Banting. As Banting’s temper flared and he lacked understanding of how institutional science worked, Macleod became frustrated.
At one point, Banting even threatened to leave the university entirely and take his research elsewhere. This forced university governors to intervene to keep the peace long enough to secure the patents and publish the findings.
The 1923 Nobel Prize controversy
The feud reached its boiling point in October 1923, when the Karolinska Institute in Stockholm announced the Nobel Prize winner inthe Nobel Prize winner in Physiology or Medicine.
The committee awarded the prize jointly to Frederick Banting and John Macleod.
The decision caused an immediate crisis:
- Banting was furious. He felt it was a deep insult that Charles Best had been omitted while MacLeod was included. Banting publicly announced that he split his half of Nobel Prize money equally with Best.
- Macleod was deeply hurt. While Macleod acknowledged Banting’s original initiative, he felt his own months of scientific direction, administrative risk, and laboratory organization fully justified his share. To maintain fairness and protect his colleague, Macleod announced he would split his half of the prize money equally between James Collip and
The public spectacle created two opposing camps in the medical world. In Canada, public sympathy sided overwhelmingly with Banting, who was celebrated as a rugged home-grown hero, while Macleod was often cast as an arrogant, credit-stealing administrator.
Exile from Toronto and return to Scotland
During Macleod’s stay in Toronto, the atmosphere became increasingly toxic. Despite his internationally renowned status, he felt isolated within the university community. Day-to-day academic life was made uneasy by Banting’s supporters, who constantly questioned Macleod’s integrity.
Afraid of the friction and eager to return to a quieter research environment, Macleod resigned from the University of Toronto in 1928.
In his native Scotland, he accepted the Regius Professorship in Physiology at the University of Aberdeen, eventually becoming the Dean of the Medical Faculty there.
At Aberdeen, Macleod returned to his first love: fundamental laboratory research. Working on diabetes treatments, he published papers on carbohydrate metabolism, and he consulted for international health organizations. He rarely spoke publicly about the painful events in Toronto, preferring instead to let his scientific record speak for itself.
During Macleod’s final years, he suffered from severe arthritis that crippled him. At the age of 58, he died in March 1935, leaving behind a complex, misunderstood legacy.
History’s Long Journey to Rehabilitation
Macleod was portrayed in history books, films, and biographies for decades after his death as a secondary figure who provided lab space and tried to claim credit for another’s genius.
In the late twentieth century, medical historians reexamined laboratory archives, personal journals, and institutional correspondence from 1921 to 1923.
In 1982, historian Michael Bliss published The Discovery of Insulin, a thorough re-examination of the hypothesis. As a result of his comprehensive analysis of every document from the period, Bliss delivered a balanced, objective verdict that altered the historical consensus:
- The initial hypothesis of Banting was scientifically flawed. Macleod’s decision to use adult bovine pancreases instead of the pancreatic ducts was the key to mass production of insulin.
- The scientific leadership of Macleod was essential. Without Macleod’s knowledge of carbohydrate metabolism, his experimental design, and his decision to bring in James Collip, the summer experiments would likely have remained isolated, crude results rather than a global cure.
- The Nobel Committee made a sound decision. It was the committee’s intent to honor Banting as the person who conceived the initiative and Macleod as the scientist who guided the discovery into clinical practice.
A dynamic, four-person team designed insulin, not a lone genius: Banting, Best, Collip, and Macleod. Today, modern medicine recognizes that insulin was not developed by one person.
Macleod’s Experience: Key Takeaways
A vital lesson about the realities of scientific discovery can be learned from the life and career of John Macleod:
- Findings require direction: Turning a crude laboratory finding into a safe, reliable medical treatment requires specialized expertise and strategic leadership.
- Partnerships are Ruined by Communication Gaps: The rivalry between Banting and Macleod was largely driven by miscommunication, culture differences, and insecure egos.
- Having institutional support is crucial: Without Macleod’s commitment to risking university resources, lab space, and equipment on a young surgeon who was unproven, insulin might never have been discovered.
- Research into historical archives restores balance and truth when it is backed up by objective evidence: Public emotions can sway historical reputations, but they can also be distorted by archival research.
Lastly,
The legacy of John James Rickard Macleod reaches far beyond the handing over of laboratory keys. World-class physiologist whose scientific rigor, strategic vision, and decisive leadership transformed a rough hypothesis into human history’s greatest medical breakthrough.
Although personal feuds and public controversy overshadowed his contributions during his lifetime, history has taken a more unbiased view. It was John Macleod’s dedication to scientific excellence that helped save millions of lives around the world as one of the four co-discoverers of insulin.
