The Internal Secretion of the Pancreas
An extract of the pancreas pulled a dying diabetic dog's blood sugar back down — and gave the world insulin.
A century ago, a diabetes diagnosis was a death sentence — until two young Canadians made an extract from a dog's pancreas that brought a dying animal's blood sugar back from the brink.
The big idea
Your pancreas does two jobs at once. Most of it makes digestive juices; tiny scattered clusters of cells, the islets of Langerhans, make a hormone — insulin — that lets your body use sugar for fuel. In diabetes, those islet cells fail, sugar piles up dangerously in the blood, and before 1922 there was nothing to do about it.
Banting and Best reasoned that you could rescue the islets' hormone if you first got rid of the digestive part of the gland — which, they suspected, was chewing up the hormone whenever anyone tried to extract it. So they tied off the tubes that drain those digestive juices. Starved, the digestive tissue withered away over weeks, leaving the precious islets behind. From that shrunken gland they squeezed an extract — and when they injected it into a diabetic dog, its sky-high blood sugar dropped, again and again, with the bigger doses doing more.
How it came about
Frederick Banting was a young surgeon with little research experience and a single stubborn idea, scribbled in a notebook one night in 1920. He took it to J. J. R. Macleod, a respected physiologist at the University of Toronto, who was sceptical but gave Banting a corner of his lab over the summer of 1921, ten dogs, and a student assistant — Charles Best — to run the blood-sugar tests.
The summer was brutal: dogs died, extracts failed, money ran short. But by autumn they had a dog kept alive on their extract. Macleod threw the whole lab behind the work and brought in the biochemist James Collip, who purified the extract enough to try it on a human. In January 1922, a dying 14-year-old boy named Leonard Thompson received it; his blood sugar fell and he recovered. The race from idea to medicine had taken barely eighteen months.
Why it mattered
Insulin didn't cure diabetes — it still doesn't — but it turned a swift, certain death into a condition people could live with for decades. Within two years it was being made by the ton and shipped around the world. Few discoveries have so directly and quickly saved so many lives.
It also carried a quiet act of conscience: Banting, Best, and Collip sold the patent to the University of Toronto for one dollar each, believing that a discovery this important should belong to everyone rather than make them rich — a stance that still echoes in today's arguments over the price of insulin.
A way to picture it
Think of a fruit orchard with a cannery built right next to it. The cannery (the digestive part of the pancreas) is so close that every time you try to harvest the fruit (the hormone from the islets), the machinery mangles it. Banting and Best's trick was to shut down the cannery first — block its supply line and let it rust away — so that the fruit could finally be picked whole. Cut off the digestive tissue, and the hormone survives long enough to collect.
Where it sits
Insulin is the first great triumph of endocrinology — the study of the body's chemical messengers. It followed the realisation that glands could control the body from a distance through the bloodstream, and it preceded the modern molecular biology that would later read insulin's structure letter by letter and even grow it in bacteria. The story also rhymes with another in this Library: Alexander Fleming's penicillin, another extract from a humble source that changed what medicine could do — though insulin moved from bench to bedside far faster.
Intravenous injections of extract from dog's pancreas, removed from seven to ten weeks after ligation of the ducts, invariably exercises a reducing influence upon the percentage sugar of the blood and the amount of sugar excreted in the urine.