In January 1922, 14-year-old Leonard Thompson was in hospital in Toronto seriously ill with Type 1 diabetes.
The only treatment available was starving the body of sugar, so he was very thin and expected to die. But he was lucky enough to be in the first recipient of insulin extracted from cows, given by Frederick Banting.
He had an allergic reaction to the first injection but the second, of a purer extract, had dramatic positive effects and he lived for another 13 years.
Doctors had known there was something wrong with the way the pancreas worked in type 1 diabetes that led to a build up of sugar in the blood.
But until the work of Banting and others, they could not find a way of extracting the substance that we now know as insulin.
An account of the work was published in the Canadian Medical Journal just two months after Leonard's first treatment.
Banting, and a colleague John McLeod, were awarded the Nobel Prize for Medicine or Physiology in 1923.
Millions of lives have since been saved by the discovery of insulin.