Discovery of insulin

Charles Best (left) and Frederick Banting (Right) Photo credit

For years, diabetes was a disease that had no better treatment than following diets that would restrict sugar and carbohydrate intake, so that blood sugar levels would not spike out of control. However, some of the diets were so severe that its followers died of starvation. It was already known that diabetes was the result of a pancreatic protein hormone deficiency, and there had already been attempts to feed or inject patients with "pancreas extracts", however, attempts failed because of proteolytic enzyme, trypsin, present in the pancreas. Frederick Banting and colleague, Charles Best, did experiments in which they ligated a duct of the pancreas which prevented trypsin from being secreted, thereby maintaining the function of insulin. They did their experiments on dogs that had induced diabetes. They are credited with being the first to isolate insulin properly. Banting won a Nobel Prize (joint award with John Macleod!) for this and shared his prize with Best.

• Read their paper published in 1922 in the Canadian Medical Association Journal: Pancreatic Extracts in the Treatment of Diabetes Mellitus 

Another Paper: Further Clinical Experience with Insulin
A little information about Frederick Banting: Biography from NobelPrize.org