In 1889, the physician Oskar Minkowski, in collaboration with Joseph von Mering, removed the pancreas from a healthy dog to test its assumed role in digestion. The dog developed diabetes. But if the duct that the pancreatic juices flow through to the intestine was surgically tied off so that the juices could not reach the intestine, the dog developed minor digestive problems, but no diabetes.
They came to the conclusion that the pancreas must need to produce digestive juices, and too produce a substance that regulates glucose levels. If a substance could actually be isolated, the mystery of diabetes would be solved. Progress, however, was slow. Banting's Idea Frederick Banting, an unknown surgeon with a bachelor's degree in medicine, had the idea that the pancreatic digestive juices could be harmful to the secretion of the pancreas produced by the islets of Langerhans. He therefore wanted to ligate the pancreatic ducts in order to stop the flow of nourishment to the pancreas. This would cause the pancreas to degenerate, making it shrink and lose its ability to secrete the digestive juices.
Early in 1921, Banting took his idea to Professor John Macleod at the University of Toronto, who was a leading figure in the study of diabetes in Canada. Macleod didn't think much of Banting's theories. Despite this, Banting managed to convince him that his idea was worth trying. Macleod gave Banting a laboratory with a minimum of equipment and ten dogs. Banting also got an assistant, a student by the name of Charles Best. The Experiment Begins