Exubera, an inhalable form of insulin. Credit: Frank Rumpenhorst—dpa /Landov. For people with diabetes mellitus, the year 1921 is a meaningful one. That was the year Canadian physician Frederick Banting and medical student Charles H. Best discovered the hormone insulin in pancreatic extracts of dogs.On July 30, 1921, they injected the hormone into a diabetic dog and found that it effectively lowered the dog’s blood glucose levels to normal.hat was the year Canadian physician Frederick Banting and medical student Charles H. Best discovered the hormone insulin in pancreatic extracts of dogs. On July 30, 1921, they injected the hormone into a diabetic dog and found that it effectively lowered the dog’s blood glucose levels to normal.