The discovery of insulin
In May 1921, Banting and Best began to conduct experiments on dogs. They removed the pancreas of some dogs and tied off the pancreatic duct of others. The dogs whose pancreas had been removed altogether developed diabetes, as expected, while the dogs whose ducts had been tied did not. While the pancreatic cells that produced digestive secretions degenerated in the dogs whose pancreatic duct had been tied, the islets of Langerhans remained undamaged. Clearly, the islets of Langerhans produced the secretions that prevented diabetes occurring Banting and Best wanted to extract and isolate these secretions, but it was difficult to keep the dogs alive long enough to carry out tests.
Alter numerous setbacks, resulting in the deaths of several dogs, they succeeded in keeping a severely diabetic dog alive with injections of an extract made from the tied-off pancreas. They called this extract isletin. Their next challenge was to find a way of producing enough extract to make it a practicable treatment for diabetes. Realizing that relying on a supply of dogs was going to hold back research, Banting and Best moved on to using the pancreas of cows, obtained from a local slaughterhouse. They managed to extract a substance that contained a greater amount of the active ingredient and injected it into one of the laboratory dogs that had had its pancreas removed. The dog's blood sugar dropped significantly.
Human testing
At the end of 1921, Macleod invited James Collip, a skilled biochemist to help purity Banting and Best pancreatic extract for clinical testing in humans. On 11 January 1922, the extract was injected into 14-year-old Leonard Ihompson a diabetic patient who was close to death, at the loronto Gene Hospital. The first test proved disappointing, but it was repeated with a purer version of the extract around two weeks later, this time with much better results.
Thompson's blood sugar returned to normal levels and his other symptoms abated. 'In May 1922, Macleod delivered a paper, "The Effects Produced on Diabetes by Extracts of Pancreas", on behalf of the team at the annual conference of the Association of American Physicians. He received a standing ovation. The paper used the word "insulin"for the first time.