Frederick Banting upon the idea of obtaining insulin from the fetal pancreas. He removed the pancreases from fetal calves at a William Davies slaughterhouse and found the extracts to be just as potent as those extracted from the dog pancreases. By December 1921, he had also succeeded in extracting insulin from the adult pancreas. Pork and beef would remain the primary commercial sources of insulin until they were replaced by genetically-engineered bacteria in the late 20th century. In spring of 1922, Banting established a private practice in Toronto and began to treat diabetic patients. His first American patient was Elizabeth Hughes Gossett,
Frederick Banting medicine and, in 1919–1920, was Resident Surgeon at The Hospital for Sick Children. Banting was unable to gain a place on the hospital staff and so he decided to move to London, Ontario to set up a medical practice. From July 1920 to May 1921, he continued his general practice, while teaching orthopedics and anthropology part-time at the University of Western Ontario in London because his medical practice had not been particularly successful. From 1921 to 1922 he lectured in pharmacology at the University of Toronto. He received his M.D. degree in 1922, and was also awarded a gold medal.