In 1921, Frederick Banting and Charles Best who extracted the hormone insulin from the pancreas’ of dogs in 1921 administered the extract to a Leonard Thompson, a 14-year-old boy dying from type I diabetes mellitus in a Toronto hospital, saving his life and proving insulin’s efficacy in treating human diabetes.

Following their discovery, virtually all insulin for human use was harvested from slaughterhouse animals, usually porcine or bovine.

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