Leia o trecho a seguir.
A short history of insulin
In the summer of 1921, at the University of Toronto, the surgeon Frederick Banting and his student assistant Charles Best extracted a substance from the pancreas of dogs that lowered blood glucose. In January 1922, the extract was first injected into a 14-year-old boy with type 1 diabetes who was close to death. This first injection was impure: it caused a reaction at the injection site and had little effect. The biochemist James Collip then purified the extract, and a second dose, given twelve days later, reduced the boy's blood glucose dramatically. In 1923, Banting and the laboratory director John Macleod received the Nobel Prize in Physiology or Medicine. Banting shared his part of the prize money with Best, and Macleod shared his with Collip.
(Adapted from a history of medicine textbook)
Segundo o texto, qual foi o intervalo entre a primeira e a segunda dose aplicadas ao menino, e quem purificou o extrato?