On this day in 1721, Boston doctor Zabdiel Boylston took a gamble with his young son's life and inoculated him against smallpox. Puritan minister Cotton Mather had learned from one of his slaves that in Africa people did not fear the disease that so terrified Europeans. The Africans placed a small amount of smallpox pus into a scratch on children's arms, thus making them immune to the disease. When an epidemic broke out in Boston in 1721, Mather wanted to try this method. He convinced Dr. Boylston, but other physicians and the public thought the idea barbaric, even sinful. However, when those Boylston inoculated survived, the tide of public opinion began to turn. Within a few years, the once-controversial practice would be routine.