Cotton Mather was a Puritan minister and lay scientist in Boston and had come into possession of an African man named Onesimus. The enslaved African told of a procedure he had undergone back in his homeland that protected him from this illness. People in West Africa had discovered that they could fend off contagions by inoculating themselves with a specimen of fluid from an infected person. Mather was intrigued by the idea Onesimus described. He researched it, and decided to call it “variolation.” It would become the precursor to immunization and “the Holy Grail of smallpox prevention for
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