How did Cotton Mather learn about smallpox variolation?

Cotton Mather learned about the practice of variolation from Onesimus, an enslaved West African man living in his household. Onesimus, who had himself been inoculated in Africa, described the procedure to Mather, explaining how it could provide protection against smallpox.123

Intrigued by this information, Mather became a vocal advocate for the practice in the American colonies. During the Boston smallpox epidemic of 1721, he urged physician Zabdiel Boylston to perform inoculations. Despite facing intense public and professional opposition, Mather’s support helped introduce the method to the region, and he later published an account of the experience in the transactions of the Royal Society.32