Myths about physical racial differences were used to justify slavery — and are still believed by doctors today.

The excruciatingly painful medical experiments went on until his body was disfigured by a network of scars. John Brown, an enslaved man on a Baldwin County, Ga., plantation in the 1820s and ’30s, was lent to a physician, Dr. Thomas Hamilton, who was obsessed with proving that physiological differences between black and white people existed.