Anna Pierce Hobbs Bixby, sometimes spelled Bigsby born Anna Pierce (1812–1873), was a midwife, frontier doctor, dentist, herbologist, and scientist in southern Illinois. Bixby discovered that white snakeroot (Ageratina altissima) contains a toxin. When cattle consume the plant, their meat and milk become contaminated and cause the sometimes fatal condition milk sickness. One of the most notable and tragic cases of the "milk sickness" was that of Nancy Hanks Lincoln, the mother of Abraham Lincoln, who died at 34 years old in 1818.