He drew from his medical training to discredit popular ideas about differences among the races. In 1843 he gave a lecture series, "Comparative Anatomy and Physiology of the Races", to demonstrate the failings of phrenology, which was a so-called scientific practice of the time that was applied in a way to draw racist conclusions and attribute negative characteristics to ethnic Africans. He rejected the practice of homeopathy, an alternative to the scientific medicine being taught in universities. Although he had a successful medical career, Smith was never admitted to the American Medical Association or local associations because of racial discrimination.