Nancy, my notes on Alfred Harris Abernathy (22 Feb 1822-7 May 1889), stepbrother to Alfred Sidney Abernathy, do not hint at any involvement in the medical profession. The Giles Cemetery Records book (p. 323) shows him as merely Col. Alfred Harris Abernathy. I believe he enlisted in the CSA as a Captain and later became Colonel. He is shown on the 1850 census as a school teacher, on the 1860 census as Circuit Clerk, on the 1870 census as Farmer, and on the 1880 census as County Superintendent of Public Schools. He and his wife are burried in the Old White section of the Maplewood Cemetery in Giles County. They had a son who was named Charles Alfred Abernathy, who shows up on the 1880 census as a Physician. He is also buried in the Old White section of the Maplewood Cemetery (p. 311, Dr Charles Alfred Abernathy, 1853 - 1928).
While these are John Abernathy Smith's cousins, not direct ancestors, he has oodles of information on them, so I urge you to email him.