Who is Dr. Johns. from The Truest Pleasure and what is their importance?

Mama's brother, Dr. Johns, is small, unmarried man, who prescribes nothing but whiskey for his patients. He gives whiskey concoctions to Ginny when she is just a teenager to brong on her cycles, which haven't yet started. He also prescribes whiskey for pneumonia and typhoid. Note..... his prescriptions never work.