Dr. Leah Dickstein, who worked with Mason in her later years, stands by her assessment of Mason as a multiple. Professionals and staff at Wilbur's Lexington, Kentucky clinic confirm that Mason was multiple, and that she attempted to integrate several times, without success. Dr. Leah Dickstein, whose mentor was Dr. Wilbur stated that she was in touch with Mason for many years after Wilbur died. She remembers Mason telling her that "every word in the book is true." She stated that Wilbur had "no need to make this up."
http://www.nlm.nih.gov/changingthefaceofmedicine/physicians/biography_85.html
