Early in his career, Blackfan did work that identified the origin of cerebrospinal fluid.
Initially, he returned home to join his father in general practice.
Encouraged by Richard Pearse, he decided to do some pediatric training in the Founding Hospital in Philadelphia.
Walker and Blackfan discovered where cerebrospinal fluid originated by tracking dye injected into the cerebral ventricle of a dog.
He was Louis K. Diamond’s mentor, and together they wrote the first collection of photographs of microscopic appearances of the Blood in Childhood disease.