Who is Dr. Gaghan from Shaking the Nickel Bush and what is their importance?

Dr. Gaghan is Ralph's physician. It is Dr. Gaghan that initially diagnoses Ralph's diabetes, and who provides him with a diet he must follow the rest of his life. He also instructs to move out west to get plenty of sunshine. Ralph send postcards to Dr. Gaghan regularly, and in return, the doctor is able to share Ralph's whereabouts with his mother.