What was Pershing's connection to singer and musician Ray Charles as noted in the nonfiction book, The Warmth of Other Suns?

Just before singer and musician Ray Charles hit it big, he had an appointment with Dr. Pershing Foster. The two immediately struck up a friendship that lasted until Pershing’s death. On one occasion, Charles had suffered a severe cut to his hand. Pershing advised him to cancel a tour that he had scheduled but Charles wasn’t about to. Pershing went on the tour with him to tend to make sure his injury didn’t become infected. Charles wrote a song in Pershing’s honor called, “Hide Nor Hair” that spent seven weeks on the Billboard Chart.