William Bosworth Castle (October 21, 1897 – August 9, 1990) was an American physician and physiologist who transformed hematology from a "descriptive art to a dynamic interdisciplinary science.
His father was a professor of zoology at Harvard, a pioneer in mammalian genetics, and a member of the U.S. National Academy of Sciences.
At the Mass General, he had his first direct exposure to some of the great clinicians of the time, including Chester M. Jones, with whom he collaborated on his first medical publication, and George R. Minot, who later became Castle's mentor and unflagging supporter.
In 1925 Castle went back into a clinical setting at the Thorndike Memorial Laboratory on the Harvard service at the Boston City Hospital.
Whipple, Minot and Murphy were awarded the Nobel Prize for Physiology and Medicine, in 1934, for the discovery of the "anti-pernicious anæmia factor" from their experiments with liver in the diet.
Anemia was widespread on the island because of the endemic parasite hookworm and tropical sprue, the latter a disease which scientists thought possibly related to diet.
Castle was assisted by Cornelius P. Rhoads, known as Dusty, who was affiliated with the Rockefeller Institute in New York and later became head of Memorial Hospital for Cancer Care and Research.
Castle and his team later characterized the red blood cell defects that are responsible for paroxysmal nocturnal hemoglobinuria and hereditary spherocytosis.
The following year, Pauling and his colleagues at Caltech began the studies that eventually showed that the hemoglobin in sickle cell disease was abnormal.