Complex sentence: While working for the Rockefeller Institute, Rhoads was assigned to a William B. Castle's anemia research commission at Presbyterian Hospital in San Juan, Puerto Rico, in 1931 as part of the Rockefeller Foundation's sanitary commission there (later the International Health Board).
Split into simpler sentences: While working for the Rockefeller Institute, Rhoads was assigned in 1931 to a William B. Castle's anemia research commission at Presbyterian Hospital in San Juan, Puerto Rico. This was part of the Rockefeller Foundation's sanitary commission there (later the International Health Board).