Complex sentence: Mendelsohn did his internship at Cook County Hospital 1951-1952 and residency at Michael Reese Hospital (1952-1954) and later worked there as an attending (1955-1988).
Split into simpler sentences: Mendelsohn did his internship at Cook County Hospital 1951-1952. He completed his residency at Michael Reese Hospital (1952-1954) and later worked there as an attending (1955-1988).