Mixed-use right medicine for old hospital? Cook County Board commissioners in Chicago are debating the fate of the venerable Cook County Hospital, which was replaced last year by a new 1.2 million-sq.-ft. facility next door. The original Beaux Arts building, which opened in 1914, is to be torn down at the end of the year. But preservationists floated a plan last month to convert the structure to a mixed-use residential/retail development. The proposal includes 300 units of residential space, including possible senior living units, and a 90,000-sq.-ft. health club. Though the plan has support among some board members, it has no developer. The board takes a final vote this month.