The New England Journal of Medicine Downloaded from nejm.org at EDWARD G MINER LIBRARY on January 21, 2014. For personal use only. No other uses without permission.

Copyright © 1991 Massachusetts Medical Society. All rights reserved.

The New England Journal of Medicine Downloaded from nejm.org at EDWARD G MINER LIBRARY on January 21, 2014. For personal use only. No other uses without permission.

Copyright © 1991 Massachusetts Medical Society. All rights reserved.

The New England Journal of Medicine Downloaded from nejm.org at EDWARD G MINER LIBRARY on January 21, 2014. For personal use only. No other uses without permission.

Copyright © 1991 Massachusetts Medical Society. All rights reserved.

The New England Journal of Medicine Downloaded from nejm.org at EDWARD G MINER LIBRARY on January 21, 2014. For personal use only. No other uses without permission.

Copyright © 1991 Massachusetts Medical Society. All rights reserved.

The New England Journal of Medicine Downloaded from nejm.org at EDWARD G MINER LIBRARY on January 21, 2014. For personal use only. No other uses without permission.

Copyright © 1991 Massachusetts Medical Society. All rights reserved.

The New England Journal of Medicine Downloaded from nejm.org at EDWARD G MINER LIBRARY on January 21, 2014. For personal use only. No other uses without permission.

Copyright © 1991 Massachusetts Medical Society. All rights reserved.

The New England Journal of Medicine Downloaded from nejm.org at EDWARD G MINER LIBRARY on January 21, 2014. For personal use only. No other uses without permission.

Copyright © 1991 Massachusetts Medical Society. All rights reserved.

The New England Journal of Medicine Downloaded from nejm.org at EDWARD G MINER LIBRARY on January 21, 2014. For personal use only. No other uses without permission.

Copyright © 1991 Massachusetts Medical Society. All rights reserved.

The New England Journal of Medicine Downloaded from nejm.org at EDWARD G MINER LIBRARY on January 21, 2014. For personal use only. No other uses without permission.

Copyright © 1991 Massachusetts Medical Society. All rights reserved.