Official websites use .gov A .gov website belongs to an official government organization in the United States.
Secure .gov websites use HTTPS A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.
Bethesda, Md. : U.S. Dept. of Health and Human Services, Public Health Service, National Institutes of Health, National Library of Medicine ; Washington, D.C. : For sale by the Supt. of Docs., U.S. G.P.O., 1994