An official website of the United States government
The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before
sharing sensitive information, make sure you’re on a federal
government site.
The site is secure.
The https:// ensures that you are connecting to the
official website and that any information you provide is encrypted
and transmitted securely.
Brooks CM, Lange G.Brooks CM, et al.Proc Natl Acad Sci U S A. 1977 Apr;74(4):1761-2. doi: 10.1073/pnas.74.4.1761.Proc Natl Acad Sci U S A. 1977.PMID: 266218Free PMC article.