Full text
PDF
. 1969 Mar;59(3):442–447. doi: 10.2105/ajph.59.3.442
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.