Full text
PDF
letter . 1989 Jun 3;298(6686):1519–1520. doi: 10.1136/bmj.298.6686.1519-d
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.