Full text
PDF
. 1956 Jun 9;1(4979):1337–1340. doi: 10.1136/bmj.1.4979.1337
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.