Full text
PDF
. 1958 Apr;33(168):165–170. doi: 10.1136/adc.33.168.165
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.