Figure - PMC

Skip to main content

An official website of the United States government

Here's how you know

Here's how you know

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.

View full-text article in PMC

. 1989 Oct;23(4):221–227.

Search in PMC
Search in PubMed
View in NLM Catalog
Add to search

© Journal of the Royal College of Physicians of London 1989

This article is distributed under the terms of the Creative Commons Attribution-NonCommercial 4.0 International License, which permits non-commercial use and redistribution provided that the original author and source are credited.

PMC Copyright notice

graphic file with name jrcollphyslond90346-0017-b.jpg