London's medicine.Br Med J 1980; 280 doi: https://doi.org/10.1136/bmj.280.6218.935 (Published 29 March 1980) Cite this as: Br Med J 1980;280:935
Log in using your username and password
Log in through your institution
Register for a free trial to thebmj.com to receive unlimited access to all content on thebmj.com for 14 days.
Sign up for a free trial