The WeekBr Med J 1979; 2 doi: https://doi.org/10.1136/bmj.2.6193.806 (Published 29 September 1979) Cite this as: Br Med J 1979;2:806
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