Abstract

References
1.
Ryder
W
. (1970 ) Proc. roy. Soc. Med.
63 , 32 .
2.
Shafto
C E
. (1969 ) Brit. J. Anæsth.
41 , 407 .
3.
Wise
C C
Robinson
J S
Heath
M J
Tomlin
P J
. (1969 ) Brit. med. J.
ii , 540 .
