SOUNDS OF MUSIC

any secular variation in incidence during the period of the survey. In their second paper Laurence et alii study various Ipregnancy factors, seasonal variations, and social class effe.cts. Though a marked seasonal effect has been found in some previous surveys, with an excess of winter births, it was not possible to demonstrate any consistent seasonal variation in the present survey. As in other surveys of this type, a marked social class effect was noted for spina bifida, which was proportionately more frequent in social classes IV and V, but no such effect was evident for anencephaly, a fact which Laurence and his colleagues find hard to explain, since. the two conditions are in all other epidemiological respects closely linked.