MALARIA, MOSQUITOES AND THE ESSEX MARSHES 49
1938, there were 18 in which the locality where the disease was
contracted is unknown. Of the remaining 506 cases, 398, or 79%
were contracted in this area. Hence its designation as a 'Very
Dangerous Area'. Area B was classified as a 'Dangerous Area'. It
is not possible to explain why in this area there were so few cases
compared with Area A. Observations have shown that in at least
part of the area, the mosquito density is just as high as it is in
area A. It is possible that the association between man and
Anopheles is not quite so close as it is in certain parts of Area A.
Area C was the 'Potentially Dangerous Area'. A. maculipennis
can be found in almost every village in England and Wales where