48 THE ESSEX NATURALIST
east. With a knowledge of the breeding habits of A. maculipennis
atroparvus, this is not really surprising although it does not fully
explain why it was that such a high proportion of cases occurred
in the south and south-east. Shute believes that it is the density
of the atroparvus population which is very important.
In 1917-1918, the following cases of indigenous malaria were
recorded:—
The experiences of these years revealed: —
(a) that in a number of places which harboured
many carriers and numerous anopheles, no new
cases of malaria arose.
(b) that some of the new cases recorded, arose in
areas which harboured one or two carriers and
exceedingly few anopheles.
James, in a report to the Local Government Board in 1920,
concluded that the factor which determines whether or not new
cases of malaria will occur in a potentially malarious locality, and
the extent to which the disease will spread, is neither the abun-
dance of the anopheles in the locality generally, nor of carriers,
but it is the degree to which there is a close and continuous
association between the malaria carrier, the anopheline and the
susceptible person—and this degree is likely to occur only in the
particular type of dwelling which A. maculipennis selects as its
permanent resting place and feeding place, e.g., stuffy dwellings,
ill-lighted and ill-ventilated, with dark recesses, cupboards, old
drapery and much furniture with overcrowding of inmates.
In the second World War, some of the earlier lessons had been
learned. In 1942, a map (fig. 6) was sent to the Director of
Hygiene of each of the fighting services with the request that,
as far as possible, potentially relapsing cases of malaria should not
be congregated in Areas A or B on the map. This map was
prepared by P. G. Shute, to whom I am indebted for the following
comments. So far as mosquito survey work had enabled an esti-
mate to be made, A. maculipennis density is greater in Area A
than in any other part of the country. Of the 524 cases of true
indigenous malaria that occurred in England between 1917 and