50 THE ESSEX NATURALIST
suitable breeding grounds exist, although in central and western
England they are seldom abundant. The area to the west of
Oxford was considered reasonably safe. North of south Yorkshire,
however numerous the Anopheles may be, and however many
human gametocyte carriers may be living in this area, the atmos-
pheric temperature is seldom high enough for continuous periods
to enable the parasite to complete its cycle in the insect host.
Notified cases were strictly controlled and carefully investi-
gated, and only twenty-seven cases occurred in the country in the
six years after the War.
I am indebted to Mr. Shute for the following table, which sets
out the number of cases of indigenous malaria in Essex from 1917.
It is not easy to state definitely any one changed condition
which led to malaria ceasing to be endemic in England. The
introduction of quinine, land drainage, better houses and accurate
diagnosis followed by appropriate treatment have all contributed.
This is a subject which might well repay further study.
In a prefatory note to the Ministry of Health's Memorandum
on Mosquito Control, Sir John Charles, Chief Medical Officer,
states, "The presence of anopheline mosquitoes in substantial
numbers in certain areas of England can still constitute a threat
of indigenous malaria. This threat is admittedly a small one,
but in these clays of world-wide travel it can never be dismissed
as of negligible significance".
This address has been built up, in the main, from the re-
searches and writings of others. I have made use of, and
acknowledge my thanks to, the Essex Record Office and the
libraries of the Essex County Council and of the Royal Society of
Health. I have been extremely fortunate in receiving the advice