BACOT : MOSQUITOES AND THE DANGER OF MALARIA. 261
with wire netting. Lily-ponds. rock-gardens, and swamps should
be inspected and their owners fined if any mosquito larvae
are found in them. Certain kinds of trapped surface-water
drains, which afford excellent breeding places for Culicine mos-
quitoes, should be treated during dry weather with crude
naphthalene or disinfectants. In beech woods containing old
trees with gnarled roots, water-holes or pockets often form
about the roots (Pl. vii.), and these should be filled as far as possi-
ble with sand or leaf mould, so as to prevent the breeding
of mosquitoes, which, even although they may be of species not
known to convey disease, cause annoyance to picnickers. In
Epping Forest, this might not make much difference, as there
are possibly many water-pockets out of sight and reach.
The choice of Larvicides is a matter which requires know-
ledge, if economy and effectiveness are to be achieved. Heavy
oils are best in hot climates, because they evaporate less rapidly
than light ones, but they have the defect of making less contin-
uous films. They are possibly better also for use in swamps
where frequent repetition is impracticable ; but it is necessary,
in this case, for the few applications to be heavy. In cool cli-
mates, light oils are probably quite as effective as heavier ones,
A much quicker and more certain effect can be obtained by
emulsifying the oil with soap and using a watery solution, as
this spreads throughout the water and kills both larvae and
pupae beneath the surface. This method is especially applicable
to species which can dispense with air breathing for long periods.
A good emulsified larvicide will kill at a dilution of 1 in 20.000.
In such places as West Africa, it has the added advantage that,
as the oil after emulsification cannot be used for burning, it is
less likely to be stolen.
For Anopheles in running water and for any species which
breed in salt water, the Panama larvicide, which is composed
of crude Carbolic Acid and Rosin soap, may be recommended.
If any anti-mosquito campaign is undertaken in this country,
it is to be hoped that it will be centrally controlled by a com-
mittee of experts having powers and sufficient staff to see that
the necessary measures are carried out effectively. Any system
which leaves the administrative work to local councils directed
by leaflets from the Local Government Board is to be deprecated
strongly ; for, in many cases, the leaflets would not be understood