drainage and filling in malaria control 
319 
Special Problems 
Rice field workers in foreign countries 
have been able to control mosquito breeding 
in rice field by intermittent irrigation. If 
the rice field is irrigated for 3 days out of 
every 6, it will be dry for at least 24 hours 
in every interval of 6 days, and breeding 
is thereby prevented. Any small un¬ 
drained pools containing larvae should be 
treated with Paris green. In the Southern 
States rice fields are prolific sources of 
anopheles mosquitoes, but they have not 
been thought to be of much importance 
from a malaria standpoint. 
Irrigation. There should not be much 
mosquito breeding on irrigation projects if 
they are well planned and well operated. 
In other words, the system should be 
planned to waste no water and to provide 
drainage ditches to take care of any seep¬ 
age or waste. Unfortunately, but few are 
so prepared. 
Pumping. In a few countries where 
there is insufficient fall, ditches discharge 
into a sump from which the water is 
pumped over the bank or levee into the 
outlet. 
Modification of drainage structures. If 
the flow line of existing bridges or culverts 
is at a higher elevation than the territory 
directly above it, it is necessary to cut a 
trench through the bridge floor slab with 
air hammers. Care must be taken to con¬ 
struct adequate footings under the slab at 
the same time that the invert is made. This 
procedure must not be undertaken without 
first obtaining the written permission of the 
engineer in charge of the structure. An¬ 
other means for securing additional fall is 
to utilize hydraulic jacks for pushing a pipe 
through the embankment at the correct 
elevation. 
Permanent Drainage 
Three types of drainage will be discussed 
under this heading; namely, invert con¬ 
struction, the laying of tile or underground 
drains, and the filling of swamps and ponds. 
Inverts 
A few years after the discovery of the 
mode of transmission of malaria, our Gov¬ 
ernment initiated the construction of the 
Panama Canal. Officials of the United 
States Government, profiting by the mis¬ 
takes of the French, incorporated malaria 
control and sanitation as a part of the con¬ 
struction work. LePrince and Orenstein 
(1916), in their book entitled Mosquito 
Control in Panama, described in detail the 
permanent malaria control work executed 
in Panama (1904-1910) and stated that the 
cost of the permanent construction was less 
than the maintenance cost on open earth 
ditches. The British studied this epoch- 
making work of Gorgas, Carter, and Le¬ 
Prince and began to copy it almost imme¬ 
diately in the far corners of the British 
Fig. 3. Artesia, Mississippi. Left, before malarial 
control drainage; right, after construction of rein¬ 
forced concrete invert with sodded banks. 
Empire. But Americans waited approxi¬ 
mately 30 years to imitate their own work. 
Some of the first invert construction was 
done in connection with field experiments 
of the U. S. Public Health Service in and 
near Memphis, Tennessee. It has been re¬ 
ported recently that the City of Memphis 
has lined more than 75 per cent of its water 
courses (anon. 1940) and several towns in 
other states are approaching this enviable 
situation. 
Definition of inverts. The term ‘ ‘ invert ’ ’ 
means the bottom lining of an open ditch 
or water course with durable material. 
Inverts are of three types: masonry, mono¬ 
lithic, and precast: Masonry inverts are 
