NATURALISTIC METHODS OF MALARIA CONTROL 
349 
not breed abundantly in water polluted by 
industrial wastes, sewage, or sullage water. 
Tolerance to environment varies with spe¬ 
cies, and both in the laboratory (Russell 
and Mohan*1939, 1940, 1941) and in nature 
there are wide limits for a given species. 
The effect of pollution is probably due not 
only to toxic action but to some extent to 
microbie and physical effects on larvae 
and their food supply. 
One seldom finds larvae of malarial vec¬ 
tors in buffalo wallows or in piggery 
waters. Streams polluted with bagasse 
from a Philippine sugarcane mill, pools 
catching refuse from a Ceylon sisal fac¬ 
tory, and pits used for macerating canepa 
hemp in Italy were not patronized by 
malarial vectors (Hackett et al. 1938). 
Williamson (1935) was perhaps the first 
to experiment with pollution. He tried 
herbage cover, a measure which covers 
shallow water in pools or ditches with 
green-cut grass, herbage, or leaves. The 
herbage is trampled into a compact mass 
a foot or more high. It should extend a 
foot or so beyond the edge of a pool to allow 
for rainy weather extension. In a ditch or 
small stream the packing may be held down 
by a double row of stakes. In the Philip¬ 
pines, good results have followed use of 
cocoanut husks and fronds in narrow 
streams. In Madras macerated cactus has 
been used in agricultural wells and tobacco 
stubble in borrow pits with success against 
anophelines. 
Malariologists should be alert for oppor¬ 
tunities to cheapen control by using in¬ 
dustrial, agricultural, or home waste to pol¬ 
lute breeding places. Pig-raising may im¬ 
prove the economic status of a community 
while, with a little direction, it tends to 
free pools or ponds of malarial vectors. 
Changing salt content of water. Ento¬ 
mologists have noted many instances of 
natural control of anopheline larvae fol¬ 
lowing freshening or salting of a breeding 
place. Successful attempts at control have 
been based on this natural and potentially 
destructive force. Strictly speaking, the 
method probably should be classed under 
management of water rather than as a 
naturalistic method. 
At Durazzo, in Albania, by using Calco 
tide-gates in reverse position, a brackish 
marsh was transformed into a sea-water 
lagoon, thus inhibiting A. elutus. 
“Within two years, breeding over an area 
of fifteen square kilometers was reduced to 
zero, while the profits to the Government 
of an existing fish concession, which has 
been greatly benefited, more than equalled 
the cost of the operations” (Hackett et al. 
1938). 
Excluding salt water has been useful in 
controlling both A. sundaicus and A. bar- 
birostris in Malaya (Hodgkin 1938). In 
North Holland it has been found that abun¬ 
dant irrigation in the new polders gradu¬ 
ally washes salt out of the soil, causing the 
vector anopheline to disappear. 
Before altering natural lagoons, a care¬ 
ful study should be made of the probable 
effect on anophelines. Washburn (1933) 
reported that in a malaria-free Jamaica 
town some seaside mangrove swamps be¬ 
came land-locked and partially dry. Then 
came heavy rains which filled them with 
water. A. albimanus soon appeared, with 
disastrous results. Spleen rates rose from 
5 to 90 per cent, and there were 4400 cases 
of malaria with 138 deaths in a population 
of 8000. When the fresh water was drained 
off and sea water readmitted, A. grabhami 
replaced A. albimanus and malaria sub¬ 
sided. 
Shading. It has long been known in 
Malaya, Assam and elsewhere that clearing 
a jungle ravine of trees and shrubs, thus 
exposing a stream to sunlight, is frequently 
the prelude to epidemic malaria. So, too, 
for many years entomologists have noted 
that some anophelines, like A. umbrosus, 
prefer shaded breeding places, whereas 
others, like A. albimanus, prefer open, 
sunny places. This natural phenomenon 
has been developed into naturalistic con¬ 
trol by shading, as for example, by Ram¬ 
say and Macdonald (1936) in Assam, 
Overbeek and Stoker (1938) in Java, and 
Carr (1938) in Cuba. The reverse, expos¬ 
ing to sunlight, has more often resulted 
disastrously than helpfully. 
Shading may not control breeding di¬ 
rectly; in fact, Thompson (1940) found 
