MANAGEMENT OF WATER FOR MALARIA CONTROL 
331 
the Philippine Islands. Periodic closing 
and opening of a dam, situated about half 
way along the length of the stream, twice 
on one day a week, brought about a marked 
reduction in larvae. This author has called 
attention to the fact that Bentley and others 
have advocated flushing as a method of mos¬ 
quito control in Bengal. Blacklock (1939) 
refers to siphons which have been employed 
in anti-mosquito work, particularly in 
Malaya where Scharff, de Yilliers, William¬ 
son and others have developed their use. If 
sufficient fall can be obtained, it is possible, 
by means of a siphon, to produce a rapid 
transient rise of the water level in a stream 
in which anophelines are breeding. This 
author gives consideration to the various 
requirements of siphons, stressing particu¬ 
larly that for efficiency of flushing their 
action must be automatic. Various techni¬ 
cal aspects of the utilization of siphons are 
considered and his paper should be read by 
all who have the opportunity of utilizing 
this unique method of malaria control. 
MacDonald (1939) has described a design 
of flushing siphon which has proven satis¬ 
factory in the control of anophelines in 
Malaya, Ismailia and Ceylon. The princi¬ 
ple of control in this design is that a con¬ 
tinuous flow, normally sufficiently slow to 
allow anopheline breeding in the stream or 
in the neighboring pools, is converted into 
an intermittent strong flow sufficient to de¬ 
stroy larvae. It is agreed by MacDonald 
and others that a very strong current is not 
necessary for this purpose and that any 
notable variation in the flow of water will 
destroy them by stranding or by washing 
them into the main current. Nicholas 
(1939) has described a four-day sluice. 
It is not possible to summarize here the 
entire literature dealing with the control of 
anopheline larvae in running water by 
means of mechanical devices and flushing 
and flooding. However, reference must be 
made tb the work of Ram (1935) Ejercito 
(1935) and Williamson and Scharff (1936). 
The latter authors have emphasized that 
sluicing can be effective only when used 
with other methods. The danger of anoph¬ 
eline breeding in impounded headwaters 
may be eliminated by erecting the sluices as 
high upstream as possible and by the use of 
Paris green. 
Hackett, Russell, .Scharff and Senior- 
White (1938) summarized the main prin¬ 
ciples for making an efficient sluice for 
anti-larval fluctuation as follows: “That a 
sufficiently large volume of water should be 
discharged suddenly at a minimum of once 
a week, oftener in some cases, with the ob¬ 
ject of causing a wave to pass down the 
channel of the stream. This wave, as it 
flows onward, causes the stranding of mos¬ 
quito larvae, pupae and eggs. Larvae 
which are not stranded are drowned by the 
turbulence of the flowing water. There is 
no doubt, too, that in sluiced channels, par¬ 
ticularly those in fairly flat country, the 
soil disturbance and the liberation of silt 
and organic debris has a deterring effect 
upon further larval breeding. ’ ’ They have 
pointed out that the soft friable banks re¬ 
quire special protection against erosion for 
a few yards below the outfall of sluices; 
also it may be necessary to eliminate side 
pools and seepages not reached by the flush. 
If a channel is too wide it is sometimes 
advisable to obstruct it with rocks in order 
to promote stranding or turbulence. They 
admit that the method’s usefulness is re¬ 
stricted at present to fairly small streams 
and channels where there is plenty of water 
available. 
Irrigation 
The close association of malaria with the 
cultivation of rice and other crops requir¬ 
ing irrigation has long been recognized. 
Geiger and Purdy (1920) have considered 
the malaria problem of the rice fields of the 
United States. Earle (1925) has reported 
on the relation of irrigation on cane fields 
to the malaria problem of Puerto Rico and 
pointed out how the proper management of 
smaller irrigation ditches, which is in the 
hands of the cultivators, is of the greatest 
importance in malaria control. Sweet 
(1938) discussed the three types of irriga¬ 
tions systems in Mysore State and points 
out that lack of drainage remains as a com¬ 
mon difficulty to all types. Herms and 
Gray (1940) state “it is a strange com- 
