332 
MALARIA 
mentary on human intelligence that most 
irrigation districts have been organized, 
financed and constructed without any con¬ 
sideration of the problem of removing the 
inevitable seepage and surplus irrigation 
water.” Russell (1938) has discussed ma¬ 
laria due to defective and untidy irrigation. 
From his recent personal observations he is 
of the opinion that the situation as regards 
irrigation and malaria is probably worse 
than ever before. He has summarized the 
specific ways in which irrigation produces 
malaria as follows: (a) Malaria-producing 
defects in construction, operations and 
maintenance on an irrigation system, and 
(b) general results of irrigation. 
Russell’s paper is amply illustrated with 
photographs of examples of most of these 
difficulties. He emphasizes the outstanding 
need for organization and cooperation be¬ 
tween malariologists and irrigation engi¬ 
neers before and after an irrigation project 
is undertaken. It is not irrigation per se 
but defective and untidy irrigation which 
is the important source of malaria. 
One hopeful approach to the control of 
malaria under systems of irrigation is that 
of intermittent irrigation. Smalt (1937) 
tried periodic draining in rice fields of the 
island of Bali and a 67 to 73 per cent reduc¬ 
tion of anopheline larvae followed. In the 
laboratory, larvae of A. annularis and A. 
minimus survived for 145 and 175 minutes 
respectively in trays after they had been 
drained and for 40 and 60 minutes in dishes 
after the water had been removed. 
Hill (1937) pointed out the possibility 
of utilizing intermittent irrigation of rice 
fields for malaria control in Portugal. 
Hill and Cambournac (in press) presented 
the results of their studies since 1935 at the 
Louisville meeting of the American Society 
of Tropical Medicine, November, 1940. 
They found that periodic drying greatly 
decreases the number of mosquito larvae or 
completely suppresses them. Furthermore, 
the amount of water used is less than with 
the usual method of continuous irrigation 
and there is an increase in yield of certain 
species of rice per acre without detriment 
to its quality. As a result of these studies, 
the government of Portugal has passed a 
law making intermittent irrigation obliga¬ 
tory when recommended by the malarial 
service. A 17-day cycle was utilized by 
these workers. 
Summary 
The most important factor in the manage¬ 
ment of water for malaria control is the 
incorporation in the design of the project 
a provision for effective variation of water 
level. This requires the collaboration of 
malariologists and the engineers charged 
with the design of the project. In the case 
of artificial impoundages, proper reservoir 
preparation, followed by pool level fluctua¬ 
tion and supplemented by shoreline main¬ 
tenance, are the cardinal features. Neces¬ 
sary maintenance of irrigation projects and 
sluices are likewise important. In all of 
these procedures it must be realized that 
the efficacy of variation of pool level for 
malaria control depends to a large extent 
on creating an environment unsuitable for 
breeding; actual destruction of the larvae 
may also be important. 
