346 
MALARIA 
a house. The work must be begun properly 
by determining the dosage and method of 
application of the larvicides. Then during 
the season the work must be kept under 
observation and results must be measured 
by the density of mosquitoes in certain rest¬ 
ing places or in suitable traps. The final 
test, that of the diminution of malaria, may 
have to be deferred to the end of the season 
or to some later time. 
All of this is the essential bookkeeping of 
the business. Good inspectorship is the 
more essential since the results of the work 
may not stand out as would a finished 
bridge or wall, but appear in the far less 
conspicuous form of larvae in a pool or 
adult mosquitoes in a barn. Sometimes a 
conscientious workman will do wonders- 
after but little training, but such cases are 
unfortunately rare. 
Controls are of course essential. Long 
observation has taught me that a single 
control village or pond is unsatisfactory 
because of the liability to wide natural vari¬ 
ability. A group of such controls is far 
better. 
Discussion 
It is hardly necessary to state that in 
anti-mosquito work one prefers such perma¬ 
nent measures as filling or drainage. But 
there are many cases such as that of im¬ 
pounded water where such measures are 
impossible. Again, larvicides must often 
supplement engineering measures by pre¬ 
venting mosquito production in ditches and 
canals. 
So that larvicides will be always useful, 
the development of new reagents and new 
methods of application should be encour¬ 
aged. 
Summary 
1. Paris green (aceto arsenite of copper) 
is effective because of its high toxicity to 
mosquito larvae, low solubility in water, 
ease of application and relative cheapness. 
2. Its disadvantages are its failure to 
affect pupae or eggs of mosquitoes and its 
inefficacy against culicine mosquitoes in 
certain types of breeding place. 
3. It may be diluted with dry inert 
powders, with water after treatment with 
kerosene, or if made more or less floatable 
by any means it may be diluted without 
kerosene in water, in dry dust or in moist 
sand or gravel. 
4. The quantity suitable per unit of 
breeding area varies with the nature of the 
breeding place and must be determined by 
preliminary tests. Frequency of applica¬ 
tion must also be predetermined by some 
tests, for this factor varies with tempera¬ 
ture and species of mosquito. Some ap¬ 
proximations are given here of both quan¬ 
tity and intervals. 
5. If properly used, Paris green should 
be harmless to man, domestic animals, fish 
and rice plants. 
6. Culicine larvae are killed by Paris 
green when it is within their feeding radius, 
as in shallow water or in water provided 
with certain types of vegetation. 
7. Paris green has been spread by air¬ 
planes, autogiro, and boat-carried machines. 
Large-scale dusting should be useful even 
if it only diminishes the density of malaria 
vectors. 
8. Experiments with larvicides other 
than Paris green and with various methods 
of distribution of larvicides are described. 
9. The necessity of proper inspectorship 
for any kind of anti-malaria work is 
stressed. 
