340 
MALARIA 
of Paris green-kerosene treated sand about 
1 mm in diameter practically cleared of 
living larvae an area 10 cm in diameter— 
about the size of that in a large track-pool. 
We have found the Paris green-kerosene- 
moist sand method very useful against 
larvae of A. gambiae in the partially dried 
river beds of Brazil (Barber 1940). 
I have experimented in the laboratory 
with a Paris green made more or less float¬ 
able by treating it with a small amount of 
paraffin dissolved in kerosene. The kerosene 
was drained off by filtration and the powder 
subsequently well dried. This powder was 
mixed with moist sand and spread in some 
experimental bowls with very promising 
results. 
Aziz (1939) used a “light Continental 
paris green” mixed with water from the 
breeding place with no addition of kerosene 
or egg albumen. In his earlier experi¬ 
ments he used a stock solution of about 1,000 
cc of Paris green in 2,000 cc of water, which 
at the breeding place was diluted with 
stream water in the proportion of 20 to 25 
cc of stock solution to 6 or 8 liters of water. 
This final dilution was applied by means of 
a sprayer. Later he discontinued the use of 
the stock solution and carried the Paris 
green to the breeding places in packages of 
a quantity sufficient to make one charge or 
a half-charge of the sprayer. It was then 
mixed just before use, either by pouring it 
into the sprayer and adding water or by 
mixing first in some container and then 
pouring it into the sprayer. Each liter of 
the mixture in the strength described should 
suffice to treat an area of about 60 square 
yards, the amount varying with the nature 
of the breeding place. Aziz thinks that in 
Cyprus conditions the Paris green-water 
method is less expensive and more effective 
than either the Paris green-dust or the Paris 
green-kerosene methods. 
It seems to me that the modification of 
Aziz is promising, especially where a more 
or less floatable Paris green is available; 
and the method should be suitable for con¬ 
ditions other than those of Cyprus. It is to 
be remembered that the purpose of the kero¬ 
sene is not only to make the Paris green 
more floatable, but also to aid in spreading 
it, for kerosene tends to spread widely before 
it evaporates. This filming, which is ad¬ 
vantageous for most still waters, might be 
less useful in Cyprus, where anopheles 
larvae (mostly A. superpictus ) are often 
found in flowing waters. 
Dosage, or Quantity op Paris Green to 
Be Used Per Unit op Breeding Area 
The toxicity of the larvicide is a prime 
factor; the minimum lethal dose for a single 
larva is, however, hard to determine. It 
might be done by picking out with a capil¬ 
lary pipette under microscopical control 
fragments of a crystal of a floatable sample 
of Paris green and later testing this dose on 
a single larva. One can get an approxima¬ 
tion of a lethal dose by a simple experiment: 
A larva is put into a Petri dish containing 
water and kept under observation under a 
hand lens. When it is feeding well, a very 
small amount of Paris green is carefully put 
on the water surface near it. When it has 
ingested a small particle, it is removed by 
a pipette to a second dish, washed, and put 
into a third where the time of its survival 
is noted. 
The size of particles efficiently toxic can 
be determined by another procedure: The 
sample of Paris green to be tested is mixed 
in ether and filtered through a paper filter 
of known permeability. The filtrate is 
placed on water in a suitable container and 
beside it a control with ether but no Paris 
green on its surface. When the ether has 
evaporated, which may require a day or two 
according to the temperature and amount, 
anopheline larvae are introduced into both 
control and treated containers, and the de¬ 
gree and time of mortality observed. The 
purpose of the ether is to afford a volatile 
substance which will leave the particles of 
larvicide on the surface of the water. 
Laboratory experiments show clearly that 
amounts of Paris green so small as to escape 
visibility under the hand lens may poison all 
larvae in a container. In one laboratory we 
had a good deal of mortality among 
anopheline larvae in our routine breeding 
containers, an occurrence puzzling until we 
