338 
MALARIA 
dust, the diluent being used to prevent 
overdosage and to insure better distribution 
over the breeding place. Many sorts of dust 
have been used: road dust, fine gravel, 
sand, charcoal dust, talcum, soapstone, silica 
earth, ashes and slaked lime are examples. 
A dilution in common use is 1 part Paris 
green to 100 parts of inert dust by volume. 
Dust mixtures should be deposited as 
nearly as possible only on the surface of 
the water and not made to penetrate the 
surface-tension layer. Therefore dusts 
must be dry, for particles of Paris green 
will stick to a moist vehicle and may be 
carried under the water. Some dusts, as 
slaked lime, sometimes cohere in small 
masses and submerge the poison. Dry sand 
or gravel is especially good for the treat¬ 
ment of certain less accessible breeding 
places, for one may project them consider¬ 
able distances even through trees and brush. 
The greenish cloud which separates from 
the sand or gravel is particularly larvicidal. 
Larger particles of the vehicle are bound to 
sink, but we have shown by experiment that 
an effective percentage of Paris green will 
adhere to a large particle of dry gravel, 
even when projected several yards against 
the wind, and will be left on the surface 
when the gravel strikes the water. 
The choice of a dust often depends on 
what is most available during the breeding 
season of the mosquitoes. Usually nearness 
to breeding places is an important factor, 
although dusts may be collected, sifted if 
necessary, and stored at any convenient 
time or place. Airplane dusting or the use 
of dust blowers may demand special- re¬ 
quirements. 
Anopheline larvae ingest almost anything 
on the surface of the water if fine enough to 
enter the gut unless it consists of some sub¬ 
stance distinctly repulsive to them. 
Dusts are commonly thrown by hand or 
spread by dust blowers (also called “dust 
guns” or “dusters”). Spreading by hand 
has the advantage of requiring no ma¬ 
chinery which must be carried by the work¬ 
men and which is likely to get out of order. 
Where dry dust, sand or fine gravel is pres¬ 
ent at the breeding place, spreading by hand 
is especially advantageous, for no transpor¬ 
tation or sifting of the dust is required. 
There is perhaps greater danger of over 
treatment of a breeding place where dust 
is spread by hand, although I have seen 
great abuse in this respect where blowers 
were used. “Dumping” of the larvicide 
burden instead of proper spreading may 
happen in any case—perhaps more often 
when the workman is burdened by the dust- 
blower as well as by the dust. 
Workmen accustomed to the use of dust- 
blowers in agriculture make better distribu¬ 
tors of larvicides because of their greater 
experience with the machinery and its op¬ 
eration. Such workmen have proved to be 
valuable in application of larvicides in Italy 
(Hackett 1925). 
Dusts should be mixed well with the 
Paris green before spreading. Various sorts 
of mechanical mixers have been described, 
most of them consisting of a revolving box 
or barrel provided with baffles inside. 
Where no blower is carried and the dusts 
at the breeding place are employed, we have 
done successful mixing by hand in the pail 
in which the larvicides are carried. 
Application of dusts by airplane will be 
described in another part of this paper. 
Dilution with Water of a Kerosene- 
treated Paris Green 
Barber, Rice and Mandekos (1936) have 
described a method by which Paris green is 
made more floatable by mixing with kero¬ 
sene and is subsequently diluted with water 
at the breeding place. The ingredients are 
mixed in the proportion of 10 gm of Paris 
green, 20 cc of kerosene and one cc of a 
solution of egg albumen. This mixture may 
be stored in bulk and eventually carried to 
the field in containers each with capacity 
of 15 cc or 20 cc, quantities suited to the 
capacity of the sprayer. These containers 
are well closed and may be carried in a belt, 
cartridge-fashion. 
At the breeding place (where water is al¬ 
ways present) the mixture is thoroughly 
mixed with about 250 volumes of water. 
For breeding places little encumbered with 
debris of any kind, this proportion may be 
