344 
MALARIA 
depending on their distance from the line 
of flight. The effective swath was at least 
50 feet in width. 
In these experiments the spray remained 
moist enough to sink and act on the culicine 
larvae. One would expect success on anoph¬ 
eles with a floatable larvicide or with a dry 
larvicide also spread by autogiro. The ex¬ 
periments of King and McNeel are of great 
importance in indicating the use of auto- 
giros or other modifications of the airplane 
for various sorts of breeding places. 
Distribution bt a Power Dusting 
Machine Carried in a Boat 
LePrince and Johnson (1929) have de¬ 
vised an apparatus designed for the treat¬ 
ment of lakes or other larger bodies of 
water. The blower can be operated by one 
man and the whole unit placed in a small 
boat. Hydrated lime containing 15 per 
cent of Paris green gave the most satisfac¬ 
tory results. In moderate breezes such a 
mixture gave a lethal path at least 525 feet 
wide. Material costs were as low as $0.15 
per acre. 
It is well worth trying to devise a similar 
apparatus for spreading a Paris green made 
floatable by kerosene or by some other 
means and diluted with the water of the 
breeding place. 
In connection with the spread of larvicide 
by airplane or other mechanical means, it is 
encouraging to remember that a partial de¬ 
struction of anopheles in large breeding 
places may be very useful, because generally 
malarial transmission depends on the den¬ 
sity of the mosquito vector. I have studied 
for a period of some years a pond in Greek 
Macedonia which supplies A. elutus and 
intense malaria to 5 or 6 different villages 
all situated within a radius of 5 kilometers. 
A partial control of this pond might at least 
protect the more distant villages. Certain 
anopheles, as A. pseudopunctipennis in Old 
Mexico and A. pharoensis in Egypt, appar¬ 
ently are serious vectors only where their 
density is great. 
Howard and Andrews (1940) mixed 
Paris green with hydrated lime and applied 
it over a large breeding place. They deter¬ 
mined the character of the dust deposits at 
varying distances from the point of distri¬ 
bution and found that the lime went a 
greater distance than the Paris green. 
They warn against judging the area effec¬ 
tively treated by the visible clouds of dust. 
Improvement of Larvicides and of the 
Methods of Application 
In testing new stomach poisons for larvae 
the following points should be kept in 
mind: The larvicide must be very toxic in 
the gut of the larvae and practically insolu¬ 
ble in water. The larvicide should be inex¬ 
pensive. Whatever success one has with a 
larvicide in the laboratory, it must be re¬ 
tested in the natural breeding places. 
These should include both shallow and deep 
water and scattered track-pools; also water 
with various surface covering. 
These requirements hold for a larvicide 
which is designed for all sorts of breeding 
places. For special places, such as wells, 
cheapness may not be so essential. 
My colleagues and I have made many 
attempts to find new larvicides and to im¬ 
prove the method of application of those we 
have; and a short account of some of our 
failures or partial successes may be useful. 
Carbonate of copper filled the require¬ 
ments of cheapness, insolubility and ease of 
spread, and in the laboratory killed the 
anopheline larvae. But in the field we 
found that its low toxicity required too 
heavy a dosage to make it practicable. 
In certain field tests we found that iodo¬ 
form diluted in road dust was practically 
as effective as Paris green. Iodoform has 
two disadvantages: It is relatively expen¬ 
sive and must be fresh or carefully pre¬ 
served in order to be effective against lar¬ 
vae. But it might prove useful in wells 
where only small quantities are needed; 
and in the crude form at least it is easily 
manufactured, so that long storage would 
not be necessary. It is doubtful if persons 
with no hospital experience would object 
to the odor, at all events where very small 
quantities are employed. 
For breeding places such as smaller 
ponds, pools and the like we have used Paris 
