PARIS GREEN AND OTHER POISONS AS MOSQUITO LARVICIDES 
345 
green incorporated in small masses or cakes 
These have the property of floating on the 
surface of the breeding place, slowly dis¬ 
integrating and giving up a floatable Paris 
green to the surface of the water. The 
essential ingredients are: Paris green made 
floatable by treating it with paraffin dis¬ 
solved in carbon tetrachloride, a plaster of 
Paris matrix to attain slow disintegration, 
and sufficient cork dust mixed in to make 
the whole mass floatable. It was found in 
field experiments that if a cake of larvicide 
sank it got lost in the mud of the bottom. 
This sort of larvicide should be easily dis¬ 
tributed. In treating a series of pools one 
could throw a cake or two of larvicide into 
each, and theoretically one treatment should 
suffice for several weeks. 
In the laboratory these cakes worked per¬ 
fectly; but in the field, where pond levels 
varied considerably, the released Paris 
green did not spread well, sometimes be¬ 
cause the cakes got lodged on the shore. I 
still think the idea a fertile one and that 
the technique of manufacture and distribu¬ 
tion of this larvicide can be improved. In 
their present form, the cakes might be use¬ 
ful in places where rains are almost con¬ 
tinuous. The rains would aid in the spread 
of a floatable larvicide but might render 
difficult the use of ordinary powders. 
For a time we hoped that the mixture of 
stomach poisons in some non-evaporating 
oil or resin might aid in their application. 
Such substances spread widely, in broken 
patches if not in a film, and wind or rain 
should aid in their dispersal; so that appli¬ 
cation of the larvicide in one place might 
be sufficient for a whole pond. It is possi¬ 
ble to get larvicides in solution in oils or to 
incorporate them in the form of fine gran¬ 
ules. Larvae readily ingest particles of oil, 
as the dissection of anopheline larvae from 
oil-treated waters shows. Quantities of oil 
much smaller than those necessary for 
respiratory poisons should suffice. But we 
found that larvicides in oil pass into the gut 
and cause little mortality among the larvae. 
It seems that the oils or resins prevent the 
solution of the poison or otherwise prevent 
its entrance into the larval cells. 
These experiments have served one use— 
to warn against the use of too much paraffin 
or other insoluble substance in making 
Paris green more floatable. 
Several brands of Paris green are on the 
market, some of them claiming greater 
fineness and floatability, both good quali¬ 
ties when there is no accompanying loss of 
toxicity for larvae. The toxicity of very 
fine particles can be determined by filtra¬ 
tion through filters of known permeability 
(see under the topic “The dosage or quan¬ 
tity of Paris green, etc.).” Floatability 
can be estimated roughly by shaking a sam¬ 
ple with water in a test tube and noting the 
percentage of green which comes to the sur¬ 
face. 
The Choice op a Stomach Larvicide and 
op Method op Application 
The choice of a stomach larvicide and 
method of application must depend on the 
conditions. For the present, it appears 
that Paris green is the most suitable larvi¬ 
cide. The method of application will de¬ 
pend on circumstances. In partially dry 
river beds with much sand and gravel I 
should try a moist vehicle mixed with Paris 
green made floatable by kerosene or by some 
other method. For continuously rainy 
weather some of the floatable Paris green 
methods may be especially suitable. In 
semi-desert countries with stony streams 
and a fair amount of dry dust available, 
I should prefer the distribution in dust by 
hand or the modification of Aziz. For very 
large bodies of water out of the reach of 
small dust blowers or of hand treatment, 
airplanes or other mechanical methods are 
most suitable. 
The Necessity op a Trained Inspector 
in Larvicidal Work 
In some larvicidal enterprises which I 
have observed, the workman was given a 
bag of Paris green or a can of oil and left 
to look after the work with little or no 
supervision. The results were about as one 
would expect if brick layers or carpenters 
were given a blue print and told to build 
