PARIS GREEN AND OTHER POISONS AS MOSQUITO LARVICIDES 
341 
learned that Paris green was being mixed 
in another part of the building and that 
enough of it came through the open doors 
to kill our larvae. 
Dosages of larvicide determined in the 
laboratory are applicable in open field work 
only to waters practically free from sur¬ 
face obstruction of any kind. In these 
waters the larvicides tend to disperse widely 
after they reach the water. When the 
spread of the larvicide is obstructed by 
scums, floating particles of wood, algae, or 
debris of any kind, the dosage of larvicide 
has to be increased. The dry larvicide may 
penetrate vertical vegetation, but some of 
it will be lost in passing through. Rain 
tends to break up scums and beat down algae 
and a treatment soon after a heavy shower 
may require comparatively little larvicide. 
Flowing streams require more than still 
water and often more careful spreading of 
the larvicide. 
It is evident that to prescribe a definite 
dosage of larvicide may more often mislead 
than assist. The best procedure is first to 
determine roughly by dipping the numbers 
of larvae in the water to be treated. Try 
at first a light treatment of larvicide, then 
determine preferably on the following day, 
the results of this dosage. The presence of 
dead larvae on the surface of the water will 
often help in ascertaining results if the 
examination be not too long delayed. Such 
preliminary tests are almost necessary in 
beginning work in a new terrain. 
The commonest fault is over-treatment. 
One sometimes sees treated pools fairly 
green with larvicide. A preliminary test 
would have shown that for such pools a 
dosage one-tenth as great would have suf¬ 
ficed. Generally the appearance of a green 
eolor on the water or the banks indicates 
that a part of the larvicide has been wasted. 
Some approximation of proper dosages 
may be useful, at all events as a guide to 
preliminary tests. We have indicated the 
results of certain dosage in the Paris green- 
kerosene experiments. In dusting, Hackett 
(1925) showed that in waters with algae 
but with banks clean, the use of 0.02 cc of 
Paris green per square meter gave 96.0 per 
cent killing of anopheles larvae; among 
reeds, a dosage of 0.04 ec per square meter 
gave a killing of 99.4 per cent; in heavy 
brush and cane, 0.05 cc per square meter, 
a killing of 98.0 per cent. 
Danger of Poisoning Man or Domestic 
Animals by Paris Green 
In considering the danger to man or 
domestic animals by drinking waters treated 
by Paris green or other little soluble arse- 
nicals, one should keep in mind the fact 
that such larvicides rest on the surface of 
the water and are effective against larvae 
not by arsenic in solution in water but by 
that in solution in the gut of the larva. 
Only a tiny amount scarcely detectible by 
chemical means is in solution in water, and 
this amount is negligible where a brand of 
Paris green little soluble in water is used 
and is applied in proper dosage. Even if 
the surface of the water is thickly covered 
by Paris green, it is unlikely that an animal 
drinking in the ordinary manner would get 
a toxic dose. 
Although Paris green has been used for 
nearly 20 years as a larvicide for anopheline 
larvae, there is scarcely an authenticated 
case of serious poisoning of man or domestic 
animals from its use, at all events when 
applied in a proper manner. Hackett 
(1925) states that its use in wells, one gram 
to 20 square feet, is quite safe. Sweet and 
Rao (1934) treated wells in Bangalore City, 
India. Their routine was to treat a well 
weekly with 6 puffs with a hand-blower of 
a 2 per cent mixture of Paris green in road 
dust. Except immediately after the appli¬ 
cation of Paris green, the most delicate tests 
available failed to show its presence either 
in the water or in deposits from the bottom 
of wells which had been treated weekly for 
considerably over a year. 
Missiroli (1917) states that accumulation 
of arsenic through long application in the 
same water does not take place because any 
dissolved arsenic is volatized by the micro¬ 
flora of the water. He used as a test of 
arsenic in water the fungus Penicillium 
brevicaule, the growth of which produces 
a garlic odor in the presence of arsenic. 
