August, ’20] 
ZETEK: MOSQUITO CONTROL 
349 
where the chemicals were, but if they did, they would react suddenly 
upward upon coming into contact with same. 
The jars with the powdered insecticides told a different story. Three 
hours after the larvae were placed in them, many dead larvae were found. 
In the camphor jar only four larvae were alive; para-dichlorobenzene 
had six live ones; naphthalene had twelve alive. Two hours later 
showed no change in the latter jar, but in the camphor and para-dich¬ 
lorobenzene lots, all were dead. The following morning at 7:30, 
there were still two live larvae in the powdered naphthalene jar, but 
these were dead by noon. At this same hour the lump naphthalene 
had all of the 25 larvae alive and active , as if nothing out of the ordinary 
had happened. The lump camphor had but four live larvae, while 
the lump para-dichlorobenzene had sixteen live ones. At 4:30 p. m. 
that same day, all larvae in the lump camphor jar were dead, while in 
the para-dichlorobenzene there were still ten alive. There were no 
deaths in the naphthalene jar. 
The next day at 4:30 p. m. there were four live larvae in the lump 
para-dichlorobenzene jar, and eighteen in the lump naphthalene one. 
' Twenty-four hours later all larvae in the para-dichlorobenzene were 
dead, but in the lump naphthalene there were still about twelve alive, 
of which two had pupated. These tests show that the substances in 
powdered form are most effective, that camphor and para-dichloro¬ 
benzene are the best, and that naphthalene is uncertain. For ant- 
guards powdered para-dichlorobenzene is best, but for flower vases 
and holy-water urns, lump camphor may be used. 
(7) A similar test was made with pupae only. Only camphor and 
para-dichlorobenzene were used. The lump chemicals were inefficient. 
The powdered forms killed all pupae in four hours. 
(8) If equal amounts (by weight) of camphor and para-dichloro¬ 
benzene are heated in a flask, they melt and form a liquid which 
remains a liquid at ordinary room temperatures. Preliminary tests 
showed this combination had good insecticidal properties, and should 
have ready applications under special environmental conditions. 
However, not enough experimental work was done with this to warrant 
making any deductions at this moment. This liquid settles on the 
bottom in the form of a flattened sphere, and may, therefore, be used 
with good results in holy-water urns, being less objectionable than the 
powdered substances. 
Summary 
About two grams or more of para-dichlorobenzene, repeated every 
seven days during the rainy season, or every ten days during the dry 
season, was found to prevent the breeding of yellow fever mosquitoes 
