June, ’18] FREEBORN AND ATS ATT: PETROLEUM AND MOSQUITO LARVAE 301 
(4) The oil in entering the siphon and tracheal tubes blocks them 
and effectually impairs respiration. 
(5) The oil on entering the siphon and trachese acts as a contact 
poison through a direct action on the tissues. 
(6) The theory which we will endeavor to prove in this paper is that 
it is the oil vapor from the inspired oil through its extremely rapid 
penetration of the tracheal tissues, which produces the marked lethal 
effects. 
(1) Surface Tension 
Ross in 1911 suggested that the oiling of a water surface so changed 
the physical conditions that the “larvae are no longer able to keep the 
surface by surface-tension and quickly drown.” In all our observa¬ 
tions in this laboratory we have noticed a marked contradiction to this 
theory in that the larvae under a film of oil are very prone to remain at 
the surface for considerable lengths of time, either in a quiescent con¬ 
dition or in what seems a definite struggle to pierce the film. It is very 
true that in a small shell vial with a steep meniscus, the larva under a 
film of oil is unable to hold his relative position on the meniscus, but 
continually slides toward the apex of the concavity, but when the 
meniscus is less steep, there seems to be no difficulty in maintaining 
the position at the surface. 
(2) Suffocation 
. . ' ' . i 
Celli (1904) in discussing the various larvicides states that petroleum 
oils exert “a mechanical action only, that is, by intercepting the air 
from the larvae.” A simple experiment was conducted by us in which 
this theory was tested. Larvae were placed in several tubes with equal 
volumes of the same water and a previously moistened small cotton 
plug introduced into each tube until the water rose a short distance 
above it. Thus an effectual mechanical obstruction was introduced 
between the larvae and the surface air which could have no other effect 
than that for which it was intended. At the same time, larvae were 
placed in the same volume of the same water and a thin film of kero¬ 
sene poured on the surface. The rapid death of those larvae under the 
kerosene (45 minutes) as compared with those which were kept from 
the air through a simple mechanical means (30 hours) shows clearly 
that since the time required for uncomplicated suffocation was so much 
greater’than that which is required for death under a layer of oil, the 
possibility of suffocation is but a slight factor in the larvicidal action 
of the oils. 
Another set of larvae in tubes containing equal volumes of water 
were covered with films of the various oils in the series with which we 
