June, *18] FREEBORN AND ATSATT: PETROLEUM AND MOSQUITO LARVAE 303 
In experiments in which we allowed the mosquitoes to draw into 
their tracheal systems repeated doses of the oil, which we had previ¬ 
ously colored with Sudan III, an oil soluble stain not soluble in water, 
we found upon dissection that the oil had thoroughly penetrated even 
to the finest branches of the tracheae and had through its viscosity and 
capillary action almost completely collapsed the delicate walls of the 
larger tracheae. In the smaller division of the respiratory system the 
intermingled drops of oil and bubbles of air filling the whole diameter 
of the tube could be plainly seen. There can be no doubt that the oil, 
no matter whether a light oil such as kerosene, or a heavy oil-like liquid 
petrolatum does flow into the anal siphon, the main tracheae and into 
even the very finest subdivisions, and does this in sufficient quantity 
to completely block them and render the passage of air impossible. 
Here we must preclude, too, any possible application of the sugges¬ 
tion of Schafer, concerning terrestrial insects, that it may be possible 
for them to continue to breathe after having inhaled a quantity of 
kerosene or other oils, due to the penetration of the oil by the respira¬ 
tory gases, for in our experiments the mass of the oil is without ques¬ 
tion too great. 
We will agree then that this form of suffocation of the larva, due to 
-an effectual plugging of the tracheal tubes by the inspired oil, could be 
considered as a very potent factor in the efficiency of the larvicide if 
time were allowed for this mode of killing to take place. One set of 
larvae which were shut off from the air surface by a layer of paraffine 
-and another set which were shut off from the air by inhaling a quan¬ 
tity of non-toxic petrolatum which plugged their tracheae, were found 
to live for approximately the same length of time, while larvae with 
petrolatum and kerosene in their respiratory tracts showed a decided 
difference, the kerosene producing lethal effects in 45 minutes while 
the non-toxic petrolatum required 4J hours. 
As a further check upon this series of experiments and to show that 
the more rapid penetration of the kerosene into the tubes of the larvae 
as compared with the slower penetration into the tracheae of the heavier 
oils was not the primary cause of the difference in toxicity, it was 
repeated using the non-toxic petrolatum and a toxic petroleum oil of 
the same viscosity, and here again the toxic oil produced a much 
earlier death than the non-toxic petrolatum. 
(5) The Oils as Contact Poisons 
As we have shown above, by the use of our colored oils, these sub¬ 
stances actually flow into the trachea and even into the very finest 
branches of the respiratory system, so that we have here a splendid 
basis for the conclusion that the oil in its close relation to the body 
