December, ’20] 
VICKERY: PETROLEUM INSECTICIDES 
445 
No one knows what compounds in petroleum are actually toxic to 
insects. Chemically, petroleum is a complex solution of hundreds of 
compounds, and oils from different fields are composed of different 
proportions and arrangements of these. The present knowledge of 
the chemistry of petroleum is very limited. Certain structural series 
have been identified, but practically no compounds have been isolated 
or synthesized. At one time I was able to get a pure sample of Pentane. 
It had the physical properties of gasoline and its vapor proved equally 
toxic to the silkworm. 
There is good evidence to show that not all petroleum products are 
toxic to insects. Kerosene, particularly in California, sometimes fails 
unaccountably to kill scale insects. Freeborn and Atsatt report that 
oil refined for medicinal purposes is not toxic to mosquito larvae. The 
writer once tried to use a residual oil in mosquito work that failed to 
control when applied to the water in the usual thin film. Combining 
10 per cent of kerosene or crude distillate restored its toxic properties. 
It is possible that research might reveal that certain compounds in 
petroleum are particularly valuable insecticides. Economic demand 
might make it profitable to prepare these synthetically. To carry out 
such an investigation a closer study should be made of the physiology 
of petroleum as an insect poison. Shafer has made some progress along 
this line, using chemical methods, and has offered the suggestion that 
insects are killed with petroleum by an upsetting of the balance between 
the oxidizing and reducing enzymes in the body fluid. 
At one time I took up this problem using histologic methods. The 
larvae of the silkworm and the California oak moth, Phryganidia cali- 
fornica, proved to be the most satisfactory material on account of the 
ease with which the different organs could be dissected out. Two 
series of slides were made of each of these two species. In one series 
the larvae were all killed by being exposed to the vapors of gasoline. 
The other series was made as a control. Both series received identical 
treatment. Some larvae were treated by the hot water killing method 
and others by a modified fluid of Carnoy. Some of the larvae of both 
series were not dissected but, hardened, cleared and mounted in paraf¬ 
fine so that complete serial sections could be prepared of the entire 
insect. Other slides were made of the various organs. These slides 
were stained with iron haemotoxylin and counterstained to bring out 
the different tissues. It was almost impossible to find any difference 
between the gasoline killed and control material. The only consistent 
difference was in the ductless glands, the cenocytes, which showed great 
activity in the gasoline killed insects. This activity was shown by 
large drops of fluid around the inner periphery of the cell. Glazer 
found that the oenocytes secrete an oxidizing enzyme. Located, as 
