Circular 21 - Insecticides and Subsidiary Materials 67 
injurious to the animals, not to stain the coat, 
and in the case of cows not to taint the milk. 
They are made up with a less volatile oil than 
household sprays "but to about the same pyre- 
thrin content plus 5 percent pine oil, oil of 
camphor, cloves, safrol, or other aromatic, 
A special pyrethrum oil emulsion is 
prepared from kerosene and pyrethrum extract 
as explained in the circular on mosquitoes. 
This larvicide is useful in killing the l.^.rvae 
of both malaria-carrying mosquitoes and buf- 
falo gnats in infested water. The extract 
used with petrolatum or liquid vaseline may 
be applied to the skin to repel mosquitoes. 
The extracts of pyrethrum may also be 
mixed with fine talcs, powdered charcoal, 
tobacco dust, sulfur, or various inert earths 
to make insecticides to be applied as dusts. 
These should not be confused with the dusts 
prepared from pov;dered flowers discussed above. 
As previously stated, pyrethruia is very 
toxic to insects but is generally considered 
nonpoisonous to man. Certain individuals may 
be allergic to it and experience an irritation 
to the respiratory passages. 
Pyrethrum is packed in barrels in the 
form of ground flowers and fine powders for 
sale at 21 to 22 cents per pound. The liquid 
extract, 20 to 1, may be purchased in drums at 
$U»UO to $/^.60 per gallon. Smaller lots are 
also obtainable at a slightly higher rate. 
For manufacturers end distributors 
see numbers 6, 11, 19, U3, 54, SO, 98, 102, 
and 107 of list at end of this circular. 
