30 BULLETIN 1472, U. S. DEPARTMENT OF AGRICULTURE 
The following compounds were used during the World War as 
" tear gases " and are characterized by causing intense irritation to the 
eyes: Benzyl chloride, para-xylyl bromide, chloroacetone, chloroace- 
tophenone, beta-chloroethyl acetate, beta-bromoethyl acetate, and 
chloropicrin. 
In regard to attractiveness for the screw-worm fly, ethyl mercaptan 
was the best in this respect. Chloroform shows some attractiveness^ 
also denatured alcohol and valeric acid. 
Practically all of the materials which are effective in repelling 
screw-worm flies are also very effective in preventing the deposition 
of eggs. The emergence data show that almost no Cochliomyia 
emerged from any of the jars treated with these repellents. In other 
words, the fly-repellent value of a material is an index of its value in 
preventing infestation by Cochliomyia. 
MATERIALS EXHIBITING A PERFECT REPELLENT ACTION FOR PERIODS OF FROM 
TWO TO FIVE DAYS 
Each of the following materials was tested not less than four times, 
and when the number of flies visiting all the comparable check jars 
was 100 or over: 
(1) Materials which repelled all flies for a period of two days: Allyl 
isothiocyanate plus kaolin, and cade oil. 
(2) Materials which repelled all flies for a period of three days: 
Pine-tar oil, refined. 
(3) Materials which repelled all flies for a period of four days: 
Para-xylyl bromide, refined pine oil, and pine oil No. 4. 
(4) Materials which repelled all flies for a period of five days: 
Wood naptha, heavy pine tar, medium pine tar, thin pine tar, com- 
mercial pine-tar oil, commercial pine-tar oil (3) plus safrol (1), 
commercial pine-tar oil (3) plus salicylic aldehyde (1). 
Inasmuch as both allyl isothiocyanate and fennel oil, when applied 
undiluted to meat, failed to keep all screw-worm flies away for the first 
two days, it is probable that additional tests with mixtures of these 
compounds with kaolin and petrolatum will indicate that they have 
less repellent value than present tests show. 
The above grouping of materials is of interest because it is the 
experience of stockmen that a material which effectively repels flies 
for at least two days is suitable for use on animals as a fly-repelling 
wound dressing, provided, of course, there are no practical objections 
to its use, such as injurious effects on the animal tissues. 
RELATION BETWEEN REPELLENT ACTION OF COMPOUNDS AND 
THEIR CHEMICAL CONSTITUTION AND VOLATILITY 
An examination of the data fails to show any consistent relation 
between the fly-repellent properties of the compounds and their 
chemical constitution. There is no clear difference in the repellent 
action of the aliphatic and aromatic compounds, nor in that of the 
various classes of compounds, such as aldehydes, phenols, etc. 
The introduction of a halogen atom into a compound in some cases 
greatly increases its repellent action toward screw-worm flies. For 
example : 
Compound Coefficient Compound Coefficient 
Toluene 68 j Benzyl chloride 0.8 
Dextro-pinene 58 Pinene hydrochloride . 27 
Naphthalene 65 Alpha-bromonaphthalene 7. 1 
Acetone 76 i Monochloroacetone .16 
