CHEMOTEOPIC TESTS WITH THE SCREW-WORM FLY O 
practical repellents. Representatives of the different classes of the 
more common and easily procurable organic compounds were selected. 
The formulae and boiling points of these are shown in Table 1 with the 
purpose of ascertaining whether or not there is a relation between the 
repellent action of organic compounds and their chemical consti- 
tution and their volatility (which is measured roughly by their boiling 
points). On account of the widespread use of certain essential oils, 
especially citronella and pennyroyal, as mosquito repellents, many 
tests were made with these. Fish oil, pine tar, and turpentine have 
been recommended for use in keeping flies off dairy cattle, and it was 
thought worth while to subject these to careful tests also. 
The lubricating oil referred to in the table was automobile motor 
oil, specific gravity 0.930, Saybolt viscosity at 104° F. 495, manufac- 
tured from crude oils of different bases; petrolatum was U. S. P.; 
the petroleum was north Texas crude which consists principally of 
paraffin oils. The mineral oil referred to in a few tests was a spindle 
oil with a specific gravity at 60° F. of about 0.88 and boiling range 
from 569 to 750° F. Most of the chemical compounds were chemi- 
cally pure and the essential oils and crude drugs were of the best 
commercial grade. 
PROCEDURE 
In some preliminary tests fresh meat was exposed on paper plates 
in places where flies were abundant, and the materials, the repellent 
values of which were to be tested, were sprayed with a hand atomizer 
over the meat until the latter was well covered. About one-half 
pound of fresh beef was used to each plate. This method proved 
unsatisfactory, as the number and species of flies present could not 
be determined accurately. 
The baits were next placed in small cone flytraps, but when deter- 
mination of the flies was made frequently this method was found to 
be very cumbersome. 
The next procedure was to put into a pint Mason jar enough sand 
to make a layer 1 inch in depth, place 4 ounces of fresh meat on the 
sand, and then spread a measured quantity of the repellent over the 
surface of the meat. Rabbit meat was used in some of the tests, 
but as a rule fresh beef liver was employed. It was found that 
5 cubic centimeters of the liquid repellents sufficed to thoroughly 
cover the meat, and all the tests were accordingly made with this 
quantity. In the case of the solid materials, 5 grams were used. 
Since the densities of the liquids differed considerably, the same 
quantity by weight was not used in the different tests, and in only a 
few cases did 5 cubic centimeters equal 5 grams. However, for a 
rapid survey of the field of possible repellents these differences are 
negligible. 
As a rule, each repellent was tested in duplicate at the same time. 
A series of 30 to 40 jars would be prepared, 2 of which (sometimes 
3 to 5) were left untreated and served as checks. The meat in the 
other jars was covered with the materials to be tested, and the series 
of jars exposed in a favorable environment where flies were plentiful. 
Identical tests were made in Dallas and in Uvalde, Tex. In Dallas 
the jars were exposed in a large roofed shed in the yard of a large 
packing plant, and were usually first set out about noon. The 
distance between jars varied from 4 to 6 feet. Observations were 
