THE CATTLE GRUBS OR OX WARBLES 91 
kept under the most favorable conditions, hence there is difficulty 
in determining the percentage of mortality chargeable directly to 
the treatment. The tests made show clearly, however, that Hypo- 
derma larvee, especially in the later stages of their development, 
are very resistant to contact insecticides. In these tests some 25 
or 30 different materials were used. Those were selected which 
would seem to be adapted to use in the destruction of grubs in the 
eysts in the backs of the hosts. The period of submergence in most 
cases was about two minutes. 
Mention will be made of only a few of the results obtained, since 
it appears impractical to determine by this method the efficiency 
of the various materials when applied to the warbles in the cysts. 
In these experiments it appeared that the saponified coal-tar creo- 
sote products gave the highest percentage of mortality within the 
first 24 hours. Tincture of iodine U. S. P. also gave a high per- 
centage of kill soon after treatment. Certain other materials such 
as iodoform with neutral carriers and 5 per cent solutions of silver 
nitrate destroyed a high percentage of the grubs but the action was 
siower. To illustrate the resistance of the larve to the action of 
certain insecticides it might be mentioned that submergence for 
two minutes in such materials as crude petroleum and spirits of tur- 
pentine killed a comparatively small number. 
APPLICATION OF MATERIALS TO GRUBS IN THE BACKS OF CATTLE 
Many years ago the application of various smears to the backs of 
cattle was advocated by many, including such authorities as Ormerod 
(77) in England. The object in view, however, was not the destruc- 
tion of the larve in the subcutaneous tissues but the prevention of 
infestation. In connection with their work the present writers have 
learned of the use by farmers and dairymen of the injection of such 
substances as kerosene oil and turpentine into the cysts for the pur- 
pose of destroying the grubs. Some men have practiced this method 
for years and are well pleased with the results. In Germany the 
warble commission (67) advocated the application of birch tar oil to 
the grubs individually in the backs of cattle. In Ireland and Eng- 
land, as a result of experiments carried out by Carpenter (78), the 
application of a tobacco decoction in the form of a wash has been 
advocated. Réne (87) advises, among other methods of control, the 
injection of 1 cc. of tincture of iodine into the warble. 
Attempts to employ gas against the grubs in the backs of cattle 
have been reported on by Greve (37) and Duncan, Hewitt, and Jar- 
dine (28). ‘The results were not encouraging. 
In their own work, experiments along these lines have been carried 
out by the writers on a rather extensive scale since 1918. Most of 
these tests have been conducted in a way which made it possible to 
secure accurate records on the percentage of grubs destroyed by the 
various treatments. In this work various dairy herds were utilized 
in the vicinity of Dallas and other points in Texas, in Peoria, Ill., and 
in Orange and Herkimer Counties, N. Y. 
Three different classes of materials were employed—powders, oint- 
ments, and liquids. The powders were usually applied directly into 
the grub holes by means of a shaker can. The ointments were in 
