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THE CATTLE GRUBS OR OX WARBLES 5 
They have also expressed the opinion that it is not improbable 
that the larve may go from the legs to the gullet and thus to the 
back. Hadwen, working in British Columbia, has also made some 
valuable contributions to our knowledge of Hypoderma. In a paper 
published in 1912 (32), he presents data on the injuriousness of the 
cattle grubs in Canada and adds some valuable information on the 
method of egg laying of ZH. bovis. 
The seriousness of injury by cattle grubs in Germany led to the 
appointment of a commission to study all phases of this subject. 
Several years were spent in this investigational work and the results 
were published in. parts in the years 1912 to 1919 (67). A large 
amount of information was obtained on the losses due to the pests, 
relative numbers of the two species, life histories and habits, and 
control work. 
C. Stub (95-99) carried on observations on cattle grubs in Den- 
_ mark and published his records in 1912, 1913, 1915, and 1919. He 
added to the information on the life history and habits of the 
insect and reported that, in collaboration with Prof. Phil Boas, he 
found beneath a number of eggs a burrow through the skin which 
they interpreted as the entrance hole of a newly hatched larva. 
Stub also found larve from 2 to 7 millimeters long in the subdermal 
connective tissue of calves. In early records, he concluded that the 
larvee burrow directly through the skin, but was under the erroneous 
impression that the eggs are laid on the back. In 1919 (99) he 
definitely traced the course of young larvee from the inside of the 
~right tibia to the esophagus. 
Hadwen published further observations on the life history and 
seasonal development of both species in 1915 (33). In this paper he. 
showed that larve removed from the gullet and placed under the 
skin on the leg of calves would work upward rapidly through the 
connective tissues and ultimately reach the back. In 1916, Hadwen 
and Bruce (38) attempted to trace the larve as they left the gullet 
and suggested that they pass up the crura of the diaphragm or along 
the posterior borders of the ribs to the neural canal and out through 
the posterior foramen to the subcutaneous tissues of the back. In 
another paper (34), in 1916, Hadwen added further data on the 
seasonal development of the larve and demonstrated the ability of 
the newly hatched larve to penetrate bovine skin. He also described 
lesions on cattle chargeable to the penetration of Hypoderma larve. 
Later a concise account of the cattle grub problem was issued by 
Hadwen (36). 
In 1920 Carpenter and Hewitt (78) described in detail a successful 
experiment with warble eradication on Clare Island, Ireland; and in 
1922 in the sixth report (79) on the problem, Carpenter, Phibbs, and 
Slattery presented further information on the life and seasonal his- 
tory of both species of Hypoderma and further experimental evi- 
dence that larve enter the host through the skin only and not by 
way of the mouth. This report also summarizes tests with various 
dressings applied to the backs of cattle to kill the grubs, especially 
tobacco-powder wash. The biologies of Hypoderma and _ other 
aspects of the grub problem were summarized by Seymour-Jones 
(91) and Warburton (770) in 1922. 
