ie ~ “ Ror 
THE CATTLE GRUBS OR OX WARBLES rah 3 
productivity and health of the host. When the larve reach the 
esophagus 1n numbers, however, marked irritation is often in evi- 
dence. The submucous tissues are edematous, usually yellowish, and 
sometimes bloody in the region of the larve. Cases are on record | 
in which heavy infestations of the esophagus produced edematose 
conditions with large swellings. Instances are also recorded in 
which the larve burrowing along the spinal canal have caused 
paralysis of the posterior parts, although this seems to be unusual, 
considering the large number of cases in which infestation of the 
canal occurs. 
Abundant testimony is at hand as to the injurious effect-of the 
last-stage larvee under the skin in the backs of cattle. Many stock- 
men believe, and their opinion in most cases seems well founded, 
that heavy infestations of the grubs in the backs of calves are a 
prime factor in causing their death. It has been observed repeatedly 
that where these larve are removed, the calves begin to “ pick up” 
promptly. ‘The effect of heavy infestations in the backs of dairy 
cattle is also responsible for decreased milk flow. Danish literature 
contains a reference to a case observed by Boas (6), in which a 
cow producing daily from 30 to 32 pounds of milk increased the 
yield to 40 pounds a few days after 80 larve had been extracted 
from the back. Feeders frequently comment on the difficulty of 
fattening animals in which a considerable number of grubs are 
present. Those who feed steers on an extensive scale during the 
winter have informed the writers that in most cases when an animal 
-is not making proper gains, it will be found upon examination to 
have a heavy infestation of grubs in the back. When these are ex- 
tracted the animals usually respond well to the feed. Exact in- 
formation on this subject is meager. Schottler and Glaser (88) 
have reported upon an experiment which they performed in Ger- 
many on the effect of grubs on the fattening of cattle. The grubs 
were extracted from one-half of the herd and the other half kept 
as a check. The portion from which the grubs were removed showed 
a gain in weight of 5.16 per cent over the infested portion of the herd. 
Aside from the damage produced by the holes cut in the skin, 
there is other injury produced to the host itself by the grubs while 
located in the subdermal tissues of the back. When the young larve 
first reach the subcutaneous tissues along the back, marked swellings 
are often produced. These are evidently painful, as indicated by 
the action of the host when they are touched. Just how much irri- 
tation is produced after this is problematical. Undoubtedly the 
spiny armature of the fourth and fifth stages causes considerable 
irritation, but it is supposed that the encystment sac surrounding the 
larger larve is practically free from nerves, and for this reason 
the host probably does not experience any considerable amount of 
pain or annoyance. Not infrequently, however, pus organisms gain 
entrance to the openings, and often large abscesses are formed under 
the skin. These are associated usually with the death of the larva, 
either by crushing or by its imprisonment and suffocation from the 
firm plugging up or scabbing over of the hole in the skin. In a 
number of instances abscesses have been observed which were half 
as large as the crown of a man’s hat and very sore. If these are 
well opened and drained they soon heal, but where they are not 
