PARASITES AND PARASITIC DISEASES OF HORSES Zi. 
region in the form of yellow crusts. In either case, the eggs develop 
outside of the body, as do those of the large intestinal roundworm, 
and in a few days they reach the infective stage. Each egg which 
develops normally contains a small worm within the shell. Ordi- 
narily the eggs do not hatch outside the horse’s body. Horses become 
infested with pinworms as a result of swallowing the infective eggs 
in feed or water. 
Symptoms and lesions—The most evident injury produced by 
pinworms is the irritation of the anus, which causes a horse to rub 
its tail and buttocks against any convenient object. This irritation 
may result from the passage of the worms out of the anus, from the 
crushing of the female worms as they pass out, or from some irritant 
property of the eggs. It is also reported that aside from causing 
this irritation, pinworms are responsible for digestive disturbances, 
and that, when present in large numbers, they produce anemia. 
If. reatment. —Oil of chenopodium, administered as for large stron- 
gyles, is effective for the removal of pinworms from the horse. Oil 
of turpentine is also 
an effective treatment 
and should be given 
in a dose of 2 fluid 
ounces (60 cubic cen- 
timeters) for a 1,000- 
pound animal, imme- 
diately preceded or 
followed by 1 quart 
of raw linseed oil or 
by the proper dose of 
the mixture of castor 
oil and neutral oil, as 
given under the treat- 
ment for large 
strongyles. 
Prevention. — Pre- 
ventive measures with FIGURE Bea OTE: Crue ised (females), of the 
reference to the con- 
trol of pinworms are similar to those recommended for the large 
intestinal roundworms and for blood strongyles. 
LUNGWORMS 
Lungworms, Dictyocaulus arnfieldi, are long, slender, whitish 
worms and range from about 1 inch to a little over 2 inches in length. 
They occur in the bronchi and in the bronchioles (branches of the 
bronchi). 
Life history—The egg contains an embryo at the time it is depos- 
ited by the female. The eggs hatch in the lungs, and presumably 
the larvee are coughed up, swallowed, and eliminated from the body 
with the manure. It is also likely that larve are expelled with 
mucus during coughing or sneezing. In either event, the larve 
undergo their development on the eround and attain the infective 
stage in a few days. On the basis of what is known regarding the 
method of infestation with closely related species of “lungworms 
