Scab 321 
are the mites. If they are examined with a lens, their 
outlines can be seen. 
Scab of Sheep 
(Psoroptes communis, var. ovis) 
At first, itching of the skin is shown by the 
animal’s scratching with its hind feet, or biting 
and pulling wool. In bad cases, the wool may be 
shed over very large surfaces; but in ordinary cases the 
fleece has a ragged appearance and is wet and matted 
where the animal has bitten at it and pulled out tags 
of wool. The itching is more intense when the animals 
are warm with exercise. If the wool is parted over an 
itching spot and the skin examined closely, yellow pim- 
ples will be found which, on being pinched, exude a 
watery fluid. This fluid dries on the skin into yellow- 
ish, greasy scabs, which increase. in area and thickness. 
These scabs are often torn off by the sheep, thus in- 
creasing the irritation. 
An animal affected with scab falls away in flesh, 
becomes weak and debilitated, and presents an unthrifty, 
ragged appearance. The disease is most severe during 
the fall and winter months, when sheep are closely con- 
fined and are fed on dry food. In the large sheep- 
growing regions of the Southwest, scab is a common 
and very serious disease, causing heavy losses, not so 
much from the death of animals as from the general 
debility which it produces in large herds, and the con- 
sequent loss of flesh. The scab mites are transmitted 
by direct contact and by means of the tags and scabs 
seattered on the ground in yards and pens. Infested 
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