_The common sucking lice_ occurring on animals are the large-headed horse
louse, _H. macrocephalus_; the long-nosed ox louse, _H. tenuirostris_; the
large-bellied ox louse, _H. curysternus_; the _H. stenopses_ of sheep; _H.
suis_ of swine; and the _H. piliferus_ of the dog.

The _common biting lice_ (Fig. 63) that are found on domestic animals are
the _T. pilosus_ and _T. pubescens_ of solipeds, _T. scalaris_ of the ox,
_T. spoerocephalus_ of sheep and goats, _T. latus_ and _T. subrostratus_ of
the dog and cat. _Menopon palidum, Lipiurus variabilis_ and _Gonoides
dissimilis_ are the common lice found on poultry.

[Illustration: FIG. 63.--Biting louse.]

SYMPTOMS OF LICE.--The symptoms of lousiness depend on the variety of lice
present, the degree to which the animal is infested with them, its physical
condition and the care that it receives. Lice multiply more rapidly and
cause greater loss during the winter months than they do in the summer,
when the animals are not housed and the opportunity for infection from the
surroundings is not so great. The sucking louse (Fig. 64) is the most
injurious and irritating. The irritation and loss of blood that the animal
may suffer when badly infested by this parasite may result in marked
unthriftiness. Young and old animals that are not well cared for suffer
most. The biting louse may bite through the superficial layer of the skin,
and cause the animal to bite and rub the part. This irritation to the skin
prevents the animal from becoming rested, and after a time seriously
interferes with its thriftiness.

_Horses and mules_ show a staring, dirty, rough coat. The mane and tail may
become broken and matted. The animal rubs against the stall, fences and