ation: FIG. 24.--Lung worm (_Dictyocaulus viviparus_) of cattle.
Outlines showing natural size of male (above) and female.]

PARASITES OF THE BLOOD.

Certain flukes (_Schistosoma bovis_ and related species) which live in the
blood vessels (the large veins) of cattle in tropical and sub-tropical
countries cause bloody urine and diarrhea, the feces being mixed with
blood. These parasites have not yet been discovered in the United States,
although the natural conditions are such in some parts of the country that
they are liable to become established if introduced.

The embryos of _Setaria labiato-papillosa_ (p. 529) which occur in the
blood may be found by microscopical examination. They apparently cause no
trouble.

The organism which causes Texas fever is a protozoan parasite (_Piroplasma
bigeminum_) of microscopic size, which lives in the blood and attacks the
red blood corpuscles. For a discussion of this parasite and the disease
which it produces see page 476 of this volume.

Other parasites which live in the blood cause serious diseases known as
surra and nagana (p. 500), but as yet neither of these diseases has gained
a foothold in the United States.

PARASITES OF THE EYE.

Small roundworms, one-third to four-fifths of an inch in length, may occur
in the ducts of the lacrimal glands. Several species all belonging to the
same genus (_Thelazia_) are known. They sometimes escape from their usual
location and may be found on the surface of the eyeball beneath the lids,
or even in the eyeball. It has been supposed by some writers that the worms
seen in the interior of the eyeball ("snakes in the eye") are immature
stages of _Setaria labiato-papilosa_ (see p. 529) which have gone astray
from the normal course of their migration, but the correctness of this
supposition is uncertain.

Worms in the eyes and lacrimal ducts may cause inflammation, in which case
the eyes may be syringed with an antiseptic, such as a weak solution of
coal-tar stock dip, and iodoform ointment applied if the condition is
severe.

When worms are present in the eyeball itself, their removal depends upon
surgical treatment, usually not advisable, as the worms in that location
either cause but little trouble or disappear without treatment.

FOOTNOTES:

[11] Further information may be found in a very full report on "Insects
Affecting Domestic Animals," issued as Bulletin 5, new series, of the
Bureau of Entomology of this department