INTESTINAL PARASITES OF HOGS.--The _Ascaris suis_ or _common round_ worm is
very commonly found in the small intestine. It is quite frequently found in
large numbers, almost filling the lumen of the intestine of an unthrifty
pig (Fig. 75). It may also work its way into the bile duct. Sometimes,
after a hog has died, this parasite migrates forward into the stomach and
gullet. The _A. suis_ is from 4 to 10 inches (10 to 26 cm.) long.

_The Echinorhynchus gigas_ or _thorn-headed_ worm is the most dangerous of
all intestinal worms (Fig. 74). It is usually found with its proboscis or
thorn imbedded in the wall of the small intestine. The Echinorhynchus is
not as common a parasite as the Ascaride, and it is not usually present in
large numbers. Usually, not more than a half-dozen of these worms are found
in the intestine of a hog, but in some localities and in hogs that are
allowed to root around manure piles and in clover pastures the herd may
become badly infected with them and serious losses occur. The average
length of the male is about 3 inches (8 cm.) and the female 10 inches (26
cm.).

[Illustration: FIG. 77.--Whip-worms attached to wall of intestine.]

[Illustration: FIG. 78.--Pin-worms in intestine.]

The _Trichocephalus crenatus_ or _whip worm_ (Fig. 77) is slender or
hair-like in its anterior two-thirds and thick posteriorly. It is from 1.5
to 2 inches (40 to 45 mm.) long. It is found in the caecum attached to the
wall by the hair-like portion.

The _OEsophagostomum dentatum_ or _pin worm_ is from 0.3 to 0.6 inch (8 to
15 mm.) long. It is found in the large intestine (Fig. 78).