Gid — Intestinal Worms 343 
are convulsions and trembling of the muscles. The 
animal gradually becomes weaker, until it is unable to 
walk, and finally dies. 
In rare cases, the larvee have been removed surgically 
by cutting out a section of the skull-bone. But the only 
practical treatment is preventive. Sheep must be kept 
off infected pastures and away from dogs or other 
animals that seatter the infection. The heads of sheep 
dying from gid should be destroyed by boiling or burn- 
ing, so that the cysts will not be eaten by dogs and 
spread the contamination. 
INTESTINAL WORMS 
The digestive tract is frequently infested with para- 
sitic worms. These are found particularly in the stomach 
and intestines. They are common in the dog, cat, pig, 
horse and sheep, and occasionally are found in cattle. 
In most cases, intestinal worms gain their nourishment 
from the partially digested food, but some may live on 
blood, or pus or serum which exudes from irritated 
tissues to which the worm may be attached. 
Intestinal and related worms may be divided into 
four classes: the flat, segmented, and usually long, 
tape-worm ; the flat, lance-shaped fluke- worms, found 
in the liver; the thorn-headed round-worms; and the 
common round-worms. 
The tape- worms (Fig. 53) are usually long, often mea- 
suring many feet, but in some cases they may not be over 
a half inch in length. Part of their life-history is as fol- 
lows: he adult worm infesting the intestine of the host 
