n inch in
length. It lives in small cysts in the wall of the fourth stomach (fig. 17)
and is also found free in the cavity of the stomach. When numerous, these
parasites cause a thickening of the stomach wall and disturb its digestive
functions. The symptoms caused by this parasite are very similar to those
produced by the twisted stomach worm. The life history of the encysted
stomach worm is not known in detail, but it is undoubtedly very much the
same as that of the twisted stomach worm. The same measures as recommended
above for preventing infection with the twisted stomach worm should be
used. Medicinal treatment would seem to be of little use, owing to the
protected position in which the parasite occurs.

[Illustration: FIG. 17.--Piece of lining of fourth stomach, showing
cysts of the encysted stomach worm (_Ostertagia ostertagi_).]

INTESTINAL PARASITES.

TAPEWORMS.

Two species of tapeworms (fig. 18) are known to occur in the small
intestine of American cattle. They sometimes grow to a length of several
yards and to a breadth of three-fourths of an inch. Small portions of
tapeworms, consisting of one or more segments, are occasionally seen in the
droppings of infested cattle. The life history is not known, but the
infectious stage is undoubtedly taken in with the feed or water, infection
being spread by the eggs of the parasite contained in the feces of infested
animals. The eggs are perhaps swallowed by some small creature (an insect,
worm, or snail) which acts as an intermediate host, and which when
accidentally swallowed by a cow while grazing or drinking carries with it
into her stomach the infectious stage of the tapeworm.

Adult cattle do not seem to suffer much from infestation with tapeworms,
but in calves these parasites may cause scouring and emaciation.

_Treatment._--Medicinal treatment for tapeworms in cattle is usually
unsatisfactory, but the bluestone treatment used for stomach worms and
mentioned above (p. 522) sometimes expels tapeworms. Arsenic in doses of
1-1/2 to 3 grains has been claimed to give good results in the treatment of
calves for tapeworms. From results obtained at the Oklahoma Experiment
Station in the treatment of tapeworms of sheep it would appear that the
efficacy of the bluestone treatment against these parasites may be
increased by the addition of tobacco. For use on cattle the bluestone and
tobacco mixture may be prepared as follows: 13 ounces of snuff or powdered