. The dog as a carrier of parasites and diseases. Dogs as carriers of disease; Dogs. 10 BULLETIN 260, U. S. DEPARTMENT OF AGRICULTUBE. may attain a length of 2 or 3 feet. In the terminal segments are eggs, and these segments with the contained eggs pass out in the feces of the dog and contaminate vegetation, soil, and water. Such herbivorous animals as sheep, which graze over range or pasture contaminated in this way, pick up these eggs as they feed and swal- low them. In the stomach of the sheep the shell is digested and the small, hooked embryo released. The embryo bores its way through the
. The dog as a carrier of parasites and diseases. Dogs as carriers of disease; Dogs. 10 BULLETIN 260, U. S. DEPARTMENT OF AGRICULTUBE. may attain a length of 2 or 3 feet. In the terminal segments are eggs, and these segments with the contained eggs pass out in the feces of the dog and contaminate vegetation, soil, and water. Such herbivorous animals as sheep, which graze over range or pasture contaminated in this way, pick up these eggs as they feed and swal- low them. In the stomach of the sheep the shell is digested and the small, hooked embryo released. The embryo bores its way through the wall of the digestive tract and into the blood vessels and is carried around until it lodges somewhere. Embryos which do not lodge in the central nervous system start to grow, but very soon perish. Very commonly, however, the para- site makes its way to the central nervous system, lodging as a rule in the brain, though it occasionally oc- curs in the spinal cord. In the brain the embryo grows to form the blad- der worm or ccenurus, and this may attain the size of an egg, or even a larger size. As it grows it presses upon the adjacent portion of the brain and destroys it. The pressure and the irritation, due to the hooks with which the tapeworm heads of the coenurus are provided, cause verj' distinctive symptoms, the sheep com- monly holding its head in an odd position and walking in a circle toward one side or the other. Un- less the ccenurus is removed by oper- ation the sheep invariably dies. When the brain of such a sheep is eaten by dogs—and dogs very read- ily eat the brains of sheep by licking them out through the large opening at the base of the skull—^the ccenurus is ingested with the brains and the tapeworm heads pass to the intestines of the dog and give rise to the adult tapeworms. As in the case of the hydatid, the gid parasite must always be transmitted from the dog to other animals which eat the eggs from the dog tapeworm, and from the other ani- mals to the d
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