THE DOG AS A CARRIER OP PARASITES AND DISEASE. 
13 
by sheep as they graze over range or pasture or drink water con- 
taminated by these feces. In the sheep the eggshell is digested, the 
released embryo bores through the tissues and comes to rest usually 
in the edible musculature, and the bladder worm develops to the 
cysticercus capable of again infecting the dog. In cases of heavy 
infestation sheep are liable to die in the course of two to three weeks, 
but as a rule the health is not perceptibly affected. Here, as in all 
similar cases, the parasite must pass from the dog to the sheep and 
from the sheep to the dog. 
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1 
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Fig. 7. — Tapeworm {Taenia ovis) developed by feeding bladder worm {Cysticercus ovis) 
to a dog. (From Ransom.) 
The parasite has been found in Europe, Africa, and New Zealand. 
It has been found thus far in seven States in this country. It appears 
to be particularly prevalent in the West, a fact that is possibly re- 
lated to carelessness on the part of the western sheepmen as regards 
the disposal of carcasses of sheep dying on the range. Such sheep 
are usually left lying where they die, a practice which aids in the 
spread and continuance of gid, and which serves the same purpose 
in the case of the " sheep measles " parasite that throwing diseased 
viscera of hogs onto the fields does in the case of the hydatid para- 
site. The sheep dog is probably the principal carrier of the parasite, 
