340 The Diseases of Animals 



There are a number of species of ticks in the South 

 that infest cattle and other animals, but this cattle tick 

 is the most important. The sheep tick, so called, is not 

 a tick, but a fly. It is of a reddish or grayish color, 

 about one -fourth of an inch long. It is readily de- 

 stroyed by any of the dips which are effective for scab. 



LIVEB FLUKES 



Liver flukes {Distoma hepaticum) are small, flat, 

 lance-shaped worms, varying in length from one-fourth 

 to one-half an inch. The worm attacks cattle, sheep, 

 goats and pigs. It is most frequently found in warm, 

 moist climates and on low, wet lands where there is 

 stagnant water. It usually attacks young animals. 

 It causes heavy losses among sheep and calves in some 

 countries. It has been estimated that a million sheep 

 die annually from this disease. It is common in the 

 southern part of the United States. An adult fluke, 

 infesting the liver of an animal, lays a large number 

 of eggs, which pass out with the dung and fall into 

 water, where they soon hatch, and attack snails, pass- 

 ing one stage of their life -history as a parasite of 

 this animal. From the snail, another free-swimming 

 form of the parasite escapes, and infests drinking water. 

 When these parasites are taken in by a susceptible ani- 

 mal they work their way to the liver and there become 

 adult parasites. 



In a few eases, in the early stages, an animal may 

 die from apoplexy, caused by some of the parasites 

 lodging in the brain; but in most cases the symptoms 



