TRICHINA, HOOKWORMS, FILARIA, ETC. 81 



the parasites may emigrate to other parts of the host, but 

 ordinarily they remain in the alimentary tract. 



The life history and mode of infection are similar to those of 

 the preceding species. The eggs may be washed from the 

 f eces into drinking water, or they may become dry and be blown 

 about as dust or become attached to fruit or vegetables. 

 Soon after they reach the stomach of their host they begin 

 their development. Strong vermifuges are necessary to re- 

 move them, but such medicines should be used only under 

 the doctor's advice. 



Still another species, Ascaris canis, is a very serious pest of 

 dogs, especially puppies, and often causes serious losses to 

 breeders of these animals. It occurs also in cats, lynxes and 

 lions. 



The stomach worm of sheep, Hcemonchus (Strongylus) 

 contortus, is another important intestinal parasite belonging 

 to the group. It is a very small thread-like species occurring 

 in the fourth stomach of sheep, cattle and goats. The larvae 

 which hatch from eggs that pass out with the feces get on the 

 grass blades and so into the stomach of new hosts. As the 

 infection is direct the disease often spreads rapidly and does 

 serious damage, particularly to lambs, which may die in con- 

 siderable numbers. 



Uncinariasis, or Hookworm Disease. Perhaps no other 

 disease has attracted so much attention in the United States 

 during the past few years as the hookworm disease. It 

 is caused by a small round-worm from one-half to four-fifths 

 of an inch in length. On the anterior end, which is bent 

 back giving it the suggestive hook shape, is the cup-like mouth 

 by means of which the parasites attach themselves to the 

 mucous membrane of the walls of the intestine, where, in ad- 

 dition to sucking the blood of the victim and affecting the 

 mucous membrane, they produce a poison which may affect 

 the host in a variety of ways. The most pronounced symp- 

 toms are anemia and aberrations of appetite. The skin be- 

 comes dry, waxy white, or dirty yellow, and the patient may 

 eat too little or too much. In severe cases there seems to be 

 an uncontrollable desire for such things as chalk, rotten 



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