PARASITISM 



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ulcerated. They may also produce systemic disorders such as allergy 

 and anemia. 



Those intestinal parasites that feed on the intestinal wall include 

 protozoa, the intestinal flukes, a lew roundworms and a few fly larvae. 

 Man is attacked by an ameba, a flagellate and a ciliate, all of which 

 live in the large intestine. The ameba, Ent(unoeba histolytica, is the 

 most harmful and has already been described. The flagellate, Triclio- 

 mojias honinis, is the least harmful. It feeds primarily on bacteria and 

 debris and only occasionally produces diarrhea or other signs of dis- 

 tress. At such times it is suspected of feeding on the intestinal lining. 

 The ciliate, Balantidium coli, is injurious but uncommon. It digests the 

 intestinal mucosa, produces ulcers like those of the ameba, and can 

 cause death. 



Several families of flukes live in the intestine and its associated 

 passages (bile ducts, etc.). Like their ectoparasitic relatives on the gills 

 of fishes, these trematodes attach by the ventral or posterior sucker and 

 feed through the oral sucker, scraping oft the superficial layer of cells. 

 Their damage is slight unless they become numerous. 



The most injurious group of intestinal parasites is the bloodsuck- 

 ing hookworms, a group of nematodes. Their effect is seldom sudden 

 or catastrophic but is chronic and insidious, sapping the vitality of the 



Fiaure 39 8 Giardia lamblia. A, Ventral view showing two nuclei. B, Lateral 

 view showing attachment to host intestinal cell. C, Cyst passed in the feces, capable 

 of infecting a new host. (After Chandler.) 



