DISEASES DUE TO ANIMAL PARASITES 195 



reach enormous size, or the parasite may die and the 

 cyst shrivel and disappear. 



Morbid Anatomy. The increasing size of the cyst 

 causes destruction of surrounding tissue and pressure- 

 atrophy. In the brain, death may occur early with 

 pressure symptoms. 



Morbid Physiology. This depends upon the location 

 of the cyst and its size. 



DISEASES CAUSED BY NEMATODES OR ROUND-WORMS 



ASCARIS LUMBRICOIDES 



This is one of the most common small parasites affect- 

 ing man. The worm develops in the small intestine 

 after swallowing of the eggs in food or drink. The 

 worm resembles in appearance the earthworm or common 

 angleworm. While it inhabits the small intestine prin- 

 cipally, it sometimes migrates to other parts, as the 

 gall-ducts, the stomach, the esophagus, or even the 

 larynx. They give rise to few symptoms aside from 

 intestinal irritation. Large masses have caused intesti- 

 nal obstruction. 



OXYURIS VERMICULARIS 



This parasite is termed the thread-worm or seat- worm. 

 It inhabits the colon or rectum commonly in children. 

 It may migrate to the vagina. It causes intense itching 

 and irritation. 



