158 ANIMAL PARASITES IN THE STOMACH 



they hatch producing the larval form. The larvae are taken 

 up with contaminated food and bedding by healthy horses 

 and reach the intestines. From the lumen of the intestines 

 they pass probably into the veins of the mucous membrane 

 and reach the liver through the portal circulation; or they 

 may pass into the lungs through the right heart and from 

 the lungs enter the general arterial circulation. In the 

 trunk of the anterior mesenteric artery they form the worm 

 aneurysm which is one of the causes of colic (embolic) in 

 the horse. The emigration of the larvse from the aneiu-ysm 

 back to the intestine occurs in that they are carried by the 

 arterial blood to the peripheral intestinal arteries. They 

 then form embolic worm nodules in the bowel walls. Later 

 the larvae perforate the mucous membrane, re-enter the 

 bowel and attain sexual maturity. 



Sclerostomum Edentatum. — This parasite is found in the 

 large intestines in about one-half of the horses. The eggs 

 are passed out with the feces. The embryos are taken 

 up with the food and water and enter the digestive tract 

 of healthy horses. They pass into the bowel walls and 

 reach the subserosa of the parietal peritoneum, where they 

 produce hemorrhages in the peritoneum. Occasionally in 

 colts they cause anemia. Their presence frequently induces 

 an adhesive peritonitis. Rarely the parasite is found free 

 in the abdominal cavity or in the scrotum. From the sub- 

 serosa the larvse wander between the leaves of the mesentery 

 back to the large intestines, in the wall of which they become 

 encysted. They later enter the lumen of the bowel and 

 attain sexual maturity. 



Sclerostomum Quadridentatum. — Sclerostomum quadridenta- 

 tum is very rare and does not seem to have a pathogenic 

 action. 



StTong-ylus Tetracanthus. — This palisade worm lives in 

 the mature state in the colon where often large numbers 

 appear in colts. They produce a hemorrhage and even 

 necrotic enteritis with colic and bloody diarrhea. In the 

 feces large numbers of very small strongyli are found. 

 Sometimes death results from bowel hemorrhage. The 

 eggs pass out with the feces and from them rod-shaped 



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