CHAPTER XIV 

 THE ROUND WORMS AND FLAT WORMS 



The round worms, or nematodes, have an unsegmented 

 and nearly cylindrical body commonly tapering toward 

 one or both ends. Many species live in the soil or in 

 decaying organic matter, while numerous others are 

 parasitic in the bodies of animals. Some of the species, 

 such as the large round worm of the horse, Ascaris megalo- 

 cephala and the related species, Ascaris lumbricoides 

 found in pigs and sometimes in man, attain a length of 

 several inches. Others are of almost microscopic size, such 

 as the vinegar-eels which are very frequently seen in 

 cider vinegar. These forms are easily obtained and when 

 observed with a microscope the principal internal organs 

 may be seen in their semi-transparent bodies. They are 

 entirely harmless, and there is no need to be fastidious 

 about taking them in with our food. 



One of the most dangerous of the many nematode 

 parasites of man is the Trichina (Trichinella spiralis). 

 The worms are commonly taken into the body by eating 

 insufficiently cooked pork, for the Trichina is a common 

 parasite of the pig. In the pork the worms are in an 

 encysted state in the muscle; when this is digested, the 

 worms are liberated, after which they grow to maturity 

 in the intestine where they produce new worms. These 

 young worms bore through the intestinal walls and get 

 into the blood vessels where they are carried to various 

 parts of the body; they then work into the tissues, com- 

 monly the muscles, and there encyst. It is during the 



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