NEMATHELMINTHES 95 



Family 5. Trichinellidae. (Figure 38, A, B and C.)— In the 

 minute Trichinella spiralis, the body is thicker posteriorly and 

 not so slender and filamentous anteriorly, as in the Trichuridae. 

 The embryos develop in the uterus and are hatched there, so that 

 the young are brought forth alive (viviparous). 



The Trichinellidae are found in the muscles of pigs, rats, mice, 

 man, rabbits, guinea pigs, and dogs. They are not found in birds. 

 Each larval worm is encysted in an oval capsule 0.4 to 0.6 mm. 

 long. Cysts may number 100,000 to 125,000 per cubic inch of meat. 



Life History of Trichinella spiralis. — If the cysts are eaten, the 

 digestive juices free the worms from the meat in which they are 

 encysted. They then enter the small intestine and become mature 

 in a few days. The female, 3 to 4 mm. long (male 1.5 mm.), 

 penetrates the intestinal mucous membrane and in a month gives 

 birth to 1,500-10,000 living young and then dies. Young are 

 carried from the lymph vessels through the thoracic duct to the 

 veins, and finally from the blood vessels they wander into the 

 most actively used muscles of the body, such as the diaphragm, eye- 

 muscles, and muscles of the neck. They destroy the sarcolemma 

 and become encapsulated in cysts about 1.5 mm. long. High fever 

 is a symptom of trichinosis. In Emmerslaben, Saxony, in 1884, 

 there was an historic instance of one infected pig producing serious 

 illness in 364 people, 57 of whom died in the space of one month. 



Within the past five years, a number of fatalities have been 

 recorded, due to Trichinella infections, in these United States. 



Family 6. Filaridae. — These extremely minute elongated worms 

 live in blood and lymph vessels, serous cavities of the body, and in 

 subcutaneous connective tissue. The males usually have a spirally 

 rolled tail, and the females have two ovaries. The majority of them 

 are viviparous. None of the family are blood suckers. 



Filaria bancrojti, formerly called Filaria sanguinis hominis, 

 is a slender, threadlike worm, the male about 40 mm. in length and 

 the female about 100 mm. (4 inches). They live in the lymphatic 

 glarids of man, and pass from the eggs into the blood and sometimes 

 into the kidneys. They are supposed to cause elephantiasis by 

 obstructing the flow of lymph. They are transmitted by night- 

 flying mosquitoes. Loa loa, a smaller form, is transmitted by a 

 biting fly ( Chrysops), which is day-flying. Filaria perstans is trans- 

 mitted by a midge (Culicoides). It is essentially a parasite of the 

 dark skinned races, rarely attacking the whites of West Africa. 



