Flatworms and Threadworms 303 



vomited forth, or it may crawl up the oesophagus and then pass into 

 the larynx and asphyxiate the patient. In fact, it may enter any ducts 

 or tubes in the body. 



Oxyuris vermicularis (commonly called pin-worms 

 or thread- worms), (Fig. 188), are parasites of the rec- 

 tum and colon. The male is about 4 mm. long and 

 the female about 10 mm. The parasites migrate and 

 come close to the surface during the night, thus caus- 

 ing accentuated irritation and itching about the rec- 

 tum and genital organs. Many eggs are found in the 

 faeces of infected children. It is essential that the dis- 

 Fig - 19 °- tinguishing and diagnostic difference between oxyuris 



a., e mai°e°; °b™ fe- e gg s an d trichocephalus eggs be known. Both types 

 ^p a eniW 'ford*s h c'har^e are <l uit ? alike exce Pt that trichocephalus eggs have a 

 of e gg s - (After button-like lighter area (Fig. 189, 16). Re-infection 

 must be guarded against. These worms often find 

 their way into the appendix of children where they drill into the mucous 

 membrane and cause appendicitis. Trichina (Fig. 187), (also called 

 Trichinella spiralis), lives in the small intestine when adult. The disease 

 trichiniasis is caused by the embryos after they pass from the intestines 

 to the voluntary muscles where they encapsulate themselves as larvae. 



The female is 3 to 4 mm. long and the male 1.5 mm. There are two 

 tiny projections from the posterior end of the worm. The larvae, when 

 encased in the muscle, are about 1 mm. long. Trichina has a pointed 

 head and a somewhat rounded tail. The parasites are ingested by man 

 when eating inadequately cooked pork. Each worm may produce as 

 high as 10,000 young, which are either placed directly into the lymphatics 

 by the female or burrow through the intestinal wall. They then encyst 

 in the muscle tissue. Pigs acquire the disease by eating offal or infected 

 rats. 



Twenty-six different kinds of animals have been found to harbor 

 trichinae, and as many as 15,000 of these parasites have been found in 

 one gram of muscle. 



It may take about six weeks for complete encapsulation, but once 

 encapsulated, they may remain alive in the muscle for twenty or twenty- 

 five years. 



Pigs may be literally "filled" with these parasites, although they 

 may show no external sign of infection. The result is what is known 

 as "measly" pork. Many countries now insist on pork inspection to 

 prevent a spread of infection. 



The patient usually suffers with a fever, anaemia, muscle pains 

 (myositis), which are often mistaken for rheumatism, and intestinal 

 disturbances (gastro-enteritis) . 



Ankylostoma duodenale in the old world, and Necator americanus 

 in this country are the Hook-worms (Fig. 190). The disease caused 

 by hook-worm is variously known as ankylostomiasis, uncinariasis, 



