282 OTHER INTESTINAL ROUNDWORMS 



some other causes, the strongyloids increase in number and un- 

 doubtedly intensify the bad condition. 



The worms are not so readily expelled by drugs as are most of 

 the intestinal parasites, being able, on account of their small size, 

 to stow themselves away in the folds and villi of the intestine 

 where drugs do not reach them. 



Since the strongyloid occurs in the same countries as do the 

 hookworms, though more limited in distribution, and has a 

 similar mode of transmission and infection, the same preventive 

 measures which are used against hookworm are of service against 

 this comparatively harmless companion of it. 



Other Species. There are a great many other worms which 

 occasionally make their home in the human digestive tract, some 

 being locally common, others merely sporadic in their occurrence ; 

 some, in fact, are not truly parasites at all, but have merely 

 established themselves temporarily after having been swallowed 

 with infected food. Stephens lists 59 species of nematodes as 

 having been observed in man. None of those not already 

 mentioned can be considered of great importance, since they 

 seldom cause serious ailments and are most of them rare. Only 

 those which are true parasites and have been recorded from man 

 more than once need be mentioned here. 



Belonging to the same family as Ascaris (Ascaridae) or to 

 closely allied families are: Belascaris cati (or Ascaris mystax) 

 (Fig. 106) and Toxascaris limbata (or Ascaris marginata) , small 

 Ascarids two or three inches in length, normally parasitic in cats 

 and dogs respectively, found practically all over the world but 

 only occasionally in man; and Physaloptera mordens (Fig. 106), 

 a worm one and a half to two inches long, which appears to be 

 not uncommon in negroes in central East Africa. 



Allied to the hookworms and having an expanded umbrella- 

 like " bursa " at the posterior end of the male are several species 

 of Trichostrongylus (or Strongylus). T. instabilis (subtilis) (Figs. 

 106 and 114) is a smalFwornTTrom four to six mm. (one-fifth of 

 an inch) in length, somewhat resembling a hookworm but much 

 more slender. It is normally parasitic in the small intestine 

 (duodenum) of sheep, camels, baboons and other animals and 

 occasionally occurs in Egyptian " fellahs." A closely allied 

 species, T. orientalis, is found in the duodenum of Japanese. 

 Other species of this genus normally found in herbivorous ani- 



