54 ENTOZOA FOUND IN MAN. 



affected by special worms ; for instance the csecum 

 is iafested by the tricocephalus, the rectum by the 

 oxynris, the biliary passages by the distomum hepa- 

 ticum, and the urinary organs by the strongylus 

 gigas. 



Like the viscera, the other parts of the body 

 have their peculiar entozoa ; the trichina spiralis is 

 found in the voluntary muscular tissue, the coenurus 

 is found in the central nervous system, and the 

 cysticercus and the echinococcus are met with only 

 in natural or adventitious serous cavities. 



This limitation of certain worms to certain regions 

 is observed with such regularity that it may be con- 

 sidered as the result of a general law. 



The development and the propagation of entozoa 

 are influenced by various conditions, which are some- 

 times external, such as the geographical position, the 

 climate, and the seasons, and sometimes pecuhar to 

 the individual affected, such as the age and the sex. 



Of all the influences which bear upon the exist- 

 ence of entozoa, that of geographical position is the 

 most evident, and was even well-known to the 

 ancients. This question may be considered from 

 two points of view ; 1 . That there exist in certain 

 countries entozoa which are not observed elsewhere ; 

 2. That the number of persons affected by worms is 

 much more considerable in some countries than in 

 others. 



The filaria medinensis is developed exclusively in 

 tropical countries ; the anchylostomum duodenale has, 

 as yet, only been observed in Italy (at Milan), and 

 in Egypt ; the taenia nana and the distomum haema- 

 tobium have never been met with excepting in the 



