184 TROPICAL MEDICINE AND HYGIENE 



probably through various insects, parts of them being 

 accidentally swallowed. 



The Bothriocephalus is introduced by swallowing 

 imperfectly cooked fish containing the plerocercoid larvae. 



In the instances when man is the intermediate host, as 

 when the Cysticercus cellulosce develops in him or the 

 Echinococcus cysticercus hydatid cyst he must have 

 swallowed the oncospheres, probably with uncooked 

 vegetables. 



Trichina spiralis can only be introduced by swallowing 

 imperfectly cooked and infected meat of various species 

 of animals, usually pork though flesh of man or rats 

 would be equally effective. 



Prevention. The exact measures required for prevention 

 in each worm must differ, but there are a few general 

 problems involved. 



It will be seen that verminous infection is rarely 

 carried by drinking water, and even when it is so, as 

 in the case of the Guinea-worm, the actual carriers, 

 the Cyclops, are objects visible to the naked eye ; or, 

 as in the case of cercariae of flukes, bodies sufficiently 

 large to be removed by any rudimentary method of 

 filtration. Though eggs and encysted larvae may be 

 found in the mud at the bottom of tanks they are not 

 found in the superjacent water, as they are heavy and 

 sink to the bottom. Water, therefore, that appears clear 

 and free from visible parasites is not an important cause 

 of verminous infection when drunk. 



Bathing is more important, as in the mud at the edges 

 and bottoms of pools or streams such worms as are able 

 to penetrate the skin have every chance of doing so. 

 Ponds, pools, and streams used for bathing are also 

 often used for defaecation, many natives defecating in 

 water. Others defaecate in the luxurious vegetation often 

 found at the edges of such watering places, and in 

 either case the ground on the banks and at the edges 

 will contain larvae of ankylostomes, of Strongyloides, and 

 possibly the supposed developmental forms of the Schisto- 





