182 



METAZOAN PHYLA 



Mou-fh 

 Esophagus- 



Nerve 



This journey through the body is injurious to the young pig, retarding 

 its growth. The passage of the worm through the kings causes serious 

 pulmonary disturbances, and young pigs harboring many parasites remain 

 poorly nourished, weak, and unprofitable to the grower. Infection is 

 avoided by carefully cleaning the body of the mother before the time for 

 farrowing, by placing her at this time in a perfectly clean pen with clean 

 straw, and by removing both her and the young pigs to clean pasture 



just as soon as they can be taken out 

 of the farrowing pen. It is also not 

 advisable to use the same hog lot year 

 after year. 



As already noted, the ascaris occur- 

 ring in the intestine of man is morpho- 

 logically identical with the pig ascaris. 

 Some physiological difference exists, 

 however, in that eggs from the human 

 ascaris will not complete their develop- 

 ment in pigs and eggs from the pig 

 ascaris will not reach maturity in man. 

 The larval migration, however, occurs 

 in cross infections. 



213. American Hookworm. — 

 Another nematode that makes an 

 interesting journey through the body 

 of the host, which is man, is the hook- 

 worm, Necator americanus (Stiles). In 

 our southern states this worm (Fig. 92) 

 formerly affected a large population, 

 estimated to number two milhons, 

 known as "poor whites," who were 

 noteworthy for their shiftlessness, 



"Tropical Diseases," after Paclencia, by although they were the descendants of 

 the courtesy of Cassell & Comimny.) , . . , , i rm 



very good immigrant stock. These 

 people lived in cabins, frequently with no other floor than the bare earth, 

 were in the habit of going barefooted, and were unsanitary in the disposal 

 of fecal waste. The eggs of the hookworm produced in the bodies of the 

 persons afflicted with this parasite are passed out with the feces and 

 deposited on moist earth. The larvae which hatch from these eggs 

 moult twice before they become infective. Then when the skin of another 

 person, most frequently that on the foot or the hand, comes in con- 

 tact with this infested earth, the larvae enter the body by boring through 

 the epidermis and thus reaching the lymphatics or capillaries immedi- 

 ately under it. They may enter the body by means of water or food 

 but this is not the usual mode of infection. From the point of entrance 



vesic/e 



Anus 



Fig. 92. — N ecator americanus (Stiles). 

 A, male. B, female. {From Manson, 



