PHYLUM NEMATHELMINTHES 



179 



Motjih — i 



Nerve 



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

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

 puhnonary disturbances, and young pigs harboring the parasite 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. 



211. 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. 86) 

 formerly affected a large population, 

 estimated to number two millions, 

 known as "poor whites," who were 

 noteworthy for their shiftlessness, 

 although they were the descendants of 

 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 



vesic/e 



C/oi^ccf 



BurSCt 



A B 



Fig. 86. — Necator americajius (Stiles) . 

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

 " Tropical Diseases," after Placencia, by 

 the courtesy of Cassell & Company.) 



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 bor- 

 ing through the epidermis and thus reaching the lymphatics or 

 capillaries immediately 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 the larvae pass either by the veins alone or by lymphatic 

 vessels and veins to the heart and from there, still following the stream 

 of venous blood, through the pulmonary artery to the lungs. Leaving 

 the blood, they pierce the walls of the lung cavities, enter those cavities 

 and follow the air passages to the pharynx, from which, by way of the 



