Phylum Nemathelminthes and Related Phyla 433 



americaniis being the common species in the southeastern portion of 

 this country. 



Hookworm infections are seldom fatal; thus this worm can rarely 

 be accused of causing death. The most severe effects of these infections 

 are to be found in the economic and social upsets. If a population is 

 affected, the people soon become weak and unable to work effectively. 

 Thus the population of a w'hole area may soon become run down 

 physically and mentally. At one time, some of our southeastern rural 

 areas were held up as examples of the depressing effect of hookworm 

 infections. Fortunately, with the discovery of control methods and 

 the educational work of the Rockefeller Foundation, this condition 

 has largely changed. Areas that were once poor and ill-housed are 

 now prosperous. 



The adults of A^. americaniis are found in the intestinal tract. 

 The females are 10 to 11 mm. in length, w^hile the males are from 7 

 to 8 mm. Within the cup-shaped mouth cavity is a pair of chitinized 

 plates bearing sharp edges. The worm utilizes these cutting edges to 

 grasp the intestinal mucosa and obtain the blood and tissue which form 

 its food. The resulting loss of blood and intestinal injury is harm- 

 ful to the host. The female hookworm is able to produce 5,000 to 

 10,000 eggs per day. These eggs pass out with the feces when 

 they are in the four-cell stage. If the soil has the proper temperature 

 and moisture content, the embryo hatches within twenty-four hours 

 into the first larval stage. These larvae are able to move about 

 in the soil and subsist on bacteria and other organic materials. 

 After two days, the larvae molt and continue to grow; five days 

 later another molt occurs and the larvae are read\^ to infect a new 

 host. Interestingly enough after this last molt, the larvae move but 

 very slightly through the soil, but may move upward for a considerable 

 distance. At times they will crawl up on vegetation and wait for a 

 new host. Once a bare foot or some other exposed portion of human 

 skin comes in contact with this waiting larva, it burrows in and gets 

 into the blood stream. The blood soon carries the larva to the lungs. 

 Here it is caught in the capillaries and burrows into the spaces of the 

 lungs. Like Ascaris, the larva makes its way to the throat where it 

 may be swallowed. In the human being, two more molts occur before 

 adulthood is reached. It takes about six weeks before eggs are pro- 

 duced by the females. 



