258 



GENERAL ZOOLOGY 



Hookworms. One of the most spectacular members of 

 this group of roundworms is the hookworm. There are two 

 species, known, respectively, as the Old World hookworm 



{Ancylos'toma duodena'le) 

 and the New World hook- 

 worm (Neca'tor america'- 

 nus). The story of the 

 conquest of the latter in 

 the southern part of the 

 United States is one of 

 the brightest chapters in 

 the history of preventive 

 medicine in this country. 

 The hookworms live 

 in the large intestine of 

 man. Though each hook- 

 worm is only about one- 

 half inch long, when they 

 are present in consider- 

 able numbers they pro- 

 duce serious diseased 

 conditions (Fig. 135). 

 These conditions are due 

 chiefly to two causes. 

 First, the mouth of the 

 worm is provided with 

 sharp tooth-like struc- 

 tures which pierce the 

 wall of the intestine and 

 cause constant loss of blood, upon which the worms feed. 

 In the second place, they produce poisons, which seriously 

 interfere with normal physical and mental development of 

 the infected person. The patient becomes lazy and shiftless 

 and, if a young person, fails to develop properly. A young 



Fig. 135. The effects of hookworm 



Two boys of about the same age, the one on 

 the left suffering from hookworm. (Photo- 

 graph by courtesy of the International 

 Health Board) 



