DESCRIPTION OF SPECIES 255 



opilag^o in Brazil, tunnel disease and miner's itch in Europe, 

 and chlorosis in Egypt. 



The American hookworm, Necator americanus, was probably 

 introduced into America from Africa by slaves. In many parts 

 of the latter continent as well as in parts of Asia, especially 

 Ceylon, this hookworm is very common. It occurs in the 

 gorilla as well as in man. In the United States it is occasionally 

 found in all but the most northern states, but is a great menace 

 only in the southern ones — North and South Carolina, Georgia, 

 Florida, Alabama, Mississippi, Louisiana and Texas. It also 

 presents a serious problem in Cuba, Porto Rico and Brazil. In 

 most other warm parts of the world a closely allied species, the 

 Old World hookworm, Ancylostoma duodenale, is more prev- 

 alent. It is impossible now to know what was the origin or 

 natural distribution of either species, since both worms have 

 been introduced by infected travelers into every quarter of the 

 globe. In Europe Ancylostoma duodenale is far the more com- 

 mon. It first attracted attention there as the cause of " tunnel 

 disease " at the time of the building of the St. Gothard tunnel. 

 The infected laborers, dispersing after the completion of the 

 tunnel, spread the infection to all parts of Europe, and serious 

 epidemics broke out in the coal-mining districts of Hungary, 

 Germany and Belgium. 



The Parasites. — The two species of human hookworms are 

 similar in structure; they agree in all important details of life 

 history; and both produce the same symptoms, require the 

 same treatment, and can be prevented in the same ways. They 

 are round worms, belonging to the great group of nematodes, 

 which as adults live in the small intestine of their hosts and suck 

 blood. An allied species, A. ceylanicum, found in civet cats and 

 dogs in southern Asia occasionally occurs in man. The American 

 hookworm, Necator americanus (Fig. 100), is smaller than the 

 Old World species, Ancylostoma duodenale, the measurements 

 being about eight mm. (one-third of an inch) and ten mm. (two- 

 fifths of an inch) respectively in the males, and ten mm. and 15 

 mm. (three-fifths of an inch) respectively in the females. They 

 are normally whitish in color but when gorged with blood they 

 are reddish brown. The females, which are much more numerous 

 than the males, have simple cylindrical bodies, largely occupied 

 by the threadlike ovaries and egg-filled oviducts. In the Old 



