ANIMAL PARASITES. 127 



Infestment is common in both the Old and the New 

 World, although two distinct species of worms are con- 

 cerned; the Old-World Uncinaria duodenalis, and the 

 New- World Uncinaria Americana. The disease, which 

 is characterized by a grave anaemia, and in untreated 

 cases has a large mortality, is widely distributed in 

 tropical and sub-tropical countries. There are also 

 endemic foci in temperate climates. The island of 

 Porto Rico seems to suffer more from this parasite 

 than any other country, one-fourth of the total deaths 

 in a single year (1903) having been ascribed to it. The 

 anaemia prevalent in our own Southern states has been 

 demonstrated by Stiles to have the same origin. In 

 temperate climates, infestment is common in tunnel- 

 workers and miners. 



The adult worms, which jneasure from 8-10 milli- 

 meters (males) to 12-18 millimeters (females), live in 

 the small intestines. From a bending backwards of 

 the anterior extremity the name hook-worm has been 

 derived. They are blood-sucking parasites, and by 

 means of teeth and a powerful sucking apparatus attach 

 themselves to the mucous membrane lining the gut. 

 A few parasites do not cause symptoms, but where their 

 numbers are large — in many cases 1000 or more — the 

 drain upon the body is considerable, often ending 

 fatally. In children their presence interferes with 

 development. Only the eggs of the parasite appear in 

 the stools, where they are usually present in enormous 



