34 



ECONOMIC ZOOLOGY 



deficient mentally; many are tuberculous. One of the curious and 

 disgusting characteristics of these people, at times, is the habit of 

 eating dirt, wood, hair, clothing, etc., although the victim usually will 

 deny the habit. 



About the beginning of the present century Dr. C. W. Stiles, 

 a zoologist, then in the Bureau of Animal Industry, now in the Marine 

 Hospital Service, knowing the effect of hookworm upon the lower 

 animals, made the prediction that it would be found that the condition 

 of these supposedly lazy "poor whites" of the south was due to their 

 being infected with hookworm. The newspapers made great sport 

 of Dr. Stiles' "lazy germ" but the prediction was very soon fulfilled, 



FIG. 25. Hookworm, Necator americanus. A, male; B, female. Xio. (After 

 V. L. Kellogg and Doane, Economic Zoology and Entomology, from Wilder.) 



and we now know that these "poor whites" are not degenerates 

 but are sufferers from a serious, though usually easily cured, disease, 

 named from the worm that is its cause. 



The worm, Fig. 25, is a small nematode about i cm. in length and 

 about the diameter and color of a very dirty piece of sewing cotton. 

 The male may be easily distinguished from the female by the flaring, 

 fin-like posterior extremity. At the anterior end is the tiny mouth, 

 armed with sharp teeth for puncturing the soft mucosa of the digestive 

 tract; it is in the jejunum that they are chiefly found. They vary in 

 number, in a single individual, from about a dozen to over 4000; 

 but the severity of the attack is not always in proportion to the 

 number of worms found, death having resulted with the former 

 number of worms and recovery with a latter number. They may live 

 in the intestine for five or six years, or even longer. The complete 



