82 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



wood, sand, gravel and all kinds of dirt. This has given the 

 popular name of "dirt eaters" to those affected with this 

 parasite. 



The myriad eggs produced by the adult hookworms pass 

 out of the body of the host with the feces, and if these fall on 

 the ground and the temperature and moisture conditions are 

 suitable, as they usually are in the tropical and semi-tropical 

 regions where this disease is worst, the young larvae soon hatch 

 and grow for a few days before they become encysted. In this 

 latter condition they may remain for some time, even several 

 months, until they are in some way introduced into a new 

 host. There are two possible ways of infection, through the 



FIG. 27. Hookworm, Necator americanus. a, Male; b, female. (Greatly 



enlarged; after Wilder.) 



mouth or through the skin and the circulatory system. For a 

 long while it was thought that infection was wholly through the 

 mouth, but it is now known that this is not even the usual 

 mode of infection. When the encysted larvae come in contact 

 with the skin of some person, such as the bare foot of a child, 

 they break from their covering and burrow their way into the 

 skin through some of the pores or hair follicles. They soon 

 find their way into the circulation and later into the lungs or 

 larynx and finally are swallowed and attach themselves to the 

 walls of the alimentary canal. 



In passing through the skin they produce certain symptoms 

 commonly known as ground itch which often causes much 

 suffering. It will be seen that children are, under ordinary 



