SOME REACTIONS AMONG ANIMALS 



157 



Write a paragraph summing up all you know about the 

 trichina. 



Observations. 1. Examine a slide of the hookworm (Unci- 

 naria americana), and Figure 48. See if you can tell why it is 

 called the hookworm. 



2. In addition to hooks 

 for hanging on to the lining 

 of the intestine, these 

 worms are provided with a 

 fanglike hook for drawing- 

 blood from their victim. 

 This fanglike hook is also 

 poisonous. The poison is 

 supposed to prevent the 

 blood from clotting that 

 runs from the small wounds 

 they inflict. How might 

 continuous bleeding from 

 small wounds at last affect 

 the host ? 



Note. As many as from 

 600 to 4000 have been found in the bodies of their victims. 



3. The poison set free is also said to affect the red marrow 

 of the bones where much blood is made. How might the 

 victims indeed become lazy ? 



Conclusion. Explain how the hookworm, came to be called 

 the " lazy worm." 



Observations. 1. The female hookworm lays her eggs in the 

 intestines of her victim, but they cannot develop without 

 oxygen. They therefore pass from the body to hatch. 



2. More than 70% of the "poor whites" and negroes of the 

 South have no toilet closets. The few there are might be easily 

 accessible to pigs and chickens. How might hookworm larvae 

 be scattered through the damp soil ? 



3. The larvae of these worms are able to bore through the 

 skin through the hair pores. 



FIG. 48. Anterior end of a hookworm. 

 Note the tiny hooks on the anterior end. 

 (Photograph by Mr. J. J. Schoonhoven.) 



