NEMATHELMINTHES. ROUND-WORMS 39 



to prevent the worm from withdrawing into the body, each day a little 

 more of the worm is wound on the stick until it is all out of the skin. 

 It may also be removed by surgery or may be killed by injections of 

 bichloride of mercury. 



Pinworm, whipworm and various other small nematodes are some- 

 times parasitic in the human digestive tract. 



