PINWORMS:
DEFINITION: Pinworms are small parasites (about 1/4 inch long) which
live in the large intestine.  They come out at night to lay eggs around
the anus.  Anal itching results.  The victim scratches, picking up some
eggs on the fingers.  The microscopic eggs then get into the victim's
mouth from his fingers, or may be passed on to another person. 
Abdominal cramping may result when the infestation is severe. 
Treatment is aimed at killing the worms, and preventing the egg -->
finger --> mouth --> worm --> egg cycle.  It is often necessary to
treat the whole family with medication.  Good handwashing, short
fingernails, and daily washing of all bedclothes and underwear help
prevent re-infection.  Call the doctor if you develop abdominal pain,
frequent vomiting, fever, or blood in the stools.