托福考试阅读材料之Bedtime Blues

　　Never a happy topic, bed wetting is a very distressing problem for five to seven million American kids. If we can’t explain why some people like to pick on these kids, can we at least shed some light on what causes bed wetting?

　　At one time, people punished bed-wetters for acting badly, but today scientists believe that this condition has several physical causes. Some kids suffer from problems like infections or anatomical defects that can be easily identified and treated.

　　Other causes are harder to pin down. One promising area of research is on the kidney hormone ADH. We all produce more ADH hormone at night. ADH signals the kidney to slow down production. This is why we don’t go to the bathroom for eight hours at night but could never last that long between bathroom breaks during the day. Some children who wet their beds do not produce enough ADH at night. When given drugs that boost this hormone, they stop bed wetting.

　　Finally, some kids simply have small bladders and an undeveloped nervous system. The good news is that these kids, like most bed wetters, will grow out of it as their bodies develop and mature.