Dictionaries say that "spring fever" is a lazy or restless feeling . People usually have the feeling on the first warm day of spring. Everyone has probably felt it at one time or another . people have talked about it for years. Recently, scientists have taken a good look at spring fever. What they found is quite surprising. In many places we live in , the winter months often seem dark and dreary. When spring comes late March , the world becomes colorful . The number of daylight hours grows with each passing day. According to many scientists, all the sunlight sets off chemicals in the brain  . The chemicals make our feeling change and bring on spring fever. Scientists think that   _   cause(s) spring fever .
colors sunlight dark illness