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A Biological Clock
Every living thing has what scientists call a biological clock that controls behavior. The biological clock tells _plants_ when to form flowers and when the flowers should open. It tells_insects_ when to leave the protective cocoons and fly away，and it tells animals and human beings when to eat, sleep and wake.
Events outside the plant and animal _affect_ the actions of some biological clocks. Scientists recently found, for example, that a tiny animal changes the color of its fur _because of _the number of hours of daylight. In the short _days_ of winter, its fur becomes white. The fur becomes gray brown in color in the longer hours of daylight in summer.
Inner signals control other biological clocks. German scientists found that some kind of internal clock seems to order birds to begin their long migration _flight_ twice each year. Birds_prevented from _ flying become restless when it is time for the trip， _but_ they become calm again when the time of the flight has ended.
Scientists say they are beginning to learn which _parts_ of the brain contain biological clocks. An American researcher, Martin Moorhead, said a small group of cells near the front of the brain _seems_ to control the timing of some of our actions. These _cells_ tell a person when to _awaken_ ，when to sleep and when to seek food . Scientists say there probably are other biological clock cells that control other body activities.
Dr. Moorhead is studying _ how _ our biological clocks affect the way we do our work. For example, most of us have great difficulty if we must often change to different work hours.
_It_ can take many days for a human body to accept the major change in work hours. Dr. Moorhead said industrial officials should have a better understanding of biological clocks and how they affect workers. He said _such_ understanding could cut sickness and accidents at work and would help increase a factory’s production.
譯文：
生物鐘
每一種生物都有控制它們行為的時鐘，科學家們稱之為生物鐘。生物鐘告訴植物的花朵何時生長，何時開放;生物鐘告訴昆蟲何時離開防護卵袋，遠遠飛去;生物鐘還告訴動物和人類何時進食、睡眠，何時甦醒。
外界的變化會影響某些動植物的生物鐘。例如，科學家最近發現，有一種很小的動物，會隨著白天日照時間的長短改變其毛髮的顏色。冬季日照時間短，它的.毛變成白色。夏季白天日照時間長，它的毛又變成棕灰色。
還有的生物，它們的生物鐘受體內訊號控制。德國的科學家發現，鳥類體內的某種生物鐘迫 使它們每年做兩次長距離遷移。那些被迫不能遷移的鳥，當遷移時間到來時，會顯得煩躁不安，而當這段時間過後，它們又恢復了平靜。
科學家們指出，他們開始探索大腦內部的哪些部位存在生物鐘。一位美國的研究員，馬丁• 莫亥德(Martin Moorhead)曾指出，好像是人腦前部的一小群細胞控制著人體的行為。這些細胞控制著人體睡眠、甦醒和覓食的時間。另外，科學工作者推測，可能還有另外的生物鐘細胞控制人體的其他行為。
目前，莫亥德博士正在研究生物鐘對人們工作方面的影響。比如，如果經常改變工作時間， 絕大多數人會感覺不適應。要適應工作時間上的較大變動，可能需要相當長一段日子。莫亥德博士說，工廠的領導應該對生物鐘有進一步的瞭解，懂得生物鐘對工人的影響，如此則會減少工作中的不適和事故，對提高生產大有裨益。
