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.

　　译文：

　　生物钟

　　每一种生物都有控制它们行为的时钟，科学家们称之为生物钟。生物钟告诉植物的花朵何时生长，何时开放;生物钟告诉昆虫何时离开防护卵袋，远远飞去;生物钟还告诉动物和人类何时进食、睡眠，何时苏醒。

　　外界的变化会影响某些动植物的生物钟。例如，科学家最近发现，有一种很小的动物，会随着白天日照时间的长短改变其毛发的颜色。冬季日照时间短，它的毛变成白色。夏季白天日照时间长，它的毛又变成棕灰色。

　　还有的生物，它们的生物钟受体内信号控制。德国的科学家发现，鸟类体内的某种生物钟迫 使它们每年做两次长距离迁移。那些被迫不能迁移的鸟，当迁移时间到来时，会显得烦躁不安，而当这段时间过后，它们又恢复了平静。

　　科学家们指出，他们开始探索大脑内部的哪些部位存在生物钟。一位美国的研究员，马丁• 莫亥德(Martin Moorhead)曾指出，好像是人脑前部的一小群细胞控制着人体的行为。这些细胞控制着人体睡眠、苏醒和觅食的时间。另外，科学工作者推测，可能还有另外的生物钟细胞控制人体的其他行为。

　　目前，莫亥德博士正在研究生物钟对人们工作方面的影响。比如，如果经常改变工作时间， 绝大多数人会感觉不适应。要适应工作时间上的较大变动，可能需要相当长一段日子。莫亥德博士说，工厂的领导应该对生物钟有进一步的了解，懂得生物钟对工人的影响，如此则会减少工作中的不适和事故，对提高生产大有裨益。

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（责任编辑：何莹莹）