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Electricity
The modern age is an age of electricity. People are so used to electriclights, radio, televisions, and telephones that it is hard to imagine whatlife would be like without them. When there is a power failure, people gropeabout in flickering candlelight, cars hesitate in the streets becausethere are no traffic lights to guide them, and food spoils in silent refrigerators.
Yet, peoplebegan to understand how electricity works only a little more than two centuriesago. Nature has apparently been experimenting in this field for millionsof years. Scientists are discovering more and more that the living worldmay hold many interesting secrets of electricity that could benefit humanity.
All livingcells send out tiny pulses of electricity. As the heart beats, it sends outpulses of record; they form an electrocardiogram, which adoctor can study to determine how well the heart is working. Thebrain, too, sends out brain waves of electricity, which can be recorded inan electroencephalogram. The electric currents generated bymost living cells are extremely small -- often so small that sensitiveinstruments are needed to record them. But in some animals, certain musclecells have become so specialized as electrical generators that they do not workas muscle cells at all. When large numbers of these cells are linked together, the effects can beastonishing.
The electriceel is an amazing storage battery. It can send a jolt of as much as eighthundred volts of electricity through the water in which it lives. (An electric house current is only one hundred twentyvolts.) As many as four-fifths of all the cells in the electric eel's body are specialized for generatingelectricity, and the strength of the shock it can delivercorresponds roughly to the length of its body.
电当今时代是电气时代。 人们对电灯、收音机、电视和电话早已司空见惯以致很难想 象没有它们生活会变成什么样。
当停电时，人们在摇曳不定的烛光下暗中摸索; 因没有红 绿灯的指示，汽车在道路上迟疑不前;冰箱也停止工作，导致食物变质。人们只是在两个世 纪前一点才开始了解电的使用原理，自然界却显然在这方面经历过了数百万年。 科学家不 断发现许多生物世界里可能有益于人类的关于电的有趣秘密。所有生物细胞都会发出微小的 电脉冲。
当心脏跳动时，把它发出的脉冲记录下来就成了心电图，这可让医生了解心脏的 工作状况。大脑也发出脑电波，这可在脑电图上记录下来。
许多生物细胞发出的电流都是 极微小的，小到要用灵敏仪器才能记录和测量。 但一些动物的某些肌肉细胞能转化成一个 个发电机，以致完全失去肌肉细胞的功能。
这种细胞大量地连接在一起时产生的效果将是 非常令人吃惊的。电鳗就是一种令人惊异的蓄电池。 它可以在水中发出相当于 800 伏特电 压电流(家庭用户的电压只有 120 伏特)。 在电鳗的身体里，多至五分之四的细胞都专门用 来发电，而且发出的电流的强度大约和它身体的长度成正比。
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