Electricity

　　Themodernageisanageofelectricity.Peoplearesousedtoelectriclights,radio,televisions,andtelephonesthatitishardtoimaginewhatlifewouldbelikewithoutthem.Whenthereisapowerfailure,peoplegropeaboutinflickeringcandlelight,carshesitateinthestreetsbecausetherearenotrafficlightstoguidethem,andfoodspoilsinsilentrefrigerators.

　　Yet,peoplebegantounderstandhowelectricityworksonlyalittlemorethantwocenturiesago.Naturehasapparentlybeenexperimentinginthisfieldformillionsofyears.Scientistsarediscoveringmoreandmorethatthelivingworldmayholdmanyinterestingsecretsofelectricitythatcouldbenefithumanity.

　　Alllivingcellssendouttinypulsesofelectricity.Astheheartbeats,itsendsoutpulsesofrecord;theyformanelectrocardiogram,whichadoctorcanstudytodeterminehowwelltheheartisworking.Thebrain,too,sendsoutbrainwavesofelectricity,whichcanberecordedinanelectroencephalogram.Theelectriccurrentsgeneratedbymostlivingcellsareextremelysmall--oftensosmallthatsensitiveinstrumentsareneededtorecordthem.Butinsomeanimals,certainmusclecellshavebecomesospecializedaselectricalgeneratorsthattheydonotworkasmusclecellsatall.Whenlargenumbersofthesecellsarelinkedtogether,theeffectscanbeastonishing.

　　Theelectriceelisanamazingstoragebattery.Itcansendajoltofasmuchaseighthundredvoltsofelectricitythroughthewaterinwhichitlives.(Anelectrichousecurrentisonlyonehundredtwentyvolts.)Asmanyasfour-fifthsofallthecellsintheelectriceel'sbodyarespecializedforgeneratingelectricity,andthestrengthoftheshockitcandelivercorrespondsroughlytothelengthofitsbody.

　　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