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

　　Yet,peoplebegantounderstandhowelectricityworksonlyalittlemorethantwocenturiesago.Naturehasapparentlybeenexperimentinginthisfieldformillionofyears.Scientistsarediscoveringmoreandmorethatthelivingworldmayholdmanyinterestingsecretsofelectricitythatcouldbenefithumanity.

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

　　Theelectriceelisanamazingstoragebattery.Itcanseedajoltofasmuchaseighthundredvoltsofelectricitythroughthewaterinwhichitlive.(Anelectrichousecurrentisonlyonehundredtwentyvolts.)Asmanyasfour-fifthsofallthecellsintheelectriceel'sbodyarespecializedforgeneratingelectricity,andthestrengthoftheshockitcandelivercorrespondsroughlytolengthofitsbody.