Themodernageisanageofelectricity.Peoplearesousedtoelectriclightsradiotelevisionsandtelephonesthatitishardtoimaginewhatlifewouldbelikewithoutthem.Whenthereisapowerfailurepeoplegropeaboutinflickeringcandlelightcarshesitateinthestreetsbecausetherearenotrafficlightstoguidethemandfoodspoilsinsilentrefrigerators.Yetpeoplebegantounderstandhowelectricityworksonlyalittlemorethantwocenturiesago.Naturehasapparentlybeenexperimentinginthisfieldformillionofyears.Scientistsarediscoveringmoreandmorethatthelivingworldmayholdmanyinterestingsecretsofelectricitythatcouldbenefithumanity.Alllivingcellsendouttinypulsesofelectricity.Astheheartbeatsitsendsoutpulsesofrecord;theyformanelectrocardiogramwhichadoctorcanstudytodeterminehowwelltheheartisworking.Thebraintoosendsoutbrainwavesofelectricitywhichcanberecordedinanelectroencephalogram.Theelectriccurrentsgeneratedbymostlivingcellsareextremelysmall-oftensosmallthatsensitiveinstrumentsareneededtorecordthem.Butinsomeanimalscertainmusclecellshavebecomesospecializedaselectricalgeneratorsthattheydonotworkasmusclecellsatall.Whenlargenumbersofthesecellarelinkedtogethertheeffectscanbeastonishing.Theelectriceelisanamazingstoragebattery.Itcanseedajoltofasmuchaseighthundredvoltsofelectricitythroughthewaterinwhichitlive.(Anelectrichousecurrentisonlyonehundredtwentyvolts.)Asmanyasfour-fifthsofallthecellsintheelectriceelsbodyarespecializedforgeneratingelectricityandthestrengthoftheshockitcandelivercorrespondsroughlytolengthofitsbody.
