《经济学人》杂志原版英文整理完整版之欧阳体创编.docx
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《经济学人》杂志原版英文整理完整版之欧阳体创编.docx
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《经济学人》杂志原版英文整理完整版之欧阳体创编
DigestOfThe.Economist.2006(6-7)
时间:
2021.02.03
创作:
欧阳体
Hardtodigest
Awealthofgeneticinformationistobefoundinthehumangut
BACTERIA,likepeople,canbedividedintofriendandfoe.Inspiredbyevidencethatthefriendlysortmayhelpwitharangeofailments,manypeopleconsumebacteriaintheformofyogurtsanddietarysupplements.Suchasmatteringofartificialadditions,however,representsbutadropintheocean.Thereareatleast800typesofbacterialivinginthehumangut.AndresearchbyStevenGilloftheInstituteforGenomicResearchinRockville,Maryland,andhiscolleagues,publishedinthisweek'sScience,suggeststhatthecollectivegenomeoftheseorganismsissolargethatitcontains100timesasmanygenesasthehumangenomeitself.
DrGillandhisteamwereabletocometothisconclusionbyextractingbacterialDNAfromthefaecesoftwovolunteers.Becauseofthecomplexityofthesamples,theywerenotabletoreconstructtheentiregenomesofeachofthegutbacteria,justtheindividualgenes.Butthatallowedthemtomakeanestimateofnumbers.
Whatallthesebacteriaaredoingistrickytoidentify—thebacteriathemselvesaredifficulttocultivate.Sotheresearchersguessedatwhattheymightbeuptobycomparingthegenestheydiscoveredwithpublisheddatabasesofgeneswhosefunctionsarealreadyknown.
ThiscomparisonhelpedDrGillidentifyforthefirsttimetheprobableenzymaticprocessesbywhichbacteriahelphumanstodigestthecomplexcarbohydratesinplants.Thebacteriaalsocontainaplentifulsupplyofgenesinvolvedinthesynthesisofchemicalsessentialtohumanlife—includingtwoBvitaminsandcertainessentialaminoacids—althoughtheteammerelyshowedthatthesemetabolicpathwaysexistratherthanprovingthattheyareused.Nevertheless,thepathwaystheyfoundleavehumanslookingmorelikeruminants:
animalssuchasgoatsandsheepthatusebacteriatobreakdownotherwiseindigestiblematterintheplantstheyeat.
ThebroaderconclusionDrGilldrawsisthatpeoplearesuperorganismswhosemetabolismrepresentsanamalgamationofhumanandmicrobialattributes.Thenotionofasuperorganismhasemergedbefore,asresearchersinotherfieldshavecometoviewhumansashavingadiverseinternalecosystem.This,suggestsome,willbecrucialtothesuccessofpersonalisedmedicine,asdifferentpeoplewillhavedifferentresponsestodrugs,dependingontheirmicrobialflora.Accordingly,thenextstep,saysDrGill,istoseehowmicrobialpopulationsvarybetweenpeopleofdifferentages,backgroundsanddiets.
Anotherareaofresearchistheprocessbywhichthesehelpfulbacteriafirstcolonisethedigestivetract.Babiesacquiretheirgutfloraastheypassdownthebirthcanalandtakeagene-filledgulpoftheirmother'svaginalandfaecalflora.Itmightnotbethemostdeliciousoffirstmeals,butitcouldwellbeanimportantone.
Zappingtheblues
Therebirthofelectric-shocktreatment
ELECTRICITYhaslongbeenusedtotreatmedicaldisorders.AsearlyasthesecondcenturyAD,Galen,aGreekphysician,recommendedtheuseofelectriceelsfortreatingheadachesandfacialpain.Inthe1930sUgoCerlettiandLucioBini,twoItalianpsychiatrists,usedelectroconvulsivetherapytotreatschizophrenia.Thesedays,suchrigoroustechniquesarepractisedlesswidely.Butresearchersarestillinvestigatinghowagentlerelectrictherapyappearstotreatdepression.
Vagus-nervestimulation,togiveititspropername,wasoriginallydevelopedtotreatsevereepilepsy.Itrequiresapacemaker-likedevicetobeimplantedinapatient'schestandwiresfromitthreadeduptothevagusnerveontheleftsideofhisneck.Inthenormalcourseofevents,thisprovidesanelectricalpulsetothevagusnervefor30secondseveryfiveminutes.
Thistreatmentdoesnotalwayswork,butinsomecaseswhereitfailed(thenumberofepilepticseizuresexperiencedbyapatientremainingthesame),thatpatientneverthelessreportedfeelingmuchbetterafterreceivingtheimplant.Thissecondaryeffectledtotrialsfortreatingdepressionand,in2005,America'sFoodandDrugAdministrationapprovedthetherapyfordepressionthatfailstorespondtoallconventionaltreatments,includingdrugsandpsychotherapy.
Notonlydoesthetreatmentwork,butitseffectsappeartobelonglasting.AstudyledbyCharlesConwayofSaintLouisUniversityinMissouri,andpresentedtoarecentmeetingoftheAmericanPsychiatricAssociation,hasfoundthat70%ofpatientswhoarebetterafteroneyearstaybetteraftertwoyearsaswell.
Thetechniquebuildsonaprocedurecalleddeep-brainstimulation,inwhichelectrodesareimplanteddeepintothewhitematterofpatients'brainsandusedto“reboot”faultyneuralcircuitry.Suchanoperationisabigundertaking,requiringafulldayofsurgeryandcarryingariskofthepatientsufferingastroke.Onlyasmallnumberofpeoplehavebeentreatedthisway.Incontrast,thedevicethatstimulatesthevagusnervecanbeimplantedin45minuteswithoutastayinhospital.
Thetroubleisthatvagus-nervestimulationcantakealongtimetoproduceitsfullbeneficialeffect.AccordingtoDrConway,scanstakenusingatechniquecalledpositron-emissiontomographyshowsignificantchangesinbrainactivitystartingthreemonthsaftertreatmentbegins.Thechangesaresimilartotheimprovementsseeninpatientswhoundergootherformsofantidepressiontreatment.Thebraincontinuestochangeoverthefollowing21months.DrConwaysaysthatpatientsshouldbetoldthattheantidepressanteffectscouldbeslowincoming.
However,RichardSelwayofKing'sCollegeHospital,London,foundthathispatients'moodsimprovedjustweeksaftertheimplant.Althoughbrainscansareusefulindeterminingthelongevityofthetreatment,MrSelwaynotesthatvisiblechangesinthebraindonotnecessarilycorrelateperfectlywithchangesinmood.
Nobodyknowswhystimulatingthevagusnerveimprovesthemoodofdepressedpatients,butMrSelwayhasatheory.Hebelievesthattheelectricalstimulationcausesaregioninthebrainstemcalledthelocuscaeruleus(Latin,ironically,for“blueplace”)tofloodthebrainwithnorepinephrine,aneurotransmitterimplicatedinalertness,concentrationandmotivation—thatis,themoodstatesmissingindepressedpatients.Whateverthemechanism,forthedepressedatherapythatisrelativelysafeandlonglastingisrarecauseforcheer.
Theshapeofthingstocome
Howtomorrow'snuclearpowerstationswilldifferfromtoday's
THEagencyinchargeofpromotingnuclearpowerinAmericadescribesanewgenerationofreactorsthatwillbe“highlyeconomical”with“enhancedsafety”,that“minimisewastes”andwillprove“proliferationresistant”.Nodoubttheywillbakeameanapplepie,too.
Unfortunately,intheworldofnuclearenergy,finewordsarenotenough.Americagotawaylightlywithitsnuclearaccident.WhentheThreeMileIslandplantinPennsylvaniaoverheatedin1979verylittleradiationleaked,andtherewerenoinjuries.Europewasnotsolucky.TheaccidentatChernobylinUkrainein1986killeddozensimmediatelyandhasaffected(sometimesfatally)thehealthoftensofthousandsattheleast.Evendiscountingtheassociationofnuclearpowerwithnuclearweaponry,peoplehavegoodreasontobesuspiciousofclaimsthatreactorsaresafe.
Yetpoliticalinterestinnuclearpowerisrevivingacrosstheworld,thanksinparttoconcernsaboutglobalwarmingandenergysecurity.Already,some441commercialreactorsoperatein31countriesandprovide17%oftheplanet'selectricity,accordingtoAmerica'sDepartmentofEnergy.Untilrecently,thetalkwasofhowtoretirethesereactorsgracefully.Nowitisofhowtoextendtheirlives.Inaddition,another32reactorsarebeingbuilt,mostlyinIndia,Chinaandtheirneighbours.Thesenewpowerstationsbelongtowhathasbeencalledthethirdgenerationofreactors,designsthathavebeeninformedbyexperienceandthatareconsideredbytheircreatorstobeadvanced.Butwillthesenewstationsreallybesaferthantheirpredecessors?
Clearly,moderndesignsneedtobelessaccidentprone.Themostimportantfeatureofasafedesignisthatit“failssafe”.Forareactor,thismeansthatifitscontrolsystemsstopworkingitshutsdownautomatically,safelydissipatestheheatproducedbythereactionsinitscore,andstopsboththefuelandtheradioactivewasteproducedbynuclearreactionsfromescapingbykeepingthemwithinsomesortofcontainmentvessel.Reactorsthatfollowsuchrulesarecalled“passive”.Mostmoderndesignsarepassivetosomeextentandsomeneweronesaretrulyso.However,someofthegenuinelypassivereactorsarealsolikelytobemoreexpensivetorun.
Nuclearenergyisproducedbyatomicfission.Alargeatom(usuallyuraniumorplutonium)breaksintotwosmallerones,releasingenergyandneutrons.Theneutronsthentriggerfurtherbreak-ups.Andsoon.Ifthis“chainreaction”canbecontrolled,theenergyreleasedcanbeusedtoboilwater,producesteamanddriveaturbinethatgenerateselectricity.Ifitrunsaway,theresultisameltdownandanaccident(or,inextremecircumstances,anuclearexplosion—thoughcircumstancesareneverthatextremeinareactorbecausethefuelislessfissilethanthematerialinabomb).Inmanynewdesignstheneutrons,andthusthechainreaction,arekeptundercontrolbypassingthemthroughwatertoslowthemdown.(Slowneutronstriggermorebreakupsthanfastones.)Thiswaterisexposedtoapressureofabout150atmospheres—apressurethatmeansitremainsliquidevenathightemperatures.Whennuclearreactionswarmthewater,itsdensitydro
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