万物简史英文版_比尔·布莱森-第71章

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re　like　50　percent；　it　depends；　apparently；　on　what　youmean　by　鈥渦nderstand。鈥潱﹕urprises　at　the　cellular　level　turn　up　all　the　time。　in　nature；　nitric　oxide　is　a　formidabletoxin　and　a　mon　ponent　of　air　pollution。　so　scientists　were　naturally　a　little　surprisedwhen；　in　the　mid…1980s；　they　found　it　being　produced　in　a　curiously　devoted　manner　inhuman　cells。　its　purpose　was　at　first　a　mystery；　but　then　scientists　began　to　find　it　all　over　theplace鈥攃ontrolling　the　flow　of　blood　and　the　energy　levels　of　cells；　attacking　cancers　andother　pathogens；　regulating　the　sense　of　smell；　even　assisting　in　penile　erections。　it　alsoexplained　why　nitroglycerine；　the　well…known　explosive；　soothes　the　heart　pain　known　asangina。　（it　is　converted　into　nitric　oxide　in　the　bloodstream；　relaxing　the　muscle　linings　ofvessels；　allowing　blood　to　flow　more　freely。）　in　barely　the　space　of　a　decade　this　one　gassysubstance　went　from　extraneous　toxin　to　ubiquitous　elixir。

you　　possess　　鈥渟ome　　few　　hundred鈥潯　�different　　types　of　cell；　according　to　the　belgianbiochemist　christian　de　duve；　and　they　vary　enormously　in　size　and　shape；　from　nerve　cellswhose　filaments　can　stretch　to　several　feet　to　tiny；　disc…shaped　red　blood　cells　to　the　rod…shaped　photocells　that　help　to　give　us　vision。　they　also　e　in　a　sumptuously　wide　range　ofsizes鈥攏owhere　more　strikingly　than　at　the　moment　of　conception；　when　a　single　beatingsperm　confronts　an　egg　eighty…five　thousand　times　bigger　than　it　（which　rather　puts　the　notionof　male　conquest　into　perspective）。　on　average；　however；　a　human　cell　is　about　twentymicrons　wide鈥攖hat　is　about　two　hundredths　of　a　millimeter鈥攚hich　is　too　small　to　be　seenbut　roomy　enough　to　hold　thousands　of　plicated　structures　like　mitochondria；　and　millionsupon　millions　of　molecules。　in　the　most　literal　way；　cells　also　vary　in　liveliness。　your　skincells　are　all　dead。　it鈥檚　a　somewhat　galling　notion　to　reflect　that　every　inch　of　your　surface　isdeceased。　if　you　are　an　average…sized　adult　you　are　lugging　around　about　five　pounds　of　deadskin；　of　which　several　billion　tiny　fragments　are　sloughed　off　each　day。　run　a　finger　along　adusty　shelf　and　you　are　drawing　a　pattern　very　largely　in　old　skin。

most　living　cells　seldom　last　more　than　a　month　or　so；　but　there　are　some　notableexceptions。　liver　cells　can　survive　for　years；　though　the　ponents　within　them　may　berenewed　every　few　days。　brain　cells　last　as　long　as　you　do。　you　are　issued　a　hundred　billionor　so　at　birth；　and　that　is　all　you　are　ever　going　to　get。　it　has　been　estimated　that　you　lose　fivehundred　of　them　an　hour；　so　if　you　have　any　serious　thinking　to　do　there　really　isn鈥檛　a　momentto　waste。　the　good　news　is　that　the　individual　ponents　of　your　brain　cells　are　constantlyrenewed　so　that；　as　with　the　liver　cells；　no　part　of　them　is　actually　likely　to　be　more　than　abouta　month　old。　indeed；　it　has　been　suggested　that　there　isn鈥檛　a　single　bit　of　any　of　us鈥攏ot　somuch　as　a　stray　molecule鈥攖hat　was　part　of　us　nine　years　ago。　it　may　not　feel　like　it；　but　at　thecellular　level　we　are　all　youngsters。

the　first　person　to　describe　a　cell　was　robert　hooke；　whom　we　last　encounteredsquabbling　with　isaac　newton　over　credit　for　the　invention　of　the　inverse　square　law。　hookeachieved　many　things　in　his　sixty…eight　years鈥攈e　was　both　an　acplished　theoretician　anda　dab　hand　at　making　ingenious　and　useful　instruments鈥攂ut　nothing　he　did　brought　himgreater　admiration　than　his　popular　book　microphagia：　or　some　physiological　descriptions　ofminiature　bodies　made　by　magnifying　glasses；　produced　in　1665。　it　revealed　to　an　enchantedpublic　a　universe　of　the　very　small　that　was　far　more　diverse；　crowded；　and　finely　structuredthan　anyone　had　ever　e　close　to　imagining。

among　the　microscopic　features　first　identified　by　hooke　were　little　chambers　in　plantsthat　he　called　鈥渃ells鈥潯�because　they　reminded　him　of　monks鈥櫋�cells。　hooke　calculated　that　aone…inch　square　of　cork　would　contain　1；259；712；000　of　these　tiny　chambers鈥攖he　firstappearance　of　such　a　very　large　number　anywhere　in　science。　microscopes　by　this　time　hadbeen　around　for　a　generation　or　so；　but　what　set　hooke鈥檚　apart　were　their　technicalsupremacy。　they　achieved　magnifications　of　thirty　times；　making　them　the　last　word　inseventeenth…century　optical　technology。

so　it　came　as　something　of　a　shock　when　just　a　decade　later　hooke　and　the　other　membersof　london鈥檚　royal　society　began　to　receive　drawings　and　reports　from　an　unlettered　linendraper　in　holland　employing　magnifications　of　up　to　275　times。　the　draper鈥檚　name　wasantoni　van　leeuwenhoek。　though　he　had　little　formal　education　and　no　background　inscience；　he　was　a　perceptive　and　dedicated　observer　and　a　technical　genius。

to　this　day　it　is　not　known　how　he　got　such　magnificent　magnifications　from　simplehandheld　devices；　which　were　little　more　than　modest　wooden　dowels　with　a　tiny　bubble　ofglass　embedded　in　them；　far　more　like　magnifying　glasses　than　what　most　of　us　think　of　asmicroscopes；　but　really　not　much　like　either。　leeuwenhoek　made　a　new　instrument　for　everyexperiment　he　performed　and　was　extremely　secretive　about　his　techniques；　though　he　didsometimes　offer　tips　to　the　british　on　how　they　might　improve　their　resolutions。

2over　a　period　of　fifty　years鈥攂eginning；　remarkably　enough；　when　he　was　already　pastforty鈥攈e　made　almost　two　hundred　reports　to　the　royal　society；　all　written　in　low　dutch；the　only　tongue　of　which　he　was　master。　leeuwenhoek　offered　no　interpretations；　but　simplythe　facts　of　what　he　had　found；　acpanied　by　exquisite　drawings。　he　sent　reports　on　almosteverything　that　could　be　usefully　examined鈥攂read　mold；　a　bee鈥檚　stinger；　blood　cells；　teeth；hair；　his　own　saliva；　excrement；　and　semen　（these　last　with　fretful　apologies　for　their　unsavorynature）鈥攏early　all　of　which　had　never　been　seen　microscopically　before。

after　he　reported　finding　鈥渁nimalcules鈥潯�in　a　sample　of　pepper　water　in　1676；　the　membersof　the　royal　society　spent　a　year　with　the　best　devices　english　technology　could　producesearching　for　the　鈥渓ittle　animals鈥潯�before　finally　getting　the　magnification　right。　whatleeuwenhoek　had　found　were　protozoa。　he　calculated　that　there　were　8；280；000　of　these　tinybeings　in　a　single　drop　of　water鈥攎ore　than　the　number　of　people　in　holland。　the　worldteemed　with　life　in　ways　and　numbers　that　no　one　had　previously　suspected。

inspired　by　leeuwenhoek鈥檚　fantastic　findings；　others　began　to　peer　into　microscopes　withsuch　keenness　that　they　sometimes　found　things　that　weren鈥檛　in　fact　there。　one　respecteddutch　observer；　nicolaus　hartsoecker；　was　convinced　he　saw　鈥渢iny　preformed　men鈥潯�in　spermcells。　he　called　the　little　beings　鈥渉omunculi鈥潯�and　for　some　time　many　people　believed　that　allhumans鈥攊ndeed；　all　creatures鈥攚ere　simply　vastly　inflated　versions　of　tiny　but　pleteprecursor　beings。　leeuwenhoek　himself　occasionally　got　carried　away　with　his　enthusiasms。

in　one　of　his　least　successful　experiments　he　tried　to　study　the　explosive　properties　ofgunpowder　by　observing　a　small　blast　at　close　range；　he　nearly　blinded　himself　in　the　process。

2leeuwenhoek　was　close　friends　with　another　delft　notable；　the　artist　jan　vermeer。　in　the　mid…1660s；　vermeer；who　previously　had　been　a　petent　but　not　outstanding　artist；　suddenly　developed　the　mastery　of　light　andperspective　for　which　he　has　been　celebrated　ever　since。　though　it　has　never　been　proved；　it　has　long　beensuspected　that　he　used　a　camera　obscura；　a　device　for　projecting　images　onto　a　flat　surface　through　a　lens。　nosuch　device　was　listed　among　vermeers　personal　effects　after　his　death；　but　it　happens　that　the　executor　ofvermeers　estate　was　none　other　than　antoni　van　leeuwenhoek；　the　most　secretive　lens…maker　of　his　day。

in　1683　leeuwenhoek　discovered　bacteria；　but　that　was　about　as　far　as　progress　could　getfor　the　next　century　and　a　half　because　of　the　limitations　of　microscope　technology。　not　until1831　would　anyone　first　see　the　nucleus　of　a　cell鈥攊t　was　found　by　the　scottish　botanistrobert　brown；　that　frequent　but　always　shadowy　visitor　to　the　history　of　science。　brown；　wholived　from　1773　to　1858；　called　it　nucleus　from　the　latin　nucula；　meaning　little　nut　or　kernel。

not　until　1839；　however；　did　anyone　realize　that　all　living　matter　is　cellular。　it　was　theodorschwann；　a　german；　who　had　this　insight；　and　it　was　not　only　paratively　late；　as　scientificinsights　go；　but　not　widely　embraced　at　first。　it　wasn鈥檛　until　the　1860s；　and　some　landmarkwork　by　louis　pasteur　in　france；　that　it　was　shown　conclusively　that　life　cannot　arisespontaneously　but　must　e　from　preexisting　cells。　the　belief　became　known　as　the　鈥渃elltheory；鈥潯�and　it　is　the　basis　of　all　modern　biology。

the　cell　has　been　pared　to　many　things；　from　鈥渁　plex　chemical　refinery鈥潯。╞y　thephysicist　james　trefil）　to　鈥渁　vast；　teeming　metropolis鈥潯。╰he　biochemist　guy　brown）。　a　cell　isboth　of　those　things　and　neither。　it　is　like　a　refinery　in　that　it　is　devoted　to　chemical　activityon　a　grand　scale；　and　like　a　metropolis　in　that　it　is　crowded　and　busy　and　filled　withinteractions　that　seem　confused　and　random　but　clearly　have　some　system　to　them。　but　it　is　amuch　more　nightmarish　place　than　any　city　or　factory　that　you　have　ever　seen。　to　begin　withthere　is　no　up　or　down　inside　the　cell　（gravity　doesn鈥檛　meaningfully　apply　at　the　cellularscale）；　and　not　an　atom鈥檚　width　of　space　is　unused。　there　is　activity　every　where　and　aceaseless　thrum　of　electrical　energy。　you　may　not　feel　terribly　electrical；　but　you　are。　thefood　we　eat　and　the　oxygen　we　breathe　are　bined　in　the　cells　into　electricity。　the　reasonwe　don鈥檛　give　each　other　massive　shocks　or　scorch　the　sofa　when　we　sit　is　that　it　is　allhappening　on　a　tiny　scale：　a　mere　0。1　volts　traveling　distances　measured　in　nanometers。

however；　scale　that　up　and　it　would　translate　as　a　jolt　of　twenty　million　volts　per　meter；　aboutthe　same　as　the　charge　carried　by　the　main　body　of　a　thunderstorm。

whatever　their　size　or　shape；　nearly　all　your　cells　are　built　to　fundamentally　the　same　plan：

they　have　an　outer　casing　or　membrane；　a　nucleus　wherein　resides　the　necessary　geneticinformation　to　keep　you　going；　and　a　busy　space　between　the　two　called　the　cytoplasm。　themembrane　is　not；　as　most　of　us　imagine　it；　a　durable；　rubbery　casing；　something　that　youwould　need　a　sharp　pin　to　prick。　rather；　it　is　made　up　of　a　type　of　fatty　material　known　as　alipid；　which　has　the　approximate　consistency　鈥渙f　a　light　grade　of　machine　oil；鈥潯�to　quotesherwin　b。　nuland。　if　that　seems　surprisingly　insubstantial；　bear　in　mind　that　at　themicroscopic　level　things　behave　differently。　to　anything　on　a　molecular　scale　water　beesa　kind　of　heavy…duty　gel；　and　a　lipid　is　like　iron。

if　you　could　visit　a　cell；　you　wouldn鈥檛　like　it。　blown　up　to　a　scale　at　which　atoms　wereabout　the　size　of　peas；　a　cell　itself　would　be　a　sphere　roughly　half　a　mile　across；　and　supportedby　a　plex　framework　of　girders　called　the　cytoskeleton。　within　it；　millions　upon　millionsof　objects鈥攕ome　the　size　of　basketballs；　others　the　size　of　cars鈥攚ould　whiz　about　likebullets。　there　wouldn鈥檛　be　a　place　you　could　stand　without　being　pummeled　and　rippedthousands　of　times　every　second　from　every　direction。　even　for　its　full…time　occupants　theinside　of　a　cell　is　a　hazardous