a history of science-2-第30节

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as　appointed　physician　extraordinary　to　the　king；　and；　a　little　later；　physician　in　ordinary。　He　was　in　attendance　upon　Charles　I。　at　the　battle　of　Edgehill；　in　1642；　where；　with　the　young　Prince　of　Wales　and　the　Duke　of　York；　after　seeking　shelter　under　a　hedge；　he　drew　a　book　out　of　his　pocket　and；　forgetful　of　the　battle；　became　absorbed　in　study；　until　finally　the　cannon…balls　from　the　enemy's　artillery　made　him　seek　a　more　sheltered　position。　On　the　fall　of　Charles　I。　he　retired　from　practice；　and　lived　in　retirement　with　his　brother。　He　was　then　well　along　in　years；　but　still　pursued　his　scientific　researches　with　the　same　vigor　as　before；　directing　his　attention　chiefly　to　the　study　of　embryology。　On　June　3；　1657；　he　was　attacked　by　paralysis　and　died；　in　his　eightieth　year。　He　had　lived　to　see　his　theory　of　the　circulation　accepted；　several　years　before；　by　all　the　eminent　anatomists　of　the　civilized　world。　A　keenness　in　the　observation　of　facts；　characteristic　of　the　mind　of　the　man；　had　led　Harvey　to　doubt　the　truth　of　existing　doctrines　as　to　the　phenomena　of　the　circulation。　Galen　had　taught　that　〃the　arteries　are　filled；　like　bellows；　because　they　are　expanded；〃　but　Harvey　thought　that　the　action　of　spurting　blood　from　a　severed　vessel　disproved　this。　For　the　spurting　was　remittant；　〃now　with　greater；　now　with　less　impetus；〃　and　its　greater　force　always　corresponded　to　the　expansion　（diastole）；　not　the　contraction　（systole）　of　the　vessel。　Furthermore；　it　was　evident　that　contraction　of　the　heart　and　the　arteries　was　not　simultaneous；　as　was　commonly　taught；　because　in　that　case　there　would　be　no　marked　propulsion　of　the　blood　in　any　direction；　and　there　was　no　gainsaying　the　fact　that　the　blood　was　forcibly　propelled　in　a　definite　direction；　and　that　direction　away　from　the　heart。　Harvey's　investigations　led　him　to　doubt　also　the　accepted　theory　that　there　was　a　porosity　in　the　septum　of　tissue　that　divides　the　two　ventricles　of　the　heart。　It　seemed　unreasonable　to　suppose　that　a　thick　fluid　like　the　blood　could　find　its　way　through　pores　so　small　that　they　could　not　be　demonstrated　by　any　means　devised　by　man。　In　evidence　that　there　could　be　no　such　openings　he　pointed　out　that；　since　the　two　ventricles　contract　at　the　same　time；　this　process　would　impede　rather　than　facilitate　such　an　intra…ventricular　passage　of　blood。　But　what　seemed　the　most　conclusive　proof　of　all　was　the　fact　that　in　the　foetus　there　existed　a　demonstrable　opening　between　the　two　ventricles；　and　yet　this　is　closed　in　the　fully　developed　heart。　Why　should　Nature；　if　she　intended　that　blood　should　pass　between　the　two　cavities；　choose　to　close　this　opening　and　substitute　microscopic　openings　in　place　of　it？　It　would　surely　seem　more　reasonable　to　have　the　small　perforations　in　the　thin；　easily　permeable　membrane　of　the　foetus；　and　the　opening　in　the　adult　heart；　rather　than　the　reverse。　From　all　this　Harvey　drew　his　correct　conclusions；　declaring　earnestly；　〃By　Hercules；　there　ARE　no　such　porosities；　and　they　cannot　be　demonstrated。〃　Having　convinced　himself　that　no　intra…ventricular　opening　existed；　he　proceeded　to　study　the　action　of　the　heart　itself；　untrammelled　by　too　much　faith　in　established　theories；　and；　as　yet；　with　no　theory　of　his　own。　He　soon　discovered　that　the　commonly　accepted　theory　of　the　heart　striking　against　the　chest…wall　during　the　period　of　relaxation　was　entirely　wrong；　and　that　its　action　was　exactly　the　reverse　of　this；　the　heart　striking　the　chest…wall　during　contraction。　Having　thus　disproved　the　accepted　theory　concerning　the　heart's　action；　he　took　up　the　subject　of　the　action　of　arteries；　and　soon　was　able　to　demonstrate　by　vivisection　that　the　contraction　of　the　arteries　was　not　simultaneous　with　contractions　of　the　heart。　His　experiments　demonstrated　that　these　vessels　were　simply　elastic　tubes　whose　pulsations　were　〃nothing　else　than　the　impulse　of　the　blood　within　them。〃　The　reason　that　the　arterial　pulsation　was　not　simultaneous　with　the　heart…beat　he　found　to　be　because　of　the　time　required　to　carry　the　impulse　along　the　tube；　By　a　series　of　further　careful　examinations　and　experiments；　which　are　too　extended　to　be　given　here；　he　was　soon　able　further　to　demonstrate　the　action　and　course　of　the　blood　during　the　contractions　of　the　heart。　His　explanations　were　practically　the　same　as　those　given　to…dayfirst　the　contraction　of　the　auricle；　sending　blood　into　the　ventricle；　then　ventricular　contraction；　making　the　pulse；　and　sending　the　blood　into　the　arteries。　He　had　thus　demonstrated　what　had　not　been　generally　accepted　before；　that　the　heart　was　an　organ　for　the　propulsion　of　blood。　To　make　such　a　statement　to…day　seems　not　unlike　the　sober　announcement　that　the　earth　is　round　or　that　the　sun　does　not　revolve　about　it。　Before　Harvey's　time；　however；　it　was　considered　as　an　organ　that　was　〃in　some　mysterious　way　the　source　of　vitality　and　warmth；　as　an　animated　crucible　for　the　concoction　of　blood　and　the　generation　of　vital　spirits。〃＇3＇　In　watching　the　rapid　and　ceaseless　contractions　of　the　heart；　Harvey　was　impressed　with　the　fact　that；　even　if　a　very　small　amount　of　blood　was　sent　out　at　each　pulsation；　an　enormous　quantity　must　pass　through　the　organ　in　a　day；　or　even　in　an　hour。　Estimating　the　size　of　the　cavities　of　the　heart；　and　noting　that　at　least　a　drachm　must　be　sent　out　with　each　pulsation；　it　was　evident　that　the　two　thousand　beats　given　by　a　very　slow　human　heart　in　an　hour　must　send　out　some　forty　pounds　of　bloodmore　than　twice　the　amount　in　the　entire　body。　The　question　was；　what　became　of　it　all？　For　it　should　be　remembered　that　the　return　of　the　blood　by　the　veins　was　unknown；　and　nothing　like　a　〃circulation〃　more　than　vaguely　conceived　even　by　Harvey　himself。　Once　it　could　be　shown　that　the　veins　were　constantly　returning　blood　to　the　heart；　the　discovery　that　the　blood　in　some　way　passes　from　the　arteries　to　the　veins　was　only　a　short　step。　Harvey；　by　resorting　to　vivisections　of　lower　animals　and　reptiles；　soon　demonstrated　beyond　question　the　fact　that　the　veins　do　carry　the　return　blood。　〃But　this；　in　particular；　can　be　shown　clearer　than　daylight；〃　says　Harvey。　〃The　vena　cava　enters　the　heart　at　an　inferior　portion；　while　the　artery　passes　out　above。　Now　if　the　vena　cava　be　taken　up　with　forceps　or　the　thumb　and　finger；　and　the　course　of　the　blood　intercepted　for　some　distance　below　the　heart；　you　will　at　once　see　it　almost　emptied　between　the　fingers　and　the　heart；　the　blood　being　exhausted　by　the　heart's　pulsation；　the　heart　at　the　same　time　becoming　much　paler　even　in　its　dilatation；　smaller　in　size；　owing　to　the　deficiency　of　blood；　and　at　length　languid　in　pulsation；　as　if　about　to　die。　On　the　other　hand；　when　you　release　the　vein　the　heart　immediately　regains　its　color　and　dimensions。　After　that；　if　you　leave　the　vein　free　and　tie　and　compress　the　arteries　at　some　distance　from　the　heart；　you　will　see；　on　the　contrary；　their　included　portion　grow　excessively　turgid；　the　heart　becoming　so　beyond　measure；　assuming　a　dark…red　color；　even　to　lividity；　and　at　length　so　overloaded　with　blood　as　to　seem　in　danger　of　suffocation；　but　when　the　obstruction　is　removed　it　returns　to　its　normal　condition；　in　size；　color；　and　movement。〃＇4＇　This　conclusive　demonstration　that　the　veins　return　the　blood　to　the　heart　must　have　been　most　impressive　to　Harvey；　who　had　been　taught　to　believe　that　the　blood　current　in　the　veins　pursued　an　opposite　course；　and　must　have　tended　to　shake　his　faith　in　all　existing　doctrines　of　the　day。　His　next　step　was　the　natural　one　of　demonstrating　that　the　blood　passes　from　the　arteries　to　the　veins。　He　demonstrated　conclusively　that　this　did　occur；　but　for　once　his　rejection　of　the　ancient　writers　and　one　modern　one　was　a　mistake。　For　Galen　had　taught；　and　had　attempted　to　demonstrate；　that　there　are　sets　of　minute　vessels　connecting　the　arteries　and　the　veins；　and　Servetus　had　shown　that　there　must　be　such　vessels；　at　least　in　the　lungs。　However；　the　little　flaw　in　the　otherwise　complete　demonstration　of　Harvey　detracts　nothing　from　the　main　issue　at　stake。　It　was　for　others　who　followed　to　show　just　how　these　small　vessels　acted　in　effecting　the　transfer　of　the　blood　from　artery　to　vein；　and　the　grand　general　statement　that　such　a　transfer　does　take　place　was；　after　all；　the　all…important　one；　and　the　exact　method　of　how　it　takes　place　a　detail。　Harvey's　experiments　to　demonstrate　that　the　blood　passes　from　the　arteries　to　the　veins　are　so　simply　and　concisely　stated　that　they　may　best　be　given　in　his　own　words。　〃I　have　here　to　cite　certain　experiments；〃　he　wrote；　〃from　which　it　seems　obvious　that　the　blood　enters　a　limb　by　the　arteries；　and　returns　from　it　by　the　veins；　that　the　arteries　are　the　vessels　carrying　the　blood　from　the　heart；　and　the　veins　the　returning　channels　of　the　blood　to　the　heart；　that　in　the　limbs　and　extreme　parts　of　the　body　the　blood　passes　either　by　anastomosis　from　the　arteries　into　the　veins；　or　immediately　by　the　pores　of　the　flesh；　or　in　both　ways；　as　has　already　been　said　in　speaking　of　the　passage　of　the　blood　through　the　lungs；　whence　it　appears　manifest　that　in　the　circuit　the　blood　moves　from　thence　hither；　and　hence　thither；　from　the　c