a history of science-4-第15部分

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Simply　stated；　every　organ　or　muscle　of　the　body　is　supplied　by　one　large　artery；　whose　main　trunk　distributes　the　blood　into　its　lesser　branches；　and　thence　through　the　capillaries。　Cutting　off　this　main　artery；　it　would　seem；　should　cut　off　entirely　the　blood…supply　to　the　particular　organ　which　is　supplied　by　this　vessel；　and　until　the　time　of　Hunter's　demonstration　this　belief　was　held　by　most　physiologists。　But　nature　has　made　a　provision　for　this　possible　stoppage　of　blood…supply　from　a　single　source；　and　has　so　arranged　that　some　of　the　small　arterial　branches　coming　from　the　main　supply…trunk　are　connected　with　other　arterial　branches　coming　from　some　other　supply…trunk。　Under　normal　conditions　the　main　arterial　trunks　supply　their　respective　organs；　the　little　connecting　arterioles　playing　an　insignificant　part。　But　let　the　main　supply…trunk　be　cut　off　or　stopped　for　whatever　reason；　and　a　remarkable　thing　takes　place。　The　little　connecting　branches　begin　at　once　to　enlarge　and　draw　blood　from　the　neighboring　uninjured　supply…trunk；　This　enlargement　continues　until　at　last　a　new　route　for　the　circulation　has　been　established；　the　organ　no　longer　depending　on　the　now　defunct　original　arterial　trunk；　but　getting　on　as　well　as　before　by　this　〃collateral〃　circulation　that　has　been　established。

The　thorough　understanding　of　this　collateral　circulation　is　one　of　the　most　important　steps　in　surgery；　for　until　it　was　discovered　amputations　were　thought　necessary　in　such　cases　as　those　involving　the　artery　supplying　a　leg　or　arm；　since　it　was　supposed　that；　the　artery　being　stopped；　death　of　the　limb　and　the　subsequent　necessity　for　amputation　were　sure　to　follow。　Hunter　solved　this　problem　by　a　single　operation　upon　a　deer；　and　his　practicality　as　a　surgeon　led　him　soon　after　to　apply　this　knowledge　to　a　certain　class　of　surgical　cases　in　a　most　revolutionary　and　satisfactory　manner。

What　led　to　Hunter's　far…reaching　discovery　was　his　investigation　as　to　the　cause　of　the　growth　of　the　antlers　of　the　deer。　Wishing　to　ascertain　just　what　part　the　blood…supply　on　the　opposite　sides　of　the　neck　played　in　the　process　of　development；　or；　perhaps　more　correctly；　to　see　what　effect　cutting　off　the　main　blood…supply　would　have；　Hunter　had　one　of　the　deer　of　Richmond　Park　caught　and　tied；　while　he　placed　a　ligature　around　one　of　the　carotid　arteriesone　of　the　two　principal　arteries　that　supply　the　head　with　blood。　He　observed　that　shortly　after　this　the　antler　（which　was　only　half　grown　and　consequently　very　vascular）　on　the　side　of　the　obliterated　artery　became　cold　to　the　touchfrom　the　lack　of　warmth…giving　blood。　There　was　nothing　unexpected　in　this；　and　Hunter　thought　nothing　of　it　until　a　few　days　later；　when　he　found；　to　his　surprise；　that　the　antler　had　become　as　warm　as　its　fellow；　and　was　apparently　increasing　in　size。　Puzzled　as　to　how　this　could　be；　and　suspecting　that　in　some　way　his　ligature　around　the　artery　had　not　been　effective；　he　ordered　the　deer　killed；　and　on　examination　was　astonished　to　find　that　while　his　ligature　had　completely　shut　off　the　blood…supply　from　the　source　of　that　carotid　artery；　the　smaller　arteries　had　become　enlarged　so　as　to　supply　the　antler　with　blood　as　well　as　ever；　only　by　a　different　route。

Hunter　soon　had　a　chance　to　make　a　practical　application　of　the　knowledge　thus　acquired。　　This　was　a　case　of　popliteal　aneurism；　operations　for　which　had　heretofore　proved　pretty　uniformly　fatal。　An　aneurism；　as　is　generally　understood；　is　an　enlargement　of　a　certain　part　of　an　artery；　this　enlargement　sometimes　becoming　of　enormous　size；　full　of　palpitating　blood；　and　likely　to　rupture　with　fatal　results　at　any　time。　　If　by　any　means　the　blood　can　be　allowed　to　remain　quiet　for　even　a　few　hours　in　this　aneurism　it　will　form　a　clot；　contract；　and　finally　be　absorbed　and　disappear　without　any　evil　results。　The　problem　of　keeping　the　blood　quiet；　with　the　heart　continually　driving　it　through　the　vessel；　is　not　a　simple　one；　and　in　Hunter's　time　was　considered　so　insurmountable　that　some　surgeons　advocated　amputation　of　any　member　having　an　aneurism；　while　others　cut　down　upon　the　tumor　itself　and　attempted　to　tie　off　the　artery　above　and　below。　The　first　of　these　operations　maimed　the　patient　for　life；　while　the　second　was　likely　to　prove　fatal。

In　pondering　over　what　he　had　learned　about　collateral　circulation　and　the　time　required　for　it　to　become　fully　established；　Hunter　conceived　the　idea　that　if　the　blood…supply　was　cut　off　from　above　the　aneurism；　thus　temporarily　preventing　the　ceaseless　pulsations　from　the　heart；　this　blood　would　coagulate　and　form　a　clot　before　the　collateral　circulation　could　become　established　or　could　affect　it。　　The　patient　upon　whom　he　performed　his　now　celebrated　operation　was　afflicted　with　a　popliteal　aneurismthat　is；　the　aneurism　was　located　on　the　large　popliteal　artery　just　behind　the　knee…joint。　Hunter；　therefore；　tied　off　the　femoral；　or　main　supplying　artery　in　the　thigh；　a　little　distance　above　the　aneurism。　The　operation　was　entirely　successful；　and　in　six　weeks'　time　the　patient　was　able　to　leave　the　hospital；　and　with　two　sound　limbs。　Naturally　the　simplicity　and　success　of　this　operation　aroused　the　attention　of　Europe；　and；　alone；　would　have　made　the　name　of　Hunter　immortal　in　the　annals　of　surgery。　　The　operation　has　ever　since　been　called　the　〃Hunterian〃　operation　for　aneurism；　but　there　is　reason　to　believe　that　Dominique　Anel　（born　about　1679）　performed　a　somewhat　similar　operation　several　years　earlier。　It　is　probable；　however；　that　Hunter　had　never　heard　of　this　work　of　Anel；　and　that　his　operation　was　the　outcome　of　his　own　independent　reasoning　from　the　facts　he　had　learned　about　collateral　circulation。　Furthermore；　Hunter's　mode　of　operation　was　a　much　better　one　than　Anel's；　and；　while　Anel's　must　claim　priority；　the　credit　of　making　it　widely　known　will　always　be　Hunter's。

The　great　services　of　Hunter　were　recognized　both　at　home　and　abroad；　and　honors　and　positions　of　honor　and　responsibility　were　given　him。　In　1776　he　was　appointed　surgeon…extraordinary　to　the　king；　in　1783　he　was　elected　a　member　of　the　Royal　Society　of　Medicine　and　of　the　Royal　Academy　of　Surgery　at　Paris；　in　1786　he　became　deputy　surgeon…general　of　the　army；　and　in　1790　he　was　appointed　surgeon…general　and　inspector…general　of　hospitals。　All　these　positions　he　filled　with　credit；　and　he　was　actively　engaged　in　his　tireless　pursuit　of　knowledge　and　in　discharging　his　many　duties　when　in　October；　1793；　he　was　stricken　while　addressing　some　colleagues；　and　fell　dead　in　the　arms　of　a　fellow…physician。


LAZZARO　SPALLANZANI

Hunter's　great　rival　among　contemporary　physiologists　was　the　Italian　Lazzaro　Spallanzani　（1729…1799）；　one　of　the　most　picturesque　figures　in　the　history　of　science。　He　was　not　educated　either　as　a　scientist　or　physician；　devoting；　himself　at　first　to　philosophy　and　the　languages；　afterwards　studying　law；　and　later　taking　orders。　But　he　was　a　keen　observer　of　nature　and　of　a　questioning　and　investigating　mind；　so　that　he　is　remembered　now　chiefly　for　his　discoveries　and　investigations　in　the　biological　sciences。　One　important　demonstration　was　his　controversion　of　the　theory　of　abiogenesis；　or　〃spontaneous　generation；〃　as　propounded　by　Needham　and　Buffon。　　At　the　time　of　Needham's　experiments　it　had　long　been　observed　that　when　animal　or　vegetable　matter　had　lain　in　water　for　a　little　timelong　enough　for　it　to　begin　to　undergo　decompositionthe　water　became　filled　with　microscopic　creatures；　the　〃infusoria　animalculis。〃　This　would　tend　to　show；　either　that　the　water　or　the　animal　or　vegetable　substance　contained　the　〃germs〃　of　these　minute　organisms；　or　else　that　they　were　generated　spontaneously。　It　was　known　that　boiling　killed　these　animalcules；　and　Needham　agreed；　therefore；　that　if　he　first　heated　the　meat　or　vegetables；　and　also　the　water　containing　them；　and　then　placed　them　in　hermetically　scaled　jarsif　he　did　this；　and　still　the　animalcules　made　their　appearance；　it　would　be　proof…positive　that　they　had　been　generated　spontaneously。　　Accordingly　be　made　numerous　experiments；　always　with　the　same　resultsthat　after　a　few　days　the　water　was　found　to　swarm　with　the　microscopic　creatures。　The　thing　seemed　proven　beyond　questionproviding；　of　course；　that　there　had　been　no　slips　in　the　experiments。

But　Abbe　Spallanzani　thought　that　he　detected　such　slips　in　Needham's　experiment。　　The　possibility　of　such　slips　might　come　in　several　ways：　　the　contents　of　the　jar　might　not　have　been　boiled　for　a　sufficient　length　of　time　to　kill　all　the　germs；　or　the　air　might　not　have　been　excluded　completely　by　the　sealing　process。　To　cover　both　these　contingencies；　Spallanzani　first　hermetically　sealed　the　glass　vessels　and　then　boiled　them　for　three…quarters　of　an　hour。　Under　these　circumstances　no　animalcules　ever　made　their　appearancea　conclusive　demonstration　that　rendered　Needham's　grounds　for　his　theory　at　once　untenable。＇2＇

Allied　to　these　studies　of　spontaneous　generation　were　Spallanzani's　experiments　and　observations　on　the　physiological　processes　of　generation　among　higher　animals。　　He　experimented　with　frogs；　tortoises；　and　dogs；　and　settled　beyon