a history of science-4-第21章

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h　have　disappeared　previous　to　their　incrustation。　It　is　also　very　rare　to　find　any　fossil　skeletons　of　quadrupeds　in　any　degree　approaching　to　a　complete　state；　as　the　strata　for　the　most　part　only　contain　separate　bones；　scattered　confusedly　and　almost　always　broken　and　reduced　to　fragments；　which　are　the　only　means　left　to　naturalists　for　ascertaining　the　species　or　genera　to　which　they　have　belonged。

〃Fortunately　comparative　anatomy；　when　thoroughly　understood；　enables　us　to　surmount　all　these　difficulties；　as　a　careful　application　of　its　principles　instructs　us　in　the　correspondences　and　dissimilarities　of　the　forms　of　organized　bodies　of　different　kinds；　by　which　each　may　be　rigorously　ascertained　from　almost　every　fragment　of　its　various　parts　and　organs。

〃Every　organized　individual　forms　an　entire　system　of　its　own；　all　the　parts　of　which　naturally　correspond；　and　concur　to　produce　a　certain　definite　purpose；　by　reciprocal　reaction；　or　by　combining　towards　the　same　end。　　Hence　none　of　these　separate　parts　can　change　their　forms　without　a　corresponding　change　in　the　other　parts　of　the　same　animal；　and　consequently　each　of　these　parts；　taken　separately；　indicates　all　the　other　parts　to　which　it　has　belonged。　　Thus；　as　I　have　elsewhere　shown；　if　the　viscera　of　an　animal　are　so　organized　as　only　to　be　fitted　for　the　digestion　of　recent　flesh；　it　is　also　requisite　that　the　jaws　should　be　so　constructed　as　to　fit　them　for　devouring　prey；　the　claws　must　be　constructed　for　seizing　and　tearing　it　to　pieces；　the　teeth　for　cutting　and　dividing　its　flesh；　the　entire　system　of　the　limbs；　or　organs　of　motion；　for　pursuing　and　overtaking　it；　and　the　organs　of　sense　for　discovering　it　at　a　distance。　Nature　must　also　have　endowed　the　brain　of　the　animal　with　instincts　sufficient　for　concealing　itself　and　for　laying　plans　to　catch　its　necessary　victims。　　。　。　。　。　。　。　。　。　。

〃To　enable　the　animal　to　carry　off　its　prey　when　seized；　a　corresponding　force　is　requisite　in　the　muscles　which　elevate　the　head；　and　this　necessarily　gives　rise　to　a　determinate　form　of　the　vertebrae　to　which　these　muscles　are　attached　and　of　the　occiput　into　which　they　are　inserted。　In　order　that　the　teeth　of　a　carnivorous　animal　may　be　able　to　cut　the　flesh；　they　require　to　be　sharp；　more　or　less　so　in　proportion　to　the　greater　or　less　quantity　of　flesh　that　they　have　to　cut。　It　is　requisite　that　their　roots　should　be　solid　and　strong；　in　proportion　to　the　quantity　and　size　of　the　bones　which　they　have　to　break　to　pieces。　The　whole　of　these　circumstances　must　necessarily　influence　the　development　and　form　of　all　the　parts　which　contribute　to　move　the　jaws。　。　。　。　。　。　。　。　。　。

After　these　observations；　it　will　be　easily　seen　that　similar　conclusions　may　be　drawn　with　respect　to　the　limbs　of　carnivorous　animals；　which　require　particular　conformations　to　fit　them　for　rapidity　of　motion　in　general；　and　that　similar　considerations　must　influence　the　forms　and　connections　of　the　vertebrae　and　other　bones　constituting　the　trunk　of　the　body；　to　fit　them　for　flexibility　and　readiness　of　motion　in　all　directions。　The　bones　also　of　the　nose；　of　the　orbit；　and　of　the　ears　require　certain　forms　and　structures　to　fit　them　for　giving　perfection　to　the　senses　of　smell；　sight；　and　hearing；　so　necessary　to　animals　of　prey。　In　short；　the　shape　and　structure　of　the　teeth　regulate　the　forms　of　the　condyle；　of　the　shoulder…blade；　and　of　the　claws；　in　the　same　manner　as　the　equation　of　a　curve　regulates　all　its　other　properties；　and　as　in　regard　to　any　particular　curve　all　its　properties　may　be　ascertained　by　assuming　each　separate　property　as　the　foundation　of　a　particular　equation；　in　the　same　manner　a　claw；　a　shoulder…blade；　a　condyle；　a　leg　or　arm　bone；　or　any　other　bone　separately　considered；　enables　us　to　discover　the　description　of　teeth　to　which　they　have　belonged；　and　so　also　reciprocally　we　may　determine　the　forms　of　the　other　bones　from　the　teeth。　　Thus　commencing　our　investigations　by　a　careful　survey　of　any　one　bone　by　itself；　a　person　who　is　sufficiently　master　of　the　laws　of　organic　structure　may；　as　it　were；　reconstruct　the　whole　animal　to　which　that　bone　belonged。〃＇1＇

We　have　already　pointed　out　that　no　one　is　quite　able　to　perform　the　necromantic　feat　suggested　in　the　last　sentence；　but　the　exaggeration　is　pardonable　in　the　enthusiast　to　whom　the　principle　meant　so　much　and　in　whose　hands　it　extended　so　far。

Of　course　this　entire　principle；　in　its　broad　outlines；　is　something　with　which　every　student　of　anatomy　had　been　familiar　from　the　time　when　anatomy　was　first　studied；　but　the　full　expression　of　the　〃law　of　co…ordination；〃　as　Cuvier　called　it；　had　never　been　explicitly　made　before；　and；　notwithstanding　its　seeming　obviousness；　the　exposition　which　Cuvier　made　of　it　in　the　introduction　to　his　classical　work　on　comparative　anatomy；　which　was　published　during　the　first　decade　of　the　nineteenth　century；　ranks　as　a　great　discovery。　It　is　one　of　those　generalizations　which　serve　as　guideposts　to　other　discoveries。


BICHAT　AND　THE　BODILY　TISSUES

Much　the　same　thing　may　be　said　of　another　generalization　regarding　the　animal　body；　which　the　brilliant　young　French　physician　Marie　Francois　Bichat　made　in　calling　attention　to　the　fact　that　each　vertebrate　organism；　including　man；　has　really　two　quite　different　sets　of　organsone　set　under　volitional　control；　and　serving　the　end　of　locomotion；　the　other　removed　from　volitional　control；　and　serving　the　ends　of　the　〃vital　processes〃　of　digestion；　assimilation；　and　the　like。　He　called　these　sets　of　organs　the　animal　system　and　the　organic　system；　respectively。　　The　division　thus　pointed　out　was　not　quite　new；　for　Grimaud；　professor　of　physiology　in　the　University　of　Montpellier；　had　earlier　made　what　was　substantially　the　same　classification　of　the　functions　into　〃internal　or　digestive　and　external　or　locomotive〃；　but　it　was　Bichat's　exposition　that　gave　currency　to　the　idea。

Far　more　important；　however；　was　another　classification　which　Bichat　put　forward　in　his　work　on　anatomy；　published　just　at　the　beginning　of　the　last　century。　　This　was　the　division　of　all　animal　structures　into　what　Bichat　called　tissues；　and　the　pointing　out　that　there　are　really　only　a　few　kinds　of　these　in　the　body；　making　up　all　the　diverse　organs。　Thus　muscular　organs　form　one　system；　membranous　organs　another；　glandular　organs　a　third；　the　vascular　mechanism　a　fourth；　and　so　on。　　The　distinction　is　so　obvious　that　it　seems　rather　difficult　to　conceive　that　it　could　have　been　overlooked　by　the　earliest　anatomists；　but；　in　point　of　fact；　it　is　only　obvious　because　now　it　has　been　familiarly　taught　for　almost　a　century。　It　had　never　been　given　explicit　expression　before　the　time　of　Bichat；　though　it　is　said　that　Bichat　himself　was　somewhat　indebted　for　it　to　his　master；　Desault；　and　to　the　famous　alienist　Pinel。

However　that　may　be；　it　is　certain　that　all　subsequent　anatomists　have　found　Bichat's　classification　of　the　tissues　of　the　utmost　value　in　their　studies　of　the　animal　functions。　Subsequent　advances　were　to　show　that　the　distinction　between　the　various　tissues　is　not　really　so　fundamental　as　Bichat　supposed；　but　that　takes　nothing　from　the　practical　value　of　the　famous　classification。

It　was　but　a　step　from　this　scientific　classification　of　tissues　to　a　similar　classification　of　the　diseases　affecting　them；　and　this　was　one　of　the　greatest　steps　towards　placing　medicine　on　the　plane　of　an　exact　science。　This　subject　of　these　branches　completely　fascinated　Bichat；　and　he　exclaimed；　enthusiastically：　　〃Take　away　some　fevers　and　nervous　trouble；　and　all　else　belongs　to　the　kingdom　of　pathological　anatomy。〃　But　out　of　this　enthusiasm　came　great　results。　　Bichat　practised　as　he　preached；　and；　believing　that　it　was　only　possible　to　understand　disease　by　observing　the　symptoms　carefully　at　the　bedside；　and；　if　the　disease　terminated　fatally；　by　post…mortem　examination；　he　was　so　arduous　in　his　pursuit　of　knowledge　that　within　a　period　of　less　than　six　months　he　had　made　over　six　hundred　autopsiesa　record　that　has　seldom；　if　ever；　been　equalled。　Nor　were　his　efforts　fruitless；　as　a　single　example　will　suffice　to　show。　By　his　examinati