medical essays-第47部分

快捷操作: 按键盘上方向键 ← 或 → 可快速上下翻页 按键盘上的 Enter 键可回到本书目录页 按键盘上方向键 ↑ 可回到本页顶部! 如果本书没有阅读完，想下次继续接着阅读，可使用上方 "收藏到我的浏览器" 功能 和 "加入书签" 功能！


I　will　only　call　your　attention　to　the　fact；　that　the　exceptional　phenomenon　of　the　laboratory　is　the　prevailing　law　of　the　organism。　Nutrition　itself　is　but　one　great　catalytic　process。　　As　the　blood　travels　its　rounds；　each　part　selects　its　appropriate　element　and　transforms　it　to　its　own　likeness。　　Whether　the　appropriating　agent　be　cell　or　nucleus；　or　a　structureless　solid　like　the　intercellular　substance　of　cartilage；　the　fact　of　its　presence　determines　the　separation　of　its　proper　constituents　from　the　circulating　fluid；　so　that　even　when　we　are　wounded　bone　is　replaced　by　bone；　skin　by　skin；　and　nerve　by　nerve。

It　is　hardly　without　a　smile　that　we　resuscitate　the　old　question　of　the　vis　insita　of　the　muscular　fibre；　so　famous　in　the　discussions　of　Haller　and　his　contemporaries。　　Speaking　generally；　I　think　we　may　say　that　Haller's　doctrine　is　the　one　now　commonly　received；　namely；　that　the　muscles　contract　in　virtue　of　their　own　inherent　endowments。　It　is　true　that　Kolliker　says　no　perfectly　decisive　fact　has　been　brought　forward　to　prove　that　the　striated　muscles　contract　with。　out　having　been　acted　on　by　nerves。　　Yet　Mr。　Bowman's　observations　on　the　contraction　of　isolated　fibres　appear　decisive　enough　（unless　we　consider　them　invalidated　by　Dr。　Lionel　Beale's　recent　researches；　tending　to　show　that　each　elementary　fibre　is　supplied　with　nerves；　and　as　to　the　smooth　muscular　fibres；　we　have　Virchow's　statement　respecting　the　contractility　of　those　of　the　umbilical　cord；　where　there　is　not　a　trace　of　any　nerves。

In　the　investigation　of　the　nervous　system；　anatomy　and　physiology　have　gone　hand　in　hand。　　It　is　very　singular　that　so　important；　and　seemingly　simple；　a　fact　as　the　connection　of　the　nerve…tubes；　at　their　origin　or　in　their　course；　with　the　nerve…cells；　should　have　so　long　remained　open　to　doubt；　as　you　may　see　that　it　did　by　referring　to　the　very　complete　work　of　Sharpey　and　Quain　（edition　of　1849）；　the　histological　portion　of　which　is　cordially　approved　by　Kolliker　himself。

Several　most　interesting　points　of　the　minute　anatomy　of　the　nervous　centres　have　been　laboriously　and　skilfully　worked　out　by　a　recent　graduate　of　this　Medical　School；　in　a　monograph　worthy　to　stand　in　line　with　those　of　Lockhart　Clarke；　Stilling；　and　Schroder　van　der　Kolk。　I　have　had　the　privilege　of　examining　and　of　showing　some　of　you　a　number　of　Dr。　Dean's　skilful　preparations。　　I　have　no　space　to　give　even　an　abstract　of　his　conclusions。　　I　can　only　refer　to　his　proof　of　the　fact；　that　a　single　cell　may　send　its　processes　into　several　different　bundles　of　nerve…roots；　and　to　his　demonstration　of　the　curved　ascending　and　descending　fibres　from　the　posterior　nerveroots；　to　reach　what　he　has　called　the　longitudinal　columns　of　the　cornea。　　I　must　also　mention　Dr。　Dean's　exquisite　microscopic　photographs　from　sections　of　the　medulla　oblongata；　which　appear　to　me　to　promise　a　new　development；　if　not　a　new　epoch；　in　anatomical　art。

It　having　been　settled　that　the　nerve…tubes　can　very　commonly　be　traced　directly　to　the　nerve…cells；　the　object　of　all　the　observers　in　this　department　of　anatomy　is　to　follow　these　tubes　to　their　origin。　　We　have　an　infinite　snarl　of　telegraph　wires；　and　we　may　be　reasonably　sure；　that；　if　we　can　follow　them　up；　we　shall　find　each　of　them　ends　in　a　battery　somewhere。　　One　of　the　most　interesting　problems　is　to　find　the　ganglionic　origin　of　the　great　nerves　of　the　medulla　oblongata；　and　this　is　the　end　to　which；　by　the　aid　of　the　most　delicate　sections；　colored　so　as　to　bring　out　their　details；　mounted　so　as　to　be　imperishable；　magnified　by　the　best　instruments；　and　now　self…recorded　in　the　light　of　the　truth…telling　sunbeam；　our　fellow…student　is　making　a　steady　progress　in　a　labor　which　I　think　bids　fair　to　rank　with　the　most　valuable　contributions　to　histology　that　we　have　had　from　this　side　of　the　Atlantic。

It　is　interesting　to　see　how　old　questions　are　incidentally　settled　in　the　course　of　these　new　investigations。　　Thus；　Mr。　Clarke's　dissections；　confirmed　by　preparations　of　Mr。　Dean's　which　I　have　myself　examined；　placed　the　fact　of　the　decussation　of　the　pyramids　denied　by　Haller；　by　Morgagni；　and　even　by　Stillingbeyond　doubt。　So　the　spinal　canal；　the　existence　of　which；　at　least　in　the　adult；　has　been　so　often　disputed；　appears　as　a　coarse　and　unequivocal　anatomical　fact　in　many　of　the　preparations　referred　to。

While　these　studies　of　the　structure　of　the　cord　have　been　going　on；　the　ingenious　and　indefatigable　Brown…Sequard　has　been　investigating　the　functions　of　its　different　parts　with　equal　diligence。　　The　microscopic　anatomists　had　shown　that　the　ganglionic　corpuscles　of　the　gray　matter　of　the　cord　are　connected　with　each　other　by　their　processes；　as　well　as　with　the　nerve…roots。　　M。　　Brown…Sequard　has　proved　by　numerous　experiments　that　the　gray　substance　transmits　sensitive　impressions　and　muscular　stimulation。　　The　oblique　ascending　and　descending　fibres　from　the　posterior　nerve…roots；　joining　the　〃longitudinal　columns　of　the　cornua；〃　account　for　the　results　of　Brown…Sequard's　sections　of　the　posterior　columns。　　The　physiological　experimenter　has　also　made　it　evident　that　the　decussation　of　the　conductors　of　sensitive　impressions　has　its　seat　in　the　spinal　core；　and　not　in　the　encephalon；　as　had　been　supposed。　Not　less　remarkable　than　these　results　are　the　facts；　which　I　with　others　of　my　audience　have　had　the　opportunity　of　observing；　as　shown　by　M。　Brown…S6quard；　of　the　artificial　production　of　epilepsy　in　animals　by　injuring　the　spinal　cord；　and　the　induction　of　the　paroxysm　by　pinching　a　certain　portion　of　the　skin。　　I　would　also　call　the　student's　attention　to　his　account　of　the　relations　of　the　nervous　centres　to　nutrition　and　secretion；　the　last　of　which　relations　has　been　made　the　subject　of　an　extended　essay　by　our　fellow　countryman；　Dr。　H。　F。　Campbell　of　Georgia。

The　physiology　of　the　spinal　cord　seems　a　simple　matter　as　you　study　it　in　Longet。　　The　experiments　of　Brown…Sequard　have　shown　the　problem　to　be　a　complex　one；　and　raised　almost　as　many　doubts　as　they　have　solved　questions；　at　any　rate；　I　believe　all　lecturers　on　physiology　agree　that　there　is　no　part　of　their　task　they　dread　so　much　as　the　analysis　of　the　evidence　relating　to　the　special　offices　of　the　different　portions　of　the　medulla　spinalis。　　In　the　brain　we　are　sure　that　we　do　not　know　how　to　localize　functions；　in　the　spinal　cord；　we　think　we　do　know　something；　but　there　are　so　many　anomalies；　and　seeming　contradictions；　and　sources　of　fallacy；　that　beyond　the　facts　of　crossed　paralysis　of　sensation；　and　the　conducting　agency　of　the　gray　substance；　I　am　afraid　we　retain　no　cardinal　principles　discovered　since　the　development　of　the　reflex　function　took　its　place　by　Sir　Charles　Bell's　great　discovery。

By　the　manner　in　which　I　spoke　of　the　brain；　you　will　see　that　I　am　obliged　to　leave　phrenology　sub　Jove；out　in　the　cold；as　not　one　of　the　household　of　science。　　I　am　not　one　of　its　haters；　on　the　contrary；　I　am　grateful　for　the　incidental　good　it　has　done。　　I　love　to　amuse　myself　in　its　plaster　Golgothas；　and　listen　to　the　glib　professor；　as　he　discovers　by　his　manipulations

　　　　　〃All　that　disgraced　my　betters　met　in　me。〃

I　loved　of　old　to　see　square…headed；　heavy…jawed　Spurzheim　make　a　brain　flower　out　into　a　corolla　of　marrowy　filaments；　as　Vieussens　had　done　before　him；　and　to　hear　the　dry…fibred　but　human…hearted　George　Combe　teach　good　sense　under　the　disguise　of　his　equivocal　system。　　But　the　pseudo…sciences；　phrenology　and　the　rest；　seem　to　me　only　appeals　to　weak　minds　and　the　weak　points　of　strong　ones。　　There　is　a　pica　or　false　appetite　in　many　intelligences；　they　take　to　odd　fancies　in　place　of　wholesome　truth；　as　girls　gnaw　at　chalk　and　charcoal。　　Phrenology　juggles　with　nature。　　It　is　so　adjusted　as　to　soak　up　all　evidence　that　helps　it；　and　shed　all　that　harms　it。　　It　crawls　forward　in　all　weathers；　like　Richard　Edgeworth's　hygrometer。　It　does　not　stand　at　the　boundary　of　our　ignorance；　it　seems　to　me；　but　is　one　of　the　will…o'…the…wisps　of　its　undisputed　central　domain　of　bog　and　quicksand。　　Yet　I　should　not　have　devoted　so　many　words　to　it；　did　I　not　recognize　the　light　it　has　thrown　on　human　actions　by　its　study　of　congenital　organic　tendencies。　　Its　maps　of　the。　surface　of　the　head　are；　I　feel　sure；　founded　on　a　delusion；　but　its　studies　of　individual　character　are　always　interesting　and　instructive。

The　〃snapping…turtle〃　strikes　after　its　natural　fashion　when　it　first　comes　out　of　the　egg。　　Children　betray　their　tendencies　in　their　way　of　dealing　with　the　breasts　that　nourish　them；　nay；　lean　venture　to　affirm；　that　long　before　they　are　born　they　teach　their　mothers　something　of　their　turbulent　or　quiet　tempers。

　　　　　〃Castor　gaudet　equis；　ovo　proanatus　eodem　　　　　　　　　　　Pugnis。〃

Strike　out　the　false　pretensions　of　phrenology；　call　it　anthropology；　let　it　study　man　the　individual　in　distinction　from　man　the　abstraction；　the　metaphysical　or　theological　lay…figure；　and　it　becomes　〃the　proper　study　of　mankind；〃　one　of　the　noblest　and　most　interesting　of　pursuits。

The　whole　physiology　of　the　nervous　system；　from　the　simplest　manifestation　of　its　power　in　an　insect　up　to　the　supre