medical essays-第42部分

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　of　man　in　different　climates；　and　of　numerous　experiments　in　the　feeding　of　animals。　　I　must　return　to　this　subject　in　connection　with　the　respiratory　function。

The　sugar…making　faculty　of　the　liver　is　another　〃catalytic〃　mystery；　as　great　as　the　rest　of　them；　and　no　greater。　　Liver…tissue　brings　sugar　out　of　the　blood；　or　out　of　its　own　substance；why？

　　　　　　　　　　Quia　est　in　eo　　　　　　　　　　　Virtus　saccharitiva。

Just　what　becomes　of　the　sugar　beyond　the　fact　of　its　disappearance　before　it　can　get　into　the　general　circulation　and　sweeten　our　tempers；　it　is　hard　to　say。

The　pancreatic　fluid　makes　an　emulsion　of　the　fat　contained　in　our　food；　but　just　how　the　fatty　particles　get　into　the　villi　we　must　leave　Brucke　and　Kolliker　to　settle　if　they　can。

No　one　has　shown　satisfactorily　the　process　by　which　the　blood…　corpuscles　are　formed　out　of　the　lymph…corpuscles；　nor　what　becomes　of　them。　　These　two　questions　are　like　those　famous　household　puzzles；Where　do　the　flies　come　from？　　and；　Where　do　the　pins　go　to？

There　is　a　series　of　organs　in　the　body　which　has　long　puzzled　physiologists；organs　of　glandular　aspect；　but　having　no　ducts；the　spleen；　the　thyroid　and　thymus　bodies；　and　the　suprarenal　capsules。　We　call　them　vascular　glands；　and　we　believe　that　they　elaborate　colored　and　uncolored　blood…cells；　but　just　what　changes　they　effect；　and　just　how　they　effect　them；　it　has　proved　a　very　difficult　matter　to　determine。　　So　of　the　noted　glandules　which　form　Peyer's　patches；　their　precise　office；　though　seemingly　like　those　of　the　lymphatic　glands；　cannot　be　positively　assigned；　so　far　as　I　know；　at　the　present　time。　　It　is　of　obvious　interest　to　learn　it　with　reference　to　the　pathology　of　typhoid　fever。　　It　will　be　remarked　that　the　coincidence　of　their　changes　in　this　disease　with　enlargement　of　the　spleen　suggests　the　idea　of　a　similarity　of　function　in　these　two　organs。

The　theories　of　the　production　of　animal　heat；　from　the　times　of　Black；　Lavoisier；　and　Crawford　to　those　of　Liebig；　are　familiar　to　all　who　have　paid　any　attention　to　physiological　studies。　　The　simplicity　of　Liebig's　views；　and　the　popular　form　in　which　they　have　been　presented；　have　given　them　wide　currency；　and　incorporated　them　in　the　common　belief　and　language　of　our　text…books。　　Direct　oxidation　or　combustion　of　the　carbon　and　hydrogen　contained　in　the　food；　or　in　the　tissues　themselves；　the　division　of　alimentary　substances　into　respiratory；　or　non…azotized；　and　azotized；these　doctrines　are　familiar　even　to　the　classes　in　our　high…schools。　　But　this　simple　statement　is　boldly　questioned。　　Nothing　proves　that　oxygen　combines　（in　the　system）　with　hydrogen　and　carbon　in　particular；　rather　than　with　sulphur　and　azote。　　Such　is　the　well…　grounded　statement　of　Robin　and　Verdeil。　　〃It　is　very　probable　that　animal　heat　is　entirely　produced　by　the　chemical　actions　which　take　place　in　the　organism；　but　the　phenomenon　is　too　complex　to　admit　of　our　calculating　it　according　to　the　quality　of　oxygen　consumed。〃　These　last　are　the　words　of　Regnault；　as　cited　by　Mr。　Lewes；　whose　intelligent　discussion　of　this　and　many　of　the　most　interesting　physiological　problems　I　strongly　recommend　to　your　attention。

This　single　illustration　covers　a　wider　ground　than　the　special　function　to　which　it　belongs。　　We　are　learning　that　the　chemistry　of　the　body　must　be　studied；　not　simply　by　its　ingesta　and　egesta；　but　that　there　is　a　long　intermediate　series　of　changes　which　must　be　investigated　in　their　own　light；　under　their　own　special　conditions。　The　expression　〃sum　of　vital　unities〃　applies　to　the　chemical　actions；　as　well　as　to　other　actions　localized　in　special　parts；　and　when　the　distinguished　chemists　whom　I　have　just　cited　entitle　their　work　a　treatise　on　the　immediate　principles　of　the　body；　they　only　indicate　the　nature　of　that　profound　and　subtile　analysis　which　must　take　the　place　of　all　hasty　generalizations　founded　on　a　comparison　of　the　food　with　residual　products。

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　specia