medical essays-第39章

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enied　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　supreme　act　of　the　human　intelligence　working　through　the　brain；　is　full　of　the　most　difficult　yet　profoundly　interesting　questions。　　The　singular　relations　between　electricity　and　nerve…force；　relations　which　it　has　been　attempted　to　interpret　as　meaning　identity；　in　the　face　of　palpable　differences；　require　still　more　extended　studies。　　You　may　be　interested　by　Professor　Faraday's　statement　of　his　opinion　on　the　matter。　　〃Though　I　am　not　satisfied　that　the　nervous　fluid　is　only　electricity；　still　I　think　that　the　agent　in　the　nervous　system　maybe　an　inorganic　force；　and　if　there　be　reason　for　supposing　that　magnetism　is　a　higher　relation　of　force　than　electricity；　so　it　may　well　be　imagined　that　the　nervous　power　may　be　of　a　still　more　exalted　character；　and　yet　within　the　reach　of　experiment。〃

In　connection　with　this　statement；　it　is　interesting　to　refer　to　the　experiments　of　Helmholtz　on　the　rapidity　of　transmission　of　the　nervous　actions。　　The　rate　is　given　differently　in　Valentin's　report　of　these　experiments　and　in　that　found　in　the　〃Scientific　Annual〃　for　1858。　　One　hundred　and　eighty　to　three　hundred　feet　per　second　is　the　rate　of　movement　assigned　for　sensation；　but　all　such　results　must　be　very　vaguely　approximative。　　Boxers；　fencers；　players　at　the　Italian　game　of　morn；　〃prestidigitators；〃　and　all　who　depend　for　their　success　on　rapidity　of　motion；　know　what　differences　there　are　in　the　personal　equation　of　movement。

Reflex　action；　the　mechanical　sympathy；　if　I　may　so　call　it；　of　distant　parts；　Instinct；　which　is　crystallized　intelligence；an　absolute　law　with　its　invariable　planes　and　angles　introduced　into　the　sphere　of　consciousness；　as　raphides　are　inclosed　in　the　living　cells　of　plants；　Intellect；the　operation　of　the　thinking　principle　through　material　organs；　with　an　appreciable　waste　of　tissue　in　every　act　of　thought；　so　that　our　clergymen's　blood　has　more　phosphates　to　get　rid　of　on　Monday　than　on　any　other　day　of　the　week；　Will；　theoretically　the　absolute　determining　power；　practically　limited　in　different　degrees　by　the　varying　organization　of　races　and　individuals；　annulled　or　perverted　by　different　ill…understood　organic　changes；　on　all　these　subjects　our　knowledge　is　in　its　infancy；　and　from　the　study　of　some　of　them　the　interdict　of　the　Vatican　is　hardly　yet　removed。

I　must　allude　to　one　or　two　points　in　the　histology　and　physiology　of　the　organs　of　sense。　　The　anterior　continuation　of　the　retina　beyond　the　ora　serrata　has　been　a　subject　of　much　discussion。　　If　H。　Muller　and　Kolliker　can　be　relied　upon；　this　question　is　settled　by　recognizing　that　a　layer　of　cells；　continued　from　the　retina；　passes　over　the　surface　of　the　zonula　Zinnii；　but　that　no　proper　nervous　element　is　so　prolonged　forward。

I　observe　that　Kolliker　calls　the　true　nervous　elements　of　the　retina　〃the　layer　of　gray　cerebral　substance。〃　　In　fact；　the　ganglionic　corpuscles　of　each　eye　may　be　considered　as　constituting　a　little　brain；　connected　with　the　masses　behind　by　the　commissure；　commonly　called　the　optic　nerve。　　We　are　prepared；　therefore；　to　find　these　two　little　brains　in　the　most　intimate　relations　with　each　other；　as　we　find　the　cerebral　hemispheres。　　We　know　that　they　are　directly　connected　by　fibres　that　arch　round　through　the　chiasma。

I　mention　these　anatomical　facts　to　introduce　a　physiological　observation　of　my　own；　first　announced　in　one　of　the　lectures　before　the　Medical　Class；　subsequently　communicated　to　the　American　Academy　of　Arts　and　Sciences；　and　printed　in　its　〃Transactions〃　for　February　14；　1860。　　I　refer　to　the　apparent　transfer　of　impressions　from　one　retina　to　the　other；　to　which　I　have　given　the　name　reflex　vision。　The　idea　was　suggested　to　me　in　consequence　of　certain　effects　noticed　in　employing　the　stereoscope。　　Professor　William　B。　Rodgers　has　since　called　the　attention　of　the　American　Scientific　Association　to　some　facts　bearing　on　the　subject；　and　to　a　very　curious　experiment　of　Leonardo　da　Vinci's；　which　enables　the　observer　to　look　through　the　palm　of　his　hand　（or　seem　to）；　as　if　it　had　a　hole　bored　through　it。　　As　he　and　others　hesitated　to　accept　my　explanation；　I　was　not　sorry　to　find　recently　the　following　words　in　the　〃Observations　on　Man〃　of　that　acute　observer　and　thinker；　David　Hartley。　　〃An　impression　made　on　the　right　eye　alone　by　a　single　object　may　propagate　itself　into　the　left；　and　there　raise　up　an　image　almost　equal　in　vividness　to　itself；　and　consequently　when　we　see　with　one　eye　only；　we　may；　however；　have　pictures　in　both　eyes。〃　Hartley；　in　1784；　had　anticipated　many　of　the　doctrines　which　have　since　been　systematized　into　the　theory　of　reflex　actions；　and　with　which　I　have　attempted　to　associate　this　act　of　reflex　vision。　　My　sixth　experiment；　however；　in　the　communication　referred　to；　appears　to　me　to　be　a　crucial　one；　proving　the　correctness　of　my　explanation；　and　I　am　not　aware　that　it　has　been　before　instituted。

Another　point　of　great　interest　connected　with　the　physiology　of　vision；　and　involved　for　a　long　time　in　great　obscurity；　is　that　of　the　adjustment　of　the　eye　to　different　distances。　　Dr。　Clay　Wallace　of　New　York；　who　published　a　very　ingenious　little　book　on　the　eye　about　twenty　years　ago；　with　vignettes　reminding　one　of　Bewick；　was　among　the　first；　if　not　the　first；　to　describe　the　ciliary　muscle；　to　which　the　power　of　adjustment　is　generally　ascribed。　　It　is　ascertained；　by　exact　experiment　with　the　phacueidoscope；　that　accommodation　depends　on　change　of　form　of　the　crystalline　lens。　Where　the　crystalline　is　wanting；　as　Mr。　Ware　long　ago　taught；　no　power　of　accommodation　remains。　　The　ciliary　muscle　is　generally　thought　to　effect　the　change　of　form　of　the　crystalline。　　The　power　of　accommodation　is　lost　after　the　application　of　atropine；　in　consequence；　as　is　supposed；　of　the　paralysis　of　this　muscle。　　This；　I　believe；　is　the　nearest　approach　to　a　demonstration　we　have　on　this　point。

I　have　only　time　briefly　to　refer　to　Professor　Draper's　most　ingenious　theory　as　to　the　photographic　nature　of　vision；　for　an　account　of　which　I　must　refer　to　his　original　and　interesting　Treatise　on　Physiology。

It　were　to　be　wished　that　the　elaborate　an