the expression of emotion in man and animals-第8节

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！
————未阅读完？加入书签已便下次继续阅读！


akes　his　spring；　many　of　the　spectators；　generally　men　and　boys；　move　their　feet；　but　here　again　habit　probably　comes　into　play；　for　it　is　very　doubtful　whether　women　would　thus　act。

_Reflex　actions_Reflex　actions；　in　the　strict　sense　of　the　term；　are　due　to　the　excitement　of　a　peripheral　nerve；　which　transmits　its　influence　to　certain　nerve…cells；　and　these　in　their　turn　excite　certain　muscles　or　glands　into　action；　and　all　this　may　take　place　without　any　sensation　or　consciousness　on　our　part；　though　often　thus　accompanied。　　As　many　reflex　actions　are　highly　expressive；　the　subject　must　here　be　noticed　at　some　little　length。　We　shall　also　see　that　some　of　them　graduate　into；　and　can　hardly　be　distinguished　from　actions　which　have　arisen　through　habit？　Coughing　and　sneezing　are　familiar　instances　of　reflex　actions。　With　infants　the　first　act　of　respiration　is　often　a　sneeze；　although　this　requires　the　co…ordinated　movement　of　numerous　muscles。　Respiration　is　partly　voluntary；　but　mainly　reflex；　and　is　performed　in　the　most　natural　and　best　manner　without　the　interference　of　the　will。　A　vast　number　of　complex　movements　are　reflex。　　As　good　an　instance　as　can　be　given　is　the　often…quoted　one　of　a　decapitated　frog；　which　cannot　of　course　feel；　and　cannot　consciously　perform；　any　movement。　Yet　if　a　drop　of　acid　be　placed　on　the　lower　surface　of　the　thigh　of　a　frog　in　this　state；　it　will　rub　off　the　drop　with　the　upper　surface　of　the　foot　of　the　same　leg。　　If　this　foot　be　cut　off；　it　cannot　thus　act。　　〃After　some　fruitless　efforts；　therefore；　it　gives　up　trying　in　that　way；　seems　restless；　as　though；　says　Pfluger；　it　was　seeking　some　other　way；　and　at　last　it　makes　use　of　the　foot　of　the　other　leg　and　succeeds　in　rubbing　off　the　acid。　Notably　we　have　here　not　merely　contractions　of　muscles；　but　combined　and　harmonized　contractions　in　due　sequence　for　a　special　purpose。　These　are　actions　that　have　all　the　appearance　of　being　guided　by　intelligence　and　instigated　by　will　in　an　animal；　the　recognized　organ　of　whose　intelligence　and　will　has　been　removed。〃＇10＇


＇9＇　Prof。　Huxley　remarks　（‘Elementary　Physiology；'　5th　edit。　　p。　　305）　that　reflex　actions　proper　to　the　spinal　cord　are　NATURAL；　but；　by　the　help　of　the　brain；　that　is　through　habit；　an　infinity　of　ARTIFICIAL　reflex　actions　may　be　acquired。　Virchow　admits　（‘Sammlung　wissenschaft。　　Vortrage；'　&c。；　〃Ueber　das　Ruckeninark；〃　1871；　ss。　　24；　31）　that　some　reflex　actions　can　hardly　be　distinguished　from　instincts；　and；　of　the　latter；　it　may　be　added；　some　cannot　be　distinguished　from　inherited　habits。

We　see　the　difference　between　reflex　and　voluntary　movements　in　very　young　children　not　being　able　to　perform；　as　I　am　informed　by　Sir　Henry　Holland；　certain　acts　somewhat　analogous　to　those　of　sneezing　and　coughing；　namely；　in　their　not　being　able　to　blow　their　noses　（i。　e。　to　compress　the　nose　and　blow　violently　through　the　passage）；　and　in　their　not　being　able　to　clear　their　throats　of　phlegm。　They　have　to　learn　to　perform　these　acts；　yet　they　are　performed　by　us；　when　a　little　older；　almost　as　easily　as　reflex　actions。　Sneezing　and　coughing；　however；　can　be　controlled　by　the　will　only　partially　or　not　at　all；　whilst　the　clearing　the　throat　and　blowing　the　nose　are　completely　under　our　command。


＇10＇　〃Dr。　Maudsley；　‘Body　and　Mind；'　1870；　p。　　8。

When　we　are　conscious　of　the　presence　of　an　irritating　particle　in　our　nostrils　or　windpipethat　is；　when　the　same　sensory　nerve…cells　are　excited；　as　in　the　case　of　sneezing　and　coughing　we　can　voluntarily　expel　the　particle　by　forcibly　driving　air　through　these　passages；　but　we　cannot　do　this　with　nearly　the　same　force；　rapidity；　and　precision；　as　by　a　reflex　action。　In　this　latter　case　the　sensory　nerve…cells　apparently　excite　the　motor　nerve…cells　without　any　waste　of　power　by　first　communicating　with　the　cerebral　hemispheresthe　seat　of　our　consciousness　and　volition。　　In　all　cases　there　seems　to　exist　a　profound　antagonism　between　the　same　movements；　as　directed　by　the　will　and　by　a　reflex　stimulant；　in　the　force　with　which　they　are　performed　and　in　the　facility　with　which　they　are　excited。　As　Claude　Bernard　asserts；　〃L'influence　du　cerveau　tend　donc　a　entraver　les　mouvements　reflexes；　a　limiter　leur　force　et　leur　etendue。〃＇11＇

The　conscious　wish　to　perform　a　reflex　action　sometimes　stops　or　interrupts　its　performance；　though　the　proper　sensory　nerves　may　be　stimulated。　For　instance；　many　years　ago　I　laid　a　small　wager　with　a　dozen　young　men　that　they　would　not　sneeze　if　they　took　snuff；　although　they　all　declared　that　they　invariably　did　so；　accordingly　they　all　took　a　pinch；　but　from　wishing　much　to　succeed；　not　one　sneezed；　though　their　eyes　watered；　and　all；　without　exception；　had　to　pay　me　the　wager。　Sir　H。　Holland　remarks＇12＇　that　attention　paid　to　the　act　of　swallowing　interferes　with　the　proper　movements；　from　which　it　probably　follows；　at　least　in　part；　that　some　persons　find　it　so　difficult　to　swallow　a　pill。


＇11＇　〃See　the　very　interesting　discussion　on　the　whole　subject　by　Claude　Bernard；　‘Tissus　Vivants；'　1866；　p。　　353…356。

＇12＇　‘Chapters　on　Mental　Physiology；'　1858；　p。　　85。

Another　familiar　instance　of　a　reflex　action　is　the　involuntary　closing　of　the　eyelids　when　the　surface　of　the　eye　is　touched。　A　similar　winking　movement　is　caused　when　a　blow　is　directed　towards　the　face；　but　this　is　an　habitual　and　not　a　strictly　reflex　action；　as　the　stimulus　is　conveyed　through　the　mind　and　not　by　the　excitement　of　a　peripheral　nerve。　　The　whole　body　and　head　are　generally　at　the　same　time　drawn　suddenly　backwards。　These　latter　movements；　however；　can　be　prevented；　if　the　danger　does　not　appear　to　the　imagination　imminent；　but　our　reason　telling　us　that　there　is　no　danger　does　not　suffice。　I　may　mention　a　trifling　fact；　illustrating　this　point；　and　which　at　the　time　amused　me。　　I　put　my　face　close　to　the　thick　glass…plate　in　front　of　a　puff…adder　in　the　Zoological　Gardens；　with　the　firm　determination　of　not　starting　back　if　the　snake　struck　at　me；　but；　as　soon　as　the　blow　was　struck；　my　resolution　went　for　nothing；　and　I　jumped　a　yard　or　two　backwards　with　astonishing　rapidity。　My　will　and　reason　were　powerless　against　the　imagination　of　a　danger　which　had　never　been　experienced。

The　violence　of　a　start　seems　to　depend　partly　on　the　vividness　of　the　imagination；　and　partly　on　the　condition；　either　habitual　or　temporary；　of　the　nervous　system。　He　who　will　attend　to　the　starting　of　his　horse；　when　tired　and　fresh；　will　perceive　how　perfect　is　the　gradation　from　a　mere　glance　at　some　unexpected　object；　with　a　momentary　doubt　whether　it　is　dangerous；　to　a　jump　so　rapid　and　violent；　that　the　animal　probably　could　not　voluntarily　whirl　round　in　so　rapid　a　manner。　The　nervous　system　of　a　fresh　and　highly…fed　horse　sends　its　order　to　the　motory　system　so　quickly；　that　no　time　is　allowed　for　him　to　consider　whether　or　not　the　danger　is　real。　After　one　violent　start；　when　he　is　excited　and　the　blood　flows　freely　through　his　brain；　he　is　very　apt　to　start　again；　and　so　it　is；　as　I　have　noticed；　with　young　infants。

A　start　from　a　sudden　noise；　when　the　stimulus　is　conveyed　through　the　auditory　nerves；　is　always　accompanied　in　grown…up　persons　by　the　winking　of　the　eyelids。＇13＇　I　observed；　however；　that　though　my　infants　started　at　sudden　sounds；　when　under　a　fortnight　old；　they　certainly　did　not　always　wink　their　eyes；　and　I　believe　never　did　so。　　The　start　of　an　older　infant　apparently　represents　a　vague　catching　hold　of　something　to　prevent　falling。　I　shook　a　pasteboard　box　close　before　the　eyes　of　one　of　my　infants；　when　114　days　old；　and　it　did　not　in　the　least　wink；　but　when　I　put　a　few　comfits　into　the　box；　holding　it　in　the　same　position　as　before；　and　rattled　them；　the　child　blinked　its　eyes　violently　every　time；　and　started　a　little。　It　was　obviously　impossible　that　a　carefully…guarded　infant　could　have　learnt　by　experience　that　a　rattling　sound　near　its　eyes　indicated　danger　to　them。　But　such　experience　will　have　been　slowly　gained　at　a　later　age　during　a　long　series　of　generations；　and　from　what　we　know　of　inheritance；　there　is　nothing　improbable　in　the　transmission　of　a　habit　to　the　offspring　at　an　earlier　age　than　that　at　which　it　was　first　acquired　by　the　parents。

From　the　foregoing　remarks　it　seems　probable　that　some　actions；　which　were　at　first　performed　consciously；　have　become　through　habit　and　association　converted　into　reflex　actions；　and　are　now　so　firmly　fixed　and　inherited；　that　they　are　performed；　even　when　not　of　the　least　use；＇14＇　as　often　as　the　same　causes　arise；　which　originally　excited　them　in　us　through　the　volition。　　In　such　cases　the　sensory　nerve…cells　excite　the　motor　cells；　without　first　communicating　with　those　cells　on　which　our　consciousness　and　volition　depend。　It　is　probable　that　sneezing　and　coughing　were　originally　acquired　by　the　habit　of　expelling；　as　violently　as　possible；　any　irritating　particle　from　the　sensitive　air…passages。　As　far　as　time　is　concerned；　there　has　been　more　than　enough　for　these　habits　to　have　become　innate　or　converted　into　reflex　actions；　for　they　are　common　to　most　or　all　of　the　higher　quadrupeds；　and　must　therefore　have　been　first　acquired　at　a　very　re