the origin and nature of emotions-第13部分

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；　while　there　is　absolutely　no　pain　in　the　diseases　or　injuries　which　affect　those　regions　of　the　body　in　which　in　the　course　of　evolution　no　pain　receptors　were　placed；　or　in　those　diseases　in　which　muscular　inhibition　or　contraction　is　of　no　help。　In　a　biologic　sense　pain　is　closely　associated　with　the　emotional　stimuli；　for　both　pain　and　the　emotions　incite　motor　activity　for　the　good　of　the　individual。　　The　frequent　occurrence　of　post…operative　and　post…　traumatic　pain　is　accounted　for　by　the　fact　that　the　operation　or　the　injury　has　lowered　the　threshold　of　the　brain…　cells　to　trauma；　the　brain　and　not　the　local　sensitive　field　is　the　site　of　the　pain。　I　have　found　that；　by　blockingthe　field　of　operation　with　local　anesthesia；　post…operative　pain　is　diminished；　that　is；　since　the　local　anesthesia　prevents　the　strong　stimuli　of　the　trauma　from　reaching　the　brain；　its　threshold　is　not　lowered。　There　is　a　close　resemblance　between　the　phenomena　of　pain　habit；　of　education；　of　physical　training；　of　love　and　of　hate。　　In　education；　in　pain　habit；　in　all　emotional　relations；　a　low　brain…　cell　threshold　is　established　which　facilitates　the　reception　of　specific　stimuli；　all　these　processes　are　motor　acts；　or　are　symbolic　of　motor　acts；　and　we　may　be　trained　to　perceive　misfortune　and　pain　as　readily　as　we　are　trained　to　perceive　mathematical　formulae　or　moral　precepts。　In　each　and　every　case；　readiness　of　perception　depends；　as　it　seems　to　me；　upon　a　modified　state　of　the　brain…cells；　their　threshold　especially；　the　final　degree　of　perception　possible　in　any　individual　being　perhaps　based　on　the　type　of　potential　molecules　of　which　the　brain　is　built。　We　must　believe　also　that　every　impression　is　permanent；　as　only　thus　could　an　individual　animal　or　a　man　be　fitted　by　his　own　experience　for　life's　battles。　　LAUGHTER　AND　CRYING　What　is　laughter？　What　is　its　probable　origin；　its　distribution；　and　its　purpose？　Laughter　is　an　involuntary　rhythmic　contraction　of　certain　respiratory　muscles；　usually　accompanied　by　certain　vocal　sounds。　It　is　a　motor　act　of　the　respiratory　apparatus　primarily；　although　if　intense　it　may　involve　not　only　the　extraordinary　muscles　of　respiration；　but　most　of　the　muscles　of　the　body。　　There　are　many　degrees　of　laughter；　from　the　mere　brightening　of　the　eyes；　a　fleeting　smile；　tittering　andgiggling；　to　hysteric　and　convulsive　laughter。　Under　certain　circumstances；　laughter　may　be　so　intense　and　so　long　continued　that　it　leads　to　considerable　exhaustion。　The　formation　of　tears　is　sometimes　associated　with　laughter。　When　integrated　with　laughter；　the　nervous　system　can　perform　no　other　function。　　Crying　is　closely　associated　with　laughter；　and　in　children　especially　laughter　and　crying　are　readily　interchanged。　We　postulate　that　laughter　and　weeping　serve　a　useful　purpose。　According　to　Darwin；　only　man　and　monkeys　laugh　（Fig。　26）；　other　animals　exhibit　certain　types　of　facial　expression　accompanying　various　emotions；　but　laughter　in　the　sense　in　which　that　word　is　commonly　used　is　probably　an　attribute　of　the　primates　only；　although　it　is　probable　that　many　animals　find　substitutes　for　laughter。　The　proneness　of　man　to　laughter　is　modified　by　age；　sex；　training；　mental　state；　health；　and　by　many　other　factors。　　Healthy；　happy　children　are　especially　prone　to　laughter；　while　disease；　strong　emotions；　fatigue；　and　age　diminish　laughter。　　Women　laugh　more　than　do　men。　The　healthy；　happy　maturing　young　woman　perhaps　laughs　most；　especially　when　she　is　slightly　embarrassed。　　What　causes　laughter？　　Good　news；　high　spirits；　tickling；　hearing　and　seeing　others　laugh；　droll　stories；　flashes　of　wit；　passages　of　humor；　averted　injury；　threatened　breach　of　the　conventions；　and　numerous　other　causes　might　be　added。　It　is　obvious　that　laughter　may　be　produced　by　diverse　influences；　many　of　which　are　so　unlike　each　other　that　it　would　at　first　sight　seem　improbable　that　a　single　general　principle　underlies　all。　Before　presenting　a　hypothesis　which　harmonizes　most　of　the　facts；　and　which　mayoffer　an　explanation　of　the　origin　and　purpose　of　laughter；　let　us　return　for　a　moment　to　some　previous　considerations　that　man　is　essentially　a　motor　being；　that　all　his　responses　to　the　physical　forces　of　his　environment　are　motor；　｛illust。　caption　=　FIG。　　26。LAUGHING　CHIMPANZEE。　　〃Mike；〃　the　clever　chimpanzee　in　the　London　Zoo；　evidently　enjoys　a　joke　as　well　as　any　one　else。　（Photo　by　Underwood　and　Underwood；　N。　Y。）｝


that　thoughts　and　words　even　are　symbolic　of　motor　acts；　that　in　the　emotions　of　fear；　of　anger；　and　of　sexual　love　the　whole　body　is　integrated　for　acts　which　are　not　performed。　These　integrations　stimulate　the　brain…cells；　the　ductless　glands；　and　other　parts；　and　the　energizing　secretions；　among　which　are　epinephrin；　thyroid　and　hypophyseal　secretions；　are　thrown　into　the　blood…stream；　while　that　most　available　fuel；　glycogen；　is　also　mobilized　in　the　blood。　This　body…wide　preparation　for　action　may　be　designated　kinetic　reaction。　The　fact　that　emotion　is　more　injurious　to　the　body　than　is　muscular　action　is　well　known；　the　difference　being　probably　caused　by　the　fact　that　when　there　is　action　the　above…mentioned　products　of　stimulation　are　consumed；　while　in　stimulation　without　action　they　are　not　consumed　and　must　be　eliminated　as　waste　products。　Now　these　activating　substances　and　the　fuel　glycogen　may　be　consumed　by　any　muscular　action　as　well　as　by　the　particular　muscular　action　for　which　the　integration　and　consequent　stimulation　were　made；　that　is；　if　one　were　provoked　to　such　anger　that　he　felt　impelled　to　attack　the　object　of　his　anger；　one　of　three　things　might　happen：　First；　he　might　perform　no　physical　act　but　give　expression　to　the　emotion　of　anger；　second；　he　might　engage　in　a　physical　struggle　and　completely　satisfy　his　anger；　third；　he　might　immediately　engage　in　violent　gymnastic　exercises　and　thus　consume　all　the　motor…producing　elements　mobilized　by　the　anger　and　thus　clarify　his　body。

In　these　premises　we　find　our　explanation　of　the　origin　and　purpose　of　laughter　and　crying；　for　since　they　consist　almost　wholly　of　muscular　exertion；　they　serve　precisely　such　clarifying　purposes　as　would　be　served　by　the　gymnastic　exercises　of　an　angry　man。　As　it　seems　to　me；　the　muscular　action　of　laughter　clears　the　system　of　the　energizing　substances　which　have　been　mobilized　in　various　parts　of　the　body　for　the　performance　of　other　actions　（Figs。　27　to　29）。　If　this　be　true；　the　first　question　that　presents　itself　is；　Why　is　the　respiratory　system　utilized　for　such　a　clarifying　purpose？　Why　do　we　not　laugh　with　our　feet　and　hands　as　well？　Were　laughter　expressed　with　the　hands；　the　monkey　might　fall　from　the　tree　and；　if　by　the　feet；　man　might　fall　to　the　ground。　He　would　at　least　be　ataxic。　　In　fact；　laughter　has　the　great　advantage　of　utilizing　a　group　of　powerful　muscles　which　can　be　readily　spared　without　seriously　interfering　with　the　maintenance　of　posture。　　Laughter；　however；　is　only　one　form　of　muscular　action　which　may　consume　the　fuel　thrown　into　the　blood　by　excitation。　That　these　products　of　excitation　are　often　consumed　by　other　motor　acts　than　laughter　is　frequently　seen　in　public　meetings　when　the　stamping　of　feet　and　the　clapping　of　hands　in　applause　gives　relief　to　the　excitation　（Fig。　30）。　Why　the　noise　of　laughter？　In　order　that　the　products　of　excitation　may　be　quickly　and　completely　consumed；　the　powerful　group　of　expiratory　muscles　must　have　some　resistance　against　which　they　can　exert　themselves　strongly　and　at　the　same　time　provide　for　adequate　respiratory　exchange。　The　intermittent　closure　of　the　epiglottis　serves　this　purpose　admirably；　just　as　the　horizontal　bars　afford　the　resistance　against　which　muscles　may　be　exercised。　　The　facial　muscles　are　not　in　use　for　other　purposes；　hence　their　contractions　will　consume　a　little　of　the　fuel。　An　audience　excited　by　the　words　of　an　impassioned　speaker　undergoes　a　body…wide　stimulation　for　action；　all　of　which　may　be　eliminated　by　laughter　or　by　applause　（Fig。　31）。

Let　us　test　this　hypothesis　by　some　practical　examples。　The　first　is　an　incident　that　accidentally　occurred　in　our　laboratory　during　experiments　on　fear　which　were　performed　as　follows：　A　keen；　snappy　fox　terrier　was　completely　muzzled　by　winding　a　broad　strip　of　adhesive　plaster　around　his　jaw　so　as　to　include　all　but　the　nostrils。　When　this　aggressive　little　terrier　and　the　rabbit　found　themselves　in　close　quarters　each　animal　became　completely　governed　by　instinct；　the　rabbit　crouched　in　fear；　while　the　terrier；　with　all　the　ancestral　assurance　of　seizing　his　prey；　rushed；　upon　the　rabbit；　his　muzzle　always　glancing　off　and　his　attack　ending　in　awkward　failure。

This　experiment　was　repeated　many　times　and　each　time　provoked　the　serious…minded　scientific　visitors　who　witnessed　it　to　laughter。　　Why？　　Because　the　spectacle　of　a　savage　little　terrier　rushing　upon　an　innocent　rabbit　as　if　to　mangle　it　integrated　the　body　of　the　onlooker　with　a　strong　desire　to　exert　muscular　action　to　prevent　the　cruelty。　　This　integration　caused　a　conversion　of　the　potential　energy　in　the　brain…cells　into　kinetic　energy；　and　there　resulted　a　discharge　into　the　blood…stream　of　activating　internal　secretions　for　the　purpose　of　producing　muscular　action。　Instantly　and　unexpectedly　the　danger　passed　and　the　preparation　for　muscular　action　intended　for　use　in　the　protection　of　the　rabbit　was　not　needed。　　This　fuel　was　consumed　by　the　neutral　muscular　action　of　laughter；　which　thus　afforded　relief。

A　common　example　of　the　same　nature　is　that　encountered　on　the　street　when　a　pedestrian　slips　on　a　banana　peel　and；　just　as　he　is　about　to　tumble；　recovers　his　equilibrium。　　The　onlookers　secure　relief　from　the　integration　to　run　to　his　rescue　by　laughing。　On　the　other　hand；　should　the　same　pedestrian　fall　and　fracture　his　skull　the　motor　integration　of　the　onlookers　would　be　consumed　by　rendering　physical　assistancehence　there　would　be　no　laughter。　In　children　almost　any　unexpected　phenomenon；　such　as　a　sudden　〃booing〃　from　behind　a　door；　is　attended　by　laughter；　and　in　like　manner　the　kinetic　reaction　produced　by　the　innumerable　threats　of　danger　which　are　suddenly　averted；　a　breach　of　the　conventions；　a　sudden