the origin and nature of emotions-第4章

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ly　conducted　experiments　on　skunks　and　two　on　armadillos　（an　insufficient　number）　the　energy　discharged　in　response　to　severe　and　protracted　trauma　of　the　abdominal　viscera　was　very　much　less　than　in　similar　experiments　on　dogs；　opossums；　pigs；　sheep；　and　rabbits。　It　was　indeed　relatively　difficult　to　exhaust　the　skunks　and　armadillos　by　trauma。　　These　experiments　are　too　few　to　be　conclusive；　but　they　are　of　some　value　and　furnish　an　excellent　lead。　It　seems　more　than　a　coincidence　that　proneness　to　fear；　distribution　of　nociceptors；　and　susceptibility　to　shock　go　hand…in…hand　in　these　comparative　observations　（Figs。　6；　7；　and　8）。

The　discharge　of　energy　caused　by　an　adequate　mechanical　stimulation　of　the　nociceptors　is　best　explained　in　accordance　with　the　law　of　phylogenetic　association。　　That　is；　injuries　awaken　those　reflex　actions　which　by　natural　selection　have　been　developed　for　the　purpose　of　self…protection。　Adequate　stimulation　of　the　nociceptors　for　pain　is　not　the　only　means　by　which　a　discharge　of　nervous　energy　is　caused。　Nervous　energy　may　be　discharged　also　by　adequate　stimulation　of　the　various　ticklish　regions　of　the　body；　the　entire　skin　surface　of　the　body　contains　delicate　ticklish　receptors。　These　receptors　are　closely　related　to　the　nociceptors　for　pain；　and　their　adequate　stimulation　by　an　insect…like　touch　causes　a　discharge　of　energy；a　nerve…muscular　reaction；　resembling　that　developed　for　the　purpose　of　brushing　off　insects。　This　reflex　is　similar　to　the　scratch　reflex　in　the　dog。　The　discharge　of　energy　is　almost　wholly　independent　of　the　will　and　is　a　self…protective　action　in　the　same　sense　as　is　the　response　to　pain　stimuli。　　The　ear　in　man　and　in　animals　is　acutely　ticklish；　the　adequate　stimulus　being　any　foreign　body；　especially　a　buzzing；　insect…like　contact。　　The　discharge　of　nervous　energy　in　horses　and　in　cattle　on　adequate　stimulation　of　the　ticklish　receptors　of　the　ear　is　so　extraordinary　that　in　the　course　of　evolution　it　must　have　been　of　great　importance　to　the　safety　of　the　animal。　A　similar　ticklish　zone　guards　the　nasal　chambers；　the　discharge　of　energy　here　taking　a　form　which　effectively　dislodges　the　foreign　body。　The　larynx　is　exquisitely　ticklish；　and；　in　response　to　any　adequate　stimulus；　energy　is　discharged　in　the　production　of　a　vigorous　cough。　The　mouth　and　pharynx　have　active　receptors　which　cause　the　rejection　of　noxious　substances。　　The　conjunctival　reflex；　though　not　classed　as　ticklish；　is　a　most　efficient　self…protective　reflex。　I　assume　that　there　is　no　doubt　as　to　the　relation　between　the　adequate　stimuli　and　the　nerve…muscular　response　of　the　various　ticklish　receptors　of　the　surface　of　the　skin；　of　the　ear；　the　nose；　the　eye；　and　the　larynx。　　These　mechanisms　were　developed　by　natural　selection　as　protective　measures　against　the　intrusion　of　insects　and　foreign　bodies　into　regions　of　great　importance。　The　discharge　of　energy　in　these　instances　is　in　accordance　with　the　laws　of　inheritance　and　association。　　The　other　ticklish　points　which　are　capable　of　discharging　vast　amounts　of　energy　are　the　lateral　chest…wall；　the　abdomen；　the　loins；　the　neck；　and　the　soles　of　the　feet。　　The　type　of　adequate　stimuli　of　the　soles　of　the　feet；　the　distribution　of　the　ticklish　points　upon　them；　and　the　associated　response；　leave　no　doubt　that　these　ticklish　points　were　long　ago　established　as　a　means　of　protection　from　injury。　Under　present　conditions　they　are　of　little　value　to　man。

The　adequate　stimulus　for　the　ticklish　points　of　the　ribs；　the　loins；　the　abdomen；　and　the　neck　is　deep　isolated　pressure；　probably　the　most　adequate　being　pressure　by　a　tooth…shaped　body。　The　response　to　tickling　in　these　regions　is　actively　and　obviously　self…defensive。　The　horse　discharges　energy　in　the　form　of　a　kick；　the　dog　wriggles　and　makes　a　counter…bite；　the　man　makes　efforts　at　defense　and　escape。

There　is　strong　evidence　that　the　deep　ticklish　points　of　the　body　were　developed　through　vast　periods　of　fighting　with　teeth　and　claws　（Fig。　9）。　Even　puppies　at　play　bite　each　other　in　their　ticklish　points　and　thus　give　a　recapitulation　of　their　ancestral　battles　and　of　the　real　battles　to　come　（Fig。　10）。　The　mere　fact　that　animals　fight　effectively　in　the　dark　and　always　according　to　the　habit　of　their　species　supports　the　belief　that　the　fighting　of　animals　is　not　an　intellectual　but　a　reflex　process。　　There　are　no　rules　which　govern　the　conduct　of　a　fight　between　animals。　　The　events　follow　each　other　with　such　kaleidoscopic　rapidity　that　the　process　is　but　a　series　of　automatic　stimulations　and　physiologic　reactions。　Whatever　their　significance；　therefore；　it　is　certain　that　man　did　not　come　either　accidentally　or　without　purpose　into　possession　of　the　deep　ticklish　regions　of　his　chest　and　abdomen。　Should　any　one　doubt　the　vast　power　that　adequate　stimulation　of　these　regions　possesses　in　causing　the　discharge　of　energy；　let　him　be　bound　hand　and　foot　and　vigorously　tickled　for　an　hour。　What　would　happen？　　He　would　be　as　completely　exhausted　as　though　he　had　experienced　a　major　surgical　operation　or　had　run　a　Marathon　race。

A　close　analogy　to　the　reflex　process　in　the　fighting　of　animals　is　shown　in　the　role　played　by　the　sexual　receptors　in　conjugation。　Adequate　stimulation　of　either　of　these　two　distinct　groups　of　receptors；　the　sexual　and　the　noci；　causes　specific　behavior　the　one　toward　embrace；　the　other　toward　repulsion。　　Again；　one　of　the　most　peremptory　causes　of　the　discharge　of　energy　is　that　due　to　an　attempt　to　obstruct　forcibly　the　mouth　and　the　nose　so　that　asphyxia　is　threatened。　　Under　such　conditions　neither　friend　nor　foe　is　trusted；　and　a　desperate　struggle　for　air　ensues。　It　will　be　readily　granted　that　the　reactions　to　prevent　suffocation　were　established　for　the　purpose　of　self…preservation；　but　the　discharge　of　nerve…muscular　energy　to　this　particular　end　is　no　more　specific　and　no　more　shows　adaptive　qualities　than　do　the　preceding　examples。　Even　the　proposal　to　bind　one　down　hand　and　foot　excites　resentment；　a　feeling　originally　suggested　by　the　need　for　self…preservation。　No　patient　views　with　equanimity　the　application　of　shackles　as　a　preparation　for　anesthesia。

We　have　now　considered　some　of　the　causes　of　those　discharges　of　nervous　energy　which　result　from　various　types　of　harmful　physical　contact；　and　have　referred　to　the　analogous；　though　antithetical；　response　to　the　stimulation　of　the　sexual　receptors。　The　response　to　the　adequate　stimuli　of　each　of　the　several　receptors　is　a　discharge　of　nerve…muscular　energy　of　a　specific　type；　that　is；　there　is　one　type　of　response　for　the　ear；　one　for　the　larynx；　one　for　the　pharynx；　another　for　the　nose；　another　for　the　eye；　another　for　the　deep　ticklish　points　of　the　chest　and　the　abdomen；　quite　another　for　the　delicate　tickling　of　the　skin；　and　still　another　type　of　response　to　sexual　stimuli。

According　to　Sherrington；　a　given　receptor　has　a　low　threshold　for　only　one；　its　own　specific　stimulus；　and　a　high　threshold　for　all　others；　that　is；　the　doors　that　guard　the　nerve…paths　to　the　brain　are　opened　only　when　the　proper　password　is　received。　According　to　Sherrington's　law；　the　individual　as　a　whole　responds　to　but　one　stimulus　at　a　time；　that　is；　only　one　stimulus　occupies　the　nerve…paths　which　carry　the　impulses　as　a　result　of　which　acts　are　performed；　_i。　　e_。；　the　final　common　path。　As　soon　as　a　stronger　stimulus　reaches　the　brain　it　dispossesses　whatever　other　stimulus　is　then　occupying　the　final　common　path　the　path　of　action。　　The　various　receptors　have　a　definite　order　of　precedence　over　each　other　（Sherrington）。　For　example；　the　impulse　from　the　delicate　ticklish　points　of　the　skin；　whose　adequate　stimulus　is　an　insect…like　contact；　could　not　successfully　compete　for　the　final　common　path　with　the　stimulus　of　a　nociceptor。　The　stimulus　of　a　fly　on　the　nose　would　be　at　once　superseded　by　the　crushing　of　a　finger。　　In　quick　succession　do　the　various　receptors　（Sherrington）　occupy　the　final　common　path；　but　each　stimulus　is　for　the　time　the　sole　possessor；　hence　the　nervous　system　is　integrated　（connected）　to　act　as　a　whole。　　Each　individual　at　every　moment　of　life　has　a　limited　amount　of　dischar