the origin and nature of emotions-第3节

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　purposes　were　achieved：　（1）　Self…defense　against　or　escape　from　enemies；　（2）　the　acquisition　of　food；　and　（3）　procreation；　and　these　were　virtually　the　only　purposes　for　which　nervous　energy　was　discharged。　　In　its　last　analysis；　in　a　biologic　sense；　this　statement　holds　true　of　man　today。　Disregarding　for　the　present　the　expenditure　of　energy　for　procuring　food　and　for　procreation；　let　us　consider　the　discharge　of　energy　for　self…preservation。　The　mechanisms　for　self…defense　which　we　now　possess　were　developed　in　the　course　of　vast　periods　of　time　through　innumerable　intermediary　stages　from　those　possessed　by　the　lowest　forms　of　life。　　One　would　suppose；　therefore；　that　we　must　now　be　in　possession　of　mechanisms　which　still　discharge　energy　on　adequate　stimulation；　but　which　are　not　suited　to　our　present　needs。　We　shall　point　out　some　examples　of　such　unnecessary　mechanisms。　As　Sherrington　has　stated；　our　skin；　in　which　are　implanted　many　receptors　for　receiving　specific　stimuli　which　are　transmitted　to　the　brain；　is　interposed　between　ourselves　and　the　environment　in　which　we　are　immersed。　　When　these　stimuli　reach　the　brain；　there　is　a　specific　response；　principally　in　the　form　of　muscular　action。　　Now；　each　receptor　can　be　adequately　stimulated　only　by　the　particular　factor　or　factors　in　the　environment　which　created　the　necessity　for　the　existence　of　that　receptor。　Thus　there　have　arisen　receptors　for　touch；　for　temperature；　for　pain；　etc。　　The　receptors　for　pain　have　been　designated　_nociceptors_　（nocuous　or　harmful）　by　Sherrington。

On　the　basis　of　natural　selection；　nociceptors　could　have　developed　in　only　those　regions　of　the　body　which　have　been　exposed　to　injury　during　long　periods　of　time。　　On　this　ground　the　finger；　because　it　is　exposed；　should　have　many　nociceptors；　while　the　brain；　though　the　most　important　organ　of　the　body；　should　have　no　nociceptors　because；　during　a　vast　period　of　time；　it　has　been　protected　by　a　skull。　Realizing　that　this　point　is　a　crucial　one；　Dr。　Sloan　and　I　made　a　series　of　careful　experiments。　　The　cerebral　hemispheres　of　dogs　were　exposed　by　removing　the　skull　and　dura　under　ether　and　local　anesthesia。　Then　various　portions　of　the　hemispheres　were　slowly　but　completely　destroyed　by　rubbing　them　with　pieces　of　gauze。　In　some　instances　a　hemisphere　was　destroyed　by　burning。　In　no　case　was　there　more　than　a　slight　response　of　the　centers　governing　circulation　and　respiration；　and　no　morphologic　change　was　noted　in　an　histologic　study　of　the　brain…cells　of　the　uninjured　hemisphere。　The　experiment　was　as　completely　negative　as　were　the　experiments　on　the　〃spinal　dog。〃　　Clinically　I　have　confirmed　these　experimental　findings　when　I　have　explored　the　brains　of　conscious　patients　with　a　probe　to　determine　the　presence　of　brain　tumors。　Such　explorations　elicited　neither　pain　nor　any　evidence　of　altered　physiologic　functions。　　The　brain；　therefore；　contains　no　mechanism　no　nociceptorsthe　direct　stimulation　of　which　can　cause　a　discharge　of　nervous　energy　in　a　self…defensive　action。　That　is　to　say；　direct　injury　of　the　brain　can　cause　no　purposeful　nerve…muscular　action；　while　direct　injury　of　the　finger　does　cause　purposeful　nerve…muscular　action。　　In　like　manner；　the　deeper　portions　of　the　spinal　region　have　been　sheltered　from　trauma　and　they；　too；　show　but　little　power　of　causing　a　discharge　of　nervous　energy　on　receiving　trauma。　　The　various　tissues　and　organs　of　the　body　are　differently　endowed　with　injury　receptorsthe　nociceptors　of　Sherrington。　　The　abdomen　and　chest　when　traumatized　stand　first　in　their　facility　for　causing　the　discharge　of　nervous　energy；　_i。　e_。；　THEY　STAND　FIRST　IN　SHOCK　PRODUCTION。　　Then　follow　the　extremities；　the　neck；　and　the　back。　　It　is　an　interesting　fact　also　that　different　types　of　trauma　elicit　different　responses　as　far　as　the　consequent　discharge　of　energy　is　concerned。

Because　it　is　such　a　commonplace　observation；　one　scarcely　realizes　the　importance　of　the　fact　that　clean…cut　wounds　inflicted　by　a　razor…like　knife　cause　the　least　reaction；　while　a　tearing；　crushing　trauma　causes　the　greatest　response。　　It　is　a　suggestive　fact　that　the　greatest　shock　is　produced　by　any　technic　which　imitates　the　methods　of　attack　and　of　slaughter　used　by　the　carnivora。　_*In　the　course　of　evolution；　injuries　thus　produced　may　well　have　been　the　predominating　type　of　traumata　to　which　our　progenitors　were　subjected_。　　In　one　particular　respect　there　is　an　analogy　between　the　response　to　trauma　of　some　parts　of　the　body　of　the　individuals　of　a　species　susceptible　to　shock　and　the　response　to　trauma　of　the　individuals　in　certain　other　great　divisions　of　the　animal　kingdom。　Natural　selection　has　protected　the　crustaceans　against　their　enemies　by　protective　armor；　_e。　　g_。；　the　turtle　and　the　armadillo；　to　the　birds；　it　has　given　sharp　eyes　and　wings；　as；　for　instance；　the　wild　goose　to　another　speciesthe　skunkit　has　given　a　noisome　odor　for　its　protection。　　The　turtle；　protected　by　its　armor　against　trauma；　is　in　a　very　similar　position　to　that　of　the　sheltered　brain　of　man　and；　like　the　brain；　the　turtle　does　not　respond　to　trauma　by　an　especially　active　self…protective　nerve…muscular　response；　but　merely　withdraws　its　head　and　legs　within　the　armored　protection。　It　is　proverbially　difficult　to　exhaust　or　to　kill　this　animal　by　trauma。　The　brain　and　other　phylogenetically　sheltered　parts　likewise　give　no　exhausting　self…protective　nerve…muscular　response　to　trauma。　　The　skunk　is　quite　effectively　protected　from　violence　by　its　peculiar　odor。　This　is　indicated　not　only　by　the　protective　value　of　the　odor　itself；　but　also　by　the　fact　that　the　skunk　has　no　efficient　nerve…muscular　mechanism　for　escape　or　defense；　it　can　neither　run　fast　nor　can　it　climb　a　tree。　　Moreover；　in　encounters　it　shows　no　fear　and　backs　rather　than　runs。　　The　armadillo　rolls　itself　into　a　ball　for　defense。　On　these　premises　we　should　conclude　that　the　turtle；　the　armadillo；　and　the　skunk　have　fewer　nociceptors　than　has　a　dog　or　man；　and　that　they　would　show　less　response　to　trauma。　In　two　carefully　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　nec