the origin and nature of emotions-第3章

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The　Cause　of　the　Discharge　of　Nervous　Energy　as　a　Result　of　Trauma　under　Inhalation　Anesthesia　and　under　Normal　Conditions


I　looked　into　this　problem　from　many　viewpoints　and　there　seemed　to　be　no　solution　until　it　occurred　to　me　to　seek　the　explanation　in　certain　of　the　postulates　which　make　up　the　doctrine　of　evolution。　I　realize　fully　the　difficulty　and　the　danger　in　attempting　to　reach　the　generalization　which　I　shall　make　later　and　in　the　hypothesis　I　shall　propose；　for　there　is；　of　course；　no　direct　final　proof　of　the　truth　of　even　the　doctrine　of　evolution。　It　is　idle　to　consider　any　experimental　research　into　the　cause　of　phenomena　that　have　developed　by　natural　selection　during　millions　of　years。　　Nature　herself　has　made　the　experiments　on　a　world…wide　scale　and　the　data　are　before　us　for　interpretation。　Darwin　could　do　no　more　than　to　collect　all　available　facts　and　then　to　frame　the　hypothesis　by　which　the　facts　were　best　harmonized。　Sherrington；　that　masterly　physiologist；　in　his　volume　entitled　〃The　Integrative　Action　of　the　Nervous　System；〃　shows　clearly　how　the　central　nervous　system　was　built　up　in　the　process　of　evolution。　Sherrington　has　made　free　use　of　Darwin's　doctrine　in　explaining　physiologic　functions；　just　as　anatomists　have　extensively　utilized　it　in　the　explanation　of　the　genesis　of　anatomic　forms。　I　shall　assume；　therefore；　that　the　discharge　of　nervous　energy　is　accomplished　by　the　application　of　the　laws　of　inheritance　and　association；　and　I　conclude　that　this　hypothesis　will　explain　many　clinical　phenomena。　I　shall　now　present　such　evidence　in　favor　of　this　hypothesis　as　time　and　my　limitations　will　admit；　after　which　I　shall　point　out　certain　clinical　facts　that　may　be　explained　by　this　hypothesis。

According　to　the　doctrine　of　evolution；　every　function　owes　its　origin　to　natural　selection　in　the　struggle　for　existence。　In　the　lower　and　simpler　forms　of　animal　life；　indeed；　in　our　human　progenitors　as　well；　existence　depended　principally　upon　the　success　with　which　three　great　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　d