on the motion of animals-第4节

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potency　must　be　two　in　action；　and　so　be　a　definite　spatial



magnitude　not　a　mathematical　point。　Again；　C　may　be　moved



simultaneously　with　B。　Both　the　originals　then　in　A　must　move　and



be；　and　so　there　must　be　something　other　than　them　which　moves　but



is　not　moved。　For　otherwise；　when　the　movement　begins；　the　extremes；



i。e。　the　originals；　in　A　would　rest　upon　one　another；　like　two　men



putting　themselves　back　to　back　and　so　moving　their　legs。　There　must



then　be　some　one　thing　which　moves　both。　This　something　is　the　soul；



distinct　from　the　spatial　magnitude　just　described　and　yet　located



therein。



　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　10







　　Although　from　the　point　of　view　of　the　definition　of　movement…　a



definition　which　gives　the　cause…　desire　is　the　middle　term　or



cause；　and　desire　moves　being　moved；　still　in　the　material　animated



body　there　must　be　some　material　which　itself　moves　being　moved。　Now



that　which　is　moved；　but　whose　nature　is　not　to　initiate　movement；



is　capable　of　being　passive　to　an　external　force；　while　that　which



initiates　movement　must　needs　possess　a　kind　of　force　and　power。　Now



experience　shows　us　that　animals　do　both　possess　connatural　spirit　and



derive　power　from　this。　（How　this　connatural　spirit　is　maintained　in



the　body　is　explained　in　other　passages　of　our　works。）　And　this　spirit



appears　to　stand　to　the　soul…centre　or　original　in　a　relation



analogous　to　that　between　the　point　in　a　joint　which　moves　being　moved



and　the　unmoved。　Now　since　this　centre　is　for　some　animals　in　the



heart；　in　the　rest　in　a　part　analogous　with　the　heart；　we　further



see　the　reason　for　the　connatural　spirit　being　situate　where　it



actually　is　found。　The　question　whether　the　spirit　remains　always



the　same　or　constantly　changes　and　is　renewed；　like　the　cognate



question　about　the　rest　of　the　parts　of　the　body；　is　better　postponed。



At　all　events　we　see　that　it　is　well　disposed　to　excite　movement　and



to　exert　power；　and　the　functions　of　movement　are　thrusting　and



pulling。　Accordingly；　the　organ　of　movement　must　be　capable　of



expanding　and　contracting；　and　this　is　precisely　the　characteristic　of



spirit。　It　contracts　and　expands　naturally；　and　so　is　able　to　pull　and



to　thrust　from　one　and　the　same　cause；　exhibiting　gravity　compared



with　the　fiery　element；　and　levity　by　comparison　with　the　opposites　of



fire。　Now　that　which　is　to　initiate　movement　without　change　of



structure　must　be　of　the　kind　described；　for　the　elementary　bodies



prevail　over　one　another　in　a　compound　body　by　dint　of



disproportion；　the　light　is　overcome　and　kept　down　by　the　heavier；　and



the　heavy　kept　up　by　the　lighter。



　　We　have　now　explained　what　the　part　is　which　is　moved　when　the



soul　originates　movement　in　the　body；　and　what　is　the　reason　for　this。



And　the　animal　organism　must　be　conceived　after　the　similitude　of　a



well…governed　commonwealth。　When　order　is　once　established　in　it　there



is　no　more　need　of　a　separate　monarch　to　preside　over　each　several



task。　The　individuals　each　play　their　assigned　part　as　it　is



ordered；　and　one　thing　follows　another　in　its　accustomed　order。　So



in　animals　there　is　the　same　orderliness…　nature　taking　the　place　of



custom…　and　each　part　naturally　doing　his　own　work　as　nature　has



composed　them。　There　is　no　need　then　of　a　soul　in　each　part；　but　she



resides　in　a　kind　of　central　governing　place　of　the　body；　and　the



remaining　parts　live　by　continuity　of　natural　structure；　and　play



the　parts　Nature　would　have　them　play。



　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　　11







　　So　much　then　for　the　voluntary　movements　of　animal　bodies；　and　the



reasons　for　them。　These　bodies；　however；　display　in　certain　members



involuntary　movements　too；　but　most　often　non…voluntary　movements。



By　involuntary　I　mean　motions　of　the　heart　and　of　the　privy　member；



for　often　upon　an　image　arising　and　without　express　mandate　of　the



reason　these　parts　are　moved。　By　non…voluntary　I　mean　sleep　and　waking



and　respiration；　and　other　similar　organic　movements。　For　neither



imagination　nor　desire　is　properly　mistress　of　any　of　these；　but　since



the　animal　body　must　undergo　natural　changes　of　quality；　and　when



the　parts　are　so　altered　some　must　increase　and　other　decrease；　the



body　must　straightway　be　moved　and　change　with　the　changes　that　nature



makes　dependent　upon　one　another。　Now　the　causes　of　the　movements



are　natural　changes　of　temperature；　both　those　coming　from　outside　the



body；　and　those　taking　place　within　it。　So　the　involuntary　movements



which　occur　in　spite　of　reason　in　the　aforesaid　parts　occur　when　a



change　of　quality　supervenes。　For　conception　and　imagination；　as　we



said　above；　produce　the　conditions　necessary　to　affections；　since　they



bring　to　bear　the　images　or　forms　which　tend　to　create　these　states。



And　the　two　parts　aforesaid　display　this　motion　more　conspicuously



than　the　rest；　because　each　is　in　a　sense　a　separate　vital　organism；



the　reason　being　that　each　contains　vital　moisture。　In　the　case　of　the



heart　the　cause　is　plain；　for　the　heart　is　the　seat　of　the　senses；



while　an　indication　that　the　generative　organ　too　is　vital　is　that



there　flows　from　it　the　seminal　potency；　itself　a　kind　of　organism。



Again；　it　is　a　reasonable　arrangement　that　the　movements　arise　in



the　centre　upon　movements　in　the　parts；　and　in　the　parts　upon



movements　in　the　centre；　and　so　reach　one　another。　Conceive　A　to　be



the　centre　or　starting　point。　The　movements　then　arrive　at　the



centre　from　each　letter　in　the　diagram　we　have　drawn；　and　flow　back



again　from　the　centre　which　is　moved　and　changes；　（for　the　centre　is



potentially　multiple）　the　movement　of　B　goes　to　B；　that　of　C　to　C；　the



movement　of　both　to　both；　but　from　B　to　C　the　movements　flow　by　dint



of　going　from　B　to　A　as　to　a　centre；　and　then　from　A　to　C　as　from　a



centre。



　　Moreover　a　movement　contrary　to　reason　sometimes　does　and



sometimes　does　not　arise　in　the　organs　on　the　occasion　of　the　same



thoughts；　the　reason　is　that　sometimes　the　matter　which　is　passive



to　the　impressions　is　there　in　sufficient　quantity　and　of　the　right



quality　and　sometimes　not。



　　And　so　we　have　finished　our　account　of　the　reasons　for　the　parts



of　each　kind　of　animal；　of　the　soul；　and　furthere　of　sense…perception；



of　sleep；　of　memory；　and　of　movement　in　general；　it　remains　to　speak



of　animal　generation。











　　　　　　　　　　　　　　　　　　　　　　　　　　　　　…THE　END…



。