a discourse on method-第9节

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enable　me　to　treat　of　these　in　the　same　manner　as　of　the　rest；　that　is　to　say；　by　deducing　effects　from　their　causes；　and　by　showing　from　what　elements　and　in　what　manner　nature　must　produce　them；　I　remained　satisfied　with　the　supposition　that　God　formed　the　body　of　man　wholly　like　to　one　of　ours；　as　well　in　the　external　shape　of　the　members　as　in　the　internal　conformation　of　the　organs；　of　the　same　matter　with　that　I　had　described；　and　at　first　placed　in　it　no　rational　soul；　nor　any　other　principle；　in　room　of　the　vegetative　or　sensitive　soul；　beyond　kindling　in　the　heart　one　of　those　fires　without　light；　such　as　I　had　already　described；　and　which　I　thought　was　not　different　from　the　heat　in　hay　that　has　been　heaped　together　before　it　is　dry；　or　that　which　causes　fermentation　in　new　wines　before　they　are　run　clear　of　the　fruit。　　For；　when　I　examined　the　kind　of　functions　which　might；　as　consequences　of　this　supposition；　exist　in　this　body；　I　found　precisely　all　those　which　may　exist　in　us　independently　of　all　power　of　thinking；　and　consequently　without　being　in　any　measure　owing　to　the　soul；　in　other　words；　to　that　part　of　us　which　is　distinct　from　the　body；　and　of　which　it　has　been　said　above　that　the　nature　distinctively　consists　in　thinking；　functions　in　which　the　animals　void　of　reason　may　be　said　wholly　to　resemble　us；　but　among　which　I　could　not　discover　any　of　those　that；　as　dependent　on　thought　alone；　belong　to　us　as　men；　while；　on　the　other　hand；　I　did　afterwards　discover　these　as　soon　as　I　supposed　God　to　have　created　a　rational　soul；　and　to　have　annexed　it　to　this　body　in　a　particular　manner　which　I　described。

But；　in　order　to　show　how　I　there　handled　this　matter；　I　mean　here　to　give　the　explication　of　the　motion　of　the　heart　and　arteries；　which；　as　the　first　and　most　general　motion　observed　in　animals；　will　afford　the　means　of　readily　determining　what　should　be　thought　of　all　the　rest。　　And　that　there　may　be　less　difficulty　in　understanding　what　I　am　about　to　say　on　this　subject；　I　advise　those　who　are　not　versed　in　anatomy；　before　they　commence　the　perusal　of　these　observations；　to　take　the　trouble　of　getting　dissected　in　their　presence　the　heart　of　some　large　animal　possessed　of　lungs　（for　this　is　throughout　sufficiently　like　the　human）；　and　to　have　shown　to　them　its　two　ventricles　or　cavities：　　in　the　first　place；　that　in　the　right　side；　with　which　correspond　two　very　ample　tubes；　viz。；　the　hollow　vein　（vena　cava）；　which　is　the　principal　receptacle　of　the　blood；　and　the　trunk　of　the　tree；　as　it　were；　of　which　all　the　other　veins　in　the　body　are　branches；　and　the　arterial　vein　（vena　arteriosa）；　inappropriately　so　denominated；　since　it　is　in　truth　only　an　artery；　which；　taking　its　rise　in　the　heart；　is　divided；　after　passing　out　from　it；　into　many　branches　which　presently　disperse　themselves　all　over　the　lungs；　in　the　second　place；　the　cavity　in　the　left　side；　with　which　correspond　in　the　same　manner　two　canals　in　size　equal　to　or　larger　than　the　preceding；　viz。；　the　venous　artery　（arteria　venosa）；　likewise　inappropriately　thus　designated；　because　it　is　simply　a　vein　which　comes　from　the　lungs；　where　it　is　divided　into　many　branches；　interlaced　with　those　of　the　arterial　vein；　and　those　of　the　tube　called　the　windpipe；　through　which　the　air　we　breathe　enters；　and　the　great　artery　which；　issuing　from　the　heart；　sends　its　branches　all　over　the　body。　　I　should　wish　also　that　such　persons　were　carefully　shown　the　eleven　pellicles　which；　like　so　many　small　valves；　open　and　shut　the　four　orifices　that　are　in　these　two　cavities；　viz。；　three　at　the　entrance　of　the　hollow　veins　where　they　are　disposed　in　such　a　manner　as　by　no　means　to　prevent　the　blood　which　it　contains　from　flowing　into　the　right　ventricle　of　the　heart；　and　yet　exactly　to　prevent　its　flowing　out；　three　at　the　entrance　to　the　arterial　vein；　which；　arranged　in　a　manner　exactly　the　opposite　of　the　former；　readily　permit　the　blood　contained　in　this　cavity　to　pass　into　the　lungs；　but　hinder　that　contained　in　the　lungs　from　returning　to　this　cavity；　and；　in　like　manner；　two　others　at　the　mouth　of　the　venous　artery；　which　allow　the　blood　from　the　lungs　to　flow　into　the　left　cavity　of　the　heart；　but　preclude　its　return；　and　three　at　the　mouth　of　the　great　artery；　which　suffer　the　blood　to　flow　from　the　heart；　but　prevent　its　reflux。　　Nor　do　we　need　to　seek　any　other　reason　for　the　number　of　these　pellicles　beyond　this　that　the　orifice　of　the　venous　artery　being　of　an　oval　shape　from　the　nature　of　its　situation；　can　be　adequately　closed　with　two；　whereas　the　others　being　round　are　more　conveniently　closed　with　three。　　Besides；　I　wish　such　persons　to　observe　that　the　grand　artery　and　the　arterial　vein　are　of　much　harder　and　firmer　texture　than　the　venous　artery　and　the　hollow　vein；　and　that　the　two　last　expand　before　entering　the　heart；　and　there　form；　as　it　were；　two　pouches　denominated　the　auricles　of　the　heart；　which　are　composed　of　a　substance　similar　to　that　of　the　heart　itself；　and　that　there　is　always　more　warmth　in　the　heart　than　in　any　other　part　of　the　body…　and　finally；　that　this　heat　is　capable　of　causing　any　drop　of　blood　that　passes　into　the　cavities　rapidly　to　expand　and　dilate；　just　as　all　liquors　do　when　allowed　to　fall　drop　by　drop　into　a　highly　heated　vessel。

For；　after　these　things；　it　is　not　necessary　for　me　to　say　anything　more　with　a　view　to　explain　the　motion　of　the　heart；　except　that　when　its　cavities　are　not　full　of　blood；　into　these　the　blood　of　necessity　flows；　…　…　from　the　hollow　vein　into　the　right；　and　from　the　venous　artery　into　the　left；　because　these　two　vessels　are　always　full　of　blood；　and　their　orifices；　which　are　turned　towards　the　heart；　cannot　then　be　closed。　　But　as　soon　as　two　drops　of　blood　have　thus　passed；　one　into　each　of　the　cavities；　these　drops　which　cannot　but　be　very　large；　because　the　orifices　through　which　they　pass　are　wide；　and　the　vessels　from　which　they　come　full　of　blood；　are　immediately　rarefied；　and　dilated　by　the　heat　they　meet　with。　　In　this　way　they　cause　the　whole　heart　to　expand；　and　at　the　same　time　press　home　and　shut　the　five　small　valves　that　are　at　the　entrances　of　the　two　vessels　from　which　they　flow；　and　thus　prevent　any　more　blood　from　coming　down　into　the　heart；　and　becoming　more　and　more　rarefied；　they　push　open　the　six　small　valves　that　are　in　the　orifices　of　the　other　two　vessels；　through　which　they　pass　out；　causing　in　this　way　all　the　branches　of　the　arterial　vein　and　of　the　grand　artery　to　expand　almost　simultaneously　with　the　heart　which　immediately　thereafter　begins　to　contract；　as　do　also　the　arteries；　because　the　blood　that　has　entered　them　has　cooled；　and　the　six　small　valves　close；　and　the　five　of　the　hollow　vein　and　of　the　venous　artery　open　anew　and　allow　a　passage　to　other　two　drops　of　blood；　which　cause　the　heart　and　the　arteries　again　to　expand　as　before。　　And；　because　the　blood　which　thus　enters　into　the　heart　passes　through　these　two　pouches　called　auricles；　it　thence　happens　that　their　motion　is　the　contrary　of　that　of　the　heart；　and　that　when　it　expands　they　contract。　　But　lest　those　who　are　ignorant　of　the　force　of　mathematical　demonstrations　and　who　are　not　accustomed　to　distinguish　true　reasons　from　mere　verisimilitudes；　should　venture。　　without　examination；　to　deny　what　has　been　said；　I　wish　it　to　be　considered　that　the　motion　which　I　have　now　explained　follows　as　necessarily　from　the　very　arrangement　of　the　parts；　which　may　be　observed　in　the　heart　by　the　eye　alone；　and　from　the　heat　which　may　be　felt　with　the　fingers；　and　from　the　nature　of　the　blood　as　learned　from　experience；　as　does　the　motion　of　a　clock　from　the　power；　the　situation；　and　shape　of　its　counterweights　and　wheels。

But　if　it　be　asked　how　it　happens　that　the　blood　in　the　veins；　flowing　in　this　way　continually　into　the　heart；　is　not　exhausted；　and　why　the　arteries　do　not　become　too　full；　since　all　the　blood　which　passes　through　the　heart　flows　into　them；　I　need　only　mention　in　reply　what　has　been　written　by　a　physician　1　of　England；　who　has　the　honor　of　having　broken　the　ice　on　this　subject；　and　of　having　been　the　first　to　teach　that　there　are　many　small　passages　at　the　extremities　of　the　arteries；　through　which　the　blood　received　by　them　from　the　heart　passes　into　the　small　branches　of　the　veins；　whence　it　again　returns　to　the　heart；　so　that　its　course　amounts　precisely　to　a　perpetual　circulation。　　Of　this　we　have　abundant　proof　in　the　ordinary　experience　of　surgeons；　who；　by　binding　the　arm　with　a　tie　of　moderate　straitness　above　the　part　where　they　open　the　vein；　cause　the　blood　to　flow　more　copiously　than　it　would　have　done　without　any　ligature；　whereas　quite　the　contrary　would　happen　were　they　to　bind　it　below；　that　is；　between　the　hand　and　the　opening；　or　were　to　make　the　ligature　above　the　opening　very　tight。　　For　it　is　manifest　that　the　tie；　moderately　straightened；　while　adequate　to　hinder　the　blood　already　in　the　arm　from　returning　towards　the　heart　by　the　veins；　cannot　on　that　account　prevent　new　blood　from　coming　forward　through　the　arteries；　because　these　are　situated　below　the　veins；　and　their　coverings；　from　their　greater　consistency；　are　more　difficult　to　compress；　and　also　that　the　bloo