a history of science-4- 第43部分

These　studies　of　the　psychologists　and　pathologists　bring　the　relations　of　mind　and　body　into　sharp　relief。　　But　even　more　definite　in　this　regard　was　the　work　of　the　brain　physiologists。　Chief　of　these；　during　the　middle　period　of　the　century；　was　the　man　who　is　sometimes　spoken　of　as　the　〃father　of　brain　physiology；〃　Marie　Jean　Pierre　Flourens；　of　the　Jardin　des　Plantes　of　Paris；　the　pupil　and　worthy　successor　of　Magendie。　　His　experiments　in　nerve　physiology　were　begun　in　the　first　quarter　of　the　century；　but　his　local　experiments　upon　the　brain　itself　were　not　culminated　until　about　1842。　At　this　time　the　old　dispute　over　phrenology　had　broken　out　afresh；　and　the　studies　of　Flourens　were　aimed；　in　part　at　least；　at　the　strictly　scientific　investigation　of　this　troublesome　topic。

In　the　course　of　these　studies　Flourens　discovered　that　in　the　medulla　oblongata；　the　part　of　the　brain　which　connects　that　organ　with　the　spinal　cord；　there　is　a　centre　of　minute　size　which　cannot　be　injured　in　the　least　without　causing　the　instant　death　of　the　animal　operated　upon。　　It　may　be　added　that　it　is　this　spot　which　is　reached　by　the　needle　of　the　garroter　in　Spanish　executions；　and　that　the　same　centre　also　is　destroyed　when　a　criminal　is　〃successfully〃　hanged；　this　time　by　the　forced　intrusion　of　a　process　of　the　second　cervical　vertebra。　Flourens　named　this　spot　the　〃vital　knot。〃　　Its　extreme　importance；　as　is　now　understood；　is　due　to　the　fact　that　it　is　the　centre　of　nerves　that　supply　the　heart；　but　this　simple　explanation；　annulling　the　conception　of　a　specific　〃life　centre；〃　was　not　at　once　apparent。

Other　experiments　of　Flourens　seemed　to　show　that　the　cerebellum　is　the　seat　of　the　centres　that　co…ordinate　muscular　activities；　and　that　the　higher　intellectual　faculties　are　relegated　to　the　cerebrum。　But　beyond　this；　as　regards　localization；　experiment　faltered。　Negative　results；　as　regards　specific　faculties；　were　obtained　from　all　localized　irritations　of　the　cerebrum；　and　Flourens　was　forced　to　conclude　that　the　cerebral　lobe；　while　being　undoubtedly　the　seat　of　higher　intellection；　performs　its　functions　with　its　entire　structure。　This　conclusion；　which　incidentally　gave　a　quietus　to　phrenology；　was　accepted　generally；　and　became　the　stock　doctrine　of　cerebral　physiology　for　a　generation。

It　will　be　seen；　however；　that　these　studies　of　Flourens　had　a　double　bearing。　　They　denied　localization　of　cerebral　functions；　but　they　demonstrated　the　localization　of　certain　nervous　processes　in　other　portions　of　the　brain。　　On　the　whole；　then；　they　spoke　positively　for　the　principle　of　localization　of　function　in　the　brain；　for　which　a　certain　number　of　students　contended；　while　their　evidence　against　cerebral　localization　was　only　negative。　There　was　here　and　there　an　observer　who　felt　that　this　negative　testimony　was　not　conclusive。　　In　particular；　the　German　anatomist　Meynert；　who　had　studied　the　disposition　of　nerve　tracts　in　the　cerebrum；　was　led　to　believe　that　the　anterior　portions　of　the　cerebrum　must　have　motor　functions　in　preponderance；　the　posterior　positions；　sensory　functions。　　Somewhat　similar　conclusions　were　reached　also　by　Dr。　Hughlings…Jackson；　in　England；　from　his　studies　of　epilepsy。　But　no　positive　evidence　was　forthcoming　until　1861；　when　Dr。　Paul　Broca　brought　before　the　Academy　of　Medicine　in　Paris　a　case　of　brain　lesion　which　he　regarded　as　having　most　important　bearings　on　the　question　of　cerebral　localization。

The　case　was　that　of　a　patient　at　the　Bicetre；　who　for　twenty　years　had　been　deprived　of　the　power　of　speech；　seemingly　through　loss　of　memory　of　words。　In　1861　this　patient　died；　and　an　autopsy　revealed　that　a　certain　convolution　of　the　left　frontal　lobe　of　his　cerebrum　had　been　totally　destroyed　by　disease；　the　remainder　of　his　brain　being　intact。　Broca　felt　that　this　observation　pointed　strongly　to　a　localization　of　the　memory　of　words　in　a　definite　area　of　the　brain。　　Moreover；　it　transpired　that　the　case　was　not　without　precedent。　　As　long　ago　as　1825　Dr。　Boillard　had　been　led；　through　pathological　studies；　to　locate　definitely　a　centre　for　the　articulation　of　words　in　the　frontal　lobe；　and　here　and　there　other　observers　had　made　tentatives　in　the　same　direction。　Boillard　had　even　followed　the　matter　up　with　pertinacity；　but　the　world　was　not　ready　to　listen　to　him。　　Now；　however；　in　the　half…decade　that　followed　Broca's　announcements；　interest　rose　to　fever…beat；　and　through　the　efforts　of　Broca；　Boillard；　and　numerous　others　it　was　proved　that　a　veritable　centre　having　a　strange　domination　over　the　memory　of　articulate　words　has　its　seat　in　the　third　convolution　of　the　frontal　lobe　of　the　cerebrum；　usually　in　the　left　hemisphere。　That　part　of　the　brain　has　since　been　known　to　the　English…speaking　world　as　the　convolution　of　Broca；　a　name　which；　strangely　enough；　the　discoverer's　compatriots　have　been　slow　to　accept。

This　discovery　very　naturally　reopened　the　entire　subject　of　brain　localization。　　It　was　but　a　short　step　to　the　inference　that　there　must　be　other　definite　centres　worth　the　seeking；　and　various　observers　set　about　searching　for　them。　　In　1867　a　clew　was　gained　by　Eckhard；　who；　repeating　a　forgotten　experiment　by　Haller　and　Zinn　of　the　previous　century；　removed　portions　of　the　brain　cortex　of　animals；　with　the　result　of　producing　convulsions。　But　the　really　vital　departure　was　made　in　1870　by　the　German　investigators　Fritsch　and　Hitzig；　who；　by　stimulating　definite　areas　of　the　cortex　of　animals　with　a　galvanic　current；　produced　contraction　of　definite　sets　of　muscles　of　the　opposite　side　of　the　body。　These　most　important　experiments；　received　at　first　with　incredulity；　were　repeated　and　extended　in　1873　by　Dr。　David　Ferrier；　of　London；　and　soon　afterwards　by　a　small　army　of　independent　workers　everywhere；　prominent　among　whom　were　Franck　and　Pitres　in　France；　Munck　and　Goltz　in　Germany；　and　Horsley　and　Schafer　in　England。　　The　detailed　results；　naturally　enough；　were　not　at　first　all　in　harmony。　　Some　observers；　as　Goltz；　even　denied　the　validity　of　the　conclusions　in　toto。　But　a　consensus　of　opinion；　based　on　multitudes　of　experiments；　soon　placed　the　broad　general　facts　for　which　Fritsch　and　Hitzig　contended　beyond　controversy。　　It　was　found；　indeed；　that　the　cerebral　centres　of　motor　activities　have　not　quite　the　finality　at　first　ascribed　to　them　by　some　observers；　since　it　may　often　happen　that　after　the　destruction　of　a　centre；　with　attending　loss　of　function；　there　may　be　a　gradual　restoration　of　the　lost　function；　proving　that　other　centres　have　acquired　the　capacity　to　take　the　place　of　the　one　destroyed。　　There　are　limits　to　this　capacity　for　substitution；　however；　and　with　this　qualification　the　definiteness　of　the　localization　of　motor　functions　in　the　cerebral　cortex　has　become　an　accepted　part　of　brain　physiology。

Nor　is　such　localization　confined　to　motor　centres。　Later　experiments；　particularly　of　Ferrier　and　of　Munck；　proved　that　the　centres　of　vision　are　equally　restricted　in　their　location；　this　time　in　the　posterior　lobes　of　the　brain；　and　that　hearing　has　likewise　its　local　habitation。　Indeed；　there　is　every　reason　to　believe　that　each　form　of　primary　sensation　is　based　on　impressions　which　mainly　come　to　a　definitely　localized　goal　in　the　brain。　　But　all　this；　be　it　understood；　has　no　reference　to　the　higher　forms　of　intellection。　All　experiment　has　proved　futile　to　localize　these　functions；　except　indeed　to　the　extent　of　corroborating　the　familiar　fact　of　their　dependence　upon　the　brain；　and；　somewhat　problematically；　upon　the　anterior　lobes　of　the　cerebrum　in　particular。　But　this　is　precisely　what　should　be　expected；　for　the　clearer　insight　into　the　nature　of　mental　processes　makes　it　plain　that　in　the　main　these　alleged　〃faculties〃　are　not　in　themselves　localized。　Thus；　for　example；　the　〃faculty〃　of　language　is　associated　irrevocably　with　centres　of　vision；　of　hearing；　and　of　muscular　activity；　to　go　no　further；　and　only　becomes　possible　through　the　association　of　these　widely　separated　centres。　The　destruction　of　Broca's　centre；　as　was　early　discovered；　does　not　altogether　deprive　a　patient　of　his　knowledge　of　language。　He　may　be　totally　unable　to　speak　（though　as　to　this　there　are　all　degrees　of　variation）；　and　yet　may　comprehend　what　is　said　to　him；　and　be　able　to　read；　think；　and　even　write　correctly。　Thus　it　appears　that　Broca's　centre　is　peculiarly　bound　up　with　the　capacity　for　articulate　speech；　but　is　far　enough　from　being　the　seat　of　the　faculty　of　language　in　its　entirety。

In　a　similar　way；　most　of　the　supposed　isolated　〃faculties〃　of　higher　intellection　appear；　upon　clearer　analysis；　as　complex　aggregations　of　primary　sensations；　and　hence　necessarily　dependent　upon　numerous　and　scattered　centres。　Some　〃faculties；〃　as　memory　and　volition；　may　be　said　in　a　sense　to　be　primordial　endowments　of　every　nerve　celleven　of　every　body　cell。　　Indeed；　an　ultimate　analysis　relegates　all　intellection；　in　its　primordial　adumbrations；　to　every　particle　of　living　matter。　But　such　refinements　of　analysis；　after　all；　cannot　hide　the　fact　that　certain　forms　of　higher　intellection　involve　a　pretty　definite　collocation　and　elaboration　of　special　sensations。　Such　specialization；　indeed；　seems　a　necessary　accompaniment　of　mental　evolution。　　That　every　such　specialized　function　has　its　localized　centres　of　co…ordination；　of　some　such　significance　as　the　demonstrated　centres　of　articulate　speech；　can　hardly　be　in　doubtthough　this；　be　it　understood；　is　an　induction；　not　as　yet　a　demonstration。　　In　other　words；　there　is　every　reason　to　believe　that　numerous　〃centres；〃　in　this　restricted　sense；　exist　in　the　brain　that　have　as　yet　eluded　the　investigator。　Indeed；　the　current　conception　regards　the　entire　cerebral　cortex　as　chiefly　composed　of　centres　of　ultimate　co…ordination　of　impressions；　which　in　their　cruder　form　are　received　by　more　primitive　nervous　tissuesthe　basal　ganglia；　the　cerebellum　and　medulla；　and　the　spinal　cord。

This；　of　course；　is　equivalent　to　postulating　the　cerebral　cortex　as　the　exclusive　seat　of　higher　intellection。　This　proposition；　however；　to　which　a　safe　induction　seems　to　lead；　is　far　afield　from　the　substantiation　of　the　old　conception