a history of science-4-第53章

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arned　as　to　conditions　that　modify　this　time。　　Thus　it　was　found　that　different　persons　vary　in　the　rate　of　their　central　nervous　activitywhich　explained　the　〃personal　equation〃　that　the　astronomer　Bessel　had　noted　a　half…century　before。　It　was　found；　too；　that　the　rate　of　activity　varies　also　for　the　same　person　under　different　conditions；　becoming　retarded；　for　example；　under　influence　of　fatigue；　or　in　case　of　certain　diseases　of　the　brain。　　All　details　aside；　the　essential　fact　emerges；　as　an　experimental　demonstration；　that　the　intellectual　processessensation；　apperception；　volitionare　linked　irrevocably　with　the　activities　of　the　central　nervous　tissues；　and　that　these　activities；　like　all　other　physical　processes；　have　a　time　element。　　To　that　old　school　of　psychologists；　who　scarcely　cared　more　for　the　human　head　than　for　the　heelsbeing　interested　only　in　the　mindsuch　a　linking　of　mind　and　body　as　was　thus　demonstrated　was　naturally　disquieting。　But　whatever　the　inferences；　there　was　no　escaping　the　facts。

Of　course　this　new　movement　has　not　been　confined　to　Germany。　　Indeed；　it　had　long　had　exponents　elsewhere。　Thus　in　England；　a　full　century　earlier；　Dr。　Hartley　had　championed　the　theory　of　the　close　and　indissoluble　dependence　of　the　mind　upon　the　brain；　and　formulated　a　famous　vibration　theory　of　association　that　still　merits　careful　consideration。　Then；　too；　in　France；　at　the　beginning　of　the　century；　there　was　Dr。　Cabanis　with　his　tangible；　if　crudely　phrased；　doctrine　that　the　brain　digests　impressions　and　secretes　thought　as　the　stomach　digests　food　and　the　liver　secretes　bile。　Moreover；　Herbert　Spencer's　Principles　of　Psychology；　with　its　avowed　co…ordination　of　mind　and　body　and　its　vitalizing　theory　of　evolution；　appeared　in　1855；　half　a　decade　before　the　work　of　Fechner。　　But　these　influences；　though　of　vast　educational　value；　were　theoretical　rather　than　demonstrative；　and　the　fact　remains　that　the　experimental　work　which　first　attempted　to　gauge　mental　operations　by　physical　principles　was　mainly　done　in　Germany。　　Wundt's　Physiological　Psychology；　with　its　full　preliminary　descriptions　of　the　anatomy　of　the　nervous　system；　gave　tangible　expression　to　the　growth　of　the　new　movement　in　1874；　and　four　years　later；　with　the　opening　of　his　laboratory　of　physiological　psychology　at　the　University　of　Leipzig；　the　new　psychology　may　be　said　to　have　gained　a　permanent　foothold　and　to　have　forced　itself　into　official　recognition。　From　then　on　its　conquest　of　the　world　was　but　a　matter　of　time。

It　should　be　noted；　however；　that　there　is　one　other　method　of　strictly　experimental　examination　of　the　mental　field；　latterly　much　in　vogue；　which　had　a　different　origin。　This　is　the　scientific　investigation　of　the　phenomena　of　hypnotism。　This　subject　was　rescued　from　the　hands　of　charlatans；　rechristened；　and　subjected　to　accurate　investigation　by　Dr。　James　Braid；　of　Manchester；　as　early　as　1841。　But　his　results；　after　attracting　momentary　attention；　fell　from　view；　and；　despite　desultory　efforts；　the　subject　was　not　again　accorded　a　general　hearing　from　the　scientific　world　until　1878；　when　Dr。　Charcot　took　it　up　at　the　Salpetriere；　in　Paris；　followed　soon　afterwards　by　Dr。　Rudolf　Heidenhain；　of　Breslau；　and　a　host　of　other　experimenters。　　The　value　of　the　method　in　the　study　of　mental　states　was　soon　apparent。　Most　of　Braid's　experiments　were　repeated；　and　in　the　main　his　results　were　confirmed。　　His　explanation　of　hypnotism；　or　artificial　somnambulism；　as　a　self…induced　state；　independent　of　any　occult　or　supersensible　influence；　soon　gained　general　credence。　　His　belief　that　the　initial　stages　are　due　to　fatigue　of　nervous　centres；　usually　from　excessive　stimulation；　has　not　been　supplanted；　though　supplemented　by　notions　growing　out　of　the　new　knowledge　as　to　subconscious　mentality　in　general；　and　the　inhibitory　influence　of　one　centre　over　another　in　the　central　nervous　mechanism。


THE　BRAIN　AS　THE　ORGAN　OF　MIND

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。　B