autobiography and selected essays-第28章

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complicated　activities　of　man　are　comprehensible　under　three

categories。　　Either　they　are　immediately　directed　towards　the

maintenance　and　development　of　the　body；　or　they　effect　transitory

changes　in　the　relative　positions　of　parts　of　the　body；　or　they

tend　towards　the　continuance　of　the　species。　　Even　those

manifestations　of　intellect；　of　feeling；　and　of　will；　which　we

rightly　name　the　higher　faculties；　are　not　excluded　from　this

classification；　inasmuch　as　to　every　one　but　the　subject　of　them；

they　are　known　only　as　transitory　changes　in　the　relative　positions

of　parts　of　the　body。　　Speech；　gesture；　and　every　other　form　of

human　action　are；　in　the　long　run；　resolvable　into　muscular

contraction；　and　muscular　contraction　is　but　a　transitory　change　in

the　relative　positions　of　the　parts　of　a　muscle。　　But　the　scheme

which　is　large　enough　to　embrace　the　activities　of　the　highest　form

of　life；　covers　all　those　of　the　lower　creatures。　　The　lowest

plant；　or　animalcule；　feeds；　grows；　and　reproduces　its　kind。　　In

addition；　all　animals　manifest　those　transitory　changes　of　form

which　we　class　under　irritability　and　contractility；　and；　it　is

more　than　probable；　that　when　the　vegetable　world　is　thoroughly

explored；　we　shall　find　all　plants　in　possession　of　the　same

powers；　at　one　time　or　other　of　their　existence。



I　am　not　now　alluding　to　such　phaenomena；　at　once　rare　and

conspicuous；　as　those　exhibited　by　the　leaflets　of　the　sensitive

plants；　or　the　stamens　of　the　barberry；　but　to　much　more　widely

spread；　and　at　the　same　time；　more　subtle　and　hidden；

manifestations　of　vegetable　contractility。　　You　are　doubtless　aware

that　the　common　nettle　owes　its　stinging　property　to　the

innumerable　stiff　and　needle…like；　though　exquisitely　delicate；

hairs　which　cover　its　surface。　　Each　stinging…needle　tapers　from　a

broad　base　to　a　slender　summit；　which；　though　rounded　at　the　end；

is　of　such　microscopic　fineness　that　it　readily　penetrates；　and

breaks　off　in；　the　skin。　　The　whole　hair　consists　of　a　very

delicate　outer　case　of　wood；　closely　applied　to　the　inner　surface

of　which　is　a　layer　of　semi…fluid　matter；　full　of　innumerable

granules　of　extreme　minuteness。　　This　semi…fluid　lining　is

protoplasm；　which　thus　constitutes　a　kind　of　bag；　full　of　a　limpid

liquid；　and　roughly　corresponding　in　form　with　the　interior　of　the

hair　which　it　fills。　　When　viewed　with　a　sufficiently　high

magnifying　power；　the　protoplasmic　layer　of　the　nettle　hair　is　seen

to　be　in　a　condition　of　unceasing　activity。　　Local　contractions　of

the　whole　thickness　of　its　substance　pass　slowly　and　gradually　from

point　to　point；　and　give　rise　to　the　appearance　of　progressive

waves；　just　as　the　bending　of　successive　stalks　of　corn　by　a　breeze

produces　the　apparent　billows　of　a　cornfield。



But；　in　addition　to　these　movements；　and　independently　of　them；　the

granules　are　driven；　in　relatively　rapid　streams；　through　channels

in　the　protoplasm　which　seem　to　have　a　considerable　amount　of

persistence。　　Most　commonly；　the　currents　in　adjacent　parts　of　the

protoplasm　take　similar　directions；　and；　thus；　there　is　a　general

stream　up　one　side　of　the　hair　and　down　the　other。　　But　this　does

not　prevent　the　existence　of　partial　currents　which　take　different

routes；　and　sometimes　trains　of　granules　may　be　seen　coursing

swiftly　in　opposite　directions　within　a　twenty…thousandth　of　an

inch　of　one　another；　while；　occasionally；　opposite　streams　come

into　direct　collision；　and；　after　a　longer　or　shorter　struggle；　one

predominates。　　The　cause　of　these　currents　seems　to　lie　in

contractions　of　the　protoplasm　which　bounds　the　channels　in　which

they　flow；　but　which　are　so　minute　that　the　best　microscopes　show

only　their　effects；　and　not　themselves。



The　spectacle　afforded　by　the　wonderful　energies　prisoned　within

the　compass　of　the　microscopic　hair　of　a　plant；　which　we　commonly

regard　as　a　merely　passive　organism；　is　not　easily　forgotten　by　one

who　has　watched　its　display；　continued　hour　after　hour；　without

pause　or　sign　of　weakening。　　The　possible　complexity　of　many　other

organic　forms；　seemingly　as　simple　as　the　protoplasm　of　the　nettle；

dawns　upon　one；　and　the　comparison　of　such　a　protoplasm　to　a　body

with　an　internal　circulation；　which　has　been　put　forward　by　an

eminent　physiologist；　loses　much　of　its　startling　character。

Currents　similar　to　those　of　the　hairs　of　the　nettle　have　been

observed　in　a　great　multitude　of　very　different　plants；　and　weighty

authorities　have　suggested　that　they　probably　occur；　in　more　or

less　perfection；　in　all　young　vegetable　cells。　　If　such　be　the

case；　the　wonderful　noonday　silence　of　a　tropical　forest　is；　after

all；　due　only　to　the　dulness　of　our　hearing；　and　could　our　ears

catch　the　murmur　of　these　tiny　Maelstroms；　＇96＇　as　they　whirl　in　the

innumerable　myriads　of　living　cells　which　constitute　each　tree；　we

should　be　stunned；　as　with　the　roar　of　a　great　city。



Among　the　lower　plants；　it　is　the　rule　rather　than　the　exception；

that　contractility　should　be　still　more　openly　manifested　at　some

periods　of　their　existence。　　The　protoplasm　of　Algae　and　Fungi

becomes；　under　many　circumstances；　partially；　or　completely；　freed

from　its　woody　case；　and　exhibits　movements　of　its　whole　mass；　or

is　propelled　by　the　contractility　of　one；　or　more；　hair…like

prolongations　of　its　body；　which　are　called　vibratile　cilia。　　And；

so　far　as　the　conditions　of　the　manifestation　of　the　phaenomena　of

contractility　have　yet　been　studied；　they　are　the　same　for　the

plant　as　for　the　animal。　　Heat　and　electric　shocks　influence　both；

and　in　the　same　way；　though　it　may　be　in　different　degrees。　　It　is

by　no　means　my　intention　to　suggest　that　there　is　no　difference　in

faculty　between　the　lowest　plant　and　the　highest；　or　between　plants

and　animals。　　But　the　difference　between　the　powers　of　the　lowest

plant；　or　animal；　and　those　of　the　highest；　is　one　of　degree；　not

of　kind；　and　depends；　as　Milne…Edwards　＇97＇　long　ago　so　well　pointed

out；　upon　the　extent　to　which　the　principle　of　the　division　of

labour　is　carried　out　in　the　living　economy。　　In　the　lowest

organism　all　parts　are　competent　to　perform　all　functions；　and　one

and　the　same　portion　of　protoplasm　may　successfully　take　on　the

function　of　feeding；　moving；　or　reproducing　apparatus。　　In　the

highest；　on　the　contrary；　a　great　number　of　parts　combine　to

perform　each　function；　each　part　doing　its　allotted　share　of　the

work　with　great　accuracy　and　efficiency；　but　being　useless　for　any

other　purpose。



On　the　other　hand；　notwithstanding　all　the　fundamental　resemblances

which　exist　between　the　powers　of　the　protoplasm　in　plants　and　in

animals；　they　present　a　striking　difference　（to　which　I　shall

advert　more　at　length　presently）；　in　the　fact　that　plants　can

manufacture　fresh　protoplasm　out　of　mineral　compounds；　whereas

animals　are　obliged　to　procure　it　ready　made；　and　hence；　in　the

long　run；　depend　upon　plants。　　Upon　what　condition　this　difference

in　the　powers　of　the　two　great　divisions　of　the　world　of　life

depends；　nothing　is　at　present　known。



With　such　qualifications　as　arises　＇98＇　out　of　the　last…mentioned

fact；　it　may　be　truly　said　that　the　acts　of　all　living　things　are

fundamentally　one。　　Is　any　such　unity　predicable　of　their　forms？

Let　us　seek　in　easily　verified　facts　for　a　reply　to　this　question。

If　a　drop　of　blood　be　drawn　by　pricking　one's　finger；　and　viewed

with　proper　precautions；　and　under　a　sufficiently　high　microscopic

power；　there　will　be　seen；　among　the　innumerable　multitude　of

little；　circular；　discoidal　bodies；　or　corpuscles；　which　float　in

it　and　give　it　its　colour；　a　comparatively　small　number　of

colourless　corpuscles；　of　somewhat　larger　size　and　very　irregular

shape。　　If　the　drop　of　blood　be　kept　at　the　temperature　of　the

body；　these　colourless　corpuscles　will　be　seen　to　exhibit　a

marvellous　activity；　changing　their　forms　with　great　rapidity；

drawing　in　and　thrusting　out　prolong