essays on life, art and science-第35节

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sympathetic　nerve。

〃'4th。　　Partial　closure　of　the　eyelids　in　animals　born　of　parents　in
which　that　state　of　the　eyelids　had　been　caused　either　by　the
section　of　the　cervical　sympathetic　nerve　or　the　removal　of　the
superior　cervical　ganglion。

〃'5th。　　Exophthalmia　in　animals　born　of　parents　in　which　an　injury
to　the　restiform　body　had　produced　that　protrusion　of　the　eyeball。
This　interesting　fact　I　have　witnessed　a　good　many　times；　and　I　have
seen　the　transmission　of　the　morbid　state　of　the　eye　continue
through　four　generations。　　In　these　animals　modified　by　heredity；
the　two　eyes　generally　protruded；　although　in　the　parents　usually
only　one　showed　exophthalmia；　the　lesion　having　been　made　in　most
cases　only　on　one　of　the　corpora　restiformia。

〃'6th。　　Haematoma　and　dry　gangrene　of　the　ears　in　animals　born　of
parents　in　which　these　ear…alterations　had　been　caused　by　an　injury
to　the　restiform　body　near　the　nib　of　the　calamus。

〃'7th。　　Absence　of　two　toes　out　of　the　three　of　the　hind　leg；　and
sometimes　of　the　three；　in　animals　whose　parents　had　eaten　up　their
hind…leg　toes　which　had　become　anaesthetic　from　a　section　of　the
sciatic　nerve　alone；　or　of　that　nerve　and　also　of　the　crural。
Sometimes；　instead　of　complete　absence　of　the　toes；　only　a　part　of
one　or　two　or　three　was　missing　in　the　young；　although　in　the　parent
not　only　the　toes　but　the　whole　foot　was　absent　（partly　eaten　off；
partly　destroyed　by　inflammation；　ulceration；　or　gangrene）。

〃'8th。　　Appearance　of　various　morbid　states　of　the　skin　and　hair　of
the　neck　and　face　in　animals　born　of　parents　having　had　similar
alterations　in　the　same　parts；　as　effects　of　an　injury　to　the
sciatic　nerve。'

〃It　should　be　especially　observed　that　Brown…Sequard　has　bred　during
thirty　years　many　thousand　guinea…pigs　from　animals　which　had　not
been　operated　upon；　and　not　one　of　these　manifested　the　epileptic
tendency。　　Nor　has　he　ever　seen　a　guinea…pig　born　without　toes；
which　was　not　the　offspring　of　parents　which　had　gnawed　off　their
own　toes　owing　to　the　sciatic　nerve　having　been　divided。　　Of　this
latter　fact　thirteen　instances　were　carefully　recorded；　and　a
greater　number　were　seen；　yet　Brown…Sequard　speaks　of　such　cases　as
one　of　the　rarer　forms　of　inheritance。　　It　is　a　still　more
interesting　fact；　'that　the　sciatic　nerve　in　the　congenitally
toeless　animal　has　inherited　the　power　of　passing　through　all　the
different　morbid　states　which　have　occurred　in　one　of　its　parents
from　the　time　of　the　division　till　after　its　reunion　with　the
peripheric　end。　　It　is　not；　therefore；　simply　the　power　of
performing　an　action　which　is　inherited；　but　the　power　of　performing
a　whole　series　of　actions；　in　a　certain　order。'

〃In　most　of　the　cases　of　inheritance　recorded　by　Brown…Sequard　only
one　of　the　two　parents　had　been　operated　upon　and　was　affected。　　He
concludes　by　expressing　his　belief　that　'what　is　transmitted　is　the
morbid　state　of　the　nervous　system；'　due　to　the　operation　performed
on　the　parents。〃

Mr。　Darwin　proceeds　to　give　other　instances　of　inherited　effects　of
mutilations：…

〃With　the　horse　there　seems　hardly　a　doubt　that　exostoses　on　the
legs；　caused　by　too　much　travelling　on　hard　roads；　are　inherited。
Blumenbach　records　the　case　of　a　man　who　had　his　little　finger　on
the　right　hand　almost　cut　off；　and　which　in　consequence　grew
crooked；　and　his　sons　had　the　same　finger　on　the　same　hand　similarly
crooked。　　A　soldier；　fifteen　years　before　his　marriage；　lost　his
left　eye　from　purulent　ophthalmia；　and　his　two　sons　were
microphthalmic　on　the　same　side。〃

The　late　Professor　Rolleston；　whose　competence　as　an　observer　no　one
is　likely　to　dispute；　gave　Mr。　Darwin　two　cases　as　having　fallen
under　his　own　notice；　one　of　a　man　whose　knee　had　been　severely
wounded；　and　whose　child　was　born　with　the　same　spot　marked　or
scarred；　and　the　other　of　one　who　was　severely　cut　upon　the　cheek；
and　whose　child　was　born　scarred　in　the　same　place。　　Mr。　Darwin's
conclusion　was　that　〃the　effects　of　injuries；　especially　when
followed　by　disease；　or　perhaps　exclusively　when　thus　followed；　are
occasionally　inherited。〃

Let　us　now　see　what　Professor　Weismann　has　to　say　against　this。　　He
writes：…

〃The　only　cases　worthy　of　discussion　are　the　well…known　experiments
upon　guinea…pigs　conducted　by　the　French　physiologist；　Brown…
Sequard。　　But　the　explanation　of　his　results　is；　in　my　opinion；　open
to　discussion。　　In　these　cases　we　have　to　do　with　the　apparent
transmission　of　artificially　produced　malformations　。　。　。　All　these
effects　were　said　to　be　transmitted　to　descendants　as　far　as　the
fifth　or　sixth　generation。

〃But　we　must　inquire　whether　these　cases　are　really　due　to　heredity；
and　not　to　simple　infection。　　In　the　case　of　epilepsy；　at　any　rate；
it　is　easy　to　imagine　that　the　passage　of　some　specific　organism
through　the　reproductive　cells　may　take　place；　as　in　the　case　of
syphilis。　　We　are；　however；　entirely　ignorant　of　the　nature　of　the
former　disease。　　This　suggested　explanation　may　not　perhaps　apply　to
the　other　cases；　but　we　must　remember　that　animals　which　have　been
subjected　to　such　severe　operations　upon　the　nervous　system　have
sustained　a　great　shock；　and　if　they　are　capable　of　breeding；　it　is
only　probable　that　they　will　produce　weak　descendants；　and　such　as
are　easily　affected　by　disease。　　Such　a　result　does　not；　however；
explain　why　the　offspring　should　suffer　from　the　same　disease　as
that　which　was　artificially　induced　in　the　parents。　　But　this　does
not　appear　to　have　been　by　any　means　invariably　the　case。　　Brown…
Sequard　himself　says：　　'The　changes　in　the　eye　of　the　offspring　were
of　a　very　variable　nature；　and　were　only　occasionally　exactly
similar　to　those　observed　in　the　parents。'

〃There　is　no　doubt；　however；　that　these　experiments　demand　careful
consideration；　but　before　they　can　claim　scientific　recognition；
they　must　be　subjected　to　rigid　criticism　as　to　the　precautions
taken；　the　nature　and　number　of　the　control　experiments；　&c。

〃Up　to　the　present　time　such　necessary　conditions　have　not　been
sufficiently　observed。　　The　recent　experiments　themselves　are　only
described　in　short　preliminary　notices；　which；　as　regards　their
accuracy；　the　possibility　of　mistake；　the　precautions　taken；　and　the
exact　succession　of　individuals　affected；　afford　no　data　on　which　a
scientific　opinion　can　be　founded〃　（pp。　81；　82）。

The　line　Professor　Weismann　takes；　therefore；　is　to　discredit　the
facts；　yet　on　a　later　page　we　find　that　the　experiments　have　since
been　repeated　by　Obersteiner；　〃who　has　described　them　in　a　very
exact　and　unprejudiced　manner；〃　and　that　〃the　fact〃（I　imagine　that
Professor　Weismann　intends　〃the　facts〃）〃cannot　be　doubted。〃

On　a　still　later　page；　however；　we　read：…

〃If；　for　instance；　it　could　be　shown　that　artificial　mutilation
spontaneously　reappears　in　the　offspring　with　sufficient　frequency
to　exclude　all　possibilities　of　chance；　then　such　proof　＇i。e。；　that
acquired　characters　can　be　transmitted＇　would　be　forthcoming。　　The
transmission　of　mutilations　has　been　frequently　asserted；　and　has
been　even　recently　again　brought　forward；　but　all　the　supposed
instances　have　broken　down　when　carefully　examined〃　（p。　390）。

Here；　then；　we　are　told　that　proof　of　the　occasional　transmission　of
mutilations　would　be　sufficient　to　establish　the　fact；　but　on　p。　267
we　find　that　no　single　fact　is　known　which　really　proves　that
acquired　characters　can　be　transmitted；　〃FOR　THE　ASCERTAINED　FACTS
WHICH　SEEM　TO　POINT　TO　THE　TRANSMISSION　OF　ARTIFICIALLY　PRODUCED
DISEASES　CANNOT　BE　CONSIDERED　AS　PROOF〃　＇Italics　mine。＇　　Perhaps；
but　it　was　mutilation　in　many　cases　that　Professor　Weismann
practically　admitted　to　have　been　transmitted　when　he　declared　that
Obersteiner　had　verified　Brown…Sequard's　experiments。

That　Professor　Weismann　recognises　the　vital　importance　to　his　own
theory　of　the　question　whether　or　no　mutilations　can　be　transmitted
under　any　circumstances；　is　evident　from　a　passage　on　p。　425　of　his
work；　on　which　he　says：　　〃It　can　hardly　be　doubted　that　mutilations
are　acquired　characters；　they　do　not　arise　from　any　tendency
contained　in　the　germ；　but　are　merely　the　reaction　of　the　body　under
certain　external　influences。　　They　are；　as　I　have　recently　expressed
it；　purely　somatogenic　charactersviz。；　characters　which　emanate
from　the　body　（soma）　only；　as　opposed　to　the　germ…cells；　they　are；
therefore；　characters　that　do　not　arise　from　the　germ　itself。

〃If　mutilations　must　necessarily　be　transmitted〃　＇which　no　one　that
I　know　of　has　maintained＇；　〃or　even　if　they　might　occasionally　be
transmitted〃　＇which　cannot；　I　imagine；　be　reasonably　questioned＇；　〃a
powerful　support　would　be　given　to　the　Lamarckian　principle；　and　the
transmission　of　functional　hypertrophy　or　atrophy　would　thus　become
highly　probable。〃

I　have　not　found　any　further　attempt　in　Professor　Weismann's　book　to
deal　with　the　evidence　adduced　by　Mr。　Darwin　to　show　that
mutilations；　if　followed　by　diseases；　are　sometimes　inherited；　and　I
must　leave　it　to　the　reader　to　determine　how　far　Professor　Weismann
has　shown　reason　for　rejecting　Mr。　Darwin's　conclusion。　　I　do　not；
however；　dwell　upon　these　facts　no