the origination of living beings-第4部分

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which　forms　one　of　the　waste　products　of　animal　structures。　　And　of
late　years　a　number　of　other　compounds；　such　as　Butyric　Acid；　and
others；　have　been　added　to　the　list。　　I　need　not　tell　you　that
chemistry　is　an　enormous　distance　from　the　goal　I　indicate；　all　I　wish
to　point　out　to　you　is；　that　it　is　by　no　means　safe　to　say　that　that
goal　may　not　be　reached　one　day。　　It　may　be　that　it　is　impossible　for
us　to　produce　the　conditions　requisite　to　the　origination　of　life；　but
we　must　speak　modestly　about　the　matter；　and　recollect　that　Science　has
put　her　foot　upon　the　bottom　round　of　the　ladder。　　Truly　he　would　be　a
bold　man　who　would　venture　to　predict　where　she　will　be　fifty　years
hence。

There　is　another　inquiry　which　bears　indirectly　upon　this　question；　and
upon　which　I　must　say　a　few　words。　　You　are　all　of　you　aware　of　the
phenomena　of　what　is　called　spontaneous　generation。　　Our　forefathers；
down　to　the　seventeenth　century；　or　thereabouts；　all　imagined；　in
perfectly　good　faith；　that　certain　vegetable　and　animal　forms　gave
birth；　in　the　process　of　their　decomposition；　to　insect　life。　　Thus；　if
you　put　a　piece　of　meat　in　the　sun；　and　allowed　it　to　putrefy；　they
conceived　that　the　grubs　which　soon　began　to　appear　were　the　result　of
the　action　of　a　power　of　spontaneous　generation　which　the　meat
contained。　　And　they　could　give　you　receipts　for　making　various　animal
and　vegetable　preparations　which　would　produce　particular　kinds　of
animals。　　A　very　distinguished　Italian　naturalist；　named　Redi；　took　up
the　question；　at　a　time　when　everybody　believed　in　it；　among　others　our
own　great　Harvey；　the　discoverer　of　the　circulation　of　the　blood。　　You
will　constantly　find　his　name　quoted；　however；　as　an　opponent　of　the
doctrine　of　spontaneous　generation；　but　the　fact　is；　and　you　will　see　it
if　you　will　take　the　trouble　to　look　into　his　works；　Harvey　believed　it
as　profoundly　as　any　man　of　his　time；　but　he　happened　to　enunciate　a
very　curious　propositionthat　every　living　thing　came　from　an　'egg'；
he　did　not　mean　to　use　the　word　in　the　sense　in　which　we　now　employ　it；
he　only　meant　to　say　that　every　living　thing　originated　in　a　little
rounded　particle　of　organized　substance；　and　it　is　from　this
circumstance；　probably；　that　the　notion　of　Harvey　having　opposed　the
doctrine　originated。　　Then　came　Redi；　and　he　proceeded　to　upset　the
doctrine　in　a　very　simple　manner。　　He　merely　covered　the　piece　of　meat
with　some　very　fine　gauze；　and　then　he　exposed　it　to　the　same
conditions。　　The　result　of　this　was　that　no　grubs　or　insects　were
produced；　he　proved　that　the　grubs　originated　from　the　insects　who　came
and　deposited　their　eggs　in　the　meat；　and　that　they　were　hatched　by　the
heat　of　the　sun。　　By　this　kind　of　inquiry　he　thoroughly　upset　the
doctrine　of　spontaneous　generation；　for　his　time　at　least。

Then　came　the　discovery　and　application　of　the　microscope　to　scientific
inquiries；　which　showed　to　naturalists　that　besides　the　organisms　which
they　already　knew　as　living　beings　and　plants；　there　were　an　immense
number　of　minute　things　which　could　be　obtained　apparently　almost　at
will　from　decaying　vegetable　and　animal　forms。　　Thus；　if　you　took　some
ordinary　black　pepper　or　some　hay；　and　steeped　it　in　water；　you　would
find　in　the　course　of　a　few　days　that　the　water　had　become　impregnated
with　an　immense　number　of　animalcules　swimming　about　in　all
directions。　　From　facts　of　this　kind　naturalists　were　led　to　revive　the
theory　of　spontaneous　generation。　　They　were　headed　here　by　an　English
naturalist；Needham；and　afterwards　in　France　by　the　learned　Buffon。
They　said　that　these　things　were　absolutely　begotten　in　the　water　of
the　decaying　substances　out　of　which　the　infusion　was　made。　　It　did　not
matter　whether　you　took　animal　or　vegetable　matter；　you　had　only　to
steep　it　in　water　and　expose　it；　and　you　would　soon　have　plenty　of
animalcules。　　They　made　an　hypothesis　about　this　which　was　a　very　fair
one。　　They　said；　this　matter　of　the　animal　world；　or　of　the　higher
plants；　appears　to　be　dead；　but　in　reality　it　has　a　sort　of　dim　life
about　it；　which；　if　it　is　placed　under　fair　conditions；　will　cause　it
to　break　up　into　the　forms　of　these　little　animalcules；　and　they　will
go　through　their　lives　in　the　same　way　as　the　animal　or　plant　of　which
they　once　formed　a　part。

The　question　now　became　very　hotly　debated。　　Spallanzani；　an　Italian
naturalist；　took　up　opposite　views　to　those　of　Needham　and　Buffon；　and
by　means　of　certain　experiments　he　showed　that　it　was　quite　possible　to
stop　the　process　by　boiling　the　water；　and　closing　the　vessel　in　which
it　was　contained。　　〃Oh！〃　said　his　opponents；　〃but　what　do　you　know　you
may　be　doing　when　you　heat　the　air　over　the　water　in　this　way？　　You　may
be　destroying　some　property　of　the　air　requisite　for　the　spontaneous
generation　of　the　animalcules。〃

However；　Spallanzani's　views　were　supposed　to　be　upon　the　right　side；
and　those　of　the　others　fell　into　discredit；　although　the　fact　was　that
Spallanzani　had　not　made　good　his　views。　　Well；　then；　the　subject
continued　to　be　revived　from　time　to　time；　and　experiments　were　made　by
several　persons；　but　these　experiments　were　not　altogether　satisfactory。
It　was　found　that　if　you　put　an　infusion　in　which　animalcules　would
appear　if　it　were　exposed　to　the　air　into　a　vessel　and　boiled　it；　and
then　sealed　up　the　mouth　of　the　vessel；　so　that　no　air；　save　such　as
had　been　heated　to　212　degrees；　could　reach　its　contents；　that　then　no
animalcules　would　be　found；　but　if　you　took　the　same　vessel　and　exposed
the　infusion　to　the　air；　then　you　would　get　animalcules。　　Furthermore；
it　was　found　that　if　you　connected　the　mouth　of　the　vessel　with　a
red…hot　tube　in　such　a　way　that　the　air　would　have　to　pass　through　the
tube　before　reaching　the　infusion；　that　then　you　would　get　no
animalcules。　　Yet　another　thing　was　noticed：　if　you　took　two　flasks
containing　the　same　kind　of　infusion；　and　left　one　entirely　exposed　to
the　air；　and　in　the　mouth　of　the　other　placed　a　ball　of　cotton　wool；　so
that　the　air　would　have　to　filter　itself　through　it　before　reaching　the
infusion；　that　then；　although　you　might　have　plenty　of　animalcules　in
the　first　flask；　you　would　certainly　obtain　none　from　the　second。

These　experiments；　you　see；　all　tended　towards　one　conclusionthat　the
infusoria　were　developed　from　little　minute　spores　or　eggs　which　were
constantly　floating　in　the　atmosphere；　which　lose　their　power　of
germination　if　subjected　to　heat。　　But　one　observer　now　made　another
experiment　which　seemed　to　go　entirely　the　other　way；　and　puzzled　him
altogether。　He　took　some　of　this　boiled　infusion　that　I　have　been
speaking　of；　and　by　the　use　of　a　mercurial　batha　kind　of　trough　used
in　laboratorieshe　deftly　inverted　a　vessel　containing　the　infusion
into　the　mercury；　so　that　the　latter　reached　a　little　beyond　the　level
of　the　mouth　of　the　'inverted'　vessel。　　You　see　that　he　thus　had　a
quantity　of　the　infusion　shut　off　from　any　possible　communication　with
the　outer　air　by　being　inverted　upon　a　bed　of　mercury。

He　then　prepared　some　pure　oxygen　and　nitrogen　gases；　and　passed　them　by
means　of　a　tube　going　from　the　outside　of　the　vessel；　up　through　the
mercury　into　the　infusion；　so　that　he　thus　had　it　exposed　to　a
perfectly　pure　atmosphere　of　the　same　constituents　as　the　external　air。
Of　course；　he　expected　he　would　get　no　infusorial　animalcules　at　all　in
that　infusion；　but；　to　his　great　dismay　and　discomfiture；　he　found　he
almost　always　did　get　them。

Furthermore；　it　has　been　found　that　experiments　made　in　the　manner
described　above　answer　well　with　most　infusions；　but　that　if　you　fill
the　vessel　with　boiled　milk；　and　then　stop　the　neck　with　cotton…wool；
you　'will'　have　infusoria。　　So　that　you　see　there　were　two　experiments
that　brought　you　to　one　kind　of　conclusion；　and　three　to　another；　which
was　a　most　unsatisfactory　state　of　things　to　arrive　at　in　a　scientific
inquiry。

Some　few　years　after　this；　the　question　began　to　be　very　hotly　discussed
in　France。　　There　was　M。　Pouchet；　a　professor　at　Rouen；　a　very　learned
man；　but　certainly　not　a　very　rigid　experimentalist。　　He　published　a
number　of　experiments　of　his　own；　some　of　which　were　very　ingenious；　to
show　that　if　you　went　to　work　in　a　proper　way；　there　was　a　truth　in　the
doctrine　of　spontaneous　generation。　　Well；　it　was　one　of　the　most
fortunate　things　in　the　world　that　M。　　Pouchet　took　up　this　question；
because　it　induced　a　distinguished　French　chemist；　M。　Pasteur；　to　take
up　the　question　on　the　other　side；　and　he　has　certainly　worked　it　out　in
the　most　perfect　manner。　　I　am　glad　to　say；　too；　that　he　has　published
his　researches　in　time　to　enable　me　to　give　you　an　account　of　them。　　He
verified　all　the　experiments　which　I　have　just　mentioned　to　youand
then　finding　those　extraordinary　anomalies；　as　in　the　case　of　the
mercury　bath　and　the　milk；　he　set　himself　to　work　to　discover　their
nature。　　In　the　case　of　milk　he　found　it　to　be　a　question　of
temperature。　　Milk　in　a　fresh　state　is　slightly　alkaline；　and　it　is　a
very　curious　circumstance；　but　this　very　slight　degree　of　alkalinity
seems　to　have　the　effect　of　preserving　the　organisms　which　fall　into　it
from　the　air　from　being　destroyed　at　a　temperature　of　212　degrees；
which　is　the　boiling　point。　　But　if　you　raise　the　temperature　10　degrees
when　you　boil　it；　the　milk　behaves　like　everything　else；　and　if　the　air
with　which　it　comes　in　contact；　after　being　boiled　at　this　temperature；
is　passed　through　a　red…hot　tube；　you　will　not　get　a　trace　of
organisms。

He　then　turned　his　attention　to　the　mercury　bath；　and　found　on
examination　that　the　surface　of　the　mercury　was　almost　always　covered
with　a　very　fine　dust。　　He　found　that　even　the　mercury　itself　was
positively　full　of　organic　matters；　that　from　being　constantly　exposed
to　the　air；　it　had　collected　an　immense　number　of　these　infusorial
organisms　from　the　air。　　Well；　under　these　circumstances　he　felt　that
the　case　was　quite　clear；　and　that　the　mercury　was　not　what　it　had
appeared　to　M。　Schwann　to　be；a　bar　to　the　admission　of　these
organisms；　but　that；　in　reality；　it　acted　as　a　reservoir　from　which　the
infusion　was　immediately　supplied　with　the