the origination of living beings-第6章

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organisms；　but　that；　in　reality；　it　acted　as　a　reservoir　from　which　the
infusion　was　immediately　supplied　with　the　large　quantity　that　had　so
puzzled　him。

But　not　content　with　explaining　the　experiments　of　others；　M。　Pasteur
went　to　work　to　satisfy　himself　completely。　　He　said　to　himself：　〃If　my
view　is　right；　and　if；　in　point　of　fact；　all　these　appearances　of
spontaneous　generation　are　altogether　due　to　the　falling　of　minute
germs　suspended　in　the　atmosphere；why；　I　ought　not　only　to　be　able　to
show　the　germs；　but　I　ought　to　be　able　to　catch　and　sow　them；　and
produce　the　resulting　organisms。〃　　He；　accordingly；　constructed　a　very
ingenious　apparatus　to　enable　him　to　accomplish　this　trapping　of　this
〃germ　dust〃　in　the　air。　　He　fixed　in　the　window　of　his　room　a　glass
tube；　in　the　centre　of　which　he　had　placed　a　ball　of　gun…cotton；　which；
as　you　all　know；　is　ordinary　cotton…wool；　which；　from　having　been
steeped　in　strong　acid；　is　converted　into　a　substance　of　great　explosive
power。　　It　is　also　soluble　in　alcohol　and　ether。　　One　end　of　the　glass
tube　was；　of　course；　open　to　the　external　air；　and　at　the　other　end　of
it　he　placed　an　aspirator；　a　contrivance　for　causing　a　current　of　the
external　air　to　pass　through　the　tube。　　He　kept　this　apparatus　going
for　four…and…twenty　hours；　and　then　removed　the　'dusted'　gun…cotton；
and　dissolved　it　in　alcohol　and　ether。　　He　then　allowed　this　to　stand
for　a　few　hours；　and　the　result　was；　that　a　very　fine　dust　was
gradually　deposited　at　the　bottom　of　it。　　That　dust；　on　being
transferred　to　the　stage　of　a　microscope；　was　found　to　contain　an
enormous　number　of　starch　grains。　　You　know　that　the　materials　of　our
food　and　the　greater　portion　of　plants　are　composed　of　starch；　and　we
are　constantly　making　use　of　it　in　a　variety　of　ways；　so　that　there　is
always　a　quantity　of　it　suspended　in　the　air。　　It　is　these　starch
grains　which　form　many　of　those　bright　specks　that　we　see　dancing　in　a
ray　of　light　sometimes。　　But　besides　these；　M。　Pasteur　found　also　an
immense　number　of　other　organic　substances　such　as　spores　of　fungi；
which　had　been　floating　about　in　the　air　and　had　got　caged　in　this　way。

He　went　farther；　and　said　to　himself；　〃If　these　really　are　the　things
that　give　rise　to　the　appearance　of　spontaneous　generation；　I　ought　to
be　able　to　take　a　ball　of　this　'dusted'　gun…cotton　and　put　it　into　one
of　my　vessels；　containing　that　boiled　infusion　which　has　been　kept　away
from　the　air；　and　in　which　no　infusoria　are　at　present　developed；　and
then；　if　I　am　right；　the　introduction　of　this　gun…cotton　will　give　rise
to　organisms。〃

Accordingly；　he　took　one　of　these　vessels　of　infusion；　which　had　been
kept　eighteen　months；　without　the　least　appearance　of　life；　and　by　a
most　ingenious　contrivance；　he　managed　to　break　it　open　and　introduce
such　a　ball　of　gun…cotton；　without　allowing　the　infusion　or　the　cotton
ball　to　come　into　contact　with　any　air　but　that　which　had　been　subjected
to　a　red　heat；　and　in　twenty…four　hours　he　had　the　satisfaction　of
finding　all　the　indications　of　what　had　been　hitherto　called
spontaneous　generation。　　He　had　succeeded　in　catching　the　germs　and
developing　organisms　in　the　way　he　had　anticipated。

It　now　struck　him　that　the　truth　of　his　conclusions　might　be
demonstrated　without　all　the　apparatus　he　had　employed。　　To　do　this；　he
took　some　decaying　animal　or　vegetable　substance；　such　as　urine；　which
is　an　extremely　decomposable　substance；　or　the　juice　of　yeast；　or
perhaps　some　other　artificial　preparation；　and　filled　a　vessel　having　a
long　tubular　neck　with　it。　　He　then　boiled　the　liquid　and　bent　that
long　neck　into　an　S　shape　or　zig…zag；　leaving　it　open　at　the　end。　　The
infusion　then　gave　no　trace　of　any　appearance　of　spontaneous
generation；　however　long　it　might　be　left；　as　all　the　germs　in　the　air
were　deposited　in　the　beginning　of　the　bent　neck。　　He　then　cut　the　tube
close　to　the　vessel；　and　allowed　the　ordinary　air　to　have　free　and
direct　access；　and　the　result　of　that　was　the　appearance　of　organisms　in
it；　as　soon　as　the　infusion　had　been　allowed　to　stand　long　enough　to
allow　of　the　growth　of　those　it　received　from　the　air；　which　was　about
forty…eight　hours。　　The　result　of　M。　Pasteur's　experiments　proved；
therefore；　in　the　most　conclusive　manner；　that　all　the　appearances　of
spontaneous　generation　arose　from　nothing　more　than　the　deposition　of
the　germs　of　organisms　which　were　constantly　floating　in　the　air。

To　this　conclusion；　however；　the　objection　was　made；　that　if　that　were
the　cause；　then　the　air　would　contain　such　an　enormous　number　of　these
germs；　that　it　would　be　a　continual　fog。　　But　M。　Pasteur　replied　that
they　are　not　there　in　anything　like　the　number　we　might　suppose；　and
that　an　exaggerated　view　has　been　held　on　that　subject；　he　showed　that
the　chances　of　animal　or　vegetable　life　appearing　in　infusions；　depend
entirely　on　the　conditions　under　which　they　are　exposed。　　If　they　are
exposed　to　the　ordinary　atmosphere　around　us；　why；　of　course；　you　may
have　organisms　appearing　early。　　But；　on　the　other　hand；　if　they　are
exposed　to　air　from　a　great　height；　or　from　some　very　quiet　cellar；　you
will　often　not　find　a　single　trace　of　life。

So　that　M。　Pasteur　arrived　at　last　at　the　clear　and　definite　result；
that　all　these　appearances　are　like　the　case　of　the　worms　in　the　piece
of　meat；　which　was　refuted　by　Redi；　simply　germs　carried　by　the　air　and
deposited　in　the　liquids　in　which　they　afterwards　appear。　　For　my　own
part；　I　conceive　that；　with　the　particulars　of　M。　Pasteur's　experiments
before　us；　we　cannot　fail　to　arrive　at　his　conclusions；　and　that　the
doctrine　of　spontaneous　generation　has　received　a　final　'coup　de
grace'。

You；　of　course；　understand　that　all　this　in　no　way　interferes　with　the
'possibility'　of　the　fabrication　of　organic　matters　by　the　direct
method　to　which　I　have　referred；　remote　as　that　possibility　may　be。


　　　　＇Footnote＇　1　Those　who　wish　to　study　fully　the　doctrines　of
　　　　which　I　have　endeavoured　to　give　some　rough　and　ready
　　　　illustrations；　must　read　Mr。　John　Stuart　Mill's　'System　of
　　　　Logic'。







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