yeast-第3章

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common　air。　　He　was　the　man　who　invented　the　term　〃gas；〃　and　he　called
this　kind　of　gas　〃gas　silvestre〃so　to　speak　gas　that　is　wild；　and
lives　in　out　of　the　way　placeshaving　in　his　mind　the　identity　of　this
particular　kind　of　air　with　that　which　is　found　in　some　caves　and
cellars。　　Then；　the　gradual　process　of　investigation　going　on；　it　was
discovered　that　this　substance；　then　called　〃fixed　air；〃　was　a　poisonous
gas；　and　it　was　finally　identified　with　that　kind　of　gas　which　is
obtained　by　burning　charcoal　in　the　air；　which　is　called　〃carbonic
acid。〃　　Then　the　substance　alcohol　was　subjected　to　examination；　and　it
was　found　to　be　a　combination　of　carbon；　and　hydrogen；　and　oxygen。　Then
the　sugar　which　was　contained　in　the　fermenting　liquid　was　examined　and
that　was　found　to　contain　the　three　elements　carbon；　hydrogen；　and
oxygen。　　So　that　it　was　clear　there　were　in　sugar　the　fundamental
elements　which　are　contained　in　the　carbonic　acid；　and　in　the　alcohol。
And　then　came　that　great　chemist　Lavoisier；　and　he　examined　into　the
subject　carefully；　and　possessed　with　that　brilliant　thought　of　his
which　happens　to　be　propounded　exactly　apropos　to　this　matter　of
fermentationthat　no　matter　is　ever　lost；　but　that　matter　only　changes
its　form　and　changes　its　combinationshe　endeavoured　to　make　out　what
became　of　the　sugar　which　was　subjected　to　fermentation。　　He　thought　he
discovered　that　the　whole　weight　of　the　sugar　was　represented　by　the
carbonic　acid　produced；　that　in　other　words；　supposing　this　tumbler　to
represent　the　sugar；　that　the　action　of　fermentation　was　as　it　were　the
splitting　of　it；　the　one　half　going　away　in　the　shape　of　carbonic　acid；
and　the　other　half　going　away　in　the　shape　of　alcohol。　　Subsequent
inquiry；　careful　research　with　the　refinements　of　modern　chemistry；
have　been　applied　to　this　problem；　and　they　have　shown　that　Lavoisier
was　not　quite　correct；　that　what　he　says　is　quite　true　for　about　95　per
cent。　of　the　sugar；　but　that　the　other　5　per　cent。；　or　nearly　so；　is
converted　into　two　other　things；　one　of　them；　matter　which　is　called
succinic　acid；　and　the　other　matter　which　is　called　glycerine；　which
you　all　know　now　as　one　of　the　commonest　of　household　matters。　　It　may
be　that　we　have　not　got　to　the　end　of　this　refined　analysis　yet；　but　at
any　rate；　I　suppose　I　may　sayand　I　speak　with　some　little　hesitation
for　fear　my　friend　Professor　Roscoe　here　may　pick　me　up　for　trespassing
upon　his　provincebut　I　believe　I　may　say　that　now　we　can　account　for
99　per　cent。　at　least　of　the　sugar；　and　that　99　per　cent。　is　split　up
into　these　four　things；　carbonic　acid；　alcohol；　succinic　acid；　and
glycerine。　So　that　it　may　be　that　none　of　the　sugar　whatever
disappears；　and　that　only　its　parts；　so　to　speak；　are　re…arranged；　and
if　any　of　it　disappears；　certainly　it　is　a　very　small　portion。

Now　these　are　the　facts　of　the　case。　　There　is　the　fact　of　the　growth　of
the　yeast　plant；　and　there　is　the　fact　of　the　splitting　up　of　the
sugar。　　What　relation　have　these　two　facts　to　one　another？

For　a　very　long　time　that　was　a　great　matter　of　dispute。　　The　early
French　observers；　to　do　them　justice；　discerned　the　real　state　of　the
case；　namely；　that　there　was　a　very　close　connection　between　the　actual
life　of　the　yeast　plant　and　this　operation　of　the　splitting　up　of　the
sugar；　and　that　one　was　in　some　way　or　other　connected　with　the　other。
All　investigation　subsequently　has　confirmed　this　original　idea。　　It
has　been　shown　that　if　you　take　any　measures　by　which　other　plants　of
like　kind　to　the　torula　would　be　killed；　and　by　which　the　yeast　plant
is　killed；　then　the　yeast　loses　its　efficiency。　　But　a　capital
experiment　upon　this　subject　was　made　by　a　very　distinguished　man；
Helmholz；　who　performed　an　experiment　of　this　kind。　　He　had　two
vesselsone　of　them　we　will　suppose　full　of　yeast；　but　over　the　bottom
of　it；　as　this　might　be；　was　tied　a　thin　film　of　bladder；　consequently；
through　that　thin　film　of　bladder　all　the　liquid　parts　of　the　yeast
would　go；　but　the　solid　parts　would　be　stopped　behind；　the　torula　would
be　stopped；　the　liquid　parts　of　the　yeast　would　go。　　And　then　he　took
another　vessel　containing　a　fermentable　solution　of　sugar；　and　he　put
one　inside　the　other；　and　in　this　way　you　see　the　fluid　parts　of　the
yeast　were　able　to　pass　through　with　the　utmost　ease　into　the　sugar；　but
the　solid　parts　could　not　get　through　at　all。　　And　he　judged　thus：　　if
the　fluid　parts　are　those　which　excite　fermentation；　then；　inasmuch　as
these　are　stopped；　the　sugar　will　not　ferment；　and　the　sugar　did　not
ferment；　showing　quite　clearly；　that　an　immediate　contact　with　the
solid；　living　torula　was　absolutely　necessary　to　excite　this　process　of
splitting　up　of　the　sugar。　　This　experiment　was　quite　conclusive　as　to
this　particular　point；　and　has　had　very　great　fruits　in　other
directions。

Well；　then；　the　yeast　plant　being　essential　to　the　production　of
fermentation；　where　does　the　yeast　plant　come　from？　　Here；　again；　was
another　great　problem　opened　up；　for；　as　I　said　at　starting；　you　have；
under　ordinary　circumstances　in　warm　weather；　merely　to　expose　some
fluid　containing　a　solution　of　sugar；　or　any　form　of　syrup　or　vegetable
juice　to　the　air；　in　order；　after　a　comparatively　short　time；　to　see
all　these　phenomena　of　fermentation。　　Of　course　the　first　obvious
suggestion　is；　that　the　torula　has　been　generated　within　the　fluid。　　In
fact；　it　seems　at　first　quite　absurd　to　entertain　any　other　conviction；
but　that　belief　would　most　assuredly　be　an　erroneous　one。

Towards　the　beginning　of　this　century；　in　the　vigorous　times　of　the　old
French　wars；　there　was　a　Monsieur　Appert；　who　had　his　attention
directed　to　the　preservation　of　things　that　ordinarily　perish；　such　as
meats　and　vegetables；　and　in　fact　he　laid　the　foundation　of　our　modern
method　of　preserving　meats；　and　he　found　that　if　he　boiled　any　of　these
substances　and　then　tied　them　so　as　to　exclude　the　air；　that　they　would
be　preserved　for　any　time。　　He　tried　these　experiments；　particularly
with　the　must　of　wine　and　with　the　wort　of　beer；　and　he　found　that　if
the　wort　of　beer　had　been　carefully　boiled　and　was　stopped　in　such　a　way
that　the　air　could　not　get　at　it；　it　would　never　ferment。　　What　was　the
reason　of　this？　　That；　again；　became　the　subject　of　a　long　string　of
experiments；　with　this　ultimate　result；　that　if　you　take　precautions　to
prevent　any　solid　matters　from　getting　into　the　must　of　wine　or　the　wort
of　beer；　under　these　circumstancesthat　is　to　say；　if　the　fluid　has
been　boiled　and　placed　in　a　bottle；　and　if　you　stuff　the　neck　of　the
bottle　full　of　cotton　wool；　which　allows　the　air　to　go　through　and
stops　anything　of　a　solid　character　however　fine；　then　you　may　let　it
be　for　ten　years　and　it　will　not　ferment。　　But　if　you　take　that　plug
out　and　give　the　air　free　access；　then；　sooner　or　later　fermentation
will　set　up。　　And　there　is　no　doubt　whatever　that　fermentation　is
excited　only　by　the　presence　of　some　torula　or　other；　and　that　that
torula　proceeds　in　our　present　experience；　from　pre…existing　torulae。
These　little　bodies　are　excessively　light。　　You　can　easily　imagine　what
must　be　the　weight　of　little　particles；　but　slightly　heavier　than　water；
and　not　more　than　the　two…thousandth　or　perhaps　seven…thousandth　of　an
inch　in　diameter。　　They　are　capable　of　floating　about　and　dancing　like
motes　in　the　sunbeam；　they　are　carried　about　by　all　sorts　of　currents
of　air；　the　great　majority　of　them　perish；　but　one　or　two；　which　may
chance　to　enter　into　a　sugary　solution；　immediately　enter　into　active
life；　find　there　the　conditions　of　their　nourishment；　increase　and
multiply；　and　may　give　rise　to　any　quantity　whatever　of　this　substance
yeast。　　And；　whatever　may　be　true　or　not　be　true　about　this
〃spontaneous　generation；〃　as　it　is　called　in　regard　to　all　other　kinds
of　living　things；　it　is　perfectly　certain；　as　regards　yeast；　that　it
always　owes　its　origin　to　this　process　of　transportation　or　inoculation；
if　you　like　so　to　call　it；　from　some　other　living　yeast　organism；　and
so　far　as　yeast　is　concerned；　the　doctrine　of　spontaneous　generation　is
absolutely　out　of　court。　　And　not　only　so；　but　the　ye