yeast-第2部分

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of　the　attempt　to　understand　the　relation　between　the　yeast　and　the
products；　and　lastly；　what　very　curious　side　issues　if　I　may　so　call
themhave　branched　out　in　the　course　of　this　inquiry；　which　has　now
occupied　somewhere　about　two　centuries。

The　first　thing　was　to　make　out　precisely　and　clearly　what　was　the
nature　of　this　substance；　this　apparently　mere　scum　and　mud　that　we
call　yeast。　　And　that　was　first　commenced　seriously　by　a　wonderful　old
Dutchman　of　the　name　of　Leeuwenhoek；　who　lived　some　two　hundred　years
ago；　and　who　was　the　first　person　to　invent　thoroughly　trustworthy
microscopes　of　high　powers。　　Now；　Leeuwenhoek　went　to　work　upon　this
yeast　mud；　and　by　applying　to　it　high　powers　of　the　microscope；　he
discovered　that　it　was　no　mere　mud　such　as　you　might　at　first　suppose；
but　that　it　was　a　substance　made　up　of　an　enormous　multitude　of　minute
grains；　each　of　which　had　just　as　definite　a　form　as　if　it　were　a　grain
of　corn；　although　it　was　vastly　smaller；　the　largest　of　these　not　being
more　than　the　two…thousandth　of　an　inch　in　diameter；　while；　as　you
know；　a　grain　of　corn　is　a　large　thing；　and　the　very　smallest　of　these
particles　were　not　more　than　the　seven…thousandth　of　an　inch　in
diameter。　　Leeuwenhoek　saw　that　this　muddy　stuff　was　in　reality　a
liquid；　in　which　there　were　floating　this　immense　number　of　definitely
shaped　particles；　all　aggregated　in　heaps　and　lumps　and　some　of　them
separate。　That　discovery　remained；　so　to　speak；　dormant　for　fully　a
century；　and　then　the　question　was　taken　up　by　a　French　discoverer；
who；　paying　great　attention　and　having　the　advantage　of　better
instruments　than　Leeuwenhoek　had；　watched　these　things　and　made　the
astounding　discovery　that　they　were　bodies　which　were　constantly　being
reproduced　and　growing；　than　when　one　of　these　rounded　bodies　was　once
formed　and　had　grown　to　its　full　size；　it　immediately　began　to　give　off
a　little　bud　from　one　side；　and　then　that　bud　grew　out　until　it　had
attained　the　full　size　of　the　first；　and　that；　in　this　way；　the　yeast
particle　was　undergoing　a　process　of　multiplication　by　budding；　just　as
effectual　and　just　as　complete　as　the　process　of　multiplication　of　a
plant　by　budding；　and　thus　this　Frenchman；　Cagniard　de　la　Tour；　arrived
at　the　conclusionvery　creditable　to　his　sagacity；　and　which　has　been
confirmed　by　every　observation　and　reasoning　sincethat　this
apparently　muddy　refuse　was　neither　more　nor　less　than　a　mass　of
plants；　of　minute　living　plants；　growing　and　multiplying　in　the　sugary
fluid　in　which　the　yeast　is　formed。　　And　from　that　time　forth　we　have
known　this　substance　which　forms　the　scum　and　the　lees　as　the　yeast
plant；　and　it　has　received　a　scientific　namewhich　I　may　use　without
thinking　of　it；　and　which　I　will　therefore　give　younamely；　〃Torula。〃
Well；　this　was　a　capital　discovery。　　The　next　thing　to　do　was　to　make
out　how　this　torula　was　related　to　the　other　plants。　　I　won't　weary　you
with　the　whole　course　of　investigation；　but　I　may　sum　up　its　results；
and　they　are　thesethat　the　torula　is　a　particular　kind　of　a　fungus；　a
particular　state　rather；　of　a　fungus　or　mould。　　There　are　many　moulds
which　under　certain　conditions　give　rise　to　this　torula　condition；　to　a
substance　which　is　not　distinguishable　from　yeast；　and　which　has　the
same　properties　as　yeastthat　is　to　say；　which　is　able　to　decompose
sugar　in　the　curious　way　that　we　shall　consider　by…and…by。　　So　that　the
yeast　plant　is　a　plant　belonging　to　a　group　of　the　Fungi；　multiplying
and　growing　and　living　in　this　very　remarkable　manner　in　the　sugary
fluid　which　is；　so　to　speak；　the　nidus　or　home　of　the　yeast。

That；　in　a　few　words；　is；　as　far　as　investigationby　the　help　of　one's
eye　and　by　the　help　of　the　microscopehas　taken　us。　　But　now　there　is
an　observer　whose　methods　of　observation　are　more　refined　than　those　of
men　who　use　their　eye；　even　though　it　be　aided　by　the　microscope；　a　man
who　sees　indirectly　further　than　we　can　see　directlythat　is；　the
chemist；　and　the　chemist　took　up　this　question；　and　his　discovery　was
not　less　remarkable　than　that　of　the　microscopist。　　The　chemist
discovered　that　the　yeast　plant　being　composed　of　a　sort　of　bag；　like　a
bladder；　inside　which　is　a　peculiar　soft；　semifluid　materialthe
chemist　found　that　this　outer　bladder　has　the　same　composition　as　the
substance　of　wood；　that　material　which　is　called　〃cellulose；〃　and　which
consists　of　the　elements　carbon　and　hydrogen　and　oxygen；　without　any
nitrogen。　　But　then　he　also　found　（the　first　person　to　discover　it　was
an　Italian　chemist；　named

Fabroni；　in　the　end　of　the　last　century）　that　this　inner　matter　which
was　contained　in　the　bag；　which　constitutes　the　yeast　plant；　was　a
substance　containing　the　elements　carbon　and　hydrogen　and　oxygen　and
nitrogen；　that　it　was　what　Fabroni　called　a　vegeto…animal　substance；
and　that　it　had　the　peculiarities　of　what　are　commonly　called　〃animal
products。〃

This　again　was　an　exceedingly　remarkable　discovery。　　It　lay　neglected
for　a　time；　until　it　was　subsequently　taken　up　by　the　great　chemists　of
modern　times；　and　they；　with　their　delicate　methods　of　analysis；　have
finally　decided　that；　in　all　essential　respects；　the　substance　which
forms　the　chief　part　of　the　contents　of　the　yeast　plant　is　identical
with　the　material　which　forms　the　chief　part　of　our　own　muscles；　which
forms　the　chief　part　of　our　own　blood；　which　forms　the　chief　part　of
the　white　of　the　egg；　that；　in　fact；　although　this　little　organism　is　a
plant；　and　nothing　but　a　plant；　yet　that　its　active　living　contents
contain　a　substance　which　is　called　〃protein；〃　which　is　of　the　same
nature　as　the　substance　which　forms　the　foundation　of　every　animal
organism　whatever。

Now　we　come　next　to　the　question　of　the　analysis　of　the　products；　of
that　which　is　produced　during　the　process　of　fermentation。　　So　far　back
as　the　beginning　of　the　16th　century；　in　the　times　of　transition
between　the　old　alchemy　and　the　modern　chemistry；　there　was　a
remarkable　man；　Von　Helmont；　a　Dutchman；　who　saw　the　difference　between
the　air　which　comes　out　of　a　vat　where　something　is　fermenting　and
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；　th