a history of science-4-第39节

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hat　putrefaction；　in　short；　has　its　foundation　in　the　activities　of　these　so…called　anaerobic　bacteria。

In　a　word；　Pasteur　showed　that　all　the　many　familiar　processes　of　the　decay　of　organic　tissues　are；　in　effect；　forms　of　fermentation；　and　would　not　take　place　at　all　except　for　the　presence　of　the　living　micro…organisms。　A　piece　of　meat；　for　example；　suspended　in　an　atmosphere　free　from　germs；　will　dry　up　gradually；　without　the　slightest　sign　of　putrefaction；　regardless　of　the　temperature　or　other　conditions　to　which　it　may　have　been　subjected。　Let　us　witness　one　or　two　series　of　these　experiments　as　presented　by　Pasteur　himself　in　one　of　his　numerous　papers　before　the　Academy　of　Sciences。


EXPERIMENTS　WITH　GRAPE　SUGAR

〃In　the　course　of　the　discussion　which　took　place　before　the　Academy　upon　the　subject　of　the　generation　of　ferments　properly　so…called；　there　was　a　good　deal　said　about　that　of　wine；　the　oldest　fermentation　known。　On　this　account　I　decided　to　disprove　the　theory　of　M。　Fremy　by　a　decisive　experiment　bearing　solely　upon　the　juice　of　grapes。

〃I　prepared　forty　flasks　of　a　capacity　of　from　two　hundred　and　fifty　to　three　hundred　cubic　centimetres　and　filled　them　half　full　with　filtered　grape…must；　perfectly　clear；　and　which；　as　is　the　case　of　all　acidulated　liquids　that　have　been　boiled　for　a　few　seconds；　remains　uncontaminated　although　the　curved　neck　of　the　flask　containing　them　remain　constantly　open　during　several　months　or　years。

〃In　a　small　quantity　of　water　I　washed　a　part　of　a　bunch　of　grapes；　the　grapes　and　the　stalks　together；　and　the　stalks　separately。　This　washing　was　easily　done　by　means　of　a　small　badger's…hair　brush。　The　washing…water　collected　the　dust　upon　the　surface　of　the　grapes　and　the　stalks；　and　it　was　easily　shown　under　the　microscope　that　this　water　held　in　suspension　a　multitude　of　minute　organisms　closely　resembling　either　fungoid　spores；　or　those　of　alcoholic　Yeast；　or　those　of　Mycoderma　vini；　etc。　This　being　done；　ten　of　the　forty　flasks　were　preserved　for　reference；　in　ten　of　the　remainder；　through　the　straight　tube　attached　to　each；　some　drops　of　the　washing…water　were　introduced；　in　a　third　series　of　ten　flasks　a　few　drops　of　the　same　liquid　were　placed　after　it　had　been　boiled；　and；　finally；　in　the　ten　remaining　flasks　were　placed　some　drops　of　grape…juice　taken　from　the　inside　of　a　perfect　fruit。　　In　order　to　carry　out　this　experiment；　the　straight　tube　of　each　flask　was　drawn　out　into　a　fine　and　firm　point　in　the　lamp；　and　then　curved。　This　fine　and　closed　point　was　filed　round　near　the　end　and　inserted　into　the　grape　while　resting　upon　some　hard　substance。　When　the　point　was　felt　to　touch　the　support　of　the　grape　it　was　by　a　slight　pressure　broken　off　at　the　point　file　mark。　Then；　if　care　had　been　taken　to　create　a　slight　vacuum　in　the　flask；　a　drop　of　the　juice　of　the　grape　got　into　it；　the　filed　point　was　withdrawn；　and　the　aperture　immediately　closed　in　the　alcohol　lamp。　　This　decreased　pressure　of　the　atmosphere　in　the　flask　was　obtained　by　the　following　means：　After　warming　the　sides　of　the　flask　either　in　the　hands　or　in　the　lamp…flame；　thus　causing　a　small　quantity　of　air　to　be　driven　out　of　the　end　of　the　curved　neck；　this　end　was　closed　in　the　lamp。　After　the　flask　was　cooled；　there　was　a　tendency　to　suck　in　the　drop　of　grape…juice　in　the　manner　just　described。

〃The　drop　of　grape…juice　which　enters　into　the　flask　by　this　suction　ordinarily　remains　in　the　curved　part　of　the　tube；　so　that　to　mix　it　with　the　must　it　was　necessary　to　incline　the　flask　so　as　to　bring　the　must　into　contact　with　the　juice　and　then　replace　the　flask　in　its　normal　position。　The　four　series　of　comparative　experiments　produced　the　following　results：

〃The　first　ten　flasks　containing　the　grape…must　boiled　in　pure　air　did　not　show　the　production　of　any　organism。　The　grape…must　could　possibly　remain　in　them　for　an　indefinite　number　of　years。　　Those　in　the　second　series；　containing　the　water　in　which　the　grapes　had　been　washed　separately　and　together；　showed　without　exception　an　alcoholic　fermentation　which　in　several　cases　began　to　appear　at　the　end　of　forty…eight　hours　when　the　experiment　took　place　at　ordinary　summer　temperature。　At　the　same　time　that　the　yeast　appeared；　in　the　form　of　white　traces；　which　little　by　little　united　themselves　in　the　form　of　a　deposit　on　the　sides　of　all　the　flasks；　there　were　seen　to　form　little　flakes　of　Mycellium；　often　as　a　single　fungoid　growth　or　in　combination；　these　fungoid　growths　being　quite　independent　of　the　must　or　of　any　alcoholic　yeast。　　Often；　also；　the　Mycoderma　vini　appeared　after　some　days　upon　the　surface　of　the　liquid。　The　Vibria　and　the　lactic　ferments　properly　so　called　did　not　appear　on　account　of　the　nature　of　the　liquid。

〃The　third　series　of　flasks；　the　washing…water　in　which　had　been　previously　boiled；　remained　unchanged；　as　in　the　first　series。　Those　of　the　fourth　series；　in　which　was　the　juice　of　the　interior　of　the　grapes；　remained　equally　free　from　change；　although　I　was　not　always　able；　on　account　of　the　delicacy　of　the　experiment；　to　eliminate　every　chance　of　error。　These　experiments　cannot　leave　the　least　doubt　in　the　mind　as　to　the　following　facts：

Grape…must；　after　heating；　never　ferments　on　contact　with　the　air；　when　the　air　has　been　deprived　of　the　germs　which　it　ordinarily　holds　in　a　state　of　suspension。

〃The　boiled　grape…must　ferments　when　there　is　introduced　into　it　a　very　small　quantity　of　water　in　which　the　surface　of　the　grapes　or　their　stalks　have　been　washed。

〃The　grape…must　does　not　ferment　when　this　washing…water　has　been　boiled　and　afterwards　cooled。

〃The　grape…must　does　not　ferment　when　there　is　added　to　it　a　small　quantity　of　the　juice　of　the　inside　of　the　grape。

〃The　yeast；　therefore；　which　causes　the　fermentation　of　the　grapes　in　the　vintage…tub　comes　from　the　outside　and　not　from　the　inside　of　the　grapes。　　Thus　is　destroyed　the　hypothesis　of　MM。　　Trecol　and　Fremy；　who　surmised　that　the　albuminous　matter　transformed　itself　into　yeast　on　account　of　the　vital　germs　which　were　natural　to　it。　With　greater　reason；　therefore；　there　is　no　longer　any　question　of　the　theory　of　Liebig　of　the　transformation　of　albuminoid　matter　into　ferments　on　account　of　the　oxidation。〃


FOREIGN　ORGANISMS　AND　THE　WORT　OF　BEER

〃The　method　which　I　have　just　followed；〃　Pasteur　continues；　〃in　order　to　show　that　there　exists　a　correlation　between　the　diseases　of　beer　and　certain　microscopic　organisms　leaves　no　room　for　doubt；　it　seems　to　me；　in　regard　to　the　principles　I　am　expounding。

〃Every　time　that　the　microscope　reveals　in　the　leaven；　and　especially　in　the　active　yeast；　the　production　of　organisms　foreign　to　the　alcoholic　yeast　properly　so　called；　the　flavor　of　the　beer　leaves　something　to　be　desired；　much　or　little；　according　to　the　abundance　and　the　character　of　these　little　germs。　Moreover；　when　a　finished　beer　of　good　quality　loses　after　a　time　its　agreeable　flavor　and　becomes　sour；　it　can　be　easily　shown　that　the　alcoholic　yeast　deposited　in　the　bottles　or　the　casks；　although　originally　pure；　at　least　in　appearance；　is　found　to　be　contaminated　gradually　with　these　filiform　or　other　ferments。　All　this　can　be　deduced　from　the　facts　already　given；　but　some　critics　may　perhaps　declare　that　these　foreign　ferments　are　the　consequences　of　the　diseased　condition；　itself　produced　by　unknown　causes。

〃Although　this　gratuitous　hypothesis　may　be　difficult　to　uphold；　I　will　endeavor　to　corroborate　the　preceding　observations　by　a　clearer　method　of　investigation。　　This　consists　in　showing　that　the　beer　never　has　any　unpleasant　taste　in　all　cases　when　the　alcoholic　ferment　properly　so　called　is　not　mixed　with　foreign　ferments；　that　it　is　the　same　in　the　case　of　wort；　and　that　wort；　liable　to　changes　as　it　is；　can　be　preserved　unaltered　if　it　is　kept　from　those　microscopic　parasites　which　find　in　it　a　suitable　nourishment　and　a　field　for　growth。

〃The　employment　of　this　second　method　has；　moreover；　the　advantage　of　proving　with　certainty　the　proposition　that　I　advanced　at　firstnamely；　that　the　germs　of　these　organisms　are　derived　from　the　dust　of　the　atmosphere；　carried　about　and　deposited　upon　all　objects；　or　scattered　over　the　utensils　and　the　materials　used　in　a　brewery…materials　naturally　charged　with　microscopic　germs；　and　which　the　various　operations　in　the　store…rooms　and　the　malt…house　may　multiply　indefinitely。

〃Let　us　take　a　glass　flask　with　a　long　neck　of　from　two　hundred　and　fifty　to　three　hundred　cubic　centimetres　capacity；　and　place　in　it　some　wort；　with　or　without　hops；　and　then　in　the　flame　of　a　lamp　draw　out　the　neck　of　the　flask　to　a　fine　point；　afterwards　heating　the　liquid　until　the　steam　comes　out　of　the　end　of　the　neck。　It　can　then　be　allowed　to　cool　without　any　other　precautions；　but　for　additional　safety　there　can　be　introduced　into　the　little　point　a　small　wad　of　asbestos　at　the　moment　that　the　flame　is　withdrawn　from　beneath　the　flask。　　Before　thus　placing　the　asbestos　it　also　can　be　passed　through　the　flame；　as　well　as　after　it　has　been　put　into　the　end　of　the　tube。　The　air　which　then　first　re…enters　the　flask　will　thus　come　into　contact　with　the　heated　glass　and　the　heated　liquid；　so　as