a history of science-4-第41节

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working　microbiologist。

As　it　happened；　the　world　was　not　kept　long　in　suspense。　Almost　before　the　proposition　had　taken　shape　in　the　minds　of　the　other　leaders；　Pasteur　had　found　a　solution。　Guided　by　the　empirical　success　of　Jenner；　he；　like　many　others；　had　long　practised　inoculation　experiments；　and　on　February　9；　1880；　he　announced　to　the　French　Academy　of　Sciences　that　he　had　found　a　method　of　so　reducing　the　virulence　of　a　disease　germ　that　when　introduced　into　the　system　of　a　susceptible　animal　it　produced　only　a　mild　form　of　the　disease；　which；　however；　sufficed　to　protect　against　the　usual　virulent　form　exactly　as　vaccinia　protects　against　small…pox。　The　particular　disease　experimented　with　was　that　infectious　malady　of　poultry　known　familiarly　as　〃chicken　cholera。〃　　In　October　of　the　same　year　Pasteur　announced　the　method　by　which　this　〃attenuation　of　the　virus；〃　as　he　termed　it；　had　been　brought　aboutby　cultivation　of　the　disease　germs　in　artificial　media；　exposed　to　the　air；　and　he　did　not　hesitate　to　assert　his　belief　that　the　method　would　prove　〃susceptible　of　generalization〃that　is　to　say；　of　application　to　other　diseases　than　the　particular　one　in　question。

Within　a　few　months　he　made　good　this　prophecy；　for　in　February；　1881；　he　announced　to　the　Academy　that　with　the　aid；　as　before；　of　his　associates　MM。　　Chamberland　and　Roux；　he　had　produced　an　attenuated　virus　of　the　anthrax　microbe　by　the　use　of　which；　as　he　affirmed　with　great　confidence；　he　could　protect　sheep；　and　presumably　cattle；　against　that　fatal　malady。　　〃In　some　recent　publications；〃　said　Pasteur；　〃I　announced　the　first　case　of　the　attenuation　of　a　virus　by　experimental　methods　only。　Formed　of　a　special　microbe　of　an　extreme　minuteness；　this　virus　may　be　multiplied　by　artificial　culture　outside　the　animal　body。　These　cultures；　left　alone　without　any　possible　external　contamination；　undergo；　in　the　course　of　time；　modifications　of　their　virulency　to　a　greater　or　less　extent。　　The　oxygen　of　the　atmosphere　is　said　to　be　the　chief　cause　of　these　attenuationsthat　is；　this　lessening　of　the　facilities　of　multiplication　of　the　microbe；　for　it　is　evident　that　the　difference　of　virulence　is　in　some　way　associated　with　differences　of　development　in　the　parasitic　economy。

〃There　is　no　need　to　insist　upon　the　interesting　character　of　these　results　and　the　deductions　to　be　made　therefrom。　To　seek　to　lessen　the　virulence　by　rational　means　would　be　to　establish；　upon　an　experimental　basis；　the　hope　of　preparing　from　an　active　virus；　easily　cultivated　either　in　the　human　or　animal　body；　a　vaccine…virus　of　restrained　development　capable　of　preventing　the　fatal　effects　of　the　former。　Therefore；　we　have　applied　all　our　energies　to　investigate　the　possible　generalizing　action　of　atmospheric　oxygen　in　the　attenuation　of　virus。

〃The　anthrax　virus；　being　one　that　has　been　most　carefully　studied；　seemed　to　be　the　first　that　should　attract　our　attention。　Every　time；　however；　we　encountered　a　difficulty。　Between　the　microbe　of　chicken　cholera　and　the　microbe　of　anthrax　there　exists　an　essential　difference　which　does　not　allow　the　new　experiment　to　be　verified　by　the　old。　The　microbes　of　chicken　cholera　do　not；　in　effect；　seem　to　resolve　themselves；　in　their　culture；　into　veritable　germs。　The　latter　are　merely　cells；　or　articulations　always　ready　to　multiply　by　division；　except　when　the　particular　conditions　in　which　they　become　true　germs　are　known。

〃The　yeast　of　beer　is　a　striking　example　of　these　cellular　productions；　being　able　to　multiply　themselves　indefinitely　without　the　apparition　of　their　original　spores。　　There　exist　many　mucedines　（Mucedinae？）　of　tubular　mushrooms；　which　in　certain　conditions　of　culture　produce　a　chain　of　more　or　less　spherical　cells　called　Conidae。　　The　latter；　detached　from　their　branches；　are　able　to　reproduce　themselves　in　the　form　of　cells；　without　the　appearance；　at　least　with　a　change　in　the　conditions　of　culture；　of　the　spores　of　their　respective　mucedines。　These　vegetable　organisms　can　be　compared　to　plants　which　are　cultivated　by　slipping；　and　to　produce　which　it　is　not　necessary　to　have　the　fruits　or　the　seeds　of　the　mother　plant。

The　anthrax　bacterium；　in　its　artificial　cultivation；　behaves　very　differently。　　Its　mycelian　filaments；　if　one　may　so　describe　them；　have　been　produced　scarcely　for　twenty…four　or　forty…eight　hours　when　they　are　seen　to　transform　themselves；　those　especially　which　are　in　free　contact　with　the　air；　into　very　refringent　corpuscles；　capable　of　gradually　isolating　themselves　into　true　germs　of　slight　organization。　　Moreover；　observation　shows　that　these　germs；　formed　so　quickly　in　the　culture；　do　not　undergo；　after　exposure　for　a　time　to　atmospheric　air；　any　change　either　in　their　vitality　or　their　virulence。　I　was　able　to　present　to　the　Academy　a　tube　containing　some　spores　of　anthrax　bacteria　produced　four　years　ago；　on　March　21；　1887。　Each　year　the　germination　of　these　little　corpuscles　has　been　tried；　and　each　year　the　germination　has　been　accomplished　with　the　same　facility　and　the　same　rapidity　as　at　first。　Each　year　also　the　virulence　of　the　new　cultures　has　been　tested；　and　they　have　not　shown　any　visible　falling　off。　　Therefore；　how　can　we　experiment　with　the　action　of　the　air　upon　the　anthrax　virus　with　any　expectation　of　making　it　less　virulent？

〃The　crucial　difficulty　lies　perhaps　entirely　in　this　rapid　reproduction　of　the　bacteria　germs　which　we　have　just　related。　In　its　form　of　a　filament；　and　in　its　multiplication　by　division；　is　not　this　organism　at　all　points　comparable　with　the　microbe　of　the　chicken　cholera？

〃That　a　germ；　properly　so　called；　that　a　seed；　does　not　suffer　any　modification　on　account　of　the　air　is　easily　conceived；　but　it　is　conceivable　not　less　easily　that　if　there　should　be　any　change　it　would　occur　by　preference　in　the　case　of　a　mycelian　fragment。　It　is　thus　that　a　slip　which　may　have　been　abandoned　in　the　soil　in　contact　with　the　air　does　not　take　long　to　lose　all　vitality；　while　under　similar　conditions　a　seed　is　preserved　in　readiness　to　reproduce　the　plant。　　If　these　views　have　any　foundation；　we　are　led　to　think　that　in　order　to　prove　the　action　of　the　air　upon　the　anthrax　bacteria　it　will　be　indispensable　to　submit　to　this　action　the　mycelian　development　of　the　minute　organism　under　conditions　where　there　cannot　be　the　least　admixture　of　corpuscular　germs。　Hence　the　problem　of　submitting　the　bacteria　to　the　action　of　oxygen　comes　back　to　the　question　of　presenting　entirely　the　formation　of　spores。　The　question　being　put　in　this　way；　we　are　beginning　to　recognize　that　it　is　capable　of　being　solved。

〃We　can；　in　fact；　prevent　the　appearance　of　spores　in　the　artificial　cultures　of　the　anthrax　parasite　by　various　artifices。　At　the　lowest　temperature　at　which　this　parasite　can　be　cultivatedthat　is　to　say；　about　＋16　degrees　Centigradethe　bacterium　does　not　produce　germsat　any　rate；　for　a　very　long　time。　The　shapes　of　the　minute　microbe　at　this　lowest　limit　of　its　development　are　irregular；　in　the　form　of　balls　and　pearsin　a　word；　they　are　monstrositiesbut　they　are　without　spores。　In　the　last　regard　also　it　is　the　same　at　the　highest　temperatures　at　which　the　parasite　can　be　cultivated；　temperatures　which　vary　slightly　according　to　the　means　employed。　In　neutral　chicken　bouillon　the　bacteria　cannot　be　cultivated　above　45　degrees。　Culture；　however；　is　easy　and　abundant　at　42　to　43　degrees；　but　equally　without　any　formation　of　spores。　　Consequently　a　culture　of　mycelian　bacteria　can　be　kept　entirely　free　from　germs　while　in　contact　with　the　open　air　at　a　temperature　of　from　42　to　43　degrees　Centigrade。　　Now　appear　the　three　remarkable　results。　After　about　one　month　of　waiting　the　culture　diesthat　is　to　say；　if　put　into　a　fresh　bouillon　it　becomes　absolutely　sterile。

〃So　much　for　the　life　and　nutrition　of　this　organism。　In　respect　to　its　virulence；　it　is　an　extraordinary　fact　that　it　disappears　entirely　after　eight　days'　culture　at　42　to　43　degrees　Centigrade；　or；　at　any　rate；　the　cultures　are　innocuous　for　the　guinea…pig；　the　rabbit；　and　the　sheep；　the　three　kinds　of　animals　most　apt　to　contract　anthrax。　We　are　thus　able　to　obtain；　not　only　the　attenuation　of　the　virulence；　but　also　its　complete　suppression　by　a　simple　method　of　cultivation。　Moreover；　we　see　also　the　possibility　of　preserving　and　cultivating　the　terrible　microbe　in　an　inoffensive　state。　What　is　it　that　happens　in　these　eight　days　at　43　degrees　that　suffices　to　take　away　the　virulence　of　the　bacteria？　Let　us　remember　that　the　microbe　of　chicken　cholera　dies　in　contact　with　the　air；　in　a　period　somewhat　protracted；　it　is　true；　but　after　successive　attenuations。　　Are　we　justified　in　thinking　that　it　ought　to　be　the　same　in　regard　to　the　microbe　of　anthrax？　　This　hypothesis　is　confirmed　by　experiment。　Before　the　disappearance　of　its　virulence　the　anthrax　microbe　passes　through　various　degrees　of　attenuation；　and；　moreover；　as　is　also　the　case　with　the　microbe　of　chicken　cholera；　each　of　these　attenuated　states　of　virulence　can　be　obtained　by　cultivation。　Moreover；　since；　according　to　one　of　our　recent　Communications；　anthrax　is　not　recurrent；　each　of　our　attenuated　anthrax　microbes　is；　for　the　bette