othing；　etc。；　all　gave　support　to　the　view　that　the　actual　cause　was　something　alive；　a　contagium　vivum。　It　was　really　a　very　old　view；　the　germs　of　which　may　be　found　in　the　Fathers；　but　which　was　first　clearly　expressedso　far　as　I　knowby　Fracastorius；　the　Veronese　physician；　in　the　sixteenth　century；　who　spoke　of　the　seeds　of　contagion　passing　from　one　person　to　another；＇12＇　and　he　first　drew　a　parallel　between　the　processes　of　contagion　and　the　fermentation　of　wine。　This　was　more　than　one　hundred　years　before　Kircher；　Leeuwenhoek　and　others　began　to　use　the　microscope　and　to　see　animalcula；；　etc。；　in　water；　and　so　give　a　basis　for　the　〃infinitely　little〃　view　of　the　nature　of　disease　germs。　And　it　was　a　study　of　the　processes　of　fermentation　that　led　Pasteur　to　the　sure　ground　on　which　we　now　stand。
  ＇12＇　Varro；　in　De　Re　Rustica；　Bk。　I；　12　（circa　40　B。C。）；　speaks　of　minute　organisms　which　the　eye　cannot　see　and　which　enter　the　body　and　cause　disease。
  Out　of　these　researches　arose　a　famous　battle　which　kept　Pasteur　hard　at　work　for　four　or　five　yearsthe　struggle　over　spontaneous　generation。　It　was　an　old　warfare；　but　the　microscope　had　revealed　a　new　world；　and　the　experiments　on　fermentation　had　lent　great　weight　to　the　omne　vivum　ex　ovo　doctrine。　　The　famous　Italians；　Redi　and　Spallanzani；　had　led　the　way　in　their　experiments；　and　the　latter　had　reached　the　conclusion　that　there　is　no　vegetable　and　no　animal　that　has　not　its　own　germ。　But　heterogenesis　became　the　burning　question；　and　Pouchet　in　France；　and　Bastian　in　England；　led　the　opposition　to　Pasteur。　　The　many　famous　experiments　carried　conviction　to　the　minds　of　scientific　men；　and　destroyed　forever　the　old　belief　in　spontaneous　generation。　All　along；　the　analogy　between　disease　and　fermentation　must　have　been　in　Pasteur's　mind；　and　then　came　the　suggestion；　〃What　would　be　most　desirable　is　to　push　those　studies　far　enough　to　prepare　the　road　for　a　serious　research　into　the　origin　of　various　diseases。〃　If　the　changes　in　lactic；　alcoholic　and　butyric　fermentations　are　due　to　minute　living　organisms；　why　should　not　the　same　tiny　creatures　make　the　changes　which　occur　in　the　body　in　the　putrid　and　suppurative　diseases？　With　an　accurate　training　as　a　chemist；　having　been　diverted　in　his　studies　upon　fermentation　into　the　realm　of　biology；　and　nourishing　a　strong　conviction　of　the　identity　between　putrefactive　changes　of　the　body　and　fermentation；　Pasteur　was　well　prepared　to　undertake　investigations　which　had　hitherto　been　confined　to　physicians　alone。
  So　impressed　was　he　with　the　analogy　between　fermentation　and　the　infectious　diseases　that；　in　1863；　he　assured　the　French　Emperor　of　his　ambition　〃to　arrive　at　the　knowledge　of　the　causes　of　putrid　and　contagious　diseases。〃　After　a　study　upon　the　diseases　of　wines；　which　has　had　most　important　practical　bearings；　an　opportunity　arose　which　changed　the　whole　course　of　his　career；　and　profoundly　influenced　the　development　of　medical　science。　　A　disease　of　the　silkworm　had；　for　some　years；　ruined　one　of　the　most　important　industries　in　France；　and　in　1865　the　Government　asked　Pasteur　to　give　up　his　laboratory　work　and　teaching；　and　to　devote　his　whole　energies　to　the　task　of　investigating　it。　The　story　of　the　brilliant　success　which　followed　years　of　application　to　the　problem　will　be　read　with　deep　interest　by　every　student　of　science。　It　was　the　first　of　his　victories　in　the　application　of　the　experimental　methods　of　a　trained　chemist　to　the　problems　of　biology；　and　it　placed　his　name　high　in　the　group　of　the　most　illustrious　benefactors　of　practical　industries。
  In　a　series　of　studies　on　the　diseases　of　beer；　and　on　the　mode　of　production　of　vinegar；　he　became　more　and　more　convinced　that　these　studies　on　fermentation　had　given　him　the　key　to　the　nature　of　the　infectious　diseases。　It　is　a　remarkable　fact　that　the　distinguished　English　philosopher　of　the　seventeenth　century；　the　man　who　more　than　anyone　else　of　his　century　appreciated　the　importance　of　the　experimental　method；　Robert　Boyle；　had　said　that　he　who　could　discover　the　nature　of　ferments　and　fermentation；　would　be　more　capable　than　anyone　else　of　explaining　the　nature　of　certain　diseases。
  In　1876　there　appeared　in　Cohn's　〃Beitrage　zur　Morphologie　der　Pflanzen〃　（II；　277…310）；　a　paper　on　the　〃AEtiology　of　Anthrax〃　by　a　German　district　physician　in　Wollstein；　Robert　Koch；　which　is　memorable　in　our　literature　as　the　starting　point　of　a　new　method　of　research　into　the　causation　of　infectious　diseases。　Koch　demonstrated　the　constant　presence　of　germs　in　the　blood　of　animals　dying　from　the　disease。　　Years　before；　those　organisms　had　been　seen　by　Pollender　and　Davaine；　but　the　epoch…making　advance　of　Koch　was　to　grow　those　organisms　in　a　pure　culture　outside　the　body；　and　to　produce　the　disease　artificially　by　inoculating　animals　with　the　cultures　Koch　is　really　our　medical　Galileo；　who；　by　means　of　a　new　technique；pure　cultures　and　isolated　staining；　introduced　us　to　a　new　world。　　In　1878；　followed　his　study　on　the　〃AEtiology　of　Wound　Infections；〃　in　which　he　was　able　to　demonstrate　conclusively　the　association　of　micro…organisms　with　the　disease。　Upon　those　two　memorable　researches　made　by　a　country　doctor　rests　the　modern　science　of　bacteriology。
  The　next　great　advance　was　the　discovery　by　Pasteur　of　the　possibility　of　so　attenuating；　or　weakening；　the　poison　that　an　animal　inoculated　had　a　slight　attack；　recovered　and　was　then　protected　against　the　disease。　More　than　eighty　years　had　passed　since　on　May　14；　1796；　Jenner　had　vaccinated　a　child　with　cowpox　and　proved　that　a　slight　attack　of　one　disease　protected　the　body　from　a　disease　of　an　allied　nature。　An　occasion　equally　famous　in　the　history　of　medicine　was　a　day　in　1881；　when　Pasteur　determined　that　a　flock　of　sheep　vaccinated　with　the　attenuated　virus　of　anthrax　remained　well；　when　every　one　of　the　unvaccinated　infected　from　the　same　material　had　died。　Meanwhile；　from　Pasteur's　researches　on　fermentation　and　spontaneous　generation；　a　transformation　had　been　initiated　in　the　practice　of　surgery；　which；　it　is　not　too　much　to　say；　has　proved　one　of　the　greatest　boons　ever　conferred　upon　humanity。　It　had　long　been　recognized　that；　now　and　again；　a　wound　healed　without　the　formation　of　pus；　that　is；　without　suppuration；　but　both　spontaneous　and　operative　wounds　were　almost　invariably　associated　with　that　process；　and；　moreover；　they　frequently　became　putrid；　as　it　was　then　called；infected；　as　we　should　say；the　general　system　became　involved　and　the　patient　died　of　blood　poisoning。　So　common　was　this；　particularly　in　old；　ill…equipped　hospitals；　that　many　surgeons　feared　to　operate；　and　the　general　mortality　in　all　surgical　cases　was　very　high。　Believing　that　it　was　from　outside　that　the　germs　came　which　caused　the　decomposition　of　wounds；　just　as　from　the　atmosphere　the　sugar　solution　got　the　germs　which　caused　the　fermentation；　a　young　surgeon　in　Glasgow；　Joseph　Lister；　applied　the　principles　of　Pasteur's　experiments　to　their　treatment。　From　Lister's　original　paper＇*＇　I　quote　the　following：　〃Turning　now　to　the　question　how　the　atmosphere　produces　decomposition　of　organic　substances；　we　find　that　a　flood　of　light　has　been　thrown　upon　this　most　important　subject　by　the　philosophic　researches　of　M。　Pasteur；　who　has　demonstrated　by　thoroughly　convincing　evidence　that　it　is　not　to　its　oxygen　or　to　any　of　its　gaseous　constituents　that　the　air　owes　this　property；　but　to　minute　particles　suspended　in　it；　which　are　the　germs　of　various　low　forms　of　life；　long　since　revealed　by　the　microscope；　and　regarded　as　merely　accidental　concomitants　of　putrescence；　but　now　shown　by　Pasteur　to　be　its　essential　cause；　resolving　the　complex　organic　compounds　into　substances　of　simpler　chemical　constitution；　just　as　the　yeast…plant　converts　sugar　into　alcohol　and　carbonic　acid。〃　From　these　beginnings　modern　surgery　took　its　rise；　and　the　whole　subject　of　wound　infection；　not　only　in　relation　to　surgical　diseases；　but　to　child…bed　fever；　forms　now　one　of　the　most　brilliant　chapters　in　the　history　of　preventive　medicine。
  ＇*＇　Lancet；　March　16；　1867。　　＇Cf。　Camac：　　Epoch…making　Contributions；　etc。；　1909；　p。　7。Ed。＇
  With　the　new　technique　and　experimental　methods；　the　discovery　of　the　specific　germs　of　many　of　the　more　important　acute　infections　followed　each　other　with　bewildering　rapidity：　　typhoid　fever；　diphtheria；　cholera；　tetanus；　plague；　pneumonia；　gonorrhoea　and；　most　important　of　all；　tuberculosis。　　It　is　not　too　much　to　say　that　the　demonstration　by　Koch　of　the　〃bacillus　tuberculosis〃　（1882）　is；　in　its　far…reaching　results；　one　of　the　most　momentous　discoveries　ever　made。
  Of　almost　equal　value　have　been　the　researches　upon　the　protozoan　forms　of　animal　life；　as　causes　of　disease。　As　early　as　1873；　spirilla　were　demonstrated　in　relapsing　fever。　Laveran　proved　the　association　of　haematozoa　with　malaria　in　1880。　In　the　same　year；　Griffith　Evans　discovered　trypanosomes　in　a　disease　of　horses　and　cattle　in　India；　and　the　same　type　of　parasite　was　found　in　the　sleeping　sickness。　Amoebae　were　demonstrated　in　one　form　of　dysentery；　and　in　other　tropical　diseases　protozoa　were　discovered；　so　that　we　were　really　prepared　for