the　louse；　the　bedbug；　the　house　fly；　the　mosquito；　the　tick；　have　all　within　a　few　years　taken　their　places　as　important　transmitters　of　disease。　The　fly　population　may　be　taken　as　the　sanitary　index　of　a　place。　The　discovery；　too；　that　insects　are　porters　of　disease　has　led　to　a　great　extension　of　our　knowledge　of　their　life　history。　Early　in　the　nineties；　when　Dr。　Thayer　and　I　were　busy　with　the　study　of　malaria　in　Baltimore；　we　began　experiments　on　the　possible　transmission　of　the　parasites；　and　a　tramp；　who　had　been　a　medical　student；　offered　himself　as　a　subject。　Before　we　began；　Dr。　Thayer　sought　information　as　to　the　varieties　of　mosquitoes　known　in　America；　but　sought　in　vain：　　there　had　at　that　time　been　no　systematic　study。　　The　fundamental　study　which　set　us　on　the　track　was　a　demonstration　by　Patrick　Manson；＇3＇　in　1879；　of　the　association　of　filarian　disease　with　the　mosquito。　Many　observations　had　already　been　made；　and　were　made　subsequently；　on　the　importance　of　insects　as　intermediary　hosts　in　the　animal　parasites；　but　the　first　really　great　scientific　demonstration　of　a　widespread　infection　through　insects　was　by　Theobald　Smith；　now　of　Harvard　University；　in　1889；　in　a　study　of　Texas　fever　of　cattle。＇4＇　I　well　remember　the　deep　impression　made　upon　me　by　his　original　communication；　which　in　completeness；　in　accuracy　of　detail；　in　Harveian　precision　and　in　practical　results　remains　one　of　the　most　brilliant　pieces　of　experimental　work　ever　undertaken。　It　is　difficult　to　draw　comparisons　in　pathology；　but　I　think；　if　a　census　were　taken　among　the　world's　workers　on　disease；　the　judgment　to　be　based　on　the　damage　to　health　and　direct　mortality；　the　votes　would　be　given　to　malaria　as　the　greatest　single　destroyer　of　the　human　race。　　Cholera　kills　its　thousands；　plague；　in　its　bad　years；　its　hundreds　of　thousands；　yellow　fever；　hookworm　disease；　pneumonia；　tuberculosis；　are　all　terribly　destructive；　some　only　in　the　tropics；　others　in　more　temperate　regions：　but　malaria　is　today；　as　it　ever　was；　a　disease　to　which　the　word　pandemic　is　specially　applicable。　　In　this　country　and　in　Europe；　its　ravages　have　lessened　enormously　during　the　past　century；　but　in　the　tropics　it　is　everywhere　and　always　present；　the　greatest　single　foe　of　the　white　man；　and　at　times　and　places　it　assumes　the　proportions　of　a　terrible　epidemic。　　In　one　district　of　India　alone；　during　the　last　four　months　of　1908；　one　quarter　of　the　total　population　suffered　from　the　disease　and　there　were　400；000　deaths　practically　all　from　malaria。　　Today；　the　control　of　this　terrible　scourge　is　in　our　hands；　and；　as　I　shall　tell　you　in　a　few　minutes；　largely　because　of　this　control；　the　Panama　Canal　is　being　built。　No　disease　illustrates　better　the　progressive　evolution　of　scientific　medicine。　　It　is　one　of　the　oldest　of　known　diseases。　The　Greeks　and　Graeco…Romans　knew　it　well。　　It　seems　highly　probable；　as　brought　out　by　the　studies　of　W。H。S。　Jones　of　Cambridge；　that；　in　part　at　least；　the　physical　degeneration　in　Greece　and　Rome　may　have　been　due　to　the　great　increase　of　this　disease。　Its　clinical　manifestations　were　well　known　and　admirably　described　by　the　older　writers。　　In　the　seventeenth　century；　as　I　have　already　told　you；　the　remarkable　discovery　was　made　that　the　bark　of　the　cinchona　tree　was　a　specific。　Between　the　date　of　the　Countess's　recovery　in　Lima　and　the　year　1880　a　colossal　literature　on　the　disease　had　accumulated。　Literally　thousands　of　workers　had　studied　the　various　aspects　of　its　many　problems；　the　literature　of　this　country；　particularly　of　the　Southern　States；　in　the　first　half　of　the　last　century　may　be　said　to　be　predominantly　malarial。　Ordinary　observation　carried　on　for　long　centuries　had　done　as　much　as　was　possible。　　In　1880；　a　young　French　army　surgeon；　Laveran　by　name；　working　in　Algiers；　found　in　the　microscopic　examination　of　the　blood　that　there　were　little　bodies　in　the　red　blood　corpuscles；　amoeboid　in　character；　which　he　believed　to　be　the　germs　of　the　disease。　　Very　little　attention　at　first　was　paid　to　his　work；　and　it　is　not　surprising。　It　was　the　old　story　of　〃Wolf；　wolf〃；　there　had　been　so　many　supposed　〃germs〃　that　the　profession　had　become　suspicious。　Several　years　elapsed　before　Surgeon…General　Sternberg　called　the　attention　of　the　English…speaking　world　to　Laveran's　work：　it　was　taken　up　actively　in　Italy；　and　in　America　by　Councilman；　Abbott　and　by　others　among　us　in　Baltimore。　　The　result　of　these　widespread　observations　was　the　confirmation　in　every　respect　of　Laveran's　discovery　of　the　association　with　malaria　of　a　protozoan　parasite。　This　was　step　number　three。　　Clinical　observation；　empirical　discovery　of　the　cure；　determination　of　the　presence　of　a　parasite。　Two　other　steps　followed　rapidly。　　Another　army　surgeon；　Ronald　Ross；　working　in　India；　influenced　by　the　work　of　Manson；　proved　that　the　disease　was　transmitted　by　certain　varieties　of　mosquitoes。　Experiments　came　in　to　support　the　studies　in　etiology；　two　of　those　may　be　quoted。　　Mosquitoes　which　had　bitten　malarial　patients　in　Italy　were　sent　to　London　and　there　allowed　to　bite　Mr。　Manson；　son　of　Dr。　Manson。　　This　gentleman　had　not　lived　out　of　England；　where　there　is　now　no　acute　malaria。　He　had　been　a　perfectly　healthy；　strong　man。　　In　a　few　days　following　the　bites　of　the　infected　mosquitoes；　he　had　a　typical　attack　of　malarial　fever。
  ＇3＇　Journal　Linnaean　Society；　London；　1879；　XIV；　304…311。
  ＇4＇　Medical　News；　Philadelphia；　1889；　LV；　689…693；　and　monograph　with　Kilborne；　Washington；　1893。
  The　other　experiment；　though　of　a　different　character；　is　quite　as　convincing。　In　certain　regions　about　Rome；　in　the　Campania；　malaria　is　so　prevalent　that；　in　the　autumn；　almost　everyone　in　the　district　is　attacked；　particularly　if　he　is　a　newcomer。　　Dr。　Sambon　and　a　friend　lived　in　this　district　from　June　1　to　September　1；　1900。　The　test　was　whether　they　could　live　in　this　exceedingly　dangerous　climate　for　the　three　months　without　catching　malaria；　if　they　used　stringent　precautions　against　the　bites　of　mosquitoes。　For　this　purpose　the　hut　in　which　they　lived　was　thoroughly　wired；　and　they　slept　under　netting。　　Both　of　these　gentlemen；　at　the　end　of　the　period；　had　escaped　the　disease。
  Then　came　the　fifth　and　final　triumphthe　prevention　of　the　disease。　The　anti…malarial　crusade　which　has　been　preached　by　Sir　Ronald　Ross　and　has　been　carried　out　successfully　on　a　wholesale　scale　in　Italy　and　in　parts　of　India　and　Africa；　has　reduced　enormously　the　incidence　of　the　disease。　　Professor　Celli　of　Rome；　in　his　lecture　room；　has　an　interesting　chart　which　shows　the　reduction　in　the　mortality　from　malaria　in　Italy　since　the　preventive　measures　have　been　adoptedthe　deaths　have　fallen　from　above　28；000　in　1888　to　below　2000　in　1910。　There　is　needed　a　stirring　campaign　against　the　disease　throughout　the　Southern　States　of　this　country。
  The　story　of　yellow　fever　illustrates　one　of　the　greatest　practical　triumphs　of　scientific　medicine；　indeed；　in　view　of　its　far…reaching　commercial　consequences；　it　may　range　as　one　of　the　first　achievements　of　the　race。　　Ever　since　the　discovery　of　America；　the　disease　has　been　one　of　its　great　scourges；　permanently　endemic　in　the　Spanish　Main；　often　extending　to　the　Southern　States；　occasionally　into　the　North；　and　not　infrequently　it　has　crossed　the　Atlantic。　　The　records　of　the　British　Army　in　the　West　Indies　show　an　appalling　death　rate；　chiefly　from　this　disease。　At　Jamaica；　for　the　twenty　years　ending　in　1836；　the　average　mortality　was　101　per　thousand；　and　in　certain　instances　as　high　as　178。　One　of　the　most　dreaded　of　all　infections；　the　periods　of　epidemics　in　the　Southern　States　have　been　the　occasions　of　a　widespread　panic　with　complete　paralysis　of　commerce。　　How　appalling　the　mortality　is　may　be　judged　from　the　outbreak　in　Philadelphia　in　1793；　when　ten　thousand　people　died　in　three　months。＇5＇　The　epidemics　in　Spain　in　the　early　part　of　the　nineteenth　century　were　of　great　severity。　A　glance　through　La　Roche's　great　book＇6＇　on　the　subject　soon　gives　one　an　idea　of　the　enormous　importance　of　the　disease　in　the　history　of　the　Southern　States。　　Havana；　ever　since　its　foundation；　had　been　a　hotbed　of　yellow　fever。　　The　best　minds　of　the　profession　had　been　attracted　to　a　solution　of　the　problem；　but　all　in　vain。　Commission　after　commission　had　been　appointed；　with　negative　results；　various　organisms　had　been　described　as　the　cause；　and　there　were　sad　illustrations　of　the　tragedy　associated　with　investigations　undertaken　without　proper　training　or　proper　technique。　　By　the　year　1900；　not　only　had　the　ground　been　cleared；　but　the　work　on　insect…borne　disease　by　Manson　and　by　Ross　had　given　observers　an　important　clue。　It　had　repeatedly　been　suggested　that　some　relation　existed　between　the　bites　of　mosquitoes　and　the　tropical　fevers；　particularly　by　that　remarkable　student；　Nott　of　Mobile；　and　the　French　physician；　Beauperthuy。　　But　the　first　to　announce　clearly　the　mosquito　theory　of　the　disease　was　Carlos　Finlay　of　Havana。　　Early　in　the　spring　of　1900；　during　the　occupation　of　Cuba　by　the　United　States；　a　commission　appointed　by　Surgeon…General　Sternberg　（himself　one　of　the　most　energetic　students　of　the　disease）　under