The　freedom　with　which　each　of　us　speaks　his　thought　in　this　presence；　belongs　in　part　to　the　assured　position　of　the　Profession　in　our　Commonwealth；　to　the　attitude　of　Science；　which　is　always　fearless；　and　to　the　genius　of　the　soil　on　which　we　stand；　from　which　Nature　withheld　the　fatal　gift　of　malaria　only　to　fill　it　with　exhalations　that　breed　the　fever　of　inquiry　in　our　blood　and　in　our　brain。　　But　mainly　we　owe　the　large　license　of　speech　we　enjoy　to　those　influences　and　privileges　common　to　us　all　as　self…governing　Americans。
  This　Republic　is　the　chosen　home　of　minorities；　of　the　less　power　in　the　presence　of　the　greater。　　It　is　a　common　error　to　speak　of　our　distinction　as　consisting　in　the　rule　of　the　majority。　　Majorities；　the　greater　material　powers；　have　always　ruled　before。　　The　history　of　most　countries　has　been　that　of　majorities；　mounted　majorities；　clad　in　iron；　armed　with　death　treading　down　the　tenfold　more　numerous　minorities。　　In　the　old　civilizations　they　root　themselves　like　oaks　in　the　soil；　men　must　live　in　their　shadow　or　cut　them　down。　　With　us　the　majority　is　only　the　flower　of　the　passing　noon；　and　the　minority　is　the　bud　which　may　open　in　the　next　morning's　sun。　We　must　be　tolerant；　for　the　thought　which　stammers　on　a　single　tongue　today　may　organize　itself　in　the　growing　consciousness　of　the　time；　and　come　back　to　us　like　the　voice　of　the　multitudinous　waves　of　the　ocean　on　the　morrow。
  Twenty…five　years　have　passed　since　one　of　your　honored　Presidents　spoke　to　this　Society　of　certain　limitations　to　the　power　of　our　Art；　now　very　generally　conceded。　　Some　were　troubled；　some　were　almost　angry；　thinking　the　Profession　might　suffer　from　such　concessions。　It　has　certainly　not　suffered　here；　if；　as　some　affirm；　it　has　lost　respect　anywhere；　it　was　probably　for　other；　and　no　doubt　sufficient　reasons。
  Since　that　time　the　civilization　of　this　planet　has　changed　hands。　Strike　out　of　existence　at　this　moment　every　person　who　was　breathing　on　that　day；　May　27；　1835；　and　every　institution　of　society；　every　art　and　every　science　would　remain　intact　and　complete　in　the　living　that　would　be　left。　　Every　idea　the　world　then　held　has　been　since　dissolved　and　recrystallized。
  We　are　repeating　the　same　process。　　Not　to　make　silver　shrines　for　our　old　divinities；　even　though　by　this　craft　we　should　have　our　wealth；　was　this　Society　organized　and　carried　on　by　the　good　men　and　true　who　went　before　us。　　Not　for　this；　but　to　melt　the　gold　out　of　the　past；　though　its　dross　should　fly　in　dust　to　all　the　winds　of　heaven；　to　save　all　our　old　treasures　of　knowledge　and　mine　deeply　for　new；　to　cultivate　that　mutual　respect　of　which　outward　courtesy　is　the　sign；　to　work　together；　to　feel　together；　to　take　counsel　together；　and　to　stand　together　for　the　truth；　now；　always；　here；　everywhere；　for　this　our　fathers　instituted；　and　we　accept；　the　offices　and　duties　of　this　time…honored　Society。
  BORDER　LINES　OF　KNOWLEDGE　IN　SOME　PROVINCES　OF　MEDICAL　SCIENCE。
  An　Introductory　Lecture　delivered　before　the　Medical　Class　of　Harvard　University；　November　6；　1861。
  ＇This　Lecture　appears　as　it　would　have　been　delivered　had　the　time　allowed　been　less　strictly；　limited。　　Passages　necessarily　omitted　have　been　restored；　and　points　briefly　touched　have　been　more　fully　considered。　　A　few　notes　have　been　added　for　the　benefit　of　that　limited　class　of　students　who　care　to　track　an　author　through　the　highways　and　by…ways　of　his　reading。　　I　owe　my　thanks　to　several　of　my　professional　brethren　who　have　communicated　with　me　on　subjects　with　which　they　are　familiar；　especially　to　Dr。　John　Dean；　for　the　opportunity　of　profiting　by　his　unpublished　labors；　and　to　Dr。　Hasket　Derby；　for　information　and　references　to　recent　authorities　relating　to　the　anatomy　and　physiology　of　the　eye。＇
  The　entrance　upon　a　new　course　of　Lectures　is　always　a　period　of　interest　to　instructors　and　pupils。　　As　the　birth　of　a　child　to　a　parent；　so　is　the　advent　of　a　new　class　to　a　teacher。　　As　the　light　of　the　untried　world　to　the　infant；　so　is　the　dawning　of　the　light　resting　over　the　unexplored　realms　of　science　to　the　student。　　In　the　name　of　the　Faculty　I　welcome　you；　Gentlemen　of　the　Medical　Class；　new…born　babes　of　science；　or　lustier　nurslings；　to　this　morning　of　your　medical　life；　and　to　the　arms　and　the　bosom　of　this　ancient　University。　　Fourteen　years　ago　I　stood　in　this　place　for　the　first　time　to　address　those　who　occupied　these　benches。　　As　I　recall　these　past　seasons　of　our　joint　labors；　I　feel　that　they　have　been　on　the　whole　prosperous；　and　not　undeserving　of　their　prosperity。
  For　it　has　been　my　privilege　to　be　associated　with　a　body　of　true　and　faithful　workers；　I　cannot　praise　them　freely　to　their　faces；　or　I　should　be　proud　to　discourse　of　the　harmonious　diligence　and　the　noble　spirit　in　which　they　have　toiled　together；　not　merely　to　teach　their　several　branches；　but　to　elevate　the　whole　standard　of　teaching。
  I　may　speak　with　less　restraint　of　those　gentlemen　who　have　aided　me　in　the　most　laborious　part　of　my　daily　duties；　the　Demonstrators；　to　whom　the　successive　classes　have　owed　so　much　of　their　instruction。　They　rise　before　me；　the　dead　and　the　living；　in　the　midst　of　the　most　grateful　recollections。　　The　fair；　manly　face　and　stately　figure　of　my　friend；　Dr。　Samuel　Parkman；　himself　fit　for　the　highest　offices　of　teaching；　yet　willing　to　be　my　faithful　assistant　in　the　time　of　need；　come　back　to　me　with　the　long　sigh　of　regret　for　his　early　loss　to　our　earthly　companionship。　　Every　year　I　speak　the　eulogy　of　Dr。　Ainsworth's　patient　toil　as　I　show　his　elaborate　preparations：　When　I　take　down　my　〃American　Cyclopaedia〃　and　borrow　instruction　from　the　learned　articles　of　Dr。　Kneeland；　I　cease　to　regret　that　his　indefatigable　and　intelligent　industry　was　turned　into　a　broader　channel。　　And　what　can　I　say　too　cordial　of　my　long　associated　companion　and　friend；　Dr。　Hodges；　whose　admirable　skill；　working　through　the　swiftest　and　surest　fingers　that　ever　held　a　scalpel　among　us；　has　delighted　class　after　class；　and　filled　our　Museum　with　monuments　which　will　convey　his　name　to　unborn　generations？
  This　day　belongs；　however；　not　to　myself　and　my　recollections；　but　to　all　of　us　who　teach　and　all　of　you　who　listen；　whether　experts　in　our　specialties　or　aliens　to　their　mysteries；　or　timid　neophytes　just　entering　the　portals　of　the　hall　of　science。　　Look　in　with　me；　then；　while　I　attempt　to　throw　some　rays　into　its　interior；　which　shall　illuminate　a　few　of　its　pillars　and　cornices；　and　show　at　the　same　time　how　many　niches　and　alcoves　remain　in　darkness。
  SCIENCE　is　the　topography　of　ignorance。　　From　a　few　elevated　points　we　triangulate　vast　spaces；　inclosing　infinite　unknown　details。　　We　cast　the　lead；　and　draw　up　a　little　sand　from　abysses　we　may　never　reach　with　our　dredges。
  The　best　part　of　our　knowledge　is　that　which　teaches　us　where　knowledge　leaves　off　and　ignorance　begins。　　Nothing　more　clearly　separates　a　vulgar　from　a　superior　mind；　than　the　confusion　in　the　first　between　the　little　that　it　truly　knows；　on　the　one　hand；　and　what　it　half　knows　and　what　it　thinks　it　knows　on　the　other。
  That　which　is　true　of　every　subject　is　especially　true　of　the　branch　of　knowledge　which　deals　with　living　beings。　　Their　existence　is　a　perpetual　death　and　reanimation。　　Their　identity　is　only　an　idea；　for　we　put　off　our　bodies　many　times　during　our　lives；　and　dress　in　new　suits　of　bones　and　muscles。
  〃Thou　art　not　thyself；　　　　　　For　thou　exist'st　on　many　a　thousand　grains　　　　　　That　issue　out　of　dust。〃
  If　it　is　true　that　we　understand　ourselves　but　imperfectly　in　health；　this　truth　is　more　signally　manifested　in　disease；　where　natural　actions　imperfectly　understood；　disturbed　in　an　obscure　way　by　half…　seen　causes；　are　creeping　and　winding　along　in　the　dark　toward　their　destined　issue；　sometimes　using　our　remedies　as　safe　stepping…stones；　occasionally；　it　may　be；　stumbling　over　them　as　obstacles。
  I　propose　in　this　lecture　to　show　you　some　points　of　contact　between　our　ignorance　and　our　knowledge　in　several　of　the　branches　upon　the　study　of　which　you　are　entering。　　I　may　teach　you　a　very　little　directly；　but　I　hope　much　more　from　the　trains　of　thought　I　shall　suggest。　　Do　not　expect　too　much　ground　to　be　covered　in　this　rapid　survey。　　Our　task　is　only　that　of　sending　out　a　few　pickets　under　the　starry　flag　of　science　to　the　edge　of　that　dark　domain　where　the　ensigns　of　the　obstinate　rebel；　Ignorance；　are　flying　undisputed。　　We　are　not　making　a　reconnoissance　in　force；　still　less　advancing　with　the　main　column。　　But　here　are　a　few　roads　along　which　we　have　to　march　together；　and　we　wish　to　see　clearly　how　far　our　lines　extend；　and　where　the　enemy's　outposts　begin。
  Before　touching　the　branches　of　knowledge　that　deal　with　organization　and　vital　functions；　let　us　glance　at　that　science　which　meets　you　at　the　threshold　of　your　study；　and　prepares　you　in　some　measure　to　deal　with　the　more　complex　problems　of　the　living　laboratory。
  CHEMISTRY。　　includes　the　art　of　separating　and　combining　the　elements　of　matter；　and　the　study　of　the　changes　produced　by　these　operations。　We　can　hardly　say　too　much　of　what　it　has　contri