eachwhich　is　its　rate　of　goingwill　be　performed　in　the　same　manner；
  and　you　shall　be　able　to　distinguish　no　difference　between　them；　but　let
  me　take　a　pair　of　pincers；　and　if　my　hand　is　steady　enough　to　do　it；
  let　me　just　lightly　crush　together　the　bearings　of　the　balance…wheel；
  or　force　to　a　slightly　different　angle　the　teeth　of　the　escapement　of
  one　of　them；　and　of　course　you　know　the　immediate　result　will　be　that
  the　watch；　so　treated；　from　that　moment　will　cease　to　go。　　But　what
  proportion　is　there　between　the　structural　alteration　and　the
  functional　result？　　Is　it　not　perfectly　obvious　that　the　alteration　is
  of　the　minutest　kind；　yet　that　slight　as　it　is；　it　has　produced　an
  infinite　difference　in　the　performance　of　the　functions　of　these　two
  instruments？
  Well；　now；　apply　that　to　the　present　question。　　What　is　it　that
  constitutes　and　makes　man　what　he　is？　　What　is　it　but　his　power　of
  languagethat　language　giving　him　the　means　of　recording　his
  experiencemaking　every　generation　somewhat　wiser　than　its
  predecessor；more　in　accordance　with　the　established　order　of　the
  universe？
  What　is　it　but　this　power　of　speech；　of　recording　experience；　which
  enables　men　to　be　menlooking　before　and　after　and；　in　some　dim　sense；
  understanding　the　working　of　this　wondrous　universeand　which
  distinguishes　man　from　the　whole　of　the　brute　world？　　I　say　that　this
  functional　difference　is　vast；　unfathomable；　and　truly　infinite　in　its
  consequences；　and　I　say　at　the　same　time；　that　it　may　depend　upon
  structural　differences　which　shall　be　absolutely　inappreciable　to　us
  with　our　present　means　of　investigation。　　What　is　this　very　speech　that
  we　are　talking　about？　　I　am　speaking　to　you　at　this　moment；　but　if　you
  were　to　alter；　in　the　minutest　degree；　the　proportion　of　the　nervous
  forces　now　active　in　the　two　nerves　which　supply　the　muscles　of　my
  glottis；　I　should　become　suddenly　dumb。　　The　voice　is　produced　only　so
  long　as　the　vocal　chords　are　parallel；　and　these　are　parallel　only　so
  long　as　certain　muscles　contract　with　exact　equality；　and　that　again
  depends　on　the　equality　of　action　of　those　two　nerves　I　spoke　of。　　So
  that　a　change　of　the　minutest　kind　in　the　structure　of　one　of　these
  nerves；　or　in　the　structure　of　the　part　in　which　it　originates；　or　of
  the　supply　of　blood　to　that　part；　or　of　one　of　the　muscles　to　which　it
  is　distributed；　might　render　all　of　us　dumb。　　But　a　race　of　dumb　men；
  deprived　of　all　communication　with　those　who　could　speak；　would　be
  little　indeed　removed　from　the　brutes。　　And　the　moral　and　intellectual
  difference　between　them　and　ourselves　would　be　practically　infinite；
  though　the　naturalist　should　not　be　able　to　find　a　single　shadow　of
  even　specific　structural　difference。
  But　let　me　dismiss　this　question　now；　and；　in　conclusion；　let　me　say
  that　you　may　go　away　with　it　as　my　mature　conviction；　that　Mr。　Darwin's
  work　is　the　greatest　contribution　which　has　been　made　to　biological
  science　since　the　publication　of　the　'Regne　Animal'　of　Cuvier；　and
  since　that　of　the　'History　of　Development'　of　Von　Baer。　　I　believe　that
  if　you　strip　it　of　its　theoretical　part　it　still　remains　one　of　the
  greatest　encyclopaedias　of　biological　doctrine　that　any　one　man　ever
  brought　forth；　and　I　believe　that；　if　you　take　it　as　the　embodiment　of
  an　hypothesis；　it　is　destined　to　be　the　guide　of　biological　and
  psychological　speculation　for　the　next　three　or　four　generations。
  End