whole　lot。　　You　may　imagine　with　what　interest　I　put　the　page　I
  wished　to　examine　under　my　microscope　and　laid　beside　it　the　piece
  of　glass　which；　you　will　perhaps　remember；　I　cut　from　a　window　of
  the　room　in　which　the　murder　was　committed。　　I　believe　I　have　never
  yet　explained　to　Miss　Darrow　why　I　preserved　that　bit　of　glass。
  There　were　two　reasons　for　it。　　The　house　had　been　primed　that　day
  and　there　were　two　smutches　of　paint　upon　the　glass　and　two　almost
  identical　smutches　upon　the　sill。　　One　was　a　sinuous　line；　as　if
  the　glass　had　been　struck　with　a　short　bit　of　rope；　…　or　possibly
  rubber　tubing　since　no　rope…like　texture　was　visible；　…　which　had
  previously　been　soiled　with　the　paint　from　the　sill。　　The　other　mark
  was　that　of　a　human　thumb。　　I　had　seen　at　the　World's　Fair　an　exhibit
  of　these　thumbmarks　collected　by　a　Frenchman　who　has　made　an
  exhaustive　study　of　the　subject；　and　had　learned　there　for　the　first
  time　that　no　two　thumbs　in　the　world　can　make　the　same　mark。　　I　knew；
  therefore；　that　this　slip　of　glass　would　at　any　time　tell　me　whether
  or　not　a　suspected　man　were　guilty。　　I　had　not　failed　to　get　the
  thumb…marks　of　the　men　who　painted　the　house　on　that　day；　as　well
  as　those　of　every　other　person　known　to　be　about　the　place。　　The
  marks　upon　the　glass　could　not；　by　any　possibility；　have　been　made
  by　any　of　them。　　　The　deduction　was　inevitable。　　They　were　made　by
  the　man　who　stood　by　the　window　when　the　murder　was　committed。
  〃You　will　be　surprised　when　I　tell　you　it　was　some　moments　before
  I　could　summon　up　courage　to　look　through　my　microscope　upon　the
  page　beneath　it。　　You　see；　I　had　been　seized　by　an　unaccountable
  conviction　that　I　had　at　last　found　a　real　clue　to　the　murderer；
  and　I　dreaded　lest　the　first　glance　should　show　this　to　have　been
  an　idle　delusion。　　At　length　I　looked。　　The　thumb　that　had　pressed
  the　paper　was　the　thumb　that　had　pressed　the　glass！　　There　was　not
  a　doubt　of　it。　　My　suspicions　were　confirmed。　　Everything　now
  regarding　this　book　was　of　immense　importance。　　The　page　upon　which
  the　mark　was　found　…　well；　I　think　you　would　open　your　eyes　if　I
  were　to　read　it　to　you。　　I　will　defer　this　pleasure；　however；　till
  I　see　if　my　suspicions　are　correct。　　The　thumb…mark　is　upon　page
  469　of　'Poisons；　Their　Effects　and　Detection；'　by　Alexander　Wynter
  Blyth。
  〃No　sooner　had　I　made　sure　of　my　discovery　than　I　set　out　for　No。　5
  Oak　Street；　the　address　given　by　Rizzi。　　There　was　no　such　person
  there；　nor　had　there　been　anyone　of　that　name　in　the　house　during
  the　three　years　of　the　present　tenant's　occupancy。　　I　went　to　15
  Staniford　Place　with　the　same　result。　　A　young　woman　about
  twenty…five　years　of　age　came　to　the　door。　　She　informed　me　that
  she　had　been　born　in　the　house　and　had　always　lived　there。　　She　had
  never　known　anyone　by　the　name　of　Weltz。　　This　was　just　what　I　had
  expected。　　The　man　for　whom　we　are　searching　is　shrewd　almost　beyond
  belief；　and　if　we　succeed　in　finding　him　it　will　not；　we　may　be
  assured；　be　the　result　of　any　bungling　on　his　part。
  〃I　have　now　told　you　all　I　have　learned；　or　rather　all　that　is
  sufficiently　definite　to　communicate　…　it　is　not　much；　yet　it　is　a
  clue　and　may　serve　to　give　our　hope　a　new　lease　of　life。　　What　do
  you　think　of　it；　Miss　Darrow？〃
  〃I　think　what　you　have　learned；〃　Gwen　replied；　〃will　be　of　the
  utmost　importance。　　You　have　now　something　definite　to　guide　you。
  I　am　most　fortunate　in　having　the　services　of　such　a　detective；
  …　indeed；　I　am　at　a　loss　to　know　how　to　thank　you　for　all　you　have
  done；　…　for　all　you　are　doing；　I　…　〃
  〃My　dear　Miss　Darrow；〃　Maitland　interrupted；　〃I　need　no　thanks。　　Be
  assured　I　am　selfish　in　all　I　do。　　It　is　a　pleasure　to　me；　therefore
  I　do　it。　　You　see　I　deserve　no　credit。　　If　I　am　able　to　free　you
  from　the　danger　of　sacrificing　yourself；　I　shall　be　more　than
  repaid。〃
  Gwen　made　no　reply；　but　I；　sitting　as　I　did　close　beside　her；　saw
  the　moisture　gather　between　her　drooping　lids。　　Maitland　took　his
  leave　almost　immediately；　having；　he　said；　a　long　evening's　work
  before　him；　while　Gwen；　Alice；　and　I　discussed　the　news　he　had
  brought　us；　until　far　into　the　night。　　I　did　not　see　him　the　next
  day；　which　was　Tuesday；　and　I　believe　not　on　Wednesday。　　It　was
  Thursday　afternoon；　if　I　do　not　mistake；　that　he　sent　me　a　note
  asking　me　to　call　on　him　at　his　office。　　I　went　at　once；　thinking
  it　might　be　something　very　important。　　I　found　him　alone　and
  waiting　for　me。
  〃I　wanted；〃　he　began　as　soon　as　I　was　seated；　〃to　talk　this　matter
  over　with　you。　　You　see　the　great　difficulty　which　besets　me　in　this
  case　is　that　nearly　all　our　evidence；　while　it　is　of　a　nature　to
  enable　us　to　convict　our　man　once　we　have　him；　is　yet　of　almost　no
  assistance　to　us　in　finding　him。　　　What　do　we　know　of　him　up　to　date；
  or　at　least　of　what　do　we　feel　reasonably　assured？　　Let　us　see。
  John　Darrow　was　poisoned　in　some　mysterious　way　by　a　man　who　was
  stationed　just　outside　the　partly　opened　window。　　The　weapon；　or
  whatever　was　used　as　such；　was　taken　away　by　the　murderer。　　Nothing
  in　the　nature　of　a　projectile　could　have　been　employed；　since　the
  wound　was　upon　a　part　of　the　victim's　throat　known　to　have　been
  turned　away　from　the　window　and　to　have　been　completely　shielded
  upon　that　side　by　the　high　and　massive　back　of　the　chair　in　which
  the　victim　sat。
  〃He　was　fully　eight　feet　from　the　casement；　so　that　the　assassin
  could　not　have　reached　in　and　struck　him。　　　There　were　no　footprints
  by　the　window；　as　the　assassin　had　strapped　small　boards　upon　his
  feet。　　It　is　most　likely；　therefore；　that　he　has　some　peculiarity
  about　his　feet　which　he　thought　best　to　conceal。　　He　is　about　five
  feet　five　inches　tall；　weighs　about　one　hundred　and　thirty…five
  pounds；　and　steps　three　or　four　inches　longer　when　the　right　foot
  is　thrown　forward　than　he　does　when　the　left　foot　leads。　　We　have　a
  cast　of　the　assassin's　hand　showing　unmistakable　evidence　of　the
  habit　of　biting　the　nails；　with　the　exception　of　that　of　the　little
  finger；　which　nail；　by　the　way；　is　abnormally　long；　and　could　only
  have　been　spared　for　some　special　reason。　　The　murderer　is　most
  likely　a　foreigner。　　His　handwriting　would　indicate　this　even　if　we
  did　not　know；　from　the　books　he　read；　how　conversant　he　is　with　at
  least　one　foreign　tongue。　　Again；　he　has　some　decided　interest　in
  the　subject　of　cancers　and；　perhaps；　some　interest　in　legerdemain；
  if　we　may　judge　from　his　perusal　of　Robert　Houdin's　book。
  〃There　are　one　or　two　other　things　I　have　learned；　but　this；　so　far
  as　any　present　effect　is　concerned；　is　about　all　we　know；　and　it
  doesn't　seem　to　make　the　conduct　of　our　search　a　very　easy　matter。
  We　have　clearly　to　deal　with　a　man　who　is　possessed　not　merely　of
  low　criminal　cunning；　but；　I　have　reason　to　believe；　with　one　who
  has　education　and　culture；　and；　if　anything　can　be　judged　from
  handwriting；　rare　strength　of　character　as　well。　　If　we　could　only
  find　some　motive！　　No　one　but　a　maniac　would　do　such　a　deed　without
  a　motive；　yet　we　can't　find　one。　　A　maniac！　　By　Jove！　　I　hadn't
  thought　of　that。　　What　do　you　think　of　the　idea？　　'Though　this　be
  madness；　yet　there　is　method　in't；'　eh？〃
  I　told　him　that　the　maniac　theory　did　not　appeal　to　me　very　strongly。
  〃Madness；　to　be　sure；　is　often　exceedingly　cunning；〃　I　said；　〃but
  it　is　hardly　capable　of　such　sustained　masterfulness　as　our　criminal
  has　evinced。〃
  〃Look　here；　Doc；〃　Maitland　said；　breaking　out　suddenly；　〃I've　an
  idea。　　Might　not　this　fellow's　interest　in　cancers　be　due　to　his
  having　one　himself？　　Suppose　you　make　a　canvass　of　the　specialists
  on　cancer　in　Boston　and　vicinity；　and　see　if　any　of　them　remember
  being　consulted　by　a　patient　answering　the　description　with　which　I
  will　provide　you。　　In　addition　to　this　I　will　insert　an　ad　in　the
  papers　calling　attention　to　a　new　method　for　the　cure　of　cancer；
  and　asking　all　interested　to　call　at　your　office　for　further
  particulars。　　The　plan　does　not　promise　much；　still　it　may　bring
  him。　　　What　do　you　say？〃
  I　expressed　my　willingness　to　do　all　in　my　power　to　aid　him；　and　he
  left　me。　　The　next　morning's　papers　contained　the　advertisement　and
  I　had　several　calls　in　answer　to　it。　　These　would　have　caused　me
  much　inconvenience　had　I　not　explained　the　whole　ruse　in　confidence
  to　a　medical　friend　who　made　a　specialty　of　the　treatment　of　cancers；
  and　persuaded　him　to　come　to　my　office　during　the　hours　specified
  in　the　advertisement。　　When　a　patient　would　call　I　would　satisfy
  myself　that　it　was　neither　the　person　we　were　searching　for；　nor
  anyone　sent　by　him　to　make　inquiries；　and　then　turn　him　over　to　my
  colleague；　Dr。　Rhodes。　　It　would　never　have　occurred　to　me　to
  interest　myself　in　any　patient　who　did　not　answer　the　description
  given　me　by　Maitland；　had　he　not　especially　cautioned　me　in　this
  regard。
  〃We　have；〃　he　said；　〃to　deal　with　a　man　possessed　of　ability　of　no
  common　order。　　We　have　already　seen　that　he　never　runs　a　risk；
  however　slight；　which　he　can　avoid。　　It　is　more　than　likely；
  therefore；　if　our　advertisement　meets　his　eye　and　interests　him；　he
  will　inquire　into　it　through　some　second　party。　　Again；　we　are　by
  no　means　certain　that　his　interest　in　cancers　is　a　purely　p