committed by a woman？' was my next question； and my answer was； 'Yes；
a possibility； but it is so decidedly improbable that I may count it
out for the time being。' Accordingly； I set aside all the female
names； which cut my list down to eighteen。 Several of the applicants
had only signed the initials of their given names； and the attendant；
copying them from the slips； had done likewise； so I was obliged to
go to the registration clerk to determine this question of sex； and；
while there； I also ascertained the age of each applicant … that is；
of all but two。 The registrar could give me no information regarding
J。 Z。 Weltz； or B。 W。 Rizzi。 When I told him that one of the clerks
had copied the names for me from application slips； he informed me
that if I would go back to her I would undoubtedly find she had taken
the two last…mentioned names from the green slips used in applying
for books for hall use； as neither J。 Z。 Weltz nor B。 W。 Rizzi was a
card…holder。
〃I decided to let these two names rest a while； and to give my
attention to the others。 After careful deliberation I felt
reasonably sure your father's assassin could not fail to be a man
of mature judgment and extraordinary cunning； probably a man past
middle life … at all events； I could safely say he was over
twenty…one years of age。 Proceeding upon this assumption my list
was reduced to ten names。 But how should I further continue this
process of exclusion？ This was the question which now confronted
me。 I could think of but one way； apart from personally making the
gentlemen's acquaintance； which I did not then wish to do； and that
was to ascertain what other books they had borrowed immediately
before and after they had read 'The Sign of the Four。' This was
the course I determined to pursue。
〃If you ask me why I so persistently followed an investigation； a
successful outcome of which anyone must recognise would be little
short of miraculous； I can only say that I felt impelled to do so。
Perhaps the impulse was due to my habit of testing patiently and
thoroughly each new theory which impresses me as having any degree
of probability； and perhaps it was due to something else … Cleopatra；
perhaps； eh； Doctor？ … I don't know。 I determined； however； to
thoroughly satisfy myself regarding these ten men。 I made a careful
list； with the assistance of an attendant； of ten books taken by
each man； five taken just prior to 'The Sign of the Four；' and the
other five just following it。 I made no deductions until the list
was completed； although I began to see certain things of interest
as we worked upon it。 At length the whole hundred titles were spread
before me； and I sat down to see what I could make of them。 I
purposely reserved consideration of the books borrowed by Weltz and
Rizzi until the last； because I had been able to learn nothing of
them； and considered； therefore； that they were the most difficult
persons in the list about whom to satisfy myself。 I found the
other eight exhibited no system in their reading。 One had read
… I think I can remember the books in the order in which they were
borrowed … 'Thelma；' 'Under Two Flags；' 'David Copperfield；' 'The
Story of an African Farm；' 'A Study in Scarlet；' 'The Sign of the
Four；' 'The Prisoner of Zenda；' 'The Dolly Dialogues；' 'The Yellow
Aster；' 'The Superfluous Woman；' and 'Ideala。' This is a fair sample
of the other seven。 Not so； however； with Messrs。 Weltz and Rizzi。
The reading of these men at once impressed me as having a purpose
behind it。
〃I will read you a list of the books taken by Weltz and Rizzi； just
to see what you will make out of it：
WELTZ RIZZI
I。〃Lecons de Toxicologic；〃 1。〃Traite de Toxicologic；〃
par M。 Orifia。 par C。 P。 Galtier。
2。〃The Poisons of Asps and 2。〃The Poisons of Asps and
Other Stories；〃 by Florence Other Stories；〃 by Florence
Marryat。 Marryat。
3。〃A Practical Essay on 3。〃A Practical Essay on
Cancer；〃 by C。 T。 Johnson。 Cancer；〃 by C。 T。 Johnson。
4。〃The Sharper Detected 4。〃The Sharper Detected
and Exposed；〃 by R。 Houdin。 and Exposed；〃 by R。 Houdin。
5。〃The Sign of the Four；〃 5。〃The Sign of the Four；〃
by A。 Conan Doyle。 by A。 Conan Doyle。
6。〃Cancer； a New Method of 6。〃Legal Chemistry： A
Treatment；〃 by W。 H。 Guide to the Detection of
Broadbent。 Poisons； Examinations of
Stains； etc。； as Applied to=20
Chemical Jurisprudence。〃
From the French of A。 Naquet=20
by J。 P。 Battershall； Nat。Sc。D。
7。〃Reports of Trials for 7。〃Traite Pratique des =20
Murder by Poisoning；〃 Maladies Cancerences；〃
by G。 L。 Browne and C。 par H。 Lebert。
G。Stewart。 =20
8。〃A Practical Treatise on 8。〃A Practical Treatise on
Poisons；〃 by 0。 H。 Costill。 Poisons；〃 by 0。 H。 Costill。
9。〃Poisons； Their Effects 9。〃A Treatise on Poisons in
and Detection；〃 by Alexander Relation to Medical=20
Wynter Blyth。 Jurisprudence； Physiology；
and the Practice of Physic；〃=20
by R。 Christison；M。D。； F。R。S。E。
10。〃Poisons； Their Effects 10。〃Poisons； Their Effects
and Detection；〃 by Alexander and Detection；〃 by Alexander =20
Wynter Blyth。 Wynter Blyth。
〃There； do you wonder that the perusal of that list excited me？
Come； now； before I go any further； tell me what you make of it；
Doc；〃 and he passed it to me。
〃There seems to me to be a singular unanimity of purpose existing
between these two men；〃 I said； 〃not only as regards the
subject…matter of their reading； but in no less than six cases they
have both perused the same volume。 This never happened by chance。
Clearly； they are acquaintances； and are working together toward
some common end。 I should think it very likely； judging from their
interest in cancers and toxicology； that they were medical students。
Numbers four and five don't exactly seem to strengthen my medical
hypothesis； but they are only two out of the ten。 That's about all
I can make out of it；〃 and I returned the list to him。
〃Your views in the matter；〃 replied Maitland； 〃are precisely those
which first occurred to me； and I am not sure but I should still
hold them； had I been obliged to decide solely from the evidence I
have submitted to you。 It was clear to my mind from the first that
some common purpose actuated both Weltz and Rizzi。 With a view to
ascertaining where they lived as a preparatory step toward learning
more of them； I consulted a Boston directory； only to learn that it
contained no such names。 I was about to examine some of the
directories of neighbouring towns when it occurred to me that the
easiest way to find their places of residence would be to consult
the green slips upon which they had procured their books； and I
accordingly asked the attendant to kindly let me look at them。
While she was collecting the slips I re…examined the list of books
taken by Weltz and Rizzi； especially those which had been taken by
both men。 One thing at once struck my attention； and that was that
most of these latter were large books which would take a long time
to peruse and would require to be borrowed several times for hall
use； were they to be examined with any care。 I put this fact down
for future reference and gave my attention to the green slips； the
whole twenty of which the attendant now placed before me。 The
residence of Weltz was given as No。 15 Staniford Place； Boston；
while that of Rizzi was No。 5 Oak Street； Boston。 I was about to
walk over to Oak Street to see if Rizzi were still there when； in
returning the slips to the attendant； I noticed a peculiarity
in Weltz's 'z' which I had thought I had seen in Rizzi's signature。
I immediately compared the slips。 There was the same oddly shaped
'z' in both。 It was made like this〃 … and he handed us a slip of
paper with this z* upon it。
〃You see；〃 he continued； 〃it is so unusual a way of making the
letter that it at once attracted my attention； notwithstanding the
fact that Rizzi wrote with his left hand。 Closer examination
revealed other peculiarities； as in the r*'s； common to both hands。
Well； to make a long story short； I satisfied myself that the same
person wrote the whole twenty slips and was； moreover； ambidextrous。
This I considered as a very promising discovery； so much so； indeed；
that I gave up an engagement I had for the evening and decided to
camp right there until the Library closed。 Happily the books I had
been consulting were still on the table。 I picked out those borrowed
under the names of Weltz and Rizzi； and began a most careful
examination of them。 I had been working about two hours when I
discovered something that fairly took my breath away。 I was not
sure that I was right； but I knew that； if my microscope bore me out；
I would be able to stake my life that the murderer of John Darrow
had read that book。 I was aware； however； that even then I should
not be able to name the man who had put his mark upon the book； but
I could take oath that the record was made by the same hand that
committed the murder。
___________________________________________________________________
transcriber's note： the symbols designated z* and r* are shown as
script which is not reproducible here。
___________________________________________________________________
〃I was too excited to do more till this had been settled； so I
besought the official in charge to let me take all the books home
with me； if only for a day； explaining to him the vital importance
of my request。 He readily consented and I hastened home with the
whole lot。 You may imagine with what interest I put the page I
wished to examine under my microscope and laid beside it the pie