The Classic Mystery Collection - Arthur Conan Doyle [5801]
"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.
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transcriber's note: the symbols designated z* and r* are shown as script which is not reproducible here.
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"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 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.