k which is due not to any peculiarity of the
thumb, but to a peculiarity of the paper. On the theory of coincidences
it is necessary to suppose that each piece of paper had a loose fibre of
exactly identical shape and size and that this fibre came, by accident,
in contact with the thumb at exactly the same spot. But such a
supposition would be more opposed to probabilities even than the
supposition that two exactly similar thumb-prints should have been made
by different persons. And then there is the further fact that the paper
found in the safe had no loose fibre to account for the mark."

"What is your explanation of the presence of defibrinated blood in the
safe?"

"It was probably used by the forger in making the thumb-print, for which
purpose fresh blood would be less suitable by reason of its clotting. He
would probably have carried a small quantity in a bottle, together with
the pocket slab and roller invented by Mr. Galton. It would thus be
possible for him to put a drop on the slab, roll it out into a thin film
and take a clean impression with his stamp. It must be remembered that
these precautions were quite necessary, since he had to make a
recognisable print at the first attempt. A failure and a second trial
would have destroyed the accidental appearance, and might have aroused
suspicion."

"You have made some enlarged photographs of the thumb-prints, have you
not?"

"Yes. I have here two enlarged photographs, one of the 'Thumbograph'
print and one of the red thumb-print. They both show the white mark very
clearly and will assist comparison of the originals, in which the mark
is plainly visible through a lens."

He handed the two photographs up to the judge, together with the
'Thumbograph,' the memorandum slip, and a powerful doublet lens with
which to examine them.

The judge inspected the two original documents with the aid of the lens
and compared them with the photographs, nodding approvingly as he made
out the points of agreement. Then he passed them on to the jury and made
an entry in his notes.

While this was going on my attention was attracted by Walter Hornby. An
expression of terror and wild despair had settled on his face, which was
ghastly in its pallor and bedewed with sweat. He looked furtively at
Thorndyke and, as I noted the murderous hate in his eyes, I recalled our
midnight adventure in John Street and the mysterious cigar.

Suddenly he rose to his feet, wiping his brow and ste