the
finger. Hence it follows that the gelatine plate is acted upon by light
only on the parts corresponding to the ridges; and in these parts the
gelatine is rendered insoluble, while all the rest of the gelatine is
soluble. The gelatine plate, which is cemented to a thin plate of metal
for support, is now carefully washed with hot water, by which the
soluble part of the gelatine is dissolved away leaving the insoluble
part (corresponding to the ridges) standing up from the surface. Thus
there is produced a _facsimile_ in relief of the finger-print having
actual ridges and furrows identical in character with the ridges and
furrows of the finger-tip. If an inked roller is passed over this
relief, or if the relief is pressed lightly on an inked slab, and then
pressed on a sheet of paper, a finger-print will be produced which will
be absolutely identical with the original, even to the little white
spots which mark the orifices of the sweat glands. It will be impossible
to discover any difference between the real finger-print and the
counterfeit because, in fact, no difference exists."

"But surely the process you have described is a very difficult and
intricate one?"

"Not at all; it is very little more difficult than ordinary carbon
printing, which is practised successfully by numbers of amateurs.
Moreover, such a relief as I have described--which is practically
nothing more than an ordinary process block--could be produced by any
photo-engraver. The process that I have described is, in all essentials,
that which is used in the reproduction of pen-and-ink drawings, and any
of the hundreds of workmen who are employed in that industry could make
a relief-block of a finger-print, with which an undetectable forgery
could be executed."

"You have asserted that the counterfeit finger-print could not be
distinguished from the original. Are you prepared to furnish proof that
this is the case?"

"Yes. I am prepared to execute a counterfeit of the prisoner's
thumb-print in the presence of the Court."

"And do you say that such a counterfeit would be indistinguishable from
the original, even by the experts?"

"I do."

Anstey turned towards the judge. "Would your lordship give your
permission for a demonstration such as the witness proposes?"

"Certainly," replied the judge. "The evidence is highly material. How do
you propose that the comparison should be made?" he added, addressing
Thorndyke.

"I have brought, for the