"What did you do then?"
"I asked Mrs. Hornby to lend me the 'Thumbograph' so that I might show it to the Chief of the Finger-print Department, to which she consented. I had not intended to tell her of my discovery, but, as I was leaving, Mr. Hornby arrived home, and when he heard of what had taken place, he asked me why I wanted the book, and then I told him. He was greatly astonished and horrified, and wished me to return the book at once. He proposed to let the whole matter drop and take the loss of the diamonds on himself; but I pointed out that this was impossible as it would practically amount to compounding a felony. Seeing that Mrs. Hornby was so distressed at the idea of her book being used in evidence against her nephew, I promised her that I would return it to her if I could obtain a thumb-print in any other way.
"I then took the 'Thumbograph' to Scotland Yard and showed it to Mr. Singleton, who agreed that the print of the left thumb of Reuben Hornby was in every respect identical with the thumb-print on the paper found in the safe. On this I applied for a warrant for the arrest of Reuben Hornby, which I executed on the following morning. I told the prisoner what I had promised Mrs. Hornby, and he then offered to allow me to take a print of his left thumb so that his aunt's book should not have to be used in evidence."
"How is it, then," asked the judge, "that it has been put in evidence?"
"It has been put in by the defence, my lord," said Sir Hector Trumpler.
"I see," said the judge. "'A hair of the dog that bit him.' The 'Thumbograph' is to be applied as a remedy on the principle that similia similibus curantur. Well?"
"When I arrested him, I administered the usual caution, and the prisoner then said, 'I am innocent. I know nothing about the robbery.'"
The counsel for the prosecution sat down, and Anstey rose to cross-examine.
"You have told us," said he, in his clear musical voice, "that you found at the bottom of the safe two rather large drops of a dark fluid which you considered to be blood. Now, what led you to believe that fluid to be blood?"
"I took some of the fluid up on a piece of white paper, and it had the appearance and colour of blood."