"My object was to ascertain whether fingers wet with fresh blood would yield distinct and characteristic prints. I made a great number of trials, and as a result found that it is extremely difficult to obtain a clear print when the finger is wetted with fresh blood. The usual result is a mere red blot showing no ridge pattern at all, owing to the blood filling the furrows between the ridges. But if the blood is allowed to dry almost completely on the finger, a very clear print is obtained."
"Is it possible to recognise a print that has been made by a nearly dry finger?"
"Yes; quite easily. The half-dried blood is nearly solid and adheres to the paper in a different way from the liquid, and it shows minute details, such as the mouths of the sweat glands, which are always obliterated by the liquid."
"Look carefully at this paper, which was found in the safe, and tell me what you see."
The witness took the paper and examined it attentively, first with the naked eye and then with a pocket-lens.
"I see," said he, "two blood-marks and a print, apparently of a thumb. Of the two marks, one is a blot, smeared slightly by a finger or thumb; the other is a smear only. Both were evidently produced with quite liquid blood. The thumb-print was also made with liquid blood."
"You are quite sure that the thumb-print was made with liquid blood?"
"Quite sure."
"Is there anything unusual about the thumb-print?"
"Yes. It is extraordinarily clear and distinct. I have made a great number of trials and have endeavoured to obtain the clearest prints possible with fresh blood; but none of my prints are nearly as distinct as this one."