screen with extreme care and then, slipping a small leather cap over the
objective, introduced the dark slide and drew out the shutter.

"I will ask you to sit down and remain quite still while I make the
exposure," he said to me and the inspector. "A very little vibration is
enough to destroy the sharpness of the image."

We seated ourselves accordingly, and Thorndyke then removed the cap,
standing motionless, watch in hand, while he exposed the first plate.

"We may as well take a second, in case this should not turn out quite
perfect," he said, as he replaced the cap and closed the shutter.

He reversed the dark slide and made another exposure in the same way,
and then, having removed the micrometer and replaced it by a slip of
plain glass, he made two more exposures.

"There are two plates left," he remarked, as he drew out the second dark
slide. "I think I will take a record of the blood-stain on them."

He accordingly made two more exposures--one of the larger blood-stain
and one of the smaller smears.

"There," said he, with an air of satisfaction, as he proceeded to pack
up what the inspector described as his "box of tricks." "I think we have
all the data that we can squeeze out of Scotland Yard, and I am very
much obliged to you, Mr. Singleton, for giving so many facilities to
your natural enemy, the counsel for the defence."

"Not our natural enemies, doctor," protested Mr. Singleton. "We work for