"What, are you going to put it under the microscope?" exclaimed Mr.
Singleton, looking round with a broad smile.

"Must do something for my fee, you know," replied Thorndyke, as he set
up the microscope and screwed on two extra objectives to the triple
nose-piece. "You observe that there is no deception," he added to the
inspector, as he took the paper from Mr. Singleton's table and placed it
between two slips of glass.

"I'm watching you, sir," replied the officer, with a chuckle; and he did
watch, with close attention and great interest, while Thorndyke laid the
glass slips on the microscope stage and proceeded to focus.

I also watched, and was a good deal exercised in my mind by my
colleague's proceedings. After a preliminary glance with the six-inch
glass, he swung round the nose-piece to the half-inch objective and
slipped in a more powerful eye-piece, and with this power he examined
the blood-stains carefully, and then moved the thumb-print into the
field of vision. After looking at this for some time with deep
attention, he drew from the case a tiny spirit lamp which was evidently
filled with an alcoholic solution of some sodium salt, for when he lit
it I recognised the characteristic yellow sodium flame. Then he replaced
one of the objectives by a spectroscopic attachment, and having placed
the little lamp close to the microscope mirror, adjusted the
spectroscope. Evidently my friend was fixing the position of the "D"
line (or sodium line) in the spectrum.

Having completed the adjustments, he now examined afresh the
blood-smears and the thumb-print, both by transmitted and reflected