too general to be of any use in tracing the owner."
"I am afraid you are right," said Thorndyke, laying the coat on the laboratory bench; "but we shall soon see, if Polton will let us have his patent dust-extractor."
The little apparatus to which my colleague referred was the invention of our ingenious laboratory assistant, and resembled in principle the "vacuum cleaners" used for restoring carpets. It had, however, one special feature: the receiver was made to admit a microscope-slide, and on this the dust-laden air was delivered from a jet.
The "extractor" having been clamped to the bench by its proud inventor, and a wetted slide introduced into the receiver, Thorndyke applied the nozzle of the instrument to the collar of the coat while Polton worked the pump. The slide was then removed and, another having been substituted, the nozzle was applied to the right sleeve near the shoulder, and the exhauster again worked by Polton. By repeating this process, half-a-dozen slides were obtained charged with dust from different parts of the garment, and then, setting up our respective microscopes, we proceeded to examine the samples.
A very brief inspection showed me that this dust contained matter not usually met with—at any rate, in appreciable quantities. There were, of
