I followed my colleague out into the street, and for some time we walked on without speaking. "You guessed what the sergeant had in that paper, of course," said Thorndyke at length.
"Yes. It was the hair from the dead woman's hand; and I thought that he had much better have left it there."
"Undoubtedly. But that is the way in which well-meaning policemen destroy valuable evidence. Not that it matters much in this particular instance; but it might have been a fatal mistake."
"Do you intend to take any active part in this case?" I asked.
"That depends on circumstances. I have collected some evidence, but what it is worth I don't yet know. Neither do I know whether the police have observed the same set of facts; but I need not say that I shall do anything that seems necessary to assist the authorities. That is a matter of common citizenship."
The inroads made upon our time by the morning's adventures made it necessary that we should go each about his respective business without delay; so, after a perfunctory lunch at a tea-shop, we separated, and I did not see my colleague again until the day's work was finished, and I turned into our chambers just before dinner-time.
Here I found Thorndyke seated at the table, and evidently full of business. A microscope stood close by, with a condenser throwing a spot of light on to a pinch of powder that had been sprinkled on to the slide; his collecting-box lay open before him, and he was engaged, rather mysteriously, in squeezing a thick white cement from a tube on to three little pieces of moulding-wax.
"Useful stuff, this Fortafix," he remarked; "it makes excellent casts, and saves the trouble and mess of mixing plaster, which is a consideration for small work like this. By the way, if you want to know what was on that poor girl's pillow, just take a peep through the microscope. It is rather a pretty specimen."
I stepped across, and applied my eye to the instrument. The specimen was, indeed, pretty in more than a technical sense. Mingled with crystalline grains of quartz, glassy spicules, and water-worn fragments of coral, were a number of lovely little shells, some of the texture of fine porcelain, others like blown Venetian glass.