"With this train of reasoning in my head I naturally looked about in Mortimer Tregennis's room to find some remains of this substance. The obvious place to look was the talc shelf or smoke-guard of the lamp. There, sure enough, I perceived a number of flaky ashes, and round the edges a fringe of brownish powder, which had not yet been consumed. Half of this I took, as you saw, and I placed it in an envelope."
"Why half, Holmes?"
"It is not for me, my dear Watson, to stand in the way of the official police force. I leave them all the evidence which I found. The poison still remained upon the talc had they the wit to find it. Now, Watson, we will light our lamp; we will, however, take the precaution to open our window to avoid the premature decease of two deserving members of society, and
