the room fell
into a chair? You had forgotten? Well I can answer for it that it was
so. Now, you will remember also that Mrs. Porter, the housekeeper, told
us that she herself fainted upon entering the room and had afterwards
opened the window. In the second case--that of Mortimer Tregennis
himself--you cannot have forgotten the horrible stuffiness of the room
when we arrived, though the servant had thrown open the window. That
servant, I found upon inquiry, was so ill that she had gone to her bed.
You will admit, Watson, that these facts are very suggestive. In each
case there is evidence of a poisonous atmosphere. In each case, also,
there is combustion going on in the room--in the one case a fire, in
the other a lamp. The fire was needed, but the lamp was lit--as a
comparison of the oil consumed will show--long after it was broad
daylight. Why? Surely because there is some connection between three
things--the burning, the stuffy atmosphere, and, finally, the madness
or death of those unfortunate people. That is clear, is it not?"

"It would appear so."

"At least we may accept it as a working hypothesis. We will suppose,
then, that something was burned in each case which produced an
atmosphere causing strange toxic effects. Very good. In the first
instance--that of the Tregennis family--this substance was placed in
the fire. Now the window was shut, but the fire would naturally carry
fumes to some extent up the chimney. Hence one would expect the
effects of the poison to be less than in the second case, where there
was less escape for the vapour. The result seems to indicate that it
was so, since in the first case only the woman, who had presumably the
more sensitive organism, was killed, the others exhibiting that
temporary or permanent lunacy which is evidently the first effect of
the drug. In the second case the result was complete. The facts,
therefore, seem to bear out the theory of a poison which worked by
combustion.

"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