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 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 pre-