I knew that seclusion and solitude were very necessary for my friend in those hours of intense mental concentration during which he weighed every particle of evidence, constructed alternative theories, balanced one against the other, and made up his mind as to which points were essential and which immaterial. I therefore spent the day at my club and did not return to Baker Street until evening. It was nearly nine o'clock when I found myself in the sitting-room once more.
My first impression as I opened the door was that a fire had broken out, for the room was so filled with smoke that the light of the lamp upon the table was blurred by it. As I entered, however, my fears were set at rest, for it was the acrid fumes of strong coarse tobacco which took me by the throat and set me coughing. Through the haze I had a vague vision of Holmes in his dressing-gown coiled up in an armchair with his black clay pipe between his lips. Several rolls of paper lay around him.
"Caught cold, Watson?" said he.
"No, it's this poisonous atmosphere."
"I suppose it is pretty thick, now that you mention it."
"Thick! It is intolerable."
"Open the window, then! You have been at your club all day, I perceive."
"My dear Holmes!"
"Am I right?"
"Certainly, but how---------?"
He laughed at my bewildered expression.
Arthur Conan Doyle. The Hound of the Baskervilles (1902). Dover Publications, 1994. p. 18