The Disappearance of Lady Frances Carfax, The Adventure of the Devil's Foot, The Adventure of Wisteria Lodge

"But why Turkish?" asked Mr. Sherlock Holmes, gazing fixedly at my boots. I was reclining in a cane-backed chair at the moment, and my protruded feet had attracted his ever-active attention.
"English," I answered in some surprise. "I got them at Latimer's, in Oxford Street."
Holmes smiled with an expression of weary patience.
"The bath!" he said; "the bath! Why the relaxing and expensive Turkish rather than the invigorating home-made article?"
"Because for the last few days I have been feeling rheumatic and old. A Turkish bath is what we call an alterative in medicine--a fresh starting-point, a cleanser of the system.
"By the way, Holmes," I added, "I have no doubt the connection between my boots and a Turkish bath is a perfectly self-evident one to a logical mind, and yet I should be obliged to you if you would indicate it."
"The train of reasoning is not very obscure, Watson," said Holmes with a mischievous twinkle. "It belongs to the same elementary class of deduction which I should illustrate if I were to ask you who shared your cab in your drive this morning."