A Study in Scarlet. and The Country of the Saints

[...]
"Criminal cases are continually hinging upon that one point. A man is suspected of a crime months perhaps after it has been committed. His linen or clothes are examined, and brownish stains discovered upon them. Are they blood stains, or mud stains, or rust stains, or fruit stains, or what are they? That is a question which has puzzled many an expert, and why? Because there was no reliable test. Now we have the Sherlock Holmes' test, and there will no longer be any difficulty."
His eyes fairly glittered as he spoke, and he put his hand over his heart and bowed as if to some applauding crowd conjured up by his imagination.
"You are to be congratulated," I remarked, considerably surprised at his enthusiasm.
"There was the case of Von Bischoff at Frankfort last year. He would certainly have been hung had this test been in existence. Then there was Mason of Bradford, and the notorious Muller, and Lefevre of Montpellier, and Samson of New Orleans. I could name a score of cases in which it would have been decisive."
"You seem to be a walking calendar of crime," said Stamford with a laugh. "You might start a paper on those lines. Call it the 'Police News of the Past.'"
"Very interesting reading it might be made, too," remarked Sherlock Holmes, sticking a small piece of plaster over the prick on his finger. "I have to be careful," he continued, turning to me with a smile, "for I dabble with poisons a good deal." He held out his hand as he spoke, and I noticed that it was all mottled over with similar pieces of plaster, and discoloured with strong acids.
"We came here on business," said Stamford, sitting down on a high three-legged stool, and pushing another one in my direction with his foot. "My friend here wants to take diggings, and as you were complaining that you could get no one to go halves with you, I thought that I had better bring you together."
Sherlock Holmes seemed delighted at the idea of sharing his rooms with me. "I have my eye on a suite in Baker Street," he said, "which would suit us down to the ground. You don't mind the smell of strong tobacco, I hope?"
"I always smoke 'ship's' myself," I answered.
[...]

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