A Study in Scarlet (Sherlock Holmes)

The first Sherlock Holmes adventure where John Watson meets the great detective: This was a lofty chamber, lined and littered with countless bottles. Broad, low tables were scattered about, which bristled with retorts, test-tubes, and little Bunsen lamps, with their blue flickering flames. There was only one student in the room, who was bending over a distant table absorbed in his work. At the sound of our steps he glanced round and sprang to his feet with a cry of pleasure. "I've found it! I've found it," he shouted to my companion, running towards us with a test-tube in his hand. "I have found a re-agent which is precipitated by hoemoglobin, and by nothing else." Had he discovered a gold mine, greater delight could not have shone upon his features.
"Dr. Watson, Mr. Sherlock Holmes," said Stamford, introducing us.
"How are you?" he said cordially, gripping my hand with a strength for which I should hardly have given him credit. "You have been in Afghanistan, I perceive."
"How on earth did you know that?" I asked in astonishment.
"Never mind," said he, chuckling to himself. "The question now is about hoemoglobin. No doubt you see the significance of this discovery of mine?"