221B Baker Street

"In a world of locked rooms, the man with the key is king."

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 haemoglobin, 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 haemoglobin. No doubt you see the significance of this discovery of mine?'

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