“It is not easy to express the inexpressible,” he answered with a laugh. “Holmes is a little too scientific for my tastes—it approaches to cold-bloodedness. I could imagine his giving a friend a little pinch of the latest vegetable alkaloid, not out of malevolence, you understand, but simply out of a spirit of inquiry in order to have an accurate idea of the effects. To do him justice, I think that he would take it himself with the same readiness. He appears to have a passion for definite and exact knowledge.”

“Very right too.”

“Yes, but it may be pushed to excess. When it comes to beating the subjects in the dissecting-rooms with a stick, it is certainly taking rather a bizarre shape.”

“Beating the subjects!”

“Yes, to verify how far bruises may be produced after death. I saw him at it with my own eyes.”

“And yet you say he is not a medical student?”

“No. Heaven knows what the objects of his studies are. But here we are, and you must form your own impressions about him.” As he spoke, we turned down a narrow lane and passed through a small side- door, which opened into a wing of the great hospital. It was familiar ground to me, and I needed no guiding as we ascended the bleak stone staircase and made our way down the long corridor with its vista of whitewashed wall and dun-coloured doors. Near the farther end a low arched passage branched away from it and led to the chemical laboratory.

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 hæmoglobin, 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 hæmoglobin. No doubt you see the significance of this discovery of mine?”

“It is interesting, chemically, no doubt,” I answered, “but practically—”

“Why, man, it is the most practical medico-legal discovery for years. Don’t you see that it gives us an infallible test for blood stains? Come over here now!” He seized me by the coat-sleeve in his eagerness, and drew me over to the table at which he had been working. “Let us have some fresh blood,” he said, digging a long bodkin into his finger, and drawing off the resulting drop of blood in a chemical pipette. “Now, I add this small quantity of blood to a litre of water. You perceive that the resulting mixture has the appearance of pure water. The proportion of blood cannot be more than one in a million. I have no doubt, however, that we shall be able to obtain the characteristic reaction.” As he spoke, he threw into the vessel a few white crystals, and then added some drops of a transparent fluid. In an instant the contents assumed a dull mahogany colour, and a brownish dust was precipitated to the bottom of the glass jar.