“He is sure to be at the laboratory，” returned my companion.
“He either avoids the place for weeks， or else he works there frommorning till night. If you like， we will drive round together afterluncheon.”
“Certainly，” I answered， and the conversation drifted away intoother channels.
As we made our way to the hospital after leaving the Holborn，Stamford gave me a few more particulars about the gentlemanwhom I proposed to take as a fellow-lodger.
“You mustn’t blame me if you don’t get on with him，” he said； “Iknow nothing more of him than I have learned from meeting himoccasionally in the laboratory. You proposed this arrangement， soyou must not hold me responsible.”
“If we don’t get on it will be easy to part company，” I answered.
“It seems to me， Stamford，” I added， looking hard at mycompanion， “that you have some reason for washing your handsof the matter. Is this fellow’s temper so formidable， or what is it？
Don’t be mealy-mouthed about it.”
“It is not easy to express the inexpressible，” he answeredwith a laugh. “Holmes is a little too scientific for my tastes—itapproaches to cold-bloodedness. I could imagine his giving afriend a little pinch of the latest vegetable alkaloid， not out ofmalevolence， you understand， but simply out of a spirit of inquiryin 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. Heappears to have a passion for definite and exact knowledge.”
“Very right too.”
“Yes， but it may be pushed to excess. When it comes to beatingthe subjects in the dissecting-rooms with a stick， it is certainlytaking rather a bizarre shape.”
“Beating the subjects！”
“Yes， to verify how far bruises may be produced after death. Isaw 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 herewe are， and you must form your own impressions about him.” Ashe spoke， we turned down a narrow lane and passed through asmall side-door， which opened into a wing of the great hospital.
It was familiar ground to me， and I needed no guiding as weascended the bleak stone staircase and made our way down thelong corridor with its vista of whitewashed wall and dun-coloureddoors. Near the further end a low arched passage branched awayfrom it and led to the chemical laboratory.
This was a lofty chamber， lined and littered with countlessbottles. Broad， low tables were scattered about， which bristledwith retorts， test-tubes， and little Bunsen lamps， with their blueflickering flames. There was only one student in the room， whowas bending over a distant table absorbed in his work. At thesound of our steps he glanced round and sprang to his feet witha cry of pleasure. “I’ve found it！ I’ve found it，” he shouted to mycompanion， running towards us with a test-tube in his hand. “Ihave found a re-agent which is precipitated by h.moglobin， andby nothing else.” Had he discovered a gold mine， greater delightcould not have shone upon his features.
“Dr. Watson， Mr. Sherlock Holmes，” said Stamford， introducingus.
“How are you？” he said cordially， gripping my hand with astrength for which I should hardly have given him credit. “Youhave 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 nowis about h.moglobin. No doubt you see the significance of thisdiscovery of mine？”
“It is interesting， chemically， no doubt，” I answered， “butpractically——”
“Why， man， it is the most practical medico-legal discovery foryears？ Don’t you see that it gives us an infallible test for bloodstains？ Come over here now！” He seized me by the coat-sleeve inhis eagerness， and drew me over to the table at which he had beenworking. “Let us have some fresh blood，” he said， digging a longbodkin into his finger， and drawing off the resulting drop of blood ina chemical pipette. “Now， I add this small quantity of blood to a litreof water. You perceive that the resulting mixture has the appearanceof pure water. The proportion of blood cannot be more than one ina million. I have no doubt， however， that we shall be able to obtainthe characteristic reaction.” As he spoke， he threw into the vessela few white crystals， and then added some drops of a transparentfluid. In an instant the contents assumed a dull mahogany colour，and a brownish dust was precipitated to the bottom of the glass jar.
“Ha！ ha！” he cried， clapping his hands， and looking as delightedas a child with a new toy. “What do you think of that？”
“It seems to be a very delicate test，” I remarked.
“Beautiful！ beautiful！ The old Guaiacum test was very clumsy anduncertain. So is the microscopic examination for blood corpuscles.
The latter is valueless if the stains are a few hours old. Now， thisappears to act as well whether the blood is old or new. Had thistest been invented， there are hundreds of men now walking theearth who would long ago have paid the penalty of their crimes.”
“Indeed！” I murmured.
“Criminal cases are continually hinging upon that one point.
A man is suspected of a crime months perhaps after it has beencommitted. His linen or clothes are examined and brownish stainsdiscovered upon them. Are they blood stains， or mud stains， orrust stains， or fruit stains， or what are they？ That is a questionwhich has puzzled many an expert， and why？ Because there was noreliable test. Now we have the Sherlock Holmes’ test， and therewill no longer be any difficulty.”
His eyes fairly glittered as he spoke， and he put his hand overhis heart and bowed as if to some applauding crowd conjured upby his imagination.
“You are to be congratulated，” I remarked， considerably surprisedat his enthusiasm.
“There was the case of Von Bischoff at Frankfort last year. Hewould certainly have been hung had this test been in existence.