There was only one student in the room, who was bending over(俯身，弯腰) a table, intensely focused on 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(试管) in his hand.

“I have found a reagent(试剂) which is precipitated(被沉淀) by hemoglobin(血红素，血红蛋白), and by nothing else.”

He could not have been more delighted if he had discovered a gold mine.

“Dr. Watson, Mr. Sherlock Holmes,” said Stamford, introducing us.

“How are you?” he said kindly, shaking my hand with unbelievable strength.

“You have been in Afghanistan, I observe.”

“How on earth did you know that?” I asked in shock.

“Never mind,” he said, laughing to himself.

“The question now is about hemoglobin(血红素，血红蛋白). No doubt you see the significance(意义) of this discovery of mine?”

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

“Well, man, it is the most practical medico-legal(法医学的) discovery for years.

Don’t you see that it gives us an infallible(万无一失的) test for blood stains(血迹). 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, sticking a long needle into his finger.

“Now, I add this small quantity of blood to a litre of water.

You can see that the resulting mixture looks like pure water.

The proportion(比例) of blood cannot be more than one in a million. But look now!”

As he spoke, he threw into the water a few white crystals(晶体), and then added some drops of a transparent(透明的) liquid.

In an instant the contents turned a reddish-brown color, and a brownish dust was precipitated(沉淀) to the bottom of the glass jar.

“Ha! ha!” he cried, clapping his hands, and looking as delighted as a child with a new toy.

“What do you think of that?”

“It seems to be a very sensitive(灵敏的) test,” I remarked.

“Beautiful! Beautiful! The old guaiacum test was very clumsy(笨拙的) and uncertain.

So is the microscopic(显微镜) examination for blood cells(细胞).

The latter is also useless if the stains(污渍) are even a few hours old.

Now, this appears to act as well whether the blood is old or new.

If this test had been invented, there are hundreds of men now walking the earth who would long ago have paid the penalty(处罚) of their crimes.”

“Indeed!” I murmured(低声道).

“Criminal cases often depend upon(取决于) that one point.

A man is suspected(被怀疑) of a crime months perhaps after it has been committed.

His clothes are examined, and brownish stains(污渍) discovered upon them.

Are they blood stains(血渍), or mud stains(泥渍), or rust stains(锈渍), or fruit stains(果渍), or what are they?

That is a question which has puzzled(困扰) many an(许多) expert, and why?

Because there was no reliable(可靠的) test.

Now we have the Sherlock Holmes’ test, and there will no longer be any difficulty.”

His eyes fairly glittered(闪光) as he spoke, and he put his hand over his heart and bowed as if to some applauding(鼓掌的) crowd created 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 if this test had been in existence.

Then there was Mason of Bradford, and the notorious(臭名昭著的) Muller, and Lefevre of Montpellier, and Samson of New Orleans.

I could name twenty cases, or more, in which this test would have decided the result.”

“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.’ ”

“It might make very interesting reading, too,” remarked Sherlock Holmes, sticking a small bandage over the place where his finger was bleeding.

“I have to be careful,” he continued, turning to me with a smile, “for I experiment with poisons a good deal.”

He held out his hand as he spoke, and I noticed that it was covered with similar bandages.

“We came here on business,” said Stamford, turning to Sherlock Holmes.

“My friend here is looking for somewhere to live, and as you were complaining(抱怨) that you could get no one to share rooms 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 an apartment(公寓) in Baker Street,” he said, “which would suit us perfectly.

You don’t mind the smell of strong tobacco, I hope?”

“I’m a pipe smoker myself,” I answered.

“That’s good enough. I generally have chemicals everywhere, and occasionally do experiments. Would that bother(打扰) you?”

“Not at all.”

“Let me see—what my other faults are.

I get very withdrawn(沉默寡言的) at times, and don’t open my mouth for days.

You must not think I am angry at you when I do that.

Just leave me alone, and I’ll soon be all right.

What have you to confess(坦白) now? It’s just as well for two people to know the worst of one another before they begin to live together.”

I laughed at this cross-examination(盘问).

“I keep a small dog,” I said, “and I object to noise because my nerves(神经) are shaken, and I get up at all sorts of strange hours, and I am extremely lazy.

I have another set of faults when I’m well, but those are the main ones at present.”

“Do you include violin-playing in your category(范畴) of noise?” he asked, anxiously.

“It depends on(取决于) the player,” I answered.

“A well-played violin is a treat for the gods—a badly-played one—”

“Oh, that’s all right,” he cried, with a happy laugh.

“I think we may consider the thing as settled—that is, if the rooms are acceptable to you.”

“When shall we see them?”

“Call for me here at noon tomorrow, and we’ll go together and settle everything,” he answered.

“All right—noon exactly,” said I, shaking his hand.

We left him working among his chemicals, and we walked together towards my hotel.

“By the way,” I asked suddenly, stopping and turning upon Stamford, “how did he know that I had come from Afghanistan?”

My companion smiled. “That’s just his special little talent,” he said.

“Many people have wanted to know how he finds things out.”

“Oh! A mystery(谜) is it?” I cried, rubbing(搓着) my hands. “This is very interesting.

I am very grateful to you for bringing us together. Good-bye.”

I said, and walked into my hotel, considerably interested in my new acquaintance(相识之人).