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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, {4}
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?"

"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.

"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 delicate test," I remarked.

"Beautiful! beautiful! The old Guiacum test was very clumsy
and uncertain. So is the microscopic examination for blood
corpuscles. The latter is valueless if the stains are a few
hours old. Now, this appears to act as well whether the
blood is old or new. Had this test been invented, there are
hundreds of men now walking the earth 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
been committed. His linen or clothes are examined, and
brownish stains discovered upon them. Are they blood stains,

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