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