"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.