“Wrapped up in this paper I have the scrapings of the spot which I found on the floor—­just a few grains of dark, dried powder.  To show how sensitive the test is, I will take only one of the smallest of these minute scrapings.  I dissolve it in this third tube with distilled water.  I will even divide it in half, and place the other half in this fourth tube.

“Next I add some of the serum of the uninoculated rabbit to the half in this tube.  You observe, nothing happens.  I add a little of the serum of the inoculated rabbit to the other half in this other tube.  Observe how delicate the test is—­”

Kennedy was leaning forward, almost oblivious of the rest of us in the room, talking almost as if to himself.  We, too, had riveted our eyes on the tubes.

As he added the serum from the inoculated rabbit, a cloudy milky ring formed almost immediately in the hitherto colourless, very dilute blood-solution.

“That,” concluded Craig, triumphantly holding the tube aloft, “that conclusively proves that the little round spot on the hardwood floor was not paint, was not anything in this wide world but blood.”

No one in the room said a word, but I knew there must have been someone there who thought volumes in the few minutes that elapsed.

“Having found one blood-spot, I began to look about for more, but was able to find only two or three traces where spots seemed to have been.  The fact is that the blood spots had been apparently carefully wiped up.  That is an easy matter.  Hot water and salt, or hot water alone, or even cold water, will make quite short work of fresh blood-spots—­at least to all outward appearances.  But nothing but a most thorough cleaning can conceal them from the Uhlenhuth test, even when they are apparently wiped out.  It is a case of Lady Macbeth over again, crying in the face of modern science, ‘Out, out, damned spot.’

“I was able with sufficient definiteness to trace roughly a course of blood-spots from the fireplace to a point near the door of the living-room.  But beyond the door, in the hall, nothing.”

“Still,” interrupted Harrington, “to get back to the facts in the case.  They are perfectly in accord either with my theory of the cigar or the Record’s of spontaneous combustion.  How do you account for the facts?”

“I suppose you refer to the charred head, the burned neck, the upper chest cavity, while the arms and legs were untouched?”

“Yes, and then the body was found in the midst of combustible furniture that was not touched.  It seems to me that even the spontaneous-combustion theory has considerable support in spite of this very interesting circumstantial evidence about blood-spots.  Next to my own theory, the combustion theory seems most in harmony with the facts.”