“If you will go over in your mind all the points proved to have been discovered—­not the added points in the Record story—­I think you will agree with me that mine is a more logical interpretation than spontaneous combustion,” reasoned Craig.  “Hear me out and you will see that the facts are more in harmony with my less fanciful explanation.  No, someone struck Lewis Langley down either in passion or in cold blood, and then, seeing what he had done, made a desperate effort to destroy the evidence of violence.  Consider my next discovery.”

Kennedy placed the five glasses which I had carefully sealed and labelled on the table before us.

“The next step,” he said, “was to find out whether any articles of clothing in the house showed marks that might be suspected of being blood-spots.  And here I must beg the pardon of all in the room for intruding in their private wardrobes.  But in this crisis it was absolutely necessary, and under such circumstances I never let ceremony stand before justice.

“In these five glasses on the table I have the washings of spots from the clothing worn by Tom, Mr. James Langley, Junior, Harrington Brown, and Doctor Putnam.  I am not going to tell you which is which—­indeed I merely have them marked, and I do not know them myself.  But Mr. Jameson has the marks with the names opposite on a piece of paper in his pocket.  I am simply going to proceed with the tests to see if any of the stains on the coats were of blood.”

Just then Doctor Putnam interposed.  “One question, Professor Kennedy.  It is a comparatively easy thing to recognise a blood-stain, but it is difficult, usually impossible, to tell whether the blood is that of a man or of an animal.  I recall that we were all in our hunting-jackets that day, had been all day.  Now, in the morning there had been an operation on one of the horses at the stable, and I assisted the veterinary from town.  I may have got a spot or two of blood on my coat from that operation.  Do I understand that this test would show that?”

“No,” replied Craig, “this test would not show that.  Other tests would, but not this.  But if the spot of human blood were less than the size of a pin-head, it would show—­it would show if the spot contained even so little as one twenty-thousandth of a gram of albumin.  Blood from a horse, a deer, a sheep, a pig, a dog, could be obtained, but when the test was applied the liquid in which they were diluted would remain clear.  No white precipitin, as it is called, would form.  But let human blood, ever so diluted, be added to the serum of the inoculated rabbit, and the test is absolute.”

A death-like silence seemed to pervade the room.  Kennedy slowly and deliberately began to test the contents of the glasses.  Dropping into each, as he broke the seal, some of the serum of the rabbit, he waited a moment to see if any change occurred.

It was thrilling.  I think no one could have gone through that fifteen minutes without having it indelibly impressed on his memory.  I recall thinking as Kennedy took each glass, “Which is it to be, guilt or innocence, life or death?” Could it be possible that a man’s life might hang on such a slender thread?  I knew Kennedy was too accurate and serious to deceive us.  It was not only possible, it was actually a fact.