He displayed on his table a number of enlarged micro-photographs.  Some were labelled, “Characteristic crystals of white man’s blood”; others “Crystallisation of negro blood”; still others, “Blood-crystals of the cat.”

“I have here,” he resumed, after we had all examined the photographs and had seen that there was indeed a vast amount of difference, “three characteristic kinds of crystals, all of which I found in the various spots in the kitchen of Mr. Pitts.  There were three kinds of blood, by the infallible Reichert test.”

I had been prepared for his discovery of two kinds, but three heightened the mystery still more.

“There was only a very little of the blood which was that of the poor, faithful, unfortunate Sam, the negro chef,” Kennedy went on.  “A little more, found far from his body, is that of a white person.  But most of it is not human blood at all.  It was the blood of a cat.”

The revelation was startling.  Before any of us could ask, he hastened to explain.

“It was placed there by some one who wished to exaggerate the struggle in order to divert suspicion.  That person had indeed been wounded slightly, but wished it to appear that the wounds were very serious.  The fact of the matter is that the carving-knife is spotted deeply with blood, but it is not human blood.  It is the blood of a cat.  A few years ago even a scientific detective would have concluded that a fierce hand-to-hand struggle had been waged and that the murderer was, perhaps, fatally wounded.  Now, another conclusion stands, proved infallibly by this Reichert test.  The murderer was wounded, but not badly.  That person even went out of the room and returned later, probably with a can of animal blood, sprinkled it about to give the appearance of a struggle, perhaps thought of preparing in this way a plea of self-defence.  If that latter was the case, this Reichert test completely destroys it, clever though it was.”  No one spoke, but the same thought was openly in all our minds.  Who was this wounded criminal?

I asked myself the usual query of the lawyers and the detectives—­ Who would benefit most by the death of Pitts?  There was but one answer, apparently, to that.  It was Minna Pitts.  Yet it was difficult for me to believe that a woman of her ordinary gentleness could be here to-night, faced even by so great exposure, yet be so solicitous for him as she had been and then at the same time be plotting against him.  I gave it up, determining to let Kennedy unravel it in his own way.

Craig evidently had the same thought in his mind, however, for he continued:  “Was it a woman who killed the chef?  No, for the third specimen of blood, that of the white person, was the blood of a man; not of a woman.”

Pitts had been following closely, his unnatural eyes now gleaming.  “You said he was wounded, you remember,” he interrupted, as if casting about in his mind to recall some one who bore a recent wound.  “Perhaps it was not a bad wound, but it was a wound nevertheless, and some one must have seen it, must know about it.  It is not three days.”