over the slight form of Mrs. Pitts, as she must have realised that this was the point where Kennedy had left off, in his questioning her the night before.
"There is," he went on slowly, "a blood test so delicute that one might almost say that he could identify a criminal by his very blood-crystals—the fingerprints, so to speak, of his blood. It was by means of these 'hemoglobin clues,' if I may call them so, that I was able to get on the right trail. For the fact is that a man's blood is not like that of any other living creature. Blood of different men, of men and women differ. I believe that in time we shall be able to refine this test to tell the exact individual, too.
"What is this principle? It is that the hemoglobin or red colouring-matter of the blood forms crystals. That has long been known, but working on this fact Dr. Reichert and Professor Brown of the University of Pennsylvania have made some wonderful discoveries.
"We could distinguish human from animal blood before, it is true. But the discovery of these two scientists takes us much further. By means of blood-crystals we can distinguish the blood of man from that of the animals and in addition that of white men from that of negroes and other races. It is often the only way of differentiating between various kinds of blood.
"The variations in crystals in the blood are in part of form and in part of molecular structure, the latter being discovered only by means of the polarising microscope. A blood-crystal is only one two-thousand-two-hundred-and-fiftieth of an inch in length and
