Craig went to work abruptly without a word. On the laboratory table he placed his splendid microscope and several cases of slides as well as innumerable micro-photographs. He had been working for some time when he looked up.
"Ever hear of Dr. Edward Reichert of the University of Pennsylvania and his wonderful discoveries of how blood crystals vary in different species?" he asked.
I had not, but did not admit it.
"Well," he went on, "there is a blood test so delicate that one might almost say that he could identify a criminal by the finger prints, so to speak, of his blood crystals. The hemoglobin or red coloring matter forms crystals and the variations of these crystals both in form and molecular construction are such that they set apart every species of animal from every other, and even the races of men—perhaps may even set apart individuals. Here, Walter, we have sample of human blood crystals."
I looked through the microscope as he directed. There I could see the crystals sharply defined.
"And here," he added, "are the crystals of the blood on Elaine's handkerchief."
I looked again as he changed the slides. There was a marked difference and I looked up at him quickly.
"It is dog's blood—not human blood," he said simply.
I looked again at the two sets of slides. There could be no doubt that there was a plain difference.
"Wonderful!" I exclaimed.