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was morally certain that his ideas were cor rect, and knew that he could scientifically prove it, but still the basis of his reckoning was so narrow that he was unwilling to stand upon it when human life and liberty were at stake. In explaining Dr. Edson's discovery, two things should be noted. First, the fact that it is as simple as the alphabet (at least onethird of the important discoveries have been), and, second, the formation and character of the blood must be fully understood. Blood is composed of watery elements and corpus cles. A blood corpuscle is a bi-concave disk. Viewed from the side it seems a per fect circle. Viewed on end it looks like a dumb-bell. The only difference in the blood of different creatures is in the size and shape of the corpuscles. The blood corpuscles of a fish are large and flat, and in their centre is a small spot or nucleus. The blood of all birds and fowls is similar, but the corpus cles are smaller. The blood of all animals, aside from birds, fishes, and reptiles, has smaller corpuscles without the nucleus. The presence of this nucleus has for many years made it possible to throw out the blood -of fishes and birds in murder cases. Not long ago a case attracting much attention was tried in England. The issue hung on the statement of the defense that the blood on a knife found in the possession of the pris oner was that of a turkey. This was abun dantly disproven, because of the absence of the central nucleus in the corpuscles. Mi croscopic examination showed this plainly to the jury, and, as no claim had been made that the blood was that of any other animal, the argument was thrown out, and the man convicted and hanged. But no point exists by which it is equally possible to show the difference between the blood of a human being and the blood of a four-footed beast. It has been proven that a difference exists in the size of the blood corpuscles of all animals, including man. The corpuscles have been accurately measured by micro

scopic examination, and no doubt whatever exists as to the truth of these measurements. It has long been quite possible for a scien tist to take the blood found on a prisoner's person, and measure its corpuscles so ex actly that the scientist would have no moral doubt in pronouncing them human or other wise. But, as the figures following will show, the difference in measurements is so slight — a particle of dust, an unexpected refraction of light, the most minute optical illusion, might throw his calculations all awry — that no scientist has been willing to swear to the accuracy of his deductions on this basis. Here are his measurements : A blood corpuscle of a man has a diameter of 1-3200 of an inch, the diameter of a dog's blood is 1-3570 of an inch, that of a mouse 1-3840 of an inch, that of an ox 1-4580 of an inch, that of a sheep 1-5000, that of a goat 1-5200 of an inch. A microscope will measure with fair ac curacy to within 1-200000 of an inch, but as has been said, these measurements are so very delicate that a shade or the most min ute difference in focus would derange and destroy their accuracy. For this reason they have not been useful in murder cases. Dr. Edson, in reflecting upon this subject not long ago, thought fantastically of the advantage that would accrue to justice if one could only enlarge these corpuscles so that a minute error in measurement would be less important. Suddenly, it occurred to him that by the very simplest method they might readily be enlarged, and it is because he thought of this simple method, and not because of any extraordinary learning in volved in carrying it out, that he has made an important discovery. For many years it has been customary in cases of forgery to throw the suspected sig nature in enlarged form upon a screen with a magic-lantern. He saw at once that this might as readily be done with blood corpus cles as with a forged signature. So he did it. First, he set about to measure 3,000