“Without prejudice,” he replied. “I don’t know Fletcher, but the balance of probabilities is in his favour. Still, that blood-track in the hall is a curious feature. It certainly requires explanation.” “It does, indeed!” I exclaimed, “and you have got to find the explanation! Well, I wish you joy of the job. I suppose you will carry out the farce to the bitter end as you have promised?” “Certainly,” he replied. “But it is hardly a farce. I should have looked the specimens over in any case. One never knows what illuminating fact a chance observation may bring into view.” I smiled sceptically. “The fact that you are asked to ascertain is that these two samples of blood came from the same person. If there are any means of proving that, they are unknown to me. I should have said it was an impossibility.” “Of course,” he rejoined, “you are quite right, speaking academically and in general terms. No method of identifying the blood of individual persons has hitherto been discovered. But yet I can imagine the possibility, in particular and exceptional cases, of an actual, personal identification by means of blood. What does my learned friend think?” “He thinks that his imagination is not equal to the required effort,” I answered; and with that I picked up my brief bag and went forth to my duties at the courts. That Thorndyke would keep his promise to poor Lilian Markham was a foregone conclusion, preposterous as the examination seemed. But even my long experience of my colleague’s scrupulous conscientiousness had not prepared me for the spectacle which met my eyes when I returned to our chambers. On the table stood the microscope, flanked by three slide-boxes. Each box held six trays, and each tray held six slides--a hundred and eight slides in all! But why three boxes? I opened one. The slides--carefully mounted blood-films--were labelled “Joseph Riggs.” Those in the second box were labelled, “Blood from hall floor.” But when I opened the third box, I beheld a collection of empty slides labelled “Robert Fletcher”! I chuckled aloud. Prodigious! Thorndyke was going even one better than his promise. He was not only going to examine--probably had examined--the two samples produced; he was actually going to collect a third sample for himself! I picked out one of Mr. Riggs’s slides and laid it on the stage of the microscope. Thorndyke seemed to have been using a low-power objective--the inch-and-a-half. After a glance through this, I swung round the nose-piece to the high power. And then I got a further surprise. The brightly-coloured “white” corpuscles showed that Thorndyke had actually been to the trouble of staining the films with eosin! Again I murmured, “Prodigious!” and put the slide back in its box. For, of course, it showed just what one expected: blood--or rather, broken-up blood-clot. From its appearance, I could not even have sworn that it was human blood.