The ape, who had been an interested listener, now stepped forward. "Oh, please, I pray you," it mumbled, "do not again condemn me to these horrid shelves. I recall the day that I was brought here securely bound, and though I have no recollection of what has transpired since I can but guess from the appearance of my own skin and that of these dusty corpses that I have lain here long. I beg that you will permit me to live and either restore me to my fellows or allow me to serve in some capacity in this establishment, of which I saw something between the time of my capture and the day that I was carried into this laboratory, bound and helpless, to one of your cold, ersite slabs."

Ras Thavas made a gesture of impatience. "Nonsense!" he cried. "You are better off here, where you can be preserved in the interests of science."

"Accede to his request," I begged, "and I will myself take over all responsibility for him while I profit by the study that he will afford me."

"Do as you are directed," snapped Ras Thavas as he quit the room.

I shrugged my shoulders. "There is nothing for it, then," I said.

"I might dispatch you all and escape," mused the ape, aloud, "but you would have helped me. I could not kill one who would have befriended me — yet I shrink from the thought of another death. How long have I lain here?"

I referred to the history of his case that had been brought and suspended at the head of the table. "Twelve years," I told him.

"And yet, why not?" he demanded of himself. "This man would slay me- why should I not slay him first."

"It would do you no good," I assured him, "for you could never escape. Instead you would be really killed, dying a death from which Ras Thavas would probably think it not worth while ever to recall you, while I, who might find the opportunity at some later date and who have the inclination, would be dead at your hands and thus incapable of saving you."

I had been speaking in a low voice, close to his ear, that the attendants might not overhear me. The ape listened intently.

"You will do as you suggest?" he asked.

"At the first opportunity that presents itself," I assured him.

"Very well," he said, "I will submit, trusting to you."

A half hour later both subjects had been returned to their shelves.

Days ran into weeks, weeks into months, as day by day I labored at the side of Ras Thavas, and more and more the old surgeon took me into his confidence, more and more he imparted to me the secrets of his skill and his profession.

Gradually he permitted me to perform more and more important functions in the actual practice of his vast laboratory. I started transferring limbs from one subject to another, then internal organs of the digestive tract. Then he entrusted to me a complete operation upon a paying client I removed the kidneys from a rich old man, replacing them with healthy ones from a young subject The following day I gave a stunted child new thyroid glands. A week later I transferred two hearts and then, at last, came the great day for me-unassisted, with Ras Thavas standing silently beside me, I took the brain of an old man and transplanted it within the cranium of a youth.

When I had done Ras Thavas laid a hand upon my shoulder. "I could not have done better myself," he said. He seemed much elated and I could not but wonder at this unusual demonstration of emotion upon his part, he who so prided himself upon his lack of emotionalism. I had often pondered the purpose which influenced Ras Thavas to devote so much time to my training, but never had I hit upon any more satisfactory explanation than that he had need of assistance in his growing practice. Yet when I consulted the records, that were now open to me, I discovered that his practice was no greater than it had been for many years; and even had it been there was really no reason why he should have trained me in preference to one of his red-Martian assistants, his belief in my loyalty not being sufficient warrant, in my mind, for this preferment when he could, as well as not have kept me for a bodyguard and trained one of his own kind to aid him in his surgical work.

But I was presently to learn that he had an excellent reason for what he was doing-Ras Thavas always had an excellent reason for whatever he did. One night after we had finished our evening meal he sat looking at me intently as he so often did, as though he would read my mind, which, by the way, he was totally unable to do, much to his surprise and chagrin; for unless a Martian is constantly upon the alert any other Martian can read clearly his every thought; but Ras Thavas was unable to read mine. He said that it was due to the fact that I was not a Barsoomian. Yet I could often read the minds of his assistants, when they were off their guard, though never had I read aught of Ras Thavas' thoughts, nor, I am sure, had any other read them. He kept his brain sealed like one of his own blood jars, nor was he ever for a moment found with his barriers down.

He sat looking at me this evening for a long time, nor did it in the least embarrass me, so accustomed was I to his peculiarities. "Perhaps," he said presently, "one of the reasons that I trust you is due to the fact that I cannot ever, at any time, fathom your mind; so, if you harbor traitorous thoughts concerning me I do not know it, while the others, every one of them, reveal their inmost souls to my searching mind and in each one there is envy, jealousy or hatred of me. Them, I know, I cannot trust. Therefore I must accept the risk and place all my dependence upon you, and my reason tells me that my choice is a wise one-I have told you upon what grounds it based my selection of you as my bodyguard. The same holds true in my selection of you for the thing I have in mind. You cannot harm me without harming yourself and no man will intentionally do that; nor is there any reason why you should feel any deep antagonism towards me.

"You are, of course, a sentimentalist and doubtless you look with horror upon many of the acts of a sane, rational, scientific mind; but you are also highly intelligent and can, therefore, appreciate better than another, even though you may not approve them, the motives that prompt me to do many of those things of which your sentimentality disapproves. I may have offended you, but I have never wronged you, nor have I wronged any creature for which you might have felt some of your so-called friendship or love. Are my premises incorrect, or my reasoning faulty?"

I assured him to the contrary.

"Very well! Now let me explain why I have gone to such pains to train you as no other human being, aside from myself, has ever been trained. I am not ready to use you yet, or rather you are not ready; but if you know my purpose you will realize the necessity for bending your energy to the consummation of my purpose, and to that end you will strive even more diligently than you have to perfect yourself in the high, scientific art I am imparting to you.

"I am a very old man," he continued after a brief pause, "even as age goes upon Barsoom. I have lived more than a thousand years. I have passed the allotted natural span of life, but I am not through with my life's work-I have but barely started it. I must not die. Barsoom must not be robbed of this wondrous brain and skill of mine. I have long had in mind a plan to thwart death, but it required another with skill equal to mine-two such might live for ever. I have selected you to be that other, for reasons that I already have explained-they are undefiled by sentimentalism. I did not choose you because I love you, or because I feel friendship for you, or because I think that you love me, or feel friendship towards me. I chose you because I knew that of all the inhabitants of a world you were the one least likely to fail me. For a time you will have my life in your hands. You will understand now why I have not been able to choose carelessly.