"Because your brain is not in your head, and it is not small. Come, I may as well show it to you; I've told you enough that it won't matter if you know a little more. There are few who are taken on personally conducted sight-seeing tours of their own brains. You should be grateful. "Gratitude seems a little tardy." They went into the barred area, down into the bowels of the main building of the center. And they looked at the brain of Anthony Trotz, a restricted person in its special meaning. "It is the largest in the world," said Colonel Cooper. "How large?" "A little over twelve hundred cubic meters." "What a brain! And it is mine?" "You are an adjunct to it, a runner for it, an appendage, inasmuch as you are anything at all." "Colonel Cooper, how long have I been alive?" "You are not." "How long have I been as I am now?" "It is three days since you were last reassigned, since you were assigned to this. At that time your nervousness and apprehensions were introduced. An apprehensive unit will be more inclined to notice details just a little out of the ordinary." "And what is my purpose?" They were walking now back to the office work area, and Anthony had a sad feeling at leaving his brain behind him. "This is a filter center, and your purpose is to serve as a filter, of a sort. Every person has a slight aura around him. It is a characteristic of his, and is part of his personality and purpose. And it can be detected, electrically, magnetically, even visually under special conditions. The accumulator at which we were looking (your brain) is designed to maintain contact with all the auras in the world, and to keep a running and complete data on them all. It contains a multiplicity of circuits for each of its three billion and some subjects. However, as aid to its operation, it was necessary to assign several artificial consciousnesses to it. You are one of these." * * * * * The dogs and the children had found a new victim in the streets below. Anthony's heart went out to him. "The purpose," continued Colonel Cooper, "was to notice anything just a little bit peculiar in the auras and the persons they represent, anything at all odd in their comings and goings. Anything like what you have come here to report to me." "Like the seven persons who recently arrived in the world, and not by way of birth?" "Yes. We have been expecting the first of the aliens for months. We must know their area, and at once. Now tell me." "What if they are not aliens at all. What if they are restricted persons like myself?" "Restricted persons have no aura, are not persons, are not alive. And you would not receive knowledge of them." "Then how do I know the other restricted persons here, Adrian and Wellington, and such?"