I fancy that many of you, like myself, have woken up in the night with a "sleeping" arm or leg. It is a very peculiar feeling to have that arm or leg, cold and lifeless, hanging there at your side as if it were something which does not belong to you. In such situations you recover some of the motor functions before the sensory functions, which en ables you to move the limb like a pendulum. For a few sec onds the arm functions as an artificial limb - a prosthesis without sensors. In general we are not aware of the importance of our sensory organs until we lose them. You do not feel the...