"I must confess that I have not given the subject a thought," I replied. "As I predicted," he said. "It is a step toward a new idea, and simple as it seems, now that the subject has been suggested, you must agree that thousands of intelligent men have not been able to formulate the thought. The idea had never occurred to them. Even after our previous conversation concerning the possibility of showing you your own brain, you were powerless and could not conceive of the train of thought which I started, and along which I shall now further direct your senses." "The eye is so constituted that light produces an impression on a nervous film in the rear of that organ, this film is named the retina, the impression being carried backward therefrom through a magma of nerve fibers (the optic nerve), and reaching the brain, is recorded on that organ and thus affects the mind. Is it not rational to suppose it possible for this sequence to be reversed? In other words, if the order were reversed could not the same set of nerves carry an impression from behind to the retina, and picture thereon an image of the object which lies anterior thereto, to be again, by reflex action, carried back to the brain, thus bringing the brain substance itself to the view of the mind, and thus impress the senses? To recapitulate: If the nerve sensation, or force expression, should travel from the brain to the retina, instead of from an outward object, it will on the reverse of the retina produce the image of that which lies behind, and then if the optic nerve carry the image back to the brain, the mind will bring to the senses the appearance of the image depicted thereon." [Illustration: "FACING THE OPEN WINDOW HE TURNED THE PUPILS OF HIS EYES UPWARD."] "This is my first consideration of the subject," I replied. "Exactly," he said; "you have passed through life looking at outside objects, and have been heedlessly ignorant of your own brain. You have never made an exclamation of surprise at the statement that you really see a star that exists in the depths of space millions of miles beyond our solar system, and yet you became incredulous and scornful when it was suggested that I could show you how you could see the configuration of your brain, an object with which the organ of sight is nearly in contact. How inconsistent." "The chain of reasoning is certainly novel, and yet I can not think of a mode by which I can reverse my method of sight and look backward," I now respectfully answered. "It is very simple; all that is required is a counter excitation of the nerve, and we have with us to-night what any person who cares to consider the subject can employ at any time, and thus behold an outline of a part of his own brain. I will give you the lesson."