"Beware of the science of man, I repeat," he replied; "now, before you are deep in the toils, and can not foresee the end, beware of the science of human biology. Remember the story recently related, that of the physician who was led to destruction by the alluring voice." I made no reply, but stood with my face fixed, slowly moving the candle backward and forward, gazing intently into the depths of my own brain. After a time the old man removed the candle from my hand, and said: "Do you accept the fact? Have I demonstrated the truth of the assertion?" "Yes," I replied; "but tell me further, now that you have excited my interest, have I seen and learned all that man can discover in this direction?" "No; you have seen but a small portion of the brain convolutions, only those that lie directly back of the optic nerve. By systematic research, under proper conditions, every part of the living brain may become as plainly pictured as that which you have seen." "And is that all that could be learned?" I asked. "No," he continued. "Further development may enable men to picture the figures engraved on the convolutions, and at last to read the thoughts that are engraved within the brains of others, and thus through material investigation the observer will perceive the recorded thought of another person. An instrument capable of searching and illuminating the retina could be easily affixed to the eye of a criminal, after which, if the mind of the person operated upon were stimulated by the suggestion of an occurrence either remote or recent, the mind facility would excite the brain, produce the record, and spread the circumstances as a picture before the observer. The brain would tell its own story, and the investigator could read the truth as recorded in the brain of the other man. A criminal subjected to such an examination could not tell an untruth, or equivocate; his very brain would present itself to the observer." "And you make this assertion, and then ask me to go no further into the subject?" "Yes; decidedly yes." "Tell me, then, could you not have performed this experiment in my room, or in the dark cellar of my house?" "Any one can repeat it with a candle in any room not otherwise lighted, by looking at a blackboard, a blank wall, or black space," he said. I was indignant. "Why have you treated me so inhumanly? Was there a necessity for this journey, these mysterious movements, this physical exertion? Look at the mud with which I am covered, and consider the return trip which yet lies before me, and which must prove even more exhausting?"