The brain may be deficient in thinking power; the body may react on thought, and sometimes the thought may react on the body. Could not the mind produce decay in the brain, or is it true that it is always bodily strain that brings strain of mind? Or does anger bring a strain on the body? The trouble usually comes from within. Hallucinations sometimes arise from thought and mind, either the same person or in some other person. We call it obsession when it comes from without.