In other words, man wondered countless ages before he reasoned; because feeling travels along the line of least resistance, while thought, or the challenge by inquiry--therefore the assumption that there may be two sides to a question--must pursue a path obstructed by the dominance of custom, the force of imitation, and the strength of prejudice and fear. It is here that anthropology, notably that psychical branch of it comprehended under folk-lore, takes up the cue from the momentous doctrine of heredity; explains the persistence of the primitive; and the causes of man's tardy escape from the illusions of the senses, and the general conservatism of human nature. "Born into life! in vain, Opinions, those or these, unalter'd to retain the obstinate mind decrees," as in the striking illustration cited in Heine's Travel-Pictures. "A few years ago Bullock dug up an ancient stone idol in Mexico, and the next day he found that it had been crowned during the night with flowers. And yet the Spaniard had exterminated the old Mexican religion with fire and sword, and for three centuries had been engaged in ploughing and harrowing their minds and implanting the seed of Christianity." The causes of error and delusion, and of the spiritual nightmares of olden time, being made clear, there is begotten a generous sympathy with that which empirical notions of human nature attributed to wilfulness or to man's fall from a high estate. Superstitions which are the outcome of ignorance can only awaken pity. Where the corrective of knowledge is absent, we see that it could not be otherwise. Where that corrective is present, but either perverted or not exercised, pity is supplanted by blame. In either case, we learn that the art of life largely consists in that control of the emotions and that diversion of them into wholesome channels, which the intellect, braced with the latest knowledge, can alone effect. Therefore, discarding theories of revelation, spiritual illumination, and other assumed supra-mundane sources of knowledge, sufficing causes of abnormal mental phenomena are found in abnormal working of the mental apparatus. The investigation of hallucinations (Lat. _alucinor_, to wander in mind) leaves no doubt that they are the effect of a morbid condition of that intricate, delicately poised structure, the nervous system, under which objects are seen and sensations felt when no corresponding impression has been made through the medium of the senses. When the nervous system is out of gear, voices, whether divine or of the dead, may be heard; and actual figures may be seen. A mental image becomes a visual image; an imagined pain a real pain, as the great physiologist, John Hunter, testified when he said, "I am confident that I can fix my attention to any part until I have a sensation in that part." Shakespere portrays the like condition when Macbeth attempts to clutch the dagger wherewith to stab Duncan: