The soul, or psychic being, has external and internal perceptions (for which it has cerebral organs). When the former predominate too greatly, the human body and all external objects are realized most vividly, and the reality of psychic life is not so well realized or understood. Hence persons so organized are disposed to materialism, and either doubt the existence of their psychic being, or are indifferent to it. On the other hand, those in whom the interior faculties predominate too greatly vividly realize their psychic life, but have more vague and feeble conceptions of material objects, including their own bodies, and attach undue importance to the imaginary and subjective in preference to the objective. The materialists and the illusionists, however, are not entirely composed of these two classes of subjective and objective thinkers. The majority consists of persons of moderate reasoning capacity, who simply follow their leaders. In making a critical distinction between the psycho-organic brain and non-psychic body, the former may be confined strictly within the cranium, leaving the exterior portions of the head as a part of the non-psychic body; but as they are more intimately associated with the brain than any part below the neck, this distinction is not important; and if the whole head, as the environment of the psychic brain, be grouped with it, it may not lead to any material error. The brain is intimately associated with the entire physical person by twelve pairs of cranial or cerebral nerves, and by the spinal cord, which descends from the base of the brain through a great foramen or opening midway between the ears, and while passing down the spinal column gives off thirty pairs of nerves. The cranial nerves are all for the head, except the _pneumogastric_ or lung-stomach nerve, which belongs to the organs of respiration, voice, and digestion; and the spinal nerves are all for the body, except a few which ramify in the neck and in the scalp. The entire nervous system is so instantaneously prompt in conveying to the brain the impressions which originate feeling, and in conveying from the brain the nervous energies that produce voluntary motion and modify all the processes of life, that we feel as if we had sensation and volition in every part of the body; or, in other words, that our conscious existence was in the body; but we rationally know that the sensation and volition occur in the brain, for neither sensation nor voluntary motion can occur if the nervous connection with the brain is interrupted by compression and section, or if the brain itself be sufficiently compressed. When the brain is exposed by an injury of the cranium, the pressure of a finger suspends all consciousness and volition, making a blank in the life of the individual.