An exact and detailed explanation of the difference would lead us into rather recondite technicalities, but perhaps the general idea of the distinction between the two may be caught from an example taken from the very lowest plane of clairvoyance, in close contact with the denser physical. The etheric double in man is in exceedingly close relation to his nervous system, and any kind of action upon one of them speedily reacts on the other. Now in the sporadic appearance of etheric sight in the savage, whether of Central Africa or of Western Europe, it has been observed that the corresponding nervous disturbance is almost entirely in the sympathetic system, and that the whole affair is practically beyond the man's control--is in fact a sort of massive sensation vaguely belonging to the whole etheric body, rather than an exact and definite sense-perception communicated through a specialized organ. As in later races and amid higher development the strength of the man is more and more thrown into the evolution of the mental faculties, this vague sensitiveness usually disappears; but still later, when the spiritual man begins to unfold, he regains his clairvoyant power. This time, however, the faculty is a precise and exact one, under the control of the man's will, and exercised through a definite sense-organ; and it is noteworthy that any nervous action set up in sympathy with it is now almost exclusively in the cerebro-spinal system. On this subject Mrs. Besant writes:--"The lower forms of psychism are more frequent in animals and in very unintelligent human beings than in men and women in whom the intellectual powers are well developed. They appear to be connected with the sympathetic system, not with the cerebro-spinal. The large nucleated ganglionic cells in this system contain a very large proportion of etheric matter, and are hence more easily affected by the coarser astral vibrations than are the cells in which the proportion is less. As the cerebro-spinal system develops, and the brain becomes more highly evolved, the sympathetic system subsides into a subordinate position, and the sensitiveness to psychic vibrations is dominated by the stronger and more active vibrations of the higher nervous system. It is true that at a later stage of evolution psychic sensitiveness reappears, but it is then developed in connection with the cerebro-spinal centres, and is brought under the control of the will. But the hysterical and ill-regulated psychism of which we see so many lamentable examples is due to the small development of the brain and the dominance of the sympathetic system."