Anatomy teaches us that there are nerve centres and nerve fibres all over the body. To the naked eye a difference is obvious between certain portions of the brain and spinal cord, viz the grey matter and the white matter. The grey matter is largely composed of nerve-cells, while the white matter contains only their long processes, the nerve fibres. It is the grey matter that nervous impressions and impulses originate and the nerve fibres conduct these impulses. Hence the functions of nerve-cells is consciousness. There are two systems of nerve-cells and fibres in the body viz, cerebro-spinal and Sympathetic Systems. The Sympathetic System of cells apparently have no consciousness. The functions of the body such as digestion, exertion, peristaltie action of the intestines are governed by this Sympathetic System, which are not normally under the control of the will. In the Yoga Sadhana of Siddhis, an effort is made to gain control over this System of nerve-cells which pertain to “Annamaya-kosha” (physical body) and “Pranamaya-Kosha” (psychological sheath).
