Raja Yoga (the Yoga Sūtras with commentary) — trans. Swami Vivekananda (1896)

This Susumna is, in ordinary persons, closed up at the lower extremity ; no action comes through it. The Yogi proposes a practice by which it can be opened, and the nerve currents made to travel through. When a sensation is carried to a centre, the centre reacts. This 2reaction, in the case of automatic centres, is followed by motion ; in the case of conscious centres it is followed first by perception, and secondly by motion. All perception is the reaction to action from outside. How, then, do perceptions in dreams arise ? There is then no action from outside. The sensory motions, therefore, are coiled up somew'here, just as the motor motions are known to be in different centres. For instance, I see a city ; the perception of that city was from the reaction to the sensations brought from outside objects comprising that city. That is to say, a certain motion in the brain molecules ' has been set up by the motion in the incarrying nerves,' which again were set in motion by external objects in the city. Now, even after a long time I can remember the city. This memory is exactly the same phenomenon, only it is in a milder form. But whence is the action that set up even the milder form of similar vibrations in the brain. Not certainly from the primary sensations. Therefore it must be that the sensations are coiled up somewhere, and they, by their acting, bring out the mild reaction which w-e call dream perception. Now the centre where all these residual sensations are, as it were, stored up, is called the Muladhara, the root receptacle, and the coiled up energy of action is Kundalini, the *' coiled up." It is very probable that the residual motor energy is also stored up in the same centre as, after deep study or meditation on external objects, the part of the body w^here the Muladhara centre is situated (probably the sacral plexus) gets heated. Now, if this 3coiled-up energy be roused and made active, and then consciously made to travel up the Susumna canal, as it acts upon centre after centre, a tremendous reaction will set in. 'When a minute portion of the energy of action travels along a nerve fibre and causes reaction from centres, the perception is either dream or imagination. But when the vast mass of this energy stored up by the power of long internal meditation travels along the Susunma, and strikes the centres, the reaction is tremendous, immensely superior to the reaction of dream or imagination, immensely more intense than the reaction of sense perception. It is super-sensuous perception, and the mind in that state is called super-conscious. And when it reaches the metropolis of all sensations, the brain, the whole brain, as it were, reacts, and every percei\ing molecule in the body, as it were, reacts, and the result is the full blaze of illumination, the perception of the Self. As this Kundalini force travels from centre to centre, layer after layer of the mind, as it were, will be opened up, and this universe will be perceived by the Yogi in its fine, or coarse, form. Then alone the causes of this universe, both as sensation and reaction, will be known as they are, and hence will come all knowledge. The causes being known, the knowledge of the effects is sure to follow.