The physical body is made of matter, its substance is matter; but the centers of perception are of still finer matter, and though they are located in the physical body, no nourishment can reach them, except that which is drawn through the breath, the fine substance which is not even visible. In the language of the mystics it is called Nur, which means light. The body does not only want food, but also breath, in other words vibration, and that vibration is given to it by the repetition of sacred words. The sounds, the vowels, and the composition of the sacred words is chemical, and it is this process which was called by the ancient philosophers Alchemy. These centers are the Akashas or domes where every sound has its echo, and the echo once produced in this Akasha or Asman reaches all other Asmans which exist within and without. Therefore the repetition of a sacred word has not only to do with oneself and one's life, but it spreads and rises higher than man can imagine, and wider than he can perceive. Verily every action sets in movement every atom of the universe.