Yoga Nadis
Nadis are the astral tubes made up of astral matter that carry psychic currents. The Sanskrit term ‘Nadi’ comes from the root ‘Nad’ which means ‘motion’. It is through these Nadis (Sukshma, subtle passages), that the vital force or Pranic current moves or flows. Since they are made up of subtle matter they cannot be seen by the naked physical eyes and you cannot make any test-tube experiments in the physical plane. These Yoga Nadis are not the ordinary nerves, arteries and veins that are known to the Vaidya Shastra (Anatomy and Physiology). Yoga Nadis are quite different from these.http://www.yoga-age.com/modern/kun4.html