The life of a physical body is one of perpetual change and in order that it shall live, it needs constantly to be supplied from three distinct sources. It must have food for its digestion, air for its breathing, and vitality for its absorption. This vitality is essentially a force, but when clothed in matter it appears to us as a definite element, which exists in all the worlds of which we have spoken. At the moment we are concerned with that manifestation of it which we find in the highest subdivision of the physical world. Just as the blood circulates through the veins, so does the vitality circulate along the nerves; and precisely as any abnormality in the flow of the blood at once affects the physical body, so does the slightest irregularity in the absorption or flow of the vitality affect this higher part of the physical body. Vitality is a force which comes originally from the sun. When an ultimate physical atom is charged with it, it draws round itself six other atoms, and makes itself into an etheric element. The original force of vitality is then subdivided into seven, each of the atoms carrying a separate charge. The element thus made is absorbed into the human body through the etheric part of the spleen. It is there split up into its component parts, which at once low to the various parts of the body assigned to them. The spleen is one of the seven force centres in the etheric part of the physical body. In each of our vehicles seven such centres should be in activity, and when they are thus active they are visible to clairvoyant sight. They appear usually as shallow vortices, for they are the points at which the force from the higher bodies enters the lower. In the physical body these centres are: (1) at the base of the spine, (2) at the solar plexus, (3) at the spleen, (4) over the heart, (5) at the throat, (6) between the eyebrows, and (7) at the top of the head. There are other dormant centres, but their awakening is undesirable. The shape of all the higher bodies as seen by the clairvoyant is ovoid, but the matter composing them is not equally distributed throughout the egg. In the midst of this ovoid is the physical body. The physical body strongly attracts astral matter, and in its turn the astral matter strongly attracts mental matter. Therefore by far the greater part of the matter of the astral body is gathered within the physical frame; and the same is true of the mental vehicle. If we see the astral body of a man in its own world, apart from the physical body we shall still perceive the astral matter aggregated in exactly the shape of the physical, although, as the matter is more fluidic in its nature, what we see is a body built of dense mist, in the midst of an ovoid of much finer mist. The same is true for the mental body. Therefore, if in the astral or the mental world we should meet an acquaintance, we should recognise him by his appearance just as instantly as in the physical world.