In my next step, however, I cannot by any stretching of ordinary science persuade it to accompany me, or give me a foundation; for the point is that your consciousness, working on the next plane above the one on which the organ of consciousness is being built, is the shaper of that mechanism. To put it concretely: your physical brain is built up from the astral plane, and it is your consciousness working in matter finer than the physical which builds up the brain in the forming child within the limits laid down by karma. Now, that is a general law for healthy evolution. You will see the importance of this law a little further on. Every body which we possess--physical, astral, mental, buḍḍhic--is always built up by consciousness working in the plane next above it; the next plane, or world, is a world very much more "next" than you are next each other sitting here--not far away beyond the stars, removed by great spaces. It is interpenetrating you in every portion of your being. It is only "next" in the sense that the solids, liquids, and gases of your bodies are next each other in the body--not far away, but here. So that the working is of the closest and most intimate kind. Some of you who are students of Theosophical literature will remember that H.P.B. has spoken of all of us as working in the astral consciousness. You will see that you are not working with a physical consciousness in the literal sense of the term, if you think for a moment. How much do you know of the consciousness working in the various cells and tissues of your physical body? Practically nothing, except when you are ill. Only when the body is disorganised do you become conscious of that working. Normally, the motion of your blood, the building up by assimilation of your muscles and nerves, the life of your cells, the protective action of some of the living cells in your body--the "devourers," as they are called--go on without your knowledge, without your thought, without your giving one moment's conscious attention to them. In the Perfect Man, the consciousness of all this is ever present, but in us, imperfect, it is not; we are not yet sufficiently vitalised and unfolded to carry on the whole of our consciousness, with full awareness of all its activities. We are only able to manage a very small part of it, and so have let go the consciousness that keeps at work the physical body, to concentrate ourselves in a higher world, and utilise the nervous mechanism as the apparatus of our thinking. That law obtains, then, all through. If you want to organise and build up your astral body, you can only do it from the mental plane. You must raise your thought to a higher power by concentration, by regular meditation, by deliberately working on the consciousness, before you can raise it to that power from which it shall be able to organise your astral body, as it has already organised your physical body. That is the reason why meditation is necessary in all these things; because