For instance, just as the physical body has need of the outer world, which is of like substance with itself, for its supply of food, something of the same kind takes place in the case of the astral body. Let us imagine a physical human body removed from the surrounding world: it would die. That shows that physical life is an impossibility without the entire physical environment. In fact, the whole earth must be just as it is if physical human bodies are to exist upon it. For, in reality, the whole human body is only a part of the earth,—indeed, in a wider sense, part of the whole physical universe. In this respect it is related in the same sense as, for example, the finger of a hand to the entire human body. Separate the finger from the hand and it cannot remain a finger: it withers away. Such would also be the fate of the human body were it removed from that body of which it is a member,—from the conditions of life with which the earth provides it. Let it be raised above the surface of the earth but a sufficient number of miles and it will perish as the finger perishes when cut off from the hand. If this fact is less apparent in the case of a man’s physical organism than in that of his finger and his body, it is merely because the finger cannot walk about on the body as man is able to do on the earth, and because on that account the dependence of the former is more obvious. In the same way that the physical body is embedded in the physical world to which it belongs, so does the astral body form a part of its own world, only it is torn out of it in waking life. We can form a clear idea of what happens by having recourse to an analogy. Imagine a vessel filled with water. No one drop is a separate thing in itself within that entire mass of water. But let us take a little sponge and with it suck up a single drop from the whole mass of water. Something of this kind happens to the human astral body on awaking. During sleep it is in a world resembling its own nature. In a certain sense it forms part of it. On awaking, the physical and etheric bodies suck it up: they absorb it; they contain the organs through which it perceives the outer world. In order to achieve this perception it has to leave its own world, for it is in that world alone that it can receive the models which it needs for the etheric body.