Each of these bodies serves as a vehicle of consciousness on the plane to which it belongs. The soul is evolving simultaneously in each of the worlds, physical, astral and mental, and these various bodies enable it to receive the vibrations of the plane they belong to and thus to be conscious there. The mental body is the seat of intellectual activity. Thought arises as a vibration in it and passes through the astral body into the physical brain. Whenever we think we are using the mental body. The astral body is the seat of emotion. With it we feel. All emotion passes from it to the physical body to be expressed in the material world. The astral world is also called the emotional world, as the mental plane is called the mental world. The physical body is the soul's instrument of action. It attaches it to the physical world, enables the consciousness to contact material objects and to move and express on the material plane the thoughts and emotions generated in the mental and astral bodies. Another part of the mechanism of consciousness is known as the etheric double. But it is only a link in the chain and not a body through which the soul can function. It is composed of the etheric matter of the physical world and connects the astral body with the physical body. As every atom of physical matter is surrounded and permeated by etheric matter, it follows that the physical body has its duplicate in etheric matter. "Etheric double" is a very appropriate name since it is a perfect duplicate of the physical body in etheric matter. It serves the purpose of supplying the life force to the nervous system and is the medium through which sensation is conveyed. The action of an anaesthetic drives out so much of the matter of the etheric double that the connection is broken and sensation in the physical body ceases.