which express them are impossible for the higher mental matter of which the
causal body is constructed.

So far, we have described vehicles which are the expression of the ego in
their respective worlds--vehicles, which he provides for himself; in the
physical world we come to a vehicle which is provided for him by Nature
under laws which will be later explained--which though also in some sense
an expression of him, is by no means a perfect manifestation. In ordinary
life we see only a small part of this physical body--only that which is
built of the solid and liquid subdivisions of physical matter. The body
contains matter of all the seven subdivisions, and all of them play their
part in its life and are of equal importance, to it.

We usually speak of the invisible part of the physical body as the etheric
double; "double" because it exactly reproduces the size and shape of the
part of the body that we can see, and "etheric" because it is built--of
that finer kind of matter by the vibrations of which light is conveyed to
the retina of the eye. (This must not be confused with the true æther of
space--that of which matter is the negation.) This invisible part of the
physical body is of great importance to us, since it is the vehicle through
which flow the streams of vitality which keep the body alive, and without
it, as a bridge to convey undulations of thought and feeling from the
astral to the visible denser physical matter, the ego could make no use of
the cells of his brain.

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