awareness of the momentary positions of the parts of the body involved,
so that we know whether or not they are moving in the intended manner.
This awareness is due to a particular sense, the 'sense of movement' or
'muscular sense' - one of those senses whose existence physiology has
lately come to acknowledge. Nothing, however, is known to us of all the
complex changes which are set into play within the muscles themselves
in order to carry out some intended movement. And it is these that are
the direct outcome of the activity of our will.

Regarding man's psycho-physical organization thus, we come to see in it
a kind of polarity - a death-pole, as it were, represented by the
nerves including their extension into the senses, and a life-pole,
represented by the metabolic and muscular systems; and connected with
them a pole of consciousness and one of unconsciousness - or as we can
also say, of waking and sleeping consciousness. For the degree of
consciousness on the side of the life-pole is not different from the
state in which the entire human being dwells during sleep.

It is by thus recognizing the dependence of consciousness on processes
of bodily disintegration that we first come to understand why
consciousness, once it has reached a certain degree of brightness, is
bound to suffer repeated interruptions. Every night, when we sleep, our
nervous system becomes alive (though with gradually decreasing
intensity) in order that what has been destroyed during the day may be
restored. While the system is kept in this condition, no consciousness
can obtain in it.

In between the two polarically opposite systems there is a third, again
of clearly distinct character, which functions as a mediator between
the two. Here all processes are of a strictly rhythmic nature, as is