eling of
something that is the same, or is not the same, as the first. So
immediately perception is established. The baby consciousness recognizes
that the vague feeling is, or is not, _that same thing_. And from
perception to a complex consciousness of perceptions, of ideas, of
memories and relations, and judgments, is so short a step that we cannot
use our measuring rods to span it.

Thus through the various stages of life, from infancy to maturity, the
conscious is passing into the unconscious, only to help form later a new
conscious thought. Hence the conscious thought is determined by the
great mass of the unconscious, plus the external world.

But every thought, relegated to the unconscious, through its association
there--for it is plastic by nature--comes back to consciousness never
quite the same, and meets never quite the same stimulus. And as a result
a repeated mental experience is never twice exactly the same. So the
conscious becomes the unconscious and the unconscious the conscious, and
neither can be without the other.

Our problem is to understand the workings of the mind as it exists
today, and to try to find some of its most constructive uses; and on
that we shall focus attention. To that end we must first examine the
various ways in which consciousness expresses itself.

We have recognized two distinct mental states--the conscious and the
unconscious--and have found them constantly pressing each on the other's
domain. Our study of consciousness reveals the normal in the aspects of
sleeping and waking, also various abnormal states. Consciousness may
become excited, depressed, confused, delirious, or insane. We shall
consider later some of the mental workings that account for these
abnormal expressions. At present let us examine the mind's activities in
sleep and in delirium.

CONSCIOUSNESS IN SLEEP

Sleep seldom, if ever, is a condition of utter unconsciousness. We so
frequently have at least a vague recollection, when we wake, of
dreaming--whether or not we remember the dream material--that we are
inclined to accept sleep as always a state of some kind of mental
activity, though waking so often wipes the slate clean. A new word which
serves our purpose well has come into common use these last years, and
we describe sleep as a state of rest of the conscious mind made possible
as weariness overpowers the _censor_, and this guard at the gate naps.
The censor is merely that mental activity which