When we are asleep, the part of us that is usually conscious is
dissociated and the submerged part takes the stage. When we forget our
surroundings in concentration or absent-mindedness, a part of us is
dissociated and our friends say that we are "not all there," or as
popular slang has it, "Nobody home." When a mood or system of
complexes drives out all other moods, one becomes "a different
person." But if this normal dissociation is carried a step farther, we
may lose the power to put ourselves together again, and then we may
truly be said to be dissociated. Almost any part of us is subject to
this kind of apparent loss. In neurasthenia the happy, healthy
complexes which have hitherto dominated our lives may be split off and
left lying dormant in the subconscious; or the power of will or
concentration may seem to be gone. In hysteria we may seem to lose the
ability to see or feel or walk, or we may lose for the time all
recollection of certain past events, or of whole periods of our lives,
or of everything but one system of ideas which monopolizes the field
of attention. Sometimes great systems of memories, instincts, and
complexes are alternately shifted in and out of gear, leaving first
one kind of person on top and then another.[25] Stevenson's _Dr.
Jekyll_ and _Mr. Hyde_ is not so fantastic a character as he seems.
Any one who doubts the ability of the mind to split itself up into two
or more distinct personalities, entertaining totally different
conceptions of life, disliking each other, playing tricks on each
other, writing notes to each other, and carrying on a perpetual feud
as each tries to get the upper hand, should read Morton Prince's
"Dissociation of a Personality," a fascinating account of his famous
case, Miss Beauchamp.

[Footnote 25: When a memory or system of memories is suddenly lost
from consciousness the person is said to be suffering from amnesia or