d in the protozooen, the simplest form in which
animal life is known to exist, by what we call its response to stimuli.
The protozooen has a limited power of self-movement, and will accept or
reject certain environments. But while we see that mind expresses itself
in consciousness as vague, as dubious as that of the protozooen, we find
it also as clear, as definite, as far reaching as that of the statesman,
the chemist, the philosopher. Hence, the "phenomena of mental life"
embrace the entire realms of feeling, knowing, willing--not of man
alone, but of all creatures.

In our study, however, we shall limit ourselves to the psychology of the
human mind, since that concerns us vitally as nurses. Animal psychology,
race psychology, comparative psychology are not within the realm of our
practical needs in hospital life. We would know the workings of man's
mind in disease and health. What are the instinctive responses to fear,
as shown by babies and children and primitive races? What are the normal
expressions of joy, of anger, or desire? What external conditions call
forth these evidences? What are the acquired responses to the things
which originally caused fear, or joy, or anger? How do grown-ups differ
in their reactions to the same stimuli? Why do they differ? Why does one
man walk firmly, with stern, set face, to meet danger? Why does another
quake and run? Why does a third man approach it with a swagger, face it
with a confident, reckless smile of defiance?

All these are legitimate questions for the psychologist. He will
approach the study of man's mind by finding how his body acts--that is,
by watching the phenomena of mental life--under various conditions; then
he will seek for the "why" of the action. For we can only conclude what
is in the mind of another by interpreting his expression of his thinking
and feeling. We cannot see within his mind. But experience with
ourselves and others has taught us that certain attitudes of body,
certain shades of countenance, certain gestures, tones of voice,
spontaneous or willed actions, represent anger or joy, impatience or
irritability, stern control or poise of mind. We realize that the
average man has learned to conceal his mental reactions from the casual
observer at will. But if we see him at an unguarded moment, we can very
often get a fair idea of his mental attitude. Through these outward
expressions we are able to judge to some extent of the phenomena of his
mental