d refuse to call up the emotion.

=The Right of Way.= There is a law that comes to the aid of reason in
this dilemma and that is the "law of the common path."[7] By this is
meant that man is capable of but one intense emotion at a time. No one
can imagine himself strenuously making love while he is shaken by an
agony of fear, or ravenously eating while he is in a passion of rage.
The stronger emotion gets the right of way, obtains control of mental
and bodily machinery, and leaves no room for opposite states. If the
two emotions are not antagonistic, they may blend together to form a
compound emotion, but if in the nature of the case such a blending is
impossible, the weaker is for the time being forgotten in the
intensity of the stronger. "The expulsive power of a new affection" is
not merely a happy phrase; it is a fact in every day life. The
problem, then, resolves itself into ways of making the desirable
emotion the stronger, of learning how to form the habit of giving it
the head start and the right of way. In our chapter on "Choosing the
Emotions," we shall find that much depends on building up the right
kind of sentiments, or the permanent organization of instincts around
ideas. However, we must first look more closely at the separate
instincts to acquaint ourselves with the purpose and the ways of each,
and to discover the nature of the forces with which we have to deal.

[Footnote 7: Sherrington: _Integrative Action of the Nervous System_.]

I THE SELF-PRESERVATIVE INSTINCTS

=Hunger.= Hunger is the most pressing desire of the egoistic or
self-preserving impulse. The yearning for food and the impulse to seek
and eat it are aroused organically within the body and are behind much
of the activity of every type of life. As the impulse is so familiar,
and its promptings are so little subject to psychic control, it seems
unnecessary to do more than mention its importance.

=Flight and Fear.= All through the ages the race has been subject to
injury. Species has been pitted against species, individual against
individual. He who could fight hardest or run fastest has survived and
passed his abilities on to his offspring. Not all could be strongest
for fight, and many species have owed their existence to their ability
to run and to know when to run. Thus it is that one of the strongest
and most universal tendencies is the instinct for flight, and its
emotion, fear. "Fear is the representation of injury and is born