y to
consider the matter in the same way as we considered thirst just
above.

Breathing and air-getting.

Breathing, obviously a native reaction, is ordinarily automatic and
needs no preparatory reactions, simply because air is so easy to get.
But let breathing be difficult, for any reason, and the stifling
sensation is as impulsive as hunger or thirst. The stuffy air in a
cave or in a hole under a haymow will lead a child to frantic escape.
Possibly the delight in being out of doors which shows itself in young
children, and is not lost in adults, represents a sort of air-hunting
instinct, parallel to food-hunting. Closely connected with breathing
is the function of circulation, automatic for the most part; and we
should mention also the organic needs of waste-elimination, which give
impulsive sensations akin to hunger and thirst, and lead to more or
less organized instinctive reactions.

Responses to heat and cold.

The warm-blooded animals, birds and mammals, have the remarkable power
of keeping the body temperature constant (at 98-99 degrees Fahrenheit,
in man, somewhat higher in birds), in spite of great variations in the
external temperature to which the body is exposed, and in spite of
great variations in the {142} amount of heat generated in the body by
muscular exercise. Sweating and flushing of the skin are reactions to
heat, and prevent the body temperature from rising; paling of the
skin, shivering and general muscular activity are responses to cold
and prevent the body temperature from falling. Shrinking from great
heat or cold are also instinctive, while seeking shelter from the heat
or cold is a preparatory reaction that is not definitely organized in
the native constitution of man, but gives rise to a great variety of
learned reactions, and plays a considerable part in life.

Shrinking from injury.

The "flexion reflex" of the arm or leg, which pulls it away from a
pinch, prick or burn, is the type of a host of defensive
reactions--winking, scratching, rubbing the skin, coughing, sneezing,
clearing the throat, wincing, limping, squirming, changing from an
uncomfortable position--most or all of them instinctive reactions.
With each goes some sort of irritating sensation, as pain, itching,
tickling, discomfort; and a conscious impulse to get rid of the
irritation is often present. When the simpler avoiding reactions do
not remove the irritating stimulus, they are repeated more vigorously
or giv