, and a large share of simple
mental performances, are essentially associative reactions. In most
cases from ordinary life, the _preparation_ is less complete than in
the laboratory experiments, and the reaction time is accordingly
longer.

Reflex Action

The simple reaction has some points of resemblance with the "reflex",
which, also, is a prompt motor response to a sensory stimulus. A
familiar example is the reflex wink of the eyes in response to
anything touching the eyeball, or in response to an object suddenly
approaching the eye. This "lid reflex" is quicker than the quickest
simple reaction, taking about .05 second. The knee jerk or "patellar
reflex", aroused by a blow on the patellar tendon just below the knee
when the knee is bent and the lower leg hanging freely, is quicker
still, taking about .03 second. The reason for this extreme quickness
of the reflex will appear as we proceed. However, not every reflex is
as quick as those mentioned, and some are slower than the quickest of
the simple reactions.

A few other examples of reflexes may be given. The "pupillary reflex"
is the narrowing of the pupil of the eye {25} in response to a bright
light suddenly shining into the eye. The "flexion reflex" is the
pulling up of the leg in response to a pinch, prick or burn on the
foot. Coughing and sneezing are like this in being protective
reflexes, and the scratching of the dog belongs here also.

There are many internal reflexes: movements of the stomach and
intestines, swallowing and hiccoughing, widening and narrowing of the
arteries resulting in flushing and paling of the skin. These are
muscular responses; and there are also glandular reflexes, such as the
discharge of saliva from the salivary glands into the mouth, in
response to a tasting substance, the flow of the gastric juice when
food reaches the stomach, the flow of tears when a cinder gets into
the eye. There are also inhibitory reflexes, such as the momentary
stoppage of breathing in response to a dash of cold water. All in all,
a large number of reflexes are to be found.

Most reflexes can be seen to be _useful_ to the organism. A large
proportion of them are protective in one way or another, while others
might be called regulative, in that they adjust the organism to the
conditions affecting it.

Now comparing the reflex with the simple reaction, we see first that
the reflex is more deep-seated in the organism, and more essential to
its welf