system is reflex action. For instance, when the foot of a frog, or the
hand of a soundly sleeping person, is tickled very gently, the limb is
moved away from the irritation, without any mental action, and entirely
without will being exercised. And when we go from light into darkness,
the pupil of the eye enlarges, without any direct consciousness of the
change of its shape on our part. Similarly, the presence or food in the
pharynx initiates a series of movements-- swallowing, the digestive
movements, and so on-- which in health are entirely beyond our
mental scope.