he natural stimulus
being present.

Voluntary control includes also the ability to omit a response even if
the natural stimulus is present. Holding the breath, keeping the eyes
wide open in spite of the tendency to wink, not swallowing though the
mouth is full of saliva, holding the hand steady when it is being
pricked, and many {299} similar instances of control over reflexes are
cases of _detachment_ of a native reaction from its natural stimulus.
Not "starting" at a sudden sound to which we have grown used and not
turning the eyes to look at a very familiar object, are other
instances of this detachment.

The _substitute response_ is another modification to be placed
alongside of the substitute stimulus. Here a natural stimulus calls
out a motor response different from its natural response. The muttered
imprecation of the adult takes the place of the child's scream of
pain. The loose holding of the pen between the thumb and the first two
fingers takes the place of the child's full-fisted grasp.

Finally, an important type of modification consists in the
_combination_ of reflex movements into larger cooerdinations. One hand
grasps an object, while the other hand pulls, pushes or strikes it.
Or, both hands grasp the object but in different ways, as in handling
an ax or shovel. These cases illustrate simultaneous cooerdination, and
there is also a serial cooerdination, in which a number of simple
instinctive movements become hitched together in a fixed order.
Examples of this are seen in dancing, writing a word, and, most
notably, in speaking a word or familiar phrase.

In these ways, by strengthening, fixing and combining movements, and
by new attachments and detachments between stimulus and response, the
instinctive motor activity of the baby passes over into the skilled
and habitual movement of the adult.

Acquired Tendencies

In the sphere of _impulse_ and _emotion_ the same kinds of
modification occur. Detachment of an impulse or emotion from its
natural stimulus is very much in evidence, since {300} what frightens
or angers or amuses the little child may have no such power with the
adult. One little boy of two could be thrown into gales of laughter by
letting a spoon drop with a bang to the floor; and you could repeat
this a dozen times in quick succession and get the response every
time. But this stimulus no longer worked when he had advanced to the
age of four.

The emotions get attached to substitut