Normally, we communicate with one another in three ways; by means of
marks upon paper (writing), by movements (sign language), and by means
of air vibrations issuing from the vocal chords (speech). The question
of the origin of speech is a much disputed one, some authorities
contending that we gradually attached meanings to certain primitive
sounds; others that we learned to express ourselves in speech in order
to express our thoughts.
There are certain definite areas in the brain which send out the
necessary motor currents, rendering speech possible. We have two such
centers, one in each hemisphere, but we ordinarily use but one of
them. Right-handed people use the one in the left hemisphere, while
left-handed persons utilize the one in the right hemisphere. Should
this active area be injured, the subject becomes _dumb_--though the
corresponding area in the other hemisphere may be quite intact. Hence
the importance of teaching children to become “ambidextrous”; _both_
centers are thereby cultivated, and, if one is injured, the patient can
still talk. An extended discussion of this entire subject may be found
in Dr. N. C. MacNamara’s “Human Speech; its Physical Basis.”