he lungs.

*Pitch and Intensity of the Voice.*--Changes in the pitch of the voice are
caused mainly by variations in the tension of the cords, due to the
movements of the thyroid and cricoid cartilages upon each other.(118) In
the production of tones of very high pitch, the vibrating portions of the
cords are thought to be actually shortened by their margins being drawn
into contact at the back. This raises the pitch in the same manner as does
the shortening of the vibrating portion of a violin string.

The _intensity_, or loudness, of the voice is governed by the force with
which the air is expelled from the lungs. The vibrations of the cords,
however, are greatly reenforced by the peculiar structure of the upper air
passages, as stated above.

*Production of Speech.*--The sounds that form our speech or language are
produced by modifying the vibrations from the vocal cords. This is
accomplished by "mouthing" the sounds from the larynx. The distinct
sounds, or words, are usually complex in nature, being made up of two or
more elementary sounds. These are classed either as _vowels_ or
_consonants_ and are represented by the different letters of the alphabet.
The vowel sounds are made with the mouth open and are more nearly the pure
vibrations of the vocal cords. The consonants are modifications of the
vocal cord vibrations produced by the tongue, teeth, lips, and throat.

*Words and their Significance.*--In the development of language certain
ideas have become associated with certain sounds so that the hearing of
these sounds suggests the ideas. Our words, therefore, consist of so many
sound signals, each capable of arousing a definite idea in the mind. To
talk is to express ideas through these signals, and to listen is to assume
an attitude of mind such that the signals may be interpreted. In learning
a language, both the sounds of the words and their associated ideas are
mastered, this being necessary to their practical use in exchanging ideas.
From spoken language man has advanced to written language, so that the
sight of the written or printed word also arouses in the mind the
associated idea.

THE EAR

*The Ear* is the sense organ which enables sound waves to so act upon
afferent neurons as to excite impulses in them. The effect upon the mind
which these impulses produce is known as the _sensation of hearing_. In
the performance of its function the ear receives and transmits sound waves
and also concentr