onsist of a number of sets of voluntary
muscles, of the bones and cartilages to which these muscles are
attached, and of the nerves and nerve centers governing their actions.
The precise nature of the muscular contractions of tone-production,
whether correct or incorrect, is not known. These contractions occur in
accordance with established laws of acoustics and mechanics. Under
normal conditions the vocal organs instinctively respond to the demands
of the singer, through the guidance of the sense of hearing. The ability
of the vocal organs to adjust themselves properly may be upset by some
influence apparently outside the singer's voluntary control. Study of
the vocal mechanism does not inform us of the meaning of the correct
vocal action, nor of the difference between this action and any other
mode of operation of the voice.

Empirically considered, there is a striking difference between the
correct vocal action and any other manner of tone-production. A perfect
vocal tone awakens in the hearer a distinct set of auditory and muscular
sensations. Attentively observed, the muscular sensations of the hearer
indicate that the perfect vocal tone is produced by the balanced and
harmonious action of all the muscles of the singer's vocal mechanism. In
listening to perfect singing the hearer feels that every muscle of the
singer's vocal organs is contracted with exactly the appropriate degree
of strength. Any vocal tone of unsatisfactory sound awakens in the
hearer a set of muscular sensations, the direct opposite of those
indicating the correct vocal action. An incorrectly produced tone
imparts to the hearer a sensation of stiffness and undue muscular
tension, located more or less definitely in the throat. This sensation
indicates that the singer's throat is stiffened by excessive muscular
contraction. Further, this feeling of throat stiffness indicates to the
hearer that the singer's vocal action would become correct if the undue
muscular tension were relaxed.

Combining now the results of empirical and scientific investigation of
the voice, throat stiffness is seen to be the interfering influence
which disturbs the instinctive connection between voice and ear. Let us
now consider the meaning of throat stiffness as a feature of incorrect
tone-production. First, what is muscular stiffness?

All the voluntary muscles of the body are arranged in opposed pairs,
sets, or groups. A typical pair of opposed muscles are the biceps