As a rule, vocal teachers pay little attention to this form of resonance. The subject of enunciation is generally treated as distinct from tone-production strictly speaking. While the correct emission of the tone, in its passage from the vocal cords to the lips, is considered a very important topic, this feature of tone-production has no reference to resonance. One exception must be made to the statement that no attention is paid to mouth-pharynx resonance. This is found in an interpretation of the empirical precept, "Sing with open throat." Several vocal theorists take this precept literally, and hold that it describes a function of mouth-pharynx resonance. According to their idea the cavity must be expanded to the largest size possible, on the theory that a large resonance cavity secures a proportionately greater reinforcement of the tone. "The greater the size of the pharynx, whether through practice or natural gifts, the stronger in proportion is the tone." (_Die Kunst der idealen Tonbildung_, Dr. W. Reinecke, Leipzig, 1906.) This theory is of course rather loose and unscientific. Still this idea,--a literal interpretation of the "open throat" precept,--receives much attention in practical instruction. Only one muscular action has ever been defined by which the throat might be "opened." That is, the lowering of the larynx and the raising of the soft palate. Many teachers therefore direct that the throat be "opened" gradually in this way for the swelling of the tone. It is assumed that the power of the voice is developed by singing with the larynx low in the throat. This manner of instruction is, however, very loosely given. The supposedly scientific interpretation of the "open throat" precept shades off into a purely empirical application. _Chest Resonance_ In no other topic of Vocal Science is the gap between theory and practice more striking than in the doctrine of chest resonance. Vocal teachers are in fair accord in believing the resonance of the air in the chest to be the most important influence in imparting power and "color" to the voice, and particularly to the lower notes of its compass. Students of singing are in almost all cases urged to acquire a proper command of chest resonance. But when it comes to telling the student how to learn to govern the chest resonance, the teacher has practically nothing to offer. No direct means has ever been found for causing the air in the thorax to vibrate; this cannot be effected, so far as has yet been determined, by any voluntary muscular action on the part of the singer.