For the production of tone the vocal cords are brought together and held on tension with sufficient strength momentarily to close the glottis and check the outflow of the expired breath. As a slight degree of condensation takes place in the air behind the cords, they are forced apart and a tiny puff of air is allowed to escape. Immediately the cords spring back, once more close the glottis, and again check the outflow of the breath. This is repeated a varying number of times per second, the rate of rapidity of the succession of puffs being regulated by the degree of tension of the vocal cords, and by their effective vibrating length. The pitch of the tone thus produced is determined by the rate of the air puffs; these range from 75 per second for the lowest usual bass note, [Illustration: Music score] to 1,417 per second for the highest usual soprano note, [Illustration: Music score]. The tone produced by the vibration of the vocal cords is complex in its acoustic character, containing the fundamental note and a large number of its overtones. Yet as it leaves the cords the tone is weak in power and of rather characterless quality. In order to be of musical quality, volume, and carrying power, the primary or vocal cord tone requires to be modified and reinforced by the resonance cavities. The resonating cavities of the voice, mastery of which is considered essential to the scientific management of the voice, are the chest, the mouth-pharynx, the nasal passages, and the sphenoid, ethnoid, and frontal sinuses. Each of these is adapted by its size and shape to reinforce either the fundamental note or certain of its overtones with especial prominence. In order to produce a satisfactory tone each resonance cavity must exercise its particular influence in the proper way, their combined effect being necessary to a correct use of the voice. Much importance is attached by most vocal authorities to the subject of chest resonance. It is believed that the size of the chest cavity,[1] much greater than that of the other resonating spaces, adapts it especially to the reinforcement of the fundamental note and its lower overtones.[2] The mouth-pharynx cavity is capable of extreme variability in both size and shape. This mobility enables it to reinforce a wide variety of overtones, and so to exercise a most important influence in determining the quality of the tone. Another function of this cavity is to increase the power of the primary or vocal cord tone. To secure the effect of crescendo in a single tone, the force of the expiratory blast is gradually increased. In order that the tone may be of uniform musical quality as it swells from soft to loud, a corresponding increase must take place in the size of the mouth-pharynx cavity. This is effected by the gradual opening of the mouth by a lateral expansion of the pharynx and by a lowering of the base of the tongue. A slight elevation of the soft palate may also contribute to the expansion of the cavity.