570 PHYSIOLOGY. 



The number of vibrations would then depend upon the state of tension 

 and the length of the cords themselves. The greater the number of 

 vibrations during a second, the higher will be the tone, and vice versa. 



The range of the human voice, as regards height, is usually 

 between 87 and 768 vibrations per second. Not all persons have 

 such a range. Each type of voice includes about two octaves. When 

 a man speaks that is, when he uses the articulate voice his voice 

 does not exceed the height of a half -octave. When he sings, his 

 vocal range is more extended. 



The Intensity of sound depends upon- the extent of the vibra- 

 tions of the vocal cords, produced especially by the force of the cur- 

 rent of air. 



The height of the voice depends, to a considerable extent, upon 

 different lengths of the vocal cords. The result is that in adult man 



Fig. 213. Position of Vocal Cords on Uttering a High Note. 

 (LANDOIS.) 



the bass, baritone, and tenor voices are found, because of the greater 

 length of the vocal cords in man. On the contrary, the contralto, 

 mezzosopmiw, and soprano voices belong to women and boys, for they 

 have cords shorter in length. 



Timbre of sound depends upon the nature of the vibrating body 

 and of the other parts vibrating at the same time with it for the 

 production of harmonious sounds. 



Resonance. The normal voice of man is sonorous; that is, it 

 is composed of vibrations regular in extent and isochronous. Its 

 resonance comes either from the air-tube or from the resonators. By 

 the former is understood the trachea, bronchi, walls of the lungs, and 

 thoracic case; by the latter, the ventricles, pharynx, mouth, and 

 nasal cavities. The resonance within the thorax in an adult causes 

 a fremitus of the thoracic wall. This is greatly increased in low 

 sounds and diminishes until it disappears in high sounds. 



Ordinarily, in speaking and singing, the air put in vibration in 

 the larynx issues from the mouth while the nostrils are open. If 





