350 



APPLIED PHYSIOLOGY 



together. Expiring air between these bands, while they 

 are tight and close together, causes them to vibrate and 

 produce a sound which is called the voice. Hence the 



Top view of the larynx, with the 



vocal cords closed, as in speaking. 



a epiglottis. b vocal cords. 



Top view of the larynx, with the 

 vocal cords open, as in breathing. 



a epiglottis. b vocal cords. 



bands are called the vocal cords. The whole larynx, ex- 

 cept the edges of the vocal cords, is covered with loose 

 mucous membrane. 



628. Pitch of the voice. All sound has the four char- 

 acteristics of pitch, intensity, quality, and duration. The 

 same characteristics apply to the voice. 



Pitch depends upon the number of vibrations which 

 occur each second. In order that the vibrations of the 

 air shall blend into a musical note they must occur at the 

 rate of sixteen times a second, but until they reach a rate 

 of fifty the sound is more like a buzz than music. Upper 

 C of the bass voice which corresponds to lower C of a 

 soprano, is produced by 256 vibrations per second. The 

 shorter or tighter the vocal cords are, the higher will be 

 the pitch. In men the cords are longer than in women, 

 making a man's voice an octave lower in pitch. The 

 larynx and voice of a boy resemble those of a girl. At 

 about the age of fifteen the voice of a boy becomes like 

 a man's, while in a girl it remains unchanged. 



629. The intensity of the voice depends upon the force 

 with which air is expelled through the larynx. In making 



