352 ELEMENTS OF PHYSIOLOGY 



Two persons sing a song together in the same pitch and 

 with the same loudness; yet you can readily distinguish 

 a difference in the two voices. This is because of a dif- 

 ference in 



Quality, which is the third variation possible in a voice. 

 Sound in wind instruments is strengthened by resonance, 

 which is a kind of instantaneous echo in the pipes. 



635. The vibration of the vocal cords alone produces a 

 weak, squeaky sound, but their vibrations are reenforced or 

 strengthened by the vibration of the walls of the lungs and 

 windpipe below, and of the nose and mouth above. These 

 echoes, combining with and reenforcing the vibration of 

 the cords, determine the quality of the voice. Just as the 

 shape and material of the walls of the violin give the quality 

 to its tone, so the shape and condition of the nasal passages, 

 throat, etc., give characteristic quality to each human voice. 

 If the nasal passages are stopped up by catarrh, the per- 

 son is said to speak in a nasal tone, or through the nose, 

 but a "nasal" tone really results only when the sound 

 cannot come through the nose. Such a person's voice 

 does not change its quality, when he speaks with his nose 

 stopped with his fingers. But a voice which has correct 

 nasal resonance will change its quality when the nose is held. 

 Try it, and see whether your voice retains its nasal reso- 

 nance. Let one pupil read aloud at the back of the room 

 where the others do not see him, and find whether they 

 can tell, by the change in his voice, at which word he 

 closes his nose in the midst of the reading. The vocal 

 cords are not used at all in whispering. It is akin to 

 whistling. 



636. Duration of Sound. In singing, single sounds are 

 more or less prolonged. In speech, the principal changes 

 are in the duration of the sound, and in the resonance in 

 the mouth. In whispering, audible breathing is cut off by 

 the tongue and lips, and words are articulated, although 



