MECHANISM AND CHEMISTRY OF RESPIRATION 213 



rapidly even though one blows on it steadily. For similar 

 reasons the vocal cords, stretched across the trachea, will 

 vibrate when a strong, steady current of air is sent through 

 them, thus producing air waves which give rise to sound. 



Pitch of Voice. The short strings on a piano give out 

 higher tones than the longer ones; but the pitch of any of the 

 strings may be made higher by tightening them. In the 



Cartilage 



Vocal Cords 



Talking 



Vocal Cords 



Bredhlnq 



FIG. 107. THE LARYNX AS VIEWED FROM ABOVE WITH THE MEMBRANES 



IN POSITION 



The figure at the left shows the vocal cords tightened to produce a sound as in talking 

 and that at the right shows them slackened and widely open as in quiet breathing. 



larynx, the length of the vocal cords cannot be changed, so 

 pitch must be modified by varying their tension. If the 

 muscles that tighten the vocal cords contract, the cords will 

 give out a high tone; if these muscles relax a little and the 

 opposite muscles (Fig. 106) shorten, the vocal cords will 

 loosen and a lower tone result. Under ordinary circum- 

 stances these differences in tension are brought about in- 

 voluntarily, but in singing, conscious determination of theii 

 tension occurs to a certain extent. 



Difference in Voice in Women and Men. The reason why 

 ;he voice in women is so much higher in pitch than it is in 

 len, is that a woman's larynx is actually smaller than a man's, 

 hen a boy is about fifteen years of age, his larynx begins tc 



