5 8o TEXT-BOOK OF PHYSIOLOGY. 



which the laryngeal vibrations are reinforced. The degree of pres- 

 sure to which the air in the lungs and trachea is subjected was 

 determined by Latour to vary from 160 mm. of water for sounds of 

 moderate, to 940 mm. of water for sounds of highest intensity. With 

 the escape of the air or the separation of the vocal bands the vibra- 

 tion ceases and the sound dies away. 



The Characteristics of Vocal Sounds. In common with the 

 sounds produced by all other music instruments, all vocal sounds 

 are characterized by intensity, pitch and quality, tone or color. 



The intensity or loudness of a sound depends on the extent or 

 amplitude of the up-and-down vibration or the extent of the excur- 

 sion of the vocal band on either side of the position of equilibrium 

 or rest ; and this in turn depends on the force with which the blast of 

 air strikes the band. The more forceful the blast of air, the larger, 

 other things being equal, will be the primary vibrations of the bands, 



FIG. 267. POSITION OF THE VOCAL 

 BANDS PREVIOUS TO THE EMISSION 

 or A SOUND, b. Epiglottis, rs. False 

 vocal band. ri. True vocal band. 

 ar. Arytenoid cartilages. 



rap 



FIG. 268. POSITION OF THE VOCAL 

 BANDS IN THE PRODUCTION OF 

 NOTES OF Low PITCH. /. Epiglottis. 

 or. Glottis, ns. False vocal cord. 

 ni. True vocal cord. ar. Arytenoid 

 cartilages. (Mandl.) 



and hence the secondary vibrations of the air in the upper air- 

 passages. 



The pitch of the voice depends on the number of vibrations in 

 a unit of time, a second. This will be conditioned by the length of 

 the bands in vibration or the length and width of the aperture through 

 which the air passes and the degree of tension to which the bands are 

 subjected. In the emission of sounds of highest pitch the tension of 

 the vocal bands and the narrowing of the glottis attain their maxi- 

 mum. In the emission of sounds of lowest pitch the reverse conditions 

 obtain. In passing from the lowest to the highest pitched sounds in 

 the range of the voice peculiar to any one individual, there is a pro- 

 gressive increase in both the tension of the vocal bands and the 

 narrowing of the glottic aperture. In the production of low-pitched 

 notes of men, those due to vibrations lying between 80 and 240 per 

 second, the tension is regulated by the crico-thyroid muscle; the 



