208 SPECIAL PHYSIOLOGY. 



opening. The escape of the air propelled upwards through the trachea, 

 being thus retarded, the margins of the vocal cords are forced upwards, 

 and slightly separated from each other ; the elasticity of the cords is 

 now called into play, so that they counteract the force of the impulse 

 communicated to them, and, by a downward recoiling movement, again 

 narrow the glottis. In this manner, the oscillations into which the 

 vocal cords are thrown by the escape of the air driven from the trachea, 

 or wind-tube, are communicated to the less tense air above the glottis, 

 and throw this into vibrations. By means of the laryngeal ventricles 

 or sacs, placed above the vocal cords, these latter are kept free, so 

 that their vibrations are easily accomplished. It has also been sup- 

 posed by some, that the superior vocal cords maintain the strength 

 and quality of the sounds, by entering into simultaneous and syn- 

 chronous vibrations. This is contrary to Senor Garcia's observations 

 with the laryngoscope ; but he found that, in elevation of the pitch of 

 the voice, whether natural or falsetto, the superior vocal cords ap- 

 proach each other, so as to narrow the part of the vocal tube above 

 the glottis. 



The human voice, from the lowest male to the highest female voice, 

 has a range of nearly 4 octaves, the lowest note being E,* caused by 

 80 vibrations per second, and the highest C,f caused by 1024 vibra- 

 tions in the second. But if extreme cases be included, the range is 

 nearly 5J octaves, the lowest note being F,J caused by 42 vibrations, 

 the highest A, by 1708 vibrations (Vierordt). In the same individual, 

 the compass of the voice, in singing, generally extends over 2 octaves ; 

 in some rare instances, however, it has been known to include even 3J 

 octaves. In ordinary speech, the range of the voice is usually about 

 half an octave. The production of these different notes is effected by 

 alterations in the length and tension of the vocal cords, and by changes 

 in the degree of approximation and separation of these ; thus, during 

 the emission of the low notes, the cords are longer, looser, and more 

 widely separated from each other, than they are during the produc- 

 tion of notes of a higher pitch, and the air passes through the glottis 

 more slowly, but in larger quantity. It has been calculated that 240 

 different states of tension of the vocal cords must be accurately pro- 

 ducible at will, to account for all the notes and intermediate tones 

 possible in a perfect human voice of ordinary range. The celebrated 

 Madame Mara could effect as many as 2000 changes. 



There are four different varieties of voice, viz., the bass, tenor, con- 

 tralto, and soprano the two former being characteristic of the male 



3 



i a^ dfc* 



IF 





