RESPIRA TION 279 



the vibrating cords. An approximation of the cords, a narrowing 

 of the glottis, is essential to the production of voice ; with a 

 widely-opened glottis the air escapes too easily, and the necessary 

 pressure cannot be attained. The pressure in the windpipe was 

 found in a woman with a tracheal fistula to be about 12 mm. of 

 mercury for a note of medium height, about 15 mm. for a high 

 note, and about 72 mm. for the highest possible note. The 

 period of vibration of structures like the vocal cords depends on 

 their length, thickness, density and tension ; the shorter, thinner, 

 more tense and less dense a stretched string is, the greater is 

 the vibration frequency, the higher the note. In the child 

 the cords are short (6 to 8 mm.), in woman longer (10 to 12 mm. 

 when slack, 13 to 15 mm. when stretched), in man longest of 

 all (14 to 18 mm. in the relaxed, and 18 to 22 mm. in the stretched 

 position) ; and the lower limit of the voice is fixed by the 

 maximum length of the relaxed cords. A boy or a woman 

 cannot utter a deep bass note, because their vocal cords are 

 relatively short, and do not vibrate with sufficient slowness. 

 It is true that by the action of the crico-thyroid muscle the 

 cords can be lengthened, and that the maximum length in a 

 woman approaches or exceeds the minimum length in a man. 

 But the lengthening of the vocal cords in one and the same 

 individual is always accompanied by other changes increase 

 of tension, decrease of breadth and thickness which tell upon 

 the vibration frequency in the opposite way, and more than 

 compensate the effect of the increase of length, so that for high 

 notes the cords are longer than for low. The contraction of the 

 thyro-arytenoid muscle is a more influential factor in altering the 

 tension of the cords than the contraction of the crico-thyroid. 

 It is probable that when the highest notes are uttered, only the 

 anterior portions of the cords are free to vibrate, their posterior 

 portions being damped by the approximation of the vocal pro- 

 cesses of the arytenoid cartilages by the contraction of the lateral 

 crico-arytenoid and transverse arytenoid muscles. The range 

 of an ordinary voice is 2 octaves ; by training 2j octaves can be 

 reached ; but in exceptional cases a range of 3, and even 3j, 

 octaves (as in the celebrated singer Catalani) has been known. 



The development of the voice in children is of great interest. At 

 the age of six years the boy's voice has a rather narrower range than 

 the girl's in both directions. The boy's voice reaches its full height 

 yi the twelfth and its full depth in the thirteenth year, when the 

 range is almost 3 octaves, its upper limit being a semitone higher 

 than the girl's, but its lower limit a whole tone deeper. When the 

 voice ' breaks ' in boys at the age of puberty it falls about an octave. 

 The control of the vocal organs becomes so incomplete that only in 

 one-fourth of the cases can notes of sufficient steadiness to be used 

 in music be produced. The vocal cords, as may be seen with the 

 laryngoscope, are frequently, though not always, congested. 



