27+ Mr. Bishop's Experimental Researches i?ito 



came loud and distinct, but possessing a more reedy quality of 

 tone than belongs to the voice in the living body. 



The difference was doubtless attributable to the absence of 

 the mouth and nasal cavities, which powerfully influence the 

 melody of the voice. 



Finding that during the production of sound the chink of 

 the glottis remained closed, excepting the parts in actual vi- 

 bration, I next minutely observed the change produced in the 

 vocal chords ; I remarked that when the gravest tones were 

 uttered, the ligaments vibrated throughout their whole length, 

 and that as the tones became more acute, a proportionably 

 smaller extent of the ligaments was thrown into vibration. 

 During the production of the most acute tones, the tension of 

 the vocal ligaments was but slightly increased, and the great- 

 est possible tension was insufficient to produce acute tones, 

 whilst these ligaments vibrated throughout their whole length. 



A very slight movement of the thyro-arytenoid muscle 

 seemed to be sufficient to vary the tones, and they would fre- 

 quently become very acute without my being sensible of hav- 

 ing altered the tension. Hence it appears demonstrated that 

 the motions of the thyro-arytenoid and crico-thyroid muscles 

 so affect the vocal chords that a portion of them only is ren- 

 dered susceptible of vibration. 



Since therefore a muscular apparatus has been shown ex- 

 pressly adapted to produce all the motions necessary for the 

 modulation of the voice, it may safely be inferred that the 

 phsenomena observed in experiments thus conducted actually 

 take place in the living body, and that this is the true mode by 

 which all the tones of the voice, whether acute or grave, are 

 effected *. The ligaments of the glottis being attached at their 

 extremities, are subject, as regards their vibrations, to the 

 laws observed in simple strings, modified perhaps in conse- 

 quence of the reflections of the mucous membrane over them, 

 owing to which a broad surface is presented to the current of 

 air rather than isolated chords or strings. 



Having now considered the manner in which the glottis is 

 made to yield all the fundamental notes, whether acute or 

 grave, of the human voice, I shall investigate the nature of 

 those changes which lake place in the vocal tube in order to 

 yield vibrations isochronous with those of the glottis. 



The intimate relation existing between the glottis and the 



* The observations of Magendie tend to confirm those deduced from 

 my experiments. He found that the glottis of a dog vibrated in a small 

 proportion of its length during the utterance of acute tones, but in a larger 

 proportion during the grave tones. This illustrates the identity of the mo- 

 tions of the glottis artificially excited, with those of the living animal. 



