144 PHYSIOLOGY CHAP. 



The trachea was connected to a bellows, and the different 

 pressures at which the air traversed the glottis were measured 

 by a manometer. 



With this method Mliller carried out a long series of experi- 

 ments which, though less valuable to-day owing to the laryngo- 

 scopical observations now made on the living subject, were of 

 epoch-making importance in the history of physiology. When 

 the cords were brought together, their tension being unchanged, 

 the laryngeal sounds became higher ; on moving the cords apart, 

 the sounds were deeper. With increased tension of the cords, the 

 note could be raised two octaves. With increased air pressure, the 

 tension of the cords being unchanged, the strength and pitch of 

 the laryngeal note could be raised a fifth. Lastly, he found that 

 everything above the true vocal cords could be removed without 

 altering the pitch of the sounds, and that the office of the accessory 

 tube, the pharyngo-buccal and nasal cavities, was limited to 

 altering the pitch. 



J. Miiller first constructed an artificial larynx with one or two 

 membranous tongues of elastic material or arterial wall stretched 

 across the mouth of a wooden pipe, on which he studied the 

 mechanical conditions for the production of sound and of variations 

 in pitch, strength, and timbre. But ,in his conclusions he fell into 

 the same error as Ferrein, who first compared the vocal cords to 

 the strings of a violin, and regarded their vibrations as the primary 

 source of the sounds, the air blast as the bow which threw them 

 into vibration, and the thorax and lungs as the hand that moves 

 the bow. Miiller supported this theory, even after W. Weber had 

 demonstrated by his classical experiments that the sounds of 

 tongued instruments are essentially due to explosions of air, viz. 

 to the periodic increments and decrements of pressure as it passes 

 through the slit that lies between the vibrating tongues. 



Direct observation on the living subject of the position of the 

 glottis during the formation of sounds was an immense advance 

 in the study of the mechanism of the laryngeal sounds. 



Magendie (1816) was the pioneer in this research. He 

 recognised that it is necessary for the emission of vocal sounds 

 that the arytenoids and vocal cords be brought together, 

 while the opening of the inter-cartilaginous glottis does not 

 prevent the formation of sounds. His method consisted in 

 exposing the glottis in dogs by an incision between the hyoid 

 bone and thyroid cartilage. The same method was adopted by 

 the surgeon Malgaigne (1831), who corrected certain errors in 

 Magendie's observations, and showed that only the pars rnern- 

 branacea of the glottis is concerned in voice formation. 



The human glottis has also been directly observed in persons 

 who have attempted suicide by cutting the throat above the vocal 

 cords (Mayo, 1883, and others). Such observations confirm the 



