126 EXPERIMENTAL PHYSIOLOGY 



shape and size of the resonating chamber formed by the throat and 

 buccal cavity. 



The production of consonants. Notice that most of the consonants 

 are produced by an interruption, complete or incomplete, of the blast 

 of air which is producing the vibration of the vocal cords, the interrup- 

 tion occurring either at the back of the palate (gutturals) or at the 

 front of the palate (linguals), or at the lips (labials). Notice also that 

 the character of the interruption is a factor in determining the quality 

 of the consonant : thus, with some, such as k t b, and t, it is sudden or 

 explosive ; with others, such as m and n, the nasal cavities are brought 

 in as resonators ; with others, such as ch, f, and s, the blast is con- 

 tinuous, but is made to traverse a narrowed part of the cavity : whilst 

 with q there is an actual vibration of the narrowed part. 



The production of sounds by vibration of the vocal cords, and the 

 dependence of the pitch of sounds on the tension of the cords. Take 

 a sheep's larynx and tie a glass tube into the trachea. Fix the larynx 

 securely on a board, with the dorsal surface downwards, by wires 

 or strong pins through the cricoid cartilage and epiglottis. Pass a 

 string through the lower part of the thyroid cartilage. When this 

 string is pulled vertically upwards, the vocal cords are stretched in 

 proportion to the pull, and become approximated. If air is blown 

 through the tube in the trachea, the edges of the cords are set in 

 vibration when thus approximated and a sound is emitted, the pitch 

 of which varies with the tension of the cords. The blast of air should 

 be of about the same strength throughout. 



Analysis of sounds of musical instruments and of the voice. The 

 analysis can be made by applying different Helmholtz resonators to 

 the ear of the observer. Konig's manometric flames, which are 

 provided with these resonators and are examined with the aid of 

 vertical rotating mirrors, are also employed for this purpose. 



Determination of range of pitch for audition. The highest and 

 lowest notes which can be appreciated are determined by the use 

 of Galton's adjustable whistle. 



Conduction of sound by the bones of the skull. Stop the ears with 

 wool. Set a small tuning-fork in vibration, and hold it with the base 

 touching the top of the skull. The sound is propagated to the cochlea 

 by the bones of the skull. 



Inspection of the tympanic membrane. Using a mirror with a 

 central aperture fired in front of the eye, throw the reflection of a 

 lamp into the meatus of the subject, whose external ear must be 

 drawn somewhat backwards and upwards. 



Propagation of sound to the internal ear. The mode of transmission 

 may be studied with the aid of a model showing the bones of the 



