THE LARYNX AND THE EAR 367 



5. Name all the parts of the body that are directly or indirectly 

 concerned in the production of sound. 



6. Describe the larynx. 



7. Describe the condition of the vocal cords in speaking and in 

 ordinary breathing. 



8. How are sounds differing in pitch and intensity produced by the 

 larynx ? 



9. How is the sound produced by the vocal cords changed into 

 speech ? 



10. What parts of the ear are concerned in transmitting sound 

 waves ? 



11. Give the purposes of the middle ear. 



12. Trace a sound wave from a bell to the basilar membrane, and 

 trace the impulse that it causes from there to the brain. 



13. Give the purpose of the Eustachian tubes ; of the rods of Corti ; 

 of the semicircular canals. 



14. Give directions for the proper care of the ear. 



PRACTICAL WORK 



To illustrate the Origin of Sound. i. Strike a bell an easy blow 

 and hold some light substance, as a pith ball attached to a thread, 

 against the side, noting the result. 2. Sound a tuning fork by striking 

 it against the table. Test it for vibrations as above, or by letting the 

 vibrating prongs touch the surface of water. 3. Pluck a string of a 

 guitar or violin, and find proof that it is vibrating while giving out 

 sound. 



To show the Transmission of Sound. i . Vibrate a tuning fork 

 and press the stem against a table or desk. The vibrations which are 

 reenforced in this way will be heard in all parts of the room. Now 

 press one end of a wooden rod, as a broom handle, against the table, 

 and bring the stem of the vibrating fork against the other end. The 

 vibrations now move down the stick to the table, from whence they 

 are communicated to the air. Observe that the sound waves, to reach 

 the ear, must pass through the rod, the table, and the air. 2. Fasten 

 the timing fork to a flat piece of cork by pressing the stem into a small 

 hole in the center. Vibrate the fork and let the cork rest on the sur- 

 face of water in a half-filled tumbler on the table. The sound will, as 

 before, pass to the table and then to the air. Observe that in this case 

 the vibrations are transmitted by a liquid, a solid, and by the air. 



