THE SENSES I 57 



membrane to bulge inward, and to be stretched so tight 

 that it cannot vibrate freely. 



The inner ear is called the labyrinth, because of its wind- 

 ing passages. There is a spiral passage called the snail 

 shell and three simpler passages called the loops (Fig. 128). 

 The inner ear is filled with a limpid liquid which conveys 

 the vibrations to the ends of the auditory nerve found in the 

 snail shell. If the auditory nerve or labyrinth becomes 

 diseased, the deafness is probably incurable. Quinine and 

 other drugs may cause deafness. 



Sense of Equilibrium. — Some fibers of the auditory nerve end in the 

 loops and are not believed to be used in hearing. It is believed that 

 each loop acts like a carpenter's level, and the varying pressure of the 

 fluid upon the nerves in the loops tells us the position of the body and 

 constitutes the sense of equilibrium. There are how many of these 

 loops in each ear ? (Fig. 128.) 



