368 ADVANCED PHYSIOLOGY 



least somewhere between them, in which case the endolymph 

 in two of the canals is moved, and from the resulting sensation 

 one judges the direction of the body motion. These facts, too, 

 explain why children who have been whirling about on their 

 feet in one direction for some time become dizzy. If a pail 

 of water is whirled long enough in one direction the water 

 will finally get to whirling with the pail; and if then the pail 

 is suddenly stopped the water will keep on moving for some 

 time. In the same way, a whirling child sets the endolymph 

 moving in the direction in which the canals go, so that the 

 latter no longer slip around outside the endolymph; when the 

 child stops whirling the endolymph keeps on moving in the 

 canals, and though the body is quite erect, messages continue 

 to go to the brain, and the resulting sensation makes the nerve 

 center feel that some other position of the body must be sought. 

 Messages are consequently sent out to some muscles to relax 

 and to others to contract. As a result the child makes stagger- 

 ing movements, or falls over. Relief can be obtained quickly 

 by whirling in the opposite direction for a moment, thus com- 

 pelling the endolymph to overcome more friction and sooner 

 become quiet. 



THE STRUCTURE AND FUNCTION OF THE COCHLEA 



The shape of the cochlea tube, as it winds into the bone of 

 this region, has already been described as that of a spiral. 

 The diagram in Figure 184, which represents the cochlea as 

 unwound and straightened out, makes this matter of the con- 

 nection between the cochlea and vestibule clear. The part of 

 the structure which has to do with hearing is the dotted 

 horizontal tube, in the walls of which the auditory nerves 

 end. The cochlea is large where it leaves the vestibule, but 

 grows smaller as it coils. It has often been likened to a 

 snail's shell, and indeed takes its name from that fact. 



Extending through the membranous tube (marked cochlea 

 in Figure 184) is a peculiar organ, a sketch of which (highly 



