524 STUDIES IN ADVANCED PHYSIOLOGY. 



this way a sensation is produced which in the mind is in- 

 terpreted in terms of position or movement. If, however, 

 the motion in a certain direction should continue, the endo- 

 lymph inside would soon adjust itself to that motion, just 

 as after a train has started the passengers no longer feel a 

 tendency to be thrown backwards. A sudden stopping now 

 of the train throws the passengers violently forward. So a 

 sudden stopping of the motion of the body, say for instance 

 from a circular motion, will cause the endolymph on ac- 

 count of its inertia to be thrown forwards and in this way 

 affect the projecting hair cells and give rise to a sensation 

 of motion. Possibly this is the explanation of the dizziness 

 which results when a rotary motion of the body suddenly 

 ceases. To the individual it seems that he is still moving. 

 One point in favor of the view that these organs are 

 wholly organs of equilibrium is the fact that the perception 

 of all sounds can be satisfactorily explained in the cochlea, 

 and so there is no necessity to begin with for attributing 

 auditory sensations to these structures. On the other hand, 

 however, none of the invertebrates have a cochlea, and yet 

 it would be entirely wrong to think that these animals are 

 without the sense of hearing. Evidently, therefore, in the 

 invertebrates at least, structures very analagous indeed to 

 utriculus, sacculus and ampulla are directly concerned in 

 the perception of sound, and it may be possible that even 

 in the human being this property has not been entirely lost, 

 but has simply been overshadowed by the addition of a new 

 structure to the ear, the cochlea. 



2. The Function of the Cochlea. The anatomy of the 

 cochlea readily shows how a vibration descending the scala 

 tympani is brought in direct contact with the basilar mem- 

 brane, and how there by sympathetic vibrations it sets into 

 motion some one of the many strings which is attuned to it. 

 Arrangement is thus made in purely physical ways to set in 

 vibration the proper string in any case, but it is an equal 

 physical necessity that such vibration should cease as soon 

 as the sound producing it ceases. It would, of course, be 



