THE EAR, HEARING, TASTE AND SMELL 199 



twenty-four thousand strands. Fourteen thousand nerve-fibers 

 communicate with the hair-cells of the organ of Corti. 



We must suppose that compound tones entering the ear set the 

 fluids of the cochlea into vibrations whose form depends upon the 

 make-up of the tone producing them. These vibrations are 

 analyzed by the basilar membrane, the particular strands having 

 the vibration rates of the fundamental and the partials which are 

 present being set into sympathetic vibration and stimulating the 

 nerve-fibers with which they communicate. 



Auditory Perceptions. Sounds, as a general rule, do not seem 

 to us to originate within the auditory apparatus; we refer them to 

 an external source, and to a certain extent can judge the distance 

 and direction of this. As already mentioned, the extrinsic reference 

 of sounds which reach the labyrinth through the general skull- 

 bones instead of through the tympanic chain is imperfect or 

 absent. The recognition of the distance of a sounding body is pos- 

 sible only when the sound is well known, and then not very accu- 

 rately; from its faintness or loudness we may make in some cases a 

 pretty good guess. Judgments as to the direction of a sound are 

 also liable to be grossly wrong, as most persons have experienced. 

 However, when a sound is heard louder by the left than the right 

 ear we can recognize that its source is on the left; when equally 

 with both ears, that it is straight in front or behind; and so on. 

 The concha has perhaps something to do with enabling us to detect 

 whether a sound originates before or behind the ear, since it col- 

 lects, and turns with more intensity into the external auditory 

 meatus, sound-waves coming from the front. By turning the head 

 and noting the accompanying changes of sensation in each ear we 

 can localize sounds better than if the head be kept motionless. The 

 large movable concha of many animals, as a rabbit or a horse, 

 which can be turned in several directions, is probably an important 

 aid to them in detecting the position of the source of a sound. That 

 the recognition of the direction of sounds is not a true sensation, 

 but a judgment, founded on experience, is illustrated by the fact 

 that we can estimate much more accurately the direction of the 

 human voice, which we hear and heed most, than that of any other 

 sound. 



Nerve-Endings in the Semicircular Canals and the Vestibule. 

 Medullated fibers (/, Fig. 75) from the vestibular branch of the 



