1919] on The Organ of Hearing from a New Point of View 509 



the auditory nerve are concerned in its transmission from the ear to 

 the brain. It is a legitimate inference to suppose that the time 

 signals carried by this code can be deciphered and sorted out at 

 nerve synapses in the central nervous system. Thus Sir Thomas 

 Wrightson's theory brings hearing into line with smell, taste, sight 

 and touch, whereas Helmholtz's theory, by presupposing that each 

 fibre in the auditory nerve has its special function, breaks the most 

 elementary law we know regarding the nature of nerve constitution. 



Recent advances in our knowledge of the evolution of the internal 

 ear throw a most definite light on the mechanism of the cochlea and 

 organ of Corti. The ear has been evolved from the balancing appa- 

 ratus of the primitive labyrinth ; the principle which has been 

 adopted by Xature in working out the organ of hearing is merely an 

 extension of the principle used in the primitive labyrinth. In the 

 low^est fishes a closed vesicle on each side of the head, filled with 

 fluid, serves as the central part of the labyrinth ; on its floor is a 

 nest or island of hair-cells. On the hairs is balanced an otolith ; 

 nerve fibrils commence in or round the hair-cells. So long as a fish 

 swims on an even keel the ciliary semaphoric system is at rest ; but 

 if it heels over, ever so slightly, then gravity comes into play ; the 

 otolith as it answers to gravity bends the hairlets right or left, as 

 the case may be, and on bending the hairlets sets up certain tensions 

 or changes in the living cells to which they are attached, and these 

 changes are transmitted as signals or impulses along the attached 

 nerves. In this simple semaphoric apparatus there are four elements : 

 (1) the otolith or titiUator : (2) the hairlet or lever on which the 

 titillator acts ; (3) the sense-cell on which the lever acts ; (-4) the 

 nerve-fibres which are acted upon or stimulated by the sense-cells. 



In the sense organs or signal stations of the semicircular canals 

 which have been evolved for the registration of body-movements we 

 find the same four elements. The cupola represents the titillator, 

 but it is no longer acted upou by gravity but by mass movements 

 of fluid set up in the canals during movements of the head. Barany 

 was the first to show that movement of the fluid in one direction 

 gave one set of signals ; movement in the reverse direction another 

 and reverse set of signals. 



With the evolution of the cochlea and the organ of hearing the 

 same four elements were used. The titillator is the tectorial mem- 

 brane ; the hairlets or levers, the sense-cells and nerves are as before, 

 save that the sense-cells are now set in an elastic scaffolding of fine 

 elastic rods and fibres. But one novel change has been introduced ; 

 in the balancing apparatus of the vestibule the sense-cells are fixed ; 

 the titillator is movable. In the cochlea Xature has reversed the 

 arrangement and set the sense-cells on a movable membrane — the 

 basilar membrane, which responds to every displacement of fluid set 

 up by waves of sound impinging on the inner ear. On the other 

 hand, the titillator is no longer free but is tethered to the containing 



