

OTOLITH SACS OF THE INNER EAR 481 



D. THE OTOLITH SACS 



It will be readily understood that a movement in a straight line will not 

 produce any current in the semicircular canals, for the reason that the influence 

 of inertia in the two halves of each canal will be found to be equal and in oppo- 

 site directions. But, as Breuer has observed, it appears that the otolith apparatus 

 may be stimulated under these circumstances. The impression which the otolith 

 will make at any time will depend on the position with reference to the direc- 

 tion of gravity, of the surface between the otolith and the subjacent epithelium, 

 and will vary, therefore, with the position of the head with reference to the line 

 of gravity. On account of the varying position of the different maculaB, the 

 impressions from the different otoliths for any given position of the head will 

 also be different. Hence, every position of the head would be accompanied by a 

 definite combination of impressions discharged by the otoliths, and hence the 

 otolith sacs would constitute an organ for the perception of the position of the 

 head with reference to a plumb line. 



Again, if we suppose, as Breuer has sought to show, that each otolith has a 

 definite " groove," so to speak, in which it may exert the pressure due to its 

 inertia, we should have an arrangement by which translocation movements in 

 any straight line could be perceived. 



Several observations on fishes have been cited in support of this function of 

 the otolith sacs, their purport being that when the sacs are injured or destroyed 

 the orientation of the animal with reference to gravity is practically lost. 



E. OBSERVATIONS ON MEN 



The rotation experiments constitute a no less valuable means of studying 

 the influence of the semicircular canals in man. When a man with normal 

 ears is rotated about the vertical axis in an apparatus suitable for the purpose, 

 the eyes are moved first slowly in the opposite direction, then quickly in the 

 same direction as the rotation. This reaction appears to be perfectly constant 

 in healthy individuals, but is often (fifty per cent of the cases 1 ) wanting 

 in the deaf and dumb (Kreidl). 



Kreidl asserts furthermore that these same deaf-and-dumb persons who 

 failed to give the eye reaction, did not suffer from dizziness when the rotation 

 ceased, as the normal persons do. and similarly, we find in James the state- 

 ment that out of 519 deaf-and-dumb persons only 199 suffered from dizziness 

 as the result of rotation. 



The explanation which Breuer has advanced with reference to the func- 

 tion of the otolith sacs in animals, namely, that they make the animal aware 

 of its position with reference to the line of gravity, appears to apply also to 

 man. Certain positions of the eyes are unquestionably dependent upon the 

 position of the head with reference to the line of gravity. Thus, for example, 

 in the blind the bending of the head forward is accompanied by an elevation 

 of the plane of vision with reference to the head, and bending the head 

 backward by a corresponding lowering of the plane of vision (Breuer). In 

 persons with normal eyes these movements do not occur. But we meet with 



1 Mygind has ascertained that in Copenhagen about fifty-six per cent of the deaf 

 and dumb have the semicircular canals affected. 



