S. S. MAXWELL 159 



That the horizontal ampulla reacts to its normal stimulus by a response 

 then is due only to its space relations, and not to a different kind of 

 physiological function. Of course my experiments have demon- 

 strated the ability of the other ampullae to produce sustained static 

 effects. 



The Static Functions of the Otolith Organ. 



In the dogfish and related forms it is comparatively easy to remove 

 all the ampullae and to see that in their absence both static and dy- 

 namic functions are retained by the remaining parts of the labyrinth; 

 that is, compensatory movements and compensatory positions of the 

 eyes and fins still occur in response to rotations in all planes except 

 the horizontal. The removal of the large otolith of the sacculus has 

 no effect whatever on these reactions; but if now, in addition, the small 

 otolith of the recessus utriculi is removed the compensatory move- 

 ments are at once abolished. 



The original suggestion of Breuer that the otolith organs constitute 

 the apparatus for the static functions of the labyrinth has been widely 

 accepted. It has also been generally believed that the pressure of the 

 otolith due to its weight is the stimulus which gives rise to the static 

 function. If, for example, the animal is rotated to the right around 

 its longitudinal axis and held in this new position, the pressure of the 

 otoliths is shifted to the right and presumably the epithelium on the 

 right side of the macula is now subjected to a relatively greater pres- 

 sure, or even a previously unstimulated portion is now brought under 

 pressure. In a previous paper^ I was inclined to accept a similar 

 explanation of the dynamic functioning of the otolith. In the light 

 of new experiments to be reported below I am led to modify this 

 view. I had, however, long ago given proof that in the compensatory 

 movements of the horned toad (Phrynosoma) the exciting cause is not 

 pressure, per se, but the torsion effect due to rotation.^ 



^ Maxwell, S. S., Labyrinth and equilibrium. II. The mechanism of the 

 dynamic functions of the labyrinth, /. Gen. Physiol., 1919-20, ii, 349. 



^ Maxwell, S. S., On the exciting cause of compensatory movements, Am. J. 

 Physiol., 1911-12, xxix, 367. 



