158 STATIC FUNCTIONS OF LABYRINTH 



contents of the vestibule returned at once to their original position 

 the stimulus would cease and the eyes would return to the primary 

 position. If, however, the new position of the vestibular structures 

 continued to exist after cessation of the movement the tension differ- 

 ences would also continue and the resulting stimuli would give rise 

 to sustained forced position of the eyes; i.e., to the static effect. The 

 latter condition could exist in case the specific gravity of the utricular 

 tissues is greater than that of the lymph. This I have found to be 

 the case. 



In most selachians the lymph of the vestibule is in free communi- 

 cation with the exterior sea water through the ductus endolymphati- 

 cus. It is reasonable therefore to expect that the density of the 

 lymph would be practically equal to that of sea water. On this 

 assumption I determined the relative weights of the membranous 

 labyrinth and sea water by dropping small bits of utricle, ampullae, 

 and semicircular canals into a tall jar of sea water and saw that they 

 all sank to the bottom. In order to be more certain, however, I 

 succeeded in getting a sufficient amount of lymph from the ears of 

 several fish killed at one time and dropped bits of the membranous 

 labyrinth into it, with the result that they sank just as in sea water. 



Since the membranous labyrinth and the lymph differ in specific 

 gravity it is evident that when the membrane is displaced to a rela- 

 tively lower position its weight will have the tendency to prevent its 

 return to the original position in the cavity as long as the new body 

 position is retained. I believe that this difference in weight, then, is 

 the cause of the continued forced position in the absence of the otolith. 



It has been frequently stated that the stimulation of an ampulla 

 gives rise only to a momentary movement, not to a sustained forced 

 position, and that therefore its function can be only dynamic and not 

 static. I have found the contrary to be very definitely true. Sus- 

 tained mechanical stimulation of an ampulla, even the ampulla of a 

 horizontal canal, causes a sustained forced position of the two eyes; 

 namely, a conjugate deviation to the side opposite to the stimulated 

 ampulla. It is self-evident that in the ordinary functioning of the 

 horizontal ampulla, when the rotation to which it responds is in a 

 horizontal plane, no changed relation to gravity can occur and hence 

 the reaction to rotation cannot continue after the rotation has ceased. 



