Physiology of the Otic Labyrinth. 203 



the nystagmus time decreases progressively with practice. They 

 find that in four persons subjected to frequent periods of rotation 

 over an extended period (20 days) the average post-rotatory 

 nystagmus time fell from 24.9 to 6.3 seconds. 



The question then arises as to whether the nystagmus time 

 can be taken as an absolute index of labyrinthine efficiency. 



In experiments on animals it has been shown that the nystagmus 

 following unilateral extirpation of the otic labyrinth disappears a 

 few days after operation and that the ocular symptoms (deviation) 

 recur after ablation of the cerebrum. This seems to indicate that 

 the disappearance of nystagmus under these circumstances is 

 dependent on the activity of a compensatory mechanism localized 

 in the cerebrum. 1 



In order to decide whether such compensation occurs after 

 repeated rotation I have tested the matter as follows: Cats were 

 subjected to interrupted horizontal rotation over a prolonged 

 period and the nystagmus time observed. The rotation tests 

 (20 turns in 20 seconds) were applied 50 to 60 times daily at 

 intervals of two minutes and were repeated for twenty consecutive 

 days. 



The duration of post-rotatory nystagmus under these condi- 

 tions was found to vary slightly in different animals. With 20 

 revolutions in 20 seconds the maximal variations in the post-rota- 

 tory nystagmus time observed in six animals were from 12 to 19 

 seconds. 



The ocular responses to rotation for each animal remained 

 fixed within narrow limits and were unaffected by prolonged 

 rotation. It may be concluded therefore that rotation tests give 

 an adequate index of labyrinthine activity. 



1 Prince, A. L., Proceedings of the Society for Experimental Biology 

 and Medicine, 1917, XIV, 133. 



