876 THE CENTRAL NERVOUS SYSTEM 



The procedure is repeated on the other ear. If it takes longer than 90 

 seconds for the nystagmus to appear, the vestibular apparatus of that 

 side is abnormal. Absence of the reaction deviation after the douching is 

 a certain sign of internal ear disease. 



It is undoubtedly essential that these tests should be most carefully 

 applied to all would-be aviators. They frequently reveal lesions of the 

 vcslibular apparatus or the cerebellum in subjects who had thought 

 themselves perfectly normal, and who indeed may have boasted of their 

 powers of equilibrium because they imagined that freedom from seasick- 

 ness or failure to become dizzy in dancing indicated a high development 

 of this function. There can be no doubt that many aviators have gone to 

 their death because of impairment in the ear mechanism. When on "terra 

 firma" the muscular sense and cutaneous sensations often make the 

 vestibular weakness of no consequence, but when deprived of these con- 

 tributory sensations and dependent on the ear-balance mechanism alone, 

 as in flying, any weakness becomes a serious menace. 



