THE BRAIN 117 



is caused by revolving the body the disturbances of the 

 ear receptors are combined with a curious ocular reac- 

 tion called nystagmus. It will be worth while to say a 

 word about this movement. 



If a person is spun around, as in an office chair, the 

 eyes behave in a characteristic fashion. Suppose the 

 rotation is toward the right. The eyes fix themselves 

 upon some object and as the body is turned away from 

 it they are swung in the opposite direction (toward the 

 left), keeping the landmark in view as long as possible. 

 When the eyes can be carried no farther they are 

 snapped very sharply to the right and another object 

 is seized upon. There is again the measured sweep to 

 the left and the quick snap to the right. The name 

 nystagmus is applied to this alternating movement of 

 the eyes in which the travel opposite in direction to the 

 rotation of the body is moderate in speed while the 

 counter-movement is extremely rapid. 



When the subject of such an experiment is brought 

 to rest, the nystagmus continues for a time. It is 

 accompanied by the distressing illusion that " every- 

 thing is going round and round." The uncontrollable 

 movements of the eyes continually shift the images upon 

 the retinas. It is thought that the quick, snapping 

 motions are not sources of sensation while the slower 

 ones are vividly effective. The result is, accordingly, 

 the impression that the surroundings are revolving in 

 one direction rather than oscillating back and forth. 

 By closing the eyes one lessens but does not entirely 

 do away with the feeling. When the shifting images can 

 no longer be seen there are still sensations from the eye 

 muscles as they go on with their unprofitable working. 



We are not justified in saying that the cerebellum is 

 the only central station through which the reflexes mak- 

 ing for equilibrium are brought about. Nevertheless, 

 it is the most obvious of such stations and it is un- 

 doubtedly traversed constantly by impulses which have 

 had their rise in the eyes, the ears, and the muscular 



