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THE AMERICAN NATURALIST [Vol. LIV 



attempt of Fisher ami liabcurk alTords no positive evi- 

 dence against the demonstrated reduction of nystagmus 

 under repetition, 4 it has suggested an experimentum 

 cruris which is designed to show that the reduction is not 

 an artefact produced by the "wilful gaze-fixing" of in- 

 convenient subjects who acquired "'the art of holding 

 the eye more or less iixed voluntarily" upon a "distant 



We have chosen the white rat as a subject in our crucial 

 experiment. The rat is admirably adapted to this sort 

 of problem. It is docile and easy to handle. The lack of 

 a fovea and of distant vision and the probable absence of 

 all clear-cut retinal images 5 seeni to provide the optimal 

 conditions of non-fixation as suggested by the otologists' 

 contentions. On the other hand, the pupil of the rat's 

 eye is easily observed, as well as those portions of the 

 sclerotic coat which project beyond the surrounding 

 cutaneous and hairy tissues. 



The following method of rotation and observation was 

 employed. Upon a pivoted wooden platform, 11 cm. X 20 

 cm., was set a glass bell-jar 11 cm. in diameter and 12 cm. 

 in height. The rat was so placed under the glass jar that 

 its center of gravity lay over the center of rotation. A 

 small motor, governed by means of a friction-brake, 

 served to provide a very regular and easily controlled 

 means of rotating the platform and the jar. Records of 

 the time of after-nystagmus were at first made with a 

 stop-watch, but later with a key connected to an electric 

 signal-marker which registered on a revolving smoked 



