Z A. C. IVY 



Observations were made upon rotatory and postrotatory nys- 

 tagmus. The animals were placed upon a turntable and rotated, 

 the speed and number of rotations being controlled. 



RESULTS 



Frog. Some observers have reported the presence of compen- 

 satory movements of the eyes of the frog, others have not. This 

 discrepancy is probably due to the condition of the frog and the 

 acuteness of observation. Out of about one hundred frogs ex- 

 amined only a few were found that did not show on rotation a 

 true vestibular nystagmus with slow and quick components. 

 The small green frog (Rana pipiens) and the jumbo bull-frog. 

 (Rana catesbiana) were used. The latter is much better than the 

 former for study, as the nystagmus reaction is more marked and 

 the eyes are larger. Several precautions are necessary in order 

 to observe the reaction. It is necessary to rotate the frog slowly : 

 if rotated too rapidly, only deviation occurs. The quick com- 

 ponent is very slight in degree (| to 32 inch, depending on the 

 size of the frog), for the deviation in the frog is not marked. It 

 is easier to observe, if the head is held between the fingers to 

 prevent head nystagmus. If the frog struggles much, it will be 

 absent. Pinning to the frog board often inhibits the reaction. 

 Postrotatory nystagmus is very infrequent. I have observed it, 

 however, consisting only of one or two movements. The tem- 

 perature of the frog is very important. The best reaction occurs 

 at 18° to 20°C. 



Decerebration in the frog never abolishes the quick compon- 

 ent of nystagmus nor interferes with the nystagmus reaction in 

 any way. If the frog is depressed as a result of the operation, 

 then deviation only is observed. 



Turtle. Wilson and Pike ('15) report that nystagmus is absent 

 in the turtle. My observations are to the contrary, provided the 

 turtle's temperature is between 10° and 39°C. On either side 

 of these temperatures the quick component is abolished and 

 deviation only is present. 



This effect of temperature upon nystagmus is only to be ex- 

 pected when it is recalled that reflexes in general are depressed 

 by temperature on either side of the normal or optimum. 



