12 A. C. IVY 



trol, the slow component, or deviation, due to stimulation of the 

 labyrinth, which exerts an intersegmental control (Sherrington, 

 '06 a) . Then, since some reflexes are more easily interfered with 

 than others (Sherrington, '06 b) it is reasonable to believe that 

 the quick component of nystagmus is a type of reflex of lower in- 

 tensity, more easily interfered with and suppressed than the 

 slow component, or deviation. 



CONCLUSIONS 



(Rotation was the stimulus used to produce vestibular nystag- 

 mus.) 



True vestibular nystagmus is present in the frog, turtle, and 

 pigeon. If the body temperature of the frog and turtle is below 

 10°C, the quick component disappears while the slow component 

 persists. 



Decerebration in the frog, turtle, and pigeon does not disturb 

 vestibular nystagmus. 



The decerebrate pigeon with extensive lesion to the thalamus 

 manifests true vestibular nystagmus, provided its body tempera- 

 ture is kept normal. Otherwise, the quick component disap- 

 pears and only deviation persists. 



Hemi-decerebration in the rabbit, cat, and dog causes an in- 

 crease in vestibular nystagmus when the slow component is di- 

 rected opposite to the side of the lesion. When the slow com- 

 ponent is directed to the side of the lesion it is not abolished, 

 although not infrequently it is diminished. 



Complete decerebration with extensive destruction of the thal- 

 amus in the rabbit does not abolish the quick component of nys- 

 tagmus, provided the body temperature is kept normal. Rogers' 

 ('18) observations of the reduction of body temperature following 

 lesions of the thalamus have been confirmed for the rabbit. 



In the dog ablation of the motor cortex in the region of the eye 

 area with the inclusion of the lateral and basal portions of the 

 temporal lobe causes a five- to fifteen-fold increase in the number 

 of movements and a two- to four-fold increase in the duration of 

 the after-nystagmus when the animal is rotated opposite to the 

 side of the lesion. There is a slight increase in the rotatory nys- 



