THE SENSE ORGANS 181 



the nystagmus, the change in the direction of the long axis of the rab- 

 bit, the change in the position of its head, and the compensating mus- 

 cular movements made by it in order to retain its equilibrium. Do not 

 repeat this experiment many times. 



Stand erect and rotate a few times around the long axis of your 

 body. Repeat this test with your eyes closed. Analyze the peculiar 

 phenomena appearing when you cease rotating. In what direction do 

 the walls move? How do you endeavor to counteract this impression? 

 Since some persons are unusually sensitive to rotation, these experiments 

 should be performed with some care. Do not rotate excessively until 

 you have determined by a few rotations just how receptive you are. 



Repeat the rotation around your vertical axis while you hold the 

 head forward. Retain this position of the head at the end of the rota- 

 tion. What canals are involved, and what is the character of the after- 

 effects? 



Repeat the rotation around your vertical axis with the head bent 

 forward. On ceasing to rotate, raise the head. Analyze the after- 

 effect. 



6. Rotation Effects in the Frog. Place a frog under a bell-jar upon 

 a revolving chair. Turn the latter slowly, noting that the frog bends 

 its head and body against the direction of the rotation. 



Place a frog upon a somewhat roughened board. Tilt the board 

 and observe that the frog bends its body, and chiefly its head, against 

 the inclination. Carefully force the frog to move and make it move 

 across the edge of the gradually raised board and down its opposite 

 side. 



7. Equilibrium a Combined Sense. Close your eyes and try to 

 stand on one leg for one minute. Open your eyes and repeat this test. 

 Employ a tactile sensation in addition to the visual. Note that you 

 can retain your equilibrium with greater ease if the sensations from the 

 labyrinth are augmented by other sensations. 



8. Railroad Nystagmus. While riding in a street car observe that 

 the eyes of the person seated opposite to you are first deviated laterally 

 and are then quickly moved into a median position. This nystagmus is 

 not of labyrinthine origin, because it may be made to cease by accom- 

 modation for a stationary object or by shielding the eyes. 



9. Otolithic Cavity in the Frog. Etherize a frog. Open its mouth 

 widely and make an incision through the membrane covering its roof 

 on the median side of the orifice of the Eustachian tube. Remove the 

 surface layer of the bone of this region, thereby exposing a white 

 otolithic mass. Thoroughly destroy this mass. Let this animal rest 

 for some time, and then observe the position of its head and limbs. 

 Rotate this frog and look for compensating movements. Does this 

 frog possess a normal power of locomotion? How do its swimming 

 movements compare with those of a normal frog? 



Destroy the otolithic cavity on the opposite side, and repeat the 

 observations just made. Compare. 



