Behavior: Equilibration and Dizziness 45 



for movement on inclined surfaces or narrow places by its 

 tendency to move in circles and zigzags. The results of 

 my own experiments indicate that the timidity of the adult 

 is greater than that of the immature animal when it is placed 

 on a bridge i or 2 cm. wide at a distance of 20 cm. from the 

 ground. Individuals three weeks old showed less hesitation 

 about trying to creep along such a narrow pathway than did 

 full-grown dancers three or four months old ; and these, in 

 turn, were not so timid apparently as an individual one year 

 old. But the younger animals fell off more frequently than 

 did the older ones. 



Additional support for these statements concerning equili- 

 brational ability is furnished by the observations of Kishi 

 (21 p. 482). He built a wooden bridge 60 cm. long, i cm. 

 wide at one end, and \ cm. at the other, and supported it 

 at a height of 30 cm. above the ground by posts at the ends. 

 On this bridge ten dancers were tested. Some attempted 

 to move sidewise, others began to whirl and fell to the ground ; 

 only one of the ten succeeded in getting all the way across 

 the bridge on the first trial. The second time he was tested 

 this individual crossed the bridge and found the post; and 

 the third time he crossed the bridge and climbed down the 

 post directly. The others did not succeed in descending the 

 post even after having crossed the bridge safely, but, instead, 

 finally fell to the floor from awkwardness or exhaustion. On 

 the basis of these and other similar observations, Kishi says 

 that the dancer possesses a fair degree of ability to orient and 

 balance itself. 



Inasmuch as equilibration occurs similarly in darkness 

 and in daylight, Zoth thinks that there is neither visual dizzi- 

 ness nor fear of heights. But it is doubtful whether he is 

 right concerning fear. There is no doubt in my mind, in 

 view of the way the mice behave when placed on an elevated 



