518 



Comparative Animal Physiology 



produced an enhancement of impulse discharge (Figs. 187, 188); rotation in 

 the opposite direction (contralateral rotation) produced a decrease of the 

 spontaneous discharge (Figs. 187, 189). The impulse frequency increases 

 (or decreases) uniformly with constant angular acceleration. Rotation at 

 constant velocity produces an initial increase (or decrease) of impulse 

 frequency, during the acceleratory phase, followed by a gradual return to 

 the spontaneous discharge level in 20 to 30 seconds (Fig. 190). Stein- 



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Fig. 187. Photograph of oscillographically recorded spike potentials obtained from a 

 nerve branch to the left horizontal ampulla of the skate. The uniformity of the large 

 spikes indicates the response of a single fiber. A, Response of a single unit to ipsilateral 

 angular accelerations. The angular acceleration (15 degrees per sec.) is indicated by the 

 broken black lines of unequal lengths. Note the spontaneous activity in other fibers 

 before and after acceleration. B, Response of the same unit to contralateral angular 

 accelerations. From Lowenstein and Sand."" 



hausen**^' "" and Dohlman-- observed and photographed the cupula in 

 intact semicircular canals of the pike. The results of both investigators 

 show that the cupula nearly fills the lumen of the ampulla and is displaced 

 sharply to one side on rotation of the animal (Fig. 191). Introduction of 

 an oil droplet into the canal (by Dohlman) shows that the displacement 

 of fluid is responsible for the movement of the cupula. Analysis of the 

 time relations indicates that a cupula displaced by sudden acceleration re- 

 turns to its resting condition in about 20 seconds. (Fig. 192). The cupula 

 thus acts as a highly damped pendulum having a period of 20 seconds. 

 The results of these investigations indicate that the movement of the 



