520 



Comparative Animal Physiology 



Equilibrium Orientation in Vertebrates. Numerous experiments on the 

 effects of labyrinthectomy have been reported on a great variety of ani- 

 ^^js 9. 14. 27. -'8. 30, :«, 34, 39, 50, 68 Removal of onc labyrinth produces an ab- 

 normal posture in which the head and neck are bent toward the operated side. 

 In the absence of other sensory cues (see below), this abnormal reaction is 

 always present and is called a primary symptom. Other symptoms of ab- 

 normal posture appear after the operation but gradually subside, until the 

 orientation and response of the organism is normal. These are called 

 secondary symptoms. Most animals with only one labyrinth typically re- 



^ 25 = 



seconds 



Fig. 190. Relation of spike potential discharge frequency to rotation (A, ipsilateral, 

 and B, contralateral) at constant speed of 36 degrees per second, as a function of time. 

 The horizontal lines indicate the frequency level of spontaneous activity at the onset of 

 each experiment. Note the early occurrence of a maximum change followed by tendency 

 to level off above and below the spontaneous discharge level. From Lowenstein and Sand."' 



spond to rotation in both directions, suggesting that onc labyrinth is capable 

 of serving an organism satisfactorily, a suggestion confirmed by the study 

 (;f impulses in labyrinthine nerves. 



The removal of both labyrinths produces effects which differ in animals. 

 Frogs thus prepared'' maintain an\' imposed posture of which they are 

 capable. Mammals, except rabbits and guinea pigs, seem to behave quite 

 normally, provided the eyes are intact, except under two circumstances. 

 When a bilaterally labyrinthcctomized animal is placed in water, orienta- 



