658' 



A TEXTBOOK OF PHYSIOLOGY 



Similar phenomena may be evoked by changes of temperature 

 applied to the outer wall of the labyrinth as, for example, by irriga- 

 tion of the middle ear with tepid water. In irrigation experiments 

 upon the superior canal, it has also been shown that reflex forced 

 movements of the head, eyes, and trunk, are produced in the same 

 direction as the wave of increased pressure in the endolymph. 

 Stimulation of the labyrinth by means of the galvanic current has 

 confirmed these results both in animals and in man. 



Passive rotation upon a turn-table causes the subject to turn 

 his head in the opposite direction, and on stopping in the direc- 

 tion of rotation, with a sensation of actual rotation in the opposite 

 direction. Cases of vestibular trouble may be investigated by means 

 of the turn-table, and their behaviour compared with that of normal 

 subjects. The giddiness and upset of equilibration produced by 



i 



UK INKUVK-EIBKKS ix A MUSCLE SI-IXDLE. 

 " Quain's Anatomy.") 



(Ruffini, from 



it, Nerve-ribres to spindle; a, annular endings of axon: .-, spiral endings: >1, dendritic 

 endings; sh, connective-tissue sh.ath of spindle. 



shifting the head from one plane to another after rotation is familiar 

 in the children's game, where, after turning round quickly with the 

 forehead resting on the poker, the subject stands up and tries i<> 

 walk straight out of the door or to touch a certain person. 



Comparative anatomy also supports these results. It has been 

 shown that Japanese waltzing mice and tumbler pigeons have ab- 

 normal semicircular canals. 



The mode of excitation of the receptor mechanism is generally 

 believed to be due to the inertia of the fluid within the canals. Rota- 

 tion of the head causes a lag of fluid and pressure in the opposite 

 direction, which acts upon the hair cells of the ampulla. Owing to 

 the small size of the canals, there is probably no actual movement of 

 the fluid, but merely positive and negative alterations of the fluid- 

 pressure within the canals. 



