SEMICIRCULAR CANALS AND THE VESTIBULE. 385 



not constant nor striking, but chemical and especially mechanical 

 stimulation in the hands of many observers has called forth definite 

 movements of head or eyes similar in a general way to those caused 

 by section of the canal, but lasting, of course, for a short time only. 

 In the dog-fish Lee* finds that pressure upon an ampulla causes 

 movements of the eyes and fins such as would occur normally if 

 the animal's body were rotated in the plane of the canal stimulated. 



Effect of Section of the Ampullary or the Acoustic Nerve. 

 Many of the older and newer observers have 'cut one or both of the 

 acoustic nerves or destroyed the entire labyrinth on one or both 

 sides. The effects described vary somewhat with the animals used, 

 but, in general, section of the nerve on one side is followed by 

 forced movements, especially by rolling movements around the 

 long axis of the body. When the nerves are cut on both sides 

 disturbances in the power to maintain equilibrium perfectly are 

 more or less distinctly marked. In fishes (dog-fish) the animal may 

 swim or come to rest in unusual positions, on the back or side, for 

 instance. 



Is the Effect of Section of the Canals Due to Stimulation? 

 The movements that result from section of one or more of the canals 

 have been attributed by some authors to stimulations set up by the 

 injury caused by the operation, and by others have been considered 

 as a result of the falling out of the stimuli normally and constantly 

 proceeding from the canals. This fundamental question has not 

 been decided. On the one hand, the movements observed are simi- 

 lar to those caused by excitation, which would indicate that a stimu- 

 lation is set up by the operation. On the other hand, the effects are 

 so long lasting as to make it improbable that they are entirely due to 

 the irritation of the operation. Moreover, Gaglio f states that when 

 the spot operated upon is cocainized the same effects follow. Indeed, 

 cocainizing the membranous canals gives the same results as cutting 

 them. It is possible, of course, that both processes take place, an 

 irritative stimulation and a falling out of normal impulses, the 

 effects of the latter being longer lasting. 



Theories of the Functions of the Semicircular Canals. As 

 indicated briefly above, the facts regarding injury to and stimulation 

 of the semicircular canals are very numerous and, on the whole, fairly 

 concordant. Their interpretation, however, has offered great dif- 

 ficulties, and many views have been proposed; almost every inves- 

 tigator, in fact, has, to some extent, varied in his interpretation of 

 the precise functional significance of these organs. t These views 

 may be classified, although imperfectly, under the following heads : 



* Lee, "Journal of Physiology," 15, 328, 1903. 



t Gaglio, "Archives ital. de biologic," 31, 377, 1899. 



t For a detailed and complete account of these views to 1892 see Stein, 

 "Die Lehren von den Funktionen der eizelnen Theile des Ohrlabyrinths." 

 Jena, 1894. 



