SEMICIRCULAR CANALS AND THE VESTIBULE. 407 



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 equilil:)rium 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 * 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 possi]:)le, 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 : 



1. The old view, first propossd by Autenrieth (1802), that the 

 canals or their sense cells are stimulated by sound waves and give 

 us the means of determining the direction of sound in accordance 

 with their position in three planes at right angles to one another. 

 This view has been revived from time to time by recent writers. 



2. Flourens himself believed that the impulses normally proceed- 

 ing from these organs serve to moderate, or, as we should say now, 

 to inhil^it the movements of the head. As soon as the canals are cut 

 the movements that have been kept under control by their influence 

 are unrestrained. On this view the semicircular canals are 

 organs which reflexly inhibit or restrain the voluntary movements, 

 and thus take an essential part in the proper co-ordination of such 



* Gaglio, "Archives ital. de biologie," 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 Ohrlab>Tinths," 

 Jena, 1894. 



