SEMICIRCULAR CANALS AND THE VESTIBULE. 383 



Flourens's Experiments upon the Semicircular Canals. 



Modern experiments and theories concerning the functions of the 

 semicircular canals date from the classical researches of Flourens* 

 (1824). This investigator laid bare the canals in birds and mam- 

 mals and studied the effects of sections of one or more of them. 

 The experiments have since been repeated by numerous observers, 

 and the results obtained have,, been described in great detail, for an 

 account of which reference must be made to original sources.f In 

 general, it may be said that injuries to the canals are followed by 

 certain more or less definite movements of the head, eyes, and body, 

 and by a disturbance in the power of the animal to co-ordinate nor- 

 mally the muscles used in standing, locomotion, or flying. The 

 character and extent of these results vary with the number of 

 canals injured, and, indeed, show a more or less definite relationship 

 to the several canals. When the horizontal canal is cut on one side 

 in pigeons the animal makes movements of the head in the plane of 

 that canal, and if the similar canal on the other side is also sec- 

 tioned these movements are more pronounced. The animal may 

 also in moving show an inability to walk normally and a tendency, 

 especially when excited, to make abnormal forced movements of 

 rotation of the whole body. After such an operation the pigeon will 

 not fly voluntarily and if thrown into the air is not able to guide 

 its flight with accuracy and soon descends. Similar operations 

 on the anterior or the posterior canals cause movements of the head 

 in the corresponding planes and a tendency in walking or flying 

 to make forced movements somersaults forward or backward. 

 When all three canals are cut on one or both sides the animal shows 

 a distressing inability to maintain a normal position. The head is 

 twisted, it is not able to stand unless supported, and any attempt 

 at walking or flying results in violent forced and inco-ordinated 

 movements. The animal makes continual somersaults at each 

 attempt to stand or walk and the head is kept in spasmodic, forceful 

 movements, which may produce injury or death. To preserve the 

 animal from injury after such an extensive operation it is necessary 

 to keep it wrapped in bandages. It should be added that results 

 of this character are obtained only when the membranous canals 

 are injured. If the bony canal alone is cut and even if the peri- 

 lymph is removed by suction no such effects are obtained. At 

 most slight and relatively transient movements of the head are 

 observed. If the exposed membranous canal is pricked with a 



* Flourens, " Recherches experimentales sur les proprietes et les fonctions 

 du systeme nerveux," second edition, 1842. 



f The literature of the semicircular canals and the vestibule is very ex- 

 tensive. The complete bibliography may be obtained from the following 

 sources : " Die Lehren von den Funktionen der einzelnen Theile des Ohrlaby- 

 rinths," by von Stein, 1894; Richet's " Dictionnaire de Physiologic," article 

 by Cyon, on "Espace," 1900. Ewald, ''Physiolog. Untersuchungen u. d. 

 Endorgan des nervus octavus, " 1892. 



