Experimental Removal of Otic Labyrinth. 157 



musculature on the side of the lesion. Although this investigation 

 is as yet incomplete, it is considered desirable to report the fol- 

 lowing facts. 



As a means of determining the effect of impaired tonus on torsion 

 of the head, apart from that arising from destruction of the laby- 

 rinth, the following procedure was adopted: 



1. Unilateral section of the dorsal roots of the cer- 



vical NERVES. 



Accompanying the impairment of muscular tonus occasioned 

 by this procedure, there is torsion of the head to the side of the 

 injury. This torsion can only be attributed to the unbalanced 

 activity of the neck muscles on the intact side. It is to be noted 

 that the character of torsion following section of the dorsal roots 

 of the cervical nerves does not differ greatly from that seen after 

 unilateral removal of the labyrinth. In a dog, which has not 

 yet come to autopsy, section of the dorsal roots was followed by 

 torsion of the head to the side away from the lesion. 



The remaining series illustrate the torsional effect of various 

 combined lesions. 



2. Unilateral removal of the labyrinth and section of 



the dorsal roots of the cervical nerves on 

 the opposite side. 

 As stated before, unilateral removal of the labyrinth is fol- 

 lowed by torsion of the head to the side of the injury. Upon 

 subsequent section of the dorsal roots of the cervical nerves on the 

 opposite side this torsion is greatly reduced and in some cases 

 entirely disappears. Reversal in the order of the experiment 

 does not affect the end result; the torsion resulting from the first 

 procedure is always decreased or abolished by the second. 



3. Unilateral removal of the labyrinth and section of 

 the dorsal roots of the cervical nerves on the opposite 



side followed by either (a) removal of the re- 

 maining labyrinth, or (b) section of the re- 

 maining dorsal cervical roots. 

 In these experiments the final procedure is followed by a 

 reappearance of the head torsion. The direction of the torsion, 

 however, is always to the side on which two lesions are combined. 



