454 Beijf. J. Griieuherg 



2 The manner in which the semicircular canals operate to 

 bring about perception of space has been variously explained as 

 resulting from [a) static inertia of the endolymph; [b) variation 

 in pressure of the endolymph; and {c) movements or acceleration 

 of the endolymph, or of the perilymph, or of both; brought about 

 by movements of the head. 



3 Theoretical considerations seem to show that this function 

 cannot be ascribed to the canals for the reason that identical reac- 

 tions are produced under conditions in which the sense of the 

 acceleration may be opposite. (As explained in connection with 

 Fig. I.) 



4 But operations to remove or destroy the semicircular canals, 

 or to sever the connections of the VIII nerve, show {a) in some 

 cases that the movements of the animals are seriously affected, 

 and {b) in other cases that the animals continue to respond to 

 rotation as do the normal animals. 



5 Mechanical, thermal and electrical stimulations of the single 

 canals show {a) in some cases decided disturbances of movement 

 related to the planes of the respective canals, and {b) in other 

 cases the absence of related responses. 



On examining again the movements represented in Fig. i, it 

 will be seen that a given rotation will produce for the frog a dis- 

 placement of the retinal image or "view," and always in the same 

 direction without regard to the position of the animal on the turn- 

 table. Whereas the actions of centrifugal force and of acceleration 

 depend upon the position of the animal with relation to the axis 

 of rotation, the sense of displacement of the field of vision does 

 not so depend, and it may therefore be supposed that the uniform 

 turnings of the head are in response to the changing view; the 

 frog seems to be trying to keep the same view before him. 



To test the responsiveness of the frog to the apparent displace- 

 ment of his surroundings, a "revolving environment" was ar- 

 ranged, consisting of a cylinder of stout paper about 6o cm. in 

 diameter and about 35 cm. high, attached to a wooden hoop which 

 was suspended so that it could be readily rotated in either direc- 

 tion. A portion of the cylinder consisted of light colored material 

 bearing black vertical stripes about 5 mm. wide and from 2 to 5 



