45^ Bejij. C. Grueuherg 



"responses" to rotation even in a wooden frog; and these re- 

 sponses agree in sense with those described for the Uve frog. That 

 is to say, with a given rotation of the turntable the "turning" of 

 the head is constant, without regard to the position of the body in 

 relation to the axis of rotation. These considerations in detail 

 have led many physiologists to abandon the theory that the canals 

 are the organs for the perception of movement or acceleration, 

 since they so obviously arouse the same response to opposite sets 

 of stimuli, and since the responses can be obtained from wooden 

 animals as well as from Nature's own. But there is one element 

 in the mechanical theory that seems to have been overlooked as a 

 constant source of rotation stimuli. 



The inertia of a loosely jointed head as an explanation of the 

 phenomena may be left entirely out of account because in the first 

 place it cannot account for the back-jerk, in the second place the 

 inertia is overbalanced by the centrifugal force when a certain 

 rate of rotation is reached, whereas the responses do not dis- 

 appear at this point, and in the third place the responses can be 

 inhibited by stimuli that do not seem to affect the freedom of the 

 head articulation. 



Steiner ('85) has described the reactions of the frog in response 

 to rotation essentially as given here, and analyzed the movements 

 in terms of tangential force; but he concludes from the persistence 

 of the reactions after the division of the eighth nerve, that the 

 canals are not concerned in the matter at all. It is to be noticed 

 that when the animal is rotated on a turntable, the posterior end of 

 the body is constantly changing its position with reference to the 

 anterior end, as is the right side with reference to the left, etc. 

 This movement is constant in direction, and parallel (in direction) 

 to the rotation. That this is a real motion and quite distinct from 

 the motion of translation or rotation, is known to every physicist 

 and to some laymen; but the physicist has a name for it. 



Prof. Albert P. Wills, of the Department of Physics of Colum- 

 bia University, has kindly helped me to get the matter clear by 

 assuring me that this kind of motion is well recognized in mechan- 

 ics, and by giving me the technical name for it. It is known as 

 the "spin." This spin it is that remains constant in direction on 



