THE CENTRAL NERVOUS SYSTEM 379 



which the whole brain has been destroyed with 

 the seeker, in respect to posture, power to regain 

 feet when laid on back, respiratory movements, 

 position of eyelids, leaping and swimming. 



2. Balancing Experiment. Place the frog oh a 

 somewhat roughened board, about 20 inches long, 

 8 inches wide, and 1 inch thick. Tilt the 

 board gradually. 



The frog remains motionless until his centre 

 of gravity is disturbed. He then moves forward 

 in an attempt to reach a stable position. By 

 careful management, he can be made to climb up 

 the inclined board, perch upon the narrow edge, 

 and, the board still turning, descend head-first on 

 the opposite side. 



3. Retinal Reflex. Place the frog deprived of 

 cerebral hemispheres in front of a bright light ; 

 for example, an incandescent electric lamp. In- 

 terpose some object, such as a small instrument 

 case, between the light and the frog, so that a 

 strong shadow is cast upon the frog's eyes. 

 Stimulate the frog by pinching the skin of the 

 back. 



The frog will jump, but will avoid the object 

 which casts the shadow, 



4. Croak Reflex. Sever the large hemispheres 

 from the remainder of the brain of another frog 

 by passing a knife through the cranium to the 



