CHAPTER VI. 

 THE BRAIN. 



SEC. 1. ON THE PHENOMENA EXHIBITED BY AN ANIMAL 

 DEPRIVED OF ITS CEREBRAL HEMISPHERES. 



A FEOG from which the cerebral lobes have been removed, even 

 though all the rest of the brain has been left intact, seems to 

 possess no volition. The apparently spontaneous movements which 

 it executes are so few and seldom that it is much more rational 

 to attribute those which do occur to the action of some stimulus 

 which has escaped observation, than to suppose that they are the 

 products of a will acting only at long intervals and in a feeble 

 manner. 



By the application however of appropriate stimuli, such an 

 animal can be induced to perform all the movements which an 

 entire frog is capable of executing. It can be made to swim, to 

 leap, and to crawl. When placed on its back, it immediately 

 regains its natural position. When placed on a board, it does not 

 fall from the board when the latter is tilted up so as to displace 

 the animal's centre of gravity : it crawls up the board until it 

 gains a new position in which its centre of gravity is restored to 

 its proper place. Its movements are exactly those of an entire 

 frog except that they need an external stimulus to call them forth. 

 They inevitably follow when the stimulus is applied ; they come 

 to an end when the stimulus ceases to act. By continually varying 

 the inclination of a board on which it is placed, the frog may 

 be made to continue crawling almost indefinitely ; but directly 

 the board is made to assume such a position that the body of 

 the frog is in equilibrium, the crawling ceases ; and if the position 

 be not disturbed the animal will remain impassive and quiet for 

 an almost indefinite time. When thrown into water, the creature 



