THE CENTRAL NERVOUS SYSTEM 739 



Functions of the Cerebral Cortex. When an animal, like a 

 frog, is deprived of its cerebral hemispheres, the power of 

 automatic voluntary movement appears to be definitively 

 and entirely lost. The animal, as soon as the effects of the 

 anaesthetic and the shock of the operation have passed away, 

 draws up its legs, erects its head, and assumes the charac- 

 teristic position of a normal frog at rest. So close may be 

 the resemblance, that if all external signs of the operation 

 have been concealed, it may not be possible for a casual 

 observer to tell merely by inspection which is the intact and 

 which the ' brainless ' frog. The latter will jump if it be 

 touched or otherwise stimulated. It will croak if its flanks 

 be stroked or gently squeezed together. It will swim if 

 thrown into water. If placed on its back, it will promptly 

 recover its normal position. But it will do all these things 

 as a machine would do them, without purpose, without 

 regard to its environment, with a kind of * fatal ' regularity. 

 Every time it is stimulated it will jump, every time its flanks 

 are squeezed it will croak, and, in the absence of all stimu- 

 lation, it will sit still till it withers to a mummy, even by the 

 side of the water that might for a while preserve it. 



A Menobranchus, without its cerebral hemispheres, will, 

 like the frog, refuse to lie on its back. On stimulation it 

 moves its feet or tail, or its whole body ; but if not interfered 

 with, it lies for an indefinite time in the same position. Its 

 gills are seen to execute rhythmic movements, which never 

 stop, and rarely slacken, except for an instant, when some 

 part of the skin, particularly in the region of the head, is 

 mechanically or electrically stimulated. The normal Meno- 

 branchus, on the other hand, lies for long periods with its 

 gills at perfect rest, and when stimulated moves for a con- 

 siderable distance. After a time, two months or more, it is 

 true the * brainless frog,' if it be kept alive, as may be done 

 by careful attention, will recover a certain portion of the 

 powers which it has lost by removal of the cerebral hemi- 

 spheres; and, indeed, the longer it lives, the nearer it 

 approximates to the condition of a normal frog. A brain- 

 less frog has been seen to catch flies and to bury itself as 

 winter drew on. A fish even three days after the destruction 



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