CHAP, vi.] THE BRAIN. 611 



highly differentiated bird or mammal. On the other hand, when 

 the cerebral hemispheres are bodily removed by the knife, the 

 portions of the brain left behind are so profoundly affected by the 

 ' shock ' of the operation, are for a while so obviously in an ab- 

 normal condition, that no just deductions can then be made as to 

 what are their normal functions. And the animals generally die 

 before they have entirely recovered from these immediate effects of 

 the operation. 



In the case of the bird, it has been found possible to keep the 

 creature alive for months, after apparently complete removal of 

 the hemispheres, and the following phenomena have then been ob- 

 served. The bird is able to maintain a completely normal posture, 

 and will balance itself on one leg, after the fashion of a bird which 

 has in a natural way gone to sleep. In fact, its appearance and be- 

 haviour are strikingly similar to those of a bird sleepy and stupid. 

 Left alone in perfect quiet, it will remain impassive and motionless 

 for a long, it may be for an almost indefinite, time. When stirred 

 it moves, shifts its position ; and then on being left alone returns 

 to a natural, easy posture. Placed on its side or its back it will 

 regain its feet ; thrown into the air, it flies with considerable pre- 

 cision for some distance before it returns to rest. It frequently 

 tucks its head under its wings, and at times may be seen to 

 clean its feathers and to pick up corn or to drink water presented 

 to its beak. It may be induced to move not only by ordinary 

 stimuli applied to the skin, but also by sudden sharp sounds, or 

 flashes of light ; and it is evident that its movements are to a 

 certain extent guided by visual sensations, for in its flight it will, 

 though imperfectly, avoid obstacles. Save that all clear signs of 

 distinct volition are absent, that all satisfactory indications of 

 intelligence are wanting, and that the movements are on the 

 whole clumsy, resembling rather those of a stupid drowsy bird 

 than those of one quite wide awake, there is very little to dis- 

 tinguish such a bird from one in full possession of its cerebral 

 hemispheres. 



In a mammal, during the few hours which intervene between 

 the sudden removal of the whole of both hemispheres and death, 

 very much the same phenomena may be observed. The rabbit, or 

 rat, operated on can stand, run and leap ; placed on its side or 

 back it at once regains its feet. Left alone, it remains as motion- 

 less and impassive as a statue, save now and then when a passing 

 impulse seems to stir it to a sudden but brief movement. Such a 

 rabbit will remain for minutes together utterly heedless of a carrot 

 or cabbage-leaf placed just before its nose, though if a morsel be 

 placed in its mouth it at once begins to gnaw and eat. When 

 stirred, it will with perfect ease and steadiness run or leap forward ; 

 and obstacles in its course are very frequently, with more or less 

 success, avoided. It will often follow by movements of the head a 

 bright light held in front of it (provided that the optic nerves and 



392 



