THE BRAIN 717 



When the worm was attached to a thread, and the observer retired 

 from view, the fish swallowed both worm and thread. The fish also' 

 apparently " played " in normal fashion with, fish which had not been 

 operated upon. These fish depend mainly upon vision for their 

 activities, and in the operation the optic lobes are not destroyed, 



In selachean or cartilaginous fishes, such as the shark, the result' 

 was different. These fish depend largely upon the sense of smell,- 

 and in them the prosencephalon is represented almost entirely by' 

 the primitive rhinencephalon, or smell-brain. Thus, when sardines 

 were thrown into an aquarium, the teleostea immediately seized their 

 booty, the selachea gradually approached in circles. When, in selachea, 

 the olfactory lobes, the representatives of the cerebrum, were taken 

 away, the fish was reduced from a state of activity to one of complete 

 quiescence. 



In the frog, after removal of the cerebral hemispheres, the animal 

 appears at first sight quite normal. It sits in normal fashion, jumps 

 when pinched, and starts swimming after stimulation just as quickly 

 as the normal animal. It will catch its food as normally, but shows 

 no power of differentiating between what is food and what is not; 

 It will snap at anything moving like a fly. 



In lizards, the loss of spontaneity is marked ; the animals lie about 

 as if sleeping. When roused, they just move away. The movement^ 

 are normal, obstacles are avoided, but the animal does not feed spon- 

 taneously, and exhibits no fear, as does the normal animal. 



In birds, such as pigeons, the results are somewhat similar to those 

 on reptiles. The bird can balance itself, and, when thrown in the air* 

 can fly, avoiding obstacles. When undisturbed, it remains still, 

 sleepy and motionless. It does not feed of itself, and manifests no 

 feelings of any sort. It was observed that a brainless female pigeon 

 responded in no way to the wooing of a male> nor showed any affection 

 or interest in the young which followed her, crying aloud for food. 

 It would push another pigeon out of the way, as if it 'were a stone, or 

 climb over it. It had no fear of anything e.g., cat or dog; it knew 

 neither friend nor foe. The cerebral processes of birds are localized 

 chiefly in a great development of the corpus striatum; in mammals, 

 on the other hand, they are more particularly dependent on the great 

 development of the cerebral hemispheres. 



In mammals, the operation of removal of the cerebrum is one of 

 considerable difficulty, and has only been successfully performed by 

 removing the brain piecemeal in successive operations. It has been 

 done by several observers, chiefly upon dogs, but also upon apes. In 

 the case of a dog which remained healthy after the final operation, 

 and was killed at the end of eighteen months, it was found post 

 mortem that, of the cerebral hemispheres, only such traces had been 

 left as were necessary to preserve the optic nerves from injury by 

 the operation. This, however, was successful only on the right side; 

 on the left side the nerve had atrophied. The optic thalami were 

 not injured by the operation, although the grey matter of the anterior 

 part was found to be atrophied. 



