576 THE NERVOUS SYSTEM 



ation has reduced the animal to the condition of an automaton capable of 

 carrying on complex activities, but only after receiving some definite stimulus. 

 This condition contrasts with that resulting from the removal of the entire 

 brain, leaving only the spinal cord. In this case only the simpler reflex actions 

 can take place. The frog does not breathe ; he lies flat on the table instead of 

 sitting up; when thrown into a vessel of water he sinks to the bottom; when 

 his legs are pinched he kicks out, but does not leap away. 



If the cerebrum of the frog be removed, taking special care not to interfere 

 with the optic nerves or the optic thalami, then he acts somewhat differently. 

 Whereas with the entire cerebrum removed he makes no effort to take food, 

 now he will attempt to catch flies or other insects, and will show other signs of 

 spontaneous activity. He will avoid an object and shows signs of responding 

 to visual sensations, such as the attempt to feed just mentioned. 



The cerebral lobes of the frog, however, are very low in the scale of de- 

 velopment as compared with other vertebrates. The cortex is a single layer 

 of rather small cells, and the total volume of the cortex as compared with other 

 portions of the brain is small. 



The case of the pigeon, which represents a higher animal in the scale^ 

 has been extensively studied by Flourens and others. They have shown that 

 when the cerebrum is carefully removed, leaving the basal nuclei undisturbed, 

 and the animal has recovered from the immediate effects of the shock, it is 

 able to carry on many Coordinate activities. In the first place it can stand 

 or perch without difficulty; if placed on its back it immediately regains its 

 equilibrium; if tossed in the air it flies until it comes in contact with a firm 

 support. If disturbed on its perch it will walk away, showing the power 

 to coordinate not only wing muscles, but the leg muscles. If left undisturbed, 

 such a pigeon will occasionally make motions, i.e., open its eyes, move its head, 

 preen its feathers, or even take a step or two. It spends most of its time, how- 

 ever, sitting quietly as though asleep. If aroused, the animal shows little or no 

 signs of excitement or fright. 



After several months such pigeons are said usually to increase the motions 

 of spontaneity or take short flights, avoiding obstacles in the way and alighting 

 definitely on the perch. They will pick around among food for definite articles, 

 apparently intending to select the food. Early after the operation the pigeon 

 will pick at objects indiscriminately, but does not take food unless it is placed 

 in the mouth. 



Apparently the main effect produced here is to diminish the complexity and 

 efficiency of those activities which we call spontaneous. The surprising thing 

 is that there is as little disturbance among the motor functions as is found. 



In mammals it is difficult to remove the cerebral hemispheres, but in those 

 animals, in which the operation has been carried out, as for example in the rab- 

 bit and rat, a result very similar to those observed in the case of the frog and 

 pigeon has been obtained. The animal is able to maintain its equilibrium, 



