CHAPTER II. 

 THE BRAIN. 



SEC. 1. ON THE PHENOMENA EXHIBITED BY AN 

 ANIMAL DEPRIVED OF ITS CEREBRAL HEMISPHERES. 



473. THE cerebral hemispheres, as we have more than 

 once insisted, seem to stand apart from the rest of the brain. In 

 the case of some animals it is possible to remove the cerebral 

 hemispheres and to keep the animal not only alive, but in good 

 health for a long time, days, weeks or even months after the 

 operation. In such case we are able to study the behaviour of 

 an animal possessing no cerebral hemispheres and to compare it 

 with that of an intact animal. Such an experiment is best carried 

 out on a frog. In this animal it is comparatively easy to re- 

 move the cerebral hemispheres, including the parts correspond- 

 ing to the corpora striata, leaving behind intact and uninjured 

 the optic thalami with the optic nerves, the optic lobes (or rep- 

 resentatives of the corpora quadrigemina), the small cerebellum 

 and the bulb. If the animal be carefully fed and attended to, 

 it may be kept alive for a very long time, for more than a year 

 for instance. 



The salient fact about a frog lacking the cerebral hemis- 

 pheres, is that, as in the case of a frog deprived of its whole 

 brain, the signs of the working of an intelligent volition are 

 either wholly absent or extremely rare. The presence of the 

 bulb and the middle parts of the brain (for so we may con- 

 veniently call the cerebral structures lying between the cerebral 

 hemispheres and the bulb) ensures the healthy action of the 

 vascular, respiratory and other nutritive systems ; food placed 

 in the mouth is readily and easily swallowed ; the animal wln-n 

 stimulated executes various movements; but if it be left entirely 

 to itself, and care be taken to shield it from adventitious stimuli, 

 either it remains perfectly and permanently quiescent, or the 

 apparently spontaneous movements which it carries out are so 



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