128 HAND-BOOK OF PHYSIOLOGY. 



impressions of sensible things, and reproducing them in subjective sensa- 

 tions and ideas. (4.) It is the medium of all the higher emotions and 

 feelings, and of the faculties of judgment, understanding, memory, reflec- 

 tion, induction, imagination and the like. 



Evidence regarding the physiology of the cerebral hemispheres has 

 been obtained, as in the case of other parts of the nervous system, from the 

 study of Comparative Anatomy, from Pathology, and from Experiments 

 on the lower animals. The chief evidences regarding- the functions of 

 the Cerebral hemispheres derived from these various* sources, are briefly 

 these: 1. Any severe injury of them, such as a general concussion, or 

 sudden pressure by apoplexy, may instantly deprive a man of all power of 

 manifesting externally any mental faculty. 2. In the same general pro- 

 portion as the higher mental faculties are developed in the Vertebrate ani- 

 mals, and in man at different ages and in different individuals, the more 

 is the size of the cerebral hemispheres developed in comparison with the 

 rest of the cerebro-spinal system. 3. No other part of the nervous system 

 bears a corresponding proportion to the development of the mental facul- 

 ties. 4. Congenital and other morbid defects of the cerebral hemisphere 

 are, in general, accompanied by corresponding deficiency in the range or 

 power of the intellectual faculties and the higli3r instincts. 5. Removal 

 of the cerebral hemispheres in one of the lower animals produces effects 

 corresponding with what might be anticipated from the foregoing facts. 

 The animal, although retaining mere sensation, . and the power of per- 

 forming even complicated reflex acts, remains in a state of stupor, and 

 performs no voluntary movement of any kind. (See below.) 



Effects of the Removal of the Cerebrum. The removal of the 

 cerebrum in the lower animals appears to reduce them to the condition of 

 a mechanism without spontaneity. A pigeon from which the cerebrum 

 has been removed will remain motionless and apparently unconscious 

 unless disturbed. When disturbed in any way it soon recovers its former 

 position; when thrown into the air it flies. 



In the case of the frog, when the cerebral lobes have been removed, 

 the animal appears similarly deprived of all power of spontaneous move- 

 ment. But it sits up in a natural attitude, breathing quietly; when 

 pricked it jumps away; when thrown into the water it swims; when placed 

 upon the palm of the hand it remains motionless, although, if the hand 

 be gradually tilted over till the frog is on the point of losing his balance, 

 he will crawl up till he regains his equilibrium, and comes to be perched 

 quite on the edge of the hand. This condition contrasts with that result- 

 ing 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. 



