51 '2 HANDBOOK OF PHYSIOLOGY. 



faculties of judgment, understanding, memory, reflection, 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 Experi- 

 ments on the lower animals. The chief evidences regarding the func- 

 tions of the Cerebral hemispheres derived from these various sources, are 

 briefly these: 1. Any severe injury of them, such as a general concus- 

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

 power of manifesting externally any mental faculty. 2. In the same 

 general proportion as the higher mental faculties are developed in the 

 Vertebrate animals, and in man at different ages and in different indi- 

 viduals, the more is the size of the cerebral hemispheres developed in com- 

 parison 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 faculties. 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 

 higher instincts. 5. Eemoval of the cerebral hemispheres in one of the 

 lower animals produces effects corresponding with what might be antici- 

 pated from the foregoing facts. 



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 mech- 

 anism without spontaneity. A pigeon from which the cerebrum has been 

 removed will remain motionless and apparently unconscious unless dis- 

 turbed. When disturbed in any way it soon recovers its former position; 

 when thrown into the air it flies. 



In the case of the/ro^, 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 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. 



Unilateral Action. Respecting the mode in which the brain dis- 

 charges its functions, there is no evidence whatever. But it appears 

 that, for all but its highest intellectual acts, one of the cerebral hemi- 

 spheres is sufficient. For numerou scases are recorded in which no men- 



