HEMISPHERES. 423 



His mental derangement is often shown in the undue estimate which 

 he forms of passing events. He is no longer able to appreciate the 

 true relation between different objects and different phenomena. 

 Thus, he will show an exaggerated degree of solicitude about a 

 trivial occurrence, and will pay no attention to other matters of 

 real importance. As the difficulty increases, he becomes careless 

 of the directions and advice of his attendants, and must be watched 

 and managed like a child or an imbecile. After a certain period, 

 he no longer appreciates the lapse of time, and even loses the dis- 

 tinction between day and night. Finally, when the injury to the 

 hemispheres is complete, the senses may still remain active and 

 impressible, while the patient is completely deprived of intelligence, 

 memory, and judgment. 



If we examine the comparative development of the hemispheres 

 in different species of animals, and in different races of men, we 

 shall find that the size of these ganglia corresponds very closely 

 with the degree of intelligence possessed by the individual. We 

 have already traced, in a preceding chapter, the gradual increase 

 in size of the hemispheres in fish, reptiles, birds, and quadrupeds : 

 four classes of animals which may be arranged, with regard to the 

 amount of intelligence possessed by each, in precisely the same 

 order of succession. Among quadrupeds, the elephant has much 

 the largest and most perfectly formed cerebrum, in proportion to 

 the size of the entire body ; and of all quadrupeds he is proverbially 

 the most intelligent and the most teachable. It is important to 

 observe in this connection, that the kind of intelligence which 

 characterizes the elephant and some other of the lower animals, 

 and which most nearly resembles that of man, is a teachable intelli- 

 gence ; a very different thing from the intelligence which depends 

 upon instinct, such as that of insects, for example, or birds of pas- 

 sage. Instinct is unvarying, and always does the same thing in the 

 same manner, with endless repetition ; but intelligence is a power 

 which adapts itself to new circumstances, and enables its possessor, 

 by comprehending and retaining new ideas, to profit by experience. 

 It is this quality which distinguishes the higher classes of animals 

 from the lower ; and which, in a very much greater degree, con- 

 stitutes the intellectual superiority of man himself. The size of 

 the cerebrum in man is accordingly very much greater, in propor- 

 tion to that of the entire body, than in any of the lower animals : 

 while other parts of the brain, on the contrary, such as the olfactory 

 ganglia or the optic tubercles, are frequently smaller in him than 



