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THE NERVOUS SYSTEM. 



or change its position unless some stimulus was applied, and 

 that as soon as this stimulus was withdrawn it lapsed into its 

 original position, remaining therein until again disturbed. If the 

 hemispheres are removed from a pigeon, it will act very much as 

 does the frog. If disturbed, it may fly for a short distance, but at 

 once lapses into a state of apparent unconsciousness, with eyes 

 closed. When the foot is pinched, it will be withdrawn. If a pistol 

 is discharged, the bird will open its eyes and show unmistakably 

 that the report was heard, but the discharge seems to produce no 

 other effect. The fact that there is danger is not appreciated. It 

 seems, therefore, that the faculty is absent by which the bird in 

 health associates danger with such sounds. When the human brain 

 is diseased or injured, something of the same kind is witnessed, and 

 in idiots, whose brains are imperfectly developed, the intellectual 

 faculties are very deficient. Human intelligence is manifested 

 through memory, reason, and judgment. 



Memory is the basis for the action of the other two faculties ; 

 without it there could be neither reason nor judgment. It is the 

 faculty of the mind by which it retains the knowledge of previous 

 thoughts or events, the actual and distinct retention and recogni- 

 tion of past ideas in the mind. Afferent impulses are continually 

 reaching the cells of the cortex of the brain, and these impulses 

 produce impressions more or less permanent. If they were evanes- 

 cent, passing away almost as soon as received, memory would be 

 impossible ; but it is this retention which constitutes memory. 

 If the ideas produced by these impulses come again into existence 

 spontaneously and without effort, this is remembrance; if this 

 requires an effort, this is recollection, a re-collecting of the im- 

 pressions originally produced on the cells by afferent impulses. 



Reason is the faculty of the mind by which is appreciated the 

 nature of nervous impulses, and by which they are referred to 

 their external source by which an effect is referred to its cause. 

 This reference an idiot cannot make ; hence he is said to be 

 " un-reasonable." 



Judgment is the faculty of the mind by which a selection is 

 made of the proper means to be used in the attainment of a par- 

 ticular end. Thus if one selects inadequate means for the accom- 

 plishment of a given object, it is said that one " lacks judgment." 



The cerebrum is the seat of conscious sensation, as opposed to 

 sensation alone. The gray matter of the spinal cord is said to be 

 sensitive- that is, it responds to stimuli. If the finger is burned, 

 the afferent impulse is received by the gray matter of the cord 

 and a motor impulse passes out to the muscles. But if the impulse 

 travels no farther than the cord, there is no conscious sensation. 

 To excite this sensation it must proceed to the gray matter of the 

 cerebral cortex. It is in the cells of the cortex that volitional 

 impulses have their origin. The gray matter, then, is the seat of 



