20 PSTCHOLOQY. 



GENERAL NOTION OF HEMISPHERES. 



All these facts lead us, when we think about them, to 

 some such explauatorj conception as this : The lower centres 

 act from present sensational stimuli alone; the hemispheres act 

 from perceptions and considerations, the sensations which they 

 may receive serving only as suggesters of these. But what 

 are perceptions but sensations grouped together ? and what 

 are considerations but expectations, in the fancy, of sensa- 

 tions which Avill be felt one Avay or another according as 

 action takes this course or that ? If I step aside on seeing 

 a rattlesnake, from considering how dangerous an animal 

 he is, the mental materials which constitute mj jDrudential 

 reflection are images more or less vivid of the movement 

 of his head, of a sudden pain in my leg, of a state of terror, 

 a swelling of the limb, a chill, delirium, unconsciousness, 

 etc., etc., and the ruin of my hopes. But all these images 

 are constructed out of my past experiences. They are repro- 

 ductions of what I have felt or witnessed. They are, in 

 short, remote sensations ; and the difference between the hemi- 

 spherdess animal and the ivhole one may be concisely ex- 

 pressed by saying that the one obeys absent, the other only 

 present, objects. 



The hemispheres would then seem to be the seat of mem- 

 ory. Yestiges of past experience must in some way be 

 stored up in them, and must, when aroused by present 

 stimuli, first appear as representations of distant goods 

 and evils; and then miist discharge into the appropriate 

 motor channels for warding off the evil and securing the 

 benefits of the good. If we liken the nervous currents to 

 electric currents, we can compare the nervous system, C, 

 below the hemispheres to a direct circuit from sense- 

 organ to muscle along the line S .. . C .. . M oi Fig. 2 (p. 21). 

 The hemisphere, H, adds the long circuit or loop-line 

 through which the current may pass when for any reason 

 the direct line is not used. 



Thus, a tired wayfarer on a hot day throws himself on 



