MOVEMENT 



chemical process like unconscious and involuntary move- 

 ment (and unconscious feeling). They are both equally 

 subject to the law of substance. However, only the 

 external stimuli which cause reflex movements are 

 known to us to any great extent and experimentally 

 recognizable; the internal stimuli, which affect the will, 

 are mostly unknown, and are not directly accessible to 

 investigation. They are determined by the compHcated 

 structure of the psychoplasm, which has been gradually 

 acquired by phylogenetic processes in the course of 

 millions of years. 



The great problem of the will and its freedom — the 

 seventh and last of Dubois-Reymond's world-riddles — 

 has been dealt with fully in the Riddle (chapter vii.). But 

 as we still meet with the most glaring contradictions 

 and confusion in regard to this difficult psychological 

 question, I must touch upon it briefly once more. In 

 the first place, I would remind the reader that it is best 

 to restrict the name "will" to the purposive and con- 

 scious movements in the central nervous system of man 

 and the higher animals, and to give the name of impulses 

 (tropisms) to the corresponding unconscious processes in 

 the psychoplasm of the lower animals, as well as of the 

 plants and protists. For it is only the complicated 

 mechanism of the advanced brain structure in the higher 

 animals, in conjunction with the differentiated sense- 

 organs on the one side and the muscles on the other, 

 that accomplishes the purposive and deliberate actions 

 which we are accustomed to call acts of will. 



But the distinction between voluntary (autonomous) 

 and involuntary (reflex) movements is as difficult to 

 carry out in practice as it is clear in theory. We can 

 easily see that the two forms of movement pass into 

 each other without any sharp boundary (like conscious 

 and unconscious sensation). The same action, which 

 seems at first a conscious act of the will (for instance, in 



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