CHAPTER XX 

 REFLEXES, INSTINCT, AND REASON 



We live in a world which is full of misery and ignorance, and the 

 plain duty of each and all of us is to try to make the little corner he can 

 influence somewhat less miserable and somewhat less ignorant than it 

 was before he entered it. To do this effectually it is necessary to be 

 fully possessed of two beliefs the first, that the order of nature is 

 ascertainable by our faculties to an extent which is practically un- 

 limited ; the second, that our volition counts for something as a condi- 

 tion of the course of events. 



Each of these beliefs can be verified experimentally as often as we 

 like to try. Each, therefore, stands upon the strongest foundation upon 

 which any belief can rest, and forms one of our highest truths. If we 

 find that the ascertainment of the order of nature is facilitated by using 

 one terminology or one set of symbols rather than another, it is our 

 clear duty to use the former; and no harm can accrue so long as we 

 bear in mind that we are dealing merely with terms and symbols. 

 HUXLEY. 



ALL animals of whatever degree of organization show in 

 life the quality of irritability^ or response to external stimulus. 

 Contact with external things produces some effect on each of 

 them, and this effect seems to be something more than the 

 mere mechanical effect on the matter of which the animal is 

 composed. In the one-celled animals, the functions of response 

 to external stimulus are not localized. They are the property 

 of any part of the protoplasm of the body. Just as breathing 

 or digestion is a function of the whole cell, so are sensation and 

 response in action. In the higher or many-celled animals 

 each of these functions is specialized and localized. A certain 

 set of cells is set apart for each function, and each organ or 

 series of cells is released from all functions save its own. 



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