CHAPTER IV 



REFLEX ACTION 



i. THE organism maintains itself by continual adapta- 

 tions. There is adaptation in every process of life, inward 

 as well as outward, in absorption, secretion, respiration, no 

 less than in those movements of the limbs which for the 

 observer constitute pre-eminently theactions of an organism. 

 These actions, however, whereby it modifies its relations to 

 other organisms and the outer world generally, form one 

 case, and for us the most important case, of the exercise 

 of its powers of adaptation. 



Actions whether inward or outwardly apparent may be 

 due to purely internal changes. Just as the kettle goes 

 on quietly simmering till presently the lid lifts and the 

 water boils over, so in a nerve centre, or for that matter 

 in any mass of protoplasm, internal changes may go on, 

 while for the outward observer all is peace, till suddenly 

 a culminating point is reached, and a limb or the whole 

 body is thrown into decided, perhaps sudden and violent, 

 movement. Internally initiated movements are found in 

 the foetal life of the higher animals. Movements of the 

 chick in the egg from the fifth day are reported by Preyer, 1 

 and according to the same observer the " outstretching 

 and bending of the arms and legs " of new-born children 

 is " nothing else than a continuation of the intra-uterine 

 movements. 2 The aimless waving about of arms and 

 legs noticeable up to the third quarter of the first year 

 are referred by him to the same class. 3 Actions of this 



1 Preyer, I. p. 201. 2 Id. p. 205. 



3 Ib. p. 207. It may be, of course, that these motions have a casual 

 good effect as exercise, but this would not exclude them from the scope 

 of our definition. 



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