424 BIOLOGY. 



newed and indefatigable severance, by a desertion or 

 falling off from Nature. 



2529. In so doing, however, it detaches itself from 

 Nature, as being a part thereof ; the severance is there- 

 fore a conversion of the nature into an animal. In this 

 consists the reciprocal action of both, viz. that the animal 

 is constantly seeking to assimilate the nature unto itself. 



2530. The ability or power to assimilate the nature, is 

 called excitability. 



2531. Excitability is the most general phenomenon 

 of the organic mass, and appertains both to plants and 

 animals. 



2532. But in the animal excitability, the free self-sen- 

 sation, within which a free motion is necessarily inherent, 

 is super added or originates. This excitability unto motion 

 I call irritability. 



2533. Thus this irritability belongs only to animals. 



2534. Irritability does not depend directly upon motion, 

 but throughout upon sensation. Without sensation no 

 irritability is possible. If the sensation ceases, so also 

 does mobility, or the capacity for motion, cease. 



2535. Since irritability originates from the antagonism 

 of the animal with the world ; so is it parallel to an anta- 

 gonism of the heavenly bodies, or to that of sun and 

 planets. The mutual operation of these two heavenly 

 bodies is, however, an interchange of polarity, a polar 

 excitation. The irritability is a polar process ; but one 

 which is pure and devoid of material excretions, just as 



A the sun excites the earth without eliciting therein any 

 material change or transition. The animal becomes 

 polarized by the incentive agent or stimulus. 



2536. Through the irritability there originates a 

 double polarity in the animal. In the first place one 

 between the world arid the animal ; in the second, one 

 between the exterior of the animal and its interior. The 

 world-polarity gives the feeling or sensation, the body's 

 polarity the motion. 



2537. In the sensation the animal always transcends 

 itself ; there is thus only excitability. In the motion the 



