SUMMARY OF THE ARGUMENT. 438 



substance of the living body, by a constructive force which 

 (in so far as it is not supplied by the direct agency of external 

 heat) is developed by the retrograde metamorphosis of another 

 portion (6) of the food. And whilst the ultimate descent of 

 the first-named portion (a) to the simple condition from which 

 it was originally drawn, becomes one source of the peculiarly 

 animal powers the psychical and the motor exerted by the 

 organism, another source of these may be found in a like 

 metamorphosis of a further portion (c) of the food which has 

 never been converted into living tissue. 



Thus, during the whole life of the animal, the organism 

 is restoring to the world around both the materials and the 

 forces which it draws from it ; and after its death this resto- 

 ration is completed, as in plants, by the final decomposition 

 of its substance. But there is this marked contrast between 

 the two kingdoms of organic nature in their material and 

 dynamical relations to the inorganic world that whilst the 

 vegetable is constantly engaged (so to speak) in raising its 

 component materials from a lower plane to the higher, by 

 means of the power which it draws from the solar rays, the 

 animal, whilst raising one portion of these to a still higher 

 level by the descent of another portion to a lower, ultimately 

 lets down the whole of what the plant had raised ; in so 

 doing, however, giving' back to the universe, in the form of 

 heat and motion, the equivalent of the light and heat which 

 the plant had taken from it. 



19 



