KATABOLISM. 435 



of vital energy, and therefore the katabolic descent must 

 go far below the plane from which material is drawn by 

 anabolism. Plants, on the contrary, take much energy, 

 viz., that expended in making organic matter, directly 

 from the sun ; an energy generated by a katabolic pro- 

 cess, true — viz., decomposition of C0 2 — but determined 

 by an external force, sunlight. So that in the eternal 

 circulation of matter from the plane of minerals to that 

 of animal life and back again to the plane of minerals 

 the anabolic ascent begins in plants and completes itself 

 in animals ; but the katabolic descent completes itself at 

 once in animal katabolism. So that the whole circula- 

 tion may be represented by an endless chain, as in the 

 adjoining figure (295). This circulation must be driven 

 in part by a force external to the chain. That force is 

 the sun. It is evident that animal force in activity, in 

 excess of maintenance of tissues, is the equivalent of 

 the excess of katabolism over anabolism — of the excess 

 (2, j) of the katabolic branch of the siphon. But this 

 is exactly equal to the lift by the sun (/, 2). Therefore 

 animal force or activity is equivalent to sun force in 

 making organic matter. 



SECTION III. 

 Tke Kidneys : The Organ and its Function. 



The Organ. — We have already said that the lungs 

 and kidneys are the two great organs for elimination of 

 the products of katabolism. They are also correlative, 

 since they divide between them the final disposal of the 

 albuminoid food and the waste. The kidneys, therefore, 

 must be our next subject. 



Place and Form. — The kidneys are in the abdomi- 

 nal cavity, in the hollow on each side of the lumbar ver- 

 tebra, and just below the roots of the diaphragm. The 



