Nitrogen. 197 



place. We may not fully understand why this con- 

 stant change should be necessarv. lUit we know 

 that it is necessary under our present constitution, 

 and that by it heat and muscular power are both 

 produced. And since this rapid change of particles 

 is necessary for the body, we see how beautifully 

 adapted hydrogen is for the important place it occu- 

 I in the animal system. Its oxidation evolves 

 more heat than the same weight of any other sub- 

 stance ; and its product, water, is not only readily 

 eliminated from the system, but it aids in bearing 

 away the other substances that in the form of salts 

 must be eliminated by solution. 



Hydrogen has also important relations to nitro- 

 , so that in the decomposition of nitrogen com- 

 pounds, and probably also as water in the air, it 

 forms ammonia, and thus brings nitrogen into the 

 most favorable condition for the nourishment of 

 vegetation. 



The third element to be considered is nitrogen. 

 Design may be learned from results as well as from 

 the means by which the results are produced. As 

 already intimated, a clock would indicate design by the 

 movement of its hands marking the hours, though 

 its wheels were never seen. It is by its results, 

 rather than by knowledge of the methods of its 

 changes, that we must recognise design in nitrogen. 

 We are not, by any means, so sure of its methods 

 and conditions of combinations as in the case of 

 the two elements already considered. It constitutes 

 four-fifths of the atmosphere, but as a portion of the 



